1 /*
2 * Copyright (c) 1998, 2016, 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 // The "core" versions of monitor enter and exit reside in this file.
52 // The interpreter and compilers contain specialized transliterated
53 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
54 // for instance. If you make changes here, make sure to modify the
55 // interpreter, and both C1 and C2 fast-path inline locking code emission.
56 //
57 // -----------------------------------------------------------------------------
58
59 #ifdef DTRACE_ENABLED
60
61 // Only bother with this argument setup if dtrace is available
62 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
63
64 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
65 char* bytes = NULL; \
66 int len = 0; \
67 jlong jtid = SharedRuntime::get_java_tid(thread); \
68 Symbol* klassname = ((oop)(obj))->klass()->name(); \
69 if (klassname != NULL) { \
70 bytes = (char*)klassname->bytes(); \
71 len = klassname->utf8_length(); \
72 }
73
74 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
75 { \
76 if (DTraceMonitorProbes) { \
77 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
78 HOTSPOT_MONITOR_WAIT(jtid, \
79 (uintptr_t)(monitor), bytes, len, (millis)); \
80 } \
81 }
82
83 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
84 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
85 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
86
87 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
88 { \
89 if (DTraceMonitorProbes) { \
90 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
91 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
92 (uintptr_t)(monitor), bytes, len); \
93 } \
94 }
95
96 #else // ndef DTRACE_ENABLED
97
98 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
99 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
100
101 #endif // ndef DTRACE_ENABLED
102
103 // This exists only as a workaround of dtrace bug 6254741
104 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
105 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
106 return 0;
107 }
108
109 #define NINFLATIONLOCKS 256
110 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
111
112 // global list of blocks of monitors
113 // gBlockList is really PaddedEnd<ObjectMonitor> *, but we don't
114 // want to expose the PaddedEnd template more than necessary.
115 ObjectMonitor * volatile ObjectSynchronizer::gBlockList = NULL;
116 // global monitor free list
117 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL;
118 // global monitor in-use list, for moribund threads,
119 // monitors they inflated need to be scanned for deflation
120 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL;
121 // count of entries in gOmInUseList
122 int ObjectSynchronizer::gOmInUseCount = 0;
123
124 static volatile intptr_t gListLock = 0; // protects global monitor lists
125 static volatile int gMonitorFreeCount = 0; // # on gFreeList
126 static volatile int gMonitorPopulation = 0; // # Extant -- in circulation
127
128 static void post_monitor_inflate_event(EventJavaMonitorInflate&,
129 const oop,
130 const ObjectSynchronizer::InflateCause);
131
132 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
133
134
135 // =====================> Quick functions
136
137 // The quick_* forms are special fast-path variants used to improve
138 // performance. In the simplest case, a "quick_*" implementation could
139 // simply return false, in which case the caller will perform the necessary
140 // state transitions and call the slow-path form.
141 // The fast-path is designed to handle frequently arising cases in an efficient
142 // manner and is just a degenerate "optimistic" variant of the slow-path.
143 // returns true -- to indicate the call was satisfied.
144 // returns false -- to indicate the call needs the services of the slow-path.
145 // A no-loitering ordinance is in effect for code in the quick_* family
146 // operators: safepoints or indefinite blocking (blocking that might span a
147 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
148 // entry.
149 //
150 // Consider: An interesting optimization is to have the JIT recognize the
151 // following common idiom:
152 // synchronized (someobj) { .... ; notify(); }
153 // That is, we find a notify() or notifyAll() call that immediately precedes
154 // the monitorexit operation. In that case the JIT could fuse the operations
155 // into a single notifyAndExit() runtime primitive.
156
157 bool ObjectSynchronizer::quick_notify(oopDesc * obj, Thread * self, bool all) {
158 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
159 assert(self->is_Java_thread(), "invariant");
160 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
161 NoSafepointVerifier nsv;
162 if (obj == NULL) return false; // slow-path for invalid obj
163 const markOop mark = obj->mark();
164
165 if (mark->has_locker() && self->is_lock_owned((address)mark->locker())) {
166 // Degenerate notify
167 // stack-locked by caller so by definition the implied waitset is empty.
168 return true;
169 }
170
171 if (mark->has_monitor()) {
172 ObjectMonitor * const mon = mark->monitor();
173 assert(mon->object() == obj, "invariant");
174 if (mon->owner() != self) return false; // slow-path for IMS exception
175
176 if (mon->first_waiter() != NULL) {
177 // We have one or more waiters. Since this is an inflated monitor
178 // that we own, we can transfer one or more threads from the waitset
179 // to the entrylist here and now, avoiding the slow-path.
180 if (all) {
181 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
182 } else {
183 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
184 }
185 int tally = 0;
186 do {
187 mon->INotify(self);
188 ++tally;
189 } while (mon->first_waiter() != NULL && all);
190 OM_PERFDATA_OP(Notifications, inc(tally));
191 }
192 return true;
193 }
194
195 // biased locking and any other IMS exception states take the slow-path
196 return false;
197 }
198
199
200 // The LockNode emitted directly at the synchronization site would have
201 // been too big if it were to have included support for the cases of inflated
202 // recursive enter and exit, so they go here instead.
203 // Note that we can't safely call AsyncPrintJavaStack() from within
204 // quick_enter() as our thread state remains _in_Java.
205
206 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
207 BasicLock * Lock) {
208 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
209 assert(Self->is_Java_thread(), "invariant");
210 assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
211 NoSafepointVerifier nsv;
212 if (obj == NULL) return false; // Need to throw NPE
213 const markOop mark = obj->mark();
214
215 if (mark->has_monitor()) {
216 ObjectMonitor * const m = mark->monitor();
217 assert(m->object() == obj, "invariant");
218 Thread * const owner = (Thread *) m->_owner;
219
220 // Lock contention and Transactional Lock Elision (TLE) diagnostics
221 // and observability
222 // Case: light contention possibly amenable to TLE
223 // Case: TLE inimical operations such as nested/recursive synchronization
224
225 if (owner == Self) {
226 m->_recursions++;
227 return true;
228 }
229
230 if (owner == NULL &&
231 Atomic::cmpxchg_ptr(Self, &(m->_owner), NULL) == NULL) {
232 assert(m->_recursions == 0, "invariant");
233 assert(m->_owner == Self, "invariant");
234 return true;
235 }
236 }
237
238 // Note that we could inflate in quick_enter.
239 // This is likely a useful optimization
240 // Critically, in quick_enter() we must not:
241 // -- perform bias revocation, or
242 // -- block indefinitely, or
243 // -- reach a safepoint
244
245 return false; // revert to slow-path
246 }
247
248 // -----------------------------------------------------------------------------
249 // Fast Monitor Enter/Exit
250 // This the fast monitor enter. The interpreter and compiler use
251 // some assembly copies of this code. Make sure update those code
252 // if the following function is changed. The implementation is
253 // extremely sensitive to race condition. Be careful.
254
255 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
256 bool attempt_rebias, TRAPS) {
257 if (UseBiasedLocking) {
258 if (!SafepointSynchronize::is_at_safepoint()) {
259 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
260 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
261 return;
262 }
263 } else {
264 assert(!attempt_rebias, "can not rebias toward VM thread");
265 BiasedLocking::revoke_at_safepoint(obj);
266 }
267 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
268 }
269
270 slow_enter(obj, lock, THREAD);
271 }
272
273 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
274 assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here");
275 // if displaced header is null, the previous enter is recursive enter, no-op
276 markOop dhw = lock->displaced_header();
277 markOop mark;
278 if (dhw == NULL) {
279 // Recursive stack-lock.
280 // Diagnostics -- Could be: stack-locked, inflating, inflated.
281 mark = object->mark();
282 assert(!mark->is_neutral(), "invariant");
283 if (mark->has_locker() && mark != markOopDesc::INFLATING()) {
284 assert(THREAD->is_lock_owned((address)mark->locker()), "invariant");
285 }
286 if (mark->has_monitor()) {
287 ObjectMonitor * m = mark->monitor();
288 assert(((oop)(m->object()))->mark() == mark, "invariant");
289 assert(m->is_entered(THREAD), "invariant");
290 }
291 return;
292 }
293
294 mark = object->mark();
295
296 // If the object is stack-locked by the current thread, try to
297 // swing the displaced header from the box back to the mark.
