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 PaddedObjectMonitor* volatile ObjectSynchronizer::g_block_list = NULL;
121 // Global ObjectMonitor free list. Newly allocated and deflated
122 // ObjectMonitors are prepended here.
123 ObjectMonitor* volatile ObjectSynchronizer::g_free_list = NULL;
124 // Global ObjectMonitor in-use list. When a JavaThread is exiting,
125 // ObjectMonitors on its per-thread in-use list are prepended here.
126 ObjectMonitor* volatile ObjectSynchronizer::g_om_in_use_list = NULL;
127 int ObjectSynchronizer::g_om_in_use_count = 0; // # on g_om_in_use_list
128
129 static volatile intptr_t gListLock = 0; // protects global monitor lists
130 static volatile int g_om_free_count = 0; // # on g_free_list
131 static volatile int g_om_population = 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 free_count = 0;
187 do {
188 mon->INotify(self);
189 ++free_count;
190 } while (mon->first_waiter() != NULL && all);
191 OM_PERFDATA_OP(Notifications, inc(free_count));
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 do_lock) {
420 _dolock = do_lock;
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::wait_uninterruptibly(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 stw_random;
524 volatile int stw_cycle;
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 hc_sequence;
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 read_stable_mark(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 read_stable_mark() 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,stw_random}
605 // * CRC32 of {obj,stw_random} 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.stw_random ;
610 // * A variation of Marsaglia's shift-xor RNG scheme.
611 // * (obj ^ stw_random) 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 addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
630 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
631 } else if (hashCode == 2) {
632 value = 1; // for sensitivity testing
633 } else if (hashCode == 3) {
634 value = ++GVars.hc_sequence;
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 = read_stable_mark(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 non-deflation update to the ObjectMonitor's
752 // header/dmw field is to merge in the hash code. If someone
753 // adds a new usage of the header/dmw field, please update
754 // this code.
755 hash = test.hash();
756 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
757 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
758 }
759 }
760 // We finally get the hash
761 return hash;
762 }
763
764 // Deprecated -- use FastHashCode() instead.
765
766 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
767 return FastHashCode(Thread::current(), obj());
768 }
769
770
771 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
772 Handle h_obj) {
773 if (UseBiasedLocking) {
774 BiasedLocking::revoke(h_obj, thread);
775 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
776 }
777
778 assert(thread == JavaThread::current(), "Can only be called on current thread");
779 oop obj = h_obj();
780
781 markWord mark = read_stable_mark(obj);
782
783 // Uncontended case, header points to stack
784 if (mark.has_locker()) {
785 return thread->is_lock_owned((address)mark.locker());
786 }
787 // Contended case, header points to ObjectMonitor (tagged pointer)
788 if (mark.has_monitor()) {
789 ObjectMonitor* monitor = mark.monitor();
790 return monitor->is_entered(thread) != 0;
791 }
792 // Unlocked case, header in place
793 assert(mark.is_neutral(), "sanity check");
794 return false;
795 }
796
797 // Be aware of this method could revoke bias of the lock object.
798 // This method queries the ownership of the lock handle specified by 'h_obj'.
799 // If the current thread owns the lock, it returns owner_self. If no
800 // thread owns the lock, it returns owner_none. Otherwise, it will return
801 // owner_other.
802 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
803 (JavaThread *self, Handle h_obj) {
804 // The caller must beware this method can revoke bias, and
805 // revocation can result in a safepoint.
806 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
807 assert(self->thread_state() != _thread_blocked, "invariant");
808
809 // Possible mark states: neutral, biased, stack-locked, inflated
810
811 if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) {
812 // CASE: biased
813 BiasedLocking::revoke(h_obj, self);
814 assert(!h_obj->mark().has_bias_pattern(),
815 "biases should be revoked by now");
816 }
817
818 assert(self == JavaThread::current(), "Can only be called on current thread");
819 oop obj = h_obj();
820 markWord mark = read_stable_mark(obj);
821
822 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
823 if (mark.has_locker()) {
824 return self->is_lock_owned((address)mark.locker()) ?
825 owner_self : owner_other;
826 }
827
828 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
829 // The Object:ObjectMonitor relationship is stable as long as we're
830 // not at a safepoint.
831 if (mark.has_monitor()) {
832 void* owner = mark.monitor()->_owner;
833 if (owner == NULL) return owner_none;
834 return (owner == self ||
835 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
836 }
837
838 // CASE: neutral
839 assert(mark.is_neutral(), "sanity check");
840 return owner_none; // it's unlocked
841 }
842
843 // FIXME: jvmti should call this
844 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
845 if (UseBiasedLocking) {
846 if (SafepointSynchronize::is_at_safepoint()) {
847 BiasedLocking::revoke_at_safepoint(h_obj);
848 } else {
849 BiasedLocking::revoke(h_obj, JavaThread::current());
850 }
851 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
852 }
853
854 oop obj = h_obj();
855 address owner = NULL;
856
857 markWord mark = read_stable_mark(obj);
858
859 // Uncontended case, header points to stack
860 if (mark.has_locker()) {
861 owner = (address) mark.locker();
862 }
863
864 // Contended case, header points to ObjectMonitor (tagged pointer)
865 else if (mark.has_monitor()) {
866 ObjectMonitor* monitor = mark.monitor();
867 assert(monitor != NULL, "monitor should be non-null");
868 owner = (address) monitor->owner();
869 }
870
871 if (owner != NULL) {
872 // owning_thread_from_monitor_owner() may also return NULL here
873 return Threads::owning_thread_from_monitor_owner(t_list, owner);
874 }
875
876 // Unlocked case, header in place
877 // Cannot have assertion since this object may have been
878 // locked by another thread when reaching here.
879 // assert(mark.is_neutral(), "sanity check");
880
881 return NULL;
882 }
883
884 // Visitors ...
885
886 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
887 PaddedObjectMonitor* block = OrderAccess::load_acquire(&g_block_list);
888 while (block != NULL) {
889 assert(block->object() == CHAINMARKER, "must be a block header");
890 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
891 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
892 oop object = (oop)mid->object();
893 if (object != NULL) {
894 // Only process with closure if the object is set.
895 closure->do_monitor(mid);
896 }
897 }
898 block = (PaddedObjectMonitor*)block->_next_om;
899 }
900 }
901
902 static bool monitors_used_above_threshold() {
903 if (g_om_population == 0) {
904 return false;
905 }
906 int monitors_used = g_om_population - g_om_free_count;
907 int monitor_usage = (monitors_used * 100LL) / g_om_population;
908 return monitor_usage > MonitorUsedDeflationThreshold;
909 }
910
911 bool ObjectSynchronizer::is_cleanup_needed() {
912 if (MonitorUsedDeflationThreshold > 0) {
913 return monitors_used_above_threshold();
914 }
915 return false;
916 }
917
918 void ObjectSynchronizer::oops_do(OopClosure* f) {
919 // We only scan the global used list here (for moribund threads), and
920 // the thread-local monitors in Thread::oops_do().
