--- /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<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