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 enter
280 bool ObjectSynchronizer::jni_try_enter(Handle obj, Thread* THREAD) {
281 if (UseBiasedLocking) {
282 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
283 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
284 }
285
286 ObjectMonitor* monitor = ObjectSynchronizer::inflate_helper(obj());
287 return monitor->try_enter(THREAD);
288 }
289
290
291 // NOTE: must use heavy weight monitor to handle jni monitor exit
292 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
293 TEVENT(jni_exit);
294 if (UseBiasedLocking) {
295 Handle h_obj(THREAD, obj);
296 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
297 obj = h_obj();
298 }
299 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
300
301 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj);
302 // If this thread has locked the object, exit the monitor. Note: can't use
303 // monitor->check(CHECK); must exit even if an exception is pending.
304 if (monitor->check(THREAD)) {
305 monitor->exit(true, THREAD);
306 }
307 }
308
309 // -----------------------------------------------------------------------------
310 // Internal VM locks on java objects
311 // standard constructor, allows locking failures
312 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
313 _dolock = doLock;
314 _thread = thread;
315 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
316 _obj = obj;
317
318 if (_dolock) {
319 TEVENT(ObjectLocker);
320
321 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
322 }
323 }
324
325 ObjectLocker::~ObjectLocker() {
326 if (_dolock) {
327 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
328 }
329 }
330
331
332 // -----------------------------------------------------------------------------
333 // Wait/Notify/NotifyAll
334 // NOTE: must use heavy weight monitor to handle wait()
335 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
336 if (UseBiasedLocking) {
337 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
338 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
339 }
340 if (millis < 0) {
341 TEVENT(wait - throw IAX);
342 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
343 }
344 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
345 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
346 monitor->wait(millis, true, THREAD);
347
348 // This dummy call is in place to get around dtrace bug 6254741. Once
349 // that's fixed we can uncomment the following line, remove the call
350 // and change this function back into a "void" func.
351 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
352 return dtrace_waited_probe(monitor, obj, THREAD);
353 }
354
355 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, 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 if (millis < 0) {
361 TEVENT(wait - throw IAX);
362 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
363 }
364 ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD);
365 }
366
367 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
368 if (UseBiasedLocking) {
369 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
370 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
371 }
372
373 markOop mark = obj->mark();
374 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
375 return;
376 }
377 ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD);
378 }
379
380 // NOTE: see comment of notify()
381 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
382 if (UseBiasedLocking) {
383 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
384 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
385 }
386
387 markOop mark = obj->mark();
388 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
389 return;
390 }
391 ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD);
392 }
393
394 // -----------------------------------------------------------------------------
395 // Hash Code handling
396 //
397 // Performance concern:
398 // OrderAccess::storestore() calls release() which at one time stored 0
399 // into the global volatile OrderAccess::dummy variable. This store was
400 // unnecessary for correctness. Many threads storing into a common location
401 // causes considerable cache migration or "sloshing" on large SMP systems.
402 // As such, I avoided using OrderAccess::storestore(). In some cases
403 // OrderAccess::fence() -- which incurs local latency on the executing
404 // processor -- is a better choice as it scales on SMP systems.
405 //
406 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
407 // a discussion of coherency costs. Note that all our current reference
408 // platforms provide strong ST-ST order, so the issue is moot on IA32,
409 // x64, and SPARC.
410 //
411 // As a general policy we use "volatile" to control compiler-based reordering
412 // and explicit fences (barriers) to control for architectural reordering
413 // performed by the CPU(s) or platform.
414
415 struct SharedGlobals {
416 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
417 // These are highly shared mostly-read variables.
418 // To avoid false-sharing they need to be the sole occupants of a cache line.
419 volatile int stwRandom;
420 volatile int stwCycle;
421 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
422 // Hot RW variable -- Sequester to avoid false-sharing
423 volatile int hcSequence;
424 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
425 };
426
427 static SharedGlobals GVars;
428 static int MonitorScavengeThreshold = 1000000;
429 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
430
431 static markOop ReadStableMark(oop obj) {
432 markOop mark = obj->mark();
433 if (!mark->is_being_inflated()) {
434 return mark; // normal fast-path return
435 }
436
437 int its = 0;
438 for (;;) {
439 markOop mark = obj->mark();
440 if (!mark->is_being_inflated()) {
441 return mark; // normal fast-path return
442 }
443
444 // The object is being inflated by some other thread.
445 // The caller of ReadStableMark() must wait for inflation to complete.
446 // Avoid live-lock
447 // TODO: consider calling SafepointSynchronize::do_call_back() while
448 // spinning to see if there's a safepoint pending. If so, immediately
449 // yielding or blocking would be appropriate. Avoid spinning while
450 // there is a safepoint pending.
451 // TODO: add inflation contention performance counters.
452 // TODO: restrict the aggregate number of spinners.
453
454 ++its;
455 if (its > 10000 || !os::is_MP()) {
456 if (its & 1) {
457 os::naked_yield();
458 TEVENT(Inflate: INFLATING - yield);
459 } else {
460 // Note that the following code attenuates the livelock problem but is not
461 // a complete remedy. A more complete solution would require that the inflating
462 // thread hold the associated inflation lock. The following code simply restricts
463 // the number of spinners to at most one. We'll have N-2 threads blocked
464 // on the inflationlock, 1 thread holding the inflation lock and using
465 // a yield/park strategy, and 1 thread in the midst of inflation.
466 // A more refined approach would be to change the encoding of INFLATING
467 // to allow encapsulation of a native thread pointer. Threads waiting for
468 // inflation to complete would use CAS to push themselves onto a singly linked
469 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
470 // and calling park(). When inflation was complete the thread that accomplished inflation
471 // would detach the list and set the markword to inflated with a single CAS and
472 // then for each thread on the list, set the flag and unpark() the thread.
473 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
474 // wakes at most one thread whereas we need to wake the entire list.
475 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
476 int YieldThenBlock = 0;
477 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
478 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
479 Thread::muxAcquire(InflationLocks + ix, "InflationLock");
480 while (obj->mark() == markOopDesc::INFLATING()) {
481 // Beware: NakedYield() is advisory and has almost no effect on some platforms
482 // so we periodically call Self->_ParkEvent->park(1).
483 // We use a mixed spin/yield/block mechanism.
