1 /*
2 * Copyright (c) 1998, 2015, 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 "memory/padded.hpp"
28 #include "memory/resourceArea.hpp"
29 #include "oops/markOop.hpp"
30 #include "oops/oop.inline.hpp"
31 #include "runtime/atomic.inline.hpp"
32 #include "runtime/biasedLocking.hpp"
33 #include "runtime/handles.inline.hpp"
34 #include "runtime/interfaceSupport.hpp"
35 #include "runtime/mutexLocker.hpp"
36 #include "runtime/objectMonitor.hpp"
37 #include "runtime/objectMonitor.inline.hpp"
38 #include "runtime/osThread.hpp"
39 #include "runtime/stubRoutines.hpp"
40 #include "runtime/synchronizer.hpp"
41 #include "runtime/thread.inline.hpp"
42 #include "utilities/dtrace.hpp"
43 #include "utilities/events.hpp"
44 #include "utilities/preserveException.hpp"
45
46 #if defined(__GNUC__) && !defined(PPC64)
47 // Need to inhibit inlining for older versions of GCC to avoid build-time failures
48 #define NOINLINE __attribute__((noinline))
49 #else
50 #define NOINLINE
51 #endif
52
53 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
54
55 // The "core" versions of monitor enter and exit reside in this file.
56 // The interpreter and compilers contain specialized transliterated
57 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
58 // for instance. If you make changes here, make sure to modify the
59 // interpreter, and both C1 and C2 fast-path inline locking code emission.
60 //
61 // -----------------------------------------------------------------------------
62
63 #ifdef DTRACE_ENABLED
64
65 // Only bother with this argument setup if dtrace is available
66 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
67
68 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
69 char* bytes = NULL; \
70 int len = 0; \
71 jlong jtid = SharedRuntime::get_java_tid(thread); \
72 Symbol* klassname = ((oop)(obj))->klass()->name(); \
73 if (klassname != NULL) { \
74 bytes = (char*)klassname->bytes(); \
75 len = klassname->utf8_length(); \
76 }
77
78 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
79 { \
80 if (DTraceMonitorProbes) { \
81 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
82 HOTSPOT_MONITOR_WAIT(jtid, \
83 (uintptr_t)(monitor), bytes, len, (millis)); \
84 } \
85 }
86
87 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
88
89 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
90 { \
91 if (DTraceMonitorProbes) { \
92 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
93 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
94 (uintptr_t)(monitor), bytes, len); \
95 } \
96 }
97
98 #else // ndef DTRACE_ENABLED
99
100 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
101 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
102
103 #endif // ndef DTRACE_ENABLED
104
105 // This exists only as a workaround of dtrace bug 6254741
106 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
107 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
108 return 0;
109 }
110
111 #define NINFLATIONLOCKS 256
112 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
113
114 // global list of blocks of monitors
115 // gBlockList is really PaddedEnd<ObjectMonitor> *, but we don't
116 // want to expose the PaddedEnd template more than necessary.
117 ObjectMonitor * ObjectSynchronizer::gBlockList = NULL;
118 // global monitor free list
119 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL;
120 // global monitor in-use list, for moribund threads,
121 // monitors they inflated need to be scanned for deflation
122 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL;
123 // count of entries in gOmInUseList
124 int ObjectSynchronizer::gOmInUseCount = 0;
125
126 static volatile intptr_t gListLock = 0; // protects global monitor lists
127 static volatile int gMonitorFreeCount = 0; // # on gFreeList
128 static volatile int gMonitorPopulation = 0; // # Extant -- in circulation
129
130 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
131
132
133 // =====================> Quick functions
134
135 // The quick_* forms are special fast-path variants used to improve
136 // performance. In the simplest case, a "quick_*" implementation could
137 // simply return false, in which case the caller will perform the necessary
138 // state transitions and call the slow-path form.
139 // The fast-path is designed to handle frequently arising cases in an efficient
140 // manner and is just a degenerate "optimistic" variant of the slow-path.
141 // returns true -- to indicate the call was satisfied.
142 // returns false -- to indicate the call needs the services of the slow-path.
143 // A no-loitering ordinance is in effect for code in the quick_* family
144 // operators: safepoints or indefinite blocking (blocking that might span a
145 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
146 // entry.
147
148 // The LockNode emitted directly at the synchronization site would have
149 // been too big if it were to have included support for the cases of inflated
150 // recursive enter and exit, so they go here instead.
151 // Note that we can't safely call AsyncPrintJavaStack() from within
152 // quick_enter() as our thread state remains _in_Java.
153
154 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
155 BasicLock * Lock) {
156 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
157 assert(Self->is_Java_thread(), "invariant");
158 assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
159 No_Safepoint_Verifier nsv;
160 if (obj == NULL) return false; // Need to throw NPE
161 const markOop mark = obj->mark();
162
163 if (mark->has_monitor()) {
164 ObjectMonitor * const m = mark->monitor();
165 assert(m->object() == obj, "invariant");
166 Thread * const owner = (Thread *) m->_owner;
167
168 // Lock contention and Transactional Lock Elision (TLE) diagnostics
169 // and observability
170 // Case: light contention possibly amenable to TLE
171 // Case: TLE inimical operations such as nested/recursive synchronization
172
173 if (owner == Self) {
174 m->_recursions++;
175 return true;
176 }
177
178 if (owner == NULL &&
179 Atomic::cmpxchg_ptr(Self, &(m->_owner), NULL) == NULL) {
180 assert(m->_recursions == 0, "invariant");
181 assert(m->_owner == Self, "invariant");
182 return true;
183 }
184 }
185
186 // Note that we could inflate in quick_enter.
187 // This is likely a useful optimization
188 // Critically, in quick_enter() we must not:
189 // -- perform bias revocation, or
190 // -- block indefinitely, or
191 // -- reach a safepoint
192
193 return false; // revert to slow-path
194 }
195
196 // -----------------------------------------------------------------------------
197 // Fast Monitor Enter/Exit
198 // This the fast monitor enter. The interpreter and compiler use
199 // some assembly copies of this code. Make sure update those code
200 // if the following function is changed. The implementation is
201 // extremely sensitive to race condition. Be careful.
202
203 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
204 bool attempt_rebias, TRAPS) {
205 if (UseBiasedLocking) {
206 if (!SafepointSynchronize::is_at_safepoint()) {
207 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
208 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
209 return;
210 }
211 } else {
212 assert(!attempt_rebias, "can not rebias toward VM thread");
213 BiasedLocking::revoke_at_safepoint(obj);
214 }
215 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
216 }
217
218 slow_enter(obj, lock, THREAD);
219 }
220
221 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
222 assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here");
223 // if displaced header is null, the previous enter is recursive enter, no-op
224 markOop dhw = lock->displaced_header();
225 markOop mark;
226 if (dhw == NULL) {
227 // Recursive stack-lock.
228 // Diagnostics -- Could be: stack-locked, inflating, inflated.
229 mark = object->mark();
230 assert(!mark->is_neutral(), "invariant");
231 if (mark->has_locker() && mark != markOopDesc::INFLATING()) {
232 assert(THREAD->is_lock_owned((address)mark->locker()), "invariant");
233 }
234 if (mark->has_monitor()) {
235 ObjectMonitor * m = mark->monitor();
236 assert(((oop)(m->object()))->mark() == mark, "invariant");
237 assert(m->is_entered(THREAD), "invariant");
238 }
239 return;
240 }
241
242 mark = object->mark();
243
244 // If the object is stack-locked by the current thread, try to
245 // swing the displaced header from the box back to the mark.
246 if (mark == (markOop) lock) {
247 assert(dhw->is_neutral(), "invariant");
248 if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) {
249 TEVENT(fast_exit: release stacklock);
250 return;
251 }
252 }
253
254 ObjectSynchronizer::inflate(THREAD, object)->exit(true, THREAD);
255 }
256
257 // -----------------------------------------------------------------------------
258 // Interpreter/Compiler Slow Case
259 // This routine is used to handle interpreter/compiler slow case
260 // We don't need to use fast path here, because it must have been
261 // failed in the interpreter/compiler code.
