1 /*
2 * Copyright (c) 1998, 2014, 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 "memory/padded.hpp"
28 #include "memory/resourceArea.hpp"
29 #include "oops/markOop.hpp"
30 #include "oops/oop.inline.hpp"
31 #include "runtime/atomic.inline.hpp"
32 #include "runtime/biasedLocking.hpp"
33 #include "runtime/handles.inline.hpp"
34 #include "runtime/interfaceSupport.hpp"
35 #include "runtime/mutexLocker.hpp"
36 #include "runtime/objectMonitor.hpp"
37 #include "runtime/objectMonitor.inline.hpp"
38 #include "runtime/osThread.hpp"
39 #include "runtime/stubRoutines.hpp"
40 #include "runtime/synchronizer.hpp"
41 #include "runtime/thread.inline.hpp"
42 #include "utilities/dtrace.hpp"
43 #include "utilities/events.hpp"
44 #include "utilities/preserveException.hpp"
45
46 #if defined(__GNUC__) && !defined(PPC64)
47 // Need to inhibit inlining for older versions of GCC to avoid build-time failures
48 #define NOINLINE __attribute__((noinline))
49 #else
50 #define NOINLINE
51 #endif
52
53 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
54
55 // The "core" versions of monitor enter and exit reside in this file.
56 // The interpreter and compilers contain specialized transliterated
57 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
58 // for instance. If you make changes here, make sure to modify the
59 // interpreter, and both C1 and C2 fast-path inline locking code emission.
60 //
61 // -----------------------------------------------------------------------------
62
63 #ifdef DTRACE_ENABLED
64
65 // Only bother with this argument setup if dtrace is available
66 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
67
68 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
69 char* bytes = NULL; \
70 int len = 0; \
71 jlong jtid = SharedRuntime::get_java_tid(thread); \
72 Symbol* klassname = ((oop)(obj))->klass()->name(); \
73 if (klassname != NULL) { \
74 bytes = (char*)klassname->bytes(); \
75 len = klassname->utf8_length(); \
76 }
77
78 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
79 { \
80 if (DTraceMonitorProbes) { \
81 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
82 HOTSPOT_MONITOR_WAIT(jtid, \
83 (uintptr_t)(monitor), bytes, len, (millis)); \
84 } \
85 }
86
87 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
88
89 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
90 { \
91 if (DTraceMonitorProbes) { \
92 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
93 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
94 (uintptr_t)(monitor), bytes, len); \
95 } \
96 }
97
98 #else // ndef DTRACE_ENABLED
99
100 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
101 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
102
103 #endif // ndef DTRACE_ENABLED
104
105 // This exists only as a workaround of dtrace bug 6254741
106 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
107 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
108 return 0;
109 }
110
111 #define NINFLATIONLOCKS 256
112 static volatile intptr_t InflationLocks[NINFLATIONLOCKS];
113
114 // gBlockList is really PaddedEnd<ObjectMonitor> *, but we don't
115 // want to expose the PaddedEnd template more than necessary.
116 ObjectMonitor * ObjectSynchronizer::gBlockList = NULL;
117 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL;
118 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL;
119 int ObjectSynchronizer::gOmInUseCount = 0;
120 static volatile intptr_t ListLock = 0; // protects global monitor free-list cache
121 static volatile int MonitorFreeCount = 0; // # on gFreeList
122 static volatile int MonitorPopulation = 0; // # Extant -- in circulation
123 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
124
125 // -----------------------------------------------------------------------------
126 // Fast Monitor Enter/Exit
127 // This the fast monitor enter. The interpreter and compiler use
128 // some assembly copies of this code. Make sure update those code
129 // if the following function is changed. The implementation is
130 // extremely sensitive to race condition. Be careful.
131
132 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
133 bool attempt_rebias, TRAPS) {
134 if (UseBiasedLocking) {
135 if (!SafepointSynchronize::is_at_safepoint()) {
136 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
137 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
138 return;
139 }
140 } else {
141 assert(!attempt_rebias, "can not rebias toward VM thread");
142 BiasedLocking::revoke_at_safepoint(obj);
143 }
144 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
145 }
146
147 slow_enter(obj, lock, THREAD);
148 }
149
150 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
151 assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here");
152 // if displaced header is null, the previous enter is recursive enter, no-op
153 markOop dhw = lock->displaced_header();
154 markOop mark;
155 if (dhw == NULL) {
156 // Recursive stack-lock.
157 // Diagnostics -- Could be: stack-locked, inflating, inflated.
158 mark = object->mark();
159 assert(!mark->is_neutral(), "invariant");
160 if (mark->has_locker() && mark != markOopDesc::INFLATING()) {
161 assert(THREAD->is_lock_owned((address)mark->locker()), "invariant");
162 }
163 if (mark->has_monitor()) {
164 ObjectMonitor * m = mark->monitor();
165 assert(((oop)(m->object()))->mark() == mark, "invariant");
166 assert(m->is_entered(THREAD), "invariant");
167 }
168 return;
169 }
170
171 mark = object->mark();
172
173 // If the object is stack-locked by the current thread, try to
174 // swing the displaced header from the box back to the mark.
175 if (mark == (markOop) lock) {
176 assert(dhw->is_neutral(), "invariant");
177 if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) {
178 TEVENT(fast_exit: release stacklock);
179 return;
180 }
181 }
182
183 ObjectSynchronizer::inflate(THREAD, object)->exit(true, THREAD);
184 }
185
186 // -----------------------------------------------------------------------------
187 // Interpreter/Compiler Slow Case
188 // This routine is used to handle interpreter/compiler slow case
189 // We don't need to use fast path here, because it must have been
190 // failed in the interpreter/compiler code.
191 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
192 markOop mark = obj->mark();
193 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
194
195 if (mark->is_neutral()) {
196 // Anticipate successful CAS -- the ST of the displaced mark must
197 // be visible <= the ST performed by the CAS.
198 lock->set_displaced_header(mark);
199 if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) {
200 TEVENT(slow_enter: release stacklock);
201 return;
202 }
203 // Fall through to inflate() ...
204 } else if (mark->has_locker() &&
205 THREAD->is_lock_owned((address)mark->locker())) {
206 assert(lock != mark->locker(), "must not re-lock the same lock");
207 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
208 lock->set_displaced_header(NULL);
209 return;
210 }
211
212 // The object header will never be displaced to this lock,
213 // so it does not matter what the value is, except that it
214 // must be non-zero to avoid looking like a re-entrant lock,
215 // and must not look locked either.
216 lock->set_displaced_header(markOopDesc::unused_mark());
217 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
218 }
219
220 // This routine is used to handle interpreter/compiler slow case
221 // We don't need to use fast path here, because it must have
222 // failed in the interpreter/compiler code. Simply use the heavy
223 // weight monitor should be ok, unless someone find otherwise.
