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 "oops/markOop.hpp"
35 #include "oops/oop.inline.hpp"
36 #include "runtime/atomic.hpp"
37 #include "runtime/biasedLocking.hpp"
38 #include "runtime/handles.inline.hpp"
39 #include "runtime/interfaceSupport.inline.hpp"
40 #include "runtime/mutexLocker.hpp"
41 #include "runtime/objectMonitor.hpp"
42 #include "runtime/objectMonitor.inline.hpp"
43 #include "runtime/osThread.hpp"
44 #include "runtime/safepointVerifiers.hpp"
45 #include "runtime/sharedRuntime.hpp"
46 #include "runtime/stubRoutines.hpp"
47 #include "runtime/synchronizer.hpp"
48 #include "runtime/thread.inline.hpp"
49 #include "runtime/timer.hpp"
50 #include "runtime/vframe.hpp"
51 #include "runtime/vmThread.hpp"
52 #include "utilities/align.hpp"
53 #include "utilities/dtrace.hpp"
54 #include "utilities/events.hpp"
55 #include "utilities/preserveException.hpp"
56
57 // The "core" versions of monitor enter and exit reside in this file.
58 // The interpreter and compilers contain specialized transliterated
59 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
60 // for instance. If you make changes here, make sure to modify the
61 // interpreter, and both C1 and C2 fast-path inline locking code emission.
62 //
63 // -----------------------------------------------------------------------------
64
65 #ifdef DTRACE_ENABLED
66
67 // Only bother with this argument setup if dtrace is available
68 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
69
70 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
71 char* bytes = NULL; \
72 int len = 0; \
73 jlong jtid = SharedRuntime::get_java_tid(thread); \
74 Symbol* klassname = ((oop)(obj))->klass()->name(); \
75 if (klassname != NULL) { \
76 bytes = (char*)klassname->bytes(); \
77 len = klassname->utf8_length(); \
78 }
79
80 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
81 { \
82 if (DTraceMonitorProbes) { \
83 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
84 HOTSPOT_MONITOR_WAIT(jtid, \
85 (uintptr_t)(monitor), bytes, len, (millis)); \
86 } \
87 }
88
89 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
90 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
91 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
92
93 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
94 { \
95 if (DTraceMonitorProbes) { \
96 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
97 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
98 (uintptr_t)(monitor), bytes, len); \
99 } \
100 }
101
102 #else // ndef DTRACE_ENABLED
103
104 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
105 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
106
107 #endif // ndef DTRACE_ENABLED
108
109 // This exists only as a workaround of dtrace bug 6254741
110 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
111 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
112 return 0;
113 }
114
115 #define NINFLATIONLOCKS 256
116 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
117
118 // global list of blocks of monitors
119 PaddedEnd<ObjectMonitor> * volatile ObjectSynchronizer::gBlockList = NULL;
120 // global monitor free list
121 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL;
122 // global monitor in-use list, for moribund threads,
123 // monitors they inflated need to be scanned for deflation
124 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL;
125 // count of entries in gOmInUseList
126 int ObjectSynchronizer::gOmInUseCount = 0;
127 bool ObjectSynchronizer::_gOmShouldDeflateIdleMonitors = false;
128 bool volatile ObjectSynchronizer::_is_cleanup_requested = false;
129
130 static volatile intptr_t gListLock = 0; // protects global monitor lists
131 static volatile int gMonitorFreeCount = 0; // # on gFreeList
132 static volatile int gMonitorPopulation = 0; // # Extant -- in circulation
133
134 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
135
136
137 // =====================> Quick functions
138
139 // The quick_* forms are special fast-path variants used to improve
140 // performance. In the simplest case, a "quick_*" implementation could
141 // simply return false, in which case the caller will perform the necessary
142 // state transitions and call the slow-path form.
143 // The fast-path is designed to handle frequently arising cases in an efficient
144 // manner and is just a degenerate "optimistic" variant of the slow-path.
145 // returns true -- to indicate the call was satisfied.
146 // returns false -- to indicate the call needs the services of the slow-path.
147 // A no-loitering ordinance is in effect for code in the quick_* family
148 // operators: safepoints or indefinite blocking (blocking that might span a
149 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
150 // entry.
151 //
152 // Consider: An interesting optimization is to have the JIT recognize the
153 // following common idiom:
154 // synchronized (someobj) { .... ; notify(); }
155 // That is, we find a notify() or notifyAll() call that immediately precedes
156 // the monitorexit operation. In that case the JIT could fuse the operations
157 // into a single notifyAndExit() runtime primitive.
158
159 bool ObjectSynchronizer::quick_notify(oopDesc * obj, Thread * self, bool all) {
160 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
161 assert(self->is_Java_thread(), "invariant");
162 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
163 NoSafepointVerifier nsv;
164 if (obj == NULL) return false; // slow-path for invalid obj
165 const markOop mark = obj->mark();
166
167 if (mark->has_locker() && self->is_lock_owned((address)mark->locker())) {
168 // Degenerate notify
169 // stack-locked by caller so by definition the implied waitset is empty.
170 return true;
171 }
172
173 if (mark->has_monitor()) {
174 ObjectMonitor * const mon = mark->monitor();
175 assert(oopDesc::equals((oop) mon->object(), obj), "invariant");
176 if (mon->owner() != self) return false; // slow-path for IMS exception
177
178 if (mon->first_waiter() != NULL) {
179 // We have one or more waiters. Since this is an inflated monitor
180 // that we own, we can transfer one or more threads from the waitset
181 // to the entrylist here and now, avoiding the slow-path.
182 if (all) {
183 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
184 } else {
185 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
186 }
187 int tally = 0;
188 do {
189 mon->INotify(self);
190 ++tally;
191 } while (mon->first_waiter() != NULL && all);
192 OM_PERFDATA_OP(Notifications, inc(tally));
193 }
194 return true;
195 }
196
197 // biased locking and any other IMS exception states take the slow-path
198 return false;
199 }
200
201
202 // The LockNode emitted directly at the synchronization site would have
203 // been too big if it were to have included support for the cases of inflated
204 // recursive enter and exit, so they go here instead.
205 // Note that we can't safely call AsyncPrintJavaStack() from within
206 // quick_enter() as our thread state remains _in_Java.
207
208 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
209 BasicLock * lock) {
210 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
211 assert(Self->is_Java_thread(), "invariant");
212 assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
213 NoSafepointVerifier nsv;
214 if (obj == NULL) return false; // Need to throw NPE
215
216 while (true) {
217 const markOop mark = obj->mark();
218
219 if (mark->has_monitor()) {
220 ObjectMonitorHandle omh;
221 if (!omh.save_om_ptr(obj, mark)) {
222 // Lost a race with async deflation so try again.
223 assert(AsyncDeflateIdleMonitors, "sanity check");
224 continue;
225 }
226 ObjectMonitor * const m = omh.om_ptr();
227 assert(oopDesc::equals((oop) m->object(), obj), "invariant");
228 Thread * const owner = (Thread *) m->_owner;
229
230 // Lock contention and Transactional Lock Elision (TLE) diagnostics
231 // and observability
232 // Case: light contention possibly amenable to TLE
233 // Case: TLE inimical operations such as nested/recursive synchronization
234
235 if (owner == Self) {
236 m->_recursions++;
237 return true;
238 }
239
240 // This Java Monitor is inflated so obj's header will never be
241 // displaced to this thread's BasicLock. Make the displaced header
242 // non-NULL so this BasicLock is not seen as recursive nor as
243 // being locked. We do this unconditionally so that this thread's
244 // BasicLock cannot be mis-interpreted by any stack walkers. For
245 // performance reasons, stack walkers generally first check for
246 // Biased Locking in the object's header, the second check is for
247 // stack-locking in the object's header, the third check is for
248 // recursive stack-locking in the displaced header in the BasicLock,
249 // and last are the inflated Java Monitor (ObjectMonitor) checks.
250 lock->set_displaced_header(markOopDesc::unused_mark());
251
252 if (owner == NULL && Atomic::replace_if_null(Self, &(m->_owner))) {
253 assert(m->_recursions == 0, "invariant");
254 assert(m->_owner == Self, "invariant");
255 return true;
256 }
257 }
258 break;
259 }
260
261 // Note that we could inflate in quick_enter.
262 // This is likely a useful optimization
263 // Critically, in quick_enter() we must not:
264 // -- perform bias revocation, or
265 // -- block indefinitely, or
266 // -- reach a safepoint
267
268 return false; // revert to slow-path
269 }
270
271 // -----------------------------------------------------------------------------
272 // Fast Monitor Enter/Exit
273 // This the fast monitor enter. The interpreter and compiler use
274 // some assembly copies of this code. Make sure update those code
275 // if the following function is changed. The implementation is
276 // extremely sensitive to race condition. Be careful.
277
278 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
279 bool attempt_rebias, TRAPS) {
280 if (UseBiasedLocking) {
281 if (!SafepointSynchronize::is_at_safepoint()) {
282 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
283 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
284 return;
285 }
286 } else {
287 assert(!attempt_rebias, "can not rebias toward VM thread");
288 BiasedLocking::revoke_at_safepoint(obj);
289 }
290 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
291 }
292
293 slow_enter(obj, lock, THREAD);
294 }
295
296 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
297 markOop mark = object->mark();
298 // We cannot check for Biased Locking if we are racing an inflation.
299 assert(mark == markOopDesc::INFLATING() ||
300 !mark->has_bias_pattern(), "should not see bias pattern here");
301
302 markOop dhw = lock->displaced_header();
303 if (dhw == NULL) {
304 // If the displaced header is NULL, then this exit matches up with
305 // a recursive enter. No real work to do here except for diagnostics.
306 #ifndef PRODUCT
307 if (mark != markOopDesc::INFLATING()) {
308 // Only do diagnostics if we are not racing an inflation. Simply
309 // exiting a recursive enter of a Java Monitor that is being
310 // inflated is safe; see the has_monitor() comment below.
311 assert(!mark->is_neutral(), "invariant");
312 assert(!mark->has_locker() ||
313 THREAD->is_lock_owned((address)mark->locker()), "invariant");
314 if (mark->has_monitor()) {
315 // The BasicLock's displaced_header is marked as a recursive
316 // enter and we have an inflated Java Monitor (ObjectMonitor).
317 // This is a special case where the Java Monitor was inflated
318 // after this thread entered the stack-lock recursively. When a
319 // Java Monitor is inflated, we cannot safely walk the Java
320 // Monitor owner's stack and update the BasicLocks because a
321 // Java Monitor can be asynchronously inflated by a thread that
322 // does not own the Java Monitor.
323 ObjectMonitor * m = mark->monitor();
324 assert(((oop)(m->object()))->mark() == mark, "invariant");
325 assert(m->is_entered(THREAD), "invariant");
326 }
327 }
328 #endif
329 return;
330 }
331
332 if (mark == (markOop) lock) {
333 // If the object is stack-locked by the current thread, try to
334 // swing the displaced header from the BasicLock back to the mark.
335 assert(dhw->is_neutral(), "invariant");
336 if (object->cas_set_mark(dhw, mark) == mark) {
337 return;
338 }
339 }
340
341 // We have to take the slow-path of possible inflation and then exit.
342 ObjectMonitorHandle omh;
343 inflate(&omh, THREAD, object, inflate_cause_vm_internal);
344 omh.om_ptr()->exit(true, THREAD);
345 }
346
347 // -----------------------------------------------------------------------------
348 // Interpreter/Compiler Slow Case
349 // This routine is used to handle interpreter/compiler slow case
350 // We don't need to use fast path here, because it must have been
351 // failed in the interpreter/compiler code.
352 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
353 markOop mark = obj->mark();
354 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
355
356 if (mark->is_neutral()) {
357 // Anticipate successful CAS -- the ST of the displaced mark must
358 // be visible <= the ST performed by the CAS.
359 lock->set_displaced_header(mark);
360 if (mark == obj()->cas_set_mark((markOop) lock, mark)) {
361 return;
362 }
363 // Fall through to inflate() ...
364 } else if (mark->has_locker() &&
365 THREAD->is_lock_owned((address)mark->locker())) {
366 assert(lock != mark->locker(), "must not re-lock the same lock");
367 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
368 lock->set_displaced_header(NULL);
369 return;
370 }
371
372 // The object header will never be displaced to this lock,
373 // so it does not matter what the value is, except that it
374 // must be non-zero to avoid looking like a re-entrant lock,
375 // and must not look locked either.
376 lock->set_displaced_header(markOopDesc::unused_mark());
377 ObjectMonitorHandle omh;
378 inflate(&omh, THREAD, obj(), inflate_cause_monitor_enter);
379 omh.om_ptr()->enter(THREAD);
380 }
381
382 // This routine is used to handle interpreter/compiler slow case
383 // We don't need to use fast path here, because it must have
384 // failed in the interpreter/compiler code. Simply use the heavy
385 // weight monitor should be ok, unless someone find otherwise.
