1 /*
2 * Copyright (c) 1998, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/vmSymbols.hpp"
27 #include "logging/log.hpp"
28 #include "logging/logStream.hpp"
29 #include "jfr/jfrEvents.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "memory/metaspaceShared.hpp"
32 #include "memory/padded.hpp"
33 #include "memory/resourceArea.hpp"
34 #include "memory/universe.hpp"
35 #include "oops/markWord.hpp"
36 #include "oops/oop.inline.hpp"
37 #include "runtime/atomic.hpp"
38 #include "runtime/biasedLocking.hpp"
39 #include "runtime/handles.inline.hpp"
40 #include "runtime/interfaceSupport.inline.hpp"
41 #include "runtime/mutexLocker.hpp"
42 #include "runtime/objectMonitor.hpp"
43 #include "runtime/objectMonitor.inline.hpp"
44 #include "runtime/osThread.hpp"
45 #include "runtime/safepointVerifiers.hpp"
46 #include "runtime/sharedRuntime.hpp"
47 #include "runtime/stubRoutines.hpp"
48 #include "runtime/synchronizer.hpp"
49 #include "runtime/thread.inline.hpp"
50 #include "runtime/timer.hpp"
51 #include "runtime/vframe.hpp"
52 #include "runtime/vmThread.hpp"
53 #include "utilities/align.hpp"
54 #include "utilities/dtrace.hpp"
55 #include "utilities/events.hpp"
56 #include "utilities/preserveException.hpp"
57
58 // The "core" versions of monitor enter and exit reside in this file.
59 // The interpreter and compilers contain specialized transliterated
60 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
61 // for instance. If you make changes here, make sure to modify the
62 // interpreter, and both C1 and C2 fast-path inline locking code emission.
63 //
64 // -----------------------------------------------------------------------------
65
66 #ifdef DTRACE_ENABLED
67
68 // Only bother with this argument setup if dtrace is available
69 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
70
71 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
72 char* bytes = NULL; \
73 int len = 0; \
74 jlong jtid = SharedRuntime::get_java_tid(thread); \
75 Symbol* klassname = ((oop)(obj))->klass()->name(); \
76 if (klassname != NULL) { \
77 bytes = (char*)klassname->bytes(); \
78 len = klassname->utf8_length(); \
79 }
80
81 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
82 { \
83 if (DTraceMonitorProbes) { \
84 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
85 HOTSPOT_MONITOR_WAIT(jtid, \
86 (uintptr_t)(monitor), bytes, len, (millis)); \
87 } \
88 }
89
90 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
91 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
92 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
93
94 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
95 { \
96 if (DTraceMonitorProbes) { \
97 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
98 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
99 (uintptr_t)(monitor), bytes, len); \
100 } \
101 }
102
103 #else // ndef DTRACE_ENABLED
104
105 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
106 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
107
108 #endif // ndef DTRACE_ENABLED
109
110 // This exists only as a workaround of dtrace bug 6254741
111 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
112 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
113 return 0;
114 }
115
116 #define NINFLATIONLOCKS 256
117 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
118
119 // global list of blocks of monitors
120 PaddedObjectMonitor* volatile ObjectSynchronizer::g_block_list = NULL;
121 // Global ObjectMonitor free list. Newly allocated and deflated
122 // ObjectMonitors are prepended here.
123 ObjectMonitor* volatile ObjectSynchronizer::g_free_list = NULL;
124 // Global ObjectMonitor in-use list. When a JavaThread is exiting,
125 // ObjectMonitors on its per-thread in-use list are prepended here.
126 ObjectMonitor* volatile ObjectSynchronizer::g_om_in_use_list = NULL;
127 int ObjectSynchronizer::g_om_in_use_count = 0; // # on g_om_in_use_list
128
129 static volatile intptr_t gListLock = 0; // protects global monitor lists
130 static volatile int g_om_free_count = 0; // # on g_free_list
131 static volatile int g_om_population = 0; // # Extant -- in circulation
132
133 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
134
135
136 // =====================> Quick functions
137
138 // The quick_* forms are special fast-path variants used to improve
139 // performance. In the simplest case, a "quick_*" implementation could
140 // simply return false, in which case the caller will perform the necessary
141 // state transitions and call the slow-path form.
142 // The fast-path is designed to handle frequently arising cases in an efficient
143 // manner and is just a degenerate "optimistic" variant of the slow-path.
144 // returns true -- to indicate the call was satisfied.
145 // returns false -- to indicate the call needs the services of the slow-path.
146 // A no-loitering ordinance is in effect for code in the quick_* family
147 // operators: safepoints or indefinite blocking (blocking that might span a
148 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
149 // entry.
150 //
151 // Consider: An interesting optimization is to have the JIT recognize the
152 // following common idiom:
153 // synchronized (someobj) { .... ; notify(); }
154 // That is, we find a notify() or notifyAll() call that immediately precedes
155 // the monitorexit operation. In that case the JIT could fuse the operations
156 // into a single notifyAndExit() runtime primitive.
157
158 bool ObjectSynchronizer::quick_notify(oopDesc* obj, Thread* self, bool all) {
159 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
160 assert(self->is_Java_thread(), "invariant");
161 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
162 NoSafepointVerifier nsv;
163 if (obj == NULL) return false; // slow-path for invalid obj
164 const markWord mark = obj->mark();
165
166 if (mark.has_locker() && self->is_lock_owned((address)mark.locker())) {
167 // Degenerate notify
168 // stack-locked by caller so by definition the implied waitset is empty.
169 return true;
170 }
171
172 if (mark.has_monitor()) {
173 ObjectMonitor* const mon = mark.monitor();
174 assert(mon->object() == obj, "invariant");
175 if (mon->owner() != self) return false; // slow-path for IMS exception
176
177 if (mon->first_waiter() != NULL) {
178 // We have one or more waiters. Since this is an inflated monitor
179 // that we own, we can transfer one or more threads from the waitset
180 // to the entrylist here and now, avoiding the slow-path.
181 if (all) {
182 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
183 } else {
184 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
185 }
186 int free_count = 0;
187 do {
188 mon->INotify(self);
189 ++free_count;
190 } while (mon->first_waiter() != NULL && all);
191 OM_PERFDATA_OP(Notifications, inc(free_count));
192 }
193 return true;
194 }
195
196 // biased locking and any other IMS exception states take the slow-path
197 return false;
198 }
199
200
201 // The LockNode emitted directly at the synchronization site would have
202 // been too big if it were to have included support for the cases of inflated
203 // recursive enter and exit, so they go here instead.
204 // Note that we can't safely call AsyncPrintJavaStack() from within
205 // quick_enter() as our thread state remains _in_Java.
206
207 bool ObjectSynchronizer::quick_enter(oop obj, Thread* self,
208 BasicLock * lock) {
209 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
210 assert(self->is_Java_thread(), "invariant");
211 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
212 NoSafepointVerifier nsv;
213 if (obj == NULL) return false; // Need to throw NPE
214 const markWord mark = obj->mark();
215
216 if (mark.has_monitor()) {
217 ObjectMonitor* const m = mark.monitor();
218 assert(m->object() == obj, "invariant");
219 Thread* const owner = (Thread *) m->_owner;
220
221 // Lock contention and Transactional Lock Elision (TLE) diagnostics
222 // and observability
223 // Case: light contention possibly amenable to TLE
224 // Case: TLE inimical operations such as nested/recursive synchronization
225
226 if (owner == self) {
227 m->_recursions++;
228 return true;
229 }
230
231 // This Java Monitor is inflated so obj's header will never be
232 // displaced to this thread's BasicLock. Make the displaced header
233 // non-NULL so this BasicLock is not seen as recursive nor as
234 // being locked. We do this unconditionally so that this thread's
235 // BasicLock cannot be mis-interpreted by any stack walkers. For
236 // performance reasons, stack walkers generally first check for
237 // Biased Locking in the object's header, the second check is for
238 // stack-locking in the object's header, the third check is for
239 // recursive stack-locking in the displaced header in the BasicLock,
240 // and last are the inflated Java Monitor (ObjectMonitor) checks.
241 lock->set_displaced_header(markWord::unused_mark());
242
243 if (owner == NULL && m->try_set_owner_from(NULL, self) == NULL) {
244 assert(m->_recursions == 0, "invariant");
245 return true;
246 }
247 }
248
249 // Note that we could inflate in quick_enter.
250 // This is likely a useful optimization
251 // Critically, in quick_enter() we must not:
252 // -- perform bias revocation, or
253 // -- block indefinitely, or
254 // -- reach a safepoint
255
256 return false; // revert to slow-path
257 }
258
259 // -----------------------------------------------------------------------------
260 // Monitor Enter/Exit
261 // The interpreter and compiler assembly code tries to lock using the fast path
262 // of this algorithm. Make sure to update that code if the following function is
263 // changed. The implementation is extremely sensitive to race condition. Be careful.
264
265 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, TRAPS) {
266 if (UseBiasedLocking) {
267 if (!SafepointSynchronize::is_at_safepoint()) {
268 BiasedLocking::revoke(obj, THREAD);
269 } else {
270 BiasedLocking::revoke_at_safepoint(obj);
271 }
272 }
273
274 markWord mark = obj->mark();
275 assert(!mark.has_bias_pattern(), "should not see bias pattern here");
276
277 if (mark.is_neutral()) {
278 // Anticipate successful CAS -- the ST of the displaced mark must
279 // be visible <= the ST performed by the CAS.
280 lock->set_displaced_header(mark);
281 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
282 return;
283 }
284 // Fall through to inflate() ...
285 } else if (mark.has_locker() &&
286 THREAD->is_lock_owned((address)mark.locker())) {
287 assert(lock != mark.locker(), "must not re-lock the same lock");
288 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
289 lock->set_displaced_header(markWord::from_pointer(NULL));
290 return;
291 }
292
293 // The object header will never be displaced to this lock,
294 // so it does not matter what the value is, except that it
295 // must be non-zero to avoid looking like a re-entrant lock,
296 // and must not look locked either.
297 lock->set_displaced_header(markWord::unused_mark());
298 inflate(THREAD, obj(), inflate_cause_monitor_enter)->enter(THREAD);
299 }
300
301 void ObjectSynchronizer::exit(oop object, BasicLock* lock, TRAPS) {
302 markWord mark = object->mark();
303 // We cannot check for Biased Locking if we are racing an inflation.
