1 /*
2 * Copyright (c) 1998, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/vmSymbols.hpp"
27 #include "logging/log.hpp"
28 #include "logging/logStream.hpp"
29 #include "jfr/jfrEvents.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "memory/metaspaceShared.hpp"
32 #include "memory/padded.hpp"
33 #include "memory/resourceArea.hpp"
34 #include "memory/universe.hpp"
35 #include "oops/markWord.hpp"
36 #include "oops/oop.inline.hpp"
37 #include "runtime/atomic.hpp"
38 #include "runtime/biasedLocking.hpp"
39 #include "runtime/handles.inline.hpp"
40 #include "runtime/interfaceSupport.inline.hpp"
41 #include "runtime/mutexLocker.hpp"
42 #include "runtime/objectMonitor.hpp"
43 #include "runtime/objectMonitor.inline.hpp"
44 #include "runtime/osThread.hpp"
45 #include "runtime/safepointVerifiers.hpp"
46 #include "runtime/sharedRuntime.hpp"
47 #include "runtime/stubRoutines.hpp"
48 #include "runtime/synchronizer.hpp"
49 #include "runtime/thread.inline.hpp"
50 #include "runtime/timer.hpp"
51 #include "runtime/vframe.hpp"
52 #include "runtime/vmThread.hpp"
53 #include "utilities/align.hpp"
54 #include "utilities/dtrace.hpp"
55 #include "utilities/events.hpp"
56 #include "utilities/preserveException.hpp"
57
58 // The "core" versions of monitor enter and exit reside in this file.
59 // The interpreter and compilers contain specialized transliterated
60 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
61 // for instance. If you make changes here, make sure to modify the
62 // interpreter, and both C1 and C2 fast-path inline locking code emission.
63 //
64 // -----------------------------------------------------------------------------
65
66 #ifdef DTRACE_ENABLED
67
68 // Only bother with this argument setup if dtrace is available
69 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
70
71 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
72 char* bytes = NULL; \
73 int len = 0; \
74 jlong jtid = SharedRuntime::get_java_tid(thread); \
75 Symbol* klassname = ((oop)(obj))->klass()->name(); \
76 if (klassname != NULL) { \
77 bytes = (char*)klassname->bytes(); \
78 len = klassname->utf8_length(); \
79 }
80
81 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
82 { \
83 if (DTraceMonitorProbes) { \
84 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
85 HOTSPOT_MONITOR_WAIT(jtid, \
86 (uintptr_t)(monitor), bytes, len, (millis)); \
87 } \
88 }
89
90 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
91 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
92 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
93
94 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
95 { \
96 if (DTraceMonitorProbes) { \
97 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
98 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
99 (uintptr_t)(monitor), bytes, len); \
100 } \
101 }
102
103 #else // ndef DTRACE_ENABLED
104
105 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
106 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
107
108 #endif // ndef DTRACE_ENABLED
109
110 // This exists only as a workaround of dtrace bug 6254741
111 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
112 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
113 return 0;
114 }
115
116 #define NINFLATIONLOCKS 256
117 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
118
119 // global list of blocks of monitors
120 PaddedEnd<ObjectMonitor> * volatile ObjectSynchronizer::gBlockList = NULL;
121 // global monitor free list
122 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL;
123 // global monitor in-use list, for moribund threads,
124 // monitors they inflated need to be scanned for deflation
125 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL;
126 // count of entries in gOmInUseList
127 int ObjectSynchronizer::gOmInUseCount = 0;
128
129 static volatile intptr_t gListLock = 0; // protects global monitor lists
130 static volatile int gMonitorFreeCount = 0; // # on gFreeList
131 static volatile int gMonitorPopulation = 0; // # Extant -- in circulation
132
133 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
134
135
136 // =====================> Quick functions
137
138 // The quick_* forms are special fast-path variants used to improve
139 // performance. In the simplest case, a "quick_*" implementation could
140 // simply return false, in which case the caller will perform the necessary
141 // state transitions and call the slow-path form.
142 // The fast-path is designed to handle frequently arising cases in an efficient
143 // manner and is just a degenerate "optimistic" variant of the slow-path.
144 // returns true -- to indicate the call was satisfied.
145 // returns false -- to indicate the call needs the services of the slow-path.
146 // A no-loitering ordinance is in effect for code in the quick_* family
147 // operators: safepoints or indefinite blocking (blocking that might span a
148 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
149 // entry.
150 //
151 // Consider: An interesting optimization is to have the JIT recognize the
152 // following common idiom:
153 // synchronized (someobj) { .... ; notify(); }
154 // That is, we find a notify() or notifyAll() call that immediately precedes
155 // the monitorexit operation. In that case the JIT could fuse the operations
156 // into a single notifyAndExit() runtime primitive.
157
158 bool ObjectSynchronizer::quick_notify(oopDesc * obj, Thread * self, bool all) {
159 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
160 assert(self->is_Java_thread(), "invariant");
161 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
162 NoSafepointVerifier nsv;
163 if (obj == NULL) return false; // slow-path for invalid obj
164 const markWord mark = obj->mark();
165
166 if (mark.has_locker() && self->is_lock_owned((address)mark.locker())) {
167 // Degenerate notify
168 // stack-locked by caller so by definition the implied waitset is empty.
169 return true;
170 }
171
172 if (mark.has_monitor()) {
173 ObjectMonitor * const mon = mark.monitor();
174 assert(oopDesc::equals((oop) mon->object(), obj), "invariant");
175 if (mon->owner() != self) return false; // slow-path for IMS exception
176
177 if (mon->first_waiter() != NULL) {
178 // We have one or more waiters. Since this is an inflated monitor
179 // that we own, we can transfer one or more threads from the waitset
180 // to the entrylist here and now, avoiding the slow-path.
181 if (all) {
182 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
183 } else {
184 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
185 }
186 int tally = 0;
187 do {
188 mon->INotify(self);
189 ++tally;
190 } while (mon->first_waiter() != NULL && all);
191 OM_PERFDATA_OP(Notifications, inc(tally));
192 }
193 return true;
194 }
195
196 // biased locking and any other IMS exception states take the slow-path
197 return false;
198 }
199
200
201 // The LockNode emitted directly at the synchronization site would have
202 // been too big if it were to have included support for the cases of inflated
203 // recursive enter and exit, so they go here instead.
204 // Note that we can't safely call AsyncPrintJavaStack() from within
205 // quick_enter() as our thread state remains _in_Java.
206
207 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
208 BasicLock * lock) {
209 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
210 assert(Self->is_Java_thread(), "invariant");
211 assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
212 NoSafepointVerifier nsv;
213 if (obj == NULL) return false; // Need to throw NPE
214 const markWord mark = obj->mark();
215
216 if (mark.has_monitor()) {
217 ObjectMonitor * const m = mark.monitor();
218 assert(oopDesc::equals((oop) m->object(), obj), "invariant");
219 Thread * const owner = (Thread *) m->_owner;
220
221 // Lock contention and Transactional Lock Elision (TLE) diagnostics
222 // and observability
223 // Case: light contention possibly amenable to TLE
224 // Case: TLE inimical operations such as nested/recursive synchronization
225
226 if (owner == Self) {
227 m->_recursions++;
228 return true;
229 }
230
231 // This Java Monitor is inflated so obj's header will never be
232 // displaced to this thread's BasicLock. Make the displaced header
233 // non-NULL so this BasicLock is not seen as recursive nor as
234 // being locked. We do this unconditionally so that this thread's
235 // BasicLock cannot be mis-interpreted by any stack walkers. For
236 // performance reasons, stack walkers generally first check for
237 // Biased Locking in the object's header, the second check is for
238 // stack-locking in the object's header, the third check is for
239 // recursive stack-locking in the displaced header in the BasicLock,
240 // and last are the inflated Java Monitor (ObjectMonitor) checks.
241 lock->set_displaced_header(markWord::unused_mark());
242
243 if (owner == NULL && Atomic::replace_if_null(Self, &(m->_owner))) {
244 assert(m->_recursions == 0, "invariant");
245 return true;
246 }
247 }
248
249 // Note that we could inflate in quick_enter.
250 // This is likely a useful optimization
251 // Critically, in quick_enter() we must not:
252 // -- perform bias revocation, or
253 // -- block indefinitely, or
254 // -- reach a safepoint
255
256 return false; // revert to slow-path
257 }
258
259 // -----------------------------------------------------------------------------
260 // Monitor Enter/Exit
261 // The interpreter and compiler assembly code tries to lock using the fast path
262 // of this algorithm. Make sure to update that code if the following function is
263 // changed. The implementation is extremely sensitive to race condition. Be careful.
264
265 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, TRAPS) {
266 if (UseBiasedLocking) {
267 if (!SafepointSynchronize::is_at_safepoint()) {
268 BiasedLocking::revoke(obj, THREAD);
269 } else {
270 BiasedLocking::revoke_at_safepoint(obj);
271 }
272 }
273
274 markWord mark = obj->mark();
275 assert(!mark.has_bias_pattern(), "should not see bias pattern here");
276
277 if (mark.is_neutral()) {
278 // Anticipate successful CAS -- the ST of the displaced mark must
279 // be visible <= the ST performed by the CAS.
280 lock->set_displaced_header(mark);
281 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
282 return;
283 }
284 // Fall through to inflate() ...
285 } else if (mark.has_locker() &&
286 THREAD->is_lock_owned((address)mark.locker())) {
287 assert(lock != mark.locker(), "must not re-lock the same lock");
288 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
289 lock->set_displaced_header(markWord::from_pointer(NULL));
290 return;
291 }
292
293 // The object header will never be displaced to this lock,
294 // so it does not matter what the value is, except that it
295 // must be non-zero to avoid looking like a re-entrant lock,
296 // and must not look locked either.