386 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
387 fast_exit(object, lock, THREAD);
388 }
389
390 // -----------------------------------------------------------------------------
391 // Class Loader support to workaround deadlocks on the class loader lock objects
392 // Also used by GC
393 // complete_exit()/reenter() are used to wait on a nested lock
394 // i.e. to give up an outer lock completely and then re-enter
395 // Used when holding nested locks - lock acquisition order: lock1 then lock2
396 // 1) complete_exit lock1 - saving recursion count
397 // 2) wait on lock2
398 // 3) when notified on lock2, unlock lock2
399 // 4) reenter lock1 with original recursion count
400 // 5) lock lock2
401 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
402 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
403 if (UseBiasedLocking) {
404 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
405 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
406 }
407
408 ObjectMonitorHandle omh;
409 inflate(&omh, THREAD, obj(), inflate_cause_vm_internal);
410 intptr_t ret_code = omh.om_ptr()->complete_exit(THREAD);
411 return ret_code;
412 }
413
414 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
415 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
416 if (UseBiasedLocking) {
417 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
418 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
419 }
420
421 ObjectMonitorHandle omh;
422 inflate(&omh, THREAD, obj(), inflate_cause_vm_internal);
423 omh.om_ptr()->reenter(recursion, THREAD);
424 }
425 // -----------------------------------------------------------------------------
426 // JNI locks on java objects
427 // NOTE: must use heavy weight monitor to handle jni monitor enter
428 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
429 // the current locking is from JNI instead of Java code
430 if (UseBiasedLocking) {
431 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
432 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
433 }
434 THREAD->set_current_pending_monitor_is_from_java(false);
435 ObjectMonitorHandle omh;
436 inflate(&omh, THREAD, obj(), inflate_cause_jni_enter);
437 omh.om_ptr()->enter(THREAD);
438 THREAD->set_current_pending_monitor_is_from_java(true);
439 }
440
441 // NOTE: must use heavy weight monitor to handle jni monitor exit
442 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
443 if (UseBiasedLocking) {
444 Handle h_obj(THREAD, obj);
445 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
446 obj = h_obj();
447 }
448 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
449
450 ObjectMonitorHandle omh;
451 inflate(&omh, THREAD, obj, inflate_cause_jni_exit);
452 ObjectMonitor * monitor = omh.om_ptr();
453 // If this thread has locked the object, exit the monitor. Note: can't use
454 // monitor->check(CHECK); must exit even if an exception is pending.
455 if (monitor->check(THREAD)) {
456 monitor->exit(true, THREAD);
457 }
458 }
459
460 // -----------------------------------------------------------------------------
461 // Internal VM locks on java objects
462 // standard constructor, allows locking failures
463 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
464 _dolock = doLock;
465 _thread = thread;
466 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
467 _obj = obj;
468
469 if (_dolock) {
470 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
471 }
472 }
473
474 ObjectLocker::~ObjectLocker() {
475 if (_dolock) {
476 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
477 }
478 }
479
480
481 // -----------------------------------------------------------------------------
482 // Wait/Notify/NotifyAll
483 // NOTE: must use heavy weight monitor to handle wait()
484 int ObjectSynchronizer::wait(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_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
491 }
492 ObjectMonitorHandle omh;
493 inflate(&omh, THREAD, obj(), inflate_cause_wait);
494 ObjectMonitor * monitor = omh.om_ptr();
495
496 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
497 monitor->wait(millis, true, THREAD);
498
499 // This dummy call is in place to get around dtrace bug 6254741. Once
500 // that's fixed we can uncomment the following line, remove the call
501 // and change this function back into a "void" func.
502 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
503 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
504 return ret_code;
505 }
506
507 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
508 if (UseBiasedLocking) {
509 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
510 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
511 }
512 if (millis < 0) {
513 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
514 }
515 ObjectMonitorHandle omh;
516 inflate(&omh, THREAD, obj(), inflate_cause_wait);
517 omh.om_ptr()->wait(millis, false, THREAD);
518 }
519
520 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
521 if (UseBiasedLocking) {
522 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
523 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
524 }
525
526 markOop mark = obj->mark();
527 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
528 return;
529 }
530 ObjectMonitorHandle omh;
531 inflate(&omh, THREAD, obj(), inflate_cause_notify);
532 omh.om_ptr()->notify(THREAD);
533 }
534
535 // NOTE: see comment of notify()
536 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
537 if (UseBiasedLocking) {
538 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
539 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
540 }
541
542 markOop mark = obj->mark();
543 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
544 return;
545 }
546 ObjectMonitorHandle omh;
547 inflate(&omh, THREAD, obj(), inflate_cause_notify);
548 omh.om_ptr()->notifyAll(THREAD);
549 }
550
551 // -----------------------------------------------------------------------------
552 // Hash Code handling
553 //
554 // Performance concern:
555 // OrderAccess::storestore() calls release() which at one time stored 0
556 // into the global volatile OrderAccess::dummy variable. This store was
557 // unnecessary for correctness. Many threads storing into a common location
558 // causes considerable cache migration or "sloshing" on large SMP systems.
559 // As such, I avoided using OrderAccess::storestore(). In some cases
560 // OrderAccess::fence() -- which incurs local latency on the executing
561 // processor -- is a better choice as it scales on SMP systems.
562 //
563 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
564 // a discussion of coherency costs. Note that all our current reference
565 // platforms provide strong ST-ST order, so the issue is moot on IA32,
566 // x64, and SPARC.
567 //
568 // As a general policy we use "volatile" to control compiler-based reordering
569 // and explicit fences (barriers) to control for architectural reordering
570 // performed by the CPU(s) or platform.
571
572 struct SharedGlobals {
573 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
574 // These are highly shared mostly-read variables.
575 // To avoid false-sharing they need to be the sole occupants of a cache line.
576 volatile int stwRandom;
577 volatile int stwCycle;
578 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
579 // Hot RW variable -- Sequester to avoid false-sharing
580 volatile int hcSequence;
581 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
582 };
583
584 static SharedGlobals GVars;
585 static int MonitorScavengeThreshold = 1000000;
586 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
587
588 static markOop ReadStableMark(oop obj) {
589 markOop mark = obj->mark();
590 if (!mark->is_being_inflated()) {
591 return mark; // normal fast-path return
592 }
593
594 int its = 0;
595 for (;;) {
596 markOop mark = obj->mark();
597 if (!mark->is_being_inflated()) {
598 return mark; // normal fast-path return
599 }
600
601 // The object is being inflated by some other thread.
602 // The caller of ReadStableMark() must wait for inflation to complete.
603 // Avoid live-lock
604 // TODO: consider calling SafepointSynchronize::do_call_back() while
605 // spinning to see if there's a safepoint pending. If so, immediately
606 // yielding or blocking would be appropriate. Avoid spinning while
607 // there is a safepoint pending.
608 // TODO: add inflation contention performance counters.
609 // TODO: restrict the aggregate number of spinners.
610
611 ++its;
612 if (its > 10000 || !os::is_MP()) {
613 if (its & 1) {
614 os::naked_yield();
615 } else {
616 // Note that the following code attenuates the livelock problem but is not
617 // a complete remedy. A more complete solution would require that the inflating
618 // thread hold the associated inflation lock. The following code simply restricts
619 // the number of spinners to at most one. We'll have N-2 threads blocked
620 // on the inflationlock, 1 thread holding the inflation lock and using
621 // a yield/park strategy, and 1 thread in the midst of inflation.
622 // A more refined approach would be to change the encoding of INFLATING
623 // to allow encapsulation of a native thread pointer. Threads waiting for
624 // inflation to complete would use CAS to push themselves onto a singly linked
625 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
626 // and calling park(). When inflation was complete the thread that accomplished inflation
627 // would detach the list and set the markword to inflated with a single CAS and
628 // then for each thread on the list, set the flag and unpark() the thread.
629 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
630 // wakes at most one thread whereas we need to wake the entire list.
631 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
632 int YieldThenBlock = 0;
633 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
634 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
635 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
636 while (obj->mark() == markOopDesc::INFLATING()) {
637 // Beware: NakedYield() is advisory and has almost no effect on some platforms
638 // so we periodically call Self->_ParkEvent->park(1).
639 // We use a mixed spin/yield/block mechanism.
640 if ((YieldThenBlock++) >= 16) {
641 Thread::current()->_ParkEvent->park(1);
642 } else {
643 os::naked_yield();
644 }
645 }
646 Thread::muxRelease(gInflationLocks + ix);
647 }
648 } else {
649 SpinPause(); // SMP-polite spinning
650 }
651 }
652 }
653
654 // hashCode() generation :
655 //
656 // Possibilities:
657 // * MD5Digest of {obj,stwRandom}
658 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
659 // * A DES- or AES-style SBox[] mechanism
660 // * One of the Phi-based schemes, such as:
661 // 2654435761 = 2^32 * Phi (golden ratio)
662 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
663 // * A variation of Marsaglia's shift-xor RNG scheme.
664 // * (obj ^ stwRandom) is appealing, but can result
665 // in undesirable regularity in the hashCode values of adjacent objects
666 // (objects allocated back-to-back, in particular). This could potentially
667 // result in hashtable collisions and reduced hashtable efficiency.
668 // There are simple ways to "diffuse" the middle address bits over the
669 // generated hashCode values:
670
671 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
672 intptr_t value = 0;
673 if (hashCode == 0) {
674 // This form uses global Park-Miller RNG.
675 // On MP system we'll have lots of RW access to a global, so the
676 // mechanism induces lots of coherency traffic.
677 value = os::random();
678 } else if (hashCode == 1) {
679 // This variation has the property of being stable (idempotent)
680 // between STW operations. This can be useful in some of the 1-0
681 // synchronization schemes.
682 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
683 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
684 } else if (hashCode == 2) {
685 value = 1; // for sensitivity testing
686 } else if (hashCode == 3) {
687 value = ++GVars.hcSequence;
688 } else if (hashCode == 4) {
689 value = cast_from_oop<intptr_t>(obj);
690 } else {
691 // Marsaglia's xor-shift scheme with thread-specific state
692 // This is probably the best overall implementation -- we'll
693 // likely make this the default in future releases.
694 unsigned t = Self->_hashStateX;
695 t ^= (t << 11);
696 Self->_hashStateX = Self->_hashStateY;
697 Self->_hashStateY = Self->_hashStateZ;
698 Self->_hashStateZ = Self->_hashStateW;
699 unsigned v = Self->_hashStateW;
700 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
701 Self->_hashStateW = v;
702 value = v;
703 }
704
705 value &= markOopDesc::hash_mask;
706 if (value == 0) value = 0xBAD;
707 assert(value != markOopDesc::no_hash, "invariant");
708 return value;
709 }
710
711 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
712 if (UseBiasedLocking) {
713 // NOTE: many places throughout the JVM do not expect a safepoint
714 // to be taken here, in particular most operations on perm gen
715 // objects. However, we only ever bias Java instances and all of
716 // the call sites of identity_hash that might revoke biases have
717 // been checked to make sure they can handle a safepoint. The
718 // added check of the bias pattern is to avoid useless calls to
719 // thread-local storage.
720 if (obj->mark()->has_bias_pattern()) {
721 // Handle for oop obj in case of STW safepoint
722 Handle hobj(Self, obj);
723 // Relaxing assertion for bug 6320749.
724 assert(Universe::verify_in_progress() ||
725 !SafepointSynchronize::is_at_safepoint(),
726 "biases should not be seen by VM thread here");
727 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
728 obj = hobj();
729 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
730 }
731 }
732
733 // hashCode() is a heap mutator ...
734 // Relaxing assertion for bug 6320749.
735 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
736 !SafepointSynchronize::is_at_safepoint(), "invariant");
737 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
738 Self->is_Java_thread() , "invariant");
739 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
740 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
741
742 while (true) {
743 ObjectMonitor* monitor = NULL;
744 markOop temp, test;
745 intptr_t hash;
746 markOop mark = ReadStableMark(obj);
747
748 // object should remain ineligible for biased locking
749 assert(!mark->has_bias_pattern(), "invariant");
750
751 if (mark->is_neutral()) {
752 hash = mark->hash(); // this is a normal header
753 if (hash != 0) { // if it has hash, just return it
754 return hash;
755 }
756 hash = get_next_hash(Self, obj); // allocate a new hash code
757 temp = mark->copy_set_hash(hash); // merge the hash code into header
758 // use (machine word version) atomic operation to install the hash
759 test = obj->cas_set_mark(temp, mark);
760 if (test == mark) {
761 return hash;
762 }
763 // If atomic operation failed, we must inflate the header
764 // into heavy weight monitor. We could add more code here
765 // for fast path, but it does not worth the complexity.
766 } else if (mark->has_monitor()) {
767 ObjectMonitorHandle omh;
768 if (!omh.save_om_ptr(obj, mark)) {
769 // Lost a race with async deflation so try again.