298 if (mark == (markOop) lock) {
299 assert(dhw->is_neutral(), "invariant");
300 if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) {
301 TEVENT(fast_exit: release stacklock);
302 return;
303 }
304 }
305
306 ObjectSynchronizer::inflate(THREAD,
307 object,
308 inflate_cause_vm_internal)->exit(true, THREAD);
309 }
310
311 // -----------------------------------------------------------------------------
312 // Interpreter/Compiler Slow Case
313 // This routine is used to handle interpreter/compiler slow case
314 // We don't need to use fast path here, because it must have been
315 // failed in the interpreter/compiler code.
316 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
317 markOop mark = obj->mark();
318 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
319
320 if (mark->is_neutral()) {
321 // Anticipate successful CAS -- the ST of the displaced mark must
322 // be visible <= the ST performed by the CAS.
323 lock->set_displaced_header(mark);
324 if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) {
325 TEVENT(slow_enter: release stacklock);
326 return;
327 }
328 // Fall through to inflate() ...
329 } else if (mark->has_locker() &&
330 THREAD->is_lock_owned((address)mark->locker())) {
331 assert(lock != mark->locker(), "must not re-lock the same lock");
332 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
333 lock->set_displaced_header(NULL);
334 return;
335 }
336
337 // The object header will never be displaced to this lock,
338 // so it does not matter what the value is, except that it
339 // must be non-zero to avoid looking like a re-entrant lock,
340 // and must not look locked either.
341 lock->set_displaced_header(markOopDesc::unused_mark());
342 ObjectSynchronizer::inflate(THREAD,
343 obj(),
344 inflate_cause_monitor_enter)->enter(THREAD);
345 }
346
347 // This routine is used to handle interpreter/compiler slow case
348 // We don't need to use fast path here, because it must have
349 // failed in the interpreter/compiler code. Simply use the heavy
350 // weight monitor should be ok, unless someone find otherwise.
351 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
352 fast_exit(object, lock, THREAD);
353 }
354
355 // -----------------------------------------------------------------------------
356 // Class Loader support to workaround deadlocks on the class loader lock objects
357 // Also used by GC
358 // complete_exit()/reenter() are used to wait on a nested lock
359 // i.e. to give up an outer lock completely and then re-enter
360 // Used when holding nested locks - lock acquisition order: lock1 then lock2
361 // 1) complete_exit lock1 - saving recursion count
362 // 2) wait on lock2
363 // 3) when notified on lock2, unlock lock2
364 // 4) reenter lock1 with original recursion count
365 // 5) lock lock2
366 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
367 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
368 TEVENT(complete_exit);
369 if (UseBiasedLocking) {
370 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
371 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
372 }
373
374 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
375 obj(),
376 inflate_cause_vm_internal);
377
378 return monitor->complete_exit(THREAD);
379 }
380
381 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
382 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
383 TEVENT(reenter);
384 if (UseBiasedLocking) {
385 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
386 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
387 }
388
389 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
390 obj(),
391 inflate_cause_vm_internal);
392
393 monitor->reenter(recursion, THREAD);
394 }
395 // -----------------------------------------------------------------------------
396 // JNI locks on java objects
397 // NOTE: must use heavy weight monitor to handle jni monitor enter
398 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
399 // the current locking is from JNI instead of Java code
400 TEVENT(jni_enter);
401 if (UseBiasedLocking) {
402 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
403 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
404 }
405 THREAD->set_current_pending_monitor_is_from_java(false);
406 ObjectSynchronizer::inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);
407 THREAD->set_current_pending_monitor_is_from_java(true);
408 }
409
410 // NOTE: must use heavy weight monitor to handle jni monitor exit
411 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
412 TEVENT(jni_exit);
413 if (UseBiasedLocking) {
414 Handle h_obj(THREAD, obj);
415 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
416 obj = h_obj();
417 }
418 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
419
420 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
421 obj,
422 inflate_cause_jni_exit);
423 // If this thread has locked the object, exit the monitor. Note: can't use
424 // monitor->check(CHECK); must exit even if an exception is pending.
425 if (monitor->check(THREAD)) {
426 monitor->exit(true, THREAD);
427 }
428 }
429
430 // -----------------------------------------------------------------------------
431 // Internal VM locks on java objects
432 // standard constructor, allows locking failures
433 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
434 _dolock = doLock;
435 _thread = thread;
436 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
437 _obj = obj;
438
439 if (_dolock) {
440 TEVENT(ObjectLocker);
441
442 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
443 }
444 }
445
446 ObjectLocker::~ObjectLocker() {
447 if (_dolock) {
448 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
449 }
450 }
451
452
453 // -----------------------------------------------------------------------------
454 // Wait/Notify/NotifyAll
455 // NOTE: must use heavy weight monitor to handle wait()
456 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
457 if (UseBiasedLocking) {
458 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
459 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
460 }
461 if (millis < 0) {
462 TEVENT(wait - throw IAX);
463 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
464 }
465 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
466 obj(),
467 inflate_cause_wait);
468
469 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
470 monitor->wait(millis, true, THREAD);
471
472 // This dummy call is in place to get around dtrace bug 6254741. Once
473 // that's fixed we can uncomment the following line, remove the call
474 // and change this function back into a "void" func.
475 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
476 return dtrace_waited_probe(monitor, obj, THREAD);
477 }
478
479 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
480 if (UseBiasedLocking) {
481 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
482 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
483 }
484 if (millis < 0) {
485 TEVENT(wait - throw IAX);
486 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
487 }
488 ObjectSynchronizer::inflate(THREAD,
489 obj(),
490 inflate_cause_wait)->wait(millis, false, THREAD);
491 }
492
493 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
494 if (UseBiasedLocking) {
495 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
496 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
497 }
498
499 markOop mark = obj->mark();
500 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
501 return;
502 }
503 ObjectSynchronizer::inflate(THREAD,
504 obj(),
505 inflate_cause_notify)->notify(THREAD);
506 }
507
508 // NOTE: see comment of notify()
509 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
510 if (UseBiasedLocking) {
511 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
512 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
513 }
514
515 markOop mark = obj->mark();
516 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
517 return;
518 }
519 ObjectSynchronizer::inflate(THREAD,
520 obj(),
521 inflate_cause_notify)->notifyAll(THREAD);
522 }
523
524 // -----------------------------------------------------------------------------
525 // Hash Code handling
526 //
527 // Performance concern:
528 // OrderAccess::storestore() calls release() which at one time stored 0
529 // into the global volatile OrderAccess::dummy variable. This store was
530 // unnecessary for correctness. Many threads storing into a common location
531 // causes considerable cache migration or "sloshing" on large SMP systems.
532 // As such, I avoided using OrderAccess::storestore(). In some cases
533 // OrderAccess::fence() -- which incurs local latency on the executing
534 // processor -- is a better choice as it scales on SMP systems.
535 //
536 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
537 // a discussion of coherency costs. Note that all our current reference
538 // platforms provide strong ST-ST order, so the issue is moot on IA32,
539 // x64, and SPARC.
540 //
541 // As a general policy we use "volatile" to control compiler-based reordering
542 // and explicit fences (barriers) to control for architectural reordering
543 // performed by the CPU(s) or platform.
544
545 struct SharedGlobals {
546 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
547 // These are highly shared mostly-read variables.
548 // To avoid false-sharing they need to be the sole occupants of a cache line.
549 volatile int stwRandom;
550 volatile int stwCycle;
551 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
552 // Hot RW variable -- Sequester to avoid false-sharing
553 volatile int hcSequence;
554 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
555 };
556
557 static SharedGlobals GVars;
558 static int MonitorScavengeThreshold = 1000000;
559 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
560
561 static markOop ReadStableMark(oop obj) {
562 markOop mark = obj->mark();
563 if (!mark->is_being_inflated()) {
564 return mark; // normal fast-path return
565 }
566
567 int its = 0;
568 for (;;) {
569 markOop mark = obj->mark();
570 if (!mark->is_being_inflated()) {
571 return mark; // normal fast-path return
572 }
573
574 // The object is being inflated by some other thread.
