| /* |
| * Copyright (c) 1998, 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/vmSymbols.hpp" |
| #include "memory/resourceArea.hpp" |
| #include "oops/markOop.hpp" |
| #include "oops/oop.inline.hpp" |
| #include "runtime/biasedLocking.hpp" |
| #include "runtime/handles.inline.hpp" |
| #include "runtime/interfaceSupport.hpp" |
| #include "runtime/mutexLocker.hpp" |
| #include "runtime/objectMonitor.hpp" |
| #include "runtime/objectMonitor.inline.hpp" |
| #include "runtime/osThread.hpp" |
| #include "runtime/stubRoutines.hpp" |
| #include "runtime/synchronizer.hpp" |
| #include "runtime/thread.inline.hpp" |
| #include "utilities/dtrace.hpp" |
| #include "utilities/events.hpp" |
| #include "utilities/preserveException.hpp" |
| #ifdef TARGET_OS_FAMILY_linux |
| # include "os_linux.inline.hpp" |
| #endif |
| #ifdef TARGET_OS_FAMILY_solaris |
| # include "os_solaris.inline.hpp" |
| #endif |
| #ifdef TARGET_OS_FAMILY_windows |
| # include "os_windows.inline.hpp" |
| #endif |
| #ifdef TARGET_OS_FAMILY_bsd |
| # include "os_bsd.inline.hpp" |
| #endif |
| |
| #if defined(__GNUC__) && !defined(PPC64) |
| // Need to inhibit inlining for older versions of GCC to avoid build-time failures |
| #define ATTR __attribute__((noinline)) |
| #else |
| #define ATTR |
| #endif |
| |
| PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC |
| |
| // The "core" versions of monitor enter and exit reside in this file. |
| // The interpreter and compilers contain specialized transliterated |
| // variants of the enter-exit fast-path operations. See i486.ad fast_lock(), |
| // for instance. If you make changes here, make sure to modify the |
| // interpreter, and both C1 and C2 fast-path inline locking code emission. |
| // |
| // |
| // ----------------------------------------------------------------------------- |
| |
| #ifdef DTRACE_ENABLED |
| |
| // Only bother with this argument setup if dtrace is available |
| // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly. |
| |
| #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \ |
| char* bytes = NULL; \ |
| int len = 0; \ |
| jlong jtid = SharedRuntime::get_java_tid(thread); \ |
| Symbol* klassname = ((oop)(obj))->klass()->name(); \ |
| if (klassname != NULL) { \ |
| bytes = (char*)klassname->bytes(); \ |
| len = klassname->utf8_length(); \ |
| } |
| |
| #ifndef USDT2 |
| HS_DTRACE_PROBE_DECL5(hotspot, monitor__wait, |
| jlong, uintptr_t, char*, int, long); |
| HS_DTRACE_PROBE_DECL4(hotspot, monitor__waited, |
| jlong, uintptr_t, char*, int); |
| |
| #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \ |
| { \ |
| if (DTraceMonitorProbes) { \ |
| DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ |
| HS_DTRACE_PROBE5(hotspot, monitor__wait, jtid, \ |
| (monitor), bytes, len, (millis)); \ |
| } \ |
| } |
| |
| #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \ |
| { \ |
| if (DTraceMonitorProbes) { \ |
| DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ |
| HS_DTRACE_PROBE4(hotspot, monitor__##probe, jtid, \ |
| (uintptr_t)(monitor), bytes, len); \ |
| } \ |
| } |
| |
| #else /* USDT2 */ |
| |
| #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \ |
| { \ |
| if (DTraceMonitorProbes) { \ |
| DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ |
| HOTSPOT_MONITOR_WAIT(jtid, \ |
| (uintptr_t)(monitor), bytes, len, (millis)); \ |
| } \ |
| } |
| |
| #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED |
| |
| #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \ |
| { \ |
| if (DTraceMonitorProbes) { \ |
| DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ |
| HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \ |
| (uintptr_t)(monitor), bytes, len); \ |
| } \ |
| } |
| |
| #endif /* USDT2 */ |
| #else // ndef DTRACE_ENABLED |
| |
| #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;} |
| #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;} |
| |
| #endif // ndef DTRACE_ENABLED |
| |
| // This exists only as a workaround of dtrace bug 6254741 |
| int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) { |
| DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr); |
| return 0; |
| } |
| |
| #define NINFLATIONLOCKS 256 |
| static volatile intptr_t InflationLocks [NINFLATIONLOCKS] ; |
| |
| ObjectMonitor * ObjectSynchronizer::gBlockList = NULL ; |
| ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL ; |
| ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL ; |
| int ObjectSynchronizer::gOmInUseCount = 0; |
| static volatile intptr_t ListLock = 0 ; // protects global monitor free-list cache |
| static volatile int MonitorFreeCount = 0 ; // # on gFreeList |
| static volatile int MonitorPopulation = 0 ; // # Extant -- in circulation |
| #define CHAINMARKER (cast_to_oop<intptr_t>(-1)) |
| |
| // ----------------------------------------------------------------------------- |
| // Fast Monitor Enter/Exit |
| // This the fast monitor enter. The interpreter and compiler use |
| // some assembly copies of this code. Make sure update those code |
| // if the following function is changed. The implementation is |
| // extremely sensitive to race condition. Be careful. |
| |
| void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock, bool attempt_rebias, TRAPS) { |
| if (UseBiasedLocking) { |
| if (!SafepointSynchronize::is_at_safepoint()) { |
| BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD); |
| if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) { |
| return; |
| } |
| } else { |
| assert(!attempt_rebias, "can not rebias toward VM thread"); |
| BiasedLocking::revoke_at_safepoint(obj); |
| } |
| assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
| } |
| |
| slow_enter (obj, lock, THREAD) ; |
| } |
| |
| void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) { |
| assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here"); |
| // if displaced header is null, the previous enter is recursive enter, no-op |
| markOop dhw = lock->displaced_header(); |
| markOop mark ; |
| if (dhw == NULL) { |
| // Recursive stack-lock. |
| // Diagnostics -- Could be: stack-locked, inflating, inflated. |
| mark = object->mark() ; |
| assert (!mark->is_neutral(), "invariant") ; |
| if (mark->has_locker() && mark != markOopDesc::INFLATING()) { |
| assert(THREAD->is_lock_owned((address)mark->locker()), "invariant") ; |
| } |
| if (mark->has_monitor()) { |
| ObjectMonitor * m = mark->monitor() ; |
| assert(((oop)(m->object()))->mark() == mark, "invariant") ; |
| assert(m->is_entered(THREAD), "invariant") ; |
| } |
| return ; |
| } |
| |
| mark = object->mark() ; |
| |
| // If the object is stack-locked by the current thread, try to |
| // swing the displaced header from the box back to the mark. |
| if (mark == (markOop) lock) { |
| assert (dhw->is_neutral(), "invariant") ; |
| if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) { |
| TEVENT (fast_exit: release stacklock) ; |
| return; |
| } |
| } |
| |
| ObjectSynchronizer::inflate(THREAD, object)->exit (true, THREAD) ; |
| } |
| |
| // ----------------------------------------------------------------------------- |
| // Interpreter/Compiler Slow Case |
| // This routine is used to handle interpreter/compiler slow case |
| // We don't need to use fast path here, because it must have been |
| // failed in the interpreter/compiler code. |
| void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) { |
| markOop mark = obj->mark(); |
| assert(!mark->has_bias_pattern(), "should not see bias pattern here"); |
| |
| if (mark->is_neutral()) { |
| // Anticipate successful CAS -- the ST of the displaced mark must |
| // be visible <= the ST performed by the CAS. |
| lock->set_displaced_header(mark); |
| if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) { |
| TEVENT (slow_enter: release stacklock) ; |
| return ; |
| } |
| // Fall through to inflate() ... |
| } else |
| if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { |
| assert(lock != mark->locker(), "must not re-lock the same lock"); |
| assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock"); |
| lock->set_displaced_header(NULL); |
| return; |
| } |
| |
| #if 0 |
| // The following optimization isn't particularly useful. |
| if (mark->has_monitor() && mark->monitor()->is_entered(THREAD)) { |
| lock->set_displaced_header (NULL) ; |
