| /* |
| * Copyright (c) 1998, 2017, 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 "logging/log.hpp" |
| #include "memory/metaspaceShared.hpp" |
| #include "memory/padded.hpp" |
| #include "memory/resourceArea.hpp" |
| #include "oops/markOop.hpp" |
| #include "oops/oop.inline.hpp" |
| #include "runtime/atomic.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 "runtime/vframe.hpp" |
| #include "trace/traceMacros.hpp" |
| #include "trace/tracing.hpp" |
| #include "utilities/align.hpp" |
| #include "utilities/dtrace.hpp" |
| #include "utilities/events.hpp" |
| #include "utilities/preserveException.hpp" |
| |
| // 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(); \ |
| } |
| |
| #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_notify HOTSPOT_MONITOR_NOTIFY |
| #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL |
| #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); \ |
| } \ |
| } |
| |
| #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 gInflationLocks[NINFLATIONLOCKS]; |
| |
| // global list of blocks of monitors |
| // gBlockList is really PaddedEnd<ObjectMonitor> *, but we don't |
| // want to expose the PaddedEnd template more than necessary. |
| ObjectMonitor * volatile ObjectSynchronizer::gBlockList = NULL; |
| // global monitor free list |
| ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL; |
| // global monitor in-use list, for moribund threads, |
| // monitors they inflated need to be scanned for deflation |
| ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL; |
| // count of entries in gOmInUseList |
| int ObjectSynchronizer::gOmInUseCount = 0; |
| |
| static volatile intptr_t gListLock = 0; // protects global monitor lists |
| static volatile int gMonitorFreeCount = 0; // # on gFreeList |
| static volatile int gMonitorPopulation = 0; // # Extant -- in circulation |
| |
| static void post_monitor_inflate_event(EventJavaMonitorInflate&, |
| const oop, |
| const ObjectSynchronizer::InflateCause); |
| |
| #define CHAINMARKER (cast_to_oop<intptr_t>(-1)) |
| |
| |
| // =====================> Quick functions |
| |
| // The quick_* forms are special fast-path variants used to improve |
| // performance. In the simplest case, a "quick_*" implementation could |
| // simply return false, in which case the caller will perform the necessary |
| // state transitions and call the slow-path form. |
| // The fast-path is designed to handle frequently arising cases in an efficient |
| // manner and is just a degenerate "optimistic" variant of the slow-path. |
| // returns true -- to indicate the call was satisfied. |
| // returns false -- to indicate the call needs the services of the slow-path. |
| // A no-loitering ordinance is in effect for code in the quick_* family |
| // operators: safepoints or indefinite blocking (blocking that might span a |
| // safepoint) are forbidden. Generally the thread_state() is _in_Java upon |
| // entry. |
| // |
| // Consider: An interesting optimization is to have the JIT recognize the |
| // following common idiom: |
| // synchronized (someobj) { .... ; notify(); } |
| // That is, we find a notify() or notifyAll() call that immediately precedes |
| // the monitorexit operation. In that case the JIT could fuse the operations |
| // into a single notifyAndExit() runtime primitive. |
| |
| bool ObjectSynchronizer::quick_notify(oopDesc * obj, Thread * self, bool all) { |
| assert(!SafepointSynchronize::is_at_safepoint(), "invariant"); |
| assert(self->is_Java_thread(), "invariant"); |
| assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant"); |
| NoSafepointVerifier nsv; |
| if (obj == NULL) return false; // slow-path for invalid obj |
| const markOop mark = obj->mark(); |
| |
| if (mark->has_locker() && self->is_lock_owned((address)mark->locker())) { |
| // Degenerate notify |
| // stack-locked by caller so by definition the implied waitset is empty. |
| return true; |
| } |
| |
| if (mark->has_monitor()) { |
| ObjectMonitor * const mon = mark->monitor(); |
| assert(mon->object() == obj, "invariant"); |
| if (mon->owner() != self) return false; // slow-path for IMS exception |
| |
