| /* |
| * Copyright (c) 2001, 2014, 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/javaClasses.hpp" |
| #include "classfile/systemDictionary.hpp" |
| #include "gc_implementation/shared/gcTimer.hpp" |
| #include "gc_implementation/shared/gcTraceTime.hpp" |
| #include "gc_interface/collectedHeap.hpp" |
| #include "gc_interface/collectedHeap.inline.hpp" |
| #include "memory/referencePolicy.hpp" |
| #include "memory/referenceProcessor.hpp" |
| #include "oops/oop.inline.hpp" |
| #include "runtime/java.hpp" |
| #include "runtime/jniHandles.hpp" |
| |
| PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC |
| |
| ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL; |
| ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL; |
| bool ReferenceProcessor::_pending_list_uses_discovered_field = false; |
| jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0; |
| |
| void referenceProcessor_init() { |
| ReferenceProcessor::init_statics(); |
| } |
| |
| void ReferenceProcessor::init_statics() { |
| // We need a monotonically non-deccreasing time in ms but |
| // os::javaTimeMillis() does not guarantee monotonicity. |
| jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; |
| |
| // Initialize the soft ref timestamp clock. |
| _soft_ref_timestamp_clock = now; |
| // Also update the soft ref clock in j.l.r.SoftReference |
| java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock); |
| |
| _always_clear_soft_ref_policy = new AlwaysClearPolicy(); |
| _default_soft_ref_policy = new COMPILER2_PRESENT(LRUMaxHeapPolicy()) |
| NOT_COMPILER2(LRUCurrentHeapPolicy()); |
| if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) { |
| vm_exit_during_initialization("Could not allocate reference policy object"); |
| } |
| guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery || |
| RefDiscoveryPolicy == ReferentBasedDiscovery, |
| "Unrecongnized RefDiscoveryPolicy"); |
| _pending_list_uses_discovered_field = JDK_Version::current().pending_list_uses_discovered_field(); |
| } |
| |
| void ReferenceProcessor::enable_discovery(bool verify_disabled, bool check_no_refs) { |
| #ifdef ASSERT |
| // Verify that we're not currently discovering refs |
| assert(!verify_disabled || !_discovering_refs, "nested call?"); |
| |
| if (check_no_refs) { |
| // Verify that the discovered lists are empty |
| verify_no_references_recorded(); |
| } |
| #endif // ASSERT |
| |
| // Someone could have modified the value of the static |
| // field in the j.l.r.SoftReference class that holds the |
| // soft reference timestamp clock using reflection or |
| // Unsafe between GCs. Unconditionally update the static |
| // field in ReferenceProcessor here so that we use the new |
| // value during reference discovery. |
| |
| _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); |
| _discovering_refs = true; |
| } |
| |
| ReferenceProcessor::ReferenceProcessor(MemRegion span, |
| bool mt_processing, |
| uint mt_processing_degree, |
| bool mt_discovery, |
| uint mt_discovery_degree, |
| bool atomic_discovery, |
| BoolObjectClosure* is_alive_non_header) : |
| _discovering_refs(false), |
| _enqueuing_is_done(false), |
| _is_alive_non_header(is_alive_non_header), |
| _processing_is_mt(mt_processing), |
| _next_id(0) |
| { |
| _span = span; |
| _discovery_is_atomic = atomic_discovery; |
| _discovery_is_mt = mt_discovery; |
| _num_q = MAX2(1U, mt_processing_degree); |
| _max_num_q = MAX2(_num_q, mt_discovery_degree); |
| _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList, |
| _max_num_q * number_of_subclasses_of_ref(), mtGC); |
| |
| if (_discovered_refs == NULL) { |
| vm_exit_during_initialization("Could not allocated RefProc Array"); |
| } |
| _discoveredSoftRefs = &_discovered_refs[0]; |
| _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q]; |
| _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q]; |
| _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q]; |
| _discoveredCleanerRefs = &_discoveredPhantomRefs[_max_num_q]; |
| |
| // Initialize all entries to NULL |
| for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
| _discovered_refs[i].set_head(NULL); |
| _discovered_refs[i].set_length(0); |
| } |
| |
| setup_policy(false /* default soft ref policy */); |
| } |
| |
| #ifndef PRODUCT |
| void ReferenceProcessor::verify_no_references_recorded() { |
| guarantee(!_discovering_refs, "Discovering refs?"); |
| for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
| guarantee(_discovered_refs[i].is_empty(), |
| "Found non-empty discovered list"); |
| } |
| } |
| #endif |
| |
| void ReferenceProcessor::weak_oops_do(OopClosure* f) { |
| for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
| if (UseCompressedOops) { |
| f->do_oop((narrowOop*)_discovered_refs[i].adr_head()); |
| } else { |
| f->do_oop((oop*)_discovered_refs[i].adr_head()); |
| } |
| } |
| } |
| |
| void ReferenceProcessor::update_soft_ref_master_clock() { |
| // Update (advance) the soft ref master clock field. This must be done |
| // after processing the soft ref list. |
| |
| // We need a monotonically non-deccreasing time in ms but |
| // os::javaTimeMillis() does not guarantee monotonicity. |
| jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; |
| jlong soft_ref_clock = java_lang_ref_SoftReference::clock(); |
| assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync"); |
| |
| NOT_PRODUCT( |
| if (now < _soft_ref_timestamp_clock) { |
| warning("time warp: "INT64_FORMAT" to "INT64_FORMAT, |
| _soft_ref_timestamp_clock, now); |
| } |
| ) |
| // The values of now and _soft_ref_timestamp_clock are set using |
| // javaTimeNanos(), which is guaranteed to be monotonically |
| // non-decreasing provided the underlying platform provides such |
| // a time source (and it is bug free). |
| // In product mode, however, protect ourselves from non-monotonicty. |
| if (now > _soft_ref_timestamp_clock) { |
| _soft_ref_timestamp_clock = now; |
| java_lang_ref_SoftReference::set_clock(now); |
| } |
| // Else leave clock stalled at its old value until time progresses |
| // past clock value. |
| } |
| |
| size_t ReferenceProcessor::total_count(DiscoveredList lists[]) { |
| size_t total = 0; |
| for (uint i = 0; i < _max_num_q; ++i) { |
| total += lists[i].length(); |
| } |
| return total; |
| } |
| |
| ReferenceProcessorStats ReferenceProcessor::process_discovered_references( |
