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 "logging/log.hpp"
28 #include "memory/metaspaceShared.hpp"
29 #include "memory/padded.hpp"
30 #include "memory/resourceArea.hpp"
31 #include "oops/markOop.hpp"
32 #include "oops/oop.inline.hpp"
33 #include "runtime/atomic.inline.hpp"
34 #include "runtime/biasedLocking.hpp"
35 #include "runtime/handles.inline.hpp"
36 #include "runtime/interfaceSupport.hpp"
37 #include "runtime/mutexLocker.hpp"
38 #include "runtime/objectMonitor.hpp"
39 #include "runtime/objectMonitor.inline.hpp"
40 #include "runtime/osThread.hpp"
41 #include "runtime/stubRoutines.hpp"
42 #include "runtime/synchronizer.hpp"
43 #include "runtime/thread.inline.hpp"
44 #include "runtime/vframe.hpp"
45 #include "trace/traceMacros.hpp"
46 #include "trace/tracing.hpp"
47 #include "utilities/dtrace.hpp"
48 #include "utilities/events.hpp"
49 #include "utilities/preserveException.hpp"
50
51 #if defined(__GNUC__) && !defined(PPC64)
52 // Need to inhibit inlining for older versions of GCC to avoid build-time failures
53 #define NOINLINE __attribute__((noinline))
54 #else
55 #define NOINLINE
56 #endif
57
58 // The "core" versions of monitor enter and exit reside in this file.
59 // The interpreter and compilers contain specialized transliterated
60 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
61 // for instance. If you make changes here, make sure to modify the
62 // interpreter, and both C1 and C2 fast-path inline locking code emission.
63 //
64 // -----------------------------------------------------------------------------
65
66 #ifdef DTRACE_ENABLED
67
68 // Only bother with this argument setup if dtrace is available
69 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
70
71 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
72 char* bytes = NULL; \
73 int len = 0; \
74 jlong jtid = SharedRuntime::get_java_tid(thread); \
75 Symbol* klassname = ((oop)(obj))->klass()->name(); \
76 if (klassname != NULL) { \
77 bytes = (char*)klassname->bytes(); \
78 len = klassname->utf8_length(); \
79 }
80
81 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
82 { \
83 if (DTraceMonitorProbes) { \
84 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
85 HOTSPOT_MONITOR_WAIT(jtid, \
86 (uintptr_t)(monitor), bytes, len, (millis)); \
87 } \
88 }
89
90 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
91 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
92 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
93
94 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
95 { \
96 if (DTraceMonitorProbes) { \
97 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
98 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
99 (uintptr_t)(monitor), bytes, len); \
100 } \
101 }
102
103 #else // ndef DTRACE_ENABLED
104
105 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
106 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
107
108 #endif // ndef DTRACE_ENABLED
109
110 // This exists only as a workaround of dtrace bug 6254741
111 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
112 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
113 return 0;
114 }
115
116 #define NINFLATIONLOCKS 256
117 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
118
119 // global list of blocks of monitors
120 // gBlockList is really PaddedEnd<ObjectMonitor> *, but we don't
121 // want to expose the PaddedEnd template more than necessary.
122 ObjectMonitor * volatile ObjectSynchronizer::gBlockList = NULL;
123 // global monitor free list
124 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL;
125 // global monitor in-use list, for moribund threads,
126 // monitors they inflated need to be scanned for deflation
127 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL;
128 // count of entries in gOmInUseList
129 int ObjectSynchronizer::gOmInUseCount = 0;
130
131 static volatile intptr_t gListLock = 0; // protects global monitor lists
132 static volatile int gMonitorFreeCount = 0; // # on gFreeList
133 static volatile int gMonitorPopulation = 0; // # Extant -- in circulation
134
135 static void post_monitor_inflate_event(EventJavaMonitorInflate&,
136 const oop,
137 const ObjectSynchronizer::InflateCause);
138
139 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
140
141
142 // =====================> Quick functions
143
144 // The quick_* forms are special fast-path variants used to improve
145 // performance. In the simplest case, a "quick_*" implementation could
146 // simply return false, in which case the caller will perform the necessary
147 // state transitions and call the slow-path form.
148 // The fast-path is designed to handle frequently arising cases in an efficient
149 // manner and is just a degenerate "optimistic" variant of the slow-path.
150 // returns true -- to indicate the call was satisfied.
151 // returns false -- to indicate the call needs the services of the slow-path.
152 // A no-loitering ordinance is in effect for code in the quick_* family
153 // operators: safepoints or indefinite blocking (blocking that might span a
154 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
155 // entry.
156 //
157 // Consider: An interesting optimization is to have the JIT recognize the
158 // following common idiom:
159 // synchronized (someobj) { .... ; notify(); }
160 // That is, we find a notify() or notifyAll() call that immediately precedes
161 // the monitorexit operation. In that case the JIT could fuse the operations
162 // into a single notifyAndExit() runtime primitive.
163
164 bool ObjectSynchronizer::quick_notify(oopDesc * obj, Thread * self, bool all) {
165 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
166 assert(self->is_Java_thread(), "invariant");
167 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
168 NoSafepointVerifier nsv;
169 if (obj == NULL) return false; // slow-path for invalid obj
170 const markOop mark = obj->mark();
171
172 if (mark->has_locker() && self->is_lock_owned((address)mark->locker())) {
173 // Degenerate notify
174 // stack-locked by caller so by definition the implied waitset is empty.
175 return true;
176 }
177
178 if (mark->has_monitor()) {
179 ObjectMonitor * const mon = mark->monitor();
180 assert(mon->object() == obj, "invariant");
181 if (mon->owner() != self) return false; // slow-path for IMS exception
182
183 if (mon->first_waiter() != NULL) {
184 // We have one or more waiters. Since this is an inflated monitor
185 // that we own, we can transfer one or more threads from the waitset
186 // to the entrylist here and now, avoiding the slow-path.
187 if (all) {
188 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
189 } else {
190 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
191 }
192 int tally = 0;
193 do {
194 mon->INotify(self);
195 ++tally;
196 } while (mon->first_waiter() != NULL && all);
197 OM_PERFDATA_OP(Notifications, inc(tally));
198 }
199 return true;
200 }
201
202 // biased locking and any other IMS exception states take the slow-path
203 return false;
204 }
205
206
207 // The LockNode emitted directly at the synchronization site would have
208 // been too big if it were to have included support for the cases of inflated
209 // recursive enter and exit, so they go here instead.
210 // Note that we can't safely call AsyncPrintJavaStack() from within
211 // quick_enter() as our thread state remains _in_Java.
212
213 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
214 BasicLock * Lock) {
215 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
216 assert(Self->is_Java_thread(), "invariant");
217 assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
218 NoSafepointVerifier nsv;
219 if (obj == NULL) return false; // Need to throw NPE
220 const markOop mark = obj->mark();
221
222 if (mark->has_monitor()) {
223 ObjectMonitor * const m = mark->monitor();
224 assert(m->object() == obj, "invariant");
225 Thread * const owner = (Thread *) m->_owner;
226
227 // Lock contention and Transactional Lock Elision (TLE) diagnostics
228 // and observability
229 // Case: light contention possibly amenable to TLE
230 // Case: TLE inimical operations such as nested/recursive synchronization
231
232 if (owner == Self) {
233 m->_recursions++;
234 return true;
235 }
236
237 if (owner == NULL &&
238 Atomic::cmpxchg_ptr(Self, &(m->_owner), NULL) == NULL) {
239 assert(m->_recursions == 0, "invariant");
240 assert(m->_owner == Self, "invariant");
241 return true;
242 }
243 }
244
245 // Note that we could inflate in quick_enter.
246 // This is likely a useful optimization
247 // Critically, in quick_enter() we must not:
248 // -- perform bias revocation, or
249 // -- block indefinitely, or
250 // -- reach a safepoint
251
252 return false; // revert to slow-path
253 }
254
255 // -----------------------------------------------------------------------------
256 // Fast Monitor Enter/Exit
257 // This the fast monitor enter. The interpreter and compiler use
258 // some assembly copies of this code. Make sure update those code
259 // if the following function is changed. The implementation is
260 // extremely sensitive to race condition. Be careful.
261
262 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
263 bool attempt_rebias, TRAPS) {
264 if (UseBiasedLocking) {
265 if (!SafepointSynchronize::is_at_safepoint()) {
266 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
267 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
268 return;
269 }
270 } else {
271 assert(!attempt_rebias, "can not rebias toward VM thread");
272 BiasedLocking::revoke_at_safepoint(obj);
273 }
274 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
275 }
276
277 slow_enter(obj, lock, THREAD);
278 }
279
280 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
281 assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here");
282 // if displaced header is null, the previous enter is recursive enter, no-op
283 markOop dhw = lock->displaced_header();
284 markOop mark;
285 if (dhw == NULL) {
286 // Recursive stack-lock.
