| /* |
| * Copyright (c) 2001, 2012, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| * |
| */ |
| |
| #include "precompiled.hpp" |
| #include "classfile/symbolTable.hpp" |
| #include "classfile/systemDictionary.hpp" |
| #include "code/codeCache.hpp" |
| #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp" |
| #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp" |
| #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp" |
| #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp" |
| #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp" |
| #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp" |
| #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp" |
| #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp" |
| #include "gc_implementation/parNew/parNewGeneration.hpp" |
| #include "gc_implementation/shared/collectorCounters.hpp" |
| #include "gc_implementation/shared/isGCActiveMark.hpp" |
| #include "gc_interface/collectedHeap.inline.hpp" |
| #include "memory/cardTableRS.hpp" |
| #include "memory/collectorPolicy.hpp" |
| #include "memory/gcLocker.inline.hpp" |
| #include "memory/genCollectedHeap.hpp" |
| #include "memory/genMarkSweep.hpp" |
| #include "memory/genOopClosures.inline.hpp" |
| #include "memory/iterator.hpp" |
| #include "memory/referencePolicy.hpp" |
| #include "memory/resourceArea.hpp" |
| #include "oops/oop.inline.hpp" |
| #include "prims/jvmtiExport.hpp" |
| #include "runtime/globals_extension.hpp" |
| #include "runtime/handles.inline.hpp" |
| #include "runtime/java.hpp" |
| #include "runtime/vmThread.hpp" |
| #include "services/memoryService.hpp" |
| #include "services/runtimeService.hpp" |
| |
| // statics |
| CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL; |
| bool CMSCollector::_full_gc_requested = false; |
| |
| ////////////////////////////////////////////////////////////////// |
| // In support of CMS/VM thread synchronization |
| ////////////////////////////////////////////////////////////////// |
| // We split use of the CGC_lock into 2 "levels". |
| // The low-level locking is of the usual CGC_lock monitor. We introduce |
| // a higher level "token" (hereafter "CMS token") built on top of the |
| // low level monitor (hereafter "CGC lock"). |
| // The token-passing protocol gives priority to the VM thread. The |
| // CMS-lock doesn't provide any fairness guarantees, but clients |
| // should ensure that it is only held for very short, bounded |
| // durations. |
| // |
| // When either of the CMS thread or the VM thread is involved in |
| // collection operations during which it does not want the other |
| // thread to interfere, it obtains the CMS token. |
| // |
| // If either thread tries to get the token while the other has |
| // it, that thread waits. However, if the VM thread and CMS thread |
| // both want the token, then the VM thread gets priority while the |
| // CMS thread waits. This ensures, for instance, that the "concurrent" |
| // phases of the CMS thread's work do not block out the VM thread |
| // for long periods of time as the CMS thread continues to hog |
| // the token. (See bug 4616232). |
| // |
| // The baton-passing functions are, however, controlled by the |
| // flags _foregroundGCShouldWait and _foregroundGCIsActive, |
| // and here the low-level CMS lock, not the high level token, |
| // ensures mutual exclusion. |
| // |
| // Two important conditions that we have to satisfy: |
| // 1. if a thread does a low-level wait on the CMS lock, then it |
| // relinquishes the CMS token if it were holding that token |
| // when it acquired the low-level CMS lock. |
| // 2. any low-level notifications on the low-level lock |
| // should only be sent when a thread has relinquished the token. |
| // |
| // In the absence of either property, we'd have potential deadlock. |
| // |
| // We protect each of the CMS (concurrent and sequential) phases |
| // with the CMS _token_, not the CMS _lock_. |
| // |
| // The only code protected by CMS lock is the token acquisition code |
| // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the |
| // baton-passing code. |
| // |
| // Unfortunately, i couldn't come up with a good abstraction to factor and |
| // hide the naked CGC_lock manipulation in the baton-passing code |
| // further below. That's something we should try to do. Also, the proof |
| // of correctness of this 2-level locking scheme is far from obvious, |
| // and potentially quite slippery. We have an uneasy supsicion, for instance, |
| // that there may be a theoretical possibility of delay/starvation in the |
| // low-level lock/wait/notify scheme used for the baton-passing because of |
| // potential intereference with the priority scheme embodied in the |
| // CMS-token-passing protocol. See related comments at a CGC_lock->wait() |
| // invocation further below and marked with "XXX 20011219YSR". |
| // Indeed, as we note elsewhere, this may become yet more slippery |
| // in the presence of multiple CMS and/or multiple VM threads. XXX |
| |
| class CMSTokenSync: public StackObj { |
| private: |
| bool _is_cms_thread; |
| public: |
| CMSTokenSync(bool is_cms_thread): |
| _is_cms_thread(is_cms_thread) { |
| assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(), |
| "Incorrect argument to constructor"); |
| ConcurrentMarkSweepThread::synchronize(_is_cms_thread); |
| } |
| |
| ~CMSTokenSync() { |
| assert(_is_cms_thread ? |
| ConcurrentMarkSweepThread::cms_thread_has_cms_token() : |
| ConcurrentMarkSweepThread::vm_thread_has_cms_token(), |
| "Incorrect state"); |
| ConcurrentMarkSweepThread::desynchronize(_is_cms_thread); |
| } |
| }; |
| |
| // Convenience class that does a CMSTokenSync, and then acquires |
| // upto three locks. |
| class CMSTokenSyncWithLocks: public CMSTokenSync { |
| private: |
| // Note: locks are acquired in textual declaration order |
| // and released in the opposite order |
| MutexLockerEx _locker1, _locker2, _locker3; |
| public: |
| CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1, |
| Mutex* mutex2 = NULL, Mutex* mutex3 = NULL): |
| CMSTokenSync(is_cms_thread), |
| _locker1(mutex1, Mutex::_no_safepoint_check_flag), |
| _locker2(mutex2, Mutex::_no_safepoint_check_flag), |
| _locker3(mutex3, Mutex::_no_safepoint_check_flag) |
| { } |
| }; |
| |
| |
| // Wrapper class to temporarily disable icms during a foreground cms collection. |
| class ICMSDisabler: public StackObj { |
| public: |
| // The ctor disables icms and wakes up the thread so it notices the change; |
| // the dtor re-enables icms. Note that the CMSCollector methods will check |
| // CMSIncrementalMode. |
| ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); } |
| ~ICMSDisabler() { CMSCollector::enable_icms(); } |
| }; |
| |
| ////////////////////////////////////////////////////////////////// |
| // Concurrent Mark-Sweep Generation ///////////////////////////// |
| ////////////////////////////////////////////////////////////////// |
| |
| NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;) |
| |
| // This struct contains per-thread things necessary to support parallel |
| // young-gen collection. |
| class CMSParGCThreadState: public CHeapObj { |
| public: |
| CFLS_LAB lab; |
| PromotionInfo promo; |
| |
| // Constructor. |
| CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) { |
| promo.setSpace(cfls); |
| } |
| }; |
| |
| ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration( |
| ReservedSpace rs, size_t initial_byte_size, int level, |
| CardTableRS* ct, bool use_adaptive_freelists, |
| FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) : |
| CardGeneration(rs, initial_byte_size, level, ct), |
| _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))), |
| _debug_collection_type(Concurrent_collection_type) |
| { |
| HeapWord* bottom = (HeapWord*) _virtual_space.low(); |
| HeapWord* end = (HeapWord*) _virtual_space.high(); |
| |
| _direct_allocated_words = 0; |
| NOT_PRODUCT( |
| _numObjectsPromoted = 0; |
| _numWordsPromoted = 0; |
| _numObjectsAllocated = 0; |
| _numWordsAllocated = 0; |
| ) |
| |
| _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end), |
| use_adaptive_freelists, |
| dictionaryChoice); |
| NOT_PRODUCT(debug_cms_space = _cmsSpace;) |
| if (_cmsSpace == NULL) { |
| vm_exit_during_initialization( |
| "CompactibleFreeListSpace allocation failure"); |
| } |
| _cmsSpace->_gen = this; |
| |
| _gc_stats = new CMSGCStats(); |
| |
| // Verify the assumption that FreeChunk::_prev and OopDesc::_klass |
| // offsets match. The ability to tell free chunks from objects |
| // depends on this property. |
| debug_only( |
| FreeChunk* junk = NULL; |
| assert(UseCompressedOops || |
| junk->prev_addr() == (void*)(oop(junk)->klass_addr()), |
| "Offset of FreeChunk::_prev within FreeChunk must match" |
| " that of OopDesc::_klass within OopDesc"); |
| ) |
| if (CollectedHeap::use_parallel_gc_threads()) { |
| typedef CMSParGCThreadState* CMSParGCThreadStatePtr; |
| _par_gc_thread_states = |
| NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads); |
| if (_par_gc_thread_states == NULL) { |
| vm_exit_during_initialization("Could not allocate par gc structs"); |
| } |
| for (uint i = 0; i < ParallelGCThreads; i++) { |
| _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace()); |
| if (_par_gc_thread_states[i] == NULL) { |
| vm_exit_during_initialization("Could not allocate par gc structs"); |
| } |
| } |
| } else { |
| _par_gc_thread_states = NULL; |
| } |
| _incremental_collection_failed = false; |
| // The "dilatation_factor" is the expansion that can occur on |
| // account of the fact that the minimum object size in the CMS |
| // generation may be larger than that in, say, a contiguous young |
| // generation. |
| // Ideally, in the calculation below, we'd compute the dilatation |
| // factor as: MinChunkSize/(promoting_gen's min object size) |
| // Since we do not have such a general query interface for the |
| // promoting generation, we'll instead just use the mimimum |
| // object size (which today is a header's worth of space); |
| // note that all arithmetic is in units of HeapWords. |
| assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking"); |
| assert(_dilatation_factor >= 1.0, "from previous assert"); |
| } |
| |
| |
| // The field "_initiating_occupancy" represents the occupancy percentage |
| // at which we trigger a new collection cycle. Unless explicitly specified |
| // via CMSInitiating[Perm]OccupancyFraction (argument "io" below), it |
| // is calculated by: |
| // |
| // Let "f" be MinHeapFreeRatio in |
| // |
| // _intiating_occupancy = 100-f + |
| // f * (CMSTrigger[Perm]Ratio/100) |
| // where CMSTrigger[Perm]Ratio is the argument "tr" below. |
| // |
| // That is, if we assume the heap is at its desired maximum occupancy at the |
| // end of a collection, we let CMSTrigger[Perm]Ratio of the (purported) free |
| // space be allocated before initiating a new collection cycle. |
| // |
| void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) { |
| assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments"); |
| if (io >= 0) { |
| _initiating_occupancy = (double)io / 100.0; |
| } else { |
| _initiating_occupancy = ((100 - MinHeapFreeRatio) + |
| (double)(tr * MinHeapFreeRatio) / 100.0) |
| / 100.0; |
| } |
| } |
| |
| void ConcurrentMarkSweepGeneration::ref_processor_init() { |
| assert(collector() != NULL, "no collector"); |
| collector()->ref_processor_init(); |
| } |
| |
| void CMSCollector::ref_processor_init() { |
| if (_ref_processor == NULL) { |
| // Allocate and initialize a reference processor |
| _ref_processor = |
| new ReferenceProcessor(_span, // span |
| (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing |
| (int) ParallelGCThreads, // mt processing degree |
| _cmsGen->refs_discovery_is_mt(), // mt discovery |
| (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree |
| _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic |
| &_is_alive_closure, // closure for liveness info |
| false); // next field updates do not need write barrier |
| // Initialize the _ref_processor field of CMSGen |
| _cmsGen->set_ref_processor(_ref_processor); |
| |
| // Allocate a dummy ref processor for perm gen. |
| ReferenceProcessor* rp2 = new ReferenceProcessor(); |
| if (rp2 == NULL) { |
| vm_exit_during_initialization("Could not allocate ReferenceProcessor object"); |
| } |
| _permGen->set_ref_processor(rp2); |
| } |
| } |
| |
| CMSAdaptiveSizePolicy* CMSCollector::size_policy() { |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| assert(gch->kind() == CollectedHeap::GenCollectedHeap, |
| "Wrong type of heap"); |
| CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*) |
| gch->gen_policy()->size_policy(); |
| assert(sp->is_gc_cms_adaptive_size_policy(), |
| "Wrong type of size policy"); |
| return sp; |
| } |
| |
| CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() { |
| CMSGCAdaptivePolicyCounters* results = |
| (CMSGCAdaptivePolicyCounters*) collector_policy()->counters(); |
| assert( |
| results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind, |
| "Wrong gc policy counter kind"); |
| return results; |
| } |
| |
| |
| void ConcurrentMarkSweepGeneration::initialize_performance_counters() { |
| |
| const char* gen_name = "old"; |
| |
| // Generation Counters - generation 1, 1 subspace |
| _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space); |
| |
| _space_counters = new GSpaceCounters(gen_name, 0, |
| _virtual_space.reserved_size(), |
| this, _gen_counters); |
| } |
| |
| CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha): |
| _cms_gen(cms_gen) |
| { |
| assert(alpha <= 100, "bad value"); |
| _saved_alpha = alpha; |
| |
| // Initialize the alphas to the bootstrap value of 100. |
| _gc0_alpha = _cms_alpha = 100; |
| |
| _cms_begin_time.update(); |
| _cms_end_time.update(); |
| |
| _gc0_duration = 0.0; |
| _gc0_period = 0.0; |
| _gc0_promoted = 0; |
| |
| _cms_duration = 0.0; |
| _cms_period = 0.0; |
| _cms_allocated = 0; |
| |
| _cms_used_at_gc0_begin = 0; |
| _cms_used_at_gc0_end = 0; |
| _allow_duty_cycle_reduction = false; |
| _valid_bits = 0; |
| _icms_duty_cycle = CMSIncrementalDutyCycle; |
| } |
| |
| double CMSStats::cms_free_adjustment_factor(size_t free) const { |
| // TBD: CR 6909490 |
| return 1.0; |
| } |
| |
| void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) { |
| } |
| |
| // If promotion failure handling is on use |
| // the padded average size of the promotion for each |
| // young generation collection. |
| double CMSStats::time_until_cms_gen_full() const { |
| size_t cms_free = _cms_gen->cmsSpace()->free(); |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(), |
| (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average()); |
| if (cms_free > expected_promotion) { |
| // Start a cms collection if there isn't enough space to promote |
| // for the next minor collection. Use the padded average as |
| // a safety factor. |
| cms_free -= expected_promotion; |
| |
| // Adjust by the safety factor. |
| double cms_free_dbl = (double)cms_free; |
| double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0; |
| // Apply a further correction factor which tries to adjust |
| // for recent occurance of concurrent mode failures. |
| cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free); |
| cms_free_dbl = cms_free_dbl * cms_adjustment; |
| |
| if (PrintGCDetails && Verbose) { |
| gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free " |
| SIZE_FORMAT " expected_promotion " SIZE_FORMAT, |
| cms_free, expected_promotion); |
| gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f", |
| cms_free_dbl, cms_consumption_rate() + 1.0); |
| } |
| // Add 1 in case the consumption rate goes to zero. |
| return cms_free_dbl / (cms_consumption_rate() + 1.0); |
| } |
| return 0.0; |
| } |
| |
| // Compare the duration of the cms collection to the |
| // time remaining before the cms generation is empty. |
| // Note that the time from the start of the cms collection |
| // to the start of the cms sweep (less than the total |
| // duration of the cms collection) can be used. This |
| // has been tried and some applications experienced |
| // promotion failures early in execution. This was |
| // possibly because the averages were not accurate |
| // enough at the beginning. |
| double CMSStats::time_until_cms_start() const { |
| // We add "gc0_period" to the "work" calculation |
| // below because this query is done (mostly) at the |
| // end of a scavenge, so we need to conservatively |
| // account for that much possible delay |
| // in the query so as to avoid concurrent mode failures |
| // due to starting the collection just a wee bit too |
| // late. |
| double work = cms_duration() + gc0_period(); |
| double deadline = time_until_cms_gen_full(); |
| // If a concurrent mode failure occurred recently, we want to be |
| // more conservative and halve our expected time_until_cms_gen_full() |
| if (work > deadline) { |
| if (Verbose && PrintGCDetails) { |
| gclog_or_tty->print( |
| " CMSCollector: collect because of anticipated promotion " |
| "before full %3.7f + %3.7f > %3.7f ", cms_duration(), |
| gc0_period(), time_until_cms_gen_full()); |
| } |
| return 0.0; |
| } |
| return work - deadline; |
| } |
| |
| // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the |
| // amount of change to prevent wild oscillation. |
| unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle, |
| unsigned int new_duty_cycle) { |
| assert(old_duty_cycle <= 100, "bad input value"); |
| assert(new_duty_cycle <= 100, "bad input value"); |
| |
| // Note: use subtraction with caution since it may underflow (values are |
| // unsigned). Addition is safe since we're in the range 0-100. |
| unsigned int damped_duty_cycle = new_duty_cycle; |
| if (new_duty_cycle < old_duty_cycle) { |
| const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U); |
| if (new_duty_cycle + largest_delta < old_duty_cycle) { |
| damped_duty_cycle = old_duty_cycle - largest_delta; |
| } |
| } else if (new_duty_cycle > old_duty_cycle) { |
| const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U); |
| if (new_duty_cycle > old_duty_cycle + largest_delta) { |
| damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U); |
| } |
| } |
| assert(damped_duty_cycle <= 100, "invalid duty cycle computed"); |
| |
| if (CMSTraceIncrementalPacing) { |
| gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ", |
| old_duty_cycle, new_duty_cycle, damped_duty_cycle); |
| } |
| return damped_duty_cycle; |
| } |
| |
| unsigned int CMSStats::icms_update_duty_cycle_impl() { |
| assert(CMSIncrementalPacing && valid(), |
| "should be handled in icms_update_duty_cycle()"); |
| |
| double cms_time_so_far = cms_timer().seconds(); |
| double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M; |
| double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far); |
| |
| // Avoid division by 0. |
| double time_until_full = MAX2(time_until_cms_gen_full(), 0.01); |
| double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full; |
| |
| unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U); |
| if (new_duty_cycle > _icms_duty_cycle) { |
| // Avoid very small duty cycles (1 or 2); 0 is allowed. |
| if (new_duty_cycle > 2) { |
| _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, |
| new_duty_cycle); |
| } |
| } else if (_allow_duty_cycle_reduction) { |
| // The duty cycle is reduced only once per cms cycle (see record_cms_end()). |
| new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle); |
| // Respect the minimum duty cycle. |
| unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin; |
| _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle); |
| } |
| |
| if (PrintGCDetails || CMSTraceIncrementalPacing) { |
| gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle); |
| } |
| |
| _allow_duty_cycle_reduction = false; |
| return _icms_duty_cycle; |
| } |
| |
| #ifndef PRODUCT |
| void CMSStats::print_on(outputStream *st) const { |
| st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha); |
| st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT, |
| gc0_duration(), gc0_period(), gc0_promoted()); |
| st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT, |
| cms_duration(), cms_duration_per_mb(), |
| cms_period(), cms_allocated()); |
| st->print(",cms_since_beg=%g,cms_since_end=%g", |
| cms_time_since_begin(), cms_time_since_end()); |
| st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT, |
| _cms_used_at_gc0_begin, _cms_used_at_gc0_end); |
| if (CMSIncrementalMode) { |
| st->print(",dc=%d", icms_duty_cycle()); |
| } |
| |
| if (valid()) { |
| st->print(",promo_rate=%g,cms_alloc_rate=%g", |
| promotion_rate(), cms_allocation_rate()); |
| st->print(",cms_consumption_rate=%g,time_until_full=%g", |
| cms_consumption_rate(), time_until_cms_gen_full()); |
| } |
| st->print(" "); |
| } |
| #endif // #ifndef PRODUCT |
| |
| CMSCollector::CollectorState CMSCollector::_collectorState = |
| CMSCollector::Idling; |
| bool CMSCollector::_foregroundGCIsActive = false; |
| bool CMSCollector::_foregroundGCShouldWait = false; |
| |
| CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen, |
| ConcurrentMarkSweepGeneration* permGen, |
| CardTableRS* ct, |
| ConcurrentMarkSweepPolicy* cp): |
| _cmsGen(cmsGen), |
| _permGen(permGen), |
| _ct(ct), |
| _ref_processor(NULL), // will be set later |
| _conc_workers(NULL), // may be set later |
| _abort_preclean(false), |
| _start_sampling(false), |
| _between_prologue_and_epilogue(false), |
| _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"), |
| _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"), |
| _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize), |
| -1 /* lock-free */, "No_lock" /* dummy */), |
| _modUnionClosure(&_modUnionTable), |
| _modUnionClosurePar(&_modUnionTable), |
| // Adjust my span to cover old (cms) gen and perm gen |
| _span(cmsGen->reserved()._union(permGen->reserved())), |
| // Construct the is_alive_closure with _span & markBitMap |
| _is_alive_closure(_span, &_markBitMap), |
| _restart_addr(NULL), |
| _overflow_list(NULL), |
| _stats(cmsGen), |
| _eden_chunk_array(NULL), // may be set in ctor body |
| _eden_chunk_capacity(0), // -- ditto -- |
| _eden_chunk_index(0), // -- ditto -- |
| _survivor_plab_array(NULL), // -- ditto -- |
| _survivor_chunk_array(NULL), // -- ditto -- |
| _survivor_chunk_capacity(0), // -- ditto -- |
| _survivor_chunk_index(0), // -- ditto -- |
| _ser_pmc_preclean_ovflw(0), |
| _ser_kac_preclean_ovflw(0), |
| _ser_pmc_remark_ovflw(0), |
| _par_pmc_remark_ovflw(0), |
| _ser_kac_ovflw(0), |
| _par_kac_ovflw(0), |
| #ifndef PRODUCT |
| _num_par_pushes(0), |
| #endif |
| _collection_count_start(0), |
| _verifying(false), |
| _icms_start_limit(NULL), |
| _icms_stop_limit(NULL), |
| _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"), |
| _completed_initialization(false), |
| _collector_policy(cp), |
| _should_unload_classes(false), |
| _concurrent_cycles_since_last_unload(0), |
| _roots_scanning_options(0), |
| _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding), |
| _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding) |
| { |
| if (ExplicitGCInvokesConcurrentAndUnloadsClasses) { |
| ExplicitGCInvokesConcurrent = true; |
| } |
| // Now expand the span and allocate the collection support structures |
| // (MUT, marking bit map etc.) to cover both generations subject to |
| // collection. |
| |
| // First check that _permGen is adjacent to _cmsGen and above it. |
| assert( _cmsGen->reserved().word_size() > 0 |
| && _permGen->reserved().word_size() > 0, |
| "generations should not be of zero size"); |
| assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(), |
| "_cmsGen and _permGen should not overlap"); |
| assert(_cmsGen->reserved().end() == _permGen->reserved().start(), |
| "_cmsGen->end() different from _permGen->start()"); |
| |
| // For use by dirty card to oop closures. |
| _cmsGen->cmsSpace()->set_collector(this); |
| _permGen->cmsSpace()->set_collector(this); |
| |
| // Allocate MUT and marking bit map |
| { |
| MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag); |
| if (!_markBitMap.allocate(_span)) { |
| warning("Failed to allocate CMS Bit Map"); |
| return; |
| } |
| assert(_markBitMap.covers(_span), "_markBitMap inconsistency?"); |
| } |
| { |
| _modUnionTable.allocate(_span); |
| assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?"); |
| } |
| |
| if (!_markStack.allocate(MarkStackSize)) { |
| warning("Failed to allocate CMS Marking Stack"); |
| return; |
| } |
| if (!_revisitStack.allocate(CMSRevisitStackSize)) { |
| warning("Failed to allocate CMS Revisit Stack"); |
| return; |
| } |
| |
| // Support for multi-threaded concurrent phases |
| if (CMSConcurrentMTEnabled) { |
| if (FLAG_IS_DEFAULT(ConcGCThreads)) { |
| // just for now |
| FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4); |
| } |
| if (ConcGCThreads > 1) { |
| _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads", |
| ConcGCThreads, true); |
| if (_conc_workers == NULL) { |
| warning("GC/CMS: _conc_workers allocation failure: " |
| "forcing -CMSConcurrentMTEnabled"); |
| CMSConcurrentMTEnabled = false; |
| } else { |
| _conc_workers->initialize_workers(); |
| } |
| } else { |
| CMSConcurrentMTEnabled = false; |
| } |
| } |
| if (!CMSConcurrentMTEnabled) { |
| ConcGCThreads = 0; |
| } else { |
| // Turn off CMSCleanOnEnter optimization temporarily for |
| // the MT case where it's not fixed yet; see 6178663. |
| CMSCleanOnEnter = false; |
| } |
| assert((_conc_workers != NULL) == (ConcGCThreads > 1), |
| "Inconsistency"); |
| |
| // Parallel task queues; these are shared for the |
| // concurrent and stop-world phases of CMS, but |
| // are not shared with parallel scavenge (ParNew). |
| { |
| uint i; |
| uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads); |
| |
| if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled |
| || ParallelRefProcEnabled) |
| && num_queues > 0) { |
| _task_queues = new OopTaskQueueSet(num_queues); |
| if (_task_queues == NULL) { |
| warning("task_queues allocation failure."); |
| return; |
| } |
| _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues); |
| if (_hash_seed == NULL) { |
| warning("_hash_seed array allocation failure"); |
| return; |
| } |
| |
| typedef Padded<OopTaskQueue> PaddedOopTaskQueue; |
| for (i = 0; i < num_queues; i++) { |
| PaddedOopTaskQueue *q = new PaddedOopTaskQueue(); |
| if (q == NULL) { |
| warning("work_queue allocation failure."); |
| return; |
| } |
| _task_queues->register_queue(i, q); |
| } |
| for (i = 0; i < num_queues; i++) { |
| _task_queues->queue(i)->initialize(); |
| _hash_seed[i] = 17; // copied from ParNew |
| } |
| } |
| } |
| |
| _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio); |
| _permGen->init_initiating_occupancy(CMSInitiatingPermOccupancyFraction, CMSTriggerPermRatio); |
| |
| // Clip CMSBootstrapOccupancy between 0 and 100. |
| _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy))) |
| /(double)100; |
| |
| _full_gcs_since_conc_gc = 0; |
| |
| // Now tell CMS generations the identity of their collector |
| ConcurrentMarkSweepGeneration::set_collector(this); |
| |
| // Create & start a CMS thread for this CMS collector |
| _cmsThread = ConcurrentMarkSweepThread::start(this); |
| assert(cmsThread() != NULL, "CMS Thread should have been created"); |
| assert(cmsThread()->collector() == this, |
| "CMS Thread should refer to this gen"); |
| assert(CGC_lock != NULL, "Where's the CGC_lock?"); |
| |
| // Support for parallelizing young gen rescan |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| _young_gen = gch->prev_gen(_cmsGen); |
| if (gch->supports_inline_contig_alloc()) { |
| _top_addr = gch->top_addr(); |
| _end_addr = gch->end_addr(); |
| assert(_young_gen != NULL, "no _young_gen"); |
| _eden_chunk_index = 0; |
| _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain; |
| _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity); |
| if (_eden_chunk_array == NULL) { |
| _eden_chunk_capacity = 0; |
| warning("GC/CMS: _eden_chunk_array allocation failure"); |
| } |
| } |
| assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error"); |
| |
| // Support for parallelizing survivor space rescan |
| if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) { |
| const size_t max_plab_samples = |
| ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize; |
| |
| _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads); |
| _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples); |
| _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads); |
| if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL |
| || _cursor == NULL) { |
| warning("Failed to allocate survivor plab/chunk array"); |
| if (_survivor_plab_array != NULL) { |
| FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array); |
| _survivor_plab_array = NULL; |
| } |
| if (_survivor_chunk_array != NULL) { |
| FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array); |
| _survivor_chunk_array = NULL; |
| } |
| if (_cursor != NULL) { |
| FREE_C_HEAP_ARRAY(size_t, _cursor); |
| _cursor = NULL; |
| } |
| } else { |
| _survivor_chunk_capacity = 2*max_plab_samples; |
| for (uint i = 0; i < ParallelGCThreads; i++) { |
| HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples); |
| if (vec == NULL) { |
| warning("Failed to allocate survivor plab array"); |
| for (int j = i; j > 0; j--) { |
| FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array()); |
| } |
| FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array); |
| FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array); |
| _survivor_plab_array = NULL; |
| _survivor_chunk_array = NULL; |
| _survivor_chunk_capacity = 0; |
| break; |
| } else { |
| ChunkArray* cur = |
| ::new (&_survivor_plab_array[i]) ChunkArray(vec, |
| max_plab_samples); |
| assert(cur->end() == 0, "Should be 0"); |
| assert(cur->array() == vec, "Should be vec"); |
| assert(cur->capacity() == max_plab_samples, "Error"); |
| } |
| } |
| } |
| } |
| assert( ( _survivor_plab_array != NULL |
| && _survivor_chunk_array != NULL) |
| || ( _survivor_chunk_capacity == 0 |
| && _survivor_chunk_index == 0), |
| "Error"); |
| |
| // Choose what strong roots should be scanned depending on verification options |
| // and perm gen collection mode. |
| if (!CMSClassUnloadingEnabled) { |
| // If class unloading is disabled we want to include all classes into the root set. |
| add_root_scanning_option(SharedHeap::SO_AllClasses); |
| } else { |
| add_root_scanning_option(SharedHeap::SO_SystemClasses); |
| } |
| |
| NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;) |
| _gc_counters = new CollectorCounters("CMS", 1); |
| _completed_initialization = true; |
| _inter_sweep_timer.start(); // start of time |
| #ifdef SPARC |
| // Issue a stern warning, but allow use for experimentation and debugging. |
| if (VM_Version::is_sun4v() && UseMemSetInBOT) { |
| assert(!FLAG_IS_DEFAULT(UseMemSetInBOT), "Error"); |
| warning("Experimental flag -XX:+UseMemSetInBOT is known to cause instability" |
| " on sun4v; please understand that you are using at your own risk!"); |
| } |
| #endif |
| } |
| |
| const char* ConcurrentMarkSweepGeneration::name() const { |
| return "concurrent mark-sweep generation"; |
| } |
| void ConcurrentMarkSweepGeneration::update_counters() { |
| if (UsePerfData) { |
| _space_counters->update_all(); |
| _gen_counters->update_all(); |
| } |
| } |
| |
| // this is an optimized version of update_counters(). it takes the |
| // used value as a parameter rather than computing it. |
| // |
| void ConcurrentMarkSweepGeneration::update_counters(size_t used) { |
| if (UsePerfData) { |
| _space_counters->update_used(used); |
| _space_counters->update_capacity(); |
| _gen_counters->update_all(); |
| } |
| } |
| |
| void ConcurrentMarkSweepGeneration::print() const { |
| Generation::print(); |
| cmsSpace()->print(); |
| } |
| |
| #ifndef PRODUCT |
| void ConcurrentMarkSweepGeneration::print_statistics() { |
| cmsSpace()->printFLCensus(0); |
| } |
| #endif |
| |
| void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) { |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| if (PrintGCDetails) { |
| if (Verbose) { |
| gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]", |
| level(), short_name(), s, used(), capacity()); |
| } else { |
| gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]", |
| level(), short_name(), s, used() / K, capacity() / K); |
| } |
| } |
| if (Verbose) { |
| gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")", |
| gch->used(), gch->capacity()); |
| } else { |
| gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)", |
| gch->used() / K, gch->capacity() / K); |
| } |
| } |
| |
| size_t |
| ConcurrentMarkSweepGeneration::contiguous_available() const { |
| // dld proposes an improvement in precision here. If the committed |
| // part of the space ends in a free block we should add that to |
| // uncommitted size in the calculation below. Will make this |
| // change later, staying with the approximation below for the |
| // time being. -- ysr. |
| return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc()); |
| } |
| |
| size_t |
| ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const { |
| return _cmsSpace->max_alloc_in_words() * HeapWordSize; |
| } |
| |
| size_t ConcurrentMarkSweepGeneration::max_available() const { |
| return free() + _virtual_space.uncommitted_size(); |
| } |
| |
| bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const { |
| size_t available = max_available(); |
| size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average(); |
| bool res = (available >= av_promo) || (available >= max_promotion_in_bytes); |
| if (Verbose && PrintGCDetails) { |
| gclog_or_tty->print_cr( |
| "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT")," |
| "max_promo("SIZE_FORMAT")", |
| res? "":" not", available, res? ">=":"<", |
| av_promo, max_promotion_in_bytes); |
| } |
| return res; |
| } |
| |
| // At a promotion failure dump information on block layout in heap |
| // (cms old generation). |
| void ConcurrentMarkSweepGeneration::promotion_failure_occurred() { |
| if (CMSDumpAtPromotionFailure) { |
| cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty); |
| } |
| } |
| |
| CompactibleSpace* |
| ConcurrentMarkSweepGeneration::first_compaction_space() const { |
| return _cmsSpace; |
| } |
| |
| void ConcurrentMarkSweepGeneration::reset_after_compaction() { |
| // Clear the promotion information. These pointers can be adjusted |
| // along with all the other pointers into the heap but |
| // compaction is expected to be a rare event with |
| // a heap using cms so don't do it without seeing the need. |
| if (CollectedHeap::use_parallel_gc_threads()) { |
| for (uint i = 0; i < ParallelGCThreads; i++) { |
| _par_gc_thread_states[i]->promo.reset(); |
| } |
| } |
| } |
| |
| void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) { |
| blk->do_space(_cmsSpace); |
| } |
| |
| void ConcurrentMarkSweepGeneration::compute_new_size() { |
| assert_locked_or_safepoint(Heap_lock); |
| |
| // If incremental collection failed, we just want to expand |
| // to the limit. |
| if (incremental_collection_failed()) { |
| clear_incremental_collection_failed(); |
| grow_to_reserved(); |
| return; |
| } |
| |
| size_t expand_bytes = 0; |
| double free_percentage = ((double) free()) / capacity(); |
| double desired_free_percentage = (double) MinHeapFreeRatio / 100; |
| double maximum_free_percentage = (double) MaxHeapFreeRatio / 100; |
| |
| // compute expansion delta needed for reaching desired free percentage |
| if (free_percentage < desired_free_percentage) { |
| size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); |
| assert(desired_capacity >= capacity(), "invalid expansion size"); |
| expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes); |
| } |
| if (expand_bytes > 0) { |
| if (PrintGCDetails && Verbose) { |
| size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); |
| gclog_or_tty->print_cr("\nFrom compute_new_size: "); |
| gclog_or_tty->print_cr(" Free fraction %f", free_percentage); |
| gclog_or_tty->print_cr(" Desired free fraction %f", |
| desired_free_percentage); |
| gclog_or_tty->print_cr(" Maximum free fraction %f", |
| maximum_free_percentage); |
| gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000); |
| gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT, |
| desired_capacity/1000); |
| int prev_level = level() - 1; |
| if (prev_level >= 0) { |
| size_t prev_size = 0; |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| Generation* prev_gen = gch->_gens[prev_level]; |
| prev_size = prev_gen->capacity(); |
| gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT, |
| prev_size/1000); |
| } |
| gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT, |
| unsafe_max_alloc_nogc()/1000); |
| gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT, |
| contiguous_available()/1000); |
| gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)", |
| expand_bytes); |
| } |
| // safe if expansion fails |
| expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio); |
| if (PrintGCDetails && Verbose) { |
| gclog_or_tty->print_cr(" Expanded free fraction %f", |
| ((double) free()) / capacity()); |
| } |
| } |
| } |
| |
| Mutex* ConcurrentMarkSweepGeneration::freelistLock() const { |
| return cmsSpace()->freelistLock(); |
| } |
| |
| HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, |
| bool tlab) { |
| CMSSynchronousYieldRequest yr; |
| MutexLockerEx x(freelistLock(), |
| Mutex::_no_safepoint_check_flag); |
| return have_lock_and_allocate(size, tlab); |
| } |
| |
| HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size, |
| bool tlab /* ignored */) { |
| assert_lock_strong(freelistLock()); |
| size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size); |
| HeapWord* res = cmsSpace()->allocate(adjustedSize); |
| // Allocate the object live (grey) if the background collector has |
| // started marking. This is necessary because the marker may |
| // have passed this address and consequently this object will |
| // not otherwise be greyed and would be incorrectly swept up. |
| // Note that if this object contains references, the writing |
| // of those references will dirty the card containing this object |
| // allowing the object to be blackened (and its references scanned) |
| // either during a preclean phase or at the final checkpoint. |
| if (res != NULL) { |
| // We may block here with an uninitialized object with |
| // its mark-bit or P-bits not yet set. Such objects need |
| // to be safely navigable by block_start(). |
| assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here."); |
| assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size"); |
| collector()->direct_allocated(res, adjustedSize); |
| _direct_allocated_words += adjustedSize; |
| // allocation counters |
| NOT_PRODUCT( |
| _numObjectsAllocated++; |
| _numWordsAllocated += (int)adjustedSize; |
| ) |
| } |
| return res; |
| } |
| |
| // In the case of direct allocation by mutators in a generation that |
| // is being concurrently collected, the object must be allocated |
| // live (grey) if the background collector has started marking. |
| // This is necessary because the marker may |
| // have passed this address and consequently this object will |
| // not otherwise be greyed and would be incorrectly swept up. |
| // Note that if this object contains references, the writing |
| // of those references will dirty the card containing this object |
| // allowing the object to be blackened (and its references scanned) |
| // either during a preclean phase or at the final checkpoint. |
| void CMSCollector::direct_allocated(HeapWord* start, size_t size) { |
| assert(_markBitMap.covers(start, size), "Out of bounds"); |
| if (_collectorState >= Marking) { |
| MutexLockerEx y(_markBitMap.lock(), |
| Mutex::_no_safepoint_check_flag); |
| // [see comments preceding SweepClosure::do_blk() below for details] |
| // 1. need to mark the object as live so it isn't collected |
| // 2. need to mark the 2nd bit to indicate the object may be uninitialized |
| // 3. need to mark the end of the object so marking, precleaning or sweeping |
| // can skip over uninitialized or unparsable objects. An allocated |
| // object is considered uninitialized for our purposes as long as |
| // its klass word is NULL. (Unparsable objects are those which are |
| // initialized in the sense just described, but whose sizes can still |
| // not be correctly determined. Note that the class of unparsable objects |
| // can only occur in the perm gen. All old gen objects are parsable |
| // as soon as they are initialized.) |
| _markBitMap.mark(start); // object is live |
| _markBitMap.mark(start + 1); // object is potentially uninitialized? |
| _markBitMap.mark(start + size - 1); |
| // mark end of object |
| } |
| // check that oop looks uninitialized |
| assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL"); |
| } |
| |
| void CMSCollector::promoted(bool par, HeapWord* start, |
| bool is_obj_array, size_t obj_size) { |
| assert(_markBitMap.covers(start), "Out of bounds"); |
| // See comment in direct_allocated() about when objects should |
| // be allocated live. |
| if (_collectorState >= Marking) { |
| // we already hold the marking bit map lock, taken in |
| // the prologue |
| if (par) { |
| _markBitMap.par_mark(start); |
| } else { |
| _markBitMap.mark(start); |
| } |
| // We don't need to mark the object as uninitialized (as |
| // in direct_allocated above) because this is being done with the |
| // world stopped and the object will be initialized by the |
| // time the marking, precleaning or sweeping get to look at it. |
| // But see the code for copying objects into the CMS generation, |
| // where we need to ensure that concurrent readers of the |
| // block offset table are able to safely navigate a block that |
| // is in flux from being free to being allocated (and in |
| // transition while being copied into) and subsequently |
| // becoming a bona-fide object when the copy/promotion is complete. |
| assert(SafepointSynchronize::is_at_safepoint(), |
| "expect promotion only at safepoints"); |
| |
| if (_collectorState < Sweeping) { |
| // Mark the appropriate cards in the modUnionTable, so that |
| // this object gets scanned before the sweep. If this is |
| // not done, CMS generation references in the object might |
| // not get marked. |
| // For the case of arrays, which are otherwise precisely |
| // marked, we need to dirty the entire array, not just its head. |
| if (is_obj_array) { |
| // The [par_]mark_range() method expects mr.end() below to |
| // be aligned to the granularity of a bit's representation |
| // in the heap. In the case of the MUT below, that's a |
| // card size. |
| MemRegion mr(start, |
| (HeapWord*)round_to((intptr_t)(start + obj_size), |
| CardTableModRefBS::card_size /* bytes */)); |
| if (par) { |
| _modUnionTable.par_mark_range(mr); |
| } else { |
| _modUnionTable.mark_range(mr); |
| } |
| } else { // not an obj array; we can just mark the head |
| if (par) { |
| _modUnionTable.par_mark(start); |
| } else { |
| _modUnionTable.mark(start); |
| } |
| } |
| } |
| } |
| } |
| |
| static inline size_t percent_of_space(Space* space, HeapWord* addr) |
| { |
| size_t delta = pointer_delta(addr, space->bottom()); |
| return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize)); |
| } |
| |
| void CMSCollector::icms_update_allocation_limits() |
| { |
| Generation* gen0 = GenCollectedHeap::heap()->get_gen(0); |
| EdenSpace* eden = gen0->as_DefNewGeneration()->eden(); |
| |
| const unsigned int duty_cycle = stats().icms_update_duty_cycle(); |
| if (CMSTraceIncrementalPacing) { |
| stats().print(); |
| } |
| |
| assert(duty_cycle <= 100, "invalid duty cycle"); |
| if (duty_cycle != 0) { |
| // The duty_cycle is a percentage between 0 and 100; convert to words and |
| // then compute the offset from the endpoints of the space. |
| size_t free_words = eden->free() / HeapWordSize; |
| double free_words_dbl = (double)free_words; |
| size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0); |
| size_t offset_words = (free_words - duty_cycle_words) / 2; |
| |
| _icms_start_limit = eden->top() + offset_words; |
| _icms_stop_limit = eden->end() - offset_words; |
| |
| // The limits may be adjusted (shifted to the right) by |
| // CMSIncrementalOffset, to allow the application more mutator time after a |
| // young gen gc (when all mutators were stopped) and before CMS starts and |
| // takes away one or more cpus. |
| if (CMSIncrementalOffset != 0) { |
| double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0; |
| size_t adjustment = (size_t)adjustment_dbl; |
| HeapWord* tmp_stop = _icms_stop_limit + adjustment; |
| if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) { |
| _icms_start_limit += adjustment; |
| _icms_stop_limit = tmp_stop; |
| } |
| } |
| } |
| if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) { |
| _icms_start_limit = _icms_stop_limit = eden->end(); |
| } |
| |
| // Install the new start limit. |
| eden->set_soft_end(_icms_start_limit); |
| |
| if (CMSTraceIncrementalMode) { |
| gclog_or_tty->print(" icms alloc limits: " |
| PTR_FORMAT "," PTR_FORMAT |
| " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ", |
| _icms_start_limit, _icms_stop_limit, |
| percent_of_space(eden, _icms_start_limit), |
| percent_of_space(eden, _icms_stop_limit)); |
| if (Verbose) { |
| gclog_or_tty->print("eden: "); |
| eden->print_on(gclog_or_tty); |
| } |
| } |
| } |
| |
| // Any changes here should try to maintain the invariant |
| // that if this method is called with _icms_start_limit |
| // and _icms_stop_limit both NULL, then it should return NULL |
| // and not notify the icms thread. |
| HeapWord* |
| CMSCollector::allocation_limit_reached(Space* space, HeapWord* top, |
| size_t word_size) |
| { |
| // A start_limit equal to end() means the duty cycle is 0, so treat that as a |
| // nop. |
| if (CMSIncrementalMode && _icms_start_limit != space->end()) { |
| if (top <= _icms_start_limit) { |
| if (CMSTraceIncrementalMode) { |
| space->print_on(gclog_or_tty); |
| gclog_or_tty->stamp(); |
| gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT |
| ", new limit=" PTR_FORMAT |
| " (" SIZE_FORMAT "%%)", |
| top, _icms_stop_limit, |
| percent_of_space(space, _icms_stop_limit)); |
| } |
| ConcurrentMarkSweepThread::start_icms(); |
| assert(top < _icms_stop_limit, "Tautology"); |
| if (word_size < pointer_delta(_icms_stop_limit, top)) { |
| return _icms_stop_limit; |
| } |
| |
| // The allocation will cross both the _start and _stop limits, so do the |
| // stop notification also and return end(). |
| if (CMSTraceIncrementalMode) { |
| space->print_on(gclog_or_tty); |
| gclog_or_tty->stamp(); |
| gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT |
| ", new limit=" PTR_FORMAT |
| " (" SIZE_FORMAT "%%)", |
| top, space->end(), |
| percent_of_space(space, space->end())); |
| } |
| ConcurrentMarkSweepThread::stop_icms(); |
| return space->end(); |
| } |
| |
| if (top <= _icms_stop_limit) { |
| if (CMSTraceIncrementalMode) { |
| space->print_on(gclog_or_tty); |
| gclog_or_tty->stamp(); |
| gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT |
| ", new limit=" PTR_FORMAT |
| " (" SIZE_FORMAT "%%)", |
| top, space->end(), |
| percent_of_space(space, space->end())); |
| } |
| ConcurrentMarkSweepThread::stop_icms(); |
| return space->end(); |
| } |
| |
| if (CMSTraceIncrementalMode) { |
| space->print_on(gclog_or_tty); |
| gclog_or_tty->stamp(); |
| gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT |
| ", new limit=" PTR_FORMAT, |
| top, NULL); |
| } |
| } |
| |
| return NULL; |
| } |
| |
| oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) { |
| assert(obj_size == (size_t)obj->size(), "bad obj_size passed in"); |
| // allocate, copy and if necessary update promoinfo -- |
| // delegate to underlying space. |
| assert_lock_strong(freelistLock()); |
| |
| #ifndef PRODUCT |
| if (Universe::heap()->promotion_should_fail()) { |
| return NULL; |
| } |
| #endif // #ifndef PRODUCT |
| |
| oop res = _cmsSpace->promote(obj, obj_size); |
| if (res == NULL) { |
| // expand and retry |
| size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords |
| expand(s*HeapWordSize, MinHeapDeltaBytes, |
| CMSExpansionCause::_satisfy_promotion); |
| // Since there's currently no next generation, we don't try to promote |
| // into a more senior generation. |
| assert(next_gen() == NULL, "assumption, based upon which no attempt " |
| "is made to pass on a possibly failing " |
| "promotion to next generation"); |
| res = _cmsSpace->promote(obj, obj_size); |
| } |
| if (res != NULL) { |
| // See comment in allocate() about when objects should |
| // be allocated live. |
| assert(obj->is_oop(), "Will dereference klass pointer below"); |
| collector()->promoted(false, // Not parallel |
| (HeapWord*)res, obj->is_objArray(), obj_size); |
| // promotion counters |
| NOT_PRODUCT( |
| _numObjectsPromoted++; |
| _numWordsPromoted += |
| (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size())); |
| ) |
| } |
| return res; |
| } |
| |
| |
| HeapWord* |
| ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space, |
| HeapWord* top, |
| size_t word_sz) |
| { |
| return collector()->allocation_limit_reached(space, top, word_sz); |
| } |
| |
| // IMPORTANT: Notes on object size recognition in CMS. |
| // --------------------------------------------------- |
| // A block of storage in the CMS generation is always in |
| // one of three states. A free block (FREE), an allocated |
| // object (OBJECT) whose size() method reports the correct size, |
| // and an intermediate state (TRANSIENT) in which its size cannot |
| // be accurately determined. |
| // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS) |
| // ----------------------------------------------------- |
| // FREE: klass_word & 1 == 1; mark_word holds block size |
| // |
| // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0; |
| // obj->size() computes correct size |
| // [Perm Gen objects needs to be "parsable" before they can be navigated] |
| // |
| // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT |
| // |
| // STATE IDENTIFICATION: (64 bit+COOPS) |
| // ------------------------------------ |
| // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size |
| // |
| // OBJECT: klass_word installed; klass_word != 0; |
| // obj->size() computes correct size |
| // [Perm Gen comment above continues to hold] |
| // |
| // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT |
| // |
| // |
| // STATE TRANSITION DIAGRAM |
| // |
| // mut / parnew mut / parnew |
| // FREE --------------------> TRANSIENT ---------------------> OBJECT --| |
| // ^ | |
| // |------------------------ DEAD <------------------------------------| |
| // sweep mut |
| // |
| // While a block is in TRANSIENT state its size cannot be determined |
| // so readers will either need to come back later or stall until |
| // the size can be determined. Note that for the case of direct |
| // allocation, P-bits, when available, may be used to determine the |
| // size of an object that may not yet have been initialized. |
| |
| // Things to support parallel young-gen collection. |
| oop |
| ConcurrentMarkSweepGeneration::par_promote(int thread_num, |
| oop old, markOop m, |
| size_t word_sz) { |
| #ifndef PRODUCT |
| if (Universe::heap()->promotion_should_fail()) { |
| return NULL; |
| } |
| #endif // #ifndef PRODUCT |
| |
| CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; |
| PromotionInfo* promoInfo = &ps->promo; |
| // if we are tracking promotions, then first ensure space for |
| // promotion (including spooling space for saving header if necessary). |
| // then allocate and copy, then track promoted info if needed. |
| // When tracking (see PromotionInfo::track()), the mark word may |
| // be displaced and in this case restoration of the mark word |
| // occurs in the (oop_since_save_marks_)iterate phase. |
| if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) { |
| // Out of space for allocating spooling buffers; |
| // try expanding and allocating spooling buffers. |
| if (!expand_and_ensure_spooling_space(promoInfo)) { |
| return NULL; |
| } |
| } |
| assert(promoInfo->has_spooling_space(), "Control point invariant"); |
| const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz); |
| HeapWord* obj_ptr = ps->lab.alloc(alloc_sz); |
| if (obj_ptr == NULL) { |
| obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz); |
| if (obj_ptr == NULL) { |
| return NULL; |
| } |
| } |
| oop obj = oop(obj_ptr); |
| OrderAccess::storestore(); |
| assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); |
| assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); |
| // IMPORTANT: See note on object initialization for CMS above. |
| // Otherwise, copy the object. Here we must be careful to insert the |
| // klass pointer last, since this marks the block as an allocated object. |
| // Except with compressed oops it's the mark word. |
| HeapWord* old_ptr = (HeapWord*)old; |
| // Restore the mark word copied above. |
| obj->set_mark(m); |
| assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); |
| assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); |
| OrderAccess::storestore(); |
| |
| if (UseCompressedOops) { |
| // Copy gap missed by (aligned) header size calculation below |
| obj->set_klass_gap(old->klass_gap()); |
| } |
| if (word_sz > (size_t)oopDesc::header_size()) { |
| Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(), |
| obj_ptr + oopDesc::header_size(), |
| word_sz - oopDesc::header_size()); |
| } |
| |
| // Now we can track the promoted object, if necessary. We take care |
| // to delay the transition from uninitialized to full object |
| // (i.e., insertion of klass pointer) until after, so that it |
| // atomically becomes a promoted object. |
| if (promoInfo->tracking()) { |
| promoInfo->track((PromotedObject*)obj, old->klass()); |
| } |
| assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); |
| assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); |
| assert(old->is_oop(), "Will use and dereference old klass ptr below"); |
| |
| // Finally, install the klass pointer (this should be volatile). |
| OrderAccess::storestore(); |
| obj->set_klass(old->klass()); |
| // We should now be able to calculate the right size for this object |
| assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object"); |
| |
| collector()->promoted(true, // parallel |
| obj_ptr, old->is_objArray(), word_sz); |
| |
| NOT_PRODUCT( |
| Atomic::inc_ptr(&_numObjectsPromoted); |
| Atomic::add_ptr(alloc_sz, &_numWordsPromoted); |
| ) |
| |
| return obj; |
| } |
| |
| void |
| ConcurrentMarkSweepGeneration:: |
| par_promote_alloc_undo(int thread_num, |
| HeapWord* obj, size_t word_sz) { |
| // CMS does not support promotion undo. |
| ShouldNotReachHere(); |
| } |
| |
| void |
| ConcurrentMarkSweepGeneration:: |
| par_promote_alloc_done(int thread_num) { |
| CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; |
| ps->lab.retire(thread_num); |
| } |
| |
| void |
| ConcurrentMarkSweepGeneration:: |
| par_oop_since_save_marks_iterate_done(int thread_num) { |
| CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; |
| ParScanWithoutBarrierClosure* dummy_cl = NULL; |
| ps->promo.promoted_oops_iterate_nv(dummy_cl); |
| } |
| |
| // XXXPERM |
| bool ConcurrentMarkSweepGeneration::should_collect(bool full, |
| size_t size, |
| bool tlab) |
| { |
| // We allow a STW collection only if a full |
| // collection was requested. |
| return full || should_allocate(size, tlab); // FIX ME !!! |
| // This and promotion failure handling are connected at the |
| // hip and should be fixed by untying them. |
| } |
| |
| bool CMSCollector::shouldConcurrentCollect() { |
| if (_full_gc_requested) { |
| if (Verbose && PrintGCDetails) { |
| gclog_or_tty->print_cr("CMSCollector: collect because of explicit " |
| " gc request (or gc_locker)"); |
| } |
| return true; |
| } |
| |
| // For debugging purposes, change the type of collection. |
| // If the rotation is not on the concurrent collection |
| // type, don't start a concurrent collection. |
| NOT_PRODUCT( |
| if (RotateCMSCollectionTypes && |
| (_cmsGen->debug_collection_type() != |
| ConcurrentMarkSweepGeneration::Concurrent_collection_type)) { |
| assert(_cmsGen->debug_collection_type() != |
| ConcurrentMarkSweepGeneration::Unknown_collection_type, |
| "Bad cms collection type"); |
| return false; |
| } |
| ) |
| |
| FreelistLocker x(this); |
| // ------------------------------------------------------------------ |
| // Print out lots of information which affects the initiation of |
| // a collection. |
| if (PrintCMSInitiationStatistics && stats().valid()) { |
| gclog_or_tty->print("CMSCollector shouldConcurrentCollect: "); |
| gclog_or_tty->stamp(); |
| gclog_or_tty->print_cr(""); |
| stats().print_on(gclog_or_tty); |
| gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f", |
| stats().time_until_cms_gen_full()); |
| gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free()); |
| gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT, |
| _cmsGen->contiguous_available()); |
| gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate()); |
| gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate()); |
| gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy()); |
| gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy()); |
| gclog_or_tty->print_cr("initiatingPermOccupancy=%3.7f", _permGen->initiating_occupancy()); |
| } |
| // ------------------------------------------------------------------ |
| |
| // If the estimated time to complete a cms collection (cms_duration()) |
| // is less than the estimated time remaining until the cms generation |
| // is full, start a collection. |
| if (!UseCMSInitiatingOccupancyOnly) { |
| if (stats().valid()) { |
| if (stats().time_until_cms_start() == 0.0) { |
| return true; |
| } |
| } else { |
| // We want to conservatively collect somewhat early in order |
| // to try and "bootstrap" our CMS/promotion statistics; |
| // this branch will not fire after the first successful CMS |
| // collection because the stats should then be valid. |
| if (_cmsGen->occupancy() >= _bootstrap_occupancy) { |
| if (Verbose && PrintGCDetails) { |
| gclog_or_tty->print_cr( |
| " CMSCollector: collect for bootstrapping statistics:" |
| " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(), |
| _bootstrap_occupancy); |
| } |
| return true; |
| } |
| } |
| } |
| |
| // Otherwise, we start a collection cycle if either the perm gen or |
| // old gen want a collection cycle started. Each may use |
| // an appropriate criterion for making this decision. |
| // XXX We need to make sure that the gen expansion |
| // criterion dovetails well with this. XXX NEED TO FIX THIS |
| if (_cmsGen->should_concurrent_collect()) { |
| if (Verbose && PrintGCDetails) { |
| gclog_or_tty->print_cr("CMS old gen initiated"); |
| } |
| return true; |
| } |
| |
| // We start a collection if we believe an incremental collection may fail; |
| // this is not likely to be productive in practice because it's probably too |
| // late anyway. |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| assert(gch->collector_policy()->is_two_generation_policy(), |
| "You may want to check the correctness of the following"); |
| if (gch->incremental_collection_will_fail(true /* consult_young */)) { |
| if (Verbose && PrintGCDetails) { |
| gclog_or_tty->print("CMSCollector: collect because incremental collection will fail "); |
| } |
| return true; |
| } |
| |
| if (CMSClassUnloadingEnabled && _permGen->should_concurrent_collect()) { |
| bool res = update_should_unload_classes(); |
| if (res) { |
| if (Verbose && PrintGCDetails) { |
| gclog_or_tty->print_cr("CMS perm gen initiated"); |
| } |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| // Clear _expansion_cause fields of constituent generations |
| void CMSCollector::clear_expansion_cause() { |
| _cmsGen->clear_expansion_cause(); |
| _permGen->clear_expansion_cause(); |
| } |
| |
| // We should be conservative in starting a collection cycle. To |
| // start too eagerly runs the risk of collecting too often in the |
| // extreme. To collect too rarely falls back on full collections, |
| // which works, even if not optimum in terms of concurrent work. |
| // As a work around for too eagerly collecting, use the flag |
| // UseCMSInitiatingOccupancyOnly. This also has the advantage of |
| // giving the user an easily understandable way of controlling the |
| // collections. |
| // We want to start a new collection cycle if any of the following |
| // conditions hold: |
| // . our current occupancy exceeds the configured initiating occupancy |
| // for this generation, or |
| // . we recently needed to expand this space and have not, since that |
| // expansion, done a collection of this generation, or |
| // . the underlying space believes that it may be a good idea to initiate |
| // a concurrent collection (this may be based on criteria such as the |
| // following: the space uses linear allocation and linear allocation is |
| // going to fail, or there is believed to be excessive fragmentation in |
| // the generation, etc... or ... |
| // [.(currently done by CMSCollector::shouldConcurrentCollect() only for |
| // the case of the old generation, not the perm generation; see CR 6543076): |
| // we may be approaching a point at which allocation requests may fail because |
| // we will be out of sufficient free space given allocation rate estimates.] |
| bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const { |
| |
| assert_lock_strong(freelistLock()); |
| if (occupancy() > initiating_occupancy()) { |
| if (PrintGCDetails && Verbose) { |
| gclog_or_tty->print(" %s: collect because of occupancy %f / %f ", |
| short_name(), occupancy(), initiating_occupancy()); |
| } |
| return true; |
| } |
| if (UseCMSInitiatingOccupancyOnly) { |
| return false; |
| } |
| if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) { |
| if (PrintGCDetails && Verbose) { |
| gclog_or_tty->print(" %s: collect because expanded for allocation ", |
| short_name()); |
| } |
| return true; |
| } |
| if (_cmsSpace->should_concurrent_collect()) { |
| if (PrintGCDetails && Verbose) { |
| gclog_or_tty->print(" %s: collect because cmsSpace says so ", |
| short_name()); |
| } |
| return true; |
| } |
| return false; |
| } |
| |
| void ConcurrentMarkSweepGeneration::collect(bool full, |
| bool clear_all_soft_refs, |
| size_t size, |
| bool tlab) |
| { |
| collector()->collect(full, clear_all_soft_refs, size, tlab); |
| } |
| |
| void CMSCollector::collect(bool full, |
| bool clear_all_soft_refs, |
| size_t size, |
| bool tlab) |
| { |
| if (!UseCMSCollectionPassing && _collectorState > Idling) { |
| // For debugging purposes skip the collection if the state |
| // is not currently idle |
| if (TraceCMSState) { |
| gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d", |
| Thread::current(), full, _collectorState); |
| } |
| return; |
| } |
| |
| // The following "if" branch is present for defensive reasons. |
| // In the current uses of this interface, it can be replaced with: |
| // assert(!GC_locker.is_active(), "Can't be called otherwise"); |
| // But I am not placing that assert here to allow future |
| // generality in invoking this interface. |
| if (GC_locker::is_active()) { |
| // A consistency test for GC_locker |
| assert(GC_locker::needs_gc(), "Should have been set already"); |
| // Skip this foreground collection, instead |
| // expanding the heap if necessary. |
| // Need the free list locks for the call to free() in compute_new_size() |
| compute_new_size(); |
| return; |
| } |
| acquire_control_and_collect(full, clear_all_soft_refs); |
| _full_gcs_since_conc_gc++; |
| |
| } |
| |
| void CMSCollector::request_full_gc(unsigned int full_gc_count) { |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| unsigned int gc_count = gch->total_full_collections(); |
| if (gc_count == full_gc_count) { |
| MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag); |
| _full_gc_requested = true; |
| CGC_lock->notify(); // nudge CMS thread |
| } else { |
| assert(gc_count > full_gc_count, "Error: causal loop"); |
| } |
| } |
| |
| |
| // The foreground and background collectors need to coordinate in order |
| // to make sure that they do not mutually interfere with CMS collections. |
| // When a background collection is active, |
| // the foreground collector may need to take over (preempt) and |
| // synchronously complete an ongoing collection. Depending on the |
| // frequency of the background collections and the heap usage |
| // of the application, this preemption can be seldom or frequent. |
| // There are only certain |
| // points in the background collection that the "collection-baton" |
| // can be passed to the foreground collector. |
| // |
| // The foreground collector will wait for the baton before |
| // starting any part of the collection. The foreground collector |
| // will only wait at one location. |
| // |
| // The background collector will yield the baton before starting a new |
| // phase of the collection (e.g., before initial marking, marking from roots, |
| // precleaning, final re-mark, sweep etc.) This is normally done at the head |
| // of the loop which switches the phases. The background collector does some |
| // of the phases (initial mark, final re-mark) with the world stopped. |
| // Because of locking involved in stopping the world, |
| // the foreground collector should not block waiting for the background |
| // collector when it is doing a stop-the-world phase. The background |
| // collector will yield the baton at an additional point just before |
| // it enters a stop-the-world phase. Once the world is stopped, the |
| // background collector checks the phase of the collection. If the |
| // phase has not changed, it proceeds with the collection. If the |
| // phase has changed, it skips that phase of the collection. See |
| // the comments on the use of the Heap_lock in collect_in_background(). |
| // |
| // Variable used in baton passing. |
| // _foregroundGCIsActive - Set to true by the foreground collector when |
| // it wants the baton. The foreground clears it when it has finished |
| // the collection. |
| // _foregroundGCShouldWait - Set to true by the background collector |
| // when it is running. The foreground collector waits while |
| // _foregroundGCShouldWait is true. |
| // CGC_lock - monitor used to protect access to the above variables |
| // and to notify the foreground and background collectors. |
| // _collectorState - current state of the CMS collection. |
| // |
| // The foreground collector |
| // acquires the CGC_lock |
| // sets _foregroundGCIsActive |
| // waits on the CGC_lock for _foregroundGCShouldWait to be false |
| // various locks acquired in preparation for the collection |
| // are released so as not to block the background collector |
| // that is in the midst of a collection |
| // proceeds with the collection |
| // clears _foregroundGCIsActive |
| // returns |
| // |
| // The background collector in a loop iterating on the phases of the |
| // collection |
| // acquires the CGC_lock |
| // sets _foregroundGCShouldWait |
| // if _foregroundGCIsActive is set |
| // clears _foregroundGCShouldWait, notifies _CGC_lock |
| // waits on _CGC_lock for _foregroundGCIsActive to become false |
| // and exits the loop. |
| // otherwise |
| // proceed with that phase of the collection |
| // if the phase is a stop-the-world phase, |
| // yield the baton once more just before enqueueing |
| // the stop-world CMS operation (executed by the VM thread). |
| // returns after all phases of the collection are done |
| // |
| |
| void CMSCollector::acquire_control_and_collect(bool full, |
| bool clear_all_soft_refs) { |
| assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint"); |
| assert(!Thread::current()->is_ConcurrentGC_thread(), |
| "shouldn't try to acquire control from self!"); |
| |
| // Start the protocol for acquiring control of the |
| // collection from the background collector (aka CMS thread). |
| assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), |
| "VM thread should have CMS token"); |
| // Remember the possibly interrupted state of an ongoing |
| // concurrent collection |
| CollectorState first_state = _collectorState; |
| |
| // Signal to a possibly ongoing concurrent collection that |
| // we want to do a foreground collection. |
| _foregroundGCIsActive = true; |
| |
| // Disable incremental mode during a foreground collection. |
| ICMSDisabler icms_disabler; |
| |
| // release locks and wait for a notify from the background collector |
| // releasing the locks in only necessary for phases which |
| // do yields to improve the granularity of the collection. |
| assert_lock_strong(bitMapLock()); |
| // We need to lock the Free list lock for the space that we are |
| // currently collecting. |
| assert(haveFreelistLocks(), "Must be holding free list locks"); |
| bitMapLock()->unlock(); |
| releaseFreelistLocks(); |
| { |
| MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); |
| if (_foregroundGCShouldWait) { |
| // We are going to be waiting for action for the CMS thread; |
| // it had better not be gone (for instance at shutdown)! |
| assert(ConcurrentMarkSweepThread::cmst() != NULL, |
| "CMS thread must be running"); |
| // Wait here until the background collector gives us the go-ahead |
| ConcurrentMarkSweepThread::clear_CMS_flag( |
| ConcurrentMarkSweepThread::CMS_vm_has_token); // release token |
| // Get a possibly blocked CMS thread going: |
| // Note that we set _foregroundGCIsActive true above, |
| // without protection of the CGC_lock. |
| CGC_lock->notify(); |
| assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(), |
| "Possible deadlock"); |
| while (_foregroundGCShouldWait) { |
| // wait for notification |
| CGC_lock->wait(Mutex::_no_safepoint_check_flag); |
| // Possibility of delay/starvation here, since CMS token does |
| // not know to give priority to VM thread? Actually, i think |
| // there wouldn't be any delay/starvation, but the proof of |
| // that "fact" (?) appears non-trivial. XXX 20011219YSR |
| } |
| ConcurrentMarkSweepThread::set_CMS_flag( |
| ConcurrentMarkSweepThread::CMS_vm_has_token); |
| } |
| } |
| // The CMS_token is already held. Get back the other locks. |
| assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), |
| "VM thread should have CMS token"); |
| getFreelistLocks(); |
| bitMapLock()->lock_without_safepoint_check(); |
| if (TraceCMSState) { |
| gclog_or_tty->print_cr("CMS foreground collector has asked for control " |
| INTPTR_FORMAT " with first state %d", Thread::current(), first_state); |
| gclog_or_tty->print_cr(" gets control with state %d", _collectorState); |
| } |
| |
| // Check if we need to do a compaction, or if not, whether |
| // we need to start the mark-sweep from scratch. |
| bool should_compact = false; |
| bool should_start_over = false; |
| decide_foreground_collection_type(clear_all_soft_refs, |
| &should_compact, &should_start_over); |
| |
| NOT_PRODUCT( |
| if (RotateCMSCollectionTypes) { |
| if (_cmsGen->debug_collection_type() == |
| ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) { |
| should_compact = true; |
| } else if (_cmsGen->debug_collection_type() == |
| ConcurrentMarkSweepGeneration::MS_foreground_collection_type) { |
| should_compact = false; |
| } |
| } |
| ) |
| |
| if (PrintGCDetails && first_state > Idling) { |
| GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause(); |
| if (GCCause::is_user_requested_gc(cause) || |
| GCCause::is_serviceability_requested_gc(cause)) { |
| gclog_or_tty->print(" (concurrent mode interrupted)"); |
| } else { |
| gclog_or_tty->print(" (concurrent mode failure)"); |
| } |
| } |
| |
| if (should_compact) { |
| // If the collection is being acquired from the background |
| // collector, there may be references on the discovered |
| // references lists that have NULL referents (being those |
| // that were concurrently cleared by a mutator) or |
| // that are no longer active (having been enqueued concurrently |
| // by the mutator). |
| // Scrub the list of those references because Mark-Sweep-Compact |
| // code assumes referents are not NULL and that all discovered |
| // Reference objects are active. |
| ref_processor()->clean_up_discovered_references(); |
| |
| do_compaction_work(clear_all_soft_refs); |
| |
| // Has the GC time limit been exceeded? |
| DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration(); |
| size_t max_eden_size = young_gen->max_capacity() - |
| young_gen->to()->capacity() - |
| young_gen->from()->capacity(); |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| GCCause::Cause gc_cause = gch->gc_cause(); |
| size_policy()->check_gc_overhead_limit(_young_gen->used(), |
| young_gen->eden()->used(), |
| _cmsGen->max_capacity(), |
| max_eden_size, |
| full, |
| gc_cause, |
| gch->collector_policy()); |
| } else { |
| do_mark_sweep_work(clear_all_soft_refs, first_state, |
| should_start_over); |
| } |
| // Reset the expansion cause, now that we just completed |
| // a collection cycle. |
| clear_expansion_cause(); |
| _foregroundGCIsActive = false; |
| return; |
| } |
| |
| // Resize the perm generation and the tenured generation |
| // after obtaining the free list locks for the |
| // two generations. |
| void CMSCollector::compute_new_size() { |
| assert_locked_or_safepoint(Heap_lock); |
| FreelistLocker z(this); |
| _permGen->compute_new_size(); |
| _cmsGen->compute_new_size(); |
| } |
| |
| // A work method used by foreground collection to determine |
| // what type of collection (compacting or not, continuing or fresh) |
| // it should do. |
| // NOTE: the intent is to make UseCMSCompactAtFullCollection |
| // and CMSCompactWhenClearAllSoftRefs the default in the future |
| // and do away with the flags after a suitable period. |
| void CMSCollector::decide_foreground_collection_type( |
| bool clear_all_soft_refs, bool* should_compact, |
| bool* should_start_over) { |
| // Normally, we'll compact only if the UseCMSCompactAtFullCollection |
| // flag is set, and we have either requested a System.gc() or |
| // the number of full gc's since the last concurrent cycle |
| // has exceeded the threshold set by CMSFullGCsBeforeCompaction, |
| // or if an incremental collection has failed |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| assert(gch->collector_policy()->is_two_generation_policy(), |
| "You may want to check the correctness of the following"); |
| // Inform cms gen if this was due to partial collection failing. |
| // The CMS gen may use this fact to determine its expansion policy. |
| if (gch->incremental_collection_will_fail(false /* don't consult_young */)) { |
| assert(!_cmsGen->incremental_collection_failed(), |
| "Should have been noticed, reacted to and cleared"); |
| _cmsGen->set_incremental_collection_failed(); |
| } |
| *should_compact = |
| UseCMSCompactAtFullCollection && |
| ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) || |
| GCCause::is_user_requested_gc(gch->gc_cause()) || |
| gch->incremental_collection_will_fail(true /* consult_young */)); |
| *should_start_over = false; |
| if (clear_all_soft_refs && !*should_compact) { |
| // We are about to do a last ditch collection attempt |
| // so it would normally make sense to do a compaction |
| // to reclaim as much space as possible. |
| if (CMSCompactWhenClearAllSoftRefs) { |
| // Default: The rationale is that in this case either |
| // we are past the final marking phase, in which case |
| // we'd have to start over, or so little has been done |
| // that there's little point in saving that work. Compaction |
| // appears to be the sensible choice in either case. |
| *should_compact = true; |
| } else { |
| // We have been asked to clear all soft refs, but not to |
| // compact. Make sure that we aren't past the final checkpoint |
| // phase, for that is where we process soft refs. If we are already |
| // past that phase, we'll need to redo the refs discovery phase and |
| // if necessary clear soft refs that weren't previously |
| // cleared. We do so by remembering the phase in which |
| // we came in, and if we are past the refs processing |
| // phase, we'll choose to just redo the mark-sweep |
| // collection from scratch. |
| if (_collectorState > FinalMarking) { |
| // We are past the refs processing phase; |
| // start over and do a fresh synchronous CMS cycle |
| _collectorState = Resetting; // skip to reset to start new cycle |
| reset(false /* == !asynch */); |
| *should_start_over = true; |
| } // else we can continue a possibly ongoing current cycle |
| } |
| } |
| } |
| |
| // A work method used by the foreground collector to do |
| // a mark-sweep-compact. |
| void CMSCollector::do_compaction_work(bool clear_all_soft_refs) { |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty); |
| if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) { |
| gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d " |
| "collections passed to foreground collector", _full_gcs_since_conc_gc); |
| } |
| |
| // Sample collection interval time and reset for collection pause. |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->msc_collection_begin(); |
| } |
| |
| // Temporarily widen the span of the weak reference processing to |
| // the entire heap. |
| MemRegion new_span(GenCollectedHeap::heap()->reserved_region()); |
| ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span); |
| // Temporarily, clear the "is_alive_non_header" field of the |
| // reference processor. |
| ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL); |
| // Temporarily make reference _processing_ single threaded (non-MT). |
| ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false); |
| // Temporarily make refs discovery atomic |
| ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true); |
| // Temporarily make reference _discovery_ single threaded (non-MT) |
| ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false); |
| |
| ref_processor()->set_enqueuing_is_done(false); |
| ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/); |
| ref_processor()->setup_policy(clear_all_soft_refs); |
| // If an asynchronous collection finishes, the _modUnionTable is |
| // all clear. If we are assuming the collection from an asynchronous |
| // collection, clear the _modUnionTable. |
| assert(_collectorState != Idling || _modUnionTable.isAllClear(), |
| "_modUnionTable should be clear if the baton was not passed"); |
| _modUnionTable.clear_all(); |
| |
| // We must adjust the allocation statistics being maintained |
| // in the free list space. We do so by reading and clearing |
| // the sweep timer and updating the block flux rate estimates below. |
| assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive"); |
| if (_inter_sweep_timer.is_active()) { |
| _inter_sweep_timer.stop(); |
| // Note that we do not use this sample to update the _inter_sweep_estimate. |
| _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()), |
| _inter_sweep_estimate.padded_average(), |
| _intra_sweep_estimate.padded_average()); |
| } |
| |
| GenMarkSweep::invoke_at_safepoint(_cmsGen->level(), |
| ref_processor(), clear_all_soft_refs); |
| #ifdef ASSERT |
| CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); |
| size_t free_size = cms_space->free(); |
| assert(free_size == |
| pointer_delta(cms_space->end(), cms_space->compaction_top()) |
| * HeapWordSize, |
| "All the free space should be compacted into one chunk at top"); |
| assert(cms_space->dictionary()->total_chunk_size( |
| debug_only(cms_space->freelistLock())) == 0 || |
| cms_space->totalSizeInIndexedFreeLists() == 0, |
| "All the free space should be in a single chunk"); |
| size_t num = cms_space->totalCount(); |
| assert((free_size == 0 && num == 0) || |
| (free_size > 0 && (num == 1 || num == 2)), |
| "There should be at most 2 free chunks after compaction"); |
| #endif // ASSERT |
| _collectorState = Resetting; |
| assert(_restart_addr == NULL, |
| "Should have been NULL'd before baton was passed"); |
| reset(false /* == !asynch */); |
| _cmsGen->reset_after_compaction(); |
| _concurrent_cycles_since_last_unload = 0; |
| |
| if (verifying() && !should_unload_classes()) { |
| perm_gen_verify_bit_map()->clear_all(); |
| } |
| |
| // Clear any data recorded in the PLAB chunk arrays. |
| if (_survivor_plab_array != NULL) { |
| reset_survivor_plab_arrays(); |
| } |
| |
| // Adjust the per-size allocation stats for the next epoch. |
| _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */); |
| // Restart the "inter sweep timer" for the next epoch. |
| _inter_sweep_timer.reset(); |
| _inter_sweep_timer.start(); |
| |
| // Sample collection pause time and reset for collection interval. |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->msc_collection_end(gch->gc_cause()); |
| } |
| |
| // For a mark-sweep-compact, compute_new_size() will be called |
| // in the heap's do_collection() method. |
| } |
| |
| // A work method used by the foreground collector to do |
| // a mark-sweep, after taking over from a possibly on-going |
| // concurrent mark-sweep collection. |
| void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs, |
| CollectorState first_state, bool should_start_over) { |
| if (PrintGC && Verbose) { |
| gclog_or_tty->print_cr("Pass concurrent collection to foreground " |
| "collector with count %d", |
| _full_gcs_since_conc_gc); |
| } |
| switch (_collectorState) { |
| case Idling: |
| if (first_state == Idling || should_start_over) { |
| // The background GC was not active, or should |
| // restarted from scratch; start the cycle. |
| _collectorState = InitialMarking; |
| } |
| // If first_state was not Idling, then a background GC |
| // was in progress and has now finished. No need to do it |
| // again. Leave the state as Idling. |
| break; |
| case Precleaning: |
| // In the foreground case don't do the precleaning since |
| // it is not done concurrently and there is extra work |
| // required. |
| _collectorState = FinalMarking; |
| } |
| if (PrintGCDetails && |
| (_collectorState > Idling || |
| !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) { |
| gclog_or_tty->print(" (concurrent mode failure)"); |
| } |
| collect_in_foreground(clear_all_soft_refs); |
| |
| // For a mark-sweep, compute_new_size() will be called |
| // in the heap's do_collection() method. |
| } |
| |
| |
| void CMSCollector::getFreelistLocks() const { |
| // Get locks for all free lists in all generations that this |
| // collector is responsible for |
| _cmsGen->freelistLock()->lock_without_safepoint_check(); |
| _permGen->freelistLock()->lock_without_safepoint_check(); |
| } |
| |
| void CMSCollector::releaseFreelistLocks() const { |
| // Release locks for all free lists in all generations that this |
| // collector is responsible for |
| _cmsGen->freelistLock()->unlock(); |
| _permGen->freelistLock()->unlock(); |
| } |
| |
| bool CMSCollector::haveFreelistLocks() const { |
| // Check locks for all free lists in all generations that this |
| // collector is responsible for |
| assert_lock_strong(_cmsGen->freelistLock()); |
| assert_lock_strong(_permGen->freelistLock()); |
| PRODUCT_ONLY(ShouldNotReachHere()); |
| return true; |
| } |
| |
| // A utility class that is used by the CMS collector to |
| // temporarily "release" the foreground collector from its |
| // usual obligation to wait for the background collector to |
| // complete an ongoing phase before proceeding. |
| class ReleaseForegroundGC: public StackObj { |
| private: |
| CMSCollector* _c; |
| public: |
| ReleaseForegroundGC(CMSCollector* c) : _c(c) { |
| assert(_c->_foregroundGCShouldWait, "Else should not need to call"); |
| MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); |
| // allow a potentially blocked foreground collector to proceed |
| _c->_foregroundGCShouldWait = false; |
| if (_c->_foregroundGCIsActive) { |
| CGC_lock->notify(); |
| } |
| assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| "Possible deadlock"); |
| } |
| |
| ~ReleaseForegroundGC() { |
| assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?"); |
| MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); |
| _c->_foregroundGCShouldWait = true; |
| } |
| }; |
| |
| // There are separate collect_in_background and collect_in_foreground because of |
| // the different locking requirements of the background collector and the |
| // foreground collector. There was originally an attempt to share |
| // one "collect" method between the background collector and the foreground |
| // collector but the if-then-else required made it cleaner to have |
| // separate methods. |
| void CMSCollector::collect_in_background(bool clear_all_soft_refs) { |
| assert(Thread::current()->is_ConcurrentGC_thread(), |
| "A CMS asynchronous collection is only allowed on a CMS thread."); |
| |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| { |
| bool safepoint_check = Mutex::_no_safepoint_check_flag; |
| MutexLockerEx hl(Heap_lock, safepoint_check); |
| FreelistLocker fll(this); |
| MutexLockerEx x(CGC_lock, safepoint_check); |
| if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) { |
| // The foreground collector is active or we're |
| // not using asynchronous collections. Skip this |
| // background collection. |
| assert(!_foregroundGCShouldWait, "Should be clear"); |
| return; |
| } else { |
| assert(_collectorState == Idling, "Should be idling before start."); |
| _collectorState = InitialMarking; |
| // Reset the expansion cause, now that we are about to begin |
| // a new cycle. |
| clear_expansion_cause(); |
| } |
| // Decide if we want to enable class unloading as part of the |
| // ensuing concurrent GC cycle. |
| update_should_unload_classes(); |
| _full_gc_requested = false; // acks all outstanding full gc requests |
| // Signal that we are about to start a collection |
| gch->increment_total_full_collections(); // ... starting a collection cycle |
| _collection_count_start = gch->total_full_collections(); |
| } |
| |
| // Used for PrintGC |
| size_t prev_used; |
| if (PrintGC && Verbose) { |
| prev_used = _cmsGen->used(); // XXXPERM |
| } |
| |
| // The change of the collection state is normally done at this level; |
| // the exceptions are phases that are executed while the world is |
| // stopped. For those phases the change of state is done while the |
| // world is stopped. For baton passing purposes this allows the |
| // background collector to finish the phase and change state atomically. |
| // The foreground collector cannot wait on a phase that is done |
| // while the world is stopped because the foreground collector already |
| // has the world stopped and would deadlock. |
| while (_collectorState != Idling) { |
| if (TraceCMSState) { |
| gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d", |
| Thread::current(), _collectorState); |
| } |
| // The foreground collector |
| // holds the Heap_lock throughout its collection. |
| // holds the CMS token (but not the lock) |
| // except while it is waiting for the background collector to yield. |
| // |
| // The foreground collector should be blocked (not for long) |
| // if the background collector is about to start a phase |
| // executed with world stopped. If the background |
| // collector has already started such a phase, the |
| // foreground collector is blocked waiting for the |
| // Heap_lock. The stop-world phases (InitialMarking and FinalMarking) |
| // are executed in the VM thread. |
| // |
| // The locking order is |
| // PendingListLock (PLL) -- if applicable (FinalMarking) |
| // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue()) |
| // CMS token (claimed in |
| // stop_world_and_do() --> |
| // safepoint_synchronize() --> |
| // CMSThread::synchronize()) |
| |
| { |
| // Check if the FG collector wants us to yield. |
| CMSTokenSync x(true); // is cms thread |
| if (waitForForegroundGC()) { |
| // We yielded to a foreground GC, nothing more to be |
| // done this round. |
| assert(_foregroundGCShouldWait == false, "We set it to false in " |
| "waitForForegroundGC()"); |
| if (TraceCMSState) { |
| gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT |
| " exiting collection CMS state %d", |
| Thread::current(), _collectorState); |
| } |
| return; |
| } else { |
| // The background collector can run but check to see if the |
| // foreground collector has done a collection while the |
| // background collector was waiting to get the CGC_lock |
| // above. If yes, break so that _foregroundGCShouldWait |
| // is cleared before returning. |
| if (_collectorState == Idling) { |
| break; |
| } |
| } |
| } |
| |
| assert(_foregroundGCShouldWait, "Foreground collector, if active, " |
| "should be waiting"); |
| |
| switch (_collectorState) { |
| case InitialMarking: |
| { |
| ReleaseForegroundGC x(this); |
| stats().record_cms_begin(); |
| |
| VM_CMS_Initial_Mark initial_mark_op(this); |
| VMThread::execute(&initial_mark_op); |
| } |
| // The collector state may be any legal state at this point |
| // since the background collector may have yielded to the |
| // foreground collector. |
| break; |
| case Marking: |
| // initial marking in checkpointRootsInitialWork has been completed |
| if (markFromRoots(true)) { // we were successful |
| assert(_collectorState == Precleaning, "Collector state should " |
| "have changed"); |
| } else { |
| assert(_foregroundGCIsActive, "Internal state inconsistency"); |
| } |
| break; |
| case Precleaning: |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->concurrent_precleaning_begin(); |
| } |
| // marking from roots in markFromRoots has been completed |
| preclean(); |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->concurrent_precleaning_end(); |
| } |
| assert(_collectorState == AbortablePreclean || |
| _collectorState == FinalMarking, |
| "Collector state should have changed"); |
| break; |
| case AbortablePreclean: |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->concurrent_phases_resume(); |
| } |
| abortable_preclean(); |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->concurrent_precleaning_end(); |
| } |
| assert(_collectorState == FinalMarking, "Collector state should " |
| "have changed"); |
| break; |
| case FinalMarking: |
| { |
| ReleaseForegroundGC x(this); |
