1 /*
2 * Copyright (c) 1998, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/vmSymbols.hpp"
27 #include "logging/log.hpp"
28 #include "logging/logStream.hpp"
29 #include "jfr/jfrEvents.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "memory/metaspaceShared.hpp"
32 #include "memory/padded.hpp"
33 #include "memory/resourceArea.hpp"
34 #include "memory/universe.hpp"
35 #include "oops/markOop.hpp"
36 #include "oops/oop.inline.hpp"
37 #include "runtime/atomic.hpp"
38 #include "runtime/biasedLocking.hpp"
39 #include "runtime/handles.inline.hpp"
40 #include "runtime/interfaceSupport.inline.hpp"
41 #include "runtime/mutexLocker.hpp"
42 #include "runtime/objectMonitor.hpp"
43 #include "runtime/objectMonitor.inline.hpp"
44 #include "runtime/osThread.hpp"
45 #include "runtime/safepointVerifiers.hpp"
46 #include "runtime/sharedRuntime.hpp"
47 #include "runtime/stubRoutines.hpp"
48 #include "runtime/synchronizer.hpp"
49 #include "runtime/thread.inline.hpp"
50 #include "runtime/timer.hpp"
51 #include "runtime/vframe.hpp"
52 #include "runtime/vmThread.hpp"
53 #include "utilities/align.hpp"
54 #include "utilities/dtrace.hpp"
55 #include "utilities/events.hpp"
56 #include "utilities/preserveException.hpp"
57
58 // The "core" versions of monitor enter and exit reside in this file.
59 // The interpreter and compilers contain specialized transliterated
60 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
61 // for instance. If you make changes here, make sure to modify the
62 // interpreter, and both C1 and C2 fast-path inline locking code emission.
63 //
64 // -----------------------------------------------------------------------------
65
66 #ifdef DTRACE_ENABLED
67
68 // Only bother with this argument setup if dtrace is available
69 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
70
71 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
72 char* bytes = NULL; \
73 int len = 0; \
74 jlong jtid = SharedRuntime::get_java_tid(thread); \
75 Symbol* klassname = ((oop)(obj))->klass()->name(); \
76 if (klassname != NULL) { \
77 bytes = (char*)klassname->bytes(); \
78 len = klassname->utf8_length(); \
79 }
80
81 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
82 { \
83 if (DTraceMonitorProbes) { \
84 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
85 HOTSPOT_MONITOR_WAIT(jtid, \
86 (uintptr_t)(monitor), bytes, len, (millis)); \
87 } \
88 }
89
90 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
91 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
92 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
93
94 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
95 { \
96 if (DTraceMonitorProbes) { \
97 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
98 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
99 (uintptr_t)(monitor), bytes, len); \
100 } \
101 }
102
103 #else // ndef DTRACE_ENABLED
104
105 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
106 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
107
108 #endif // ndef DTRACE_ENABLED
109
110 // This exists only as a workaround of dtrace bug 6254741
111 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
112 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
113 return 0;
114 }
115
116 #define NINFLATIONLOCKS 256
117 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
118
119 // global list of blocks of monitors
120 PaddedEnd<ObjectMonitor> * volatile ObjectSynchronizer::gBlockList = NULL;
121 // global monitor free list
122 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL;
123 // global monitor in-use list, for moribund threads,
124 // monitors they inflated need to be scanned for deflation
125 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL;
126 // count of entries in gOmInUseList
127 int ObjectSynchronizer::gOmInUseCount = 0;
128 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
129 bool volatile ObjectSynchronizer::_is_special_deflation_requested = false;
130 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
131
132 static volatile intptr_t gListLock = 0; // protects global monitor lists
133 static volatile int gMonitorFreeCount = 0; // # on gFreeList
134 static volatile int gMonitorPopulation = 0; // # Extant -- in circulation
135
136 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
137
138
139 // =====================> Quick functions
140
141 // The quick_* forms are special fast-path variants used to improve
142 // performance. In the simplest case, a "quick_*" implementation could
143 // simply return false, in which case the caller will perform the necessary
144 // state transitions and call the slow-path form.
145 // The fast-path is designed to handle frequently arising cases in an efficient
146 // manner and is just a degenerate "optimistic" variant of the slow-path.
147 // returns true -- to indicate the call was satisfied.
148 // returns false -- to indicate the call needs the services of the slow-path.
149 // A no-loitering ordinance is in effect for code in the quick_* family
150 // operators: safepoints or indefinite blocking (blocking that might span a
151 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
152 // entry.
153 //
154 // Consider: An interesting optimization is to have the JIT recognize the
155 // following common idiom:
156 // synchronized (someobj) { .... ; notify(); }
157 // That is, we find a notify() or notifyAll() call that immediately precedes
158 // the monitorexit operation. In that case the JIT could fuse the operations
159 // into a single notifyAndExit() runtime primitive.
160
161 bool ObjectSynchronizer::quick_notify(oopDesc * obj, Thread * self, bool all) {
162 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
163 assert(self->is_Java_thread(), "invariant");
164 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
165 NoSafepointVerifier nsv;
166 if (obj == NULL) return false; // slow-path for invalid obj
167 const markOop mark = obj->mark();
168
169 if (mark->has_locker() && self->is_lock_owned((address)mark->locker())) {
170 // Degenerate notify
171 // stack-locked by caller so by definition the implied waitset is empty.
172 return true;
173 }
174
175 if (mark->has_monitor()) {
176 ObjectMonitor * const mon = mark->monitor();
177 assert(oopDesc::equals((oop) mon->object(), obj), "invariant");
178 if (mon->owner() != self) return false; // slow-path for IMS exception
179
180 if (mon->first_waiter() != NULL) {
181 // We have one or more waiters. Since this is an inflated monitor
182 // that we own, we can transfer one or more threads from the waitset
183 // to the entrylist here and now, avoiding the slow-path.
184 if (all) {
185 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
186 } else {
187 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
188 }
189 int tally = 0;
190 do {
191 mon->INotify(self);
192 ++tally;
193 } while (mon->first_waiter() != NULL && all);
194 OM_PERFDATA_OP(Notifications, inc(tally));
195 }
196 return true;
197 }
198
199 // biased locking and any other IMS exception states take the slow-path
200 return false;
201 }
202
203
204 // The LockNode emitted directly at the synchronization site would have
205 // been too big if it were to have included support for the cases of inflated
206 // recursive enter and exit, so they go here instead.
207 // Note that we can't safely call AsyncPrintJavaStack() from within
208 // quick_enter() as our thread state remains _in_Java.
209
210 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
211 BasicLock * lock) {
212 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
213 assert(Self->is_Java_thread(), "invariant");
214 assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
215 NoSafepointVerifier nsv;
216 if (obj == NULL) return false; // Need to throw NPE
217
218 while (true) {
219 const markOop mark = obj->mark();
220
221 if (mark->has_monitor()) {
222 ObjectMonitorHandle omh;
223 if (!omh.save_om_ptr(obj, mark)) {
224 // Lost a race with async deflation so try again.
225 assert(AsyncDeflateIdleMonitors, "sanity check");
226 continue;
227 }
228 ObjectMonitor * const m = omh.om_ptr();
229 assert(oopDesc::equals((oop) m->object(), obj), "invariant");
230 Thread * const owner = (Thread *) m->_owner;
231
232 // Lock contention and Transactional Lock Elision (TLE) diagnostics
233 // and observability
234 // Case: light contention possibly amenable to TLE
235 // Case: TLE inimical operations such as nested/recursive synchronization
236
237 if (owner == Self) {
238 m->_recursions++;
239 return true;
240 }
241
242 // This Java Monitor is inflated so obj's header will never be
243 // displaced to this thread's BasicLock. Make the displaced header
244 // non-NULL so this BasicLock is not seen as recursive nor as
245 // being locked. We do this unconditionally so that this thread's
246 // BasicLock cannot be mis-interpreted by any stack walkers. For
247 // performance reasons, stack walkers generally first check for
248 // Biased Locking in the object's header, the second check is for
249 // stack-locking in the object's header, the third check is for
250 // recursive stack-locking in the displaced header in the BasicLock,
251 // and last are the inflated Java Monitor (ObjectMonitor) checks.
252 lock->set_displaced_header(markOopDesc::unused_mark());
253
254 if (owner == NULL && Atomic::replace_if_null(Self, &(m->_owner))) {
255 assert(m->_recursions == 0, "invariant");
256 return true;
257 }
258 }
259 break;
260 }
261
262 // Note that we could inflate in quick_enter.
263 // This is likely a useful optimization
264 // Critically, in quick_enter() we must not:
265 // -- perform bias revocation, or
266 // -- block indefinitely, or
267 // -- reach a safepoint
268
269 return false; // revert to slow-path
270 }
271
272 // -----------------------------------------------------------------------------
273 // Fast Monitor Enter/Exit
274 // This the fast monitor enter. The interpreter and compiler use
275 // some assembly copies of this code. Make sure update those code
276 // if the following function is changed. The implementation is
277 // extremely sensitive to race condition. Be careful.
278
279 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
280 bool attempt_rebias, TRAPS) {
281 if (UseBiasedLocking) {
282 if (!SafepointSynchronize::is_at_safepoint()) {
283 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
284 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
285 return;
286 }
287 } else {
288 assert(!attempt_rebias, "can not rebias toward VM thread");
289 BiasedLocking::revoke_at_safepoint(obj);
290 }
291 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
292 }
293
294 slow_enter(obj, lock, THREAD);
295 }
296
297 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
298 markOop mark = object->mark();
299 // We cannot check for Biased Locking if we are racing an inflation.
300 assert(mark == markOopDesc::INFLATING() ||
301 !mark->has_bias_pattern(), "should not see bias pattern here");
302
303 markOop dhw = lock->displaced_header();
304 if (dhw == NULL) {
305 // If the displaced header is NULL, then this exit matches up with
306 // a recursive enter. No real work to do here except for diagnostics.
307 #ifndef PRODUCT
308 if (mark != markOopDesc::INFLATING()) {
309 // Only do diagnostics if we are not racing an inflation. Simply
310 // exiting a recursive enter of a Java Monitor that is being
311 // inflated is safe; see the has_monitor() comment below.
312 assert(!mark->is_neutral(), "invariant");
313 assert(!mark->has_locker() ||
314 THREAD->is_lock_owned((address)mark->locker()), "invariant");
315 if (mark->has_monitor()) {
316 // The BasicLock's displaced_header is marked as a recursive
317 // enter and we have an inflated Java Monitor (ObjectMonitor).
318 // This is a special case where the Java Monitor was inflated
319 // after this thread entered the stack-lock recursively. When a
320 // Java Monitor is inflated, we cannot safely walk the Java
321 // Monitor owner's stack and update the BasicLocks because a
322 // Java Monitor can be asynchronously inflated by a thread that
323 // does not own the Java Monitor.
324 ObjectMonitor * m = mark->monitor();
325 assert(((oop)(m->object()))->mark() == mark, "invariant");
326 assert(m->is_entered(THREAD), "invariant");
327 }
328 }
329 #endif
330 return;
331 }
332
333 if (mark == (markOop) lock) {
334 // If the object is stack-locked by the current thread, try to
335 // swing the displaced header from the BasicLock back to the mark.
336 assert(dhw->is_neutral(), "invariant");
337 if (object->cas_set_mark(dhw, mark) == mark) {
338 return;
339 }
340 }
341
342 // We have to take the slow-path of possible inflation and then exit.
343 ObjectMonitorHandle omh;
344 inflate(&omh, THREAD, object, inflate_cause_vm_internal);
345 omh.om_ptr()->exit(true, THREAD);
346 }
347
348 // -----------------------------------------------------------------------------
349 // Interpreter/Compiler Slow Case
350 // This routine is used to handle interpreter/compiler slow case
351 // We don't need to use fast path here, because it must have been
352 // failed in the interpreter/compiler code.
353 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
354 markOop mark = obj->mark();
355 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
356
357 if (mark->is_neutral()) {
358 // Anticipate successful CAS -- the ST of the displaced mark must
359 // be visible <= the ST performed by the CAS.
360 lock->set_displaced_header(mark);
361 if (mark == obj()->cas_set_mark((markOop) lock, mark)) {
362 return;
363 }
364 // Fall through to inflate() ...
365 } else if (mark->has_locker() &&
366 THREAD->is_lock_owned((address)mark->locker())) {
367 assert(lock != mark->locker(), "must not re-lock the same lock");
368 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
369 lock->set_displaced_header(NULL);
370 return;
371 }
372
373 // The object header will never be displaced to this lock,
374 // so it does not matter what the value is, except that it
375 // must be non-zero to avoid looking like a re-entrant lock,
376 // and must not look locked either.
377 lock->set_displaced_header(markOopDesc::unused_mark());
378 ObjectMonitorHandle omh;
379 inflate(&omh, THREAD, obj(), inflate_cause_monitor_enter);
380 omh.om_ptr()->enter(THREAD);
381 }
382
383 // This routine is used to handle interpreter/compiler slow case
384 // We don't need to use fast path here, because it must have
385 // failed in the interpreter/compiler code. Simply use the heavy
386 // weight monitor should be ok, unless someone find otherwise.