484 if ((YieldThenBlock++) >= 16) {
485 Thread::current()->_ParkEvent->park(1);
486 } else {
487 os::naked_yield();
488 }
489 }
490 Thread::muxRelease(InflationLocks + ix);
491 TEVENT(Inflate: INFLATING - yield/park);
492 }
493 } else {
494 SpinPause(); // SMP-polite spinning
495 }
496 }
497 }
498
499 // hashCode() generation :
500 //
501 // Possibilities:
502 // * MD5Digest of {obj,stwRandom}
503 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
504 // * A DES- or AES-style SBox[] mechanism
505 // * One of the Phi-based schemes, such as:
506 // 2654435761 = 2^32 * Phi (golden ratio)
507 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
508 // * A variation of Marsaglia's shift-xor RNG scheme.
509 // * (obj ^ stwRandom) is appealing, but can result
510 // in undesirable regularity in the hashCode values of adjacent objects
511 // (objects allocated back-to-back, in particular). This could potentially
512 // result in hashtable collisions and reduced hashtable efficiency.
513 // There are simple ways to "diffuse" the middle address bits over the
514 // generated hashCode values:
515
516 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
517 intptr_t value = 0;
518 if (hashCode == 0) {
519 // This form uses an unguarded global Park-Miller RNG,
520 // so it's possible for two threads to race and generate the same RNG.
521 // On MP system we'll have lots of RW access to a global, so the
522 // mechanism induces lots of coherency traffic.
523 value = os::random();
524 } else if (hashCode == 1) {
525 // This variation has the property of being stable (idempotent)
526 // between STW operations. This can be useful in some of the 1-0
527 // synchronization schemes.
528 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
529 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
530 } else if (hashCode == 2) {
531 value = 1; // for sensitivity testing
532 } else if (hashCode == 3) {
533 value = ++GVars.hcSequence;
534 } else if (hashCode == 4) {
535 value = cast_from_oop<intptr_t>(obj);
536 } else {
537 // Marsaglia's xor-shift scheme with thread-specific state
538 // This is probably the best overall implementation -- we'll
539 // likely make this the default in future releases.
540 unsigned t = Self->_hashStateX;
541 t ^= (t << 11);
542 Self->_hashStateX = Self->_hashStateY;
543 Self->_hashStateY = Self->_hashStateZ;
544 Self->_hashStateZ = Self->_hashStateW;
545 unsigned v = Self->_hashStateW;
546 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
547 Self->_hashStateW = v;
548 value = v;
549 }
550
551 value &= markOopDesc::hash_mask;
552 if (value == 0) value = 0xBAD;
553 assert(value != markOopDesc::no_hash, "invariant");
554 TEVENT(hashCode: GENERATE);
555 return value;
556 }
557
558 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
559 if (UseBiasedLocking) {
560 // NOTE: many places throughout the JVM do not expect a safepoint
561 // to be taken here, in particular most operations on perm gen
562 // objects. However, we only ever bias Java instances and all of
563 // the call sites of identity_hash that might revoke biases have
564 // been checked to make sure they can handle a safepoint. The
565 // added check of the bias pattern is to avoid useless calls to
566 // thread-local storage.
567 if (obj->mark()->has_bias_pattern()) {
568 // Handle for oop obj in case of STW safepoint
569 Handle hobj(Self, obj);
570 // Relaxing assertion for bug 6320749.
571 assert(Universe::verify_in_progress() ||
572 !SafepointSynchronize::is_at_safepoint(),
573 "biases should not be seen by VM thread here");
574 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
575 obj = hobj();
576 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
577 }
578 }
579
580 // hashCode() is a heap mutator ...
581 // Relaxing assertion for bug 6320749.
582 assert(Universe::verify_in_progress() ||
583 !SafepointSynchronize::is_at_safepoint(), "invariant");
584 assert(Universe::verify_in_progress() ||
585 Self->is_Java_thread() , "invariant");
586 assert(Universe::verify_in_progress() ||
587 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
588
589 ObjectMonitor* monitor = NULL;
590 markOop temp, test;
591 intptr_t hash;
592 markOop mark = ReadStableMark(obj);
593
594 // object should remain ineligible for biased locking
595 assert(!mark->has_bias_pattern(), "invariant");
596
597 if (mark->is_neutral()) {
598 hash = mark->hash(); // this is a normal header
599 if (hash) { // if it has hash, just return it
600 return hash;
601 }
602 hash = get_next_hash(Self, obj); // allocate a new hash code
603 temp = mark->copy_set_hash(hash); // merge the hash code into header
604 // use (machine word version) atomic operation to install the hash
605 test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark);
606 if (test == mark) {
607 return hash;
608 }
609 // If atomic operation failed, we must inflate the header
610 // into heavy weight monitor. We could add more code here
611 // for fast path, but it does not worth the complexity.
612 } else if (mark->has_monitor()) {
613 monitor = mark->monitor();
614 temp = monitor->header();
615 assert(temp->is_neutral(), "invariant");
616 hash = temp->hash();
617 if (hash) {
618 return hash;
619 }
620 // Skip to the following code to reduce code size
621 } else if (Self->is_lock_owned((address)mark->locker())) {
622 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
623 assert(temp->is_neutral(), "invariant");
624 hash = temp->hash(); // by current thread, check if the displaced
625 if (hash) { // header contains hash code
626 return hash;
627 }
628 // WARNING:
629 // The displaced header is strictly immutable.
630 // It can NOT be changed in ANY cases. So we have
631 // to inflate the header into heavyweight monitor
632 // even the current thread owns the lock. The reason
633 // is the BasicLock (stack slot) will be asynchronously
634 // read by other threads during the inflate() function.
635 // Any change to stack may not propagate to other threads
636 // correctly.
637 }
638
639 // Inflate the monitor to set hash code
640 monitor = ObjectSynchronizer::inflate(Self, obj);
641 // Load displaced header and check it has hash code
642 mark = monitor->header();
643 assert(mark->is_neutral(), "invariant");
644 hash = mark->hash();
645 if (hash == 0) {
646 hash = get_next_hash(Self, obj);
647 temp = mark->copy_set_hash(hash); // merge hash code into header
648 assert(temp->is_neutral(), "invariant");
649 test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark);
650 if (test != mark) {
651 // The only update to the header in the monitor (outside GC)
652 // is install the hash code. If someone add new usage of
653 // displaced header, please update this code
654 hash = test->hash();
655 assert(test->is_neutral(), "invariant");
656 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
657 }
658 }
659 // We finally get the hash
660 return hash;
661 }
662
663 // Deprecated -- use FastHashCode() instead.