297 lock->set_displaced_header(markWord::unused_mark());
298 inflate(THREAD, obj(), inflate_cause_monitor_enter)->enter(THREAD);
299 }
300
301 void ObjectSynchronizer::exit(oop object, BasicLock* lock, TRAPS) {
302 markWord mark = object->mark();
303 // We cannot check for Biased Locking if we are racing an inflation.
304 assert(mark == markWord::INFLATING() ||
305 !mark.has_bias_pattern(), "should not see bias pattern here");
306
307 markWord dhw = lock->displaced_header();
308 if (dhw.value() == 0) {
309 // If the displaced header is NULL, then this exit matches up with
310 // a recursive enter. No real work to do here except for diagnostics.
311 #ifndef PRODUCT
312 if (mark != markWord::INFLATING()) {
313 // Only do diagnostics if we are not racing an inflation. Simply
314 // exiting a recursive enter of a Java Monitor that is being
315 // inflated is safe; see the has_monitor() comment below.
316 assert(!mark.is_neutral(), "invariant");
317 assert(!mark.has_locker() ||
318 THREAD->is_lock_owned((address)mark.locker()), "invariant");
319 if (mark.has_monitor()) {
320 // The BasicLock's displaced_header is marked as a recursive
321 // enter and we have an inflated Java Monitor (ObjectMonitor).
322 // This is a special case where the Java Monitor was inflated
323 // after this thread entered the stack-lock recursively. When a
324 // Java Monitor is inflated, we cannot safely walk the Java
325 // Monitor owner's stack and update the BasicLocks because a
326 // Java Monitor can be asynchronously inflated by a thread that
327 // does not own the Java Monitor.
328 ObjectMonitor * m = mark.monitor();
329 assert(((oop)(m->object()))->mark() == mark, "invariant");
330 assert(m->is_entered(THREAD), "invariant");
331 }
332 }
333 #endif
334 return;
335 }
336
337 if (mark == markWord::from_pointer(lock)) {
338 // If the object is stack-locked by the current thread, try to
339 // swing the displaced header from the BasicLock back to the mark.
340 assert(dhw.is_neutral(), "invariant");
341 if (object->cas_set_mark(dhw, mark) == mark) {
342 return;
343 }
344 }
345
346 // We have to take the slow-path of possible inflation and then exit.
347 inflate(THREAD, object, inflate_cause_vm_internal)->exit(true, THREAD);
348 }
349
350 // -----------------------------------------------------------------------------
351 // Class Loader support to workaround deadlocks on the class loader lock objects
352 // Also used by GC
353 // complete_exit()/reenter() are used to wait on a nested lock
354 // i.e. to give up an outer lock completely and then re-enter
355 // Used when holding nested locks - lock acquisition order: lock1 then lock2
356 // 1) complete_exit lock1 - saving recursion count
357 // 2) wait on lock2
358 // 3) when notified on lock2, unlock lock2
359 // 4) reenter lock1 with original recursion count
360 // 5) lock lock2
361 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
362 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
363 if (UseBiasedLocking) {
364 BiasedLocking::revoke(obj, THREAD);
365 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
366 }
367
368 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
369
370 return monitor->complete_exit(THREAD);
371 }
372
373 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
374 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
375 if (UseBiasedLocking) {
376 BiasedLocking::revoke(obj, THREAD);
377 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
378 }
379
380 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
381
382 monitor->reenter(recursion, THREAD);
383 }
384 // -----------------------------------------------------------------------------
385 // JNI locks on java objects
386 // NOTE: must use heavy weight monitor to handle jni monitor enter
387 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
388 // the current locking is from JNI instead of Java code
389 if (UseBiasedLocking) {
390 BiasedLocking::revoke(obj, THREAD);
391 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
392 }
393 THREAD->set_current_pending_monitor_is_from_java(false);
394 inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);
395 THREAD->set_current_pending_monitor_is_from_java(true);
396 }
397
398 // NOTE: must use heavy weight monitor to handle jni monitor exit
399 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
400 if (UseBiasedLocking) {
401 Handle h_obj(THREAD, obj);
402 BiasedLocking::revoke(h_obj, THREAD);
403 obj = h_obj();
404 }
405 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
406
407 ObjectMonitor* monitor = inflate(THREAD, obj, inflate_cause_jni_exit);
408 // If this thread has locked the object, exit the monitor. We
409 // intentionally do not use CHECK here because we must exit the
410 // monitor even if an exception is pending.
411 if (monitor->check_owner(THREAD)) {
412 monitor->exit(true, THREAD);
413 }
414 }
415
416 // -----------------------------------------------------------------------------
417 // Internal VM locks on java objects
418 // standard constructor, allows locking failures
419 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
420 _dolock = doLock;
421 _thread = thread;
422 _thread->check_for_valid_safepoint_state(false);
423 _obj = obj;
424
425 if (_dolock) {
426 ObjectSynchronizer::enter(_obj, &_lock, _thread);
427 }
428 }
429
430 ObjectLocker::~ObjectLocker() {
431 if (_dolock) {
432 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
433 }
434 }
435
436
437 // -----------------------------------------------------------------------------
438 // Wait/Notify/NotifyAll
439 // NOTE: must use heavy weight monitor to handle wait()
440 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
441 if (UseBiasedLocking) {
442 BiasedLocking::revoke(obj, THREAD);
443 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
444 }
445 if (millis < 0) {
446 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
447 }
448 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
449
450 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
451 monitor->wait(millis, true, THREAD);
452
453 // This dummy call is in place to get around dtrace bug 6254741. Once
454 // that's fixed we can uncomment the following line, remove the call
455 // and change this function back into a "void" func.
456 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
457 return dtrace_waited_probe(monitor, obj, THREAD);
458 }
459
460 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
461 if (UseBiasedLocking) {
462 BiasedLocking::revoke(obj, THREAD);
463 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
464 }
465 if (millis < 0) {
466 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
467 }
468 inflate(THREAD, obj(), inflate_cause_wait)->wait(millis, false, THREAD);
469 }
470
471 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
472 if (UseBiasedLocking) {
473 BiasedLocking::revoke(obj, THREAD);
474 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
475 }
476
477 markWord mark = obj->mark();
478 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
479 return;
480 }
481 inflate(THREAD, obj(), inflate_cause_notify)->notify(THREAD);
482 }
483
484 // NOTE: see comment of notify()
485 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
486 if (UseBiasedLocking) {
487 BiasedLocking::revoke(obj, THREAD);
488 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
489 }
490
491 markWord mark = obj->mark();
492 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
493 return;
494 }
495 inflate(THREAD, obj(), inflate_cause_notify)->notifyAll(THREAD);
496 }
497
498 // -----------------------------------------------------------------------------
499 // Hash Code handling
500 //
501 // Performance concern:
502 // OrderAccess::storestore() calls release() which at one time stored 0
503 // into the global volatile OrderAccess::dummy variable. This store was
504 // unnecessary for correctness. Many threads storing into a common location
505 // causes considerable cache migration or "sloshing" on large SMP systems.
506 // As such, I avoided using OrderAccess::storestore(). In some cases
507 // OrderAccess::fence() -- which incurs local latency on the executing
508 // processor -- is a better choice as it scales on SMP systems.
509 //
510 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
511 // a discussion of coherency costs. Note that all our current reference
512 // platforms provide strong ST-ST order, so the issue is moot on IA32,
513 // x64, and SPARC.
514 //
515 // As a general policy we use "volatile" to control compiler-based reordering
516 // and explicit fences (barriers) to control for architectural reordering
517 // performed by the CPU(s) or platform.
518
519 struct SharedGlobals {
520 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
521 // These are highly shared mostly-read variables.
522 // To avoid false-sharing they need to be the sole occupants of a cache line.
523 volatile int stwRandom;
524 volatile int stwCycle;
525 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
526 // Hot RW variable -- Sequester to avoid false-sharing
527 volatile int hcSequence;
528 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
529 };
530
531 static SharedGlobals GVars;
532 static int MonitorScavengeThreshold = 1000000;
533 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
534
535 static markWord ReadStableMark(oop obj) {
536 markWord mark = obj->mark();
537 if (!mark.is_being_inflated()) {
538 return mark; // normal fast-path return
539 }
540
541 int its = 0;
542 for (;;) {
543 markWord mark = obj->mark();
544 if (!mark.is_being_inflated()) {
545 return mark; // normal fast-path return
546 }
547
548 // The object is being inflated by some other thread.
549 // The caller of ReadStableMark() must wait for inflation to complete.
550 // Avoid live-lock
551 // TODO: consider calling SafepointSynchronize::do_call_back() while
552 // spinning to see if there's a safepoint pending. If so, immediately
553 // yielding or blocking would be appropriate. Avoid spinning while
554 // there is a safepoint pending.
555 // TODO: add inflation contention performance counters.
556 // TODO: restrict the aggregate number of spinners.
557
558 ++its;
559 if (its > 10000 || !os::is_MP()) {
560 if (its & 1) {
561 os::naked_yield();
562 } else {
563 // Note that the following code attenuates the livelock problem but is not
564 // a complete remedy. A more complete solution would require that the inflating
565 // thread hold the associated inflation lock. The following code simply restricts
566 // the number of spinners to at most one. We'll have N-2 threads blocked
567 // on the inflationlock, 1 thread holding the inflation lock and using
568 // a yield/park strategy, and 1 thread in the midst of inflation.
569 // A more refined approach would be to change the encoding of INFLATING
570 // to allow encapsulation of a native thread pointer. Threads waiting for
571 // inflation to complete would use CAS to push themselves onto a singly linked
572 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
573 // and calling park(). When inflation was complete the thread that accomplished inflation
574 // would detach the list and set the markword to inflated with a single CAS and
575 // then for each thread on the list, set the flag and unpark() the thread.
576 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
577 // wakes at most one thread whereas we need to wake the entire list.