| return ; |
| } |
| #endif |
| |
| // The object header will never be displaced to this lock, |
| // so it does not matter what the value is, except that it |
| // must be non-zero to avoid looking like a re-entrant lock, |
| // and must not look locked either. |
| lock->set_displaced_header(markOopDesc::unused_mark()); |
| ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD); |
| } |
| |
| // This routine is used to handle interpreter/compiler slow case |
| // We don't need to use fast path here, because it must have |
| // failed in the interpreter/compiler code. Simply use the heavy |
| // weight monitor should be ok, unless someone find otherwise. |
| void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) { |
| fast_exit (object, lock, THREAD) ; |
| } |
| |
| // ----------------------------------------------------------------------------- |
| // Class Loader support to workaround deadlocks on the class loader lock objects |
| // Also used by GC |
| // complete_exit()/reenter() are used to wait on a nested lock |
| // i.e. to give up an outer lock completely and then re-enter |
| // Used when holding nested locks - lock acquisition order: lock1 then lock2 |
| // 1) complete_exit lock1 - saving recursion count |
| // 2) wait on lock2 |
| // 3) when notified on lock2, unlock lock2 |
| // 4) reenter lock1 with original recursion count |
| // 5) lock lock2 |
| // NOTE: must use heavy weight monitor to handle complete_exit/reenter() |
| intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) { |
| TEVENT (complete_exit) ; |
| if (UseBiasedLocking) { |
| BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
| assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
| } |
| |
| ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); |
| |
| return monitor->complete_exit(THREAD); |
| } |
| |
| // NOTE: must use heavy weight monitor to handle complete_exit/reenter() |
| void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) { |
| TEVENT (reenter) ; |
| if (UseBiasedLocking) { |
| BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
| assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
| } |
| |
| ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); |
| |
| monitor->reenter(recursion, THREAD); |
| } |
| // ----------------------------------------------------------------------------- |
| // JNI locks on java objects |
| // NOTE: must use heavy weight monitor to handle jni monitor enter |
| void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) { // possible entry from jni enter |
| // the current locking is from JNI instead of Java code |
| TEVENT (jni_enter) ; |
| if (UseBiasedLocking) { |
| BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
| assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
| } |
| THREAD->set_current_pending_monitor_is_from_java(false); |
| ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD); |
| THREAD->set_current_pending_monitor_is_from_java(true); |
| } |
| |
| // NOTE: must use heavy weight monitor to handle jni monitor enter |
| bool ObjectSynchronizer::jni_try_enter(Handle obj, Thread* THREAD) { |
| if (UseBiasedLocking) { |
| BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
| assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
| } |
| |
| ObjectMonitor* monitor = ObjectSynchronizer::inflate_helper(obj()); |
| return monitor->try_enter(THREAD); |
| } |
| |
| |
| // NOTE: must use heavy weight monitor to handle jni monitor exit |
| void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) { |
| TEVENT (jni_exit) ; |
| if (UseBiasedLocking) { |
| Handle h_obj(THREAD, obj); |
| BiasedLocking::revoke_and_rebias(h_obj, false, THREAD); |
| obj = h_obj(); |
| } |
| assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
| |
| ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj); |
| // If this thread has locked the object, exit the monitor. Note: can't use |
| // monitor->check(CHECK); must exit even if an exception is pending. |
| if (monitor->check(THREAD)) { |
| monitor->exit(true, THREAD); |
| } |
| } |
| |
| // ----------------------------------------------------------------------------- |
| // Internal VM locks on java objects |
| // standard constructor, allows locking failures |
| ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) { |
| _dolock = doLock; |
| _thread = thread; |
| debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);) |
| _obj = obj; |
| |
| if (_dolock) { |
| TEVENT (ObjectLocker) ; |
| |
| ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread); |
| } |
| } |
| |
| ObjectLocker::~ObjectLocker() { |
| if (_dolock) { |
| ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread); |
| } |
| } |
| |
| |
| // ----------------------------------------------------------------------------- |
| // Wait/Notify/NotifyAll |
| // NOTE: must use heavy weight monitor to handle wait() |
| void ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) { |
| if (UseBiasedLocking) { |
| BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
| assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
| } |
| if (millis < 0) { |
| TEVENT (wait - throw IAX) ; |
| THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); |
| } |
| ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); |
| DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis); |
| monitor->wait(millis, true, THREAD); |
| |
| /* This dummy call is in place to get around dtrace bug 6254741. Once |
| that's fixed we can uncomment the following line and remove the call */ |
| // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD); |
| dtrace_waited_probe(monitor, obj, THREAD); |
| } |
| |
| void ObjectSynchronizer::waitUninterruptibly (Handle obj, jlong millis, TRAPS) { |
| if (UseBiasedLocking) { |
| BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
| assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
| } |
| if (millis < 0) { |
| TEVENT (wait - throw IAX) ; |
| THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); |
| } |
| ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD) ; |
| } |
| |
| void ObjectSynchronizer::notify(Handle obj, TRAPS) { |
| if (UseBiasedLocking) { |
| BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
| assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
| } |
| |
| markOop mark = obj->mark(); |
| if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { |
| return; |
| } |
| ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD); |
| } |
| |
| // NOTE: see comment of notify() |
| void ObjectSynchronizer::notifyall(Handle obj, TRAPS) { |
| if (UseBiasedLocking) { |
| BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
| assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
| } |
| |
| markOop mark = obj->mark(); |
| if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { |
| return; |
| } |
| ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD); |
| } |
| |
| // ----------------------------------------------------------------------------- |
| // Hash Code handling |
| // |
| // Performance concern: |
| // OrderAccess::storestore() calls release() which at one time stored 0 |
| // into the global volatile OrderAccess::dummy variable. This store was |
| // unnecessary for correctness. Many threads storing into a common location |
| // causes considerable cache migration or "sloshing" on large SMP systems. |
| // As such, I avoided using OrderAccess::storestore(). In some cases |
| // OrderAccess::fence() -- which incurs local latency on the executing |
| // processor -- is a better choice as it scales on SMP systems. |
| // |
| // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for |
| // a discussion of coherency costs. Note that all our current reference |
| // platforms provide strong ST-ST order, so the issue is moot on IA32, |
| // x64, and SPARC. |
| // |
| // As a general policy we use "volatile" to control compiler-based reordering |
| // and explicit fences (barriers) to control for architectural reordering |
| // performed by the CPU(s) or platform. |
| |
| struct SharedGlobals { |
| // These are highly shared mostly-read variables. |
| // To avoid false-sharing they need to be the sole occupants of a $ line. |
| double padPrefix [8]; |
| volatile int stwRandom ; |
| volatile int stwCycle ; |
