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