578 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
579 int YieldThenBlock = 0;
580 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
581 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
582 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
583 while (obj->mark() == markWord::INFLATING()) {
584 // Beware: NakedYield() is advisory and has almost no effect on some platforms
585 // so we periodically call Self->_ParkEvent->park(1).
586 // We use a mixed spin/yield/block mechanism.
587 if ((YieldThenBlock++) >= 16) {
588 Thread::current()->_ParkEvent->park(1);
589 } else {
590 os::naked_yield();
591 }
592 }
593 Thread::muxRelease(gInflationLocks + ix);
594 }
595 } else {
596 SpinPause(); // SMP-polite spinning
597 }
598 }
599 }
600
601 // hashCode() generation :
602 //
603 // Possibilities:
604 // * MD5Digest of {obj,stwRandom}
605 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
606 // * A DES- or AES-style SBox[] mechanism
607 // * One of the Phi-based schemes, such as:
608 // 2654435761 = 2^32 * Phi (golden ratio)
609 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
610 // * A variation of Marsaglia's shift-xor RNG scheme.
611 // * (obj ^ stwRandom) is appealing, but can result
612 // in undesirable regularity in the hashCode values of adjacent objects
613 // (objects allocated back-to-back, in particular). This could potentially
614 // result in hashtable collisions and reduced hashtable efficiency.
615 // There are simple ways to "diffuse" the middle address bits over the
616 // generated hashCode values:
617
618 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
619 intptr_t value = 0;
620 if (hashCode == 0) {
621 // This form uses global Park-Miller RNG.
622 // On MP system we'll have lots of RW access to a global, so the
623 // mechanism induces lots of coherency traffic.
624 value = os::random();
625 } else if (hashCode == 1) {
626 // This variation has the property of being stable (idempotent)
627 // between STW operations. This can be useful in some of the 1-0
628 // synchronization schemes.
629 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
630 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
631 } else if (hashCode == 2) {
632 value = 1; // for sensitivity testing
633 } else if (hashCode == 3) {
634 value = ++GVars.hcSequence;
635 } else if (hashCode == 4) {
636 value = cast_from_oop<intptr_t>(obj);
637 } else {
638 // Marsaglia's xor-shift scheme with thread-specific state
639 // This is probably the best overall implementation -- we'll
640 // likely make this the default in future releases.
641 unsigned t = Self->_hashStateX;
642 t ^= (t << 11);
643 Self->_hashStateX = Self->_hashStateY;
644 Self->_hashStateY = Self->_hashStateZ;
645 Self->_hashStateZ = Self->_hashStateW;
646 unsigned v = Self->_hashStateW;
647 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
648 Self->_hashStateW = v;
649 value = v;
650 }
651
652 value &= markWord::hash_mask;
653 if (value == 0) value = 0xBAD;
654 assert(value != markWord::no_hash, "invariant");
655 return value;
656 }
657
658 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
659 if (UseBiasedLocking) {
660 // NOTE: many places throughout the JVM do not expect a safepoint
661 // to be taken here, in particular most operations on perm gen
662 // objects. However, we only ever bias Java instances and all of
663 // the call sites of identity_hash that might revoke biases have
664 // been checked to make sure they can handle a safepoint. The
665 // added check of the bias pattern is to avoid useless calls to
666 // thread-local storage.
667 if (obj->mark().has_bias_pattern()) {
668 // Handle for oop obj in case of STW safepoint
669 Handle hobj(Self, obj);
670 // Relaxing assertion for bug 6320749.
671 assert(Universe::verify_in_progress() ||
672 !SafepointSynchronize::is_at_safepoint(),
673 "biases should not be seen by VM thread here");
674 BiasedLocking::revoke(hobj, JavaThread::current());
675 obj = hobj();
676 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
677 }
678 }
679
680 // hashCode() is a heap mutator ...
681 // Relaxing assertion for bug 6320749.
682 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
683 !SafepointSynchronize::is_at_safepoint(), "invariant");
684 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
685 Self->is_Java_thread() , "invariant");
686 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
687 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
688
689 ObjectMonitor* monitor = NULL;
690 markWord temp, test;
691 intptr_t hash;
692 markWord mark = ReadStableMark(obj);
693
694 // object should remain ineligible for biased locking
695 assert(!mark.has_bias_pattern(), "invariant");
696
697 if (mark.is_neutral()) {
698 hash = mark.hash(); // this is a normal header
699 if (hash != 0) { // if it has hash, just return it
700 return hash;
701 }
702 hash = get_next_hash(Self, obj); // allocate a new hash code
703 temp = mark.copy_set_hash(hash); // merge the hash code into header
704 // use (machine word version) atomic operation to install the hash
705 test = obj->cas_set_mark(temp, mark);
706 if (test == mark) {
707 return hash;
708 }
709 // If atomic operation failed, we must inflate the header
710 // into heavy weight monitor. We could add more code here
711 // for fast path, but it does not worth the complexity.
712 } else if (mark.has_monitor()) {
713 monitor = mark.monitor();
714 temp = monitor->header();
715 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
716 hash = temp.hash();
717 if (hash != 0) {
718 return hash;
719 }
720 // Skip to the following code to reduce code size
721 } else if (Self->is_lock_owned((address)mark.locker())) {
722 temp = mark.displaced_mark_helper(); // this is a lightweight monitor owned
723 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
724 hash = temp.hash(); // by current thread, check if the displaced
725 if (hash != 0) { // header contains hash code
726 return hash;
727 }
728 // WARNING:
729 // The displaced header in the BasicLock on a thread's stack
730 // is strictly immutable. It CANNOT be changed in ANY cases.
731 // So we have to inflate the stack lock into an ObjectMonitor
732 // even if the current thread owns the lock. The BasicLock on
733 // a thread's stack can be asynchronously read by other threads
734 // during an inflate() call so any change to that stack memory
735 // may not propagate to other threads correctly.
736 }
737
738 // Inflate the monitor to set hash code
739 monitor = inflate(Self, obj, inflate_cause_hash_code);
740 // Load displaced header and check it has hash code
741 mark = monitor->header();
742 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
743 hash = mark.hash();
744 if (hash == 0) {
745 hash = get_next_hash(Self, obj);
746 temp = mark.copy_set_hash(hash); // merge hash code into header
747 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
748 uintptr_t v = Atomic::cmpxchg(temp.value(), (volatile uintptr_t*)monitor->header_addr(), mark.value());
749 test = markWord(v);
750 if (test != mark) {
751 // The only update to the ObjectMonitor's header/dmw field
752 // is to merge in the hash code. If someone adds a new usage
753 // of the header/dmw field, please update this code.
754 hash = test.hash();
755 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
756 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
757 }
758 }
759 // We finally get the hash
760 return hash;
761 }
762
763 // Deprecated -- use FastHashCode() instead.
764
765 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
766 return FastHashCode(Thread::current(), obj());
767 }
768
769
770 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
771 Handle h_obj) {
772 if (UseBiasedLocking) {
773 BiasedLocking::revoke(h_obj, thread);
774 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
775 }
776
777 assert(thread == JavaThread::current(), "Can only be called on current thread");
778 oop obj = h_obj();
779
780 markWord mark = ReadStableMark(obj);
781
782 // Uncontended case, header points to stack
783 if (mark.has_locker()) {
784 return thread->is_lock_owned((address)mark.locker());
785 }
786 // Contended case, header points to ObjectMonitor (tagged pointer)
787 if (mark.has_monitor()) {
788 ObjectMonitor* monitor = mark.monitor();
789 return monitor->is_entered(thread) != 0;
790 }
791 // Unlocked case, header in place
792 assert(mark.is_neutral(), "sanity check");
793 return false;
794 }
795
796 // Be aware of this method could revoke bias of the lock object.
797 // This method queries the ownership of the lock handle specified by 'h_obj'.
798 // If the current thread owns the lock, it returns owner_self. If no
799 // thread owns the lock, it returns owner_none. Otherwise, it will return
800 // owner_other.
801 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
802 (JavaThread *self, Handle h_obj) {
803 // The caller must beware this method can revoke bias, and
804 // revocation can result in a safepoint.
805 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
806 assert(self->thread_state() != _thread_blocked, "invariant");
807
808 // Possible mark states: neutral, biased, stack-locked, inflated
809
810 if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) {
811 // CASE: biased
812 BiasedLocking::revoke(h_obj, self);
813 assert(!h_obj->mark().has_bias_pattern(),
814 "biases should be revoked by now");
815 }
816
817 assert(self == JavaThread::current(), "Can only be called on current thread");
818 oop obj = h_obj();
819 markWord mark = ReadStableMark(obj);
820
821 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
822 if (mark.has_locker()) {
823 return self->is_lock_owned((address)mark.locker()) ?
824 owner_self : owner_other;
825 }
826
827 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
828 // The Object:ObjectMonitor relationship is stable as long as we're
829 // not at a safepoint.
830 if (mark.has_monitor()) {
831 void * owner = mark.monitor()->_owner;
832 if (owner == NULL) return owner_none;
833 return (owner == self ||
834 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
835 }
836
837 // CASE: neutral
838 assert(mark.is_neutral(), "sanity check");
839 return owner_none; // it's unlocked
840 }
841
842 // FIXME: jvmti should call this
843 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
844 if (UseBiasedLocking) {
845 if (SafepointSynchronize::is_at_safepoint()) {
846 BiasedLocking::revoke_at_safepoint(h_obj);
847 } else {
848 BiasedLocking::revoke(h_obj, JavaThread::current());
849 }
850 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
851 }
852
853 oop obj = h_obj();
854 address owner = NULL;
855
856 markWord mark = ReadStableMark(obj);
857
858 // Uncontended case, header points to stack
859 if (mark.has_locker()) {
860 owner = (address) mark.locker();
861 }
862
863 // Contended case, header points to ObjectMonitor (tagged pointer)
864 else if (mark.has_monitor()) {
865 ObjectMonitor* monitor = mark.monitor();
866 assert(monitor != NULL, "monitor should be non-null");
867 owner = (address) monitor->owner();
868 }
869
870 if (owner != NULL) {
871 // owning_thread_from_monitor_owner() may also return NULL here
872 return Threads::owning_thread_from_monitor_owner(t_list, owner);
873 }
874
875 // Unlocked case, header in place
876 // Cannot have assertion since this object may have been
877 // locked by another thread when reaching here.