224 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
225 fast_exit(object, lock, THREAD);
226 }
227
228 // -----------------------------------------------------------------------------
229 // Class Loader support to workaround deadlocks on the class loader lock objects
230 // Also used by GC
231 // complete_exit()/reenter() are used to wait on a nested lock
232 // i.e. to give up an outer lock completely and then re-enter
233 // Used when holding nested locks - lock acquisition order: lock1 then lock2
234 // 1) complete_exit lock1 - saving recursion count
235 // 2) wait on lock2
236 // 3) when notified on lock2, unlock lock2
237 // 4) reenter lock1 with original recursion count
238 // 5) lock lock2
239 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
240 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
241 TEVENT(complete_exit);
242 if (UseBiasedLocking) {
243 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
244 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
245 }
246
247 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
248
249 return monitor->complete_exit(THREAD);
250 }
251
252 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
253 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
254 TEVENT(reenter);
255 if (UseBiasedLocking) {
256 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
257 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
258 }
259
260 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
261
262 monitor->reenter(recursion, THREAD);
263 }
264 // -----------------------------------------------------------------------------
265 // JNI locks on java objects
266 // NOTE: must use heavy weight monitor to handle jni monitor enter
267 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
268 // the current locking is from JNI instead of Java code
269 TEVENT(jni_enter);
270 if (UseBiasedLocking) {
271 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
272 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
273 }
274 THREAD->set_current_pending_monitor_is_from_java(false);
275 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
276 THREAD->set_current_pending_monitor_is_from_java(true);
277 }
278
279 // NOTE: must use heavy weight monitor to handle jni monitor exit
280 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
281 TEVENT(jni_exit);
282 if (UseBiasedLocking) {
283 Handle h_obj(THREAD, obj);
284 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
285 obj = h_obj();
286 }
287 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
288
289 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj);
290 // If this thread has locked the object, exit the monitor. Note: can't use
291 // monitor->check(CHECK); must exit even if an exception is pending.
292 if (monitor->check(THREAD)) {
293 monitor->exit(true, THREAD);
294 }
295 }
296
297 // -----------------------------------------------------------------------------
298 // Internal VM locks on java objects
299 // standard constructor, allows locking failures
300 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
301 _dolock = doLock;
302 _thread = thread;
303 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
304 _obj = obj;
305
306 if (_dolock) {
307 TEVENT(ObjectLocker);
308
309 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
310 }
311 }
312
313 ObjectLocker::~ObjectLocker() {
314 if (_dolock) {
315 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
316 }
317 }
318
319
320 // -----------------------------------------------------------------------------
321 // Wait/Notify/NotifyAll
322 // NOTE: must use heavy weight monitor to handle wait()
323 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
324 if (UseBiasedLocking) {
325 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
326 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
327 }
328 if (millis < 0) {
329 TEVENT(wait - throw IAX);
330 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
331 }
332 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
333 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
334 monitor->wait(millis, true, THREAD);
335
336 // This dummy call is in place to get around dtrace bug 6254741. Once
337 // that's fixed we can uncomment the following line, remove the call
338 // and change this function back into a "void" func.
339 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
340 return dtrace_waited_probe(monitor, obj, THREAD);
341 }
342
343 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
344 if (UseBiasedLocking) {
345 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
346 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
347 }
348 if (millis < 0) {
349 TEVENT(wait - throw IAX);
350 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
351 }
352 ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD);
353 }
354
355 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
356 if (UseBiasedLocking) {
357 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
358 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
359 }
360
361 markOop mark = obj->mark();
362 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
363 return;
364 }
365 ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD);
366 }
367
368 // NOTE: see comment of notify()
369 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
370 if (UseBiasedLocking) {
371 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
372 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
373 }
374
375 markOop mark = obj->mark();
376 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
377 return;
378 }
379 ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD);
380 }
381
382 // -----------------------------------------------------------------------------
383 // Hash Code handling
384 //
385 // Performance concern:
386 // OrderAccess::storestore() calls release() which at one time stored 0
387 // into the global volatile OrderAccess::dummy variable. This store was
388 // unnecessary for correctness. Many threads storing into a common location
389 // causes considerable cache migration or "sloshing" on large SMP systems.
390 // As such, I avoided using OrderAccess::storestore(). In some cases
391 // OrderAccess::fence() -- which incurs local latency on the executing
392 // processor -- is a better choice as it scales on SMP systems.
393 //
394 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
395 // a discussion of coherency costs. Note that all our current reference
396 // platforms provide strong ST-ST order, so the issue is moot on IA32,
397 // x64, and SPARC.
398 //
399 // As a general policy we use "volatile" to control compiler-based reordering
400 // and explicit fences (barriers) to control for architectural reordering
401 // performed by the CPU(s) or platform.
402
403 struct SharedGlobals {
404 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
405 // These are highly shared mostly-read variables.
406 // To avoid false-sharing they need to be the sole occupants of a cache line.
407 volatile int stwRandom;
408 volatile int stwCycle;
409 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
410 // Hot RW variable -- Sequester to avoid false-sharing
411 volatile int hcSequence;
412 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
413 };
414
415 static SharedGlobals GVars;
416 static int MonitorScavengeThreshold = 1000000;
417 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
418
419 static markOop ReadStableMark(oop obj) {
420 markOop mark = obj->mark();
421 if (!mark->is_being_inflated()) {
422 return mark; // normal fast-path return
423 }
424
425 int its = 0;
426 for (;;) {
427 markOop mark = obj->mark();
428 if (!mark->is_being_inflated()) {
429 return mark; // normal fast-path return
430 }
431
432 // The object is being inflated by some other thread.
433 // The caller of ReadStableMark() must wait for inflation to complete.
434 // Avoid live-lock
435 // TODO: consider calling SafepointSynchronize::do_call_back() while
436 // spinning to see if there's a safepoint pending. If so, immediately
437 // yielding or blocking would be appropriate. Avoid spinning while
438 // there is a safepoint pending.
439 // TODO: add inflation contention performance counters.
440 // TODO: restrict the aggregate number of spinners.
441
442 ++its;
443 if (its > 10000 || !os::is_MP()) {
444 if (its & 1) {
445 os::naked_yield();
446 TEVENT(Inflate: INFLATING - yield);
447 } else {
448 // Note that the following code attenuates the livelock problem but is not
449 // a complete remedy. A more complete solution would require that the inflating
450 // thread hold the associated inflation lock. The following code simply restricts
451 // the number of spinners to at most one. We'll have N-2 threads blocked
452 // on the inflationlock, 1 thread holding the inflation lock and using
453 // a yield/park strategy, and 1 thread in the midst of inflation.
454 // A more refined approach would be to change the encoding of INFLATING
455 // to allow encapsulation of a native thread pointer. Threads waiting for
456 // inflation to complete would use CAS to push themselves onto a singly linked
457 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
458 // and calling park(). When inflation was complete the thread that accomplished inflation
459 // would detach the list and set the markword to inflated with a single CAS and
460 // then for each thread on the list, set the flag and unpark() the thread.
461 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
462 // wakes at most one thread whereas we need to wake the entire list.
463 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
464 int YieldThenBlock = 0;
465 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
466 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
467 Thread::muxAcquire(InflationLocks + ix, "InflationLock");
468 while (obj->mark() == markOopDesc::INFLATING()) {
469 // Beware: NakedYield() is advisory and has almost no effect on some platforms
470 // so we periodically call Self->_ParkEvent->park(1).
471 // We use a mixed spin/yield/block mechanism.
472 if ((YieldThenBlock++) >= 16) {
473 Thread::current()->_ParkEvent->park(1);
474 } else {
475 os::naked_yield();
476 }
477 }
478 Thread::muxRelease(InflationLocks + ix);
479 TEVENT(Inflate: INFLATING - yield/park);
480 }
481 } else {
482 SpinPause(); // SMP-polite spinning
483 }
484 }
485 }
486
487 // hashCode() generation :
488 //
489 // Possibilities:
490 // * MD5Digest of {obj,stwRandom}
491 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
492 // * A DES- or AES-style SBox[] mechanism
493 // * One of the Phi-based schemes, such as:
494 // 2654435761 = 2^32 * Phi (golden ratio)
495 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
496 // * A variation of Marsaglia's shift-xor RNG scheme.
497 // * (obj ^ stwRandom) is appealing, but can result
498 // in undesirable regularity in the hashCode values of adjacent objects
499 // (objects allocated back-to-back, in particular). This could potentially
500 // result in hashtable collisions and reduced hashtable efficiency.