262 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
263 markOop mark = obj->mark();
264 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
265
266 if (mark->is_neutral()) {
267 // Anticipate successful CAS -- the ST of the displaced mark must
268 // be visible <= the ST performed by the CAS.
269 lock->set_displaced_header(mark);
270 if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) {
271 TEVENT(slow_enter: release stacklock);
272 return;
273 }
274 // Fall through to inflate() ...
275 } else if (mark->has_locker() &&
276 THREAD->is_lock_owned((address)mark->locker())) {
277 assert(lock != mark->locker(), "must not re-lock the same lock");
278 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
279 lock->set_displaced_header(NULL);
280 return;
281 }
282
283 // The object header will never be displaced to this lock,
284 // so it does not matter what the value is, except that it
285 // must be non-zero to avoid looking like a re-entrant lock,
286 // and must not look locked either.
287 lock->set_displaced_header(markOopDesc::unused_mark());
288 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
289 }
290
291 // This routine is used to handle interpreter/compiler slow case
292 // We don't need to use fast path here, because it must have
293 // failed in the interpreter/compiler code. Simply use the heavy
294 // weight monitor should be ok, unless someone find otherwise.
295 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
296 fast_exit(object, lock, THREAD);
297 }
298
299 // -----------------------------------------------------------------------------
300 // Class Loader support to workaround deadlocks on the class loader lock objects
301 // Also used by GC
302 // complete_exit()/reenter() are used to wait on a nested lock
303 // i.e. to give up an outer lock completely and then re-enter
304 // Used when holding nested locks - lock acquisition order: lock1 then lock2
305 // 1) complete_exit lock1 - saving recursion count
306 // 2) wait on lock2
307 // 3) when notified on lock2, unlock lock2
308 // 4) reenter lock1 with original recursion count
309 // 5) lock lock2
310 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
311 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
312 TEVENT(complete_exit);
313 if (UseBiasedLocking) {
314 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
315 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
316 }
317
318 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
319
320 return monitor->complete_exit(THREAD);
321 }
322
323 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
324 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
325 TEVENT(reenter);
326 if (UseBiasedLocking) {
327 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
328 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
329 }
330
331 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
332
333 monitor->reenter(recursion, THREAD);
334 }
335 // -----------------------------------------------------------------------------
336 // JNI locks on java objects
337 // NOTE: must use heavy weight monitor to handle jni monitor enter
338 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
339 // the current locking is from JNI instead of Java code
340 TEVENT(jni_enter);
341 if (UseBiasedLocking) {
342 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
343 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
344 }
345 THREAD->set_current_pending_monitor_is_from_java(false);
346 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
347 THREAD->set_current_pending_monitor_is_from_java(true);
348 }
349
350 // NOTE: must use heavy weight monitor to handle jni monitor exit
351 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
352 TEVENT(jni_exit);
353 if (UseBiasedLocking) {
354 Handle h_obj(THREAD, obj);
355 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
356 obj = h_obj();
357 }
358 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
359
360 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj);
361 // If this thread has locked the object, exit the monitor. Note: can't use
362 // monitor->check(CHECK); must exit even if an exception is pending.
363 if (monitor->check(THREAD)) {
364 monitor->exit(true, THREAD);
365 }
366 }
367
368 // -----------------------------------------------------------------------------
369 // Internal VM locks on java objects
370 // standard constructor, allows locking failures
371 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
372 _dolock = doLock;
373 _thread = thread;
374 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
375 _obj = obj;
376
377 if (_dolock) {
378 TEVENT(ObjectLocker);
379
380 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
381 }
382 }
383
384 ObjectLocker::~ObjectLocker() {
385 if (_dolock) {
386 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
387 }
388 }
389
390
391 // -----------------------------------------------------------------------------
392 // Wait/Notify/NotifyAll
393 // NOTE: must use heavy weight monitor to handle wait()
394 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
395 if (UseBiasedLocking) {
396 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
397 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
398 }
399 if (millis < 0) {
400 TEVENT(wait - throw IAX);
401 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
402 }
403 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
404 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
405 monitor->wait(millis, true, THREAD);
406
407 // This dummy call is in place to get around dtrace bug 6254741. Once
408 // that's fixed we can uncomment the following line, remove the call
409 // and change this function back into a "void" func.
410 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
411 return dtrace_waited_probe(monitor, obj, THREAD);
412 }
413
414 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
415 if (UseBiasedLocking) {
416 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
417 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
418 }
419 if (millis < 0) {
420 TEVENT(wait - throw IAX);
421 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
422 }
423 ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD);
424 }
425
426 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
427 if (UseBiasedLocking) {
428 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
429 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
430 }
431
432 markOop mark = obj->mark();
433 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
434 return;
435 }
436 ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD);
437 }
438
439 // NOTE: see comment of notify()
440 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
441 if (UseBiasedLocking) {
442 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
443 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
444 }
445
446 markOop mark = obj->mark();
447 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
448 return;
449 }
450 ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD);
451 }
452
453 // -----------------------------------------------------------------------------
454 // Hash Code handling
455 //
456 // Performance concern:
457 // OrderAccess::storestore() calls release() which at one time stored 0
458 // into the global volatile OrderAccess::dummy variable. This store was
459 // unnecessary for correctness. Many threads storing into a common location
460 // causes considerable cache migration or "sloshing" on large SMP systems.
461 // As such, I avoided using OrderAccess::storestore(). In some cases
462 // OrderAccess::fence() -- which incurs local latency on the executing
463 // processor -- is a better choice as it scales on SMP systems.
464 //
465 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
466 // a discussion of coherency costs. Note that all our current reference
467 // platforms provide strong ST-ST order, so the issue is moot on IA32,
468 // x64, and SPARC.
469 //
470 // As a general policy we use "volatile" to control compiler-based reordering
471 // and explicit fences (barriers) to control for architectural reordering
472 // performed by the CPU(s) or platform.
473
474 struct SharedGlobals {
475 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
476 // These are highly shared mostly-read variables.
477 // To avoid false-sharing they need to be the sole occupants of a cache line.
478 volatile int stwRandom;
479 volatile int stwCycle;
480 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
481 // Hot RW variable -- Sequester to avoid false-sharing
482 volatile int hcSequence;
483 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
484 };
485
486 static SharedGlobals GVars;
487 static int MonitorScavengeThreshold = 1000000;
488 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
489
490 static markOop ReadStableMark(oop obj) {
491 markOop mark = obj->mark();
492 if (!mark->is_being_inflated()) {
493 return mark; // normal fast-path return
494 }
495
496 int its = 0;
497 for (;;) {
498 markOop mark = obj->mark();
499 if (!mark->is_being_inflated()) {
500 return mark; // normal fast-path return
501 }
502
503 // The object is being inflated by some other thread.
504 // The caller of ReadStableMark() must wait for inflation to complete.
505 // Avoid live-lock
506 // TODO: consider calling SafepointSynchronize::do_call_back() while
507 // spinning to see if there's a safepoint pending. If so, immediately
508 // yielding or blocking would be appropriate. Avoid spinning while
509 // there is a safepoint pending.
510 // TODO: add inflation contention performance counters.
511 // TODO: restrict the aggregate number of spinners.
512
513 ++its;
514 if (its > 10000 || !os::is_MP()) {
515 if (its & 1) {
516 os::naked_yield();
517 TEVENT(Inflate: INFLATING - yield);
518 } else {
519 // Note that the following code attenuates the livelock problem but is not
520 // a complete remedy. A more complete solution would require that the inflating
521 // thread hold the associated inflation lock. The following code simply restricts
522 // the number of spinners to at most one. We'll have N-2 threads blocked
523 // on the inflationlock, 1 thread holding the inflation lock and using
524 // a yield/park strategy, and 1 thread in the midst of inflation.
