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 Retry:
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 goto Retry;
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 update to the ObjectMonitor's header/dmw field
822 // is to merge in the hash code. If someone adds a new usage
823 // of the header/dmw field, please update this code.
824 hash = test->hash();
825 assert(test->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(test));
826 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
827 }
828 }
829 // We finally get the hash
830 return hash;
831 }
832
833 // Deprecated -- use FastHashCode() instead.
834
835 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
836 return FastHashCode(Thread::current(), obj());
837 }
838
839
840 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
841 Handle h_obj) {
842 if (UseBiasedLocking) {
843 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
844 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
845 }
846
847 assert(thread == JavaThread::current(), "Can only be called on current thread");
848 oop obj = h_obj();
849
850 while (true) {
851 markOop mark = ReadStableMark(obj);
852
853 // Uncontended case, header points to stack
854 if (mark->has_locker()) {
855 return thread->is_lock_owned((address)mark->locker());
856 }
857 // Contended case, header points to ObjectMonitor (tagged pointer)
858 if (mark->has_monitor()) {
859 ObjectMonitorHandle omh;
860 if (!omh.save_om_ptr(obj, mark)) {
861 // Lost a race with async deflation so try again.
862 assert(AsyncDeflateIdleMonitors, "sanity check");
863 continue;
864 }
865 bool ret_code = omh.om_ptr()->is_entered(thread) != 0;
866 return ret_code;
867 }
868 // Unlocked case, header in place
869 assert(mark->is_neutral(), "sanity check");
870 return false;
871 }
872 }
873
874 // Be aware of this method could revoke bias of the lock object.
875 // This method queries the ownership of the lock handle specified by 'h_obj'.
876 // If the current thread owns the lock, it returns owner_self. If no
877 // thread owns the lock, it returns owner_none. Otherwise, it will return
878 // owner_other.
879 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
880 (JavaThread *self, Handle h_obj) {
881 // The caller must beware this method can revoke bias, and
882 // revocation can result in a safepoint.
883 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
884 assert(self->thread_state() != _thread_blocked, "invariant");
885
886 // Possible mark states: neutral, biased, stack-locked, inflated
887
888 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
889 // CASE: biased
890 BiasedLocking::revoke_and_rebias(h_obj, false, self);
891 assert(!h_obj->mark()->has_bias_pattern(),
892 "biases should be revoked by now");
893 }
894
895 assert(self == JavaThread::current(), "Can only be called on current thread");
896 oop obj = h_obj();
897
898 while (true) {
899 markOop mark = ReadStableMark(obj);
900
901 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
902 if (mark->has_locker()) {
903 return self->is_lock_owned((address)mark->locker()) ?
904 owner_self : owner_other;
905 }
906
907 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
908 // The Object:ObjectMonitor relationship is stable as long as we're
909 // not at a safepoint and AsyncDeflateIdleMonitors is false.
910 if (mark->has_monitor()) {
911 ObjectMonitorHandle omh;
912 if (!omh.save_om_ptr(obj, mark)) {
913 // Lost a race with async deflation so try again.
914 assert(AsyncDeflateIdleMonitors, "sanity check");
915 continue;
916 }
917 ObjectMonitor * monitor = omh.om_ptr();
918 void * owner = monitor->_owner;
919 if (owner == NULL) return owner_none;
920 return (owner == self ||
921 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
922 }
923
924 // CASE: neutral
925 assert(mark->is_neutral(), "sanity check");
926 return owner_none; // it's unlocked
927 }
928 }
929
930 // FIXME: jvmti should call this
931 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
932 if (UseBiasedLocking) {
933 if (SafepointSynchronize::is_at_safepoint()) {
934 BiasedLocking::revoke_at_safepoint(h_obj);
935 } else {
936 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
937 }
938 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
939 }
940
941 oop obj = h_obj();
942
943 while (true) {
944 address owner = NULL;
945 markOop mark = ReadStableMark(obj);
946
947 // Uncontended case, header points to stack
948 if (mark->has_locker()) {
949 owner = (address) mark->locker();
950 }
951
952 // Contended case, header points to ObjectMonitor (tagged pointer)
953 else if (mark->has_monitor()) {
954 ObjectMonitorHandle omh;
955 if (!omh.save_om_ptr(obj, mark)) {
956 // Lost a race with async deflation so try again.
957 assert(AsyncDeflateIdleMonitors, "sanity check");
958 continue;
959 }
960 ObjectMonitor* monitor = omh.om_ptr();
961 assert(monitor != NULL, "monitor should be non-null");
962 owner = (address) monitor->owner();
963 }
964
965 if (owner != NULL) {
966 // owning_thread_from_monitor_owner() may also return NULL here
967 return Threads::owning_thread_from_monitor_owner(t_list, owner);
968 }
969
970 // Unlocked case, header in place
971 // Cannot have assertion since this object may have been
972 // locked by another thread when reaching here.
973 // assert(mark->is_neutral(), "sanity check");
974
975 return NULL;
976 }
977 }
978
979 // Visitors ...
980
981 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
982 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
983 while (block != NULL) {
984 assert(block->object() == CHAINMARKER, "must be a block header");
985 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
986 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
987 if (mid->is_active()) {
988 ObjectMonitorHandle omh(mid);
989
990 if (mid->object() == NULL ||
991 (AsyncDeflateIdleMonitors && mid->_owner == DEFLATER_MARKER)) {
992 // Only process with closure if the object is set.
993 // For async deflation, race here if monitor is not owned!
994 // The above ref_count bump (in ObjectMonitorHandle ctr)
995 // will cause subsequent async deflation to skip it.
996 // However, previous or concurrent async deflation is a race.
997 continue;
998 }
999 closure->do_monitor(mid);
1000 }
1001 }
1002 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
1003 }
1004 }
1005
1006 // Get the next block in the block list.
1007 static inline PaddedEnd<ObjectMonitor>* next(PaddedEnd<ObjectMonitor>* block) {
1008 assert(block->object() == CHAINMARKER, "must be a block header");
1009 block = (PaddedEnd<ObjectMonitor>*) block->FreeNext;
1010 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
1011 return block;
1012 }
1013
1014 static bool monitors_used_above_threshold() {
1015 if (gMonitorPopulation == 0) {
1016 return false;
1017 }
1018 int monitors_used = gMonitorPopulation - gMonitorFreeCount;
1019 int monitor_usage = (monitors_used * 100LL) / gMonitorPopulation;
1020 return monitor_usage > MonitorUsedDeflationThreshold;
1021 }
1022
1023 bool ObjectSynchronizer::is_cleanup_needed() {
1024 if (MonitorUsedDeflationThreshold > 0) {
1025 return monitors_used_above_threshold();
1026 }
1027 return false;
1028 }
1029
1030 void ObjectSynchronizer::oops_do(OopClosure* f) {
1031 // We only scan the global used list here (for moribund threads), and
1032 // the thread-local monitors in Thread::oops_do().
1033 global_used_oops_do(f);
1034 }
1035
1036 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
1037 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1038 list_oops_do(gOmInUseList, f);
1039 }
1040
1041 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
1042 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1043 list_oops_do(thread->omInUseList, f);
1044 }
1045
1046 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
1047 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1048 ObjectMonitor* mid;
1049 for (mid = list; mid != NULL; mid = mid->FreeNext) {
1050 if (mid->object() != NULL) {
1051 f->do_oop((oop*)mid->object_addr());
1052 }
1053 }
1054 }
1055
1056
1057 // -----------------------------------------------------------------------------
1058 // ObjectMonitor Lifecycle
1059 // -----------------------
1060 // Inflation unlinks monitors from the global gFreeList and
1061 // associates them with objects. Deflation -- which occurs at
1062 // STW-time -- disassociates idle monitors from objects. Such
1063 // scavenged monitors are returned to the gFreeList.
1064 //
1065 // The global list is protected by gListLock. All the critical sections
1066 // are short and operate in constant-time.
1067 //
1068 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1069 //
1070 // Lifecycle:
1071 // -- unassigned and on the global free list
1072 // -- unassigned and on a thread's private omFreeList
1073 // -- assigned to an object. The object is inflated and the mark refers
1074 // to the objectmonitor.
1075
1076
1077 // Constraining monitor pool growth via MonitorBound ...
1078 //
1079 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
1080 // the rate of scavenging is driven primarily by GC. As such, we can find
1081 // an inordinate number of monitors in circulation.
1082 // To avoid that scenario we can artificially induce a STW safepoint
1083 // if the pool appears to be growing past some reasonable bound.
1084 // Generally we favor time in space-time tradeoffs, but as there's no
1085 // natural back-pressure on the # of extant monitors we need to impose some
1086 // type of limit. Beware that if MonitorBound is set to too low a value
1087 // we could just loop. In addition, if MonitorBound is set to a low value
1088 // we'll incur more safepoints, which are harmful to performance.
1089 // See also: GuaranteedSafepointInterval
1090 //
1091 // The current implementation uses asynchronous VM operations.
1092
1093 static void InduceScavenge(Thread * Self, const char * Whence) {
1094 // Induce STW safepoint to trim monitors
1095 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1096 // More precisely, trigger an asynchronous STW safepoint as the number
1097 // of active monitors passes the specified threshold.
1098 // TODO: assert thread state is reasonable
1099
1100 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1101 // Induce a 'null' safepoint to scavenge monitors
1102 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1103 // to the VMthread and have a lifespan longer than that of this activation record.
1104 // The VMThread will delete the op when completed.