575 // The caller of ReadStableMark() must wait for inflation to complete.
576 // Avoid live-lock
577 // TODO: consider calling SafepointSynchronize::do_call_back() while
578 // spinning to see if there's a safepoint pending. If so, immediately
579 // yielding or blocking would be appropriate. Avoid spinning while
580 // there is a safepoint pending.
581 // TODO: add inflation contention performance counters.
582 // TODO: restrict the aggregate number of spinners.
583
584 ++its;
585 if (its > 10000 || !os::is_MP()) {
586 if (its & 1) {
587 os::naked_yield();
588 TEVENT(Inflate: INFLATING - yield);
589 } else {
590 // Note that the following code attenuates the livelock problem but is not
591 // a complete remedy. A more complete solution would require that the inflating
592 // thread hold the associated inflation lock. The following code simply restricts
593 // the number of spinners to at most one. We'll have N-2 threads blocked
594 // on the inflationlock, 1 thread holding the inflation lock and using
595 // a yield/park strategy, and 1 thread in the midst of inflation.
596 // A more refined approach would be to change the encoding of INFLATING
597 // to allow encapsulation of a native thread pointer. Threads waiting for
598 // inflation to complete would use CAS to push themselves onto a singly linked
599 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
600 // and calling park(). When inflation was complete the thread that accomplished inflation
601 // would detach the list and set the markword to inflated with a single CAS and
602 // then for each thread on the list, set the flag and unpark() the thread.
603 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
604 // wakes at most one thread whereas we need to wake the entire list.
605 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
606 int YieldThenBlock = 0;
607 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
608 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
609 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
610 while (obj->mark() == markOopDesc::INFLATING()) {
611 // Beware: NakedYield() is advisory and has almost no effect on some platforms
612 // so we periodically call Self->_ParkEvent->park(1).
613 // We use a mixed spin/yield/block mechanism.
614 if ((YieldThenBlock++) >= 16) {
615 Thread::current()->_ParkEvent->park(1);
616 } else {
617 os::naked_yield();
618 }
619 }
620 Thread::muxRelease(gInflationLocks + ix);
621 TEVENT(Inflate: INFLATING - yield/park);
622 }
623 } else {
624 SpinPause(); // SMP-polite spinning
625 }
626 }
627 }
628
629 // hashCode() generation :
630 //
631 // Possibilities:
632 // * MD5Digest of {obj,stwRandom}
633 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
634 // * A DES- or AES-style SBox[] mechanism
635 // * One of the Phi-based schemes, such as:
636 // 2654435761 = 2^32 * Phi (golden ratio)
637 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
638 // * A variation of Marsaglia's shift-xor RNG scheme.
639 // * (obj ^ stwRandom) is appealing, but can result
640 // in undesirable regularity in the hashCode values of adjacent objects
641 // (objects allocated back-to-back, in particular). This could potentially
642 // result in hashtable collisions and reduced hashtable efficiency.
643 // There are simple ways to "diffuse" the middle address bits over the
644 // generated hashCode values:
645
646 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
647 intptr_t value = 0;
648 if (hashCode == 0) {
649 // This form uses an unguarded global Park-Miller RNG,
650 // so it's possible for two threads to race and generate the same RNG.
651 // On MP system we'll have lots of RW access to a global, so the
652 // mechanism induces lots of coherency traffic.
653 value = os::random();
654 } else if (hashCode == 1) {
655 // This variation has the property of being stable (idempotent)
656 // between STW operations. This can be useful in some of the 1-0
657 // synchronization schemes.
658 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
659 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
660 } else if (hashCode == 2) {
661 value = 1; // for sensitivity testing
662 } else if (hashCode == 3) {
663 value = ++GVars.hcSequence;
664 } else if (hashCode == 4) {
665 value = cast_from_oop<intptr_t>(obj);
666 } else {
667 // Marsaglia's xor-shift scheme with thread-specific state
668 // This is probably the best overall implementation -- we'll
669 // likely make this the default in future releases.
670 unsigned t = Self->_hashStateX;
671 t ^= (t << 11);
672 Self->_hashStateX = Self->_hashStateY;
673 Self->_hashStateY = Self->_hashStateZ;
674 Self->_hashStateZ = Self->_hashStateW;
675 unsigned v = Self->_hashStateW;
676 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
677 Self->_hashStateW = v;
678 value = v;
679 }
680
681 value &= markOopDesc::hash_mask;
682 if (value == 0) value = 0xBAD;
683 assert(value != markOopDesc::no_hash, "invariant");
684 TEVENT(hashCode: GENERATE);
685 return value;
686 }
687
688 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
689 if (UseBiasedLocking) {
690 // NOTE: many places throughout the JVM do not expect a safepoint
691 // to be taken here, in particular most operations on perm gen
692 // objects. However, we only ever bias Java instances and all of
693 // the call sites of identity_hash that might revoke biases have
694 // been checked to make sure they can handle a safepoint. The
695 // added check of the bias pattern is to avoid useless calls to
696 // thread-local storage.
697 if (obj->mark()->has_bias_pattern()) {
698 // Handle for oop obj in case of STW safepoint
699 Handle hobj(Self, obj);
700 // Relaxing assertion for bug 6320749.
701 assert(Universe::verify_in_progress() ||
702 !SafepointSynchronize::is_at_safepoint(),
703 "biases should not be seen by VM thread here");
704 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
705 obj = hobj();
706 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
707 }
708 }
709
710 // hashCode() is a heap mutator ...
711 // Relaxing assertion for bug 6320749.
712 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
713 !SafepointSynchronize::is_at_safepoint(), "invariant");
714 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
715 Self->is_Java_thread() , "invariant");
716 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
717 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
718
719 ObjectMonitor* monitor = NULL;
720 markOop temp, test;
721 intptr_t hash;
722 markOop mark = ReadStableMark(obj);
723
724 // object should remain ineligible for biased locking
725 assert(!mark->has_bias_pattern(), "invariant");
726
727 if (mark->is_neutral()) {
728 hash = mark->hash(); // this is a normal header
729 if (hash) { // if it has hash, just return it
730 return hash;
731 }
732 hash = get_next_hash(Self, obj); // allocate a new hash code
733 temp = mark->copy_set_hash(hash); // merge the hash code into header
734 // use (machine word version) atomic operation to install the hash
735 test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark);
736 if (test == mark) {
737 return hash;
738 }
739 // If atomic operation failed, we must inflate the header
740 // into heavy weight monitor. We could add more code here
741 // for fast path, but it does not worth the complexity.
742 } else if (mark->has_monitor()) {
743 monitor = mark->monitor();
744 temp = monitor->header();
745 assert(temp->is_neutral(), "invariant");
746 hash = temp->hash();
747 if (hash) {
748 return hash;
749 }
750 // Skip to the following code to reduce code size
751 } else if (Self->is_lock_owned((address)mark->locker())) {
752 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
753 assert(temp->is_neutral(), "invariant");
754 hash = temp->hash(); // by current thread, check if the displaced
755 if (hash) { // header contains hash code
756 return hash;
757 }
758 // WARNING:
759 // The displaced header is strictly immutable.
760 // It can NOT be changed in ANY cases. So we have
761 // to inflate the header into heavyweight monitor
762 // even the current thread owns the lock. The reason
763 // is the BasicLock (stack slot) will be asynchronously
764 // read by other threads during the inflate() function.
765 // Any change to stack may not propagate to other threads
766 // correctly.
767 }
768
769 // Inflate the monitor to set hash code
770 monitor = ObjectSynchronizer::inflate(Self, obj, inflate_cause_hash_code);
771 // Load displaced header and check it has hash code
772 mark = monitor->header();
773 assert(mark->is_neutral(), "invariant");
774 hash = mark->hash();
775 if (hash == 0) {
776 hash = get_next_hash(Self, obj);
777 temp = mark->copy_set_hash(hash); // merge hash code into header
778 assert(temp->is_neutral(), "invariant");
779 test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark);
780 if (test != mark) {
781 // The only update to the header in the monitor (outside GC)
782 // is install the hash code. If someone add new usage of
783 // displaced header, please update this code
784 hash = test->hash();
785 assert(test->is_neutral(), "invariant");
786 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
787 }
788 }
789 // We finally get the hash
790 return hash;
791 }
792
793 // Deprecated -- use FastHashCode() instead.