| if (mon->first_waiter() != NULL) { |
| // We have one or more waiters. Since this is an inflated monitor |
| // that we own, we can transfer one or more threads from the waitset |
| // to the entrylist here and now, avoiding the slow-path. |
| if (all) { |
| DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self); |
| } else { |
| DTRACE_MONITOR_PROBE(notify, mon, obj, self); |
| } |
| int tally = 0; |
| do { |
| mon->INotify(self); |
| ++tally; |
| } while (mon->first_waiter() != NULL && all); |
| OM_PERFDATA_OP(Notifications, inc(tally)); |
| } |
| return true; |
| } |
| |
| // biased locking and any other IMS exception states take the slow-path |
| return false; |
| } |
| |
| |
| // The LockNode emitted directly at the synchronization site would have |
| // been too big if it were to have included support for the cases of inflated |
| // recursive enter and exit, so they go here instead. |
| // Note that we can't safely call AsyncPrintJavaStack() from within |
| // quick_enter() as our thread state remains _in_Java. |
| |
| bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self, |
| BasicLock * lock) { |
| assert(!SafepointSynchronize::is_at_safepoint(), "invariant"); |
| assert(Self->is_Java_thread(), "invariant"); |
| assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant"); |
| NoSafepointVerifier nsv; |
| if (obj == NULL) return false; // Need to throw NPE |
| const markOop mark = obj->mark(); |
| |
| if (mark->has_monitor()) { |
| ObjectMonitor * const m = mark->monitor(); |
| assert(m->object() == obj, "invariant"); |
| Thread * const owner = (Thread *) m->_owner; |
| |
| // Lock contention and Transactional Lock Elision (TLE) diagnostics |
| // and observability |
| // Case: light contention possibly amenable to TLE |
| // Case: TLE inimical operations such as nested/recursive synchronization |
| |
| if (owner == Self) { |
| m->_recursions++; |
| return true; |
| } |
| |
| // This Java Monitor is inflated so obj's header will never be |
| // displaced to this thread's BasicLock. Make the displaced header |
| // non-NULL so this BasicLock is not seen as recursive nor as |
| // being locked. We do this unconditionally so that this thread's |
| // BasicLock cannot be mis-interpreted by any stack walkers. For |
| // performance reasons, stack walkers generally first check for |
| // Biased Locking in the object's header, the second check is for |
| // stack-locking in the object's header, the third check is for |
| // recursive stack-locking in the displaced header in the BasicLock, |
| // and last are the inflated Java Monitor (ObjectMonitor) checks. |
| lock->set_displaced_header(markOopDesc::unused_mark()); |
| |
| if (owner == NULL && |
| Atomic::cmpxchg_ptr(Self, &(m->_owner), NULL) == NULL) { |
| assert(m->_recursions == 0, "invariant"); |
| assert(m->_owner == Self, "invariant"); |
| return true; |
| } |
| } |
| |
| // Note that we could inflate in quick_enter. |
| // This is likely a useful optimization |
| // Critically, in quick_enter() we must not: |
| // -- perform bias revocation, or |
| // -- block indefinitely, or |
| // -- reach a safepoint |
| |
| return false; // revert to slow-path |
| } |
| |
| // ----------------------------------------------------------------------------- |
| // 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) { |
| markOop mark = object->mark(); |
| // We cannot check for Biased Locking if we are racing an inflation. |
| assert(mark == markOopDesc::INFLATING() || |
| !mark->has_bias_pattern(), "should not see bias pattern here"); |
| |
| markOop dhw = lock->displaced_header(); |
| if (dhw == NULL) { |
| // If the displaced header is NULL, then this exit matches up with |
| // a recursive enter. No real work to do here except for diagnostics. |
| #ifndef PRODUCT |
| if (mark != markOopDesc::INFLATING()) { |
| // Only do diagnostics if we are not racing an inflation. Simply |
| // exiting a recursive enter of a Java Monitor that is being |
| // inflated is safe; see the has_monitor() comment below. |
| assert(!mark->is_neutral(), "invariant"); |
| assert(!mark->has_locker() || |