387 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
388 fast_exit(object, lock, THREAD);
389 }
390
391 // -----------------------------------------------------------------------------
392 // Class Loader support to workaround deadlocks on the class loader lock objects
393 // Also used by GC
394 // complete_exit()/reenter() are used to wait on a nested lock
395 // i.e. to give up an outer lock completely and then re-enter
396 // Used when holding nested locks - lock acquisition order: lock1 then lock2
397 // 1) complete_exit lock1 - saving recursion count
398 // 2) wait on lock2
399 // 3) when notified on lock2, unlock lock2
400 // 4) reenter lock1 with original recursion count
401 // 5) lock lock2
402 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
403 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
404 if (UseBiasedLocking) {
405 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
406 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
407 }
408
409 ObjectMonitorHandle omh;
410 inflate(&omh, THREAD, obj(), inflate_cause_vm_internal);
411 intptr_t ret_code = omh.om_ptr()->complete_exit(THREAD);
412 return ret_code;
413 }
414
415 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
416 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
417 if (UseBiasedLocking) {
418 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
419 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
420 }
421
422 ObjectMonitorHandle omh;
423 inflate(&omh, THREAD, obj(), inflate_cause_vm_internal);
424 omh.om_ptr()->reenter(recursion, THREAD);
425 }
426 // -----------------------------------------------------------------------------
427 // JNI locks on java objects
428 // NOTE: must use heavy weight monitor to handle jni monitor enter
429 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
430 // the current locking is from JNI instead of Java code
431 if (UseBiasedLocking) {
432 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
433 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
434 }
435 THREAD->set_current_pending_monitor_is_from_java(false);
436 ObjectMonitorHandle omh;
437 inflate(&omh, THREAD, obj(), inflate_cause_jni_enter);
438 omh.om_ptr()->enter(THREAD);
439 THREAD->set_current_pending_monitor_is_from_java(true);
440 }
441
442 // NOTE: must use heavy weight monitor to handle jni monitor exit
443 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
444 if (UseBiasedLocking) {
445 Handle h_obj(THREAD, obj);
446 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
447 obj = h_obj();
448 }
449 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
450
451 ObjectMonitorHandle omh;
452 inflate(&omh, THREAD, obj, inflate_cause_jni_exit);
453 ObjectMonitor * monitor = omh.om_ptr();
454 // If this thread has locked the object, exit the monitor. Note: can't use
455 // monitor->check(CHECK); must exit even if an exception is pending.
456 if (monitor->check(THREAD)) {
457 monitor->exit(true, THREAD);
458 }
459 }
460
461 // -----------------------------------------------------------------------------
462 // Internal VM locks on java objects
463 // standard constructor, allows locking failures
464 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
465 _dolock = doLock;
466 _thread = thread;
467 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
468 _obj = obj;
469
470 if (_dolock) {
471 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
472 }
473 }
474
475 ObjectLocker::~ObjectLocker() {
476 if (_dolock) {
477 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
478 }
479 }
480
481
482 // -----------------------------------------------------------------------------
483 // Wait/Notify/NotifyAll
484 // NOTE: must use heavy weight monitor to handle wait()
485 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
486 if (UseBiasedLocking) {
487 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
488 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
489 }
490 if (millis < 0) {
491 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
492 }
493 ObjectMonitorHandle omh;
494 inflate(&omh, THREAD, obj(), inflate_cause_wait);
495 ObjectMonitor * monitor = omh.om_ptr();
496
497 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
498 monitor->wait(millis, true, THREAD);
499
500 // This dummy call is in place to get around dtrace bug 6254741. Once
501 // that's fixed we can uncomment the following line, remove the call
502 // and change this function back into a "void" func.
503 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
504 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
505 return ret_code;
506 }
507
508 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
509 if (UseBiasedLocking) {
510 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
511 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
512 }
513 if (millis < 0) {
514 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
515 }
516 ObjectMonitorHandle omh;
517 inflate(&omh, THREAD, obj(), inflate_cause_wait);
518 omh.om_ptr()->wait(millis, false, THREAD);
519 }
520
521 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
522 if (UseBiasedLocking) {
523 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
524 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
525 }
526
527 markOop mark = obj->mark();
528 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
529 return;
530 }
531 ObjectMonitorHandle omh;
532 inflate(&omh, THREAD, obj(), inflate_cause_notify);
533 omh.om_ptr()->notify(THREAD);
534 }
535
536 // NOTE: see comment of notify()
537 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
538 if (UseBiasedLocking) {
539 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
540 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
541 }
542
543 markOop mark = obj->mark();
544 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
545 return;
546 }
547 ObjectMonitorHandle omh;
548 inflate(&omh, THREAD, obj(), inflate_cause_notify);
549 omh.om_ptr()->notifyAll(THREAD);
550 }
551
552 // -----------------------------------------------------------------------------
553 // Hash Code handling
554 //
555 // Performance concern:
556 // OrderAccess::storestore() calls release() which at one time stored 0
557 // into the global volatile OrderAccess::dummy variable. This store was
558 // unnecessary for correctness. Many threads storing into a common location
559 // causes considerable cache migration or "sloshing" on large SMP systems.
560 // As such, I avoided using OrderAccess::storestore(). In some cases
561 // OrderAccess::fence() -- which incurs local latency on the executing
562 // processor -- is a better choice as it scales on SMP systems.
563 //
564 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
565 // a discussion of coherency costs. Note that all our current reference
566 // platforms provide strong ST-ST order, so the issue is moot on IA32,
567 // x64, and SPARC.
568 //
569 // As a general policy we use "volatile" to control compiler-based reordering
570 // and explicit fences (barriers) to control for architectural reordering
571 // performed by the CPU(s) or platform.
572
573 struct SharedGlobals {
574 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
575 // These are highly shared mostly-read variables.
576 // To avoid false-sharing they need to be the sole occupants of a cache line.
577 volatile int stwRandom;
578 volatile int stwCycle;
579 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
580 // Hot RW variable -- Sequester to avoid false-sharing
581 volatile int hcSequence;
582 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
583 };
584
585 static SharedGlobals GVars;
586 static int MonitorScavengeThreshold = 1000000;
587 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
588
589 static markOop ReadStableMark(oop obj) {
590 markOop mark = obj->mark();
591 if (!mark->is_being_inflated()) {
592 return mark; // normal fast-path return
593 }
594
595 int its = 0;
596 for (;;) {
597 markOop mark = obj->mark();
598 if (!mark->is_being_inflated()) {
599 return mark; // normal fast-path return
600 }
601
602 // The object is being inflated by some other thread.
603 // The caller of ReadStableMark() must wait for inflation to complete.
604 // Avoid live-lock
605 // TODO: consider calling SafepointSynchronize::do_call_back() while
606 // spinning to see if there's a safepoint pending. If so, immediately
607 // yielding or blocking would be appropriate. Avoid spinning while
608 // there is a safepoint pending.
609 // TODO: add inflation contention performance counters.
610 // TODO: restrict the aggregate number of spinners.
611
612 ++its;
613 if (its > 10000 || !os::is_MP()) {
614 if (its & 1) {
615 os::naked_yield();
616 } else {
617 // Note that the following code attenuates the livelock problem but is not
618 // a complete remedy. A more complete solution would require that the inflating
619 // thread hold the associated inflation lock. The following code simply restricts
620 // the number of spinners to at most one. We'll have N-2 threads blocked
621 // on the inflationlock, 1 thread holding the inflation lock and using
622 // a yield/park strategy, and 1 thread in the midst of inflation.
623 // A more refined approach would be to change the encoding of INFLATING
624 // to allow encapsulation of a native thread pointer. Threads waiting for
625 // inflation to complete would use CAS to push themselves onto a singly linked
626 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
627 // and calling park(). When inflation was complete the thread that accomplished inflation
628 // would detach the list and set the markword to inflated with a single CAS and
629 // then for each thread on the list, set the flag and unpark() the thread.
630 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
631 // wakes at most one thread whereas we need to wake the entire list.
632 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
633 int YieldThenBlock = 0;
634 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
635 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
636 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
637 while (obj->mark() == markOopDesc::INFLATING()) {
638 // Beware: NakedYield() is advisory and has almost no effect on some platforms
639 // so we periodically call Self->_ParkEvent->park(1).
640 // We use a mixed spin/yield/block mechanism.
641 if ((YieldThenBlock++) >= 16) {
642 Thread::current()->_ParkEvent->park(1);
643 } else {
644 os::naked_yield();
645 }
646 }
647 Thread::muxRelease(gInflationLocks + ix);
648 }
649 } else {
650 SpinPause(); // SMP-polite spinning
651 }
652 }
653 }
654
655 // hashCode() generation :
656 //
657 // Possibilities:
658 // * MD5Digest of {obj,stwRandom}
659 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
660 // * A DES- or AES-style SBox[] mechanism
661 // * One of the Phi-based schemes, such as:
662 // 2654435761 = 2^32 * Phi (golden ratio)
663 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
664 // * A variation of Marsaglia's shift-xor RNG scheme.
665 // * (obj ^ stwRandom) is appealing, but can result
666 // in undesirable regularity in the hashCode values of adjacent objects
667 // (objects allocated back-to-back, in particular). This could potentially
668 // result in hashtable collisions and reduced hashtable efficiency.
669 // There are simple ways to "diffuse" the middle address bits over the
670 // generated hashCode values:
671
672 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
673 intptr_t value = 0;
674 if (hashCode == 0) {
675 // This form uses global Park-Miller RNG.
676 // On MP system we'll have lots of RW access to a global, so the
677 // mechanism induces lots of coherency traffic.
678 value = os::random();
679 } else if (hashCode == 1) {
680 // This variation has the property of being stable (idempotent)
681 // between STW operations. This can be useful in some of the 1-0
682 // synchronization schemes.
683 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
684 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
685 } else if (hashCode == 2) {
686 value = 1; // for sensitivity testing
687 } else if (hashCode == 3) {
688 value = ++GVars.hcSequence;
689 } else if (hashCode == 4) {
690 value = cast_from_oop<intptr_t>(obj);
691 } else {
692 // Marsaglia's xor-shift scheme with thread-specific state
693 // This is probably the best overall implementation -- we'll
694 // likely make this the default in future releases.
695 unsigned t = Self->_hashStateX;
696 t ^= (t << 11);
697 Self->_hashStateX = Self->_hashStateY;
698 Self->_hashStateY = Self->_hashStateZ;
699 Self->_hashStateZ = Self->_hashStateW;
700 unsigned v = Self->_hashStateW;
701 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
702 Self->_hashStateW = v;
703 value = v;
704 }
705
706 value &= markOopDesc::hash_mask;
707 if (value == 0) value = 0xBAD;
708 assert(value != markOopDesc::no_hash, "invariant");
709 return value;
710 }
711
712 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
713 if (UseBiasedLocking) {
714 // NOTE: many places throughout the JVM do not expect a safepoint
715 // to be taken here, in particular most operations on perm gen
716 // objects. However, we only ever bias Java instances and all of
717 // the call sites of identity_hash that might revoke biases have
718 // been checked to make sure they can handle a safepoint. The
719 // added check of the bias pattern is to avoid useless calls to
720 // thread-local storage.
721 if (obj->mark()->has_bias_pattern()) {
722 // Handle for oop obj in case of STW safepoint
723 Handle hobj(Self, obj);
724 // Relaxing assertion for bug 6320749.
725 assert(Universe::verify_in_progress() ||
726 !SafepointSynchronize::is_at_safepoint(),
727 "biases should not be seen by VM thread here");
728 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
729 obj = hobj();
730 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
731 }
732 }
733
734 // hashCode() is a heap mutator ...
735 // Relaxing assertion for bug 6320749.
736 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
737 !SafepointSynchronize::is_at_safepoint(), "invariant");
738 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
739 Self->is_Java_thread() , "invariant");
740 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
741 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
742
743 while (true) {
744 ObjectMonitor* monitor = NULL;
745 markOop temp, test;
746 intptr_t hash;
747 markOop mark = ReadStableMark(obj);
748
749 // object should remain ineligible for biased locking
750 assert(!mark->has_bias_pattern(), "invariant");
751
752 if (mark->is_neutral()) {
753 hash = mark->hash(); // this is a normal header
754 if (hash != 0) { // if it has hash, just return it
755 return hash;
756 }
757 hash = get_next_hash(Self, obj); // allocate a new hash code
758 temp = mark->copy_set_hash(hash); // merge the hash code into header
759 // use (machine word version) atomic operation to install the hash
760 test = obj->cas_set_mark(temp, mark);
761 if (test == mark) {
762 return hash;
763 }
764 // If atomic operation failed, we must inflate the header
765 // into heavy weight monitor. We could add more code here
766 // for fast path, but it does not worth the complexity.
767 } else if (mark->has_monitor()) {
768 ObjectMonitorHandle omh;
769 if (!omh.save_om_ptr(obj, mark)) {
770 // Lost a race with async deflation so try again.
771 assert(AsyncDeflateIdleMonitors, "sanity check");
772 continue;
773 }
774 monitor = omh.om_ptr();
775 temp = monitor->header();
776 assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(temp));
777 hash = temp->hash();
778 if (hash != 0) {
779 return hash;
780 }
781 // Skip to the following code to reduce code size
782 } else if (Self->is_lock_owned((address)mark->locker())) {
783 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
784 assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(temp));
785 hash = temp->hash(); // by current thread, check if the displaced
786 if (hash != 0) { // header contains hash code
787 return hash;
788 }
789 // WARNING:
790 // The displaced header in the BasicLock on a thread's stack
791 // is strictly immutable. It CANNOT be changed in ANY cases.