501 // There are simple ways to "diffuse" the middle address bits over the
502 // generated hashCode values:
503
504 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
505 intptr_t value = 0;
506 if (hashCode == 0) {
507 // This form uses an unguarded global Park-Miller RNG,
508 // so it's possible for two threads to race and generate the same RNG.
509 // On MP system we'll have lots of RW access to a global, so the
510 // mechanism induces lots of coherency traffic.
511 value = os::random();
512 } else if (hashCode == 1) {
513 // This variation has the property of being stable (idempotent)
514 // between STW operations. This can be useful in some of the 1-0
515 // synchronization schemes.
516 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
517 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
518 } else if (hashCode == 2) {
519 value = 1; // for sensitivity testing
520 } else if (hashCode == 3) {
521 value = ++GVars.hcSequence;
522 } else if (hashCode == 4) {
523 value = cast_from_oop<intptr_t>(obj);
524 } else {
525 // Marsaglia's xor-shift scheme with thread-specific state
526 // This is probably the best overall implementation -- we'll
527 // likely make this the default in future releases.
528 unsigned t = Self->_hashStateX;
529 t ^= (t << 11);
530 Self->_hashStateX = Self->_hashStateY;
531 Self->_hashStateY = Self->_hashStateZ;
532 Self->_hashStateZ = Self->_hashStateW;
533 unsigned v = Self->_hashStateW;
534 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
535 Self->_hashStateW = v;
536 value = v;
537 }
538
539 value &= markOopDesc::hash_mask;
540 if (value == 0) value = 0xBAD;
541 assert(value != markOopDesc::no_hash, "invariant");
542 TEVENT(hashCode: GENERATE);
543 return value;
544 }
545
546 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
547 if (UseBiasedLocking) {
548 // NOTE: many places throughout the JVM do not expect a safepoint
549 // to be taken here, in particular most operations on perm gen
550 // objects. However, we only ever bias Java instances and all of
551 // the call sites of identity_hash that might revoke biases have
552 // been checked to make sure they can handle a safepoint. The
553 // added check of the bias pattern is to avoid useless calls to
554 // thread-local storage.
555 if (obj->mark()->has_bias_pattern()) {
556 // Handle for oop obj in case of STW safepoint
557 Handle hobj(Self, obj);
558 // Relaxing assertion for bug 6320749.
559 assert(Universe::verify_in_progress() ||
560 !SafepointSynchronize::is_at_safepoint(),
561 "biases should not be seen by VM thread here");
562 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
563 obj = hobj();
564 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
565 }
566 }
567
568 // hashCode() is a heap mutator ...
569 // Relaxing assertion for bug 6320749.
570 assert(Universe::verify_in_progress() ||
571 !SafepointSynchronize::is_at_safepoint(), "invariant");
572 assert(Universe::verify_in_progress() ||
573 Self->is_Java_thread() , "invariant");
574 assert(Universe::verify_in_progress() ||
575 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
576
577 ObjectMonitor* monitor = NULL;
578 markOop temp, test;
579 intptr_t hash;
580 markOop mark = ReadStableMark(obj);
581
582 // object should remain ineligible for biased locking
583 assert(!mark->has_bias_pattern(), "invariant");
584
585 if (mark->is_neutral()) {
586 hash = mark->hash(); // this is a normal header
587 if (hash) { // if it has hash, just return it
588 return hash;
589 }
590 hash = get_next_hash(Self, obj); // allocate a new hash code
591 temp = mark->copy_set_hash(hash); // merge the hash code into header
592 // use (machine word version) atomic operation to install the hash
593 test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark);
594 if (test == mark) {
595 return hash;
596 }
597 // If atomic operation failed, we must inflate the header
598 // into heavy weight monitor. We could add more code here
599 // for fast path, but it does not worth the complexity.
600 } else if (mark->has_monitor()) {
601 monitor = mark->monitor();
602 temp = monitor->header();
603 assert(temp->is_neutral(), "invariant");
604 hash = temp->hash();
605 if (hash) {
606 return hash;
607 }
608 // Skip to the following code to reduce code size
609 } else if (Self->is_lock_owned((address)mark->locker())) {
610 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
611 assert(temp->is_neutral(), "invariant");
612 hash = temp->hash(); // by current thread, check if the displaced
613 if (hash) { // header contains hash code
614 return hash;
615 }
616 // WARNING:
617 // The displaced header is strictly immutable.
618 // It can NOT be changed in ANY cases. So we have
619 // to inflate the header into heavyweight monitor
620 // even the current thread owns the lock. The reason
621 // is the BasicLock (stack slot) will be asynchronously
622 // read by other threads during the inflate() function.
623 // Any change to stack may not propagate to other threads
624 // correctly.
625 }
626
627 // Inflate the monitor to set hash code
628 monitor = ObjectSynchronizer::inflate(Self, obj);
629 // Load displaced header and check it has hash code
630 mark = monitor->header();
631 assert(mark->is_neutral(), "invariant");
632 hash = mark->hash();
633 if (hash == 0) {
634 hash = get_next_hash(Self, obj);
635 temp = mark->copy_set_hash(hash); // merge hash code into header
636 assert(temp->is_neutral(), "invariant");
637 test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark);
638 if (test != mark) {
639 // The only update to the header in the monitor (outside GC)
640 // is install the hash code. If someone add new usage of
641 // displaced header, please update this code
642 hash = test->hash();
643 assert(test->is_neutral(), "invariant");
644 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
645 }
646 }
647 // We finally get the hash
648 return hash;
649 }
650
651 // Deprecated -- use FastHashCode() instead.
652
653 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
654 return FastHashCode(Thread::current(), obj());
655 }
656
657
658 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
659 Handle h_obj) {
660 if (UseBiasedLocking) {
661 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
662 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
663 }
664
665 assert(thread == JavaThread::current(), "Can only be called on current thread");
666 oop obj = h_obj();
667
668 markOop mark = ReadStableMark(obj);
669
670 // Uncontended case, header points to stack
671 if (mark->has_locker()) {
672 return thread->is_lock_owned((address)mark->locker());
673 }
674 // Contended case, header points to ObjectMonitor (tagged pointer)
675 if (mark->has_monitor()) {
676 ObjectMonitor* monitor = mark->monitor();
677 return monitor->is_entered(thread) != 0;
678 }
679 // Unlocked case, header in place
680 assert(mark->is_neutral(), "sanity check");
681 return false;
682 }
683
684 // Be aware of this method could revoke bias of the lock object.
685 // This method queries the ownership of the lock handle specified by 'h_obj'.
686 // If the current thread owns the lock, it returns owner_self. If no
687 // thread owns the lock, it returns owner_none. Otherwise, it will return
688 // owner_other.
689 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
690 (JavaThread *self, Handle h_obj) {
691 // The caller must beware this method can revoke bias, and
692 // revocation can result in a safepoint.
693 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
694 assert(self->thread_state() != _thread_blocked, "invariant");
695
696 // Possible mark states: neutral, biased, stack-locked, inflated
697
698 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
699 // CASE: biased
700 BiasedLocking::revoke_and_rebias(h_obj, false, self);
701 assert(!h_obj->mark()->has_bias_pattern(),
702 "biases should be revoked by now");
703 }
704
705 assert(self == JavaThread::current(), "Can only be called on current thread");
706 oop obj = h_obj();
707 markOop mark = ReadStableMark(obj);
708
709 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
710 if (mark->has_locker()) {
711 return self->is_lock_owned((address)mark->locker()) ?