| THREAD->is_lock_owned((address)mark->locker()), "invariant"); |
| if (mark->has_monitor()) { |
| // The BasicLock's displaced_header is marked as a recursive |
| // enter and we have an inflated Java Monitor (ObjectMonitor). |
| // This is a special case where the Java Monitor was inflated |
| // after this thread entered the stack-lock recursively. When a |
| // Java Monitor is inflated, we cannot safely walk the Java |
| // Monitor owner's stack and update the BasicLocks because a |
| // Java Monitor can be asynchronously inflated by a thread that |
| // does not own the Java Monitor. |
| ObjectMonitor * m = mark->monitor(); |
| assert(((oop)(m->object()))->mark() == mark, "invariant"); |
| assert(m->is_entered(THREAD), "invariant"); |
| } |
| } |
| #endif |
| return; |
| } |
| |
| if (mark == (markOop) lock) { |
| // If the object is stack-locked by the current thread, try to |
| // swing the displaced header from the BasicLock back to the mark. |
| assert(dhw->is_neutral(), "invariant"); |
| if (object->cas_set_mark(dhw, mark) == mark) { |
| TEVENT(fast_exit: release stack-lock); |
| return; |
| } |
| } |
| |
| // We have to take the slow-path of possible inflation and then exit. |
| ObjectSynchronizer::inflate(THREAD, |
| object, |
| inflate_cause_vm_internal)->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 == obj()->cas_set_mark((markOop) lock, 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; |
| } |
| |
| // 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(), |
| inflate_cause_monitor_enter)->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(), |
| inflate_cause_vm_internal); |
| |
| 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(), |
| inflate_cause_vm_internal); |
| |
| 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) { |
| // 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(), inflate_cause_jni_enter)->enter(THREAD); |
| THREAD->set_current_pending_monitor_is_from_java(true); |
| } |
| |
| // 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, |
| inflate_cause_jni_exit); |
| // 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() |
| int 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_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); |
| } |
| ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, |
| obj(), |
| inflate_cause_wait); |
| |
| 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, remove the call |
| // and change this function back into a "void" func. |
| // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD); |
| return 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(), |
| inflate_cause_wait)->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(), |
| inflate_cause_notify)->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(), |
| inflate_cause_notify)->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 { |
| char _pad_prefix[DEFAULT_CACHE_LINE_SIZE]; |
| // These are highly shared mostly-read variables. |
| // To avoid false-sharing they need to be the sole occupants of a cache line. |
| volatile int stwRandom; |
| volatile int stwCycle; |
| DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2); |
| // Hot RW variable -- Sequester to avoid false-sharing |
| volatile int hcSequence; |
| DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int)); |
| }; |
| |
| 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::naked_yield(); |
| 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(gInflationLocks + ix, "gInflationLock"); |
| 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::naked_yield(); |
| } |
| } |
| Thread::muxRelease(gInflationLocks + 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 global Park-Miller 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()) { |
| // Handle for oop obj in case of 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() || DumpSharedSpaces || |
| !SafepointSynchronize::is_at_safepoint(), "invariant"); |
| assert(Universe::verify_in_progress() || DumpSharedSpaces || |
| Self->is_Java_thread() , "invariant"); |
| assert(Universe::verify_in_progress() || DumpSharedSpaces || |