1105 VMThread::execute(new VM_ScavengeMonitors());
1106 }
1107 }
1108
1109 ObjectMonitor* ObjectSynchronizer::omAlloc(Thread * Self,
1110 const InflateCause cause) {
1111 // A large MAXPRIVATE value reduces both list lock contention
1112 // and list coherency traffic, but also tends to increase the
1113 // number of objectMonitors in circulation as well as the STW
1114 // scavenge costs. As usual, we lean toward time in space-time
1115 // tradeoffs.
1116 const int MAXPRIVATE = 1024;
1117
1118 if (AsyncDeflateIdleMonitors) {
1119 JavaThread * jt = (JavaThread *)Self;
1120 if (jt->omShouldDeflateIdleMonitors && jt->omInUseCount > 0 &&
1121 cause != inflate_cause_vm_internal) {
1122 // Deflate any per-thread idle monitors for this JavaThread if
1123 // this is not an internal inflation. Clean up your own mess.
1124 // (Gibbs Rule 45) Otherwise, skip this cleanup.
1125 // deflate_global_idle_monitors_using_JT() is called by the ServiceThread.
1126 debug_only(jt->check_for_valid_safepoint_state(false);)
1127 ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT();
1128 }
1129 }
1130
1131 for (;;) {
1132 ObjectMonitor * m;
1133
1134 // 1: try to allocate from the thread's local omFreeList.
1135 // Threads will attempt to allocate first from their local list, then
1136 // from the global list, and only after those attempts fail will the thread
1137 // attempt to instantiate new monitors. Thread-local free lists take
1138 // heat off the gListLock and improve allocation latency, as well as reducing
1139 // coherency traffic on the shared global list.
1140 m = Self->omFreeList;
1141 if (m != NULL) {
1142 Self->omFreeList = m->FreeNext;
1143 Self->omFreeCount--;
1144 guarantee(m->object() == NULL, "invariant");
1145 m->set_allocation_state(ObjectMonitor::New);
1146 m->FreeNext = Self->omInUseList;
1147 Self->omInUseList = m;
1148 Self->omInUseCount++;
1149 return m;
1150 }
1151
1152 // 2: try to allocate from the global gFreeList
1153 // CONSIDER: use muxTry() instead of muxAcquire().
1154 // If the muxTry() fails then drop immediately into case 3.
1155 // If we're using thread-local free lists then try
1156 // to reprovision the caller's free list.
1157 if (gFreeList != NULL) {
1158 // Reprovision the thread's omFreeList.
1159 // Use bulk transfers to reduce the allocation rate and heat
1160 // on various locks.
1161 Thread::muxAcquire(&gListLock, "omAlloc(1)");
1162 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1163 gMonitorFreeCount--;
1164 ObjectMonitor * take = gFreeList;
1165 gFreeList = take->FreeNext;
1166 guarantee(take->object() == NULL, "invariant");
1167 if (AsyncDeflateIdleMonitors) {
1168 take->set_owner(NULL);
1169 take->_contentions = 0;
1170 }
1171 guarantee(!take->is_busy(), "invariant");
1172 take->Recycle();
1173 assert(take->is_free(), "invariant");
1174 omRelease(Self, take, false);
1175 }
1176 Thread::muxRelease(&gListLock);
1177 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1178 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1179
1180 const int mx = MonitorBound;
1181 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1182 // We can't safely induce a STW safepoint from omAlloc() as our thread
1183 // state may not be appropriate for such activities and callers may hold
1184 // naked oops, so instead we defer the action.
1185 InduceScavenge(Self, "omAlloc");
1186 }
1187 continue;
1188 }
1189
1190 // 3: allocate a block of new ObjectMonitors
1191 // Both the local and global free lists are empty -- resort to malloc().
1192 // In the current implementation objectMonitors are TSM - immortal.
1193 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1194 // each ObjectMonitor to start at the beginning of a cache line,
1195 // so we use align_up().
1196 // A better solution would be to use C++ placement-new.
1197 // BEWARE: As it stands currently, we don't run the ctors!
1198 assert(_BLOCKSIZE > 1, "invariant");
1199 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
1200 PaddedEnd<ObjectMonitor> * temp;
1201 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1202 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
1203 mtInternal);
1204 temp = (PaddedEnd<ObjectMonitor> *)
1205 align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE);
1206
1207 // NOTE: (almost) no way to recover if allocation failed.
1208 // We might be able to induce a STW safepoint and scavenge enough
1209 // objectMonitors to permit progress.
1210 if (temp == NULL) {
1211 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1212 "Allocate ObjectMonitors");
1213 }
1214 (void)memset((void *) temp, 0, neededsize);
1215
1216 // Format the block.
1217 // initialize the linked list, each monitor points to its next
1218 // forming the single linked free list, the very first monitor
1219 // will points to next block, which forms the block list.
1220 // The trick of using the 1st element in the block as gBlockList
1221 // linkage should be reconsidered. A better implementation would
1222 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1223
1224 for (int i = 1; i < _BLOCKSIZE; i++) {
1225 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1226 assert(temp[i].is_free(), "invariant");
1227 }
1228
1229 // terminate the last monitor as the end of list
1230 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1231
1232 // Element [0] is reserved for global list linkage
1233 temp[0].set_object(CHAINMARKER);
1234
1235 // Consider carving out this thread's current request from the
1236 // block in hand. This avoids some lock traffic and redundant
1237 // list activity.
1238
1239 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1240 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1241 Thread::muxAcquire(&gListLock, "omAlloc(2)");
1242 gMonitorPopulation += _BLOCKSIZE-1;
1243 gMonitorFreeCount += _BLOCKSIZE-1;
1244
1245 // Add the new block to the list of extant blocks (gBlockList).
1246 // The very first objectMonitor in a block is reserved and dedicated.
1247 // It serves as blocklist "next" linkage.
1248 temp[0].FreeNext = gBlockList;
1249 // There are lock-free uses of gBlockList so make sure that
1250 // the previous stores happen before we update gBlockList.
1251 OrderAccess::release_store(&gBlockList, temp);
1252
1253 // Add the new string of objectMonitors to the global free list
1254 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1255 gFreeList = temp + 1;
1256 Thread::muxRelease(&gListLock);
1257 }
1258 }
1259
1260 // Place "m" on the caller's private per-thread omFreeList.
1261 // In practice there's no need to clamp or limit the number of
1262 // monitors on a thread's omFreeList as the only time we'll call
1263 // omRelease is to return a monitor to the free list after a CAS
1264 // attempt failed. This doesn't allow unbounded #s of monitors to
1265 // accumulate on a thread's free list.
1266 //
1267 // Key constraint: all ObjectMonitors on a thread's free list and the global
1268 // free list must have their object field set to null. This prevents the
1269 // scavenger -- deflate_monitor_list() or deflate_monitor_list_using_JT()
1270 // -- from reclaiming them while we are trying to release them.
1271
1272 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1273 bool fromPerThreadAlloc) {
1274 guarantee(m->header() == NULL, "invariant");
1275 guarantee(m->object() == NULL, "invariant");
1276 guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor");
1277 m->set_allocation_state(ObjectMonitor::Free);
1278 // Remove from omInUseList
1279 if (fromPerThreadAlloc) {
1280 ObjectMonitor* cur_mid_in_use = NULL;
1281 bool extracted = false;
1282 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1283 if (m == mid) {
1284 // extract from per-thread in-use list
1285 if (mid == Self->omInUseList) {
1286 Self->omInUseList = mid->FreeNext;
1287 } else if (cur_mid_in_use != NULL) {
1288 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1289 }
1290 extracted = true;
1291 Self->omInUseCount--;
1292 break;
1293 }
1294 }
1295 assert(extracted, "Should have extracted from in-use list");
1296 }
1297
1298 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1299 m->FreeNext = Self->omFreeList;
1300 guarantee(m->is_free(), "invariant");
1301 Self->omFreeList = m;
1302 Self->omFreeCount++;
1303 }
1304
1305 // Return the monitors of a moribund thread's local free list to
1306 // the global free list. Typically a thread calls omFlush() when
1307 // it's dying. We could also consider having the VM thread steal
1308 // monitors from threads that have not run java code over a few
1309 // consecutive STW safepoints. Relatedly, we might decay
1310 // omFreeProvision at STW safepoints.
1311 //
1312 // Also return the monitors of a moribund thread's omInUseList to
1313 // a global gOmInUseList under the global list lock so these
1314 // will continue to be scanned.
1315 //
1316 // We currently call omFlush() from Threads::remove() _before the thread
1317 // has been excised from the thread list and is no longer a mutator.
1318 // This means that omFlush() cannot run concurrently with a safepoint and
1319 // interleave with the deflate_idle_monitors scavenge operator. In particular,
1320 // this ensures that the thread's monitors are scanned by a GC safepoint,
1321 // either via Thread::oops_do() (if safepoint happens before omFlush()) or via
1322 // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's
1323 // monitors have been transferred to the global in-use list).
1324 //
1325 // With AsyncDeflateIdleMonitors, deflate_global_idle_monitors_using_JT()
1326 // and deflate_per_thread_idle_monitors_using_JT() (in another thread) can
1327 // run at the same time as omFlush() so we have to be careful.