792 // So we have to inflate the stack lock into an ObjectMonitor
793 // even if the current thread owns the lock. The BasicLock on
794 // a thread's stack can be asynchronously read by other threads
795 // during an inflate() call so any change to that stack memory
796 // may not propagate to other threads correctly.
797 }
798
799 // Inflate the monitor to set hash code
800 ObjectMonitorHandle omh;
801 inflate(&omh, Self, obj, inflate_cause_hash_code);
802 monitor = omh.om_ptr();
803 // Load displaced header and check it has hash code
804 mark = monitor->header();
805 assert(mark->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(mark));
806 hash = mark->hash();
807 if (hash == 0) {
808 hash = get_next_hash(Self, obj);
809 temp = mark->copy_set_hash(hash); // merge hash code into header
810 assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(temp));
811 test = Atomic::cmpxchg(temp, monitor->header_addr(), mark);
812 if (test != mark) {
813 // The only non-deflation update to the ObjectMonitor's
814 // header/dmw field is to merge in the hash code. If someone
815 // adds a new usage of the header/dmw field, please update
816 // this code.
817 // ObjectMonitor::install_displaced_markword_in_object()
818 // does mark the header/dmw field as part of async deflation,
819 // but that protocol cannot happen now due to the
820 // ObjectMonitorHandle above.
821 hash = test->hash();
822 assert(test->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(test));
823 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
824 }
825 }
826 // We finally get the hash
827 return hash;
828 }
829 }
830
831 // Deprecated -- use FastHashCode() instead.
832
833 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
834 return FastHashCode(Thread::current(), obj());
835 }
836
837
838 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
839 Handle h_obj) {
840 if (UseBiasedLocking) {
841 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
842 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
843 }
844
845 assert(thread == JavaThread::current(), "Can only be called on current thread");
846 oop obj = h_obj();
847
848 while (true) {
849 markOop mark = ReadStableMark(obj);
850
851 // Uncontended case, header points to stack
852 if (mark->has_locker()) {
853 return thread->is_lock_owned((address)mark->locker());
854 }
855 // Contended case, header points to ObjectMonitor (tagged pointer)
856 if (mark->has_monitor()) {
857 ObjectMonitorHandle omh;
858 if (!omh.save_om_ptr(obj, mark)) {
859 // Lost a race with async deflation so try again.
860 assert(AsyncDeflateIdleMonitors, "sanity check");
861 continue;
862 }
863 bool ret_code = omh.om_ptr()->is_entered(thread) != 0;
864 return ret_code;
865 }
866 // Unlocked case, header in place
867 assert(mark->is_neutral(), "sanity check");
868 return false;
869 }
870 }
871
872 // Be aware of this method could revoke bias of the lock object.
873 // This method queries the ownership of the lock handle specified by 'h_obj'.
874 // If the current thread owns the lock, it returns owner_self. If no
875 // thread owns the lock, it returns owner_none. Otherwise, it will return
876 // owner_other.
877 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
878 (JavaThread *self, Handle h_obj) {
879 // The caller must beware this method can revoke bias, and
880 // revocation can result in a safepoint.
881 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
882 assert(self->thread_state() != _thread_blocked, "invariant");
883
884 // Possible mark states: neutral, biased, stack-locked, inflated
885
886 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
887 // CASE: biased
888 BiasedLocking::revoke_and_rebias(h_obj, false, self);
889 assert(!h_obj->mark()->has_bias_pattern(),
890 "biases should be revoked by now");
891 }
892
893 assert(self == JavaThread::current(), "Can only be called on current thread");
894 oop obj = h_obj();
895
896 while (true) {
897 markOop mark = ReadStableMark(obj);
898
899 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
900 if (mark->has_locker()) {
901 return self->is_lock_owned((address)mark->locker()) ?
902 owner_self : owner_other;
903 }
904
905 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
906 // The Object:ObjectMonitor relationship is stable as long as we're
907 // not at a safepoint and AsyncDeflateIdleMonitors is false.
908 if (mark->has_monitor()) {
909 ObjectMonitorHandle omh;
910 if (!omh.save_om_ptr(obj, mark)) {
911 // Lost a race with async deflation so try again.
912 assert(AsyncDeflateIdleMonitors, "sanity check");
913 continue;
914 }
915 ObjectMonitor * monitor = omh.om_ptr();
916 void * owner = monitor->_owner;
917 if (owner == NULL) return owner_none;
918 return (owner == self ||
919 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
920 }
921
922 // CASE: neutral
923 assert(mark->is_neutral(), "sanity check");
924 return owner_none; // it's unlocked
925 }
926 }
927
928 // FIXME: jvmti should call this
929 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
930 if (UseBiasedLocking) {
931 if (SafepointSynchronize::is_at_safepoint()) {
932 BiasedLocking::revoke_at_safepoint(h_obj);
933 } else {
934 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
935 }
936 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
937 }
938
939 oop obj = h_obj();
940
941 while (true) {
942 address owner = NULL;
943 markOop mark = ReadStableMark(obj);
944
945 // Uncontended case, header points to stack
946 if (mark->has_locker()) {
947 owner = (address) mark->locker();
948 }
949
950 // Contended case, header points to ObjectMonitor (tagged pointer)
951 else if (mark->has_monitor()) {
952 ObjectMonitorHandle omh;
953 if (!omh.save_om_ptr(obj, mark)) {
954 // Lost a race with async deflation so try again.
955 assert(AsyncDeflateIdleMonitors, "sanity check");
956 continue;
957 }
958 ObjectMonitor* monitor = omh.om_ptr();
959 assert(monitor != NULL, "monitor should be non-null");
960 owner = (address) monitor->owner();
961 }
962
963 if (owner != NULL) {
964 // owning_thread_from_monitor_owner() may also return NULL here
965 return Threads::owning_thread_from_monitor_owner(t_list, owner);
966 }
967
968 // Unlocked case, header in place
969 // Cannot have assertion since this object may have been
970 // locked by another thread when reaching here.
971 // assert(mark->is_neutral(), "sanity check");
972
973 return NULL;
974 }
975 }
976
977 // Visitors ...
978
979 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
980 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
981 while (block != NULL) {
982 assert(block->object() == CHAINMARKER, "must be a block header");
983 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
984 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
985 if (mid->is_active()) {
986 ObjectMonitorHandle omh(mid);
987
988 if (mid->object() == NULL ||
989 (AsyncDeflateIdleMonitors && mid->_owner == DEFLATER_MARKER)) {
990 // Only process with closure if the object is set.
991 // For async deflation, race here if monitor is not owned!
992 // The above ref_count bump (in ObjectMonitorHandle ctr)
993 // will cause subsequent async deflation to skip it.
994 // However, previous or concurrent async deflation is a race.
995 continue;
996 }
997 closure->do_monitor(mid);
998 }
999 }
1000 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
1001 }
1002 }
1003
1004 // Get the next block in the block list.
1005 static inline PaddedEnd<ObjectMonitor>* next(PaddedEnd<ObjectMonitor>* block) {
1006 assert(block->object() == CHAINMARKER, "must be a block header");
1007 block = (PaddedEnd<ObjectMonitor>*) block->FreeNext;
1008 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
1009 return block;
1010 }
1011
1012 static bool monitors_used_above_threshold() {
1013 if (gMonitorPopulation == 0) {
1014 return false;
1015 }
1016 if (MonitorUsedDeflationThreshold > 0) {
1017 int monitors_used = gMonitorPopulation - gMonitorFreeCount;
1018 int monitor_usage = (monitors_used * 100LL) / gMonitorPopulation;
1019 return monitor_usage > MonitorUsedDeflationThreshold;
1020 }
1021 return false;
1022 }
1023
1024 bool ObjectSynchronizer::is_async_deflation_needed() {
1025 if (!AsyncDeflateIdleMonitors) {
1026 return false;
1027 }
1028 if (is_async_deflation_requested()) {
1029 // Async deflation request.
1030 return true;
1031 }
1032 if (AsyncDeflationInterval > 0 &&
1033 time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1034 monitors_used_above_threshold()) {
1035 // It's been longer than our specified deflate interval and there
1036 // are too many monitors in use. We don't deflate more frequently
1037 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1038 // in order to not swamp the ServiceThread.
1039 _last_async_deflation_time_ns = os::javaTimeNanos();
1040 return true;
1041 }
1042 return false;
1043 }
1044
1045 bool ObjectSynchronizer::is_safepoint_deflation_needed() {
1046 if (!AsyncDeflateIdleMonitors) {
1047 if (monitors_used_above_threshold()) {
1048 // Too many monitors in use.
1049 return true;
1050 }
1051 return false;
1052 }
1053 if (is_special_deflation_requested()) {
1054 // For AsyncDeflateIdleMonitors only do a safepoint deflation
1055 // if there is a special deflation request.
1056 return true;
1057 }
1058 return false;
1059 }
1060
1061 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1062 return (os::javaTimeNanos() - _last_async_deflation_time_ns) / (NANOUNITS / MILLIUNITS);
1063 }
1064
1065 void ObjectSynchronizer::oops_do(OopClosure* f) {
1066 // We only scan the global used list here (for moribund threads), and
1067 // the thread-local monitors in Thread::oops_do().
1068 global_used_oops_do(f);
1069 }
1070
1071 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
1072 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1073 list_oops_do(gOmInUseList, f);
1074 }
1075
1076 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
1077 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1078 list_oops_do(thread->omInUseList, f);
1079 }
1080
1081 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
1082 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1083 ObjectMonitor* mid;
1084 for (mid = list; mid != NULL; mid = mid->FreeNext) {
1085 if (mid->object() != NULL) {
1086 f->do_oop((oop*)mid->object_addr());
1087 }
1088 }
1089 }
1090
1091
1092 // -----------------------------------------------------------------------------
1093 // ObjectMonitor Lifecycle
1094 // -----------------------
1095 // Inflation unlinks monitors from the global gFreeList and
1096 // associates them with objects. Deflation -- which occurs at
1097 // STW-time -- disassociates idle monitors from objects. Such
1098 // scavenged monitors are returned to the gFreeList.
1099 //
1100 // The global list is protected by gListLock. All the critical sections
1101 // are short and operate in constant-time.
1102 //
1103 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1104 //
1105 // Lifecycle:
1106 // -- unassigned and on the global free list
1107 // -- unassigned and on a thread's private omFreeList
1108 // -- assigned to an object. The object is inflated and the mark refers
1109 // to the objectmonitor.
1110
1111
1112 // Constraining monitor pool growth via MonitorBound ...
1113 //
1114 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
1115 // the rate of scavenging is driven primarily by GC. As such, we can find
1116 // an inordinate number of monitors in circulation.
1117 // To avoid that scenario we can artificially induce a STW safepoint
1118 // if the pool appears to be growing past some reasonable bound.
1119 // Generally we favor time in space-time tradeoffs, but as there's no
1120 // natural back-pressure on the # of extant monitors we need to impose some
1121 // type of limit. Beware that if MonitorBound is set to too low a value
1122 // we could just loop. In addition, if MonitorBound is set to a low value
1123 // we'll incur more safepoints, which are harmful to performance.
1124 // See also: GuaranteedSafepointInterval
1125 //
1126 // The current implementation uses asynchronous VM operations.
1127
1128 static void InduceScavenge(Thread * Self, const char * Whence) {
1129 // Induce STW safepoint to trim monitors
1130 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1131 // More precisely, trigger an asynchronous STW safepoint as the number
1132 // of active monitors passes the specified threshold.
1133 // TODO: assert thread state is reasonable
1134
1135 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1136 // Induce a 'null' safepoint to scavenge monitors
1137 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1138 // to the VMthread and have a lifespan longer than that of this activation record.
1139 // The VMThread will delete the op when completed.
1140 VMThread::execute(new VM_ScavengeMonitors());
1141 }
1142 }
1143
1144 ObjectMonitor* ObjectSynchronizer::omAlloc(Thread * Self,
1145 const InflateCause cause) {
1146 // A large MAXPRIVATE value reduces both list lock contention
1147 // and list coherency traffic, but also tends to increase the
1148 // number of objectMonitors in circulation as well as the STW
1149 // scavenge costs. As usual, we lean toward time in space-time
1150 // tradeoffs.
1151 const int MAXPRIVATE = 1024;
1152
1153 if (AsyncDeflateIdleMonitors) {
1154 JavaThread * jt = (JavaThread *)Self;
1155 if (jt->omShouldDeflateIdleMonitors && jt->omInUseCount > 0 &&
1156 cause != inflate_cause_vm_internal) {
1157 // Deflate any per-thread idle monitors for this JavaThread if
1158 // this is not an internal inflation; internal inflations can
1159 // occur in places where it is not safe to pause for a safepoint.
1160 // Clean up your own mess. (Gibbs Rule 45) Otherwise, skip this
1161 // deflation. deflate_global_idle_monitors_using_JT() is called
1162 // by the ServiceThread.
1163 debug_only(jt->check_for_valid_safepoint_state(false);)
1164 ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT();
1165 }
1166 }
1167
1168 stringStream ss;
1169 for (;;) {
1170 ObjectMonitor * m;
1171
1172 // 1: try to allocate from the thread's local omFreeList.