525 // A more refined approach would be to change the encoding of INFLATING
526 // to allow encapsulation of a native thread pointer. Threads waiting for
527 // inflation to complete would use CAS to push themselves onto a singly linked
528 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
529 // and calling park(). When inflation was complete the thread that accomplished inflation
530 // would detach the list and set the markword to inflated with a single CAS and
531 // then for each thread on the list, set the flag and unpark() the thread.
532 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
533 // wakes at most one thread whereas we need to wake the entire list.
534 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
535 int YieldThenBlock = 0;
536 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
537 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
538 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
539 while (obj->mark() == markOopDesc::INFLATING()) {
540 // Beware: NakedYield() is advisory and has almost no effect on some platforms
541 // so we periodically call Self->_ParkEvent->park(1).
542 // We use a mixed spin/yield/block mechanism.
543 if ((YieldThenBlock++) >= 16) {
544 Thread::current()->_ParkEvent->park(1);
545 } else {
546 os::naked_yield();
547 }
548 }
549 Thread::muxRelease(gInflationLocks + ix);
550 TEVENT(Inflate: INFLATING - yield/park);
551 }
552 } else {
553 SpinPause(); // SMP-polite spinning
554 }
555 }
556 }
557
558 // hashCode() generation :
559 //
560 // Possibilities:
561 // * MD5Digest of {obj,stwRandom}
562 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
563 // * A DES- or AES-style SBox[] mechanism
564 // * One of the Phi-based schemes, such as:
565 // 2654435761 = 2^32 * Phi (golden ratio)
566 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
567 // * A variation of Marsaglia's shift-xor RNG scheme.
568 // * (obj ^ stwRandom) is appealing, but can result
569 // in undesirable regularity in the hashCode values of adjacent objects
570 // (objects allocated back-to-back, in particular). This could potentially
571 // result in hashtable collisions and reduced hashtable efficiency.
572 // There are simple ways to "diffuse" the middle address bits over the
573 // generated hashCode values:
574
575 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
576 intptr_t value = 0;
577 if (hashCode == 0) {
578 // This form uses an unguarded global Park-Miller RNG,
579 // so it's possible for two threads to race and generate the same RNG.
580 // On MP system we'll have lots of RW access to a global, so the
581 // mechanism induces lots of coherency traffic.
582 value = os::random();
583 } else if (hashCode == 1) {
584 // This variation has the property of being stable (idempotent)
585 // between STW operations. This can be useful in some of the 1-0
586 // synchronization schemes.
587 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
588 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
589 } else if (hashCode == 2) {
590 value = 1; // for sensitivity testing
591 } else if (hashCode == 3) {
592 value = ++GVars.hcSequence;
593 } else if (hashCode == 4) {
594 value = cast_from_oop<intptr_t>(obj);
595 } else {
596 // Marsaglia's xor-shift scheme with thread-specific state
597 // This is probably the best overall implementation -- we'll
598 // likely make this the default in future releases.
599 unsigned t = Self->_hashStateX;
600 t ^= (t << 11);
601 Self->_hashStateX = Self->_hashStateY;
602 Self->_hashStateY = Self->_hashStateZ;
603 Self->_hashStateZ = Self->_hashStateW;
604 unsigned v = Self->_hashStateW;
605 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
606 Self->_hashStateW = v;
607 value = v;
608 }
609
610 value &= markOopDesc::hash_mask;
611 if (value == 0) value = 0xBAD;
612 assert(value != markOopDesc::no_hash, "invariant");
613 TEVENT(hashCode: GENERATE);
614 return value;
615 }
616
617 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
618 if (UseBiasedLocking) {
619 // NOTE: many places throughout the JVM do not expect a safepoint
620 // to be taken here, in particular most operations on perm gen
621 // objects. However, we only ever bias Java instances and all of
622 // the call sites of identity_hash that might revoke biases have
623 // been checked to make sure they can handle a safepoint. The
624 // added check of the bias pattern is to avoid useless calls to
625 // thread-local storage.
626 if (obj->mark()->has_bias_pattern()) {
627 // Handle for oop obj in case of STW safepoint
628 Handle hobj(Self, obj);
629 // Relaxing assertion for bug 6320749.
630 assert(Universe::verify_in_progress() ||
631 !SafepointSynchronize::is_at_safepoint(),
632 "biases should not be seen by VM thread here");
633 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
634 obj = hobj();
635 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
636 }
637 }
638
639 // hashCode() is a heap mutator ...
640 // Relaxing assertion for bug 6320749.
641 assert(Universe::verify_in_progress() ||
642 !SafepointSynchronize::is_at_safepoint(), "invariant");
643 assert(Universe::verify_in_progress() ||
644 Self->is_Java_thread() , "invariant");
645 assert(Universe::verify_in_progress() ||
646 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
647
648 ObjectMonitor* monitor = NULL;
649 markOop temp, test;
650 intptr_t hash;
651 markOop mark = ReadStableMark(obj);
652
653 // object should remain ineligible for biased locking
654 assert(!mark->has_bias_pattern(), "invariant");
655
656 if (mark->is_neutral()) {
657 hash = mark->hash(); // this is a normal header
658 if (hash) { // if it has hash, just return it
659 return hash;
660 }
661 hash = get_next_hash(Self, obj); // allocate a new hash code
662 temp = mark->copy_set_hash(hash); // merge the hash code into header
663 // use (machine word version) atomic operation to install the hash
664 test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark);
665 if (test == mark) {
666 return hash;
667 }
668 // If atomic operation failed, we must inflate the header
669 // into heavy weight monitor. We could add more code here
670 // for fast path, but it does not worth the complexity.
671 } else if (mark->has_monitor()) {
672 monitor = mark->monitor();
673 temp = monitor->header();
674 assert(temp->is_neutral(), "invariant");
675 hash = temp->hash();
676 if (hash) {
677 return hash;
678 }
679 // Skip to the following code to reduce code size
680 } else if (Self->is_lock_owned((address)mark->locker())) {
681 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
682 assert(temp->is_neutral(), "invariant");
683 hash = temp->hash(); // by current thread, check if the displaced
684 if (hash) { // header contains hash code
685 return hash;
686 }
687 // WARNING:
688 // The displaced header is strictly immutable.
689 // It can NOT be changed in ANY cases. So we have
690 // to inflate the header into heavyweight monitor
691 // even the current thread owns the lock. The reason
692 // is the BasicLock (stack slot) will be asynchronously
693 // read by other threads during the inflate() function.
694 // Any change to stack may not propagate to other threads
695 // correctly.
696 }
697
698 // Inflate the monitor to set hash code
699 monitor = ObjectSynchronizer::inflate(Self, obj);
700 // Load displaced header and check it has hash code
701 mark = monitor->header();
702 assert(mark->is_neutral(), "invariant");
703 hash = mark->hash();
704 if (hash == 0) {
705 hash = get_next_hash(Self, obj);
706 temp = mark->copy_set_hash(hash); // merge hash code into header
707 assert(temp->is_neutral(), "invariant");
708 test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark);
709 if (test != mark) {
710 // The only update to the header in the monitor (outside GC)
711 // is install the hash code. If someone add new usage of
712 // displaced header, please update this code
713 hash = test->hash();
714 assert(test->is_neutral(), "invariant");
715 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
716 }
717 }
718 // We finally get the hash
719 return hash;
720 }
721
722 // Deprecated -- use FastHashCode() instead.
723
724 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
725 return FastHashCode(Thread::current(), obj());
726 }
727
728
729 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
730 Handle h_obj) {
731 if (UseBiasedLocking) {
732 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
733 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
734 }
735
736 assert(thread == JavaThread::current(), "Can only be called on current thread");
737 oop obj = h_obj();
738
739 markOop mark = ReadStableMark(obj);
740
741 // Uncontended case, header points to stack
742 if (mark->has_locker()) {
743 return thread->is_lock_owned((address)mark->locker());
744 }
745 // Contended case, header points to ObjectMonitor (tagged pointer)
746 if (mark->has_monitor()) {
747 ObjectMonitor* monitor = mark->monitor();
748 return monitor->is_entered(thread) != 0;
749 }
750 // Unlocked case, header in place
751 assert(mark->is_neutral(), "sanity check");
752 return false;
753 }
754
755 // Be aware of this method could revoke bias of the lock object.
