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/markOop.hpp"
36 #include "oops/oop.inline.hpp"
37 #include "runtime/atomic.hpp"
38 #include "runtime/biasedLocking.hpp"
39 #include "runtime/handles.inline.hpp"
40 #include "runtime/interfaceSupport.inline.hpp"
41 #include "runtime/mutexLocker.hpp"
42 #include "runtime/objectMonitor.hpp"
43 #include "runtime/objectMonitor.inline.hpp"
44 #include "runtime/osThread.hpp"
45 #include "runtime/safepointVerifiers.hpp"
46 #include "runtime/sharedRuntime.hpp"
47 #include "runtime/stubRoutines.hpp"
48 #include "runtime/synchronizer.hpp"
49 #include "runtime/thread.inline.hpp"
50 #include "runtime/timer.hpp"
51 #include "runtime/vframe.hpp"
52 #include "runtime/vmThread.hpp"
53 #include "utilities/align.hpp"
54 #include "utilities/dtrace.hpp"
55 #include "utilities/events.hpp"
56 #include "utilities/preserveException.hpp"
57
58 // The "core" versions of monitor enter and exit reside in this file.
59 // The interpreter and compilers contain specialized transliterated
60 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
61 // for instance. If you make changes here, make sure to modify the
62 // interpreter, and both C1 and C2 fast-path inline locking code emission.
63 //
64 // -----------------------------------------------------------------------------
65
66 #ifdef DTRACE_ENABLED
67
68 // Only bother with this argument setup if dtrace is available
69 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
70
71 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
72 char* bytes = NULL; \
73 int len = 0; \
74 jlong jtid = SharedRuntime::get_java_tid(thread); \
75 Symbol* klassname = ((oop)(obj))->klass()->name(); \
76 if (klassname != NULL) { \
77 bytes = (char*)klassname->bytes(); \
78 len = klassname->utf8_length(); \
79 }
80
81 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
82 { \
83 if (DTraceMonitorProbes) { \
84 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
85 HOTSPOT_MONITOR_WAIT(jtid, \
86 (uintptr_t)(monitor), bytes, len, (millis)); \
87 } \
88 }
89
90 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
91 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
92 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
93
94 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
95 { \
96 if (DTraceMonitorProbes) { \
97 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
98 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
99 (uintptr_t)(monitor), bytes, len); \
100 } \
101 }
102
103 #else // ndef DTRACE_ENABLED
104
105 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
106 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
107
108 #endif // ndef DTRACE_ENABLED
109
110 // This exists only as a workaround of dtrace bug 6254741
111 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
112 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
113 return 0;
114 }
115
116 #define NINFLATIONLOCKS 256
117 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
118
119 // global list of blocks of monitors
120 PaddedEnd<ObjectMonitor> * volatile ObjectSynchronizer::gBlockList = NULL;
121 // global monitor free list
122 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL;
123 // global monitor in-use list, for moribund threads,
124 // monitors they inflated need to be scanned for deflation
125 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL;
126 // count of entries in gOmInUseList
127 int ObjectSynchronizer::gOmInUseCount = 0;
128
129 static volatile intptr_t gListLock = 0; // protects global monitor lists
130 static volatile int gMonitorFreeCount = 0; // # on gFreeList
131 static volatile int gMonitorPopulation = 0; // # Extant -- in circulation
132
133 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
134
135
136 // =====================> Quick functions
137
138 // The quick_* forms are special fast-path variants used to improve
139 // performance. In the simplest case, a "quick_*" implementation could
140 // simply return false, in which case the caller will perform the necessary
141 // state transitions and call the slow-path form.
142 // The fast-path is designed to handle frequently arising cases in an efficient
143 // manner and is just a degenerate "optimistic" variant of the slow-path.
144 // returns true -- to indicate the call was satisfied.
145 // returns false -- to indicate the call needs the services of the slow-path.
146 // A no-loitering ordinance is in effect for code in the quick_* family
147 // operators: safepoints or indefinite blocking (blocking that might span a
148 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
149 // entry.
150 //
151 // Consider: An interesting optimization is to have the JIT recognize the
152 // following common idiom:
153 // synchronized (someobj) { .... ; notify(); }
154 // That is, we find a notify() or notifyAll() call that immediately precedes
155 // the monitorexit operation. In that case the JIT could fuse the operations
156 // into a single notifyAndExit() runtime primitive.
157
158 bool ObjectSynchronizer::quick_notify(oopDesc * obj, Thread * self, bool all) {
159 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
160 assert(self->is_Java_thread(), "invariant");
161 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
162 NoSafepointVerifier nsv;
163 if (obj == NULL) return false; // slow-path for invalid obj
164 const markOop mark = obj->mark();
165
166 if (mark->has_locker() && self->is_lock_owned((address)mark->locker())) {
167 // Degenerate notify
168 // stack-locked by caller so by definition the implied waitset is empty.
169 return true;
170 }
171
172 if (mark->has_monitor()) {
173 ObjectMonitor * const mon = mark->monitor();
174 assert(oopDesc::equals((oop) mon->object(), obj), "invariant");
175 if (mon->owner() != self) return false; // slow-path for IMS exception
176
177 if (mon->first_waiter() != NULL) {
178 // We have one or more waiters. Since this is an inflated monitor
179 // that we own, we can transfer one or more threads from the waitset
180 // to the entrylist here and now, avoiding the slow-path.
181 if (all) {
182 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
183 } else {
184 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
185 }
186 int tally = 0;
187 do {
188 mon->INotify(self);
189 ++tally;
190 } while (mon->first_waiter() != NULL && all);
191 OM_PERFDATA_OP(Notifications, inc(tally));
192 }
193 return true;
194 }
195
196 // biased locking and any other IMS exception states take the slow-path
197 return false;
198 }
199
200
201 // The LockNode emitted directly at the synchronization site would have
202 // been too big if it were to have included support for the cases of inflated
203 // recursive enter and exit, so they go here instead.
204 // Note that we can't safely call AsyncPrintJavaStack() from within
205 // quick_enter() as our thread state remains _in_Java.
206
207 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
208 BasicLock * lock) {
209 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
210 assert(Self->is_Java_thread(), "invariant");
211 assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
212 NoSafepointVerifier nsv;
213 if (obj == NULL) return false; // Need to throw NPE
214 const markOop mark = obj->mark();
215
216 if (mark->has_monitor()) {
217 ObjectMonitor * const m = mark->monitor();
218 assert(oopDesc::equals((oop) m->object(), obj), "invariant");
219 Thread * const owner = (Thread *) m->_owner;
220
221 // Lock contention and Transactional Lock Elision (TLE) diagnostics
222 // and observability
223 // Case: light contention possibly amenable to TLE
224 // Case: TLE inimical operations such as nested/recursive synchronization
225
226 if (owner == Self) {
227 m->_recursions++;
228 return true;
229 }
230
231 // This Java Monitor is inflated so obj's header will never be
232 // displaced to this thread's BasicLock. Make the displaced header
233 // non-NULL so this BasicLock is not seen as recursive nor as
234 // being locked. We do this unconditionally so that this thread's
235 // BasicLock cannot be mis-interpreted by any stack walkers. For
236 // performance reasons, stack walkers generally first check for
237 // Biased Locking in the object's header, the second check is for
238 // stack-locking in the object's header, the third check is for
239 // recursive stack-locking in the displaced header in the BasicLock,
240 // and last are the inflated Java Monitor (ObjectMonitor) checks.
241 lock->set_displaced_header(markOopDesc::unused_mark());
242
243 if (owner == NULL && Atomic::replace_if_null(Self, &(m->_owner))) {
244 assert(m->_recursions == 0, "invariant");
245 assert(m->_owner == Self, "invariant");
246 return true;
247 }
248 }
249
250 // Note that we could inflate in quick_enter.
251 // This is likely a useful optimization
252 // Critically, in quick_enter() we must not:
253 // -- perform bias revocation, or
254 // -- block indefinitely, or
255 // -- reach a safepoint
256
257 return false; // revert to slow-path
258 }
259
260 // -----------------------------------------------------------------------------
261 // Fast Monitor Enter/Exit
262 // This the fast monitor enter. The interpreter and compiler use
263 // some assembly copies of this code. Make sure update those code
264 // if the following function is changed. The implementation is
265 // extremely sensitive to race condition. Be careful.
266
267 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
268 bool attempt_rebias, TRAPS) {
269 if (UseBiasedLocking) {
270 if (!SafepointSynchronize::is_at_safepoint()) {
271 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
272 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
273 return;
274 }
275 } else {
276 assert(!attempt_rebias, "can not rebias toward VM thread");
277 BiasedLocking::revoke_at_safepoint(obj);
278 }
279 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
280 }
281
282 slow_enter(obj, lock, THREAD);
283 }
284
285 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
286 markOop mark = object->mark();
287 // We cannot check for Biased Locking if we are racing an inflation.
288 assert(mark == markOopDesc::INFLATING() ||
289 !mark->has_bias_pattern(), "should not see bias pattern here");
290
291 markOop dhw = lock->displaced_header();
292 if (dhw == NULL) {
293 // If the displaced header is NULL, then this exit matches up with
294 // a recursive enter. No real work to do here except for diagnostics.
295 #ifndef PRODUCT
296 if (mark != markOopDesc::INFLATING()) {
297 // Only do diagnostics if we are not racing an inflation. Simply
298 // exiting a recursive enter of a Java Monitor that is being
299 // inflated is safe; see the has_monitor() comment below.
300 assert(!mark->is_neutral(), "invariant");
301 assert(!mark->has_locker() ||
302 THREAD->is_lock_owned((address)mark->locker()), "invariant");
303 if (mark->has_monitor()) {
304 // The BasicLock's displaced_header is marked as a recursive
305 // enter and we have an inflated Java Monitor (ObjectMonitor).