770 assert(AsyncDeflateIdleMonitors, "sanity check");
771 continue;
772 }
773 monitor = omh.om_ptr();
774 temp = monitor->header();
775 assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(temp));
776 hash = temp->hash();
777 if (hash != 0) {
778 return hash;
779 }
780 // Skip to the following code to reduce code size
781 } else if (Self->is_lock_owned((address)mark->locker())) {
782 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
783 assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(temp));
784 hash = temp->hash(); // by current thread, check if the displaced
785 if (hash != 0) { // header contains hash code
786 return hash;
787 }
788 // WARNING:
789 // The displaced header in the BasicLock on a thread's stack
790 // is strictly immutable. It CANNOT be changed in ANY cases.
791 // So we have to inflate the stack lock into an ObjectMonitor
792 // even if the current thread owns the lock. The BasicLock on
793 // a thread's stack can be asynchronously read by other threads
794 // during an inflate() call so any change to that stack memory
795 // may not propagate to other threads correctly.
796 }
797
798 // Inflate the monitor to set hash code
799 ObjectMonitorHandle omh;
800 inflate(&omh, Self, obj, inflate_cause_hash_code);
801 monitor = omh.om_ptr();
802 // Load displaced header and check it has hash code
803 mark = monitor->header();
804 assert(mark->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(mark));
805 hash = mark->hash();
806 if (hash == 0) {
807 hash = get_next_hash(Self, obj);
808 temp = mark->copy_set_hash(hash); // merge hash code into header
809 assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(temp));
810 test = Atomic::cmpxchg(temp, monitor->header_addr(), mark);
811 if (test != mark) {
812 // The only non-deflation update to the ObjectMonitor's
813 // header/dmw field is to merge in the hash code. If someone
814 // adds a new usage of the header/dmw field, please update
815 // this code.
816 // ObjectMonitor::install_displaced_markword_in_object()
817 // does mark the header/dmw field as part of async deflation,
818 // but that protocol cannot happen now due to the
819 // ObjectMonitorHandle above.
820 hash = test->hash();
821 assert(test->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(test));
822 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
823 }
824 }
825 // We finally get the hash
826 return hash;
827 }
828 }
829
830 // Deprecated -- use FastHashCode() instead.
831
832 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
833 return FastHashCode(Thread::current(), obj());
834 }
835
836
837 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
838 Handle h_obj) {
839 if (UseBiasedLocking) {
840 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
841 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
842 }
843
844 assert(thread == JavaThread::current(), "Can only be called on current thread");
845 oop obj = h_obj();
846
847 while (true) {
848 markOop mark = ReadStableMark(obj);
849
850 // Uncontended case, header points to stack
851 if (mark->has_locker()) {
852 return thread->is_lock_owned((address)mark->locker());
853 }
854 // Contended case, header points to ObjectMonitor (tagged pointer)
855 if (mark->has_monitor()) {
856 ObjectMonitorHandle omh;
857 if (!omh.save_om_ptr(obj, mark)) {
858 // Lost a race with async deflation so try again.
859 assert(AsyncDeflateIdleMonitors, "sanity check");
860 continue;
861 }
862 bool ret_code = omh.om_ptr()->is_entered(thread) != 0;
863 return ret_code;
864 }
865 // Unlocked case, header in place
866 assert(mark->is_neutral(), "sanity check");
867 return false;
868 }
869 }
870
871 // Be aware of this method could revoke bias of the lock object.
872 // This method queries the ownership of the lock handle specified by 'h_obj'.
873 // If the current thread owns the lock, it returns owner_self. If no
874 // thread owns the lock, it returns owner_none. Otherwise, it will return
875 // owner_other.
876 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
877 (JavaThread *self, Handle h_obj) {
878 // The caller must beware this method can revoke bias, and
879 // revocation can result in a safepoint.
880 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
881 assert(self->thread_state() != _thread_blocked, "invariant");
882
883 // Possible mark states: neutral, biased, stack-locked, inflated
884
885 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
886 // CASE: biased
887 BiasedLocking::revoke_and_rebias(h_obj, false, self);
888 assert(!h_obj->mark()->has_bias_pattern(),
889 "biases should be revoked by now");
890 }
891
892 assert(self == JavaThread::current(), "Can only be called on current thread");
893 oop obj = h_obj();
894
895 while (true) {
896 markOop mark = ReadStableMark(obj);
897
898 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
899 if (mark->has_locker()) {
900 return self->is_lock_owned((address)mark->locker()) ?
901 owner_self : owner_other;
902 }
903
904 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
905 // The Object:ObjectMonitor relationship is stable as long as we're
906 // not at a safepoint and AsyncDeflateIdleMonitors is false.
907 if (mark->has_monitor()) {
908 ObjectMonitorHandle omh;
909 if (!omh.save_om_ptr(obj, mark)) {
910 // Lost a race with async deflation so try again.
911 assert(AsyncDeflateIdleMonitors, "sanity check");
912 continue;
913 }
914 ObjectMonitor * monitor = omh.om_ptr();
915 void * owner = monitor->_owner;
916 if (owner == NULL) return owner_none;
917 return (owner == self ||
918 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
919 }
920
921 // CASE: neutral
922 assert(mark->is_neutral(), "sanity check");
923 return owner_none; // it's unlocked
924 }
925 }
926
927 // FIXME: jvmti should call this
928 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
929 if (UseBiasedLocking) {
930 if (SafepointSynchronize::is_at_safepoint()) {
931 BiasedLocking::revoke_at_safepoint(h_obj);
932 } else {
933 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
934 }
935 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
936 }
937
938 oop obj = h_obj();
939
940 while (true) {
941 address owner = NULL;
942 markOop mark = ReadStableMark(obj);
943
944 // Uncontended case, header points to stack
945 if (mark->has_locker()) {
946 owner = (address) mark->locker();
947 }
948
949 // Contended case, header points to ObjectMonitor (tagged pointer)
950 else if (mark->has_monitor()) {
951 ObjectMonitorHandle omh;
952 if (!omh.save_om_ptr(obj, mark)) {
953 // Lost a race with async deflation so try again.
954 assert(AsyncDeflateIdleMonitors, "sanity check");
955 continue;
956 }
957 ObjectMonitor* monitor = omh.om_ptr();
958 assert(monitor != NULL, "monitor should be non-null");
959 owner = (address) monitor->owner();
960 }
961
962 if (owner != NULL) {
963 // owning_thread_from_monitor_owner() may also return NULL here
964 return Threads::owning_thread_from_monitor_owner(t_list, owner);
965 }
966
967 // Unlocked case, header in place
968 // Cannot have assertion since this object may have been
969 // locked by another thread when reaching here.
970 // assert(mark->is_neutral(), "sanity check");
971
972 return NULL;
973 }
974 }
975
976 // Visitors ...
977
978 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
979 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
980 while (block != NULL) {
981 assert(block->object() == CHAINMARKER, "must be a block header");
982 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
983 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
984 if (mid->is_active()) {
985 ObjectMonitorHandle omh(mid);
986
987 if (mid->object() == NULL ||
988 (AsyncDeflateIdleMonitors && mid->_owner == DEFLATER_MARKER)) {
989 // Only process with closure if the object is set.
990 // For async deflation, race here if monitor is not owned!
991 // The above ref_count bump (in ObjectMonitorHandle ctr)
992 // will cause subsequent async deflation to skip it.
993 // However, previous or concurrent async deflation is a race.
994 continue;
995 }
996 closure->do_monitor(mid);
997 }
998 }
999 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
1000 }
1001 }
1002
1003 // Get the next block in the block list.
1004 static inline PaddedEnd<ObjectMonitor>* next(PaddedEnd<ObjectMonitor>* block) {
1005 assert(block->object() == CHAINMARKER, "must be a block header");
1006 block = (PaddedEnd<ObjectMonitor>*) block->FreeNext;
1007 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
1008 return block;
1009 }
1010
1011 static bool monitors_used_above_threshold() {
1012 if (gMonitorPopulation == 0) {
1013 return false;
1014 }
1015 int monitors_used = gMonitorPopulation - gMonitorFreeCount;
1016 int monitor_usage = (monitors_used * 100LL) / gMonitorPopulation;
1017 return monitor_usage > MonitorUsedDeflationThreshold;
1018 }
1019
1020 bool ObjectSynchronizer::is_cleanup_needed() {
1021 if (MonitorUsedDeflationThreshold > 0) {
1022 return monitors_used_above_threshold();
1023 }
1024 return false;
1025 }
1026
1027 void ObjectSynchronizer::oops_do(OopClosure* f) {
1028 // We only scan the global used list here (for moribund threads), and
1029 // the thread-local monitors in Thread::oops_do().
1030 global_used_oops_do(f);
1031 }
1032
1033 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
1034 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1035 list_oops_do(gOmInUseList, f);
1036 }
1037
1038 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
1039 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1040 list_oops_do(thread->omInUseList, f);
1041 }
1042
1043 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
1044 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1045 ObjectMonitor* mid;
1046 for (mid = list; mid != NULL; mid = mid->FreeNext) {
1047 if (mid->object() != NULL) {
1048 f->do_oop((oop*)mid->object_addr());
1049 }
1050 }
1051 }
1052
1053
1054 // -----------------------------------------------------------------------------
1055 // ObjectMonitor Lifecycle
1056 // -----------------------
1057 // Inflation unlinks monitors from the global gFreeList and
1058 // associates them with objects. Deflation -- which occurs at
1059 // STW-time -- disassociates idle monitors from objects. Such
1060 // scavenged monitors are returned to the gFreeList.
1061 //
1062 // The global list is protected by gListLock. All the critical sections
1063 // are short and operate in constant-time.
1064 //
1065 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1066 //
1067 // Lifecycle:
1068 // -- unassigned and on the global free list
1069 // -- unassigned and on a thread's private omFreeList
1070 // -- assigned to an object. The object is inflated and the mark refers
1071 // to the objectmonitor.
1072
1073
1074 // Constraining monitor pool growth via MonitorBound ...
1075 //
1076 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
1077 // the rate of scavenging is driven primarily by GC. As such, we can find
1078 // an inordinate number of monitors in circulation.
1079 // To avoid that scenario we can artificially induce a STW safepoint
1080 // if the pool appears to be growing past some reasonable bound.
1081 // Generally we favor time in space-time tradeoffs, but as there's no
1082 // natural back-pressure on the # of extant monitors we need to impose some
1083 // type of limit. Beware that if MonitorBound is set to too low a value
1084 // we could just loop. In addition, if MonitorBound is set to a low value
1085 // we'll incur more safepoints, which are harmful to performance.
1086 // See also: GuaranteedSafepointInterval
1087 //
1088 // The current implementation uses asynchronous VM operations.
1089
1090 static void InduceScavenge(Thread * Self, const char * Whence) {
1091 // Induce STW safepoint to trim monitors
1092 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1093 // More precisely, trigger an asynchronous STW safepoint as the number
1094 // of active monitors passes the specified threshold.
1095 // TODO: assert thread state is reasonable
1096
1097 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1098 // Induce a 'null' safepoint to scavenge monitors
1099 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1100 // to the VMthread and have a lifespan longer than that of this activation record.
1101 // The VMThread will delete the op when completed.
1102 VMThread::execute(new VM_ScavengeMonitors());
1103 }
1104 }
1105
1106 ObjectMonitor* ObjectSynchronizer::omAlloc(Thread * Self,
1107 const InflateCause cause) {
1108 // A large MAXPRIVATE value reduces both list lock contention
1109 // and list coherency traffic, but also tends to increase the
1110 // number of objectMonitors in circulation as well as the STW
1111 // scavenge costs. As usual, we lean toward time in space-time
1112 // tradeoffs.
1113 const int MAXPRIVATE = 1024;
1114
1115 if (AsyncDeflateIdleMonitors) {
1116 JavaThread * jt = (JavaThread *)Self;
1117 if (jt->omShouldDeflateIdleMonitors && jt->omInUseCount > 0 &&
1118 cause != inflate_cause_vm_internal) {
1119 // Deflate any per-thread idle monitors for this JavaThread if
1120 // this is not an internal inflation. Clean up your own mess.
1121 // (Gibbs Rule 45) Otherwise, skip this cleanup.
1122 // deflate_global_idle_monitors_using_JT() is called by the ServiceThread.
1123 debug_only(jt->check_for_valid_safepoint_state(false);)
1124 ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT();
1125 }
1126 }
1127
1128 for (;;) {
1129 ObjectMonitor * m;
1130
1131 // 1: try to allocate from the thread's local omFreeList.
1132 // Threads will attempt to allocate first from their local list, then
1133 // from the global list, and only after those attempts fail will the thread
1134 // attempt to instantiate new monitors. Thread-local free lists take
1135 // heat off the gListLock and improve allocation latency, as well as reducing
1136 // coherency traffic on the shared global list.
1137 m = Self->omFreeList;
1138 if (m != NULL) {
1139 Self->omFreeList = m->FreeNext;
1140 Self->omFreeCount--;
1141 guarantee(m->object() == NULL, "invariant");
1142 m->set_allocation_state(ObjectMonitor::New);
1143 m->FreeNext = Self->omInUseList;
1144 Self->omInUseList = m;
1145 Self->omInUseCount++;
1146 return m;
1147 }
1148
1149 // 2: try to allocate from the global gFreeList
1150 // CONSIDER: use muxTry() instead of muxAcquire().