287 // Diagnostics -- Could be: stack-locked, inflating, inflated.
288 mark = object->mark();
289 assert(!mark->is_neutral(), "invariant");
290 if (mark->has_locker() && mark != markOopDesc::INFLATING()) {
291 assert(THREAD->is_lock_owned((address)mark->locker()), "invariant");
292 }
293 if (mark->has_monitor()) {
294 ObjectMonitor * m = mark->monitor();
295 assert(((oop)(m->object()))->mark() == mark, "invariant");
296 assert(m->is_entered(THREAD), "invariant");
297 }
298 return;
299 }
300
301 mark = object->mark();
302
303 // If the object is stack-locked by the current thread, try to
304 // swing the displaced header from the box back to the mark.
305 if (mark == (markOop) lock) {
306 assert(dhw->is_neutral(), "invariant");
307 if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) {
308 TEVENT(fast_exit: release stacklock);
309 return;
310 }
311 }
312
313 ObjectSynchronizer::inflate(THREAD,
314 object,
315 inflate_cause_vm_internal)->exit(true, THREAD);
316 }
317
318 // -----------------------------------------------------------------------------
319 // Interpreter/Compiler Slow Case
320 // This routine is used to handle interpreter/compiler slow case
321 // We don't need to use fast path here, because it must have been
322 // failed in the interpreter/compiler code.
323 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
324 markOop mark = obj->mark();
325 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
326
327 if (mark->is_neutral()) {
328 // Anticipate successful CAS -- the ST of the displaced mark must
329 // be visible <= the ST performed by the CAS.
330 lock->set_displaced_header(mark);
331 if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) {
332 TEVENT(slow_enter: release stacklock);
333 return;
334 }
335 // Fall through to inflate() ...
336 } else if (mark->has_locker() &&
337 THREAD->is_lock_owned((address)mark->locker())) {
338 assert(lock != mark->locker(), "must not re-lock the same lock");
339 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
340 lock->set_displaced_header(NULL);
341 return;
342 }
343
344 // The object header will never be displaced to this lock,
345 // so it does not matter what the value is, except that it
346 // must be non-zero to avoid looking like a re-entrant lock,
347 // and must not look locked either.
348 lock->set_displaced_header(markOopDesc::unused_mark());
349 ObjectSynchronizer::inflate(THREAD,
350 obj(),
351 inflate_cause_monitor_enter)->enter(THREAD);
352 }
353
354 // This routine is used to handle interpreter/compiler slow case
355 // We don't need to use fast path here, because it must have
356 // failed in the interpreter/compiler code. Simply use the heavy
357 // weight monitor should be ok, unless someone find otherwise.
358 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
359 fast_exit(object, lock, THREAD);
360 }
361
362 // -----------------------------------------------------------------------------
363 // Class Loader support to workaround deadlocks on the class loader lock objects
364 // Also used by GC
365 // complete_exit()/reenter() are used to wait on a nested lock
366 // i.e. to give up an outer lock completely and then re-enter
367 // Used when holding nested locks - lock acquisition order: lock1 then lock2
368 // 1) complete_exit lock1 - saving recursion count
369 // 2) wait on lock2
370 // 3) when notified on lock2, unlock lock2
371 // 4) reenter lock1 with original recursion count
372 // 5) lock lock2
373 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
374 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
375 TEVENT(complete_exit);
376 if (UseBiasedLocking) {
377 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
378 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
379 }
380
381 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
382 obj(),
383 inflate_cause_vm_internal);
384
385 return monitor->complete_exit(THREAD);
386 }
387
388 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
389 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
390 TEVENT(reenter);
391 if (UseBiasedLocking) {
392 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
393 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
394 }
395
396 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
397 obj(),
398 inflate_cause_vm_internal);
399
400 monitor->reenter(recursion, THREAD);
401 }
402 // -----------------------------------------------------------------------------
403 // JNI locks on java objects
404 // NOTE: must use heavy weight monitor to handle jni monitor enter
405 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
406 // the current locking is from JNI instead of Java code
407 TEVENT(jni_enter);
408 if (UseBiasedLocking) {
409 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
410 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
411 }
412 THREAD->set_current_pending_monitor_is_from_java(false);
413 ObjectSynchronizer::inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);
414 THREAD->set_current_pending_monitor_is_from_java(true);
415 }
416
417 // NOTE: must use heavy weight monitor to handle jni monitor exit
418 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
419 TEVENT(jni_exit);
420 if (UseBiasedLocking) {
421 Handle h_obj(THREAD, obj);
422 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
423 obj = h_obj();
424 }
425 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
426
427 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
428 obj,
429 inflate_cause_jni_exit);
430 // If this thread has locked the object, exit the monitor. Note: can't use
431 // monitor->check(CHECK); must exit even if an exception is pending.
432 if (monitor->check(THREAD)) {
433 monitor->exit(true, THREAD);
434 }
435 }
436
437 // -----------------------------------------------------------------------------
438 // Internal VM locks on java objects
439 // standard constructor, allows locking failures
440 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
441 _dolock = doLock;
442 _thread = thread;
443 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
444 _obj = obj;
445
446 if (_dolock) {
447 TEVENT(ObjectLocker);
448
449 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
450 }
451 }
452
453 ObjectLocker::~ObjectLocker() {
454 if (_dolock) {
455 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
456 }
457 }
458
459
460 // -----------------------------------------------------------------------------
461 // Wait/Notify/NotifyAll
462 // NOTE: must use heavy weight monitor to handle wait()
463 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
464 if (UseBiasedLocking) {
465 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
466 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
467 }
468 if (millis < 0) {
469 TEVENT(wait - throw IAX);
470 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
471 }
472 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
473 obj(),
474 inflate_cause_wait);
475
476 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
477 monitor->wait(millis, true, THREAD);
478
479 // This dummy call is in place to get around dtrace bug 6254741. Once
480 // that's fixed we can uncomment the following line, remove the call
481 // and change this function back into a "void" func.
482 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
483 return dtrace_waited_probe(monitor, obj, THREAD);
484 }
485
486 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
487 if (UseBiasedLocking) {
488 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
489 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
490 }
491 if (millis < 0) {
492 TEVENT(wait - throw IAX);
493 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
494 }
495 ObjectSynchronizer::inflate(THREAD,
496 obj(),
497 inflate_cause_wait)->wait(millis, false, THREAD);
498 }
499
500 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
501 if (UseBiasedLocking) {
502 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
503 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
504 }
505
506 markOop mark = obj->mark();
507 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
508 return;
509 }
510 ObjectSynchronizer::inflate(THREAD,
511 obj(),
512 inflate_cause_notify)->notify(THREAD);
513 }
514
515 // NOTE: see comment of notify()
516 void ObjectSynchronizer::notifyall(Handle obj, 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
522 markOop mark = obj->mark();
523 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
524 return;
525 }
526 ObjectSynchronizer::inflate(THREAD,
527 obj(),
528 inflate_cause_notify)->notifyAll(THREAD);
529 }
530
531 // -----------------------------------------------------------------------------
532 // Hash Code handling
533 //
534 // Performance concern:
535 // OrderAccess::storestore() calls release() which at one time stored 0
536 // into the global volatile OrderAccess::dummy variable. This store was
537 // unnecessary for correctness. Many threads storing into a common location
538 // causes considerable cache migration or "sloshing" on large SMP systems.
539 // As such, I avoided using OrderAccess::storestore(). In some cases
540 // OrderAccess::fence() -- which incurs local latency on the executing
541 // processor -- is a better choice as it scales on SMP systems.
542 //
543 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
544 // a discussion of coherency costs. Note that all our current reference
545 // platforms provide strong ST-ST order, so the issue is moot on IA32,
546 // x64, and SPARC.
547 //
548 // As a general policy we use "volatile" to control compiler-based reordering
549 // and explicit fences (barriers) to control for architectural reordering
550 // performed by the CPU(s) or platform.
551
552 struct SharedGlobals {
553 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
554 // These are highly shared mostly-read variables.
555 // To avoid false-sharing they need to be the sole occupants of a cache line.