921 global_used_oops_do(f);
922 }
923
924 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
925 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
926 list_oops_do(g_om_in_use_list, f);
927 }
928
929 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
930 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
931 list_oops_do(thread->om_in_use_list, f);
932 }
933
934 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
935 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
936 ObjectMonitor* mid;
937 for (mid = list; mid != NULL; mid = mid->_next_om) {
938 if (mid->object() != NULL) {
939 f->do_oop((oop*)mid->object_addr());
940 }
941 }
942 }
943
944
945 // -----------------------------------------------------------------------------
946 // ObjectMonitor Lifecycle
947 // -----------------------
948 // Inflation unlinks monitors from the global g_free_list and
949 // associates them with objects. Deflation -- which occurs at
950 // STW-time -- disassociates idle monitors from objects. Such
951 // scavenged monitors are returned to the g_free_list.
952 //
953 // The global list is protected by gListLock. All the critical sections
954 // are short and operate in constant-time.
955 //
956 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
957 //
958 // Lifecycle:
959 // -- unassigned and on the global free list
960 // -- unassigned and on a thread's private om_free_list
961 // -- assigned to an object. The object is inflated and the mark refers
962 // to the objectmonitor.
963
964
965 // Constraining monitor pool growth via MonitorBound ...
966 //
967 // If MonitorBound is not set (<= 0), MonitorBound checks are disabled.
968 //
969 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
970 // the rate of scavenging is driven primarily by GC. As such, we can find
971 // an inordinate number of monitors in circulation.
972 // To avoid that scenario we can artificially induce a STW safepoint
973 // if the pool appears to be growing past some reasonable bound.
974 // Generally we favor time in space-time tradeoffs, but as there's no
975 // natural back-pressure on the # of extant monitors we need to impose some
976 // type of limit. Beware that if MonitorBound is set to too low a value
977 // we could just loop. In addition, if MonitorBound is set to a low value
978 // we'll incur more safepoints, which are harmful to performance.
979 // See also: GuaranteedSafepointInterval
980 //
981 // The current implementation uses asynchronous VM operations.
982 //
983 // If MonitorBound is set, the boundry applies to
984 // (g_om_population - g_om_free_count)
985 // i.e., if there are not enough ObjectMonitors on the global free list,
986 // then a safepoint deflation is induced. Picking a good MonitorBound value
987 // is non-trivial.
988
989 static void InduceScavenge(Thread* self, const char * Whence) {
990 // Induce STW safepoint to trim monitors
991 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
992 // More precisely, trigger an asynchronous STW safepoint as the number
993 // of active monitors passes the specified threshold.
994 // TODO: assert thread state is reasonable
995
996 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
997 // Induce a 'null' safepoint to scavenge monitors
998 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
999 // to the VMthread and have a lifespan longer than that of this activation record.
1000 // The VMThread will delete the op when completed.
1001 VMThread::execute(new VM_ScavengeMonitors());
1002 }
1003 }
1004
1005 ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self) {
1006 // A large MAXPRIVATE value reduces both list lock contention
1007 // and list coherency traffic, but also tends to increase the
1008 // number of ObjectMonitors in circulation as well as the STW
1009 // scavenge costs. As usual, we lean toward time in space-time
1010 // tradeoffs.
1011 const int MAXPRIVATE = 1024;
1012 stringStream ss;
1013 for (;;) {
1014 ObjectMonitor* m;
1015
1016 // 1: try to allocate from the thread's local om_free_list.
1017 // Threads will attempt to allocate first from their local list, then
1018 // from the global list, and only after those attempts fail will the thread
1019 // attempt to instantiate new monitors. Thread-local free lists take
1020 // heat off the gListLock and improve allocation latency, as well as reducing
1021 // coherency traffic on the shared global list.
1022 m = self->om_free_list;
1023 if (m != NULL) {
1024 self->om_free_list = m->_next_om;
1025 self->om_free_count--;
1026 guarantee(m->object() == NULL, "invariant");
1027 m->_next_om = self->om_in_use_list;
1028 self->om_in_use_list = m;
1029 self->om_in_use_count++;
1030 return m;
1031 }
1032
1033 // 2: try to allocate from the global g_free_list
1034 // CONSIDER: use muxTry() instead of muxAcquire().
1035 // If the muxTry() fails then drop immediately into case 3.
1036 // If we're using thread-local free lists then try
1037 // to reprovision the caller's free list.
1038 if (g_free_list != NULL) {
1039 // Reprovision the thread's om_free_list.
1040 // Use bulk transfers to reduce the allocation rate and heat
1041 // on various locks.
1042 Thread::muxAcquire(&gListLock, "om_alloc(1)");
1043 for (int i = self->om_free_provision; --i >= 0 && g_free_list != NULL;) {
1044 g_om_free_count--;
1045 ObjectMonitor* take = g_free_list;
1046 g_free_list = take->_next_om;
1047 guarantee(take->object() == NULL, "invariant");
1048 take->Recycle();
1049 om_release(self, take, false);
1050 }
1051 Thread::muxRelease(&gListLock);
1052 self->om_free_provision += 1 + (self->om_free_provision/2);
1053 if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE;
1054
1055 const int mx = MonitorBound;
1056 if (mx > 0 && (g_om_population-g_om_free_count) > mx) {
1057 // Not enough ObjectMonitors on the global free list.
1058 // We can't safely induce a STW safepoint from om_alloc() as our thread
1059 // state may not be appropriate for such activities and callers may hold
1060 // naked oops, so instead we defer the action.
1061 InduceScavenge(self, "om_alloc");
1062 }
1063 continue;
1064 }
1065
1066 // 3: allocate a block of new ObjectMonitors
1067 // Both the local and global free lists are empty -- resort to malloc().
1068 // In the current implementation ObjectMonitors are TSM - immortal.
1069 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1070 // each ObjectMonitor to start at the beginning of a cache line,
1071 // so we use align_up().
1072 // A better solution would be to use C++ placement-new.
1073 // BEWARE: As it stands currently, we don't run the ctors!
1074 assert(_BLOCKSIZE > 1, "invariant");
1075 size_t neededsize = sizeof(PaddedObjectMonitor) * _BLOCKSIZE;
1076 PaddedObjectMonitor* temp;
1077 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1078 void* real_malloc_addr = (void*)NEW_C_HEAP_ARRAY(char, aligned_size,
1079 mtInternal);
1080 temp = (PaddedObjectMonitor*)align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE);
1081
1082 // NOTE: (almost) no way to recover if allocation failed.
1083 // We might be able to induce a STW safepoint and scavenge enough
1084 // ObjectMonitors to permit progress.
1085 if (temp == NULL) {
1086 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1087 "Allocate ObjectMonitors");
1088 }
1089 (void)memset((void *) temp, 0, neededsize);
1090
1091 // Format the block.
1092 // initialize the linked list, each monitor points to its next
1093 // forming the single linked free list, the very first monitor
1094 // will points to next block, which forms the block list.
1095 // The trick of using the 1st element in the block as g_block_list
1096 // linkage should be reconsidered. A better implementation would
1097 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1098
1099 for (int i = 1; i < _BLOCKSIZE; i++) {
1100 temp[i]._next_om = (ObjectMonitor *)&temp[i+1];
1101 }
1102
1103 // terminate the last monitor as the end of list
1104 temp[_BLOCKSIZE - 1]._next_om = NULL;
1105
1106 // Element [0] is reserved for global list linkage
1107 temp[0].set_object(CHAINMARKER);
1108
1109 // Consider carving out this thread's current request from the
1110 // block in hand. This avoids some lock traffic and redundant
1111 // list activity.