| |
| // Hot RW variables -- Sequester to avoid false-sharing |
| double padSuffix [16]; |
| volatile int hcSequence ; |
| double padFinal [8] ; |
| } ; |
| |
| static SharedGlobals GVars ; |
| static int MonitorScavengeThreshold = 1000000 ; |
| static volatile int ForceMonitorScavenge = 0 ; // Scavenge required and pending |
| |
| static markOop ReadStableMark (oop obj) { |
| markOop mark = obj->mark() ; |
| if (!mark->is_being_inflated()) { |
| return mark ; // normal fast-path return |
| } |
| |
| int its = 0 ; |
| for (;;) { |
| markOop mark = obj->mark() ; |
| if (!mark->is_being_inflated()) { |
| return mark ; // normal fast-path return |
| } |
| |
| // The object is being inflated by some other thread. |
| // The caller of ReadStableMark() must wait for inflation to complete. |
| // Avoid live-lock |
| // TODO: consider calling SafepointSynchronize::do_call_back() while |
| // spinning to see if there's a safepoint pending. If so, immediately |
| // yielding or blocking would be appropriate. Avoid spinning while |
| // there is a safepoint pending. |
| // TODO: add inflation contention performance counters. |
| // TODO: restrict the aggregate number of spinners. |
| |
| ++its ; |
| if (its > 10000 || !os::is_MP()) { |
| if (its & 1) { |
| os::NakedYield() ; |
| TEVENT (Inflate: INFLATING - yield) ; |
| } else { |
| // Note that the following code attenuates the livelock problem but is not |
| // a complete remedy. A more complete solution would require that the inflating |
| // thread hold the associated inflation lock. The following code simply restricts |
| // the number of spinners to at most one. We'll have N-2 threads blocked |
| // on the inflationlock, 1 thread holding the inflation lock and using |
| // a yield/park strategy, and 1 thread in the midst of inflation. |
| // A more refined approach would be to change the encoding of INFLATING |
| // to allow encapsulation of a native thread pointer. Threads waiting for |
| // inflation to complete would use CAS to push themselves onto a singly linked |
| // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag |
| // and calling park(). When inflation was complete the thread that accomplished inflation |
| // would detach the list and set the markword to inflated with a single CAS and |
| // then for each thread on the list, set the flag and unpark() the thread. |
| // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease |
| // wakes at most one thread whereas we need to wake the entire list. |
| int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1) ; |
| int YieldThenBlock = 0 ; |
| assert (ix >= 0 && ix < NINFLATIONLOCKS, "invariant") ; |
| assert ((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant") ; |
| Thread::muxAcquire (InflationLocks + ix, "InflationLock") ; |
| while (obj->mark() == markOopDesc::INFLATING()) { |
| // Beware: NakedYield() is advisory and has almost no effect on some platforms |
| // so we periodically call Self->_ParkEvent->park(1). |
| // We use a mixed spin/yield/block mechanism. |
| if ((YieldThenBlock++) >= 16) { |
| Thread::current()->_ParkEvent->park(1) ; |
| } else { |
| os::NakedYield() ; |
| } |
| } |
| Thread::muxRelease (InflationLocks + ix ) ; |
| TEVENT (Inflate: INFLATING - yield/park) ; |
| } |
| } else { |
| SpinPause() ; // SMP-polite spinning |
| } |
| } |
| } |
| |
| // hashCode() generation : |
| // |
| // Possibilities: |
| // * MD5Digest of {obj,stwRandom} |
| // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function. |
| // * A DES- or AES-style SBox[] mechanism |
| // * One of the Phi-based schemes, such as: |
| // 2654435761 = 2^32 * Phi (golden ratio) |
| // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ; |
| // * A variation of Marsaglia's shift-xor RNG scheme. |
| // * (obj ^ stwRandom) is appealing, but can result |
| // in undesirable regularity in the hashCode values of adjacent objects |
| // (objects allocated back-to-back, in particular). This could potentially |
| // result in hashtable collisions and reduced hashtable efficiency. |
| // There are simple ways to "diffuse" the middle address bits over the |
| // generated hashCode values: |
| // |
| |
| static inline intptr_t get_next_hash(Thread * Self, oop obj) { |
| intptr_t value = 0 ; |
| if (hashCode == 0) { |
| // This form uses an unguarded global Park-Miller RNG, |
| // so it's possible for two threads to race and generate the same RNG. |
| // On MP system we'll have lots of RW access to a global, so the |
| // mechanism induces lots of coherency traffic. |
| value = os::random() ; |
| } else |
| if (hashCode == 1) { |
| // This variation has the property of being stable (idempotent) |
| // between STW operations. This can be useful in some of the 1-0 |
| // synchronization schemes. |
| intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3 ; |
| value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom ; |
| } else |
| if (hashCode == 2) { |
| value = 1 ; // for sensitivity testing |
| } else |
| if (hashCode == 3) { |
| value = ++GVars.hcSequence ; |
| } else |
| if (hashCode == 4) { |
| value = cast_from_oop<intptr_t>(obj) ; |
| } else { |
| // Marsaglia's xor-shift scheme with thread-specific state |
| // This is probably the best overall implementation -- we'll |
| // likely make this the default in future releases. |
| unsigned t = Self->_hashStateX ; |
| t ^= (t << 11) ; |
| Self->_hashStateX = Self->_hashStateY ; |
| Self->_hashStateY = Self->_hashStateZ ; |
| Self->_hashStateZ = Self->_hashStateW ; |
| unsigned v = Self->_hashStateW ; |
| v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)) ; |
| Self->_hashStateW = v ; |
| value = v ; |
| } |
| |
| value &= markOopDesc::hash_mask; |
| if (value == 0) value = 0xBAD ; |
| assert (value != markOopDesc::no_hash, "invariant") ; |
| TEVENT (hashCode: GENERATE) ; |
| return value; |
| } |
| // |
| intptr_t ObjectSynchronizer::FastHashCode (Thread * Self, oop obj) { |
| if (UseBiasedLocking) { |
| // NOTE: many places throughout the JVM do not expect a safepoint |
| // to be taken here, in particular most operations on perm gen |
| // objects. However, we only ever bias Java instances and all of |
| // the call sites of identity_hash that might revoke biases have |
| // been checked to make sure they can handle a safepoint. The |
| // added check of the bias pattern is to avoid useless calls to |
| // thread-local storage. |
| if (obj->mark()->has_bias_pattern()) { |
| // Box and unbox the raw reference just in case we cause a STW safepoint. |
| Handle hobj (Self, obj) ; |
| // Relaxing assertion for bug 6320749. |
| assert (Universe::verify_in_progress() || |
| !SafepointSynchronize::is_at_safepoint(), |
| "biases should not be seen by VM thread here"); |
| BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current()); |
| obj = hobj() ; |
| assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
| } |
| } |
| |
| // hashCode() is a heap mutator ... |
| // Relaxing assertion for bug 6320749. |
| assert (Universe::verify_in_progress() || |
| !SafepointSynchronize::is_at_safepoint(), "invariant") ; |
| assert (Universe::verify_in_progress() || |
| Self->is_Java_thread() , "invariant") ; |
| assert (Universe::verify_in_progress() || |
| ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ; |
| |
| ObjectMonitor* monitor = NULL; |
| markOop temp, test; |
| intptr_t hash; |
| markOop mark = ReadStableMark (obj); |
| |
| // object should remain ineligible for biased locking |
| assert (!mark->has_bias_pattern(), "invariant") ; |
| |
| if (mark->is_neutral()) { |
| hash = mark->hash(); // this is a normal header |
| if (hash) { // if it has hash, just return it |
| return hash; |
| } |
| hash = get_next_hash(Self, obj); // allocate a new hash code |
| temp = mark->copy_set_hash(hash); // merge the hash code into header |
| // use (machine word version) atomic operation to install the hash |
| test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark); |
| if (test == mark) { |
| return hash; |
| } |
| // If atomic operation failed, we must inflate the header |
| // into heavy weight monitor. We could add more code here |
| // for fast path, but it does not worth the complexity. |
| } else if (mark->has_monitor()) { |
| monitor = mark->monitor(); |