| |
| VM_CMS_Final_Remark final_remark_op(this); |
| VMThread::execute(&final_remark_op); |
| } |
| assert(_foregroundGCShouldWait, "block post-condition"); |
| break; |
| case Sweeping: |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->concurrent_sweeping_begin(); |
| } |
| // final marking in checkpointRootsFinal has been completed |
| sweep(true); |
| assert(_collectorState == Resizing, "Collector state change " |
| "to Resizing must be done under the free_list_lock"); |
| _full_gcs_since_conc_gc = 0; |
| |
| // Stop the timers for adaptive size policy for the concurrent phases |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->concurrent_sweeping_end(); |
| size_policy()->concurrent_phases_end(gch->gc_cause(), |
| gch->prev_gen(_cmsGen)->capacity(), |
| _cmsGen->free()); |
| } |
| |
| case Resizing: { |
| // Sweeping has been completed... |
| // At this point the background collection has completed. |
| // Don't move the call to compute_new_size() down |
| // into code that might be executed if the background |
| // collection was preempted. |
| { |
| ReleaseForegroundGC x(this); // unblock FG collection |
| MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag); |
| CMSTokenSync z(true); // not strictly needed. |
| if (_collectorState == Resizing) { |
| compute_new_size(); |
| _collectorState = Resetting; |
| } else { |
| assert(_collectorState == Idling, "The state should only change" |
| " because the foreground collector has finished the collection"); |
| } |
| } |
| break; |
| } |
| case Resetting: |
| // CMS heap resizing has been completed |
| reset(true); |
| assert(_collectorState == Idling, "Collector state should " |
| "have changed"); |
| stats().record_cms_end(); |
| // Don't move the concurrent_phases_end() and compute_new_size() |
| // calls to here because a preempted background collection |
| // has it's state set to "Resetting". |
| break; |
| case Idling: |
| default: |
| ShouldNotReachHere(); |
| break; |
| } |
| if (TraceCMSState) { |
| gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d", |
| Thread::current(), _collectorState); |
| } |
| assert(_foregroundGCShouldWait, "block post-condition"); |
| } |
| |
| // Should this be in gc_epilogue? |
| collector_policy()->counters()->update_counters(); |
| |
| { |
| // Clear _foregroundGCShouldWait and, in the event that the |
| // foreground collector is waiting, notify it, before |
| // returning. |
| MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); |
| _foregroundGCShouldWait = false; |
| if (_foregroundGCIsActive) { |
| CGC_lock->notify(); |
| } |
| assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| "Possible deadlock"); |
| } |
| if (TraceCMSState) { |
| gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT |
| " exiting collection CMS state %d", |
| Thread::current(), _collectorState); |
| } |
| if (PrintGC && Verbose) { |
| _cmsGen->print_heap_change(prev_used); |
| } |
| } |
| |
| void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) { |
| assert(_foregroundGCIsActive && !_foregroundGCShouldWait, |
| "Foreground collector should be waiting, not executing"); |
| assert(Thread::current()->is_VM_thread(), "A foreground collection" |
| "may only be done by the VM Thread with the world stopped"); |
| assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), |
| "VM thread should have CMS token"); |
| |
| NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose, |
| true, gclog_or_tty);) |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->ms_collection_begin(); |
| } |
| COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact); |
| |
| HandleMark hm; // Discard invalid handles created during verification |
| |
| if (VerifyBeforeGC && |
| GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { |
| Universe::verify(true); |
| } |
| |
| // Snapshot the soft reference policy to be used in this collection cycle. |
| ref_processor()->setup_policy(clear_all_soft_refs); |
| |
| bool init_mark_was_synchronous = false; // until proven otherwise |
| while (_collectorState != Idling) { |
| if (TraceCMSState) { |
| gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d", |
| Thread::current(), _collectorState); |
| } |
| switch (_collectorState) { |
| case InitialMarking: |
| init_mark_was_synchronous = true; // fact to be exploited in re-mark |
| checkpointRootsInitial(false); |
| assert(_collectorState == Marking, "Collector state should have changed" |
| " within checkpointRootsInitial()"); |
| break; |
| case Marking: |
| // initial marking in checkpointRootsInitialWork has been completed |
| if (VerifyDuringGC && |
| GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { |
| gclog_or_tty->print("Verify before initial mark: "); |
| Universe::verify(true); |
| } |
| { |
| bool res = markFromRoots(false); |
| assert(res && _collectorState == FinalMarking, "Collector state should " |
| "have changed"); |
| break; |
| } |
| case FinalMarking: |
| if (VerifyDuringGC && |
| GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { |
| gclog_or_tty->print("Verify before re-mark: "); |
| Universe::verify(true); |
| } |
| checkpointRootsFinal(false, clear_all_soft_refs, |
| init_mark_was_synchronous); |
| assert(_collectorState == Sweeping, "Collector state should not " |
| "have changed within checkpointRootsFinal()"); |
| break; |
| case Sweeping: |
| // final marking in checkpointRootsFinal has been completed |
| if (VerifyDuringGC && |
| GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { |
| gclog_or_tty->print("Verify before sweep: "); |
| Universe::verify(true); |
| } |
| sweep(false); |
| assert(_collectorState == Resizing, "Incorrect state"); |
| break; |
| case Resizing: { |
| // Sweeping has been completed; the actual resize in this case |
| // is done separately; nothing to be done in this state. |
| _collectorState = Resetting; |
| break; |
| } |
| case Resetting: |
| // The heap has been resized. |
| if (VerifyDuringGC && |
| GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { |
| gclog_or_tty->print("Verify before reset: "); |
| Universe::verify(true); |
| } |
| reset(false); |
| assert(_collectorState == Idling, "Collector state should " |
| "have changed"); |
| break; |
| case Precleaning: |
| case AbortablePreclean: |
| // Elide the preclean phase |
| _collectorState = FinalMarking; |
| break; |
| default: |
| ShouldNotReachHere(); |
| } |
| if (TraceCMSState) { |
| gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d", |
| Thread::current(), _collectorState); |
| } |
| } |
| |
| if (UseAdaptiveSizePolicy) { |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| size_policy()->ms_collection_end(gch->gc_cause()); |
| } |
| |
| if (VerifyAfterGC && |
| GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { |
| Universe::verify(true); |
| } |
| if (TraceCMSState) { |
| gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT |
| " exiting collection CMS state %d", |
| Thread::current(), _collectorState); |
| } |
| } |
| |
| bool CMSCollector::waitForForegroundGC() { |
| bool res = false; |
| assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| "CMS thread should have CMS token"); |
| // Block the foreground collector until the |
| // background collectors decides whether to |
| // yield. |
| MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); |
| _foregroundGCShouldWait = true; |
| if (_foregroundGCIsActive) { |
| // The background collector yields to the |
| // foreground collector and returns a value |
| // indicating that it has yielded. The foreground |
| // collector can proceed. |
| res = true; |
| _foregroundGCShouldWait = false; |
| ConcurrentMarkSweepThread::clear_CMS_flag( |
| ConcurrentMarkSweepThread::CMS_cms_has_token); |
| ConcurrentMarkSweepThread::set_CMS_flag( |
| ConcurrentMarkSweepThread::CMS_cms_wants_token); |
| // Get a possibly blocked foreground thread going |
| CGC_lock->notify(); |
| if (TraceCMSState) { |
| gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d", |
| Thread::current(), _collectorState); |
| } |
| while (_foregroundGCIsActive) { |
| CGC_lock->wait(Mutex::_no_safepoint_check_flag); |
| } |
| ConcurrentMarkSweepThread::set_CMS_flag( |
| ConcurrentMarkSweepThread::CMS_cms_has_token); |
| ConcurrentMarkSweepThread::clear_CMS_flag( |
| ConcurrentMarkSweepThread::CMS_cms_wants_token); |
| } |
| if (TraceCMSState) { |
| gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d", |
| Thread::current(), _collectorState); |
| } |
| return res; |
| } |
| |
| // Because of the need to lock the free lists and other structures in |
| // the collector, common to all the generations that the collector is |
| // collecting, we need the gc_prologues of individual CMS generations |
| // delegate to their collector. It may have been simpler had the |
| // current infrastructure allowed one to call a prologue on a |
| // collector. In the absence of that we have the generation's |
| // prologue delegate to the collector, which delegates back |
| // some "local" work to a worker method in the individual generations |
| // that it's responsible for collecting, while itself doing any |
| // work common to all generations it's responsible for. A similar |
| // comment applies to the gc_epilogue()'s. |
| // The role of the varaible _between_prologue_and_epilogue is to |
| // enforce the invocation protocol. |
| void CMSCollector::gc_prologue(bool full) { |
| // Call gc_prologue_work() for each CMSGen and PermGen that |
| // we are responsible for. |
| |
| // The following locking discipline assumes that we are only called |
| // when the world is stopped. |
| assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption"); |
| |
| // The CMSCollector prologue must call the gc_prologues for the |
| // "generations" (including PermGen if any) that it's responsible |
| // for. |
| |
| assert( Thread::current()->is_VM_thread() |
| || ( CMSScavengeBeforeRemark |
| && Thread::current()->is_ConcurrentGC_thread()), |
| "Incorrect thread type for prologue execution"); |
| |
| if (_between_prologue_and_epilogue) { |
| // We have already been invoked; this is a gc_prologue delegation |
| // from yet another CMS generation that we are responsible for, just |
| // ignore it since all relevant work has already been done. |
| return; |
| } |
| |
| // set a bit saying prologue has been called; cleared in epilogue |
| _between_prologue_and_epilogue = true; |
| // Claim locks for common data structures, then call gc_prologue_work() |
| // for each CMSGen and PermGen that we are responsible for. |
| |
| getFreelistLocks(); // gets free list locks on constituent spaces |
| bitMapLock()->lock_without_safepoint_check(); |
| |
| // Should call gc_prologue_work() for all cms gens we are responsible for |
| bool registerClosure = _collectorState >= Marking |
| && _collectorState < Sweeping; |
| ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ? |
| &_modUnionClosurePar |
| : &_modUnionClosure; |
| _cmsGen->gc_prologue_work(full, registerClosure, muc); |
| _permGen->gc_prologue_work(full, registerClosure, muc); |
| |
| if (!full) { |
| stats().record_gc0_begin(); |
| } |
| } |
| |
| void ConcurrentMarkSweepGeneration::gc_prologue(bool full) { |
| // Delegate to CMScollector which knows how to coordinate between |
| // this and any other CMS generations that it is responsible for |
| // collecting. |
| collector()->gc_prologue(full); |
| } |
| |
| // This is a "private" interface for use by this generation's CMSCollector. |
| // Not to be called directly by any other entity (for instance, |
| // GenCollectedHeap, which calls the "public" gc_prologue method above). |
| void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full, |
| bool registerClosure, ModUnionClosure* modUnionClosure) { |
| assert(!incremental_collection_failed(), "Shouldn't be set yet"); |
| assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL, |
| "Should be NULL"); |
| if (registerClosure) { |
| cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure); |
| } |
| cmsSpace()->gc_prologue(); |
| // Clear stat counters |
| NOT_PRODUCT( |
| assert(_numObjectsPromoted == 0, "check"); |
| assert(_numWordsPromoted == 0, "check"); |
| if (Verbose && PrintGC) { |
| gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, " |
| SIZE_FORMAT" bytes concurrently", |
| _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord)); |
| } |
| _numObjectsAllocated = 0; |
| _numWordsAllocated = 0; |
| ) |
| } |
| |
| void CMSCollector::gc_epilogue(bool full) { |
| // The following locking discipline assumes that we are only called |
| // when the world is stopped. |
| assert(SafepointSynchronize::is_at_safepoint(), |
| "world is stopped assumption"); |
| |
| // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks |
| // if linear allocation blocks need to be appropriately marked to allow the |
| // the blocks to be parsable. We also check here whether we need to nudge the |
| // CMS collector thread to start a new cycle (if it's not already active). |
| assert( Thread::current()->is_VM_thread() |
| || ( CMSScavengeBeforeRemark |
| && Thread::current()->is_ConcurrentGC_thread()), |
| "Incorrect thread type for epilogue execution"); |
| |
| if (!_between_prologue_and_epilogue) { |
| // We have already been invoked; this is a gc_epilogue delegation |
| // from yet another CMS generation that we are responsible for, just |
| // ignore it since all relevant work has already been done. |
| return; |
| } |
| assert(haveFreelistLocks(), "must have freelist locks"); |
| assert_lock_strong(bitMapLock()); |
| |
| _cmsGen->gc_epilogue_work(full); |
| _permGen->gc_epilogue_work(full); |
| |
| if (_collectorState == AbortablePreclean || _collectorState == Precleaning) { |
| // in case sampling was not already enabled, enable it |
| _start_sampling = true; |
| } |
| // reset _eden_chunk_array so sampling starts afresh |
| _eden_chunk_index = 0; |
| |
| size_t cms_used = _cmsGen->cmsSpace()->used(); |
| size_t perm_used = _permGen->cmsSpace()->used(); |
| |
| // update performance counters - this uses a special version of |
| // update_counters() that allows the utilization to be passed as a |
| // parameter, avoiding multiple calls to used(). |
| // |
| _cmsGen->update_counters(cms_used); |
| _permGen->update_counters(perm_used); |
| |
| if (CMSIncrementalMode) { |
| icms_update_allocation_limits(); |
| } |
| |
| bitMapLock()->unlock(); |
| releaseFreelistLocks(); |
| |
| if (!CleanChunkPoolAsync) { |
| Chunk::clean_chunk_pool(); |
| } |
| |
| _between_prologue_and_epilogue = false; // ready for next cycle |
| } |
| |
| void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) { |
| collector()->gc_epilogue(full); |
| |
| // Also reset promotion tracking in par gc thread states. |
| if (CollectedHeap::use_parallel_gc_threads()) { |
| for (uint i = 0; i < ParallelGCThreads; i++) { |
| _par_gc_thread_states[i]->promo.stopTrackingPromotions(i); |
| } |
| } |
| } |
| |
| void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) { |
| assert(!incremental_collection_failed(), "Should have been cleared"); |
| cmsSpace()->setPreconsumptionDirtyCardClosure(NULL); |
| cmsSpace()->gc_epilogue(); |
| // Print stat counters |
| NOT_PRODUCT( |
| assert(_numObjectsAllocated == 0, "check"); |
| assert(_numWordsAllocated == 0, "check"); |
| if (Verbose && PrintGC) { |
| gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, " |
| SIZE_FORMAT" bytes", |
| _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord)); |
| } |
| _numObjectsPromoted = 0; |
| _numWordsPromoted = 0; |
| ) |
| |
| if (PrintGC && Verbose) { |
| // Call down the chain in contiguous_available needs the freelistLock |
| // so print this out before releasing the freeListLock. |
| gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ", |
| contiguous_available()); |
| } |
| } |
| |
| #ifndef PRODUCT |
| bool CMSCollector::have_cms_token() { |
| Thread* thr = Thread::current(); |
| if (thr->is_VM_thread()) { |
| return ConcurrentMarkSweepThread::vm_thread_has_cms_token(); |
| } else if (thr->is_ConcurrentGC_thread()) { |
| return ConcurrentMarkSweepThread::cms_thread_has_cms_token(); |
| } else if (thr->is_GC_task_thread()) { |
| return ConcurrentMarkSweepThread::vm_thread_has_cms_token() && |
| ParGCRareEvent_lock->owned_by_self(); |
| } |
| return false; |
| } |
| #endif |
| |
| // Check reachability of the given heap address in CMS generation, |
| // treating all other generations as roots. |
| bool CMSCollector::is_cms_reachable(HeapWord* addr) { |
| // We could "guarantee" below, rather than assert, but i'll |
| // leave these as "asserts" so that an adventurous debugger |
| // could try this in the product build provided some subset of |
| // the conditions were met, provided they were intersted in the |
| // results and knew that the computation below wouldn't interfere |
| // with other concurrent computations mutating the structures |
| // being read or written. |
| assert(SafepointSynchronize::is_at_safepoint(), |
| "Else mutations in object graph will make answer suspect"); |
| assert(have_cms_token(), "Should hold cms token"); |
| assert(haveFreelistLocks(), "must hold free list locks"); |
| assert_lock_strong(bitMapLock()); |
| |
| // Clear the marking bit map array before starting, but, just |
| // for kicks, first report if the given address is already marked |
| gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr, |
| _markBitMap.isMarked(addr) ? "" : " not"); |
| |
| if (verify_after_remark()) { |
| MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag); |
| bool result = verification_mark_bm()->isMarked(addr); |
| gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr, |
| result ? "IS" : "is NOT"); |
| return result; |
| } else { |
| gclog_or_tty->print_cr("Could not compute result"); |
| return false; |
| } |
| } |
| |
| //////////////////////////////////////////////////////// |
| // CMS Verification Support |
| //////////////////////////////////////////////////////// |
| // Following the remark phase, the following invariant |
| // should hold -- each object in the CMS heap which is |
| // marked in markBitMap() should be marked in the verification_mark_bm(). |
| |
| class VerifyMarkedClosure: public BitMapClosure { |
| CMSBitMap* _marks; |
| bool _failed; |
| |
| public: |
| VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {} |
| |
| bool do_bit(size_t offset) { |
| HeapWord* addr = _marks->offsetToHeapWord(offset); |
| if (!_marks->isMarked(addr)) { |
| oop(addr)->print_on(gclog_or_tty); |
| gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr); |
| _failed = true; |
| } |
| return true; |
| } |
| |
| bool failed() { return _failed; } |
| }; |
| |
| bool CMSCollector::verify_after_remark() { |
| gclog_or_tty->print(" [Verifying CMS Marking... "); |
| MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag); |
| static bool init = false; |
| |
| assert(SafepointSynchronize::is_at_safepoint(), |
| "Else mutations in object graph will make answer suspect"); |
| assert(have_cms_token(), |
| "Else there may be mutual interference in use of " |
| " verification data structures"); |
| assert(_collectorState > Marking && _collectorState <= Sweeping, |
| "Else marking info checked here may be obsolete"); |
| assert(haveFreelistLocks(), "must hold free list locks"); |
| assert_lock_strong(bitMapLock()); |
| |
| |
| // Allocate marking bit map if not already allocated |
| if (!init) { // first time |
| if (!verification_mark_bm()->allocate(_span)) { |
| return false; |
| } |
| init = true; |
| } |
| |
| assert(verification_mark_stack()->isEmpty(), "Should be empty"); |
| |
| // Turn off refs discovery -- so we will be tracing through refs. |
| // This is as intended, because by this time |
| // GC must already have cleared any refs that need to be cleared, |
| // and traced those that need to be marked; moreover, |
| // the marking done here is not going to intefere in any |
| // way with the marking information used by GC. |
| NoRefDiscovery no_discovery(ref_processor()); |
| |
| COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;) |
| |
| // Clear any marks from a previous round |
| verification_mark_bm()->clear_all(); |
| assert(verification_mark_stack()->isEmpty(), "markStack should be empty"); |
| verify_work_stacks_empty(); |
| |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| gch->ensure_parsability(false); // fill TLABs, but no need to retire them |
| // Update the saved marks which may affect the root scans. |
| gch->save_marks(); |
| |
| if (CMSRemarkVerifyVariant == 1) { |
| // In this first variant of verification, we complete |
| // all marking, then check if the new marks-verctor is |
| // a subset of the CMS marks-vector. |
| verify_after_remark_work_1(); |
| } else if (CMSRemarkVerifyVariant == 2) { |
| // In this second variant of verification, we flag an error |
| // (i.e. an object reachable in the new marks-vector not reachable |
| // in the CMS marks-vector) immediately, also indicating the |
| // identify of an object (A) that references the unmarked object (B) -- |
| // presumably, a mutation to A failed to be picked up by preclean/remark? |
| verify_after_remark_work_2(); |
| } else { |
| warning("Unrecognized value %d for CMSRemarkVerifyVariant", |
| CMSRemarkVerifyVariant); |
| } |
| gclog_or_tty->print(" done] "); |
| return true; |
| } |
| |
| void CMSCollector::verify_after_remark_work_1() { |
| ResourceMark rm; |
| HandleMark hm; |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| |
| // Mark from roots one level into CMS |
| MarkRefsIntoClosure notOlder(_span, verification_mark_bm()); |
| gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. |
| |
| gch->gen_process_strong_roots(_cmsGen->level(), |
| true, // younger gens are roots |
| true, // activate StrongRootsScope |
| true, // collecting perm gen |
| SharedHeap::ScanningOption(roots_scanning_options()), |
| ¬Older, |
| true, // walk code active on stacks |
| NULL); |
| |
| // Now mark from the roots |
| assert(_revisitStack.isEmpty(), "Should be empty"); |
| MarkFromRootsClosure markFromRootsClosure(this, _span, |
| verification_mark_bm(), verification_mark_stack(), &_revisitStack, |
| false /* don't yield */, true /* verifying */); |
| assert(_restart_addr == NULL, "Expected pre-condition"); |
| verification_mark_bm()->iterate(&markFromRootsClosure); |
| while (_restart_addr != NULL) { |
| // Deal with stack overflow: by restarting at the indicated |
| // address. |
| HeapWord* ra = _restart_addr; |
| markFromRootsClosure.reset(ra); |
| _restart_addr = NULL; |
| verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end()); |
| } |
| assert(verification_mark_stack()->isEmpty(), "Should have been drained"); |
| verify_work_stacks_empty(); |
| // Should reset the revisit stack above, since no class tree |
| // surgery is forthcoming. |
| _revisitStack.reset(); // throwing away all contents |
| |
| // Marking completed -- now verify that each bit marked in |
| // verification_mark_bm() is also marked in markBitMap(); flag all |
| // errors by printing corresponding objects. |
| VerifyMarkedClosure vcl(markBitMap()); |
| verification_mark_bm()->iterate(&vcl); |
| if (vcl.failed()) { |
| gclog_or_tty->print("Verification failed"); |
| Universe::heap()->print_on(gclog_or_tty); |
| fatal("CMS: failed marking verification after remark"); |
| } |
| } |
| |
| void CMSCollector::verify_after_remark_work_2() { |
| ResourceMark rm; |
| HandleMark hm; |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| |
| // Mark from roots one level into CMS |
| MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(), |
| markBitMap()); |
| gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. |
| gch->gen_process_strong_roots(_cmsGen->level(), |
| true, // younger gens are roots |
| true, // activate StrongRootsScope |
| true, // collecting perm gen |
| SharedHeap::ScanningOption(roots_scanning_options()), |
| ¬Older, |
| true, // walk code active on stacks |
| NULL); |
| |
| // Now mark from the roots |
| assert(_revisitStack.isEmpty(), "Should be empty"); |
| MarkFromRootsVerifyClosure markFromRootsClosure(this, _span, |
| verification_mark_bm(), markBitMap(), verification_mark_stack()); |
| assert(_restart_addr == NULL, "Expected pre-condition"); |
| verification_mark_bm()->iterate(&markFromRootsClosure); |
| while (_restart_addr != NULL) { |
| // Deal with stack overflow: by restarting at the indicated |
| // address. |
| HeapWord* ra = _restart_addr; |
| markFromRootsClosure.reset(ra); |
| _restart_addr = NULL; |
| verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end()); |
| } |
| assert(verification_mark_stack()->isEmpty(), "Should have been drained"); |
| verify_work_stacks_empty(); |
| // Should reset the revisit stack above, since no class tree |
| // surgery is forthcoming. |
| _revisitStack.reset(); // throwing away all contents |
| |
| // Marking completed -- now verify that each bit marked in |
| // verification_mark_bm() is also marked in markBitMap(); flag all |
| // errors by printing corresponding objects. |
| VerifyMarkedClosure vcl(markBitMap()); |
| verification_mark_bm()->iterate(&vcl); |
| assert(!vcl.failed(), "Else verification above should not have succeeded"); |
| } |
| |
| void ConcurrentMarkSweepGeneration::save_marks() { |
| // delegate to CMS space |
| cmsSpace()->save_marks(); |
| for (uint i = 0; i < ParallelGCThreads; i++) { |
| _par_gc_thread_states[i]->promo.startTrackingPromotions(); |
| } |
| } |
| |
| bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() { |
| return cmsSpace()->no_allocs_since_save_marks(); |
| } |
| |
| #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \ |
| \ |
| void ConcurrentMarkSweepGeneration:: \ |
| oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \ |
| cl->set_generation(this); \ |
| cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \ |
| cl->reset_generation(); \ |
| save_marks(); \ |
| } |
| |
| ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN) |
| |
| void |
| ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk) |
| { |
| // Not currently implemented; need to do the following. -- ysr. |
| // dld -- I think that is used for some sort of allocation profiler. So it |
| // really means the objects allocated by the mutator since the last |
| // GC. We could potentially implement this cheaply by recording only |
| // the direct allocations in a side data structure. |
| // |
| // I think we probably ought not to be required to support these |
| // iterations at any arbitrary point; I think there ought to be some |
| // call to enable/disable allocation profiling in a generation/space, |
| // and the iterator ought to return the objects allocated in the |
| // gen/space since the enable call, or the last iterator call (which |
| // will probably be at a GC.) That way, for gens like CM&S that would |
| // require some extra data structure to support this, we only pay the |
| // cost when it's in use... |
| cmsSpace()->object_iterate_since_last_GC(blk); |
| } |
| |
| void |
| ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) { |
| cl->set_generation(this); |
| younger_refs_in_space_iterate(_cmsSpace, cl); |
| cl->reset_generation(); |
| } |
| |
| void |
| ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) { |
| if (freelistLock()->owned_by_self()) { |
| Generation::oop_iterate(mr, cl); |
| } else { |
| MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); |
| Generation::oop_iterate(mr, cl); |
| } |
| } |
| |
| void |
| ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) { |
| if (freelistLock()->owned_by_self()) { |
| Generation::oop_iterate(cl); |
| } else { |
| MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); |
| Generation::oop_iterate(cl); |
| } |
| } |
| |
| void |
| ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) { |
| if (freelistLock()->owned_by_self()) { |
| Generation::object_iterate(cl); |
| } else { |
| MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); |
| Generation::object_iterate(cl); |
| } |
| } |
| |
| void |
| ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) { |
| if (freelistLock()->owned_by_self()) { |
| Generation::safe_object_iterate(cl); |
| } else { |
| MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); |
| Generation::safe_object_iterate(cl); |
| } |
| } |
| |
| void |
| ConcurrentMarkSweepGeneration::pre_adjust_pointers() { |
| } |
| |
| void |
| ConcurrentMarkSweepGeneration::post_compact() { |
| } |
| |
| void |
| ConcurrentMarkSweepGeneration::prepare_for_verify() { |
| // Fix the linear allocation blocks to look like free blocks. |
| |
| // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those |
| // are not called when the heap is verified during universe initialization and |
| // at vm shutdown. |
| if (freelistLock()->owned_by_self()) { |
| cmsSpace()->prepare_for_verify(); |
| } else { |
| MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag); |
| cmsSpace()->prepare_for_verify(); |
| } |
| } |
| |
| void |
| ConcurrentMarkSweepGeneration::verify() { |
| // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those |
| // are not called when the heap is verified during universe initialization and |
| // at vm shutdown. |
| if (freelistLock()->owned_by_self()) { |
| cmsSpace()->verify(); |
| } else { |
| MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag); |
| cmsSpace()->verify(); |
| } |
| } |
| |
| void CMSCollector::verify() { |
| _cmsGen->verify(); |
| _permGen->verify(); |
| } |
| |
| #ifndef PRODUCT |
| bool CMSCollector::overflow_list_is_empty() const { |
| assert(_num_par_pushes >= 0, "Inconsistency"); |
| if (_overflow_list == NULL) { |
| assert(_num_par_pushes == 0, "Inconsistency"); |
| } |
| return _overflow_list == NULL; |
| } |
| |
| // The methods verify_work_stacks_empty() and verify_overflow_empty() |
| // merely consolidate assertion checks that appear to occur together frequently. |
| void CMSCollector::verify_work_stacks_empty() const { |
| assert(_markStack.isEmpty(), "Marking stack should be empty"); |
| assert(overflow_list_is_empty(), "Overflow list should be empty"); |
| } |
| |
| void CMSCollector::verify_overflow_empty() const { |
| assert(overflow_list_is_empty(), "Overflow list should be empty"); |
| assert(no_preserved_marks(), "No preserved marks"); |
| } |
| #endif // PRODUCT |
| |
| // Decide if we want to enable class unloading as part of the |
| // ensuing concurrent GC cycle. We will collect the perm gen and |
| // unload classes if it's the case that: |
| // (1) an explicit gc request has been made and the flag |
| // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR |
| // (2) (a) class unloading is enabled at the command line, and |
| // (b) (i) perm gen threshold has been crossed, or |
| // (ii) old gen is getting really full, or |
| // (iii) the previous N CMS collections did not collect the |
| // perm gen |
| // NOTE: Provided there is no change in the state of the heap between |
| // calls to this method, it should have idempotent results. Moreover, |
| // its results should be monotonically increasing (i.e. going from 0 to 1, |
| // but not 1 to 0) between successive calls between which the heap was |
| // not collected. For the implementation below, it must thus rely on |
| // the property that concurrent_cycles_since_last_unload() |
| // will not decrease unless a collection cycle happened and that |
| // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are |
| // themselves also monotonic in that sense. See check_monotonicity() |
| // below. |
| bool CMSCollector::update_should_unload_classes() { |
| _should_unload_classes = false; |
| // Condition 1 above |
| if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) { |
| _should_unload_classes = true; |
| } else if (CMSClassUnloadingEnabled) { // Condition 2.a above |
| // Disjuncts 2.b.(i,ii,iii) above |
| _should_unload_classes = (concurrent_cycles_since_last_unload() >= |
| CMSClassUnloadingMaxInterval) |
| || _permGen->should_concurrent_collect() |
| || _cmsGen->is_too_full(); |
| } |
| return _should_unload_classes; |
| } |
| |
| bool ConcurrentMarkSweepGeneration::is_too_full() const { |
| bool res = should_concurrent_collect(); |
| res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0); |
| return res; |
| } |
| |
| void CMSCollector::setup_cms_unloading_and_verification_state() { |
| const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC |
| || VerifyBeforeExit; |
| const int rso = SharedHeap::SO_Strings | SharedHeap::SO_CodeCache; |
| |
| if (should_unload_classes()) { // Should unload classes this cycle |
| remove_root_scanning_option(rso); // Shrink the root set appropriately |
| set_verifying(should_verify); // Set verification state for this cycle |
| return; // Nothing else needs to be done at this time |
| } |
| |
| // Not unloading classes this cycle |
| assert(!should_unload_classes(), "Inconsitency!"); |
| if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) { |
| // We were not verifying, or we _were_ unloading classes in the last cycle, |
| // AND some verification options are enabled this cycle; in this case, |
| // we must make sure that the deadness map is allocated if not already so, |
| // and cleared (if already allocated previously -- |
| // CMSBitMap::sizeInBits() is used to determine if it's allocated). |
| if (perm_gen_verify_bit_map()->sizeInBits() == 0) { |
| if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) { |
| warning("Failed to allocate permanent generation verification CMS Bit Map;\n" |
| "permanent generation verification disabled"); |
| return; // Note that we leave verification disabled, so we'll retry this |
| // allocation next cycle. We _could_ remember this failure |
| // and skip further attempts and permanently disable verification |
| // attempts if that is considered more desirable. |
| } |
| assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()), |
| "_perm_gen_ver_bit_map inconsistency?"); |
| } else { |
| perm_gen_verify_bit_map()->clear_all(); |
| } |
| // Include symbols, strings and code cache elements to prevent their resurrection. |
| add_root_scanning_option(rso); |
| set_verifying(true); |
| } else if (verifying() && !should_verify) { |
| // We were verifying, but some verification flags got disabled. |
| set_verifying(false); |
| // Exclude symbols, strings and code cache elements from root scanning to |
| // reduce IM and RM pauses. |
| remove_root_scanning_option(rso); |
| } |
| } |
| |
| |
| #ifndef PRODUCT |
| HeapWord* CMSCollector::block_start(const void* p) const { |
| const HeapWord* addr = (HeapWord*)p; |
| if (_span.contains(p)) { |
| if (_cmsGen->cmsSpace()->is_in_reserved(addr)) { |
| return _cmsGen->cmsSpace()->block_start(p); |
| } else { |
| assert(_permGen->cmsSpace()->is_in_reserved(addr), |
| "Inconsistent _span?"); |
| return _permGen->cmsSpace()->block_start(p); |
| } |
| } |
| return NULL; |
| } |
| #endif |
| |
| HeapWord* |
| ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size, |
| bool tlab, |
| bool parallel) { |
| CMSSynchronousYieldRequest yr; |
| assert(!tlab, "Can't deal with TLAB allocation"); |
| MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); |
| expand(word_size*HeapWordSize, MinHeapDeltaBytes, |
| CMSExpansionCause::_satisfy_allocation); |
| if (GCExpandToAllocateDelayMillis > 0) { |
| os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); |
| } |
| return have_lock_and_allocate(word_size, tlab); |
| } |
| |
| // YSR: All of this generation expansion/shrinking stuff is an exact copy of |
| // OneContigSpaceCardGeneration, which makes me wonder if we should move this |
| // to CardGeneration and share it... |
| bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) { |
| return CardGeneration::expand(bytes, expand_bytes); |
| } |
| |
| void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes, |
| CMSExpansionCause::Cause cause) |
| { |
| |
| bool success = expand(bytes, expand_bytes); |
| |
| // remember why we expanded; this information is used |
| // by shouldConcurrentCollect() when making decisions on whether to start |
| // a new CMS cycle. |
| if (success) { |
| set_expansion_cause(cause); |
| if (PrintGCDetails && Verbose) { |
| gclog_or_tty->print_cr("Expanded CMS gen for %s", |
| CMSExpansionCause::to_string(cause)); |
| } |
| } |
| } |
| |
| HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) { |
| HeapWord* res = NULL; |
| MutexLocker x(ParGCRareEvent_lock); |
| while (true) { |
| // Expansion by some other thread might make alloc OK now: |
| res = ps->lab.alloc(word_sz); |
| if (res != NULL) return res; |
| // If there's not enough expansion space available, give up. |
| if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) { |
| return NULL; |
| } |
| // Otherwise, we try expansion. |
| expand(word_sz*HeapWordSize, MinHeapDeltaBytes, |
| CMSExpansionCause::_allocate_par_lab); |
| // Now go around the loop and try alloc again; |
| // A competing par_promote might beat us to the expansion space, |
| // so we may go around the loop again if promotion fails agaion. |
| if (GCExpandToAllocateDelayMillis > 0) { |
| os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); |
| } |
| } |
| } |
| |
| |
| bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space( |
| PromotionInfo* promo) { |
| MutexLocker x(ParGCRareEvent_lock); |
| size_t refill_size_bytes = promo->refillSize() * HeapWordSize; |
| while (true) { |
| // Expansion by some other thread might make alloc OK now: |
| if (promo->ensure_spooling_space()) { |
| assert(promo->has_spooling_space(), |
| "Post-condition of successful ensure_spooling_space()"); |
| return true; |
| } |
| // If there's not enough expansion space available, give up. |
| if (_virtual_space.uncommitted_size() < refill_size_bytes) { |
| return false; |
| } |
| // Otherwise, we try expansion. |
| expand(refill_size_bytes, MinHeapDeltaBytes, |
| CMSExpansionCause::_allocate_par_spooling_space); |
| // Now go around the loop and try alloc again; |
| // A competing allocation might beat us to the expansion space, |
| // so we may go around the loop again if allocation fails again. |
| if (GCExpandToAllocateDelayMillis > 0) { |
| os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); |
| } |
| } |
| } |
| |
| |
| |
| void ConcurrentMarkSweepGeneration::shrink(size_t bytes) { |
| assert_locked_or_safepoint(Heap_lock); |
| size_t size = ReservedSpace::page_align_size_down(bytes); |
| if (size > 0) { |
| shrink_by(size); |
| } |
| } |
| |
| bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) { |
| assert_locked_or_safepoint(Heap_lock); |
| bool result = _virtual_space.expand_by(bytes); |
| if (result) { |
| HeapWord* old_end = _cmsSpace->end(); |
| size_t new_word_size = |
| heap_word_size(_virtual_space.committed_size()); |
| MemRegion mr(_cmsSpace->bottom(), new_word_size); |
| _bts->resize(new_word_size); // resize the block offset shared array |
| Universe::heap()->barrier_set()->resize_covered_region(mr); |
| // Hmmmm... why doesn't CFLS::set_end verify locking? |
| // This is quite ugly; FIX ME XXX |
| _cmsSpace->assert_locked(freelistLock()); |
| _cmsSpace->set_end((HeapWord*)_virtual_space.high()); |
| |
| // update the space and generation capacity counters |
| if (UsePerfData) { |
| _space_counters->update_capacity(); |
| _gen_counters->update_all(); |
| } |
| |
| if (Verbose && PrintGC) { |
| size_t new_mem_size = _virtual_space.committed_size(); |
| size_t old_mem_size = new_mem_size - bytes; |
| gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK", |
| name(), old_mem_size/K, bytes/K, new_mem_size/K); |
| } |
| } |
| return result; |
| } |
| |
| bool ConcurrentMarkSweepGeneration::grow_to_reserved() { |
| assert_locked_or_safepoint(Heap_lock); |
| bool success = true; |
| const size_t remaining_bytes = _virtual_space.uncommitted_size(); |
| if (remaining_bytes > 0) { |
| success = grow_by(remaining_bytes); |
| DEBUG_ONLY(if (!success) warning("grow to reserved failed");) |
| } |
| return success; |
| } |
| |
| void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) { |
| assert_locked_or_safepoint(Heap_lock); |
| assert_lock_strong(freelistLock()); |
| // XXX Fix when compaction is implemented. |
| warning("Shrinking of CMS not yet implemented"); |
| return; |
| } |
| |
| |
| // Simple ctor/dtor wrapper for accounting & timer chores around concurrent |
| // phases. |
| class CMSPhaseAccounting: public StackObj { |
| public: |
| CMSPhaseAccounting(CMSCollector *collector, |
| const char *phase, |
| bool print_cr = true); |
| ~CMSPhaseAccounting(); |
| |
| private: |
| CMSCollector *_collector; |
| const char *_phase; |
| elapsedTimer _wallclock; |
| bool _print_cr; |
| |
| public: |
| // Not MT-safe; so do not pass around these StackObj's |
| // where they may be accessed by other threads. |
| jlong wallclock_millis() { |
| assert(_wallclock.is_active(), "Wall clock should not stop"); |
| _wallclock.stop(); // to record time |
| jlong ret = _wallclock.milliseconds(); |
| _wallclock.start(); // restart |
| return ret; |
| } |
| }; |
| |
| CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector, |
| const char *phase, |
| bool print_cr) : |
| _collector(collector), _phase(phase), _print_cr(print_cr) { |
| |
| if (PrintCMSStatistics != 0) { |
| _collector->resetYields(); |
| } |
| if (PrintGCDetails && PrintGCTimeStamps) { |
| gclog_or_tty->date_stamp(PrintGCDateStamps); |
| gclog_or_tty->stamp(); |
| gclog_or_tty->print_cr(": [%s-concurrent-%s-start]", |
| _collector->cmsGen()->short_name(), _phase); |
| } |
| _collector->resetTimer(); |
| _wallclock.start(); |
| _collector->startTimer(); |
| } |
| |
| CMSPhaseAccounting::~CMSPhaseAccounting() { |
| assert(_wallclock.is_active(), "Wall clock should not have stopped"); |
| _collector->stopTimer(); |
| _wallclock.stop(); |
| if (PrintGCDetails) { |
| gclog_or_tty->date_stamp(PrintGCDateStamps); |
| if (PrintGCTimeStamps) { |
| gclog_or_tty->stamp(); |
| gclog_or_tty->print(": "); |
| } |
| gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]", |
| _collector->cmsGen()->short_name(), |
| _phase, _collector->timerValue(), _wallclock.seconds()); |
| if (_print_cr) { |
| gclog_or_tty->print_cr(""); |
| } |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase, |
| _collector->yields()); |
| } |
| } |
| } |
| |
| // CMS work |
| |
| // Checkpoint the roots into this generation from outside |
| // this generation. [Note this initial checkpoint need only |
| // be approximate -- we'll do a catch up phase subsequently.] |
| void CMSCollector::checkpointRootsInitial(bool asynch) { |
| assert(_collectorState == InitialMarking, "Wrong collector state"); |
| check_correct_thread_executing(); |
| TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause()); |
| |
| ReferenceProcessor* rp = ref_processor(); |
| SpecializationStats::clear(); |
| assert(_restart_addr == NULL, "Control point invariant"); |
| if (asynch) { |
| // acquire locks for subsequent manipulations |
| MutexLockerEx x(bitMapLock(), |
| Mutex::_no_safepoint_check_flag); |
| checkpointRootsInitialWork(asynch); |
| // enable ("weak") refs discovery |
| rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/); |
| _collectorState = Marking; |
| } else { |
| // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection |
| // which recognizes if we are a CMS generation, and doesn't try to turn on |
| // discovery; verify that they aren't meddling. |
| assert(!rp->discovery_is_atomic(), |
| "incorrect setting of discovery predicate"); |
| assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control " |
| "ref discovery for this generation kind"); |
| // already have locks |
| checkpointRootsInitialWork(asynch); |
| // now enable ("weak") refs discovery |
| rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/); |
| _collectorState = Marking; |
| } |
| SpecializationStats::print(); |
| } |
| |
| void CMSCollector::checkpointRootsInitialWork(bool asynch) { |
| assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped"); |
| assert(_collectorState == InitialMarking, "just checking"); |
| |
| // If there has not been a GC[n-1] since last GC[n] cycle completed, |
| // precede our marking with a collection of all |
| // younger generations to keep floating garbage to a minimum. |
| // XXX: we won't do this for now -- it's an optimization to be done later. |
| |
| // already have locks |
| assert_lock_strong(bitMapLock()); |
| assert(_markBitMap.isAllClear(), "was reset at end of previous cycle"); |
| |
| // Setup the verification and class unloading state for this |
| // CMS collection cycle. |
| setup_cms_unloading_and_verification_state(); |
| |
| NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork", |
| PrintGCDetails && Verbose, true, gclog_or_tty);) |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->checkpoint_roots_initial_begin(); |
| } |
| |
| // Reset all the PLAB chunk arrays if necessary. |
| if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) { |
| reset_survivor_plab_arrays(); |
| } |
| |
| ResourceMark rm; |
| HandleMark hm; |
| |
| FalseClosure falseClosure; |
| // In the case of a synchronous collection, we will elide the |
| // remark step, so it's important to catch all the nmethod oops |
| // in this step. |
| // The final 'true' flag to gen_process_strong_roots will ensure this. |