| BoolObjectClosure* is_alive, |
| OopClosure* keep_alive, |
| VoidClosure* complete_gc, |
| AbstractRefProcTaskExecutor* task_executor, |
| GCTimer* gc_timer, |
| GCId gc_id) { |
| NOT_PRODUCT(verify_ok_to_handle_reflists()); |
| |
| assert(!enqueuing_is_done(), "If here enqueuing should not be complete"); |
| // Stop treating discovered references specially. |
| disable_discovery(); |
| |
| // If discovery was concurrent, someone could have modified |
| // the value of the static field in the j.l.r.SoftReference |
| // class that holds the soft reference timestamp clock using |
| // reflection or Unsafe between when discovery was enabled and |
| // now. Unconditionally update the static field in ReferenceProcessor |
| // here so that we use the new value during processing of the |
| // discovered soft refs. |
| |
| _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); |
| |
| bool trace_time = PrintGCDetails && PrintReferenceGC; |
| |
| // Soft references |
| size_t soft_count = 0; |
| { |
| GCTraceTime tt("SoftReference", trace_time, false, gc_timer, gc_id); |
| soft_count = |
| process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true, |
| is_alive, keep_alive, complete_gc, task_executor); |
| } |
| |
| update_soft_ref_master_clock(); |
| |
| // Weak references |
| size_t weak_count = 0; |
| { |
| GCTraceTime tt("WeakReference", trace_time, false, gc_timer, gc_id); |
| weak_count = |
| process_discovered_reflist(_discoveredWeakRefs, NULL, true, |
| is_alive, keep_alive, complete_gc, task_executor); |
| } |
| |
| // Final references |
| size_t final_count = 0; |
| { |
| GCTraceTime tt("FinalReference", trace_time, false, gc_timer, gc_id); |
| final_count = |
| process_discovered_reflist(_discoveredFinalRefs, NULL, false, |
| is_alive, keep_alive, complete_gc, task_executor); |
| } |
| |
| // Phantom references |
| size_t phantom_count = 0; |
| { |
| GCTraceTime tt("PhantomReference", trace_time, false, gc_timer, gc_id); |
| phantom_count = |
| process_discovered_reflist(_discoveredPhantomRefs, NULL, false, |
| is_alive, keep_alive, complete_gc, task_executor); |
| |
| // Process cleaners, but include them in phantom statistics. We expect |
| // Cleaner references to be temporary, and don't want to deal with |
| // possible incompatibilities arising from making it more visible. |
| phantom_count += |
| process_discovered_reflist(_discoveredCleanerRefs, NULL, true, |
| is_alive, keep_alive, complete_gc, task_executor); |
| } |
| |
| // Weak global JNI references. It would make more sense (semantically) to |
| // traverse these simultaneously with the regular weak references above, but |
| // that is not how the JDK1.2 specification is. See #4126360. Native code can |
| // thus use JNI weak references to circumvent the phantom references and |
| // resurrect a "post-mortem" object. |
| { |
| GCTraceTime tt("JNI Weak Reference", trace_time, false, gc_timer, gc_id); |
| if (task_executor != NULL) { |
| task_executor->set_single_threaded_mode(); |
| } |
| process_phaseJNI(is_alive, keep_alive, complete_gc); |
| } |
| |
| return ReferenceProcessorStats(soft_count, weak_count, final_count, phantom_count); |
| } |
| |
| #ifndef PRODUCT |
| // Calculate the number of jni handles. |
| uint ReferenceProcessor::count_jni_refs() { |
| class AlwaysAliveClosure: public BoolObjectClosure { |
| public: |
| virtual bool do_object_b(oop obj) { return true; } |
| }; |
| |
| class CountHandleClosure: public OopClosure { |
| private: |
| int _count; |
| public: |
| CountHandleClosure(): _count(0) {} |
| void do_oop(oop* unused) { _count++; } |
| void do_oop(narrowOop* unused) { ShouldNotReachHere(); } |
| int count() { return _count; } |
| }; |
| CountHandleClosure global_handle_count; |
| AlwaysAliveClosure always_alive; |
| JNIHandles::weak_oops_do(&always_alive, &global_handle_count); |
| return global_handle_count.count(); |
| } |
| #endif |
| |
| void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive, |
| OopClosure* keep_alive, |
| VoidClosure* complete_gc) { |
| #ifndef PRODUCT |
| if (PrintGCDetails && PrintReferenceGC) { |
| unsigned int count = count_jni_refs(); |
| gclog_or_tty->print(", %u refs", count); |
| } |
| #endif |
| JNIHandles::weak_oops_do(is_alive, keep_alive); |
| complete_gc->do_void(); |
| } |
| |
| |
| template <class T> |
| bool enqueue_discovered_ref_helper(ReferenceProcessor* ref, |
| AbstractRefProcTaskExecutor* task_executor) { |
| |
| // Remember old value of pending references list |
| T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr(); |
| T old_pending_list_value = *pending_list_addr; |
| |
| // Enqueue references that are not made active again, and |
| // clear the decks for the next collection (cycle). |
| ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor); |
| // Do the post-barrier on pending_list_addr missed in |
| // enqueue_discovered_reflist. |
| oopDesc::bs()->write_ref_field(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr)); |
| |
| // Stop treating discovered references specially. |
| ref->disable_discovery(); |
| |
| // Return true if new pending references were added |
| return old_pending_list_value != *pending_list_addr; |
| } |
| |
| bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) { |
| NOT_PRODUCT(verify_ok_to_handle_reflists()); |
| if (UseCompressedOops) { |
| return enqueue_discovered_ref_helper<narrowOop>(this, task_executor); |
| } else { |
| return enqueue_discovered_ref_helper<oop>(this, task_executor); |
| } |
| } |
| |
| void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list, |
| HeapWord* pending_list_addr) { |
| // Given a list of refs linked through the "discovered" field |
| // (java.lang.ref.Reference.discovered), self-loop their "next" field |
| // thus distinguishing them from active References, then |
| // prepend them to the pending list. |
| // |
| // The Java threads will see the Reference objects linked together through |
| // the discovered field. Instead of trying to do the write barrier updates |
| // in all places in the reference processor where we manipulate the discovered |
| // field we make sure to do the barrier here where we anyway iterate through |
| // all linked Reference objects. Note that it is important to not dirty any |
| // cards during reference processing since this will cause card table |