1151 // If the muxTry() fails then drop immediately into case 3.
1152 // If we're using thread-local free lists then try
1153 // to reprovision the caller's free list.
1154 if (gFreeList != NULL) {
1155 // Reprovision the thread's omFreeList.
1156 // Use bulk transfers to reduce the allocation rate and heat
1157 // on various locks.
1158 Thread::muxAcquire(&gListLock, "omAlloc(1)");
1159 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1160 gMonitorFreeCount--;
1161 ObjectMonitor * take = gFreeList;
1162 gFreeList = take->FreeNext;
1163 guarantee(take->object() == NULL, "invariant");
1164 if (AsyncDeflateIdleMonitors) {
1165 // Clear any values we allowed to linger during async deflation.
1166 take->_header = NULL;
1167 take->set_owner(NULL);
1168
1169 if (take->ref_count() < 0) {
1170 // Add back max_jint to restore the ref_count field to its
1171 // proper value.
1172 Atomic::add(max_jint, &take->_ref_count);
1173
1174 assert(take->ref_count() >= 0, "must not be negative: ref_count=%d",
1175 take->ref_count());
1176 }
1177 }
1178 guarantee(!take->is_busy(), "invariant");
1179 take->Recycle();
1180 assert(take->is_free(), "invariant");
1181 omRelease(Self, take, false);
1182 }
1183 Thread::muxRelease(&gListLock);
1184 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1185 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1186
1187 const int mx = MonitorBound;
1188 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1189 // We can't safely induce a STW safepoint from omAlloc() as our thread
1190 // state may not be appropriate for such activities and callers may hold
1191 // naked oops, so instead we defer the action.
1192 InduceScavenge(Self, "omAlloc");
1193 }
1194 continue;
1195 }
1196
1197 // 3: allocate a block of new ObjectMonitors
1198 // Both the local and global free lists are empty -- resort to malloc().
1199 // In the current implementation objectMonitors are TSM - immortal.
1200 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1201 // each ObjectMonitor to start at the beginning of a cache line,
1202 // so we use align_up().
1203 // A better solution would be to use C++ placement-new.
1204 // BEWARE: As it stands currently, we don't run the ctors!
1205 assert(_BLOCKSIZE > 1, "invariant");
1206 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
1207 PaddedEnd<ObjectMonitor> * temp;
1208 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1209 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
1210 mtInternal);
1211 temp = (PaddedEnd<ObjectMonitor> *)
1212 align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE);
1213
1214 // NOTE: (almost) no way to recover if allocation failed.
1215 // We might be able to induce a STW safepoint and scavenge enough
1216 // objectMonitors to permit progress.
1217 if (temp == NULL) {
1218 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1219 "Allocate ObjectMonitors");
1220 }
1221 (void)memset((void *) temp, 0, neededsize);
1222
1223 // Format the block.
1224 // initialize the linked list, each monitor points to its next
1225 // forming the single linked free list, the very first monitor
1226 // will points to next block, which forms the block list.
1227 // The trick of using the 1st element in the block as gBlockList
1228 // linkage should be reconsidered. A better implementation would
1229 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1230
1231 for (int i = 1; i < _BLOCKSIZE; i++) {
1232 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1233 assert(temp[i].is_free(), "invariant");
1234 }
1235
1236 // terminate the last monitor as the end of list
1237 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1238
1239 // Element [0] is reserved for global list linkage
1240 temp[0].set_object(CHAINMARKER);
1241
1242 // Consider carving out this thread's current request from the
1243 // block in hand. This avoids some lock traffic and redundant
1244 // list activity.
1245
1246 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1247 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1248 Thread::muxAcquire(&gListLock, "omAlloc(2)");
1249 gMonitorPopulation += _BLOCKSIZE-1;
1250 gMonitorFreeCount += _BLOCKSIZE-1;
1251
1252 // Add the new block to the list of extant blocks (gBlockList).
1253 // The very first objectMonitor in a block is reserved and dedicated.
1254 // It serves as blocklist "next" linkage.
1255 temp[0].FreeNext = gBlockList;
1256 // There are lock-free uses of gBlockList so make sure that
1257 // the previous stores happen before we update gBlockList.
1258 OrderAccess::release_store(&gBlockList, temp);
1259
1260 // Add the new string of objectMonitors to the global free list
1261 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1262 gFreeList = temp + 1;
1263 Thread::muxRelease(&gListLock);
1264 }
1265 }
1266
1267 // Place "m" on the caller's private per-thread omFreeList.
1268 // In practice there's no need to clamp or limit the number of
1269 // monitors on a thread's omFreeList as the only time we'll call
1270 // omRelease is to return a monitor to the free list after a CAS
1271 // attempt failed. This doesn't allow unbounded #s of monitors to
1272 // accumulate on a thread's free list.
1273 //
1274 // Key constraint: all ObjectMonitors on a thread's free list and the global
1275 // free list must have their object field set to null. This prevents the
1276 // scavenger -- deflate_monitor_list() or deflate_monitor_list_using_JT()
1277 // -- from reclaiming them while we are trying to release them.
1278
1279 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1280 bool fromPerThreadAlloc) {
1281 guarantee(m->header() == NULL, "invariant");
1282 guarantee(m->object() == NULL, "invariant");
1283 guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor");
1284 m->set_allocation_state(ObjectMonitor::Free);
1285 // Remove from omInUseList
1286 if (fromPerThreadAlloc) {
1287 ObjectMonitor* cur_mid_in_use = NULL;
1288 bool extracted = false;
1289 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1290 if (m == mid) {
1291 // extract from per-thread in-use list
1292 if (mid == Self->omInUseList) {
1293 Self->omInUseList = mid->FreeNext;
1294 } else if (cur_mid_in_use != NULL) {
1295 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1296 }
1297 extracted = true;
1298 Self->omInUseCount--;
1299 break;
1300 }
1301 }
1302 assert(extracted, "Should have extracted from in-use list");
1303 }
1304
1305 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1306 m->FreeNext = Self->omFreeList;
1307 guarantee(m->is_free(), "invariant");
1308 Self->omFreeList = m;
1309 Self->omFreeCount++;
1310 }
1311
1312 // Return the monitors of a moribund thread's local free list to
1313 // the global free list. Typically a thread calls omFlush() when
1314 // it's dying. We could also consider having the VM thread steal
1315 // monitors from threads that have not run java code over a few
1316 // consecutive STW safepoints. Relatedly, we might decay
1317 // omFreeProvision at STW safepoints.
1318 //
1319 // Also return the monitors of a moribund thread's omInUseList to
1320 // a global gOmInUseList under the global list lock so these
1321 // will continue to be scanned.
1322 //
1323 // We currently call omFlush() from Threads::remove() _before the thread
1324 // has been excised from the thread list and is no longer a mutator.
1325 // This means that omFlush() cannot run concurrently with a safepoint and
1326 // interleave with the deflate_idle_monitors scavenge operator. In particular,
1327 // this ensures that the thread's monitors are scanned by a GC safepoint,
1328 // either via Thread::oops_do() (if safepoint happens before omFlush()) or via
1329 // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's
1330 // monitors have been transferred to the global in-use list).
1331 //
1332 // With AsyncDeflateIdleMonitors, deflate_global_idle_monitors_using_JT()
1333 // and deflate_per_thread_idle_monitors_using_JT() (in another thread) can
1334 // run at the same time as omFlush() so we have to be careful.
1335
1336 void ObjectSynchronizer::omFlush(Thread * Self) {
1337 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1338 ObjectMonitor * tail = NULL;
1339 int tally = 0;
1340 if (list != NULL) {
1341 ObjectMonitor * s;
1342 // The thread is going away, the per-thread free monitors
1343 // are freed via set_owner(NULL)
1344 // Link them to tail, which will be linked into the global free list
1345 // gFreeList below, under the gListLock
1346 for (s = list; s != NULL; s = s->FreeNext) {
1347 tally++;
1348 tail = s;
1349 guarantee(s->object() == NULL, "invariant");
1350 guarantee(!s->is_busy(), "invariant");
1351 s->set_owner(NULL); // redundant but good hygiene
1352 }
1353 guarantee(tail != NULL, "invariant");
1354 ADIM_guarantee(Self->omFreeCount == tally, "free-count off");
1355 Self->omFreeList = NULL;
1356 Self->omFreeCount = 0;
1357 }
1358
1359 ObjectMonitor * inUseList = Self->omInUseList;
1360 ObjectMonitor * inUseTail = NULL;
1361 int inUseTally = 0;
1362 if (inUseList != NULL) {
1363 ObjectMonitor *cur_om;
1364 // The thread is going away, however the omInUseList inflated
1365 // monitors may still be in-use by other threads.
1366 // Link them to inUseTail, which will be linked into the global in-use list
1367 // gOmInUseList below, under the gListLock
1368 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1369 inUseTail = cur_om;
1370 inUseTally++;
1371 ADIM_guarantee(cur_om->is_active(), "invariant");
1372 }
1373 guarantee(inUseTail != NULL, "invariant");
1374 ADIM_guarantee(Self->omInUseCount == inUseTally, "in-use count off");
1375 Self->omInUseList = NULL;
1376 Self->omInUseCount = 0;
1377 }
1378
1379 Thread::muxAcquire(&gListLock, "omFlush");
1380 if (tail != NULL) {
1381 tail->FreeNext = gFreeList;
1382 gFreeList = list;
1383 gMonitorFreeCount += tally;
1384 }
1385
1386 if (inUseTail != NULL) {
1387 inUseTail->FreeNext = gOmInUseList;
1388 gOmInUseList = inUseList;
1389 gOmInUseCount += inUseTally;
1390 }
1391
1392 Thread::muxRelease(&gListLock);
1393
1394 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1395 LogStreamHandle(Info, monitorinflation) lsh_info;
1396 LogStream * ls = NULL;
1397 if (log_is_enabled(Debug, monitorinflation)) {
1398 ls = &lsh_debug;
1399 } else if ((tally != 0 || inUseTally != 0) &&
1400 log_is_enabled(Info, monitorinflation)) {
1401 ls = &lsh_info;
1402 }
1403 if (ls != NULL) {
1404 ls->print_cr("omFlush: jt=" INTPTR_FORMAT ", free_monitor_tally=%d"
1405 ", in_use_monitor_tally=%d" ", omFreeProvision=%d",
1406 p2i(Self), tally, inUseTally, Self->omFreeProvision);
1407 }
1408 }
1409
1410 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1411 const oop obj,
1412 ObjectSynchronizer::InflateCause cause) {
1413 assert(event != NULL, "invariant");
1414 assert(event->should_commit(), "invariant");
1415 event->set_monitorClass(obj->klass());
1416 event->set_address((uintptr_t)(void*)obj);
1417 event->set_cause((u1)cause);
1418 event->commit();
1419 }
1420
1421 // Fast path code shared by multiple functions
1422 void ObjectSynchronizer::inflate_helper(ObjectMonitorHandle * omh_p, oop obj) {
1423 while (true) {
1424 markOop mark = obj->mark();
1425 if (mark->has_monitor()) {
1426 if (!omh_p->save_om_ptr(obj, mark)) {
1427 // Lost a race with async deflation so try again.
1428 assert(AsyncDeflateIdleMonitors, "sanity check");
1429 continue;
1430 }
1431 ObjectMonitor * monitor = omh_p->om_ptr();
1432 assert(ObjectSynchronizer::verify_objmon_isinpool(monitor), "monitor is invalid");
1433 markOop dmw = monitor->header();
1434 assert(dmw->is_neutral(), "sanity check: header=" INTPTR_FORMAT, p2i(dmw));
1435 return;
1436 }
1437 inflate(omh_p, Thread::current(), obj, inflate_cause_vm_internal);
1438 return;
1439 }
1440 }
1441
1442 void ObjectSynchronizer::inflate(ObjectMonitorHandle * omh_p, Thread * Self,
1443 oop object, const InflateCause cause) {
1444 // Inflate mutates the heap ...
1445 // Relaxing assertion for bug 6320749.
1446 assert(Universe::verify_in_progress() ||
1447 !SafepointSynchronize::is_at_safepoint(), "invariant");
1448
1449 EventJavaMonitorInflate event;
1450
1451 for (;;) {
1452 const markOop mark = object->mark();
1453 assert(!mark->has_bias_pattern(), "invariant");
1454
1455 // The mark can be in one of the following states:
1456 // * Inflated - just return
1457 // * Stack-locked - coerce it to inflated
1458 // * INFLATING - busy wait for conversion to complete
1459 // * Neutral - aggressively inflate the object.
1460 // * BIASED - Illegal. We should never see this
1461
1462 // CASE: inflated
1463 if (mark->has_monitor()) {
1464 if (!omh_p->save_om_ptr(object, mark)) {
1465 // Lost a race with async deflation so try again.
1466 assert(AsyncDeflateIdleMonitors, "sanity check");
1467 continue;
1468 }
1469 ObjectMonitor * inf = omh_p->om_ptr();
1470 markOop dmw = inf->header();
1471 assert(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1472 assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1473 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1474 return;
1475 }
1476
1477 // CASE: inflation in progress - inflating over a stack-lock.