1173 // Threads will attempt to allocate first from their local list, then
1174 // from the global list, and only after those attempts fail will the thread
1175 // attempt to instantiate new monitors. Thread-local free lists take
1176 // heat off the gListLock and improve allocation latency, as well as reducing
1177 // coherency traffic on the shared global list.
1178 m = Self->omFreeList;
1179 if (m != NULL) {
1180 Self->omFreeList = m->FreeNext;
1181 Self->omFreeCount--;
1182 guarantee(m->object() == NULL, "invariant");
1183 m->set_allocation_state(ObjectMonitor::New);
1184 m->FreeNext = Self->omInUseList;
1185 Self->omInUseList = m;
1186 Self->omInUseCount++;
1187 return m;
1188 }
1189
1190 // 2: try to allocate from the global gFreeList
1191 // CONSIDER: use muxTry() instead of muxAcquire().
1192 // If the muxTry() fails then drop immediately into case 3.
1193 // If we're using thread-local free lists then try
1194 // to reprovision the caller's free list.
1195 if (gFreeList != NULL) {
1196 // Reprovision the thread's omFreeList.
1197 // Use bulk transfers to reduce the allocation rate and heat
1198 // on various locks.
1199 Thread::muxAcquire(&gListLock, "omAlloc(1)");
1200 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1201 gMonitorFreeCount--;
1202 ObjectMonitor * take = gFreeList;
1203 gFreeList = take->FreeNext;
1204 guarantee(take->object() == NULL, "invariant");
1205 if (AsyncDeflateIdleMonitors) {
1206 // Clear any values we allowed to linger during async deflation.
1207 take->_header = NULL;
1208 take->set_owner(NULL);
1209
1210 if (take->ref_count() < 0) {
1211 // Add back max_jint to restore the ref_count field to its
1212 // proper value.
1213 Atomic::add(max_jint, &take->_ref_count);
1214
1215 assert(take->ref_count() >= 0, "must not be negative: ref_count=%d",
1216 take->ref_count());
1217 }
1218 }
1219 take->Recycle();
1220 assert(take->is_free(), "invariant");
1221 omRelease(Self, take, false);
1222 }
1223 Thread::muxRelease(&gListLock);
1224 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1225 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1226
1227 const int mx = MonitorBound;
1228 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1229 // We can't safely induce a STW safepoint from omAlloc() as our thread
1230 // state may not be appropriate for such activities and callers may hold
1231 // naked oops, so instead we defer the action.
1232 InduceScavenge(Self, "omAlloc");
1233 }
1234 continue;
1235 }
1236
1237 // 3: allocate a block of new ObjectMonitors
1238 // Both the local and global free lists are empty -- resort to malloc().
1239 // In the current implementation objectMonitors are TSM - immortal.
1240 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1241 // each ObjectMonitor to start at the beginning of a cache line,
1242 // so we use align_up().
1243 // A better solution would be to use C++ placement-new.
1244 // BEWARE: As it stands currently, we don't run the ctors!
1245 assert(_BLOCKSIZE > 1, "invariant");
1246 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
1247 PaddedEnd<ObjectMonitor> * temp;
1248 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1249 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
1250 mtInternal);
1251 temp = (PaddedEnd<ObjectMonitor> *)
1252 align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE);
1253
1254 // NOTE: (almost) no way to recover if allocation failed.
1255 // We might be able to induce a STW safepoint and scavenge enough
1256 // objectMonitors to permit progress.
1257 if (temp == NULL) {
1258 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1259 "Allocate ObjectMonitors");
1260 }
1261 (void)memset((void *) temp, 0, neededsize);
1262
1263 // Format the block.
1264 // initialize the linked list, each monitor points to its next
1265 // forming the single linked free list, the very first monitor
1266 // will points to next block, which forms the block list.
1267 // The trick of using the 1st element in the block as gBlockList
1268 // linkage should be reconsidered. A better implementation would
1269 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1270
1271 for (int i = 1; i < _BLOCKSIZE; i++) {
1272 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1273 assert(temp[i].is_free(), "invariant");
1274 }
1275
1276 // terminate the last monitor as the end of list
1277 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1278
1279 // Element [0] is reserved for global list linkage
1280 temp[0].set_object(CHAINMARKER);
1281
1282 // Consider carving out this thread's current request from the
1283 // block in hand. This avoids some lock traffic and redundant
1284 // list activity.
1285
1286 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1287 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1288 Thread::muxAcquire(&gListLock, "omAlloc(2)");
1289 gMonitorPopulation += _BLOCKSIZE-1;
1290 gMonitorFreeCount += _BLOCKSIZE-1;
1291
1292 // Add the new block to the list of extant blocks (gBlockList).
1293 // The very first objectMonitor in a block is reserved and dedicated.
1294 // It serves as blocklist "next" linkage.
1295 temp[0].FreeNext = gBlockList;
1296 // There are lock-free uses of gBlockList so make sure that
1297 // the previous stores happen before we update gBlockList.
1298 OrderAccess::release_store(&gBlockList, temp);
1299
1300 // Add the new string of objectMonitors to the global free list
1301 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1302 gFreeList = temp + 1;
1303 Thread::muxRelease(&gListLock);
1304 }
1305 }
1306
1307 // Place "m" on the caller's private per-thread omFreeList.
1308 // In practice there's no need to clamp or limit the number of
1309 // monitors on a thread's omFreeList as the only time we'll call
1310 // omRelease is to return a monitor to the free list after a CAS
1311 // attempt failed. This doesn't allow unbounded #s of monitors to
1312 // accumulate on a thread's free list.
1313 //
1314 // Key constraint: all ObjectMonitors on a thread's free list and the global
1315 // free list must have their object field set to null. This prevents the
1316 // scavenger -- deflate_monitor_list() or deflate_monitor_list_using_JT()
1317 // -- from reclaiming them while we are trying to release them.
1318
1319 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1320 bool fromPerThreadAlloc) {
1321 guarantee(m->header() == NULL, "invariant");
1322 guarantee(m->object() == NULL, "invariant");
1323 stringStream ss;
1324 guarantee((m->is_busy() | m->_recursions) == 0, "freeing in-use monitor: "
1325 "%s, recursions=" INTPTR_FORMAT, m->is_busy_to_string(&ss),
1326 m->_recursions);
1327 m->set_allocation_state(ObjectMonitor::Free);
1328 // Remove from omInUseList
1329 if (fromPerThreadAlloc) {
1330 ObjectMonitor* cur_mid_in_use = NULL;
1331 bool extracted = false;
1332 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1333 if (m == mid) {
1334 // extract from per-thread in-use list
1335 if (mid == Self->omInUseList) {
1336 Self->omInUseList = mid->FreeNext;
1337 } else if (cur_mid_in_use != NULL) {
1338 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1339 }
1340 extracted = true;
1341 Self->omInUseCount--;
1342 break;
1343 }
1344 }
1345 assert(extracted, "Should have extracted from in-use list");
1346 }
1347
1348 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1349 m->FreeNext = Self->omFreeList;
1350 guarantee(m->is_free(), "invariant");
1351 Self->omFreeList = m;
1352 Self->omFreeCount++;
1353 }
1354
1355 // Return the monitors of a moribund thread's local free list to
1356 // the global free list. Typically a thread calls omFlush() when
1357 // it's dying. We could also consider having the VM thread steal
1358 // monitors from threads that have not run java code over a few
1359 // consecutive STW safepoints. Relatedly, we might decay
1360 // omFreeProvision at STW safepoints.
1361 //
1362 // Also return the monitors of a moribund thread's omInUseList to
1363 // a global gOmInUseList under the global list lock so these
1364 // will continue to be scanned.
1365 //
1366 // We currently call omFlush() from Threads::remove() _before the thread
1367 // has been excised from the thread list and is no longer a mutator.
1368 // This means that omFlush() cannot run concurrently with a safepoint and
1369 // interleave with the deflate_idle_monitors scavenge operator. In particular,
1370 // this ensures that the thread's monitors are scanned by a GC safepoint,
1371 // either via Thread::oops_do() (if safepoint happens before omFlush()) or via
1372 // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's
1373 // monitors have been transferred to the global in-use list).
1374 //
1375 // With AsyncDeflateIdleMonitors, deflate_global_idle_monitors_using_JT()
1376 // and deflate_per_thread_idle_monitors_using_JT() (in another thread) can
1377 // run at the same time as omFlush() so we have to be careful.
1378
1379 void ObjectSynchronizer::omFlush(Thread * Self) {
1380 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1381 ObjectMonitor * tail = NULL;
1382 int tally = 0;
1383 if (list != NULL) {
1384 ObjectMonitor * s;
1385 // The thread is going away. Set 'tail' to the last per-thread free
1386 // monitor which will be linked to gFreeList below under the gListLock.
1387 stringStream ss;
1388 for (s = list; s != NULL; s = s->FreeNext) {
1389 tally++;
1390 tail = s;
1391 guarantee(s->object() == NULL, "invariant");
1392 guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss));
1393 }
1394 guarantee(tail != NULL, "invariant");
1395 ADIM_guarantee(Self->omFreeCount == tally, "free-count off");
1396 Self->omFreeList = NULL;
1397 Self->omFreeCount = 0;
1398 }
1399
1400 ObjectMonitor * inUseList = Self->omInUseList;
1401 ObjectMonitor * inUseTail = NULL;
1402 int inUseTally = 0;
1403 if (inUseList != NULL) {
1404 ObjectMonitor *cur_om;
1405 // The thread is going away, however the omInUseList inflated
1406 // monitors may still be in-use by other threads.
1407 // Link them to inUseTail, which will be linked into the global in-use list
1408 // gOmInUseList below, under the gListLock
1409 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1410 inUseTail = cur_om;
1411 inUseTally++;
1412 ADIM_guarantee(cur_om->is_active(), "invariant");
1413 }
1414 guarantee(inUseTail != NULL, "invariant");
1415 ADIM_guarantee(Self->omInUseCount == inUseTally, "in-use count off");
1416 Self->omInUseList = NULL;
1417 Self->omInUseCount = 0;
1418 }
1419
1420 Thread::muxAcquire(&gListLock, "omFlush");
1421 if (tail != NULL) {
1422 tail->FreeNext = gFreeList;
1423 gFreeList = list;
1424 gMonitorFreeCount += tally;
1425 }
1426
1427 if (inUseTail != NULL) {
1428 inUseTail->FreeNext = gOmInUseList;
1429 gOmInUseList = inUseList;
1430 gOmInUseCount += inUseTally;
1431 }
1432
1433 Thread::muxRelease(&gListLock);
1434
1435 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1436 LogStreamHandle(Info, monitorinflation) lsh_info;
1437 LogStream * ls = NULL;
1438 if (log_is_enabled(Debug, monitorinflation)) {
1439 ls = &lsh_debug;
1440 } else if ((tally != 0 || inUseTally != 0) &&
1441 log_is_enabled(Info, monitorinflation)) {
1442 ls = &lsh_info;
1443 }
1444 if (ls != NULL) {
1445 ls->print_cr("omFlush: jt=" INTPTR_FORMAT ", free_monitor_tally=%d"
1446 ", in_use_monitor_tally=%d" ", omFreeProvision=%d",
1447 p2i(Self), tally, inUseTally, Self->omFreeProvision);
1448 }
1449 }
1450
1451 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1452 const oop obj,
1453 ObjectSynchronizer::InflateCause cause) {
1454 assert(event != NULL, "invariant");
1455 assert(event->should_commit(), "invariant");
1456 event->set_monitorClass(obj->klass());
1457 event->set_address((uintptr_t)(void*)obj);
1458 event->set_cause((u1)cause);
1459 event->commit();
1460 }
1461
1462 // Fast path code shared by multiple functions
1463 void ObjectSynchronizer::inflate_helper(ObjectMonitorHandle * omh_p, oop obj) {
1464 while (true) {
1465 markOop mark = obj->mark();
1466 if (mark->has_monitor()) {
1467 if (!omh_p->save_om_ptr(obj, mark)) {
1468 // Lost a race with async deflation so try again.
1469 assert(AsyncDeflateIdleMonitors, "sanity check");
1470 continue;
1471 }
1472 ObjectMonitor * monitor = omh_p->om_ptr();
1473 assert(ObjectSynchronizer::verify_objmon_isinpool(monitor), "monitor is invalid");
1474 markOop dmw = monitor->header();
1475 assert(dmw->is_neutral(), "sanity check: header=" INTPTR_FORMAT, p2i(dmw));
1476 return;
1477 }
1478 inflate(omh_p, Thread::current(), obj, inflate_cause_vm_internal);
1479 return;
1480 }
1481 }
1482
1483 void ObjectSynchronizer::inflate(ObjectMonitorHandle * omh_p, Thread * Self,
1484 oop object, const InflateCause cause) {
1485 // Inflate mutates the heap ...
1486 // Relaxing assertion for bug 6320749.
1487 assert(Universe::verify_in_progress() ||
1488 !SafepointSynchronize::is_at_safepoint(), "invariant");
1489
1490 EventJavaMonitorInflate event;
1491
1492 for (;;) {
1493 const markOop mark = object->mark();
1494 assert(!mark->has_bias_pattern(), "invariant");
1495
1496 // The mark can be in one of the following states:
1497 // * Inflated - just return
1498 // * Stack-locked - coerce it to inflated
1499 // * INFLATING - busy wait for conversion to complete
1500 // * Neutral - aggressively inflate the object.