306 // This is a special case where the Java Monitor was inflated
307 // after this thread entered the stack-lock recursively. When a
308 // Java Monitor is inflated, we cannot safely walk the Java
309 // Monitor owner's stack and update the BasicLocks because a
310 // Java Monitor can be asynchronously inflated by a thread that
311 // does not own the Java Monitor.
312 ObjectMonitor * m = mark->monitor();
313 assert(((oop)(m->object()))->mark() == mark, "invariant");
314 assert(m->is_entered(THREAD), "invariant");
315 }
316 }
317 #endif
318 return;
319 }
320
321 if (mark == (markOop) lock) {
322 // If the object is stack-locked by the current thread, try to
323 // swing the displaced header from the BasicLock back to the mark.
324 assert(dhw->is_neutral(), "invariant");
325 if (object->cas_set_mark(dhw, mark) == mark) {
326 return;
327 }
328 }
329
330 // We have to take the slow-path of possible inflation and then exit.
331 inflate(THREAD, object, inflate_cause_vm_internal)->exit(true, THREAD);
332 }
333
334 // -----------------------------------------------------------------------------
335 // Interpreter/Compiler Slow Case
336 // This routine is used to handle interpreter/compiler slow case
337 // We don't need to use fast path here, because it must have been
338 // failed in the interpreter/compiler code.
339 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
340 markOop mark = obj->mark();
341 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
342
343 if (mark->is_neutral()) {
344 // Anticipate successful CAS -- the ST of the displaced mark must
345 // be visible <= the ST performed by the CAS.
346 lock->set_displaced_header(mark);
347 if (mark == obj()->cas_set_mark((markOop) lock, mark)) {
348 return;
349 }
350 // Fall through to inflate() ...
351 } else if (mark->has_locker() &&
352 THREAD->is_lock_owned((address)mark->locker())) {
353 assert(lock != mark->locker(), "must not re-lock the same lock");
354 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
355 lock->set_displaced_header(NULL);
356 return;
357 }
358
359 // The object header will never be displaced to this lock,
360 // so it does not matter what the value is, except that it
361 // must be non-zero to avoid looking like a re-entrant lock,
362 // and must not look locked either.
363 lock->set_displaced_header(markOopDesc::unused_mark());
364 inflate(THREAD, obj(), inflate_cause_monitor_enter)->enter(THREAD);
365 }
366
367 // This routine is used to handle interpreter/compiler slow case
368 // We don't need to use fast path here, because it must have
369 // failed in the interpreter/compiler code. Simply use the heavy
370 // weight monitor should be ok, unless someone find otherwise.
371 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
372 fast_exit(object, lock, THREAD);
373 }
374
375 // -----------------------------------------------------------------------------
376 // Class Loader support to workaround deadlocks on the class loader lock objects
377 // Also used by GC
378 // complete_exit()/reenter() are used to wait on a nested lock
379 // i.e. to give up an outer lock completely and then re-enter
380 // Used when holding nested locks - lock acquisition order: lock1 then lock2
381 // 1) complete_exit lock1 - saving recursion count
382 // 2) wait on lock2
383 // 3) when notified on lock2, unlock lock2
384 // 4) reenter lock1 with original recursion count
385 // 5) lock lock2
386 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
387 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
388 if (UseBiasedLocking) {
389 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
390 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
391 }
392
393 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
394
395 return monitor->complete_exit(THREAD);
396 }
397
398 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
399 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
400 if (UseBiasedLocking) {
401 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
402 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
403 }
404
405 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
406
407 monitor->reenter(recursion, THREAD);
408 }
409 // -----------------------------------------------------------------------------
410 // JNI locks on java objects
411 // NOTE: must use heavy weight monitor to handle jni monitor enter
412 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
413 // the current locking is from JNI instead of Java code
414 if (UseBiasedLocking) {
415 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
416 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
417 }
418 THREAD->set_current_pending_monitor_is_from_java(false);
419 inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);
420 THREAD->set_current_pending_monitor_is_from_java(true);
421 }
422
423 // NOTE: must use heavy weight monitor to handle jni monitor exit
424 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
425 if (UseBiasedLocking) {
426 Handle h_obj(THREAD, obj);
427 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
428 obj = h_obj();
429 }
430 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
431
432 ObjectMonitor* monitor = inflate(THREAD, obj, inflate_cause_jni_exit);
433 // If this thread has locked the object, exit the monitor. Note: can't use
434 // monitor->check(CHECK); must exit even if an exception is pending.
435 if (monitor->check(THREAD)) {
436 monitor->exit(true, THREAD);
437 }
438 }
439
440 // -----------------------------------------------------------------------------
441 // Internal VM locks on java objects
442 // standard constructor, allows locking failures
443 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
444 _dolock = doLock;
445 _thread = thread;
446 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
447 _obj = obj;
448
449 if (_dolock) {
450 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
451 }
452 }
453
454 ObjectLocker::~ObjectLocker() {
455 if (_dolock) {
456 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
457 }
458 }
459
460
461 // -----------------------------------------------------------------------------
462 // Wait/Notify/NotifyAll
463 // NOTE: must use heavy weight monitor to handle wait()
464 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
465 if (UseBiasedLocking) {
466 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
467 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
468 }
469 if (millis < 0) {
470 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
471 }
472 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
473
474 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
475 monitor->wait(millis, true, THREAD);
476
477 // This dummy call is in place to get around dtrace bug 6254741. Once
478 // that's fixed we can uncomment the following line, remove the call
479 // and change this function back into a "void" func.
480 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
481 return dtrace_waited_probe(monitor, obj, THREAD);
482 }
483
484 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
485 if (UseBiasedLocking) {
486 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
487 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
488 }
489 if (millis < 0) {
490 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
491 }
492 inflate(THREAD, obj(), inflate_cause_wait)->wait(millis, false, THREAD);
493 }
494
495 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
496 if (UseBiasedLocking) {
497 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
498 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
499 }
500
501 markOop mark = obj->mark();
502 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
503 return;
504 }
505 inflate(THREAD, obj(), inflate_cause_notify)->notify(THREAD);
506 }
507
508 // NOTE: see comment of notify()
509 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
510 if (UseBiasedLocking) {
511 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
512 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
513 }
514
515 markOop mark = obj->mark();
516 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
517 return;
518 }
519 inflate(THREAD, obj(), inflate_cause_notify)->notifyAll(THREAD);
520 }
521
522 // -----------------------------------------------------------------------------
523 // Hash Code handling
524 //
525 // Performance concern:
526 // OrderAccess::storestore() calls release() which at one time stored 0
527 // into the global volatile OrderAccess::dummy variable. This store was
528 // unnecessary for correctness. Many threads storing into a common location
529 // causes considerable cache migration or "sloshing" on large SMP systems.
530 // As such, I avoided using OrderAccess::storestore(). In some cases
531 // OrderAccess::fence() -- which incurs local latency on the executing
532 // processor -- is a better choice as it scales on SMP systems.
533 //
534 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
535 // a discussion of coherency costs. Note that all our current reference
536 // platforms provide strong ST-ST order, so the issue is moot on IA32,
537 // x64, and SPARC.
538 //
539 // As a general policy we use "volatile" to control compiler-based reordering
540 // and explicit fences (barriers) to control for architectural reordering
541 // performed by the CPU(s) or platform.
542
543 struct SharedGlobals {
544 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
545 // These are highly shared mostly-read variables.
546 // To avoid false-sharing they need to be the sole occupants of a cache line.
547 volatile int stwRandom;
548 volatile int stwCycle;
549 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
550 // Hot RW variable -- Sequester to avoid false-sharing
551 volatile int hcSequence;
552 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
553 };
554
555 static SharedGlobals GVars;
556 static int MonitorScavengeThreshold = 1000000;
557 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
558
559 static markOop ReadStableMark(oop obj) {
560 markOop mark = obj->mark();
561 if (!mark->is_being_inflated()) {
562 return mark; // normal fast-path return
563 }
564
565 int its = 0;
566 for (;;) {
567 markOop mark = obj->mark();
568 if (!mark->is_being_inflated()) {
569 return mark; // normal fast-path return
570 }
571
572 // The object is being inflated by some other thread.
573 // The caller of ReadStableMark() must wait for inflation to complete.
574 // Avoid live-lock
575 // TODO: consider calling SafepointSynchronize::do_call_back() while
576 // spinning to see if there's a safepoint pending. If so, immediately
577 // yielding or blocking would be appropriate. Avoid spinning while
578 // there is a safepoint pending.
579 // TODO: add inflation contention performance counters.
580 // TODO: restrict the aggregate number of spinners.
581
582 ++its;
583 if (its > 10000 || !os::is_MP()) {
584 if (its & 1) {
585 os::naked_yield();
586 } else {
587 // Note that the following code attenuates the livelock problem but is not
588 // a complete remedy. A more complete solution would require that the inflating
589 // thread hold the associated inflation lock. The following code simply restricts
590 // the number of spinners to at most one. We'll have N-2 threads blocked
591 // on the inflationlock, 1 thread holding the inflation lock and using
592 // a yield/park strategy, and 1 thread in the midst of inflation.
593 // A more refined approach would be to change the encoding of INFLATING
594 // to allow encapsulation of a native thread pointer. Threads waiting for
595 // inflation to complete would use CAS to push themselves onto a singly linked
596 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
597 // and calling park(). When inflation was complete the thread that accomplished inflation
598 // would detach the list and set the markword to inflated with a single CAS and
599 // then for each thread on the list, set the flag and unpark() the thread.
600 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
601 // wakes at most one thread whereas we need to wake the entire list.
602 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
603 int YieldThenBlock = 0;
604 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
605 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
606 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
607 while (obj->mark() == markOopDesc::INFLATING()) {
608 // Beware: NakedYield() is advisory and has almost no effect on some platforms
609 // so we periodically call Self->_ParkEvent->park(1).