1478 // Some other thread is converting from stack-locked to inflated.
1479 // Only that thread can complete inflation -- other threads must wait.
1480 // The INFLATING value is transient.
1481 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1482 // We could always eliminate polling by parking the thread on some auxiliary list.
1483 if (mark == markOopDesc::INFLATING()) {
1484 ReadStableMark(object);
1485 continue;
1486 }
1487
1488 // CASE: stack-locked
1489 // Could be stack-locked either by this thread or by some other thread.
1490 //
1491 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1492 // to install INFLATING into the mark word. We originally installed INFLATING,
1493 // allocated the objectmonitor, and then finally STed the address of the
1494 // objectmonitor into the mark. This was correct, but artificially lengthened
1495 // the interval in which INFLATED appeared in the mark, thus increasing
1496 // the odds of inflation contention.
1497 //
1498 // We now use per-thread private objectmonitor free lists.
1499 // These list are reprovisioned from the global free list outside the
1500 // critical INFLATING...ST interval. A thread can transfer
1501 // multiple objectmonitors en-mass from the global free list to its local free list.
1502 // This reduces coherency traffic and lock contention on the global free list.
1503 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1504 // before or after the CAS(INFLATING) operation.
1505 // See the comments in omAlloc().
1506
1507 LogStreamHandle(Trace, monitorinflation) lsh;
1508
1509 if (mark->has_locker()) {
1510 ObjectMonitor * m;
1511 if (!AsyncDeflateIdleMonitors || cause == inflate_cause_vm_internal) {
1512 // If !AsyncDeflateIdleMonitors or if an internal inflation, then
1513 // we won't stop for a potential safepoint in omAlloc.
1514 m = omAlloc(Self, cause);
1515 } else {
1516 // If AsyncDeflateIdleMonitors and not an internal inflation, then
1517 // we may stop for a safepoint in omAlloc() so protect object.
1518 Handle h_obj(Self, object);
1519 m = omAlloc(Self, cause);
1520 object = h_obj(); // Refresh object.
1521 }
1522 // Optimistically prepare the objectmonitor - anticipate successful CAS
1523 // We do this before the CAS in order to minimize the length of time
1524 // in which INFLATING appears in the mark.
1525 m->Recycle();
1526 m->_Responsible = NULL;
1527 m->_recursions = 0;
1528 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1529
1530 markOop cmp = object->cas_set_mark(markOopDesc::INFLATING(), mark);
1531 if (cmp != mark) {
1532 omRelease(Self, m, true);
1533 continue; // Interference -- just retry
1534 }
1535
1536 // We've successfully installed INFLATING (0) into the mark-word.
1537 // This is the only case where 0 will appear in a mark-word.
1538 // Only the singular thread that successfully swings the mark-word
1539 // to 0 can perform (or more precisely, complete) inflation.
1540 //
1541 // Why do we CAS a 0 into the mark-word instead of just CASing the
1542 // mark-word from the stack-locked value directly to the new inflated state?
1543 // Consider what happens when a thread unlocks a stack-locked object.
1544 // It attempts to use CAS to swing the displaced header value from the
1545 // on-stack basiclock back into the object header. Recall also that the
1546 // header value (hash code, etc) can reside in (a) the object header, or
1547 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1548 // header in an objectMonitor. The inflate() routine must copy the header
1549 // value from the basiclock on the owner's stack to the objectMonitor, all
1550 // the while preserving the hashCode stability invariants. If the owner
1551 // decides to release the lock while the value is 0, the unlock will fail
1552 // and control will eventually pass from slow_exit() to inflate. The owner
1553 // will then spin, waiting for the 0 value to disappear. Put another way,
1554 // the 0 causes the owner to stall if the owner happens to try to
1555 // drop the lock (restoring the header from the basiclock to the object)
1556 // while inflation is in-progress. This protocol avoids races that might
1557 // would otherwise permit hashCode values to change or "flicker" for an object.
1558 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1559 // 0 serves as a "BUSY" inflate-in-progress indicator.
1560
1561
1562 // fetch the displaced mark from the owner's stack.
1563 // The owner can't die or unwind past the lock while our INFLATING
1564 // object is in the mark. Furthermore the owner can't complete
1565 // an unlock on the object, either.
1566 markOop dmw = mark->displaced_mark_helper();
1567 // Catch if the object's header is not neutral (not locked and
1568 // not marked is what we care about here).
1569 ADIM_guarantee(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1570
1571 // Setup monitor fields to proper values -- prepare the monitor
1572 m->set_header(dmw);
1573
1574 // Optimization: if the mark->locker stack address is associated
1575 // with this thread we could simply set m->_owner = Self.
1576 // Note that a thread can inflate an object
1577 // that it has stack-locked -- as might happen in wait() -- directly
1578 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1579 m->set_owner(mark->locker());
1580 m->set_object(object);
1581 // TODO-FIXME: assert BasicLock->dhw != 0.
1582
1583 omh_p->set_om_ptr(m);
1584 assert(m->is_new(), "freshly allocated monitor must be new");
1585 m->set_allocation_state(ObjectMonitor::Old);
1586
1587 // Must preserve store ordering. The monitor state must
1588 // be stable at the time of publishing the monitor address.
1589 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1590 object->release_set_mark(markOopDesc::encode(m));
1591
1592 // Hopefully the performance counters are allocated on distinct cache lines
1593 // to avoid false sharing on MP systems ...
1594 OM_PERFDATA_OP(Inflations, inc());
1595 if (log_is_enabled(Trace, monitorinflation)) {
1596 ResourceMark rm(Self);
1597 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1598 INTPTR_FORMAT ", type='%s'", p2i(object),
1599 p2i(object->mark()), object->klass()->external_name());
1600 }
1601 if (event.should_commit()) {
1602 post_monitor_inflate_event(&event, object, cause);
1603 }
1604 ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free");
1605 return;
1606 }
1607
1608 // CASE: neutral
1609 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1610 // If we know we're inflating for entry it's better to inflate by swinging a
1611 // pre-locked objectMonitor pointer into the object header. A successful
1612 // CAS inflates the object *and* confers ownership to the inflating thread.
1613 // In the current implementation we use a 2-step mechanism where we CAS()
1614 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1615 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1616 // would be useful.
1617
1618 // Catch if the object's header is not neutral (not locked and
1619 // not marked is what we care about here).
1620 ADIM_guarantee(mark->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(mark));
1621 ObjectMonitor * m;
1622 if (!AsyncDeflateIdleMonitors || cause == inflate_cause_vm_internal) {
1623 // If !AsyncDeflateIdleMonitors or if an internal inflation, then
1624 // we won't stop for a potential safepoint in omAlloc.
1625 m = omAlloc(Self, cause);
1626 } else {
1627 // If AsyncDeflateIdleMonitors and not an internal inflation, then
1628 // we may stop for a safepoint in omAlloc() so protect object.
1629 Handle h_obj(Self, object);
1630 m = omAlloc(Self, cause);
1631 object = h_obj(); // Refresh object.
1632 }
1633 // prepare m for installation - set monitor to initial state
1634 m->Recycle();
1635 m->set_header(mark);
1636 m->set_owner(NULL);
1637 m->set_object(object);
1638 m->_recursions = 0;
1639 m->_Responsible = NULL;
1640 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1641
1642 omh_p->set_om_ptr(m);
1643 assert(m->is_new(), "freshly allocated monitor must be new");
1644 m->set_allocation_state(ObjectMonitor::Old);
1645
1646 if (object->cas_set_mark(markOopDesc::encode(m), mark) != mark) {
1647 m->set_header(NULL);
1648 m->set_object(NULL);
1649 m->Recycle();
1650 omh_p->set_om_ptr(NULL);
1651 // omRelease() will reset the allocation state
1652 omRelease(Self, m, true);
1653 m = NULL;
1654 continue;
1655 // interference - the markword changed - just retry.
1656 // The state-transitions are one-way, so there's no chance of
1657 // live-lock -- "Inflated" is an absorbing state.
1658 }
1659
1660 // Hopefully the performance counters are allocated on distinct
1661 // cache lines to avoid false sharing on MP systems ...
1662 OM_PERFDATA_OP(Inflations, inc());
1663 if (log_is_enabled(Trace, monitorinflation)) {
1664 ResourceMark rm(Self);
1665 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1666 INTPTR_FORMAT ", type='%s'", p2i(object),
1667 p2i(object->mark()), object->klass()->external_name());
1668 }
1669 if (event.should_commit()) {
1670 post_monitor_inflate_event(&event, object, cause);
1671 }
1672 ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free");
1673 return;
1674 }
1675 }
1676
1677
1678 // We maintain a list of in-use monitors for each thread.
1679 //
1680 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1681 // deflate_idle_monitors() scans only a global list of in-use monitors which
1682 // is populated only as a thread dies (see omFlush()).
1683 //
1684 // These operations are called at all safepoints, immediately after mutators
1685 // are stopped, but before any objects have moved. Collectively they traverse
1686 // the population of in-use monitors, deflating where possible. The scavenged
1687 // monitors are returned to the global monitor free list.
1688 //
1689 // Beware that we scavenge at *every* stop-the-world point. Having a large
1690 // number of monitors in-use could negatively impact performance. We also want
1691 // to minimize the total # of monitors in circulation, as they incur a small
1692 // footprint penalty.
1693 //
1694 // Perversely, the heap size -- and thus the STW safepoint rate --
1695 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1696 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1697 // This is an unfortunate aspect of this design.
1698
1699 void ObjectSynchronizer::do_safepoint_work(DeflateMonitorCounters* _counters) {
1700 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1701
1702 // The per-thread in-use lists are handled in
1703 // ParallelSPCleanupThreadClosure::do_thread().
1704
1705 if (!AsyncDeflateIdleMonitors || is_cleanup_requested()) {
1706 // Use the older mechanism for the global in-use list or
1707 // if a special cleanup has been requested.
1708 ObjectSynchronizer::deflate_idle_monitors(_counters);
1709 return;
1710 }
1711
1712 log_debug(monitorinflation)("requesting deflation of idle monitors.");
1713 // Request deflation of global idle monitors by the ServiceThread:
1714 _gOmShouldDeflateIdleMonitors = true;
1715 MutexLockerEx ml(Service_lock, Mutex::_no_safepoint_check_flag);
1716 Service_lock->notify_all();
1717 }
1718
1719 // Deflate a single monitor if not in-use
1720 // Return true if deflated, false if in-use
1721 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1722 ObjectMonitor** freeHeadp,
1723 ObjectMonitor** freeTailp) {
1724 bool deflated;
1725 // Normal case ... The monitor is associated with obj.
1726 const markOop mark = obj->mark();
1727 guarantee(mark == markOopDesc::encode(mid), "should match: mark="
1728 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, p2i(mark),
1729 p2i(markOopDesc::encode(mid)));
1730 // Make sure that mark->monitor() and markOopDesc::encode() agree:
1731 guarantee(mark->monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
1732 ", mid=" INTPTR_FORMAT, p2i(mark->monitor()), p2i(mid));
1733 const markOop dmw = mid->header();
1734 guarantee(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1735
1736 if (mid->is_busy()) {
1737 deflated = false;
1738 } else {
1739 // Deflate the monitor if it is no longer being used
1740 // It's idle - scavenge and return to the global free list
1741 // plain old deflation ...
1742 if (log_is_enabled(Trace, monitorinflation)) {
1743 ResourceMark rm;
1744 log_trace(monitorinflation)("deflate_monitor: "
1745 "object=" INTPTR_FORMAT ", mark="
1746 INTPTR_FORMAT ", type='%s'", p2i(obj),
1747 p2i(mark), obj->klass()->external_name());
1748 }
1749
1750 // Restore the header back to obj
1751 obj->release_set_mark(dmw);
1752 mid->clear();
1753
1754 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
1755 p2i(mid->object()));
1756 assert(mid->is_free(), "invariant");
1757
1758 // Move the object to the working free list defined by freeHeadp, freeTailp
1759 if (*freeHeadp == NULL) *freeHeadp = mid;
1760 if (*freeTailp != NULL) {
1761 ObjectMonitor * prevtail = *freeTailp;
1762 assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1763 prevtail->FreeNext = mid;
1764 }
1765 *freeTailp = mid;
1766 deflated = true;
1767 }
1768 return deflated;
1769 }
1770
1771 // Deflate the specified ObjectMonitor if not in-use using a JavaThread.
1772 // Returns true if it was deflated and false otherwise.
1773 //
1774 // The async deflation protocol sets owner to DEFLATER_MARKER and
1775 // makes ref_count negative as signals to contending threads that
1776 // an async deflation is in progress. There are a number of checks
1777 // as part of the protocol to make sure that the calling thread has
1778 // not lost the race to a contending thread or to a thread that just
1779 // wants to use the ObjectMonitor*.
1780 //
1781 // The ObjectMonitor has been successfully async deflated when:
1782 // (owner == DEFLATER_MARKER && ref_count < 0)
1783 // Contending threads or ObjectMonitor* using threads that see those
1784 // values know to retry their operation.