712 owner_self : owner_other;
713 }
714
715 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
716 // The Object:ObjectMonitor relationship is stable as long as we're
717 // not at a safepoint.
718 if (mark->has_monitor()) {
719 void * owner = mark->monitor()->_owner;
720 if (owner == NULL) return owner_none;
721 return (owner == self ||
722 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
723 }
724
725 // CASE: neutral
726 assert(mark->is_neutral(), "sanity check");
727 return owner_none; // it's unlocked
728 }
729
730 // FIXME: jvmti should call this
731 JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) {
732 if (UseBiasedLocking) {
733 if (SafepointSynchronize::is_at_safepoint()) {
734 BiasedLocking::revoke_at_safepoint(h_obj);
735 } else {
736 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
737 }
738 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
739 }
740
741 oop obj = h_obj();
742 address owner = NULL;
743
744 markOop mark = ReadStableMark(obj);
745
746 // Uncontended case, header points to stack
747 if (mark->has_locker()) {
748 owner = (address) mark->locker();
749 }
750
751 // Contended case, header points to ObjectMonitor (tagged pointer)
752 if (mark->has_monitor()) {
753 ObjectMonitor* monitor = mark->monitor();
754 assert(monitor != NULL, "monitor should be non-null");
755 owner = (address) monitor->owner();
756 }
757
758 if (owner != NULL) {
759 // owning_thread_from_monitor_owner() may also return NULL here
760 return Threads::owning_thread_from_monitor_owner(owner, doLock);
761 }
762
763 // Unlocked case, header in place
764 // Cannot have assertion since this object may have been
765 // locked by another thread when reaching here.
766 // assert(mark->is_neutral(), "sanity check");
767
768 return NULL;
769 }
770 // Visitors ...
771
772 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
773 PaddedEnd<ObjectMonitor> * block = (PaddedEnd<ObjectMonitor> *)gBlockList;
774 ObjectMonitor* mid;
775 while (block) {
776 assert(block->object() == CHAINMARKER, "must be a block header");
777 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
778 mid = (ObjectMonitor *)(block + i);
779 oop object = (oop) mid->object();
780 if (object != NULL) {
781 closure->do_monitor(mid);
782 }
783 }
784 block = (PaddedEnd<ObjectMonitor> *) block->FreeNext;
785 }
786 }
787
788 // Get the next block in the block list.
789 static inline ObjectMonitor* next(ObjectMonitor* block) {
790 assert(block->object() == CHAINMARKER, "must be a block header");
791 block = block->FreeNext;
792 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
793 return block;
794 }
795
796
797 void ObjectSynchronizer::oops_do(OopClosure* f) {
798 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
799 for (PaddedEnd<ObjectMonitor> * block =
800 (PaddedEnd<ObjectMonitor> *)gBlockList; block != NULL;
801 block = (PaddedEnd<ObjectMonitor> *)next(block)) {
802 assert(block->object() == CHAINMARKER, "must be a block header");
803 for (int i = 1; i < _BLOCKSIZE; i++) {
804 ObjectMonitor* mid = (ObjectMonitor *)&block[i];
805 if (mid->object() != NULL) {
806 f->do_oop((oop*)mid->object_addr());
807 }
808 }
809 }
810 }
811
812
813 // -----------------------------------------------------------------------------
814 // ObjectMonitor Lifecycle
815 // -----------------------
816 // Inflation unlinks monitors from the global gFreeList and
817 // associates them with objects. Deflation -- which occurs at
818 // STW-time -- disassociates idle monitors from objects. Such
819 // scavenged monitors are returned to the gFreeList.
820 //
821 // The global list is protected by ListLock. All the critical sections
822 // are short and operate in constant-time.
823 //
824 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
825 //
826 // Lifecycle:
827 // -- unassigned and on the global free list
828 // -- unassigned and on a thread's private omFreeList
829 // -- assigned to an object. The object is inflated and the mark refers
830 // to the objectmonitor.
831
832
833 // Constraining monitor pool growth via MonitorBound ...
834 //
835 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
836 // the rate of scavenging is driven primarily by GC. As such, we can find
837 // an inordinate number of monitors in circulation.
838 // To avoid that scenario we can artificially induce a STW safepoint
839 // if the pool appears to be growing past some reasonable bound.
840 // Generally we favor time in space-time tradeoffs, but as there's no
841 // natural back-pressure on the # of extant monitors we need to impose some
842 // type of limit. Beware that if MonitorBound is set to too low a value
843 // we could just loop. In addition, if MonitorBound is set to a low value
844 // we'll incur more safepoints, which are harmful to performance.
845 // See also: GuaranteedSafepointInterval
846 //
847 // The current implementation uses asynchronous VM operations.
848
849 static void InduceScavenge(Thread * Self, const char * Whence) {
850 // Induce STW safepoint to trim monitors
851 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
852 // More precisely, trigger an asynchronous STW safepoint as the number
853 // of active monitors passes the specified threshold.
854 // TODO: assert thread state is reasonable
855
856 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
857 if (ObjectMonitor::Knob_Verbose) {
858 ::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ;
859 ::fflush(stdout);
860 }
861 // Induce a 'null' safepoint to scavenge monitors
862 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
863 // to the VMthread and have a lifespan longer than that of this activation record.
864 // The VMThread will delete the op when completed.
865 VMThread::execute(new VM_ForceAsyncSafepoint());
866
867 if (ObjectMonitor::Knob_Verbose) {
868 ::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ;
869 ::fflush(stdout);
870 }
871 }
872 }
873
874 void ObjectSynchronizer::verifyInUse(Thread *Self) {
875 ObjectMonitor* mid;
876 int inusetally = 0;
877 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) {
878 inusetally++;
879 }
880 assert(inusetally == Self->omInUseCount, "inuse count off");
881
882 int freetally = 0;
883 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) {
884 freetally++;
885 }
886 assert(freetally == Self->omFreeCount, "free count off");
887 }
888
889 ObjectMonitor * NOINLINE ObjectSynchronizer::omAlloc(Thread * Self) {
890 // A large MAXPRIVATE value reduces both list lock contention
891 // and list coherency traffic, but also tends to increase the
892 // number of objectMonitors in circulation as well as the STW
893 // scavenge costs. As usual, we lean toward time in space-time
894 // tradeoffs.
895 const int MAXPRIVATE = 1024;
896 for (;;) {
897 ObjectMonitor * m;
898
899 // 1: try to allocate from the thread's local omFreeList.
900 // Threads will attempt to allocate first from their local list, then
901 // from the global list, and only after those attempts fail will the thread
902 // attempt to instantiate new monitors. Thread-local free lists take
903 // heat off the ListLock and improve allocation latency, as well as reducing
904 // coherency traffic on the shared global list.
905 m = Self->omFreeList;
906 if (m != NULL) {
907 Self->omFreeList = m->FreeNext;
908 Self->omFreeCount--;
909 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene
910 guarantee(m->object() == NULL, "invariant");
911 if (MonitorInUseLists) {
912 m->FreeNext = Self->omInUseList;
913 Self->omInUseList = m;
914 Self->omInUseCount++;
915 if (ObjectMonitor::Knob_VerifyInUse) {
916 verifyInUse(Self);
917 }
918 } else {
919 m->FreeNext = NULL;
920 }
921 return m;
922 }
923
924 // 2: try to allocate from the global gFreeList
925 // CONSIDER: use muxTry() instead of muxAcquire().
926 // If the muxTry() fails then drop immediately into case 3.
927 // If we're using thread-local free lists then try
928 // to reprovision the caller's free list.
929 if (gFreeList != NULL) {
930 // Reprovision the thread's omFreeList.