878 // assert(mark.is_neutral(), "sanity check");
879
880 return NULL;
881 }
882
883 // Visitors ...
884
885 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
886 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
887 while (block != NULL) {
888 assert(block->object() == CHAINMARKER, "must be a block header");
889 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
890 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
891 oop object = (oop)mid->object();
892 if (object != NULL) {
893 closure->do_monitor(mid);
894 }
895 }
896 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
897 }
898 }
899
900 // Get the next block in the block list.
901 static inline PaddedEnd<ObjectMonitor>* next(PaddedEnd<ObjectMonitor>* block) {
902 assert(block->object() == CHAINMARKER, "must be a block header");
903 block = (PaddedEnd<ObjectMonitor>*) block->FreeNext;
904 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
905 return block;
906 }
907
908 static bool monitors_used_above_threshold() {
909 if (gMonitorPopulation == 0) {
910 return false;
911 }
912 int monitors_used = gMonitorPopulation - gMonitorFreeCount;
913 int monitor_usage = (monitors_used * 100LL) / gMonitorPopulation;
914 return monitor_usage > MonitorUsedDeflationThreshold;
915 }
916
917 bool ObjectSynchronizer::is_cleanup_needed() {
918 if (MonitorUsedDeflationThreshold > 0) {
919 return monitors_used_above_threshold();
920 }
921 return false;
922 }
923
924 void ObjectSynchronizer::oops_do(OopClosure* f) {
925 // We only scan the global used list here (for moribund threads), and
926 // the thread-local monitors in Thread::oops_do().
927 global_used_oops_do(f);
928 }
929
930 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
931 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
932 list_oops_do(gOmInUseList, f);
933 }
934
935 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
936 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
937 list_oops_do(thread->omInUseList, f);
938 }
939
940 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
941 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
942 ObjectMonitor* mid;
943 for (mid = list; mid != NULL; mid = mid->FreeNext) {
944 if (mid->object() != NULL) {
945 f->do_oop((oop*)mid->object_addr());
946 }
947 }
948 }
949
950
951 // -----------------------------------------------------------------------------
952 // ObjectMonitor Lifecycle
953 // -----------------------
954 // Inflation unlinks monitors from the global gFreeList and
955 // associates them with objects. Deflation -- which occurs at
956 // STW-time -- disassociates idle monitors from objects. Such
957 // scavenged monitors are returned to the gFreeList.
958 //
959 // The global list is protected by gListLock. All the critical sections
960 // are short and operate in constant-time.
961 //
962 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
963 //
964 // Lifecycle:
965 // -- unassigned and on the global free list
966 // -- unassigned and on a thread's private omFreeList
967 // -- assigned to an object. The object is inflated and the mark refers
968 // to the objectmonitor.
969
970
971 // Constraining monitor pool growth via MonitorBound ...
972 //
973 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
974 // the rate of scavenging is driven primarily by GC. As such, we can find
975 // an inordinate number of monitors in circulation.
976 // To avoid that scenario we can artificially induce a STW safepoint
977 // if the pool appears to be growing past some reasonable bound.
978 // Generally we favor time in space-time tradeoffs, but as there's no
979 // natural back-pressure on the # of extant monitors we need to impose some
980 // type of limit. Beware that if MonitorBound is set to too low a value
981 // we could just loop. In addition, if MonitorBound is set to a low value
982 // we'll incur more safepoints, which are harmful to performance.
983 // See also: GuaranteedSafepointInterval
984 //
985 // The current implementation uses asynchronous VM operations.
986
987 static void InduceScavenge(Thread * Self, const char * Whence) {
988 // Induce STW safepoint to trim monitors
989 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
990 // More precisely, trigger an asynchronous STW safepoint as the number
991 // of active monitors passes the specified threshold.
992 // TODO: assert thread state is reasonable
993
994 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
995 // Induce a 'null' safepoint to scavenge monitors
996 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
997 // to the VMthread and have a lifespan longer than that of this activation record.
998 // The VMThread will delete the op when completed.
999 VMThread::execute(new VM_ScavengeMonitors());
1000 }
1001 }
1002
1003 ObjectMonitor* ObjectSynchronizer::omAlloc(Thread * Self) {
1004 // A large MAXPRIVATE value reduces both list lock contention
1005 // and list coherency traffic, but also tends to increase the
1006 // number of objectMonitors in circulation as well as the STW
1007 // scavenge costs. As usual, we lean toward time in space-time
1008 // tradeoffs.
1009 const int MAXPRIVATE = 1024;
1010 stringStream ss;
1011 for (;;) {
1012 ObjectMonitor * m;
1013
1014 // 1: try to allocate from the thread's local omFreeList.
1015 // Threads will attempt to allocate first from their local list, then
1016 // from the global list, and only after those attempts fail will the thread
1017 // attempt to instantiate new monitors. Thread-local free lists take
1018 // heat off the gListLock and improve allocation latency, as well as reducing
1019 // coherency traffic on the shared global list.
1020 m = Self->omFreeList;
1021 if (m != NULL) {
1022 Self->omFreeList = m->FreeNext;
1023 Self->omFreeCount--;
1024 guarantee(m->object() == NULL, "invariant");
1025 m->FreeNext = Self->omInUseList;
1026 Self->omInUseList = m;
1027 Self->omInUseCount++;
1028 return m;
1029 }
1030
1031 // 2: try to allocate from the global gFreeList
1032 // CONSIDER: use muxTry() instead of muxAcquire().
1033 // If the muxTry() fails then drop immediately into case 3.
1034 // If we're using thread-local free lists then try
1035 // to reprovision the caller's free list.
1036 if (gFreeList != NULL) {
1037 // Reprovision the thread's omFreeList.
1038 // Use bulk transfers to reduce the allocation rate and heat
1039 // on various locks.
1040 Thread::muxAcquire(&gListLock, "omAlloc(1)");
1041 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1042 gMonitorFreeCount--;
1043 ObjectMonitor * take = gFreeList;
1044 gFreeList = take->FreeNext;
1045 guarantee(take->object() == NULL, "invariant");
1046 take->Recycle();
1047 omRelease(Self, take, false);
1048 }
1049 Thread::muxRelease(&gListLock);
1050 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1051 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1052
1053 const int mx = MonitorBound;
1054 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1055 // We can't safely induce a STW safepoint from omAlloc() as our thread
1056 // state may not be appropriate for such activities and callers may hold
1057 // naked oops, so instead we defer the action.
1058 InduceScavenge(Self, "omAlloc");
1059 }
1060 continue;
1061 }
1062
1063 // 3: allocate a block of new ObjectMonitors
1064 // Both the local and global free lists are empty -- resort to malloc().
1065 // In the current implementation objectMonitors are TSM - immortal.
1066 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1067 // each ObjectMonitor to start at the beginning of a cache line,
1068 // so we use align_up().
1069 // A better solution would be to use C++ placement-new.
1070 // BEWARE: As it stands currently, we don't run the ctors!
1071 assert(_BLOCKSIZE > 1, "invariant");
1072 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
1073 PaddedEnd<ObjectMonitor> * temp;
1074 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1075 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
1076 mtInternal);
1077 temp = (PaddedEnd<ObjectMonitor> *)
1078 align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE);
1079
1080 // NOTE: (almost) no way to recover if allocation failed.
1081 // We might be able to induce a STW safepoint and scavenge enough
1082 // objectMonitors to permit progress.
1083 if (temp == NULL) {
1084 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1085 "Allocate ObjectMonitors");
1086 }
1087 (void)memset((void *) temp, 0, neededsize);
1088
1089 // Format the block.
1090 // initialize the linked list, each monitor points to its next
1091 // forming the single linked free list, the very first monitor
1092 // will points to next block, which forms the block list.
1093 // The trick of using the 1st element in the block as gBlockList
1094 // linkage should be reconsidered. A better implementation would
1095 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1096
1097 for (int i = 1; i < _BLOCKSIZE; i++) {
1098 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1099 }
1100
1101 // terminate the last monitor as the end of list
1102 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1103
1104 // Element [0] is reserved for global list linkage
1105 temp[0].set_object(CHAINMARKER);
1106
1107 // Consider carving out this thread's current request from the
1108 // block in hand. This avoids some lock traffic and redundant
1109 // list activity.
1110
1111 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1112 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1113 Thread::muxAcquire(&gListLock, "omAlloc(2)");
1114 gMonitorPopulation += _BLOCKSIZE-1;
1115 gMonitorFreeCount += _BLOCKSIZE-1;
1116
1117 // Add the new block to the list of extant blocks (gBlockList).
1118 // The very first objectMonitor in a block is reserved and dedicated.
1119 // It serves as blocklist "next" linkage.
1120 temp[0].FreeNext = gBlockList;
1121 // There are lock-free uses of gBlockList so make sure that
1122 // the previous stores happen before we update gBlockList.
1123 OrderAccess::release_store(&gBlockList, temp);
1124
1125 // Add the new string of objectMonitors to the global free list
1126 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1127 gFreeList = temp + 1;
1128 Thread::muxRelease(&gListLock);
1129 }
1130 }
1131
1132 // Place "m" on the caller's private per-thread omFreeList.
1133 // In practice there's no need to clamp or limit the number of
1134 // monitors on a thread's omFreeList as the only time we'll call
1135 // omRelease is to return a monitor to the free list after a CAS
1136 // attempt failed. This doesn't allow unbounded #s of monitors to
1137 // accumulate on a thread's free list.