1785 //
1786 bool ObjectSynchronizer::deflate_monitor_using_JT(ObjectMonitor* mid,
1787 ObjectMonitor** freeHeadp,
1788 ObjectMonitor** freeTailp) {
1789 assert(AsyncDeflateIdleMonitors, "sanity check");
1790 assert(Thread::current()->is_Java_thread(), "precondition");
1791 // A newly allocated ObjectMonitor should not be seen here so we
1792 // avoid an endless inflate/deflate cycle.
1793 assert(mid->is_old(), "must be old: allocation_state=%d",
1794 (int) mid->allocation_state());
1795
1796 if (mid->is_busy() || mid->ref_count() != 0) {
1797 // Easy checks are first - the ObjectMonitor is busy or ObjectMonitor*
1798 // is in use so no deflation.
1799 return false;
1800 }
1801
1802 if (Atomic::replace_if_null(DEFLATER_MARKER, &(mid->_owner))) {
1803 // ObjectMonitor is not owned by another thread. Our setting
1804 // owner to DEFLATER_MARKER forces any contending thread through
1805 // the slow path. This is just the first part of the async
1806 // deflation dance.
1807
1808 if (mid->_contentions != 0 || mid->_waiters != 0) {
1809 // Another thread has raced to enter the ObjectMonitor after
1810 // mid->is_busy() above or has already entered and waited on
1811 // it which makes it busy so no deflation. Restore owner to
1812 // NULL if it is still DEFLATER_MARKER.
1813 Atomic::cmpxchg((void*)NULL, &mid->_owner, DEFLATER_MARKER);
1814 return false;
1815 }
1816
1817 if (Atomic::cmpxchg(-max_jint, &mid->_ref_count, (jint)0) == 0) {
1818 // Make ref_count negative to force any contending threads or
1819 // ObjectMonitor* using threads to retry. This is the second
1820 // part of the async deflation dance.
1821
1822 if (mid->_owner == DEFLATER_MARKER) {
1823 // If owner is still DEFLATER_MARKER, then we have successfully
1824 // signaled any contending threads to retry. If it is not, then we
1825 // have lost the race to an entering thread and the ObjectMonitor
1826 // is now busy. This is the third and final part of the async
1827 // deflation dance.
1828 // Note: This owner check solves the ABA problem with ref_count
1829 // where another thread acquired the ObjectMonitor, finished
1830 // using it and restored the ref_count to zero.
1831
1832 // Sanity checks for the races:
1833 guarantee(mid->_contentions == 0, "must be 0: contentions=%d",
1834 mid->_contentions);
1835 guarantee(mid->_waiters == 0, "must be 0: waiters=%d", mid->_waiters);
1836 guarantee(mid->_cxq == NULL, "must be no contending threads: cxq="
1837 INTPTR_FORMAT, p2i(mid->_cxq));
1838 guarantee(mid->_EntryList == NULL,
1839 "must be no entering threads: EntryList=" INTPTR_FORMAT,
1840 p2i(mid->_EntryList));
1841
1842 const oop obj = (oop) mid->object();
1843 if (log_is_enabled(Trace, monitorinflation)) {
1844 ResourceMark rm;
1845 log_trace(monitorinflation)("deflate_monitor_using_JT: "
1846 "object=" INTPTR_FORMAT ", mark="
1847 INTPTR_FORMAT ", type='%s'",
1848 p2i(obj), p2i(obj->mark()),
1849 obj->klass()->external_name());
1850 }
1851
1852 // Install the old mark word if nobody else has already done it.
1853 mid->install_displaced_markword_in_object(obj);
1854 mid->clear_using_JT();
1855
1856 assert(mid->object() == NULL, "must be NULL: object=" INTPTR_FORMAT,
1857 p2i(mid->object()));
1858 assert(mid->is_free(), "must be free: allocation_state=%d",
1859 (int) mid->allocation_state());
1860
1861 // Move the deflated ObjectMonitor to the working free list
1862 // defined by freeHeadp and freeTailp.
1863 if (*freeHeadp == NULL) {
1864 // First one on the list.
1865 *freeHeadp = mid;
1866 }
1867 if (*freeTailp != NULL) {
1868 // We append to the list so the caller can use mid->FreeNext
1869 // to fix the linkages in its context.
1870 ObjectMonitor * prevtail = *freeTailp;
1871 // Should have been cleaned up by the caller:
1872 assert(prevtail->FreeNext == NULL, "must be NULL: FreeNext="
1873 INTPTR_FORMAT, p2i(prevtail->FreeNext));
1874 prevtail->FreeNext = mid;
1875 }
1876 *freeTailp = mid;
1877
1878 // At this point, mid->FreeNext still refers to its current
1879 // value and another ObjectMonitor's FreeNext field still
1880 // refers to this ObjectMonitor. Those linkages have to be
1881 // cleaned up by the caller who has the complete context.
1882
1883 // We leave owner == DEFLATER_MARKER and ref_count < 0
1884 // to force any racing threads to retry.
1885 return true; // Success, ObjectMonitor has been deflated.
1886 }
1887
1888 // The owner was changed from DEFLATER_MARKER so we lost the
1889 // race since the ObjectMonitor is now busy.
1890
1891 // Add back max_jint to restore the ref_count field to its
1892 // proper value (which may not be what we saw above):
1893 Atomic::add(max_jint, &mid->_ref_count);
1894
1895 assert(mid->ref_count() >= 0, "must not be negative: ref_count=%d",
1896 mid->ref_count());
1897 return false;
1898 }
1899
1900 // The ref_count was no longer 0 so we lost the race since the
1901 // ObjectMonitor is now busy or the ObjectMonitor* is now is use.
1902 // Restore owner to NULL if it is still DEFLATER_MARKER:
1903 Atomic::cmpxchg((void*)NULL, &mid->_owner, DEFLATER_MARKER);
1904 }
1905
1906 // The owner field is no longer NULL so we lost the race since the
1907 // ObjectMonitor is now busy.
1908 return false;
1909 }
1910
1911 // Walk a given monitor list, and deflate idle monitors
1912 // The given list could be a per-thread list or a global list
1913 // Caller acquires gListLock as needed.
1914 //
1915 // In the case of parallel processing of thread local monitor lists,
1916 // work is done by Threads::parallel_threads_do() which ensures that
1917 // each Java thread is processed by exactly one worker thread, and
1918 // thus avoid conflicts that would arise when worker threads would
1919 // process the same monitor lists concurrently.
1920 //
1921 // See also ParallelSPCleanupTask and
1922 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1923 // Threads::parallel_java_threads_do() in thread.cpp.
1924 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1925 ObjectMonitor** freeHeadp,
1926 ObjectMonitor** freeTailp) {
1927 ObjectMonitor* mid;
1928 ObjectMonitor* next;
1929 ObjectMonitor* cur_mid_in_use = NULL;
1930 int deflated_count = 0;
1931
1932 for (mid = *listHeadp; mid != NULL;) {
1933 oop obj = (oop) mid->object();
1934 if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1935 // if deflate_monitor succeeded,
1936 // extract from per-thread in-use list
1937 if (mid == *listHeadp) {
1938 *listHeadp = mid->FreeNext;
1939 } else if (cur_mid_in_use != NULL) {
1940 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1941 }
1942 next = mid->FreeNext;
1943 mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list
1944 mid = next;
1945 deflated_count++;
1946 } else {
1947 cur_mid_in_use = mid;
1948 mid = mid->FreeNext;
1949 }
1950 }
1951 return deflated_count;
1952 }
1953
1954 // Walk a given ObjectMonitor list and deflate idle ObjectMonitors using
1955 // a JavaThread. Returns the number of deflated ObjectMonitors. The given
1956 // list could be a per-thread in-use list or the global in-use list.
1957 // Caller acquires gListLock as appropriate. If a safepoint has started,
1958 // then we save state via savedMidInUsep and return to the caller to
1959 // honor the safepoint.
1960 //
1961 int ObjectSynchronizer::deflate_monitor_list_using_JT(ObjectMonitor** listHeadp,
1962 ObjectMonitor** freeHeadp,
1963 ObjectMonitor** freeTailp,
1964 ObjectMonitor** savedMidInUsep) {
1965 assert(AsyncDeflateIdleMonitors, "sanity check");
1966 assert(Thread::current()->is_Java_thread(), "precondition");
1967
1968 ObjectMonitor* mid;
1969 ObjectMonitor* next;
1970 ObjectMonitor* cur_mid_in_use = NULL;
1971 int deflated_count = 0;
1972
1973 if (*savedMidInUsep == NULL) {
1974 // No saved state so start at the beginning.
1975 mid = *listHeadp;
1976 } else {
1977 // We're restarting after a safepoint so restore the necessary state
1978 // before we resume.
1979 cur_mid_in_use = *savedMidInUsep;
1980 mid = cur_mid_in_use->FreeNext;
1981 }
1982 while (mid != NULL) {
1983 // Only try to deflate if there is an associated Java object and if
1984 // mid is old (is not newly allocated and is not newly freed).
1985 if (mid->object() != NULL && mid->is_old() &&
1986 deflate_monitor_using_JT(mid, freeHeadp, freeTailp)) {
1987 // Deflation succeeded so update the in-use list.
1988 if (mid == *listHeadp) {
1989 *listHeadp = mid->FreeNext;
1990 } else if (cur_mid_in_use != NULL) {
1991 // Maintain the current in-use list.
1992 cur_mid_in_use->FreeNext = mid->FreeNext;
1993 }
1994 next = mid->FreeNext;
1995 mid->FreeNext = NULL;
1996 // At this point mid is disconnected from the in-use list
1997 // and is the current tail in the freeHeadp list.
1998 mid = next;
1999 deflated_count++;
2000 } else {
2001 // mid is considered in-use if it does not have an associated
2002 // Java object or mid is not old or deflation did not succeed.
2003 // A mid->is_new() node can be seen here when it is freshly
2004 // returned by omAlloc() (and skips the deflation code path).
2005 // A mid->is_old() node can be seen here when deflation failed.
2006 // A mid->is_free() node can be seen here when a fresh node from
2007 // omAlloc() is released by omRelease() due to losing the race
2008 // in inflate().
2009
2010 cur_mid_in_use = mid;
2011 mid = mid->FreeNext;
2012
2013 if (SafepointSynchronize::is_synchronizing() &&
2014 cur_mid_in_use != *listHeadp && cur_mid_in_use->is_old()) {
2015 // If a safepoint has started and cur_mid_in_use is not the list
2016 // head and is old, then it is safe to use as saved state. Return
2017 // to the caller so gListLock can be dropped as appropriate
2018 // before blocking.
2019 *savedMidInUsep = cur_mid_in_use;
2020 return deflated_count;
2021 }
2022 }
2023 }
2024 // We finished the list without a safepoint starting so there's
2025 // no need to save state.
2026 *savedMidInUsep = NULL;
2027 return deflated_count;
2028 }
2029
2030 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2031 counters->nInuse = 0; // currently associated with objects
2032 counters->nInCirculation = 0; // extant
2033 counters->nScavenged = 0; // reclaimed (global and per-thread)
2034 counters->perThreadScavenged = 0; // per-thread scavenge total
2035 counters->perThreadTimes = 0.0; // per-thread scavenge times
2036 }
2037
2038 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
2039 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2040
2041 if (AsyncDeflateIdleMonitors) {
2042 // Nothing to do when global idle ObjectMonitors are deflated using
2043 // a JavaThread unless a special cleanup has been requested.
2044 if (!is_cleanup_requested()) {
2045 return;
2046 }
2047 }
2048
2049 bool deflated = false;
2050
2051 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
2052 ObjectMonitor * freeTailp = NULL;
2053 elapsedTimer timer;
2054
2055 if (log_is_enabled(Info, monitorinflation)) {
2056 timer.start();
2057 }
2058
2059 // Prevent omFlush from changing mids in Thread dtor's during deflation
2060 // And in case the vm thread is acquiring a lock during a safepoint
2061 // See e.g. 6320749
2062 Thread::muxAcquire(&gListLock, "deflate_idle_monitors");
2063
2064 // Note: the thread-local monitors lists get deflated in
2065 // a separate pass. See deflate_thread_local_monitors().
2066
2067 // For moribund threads, scan gOmInUseList
2068 int deflated_count = 0;
2069 if (gOmInUseList) {
2070 counters->nInCirculation += gOmInUseCount;
2071 deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
2072 gOmInUseCount -= deflated_count;
2073 counters->nScavenged += deflated_count;
2074 counters->nInuse += gOmInUseCount;
2075 }
2076
2077 // Move the scavenged monitors back to the global free list.