| // If 'async' is true, we can relax the nmethod tracing. |
| MarkRefsIntoClosure notOlder(_span, &_markBitMap); |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| |
| verify_work_stacks_empty(); |
| verify_overflow_empty(); |
| |
| gch->ensure_parsability(false); // fill TLABs, but no need to retire them |
| // Update the saved marks which may affect the root scans. |
| gch->save_marks(); |
| |
| // weak reference processing has not started yet. |
| ref_processor()->set_enqueuing_is_done(false); |
| |
| { |
| // This is not needed. DEBUG_ONLY(RememberKlassesChecker imx(true);) |
| COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;) |
| gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. |
| gch->gen_process_strong_roots(_cmsGen->level(), |
| true, // younger gens are roots |
| true, // activate StrongRootsScope |
| true, // collecting perm gen |
| SharedHeap::ScanningOption(roots_scanning_options()), |
| ¬Older, |
| true, // walk all of code cache if (so & SO_CodeCache) |
| NULL); |
| } |
| |
| // Clear mod-union table; it will be dirtied in the prologue of |
| // CMS generation per each younger generation collection. |
| |
| assert(_modUnionTable.isAllClear(), |
| "Was cleared in most recent final checkpoint phase" |
| " or no bits are set in the gc_prologue before the start of the next " |
| "subsequent marking phase."); |
| |
| // Save the end of the used_region of the constituent generations |
| // to be used to limit the extent of sweep in each generation. |
| save_sweep_limits(); |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->checkpoint_roots_initial_end(gch->gc_cause()); |
| } |
| verify_overflow_empty(); |
| } |
| |
| bool CMSCollector::markFromRoots(bool asynch) { |
| // we might be tempted to assert that: |
| // assert(asynch == !SafepointSynchronize::is_at_safepoint(), |
| // "inconsistent argument?"); |
| // However that wouldn't be right, because it's possible that |
| // a safepoint is indeed in progress as a younger generation |
| // stop-the-world GC happens even as we mark in this generation. |
| assert(_collectorState == Marking, "inconsistent state?"); |
| check_correct_thread_executing(); |
| verify_overflow_empty(); |
| |
| bool res; |
| if (asynch) { |
| |
| // Start the timers for adaptive size policy for the concurrent phases |
| // Do it here so that the foreground MS can use the concurrent |
| // timer since a foreground MS might has the sweep done concurrently |
| // or STW. |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->concurrent_marking_begin(); |
| } |
| |
| // Weak ref discovery note: We may be discovering weak |
| // refs in this generation concurrent (but interleaved) with |
| // weak ref discovery by a younger generation collector. |
| |
| CMSTokenSyncWithLocks ts(true, bitMapLock()); |
| TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); |
| CMSPhaseAccounting pa(this, "mark", !PrintGCDetails); |
| res = markFromRootsWork(asynch); |
| if (res) { |
| _collectorState = Precleaning; |
| } else { // We failed and a foreground collection wants to take over |
| assert(_foregroundGCIsActive, "internal state inconsistency"); |
| assert(_restart_addr == NULL, "foreground will restart from scratch"); |
| if (PrintGCDetails) { |
| gclog_or_tty->print_cr("bailing out to foreground collection"); |
| } |
| } |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->concurrent_marking_end(); |
| } |
| } else { |
| assert(SafepointSynchronize::is_at_safepoint(), |
| "inconsistent with asynch == false"); |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->ms_collection_marking_begin(); |
| } |
| // already have locks |
| res = markFromRootsWork(asynch); |
| _collectorState = FinalMarking; |
| if (UseAdaptiveSizePolicy) { |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| size_policy()->ms_collection_marking_end(gch->gc_cause()); |
| } |
| } |
| verify_overflow_empty(); |
| return res; |
| } |
| |
| bool CMSCollector::markFromRootsWork(bool asynch) { |
| // iterate over marked bits in bit map, doing a full scan and mark |
| // from these roots using the following algorithm: |
| // . if oop is to the right of the current scan pointer, |
| // mark corresponding bit (we'll process it later) |
| // . else (oop is to left of current scan pointer) |
| // push oop on marking stack |
| // . drain the marking stack |
| |
| // Note that when we do a marking step we need to hold the |
| // bit map lock -- recall that direct allocation (by mutators) |
| // and promotion (by younger generation collectors) is also |
| // marking the bit map. [the so-called allocate live policy.] |
| // Because the implementation of bit map marking is not |
| // robust wrt simultaneous marking of bits in the same word, |
| // we need to make sure that there is no such interference |
| // between concurrent such updates. |
| |
| // already have locks |
| assert_lock_strong(bitMapLock()); |
| |
| // Clear the revisit stack, just in case there are any |
| // obsolete contents from a short-circuited previous CMS cycle. |
| _revisitStack.reset(); |
| verify_work_stacks_empty(); |
| verify_overflow_empty(); |
| assert(_revisitStack.isEmpty(), "tabula rasa"); |
| DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());) |
| bool result = false; |
| if (CMSConcurrentMTEnabled && ConcGCThreads > 0) { |
| result = do_marking_mt(asynch); |
| } else { |
| result = do_marking_st(asynch); |
| } |
| return result; |
| } |
| |
| // Forward decl |
| class CMSConcMarkingTask; |
| |
| class CMSConcMarkingTerminator: public ParallelTaskTerminator { |
| CMSCollector* _collector; |
| CMSConcMarkingTask* _task; |
| public: |
| virtual void yield(); |
| |
| // "n_threads" is the number of threads to be terminated. |
| // "queue_set" is a set of work queues of other threads. |
| // "collector" is the CMS collector associated with this task terminator. |
| // "yield" indicates whether we need the gang as a whole to yield. |
| CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) : |
| ParallelTaskTerminator(n_threads, queue_set), |
| _collector(collector) { } |
| |
| void set_task(CMSConcMarkingTask* task) { |
| _task = task; |
| } |
| }; |
| |
| class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator { |
| CMSConcMarkingTask* _task; |
| public: |
| bool should_exit_termination(); |
| void set_task(CMSConcMarkingTask* task) { |
| _task = task; |
| } |
| }; |
| |
| // MT Concurrent Marking Task |
| class CMSConcMarkingTask: public YieldingFlexibleGangTask { |
| CMSCollector* _collector; |
| int _n_workers; // requested/desired # workers |
| bool _asynch; |
| bool _result; |
| CompactibleFreeListSpace* _cms_space; |
| CompactibleFreeListSpace* _perm_space; |
| char _pad_front[64]; // padding to ... |
| HeapWord* _global_finger; // ... avoid sharing cache line |
| char _pad_back[64]; |
| HeapWord* _restart_addr; |
| |
| // Exposed here for yielding support |
| Mutex* const _bit_map_lock; |
| |
| // The per thread work queues, available here for stealing |
| OopTaskQueueSet* _task_queues; |
| |
| // Termination (and yielding) support |
| CMSConcMarkingTerminator _term; |
| CMSConcMarkingTerminatorTerminator _term_term; |
| |
| public: |
| CMSConcMarkingTask(CMSCollector* collector, |
| CompactibleFreeListSpace* cms_space, |
| CompactibleFreeListSpace* perm_space, |
| bool asynch, |
| YieldingFlexibleWorkGang* workers, |
| OopTaskQueueSet* task_queues): |
| YieldingFlexibleGangTask("Concurrent marking done multi-threaded"), |
| _collector(collector), |
| _cms_space(cms_space), |
| _perm_space(perm_space), |
| _asynch(asynch), _n_workers(0), _result(true), |
| _task_queues(task_queues), |
| _term(_n_workers, task_queues, _collector), |
| _bit_map_lock(collector->bitMapLock()) |
| { |
| _requested_size = _n_workers; |
| _term.set_task(this); |
| _term_term.set_task(this); |
| assert(_cms_space->bottom() < _perm_space->bottom(), |
| "Finger incorrectly initialized below"); |
| _restart_addr = _global_finger = _cms_space->bottom(); |
| } |
| |
| |
| OopTaskQueueSet* task_queues() { return _task_queues; } |
| |
| OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } |
| |
| HeapWord** global_finger_addr() { return &_global_finger; } |
| |
| CMSConcMarkingTerminator* terminator() { return &_term; } |
| |
| virtual void set_for_termination(int active_workers) { |
| terminator()->reset_for_reuse(active_workers); |
| } |
| |
| void work(uint worker_id); |
| bool should_yield() { |
| return ConcurrentMarkSweepThread::should_yield() |
| && !_collector->foregroundGCIsActive() |
| && _asynch; |
| } |
| |
| virtual void coordinator_yield(); // stuff done by coordinator |
| bool result() { return _result; } |
| |
| void reset(HeapWord* ra) { |
| assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)"); |
| assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)"); |
| assert(ra < _perm_space->end(), "ra too large"); |
| _restart_addr = _global_finger = ra; |
| _term.reset_for_reuse(); |
| } |
| |
| static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk, |
| OopTaskQueue* work_q); |
| |
| private: |
| void do_scan_and_mark(int i, CompactibleFreeListSpace* sp); |
| void do_work_steal(int i); |
| void bump_global_finger(HeapWord* f); |
| }; |
| |
| bool CMSConcMarkingTerminatorTerminator::should_exit_termination() { |
| assert(_task != NULL, "Error"); |
| return _task->yielding(); |
| // Note that we do not need the disjunct || _task->should_yield() above |
| // because we want terminating threads to yield only if the task |
| // is already in the midst of yielding, which happens only after at least one |
| // thread has yielded. |
| } |
| |
| void CMSConcMarkingTerminator::yield() { |
| if (_task->should_yield()) { |
| _task->yield(); |
| } else { |
| ParallelTaskTerminator::yield(); |
| } |
| } |
| |
| //////////////////////////////////////////////////////////////// |
| // Concurrent Marking Algorithm Sketch |
| //////////////////////////////////////////////////////////////// |
| // Until all tasks exhausted (both spaces): |
| // -- claim next available chunk |
| // -- bump global finger via CAS |
| // -- find first object that starts in this chunk |
| // and start scanning bitmap from that position |
| // -- scan marked objects for oops |
| // -- CAS-mark target, and if successful: |
| // . if target oop is above global finger (volatile read) |
| // nothing to do |
| // . if target oop is in chunk and above local finger |
| // then nothing to do |
| // . else push on work-queue |
| // -- Deal with possible overflow issues: |
| // . local work-queue overflow causes stuff to be pushed on |
| // global (common) overflow queue |
| // . always first empty local work queue |
| // . then get a batch of oops from global work queue if any |
| // . then do work stealing |
| // -- When all tasks claimed (both spaces) |
| // and local work queue empty, |
| // then in a loop do: |
| // . check global overflow stack; steal a batch of oops and trace |
| // . try to steal from other threads oif GOS is empty |
| // . if neither is available, offer termination |
| // -- Terminate and return result |
| // |
| void CMSConcMarkingTask::work(uint worker_id) { |
| elapsedTimer _timer; |
| ResourceMark rm; |
| HandleMark hm; |
| |
| DEBUG_ONLY(_collector->verify_overflow_empty();) |
| |
| // Before we begin work, our work queue should be empty |
| assert(work_queue(worker_id)->size() == 0, "Expected to be empty"); |
| // Scan the bitmap covering _cms_space, tracing through grey objects. |
| _timer.start(); |
| do_scan_and_mark(worker_id, _cms_space); |
| _timer.stop(); |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec", |
| worker_id, _timer.seconds()); |
| // XXX: need xxx/xxx type of notation, two timers |
| } |
| |
| // ... do the same for the _perm_space |
| _timer.reset(); |
| _timer.start(); |
| do_scan_and_mark(worker_id, _perm_space); |
| _timer.stop(); |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec", |
| worker_id, _timer.seconds()); |
| // XXX: need xxx/xxx type of notation, two timers |
| } |
| |
| // ... do work stealing |
| _timer.reset(); |
| _timer.start(); |
| do_work_steal(worker_id); |
| _timer.stop(); |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec", |
| worker_id, _timer.seconds()); |
| // XXX: need xxx/xxx type of notation, two timers |
| } |
| assert(_collector->_markStack.isEmpty(), "Should have been emptied"); |
| assert(work_queue(worker_id)->size() == 0, "Should have been emptied"); |
| // Note that under the current task protocol, the |
| // following assertion is true even of the spaces |
| // expanded since the completion of the concurrent |
| // marking. XXX This will likely change under a strict |
| // ABORT semantics. |
| assert(_global_finger > _cms_space->end() && |
| _global_finger >= _perm_space->end(), |
| "All tasks have been completed"); |
| DEBUG_ONLY(_collector->verify_overflow_empty();) |
| } |
| |
| void CMSConcMarkingTask::bump_global_finger(HeapWord* f) { |
| HeapWord* read = _global_finger; |
| HeapWord* cur = read; |
| while (f > read) { |
| cur = read; |
| read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur); |
| if (cur == read) { |
| // our cas succeeded |
| assert(_global_finger >= f, "protocol consistency"); |
| break; |
| } |
| } |
| } |
| |
| // This is really inefficient, and should be redone by |
| // using (not yet available) block-read and -write interfaces to the |
| // stack and the work_queue. XXX FIX ME !!! |
| bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk, |
| OopTaskQueue* work_q) { |
| // Fast lock-free check |
| if (ovflw_stk->length() == 0) { |
| return false; |
| } |
| assert(work_q->size() == 0, "Shouldn't steal"); |
| MutexLockerEx ml(ovflw_stk->par_lock(), |
| Mutex::_no_safepoint_check_flag); |
| // Grab up to 1/4 the size of the work queue |
| size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, |
| (size_t)ParGCDesiredObjsFromOverflowList); |
| num = MIN2(num, ovflw_stk->length()); |
| for (int i = (int) num; i > 0; i--) { |
| oop cur = ovflw_stk->pop(); |
| assert(cur != NULL, "Counted wrong?"); |
| work_q->push(cur); |
| } |
| return num > 0; |
| } |
| |
| void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) { |
| SequentialSubTasksDone* pst = sp->conc_par_seq_tasks(); |
| int n_tasks = pst->n_tasks(); |
| // We allow that there may be no tasks to do here because |
| // we are restarting after a stack overflow. |
| assert(pst->valid() || n_tasks == 0, "Uninitialized use?"); |
| uint nth_task = 0; |
| |
| HeapWord* aligned_start = sp->bottom(); |
| if (sp->used_region().contains(_restart_addr)) { |
| // Align down to a card boundary for the start of 0th task |
| // for this space. |
| aligned_start = |
| (HeapWord*)align_size_down((uintptr_t)_restart_addr, |
| CardTableModRefBS::card_size); |
| } |
| |
| size_t chunk_size = sp->marking_task_size(); |
| while (!pst->is_task_claimed(/* reference */ nth_task)) { |
| // Having claimed the nth task in this space, |
| // compute the chunk that it corresponds to: |
| MemRegion span = MemRegion(aligned_start + nth_task*chunk_size, |
| aligned_start + (nth_task+1)*chunk_size); |
| // Try and bump the global finger via a CAS; |
| // note that we need to do the global finger bump |
| // _before_ taking the intersection below, because |
| // the task corresponding to that region will be |
| // deemed done even if the used_region() expands |
| // because of allocation -- as it almost certainly will |
| // during start-up while the threads yield in the |
| // closure below. |
| HeapWord* finger = span.end(); |
| bump_global_finger(finger); // atomically |
| // There are null tasks here corresponding to chunks |
| // beyond the "top" address of the space. |
| span = span.intersection(sp->used_region()); |
| if (!span.is_empty()) { // Non-null task |
| HeapWord* prev_obj; |
| assert(!span.contains(_restart_addr) || nth_task == 0, |
| "Inconsistency"); |
| if (nth_task == 0) { |
| // For the 0th task, we'll not need to compute a block_start. |
| if (span.contains(_restart_addr)) { |
| // In the case of a restart because of stack overflow, |
| // we might additionally skip a chunk prefix. |
| prev_obj = _restart_addr; |
| } else { |
| prev_obj = span.start(); |
| } |
| } else { |
| // We want to skip the first object because |
| // the protocol is to scan any object in its entirety |
| // that _starts_ in this span; a fortiori, any |
| // object starting in an earlier span is scanned |
| // as part of an earlier claimed task. |
| // Below we use the "careful" version of block_start |
| // so we do not try to navigate uninitialized objects. |
| prev_obj = sp->block_start_careful(span.start()); |
| // Below we use a variant of block_size that uses the |
| // Printezis bits to avoid waiting for allocated |
| // objects to become initialized/parsable. |
| while (prev_obj < span.start()) { |
| size_t sz = sp->block_size_no_stall(prev_obj, _collector); |
| if (sz > 0) { |
| prev_obj += sz; |
| } else { |
| // In this case we may end up doing a bit of redundant |
| // scanning, but that appears unavoidable, short of |
| // locking the free list locks; see bug 6324141. |
| break; |
| } |
| } |
| } |
| if (prev_obj < span.end()) { |
| MemRegion my_span = MemRegion(prev_obj, span.end()); |
| // Do the marking work within a non-empty span -- |
| // the last argument to the constructor indicates whether the |
| // iteration should be incremental with periodic yields. |
| Par_MarkFromRootsClosure cl(this, _collector, my_span, |
| &_collector->_markBitMap, |
| work_queue(i), |
| &_collector->_markStack, |
| &_collector->_revisitStack, |
| _asynch); |
| _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end()); |
| } // else nothing to do for this task |
| } // else nothing to do for this task |
| } |
| // We'd be tempted to assert here that since there are no |
| // more tasks left to claim in this space, the global_finger |
| // must exceed space->top() and a fortiori space->end(). However, |
| // that would not quite be correct because the bumping of |
| // global_finger occurs strictly after the claiming of a task, |
| // so by the time we reach here the global finger may not yet |
| // have been bumped up by the thread that claimed the last |
| // task. |
| pst->all_tasks_completed(); |
| } |
| |
| class Par_ConcMarkingClosure: public Par_KlassRememberingOopClosure { |
| private: |
| CMSConcMarkingTask* _task; |
| MemRegion _span; |
| CMSBitMap* _bit_map; |
| CMSMarkStack* _overflow_stack; |
| OopTaskQueue* _work_queue; |
| protected: |
| DO_OOP_WORK_DEFN |
| public: |
| Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue, |
| CMSBitMap* bit_map, CMSMarkStack* overflow_stack, |
| CMSMarkStack* revisit_stack): |
| Par_KlassRememberingOopClosure(collector, collector->ref_processor(), revisit_stack), |
| _task(task), |
| _span(collector->_span), |
| _work_queue(work_queue), |
| _bit_map(bit_map), |
| _overflow_stack(overflow_stack) |
| { } |
| virtual void do_oop(oop* p); |
| virtual void do_oop(narrowOop* p); |
| void trim_queue(size_t max); |
| void handle_stack_overflow(HeapWord* lost); |
| void do_yield_check() { |
| if (_task->should_yield()) { |
| _task->yield(); |
| } |
| } |
| }; |
| |
| // Grey object scanning during work stealing phase -- |
| // the salient assumption here is that any references |
| // that are in these stolen objects being scanned must |
| // already have been initialized (else they would not have |
| // been published), so we do not need to check for |
| // uninitialized objects before pushing here. |
| void Par_ConcMarkingClosure::do_oop(oop obj) { |
| assert(obj->is_oop_or_null(true), "expected an oop or NULL"); |
| HeapWord* addr = (HeapWord*)obj; |
| // Check if oop points into the CMS generation |
| // and is not marked |
| if (_span.contains(addr) && !_bit_map->isMarked(addr)) { |
| // a white object ... |
| // If we manage to "claim" the object, by being the |
| // first thread to mark it, then we push it on our |
| // marking stack |
| if (_bit_map->par_mark(addr)) { // ... now grey |
| // push on work queue (grey set) |
| bool simulate_overflow = false; |
| NOT_PRODUCT( |
| if (CMSMarkStackOverflowALot && |
| _collector->simulate_overflow()) { |
| // simulate a stack overflow |
| simulate_overflow = true; |
| } |
| ) |
| if (simulate_overflow || |
| !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) { |
| // stack overflow |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print_cr("CMS marking stack overflow (benign) at " |
| SIZE_FORMAT, _overflow_stack->capacity()); |
| } |
| // We cannot assert that the overflow stack is full because |
| // it may have been emptied since. |
| assert(simulate_overflow || |
| _work_queue->size() == _work_queue->max_elems(), |
| "Else push should have succeeded"); |
| handle_stack_overflow(addr); |
| } |
| } // Else, some other thread got there first |
| do_yield_check(); |
| } |
| } |
| |
| void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); } |
| void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); } |
| |
| void Par_ConcMarkingClosure::trim_queue(size_t max) { |
| while (_work_queue->size() > max) { |
| oop new_oop; |
| if (_work_queue->pop_local(new_oop)) { |
| assert(new_oop->is_oop(), "Should be an oop"); |
| assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object"); |
| assert(_span.contains((HeapWord*)new_oop), "Not in span"); |
| assert(new_oop->is_parsable(), "Should be parsable"); |
| new_oop->oop_iterate(this); // do_oop() above |
| do_yield_check(); |
| } |
| } |
| } |
| |
| // Upon stack overflow, we discard (part of) the stack, |
| // remembering the least address amongst those discarded |
| // in CMSCollector's _restart_address. |
| void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) { |
| // We need to do this under a mutex to prevent other |
| // workers from interfering with the work done below. |
| MutexLockerEx ml(_overflow_stack->par_lock(), |
| Mutex::_no_safepoint_check_flag); |
| // Remember the least grey address discarded |
| HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost); |
| _collector->lower_restart_addr(ra); |
| _overflow_stack->reset(); // discard stack contents |
| _overflow_stack->expand(); // expand the stack if possible |
| } |
| |
| |
| void CMSConcMarkingTask::do_work_steal(int i) { |
| OopTaskQueue* work_q = work_queue(i); |
| oop obj_to_scan; |
| CMSBitMap* bm = &(_collector->_markBitMap); |
| CMSMarkStack* ovflw = &(_collector->_markStack); |
| CMSMarkStack* revisit = &(_collector->_revisitStack); |
| int* seed = _collector->hash_seed(i); |
| Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw, revisit); |
| while (true) { |
| cl.trim_queue(0); |
| assert(work_q->size() == 0, "Should have been emptied above"); |
| if (get_work_from_overflow_stack(ovflw, work_q)) { |
| // Can't assert below because the work obtained from the |
| // overflow stack may already have been stolen from us. |
| // assert(work_q->size() > 0, "Work from overflow stack"); |
| continue; |
| } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) { |
| assert(obj_to_scan->is_oop(), "Should be an oop"); |
| assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object"); |
| obj_to_scan->oop_iterate(&cl); |
| } else if (terminator()->offer_termination(&_term_term)) { |
| assert(work_q->size() == 0, "Impossible!"); |
| break; |
| } else if (yielding() || should_yield()) { |
| yield(); |
| } |
| } |
| } |
| |
| // This is run by the CMS (coordinator) thread. |
| void CMSConcMarkingTask::coordinator_yield() { |
| assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| "CMS thread should hold CMS token"); |
| DEBUG_ONLY(RememberKlassesChecker mux(false);) |
| // First give up the locks, then yield, then re-lock |
| // We should probably use a constructor/destructor idiom to |
| // do this unlock/lock or modify the MutexUnlocker class to |
| // serve our purpose. XXX |
| assert_lock_strong(_bit_map_lock); |
| _bit_map_lock->unlock(); |
| ConcurrentMarkSweepThread::desynchronize(true); |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| _collector->stopTimer(); |
| if (PrintCMSStatistics != 0) { |
| _collector->incrementYields(); |
| } |
| _collector->icms_wait(); |
| |
| // It is possible for whichever thread initiated the yield request |
| // not to get a chance to wake up and take the bitmap lock between |
| // this thread releasing it and reacquiring it. So, while the |
| // should_yield() flag is on, let's sleep for a bit to give the |
| // other thread a chance to wake up. The limit imposed on the number |
| // of iterations is defensive, to avoid any unforseen circumstances |
| // putting us into an infinite loop. Since it's always been this |
| // (coordinator_yield()) method that was observed to cause the |
| // problem, we are using a parameter (CMSCoordinatorYieldSleepCount) |
| // which is by default non-zero. For the other seven methods that |
| // also perform the yield operation, as are using a different |
| // parameter (CMSYieldSleepCount) which is by default zero. This way we |
| // can enable the sleeping for those methods too, if necessary. |
| // See 6442774. |
| // |
| // We really need to reconsider the synchronization between the GC |
| // thread and the yield-requesting threads in the future and we |
| // should really use wait/notify, which is the recommended |
| // way of doing this type of interaction. Additionally, we should |
| // consolidate the eight methods that do the yield operation and they |
| // are almost identical into one for better maintenability and |
| // readability. See 6445193. |
| // |
| // Tony 2006.06.29 |
| for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount && |
| ConcurrentMarkSweepThread::should_yield() && |
| !CMSCollector::foregroundGCIsActive(); ++i) { |
| os::sleep(Thread::current(), 1, false); |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| } |
| |
| ConcurrentMarkSweepThread::synchronize(true); |
| _bit_map_lock->lock_without_safepoint_check(); |
| _collector->startTimer(); |
| } |
| |
| bool CMSCollector::do_marking_mt(bool asynch) { |
| assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition"); |
| int num_workers = AdaptiveSizePolicy::calc_active_conc_workers( |
| conc_workers()->total_workers(), |
| conc_workers()->active_workers(), |
| Threads::number_of_non_daemon_threads()); |
| conc_workers()->set_active_workers(num_workers); |
| |
| CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); |
| CompactibleFreeListSpace* perm_space = _permGen->cmsSpace(); |
| |
| CMSConcMarkingTask tsk(this, |
| cms_space, |
| perm_space, |
| asynch, |
| conc_workers(), |
| task_queues()); |
| |
| // Since the actual number of workers we get may be different |
| // from the number we requested above, do we need to do anything different |
| // below? In particular, may be we need to subclass the SequantialSubTasksDone |
| // class?? XXX |
| cms_space ->initialize_sequential_subtasks_for_marking(num_workers); |
| perm_space->initialize_sequential_subtasks_for_marking(num_workers); |
| |
| // Refs discovery is already non-atomic. |
| assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic"); |
| assert(ref_processor()->discovery_is_mt(), "Discovery should be MT"); |
| DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());) |
| conc_workers()->start_task(&tsk); |
| while (tsk.yielded()) { |
| tsk.coordinator_yield(); |
| conc_workers()->continue_task(&tsk); |
| } |
| // If the task was aborted, _restart_addr will be non-NULL |
| assert(tsk.completed() || _restart_addr != NULL, "Inconsistency"); |
| while (_restart_addr != NULL) { |
| // XXX For now we do not make use of ABORTED state and have not |
| // yet implemented the right abort semantics (even in the original |
| // single-threaded CMS case). That needs some more investigation |
| // and is deferred for now; see CR# TBF. 07252005YSR. XXX |
| assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency"); |
| // If _restart_addr is non-NULL, a marking stack overflow |
| // occurred; we need to do a fresh marking iteration from the |
| // indicated restart address. |
| if (_foregroundGCIsActive && asynch) { |
| // We may be running into repeated stack overflows, having |
| // reached the limit of the stack size, while making very |
| // slow forward progress. It may be best to bail out and |
| // let the foreground collector do its job. |
| // Clear _restart_addr, so that foreground GC |
| // works from scratch. This avoids the headache of |
| // a "rescan" which would otherwise be needed because |
| // of the dirty mod union table & card table. |
| _restart_addr = NULL; |
| return false; |
| } |
| // Adjust the task to restart from _restart_addr |
| tsk.reset(_restart_addr); |
| cms_space ->initialize_sequential_subtasks_for_marking(num_workers, |
| _restart_addr); |
| perm_space->initialize_sequential_subtasks_for_marking(num_workers, |
| _restart_addr); |
| _restart_addr = NULL; |
| // Get the workers going again |
| conc_workers()->start_task(&tsk); |
| while (tsk.yielded()) { |
| tsk.coordinator_yield(); |
| conc_workers()->continue_task(&tsk); |
| } |
| } |
| assert(tsk.completed(), "Inconsistency"); |
| assert(tsk.result() == true, "Inconsistency"); |
| return true; |
| } |
| |
| bool CMSCollector::do_marking_st(bool asynch) { |
| ResourceMark rm; |
| HandleMark hm; |
| |
| // Temporarily make refs discovery single threaded (non-MT) |
| ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false); |
| MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap, |
| &_markStack, &_revisitStack, CMSYield && asynch); |
| // the last argument to iterate indicates whether the iteration |
| // should be incremental with periodic yields. |
| _markBitMap.iterate(&markFromRootsClosure); |
| // If _restart_addr is non-NULL, a marking stack overflow |
| // occurred; we need to do a fresh iteration from the |
| // indicated restart address. |
| while (_restart_addr != NULL) { |
| if (_foregroundGCIsActive && asynch) { |
| // We may be running into repeated stack overflows, having |
| // reached the limit of the stack size, while making very |
| // slow forward progress. It may be best to bail out and |
| // let the foreground collector do its job. |
| // Clear _restart_addr, so that foreground GC |
| // works from scratch. This avoids the headache of |
| // a "rescan" which would otherwise be needed because |
| // of the dirty mod union table & card table. |
| _restart_addr = NULL; |
| return false; // indicating failure to complete marking |
| } |
| // Deal with stack overflow: |
| // we restart marking from _restart_addr |
| HeapWord* ra = _restart_addr; |
| markFromRootsClosure.reset(ra); |
| _restart_addr = NULL; |
| _markBitMap.iterate(&markFromRootsClosure, ra, _span.end()); |
| } |
| return true; |
| } |
| |
| void CMSCollector::preclean() { |
| check_correct_thread_executing(); |
| assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread"); |
| verify_work_stacks_empty(); |
| verify_overflow_empty(); |
| _abort_preclean = false; |
| if (CMSPrecleaningEnabled) { |
| _eden_chunk_index = 0; |
| size_t used = get_eden_used(); |
| size_t capacity = get_eden_capacity(); |
| // Don't start sampling unless we will get sufficiently |
| // many samples. |
| if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100) |
| * CMSScheduleRemarkEdenPenetration)) { |
| _start_sampling = true; |
| } else { |
| _start_sampling = false; |
| } |
| TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); |
| CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails); |
| preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1); |
| } |
| CMSTokenSync x(true); // is cms thread |
| if (CMSPrecleaningEnabled) { |
| sample_eden(); |
| _collectorState = AbortablePreclean; |
| } else { |
| _collectorState = FinalMarking; |
| } |
| verify_work_stacks_empty(); |
| verify_overflow_empty(); |
| } |
| |
| // Try and schedule the remark such that young gen |
| // occupancy is CMSScheduleRemarkEdenPenetration %. |
| void CMSCollector::abortable_preclean() { |
| check_correct_thread_executing(); |
| assert(CMSPrecleaningEnabled, "Inconsistent control state"); |
| assert(_collectorState == AbortablePreclean, "Inconsistent control state"); |
| |
| // If Eden's current occupancy is below this threshold, |
| // immediately schedule the remark; else preclean |
| // past the next scavenge in an effort to |
| // schedule the pause as described avove. By choosing |
| // CMSScheduleRemarkEdenSizeThreshold >= max eden size |
| // we will never do an actual abortable preclean cycle. |
| if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) { |
| TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); |
| CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails); |
| // We need more smarts in the abortable preclean |
| // loop below to deal with cases where allocation |
| // in young gen is very very slow, and our precleaning |
| // is running a losing race against a horde of |
| // mutators intent on flooding us with CMS updates |
| // (dirty cards). |
| // One, admittedly dumb, strategy is to give up |
| // after a certain number of abortable precleaning loops |
| // or after a certain maximum time. We want to make |
| // this smarter in the next iteration. |
| // XXX FIX ME!!! YSR |
| size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0; |
| while (!(should_abort_preclean() || |
| ConcurrentMarkSweepThread::should_terminate())) { |
| workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2); |
| cumworkdone += workdone; |
| loops++; |
| // Voluntarily terminate abortable preclean phase if we have |
| // been at it for too long. |
| if ((CMSMaxAbortablePrecleanLoops != 0) && |
| loops >= CMSMaxAbortablePrecleanLoops) { |
| if (PrintGCDetails) { |
| gclog_or_tty->print(" CMS: abort preclean due to loops "); |
| } |
| break; |
| } |
| if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) { |
| if (PrintGCDetails) { |
| gclog_or_tty->print(" CMS: abort preclean due to time "); |
| } |
| break; |
| } |
| // If we are doing little work each iteration, we should |
| // take a short break. |
| if (workdone < CMSAbortablePrecleanMinWorkPerIteration) { |
| // Sleep for some time, waiting for work to accumulate |
| stopTimer(); |
| cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis); |
| startTimer(); |
| waited++; |
| } |
| } |
| if (PrintCMSStatistics > 0) { |
| gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ", |
| loops, waited, cumworkdone); |
| } |
| } |
| CMSTokenSync x(true); // is cms thread |
| if (_collectorState != Idling) { |
| assert(_collectorState == AbortablePreclean, |
| "Spontaneous state transition?"); |
| _collectorState = FinalMarking; |
| } // Else, a foreground collection completed this CMS cycle. |
| return; |
| } |
| |
| // Respond to an Eden sampling opportunity |
| void CMSCollector::sample_eden() { |
| // Make sure a young gc cannot sneak in between our |
| // reading and recording of a sample. |
| assert(Thread::current()->is_ConcurrentGC_thread(), |
| "Only the cms thread may collect Eden samples"); |
| assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| "Should collect samples while holding CMS token"); |
| if (!_start_sampling) { |
| return; |
| } |
| if (_eden_chunk_array) { |
| if (_eden_chunk_index < _eden_chunk_capacity) { |
| _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample |
| assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr, |
| "Unexpected state of Eden"); |
| // We'd like to check that what we just sampled is an oop-start address; |
| // however, we cannot do that here since the object may not yet have been |
| // initialized. So we'll instead do the check when we _use_ this sample |
| // later. |
| if (_eden_chunk_index == 0 || |
| (pointer_delta(_eden_chunk_array[_eden_chunk_index], |
| _eden_chunk_array[_eden_chunk_index-1]) |
| >= CMSSamplingGrain)) { |
| _eden_chunk_index++; // commit sample |
| } |
| } |
| } |
| if ((_collectorState == AbortablePreclean) && !_abort_preclean) { |
| size_t used = get_eden_used(); |
| size_t capacity = get_eden_capacity(); |
| assert(used <= capacity, "Unexpected state of Eden"); |
| if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) { |
| _abort_preclean = true; |
| } |
| } |
| } |
| |
| |
| size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) { |
| assert(_collectorState == Precleaning || |
| _collectorState == AbortablePreclean, "incorrect state"); |
| ResourceMark rm; |
| HandleMark hm; |
| |
| // Precleaning is currently not MT but the reference processor |
| // may be set for MT. Disable it temporarily here. |
| ReferenceProcessor* rp = ref_processor(); |
| ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false); |
| |
| // Do one pass of scrubbing the discovered reference lists |
| // to remove any reference objects with strongly-reachable |
| // referents. |
| if (clean_refs) { |
| CMSPrecleanRefsYieldClosure yield_cl(this); |
| assert(rp->span().equals(_span), "Spans should be equal"); |
| CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap, |
| &_markStack, &_revisitStack, |
| true /* preclean */); |
| CMSDrainMarkingStackClosure complete_trace(this, |
| _span, &_markBitMap, &_markStack, |
| &keep_alive, true /* preclean */); |
| |
| // We don't want this step to interfere with a young |
| // collection because we don't want to take CPU |
| // or memory bandwidth away from the young GC threads |
| // (which may be as many as there are CPUs). |
| // Note that we don't need to protect ourselves from |
| // interference with mutators because they can't |
| // manipulate the discovered reference lists nor affect |
| // the computed reachability of the referents, the |
| // only properties manipulated by the precleaning |
| // of these reference lists. |
| stopTimer(); |
| CMSTokenSyncWithLocks x(true /* is cms thread */, |
| bitMapLock()); |
| startTimer(); |
| sample_eden(); |
| |
| // The following will yield to allow foreground |
| // collection to proceed promptly. XXX YSR: |
| // The code in this method may need further |
| // tweaking for better performance and some restructuring |
| // for cleaner interfaces. |
| rp->preclean_discovered_references( |
| rp->is_alive_non_header(), &keep_alive, &complete_trace, |
| &yield_cl, should_unload_classes()); |
| } |
| |
| if (clean_survivor) { // preclean the active survivor space(s) |
| assert(_young_gen->kind() == Generation::DefNew || |
| _young_gen->kind() == Generation::ParNew || |
| _young_gen->kind() == Generation::ASParNew, |
| "incorrect type for cast"); |
| DefNewGeneration* dng = (DefNewGeneration*)_young_gen; |
| PushAndMarkClosure pam_cl(this, _span, ref_processor(), |
| &_markBitMap, &_modUnionTable, |
| &_markStack, &_revisitStack, |
| true /* precleaning phase */); |
| stopTimer(); |
| CMSTokenSyncWithLocks ts(true /* is cms thread */, |
| bitMapLock()); |
| startTimer(); |
| unsigned int before_count = |
| GenCollectedHeap::heap()->total_collections(); |
| SurvivorSpacePrecleanClosure |
| sss_cl(this, _span, &_markBitMap, &_markStack, |
| &pam_cl, before_count, CMSYield); |
| DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());) |
| dng->from()->object_iterate_careful(&sss_cl); |
| dng->to()->object_iterate_careful(&sss_cl); |
| } |
| MarkRefsIntoAndScanClosure |
| mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable, |
| &_markStack, &_revisitStack, this, CMSYield, |
| true /* precleaning phase */); |
| // CAUTION: The following closure has persistent state that may need to |
| // be reset upon a decrease in the sequence of addresses it |
| // processes. |
| ScanMarkedObjectsAgainCarefullyClosure |
| smoac_cl(this, _span, |
| &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield); |
| |
| // Preclean dirty cards in ModUnionTable and CardTable using |
| // appropriate convergence criterion; |
| // repeat CMSPrecleanIter times unless we find that |
| // we are losing. |
| assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large"); |
| assert(CMSPrecleanNumerator < CMSPrecleanDenominator, |
| "Bad convergence multiplier"); |
| assert(CMSPrecleanThreshold >= 100, |
| "Unreasonably low CMSPrecleanThreshold"); |
| |
| size_t numIter, cumNumCards, lastNumCards, curNumCards; |
| for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0; |
| numIter < CMSPrecleanIter; |
| numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) { |
| curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl); |
| if (CMSPermGenPrecleaningEnabled) { |
| curNumCards += preclean_mod_union_table(_permGen, &smoac_cl); |
| } |
| if (Verbose && PrintGCDetails) { |
| gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards); |
| } |
| // Either there are very few dirty cards, so re-mark |
| // pause will be small anyway, or our pre-cleaning isn't |
| // that much faster than the rate at which cards are being |
| // dirtied, so we might as well stop and re-mark since |
| // precleaning won't improve our re-mark time by much. |
| if (curNumCards <= CMSPrecleanThreshold || |
| (numIter > 0 && |
| (curNumCards * CMSPrecleanDenominator > |
| lastNumCards * CMSPrecleanNumerator))) { |
| numIter++; |
| cumNumCards += curNumCards; |
| break; |
| } |
| } |
| curNumCards = preclean_card_table(_cmsGen, &smoac_cl); |
| if (CMSPermGenPrecleaningEnabled) { |
| curNumCards += preclean_card_table(_permGen, &smoac_cl); |
| } |
| cumNumCards += curNumCards; |
| if (PrintGCDetails && PrintCMSStatistics != 0) { |
| gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)", |
| curNumCards, cumNumCards, numIter); |
| } |
| return cumNumCards; // as a measure of useful work done |
| } |
| |
| // PRECLEANING NOTES: |
| // Precleaning involves: |
| // . reading the bits of the modUnionTable and clearing the set bits. |
| // . For the cards corresponding to the set bits, we scan the |
| // objects on those cards. This means we need the free_list_lock |
| // so that we can safely iterate over the CMS space when scanning |
| // for oops. |
| // . When we scan the objects, we'll be both reading and setting |
| // marks in the marking bit map, so we'll need the marking bit map. |
| // . For protecting _collector_state transitions, we take the CGC_lock. |
| // Note that any races in the reading of of card table entries by the |
| // CMS thread on the one hand and the clearing of those entries by the |
| // VM thread or the setting of those entries by the mutator threads on the |
| // other are quite benign. However, for efficiency it makes sense to keep |
| // the VM thread from racing with the CMS thread while the latter is |
| // dirty card info to the modUnionTable. We therefore also use the |
| // CGC_lock to protect the reading of the card table and the mod union |
| // table by the CM thread. |
| // . We run concurrently with mutator updates, so scanning |
| // needs to be done carefully -- we should not try to scan |
| // potentially uninitialized objects. |
| // |
| // Locking strategy: While holding the CGC_lock, we scan over and |
| // reset a maximal dirty range of the mod union / card tables, then lock |
| // the free_list_lock and bitmap lock to do a full marking, then |
| // release these locks; and repeat the cycle. This allows for a |
| // certain amount of fairness in the sharing of these locks between |
| // the CMS collector on the one hand, and the VM thread and the |
| // mutators on the other. |
| |
| // NOTE: preclean_mod_union_table() and preclean_card_table() |
| // further below are largely identical; if you need to modify |
| // one of these methods, please check the other method too. |
| |
| size_t CMSCollector::preclean_mod_union_table( |
| ConcurrentMarkSweepGeneration* gen, |
| ScanMarkedObjectsAgainCarefullyClosure* cl) { |
| verify_work_stacks_empty(); |
| verify_overflow_empty(); |
| |
| // Turn off checking for this method but turn it back on |
| // selectively. There are yield points in this method |
| // but it is difficult to turn the checking off just around |
| // the yield points. It is simpler to selectively turn |
| // it on. |
| DEBUG_ONLY(RememberKlassesChecker mux(false);) |
| |
| // strategy: starting with the first card, accumulate contiguous |
| // ranges of dirty cards; clear these cards, then scan the region |
| // covered by these cards. |
| |
| // Since all of the MUT is committed ahead, we can just use |
| // that, in case the generations expand while we are precleaning. |
| // It might also be fine to just use the committed part of the |
| // generation, but we might potentially miss cards when the |
| // generation is rapidly expanding while we are in the midst |
| // of precleaning. |
| HeapWord* startAddr = gen->reserved().start(); |
| HeapWord* endAddr = gen->reserved().end(); |
| |
| cl->setFreelistLock(gen->freelistLock()); // needed for yielding |
| |
| size_t numDirtyCards, cumNumDirtyCards; |
| HeapWord *nextAddr, *lastAddr; |
| for (cumNumDirtyCards = numDirtyCards = 0, |
| nextAddr = lastAddr = startAddr; |
| nextAddr < endAddr; |
| nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) { |
| |
| ResourceMark rm; |
| HandleMark hm; |
| |
| MemRegion dirtyRegion; |
| { |
| stopTimer(); |
| // Potential yield point |
| CMSTokenSync ts(true); |
| startTimer(); |
| sample_eden(); |
| // Get dirty region starting at nextOffset (inclusive), |
| // simultaneously clearing it. |
| dirtyRegion = |