1138 //
1139 // Key constraint: all ObjectMonitors on a thread's free list and the global
1140 // free list must have their object field set to null. This prevents the
1141 // scavenger -- deflate_monitor_list() -- from reclaiming them.
1142
1143 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1144 bool fromPerThreadAlloc) {
1145 guarantee(m->header().value() == 0, "invariant");
1146 guarantee(m->object() == NULL, "invariant");
1147 stringStream ss;
1148 guarantee((m->is_busy() | m->_recursions) == 0, "freeing in-use monitor: "
1149 "%s, recursions=" INTPTR_FORMAT, m->is_busy_to_string(&ss),
1150 m->_recursions);
1151 // Remove from omInUseList
1152 if (fromPerThreadAlloc) {
1153 ObjectMonitor* cur_mid_in_use = NULL;
1154 bool extracted = false;
1155 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1156 if (m == mid) {
1157 // extract from per-thread in-use list
1158 if (mid == Self->omInUseList) {
1159 Self->omInUseList = mid->FreeNext;
1160 } else if (cur_mid_in_use != NULL) {
1161 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1162 }
1163 extracted = true;
1164 Self->omInUseCount--;
1165 break;
1166 }
1167 }
1168 assert(extracted, "Should have extracted from in-use list");
1169 }
1170
1171 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1172 m->FreeNext = Self->omFreeList;
1173 Self->omFreeList = m;
1174 Self->omFreeCount++;
1175 }
1176
1177 // Return the monitors of a moribund thread's local free list to
1178 // the global free list. Typically a thread calls omFlush() when
1179 // it's dying. We could also consider having the VM thread steal
1180 // monitors from threads that have not run java code over a few
1181 // consecutive STW safepoints. Relatedly, we might decay
1182 // omFreeProvision at STW safepoints.
1183 //
1184 // Also return the monitors of a moribund thread's omInUseList to
1185 // a global gOmInUseList under the global list lock so these
1186 // will continue to be scanned.
1187 //
1188 // We currently call omFlush() from Threads::remove() _before the thread
1189 // has been excised from the thread list and is no longer a mutator.
1190 // This means that omFlush() cannot run concurrently with a safepoint and
1191 // interleave with the deflate_idle_monitors scavenge operator. In particular,
1192 // this ensures that the thread's monitors are scanned by a GC safepoint,
1193 // either via Thread::oops_do() (if safepoint happens before omFlush()) or via
1194 // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's
1195 // monitors have been transferred to the global in-use list).
1196
1197 void ObjectSynchronizer::omFlush(Thread * Self) {
1198 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1199 ObjectMonitor * tail = NULL;
1200 int tally = 0;
1201 if (list != NULL) {
1202 ObjectMonitor * s;
1203 // The thread is going away. Set 'tail' to the last per-thread free
1204 // monitor which will be linked to gFreeList below under the gListLock.
1205 stringStream ss;
1206 for (s = list; s != NULL; s = s->FreeNext) {
1207 tally++;
1208 tail = s;
1209 guarantee(s->object() == NULL, "invariant");
1210 guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss));
1211 }
1212 guarantee(tail != NULL, "invariant");
1213 assert(Self->omFreeCount == tally, "free-count off");
1214 Self->omFreeList = NULL;
1215 Self->omFreeCount = 0;
1216 }
1217
1218 ObjectMonitor * inUseList = Self->omInUseList;
1219 ObjectMonitor * inUseTail = NULL;
1220 int inUseTally = 0;
1221 if (inUseList != NULL) {
1222 ObjectMonitor *cur_om;
1223 // The thread is going away, however the omInUseList inflated
1224 // monitors may still be in-use by other threads.
1225 // Link them to inUseTail, which will be linked into the global in-use list
1226 // gOmInUseList below, under the gListLock
1227 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1228 inUseTail = cur_om;
1229 inUseTally++;
1230 }
1231 guarantee(inUseTail != NULL, "invariant");
1232 assert(Self->omInUseCount == inUseTally, "in-use count off");
1233 Self->omInUseList = NULL;
1234 Self->omInUseCount = 0;
1235 }
1236
1237 Thread::muxAcquire(&gListLock, "omFlush");
1238 if (tail != NULL) {
1239 tail->FreeNext = gFreeList;
1240 gFreeList = list;
1241 gMonitorFreeCount += tally;
1242 }
1243
1244 if (inUseTail != NULL) {
1245 inUseTail->FreeNext = gOmInUseList;
1246 gOmInUseList = inUseList;
1247 gOmInUseCount += inUseTally;
1248 }
1249
1250 Thread::muxRelease(&gListLock);
1251
1252 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1253 LogStreamHandle(Info, monitorinflation) lsh_info;
1254 LogStream * ls = NULL;
1255 if (log_is_enabled(Debug, monitorinflation)) {
1256 ls = &lsh_debug;
1257 } else if ((tally != 0 || inUseTally != 0) &&
1258 log_is_enabled(Info, monitorinflation)) {
1259 ls = &lsh_info;
1260 }
1261 if (ls != NULL) {
1262 ls->print_cr("omFlush: jt=" INTPTR_FORMAT ", free_monitor_tally=%d"
1263 ", in_use_monitor_tally=%d" ", omFreeProvision=%d",
1264 p2i(Self), tally, inUseTally, Self->omFreeProvision);
1265 }
1266 }
1267
1268 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1269 const oop obj,
1270 ObjectSynchronizer::InflateCause cause) {
1271 assert(event != NULL, "invariant");
1272 assert(event->should_commit(), "invariant");
1273 event->set_monitorClass(obj->klass());
1274 event->set_address((uintptr_t)(void*)obj);
1275 event->set_cause((u1)cause);
1276 event->commit();
1277 }
1278
1279 // Fast path code shared by multiple functions
1280 void ObjectSynchronizer::inflate_helper(oop obj) {
1281 markWord mark = obj->mark();
1282 if (mark.has_monitor()) {
1283 assert(ObjectSynchronizer::verify_objmon_isinpool(mark.monitor()), "monitor is invalid");
1284 assert(mark.monitor()->header().is_neutral(), "monitor must record a good object header");
1285 return;
1286 }
1287 inflate(Thread::current(), obj, inflate_cause_vm_internal);
1288 }
1289
1290 ObjectMonitor* ObjectSynchronizer::inflate(Thread * Self,
1291 oop object,
1292 const InflateCause cause) {
1293 // Inflate mutates the heap ...
1294 // Relaxing assertion for bug 6320749.
1295 assert(Universe::verify_in_progress() ||
1296 !SafepointSynchronize::is_at_safepoint(), "invariant");
1297
1298 EventJavaMonitorInflate event;
1299
1300 for (;;) {
1301 const markWord mark = object->mark();
1302 assert(!mark.has_bias_pattern(), "invariant");
1303
1304 // The mark can be in one of the following states:
1305 // * Inflated - just return
1306 // * Stack-locked - coerce it to inflated
1307 // * INFLATING - busy wait for conversion to complete
1308 // * Neutral - aggressively inflate the object.
1309 // * BIASED - Illegal. We should never see this
1310
1311 // CASE: inflated
1312 if (mark.has_monitor()) {
1313 ObjectMonitor * inf = mark.monitor();
1314 markWord dmw = inf->header();
1315 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1316 assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1317 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1318 return inf;
1319 }
1320
1321 // CASE: inflation in progress - inflating over a stack-lock.
1322 // Some other thread is converting from stack-locked to inflated.
1323 // Only that thread can complete inflation -- other threads must wait.
1324 // The INFLATING value is transient.
1325 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1326 // We could always eliminate polling by parking the thread on some auxiliary list.
1327 if (mark == markWord::INFLATING()) {
1328 ReadStableMark(object);
1329 continue;
1330 }
1331
1332 // CASE: stack-locked
1333 // Could be stack-locked either by this thread or by some other thread.
1334 //
1335 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1336 // to install INFLATING into the mark word. We originally installed INFLATING,
1337 // allocated the objectmonitor, and then finally STed the address of the
1338 // objectmonitor into the mark. This was correct, but artificially lengthened
1339 // the interval in which INFLATED appeared in the mark, thus increasing
1340 // the odds of inflation contention.
1341 //
1342 // We now use per-thread private objectmonitor free lists.
1343 // These list are reprovisioned from the global free list outside the
1344 // critical INFLATING...ST interval. A thread can transfer
1345 // multiple objectmonitors en-mass from the global free list to its local free list.
1346 // This reduces coherency traffic and lock contention on the global free list.
1347 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1348 // before or after the CAS(INFLATING) operation.
1349 // See the comments in omAlloc().
1350
1351 LogStreamHandle(Trace, monitorinflation) lsh;
1352
1353 if (mark.has_locker()) {
1354 ObjectMonitor * m = omAlloc(Self);
1355 // Optimistically prepare the objectmonitor - anticipate successful CAS
1356 // We do this before the CAS in order to minimize the length of time
1357 // in which INFLATING appears in the mark.
1358 m->Recycle();
1359 m->_Responsible = NULL;
1360 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1361
1362 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1363 if (cmp != mark) {
1364 omRelease(Self, m, true);
1365 continue; // Interference -- just retry
1366 }
1367
1368 // We've successfully installed INFLATING (0) into the mark-word.
1369 // This is the only case where 0 will appear in a mark-word.
1370 // Only the singular thread that successfully swings the mark-word
1371 // to 0 can perform (or more precisely, complete) inflation.
1372 //
1373 // Why do we CAS a 0 into the mark-word instead of just CASing the
1374 // mark-word from the stack-locked value directly to the new inflated state?
1375 // Consider what happens when a thread unlocks a stack-locked object.