1328
1329 void ObjectSynchronizer::omFlush(Thread * Self) {
1330 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1331 ObjectMonitor * tail = NULL;
1332 int tally = 0;
1333 if (list != NULL) {
1334 ObjectMonitor * s;
1335 // The thread is going away, the per-thread free monitors
1336 // are freed via set_owner(NULL)
1337 // Link them to tail, which will be linked into the global free list
1338 // gFreeList below, under the gListLock
1339 for (s = list; s != NULL; s = s->FreeNext) {
1340 tally++;
1341 tail = s;
1342 guarantee(s->object() == NULL, "invariant");
1343 guarantee(!s->is_busy(), "invariant");
1344 s->set_owner(NULL); // redundant but good hygiene
1345 }
1346 guarantee(tail != NULL, "invariant");
1347 guarantee(Self->omFreeCount == tally, "free-count off");
1348 Self->omFreeList = NULL;
1349 Self->omFreeCount = 0;
1350 }
1351
1352 ObjectMonitor * inUseList = Self->omInUseList;
1353 ObjectMonitor * inUseTail = NULL;
1354 int inUseTally = 0;
1355 if (inUseList != NULL) {
1356 ObjectMonitor *cur_om;
1357 // The thread is going away, however the omInUseList inflated
1358 // monitors may still be in-use by other threads.
1359 // Link them to inUseTail, which will be linked into the global in-use list
1360 // gOmInUseList below, under the gListLock
1361 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1362 inUseTail = cur_om;
1363 inUseTally++;
1364 guarantee(cur_om->is_active(), "invariant");
1365 }
1366 guarantee(inUseTail != NULL, "invariant");
1367 guarantee(Self->omInUseCount == inUseTally, "in-use count off");
1368 Self->omInUseList = NULL;
1369 Self->omInUseCount = 0;
1370 }
1371
1372 Thread::muxAcquire(&gListLock, "omFlush");
1373 if (tail != NULL) {
1374 tail->FreeNext = gFreeList;
1375 gFreeList = list;
1376 gMonitorFreeCount += tally;
1377 }
1378
1379 if (inUseTail != NULL) {
1380 inUseTail->FreeNext = gOmInUseList;
1381 gOmInUseList = inUseList;
1382 gOmInUseCount += inUseTally;
1383 }
1384
1385 Thread::muxRelease(&gListLock);
1386
1387 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1388 LogStreamHandle(Info, monitorinflation) lsh_info;
1389 LogStream * ls = NULL;
1390 if (log_is_enabled(Debug, monitorinflation)) {
1391 ls = &lsh_debug;
1392 } else if ((tally != 0 || inUseTally != 0) &&
1393 log_is_enabled(Info, monitorinflation)) {
1394 ls = &lsh_info;
1395 }
1396 if (ls != NULL) {
1397 ls->print_cr("omFlush: jt=" INTPTR_FORMAT ", free_monitor_tally=%d"
1398 ", in_use_monitor_tally=%d" ", omFreeProvision=%d",
1399 p2i(Self), tally, inUseTally, Self->omFreeProvision);
1400 }
1401 }
1402
1403 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1404 const oop obj,
1405 ObjectSynchronizer::InflateCause cause) {
1406 assert(event != NULL, "invariant");
1407 assert(event->should_commit(), "invariant");
1408 event->set_monitorClass(obj->klass());
1409 event->set_address((uintptr_t)(void*)obj);
1410 event->set_cause((u1)cause);
1411 event->commit();
1412 }
1413
1414 // Fast path code shared by multiple functions
1415 void ObjectSynchronizer::inflate_helper(ObjectMonitorHandle * omh_p, oop obj) {
1416 while (true) {
1417 markOop mark = obj->mark();
1418 if (mark->has_monitor()) {
1419 if (!omh_p->save_om_ptr(obj, mark)) {
1420 // Lost a race with async deflation so try again.
1421 assert(AsyncDeflateIdleMonitors, "sanity check");
1422 continue;
1423 }
1424 ObjectMonitor * monitor = omh_p->om_ptr();
1425 assert(ObjectSynchronizer::verify_objmon_isinpool(monitor), "monitor is invalid");
1426 markOop dmw = monitor->header();
1427 assert(dmw->is_neutral(), "sanity check: header=" INTPTR_FORMAT, p2i(dmw));
1428 return;
1429 }
1430 inflate(omh_p, Thread::current(), obj, inflate_cause_vm_internal);
1431 return;
1432 }
1433 }
1434
1435 void ObjectSynchronizer::inflate(ObjectMonitorHandle * omh_p, Thread * Self,
1436 oop object, const InflateCause cause) {
1437 // Inflate mutates the heap ...
1438 // Relaxing assertion for bug 6320749.
1439 assert(Universe::verify_in_progress() ||
1440 !SafepointSynchronize::is_at_safepoint(), "invariant");
1441
1442 EventJavaMonitorInflate event;
1443
1444 for (;;) {
1445 const markOop mark = object->mark();
1446 assert(!mark->has_bias_pattern(), "invariant");
1447
1448 // The mark can be in one of the following states:
1449 // * Inflated - just return
1450 // * Stack-locked - coerce it to inflated
1451 // * INFLATING - busy wait for conversion to complete
1452 // * Neutral - aggressively inflate the object.
1453 // * BIASED - Illegal. We should never see this
1454
1455 // CASE: inflated
1456 if (mark->has_monitor()) {
1457 if (!omh_p->save_om_ptr(object, mark)) {
1458 // Lost a race with async deflation so try again.
1459 assert(AsyncDeflateIdleMonitors, "sanity check");
1460 continue;
1461 }
1462 ObjectMonitor * inf = omh_p->om_ptr();
1463 markOop dmw = inf->header();
1464 assert(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1465 assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1466 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1467 return;
1468 }
1469
1470 // CASE: inflation in progress - inflating over a stack-lock.
1471 // Some other thread is converting from stack-locked to inflated.
1472 // Only that thread can complete inflation -- other threads must wait.
1473 // The INFLATING value is transient.
1474 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1475 // We could always eliminate polling by parking the thread on some auxiliary list.
1476 if (mark == markOopDesc::INFLATING()) {
1477 ReadStableMark(object);
1478 continue;
1479 }
1480
1481 // CASE: stack-locked
1482 // Could be stack-locked either by this thread or by some other thread.
1483 //
1484 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1485 // to install INFLATING into the mark word. We originally installed INFLATING,
1486 // allocated the objectmonitor, and then finally STed the address of the
1487 // objectmonitor into the mark. This was correct, but artificially lengthened
1488 // the interval in which INFLATED appeared in the mark, thus increasing
1489 // the odds of inflation contention.
1490 //
1491 // We now use per-thread private objectmonitor free lists.
1492 // These list are reprovisioned from the global free list outside the
1493 // critical INFLATING...ST interval. A thread can transfer
1494 // multiple objectmonitors en-mass from the global free list to its local free list.
1495 // This reduces coherency traffic and lock contention on the global free list.
1496 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1497 // before or after the CAS(INFLATING) operation.
1498 // See the comments in omAlloc().
1499
1500 LogStreamHandle(Trace, monitorinflation) lsh;
1501
1502 if (mark->has_locker()) {
1503 ObjectMonitor * m;
1504 if (!AsyncDeflateIdleMonitors || cause == inflate_cause_vm_internal) {
1505 // If !AsyncDeflateIdleMonitors or if an internal inflation, then
1506 // we won't stop for a potential safepoint in omAlloc.
1507 m = omAlloc(Self, cause);
1508 } else {
1509 // If AsyncDeflateIdleMonitors and not an internal inflation, then
1510 // we may stop for a safepoint in omAlloc() so protect object.
1511 Handle h_obj(Self, object);
1512 m = omAlloc(Self, cause);
1513 object = h_obj(); // Refresh object.
1514 }
1515 // Optimistically prepare the objectmonitor - anticipate successful CAS
1516 // We do this before the CAS in order to minimize the length of time
1517 // in which INFLATING appears in the mark.
1518 m->Recycle();
1519 m->_Responsible = NULL;
1520 m->_recursions = 0;
1521 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1522
1523 markOop cmp = object->cas_set_mark(markOopDesc::INFLATING(), mark);
1524 if (cmp != mark) {
1525 omRelease(Self, m, true);
1526 continue; // Interference -- just retry
1527 }
1528
1529 // We've successfully installed INFLATING (0) into the mark-word.
1530 // This is the only case where 0 will appear in a mark-word.
1531 // Only the singular thread that successfully swings the mark-word
1532 // to 0 can perform (or more precisely, complete) inflation.
1533 //
1534 // Why do we CAS a 0 into the mark-word instead of just CASing the
1535 // mark-word from the stack-locked value directly to the new inflated state?
1536 // Consider what happens when a thread unlocks a stack-locked object.
1537 // It attempts to use CAS to swing the displaced header value from the
1538 // on-stack basiclock back into the object header. Recall also that the
1539 // header value (hash code, etc) can reside in (a) the object header, or
1540 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1541 // header in an objectMonitor. The inflate() routine must copy the header
1542 // value from the basiclock on the owner's stack to the objectMonitor, all
1543 // the while preserving the hashCode stability invariants. If the owner
1544 // decides to release the lock while the value is 0, the unlock will fail
1545 // and control will eventually pass from slow_exit() to inflate. The owner
1546 // will then spin, waiting for the 0 value to disappear. Put another way,
1547 // the 0 causes the owner to stall if the owner happens to try to
1548 // drop the lock (restoring the header from the basiclock to the object)
1549 // while inflation is in-progress. This protocol avoids races that might
1550 // would otherwise permit hashCode values to change or "flicker" for an object.
1551 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1552 // 0 serves as a "BUSY" inflate-in-progress indicator.
1553
1554
1555 // fetch the displaced mark from the owner's stack.
1556 // The owner can't die or unwind past the lock while our INFLATING
1557 // object is in the mark. Furthermore the owner can't complete
1558 // an unlock on the object, either.
1559 markOop dmw = mark->displaced_mark_helper();
1560 // Catch if the object's header is not neutral (not locked and
1561 // not marked is what we care about here).