| temp = monitor->header(); |
| assert (temp->is_neutral(), "invariant") ; |
| hash = temp->hash(); |
| if (hash) { |
| return hash; |
| } |
| // Skip to the following code to reduce code size |
| } else if (Self->is_lock_owned((address)mark->locker())) { |
| temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned |
| assert (temp->is_neutral(), "invariant") ; |
| hash = temp->hash(); // by current thread, check if the displaced |
| if (hash) { // header contains hash code |
| return hash; |
| } |
| // WARNING: |
| // The displaced header is strictly immutable. |
| // It can NOT be changed in ANY cases. So we have |
| // to inflate the header into heavyweight monitor |
| // even the current thread owns the lock. The reason |
| // is the BasicLock (stack slot) will be asynchronously |
| // read by other threads during the inflate() function. |
| // Any change to stack may not propagate to other threads |
| // correctly. |
| } |
| |
| // Inflate the monitor to set hash code |
| monitor = ObjectSynchronizer::inflate(Self, obj); |
| // Load displaced header and check it has hash code |
| mark = monitor->header(); |
| assert (mark->is_neutral(), "invariant") ; |
| hash = mark->hash(); |
| if (hash == 0) { |
| hash = get_next_hash(Self, obj); |
| temp = mark->copy_set_hash(hash); // merge hash code into header |
| assert (temp->is_neutral(), "invariant") ; |
| test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark); |
| if (test != mark) { |
| // The only update to the header in the monitor (outside GC) |
| // is install the hash code. If someone add new usage of |
| // displaced header, please update this code |
| hash = test->hash(); |
| assert (test->is_neutral(), "invariant") ; |
| assert (hash != 0, "Trivial unexpected object/monitor header usage."); |
| } |
| } |
| // We finally get the hash |
| return hash; |
| } |
| |
| // Deprecated -- use FastHashCode() instead. |
| |
| intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) { |
| return FastHashCode (Thread::current(), obj()) ; |
| } |
| |
| |
| bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread, |
| Handle h_obj) { |
| if (UseBiasedLocking) { |
| BiasedLocking::revoke_and_rebias(h_obj, false, thread); |
| assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
| } |
| |
| assert(thread == JavaThread::current(), "Can only be called on current thread"); |
| oop obj = h_obj(); |
| |
| markOop mark = ReadStableMark (obj) ; |
| |
| // Uncontended case, header points to stack |
| if (mark->has_locker()) { |
| return thread->is_lock_owned((address)mark->locker()); |
| } |
| // Contended case, header points to ObjectMonitor (tagged pointer) |
| if (mark->has_monitor()) { |
| ObjectMonitor* monitor = mark->monitor(); |
| return monitor->is_entered(thread) != 0 ; |
| } |
| // Unlocked case, header in place |
| assert(mark->is_neutral(), "sanity check"); |
| return false; |
| } |
| |
| // Be aware of this method could revoke bias of the lock object. |
| // This method querys the ownership of the lock handle specified by 'h_obj'. |
| // If the current thread owns the lock, it returns owner_self. If no |
| // thread owns the lock, it returns owner_none. Otherwise, it will return |
| // ower_other. |
| ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership |
| (JavaThread *self, Handle h_obj) { |
| // The caller must beware this method can revoke bias, and |
| // revocation can result in a safepoint. |
| assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ; |
| assert (self->thread_state() != _thread_blocked , "invariant") ; |
| |
| // Possible mark states: neutral, biased, stack-locked, inflated |
| |
| if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) { |
| // CASE: biased |
| BiasedLocking::revoke_and_rebias(h_obj, false, self); |
| assert(!h_obj->mark()->has_bias_pattern(), |
| "biases should be revoked by now"); |
| } |
| |
| assert(self == JavaThread::current(), "Can only be called on current thread"); |
| oop obj = h_obj(); |
| markOop mark = ReadStableMark (obj) ; |
| |
| // CASE: stack-locked. Mark points to a BasicLock on the owner's stack. |
| if (mark->has_locker()) { |
| return self->is_lock_owned((address)mark->locker()) ? |
| owner_self : owner_other; |
| } |
| |
| // CASE: inflated. Mark (tagged pointer) points to an objectMonitor. |
| // The Object:ObjectMonitor relationship is stable as long as we're |
| // not at a safepoint. |
| if (mark->has_monitor()) { |
| void * owner = mark->monitor()->_owner ; |
| if (owner == NULL) return owner_none ; |
| return (owner == self || |
| self->is_lock_owned((address)owner)) ? owner_self : owner_other; |
| } |
| |
| // CASE: neutral |
| assert(mark->is_neutral(), "sanity check"); |
| return owner_none ; // it's unlocked |
| } |
| |
| // FIXME: jvmti should call this |
| JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) { |
| if (UseBiasedLocking) { |
| if (SafepointSynchronize::is_at_safepoint()) { |
| BiasedLocking::revoke_at_safepoint(h_obj); |
| } else { |
| BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current()); |
| } |
| assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
| } |
| |
| oop obj = h_obj(); |
| address owner = NULL; |
| |
| markOop mark = ReadStableMark (obj) ; |
| |
| // Uncontended case, header points to stack |
| if (mark->has_locker()) { |
| owner = (address) mark->locker(); |
| } |
| |
| // Contended case, header points to ObjectMonitor (tagged pointer) |
| if (mark->has_monitor()) { |
| ObjectMonitor* monitor = mark->monitor(); |
| assert(monitor != NULL, "monitor should be non-null"); |
| owner = (address) monitor->owner(); |
| } |
| |
| if (owner != NULL) { |
| // owning_thread_from_monitor_owner() may also return NULL here |
| return Threads::owning_thread_from_monitor_owner(owner, doLock); |
| } |
| |
| // Unlocked case, header in place |
| // Cannot have assertion since this object may have been |
| // locked by another thread when reaching here. |
| // assert(mark->is_neutral(), "sanity check"); |
| |
| return NULL; |
| } |
| // Visitors ... |
| |
| void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) { |
| ObjectMonitor* block = gBlockList; |
| ObjectMonitor* mid; |
| while (block) { |
| assert(block->object() == CHAINMARKER, "must be a block header"); |
| for (int i = _BLOCKSIZE - 1; i > 0; i--) { |
| mid = block + i; |
| oop object = (oop) mid->object(); |
| if (object != NULL) { |
| closure->do_monitor(mid); |
| } |
| } |
| block = (ObjectMonitor*) block->FreeNext; |
| } |
| } |
| |
| // Get the next block in the block list. |
| static inline ObjectMonitor* next(ObjectMonitor* block) { |
| assert(block->object() == CHAINMARKER, "must be a block header"); |
| block = block->FreeNext ; |
| assert(block == NULL || block->object() == CHAINMARKER, "must be a block header"); |
| return block; |
| } |
| |
| |
| void ObjectSynchronizer::oops_do(OopClosure* f) { |
| assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); |
| for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) { |
| assert(block->object() == CHAINMARKER, "must be a block header"); |
| for (int i = 1; i < _BLOCKSIZE; i++) { |
| ObjectMonitor* mid = &block[i]; |
| if (mid->object() != NULL) { |
| f->do_oop((oop*)mid->object_addr()); |
| } |
| } |
| } |
| } |
| |
| |
| // ----------------------------------------------------------------------------- |
| // ObjectMonitor Lifecycle |
| // ----------------------- |
| // Inflation unlinks monitors from the global gFreeList and |
| // associates them with objects. Deflation -- which occurs at |
| // STW-time -- disassociates idle monitors from objects. Such |
| // scavenged monitors are returned to the gFreeList. |
| // |
| // The global list is protected by ListLock. All the critical sections |
| // are short and operate in constant-time. |
| // |
| // ObjectMonitors reside in type-stable memory (TSM) and are immortal. |
| // |
| // Lifecycle: |
| // -- unassigned and on the global free list |
| // -- unassigned and on a thread's private omFreeList |
| // -- assigned to an object. The object is inflated and the mark refers |
| // to the objectmonitor. |
| // |
| |
| |
| // Constraining monitor pool growth via MonitorBound ... |
| // |
| // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the |