756 // This method queries the ownership of the lock handle specified by 'h_obj'.
757 // If the current thread owns the lock, it returns owner_self. If no
758 // thread owns the lock, it returns owner_none. Otherwise, it will return
759 // owner_other.
760 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
761 (JavaThread *self, Handle h_obj) {
762 // The caller must beware this method can revoke bias, and
763 // revocation can result in a safepoint.
764 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
765 assert(self->thread_state() != _thread_blocked, "invariant");
766
767 // Possible mark states: neutral, biased, stack-locked, inflated
768
769 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
770 // CASE: biased
771 BiasedLocking::revoke_and_rebias(h_obj, false, self);
772 assert(!h_obj->mark()->has_bias_pattern(),
773 "biases should be revoked by now");
774 }
775
776 assert(self == JavaThread::current(), "Can only be called on current thread");
777 oop obj = h_obj();
778 markOop mark = ReadStableMark(obj);
779
780 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
781 if (mark->has_locker()) {
782 return self->is_lock_owned((address)mark->locker()) ?
783 owner_self : owner_other;
784 }
785
786 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
787 // The Object:ObjectMonitor relationship is stable as long as we're
788 // not at a safepoint.
789 if (mark->has_monitor()) {
790 void * owner = mark->monitor()->_owner;
791 if (owner == NULL) return owner_none;
792 return (owner == self ||
793 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
794 }
795
796 // CASE: neutral
797 assert(mark->is_neutral(), "sanity check");
798 return owner_none; // it's unlocked
799 }
800
801 // FIXME: jvmti should call this
802 JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) {
803 if (UseBiasedLocking) {
804 if (SafepointSynchronize::is_at_safepoint()) {
805 BiasedLocking::revoke_at_safepoint(h_obj);
806 } else {
807 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
808 }
809 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
810 }
811
812 oop obj = h_obj();
813 address owner = NULL;
814
815 markOop mark = ReadStableMark(obj);
816
817 // Uncontended case, header points to stack
818 if (mark->has_locker()) {
819 owner = (address) mark->locker();
820 }
821
822 // Contended case, header points to ObjectMonitor (tagged pointer)
823 if (mark->has_monitor()) {
824 ObjectMonitor* monitor = mark->monitor();
825 assert(monitor != NULL, "monitor should be non-null");
826 owner = (address) monitor->owner();
827 }
828
829 if (owner != NULL) {
830 // owning_thread_from_monitor_owner() may also return NULL here
831 return Threads::owning_thread_from_monitor_owner(owner, doLock);
832 }
833
834 // Unlocked case, header in place
835 // Cannot have assertion since this object may have been
836 // locked by another thread when reaching here.
837 // assert(mark->is_neutral(), "sanity check");
838
839 return NULL;
840 }
841 // Visitors ...
842
843 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
844 PaddedEnd<ObjectMonitor> * block = (PaddedEnd<ObjectMonitor> *)gBlockList;
845 ObjectMonitor* mid;
846 while (block) {
847 assert(block->object() == CHAINMARKER, "must be a block header");
848 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
849 mid = (ObjectMonitor *)(block + i);
850 oop object = (oop) mid->object();
851 if (object != NULL) {
852 closure->do_monitor(mid);
853 }
854 }
855 block = (PaddedEnd<ObjectMonitor> *) block->FreeNext;
856 }
857 }
858
859 // Get the next block in the block list.
860 static inline ObjectMonitor* next(ObjectMonitor* block) {
861 assert(block->object() == CHAINMARKER, "must be a block header");
862 block = block->FreeNext;
863 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
864 return block;
865 }
866
867
868 void ObjectSynchronizer::oops_do(OopClosure* f) {
869 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
870 for (PaddedEnd<ObjectMonitor> * block =
871 (PaddedEnd<ObjectMonitor> *)gBlockList; block != NULL;
872 block = (PaddedEnd<ObjectMonitor> *)next(block)) {
873 assert(block->object() == CHAINMARKER, "must be a block header");
874 for (int i = 1; i < _BLOCKSIZE; i++) {
875 ObjectMonitor* mid = (ObjectMonitor *)&block[i];
876 if (mid->object() != NULL) {
877 f->do_oop((oop*)mid->object_addr());
878 }
879 }
880 }
881 }
882
883
884 // -----------------------------------------------------------------------------
885 // ObjectMonitor Lifecycle
886 // -----------------------
887 // Inflation unlinks monitors from the global gFreeList and
888 // associates them with objects. Deflation -- which occurs at
889 // STW-time -- disassociates idle monitors from objects. Such
890 // scavenged monitors are returned to the gFreeList.
891 //
892 // The global list is protected by gListLock. All the critical sections
893 // are short and operate in constant-time.
894 //
895 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
896 //
897 // Lifecycle:
898 // -- unassigned and on the global free list
899 // -- unassigned and on a thread's private omFreeList
900 // -- assigned to an object. The object is inflated and the mark refers
901 // to the objectmonitor.
902
903
904 // Constraining monitor pool growth via MonitorBound ...
905 //
906 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
907 // the rate of scavenging is driven primarily by GC. As such, we can find
908 // an inordinate number of monitors in circulation.
909 // To avoid that scenario we can artificially induce a STW safepoint
910 // if the pool appears to be growing past some reasonable bound.
911 // Generally we favor time in space-time tradeoffs, but as there's no
912 // natural back-pressure on the # of extant monitors we need to impose some
913 // type of limit. Beware that if MonitorBound is set to too low a value
914 // we could just loop. In addition, if MonitorBound is set to a low value
915 // we'll incur more safepoints, which are harmful to performance.
916 // See also: GuaranteedSafepointInterval
917 //
918 // The current implementation uses asynchronous VM operations.
919
920 static void InduceScavenge(Thread * Self, const char * Whence) {
921 // Induce STW safepoint to trim monitors
922 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
923 // More precisely, trigger an asynchronous STW safepoint as the number
924 // of active monitors passes the specified threshold.
925 // TODO: assert thread state is reasonable
926
927 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
928 if (ObjectMonitor::Knob_Verbose) {
929 ::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ;
930 ::fflush(stdout);
931 }
932 // Induce a 'null' safepoint to scavenge monitors
933 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
934 // to the VMthread and have a lifespan longer than that of this activation record.
935 // The VMThread will delete the op when completed.
936 VMThread::execute(new VM_ForceAsyncSafepoint());
937
938 if (ObjectMonitor::Knob_Verbose) {
939 ::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ;
940 ::fflush(stdout);
941 }
942 }
943 }
944
945 void ObjectSynchronizer::verifyInUse(Thread *Self) {
946 ObjectMonitor* mid;
947 int in_use_tally = 0;
948 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) {
949 in_use_tally++;
950 }
951 assert(in_use_tally == Self->omInUseCount, "in-use count off");
952
953 int free_tally = 0;
954 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) {
955 free_tally++;
956 }
957 assert(free_tally == Self->omFreeCount, "free count off");
958 }
959
960 ObjectMonitor * NOINLINE ObjectSynchronizer::omAlloc(Thread * Self) {
961 // A large MAXPRIVATE value reduces both list lock contention
962 // and list coherency traffic, but also tends to increase the
963 // number of objectMonitors in circulation as well as the STW
964 // scavenge costs. As usual, we lean toward time in space-time
965 // tradeoffs.
966 const int MAXPRIVATE = 1024;
967 for (;;) {
968 ObjectMonitor * m;
969
970 // 1: try to allocate from the thread's local omFreeList.