1112
1113 // Acquire the gListLock to manipulate g_block_list and g_free_list.
1114 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1115 Thread::muxAcquire(&gListLock, "om_alloc(2)");
1116 g_om_population += _BLOCKSIZE-1;
1117 g_om_free_count += _BLOCKSIZE-1;
1118
1119 // Add the new block to the list of extant blocks (g_block_list).
1120 // The very first ObjectMonitor in a block is reserved and dedicated.
1121 // It serves as blocklist "next" linkage.
1122 temp[0]._next_om = g_block_list;
1123 // There are lock-free uses of g_block_list so make sure that
1124 // the previous stores happen before we update g_block_list.
1125 OrderAccess::release_store(&g_block_list, temp);
1126
1127 // Add the new string of ObjectMonitors to the global free list
1128 temp[_BLOCKSIZE - 1]._next_om = g_free_list;
1129 g_free_list = temp + 1;
1130 Thread::muxRelease(&gListLock);
1131 }
1132 }
1133
1134 // Place "m" on the caller's private per-thread om_free_list.
1135 // In practice there's no need to clamp or limit the number of
1136 // monitors on a thread's om_free_list as the only non-allocation time
1137 // we'll call om_release() is to return a monitor to the free list after
1138 // a CAS attempt failed. This doesn't allow unbounded #s of monitors to
1139 // accumulate on a thread's free list.
1140 //
1141 // Key constraint: all ObjectMonitors on a thread's free list and the global
1142 // free list must have their object field set to null. This prevents the
1143 // scavenger -- deflate_monitor_list() -- from reclaiming them while we
1144 // are trying to release them.
1145
1146 void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m,
1147 bool from_per_thread_alloc) {
1148 guarantee(m->header().value() == 0, "invariant");
1149 guarantee(m->object() == NULL, "invariant");
1150 stringStream ss;
1151 guarantee((m->is_busy() | m->_recursions) == 0, "freeing in-use monitor: "
1152 "%s, recursions=" INTPTR_FORMAT, m->is_busy_to_string(&ss),
1153 m->_recursions);
1154 // _next_om is used for both per-thread in-use and free lists so
1155 // we have to remove 'm' from the in-use list first (as needed).
1156 if (from_per_thread_alloc) {
1157 // Need to remove 'm' from om_in_use_list.
1158 ObjectMonitor* cur_mid_in_use = NULL;
1159 bool extracted = false;
1160 for (ObjectMonitor* mid = self->om_in_use_list; mid != NULL; cur_mid_in_use = mid, mid = mid->_next_om) {
1161 if (m == mid) {
1162 // extract from per-thread in-use list
1163 if (mid == self->om_in_use_list) {
1164 self->om_in_use_list = mid->_next_om;
1165 } else if (cur_mid_in_use != NULL) {
1166 cur_mid_in_use->_next_om = mid->_next_om; // maintain the current thread in-use list
1167 }
1168 extracted = true;
1169 self->om_in_use_count--;
1170 break;
1171 }
1172 }
1173 assert(extracted, "Should have extracted from in-use list");
1174 }
1175
1176 m->_next_om = self->om_free_list;
1177 self->om_free_list = m;
1178 self->om_free_count++;
1179 }
1180
1181 // Return ObjectMonitors on a moribund thread's free and in-use
1182 // lists to the appropriate global lists. The ObjectMonitors on the
1183 // per-thread in-use list may still be in use by other threads.
1184 //
1185 // We currently call om_flush() from Threads::remove() before the
1186 // thread has been excised from the thread list and is no longer a
1187 // mutator. This means that om_flush() cannot run concurrently with
1188 // a safepoint and interleave with deflate_idle_monitors(). In
1189 // particular, this ensures that the thread's in-use monitors are
1190 // scanned by a GC safepoint, either via Thread::oops_do() (before
1191 // om_flush() is called) or via ObjectSynchronizer::oops_do() (after
1192 // om_flush() is called).
1193
1194 void ObjectSynchronizer::om_flush(Thread* self) {
1195 ObjectMonitor* free_list = self->om_free_list;
1196 ObjectMonitor* free_tail = NULL;
1197 int free_count = 0;
1198 if (free_list != NULL) {
1199 ObjectMonitor* s;
1200 // The thread is going away. Set 'free_tail' to the last per-thread free
1201 // monitor which will be linked to g_free_list below under the gListLock.
1202 stringStream ss;
1203 for (s = free_list; s != NULL; s = s->_next_om) {
1204 free_count++;
1205 free_tail = s;
1206 guarantee(s->object() == NULL, "invariant");
1207 guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss));
1208 }
1209 guarantee(free_tail != NULL, "invariant");
1210 assert(self->om_free_count == free_count, "free-count off");
1211 self->om_free_list = NULL;
1212 self->om_free_count = 0;
1213 }
1214
1215 ObjectMonitor* in_use_list = self->om_in_use_list;
1216 ObjectMonitor* in_use_tail = NULL;
1217 int in_use_count = 0;
1218 if (in_use_list != NULL) {
1219 // The thread is going away, however the ObjectMonitors on the
1220 // om_in_use_list may still be in-use by other threads. Link
1221 // them to in_use_tail, which will be linked into the global
1222 // in-use list g_om_in_use_list below, under the gListLock.
1223 ObjectMonitor *cur_om;
1224 for (cur_om = in_use_list; cur_om != NULL; cur_om = cur_om->_next_om) {
1225 in_use_tail = cur_om;
1226 in_use_count++;
1227 }
1228 guarantee(in_use_tail != NULL, "invariant");
1229 assert(self->om_in_use_count == in_use_count, "in-use count off");
1230 self->om_in_use_list = NULL;
1231 self->om_in_use_count = 0;
1232 }
1233
1234 Thread::muxAcquire(&gListLock, "om_flush");
1235 if (free_tail != NULL) {
1236 free_tail->_next_om = g_free_list;
1237 g_free_list = free_list;
1238 g_om_free_count += free_count;
1239 }
1240
1241 if (in_use_tail != NULL) {
1242 in_use_tail->_next_om = g_om_in_use_list;
1243 g_om_in_use_list = in_use_list;
1244 g_om_in_use_count += in_use_count;
1245 }
1246
1247 Thread::muxRelease(&gListLock);
1248
1249 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1250 LogStreamHandle(Info, monitorinflation) lsh_info;
1251 LogStream* ls = NULL;
1252 if (log_is_enabled(Debug, monitorinflation)) {
1253 ls = &lsh_debug;
1254 } else if ((free_count != 0 || in_use_count != 0) &&
1255 log_is_enabled(Info, monitorinflation)) {
1256 ls = &lsh_info;
1257 }
1258 if (ls != NULL) {
1259 ls->print_cr("om_flush: jt=" INTPTR_FORMAT ", free_count=%d"
1260 ", in_use_count=%d" ", om_free_provision=%d",
1261 p2i(self), free_count, in_use_count, self->om_free_provision);
1262 }
1263 }
1264
1265 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1266 const oop obj,
1267 ObjectSynchronizer::InflateCause cause) {
1268 assert(event != NULL, "invariant");
1269 assert(event->should_commit(), "invariant");
1270 event->set_monitorClass(obj->klass());
1271 event->set_address((uintptr_t)(void*)obj);
1272 event->set_cause((u1)cause);
1273 event->commit();
1274 }
1275
1276 // Fast path code shared by multiple functions
1277 void ObjectSynchronizer::inflate_helper(oop obj) {
1278 markWord mark = obj->mark();
1279 if (mark.has_monitor()) {
1280 assert(ObjectSynchronizer::verify_objmon_isinpool(mark.monitor()), "monitor is invalid");
1281 assert(mark.monitor()->header().is_neutral(), "monitor must record a good object header");
1282 return;
1283 }
1284 inflate(Thread::current(), obj, inflate_cause_vm_internal);
1285 }
1286
1287 ObjectMonitor* ObjectSynchronizer::inflate(Thread* self,
1288 oop object,
1289 const InflateCause cause) {
1290 // Inflate mutates the heap ...