610 // We use a mixed spin/yield/block mechanism.
611 if ((YieldThenBlock++) >= 16) {
612 Thread::current()->_ParkEvent->park(1);
613 } else {
614 os::naked_yield();
615 }
616 }
617 Thread::muxRelease(gInflationLocks + ix);
618 }
619 } else {
620 SpinPause(); // SMP-polite spinning
621 }
622 }
623 }
624
625 // hashCode() generation :
626 //
627 // Possibilities:
628 // * MD5Digest of {obj,stwRandom}
629 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
630 // * A DES- or AES-style SBox[] mechanism
631 // * One of the Phi-based schemes, such as:
632 // 2654435761 = 2^32 * Phi (golden ratio)
633 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
634 // * A variation of Marsaglia's shift-xor RNG scheme.
635 // * (obj ^ stwRandom) is appealing, but can result
636 // in undesirable regularity in the hashCode values of adjacent objects
637 // (objects allocated back-to-back, in particular). This could potentially
638 // result in hashtable collisions and reduced hashtable efficiency.
639 // There are simple ways to "diffuse" the middle address bits over the
640 // generated hashCode values:
641
642 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
643 intptr_t value = 0;
644 if (hashCode == 0) {
645 // This form uses global Park-Miller RNG.
646 // On MP system we'll have lots of RW access to a global, so the
647 // mechanism induces lots of coherency traffic.
648 value = os::random();
649 } else if (hashCode == 1) {
650 // This variation has the property of being stable (idempotent)
651 // between STW operations. This can be useful in some of the 1-0
652 // synchronization schemes.
653 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
654 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
655 } else if (hashCode == 2) {
656 value = 1; // for sensitivity testing
657 } else if (hashCode == 3) {
658 value = ++GVars.hcSequence;
659 } else if (hashCode == 4) {
660 value = cast_from_oop<intptr_t>(obj);
661 } else {
662 // Marsaglia's xor-shift scheme with thread-specific state
663 // This is probably the best overall implementation -- we'll
664 // likely make this the default in future releases.
665 unsigned t = Self->_hashStateX;
666 t ^= (t << 11);
667 Self->_hashStateX = Self->_hashStateY;
668 Self->_hashStateY = Self->_hashStateZ;
669 Self->_hashStateZ = Self->_hashStateW;
670 unsigned v = Self->_hashStateW;
671 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
672 Self->_hashStateW = v;
673 value = v;
674 }
675
676 value &= markOopDesc::hash_mask;
677 if (value == 0) value = 0xBAD;
678 assert(value != markOopDesc::no_hash, "invariant");
679 return value;
680 }
681
682 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
683 if (UseBiasedLocking) {
684 // NOTE: many places throughout the JVM do not expect a safepoint
685 // to be taken here, in particular most operations on perm gen
686 // objects. However, we only ever bias Java instances and all of
687 // the call sites of identity_hash that might revoke biases have
688 // been checked to make sure they can handle a safepoint. The
689 // added check of the bias pattern is to avoid useless calls to
690 // thread-local storage.
691 if (obj->mark()->has_bias_pattern()) {
692 // Handle for oop obj in case of STW safepoint
693 Handle hobj(Self, obj);
694 // Relaxing assertion for bug 6320749.
695 assert(Universe::verify_in_progress() ||
696 !SafepointSynchronize::is_at_safepoint(),
697 "biases should not be seen by VM thread here");
698 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
699 obj = hobj();
700 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
701 }
702 }
703
704 // hashCode() is a heap mutator ...
705 // Relaxing assertion for bug 6320749.
706 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
707 !SafepointSynchronize::is_at_safepoint(), "invariant");
708 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
709 Self->is_Java_thread() , "invariant");
710 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
711 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
712
713 ObjectMonitor* monitor = NULL;
714 markOop temp, test;
715 intptr_t hash;
716 markOop mark = ReadStableMark(obj);
717
718 // object should remain ineligible for biased locking
719 assert(!mark->has_bias_pattern(), "invariant");
720
721 if (mark->is_neutral()) {
722 hash = mark->hash(); // this is a normal header
723 if (hash != 0) { // if it has hash, just return it
724 return hash;
725 }
726 hash = get_next_hash(Self, obj); // allocate a new hash code
727 temp = mark->copy_set_hash(hash); // merge the hash code into header
728 // use (machine word version) atomic operation to install the hash
729 test = obj->cas_set_mark(temp, mark);
730 if (test == mark) {
731 return hash;
732 }
733 // If atomic operation failed, we must inflate the header
734 // into heavy weight monitor. We could add more code here
735 // for fast path, but it does not worth the complexity.
736 } else if (mark->has_monitor()) {
737 monitor = mark->monitor();
738 temp = monitor->header();
739 assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(temp));
740 hash = temp->hash();
741 if (hash != 0) {
742 return hash;
743 }
744 // Skip to the following code to reduce code size
745 } else if (Self->is_lock_owned((address)mark->locker())) {
746 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
747 assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(temp));
748 hash = temp->hash(); // by current thread, check if the displaced
749 if (hash != 0) { // header contains hash code
750 return hash;
751 }
752 // WARNING:
753 // The displaced header in the BasicLock on a thread's stack
754 // is strictly immutable. It CANNOT be changed in ANY cases.
755 // So we have to inflate the stack lock into an ObjectMonitor
756 // even if the current thread owns the lock. The BasicLock on
757 // a thread's stack can be asynchronously read by other threads
758 // during an inflate() call so any change to that stack memory
759 // may not propagate to other threads correctly.
760 }
761
762 // Inflate the monitor to set hash code
763 monitor = inflate(Self, obj, inflate_cause_hash_code);
764 // Load displaced header and check it has hash code
765 mark = monitor->header();
766 assert(mark->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(mark));
767 hash = mark->hash();
768 if (hash == 0) {
769 hash = get_next_hash(Self, obj);
770 temp = mark->copy_set_hash(hash); // merge hash code into header
771 assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(temp));
772 test = Atomic::cmpxchg(temp, monitor->header_addr(), mark);
773 if (test != mark) {
774 // The only update to the ObjectMonitor's header/dmw field
775 // is to merge in the hash code. If someone adds a new usage
776 // of the header/dmw field, please update this code.
777 hash = test->hash();
778 assert(test->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(test));
779 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
780 }
781 }
782 // We finally get the hash
783 return hash;
784 }
785
786 // Deprecated -- use FastHashCode() instead.
787
788 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
789 return FastHashCode(Thread::current(), obj());
790 }
791
792
793 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
794 Handle h_obj) {
795 if (UseBiasedLocking) {
796 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
797 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
798 }
799
800 assert(thread == JavaThread::current(), "Can only be called on current thread");
801 oop obj = h_obj();
802
803 markOop mark = ReadStableMark(obj);
804
805 // Uncontended case, header points to stack
806 if (mark->has_locker()) {
807 return thread->is_lock_owned((address)mark->locker());
808 }
809 // Contended case, header points to ObjectMonitor (tagged pointer)
810 if (mark->has_monitor()) {
811 ObjectMonitor* monitor = mark->monitor();
812 return monitor->is_entered(thread) != 0;
813 }
814 // Unlocked case, header in place
815 assert(mark->is_neutral(), "sanity check");
816 return false;
817 }
818
819 // Be aware of this method could revoke bias of the lock object.
820 // This method queries the ownership of the lock handle specified by 'h_obj'.
821 // If the current thread owns the lock, it returns owner_self. If no
822 // thread owns the lock, it returns owner_none. Otherwise, it will return
823 // owner_other.
824 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
825 (JavaThread *self, Handle h_obj) {
826 // The caller must beware this method can revoke bias, and
827 // revocation can result in a safepoint.
828 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
829 assert(self->thread_state() != _thread_blocked, "invariant");
830
831 // Possible mark states: neutral, biased, stack-locked, inflated
832
833 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
834 // CASE: biased
835 BiasedLocking::revoke_and_rebias(h_obj, false, self);
836 assert(!h_obj->mark()->has_bias_pattern(),
837 "biases should be revoked by now");
838 }
839
840 assert(self == JavaThread::current(), "Can only be called on current thread");
841 oop obj = h_obj();
842 markOop mark = ReadStableMark(obj);
843
844 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
845 if (mark->has_locker()) {
846 return self->is_lock_owned((address)mark->locker()) ?
847 owner_self : owner_other;
848 }
849
850 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
851 // The Object:ObjectMonitor relationship is stable as long as we're
852 // not at a safepoint.
853 if (mark->has_monitor()) {
854 void * owner = mark->monitor()->_owner;
855 if (owner == NULL) return owner_none;
856 return (owner == self ||
857 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
858 }
859
860 // CASE: neutral
861 assert(mark->is_neutral(), "sanity check");
862 return owner_none; // it's unlocked
863 }
864
865 // FIXME: jvmti should call this
866 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
867 if (UseBiasedLocking) {
868 if (SafepointSynchronize::is_at_safepoint()) {
869 BiasedLocking::revoke_at_safepoint(h_obj);
870 } else {
871 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
872 }
873 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
874 }
875
876 oop obj = h_obj();
877 address owner = NULL;
878
879 markOop mark = ReadStableMark(obj);
880
881 // Uncontended case, header points to stack
882 if (mark->has_locker()) {
883 owner = (address) mark->locker();
884 }
885
886 // Contended case, header points to ObjectMonitor (tagged pointer)
887 else if (mark->has_monitor()) {
888 ObjectMonitor* monitor = mark->monitor();
889 assert(monitor != NULL, "monitor should be non-null");
890 owner = (address) monitor->owner();
891 }
892
893 if (owner != NULL) {
894 // owning_thread_from_monitor_owner() may also return NULL here
895 return Threads::owning_thread_from_monitor_owner(t_list, owner);
896 }
897
898 // Unlocked case, header in place
899 // Cannot have assertion since this object may have been
900 // locked by another thread when reaching here.