971 // Threads will attempt to allocate first from their local list, then
972 // from the global list, and only after those attempts fail will the thread
973 // attempt to instantiate new monitors. Thread-local free lists take
974 // heat off the gListLock and improve allocation latency, as well as reducing
975 // coherency traffic on the shared global list.
976 m = Self->omFreeList;
977 if (m != NULL) {
978 Self->omFreeList = m->FreeNext;
979 Self->omFreeCount--;
980 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene
981 guarantee(m->object() == NULL, "invariant");
982 if (MonitorInUseLists) {
983 m->FreeNext = Self->omInUseList;
984 Self->omInUseList = m;
985 Self->omInUseCount++;
986 if (ObjectMonitor::Knob_VerifyInUse) {
987 verifyInUse(Self);
988 }
989 } else {
990 m->FreeNext = NULL;
991 }
992 return m;
993 }
994
995 // 2: try to allocate from the global gFreeList
996 // CONSIDER: use muxTry() instead of muxAcquire().
997 // If the muxTry() fails then drop immediately into case 3.
998 // If we're using thread-local free lists then try
999 // to reprovision the caller's free list.
1000 if (gFreeList != NULL) {
1001 // Reprovision the thread's omFreeList.
1002 // Use bulk transfers to reduce the allocation rate and heat
1003 // on various locks.
1004 Thread::muxAcquire(&gListLock, "omAlloc");
1005 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1006 gMonitorFreeCount--;
1007 ObjectMonitor * take = gFreeList;
1008 gFreeList = take->FreeNext;
1009 guarantee(take->object() == NULL, "invariant");
1010 guarantee(!take->is_busy(), "invariant");
1011 take->Recycle();
1012 omRelease(Self, take, false);
1013 }
1014 Thread::muxRelease(&gListLock);
1015 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1016 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1017 TEVENT(omFirst - reprovision);
1018
1019 const int mx = MonitorBound;
1020 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1021 // We can't safely induce a STW safepoint from omAlloc() as our thread
1022 // state may not be appropriate for such activities and callers may hold
1023 // naked oops, so instead we defer the action.
1024 InduceScavenge(Self, "omAlloc");
1025 }
1026 continue;
1027 }
1028
1029 // 3: allocate a block of new ObjectMonitors
1030 // Both the local and global free lists are empty -- resort to malloc().
1031 // In the current implementation objectMonitors are TSM - immortal.
1032 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1033 // each ObjectMonitor to start at the beginning of a cache line,
1034 // so we use align_size_up().
1035 // A better solution would be to use C++ placement-new.
1036 // BEWARE: As it stands currently, we don't run the ctors!
1037 assert(_BLOCKSIZE > 1, "invariant");
1038 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
1039 PaddedEnd<ObjectMonitor> * temp;
1040 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1041 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
1042 mtInternal);
1043 temp = (PaddedEnd<ObjectMonitor> *)
1044 align_size_up((intptr_t)real_malloc_addr,
1045 DEFAULT_CACHE_LINE_SIZE);
1046
1047 // NOTE: (almost) no way to recover if allocation failed.
1048 // We might be able to induce a STW safepoint and scavenge enough
1049 // objectMonitors to permit progress.
1050 if (temp == NULL) {
1051 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1052 "Allocate ObjectMonitors");
1053 }
1054 (void)memset((void *) temp, 0, neededsize);
1055
1056 // Format the block.
1057 // initialize the linked list, each monitor points to its next
1058 // forming the single linked free list, the very first monitor
1059 // will points to next block, which forms the block list.
1060 // The trick of using the 1st element in the block as gBlockList
1061 // linkage should be reconsidered. A better implementation would
1062 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1063
1064 for (int i = 1; i < _BLOCKSIZE; i++) {
1065 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1066 }
1067
1068 // terminate the last monitor as the end of list
1069 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1070
1071 // Element [0] is reserved for global list linkage
1072 temp[0].set_object(CHAINMARKER);
1073
1074 // Consider carving out this thread's current request from the
1075 // block in hand. This avoids some lock traffic and redundant
1076 // list activity.
1077
1078 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1079 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1080 Thread::muxAcquire(&gListLock, "omAlloc [2]");
1081 gMonitorPopulation += _BLOCKSIZE-1;
1082 gMonitorFreeCount += _BLOCKSIZE-1;
1083
1084 // Add the new block to the list of extant blocks (gBlockList).
1085 // The very first objectMonitor in a block is reserved and dedicated.
1086 // It serves as blocklist "next" linkage.
1087 temp[0].FreeNext = gBlockList;
1088 gBlockList = temp;
1089
1090 // Add the new string of objectMonitors to the global free list
1091 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1092 gFreeList = temp + 1;
1093 Thread::muxRelease(&gListLock);
1094 TEVENT(Allocate block of monitors);
1095 }
1096 }
1097
1098 // Place "m" on the caller's private per-thread omFreeList.
1099 // In practice there's no need to clamp or limit the number of
1100 // monitors on a thread's omFreeList as the only time we'll call
1101 // omRelease is to return a monitor to the free list after a CAS
1102 // attempt failed. This doesn't allow unbounded #s of monitors to
1103 // accumulate on a thread's free list.
1104 //
1105 // Key constraint: all ObjectMonitors on a thread's free list and the global
1106 // free list must have their object field set to null. This prevents the
1107 // scavenger -- deflate_idle_monitors -- from reclaiming them.
1108
1109 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1110 bool fromPerThreadAlloc) {
1111 guarantee(m->object() == NULL, "invariant");
1112 guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor");
1113 // Remove from omInUseList
1114 if (MonitorInUseLists && fromPerThreadAlloc) {
1115 ObjectMonitor* cur_mid_in_use = NULL;
1116 bool extracted = false;
1117 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1118 if (m == mid) {
1119 // extract from per-thread in-use list
1120 if (mid == Self->omInUseList) {
1121 Self->omInUseList = mid->FreeNext;
1122 } else if (cur_mid_in_use != NULL) {
1123 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1124 }
1125 extracted = true;
1126 Self->omInUseCount--;
1127 if (ObjectMonitor::Knob_VerifyInUse) {
1128 verifyInUse(Self);
1129 }
1130 break;
1131 }
1132 }
1133 assert(extracted, "Should have extracted from in-use list");
1134 }
1135
1136 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1137 m->FreeNext = Self->omFreeList;
1138 Self->omFreeList = m;
1139 Self->omFreeCount++;
1140 }
1141
1142 // Return the monitors of a moribund thread's local free list to
1143 // the global free list. Typically a thread calls omFlush() when
1144 // it's dying. We could also consider having the VM thread steal
1145 // monitors from threads that have not run java code over a few
1146 // consecutive STW safepoints. Relatedly, we might decay
1147 // omFreeProvision at STW safepoints.
1148 //
1149 // Also return the monitors of a moribund thread's omInUseList to
1150 // a global gOmInUseList under the global list lock so these
1151 // will continue to be scanned.
1152 //
1153 // We currently call omFlush() from the Thread:: dtor _after the thread
1154 // has been excised from the thread list and is no longer a mutator.
1155 // That means that omFlush() can run concurrently with a safepoint and
1156 // the scavenge operator. Calling omFlush() from JavaThread::exit() might
1157 // be a better choice as we could safely reason that that the JVM is
1158 // not at a safepoint at the time of the call, and thus there could
1159 // be not inopportune interleavings between omFlush() and the scavenge
1160 // operator.