556 volatile int stwRandom;
557 volatile int stwCycle;
558 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
559 // Hot RW variable -- Sequester to avoid false-sharing
560 volatile int hcSequence;
561 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
562 };
563
564 static SharedGlobals GVars;
565 static int MonitorScavengeThreshold = 1000000;
566 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
567
568 static markOop ReadStableMark(oop obj) {
569 markOop mark = obj->mark();
570 if (!mark->is_being_inflated()) {
571 return mark; // normal fast-path return
572 }
573
574 int its = 0;
575 for (;;) {
576 markOop mark = obj->mark();
577 if (!mark->is_being_inflated()) {
578 return mark; // normal fast-path return
579 }
580
581 // The object is being inflated by some other thread.
582 // The caller of ReadStableMark() must wait for inflation to complete.
583 // Avoid live-lock
584 // TODO: consider calling SafepointSynchronize::do_call_back() while
585 // spinning to see if there's a safepoint pending. If so, immediately
586 // yielding or blocking would be appropriate. Avoid spinning while
587 // there is a safepoint pending.
588 // TODO: add inflation contention performance counters.
589 // TODO: restrict the aggregate number of spinners.
590
591 ++its;
592 if (its > 10000 || !os::is_MP()) {
593 if (its & 1) {
594 os::naked_yield();
595 TEVENT(Inflate: INFLATING - yield);
596 } else {
597 // Note that the following code attenuates the livelock problem but is not
598 // a complete remedy. A more complete solution would require that the inflating
599 // thread hold the associated inflation lock. The following code simply restricts
600 // the number of spinners to at most one. We'll have N-2 threads blocked
601 // on the inflationlock, 1 thread holding the inflation lock and using
602 // a yield/park strategy, and 1 thread in the midst of inflation.
603 // A more refined approach would be to change the encoding of INFLATING
604 // to allow encapsulation of a native thread pointer. Threads waiting for
605 // inflation to complete would use CAS to push themselves onto a singly linked
606 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
607 // and calling park(). When inflation was complete the thread that accomplished inflation
608 // would detach the list and set the markword to inflated with a single CAS and
609 // then for each thread on the list, set the flag and unpark() the thread.
610 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
611 // wakes at most one thread whereas we need to wake the entire list.
612 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
613 int YieldThenBlock = 0;
614 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
615 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
616 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
617 while (obj->mark() == markOopDesc::INFLATING()) {
618 // Beware: NakedYield() is advisory and has almost no effect on some platforms
619 // so we periodically call Self->_ParkEvent->park(1).
620 // We use a mixed spin/yield/block mechanism.
621 if ((YieldThenBlock++) >= 16) {
622 Thread::current()->_ParkEvent->park(1);
623 } else {
624 os::naked_yield();
625 }
626 }
627 Thread::muxRelease(gInflationLocks + ix);
628 TEVENT(Inflate: INFLATING - yield/park);
629 }
630 } else {
631 SpinPause(); // SMP-polite spinning
632 }
633 }
634 }
635
636 // hashCode() generation :
637 //
638 // Possibilities:
639 // * MD5Digest of {obj,stwRandom}
640 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
641 // * A DES- or AES-style SBox[] mechanism
642 // * One of the Phi-based schemes, such as:
643 // 2654435761 = 2^32 * Phi (golden ratio)
644 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
645 // * A variation of Marsaglia's shift-xor RNG scheme.
646 // * (obj ^ stwRandom) is appealing, but can result
647 // in undesirable regularity in the hashCode values of adjacent objects
648 // (objects allocated back-to-back, in particular). This could potentially
649 // result in hashtable collisions and reduced hashtable efficiency.
650 // There are simple ways to "diffuse" the middle address bits over the
651 // generated hashCode values:
652
653 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
654 intptr_t value = 0;
655 if (hashCode == 0) {
656 // This form uses an unguarded global Park-Miller RNG,
657 // so it's possible for two threads to race and generate the same RNG.
658 // On MP system we'll have lots of RW access to a global, so the
659 // mechanism induces lots of coherency traffic.
660 value = os::random();
661 } else if (hashCode == 1) {
662 // This variation has the property of being stable (idempotent)
663 // between STW operations. This can be useful in some of the 1-0
664 // synchronization schemes.
665 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
666 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
667 } else if (hashCode == 2) {
668 value = 1; // for sensitivity testing
669 } else if (hashCode == 3) {
670 value = ++GVars.hcSequence;
671 } else if (hashCode == 4) {
672 value = cast_from_oop<intptr_t>(obj);
673 } else {
674 // Marsaglia's xor-shift scheme with thread-specific state
675 // This is probably the best overall implementation -- we'll
676 // likely make this the default in future releases.
677 unsigned t = Self->_hashStateX;
678 t ^= (t << 11);
679 Self->_hashStateX = Self->_hashStateY;
680 Self->_hashStateY = Self->_hashStateZ;
681 Self->_hashStateZ = Self->_hashStateW;
682 unsigned v = Self->_hashStateW;
683 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
684 Self->_hashStateW = v;
685 value = v;
686 }
687
688 value &= markOopDesc::hash_mask;
689 if (value == 0) value = 0xBAD;
690 assert(value != markOopDesc::no_hash, "invariant");
691 TEVENT(hashCode: GENERATE);
692 return value;
693 }
694
695 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
696 if (UseBiasedLocking) {
697 // NOTE: many places throughout the JVM do not expect a safepoint
698 // to be taken here, in particular most operations on perm gen
699 // objects. However, we only ever bias Java instances and all of
700 // the call sites of identity_hash that might revoke biases have
701 // been checked to make sure they can handle a safepoint. The
702 // added check of the bias pattern is to avoid useless calls to
703 // thread-local storage.
704 if (obj->mark()->has_bias_pattern()) {
705 // Handle for oop obj in case of STW safepoint
706 Handle hobj(Self, obj);
707 // Relaxing assertion for bug 6320749.
708 assert(Universe::verify_in_progress() ||
709 !SafepointSynchronize::is_at_safepoint(),
710 "biases should not be seen by VM thread here");
711 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
712 obj = hobj();
713 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
714 }
715 }
716
717 // hashCode() is a heap mutator ...
718 // Relaxing assertion for bug 6320749.
719 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
720 !SafepointSynchronize::is_at_safepoint(), "invariant");
721 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
722 Self->is_Java_thread() , "invariant");
723 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
724 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
725
726 ObjectMonitor* monitor = NULL;
727 markOop temp, test;
728 intptr_t hash;
729 markOop mark = ReadStableMark(obj);
730
731 // object should remain ineligible for biased locking
732 assert(!mark->has_bias_pattern(), "invariant");
733
734 if (mark->is_neutral()) {
735 hash = mark->hash(); // this is a normal header
736 if (hash) { // if it has hash, just return it
737 return hash;
738 }
739 hash = get_next_hash(Self, obj); // allocate a new hash code
740 temp = mark->copy_set_hash(hash); // merge the hash code into header
741 // use (machine word version) atomic operation to install the hash
742 test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark);
743 if (test == mark) {
744 return hash;
745 }
746 // If atomic operation failed, we must inflate the header
747 // into heavy weight monitor. We could add more code here
748 // for fast path, but it does not worth the complexity.
749 } else if (mark->has_monitor()) {
750 monitor = mark->monitor();
751 temp = monitor->header();
752 assert(temp->is_neutral(), "invariant");
753 hash = temp->hash();
754 if (hash) {
755 return hash;
756 }
757 // Skip to the following code to reduce code size
758 } else if (Self->is_lock_owned((address)mark->locker())) {
759 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
760 assert(temp->is_neutral(), "invariant");
761 hash = temp->hash(); // by current thread, check if the displaced
762 if (hash) { // header contains hash code
763 return hash;
764 }
765 // WARNING:
766 // The displaced header is strictly immutable.
767 // It can NOT be changed in ANY cases. So we have
768 // to inflate the header into heavyweight monitor
769 // even the current thread owns the lock. The reason
770 // is the BasicLock (stack slot) will be asynchronously
771 // read by other threads during the inflate() function.
772 // Any change to stack may not propagate to other threads
773 // correctly.
774 }
775
776 // Inflate the monitor to set hash code
777 monitor = ObjectSynchronizer::inflate(Self, obj, inflate_cause_hash_code);
778 // Load displaced header and check it has hash code
779 mark = monitor->header();
780 assert(mark->is_neutral(), "invariant");
781 hash = mark->hash();
782 if (hash == 0) {
783 hash = get_next_hash(Self, obj);
784 temp = mark->copy_set_hash(hash); // merge hash code into header
785 assert(temp->is_neutral(), "invariant");
786 test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark);
787 if (test != mark) {
788 // The only update to the header in the monitor (outside GC)
789 // is install the hash code. If someone add new usage of
790 // displaced header, please update this code
791 hash = test->hash();
792 assert(test->is_neutral(), "invariant");
793 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
794 }
795 }
796 // We finally get the hash
797 return hash;
798 }
799
800 // Deprecated -- use FastHashCode() instead.