1291 // Relaxing assertion for bug 6320749.
1292 assert(Universe::verify_in_progress() ||
1293 !SafepointSynchronize::is_at_safepoint(), "invariant");
1294
1295 EventJavaMonitorInflate event;
1296
1297 for (;;) {
1298 const markWord mark = object->mark();
1299 assert(!mark.has_bias_pattern(), "invariant");
1300
1301 // The mark can be in one of the following states:
1302 // * Inflated - just return
1303 // * Stack-locked - coerce it to inflated
1304 // * INFLATING - busy wait for conversion to complete
1305 // * Neutral - aggressively inflate the object.
1306 // * BIASED - Illegal. We should never see this
1307
1308 // CASE: inflated
1309 if (mark.has_monitor()) {
1310 ObjectMonitor* inf = mark.monitor();
1311 markWord dmw = inf->header();
1312 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1313 assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1314 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1315 return inf;
1316 }
1317
1318 // CASE: inflation in progress - inflating over a stack-lock.
1319 // Some other thread is converting from stack-locked to inflated.
1320 // Only that thread can complete inflation -- other threads must wait.
1321 // The INFLATING value is transient.
1322 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1323 // We could always eliminate polling by parking the thread on some auxiliary list.
1324 if (mark == markWord::INFLATING()) {
1325 read_stable_mark(object);
1326 continue;
1327 }
1328
1329 // CASE: stack-locked
1330 // Could be stack-locked either by this thread or by some other thread.
1331 //
1332 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1333 // to install INFLATING into the mark word. We originally installed INFLATING,
1334 // allocated the objectmonitor, and then finally STed the address of the
1335 // objectmonitor into the mark. This was correct, but artificially lengthened
1336 // the interval in which INFLATED appeared in the mark, thus increasing
1337 // the odds of inflation contention.
1338 //
1339 // We now use per-thread private objectmonitor free lists.
1340 // These list are reprovisioned from the global free list outside the
1341 // critical INFLATING...ST interval. A thread can transfer
1342 // multiple objectmonitors en-mass from the global free list to its local free list.
1343 // This reduces coherency traffic and lock contention on the global free list.
1344 // Using such local free lists, it doesn't matter if the om_alloc() call appears
1345 // before or after the CAS(INFLATING) operation.
1346 // See the comments in om_alloc().
1347
1348 LogStreamHandle(Trace, monitorinflation) lsh;
1349
1350 if (mark.has_locker()) {
1351 ObjectMonitor* m = om_alloc(self);
1352 // Optimistically prepare the objectmonitor - anticipate successful CAS
1353 // We do this before the CAS in order to minimize the length of time
1354 // in which INFLATING appears in the mark.
1355 m->Recycle();
1356 m->_Responsible = NULL;
1357 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1358
1359 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1360 if (cmp != mark) {
1361 om_release(self, m, true);
1362 continue; // Interference -- just retry
1363 }
1364
1365 // We've successfully installed INFLATING (0) into the mark-word.
1366 // This is the only case where 0 will appear in a mark-word.
1367 // Only the singular thread that successfully swings the mark-word
1368 // to 0 can perform (or more precisely, complete) inflation.
1369 //
1370 // Why do we CAS a 0 into the mark-word instead of just CASing the
1371 // mark-word from the stack-locked value directly to the new inflated state?
1372 // Consider what happens when a thread unlocks a stack-locked object.
1373 // It attempts to use CAS to swing the displaced header value from the
1374 // on-stack BasicLock back into the object header. Recall also that the
1375 // header value (hash code, etc) can reside in (a) the object header, or
1376 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1377 // header in an ObjectMonitor. The inflate() routine must copy the header
1378 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1379 // the while preserving the hashCode stability invariants. If the owner
1380 // decides to release the lock while the value is 0, the unlock will fail
1381 // and control will eventually pass from slow_exit() to inflate. The owner
1382 // will then spin, waiting for the 0 value to disappear. Put another way,
1383 // the 0 causes the owner to stall if the owner happens to try to
1384 // drop the lock (restoring the header from the BasicLock to the object)
1385 // while inflation is in-progress. This protocol avoids races that might
1386 // would otherwise permit hashCode values to change or "flicker" for an object.
1387 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1388 // 0 serves as a "BUSY" inflate-in-progress indicator.
1389
1390
1391 // fetch the displaced mark from the owner's stack.
1392 // The owner can't die or unwind past the lock while our INFLATING
1393 // object is in the mark. Furthermore the owner can't complete
1394 // an unlock on the object, either.
1395 markWord dmw = mark.displaced_mark_helper();
1396 // Catch if the object's header is not neutral (not locked and
1397 // not marked is what we care about here).
1398 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1399
1400 // Setup monitor fields to proper values -- prepare the monitor
1401 m->set_header(dmw);
1402
1403 // Optimization: if the mark.locker stack address is associated
1404 // with this thread we could simply set m->_owner = self.
1405 // Note that a thread can inflate an object
1406 // that it has stack-locked -- as might happen in wait() -- directly
1407 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1408 m->set_owner(mark.locker());
1409 m->set_object(object);
1410 // TODO-FIXME: assert BasicLock->dhw != 0.
1411
1412 // Must preserve store ordering. The monitor state must
1413 // be stable at the time of publishing the monitor address.
1414 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1415 object->release_set_mark(markWord::encode(m));
1416
1417 // Hopefully the performance counters are allocated on distinct cache lines
1418 // to avoid false sharing on MP systems ...
1419 OM_PERFDATA_OP(Inflations, inc());
1420 if (log_is_enabled(Trace, monitorinflation)) {
1421 ResourceMark rm(self);
1422 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1423 INTPTR_FORMAT ", type='%s'", p2i(object),
1424 object->mark().value(), object->klass()->external_name());
1425 }
1426 if (event.should_commit()) {
1427 post_monitor_inflate_event(&event, object, cause);
1428 }
1429 return m;
1430 }
1431
1432 // CASE: neutral
1433 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1434 // If we know we're inflating for entry it's better to inflate by swinging a
1435 // pre-locked ObjectMonitor pointer into the object header. A successful
1436 // CAS inflates the object *and* confers ownership to the inflating thread.