1161
1162 void ObjectSynchronizer::omFlush(Thread * Self) {
1163 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1164 Self->omFreeList = NULL;
1165 ObjectMonitor * tail = NULL;
1166 int tally = 0;
1167 if (list != NULL) {
1168 ObjectMonitor * s;
1169 // The thread is going away, the per-thread free monitors
1170 // are freed via set_owner(NULL)
1171 // Link them to tail, which will be linked into the global free list
1172 // gFreeList below, under the gListLock
1173 for (s = list; s != NULL; s = s->FreeNext) {
1174 tally++;
1175 tail = s;
1176 guarantee(s->object() == NULL, "invariant");
1177 guarantee(!s->is_busy(), "invariant");
1178 s->set_owner(NULL); // redundant but good hygiene
1179 TEVENT(omFlush - Move one);
1180 }
1181 guarantee(tail != NULL && list != NULL, "invariant");
1182 }
1183
1184 ObjectMonitor * inUseList = Self->omInUseList;
1185 ObjectMonitor * inUseTail = NULL;
1186 int inUseTally = 0;
1187 if (inUseList != NULL) {
1188 Self->omInUseList = NULL;
1189 ObjectMonitor *cur_om;
1190 // The thread is going away, however the omInUseList inflated
1191 // monitors may still be in-use by other threads.
1192 // Link them to inUseTail, which will be linked into the global in-use list
1193 // gOmInUseList below, under the gListLock
1194 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1195 inUseTail = cur_om;
1196 inUseTally++;
1197 }
1198 assert(Self->omInUseCount == inUseTally, "in-use count off");
1199 Self->omInUseCount = 0;
1200 guarantee(inUseTail != NULL && inUseList != NULL, "invariant");
1201 }
1202
1203 Thread::muxAcquire(&gListLock, "omFlush");
1204 if (tail != NULL) {
1205 tail->FreeNext = gFreeList;
1206 gFreeList = list;
1207 gMonitorFreeCount += tally;
1208 }
1209
1210 if (inUseTail != NULL) {
1211 inUseTail->FreeNext = gOmInUseList;
1212 gOmInUseList = inUseList;
1213 gOmInUseCount += inUseTally;
1214 }
1215
1216 Thread::muxRelease(&gListLock);
1217 TEVENT(omFlush);
1218 }
1219
1220 // Fast path code shared by multiple functions
1221 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1222 markOop mark = obj->mark();
1223 if (mark->has_monitor()) {
1224 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1225 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1226 return mark->monitor();
1227 }
1228 return ObjectSynchronizer::inflate(Thread::current(), obj);
1229 }
1230
1231
1232 ObjectMonitor * NOINLINE ObjectSynchronizer::inflate(Thread * Self,
1233 oop object) {
1234 // Inflate mutates the heap ...
1235 // Relaxing assertion for bug 6320749.
1236 assert(Universe::verify_in_progress() ||
1237 !SafepointSynchronize::is_at_safepoint(), "invariant");
1238
1239 for (;;) {
1240 const markOop mark = object->mark();
1241 assert(!mark->has_bias_pattern(), "invariant");
1242
1243 // The mark can be in one of the following states:
1244 // * Inflated - just return
1245 // * Stack-locked - coerce it to inflated
1246 // * INFLATING - busy wait for conversion to complete
1247 // * Neutral - aggressively inflate the object.
1248 // * BIASED - Illegal. We should never see this
1249
1250 // CASE: inflated
1251 if (mark->has_monitor()) {
1252 ObjectMonitor * inf = mark->monitor();
1253 assert(inf->header()->is_neutral(), "invariant");
1254 assert(inf->object() == object, "invariant");
1255 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1256 return inf;
1257 }
1258
1259 // CASE: inflation in progress - inflating over a stack-lock.
1260 // Some other thread is converting from stack-locked to inflated.
1261 // Only that thread can complete inflation -- other threads must wait.
1262 // The INFLATING value is transient.
1263 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1264 // We could always eliminate polling by parking the thread on some auxiliary list.
1265 if (mark == markOopDesc::INFLATING()) {
1266 TEVENT(Inflate: spin while INFLATING);
1267 ReadStableMark(object);
1268 continue;
1269 }
1270
1271 // CASE: stack-locked
1272 // Could be stack-locked either by this thread or by some other thread.
1273 //
1274 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1275 // to install INFLATING into the mark word. We originally installed INFLATING,
1276 // allocated the objectmonitor, and then finally STed the address of the
1277 // objectmonitor into the mark. This was correct, but artificially lengthened
1278 // the interval in which INFLATED appeared in the mark, thus increasing
1279 // the odds of inflation contention.
1280 //
1281 // We now use per-thread private objectmonitor free lists.
1282 // These list are reprovisioned from the global free list outside the
1283 // critical INFLATING...ST interval. A thread can transfer
1284 // multiple objectmonitors en-mass from the global free list to its local free list.
1285 // This reduces coherency traffic and lock contention on the global free list.
1286 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1287 // before or after the CAS(INFLATING) operation.
1288 // See the comments in omAlloc().
1289
1290 if (mark->has_locker()) {
1291 ObjectMonitor * m = omAlloc(Self);
1292 // Optimistically prepare the objectmonitor - anticipate successful CAS
1293 // We do this before the CAS in order to minimize the length of time
1294 // in which INFLATING appears in the mark.
1295 m->Recycle();
1296 m->_Responsible = NULL;
1297 m->_recursions = 0;
1298 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1299
1300 markOop cmp = (markOop) Atomic::cmpxchg_ptr(markOopDesc::INFLATING(), object->mark_addr(), mark);
1301 if (cmp != mark) {
1302 omRelease(Self, m, true);
1303 continue; // Interference -- just retry
1304 }
1305
1306 // We've successfully installed INFLATING (0) into the mark-word.
1307 // This is the only case where 0 will appear in a mark-work.
1308 // Only the singular thread that successfully swings the mark-word
1309 // to 0 can perform (or more precisely, complete) inflation.
1310 //
1311 // Why do we CAS a 0 into the mark-word instead of just CASing the
1312 // mark-word from the stack-locked value directly to the new inflated state?
1313 // Consider what happens when a thread unlocks a stack-locked object.
1314 // It attempts to use CAS to swing the displaced header value from the
1315 // on-stack basiclock back into the object header. Recall also that the
1316 // header value (hashcode, etc) can reside in (a) the object header, or
1317 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1318 // header in an objectMonitor. The inflate() routine must copy the header
1319 // value from the basiclock on the owner's stack to the objectMonitor, all
1320 // the while preserving the hashCode stability invariants. If the owner
1321 // decides to release the lock while the value is 0, the unlock will fail
1322 // and control will eventually pass from slow_exit() to inflate. The owner
1323 // will then spin, waiting for the 0 value to disappear. Put another way,
1324 // the 0 causes the owner to stall if the owner happens to try to
1325 // drop the lock (restoring the header from the basiclock to the object)
1326 // while inflation is in-progress. This protocol avoids races that might
1327 // would otherwise permit hashCode values to change or "flicker" for an object.
1328 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1329 // 0 serves as a "BUSY" inflate-in-progress indicator.
1330
1331
1332 // fetch the displaced mark from the owner's stack.
1333 // The owner can't die or unwind past the lock while our INFLATING
1334 // object is in the mark. Furthermore the owner can't complete
1335 // an unlock on the object, either.
1336 markOop dmw = mark->displaced_mark_helper();
1337 assert(dmw->is_neutral(), "invariant");
1338
1339 // Setup monitor fields to proper values -- prepare the monitor
1340 m->set_header(dmw);
1341
1342 // Optimization: if the mark->locker stack address is associated
1343 // with this thread we could simply set m->_owner = Self.
1344 // Note that a thread can inflate an object
1345 // that it has stack-locked -- as might happen in wait() -- directly
1346 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1347 m->set_owner(mark->locker());
1348 m->set_object(object);
1349 // TODO-FIXME: assert BasicLock->dhw != 0.
1350
1351 // Must preserve store ordering. The monitor state must
1352 // be stable at the time of publishing the monitor address.
1353 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1354 object->release_set_mark(markOopDesc::encode(m));
1355
1356 // Hopefully the performance counters are allocated on distinct cache lines
1357 // to avoid false sharing on MP systems ...