| // the rate of scavenging is driven primarily by GC. As such, we can find |
| // an inordinate number of monitors in circulation. |
| // To avoid that scenario we can artificially induce a STW safepoint |
| // if the pool appears to be growing past some reasonable bound. |
| // Generally we favor time in space-time tradeoffs, but as there's no |
| // natural back-pressure on the # of extant monitors we need to impose some |
| // type of limit. Beware that if MonitorBound is set to too low a value |
| // we could just loop. In addition, if MonitorBound is set to a low value |
| // we'll incur more safepoints, which are harmful to performance. |
| // See also: GuaranteedSafepointInterval |
| // |
| // The current implementation uses asynchronous VM operations. |
| // |
| |
| static void InduceScavenge (Thread * Self, const char * Whence) { |
| // Induce STW safepoint to trim monitors |
| // Ultimately, this results in a call to deflate_idle_monitors() in the near future. |
| // More precisely, trigger an asynchronous STW safepoint as the number |
| // of active monitors passes the specified threshold. |
| // TODO: assert thread state is reasonable |
| |
| if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) { |
| if (ObjectMonitor::Knob_Verbose) { |
| ::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ; |
| ::fflush(stdout) ; |
| } |
| // Induce a 'null' safepoint to scavenge monitors |
| // Must VM_Operation instance be heap allocated as the op will be enqueue and posted |
| // to the VMthread and have a lifespan longer than that of this activation record. |
| // The VMThread will delete the op when completed. |
| VMThread::execute (new VM_ForceAsyncSafepoint()) ; |
| |
| if (ObjectMonitor::Knob_Verbose) { |
| ::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ; |
| ::fflush(stdout) ; |
| } |
| } |
| } |
| /* Too slow for general assert or debug |
| void ObjectSynchronizer::verifyInUse (Thread *Self) { |
| ObjectMonitor* mid; |
| int inusetally = 0; |
| for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) { |
| inusetally ++; |
| } |
| assert(inusetally == Self->omInUseCount, "inuse count off"); |
| |
| int freetally = 0; |
| for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) { |
| freetally ++; |
| } |
| assert(freetally == Self->omFreeCount, "free count off"); |
| } |
| */ |
| ObjectMonitor * ATTR ObjectSynchronizer::omAlloc (Thread * Self) { |
| // A large MAXPRIVATE value reduces both list lock contention |
| // and list coherency traffic, but also tends to increase the |
| // number of objectMonitors in circulation as well as the STW |
| // scavenge costs. As usual, we lean toward time in space-time |
| // tradeoffs. |
| const int MAXPRIVATE = 1024 ; |
| for (;;) { |
| ObjectMonitor * m ; |
| |
| // 1: try to allocate from the thread's local omFreeList. |
| // Threads will attempt to allocate first from their local list, then |
| // from the global list, and only after those attempts fail will the thread |
| // attempt to instantiate new monitors. Thread-local free lists take |
| // heat off the ListLock and improve allocation latency, as well as reducing |
| // coherency traffic on the shared global list. |
| m = Self->omFreeList ; |
| if (m != NULL) { |
| Self->omFreeList = m->FreeNext ; |
| Self->omFreeCount -- ; |
| // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene |
| guarantee (m->object() == NULL, "invariant") ; |
| if (MonitorInUseLists) { |
| m->FreeNext = Self->omInUseList; |
| Self->omInUseList = m; |
| Self->omInUseCount ++; |
| // verifyInUse(Self); |
| } else { |
| m->FreeNext = NULL; |
| } |
| return m ; |
| } |
| |
| // 2: try to allocate from the global gFreeList |
| // CONSIDER: use muxTry() instead of muxAcquire(). |
| // If the muxTry() fails then drop immediately into case 3. |
| // If we're using thread-local free lists then try |
| // to reprovision the caller's free list. |
| if (gFreeList != NULL) { |
| // Reprovision the thread's omFreeList. |
| // Use bulk transfers to reduce the allocation rate and heat |
| // on various locks. |
| Thread::muxAcquire (&ListLock, "omAlloc") ; |
| for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL; ) { |
| MonitorFreeCount --; |
| ObjectMonitor * take = gFreeList ; |
| gFreeList = take->FreeNext ; |
| guarantee (take->object() == NULL, "invariant") ; |
| guarantee (!take->is_busy(), "invariant") ; |
| take->Recycle() ; |
| omRelease (Self, take, false) ; |
| } |
| Thread::muxRelease (&ListLock) ; |
| Self->omFreeProvision += 1 + (Self->omFreeProvision/2) ; |
| if (Self->omFreeProvision > MAXPRIVATE ) Self->omFreeProvision = MAXPRIVATE ; |
| TEVENT (omFirst - reprovision) ; |
| |
| const int mx = MonitorBound ; |
| if (mx > 0 && (MonitorPopulation-MonitorFreeCount) > mx) { |
| // We can't safely induce a STW safepoint from omAlloc() as our thread |
| // state may not be appropriate for such activities and callers may hold |
| // naked oops, so instead we defer the action. |
| InduceScavenge (Self, "omAlloc") ; |
| } |
| continue; |
| } |
| |
| // 3: allocate a block of new ObjectMonitors |
| // Both the local and global free lists are empty -- resort to malloc(). |
| // In the current implementation objectMonitors are TSM - immortal. |
| assert (_BLOCKSIZE > 1, "invariant") ; |
| ObjectMonitor * temp = new ObjectMonitor[_BLOCKSIZE]; |
| |
| // NOTE: (almost) no way to recover if allocation failed. |
| // We might be able to induce a STW safepoint and scavenge enough |
| // objectMonitors to permit progress. |
| if (temp == NULL) { |
| vm_exit_out_of_memory (sizeof (ObjectMonitor[_BLOCKSIZE]), OOM_MALLOC_ERROR, |
| "Allocate ObjectMonitors"); |
| } |
| |
| // Format the block. |
| // initialize the linked list, each monitor points to its next |
| // forming the single linked free list, the very first monitor |
| // will points to next block, which forms the block list. |
| // The trick of using the 1st element in the block as gBlockList |
| // linkage should be reconsidered. A better implementation would |
| // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; } |
| |
| for (int i = 1; i < _BLOCKSIZE ; i++) { |
| temp[i].FreeNext = &temp[i+1]; |
| } |
| |
| // terminate the last monitor as the end of list |
| temp[_BLOCKSIZE - 1].FreeNext = NULL ; |
| |
| // Element [0] is reserved for global list linkage |
| temp[0].set_object(CHAINMARKER); |
| |
| // Consider carving out this thread's current request from the |
| // block in hand. This avoids some lock traffic and redundant |
| // list activity. |
| |
| // Acquire the ListLock to manipulate BlockList and FreeList. |
| // An Oyama-Taura-Yonezawa scheme might be more efficient. |
| Thread::muxAcquire (&ListLock, "omAlloc [2]") ; |
| MonitorPopulation += _BLOCKSIZE-1; |
| MonitorFreeCount += _BLOCKSIZE-1; |
| |
| // Add the new block to the list of extant blocks (gBlockList). |
| // The very first objectMonitor in a block is reserved and dedicated. |
| // It serves as blocklist "next" linkage. |
| temp[0].FreeNext = gBlockList; |
| gBlockList = temp; |
| |
| // Add the new string of objectMonitors to the global free list |
| temp[_BLOCKSIZE - 1].FreeNext = gFreeList ; |
| gFreeList = temp + 1; |
| Thread::muxRelease (&ListLock) ; |
| TEVENT (Allocate block of monitors) ; |
| } |
| } |
| |
| // Place "m" on the caller's private per-thread omFreeList. |
| // In practice there's no need to clamp or limit the number of |
| // monitors on a thread's omFreeList as the only time we'll call |
| // omRelease is to return a monitor to the free list after a CAS |
| // attempt failed. This doesn't allow unbounded #s of monitors to |
| // accumulate on a thread's free list. |
| // |
| |
| void ObjectSynchronizer::omRelease (Thread * Self, ObjectMonitor * m, bool fromPerThreadAlloc) { |
| guarantee (m->object() == NULL, "invariant") ; |
| |
| // Remove from omInUseList |
| if (MonitorInUseLists && fromPerThreadAlloc) { |
| ObjectMonitor* curmidinuse = NULL; |
| for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; ) { |
| if (m == mid) { |
| // extract from per-thread in-use-list |
| if (mid == Self->omInUseList) { |
| Self->omInUseList = mid->FreeNext; |
| } else if (curmidinuse != NULL) { |
| curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist |
| } |
| Self->omInUseCount --; |
| // verifyInUse(Self); |