801
802 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
803 return FastHashCode(Thread::current(), obj());
804 }
805
806
807 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
808 Handle h_obj) {
809 if (UseBiasedLocking) {
810 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
811 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
812 }
813
814 assert(thread == JavaThread::current(), "Can only be called on current thread");
815 oop obj = h_obj();
816
817 markOop mark = ReadStableMark(obj);
818
819 // Uncontended case, header points to stack
820 if (mark->has_locker()) {
821 return thread->is_lock_owned((address)mark->locker());
822 }
823 // Contended case, header points to ObjectMonitor (tagged pointer)
824 if (mark->has_monitor()) {
825 ObjectMonitor* monitor = mark->monitor();
826 return monitor->is_entered(thread) != 0;
827 }
828 // Unlocked case, header in place
829 assert(mark->is_neutral(), "sanity check");
830 return false;
831 }
832
833 // Be aware of this method could revoke bias of the lock object.
834 // This method queries the ownership of the lock handle specified by 'h_obj'.
835 // If the current thread owns the lock, it returns owner_self. If no
836 // thread owns the lock, it returns owner_none. Otherwise, it will return
837 // owner_other.
838 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
839 (JavaThread *self, Handle h_obj) {
840 // The caller must beware this method can revoke bias, and
841 // revocation can result in a safepoint.
842 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
843 assert(self->thread_state() != _thread_blocked, "invariant");
844
845 // Possible mark states: neutral, biased, stack-locked, inflated
846
847 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
848 // CASE: biased
849 BiasedLocking::revoke_and_rebias(h_obj, false, self);
850 assert(!h_obj->mark()->has_bias_pattern(),
851 "biases should be revoked by now");
852 }
853
854 assert(self == JavaThread::current(), "Can only be called on current thread");
855 oop obj = h_obj();
856 markOop mark = ReadStableMark(obj);
857
858 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
859 if (mark->has_locker()) {
860 return self->is_lock_owned((address)mark->locker()) ?
861 owner_self : owner_other;
862 }
863
864 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
865 // The Object:ObjectMonitor relationship is stable as long as we're
866 // not at a safepoint.
867 if (mark->has_monitor()) {
868 void * owner = mark->monitor()->_owner;
869 if (owner == NULL) return owner_none;
870 return (owner == self ||
871 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
872 }
873
874 // CASE: neutral
875 assert(mark->is_neutral(), "sanity check");
876 return owner_none; // it's unlocked
877 }
878
879 // FIXME: jvmti should call this
880 JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) {
881 if (UseBiasedLocking) {
882 if (SafepointSynchronize::is_at_safepoint()) {
883 BiasedLocking::revoke_at_safepoint(h_obj);
884 } else {
885 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
886 }
887 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
888 }
889
890 oop obj = h_obj();
891 address owner = NULL;
892
893 markOop mark = ReadStableMark(obj);
894
895 // Uncontended case, header points to stack
896 if (mark->has_locker()) {
897 owner = (address) mark->locker();
898 }
899
900 // Contended case, header points to ObjectMonitor (tagged pointer)
901 if (mark->has_monitor()) {
902 ObjectMonitor* monitor = mark->monitor();
903 assert(monitor != NULL, "monitor should be non-null");
904 owner = (address) monitor->owner();
905 }
906
907 if (owner != NULL) {
908 // owning_thread_from_monitor_owner() may also return NULL here
909 return Threads::owning_thread_from_monitor_owner(owner, doLock);
910 }
911
912 // Unlocked case, header in place
913 // Cannot have assertion since this object may have been
914 // locked by another thread when reaching here.
915 // assert(mark->is_neutral(), "sanity check");
916
917 return NULL;
918 }
919
920 // Visitors ...
921
922 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
923 PaddedEnd<ObjectMonitor> * block =
924 (PaddedEnd<ObjectMonitor> *)OrderAccess::load_ptr_acquire(&gBlockList);
925 while (block != NULL) {
926 assert(block->object() == CHAINMARKER, "must be a block header");
927 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
928 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
929 oop object = (oop)mid->object();
930 if (object != NULL) {
931 closure->do_monitor(mid);
932 }
933 }
934 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
935 }
936 }
937
938 // Get the next block in the block list.
939 static inline ObjectMonitor* next(ObjectMonitor* block) {
940 assert(block->object() == CHAINMARKER, "must be a block header");
941 block = block->FreeNext;
942 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
943 return block;
944 }
945
946
947 void ObjectSynchronizer::oops_do(OopClosure* f) {
948 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
949 PaddedEnd<ObjectMonitor> * block =
950 (PaddedEnd<ObjectMonitor> *)OrderAccess::load_ptr_acquire(&gBlockList);
951 for (; block != NULL; block = (PaddedEnd<ObjectMonitor> *)next(block)) {
952 assert(block->object() == CHAINMARKER, "must be a block header");
953 for (int i = 1; i < _BLOCKSIZE; i++) {
954 ObjectMonitor* mid = (ObjectMonitor *)&block[i];
955 if (mid->object() != NULL) {
956 f->do_oop((oop*)mid->object_addr());
957 }
958 }
959 }
960 }
961
962
963 // -----------------------------------------------------------------------------
964 // ObjectMonitor Lifecycle
965 // -----------------------
966 // Inflation unlinks monitors from the global gFreeList and
967 // associates them with objects. Deflation -- which occurs at
968 // STW-time -- disassociates idle monitors from objects. Such
969 // scavenged monitors are returned to the gFreeList.
970 //
971 // The global list is protected by gListLock. All the critical sections
972 // are short and operate in constant-time.
973 //
974 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
975 //
976 // Lifecycle:
977 // -- unassigned and on the global free list
978 // -- unassigned and on a thread's private omFreeList
979 // -- assigned to an object. The object is inflated and the mark refers
980 // to the objectmonitor.
981
982
983 // Constraining monitor pool growth via MonitorBound ...
984 //
985 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
986 // the rate of scavenging is driven primarily by GC. As such, we can find
987 // an inordinate number of monitors in circulation.
988 // To avoid that scenario we can artificially induce a STW safepoint
989 // if the pool appears to be growing past some reasonable bound.
990 // Generally we favor time in space-time tradeoffs, but as there's no
991 // natural back-pressure on the # of extant monitors we need to impose some
992 // type of limit. Beware that if MonitorBound is set to too low a value
993 // we could just loop. In addition, if MonitorBound is set to a low value
994 // we'll incur more safepoints, which are harmful to performance.
995 // See also: GuaranteedSafepointInterval
996 //
997 // The current implementation uses asynchronous VM operations.
998
999 static void InduceScavenge(Thread * Self, const char * Whence) {
1000 // Induce STW safepoint to trim monitors
1001 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1002 // More precisely, trigger an asynchronous STW safepoint as the number
1003 // of active monitors passes the specified threshold.
1004 // TODO: assert thread state is reasonable
1005
1006 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1007 if (ObjectMonitor::Knob_Verbose) {
1008 tty->print_cr("INFO: Monitor scavenge - Induced STW @%s (%d)",
1009 Whence, ForceMonitorScavenge) ;
1010 tty->flush();
1011 }
1012 // Induce a 'null' safepoint to scavenge monitors
1013 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1014 // to the VMthread and have a lifespan longer than that of this activation record.
1015 // The VMThread will delete the op when completed.
1016 VMThread::execute(new VM_ForceAsyncSafepoint());
1017
1018 if (ObjectMonitor::Knob_Verbose) {
1019 tty->print_cr("INFO: Monitor scavenge - STW posted @%s (%d)",
1020 Whence, ForceMonitorScavenge) ;
1021 tty->flush();
1022 }
1023 }
1024 }
1025
1026 void ObjectSynchronizer::verifyInUse(Thread *Self) {
1027 ObjectMonitor* mid;
1028 int in_use_tally = 0;
1029 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) {
1030 in_use_tally++;
1031 }
1032 assert(in_use_tally == Self->omInUseCount, "in-use count off");
1033
1034 int free_tally = 0;
1035 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) {
1036 free_tally++;
1037 }
1038 assert(free_tally == Self->omFreeCount, "free count off");
1039 }
1040
1041 ObjectMonitor * NOINLINE ObjectSynchronizer::omAlloc(Thread * Self) {
1042 // A large MAXPRIVATE value reduces both list lock contention
1043 // and list coherency traffic, but also tends to increase the
1044 // number of objectMonitors in circulation as well as the STW
1045 // scavenge costs. As usual, we lean toward time in space-time
1046 // tradeoffs.