2078 if (freeHeadp != NULL) {
2079 guarantee(freeTailp != NULL && counters->nScavenged > 0, "invariant");
2080 assert(freeTailp->FreeNext == NULL, "invariant");
2081 // constant-time list splice - prepend scavenged segment to gFreeList
2082 freeTailp->FreeNext = gFreeList;
2083 gFreeList = freeHeadp;
2084 }
2085 Thread::muxRelease(&gListLock);
2086 timer.stop();
2087
2088 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2089 LogStreamHandle(Info, monitorinflation) lsh_info;
2090 LogStream * ls = NULL;
2091 if (log_is_enabled(Debug, monitorinflation)) {
2092 ls = &lsh_debug;
2093 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2094 ls = &lsh_info;
2095 }
2096 if (ls != NULL) {
2097 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2098 }
2099 }
2100
2101 // Deflate global idle ObjectMonitors using a JavaThread.
2102 //
2103 void ObjectSynchronizer::deflate_global_idle_monitors_using_JT() {
2104 assert(AsyncDeflateIdleMonitors, "sanity check");
2105 assert(Thread::current()->is_Java_thread(), "precondition");
2106 JavaThread * self = JavaThread::current();
2107
2108 _gOmShouldDeflateIdleMonitors = false;
2109
2110 deflate_common_idle_monitors_using_JT(true /* is_global */, self);
2111 }
2112
2113 // Deflate per-thread idle ObjectMonitors using a JavaThread.
2114 //
2115 void ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT() {
2116 assert(AsyncDeflateIdleMonitors, "sanity check");
2117 assert(Thread::current()->is_Java_thread(), "precondition");
2118 JavaThread * self = JavaThread::current();
2119
2120 self->omShouldDeflateIdleMonitors = false;
2121
2122 deflate_common_idle_monitors_using_JT(false /* !is_global */, self);
2123 }
2124
2125 // Deflate global or per-thread idle ObjectMonitors using a JavaThread.
2126 //
2127 void ObjectSynchronizer::deflate_common_idle_monitors_using_JT(bool is_global, JavaThread * self) {
2128 int deflated_count = 0;
2129 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged ObjectMonitors
2130 ObjectMonitor * freeTailp = NULL;
2131 ObjectMonitor * savedMidInUsep = NULL;
2132 elapsedTimer timer;
2133
2134 if (log_is_enabled(Info, monitorinflation)) {
2135 timer.start();
2136 }
2137
2138 if (is_global) {
2139 Thread::muxAcquire(&gListLock, "deflate_global_idle_monitors_using_JT(1)");
2140 OM_PERFDATA_OP(MonExtant, set_value(gOmInUseCount));
2141 } else {
2142 OM_PERFDATA_OP(MonExtant, inc(self->omInUseCount));
2143 }
2144
2145 do {
2146 int local_deflated_count;
2147 if (is_global) {
2148 local_deflated_count = deflate_monitor_list_using_JT((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp, &savedMidInUsep);
2149 gOmInUseCount -= local_deflated_count;
2150 } else {
2151 local_deflated_count = deflate_monitor_list_using_JT(self->omInUseList_addr(), &freeHeadp, &freeTailp, &savedMidInUsep);
2152 self->omInUseCount -= local_deflated_count;
2153 }
2154 deflated_count += local_deflated_count;
2155
2156 if (freeHeadp != NULL) {
2157 // Move the scavenged ObjectMonitors to the global free list.
2158 guarantee(freeTailp != NULL && local_deflated_count > 0, "freeTailp=" INTPTR_FORMAT ", local_deflated_count=%d", p2i(freeTailp), local_deflated_count);
2159 assert(freeTailp->FreeNext == NULL, "invariant");
2160
2161 if (!is_global) {
2162 Thread::muxAcquire(&gListLock, "deflate_per_thread_idle_monitors_using_JT(2)");
2163 }
2164 // Constant-time list splice - prepend scavenged segment to gFreeList.
2165 freeTailp->FreeNext = gFreeList;
2166 gFreeList = freeHeadp;
2167
2168 gMonitorFreeCount += local_deflated_count;
2169 OM_PERFDATA_OP(Deflations, inc(local_deflated_count));
2170 if (!is_global) {
2171 Thread::muxRelease(&gListLock);
2172 }
2173 }
2174
2175 if (savedMidInUsep != NULL) {
2176 // deflate_monitor_list_using_JT() detected a safepoint starting.
2177 if (is_global) {
2178 Thread::muxRelease(&gListLock);
2179 }
2180 timer.stop();
2181 {
2182 if (is_global) {
2183 log_debug(monitorinflation)("pausing deflation of global idle monitors for a safepoint.");
2184 } else {
2185 log_debug(monitorinflation)("jt=" INTPTR_FORMAT ": pausing deflation of per-thread idle monitors for a safepoint.", p2i(self));
2186 }
2187 assert(SafepointSynchronize::is_synchronizing(), "sanity check");
2188 ThreadBlockInVM blocker(self);
2189 }
2190 // Prepare for another loop after the safepoint.
2191 freeHeadp = NULL;
2192 freeTailp = NULL;
2193 if (log_is_enabled(Info, monitorinflation)) {
2194 timer.start();
2195 }
2196 if (is_global) {
2197 Thread::muxAcquire(&gListLock, "deflate_global_idle_monitors_using_JT(3)");
2198 }
2199 }
2200 } while (savedMidInUsep != NULL);
2201 if (is_global) {
2202 Thread::muxRelease(&gListLock);
2203 }
2204 timer.stop();
2205
2206 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2207 LogStreamHandle(Info, monitorinflation) lsh_info;
2208 LogStream * ls = NULL;
2209 if (log_is_enabled(Debug, monitorinflation)) {
2210 ls = &lsh_debug;
2211 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2212 ls = &lsh_info;
2213 }
2214 if (ls != NULL) {
2215 if (is_global) {
2216 ls->print_cr("async-deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2217 } else {
2218 ls->print_cr("jt=" INTPTR_FORMAT ": async-deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(self), timer.seconds(), deflated_count);
2219 }
2220 }
2221 }
2222
2223 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2224 // Report the cumulative time for deflating each thread's idle
2225 // monitors. Note: if the work is split among more than one
2226 // worker thread, then the reported time will likely be more
2227 // than a beginning to end measurement of the phase.
2228 // Note: AsyncDeflateIdleMonitors only deflates per-thread idle
2229 // monitors at a safepoint when a special cleanup has been requested.
2230 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->perThreadTimes, counters->perThreadScavenged);
2231
2232 bool needs_special_cleanup = is_cleanup_requested();
2233 if (!AsyncDeflateIdleMonitors || needs_special_cleanup) {
2234 // AsyncDeflateIdleMonitors does not use these counters unless
2235 // there is a special cleanup request.
2236
2237 gMonitorFreeCount += counters->nScavenged;
2238
2239 OM_PERFDATA_OP(Deflations, inc(counters->nScavenged));
2240 OM_PERFDATA_OP(MonExtant, set_value(counters->nInCirculation));
2241 }
2242
2243 if (log_is_enabled(Debug, monitorinflation)) {
2244 // exit_globals()'s call to audit_and_print_stats() is done
2245 // at the Info level.
2246 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2247 } else if (log_is_enabled(Info, monitorinflation)) {
2248 Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors");
2249 log_info(monitorinflation)("gMonitorPopulation=%d, gOmInUseCount=%d, "
2250 "gMonitorFreeCount=%d", gMonitorPopulation,
2251 gOmInUseCount, gMonitorFreeCount);
2252 Thread::muxRelease(&gListLock);
2253 }
2254
2255 ForceMonitorScavenge = 0; // Reset
2256 GVars.stwRandom = os::random();
2257 GVars.stwCycle++;
2258 if (needs_special_cleanup) {
2259 set_is_cleanup_requested(false); // special clean up is done
2260 }
2261 }
2262
2263 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
2264 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2265
2266 if (AsyncDeflateIdleMonitors) {
2267 if (!is_cleanup_requested()) {
2268 // Mark the JavaThread for idle monitor cleanup if a special
2269 // cleanup has NOT been requested.
2270 if (thread->omInUseCount > 0) {
2271 // This JavaThread is using monitors so mark it.
2272 thread->omShouldDeflateIdleMonitors = true;
2273 }
2274 return;
2275 }
2276 }
2277
2278 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
2279 ObjectMonitor * freeTailp = NULL;
2280 elapsedTimer timer;
2281
2282 if (log_is_enabled(Info, safepoint, cleanup) ||
2283 log_is_enabled(Info, monitorinflation)) {
2284 timer.start();
2285 }
2286
2287 int deflated_count = deflate_monitor_list(thread->omInUseList_addr(), &freeHeadp, &freeTailp);
2288
2289 Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors");
2290
2291 // Adjust counters
2292 counters->nInCirculation += thread->omInUseCount;
2293 thread->omInUseCount -= deflated_count;
2294 counters->nScavenged += deflated_count;
2295 counters->nInuse += thread->omInUseCount;
2296 counters->perThreadScavenged += deflated_count;
2297
2298 // Move the scavenged monitors back to the global free list.
2299 if (freeHeadp != NULL) {
2300 guarantee(freeTailp != NULL && deflated_count > 0, "invariant");
2301 assert(freeTailp->FreeNext == NULL, "invariant");
2302
2303 // constant-time list splice - prepend scavenged segment to gFreeList
2304 freeTailp->FreeNext = gFreeList;
2305 gFreeList = freeHeadp;
2306 }
2307
2308 timer.stop();
2309 // Safepoint logging cares about cumulative perThreadTimes and
2310 // we'll capture most of the cost, but not the muxRelease() which
2311 // should be cheap.
2312 counters->perThreadTimes += timer.seconds();
2313
2314 Thread::muxRelease(&gListLock);
2315
2316 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2317 LogStreamHandle(Info, monitorinflation) lsh_info;
2318 LogStream * ls = NULL;
2319 if (log_is_enabled(Debug, monitorinflation)) {
2320 ls = &lsh_debug;
2321 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2322 ls = &lsh_info;
2323 }
2324 if (ls != NULL) {
2325 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
2326 }
2327 }
2328
2329 // Monitor cleanup on JavaThread::exit
2330
2331 // Iterate through monitor cache and attempt to release thread's monitors
2332 // Gives up on a particular monitor if an exception occurs, but continues
2333 // the overall iteration, swallowing the exception.
2334 class ReleaseJavaMonitorsClosure: public MonitorClosure {
2335 private:
2336 TRAPS;
2337
2338 public:
2339 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
2340 void do_monitor(ObjectMonitor* mid) {
2341 if (mid->owner() == THREAD) {
2342 (void)mid->complete_exit(CHECK);
2343 }
2344 }
2345 };
2346
2347 // Release all inflated monitors owned by THREAD. Lightweight monitors are
2348 // ignored. This is meant to be called during JNI thread detach which assumes
2349 // all remaining monitors are heavyweight. All exceptions are swallowed.
2350 // Scanning the extant monitor list can be time consuming.
2351 // A simple optimization is to add a per-thread flag that indicates a thread
2352 // called jni_monitorenter() during its lifetime.
2353 //
2354 // Instead of No_Savepoint_Verifier it might be cheaper to
2355 // use an idiom of the form:
2356 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
2357 // <code that must not run at safepoint>
2358 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
2359 // Since the tests are extremely cheap we could leave them enabled
2360 // for normal product builds.
2361
2362 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
2363 assert(THREAD == JavaThread::current(), "must be current Java thread");
2364 NoSafepointVerifier nsv;
2365 ReleaseJavaMonitorsClosure rjmc(THREAD);
2366 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
2367 ObjectSynchronizer::monitors_iterate(&rjmc);
2368 Thread::muxRelease(&gListLock);
2369 THREAD->clear_pending_exception();
2370 }
2371
2372 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
2373 switch (cause) {
2374 case inflate_cause_vm_internal: return "VM Internal";
2375 case inflate_cause_monitor_enter: return "Monitor Enter";
2376 case inflate_cause_wait: return "Monitor Wait";
2377 case inflate_cause_notify: return "Monitor Notify";
2378 case inflate_cause_hash_code: return "Monitor Hash Code";
2379 case inflate_cause_jni_enter: return "JNI Monitor Enter";
2380 case inflate_cause_jni_exit: return "JNI Monitor Exit";
2381 default:
2382 ShouldNotReachHere();
2383 }
2384 return "Unknown";
2385 }
2386
2387 //------------------------------------------------------------------------------
2388 // Debugging code
2389
2390 u_char* ObjectSynchronizer::get_gvars_addr() {
2391 return (u_char*)&GVars;
2392 }
2393
2394 u_char* ObjectSynchronizer::get_gvars_hcSequence_addr() {
2395 return (u_char*)&GVars.hcSequence;
2396 }
2397
2398 size_t ObjectSynchronizer::get_gvars_size() {
2399 return sizeof(SharedGlobals);
2400 }
2401
2402 u_char* ObjectSynchronizer::get_gvars_stwRandom_addr() {
2403 return (u_char*)&GVars.stwRandom;
2404 }
2405
2406 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
2407 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
2408
2409 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2410 LogStreamHandle(Info, monitorinflation) lsh_info;
2411 LogStreamHandle(Trace, monitorinflation) lsh_trace;
2412 LogStream * ls = NULL;
2413 if (log_is_enabled(Trace, monitorinflation)) {
2414 ls = &lsh_trace;
2415 } else if (log_is_enabled(Debug, monitorinflation)) {
2416 ls = &lsh_debug;
2417 } else if (log_is_enabled(Info, monitorinflation)) {
2418 ls = &lsh_info;
2419 }
2420 assert(ls != NULL, "sanity check");
2421
2422 if (!on_exit) {
2423 // Not at VM exit so grab the global list lock.