664
665 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
666 return FastHashCode(Thread::current(), obj());
667 }
668
669
670 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
671 Handle h_obj) {
672 if (UseBiasedLocking) {
673 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
674 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
675 }
676
677 assert(thread == JavaThread::current(), "Can only be called on current thread");
678 oop obj = h_obj();
679
680 markOop mark = ReadStableMark(obj);
681
682 // Uncontended case, header points to stack
683 if (mark->has_locker()) {
684 return thread->is_lock_owned((address)mark->locker());
685 }
686 // Contended case, header points to ObjectMonitor (tagged pointer)
687 if (mark->has_monitor()) {
688 ObjectMonitor* monitor = mark->monitor();
689 return monitor->is_entered(thread) != 0;
690 }
691 // Unlocked case, header in place
692 assert(mark->is_neutral(), "sanity check");
693 return false;
694 }
695
696 // Be aware of this method could revoke bias of the lock object.
697 // This method queries the ownership of the lock handle specified by 'h_obj'.
698 // If the current thread owns the lock, it returns owner_self. If no
699 // thread owns the lock, it returns owner_none. Otherwise, it will return
700 // owner_other.
701 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
702 (JavaThread *self, Handle h_obj) {
703 // The caller must beware this method can revoke bias, and
704 // revocation can result in a safepoint.
705 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
706 assert(self->thread_state() != _thread_blocked, "invariant");
707
708 // Possible mark states: neutral, biased, stack-locked, inflated
709
710 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
711 // CASE: biased
712 BiasedLocking::revoke_and_rebias(h_obj, false, self);
713 assert(!h_obj->mark()->has_bias_pattern(),
714 "biases should be revoked by now");
715 }
716
717 assert(self == JavaThread::current(), "Can only be called on current thread");
718 oop obj = h_obj();
719 markOop mark = ReadStableMark(obj);
720
721 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
722 if (mark->has_locker()) {
723 return self->is_lock_owned((address)mark->locker()) ?
724 owner_self : owner_other;
725 }
726
727 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
728 // The Object:ObjectMonitor relationship is stable as long as we're
729 // not at a safepoint.
730 if (mark->has_monitor()) {
731 void * owner = mark->monitor()->_owner;
732 if (owner == NULL) return owner_none;
733 return (owner == self ||
734 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
735 }
736
737 // CASE: neutral
738 assert(mark->is_neutral(), "sanity check");
739 return owner_none; // it's unlocked
740 }
741
742 // FIXME: jvmti should call this
743 JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) {
744 if (UseBiasedLocking) {
745 if (SafepointSynchronize::is_at_safepoint()) {
746 BiasedLocking::revoke_at_safepoint(h_obj);
747 } else {
748 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
749 }
750 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
751 }
752
753 oop obj = h_obj();
754 address owner = NULL;
755
756 markOop mark = ReadStableMark(obj);
757
758 // Uncontended case, header points to stack
759 if (mark->has_locker()) {
760 owner = (address) mark->locker();
761 }
762
763 // Contended case, header points to ObjectMonitor (tagged pointer)
764 if (mark->has_monitor()) {
765 ObjectMonitor* monitor = mark->monitor();
766 assert(monitor != NULL, "monitor should be non-null");
767 owner = (address) monitor->owner();
768 }
769
770 if (owner != NULL) {
771 // owning_thread_from_monitor_owner() may also return NULL here
772 return Threads::owning_thread_from_monitor_owner(owner, doLock);
773 }
774
775 // Unlocked case, header in place
776 // Cannot have assertion since this object may have been
777 // locked by another thread when reaching here.
778 // assert(mark->is_neutral(), "sanity check");
779
780 return NULL;
781 }
782 // Visitors ...
783
784 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
785 PaddedEnd<ObjectMonitor> * block = (PaddedEnd<ObjectMonitor> *)gBlockList;
786 ObjectMonitor* mid;
787 while (block) {
788 assert(block->object() == CHAINMARKER, "must be a block header");
789 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
790 mid = (ObjectMonitor *)(block + i);
791 oop object = (oop) mid->object();
792 if (object != NULL) {
793 closure->do_monitor(mid);
794 }
795 }
796 block = (PaddedEnd<ObjectMonitor> *) block->FreeNext;
797 }
798 }
799
800 // Get the next block in the block list.
801 static inline ObjectMonitor* next(ObjectMonitor* block) {
802 assert(block->object() == CHAINMARKER, "must be a block header");
803 block = block->FreeNext;
804 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
805 return block;
806 }
807
808
809 void ObjectSynchronizer::oops_do(OopClosure* f) {
810 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
811 for (PaddedEnd<ObjectMonitor> * block =
812 (PaddedEnd<ObjectMonitor> *)gBlockList; block != NULL;
813 block = (PaddedEnd<ObjectMonitor> *)next(block)) {
814 assert(block->object() == CHAINMARKER, "must be a block header");
815 for (int i = 1; i < _BLOCKSIZE; i++) {
816 ObjectMonitor* mid = (ObjectMonitor *)&block[i];
817 if (mid->object() != NULL) {
818 f->do_oop((oop*)mid->object_addr());
819 }
820 }
821 }
822 }
823
824
825 // -----------------------------------------------------------------------------
826 // ObjectMonitor Lifecycle
827 // -----------------------
828 // Inflation unlinks monitors from the global gFreeList and
829 // associates them with objects. Deflation -- which occurs at
830 // STW-time -- disassociates idle monitors from objects. Such
831 // scavenged monitors are returned to the gFreeList.
832 //
833 // The global list is protected by ListLock. All the critical sections
834 // are short and operate in constant-time.
835 //
836 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
837 //
838 // Lifecycle:
839 // -- unassigned and on the global free list
840 // -- unassigned and on a thread's private omFreeList
841 // -- assigned to an object. The object is inflated and the mark refers
842 // to the objectmonitor.
843
844
845 // Constraining monitor pool growth via MonitorBound ...
846 //
847 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
848 // the rate of scavenging is driven primarily by GC. As such, we can find
849 // an inordinate number of monitors in circulation.
850 // To avoid that scenario we can artificially induce a STW safepoint
851 // if the pool appears to be growing past some reasonable bound.
852 // Generally we favor time in space-time tradeoffs, but as there's no
853 // natural back-pressure on the # of extant monitors we need to impose some
854 // type of limit. Beware that if MonitorBound is set to too low a value
855 // we could just loop. In addition, if MonitorBound is set to a low value
856 // we'll incur more safepoints, which are harmful to performance.
857 // See also: GuaranteedSafepointInterval
858 //
859 // The current implementation uses asynchronous VM operations.
860
861 static void InduceScavenge(Thread * Self, const char * Whence) {
862 // Induce STW safepoint to trim monitors
863 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
864 // More precisely, trigger an asynchronous STW safepoint as the number
865 // of active monitors passes the specified threshold.