1437 // In the current implementation we use a 2-step mechanism where we CAS()
1438 // to inflate and then CAS() again to try to swing _owner from NULL to self.
1439 // An inflateTry() method that we could call from enter() would be useful.
1440
1441 // Catch if the object's header is not neutral (not locked and
1442 // not marked is what we care about here).
1443 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1444 ObjectMonitor* m = om_alloc(self);
1445 // prepare m for installation - set monitor to initial state
1446 m->Recycle();
1447 m->set_header(mark);
1448 m->set_object(object);
1449 m->_Responsible = NULL;
1450 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1451
1452 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1453 m->set_header(markWord::zero());
1454 m->set_object(NULL);
1455 m->Recycle();
1456 om_release(self, m, true);
1457 m = NULL;
1458 continue;
1459 // interference - the markword changed - just retry.
1460 // The state-transitions are one-way, so there's no chance of
1461 // live-lock -- "Inflated" is an absorbing state.
1462 }
1463
1464 // Hopefully the performance counters are allocated on distinct
1465 // cache lines to avoid false sharing on MP systems ...
1466 OM_PERFDATA_OP(Inflations, inc());
1467 if (log_is_enabled(Trace, monitorinflation)) {
1468 ResourceMark rm(self);
1469 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1470 INTPTR_FORMAT ", type='%s'", p2i(object),
1471 object->mark().value(), object->klass()->external_name());
1472 }
1473 if (event.should_commit()) {
1474 post_monitor_inflate_event(&event, object, cause);
1475 }
1476 return m;
1477 }
1478 }
1479
1480
1481 // We maintain a list of in-use monitors for each thread.
1482 //
1483 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1484 // deflate_idle_monitors() scans only a global list of in-use monitors which
1485 // is populated only as a thread dies (see om_flush()).
1486 //
1487 // These operations are called at all safepoints, immediately after mutators
1488 // are stopped, but before any objects have moved. Collectively they traverse
1489 // the population of in-use monitors, deflating where possible. The scavenged
1490 // monitors are returned to the global monitor free list.
1491 //
1492 // Beware that we scavenge at *every* stop-the-world point. Having a large
1493 // number of monitors in-use could negatively impact performance. We also want
1494 // to minimize the total # of monitors in circulation, as they incur a small
1495 // footprint penalty.
1496 //
1497 // Perversely, the heap size -- and thus the STW safepoint rate --
1498 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1499 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1500 // This is an unfortunate aspect of this design.
1501
1502 // Deflate a single monitor if not in-use
1503 // Return true if deflated, false if in-use
1504 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1505 ObjectMonitor** free_head_p,
1506 ObjectMonitor** free_tail_p) {
1507 bool deflated;
1508 // Normal case ... The monitor is associated with obj.
1509 const markWord mark = obj->mark();
1510 guarantee(mark == markWord::encode(mid), "should match: mark="
1511 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(),
1512 markWord::encode(mid).value());
1513 // Make sure that mark.monitor() and markWord::encode() agree:
1514 guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
1515 ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid));
1516 const markWord dmw = mid->header();
1517 guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1518
1519 if (mid->is_busy()) {
1520 deflated = false;
1521 } else {
1522 // Deflate the monitor if it is no longer being used
1523 // It's idle - scavenge and return to the global free list
1524 // plain old deflation ...
1525 if (log_is_enabled(Trace, monitorinflation)) {
1526 ResourceMark rm;
1527 log_trace(monitorinflation)("deflate_monitor: "
1528 "object=" INTPTR_FORMAT ", mark="
1529 INTPTR_FORMAT ", type='%s'", p2i(obj),
1530 mark.value(), obj->klass()->external_name());
1531 }
1532
1533 // Restore the header back to obj
1534 obj->release_set_mark(dmw);
1535 mid->clear();
1536
1537 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
1538 p2i(mid->object()));
1539
1540 // Move the deflated ObjectMonitor to the working free list
1541 // defined by free_head_p and free_tail_p.
1542 if (*free_head_p == NULL) *free_head_p = mid;
1543 if (*free_tail_p != NULL) {
1544 // We append to the list so the caller can use mid->_next_om
1545 // to fix the linkages in its context.
1546 ObjectMonitor* prevtail = *free_tail_p;
1547 // Should have been cleaned up by the caller:
1548 assert(prevtail->_next_om == NULL, "cleaned up deflated?");
1549 prevtail->_next_om = mid;
1550 }
1551 *free_tail_p = mid;
1552 // At this point, mid->_next_om still refers to its current
1553 // value and another ObjectMonitor's _next_om field still
1554 // refers to this ObjectMonitor. Those linkages have to be
1555 // cleaned up by the caller who has the complete context.
1556 deflated = true;
1557 }
1558 return deflated;
1559 }
1560
1561 // Walk a given monitor list, and deflate idle monitors
1562 // The given list could be a per-thread list or a global list
1563 // Caller acquires gListLock as needed.
1564 //
1565 // In the case of parallel processing of thread local monitor lists,
1566 // work is done by Threads::parallel_threads_do() which ensures that
1567 // each Java thread is processed by exactly one worker thread, and
1568 // thus avoid conflicts that would arise when worker threads would
1569 // process the same monitor lists concurrently.
1570 //
1571 // See also ParallelSPCleanupTask and
1572 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1573 // Threads::parallel_java_threads_do() in thread.cpp.
1574 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** list_p,
1575 ObjectMonitor** free_head_p,
1576 ObjectMonitor** free_tail_p) {
1577 ObjectMonitor* mid;
1578 ObjectMonitor* next;
1579 ObjectMonitor* cur_mid_in_use = NULL;
1580 int deflated_count = 0;
1581
1582 for (mid = *list_p; mid != NULL;) {
1583 oop obj = (oop) mid->object();
1584 if (obj != NULL && deflate_monitor(mid, obj, free_head_p, free_tail_p)) {
1585 // Deflation succeeded and already updated free_head_p and
1586 // free_tail_p as needed. Finish the move to the local free list
1587 // by unlinking mid from the global or per-thread in-use list.
1588 if (mid == *list_p) {
1589 *list_p = mid->_next_om;
1590 } else if (cur_mid_in_use != NULL) {
1591 cur_mid_in_use->_next_om = mid->_next_om; // maintain the current thread in-use list
1592 }
1593 next = mid->_next_om;
1594 mid->_next_om = NULL; // This mid is current tail in the free_head_p list
1595 mid = next;
1596 deflated_count++;
1597 } else {
1598 cur_mid_in_use = mid;
1599 mid = mid->_next_om;
1600 }
1601 }
1602 return deflated_count;
1603 }
1604
1605 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1606 counters->n_in_use = 0; // currently associated with objects
1607 counters->n_in_circulation = 0; // extant
1608 counters->n_scavenged = 0; // reclaimed (global and per-thread)
1609 counters->per_thread_scavenged = 0; // per-thread scavenge total
1610 counters->per_thread_times = 0.0; // per-thread scavenge times
1611 }
1612
1613 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
1614 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1615 bool deflated = false;
1616
1617 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
1618 ObjectMonitor* free_tail_p = NULL;
1619 elapsedTimer timer;
1620
1621 if (log_is_enabled(Info, monitorinflation)) {
1622 timer.start();
1623 }
1624
1625 // Prevent om_flush from changing mids in Thread dtor's during deflation
1626 // And in case the vm thread is acquiring a lock during a safepoint
1627 // See e.g. 6320749
1628 Thread::muxAcquire(&gListLock, "deflate_idle_monitors");
1629
1630 // Note: the thread-local monitors lists get deflated in
1631 // a separate pass. See deflate_thread_local_monitors().