1562 assert(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1563
1564 // Setup monitor fields to proper values -- prepare the monitor
1565 m->set_header(dmw);
1566
1567 // Optimization: if the mark->locker stack address is associated
1568 // with this thread we could simply set m->_owner = Self.
1569 // Note that a thread can inflate an object
1570 // that it has stack-locked -- as might happen in wait() -- directly
1571 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1572 m->set_owner(mark->locker());
1573 m->set_object(object);
1574 // TODO-FIXME: assert BasicLock->dhw != 0.
1575
1576 // Must preserve store ordering. The monitor state must
1577 // be stable at the time of publishing the monitor address.
1578 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1579 object->release_set_mark(markOopDesc::encode(m));
1580
1581 // Hopefully the performance counters are allocated on distinct cache lines
1582 // to avoid false sharing on MP systems ...
1583 OM_PERFDATA_OP(Inflations, inc());
1584 if (log_is_enabled(Trace, monitorinflation)) {
1585 ResourceMark rm(Self);
1586 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1587 INTPTR_FORMAT ", type='%s'", p2i(object),
1588 p2i(object->mark()), object->klass()->external_name());
1589 }
1590 if (event.should_commit()) {
1591 post_monitor_inflate_event(&event, object, cause);
1592 }
1593 assert(!m->is_free(), "post-condition");
1594 omh_p->set_om_ptr(m);
1595 return;
1596 }
1597
1598 // CASE: neutral
1599 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1600 // If we know we're inflating for entry it's better to inflate by swinging a
1601 // pre-locked objectMonitor pointer into the object header. A successful
1602 // CAS inflates the object *and* confers ownership to the inflating thread.
1603 // In the current implementation we use a 2-step mechanism where we CAS()
1604 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1605 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1606 // would be useful.
1607
1608 // Catch if the object's header is not neutral (not locked and
1609 // not marked is what we care about here).
1610 assert(mark->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(mark));
1611 ObjectMonitor * m;
1612 if (!AsyncDeflateIdleMonitors || cause == inflate_cause_vm_internal) {
1613 // If !AsyncDeflateIdleMonitors or if an internal inflation, then
1614 // we won't stop for a potential safepoint in omAlloc.
1615 m = omAlloc(Self, cause);
1616 } else {
1617 // If AsyncDeflateIdleMonitors and not an internal inflation, then
1618 // we may stop for a safepoint in omAlloc() so protect object.
1619 Handle h_obj(Self, object);
1620 m = omAlloc(Self, cause);
1621 object = h_obj(); // Refresh object.
1622 }
1623 // prepare m for installation - set monitor to initial state
1624 m->Recycle();
1625 m->set_header(mark);
1626 m->set_owner(NULL);
1627 m->set_object(object);
1628 m->_recursions = 0;
1629 m->_Responsible = NULL;
1630 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1631
1632 if (object->cas_set_mark(markOopDesc::encode(m), mark) != mark) {
1633 m->set_header(NULL);
1634 m->set_object(NULL);
1635 m->Recycle();
1636 omRelease(Self, m, true);
1637 m = NULL;
1638 continue;
1639 // interference - the markword changed - just retry.
1640 // The state-transitions are one-way, so there's no chance of
1641 // live-lock -- "Inflated" is an absorbing state.
1642 }
1643
1644 // Hopefully the performance counters are allocated on distinct
1645 // cache lines to avoid false sharing on MP systems ...
1646 OM_PERFDATA_OP(Inflations, inc());
1647 if (log_is_enabled(Trace, monitorinflation)) {
1648 ResourceMark rm(Self);
1649 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1650 INTPTR_FORMAT ", type='%s'", p2i(object),
1651 p2i(object->mark()), object->klass()->external_name());
1652 }
1653 if (event.should_commit()) {
1654 post_monitor_inflate_event(&event, object, cause);
1655 }
1656 omh_p->set_om_ptr(m);
1657 return;
1658 }
1659 }
1660
1661
1662 // We maintain a list of in-use monitors for each thread.
1663 //
1664 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1665 // deflate_idle_monitors() scans only a global list of in-use monitors which
1666 // is populated only as a thread dies (see omFlush()).
1667 //
1668 // These operations are called at all safepoints, immediately after mutators
1669 // are stopped, but before any objects have moved. Collectively they traverse
1670 // the population of in-use monitors, deflating where possible. The scavenged
1671 // monitors are returned to the global monitor free list.
1672 //
1673 // Beware that we scavenge at *every* stop-the-world point. Having a large
1674 // number of monitors in-use could negatively impact performance. We also want
1675 // to minimize the total # of monitors in circulation, as they incur a small
1676 // footprint penalty.
1677 //
1678 // Perversely, the heap size -- and thus the STW safepoint rate --
1679 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1680 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1681 // This is an unfortunate aspect of this design.
1682
1683 void ObjectSynchronizer::do_safepoint_work(DeflateMonitorCounters* _counters) {
1684 if (!AsyncDeflateIdleMonitors) {
1685 // Use the older mechanism for the global in-use list.
1686 ObjectSynchronizer::deflate_idle_monitors(_counters);
1687 return;
1688 }
1689
1690 assert(_counters == NULL, "not used with AsyncDeflateIdleMonitors");
1691
1692 log_debug(monitorinflation)("requesting deflation of idle monitors.");
1693 // Request deflation of global idle monitors by the ServiceThread:
1694 _gOmShouldDeflateIdleMonitors = true;
1695 MutexLockerEx ml(Service_lock, Mutex::_no_safepoint_check_flag);
1696 Service_lock->notify_all();
1697
1698 // Request deflation of per-thread idle monitors by each JavaThread:
1699 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
1700 if (jt->omInUseCount > 0) {
1701 // This JavaThread is using monitors so check it.
1702 jt->omShouldDeflateIdleMonitors = true;
1703 }
1704 }
1705 }
1706
1707 // Deflate a single monitor if not in-use
1708 // Return true if deflated, false if in-use
1709 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1710 ObjectMonitor** freeHeadp,
1711 ObjectMonitor** freeTailp) {
1712 bool deflated;
1713 // Normal case ... The monitor is associated with obj.
1714 const markOop mark = obj->mark();
1715 guarantee(mark == markOopDesc::encode(mid), "should match: mark="
1716 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, p2i(mark),
1717 p2i(markOopDesc::encode(mid)));
1718 // Make sure that mark->monitor() and markOopDesc::encode() agree:
1719 guarantee(mark->monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
1720 ", mid=" INTPTR_FORMAT, p2i(mark->monitor()), p2i(mid));
1721 const markOop dmw = mid->header();
1722 guarantee(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1723
1724 if (mid->is_busy()) {
1725 deflated = false;
1726 } else {
1727 // Deflate the monitor if it is no longer being used
1728 // It's idle - scavenge and return to the global free list
1729 // plain old deflation ...
1730 if (log_is_enabled(Trace, monitorinflation)) {
1731 ResourceMark rm;
1732 log_trace(monitorinflation)("deflate_monitor: "
1733 "object=" INTPTR_FORMAT ", mark="
1734 INTPTR_FORMAT ", type='%s'", p2i(obj),
1735 p2i(mark), obj->klass()->external_name());
1736 }
1737
1738 // Restore the header back to obj
1739 obj->release_set_mark(dmw);
1740 mid->clear();
1741
1742 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
1743 p2i(mid->object()));
1744 assert(mid->is_free(), "invariant");
1745
1746 // Move the object to the working free list defined by freeHeadp, freeTailp
1747 if (*freeHeadp == NULL) *freeHeadp = mid;
1748 if (*freeTailp != NULL) {
1749 ObjectMonitor * prevtail = *freeTailp;
1750 assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1751 prevtail->FreeNext = mid;
1752 }
1753 *freeTailp = mid;
1754 deflated = true;
1755 }
1756 return deflated;
1757 }
1758
1759 // Deflate the specified ObjectMonitor if not in-use using a JavaThread.
1760 // Returns true if it was deflated and false otherwise.
1761 //
1762 // The async deflation protocol sets _owner to DEFLATER_MARKER and
1763 // makes _contentions negative as signals to contending threads that
1764 // an async deflation is in progress. There are a number of checks
1765 // as part of the protocol to make sure that the calling thread has
1766 // not lost the race to a contending thread.
1767 //
1768 // The ObjectMonitor has been successfully async deflated when:
1769 // (_owner == DEFLATER_MARKER && _contentions < 0). Contending threads
1770 // that see those values know to retry their operation.
1771 //
1772 bool ObjectSynchronizer::deflate_monitor_using_JT(ObjectMonitor* mid,
1773 ObjectMonitor** freeHeadp,
1774 ObjectMonitor** freeTailp) {
1775 assert(AsyncDeflateIdleMonitors, "sanity check");
1776 assert(Thread::current()->is_Java_thread(), "precondition");
1777 // A newly allocated ObjectMonitor should not be seen here so we
1778 // avoid an endless inflate/deflate cycle.
1779 assert(mid->is_old(), "precondition");
1780
1781 if (mid->is_busy() || mid->ref_count() != 0) {
1782 // Easy checks are first - the ObjectMonitor is busy or ObjectMonitor*
1783 // is in use so no deflation.
1784 return false;
1785 }
1786
1787 if (Atomic::cmpxchg(DEFLATER_MARKER, &mid->_owner, (void*)NULL) == NULL) {
1788 // ObjectMonitor is not owned by another thread. Our setting
1789 // _owner to DEFLATER_MARKER forces any contending thread through
1790 // the slow path. This is just the first part of the async
1791 // deflation dance.