1047 const int MAXPRIVATE = 1024;
1048 for (;;) {
1049 ObjectMonitor * m;
1050
1051 // 1: try to allocate from the thread's local omFreeList.
1052 // Threads will attempt to allocate first from their local list, then
1053 // from the global list, and only after those attempts fail will the thread
1054 // attempt to instantiate new monitors. Thread-local free lists take
1055 // heat off the gListLock and improve allocation latency, as well as reducing
1056 // coherency traffic on the shared global list.
1057 m = Self->omFreeList;
1058 if (m != NULL) {
1059 Self->omFreeList = m->FreeNext;
1060 Self->omFreeCount--;
1061 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene
1062 guarantee(m->object() == NULL, "invariant");
1063 if (MonitorInUseLists) {
1064 m->FreeNext = Self->omInUseList;
1065 Self->omInUseList = m;
1066 Self->omInUseCount++;
1067 if (ObjectMonitor::Knob_VerifyInUse) {
1068 verifyInUse(Self);
1069 }
1070 } else {
1071 m->FreeNext = NULL;
1072 }
1073 return m;
1074 }
1075
1076 // 2: try to allocate from the global gFreeList
1077 // CONSIDER: use muxTry() instead of muxAcquire().
1078 // If the muxTry() fails then drop immediately into case 3.
1079 // If we're using thread-local free lists then try
1080 // to reprovision the caller's free list.
1081 if (gFreeList != NULL) {
1082 // Reprovision the thread's omFreeList.
1083 // Use bulk transfers to reduce the allocation rate and heat
1084 // on various locks.
1085 Thread::muxAcquire(&gListLock, "omAlloc");
1086 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1087 gMonitorFreeCount--;
1088 ObjectMonitor * take = gFreeList;
1089 gFreeList = take->FreeNext;
1090 guarantee(take->object() == NULL, "invariant");
1091 guarantee(!take->is_busy(), "invariant");
1092 take->Recycle();
1093 omRelease(Self, take, false);
1094 }
1095 Thread::muxRelease(&gListLock);
1096 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1097 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1098 TEVENT(omFirst - reprovision);
1099
1100 const int mx = MonitorBound;
1101 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1102 // We can't safely induce a STW safepoint from omAlloc() as our thread
1103 // state may not be appropriate for such activities and callers may hold
1104 // naked oops, so instead we defer the action.
1105 InduceScavenge(Self, "omAlloc");
1106 }
1107 continue;
1108 }
1109
1110 // 3: allocate a block of new ObjectMonitors
1111 // Both the local and global free lists are empty -- resort to malloc().
1112 // In the current implementation objectMonitors are TSM - immortal.
1113 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1114 // each ObjectMonitor to start at the beginning of a cache line,
1115 // so we use align_size_up().
1116 // A better solution would be to use C++ placement-new.
1117 // BEWARE: As it stands currently, we don't run the ctors!
1118 assert(_BLOCKSIZE > 1, "invariant");
1119 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
1120 PaddedEnd<ObjectMonitor> * temp;
1121 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1122 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
1123 mtInternal);
1124 temp = (PaddedEnd<ObjectMonitor> *)
1125 align_size_up((intptr_t)real_malloc_addr,
1126 DEFAULT_CACHE_LINE_SIZE);
1127
1128 // NOTE: (almost) no way to recover if allocation failed.
1129 // We might be able to induce a STW safepoint and scavenge enough
1130 // objectMonitors to permit progress.
1131 if (temp == NULL) {
1132 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1133 "Allocate ObjectMonitors");
1134 }
1135 (void)memset((void *) temp, 0, neededsize);
1136
1137 // Format the block.
1138 // initialize the linked list, each monitor points to its next
1139 // forming the single linked free list, the very first monitor
1140 // will points to next block, which forms the block list.
1141 // The trick of using the 1st element in the block as gBlockList
1142 // linkage should be reconsidered. A better implementation would
1143 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1144
1145 for (int i = 1; i < _BLOCKSIZE; i++) {
1146 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1147 }
1148
1149 // terminate the last monitor as the end of list
1150 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1151
1152 // Element [0] is reserved for global list linkage
1153 temp[0].set_object(CHAINMARKER);
1154
1155 // Consider carving out this thread's current request from the
1156 // block in hand. This avoids some lock traffic and redundant
1157 // list activity.
1158
1159 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1160 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1161 Thread::muxAcquire(&gListLock, "omAlloc [2]");
1162 gMonitorPopulation += _BLOCKSIZE-1;
1163 gMonitorFreeCount += _BLOCKSIZE-1;
1164
1165 // Add the new block to the list of extant blocks (gBlockList).
1166 // The very first objectMonitor in a block is reserved and dedicated.
1167 // It serves as blocklist "next" linkage.
1168 temp[0].FreeNext = gBlockList;
1169 // There are lock-free uses of gBlockList so make sure that
1170 // the previous stores happen before we update gBlockList.
1171 OrderAccess::release_store_ptr(&gBlockList, temp);
1172
1173 // Add the new string of objectMonitors to the global free list
1174 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1175 gFreeList = temp + 1;
1176 Thread::muxRelease(&gListLock);
1177 TEVENT(Allocate block of monitors);
1178 }
1179 }
1180
1181 // Place "m" on the caller's private per-thread omFreeList.
1182 // In practice there's no need to clamp or limit the number of
1183 // monitors on a thread's omFreeList as the only time we'll call
1184 // omRelease is to return a monitor to the free list after a CAS
1185 // attempt failed. This doesn't allow unbounded #s of monitors to
1186 // accumulate on a thread's free list.
1187 //
1188 // Key constraint: all ObjectMonitors on a thread's free list and the global
1189 // free list must have their object field set to null. This prevents the
1190 // scavenger -- deflate_idle_monitors -- from reclaiming them.
1191
1192 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1193 bool fromPerThreadAlloc) {
1194 guarantee(m->object() == NULL, "invariant");
1195 guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor");
1196 // Remove from omInUseList
1197 if (MonitorInUseLists && fromPerThreadAlloc) {
1198 ObjectMonitor* cur_mid_in_use = NULL;
1199 bool extracted = false;
1200 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1201 if (m == mid) {
1202 // extract from per-thread in-use list
1203 if (mid == Self->omInUseList) {
1204 Self->omInUseList = mid->FreeNext;
1205 } else if (cur_mid_in_use != NULL) {
1206 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1207 }
1208 extracted = true;
1209 Self->omInUseCount--;
1210 if (ObjectMonitor::Knob_VerifyInUse) {
1211 verifyInUse(Self);
1212 }
1213 break;
1214 }
1215 }
1216 assert(extracted, "Should have extracted from in-use list");
1217 }
1218
1219 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1220 m->FreeNext = Self->omFreeList;
1221 Self->omFreeList = m;
1222 Self->omFreeCount++;
1223 }
1224
1225 // Return the monitors of a moribund thread's local free list to
1226 // the global free list. Typically a thread calls omFlush() when
1227 // it's dying. We could also consider having the VM thread steal
1228 // monitors from threads that have not run java code over a few
1229 // consecutive STW safepoints. Relatedly, we might decay
1230 // omFreeProvision at STW safepoints.
1231 //
1232 // Also return the monitors of a moribund thread's omInUseList to
1233 // a global gOmInUseList under the global list lock so these
1234 // will continue to be scanned.
1235 //
1236 // We currently call omFlush() from the Thread:: dtor _after the thread
1237 // has been excised from the thread list and is no longer a mutator.
1238 // That means that omFlush() can run concurrently with a safepoint and
1239 // the scavenge operator. Calling omFlush() from JavaThread::exit() might
1240 // be a better choice as we could safely reason that that the JVM is
1241 // not at a safepoint at the time of the call, and thus there could
1242 // be not inopportune interleavings between omFlush() and the scavenge
1243 // operator.