1501 // * BIASED - Illegal. We should never see this
1502
1503 // CASE: inflated
1504 if (mark->has_monitor()) {
1505 if (!omh_p->save_om_ptr(object, mark)) {
1506 // Lost a race with async deflation so try again.
1507 assert(AsyncDeflateIdleMonitors, "sanity check");
1508 continue;
1509 }
1510 ObjectMonitor * inf = omh_p->om_ptr();
1511 markOop dmw = inf->header();
1512 assert(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1513 assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1514 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1515 return;
1516 }
1517
1518 // CASE: inflation in progress - inflating over a stack-lock.
1519 // Some other thread is converting from stack-locked to inflated.
1520 // Only that thread can complete inflation -- other threads must wait.
1521 // The INFLATING value is transient.
1522 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1523 // We could always eliminate polling by parking the thread on some auxiliary list.
1524 if (mark == markOopDesc::INFLATING()) {
1525 ReadStableMark(object);
1526 continue;
1527 }
1528
1529 // CASE: stack-locked
1530 // Could be stack-locked either by this thread or by some other thread.
1531 //
1532 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1533 // to install INFLATING into the mark word. We originally installed INFLATING,
1534 // allocated the objectmonitor, and then finally STed the address of the
1535 // objectmonitor into the mark. This was correct, but artificially lengthened
1536 // the interval in which INFLATED appeared in the mark, thus increasing
1537 // the odds of inflation contention.
1538 //
1539 // We now use per-thread private objectmonitor free lists.
1540 // These list are reprovisioned from the global free list outside the
1541 // critical INFLATING...ST interval. A thread can transfer
1542 // multiple objectmonitors en-mass from the global free list to its local free list.
1543 // This reduces coherency traffic and lock contention on the global free list.
1544 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1545 // before or after the CAS(INFLATING) operation.
1546 // See the comments in omAlloc().
1547
1548 LogStreamHandle(Trace, monitorinflation) lsh;
1549
1550 if (mark->has_locker()) {
1551 ObjectMonitor * m;
1552 if (!AsyncDeflateIdleMonitors || cause == inflate_cause_vm_internal) {
1553 // If !AsyncDeflateIdleMonitors or if an internal inflation, then
1554 // we won't stop for a potential safepoint in omAlloc.
1555 m = omAlloc(Self, cause);
1556 } else {
1557 // If AsyncDeflateIdleMonitors and not an internal inflation, then
1558 // we may stop for a safepoint in omAlloc() so protect object.
1559 Handle h_obj(Self, object);
1560 m = omAlloc(Self, cause);
1561 object = h_obj(); // Refresh object.
1562 }
1563 // Optimistically prepare the objectmonitor - anticipate successful CAS
1564 // We do this before the CAS in order to minimize the length of time
1565 // in which INFLATING appears in the mark.
1566 m->Recycle();
1567 m->_Responsible = NULL;
1568 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1569
1570 markOop cmp = object->cas_set_mark(markOopDesc::INFLATING(), mark);
1571 if (cmp != mark) {
1572 omRelease(Self, m, true);
1573 continue; // Interference -- just retry
1574 }
1575
1576 // We've successfully installed INFLATING (0) into the mark-word.
1577 // This is the only case where 0 will appear in a mark-word.
1578 // Only the singular thread that successfully swings the mark-word
1579 // to 0 can perform (or more precisely, complete) inflation.
1580 //
1581 // Why do we CAS a 0 into the mark-word instead of just CASing the
1582 // mark-word from the stack-locked value directly to the new inflated state?
1583 // Consider what happens when a thread unlocks a stack-locked object.
1584 // It attempts to use CAS to swing the displaced header value from the
1585 // on-stack basiclock back into the object header. Recall also that the
1586 // header value (hash code, etc) can reside in (a) the object header, or
1587 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1588 // header in an objectMonitor. The inflate() routine must copy the header
1589 // value from the basiclock on the owner's stack to the objectMonitor, all
1590 // the while preserving the hashCode stability invariants. If the owner
1591 // decides to release the lock while the value is 0, the unlock will fail
1592 // and control will eventually pass from slow_exit() to inflate. The owner
1593 // will then spin, waiting for the 0 value to disappear. Put another way,
1594 // the 0 causes the owner to stall if the owner happens to try to
1595 // drop the lock (restoring the header from the basiclock to the object)
1596 // while inflation is in-progress. This protocol avoids races that might
1597 // would otherwise permit hashCode values to change or "flicker" for an object.
1598 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1599 // 0 serves as a "BUSY" inflate-in-progress indicator.
1600
1601
1602 // fetch the displaced mark from the owner's stack.
1603 // The owner can't die or unwind past the lock while our INFLATING
1604 // object is in the mark. Furthermore the owner can't complete
1605 // an unlock on the object, either.
1606 markOop dmw = mark->displaced_mark_helper();
1607 // Catch if the object's header is not neutral (not locked and
1608 // not marked is what we care about here).
1609 ADIM_guarantee(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1610
1611 // Setup monitor fields to proper values -- prepare the monitor
1612 m->set_header(dmw);
1613
1614 // Optimization: if the mark->locker stack address is associated
1615 // with this thread we could simply set m->_owner = Self.
1616 // Note that a thread can inflate an object
1617 // that it has stack-locked -- as might happen in wait() -- directly
1618 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1619 m->set_owner(mark->locker());
1620 m->set_object(object);
1621 // TODO-FIXME: assert BasicLock->dhw != 0.
1622
1623 omh_p->set_om_ptr(m);
1624 assert(m->is_new(), "freshly allocated monitor must be new");
1625 m->set_allocation_state(ObjectMonitor::Old);
1626
1627 // Must preserve store ordering. The monitor state must
1628 // be stable at the time of publishing the monitor address.
1629 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1630 object->release_set_mark(markOopDesc::encode(m));
1631
1632 // Hopefully the performance counters are allocated on distinct cache lines
1633 // to avoid false sharing on MP systems ...
1634 OM_PERFDATA_OP(Inflations, inc());
1635 if (log_is_enabled(Trace, monitorinflation)) {
1636 ResourceMark rm(Self);
1637 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1638 INTPTR_FORMAT ", type='%s'", p2i(object),
1639 p2i(object->mark()), object->klass()->external_name());
1640 }
1641 if (event.should_commit()) {
1642 post_monitor_inflate_event(&event, object, cause);
1643 }
1644 ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free");
1645 return;
1646 }
1647
1648 // CASE: neutral
1649 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1650 // If we know we're inflating for entry it's better to inflate by swinging a
1651 // pre-locked objectMonitor pointer into the object header. A successful
1652 // CAS inflates the object *and* confers ownership to the inflating thread.
1653 // In the current implementation we use a 2-step mechanism where we CAS()
1654 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1655 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1656 // would be useful.
1657
1658 // Catch if the object's header is not neutral (not locked and
1659 // not marked is what we care about here).
1660 ADIM_guarantee(mark->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(mark));
1661 ObjectMonitor * m;
1662 if (!AsyncDeflateIdleMonitors || cause == inflate_cause_vm_internal) {
1663 // If !AsyncDeflateIdleMonitors or if an internal inflation, then
1664 // we won't stop for a potential safepoint in omAlloc.
1665 m = omAlloc(Self, cause);
1666 } else {
1667 // If AsyncDeflateIdleMonitors and not an internal inflation, then
1668 // we may stop for a safepoint in omAlloc() so protect object.
1669 Handle h_obj(Self, object);
1670 m = omAlloc(Self, cause);
1671 object = h_obj(); // Refresh object.
1672 }
1673 // prepare m for installation - set monitor to initial state
1674 m->Recycle();
1675 m->set_header(mark);
1676 m->set_object(object);
1677 m->_Responsible = NULL;
1678 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1679
1680 omh_p->set_om_ptr(m);
1681 assert(m->is_new(), "freshly allocated monitor must be new");
1682 m->set_allocation_state(ObjectMonitor::Old);
1683
1684 if (object->cas_set_mark(markOopDesc::encode(m), mark) != mark) {
1685 m->set_header(NULL);
1686 m->set_object(NULL);
1687 m->Recycle();
1688 omh_p->set_om_ptr(NULL);
1689 // omRelease() will reset the allocation state
1690 omRelease(Self, m, true);
1691 m = NULL;
1692 continue;
1693 // interference - the markword changed - just retry.
1694 // The state-transitions are one-way, so there's no chance of
1695 // live-lock -- "Inflated" is an absorbing state.
1696 }
1697
1698 // Hopefully the performance counters are allocated on distinct
1699 // cache lines to avoid false sharing on MP systems ...
1700 OM_PERFDATA_OP(Inflations, inc());
1701 if (log_is_enabled(Trace, monitorinflation)) {
1702 ResourceMark rm(Self);
1703 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1704 INTPTR_FORMAT ", type='%s'", p2i(object),
1705 p2i(object->mark()), object->klass()->external_name());
1706 }
1707 if (event.should_commit()) {
1708 post_monitor_inflate_event(&event, object, cause);
1709 }
1710 ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free");
1711 return;
1712 }
1713 }
1714
1715
1716 // We maintain a list of in-use monitors for each thread.
1717 //
1718 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1719 // deflate_idle_monitors() scans only a global list of in-use monitors which
1720 // is populated only as a thread dies (see omFlush()).
1721 //
1722 // These operations are called at all safepoints, immediately after mutators
1723 // are stopped, but before any objects have moved. Collectively they traverse
1724 // the population of in-use monitors, deflating where possible. The scavenged
1725 // monitors are returned to the global monitor free list.
1726 //
1727 // Beware that we scavenge at *every* stop-the-world point. Having a large
1728 // number of monitors in-use could negatively impact performance. We also want
1729 // to minimize the total # of monitors in circulation, as they incur a small
1730 // footprint penalty.
1731 //
1732 // Perversely, the heap size -- and thus the STW safepoint rate --
1733 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1734 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1735 // This is an unfortunate aspect of this design.
1736
1737 void ObjectSynchronizer::do_safepoint_work(DeflateMonitorCounters* _counters) {
1738 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1739
1740 // The per-thread in-use lists are handled in
1741 // ParallelSPCleanupThreadClosure::do_thread().
1742
1743 if (!AsyncDeflateIdleMonitors || is_special_deflation_requested()) {
1744 // Use the older mechanism for the global in-use list or if a
1745 // special deflation has been requested before the safepoint.
1746 ObjectSynchronizer::deflate_idle_monitors(_counters);
1747 return;
1748 }
1749
1750 log_debug(monitorinflation)("requesting async deflation of idle monitors.");
1751 // Request deflation of idle monitors by the ServiceThread:
1752 set_is_async_deflation_requested(true);
1753 MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
1754 ml.notify_all();
1755 }
1756
1757 // Deflate a single monitor if not in-use
1758 // Return true if deflated, false if in-use
1759 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1760 ObjectMonitor** freeHeadp,
1761 ObjectMonitor** freeTailp) {
1762 bool deflated;
1763 // Normal case ... The monitor is associated with obj.
1764 const markOop mark = obj->mark();
1765 guarantee(mark == markOopDesc::encode(mid), "should match: mark="
1766 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, p2i(mark),
1767 p2i(markOopDesc::encode(mid)));
1768 // Make sure that mark->monitor() and markOopDesc::encode() agree:
1769 guarantee(mark->monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
1770 ", mid=" INTPTR_FORMAT, p2i(mark->monitor()), p2i(mid));
1771 const markOop dmw = mid->header();
1772 guarantee(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1773
1774 if (mid->is_busy()) {
1775 deflated = false;
1776 } else {
1777 // Deflate the monitor if it is no longer being used
1778 // It's idle - scavenge and return to the global free list
1779 // plain old deflation ...
1780 if (log_is_enabled(Trace, monitorinflation)) {
1781 ResourceMark rm;
1782 log_trace(monitorinflation)("deflate_monitor: "
1783 "object=" INTPTR_FORMAT ", mark="
1784 INTPTR_FORMAT ", type='%s'", p2i(obj),
1785 p2i(mark), obj->klass()->external_name());
1786 }
1787
1788 // Restore the header back to obj
1789 obj->release_set_mark(dmw);
1790 mid->clear();
1791
1792 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
1793 p2i(mid->object()));
1794 assert(mid->is_free(), "invariant");
1795
1796 // Move the object to the working free list defined by freeHeadp, freeTailp
1797 if (*freeHeadp == NULL) *freeHeadp = mid;
1798 if (*freeTailp != NULL) {
1799 ObjectMonitor * prevtail = *freeTailp;
1800 assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1801 prevtail->FreeNext = mid;
1802 }
1803 *freeTailp = mid;
1804 deflated = true;
1805 }
1806 return deflated;
1807 }
1808
1809 // Deflate the specified ObjectMonitor if not in-use using a JavaThread.
1810 // Returns true if it was deflated and false otherwise.
1811 //
1812 // The async deflation protocol sets owner to DEFLATER_MARKER and
1813 // makes ref_count negative as signals to contending threads that
1814 // an async deflation is in progress. There are a number of checks
1815 // as part of the protocol to make sure that the calling thread has
1816 // not lost the race to a contending thread or to a thread that just
1817 // wants to use the ObjectMonitor*.