304 assert(mark == markWord::INFLATING() ||
305 !mark.has_bias_pattern(), "should not see bias pattern here");
306
307 markWord dhw = lock->displaced_header();
308 if (dhw.value() == 0) {
309 // If the displaced header is NULL, then this exit matches up with
310 // a recursive enter. No real work to do here except for diagnostics.
311 #ifndef PRODUCT
312 if (mark != markWord::INFLATING()) {
313 // Only do diagnostics if we are not racing an inflation. Simply
314 // exiting a recursive enter of a Java Monitor that is being
315 // inflated is safe; see the has_monitor() comment below.
316 assert(!mark.is_neutral(), "invariant");
317 assert(!mark.has_locker() ||
318 THREAD->is_lock_owned((address)mark.locker()), "invariant");
319 if (mark.has_monitor()) {
320 // The BasicLock's displaced_header is marked as a recursive
321 // enter and we have an inflated Java Monitor (ObjectMonitor).
322 // This is a special case where the Java Monitor was inflated
323 // after this thread entered the stack-lock recursively. When a
324 // Java Monitor is inflated, we cannot safely walk the Java
325 // Monitor owner's stack and update the BasicLocks because a
326 // Java Monitor can be asynchronously inflated by a thread that
327 // does not own the Java Monitor.
328 ObjectMonitor* m = mark.monitor();
329 assert(((oop)(m->object()))->mark() == mark, "invariant");
330 assert(m->is_entered(THREAD), "invariant");
331 }
332 }
333 #endif
334 return;
335 }
336
337 if (mark == markWord::from_pointer(lock)) {
338 // If the object is stack-locked by the current thread, try to
339 // swing the displaced header from the BasicLock back to the mark.
340 assert(dhw.is_neutral(), "invariant");
341 if (object->cas_set_mark(dhw, mark) == mark) {
342 return;
343 }
344 }
345
346 // We have to take the slow-path of possible inflation and then exit.
347 inflate(THREAD, object, inflate_cause_vm_internal)->exit(true, THREAD);
348 }
349
350 // -----------------------------------------------------------------------------
351 // Class Loader support to workaround deadlocks on the class loader lock objects
352 // Also used by GC
353 // complete_exit()/reenter() are used to wait on a nested lock
354 // i.e. to give up an outer lock completely and then re-enter
355 // Used when holding nested locks - lock acquisition order: lock1 then lock2
356 // 1) complete_exit lock1 - saving recursion count
357 // 2) wait on lock2
358 // 3) when notified on lock2, unlock lock2
359 // 4) reenter lock1 with original recursion count
360 // 5) lock lock2
361 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
362 intx ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
363 if (UseBiasedLocking) {
364 BiasedLocking::revoke(obj, THREAD);
365 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
366 }
367
368 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
369
370 return monitor->complete_exit(THREAD);
371 }
372
373 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
374 void ObjectSynchronizer::reenter(Handle obj, intx recursions, TRAPS) {
375 if (UseBiasedLocking) {
376 BiasedLocking::revoke(obj, THREAD);
377 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
378 }
379
380 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
381
382 monitor->reenter(recursions, THREAD);
383 }
384 // -----------------------------------------------------------------------------
385 // JNI locks on java objects
386 // NOTE: must use heavy weight monitor to handle jni monitor enter
387 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
388 // the current locking is from JNI instead of Java code
389 if (UseBiasedLocking) {
390 BiasedLocking::revoke(obj, THREAD);
391 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
392 }
393 THREAD->set_current_pending_monitor_is_from_java(false);
394 inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);
395 THREAD->set_current_pending_monitor_is_from_java(true);
396 }
397
398 // NOTE: must use heavy weight monitor to handle jni monitor exit
399 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
400 if (UseBiasedLocking) {
401 Handle h_obj(THREAD, obj);
402 BiasedLocking::revoke(h_obj, THREAD);
403 obj = h_obj();
404 }
405 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
406
407 ObjectMonitor* monitor = inflate(THREAD, obj, inflate_cause_jni_exit);
408 // If this thread has locked the object, exit the monitor. We
409 // intentionally do not use CHECK here because we must exit the
410 // monitor even if an exception is pending.
411 if (monitor->check_owner(THREAD)) {
412 monitor->exit(true, THREAD);
413 }
414 }
415
416 // -----------------------------------------------------------------------------
417 // Internal VM locks on java objects
418 // standard constructor, allows locking failures
419 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool do_lock) {
420 _dolock = do_lock;
421 _thread = thread;
422 _thread->check_for_valid_safepoint_state();
423 _obj = obj;
424
425 if (_dolock) {
426 ObjectSynchronizer::enter(_obj, &_lock, _thread);
427 }
428 }
429
430 ObjectLocker::~ObjectLocker() {
431 if (_dolock) {
432 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
433 }
434 }
435
436
437 // -----------------------------------------------------------------------------
438 // Wait/Notify/NotifyAll
439 // NOTE: must use heavy weight monitor to handle wait()
440 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
441 if (UseBiasedLocking) {
442 BiasedLocking::revoke(obj, THREAD);
443 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
444 }
445 if (millis < 0) {
446 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
447 }
448 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
449
450 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
451 monitor->wait(millis, true, THREAD);
452
453 // This dummy call is in place to get around dtrace bug 6254741. Once
454 // that's fixed we can uncomment the following line, remove the call
455 // and change this function back into a "void" func.
456 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
457 return dtrace_waited_probe(monitor, obj, THREAD);
458 }
459
460 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, jlong millis, TRAPS) {
461 if (UseBiasedLocking) {
462 BiasedLocking::revoke(obj, THREAD);
463 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
464 }
465 if (millis < 0) {
466 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
467 }
468 inflate(THREAD, obj(), inflate_cause_wait)->wait(millis, false, THREAD);
469 }
470
471 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
472 if (UseBiasedLocking) {
473 BiasedLocking::revoke(obj, THREAD);
474 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
475 }
476
477 markWord mark = obj->mark();
478 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
479 return;
480 }
481 inflate(THREAD, obj(), inflate_cause_notify)->notify(THREAD);
482 }
483
484 // NOTE: see comment of notify()
485 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
486 if (UseBiasedLocking) {
487 BiasedLocking::revoke(obj, THREAD);
488 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
489 }
490
491 markWord mark = obj->mark();
492 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
493 return;
494 }
495 inflate(THREAD, obj(), inflate_cause_notify)->notifyAll(THREAD);
496 }
497
498 // -----------------------------------------------------------------------------
499 // Hash Code handling
500 //
501 // Performance concern:
502 // OrderAccess::storestore() calls release() which at one time stored 0
503 // into the global volatile OrderAccess::dummy variable. This store was
504 // unnecessary for correctness. Many threads storing into a common location
505 // causes considerable cache migration or "sloshing" on large SMP systems.
506 // As such, I avoided using OrderAccess::storestore(). In some cases
507 // OrderAccess::fence() -- which incurs local latency on the executing
508 // processor -- is a better choice as it scales on SMP systems.
509 //
510 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
511 // a discussion of coherency costs. Note that all our current reference
512 // platforms provide strong ST-ST order, so the issue is moot on IA32,
513 // x64, and SPARC.
514 //
515 // As a general policy we use "volatile" to control compiler-based reordering
516 // and explicit fences (barriers) to control for architectural reordering
517 // performed by the CPU(s) or platform.
518
519 struct SharedGlobals {
520 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
521 // These are highly shared mostly-read variables.
522 // To avoid false-sharing they need to be the sole occupants of a cache line.
523 volatile int stw_random;
524 volatile int stw_cycle;
525 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
526 // Hot RW variable -- Sequester to avoid false-sharing
527 volatile int hc_sequence;
528 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
529 };
530
531 static SharedGlobals GVars;
532 static int _forceMonitorScavenge = 0; // Scavenge required and pending
533
534 static markWord read_stable_mark(oop obj) {
535 markWord mark = obj->mark();
536 if (!mark.is_being_inflated()) {
537 return mark; // normal fast-path return
538 }
539
540 int its = 0;
541 for (;;) {
542 markWord mark = obj->mark();
543 if (!mark.is_being_inflated()) {
544 return mark; // normal fast-path return
545 }
546
547 // The object is being inflated by some other thread.
548 // The caller of read_stable_mark() must wait for inflation to complete.
549 // Avoid live-lock
550 // TODO: consider calling SafepointSynchronize::do_call_back() while
551 // spinning to see if there's a safepoint pending. If so, immediately
552 // yielding or blocking would be appropriate. Avoid spinning while
553 // there is a safepoint pending.
554 // TODO: add inflation contention performance counters.
555 // TODO: restrict the aggregate number of spinners.
556
557 ++its;
558 if (its > 10000 || !os::is_MP()) {
559 if (its & 1) {
560 os::naked_yield();
561 } else {
562 // Note that the following code attenuates the livelock problem but is not
563 // a complete remedy. A more complete solution would require that the inflating
564 // thread hold the associated inflation lock. The following code simply restricts
565 // the number of spinners to at most one. We'll have N-2 threads blocked
566 // on the inflationlock, 1 thread holding the inflation lock and using
567 // a yield/park strategy, and 1 thread in the midst of inflation.
568 // A more refined approach would be to change the encoding of INFLATING
569 // to allow encapsulation of a native thread pointer. Threads waiting for
570 // inflation to complete would use CAS to push themselves onto a singly linked
571 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
572 // and calling park(). When inflation was complete the thread that accomplished inflation
573 // would detach the list and set the markword to inflated with a single CAS and
574 // then for each thread on the list, set the flag and unpark() the thread.
575 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
576 // wakes at most one thread whereas we need to wake the entire list.
577 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
578 int YieldThenBlock = 0;
579 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
580 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
581 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
582 while (obj->mark() == markWord::INFLATING()) {
583 // Beware: NakedYield() is advisory and has almost no effect on some platforms
584 // so we periodically call self->_ParkEvent->park(1).
585 // We use a mixed spin/yield/block mechanism.