794
795 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
796 return FastHashCode(Thread::current(), obj());
797 }
798
799
800 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
801 Handle h_obj) {
802 if (UseBiasedLocking) {
803 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
804 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
805 }
806
807 assert(thread == JavaThread::current(), "Can only be called on current thread");
808 oop obj = h_obj();
809
810 markOop mark = ReadStableMark(obj);
811
812 // Uncontended case, header points to stack
813 if (mark->has_locker()) {
814 return thread->is_lock_owned((address)mark->locker());
815 }
816 // Contended case, header points to ObjectMonitor (tagged pointer)
817 if (mark->has_monitor()) {
818 ObjectMonitor* monitor = mark->monitor();
819 return monitor->is_entered(thread) != 0;
820 }
821 // Unlocked case, header in place
822 assert(mark->is_neutral(), "sanity check");
823 return false;
824 }
825
826 // Be aware of this method could revoke bias of the lock object.
827 // This method queries the ownership of the lock handle specified by 'h_obj'.
828 // If the current thread owns the lock, it returns owner_self. If no
829 // thread owns the lock, it returns owner_none. Otherwise, it will return
830 // owner_other.
831 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
832 (JavaThread *self, Handle h_obj) {
833 // The caller must beware this method can revoke bias, and
834 // revocation can result in a safepoint.
835 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
836 assert(self->thread_state() != _thread_blocked, "invariant");
837
838 // Possible mark states: neutral, biased, stack-locked, inflated
839
840 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
841 // CASE: biased
842 BiasedLocking::revoke_and_rebias(h_obj, false, self);
843 assert(!h_obj->mark()->has_bias_pattern(),
844 "biases should be revoked by now");
845 }
846
847 assert(self == JavaThread::current(), "Can only be called on current thread");
848 oop obj = h_obj();
849 markOop mark = ReadStableMark(obj);
850
851 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
852 if (mark->has_locker()) {
853 return self->is_lock_owned((address)mark->locker()) ?
854 owner_self : owner_other;
855 }
856
857 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
858 // The Object:ObjectMonitor relationship is stable as long as we're
859 // not at a safepoint.
860 if (mark->has_monitor()) {
861 void * owner = mark->monitor()->_owner;
862 if (owner == NULL) return owner_none;
863 return (owner == self ||
864 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
865 }
866
867 // CASE: neutral
868 assert(mark->is_neutral(), "sanity check");
869 return owner_none; // it's unlocked
870 }
871
872 // FIXME: jvmti should call this
873 JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) {
874 if (UseBiasedLocking) {
875 if (SafepointSynchronize::is_at_safepoint()) {
876 BiasedLocking::revoke_at_safepoint(h_obj);
877 } else {
878 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
879 }
880 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
881 }
882
883 oop obj = h_obj();
884 address owner = NULL;
885
886 markOop mark = ReadStableMark(obj);
887
888 // Uncontended case, header points to stack
889 if (mark->has_locker()) {
890 owner = (address) mark->locker();
891 }
892
893 // Contended case, header points to ObjectMonitor (tagged pointer)
894 if (mark->has_monitor()) {
895 ObjectMonitor* monitor = mark->monitor();
896 assert(monitor != NULL, "monitor should be non-null");
897 owner = (address) monitor->owner();
898 }
899
900 if (owner != NULL) {
901 // owning_thread_from_monitor_owner() may also return NULL here
902 return Threads::owning_thread_from_monitor_owner(owner, doLock);
903 }
904
905 // Unlocked case, header in place
906 // Cannot have assertion since this object may have been
907 // locked by another thread when reaching here.
908 // assert(mark->is_neutral(), "sanity check");
909
910 return NULL;
911 }
912
913 // Visitors ...
914
915 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
916 PaddedEnd<ObjectMonitor> * block =
917 (PaddedEnd<ObjectMonitor> *)OrderAccess::load_ptr_acquire(&gBlockList);
918 while (block != NULL) {
919 assert(block->object() == CHAINMARKER, "must be a block header");
920 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
921 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
922 oop object = (oop)mid->object();
923 if (object != NULL) {
924 closure->do_monitor(mid);
925 }
926 }
927 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
928 }
929 }
930
931 // Get the next block in the block list.
932 static inline ObjectMonitor* next(ObjectMonitor* block) {
933 assert(block->object() == CHAINMARKER, "must be a block header");
934 block = block->FreeNext;
935 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
936 return block;
937 }
938
939
940 void ObjectSynchronizer::oops_do(OopClosure* f) {
941 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
942 PaddedEnd<ObjectMonitor> * block =
943 (PaddedEnd<ObjectMonitor> *)OrderAccess::load_ptr_acquire(&gBlockList);
944 for (; block != NULL; block = (PaddedEnd<ObjectMonitor> *)next(block)) {
945 assert(block->object() == CHAINMARKER, "must be a block header");
946 for (int i = 1; i < _BLOCKSIZE; i++) {
947 ObjectMonitor* mid = (ObjectMonitor *)&block[i];
948 if (mid->object() != NULL) {
949 f->do_oop((oop*)mid->object_addr());
950 }
951 }
952 }
953 }
954
955
956 // -----------------------------------------------------------------------------
957 // ObjectMonitor Lifecycle
958 // -----------------------
959 // Inflation unlinks monitors from the global gFreeList and
960 // associates them with objects. Deflation -- which occurs at
961 // STW-time -- disassociates idle monitors from objects. Such
962 // scavenged monitors are returned to the gFreeList.
963 //
964 // The global list is protected by gListLock. All the critical sections
965 // are short and operate in constant-time.
966 //
967 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
968 //
969 // Lifecycle:
970 // -- unassigned and on the global free list
971 // -- unassigned and on a thread's private omFreeList
972 // -- assigned to an object. The object is inflated and the mark refers
973 // to the objectmonitor.
974
975
976 // Constraining monitor pool growth via MonitorBound ...
977 //
978 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
979 // the rate of scavenging is driven primarily by GC. As such, we can find
980 // an inordinate number of monitors in circulation.
981 // To avoid that scenario we can artificially induce a STW safepoint
982 // if the pool appears to be growing past some reasonable bound.
983 // Generally we favor time in space-time tradeoffs, but as there's no
984 // natural back-pressure on the # of extant monitors we need to impose some
985 // type of limit. Beware that if MonitorBound is set to too low a value
986 // we could just loop. In addition, if MonitorBound is set to a low value
987 // we'll incur more safepoints, which are harmful to performance.
988 // See also: GuaranteedSafepointInterval
989 //
990 // The current implementation uses asynchronous VM operations.
991
992 static void InduceScavenge(Thread * Self, const char * Whence) {
993 // Induce STW safepoint to trim monitors
994 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
995 // More precisely, trigger an asynchronous STW safepoint as the number
996 // of active monitors passes the specified threshold.
997 // TODO: assert thread state is reasonable
998
999 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1000 if (ObjectMonitor::Knob_Verbose) {
1001 tty->print_cr("INFO: Monitor scavenge - Induced STW @%s (%d)",
1002 Whence, ForceMonitorScavenge) ;
1003 tty->flush();
1004 }
1005 // Induce a 'null' safepoint to scavenge monitors
1006 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1007 // to the VMthread and have a lifespan longer than that of this activation record.
1008 // The VMThread will delete the op when completed.