1818 //
1819 // The ObjectMonitor has been successfully async deflated when:
1820 // (owner == DEFLATER_MARKER && ref_count < 0)
1821 // Contending threads or ObjectMonitor* using threads that see those
1822 // values know to retry their operation.
1823 //
1824 bool ObjectSynchronizer::deflate_monitor_using_JT(ObjectMonitor* mid,
1825 ObjectMonitor** freeHeadp,
1826 ObjectMonitor** freeTailp) {
1827 assert(AsyncDeflateIdleMonitors, "sanity check");
1828 assert(Thread::current()->is_Java_thread(), "precondition");
1829 // A newly allocated ObjectMonitor should not be seen here so we
1830 // avoid an endless inflate/deflate cycle.
1831 assert(mid->is_old(), "must be old: allocation_state=%d",
1832 (int) mid->allocation_state());
1833
1834 if (mid->is_busy() || mid->ref_count() != 0) {
1835 // Easy checks are first - the ObjectMonitor is busy or ObjectMonitor*
1836 // is in use so no deflation.
1837 return false;
1838 }
1839
1840 if (Atomic::replace_if_null(DEFLATER_MARKER, &(mid->_owner))) {
1841 // ObjectMonitor is not owned by another thread. Our setting
1842 // owner to DEFLATER_MARKER forces any contending thread through
1843 // the slow path. This is just the first part of the async
1844 // deflation dance.
1845
1846 if (mid->_contentions != 0 || mid->_waiters != 0) {
1847 // Another thread has raced to enter the ObjectMonitor after
1848 // mid->is_busy() above or has already entered and waited on
1849 // it which makes it busy so no deflation. Restore owner to
1850 // NULL if it is still DEFLATER_MARKER.
1851 Atomic::cmpxchg((void*)NULL, &mid->_owner, DEFLATER_MARKER);
1852 return false;
1853 }
1854
1855 if (Atomic::cmpxchg(-max_jint, &mid->_ref_count, (jint)0) == 0) {
1856 // Make ref_count negative to force any contending threads or
1857 // ObjectMonitor* using threads to retry. This is the second
1858 // part of the async deflation dance.
1859
1860 if (mid->_owner == DEFLATER_MARKER) {
1861 // If owner is still DEFLATER_MARKER, then we have successfully
1862 // signaled any contending threads to retry. If it is not, then we
1863 // have lost the race to an entering thread and the ObjectMonitor
1864 // is now busy. This is the third and final part of the async
1865 // deflation dance.
1866 // Note: This owner check solves the ABA problem with ref_count
1867 // where another thread acquired the ObjectMonitor, finished
1868 // using it and restored the ref_count to zero.
1869
1870 // Sanity checks for the races:
1871 guarantee(mid->_contentions == 0, "must be 0: contentions=%d",
1872 mid->_contentions);
1873 guarantee(mid->_waiters == 0, "must be 0: waiters=%d", mid->_waiters);
1874 guarantee(mid->_cxq == NULL, "must be no contending threads: cxq="
1875 INTPTR_FORMAT, p2i(mid->_cxq));
1876 guarantee(mid->_EntryList == NULL,
1877 "must be no entering threads: EntryList=" INTPTR_FORMAT,
1878 p2i(mid->_EntryList));
1879
1880 const oop obj = (oop) mid->object();
1881 if (log_is_enabled(Trace, monitorinflation)) {
1882 ResourceMark rm;
1883 log_trace(monitorinflation)("deflate_monitor_using_JT: "
1884 "object=" INTPTR_FORMAT ", mark="
1885 INTPTR_FORMAT ", type='%s'",
1886 p2i(obj), p2i(obj->mark()),
1887 obj->klass()->external_name());
1888 }
1889
1890 // Install the old mark word if nobody else has already done it.
1891 mid->install_displaced_markword_in_object(obj);
1892 mid->clear_using_JT();
1893
1894 assert(mid->object() == NULL, "must be NULL: object=" INTPTR_FORMAT,
1895 p2i(mid->object()));
1896 assert(mid->is_free(), "must be free: allocation_state=%d",
1897 (int) mid->allocation_state());
1898
1899 // Move the deflated ObjectMonitor to the working free list
1900 // defined by freeHeadp and freeTailp.
1901 if (*freeHeadp == NULL) {
1902 // First one on the list.
1903 *freeHeadp = mid;
1904 }
1905 if (*freeTailp != NULL) {
1906 // We append to the list so the caller can use mid->FreeNext
1907 // to fix the linkages in its context.
1908 ObjectMonitor * prevtail = *freeTailp;
1909 // Should have been cleaned up by the caller:
1910 assert(prevtail->FreeNext == NULL, "must be NULL: FreeNext="
1911 INTPTR_FORMAT, p2i(prevtail->FreeNext));
1912 prevtail->FreeNext = mid;
1913 }
1914 *freeTailp = mid;
1915
1916 // At this point, mid->FreeNext still refers to its current
1917 // value and another ObjectMonitor's FreeNext field still
1918 // refers to this ObjectMonitor. Those linkages have to be
1919 // cleaned up by the caller who has the complete context.
1920
1921 // We leave owner == DEFLATER_MARKER and ref_count < 0
1922 // to force any racing threads to retry.
1923 return true; // Success, ObjectMonitor has been deflated.
1924 }
1925
1926 // The owner was changed from DEFLATER_MARKER so we lost the
1927 // race since the ObjectMonitor is now busy.
1928
1929 // Add back max_jint to restore the ref_count field to its
1930 // proper value (which may not be what we saw above):
1931 Atomic::add(max_jint, &mid->_ref_count);
1932
1933 assert(mid->ref_count() >= 0, "must not be negative: ref_count=%d",
1934 mid->ref_count());
1935 return false;
1936 }
1937
1938 // The ref_count was no longer 0 so we lost the race since the
1939 // ObjectMonitor is now busy or the ObjectMonitor* is now is use.
1940 // Restore owner to NULL if it is still DEFLATER_MARKER:
1941 Atomic::cmpxchg((void*)NULL, &mid->_owner, DEFLATER_MARKER);
1942 }
1943
1944 // The owner field is no longer NULL so we lost the race since the
1945 // ObjectMonitor is now busy.
1946 return false;
1947 }
1948
1949 // Walk a given monitor list, and deflate idle monitors
1950 // The given list could be a per-thread list or a global list
1951 // Caller acquires gListLock as needed.
1952 //
1953 // In the case of parallel processing of thread local monitor lists,
1954 // work is done by Threads::parallel_threads_do() which ensures that
1955 // each Java thread is processed by exactly one worker thread, and
1956 // thus avoid conflicts that would arise when worker threads would
1957 // process the same monitor lists concurrently.
1958 //
1959 // See also ParallelSPCleanupTask and
1960 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1961 // Threads::parallel_java_threads_do() in thread.cpp.
1962 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1963 ObjectMonitor** freeHeadp,
1964 ObjectMonitor** freeTailp) {
1965 ObjectMonitor* mid;
1966 ObjectMonitor* next;
1967 ObjectMonitor* cur_mid_in_use = NULL;
1968 int deflated_count = 0;
1969
1970 for (mid = *listHeadp; mid != NULL;) {
1971 oop obj = (oop) mid->object();
1972 if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1973 // if deflate_monitor succeeded,
1974 // extract from per-thread in-use list
1975 if (mid == *listHeadp) {
1976 *listHeadp = mid->FreeNext;
1977 } else if (cur_mid_in_use != NULL) {
1978 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1979 }
1980 next = mid->FreeNext;
1981 mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list
1982 mid = next;
1983 deflated_count++;
1984 } else {
1985 cur_mid_in_use = mid;
1986 mid = mid->FreeNext;
1987 }
1988 }
1989 return deflated_count;
1990 }
1991
1992 // Walk a given ObjectMonitor list and deflate idle ObjectMonitors using
1993 // a JavaThread. Returns the number of deflated ObjectMonitors. The given
1994 // list could be a per-thread in-use list or the global in-use list.
1995 // Caller acquires gListLock as appropriate. If a safepoint has started,
1996 // then we save state via savedMidInUsep and return to the caller to
1997 // honor the safepoint.
1998 //
1999 int ObjectSynchronizer::deflate_monitor_list_using_JT(ObjectMonitor** listHeadp,
2000 ObjectMonitor** freeHeadp,
2001 ObjectMonitor** freeTailp,
2002 ObjectMonitor** savedMidInUsep) {
2003 assert(AsyncDeflateIdleMonitors, "sanity check");
2004 assert(Thread::current()->is_Java_thread(), "precondition");
2005
2006 ObjectMonitor* mid;
2007 ObjectMonitor* next;
2008 ObjectMonitor* cur_mid_in_use = NULL;
2009 int deflated_count = 0;
2010
2011 if (*savedMidInUsep == NULL) {
2012 // No saved state so start at the beginning.
2013 mid = *listHeadp;
2014 } else {
2015 // We're restarting after a safepoint so restore the necessary state
2016 // before we resume.
2017 cur_mid_in_use = *savedMidInUsep;
2018 mid = cur_mid_in_use->FreeNext;
2019 }
2020 while (mid != NULL) {
2021 // Only try to deflate if there is an associated Java object and if
2022 // mid is old (is not newly allocated and is not newly freed).
2023 if (mid->object() != NULL && mid->is_old() &&
2024 deflate_monitor_using_JT(mid, freeHeadp, freeTailp)) {
2025 // Deflation succeeded so update the in-use list.
2026 if (mid == *listHeadp) {
2027 *listHeadp = mid->FreeNext;
2028 } else if (cur_mid_in_use != NULL) {
2029 // Maintain the current in-use list.
2030 cur_mid_in_use->FreeNext = mid->FreeNext;
2031 }
2032 next = mid->FreeNext;
2033 mid->FreeNext = NULL;
2034 // At this point mid is disconnected from the in-use list
2035 // and is the current tail in the freeHeadp list.
2036 mid = next;
2037 deflated_count++;
2038 } else {
2039 // mid is considered in-use if it does not have an associated
2040 // Java object or mid is not old or deflation did not succeed.
2041 // A mid->is_new() node can be seen here when it is freshly
2042 // returned by omAlloc() (and skips the deflation code path).
2043 // A mid->is_old() node can be seen here when deflation failed.
2044 // A mid->is_free() node can be seen here when a fresh node from
2045 // omAlloc() is released by omRelease() due to losing the race
2046 // in inflate().
2047
2048 cur_mid_in_use = mid;
2049 mid = mid->FreeNext;
2050
2051 if (SafepointSynchronize::is_synchronizing() &&
2052 cur_mid_in_use != *listHeadp && cur_mid_in_use->is_old()) {
2053 // If a safepoint has started and cur_mid_in_use is not the list
2054 // head and is old, then it is safe to use as saved state. Return
2055 // to the caller so gListLock can be dropped as appropriate
2056 // before blocking.
2057 *savedMidInUsep = cur_mid_in_use;
2058 return deflated_count;
2059 }
2060 }
2061 }
2062 // We finished the list without a safepoint starting so there's
2063 // no need to save state.
2064 *savedMidInUsep = NULL;
2065 return deflated_count;
2066 }
2067
2068 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2069 counters->nInuse = 0; // currently associated with objects
2070 counters->nInCirculation = 0; // extant
2071 counters->nScavenged = 0; // reclaimed (global and per-thread)
2072 counters->perThreadScavenged = 0; // per-thread scavenge total
2073 counters->perThreadTimes = 0.0; // per-thread scavenge times
2074 }
2075
2076 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
2077 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2078
2079 if (AsyncDeflateIdleMonitors) {
2080 // Nothing to do when global idle ObjectMonitors are deflated using
2081 // a JavaThread unless a special deflation has been requested.
2082 if (!is_special_deflation_requested()) {
2083 return;
2084 }
2085 }
2086
2087 bool deflated = false;
2088
2089 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
2090 ObjectMonitor * freeTailp = NULL;
2091 elapsedTimer timer;
2092
2093 if (log_is_enabled(Info, monitorinflation)) {
2094 timer.start();
2095 }
2096
2097 // Prevent omFlush from changing mids in Thread dtor's during deflation
2098 // And in case the vm thread is acquiring a lock during a safepoint
2099 // See e.g. 6320749
2100 Thread::muxAcquire(&gListLock, "deflate_idle_monitors");
2101
2102 // Note: the thread-local monitors lists get deflated in
2103 // a separate pass. See deflate_thread_local_monitors().
2104
2105 // For moribund threads, scan gOmInUseList
2106 int deflated_count = 0;
2107 if (gOmInUseList) {
2108 counters->nInCirculation += gOmInUseCount;
2109 deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
2110 gOmInUseCount -= deflated_count;
2111 counters->nScavenged += deflated_count;
2112 counters->nInuse += gOmInUseCount;
2113 }
2114
2115 // Move the scavenged monitors back to the global free list.