| break; |
| } else { |
| curmidinuse = mid; |
| mid = mid->FreeNext; |
| } |
| } |
| } |
| |
| // FreeNext is used for both onInUseList and omFreeList, so clear old before setting new |
| m->FreeNext = Self->omFreeList ; |
| Self->omFreeList = m ; |
| Self->omFreeCount ++ ; |
| } |
| |
| // Return the monitors of a moribund thread's local free list to |
| // the global free list. Typically a thread calls omFlush() when |
| // it's dying. We could also consider having the VM thread steal |
| // monitors from threads that have not run java code over a few |
| // consecutive STW safepoints. Relatedly, we might decay |
| // omFreeProvision at STW safepoints. |
| // |
| // Also return the monitors of a moribund thread"s omInUseList to |
| // a global gOmInUseList under the global list lock so these |
| // will continue to be scanned. |
| // |
| // We currently call omFlush() from the Thread:: dtor _after the thread |
| // has been excised from the thread list and is no longer a mutator. |
| // That means that omFlush() can run concurrently with a safepoint and |
| // the scavenge operator. Calling omFlush() from JavaThread::exit() might |
| // be a better choice as we could safely reason that that the JVM is |
| // not at a safepoint at the time of the call, and thus there could |
| // be not inopportune interleavings between omFlush() and the scavenge |
| // operator. |
| |
| void ObjectSynchronizer::omFlush (Thread * Self) { |
| ObjectMonitor * List = Self->omFreeList ; // Null-terminated SLL |
| Self->omFreeList = NULL ; |
| ObjectMonitor * Tail = NULL ; |
| int Tally = 0; |
| if (List != NULL) { |
| ObjectMonitor * s ; |
| for (s = List ; s != NULL ; s = s->FreeNext) { |
| Tally ++ ; |
| Tail = s ; |
| guarantee (s->object() == NULL, "invariant") ; |
| guarantee (!s->is_busy(), "invariant") ; |
| s->set_owner (NULL) ; // redundant but good hygiene |
| TEVENT (omFlush - Move one) ; |
| } |
| guarantee (Tail != NULL && List != NULL, "invariant") ; |
| } |
| |
| ObjectMonitor * InUseList = Self->omInUseList; |
| ObjectMonitor * InUseTail = NULL ; |
| int InUseTally = 0; |
| if (InUseList != NULL) { |
| Self->omInUseList = NULL; |
| ObjectMonitor *curom; |
| for (curom = InUseList; curom != NULL; curom = curom->FreeNext) { |
| InUseTail = curom; |
| InUseTally++; |
| } |
| // TODO debug |
| assert(Self->omInUseCount == InUseTally, "inuse count off"); |
| Self->omInUseCount = 0; |
| guarantee (InUseTail != NULL && InUseList != NULL, "invariant"); |
| } |
| |
| Thread::muxAcquire (&ListLock, "omFlush") ; |
| if (Tail != NULL) { |
| Tail->FreeNext = gFreeList ; |
| gFreeList = List ; |
| MonitorFreeCount += Tally; |
| } |
| |
| if (InUseTail != NULL) { |
| InUseTail->FreeNext = gOmInUseList; |
| gOmInUseList = InUseList; |
| gOmInUseCount += InUseTally; |
| } |
| |
| Thread::muxRelease (&ListLock) ; |
| TEVENT (omFlush) ; |
| } |
| |
| // Fast path code shared by multiple functions |
| ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) { |
| markOop mark = obj->mark(); |
| if (mark->has_monitor()) { |
| assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid"); |
| assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header"); |
| return mark->monitor(); |
| } |
| return ObjectSynchronizer::inflate(Thread::current(), obj); |
| } |
| |
| |
| // Note that we could encounter some performance loss through false-sharing as |
| // multiple locks occupy the same $ line. Padding might be appropriate. |
| |
| |
| ObjectMonitor * ATTR ObjectSynchronizer::inflate (Thread * Self, oop object) { |
| // Inflate mutates the heap ... |
| // Relaxing assertion for bug 6320749. |
| assert (Universe::verify_in_progress() || |
| !SafepointSynchronize::is_at_safepoint(), "invariant") ; |
| |
| for (;;) { |
| const markOop mark = object->mark() ; |
| assert (!mark->has_bias_pattern(), "invariant") ; |
| |
| // The mark can be in one of the following states: |
| // * Inflated - just return |
| // * Stack-locked - coerce it to inflated |
| // * INFLATING - busy wait for conversion to complete |
| // * Neutral - aggressively inflate the object. |
| // * BIASED - Illegal. We should never see this |
| |
| // CASE: inflated |
| if (mark->has_monitor()) { |
| ObjectMonitor * inf = mark->monitor() ; |
| assert (inf->header()->is_neutral(), "invariant"); |
| assert (inf->object() == object, "invariant") ; |
| assert (ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid"); |
| return inf ; |
| } |
| |
| // CASE: inflation in progress - inflating over a stack-lock. |
| // Some other thread is converting from stack-locked to inflated. |
| // Only that thread can complete inflation -- other threads must wait. |
| // The INFLATING value is transient. |
| // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish. |
| // We could always eliminate polling by parking the thread on some auxiliary list. |
| if (mark == markOopDesc::INFLATING()) { |
| TEVENT (Inflate: spin while INFLATING) ; |
| ReadStableMark(object) ; |
| continue ; |
| } |
| |
| // CASE: stack-locked |
| // Could be stack-locked either by this thread or by some other thread. |
| // |
| // Note that we allocate the objectmonitor speculatively, _before_ attempting |
| // to install INFLATING into the mark word. We originally installed INFLATING, |
| // allocated the objectmonitor, and then finally STed the address of the |
| // objectmonitor into the mark. This was correct, but artificially lengthened |
| // the interval in which INFLATED appeared in the mark, thus increasing |
| // the odds of inflation contention. |
| // |
| // We now use per-thread private objectmonitor free lists. |
| // These list are reprovisioned from the global free list outside the |
| // critical INFLATING...ST interval. A thread can transfer |
| // multiple objectmonitors en-mass from the global free list to its local free list. |
| // This reduces coherency traffic and lock contention on the global free list. |
| // Using such local free lists, it doesn't matter if the omAlloc() call appears |
| // before or after the CAS(INFLATING) operation. |
| // See the comments in omAlloc(). |
| |
| if (mark->has_locker()) { |
| ObjectMonitor * m = omAlloc (Self) ; |
| // Optimistically prepare the objectmonitor - anticipate successful CAS |
| // We do this before the CAS in order to minimize the length of time |
| // in which INFLATING appears in the mark. |
| m->Recycle(); |
| m->_Responsible = NULL ; |
| m->OwnerIsThread = 0 ; |
| m->_recursions = 0 ; |
| m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // Consider: maintain by type/class |
| |
| markOop cmp = (markOop) Atomic::cmpxchg_ptr (markOopDesc::INFLATING(), object->mark_addr(), mark) ; |
| if (cmp != mark) { |
| omRelease (Self, m, true) ; |
| continue ; // Interference -- just retry |
| } |
| |
| // We've successfully installed INFLATING (0) into the mark-word. |
| // This is the only case where 0 will appear in a mark-work. |
| // Only the singular thread that successfully swings the mark-word |
| // to 0 can perform (or more precisely, complete) inflation. |
| // |
| // Why do we CAS a 0 into the mark-word instead of just CASing the |
| // mark-word from the stack-locked value directly to the new inflated state? |
| // Consider what happens when a thread unlocks a stack-locked object. |
| // It attempts to use CAS to swing the displaced header value from the |
| // on-stack basiclock back into the object header. Recall also that the |
| // header value (hashcode, etc) can reside in (a) the object header, or |
| // (b) a displaced header associated with the stack-lock, or (c) a displaced |
| // header in an objectMonitor. The inflate() routine must copy the header |
| // value from the basiclock on the owner's stack to the objectMonitor, all |
| // the while preserving the hashCode stability invariants. If the owner |
| // decides to release the lock while the value is 0, the unlock will fail |
| // and control will eventually pass from slow_exit() to inflate. The owner |
| // will then spin, waiting for the 0 value to disappear. Put another way, |
| // the 0 causes the owner to stall if the owner happens to try to |
| // drop the lock (restoring the header from the basiclock to the object) |
| // while inflation is in-progress. This protocol avoids races that might |