931 // Use bulk transfers to reduce the allocation rate and heat
932 // on various locks.
933 Thread::muxAcquire(&ListLock, "omAlloc");
934 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
935 MonitorFreeCount--;
936 ObjectMonitor * take = gFreeList;
937 gFreeList = take->FreeNext;
938 guarantee(take->object() == NULL, "invariant");
939 guarantee(!take->is_busy(), "invariant");
940 take->Recycle();
941 omRelease(Self, take, false);
942 }
943 Thread::muxRelease(&ListLock);
944 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
945 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
946 TEVENT(omFirst - reprovision);
947
948 const int mx = MonitorBound;
949 if (mx > 0 && (MonitorPopulation-MonitorFreeCount) > mx) {
950 // We can't safely induce a STW safepoint from omAlloc() as our thread
951 // state may not be appropriate for such activities and callers may hold
952 // naked oops, so instead we defer the action.
953 InduceScavenge(Self, "omAlloc");
954 }
955 continue;
956 }
957
958 // 3: allocate a block of new ObjectMonitors
959 // Both the local and global free lists are empty -- resort to malloc().
960 // In the current implementation objectMonitors are TSM - immortal.
961 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
962 // each ObjectMonitor to start at the beginning of a cache line,
963 // so we use align_size_up().
964 // A better solution would be to use C++ placement-new.
965 // BEWARE: As it stands currently, we don't run the ctors!
966 assert(_BLOCKSIZE > 1, "invariant");
967 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
968 PaddedEnd<ObjectMonitor> * temp;
969 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
970 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
971 mtInternal);
972 temp = (PaddedEnd<ObjectMonitor> *)
973 align_size_up((intptr_t)real_malloc_addr,
974 DEFAULT_CACHE_LINE_SIZE);
975
976 // NOTE: (almost) no way to recover if allocation failed.
977 // We might be able to induce a STW safepoint and scavenge enough
978 // objectMonitors to permit progress.
979 if (temp == NULL) {
980 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
981 "Allocate ObjectMonitors");
982 }
983 (void)memset((void *) temp, 0, neededsize);
984
985 // Format the block.
986 // initialize the linked list, each monitor points to its next
987 // forming the single linked free list, the very first monitor
988 // will points to next block, which forms the block list.
989 // The trick of using the 1st element in the block as gBlockList
990 // linkage should be reconsidered. A better implementation would
991 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
992
993 for (int i = 1; i < _BLOCKSIZE; i++) {
994 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
995 }
996
997 // terminate the last monitor as the end of list
998 temp[_BLOCKSIZE - 1].FreeNext = NULL;
999
1000 // Element [0] is reserved for global list linkage
1001 temp[0].set_object(CHAINMARKER);
1002
1003 // Consider carving out this thread's current request from the
1004 // block in hand. This avoids some lock traffic and redundant
1005 // list activity.
1006
1007 // Acquire the ListLock to manipulate BlockList and FreeList.
1008 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1009 Thread::muxAcquire(&ListLock, "omAlloc [2]");
1010 MonitorPopulation += _BLOCKSIZE-1;
1011 MonitorFreeCount += _BLOCKSIZE-1;
1012
1013 // Add the new block to the list of extant blocks (gBlockList).
1014 // The very first objectMonitor in a block is reserved and dedicated.
1015 // It serves as blocklist "next" linkage.
1016 temp[0].FreeNext = gBlockList;
1017 gBlockList = temp;
1018
1019 // Add the new string of objectMonitors to the global free list
1020 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1021 gFreeList = temp + 1;
1022 Thread::muxRelease(&ListLock);
1023 TEVENT(Allocate block of monitors);
1024 }
1025 }
1026
1027 // Place "m" on the caller's private per-thread omFreeList.
1028 // In practice there's no need to clamp or limit the number of
1029 // monitors on a thread's omFreeList as the only time we'll call
1030 // omRelease is to return a monitor to the free list after a CAS
1031 // attempt failed. This doesn't allow unbounded #s of monitors to
1032 // accumulate on a thread's free list.
1033
1034 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1035 bool fromPerThreadAlloc) {
1036 guarantee(m->object() == NULL, "invariant");
1037
1038 // Remove from omInUseList
1039 if (MonitorInUseLists && fromPerThreadAlloc) {
1040 ObjectMonitor* curmidinuse = NULL;
1041 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL;) {
1042 if (m == mid) {
1043 // extract from per-thread in-use-list
1044 if (mid == Self->omInUseList) {
1045 Self->omInUseList = mid->FreeNext;
1046 } else if (curmidinuse != NULL) {
1047 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1048 }
1049 Self->omInUseCount--;
1050 if (ObjectMonitor::Knob_VerifyInUse) {
1051 verifyInUse(Self);
1052 }
1053 break;
1054 } else {
1055 curmidinuse = mid;
1056 mid = mid->FreeNext;
1057 }
1058 }
1059 }
1060
1061 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1062 m->FreeNext = Self->omFreeList;
1063 Self->omFreeList = m;
1064 Self->omFreeCount++;
1065 }
1066
1067 // Return the monitors of a moribund thread's local free list to
1068 // the global free list. Typically a thread calls omFlush() when
1069 // it's dying. We could also consider having the VM thread steal
1070 // monitors from threads that have not run java code over a few
1071 // consecutive STW safepoints. Relatedly, we might decay
1072 // omFreeProvision at STW safepoints.
1073 //
1074 // Also return the monitors of a moribund thread's omInUseList to
1075 // a global gOmInUseList under the global list lock so these
1076 // will continue to be scanned.
1077 //
1078 // We currently call omFlush() from the Thread:: dtor _after the thread
1079 // has been excised from the thread list and is no longer a mutator.
1080 // That means that omFlush() can run concurrently with a safepoint and
1081 // the scavenge operator. Calling omFlush() from JavaThread::exit() might
1082 // be a better choice as we could safely reason that that the JVM is
1083 // not at a safepoint at the time of the call, and thus there could
1084 // be not inopportune interleavings between omFlush() and the scavenge
1085 // operator.
1086
1087 void ObjectSynchronizer::omFlush(Thread * Self) {
1088 ObjectMonitor * List = Self->omFreeList; // Null-terminated SLL
1089 Self->omFreeList = NULL;
1090 ObjectMonitor * Tail = NULL;
1091 int Tally = 0;
1092 if (List != NULL) {
1093 ObjectMonitor * s;
1094 for (s = List; s != NULL; s = s->FreeNext) {
1095 Tally++;
1096 Tail = s;
1097 guarantee(s->object() == NULL, "invariant");
1098 guarantee(!s->is_busy(), "invariant");
1099 s->set_owner(NULL); // redundant but good hygiene
1100 TEVENT(omFlush - Move one);
1101 }
1102 guarantee(Tail != NULL && List != NULL, "invariant");
1103 }
1104
1105 ObjectMonitor * InUseList = Self->omInUseList;
1106 ObjectMonitor * InUseTail = NULL;
1107 int InUseTally = 0;
1108 if (InUseList != NULL) {
1109 Self->omInUseList = NULL;
1110 ObjectMonitor *curom;
1111 for (curom = InUseList; curom != NULL; curom = curom->FreeNext) {
1112 InUseTail = curom;
1113 InUseTally++;
1114 }
1115 assert(Self->omInUseCount == InUseTally, "inuse count off");
1116 Self->omInUseCount = 0;
1117 guarantee(InUseTail != NULL && InUseList != NULL, "invariant");
1118 }
1119
1120 Thread::muxAcquire(&ListLock, "omFlush");
1121 if (Tail != NULL) {
1122 Tail->FreeNext = gFreeList;
1123 gFreeList = List;
1124 MonitorFreeCount += Tally;
1125 }
1126
1127 if (InUseTail != NULL) {
1128 InUseTail->FreeNext = gOmInUseList;
1129 gOmInUseList = InUseList;
1130 gOmInUseCount += InUseTally;
1131 }
1132
1133 Thread::muxRelease(&ListLock);
1134 TEVENT(omFlush);
1135 }
1136
1137 // Fast path code shared by multiple functions
1138 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1139 markOop mark = obj->mark();
1140 if (mark->has_monitor()) {
1141 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1142 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1143 return mark->monitor();
1144 }
1145 return ObjectSynchronizer::inflate(Thread::current(), obj);
1146 }
1147
1148
1149 ObjectMonitor * NOINLINE ObjectSynchronizer::inflate(Thread * Self,
1150 oop object) {
1151 // Inflate mutates the heap ...