| ((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 = obj->cas_set_mark(temp, 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, inflate_cause_hash_code); |
| // 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 queries 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 |
| // owner_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) { |
| PaddedEnd<ObjectMonitor> * block = |
| (PaddedEnd<ObjectMonitor> *)OrderAccess::load_ptr_acquire(&gBlockList); |
| while (block != NULL) { |
| assert(block->object() == CHAINMARKER, "must be a block header"); |
| for (int i = _BLOCKSIZE - 1; i > 0; i--) { |
| ObjectMonitor* mid = (ObjectMonitor *)(block + i); |
| oop object = (oop)mid->object(); |
| if (object != NULL) { |
| closure->do_monitor(mid); |
| } |
| } |
| block = (PaddedEnd<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; |
| } |
| |
| static bool monitors_used_above_threshold() { |
| if (gMonitorPopulation == 0) { |
| return false; |
| } |
| int monitors_used = gMonitorPopulation - gMonitorFreeCount; |
| int monitor_usage = (monitors_used * 100LL) / gMonitorPopulation; |
| return monitor_usage > MonitorUsedDeflationThreshold; |
| } |
| |
| bool ObjectSynchronizer::is_cleanup_needed() { |
| if (MonitorUsedDeflationThreshold > 0) { |
| return monitors_used_above_threshold(); |
| } |
| return false; |
| } |
| |
| void ObjectSynchronizer::oops_do(OopClosure* f) { |
| if (MonitorInUseLists) { |
| // When using thread local monitor lists, we only scan the |
| // global used list here (for moribund threads), and |
| // the thread-local monitors in Thread::oops_do(). |
| global_used_oops_do(f); |
| } else { |
| global_oops_do(f); |
| } |
| } |
| |
| void ObjectSynchronizer::global_oops_do(OopClosure* f) { |
| assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); |
| PaddedEnd<ObjectMonitor> * block = |
| (PaddedEnd<ObjectMonitor> *)OrderAccess::load_ptr_acquire(&gBlockList); |
| for (; block != NULL; block = (PaddedEnd<ObjectMonitor> *)next(block)) { |
| assert(block->object() == CHAINMARKER, "must be a block header"); |
| for (int i = 1; i < _BLOCKSIZE; i++) { |
| ObjectMonitor* mid = (ObjectMonitor *)&block[i]; |
| if (mid->object() != NULL) { |
| f->do_oop((oop*)mid->object_addr()); |
| } |
| } |
| } |
| } |
| |
| void ObjectSynchronizer::global_used_oops_do(OopClosure* f) { |
| assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); |
| list_oops_do(gOmInUseList, f); |
| } |
| |
| void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) { |
| assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); |
| list_oops_do(thread->omInUseList, f); |
| } |
| |
| void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) { |
| assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); |
| ObjectMonitor* mid; |
| for (mid = list; mid != NULL; mid = mid->FreeNext) { |
| 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 gListLock. 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) { |
| tty->print_cr("INFO: Monitor scavenge - Induced STW @%s (%d)", |
| Whence, ForceMonitorScavenge) ; |
| tty->flush(); |
| } |
| // 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_ScavengeMonitors()); |
| |
| if (ObjectMonitor::Knob_Verbose) { |
| tty->print_cr("INFO: Monitor scavenge - STW posted @%s (%d)", |
| Whence, ForceMonitorScavenge) ; |
| tty->flush(); |
| } |
| } |
| } |
| |
| void ObjectSynchronizer::verifyInUse(Thread *Self) { |
| ObjectMonitor* mid; |
| int in_use_tally = 0; |
| for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) { |
| in_use_tally++; |
| } |
| assert(in_use_tally == Self->omInUseCount, "in-use count off"); |
| |
| int free_tally = 0; |
| for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) { |
| free_tally++; |
| } |
| assert(free_tally == Self->omFreeCount, "free count off"); |
| } |
| |
| ObjectMonitor* 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 gListLock 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++; |
| if (ObjectMonitor::Knob_VerifyInUse) { |
| 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(&gListLock, "omAlloc"); |
| for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) { |
| gMonitorFreeCount--; |
| ObjectMonitor * take = gFreeList; |