| _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr); |
| assert(dirtyRegion.start() >= nextAddr, |
| "returned region inconsistent?"); |
| } |
| // Remember where the next search should begin. |
| // The returned region (if non-empty) is a right open interval, |
| // so lastOffset is obtained from the right end of that |
| // interval. |
| lastAddr = dirtyRegion.end(); |
| // Should do something more transparent and less hacky XXX |
| numDirtyCards = |
| _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size()); |
| |
| // We'll scan the cards in the dirty region (with periodic |
| // yields for foreground GC as needed). |
| if (!dirtyRegion.is_empty()) { |
| assert(numDirtyCards > 0, "consistency check"); |
| HeapWord* stop_point = NULL; |
| stopTimer(); |
| // Potential yield point |
| CMSTokenSyncWithLocks ts(true, gen->freelistLock(), |
| bitMapLock()); |
| startTimer(); |
| { |
| verify_work_stacks_empty(); |
| verify_overflow_empty(); |
| sample_eden(); |
| DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());) |
| stop_point = |
| gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl); |
| } |
| if (stop_point != NULL) { |
| // The careful iteration stopped early either because it found an |
| // uninitialized object, or because we were in the midst of an |
| // "abortable preclean", which should now be aborted. Redirty |
| // the bits corresponding to the partially-scanned or unscanned |
| // cards. We'll either restart at the next block boundary or |
| // abort the preclean. |
| assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) || |
| (_collectorState == AbortablePreclean && should_abort_preclean()), |
| "Unparsable objects should only be in perm gen."); |
| _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end())); |
| if (should_abort_preclean()) { |
| break; // out of preclean loop |
| } else { |
| // Compute the next address at which preclean should pick up; |
| // might need bitMapLock in order to read P-bits. |
| lastAddr = next_card_start_after_block(stop_point); |
| } |
| } |
| } else { |
| assert(lastAddr == endAddr, "consistency check"); |
| assert(numDirtyCards == 0, "consistency check"); |
| break; |
| } |
| } |
| verify_work_stacks_empty(); |
| verify_overflow_empty(); |
| return cumNumDirtyCards; |
| } |
| |
| // NOTE: preclean_mod_union_table() above and preclean_card_table() |
| // below are largely identical; if you need to modify |
| // one of these methods, please check the other method too. |
| |
| size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen, |
| ScanMarkedObjectsAgainCarefullyClosure* cl) { |
| // strategy: it's similar to precleamModUnionTable above, in that |
| // we accumulate contiguous ranges of dirty cards, mark these cards |
| // precleaned, then scan the region covered by these cards. |
| HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high()); |
| HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low()); |
| |
| cl->setFreelistLock(gen->freelistLock()); // needed for yielding |
| |
| size_t numDirtyCards, cumNumDirtyCards; |
| HeapWord *lastAddr, *nextAddr; |
| |
| for (cumNumDirtyCards = numDirtyCards = 0, |
| nextAddr = lastAddr = startAddr; |
| nextAddr < endAddr; |
| nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) { |
| |
| ResourceMark rm; |
| HandleMark hm; |
| |
| MemRegion dirtyRegion; |
| { |
| // See comments in "Precleaning notes" above on why we |
| // do this locking. XXX Could the locking overheads be |
| // too high when dirty cards are sparse? [I don't think so.] |
| stopTimer(); |
| CMSTokenSync x(true); // is cms thread |
| startTimer(); |
| sample_eden(); |
| // Get and clear dirty region from card table |
| dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset( |
| MemRegion(nextAddr, endAddr), |
| true, |
| CardTableModRefBS::precleaned_card_val()); |
| |
| assert(dirtyRegion.start() >= nextAddr, |
| "returned region inconsistent?"); |
| } |
| lastAddr = dirtyRegion.end(); |
| numDirtyCards = |
| dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words; |
| |
| if (!dirtyRegion.is_empty()) { |
| stopTimer(); |
| CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock()); |
| startTimer(); |
| sample_eden(); |
| verify_work_stacks_empty(); |
| verify_overflow_empty(); |
| DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());) |
| HeapWord* stop_point = |
| gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl); |
| if (stop_point != NULL) { |
| // The careful iteration stopped early because it found an |
| // uninitialized object. Redirty the bits corresponding to the |
| // partially-scanned or unscanned cards, and start again at the |
| // next block boundary. |
| assert(CMSPermGenPrecleaningEnabled || |
| (_collectorState == AbortablePreclean && should_abort_preclean()), |
| "Unparsable objects should only be in perm gen."); |
| _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end())); |
| if (should_abort_preclean()) { |
| break; // out of preclean loop |
| } else { |
| // Compute the next address at which preclean should pick up. |
| lastAddr = next_card_start_after_block(stop_point); |
| } |
| } |
| } else { |
| break; |
| } |
| } |
| verify_work_stacks_empty(); |
| verify_overflow_empty(); |
| return cumNumDirtyCards; |
| } |
| |
| void CMSCollector::checkpointRootsFinal(bool asynch, |
| bool clear_all_soft_refs, bool init_mark_was_synchronous) { |
| assert(_collectorState == FinalMarking, "incorrect state transition?"); |
| check_correct_thread_executing(); |
| // world is stopped at this checkpoint |
| assert(SafepointSynchronize::is_at_safepoint(), |
| "world should be stopped"); |
| TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause()); |
| |
| verify_work_stacks_empty(); |
| verify_overflow_empty(); |
| |
| SpecializationStats::clear(); |
| if (PrintGCDetails) { |
| gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]", |
| _young_gen->used() / K, |
| _young_gen->capacity() / K); |
| } |
| if (asynch) { |
| if (CMSScavengeBeforeRemark) { |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| // Temporarily set flag to false, GCH->do_collection will |
| // expect it to be false and set to true |
| FlagSetting fl(gch->_is_gc_active, false); |
| NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark", |
| PrintGCDetails && Verbose, true, gclog_or_tty);) |
| int level = _cmsGen->level() - 1; |
| if (level >= 0) { |
| gch->do_collection(true, // full (i.e. force, see below) |
| false, // !clear_all_soft_refs |
| 0, // size |
| false, // is_tlab |
| level // max_level |
| ); |
| } |
| } |
| FreelistLocker x(this); |
| MutexLockerEx y(bitMapLock(), |
| Mutex::_no_safepoint_check_flag); |
| assert(!init_mark_was_synchronous, "but that's impossible!"); |
| checkpointRootsFinalWork(asynch, clear_all_soft_refs, false); |
| } else { |
| // already have all the locks |
| checkpointRootsFinalWork(asynch, clear_all_soft_refs, |
| init_mark_was_synchronous); |
| } |
| verify_work_stacks_empty(); |
| verify_overflow_empty(); |
| SpecializationStats::print(); |
| } |
| |
| void CMSCollector::checkpointRootsFinalWork(bool asynch, |
| bool clear_all_soft_refs, bool init_mark_was_synchronous) { |
| |
| NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);) |
| |
| assert(haveFreelistLocks(), "must have free list locks"); |
| assert_lock_strong(bitMapLock()); |
| |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->checkpoint_roots_final_begin(); |
| } |
| |
| ResourceMark rm; |
| HandleMark hm; |
| |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| |
| if (should_unload_classes()) { |
| CodeCache::gc_prologue(); |
| } |
| assert(haveFreelistLocks(), "must have free list locks"); |
| assert_lock_strong(bitMapLock()); |
| |
| DEBUG_ONLY(RememberKlassesChecker fmx(should_unload_classes());) |
| if (!init_mark_was_synchronous) { |
| // We might assume that we need not fill TLAB's when |
| // CMSScavengeBeforeRemark is set, because we may have just done |
| // a scavenge which would have filled all TLAB's -- and besides |
| // Eden would be empty. This however may not always be the case -- |
| // for instance although we asked for a scavenge, it may not have |
| // happened because of a JNI critical section. We probably need |
| // a policy for deciding whether we can in that case wait until |
| // the critical section releases and then do the remark following |
| // the scavenge, and skip it here. In the absence of that policy, |
| // or of an indication of whether the scavenge did indeed occur, |
| // we cannot rely on TLAB's having been filled and must do |
| // so here just in case a scavenge did not happen. |
| gch->ensure_parsability(false); // fill TLAB's, but no need to retire them |
| // Update the saved marks which may affect the root scans. |
| gch->save_marks(); |
| |
| { |
| COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;) |
| |
| // Note on the role of the mod union table: |
| // Since the marker in "markFromRoots" marks concurrently with |
| // mutators, it is possible for some reachable objects not to have been |
| // scanned. For instance, an only reference to an object A was |
| // placed in object B after the marker scanned B. Unless B is rescanned, |
| // A would be collected. Such updates to references in marked objects |
| // are detected via the mod union table which is the set of all cards |
| // dirtied since the first checkpoint in this GC cycle and prior to |
| // the most recent young generation GC, minus those cleaned up by the |
| // concurrent precleaning. |
| if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) { |
| TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty); |
| do_remark_parallel(); |
| } else { |
| TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false, |
| gclog_or_tty); |
| do_remark_non_parallel(); |
| } |
| } |
| } else { |
| assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode"); |
| // The initial mark was stop-world, so there's no rescanning to |
| // do; go straight on to the next step below. |
| } |
| verify_work_stacks_empty(); |
| verify_overflow_empty(); |
| |
| { |
| NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);) |
| refProcessingWork(asynch, clear_all_soft_refs); |
| } |
| verify_work_stacks_empty(); |
| verify_overflow_empty(); |
| |
| if (should_unload_classes()) { |
| CodeCache::gc_epilogue(); |
| } |
| JvmtiExport::gc_epilogue(); |
| |
| // If we encountered any (marking stack / work queue) overflow |
| // events during the current CMS cycle, take appropriate |
| // remedial measures, where possible, so as to try and avoid |
| // recurrence of that condition. |
| assert(_markStack.isEmpty(), "No grey objects"); |
| size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw + |
| _ser_kac_ovflw + _ser_kac_preclean_ovflw; |
| if (ser_ovflw > 0) { |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print_cr("Marking stack overflow (benign) " |
| "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT |
| ", kac_preclean="SIZE_FORMAT")", |
| _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, |
| _ser_kac_ovflw, _ser_kac_preclean_ovflw); |
| } |
| _markStack.expand(); |
| _ser_pmc_remark_ovflw = 0; |
| _ser_pmc_preclean_ovflw = 0; |
| _ser_kac_preclean_ovflw = 0; |
| _ser_kac_ovflw = 0; |
| } |
| if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) { |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print_cr("Work queue overflow (benign) " |
| "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")", |
| _par_pmc_remark_ovflw, _par_kac_ovflw); |
| } |
| _par_pmc_remark_ovflw = 0; |
| _par_kac_ovflw = 0; |
| } |
| if (PrintCMSStatistics != 0) { |
| if (_markStack._hit_limit > 0) { |
| gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")", |
| _markStack._hit_limit); |
| } |
| if (_markStack._failed_double > 0) { |
| gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT")," |
| " current capacity "SIZE_FORMAT, |
| _markStack._failed_double, |
| _markStack.capacity()); |
| } |
| } |
| _markStack._hit_limit = 0; |
| _markStack._failed_double = 0; |
| |
| // Check that all the klasses have been checked |
| assert(_revisitStack.isEmpty(), "Not all klasses revisited"); |
| |
| if ((VerifyAfterGC || VerifyDuringGC) && |
| GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { |
| verify_after_remark(); |
| } |
| |
| // Change under the freelistLocks. |
| _collectorState = Sweeping; |
| // Call isAllClear() under bitMapLock |
| assert(_modUnionTable.isAllClear(), "Should be clear by end of the" |
| " final marking"); |
| if (UseAdaptiveSizePolicy) { |
| size_policy()->checkpoint_roots_final_end(gch->gc_cause()); |
| } |
| } |
| |
| // Parallel remark task |
| class CMSParRemarkTask: public AbstractGangTask { |
| CMSCollector* _collector; |
| int _n_workers; |
| CompactibleFreeListSpace* _cms_space; |
| CompactibleFreeListSpace* _perm_space; |
| |
| // The per-thread work queues, available here for stealing. |
| OopTaskQueueSet* _task_queues; |
| ParallelTaskTerminator _term; |
| |
| public: |
| // A value of 0 passed to n_workers will cause the number of |
| // workers to be taken from the active workers in the work gang. |
| CMSParRemarkTask(CMSCollector* collector, |
| CompactibleFreeListSpace* cms_space, |
| CompactibleFreeListSpace* perm_space, |
| int n_workers, FlexibleWorkGang* workers, |
| OopTaskQueueSet* task_queues): |
| AbstractGangTask("Rescan roots and grey objects in parallel"), |
| _collector(collector), |
| _cms_space(cms_space), _perm_space(perm_space), |
| _n_workers(n_workers), |
| _task_queues(task_queues), |
| _term(n_workers, task_queues) { } |
| |
| OopTaskQueueSet* task_queues() { return _task_queues; } |
| |
| OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } |
| |
| ParallelTaskTerminator* terminator() { return &_term; } |
| int n_workers() { return _n_workers; } |
| |
| void work(uint worker_id); |
| |
| private: |
| // Work method in support of parallel rescan ... of young gen spaces |
| void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl, |
| ContiguousSpace* space, |
| HeapWord** chunk_array, size_t chunk_top); |
| |
| // ... of dirty cards in old space |
| void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i, |
| Par_MarkRefsIntoAndScanClosure* cl); |
| |
| // ... work stealing for the above |
| void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed); |
| }; |
| |
| // work_queue(i) is passed to the closure |
| // Par_MarkRefsIntoAndScanClosure. The "i" parameter |
| // also is passed to do_dirty_card_rescan_tasks() and to |
| // do_work_steal() to select the i-th task_queue. |
| |
| void CMSParRemarkTask::work(uint worker_id) { |
| elapsedTimer _timer; |
| ResourceMark rm; |
| HandleMark hm; |
| |
| // ---------- rescan from roots -------------- |
| _timer.start(); |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector, |
| _collector->_span, _collector->ref_processor(), |
| &(_collector->_markBitMap), |
| work_queue(worker_id), &(_collector->_revisitStack)); |
| |
| // Rescan young gen roots first since these are likely |
| // coarsely partitioned and may, on that account, constitute |
| // the critical path; thus, it's best to start off that |
| // work first. |
| // ---------- young gen roots -------------- |
| { |
| DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration(); |
| EdenSpace* eden_space = dng->eden(); |
| ContiguousSpace* from_space = dng->from(); |
| ContiguousSpace* to_space = dng->to(); |
| |
| HeapWord** eca = _collector->_eden_chunk_array; |
| size_t ect = _collector->_eden_chunk_index; |
| HeapWord** sca = _collector->_survivor_chunk_array; |
| size_t sct = _collector->_survivor_chunk_index; |
| |
| assert(ect <= _collector->_eden_chunk_capacity, "out of bounds"); |
| assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds"); |
| |
| do_young_space_rescan(worker_id, &par_mrias_cl, to_space, NULL, 0); |
| do_young_space_rescan(worker_id, &par_mrias_cl, from_space, sca, sct); |
| do_young_space_rescan(worker_id, &par_mrias_cl, eden_space, eca, ect); |
| |
| _timer.stop(); |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print_cr( |
| "Finished young gen rescan work in %dth thread: %3.3f sec", |
| worker_id, _timer.seconds()); |
| } |
| } |
| |
| // ---------- remaining roots -------------- |
| _timer.reset(); |
| _timer.start(); |
| gch->gen_process_strong_roots(_collector->_cmsGen->level(), |
| false, // yg was scanned above |
| false, // this is parallel code |
| true, // collecting perm gen |
| SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()), |
| &par_mrias_cl, |
| true, // walk all of code cache if (so & SO_CodeCache) |
| NULL); |
| assert(_collector->should_unload_classes() |
| || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache), |
| "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); |
| _timer.stop(); |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print_cr( |
| "Finished remaining root rescan work in %dth thread: %3.3f sec", |
| worker_id, _timer.seconds()); |
| } |
| |
| // ---------- rescan dirty cards ------------ |
| _timer.reset(); |
| _timer.start(); |
| |
| // Do the rescan tasks for each of the two spaces |
| // (cms_space and perm_space) in turn. |
| // "worker_id" is passed to select the task_queue for "worker_id" |
| do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl); |
| do_dirty_card_rescan_tasks(_perm_space, worker_id, &par_mrias_cl); |
| _timer.stop(); |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print_cr( |
| "Finished dirty card rescan work in %dth thread: %3.3f sec", |
| worker_id, _timer.seconds()); |
| } |
| |
| // ---------- steal work from other threads ... |
| // ---------- ... and drain overflow list. |
| _timer.reset(); |
| _timer.start(); |
| do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id)); |
| _timer.stop(); |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print_cr( |
| "Finished work stealing in %dth thread: %3.3f sec", |
| worker_id, _timer.seconds()); |
| } |
| } |
| |
| // Note that parameter "i" is not used. |
| void |
| CMSParRemarkTask::do_young_space_rescan(int i, |
| Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space, |
| HeapWord** chunk_array, size_t chunk_top) { |
| // Until all tasks completed: |
| // . claim an unclaimed task |
| // . compute region boundaries corresponding to task claimed |
| // using chunk_array |
| // . par_oop_iterate(cl) over that region |
| |
| ResourceMark rm; |
| HandleMark hm; |
| |
| SequentialSubTasksDone* pst = space->par_seq_tasks(); |
| assert(pst->valid(), "Uninitialized use?"); |
| |
| uint nth_task = 0; |
| uint n_tasks = pst->n_tasks(); |
| |
| HeapWord *start, *end; |
| while (!pst->is_task_claimed(/* reference */ nth_task)) { |
| // We claimed task # nth_task; compute its boundaries. |
| if (chunk_top == 0) { // no samples were taken |
| assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task"); |
| start = space->bottom(); |
| end = space->top(); |
| } else if (nth_task == 0) { |
| start = space->bottom(); |
| end = chunk_array[nth_task]; |
| } else if (nth_task < (uint)chunk_top) { |
| assert(nth_task >= 1, "Control point invariant"); |
| start = chunk_array[nth_task - 1]; |
| end = chunk_array[nth_task]; |
| } else { |
| assert(nth_task == (uint)chunk_top, "Control point invariant"); |
| start = chunk_array[chunk_top - 1]; |
| end = space->top(); |
| } |
| MemRegion mr(start, end); |
| // Verify that mr is in space |
| assert(mr.is_empty() || space->used_region().contains(mr), |
| "Should be in space"); |
| // Verify that "start" is an object boundary |
| assert(mr.is_empty() || oop(mr.start())->is_oop(), |
| "Should be an oop"); |
| space->par_oop_iterate(mr, cl); |
| } |
| pst->all_tasks_completed(); |
| } |
| |
| void |
| CMSParRemarkTask::do_dirty_card_rescan_tasks( |
| CompactibleFreeListSpace* sp, int i, |
| Par_MarkRefsIntoAndScanClosure* cl) { |
| // Until all tasks completed: |
| // . claim an unclaimed task |
| // . compute region boundaries corresponding to task claimed |
| // . transfer dirty bits ct->mut for that region |
| // . apply rescanclosure to dirty mut bits for that region |
| |
| ResourceMark rm; |
| HandleMark hm; |
| |
| OopTaskQueue* work_q = work_queue(i); |
| ModUnionClosure modUnionClosure(&(_collector->_modUnionTable)); |
| // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! |
| // CAUTION: This closure has state that persists across calls to |
| // the work method dirty_range_iterate_clear() in that it has |
| // imbedded in it a (subtype of) UpwardsObjectClosure. The |
| // use of that state in the imbedded UpwardsObjectClosure instance |
| // assumes that the cards are always iterated (even if in parallel |
| // by several threads) in monotonically increasing order per each |
| // thread. This is true of the implementation below which picks |
| // card ranges (chunks) in monotonically increasing order globally |
| // and, a-fortiori, in monotonically increasing order per thread |
| // (the latter order being a subsequence of the former). |
| // If the work code below is ever reorganized into a more chaotic |
| // work-partitioning form than the current "sequential tasks" |
| // paradigm, the use of that persistent state will have to be |
| // revisited and modified appropriately. See also related |
| // bug 4756801 work on which should examine this code to make |
| // sure that the changes there do not run counter to the |
| // assumptions made here and necessary for correctness and |
| // efficiency. Note also that this code might yield inefficient |
| // behaviour in the case of very large objects that span one or |
| // more work chunks. Such objects would potentially be scanned |
| // several times redundantly. Work on 4756801 should try and |
| // address that performance anomaly if at all possible. XXX |
| MemRegion full_span = _collector->_span; |
| CMSBitMap* bm = &(_collector->_markBitMap); // shared |
| CMSMarkStack* rs = &(_collector->_revisitStack); // shared |
| MarkFromDirtyCardsClosure |
| greyRescanClosure(_collector, full_span, // entire span of interest |
| sp, bm, work_q, rs, cl); |
| |
| SequentialSubTasksDone* pst = sp->conc_par_seq_tasks(); |
| assert(pst->valid(), "Uninitialized use?"); |
| uint nth_task = 0; |
| const int alignment = CardTableModRefBS::card_size * BitsPerWord; |
| MemRegion span = sp->used_region(); |
| HeapWord* start_addr = span.start(); |
| HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(), |
| alignment); |
| const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units |
| assert((HeapWord*)round_to((intptr_t)start_addr, alignment) == |
| start_addr, "Check alignment"); |
| assert((size_t)round_to((intptr_t)chunk_size, alignment) == |
| chunk_size, "Check alignment"); |
| |
| while (!pst->is_task_claimed(/* reference */ nth_task)) { |
| // Having claimed the nth_task, compute corresponding mem-region, |
| // which is a-fortiori aligned correctly (i.e. at a MUT bopundary). |
| // The alignment restriction ensures that we do not need any |
| // synchronization with other gang-workers while setting or |
| // clearing bits in thus chunk of the MUT. |
| MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size, |
| start_addr + (nth_task+1)*chunk_size); |
| // The last chunk's end might be way beyond end of the |
| // used region. In that case pull back appropriately. |
| if (this_span.end() > end_addr) { |
| this_span.set_end(end_addr); |
| assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)"); |
| } |
| // Iterate over the dirty cards covering this chunk, marking them |
| // precleaned, and setting the corresponding bits in the mod union |
| // table. Since we have been careful to partition at Card and MUT-word |
| // boundaries no synchronization is needed between parallel threads. |
| _collector->_ct->ct_bs()->dirty_card_iterate(this_span, |
| &modUnionClosure); |
| |
| // Having transferred these marks into the modUnionTable, |
| // rescan the marked objects on the dirty cards in the modUnionTable. |
| // Even if this is at a synchronous collection, the initial marking |
| // may have been done during an asynchronous collection so there |
| // may be dirty bits in the mod-union table. |
| _collector->_modUnionTable.dirty_range_iterate_clear( |
| this_span, &greyRescanClosure); |
| _collector->_modUnionTable.verifyNoOneBitsInRange( |
| this_span.start(), |
| this_span.end()); |
| } |
| pst->all_tasks_completed(); // declare that i am done |
| } |
| |
| // . see if we can share work_queues with ParNew? XXX |
| void |
| CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, |
| int* seed) { |
| OopTaskQueue* work_q = work_queue(i); |
| NOT_PRODUCT(int num_steals = 0;) |
| oop obj_to_scan; |
| CMSBitMap* bm = &(_collector->_markBitMap); |
| |
| while (true) { |
| // Completely finish any left over work from (an) earlier round(s) |
| cl->trim_queue(0); |
| size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, |
| (size_t)ParGCDesiredObjsFromOverflowList); |
| // Now check if there's any work in the overflow list |
| // Passing ParallelGCThreads as the third parameter, no_of_gc_threads, |
| // only affects the number of attempts made to get work from the |
| // overflow list and does not affect the number of workers. Just |
| // pass ParallelGCThreads so this behavior is unchanged. |
| if (_collector->par_take_from_overflow_list(num_from_overflow_list, |
| work_q, |
| ParallelGCThreads)) { |
| // found something in global overflow list; |
| // not yet ready to go stealing work from others. |
| // We'd like to assert(work_q->size() != 0, ...) |
| // because we just took work from the overflow list, |
| // but of course we can't since all of that could have |
| // been already stolen from us. |
| // "He giveth and He taketh away." |
| continue; |
| } |
| // Verify that we have no work before we resort to stealing |
| assert(work_q->size() == 0, "Have work, shouldn't steal"); |
| // Try to steal from other queues that have work |
| if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) { |
| NOT_PRODUCT(num_steals++;) |
| assert(obj_to_scan->is_oop(), "Oops, not an oop!"); |
| assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?"); |
| // Do scanning work |
| obj_to_scan->oop_iterate(cl); |
| // Loop around, finish this work, and try to steal some more |
| } else if (terminator()->offer_termination()) { |
| break; // nirvana from the infinite cycle |
| } |
| } |
| NOT_PRODUCT( |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals); |
| } |
| ) |
| assert(work_q->size() == 0 && _collector->overflow_list_is_empty(), |
| "Else our work is not yet done"); |
| } |
| |
| // Return a thread-local PLAB recording array, as appropriate. |
| void* CMSCollector::get_data_recorder(int thr_num) { |
| if (_survivor_plab_array != NULL && |
| (CMSPLABRecordAlways || |
| (_collectorState > Marking && _collectorState < FinalMarking))) { |
| assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds"); |
| ChunkArray* ca = &_survivor_plab_array[thr_num]; |
| ca->reset(); // clear it so that fresh data is recorded |
| return (void*) ca; |
| } else { |
| return NULL; |
| } |
| } |
| |
| // Reset all the thread-local PLAB recording arrays |
| void CMSCollector::reset_survivor_plab_arrays() { |
| for (uint i = 0; i < ParallelGCThreads; i++) { |
| _survivor_plab_array[i].reset(); |
| } |
| } |
| |
| // Merge the per-thread plab arrays into the global survivor chunk |
| // array which will provide the partitioning of the survivor space |
| // for CMS rescan. |
| void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv, |
| int no_of_gc_threads) { |
| assert(_survivor_plab_array != NULL, "Error"); |
| assert(_survivor_chunk_array != NULL, "Error"); |
| assert(_collectorState == FinalMarking, "Error"); |
| for (int j = 0; j < no_of_gc_threads; j++) { |
| _cursor[j] = 0; |
| } |
| HeapWord* top = surv->top(); |
| size_t i; |
| for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries |
| HeapWord* min_val = top; // Higher than any PLAB address |
| uint min_tid = 0; // position of min_val this round |
| for (int j = 0; j < no_of_gc_threads; j++) { |
| ChunkArray* cur_sca = &_survivor_plab_array[j]; |
| if (_cursor[j] == cur_sca->end()) { |
| continue; |
| } |
| assert(_cursor[j] < cur_sca->end(), "ctl pt invariant"); |
| HeapWord* cur_val = cur_sca->nth(_cursor[j]); |
| assert(surv->used_region().contains(cur_val), "Out of bounds value"); |
| if (cur_val < min_val) { |
| min_tid = j; |
| min_val = cur_val; |
| } else { |
| assert(cur_val < top, "All recorded addresses should be less"); |
| } |
| } |
| // At this point min_val and min_tid are respectively |
| // the least address in _survivor_plab_array[j]->nth(_cursor[j]) |
| // and the thread (j) that witnesses that address. |
| // We record this address in the _survivor_chunk_array[i] |
| // and increment _cursor[min_tid] prior to the next round i. |
| if (min_val == top) { |
| break; |
| } |
| _survivor_chunk_array[i] = min_val; |
| _cursor[min_tid]++; |
| } |
| // We are all done; record the size of the _survivor_chunk_array |
| _survivor_chunk_index = i; // exclusive: [0, i) |
| if (PrintCMSStatistics > 0) { |
| gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i); |
| } |
| // Verify that we used up all the recorded entries |
| #ifdef ASSERT |
| size_t total = 0; |
| for (int j = 0; j < no_of_gc_threads; j++) { |
| assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant"); |
| total += _cursor[j]; |
| } |
| assert(total == _survivor_chunk_index, "Ctl Pt Invariant"); |
| // Check that the merged array is in sorted order |
| if (total > 0) { |
| for (size_t i = 0; i < total - 1; i++) { |
| if (PrintCMSStatistics > 0) { |
| gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ", |
| i, _survivor_chunk_array[i]); |
| } |
| assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1], |
| "Not sorted"); |
| } |
| } |
| #endif // ASSERT |
| } |
| |
| // Set up the space's par_seq_tasks structure for work claiming |
| // for parallel rescan of young gen. |
| // See ParRescanTask where this is currently used. |
| void |
| CMSCollector:: |
| initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) { |
| assert(n_threads > 0, "Unexpected n_threads argument"); |
| DefNewGeneration* dng = (DefNewGeneration*)_young_gen; |
| |
| // Eden space |
| { |
| SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks(); |
| assert(!pst->valid(), "Clobbering existing data?"); |
| // Each valid entry in [0, _eden_chunk_index) represents a task. |
| size_t n_tasks = _eden_chunk_index + 1; |
| assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error"); |
| // Sets the condition for completion of the subtask (how many threads |
| // need to finish in order to be done). |
| pst->set_n_threads(n_threads); |
| pst->set_n_tasks((int)n_tasks); |
| } |
| |
| // Merge the survivor plab arrays into _survivor_chunk_array |
| if (_survivor_plab_array != NULL) { |
| merge_survivor_plab_arrays(dng->from(), n_threads); |
| } else { |
| assert(_survivor_chunk_index == 0, "Error"); |
| } |
| |
| // To space |
| { |
| SequentialSubTasksDone* pst = dng->to()->par_seq_tasks(); |
| assert(!pst->valid(), "Clobbering existing data?"); |
| // Sets the condition for completion of the subtask (how many threads |
| // need to finish in order to be done). |
| pst->set_n_threads(n_threads); |
| pst->set_n_tasks(1); |
| assert(pst->valid(), "Error"); |
| } |
| |
| // From space |
| { |
| SequentialSubTasksDone* pst = dng->from()->par_seq_tasks(); |
| assert(!pst->valid(), "Clobbering existing data?"); |
| size_t n_tasks = _survivor_chunk_index + 1; |
| assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error"); |
| // Sets the condition for completion of the subtask (how many threads |
| // need to finish in order to be done). |
| pst->set_n_threads(n_threads); |
| pst->set_n_tasks((int)n_tasks); |
| assert(pst->valid(), "Error"); |
| } |
| } |
| |
| // Parallel version of remark |
| void CMSCollector::do_remark_parallel() { |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| FlexibleWorkGang* workers = gch->workers(); |
| assert(workers != NULL, "Need parallel worker threads."); |
| // Choose to use the number of GC workers most recently set |
| // into "active_workers". If active_workers is not set, set it |
| // to ParallelGCThreads. |
| int n_workers = workers->active_workers(); |
| if (n_workers == 0) { |
| assert(n_workers > 0, "Should have been set during scavenge"); |
| n_workers = ParallelGCThreads; |
| workers->set_active_workers(n_workers); |
| } |
| CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); |
| CompactibleFreeListSpace* perm_space = _permGen->cmsSpace(); |
| |
| CMSParRemarkTask tsk(this, |
| cms_space, perm_space, |
| n_workers, workers, task_queues()); |
| |
| // Set up for parallel process_strong_roots work. |
| gch->set_par_threads(n_workers); |
| // We won't be iterating over the cards in the card table updating |
| // the younger_gen cards, so we shouldn't call the following else |
| // the verification code as well as subsequent younger_refs_iterate |
| // code would get confused. XXX |
| // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel |
| |
| // The young gen rescan work will not be done as part of |
| // process_strong_roots (which currently doesn't knw how to |
| // parallelize such a scan), but rather will be broken up into |
| // a set of parallel tasks (via the sampling that the [abortable] |
| // preclean phase did of EdenSpace, plus the [two] tasks of |
| // scanning the [two] survivor spaces. Further fine-grain |
| // parallelization of the scanning of the survivor spaces |
| // themselves, and of precleaning of the younger gen itself |
| // is deferred to the future. |
| initialize_sequential_subtasks_for_young_gen_rescan(n_workers); |
| |
| // The dirty card rescan work is broken up into a "sequence" |
| // of parallel tasks (per constituent space) that are dynamically |
| // claimed by the parallel threads. |
| cms_space->initialize_sequential_subtasks_for_rescan(n_workers); |
| perm_space->initialize_sequential_subtasks_for_rescan(n_workers); |
| |
| // It turns out that even when we're using 1 thread, doing the work in a |
| // separate thread causes wide variance in run times. We can't help this |
| // in the multi-threaded case, but we special-case n=1 here to get |
| // repeatable measurements of the 1-thread overhead of the parallel code. |
| if (n_workers > 1) { |
| // Make refs discovery MT-safe, if it isn't already: it may not |
| // necessarily be so, since it's possible that we are doing |
| // ST marking. |
| ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true); |
| GenCollectedHeap::StrongRootsScope srs(gch); |
| workers->run_task(&tsk); |
| } else { |
| ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false); |
| GenCollectedHeap::StrongRootsScope srs(gch); |
| tsk.work(0); |
| } |
| gch->set_par_threads(0); // 0 ==> non-parallel. |
| // restore, single-threaded for now, any preserved marks |
| // as a result of work_q overflow |
| restore_preserved_marks_if_any(); |
| } |
| |
| // Non-parallel version of remark |
| void CMSCollector::do_remark_non_parallel() { |
| ResourceMark rm; |
| HandleMark hm; |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false); |
| |
| MarkRefsIntoAndScanClosure |
| mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable, |
| &_markStack, &_revisitStack, this, |
| false /* should_yield */, false /* not precleaning */); |
| MarkFromDirtyCardsClosure |
| markFromDirtyCardsClosure(this, _span, |
| NULL, // space is set further below |
| &_markBitMap, &_markStack, &_revisitStack, |
| &mrias_cl); |
| { |
| TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty); |
| // Iterate over the dirty cards, setting the corresponding bits in the |
| // mod union table. |
| { |
| ModUnionClosure modUnionClosure(&_modUnionTable); |
| _ct->ct_bs()->dirty_card_iterate( |
| _cmsGen->used_region(), |
| &modUnionClosure); |
| _ct->ct_bs()->dirty_card_iterate( |
| _permGen->used_region(), |
| &modUnionClosure); |
| } |
| // Having transferred these marks into the modUnionTable, we just need |
| // to rescan the marked objects on the dirty cards in the modUnionTable. |
| // The initial marking may have been done during an asynchronous |
| // collection so there may be dirty bits in the mod-union table. |
| const int alignment = |
| CardTableModRefBS::card_size * BitsPerWord; |
| { |
| // ... First handle dirty cards in CMS gen |
| markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace()); |
| MemRegion ur = _cmsGen->used_region(); |
| HeapWord* lb = ur.start(); |
| HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment); |
| MemRegion cms_span(lb, ub); |
| _modUnionTable.dirty_range_iterate_clear(cms_span, |
| &markFromDirtyCardsClosure); |
| verify_work_stacks_empty(); |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ", |
| markFromDirtyCardsClosure.num_dirty_cards()); |
| } |
| } |
| { |
| // .. and then repeat for dirty cards in perm gen |
| markFromDirtyCardsClosure.set_space(_permGen->cmsSpace()); |
| MemRegion ur = _permGen->used_region(); |
| HeapWord* lb = ur.start(); |
| HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment); |
| MemRegion perm_span(lb, ub); |
| _modUnionTable.dirty_range_iterate_clear(perm_span, |
| &markFromDirtyCardsClosure); |
| verify_work_stacks_empty(); |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ", |
| markFromDirtyCardsClosure.num_dirty_cards()); |
| } |
| } |
| } |
| if (VerifyDuringGC && |
| GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { |
| HandleMark hm; // Discard invalid handles created during verification |
| Universe::verify(true); |
| } |
| { |
| TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty); |
| |
| verify_work_stacks_empty(); |
| |
| gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. |
| GenCollectedHeap::StrongRootsScope srs(gch); |
| gch->gen_process_strong_roots(_cmsGen->level(), |
| true, // younger gens as roots |
| false, // use the local StrongRootsScope |
| true, // collecting perm gen |
| SharedHeap::ScanningOption(roots_scanning_options()), |
| &mrias_cl, |
| true, // walk code active on stacks |
| NULL); |
| assert(should_unload_classes() |
| || (roots_scanning_options() & SharedHeap::SO_CodeCache), |
| "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); |
| } |
| verify_work_stacks_empty(); |
| // Restore evacuated mark words, if any, used for overflow list links |
| if (!CMSOverflowEarlyRestoration) { |
| restore_preserved_marks_if_any(); |
| } |
| verify_overflow_empty(); |
| } |
| |
| //////////////////////////////////////////////////////// |
| // Parallel Reference Processing Task Proxy Class |
| //////////////////////////////////////////////////////// |
| class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues { |
| typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; |
| CMSCollector* _collector; |
| CMSBitMap* _mark_bit_map; |
| const MemRegion _span; |
| ProcessTask& _task; |
| |
| public: |
| CMSRefProcTaskProxy(ProcessTask& task, |
| CMSCollector* collector, |
| const MemRegion& span, |
| CMSBitMap* mark_bit_map, |
| AbstractWorkGang* workers, |
| OopTaskQueueSet* task_queues): |
| // XXX Should superclass AGTWOQ also know about AWG since it knows |
| // about the task_queues used by the AWG? Then it could initialize |
| // the terminator() object. See 6984287. The set_for_termination() |
| // below is a temporary band-aid for the regression in 6984287. |
| AbstractGangTaskWOopQueues("Process referents by policy in parallel", |
| task_queues), |
| _task(task), |
| _collector(collector), _span(span), _mark_bit_map(mark_bit_map) |
| { |
| assert(_collector->_span.equals(_span) && !_span.is_empty(), |
| "Inconsistency in _span"); |
| set_for_termination(workers->active_workers()); |
| } |
| |
| OopTaskQueueSet* task_queues() { return queues(); } |
| |
| OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } |
| |
| void do_work_steal(int i, |
| CMSParDrainMarkingStackClosure* drain, |
| CMSParKeepAliveClosure* keep_alive, |
| int* seed); |
| |
| virtual void work(uint worker_id); |
| }; |
| |
| void CMSRefProcTaskProxy::work(uint worker_id) { |
| assert(_collector->_span.equals(_span), "Inconsistency in _span"); |
| CMSParKeepAliveClosure par_keep_alive(_collector, _span, |
| _mark_bit_map, |
| &_collector->_revisitStack, |
| work_queue(worker_id)); |
| CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span, |
| _mark_bit_map, |
| &_collector->_revisitStack, |
| work_queue(worker_id)); |
| CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map); |
| _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack); |
| if (_task.marks_oops_alive()) { |
| do_work_steal(worker_id, &par_drain_stack, &par_keep_alive, |
| _collector->hash_seed(worker_id)); |
| } |
| assert(work_queue(worker_id)->size() == 0, "work_queue should be empty"); |
| assert(_collector->_overflow_list == NULL, "non-empty _overflow_list"); |
| } |
| |
| class CMSRefEnqueueTaskProxy: public AbstractGangTask { |
| typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask; |
| EnqueueTask& _task; |
| |
| public: |
| CMSRefEnqueueTaskProxy(EnqueueTask& task) |
| : AbstractGangTask("Enqueue reference objects in parallel"), |
| _task(task) |
| { } |
| |
| virtual void work(uint worker_id) |
| { |
| _task.work(worker_id); |
| } |
| }; |
| |
| CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector, |
| MemRegion span, CMSBitMap* bit_map, CMSMarkStack* revisit_stack, |
| OopTaskQueue* work_queue): |
| Par_KlassRememberingOopClosure(collector, NULL, revisit_stack), |
| _span(span), |
| _bit_map(bit_map), |
| _work_queue(work_queue), |
| _mark_and_push(collector, span, bit_map, revisit_stack, work_queue), |
| _low_water_mark(MIN2((uint)(work_queue->max_elems()/4), |
| (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))) |
| { } |
| |
| // . see if we can share work_queues with ParNew? XXX |
| void CMSRefProcTaskProxy::do_work_steal(int i, |
| CMSParDrainMarkingStackClosure* drain, |
| CMSParKeepAliveClosure* keep_alive, |
| int* seed) { |
| OopTaskQueue* work_q = work_queue(i); |
| NOT_PRODUCT(int num_steals = 0;) |
| oop obj_to_scan; |
| |
| while (true) { |
| // Completely finish any left over work from (an) earlier round(s) |
| drain->trim_queue(0); |
| size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, |
| (size_t)ParGCDesiredObjsFromOverflowList); |
| // Now check if there's any work in the overflow list |
| // Passing ParallelGCThreads as the third parameter, no_of_gc_threads, |
| // only affects the number of attempts made to get work from the |
| // overflow list and does not affect the number of workers. Just |
| // pass ParallelGCThreads so this behavior is unchanged. |
| if (_collector->par_take_from_overflow_list(num_from_overflow_list, |
| work_q, |
| ParallelGCThreads)) { |
| // Found something in global overflow list; |
| // not yet ready to go stealing work from others. |
| // We'd like to assert(work_q->size() != 0, ...) |
| // because we just took work from the overflow list, |
| // but of course we can't, since all of that might have |
| // been already stolen from us. |
| continue; |
| } |
| // Verify that we have no work before we resort to stealing |
| assert(work_q->size() == 0, "Have work, shouldn't steal"); |
| // Try to steal from other queues that have work |
| if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) { |
| NOT_PRODUCT(num_steals++;) |
| assert(obj_to_scan->is_oop(), "Oops, not an oop!"); |
| assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?"); |
| // Do scanning work |
| obj_to_scan->oop_iterate(keep_alive); |
| // Loop around, finish this work, and try to steal some more |
| } else if (terminator()->offer_termination()) { |
| break; // nirvana from the infinite cycle |
| } |
| } |
| NOT_PRODUCT( |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals); |
| } |
| ) |
| } |
| |
| void CMSRefProcTaskExecutor::execute(ProcessTask& task) |
| { |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| FlexibleWorkGang* workers = gch->workers(); |
| assert(workers != NULL, "Need parallel worker threads."); |
| CMSRefProcTaskProxy rp_task(task, &_collector, |
| _collector.ref_processor()->span(), |
| _collector.markBitMap(), |
| workers, _collector.task_queues()); |
| workers->run_task(&rp_task); |
| } |
| |
| void CMSRefProcTaskExecutor::execute(EnqueueTask& task) |
| { |
| |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| FlexibleWorkGang* workers = gch->workers(); |
| assert(workers != NULL, "Need parallel worker threads."); |
| CMSRefEnqueueTaskProxy enq_task(task); |
| workers->run_task(&enq_task); |
| } |
| |
| void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) { |
| |
| ResourceMark rm; |
| HandleMark hm; |
| |
| ReferenceProcessor* rp = ref_processor(); |
| assert(rp->span().equals(_span), "Spans should be equal"); |
| assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete"); |
| // Process weak references. |
| rp->setup_policy(clear_all_soft_refs); |
| verify_work_stacks_empty(); |
| |
| CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap, |
| &_markStack, &_revisitStack, |
| false /* !preclean */); |
| CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this, |
| _span, &_markBitMap, &_markStack, |
| &cmsKeepAliveClosure, false /* !preclean */); |
| { |
| TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty); |
| if (rp->processing_is_mt()) { |
| // Set the degree of MT here. If the discovery is done MT, there |
| // may have been a different number of threads doing the discovery |
| // and a different number of discovered lists may have Ref objects. |
| // That is OK as long as the Reference lists are balanced (see |
| // balance_all_queues() and balance_queues()). |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| int active_workers = ParallelGCThreads; |
| FlexibleWorkGang* workers = gch->workers(); |
| if (workers != NULL) { |
| active_workers = workers->active_workers(); |
| // The expectation is that active_workers will have already |
| // been set to a reasonable value. If it has not been set, |
| // investigate. |
| assert(active_workers > 0, "Should have been set during scavenge"); |
| } |
| rp->set_active_mt_degree(active_workers); |
| CMSRefProcTaskExecutor task_executor(*this); |
| rp->process_discovered_references(&_is_alive_closure, |
| &cmsKeepAliveClosure, |
| &cmsDrainMarkingStackClosure, |
| &task_executor); |
| } else { |
| rp->process_discovered_references(&_is_alive_closure, |
| &cmsKeepAliveClosure, |
| &cmsDrainMarkingStackClosure, |
| NULL); |
| } |
| verify_work_stacks_empty(); |
| } |
| |
| if (should_unload_classes()) { |
| { |
| TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty); |
| |
| // Follow SystemDictionary roots and unload classes |
| bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure); |
| |
| // Follow CodeCache roots and unload any methods marked for unloading |
| CodeCache::do_unloading(&_is_alive_closure, |
| &cmsKeepAliveClosure, |
| purged_class); |
| |
| cmsDrainMarkingStackClosure.do_void(); |
| verify_work_stacks_empty(); |
| |
| // Update subklass/sibling/implementor links in KlassKlass descendants |
| assert(!_revisitStack.isEmpty(), "revisit stack should not be empty"); |
| oop k; |
| while ((k = _revisitStack.pop()) != NULL) { |
| ((Klass*)(oopDesc*)k)->follow_weak_klass_links( |
| &_is_alive_closure, |
| &cmsKeepAliveClosure); |
| } |
| assert(!ClassUnloading || |
| (_markStack.isEmpty() && overflow_list_is_empty()), |
| "Should not have found new reachable objects"); |
| assert(_revisitStack.isEmpty(), "revisit stack should have been drained"); |
| cmsDrainMarkingStackClosure.do_void(); |
| verify_work_stacks_empty(); |
| } |
| |
| { |
| TraceTime t("scrub symbol table", PrintGCDetails, false, gclog_or_tty); |
| // Clean up unreferenced symbols in symbol table. |
| SymbolTable::unlink(); |
| } |
| } |
| |
| if (should_unload_classes() || !JavaObjectsInPerm) { |
| TraceTime t("scrub string table", PrintGCDetails, false, gclog_or_tty); |
| // Now clean up stale oops in StringTable |
| StringTable::unlink(&_is_alive_closure); |
| } |
| |
| verify_work_stacks_empty(); |
| // Restore any preserved marks as a result of mark stack or |
| // work queue overflow |
| restore_preserved_marks_if_any(); // done single-threaded for now |
| |
| rp->set_enqueuing_is_done(true); |
| if (rp->processing_is_mt()) { |
| rp->balance_all_queues(); |
| CMSRefProcTaskExecutor task_executor(*this); |
| rp->enqueue_discovered_references(&task_executor); |
| } else { |
| rp->enqueue_discovered_references(NULL); |
| } |
| rp->verify_no_references_recorded(); |
| assert(!rp->discovery_enabled(), "should have been disabled"); |
| } |
| |
| #ifndef PRODUCT |
| void CMSCollector::check_correct_thread_executing() { |
| Thread* t = Thread::current(); |
| // Only the VM thread or the CMS thread should be here. |
| assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(), |
| "Unexpected thread type"); |
| // If this is the vm thread, the foreground process |
| // should not be waiting. Note that _foregroundGCIsActive is |
| // true while the foreground collector is waiting. |
| if (_foregroundGCShouldWait) { |
| // We cannot be the VM thread |
| assert(t->is_ConcurrentGC_thread(), |
| "Should be CMS thread"); |
| } else { |
| // We can be the CMS thread only if we are in a stop-world |
| // phase of CMS collection. |
| if (t->is_ConcurrentGC_thread()) { |
| assert(_collectorState == InitialMarking || |
| _collectorState == FinalMarking, |
| "Should be a stop-world phase"); |
| // The CMS thread should be holding the CMS_token. |
| assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| "Potential interference with concurrently " |
| "executing VM thread"); |
| } |
| } |
| } |
| #endif |
| |
| void CMSCollector::sweep(bool asynch) { |
| assert(_collectorState == Sweeping, "just checking"); |
| check_correct_thread_executing(); |
| verify_work_stacks_empty(); |
| verify_overflow_empty(); |
| increment_sweep_count(); |
| TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause()); |
| |
| _inter_sweep_timer.stop(); |
| _inter_sweep_estimate.sample(_inter_sweep_timer.seconds()); |
| size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free()); |
| |
| // PermGen verification support: If perm gen sweeping is disabled in |
| // this cycle, we preserve the perm gen object "deadness" information |
| // in the perm_gen_verify_bit_map. In order to do that we traverse |
| // all blocks in perm gen and mark all dead objects. |
| if (verifying() && !should_unload_classes()) { |
| assert(perm_gen_verify_bit_map()->sizeInBits() != 0, |
| "Should have already been allocated"); |
| MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(), |
| markBitMap(), perm_gen_verify_bit_map()); |
| if (asynch) { |
| CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(), |
| bitMapLock()); |
| _permGen->cmsSpace()->blk_iterate(&mdo); |
| } else { |
| // In the case of synchronous sweep, we already have |
| // the requisite locks/tokens. |
| _permGen->cmsSpace()->blk_iterate(&mdo); |
| } |
| } |
| |
| assert(!_intra_sweep_timer.is_active(), "Should not be active"); |
| _intra_sweep_timer.reset(); |
| _intra_sweep_timer.start(); |
| if (asynch) { |
| TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); |
| CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails); |
| // First sweep the old gen then the perm gen |
| { |
| CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(), |
| bitMapLock()); |
| sweepWork(_cmsGen, asynch); |
| } |
| |
| // Now repeat for perm gen |
| if (should_unload_classes()) { |
| CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(), |
| bitMapLock()); |
| sweepWork(_permGen, asynch); |
| } |
| |
| // Update Universe::_heap_*_at_gc figures. |
| // We need all the free list locks to make the abstract state |
| // transition from Sweeping to Resetting. See detailed note |
| // further below. |
| { |
| CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(), |
| _permGen->freelistLock()); |
| // Update heap occupancy information which is used as |
| // input to soft ref clearing policy at the next gc. |
| Universe::update_heap_info_at_gc(); |
| _collectorState = Resizing; |
| } |
| } else { |
| // already have needed locks |
| sweepWork(_cmsGen, asynch); |
| |
| if (should_unload_classes()) { |
| sweepWork(_permGen, asynch); |
| } |
| // Update heap occupancy information which is used as |
| // input to soft ref clearing policy at the next gc. |
| Universe::update_heap_info_at_gc(); |
| _collectorState = Resizing; |
| } |
| verify_work_stacks_empty(); |
| verify_overflow_empty(); |
| |
| _intra_sweep_timer.stop(); |
| _intra_sweep_estimate.sample(_intra_sweep_timer.seconds()); |
| |
| _inter_sweep_timer.reset(); |
| _inter_sweep_timer.start(); |
| |
| // We need to use a monotonically non-deccreasing time in ms |
| // or we will see time-warp warnings and os::javaTimeMillis() |
| // does not guarantee monotonicity. |
| jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; |
| update_time_of_last_gc(now); |
| |
| // NOTE on abstract state transitions: |
| // Mutators allocate-live and/or mark the mod-union table dirty |
| // based on the state of the collection. The former is done in |
| // the interval [Marking, Sweeping] and the latter in the interval |
| // [Marking, Sweeping). Thus the transitions into the Marking state |
| // and out of the Sweeping state must be synchronously visible |
| // globally to the mutators. |
| // The transition into the Marking state happens with the world |
| // stopped so the mutators will globally see it. Sweeping is |
| // done asynchronously by the background collector so the transition |
| // from the Sweeping state to the Resizing state must be done |
| // under the freelistLock (as is the check for whether to |
| // allocate-live and whether to dirty the mod-union table). |
| assert(_collectorState == Resizing, "Change of collector state to" |
| " Resizing must be done under the freelistLocks (plural)"); |
| |
| // Now that sweeping has been completed, we clear |
| // the incremental_collection_failed flag, |
| // thus inviting a younger gen collection to promote into |
| // this generation. If such a promotion may still fail, |
| // the flag will be set again when a young collection is |
| // attempted. |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up |
| gch->update_full_collections_completed(_collection_count_start); |
| } |
| |
| // FIX ME!!! Looks like this belongs in CFLSpace, with |
| // CMSGen merely delegating to it. |
| void ConcurrentMarkSweepGeneration::setNearLargestChunk() { |
| double nearLargestPercent = FLSLargestBlockCoalesceProximity; |
| HeapWord* minAddr = _cmsSpace->bottom(); |
| HeapWord* largestAddr = |
| (HeapWord*) _cmsSpace->dictionary()->find_largest_dict(); |
| if (largestAddr == NULL) { |
| // The dictionary appears to be empty. In this case |
| // try to coalesce at the end of the heap. |
| largestAddr = _cmsSpace->end(); |
| } |
| size_t largestOffset = pointer_delta(largestAddr, minAddr); |
| size_t nearLargestOffset = |
| (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize; |
| if (PrintFLSStatistics != 0) { |
| gclog_or_tty->print_cr( |
| "CMS: Large Block: " PTR_FORMAT ";" |
| " Proximity: " PTR_FORMAT " -> " PTR_FORMAT, |
| largestAddr, |
| _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset); |
| } |
| _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset); |
| } |
| |
| bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) { |
| return addr >= _cmsSpace->nearLargestChunk(); |
| } |
| |
| FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() { |
| return _cmsSpace->find_chunk_at_end(); |
| } |
| |
| void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level, |
| bool full) { |
| // The next lower level has been collected. Gather any statistics |
| // that are of interest at this point. |
| if (!full && (current_level + 1) == level()) { |
| // Gather statistics on the young generation collection. |
| collector()->stats().record_gc0_end(used()); |
| } |
| } |
| |
| CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() { |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| assert(gch->kind() == CollectedHeap::GenCollectedHeap, |
| "Wrong type of heap"); |
| CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*) |
| gch->gen_policy()->size_policy(); |
| assert(sp->is_gc_cms_adaptive_size_policy(), |
| "Wrong type of size policy"); |
| return sp; |
| } |
| |
| void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() { |
| if (PrintGCDetails && Verbose) { |
| gclog_or_tty->print("Rotate from %d ", _debug_collection_type); |
| } |
| _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1); |
| _debug_collection_type = |
| (CollectionTypes) (_debug_collection_type % Unknown_collection_type); |
| if (PrintGCDetails && Verbose) { |
| gclog_or_tty->print_cr("to %d ", _debug_collection_type); |
| } |
| } |
| |
| void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen, |
| bool asynch) { |
| // We iterate over the space(s) underlying this generation, |
| // checking the mark bit map to see if the bits corresponding |
| // to specific blocks are marked or not. Blocks that are |
| // marked are live and are not swept up. All remaining blocks |
| // are swept up, with coalescing on-the-fly as we sweep up |
| // contiguous free and/or garbage blocks: |
| // We need to ensure that the sweeper synchronizes with allocators |
| // and stop-the-world collectors. In particular, the following |
| // locks are used: |
| // . CMS token: if this is held, a stop the world collection cannot occur |
| // . freelistLock: if this is held no allocation can occur from this |
| // generation by another thread |
| // . bitMapLock: if this is held, no other thread can access or update |
| // |
| |
| // Note that we need to hold the freelistLock if we use |
| // block iterate below; else the iterator might go awry if |
| // a mutator (or promotion) causes block contents to change |
| // (for instance if the allocator divvies up a block). |
| // If we hold the free list lock, for all practical purposes |
| // young generation GC's can't occur (they'll usually need to |
| // promote), so we might as well prevent all young generation |
| // GC's while we do a sweeping step. For the same reason, we might |
| // as well take the bit map lock for the entire duration |
| |
| // check that we hold the requisite locks |
| assert(have_cms_token(), "Should hold cms token"); |
| assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token()) |
| || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()), |
| "Should possess CMS token to sweep"); |
| assert_lock_strong(gen->freelistLock()); |
| assert_lock_strong(bitMapLock()); |
| |
| assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context"); |
| assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context"); |
| gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()), |
| _inter_sweep_estimate.padded_average(), |
| _intra_sweep_estimate.padded_average()); |
| gen->setNearLargestChunk(); |
| |
| { |
| SweepClosure sweepClosure(this, gen, &_markBitMap, |
| CMSYield && asynch); |
| gen->cmsSpace()->blk_iterate_careful(&sweepClosure); |
| // We need to free-up/coalesce garbage/blocks from a |
| // co-terminal free run. This is done in the SweepClosure |
| // destructor; so, do not remove this scope, else the |
| // end-of-sweep-census below will be off by a little bit. |
| } |
| gen->cmsSpace()->sweep_completed(); |
| gen->cmsSpace()->endSweepFLCensus(sweep_count()); |
| if (should_unload_classes()) { // unloaded classes this cycle, |
| _concurrent_cycles_since_last_unload = 0; // ... reset count |
| } else { // did not unload classes, |
| _concurrent_cycles_since_last_unload++; // ... increment count |
| } |
| } |
| |
| // Reset CMS data structures (for now just the marking bit map) |
| // preparatory for the next cycle. |
| void CMSCollector::reset(bool asynch) { |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| CMSAdaptiveSizePolicy* sp = size_policy(); |
| AdaptiveSizePolicyOutput(sp, gch->total_collections()); |
| if (asynch) { |
| CMSTokenSyncWithLocks ts(true, bitMapLock()); |
| |
| // If the state is not "Resetting", the foreground thread |
| // has done a collection and the resetting. |
| if (_collectorState != Resetting) { |
| assert(_collectorState == Idling, "The state should only change" |
| " because the foreground collector has finished the collection"); |
| return; |
| } |
| |
| // Clear the mark bitmap (no grey objects to start with) |
| // for the next cycle. |
| TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); |
| CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails); |
| |
| HeapWord* curAddr = _markBitMap.startWord(); |
| while (curAddr < _markBitMap.endWord()) { |
| size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr); |
| MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining)); |
| _markBitMap.clear_large_range(chunk); |
| if (ConcurrentMarkSweepThread::should_yield() && |
| !foregroundGCIsActive() && |
| CMSYield) { |
| assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| "CMS thread should hold CMS token"); |
| assert_lock_strong(bitMapLock()); |
| bitMapLock()->unlock(); |
| ConcurrentMarkSweepThread::desynchronize(true); |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| stopTimer(); |
| if (PrintCMSStatistics != 0) { |
| incrementYields(); |
| } |
| icms_wait(); |
| |
| // See the comment in coordinator_yield() |
| for (unsigned i = 0; i < CMSYieldSleepCount && |
| ConcurrentMarkSweepThread::should_yield() && |
| !CMSCollector::foregroundGCIsActive(); ++i) { |
| os::sleep(Thread::current(), 1, false); |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| } |
| |
| ConcurrentMarkSweepThread::synchronize(true); |
| bitMapLock()->lock_without_safepoint_check(); |
| startTimer(); |
| } |
| curAddr = chunk.end(); |
| } |
| // A successful mostly concurrent collection has been done. |
| // Because only the full (i.e., concurrent mode failure) collections |
| // are being measured for gc overhead limits, clean the "near" flag |
| // and count. |
| sp->reset_gc_overhead_limit_count(); |
| _collectorState = Idling; |
| } else { |
| // already have the lock |
| assert(_collectorState == Resetting, "just checking"); |
| assert_lock_strong(bitMapLock()); |
| _markBitMap.clear_all(); |
| _collectorState = Idling; |
| } |
| |
| // Stop incremental mode after a cycle completes, so that any future cycles |
| // are triggered by allocation. |
| stop_icms(); |
| |
| NOT_PRODUCT( |
| if (RotateCMSCollectionTypes) { |
| _cmsGen->rotate_debug_collection_type(); |
| } |
| ) |
| } |
| |
| void CMSCollector::do_CMS_operation(CMS_op_type op) { |
| gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps); |
| TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); |
| TraceTime t("GC", PrintGC, !PrintGCDetails, gclog_or_tty); |
| TraceCollectorStats tcs(counters()); |
| |
| switch (op) { |
| case CMS_op_checkpointRootsInitial: { |
| SvcGCMarker sgcm(SvcGCMarker::OTHER); |
| checkpointRootsInitial(true); // asynch |
| if (PrintGC) { |
| _cmsGen->printOccupancy("initial-mark"); |
| } |
| break; |
| } |
| case CMS_op_checkpointRootsFinal: { |
| SvcGCMarker sgcm(SvcGCMarker::OTHER); |
| checkpointRootsFinal(true, // asynch |
| false, // !clear_all_soft_refs |
| false); // !init_mark_was_synchronous |
| if (PrintGC) { |
| _cmsGen->printOccupancy("remark"); |
| } |
| break; |
| } |
| default: |
| fatal("No such CMS_op"); |
| } |
| } |
| |
| #ifndef PRODUCT |
| size_t const CMSCollector::skip_header_HeapWords() { |
| return FreeChunk::header_size(); |
| } |
| |
| // Try and collect here conditions that should hold when |
| // CMS thread is exiting. The idea is that the foreground GC |
| // thread should not be blocked if it wants to terminate |
| // the CMS thread and yet continue to run the VM for a while |
| // after that. |
| void CMSCollector::verify_ok_to_terminate() const { |
| assert(Thread::current()->is_ConcurrentGC_thread(), |
| "should be called by CMS thread"); |
| assert(!_foregroundGCShouldWait, "should be false"); |
| // We could check here that all the various low-level locks |
| // are not held by the CMS thread, but that is overkill; see |
| // also CMSThread::verify_ok_to_terminate() where the CGC_lock |
| // is checked. |
| } |
| #endif |
| |
| size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const { |
| assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1), |
| "missing Printezis mark?"); |
| HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2); |
| size_t size = pointer_delta(nextOneAddr + 1, addr); |
| assert(size == CompactibleFreeListSpace::adjustObjectSize(size), |
| "alignment problem"); |
| assert(size >= 3, "Necessary for Printezis marks to work"); |
| return size; |
| } |
| |
| // A variant of the above (block_size_using_printezis_bits()) except |
| // that we return 0 if the P-bits are not yet set. |
| size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const { |
| if (_markBitMap.isMarked(addr + 1)) { |
| assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects"); |
| HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2); |
| size_t size = pointer_delta(nextOneAddr + 1, addr); |
| assert(size == CompactibleFreeListSpace::adjustObjectSize(size), |
| "alignment problem"); |
| assert(size >= 3, "Necessary for Printezis marks to work"); |
| return size; |
| } |
| return 0; |
| } |
| |
| HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const { |
| size_t sz = 0; |
| oop p = (oop)addr; |
| if (p->klass_or_null() != NULL && p->is_parsable()) { |
| sz = CompactibleFreeListSpace::adjustObjectSize(p->size()); |
| } else { |
| sz = block_size_using_printezis_bits(addr); |
| } |
| assert(sz > 0, "size must be nonzero"); |
| HeapWord* next_block = addr + sz; |
| HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block, |
| CardTableModRefBS::card_size); |
| assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) < |
| round_down((uintptr_t)next_card, CardTableModRefBS::card_size), |
| "must be different cards"); |
| return next_card; |
| } |
| |
| |
| // CMS Bit Map Wrapper ///////////////////////////////////////// |
| |
| // Construct a CMS bit map infrastructure, but don't create the |
| // bit vector itself. That is done by a separate call CMSBitMap::allocate() |
| // further below. |
| CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name): |
| _bm(), |
| _shifter(shifter), |
| _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL) |
| { |
| _bmStartWord = 0; |
| _bmWordSize = 0; |
| } |
| |
| bool CMSBitMap::allocate(MemRegion mr) { |
| _bmStartWord = mr.start(); |
| _bmWordSize = mr.word_size(); |
| ReservedSpace brs(ReservedSpace::allocation_align_size_up( |
| (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1)); |
| if (!brs.is_reserved()) { |
| warning("CMS bit map allocation failure"); |
| return false; |
| } |
| // For now we'll just commit all of the bit map up fromt. |
| // Later on we'll try to be more parsimonious with swap. |
| if (!_virtual_space.initialize(brs, brs.size())) { |
| warning("CMS bit map backing store failure"); |
| return false; |
| } |
| assert(_virtual_space.committed_size() == brs.size(), |
| "didn't reserve backing store for all of CMS bit map?"); |
| _bm.set_map((BitMap::bm_word_t*)_virtual_space.low()); |
| assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >= |
| _bmWordSize, "inconsistency in bit map sizing"); |
| _bm.set_size(_bmWordSize >> _shifter); |
| |
| // bm.clear(); // can we rely on getting zero'd memory? verify below |
| assert(isAllClear(), |
| "Expected zero'd memory from ReservedSpace constructor"); |
| assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()), |
| "consistency check"); |
| return true; |
| } |
| |
| void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) { |
| HeapWord *next_addr, *end_addr, *last_addr; |
| assert_locked(); |
| assert(covers(mr), "out-of-range error"); |
| // XXX assert that start and end are appropriately aligned |
| for (next_addr = mr.start(), end_addr = mr.end(); |
| next_addr < end_addr; next_addr = last_addr) { |
| MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr); |
| last_addr = dirty_region.end(); |
| if (!dirty_region.is_empty()) { |
| cl->do_MemRegion(dirty_region); |
| } else { |
| assert(last_addr == end_addr, "program logic"); |
| return; |
| } |
| } |
| } |
| |
| #ifndef PRODUCT |
| void CMSBitMap::assert_locked() const { |
| CMSLockVerifier::assert_locked(lock()); |
| } |
| |
| bool CMSBitMap::covers(MemRegion mr) const { |
| // assert(_bm.map() == _virtual_space.low(), "map inconsistency"); |
| assert((size_t)_bm.size() == (_bmWordSize >> _shifter), |
| "size inconsistency"); |
| return (mr.start() >= _bmStartWord) && |
| (mr.end() <= endWord()); |
| } |
| |
| bool CMSBitMap::covers(HeapWord* start, size_t size) const { |
| return (start >= _bmStartWord && (start + size) <= endWord()); |
| } |
| |
| void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) { |
| // verify that there are no 1 bits in the interval [left, right) |
| FalseBitMapClosure falseBitMapClosure; |
| iterate(&falseBitMapClosure, left, right); |
| } |
| |
| void CMSBitMap::region_invariant(MemRegion mr) |
| { |
| assert_locked(); |
| // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize)); |
| assert(!mr.is_empty(), "unexpected empty region"); |
| assert(covers(mr), "mr should be covered by bit map"); |
| // convert address range into offset range |
| size_t start_ofs = heapWordToOffset(mr.start()); |
| // Make sure that end() is appropriately aligned |
| assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(), |
| (1 << (_shifter+LogHeapWordSize))), |
| "Misaligned mr.end()"); |
| size_t end_ofs = heapWordToOffset(mr.end()); |
| assert(end_ofs > start_ofs, "Should mark at least one bit"); |
| } |
| |
| #endif |
| |
| bool CMSMarkStack::allocate(size_t size) { |
| // allocate a stack of the requisite depth |
| ReservedSpace rs(ReservedSpace::allocation_align_size_up( |
| size * sizeof(oop))); |
| if (!rs.is_reserved()) { |
| warning("CMSMarkStack allocation failure"); |
| return false; |
| } |
| if (!_virtual_space.initialize(rs, rs.size())) { |
| warning("CMSMarkStack backing store failure"); |
| return false; |
| } |
| assert(_virtual_space.committed_size() == rs.size(), |
| "didn't reserve backing store for all of CMS stack?"); |
| _base = (oop*)(_virtual_space.low()); |
| _index = 0; |
| _capacity = size; |
| NOT_PRODUCT(_max_depth = 0); |
| return true; |
| } |
| |
| // XXX FIX ME !!! In the MT case we come in here holding a |
| // leaf lock. For printing we need to take a further lock |
| // which has lower rank. We need to recallibrate the two |
| // lock-ranks involved in order to be able to rpint the |
| // messages below. (Or defer the printing to the caller. |
| // For now we take the expedient path of just disabling the |
| // messages for the problematic case.) |
| void CMSMarkStack::expand() { |
| assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted"); |
| if (_capacity == MarkStackSizeMax) { |
| if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) { |
| // We print a warning message only once per CMS cycle. |
| gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit"); |
| } |
| return; |
| } |
| // Double capacity if possible |
| size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax); |
| // Do not give up existing stack until we have managed to |
| // get the double capacity that we desired. |
| ReservedSpace rs(ReservedSpace::allocation_align_size_up( |
| new_capacity * sizeof(oop))); |
| if (rs.is_reserved()) { |
| // Release the backing store associated with old stack |
| _virtual_space.release(); |
| // Reinitialize virtual space for new stack |
| if (!_virtual_space.initialize(rs, rs.size())) { |
| fatal("Not enough swap for expanded marking stack"); |
| } |
| _base = (oop*)(_virtual_space.low()); |
| _index = 0; |
| _capacity = new_capacity; |
| } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) { |
| // Failed to double capacity, continue; |
| // we print a detail message only once per CMS cycle. |
| gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to " |
| SIZE_FORMAT"K", |
| _capacity / K, new_capacity / K); |
| } |
| } |
| |
| |
| // Closures |
| // XXX: there seems to be a lot of code duplication here; |
| // should refactor and consolidate common code. |
| |
| // This closure is used to mark refs into the CMS generation in |
| // the CMS bit map. Called at the first checkpoint. This closure |
| // assumes that we do not need to re-mark dirty cards; if the CMS |
| // generation on which this is used is not an oldest (modulo perm gen) |
| // generation then this will lose younger_gen cards! |
| |
| MarkRefsIntoClosure::MarkRefsIntoClosure( |
| MemRegion span, CMSBitMap* bitMap): |
| _span(span), |
| _bitMap(bitMap) |
| { |
| assert(_ref_processor == NULL, "deliberately left NULL"); |
| assert(_bitMap->covers(_span), "_bitMap/_span mismatch"); |
| } |
| |
| void MarkRefsIntoClosure::do_oop(oop obj) { |
| // if p points into _span, then mark corresponding bit in _markBitMap |
| assert(obj->is_oop(), "expected an oop"); |
| HeapWord* addr = (HeapWord*)obj; |
| if (_span.contains(addr)) { |
| // this should be made more efficient |
| _bitMap->mark(addr); |
| } |
| } |
| |
| void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); } |
| void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); } |
| |
| // A variant of the above, used for CMS marking verification. |
| MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure( |
| MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm): |
| _span(span), |
| _verification_bm(verification_bm), |
| _cms_bm(cms_bm) |
| { |
| assert(_ref_processor == NULL, "deliberately left NULL"); |
| assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch"); |
| } |
| |
| void MarkRefsIntoVerifyClosure::do_oop(oop obj) { |
| // if p points into _span, then mark corresponding bit in _markBitMap |
| assert(obj->is_oop(), "expected an oop"); |
| HeapWord* addr = (HeapWord*)obj; |
| if (_span.contains(addr)) { |
| _verification_bm->mark(addr); |
| if (!_cms_bm->isMarked(addr)) { |
| oop(addr)->print(); |
| gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr); |
| fatal("... aborting"); |
| } |
| } |
| } |
| |
| void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); } |
| void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); } |
| |
| ////////////////////////////////////////////////// |
| // MarkRefsIntoAndScanClosure |
| ////////////////////////////////////////////////// |
| |
| MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span, |
| ReferenceProcessor* rp, |
| CMSBitMap* bit_map, |
| CMSBitMap* mod_union_table, |
| CMSMarkStack* mark_stack, |
| CMSMarkStack* revisit_stack, |
| CMSCollector* collector, |
| bool should_yield, |
| bool concurrent_precleaning): |
| _collector(collector), |
| _span(span), |
| _bit_map(bit_map), |
| _mark_stack(mark_stack), |
| _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table, |
| mark_stack, revisit_stack, concurrent_precleaning), |
| _yield(should_yield), |
| _concurrent_precleaning(concurrent_precleaning), |
| _freelistLock(NULL) |
| { |
| _ref_processor = rp; |
| assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); |
| } |
| |
| // This closure is used to mark refs into the CMS generation at the |
| // second (final) checkpoint, and to scan and transitively follow |
| // the unmarked oops. It is also used during the concurrent precleaning |
| // phase while scanning objects on dirty cards in the CMS generation. |
| // The marks are made in the marking bit map and the marking stack is |
| // used for keeping the (newly) grey objects during the scan. |
| // The parallel version (Par_...) appears further below. |
| void MarkRefsIntoAndScanClosure::do_oop(oop obj) { |
| if (obj != NULL) { |
| assert(obj->is_oop(), "expected an oop"); |
| HeapWord* addr = (HeapWord*)obj; |
| assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)"); |
| assert(_collector->overflow_list_is_empty(), |
| "overflow list should be empty"); |
| if (_span.contains(addr) && |
| !_bit_map->isMarked(addr)) { |
| // mark bit map (object is now grey) |
| _bit_map->mark(addr); |
| // push on marking stack (stack should be empty), and drain the |
| // stack by applying this closure to the oops in the oops popped |
| // from the stack (i.e. blacken the grey objects) |
| bool res = _mark_stack->push(obj); |
| assert(res, "Should have space to push on empty stack"); |
| do { |
| oop new_oop = _mark_stack->pop(); |
| assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop"); |
| assert(new_oop->is_parsable(), "Found unparsable oop"); |
| assert(_bit_map->isMarked((HeapWord*)new_oop), |
| "only grey objects on this stack"); |
| // iterate over the oops in this oop, marking and pushing |
| // the ones in CMS heap (i.e. in _span). |
| new_oop->oop_iterate(&_pushAndMarkClosure); |
| // check if it's time to yield |
| do_yield_check(); |
| } while (!_mark_stack->isEmpty() || |
| (!_concurrent_precleaning && take_from_overflow_list())); |
| // if marking stack is empty, and we are not doing this |
| // during precleaning, then check the overflow list |
| } |
| assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); |
| assert(_collector->overflow_list_is_empty(), |
| "overflow list was drained above"); |
| // We could restore evacuated mark words, if any, used for |
| // overflow list links here because the overflow list is |
| // provably empty here. That would reduce the maximum |
| // size requirements for preserved_{oop,mark}_stack. |
| // But we'll just postpone it until we are all done |
| // so we can just stream through. |
| if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) { |
| _collector->restore_preserved_marks_if_any(); |
| assert(_collector->no_preserved_marks(), "No preserved marks"); |
| } |
| assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(), |
| "All preserved marks should have been restored above"); |
| } |
| } |
| |
| void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); } |
| void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); } |
| |
| void MarkRefsIntoAndScanClosure::do_yield_work() { |
| assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| "CMS thread should hold CMS token"); |
| assert_lock_strong(_freelistLock); |
| assert_lock_strong(_bit_map->lock()); |
| // relinquish the free_list_lock and bitMaplock() |
| DEBUG_ONLY(RememberKlassesChecker mux(false);) |
| _bit_map->lock()->unlock(); |
| _freelistLock->unlock(); |
| ConcurrentMarkSweepThread::desynchronize(true); |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| _collector->stopTimer(); |
| GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); |
| if (PrintCMSStatistics != 0) { |
| _collector->incrementYields(); |
| } |
| _collector->icms_wait(); |
| |
| // See the comment in coordinator_yield() |
| for (unsigned i = 0; |
| i < CMSYieldSleepCount && |
| ConcurrentMarkSweepThread::should_yield() && |
| !CMSCollector::foregroundGCIsActive(); |
| ++i) { |
| os::sleep(Thread::current(), 1, false); |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| } |
| |
| ConcurrentMarkSweepThread::synchronize(true); |
| _freelistLock->lock_without_safepoint_check(); |
| _bit_map->lock()->lock_without_safepoint_check(); |
| _collector->startTimer(); |
| } |
| |
| /////////////////////////////////////////////////////////// |
| // Par_MarkRefsIntoAndScanClosure: a parallel version of |
| // MarkRefsIntoAndScanClosure |
| /////////////////////////////////////////////////////////// |
| Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure( |
| CMSCollector* collector, MemRegion span, ReferenceProcessor* rp, |
| CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack* revisit_stack): |
| _span(span), |
| _bit_map(bit_map), |
| _work_queue(work_queue), |
| _low_water_mark(MIN2((uint)(work_queue->max_elems()/4), |
| (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))), |
| _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue, |
| revisit_stack) |
| { |
| _ref_processor = rp; |
| assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); |
| } |
| |
| // This closure is used to mark refs into the CMS generation at the |
| // second (final) checkpoint, and to scan and transitively follow |
| // the unmarked oops. The marks are made in the marking bit map and |
| // the work_queue is used for keeping the (newly) grey objects during |
| // the scan phase whence they are also available for stealing by parallel |
| // threads. Since the marking bit map is shared, updates are |
| // synchronized (via CAS). |
| void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) { |
| if (obj != NULL) { |
| // Ignore mark word because this could be an already marked oop |
| // that may be chained at the end of the overflow list. |
| assert(obj->is_oop(true), "expected an oop"); |
| HeapWord* addr = (HeapWord*)obj; |
| if (_span.contains(addr) && |
| !_bit_map->isMarked(addr)) { |
| // mark bit map (object will become grey): |
| // It is possible for several threads to be |
| // trying to "claim" this object concurrently; |
| // the unique thread that succeeds in marking the |
| // object first will do the subsequent push on |
| // to the work queue (or overflow list). |
| if (_bit_map->par_mark(addr)) { |
| // push on work_queue (which may not be empty), and trim the |
| // queue to an appropriate length by applying this closure to |
| // the oops in the oops popped from the stack (i.e. blacken the |
| // grey objects) |
| bool res = _work_queue->push(obj); |
| assert(res, "Low water mark should be less than capacity?"); |
| trim_queue(_low_water_mark); |
| } // Else, another thread claimed the object |
| } |
| } |
| } |
| |
| void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); } |
| void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); } |
| |
| // This closure is used to rescan the marked objects on the dirty cards |
| // in the mod union table and the card table proper. |
| size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m( |
| oop p, MemRegion mr) { |
| |
| size_t size = 0; |
| HeapWord* addr = (HeapWord*)p; |
| DEBUG_ONLY(_collector->verify_work_stacks_empty();) |
| assert(_span.contains(addr), "we are scanning the CMS generation"); |
| // check if it's time to yield |
| if (do_yield_check()) { |
| // We yielded for some foreground stop-world work, |
| // and we have been asked to abort this ongoing preclean cycle. |
| return 0; |
| } |
| if (_bitMap->isMarked(addr)) { |
| // it's marked; is it potentially uninitialized? |
| if (p->klass_or_null() != NULL) { |
| // If is_conc_safe is false, the object may be undergoing |
| // change by the VM outside a safepoint. Don't try to |
| // scan it, but rather leave it for the remark phase. |
| if (CMSPermGenPrecleaningEnabled && |
| (!p->is_conc_safe() || !p->is_parsable())) { |
| // Signal precleaning to redirty the card since |
| // the klass pointer is already installed. |
| assert(size == 0, "Initial value"); |
| } else { |
| assert(p->is_parsable(), "must be parsable."); |
| // an initialized object; ignore mark word in verification below |
| // since we are running concurrent with mutators |
| assert(p->is_oop(true), "should be an oop"); |
| if (p->is_objArray()) { |
| // objArrays are precisely marked; restrict scanning |
| // to dirty cards only. |
| size = CompactibleFreeListSpace::adjustObjectSize( |
| p->oop_iterate(_scanningClosure, mr)); |
| } else { |
| // A non-array may have been imprecisely marked; we need |
| // to scan object in its entirety. |
| size = CompactibleFreeListSpace::adjustObjectSize( |
| p->oop_iterate(_scanningClosure)); |
| } |
| #ifdef DEBUG |
| size_t direct_size = |
| CompactibleFreeListSpace::adjustObjectSize(p->size()); |
| assert(size == direct_size, "Inconsistency in size"); |
| assert(size >= 3, "Necessary for Printezis marks to work"); |
| if (!_bitMap->isMarked(addr+1)) { |
| _bitMap->verifyNoOneBitsInRange(addr+2, addr+size); |
| } else { |
| _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1); |
| assert(_bitMap->isMarked(addr+size-1), |
| "inconsistent Printezis mark"); |
| } |
| #endif // DEBUG |
| } |
| } else { |
| // an unitialized object |
| assert(_bitMap->isMarked(addr+1), "missing Printezis mark?"); |
| HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2); |
| size = pointer_delta(nextOneAddr + 1, addr); |
| assert(size == CompactibleFreeListSpace::adjustObjectSize(size), |
| "alignment problem"); |
| // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass() |
| // will dirty the card when the klass pointer is installed in the |
| // object (signalling the completion of initialization). |
| } |
| } else { |
| // Either a not yet marked object or an uninitialized object |
| if (p->klass_or_null() == NULL || !p->is_parsable()) { |
| // An uninitialized object, skip to the next card, since |
| // we may not be able to read its P-bits yet. |
| assert(size == 0, "Initial value"); |
| } else { |
| // An object not (yet) reached by marking: we merely need to |
| // compute its size so as to go look at the next block. |
| assert(p->is_oop(true), "should be an oop"); |
| size = CompactibleFreeListSpace::adjustObjectSize(p->size()); |
| } |
| } |
| DEBUG_ONLY(_collector->verify_work_stacks_empty();) |
| return size; |
| } |
| |
| void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() { |
| assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| "CMS thread should hold CMS token"); |
| assert_lock_strong(_freelistLock); |
| assert_lock_strong(_bitMap->lock()); |
| DEBUG_ONLY(RememberKlassesChecker mux(false);) |
| // relinquish the free_list_lock and bitMaplock() |
| _bitMap->lock()->unlock(); |
| _freelistLock->unlock(); |
| ConcurrentMarkSweepThread::desynchronize(true); |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| _collector->stopTimer(); |
| GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); |
| if (PrintCMSStatistics != 0) { |
| _collector->incrementYields(); |
| } |
| _collector->icms_wait(); |
| |
| // See the comment in coordinator_yield() |
| for (unsigned i = 0; i < CMSYieldSleepCount && |
| ConcurrentMarkSweepThread::should_yield() && |
| !CMSCollector::foregroundGCIsActive(); ++i) { |
| os::sleep(Thread::current(), 1, false); |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| } |
| |
| ConcurrentMarkSweepThread::synchronize(true); |
| _freelistLock->lock_without_safepoint_check(); |
| _bitMap->lock()->lock_without_safepoint_check(); |
| _collector->startTimer(); |
| } |
| |
| |
| ////////////////////////////////////////////////////////////////// |
| // SurvivorSpacePrecleanClosure |
| ////////////////////////////////////////////////////////////////// |
| // This (single-threaded) closure is used to preclean the oops in |
| // the survivor spaces. |
| size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) { |
| |
| HeapWord* addr = (HeapWord*)p; |
| DEBUG_ONLY(_collector->verify_work_stacks_empty();) |
| assert(!_span.contains(addr), "we are scanning the survivor spaces"); |
| assert(p->klass_or_null() != NULL, "object should be initializd"); |
| assert(p->is_parsable(), "must be parsable."); |
| // an initialized object; ignore mark word in verification below |
| // since we are running concurrent with mutators |
| assert(p->is_oop(true), "should be an oop"); |
| // Note that we do not yield while we iterate over |
| // the interior oops of p, pushing the relevant ones |
| // on our marking stack. |
| size_t size = p->oop_iterate(_scanning_closure); |
| do_yield_check(); |
| // Observe that below, we do not abandon the preclean |
| // phase as soon as we should; rather we empty the |
| // marking stack before returning. This is to satisfy |
| // some existing assertions. In general, it may be a |
| // good idea to abort immediately and complete the marking |
| // from the grey objects at a later time. |
| while (!_mark_stack->isEmpty()) { |
| oop new_oop = _mark_stack->pop(); |
| assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop"); |
| assert(new_oop->is_parsable(), "Found unparsable oop"); |
| assert(_bit_map->isMarked((HeapWord*)new_oop), |
| "only grey objects on this stack"); |
| // iterate over the oops in this oop, marking and pushing |
| // the ones in CMS heap (i.e. in _span). |
| new_oop->oop_iterate(_scanning_closure); |
| // check if it's time to yield |
| do_yield_check(); |
| } |
| unsigned int after_count = |
| GenCollectedHeap::heap()->total_collections(); |
| bool abort = (_before_count != after_count) || |
| _collector->should_abort_preclean(); |
| return abort ? 0 : size; |
| } |
| |
| void SurvivorSpacePrecleanClosure::do_yield_work() { |
| assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| "CMS thread should hold CMS token"); |
| assert_lock_strong(_bit_map->lock()); |
| DEBUG_ONLY(RememberKlassesChecker smx(false);) |
| // Relinquish the bit map lock |
| _bit_map->lock()->unlock(); |
| ConcurrentMarkSweepThread::desynchronize(true); |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| _collector->stopTimer(); |
| GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); |
| if (PrintCMSStatistics != 0) { |
| _collector->incrementYields(); |
| } |
| _collector->icms_wait(); |
| |
| // See the comment in coordinator_yield() |
| for (unsigned i = 0; i < CMSYieldSleepCount && |
| ConcurrentMarkSweepThread::should_yield() && |
| !CMSCollector::foregroundGCIsActive(); ++i) { |
| os::sleep(Thread::current(), 1, false); |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| } |
| |
| ConcurrentMarkSweepThread::synchronize(true); |
| _bit_map->lock()->lock_without_safepoint_check(); |
| _collector->startTimer(); |
| } |
| |
| // This closure is used to rescan the marked objects on the dirty cards |
| // in the mod union table and the card table proper. In the parallel |
| // case, although the bitMap is shared, we do a single read so the |
| // isMarked() query is "safe". |
| bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) { |
| // Ignore mark word because we are running concurrent with mutators |
| assert(p->is_oop_or_null(true), "expected an oop or null"); |
| HeapWord* addr = (HeapWord*)p; |
| assert(_span.contains(addr), "we are scanning the CMS generation"); |
| bool is_obj_array = false; |
| #ifdef DEBUG |
| if (!_parallel) { |
| assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)"); |
| assert(_collector->overflow_list_is_empty(), |
| "overflow list should be empty"); |
| |
| } |
| #endif // DEBUG |
| if (_bit_map->isMarked(addr)) { |