1632
1633 // For moribund threads, scan g_om_in_use_list
1634 int deflated_count = 0;
1635 if (g_om_in_use_list) {
1636 counters->n_in_circulation += g_om_in_use_count;
1637 deflated_count = deflate_monitor_list((ObjectMonitor **)&g_om_in_use_list, &free_head_p, &free_tail_p);
1638 g_om_in_use_count -= deflated_count;
1639 counters->n_scavenged += deflated_count;
1640 counters->n_in_use += g_om_in_use_count;
1641 }
1642
1643 if (free_head_p != NULL) {
1644 // Move the deflated ObjectMonitors back to the global free list.
1645 guarantee(free_tail_p != NULL && counters->n_scavenged > 0, "invariant");
1646 assert(free_tail_p->_next_om == NULL, "invariant");
1647 // constant-time list splice - prepend scavenged segment to g_free_list
1648 free_tail_p->_next_om = g_free_list;
1649 g_free_list = free_head_p;
1650 }
1651 Thread::muxRelease(&gListLock);
1652 timer.stop();
1653
1654 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1655 LogStreamHandle(Info, monitorinflation) lsh_info;
1656 LogStream* ls = NULL;
1657 if (log_is_enabled(Debug, monitorinflation)) {
1658 ls = &lsh_debug;
1659 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
1660 ls = &lsh_info;
1661 }
1662 if (ls != NULL) {
1663 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
1664 }
1665 }
1666
1667 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1668 // Report the cumulative time for deflating each thread's idle
1669 // monitors. Note: if the work is split among more than one
1670 // worker thread, then the reported time will likely be more
1671 // than a beginning to end measurement of the phase.
1672 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged);
1673
1674 g_om_free_count += counters->n_scavenged;
1675
1676 if (log_is_enabled(Debug, monitorinflation)) {
1677 // exit_globals()'s call to audit_and_print_stats() is done
1678 // at the Info level.
1679 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
1680 } else if (log_is_enabled(Info, monitorinflation)) {
1681 Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors");
1682 log_info(monitorinflation)("g_om_population=%d, g_om_in_use_count=%d, "
1683 "g_om_free_count=%d", g_om_population,
1684 g_om_in_use_count, g_om_free_count);
1685 Thread::muxRelease(&gListLock);
1686 }
1687
1688 ForceMonitorScavenge = 0; // Reset
1689
1690 OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged));
1691 OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation));
1692
1693 GVars.stw_random = os::random();
1694 GVars.stw_cycle++;
1695 }
1696
1697 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
1698 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1699
1700 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
1701 ObjectMonitor* free_tail_p = NULL;
1702 elapsedTimer timer;
1703
1704 if (log_is_enabled(Info, safepoint, cleanup) ||
1705 log_is_enabled(Info, monitorinflation)) {
1706 timer.start();
1707 }
1708
1709 int deflated_count = deflate_monitor_list(thread->om_in_use_list_addr(), &free_head_p, &free_tail_p);
1710
1711 Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors");
1712
1713 // Adjust counters
1714 counters->n_in_circulation += thread->om_in_use_count;
1715 thread->om_in_use_count -= deflated_count;
1716 counters->n_scavenged += deflated_count;
1717 counters->n_in_use += thread->om_in_use_count;
1718 counters->per_thread_scavenged += deflated_count;
1719
1720 if (free_head_p != NULL) {
1721 // Move the deflated ObjectMonitors back to the global free list.
1722 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
1723 assert(free_tail_p->_next_om == NULL, "invariant");
1724
1725 // constant-time list splice - prepend scavenged segment to g_free_list
1726 free_tail_p->_next_om = g_free_list;
1727 g_free_list = free_head_p;
1728 }
1729
1730 timer.stop();
1731 // Safepoint logging cares about cumulative per_thread_times and
1732 // we'll capture most of the cost, but not the muxRelease() which
1733 // should be cheap.
1734 counters->per_thread_times += timer.seconds();
1735
1736 Thread::muxRelease(&gListLock);
1737
1738 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1739 LogStreamHandle(Info, monitorinflation) lsh_info;
1740 LogStream* ls = NULL;
1741 if (log_is_enabled(Debug, monitorinflation)) {
1742 ls = &lsh_debug;
1743 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
1744 ls = &lsh_info;
1745 }
1746 if (ls != NULL) {
1747 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
1748 }
1749 }
1750
1751 // Monitor cleanup on JavaThread::exit
1752
1753 // Iterate through monitor cache and attempt to release thread's monitors
1754 // Gives up on a particular monitor if an exception occurs, but continues
1755 // the overall iteration, swallowing the exception.
1756 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1757 private:
1758 TRAPS;
1759
1760 public:
1761 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1762 void do_monitor(ObjectMonitor* mid) {
1763 if (mid->owner() == THREAD) {
1764 (void)mid->complete_exit(CHECK);
1765 }
1766 }
1767 };
1768
1769 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1770 // ignored. This is meant to be called during JNI thread detach which assumes
1771 // all remaining monitors are heavyweight. All exceptions are swallowed.
1772 // Scanning the extant monitor list can be time consuming.
1773 // A simple optimization is to add a per-thread flag that indicates a thread
1774 // called jni_monitorenter() during its lifetime.
1775 //
1776 // Instead of No_Savepoint_Verifier it might be cheaper to
1777 // use an idiom of the form:
1778 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1779 // <code that must not run at safepoint>
1780 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1781 // Since the tests are extremely cheap we could leave them enabled
1782 // for normal product builds.