| gFreeList = take->FreeNext; |
| guarantee(take->object() == NULL, "invariant"); |
| guarantee(!take->is_busy(), "invariant"); |
| take->Recycle(); |
| omRelease(Self, take, false); |
| } |
| Thread::muxRelease(&gListLock); |
| Self->omFreeProvision += 1 + (Self->omFreeProvision/2); |
| if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE; |
| TEVENT(omFirst - reprovision); |
| |
| const int mx = MonitorBound; |
| if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > 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. |
| // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want |
| // each ObjectMonitor to start at the beginning of a cache line, |
| // so we use align_up(). |
| // A better solution would be to use C++ placement-new. |
| // BEWARE: As it stands currently, we don't run the ctors! |
| assert(_BLOCKSIZE > 1, "invariant"); |
| size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE; |
| PaddedEnd<ObjectMonitor> * temp; |
| size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1); |
| void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size, |
| mtInternal); |
| temp = (PaddedEnd<ObjectMonitor> *) |
| align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE); |
| |
| // 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(neededsize, OOM_MALLOC_ERROR, |
| "Allocate ObjectMonitors"); |
| } |
| (void)memset((void *) temp, 0, neededsize); |
| |
| // 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 = (ObjectMonitor *)&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 gListLock to manipulate gBlockList and gFreeList. |
| // An Oyama-Taura-Yonezawa scheme might be more efficient. |
| Thread::muxAcquire(&gListLock, "omAlloc [2]"); |
| gMonitorPopulation += _BLOCKSIZE-1; |
| gMonitorFreeCount += _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; |
| // There are lock-free uses of gBlockList so make sure that |
| // the previous stores happen before we update gBlockList. |
| OrderAccess::release_store_ptr(&gBlockList, temp); |
| |
| // Add the new string of objectMonitors to the global free list |
| temp[_BLOCKSIZE - 1].FreeNext = gFreeList; |
| gFreeList = temp + 1; |
| Thread::muxRelease(&gListLock); |
| 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. |
| // |
| // Key constraint: all ObjectMonitors on a thread's free list and the global |
| // free list must have their object field set to null. This prevents the |
| // scavenger -- deflate_idle_monitors -- from reclaiming them. |
| |
| void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m, |
| bool fromPerThreadAlloc) { |
| guarantee(m->object() == NULL, "invariant"); |
| guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor"); |
| // Remove from omInUseList |
| if (MonitorInUseLists && fromPerThreadAlloc) { |
| ObjectMonitor* cur_mid_in_use = NULL; |
| bool extracted = false; |
| for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) { |
| if (m == mid) { |
| // extract from per-thread in-use list |
| if (mid == Self->omInUseList) { |
| Self->omInUseList = mid->FreeNext; |
| } else if (cur_mid_in_use != NULL) { |
| cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list |
| } |
| extracted = true; |
| Self->omInUseCount--; |
| if (ObjectMonitor::Knob_VerifyInUse) { |
| verifyInUse(Self); |
| } |
| break; |
| } |
| } |
| assert(extracted, "Should have extracted from in-use list"); |
| } |
| |
| // FreeNext is used for both omInUseList 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 Threads::remove() _before the thread |
| // has been excised from the thread list and is no longer a mutator. |
| // This means that omFlush() can not run concurrently with a safepoint and |
| // interleave with the scavenge operator. In particular, this ensures that |
| // the thread's monitors are scanned by a GC safepoint, either via |
| // Thread::oops_do() (if safepoint happens before omFlush()) or via |
| // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's |
| // monitors have been transferred to the global in-use list). |
| |
| 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; |
| // The thread is going away, the per-thread free monitors |