| // Obj arrays are precisely marked, non-arrays are not; |
| // so we scan objArrays precisely and non-arrays in their |
| // entirety. |
| if (p->is_objArray()) { |
| is_obj_array = true; |
| if (_parallel) { |
| p->oop_iterate(_par_scan_closure, mr); |
| } else { |
| p->oop_iterate(_scan_closure, mr); |
| } |
| } else { |
| if (_parallel) { |
| p->oop_iterate(_par_scan_closure); |
| } else { |
| p->oop_iterate(_scan_closure); |
| } |
| } |
| } |
| #ifdef DEBUG |
| if (!_parallel) { |
| assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); |
| assert(_collector->overflow_list_is_empty(), |
| "overflow list should be empty"); |
| |
| } |
| #endif // DEBUG |
| return is_obj_array; |
| } |
| |
| MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector, |
| MemRegion span, |
| CMSBitMap* bitMap, CMSMarkStack* markStack, |
| CMSMarkStack* revisitStack, |
| bool should_yield, bool verifying): |
| _collector(collector), |
| _span(span), |
| _bitMap(bitMap), |
| _mut(&collector->_modUnionTable), |
| _markStack(markStack), |
| _revisitStack(revisitStack), |
| _yield(should_yield), |
| _skipBits(0) |
| { |
| assert(_markStack->isEmpty(), "stack should be empty"); |
| _finger = _bitMap->startWord(); |
| _threshold = _finger; |
| assert(_collector->_restart_addr == NULL, "Sanity check"); |
| assert(_span.contains(_finger), "Out of bounds _finger?"); |
| DEBUG_ONLY(_verifying = verifying;) |
| } |
| |
| void MarkFromRootsClosure::reset(HeapWord* addr) { |
| assert(_markStack->isEmpty(), "would cause duplicates on stack"); |
| assert(_span.contains(addr), "Out of bounds _finger?"); |
| _finger = addr; |
| _threshold = (HeapWord*)round_to( |
| (intptr_t)_finger, CardTableModRefBS::card_size); |
| } |
| |
| // Should revisit to see if this should be restructured for |
| // greater efficiency. |
| bool MarkFromRootsClosure::do_bit(size_t offset) { |
| if (_skipBits > 0) { |
| _skipBits--; |
| return true; |
| } |
| // convert offset into a HeapWord* |
| HeapWord* addr = _bitMap->startWord() + offset; |
| assert(_bitMap->endWord() && addr < _bitMap->endWord(), |
| "address out of range"); |
| assert(_bitMap->isMarked(addr), "tautology"); |
| if (_bitMap->isMarked(addr+1)) { |
| // this is an allocated but not yet initialized object |
| assert(_skipBits == 0, "tautology"); |
| _skipBits = 2; // skip next two marked bits ("Printezis-marks") |
| oop p = oop(addr); |
| if (p->klass_or_null() == NULL || !p->is_parsable()) { |
| DEBUG_ONLY(if (!_verifying) {) |
| // We re-dirty the cards on which this object lies and increase |
| // the _threshold so that we'll come back to scan this object |
| // during the preclean or remark phase. (CMSCleanOnEnter) |
| if (CMSCleanOnEnter) { |
| size_t sz = _collector->block_size_using_printezis_bits(addr); |
| HeapWord* end_card_addr = (HeapWord*)round_to( |
| (intptr_t)(addr+sz), CardTableModRefBS::card_size); |
| MemRegion redirty_range = MemRegion(addr, end_card_addr); |
| assert(!redirty_range.is_empty(), "Arithmetical tautology"); |
| // Bump _threshold to end_card_addr; note that |
| // _threshold cannot possibly exceed end_card_addr, anyhow. |
| // This prevents future clearing of the card as the scan proceeds |
| // to the right. |
| assert(_threshold <= end_card_addr, |
| "Because we are just scanning into this object"); |
| if (_threshold < end_card_addr) { |
| _threshold = end_card_addr; |
| } |
| if (p->klass_or_null() != NULL) { |
| // Redirty the range of cards... |
| _mut->mark_range(redirty_range); |
| } // ...else the setting of klass will dirty the card anyway. |
| } |
| DEBUG_ONLY(}) |
| return true; |
| } |
| } |
| scanOopsInOop(addr); |
| return true; |
| } |
| |
| // We take a break if we've been at this for a while, |
| // so as to avoid monopolizing the locks involved. |
| void MarkFromRootsClosure::do_yield_work() { |
| // First give up the locks, then yield, then re-lock |
| // We should probably use a constructor/destructor idiom to |
| // do this unlock/lock or modify the MutexUnlocker class to |
| // serve our purpose. XXX |
| assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| "CMS thread should hold CMS token"); |
| assert_lock_strong(_bitMap->lock()); |
| DEBUG_ONLY(RememberKlassesChecker mux(false);) |
| _bitMap->lock()->unlock(); |
| ConcurrentMarkSweepThread::desynchronize(true); |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| _collector->stopTimer(); |
| GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); |
| if (PrintCMSStatistics != 0) { |
| _collector->incrementYields(); |
| } |
| _collector->icms_wait(); |
| |
| // See the comment in coordinator_yield() |
| for (unsigned i = 0; i < CMSYieldSleepCount && |
| ConcurrentMarkSweepThread::should_yield() && |
| !CMSCollector::foregroundGCIsActive(); ++i) { |
| os::sleep(Thread::current(), 1, false); |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| } |
| |
| ConcurrentMarkSweepThread::synchronize(true); |
| _bitMap->lock()->lock_without_safepoint_check(); |
| _collector->startTimer(); |
| } |
| |
| void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) { |
| assert(_bitMap->isMarked(ptr), "expected bit to be set"); |
| assert(_markStack->isEmpty(), |
| "should drain stack to limit stack usage"); |
| // convert ptr to an oop preparatory to scanning |
| oop obj = oop(ptr); |
| // Ignore mark word in verification below, since we |
| // may be running concurrent with mutators. |
| assert(obj->is_oop(true), "should be an oop"); |
| assert(_finger <= ptr, "_finger runneth ahead"); |
| // advance the finger to right end of this object |
| _finger = ptr + obj->size(); |
| assert(_finger > ptr, "we just incremented it above"); |
| // On large heaps, it may take us some time to get through |
| // the marking phase (especially if running iCMS). During |
| // this time it's possible that a lot of mutations have |
| // accumulated in the card table and the mod union table -- |
| // these mutation records are redundant until we have |
| // actually traced into the corresponding card. |
| // Here, we check whether advancing the finger would make |
| // us cross into a new card, and if so clear corresponding |
| // cards in the MUT (preclean them in the card-table in the |
| // future). |
| |
| DEBUG_ONLY(if (!_verifying) {) |
| // The clean-on-enter optimization is disabled by default, |
| // until we fix 6178663. |
| if (CMSCleanOnEnter && (_finger > _threshold)) { |
| // [_threshold, _finger) represents the interval |
| // of cards to be cleared in MUT (or precleaned in card table). |
| // The set of cards to be cleared is all those that overlap |
| // with the interval [_threshold, _finger); note that |
| // _threshold is always kept card-aligned but _finger isn't |
| // always card-aligned. |
| HeapWord* old_threshold = _threshold; |
| assert(old_threshold == (HeapWord*)round_to( |
| (intptr_t)old_threshold, CardTableModRefBS::card_size), |
| "_threshold should always be card-aligned"); |
| _threshold = (HeapWord*)round_to( |
| (intptr_t)_finger, CardTableModRefBS::card_size); |
| MemRegion mr(old_threshold, _threshold); |
| assert(!mr.is_empty(), "Control point invariant"); |
| assert(_span.contains(mr), "Should clear within span"); |
| // XXX When _finger crosses from old gen into perm gen |
| // we may be doing unnecessary cleaning; do better in the |
| // future by detecting that condition and clearing fewer |
| // MUT/CT entries. |
| _mut->clear_range(mr); |
| } |
| DEBUG_ONLY(}) |
| // Note: the finger doesn't advance while we drain |
| // the stack below. |
| PushOrMarkClosure pushOrMarkClosure(_collector, |
| _span, _bitMap, _markStack, |
| _revisitStack, |
| _finger, this); |
| bool res = _markStack->push(obj); |
| assert(res, "Empty non-zero size stack should have space for single push"); |
| while (!_markStack->isEmpty()) { |
| oop new_oop = _markStack->pop(); |
| // Skip verifying header mark word below because we are |
| // running concurrent with mutators. |
| assert(new_oop->is_oop(true), "Oops! expected to pop an oop"); |
| // now scan this oop's oops |
| new_oop->oop_iterate(&pushOrMarkClosure); |
| do_yield_check(); |
| } |
| assert(_markStack->isEmpty(), "tautology, emphasizing post-condition"); |
| } |
| |
| Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task, |
| CMSCollector* collector, MemRegion span, |
| CMSBitMap* bit_map, |
| OopTaskQueue* work_queue, |
| CMSMarkStack* overflow_stack, |
| CMSMarkStack* revisit_stack, |
| bool should_yield): |
| _collector(collector), |
| _whole_span(collector->_span), |
| _span(span), |
| _bit_map(bit_map), |
| _mut(&collector->_modUnionTable), |
| _work_queue(work_queue), |
| _overflow_stack(overflow_stack), |
| _revisit_stack(revisit_stack), |
| _yield(should_yield), |
| _skip_bits(0), |
| _task(task) |
| { |
| assert(_work_queue->size() == 0, "work_queue should be empty"); |
| _finger = span.start(); |
| _threshold = _finger; // XXX Defer clear-on-enter optimization for now |
| assert(_span.contains(_finger), "Out of bounds _finger?"); |
| } |
| |
| // Should revisit to see if this should be restructured for |
| // greater efficiency. |
| bool Par_MarkFromRootsClosure::do_bit(size_t offset) { |
| if (_skip_bits > 0) { |
| _skip_bits--; |
| return true; |
| } |
| // convert offset into a HeapWord* |
| HeapWord* addr = _bit_map->startWord() + offset; |
| assert(_bit_map->endWord() && addr < _bit_map->endWord(), |
| "address out of range"); |
| assert(_bit_map->isMarked(addr), "tautology"); |
| if (_bit_map->isMarked(addr+1)) { |
| // this is an allocated object that might not yet be initialized |
| assert(_skip_bits == 0, "tautology"); |
| _skip_bits = 2; // skip next two marked bits ("Printezis-marks") |
| oop p = oop(addr); |
| if (p->klass_or_null() == NULL || !p->is_parsable()) { |
| // in the case of Clean-on-Enter optimization, redirty card |
| // and avoid clearing card by increasing the threshold. |
| return true; |
| } |
| } |
| scan_oops_in_oop(addr); |
| return true; |
| } |
| |
| void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) { |
| assert(_bit_map->isMarked(ptr), "expected bit to be set"); |
| // Should we assert that our work queue is empty or |
| // below some drain limit? |
| assert(_work_queue->size() == 0, |
| "should drain stack to limit stack usage"); |
| // convert ptr to an oop preparatory to scanning |
| oop obj = oop(ptr); |
| // Ignore mark word in verification below, since we |
| // may be running concurrent with mutators. |
| assert(obj->is_oop(true), "should be an oop"); |
| assert(_finger <= ptr, "_finger runneth ahead"); |
| // advance the finger to right end of this object |
| _finger = ptr + obj->size(); |
| assert(_finger > ptr, "we just incremented it above"); |
| // On large heaps, it may take us some time to get through |
| // the marking phase (especially if running iCMS). During |
| // this time it's possible that a lot of mutations have |
| // accumulated in the card table and the mod union table -- |
| // these mutation records are redundant until we have |
| // actually traced into the corresponding card. |
| // Here, we check whether advancing the finger would make |
| // us cross into a new card, and if so clear corresponding |
| // cards in the MUT (preclean them in the card-table in the |
| // future). |
| |
| // The clean-on-enter optimization is disabled by default, |
| // until we fix 6178663. |
| if (CMSCleanOnEnter && (_finger > _threshold)) { |
| // [_threshold, _finger) represents the interval |
| // of cards to be cleared in MUT (or precleaned in card table). |
| // The set of cards to be cleared is all those that overlap |
| // with the interval [_threshold, _finger); note that |
| // _threshold is always kept card-aligned but _finger isn't |
| // always card-aligned. |
| HeapWord* old_threshold = _threshold; |
| assert(old_threshold == (HeapWord*)round_to( |
| (intptr_t)old_threshold, CardTableModRefBS::card_size), |
| "_threshold should always be card-aligned"); |
| _threshold = (HeapWord*)round_to( |
| (intptr_t)_finger, CardTableModRefBS::card_size); |
| MemRegion mr(old_threshold, _threshold); |
| assert(!mr.is_empty(), "Control point invariant"); |
| assert(_span.contains(mr), "Should clear within span"); // _whole_span ?? |
| // XXX When _finger crosses from old gen into perm gen |
| // we may be doing unnecessary cleaning; do better in the |
| // future by detecting that condition and clearing fewer |
| // MUT/CT entries. |
| _mut->clear_range(mr); |
| } |
| |
| // Note: the local finger doesn't advance while we drain |
| // the stack below, but the global finger sure can and will. |
| HeapWord** gfa = _task->global_finger_addr(); |
| Par_PushOrMarkClosure pushOrMarkClosure(_collector, |
| _span, _bit_map, |
| _work_queue, |
| _overflow_stack, |
| _revisit_stack, |
| _finger, |
| gfa, this); |
| bool res = _work_queue->push(obj); // overflow could occur here |
| assert(res, "Will hold once we use workqueues"); |
| while (true) { |
| oop new_oop; |
| if (!_work_queue->pop_local(new_oop)) { |
| // We emptied our work_queue; check if there's stuff that can |
| // be gotten from the overflow stack. |
| if (CMSConcMarkingTask::get_work_from_overflow_stack( |
| _overflow_stack, _work_queue)) { |
| do_yield_check(); |
| continue; |
| } else { // done |
| break; |
| } |
| } |
| // Skip verifying header mark word below because we are |
| // running concurrent with mutators. |
| assert(new_oop->is_oop(true), "Oops! expected to pop an oop"); |
| // now scan this oop's oops |
| new_oop->oop_iterate(&pushOrMarkClosure); |
| do_yield_check(); |
| } |
| assert(_work_queue->size() == 0, "tautology, emphasizing post-condition"); |
| } |
| |
| // Yield in response to a request from VM Thread or |
| // from mutators. |
| void Par_MarkFromRootsClosure::do_yield_work() { |
| assert(_task != NULL, "sanity"); |
| _task->yield(); |
| } |
| |
| // A variant of the above used for verifying CMS marking work. |
| MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector, |
| MemRegion span, |
| CMSBitMap* verification_bm, CMSBitMap* cms_bm, |
| CMSMarkStack* mark_stack): |
| _collector(collector), |
| _span(span), |
| _verification_bm(verification_bm), |
| _cms_bm(cms_bm), |
| _mark_stack(mark_stack), |
| _pam_verify_closure(collector, span, verification_bm, cms_bm, |
| mark_stack) |
| { |
| assert(_mark_stack->isEmpty(), "stack should be empty"); |
| _finger = _verification_bm->startWord(); |
| assert(_collector->_restart_addr == NULL, "Sanity check"); |
| assert(_span.contains(_finger), "Out of bounds _finger?"); |
| } |
| |
| void MarkFromRootsVerifyClosure::reset(HeapWord* addr) { |
| assert(_mark_stack->isEmpty(), "would cause duplicates on stack"); |
| assert(_span.contains(addr), "Out of bounds _finger?"); |
| _finger = addr; |
| } |
| |
| // Should revisit to see if this should be restructured for |
| // greater efficiency. |
| bool MarkFromRootsVerifyClosure::do_bit(size_t offset) { |
| // convert offset into a HeapWord* |
| HeapWord* addr = _verification_bm->startWord() + offset; |
| assert(_verification_bm->endWord() && addr < _verification_bm->endWord(), |
| "address out of range"); |
| assert(_verification_bm->isMarked(addr), "tautology"); |
| assert(_cms_bm->isMarked(addr), "tautology"); |
| |
| assert(_mark_stack->isEmpty(), |
| "should drain stack to limit stack usage"); |
| // convert addr to an oop preparatory to scanning |
| oop obj = oop(addr); |
| assert(obj->is_oop(), "should be an oop"); |
| assert(_finger <= addr, "_finger runneth ahead"); |
| // advance the finger to right end of this object |
| _finger = addr + obj->size(); |
| assert(_finger > addr, "we just incremented it above"); |
| // Note: the finger doesn't advance while we drain |
| // the stack below. |
| bool res = _mark_stack->push(obj); |
| assert(res, "Empty non-zero size stack should have space for single push"); |
| while (!_mark_stack->isEmpty()) { |
| oop new_oop = _mark_stack->pop(); |
| assert(new_oop->is_oop(), "Oops! expected to pop an oop"); |
| // now scan this oop's oops |
| new_oop->oop_iterate(&_pam_verify_closure); |
| } |
| assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition"); |
| return true; |
| } |
| |
| PushAndMarkVerifyClosure::PushAndMarkVerifyClosure( |
| CMSCollector* collector, MemRegion span, |
| CMSBitMap* verification_bm, CMSBitMap* cms_bm, |
| CMSMarkStack* mark_stack): |
| OopClosure(collector->ref_processor()), |
| _collector(collector), |
| _span(span), |
| _verification_bm(verification_bm), |
| _cms_bm(cms_bm), |
| _mark_stack(mark_stack) |
| { } |
| |
| void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); } |
| void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); } |
| |
| // Upon stack overflow, we discard (part of) the stack, |
| // remembering the least address amongst those discarded |
| // in CMSCollector's _restart_address. |
| void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) { |
| // Remember the least grey address discarded |
| HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost); |
| _collector->lower_restart_addr(ra); |
| _mark_stack->reset(); // discard stack contents |
| _mark_stack->expand(); // expand the stack if possible |
| } |
| |
| void PushAndMarkVerifyClosure::do_oop(oop obj) { |
| assert(obj->is_oop_or_null(), "expected an oop or NULL"); |
| HeapWord* addr = (HeapWord*)obj; |
| if (_span.contains(addr) && !_verification_bm->isMarked(addr)) { |
| // Oop lies in _span and isn't yet grey or black |
| _verification_bm->mark(addr); // now grey |
| if (!_cms_bm->isMarked(addr)) { |
| oop(addr)->print(); |
| gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", |
| addr); |
| fatal("... aborting"); |
| } |
| |
| if (!_mark_stack->push(obj)) { // stack overflow |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print_cr("CMS marking stack overflow (benign) at " |
| SIZE_FORMAT, _mark_stack->capacity()); |
| } |
| assert(_mark_stack->isFull(), "Else push should have succeeded"); |
| handle_stack_overflow(addr); |
| } |
| // anything including and to the right of _finger |
| // will be scanned as we iterate over the remainder of the |
| // bit map |
| } |
| } |
| |
| PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector, |
| MemRegion span, |
| CMSBitMap* bitMap, CMSMarkStack* markStack, |
| CMSMarkStack* revisitStack, |
| HeapWord* finger, MarkFromRootsClosure* parent) : |
| KlassRememberingOopClosure(collector, collector->ref_processor(), revisitStack), |
| _span(span), |
| _bitMap(bitMap), |
| _markStack(markStack), |
| _finger(finger), |
| _parent(parent) |
| { } |
| |
| Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector, |
| MemRegion span, |
| CMSBitMap* bit_map, |
| OopTaskQueue* work_queue, |
| CMSMarkStack* overflow_stack, |
| CMSMarkStack* revisit_stack, |
| HeapWord* finger, |
| HeapWord** global_finger_addr, |
| Par_MarkFromRootsClosure* parent) : |
| Par_KlassRememberingOopClosure(collector, |
| collector->ref_processor(), |
| revisit_stack), |
| _whole_span(collector->_span), |
| _span(span), |
| _bit_map(bit_map), |
| _work_queue(work_queue), |
| _overflow_stack(overflow_stack), |
| _finger(finger), |
| _global_finger_addr(global_finger_addr), |
| _parent(parent) |
| { } |
| |
| // Assumes thread-safe access by callers, who are |
| // responsible for mutual exclusion. |
| void CMSCollector::lower_restart_addr(HeapWord* low) { |
| assert(_span.contains(low), "Out of bounds addr"); |
| if (_restart_addr == NULL) { |
| _restart_addr = low; |
| } else { |
| _restart_addr = MIN2(_restart_addr, low); |
| } |
| } |
| |
| // Upon stack overflow, we discard (part of) the stack, |
| // remembering the least address amongst those discarded |
| // in CMSCollector's _restart_address. |
| void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) { |
| // Remember the least grey address discarded |
| HeapWord* ra = (HeapWord*)_markStack->least_value(lost); |
| _collector->lower_restart_addr(ra); |
| _markStack->reset(); // discard stack contents |
| _markStack->expand(); // expand the stack if possible |
| } |
| |
| // Upon stack overflow, we discard (part of) the stack, |
| // remembering the least address amongst those discarded |
| // in CMSCollector's _restart_address. |
| void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) { |
| // We need to do this under a mutex to prevent other |
| // workers from interfering with the work done below. |
| MutexLockerEx ml(_overflow_stack->par_lock(), |
| Mutex::_no_safepoint_check_flag); |
| // Remember the least grey address discarded |
| HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost); |
| _collector->lower_restart_addr(ra); |
| _overflow_stack->reset(); // discard stack contents |
| _overflow_stack->expand(); // expand the stack if possible |
| } |
| |
| void PushOrMarkClosure::do_oop(oop obj) { |
| // Ignore mark word because we are running concurrent with mutators. |
| assert(obj->is_oop_or_null(true), "expected an oop or NULL"); |
| HeapWord* addr = (HeapWord*)obj; |
| if (_span.contains(addr) && !_bitMap->isMarked(addr)) { |
| // Oop lies in _span and isn't yet grey or black |
| _bitMap->mark(addr); // now grey |
| if (addr < _finger) { |
| // the bit map iteration has already either passed, or |
| // sampled, this bit in the bit map; we'll need to |
| // use the marking stack to scan this oop's oops. |
| bool simulate_overflow = false; |
| NOT_PRODUCT( |
| if (CMSMarkStackOverflowALot && |
| _collector->simulate_overflow()) { |
| // simulate a stack overflow |
| simulate_overflow = true; |
| } |
| ) |
| if (simulate_overflow || !_markStack->push(obj)) { // stack overflow |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print_cr("CMS marking stack overflow (benign) at " |
| SIZE_FORMAT, _markStack->capacity()); |
| } |
| assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded"); |
| handle_stack_overflow(addr); |
| } |
| } |
| // anything including and to the right of _finger |
| // will be scanned as we iterate over the remainder of the |
| // bit map |
| do_yield_check(); |
| } |
| } |
| |
| void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); } |
| void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); } |
| |
| void Par_PushOrMarkClosure::do_oop(oop obj) { |
| // Ignore mark word because we are running concurrent with mutators. |
| assert(obj->is_oop_or_null(true), "expected an oop or NULL"); |
| HeapWord* addr = (HeapWord*)obj; |
| if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) { |
| // Oop lies in _span and isn't yet grey or black |
| // We read the global_finger (volatile read) strictly after marking oop |
| bool res = _bit_map->par_mark(addr); // now grey |
| volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr; |
| // Should we push this marked oop on our stack? |
| // -- if someone else marked it, nothing to do |
| // -- if target oop is above global finger nothing to do |
| // -- if target oop is in chunk and above local finger |
| // then nothing to do |
| // -- else push on work queue |
| if ( !res // someone else marked it, they will deal with it |
| || (addr >= *gfa) // will be scanned in a later task |
| || (_span.contains(addr) && addr >= _finger)) { // later in this chunk |
| return; |
| } |
| // the bit map iteration has already either passed, or |
| // sampled, this bit in the bit map; we'll need to |
| // use the marking stack to scan this oop's oops. |
| bool simulate_overflow = false; |
| NOT_PRODUCT( |
| if (CMSMarkStackOverflowALot && |
| _collector->simulate_overflow()) { |
| // simulate a stack overflow |
| simulate_overflow = true; |
| } |
| ) |
| if (simulate_overflow || |
| !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) { |
| // stack overflow |
| if (PrintCMSStatistics != 0) { |
| gclog_or_tty->print_cr("CMS marking stack overflow (benign) at " |
| SIZE_FORMAT, _overflow_stack->capacity()); |
| } |
| // We cannot assert that the overflow stack is full because |
| // it may have been emptied since. |
| assert(simulate_overflow || |
| _work_queue->size() == _work_queue->max_elems(), |
| "Else push should have succeeded"); |
| handle_stack_overflow(addr); |
| } |
| do_yield_check(); |
| } |
| } |
| |
| void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); } |
| void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); } |
| |
| KlassRememberingOopClosure::KlassRememberingOopClosure(CMSCollector* collector, |
| ReferenceProcessor* rp, |
| CMSMarkStack* revisit_stack) : |
| OopClosure(rp), |
| _collector(collector), |
| _revisit_stack(revisit_stack), |
| _should_remember_klasses(collector->should_unload_classes()) {} |
| |
| PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector, |
| MemRegion span, |
| ReferenceProcessor* rp, |
| CMSBitMap* bit_map, |
| CMSBitMap* mod_union_table, |
| CMSMarkStack* mark_stack, |
| CMSMarkStack* revisit_stack, |
| bool concurrent_precleaning): |
| KlassRememberingOopClosure(collector, rp, revisit_stack), |
| _span(span), |
| _bit_map(bit_map), |
| _mod_union_table(mod_union_table), |
| _mark_stack(mark_stack), |
| _concurrent_precleaning(concurrent_precleaning) |
| { |
| assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); |
| } |
| |
| // Grey object rescan during pre-cleaning and second checkpoint phases -- |
| // the non-parallel version (the parallel version appears further below.) |
| void PushAndMarkClosure::do_oop(oop obj) { |
| // Ignore mark word verification. If during concurrent precleaning, |
| // the object monitor may be locked. If during the checkpoint |
| // phases, the object may already have been reached by a different |
| // path and may be at the end of the global overflow list (so |
| // the mark word may be NULL). |
| assert(obj->is_oop_or_null(true /* ignore mark word */), |
| "expected an oop or NULL"); |
| HeapWord* addr = (HeapWord*)obj; |
| // Check if oop points into the CMS generation |
| // and is not marked |
| if (_span.contains(addr) && !_bit_map->isMarked(addr)) { |
| // a white object ... |
| _bit_map->mark(addr); // ... now grey |
| // push on the marking stack (grey set) |
| bool simulate_overflow = false; |
| NOT_PRODUCT( |
| if (CMSMarkStackOverflowALot && |
| _collector->simulate_overflow()) { |
| // simulate a stack overflow |
| simulate_overflow = true; |
| } |
| ) |
| if (simulate_overflow || !_mark_stack->push(obj)) { |
| if (_concurrent_precleaning) { |
| // During precleaning we can just dirty the appropriate card(s) |
| // in the mod union table, thus ensuring that the object remains |
| // in the grey set and continue. In the case of object arrays |
| // we need to dirty all of the cards that the object spans, |
| // since the rescan of object arrays will be limited to the |
| // dirty cards. |
| // Note that no one can be intefering with us in this action |
| // of dirtying the mod union table, so no locking or atomics |
| // are required. |
| if (obj->is_objArray()) { |
| size_t sz = obj->size(); |
| HeapWord* end_card_addr = (HeapWord*)round_to( |
| (intptr_t)(addr+sz), CardTableModRefBS::card_size); |
| MemRegion redirty_range = MemRegion(addr, end_card_addr); |
| assert(!redirty_range.is_empty(), "Arithmetical tautology"); |
| _mod_union_table->mark_range(redirty_range); |
| } else { |
| _mod_union_table->mark(addr); |
| } |
| _collector->_ser_pmc_preclean_ovflw++; |
| } else { |
| // During the remark phase, we need to remember this oop |
| // in the overflow list. |
| _collector->push_on_overflow_list(obj); |
| _collector->_ser_pmc_remark_ovflw++; |
| } |
| } |
| } |
| } |
| |
| Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector, |
| MemRegion span, |
| ReferenceProcessor* rp, |
| CMSBitMap* bit_map, |
| OopTaskQueue* work_queue, |
| CMSMarkStack* revisit_stack): |
| Par_KlassRememberingOopClosure(collector, rp, revisit_stack), |
| _span(span), |
| _bit_map(bit_map), |
| _work_queue(work_queue) |
| { |
| assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); |
| } |
| |
| void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); } |
| void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); } |
| |
| // Grey object rescan during second checkpoint phase -- |
| // the parallel version. |
| void Par_PushAndMarkClosure::do_oop(oop obj) { |
| // In the assert below, we ignore the mark word because |
| // this oop may point to an already visited object that is |
| // on the overflow stack (in which case the mark word has |
| // been hijacked for chaining into the overflow stack -- |
| // if this is the last object in the overflow stack then |
| // its mark word will be NULL). Because this object may |
| // have been subsequently popped off the global overflow |
| // stack, and the mark word possibly restored to the prototypical |
| // value, by the time we get to examined this failing assert in |
| // the debugger, is_oop_or_null(false) may subsequently start |
| // to hold. |
| assert(obj->is_oop_or_null(true), |
| "expected an oop or NULL"); |
| HeapWord* addr = (HeapWord*)obj; |
| // Check if oop points into the CMS generation |
| // and is not marked |
| if (_span.contains(addr) && !_bit_map->isMarked(addr)) { |
| // a white object ... |
| // If we manage to "claim" the object, by being the |
| // first thread to mark it, then we push it on our |
| // marking stack |
| if (_bit_map->par_mark(addr)) { // ... now grey |
| // push on work queue (grey set) |
| bool simulate_overflow = false; |
| NOT_PRODUCT( |
| if (CMSMarkStackOverflowALot && |
| _collector->par_simulate_overflow()) { |
| // simulate a stack overflow |
| simulate_overflow = true; |
| } |
| ) |
| if (simulate_overflow || !_work_queue->push(obj)) { |
| _collector->par_push_on_overflow_list(obj); |
| _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS |
| } |
| } // Else, some other thread got there first |
| } |
| } |
| |
| void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); } |
| void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); } |
| |
| void PushAndMarkClosure::remember_mdo(DataLayout* v) { |
| // TBD |
| } |
| |
| void Par_PushAndMarkClosure::remember_mdo(DataLayout* v) { |
| // TBD |
| } |
| |
| void CMSPrecleanRefsYieldClosure::do_yield_work() { |
| DEBUG_ONLY(RememberKlassesChecker mux(false);) |
| Mutex* bml = _collector->bitMapLock(); |
| assert_lock_strong(bml); |
| assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| "CMS thread should hold CMS token"); |
| |
| bml->unlock(); |
| ConcurrentMarkSweepThread::desynchronize(true); |
| |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| |
| _collector->stopTimer(); |
| GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); |
| if (PrintCMSStatistics != 0) { |
| _collector->incrementYields(); |
| } |
| _collector->icms_wait(); |
| |
| // See the comment in coordinator_yield() |
| for (unsigned i = 0; i < CMSYieldSleepCount && |
| ConcurrentMarkSweepThread::should_yield() && |
| !CMSCollector::foregroundGCIsActive(); ++i) { |
| os::sleep(Thread::current(), 1, false); |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| } |
| |
| ConcurrentMarkSweepThread::synchronize(true); |
| bml->lock(); |
| |
| _collector->startTimer(); |
| } |
| |
| bool CMSPrecleanRefsYieldClosure::should_return() { |
| if (ConcurrentMarkSweepThread::should_yield()) { |
| do_yield_work(); |
| } |
| return _collector->foregroundGCIsActive(); |
| } |
| |
| void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) { |
| assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0, |
| "mr should be aligned to start at a card boundary"); |
| // We'd like to assert: |
| // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0, |
| // "mr should be a range of cards"); |
| // However, that would be too strong in one case -- the last |
| // partition ends at _unallocated_block which, in general, can be |
| // an arbitrary boundary, not necessarily card aligned. |
| if (PrintCMSStatistics != 0) { |
| _num_dirty_cards += |
| mr.word_size()/CardTableModRefBS::card_size_in_words; |
| } |
| _space->object_iterate_mem(mr, &_scan_cl); |
| } |
| |
| SweepClosure::SweepClosure(CMSCollector* collector, |
| ConcurrentMarkSweepGeneration* g, |
| CMSBitMap* bitMap, bool should_yield) : |
| _collector(collector), |
| _g(g), |
| _sp(g->cmsSpace()), |
| _limit(_sp->sweep_limit()), |
| _freelistLock(_sp->freelistLock()), |
| _bitMap(bitMap), |
| _yield(should_yield), |
| _inFreeRange(false), // No free range at beginning of sweep |
| _freeRangeInFreeLists(false), // No free range at beginning of sweep |
| _lastFreeRangeCoalesced(false), |
| _freeFinger(g->used_region().start()) |
| { |
| NOT_PRODUCT( |
| _numObjectsFreed = 0; |
| _numWordsFreed = 0; |
| _numObjectsLive = 0; |
| _numWordsLive = 0; |
| _numObjectsAlreadyFree = 0; |
| _numWordsAlreadyFree = 0; |
| _last_fc = NULL; |
| |
| _sp->initializeIndexedFreeListArrayReturnedBytes(); |
| _sp->dictionary()->initialize_dict_returned_bytes(); |
| ) |
| assert(_limit >= _sp->bottom() && _limit <= _sp->end(), |
| "sweep _limit out of bounds"); |
| if (CMSTraceSweeper) { |
| gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT, |
| _limit); |
| } |
| } |
| |
| void SweepClosure::print_on(outputStream* st) const { |
| tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")", |
| _sp->bottom(), _sp->end()); |
| tty->print_cr("_limit = " PTR_FORMAT, _limit); |
| tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger); |
| NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);) |
| tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d", |
| _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced); |
| } |
| |
| #ifndef PRODUCT |
| // Assertion checking only: no useful work in product mode -- |
| // however, if any of the flags below become product flags, |
| // you may need to review this code to see if it needs to be |
| // enabled in product mode. |
| SweepClosure::~SweepClosure() { |
| assert_lock_strong(_freelistLock); |
| assert(_limit >= _sp->bottom() && _limit <= _sp->end(), |
| "sweep _limit out of bounds"); |
| if (inFreeRange()) { |
| warning("inFreeRange() should have been reset; dumping state of SweepClosure"); |
| print(); |
| ShouldNotReachHere(); |
| } |
| if (Verbose && PrintGC) { |
| gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes", |
| _numObjectsFreed, _numWordsFreed*sizeof(HeapWord)); |
| gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, " |
| SIZE_FORMAT" bytes " |
| "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes", |
| _numObjectsLive, _numWordsLive*sizeof(HeapWord), |
| _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord)); |
| size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) |
| * sizeof(HeapWord); |
| gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes); |
| |
| if (PrintCMSStatistics && CMSVerifyReturnedBytes) { |
| size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes(); |
| size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes(); |
| size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes; |
| gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes); |
| gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes", |
| indexListReturnedBytes); |
| gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes", |
| dict_returned_bytes); |
| } |
| } |
| if (CMSTraceSweeper) { |
| gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================", |
| _limit); |
| } |
| } |
| #endif // PRODUCT |
| |
| void SweepClosure::initialize_free_range(HeapWord* freeFinger, |
| bool freeRangeInFreeLists) { |
| if (CMSTraceSweeper) { |
| gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n", |
| freeFinger, freeRangeInFreeLists); |
| } |
| assert(!inFreeRange(), "Trampling existing free range"); |
| set_inFreeRange(true); |
| set_lastFreeRangeCoalesced(false); |
| |
| set_freeFinger(freeFinger); |
| set_freeRangeInFreeLists(freeRangeInFreeLists); |
| if (CMSTestInFreeList) { |
| if (freeRangeInFreeLists) { |
| FreeChunk* fc = (FreeChunk*) freeFinger; |
| assert(fc->is_free(), "A chunk on the free list should be free."); |
| assert(fc->size() > 0, "Free range should have a size"); |
| assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists"); |
| } |
| } |
| } |
| |
| // Note that the sweeper runs concurrently with mutators. Thus, |
| // it is possible for direct allocation in this generation to happen |
| // in the middle of the sweep. Note that the sweeper also coalesces |
| // contiguous free blocks. Thus, unless the sweeper and the allocator |
| // synchronize appropriately freshly allocated blocks may get swept up. |
| // This is accomplished by the sweeper locking the free lists while |
| // it is sweeping. Thus blocks that are determined to be free are |
| // indeed free. There is however one additional complication: |
| // blocks that have been allocated since the final checkpoint and |
| // mark, will not have been marked and so would be treated as |
| // unreachable and swept up. To prevent this, the allocator marks |
| // the bit map when allocating during the sweep phase. This leads, |
| // however, to a further complication -- objects may have been allocated |
| // but not yet initialized -- in the sense that the header isn't yet |
| // installed. The sweeper can not then determine the size of the block |
| // in order to skip over it. To deal with this case, we use a technique |
| // (due to Printezis) to encode such uninitialized block sizes in the |
| // bit map. Since the bit map uses a bit per every HeapWord, but the |
| // CMS generation has a minimum object size of 3 HeapWords, it follows |
| // that "normal marks" won't be adjacent in the bit map (there will |
| // always be at least two 0 bits between successive 1 bits). We make use |
| // of these "unused" bits to represent uninitialized blocks -- the bit |
| // corresponding to the start of the uninitialized object and the next |
| // bit are both set. Finally, a 1 bit marks the end of the object that |
| // started with the two consecutive 1 bits to indicate its potentially |
| // uninitialized state. |
| |
| size_t SweepClosure::do_blk_careful(HeapWord* addr) { |
| FreeChunk* fc = (FreeChunk*)addr; |
| size_t res; |
| |
| // Check if we are done sweeping. Below we check "addr >= _limit" rather |
| // than "addr == _limit" because although _limit was a block boundary when |
| // we started the sweep, it may no longer be one because heap expansion |
| // may have caused us to coalesce the block ending at the address _limit |
| // with a newly expanded chunk (this happens when _limit was set to the |
| // previous _end of the space), so we may have stepped past _limit: |
| // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740. |
| if (addr >= _limit) { // we have swept up to or past the limit: finish up |
| assert(_limit >= _sp->bottom() && _limit <= _sp->end(), |
| "sweep _limit out of bounds"); |
| assert(addr < _sp->end(), "addr out of bounds"); |
| // Flush any free range we might be holding as a single |
| // coalesced chunk to the appropriate free list. |
| if (inFreeRange()) { |
| assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit, |
| err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger())); |
| flush_cur_free_chunk(freeFinger(), |
| pointer_delta(addr, freeFinger())); |
| if (CMSTraceSweeper) { |
| gclog_or_tty->print("Sweep: last chunk: "); |
| gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") " |
| "[coalesced:"SIZE_FORMAT"]\n", |
| freeFinger(), pointer_delta(addr, freeFinger()), |
| lastFreeRangeCoalesced()); |
| } |
| } |
| |
| // help the iterator loop finish |
| return pointer_delta(_sp->end(), addr); |
| } |
| |
| assert(addr < _limit, "sweep invariant"); |
| // check if we should yield |
| do_yield_check(addr); |
| if (fc->is_free()) { |
| // Chunk that is already free |
| res = fc->size(); |
| do_already_free_chunk(fc); |
| debug_only(_sp->verifyFreeLists()); |
| // If we flush the chunk at hand in lookahead_and_flush() |
| // and it's coalesced with a preceding chunk, then the |
| // process of "mangling" the payload of the coalesced block |
| // will cause erasure of the size information from the |
| // (erstwhile) header of all the coalesced blocks but the |
| // first, so the first disjunct in the assert will not hold |
| // in that specific case (in which case the second disjunct |
| // will hold). |
| assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit, |
| "Otherwise the size info doesn't change at this step"); |
| NOT_PRODUCT( |
| _numObjectsAlreadyFree++; |
| _numWordsAlreadyFree += res; |
| ) |
| NOT_PRODUCT(_last_fc = fc;) |
| } else if (!_bitMap->isMarked(addr)) { |
| // Chunk is fresh garbage |
| res = do_garbage_chunk(fc); |
| debug_only(_sp->verifyFreeLists()); |
| NOT_PRODUCT( |
| _numObjectsFreed++; |
| _numWordsFreed += res; |
| ) |
| } else { |
| // Chunk that is alive. |
| res = do_live_chunk(fc); |
| debug_only(_sp->verifyFreeLists()); |
| NOT_PRODUCT( |
| _numObjectsLive++; |
| _numWordsLive += res; |
| ) |
| } |
| return res; |
| } |
| |
| // For the smart allocation, record following |
| // split deaths - a free chunk is removed from its free list because |
| // it is being split into two or more chunks. |
| // split birth - a free chunk is being added to its free list because |
| // a larger free chunk has been split and resulted in this free chunk. |
| // coal death - a free chunk is being removed from its free list because |
| // it is being coalesced into a large free chunk. |
| // coal birth - a free chunk is being added to its free list because |
| // it was created when two or more free chunks where coalesced into |
| // this free chunk. |
| // |
| // These statistics are used to determine the desired number of free |
| // chunks of a given size. The desired number is chosen to be relative |
| // to the end of a CMS sweep. The desired number at the end of a sweep |
| // is the |
| // count-at-end-of-previous-sweep (an amount that was enough) |
| // - count-at-beginning-of-current-sweep (the excess) |
| // + split-births (gains in this size during interval) |
| // - split-deaths (demands on this size during interval) |
| // where the interval is from the end of one sweep to the end of the |
| // next. |
| // |
| // When sweeping the sweeper maintains an accumulated chunk which is |
| // the chunk that is made up of chunks that have been coalesced. That |
| // will be termed the left-hand chunk. A new chunk of garbage that |
| // is being considered for coalescing will be referred to as the |
| // right-hand chunk. |
| // |
| // When making a decision on whether to coalesce a right-hand chunk with |
| // the current left-hand chunk, the current count vs. the desired count |
| // of the left-hand chunk is considered. Also if the right-hand chunk |
| // is near the large chunk at the end of the heap (see |
| // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the |
| // left-hand chunk is coalesced. |
| // |
| // When making a decision about whether to split a chunk, the desired count |
| // vs. the current count of the candidate to be split is also considered. |
| // If the candidate is underpopulated (currently fewer chunks than desired) |
| // a chunk of an overpopulated (currently more chunks than desired) size may |
| // be chosen. The "hint" associated with a free list, if non-null, points |
| // to a free list which may be overpopulated. |
| // |
| |
| void SweepClosure::do_already_free_chunk(FreeChunk* fc) { |
| const size_t size = fc->size(); |
| // Chunks that cannot be coalesced are not in the |
| // free lists. |
| if (CMSTestInFreeList && !fc->cantCoalesce()) { |
| assert(_sp->verify_chunk_in_free_list(fc), |
| "free chunk should be in free lists"); |
| } |
| // a chunk that is already free, should not have been |
| // marked in the bit map |
| HeapWord* const addr = (HeapWord*) fc; |
| assert(!_bitMap->isMarked(addr), "free chunk should be unmarked"); |
| // Verify that the bit map has no bits marked between |
| // addr and purported end of this block. |
| _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); |
| |
| // Some chunks cannot be coalesced under any circumstances. |
| // See the definition of cantCoalesce(). |
| if (!fc->cantCoalesce()) { |
| // This chunk can potentially be coalesced. |
| if (_sp->adaptive_freelists()) { |
| // All the work is done in |
| do_post_free_or_garbage_chunk(fc, size); |
| } else { // Not adaptive free lists |
| // this is a free chunk that can potentially be coalesced by the sweeper; |
| if (!inFreeRange()) { |
| // if the next chunk is a free block that can't be coalesced |
| // it doesn't make sense to remove this chunk from the free lists |
| FreeChunk* nextChunk = (FreeChunk*)(addr + size); |
| assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?"); |
| if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ... |
| nextChunk->is_free() && // ... which is free... |
| nextChunk->cantCoalesce()) { // ... but can't be coalesced |
| // nothing to do |
| } else { |
| // Potentially the start of a new free range: |
| // Don't eagerly remove it from the free lists. |
| // No need to remove it if it will just be put |
| // back again. (Also from a pragmatic point of view |
| // if it is a free block in a region that is beyond |
| // any allocated blocks, an assertion will fail) |
| // Remember the start of a free run. |
| initialize_free_range(addr, true); |
| // end - can coalesce with next chunk |
| } |
| } else { |