866 // TODO: assert thread state is reasonable
867
868 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
869 if (ObjectMonitor::Knob_Verbose) {
870 ::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ;
871 ::fflush(stdout);
872 }
873 // Induce a 'null' safepoint to scavenge monitors
874 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
875 // to the VMthread and have a lifespan longer than that of this activation record.
876 // The VMThread will delete the op when completed.
877 VMThread::execute(new VM_ForceAsyncSafepoint());
878
879 if (ObjectMonitor::Knob_Verbose) {
880 ::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ;
881 ::fflush(stdout);
882 }
883 }
884 }
885
886 void ObjectSynchronizer::verifyInUse(Thread *Self) {
887 ObjectMonitor* mid;
888 int inusetally = 0;
889 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) {
890 inusetally++;
891 }
892 assert(inusetally == Self->omInUseCount, "inuse count off");
893
894 int freetally = 0;
895 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) {
896 freetally++;
897 }
898 assert(freetally == Self->omFreeCount, "free count off");
899 }
900
901 ObjectMonitor * NOINLINE ObjectSynchronizer::omAlloc(Thread * Self) {
902 // A large MAXPRIVATE value reduces both list lock contention
903 // and list coherency traffic, but also tends to increase the
904 // number of objectMonitors in circulation as well as the STW
905 // scavenge costs. As usual, we lean toward time in space-time
906 // tradeoffs.
907 const int MAXPRIVATE = 1024;
908 for (;;) {
909 ObjectMonitor * m;
910
911 // 1: try to allocate from the thread's local omFreeList.
912 // Threads will attempt to allocate first from their local list, then
913 // from the global list, and only after those attempts fail will the thread
914 // attempt to instantiate new monitors. Thread-local free lists take
915 // heat off the ListLock and improve allocation latency, as well as reducing
916 // coherency traffic on the shared global list.
917 m = Self->omFreeList;
918 if (m != NULL) {
919 Self->omFreeList = m->FreeNext;
920 Self->omFreeCount--;
921 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene
922 guarantee(m->object() == NULL, "invariant");
923 if (MonitorInUseLists) {
924 m->FreeNext = Self->omInUseList;
925 Self->omInUseList = m;
926 Self->omInUseCount++;
927 if (ObjectMonitor::Knob_VerifyInUse) {
928 verifyInUse(Self);
929 }
930 } else {
931 m->FreeNext = NULL;
932 }
933 return m;
934 }
935
936 // 2: try to allocate from the global gFreeList
937 // CONSIDER: use muxTry() instead of muxAcquire().
938 // If the muxTry() fails then drop immediately into case 3.
939 // If we're using thread-local free lists then try
940 // to reprovision the caller's free list.
941 if (gFreeList != NULL) {
942 // Reprovision the thread's omFreeList.
943 // Use bulk transfers to reduce the allocation rate and heat
944 // on various locks.
945 Thread::muxAcquire(&ListLock, "omAlloc");
946 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
947 MonitorFreeCount--;
948 ObjectMonitor * take = gFreeList;
949 gFreeList = take->FreeNext;
950 guarantee(take->object() == NULL, "invariant");
951 guarantee(!take->is_busy(), "invariant");
952 take->Recycle();
953 omRelease(Self, take, false);
954 }
955 Thread::muxRelease(&ListLock);
956 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
957 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
958 TEVENT(omFirst - reprovision);
959
960 const int mx = MonitorBound;
961 if (mx > 0 && (MonitorPopulation-MonitorFreeCount) > mx) {
962 // We can't safely induce a STW safepoint from omAlloc() as our thread
963 // state may not be appropriate for such activities and callers may hold
964 // naked oops, so instead we defer the action.
965 InduceScavenge(Self, "omAlloc");
966 }
967 continue;
968 }
969
970 // 3: allocate a block of new ObjectMonitors
971 // Both the local and global free lists are empty -- resort to malloc().
972 // In the current implementation objectMonitors are TSM - immortal.
973 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
974 // each ObjectMonitor to start at the beginning of a cache line,
975 // so we use align_size_up().
976 // A better solution would be to use C++ placement-new.
977 // BEWARE: As it stands currently, we don't run the ctors!
978 assert(_BLOCKSIZE > 1, "invariant");
979 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
980 PaddedEnd<ObjectMonitor> * temp;
981 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
982 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
983 mtInternal);
984 temp = (PaddedEnd<ObjectMonitor> *)
985 align_size_up((intptr_t)real_malloc_addr,
986 DEFAULT_CACHE_LINE_SIZE);
987
988 // NOTE: (almost) no way to recover if allocation failed.
989 // We might be able to induce a STW safepoint and scavenge enough
990 // objectMonitors to permit progress.
991 if (temp == NULL) {
992 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
993 "Allocate ObjectMonitors");
994 }
995 (void)memset((void *) temp, 0, neededsize);
996
997 // Format the block.
998 // initialize the linked list, each monitor points to its next
999 // forming the single linked free list, the very first monitor
1000 // will points to next block, which forms the block list.
1001 // The trick of using the 1st element in the block as gBlockList
1002 // linkage should be reconsidered. A better implementation would
1003 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1004
1005 for (int i = 1; i < _BLOCKSIZE; i++) {
1006 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1007 }
1008
1009 // terminate the last monitor as the end of list
1010 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1011
1012 // Element [0] is reserved for global list linkage
1013 temp[0].set_object(CHAINMARKER);
1014
1015 // Consider carving out this thread's current request from the
1016 // block in hand. This avoids some lock traffic and redundant
1017 // list activity.
1018
1019 // Acquire the ListLock to manipulate BlockList and FreeList.
1020 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1021 Thread::muxAcquire(&ListLock, "omAlloc [2]");
1022 MonitorPopulation += _BLOCKSIZE-1;
1023 MonitorFreeCount += _BLOCKSIZE-1;
1024
1025 // Add the new block to the list of extant blocks (gBlockList).
1026 // The very first objectMonitor in a block is reserved and dedicated.
1027 // It serves as blocklist "next" linkage.
1028 temp[0].FreeNext = gBlockList;
1029 gBlockList = temp;
1030
1031 // Add the new string of objectMonitors to the global free list
1032 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1033 gFreeList = temp + 1;
1034 Thread::muxRelease(&ListLock);
1035 TEVENT(Allocate block of monitors);
1036 }
1037 }
1038
1039 // Place "m" on the caller's private per-thread omFreeList.
1040 // In practice there's no need to clamp or limit the number of
1041 // monitors on a thread's omFreeList as the only time we'll call
1042 // omRelease is to return a monitor to the free list after a CAS
1043 // attempt failed. This doesn't allow unbounded #s of monitors to
1044 // accumulate on a thread's free list.