901 // assert(mark->is_neutral(), "sanity check");
902
903 return NULL;
904 }
905
906 // Visitors ...
907
908 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
909 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
910 while (block != NULL) {
911 assert(block->object() == CHAINMARKER, "must be a block header");
912 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
913 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
914 oop object = (oop)mid->object();
915 if (object != NULL) {
916 closure->do_monitor(mid);
917 }
918 }
919 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
920 }
921 }
922
923 // Get the next block in the block list.
924 static inline PaddedEnd<ObjectMonitor>* next(PaddedEnd<ObjectMonitor>* block) {
925 assert(block->object() == CHAINMARKER, "must be a block header");
926 block = (PaddedEnd<ObjectMonitor>*) block->FreeNext;
927 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
928 return block;
929 }
930
931 static bool monitors_used_above_threshold() {
932 if (gMonitorPopulation == 0) {
933 return false;
934 }
935 int monitors_used = gMonitorPopulation - gMonitorFreeCount;
936 int monitor_usage = (monitors_used * 100LL) / gMonitorPopulation;
937 return monitor_usage > MonitorUsedDeflationThreshold;
938 }
939
940 bool ObjectSynchronizer::is_cleanup_needed() {
941 if (MonitorUsedDeflationThreshold > 0) {
942 return monitors_used_above_threshold();
943 }
944 return false;
945 }
946
947 void ObjectSynchronizer::oops_do(OopClosure* f) {
948 // We only scan the global used list here (for moribund threads), and
949 // the thread-local monitors in Thread::oops_do().
950 global_used_oops_do(f);
951 }
952
953 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
954 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
955 list_oops_do(gOmInUseList, f);
956 }
957
958 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
959 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
960 list_oops_do(thread->omInUseList, f);
961 }
962
963 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
964 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
965 ObjectMonitor* mid;
966 for (mid = list; mid != NULL; mid = mid->FreeNext) {
967 if (mid->object() != NULL) {
968 f->do_oop((oop*)mid->object_addr());
969 }
970 }
971 }
972
973
974 // -----------------------------------------------------------------------------
975 // ObjectMonitor Lifecycle
976 // -----------------------
977 // Inflation unlinks monitors from the global gFreeList and
978 // associates them with objects. Deflation -- which occurs at
979 // STW-time -- disassociates idle monitors from objects. Such
980 // scavenged monitors are returned to the gFreeList.
981 //
982 // The global list is protected by gListLock. All the critical sections
983 // are short and operate in constant-time.
984 //
985 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
986 //
987 // Lifecycle:
988 // -- unassigned and on the global free list
989 // -- unassigned and on a thread's private omFreeList
990 // -- assigned to an object. The object is inflated and the mark refers
991 // to the objectmonitor.
992
993
994 // Constraining monitor pool growth via MonitorBound ...
995 //
996 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
997 // the rate of scavenging is driven primarily by GC. As such, we can find
998 // an inordinate number of monitors in circulation.
999 // To avoid that scenario we can artificially induce a STW safepoint
1000 // if the pool appears to be growing past some reasonable bound.
1001 // Generally we favor time in space-time tradeoffs, but as there's no
1002 // natural back-pressure on the # of extant monitors we need to impose some
1003 // type of limit. Beware that if MonitorBound is set to too low a value
1004 // we could just loop. In addition, if MonitorBound is set to a low value
1005 // we'll incur more safepoints, which are harmful to performance.
1006 // See also: GuaranteedSafepointInterval
1007 //
1008 // The current implementation uses asynchronous VM operations.
1009
1010 static void InduceScavenge(Thread * Self, const char * Whence) {
1011 // Induce STW safepoint to trim monitors
1012 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1013 // More precisely, trigger an asynchronous STW safepoint as the number
1014 // of active monitors passes the specified threshold.
1015 // TODO: assert thread state is reasonable
1016
1017 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1018 // Induce a 'null' safepoint to scavenge monitors
1019 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1020 // to the VMthread and have a lifespan longer than that of this activation record.
1021 // The VMThread will delete the op when completed.
1022 VMThread::execute(new VM_ScavengeMonitors());
1023 }
1024 }
1025
1026 ObjectMonitor* ObjectSynchronizer::omAlloc(Thread * Self) {
1027 // A large MAXPRIVATE value reduces both list lock contention
1028 // and list coherency traffic, but also tends to increase the
1029 // number of objectMonitors in circulation as well as the STW
1030 // scavenge costs. As usual, we lean toward time in space-time
1031 // tradeoffs.
1032 const int MAXPRIVATE = 1024;
1033 for (;;) {
1034 ObjectMonitor * m;
1035
1036 // 1: try to allocate from the thread's local omFreeList.
1037 // Threads will attempt to allocate first from their local list, then
1038 // from the global list, and only after those attempts fail will the thread
1039 // attempt to instantiate new monitors. Thread-local free lists take
1040 // heat off the gListLock and improve allocation latency, as well as reducing
1041 // coherency traffic on the shared global list.
1042 m = Self->omFreeList;
1043 if (m != NULL) {
1044 Self->omFreeList = m->FreeNext;
1045 Self->omFreeCount--;
1046 guarantee(m->object() == NULL, "invariant");
1047 m->FreeNext = Self->omInUseList;
1048 Self->omInUseList = m;
1049 Self->omInUseCount++;
1050 return m;
1051 }
1052
1053 // 2: try to allocate from the global gFreeList
1054 // CONSIDER: use muxTry() instead of muxAcquire().
1055 // If the muxTry() fails then drop immediately into case 3.
1056 // If we're using thread-local free lists then try
1057 // to reprovision the caller's free list.
1058 if (gFreeList != NULL) {
1059 // Reprovision the thread's omFreeList.
1060 // Use bulk transfers to reduce the allocation rate and heat
1061 // on various locks.
1062 Thread::muxAcquire(&gListLock, "omAlloc(1)");
1063 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1064 gMonitorFreeCount--;
1065 ObjectMonitor * take = gFreeList;
1066 gFreeList = take->FreeNext;
1067 guarantee(take->object() == NULL, "invariant");
1068 guarantee(!take->is_busy(), "invariant");
1069 take->Recycle();
1070 omRelease(Self, take, false);
1071 }
1072 Thread::muxRelease(&gListLock);
1073 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1074 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1075
1076 const int mx = MonitorBound;
1077 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1078 // We can't safely induce a STW safepoint from omAlloc() as our thread
1079 // state may not be appropriate for such activities and callers may hold
1080 // naked oops, so instead we defer the action.
1081 InduceScavenge(Self, "omAlloc");
1082 }
1083 continue;
1084 }
1085
1086 // 3: allocate a block of new ObjectMonitors
1087 // Both the local and global free lists are empty -- resort to malloc().
1088 // In the current implementation objectMonitors are TSM - immortal.
1089 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1090 // each ObjectMonitor to start at the beginning of a cache line,
1091 // so we use align_up().
1092 // A better solution would be to use C++ placement-new.
1093 // BEWARE: As it stands currently, we don't run the ctors!
1094 assert(_BLOCKSIZE > 1, "invariant");
1095 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
1096 PaddedEnd<ObjectMonitor> * temp;
1097 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1098 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
1099 mtInternal);
1100 temp = (PaddedEnd<ObjectMonitor> *)
1101 align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE);
1102
1103 // NOTE: (almost) no way to recover if allocation failed.
1104 // We might be able to induce a STW safepoint and scavenge enough
1105 // objectMonitors to permit progress.
1106 if (temp == NULL) {
1107 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1108 "Allocate ObjectMonitors");
1109 }
1110 (void)memset((void *) temp, 0, neededsize);
1111
1112 // Format the block.
1113 // initialize the linked list, each monitor points to its next
1114 // forming the single linked free list, the very first monitor
1115 // will points to next block, which forms the block list.
1116 // The trick of using the 1st element in the block as gBlockList
1117 // linkage should be reconsidered. A better implementation would
1118 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1119
1120 for (int i = 1; i < _BLOCKSIZE; i++) {
1121 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1122 }
1123
1124 // terminate the last monitor as the end of list
1125 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1126
1127 // Element [0] is reserved for global list linkage
1128 temp[0].set_object(CHAINMARKER);
1129
1130 // Consider carving out this thread's current request from the
1131 // block in hand. This avoids some lock traffic and redundant
1132 // list activity.
1133
1134 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1135 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1136 Thread::muxAcquire(&gListLock, "omAlloc(2)");
1137 gMonitorPopulation += _BLOCKSIZE-1;
1138 gMonitorFreeCount += _BLOCKSIZE-1;
1139
1140 // Add the new block to the list of extant blocks (gBlockList).
1141 // The very first objectMonitor in a block is reserved and dedicated.
1142 // It serves as blocklist "next" linkage.
1143 temp[0].FreeNext = gBlockList;
1144 // There are lock-free uses of gBlockList so make sure that
1145 // the previous stores happen before we update gBlockList.
1146 OrderAccess::release_store(&gBlockList, temp);
1147
1148 // Add the new string of objectMonitors to the global free list
1149 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1150 gFreeList = temp + 1;
1151 Thread::muxRelease(&gListLock);
1152 }
1153 }
1154
1155 // Place "m" on the caller's private per-thread omFreeList.
1156 // In practice there's no need to clamp or limit the number of
1157 // monitors on a thread's omFreeList as the only time we'll call
1158 // omRelease is to return a monitor to the free list after a CAS
1159 // attempt failed. This doesn't allow unbounded #s of monitors to
1160 // accumulate on a thread's free list.
1161 //
1162 // Key constraint: all ObjectMonitors on a thread's free list and the global
1163 // free list must have their object field set to null. This prevents the
1164 // scavenger -- deflate_monitor_list() -- from reclaiming them.