1009 VMThread::execute(new VM_ForceAsyncSafepoint());
1010
1011 if (ObjectMonitor::Knob_Verbose) {
1012 tty->print_cr("INFO: Monitor scavenge - STW posted @%s (%d)",
1013 Whence, ForceMonitorScavenge) ;
1014 tty->flush();
1015 }
1016 }
1017 }
1018
1019 void ObjectSynchronizer::verifyInUse(Thread *Self) {
1020 ObjectMonitor* mid;
1021 int in_use_tally = 0;
1022 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) {
1023 in_use_tally++;
1024 }
1025 assert(in_use_tally == Self->omInUseCount, "in-use count off");
1026
1027 int free_tally = 0;
1028 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) {
1029 free_tally++;
1030 }
1031 assert(free_tally == Self->omFreeCount, "free count off");
1032 }
1033
1034 ObjectMonitor* ObjectSynchronizer::omAlloc(Thread * Self) {
1035 // A large MAXPRIVATE value reduces both list lock contention
1036 // and list coherency traffic, but also tends to increase the
1037 // number of objectMonitors in circulation as well as the STW
1038 // scavenge costs. As usual, we lean toward time in space-time
1039 // tradeoffs.
1040 const int MAXPRIVATE = 1024;
1041 for (;;) {
1042 ObjectMonitor * m;
1043
1044 // 1: try to allocate from the thread's local omFreeList.
1045 // Threads will attempt to allocate first from their local list, then
1046 // from the global list, and only after those attempts fail will the thread
1047 // attempt to instantiate new monitors. Thread-local free lists take
1048 // heat off the gListLock and improve allocation latency, as well as reducing
1049 // coherency traffic on the shared global list.
1050 m = Self->omFreeList;
1051 if (m != NULL) {
1052 Self->omFreeList = m->FreeNext;
1053 Self->omFreeCount--;
1054 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene
1055 guarantee(m->object() == NULL, "invariant");
1056 if (MonitorInUseLists) {
1057 m->FreeNext = Self->omInUseList;
1058 Self->omInUseList = m;
1059 Self->omInUseCount++;
1060 if (ObjectMonitor::Knob_VerifyInUse) {
1061 verifyInUse(Self);
1062 }
1063 } else {
1064 m->FreeNext = NULL;
1065 }
1066 return m;
1067 }
1068
1069 // 2: try to allocate from the global gFreeList
1070 // CONSIDER: use muxTry() instead of muxAcquire().
1071 // If the muxTry() fails then drop immediately into case 3.
1072 // If we're using thread-local free lists then try
1073 // to reprovision the caller's free list.
1074 if (gFreeList != NULL) {
1075 // Reprovision the thread's omFreeList.
1076 // Use bulk transfers to reduce the allocation rate and heat
1077 // on various locks.
1078 Thread::muxAcquire(&gListLock, "omAlloc");
1079 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1080 gMonitorFreeCount--;
1081 ObjectMonitor * take = gFreeList;
1082 gFreeList = take->FreeNext;
1083 guarantee(take->object() == NULL, "invariant");
1084 guarantee(!take->is_busy(), "invariant");
1085 take->Recycle();
1086 omRelease(Self, take, false);
1087 }
1088 Thread::muxRelease(&gListLock);
1089 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1090 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1091 TEVENT(omFirst - reprovision);
1092
1093 const int mx = MonitorBound;
1094 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1095 // We can't safely induce a STW safepoint from omAlloc() as our thread
1096 // state may not be appropriate for such activities and callers may hold
1097 // naked oops, so instead we defer the action.
1098 InduceScavenge(Self, "omAlloc");
1099 }
1100 continue;
1101 }
1102
1103 // 3: allocate a block of new ObjectMonitors
1104 // Both the local and global free lists are empty -- resort to malloc().
1105 // In the current implementation objectMonitors are TSM - immortal.
1106 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1107 // each ObjectMonitor to start at the beginning of a cache line,
1108 // so we use align_size_up().
1109 // A better solution would be to use C++ placement-new.
1110 // BEWARE: As it stands currently, we don't run the ctors!
1111 assert(_BLOCKSIZE > 1, "invariant");
1112 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
1113 PaddedEnd<ObjectMonitor> * temp;
1114 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1115 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
1116 mtInternal);
1117 temp = (PaddedEnd<ObjectMonitor> *)
1118 align_size_up((intptr_t)real_malloc_addr,
1119 DEFAULT_CACHE_LINE_SIZE);
1120
1121 // NOTE: (almost) no way to recover if allocation failed.
1122 // We might be able to induce a STW safepoint and scavenge enough
1123 // objectMonitors to permit progress.
1124 if (temp == NULL) {
1125 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1126 "Allocate ObjectMonitors");
1127 }
1128 (void)memset((void *) temp, 0, neededsize);
1129
1130 // Format the block.
1131 // initialize the linked list, each monitor points to its next
1132 // forming the single linked free list, the very first monitor
1133 // will points to next block, which forms the block list.
1134 // The trick of using the 1st element in the block as gBlockList
1135 // linkage should be reconsidered. A better implementation would
1136 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1137
1138 for (int i = 1; i < _BLOCKSIZE; i++) {
1139 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1140 }
1141
1142 // terminate the last monitor as the end of list
1143 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1144
1145 // Element [0] is reserved for global list linkage
1146 temp[0].set_object(CHAINMARKER);
1147
1148 // Consider carving out this thread's current request from the
1149 // block in hand. This avoids some lock traffic and redundant
1150 // list activity.
1151
1152 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1153 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1154 Thread::muxAcquire(&gListLock, "omAlloc [2]");
1155 gMonitorPopulation += _BLOCKSIZE-1;
1156 gMonitorFreeCount += _BLOCKSIZE-1;
1157
1158 // Add the new block to the list of extant blocks (gBlockList).
1159 // The very first objectMonitor in a block is reserved and dedicated.
1160 // It serves as blocklist "next" linkage.
1161 temp[0].FreeNext = gBlockList;
1162 // There are lock-free uses of gBlockList so make sure that
1163 // the previous stores happen before we update gBlockList.
1164 OrderAccess::release_store_ptr(&gBlockList, temp);
1165
1166 // Add the new string of objectMonitors to the global free list
1167 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1168 gFreeList = temp + 1;
1169 Thread::muxRelease(&gListLock);
1170 TEVENT(Allocate block of monitors);
1171 }
1172 }
1173
1174 // Place "m" on the caller's private per-thread omFreeList.
1175 // In practice there's no need to clamp or limit the number of
1176 // monitors on a thread's omFreeList as the only time we'll call
1177 // omRelease is to return a monitor to the free list after a CAS
1178 // attempt failed. This doesn't allow unbounded #s of monitors to
1179 // accumulate on a thread's free list.
1180 //
1181 // Key constraint: all ObjectMonitors on a thread's free list and the global
1182 // free list must have their object field set to null. This prevents the
1183 // scavenger -- deflate_idle_monitors -- from reclaiming them.
1184
1185 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1186 bool fromPerThreadAlloc) {
1187 guarantee(m->object() == NULL, "invariant");
1188 guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor");
1189 // Remove from omInUseList
1190 if (MonitorInUseLists && fromPerThreadAlloc) {
1191 ObjectMonitor* cur_mid_in_use = NULL;
1192 bool extracted = false;
1193 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1194 if (m == mid) {
1195 // extract from per-thread in-use list
1196 if (mid == Self->omInUseList) {
1197 Self->omInUseList = mid->FreeNext;
1198 } else if (cur_mid_in_use != NULL) {
1199 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1200 }
1201 extracted = true;
1202 Self->omInUseCount--;
1203 if (ObjectMonitor::Knob_VerifyInUse) {
1204 verifyInUse(Self);
1205 }
1206 break;
1207 }
1208 }
1209 assert(extracted, "Should have extracted from in-use list");
1210 }
1211
1212 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1213 m->FreeNext = Self->omFreeList;
1214 Self->omFreeList = m;
1215 Self->omFreeCount++;
1216 }
1217
1218 // Return the monitors of a moribund thread's local free list to
1219 // the global free list. Typically a thread calls omFlush() when
1220 // it's dying. We could also consider having the VM thread steal
1221 // monitors from threads that have not run java code over a few
1222 // consecutive STW safepoints. Relatedly, we might decay
1223 // omFreeProvision at STW safepoints.
1224 //
1225 // Also return the monitors of a moribund thread's omInUseList to
1226 // a global gOmInUseList under the global list lock so these
1227 // will continue to be scanned.