1783
1784 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1785 assert(THREAD == JavaThread::current(), "must be current Java thread");
1786 NoSafepointVerifier nsv;
1787 ReleaseJavaMonitorsClosure rjmc(THREAD);
1788 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
1789 ObjectSynchronizer::monitors_iterate(&rjmc);
1790 Thread::muxRelease(&gListLock);
1791 THREAD->clear_pending_exception();
1792 }
1793
1794 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1795 switch (cause) {
1796 case inflate_cause_vm_internal: return "VM Internal";
1797 case inflate_cause_monitor_enter: return "Monitor Enter";
1798 case inflate_cause_wait: return "Monitor Wait";
1799 case inflate_cause_notify: return "Monitor Notify";
1800 case inflate_cause_hash_code: return "Monitor Hash Code";
1801 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1802 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1803 default:
1804 ShouldNotReachHere();
1805 }
1806 return "Unknown";
1807 }
1808
1809 //------------------------------------------------------------------------------
1810 // Debugging code
1811
1812 u_char* ObjectSynchronizer::get_gvars_addr() {
1813 return (u_char*)&GVars;
1814 }
1815
1816 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1817 return (u_char*)&GVars.hc_sequence;
1818 }
1819
1820 size_t ObjectSynchronizer::get_gvars_size() {
1821 return sizeof(SharedGlobals);
1822 }
1823
1824 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1825 return (u_char*)&GVars.stw_random;
1826 }
1827
1828 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1829 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1830
1831 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1832 LogStreamHandle(Info, monitorinflation) lsh_info;
1833 LogStreamHandle(Trace, monitorinflation) lsh_trace;
1834 LogStream* ls = NULL;
1835 if (log_is_enabled(Trace, monitorinflation)) {
1836 ls = &lsh_trace;
1837 } else if (log_is_enabled(Debug, monitorinflation)) {
1838 ls = &lsh_debug;
1839 } else if (log_is_enabled(Info, monitorinflation)) {
1840 ls = &lsh_info;
1841 }
1842 assert(ls != NULL, "sanity check");
1843
1844 if (!on_exit) {
1845 // Not at VM exit so grab the global list lock.
1846 Thread::muxAcquire(&gListLock, "audit_and_print_stats");
1847 }
1848
1849 // Log counts for the global and per-thread monitor lists:
1850 int chk_om_population = log_monitor_list_counts(ls);
1851 int error_cnt = 0;
1852
1853 ls->print_cr("Checking global lists:");
1854
1855 // Check g_om_population:
1856 if (g_om_population == chk_om_population) {
1857 ls->print_cr("g_om_population=%d equals chk_om_population=%d",
1858 g_om_population, chk_om_population);
1859 } else {
1860 ls->print_cr("ERROR: g_om_population=%d is not equal to "
1861 "chk_om_population=%d", g_om_population,
1862 chk_om_population);
1863 error_cnt++;
1864 }
1865
1866 // Check g_om_in_use_list and g_om_in_use_count:
1867 chk_global_in_use_list_and_count(ls, &error_cnt);
1868
1869 // Check g_free_list and g_om_free_count:
1870 chk_global_free_list_and_count(ls, &error_cnt);
1871
1872 if (!on_exit) {
1873 Thread::muxRelease(&gListLock);
1874 }
1875
1876 ls->print_cr("Checking per-thread lists:");
1877
1878 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
1879 // Check om_in_use_list and om_in_use_count:
1880 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
1881
1882 // Check om_free_list and om_free_count:
1883 chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
1884 }
1885
1886 if (error_cnt == 0) {
1887 ls->print_cr("No errors found in monitor list checks.");
1888 } else {
1889 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
1890 }
1891
1892 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1893 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1894 // When exiting this log output is at the Info level. When called
1895 // at a safepoint, this log output is at the Trace level since
1896 // there can be a lot of it.
1897 log_in_use_monitor_details(ls, on_exit);
1898 }
1899
1900 ls->flush();
1901
1902 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1903 }
1904
1905 // Check a free monitor entry; log any errors.
1906 void ObjectSynchronizer::chk_free_entry(JavaThread* jt, ObjectMonitor* n,
1907 outputStream * out, int *error_cnt_p) {
1908 stringStream ss;
1909 if (n->is_busy()) {
1910 if (jt != NULL) {
1911 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1912 ": free per-thread monitor must not be busy: %s", p2i(jt),
1913 p2i(n), n->is_busy_to_string(&ss));
1914 } else {
1915 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1916 "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
1917 }
1918 *error_cnt_p = *error_cnt_p + 1;
1919 }
1920 if (n->header().value() != 0) {
1921 if (jt != NULL) {
1922 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1923 ": free per-thread monitor must have NULL _header "
1924 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
1925 n->header().value());
1926 } else {
1927 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1928 "must have NULL _header field: _header=" INTPTR_FORMAT,
1929 p2i(n), n->header().value());
1930 }
1931 *error_cnt_p = *error_cnt_p + 1;
1932 }
1933 if (n->object() != NULL) {
1934 if (jt != NULL) {
1935 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1936 ": free per-thread monitor must have NULL _object "
1937 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
1938 p2i(n->object()));
1939 } else {
1940 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1941 "must have NULL _object field: _object=" INTPTR_FORMAT,
1942 p2i(n), p2i(n->object()));
1943 }
1944 *error_cnt_p = *error_cnt_p + 1;
1945 }
1946 }
1947
1948 // Check the global free list and count; log the results of the checks.
1949 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
1950 int *error_cnt_p) {
1951 int chk_om_free_count = 0;
1952 for (ObjectMonitor* n = g_free_list; n != NULL; n = n->_next_om) {
1953 chk_free_entry(NULL /* jt */, n, out, error_cnt_p);
1954 chk_om_free_count++;
1955 }
1956 if (g_om_free_count == chk_om_free_count) {
1957 out->print_cr("g_om_free_count=%d equals chk_om_free_count=%d",
1958 g_om_free_count, chk_om_free_count);
1959 } else {
1960 out->print_cr("ERROR: g_om_free_count=%d is not equal to "
1961 "chk_om_free_count=%d", g_om_free_count,
1962 chk_om_free_count);
1963 *error_cnt_p = *error_cnt_p + 1;
1964 }
1965 }
1966
1967 // Check the global in-use list and count; log the results of the checks.
1968 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
1969 int *error_cnt_p) {
1970 int chk_om_in_use_count = 0;
1971 for (ObjectMonitor* n = g_om_in_use_list; n != NULL; n = n->_next_om) {
1972 chk_in_use_entry(NULL /* jt */, n, out, error_cnt_p);
1973 chk_om_in_use_count++;
1974 }
1975 if (g_om_in_use_count == chk_om_in_use_count) {
1976 out->print_cr("g_om_in_use_count=%d equals chk_om_in_use_count=%d", g_om_in_use_count,
1977 chk_om_in_use_count);
1978 } else {
1979 out->print_cr("ERROR: g_om_in_use_count=%d is not equal to chk_om_in_use_count=%d",
1980 g_om_in_use_count, chk_om_in_use_count);
1981 *error_cnt_p = *error_cnt_p + 1;
1982 }
1983 }
1984
1985 // Check an in-use monitor entry; log any errors.