1792
1793 if (mid->_waiters != 0 || mid->ref_count() != 0) {
1794 // Another thread has raced to enter the ObjectMonitor after
1795 // mid->is_busy() above and has already waited on it which
1796 // makes it busy so no deflation. Or the ObjectMonitor* is
1797 // in use for some other operation like inflate(). Restore
1798 // _owner to NULL if it is still DEFLATER_MARKER.
1799 Atomic::cmpxchg((void*)NULL, &mid->_owner, DEFLATER_MARKER);
1800 return false;
1801 }
1802
1803 if (Atomic::cmpxchg(-max_jint, &mid->_contentions, (jint)0) == 0) {
1804 // Make _contentions negative to force racing threads to retry.
1805 // This is the second part of the async deflation dance.
1806
1807 if (mid->_owner == DEFLATER_MARKER) {
1808 // If _owner is still DEFLATER_MARKER, then we have successfully
1809 // signaled any racing threads to retry. If it is not, then we
1810 // have lost the race to another thread and the ObjectMonitor is
1811 // now busy. This is the third and final part of the async
1812 // deflation dance.
1813 // Note: This _owner check solves the ABA problem with _contentions
1814 // where another thread acquired the ObjectMonitor, finished
1815 // using it and restored the _contentions to zero.
1816
1817 // Sanity checks for the races:
1818 guarantee(mid->_waiters == 0, "should be no waiters");
1819 guarantee(mid->_cxq == NULL, "should be no contending threads");
1820 guarantee(mid->_EntryList == NULL, "should be no entering threads");
1821
1822 if (log_is_enabled(Trace, monitorinflation)) {
1823 oop obj = (oop) mid->object();
1824 assert(obj != NULL, "sanity check");
1825 if (obj->is_instance()) {
1826 ResourceMark rm;
1827 log_trace(monitorinflation)("deflate_monitor_using_JT: "
1828 "object=" INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", type='%s'",
1829 p2i(obj), p2i(obj->mark()),
1830 obj->klass()->external_name());
1831 }
1832 }
1833
1834 // Install the old mark word if nobody else has already done it.
1835 mid->install_displaced_markword_in_object();
1836 mid->clear_using_JT();
1837
1838 assert(mid->object() == NULL, "invariant");
1839 assert(mid->is_free(), "invariant");
1840
1841 // Move the deflated ObjectMonitor to the working free list
1842 // defined by freeHeadp and freeTailp.
1843 if (*freeHeadp == NULL) {
1844 // First one on the list.
1845 *freeHeadp = mid;
1846 }
1847 if (*freeTailp != NULL) {
1848 // We append to the list so the caller can use mid->FreeNext
1849 // to fix the linkages in its context.
1850 ObjectMonitor * prevtail = *freeTailp;
1851 assert(prevtail->FreeNext == NULL, "not cleaned up by the caller");
1852 prevtail->FreeNext = mid;
1853 }
1854 *freeTailp = mid;
1855
1856 // At this point, mid->FreeNext still refers to its current
1857 // value and another ObjectMonitor's FreeNext field still
1858 // refers to this ObjectMonitor. Those linkages have to be
1859 // cleaned up by the caller who has the complete context.
1860
1861 // We leave _owner == DEFLATER_MARKER and _contentions < 0
1862 // to force any racing threads to retry.
1863 return true; // Success, ObjectMonitor has been deflated.
1864 }
1865
1866 // The _owner was changed from DEFLATER_MARKER so we lost the
1867 // race since the ObjectMonitor is now busy. Add back max_jint
1868 // to restore the _contentions field to its proper value (which
1869 // may not be what we saw above).
1870 Atomic::add(max_jint, &mid->_contentions);
1871
1872 assert(mid->_contentions >= 0, "_contentions should not be negative");
1873 }
1874
1875 // The _contentions was no longer 0 so we lost the race since the
1876 // ObjectMonitor is now busy.
1877 assert(mid->_owner != DEFLATER_MARKER, "should no longer be set");
1878 }
1879
1880 // The _owner field is no longer NULL so we lost the race since the
1881 // ObjectMonitor is now busy.
1882 return false;
1883 }
1884
1885 // Walk a given monitor list, and deflate idle monitors
1886 // The given list could be a per-thread list or a global list
1887 // Caller acquires gListLock as needed.
1888 //
1889 // In the case of parallel processing of thread local monitor lists,
1890 // work is done by Threads::parallel_threads_do() which ensures that
1891 // each Java thread is processed by exactly one worker thread, and
1892 // thus avoid conflicts that would arise when worker threads would
1893 // process the same monitor lists concurrently.
1894 //
1895 // See also ParallelSPCleanupTask and
1896 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1897 // Threads::parallel_java_threads_do() in thread.cpp.
1898 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1899 ObjectMonitor** freeHeadp,
1900 ObjectMonitor** freeTailp) {
1901 ObjectMonitor* mid;
1902 ObjectMonitor* next;
1903 ObjectMonitor* cur_mid_in_use = NULL;
1904 int deflated_count = 0;
1905
1906 for (mid = *listHeadp; mid != NULL;) {
1907 oop obj = (oop) mid->object();
1908 if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1909 // if deflate_monitor succeeded,
1910 // extract from per-thread in-use list
1911 if (mid == *listHeadp) {
1912 *listHeadp = mid->FreeNext;
1913 } else if (cur_mid_in_use != NULL) {
1914 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1915 }
1916 next = mid->FreeNext;
1917 mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list
1918 mid = next;
1919 deflated_count++;
1920 } else {
1921 cur_mid_in_use = mid;
1922 mid = mid->FreeNext;
1923 }
1924 }
1925 return deflated_count;
1926 }
1927
1928 // Walk a given ObjectMonitor list and deflate idle ObjectMonitors using
1929 // a JavaThread. Returns the number of deflated ObjectMonitors. The given
1930 // list could be a per-thread in-use list or the global in-use list.
1931 // Caller acquires gListLock as appropriate. If a safepoint has started,
1932 // then we save state via savedMidInUsep and return to the caller to
1933 // honor the safepoint.
1934 //
1935 int ObjectSynchronizer::deflate_monitor_list_using_JT(ObjectMonitor** listHeadp,
1936 ObjectMonitor** freeHeadp,
1937 ObjectMonitor** freeTailp,
1938 ObjectMonitor** savedMidInUsep) {
1939 assert(AsyncDeflateIdleMonitors, "sanity check");
1940 assert(Thread::current()->is_Java_thread(), "precondition");
1941
1942 ObjectMonitor* mid;
1943 ObjectMonitor* next;
1944 ObjectMonitor* cur_mid_in_use = NULL;
1945 int deflated_count = 0;
1946
1947 if (*savedMidInUsep == NULL) {
1948 // No saved state so start at the beginning.
1949 mid = *listHeadp;
1950 } else {
1951 // We're restarting after a safepoint so restore the necessary state
1952 // before we resume.
1953 cur_mid_in_use = *savedMidInUsep;
1954 mid = cur_mid_in_use->FreeNext;
1955 }
1956 while (mid != NULL) {
1957 // Only try to deflate if there is an associated Java object and if
1958 // mid is old (is not newly allocated and is not newly freed).
1959 if (mid->object() != NULL && mid->is_old() &&
1960 deflate_monitor_using_JT(mid, freeHeadp, freeTailp)) {
1961 // Deflation succeeded so update the in-use list.
1962 if (mid == *listHeadp) {
1963 *listHeadp = mid->FreeNext;
1964 } else if (cur_mid_in_use != NULL) {
1965 // Maintain the current in-use list.
1966 cur_mid_in_use->FreeNext = mid->FreeNext;
1967 }
1968 next = mid->FreeNext;
1969 mid->FreeNext = NULL;
1970 // At this point mid is disconnected from the in-use list
1971 // and is the current tail in the freeHeadp list.
1972 mid = next;
1973 deflated_count++;
1974 } else {
1975 // mid is considered in-use if it does not have an associated
1976 // Java object or mid is not old or deflation did not succeed.
1977 // A mid->is_new() node can be seen here when it is freshly returned
1978 // by omAlloc() (and skips the deflation code path).
1979 // A mid->is_old() node can be seen here when deflation failed.
1980 // A mid->is_free() node can be seen here when a fresh node from
1981 // omAlloc() is released by omRelease() due to losing the race
1982 // in inflate().
1983
1984 if (mid->object() != NULL && mid->is_new()) {
1985 // mid has an associated Java object and has now been seen
1986 // as newly allocated so mark it as "old".
1987 mid->set_allocation_state(ObjectMonitor::Old);
1988 }
1989 cur_mid_in_use = mid;
1990 mid = mid->FreeNext;
1991
1992 if (SafepointSynchronize::is_synchronizing() &&
1993 cur_mid_in_use != *listHeadp && cur_mid_in_use->is_old()) {
1994 // If a safepoint has started and cur_mid_in_use is not the list
1995 // head and is old, then it is safe to use as saved state. Return
1996 // to the caller so gListLock can be dropped as appropriate
1997 // before blocking.
1998 *savedMidInUsep = cur_mid_in_use;
1999 return deflated_count;
2000 }
2001 }
2002 }
2003 // We finished the list without a safepoint starting so there's
2004 // no need to save state.