| // verification to fail for G1. |
| // |
| // BKWRD COMPATIBILITY NOTE: For older JDKs (prior to the fix for 4956777), |
| // the "next" field is used to chain the pending list, not the discovered |
| // field. |
| if (TraceReferenceGC && PrintGCDetails) { |
| gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list " |
| INTPTR_FORMAT, (address)refs_list.head()); |
| } |
| |
| oop obj = NULL; |
| oop next_d = refs_list.head(); |
| if (pending_list_uses_discovered_field()) { // New behavior |
| // Walk down the list, self-looping the next field |
| // so that the References are not considered active. |
| while (obj != next_d) { |
| obj = next_d; |
| assert(obj->is_instanceRef(), "should be reference object"); |
| next_d = java_lang_ref_Reference::discovered(obj); |
| if (TraceReferenceGC && PrintGCDetails) { |
| gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, |
| (void *)obj, (void *)next_d); |
| } |
| assert(java_lang_ref_Reference::next(obj) == NULL, |
| "Reference not active; should not be discovered"); |
| // Self-loop next, so as to make Ref not active. |
| java_lang_ref_Reference::set_next_raw(obj, obj); |
| if (next_d != obj) { |
| oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d); |
| } else { |
| // This is the last object. |
| // Swap refs_list into pending_list_addr and |
| // set obj's discovered to what we read from pending_list_addr. |
| oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr); |
| // Need post-barrier on pending_list_addr. See enqueue_discovered_ref_helper() above. |
| java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL |
| oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old); |
| } |
| } |
| } else { // Old behaviour |
| // Walk down the list, copying the discovered field into |
| // the next field and clearing the discovered field. |
| while (obj != next_d) { |
| obj = next_d; |
| assert(obj->is_instanceRef(), "should be reference object"); |
| next_d = java_lang_ref_Reference::discovered(obj); |
| if (TraceReferenceGC && PrintGCDetails) { |
| gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, |
| (void *)obj, (void *)next_d); |
| } |
| assert(java_lang_ref_Reference::next(obj) == NULL, |
| "The reference should not be enqueued"); |
| if (next_d == obj) { // obj is last |
| // Swap refs_list into pendling_list_addr and |
| // set obj's next to what we read from pending_list_addr. |
| oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr); |
| // Need oop_check on pending_list_addr above; |
| // see special oop-check code at the end of |
| // enqueue_discovered_reflists() further below. |
| if (old == NULL) { |
| // obj should be made to point to itself, since |
| // pending list was empty. |
| java_lang_ref_Reference::set_next(obj, obj); |
| } else { |
| java_lang_ref_Reference::set_next(obj, old); |
| } |
| } else { |
| java_lang_ref_Reference::set_next(obj, next_d); |
| } |
| java_lang_ref_Reference::set_discovered(obj, (oop) NULL); |
| } |
| } |
| } |
| |
| // Parallel enqueue task |
| class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask { |
| public: |
| RefProcEnqueueTask(ReferenceProcessor& ref_processor, |
| DiscoveredList discovered_refs[], |
| HeapWord* pending_list_addr, |
| int n_queues) |
| : EnqueueTask(ref_processor, discovered_refs, |
| pending_list_addr, n_queues) |
| { } |
| |
| virtual void work(unsigned int work_id) { |
| assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds"); |
| // Simplest first cut: static partitioning. |
| int index = work_id; |
| // The increment on "index" must correspond to the maximum number of queues |
| // (n_queues) with which that ReferenceProcessor was created. That |
| // is because of the "clever" way the discovered references lists were |
| // allocated and are indexed into. |
| assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected"); |
| for (int j = 0; |
| j < ReferenceProcessor::number_of_subclasses_of_ref(); |
| j++, index += _n_queues) { |
| _ref_processor.enqueue_discovered_reflist( |
| _refs_lists[index], _pending_list_addr); |
| _refs_lists[index].set_head(NULL); |
| _refs_lists[index].set_length(0); |
| } |
| } |
| }; |
| |
| // Enqueue references that are not made active again |
| void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr, |
| AbstractRefProcTaskExecutor* task_executor) { |
| if (_processing_is_mt && task_executor != NULL) { |
| // Parallel code |
| RefProcEnqueueTask tsk(*this, _discovered_refs, |
| pending_list_addr, _max_num_q); |
| task_executor->execute(tsk); |
| } else { |
| // Serial code: call the parent class's implementation |
| for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
| enqueue_discovered_reflist(_discovered_refs[i], pending_list_addr); |
| _discovered_refs[i].set_head(NULL); |
| _discovered_refs[i].set_length(0); |
| } |
| } |
| } |
| |
| void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) { |
| _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref); |
| oop discovered = java_lang_ref_Reference::discovered(_ref); |
| assert(_discovered_addr && discovered->is_oop_or_null(), |
| "discovered field is bad"); |
| _next = discovered; |
| _referent_addr = java_lang_ref_Reference::referent_addr(_ref); |
| _referent = java_lang_ref_Reference::referent(_ref); |
| assert(Universe::heap()->is_in_reserved_or_null(_referent), |
| "Wrong oop found in java.lang.Reference object"); |
| assert(allow_null_referent ? |
| _referent->is_oop_or_null() |
| : _referent->is_oop(), |
| "bad referent"); |
| } |
| |
| void DiscoveredListIterator::remove() { |
| assert(_ref->is_oop(), "Dropping a bad reference"); |
| oop_store_raw(_discovered_addr, NULL); |
| |
| // First _prev_next ref actually points into DiscoveredList (gross). |
| oop new_next; |
| if (_next == _ref) { |
| // At the end of the list, we should make _prev point to itself. |
| // If _ref is the first ref, then _prev_next will be in the DiscoveredList, |
| // and _prev will be NULL. |
| new_next = _prev; |
| } else { |
| new_next = _next; |
| } |
| // Remove Reference object from discovered list. Note that G1 does not need a |
| // pre-barrier here because we know the Reference has already been found/marked, |
| // that's how it ended up in the discovered list in the first place. |
| oop_store_raw(_prev_next, new_next); |
| NOT_PRODUCT(_removed++); |