| // would otherwise permit hashCode values to change or "flicker" for an object. |
| // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable. |
| // 0 serves as a "BUSY" inflate-in-progress indicator. |
| |
| |
| // fetch the displaced mark from the owner's stack. |
| // The owner can't die or unwind past the lock while our INFLATING |
| // object is in the mark. Furthermore the owner can't complete |
| // an unlock on the object, either. |
| markOop dmw = mark->displaced_mark_helper() ; |
| assert (dmw->is_neutral(), "invariant") ; |
| |
| // Setup monitor fields to proper values -- prepare the monitor |
| m->set_header(dmw) ; |
| |
| // Optimization: if the mark->locker stack address is associated |
| // with this thread we could simply set m->_owner = Self and |
| // m->OwnerIsThread = 1. Note that a thread can inflate an object |
| // that it has stack-locked -- as might happen in wait() -- directly |
| // with CAS. That is, we can avoid the xchg-NULL .... ST idiom. |
| m->set_owner(mark->locker()); |
| m->set_object(object); |
| // TODO-FIXME: assert BasicLock->dhw != 0. |
| |
| // Must preserve store ordering. The monitor state must |
| // be stable at the time of publishing the monitor address. |
| guarantee (object->mark() == markOopDesc::INFLATING(), "invariant") ; |
| object->release_set_mark(markOopDesc::encode(m)); |
| |
| // Hopefully the performance counters are allocated on distinct cache lines |
| // to avoid false sharing on MP systems ... |
| if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ; |
| TEVENT(Inflate: overwrite stacklock) ; |
| if (TraceMonitorInflation) { |
| if (object->is_instance()) { |
| ResourceMark rm; |
| tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", |
| (void *) object, (intptr_t) object->mark(), |
| object->klass()->external_name()); |
| } |
| } |
| return m ; |
| } |
| |
| // CASE: neutral |
| // TODO-FIXME: for entry we currently inflate and then try to CAS _owner. |
| // If we know we're inflating for entry it's better to inflate by swinging a |
| // pre-locked objectMonitor pointer into the object header. A successful |
| // CAS inflates the object *and* confers ownership to the inflating thread. |
| // In the current implementation we use a 2-step mechanism where we CAS() |
| // to inflate and then CAS() again to try to swing _owner from NULL to Self. |
| // An inflateTry() method that we could call from fast_enter() and slow_enter() |
| // would be useful. |
| |
| assert (mark->is_neutral(), "invariant"); |
| ObjectMonitor * m = omAlloc (Self) ; |
| // prepare m for installation - set monitor to initial state |
| m->Recycle(); |
| m->set_header(mark); |
| m->set_owner(NULL); |
| m->set_object(object); |
| m->OwnerIsThread = 1 ; |
| m->_recursions = 0 ; |
| m->_Responsible = NULL ; |
| m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // consider: keep metastats by type/class |
| |
| if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) { |
| m->set_object (NULL) ; |
| m->set_owner (NULL) ; |
| m->OwnerIsThread = 0 ; |
| m->Recycle() ; |
| omRelease (Self, m, true) ; |
| m = NULL ; |
| continue ; |
| // interference - the markword changed - just retry. |
| // The state-transitions are one-way, so there's no chance of |
| // live-lock -- "Inflated" is an absorbing state. |
| } |
| |
| // Hopefully the performance counters are allocated on distinct |
| // cache lines to avoid false sharing on MP systems ... |
| if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ; |
| TEVENT(Inflate: overwrite neutral) ; |
| if (TraceMonitorInflation) { |
| if (object->is_instance()) { |
| ResourceMark rm; |
| tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", |
| (void *) object, (intptr_t) object->mark(), |
| object->klass()->external_name()); |
| } |
| } |
| return m ; |
| } |
| } |
| |
| // Note that we could encounter some performance loss through false-sharing as |
| // multiple locks occupy the same $ line. Padding might be appropriate. |
| |
| |
| // Deflate_idle_monitors() is called at all safepoints, immediately |
| // after all mutators are stopped, but before any objects have moved. |
| // It traverses the list of known monitors, deflating where possible. |
| // The scavenged monitor are returned to the monitor free list. |
| // |
| // Beware that we scavenge at *every* stop-the-world point. |
| // Having a large number of monitors in-circulation negatively |
| // impacts the performance of some applications (e.g., PointBase). |
| // Broadly, we want to minimize the # of monitors in circulation. |
| // |
| // We have added a flag, MonitorInUseLists, which creates a list |
| // of active monitors for each thread. deflate_idle_monitors() |
| // only scans the per-thread inuse lists. omAlloc() puts all |
| // assigned monitors on the per-thread list. deflate_idle_monitors() |
| // returns the non-busy monitors to the global free list. |
| // When a thread dies, omFlush() adds the list of active monitors for |
| // that thread to a global gOmInUseList acquiring the |
| // global list lock. deflate_idle_monitors() acquires the global |
| // list lock to scan for non-busy monitors to the global free list. |
| // An alternative could have used a single global inuse list. The |
| // downside would have been the additional cost of acquiring the global list lock |
| // for every omAlloc(). |
| // |
| // Perversely, the heap size -- and thus the STW safepoint rate -- |
| // typically drives the scavenge rate. Large heaps can mean infrequent GC, |
| // which in turn can mean large(r) numbers of objectmonitors in circulation. |
| // This is an unfortunate aspect of this design. |
| // |
| |
| enum ManifestConstants { |
| ClearResponsibleAtSTW = 0, |
| MaximumRecheckInterval = 1000 |
| } ; |
| |
| // Deflate a single monitor if not in use |
| // Return true if deflated, false if in use |
| bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj, |
| ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) { |
| bool deflated; |
| // Normal case ... The monitor is associated with obj. |
| guarantee (obj->mark() == markOopDesc::encode(mid), "invariant") ; |
| guarantee (mid == obj->mark()->monitor(), "invariant"); |
| guarantee (mid->header()->is_neutral(), "invariant"); |
| |
| if (mid->is_busy()) { |
| if (ClearResponsibleAtSTW) mid->_Responsible = NULL ; |
| deflated = false; |
| } else { |
| // Deflate the monitor if it is no longer being used |
| // It's idle - scavenge and return to the global free list |
| // plain old deflation ... |
| TEVENT (deflate_idle_monitors - scavenge1) ; |
| if (TraceMonitorInflation) { |
| if (obj->is_instance()) { |
| ResourceMark rm; |
| tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", |
| (void *) obj, (intptr_t) obj->mark(), obj->klass()->external_name()); |
| } |
| } |
| |
| // Restore the header back to obj |
| obj->release_set_mark(mid->header()); |
| mid->clear(); |
| |
| assert (mid->object() == NULL, "invariant") ; |
| |
| // Move the object to the working free list defined by FreeHead,FreeTail. |
| if (*FreeHeadp == NULL) *FreeHeadp = mid; |
| if (*FreeTailp != NULL) { |
| ObjectMonitor * prevtail = *FreeTailp; |
| assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); // TODO KK |
| prevtail->FreeNext = mid; |
| } |
| *FreeTailp = mid; |
| deflated = true; |
| } |
| return deflated; |
| } |
| |
| // Caller acquires ListLock |
| int ObjectSynchronizer::walk_monitor_list(ObjectMonitor** listheadp, |
| ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) { |
| ObjectMonitor* mid; |
| ObjectMonitor* next; |
| ObjectMonitor* curmidinuse = NULL; |
| int deflatedcount = 0; |
| |
| for (mid = *listheadp; mid != NULL; ) { |
| oop obj = (oop) mid->object(); |
| bool deflated = false; |
| if (obj != NULL) { |
| deflated = deflate_monitor(mid, obj, FreeHeadp, FreeTailp); |
| } |
| if (deflated) { |
| // extract from per-thread in-use-list |
| if (mid == *listheadp) { |
| *listheadp = mid->FreeNext; |
| } else if (curmidinuse != NULL) { |
| curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist |
| } |
| next = mid->FreeNext; |
| mid->FreeNext = NULL; // This mid is current tail in the FreeHead list |
| mid = next; |
| deflatedcount++; |
| } else { |
| curmidinuse = mid; |
| mid = mid->FreeNext; |
| } |