1165
1166 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1167 bool fromPerThreadAlloc) {
1168 guarantee(m->header() == NULL, "invariant");
1169 guarantee(m->object() == NULL, "invariant");
1170 guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor");
1171 // Remove from omInUseList
1172 if (fromPerThreadAlloc) {
1173 ObjectMonitor* cur_mid_in_use = NULL;
1174 bool extracted = false;
1175 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1176 if (m == mid) {
1177 // extract from per-thread in-use list
1178 if (mid == Self->omInUseList) {
1179 Self->omInUseList = mid->FreeNext;
1180 } else if (cur_mid_in_use != NULL) {
1181 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1182 }
1183 extracted = true;
1184 Self->omInUseCount--;
1185 break;
1186 }
1187 }
1188 assert(extracted, "Should have extracted from in-use list");
1189 }
1190
1191 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1192 m->FreeNext = Self->omFreeList;
1193 Self->omFreeList = m;
1194 Self->omFreeCount++;
1195 }
1196
1197 // Return the monitors of a moribund thread's local free list to
1198 // the global free list. Typically a thread calls omFlush() when
1199 // it's dying. We could also consider having the VM thread steal
1200 // monitors from threads that have not run java code over a few
1201 // consecutive STW safepoints. Relatedly, we might decay
1202 // omFreeProvision at STW safepoints.
1203 //
1204 // Also return the monitors of a moribund thread's omInUseList to
1205 // a global gOmInUseList under the global list lock so these
1206 // will continue to be scanned.
1207 //
1208 // We currently call omFlush() from Threads::remove() _before the thread
1209 // has been excised from the thread list and is no longer a mutator.
1210 // This means that omFlush() cannot run concurrently with a safepoint and
1211 // interleave with the deflate_idle_monitors scavenge operator. In particular,
1212 // this ensures that the thread's monitors are scanned by a GC safepoint,
1213 // either via Thread::oops_do() (if safepoint happens before omFlush()) or via
1214 // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's
1215 // monitors have been transferred to the global in-use list).
1216
1217 void ObjectSynchronizer::omFlush(Thread * Self) {
1218 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1219 ObjectMonitor * tail = NULL;
1220 int tally = 0;
1221 if (list != NULL) {
1222 ObjectMonitor * s;
1223 // The thread is going away, the per-thread free monitors
1224 // are freed via set_owner(NULL)
1225 // Link them to tail, which will be linked into the global free list
1226 // gFreeList below, under the gListLock
1227 for (s = list; s != NULL; s = s->FreeNext) {
1228 tally++;
1229 tail = s;
1230 guarantee(s->object() == NULL, "invariant");
1231 guarantee(!s->is_busy(), "invariant");
1232 s->set_owner(NULL); // redundant but good hygiene
1233 }
1234 guarantee(tail != NULL, "invariant");
1235 assert(Self->omFreeCount == tally, "free-count off");
1236 Self->omFreeList = NULL;
1237 Self->omFreeCount = 0;
1238 }
1239
1240 ObjectMonitor * inUseList = Self->omInUseList;
1241 ObjectMonitor * inUseTail = NULL;
1242 int inUseTally = 0;
1243 if (inUseList != NULL) {
1244 ObjectMonitor *cur_om;
1245 // The thread is going away, however the omInUseList inflated
1246 // monitors may still be in-use by other threads.
1247 // Link them to inUseTail, which will be linked into the global in-use list
1248 // gOmInUseList below, under the gListLock
1249 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1250 inUseTail = cur_om;
1251 inUseTally++;
1252 }
1253 guarantee(inUseTail != NULL, "invariant");
1254 assert(Self->omInUseCount == inUseTally, "in-use count off");
1255 Self->omInUseList = NULL;
1256 Self->omInUseCount = 0;
1257 }
1258
1259 Thread::muxAcquire(&gListLock, "omFlush");
1260 if (tail != NULL) {
1261 tail->FreeNext = gFreeList;
1262 gFreeList = list;
1263 gMonitorFreeCount += tally;
1264 }
1265
1266 if (inUseTail != NULL) {
1267 inUseTail->FreeNext = gOmInUseList;
1268 gOmInUseList = inUseList;
1269 gOmInUseCount += inUseTally;
1270 }
1271
1272 Thread::muxRelease(&gListLock);
1273
1274 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1275 LogStreamHandle(Info, monitorinflation) lsh_info;
1276 LogStream * ls = NULL;
1277 if (log_is_enabled(Debug, monitorinflation)) {
1278 ls = &lsh_debug;
1279 } else if ((tally != 0 || inUseTally != 0) &&
1280 log_is_enabled(Info, monitorinflation)) {
1281 ls = &lsh_info;
1282 }
1283 if (ls != NULL) {
1284 ls->print_cr("omFlush: jt=" INTPTR_FORMAT ", free_monitor_tally=%d"
1285 ", in_use_monitor_tally=%d" ", omFreeProvision=%d",
1286 p2i(Self), tally, inUseTally, Self->omFreeProvision);
1287 }
1288 }
1289
1290 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1291 const oop obj,
1292 ObjectSynchronizer::InflateCause cause) {
1293 assert(event != NULL, "invariant");
1294 assert(event->should_commit(), "invariant");
1295 event->set_monitorClass(obj->klass());
1296 event->set_address((uintptr_t)(void*)obj);
1297 event->set_cause((u1)cause);
1298 event->commit();
1299 }
1300
1301 // Fast path code shared by multiple functions
1302 void ObjectSynchronizer::inflate_helper(oop obj) {
1303 markOop mark = obj->mark();
1304 if (mark->has_monitor()) {
1305 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1306 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1307 return;
1308 }
1309 inflate(Thread::current(), obj, inflate_cause_vm_internal);
1310 }
1311
1312 ObjectMonitor* ObjectSynchronizer::inflate(Thread * Self,
1313 oop object,
1314 const InflateCause cause) {
1315 // Inflate mutates the heap ...
1316 // Relaxing assertion for bug 6320749.
1317 assert(Universe::verify_in_progress() ||
1318 !SafepointSynchronize::is_at_safepoint(), "invariant");
1319
1320 EventJavaMonitorInflate event;
1321
1322 for (;;) {
1323 const markOop mark = object->mark();
1324 assert(!mark->has_bias_pattern(), "invariant");
1325
1326 // The mark can be in one of the following states:
1327 // * Inflated - just return
1328 // * Stack-locked - coerce it to inflated
1329 // * INFLATING - busy wait for conversion to complete
1330 // * Neutral - aggressively inflate the object.
1331 // * BIASED - Illegal. We should never see this
1332
1333 // CASE: inflated
1334 if (mark->has_monitor()) {
1335 ObjectMonitor * inf = mark->monitor();
1336 markOop dmw = inf->header();
1337 assert(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1338 assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1339 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1340 return inf;
1341 }
1342
1343 // CASE: inflation in progress - inflating over a stack-lock.
1344 // Some other thread is converting from stack-locked to inflated.
1345 // Only that thread can complete inflation -- other threads must wait.
1346 // The INFLATING value is transient.
1347 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1348 // We could always eliminate polling by parking the thread on some auxiliary list.
1349 if (mark == markOopDesc::INFLATING()) {
1350 ReadStableMark(object);
1351 continue;
1352 }
1353
1354 // CASE: stack-locked
1355 // Could be stack-locked either by this thread or by some other thread.
1356 //
1357 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1358 // to install INFLATING into the mark word. We originally installed INFLATING,
1359 // allocated the objectmonitor, and then finally STed the address of the
1360 // objectmonitor into the mark. This was correct, but artificially lengthened
1361 // the interval in which INFLATED appeared in the mark, thus increasing
1362 // the odds of inflation contention.
1363 //
1364 // We now use per-thread private objectmonitor free lists.
1365 // These list are reprovisioned from the global free list outside the
1366 // critical INFLATING...ST interval. A thread can transfer
1367 // multiple objectmonitors en-mass from the global free list to its local free list.
1368 // This reduces coherency traffic and lock contention on the global free list.
1369 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1370 // before or after the CAS(INFLATING) operation.
1371 // See the comments in omAlloc().
1372
1373 LogStreamHandle(Trace, monitorinflation) lsh;
1374
1375 if (mark->has_locker()) {
1376 ObjectMonitor * m = omAlloc(Self);
1377 // Optimistically prepare the objectmonitor - anticipate successful CAS
1378 // We do this before the CAS in order to minimize the length of time
1379 // in which INFLATING appears in the mark.
1380 m->Recycle();
1381 m->_Responsible = NULL;
1382 m->_recursions = 0;
1383 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1384
1385 markOop cmp = object->cas_set_mark(markOopDesc::INFLATING(), mark);
1386 if (cmp != mark) {
1387 omRelease(Self, m, true);
1388 continue; // Interference -- just retry
1389 }
1390
1391 // We've successfully installed INFLATING (0) into the mark-word.
1392 // This is the only case where 0 will appear in a mark-word.
1393 // Only the singular thread that successfully swings the mark-word
1394 // to 0 can perform (or more precisely, complete) inflation.
1395 //
1396 // Why do we CAS a 0 into the mark-word instead of just CASing the
1397 // mark-word from the stack-locked value directly to the new inflated state?
1398 // Consider what happens when a thread unlocks a stack-locked object.
1399 // It attempts to use CAS to swing the displaced header value from the
1400 // on-stack basiclock back into the object header. Recall also that the
1401 // header value (hash code, etc) can reside in (a) the object header, or
1402 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1403 // header in an objectMonitor. The inflate() routine must copy the header
1404 // value from the basiclock on the owner's stack to the objectMonitor, all
1405 // the while preserving the hashCode stability invariants. If the owner
1406 // decides to release the lock while the value is 0, the unlock will fail
1407 // and control will eventually pass from slow_exit() to inflate. The owner
1408 // will then spin, waiting for the 0 value to disappear. Put another way,
1409 // the 0 causes the owner to stall if the owner happens to try to
1410 // drop the lock (restoring the header from the basiclock to the object)
1411 // while inflation is in-progress. This protocol avoids races that might
1412 // would otherwise permit hashCode values to change or "flicker" for an object.