1244
1245 void ObjectSynchronizer::omFlush(Thread * Self) {
1246 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1247 Self->omFreeList = NULL;
1248 ObjectMonitor * tail = NULL;
1249 int tally = 0;
1250 if (list != NULL) {
1251 ObjectMonitor * s;
1252 // The thread is going away, the per-thread free monitors
1253 // are freed via set_owner(NULL)
1254 // Link them to tail, which will be linked into the global free list
1255 // gFreeList below, under the gListLock
1256 for (s = list; s != NULL; s = s->FreeNext) {
1257 tally++;
1258 tail = s;
1259 guarantee(s->object() == NULL, "invariant");
1260 guarantee(!s->is_busy(), "invariant");
1261 s->set_owner(NULL); // redundant but good hygiene
1262 TEVENT(omFlush - Move one);
1263 }
1264 guarantee(tail != NULL && list != NULL, "invariant");
1265 }
1266
1267 ObjectMonitor * inUseList = Self->omInUseList;
1268 ObjectMonitor * inUseTail = NULL;
1269 int inUseTally = 0;
1270 if (inUseList != NULL) {
1271 Self->omInUseList = NULL;
1272 ObjectMonitor *cur_om;
1273 // The thread is going away, however the omInUseList inflated
1274 // monitors may still be in-use by other threads.
1275 // Link them to inUseTail, which will be linked into the global in-use list
1276 // gOmInUseList below, under the gListLock
1277 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1278 inUseTail = cur_om;
1279 inUseTally++;
1280 }
1281 assert(Self->omInUseCount == inUseTally, "in-use count off");
1282 Self->omInUseCount = 0;
1283 guarantee(inUseTail != NULL && inUseList != NULL, "invariant");
1284 }
1285
1286 Thread::muxAcquire(&gListLock, "omFlush");
1287 if (tail != NULL) {
1288 tail->FreeNext = gFreeList;
1289 gFreeList = list;
1290 gMonitorFreeCount += tally;
1291 }
1292
1293 if (inUseTail != NULL) {
1294 inUseTail->FreeNext = gOmInUseList;
1295 gOmInUseList = inUseList;
1296 gOmInUseCount += inUseTally;
1297 }
1298
1299 Thread::muxRelease(&gListLock);
1300 TEVENT(omFlush);
1301 }
1302
1303 // Fast path code shared by multiple functions
1304 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1305 markOop mark = obj->mark();
1306 if (mark->has_monitor()) {
1307 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1308 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1309 return mark->monitor();
1310 }
1311 return ObjectSynchronizer::inflate(Thread::current(),
1312 obj,
1313 inflate_cause_vm_internal);
1314 }
1315
1316 ObjectMonitor * NOINLINE ObjectSynchronizer::inflate(Thread * Self,
1317 oop object,
1318 const InflateCause cause) {
1319
1320 // Inflate mutates the heap ...
1321 // Relaxing assertion for bug 6320749.
1322 assert(Universe::verify_in_progress() ||
1323 !SafepointSynchronize::is_at_safepoint(), "invariant");
1324
1325 EventJavaMonitorInflate event;
1326
1327 for (;;) {
1328 const markOop mark = object->mark();
1329 assert(!mark->has_bias_pattern(), "invariant");
1330
1331 // The mark can be in one of the following states:
1332 // * Inflated - just return
1333 // * Stack-locked - coerce it to inflated
1334 // * INFLATING - busy wait for conversion to complete
1335 // * Neutral - aggressively inflate the object.
1336 // * BIASED - Illegal. We should never see this
1337
1338 // CASE: inflated
1339 if (mark->has_monitor()) {
1340 ObjectMonitor * inf = mark->monitor();
1341 assert(inf->header()->is_neutral(), "invariant");
1342 assert(inf->object() == object, "invariant");
1343 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1344 event.cancel(); // let's not post an inflation event, unless we did the deed ourselves
1345 return inf;
1346 }
1347
1348 // CASE: inflation in progress - inflating over a stack-lock.
1349 // Some other thread is converting from stack-locked to inflated.
1350 // Only that thread can complete inflation -- other threads must wait.
1351 // The INFLATING value is transient.
1352 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1353 // We could always eliminate polling by parking the thread on some auxiliary list.
1354 if (mark == markOopDesc::INFLATING()) {
1355 TEVENT(Inflate: spin while INFLATING);
1356 ReadStableMark(object);
1357 continue;
1358 }
1359
1360 // CASE: stack-locked
1361 // Could be stack-locked either by this thread or by some other thread.
1362 //
1363 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1364 // to install INFLATING into the mark word. We originally installed INFLATING,
1365 // allocated the objectmonitor, and then finally STed the address of the
1366 // objectmonitor into the mark. This was correct, but artificially lengthened
1367 // the interval in which INFLATED appeared in the mark, thus increasing
1368 // the odds of inflation contention.
1369 //
1370 // We now use per-thread private objectmonitor free lists.
1371 // These list are reprovisioned from the global free list outside the
1372 // critical INFLATING...ST interval. A thread can transfer
1373 // multiple objectmonitors en-mass from the global free list to its local free list.
1374 // This reduces coherency traffic and lock contention on the global free list.
1375 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1376 // before or after the CAS(INFLATING) operation.
1377 // See the comments in omAlloc().
1378
1379 if (mark->has_locker()) {
1380 ObjectMonitor * m = omAlloc(Self);
1381 // Optimistically prepare the objectmonitor - anticipate successful CAS
1382 // We do this before the CAS in order to minimize the length of time
1383 // in which INFLATING appears in the mark.
1384 m->Recycle();
1385 m->_Responsible = NULL;
1386 m->_recursions = 0;
1387 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1388
1389 markOop cmp = (markOop) Atomic::cmpxchg_ptr(markOopDesc::INFLATING(), object->mark_addr(), mark);
1390 if (cmp != mark) {
1391 omRelease(Self, m, true);
1392 continue; // Interference -- just retry
1393 }
1394
1395 // We've successfully installed INFLATING (0) into the mark-word.
1396 // This is the only case where 0 will appear in a mark-word.
1397 // Only the singular thread that successfully swings the mark-word
1398 // to 0 can perform (or more precisely, complete) inflation.
1399 //
1400 // Why do we CAS a 0 into the mark-word instead of just CASing the
1401 // mark-word from the stack-locked value directly to the new inflated state?
1402 // Consider what happens when a thread unlocks a stack-locked object.
1403 // It attempts to use CAS to swing the displaced header value from the
1404 // on-stack basiclock back into the object header. Recall also that the
1405 // header value (hashcode, etc) can reside in (a) the object header, or
1406 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1407 // header in an objectMonitor. The inflate() routine must copy the header
1408 // value from the basiclock on the owner's stack to the objectMonitor, all
1409 // the while preserving the hashCode stability invariants. If the owner
1410 // decides to release the lock while the value is 0, the unlock will fail
1411 // and control will eventually pass from slow_exit() to inflate. The owner
1412 // will then spin, waiting for the 0 value to disappear. Put another way,
1413 // the 0 causes the owner to stall if the owner happens to try to
1414 // drop the lock (restoring the header from the basiclock to the object)
1415 // while inflation is in-progress. This protocol avoids races that might
1416 // would otherwise permit hashCode values to change or "flicker" for an object.
1417 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1418 // 0 serves as a "BUSY" inflate-in-progress indicator.
1419
1420
1421 // fetch the displaced mark from the owner's stack.
1422 // The owner can't die or unwind past the lock while our INFLATING
1423 // object is in the mark. Furthermore the owner can't complete
1424 // an unlock on the object, either.
1425 markOop dmw = mark->displaced_mark_helper();
1426 assert(dmw->is_neutral(), "invariant");
1427
1428 // Setup monitor fields to proper values -- prepare the monitor
1429 m->set_header(dmw);
1430
1431 // Optimization: if the mark->locker stack address is associated
1432 // with this thread we could simply set m->_owner = Self.
1433 // Note that a thread can inflate an object
1434 // that it has stack-locked -- as might happen in wait() -- directly
1435 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1436 m->set_owner(mark->locker());
1437 m->set_object(object);
1438 // TODO-FIXME: assert BasicLock->dhw != 0.
1439
1440 // Must preserve store ordering. The monitor state must
1441 // be stable at the time of publishing the monitor address.
1442 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1443 object->release_set_mark(markOopDesc::encode(m));
1444
1445 // Hopefully the performance counters are allocated on distinct cache lines
1446 // to avoid false sharing on MP systems ...
1447 OM_PERFDATA_OP(Inflations, inc());
1448 TEVENT(Inflate: overwrite stacklock);
1449 if (log_is_enabled(Debug, monitorinflation)) {
1450 if (object->is_instance()) {
1451 ResourceMark rm;
1452 log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1453 p2i(object), p2i(object->mark()),
1454 object->klass()->external_name());
1455 }
1456 }
1457 if (event.should_commit()) {
1458 post_monitor_inflate_event(event, object, cause);
1459 }
1460 return m;
1461 }
1462
1463 // CASE: neutral
1464 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1465 // If we know we're inflating for entry it's better to inflate by swinging a
1466 // pre-locked objectMonitor pointer into the object header. A successful
1467 // CAS inflates the object *and* confers ownership to the inflating thread.