1152 // Relaxing assertion for bug 6320749.
1153 assert(Universe::verify_in_progress() ||
1154 !SafepointSynchronize::is_at_safepoint(), "invariant");
1155
1156 for (;;) {
1157 const markOop mark = object->mark();
1158 assert(!mark->has_bias_pattern(), "invariant");
1159
1160 // The mark can be in one of the following states:
1161 // * Inflated - just return
1162 // * Stack-locked - coerce it to inflated
1163 // * INFLATING - busy wait for conversion to complete
1164 // * Neutral - aggressively inflate the object.
1165 // * BIASED - Illegal. We should never see this
1166
1167 // CASE: inflated
1168 if (mark->has_monitor()) {
1169 ObjectMonitor * inf = mark->monitor();
1170 assert(inf->header()->is_neutral(), "invariant");
1171 assert(inf->object() == object, "invariant");
1172 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1173 return inf;
1174 }
1175
1176 // CASE: inflation in progress - inflating over a stack-lock.
1177 // Some other thread is converting from stack-locked to inflated.
1178 // Only that thread can complete inflation -- other threads must wait.
1179 // The INFLATING value is transient.
1180 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1181 // We could always eliminate polling by parking the thread on some auxiliary list.
1182 if (mark == markOopDesc::INFLATING()) {
1183 TEVENT(Inflate: spin while INFLATING);
1184 ReadStableMark(object);
1185 continue;
1186 }
1187
1188 // CASE: stack-locked
1189 // Could be stack-locked either by this thread or by some other thread.
1190 //
1191 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1192 // to install INFLATING into the mark word. We originally installed INFLATING,
1193 // allocated the objectmonitor, and then finally STed the address of the
1194 // objectmonitor into the mark. This was correct, but artificially lengthened
1195 // the interval in which INFLATED appeared in the mark, thus increasing
1196 // the odds of inflation contention.
1197 //
1198 // We now use per-thread private objectmonitor free lists.
1199 // These list are reprovisioned from the global free list outside the
1200 // critical INFLATING...ST interval. A thread can transfer
1201 // multiple objectmonitors en-mass from the global free list to its local free list.
1202 // This reduces coherency traffic and lock contention on the global free list.
1203 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1204 // before or after the CAS(INFLATING) operation.
1205 // See the comments in omAlloc().
1206
1207 if (mark->has_locker()) {
1208 ObjectMonitor * m = omAlloc(Self);
1209 // Optimistically prepare the objectmonitor - anticipate successful CAS
1210 // We do this before the CAS in order to minimize the length of time
1211 // in which INFLATING appears in the mark.
1212 m->Recycle();
1213 m->_Responsible = NULL;
1214 m->_recursions = 0;
1215 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1216
1217 markOop cmp = (markOop) Atomic::cmpxchg_ptr(markOopDesc::INFLATING(), object->mark_addr(), mark);
1218 if (cmp != mark) {
1219 omRelease(Self, m, true);
1220 continue; // Interference -- just retry
1221 }
1222
1223 // We've successfully installed INFLATING (0) into the mark-word.
1224 // This is the only case where 0 will appear in a mark-work.
1225 // Only the singular thread that successfully swings the mark-word
1226 // to 0 can perform (or more precisely, complete) inflation.
1227 //
1228 // Why do we CAS a 0 into the mark-word instead of just CASing the
1229 // mark-word from the stack-locked value directly to the new inflated state?
1230 // Consider what happens when a thread unlocks a stack-locked object.
1231 // It attempts to use CAS to swing the displaced header value from the
1232 // on-stack basiclock back into the object header. Recall also that the
1233 // header value (hashcode, etc) can reside in (a) the object header, or
1234 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1235 // header in an objectMonitor. The inflate() routine must copy the header
1236 // value from the basiclock on the owner's stack to the objectMonitor, all
1237 // the while preserving the hashCode stability invariants. If the owner
1238 // decides to release the lock while the value is 0, the unlock will fail
1239 // and control will eventually pass from slow_exit() to inflate. The owner
1240 // will then spin, waiting for the 0 value to disappear. Put another way,
1241 // the 0 causes the owner to stall if the owner happens to try to
1242 // drop the lock (restoring the header from the basiclock to the object)
1243 // while inflation is in-progress. This protocol avoids races that might
1244 // would otherwise permit hashCode values to change or "flicker" for an object.
1245 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1246 // 0 serves as a "BUSY" inflate-in-progress indicator.
1247
1248
1249 // fetch the displaced mark from the owner's stack.
1250 // The owner can't die or unwind past the lock while our INFLATING
1251 // object is in the mark. Furthermore the owner can't complete
1252 // an unlock on the object, either.
1253 markOop dmw = mark->displaced_mark_helper();
1254 assert(dmw->is_neutral(), "invariant");
1255
1256 // Setup monitor fields to proper values -- prepare the monitor
1257 m->set_header(dmw);
1258
1259 // Optimization: if the mark->locker stack address is associated
1260 // with this thread we could simply set m->_owner = Self.
1261 // Note that a thread can inflate an object
1262 // that it has stack-locked -- as might happen in wait() -- directly
1263 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1264 m->set_owner(mark->locker());
1265 m->set_object(object);
1266 // TODO-FIXME: assert BasicLock->dhw != 0.
1267
1268 // Must preserve store ordering. The monitor state must
1269 // be stable at the time of publishing the monitor address.
1270 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1271 object->release_set_mark(markOopDesc::encode(m));
1272
1273 // Hopefully the performance counters are allocated on distinct cache lines
1274 // to avoid false sharing on MP systems ...
1275 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc();
1276 TEVENT(Inflate: overwrite stacklock);
1277 if (TraceMonitorInflation) {
1278 if (object->is_instance()) {
1279 ResourceMark rm;
1280 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1281 (void *) object, (intptr_t) object->mark(),
1282 object->klass()->external_name());
1283 }
1284 }
1285 return m;
1286 }
1287
1288 // CASE: neutral
1289 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1290 // If we know we're inflating for entry it's better to inflate by swinging a
1291 // pre-locked objectMonitor pointer into the object header. A successful
1292 // CAS inflates the object *and* confers ownership to the inflating thread.
1293 // In the current implementation we use a 2-step mechanism where we CAS()
1294 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1295 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1296 // would be useful.
1297
1298 assert(mark->is_neutral(), "invariant");
1299 ObjectMonitor * m = omAlloc(Self);
1300 // prepare m for installation - set monitor to initial state
1301 m->Recycle();
1302 m->set_header(mark);
1303 m->set_owner(NULL);
1304 m->set_object(object);
1305 m->_recursions = 0;
1306 m->_Responsible = NULL;
1307 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1308
1309 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) {
1310 m->set_object(NULL);
1311 m->set_owner(NULL);
1312 m->Recycle();
1313 omRelease(Self, m, true);
1314 m = NULL;
1315 continue;
1316 // interference - the markword changed - just retry.