1413 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1414 // 0 serves as a "BUSY" inflate-in-progress indicator.
1415
1416
1417 // fetch the displaced mark from the owner's stack.
1418 // The owner can't die or unwind past the lock while our INFLATING
1419 // object is in the mark. Furthermore the owner can't complete
1420 // an unlock on the object, either.
1421 markOop dmw = mark->displaced_mark_helper();
1422 // Catch if the object's header is not neutral (not locked and
1423 // not marked is what we care about here).
1424 assert(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1425
1426 // Setup monitor fields to proper values -- prepare the monitor
1427 m->set_header(dmw);
1428
1429 // Optimization: if the mark->locker stack address is associated
1430 // with this thread we could simply set m->_owner = Self.
1431 // Note that a thread can inflate an object
1432 // that it has stack-locked -- as might happen in wait() -- directly
1433 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1434 m->set_owner(mark->locker());
1435 m->set_object(object);
1436 // TODO-FIXME: assert BasicLock->dhw != 0.
1437
1438 // Must preserve store ordering. The monitor state must
1439 // be stable at the time of publishing the monitor address.
1440 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1441 object->release_set_mark(markOopDesc::encode(m));
1442
1443 // Hopefully the performance counters are allocated on distinct cache lines
1444 // to avoid false sharing on MP systems ...
1445 OM_PERFDATA_OP(Inflations, inc());
1446 if (log_is_enabled(Trace, monitorinflation)) {
1447 ResourceMark rm(Self);
1448 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1449 INTPTR_FORMAT ", type='%s'", p2i(object),
1450 p2i(object->mark()), object->klass()->external_name());
1451 }
1452 if (event.should_commit()) {
1453 post_monitor_inflate_event(&event, object, cause);
1454 }
1455 return m;
1456 }
1457
1458 // CASE: neutral
1459 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1460 // If we know we're inflating for entry it's better to inflate by swinging a
1461 // pre-locked objectMonitor pointer into the object header. A successful
1462 // CAS inflates the object *and* confers ownership to the inflating thread.
1463 // In the current implementation we use a 2-step mechanism where we CAS()
1464 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1465 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1466 // would be useful.
1467
1468 // Catch if the object's header is not neutral (not locked and
1469 // not marked is what we care about here).
1470 assert(mark->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(mark));
1471 ObjectMonitor * m = omAlloc(Self);
1472 // prepare m for installation - set monitor to initial state
1473 m->Recycle();
1474 m->set_header(mark);
1475 m->set_owner(NULL);
1476 m->set_object(object);
1477 m->_recursions = 0;
1478 m->_Responsible = NULL;
1479 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1480
1481 if (object->cas_set_mark(markOopDesc::encode(m), mark) != mark) {
1482 m->set_header(NULL);
1483 m->set_object(NULL);
1484 m->Recycle();
1485 omRelease(Self, m, true);
1486 m = NULL;
1487 continue;
1488 // interference - the markword changed - just retry.
1489 // The state-transitions are one-way, so there's no chance of
1490 // live-lock -- "Inflated" is an absorbing state.
1491 }
1492
1493 // Hopefully the performance counters are allocated on distinct
1494 // cache lines to avoid false sharing on MP systems ...
1495 OM_PERFDATA_OP(Inflations, inc());
1496 if (log_is_enabled(Trace, monitorinflation)) {
1497 ResourceMark rm(Self);
1498 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1499 INTPTR_FORMAT ", type='%s'", p2i(object),
1500 p2i(object->mark()), object->klass()->external_name());
1501 }
1502 if (event.should_commit()) {
1503 post_monitor_inflate_event(&event, object, cause);
1504 }
1505 return m;
1506 }
1507 }
1508
1509
1510 // We maintain a list of in-use monitors for each thread.
1511 //
1512 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1513 // deflate_idle_monitors() scans only a global list of in-use monitors which
1514 // is populated only as a thread dies (see omFlush()).
1515 //
1516 // These operations are called at all safepoints, immediately after mutators
1517 // are stopped, but before any objects have moved. Collectively they traverse
1518 // the population of in-use monitors, deflating where possible. The scavenged
1519 // monitors are returned to the global monitor free list.
1520 //
1521 // Beware that we scavenge at *every* stop-the-world point. Having a large
1522 // number of monitors in-use could negatively impact performance. We also want
1523 // to minimize the total # of monitors in circulation, as they incur a small
1524 // footprint penalty.
1525 //
1526 // Perversely, the heap size -- and thus the STW safepoint rate --
1527 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1528 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1529 // This is an unfortunate aspect of this design.
1530
1531 // Deflate a single monitor if not in-use
1532 // Return true if deflated, false if in-use
1533 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1534 ObjectMonitor** freeHeadp,
1535 ObjectMonitor** freeTailp) {
1536 bool deflated;
1537 // Normal case ... The monitor is associated with obj.
1538 const markOop mark = obj->mark();
1539 guarantee(mark == markOopDesc::encode(mid), "should match: mark="
1540 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, p2i(mark),
1541 p2i(markOopDesc::encode(mid)));
1542 // Make sure that mark->monitor() and markOopDesc::encode() agree:
1543 guarantee(mark->monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
1544 ", mid=" INTPTR_FORMAT, p2i(mark->monitor()), p2i(mid));
1545 const markOop dmw = mid->header();
1546 guarantee(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1547
1548 if (mid->is_busy()) {
1549 deflated = false;
1550 } else {
1551 // Deflate the monitor if it is no longer being used
1552 // It's idle - scavenge and return to the global free list
1553 // plain old deflation ...
1554 if (log_is_enabled(Trace, monitorinflation)) {
1555 ResourceMark rm;
1556 log_trace(monitorinflation)("deflate_monitor: "
1557 "object=" INTPTR_FORMAT ", mark="
1558 INTPTR_FORMAT ", type='%s'", p2i(obj),
1559 p2i(mark), obj->klass()->external_name());
1560 }
1561
1562 // Restore the header back to obj
1563 obj->release_set_mark(dmw);
1564 mid->clear();
1565
1566 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
1567 p2i(mid->object()));
1568
1569 // Move the object to the working free list defined by freeHeadp, freeTailp
1570 if (*freeHeadp == NULL) *freeHeadp = mid;
1571 if (*freeTailp != NULL) {
1572 ObjectMonitor * prevtail = *freeTailp;
1573 assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1574 prevtail->FreeNext = mid;
1575 }
1576 *freeTailp = mid;
1577 deflated = true;
1578 }
1579 return deflated;
1580 }
1581
1582 // Walk a given monitor list, and deflate idle monitors
1583 // The given list could be a per-thread list or a global list
1584 // Caller acquires gListLock as needed.
1585 //
1586 // In the case of parallel processing of thread local monitor lists,
1587 // work is done by Threads::parallel_threads_do() which ensures that
1588 // each Java thread is processed by exactly one worker thread, and
1589 // thus avoid conflicts that would arise when worker threads would
1590 // process the same monitor lists concurrently.
1591 //
1592 // See also ParallelSPCleanupTask and
1593 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1594 // Threads::parallel_java_threads_do() in thread.cpp.
1595 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1596 ObjectMonitor** freeHeadp,
1597 ObjectMonitor** freeTailp) {
1598 ObjectMonitor* mid;
1599 ObjectMonitor* next;
1600 ObjectMonitor* cur_mid_in_use = NULL;
1601 int deflated_count = 0;
1602
1603 for (mid = *listHeadp; mid != NULL;) {
1604 oop obj = (oop) mid->object();
1605 if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1606 // if deflate_monitor succeeded,
1607 // extract from per-thread in-use list
1608 if (mid == *listHeadp) {
1609 *listHeadp = mid->FreeNext;
1610 } else if (cur_mid_in_use != NULL) {
1611 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1612 }
1613 next = mid->FreeNext;
1614 mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list
1615 mid = next;
1616 deflated_count++;
1617 } else {
1618 cur_mid_in_use = mid;
1619 mid = mid->FreeNext;
1620 }
1621 }
1622 return deflated_count;
1623 }
1624
1625 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1626 counters->nInuse = 0; // currently associated with objects
1627 counters->nInCirculation = 0; // extant
1628 counters->nScavenged = 0; // reclaimed (global and per-thread)
1629 counters->perThreadScavenged = 0; // per-thread scavenge total
1630 counters->perThreadTimes = 0.0; // per-thread scavenge times
1631 }
1632
1633 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
1634 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1635 bool deflated = false;
1636
1637 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1638 ObjectMonitor * freeTailp = NULL;
1639 elapsedTimer timer;
1640
1641 if (log_is_enabled(Info, monitorinflation)) {
1642 timer.start();
1643 }
1644
1645 // Prevent omFlush from changing mids in Thread dtor's during deflation
1646 // And in case the vm thread is acquiring a lock during a safepoint
1647 // See e.g. 6320749
1648 Thread::muxAcquire(&gListLock, "deflate_idle_monitors");
1649
1650 // Note: the thread-local monitors lists get deflated in
1651 // a separate pass. See deflate_thread_local_monitors().
1652
1653 // For moribund threads, scan gOmInUseList
1654 int deflated_count = 0;
1655 if (gOmInUseList) {
1656 counters->nInCirculation += gOmInUseCount;
1657 deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
1658 gOmInUseCount -= deflated_count;
1659 counters->nScavenged += deflated_count;
1660 counters->nInuse += gOmInUseCount;
1661 }
1662
1663 // Move the scavenged monitors back to the global free list.