1228 //
1229 // We currently call omFlush() from the Thread:: dtor _after the thread
1230 // has been excised from the thread list and is no longer a mutator.
1231 // That means that omFlush() can run concurrently with a safepoint and
1232 // the scavenge operator. Calling omFlush() from JavaThread::exit() might
1233 // be a better choice as we could safely reason that that the JVM is
1234 // not at a safepoint at the time of the call, and thus there could
1235 // be not inopportune interleavings between omFlush() and the scavenge
1236 // operator.
1237
1238 void ObjectSynchronizer::omFlush(Thread * Self) {
1239 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1240 Self->omFreeList = NULL;
1241 ObjectMonitor * tail = NULL;
1242 int tally = 0;
1243 if (list != NULL) {
1244 ObjectMonitor * s;
1245 // The thread is going away, the per-thread free monitors
1246 // are freed via set_owner(NULL)
1247 // Link them to tail, which will be linked into the global free list
1248 // gFreeList below, under the gListLock
1249 for (s = list; s != NULL; s = s->FreeNext) {
1250 tally++;
1251 tail = s;
1252 guarantee(s->object() == NULL, "invariant");
1253 guarantee(!s->is_busy(), "invariant");
1254 s->set_owner(NULL); // redundant but good hygiene
1255 TEVENT(omFlush - Move one);
1256 }
1257 guarantee(tail != NULL && list != NULL, "invariant");
1258 }
1259
1260 ObjectMonitor * inUseList = Self->omInUseList;
1261 ObjectMonitor * inUseTail = NULL;
1262 int inUseTally = 0;
1263 if (inUseList != NULL) {
1264 Self->omInUseList = NULL;
1265 ObjectMonitor *cur_om;
1266 // The thread is going away, however the omInUseList inflated
1267 // monitors may still be in-use by other threads.
1268 // Link them to inUseTail, which will be linked into the global in-use list
1269 // gOmInUseList below, under the gListLock
1270 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1271 inUseTail = cur_om;
1272 inUseTally++;
1273 }
1274 assert(Self->omInUseCount == inUseTally, "in-use count off");
1275 Self->omInUseCount = 0;
1276 guarantee(inUseTail != NULL && inUseList != NULL, "invariant");
1277 }
1278
1279 Thread::muxAcquire(&gListLock, "omFlush");
1280 if (tail != NULL) {
1281 tail->FreeNext = gFreeList;
1282 gFreeList = list;
1283 gMonitorFreeCount += tally;
1284 }
1285
1286 if (inUseTail != NULL) {
1287 inUseTail->FreeNext = gOmInUseList;
1288 gOmInUseList = inUseList;
1289 gOmInUseCount += inUseTally;
1290 }
1291
1292 Thread::muxRelease(&gListLock);
1293 TEVENT(omFlush);
1294 }
1295
1296 // Fast path code shared by multiple functions
1297 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1298 markOop mark = obj->mark();
1299 if (mark->has_monitor()) {
1300 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1301 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1302 return mark->monitor();
1303 }
1304 return ObjectSynchronizer::inflate(Thread::current(),
1305 obj,
1306 inflate_cause_vm_internal);
1307 }
1308
1309 ObjectMonitor* ObjectSynchronizer::inflate(Thread * Self,
1310 oop object,
1311 const InflateCause cause) {
1312
1313 // Inflate mutates the heap ...
1314 // Relaxing assertion for bug 6320749.
1315 assert(Universe::verify_in_progress() ||
1316 !SafepointSynchronize::is_at_safepoint(), "invariant");
1317
1318 EventJavaMonitorInflate event;
1319
1320 for (;;) {
1321 const markOop mark = object->mark();
1322 assert(!mark->has_bias_pattern(), "invariant");
1323
1324 // The mark can be in one of the following states:
1325 // * Inflated - just return
1326 // * Stack-locked - coerce it to inflated
1327 // * INFLATING - busy wait for conversion to complete
1328 // * Neutral - aggressively inflate the object.
1329 // * BIASED - Illegal. We should never see this
1330
1331 // CASE: inflated
1332 if (mark->has_monitor()) {
1333 ObjectMonitor * inf = mark->monitor();
1334 assert(inf->header()->is_neutral(), "invariant");
1335 assert(inf->object() == object, "invariant");
1336 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1337 event.cancel(); // let's not post an inflation event, unless we did the deed ourselves
1338 return inf;
1339 }
1340
1341 // CASE: inflation in progress - inflating over a stack-lock.
1342 // Some other thread is converting from stack-locked to inflated.
1343 // Only that thread can complete inflation -- other threads must wait.
1344 // The INFLATING value is transient.
1345 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1346 // We could always eliminate polling by parking the thread on some auxiliary list.
1347 if (mark == markOopDesc::INFLATING()) {
1348 TEVENT(Inflate: spin while INFLATING);
1349 ReadStableMark(object);
1350 continue;
1351 }
1352
1353 // CASE: stack-locked
1354 // Could be stack-locked either by this thread or by some other thread.
1355 //
1356 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1357 // to install INFLATING into the mark word. We originally installed INFLATING,
1358 // allocated the objectmonitor, and then finally STed the address of the
1359 // objectmonitor into the mark. This was correct, but artificially lengthened
1360 // the interval in which INFLATED appeared in the mark, thus increasing
1361 // the odds of inflation contention.
1362 //
1363 // We now use per-thread private objectmonitor free lists.
1364 // These list are reprovisioned from the global free list outside the
1365 // critical INFLATING...ST interval. A thread can transfer
1366 // multiple objectmonitors en-mass from the global free list to its local free list.
1367 // This reduces coherency traffic and lock contention on the global free list.
1368 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1369 // before or after the CAS(INFLATING) operation.
1370 // See the comments in omAlloc().
1371
1372 if (mark->has_locker()) {
1373 ObjectMonitor * m = omAlloc(Self);
1374 // Optimistically prepare the objectmonitor - anticipate successful CAS
1375 // We do this before the CAS in order to minimize the length of time
1376 // in which INFLATING appears in the mark.
1377 m->Recycle();
1378 m->_Responsible = NULL;
1379 m->_recursions = 0;
1380 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1381
1382 markOop cmp = (markOop) Atomic::cmpxchg_ptr(markOopDesc::INFLATING(), object->mark_addr(), mark);
1383 if (cmp != mark) {
1384 omRelease(Self, m, true);
1385 continue; // Interference -- just retry
1386 }
1387
1388 // We've successfully installed INFLATING (0) into the mark-word.
1389 // This is the only case where 0 will appear in a mark-word.
1390 // Only the singular thread that successfully swings the mark-word
1391 // to 0 can perform (or more precisely, complete) inflation.
1392 //
1393 // Why do we CAS a 0 into the mark-word instead of just CASing the
1394 // mark-word from the stack-locked value directly to the new inflated state?
1395 // Consider what happens when a thread unlocks a stack-locked object.
1396 // It attempts to use CAS to swing the displaced header value from the
1397 // on-stack basiclock back into the object header. Recall also that the
1398 // header value (hashcode, etc) can reside in (a) the object header, or
1399 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1400 // header in an objectMonitor. The inflate() routine must copy the header
1401 // value from the basiclock on the owner's stack to the objectMonitor, all
1402 // the while preserving the hashCode stability invariants. If the owner
1403 // decides to release the lock while the value is 0, the unlock will fail
1404 // and control will eventually pass from slow_exit() to inflate. The owner
1405 // will then spin, waiting for the 0 value to disappear. Put another way,
1406 // the 0 causes the owner to stall if the owner happens to try to
1407 // drop the lock (restoring the header from the basiclock to the object)
1408 // while inflation is in-progress. This protocol avoids races that might
1409 // would otherwise permit hashCode values to change or "flicker" for an object.
1410 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1411 // 0 serves as a "BUSY" inflate-in-progress indicator.
1412
1413
1414 // fetch the displaced mark from the owner's stack.
1415 // The owner can't die or unwind past the lock while our INFLATING
1416 // object is in the mark. Furthermore the owner can't complete
1417 // an unlock on the object, either.