2424 Thread::muxAcquire(&gListLock, "audit_and_print_stats");
2425 }
2426
2427 // Log counts for the global and per-thread monitor lists:
2428 int chkMonitorPopulation = log_monitor_list_counts(ls);
2429 int error_cnt = 0;
2430
2431 ls->print_cr("Checking global lists:");
2432
2433 // Check gMonitorPopulation:
2434 if (gMonitorPopulation == chkMonitorPopulation) {
2435 ls->print_cr("gMonitorPopulation=%d equals chkMonitorPopulation=%d",
2436 gMonitorPopulation, chkMonitorPopulation);
2437 } else {
2438 ls->print_cr("ERROR: gMonitorPopulation=%d is not equal to "
2439 "chkMonitorPopulation=%d", gMonitorPopulation,
2440 chkMonitorPopulation);
2441 error_cnt++;
2442 }
2443
2444 // Check gOmInUseList and gOmInUseCount:
2445 chk_global_in_use_list_and_count(ls, &error_cnt);
2446
2447 // Check gFreeList and gMonitorFreeCount:
2448 chk_global_free_list_and_count(ls, &error_cnt);
2449
2450 if (!on_exit) {
2451 Thread::muxRelease(&gListLock);
2452 }
2453
2454 ls->print_cr("Checking per-thread lists:");
2455
2456 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2457 // Check omInUseList and omInUseCount:
2458 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
2459
2460 // Check omFreeList and omFreeCount:
2461 chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
2462 }
2463
2464 if (error_cnt == 0) {
2465 ls->print_cr("No errors found in monitor list checks.");
2466 } else {
2467 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
2468 }
2469
2470 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
2471 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
2472 // When exiting this log output is at the Info level. When called
2473 // at a safepoint, this log output is at the Trace level since
2474 // there can be a lot of it.
2475 log_in_use_monitor_details(ls, on_exit);
2476 }
2477
2478 ls->flush();
2479
2480 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2481 }
2482
2483 // Check a free monitor entry; log any errors.
2484 void ObjectSynchronizer::chk_free_entry(JavaThread * jt, ObjectMonitor * n,
2485 outputStream * out, int *error_cnt_p) {
2486 if ((!AsyncDeflateIdleMonitors && n->is_busy()) ||
2487 (AsyncDeflateIdleMonitors && n->is_busy_async())) {
2488 if (jt != NULL) {
2489 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2490 ": free per-thread monitor must not be busy.", p2i(jt),
2491 p2i(n));
2492 } else {
2493 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2494 "must not be busy.", p2i(n));
2495 }
2496 *error_cnt_p = *error_cnt_p + 1;
2497 }
2498 if (n->header() != NULL) {
2499 if (jt != NULL) {
2500 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2501 ": free per-thread monitor must have NULL _header "
2502 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
2503 p2i(n->header()));
2504 *error_cnt_p = *error_cnt_p + 1;
2505 } else if (!AsyncDeflateIdleMonitors) {
2506 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2507 "must have NULL _header field: _header=" INTPTR_FORMAT,
2508 p2i(n), p2i(n->header()));
2509 *error_cnt_p = *error_cnt_p + 1;
2510 }
2511 }
2512 if (n->object() != NULL) {
2513 if (jt != NULL) {
2514 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2515 ": free per-thread monitor must have NULL _object "
2516 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
2517 p2i(n->object()));
2518 } else {
2519 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2520 "must have NULL _object field: _object=" INTPTR_FORMAT,
2521 p2i(n), p2i(n->object()));
2522 }
2523 *error_cnt_p = *error_cnt_p + 1;
2524 }
2525 }
2526
2527 // Check the global free list and count; log the results of the checks.
2528 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
2529 int *error_cnt_p) {
2530 int chkMonitorFreeCount = 0;
2531 for (ObjectMonitor * n = gFreeList; n != NULL; n = n->FreeNext) {
2532 chk_free_entry(NULL /* jt */, n, out, error_cnt_p);
2533 chkMonitorFreeCount++;
2534 }
2535 if (gMonitorFreeCount == chkMonitorFreeCount) {
2536 out->print_cr("gMonitorFreeCount=%d equals chkMonitorFreeCount=%d",
2537 gMonitorFreeCount, chkMonitorFreeCount);
2538 } else {
2539 out->print_cr("ERROR: gMonitorFreeCount=%d is not equal to "
2540 "chkMonitorFreeCount=%d", gMonitorFreeCount,
2541 chkMonitorFreeCount);
2542 *error_cnt_p = *error_cnt_p + 1;
2543 }
2544 }
2545
2546 // Check the global in-use list and count; log the results of the checks.
2547 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
2548 int *error_cnt_p) {
2549 int chkOmInUseCount = 0;
2550 for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
2551 chk_in_use_entry(NULL /* jt */, n, out, error_cnt_p);
2552 chkOmInUseCount++;
2553 }
2554 if (gOmInUseCount == chkOmInUseCount) {
2555 out->print_cr("gOmInUseCount=%d equals chkOmInUseCount=%d", gOmInUseCount,
2556 chkOmInUseCount);
2557 } else {
2558 out->print_cr("ERROR: gOmInUseCount=%d is not equal to chkOmInUseCount=%d",
2559 gOmInUseCount, chkOmInUseCount);
2560 *error_cnt_p = *error_cnt_p + 1;
2561 }
2562 }
2563
2564 // Check an in-use monitor entry; log any errors.
2565 void ObjectSynchronizer::chk_in_use_entry(JavaThread * jt, ObjectMonitor * n,
2566 outputStream * out, int *error_cnt_p) {
2567 if (n->header() == NULL) {
2568 if (jt != NULL) {
2569 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2570 ": in-use per-thread monitor must have non-NULL _header "
2571 "field.", p2i(jt), p2i(n));
2572 } else {
2573 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2574 "must have non-NULL _header field.", p2i(n));
2575 }
2576 *error_cnt_p = *error_cnt_p + 1;
2577 }
2578 if (n->object() == NULL) {
2579 if (jt != NULL) {
2580 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2581 ": in-use per-thread monitor must have non-NULL _object "
2582 "field.", p2i(jt), p2i(n));
2583 } else {
2584 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2585 "must have non-NULL _object field.", p2i(n));
2586 }
2587 *error_cnt_p = *error_cnt_p + 1;
2588 }
2589 const oop obj = (oop)n->object();
2590 const markOop mark = obj->mark();
2591 if (!mark->has_monitor()) {
2592 if (jt != NULL) {
2593 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2594 ": in-use per-thread monitor's object does not think "
2595 "it has a monitor: obj=" INTPTR_FORMAT ", mark="
2596 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), p2i(mark));
2597 } else {
2598 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2599 "monitor's object does not think it has a monitor: obj="
2600 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2601 p2i(obj), p2i(mark));
2602 }
2603 *error_cnt_p = *error_cnt_p + 1;
2604 }
2605 ObjectMonitor * const obj_mon = mark->monitor();
2606 if (n != obj_mon) {
2607 if (jt != NULL) {
2608 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2609 ": in-use per-thread monitor's object does not refer "
2610 "to the same monitor: obj=" INTPTR_FORMAT ", mark="
2611 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
2612 p2i(n), p2i(obj), p2i(mark), p2i(obj_mon));
2613 } else {
2614 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2615 "monitor's object does not refer to the same monitor: obj="
2616 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2617 INTPTR_FORMAT, p2i(n), p2i(obj), p2i(mark), p2i(obj_mon));
2618 }
2619 *error_cnt_p = *error_cnt_p + 1;
2620 }
2621 }
2622
2623 // Check the thread's free list and count; log the results of the checks.
2624 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
2625 outputStream * out,
2626 int *error_cnt_p) {
2627 int chkOmFreeCount = 0;
2628 for (ObjectMonitor * n = jt->omFreeList; n != NULL; n = n->FreeNext) {
2629 chk_free_entry(jt, n, out, error_cnt_p);
2630 chkOmFreeCount++;
2631 }
2632 if (jt->omFreeCount == chkOmFreeCount) {
2633 out->print_cr("jt=" INTPTR_FORMAT ": omFreeCount=%d equals "
2634 "chkOmFreeCount=%d", p2i(jt), jt->omFreeCount, chkOmFreeCount);
2635 } else {
2636 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omFreeCount=%d is not "
2637 "equal to chkOmFreeCount=%d", p2i(jt), jt->omFreeCount,
2638 chkOmFreeCount);
2639 *error_cnt_p = *error_cnt_p + 1;
2640 }
2641 }
2642
2643 // Check the thread's in-use list and count; log the results of the checks.
2644 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
2645 outputStream * out,
2646 int *error_cnt_p) {
2647 int chkOmInUseCount = 0;
2648 for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2649 chk_in_use_entry(jt, n, out, error_cnt_p);
2650 chkOmInUseCount++;
2651 }
2652 if (jt->omInUseCount == chkOmInUseCount) {
2653 out->print_cr("jt=" INTPTR_FORMAT ": omInUseCount=%d equals "
2654 "chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2655 chkOmInUseCount);
2656 } else {
2657 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omInUseCount=%d is not "
2658 "equal to chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2659 chkOmInUseCount);
2660 *error_cnt_p = *error_cnt_p + 1;
2661 }
2662 }
2663
2664 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2665 // flags indicate why the entry is in-use, 'object' and 'object type'
2666 // indicate the associated object and its type.
2667 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out,
2668 bool on_exit) {
2669 if (!on_exit) {
2670 // Not at VM exit so grab the global list lock.
2671 Thread::muxAcquire(&gListLock, "log_in_use_monitor_details");
2672 }
2673
2674 if (gOmInUseCount > 0) {
2675 out->print_cr("In-use global monitor info:");
2676 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2677 out->print_cr("%18s %s %7s %18s %18s",
2678 "monitor", "BHL", "ref_cnt", "object", "object type");
2679 out->print_cr("================== === ======= ================== ==================");
2680 for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
2681 const oop obj = (oop) n->object();
2682 const markOop mark = n->header();
2683 ResourceMark rm;
2684 out->print_cr(INTPTR_FORMAT " %d%d%d %7d " INTPTR_FORMAT " %s",
2685 p2i(n), n->is_busy() != 0, mark->hash() != 0,
2686 n->owner() != NULL, (int)n->ref_count(), p2i(obj),
2687 obj->klass()->external_name());
2688 }
2689 }
2690
2691 if (!on_exit) {
2692 Thread::muxRelease(&gListLock);
2693 }
2694
2695 out->print_cr("In-use per-thread monitor info:");
2696 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2697 out->print_cr("%18s %18s %s %7s %18s %18s",
2698 "jt", "monitor", "BHL", "ref_cnt", "object", "object type");
2699 out->print_cr("================== ================== === ======= ================== ==================");
2700 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2701 for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2702 const oop obj = (oop) n->object();
2703 const markOop mark = n->header();
2704 ResourceMark rm;
2705 out->print_cr(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d %7d "
2706 INTPTR_FORMAT " %s", p2i(jt), p2i(n), n->is_busy() != 0,
2707 mark->hash() != 0, n->owner() != NULL, (int)n->ref_count(),
2708 p2i(obj), obj->klass()->external_name());
2709 }
2710 }
2711
2712 out->flush();
2713 }
2714
2715 // Log counts for the global and per-thread monitor lists and return
2716 // the population count.
2717 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2718 int popCount = 0;
2719 out->print_cr("%18s %10s %10s %10s",
2720 "Global Lists:", "InUse", "Free", "Total");
2721 out->print_cr("================== ========== ========== ==========");
2722 out->print_cr("%18s %10d %10d %10d", "",
2723 gOmInUseCount, gMonitorFreeCount, gMonitorPopulation);
2724 popCount += gOmInUseCount + gMonitorFreeCount;
2725
2726 out->print_cr("%18s %10s %10s %10s",
2727 "Per-Thread Lists:", "InUse", "Free", "Provision");
2728 out->print_cr("================== ========== ========== ==========");
2729
2730 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2731 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
2732 jt->omInUseCount, jt->omFreeCount, jt->omFreeProvision);
2733 popCount += jt->omInUseCount + jt->omFreeCount;
2734 }
2735 return popCount;
2736 }
2737
2738 #ifndef PRODUCT
2739
2740 // Check if monitor belongs to the monitor cache
2741 // The list is grow-only so it's *relatively* safe to traverse
2742 // the list of extant blocks without taking a lock.
2743
2744 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
2745 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
2746 while (block != NULL) {
2747 assert(block->object() == CHAINMARKER, "must be a block header");
2748 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
2749 address mon = (address)monitor;
2750 address blk = (address)block;
2751 size_t diff = mon - blk;
2752 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "must be aligned");
2753 return 1;
2754 }
2755 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
2756 }
2757 return 0;
2758 }
2759
2760 #endif