| } |
| return deflatedcount; |
| } |
| |
| void ObjectSynchronizer::deflate_idle_monitors() { |
| assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); |
| int nInuse = 0 ; // currently associated with objects |
| int nInCirculation = 0 ; // extant |
| int nScavenged = 0 ; // reclaimed |
| bool deflated = false; |
| |
| ObjectMonitor * FreeHead = NULL ; // Local SLL of scavenged monitors |
| ObjectMonitor * FreeTail = NULL ; |
| |
| TEVENT (deflate_idle_monitors) ; |
| // Prevent omFlush from changing mids in Thread dtor's during deflation |
| // And in case the vm thread is acquiring a lock during a safepoint |
| // See e.g. 6320749 |
| Thread::muxAcquire (&ListLock, "scavenge - return") ; |
| |
| if (MonitorInUseLists) { |
| int inUse = 0; |
| for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) { |
| nInCirculation+= cur->omInUseCount; |
| int deflatedcount = walk_monitor_list(cur->omInUseList_addr(), &FreeHead, &FreeTail); |
| cur->omInUseCount-= deflatedcount; |
| // verifyInUse(cur); |
| nScavenged += deflatedcount; |
| nInuse += cur->omInUseCount; |
| } |
| |
| // For moribund threads, scan gOmInUseList |
| if (gOmInUseList) { |
| nInCirculation += gOmInUseCount; |
| int deflatedcount = walk_monitor_list((ObjectMonitor **)&gOmInUseList, &FreeHead, &FreeTail); |
| gOmInUseCount-= deflatedcount; |
| nScavenged += deflatedcount; |
| nInuse += gOmInUseCount; |
| } |
| |
| } else for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) { |
| // Iterate over all extant monitors - Scavenge all idle monitors. |
| assert(block->object() == CHAINMARKER, "must be a block header"); |
| nInCirculation += _BLOCKSIZE ; |
| for (int i = 1 ; i < _BLOCKSIZE; i++) { |
| ObjectMonitor* mid = &block[i]; |
| oop obj = (oop) mid->object(); |
| |
| if (obj == NULL) { |
| // The monitor is not associated with an object. |
| // The monitor should either be a thread-specific private |
| // free list or the global free list. |
| // obj == NULL IMPLIES mid->is_busy() == 0 |
| guarantee (!mid->is_busy(), "invariant") ; |
| continue ; |
| } |
| deflated = deflate_monitor(mid, obj, &FreeHead, &FreeTail); |
| |
| if (deflated) { |
| mid->FreeNext = NULL ; |
| nScavenged ++ ; |
| } else { |
| nInuse ++; |
| } |
| } |
| } |
| |
| MonitorFreeCount += nScavenged; |
| |
| // Consider: audit gFreeList to ensure that MonitorFreeCount and list agree. |
| |
| if (ObjectMonitor::Knob_Verbose) { |
| ::printf ("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n", |
| nInCirculation, nInuse, nScavenged, ForceMonitorScavenge, |
| MonitorPopulation, MonitorFreeCount) ; |
| ::fflush(stdout) ; |
| } |
| |
| ForceMonitorScavenge = 0; // Reset |
| |
| // Move the scavenged monitors back to the global free list. |
| if (FreeHead != NULL) { |
| guarantee (FreeTail != NULL && nScavenged > 0, "invariant") ; |
| assert (FreeTail->FreeNext == NULL, "invariant") ; |
| // constant-time list splice - prepend scavenged segment to gFreeList |
| FreeTail->FreeNext = gFreeList ; |
| gFreeList = FreeHead ; |
| } |
| Thread::muxRelease (&ListLock) ; |
| |
| if (ObjectMonitor::_sync_Deflations != NULL) ObjectMonitor::_sync_Deflations->inc(nScavenged) ; |
| if (ObjectMonitor::_sync_MonExtant != NULL) ObjectMonitor::_sync_MonExtant ->set_value(nInCirculation); |
| |
| // TODO: Add objectMonitor leak detection. |
| // Audit/inventory the objectMonitors -- make sure they're all accounted for. |
| GVars.stwRandom = os::random() ; |
| GVars.stwCycle ++ ; |
| } |
| |
| // Monitor cleanup on JavaThread::exit |
| |
| // Iterate through monitor cache and attempt to release thread's monitors |
| // Gives up on a particular monitor if an exception occurs, but continues |
| // the overall iteration, swallowing the exception. |
| class ReleaseJavaMonitorsClosure: public MonitorClosure { |
| private: |
| TRAPS; |
| |
| public: |
| ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {} |
| void do_monitor(ObjectMonitor* mid) { |
| if (mid->owner() == THREAD) { |
| (void)mid->complete_exit(CHECK); |
| } |
| } |
| }; |
| |
| // Release all inflated monitors owned by THREAD. Lightweight monitors are |
| // ignored. This is meant to be called during JNI thread detach which assumes |
| // all remaining monitors are heavyweight. All exceptions are swallowed. |
| // Scanning the extant monitor list can be time consuming. |
| // A simple optimization is to add a per-thread flag that indicates a thread |
| // called jni_monitorenter() during its lifetime. |
| // |
| // Instead of No_Savepoint_Verifier it might be cheaper to |
| // use an idiom of the form: |
| // auto int tmp = SafepointSynchronize::_safepoint_counter ; |
| // <code that must not run at safepoint> |
| // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ; |
| // Since the tests are extremely cheap we could leave them enabled |
| // for normal product builds. |
| |
| void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) { |
| assert(THREAD == JavaThread::current(), "must be current Java thread"); |
| No_Safepoint_Verifier nsv ; |
| ReleaseJavaMonitorsClosure rjmc(THREAD); |
| Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread"); |
| ObjectSynchronizer::monitors_iterate(&rjmc); |
| Thread::muxRelease(&ListLock); |
| THREAD->clear_pending_exception(); |
| } |
| |
| //------------------------------------------------------------------------------ |
| // Debugging code |
| |
| void ObjectSynchronizer::sanity_checks(const bool verbose, |
| const uint cache_line_size, |
| int *error_cnt_ptr, |
| int *warning_cnt_ptr) { |
| u_char *addr_begin = (u_char*)&GVars; |
| u_char *addr_stwRandom = (u_char*)&GVars.stwRandom; |
| u_char *addr_hcSequence = (u_char*)&GVars.hcSequence; |
| |
| if (verbose) { |
| tty->print_cr("INFO: sizeof(SharedGlobals)=" SIZE_FORMAT, |
| sizeof(SharedGlobals)); |
| } |
| |
| uint offset_stwRandom = (uint)(addr_stwRandom - addr_begin); |
| if (verbose) tty->print_cr("INFO: offset(stwRandom)=%u", offset_stwRandom); |
| |
| uint offset_hcSequence = (uint)(addr_hcSequence - addr_begin); |
| if (verbose) { |
| tty->print_cr("INFO: offset(_hcSequence)=%u", offset_hcSequence); |
| } |
| |
| if (cache_line_size != 0) { |
| // We were able to determine the L1 data cache line size so |
| // do some cache line specific sanity checks |
| |
| if (offset_stwRandom < cache_line_size) { |
| tty->print_cr("WARNING: the SharedGlobals.stwRandom field is closer " |
| "to the struct beginning than a cache line which permits " |
| "false sharing."); |
| (*warning_cnt_ptr)++; |
| } |
| |
| if ((offset_hcSequence - offset_stwRandom) < cache_line_size) { |
| tty->print_cr("WARNING: the SharedGlobals.stwRandom and " |
| "SharedGlobals.hcSequence fields are closer than a cache " |
| "line which permits false sharing."); |
| (*warning_cnt_ptr)++; |
| } |
| |
| if ((sizeof(SharedGlobals) - offset_hcSequence) < cache_line_size) { |
| tty->print_cr("WARNING: the SharedGlobals.hcSequence field is closer " |
| "to the struct end than a cache line which permits false " |
| "sharing."); |
| (*warning_cnt_ptr)++; |
| } |
| } |
| } |
| |
| #ifndef PRODUCT |
| |
| // Verify all monitors in the monitor cache, the verification is weak. |
| void ObjectSynchronizer::verify() { |
| ObjectMonitor* block = gBlockList; |
| ObjectMonitor* mid; |
| while (block) { |
| assert(block->object() == CHAINMARKER, "must be a block header"); |
| for (int i = 1; i < _BLOCKSIZE; i++) { |
| mid = block + i; |
| oop object = (oop) mid->object(); |
| if (object != NULL) { |
| mid->verify(); |
| } |
| } |
| block = (ObjectMonitor*) block->FreeNext; |
| } |
| } |
| |
| // Check if monitor belongs to the monitor cache |
| // The list is grow-only so it's *relatively* safe to traverse |
| // the list of extant blocks without taking a lock. |
| |
| int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) { |
| ObjectMonitor* block = gBlockList; |
| |
| while (block) { |
| assert(block->object() == CHAINMARKER, "must be a block header"); |
| if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) { |
| address mon = (address) monitor; |
| address blk = (address) block; |
| size_t diff = mon - blk; |
| assert((diff % sizeof(ObjectMonitor)) == 0, "check"); |
| return 1; |
| } |
| block = (ObjectMonitor*) block->FreeNext; |
| } |
| return 0; |
| } |
| |
| #endif |