1986 void ObjectSynchronizer::chk_in_use_entry(JavaThread* jt, ObjectMonitor* n,
1987 outputStream * out, int *error_cnt_p) {
1988 if (n->header().value() == 0) {
1989 if (jt != NULL) {
1990 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1991 ": in-use per-thread monitor must have non-NULL _header "
1992 "field.", p2i(jt), p2i(n));
1993 } else {
1994 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
1995 "must have non-NULL _header field.", p2i(n));
1996 }
1997 *error_cnt_p = *error_cnt_p + 1;
1998 }
1999 if (n->object() == NULL) {
2000 if (jt != NULL) {
2001 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2002 ": in-use per-thread monitor must have non-NULL _object "
2003 "field.", p2i(jt), p2i(n));
2004 } else {
2005 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2006 "must have non-NULL _object field.", p2i(n));
2007 }
2008 *error_cnt_p = *error_cnt_p + 1;
2009 }
2010 const oop obj = (oop)n->object();
2011 const markWord mark = obj->mark();
2012 if (!mark.has_monitor()) {
2013 if (jt != NULL) {
2014 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2015 ": in-use per-thread monitor's object does not think "
2016 "it has a monitor: obj=" INTPTR_FORMAT ", mark="
2017 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), mark.value());
2018 } else {
2019 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2020 "monitor's object does not think it has a monitor: obj="
2021 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2022 p2i(obj), mark.value());
2023 }
2024 *error_cnt_p = *error_cnt_p + 1;
2025 }
2026 ObjectMonitor* const obj_mon = mark.monitor();
2027 if (n != obj_mon) {
2028 if (jt != NULL) {
2029 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2030 ": in-use per-thread monitor's object does not refer "
2031 "to the same monitor: obj=" INTPTR_FORMAT ", mark="
2032 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
2033 p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2034 } else {
2035 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2036 "monitor's object does not refer to the same monitor: obj="
2037 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2038 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2039 }
2040 *error_cnt_p = *error_cnt_p + 1;
2041 }
2042 }
2043
2044 // Check the thread's free list and count; log the results of the checks.
2045 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
2046 outputStream * out,
2047 int *error_cnt_p) {
2048 int chk_om_free_count = 0;
2049 for (ObjectMonitor* n = jt->om_free_list; n != NULL; n = n->_next_om) {
2050 chk_free_entry(jt, n, out, error_cnt_p);
2051 chk_om_free_count++;
2052 }
2053 if (jt->om_free_count == chk_om_free_count) {
2054 out->print_cr("jt=" INTPTR_FORMAT ": om_free_count=%d equals "
2055 "chk_om_free_count=%d", p2i(jt), jt->om_free_count, chk_om_free_count);
2056 } else {
2057 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_free_count=%d is not "
2058 "equal to chk_om_free_count=%d", p2i(jt), jt->om_free_count,
2059 chk_om_free_count);
2060 *error_cnt_p = *error_cnt_p + 1;
2061 }
2062 }
2063
2064 // Check the thread's in-use list and count; log the results of the checks.
2065 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
2066 outputStream * out,
2067 int *error_cnt_p) {
2068 int chk_om_in_use_count = 0;
2069 for (ObjectMonitor* n = jt->om_in_use_list; n != NULL; n = n->_next_om) {
2070 chk_in_use_entry(jt, n, out, error_cnt_p);
2071 chk_om_in_use_count++;
2072 }
2073 if (jt->om_in_use_count == chk_om_in_use_count) {
2074 out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals "
2075 "chk_om_in_use_count=%d", p2i(jt), jt->om_in_use_count,
2076 chk_om_in_use_count);
2077 } else {
2078 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not "
2079 "equal to chk_om_in_use_count=%d", p2i(jt), jt->om_in_use_count,
2080 chk_om_in_use_count);
2081 *error_cnt_p = *error_cnt_p + 1;
2082 }
2083 }
2084
2085 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2086 // flags indicate why the entry is in-use, 'object' and 'object type'
2087 // indicate the associated object and its type.
2088 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out,
2089 bool on_exit) {
2090 if (!on_exit) {
2091 // Not at VM exit so grab the global list lock.
2092 Thread::muxAcquire(&gListLock, "log_in_use_monitor_details");
2093 }
2094
2095 stringStream ss;
2096 if (g_om_in_use_count > 0) {
2097 out->print_cr("In-use global monitor info:");
2098 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2099 out->print_cr("%18s %s %18s %18s",
2100 "monitor", "BHL", "object", "object type");
2101 out->print_cr("================== === ================== ==================");
2102 for (ObjectMonitor* n = g_om_in_use_list; n != NULL; n = n->_next_om) {
2103 const oop obj = (oop) n->object();
2104 const markWord mark = n->header();
2105 ResourceMark rm;
2106 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(n),
2107 n->is_busy() != 0, mark.hash() != 0, n->owner() != NULL,
2108 p2i(obj), obj->klass()->external_name());
2109 if (n->is_busy() != 0) {
2110 out->print(" (%s)", n->is_busy_to_string(&ss));
2111 ss.reset();
2112 }
2113 out->cr();
2114 }
2115 }
2116
2117 if (!on_exit) {
2118 Thread::muxRelease(&gListLock);
2119 }
2120
2121 out->print_cr("In-use per-thread monitor info:");
2122 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2123 out->print_cr("%18s %18s %s %18s %18s",
2124 "jt", "monitor", "BHL", "object", "object type");
2125 out->print_cr("================== ================== === ================== ==================");
2126 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2127 for (ObjectMonitor* n = jt->om_in_use_list; n != NULL; n = n->_next_om) {
2128 const oop obj = (oop) n->object();
2129 const markWord mark = n->header();
2130 ResourceMark rm;
2131 out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT
2132 " %s", p2i(jt), p2i(n), n->is_busy() != 0,
2133 mark.hash() != 0, n->owner() != NULL, p2i(obj),
2134 obj->klass()->external_name());
2135 if (n->is_busy() != 0) {
2136 out->print(" (%s)", n->is_busy_to_string(&ss));
2137 ss.reset();
2138 }
2139 out->cr();
2140 }
2141 }
2142
2143 out->flush();
2144 }
2145
2146 // Log counts for the global and per-thread monitor lists and return
2147 // the population count.
2148 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2149 int pop_count = 0;
2150 out->print_cr("%18s %10s %10s %10s",
2151 "Global Lists:", "InUse", "Free", "Total");
2152 out->print_cr("================== ========== ========== ==========");
2153 out->print_cr("%18s %10d %10d %10d", "",
2154 g_om_in_use_count, g_om_free_count, g_om_population);
2155 pop_count += g_om_in_use_count + g_om_free_count;
2156
2157 out->print_cr("%18s %10s %10s %10s",
2158 "Per-Thread Lists:", "InUse", "Free", "Provision");
2159 out->print_cr("================== ========== ========== ==========");
2160
2161 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2162 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
2163 jt->om_in_use_count, jt->om_free_count, jt->om_free_provision);
2164 pop_count += jt->om_in_use_count + jt->om_free_count;
2165 }
2166 return pop_count;
2167 }
2168
2169 #ifndef PRODUCT
2170
2171 // Check if monitor belongs to the monitor cache
2172 // The list is grow-only so it's *relatively* safe to traverse
2173 // the list of extant blocks without taking a lock.
2174
2175 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
2176 PaddedObjectMonitor* block = OrderAccess::load_acquire(&g_block_list);
2177 while (block != NULL) {
2178 assert(block->object() == CHAINMARKER, "must be a block header");
2179 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
2180 address mon = (address)monitor;
2181 address blk = (address)block;
2182 size_t diff = mon - blk;
2183 assert((diff % sizeof(PaddedObjectMonitor)) == 0, "must be aligned");
2184 return 1;
2185 }
2186 block = (PaddedObjectMonitor*)block->_next_om;
2187 }
2188 return 0;
2189 }
2190
2191 #endif