1418 markOop dmw = mark->displaced_mark_helper();
1419 assert(dmw->is_neutral(), "invariant");
1420
1421 // Setup monitor fields to proper values -- prepare the monitor
1422 m->set_header(dmw);
1423
1424 // Optimization: if the mark->locker stack address is associated
1425 // with this thread we could simply set m->_owner = Self.
1426 // Note that a thread can inflate an object
1427 // that it has stack-locked -- as might happen in wait() -- directly
1428 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1429 m->set_owner(mark->locker());
1430 m->set_object(object);
1431 // TODO-FIXME: assert BasicLock->dhw != 0.
1432
1433 // Must preserve store ordering. The monitor state must
1434 // be stable at the time of publishing the monitor address.
1435 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1436 object->release_set_mark(markOopDesc::encode(m));
1437
1438 // Hopefully the performance counters are allocated on distinct cache lines
1439 // to avoid false sharing on MP systems ...
1440 OM_PERFDATA_OP(Inflations, inc());
1441 TEVENT(Inflate: overwrite stacklock);
1442 if (log_is_enabled(Debug, monitorinflation)) {
1443 if (object->is_instance()) {
1444 ResourceMark rm;
1445 log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1446 p2i(object), p2i(object->mark()),
1447 object->klass()->external_name());
1448 }
1449 }
1450 if (event.should_commit()) {
1451 post_monitor_inflate_event(event, object, cause);
1452 }
1453 return m;
1454 }
1455
1456 // CASE: neutral
1457 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1458 // If we know we're inflating for entry it's better to inflate by swinging a
1459 // pre-locked objectMonitor pointer into the object header. A successful
1460 // CAS inflates the object *and* confers ownership to the inflating thread.
1461 // In the current implementation we use a 2-step mechanism where we CAS()
1462 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1463 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1464 // would be useful.
1465
1466 assert(mark->is_neutral(), "invariant");
1467 ObjectMonitor * m = omAlloc(Self);
1468 // prepare m for installation - set monitor to initial state
1469 m->Recycle();
1470 m->set_header(mark);
1471 m->set_owner(NULL);
1472 m->set_object(object);
1473 m->_recursions = 0;
1474 m->_Responsible = NULL;
1475 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1476
1477 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) {
1478 m->set_object(NULL);
1479 m->set_owner(NULL);
1480 m->Recycle();
1481 omRelease(Self, m, true);
1482 m = NULL;
1483 continue;
1484 // interference - the markword changed - just retry.
1485 // The state-transitions are one-way, so there's no chance of
1486 // live-lock -- "Inflated" is an absorbing state.
1487 }
1488
1489 // Hopefully the performance counters are allocated on distinct
1490 // cache lines to avoid false sharing on MP systems ...
1491 OM_PERFDATA_OP(Inflations, inc());
1492 TEVENT(Inflate: overwrite neutral);
1493 if (log_is_enabled(Debug, monitorinflation)) {
1494 if (object->is_instance()) {
1495 ResourceMark rm;
1496 log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1497 p2i(object), p2i(object->mark()),
1498 object->klass()->external_name());
1499 }
1500 }
1501 if (event.should_commit()) {
1502 post_monitor_inflate_event(event, object, cause);
1503 }
1504 return m;
1505 }
1506 }
1507
1508
1509 // Deflate_idle_monitors() is called at all safepoints, immediately
1510 // after all mutators are stopped, but before any objects have moved.
1511 // It traverses the list of known monitors, deflating where possible.
1512 // The scavenged monitor are returned to the monitor free list.
1513 //
1514 // Beware that we scavenge at *every* stop-the-world point.
1515 // Having a large number of monitors in-circulation negatively
1516 // impacts the performance of some applications (e.g., PointBase).
1517 // Broadly, we want to minimize the # of monitors in circulation.
1518 //
1519 // We have added a flag, MonitorInUseLists, which creates a list
1520 // of active monitors for each thread. deflate_idle_monitors()
1521 // only scans the per-thread in-use lists. omAlloc() puts all
1522 // assigned monitors on the per-thread list. deflate_idle_monitors()
1523 // returns the non-busy monitors to the global free list.
1524 // When a thread dies, omFlush() adds the list of active monitors for
1525 // that thread to a global gOmInUseList acquiring the
1526 // global list lock. deflate_idle_monitors() acquires the global
1527 // list lock to scan for non-busy monitors to the global free list.
1528 // An alternative could have used a single global in-use list. The
1529 // downside would have been the additional cost of acquiring the global list lock
1530 // for every omAlloc().
1531 //
1532 // Perversely, the heap size -- and thus the STW safepoint rate --
1533 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1534 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1535 // This is an unfortunate aspect of this design.
1536
1537 enum ManifestConstants {
1538 ClearResponsibleAtSTW = 0
1539 };
1540
1541 // Deflate a single monitor if not in-use
1542 // Return true if deflated, false if in-use
1543 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1544 ObjectMonitor** freeHeadp,
1545 ObjectMonitor** freeTailp) {
1546 bool deflated;
1547 // Normal case ... The monitor is associated with obj.
1548 guarantee(obj->mark() == markOopDesc::encode(mid), "invariant");
1549 guarantee(mid == obj->mark()->monitor(), "invariant");
1550 guarantee(mid->header()->is_neutral(), "invariant");
1551
1552 if (mid->is_busy()) {
1553 if (ClearResponsibleAtSTW) mid->_Responsible = NULL;
1554 deflated = false;
1555 } else {
1556 // Deflate the monitor if it is no longer being used
1557 // It's idle - scavenge and return to the global free list
1558 // plain old deflation ...
1559 TEVENT(deflate_idle_monitors - scavenge1);
1560 if (log_is_enabled(Debug, monitorinflation)) {
1561 if (obj->is_instance()) {
1562 ResourceMark rm;
1563 log_debug(monitorinflation)("Deflating object " INTPTR_FORMAT " , "
1564 "mark " INTPTR_FORMAT " , type %s",
1565 p2i(obj), p2i(obj->mark()),
1566 obj->klass()->external_name());
1567 }
1568 }
1569
1570 // Restore the header back to obj
1571 obj->release_set_mark(mid->header());
1572 mid->clear();
1573
1574 assert(mid->object() == NULL, "invariant");
1575
1576 // Move the object to the working free list defined by freeHeadp, freeTailp
1577 if (*freeHeadp == NULL) *freeHeadp = mid;
1578 if (*freeTailp != NULL) {
1579 ObjectMonitor * prevtail = *freeTailp;
1580 assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1581 prevtail->FreeNext = mid;
1582 }
1583 *freeTailp = mid;
1584 deflated = true;
1585 }
1586 return deflated;
1587 }
1588
1589 // Walk a given monitor list, and deflate idle monitors
1590 // The given list could be a per-thread list or a global list
1591 // Caller acquires gListLock
1592 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1593 ObjectMonitor** freeHeadp,
1594 ObjectMonitor** freeTailp) {
1595 ObjectMonitor* mid;
1596 ObjectMonitor* next;
1597 ObjectMonitor* cur_mid_in_use = NULL;
1598 int deflated_count = 0;
1599
1600 for (mid = *listHeadp; mid != NULL;) {
1601 oop obj = (oop) mid->object();
1602 if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1603 // if deflate_monitor succeeded,
1604 // extract from per-thread in-use list
1605 if (mid == *listHeadp) {
1606 *listHeadp = mid->FreeNext;
1607 } else if (cur_mid_in_use != NULL) {
1608 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1609 }
1610 next = mid->FreeNext;
1611 mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list
1612 mid = next;
1613 deflated_count++;
1614 } else {
1615 cur_mid_in_use = mid;
1616 mid = mid->FreeNext;
1617 }
1618 }
1619 return deflated_count;
1620 }
1621
1622 void ObjectSynchronizer::deflate_idle_monitors() {
1623 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1624 int nInuse = 0; // currently associated with objects
1625 int nInCirculation = 0; // extant
1626 int nScavenged = 0; // reclaimed
1627 bool deflated = false;
1628
1629 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1630 ObjectMonitor * freeTailp = NULL;
1631
1632 TEVENT(deflate_idle_monitors);
1633 // Prevent omFlush from changing mids in Thread dtor's during deflation
1634 // And in case the vm thread is acquiring a lock during a safepoint
1635 // See e.g. 6320749
1636 Thread::muxAcquire(&gListLock, "scavenge - return");
1637
1638 if (MonitorInUseLists) {
1639 int inUse = 0;
1640 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) {
1641 nInCirculation+= cur->omInUseCount;
1642 int deflated_count = deflate_monitor_list(cur->omInUseList_addr(), &freeHeadp, &freeTailp);
1643 cur->omInUseCount-= deflated_count;
1644 if (ObjectMonitor::Knob_VerifyInUse) {
1645 verifyInUse(cur);
1646 }
1647 nScavenged += deflated_count;
1648 nInuse += cur->omInUseCount;
1649 }
1650
1651 // For moribund threads, scan gOmInUseList
1652 if (gOmInUseList) {
1653 nInCirculation += gOmInUseCount;
1654 int deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
1655 gOmInUseCount-= deflated_count;
1656 nScavenged += deflated_count;
1657 nInuse += gOmInUseCount;
1658 }
1659
1660 } else {
1661 PaddedEnd<ObjectMonitor> * block =
1662 (PaddedEnd<ObjectMonitor> *)OrderAccess::load_ptr_acquire(&gBlockList);
1663 for (; block != NULL; block = (PaddedEnd<ObjectMonitor> *)next(block)) {
1664 // Iterate over all extant monitors - Scavenge all idle monitors.