2005 *savedMidInUsep = NULL;
2006 return deflated_count;
2007 }
2008
2009 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2010 counters->nInuse = 0; // currently associated with objects
2011 counters->nInCirculation = 0; // extant
2012 counters->nScavenged = 0; // reclaimed (global and per-thread)
2013 counters->perThreadScavenged = 0; // per-thread scavenge total
2014 counters->perThreadTimes = 0.0; // per-thread scavenge times
2015 }
2016
2017 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
2018 assert(!AsyncDeflateIdleMonitors, "sanity check");
2019 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2020 bool deflated = false;
2021
2022 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
2023 ObjectMonitor * freeTailp = NULL;
2024 elapsedTimer timer;
2025
2026 if (log_is_enabled(Info, monitorinflation)) {
2027 timer.start();
2028 }
2029
2030 // Prevent omFlush from changing mids in Thread dtor's during deflation
2031 // And in case the vm thread is acquiring a lock during a safepoint
2032 // See e.g. 6320749
2033 Thread::muxAcquire(&gListLock, "deflate_idle_monitors");
2034
2035 // Note: the thread-local monitors lists get deflated in
2036 // a separate pass. See deflate_thread_local_monitors().
2037
2038 // For moribund threads, scan gOmInUseList
2039 int deflated_count = 0;
2040 if (gOmInUseList) {
2041 counters->nInCirculation += gOmInUseCount;
2042 deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
2043 gOmInUseCount -= deflated_count;
2044 counters->nScavenged += deflated_count;
2045 counters->nInuse += gOmInUseCount;
2046 }
2047
2048 // Move the scavenged monitors back to the global free list.
2049 if (freeHeadp != NULL) {
2050 guarantee(freeTailp != NULL && counters->nScavenged > 0, "invariant");
2051 assert(freeTailp->FreeNext == NULL, "invariant");
2052 // constant-time list splice - prepend scavenged segment to gFreeList
2053 freeTailp->FreeNext = gFreeList;
2054 gFreeList = freeHeadp;
2055 }
2056 Thread::muxRelease(&gListLock);
2057 timer.stop();
2058
2059 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2060 LogStreamHandle(Info, monitorinflation) lsh_info;
2061 LogStream * ls = NULL;
2062 if (log_is_enabled(Debug, monitorinflation)) {
2063 ls = &lsh_debug;
2064 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2065 ls = &lsh_info;
2066 }
2067 if (ls != NULL) {
2068 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2069 }
2070 }
2071
2072 // Deflate global idle ObjectMonitors using a JavaThread.
2073 //
2074 void ObjectSynchronizer::deflate_global_idle_monitors_using_JT() {
2075 assert(AsyncDeflateIdleMonitors, "sanity check");
2076 assert(Thread::current()->is_Java_thread(), "precondition");
2077 JavaThread * cur_jt = JavaThread::current();
2078
2079 _gOmShouldDeflateIdleMonitors = false;
2080
2081 int deflated_count = 0;
2082 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged ObjectMonitors
2083 ObjectMonitor * freeTailp = NULL;
2084 ObjectMonitor * savedMidInUsep = NULL;
2085 elapsedTimer timer;
2086
2087 if (log_is_enabled(Info, monitorinflation)) {
2088 timer.start();
2089 }
2090 Thread::muxAcquire(&gListLock, "deflate_global_idle_monitors_using_JT(1)");
2091 OM_PERFDATA_OP(MonExtant, set_value(gOmInUseCount));
2092
2093 do {
2094 int local_deflated_count = deflate_monitor_list_using_JT((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp, &savedMidInUsep);
2095 gOmInUseCount -= local_deflated_count;
2096 deflated_count += local_deflated_count;
2097
2098 if (freeHeadp != NULL) {
2099 // Move the scavenged ObjectMonitors to the global free list.
2100 guarantee(freeTailp != NULL && local_deflated_count > 0, "freeTailp=" INTPTR_FORMAT ", local_deflated_count=%d", p2i(freeTailp), local_deflated_count);
2101 assert(freeTailp->FreeNext == NULL, "invariant");
2102
2103 // Constant-time list splice - prepend scavenged segment to gFreeList.
2104 freeTailp->FreeNext = gFreeList;
2105 gFreeList = freeHeadp;
2106
2107 gMonitorFreeCount += local_deflated_count;
2108 OM_PERFDATA_OP(Deflations, inc(local_deflated_count));
2109 }
2110
2111 if (savedMidInUsep != NULL) {
2112 // deflate_monitor_list_using_JT() detected a safepoint starting.
2113 Thread::muxRelease(&gListLock);
2114 timer.stop();
2115 {
2116 log_debug(monitorinflation)("pausing deflation of global idle monitors for a safepoint.");
2117 assert(SafepointSynchronize::is_synchronizing(), "sanity check");
2118 ThreadBlockInVM blocker(cur_jt);
2119 }
2120 // Prepare for another loop after the safepoint.
2121 freeHeadp = NULL;
2122 freeTailp = NULL;
2123 if (log_is_enabled(Info, monitorinflation)) {
2124 timer.start();
2125 }
2126 Thread::muxAcquire(&gListLock, "deflate_global_idle_monitors_using_JT(2)");
2127 }
2128 } while (savedMidInUsep != NULL);
2129 Thread::muxRelease(&gListLock);
2130 timer.stop();
2131
2132 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2133 LogStreamHandle(Info, monitorinflation) lsh_info;
2134 LogStream * ls = NULL;
2135 if (log_is_enabled(Debug, monitorinflation)) {
2136 ls = &lsh_debug;
2137 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2138 ls = &lsh_info;
2139 }
2140 if (ls != NULL) {
2141 ls->print_cr("async-deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2142 }
2143 }
2144
2145 // Deflate per-thread idle ObjectMonitors using a JavaThread.
2146 //
2147 void ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT() {
2148 assert(AsyncDeflateIdleMonitors, "sanity check");
2149 assert(Thread::current()->is_Java_thread(), "precondition");
2150 JavaThread * cur_jt = JavaThread::current();
2151
2152 cur_jt->omShouldDeflateIdleMonitors = false;
2153
2154 int deflated_count = 0;
2155 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged ObjectMonitors
2156 ObjectMonitor * freeTailp = NULL;
2157 ObjectMonitor * savedMidInUsep = NULL;
2158 elapsedTimer timer;
2159
2160 if (log_is_enabled(Info, monitorinflation)) {
2161 timer.start();
2162 }
2163
2164 OM_PERFDATA_OP(MonExtant, inc(cur_jt->omInUseCount));
2165 do {
2166 int local_deflated_count = deflate_monitor_list_using_JT(cur_jt->omInUseList_addr(), &freeHeadp, &freeTailp, &savedMidInUsep);
2167 cur_jt->omInUseCount -= local_deflated_count;
2168 deflated_count += local_deflated_count;
2169
2170 if (freeHeadp != NULL) {
2171 // Move the scavenged ObjectMonitors to the global free list.
2172 Thread::muxAcquire(&gListLock, "deflate_per_thread_idle_monitors_using_JT");
2173 guarantee(freeTailp != NULL && local_deflated_count > 0, "freeTailp=" INTPTR_FORMAT ", local_deflated_count=%d", p2i(freeTailp), local_deflated_count);
2174 assert(freeTailp->FreeNext == NULL, "invariant");
2175
2176 // Constant-time list splice - prepend scavenged segment to gFreeList.
2177 freeTailp->FreeNext = gFreeList;
2178 gFreeList = freeHeadp;
2179
2180 gMonitorFreeCount += local_deflated_count;
2181 OM_PERFDATA_OP(Deflations, inc(local_deflated_count));
2182 Thread::muxRelease(&gListLock);
2183 // Prepare for another loop on the current JavaThread.
2184 freeHeadp = NULL;
2185 freeTailp = NULL;
2186 }
2187 timer.stop();
2188
2189 if (savedMidInUsep != NULL) {
2190 // deflate_monitor_list_using_JT() detected a safepoint starting.
2191 {
2192 log_debug(monitorinflation)("jt=" INTPTR_FORMAT ": pausing deflation of per-thread idle monitors for a safepoint.", p2i(cur_jt));
2193 assert(SafepointSynchronize::is_synchronizing(), "sanity check");
2194 ThreadBlockInVM blocker(cur_jt);
2195 }
2196 // Prepare for another loop on the current JavaThread after
2197 // the safepoint.
2198 if (log_is_enabled(Info, monitorinflation)) {
2199 timer.start();
2200 }
2201 }
2202 } while (savedMidInUsep != NULL);
2203
2204 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2205 LogStreamHandle(Info, monitorinflation) lsh_info;
2206 LogStream * ls = NULL;
2207 if (log_is_enabled(Debug, monitorinflation)) {
2208 ls = &lsh_debug;
2209 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2210 ls = &lsh_info;
2211 }
2212 if (ls != NULL) {
2213 ls->print_cr("jt=" INTPTR_FORMAT ": async-deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(cur_jt), timer.seconds(), deflated_count);
2214 }
2215 }
2216
2217 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2218 // Report the cumulative time for deflating each thread's idle
2219 // monitors. Note: if the work is split among more than one
2220 // worker thread, then the reported time will likely be more
2221 // than a beginning to end measurement of the phase.
2222 // Note: AsyncDeflateIdleMonitors only deflates per-thread idle
2223 // monitors at a safepoint when a special cleanup has been requested.
2224 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->perThreadTimes, counters->perThreadScavenged);
2225
2226 bool needs_special_cleanup = is_cleanup_requested();
2227 if (!AsyncDeflateIdleMonitors || needs_special_cleanup) {
2228 // AsyncDeflateIdleMonitors does not use these counters unless
2229 // there is a special cleanup request.
2230
2231 gMonitorFreeCount += counters->nScavenged;
2232
2233 OM_PERFDATA_OP(Deflations, inc(counters->nScavenged));
2234 OM_PERFDATA_OP(MonExtant, set_value(counters->nInCirculation));
2235 }
2236
2237 if (log_is_enabled(Debug, monitorinflation)) {
2238 // exit_globals()'s call to audit_and_print_stats() is done
2239 // at the Info level.