1317 // The state-transitions are one-way, so there's no chance of
1318 // live-lock -- "Inflated" is an absorbing state.
1319 }
1320
1321 // Hopefully the performance counters are allocated on distinct
1322 // cache lines to avoid false sharing on MP systems ...
1323 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc();
1324 TEVENT(Inflate: overwrite neutral);
1325 if (TraceMonitorInflation) {
1326 if (object->is_instance()) {
1327 ResourceMark rm;
1328 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1329 (void *) object, (intptr_t) object->mark(),
1330 object->klass()->external_name());
1331 }
1332 }
1333 return m;
1334 }
1335 }
1336
1337
1338 // Deflate_idle_monitors() is called at all safepoints, immediately
1339 // after all mutators are stopped, but before any objects have moved.
1340 // It traverses the list of known monitors, deflating where possible.
1341 // The scavenged monitor are returned to the monitor free list.
1342 //
1343 // Beware that we scavenge at *every* stop-the-world point.
1344 // Having a large number of monitors in-circulation negatively
1345 // impacts the performance of some applications (e.g., PointBase).
1346 // Broadly, we want to minimize the # of monitors in circulation.
1347 //
1348 // We have added a flag, MonitorInUseLists, which creates a list
1349 // of active monitors for each thread. deflate_idle_monitors()
1350 // only scans the per-thread inuse lists. omAlloc() puts all
1351 // assigned monitors on the per-thread list. deflate_idle_monitors()
1352 // returns the non-busy monitors to the global free list.
1353 // When a thread dies, omFlush() adds the list of active monitors for
1354 // that thread to a global gOmInUseList acquiring the
1355 // global list lock. deflate_idle_monitors() acquires the global
1356 // list lock to scan for non-busy monitors to the global free list.
1357 // An alternative could have used a single global inuse list. The
1358 // downside would have been the additional cost of acquiring the global list lock
1359 // for every omAlloc().
1360 //
1361 // Perversely, the heap size -- and thus the STW safepoint rate --
1362 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1363 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1364 // This is an unfortunate aspect of this design.
1365
1366 enum ManifestConstants {
1367 ClearResponsibleAtSTW = 0,
1368 MaximumRecheckInterval = 1000
1369 };
1370
1371 // Deflate a single monitor if not in use
1372 // Return true if deflated, false if in use
1373 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1374 ObjectMonitor** freeHeadp,
1375 ObjectMonitor** freeTailp) {
1376 bool deflated;
1377 // Normal case ... The monitor is associated with obj.
1378 guarantee(obj->mark() == markOopDesc::encode(mid), "invariant");
1379 guarantee(mid == obj->mark()->monitor(), "invariant");
1380 guarantee(mid->header()->is_neutral(), "invariant");
1381
1382 if (mid->is_busy()) {
1383 if (ClearResponsibleAtSTW) mid->_Responsible = NULL;
1384 deflated = false;
1385 } else {
1386 // Deflate the monitor if it is no longer being used
1387 // It's idle - scavenge and return to the global free list
1388 // plain old deflation ...
1389 TEVENT(deflate_idle_monitors - scavenge1);
1390 if (TraceMonitorInflation) {
1391 if (obj->is_instance()) {
1392 ResourceMark rm;
1393 tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1394 (void *) obj, (intptr_t) obj->mark(), obj->klass()->external_name());
1395 }
1396 }
1397
1398 // Restore the header back to obj
1399 obj->release_set_mark(mid->header());
1400 mid->clear();
1401
1402 assert(mid->object() == NULL, "invariant");
1403
1404 // Move the object to the working free list defined by FreeHead,FreeTail.
1405 if (*freeHeadp == NULL) *freeHeadp = mid;
1406 if (*freeTailp != NULL) {
1407 ObjectMonitor * prevtail = *freeTailp;
1408 assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); // TODO KK
1409 prevtail->FreeNext = mid;
1410 }
1411 *freeTailp = mid;
1412 deflated = true;
1413 }
1414 return deflated;
1415 }
1416
1417 // Caller acquires ListLock
1418 int ObjectSynchronizer::walk_monitor_list(ObjectMonitor** listheadp,
1419 ObjectMonitor** freeHeadp,
1420 ObjectMonitor** freeTailp) {
1421 ObjectMonitor* mid;
1422 ObjectMonitor* next;
1423 ObjectMonitor* curmidinuse = NULL;
1424 int deflatedcount = 0;
1425
1426 for (mid = *listheadp; mid != NULL;) {
1427 oop obj = (oop) mid->object();
1428 bool deflated = false;
1429 if (obj != NULL) {
1430 deflated = deflate_monitor(mid, obj, freeHeadp, freeTailp);
1431 }
1432 if (deflated) {
1433 // extract from per-thread in-use-list
1434 if (mid == *listheadp) {
1435 *listheadp = mid->FreeNext;
1436 } else if (curmidinuse != NULL) {
1437 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1438 }
1439 next = mid->FreeNext;
1440 mid->FreeNext = NULL; // This mid is current tail in the FreeHead list
1441 mid = next;
1442 deflatedcount++;
1443 } else {
1444 curmidinuse = mid;
1445 mid = mid->FreeNext;
1446 }
1447 }
1448 return deflatedcount;
1449 }
1450
1451 void ObjectSynchronizer::deflate_idle_monitors() {
1452 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1453 int nInuse = 0; // currently associated with objects
1454 int nInCirculation = 0; // extant
1455 int nScavenged = 0; // reclaimed
1456 bool deflated = false;
1457
1458 ObjectMonitor * FreeHead = NULL; // Local SLL of scavenged monitors
1459 ObjectMonitor * FreeTail = NULL;
1460
1461 TEVENT(deflate_idle_monitors);
1462 // Prevent omFlush from changing mids in Thread dtor's during deflation
1463 // And in case the vm thread is acquiring a lock during a safepoint
1464 // See e.g. 6320749
1465 Thread::muxAcquire(&ListLock, "scavenge - return");
1466
1467 if (MonitorInUseLists) {
1468 int inUse = 0;
1469 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) {
1470 nInCirculation+= cur->omInUseCount;
1471 int deflatedcount = walk_monitor_list(cur->omInUseList_addr(), &FreeHead, &FreeTail);
1472 cur->omInUseCount-= deflatedcount;
1473 if (ObjectMonitor::Knob_VerifyInUse) {
1474 verifyInUse(cur);
1475 }
1476 nScavenged += deflatedcount;
1477 nInuse += cur->omInUseCount;
1478 }
1479
1480 // For moribund threads, scan gOmInUseList
1481 if (gOmInUseList) {
1482 nInCirculation += gOmInUseCount;
1483 int deflatedcount = walk_monitor_list((ObjectMonitor **)&gOmInUseList, &FreeHead, &FreeTail);
1484 gOmInUseCount-= deflatedcount;
1485 nScavenged += deflatedcount;
1486 nInuse += gOmInUseCount;
1487 }
1488
1489 } else for (PaddedEnd<ObjectMonitor> * block =
1490 (PaddedEnd<ObjectMonitor> *)gBlockList; block != NULL;
1491 block = (PaddedEnd<ObjectMonitor> *)next(block)) {
1492 // Iterate over all extant monitors - Scavenge all idle monitors.