1376 // It attempts to use CAS to swing the displaced header value from the
1377 // on-stack basiclock back into the object header. Recall also that the
1378 // header value (hash code, etc) can reside in (a) the object header, or
1379 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1380 // header in an objectMonitor. The inflate() routine must copy the header
1381 // value from the basiclock on the owner's stack to the objectMonitor, all
1382 // the while preserving the hashCode stability invariants. If the owner
1383 // decides to release the lock while the value is 0, the unlock will fail
1384 // and control will eventually pass from slow_exit() to inflate. The owner
1385 // will then spin, waiting for the 0 value to disappear. Put another way,
1386 // the 0 causes the owner to stall if the owner happens to try to
1387 // drop the lock (restoring the header from the basiclock to the object)
1388 // while inflation is in-progress. This protocol avoids races that might
1389 // would otherwise permit hashCode values to change or "flicker" for an object.
1390 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1391 // 0 serves as a "BUSY" inflate-in-progress indicator.
1392
1393
1394 // fetch the displaced mark from the owner's stack.
1395 // The owner can't die or unwind past the lock while our INFLATING
1396 // object is in the mark. Furthermore the owner can't complete
1397 // an unlock on the object, either.
1398 markWord dmw = mark.displaced_mark_helper();
1399 // Catch if the object's header is not neutral (not locked and
1400 // not marked is what we care about here).
1401 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1402
1403 // Setup monitor fields to proper values -- prepare the monitor
1404 m->set_header(dmw);
1405
1406 // Optimization: if the mark.locker stack address is associated
1407 // with this thread we could simply set m->_owner = Self.
1408 // Note that a thread can inflate an object
1409 // that it has stack-locked -- as might happen in wait() -- directly
1410 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1411 m->set_owner(mark.locker());
1412 m->set_object(object);
1413 // TODO-FIXME: assert BasicLock->dhw != 0.
1414
1415 // Must preserve store ordering. The monitor state must
1416 // be stable at the time of publishing the monitor address.
1417 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1418 object->release_set_mark(markWord::encode(m));
1419
1420 // Hopefully the performance counters are allocated on distinct cache lines
1421 // to avoid false sharing on MP systems ...
1422 OM_PERFDATA_OP(Inflations, inc());
1423 if (log_is_enabled(Trace, monitorinflation)) {
1424 ResourceMark rm(Self);
1425 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1426 INTPTR_FORMAT ", type='%s'", p2i(object),
1427 object->mark().value(), object->klass()->external_name());
1428 }
1429 if (event.should_commit()) {
1430 post_monitor_inflate_event(&event, object, cause);
1431 }
1432 return m;
1433 }
1434
1435 // CASE: neutral
1436 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1437 // If we know we're inflating for entry it's better to inflate by swinging a
1438 // pre-locked objectMonitor pointer into the object header. A successful
1439 // CAS inflates the object *and* confers ownership to the inflating thread.
1440 // In the current implementation we use a 2-step mechanism where we CAS()
1441 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1442 // An inflateTry() method that we could call from enter() would be useful.
1443
1444 // Catch if the object's header is not neutral (not locked and
1445 // not marked is what we care about here).
1446 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1447 ObjectMonitor * m = omAlloc(Self);
1448 // prepare m for installation - set monitor to initial state
1449 m->Recycle();
1450 m->set_header(mark);
1451 m->set_object(object);
1452 m->_Responsible = NULL;
1453 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1454
1455 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1456 m->set_header(markWord::zero());
1457 m->set_object(NULL);
1458 m->Recycle();
1459 omRelease(Self, m, true);
1460 m = NULL;
1461 continue;
1462 // interference - the markword changed - just retry.
1463 // The state-transitions are one-way, so there's no chance of
1464 // live-lock -- "Inflated" is an absorbing state.
1465 }
1466
1467 // Hopefully the performance counters are allocated on distinct
1468 // cache lines to avoid false sharing on MP systems ...
1469 OM_PERFDATA_OP(Inflations, inc());
1470 if (log_is_enabled(Trace, monitorinflation)) {
1471 ResourceMark rm(Self);
1472 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1473 INTPTR_FORMAT ", type='%s'", p2i(object),
1474 object->mark().value(), object->klass()->external_name());
1475 }
1476 if (event.should_commit()) {
1477 post_monitor_inflate_event(&event, object, cause);
1478 }
1479 return m;
1480 }
1481 }
1482
1483
1484 // We maintain a list of in-use monitors for each thread.
1485 //
1486 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1487 // deflate_idle_monitors() scans only a global list of in-use monitors which
1488 // is populated only as a thread dies (see omFlush()).
1489 //
1490 // These operations are called at all safepoints, immediately after mutators
1491 // are stopped, but before any objects have moved. Collectively they traverse
1492 // the population of in-use monitors, deflating where possible. The scavenged
1493 // monitors are returned to the global monitor free list.
1494 //
1495 // Beware that we scavenge at *every* stop-the-world point. Having a large
1496 // number of monitors in-use could negatively impact performance. We also want
1497 // to minimize the total # of monitors in circulation, as they incur a small
1498 // footprint penalty.
1499 //
1500 // Perversely, the heap size -- and thus the STW safepoint rate --
1501 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1502 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1503 // This is an unfortunate aspect of this design.
1504
1505 // Deflate a single monitor if not in-use
1506 // Return true if deflated, false if in-use
1507 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1508 ObjectMonitor** freeHeadp,
1509 ObjectMonitor** freeTailp) {
1510 bool deflated;
1511 // Normal case ... The monitor is associated with obj.
1512 const markWord mark = obj->mark();
1513 guarantee(mark == markWord::encode(mid), "should match: mark="
1514 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(),
1515 markWord::encode(mid).value());
1516 // Make sure that mark.monitor() and markWord::encode() agree:
1517 guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
1518 ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid));
1519 const markWord dmw = mid->header();
1520 guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1521
1522 if (mid->is_busy()) {
1523 deflated = false;
1524 } else {
1525 // Deflate the monitor if it is no longer being used
1526 // It's idle - scavenge and return to the global free list
1527 // plain old deflation ...
1528 if (log_is_enabled(Trace, monitorinflation)) {
1529 ResourceMark rm;
1530 log_trace(monitorinflation)("deflate_monitor: "
1531 "object=" INTPTR_FORMAT ", mark="
1532 INTPTR_FORMAT ", type='%s'", p2i(obj),
1533 mark.value(), obj->klass()->external_name());
1534 }
1535
1536 // Restore the header back to obj
1537 obj->release_set_mark(dmw);
1538 mid->clear();
1539
1540 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
1541 p2i(mid->object()));
1542
1543 // Move the object to the working free list defined by freeHeadp, freeTailp
1544 if (*freeHeadp == NULL) *freeHeadp = mid;
1545 if (*freeTailp != NULL) {
1546 ObjectMonitor * prevtail = *freeTailp;
1547 assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1548 prevtail->FreeNext = mid;
1549 }
1550 *freeTailp = mid;
1551 deflated = true;
1552 }
1553 return deflated;
1554 }
1555
1556 // Walk a given monitor list, and deflate idle monitors
1557 // The given list could be a per-thread list or a global list
1558 // Caller acquires gListLock as needed.
1559 //
1560 // In the case of parallel processing of thread local monitor lists,
1561 // work is done by Threads::parallel_threads_do() which ensures that
1562 // each Java thread is processed by exactly one worker thread, and
1563 // thus avoid conflicts that would arise when worker threads would
1564 // process the same monitor lists concurrently.
1565 //
1566 // See also ParallelSPCleanupTask and
1567 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1568 // Threads::parallel_java_threads_do() in thread.cpp.
1569 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1570 ObjectMonitor** freeHeadp,
1571 ObjectMonitor** freeTailp) {
1572 ObjectMonitor* mid;
1573 ObjectMonitor* next;
1574 ObjectMonitor* cur_mid_in_use = NULL;
1575 int deflated_count = 0;
1576
1577 for (mid = *listHeadp; mid != NULL;) {
1578 oop obj = (oop) mid->object();
1579 if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1580 // if deflate_monitor succeeded,
1581 // extract from per-thread in-use list
1582 if (mid == *listHeadp) {
1583 *listHeadp = mid->FreeNext;
1584 } else if (cur_mid_in_use != NULL) {
1585 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1586 }
1587 next = mid->FreeNext;
1588 mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list
1589 mid = next;
1590 deflated_count++;
1591 } else {
1592 cur_mid_in_use = mid;
1593 mid = mid->FreeNext;
1594 }
1595 }
1596 return deflated_count;
1597 }
1598
1599 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1600 counters->nInuse = 0; // currently associated with objects
1601 counters->nInCirculation = 0; // extant
1602 counters->nScavenged = 0; // reclaimed (global and per-thread)
1603 counters->perThreadScavenged = 0; // per-thread scavenge total
1604 counters->perThreadTimes = 0.0; // per-thread scavenge times
1605 }
1606
1607 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
1608 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1609 bool deflated = false;
1610
1611 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1612 ObjectMonitor * freeTailp = NULL;
1613 elapsedTimer timer;
1614
1615 if (log_is_enabled(Info, monitorinflation)) {
1616 timer.start();
1617 }
1618
1619 // Prevent omFlush from changing mids in Thread dtor's during deflation
1620 // And in case the vm thread is acquiring a lock during a safepoint
1621 // See e.g. 6320749
1622 Thread::muxAcquire(&gListLock, "deflate_idle_monitors");
1623
1624 // Note: the thread-local monitors lists get deflated in
1625 // a separate pass. See deflate_thread_local_monitors().
1626
1627 // For moribund threads, scan gOmInUseList
1628 int deflated_count = 0;
1629 if (gOmInUseList) {
1630 counters->nInCirculation += gOmInUseCount;
1631 deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
1632 gOmInUseCount -= deflated_count;
1633 counters->nScavenged += deflated_count;
1634 counters->nInuse += gOmInUseCount;
1635 }
1636
1637 // Move the scavenged monitors back to the global free list.