1045
1046 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1047 bool fromPerThreadAlloc) {
1048 guarantee(m->object() == NULL, "invariant");
1049
1050 // Remove from omInUseList
1051 if (MonitorInUseLists && fromPerThreadAlloc) {
1052 ObjectMonitor* curmidinuse = NULL;
1053 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL;) {
1054 if (m == mid) {
1055 // extract from per-thread in-use-list
1056 if (mid == Self->omInUseList) {
1057 Self->omInUseList = mid->FreeNext;
1058 } else if (curmidinuse != NULL) {
1059 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1060 }
1061 Self->omInUseCount--;
1062 if (ObjectMonitor::Knob_VerifyInUse) {
1063 verifyInUse(Self);
1064 }
1065 break;
1066 } else {
1067 curmidinuse = mid;
1068 mid = mid->FreeNext;
1069 }
1070 }
1071 }
1072
1073 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1074 m->FreeNext = Self->omFreeList;
1075 Self->omFreeList = m;
1076 Self->omFreeCount++;
1077 }
1078
1079 // Return the monitors of a moribund thread's local free list to
1080 // the global free list. Typically a thread calls omFlush() when
1081 // it's dying. We could also consider having the VM thread steal
1082 // monitors from threads that have not run java code over a few
1083 // consecutive STW safepoints. Relatedly, we might decay
1084 // omFreeProvision at STW safepoints.
1085 //
1086 // Also return the monitors of a moribund thread's omInUseList to
1087 // a global gOmInUseList under the global list lock so these
1088 // will continue to be scanned.
1089 //
1090 // We currently call omFlush() from the Thread:: dtor _after the thread
1091 // has been excised from the thread list and is no longer a mutator.
1092 // That means that omFlush() can run concurrently with a safepoint and
1093 // the scavenge operator. Calling omFlush() from JavaThread::exit() might
1094 // be a better choice as we could safely reason that that the JVM is
1095 // not at a safepoint at the time of the call, and thus there could
1096 // be not inopportune interleavings between omFlush() and the scavenge
1097 // operator.
1098
1099 void ObjectSynchronizer::omFlush(Thread * Self) {
1100 ObjectMonitor * List = Self->omFreeList; // Null-terminated SLL
1101 Self->omFreeList = NULL;
1102 ObjectMonitor * Tail = NULL;
1103 int Tally = 0;
1104 if (List != NULL) {
1105 ObjectMonitor * s;
1106 for (s = List; s != NULL; s = s->FreeNext) {
1107 Tally++;
1108 Tail = s;
1109 guarantee(s->object() == NULL, "invariant");
1110 guarantee(!s->is_busy(), "invariant");
1111 s->set_owner(NULL); // redundant but good hygiene
1112 TEVENT(omFlush - Move one);
1113 }
1114 guarantee(Tail != NULL && List != NULL, "invariant");
1115 }
1116
1117 ObjectMonitor * InUseList = Self->omInUseList;
1118 ObjectMonitor * InUseTail = NULL;
1119 int InUseTally = 0;
1120 if (InUseList != NULL) {
1121 Self->omInUseList = NULL;
1122 ObjectMonitor *curom;
1123 for (curom = InUseList; curom != NULL; curom = curom->FreeNext) {
1124 InUseTail = curom;
1125 InUseTally++;
1126 }
1127 assert(Self->omInUseCount == InUseTally, "inuse count off");
1128 Self->omInUseCount = 0;
1129 guarantee(InUseTail != NULL && InUseList != NULL, "invariant");
1130 }
1131
1132 Thread::muxAcquire(&ListLock, "omFlush");
1133 if (Tail != NULL) {
1134 Tail->FreeNext = gFreeList;
1135 gFreeList = List;
1136 MonitorFreeCount += Tally;
1137 }
1138
1139 if (InUseTail != NULL) {
1140 InUseTail->FreeNext = gOmInUseList;
1141 gOmInUseList = InUseList;
1142 gOmInUseCount += InUseTally;
1143 }
1144
1145 Thread::muxRelease(&ListLock);
1146 TEVENT(omFlush);
1147 }
1148
1149 // Fast path code shared by multiple functions
1150 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1151 markOop mark = obj->mark();
1152 if (mark->has_monitor()) {
1153 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1154 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1155 return mark->monitor();
1156 }
1157 return ObjectSynchronizer::inflate(Thread::current(), obj);
1158 }
1159
1160
1161 ObjectMonitor * NOINLINE ObjectSynchronizer::inflate(Thread * Self,
1162 oop object) {
1163 // Inflate mutates the heap ...
1164 // Relaxing assertion for bug 6320749.
1165 assert(Universe::verify_in_progress() ||
1166 !SafepointSynchronize::is_at_safepoint(), "invariant");
1167
1168 for (;;) {
1169 const markOop mark = object->mark();
1170 assert(!mark->has_bias_pattern(), "invariant");
1171
1172 // The mark can be in one of the following states:
1173 // * Inflated - just return
1174 // * Stack-locked - coerce it to inflated
1175 // * INFLATING - busy wait for conversion to complete
1176 // * Neutral - aggressively inflate the object.
1177 // * BIASED - Illegal. We should never see this
1178
1179 // CASE: inflated
1180 if (mark->has_monitor()) {
1181 ObjectMonitor * inf = mark->monitor();
1182 assert(inf->header()->is_neutral(), "invariant");
1183 assert(inf->object() == object, "invariant");
1184 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1185 return inf;
1186 }
1187
1188 // CASE: inflation in progress - inflating over a stack-lock.
1189 // Some other thread is converting from stack-locked to inflated.
1190 // Only that thread can complete inflation -- other threads must wait.
1191 // The INFLATING value is transient.
1192 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1193 // We could always eliminate polling by parking the thread on some auxiliary list.
1194 if (mark == markOopDesc::INFLATING()) {
1195 TEVENT(Inflate: spin while INFLATING);
1196 ReadStableMark(object);
1197 continue;
1198 }
1199
1200 // CASE: stack-locked
1201 // Could be stack-locked either by this thread or by some other thread.
1202 //
1203 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1204 // to install INFLATING into the mark word. We originally installed INFLATING,
1205 // allocated the objectmonitor, and then finally STed the address of the
1206 // objectmonitor into the mark. This was correct, but artificially lengthened
1207 // the interval in which INFLATED appeared in the mark, thus increasing
1208 // the odds of inflation contention.
1209 //
1210 // We now use per-thread private objectmonitor free lists.
1211 // These list are reprovisioned from the global free list outside the
1212 // critical INFLATING...ST interval. A thread can transfer
1213 // multiple objectmonitors en-mass from the global free list to its local free list.