586 if ((YieldThenBlock++) >= 16) {
587 Thread::current()->_ParkEvent->park(1);
588 } else {
589 os::naked_yield();
590 }
591 }
592 Thread::muxRelease(gInflationLocks + ix);
593 }
594 } else {
595 SpinPause(); // SMP-polite spinning
596 }
597 }
598 }
599
600 // hashCode() generation :
601 //
602 // Possibilities:
603 // * MD5Digest of {obj,stw_random}
604 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
605 // * A DES- or AES-style SBox[] mechanism
606 // * One of the Phi-based schemes, such as:
607 // 2654435761 = 2^32 * Phi (golden ratio)
608 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
609 // * A variation of Marsaglia's shift-xor RNG scheme.
610 // * (obj ^ stw_random) is appealing, but can result
611 // in undesirable regularity in the hashCode values of adjacent objects
612 // (objects allocated back-to-back, in particular). This could potentially
613 // result in hashtable collisions and reduced hashtable efficiency.
614 // There are simple ways to "diffuse" the middle address bits over the
615 // generated hashCode values:
616
617 static inline intptr_t get_next_hash(Thread* self, oop obj) {
618 intptr_t value = 0;
619 if (hashCode == 0) {
620 // This form uses global Park-Miller RNG.
621 // On MP system we'll have lots of RW access to a global, so the
622 // mechanism induces lots of coherency traffic.
623 value = os::random();
624 } else if (hashCode == 1) {
625 // This variation has the property of being stable (idempotent)
626 // between STW operations. This can be useful in some of the 1-0
627 // synchronization schemes.
628 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
629 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
630 } else if (hashCode == 2) {
631 value = 1; // for sensitivity testing
632 } else if (hashCode == 3) {
633 value = ++GVars.hc_sequence;
634 } else if (hashCode == 4) {
635 value = cast_from_oop<intptr_t>(obj);
636 } else {
637 // Marsaglia's xor-shift scheme with thread-specific state
638 // This is probably the best overall implementation -- we'll
639 // likely make this the default in future releases.
640 unsigned t = self->_hashStateX;
641 t ^= (t << 11);
642 self->_hashStateX = self->_hashStateY;
643 self->_hashStateY = self->_hashStateZ;
644 self->_hashStateZ = self->_hashStateW;
645 unsigned v = self->_hashStateW;
646 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
647 self->_hashStateW = v;
648 value = v;
649 }
650
651 value &= markWord::hash_mask;
652 if (value == 0) value = 0xBAD;
653 assert(value != markWord::no_hash, "invariant");
654 return value;
655 }
656
657 intptr_t ObjectSynchronizer::FastHashCode(Thread* self, oop obj) {
658 if (UseBiasedLocking) {
659 // NOTE: many places throughout the JVM do not expect a safepoint
660 // to be taken here, in particular most operations on perm gen
661 // objects. However, we only ever bias Java instances and all of
662 // the call sites of identity_hash that might revoke biases have
663 // been checked to make sure they can handle a safepoint. The
664 // added check of the bias pattern is to avoid useless calls to
665 // thread-local storage.
666 if (obj->mark().has_bias_pattern()) {
667 // Handle for oop obj in case of STW safepoint
668 Handle hobj(self, obj);
669 // Relaxing assertion for bug 6320749.
670 assert(Universe::verify_in_progress() ||
671 !SafepointSynchronize::is_at_safepoint(),
672 "biases should not be seen by VM thread here");
673 BiasedLocking::revoke(hobj, JavaThread::current());
674 obj = hobj();
675 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
676 }
677 }
678
679 // hashCode() is a heap mutator ...
680 // Relaxing assertion for bug 6320749.
681 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
682 !SafepointSynchronize::is_at_safepoint(), "invariant");
683 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
684 self->is_Java_thread() , "invariant");
685 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
686 ((JavaThread *)self)->thread_state() != _thread_blocked, "invariant");
687
688 ObjectMonitor* monitor = NULL;
689 markWord temp, test;
690 intptr_t hash;
691 markWord mark = read_stable_mark(obj);
692
693 // object should remain ineligible for biased locking
694 assert(!mark.has_bias_pattern(), "invariant");
695
696 if (mark.is_neutral()) { // if this is a normal header
697 hash = mark.hash();
698 if (hash != 0) { // if it has a hash, just return it
699 return hash;
700 }
701 hash = get_next_hash(self, obj); // get a new hash
702 temp = mark.copy_set_hash(hash); // merge the hash into header
703 // try to install the hash
704 test = obj->cas_set_mark(temp, mark);
705 if (test == mark) { // if the hash was installed, return it
706 return hash;
707 }
708 // Failed to install the hash. It could be that another thread
709 // installed the hash just before our attempt or inflation has
710 // occurred or... so we fall thru to inflate the monitor for
711 // stability and then install the hash.
712 } else if (mark.has_monitor()) {
713 monitor = mark.monitor();
714 temp = monitor->header();
715 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
716 hash = temp.hash();
717 if (hash != 0) { // if it has a hash, just return it
718 return hash;
719 }
720 // Fall thru so we only have one place that installs the hash in
721 // the ObjectMonitor.
722 } else if (self->is_lock_owned((address)mark.locker())) {
723 // This is a stack lock owned by the calling thread so fetch the
724 // displaced markWord from the BasicLock on the stack.
725 temp = mark.displaced_mark_helper();
726 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
727 hash = temp.hash();
728 if (hash != 0) { // if it has a hash, just return it
729 return hash;
730 }
731 // WARNING:
732 // The displaced header in the BasicLock on a thread's stack
733 // is strictly immutable. It CANNOT be changed in ANY cases.
734 // So we have to inflate the stack lock into an ObjectMonitor
735 // even if the current thread owns the lock. The BasicLock on
736 // a thread's stack can be asynchronously read by other threads
737 // during an inflate() call so any change to that stack memory
738 // may not propagate to other threads correctly.
739 }
740
741 // Inflate the monitor to set the hash.
742 monitor = inflate(self, obj, inflate_cause_hash_code);
743 // Load ObjectMonitor's header/dmw field and see if it has a hash.
744 mark = monitor->header();
745 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
746 hash = mark.hash();
747 if (hash == 0) { // if it does not have a hash
748 hash = get_next_hash(self, obj); // get a new hash
749 temp = mark.copy_set_hash(hash); // merge the hash into header
750 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
751 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
752 test = markWord(v);
753 if (test != mark) {
754 // The attempt to update the ObjectMonitor's header/dmw field
755 // did not work. This can happen if another thread managed to
756 // merge in the hash just before our cmpxchg().
757 // If we add any new usages of the header/dmw field, this code
758 // will need to be updated.
759 hash = test.hash();
760 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
761 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
762 }
763 }
764 // We finally get the hash.
765 return hash;
766 }
767
768 // Deprecated -- use FastHashCode() instead.
769
770 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
771 return FastHashCode(Thread::current(), obj());
772 }
773
774
775 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
776 Handle h_obj) {
777 if (UseBiasedLocking) {
778 BiasedLocking::revoke(h_obj, thread);
779 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
780 }
781
782 assert(thread == JavaThread::current(), "Can only be called on current thread");
783 oop obj = h_obj();
784
785 markWord mark = read_stable_mark(obj);
786
787 // Uncontended case, header points to stack
788 if (mark.has_locker()) {
789 return thread->is_lock_owned((address)mark.locker());
790 }
791 // Contended case, header points to ObjectMonitor (tagged pointer)
792 if (mark.has_monitor()) {
793 ObjectMonitor* monitor = mark.monitor();
794 return monitor->is_entered(thread) != 0;
795 }
796 // Unlocked case, header in place
797 assert(mark.is_neutral(), "sanity check");
798 return false;
799 }
800
801 // Be aware of this method could revoke bias of the lock object.
802 // This method queries the ownership of the lock handle specified by 'h_obj'.
803 // If the current thread owns the lock, it returns owner_self. If no
804 // thread owns the lock, it returns owner_none. Otherwise, it will return
805 // owner_other.
806 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
807 (JavaThread *self, Handle h_obj) {
808 // The caller must beware this method can revoke bias, and
809 // revocation can result in a safepoint.
810 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
811 assert(self->thread_state() != _thread_blocked, "invariant");
812
813 // Possible mark states: neutral, biased, stack-locked, inflated
814
815 if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) {
816 // CASE: biased
817 BiasedLocking::revoke(h_obj, self);
818 assert(!h_obj->mark().has_bias_pattern(),
819 "biases should be revoked by now");
820 }
821
822 assert(self == JavaThread::current(), "Can only be called on current thread");
823 oop obj = h_obj();
824 markWord mark = read_stable_mark(obj);
825
826 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
827 if (mark.has_locker()) {
828 return self->is_lock_owned((address)mark.locker()) ?
829 owner_self : owner_other;
830 }
831
832 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
833 // The Object:ObjectMonitor relationship is stable as long as we're
834 // not at a safepoint.
835 if (mark.has_monitor()) {
836 void* owner = mark.monitor()->_owner;
837 if (owner == NULL) return owner_none;
838 return (owner == self ||
839 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
840 }
841
842 // CASE: neutral
843 assert(mark.is_neutral(), "sanity check");
844 return owner_none; // it's unlocked
845 }
846
847 // FIXME: jvmti should call this
848 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
849 if (UseBiasedLocking) {
850 if (SafepointSynchronize::is_at_safepoint()) {
851 BiasedLocking::revoke_at_safepoint(h_obj);
852 } else {
853 BiasedLocking::revoke(h_obj, JavaThread::current());
854 }
855 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
856 }
857
858 oop obj = h_obj();
859 address owner = NULL;
860
861 markWord mark = read_stable_mark(obj);
862
863 // Uncontended case, header points to stack
864 if (mark.has_locker()) {
865 owner = (address) mark.locker();
866 }
867
868 // Contended case, header points to ObjectMonitor (tagged pointer)
869 else if (mark.has_monitor()) {
870 ObjectMonitor* monitor = mark.monitor();
871 assert(monitor != NULL, "monitor should be non-null");
872 owner = (address) monitor->owner();
873 }
874
875 if (owner != NULL) {
876 // owning_thread_from_monitor_owner() may also return NULL here
877 return Threads::owning_thread_from_monitor_owner(t_list, owner);
878 }
879
880 // Unlocked case, header in place
881 // Cannot have assertion since this object may have been
882 // locked by another thread when reaching here.