1638 if (freeHeadp != NULL) {
1639 guarantee(freeTailp != NULL && counters->nScavenged > 0, "invariant");
1640 assert(freeTailp->FreeNext == NULL, "invariant");
1641 // constant-time list splice - prepend scavenged segment to gFreeList
1642 freeTailp->FreeNext = gFreeList;
1643 gFreeList = freeHeadp;
1644 }
1645 Thread::muxRelease(&gListLock);
1646 timer.stop();
1647
1648 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1649 LogStreamHandle(Info, monitorinflation) lsh_info;
1650 LogStream * ls = NULL;
1651 if (log_is_enabled(Debug, monitorinflation)) {
1652 ls = &lsh_debug;
1653 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
1654 ls = &lsh_info;
1655 }
1656 if (ls != NULL) {
1657 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
1658 }
1659 }
1660
1661 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1662 // Report the cumulative time for deflating each thread's idle
1663 // monitors. Note: if the work is split among more than one
1664 // worker thread, then the reported time will likely be more
1665 // than a beginning to end measurement of the phase.
1666 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->perThreadTimes, counters->perThreadScavenged);
1667
1668 gMonitorFreeCount += counters->nScavenged;
1669
1670 if (log_is_enabled(Debug, monitorinflation)) {
1671 // exit_globals()'s call to audit_and_print_stats() is done
1672 // at the Info level.
1673 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
1674 } else if (log_is_enabled(Info, monitorinflation)) {
1675 Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors");
1676 log_info(monitorinflation)("gMonitorPopulation=%d, gOmInUseCount=%d, "
1677 "gMonitorFreeCount=%d", gMonitorPopulation,
1678 gOmInUseCount, gMonitorFreeCount);
1679 Thread::muxRelease(&gListLock);
1680 }
1681
1682 ForceMonitorScavenge = 0; // Reset
1683
1684 OM_PERFDATA_OP(Deflations, inc(counters->nScavenged));
1685 OM_PERFDATA_OP(MonExtant, set_value(counters->nInCirculation));
1686
1687 GVars.stwRandom = os::random();
1688 GVars.stwCycle++;
1689 }
1690
1691 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
1692 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1693
1694 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1695 ObjectMonitor * freeTailp = NULL;
1696 elapsedTimer timer;
1697
1698 if (log_is_enabled(Info, safepoint, cleanup) ||
1699 log_is_enabled(Info, monitorinflation)) {
1700 timer.start();
1701 }
1702
1703 int deflated_count = deflate_monitor_list(thread->omInUseList_addr(), &freeHeadp, &freeTailp);
1704
1705 Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors");
1706
1707 // Adjust counters
1708 counters->nInCirculation += thread->omInUseCount;
1709 thread->omInUseCount -= deflated_count;
1710 counters->nScavenged += deflated_count;
1711 counters->nInuse += thread->omInUseCount;
1712 counters->perThreadScavenged += deflated_count;
1713
1714 // Move the scavenged monitors back to the global free list.
1715 if (freeHeadp != NULL) {
1716 guarantee(freeTailp != NULL && deflated_count > 0, "invariant");
1717 assert(freeTailp->FreeNext == NULL, "invariant");
1718
1719 // constant-time list splice - prepend scavenged segment to gFreeList
1720 freeTailp->FreeNext = gFreeList;
1721 gFreeList = freeHeadp;
1722 }
1723
1724 timer.stop();
1725 // Safepoint logging cares about cumulative perThreadTimes and
1726 // we'll capture most of the cost, but not the muxRelease() which
1727 // should be cheap.
1728 counters->perThreadTimes += timer.seconds();
1729
1730 Thread::muxRelease(&gListLock);
1731
1732 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1733 LogStreamHandle(Info, monitorinflation) lsh_info;
1734 LogStream * ls = NULL;
1735 if (log_is_enabled(Debug, monitorinflation)) {
1736 ls = &lsh_debug;
1737 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
1738 ls = &lsh_info;
1739 }
1740 if (ls != NULL) {
1741 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
1742 }
1743 }
1744
1745 // Monitor cleanup on JavaThread::exit
1746
1747 // Iterate through monitor cache and attempt to release thread's monitors
1748 // Gives up on a particular monitor if an exception occurs, but continues
1749 // the overall iteration, swallowing the exception.
1750 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1751 private:
1752 TRAPS;
1753
1754 public:
1755 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1756 void do_monitor(ObjectMonitor* mid) {
1757 if (mid->owner() == THREAD) {
1758 (void)mid->complete_exit(CHECK);
1759 }
1760 }
1761 };
1762
1763 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1764 // ignored. This is meant to be called during JNI thread detach which assumes
1765 // all remaining monitors are heavyweight. All exceptions are swallowed.
1766 // Scanning the extant monitor list can be time consuming.
1767 // A simple optimization is to add a per-thread flag that indicates a thread
1768 // called jni_monitorenter() during its lifetime.
1769 //
1770 // Instead of No_Savepoint_Verifier it might be cheaper to
1771 // use an idiom of the form:
1772 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1773 // <code that must not run at safepoint>
1774 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1775 // Since the tests are extremely cheap we could leave them enabled
1776 // for normal product builds.
1777
1778 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1779 assert(THREAD == JavaThread::current(), "must be current Java thread");
1780 NoSafepointVerifier nsv;
1781 ReleaseJavaMonitorsClosure rjmc(THREAD);
1782 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
1783 ObjectSynchronizer::monitors_iterate(&rjmc);
1784 Thread::muxRelease(&gListLock);
1785 THREAD->clear_pending_exception();
1786 }
1787
1788 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1789 switch (cause) {
1790 case inflate_cause_vm_internal: return "VM Internal";
1791 case inflate_cause_monitor_enter: return "Monitor Enter";
1792 case inflate_cause_wait: return "Monitor Wait";
1793 case inflate_cause_notify: return "Monitor Notify";
1794 case inflate_cause_hash_code: return "Monitor Hash Code";
1795 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1796 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1797 default:
1798 ShouldNotReachHere();
1799 }
1800 return "Unknown";
1801 }
1802
1803 //------------------------------------------------------------------------------
1804 // Debugging code
1805
1806 u_char* ObjectSynchronizer::get_gvars_addr() {
1807 return (u_char*)&GVars;
1808 }
1809
1810 u_char* ObjectSynchronizer::get_gvars_hcSequence_addr() {
1811 return (u_char*)&GVars.hcSequence;
1812 }
1813
1814 size_t ObjectSynchronizer::get_gvars_size() {
1815 return sizeof(SharedGlobals);
1816 }
1817
1818 u_char* ObjectSynchronizer::get_gvars_stwRandom_addr() {
1819 return (u_char*)&GVars.stwRandom;
1820 }
1821
1822 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1823 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1824
1825 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1826 LogStreamHandle(Info, monitorinflation) lsh_info;
1827 LogStreamHandle(Trace, monitorinflation) lsh_trace;
1828 LogStream * ls = NULL;
1829 if (log_is_enabled(Trace, monitorinflation)) {
1830 ls = &lsh_trace;
1831 } else if (log_is_enabled(Debug, monitorinflation)) {
1832 ls = &lsh_debug;
1833 } else if (log_is_enabled(Info, monitorinflation)) {
1834 ls = &lsh_info;
1835 }
1836 assert(ls != NULL, "sanity check");
1837
1838 if (!on_exit) {
1839 // Not at VM exit so grab the global list lock.
1840 Thread::muxAcquire(&gListLock, "audit_and_print_stats");
1841 }
1842
1843 // Log counts for the global and per-thread monitor lists:
1844 int chkMonitorPopulation = log_monitor_list_counts(ls);
1845 int error_cnt = 0;
1846
1847 ls->print_cr("Checking global lists:");
1848
1849 // Check gMonitorPopulation:
1850 if (gMonitorPopulation == chkMonitorPopulation) {
1851 ls->print_cr("gMonitorPopulation=%d equals chkMonitorPopulation=%d",
1852 gMonitorPopulation, chkMonitorPopulation);
1853 } else {
1854 ls->print_cr("ERROR: gMonitorPopulation=%d is not equal to "
1855 "chkMonitorPopulation=%d", gMonitorPopulation,
1856 chkMonitorPopulation);
1857 error_cnt++;
1858 }
1859
1860 // Check gOmInUseList and gOmInUseCount:
1861 chk_global_in_use_list_and_count(ls, &error_cnt);
1862
1863 // Check gFreeList and gMonitorFreeCount:
1864 chk_global_free_list_and_count(ls, &error_cnt);
1865
1866 if (!on_exit) {
1867 Thread::muxRelease(&gListLock);
1868 }
1869
1870 ls->print_cr("Checking per-thread lists:");
1871
1872 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
1873 // Check omInUseList and omInUseCount:
1874 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
1875
1876 // Check omFreeList and omFreeCount:
1877 chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
1878 }
1879
1880 if (error_cnt == 0) {
1881 ls->print_cr("No errors found in monitor list checks.");
1882 } else {
1883 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
1884 }
1885
1886 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1887 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1888 // When exiting this log output is at the Info level. When called
1889 // at a safepoint, this log output is at the Trace level since
1890 // there can be a lot of it.
1891 log_in_use_monitor_details(ls, on_exit);
1892 }
1893
1894 ls->flush();
1895
1896 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1897 }
1898
1899 // Check a free monitor entry; log any errors.