| // the midst of a free range, we are coalescing |
| print_free_block_coalesced(fc); |
| if (CMSTraceSweeper) { |
| gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size); |
| } |
| // remove it from the free lists |
| _sp->removeFreeChunkFromFreeLists(fc); |
| set_lastFreeRangeCoalesced(true); |
| // If the chunk is being coalesced and the current free range is |
| // in the free lists, remove the current free range so that it |
| // will be returned to the free lists in its entirety - all |
| // the coalesced pieces included. |
| if (freeRangeInFreeLists()) { |
| FreeChunk* ffc = (FreeChunk*) freeFinger(); |
| assert(ffc->size() == pointer_delta(addr, freeFinger()), |
| "Size of free range is inconsistent with chunk size."); |
| if (CMSTestInFreeList) { |
| assert(_sp->verify_chunk_in_free_list(ffc), |
| "free range is not in free lists"); |
| } |
| _sp->removeFreeChunkFromFreeLists(ffc); |
| set_freeRangeInFreeLists(false); |
| } |
| } |
| } |
| // Note that if the chunk is not coalescable (the else arm |
| // below), we unconditionally flush, without needing to do |
| // a "lookahead," as we do below. |
| if (inFreeRange()) lookahead_and_flush(fc, size); |
| } else { |
| // Code path common to both original and adaptive free lists. |
| |
| // cant coalesce with previous block; this should be treated |
| // as the end of a free run if any |
| if (inFreeRange()) { |
| // we kicked some butt; time to pick up the garbage |
| assert(freeFinger() < addr, "freeFinger points too high"); |
| flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); |
| } |
| // else, nothing to do, just continue |
| } |
| } |
| |
| size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) { |
| // This is a chunk of garbage. It is not in any free list. |
| // Add it to a free list or let it possibly be coalesced into |
| // a larger chunk. |
| HeapWord* const addr = (HeapWord*) fc; |
| const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()); |
| |
| if (_sp->adaptive_freelists()) { |
| // Verify that the bit map has no bits marked between |
| // addr and purported end of just dead object. |
| _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); |
| |
| do_post_free_or_garbage_chunk(fc, size); |
| } else { |
| if (!inFreeRange()) { |
| // start of a new free range |
| assert(size > 0, "A free range should have a size"); |
| initialize_free_range(addr, false); |
| } else { |
| // this will be swept up when we hit the end of the |
| // free range |
| if (CMSTraceSweeper) { |
| gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size); |
| } |
| // If the chunk is being coalesced and the current free range is |
| // in the free lists, remove the current free range so that it |
| // will be returned to the free lists in its entirety - all |
| // the coalesced pieces included. |
| if (freeRangeInFreeLists()) { |
| FreeChunk* ffc = (FreeChunk*)freeFinger(); |
| assert(ffc->size() == pointer_delta(addr, freeFinger()), |
| "Size of free range is inconsistent with chunk size."); |
| if (CMSTestInFreeList) { |
| assert(_sp->verify_chunk_in_free_list(ffc), |
| "free range is not in free lists"); |
| } |
| _sp->removeFreeChunkFromFreeLists(ffc); |
| set_freeRangeInFreeLists(false); |
| } |
| set_lastFreeRangeCoalesced(true); |
| } |
| // this will be swept up when we hit the end of the free range |
| |
| // Verify that the bit map has no bits marked between |
| // addr and purported end of just dead object. |
| _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); |
| } |
| assert(_limit >= addr + size, |
| "A freshly garbage chunk can't possibly straddle over _limit"); |
| if (inFreeRange()) lookahead_and_flush(fc, size); |
| return size; |
| } |
| |
| size_t SweepClosure::do_live_chunk(FreeChunk* fc) { |
| HeapWord* addr = (HeapWord*) fc; |
| // The sweeper has just found a live object. Return any accumulated |
| // left hand chunk to the free lists. |
| if (inFreeRange()) { |
| assert(freeFinger() < addr, "freeFinger points too high"); |
| flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); |
| } |
| |
| // This object is live: we'd normally expect this to be |
| // an oop, and like to assert the following: |
| // assert(oop(addr)->is_oop(), "live block should be an oop"); |
| // However, as we commented above, this may be an object whose |
| // header hasn't yet been initialized. |
| size_t size; |
| assert(_bitMap->isMarked(addr), "Tautology for this control point"); |
| if (_bitMap->isMarked(addr + 1)) { |
| // Determine the size from the bit map, rather than trying to |
| // compute it from the object header. |
| HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2); |
| size = pointer_delta(nextOneAddr + 1, addr); |
| assert(size == CompactibleFreeListSpace::adjustObjectSize(size), |
| "alignment problem"); |
| |
| #ifdef DEBUG |
| if (oop(addr)->klass_or_null() != NULL && |
| ( !_collector->should_unload_classes() |
| || (oop(addr)->is_parsable()) && |
| oop(addr)->is_conc_safe())) { |
| // Ignore mark word because we are running concurrent with mutators |
| assert(oop(addr)->is_oop(true), "live block should be an oop"); |
| // is_conc_safe is checked before performing this assertion |
| // because an object that is not is_conc_safe may yet have |
| // the return from size() correct. |
| assert(size == |
| CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()), |
| "P-mark and computed size do not agree"); |
| } |
| #endif |
| |
| } else { |
| // This should be an initialized object that's alive. |
| assert(oop(addr)->klass_or_null() != NULL && |
| (!_collector->should_unload_classes() |
| || oop(addr)->is_parsable()), |
| "Should be an initialized object"); |
| // Note that there are objects used during class redefinition, |
| // e.g. merge_cp in VM_RedefineClasses::merge_cp_and_rewrite(), |
| // which are discarded with their is_conc_safe state still |
| // false. These object may be floating garbage so may be |
| // seen here. If they are floating garbage their size |
| // should be attainable from their klass. Do not that |
| // is_conc_safe() is true for oop(addr). |
| // Ignore mark word because we are running concurrent with mutators |
| assert(oop(addr)->is_oop(true), "live block should be an oop"); |
| // Verify that the bit map has no bits marked between |
| // addr and purported end of this block. |
| size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()); |
| assert(size >= 3, "Necessary for Printezis marks to work"); |
| assert(!_bitMap->isMarked(addr+1), "Tautology for this control point"); |
| DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);) |
| } |
| return size; |
| } |
| |
| void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc, |
| size_t chunkSize) { |
| // do_post_free_or_garbage_chunk() should only be called in the case |
| // of the adaptive free list allocator. |
| const bool fcInFreeLists = fc->is_free(); |
| assert(_sp->adaptive_freelists(), "Should only be used in this case."); |
| assert((HeapWord*)fc <= _limit, "sweep invariant"); |
| if (CMSTestInFreeList && fcInFreeLists) { |
| assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists"); |
| } |
| |
| if (CMSTraceSweeper) { |
| gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize); |
| } |
| |
| HeapWord* const fc_addr = (HeapWord*) fc; |
| |
| bool coalesce; |
| const size_t left = pointer_delta(fc_addr, freeFinger()); |
| const size_t right = chunkSize; |
| switch (FLSCoalescePolicy) { |
| // numeric value forms a coalition aggressiveness metric |
| case 0: { // never coalesce |
| coalesce = false; |
| break; |
| } |
| case 1: { // coalesce if left & right chunks on overpopulated lists |
| coalesce = _sp->coalOverPopulated(left) && |
| _sp->coalOverPopulated(right); |
| break; |
| } |
| case 2: { // coalesce if left chunk on overpopulated list (default) |
| coalesce = _sp->coalOverPopulated(left); |
| break; |
| } |
| case 3: { // coalesce if left OR right chunk on overpopulated list |
| coalesce = _sp->coalOverPopulated(left) || |
| _sp->coalOverPopulated(right); |
| break; |
| } |
| case 4: { // always coalesce |
| coalesce = true; |
| break; |
| } |
| default: |
| ShouldNotReachHere(); |
| } |
| |
| // Should the current free range be coalesced? |
| // If the chunk is in a free range and either we decided to coalesce above |
| // or the chunk is near the large block at the end of the heap |
| // (isNearLargestChunk() returns true), then coalesce this chunk. |
| const bool doCoalesce = inFreeRange() |
| && (coalesce || _g->isNearLargestChunk(fc_addr)); |
| if (doCoalesce) { |
| // Coalesce the current free range on the left with the new |
| // chunk on the right. If either is on a free list, |
| // it must be removed from the list and stashed in the closure. |
| if (freeRangeInFreeLists()) { |
| FreeChunk* const ffc = (FreeChunk*)freeFinger(); |
| assert(ffc->size() == pointer_delta(fc_addr, freeFinger()), |
| "Size of free range is inconsistent with chunk size."); |
| if (CMSTestInFreeList) { |
| assert(_sp->verify_chunk_in_free_list(ffc), |
| "Chunk is not in free lists"); |
| } |
| _sp->coalDeath(ffc->size()); |
| _sp->removeFreeChunkFromFreeLists(ffc); |
| set_freeRangeInFreeLists(false); |
| } |
| if (fcInFreeLists) { |
| _sp->coalDeath(chunkSize); |
| assert(fc->size() == chunkSize, |
| "The chunk has the wrong size or is not in the free lists"); |
| _sp->removeFreeChunkFromFreeLists(fc); |
| } |
| set_lastFreeRangeCoalesced(true); |
| print_free_block_coalesced(fc); |
| } else { // not in a free range and/or should not coalesce |
| // Return the current free range and start a new one. |
| if (inFreeRange()) { |
| // In a free range but cannot coalesce with the right hand chunk. |
| // Put the current free range into the free lists. |
| flush_cur_free_chunk(freeFinger(), |
| pointer_delta(fc_addr, freeFinger())); |
| } |
| // Set up for new free range. Pass along whether the right hand |
| // chunk is in the free lists. |
| initialize_free_range((HeapWord*)fc, fcInFreeLists); |
| } |
| } |
| |
| // Lookahead flush: |
| // If we are tracking a free range, and this is the last chunk that |
| // we'll look at because its end crosses past _limit, we'll preemptively |
| // flush it along with any free range we may be holding on to. Note that |
| // this can be the case only for an already free or freshly garbage |
| // chunk. If this block is an object, it can never straddle |
| // over _limit. The "straddling" occurs when _limit is set at |
| // the previous end of the space when this cycle started, and |
| // a subsequent heap expansion caused the previously co-terminal |
| // free block to be coalesced with the newly expanded portion, |
| // thus rendering _limit a non-block-boundary making it dangerous |
| // for the sweeper to step over and examine. |
| void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) { |
| assert(inFreeRange(), "Should only be called if currently in a free range."); |
| HeapWord* const eob = ((HeapWord*)fc) + chunk_size; |
| assert(_sp->used_region().contains(eob - 1), |
| err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")" |
| " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")", |
| _limit, _sp->bottom(), _sp->end(), fc, chunk_size)); |
| if (eob >= _limit) { |
| assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit"); |
| if (CMSTraceSweeper) { |
| gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block " |
| "[" PTR_FORMAT "," PTR_FORMAT ") in space " |
| "[" PTR_FORMAT "," PTR_FORMAT ")", |
| _limit, fc, eob, _sp->bottom(), _sp->end()); |
| } |
| // Return the storage we are tracking back into the free lists. |
| if (CMSTraceSweeper) { |
| gclog_or_tty->print_cr("Flushing ... "); |
| } |
| assert(freeFinger() < eob, "Error"); |
| flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger())); |
| } |
| } |
| |
| void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) { |
| assert(inFreeRange(), "Should only be called if currently in a free range."); |
| assert(size > 0, |
| "A zero sized chunk cannot be added to the free lists."); |
| if (!freeRangeInFreeLists()) { |
| if (CMSTestInFreeList) { |
| FreeChunk* fc = (FreeChunk*) chunk; |
| fc->set_size(size); |
| assert(!_sp->verify_chunk_in_free_list(fc), |
| "chunk should not be in free lists yet"); |
| } |
| if (CMSTraceSweeper) { |
| gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists", |
| chunk, size); |
| } |
| // A new free range is going to be starting. The current |
| // free range has not been added to the free lists yet or |
| // was removed so add it back. |
| // If the current free range was coalesced, then the death |
| // of the free range was recorded. Record a birth now. |
| if (lastFreeRangeCoalesced()) { |
| _sp->coalBirth(size); |
| } |
| _sp->addChunkAndRepairOffsetTable(chunk, size, |
| lastFreeRangeCoalesced()); |
| } else if (CMSTraceSweeper) { |
| gclog_or_tty->print_cr("Already in free list: nothing to flush"); |
| } |
| set_inFreeRange(false); |
| set_freeRangeInFreeLists(false); |
| } |
| |
| // We take a break if we've been at this for a while, |
| // so as to avoid monopolizing the locks involved. |
| void SweepClosure::do_yield_work(HeapWord* addr) { |
| // Return current free chunk being used for coalescing (if any) |
| // to the appropriate freelist. After yielding, the next |
| // free block encountered will start a coalescing range of |
| // free blocks. If the next free block is adjacent to the |
| // chunk just flushed, they will need to wait for the next |
| // sweep to be coalesced. |
| if (inFreeRange()) { |
| flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); |
| } |
| |
| // First give up the locks, then yield, then re-lock. |
| // We should probably use a constructor/destructor idiom to |
| // do this unlock/lock or modify the MutexUnlocker class to |
| // serve our purpose. XXX |
| assert_lock_strong(_bitMap->lock()); |
| assert_lock_strong(_freelistLock); |
| assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| "CMS thread should hold CMS token"); |
| _bitMap->lock()->unlock(); |
| _freelistLock->unlock(); |
| ConcurrentMarkSweepThread::desynchronize(true); |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| _collector->stopTimer(); |
| GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); |
| if (PrintCMSStatistics != 0) { |
| _collector->incrementYields(); |
| } |
| _collector->icms_wait(); |
| |
| // See the comment in coordinator_yield() |
| for (unsigned i = 0; i < CMSYieldSleepCount && |
| ConcurrentMarkSweepThread::should_yield() && |
| !CMSCollector::foregroundGCIsActive(); ++i) { |
| os::sleep(Thread::current(), 1, false); |
| ConcurrentMarkSweepThread::acknowledge_yield_request(); |
| } |
| |
| ConcurrentMarkSweepThread::synchronize(true); |
| _freelistLock->lock(); |
| _bitMap->lock()->lock_without_safepoint_check(); |
| _collector->startTimer(); |
| } |
| |
| #ifndef PRODUCT |
| // This is actually very useful in a product build if it can |
| // be called from the debugger. Compile it into the product |
| // as needed. |
| bool debug_verify_chunk_in_free_list(FreeChunk* fc) { |
| return debug_cms_space->verify_chunk_in_free_list(fc); |
| } |
| #endif |
| |
| void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const { |
| if (CMSTraceSweeper) { |
| gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")", |
| fc, fc->size()); |
| } |
| } |
| |
| // CMSIsAliveClosure |
| bool CMSIsAliveClosure::do_object_b(oop obj) { |
| HeapWord* addr = (HeapWord*)obj; |
| return addr != NULL && |
| (!_span.contains(addr) || _bit_map->isMarked(addr)); |
| } |
| |
| CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector, |
| MemRegion span, |
| CMSBitMap* bit_map, CMSMarkStack* mark_stack, |
| CMSMarkStack* revisit_stack, bool cpc): |
| KlassRememberingOopClosure(collector, NULL, revisit_stack), |
| _span(span), |
| _bit_map(bit_map), |
| _mark_stack(mark_stack), |
| _concurrent_precleaning(cpc) { |
| assert(!_span.is_empty(), "Empty span could spell trouble"); |
| } |
| |
| |
| // CMSKeepAliveClosure: the serial version |
| void CMSKeepAliveClosure::do_oop(oop obj) { |
| HeapWord* addr = (HeapWord*)obj; |
| if (_span.contains(addr) && |
| !_bit_map->isMarked(addr)) { |
| _bit_map->mark(addr); |
| bool simulate_overflow = false; |
| NOT_PRODUCT( |
| if (CMSMarkStackOverflowALot && |
| _collector->simulate_overflow()) { |
| // simulate a stack overflow |
| simulate_overflow = true; |
| } |
| ) |
| if (simulate_overflow || !_mark_stack->push(obj)) { |
| if (_concurrent_precleaning) { |
| // We dirty the overflown object and let the remark |
| // phase deal with it. |
| assert(_collector->overflow_list_is_empty(), "Error"); |
| // In the case of object arrays, we need to dirty all of |
| // the cards that the object spans. No locking or atomics |
| // are needed since no one else can be mutating the mod union |
| // table. |
| if (obj->is_objArray()) { |
| size_t sz = obj->size(); |
| HeapWord* end_card_addr = |
| (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size); |
| MemRegion redirty_range = MemRegion(addr, end_card_addr); |
| assert(!redirty_range.is_empty(), "Arithmetical tautology"); |
| _collector->_modUnionTable.mark_range(redirty_range); |
| } else { |
| _collector->_modUnionTable.mark(addr); |
| } |
| _collector->_ser_kac_preclean_ovflw++; |
| } else { |
| _collector->push_on_overflow_list(obj); |
| _collector->_ser_kac_ovflw++; |
| } |
| } |
| } |
| } |
| |
| void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); } |
| void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); } |
| |
| // CMSParKeepAliveClosure: a parallel version of the above. |
| // The work queues are private to each closure (thread), |
| // but (may be) available for stealing by other threads. |
| void CMSParKeepAliveClosure::do_oop(oop obj) { |
| HeapWord* addr = (HeapWord*)obj; |
| if (_span.contains(addr) && |
| !_bit_map->isMarked(addr)) { |
| // In general, during recursive tracing, several threads |
| // may be concurrently getting here; the first one to |
| // "tag" it, claims it. |
| if (_bit_map->par_mark(addr)) { |
| bool res = _work_queue->push(obj); |
| assert(res, "Low water mark should be much less than capacity"); |
| // Do a recursive trim in the hope that this will keep |
| // stack usage lower, but leave some oops for potential stealers |
| trim_queue(_low_water_mark); |
| } // Else, another thread got there first |
| } |
| } |
| |
| void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); } |
| void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); } |
| |
| void CMSParKeepAliveClosure::trim_queue(uint max) { |
| while (_work_queue->size() > max) { |
| oop new_oop; |
| if (_work_queue->pop_local(new_oop)) { |
| assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop"); |
| assert(_bit_map->isMarked((HeapWord*)new_oop), |
| "no white objects on this stack!"); |
| assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop"); |
| // iterate over the oops in this oop, marking and pushing |
| // the ones in CMS heap (i.e. in _span). |
| new_oop->oop_iterate(&_mark_and_push); |
| } |
| } |
| } |
| |
| CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure( |
| CMSCollector* collector, |
| MemRegion span, CMSBitMap* bit_map, |
| CMSMarkStack* revisit_stack, |
| OopTaskQueue* work_queue): |
| Par_KlassRememberingOopClosure(collector, NULL, revisit_stack), |
| _span(span), |
| _bit_map(bit_map), |
| _work_queue(work_queue) { } |
| |
| void CMSInnerParMarkAndPushClosure::do_oop(oop obj) { |
| HeapWord* addr = (HeapWord*)obj; |
| if (_span.contains(addr) && |
| !_bit_map->isMarked(addr)) { |
| if (_bit_map->par_mark(addr)) { |
| bool simulate_overflow = false; |
| NOT_PRODUCT( |
| if (CMSMarkStackOverflowALot && |
| _collector->par_simulate_overflow()) { |
| // simulate a stack overflow |
| simulate_overflow = true; |
| } |
| ) |
| if (simulate_overflow || !_work_queue->push(obj)) { |
| _collector->par_push_on_overflow_list(obj); |
| _collector->_par_kac_ovflw++; |
| } |
| } // Else another thread got there already |
| } |
| } |
| |
| void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); } |
| void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); } |
| |
| ////////////////////////////////////////////////////////////////// |
| // CMSExpansionCause ///////////////////////////// |
| ////////////////////////////////////////////////////////////////// |
| const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) { |
| switch (cause) { |
| case _no_expansion: |
| return "No expansion"; |
| case _satisfy_free_ratio: |
| return "Free ratio"; |
| case _satisfy_promotion: |
| return "Satisfy promotion"; |
| case _satisfy_allocation: |
| return "allocation"; |
| case _allocate_par_lab: |
| return "Par LAB"; |
| case _allocate_par_spooling_space: |
| return "Par Spooling Space"; |
| case _adaptive_size_policy: |
| return "Ergonomics"; |
| default: |
| return "unknown"; |
| } |
| } |
| |
| void CMSDrainMarkingStackClosure::do_void() { |
| // the max number to take from overflow list at a time |
| const size_t num = _mark_stack->capacity()/4; |
| assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(), |
| "Overflow list should be NULL during concurrent phases"); |
| while (!_mark_stack->isEmpty() || |
| // if stack is empty, check the overflow list |
| _collector->take_from_overflow_list(num, _mark_stack)) { |
| oop obj = _mark_stack->pop(); |
| HeapWord* addr = (HeapWord*)obj; |
| assert(_span.contains(addr), "Should be within span"); |
| assert(_bit_map->isMarked(addr), "Should be marked"); |
| assert(obj->is_oop(), "Should be an oop"); |
| obj->oop_iterate(_keep_alive); |
| } |
| } |
| |
| void CMSParDrainMarkingStackClosure::do_void() { |
| // drain queue |
| trim_queue(0); |
| } |
| |
| // Trim our work_queue so its length is below max at return |
| void CMSParDrainMarkingStackClosure::trim_queue(uint max) { |
| while (_work_queue->size() > max) { |
| oop new_oop; |
| if (_work_queue->pop_local(new_oop)) { |
| assert(new_oop->is_oop(), "Expected an oop"); |
| assert(_bit_map->isMarked((HeapWord*)new_oop), |
| "no white objects on this stack!"); |
| assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop"); |
| // iterate over the oops in this oop, marking and pushing |
| // the ones in CMS heap (i.e. in _span). |
| new_oop->oop_iterate(&_mark_and_push); |
| } |
| } |
| } |
| |
| //////////////////////////////////////////////////////////////////// |
| // Support for Marking Stack Overflow list handling and related code |
| //////////////////////////////////////////////////////////////////// |
| // Much of the following code is similar in shape and spirit to the |
| // code used in ParNewGC. We should try and share that code |
| // as much as possible in the future. |
| |
| #ifndef PRODUCT |
| // Debugging support for CMSStackOverflowALot |
| |
| // It's OK to call this multi-threaded; the worst thing |
| // that can happen is that we'll get a bunch of closely |
| // spaced simulated oveflows, but that's OK, in fact |
| // probably good as it would exercise the overflow code |
| // under contention. |
| bool CMSCollector::simulate_overflow() { |
| if (_overflow_counter-- <= 0) { // just being defensive |
| _overflow_counter = CMSMarkStackOverflowInterval; |
| return true; |
| } else { |
| return false; |
| } |
| } |
| |
| bool CMSCollector::par_simulate_overflow() { |
| return simulate_overflow(); |
| } |
| #endif |
| |
| // Single-threaded |
| bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) { |
| assert(stack->isEmpty(), "Expected precondition"); |
| assert(stack->capacity() > num, "Shouldn't bite more than can chew"); |
| size_t i = num; |
| oop cur = _overflow_list; |
| const markOop proto = markOopDesc::prototype(); |
| NOT_PRODUCT(ssize_t n = 0;) |
| for (oop next; i > 0 && cur != NULL; cur = next, i--) { |
| next = oop(cur->mark()); |
| cur->set_mark(proto); // until proven otherwise |
| assert(cur->is_oop(), "Should be an oop"); |
| bool res = stack->push(cur); |
| assert(res, "Bit off more than can chew?"); |
| NOT_PRODUCT(n++;) |
| } |
| _overflow_list = cur; |
| #ifndef PRODUCT |
| assert(_num_par_pushes >= n, "Too many pops?"); |
| _num_par_pushes -=n; |
| #endif |
| return !stack->isEmpty(); |
| } |
| |
| #define BUSY (oop(0x1aff1aff)) |
| // (MT-safe) Get a prefix of at most "num" from the list. |
| // The overflow list is chained through the mark word of |
| // each object in the list. We fetch the entire list, |
| // break off a prefix of the right size and return the |
| // remainder. If other threads try to take objects from |
| // the overflow list at that time, they will wait for |
| // some time to see if data becomes available. If (and |
| // only if) another thread places one or more object(s) |
| // on the global list before we have returned the suffix |
| // to the global list, we will walk down our local list |
| // to find its end and append the global list to |
| // our suffix before returning it. This suffix walk can |
| // prove to be expensive (quadratic in the amount of traffic) |
| // when there are many objects in the overflow list and |
| // there is much producer-consumer contention on the list. |
| // *NOTE*: The overflow list manipulation code here and |
| // in ParNewGeneration:: are very similar in shape, |
| // except that in the ParNew case we use the old (from/eden) |
| // copy of the object to thread the list via its klass word. |
| // Because of the common code, if you make any changes in |
| // the code below, please check the ParNew version to see if |
| // similar changes might be needed. |
| // CR 6797058 has been filed to consolidate the common code. |
| bool CMSCollector::par_take_from_overflow_list(size_t num, |
| OopTaskQueue* work_q, |
| int no_of_gc_threads) { |
| assert(work_q->size() == 0, "First empty local work queue"); |
| assert(num < work_q->max_elems(), "Can't bite more than we can chew"); |
| if (_overflow_list == NULL) { |
| return false; |
| } |
| // Grab the entire list; we'll put back a suffix |
| oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list); |
| Thread* tid = Thread::current(); |
| // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was |
| // set to ParallelGCThreads. |
| size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads; |
| size_t sleep_time_millis = MAX2((size_t)1, num/100); |
| // If the list is busy, we spin for a short while, |
| // sleeping between attempts to get the list. |
| for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) { |
| os::sleep(tid, sleep_time_millis, false); |
| if (_overflow_list == NULL) { |
| // Nothing left to take |
| return false; |
| } else if (_overflow_list != BUSY) { |
| // Try and grab the prefix |
| prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list); |
| } |
| } |
| // If the list was found to be empty, or we spun long |
| // enough, we give up and return empty-handed. If we leave |
| // the list in the BUSY state below, it must be the case that |
| // some other thread holds the overflow list and will set it |
| // to a non-BUSY state in the future. |
| if (prefix == NULL || prefix == BUSY) { |
| // Nothing to take or waited long enough |
| if (prefix == NULL) { |
| // Write back the NULL in case we overwrote it with BUSY above |
| // and it is still the same value. |
| (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); |
| } |
| return false; |
| } |
| assert(prefix != NULL && prefix != BUSY, "Error"); |
| size_t i = num; |
| oop cur = prefix; |
| // Walk down the first "num" objects, unless we reach the end. |
| for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--); |
| if (cur->mark() == NULL) { |
| // We have "num" or fewer elements in the list, so there |
| // is nothing to return to the global list. |
| // Write back the NULL in lieu of the BUSY we wrote |
| // above, if it is still the same value. |
| if (_overflow_list == BUSY) { |
| (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); |
| } |
| } else { |
| // Chop off the suffix and rerturn it to the global list. |
| assert(cur->mark() != BUSY, "Error"); |
| oop suffix_head = cur->mark(); // suffix will be put back on global list |
| cur->set_mark(NULL); // break off suffix |
| // It's possible that the list is still in the empty(busy) state |
| // we left it in a short while ago; in that case we may be |
| // able to place back the suffix without incurring the cost |
| // of a walk down the list. |
| oop observed_overflow_list = _overflow_list; |
| oop cur_overflow_list = observed_overflow_list; |
| bool attached = false; |
| while (observed_overflow_list == BUSY || observed_overflow_list == NULL) { |
| observed_overflow_list = |
| (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list); |
| if (cur_overflow_list == observed_overflow_list) { |
| attached = true; |
| break; |
| } else cur_overflow_list = observed_overflow_list; |
| } |
| if (!attached) { |
| // Too bad, someone else sneaked in (at least) an element; we'll need |
| // to do a splice. Find tail of suffix so we can prepend suffix to global |
| // list. |
| for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark())); |
| oop suffix_tail = cur; |
| assert(suffix_tail != NULL && suffix_tail->mark() == NULL, |
| "Tautology"); |
| observed_overflow_list = _overflow_list; |
| do { |
| cur_overflow_list = observed_overflow_list; |
| if (cur_overflow_list != BUSY) { |
| // Do the splice ... |
| suffix_tail->set_mark(markOop(cur_overflow_list)); |
| } else { // cur_overflow_list == BUSY |
| suffix_tail->set_mark(NULL); |
| } |
| // ... and try to place spliced list back on overflow_list ... |
| observed_overflow_list = |
| (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list); |
| } while (cur_overflow_list != observed_overflow_list); |
| // ... until we have succeeded in doing so. |
| } |
| } |
| |
| // Push the prefix elements on work_q |
| assert(prefix != NULL, "control point invariant"); |
| const markOop proto = markOopDesc::prototype(); |
| oop next; |
| NOT_PRODUCT(ssize_t n = 0;) |
| for (cur = prefix; cur != NULL; cur = next) { |
| next = oop(cur->mark()); |
| cur->set_mark(proto); // until proven otherwise |
| assert(cur->is_oop(), "Should be an oop"); |
| bool res = work_q->push(cur); |
| assert(res, "Bit off more than we can chew?"); |
| NOT_PRODUCT(n++;) |
| } |
| #ifndef PRODUCT |
| assert(_num_par_pushes >= n, "Too many pops?"); |
| Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes); |
| #endif |
| return true; |
| } |
| |
| // Single-threaded |
| void CMSCollector::push_on_overflow_list(oop p) { |
| NOT_PRODUCT(_num_par_pushes++;) |
| assert(p->is_oop(), "Not an oop"); |
| preserve_mark_if_necessary(p); |
| p->set_mark((markOop)_overflow_list); |
| _overflow_list = p; |
| } |
| |
| // Multi-threaded; use CAS to prepend to overflow list |
| void CMSCollector::par_push_on_overflow_list(oop p) { |
| NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);) |
| assert(p->is_oop(), "Not an oop"); |
| par_preserve_mark_if_necessary(p); |
| oop observed_overflow_list = _overflow_list; |
| oop cur_overflow_list; |
| do { |
| cur_overflow_list = observed_overflow_list; |
| if (cur_overflow_list != BUSY) { |
| p->set_mark(markOop(cur_overflow_list)); |
| } else { |
| p->set_mark(NULL); |
| } |
| observed_overflow_list = |
| (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list); |
| } while (cur_overflow_list != observed_overflow_list); |
| } |
| #undef BUSY |
| |
| // Single threaded |
| // General Note on GrowableArray: pushes may silently fail |
| // because we are (temporarily) out of C-heap for expanding |
| // the stack. The problem is quite ubiquitous and affects |
| // a lot of code in the JVM. The prudent thing for GrowableArray |
| // to do (for now) is to exit with an error. However, that may |
| // be too draconian in some cases because the caller may be |
| // able to recover without much harm. For such cases, we |
| // should probably introduce a "soft_push" method which returns |
| // an indication of success or failure with the assumption that |
| // the caller may be able to recover from a failure; code in |
| // the VM can then be changed, incrementally, to deal with such |
| // failures where possible, thus, incrementally hardening the VM |
| // in such low resource situations. |
| void CMSCollector::preserve_mark_work(oop p, markOop m) { |
| _preserved_oop_stack.push(p); |
| _preserved_mark_stack.push(m); |
| assert(m == p->mark(), "Mark word changed"); |
| assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(), |
| "bijection"); |
| } |
| |
| // Single threaded |
| void CMSCollector::preserve_mark_if_necessary(oop p) { |
| markOop m = p->mark(); |
| if (m->must_be_preserved(p)) { |
| preserve_mark_work(p, m); |
| } |
| } |
| |
| void CMSCollector::par_preserve_mark_if_necessary(oop p) { |
| markOop m = p->mark(); |
| if (m->must_be_preserved(p)) { |
| MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag); |
| // Even though we read the mark word without holding |
| // the lock, we are assured that it will not change |
| // because we "own" this oop, so no other thread can |
| // be trying to push it on the overflow list; see |
| // the assertion in preserve_mark_work() that checks |
| // that m == p->mark(). |
| preserve_mark_work(p, m); |
| } |
| } |
| |
| // We should be able to do this multi-threaded, |
| // a chunk of stack being a task (this is |
| // correct because each oop only ever appears |
| // once in the overflow list. However, it's |
| // not very easy to completely overlap this with |
| // other operations, so will generally not be done |
| // until all work's been completed. Because we |
| // expect the preserved oop stack (set) to be small, |
| // it's probably fine to do this single-threaded. |
| // We can explore cleverer concurrent/overlapped/parallel |
| // processing of preserved marks if we feel the |
| // need for this in the future. Stack overflow should |
| // be so rare in practice and, when it happens, its |
| // effect on performance so great that this will |
| // likely just be in the noise anyway. |
| void CMSCollector::restore_preserved_marks_if_any() { |
| assert(SafepointSynchronize::is_at_safepoint(), |
| "world should be stopped"); |
| assert(Thread::current()->is_ConcurrentGC_thread() || |
| Thread::current()->is_VM_thread(), |
| "should be single-threaded"); |
| assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(), |
| "bijection"); |
| |
| while (!_preserved_oop_stack.is_empty()) { |
| oop p = _preserved_oop_stack.pop(); |
| assert(p->is_oop(), "Should be an oop"); |
| assert(_span.contains(p), "oop should be in _span"); |
| assert(p->mark() == markOopDesc::prototype(), |
| "Set when taken from overflow list"); |
| markOop m = _preserved_mark_stack.pop(); |
| p->set_mark(m); |
| } |
| assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(), |
| "stacks were cleared above"); |
| } |
| |
| #ifndef PRODUCT |
| bool CMSCollector::no_preserved_marks() const { |
| return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(); |
| } |
| #endif |
| |
| CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const |
| { |
| GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap(); |
| CMSAdaptiveSizePolicy* size_policy = |
| (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy(); |
| assert(size_policy->is_gc_cms_adaptive_size_policy(), |
| "Wrong type for size policy"); |
| return size_policy; |
| } |
| |
| void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size, |
| size_t desired_promo_size) { |
| if (cur_promo_size < desired_promo_size) { |
| size_t expand_bytes = desired_promo_size - cur_promo_size; |
| if (PrintAdaptiveSizePolicy && Verbose) { |
| gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize " |
| "Expanding tenured generation by " SIZE_FORMAT " (bytes)", |
| expand_bytes); |
| } |
| expand(expand_bytes, |
| MinHeapDeltaBytes, |
| CMSExpansionCause::_adaptive_size_policy); |
| } else if (desired_promo_size < cur_promo_size) { |
| size_t shrink_bytes = cur_promo_size - desired_promo_size; |
| if (PrintAdaptiveSizePolicy && Verbose) { |
| gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize " |
| "Shrinking tenured generation by " SIZE_FORMAT " (bytes)", |
| shrink_bytes); |
| } |
| shrink(shrink_bytes); |
| } |
| } |
| |
| CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() { |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| CMSGCAdaptivePolicyCounters* counters = |
| (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters(); |
| assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind, |
| "Wrong kind of counters"); |
| return counters; |
| } |
| |
| |
| void ASConcurrentMarkSweepGeneration::update_counters() { |
| if (UsePerfData) { |
| _space_counters->update_all(); |
| _gen_counters->update_all(); |
| CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters(); |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats(); |
| assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind, |
| "Wrong gc statistics type"); |
| counters->update_counters(gc_stats_l); |
| } |
| } |
| |
| void ASConcurrentMarkSweepGeneration::update_counters(size_t used) { |
| if (UsePerfData) { |
| _space_counters->update_used(used); |
| _space_counters->update_capacity(); |
| _gen_counters->update_all(); |
| |
| CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters(); |
| GenCollectedHeap* gch = GenCollectedHeap::heap(); |
| CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats(); |
| assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind, |
| "Wrong gc statistics type"); |
| counters->update_counters(gc_stats_l); |
| } |
| } |
| |
| // The desired expansion delta is computed so that: |
| // . desired free percentage or greater is used |
| void ASConcurrentMarkSweepGeneration::compute_new_size() { |
| assert_locked_or_safepoint(Heap_lock); |
| |
| GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap(); |
| |
| // If incremental collection failed, we just want to expand |
| // to the limit. |
| if (incremental_collection_failed()) { |
| clear_incremental_collection_failed(); |
| grow_to_reserved(); |
| return; |
| } |
| |
| assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing"); |
| |
| assert(gch->kind() == CollectedHeap::GenCollectedHeap, |
| "Wrong type of heap"); |
| int prev_level = level() - 1; |
| assert(prev_level >= 0, "The cms generation is the lowest generation"); |
| Generation* prev_gen = gch->get_gen(prev_level); |
| assert(prev_gen->kind() == Generation::ASParNew, |
| "Wrong type of young generation"); |
| ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen; |
| size_t cur_eden = younger_gen->eden()->capacity(); |
| CMSAdaptiveSizePolicy* size_policy = cms_size_policy(); |
| size_t cur_promo = free(); |
| size_policy->compute_tenured_generation_free_space(cur_promo, |
| max_available(), |
| cur_eden); |
| resize(cur_promo, size_policy->promo_size()); |
| |
| // Record the new size of the space in the cms generation |
| // that is available for promotions. This is temporary. |
| // It should be the desired promo size. |
| size_policy->avg_cms_promo()->sample(free()); |
| size_policy->avg_old_live()->sample(used()); |
| |
| if (UsePerfData) { |
| CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters(); |
| counters->update_cms_capacity_counter(capacity()); |
| } |
| } |
| |
| void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) { |
| assert_locked_or_safepoint(Heap_lock); |
| assert_lock_strong(freelistLock()); |
| HeapWord* old_end = _cmsSpace->end(); |
| HeapWord* unallocated_start = _cmsSpace->unallocated_block(); |
| assert(old_end >= unallocated_start, "Miscalculation of unallocated_start"); |
| FreeChunk* chunk_at_end = find_chunk_at_end(); |
| if (chunk_at_end == NULL) { |
| // No room to shrink |
| if (PrintGCDetails && Verbose) { |
| gclog_or_tty->print_cr("No room to shrink: old_end " |
| PTR_FORMAT " unallocated_start " PTR_FORMAT |
| " chunk_at_end " PTR_FORMAT, |
| old_end, unallocated_start, chunk_at_end); |
| } |
| return; |
| } else { |
| |
| // Find the chunk at the end of the space and determine |
| // how much it can be shrunk. |
| size_t shrinkable_size_in_bytes = chunk_at_end->size(); |
| size_t aligned_shrinkable_size_in_bytes = |
| align_size_down(shrinkable_size_in_bytes, os::vm_page_size()); |
| assert(unallocated_start <= chunk_at_end->end(), |
| "Inconsistent chunk at end of space"); |
| size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes); |
| size_t word_size_before = heap_word_size(_virtual_space.committed_size()); |
| |
| // Shrink the underlying space |
| _virtual_space.shrink_by(bytes); |
| if (PrintGCDetails && Verbose) { |
| gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:" |
| " desired_bytes " SIZE_FORMAT |
| " shrinkable_size_in_bytes " SIZE_FORMAT |
| " aligned_shrinkable_size_in_bytes " SIZE_FORMAT |
| " bytes " SIZE_FORMAT, |
| desired_bytes, shrinkable_size_in_bytes, |
| aligned_shrinkable_size_in_bytes, bytes); |
| gclog_or_tty->print_cr(" old_end " SIZE_FORMAT |
| " unallocated_start " SIZE_FORMAT, |
| old_end, unallocated_start); |
| } |
| |
| // If the space did shrink (shrinking is not guaranteed), |
| // shrink the chunk at the end by the appropriate amount. |
| if (((HeapWord*)_virtual_space.high()) < old_end) { |
| size_t new_word_size = |
| heap_word_size(_virtual_space.committed_size()); |
| |
| // Have to remove the chunk from the dictionary because it is changing |
| // size and might be someplace elsewhere in the dictionary. |
| |
| // Get the chunk at end, shrink it, and put it |
| // back. |
| _cmsSpace->removeChunkFromDictionary(chunk_at_end); |
| size_t word_size_change = word_size_before - new_word_size; |
| size_t chunk_at_end_old_size = chunk_at_end->size(); |
| assert(chunk_at_end_old_size >= word_size_change, |
| "Shrink is too large"); |
| chunk_at_end->set_size(chunk_at_end_old_size - |
| word_size_change); |
| _cmsSpace->freed((HeapWord*) chunk_at_end->end(), |
| word_size_change); |
| |
| _cmsSpace->returnChunkToDictionary(chunk_at_end); |
| |
| MemRegion mr(_cmsSpace->bottom(), new_word_size); |
| _bts->resize(new_word_size); // resize the block offset shared array |
| Universe::heap()->barrier_set()->resize_covered_region(mr); |
| _cmsSpace->assert_locked(); |
| _cmsSpace->set_end((HeapWord*)_virtual_space.high()); |
| |
| NOT_PRODUCT(_cmsSpace->dictionary()->verify()); |
| |
| // update the space and generation capacity counters |
| if (UsePerfData) { |
| _space_counters->update_capacity(); |
| _gen_counters->update_all(); |
| } |
| |
| if (Verbose && PrintGCDetails) { |
| size_t new_mem_size = _virtual_space.committed_size(); |
| size_t old_mem_size = new_mem_size + bytes; |
| gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK", |
| name(), old_mem_size/K, bytes/K, new_mem_size/K); |
| } |
| } |
| |
| assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(), |
| "Inconsistency at end of space"); |
| assert(chunk_at_end->end() == _cmsSpace->end(), |
| "Shrinking is inconsistent"); |
| return; |
| } |
| } |
| |
| // Transfer some number of overflown objects to usual marking |
| // stack. Return true if some objects were transferred. |
| bool MarkRefsIntoAndScanClosure::take_from_overflow_list() { |
| size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4, |
| (size_t)ParGCDesiredObjsFromOverflowList); |
| |
| bool res = _collector->take_from_overflow_list(num, _mark_stack); |
| assert(_collector->overflow_list_is_empty() || res, |
| "If list is not empty, we should have taken something"); |
| assert(!res || !_mark_stack->isEmpty(), |
| "If we took something, it should now be on our stack"); |
| return res; |
| } |
| |
| size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) { |
| size_t res = _sp->block_size_no_stall(addr, _collector); |
| if (_sp->block_is_obj(addr)) { |
| if (_live_bit_map->isMarked(addr)) { |
| // It can't have been dead in a previous cycle |
| guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!"); |
| } else { |
| _dead_bit_map->mark(addr); // mark the dead object |
| } |
| } |
| // Could be 0, if the block size could not be computed without stalling. |
| return res; |
| } |
| |
| TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() { |
| |
| switch (phase) { |
| case CMSCollector::InitialMarking: |
| initialize(true /* fullGC */ , |
| cause /* cause of the GC */, |
| true /* recordGCBeginTime */, |
| true /* recordPreGCUsage */, |
| false /* recordPeakUsage */, |
| false /* recordPostGCusage */, |
| true /* recordAccumulatedGCTime */, |
| false /* recordGCEndTime */, |
| false /* countCollection */ ); |
| break; |
| |
| case CMSCollector::FinalMarking: |
| initialize(true /* fullGC */ , |
| cause /* cause of the GC */, |
| false /* recordGCBeginTime */, |
| false /* recordPreGCUsage */, |
| false /* recordPeakUsage */, |
| false /* recordPostGCusage */, |
| true /* recordAccumulatedGCTime */, |
| false /* recordGCEndTime */, |
| false /* countCollection */ ); |
| break; |
| |
| case CMSCollector::Sweeping: |
| initialize(true /* fullGC */ , |
| cause /* cause of the GC */, |
| false /* recordGCBeginTime */, |
| false /* recordPreGCUsage */, |
| true /* recordPeakUsage */, |
| true /* recordPostGCusage */, |
| false /* recordAccumulatedGCTime */, |
| true /* recordGCEndTime */, |
| true /* countCollection */ ); |
| break; |
| |
| default: |
| ShouldNotReachHere(); |
| } |
| } |
| |