1214 // This reduces coherency traffic and lock contention on the global free list.
1215 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1216 // before or after the CAS(INFLATING) operation.
1217 // See the comments in omAlloc().
1218
1219 if (mark->has_locker()) {
1220 ObjectMonitor * m = omAlloc(Self);
1221 // Optimistically prepare the objectmonitor - anticipate successful CAS
1222 // We do this before the CAS in order to minimize the length of time
1223 // in which INFLATING appears in the mark.
1224 m->Recycle();
1225 m->_Responsible = NULL;
1226 m->_recursions = 0;
1227 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1228
1229 markOop cmp = (markOop) Atomic::cmpxchg_ptr(markOopDesc::INFLATING(), object->mark_addr(), mark);
1230 if (cmp != mark) {
1231 omRelease(Self, m, true);
1232 continue; // Interference -- just retry
1233 }
1234
1235 // We've successfully installed INFLATING (0) into the mark-word.
1236 // This is the only case where 0 will appear in a mark-work.
1237 // Only the singular thread that successfully swings the mark-word
1238 // to 0 can perform (or more precisely, complete) inflation.
1239 //
1240 // Why do we CAS a 0 into the mark-word instead of just CASing the
1241 // mark-word from the stack-locked value directly to the new inflated state?
1242 // Consider what happens when a thread unlocks a stack-locked object.
1243 // It attempts to use CAS to swing the displaced header value from the
1244 // on-stack basiclock back into the object header. Recall also that the
1245 // header value (hashcode, etc) can reside in (a) the object header, or
1246 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1247 // header in an objectMonitor. The inflate() routine must copy the header
1248 // value from the basiclock on the owner's stack to the objectMonitor, all
1249 // the while preserving the hashCode stability invariants. If the owner
1250 // decides to release the lock while the value is 0, the unlock will fail
1251 // and control will eventually pass from slow_exit() to inflate. The owner
1252 // will then spin, waiting for the 0 value to disappear. Put another way,
1253 // the 0 causes the owner to stall if the owner happens to try to
1254 // drop the lock (restoring the header from the basiclock to the object)
1255 // while inflation is in-progress. This protocol avoids races that might
1256 // would otherwise permit hashCode values to change or "flicker" for an object.
1257 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1258 // 0 serves as a "BUSY" inflate-in-progress indicator.
1259
1260
1261 // fetch the displaced mark from the owner's stack.
1262 // The owner can't die or unwind past the lock while our INFLATING
1263 // object is in the mark. Furthermore the owner can't complete
1264 // an unlock on the object, either.
1265 markOop dmw = mark->displaced_mark_helper();
1266 assert(dmw->is_neutral(), "invariant");
1267
1268 // Setup monitor fields to proper values -- prepare the monitor
1269 m->set_header(dmw);
1270
1271 // Optimization: if the mark->locker stack address is associated
1272 // with this thread we could simply set m->_owner = Self.
1273 // Note that a thread can inflate an object
1274 // that it has stack-locked -- as might happen in wait() -- directly
1275 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1276 m->set_owner(mark->locker());
1277 m->set_object(object);
1278 // TODO-FIXME: assert BasicLock->dhw != 0.
1279
1280 // Must preserve store ordering. The monitor state must
1281 // be stable at the time of publishing the monitor address.
1282 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1283 object->release_set_mark(markOopDesc::encode(m));
1284
1285 // Hopefully the performance counters are allocated on distinct cache lines
1286 // to avoid false sharing on MP systems ...
1287 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc();
1288 TEVENT(Inflate: overwrite stacklock);
1289 if (TraceMonitorInflation) {
1290 if (object->is_instance()) {
1291 ResourceMark rm;
1292 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1293 (void *) object, (intptr_t) object->mark(),
1294 object->klass()->external_name());
1295 }
1296 }
1297 return m;
1298 }
1299
1300 // CASE: neutral
1301 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1302 // If we know we're inflating for entry it's better to inflate by swinging a
1303 // pre-locked objectMonitor pointer into the object header. A successful
1304 // CAS inflates the object *and* confers ownership to the inflating thread.
1305 // In the current implementation we use a 2-step mechanism where we CAS()
1306 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1307 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1308 // would be useful.
1309
1310 assert(mark->is_neutral(), "invariant");
1311 ObjectMonitor * m = omAlloc(Self);
1312 // prepare m for installation - set monitor to initial state
1313 m->Recycle();
1314 m->set_header(mark);
1315 m->set_owner(NULL);
1316 m->set_object(object);
1317 m->_recursions = 0;
1318 m->_Responsible = NULL;
1319 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1320
1321 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) {
1322 m->set_object(NULL);
1323 m->set_owner(NULL);
1324 m->Recycle();
1325 omRelease(Self, m, true);
1326 m = NULL;
1327 continue;
1328 // interference - the markword changed - just retry.
1329 // The state-transitions are one-way, so there's no chance of
1330 // live-lock -- "Inflated" is an absorbing state.
1331 }
1332
1333 // Hopefully the performance counters are allocated on distinct
1334 // cache lines to avoid false sharing on MP systems ...
1335 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc();
1336 TEVENT(Inflate: overwrite neutral);
1337 if (TraceMonitorInflation) {
1338 if (object->is_instance()) {
1339 ResourceMark rm;
1340 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1341 (void *) object, (intptr_t) object->mark(),
1342 object->klass()->external_name());
1343 }
1344 }
1345 return m;
1346 }
1347 }
1348
1349
1350 // Deflate_idle_monitors() is called at all safepoints, immediately
1351 // after all mutators are stopped, but before any objects have moved.
1352 // It traverses the list of known monitors, deflating where possible.
1353 // The scavenged monitor are returned to the monitor free list.
1354 //
1355 // Beware that we scavenge at *every* stop-the-world point.
1356 // Having a large number of monitors in-circulation negatively
1357 // impacts the performance of some applications (e.g., PointBase).
1358 // Broadly, we want to minimize the # of monitors in circulation.
1359 //
1360 // We have added a flag, MonitorInUseLists, which creates a list
1361 // of active monitors for each thread. deflate_idle_monitors()
1362 // only scans the per-thread inuse lists. omAlloc() puts all
1363 // assigned monitors on the per-thread list. deflate_idle_monitors()
1364 // returns the non-busy monitors to the global free list.
1365 // When a thread dies, omFlush() adds the list of active monitors for
1366 // that thread to a global gOmInUseList acquiring the
1367 // global list lock. deflate_idle_monitors() acquires the global
1368 // list lock to scan for non-busy monitors to the global free list.
1369 // An alternative could have used a single global inuse list. The
1370 // downside would have been the additional cost of acquiring the global list lock
1371 // for every omAlloc().