883 // assert(mark.is_neutral(), "sanity check");
884
885 return NULL;
886 }
887
888 // Visitors ...
889
890 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
891 PaddedObjectMonitor* block = Atomic::load_acquire(&g_block_list);
892 while (block != NULL) {
893 assert(block->object() == CHAINMARKER, "must be a block header");
894 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
895 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
896 oop object = (oop)mid->object();
897 if (object != NULL) {
898 // Only process with closure if the object is set.
899 closure->do_monitor(mid);
900 }
901 }
902 block = (PaddedObjectMonitor*)block->_next_om;
903 }
904 }
905
906 static bool monitors_used_above_threshold() {
907 if (g_om_population == 0) {
908 return false;
909 }
910 int monitors_used = g_om_population - g_om_free_count;
911 int monitor_usage = (monitors_used * 100LL) / g_om_population;
912 return monitor_usage > MonitorUsedDeflationThreshold;
913 }
914
915 bool ObjectSynchronizer::is_cleanup_needed() {
916 if (MonitorUsedDeflationThreshold > 0) {
917 if (monitors_used_above_threshold()) {
918 return true;
919 }
920 }
921 return needs_monitor_scavenge();
922 }
923
924 bool ObjectSynchronizer::needs_monitor_scavenge() {
925 if (Atomic::load(&_forceMonitorScavenge) == 1) {
926 log_info(monitorinflation)("Monitor scavenge needed, triggering safepoint cleanup.");
927 return true;
928 }
929 return false;
930 }
931
932 void ObjectSynchronizer::oops_do(OopClosure* f) {
933 // We only scan the global used list here (for moribund threads), and
934 // the thread-local monitors in Thread::oops_do().
935 global_used_oops_do(f);
936 }
937
938 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
939 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
940 list_oops_do(g_om_in_use_list, f);
941 }
942
943 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
944 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
945 list_oops_do(thread->om_in_use_list, f);
946 }
947
948 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
949 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
950 ObjectMonitor* mid;
951 for (mid = list; mid != NULL; mid = mid->_next_om) {
952 if (mid->object() != NULL) {
953 f->do_oop((oop*)mid->object_addr());
954 }
955 }
956 }
957
958
959 // -----------------------------------------------------------------------------
960 // ObjectMonitor Lifecycle
961 // -----------------------
962 // Inflation unlinks monitors from the global g_free_list and
963 // associates them with objects. Deflation -- which occurs at
964 // STW-time -- disassociates idle monitors from objects. Such
965 // scavenged monitors are returned to the g_free_list.
966 //
967 // The global list is protected by gListLock. All the critical sections
968 // are short and operate in constant-time.
969 //
970 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
971 //
972 // Lifecycle:
973 // -- unassigned and on the global free list
974 // -- unassigned and on a thread's private om_free_list
975 // -- assigned to an object. The object is inflated and the mark refers
976 // to the objectmonitor.
977
978
979 // Constraining monitor pool growth via MonitorBound ...
980 //
981 // If MonitorBound is not set (<= 0), MonitorBound checks are disabled.
982 //
983 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
984 // the rate of scavenging is driven primarily by GC. As such, we can find
985 // an inordinate number of monitors in circulation.
986 // To avoid that scenario we can artificially induce a STW safepoint
987 // if the pool appears to be growing past some reasonable bound.
988 // Generally we favor time in space-time tradeoffs, but as there's no
989 // natural back-pressure on the # of extant monitors we need to impose some
990 // type of limit. Beware that if MonitorBound is set to too low a value
991 // we could just loop. In addition, if MonitorBound is set to a low value
992 // we'll incur more safepoints, which are harmful to performance.
993 // See also: GuaranteedSafepointInterval
994 //
995 // If MonitorBound is set, the boundry applies to
996 // (g_om_population - g_om_free_count)
997 // i.e., if there are not enough ObjectMonitors on the global free list,
998 // then a safepoint deflation is induced. Picking a good MonitorBound value
999 // is non-trivial.
1000
1001 static void InduceScavenge(Thread* self, const char * Whence) {
1002 // Induce STW safepoint to trim monitors
1003 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1004 // More precisely, trigger a cleanup safepoint as the number
1005 // of active monitors passes the specified threshold.
1006 // TODO: assert thread state is reasonable
1007
1008 if (Atomic::xchg (&_forceMonitorScavenge, 1) == 0) {
1009 VMThread::check_for_forced_cleanup();
1010 }
1011 }
1012
1013 ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self) {
1014 // A large MAXPRIVATE value reduces both list lock contention
1015 // and list coherency traffic, but also tends to increase the
1016 // number of ObjectMonitors in circulation as well as the STW
1017 // scavenge costs. As usual, we lean toward time in space-time
1018 // tradeoffs.
1019 const int MAXPRIVATE = 1024;
1020 stringStream ss;
1021 for (;;) {
1022 ObjectMonitor* m;
1023
1024 // 1: try to allocate from the thread's local om_free_list.
1025 // Threads will attempt to allocate first from their local list, then
1026 // from the global list, and only after those attempts fail will the thread
1027 // attempt to instantiate new monitors. Thread-local free lists take
1028 // heat off the gListLock and improve allocation latency, as well as reducing
1029 // coherency traffic on the shared global list.
1030 m = self->om_free_list;
1031 if (m != NULL) {
1032 self->om_free_list = m->_next_om;
1033 self->om_free_count--;
1034 guarantee(m->object() == NULL, "invariant");
1035 m->_next_om = self->om_in_use_list;
1036 self->om_in_use_list = m;
1037 self->om_in_use_count++;
1038 return m;
1039 }
1040
1041 // 2: try to allocate from the global g_free_list
1042 // CONSIDER: use muxTry() instead of muxAcquire().
1043 // If the muxTry() fails then drop immediately into case 3.
1044 // If we're using thread-local free lists then try
1045 // to reprovision the caller's free list.
1046 if (g_free_list != NULL) {
1047 // Reprovision the thread's om_free_list.
1048 // Use bulk transfers to reduce the allocation rate and heat
1049 // on various locks.
1050 Thread::muxAcquire(&gListLock, "om_alloc(1)");
1051 for (int i = self->om_free_provision; --i >= 0 && g_free_list != NULL;) {
1052 g_om_free_count--;
1053 ObjectMonitor* take = g_free_list;
1054 g_free_list = take->_next_om;
1055 guarantee(take->object() == NULL, "invariant");
1056 take->Recycle();
1057 om_release(self, take, false);
1058 }
1059 Thread::muxRelease(&gListLock);
1060 self->om_free_provision += 1 + (self->om_free_provision/2);
1061 if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE;
1062
1063 const int mx = MonitorBound;
1064 if (mx > 0 && (g_om_population-g_om_free_count) > mx) {
1065 // Not enough ObjectMonitors on the global free list.
1066 // We can't safely induce a STW safepoint from om_alloc() as our thread
1067 // state may not be appropriate for such activities and callers may hold
1068 // naked oops, so instead we defer the action.
1069 InduceScavenge(self, "om_alloc");
1070 }
1071 continue;
1072 }
1073
1074 // 3: allocate a block of new ObjectMonitors
1075 // Both the local and global free lists are empty -- resort to malloc().
1076 // In the current implementation ObjectMonitors are TSM - immortal.
1077 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1078 // each ObjectMonitor to start at the beginning of a cache line,
1079 // so we use align_up().
1080 // A better solution would be to use C++ placement-new.
1081 // BEWARE: As it stands currently, we don't run the ctors!
1082 assert(_BLOCKSIZE > 1, "invariant");
1083 size_t neededsize = sizeof(PaddedObjectMonitor) * _BLOCKSIZE;
1084 PaddedObjectMonitor* temp;
1085 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1086 void* real_malloc_addr = NEW_C_HEAP_ARRAY(char, aligned_size, mtInternal);
1087 temp = (PaddedObjectMonitor*)align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE);
1088 (void)memset((void *) temp, 0, neededsize);
1089
1090 // Format the block.
1091 // initialize the linked list, each monitor points to its next
1092 // forming the single linked free list, the very first monitor
1093 // will points to next block, which forms the block list.
1094 // The trick of using the 1st element in the block as g_block_list
1095 // linkage should be reconsidered. A better implementation would
1096 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1097
1098 for (int i = 1; i < _BLOCKSIZE; i++) {
1099 temp[i]._next_om = (ObjectMonitor *)&temp[i+1];
1100 }
1101
1102 // terminate the last monitor as the end of list
1103 temp[_BLOCKSIZE - 1]._next_om = NULL;
1104
1105 // Element [0] is reserved for global list linkage
1106 temp[0].set_object(CHAINMARKER);
1107
1108 // Consider carving out this thread's current request from the
1109 // block in hand. This avoids some lock traffic and redundant
1110 // list activity.
1111
1112 // Acquire the gListLock to manipulate g_block_list and g_free_list.
1113 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1114 Thread::muxAcquire(&gListLock, "om_alloc(2)");
1115 g_om_population += _BLOCKSIZE-1;
1116 g_om_free_count += _BLOCKSIZE-1;
1117
1118 // Add the new block to the list of extant blocks (g_block_list).
1119 // The very first ObjectMonitor in a block is reserved and dedicated.
1120 // It serves as blocklist "next" linkage.
1121 temp[0]._next_om = g_block_list;
1122 // There are lock-free uses of g_block_list so make sure that
1123 // the previous stores happen before we update g_block_list.
1124 Atomic::release_store(&g_block_list, temp);
1125
1126 // Add the new string of ObjectMonitors to the global free list
1127 temp[_BLOCKSIZE - 1]._next_om = g_free_list;
1128 g_free_list = temp + 1;
1129 Thread::muxRelease(&gListLock);
1130 }
1131 }
1132
1133 // Place "m" on the caller's private per-thread om_free_list.
1134 // In practice there's no need to clamp or limit the number of
1135 // monitors on a thread's om_free_list as the only non-allocation time
1136 // we'll call om_release() is to return a monitor to the free list after
1137 // a CAS attempt failed. This doesn't allow unbounded #s of monitors to
1138 // accumulate on a thread's free list.