1358 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc();
1359 TEVENT(Inflate: overwrite stacklock);
1360 if (TraceMonitorInflation) {
1361 if (object->is_instance()) {
1362 ResourceMark rm;
1363 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1364 (void *) object, (intptr_t) object->mark(),
1365 object->klass()->external_name());
1366 }
1367 }
1368 return m;
1369 }
1370
1371 // CASE: neutral
1372 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1373 // If we know we're inflating for entry it's better to inflate by swinging a
1374 // pre-locked objectMonitor pointer into the object header. A successful
1375 // CAS inflates the object *and* confers ownership to the inflating thread.
1376 // In the current implementation we use a 2-step mechanism where we CAS()
1377 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1378 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1379 // would be useful.
1380
1381 assert(mark->is_neutral(), "invariant");
1382 ObjectMonitor * m = omAlloc(Self);
1383 // prepare m for installation - set monitor to initial state
1384 m->Recycle();
1385 m->set_header(mark);
1386 m->set_owner(NULL);
1387 m->set_object(object);
1388 m->_recursions = 0;
1389 m->_Responsible = NULL;
1390 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1391
1392 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) {
1393 m->set_object(NULL);
1394 m->set_owner(NULL);
1395 m->Recycle();
1396 omRelease(Self, m, true);
1397 m = NULL;
1398 continue;
1399 // interference - the markword changed - just retry.
1400 // The state-transitions are one-way, so there's no chance of
1401 // live-lock -- "Inflated" is an absorbing state.
1402 }
1403
1404 // Hopefully the performance counters are allocated on distinct
1405 // cache lines to avoid false sharing on MP systems ...
1406 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc();
1407 TEVENT(Inflate: overwrite neutral);
1408 if (TraceMonitorInflation) {
1409 if (object->is_instance()) {
1410 ResourceMark rm;
1411 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1412 (void *) object, (intptr_t) object->mark(),
1413 object->klass()->external_name());
1414 }
1415 }
1416 return m;
1417 }
1418 }
1419
1420
1421 // Deflate_idle_monitors() is called at all safepoints, immediately
1422 // after all mutators are stopped, but before any objects have moved.
1423 // It traverses the list of known monitors, deflating where possible.
1424 // The scavenged monitor are returned to the monitor free list.
1425 //
1426 // Beware that we scavenge at *every* stop-the-world point.
1427 // Having a large number of monitors in-circulation negatively
1428 // impacts the performance of some applications (e.g., PointBase).
1429 // Broadly, we want to minimize the # of monitors in circulation.
1430 //
1431 // We have added a flag, MonitorInUseLists, which creates a list
1432 // of active monitors for each thread. deflate_idle_monitors()
1433 // only scans the per-thread in-use lists. omAlloc() puts all
1434 // assigned monitors on the per-thread list. deflate_idle_monitors()
1435 // returns the non-busy monitors to the global free list.
1436 // When a thread dies, omFlush() adds the list of active monitors for
1437 // that thread to a global gOmInUseList acquiring the
1438 // global list lock. deflate_idle_monitors() acquires the global
1439 // list lock to scan for non-busy monitors to the global free list.
1440 // An alternative could have used a single global in-use list. The
1441 // downside would have been the additional cost of acquiring the global list lock
1442 // for every omAlloc().
1443 //
1444 // Perversely, the heap size -- and thus the STW safepoint rate --
1445 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1446 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1447 // This is an unfortunate aspect of this design.
1448
1449 enum ManifestConstants {
1450 ClearResponsibleAtSTW = 0,
1451 MaximumRecheckInterval = 1000
1452 };
1453
1454 // Deflate a single monitor if not in-use
1455 // Return true if deflated, false if in-use
1456 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1457 ObjectMonitor** freeHeadp,
1458 ObjectMonitor** freeTailp) {
1459 bool deflated;
1460 // Normal case ... The monitor is associated with obj.
1461 guarantee(obj->mark() == markOopDesc::encode(mid), "invariant");
1462 guarantee(mid == obj->mark()->monitor(), "invariant");
1463 guarantee(mid->header()->is_neutral(), "invariant");
1464
1465 if (mid->is_busy()) {
1466 if (ClearResponsibleAtSTW) mid->_Responsible = NULL;
1467 deflated = false;
1468 } else {
1469 // Deflate the monitor if it is no longer being used
1470 // It's idle - scavenge and return to the global free list
1471 // plain old deflation ...
1472 TEVENT(deflate_idle_monitors - scavenge1);
1473 if (TraceMonitorInflation) {
1474 if (obj->is_instance()) {
1475 ResourceMark rm;
1476 tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1477 (void *) obj, (intptr_t) obj->mark(), obj->klass()->external_name());
1478 }
1479 }
1480
1481 // Restore the header back to obj
1482 obj->release_set_mark(mid->header());
1483 mid->clear();
1484
1485 assert(mid->object() == NULL, "invariant");
1486
1487 // Move the object to the working free list defined by freeHeadp, freeTailp
1488 if (*freeHeadp == NULL) *freeHeadp = mid;
1489 if (*freeTailp != NULL) {
1490 ObjectMonitor * prevtail = *freeTailp;
1491 assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1492 prevtail->FreeNext = mid;
1493 }
1494 *freeTailp = mid;
1495 deflated = true;
1496 }
1497 return deflated;
1498 }
1499
1500 // Walk a given monitor list, and deflate idle monitors
1501 // The given list could be a per-thread list or a global list
1502 // Caller acquires gListLock
1503 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1504 ObjectMonitor** freeHeadp,
1505 ObjectMonitor** freeTailp) {
1506 ObjectMonitor* mid;
1507 ObjectMonitor* next;
1508 ObjectMonitor* cur_mid_in_use = NULL;
1509 int deflated_count = 0;
1510
1511 for (mid = *listHeadp; mid != NULL;) {
1512 oop obj = (oop) mid->object();
1513 if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1514 // if deflate_monitor succeeded,
1515 // extract from per-thread in-use list
1516 if (mid == *listHeadp) {
1517 *listHeadp = mid->FreeNext;
1518 } else if (cur_mid_in_use != NULL) {
1519 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1520 }
1521 next = mid->FreeNext;
1522 mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list
1523 mid = next;
1524 deflated_count++;
1525 } else {
1526 cur_mid_in_use = mid;
1527 mid = mid->FreeNext;
1528 }
1529 }
1530 return deflated_count;
1531 }
1532
1533 void ObjectSynchronizer::deflate_idle_monitors() {
1534 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1535 int nInuse = 0; // currently associated with objects
1536 int nInCirculation = 0; // extant
1537 int nScavenged = 0; // reclaimed
1538 bool deflated = false;
1539
1540 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1541 ObjectMonitor * freeTailp = NULL;
1542
1543 TEVENT(deflate_idle_monitors);
1544 // Prevent omFlush from changing mids in Thread dtor's during deflation
1545 // And in case the vm thread is acquiring a lock during a safepoint
1546 // See e.g. 6320749
1547 Thread::muxAcquire(&gListLock, "scavenge - return");
1548
1549 if (MonitorInUseLists) {
1550 int inUse = 0;
1551 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) {
1552 nInCirculation+= cur->omInUseCount;
1553 int deflated_count = deflate_monitor_list(cur->omInUseList_addr(), &freeHeadp, &freeTailp);
1554 cur->omInUseCount-= deflated_count;
1555 if (ObjectMonitor::Knob_VerifyInUse) {
1556 verifyInUse(cur);
1557 }
1558 nScavenged += deflated_count;
1559 nInuse += cur->omInUseCount;
1560 }
1561
1562 // For moribund threads, scan gOmInUseList
1563 if (gOmInUseList) {
1564 nInCirculation += gOmInUseCount;
1565 int deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
1566 gOmInUseCount-= deflated_count;
1567 nScavenged += deflated_count;
1568 nInuse += gOmInUseCount;
1569 }
1570
1571 } else for (PaddedEnd<ObjectMonitor> * block =
1572 (PaddedEnd<ObjectMonitor> *)gBlockList; block != NULL;
1573 block = (PaddedEnd<ObjectMonitor> *)next(block)) {
1574 // Iterate over all extant monitors - Scavenge all idle monitors.