2116 if (freeHeadp != NULL) {
2117 guarantee(freeTailp != NULL && counters->nScavenged > 0, "invariant");
2118 assert(freeTailp->FreeNext == NULL, "invariant");
2119 // constant-time list splice - prepend scavenged segment to gFreeList
2120 freeTailp->FreeNext = gFreeList;
2121 gFreeList = freeHeadp;
2122 }
2123 Thread::muxRelease(&gListLock);
2124 timer.stop();
2125
2126 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2127 LogStreamHandle(Info, monitorinflation) lsh_info;
2128 LogStream * ls = NULL;
2129 if (log_is_enabled(Debug, monitorinflation)) {
2130 ls = &lsh_debug;
2131 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2132 ls = &lsh_info;
2133 }
2134 if (ls != NULL) {
2135 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2136 }
2137 }
2138
2139 // Deflate global idle ObjectMonitors using a JavaThread.
2140 //
2141 void ObjectSynchronizer::deflate_global_idle_monitors_using_JT() {
2142 assert(AsyncDeflateIdleMonitors, "sanity check");
2143 assert(Thread::current()->is_Java_thread(), "precondition");
2144 JavaThread * self = JavaThread::current();
2145
2146 deflate_common_idle_monitors_using_JT(true /* is_global */, self);
2147 }
2148
2149 // Deflate per-thread idle ObjectMonitors using a JavaThread.
2150 //
2151 void ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT() {
2152 assert(AsyncDeflateIdleMonitors, "sanity check");
2153 assert(Thread::current()->is_Java_thread(), "precondition");
2154 JavaThread * self = JavaThread::current();
2155
2156 self->omShouldDeflateIdleMonitors = false;
2157
2158 deflate_common_idle_monitors_using_JT(false /* !is_global */, self);
2159 }
2160
2161 // Deflate global or per-thread idle ObjectMonitors using a JavaThread.
2162 //
2163 void ObjectSynchronizer::deflate_common_idle_monitors_using_JT(bool is_global, JavaThread * self) {
2164 int deflated_count = 0;
2165 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged ObjectMonitors
2166 ObjectMonitor * freeTailp = NULL;
2167 ObjectMonitor * savedMidInUsep = NULL;
2168 elapsedTimer timer;
2169
2170 if (log_is_enabled(Info, monitorinflation)) {
2171 timer.start();
2172 }
2173
2174 if (is_global) {
2175 Thread::muxAcquire(&gListLock, "deflate_global_idle_monitors_using_JT(1)");
2176 OM_PERFDATA_OP(MonExtant, set_value(gOmInUseCount));
2177 } else {
2178 OM_PERFDATA_OP(MonExtant, inc(self->omInUseCount));
2179 }
2180
2181 do {
2182 int local_deflated_count;
2183 if (is_global) {
2184 local_deflated_count = deflate_monitor_list_using_JT((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp, &savedMidInUsep);
2185 gOmInUseCount -= local_deflated_count;
2186 } else {
2187 local_deflated_count = deflate_monitor_list_using_JT(self->omInUseList_addr(), &freeHeadp, &freeTailp, &savedMidInUsep);
2188 self->omInUseCount -= local_deflated_count;
2189 }
2190 deflated_count += local_deflated_count;
2191
2192 if (freeHeadp != NULL) {
2193 // Move the scavenged ObjectMonitors to the global free list.
2194 guarantee(freeTailp != NULL && local_deflated_count > 0, "freeTailp=" INTPTR_FORMAT ", local_deflated_count=%d", p2i(freeTailp), local_deflated_count);
2195 assert(freeTailp->FreeNext == NULL, "invariant");
2196
2197 if (!is_global) {
2198 Thread::muxAcquire(&gListLock, "deflate_per_thread_idle_monitors_using_JT(2)");
2199 }
2200 // Constant-time list splice - prepend scavenged segment to gFreeList.
2201 freeTailp->FreeNext = gFreeList;
2202 gFreeList = freeHeadp;
2203
2204 gMonitorFreeCount += local_deflated_count;
2205 OM_PERFDATA_OP(Deflations, inc(local_deflated_count));
2206 if (!is_global) {
2207 Thread::muxRelease(&gListLock);
2208 }
2209 }
2210
2211 if (savedMidInUsep != NULL) {
2212 // deflate_monitor_list_using_JT() detected a safepoint starting.
2213 if (is_global) {
2214 Thread::muxRelease(&gListLock);
2215 }
2216 timer.stop();
2217 {
2218 if (is_global) {
2219 log_debug(monitorinflation)("pausing deflation of global idle monitors for a safepoint.");
2220 } else {
2221 log_debug(monitorinflation)("jt=" INTPTR_FORMAT ": pausing deflation of per-thread idle monitors for a safepoint.", p2i(self));
2222 }
2223 assert(SafepointSynchronize::is_synchronizing(), "sanity check");
2224 ThreadBlockInVM blocker(self);
2225 }
2226 // Prepare for another loop after the safepoint.
2227 freeHeadp = NULL;
2228 freeTailp = NULL;
2229 if (log_is_enabled(Info, monitorinflation)) {
2230 timer.start();
2231 }
2232 if (is_global) {
2233 Thread::muxAcquire(&gListLock, "deflate_global_idle_monitors_using_JT(3)");
2234 }
2235 }
2236 } while (savedMidInUsep != NULL);
2237 if (is_global) {
2238 Thread::muxRelease(&gListLock);
2239 }
2240 timer.stop();
2241
2242 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2243 LogStreamHandle(Info, monitorinflation) lsh_info;
2244 LogStream * ls = NULL;
2245 if (log_is_enabled(Debug, monitorinflation)) {
2246 ls = &lsh_debug;
2247 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2248 ls = &lsh_info;
2249 }
2250 if (ls != NULL) {
2251 if (is_global) {
2252 ls->print_cr("async-deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2253 } else {
2254 ls->print_cr("jt=" INTPTR_FORMAT ": async-deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(self), timer.seconds(), deflated_count);
2255 }
2256 }
2257 }
2258
2259 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2260 // Report the cumulative time for deflating each thread's idle
2261 // monitors. Note: if the work is split among more than one
2262 // worker thread, then the reported time will likely be more
2263 // than a beginning to end measurement of the phase.
2264 // Note: AsyncDeflateIdleMonitors only deflates per-thread idle
2265 // monitors at a safepoint when a special deflation has been requested.
2266 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->perThreadTimes, counters->perThreadScavenged);
2267
2268 bool needs_special_deflation = is_special_deflation_requested();
2269 if (!AsyncDeflateIdleMonitors || needs_special_deflation) {
2270 // AsyncDeflateIdleMonitors does not use these counters unless
2271 // there is a special deflation request.
2272
2273 gMonitorFreeCount += counters->nScavenged;
2274
2275 OM_PERFDATA_OP(Deflations, inc(counters->nScavenged));
2276 OM_PERFDATA_OP(MonExtant, set_value(counters->nInCirculation));
2277 }
2278
2279 if (log_is_enabled(Debug, monitorinflation)) {
2280 // exit_globals()'s call to audit_and_print_stats() is done
2281 // at the Info level.
2282 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2283 } else if (log_is_enabled(Info, monitorinflation)) {
2284 Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors");
2285 log_info(monitorinflation)("gMonitorPopulation=%d, gOmInUseCount=%d, "
2286 "gMonitorFreeCount=%d", gMonitorPopulation,
2287 gOmInUseCount, gMonitorFreeCount);
2288 Thread::muxRelease(&gListLock);
2289 }
2290
2291 ForceMonitorScavenge = 0; // Reset
2292 GVars.stwRandom = os::random();
2293 GVars.stwCycle++;
2294 if (needs_special_deflation) {
2295 set_is_special_deflation_requested(false); // special deflation is done
2296 }
2297 }
2298
2299 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
2300 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2301
2302 if (AsyncDeflateIdleMonitors) {
2303 if (!is_special_deflation_requested()) {
2304 // Mark the JavaThread for idle monitor deflation if a special
2305 // deflation has NOT been requested.
2306 if (thread->omInUseCount > 0) {
2307 // This JavaThread is using monitors so mark it.
2308 thread->omShouldDeflateIdleMonitors = true;
2309 }
2310 return;
2311 }
2312 }
2313
2314 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
2315 ObjectMonitor * freeTailp = NULL;
2316 elapsedTimer timer;
2317
2318 if (log_is_enabled(Info, safepoint, cleanup) ||
2319 log_is_enabled(Info, monitorinflation)) {
2320 timer.start();
2321 }
2322
2323 int deflated_count = deflate_monitor_list(thread->omInUseList_addr(), &freeHeadp, &freeTailp);
2324
2325 Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors");
2326
2327 // Adjust counters
2328 counters->nInCirculation += thread->omInUseCount;
2329 thread->omInUseCount -= deflated_count;
2330 counters->nScavenged += deflated_count;
2331 counters->nInuse += thread->omInUseCount;
2332 counters->perThreadScavenged += deflated_count;
2333
2334 // Move the scavenged monitors back to the global free list.
2335 if (freeHeadp != NULL) {
2336 guarantee(freeTailp != NULL && deflated_count > 0, "invariant");
2337 assert(freeTailp->FreeNext == NULL, "invariant");
2338
2339 // constant-time list splice - prepend scavenged segment to gFreeList
2340 freeTailp->FreeNext = gFreeList;
2341 gFreeList = freeHeadp;
2342 }
2343
2344 timer.stop();
2345 // Safepoint logging cares about cumulative perThreadTimes and
2346 // we'll capture most of the cost, but not the muxRelease() which
2347 // should be cheap.
2348 counters->perThreadTimes += timer.seconds();
2349
2350 Thread::muxRelease(&gListLock);
2351
2352 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2353 LogStreamHandle(Info, monitorinflation) lsh_info;
2354 LogStream * ls = NULL;
2355 if (log_is_enabled(Debug, monitorinflation)) {
2356 ls = &lsh_debug;
2357 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2358 ls = &lsh_info;
2359 }
2360 if (ls != NULL) {
2361 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
2362 }
2363 }
2364
2365 // Monitor cleanup on JavaThread::exit
2366
2367 // Iterate through monitor cache and attempt to release thread's monitors
2368 // Gives up on a particular monitor if an exception occurs, but continues
2369 // the overall iteration, swallowing the exception.
2370 class ReleaseJavaMonitorsClosure: public MonitorClosure {
2371 private:
2372 TRAPS;
2373
2374 public:
2375 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
2376 void do_monitor(ObjectMonitor* mid) {
2377 if (mid->owner() == THREAD) {
2378 (void)mid->complete_exit(CHECK);
2379 }
2380 }
2381 };
2382
2383 // Release all inflated monitors owned by THREAD. Lightweight monitors are
2384 // ignored. This is meant to be called during JNI thread detach which assumes
2385 // all remaining monitors are heavyweight. All exceptions are swallowed.
2386 // Scanning the extant monitor list can be time consuming.
2387 // A simple optimization is to add a per-thread flag that indicates a thread
2388 // called jni_monitorenter() during its lifetime.
2389 //
2390 // Instead of No_Savepoint_Verifier it might be cheaper to
2391 // use an idiom of the form:
2392 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
2393 // <code that must not run at safepoint>
2394 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
2395 // Since the tests are extremely cheap we could leave them enabled
2396 // for normal product builds.
2397
2398 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
2399 assert(THREAD == JavaThread::current(), "must be current Java thread");
2400 NoSafepointVerifier nsv;
2401 ReleaseJavaMonitorsClosure rjmc(THREAD);
2402 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
2403 ObjectSynchronizer::monitors_iterate(&rjmc);
2404 Thread::muxRelease(&gListLock);
2405 THREAD->clear_pending_exception();
2406 }
2407
2408 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
2409 switch (cause) {
2410 case inflate_cause_vm_internal: return "VM Internal";
2411 case inflate_cause_monitor_enter: return "Monitor Enter";
2412 case inflate_cause_wait: return "Monitor Wait";
2413 case inflate_cause_notify: return "Monitor Notify";
2414 case inflate_cause_hash_code: return "Monitor Hash Code";
2415 case inflate_cause_jni_enter: return "JNI Monitor Enter";
2416 case inflate_cause_jni_exit: return "JNI Monitor Exit";
2417 default:
2418 ShouldNotReachHere();
2419 }
2420 return "Unknown";
2421 }
2422
2423 //------------------------------------------------------------------------------
2424 // Debugging code
2425
2426 u_char* ObjectSynchronizer::get_gvars_addr() {
2427 return (u_char*)&GVars;
2428 }
2429
2430 u_char* ObjectSynchronizer::get_gvars_hcSequence_addr() {
2431 return (u_char*)&GVars.hcSequence;
2432 }
2433
2434 size_t ObjectSynchronizer::get_gvars_size() {
2435 return sizeof(SharedGlobals);
2436 }
2437
2438 u_char* ObjectSynchronizer::get_gvars_stwRandom_addr() {
2439 return (u_char*)&GVars.stwRandom;
2440 }
2441
2442 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
2443 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
2444
2445 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2446 LogStreamHandle(Info, monitorinflation) lsh_info;
2447 LogStreamHandle(Trace, monitorinflation) lsh_trace;
2448 LogStream * ls = NULL;
2449 if (log_is_enabled(Trace, monitorinflation)) {
2450 ls = &lsh_trace;
2451 } else if (log_is_enabled(Debug, monitorinflation)) {
2452 ls = &lsh_debug;
2453 } else if (log_is_enabled(Info, monitorinflation)) {
2454 ls = &lsh_info;
2455 }
2456 assert(ls != NULL, "sanity check");
2457
2458 if (!on_exit) {
2459 // Not at VM exit so grab the global list lock.