| // are freed via set_owner(NULL) |
| // Link them to tail, which will be linked into the global free list |
| // gFreeList below, under the gListLock |
| 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 *cur_om; |
| // The thread is going away, however the omInUseList inflated |
| // monitors may still be in-use by other threads. |
| // Link them to inUseTail, which will be linked into the global in-use list |
| // gOmInUseList below, under the gListLock |
| for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) { |
| inUseTail = cur_om; |
| inUseTally++; |
| } |
| assert(Self->omInUseCount == inUseTally, "in-use count off"); |
| Self->omInUseCount = 0; |
| guarantee(inUseTail != NULL && inUseList != NULL, "invariant"); |
| } |
| |
| Thread::muxAcquire(&gListLock, "omFlush"); |
| if (tail != NULL) { |
| tail->FreeNext = gFreeList; |
| gFreeList = list; |
| gMonitorFreeCount += tally; |
| assert(Self->omFreeCount == tally, "free-count off"); |
| Self->omFreeCount = 0; |
| } |
| |
| if (inUseTail != NULL) { |
| inUseTail->FreeNext = gOmInUseList; |
| gOmInUseList = inUseList; |
| gOmInUseCount += inUseTally; |
| } |
| |
| Thread::muxRelease(&gListLock); |
| 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, |
| inflate_cause_vm_internal); |
| } |
| |
| ObjectMonitor* ObjectSynchronizer::inflate(Thread * Self, |
| oop object, |
| const InflateCause cause) { |
| |
| // Inflate mutates the heap ... |
| // Relaxing assertion for bug 6320749. |
| assert(Universe::verify_in_progress() || |
| !SafepointSynchronize::is_at_safepoint(), "invariant"); |
| |
| EventJavaMonitorInflate event; |
| |
| 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->_recursions = 0; |
| m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class |
| |
| markOop cmp = object->cas_set_mark(markOopDesc::INFLATING(), 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-word. |
| // 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. |
| // 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 ... |
| OM_PERFDATA_OP(Inflations, inc()); |
| TEVENT(Inflate: overwrite stacklock); |
| if (log_is_enabled(Debug, monitorinflation)) { |
| if (object->is_instance()) { |
| ResourceMark rm; |
| log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", |
| p2i(object), p2i(object->mark()), |
| object->klass()->external_name()); |
| } |
| } |
| if (event.should_commit()) { |
| post_monitor_inflate_event(event, object, cause); |
| } |
| 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->_recursions = 0; |
| m->_Responsible = NULL; |
| m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class |
| |
| if (object->cas_set_mark(markOopDesc::encode(m), mark) != mark) { |
| m->set_object(NULL); |
| m->set_owner(NULL); |
| 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 ... |
| OM_PERFDATA_OP(Inflations, inc()); |
| TEVENT(Inflate: overwrite neutral); |
| if (log_is_enabled(Debug, monitorinflation)) { |
| if (object->is_instance()) { |
| ResourceMark rm; |
| log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", |
| p2i(object), p2i(object->mark()), |
| object->klass()->external_name()); |
| } |
| } |
| if (event.should_commit()) { |
| post_monitor_inflate_event(event, object, cause); |
| } |
| return m; |
| } |
| } |
| |
| |
| // 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 in-use 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 in-use 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 |
| }; |
| |
| // 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 (log_is_enabled(Debug, monitorinflation)) { |
| if (obj->is_instance()) { |
| ResourceMark rm; |
| log_debug(monitorinflation)("Deflating object " INTPTR_FORMAT " , " |
| "mark " INTPTR_FORMAT " , type %s", |
| p2i(obj), p2i(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 freeHeadp, freeTailp |
| if (*freeHeadp == NULL) *freeHeadp = mid; |
| if (*freeTailp != NULL) { |
| ObjectMonitor * prevtail = *freeTailp; |
| assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); |
| prevtail->FreeNext = mid; |
| } |
| *freeTailp = mid; |
| deflated = true; |
| } |
| return deflated; |
| } |
| |