1575 assert(block->object() == CHAINMARKER, "must be a block header");
1576 nInCirculation += _BLOCKSIZE;
1577 for (int i = 1; i < _BLOCKSIZE; i++) {
1578 ObjectMonitor* mid = (ObjectMonitor*)&block[i];
1579 oop obj = (oop) mid->object();
1580
1581 if (obj == NULL) {
1582 // The monitor is not associated with an object.
1583 // The monitor should either be a thread-specific private
1584 // free list or the global free list.
1585 // obj == NULL IMPLIES mid->is_busy() == 0
1586 guarantee(!mid->is_busy(), "invariant");
1587 continue;
1588 }
1589 deflated = deflate_monitor(mid, obj, &freeHeadp, &freeTailp);
1590
1591 if (deflated) {
1592 mid->FreeNext = NULL;
1593 nScavenged++;
1594 } else {
1595 nInuse++;
1596 }
1597 }
1598 }
1599
1600 gMonitorFreeCount += nScavenged;
1601
1602 // Consider: audit gFreeList to ensure that gMonitorFreeCount and list agree.
1603
1604 if (ObjectMonitor::Knob_Verbose) {
1605 ::printf("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n",
1606 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge,
1607 gMonitorPopulation, gMonitorFreeCount);
1608 ::fflush(stdout);
1609 }
1610
1611 ForceMonitorScavenge = 0; // Reset
1612
1613 // Move the scavenged monitors back to the global free list.
1614 if (freeHeadp != NULL) {
1615 guarantee(freeTailp != NULL && nScavenged > 0, "invariant");
1616 assert(freeTailp->FreeNext == NULL, "invariant");
1617 // constant-time list splice - prepend scavenged segment to gFreeList
1618 freeTailp->FreeNext = gFreeList;
1619 gFreeList = freeHeadp;
1620 }
1621 Thread::muxRelease(&gListLock);
1622
1623 if (ObjectMonitor::_sync_Deflations != NULL) ObjectMonitor::_sync_Deflations->inc(nScavenged);
1624 if (ObjectMonitor::_sync_MonExtant != NULL) ObjectMonitor::_sync_MonExtant ->set_value(nInCirculation);
1625
1626 // TODO: Add objectMonitor leak detection.
1627 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1628 GVars.stwRandom = os::random();
1629 GVars.stwCycle++;
1630 }
1631
1632 // Monitor cleanup on JavaThread::exit
1633
1634 // Iterate through monitor cache and attempt to release thread's monitors
1635 // Gives up on a particular monitor if an exception occurs, but continues
1636 // the overall iteration, swallowing the exception.
1637 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1638 private:
1639 TRAPS;
1640
1641 public:
1642 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1643 void do_monitor(ObjectMonitor* mid) {
1644 if (mid->owner() == THREAD) {
1645 (void)mid->complete_exit(CHECK);
1646 }
1647 }
1648 };
1649
1650 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1651 // ignored. This is meant to be called during JNI thread detach which assumes
1652 // all remaining monitors are heavyweight. All exceptions are swallowed.
1653 // Scanning the extant monitor list can be time consuming.
1654 // A simple optimization is to add a per-thread flag that indicates a thread
1655 // called jni_monitorenter() during its lifetime.
1656 //
1657 // Instead of No_Savepoint_Verifier it might be cheaper to
1658 // use an idiom of the form:
1659 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1660 // <code that must not run at safepoint>
1661 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1662 // Since the tests are extremely cheap we could leave them enabled
1663 // for normal product builds.
1664
1665 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1666 assert(THREAD == JavaThread::current(), "must be current Java thread");
1667 No_Safepoint_Verifier nsv;
1668 ReleaseJavaMonitorsClosure rjmc(THREAD);
1669 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
1670 ObjectSynchronizer::monitors_iterate(&rjmc);
1671 Thread::muxRelease(&gListLock);
1672 THREAD->clear_pending_exception();
1673 }
1674
1675 //------------------------------------------------------------------------------
1676 // Debugging code
1677
1678 void ObjectSynchronizer::sanity_checks(const bool verbose,
1679 const uint cache_line_size,
1680 int *error_cnt_ptr,
1681 int *warning_cnt_ptr) {
1682 u_char *addr_begin = (u_char*)&GVars;
1683 u_char *addr_stwRandom = (u_char*)&GVars.stwRandom;
1684 u_char *addr_hcSequence = (u_char*)&GVars.hcSequence;
1685
1686 if (verbose) {
1687 tty->print_cr("INFO: sizeof(SharedGlobals)=" SIZE_FORMAT,
1688 sizeof(SharedGlobals));
1689 }
1690
1691 uint offset_stwRandom = (uint)(addr_stwRandom - addr_begin);
1692 if (verbose) tty->print_cr("INFO: offset(stwRandom)=%u", offset_stwRandom);
1693
1694 uint offset_hcSequence = (uint)(addr_hcSequence - addr_begin);
1695 if (verbose) {
1696 tty->print_cr("INFO: offset(_hcSequence)=%u", offset_hcSequence);
1697 }
1698
1699 if (cache_line_size != 0) {
1700 // We were able to determine the L1 data cache line size so
1701 // do some cache line specific sanity checks
1702
1703 if (offset_stwRandom < cache_line_size) {
1704 tty->print_cr("WARNING: the SharedGlobals.stwRandom field is closer "
1705 "to the struct beginning than a cache line which permits "
1706 "false sharing.");
1707 (*warning_cnt_ptr)++;
1708 }
1709
1710 if ((offset_hcSequence - offset_stwRandom) < cache_line_size) {
1711 tty->print_cr("WARNING: the SharedGlobals.stwRandom and "
1712 "SharedGlobals.hcSequence fields are closer than a cache "
1713 "line which permits false sharing.");
1714 (*warning_cnt_ptr)++;
1715 }
1716
1717 if ((sizeof(SharedGlobals) - offset_hcSequence) < cache_line_size) {
1718 tty->print_cr("WARNING: the SharedGlobals.hcSequence field is closer "
1719 "to the struct end than a cache line which permits false "
1720 "sharing.");
1721 (*warning_cnt_ptr)++;
1722 }
1723 }
1724 }
1725
1726 #ifndef PRODUCT
1727
1728 // Verify all monitors in the monitor cache, the verification is weak.
1729 void ObjectSynchronizer::verify() {
1730 PaddedEnd<ObjectMonitor> * block = (PaddedEnd<ObjectMonitor> *)gBlockList;
1731 ObjectMonitor* mid;
1732 while (block) {
1733 assert(block->object() == CHAINMARKER, "must be a block header");
1734 for (int i = 1; i < _BLOCKSIZE; i++) {
1735 mid = (ObjectMonitor *)(block + i);
1736 oop object = (oop) mid->object();
1737 if (object != NULL) {
1738 mid->verify();
1739 }
1740 }
1741 block = (PaddedEnd<ObjectMonitor> *) block->FreeNext;
1742 }
1743 }
1744
1745 // Check if monitor belongs to the monitor cache
1746 // The list is grow-only so it's *relatively* safe to traverse
1747 // the list of extant blocks without taking a lock.
1748
1749 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
1750 PaddedEnd<ObjectMonitor> * block = (PaddedEnd<ObjectMonitor> *)gBlockList;
1751
1752 while (block) {
1753 assert(block->object() == CHAINMARKER, "must be a block header");
1754 if (monitor > (ObjectMonitor *)&block[0] &&
1755 monitor < (ObjectMonitor *)&block[_BLOCKSIZE]) {
1756 address mon = (address) monitor;
1757 address blk = (address) block;
1758 size_t diff = mon - blk;
1759 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "check");
1760 return 1;
1761 }
1762 block = (PaddedEnd<ObjectMonitor> *) block->FreeNext;
1763 }
1764 return 0;
1765 }
1766
1767 #endif