1900 void ObjectSynchronizer::chk_free_entry(JavaThread * jt, ObjectMonitor * n,
1901 outputStream * out, int *error_cnt_p) {
1902 stringStream ss;
1903 if (n->is_busy()) {
1904 if (jt != NULL) {
1905 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1906 ": free per-thread monitor must not be busy: %s", p2i(jt),
1907 p2i(n), n->is_busy_to_string(&ss));
1908 } else {
1909 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1910 "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
1911 }
1912 *error_cnt_p = *error_cnt_p + 1;
1913 }
1914 if (n->header().value() != 0) {
1915 if (jt != NULL) {
1916 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1917 ": free per-thread monitor must have NULL _header "
1918 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
1919 n->header().value());
1920 } else {
1921 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1922 "must have NULL _header field: _header=" INTPTR_FORMAT,
1923 p2i(n), n->header().value());
1924 }
1925 *error_cnt_p = *error_cnt_p + 1;
1926 }
1927 if (n->object() != NULL) {
1928 if (jt != NULL) {
1929 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1930 ": free per-thread monitor must have NULL _object "
1931 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
1932 p2i(n->object()));
1933 } else {
1934 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1935 "must have NULL _object field: _object=" INTPTR_FORMAT,
1936 p2i(n), p2i(n->object()));
1937 }
1938 *error_cnt_p = *error_cnt_p + 1;
1939 }
1940 }
1941
1942 // Check the global free list and count; log the results of the checks.
1943 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
1944 int *error_cnt_p) {
1945 int chkMonitorFreeCount = 0;
1946 for (ObjectMonitor * n = gFreeList; n != NULL; n = n->FreeNext) {
1947 chk_free_entry(NULL /* jt */, n, out, error_cnt_p);
1948 chkMonitorFreeCount++;
1949 }
1950 if (gMonitorFreeCount == chkMonitorFreeCount) {
1951 out->print_cr("gMonitorFreeCount=%d equals chkMonitorFreeCount=%d",
1952 gMonitorFreeCount, chkMonitorFreeCount);
1953 } else {
1954 out->print_cr("ERROR: gMonitorFreeCount=%d is not equal to "
1955 "chkMonitorFreeCount=%d", gMonitorFreeCount,
1956 chkMonitorFreeCount);
1957 *error_cnt_p = *error_cnt_p + 1;
1958 }
1959 }
1960
1961 // Check the global in-use list and count; log the results of the checks.
1962 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
1963 int *error_cnt_p) {
1964 int chkOmInUseCount = 0;
1965 for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
1966 chk_in_use_entry(NULL /* jt */, n, out, error_cnt_p);
1967 chkOmInUseCount++;
1968 }
1969 if (gOmInUseCount == chkOmInUseCount) {
1970 out->print_cr("gOmInUseCount=%d equals chkOmInUseCount=%d", gOmInUseCount,
1971 chkOmInUseCount);
1972 } else {
1973 out->print_cr("ERROR: gOmInUseCount=%d is not equal to chkOmInUseCount=%d",
1974 gOmInUseCount, chkOmInUseCount);
1975 *error_cnt_p = *error_cnt_p + 1;
1976 }
1977 }
1978
1979 // Check an in-use monitor entry; log any errors.
1980 void ObjectSynchronizer::chk_in_use_entry(JavaThread * jt, ObjectMonitor * n,
1981 outputStream * out, int *error_cnt_p) {
1982 if (n->header().value() == 0) {
1983 if (jt != NULL) {
1984 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1985 ": in-use per-thread monitor must have non-NULL _header "
1986 "field.", p2i(jt), p2i(n));
1987 } else {
1988 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
1989 "must have non-NULL _header field.", p2i(n));
1990 }
1991 *error_cnt_p = *error_cnt_p + 1;
1992 }
1993 if (n->object() == NULL) {
1994 if (jt != NULL) {
1995 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1996 ": in-use per-thread monitor must have non-NULL _object "
1997 "field.", p2i(jt), p2i(n));
1998 } else {
1999 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2000 "must have non-NULL _object field.", p2i(n));
2001 }
2002 *error_cnt_p = *error_cnt_p + 1;
2003 }
2004 const oop obj = (oop)n->object();
2005 const markWord mark = obj->mark();
2006 if (!mark.has_monitor()) {
2007 if (jt != NULL) {
2008 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2009 ": in-use per-thread monitor's object does not think "
2010 "it has a monitor: obj=" INTPTR_FORMAT ", mark="
2011 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), mark.value());
2012 } else {
2013 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2014 "monitor's object does not think it has a monitor: obj="
2015 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2016 p2i(obj), mark.value());
2017 }
2018 *error_cnt_p = *error_cnt_p + 1;
2019 }
2020 ObjectMonitor * const obj_mon = mark.monitor();
2021 if (n != obj_mon) {
2022 if (jt != NULL) {
2023 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2024 ": in-use per-thread monitor's object does not refer "
2025 "to the same monitor: obj=" INTPTR_FORMAT ", mark="
2026 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
2027 p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2028 } else {
2029 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2030 "monitor's object does not refer to the same monitor: obj="
2031 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2032 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2033 }
2034 *error_cnt_p = *error_cnt_p + 1;
2035 }
2036 }
2037
2038 // Check the thread's free list and count; log the results of the checks.
2039 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
2040 outputStream * out,
2041 int *error_cnt_p) {
2042 int chkOmFreeCount = 0;
2043 for (ObjectMonitor * n = jt->omFreeList; n != NULL; n = n->FreeNext) {
2044 chk_free_entry(jt, n, out, error_cnt_p);
2045 chkOmFreeCount++;
2046 }
2047 if (jt->omFreeCount == chkOmFreeCount) {
2048 out->print_cr("jt=" INTPTR_FORMAT ": omFreeCount=%d equals "
2049 "chkOmFreeCount=%d", p2i(jt), jt->omFreeCount, chkOmFreeCount);
2050 } else {
2051 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omFreeCount=%d is not "
2052 "equal to chkOmFreeCount=%d", p2i(jt), jt->omFreeCount,
2053 chkOmFreeCount);
2054 *error_cnt_p = *error_cnt_p + 1;
2055 }
2056 }
2057
2058 // Check the thread's in-use list and count; log the results of the checks.
2059 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
2060 outputStream * out,
2061 int *error_cnt_p) {
2062 int chkOmInUseCount = 0;
2063 for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2064 chk_in_use_entry(jt, n, out, error_cnt_p);
2065 chkOmInUseCount++;
2066 }
2067 if (jt->omInUseCount == chkOmInUseCount) {
2068 out->print_cr("jt=" INTPTR_FORMAT ": omInUseCount=%d equals "
2069 "chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2070 chkOmInUseCount);
2071 } else {
2072 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omInUseCount=%d is not "
2073 "equal to chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2074 chkOmInUseCount);
2075 *error_cnt_p = *error_cnt_p + 1;
2076 }
2077 }
2078
2079 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2080 // flags indicate why the entry is in-use, 'object' and 'object type'
2081 // indicate the associated object and its type.
2082 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out,
2083 bool on_exit) {
2084 if (!on_exit) {
2085 // Not at VM exit so grab the global list lock.
2086 Thread::muxAcquire(&gListLock, "log_in_use_monitor_details");
2087 }
2088
2089 stringStream ss;
2090 if (gOmInUseCount > 0) {
2091 out->print_cr("In-use global monitor info:");
2092 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2093 out->print_cr("%18s %s %18s %18s",
2094 "monitor", "BHL", "object", "object type");
2095 out->print_cr("================== === ================== ==================");
2096 for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
2097 const oop obj = (oop) n->object();
2098 const markWord mark = n->header();
2099 ResourceMark rm;
2100 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(n),
2101 n->is_busy() != 0, mark.hash() != 0, n->owner() != NULL,
2102 p2i(obj), obj->klass()->external_name());
2103 if (n->is_busy() != 0) {
2104 out->print(" (%s)", n->is_busy_to_string(&ss));
2105 ss.reset();
2106 }
2107 out->cr();
2108 }
2109 }
2110
2111 if (!on_exit) {
2112 Thread::muxRelease(&gListLock);
2113 }
2114
2115 out->print_cr("In-use per-thread monitor info:");
2116 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2117 out->print_cr("%18s %18s %s %18s %18s",
2118 "jt", "monitor", "BHL", "object", "object type");
2119 out->print_cr("================== ================== === ================== ==================");
2120 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2121 for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2122 const oop obj = (oop) n->object();
2123 const markWord mark = n->header();
2124 ResourceMark rm;
2125 out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT
2126 " %s", p2i(jt), p2i(n), n->is_busy() != 0,
2127 mark.hash() != 0, n->owner() != NULL, p2i(obj),
2128 obj->klass()->external_name());
2129 if (n->is_busy() != 0) {
2130 out->print(" (%s)", n->is_busy_to_string(&ss));
2131 ss.reset();
2132 }
2133 out->cr();
2134 }
2135 }
2136
2137 out->flush();
2138 }
2139
2140 // Log counts for the global and per-thread monitor lists and return
2141 // the population count.
2142 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2143 int popCount = 0;
2144 out->print_cr("%18s %10s %10s %10s",
2145 "Global Lists:", "InUse", "Free", "Total");
2146 out->print_cr("================== ========== ========== ==========");
2147 out->print_cr("%18s %10d %10d %10d", "",
2148 gOmInUseCount, gMonitorFreeCount, gMonitorPopulation);
2149 popCount += gOmInUseCount + gMonitorFreeCount;
2150
2151 out->print_cr("%18s %10s %10s %10s",
2152 "Per-Thread Lists:", "InUse", "Free", "Provision");
2153 out->print_cr("================== ========== ========== ==========");
2154
2155 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2156 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
2157 jt->omInUseCount, jt->omFreeCount, jt->omFreeProvision);
2158 popCount += jt->omInUseCount + jt->omFreeCount;
2159 }
2160 return popCount;
2161 }
2162
2163 #ifndef PRODUCT
2164
2165 // Check if monitor belongs to the monitor cache
2166 // The list is grow-only so it's *relatively* safe to traverse
2167 // the list of extant blocks without taking a lock.
2168
2169 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
2170 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
2171 while (block != NULL) {
2172 assert(block->object() == CHAINMARKER, "must be a block header");
2173 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
2174 address mon = (address)monitor;
2175 address blk = (address)block;
2176 size_t diff = mon - blk;
2177 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "must be aligned");
2178 return 1;
2179 }
2180 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
2181 }
2182 return 0;
2183 }
2184
2185 #endif