2460 Thread::muxAcquire(&gListLock, "audit_and_print_stats");
2461 }
2462
2463 // Log counts for the global and per-thread monitor lists:
2464 int chkMonitorPopulation = log_monitor_list_counts(ls);
2465 int error_cnt = 0;
2466
2467 ls->print_cr("Checking global lists:");
2468
2469 // Check gMonitorPopulation:
2470 if (gMonitorPopulation == chkMonitorPopulation) {
2471 ls->print_cr("gMonitorPopulation=%d equals chkMonitorPopulation=%d",
2472 gMonitorPopulation, chkMonitorPopulation);
2473 } else {
2474 ls->print_cr("ERROR: gMonitorPopulation=%d is not equal to "
2475 "chkMonitorPopulation=%d", gMonitorPopulation,
2476 chkMonitorPopulation);
2477 error_cnt++;
2478 }
2479
2480 // Check gOmInUseList and gOmInUseCount:
2481 chk_global_in_use_list_and_count(ls, &error_cnt);
2482
2483 // Check gFreeList and gMonitorFreeCount:
2484 chk_global_free_list_and_count(ls, &error_cnt);
2485
2486 if (!on_exit) {
2487 Thread::muxRelease(&gListLock);
2488 }
2489
2490 ls->print_cr("Checking per-thread lists:");
2491
2492 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2493 // Check omInUseList and omInUseCount:
2494 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
2495
2496 // Check omFreeList and omFreeCount:
2497 chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
2498 }
2499
2500 if (error_cnt == 0) {
2501 ls->print_cr("No errors found in monitor list checks.");
2502 } else {
2503 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
2504 }
2505
2506 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
2507 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
2508 // When exiting this log output is at the Info level. When called
2509 // at a safepoint, this log output is at the Trace level since
2510 // there can be a lot of it.
2511 log_in_use_monitor_details(ls, on_exit);
2512 }
2513
2514 ls->flush();
2515
2516 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2517 }
2518
2519 // Check a free monitor entry; log any errors.
2520 void ObjectSynchronizer::chk_free_entry(JavaThread * jt, ObjectMonitor * n,
2521 outputStream * out, int *error_cnt_p) {
2522 stringStream ss;
2523 if ((!AsyncDeflateIdleMonitors && n->is_busy()) ||
2524 (AsyncDeflateIdleMonitors && n->is_busy_async())) {
2525 if (jt != NULL) {
2526 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2527 ": free per-thread monitor must not be busy: %s", p2i(jt),
2528 p2i(n), n->is_busy_to_string(&ss));
2529 } else {
2530 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2531 "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
2532 }
2533 *error_cnt_p = *error_cnt_p + 1;
2534 }
2535 if (n->header() != NULL) {
2536 if (jt != NULL) {
2537 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2538 ": free per-thread monitor must have NULL _header "
2539 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
2540 p2i(n->header()));
2541 *error_cnt_p = *error_cnt_p + 1;
2542 } else if (!AsyncDeflateIdleMonitors) {
2543 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2544 "must have NULL _header field: _header=" INTPTR_FORMAT,
2545 p2i(n), p2i(n->header()));
2546 *error_cnt_p = *error_cnt_p + 1;
2547 }
2548 }
2549 if (n->object() != NULL) {
2550 if (jt != NULL) {
2551 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2552 ": free per-thread monitor must have NULL _object "
2553 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
2554 p2i(n->object()));
2555 } else {
2556 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2557 "must have NULL _object field: _object=" INTPTR_FORMAT,
2558 p2i(n), p2i(n->object()));
2559 }
2560 *error_cnt_p = *error_cnt_p + 1;
2561 }
2562 }
2563
2564 // Check the global free list and count; log the results of the checks.
2565 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
2566 int *error_cnt_p) {
2567 int chkMonitorFreeCount = 0;
2568 for (ObjectMonitor * n = gFreeList; n != NULL; n = n->FreeNext) {
2569 chk_free_entry(NULL /* jt */, n, out, error_cnt_p);
2570 chkMonitorFreeCount++;
2571 }
2572 if (gMonitorFreeCount == chkMonitorFreeCount) {
2573 out->print_cr("gMonitorFreeCount=%d equals chkMonitorFreeCount=%d",
2574 gMonitorFreeCount, chkMonitorFreeCount);
2575 } else {
2576 out->print_cr("ERROR: gMonitorFreeCount=%d is not equal to "
2577 "chkMonitorFreeCount=%d", gMonitorFreeCount,
2578 chkMonitorFreeCount);
2579 *error_cnt_p = *error_cnt_p + 1;
2580 }
2581 }
2582
2583 // Check the global in-use list and count; log the results of the checks.
2584 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
2585 int *error_cnt_p) {
2586 int chkOmInUseCount = 0;
2587 for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
2588 chk_in_use_entry(NULL /* jt */, n, out, error_cnt_p);
2589 chkOmInUseCount++;
2590 }
2591 if (gOmInUseCount == chkOmInUseCount) {
2592 out->print_cr("gOmInUseCount=%d equals chkOmInUseCount=%d", gOmInUseCount,
2593 chkOmInUseCount);
2594 } else {
2595 out->print_cr("ERROR: gOmInUseCount=%d is not equal to chkOmInUseCount=%d",
2596 gOmInUseCount, chkOmInUseCount);
2597 *error_cnt_p = *error_cnt_p + 1;
2598 }
2599 }
2600
2601 // Check an in-use monitor entry; log any errors.
2602 void ObjectSynchronizer::chk_in_use_entry(JavaThread * jt, ObjectMonitor * n,
2603 outputStream * out, int *error_cnt_p) {
2604 if (n->header() == NULL) {
2605 if (jt != NULL) {
2606 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2607 ": in-use per-thread monitor must have non-NULL _header "
2608 "field.", p2i(jt), p2i(n));
2609 } else {
2610 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2611 "must have non-NULL _header field.", p2i(n));
2612 }
2613 *error_cnt_p = *error_cnt_p + 1;
2614 }
2615 if (n->object() == NULL) {
2616 if (jt != NULL) {
2617 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2618 ": in-use per-thread monitor must have non-NULL _object "
2619 "field.", p2i(jt), p2i(n));
2620 } else {
2621 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2622 "must have non-NULL _object field.", p2i(n));
2623 }
2624 *error_cnt_p = *error_cnt_p + 1;
2625 }
2626 const oop obj = (oop)n->object();
2627 const markOop mark = obj->mark();
2628 if (!mark->has_monitor()) {
2629 if (jt != NULL) {
2630 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2631 ": in-use per-thread monitor's object does not think "
2632 "it has a monitor: obj=" INTPTR_FORMAT ", mark="
2633 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), p2i(mark));
2634 } else {
2635 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2636 "monitor's object does not think it has a monitor: obj="
2637 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2638 p2i(obj), p2i(mark));
2639 }
2640 *error_cnt_p = *error_cnt_p + 1;
2641 }
2642 ObjectMonitor * const obj_mon = mark->monitor();
2643 if (n != obj_mon) {
2644 if (jt != NULL) {
2645 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2646 ": in-use per-thread monitor's object does not refer "
2647 "to the same monitor: obj=" INTPTR_FORMAT ", mark="
2648 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
2649 p2i(n), p2i(obj), p2i(mark), p2i(obj_mon));
2650 } else {
2651 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2652 "monitor's object does not refer to the same monitor: obj="
2653 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2654 INTPTR_FORMAT, p2i(n), p2i(obj), p2i(mark), p2i(obj_mon));
2655 }
2656 *error_cnt_p = *error_cnt_p + 1;
2657 }
2658 }
2659
2660 // Check the thread's free list and count; log the results of the checks.
2661 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
2662 outputStream * out,
2663 int *error_cnt_p) {
2664 int chkOmFreeCount = 0;
2665 for (ObjectMonitor * n = jt->omFreeList; n != NULL; n = n->FreeNext) {
2666 chk_free_entry(jt, n, out, error_cnt_p);
2667 chkOmFreeCount++;
2668 }
2669 if (jt->omFreeCount == chkOmFreeCount) {
2670 out->print_cr("jt=" INTPTR_FORMAT ": omFreeCount=%d equals "
2671 "chkOmFreeCount=%d", p2i(jt), jt->omFreeCount, chkOmFreeCount);
2672 } else {
2673 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omFreeCount=%d is not "
2674 "equal to chkOmFreeCount=%d", p2i(jt), jt->omFreeCount,
2675 chkOmFreeCount);
2676 *error_cnt_p = *error_cnt_p + 1;
2677 }
2678 }
2679
2680 // Check the thread's in-use list and count; log the results of the checks.
2681 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
2682 outputStream * out,
2683 int *error_cnt_p) {
2684 int chkOmInUseCount = 0;
2685 for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2686 chk_in_use_entry(jt, n, out, error_cnt_p);
2687 chkOmInUseCount++;
2688 }
2689 if (jt->omInUseCount == chkOmInUseCount) {
2690 out->print_cr("jt=" INTPTR_FORMAT ": omInUseCount=%d equals "
2691 "chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2692 chkOmInUseCount);
2693 } else {
2694 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omInUseCount=%d is not "
2695 "equal to chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2696 chkOmInUseCount);
2697 *error_cnt_p = *error_cnt_p + 1;
2698 }
2699 }
2700
2701 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2702 // flags indicate why the entry is in-use, 'object' and 'object type'
2703 // indicate the associated object and its type.
2704 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out,
2705 bool on_exit) {
2706 if (!on_exit) {
2707 // Not at VM exit so grab the global list lock.
2708 Thread::muxAcquire(&gListLock, "log_in_use_monitor_details");
2709 }
2710
2711 stringStream ss;
2712 if (gOmInUseCount > 0) {
2713 out->print_cr("In-use global monitor info:");
2714 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2715 out->print_cr("%18s %s %7s %18s %18s",
2716 "monitor", "BHL", "ref_cnt", "object", "object type");
2717 out->print_cr("================== === ======= ================== ==================");
2718 for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
2719 const oop obj = (oop) n->object();
2720 const markOop mark = n->header();
2721 ResourceMark rm;
2722 out->print(INTPTR_FORMAT " %d%d%d %7d " INTPTR_FORMAT " %s",
2723 p2i(n), n->is_busy() != 0, mark->hash() != 0,
2724 n->owner() != NULL, (int)n->ref_count(), p2i(obj),
2725 obj->klass()->external_name());
2726 if (n->is_busy() != 0) {
2727 out->print(" (%s)", n->is_busy_to_string(&ss));
2728 ss.reset();
2729 }
2730 out->cr();
2731 }
2732 }
2733
2734 if (!on_exit) {
2735 Thread::muxRelease(&gListLock);
2736 }
2737
2738 out->print_cr("In-use per-thread monitor info:");
2739 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2740 out->print_cr("%18s %18s %s %7s %18s %18s",
2741 "jt", "monitor", "BHL", "ref_cnt", "object", "object type");
2742 out->print_cr("================== ================== === ======= ================== ==================");
2743 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2744 for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2745 const oop obj = (oop) n->object();
2746 const markOop mark = n->header();
2747 ResourceMark rm;
2748 out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d %7d "
2749 INTPTR_FORMAT " %s", p2i(jt), p2i(n), n->is_busy() != 0,
2750 mark->hash() != 0, n->owner() != NULL, (int)n->ref_count(),
2751 p2i(obj), obj->klass()->external_name());
2752 if (n->is_busy() != 0) {
2753 out->print(" (%s)", n->is_busy_to_string(&ss));
2754 ss.reset();
2755 }
2756 out->cr();
2757 }
2758 }
2759
2760 out->flush();
2761 }
2762
2763 // Log counts for the global and per-thread monitor lists and return
2764 // the population count.
2765 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2766 int popCount = 0;
2767 out->print_cr("%18s %10s %10s %10s",
2768 "Global Lists:", "InUse", "Free", "Total");
2769 out->print_cr("================== ========== ========== ==========");
2770 out->print_cr("%18s %10d %10d %10d", "",
2771 gOmInUseCount, gMonitorFreeCount, gMonitorPopulation);
2772 popCount += gOmInUseCount + gMonitorFreeCount;
2773
2774 out->print_cr("%18s %10s %10s %10s",
2775 "Per-Thread Lists:", "InUse", "Free", "Provision");
2776 out->print_cr("================== ========== ========== ==========");
2777
2778 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2779 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
2780 jt->omInUseCount, jt->omFreeCount, jt->omFreeProvision);
2781 popCount += jt->omInUseCount + jt->omFreeCount;
2782 }
2783 return popCount;
2784 }
2785
2786 #ifndef PRODUCT
2787
2788 // Check if monitor belongs to the monitor cache
2789 // The list is grow-only so it's *relatively* safe to traverse
2790 // the list of extant blocks without taking a lock.
2791
2792 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
2793 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
2794 while (block != NULL) {
2795 assert(block->object() == CHAINMARKER, "must be a block header");
2796 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
2797 address mon = (address)monitor;
2798 address blk = (address)block;
2799 size_t diff = mon - blk;
2800 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "must be aligned");
2801 return 1;
2802 }
2803 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
2804 }
2805 return 0;
2806 }
2807
2808 #endif