1372 //
1373 // Perversely, the heap size -- and thus the STW safepoint rate --
1374 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1375 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1376 // This is an unfortunate aspect of this design.
1377
1378 enum ManifestConstants {
1379 ClearResponsibleAtSTW = 0,
1380 MaximumRecheckInterval = 1000
1381 };
1382
1383 // Deflate a single monitor if not in use
1384 // Return true if deflated, false if in use
1385 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1386 ObjectMonitor** freeHeadp,
1387 ObjectMonitor** freeTailp) {
1388 bool deflated;
1389 // Normal case ... The monitor is associated with obj.
1390 guarantee(obj->mark() == markOopDesc::encode(mid), "invariant");
1391 guarantee(mid == obj->mark()->monitor(), "invariant");
1392 guarantee(mid->header()->is_neutral(), "invariant");
1393
1394 if (mid->is_busy()) {
1395 if (ClearResponsibleAtSTW) mid->_Responsible = NULL;
1396 deflated = false;
1397 } else {
1398 // Deflate the monitor if it is no longer being used
1399 // It's idle - scavenge and return to the global free list
1400 // plain old deflation ...
1401 TEVENT(deflate_idle_monitors - scavenge1);
1402 if (TraceMonitorInflation) {
1403 if (obj->is_instance()) {
1404 ResourceMark rm;
1405 tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1406 (void *) obj, (intptr_t) obj->mark(), obj->klass()->external_name());
1407 }
1408 }
1409
1410 // Restore the header back to obj
1411 obj->release_set_mark(mid->header());
1412 mid->clear();
1413
1414 assert(mid->object() == NULL, "invariant");
1415
1416 // Move the object to the working free list defined by FreeHead,FreeTail.
1417 if (*freeHeadp == NULL) *freeHeadp = mid;
1418 if (*freeTailp != NULL) {
1419 ObjectMonitor * prevtail = *freeTailp;
1420 assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); // TODO KK
1421 prevtail->FreeNext = mid;
1422 }
1423 *freeTailp = mid;
1424 deflated = true;
1425 }
1426 return deflated;
1427 }
1428
1429 // Caller acquires ListLock
1430 int ObjectSynchronizer::walk_monitor_list(ObjectMonitor** listheadp,
1431 ObjectMonitor** freeHeadp,
1432 ObjectMonitor** freeTailp) {
1433 ObjectMonitor* mid;
1434 ObjectMonitor* next;
1435 ObjectMonitor* curmidinuse = NULL;
1436 int deflatedcount = 0;
1437
1438 for (mid = *listheadp; mid != NULL;) {
1439 oop obj = (oop) mid->object();
1440 bool deflated = false;
1441 if (obj != NULL) {
1442 deflated = deflate_monitor(mid, obj, freeHeadp, freeTailp);
1443 }
1444 if (deflated) {
1445 // extract from per-thread in-use-list
1446 if (mid == *listheadp) {
1447 *listheadp = mid->FreeNext;
1448 } else if (curmidinuse != NULL) {
1449 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1450 }
1451 next = mid->FreeNext;
1452 mid->FreeNext = NULL; // This mid is current tail in the FreeHead list
1453 mid = next;
1454 deflatedcount++;
1455 } else {
1456 curmidinuse = mid;
1457 mid = mid->FreeNext;
1458 }
1459 }
1460 return deflatedcount;
1461 }
1462
1463 void ObjectSynchronizer::deflate_idle_monitors() {
1464 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1465 int nInuse = 0; // currently associated with objects
1466 int nInCirculation = 0; // extant
1467 int nScavenged = 0; // reclaimed
1468 bool deflated = false;
1469
1470 ObjectMonitor * FreeHead = NULL; // Local SLL of scavenged monitors
1471 ObjectMonitor * FreeTail = NULL;
1472
1473 TEVENT(deflate_idle_monitors);
1474 // Prevent omFlush from changing mids in Thread dtor's during deflation
1475 // And in case the vm thread is acquiring a lock during a safepoint
1476 // See e.g. 6320749
1477 Thread::muxAcquire(&ListLock, "scavenge - return");
1478
1479 if (MonitorInUseLists) {
1480 int inUse = 0;
1481 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) {
1482 nInCirculation+= cur->omInUseCount;
1483 int deflatedcount = walk_monitor_list(cur->omInUseList_addr(), &FreeHead, &FreeTail);
1484 cur->omInUseCount-= deflatedcount;
1485 if (ObjectMonitor::Knob_VerifyInUse) {
1486 verifyInUse(cur);
1487 }
1488 nScavenged += deflatedcount;
1489 nInuse += cur->omInUseCount;
1490 }
1491
1492 // For moribund threads, scan gOmInUseList
1493 if (gOmInUseList) {
1494 nInCirculation += gOmInUseCount;
1495 int deflatedcount = walk_monitor_list((ObjectMonitor **)&gOmInUseList, &FreeHead, &FreeTail);
1496 gOmInUseCount-= deflatedcount;
1497 nScavenged += deflatedcount;
1498 nInuse += gOmInUseCount;
1499 }
1500
1501 } else for (PaddedEnd<ObjectMonitor> * block =
1502 (PaddedEnd<ObjectMonitor> *)gBlockList; block != NULL;
1503 block = (PaddedEnd<ObjectMonitor> *)next(block)) {
1504 // Iterate over all extant monitors - Scavenge all idle monitors.
1505 assert(block->object() == CHAINMARKER, "must be a block header");
1506 nInCirculation += _BLOCKSIZE;
1507 for (int i = 1; i < _BLOCKSIZE; i++) {
1508 ObjectMonitor* mid = (ObjectMonitor*)&block[i];
1509 oop obj = (oop) mid->object();
1510
1511 if (obj == NULL) {
1512 // The monitor is not associated with an object.
1513 // The monitor should either be a thread-specific private
1514 // free list or the global free list.
1515 // obj == NULL IMPLIES mid->is_busy() == 0
1516 guarantee(!mid->is_busy(), "invariant");
1517 continue;
1518 }
1519 deflated = deflate_monitor(mid, obj, &FreeHead, &FreeTail);
1520
1521 if (deflated) {
1522 mid->FreeNext = NULL;
1523 nScavenged++;
1524 } else {
1525 nInuse++;
1526 }
1527 }
1528 }
1529
1530 MonitorFreeCount += nScavenged;
1531
1532 // Consider: audit gFreeList to ensure that MonitorFreeCount and list agree.