1664 if (freeHeadp != NULL) {
1665 guarantee(freeTailp != NULL && counters->nScavenged > 0, "invariant");
1666 assert(freeTailp->FreeNext == NULL, "invariant");
1667 // constant-time list splice - prepend scavenged segment to gFreeList
1668 freeTailp->FreeNext = gFreeList;
1669 gFreeList = freeHeadp;
1670 }
1671 Thread::muxRelease(&gListLock);
1672 timer.stop();
1673
1674 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1675 LogStreamHandle(Info, monitorinflation) lsh_info;
1676 LogStream * ls = NULL;
1677 if (log_is_enabled(Debug, monitorinflation)) {
1678 ls = &lsh_debug;
1679 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
1680 ls = &lsh_info;
1681 }
1682 if (ls != NULL) {
1683 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
1684 }
1685 }
1686
1687 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1688 // Report the cumulative time for deflating each thread's idle
1689 // monitors. Note: if the work is split among more than one
1690 // worker thread, then the reported time will likely be more
1691 // than a beginning to end measurement of the phase.
1692 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->perThreadTimes, counters->perThreadScavenged);
1693
1694 gMonitorFreeCount += counters->nScavenged;
1695
1696 if (log_is_enabled(Debug, monitorinflation)) {
1697 // exit_globals()'s call to audit_and_print_stats() is done
1698 // at the Info level.
1699 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
1700 } else if (log_is_enabled(Info, monitorinflation)) {
1701 Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors");
1702 log_info(monitorinflation)("gMonitorPopulation=%d, gOmInUseCount=%d, "
1703 "gMonitorFreeCount=%d", gMonitorPopulation,
1704 gOmInUseCount, gMonitorFreeCount);
1705 Thread::muxRelease(&gListLock);
1706 }
1707
1708 ForceMonitorScavenge = 0; // Reset
1709
1710 OM_PERFDATA_OP(Deflations, inc(counters->nScavenged));
1711 OM_PERFDATA_OP(MonExtant, set_value(counters->nInCirculation));
1712
1713 GVars.stwRandom = os::random();
1714 GVars.stwCycle++;
1715 }
1716
1717 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
1718 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1719
1720 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1721 ObjectMonitor * freeTailp = NULL;
1722 elapsedTimer timer;
1723
1724 if (log_is_enabled(Info, safepoint, cleanup) ||
1725 log_is_enabled(Info, monitorinflation)) {
1726 timer.start();
1727 }
1728
1729 int deflated_count = deflate_monitor_list(thread->omInUseList_addr(), &freeHeadp, &freeTailp);
1730
1731 Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors");
1732
1733 // Adjust counters
1734 counters->nInCirculation += thread->omInUseCount;
1735 thread->omInUseCount -= deflated_count;
1736 counters->nScavenged += deflated_count;
1737 counters->nInuse += thread->omInUseCount;
1738 counters->perThreadScavenged += deflated_count;
1739
1740 // Move the scavenged monitors back to the global free list.
1741 if (freeHeadp != NULL) {
1742 guarantee(freeTailp != NULL && deflated_count > 0, "invariant");
1743 assert(freeTailp->FreeNext == NULL, "invariant");
1744
1745 // constant-time list splice - prepend scavenged segment to gFreeList
1746 freeTailp->FreeNext = gFreeList;
1747 gFreeList = freeHeadp;
1748 }
1749
1750 timer.stop();
1751 // Safepoint logging cares about cumulative perThreadTimes and
1752 // we'll capture most of the cost, but not the muxRelease() which
1753 // should be cheap.
1754 counters->perThreadTimes += timer.seconds();
1755
1756 Thread::muxRelease(&gListLock);
1757
1758 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1759 LogStreamHandle(Info, monitorinflation) lsh_info;
1760 LogStream * ls = NULL;
1761 if (log_is_enabled(Debug, monitorinflation)) {
1762 ls = &lsh_debug;
1763 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
1764 ls = &lsh_info;
1765 }
1766 if (ls != NULL) {
1767 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
1768 }
1769 }
1770
1771 // Monitor cleanup on JavaThread::exit
1772
1773 // Iterate through monitor cache and attempt to release thread's monitors
1774 // Gives up on a particular monitor if an exception occurs, but continues
1775 // the overall iteration, swallowing the exception.
1776 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1777 private:
1778 TRAPS;
1779
1780 public:
1781 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1782 void do_monitor(ObjectMonitor* mid) {
1783 if (mid->owner() == THREAD) {
1784 (void)mid->complete_exit(CHECK);
1785 }
1786 }
1787 };
1788
1789 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1790 // ignored. This is meant to be called during JNI thread detach which assumes
1791 // all remaining monitors are heavyweight. All exceptions are swallowed.
1792 // Scanning the extant monitor list can be time consuming.
1793 // A simple optimization is to add a per-thread flag that indicates a thread
1794 // called jni_monitorenter() during its lifetime.
1795 //
1796 // Instead of No_Savepoint_Verifier it might be cheaper to
1797 // use an idiom of the form:
1798 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1799 // <code that must not run at safepoint>
1800 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1801 // Since the tests are extremely cheap we could leave them enabled
1802 // for normal product builds.
1803
1804 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1805 assert(THREAD == JavaThread::current(), "must be current Java thread");
1806 NoSafepointVerifier nsv;
1807 ReleaseJavaMonitorsClosure rjmc(THREAD);
1808 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
1809 ObjectSynchronizer::monitors_iterate(&rjmc);
1810 Thread::muxRelease(&gListLock);
1811 THREAD->clear_pending_exception();
1812 }
1813
1814 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1815 switch (cause) {
1816 case inflate_cause_vm_internal: return "VM Internal";
1817 case inflate_cause_monitor_enter: return "Monitor Enter";
1818 case inflate_cause_wait: return "Monitor Wait";
1819 case inflate_cause_notify: return "Monitor Notify";
1820 case inflate_cause_hash_code: return "Monitor Hash Code";
1821 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1822 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1823 default:
1824 ShouldNotReachHere();
1825 }
1826 return "Unknown";
1827 }
1828
1829 //------------------------------------------------------------------------------
1830 // Debugging code
1831
1832 u_char* ObjectSynchronizer::get_gvars_addr() {
1833 return (u_char*)&GVars;
1834 }
1835
1836 u_char* ObjectSynchronizer::get_gvars_hcSequence_addr() {
1837 return (u_char*)&GVars.hcSequence;
1838 }
1839
1840 size_t ObjectSynchronizer::get_gvars_size() {
1841 return sizeof(SharedGlobals);
1842 }
1843
1844 u_char* ObjectSynchronizer::get_gvars_stwRandom_addr() {
1845 return (u_char*)&GVars.stwRandom;
1846 }
1847
1848 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1849 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1850
1851 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1852 LogStreamHandle(Info, monitorinflation) lsh_info;
1853 LogStreamHandle(Trace, monitorinflation) lsh_trace;
1854 LogStream * ls = NULL;
1855 if (log_is_enabled(Trace, monitorinflation)) {
1856 ls = &lsh_trace;
1857 } else if (log_is_enabled(Debug, monitorinflation)) {
1858 ls = &lsh_debug;
1859 } else if (log_is_enabled(Info, monitorinflation)) {
1860 ls = &lsh_info;
1861 }
1862 assert(ls != NULL, "sanity check");
1863
1864 if (!on_exit) {
1865 // Not at VM exit so grab the global list lock.
1866 Thread::muxAcquire(&gListLock, "audit_and_print_stats");
1867 }
1868
1869 // Log counts for the global and per-thread monitor lists:
1870 int chkMonitorPopulation = log_monitor_list_counts(ls);
1871 int error_cnt = 0;
1872
1873 ls->print_cr("Checking global lists:");
1874
1875 // Check gMonitorPopulation:
1876 if (gMonitorPopulation == chkMonitorPopulation) {
1877 ls->print_cr("gMonitorPopulation=%d equals chkMonitorPopulation=%d",
1878 gMonitorPopulation, chkMonitorPopulation);
1879 } else {
1880 ls->print_cr("ERROR: gMonitorPopulation=%d is not equal to "
1881 "chkMonitorPopulation=%d", gMonitorPopulation,
1882 chkMonitorPopulation);
1883 error_cnt++;
1884 }
1885
1886 // Check gOmInUseList and gOmInUseCount:
1887 chk_global_in_use_list_and_count(ls, &error_cnt);
1888
1889 // Check gFreeList and gMonitorFreeCount:
1890 chk_global_free_list_and_count(ls, &error_cnt);
1891
1892 if (!on_exit) {
1893 Thread::muxRelease(&gListLock);
1894 }
1895
1896 ls->print_cr("Checking per-thread lists:");
1897
1898 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
1899 // Check omInUseList and omInUseCount:
1900 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
1901
1902 // Check omFreeList and omFreeCount:
1903 chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
1904 }
1905
1906 if (error_cnt == 0) {
1907 ls->print_cr("No errors found in monitor list checks.");
1908 } else {
1909 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
1910 }
1911
1912 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1913 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1914 // When exiting this log output is at the Info level. When called
1915 // at a safepoint, this log output is at the Trace level since
1916 // there can be a lot of it.
1917 log_in_use_monitor_details(ls, on_exit);
1918 }
1919
1920 ls->flush();
1921
1922 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1923 }
1924
1925 // Check a free monitor entry; log any errors.