1139 //
1140 // Key constraint: all ObjectMonitors on a thread's free list and the global
1141 // free list must have their object field set to null. This prevents the
1142 // scavenger -- deflate_monitor_list() -- from reclaiming them while we
1143 // are trying to release them.
1144
1145 void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m,
1146 bool from_per_thread_alloc) {
1147 guarantee(m->header().value() == 0, "invariant");
1148 guarantee(m->object() == NULL, "invariant");
1149 stringStream ss;
1150 guarantee((m->is_busy() | m->_recursions) == 0, "freeing in-use monitor: "
1151 "%s, recursions=" INTX_FORMAT, m->is_busy_to_string(&ss),
1152 m->_recursions);
1153 // _next_om is used for both per-thread in-use and free lists so
1154 // we have to remove 'm' from the in-use list first (as needed).
1155 if (from_per_thread_alloc) {
1156 // Need to remove 'm' from om_in_use_list.
1157 ObjectMonitor* cur_mid_in_use = NULL;
1158 bool extracted = false;
1159 for (ObjectMonitor* mid = self->om_in_use_list; mid != NULL; cur_mid_in_use = mid, mid = mid->_next_om) {
1160 if (m == mid) {
1161 // extract from per-thread in-use list
1162 if (mid == self->om_in_use_list) {
1163 self->om_in_use_list = mid->_next_om;
1164 } else if (cur_mid_in_use != NULL) {
1165 cur_mid_in_use->_next_om = mid->_next_om; // maintain the current thread in-use list
1166 }
1167 extracted = true;
1168 self->om_in_use_count--;
1169 break;
1170 }
1171 }
1172 assert(extracted, "Should have extracted from in-use list");
1173 }
1174
1175 m->_next_om = self->om_free_list;
1176 self->om_free_list = m;
1177 self->om_free_count++;
1178 }
1179
1180 // Return ObjectMonitors on a moribund thread's free and in-use
1181 // lists to the appropriate global lists. The ObjectMonitors on the
1182 // per-thread in-use list may still be in use by other threads.
1183 //
1184 // We currently call om_flush() from Threads::remove() before the
1185 // thread has been excised from the thread list and is no longer a
1186 // mutator. This means that om_flush() cannot run concurrently with
1187 // a safepoint and interleave with deflate_idle_monitors(). In
1188 // particular, this ensures that the thread's in-use monitors are
1189 // scanned by a GC safepoint, either via Thread::oops_do() (before
1190 // om_flush() is called) or via ObjectSynchronizer::oops_do() (after
1191 // om_flush() is called).
1192
1193 void ObjectSynchronizer::om_flush(Thread* self) {
1194 ObjectMonitor* free_list = self->om_free_list;
1195 ObjectMonitor* free_tail = NULL;
1196 int free_count = 0;
1197 if (free_list != NULL) {
1198 ObjectMonitor* s;
1199 // The thread is going away. Set 'free_tail' to the last per-thread free
1200 // monitor which will be linked to g_free_list below under the gListLock.
1201 stringStream ss;
1202 for (s = free_list; s != NULL; s = s->_next_om) {
1203 free_count++;
1204 free_tail = s;
1205 guarantee(s->object() == NULL, "invariant");
1206 guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss));
1207 }
1208 guarantee(free_tail != NULL, "invariant");
1209 assert(self->om_free_count == free_count, "free-count off");
1210 self->om_free_list = NULL;
1211 self->om_free_count = 0;
1212 }
1213
1214 ObjectMonitor* in_use_list = self->om_in_use_list;
1215 ObjectMonitor* in_use_tail = NULL;
1216 int in_use_count = 0;
1217 if (in_use_list != NULL) {
1218 // The thread is going away, however the ObjectMonitors on the
1219 // om_in_use_list may still be in-use by other threads. Link
1220 // them to in_use_tail, which will be linked into the global
1221 // in-use list g_om_in_use_list below, under the gListLock.
1222 ObjectMonitor *cur_om;
1223 for (cur_om = in_use_list; cur_om != NULL; cur_om = cur_om->_next_om) {
1224 in_use_tail = cur_om;
1225 in_use_count++;
1226 }
1227 guarantee(in_use_tail != NULL, "invariant");
1228 assert(self->om_in_use_count == in_use_count, "in-use count off");
1229 self->om_in_use_list = NULL;
1230 self->om_in_use_count = 0;
1231 }
1232
1233 Thread::muxAcquire(&gListLock, "om_flush");
1234 if (free_tail != NULL) {
1235 free_tail->_next_om = g_free_list;
1236 g_free_list = free_list;
1237 g_om_free_count += free_count;
1238 }
1239
1240 if (in_use_tail != NULL) {
1241 in_use_tail->_next_om = g_om_in_use_list;
1242 g_om_in_use_list = in_use_list;
1243 g_om_in_use_count += in_use_count;
1244 }
1245
1246 Thread::muxRelease(&gListLock);
1247
1248 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1249 LogStreamHandle(Info, monitorinflation) lsh_info;
1250 LogStream* ls = NULL;
1251 if (log_is_enabled(Debug, monitorinflation)) {
1252 ls = &lsh_debug;
1253 } else if ((free_count != 0 || in_use_count != 0) &&
1254 log_is_enabled(Info, monitorinflation)) {
1255 ls = &lsh_info;
1256 }
1257 if (ls != NULL) {
1258 ls->print_cr("om_flush: jt=" INTPTR_FORMAT ", free_count=%d"
1259 ", in_use_count=%d" ", om_free_provision=%d",
1260 p2i(self), free_count, in_use_count, self->om_free_provision);
1261 }
1262 }
1263
1264 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1265 const oop obj,
1266 ObjectSynchronizer::InflateCause cause) {
1267 assert(event != NULL, "invariant");
1268 assert(event->should_commit(), "invariant");
1269 event->set_monitorClass(obj->klass());
1270 event->set_address((uintptr_t)(void*)obj);
1271 event->set_cause((u1)cause);
1272 event->commit();
1273 }
1274
1275 // Fast path code shared by multiple functions
1276 void ObjectSynchronizer::inflate_helper(oop obj) {
1277 markWord mark = obj->mark();
1278 if (mark.has_monitor()) {
1279 assert(ObjectSynchronizer::verify_objmon_isinpool(mark.monitor()), "monitor is invalid");
1280 assert(mark.monitor()->header().is_neutral(), "monitor must record a good object header");
1281 return;
1282 }
1283 inflate(Thread::current(), obj, inflate_cause_vm_internal);
1284 }
1285
1286 ObjectMonitor* ObjectSynchronizer::inflate(Thread* self,
1287 oop object,
1288 const InflateCause cause) {
1289 // Inflate mutates the heap ...
1290 // Relaxing assertion for bug 6320749.
1291 assert(Universe::verify_in_progress() ||
1292 !SafepointSynchronize::is_at_safepoint(), "invariant");
1293
1294 EventJavaMonitorInflate event;
1295
1296 for (;;) {
1297 const markWord mark = object->mark();
1298 assert(!mark.has_bias_pattern(), "invariant");
1299
1300 // The mark can be in one of the following states:
1301 // * Inflated - just return
1302 // * Stack-locked - coerce it to inflated
1303 // * INFLATING - busy wait for conversion to complete
1304 // * Neutral - aggressively inflate the object.
1305 // * BIASED - Illegal. We should never see this
1306
1307 // CASE: inflated
1308 if (mark.has_monitor()) {
1309 ObjectMonitor* inf = mark.monitor();
1310 markWord dmw = inf->header();
1311 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1312 assert(inf->object() == object, "invariant");
1313 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1314 return inf;
1315 }
1316
1317 // CASE: inflation in progress - inflating over a stack-lock.
1318 // Some other thread is converting from stack-locked to inflated.
1319 // Only that thread can complete inflation -- other threads must wait.
1320 // The INFLATING value is transient.
1321 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1322 // We could always eliminate polling by parking the thread on some auxiliary list.
1323 if (mark == markWord::INFLATING()) {
1324 read_stable_mark(object);
1325 continue;
1326 }
1327
1328 // CASE: stack-locked
1329 // Could be stack-locked either by this thread or by some other thread.
1330 //
1331 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1332 // to install INFLATING into the mark word. We originally installed INFLATING,
1333 // allocated the objectmonitor, and then finally STed the address of the
1334 // objectmonitor into the mark. This was correct, but artificially lengthened
1335 // the interval in which INFLATED appeared in the mark, thus increasing
1336 // the odds of inflation contention.
1337 //
1338 // We now use per-thread private objectmonitor free lists.
1339 // These list are reprovisioned from the global free list outside the
1340 // critical INFLATING...ST interval. A thread can transfer
1341 // multiple objectmonitors en-mass from the global free list to its local free list.
1342 // This reduces coherency traffic and lock contention on the global free list.
1343 // Using such local free lists, it doesn't matter if the om_alloc() call appears
1344 // before or after the CAS(INFLATING) operation.
1345 // See the comments in om_alloc().
1346
1347 LogStreamHandle(Trace, monitorinflation) lsh;
1348
1349 if (mark.has_locker()) {
1350 ObjectMonitor* m = om_alloc(self);
1351 // Optimistically prepare the objectmonitor - anticipate successful CAS
1352 // We do this before the CAS in order to minimize the length of time
1353 // in which INFLATING appears in the mark.
1354 m->Recycle();
1355 m->_Responsible = NULL;
1356 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1357
1358 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1359 if (cmp != mark) {
1360 om_release(self, m, true);
1361 continue; // Interference -- just retry
1362 }
1363
1364 // We've successfully installed INFLATING (0) into the mark-word.
1365 // This is the only case where 0 will appear in a mark-word.
1366 // Only the singular thread that successfully swings the mark-word
1367 // to 0 can perform (or more precisely, complete) inflation.
1368 //
1369 // Why do we CAS a 0 into the mark-word instead of just CASing the
1370 // mark-word from the stack-locked value directly to the new inflated state?
1371 // Consider what happens when a thread unlocks a stack-locked object.