1468 // In the current implementation we use a 2-step mechanism where we CAS()
1469 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1470 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1471 // would be useful.
1472
1473 assert(mark->is_neutral(), "invariant");
1474 ObjectMonitor * m = omAlloc(Self);
1475 // prepare m for installation - set monitor to initial state
1476 m->Recycle();
1477 m->set_header(mark);
1478 m->set_owner(NULL);
1479 m->set_object(object);
1480 m->_recursions = 0;
1481 m->_Responsible = NULL;
1482 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1483
1484 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) {
1485 m->set_object(NULL);
1486 m->set_owner(NULL);
1487 m->Recycle();
1488 omRelease(Self, m, true);
1489 m = NULL;
1490 continue;
1491 // interference - the markword changed - just retry.
1492 // The state-transitions are one-way, so there's no chance of
1493 // live-lock -- "Inflated" is an absorbing state.
1494 }
1495
1496 // Hopefully the performance counters are allocated on distinct
1497 // cache lines to avoid false sharing on MP systems ...
1498 OM_PERFDATA_OP(Inflations, inc());
1499 TEVENT(Inflate: overwrite neutral);
1500 if (log_is_enabled(Debug, monitorinflation)) {
1501 if (object->is_instance()) {
1502 ResourceMark rm;
1503 log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1504 p2i(object), p2i(object->mark()),
1505 object->klass()->external_name());
1506 }
1507 }
1508 if (event.should_commit()) {
1509 post_monitor_inflate_event(event, object, cause);
1510 }
1511 return m;
1512 }
1513 }
1514
1515
1516 // Deflate_idle_monitors() is called at all safepoints, immediately
1517 // after all mutators are stopped, but before any objects have moved.
1518 // It traverses the list of known monitors, deflating where possible.
1519 // The scavenged monitor are returned to the monitor free list.
1520 //
1521 // Beware that we scavenge at *every* stop-the-world point.
1522 // Having a large number of monitors in-circulation negatively
1523 // impacts the performance of some applications (e.g., PointBase).
1524 // Broadly, we want to minimize the # of monitors in circulation.
1525 //
1526 // We have added a flag, MonitorInUseLists, which creates a list
1527 // of active monitors for each thread. deflate_idle_monitors()
1528 // only scans the per-thread in-use lists. omAlloc() puts all
1529 // assigned monitors on the per-thread list. deflate_idle_monitors()
1530 // returns the non-busy monitors to the global free list.
1531 // When a thread dies, omFlush() adds the list of active monitors for
1532 // that thread to a global gOmInUseList acquiring the
1533 // global list lock. deflate_idle_monitors() acquires the global
1534 // list lock to scan for non-busy monitors to the global free list.
1535 // An alternative could have used a single global in-use list. The
1536 // downside would have been the additional cost of acquiring the global list lock
1537 // for every omAlloc().
1538 //
1539 // Perversely, the heap size -- and thus the STW safepoint rate --
1540 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1541 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1542 // This is an unfortunate aspect of this design.
1543
1544 enum ManifestConstants {
1545 ClearResponsibleAtSTW = 0
1546 };
1547
1548 // Deflate a single monitor if not in-use
1549 // Return true if deflated, false if in-use
1550 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1551 ObjectMonitor** freeHeadp,
1552 ObjectMonitor** freeTailp) {
1553 bool deflated;
1554 // Normal case ... The monitor is associated with obj.
1555 guarantee(obj->mark() == markOopDesc::encode(mid), "invariant");
1556 guarantee(mid == obj->mark()->monitor(), "invariant");
1557 guarantee(mid->header()->is_neutral(), "invariant");
1558
1559 if (mid->is_busy()) {
1560 if (ClearResponsibleAtSTW) mid->_Responsible = NULL;
1561 deflated = false;
1562 } else {
1563 // Deflate the monitor if it is no longer being used
1564 // It's idle - scavenge and return to the global free list
1565 // plain old deflation ...
1566 TEVENT(deflate_idle_monitors - scavenge1);
1567 if (log_is_enabled(Debug, monitorinflation)) {
1568 if (obj->is_instance()) {
1569 ResourceMark rm;
1570 log_debug(monitorinflation)("Deflating object " INTPTR_FORMAT " , "
1571 "mark " INTPTR_FORMAT " , type %s",
1572 p2i(obj), p2i(obj->mark()),
1573 obj->klass()->external_name());
1574 }
1575 }
1576
1577 // Restore the header back to obj
1578 obj->release_set_mark(mid->header());
1579 mid->clear();
1580
1581 assert(mid->object() == NULL, "invariant");
1582
1583 // Move the object to the working free list defined by freeHeadp, freeTailp
1584 if (*freeHeadp == NULL) *freeHeadp = mid;
1585 if (*freeTailp != NULL) {
1586 ObjectMonitor * prevtail = *freeTailp;
1587 assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1588 prevtail->FreeNext = mid;
1589 }
1590 *freeTailp = mid;
1591 deflated = true;
1592 }
1593 return deflated;
1594 }
1595
1596 // Walk a given monitor list, and deflate idle monitors
1597 // The given list could be a per-thread list or a global list
1598 // Caller acquires gListLock
1599 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1600 ObjectMonitor** freeHeadp,
1601 ObjectMonitor** freeTailp) {
1602 ObjectMonitor* mid;
1603 ObjectMonitor* next;
1604 ObjectMonitor* cur_mid_in_use = NULL;
1605 int deflated_count = 0;
1606
1607 for (mid = *listHeadp; mid != NULL;) {
1608 oop obj = (oop) mid->object();
1609 if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1610 // if deflate_monitor succeeded,
1611 // extract from per-thread in-use list
1612 if (mid == *listHeadp) {
1613 *listHeadp = mid->FreeNext;
1614 } else if (cur_mid_in_use != NULL) {
1615 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1616 }
1617 next = mid->FreeNext;
1618 mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list
1619 mid = next;
1620 deflated_count++;
1621 } else {
1622 cur_mid_in_use = mid;
1623 mid = mid->FreeNext;
1624 }
1625 }
1626 return deflated_count;
1627 }
1628
1629 void ObjectSynchronizer::deflate_idle_monitors() {
1630 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1631 int nInuse = 0; // currently associated with objects
1632 int nInCirculation = 0; // extant
1633 int nScavenged = 0; // reclaimed
1634 bool deflated = false;
1635
1636 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1637 ObjectMonitor * freeTailp = NULL;
1638
1639 TEVENT(deflate_idle_monitors);
1640 // Prevent omFlush from changing mids in Thread dtor's during deflation
1641 // And in case the vm thread is acquiring a lock during a safepoint
1642 // See e.g. 6320749
1643 Thread::muxAcquire(&gListLock, "scavenge - return");
1644
1645 if (MonitorInUseLists) {
1646 int inUse = 0;
1647 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) {
1648 nInCirculation+= cur->omInUseCount;
1649 int deflated_count = deflate_monitor_list(cur->omInUseList_addr(), &freeHeadp, &freeTailp);
1650 cur->omInUseCount-= deflated_count;
1651 if (ObjectMonitor::Knob_VerifyInUse) {
1652 verifyInUse(cur);
1653 }
1654 nScavenged += deflated_count;
1655 nInuse += cur->omInUseCount;
1656 }
1657
1658 // For moribund threads, scan gOmInUseList
1659 if (gOmInUseList) {
1660 nInCirculation += gOmInUseCount;
1661 int deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
1662 gOmInUseCount-= deflated_count;
1663 nScavenged += deflated_count;
1664 nInuse += gOmInUseCount;
1665 }
1666
1667 } else {
1668 PaddedEnd<ObjectMonitor> * block =
1669 (PaddedEnd<ObjectMonitor> *)OrderAccess::load_ptr_acquire(&gBlockList);
1670 for (; block != NULL; block = (PaddedEnd<ObjectMonitor> *)next(block)) {
1671 // Iterate over all extant monitors - Scavenge all idle monitors.
1672 assert(block->object() == CHAINMARKER, "must be a block header");
1673 nInCirculation += _BLOCKSIZE;
1674 for (int i = 1; i < _BLOCKSIZE; i++) {
1675 ObjectMonitor* mid = (ObjectMonitor*)&block[i];
1676 oop obj = (oop)mid->object();
1677
1678 if (obj == NULL) {
1679 // The monitor is not associated with an object.
1680 // The monitor should either be a thread-specific private
1681 // free list or the global free list.