1493 assert(block->object() == CHAINMARKER, "must be a block header");
1494 nInCirculation += _BLOCKSIZE;
1495 for (int i = 1; i < _BLOCKSIZE; i++) {
1496 ObjectMonitor* mid = (ObjectMonitor*)&block[i];
1497 oop obj = (oop) mid->object();
1498
1499 if (obj == NULL) {
1500 // The monitor is not associated with an object.
1501 // The monitor should either be a thread-specific private
1502 // free list or the global free list.
1503 // obj == NULL IMPLIES mid->is_busy() == 0
1504 guarantee(!mid->is_busy(), "invariant");
1505 continue;
1506 }
1507 deflated = deflate_monitor(mid, obj, &FreeHead, &FreeTail);
1508
1509 if (deflated) {
1510 mid->FreeNext = NULL;
1511 nScavenged++;
1512 } else {
1513 nInuse++;
1514 }
1515 }
1516 }
1517
1518 MonitorFreeCount += nScavenged;
1519
1520 // Consider: audit gFreeList to ensure that MonitorFreeCount and list agree.
1521
1522 if (ObjectMonitor::Knob_Verbose) {
1523 ::printf("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n",
1524 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge,
1525 MonitorPopulation, MonitorFreeCount);
1526 ::fflush(stdout);
1527 }
1528
1529 ForceMonitorScavenge = 0; // Reset
1530
1531 // Move the scavenged monitors back to the global free list.
1532 if (FreeHead != NULL) {
1533 guarantee(FreeTail != NULL && nScavenged > 0, "invariant");
1534 assert(FreeTail->FreeNext == NULL, "invariant");
1535 // constant-time list splice - prepend scavenged segment to gFreeList
1536 FreeTail->FreeNext = gFreeList;
1537 gFreeList = FreeHead;
1538 }
1539 Thread::muxRelease(&ListLock);
1540
1541 if (ObjectMonitor::_sync_Deflations != NULL) ObjectMonitor::_sync_Deflations->inc(nScavenged);
1542 if (ObjectMonitor::_sync_MonExtant != NULL) ObjectMonitor::_sync_MonExtant ->set_value(nInCirculation);
1543
1544 // TODO: Add objectMonitor leak detection.
1545 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1546 GVars.stwRandom = os::random();
1547 GVars.stwCycle++;
1548 }
1549
1550 // Monitor cleanup on JavaThread::exit
1551
1552 // Iterate through monitor cache and attempt to release thread's monitors
1553 // Gives up on a particular monitor if an exception occurs, but continues
1554 // the overall iteration, swallowing the exception.
1555 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1556 private:
1557 TRAPS;
1558
1559 public:
1560 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1561 void do_monitor(ObjectMonitor* mid) {
1562 if (mid->owner() == THREAD) {
1563 (void)mid->complete_exit(CHECK);
1564 }
1565 }
1566 };
1567
1568 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1569 // ignored. This is meant to be called during JNI thread detach which assumes
1570 // all remaining monitors are heavyweight. All exceptions are swallowed.
1571 // Scanning the extant monitor list can be time consuming.
1572 // A simple optimization is to add a per-thread flag that indicates a thread
1573 // called jni_monitorenter() during its lifetime.
1574 //
1575 // Instead of No_Savepoint_Verifier it might be cheaper to
1576 // use an idiom of the form:
1577 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1578 // <code that must not run at safepoint>
1579 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1580 // Since the tests are extremely cheap we could leave them enabled
1581 // for normal product builds.
1582
1583 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1584 assert(THREAD == JavaThread::current(), "must be current Java thread");
1585 No_Safepoint_Verifier nsv;
1586 ReleaseJavaMonitorsClosure rjmc(THREAD);
1587 Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread");
1588 ObjectSynchronizer::monitors_iterate(&rjmc);
1589 Thread::muxRelease(&ListLock);
1590 THREAD->clear_pending_exception();
1591 }
1592
1593 //------------------------------------------------------------------------------
1594 // Debugging code
1595
1596 void ObjectSynchronizer::sanity_checks(const bool verbose,
1597 const uint cache_line_size,
1598 int *error_cnt_ptr,
1599 int *warning_cnt_ptr) {
1600 u_char *addr_begin = (u_char*)&GVars;
1601 u_char *addr_stwRandom = (u_char*)&GVars.stwRandom;
1602 u_char *addr_hcSequence = (u_char*)&GVars.hcSequence;
1603
1604 if (verbose) {
1605 tty->print_cr("INFO: sizeof(SharedGlobals)=" SIZE_FORMAT,
1606 sizeof(SharedGlobals));
1607 }
1608
1609 uint offset_stwRandom = (uint)(addr_stwRandom - addr_begin);
1610 if (verbose) tty->print_cr("INFO: offset(stwRandom)=%u", offset_stwRandom);
1611
1612 uint offset_hcSequence = (uint)(addr_hcSequence - addr_begin);
1613 if (verbose) {
1614 tty->print_cr("INFO: offset(_hcSequence)=%u", offset_hcSequence);
1615 }
1616
1617 if (cache_line_size != 0) {
1618 // We were able to determine the L1 data cache line size so
1619 // do some cache line specific sanity checks
1620
1621 if (offset_stwRandom < cache_line_size) {
1622 tty->print_cr("WARNING: the SharedGlobals.stwRandom field is closer "
1623 "to the struct beginning than a cache line which permits "
1624 "false sharing.");
1625 (*warning_cnt_ptr)++;
1626 }
1627
1628 if ((offset_hcSequence - offset_stwRandom) < cache_line_size) {
1629 tty->print_cr("WARNING: the SharedGlobals.stwRandom and "
1630 "SharedGlobals.hcSequence fields are closer than a cache "
1631 "line which permits false sharing.");
1632 (*warning_cnt_ptr)++;
1633 }
1634
1635 if ((sizeof(SharedGlobals) - offset_hcSequence) < cache_line_size) {
1636 tty->print_cr("WARNING: the SharedGlobals.hcSequence field is closer "
1637 "to the struct end than a cache line which permits false "
1638 "sharing.");
1639 (*warning_cnt_ptr)++;
1640 }
1641 }
1642 }
1643
1644 #ifndef PRODUCT
1645
1646 // Verify all monitors in the monitor cache, the verification is weak.
1647 void ObjectSynchronizer::verify() {
1648 PaddedEnd<ObjectMonitor> * block = (PaddedEnd<ObjectMonitor> *)gBlockList;
1649 ObjectMonitor* mid;
1650 while (block) {
1651 assert(block->object() == CHAINMARKER, "must be a block header");
1652 for (int i = 1; i < _BLOCKSIZE; i++) {
1653 mid = (ObjectMonitor *)(block + i);
1654 oop object = (oop) mid->object();
1655 if (object != NULL) {
1656 mid->verify();
1657 }
1658 }
1659 block = (PaddedEnd<ObjectMonitor> *) block->FreeNext;
1660 }
1661 }
1662
1663 // Check if monitor belongs to the monitor cache
1664 // The list is grow-only so it's *relatively* safe to traverse
1665 // the list of extant blocks without taking a lock.
1666
1667 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
1668 PaddedEnd<ObjectMonitor> * block = (PaddedEnd<ObjectMonitor> *)gBlockList;
1669
1670 while (block) {
1671 assert(block->object() == CHAINMARKER, "must be a block header");
1672 if (monitor > (ObjectMonitor *)&block[0] &&
1673 monitor < (ObjectMonitor *)&block[_BLOCKSIZE]) {
1674 address mon = (address) monitor;
1675 address blk = (address) block;
1676 size_t diff = mon - blk;
1677 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "check");
1678 return 1;
1679 }
1680 block = (PaddedEnd<ObjectMonitor> *) block->FreeNext;
1681 }
1682 return 0;
1683 }
1684
1685 #endif