1372 // It attempts to use CAS to swing the displaced header value from the
1373 // on-stack BasicLock back into the object header. Recall also that the
1374 // header value (hash code, etc) can reside in (a) the object header, or
1375 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1376 // header in an ObjectMonitor. The inflate() routine must copy the header
1377 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1378 // the while preserving the hashCode stability invariants. If the owner
1379 // decides to release the lock while the value is 0, the unlock will fail
1380 // and control will eventually pass from slow_exit() to inflate. The owner
1381 // will then spin, waiting for the 0 value to disappear. Put another way,
1382 // the 0 causes the owner to stall if the owner happens to try to
1383 // drop the lock (restoring the header from the BasicLock to the object)
1384 // while inflation is in-progress. This protocol avoids races that might
1385 // would otherwise permit hashCode values to change or "flicker" for an object.
1386 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1387 // 0 serves as a "BUSY" inflate-in-progress indicator.
1388
1389
1390 // fetch the displaced mark from the owner's stack.
1391 // The owner can't die or unwind past the lock while our INFLATING
1392 // object is in the mark. Furthermore the owner can't complete
1393 // an unlock on the object, either.
1394 markWord dmw = mark.displaced_mark_helper();
1395 // Catch if the object's header is not neutral (not locked and
1396 // not marked is what we care about here).
1397 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1398
1399 // Setup monitor fields to proper values -- prepare the monitor
1400 m->set_header(dmw);
1401
1402 // Optimization: if the mark.locker stack address is associated
1403 // with this thread we could simply set m->_owner = self.
1404 // Note that a thread can inflate an object
1405 // that it has stack-locked -- as might happen in wait() -- directly
1406 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1407 m->set_owner_from(NULL, mark.locker());
1408 m->set_object(object);
1409 // TODO-FIXME: assert BasicLock->dhw != 0.
1410
1411 // Must preserve store ordering. The monitor state must
1412 // be stable at the time of publishing the monitor address.
1413 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1414 object->release_set_mark(markWord::encode(m));
1415
1416 // Hopefully the performance counters are allocated on distinct cache lines
1417 // to avoid false sharing on MP systems ...
1418 OM_PERFDATA_OP(Inflations, inc());
1419 if (log_is_enabled(Trace, monitorinflation)) {
1420 ResourceMark rm(self);
1421 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1422 INTPTR_FORMAT ", type='%s'", p2i(object),
1423 object->mark().value(), object->klass()->external_name());
1424 }
1425 if (event.should_commit()) {
1426 post_monitor_inflate_event(&event, object, cause);
1427 }
1428 return m;
1429 }
1430
1431 // CASE: neutral
1432 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1433 // If we know we're inflating for entry it's better to inflate by swinging a
1434 // pre-locked ObjectMonitor pointer into the object header. A successful
1435 // CAS inflates the object *and* confers ownership to the inflating thread.
1436 // In the current implementation we use a 2-step mechanism where we CAS()
1437 // to inflate and then CAS() again to try to swing _owner from NULL to self.
1438 // An inflateTry() method that we could call from enter() would be useful.
1439
1440 // Catch if the object's header is not neutral (not locked and
1441 // not marked is what we care about here).
1442 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1443 ObjectMonitor* m = om_alloc(self);
1444 // prepare m for installation - set monitor to initial state
1445 m->Recycle();
1446 m->set_header(mark);
1447 m->set_object(object);
1448 m->_Responsible = NULL;
1449 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1450
1451 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1452 m->set_header(markWord::zero());
1453 m->set_object(NULL);
1454 m->Recycle();
1455 om_release(self, m, true);
1456 m = NULL;
1457 continue;
1458 // interference - the markword changed - just retry.
1459 // The state-transitions are one-way, so there's no chance of
1460 // live-lock -- "Inflated" is an absorbing state.
1461 }
1462
1463 // Hopefully the performance counters are allocated on distinct
1464 // cache lines to avoid false sharing on MP systems ...
1465 OM_PERFDATA_OP(Inflations, inc());
1466 if (log_is_enabled(Trace, monitorinflation)) {
1467 ResourceMark rm(self);
1468 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1469 INTPTR_FORMAT ", type='%s'", p2i(object),
1470 object->mark().value(), object->klass()->external_name());
1471 }
1472 if (event.should_commit()) {
1473 post_monitor_inflate_event(&event, object, cause);
1474 }
1475 return m;
1476 }
1477 }
1478
1479
1480 // We maintain a list of in-use monitors for each thread.
1481 //
1482 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1483 // deflate_idle_monitors() scans only a global list of in-use monitors which
1484 // is populated only as a thread dies (see om_flush()).
1485 //
1486 // These operations are called at all safepoints, immediately after mutators
1487 // are stopped, but before any objects have moved. Collectively they traverse
1488 // the population of in-use monitors, deflating where possible. The scavenged
1489 // monitors are returned to the global monitor free list.
1490 //
1491 // Beware that we scavenge at *every* stop-the-world point. Having a large
1492 // number of monitors in-use could negatively impact performance. We also want
1493 // to minimize the total # of monitors in circulation, as they incur a small
1494 // footprint penalty.
1495 //
1496 // Perversely, the heap size -- and thus the STW safepoint rate --
1497 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1498 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1499 // This is an unfortunate aspect of this design.
1500
1501 // Deflate a single monitor if not in-use
1502 // Return true if deflated, false if in-use
1503 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1504 ObjectMonitor** free_head_p,
1505 ObjectMonitor** free_tail_p) {
1506 bool deflated;
1507 // Normal case ... The monitor is associated with obj.
1508 const markWord mark = obj->mark();
1509 guarantee(mark == markWord::encode(mid), "should match: mark="
1510 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(),
1511 markWord::encode(mid).value());
1512 // Make sure that mark.monitor() and markWord::encode() agree:
1513 guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
1514 ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid));
1515 const markWord dmw = mid->header();
1516 guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1517
1518 if (mid->is_busy()) {
1519 deflated = false;
1520 } else {
1521 // Deflate the monitor if it is no longer being used
1522 // It's idle - scavenge and return to the global free list
1523 // plain old deflation ...
1524 if (log_is_enabled(Trace, monitorinflation)) {
1525 ResourceMark rm;
1526 log_trace(monitorinflation)("deflate_monitor: "
1527 "object=" INTPTR_FORMAT ", mark="
1528 INTPTR_FORMAT ", type='%s'", p2i(obj),
1529 mark.value(), obj->klass()->external_name());
1530 }
1531
1532 // Restore the header back to obj
1533 obj->release_set_mark(dmw);
1534 mid->clear();
1535
1536 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
1537 p2i(mid->object()));
1538
1539 // Move the deflated ObjectMonitor to the working free list
1540 // defined by free_head_p and free_tail_p.
1541 if (*free_head_p == NULL) *free_head_p = mid;
1542 if (*free_tail_p != NULL) {
1543 // We append to the list so the caller can use mid->_next_om
1544 // to fix the linkages in its context.
1545 ObjectMonitor* prevtail = *free_tail_p;
1546 // Should have been cleaned up by the caller:
1547 assert(prevtail->_next_om == NULL, "cleaned up deflated?");
1548 prevtail->_next_om = mid;
1549 }
1550 *free_tail_p = mid;
1551 // At this point, mid->_next_om still refers to its current
1552 // value and another ObjectMonitor's _next_om field still
1553 // refers to this ObjectMonitor. Those linkages have to be
1554 // cleaned up by the caller who has the complete context.
1555 deflated = true;
1556 }
1557 return deflated;
1558 }
1559
1560 // Walk a given monitor list, and deflate idle monitors
1561 // The given list could be a per-thread list or a global list
1562 // Caller acquires gListLock as needed.
1563 //
1564 // In the case of parallel processing of thread local monitor lists,
1565 // work is done by Threads::parallel_threads_do() which ensures that
1566 // each Java thread is processed by exactly one worker thread, and
1567 // thus avoid conflicts that would arise when worker threads would
1568 // process the same monitor lists concurrently.
1569 //
1570 // See also ParallelSPCleanupTask and
1571 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1572 // Threads::parallel_java_threads_do() in thread.cpp.
1573 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** list_p,
1574 ObjectMonitor** free_head_p,
1575 ObjectMonitor** free_tail_p) {
1576 ObjectMonitor* mid;
1577 ObjectMonitor* next;
1578 ObjectMonitor* cur_mid_in_use = NULL;
1579 int deflated_count = 0;
1580
1581 for (mid = *list_p; mid != NULL;) {
1582 oop obj = (oop) mid->object();
1583 if (obj != NULL && deflate_monitor(mid, obj, free_head_p, free_tail_p)) {
1584 // Deflation succeeded and already updated free_head_p and
1585 // free_tail_p as needed. Finish the move to the local free list
1586 // by unlinking mid from the global or per-thread in-use list.
1587 if (mid == *list_p) {
1588 *list_p = mid->_next_om;
1589 } else if (cur_mid_in_use != NULL) {
1590 cur_mid_in_use->_next_om = mid->_next_om; // maintain the current thread in-use list
1591 }
1592 next = mid->_next_om;
1593 mid->_next_om = NULL; // This mid is current tail in the free_head_p list
1594 mid = next;
1595 deflated_count++;
1596 } else {
1597 cur_mid_in_use = mid;
1598 mid = mid->_next_om;
1599 }
1600 }
1601 return deflated_count;
1602 }
1603
1604 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1605 counters->n_in_use = 0; // currently associated with objects
1606 counters->n_in_circulation = 0; // extant
1607 counters->n_scavenged = 0; // reclaimed (global and per-thread)
1608 counters->per_thread_scavenged = 0; // per-thread scavenge total
1609 counters->per_thread_times = 0.0; // per-thread scavenge times
1610 }
1611
1612 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
1613 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1614 bool deflated = false;
1615
1616 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
1617 ObjectMonitor* free_tail_p = NULL;
1618 elapsedTimer timer;
1619
1620 if (log_is_enabled(Info, monitorinflation)) {
1621 timer.start();
1622 }
1623
1624 // Prevent om_flush from changing mids in Thread dtor's during deflation
1625 // And in case the vm thread is acquiring a lock during a safepoint
1626 // See e.g. 6320749
1627 Thread::muxAcquire(&gListLock, "deflate_idle_monitors");
1628
1629 // Note: the thread-local monitors lists get deflated in
1630 // a separate pass. See deflate_thread_local_monitors().