| // Walk a given monitor list, and deflate idle monitors |
| // The given list could be a per-thread list or a global list |
| // Caller acquires gListLock. |
| // |
| // In the case of parallel processing of thread local monitor lists, |
| // work is done by Threads::parallel_threads_do() which ensures that |
| // each Java thread is processed by exactly one worker thread, and |
| // thus avoid conflicts that would arise when worker threads would |
| // process the same monitor lists concurrently. |
| // |
| // See also ParallelSPCleanupTask and |
| // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and |
| // Threads::parallel_java_threads_do() in thread.cpp. |
| int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp, |
| ObjectMonitor** freeHeadp, |
| ObjectMonitor** freeTailp) { |
| ObjectMonitor* mid; |
| ObjectMonitor* next; |
| ObjectMonitor* cur_mid_in_use = NULL; |
| int deflated_count = 0; |
| |
| for (mid = *listHeadp; mid != NULL;) { |
| oop obj = (oop) mid->object(); |
| if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) { |
| // if deflate_monitor succeeded, |
| // extract from per-thread in-use list |
| if (mid == *listHeadp) { |
| *listHeadp = mid->FreeNext; |
| } else if (cur_mid_in_use != NULL) { |
| cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list |
| } |
| next = mid->FreeNext; |
| mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list |
| mid = next; |
| deflated_count++; |
| } else { |
| cur_mid_in_use = mid; |
| mid = mid->FreeNext; |
| } |
| } |
| return deflated_count; |
| } |
| |
| void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) { |
| counters->nInuse = 0; // currently associated with objects |
| counters->nInCirculation = 0; // extant |
| counters->nScavenged = 0; // reclaimed |
| } |
| |
| void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) { |
| assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); |
| bool deflated = false; |
| |
| ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors |
| ObjectMonitor * freeTailp = 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(&gListLock, "scavenge - return"); |
| |
| if (MonitorInUseLists) { |
| // Note: the thread-local monitors lists get deflated in |
| // a separate pass. See deflate_thread_local_monitors(). |
| |
| // For moribund threads, scan gOmInUseList |
| if (gOmInUseList) { |
| counters->nInCirculation += gOmInUseCount; |
| int deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp); |
| gOmInUseCount -= deflated_count; |
| counters->nScavenged += deflated_count; |
| counters->nInuse += gOmInUseCount; |
| } |
| |
| } else { |
| PaddedEnd<ObjectMonitor> * block = |
| (PaddedEnd<ObjectMonitor> *)OrderAccess::load_ptr_acquire(&gBlockList); |
| for (; block != NULL; block = (PaddedEnd<ObjectMonitor> *)next(block)) { |
| // Iterate over all extant monitors - Scavenge all idle monitors. |
| assert(block->object() == CHAINMARKER, "must be a block header"); |
| counters->nInCirculation += _BLOCKSIZE; |
| for (int i = 1; i < _BLOCKSIZE; i++) { |
| ObjectMonitor* mid = (ObjectMonitor*)&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, &freeHeadp, &freeTailp); |
| |
| if (deflated) { |
| mid->FreeNext = NULL; |
| counters->nScavenged++; |
| } else { |
| counters->nInuse++; |
| } |
| } |
| } |
| } |
| |
| // Move the scavenged monitors back to the global free list. |
| if (freeHeadp != NULL) { |
| guarantee(freeTailp != NULL && counters->nScavenged > 0, "invariant"); |
| assert(freeTailp->FreeNext == NULL, "invariant"); |
| // constant-time list splice - prepend scavenged segment to gFreeList |
| freeTailp->FreeNext = gFreeList; |
| gFreeList = freeHeadp; |
| } |
| Thread::muxRelease(&gListLock); |
| |
| } |
| |
| void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) { |
| gMonitorFreeCount += counters->nScavenged; |
| |
| // Consider: audit gFreeList to ensure that gMonitorFreeCount and list agree. |
| |
| if (ObjectMonitor::Knob_Verbose) { |
| tty->print_cr("INFO: Deflate: InCirc=%d InUse=%d Scavenged=%d " |
| "ForceMonitorScavenge=%d : pop=%d free=%d", |
| counters->nInCirculation, counters->nInuse, counters->nScavenged, ForceMonitorScavenge, |