2240 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2241 } else if (log_is_enabled(Info, monitorinflation)) {
2242 Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors");
2243 log_info(monitorinflation)("gMonitorPopulation=%d, gOmInUseCount=%d, "
2244 "gMonitorFreeCount=%d", gMonitorPopulation,
2245 gOmInUseCount, gMonitorFreeCount);
2246 Thread::muxRelease(&gListLock);
2247 }
2248
2249 ForceMonitorScavenge = 0; // Reset
2250 GVars.stwRandom = os::random();
2251 GVars.stwCycle++;
2252 if (needs_special_cleanup) {
2253 set_is_cleanup_requested(false); // special clean up is done
2254 }
2255 }
2256
2257 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
2258 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2259
2260 if (AsyncDeflateIdleMonitors) {
2261 // Nothing to do when idle ObjectMonitors are deflated using a
2262 // JavaThread unless a special cleanup has been requested.
2263 if (!is_cleanup_requested()) {
2264 return;
2265 }
2266 }
2267
2268 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
2269 ObjectMonitor * freeTailp = NULL;
2270 elapsedTimer timer;
2271
2272 if (log_is_enabled(Info, safepoint, cleanup) ||
2273 log_is_enabled(Info, monitorinflation)) {
2274 timer.start();
2275 }
2276
2277 int deflated_count = deflate_monitor_list(thread->omInUseList_addr(), &freeHeadp, &freeTailp);
2278
2279 Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors");
2280
2281 // Adjust counters
2282 counters->nInCirculation += thread->omInUseCount;
2283 thread->omInUseCount -= deflated_count;
2284 counters->nScavenged += deflated_count;
2285 counters->nInuse += thread->omInUseCount;
2286 counters->perThreadScavenged += deflated_count;
2287
2288 // Move the scavenged monitors back to the global free list.
2289 if (freeHeadp != NULL) {
2290 guarantee(freeTailp != NULL && deflated_count > 0, "invariant");
2291 assert(freeTailp->FreeNext == NULL, "invariant");
2292
2293 // constant-time list splice - prepend scavenged segment to gFreeList
2294 freeTailp->FreeNext = gFreeList;
2295 gFreeList = freeHeadp;
2296 }
2297
2298 timer.stop();
2299 // Safepoint logging cares about cumulative perThreadTimes and
2300 // we'll capture most of the cost, but not the muxRelease() which
2301 // should be cheap.
2302 counters->perThreadTimes += timer.seconds();
2303
2304 Thread::muxRelease(&gListLock);
2305
2306 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2307 LogStreamHandle(Info, monitorinflation) lsh_info;
2308 LogStream * ls = NULL;
2309 if (log_is_enabled(Debug, monitorinflation)) {
2310 ls = &lsh_debug;
2311 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2312 ls = &lsh_info;
2313 }
2314 if (ls != NULL) {
2315 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
2316 }
2317 }
2318
2319 // Monitor cleanup on JavaThread::exit
2320
2321 // Iterate through monitor cache and attempt to release thread's monitors
2322 // Gives up on a particular monitor if an exception occurs, but continues
2323 // the overall iteration, swallowing the exception.
2324 class ReleaseJavaMonitorsClosure: public MonitorClosure {
2325 private:
2326 TRAPS;
2327
2328 public:
2329 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
2330 void do_monitor(ObjectMonitor* mid) {
2331 if (mid->owner() == THREAD) {
2332 (void)mid->complete_exit(CHECK);
2333 }
2334 }
2335 };
2336
2337 // Release all inflated monitors owned by THREAD. Lightweight monitors are
2338 // ignored. This is meant to be called during JNI thread detach which assumes
2339 // all remaining monitors are heavyweight. All exceptions are swallowed.
2340 // Scanning the extant monitor list can be time consuming.
2341 // A simple optimization is to add a per-thread flag that indicates a thread
2342 // called jni_monitorenter() during its lifetime.
2343 //
2344 // Instead of No_Savepoint_Verifier it might be cheaper to
2345 // use an idiom of the form:
2346 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
2347 // <code that must not run at safepoint>
2348 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
2349 // Since the tests are extremely cheap we could leave them enabled
2350 // for normal product builds.
2351
2352 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
2353 assert(THREAD == JavaThread::current(), "must be current Java thread");
2354 NoSafepointVerifier nsv;
2355 ReleaseJavaMonitorsClosure rjmc(THREAD);
2356 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
2357 ObjectSynchronizer::monitors_iterate(&rjmc);
2358 Thread::muxRelease(&gListLock);
2359 THREAD->clear_pending_exception();
2360 }
2361
2362 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
2363 switch (cause) {
2364 case inflate_cause_vm_internal: return "VM Internal";
2365 case inflate_cause_monitor_enter: return "Monitor Enter";
2366 case inflate_cause_wait: return "Monitor Wait";
2367 case inflate_cause_notify: return "Monitor Notify";
2368 case inflate_cause_hash_code: return "Monitor Hash Code";
2369 case inflate_cause_jni_enter: return "JNI Monitor Enter";
2370 case inflate_cause_jni_exit: return "JNI Monitor Exit";
2371 default:
2372 ShouldNotReachHere();
2373 }
2374 return "Unknown";
2375 }
2376
2377 //------------------------------------------------------------------------------
2378 // Debugging code
2379
2380 u_char* ObjectSynchronizer::get_gvars_addr() {
2381 return (u_char*)&GVars;
2382 }
2383
2384 u_char* ObjectSynchronizer::get_gvars_hcSequence_addr() {
2385 return (u_char*)&GVars.hcSequence;
2386 }
2387
2388 size_t ObjectSynchronizer::get_gvars_size() {
2389 return sizeof(SharedGlobals);
2390 }
2391
2392 u_char* ObjectSynchronizer::get_gvars_stwRandom_addr() {
2393 return (u_char*)&GVars.stwRandom;
2394 }
2395
2396 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
2397 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
2398
2399 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2400 LogStreamHandle(Info, monitorinflation) lsh_info;
2401 LogStreamHandle(Trace, monitorinflation) lsh_trace;
2402 LogStream * ls = NULL;
2403 if (log_is_enabled(Trace, monitorinflation)) {
2404 ls = &lsh_trace;
2405 } else if (log_is_enabled(Debug, monitorinflation)) {
2406 ls = &lsh_debug;
2407 } else if (log_is_enabled(Info, monitorinflation)) {
2408 ls = &lsh_info;
2409 }
2410 assert(ls != NULL, "sanity check");
2411
2412 if (!on_exit) {
2413 // Not at VM exit so grab the global list lock.
2414 Thread::muxAcquire(&gListLock, "audit_and_print_stats");
2415 }
2416
2417 // Log counts for the global and per-thread monitor lists:
2418 int chkMonitorPopulation = log_monitor_list_counts(ls);
2419 int error_cnt = 0;
2420
2421 ls->print_cr("Checking global lists:");
2422
2423 // Check gMonitorPopulation:
2424 if (gMonitorPopulation == chkMonitorPopulation) {
2425 ls->print_cr("gMonitorPopulation=%d equals chkMonitorPopulation=%d",
2426 gMonitorPopulation, chkMonitorPopulation);
2427 } else {
2428 ls->print_cr("ERROR: gMonitorPopulation=%d is not equal to "
2429 "chkMonitorPopulation=%d", gMonitorPopulation,
2430 chkMonitorPopulation);
2431 error_cnt++;
2432 }
2433
2434 // Check gOmInUseList and gOmInUseCount:
2435 chk_global_in_use_list_and_count(ls, &error_cnt);
2436
2437 // Check gFreeList and gMonitorFreeCount:
2438 chk_global_free_list_and_count(ls, &error_cnt);
2439
2440 if (!on_exit) {
2441 Thread::muxRelease(&gListLock);
2442 }
2443
2444 ls->print_cr("Checking per-thread lists:");
2445
2446 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2447 // Check omInUseList and omInUseCount:
2448 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
2449
2450 // Check omFreeList and omFreeCount:
2451 chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
2452 }
2453
2454 if (error_cnt == 0) {
2455 ls->print_cr("No errors found in monitor list checks.");
2456 } else {
2457 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
2458 }
2459
2460 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
2461 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
2462 // When exiting this log output is at the Info level. When called
2463 // at a safepoint, this log output is at the Trace level since
2464 // there can be a lot of it.
2465 log_in_use_monitor_details(ls, on_exit);
2466 }
2467
2468 ls->flush();
2469
2470 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2471 }
2472
2473 // Check a free monitor entry; log any errors.
2474 void ObjectSynchronizer::chk_free_entry(JavaThread * jt, ObjectMonitor * n,
2475 outputStream * out, int *error_cnt_p) {
2476 if ((!AsyncDeflateIdleMonitors && n->is_busy()) ||
2477 (AsyncDeflateIdleMonitors && n->is_busy_async())) {
2478 if (jt != NULL) {
2479 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2480 ": free per-thread monitor must not be busy.", p2i(jt),
2481 p2i(n));
2482 } else {
2483 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2484 "must not be busy.", p2i(n));
2485 }
2486 *error_cnt_p = *error_cnt_p + 1;
2487 }
2488 if (n->header() != NULL) {
2489 if (jt != NULL) {
2490 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2491 ": free per-thread monitor must have NULL _header "
2492 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
2493 p2i(n->header()));
2494 } else {
2495 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2496 "must have NULL _header field: _header=" INTPTR_FORMAT,
2497 p2i(n), p2i(n->header()));
2498 }
2499 *error_cnt_p = *error_cnt_p + 1;
2500 }
2501 if (n->object() != NULL) {
2502 if (jt != NULL) {
2503 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2504 ": free per-thread monitor must have NULL _object "
2505 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
2506 p2i(n->object()));
2507 } else {
2508 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2509 "must have NULL _object field: _object=" INTPTR_FORMAT,
2510 p2i(n), p2i(n->object()));
2511 }
2512 *error_cnt_p = *error_cnt_p + 1;
2513 }
2514 }
2515
2516 // Check the global free list and count; log the results of the checks.