1631
1632 // For moribund threads, scan g_om_in_use_list
1633 int deflated_count = 0;
1634 if (g_om_in_use_list) {
1635 counters->n_in_circulation += g_om_in_use_count;
1636 deflated_count = deflate_monitor_list((ObjectMonitor **)&g_om_in_use_list, &free_head_p, &free_tail_p);
1637 g_om_in_use_count -= deflated_count;
1638 counters->n_scavenged += deflated_count;
1639 counters->n_in_use += g_om_in_use_count;
1640 }
1641
1642 if (free_head_p != NULL) {
1643 // Move the deflated ObjectMonitors back to the global free list.
1644 guarantee(free_tail_p != NULL && counters->n_scavenged > 0, "invariant");
1645 assert(free_tail_p->_next_om == NULL, "invariant");
1646 // constant-time list splice - prepend scavenged segment to g_free_list
1647 free_tail_p->_next_om = g_free_list;
1648 g_free_list = free_head_p;
1649 }
1650 Thread::muxRelease(&gListLock);
1651 timer.stop();
1652
1653 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1654 LogStreamHandle(Info, monitorinflation) lsh_info;
1655 LogStream* ls = NULL;
1656 if (log_is_enabled(Debug, monitorinflation)) {
1657 ls = &lsh_debug;
1658 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
1659 ls = &lsh_info;
1660 }
1661 if (ls != NULL) {
1662 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
1663 }
1664 }
1665
1666 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1667 // Report the cumulative time for deflating each thread's idle
1668 // monitors. Note: if the work is split among more than one
1669 // worker thread, then the reported time will likely be more
1670 // than a beginning to end measurement of the phase.
1671 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged);
1672
1673 g_om_free_count += counters->n_scavenged;
1674
1675 if (log_is_enabled(Debug, monitorinflation)) {
1676 // exit_globals()'s call to audit_and_print_stats() is done
1677 // at the Info level.
1678 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
1679 } else if (log_is_enabled(Info, monitorinflation)) {
1680 Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors");
1681 log_info(monitorinflation)("g_om_population=%d, g_om_in_use_count=%d, "
1682 "g_om_free_count=%d", g_om_population,
1683 g_om_in_use_count, g_om_free_count);
1684 Thread::muxRelease(&gListLock);
1685 }
1686
1687 Atomic::store(&_forceMonitorScavenge, 0); // Reset
1688
1689 OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged));
1690 OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation));
1691
1692 GVars.stw_random = os::random();
1693 GVars.stw_cycle++;
1694 }
1695
1696 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
1697 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1698
1699 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
1700 ObjectMonitor* free_tail_p = NULL;
1701 elapsedTimer timer;
1702
1703 if (log_is_enabled(Info, safepoint, cleanup) ||
1704 log_is_enabled(Info, monitorinflation)) {
1705 timer.start();
1706 }
1707
1708 int deflated_count = deflate_monitor_list(thread->om_in_use_list_addr(), &free_head_p, &free_tail_p);
1709
1710 Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors");
1711
1712 // Adjust counters
1713 counters->n_in_circulation += thread->om_in_use_count;
1714 thread->om_in_use_count -= deflated_count;
1715 counters->n_scavenged += deflated_count;
1716 counters->n_in_use += thread->om_in_use_count;
1717 counters->per_thread_scavenged += deflated_count;
1718
1719 if (free_head_p != NULL) {
1720 // Move the deflated ObjectMonitors back to the global free list.
1721 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
1722 assert(free_tail_p->_next_om == NULL, "invariant");
1723
1724 // constant-time list splice - prepend scavenged segment to g_free_list
1725 free_tail_p->_next_om = g_free_list;
1726 g_free_list = free_head_p;
1727 }
1728
1729 timer.stop();
1730 // Safepoint logging cares about cumulative per_thread_times and
1731 // we'll capture most of the cost, but not the muxRelease() which
1732 // should be cheap.
1733 counters->per_thread_times += timer.seconds();
1734
1735 Thread::muxRelease(&gListLock);
1736
1737 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1738 LogStreamHandle(Info, monitorinflation) lsh_info;
1739 LogStream* ls = NULL;
1740 if (log_is_enabled(Debug, monitorinflation)) {
1741 ls = &lsh_debug;
1742 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
1743 ls = &lsh_info;
1744 }
1745 if (ls != NULL) {
1746 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
1747 }
1748 }
1749
1750 // Monitor cleanup on JavaThread::exit
1751
1752 // Iterate through monitor cache and attempt to release thread's monitors
1753 // Gives up on a particular monitor if an exception occurs, but continues
1754 // the overall iteration, swallowing the exception.
1755 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1756 private:
1757 TRAPS;
1758
1759 public:
1760 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1761 void do_monitor(ObjectMonitor* mid) {
1762 if (mid->owner() == THREAD) {
1763 (void)mid->complete_exit(CHECK);
1764 }
1765 }
1766 };
1767
1768 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1769 // ignored. This is meant to be called during JNI thread detach which assumes
1770 // all remaining monitors are heavyweight. All exceptions are swallowed.
1771 // Scanning the extant monitor list can be time consuming.
1772 // A simple optimization is to add a per-thread flag that indicates a thread
1773 // called jni_monitorenter() during its lifetime.
1774 //
1775 // Instead of No_Savepoint_Verifier it might be cheaper to
1776 // use an idiom of the form:
1777 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1778 // <code that must not run at safepoint>
1779 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1780 // Since the tests are extremely cheap we could leave them enabled
1781 // for normal product builds.
1782
1783 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1784 assert(THREAD == JavaThread::current(), "must be current Java thread");
1785 NoSafepointVerifier nsv;
1786 ReleaseJavaMonitorsClosure rjmc(THREAD);
1787 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
1788 ObjectSynchronizer::monitors_iterate(&rjmc);
1789 Thread::muxRelease(&gListLock);
1790 THREAD->clear_pending_exception();
1791 }
1792
1793 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1794 switch (cause) {
1795 case inflate_cause_vm_internal: return "VM Internal";
1796 case inflate_cause_monitor_enter: return "Monitor Enter";
1797 case inflate_cause_wait: return "Monitor Wait";
1798 case inflate_cause_notify: return "Monitor Notify";
1799 case inflate_cause_hash_code: return "Monitor Hash Code";
1800 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1801 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1802 default:
1803 ShouldNotReachHere();
1804 }
1805 return "Unknown";
1806 }
1807
1808 //------------------------------------------------------------------------------
1809 // Debugging code
1810
1811 u_char* ObjectSynchronizer::get_gvars_addr() {
1812 return (u_char*)&GVars;
1813 }
1814
1815 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1816 return (u_char*)&GVars.hc_sequence;
1817 }
1818
1819 size_t ObjectSynchronizer::get_gvars_size() {
1820 return sizeof(SharedGlobals);
1821 }
1822
1823 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1824 return (u_char*)&GVars.stw_random;
1825 }
1826
1827 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1828 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1829
1830 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1831 LogStreamHandle(Info, monitorinflation) lsh_info;
1832 LogStreamHandle(Trace, monitorinflation) lsh_trace;
1833 LogStream* ls = NULL;
1834 if (log_is_enabled(Trace, monitorinflation)) {
1835 ls = &lsh_trace;
1836 } else if (log_is_enabled(Debug, monitorinflation)) {
1837 ls = &lsh_debug;
1838 } else if (log_is_enabled(Info, monitorinflation)) {
1839 ls = &lsh_info;
1840 }
1841 assert(ls != NULL, "sanity check");
1842
1843 if (!on_exit) {
1844 // Not at VM exit so grab the global list lock.
1845 Thread::muxAcquire(&gListLock, "audit_and_print_stats");
1846 }
1847
1848 // Log counts for the global and per-thread monitor lists:
1849 int chk_om_population = log_monitor_list_counts(ls);
1850 int error_cnt = 0;
1851
1852 ls->print_cr("Checking global lists:");
1853
1854 // Check g_om_population:
1855 if (g_om_population == chk_om_population) {
1856 ls->print_cr("g_om_population=%d equals chk_om_population=%d",
1857 g_om_population, chk_om_population);
1858 } else {
1859 ls->print_cr("ERROR: g_om_population=%d is not equal to "
1860 "chk_om_population=%d", g_om_population,
1861 chk_om_population);
1862 error_cnt++;
1863 }
1864
1865 // Check g_om_in_use_list and g_om_in_use_count:
1866 chk_global_in_use_list_and_count(ls, &error_cnt);
1867
1868 // Check g_free_list and g_om_free_count:
1869 chk_global_free_list_and_count(ls, &error_cnt);
1870
1871 if (!on_exit) {
1872 Thread::muxRelease(&gListLock);
1873 }
1874
1875 ls->print_cr("Checking per-thread lists:");
1876
1877 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
1878 // Check om_in_use_list and om_in_use_count:
1879 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
1880
1881 // Check om_free_list and om_free_count:
1882 chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
1883 }
1884
1885 if (error_cnt == 0) {
1886 ls->print_cr("No errors found in monitor list checks.");
1887 } else {
1888 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
1889 }
1890
1891 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1892 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1893 // When exiting this log output is at the Info level. When called
1894 // at a safepoint, this log output is at the Trace level since
1895 // there can be a lot of it.
1896 log_in_use_monitor_details(ls, on_exit);
1897 }
1898
1899 ls->flush();
1900
1901 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1902 }
1903
1904 // Check a free monitor entry; log any errors.
1905 void ObjectSynchronizer::chk_free_entry(JavaThread* jt, ObjectMonitor* n,
1906 outputStream * out, int *error_cnt_p) {
1907 stringStream ss;
1908 if (n->is_busy()) {
1909 if (jt != NULL) {
1910 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1911 ": free per-thread monitor must not be busy: %s", p2i(jt),
1912 p2i(n), n->is_busy_to_string(&ss));
1913 } else {
1914 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1915 "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
1916 }
1917 *error_cnt_p = *error_cnt_p + 1;
1918 }
1919 if (n->header().value() != 0) {
1920 if (jt != NULL) {
1921 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1922 ": free per-thread monitor must have NULL _header "
1923 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
1924 n->header().value());
1925 } else {
1926 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1927 "must have NULL _header field: _header=" INTPTR_FORMAT,
1928 p2i(n), n->header().value());
1929 }
1930 *error_cnt_p = *error_cnt_p + 1;
1931 }
1932 if (n->object() != NULL) {
1933 if (jt != NULL) {
1934 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1935 ": free per-thread monitor must have NULL _object "
1936 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
1937 p2i(n->object()));
1938 } else {
1939 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1940 "must have NULL _object field: _object=" INTPTR_FORMAT,
1941 p2i(n), p2i(n->object()));
1942 }
1943 *error_cnt_p = *error_cnt_p + 1;
1944 }
1945 }
1946
1947 // Check the global free list and count; log the results of the checks.