| _refs_list.dec_length(1); |
| } |
| |
| // Make the Reference object active again. |
| void DiscoveredListIterator::make_active() { |
| // The pre barrier for G1 is probably just needed for the old |
| // reference processing behavior. Should we guard this with |
| // ReferenceProcessor::pending_list_uses_discovered_field() ? |
| if (UseG1GC) { |
| HeapWord* next_addr = java_lang_ref_Reference::next_addr(_ref); |
| if (UseCompressedOops) { |
| oopDesc::bs()->write_ref_field_pre((narrowOop*)next_addr, NULL); |
| } else { |
| oopDesc::bs()->write_ref_field_pre((oop*)next_addr, NULL); |
| } |
| } |
| java_lang_ref_Reference::set_next_raw(_ref, NULL); |
| } |
| |
| void DiscoveredListIterator::clear_referent() { |
| oop_store_raw(_referent_addr, NULL); |
| } |
| |
| // NOTE: process_phase*() are largely similar, and at a high level |
| // merely iterate over the extant list applying a predicate to |
| // each of its elements and possibly removing that element from the |
| // list and applying some further closures to that element. |
| // We should consider the possibility of replacing these |
| // process_phase*() methods by abstracting them into |
| // a single general iterator invocation that receives appropriate |
| // closures that accomplish this work. |
| |
| // (SoftReferences only) Traverse the list and remove any SoftReferences whose |
| // referents are not alive, but that should be kept alive for policy reasons. |
| // Keep alive the transitive closure of all such referents. |
| void |
| ReferenceProcessor::process_phase1(DiscoveredList& refs_list, |
| ReferencePolicy* policy, |
| BoolObjectClosure* is_alive, |
| OopClosure* keep_alive, |
| VoidClosure* complete_gc) { |
| assert(policy != NULL, "Must have a non-NULL policy"); |
| DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
| // Decide which softly reachable refs should be kept alive. |
| while (iter.has_next()) { |
| iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); |
| bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive(); |
| if (referent_is_dead && |
| !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) { |
| if (TraceReferenceGC) { |
| gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy", |
| (void *)iter.obj(), iter.obj()->klass()->internal_name()); |
| } |
| // Remove Reference object from list |
| iter.remove(); |
| // Make the Reference object active again |
| iter.make_active(); |
| // keep the referent around |
| iter.make_referent_alive(); |
| iter.move_to_next(); |
| } else { |
| iter.next(); |
| } |
| } |
| // Close the reachable set |
| complete_gc->do_void(); |
| NOT_PRODUCT( |
| if (PrintGCDetails && TraceReferenceGC) { |
| gclog_or_tty->print_cr(" Dropped %d dead Refs out of %d " |
| "discovered Refs by policy, from list " INTPTR_FORMAT, |
| iter.removed(), iter.processed(), (address)refs_list.head()); |
| } |
| ) |
| } |
| |
| // Traverse the list and remove any Refs that are not active, or |
| // whose referents are either alive or NULL. |
| void |
| ReferenceProcessor::pp2_work(DiscoveredList& refs_list, |
| BoolObjectClosure* is_alive, |
| OopClosure* keep_alive) { |
| assert(discovery_is_atomic(), "Error"); |
| DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
| while (iter.has_next()) { |
| iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); |
| DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());) |
| assert(next == NULL, "Should not discover inactive Reference"); |
| if (iter.is_referent_alive()) { |
| if (TraceReferenceGC) { |
| gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)", |
| (void *)iter.obj(), iter.obj()->klass()->internal_name()); |
| } |
| // The referent is reachable after all. |
| // Remove Reference object from list. |
| iter.remove(); |
| // Update the referent pointer as necessary: Note that this |
| // should not entail any recursive marking because the |
| // referent must already have been traversed. |
| iter.make_referent_alive(); |
| iter.move_to_next(); |
| } else { |
| iter.next(); |
| } |
| } |
| NOT_PRODUCT( |
| if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) { |
| gclog_or_tty->print_cr(" Dropped %d active Refs out of %d " |
| "Refs in discovered list " INTPTR_FORMAT, |
| iter.removed(), iter.processed(), (address)refs_list.head()); |
| } |
| ) |
| } |
| |
| void |
| ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list, |
| BoolObjectClosure* is_alive, |
| OopClosure* keep_alive, |
| VoidClosure* complete_gc) { |
| assert(!discovery_is_atomic(), "Error"); |
| DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
| while (iter.has_next()) { |
| iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); |
| HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj()); |
| oop next = java_lang_ref_Reference::next(iter.obj()); |
| if ((iter.referent() == NULL || iter.is_referent_alive() || |
| next != NULL)) { |
| assert(next->is_oop_or_null(), "bad next field"); |
| // Remove Reference object from list |
| iter.remove(); |
| // Trace the cohorts |
| iter.make_referent_alive(); |
| if (UseCompressedOops) { |
| keep_alive->do_oop((narrowOop*)next_addr); |
| } else { |
| keep_alive->do_oop((oop*)next_addr); |
| } |
| iter.move_to_next(); |
| } else { |
| iter.next(); |
| } |
| } |
| // Now close the newly reachable set |
| complete_gc->do_void(); |
| NOT_PRODUCT( |
| if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) { |
| gclog_or_tty->print_cr(" Dropped %d active Refs out of %d " |
| "Refs in discovered list " INTPTR_FORMAT, |
| iter.removed(), iter.processed(), (address)refs_list.head()); |
| } |
| ) |
| } |
| |
| // Traverse the list and process the referents, by either |
| // clearing them or keeping them (and their reachable |
| // closure) alive. |
| void |
| ReferenceProcessor::process_phase3(DiscoveredList& refs_list, |
| bool clear_referent, |
| BoolObjectClosure* is_alive, |
| OopClosure* keep_alive, |
| VoidClosure* complete_gc) { |
| ResourceMark rm; |
| DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
| while (iter.has_next()) { |
| iter.update_discovered(); |
| iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); |
| if (clear_referent) { |
| // NULL out referent pointer |
| iter.clear_referent(); |
| } else { |
| // keep the referent around |
| iter.make_referent_alive(); |
| } |
| if (TraceReferenceGC) { |
| gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending", |
| clear_referent ? "cleared " : "", |
| (void *)iter.obj(), iter.obj()->klass()->internal_name()); |
| } |
| assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference"); |
| iter.next(); |
| } |
| // Remember to update the next pointer of the last ref. |
| iter.update_discovered(); |
| // Close the reachable set |
| complete_gc->do_void(); |
| } |
| |
| void |
| ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) { |
| oop obj = NULL; |
| oop next = refs_list.head(); |
| while (next != obj) { |
| obj = next; |
| next = java_lang_ref_Reference::discovered(obj); |
| java_lang_ref_Reference::set_discovered_raw(obj, NULL); |
| } |
| refs_list.set_head(NULL); |
| refs_list.set_length(0); |
| } |
| |
| void |
| ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& refs_list) { |
| clear_discovered_references(refs_list); |
| } |
| |
| void ReferenceProcessor::abandon_partial_discovery() { |
| // loop over the lists |
| for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
| if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) { |
| gclog_or_tty->print_cr("\nAbandoning %s discovered list", list_name(i)); |
| } |
| abandon_partial_discovered_list(_discovered_refs[i]); |
| } |
| } |
| |
| class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask { |
| public: |
| RefProcPhase1Task(ReferenceProcessor& ref_processor, |
| DiscoveredList refs_lists[], |
| ReferencePolicy* policy, |
| bool marks_oops_alive) |
| : ProcessTask(ref_processor, refs_lists, marks_oops_alive), |
| _policy(policy) |
| { } |
| virtual void work(unsigned int i, BoolObjectClosure& is_alive, |
| OopClosure& keep_alive, |
| VoidClosure& complete_gc) |
| { |
| Thread* thr = Thread::current(); |
| int refs_list_index = ((WorkerThread*)thr)->id(); |
| _ref_processor.process_phase1(_refs_lists[refs_list_index], _policy, |
| &is_alive, &keep_alive, &complete_gc); |
| } |
| private: |
| ReferencePolicy* _policy; |
| }; |
| |
| class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask { |
| public: |
| RefProcPhase2Task(ReferenceProcessor& ref_processor, |
| DiscoveredList refs_lists[], |
| bool marks_oops_alive) |
| : ProcessTask(ref_processor, refs_lists, marks_oops_alive) |
| { } |
| virtual void work(unsigned int i, BoolObjectClosure& is_alive, |
| OopClosure& keep_alive, |
| VoidClosure& complete_gc) |
| { |
| _ref_processor.process_phase2(_refs_lists[i], |
| &is_alive, &keep_alive, &complete_gc); |
| } |
| }; |
| |
| class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask { |
| public: |
| RefProcPhase3Task(ReferenceProcessor& ref_processor, |
| DiscoveredList refs_lists[], |
| bool clear_referent, |
| bool marks_oops_alive) |
| : ProcessTask(ref_processor, refs_lists, marks_oops_alive), |
| _clear_referent(clear_referent) |
| { } |
| virtual void work(unsigned int i, BoolObjectClosure& is_alive, |
| OopClosure& keep_alive, |
| VoidClosure& complete_gc) |
| { |
| // Don't use "refs_list_index" calculated in this way because |
| // balance_queues() has moved the Ref's into the first n queues. |
| // Thread* thr = Thread::current(); |
| // int refs_list_index = ((WorkerThread*)thr)->id(); |
| // _ref_processor.process_phase3(_refs_lists[refs_list_index], _clear_referent, |
| _ref_processor.process_phase3(_refs_lists[i], _clear_referent, |
| &is_alive, &keep_alive, &complete_gc); |
| } |
| private: |
| bool _clear_referent; |
| }; |
| |
| // Balances reference queues. |
| // Move entries from all queues[0, 1, ..., _max_num_q-1] to |
| // queues[0, 1, ..., _num_q-1] because only the first _num_q |
| // corresponding to the active workers will be processed. |
| void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[]) |
| { |
| // calculate total length |
| size_t total_refs = 0; |
| if (TraceReferenceGC && PrintGCDetails) { |
| gclog_or_tty->print_cr("\nBalance ref_lists "); |
| } |
| |
| for (uint i = 0; i < _max_num_q; ++i) { |
| total_refs += ref_lists[i].length(); |
| if (TraceReferenceGC && PrintGCDetails) { |
| gclog_or_tty->print("%d ", ref_lists[i].length()); |
| } |
| } |
| if (TraceReferenceGC && PrintGCDetails) { |
| gclog_or_tty->print_cr(" = %d", total_refs); |
| } |
| size_t avg_refs = total_refs / _num_q + 1; |
| uint to_idx = 0; |
| for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) { |
| bool move_all = false; |
| if (from_idx >= _num_q) { |
| move_all = ref_lists[from_idx].length() > 0; |
| } |
| while ((ref_lists[from_idx].length() > avg_refs) || |
| move_all) { |
| assert(to_idx < _num_q, "Sanity Check!"); |
| if (ref_lists[to_idx].length() < avg_refs) { |
| // move superfluous refs |
| size_t refs_to_move; |
| // Move all the Ref's if the from queue will not be processed. |
| if (move_all) { |
| refs_to_move = MIN2(ref_lists[from_idx].length(), |
| avg_refs - ref_lists[to_idx].length()); |
| } else { |
| refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs, |
| avg_refs - ref_lists[to_idx].length()); |
| } |
| |
| assert(refs_to_move > 0, "otherwise the code below will fail"); |
| |
| oop move_head = ref_lists[from_idx].head(); |
| oop move_tail = move_head; |
| oop new_head = move_head; |
| // find an element to split the list on |
| for (size_t j = 0; j < refs_to_move; ++j) { |
| move_tail = new_head; |
| new_head = java_lang_ref_Reference::discovered(new_head); |
| } |
| |
| // Add the chain to the to list. |
| if (ref_lists[to_idx].head() == NULL) { |
| // to list is empty. Make a loop at the end. |
| java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail); |
| } else { |
| java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head()); |
| } |
| ref_lists[to_idx].set_head(move_head); |
| ref_lists[to_idx].inc_length(refs_to_move); |
| |
| // Remove the chain from the from list. |
| if (move_tail == new_head) { |
| // We found the end of the from list. |
| ref_lists[from_idx].set_head(NULL); |
| } else { |
| ref_lists[from_idx].set_head(new_head); |
| } |
| ref_lists[from_idx].dec_length(refs_to_move); |
| if (ref_lists[from_idx].length() == 0) { |
| break; |
| } |
| } else { |
| to_idx = (to_idx + 1) % _num_q; |
| } |
| } |
| } |
| #ifdef ASSERT |
| size_t balanced_total_refs = 0; |
| for (uint i = 0; i < _max_num_q; ++i) { |
| balanced_total_refs += ref_lists[i].length(); |
| if (TraceReferenceGC && PrintGCDetails) { |
| gclog_or_tty->print("%d ", ref_lists[i].length()); |