1926 void ObjectSynchronizer::chk_free_entry(JavaThread * jt, ObjectMonitor * n,
1927 outputStream * out, int *error_cnt_p) {
1928 if (n->is_busy()) {
1929 if (jt != NULL) {
1930 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1931 ": free per-thread monitor must not be busy.", p2i(jt),
1932 p2i(n));
1933 } else {
1934 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1935 "must not be busy.", p2i(n));
1936 }
1937 *error_cnt_p = *error_cnt_p + 1;
1938 }
1939 if (n->header() != NULL) {
1940 if (jt != NULL) {
1941 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1942 ": free per-thread monitor must have NULL _header "
1943 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
1944 p2i(n->header()));
1945 } else {
1946 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1947 "must have NULL _header field: _header=" INTPTR_FORMAT,
1948 p2i(n), p2i(n->header()));
1949 }
1950 *error_cnt_p = *error_cnt_p + 1;
1951 }
1952 if (n->object() != NULL) {
1953 if (jt != NULL) {
1954 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1955 ": free per-thread monitor must have NULL _object "
1956 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
1957 p2i(n->object()));
1958 } else {
1959 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1960 "must have NULL _object field: _object=" INTPTR_FORMAT,
1961 p2i(n), p2i(n->object()));
1962 }
1963 *error_cnt_p = *error_cnt_p + 1;
1964 }
1965 }
1966
1967 // Check the global free list and count; log the results of the checks.
1968 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
1969 int *error_cnt_p) {
1970 int chkMonitorFreeCount = 0;
1971 for (ObjectMonitor * n = gFreeList; n != NULL; n = n->FreeNext) {
1972 chk_free_entry(NULL /* jt */, n, out, error_cnt_p);
1973 chkMonitorFreeCount++;
1974 }
1975 if (gMonitorFreeCount == chkMonitorFreeCount) {
1976 out->print_cr("gMonitorFreeCount=%d equals chkMonitorFreeCount=%d",
1977 gMonitorFreeCount, chkMonitorFreeCount);
1978 } else {
1979 out->print_cr("ERROR: gMonitorFreeCount=%d is not equal to "
1980 "chkMonitorFreeCount=%d", gMonitorFreeCount,
1981 chkMonitorFreeCount);
1982 *error_cnt_p = *error_cnt_p + 1;
1983 }
1984 }
1985
1986 // Check the global in-use list and count; log the results of the checks.
1987 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
1988 int *error_cnt_p) {
1989 int chkOmInUseCount = 0;
1990 for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
1991 chk_in_use_entry(NULL /* jt */, n, out, error_cnt_p);
1992 chkOmInUseCount++;
1993 }
1994 if (gOmInUseCount == chkOmInUseCount) {
1995 out->print_cr("gOmInUseCount=%d equals chkOmInUseCount=%d", gOmInUseCount,
1996 chkOmInUseCount);
1997 } else {
1998 out->print_cr("ERROR: gOmInUseCount=%d is not equal to chkOmInUseCount=%d",
1999 gOmInUseCount, chkOmInUseCount);
2000 *error_cnt_p = *error_cnt_p + 1;
2001 }
2002 }
2003
2004 // Check an in-use monitor entry; log any errors.
2005 void ObjectSynchronizer::chk_in_use_entry(JavaThread * jt, ObjectMonitor * n,
2006 outputStream * out, int *error_cnt_p) {
2007 if (n->header() == NULL) {
2008 if (jt != NULL) {
2009 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2010 ": in-use per-thread monitor must have non-NULL _header "
2011 "field.", p2i(jt), p2i(n));
2012 } else {
2013 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2014 "must have non-NULL _header field.", p2i(n));
2015 }
2016 *error_cnt_p = *error_cnt_p + 1;
2017 }
2018 if (n->object() == NULL) {
2019 if (jt != NULL) {
2020 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2021 ": in-use per-thread monitor must have non-NULL _object "
2022 "field.", p2i(jt), p2i(n));
2023 } else {
2024 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2025 "must have non-NULL _object field.", p2i(n));
2026 }
2027 *error_cnt_p = *error_cnt_p + 1;
2028 }
2029 const oop obj = (oop)n->object();
2030 const markOop mark = obj->mark();
2031 if (!mark->has_monitor()) {
2032 if (jt != NULL) {
2033 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2034 ": in-use per-thread monitor's object does not think "
2035 "it has a monitor: obj=" INTPTR_FORMAT ", mark="
2036 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), p2i(mark));
2037 } else {
2038 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2039 "monitor's object does not think it has a monitor: obj="
2040 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2041 p2i(obj), p2i(mark));
2042 }
2043 *error_cnt_p = *error_cnt_p + 1;
2044 }
2045 ObjectMonitor * const obj_mon = mark->monitor();
2046 if (n != obj_mon) {
2047 if (jt != NULL) {
2048 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2049 ": in-use per-thread monitor's object does not refer "
2050 "to the same monitor: obj=" INTPTR_FORMAT ", mark="
2051 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
2052 p2i(n), p2i(obj), p2i(mark), p2i(obj_mon));
2053 } else {
2054 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2055 "monitor's object does not refer to the same monitor: obj="
2056 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2057 INTPTR_FORMAT, p2i(n), p2i(obj), p2i(mark), p2i(obj_mon));
2058 }
2059 *error_cnt_p = *error_cnt_p + 1;
2060 }
2061 }
2062
2063 // Check the thread's free list and count; log the results of the checks.
2064 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
2065 outputStream * out,
2066 int *error_cnt_p) {
2067 int chkOmFreeCount = 0;
2068 for (ObjectMonitor * n = jt->omFreeList; n != NULL; n = n->FreeNext) {
2069 chk_free_entry(jt, n, out, error_cnt_p);
2070 chkOmFreeCount++;
2071 }
2072 if (jt->omFreeCount == chkOmFreeCount) {
2073 out->print_cr("jt=" INTPTR_FORMAT ": omFreeCount=%d equals "
2074 "chkOmFreeCount=%d", p2i(jt), jt->omFreeCount, chkOmFreeCount);
2075 } else {
2076 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omFreeCount=%d is not "
2077 "equal to chkOmFreeCount=%d", p2i(jt), jt->omFreeCount,
2078 chkOmFreeCount);
2079 *error_cnt_p = *error_cnt_p + 1;
2080 }
2081 }
2082
2083 // Check the thread's in-use list and count; log the results of the checks.
2084 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
2085 outputStream * out,
2086 int *error_cnt_p) {
2087 int chkOmInUseCount = 0;
2088 for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2089 chk_in_use_entry(jt, n, out, error_cnt_p);
2090 chkOmInUseCount++;
2091 }
2092 if (jt->omInUseCount == chkOmInUseCount) {
2093 out->print_cr("jt=" INTPTR_FORMAT ": omInUseCount=%d equals "
2094 "chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2095 chkOmInUseCount);
2096 } else {
2097 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omInUseCount=%d is not "
2098 "equal to chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2099 chkOmInUseCount);
2100 *error_cnt_p = *error_cnt_p + 1;
2101 }
2102 }
2103
2104 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2105 // flags indicate why the entry is in-use, 'object' and 'object type'
2106 // indicate the associated object and its type.
2107 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out,
2108 bool on_exit) {
2109 if (!on_exit) {
2110 // Not at VM exit so grab the global list lock.
2111 Thread::muxAcquire(&gListLock, "log_in_use_monitor_details");
2112 }
2113
2114 if (gOmInUseCount > 0) {
2115 out->print_cr("In-use global monitor info:");
2116 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2117 out->print_cr("%18s %s %18s %18s",
2118 "monitor", "BHL", "object", "object type");
2119 out->print_cr("================== === ================== ==================");
2120 for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
2121 const oop obj = (oop) n->object();
2122 const markOop mark = n->header();
2123 ResourceMark rm;
2124 out->print_cr(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(n),
2125 n->is_busy() != 0, mark->hash() != 0, n->owner() != NULL,
2126 p2i(obj), obj->klass()->external_name());
2127 }
2128 }
2129
2130 if (!on_exit) {
2131 Thread::muxRelease(&gListLock);
2132 }
2133
2134 out->print_cr("In-use per-thread monitor info:");
2135 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2136 out->print_cr("%18s %18s %s %18s %18s",
2137 "jt", "monitor", "BHL", "object", "object type");
2138 out->print_cr("================== ================== === ================== ==================");
2139 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2140 for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2141 const oop obj = (oop) n->object();
2142 const markOop mark = n->header();
2143 ResourceMark rm;
2144 out->print_cr(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT
2145 " %s", p2i(jt), p2i(n), n->is_busy() != 0,
2146 mark->hash() != 0, n->owner() != NULL, p2i(obj),
2147 obj->klass()->external_name());
2148 }
2149 }
2150
2151 out->flush();
2152 }
2153
2154 // Log counts for the global and per-thread monitor lists and return
2155 // the population count.
2156 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2157 int popCount = 0;
2158 out->print_cr("%18s %10s %10s %10s",
2159 "Global Lists:", "InUse", "Free", "Total");
2160 out->print_cr("================== ========== ========== ==========");
2161 out->print_cr("%18s %10d %10d %10d", "",
2162 gOmInUseCount, gMonitorFreeCount, gMonitorPopulation);
2163 popCount += gOmInUseCount + gMonitorFreeCount;
2164
2165 out->print_cr("%18s %10s %10s %10s",
2166 "Per-Thread Lists:", "InUse", "Free", "Provision");
2167 out->print_cr("================== ========== ========== ==========");
2168
2169 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2170 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
2171 jt->omInUseCount, jt->omFreeCount, jt->omFreeProvision);
2172 popCount += jt->omInUseCount + jt->omFreeCount;
2173 }
2174 return popCount;
2175 }
2176
2177 #ifndef PRODUCT
2178
2179 // Check if monitor belongs to the monitor cache
2180 // The list is grow-only so it's *relatively* safe to traverse
2181 // the list of extant blocks without taking a lock.
2182
2183 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
2184 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
2185 while (block != NULL) {
2186 assert(block->object() == CHAINMARKER, "must be a block header");
2187 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
2188 address mon = (address)monitor;
2189 address blk = (address)block;
2190 size_t diff = mon - blk;
2191 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "must be aligned");
2192 return 1;
2193 }
2194 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
2195 }
2196 return 0;
2197 }
2198
2199 #endif