2517 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
2518 int *error_cnt_p) {
2519 int chkMonitorFreeCount = 0;
2520 for (ObjectMonitor * n = gFreeList; n != NULL; n = n->FreeNext) {
2521 chk_free_entry(NULL /* jt */, n, out, error_cnt_p);
2522 chkMonitorFreeCount++;
2523 }
2524 if (gMonitorFreeCount == chkMonitorFreeCount) {
2525 out->print_cr("gMonitorFreeCount=%d equals chkMonitorFreeCount=%d",
2526 gMonitorFreeCount, chkMonitorFreeCount);
2527 } else {
2528 out->print_cr("ERROR: gMonitorFreeCount=%d is not equal to "
2529 "chkMonitorFreeCount=%d", gMonitorFreeCount,
2530 chkMonitorFreeCount);
2531 *error_cnt_p = *error_cnt_p + 1;
2532 }
2533 }
2534
2535 // Check the global in-use list and count; log the results of the checks.
2536 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
2537 int *error_cnt_p) {
2538 int chkOmInUseCount = 0;
2539 for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
2540 chk_in_use_entry(NULL /* jt */, n, out, error_cnt_p);
2541 chkOmInUseCount++;
2542 }
2543 if (gOmInUseCount == chkOmInUseCount) {
2544 out->print_cr("gOmInUseCount=%d equals chkOmInUseCount=%d", gOmInUseCount,
2545 chkOmInUseCount);
2546 } else {
2547 out->print_cr("ERROR: gOmInUseCount=%d is not equal to chkOmInUseCount=%d",
2548 gOmInUseCount, chkOmInUseCount);
2549 *error_cnt_p = *error_cnt_p + 1;
2550 }
2551 }
2552
2553 // Check an in-use monitor entry; log any errors.
2554 void ObjectSynchronizer::chk_in_use_entry(JavaThread * jt, ObjectMonitor * n,
2555 outputStream * out, int *error_cnt_p) {
2556 if (n->header() == NULL) {
2557 if (jt != NULL) {
2558 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2559 ": in-use per-thread monitor must have non-NULL _header "
2560 "field.", p2i(jt), p2i(n));
2561 } else {
2562 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2563 "must have non-NULL _header field.", p2i(n));
2564 }
2565 *error_cnt_p = *error_cnt_p + 1;
2566 }
2567 if (n->object() == NULL) {
2568 if (jt != NULL) {
2569 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2570 ": in-use per-thread monitor must have non-NULL _object "
2571 "field.", p2i(jt), p2i(n));
2572 } else {
2573 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2574 "must have non-NULL _object field.", p2i(n));
2575 }
2576 *error_cnt_p = *error_cnt_p + 1;
2577 }
2578 const oop obj = (oop)n->object();
2579 const markOop mark = obj->mark();
2580 if (!mark->has_monitor()) {
2581 if (jt != NULL) {
2582 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2583 ": in-use per-thread monitor's object does not think "
2584 "it has a monitor: obj=" INTPTR_FORMAT ", mark="
2585 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), p2i(mark));
2586 } else {
2587 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2588 "monitor's object does not think it has a monitor: obj="
2589 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2590 p2i(obj), p2i(mark));
2591 }
2592 *error_cnt_p = *error_cnt_p + 1;
2593 }
2594 ObjectMonitor * const obj_mon = mark->monitor();
2595 if (n != obj_mon) {
2596 if (jt != NULL) {
2597 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2598 ": in-use per-thread monitor's object does not refer "
2599 "to the same monitor: obj=" INTPTR_FORMAT ", mark="
2600 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
2601 p2i(n), p2i(obj), p2i(mark), p2i(obj_mon));
2602 } else {
2603 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2604 "monitor's object does not refer to the same monitor: obj="
2605 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2606 INTPTR_FORMAT, p2i(n), p2i(obj), p2i(mark), p2i(obj_mon));
2607 }
2608 *error_cnt_p = *error_cnt_p + 1;
2609 }
2610 }
2611
2612 // Check the thread's free list and count; log the results of the checks.
2613 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
2614 outputStream * out,
2615 int *error_cnt_p) {
2616 int chkOmFreeCount = 0;
2617 for (ObjectMonitor * n = jt->omFreeList; n != NULL; n = n->FreeNext) {
2618 chk_free_entry(jt, n, out, error_cnt_p);
2619 chkOmFreeCount++;
2620 }
2621 if (jt->omFreeCount == chkOmFreeCount) {
2622 out->print_cr("jt=" INTPTR_FORMAT ": omFreeCount=%d equals "
2623 "chkOmFreeCount=%d", p2i(jt), jt->omFreeCount, chkOmFreeCount);
2624 } else {
2625 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omFreeCount=%d is not "
2626 "equal to chkOmFreeCount=%d", p2i(jt), jt->omFreeCount,
2627 chkOmFreeCount);
2628 *error_cnt_p = *error_cnt_p + 1;
2629 }
2630 }
2631
2632 // Check the thread's in-use list and count; log the results of the checks.
2633 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
2634 outputStream * out,
2635 int *error_cnt_p) {
2636 int chkOmInUseCount = 0;
2637 for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2638 chk_in_use_entry(jt, n, out, error_cnt_p);
2639 chkOmInUseCount++;
2640 }
2641 if (jt->omInUseCount == chkOmInUseCount) {
2642 out->print_cr("jt=" INTPTR_FORMAT ": omInUseCount=%d equals "
2643 "chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2644 chkOmInUseCount);
2645 } else {
2646 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omInUseCount=%d is not "
2647 "equal to chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2648 chkOmInUseCount);
2649 *error_cnt_p = *error_cnt_p + 1;
2650 }
2651 }
2652
2653 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2654 // flags indicate why the entry is in-use, 'object' and 'object type'
2655 // indicate the associated object and its type.
2656 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out,
2657 bool on_exit) {
2658 if (!on_exit) {
2659 // Not at VM exit so grab the global list lock.
2660 Thread::muxAcquire(&gListLock, "log_in_use_monitor_details");
2661 }
2662
2663 if (gOmInUseCount > 0) {
2664 out->print_cr("In-use global monitor info:");
2665 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2666 out->print_cr("%18s %s %7s %18s %18s",
2667 "monitor", "BHL", "ref_cnt", "object", "object type");
2668 out->print_cr("================== === ======= ================== ==================");
2669 for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
2670 const oop obj = (oop) n->object();
2671 const markOop mark = n->header();
2672 ResourceMark rm;
2673 out->print_cr(INTPTR_FORMAT " %d%d%d %7d " INTPTR_FORMAT " %s",
2674 p2i(n), n->is_busy() != 0, mark->hash() != 0,
2675 n->owner() != NULL, (int)n->ref_count(), p2i(obj),
2676 obj->klass()->external_name());
2677 }
2678 }
2679
2680 if (!on_exit) {
2681 Thread::muxRelease(&gListLock);
2682 }
2683
2684 out->print_cr("In-use per-thread monitor info:");
2685 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2686 out->print_cr("%18s %18s %s %7s %18s %18s",
2687 "jt", "monitor", "BHL", "ref_cnt", "object", "object type");
2688 out->print_cr("================== ================== === ======= ================== ==================");
2689 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2690 for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2691 const oop obj = (oop) n->object();
2692 const markOop mark = n->header();
2693 ResourceMark rm;
2694 out->print_cr(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d %7d "
2695 INTPTR_FORMAT " %s", p2i(jt), p2i(n), n->is_busy() != 0,
2696 mark->hash() != 0, n->owner() != NULL, (int)n->ref_count(),
2697 p2i(obj), obj->klass()->external_name());
2698 }
2699 }
2700
2701 out->flush();
2702 }
2703
2704 // Log counts for the global and per-thread monitor lists and return
2705 // the population count.
2706 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2707 int popCount = 0;
2708 out->print_cr("%18s %10s %10s %10s",
2709 "Global Lists:", "InUse", "Free", "Total");
2710 out->print_cr("================== ========== ========== ==========");
2711 out->print_cr("%18s %10d %10d %10d", "",
2712 gOmInUseCount, gMonitorFreeCount, gMonitorPopulation);
2713 popCount += gOmInUseCount + gMonitorFreeCount;
2714
2715 out->print_cr("%18s %10s %10s %10s",
2716 "Per-Thread Lists:", "InUse", "Free", "Provision");
2717 out->print_cr("================== ========== ========== ==========");
2718
2719 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2720 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
2721 jt->omInUseCount, jt->omFreeCount, jt->omFreeProvision);
2722 popCount += jt->omInUseCount + jt->omFreeCount;
2723 }
2724 return popCount;
2725 }
2726
2727 #ifndef PRODUCT
2728
2729 // Check if monitor belongs to the monitor cache
2730 // The list is grow-only so it's *relatively* safe to traverse
2731 // the list of extant blocks without taking a lock.
2732
2733 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
2734 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
2735 while (block != NULL) {
2736 assert(block->object() == CHAINMARKER, "must be a block header");
2737 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
2738 address mon = (address)monitor;
2739 address blk = (address)block;
2740 size_t diff = mon - blk;
2741 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "must be aligned");
2742 return 1;
2743 }
2744 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
2745 }
2746 return 0;
2747 }
2748
2749 #endif