| } |
| } |
| if (TraceReferenceGC && PrintGCDetails) { |
| gclog_or_tty->print_cr(" = %d", balanced_total_refs); |
| gclog_or_tty->flush(); |
| } |
| assert(total_refs == balanced_total_refs, "Balancing was incomplete"); |
| #endif |
| } |
| |
| void ReferenceProcessor::balance_all_queues() { |
| balance_queues(_discoveredSoftRefs); |
| balance_queues(_discoveredWeakRefs); |
| balance_queues(_discoveredFinalRefs); |
| balance_queues(_discoveredPhantomRefs); |
| balance_queues(_discoveredCleanerRefs); |
| } |
| |
| size_t |
| ReferenceProcessor::process_discovered_reflist( |
| DiscoveredList refs_lists[], |
| ReferencePolicy* policy, |
| bool clear_referent, |
| BoolObjectClosure* is_alive, |
| OopClosure* keep_alive, |
| VoidClosure* complete_gc, |
| AbstractRefProcTaskExecutor* task_executor) |
| { |
| bool mt_processing = task_executor != NULL && _processing_is_mt; |
| // If discovery used MT and a dynamic number of GC threads, then |
| // the queues must be balanced for correctness if fewer than the |
| // maximum number of queues were used. The number of queue used |
| // during discovery may be different than the number to be used |
| // for processing so don't depend of _num_q < _max_num_q as part |
| // of the test. |
| bool must_balance = _discovery_is_mt; |
| |
| if ((mt_processing && ParallelRefProcBalancingEnabled) || |
| must_balance) { |
| balance_queues(refs_lists); |
| } |
| |
| size_t total_list_count = total_count(refs_lists); |
| |
| if (PrintReferenceGC && PrintGCDetails) { |
| gclog_or_tty->print(", %u refs", total_list_count); |
| } |
| |
| // Phase 1 (soft refs only): |
| // . Traverse the list and remove any SoftReferences whose |
| // referents are not alive, but that should be kept alive for |
| // policy reasons. Keep alive the transitive closure of all |
| // such referents. |
| if (policy != NULL) { |
| if (mt_processing) { |
| RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/); |
| task_executor->execute(phase1); |
| } else { |
| for (uint i = 0; i < _max_num_q; i++) { |
| process_phase1(refs_lists[i], policy, |
| is_alive, keep_alive, complete_gc); |
| } |
| } |
| } else { // policy == NULL |
| assert(refs_lists != _discoveredSoftRefs, |
| "Policy must be specified for soft references."); |
| } |
| |
| // Phase 2: |
| // . Traverse the list and remove any refs whose referents are alive. |
| if (mt_processing) { |
| RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/); |
| task_executor->execute(phase2); |
| } else { |
| for (uint i = 0; i < _max_num_q; i++) { |
| process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc); |
| } |
| } |
| |
| // Phase 3: |
| // . Traverse the list and process referents as appropriate. |
| if (mt_processing) { |
| RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/); |
| task_executor->execute(phase3); |
| } else { |
| for (uint i = 0; i < _max_num_q; i++) { |
| process_phase3(refs_lists[i], clear_referent, |
| is_alive, keep_alive, complete_gc); |
| } |
| } |
| |
| return total_list_count; |
| } |
| |
| void ReferenceProcessor::clean_up_discovered_references() { |
| // loop over the lists |
| for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
| if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) { |
| gclog_or_tty->print_cr( |
| "\nScrubbing %s discovered list of Null referents", |
| list_name(i)); |
| } |
| clean_up_discovered_reflist(_discovered_refs[i]); |
| } |
| } |
| |
| void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) { |
| assert(!discovery_is_atomic(), "Else why call this method?"); |
| DiscoveredListIterator iter(refs_list, NULL, NULL); |
| while (iter.has_next()) { |
| iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); |
| oop next = java_lang_ref_Reference::next(iter.obj()); |
| assert(next->is_oop_or_null(), "bad next field"); |
| // If referent has been cleared or Reference is not active, |
| // drop it. |
| if (iter.referent() == NULL || next != NULL) { |
| debug_only( |
| if (PrintGCDetails && TraceReferenceGC) { |
| gclog_or_tty->print_cr("clean_up_discovered_list: Dropping Reference: " |
| INTPTR_FORMAT " with next field: " INTPTR_FORMAT |
| " and referent: " INTPTR_FORMAT, |
| (void *)iter.obj(), (void *)next, (void *)iter.referent()); |
| } |
| ) |
| // Remove Reference object from list |
| iter.remove(); |
| iter.move_to_next(); |
| } else { |
| iter.next(); |
| } |
| } |
| NOT_PRODUCT( |
| if (PrintGCDetails && TraceReferenceGC) { |
| gclog_or_tty->print( |
| " Removed %d Refs with NULL referents out of %d discovered Refs", |
| iter.removed(), iter.processed()); |
| } |
| ) |
| } |
| |
| inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) { |
| uint id = 0; |
| // Determine the queue index to use for this object. |
| if (_discovery_is_mt) { |
| // During a multi-threaded discovery phase, |
| // each thread saves to its "own" list. |
| Thread* thr = Thread::current(); |
| id = thr->as_Worker_thread()->id(); |
| } else { |
| // single-threaded discovery, we save in round-robin |
| // fashion to each of the lists. |
| if (_processing_is_mt) { |
| id = next_id(); |
| } |
| } |
| assert(0 <= id && id < _max_num_q, "Id is out-of-bounds (call Freud?)"); |
| |
| // Get the discovered queue to which we will add |
| DiscoveredList* list = NULL; |
| switch (rt) { |
| case REF_OTHER: |
| // Unknown reference type, no special treatment |
| break; |
| case REF_SOFT: |
| list = &_discoveredSoftRefs[id]; |
| break; |
| case REF_WEAK: |
| list = &_discoveredWeakRefs[id]; |
| break; |
| case REF_FINAL: |
| list = &_discoveredFinalRefs[id]; |
| break; |
| case REF_PHANTOM: |
| list = &_discoveredPhantomRefs[id]; |
| break; |
| case REF_CLEANER: |
| list = &_discoveredCleanerRefs[id]; |
| break; |
| case REF_NONE: |
| // we should not reach here if we are an InstanceRefKlass |
| default: |
| ShouldNotReachHere(); |
| } |
| if (TraceReferenceGC && PrintGCDetails) { |
| gclog_or_tty->print_cr("Thread %d gets list " INTPTR_FORMAT, id, list); |
| } |
| return list; |
| } |
| |
| inline void |
| ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list, |
| oop obj, |
| HeapWord* discovered_addr) { |
| assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller"); |
| // First we must make sure this object is only enqueued once. CAS in a non null |
| // discovered_addr. |