1682 // obj == NULL IMPLIES mid->is_busy() == 0
1683 guarantee(!mid->is_busy(), "invariant");
1684 continue;
1685 }
1686 deflated = deflate_monitor(mid, obj, &freeHeadp, &freeTailp);
1687
1688 if (deflated) {
1689 mid->FreeNext = NULL;
1690 nScavenged++;
1691 } else {
1692 nInuse++;
1693 }
1694 }
1695 }
1696 }
1697
1698 gMonitorFreeCount += nScavenged;
1699
1700 // Consider: audit gFreeList to ensure that gMonitorFreeCount and list agree.
1701
1702 if (ObjectMonitor::Knob_Verbose) {
1703 tty->print_cr("INFO: Deflate: InCirc=%d InUse=%d Scavenged=%d "
1704 "ForceMonitorScavenge=%d : pop=%d free=%d",
1705 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge,
1706 gMonitorPopulation, gMonitorFreeCount);
1707 tty->flush();
1708 }
1709
1710 ForceMonitorScavenge = 0; // Reset
1711
1712 // Move the scavenged monitors back to the global free list.
1713 if (freeHeadp != NULL) {
1714 guarantee(freeTailp != NULL && nScavenged > 0, "invariant");
1715 assert(freeTailp->FreeNext == NULL, "invariant");
1716 // constant-time list splice - prepend scavenged segment to gFreeList
1717 freeTailp->FreeNext = gFreeList;
1718 gFreeList = freeHeadp;
1719 }
1720 Thread::muxRelease(&gListLock);
1721
1722 OM_PERFDATA_OP(Deflations, inc(nScavenged));
1723 OM_PERFDATA_OP(MonExtant, set_value(nInCirculation));
1724
1725 // TODO: Add objectMonitor leak detection.
1726 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1727 GVars.stwRandom = os::random();
1728 GVars.stwCycle++;
1729 }
1730
1731 // Monitor cleanup on JavaThread::exit
1732
1733 // Iterate through monitor cache and attempt to release thread's monitors
1734 // Gives up on a particular monitor if an exception occurs, but continues
1735 // the overall iteration, swallowing the exception.
1736 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1737 private:
1738 TRAPS;
1739
1740 public:
1741 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1742 void do_monitor(ObjectMonitor* mid) {
1743 if (mid->owner() == THREAD) {
1744 if (ObjectMonitor::Knob_VerifyMatch != 0) {
1745 Handle obj((oop) mid->object());
1746 tty->print("INFO: unexpected locked object:");
1747 javaVFrame::print_locked_object_class_name(tty, obj, "locked");
1748 fatal("exiting JavaThread=" INTPTR_FORMAT
1749 " unexpectedly owns ObjectMonitor=" INTPTR_FORMAT,
1750 p2i(THREAD), p2i(mid));
1751 }
1752 (void)mid->complete_exit(CHECK);
1753 }
1754 }
1755 };
1756
1757 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1758 // ignored. This is meant to be called during JNI thread detach which assumes
1759 // all remaining monitors are heavyweight. All exceptions are swallowed.
1760 // Scanning the extant monitor list can be time consuming.
1761 // A simple optimization is to add a per-thread flag that indicates a thread
1762 // called jni_monitorenter() during its lifetime.
1763 //
1764 // Instead of No_Savepoint_Verifier it might be cheaper to
1765 // use an idiom of the form:
1766 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1767 // <code that must not run at safepoint>
1768 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1769 // Since the tests are extremely cheap we could leave them enabled
1770 // for normal product builds.
1771
1772 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1773 assert(THREAD == JavaThread::current(), "must be current Java thread");
1774 NoSafepointVerifier nsv;
1775 ReleaseJavaMonitorsClosure rjmc(THREAD);
1776 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
1777 ObjectSynchronizer::monitors_iterate(&rjmc);
1778 Thread::muxRelease(&gListLock);
1779 THREAD->clear_pending_exception();
1780 }
1781
1782 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1783 switch (cause) {
1784 case inflate_cause_vm_internal: return "VM Internal";
1785 case inflate_cause_monitor_enter: return "Monitor Enter";
1786 case inflate_cause_wait: return "Monitor Wait";
1787 case inflate_cause_notify: return "Monitor Notify";
1788 case inflate_cause_hash_code: return "Monitor Hash Code";
1789 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1790 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1791 default:
1792 ShouldNotReachHere();
1793 }
1794 return "Unknown";
1795 }
1796
1797 static void post_monitor_inflate_event(EventJavaMonitorInflate& event,
1798 const oop obj,
1799 const ObjectSynchronizer::InflateCause cause) {
1800 #if INCLUDE_TRACE
1801 assert(event.should_commit(), "check outside");
1802 event.set_klass(obj->klass());
1803 event.set_address((TYPE_ADDRESS)(uintptr_t)(void*)obj);
1804 event.set_cause((u1)cause);
1805 event.commit();
1806 #endif
1807 }
1808
1809 //------------------------------------------------------------------------------
1810 // Debugging code
1811
1812 void ObjectSynchronizer::sanity_checks(const bool verbose,
1813 const uint cache_line_size,
1814 int *error_cnt_ptr,
1815 int *warning_cnt_ptr) {
1816 u_char *addr_begin = (u_char*)&GVars;
1817 u_char *addr_stwRandom = (u_char*)&GVars.stwRandom;
1818 u_char *addr_hcSequence = (u_char*)&GVars.hcSequence;
1819
1820 if (verbose) {
1821 tty->print_cr("INFO: sizeof(SharedGlobals)=" SIZE_FORMAT,
1822 sizeof(SharedGlobals));
1823 }
1824
1825 uint offset_stwRandom = (uint)(addr_stwRandom - addr_begin);
1826 if (verbose) tty->print_cr("INFO: offset(stwRandom)=%u", offset_stwRandom);
1827
1828 uint offset_hcSequence = (uint)(addr_hcSequence - addr_begin);
1829 if (verbose) {
1830 tty->print_cr("INFO: offset(_hcSequence)=%u", offset_hcSequence);
1831 }
1832
1833 if (cache_line_size != 0) {
1834 // We were able to determine the L1 data cache line size so
1835 // do some cache line specific sanity checks
1836
1837 if (offset_stwRandom < cache_line_size) {
1838 tty->print_cr("WARNING: the SharedGlobals.stwRandom field is closer "
1839 "to the struct beginning than a cache line which permits "
1840 "false sharing.");
1841 (*warning_cnt_ptr)++;
1842 }
1843
1844 if ((offset_hcSequence - offset_stwRandom) < cache_line_size) {
1845 tty->print_cr("WARNING: the SharedGlobals.stwRandom and "
1846 "SharedGlobals.hcSequence fields are closer than a cache "
1847 "line which permits false sharing.");
1848 (*warning_cnt_ptr)++;
1849 }
1850
1851 if ((sizeof(SharedGlobals) - offset_hcSequence) < cache_line_size) {
1852 tty->print_cr("WARNING: the SharedGlobals.hcSequence field is closer "
1853 "to the struct end than a cache line which permits false "
1854 "sharing.");
1855 (*warning_cnt_ptr)++;
1856 }
1857 }
1858 }
1859
1860 #ifndef PRODUCT
1861
1862 // Verify all monitors in the monitor cache, the verification is weak.
1863 void ObjectSynchronizer::verify() {
1864 PaddedEnd<ObjectMonitor> * block =
1865 (PaddedEnd<ObjectMonitor> *)OrderAccess::load_ptr_acquire(&gBlockList);
1866 while (block != NULL) {
1867 assert(block->object() == CHAINMARKER, "must be a block header");
1868 for (int i = 1; i < _BLOCKSIZE; i++) {
1869 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
1870 oop object = (oop)mid->object();
1871 if (object != NULL) {
1872 mid->verify();
1873 }
1874 }
1875 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
1876 }
1877 }
1878
1879 // Check if monitor belongs to the monitor cache
1880 // The list is grow-only so it's *relatively* safe to traverse
1881 // the list of extant blocks without taking a lock.
1882
1883 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
1884 PaddedEnd<ObjectMonitor> * block =
1885 (PaddedEnd<ObjectMonitor> *)OrderAccess::load_ptr_acquire(&gBlockList);
1886 while (block != NULL) {
1887 assert(block->object() == CHAINMARKER, "must be a block header");
1888 if (monitor > (ObjectMonitor *)&block[0] &&
1889 monitor < (ObjectMonitor *)&block[_BLOCKSIZE]) {
1890 address mon = (address)monitor;
1891 address blk = (address)block;
1892 size_t diff = mon - blk;
1893 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "must be aligned");
1894 return 1;
1895 }
1896 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
1897 }
1898 return 0;
1899 }
1900
1901 #endif