1948 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
1949 int *error_cnt_p) {
1950 int chk_om_free_count = 0;
1951 for (ObjectMonitor* n = g_free_list; n != NULL; n = n->_next_om) {
1952 chk_free_entry(NULL /* jt */, n, out, error_cnt_p);
1953 chk_om_free_count++;
1954 }
1955 if (g_om_free_count == chk_om_free_count) {
1956 out->print_cr("g_om_free_count=%d equals chk_om_free_count=%d",
1957 g_om_free_count, chk_om_free_count);
1958 } else {
1959 out->print_cr("ERROR: g_om_free_count=%d is not equal to "
1960 "chk_om_free_count=%d", g_om_free_count,
1961 chk_om_free_count);
1962 *error_cnt_p = *error_cnt_p + 1;
1963 }
1964 }
1965
1966 // Check the global in-use list and count; log the results of the checks.
1967 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
1968 int *error_cnt_p) {
1969 int chk_om_in_use_count = 0;
1970 for (ObjectMonitor* n = g_om_in_use_list; n != NULL; n = n->_next_om) {
1971 chk_in_use_entry(NULL /* jt */, n, out, error_cnt_p);
1972 chk_om_in_use_count++;
1973 }
1974 if (g_om_in_use_count == chk_om_in_use_count) {
1975 out->print_cr("g_om_in_use_count=%d equals chk_om_in_use_count=%d", g_om_in_use_count,
1976 chk_om_in_use_count);
1977 } else {
1978 out->print_cr("ERROR: g_om_in_use_count=%d is not equal to chk_om_in_use_count=%d",
1979 g_om_in_use_count, chk_om_in_use_count);
1980 *error_cnt_p = *error_cnt_p + 1;
1981 }
1982 }
1983
1984 // Check an in-use monitor entry; log any errors.
1985 void ObjectSynchronizer::chk_in_use_entry(JavaThread* jt, ObjectMonitor* n,
1986 outputStream * out, int *error_cnt_p) {
1987 if (n->header().value() == 0) {
1988 if (jt != NULL) {
1989 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1990 ": in-use per-thread monitor must have non-NULL _header "
1991 "field.", p2i(jt), p2i(n));
1992 } else {
1993 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
1994 "must have non-NULL _header field.", p2i(n));
1995 }
1996 *error_cnt_p = *error_cnt_p + 1;
1997 }
1998 if (n->object() == NULL) {
1999 if (jt != NULL) {
2000 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2001 ": in-use per-thread monitor must have non-NULL _object "
2002 "field.", p2i(jt), p2i(n));
2003 } else {
2004 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2005 "must have non-NULL _object field.", p2i(n));
2006 }
2007 *error_cnt_p = *error_cnt_p + 1;
2008 }
2009 const oop obj = (oop)n->object();
2010 const markWord mark = obj->mark();
2011 if (!mark.has_monitor()) {
2012 if (jt != NULL) {
2013 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2014 ": in-use per-thread monitor's object does not think "
2015 "it has a monitor: obj=" INTPTR_FORMAT ", mark="
2016 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), mark.value());
2017 } else {
2018 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2019 "monitor's object does not think it has a monitor: obj="
2020 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2021 p2i(obj), mark.value());
2022 }
2023 *error_cnt_p = *error_cnt_p + 1;
2024 }
2025 ObjectMonitor* const obj_mon = mark.monitor();
2026 if (n != obj_mon) {
2027 if (jt != NULL) {
2028 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2029 ": in-use per-thread monitor's object does not refer "
2030 "to the same monitor: obj=" INTPTR_FORMAT ", mark="
2031 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
2032 p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2033 } else {
2034 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2035 "monitor's object does not refer to the same monitor: obj="
2036 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2037 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2038 }
2039 *error_cnt_p = *error_cnt_p + 1;
2040 }
2041 }
2042
2043 // Check the thread's free list and count; log the results of the checks.
2044 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
2045 outputStream * out,
2046 int *error_cnt_p) {
2047 int chk_om_free_count = 0;
2048 for (ObjectMonitor* n = jt->om_free_list; n != NULL; n = n->_next_om) {
2049 chk_free_entry(jt, n, out, error_cnt_p);
2050 chk_om_free_count++;
2051 }
2052 if (jt->om_free_count == chk_om_free_count) {
2053 out->print_cr("jt=" INTPTR_FORMAT ": om_free_count=%d equals "
2054 "chk_om_free_count=%d", p2i(jt), jt->om_free_count, chk_om_free_count);
2055 } else {
2056 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_free_count=%d is not "
2057 "equal to chk_om_free_count=%d", p2i(jt), jt->om_free_count,
2058 chk_om_free_count);
2059 *error_cnt_p = *error_cnt_p + 1;
2060 }
2061 }
2062
2063 // Check the thread's in-use list and count; log the results of the checks.
2064 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
2065 outputStream * out,
2066 int *error_cnt_p) {
2067 int chk_om_in_use_count = 0;
2068 for (ObjectMonitor* n = jt->om_in_use_list; n != NULL; n = n->_next_om) {
2069 chk_in_use_entry(jt, n, out, error_cnt_p);
2070 chk_om_in_use_count++;
2071 }
2072 if (jt->om_in_use_count == chk_om_in_use_count) {
2073 out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals "
2074 "chk_om_in_use_count=%d", p2i(jt), jt->om_in_use_count,
2075 chk_om_in_use_count);
2076 } else {
2077 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not "
2078 "equal to chk_om_in_use_count=%d", p2i(jt), jt->om_in_use_count,
2079 chk_om_in_use_count);
2080 *error_cnt_p = *error_cnt_p + 1;
2081 }
2082 }
2083
2084 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2085 // flags indicate why the entry is in-use, 'object' and 'object type'
2086 // indicate the associated object and its type.
2087 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out,
2088 bool on_exit) {
2089 if (!on_exit) {
2090 // Not at VM exit so grab the global list lock.
2091 Thread::muxAcquire(&gListLock, "log_in_use_monitor_details");
2092 }
2093
2094 stringStream ss;
2095 if (g_om_in_use_count > 0) {
2096 out->print_cr("In-use global monitor info:");
2097 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2098 out->print_cr("%18s %s %18s %18s",
2099 "monitor", "BHL", "object", "object type");
2100 out->print_cr("================== === ================== ==================");
2101 for (ObjectMonitor* n = g_om_in_use_list; n != NULL; n = n->_next_om) {
2102 const oop obj = (oop) n->object();
2103 const markWord mark = n->header();
2104 ResourceMark rm;
2105 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(n),
2106 n->is_busy() != 0, mark.hash() != 0, n->owner() != NULL,
2107 p2i(obj), obj->klass()->external_name());
2108 if (n->is_busy() != 0) {
2109 out->print(" (%s)", n->is_busy_to_string(&ss));
2110 ss.reset();
2111 }
2112 out->cr();
2113 }
2114 }
2115
2116 if (!on_exit) {
2117 Thread::muxRelease(&gListLock);
2118 }
2119
2120 out->print_cr("In-use per-thread monitor info:");
2121 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2122 out->print_cr("%18s %18s %s %18s %18s",
2123 "jt", "monitor", "BHL", "object", "object type");
2124 out->print_cr("================== ================== === ================== ==================");
2125 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2126 for (ObjectMonitor* n = jt->om_in_use_list; n != NULL; n = n->_next_om) {
2127 const oop obj = (oop) n->object();
2128 const markWord mark = n->header();
2129 ResourceMark rm;
2130 out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT
2131 " %s", p2i(jt), p2i(n), n->is_busy() != 0,
2132 mark.hash() != 0, n->owner() != NULL, p2i(obj),
2133 obj->klass()->external_name());
2134 if (n->is_busy() != 0) {
2135 out->print(" (%s)", n->is_busy_to_string(&ss));
2136 ss.reset();
2137 }
2138 out->cr();
2139 }
2140 }
2141
2142 out->flush();
2143 }
2144
2145 // Log counts for the global and per-thread monitor lists and return
2146 // the population count.
2147 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2148 int pop_count = 0;
2149 out->print_cr("%18s %10s %10s %10s",
2150 "Global Lists:", "InUse", "Free", "Total");
2151 out->print_cr("================== ========== ========== ==========");
2152 out->print_cr("%18s %10d %10d %10d", "",
2153 g_om_in_use_count, g_om_free_count, g_om_population);
2154 pop_count += g_om_in_use_count + g_om_free_count;
2155
2156 out->print_cr("%18s %10s %10s %10s",
2157 "Per-Thread Lists:", "InUse", "Free", "Provision");
2158 out->print_cr("================== ========== ========== ==========");
2159
2160 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2161 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
2162 jt->om_in_use_count, jt->om_free_count, jt->om_free_provision);
2163 pop_count += jt->om_in_use_count + jt->om_free_count;
2164 }
2165 return pop_count;
2166 }
2167
2168 #ifndef PRODUCT
2169
2170 // Check if monitor belongs to the monitor cache
2171 // The list is grow-only so it's *relatively* safe to traverse
2172 // the list of extant blocks without taking a lock.
2173
2174 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
2175 PaddedObjectMonitor* block = Atomic::load_acquire(&g_block_list);
2176 while (block != NULL) {
2177 assert(block->object() == CHAINMARKER, "must be a block header");
2178 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
2179 address mon = (address)monitor;
2180 address blk = (address)block;
2181 size_t diff = mon - blk;
2182 assert((diff % sizeof(PaddedObjectMonitor)) == 0, "must be aligned");
2183 return 1;
2184 }
2185 block = (PaddedObjectMonitor*)block->_next_om;
2186 }
2187 return 0;
2188 }
2189
2190 #endif