| oop current_head = refs_list.head(); |
| // The last ref must have its discovered field pointing to itself. |
| oop next_discovered = (current_head != NULL) ? current_head : obj; |
| |
| oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr, |
| NULL); |
| if (retest == NULL) { |
| // This thread just won the right to enqueue the object. |
| // We have separate lists for enqueueing, so no synchronization |
| // is necessary. |
| refs_list.set_head(obj); |
| refs_list.inc_length(1); |
| |
| if (TraceReferenceGC) { |
| gclog_or_tty->print_cr("Discovered reference (mt) (" INTPTR_FORMAT ": %s)", |
| (void *)obj, obj->klass()->internal_name()); |
| } |
| } else { |
| // If retest was non NULL, another thread beat us to it: |
| // The reference has already been discovered... |
| if (TraceReferenceGC) { |
| gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)", |
| (void *)obj, obj->klass()->internal_name()); |
| } |
| } |
| } |
| |
| #ifndef PRODUCT |
| // Non-atomic (i.e. concurrent) discovery might allow us |
| // to observe j.l.References with NULL referents, being those |
| // cleared concurrently by mutators during (or after) discovery. |
| void ReferenceProcessor::verify_referent(oop obj) { |
| bool da = discovery_is_atomic(); |
| oop referent = java_lang_ref_Reference::referent(obj); |
| assert(da ? referent->is_oop() : referent->is_oop_or_null(), |
| err_msg("Bad referent " INTPTR_FORMAT " found in Reference " |
| INTPTR_FORMAT " during %satomic discovery ", |
| (void *)referent, (void *)obj, da ? "" : "non-")); |
| } |
| #endif |
| |
| // We mention two of several possible choices here: |
| // #0: if the reference object is not in the "originating generation" |
| // (or part of the heap being collected, indicated by our "span" |
| // we don't treat it specially (i.e. we scan it as we would |
| // a normal oop, treating its references as strong references). |
| // This means that references can't be discovered unless their |
| // referent is also in the same span. This is the simplest, |
| // most "local" and most conservative approach, albeit one |
| // that may cause weak references to be enqueued least promptly. |
| // We call this choice the "ReferenceBasedDiscovery" policy. |
| // #1: the reference object may be in any generation (span), but if |
| // the referent is in the generation (span) being currently collected |
| // then we can discover the reference object, provided |
| // the object has not already been discovered by |
| // a different concurrently running collector (as may be the |
| // case, for instance, if the reference object is in CMS and |
| // the referent in DefNewGeneration), and provided the processing |
| // of this reference object by the current collector will |
| // appear atomic to every other collector in the system. |
| // (Thus, for instance, a concurrent collector may not |
| // discover references in other generations even if the |
| // referent is in its own generation). This policy may, |
| // in certain cases, enqueue references somewhat sooner than |
| // might Policy #0 above, but at marginally increased cost |
| // and complexity in processing these references. |
| // We call this choice the "RefeferentBasedDiscovery" policy. |
| bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { |
| // Make sure we are discovering refs (rather than processing discovered refs). |
| if (!_discovering_refs || !RegisterReferences) { |
| return false; |
| } |
| // We only discover active references. |
| oop next = java_lang_ref_Reference::next(obj); |
| if (next != NULL) { // Ref is no longer active |
| return false; |
| } |
| |
| HeapWord* obj_addr = (HeapWord*)obj; |
| if (RefDiscoveryPolicy == ReferenceBasedDiscovery && |
| !_span.contains(obj_addr)) { |
| // Reference is not in the originating generation; |
| // don't treat it specially (i.e. we want to scan it as a normal |
| // object with strong references). |
| return false; |
| } |
| |
| // We only discover references whose referents are not (yet) |
| // known to be strongly reachable. |
| if (is_alive_non_header() != NULL) { |
| verify_referent(obj); |
| if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) { |
| return false; // referent is reachable |
| } |
| } |
| if (rt == REF_SOFT) { |
| // For soft refs we can decide now if these are not |
| // current candidates for clearing, in which case we |
| // can mark through them now, rather than delaying that |
| // to the reference-processing phase. Since all current |
| // time-stamp policies advance the soft-ref clock only |
| // at a major collection cycle, this is always currently |
| // accurate. |
| if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) { |
| return false; |
| } |
| } |
| |
| ResourceMark rm; // Needed for tracing. |
| |
| HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj); |
| const oop discovered = java_lang_ref_Reference::discovered(obj); |
| assert(discovered->is_oop_or_null(), "bad discovered field"); |
| if (discovered != NULL) { |
| // The reference has already been discovered... |
| if (TraceReferenceGC) { |
| gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)", |
| (void *)obj, obj->klass()->internal_name()); |
| } |
| if (RefDiscoveryPolicy == ReferentBasedDiscovery) { |
| // assumes that an object is not processed twice; |
| // if it's been already discovered it must be on another |
| // generation's discovered list; so we won't discover it. |
| return false; |
| } else { |
| assert(RefDiscoveryPolicy == ReferenceBasedDiscovery, |
| "Unrecognized policy"); |
| // Check assumption that an object is not potentially |
| // discovered twice except by concurrent collectors that potentially |
| // trace the same Reference object twice. |
| assert(UseConcMarkSweepGC || UseG1GC, |
| "Only possible with a concurrent marking collector"); |
| return true; |
| } |
| } |
| |
| if (RefDiscoveryPolicy == ReferentBasedDiscovery) { |
| verify_referent(obj); |
| // Discover if and only if EITHER: |
| // .. reference is in our span, OR |
| // .. we are an atomic collector and referent is in our span |
| if (_span.contains(obj_addr) || |
| (discovery_is_atomic() && |
| _span.contains(java_lang_ref_Reference::referent(obj)))) { |
| // should_enqueue = true; |
| } else { |
| return false; |
| } |
| } else { |
| assert(RefDiscoveryPolicy == ReferenceBasedDiscovery && |