| gMonitorPopulation, gMonitorFreeCount); |
| tty->flush(); |
| } |
| |
| ForceMonitorScavenge = 0; // Reset |
| |
| OM_PERFDATA_OP(Deflations, inc(counters->nScavenged)); |
| OM_PERFDATA_OP(MonExtant, set_value(counters->nInCirculation)); |
| |
| // TODO: Add objectMonitor leak detection. |
| // Audit/inventory the objectMonitors -- make sure they're all accounted for. |
| GVars.stwRandom = os::random(); |
| GVars.stwCycle++; |
| } |
| |
| void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) { |
| assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); |
| if (!MonitorInUseLists) return; |
| |
| ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors |
| ObjectMonitor * freeTailp = NULL; |
| |
| int deflated_count = deflate_monitor_list(thread->omInUseList_addr(), &freeHeadp, &freeTailp); |
| |
| Thread::muxAcquire(&gListLock, "scavenge - return"); |
| |
| // Adjust counters |
| counters->nInCirculation += thread->omInUseCount; |
| thread->omInUseCount -= deflated_count; |
| if (ObjectMonitor::Knob_VerifyInUse) { |
| verifyInUse(thread); |
| } |
| counters->nScavenged += deflated_count; |
| counters->nInuse += thread->omInUseCount; |
| |
| // Move the scavenged monitors back to the global free list. |
| if (freeHeadp != NULL) { |
| guarantee(freeTailp != NULL && deflated_count > 0, "invariant"); |
| assert(freeTailp->FreeNext == NULL, "invariant"); |
| |
| // constant-time list splice - prepend scavenged segment to gFreeList |
| freeTailp->FreeNext = gFreeList; |
| gFreeList = freeHeadp; |
| } |
| Thread::muxRelease(&gListLock); |
| } |
| |
| // 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) { |
| if (ObjectMonitor::Knob_VerifyMatch != 0) { |
| ResourceMark rm; |
| Handle obj(THREAD, (oop) mid->object()); |
| tty->print("INFO: unexpected locked object:"); |
| javaVFrame::print_locked_object_class_name(tty, obj, "locked"); |
| fatal("exiting JavaThread=" INTPTR_FORMAT |
| " unexpectedly owns ObjectMonitor=" INTPTR_FORMAT, |
| p2i(THREAD), p2i(mid)); |
| } |
| (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"); |
| NoSafepointVerifier nsv; |
| ReleaseJavaMonitorsClosure rjmc(THREAD); |
| Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread"); |
| ObjectSynchronizer::monitors_iterate(&rjmc); |
| Thread::muxRelease(&gListLock); |
| THREAD->clear_pending_exception(); |
| } |
| |
| const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) { |
| switch (cause) { |
| case inflate_cause_vm_internal: return "VM Internal"; |
| case inflate_cause_monitor_enter: return "Monitor Enter"; |
| case inflate_cause_wait: return "Monitor Wait"; |
| case inflate_cause_notify: return "Monitor Notify"; |
| case inflate_cause_hash_code: return "Monitor Hash Code"; |
| case inflate_cause_jni_enter: return "JNI Monitor Enter"; |
| case inflate_cause_jni_exit: return "JNI Monitor Exit"; |
| default: |
| ShouldNotReachHere(); |
| } |
| return "Unknown"; |
| } |
| |
| static void post_monitor_inflate_event(EventJavaMonitorInflate& event, |
| const oop obj, |
| const ObjectSynchronizer::InflateCause cause) { |
| #if INCLUDE_TRACE |
| assert(event.should_commit(), "check outside"); |
| event.set_monitorClass(obj->klass()); |
| event.set_address((TYPE_ADDRESS)(uintptr_t)(void*)obj); |
| event.set_cause((u1)cause); |
| event.commit(); |
| #endif |
| } |
| |
| //------------------------------------------------------------------------------ |
| // 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 |
| |
| // 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) { |
| PaddedEnd<ObjectMonitor> * block = |
| (PaddedEnd<ObjectMonitor> *)OrderAccess::load_ptr_acquire(&gBlockList); |
| while (block != NULL) { |
| assert(block->object() == CHAINMARKER, "must be a block header"); |
| if (monitor > (ObjectMonitor *)&block[0] && |
| monitor < (ObjectMonitor *)&block[_BLOCKSIZE]) { |
| address mon = (address)monitor; |
| address blk = (address)block; |
| size_t diff = mon - blk; |
| assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "must be aligned"); |
| return 1; |
| } |
| block = (PaddedEnd<ObjectMonitor> *)block->FreeNext; |
| } |
| return 0; |
| } |
| |
| #endif |