1533
1534 if (ObjectMonitor::Knob_Verbose) {
1535 ::printf("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n",
1536 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge,
1537 MonitorPopulation, MonitorFreeCount);
1538 ::fflush(stdout);
1539 }
1540
1541 ForceMonitorScavenge = 0; // Reset
1542
1543 // Move the scavenged monitors back to the global free list.
1544 if (FreeHead != NULL) {
1545 guarantee(FreeTail != NULL && nScavenged > 0, "invariant");
1546 assert(FreeTail->FreeNext == NULL, "invariant");
1547 // constant-time list splice - prepend scavenged segment to gFreeList
1548 FreeTail->FreeNext = gFreeList;
1549 gFreeList = FreeHead;
1550 }
1551 Thread::muxRelease(&ListLock);
1552
1553 if (ObjectMonitor::_sync_Deflations != NULL) ObjectMonitor::_sync_Deflations->inc(nScavenged);
1554 if (ObjectMonitor::_sync_MonExtant != NULL) ObjectMonitor::_sync_MonExtant ->set_value(nInCirculation);
1555
1556 // TODO: Add objectMonitor leak detection.
1557 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1558 GVars.stwRandom = os::random();
1559 GVars.stwCycle++;
1560 }
1561
1562 // Monitor cleanup on JavaThread::exit
1563
1564 // Iterate through monitor cache and attempt to release thread's monitors
1565 // Gives up on a particular monitor if an exception occurs, but continues
1566 // the overall iteration, swallowing the exception.
1567 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1568 private:
1569 TRAPS;
1570
1571 public:
1572 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1573 void do_monitor(ObjectMonitor* mid) {
1574 if (mid->owner() == THREAD) {
1575 (void)mid->complete_exit(CHECK);
1576 }
1577 }
1578 };
1579
1580 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1581 // ignored. This is meant to be called during JNI thread detach which assumes
1582 // all remaining monitors are heavyweight. All exceptions are swallowed.
1583 // Scanning the extant monitor list can be time consuming.
1584 // A simple optimization is to add a per-thread flag that indicates a thread
1585 // called jni_monitorenter() during its lifetime.
1586 //
1587 // Instead of No_Savepoint_Verifier it might be cheaper to
1588 // use an idiom of the form:
1589 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1590 // <code that must not run at safepoint>
1591 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1592 // Since the tests are extremely cheap we could leave them enabled
1593 // for normal product builds.
1594
1595 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1596 assert(THREAD == JavaThread::current(), "must be current Java thread");
1597 No_Safepoint_Verifier nsv;
1598 ReleaseJavaMonitorsClosure rjmc(THREAD);
1599 Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread");
1600 ObjectSynchronizer::monitors_iterate(&rjmc);
1601 Thread::muxRelease(&ListLock);
1602 THREAD->clear_pending_exception();
1603 }
1604
1605 //------------------------------------------------------------------------------
1606 // Debugging code
1607
1608 void ObjectSynchronizer::sanity_checks(const bool verbose,
1609 const uint cache_line_size,
1610 int *error_cnt_ptr,
1611 int *warning_cnt_ptr) {
1612 u_char *addr_begin = (u_char*)&GVars;
1613 u_char *addr_stwRandom = (u_char*)&GVars.stwRandom;
1614 u_char *addr_hcSequence = (u_char*)&GVars.hcSequence;
1615
1616 if (verbose) {
1617 tty->print_cr("INFO: sizeof(SharedGlobals)=" SIZE_FORMAT,
1618 sizeof(SharedGlobals));
1619 }
1620
1621 uint offset_stwRandom = (uint)(addr_stwRandom - addr_begin);
1622 if (verbose) tty->print_cr("INFO: offset(stwRandom)=%u", offset_stwRandom);
1623
1624 uint offset_hcSequence = (uint)(addr_hcSequence - addr_begin);
1625 if (verbose) {
1626 tty->print_cr("INFO: offset(_hcSequence)=%u", offset_hcSequence);
1627 }
1628
1629 if (cache_line_size != 0) {
1630 // We were able to determine the L1 data cache line size so
1631 // do some cache line specific sanity checks
1632
1633 if (offset_stwRandom < cache_line_size) {
1634 tty->print_cr("WARNING: the SharedGlobals.stwRandom field is closer "
1635 "to the struct beginning than a cache line which permits "
1636 "false sharing.");
1637 (*warning_cnt_ptr)++;
1638 }
1639
1640 if ((offset_hcSequence - offset_stwRandom) < cache_line_size) {
1641 tty->print_cr("WARNING: the SharedGlobals.stwRandom and "
1642 "SharedGlobals.hcSequence fields are closer than a cache "
1643 "line which permits false sharing.");
1644 (*warning_cnt_ptr)++;
1645 }
1646
1647 if ((sizeof(SharedGlobals) - offset_hcSequence) < cache_line_size) {
1648 tty->print_cr("WARNING: the SharedGlobals.hcSequence field is closer "
1649 "to the struct end than a cache line which permits false "
1650 "sharing.");
1651 (*warning_cnt_ptr)++;
1652 }
1653 }
1654 }
1655
1656 #ifndef PRODUCT
1657
1658 // Verify all monitors in the monitor cache, the verification is weak.
1659 void ObjectSynchronizer::verify() {
1660 PaddedEnd<ObjectMonitor> * block = (PaddedEnd<ObjectMonitor> *)gBlockList;
1661 ObjectMonitor* mid;
1662 while (block) {
1663 assert(block->object() == CHAINMARKER, "must be a block header");
1664 for (int i = 1; i < _BLOCKSIZE; i++) {
1665 mid = (ObjectMonitor *)(block + i);
1666 oop object = (oop) mid->object();
1667 if (object != NULL) {
1668 mid->verify();
1669 }
1670 }
1671 block = (PaddedEnd<ObjectMonitor> *) block->FreeNext;
1672 }
1673 }
1674
1675 // Check if monitor belongs to the monitor cache
1676 // The list is grow-only so it's *relatively* safe to traverse
1677 // the list of extant blocks without taking a lock.
1678
1679 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
1680 PaddedEnd<ObjectMonitor> * block = (PaddedEnd<ObjectMonitor> *)gBlockList;
1681
1682 while (block) {
1683 assert(block->object() == CHAINMARKER, "must be a block header");
1684 if (monitor > (ObjectMonitor *)&block[0] &&
1685 monitor < (ObjectMonitor *)&block[_BLOCKSIZE]) {
1686 address mon = (address) monitor;
1687 address blk = (address) block;
1688 size_t diff = mon - blk;
1689 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "check");
1690 return 1;
1691 }
1692 block = (PaddedEnd<ObjectMonitor> *) block->FreeNext;
1693 }
1694 return 0;
1695 }
1696
1697 #endif