| _span.contains(obj_addr), "code inconsistency"); |
| } |
| |
| // Get the right type of discovered queue head. |
| DiscoveredList* list = get_discovered_list(rt); |
| if (list == NULL) { |
| return false; // nothing special needs to be done |
| } |
| |
| if (_discovery_is_mt) { |
| add_to_discovered_list_mt(*list, obj, discovered_addr); |
| } else { |
| // We do a raw store here: the field will be visited later when processing |
| // the discovered references. |
| oop current_head = list->head(); |
| // The last ref must have its discovered field pointing to itself. |
| oop next_discovered = (current_head != NULL) ? current_head : obj; |
| |
| assert(discovered == NULL, "control point invariant"); |
| oop_store_raw(discovered_addr, next_discovered); |
| list->set_head(obj); |
| list->inc_length(1); |
| |
| if (TraceReferenceGC) { |
| gclog_or_tty->print_cr("Discovered reference (" INTPTR_FORMAT ": %s)", |
| (void *)obj, obj->klass()->internal_name()); |
| } |
| } |
| assert(obj->is_oop(), "Discovered a bad reference"); |
| verify_referent(obj); |
| return true; |
| } |
| |
| // Preclean the discovered references by removing those |
| // whose referents are alive, and by marking from those that |
| // are not active. These lists can be handled here |
| // in any order and, indeed, concurrently. |
| void ReferenceProcessor::preclean_discovered_references( |
| BoolObjectClosure* is_alive, |
| OopClosure* keep_alive, |
| VoidClosure* complete_gc, |
| YieldClosure* yield, |
| GCTimer* gc_timer, |
| GCId gc_id) { |
| |
| NOT_PRODUCT(verify_ok_to_handle_reflists()); |
| |
| // Soft references |
| { |
| GCTraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC, |
| false, gc_timer, gc_id); |
| for (uint i = 0; i < _max_num_q; i++) { |
| if (yield->should_return()) { |
| return; |
| } |
| preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive, |
| keep_alive, complete_gc, yield); |
| } |
| } |
| |
| // Weak references |
| { |
| GCTraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC, |
| false, gc_timer, gc_id); |
| for (uint i = 0; i < _max_num_q; i++) { |
| if (yield->should_return()) { |
| return; |
| } |
| preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive, |
| keep_alive, complete_gc, yield); |
| } |
| } |
| |
| // Final references |
| { |
| GCTraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC, |
| false, gc_timer, gc_id); |
| for (uint i = 0; i < _max_num_q; i++) { |
| if (yield->should_return()) { |
| return; |
| } |
| preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive, |
| keep_alive, complete_gc, yield); |
| } |
| } |
| |
| // Phantom references |
| { |
| GCTraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC, |
| false, gc_timer, gc_id); |
| for (uint i = 0; i < _max_num_q; i++) { |
| if (yield->should_return()) { |
| return; |
| } |
| preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive, |
| keep_alive, complete_gc, yield); |
| } |
| |
| // Cleaner references. Included in timing for phantom references. We |
| // expect Cleaner references to be temporary, and don't want to deal with |
| // possible incompatibilities arising from making it more visible. |
| for (uint i = 0; i < _max_num_q; i++) { |
| if (yield->should_return()) { |
| return; |
| } |
| preclean_discovered_reflist(_discoveredCleanerRefs[i], is_alive, |
| keep_alive, complete_gc, yield); |
| } |
| } |
| } |
| |
| // Walk the given discovered ref list, and remove all reference objects |
| // whose referents are still alive, whose referents are NULL or which |
| // are not active (have a non-NULL next field). NOTE: When we are |
| // thus precleaning the ref lists (which happens single-threaded today), |
| // we do not disable refs discovery to honour the correct semantics of |
| // java.lang.Reference. As a result, we need to be careful below |
| // that ref removal steps interleave safely with ref discovery steps |
| // (in this thread). |
| void |
| ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list, |
| BoolObjectClosure* is_alive, |
| OopClosure* keep_alive, |
| VoidClosure* complete_gc, |
| YieldClosure* yield) { |
| DiscoveredListIterator iter(refs_list, keep_alive, is_alive); |
| while (iter.has_next()) { |
| iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); |
| oop obj = iter.obj(); |
| oop next = java_lang_ref_Reference::next(obj); |
| if (iter.referent() == NULL || iter.is_referent_alive() || |
| next != NULL) { |
| // The referent has been cleared, or is alive, or the Reference is not |
| // active; we need to trace and mark its cohort. |
| if (TraceReferenceGC) { |
| gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)", |
| (void *)iter.obj(), iter.obj()->klass()->internal_name()); |
| } |
| // Remove Reference object from list |
| iter.remove(); |
| // Keep alive its cohort. |
| iter.make_referent_alive(); |
| if (UseCompressedOops) { |
| narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj); |
| keep_alive->do_oop(next_addr); |
| } else { |
| oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj); |
| keep_alive->do_oop(next_addr); |
| } |
| iter.move_to_next(); |
| } else { |
| iter.next(); |
| } |
| } |
| // Close the reachable set |
| complete_gc->do_void(); |
| |
| NOT_PRODUCT( |
| if (PrintGCDetails && PrintReferenceGC && (iter.processed() > 0)) { |
| gclog_or_tty->print_cr(" Dropped %d Refs out of %d " |
| "Refs in discovered list " INTPTR_FORMAT, |
| iter.removed(), iter.processed(), (address)refs_list.head()); |
| } |
| ) |
| } |
| |
| const char* ReferenceProcessor::list_name(uint i) { |
| assert(i >= 0 && i <= _max_num_q * number_of_subclasses_of_ref(), |
| "Out of bounds index"); |
| |
| int j = i / _max_num_q; |
| switch (j) { |
| case 0: return "SoftRef"; |
| case 1: return "WeakRef"; |
| case 2: return "FinalRef"; |
| case 3: return "PhantomRef"; |
| case 4: return "CleanerRef"; |
| } |
| ShouldNotReachHere(); |
| return NULL; |
| } |
| |
| #ifndef PRODUCT |
| void ReferenceProcessor::verify_ok_to_handle_reflists() { |
| // empty for now |
| } |
| #endif |
| |
| #ifndef PRODUCT |
| void ReferenceProcessor::clear_discovered_references() { |
| guarantee(!_discovering_refs, "Discovering refs?"); |
| for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { |
| clear_discovered_references(_discovered_refs[i]); |
| } |
| } |
| |
| #endif // PRODUCT |
