diff -r 4ebc2e2fb97c -r 71c04702a3d5 src/hotspot/share/runtime/synchronizer.cpp --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/hotspot/share/runtime/synchronizer.cpp Tue Sep 12 19:03:39 2017 +0200 @@ -0,0 +1,1989 @@ +/* + * 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 *, 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(-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(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(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(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 * block = + (PaddedEnd *)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 *)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 * block = + (PaddedEnd *)OrderAccess::load_ptr_acquire(&gBlockList); + for (; block != NULL; block = (PaddedEnd *)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) * _BLOCKSIZE; + PaddedEnd * 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 *) + 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 * block = + (PaddedEnd *)OrderAccess::load_ptr_acquire(&gBlockList); + for (; block != NULL; block = (PaddedEnd *)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 ; +// +// 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 * block = + (PaddedEnd *)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)) == 0, "must be aligned"); + return 1; + } + block = (PaddedEnd *)block->FreeNext; + } + return 0; +} + +#endif