1665 assert(block->object() == CHAINMARKER, "must be a block header");
1666 nInCirculation += _BLOCKSIZE;
1667 for (int i = 1; i < _BLOCKSIZE; i++) {
1668 ObjectMonitor* mid = (ObjectMonitor*)&block[i];
1669 oop obj = (oop)mid->object();
1670
1671 if (obj == NULL) {
1672 // The monitor is not associated with an object.
1673 // The monitor should either be a thread-specific private
1674 // free list or the global free list.
1675 // obj == NULL IMPLIES mid->is_busy() == 0
1676 guarantee(!mid->is_busy(), "invariant");
1677 continue;
1678 }
1679 deflated = deflate_monitor(mid, obj, &freeHeadp, &freeTailp);
1680
1681 if (deflated) {
1682 mid->FreeNext = NULL;
1683 nScavenged++;
1684 } else {
1685 nInuse++;
1686 }
1687 }
1688 }
1689 }
1690
1691 gMonitorFreeCount += nScavenged;
1692
1693 // Consider: audit gFreeList to ensure that gMonitorFreeCount and list agree.
1694
1695 if (ObjectMonitor::Knob_Verbose) {
1696 tty->print_cr("INFO: Deflate: InCirc=%d InUse=%d Scavenged=%d "
1697 "ForceMonitorScavenge=%d : pop=%d free=%d",
1698 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge,
1699 gMonitorPopulation, gMonitorFreeCount);
1700 tty->flush();
1701 }
1702
1703 ForceMonitorScavenge = 0; // Reset
1704
1705 // Move the scavenged monitors back to the global free list.
1706 if (freeHeadp != NULL) {
1707 guarantee(freeTailp != NULL && nScavenged > 0, "invariant");
1708 assert(freeTailp->FreeNext == NULL, "invariant");
1709 // constant-time list splice - prepend scavenged segment to gFreeList
1710 freeTailp->FreeNext = gFreeList;
1711 gFreeList = freeHeadp;
1712 }
1713 Thread::muxRelease(&gListLock);
1714
1715 OM_PERFDATA_OP(Deflations, inc(nScavenged));
1716 OM_PERFDATA_OP(MonExtant, set_value(nInCirculation));
1717
1718 // TODO: Add objectMonitor leak detection.
1719 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1720 GVars.stwRandom = os::random();
1721 GVars.stwCycle++;
1722 }
1723
1724 // Monitor cleanup on JavaThread::exit
1725
1726 // Iterate through monitor cache and attempt to release thread's monitors
1727 // Gives up on a particular monitor if an exception occurs, but continues
1728 // the overall iteration, swallowing the exception.
1729 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1730 private:
1731 TRAPS;
1732
1733 public:
1734 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1735 void do_monitor(ObjectMonitor* mid) {
1736 if (mid->owner() == THREAD) {
1737 if (ObjectMonitor::Knob_VerifyMatch != 0) {
1738 Handle obj((oop) mid->object());
1739 tty->print("INFO: unexpected locked object:");
1740 javaVFrame::print_locked_object_class_name(tty, obj, "locked");
1741 fatal("exiting JavaThread=" INTPTR_FORMAT
1742 " unexpectedly owns ObjectMonitor=" INTPTR_FORMAT,
1743 p2i(THREAD), p2i(mid));
1744 }
1745 (void)mid->complete_exit(CHECK);
1746 }
1747 }
1748 };
1749
1750 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1751 // ignored. This is meant to be called during JNI thread detach which assumes
1752 // all remaining monitors are heavyweight. All exceptions are swallowed.
1753 // Scanning the extant monitor list can be time consuming.
1754 // A simple optimization is to add a per-thread flag that indicates a thread
1755 // called jni_monitorenter() during its lifetime.
1756 //
1757 // Instead of No_Savepoint_Verifier it might be cheaper to
1758 // use an idiom of the form:
1759 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1760 // <code that must not run at safepoint>
1761 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1762 // Since the tests are extremely cheap we could leave them enabled
1763 // for normal product builds.
1764
1765 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1766 assert(THREAD == JavaThread::current(), "must be current Java thread");
1767 NoSafepointVerifier nsv;
1768 ReleaseJavaMonitorsClosure rjmc(THREAD);
1769 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
1770 ObjectSynchronizer::monitors_iterate(&rjmc);
1771 Thread::muxRelease(&gListLock);
1772 THREAD->clear_pending_exception();
1773 }
1774
1775 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1776 switch (cause) {
1777 case inflate_cause_vm_internal: return "VM Internal";
1778 case inflate_cause_monitor_enter: return "Monitor Enter";
1779 case inflate_cause_wait: return "Monitor Wait";
1780 case inflate_cause_notify: return "Monitor Notify";
1781 case inflate_cause_hash_code: return "Monitor Hash Code";
1782 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1783 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1784 default:
1785 ShouldNotReachHere();
1786 }
1787 return "Unknown";
1788 }
1789
1790 static void post_monitor_inflate_event(EventJavaMonitorInflate& event,
1791 const oop obj,
1792 const ObjectSynchronizer::InflateCause cause) {
1793 #if INCLUDE_TRACE
1794 assert(event.should_commit(), "check outside");
1795 event.set_klass(obj->klass());
1796 event.set_address((TYPE_ADDRESS)(uintptr_t)(void*)obj);
1797 event.set_cause((u1)cause);
1798 event.commit();
1799 #endif
1800 }
1801
1802 //------------------------------------------------------------------------------
1803 // Debugging code
1804
1805 void ObjectSynchronizer::sanity_checks(const bool verbose,
1806 const uint cache_line_size,
1807 int *error_cnt_ptr,
1808 int *warning_cnt_ptr) {
1809 u_char *addr_begin = (u_char*)&GVars;
1810 u_char *addr_stwRandom = (u_char*)&GVars.stwRandom;
1811 u_char *addr_hcSequence = (u_char*)&GVars.hcSequence;
1812
1813 if (verbose) {
1814 tty->print_cr("INFO: sizeof(SharedGlobals)=" SIZE_FORMAT,
1815 sizeof(SharedGlobals));
1816 }
1817
1818 uint offset_stwRandom = (uint)(addr_stwRandom - addr_begin);
1819 if (verbose) tty->print_cr("INFO: offset(stwRandom)=%u", offset_stwRandom);
1820
1821 uint offset_hcSequence = (uint)(addr_hcSequence - addr_begin);
1822 if (verbose) {
1823 tty->print_cr("INFO: offset(_hcSequence)=%u", offset_hcSequence);
1824 }
1825
1826 if (cache_line_size != 0) {
1827 // We were able to determine the L1 data cache line size so
1828 // do some cache line specific sanity checks
1829
1830 if (offset_stwRandom < cache_line_size) {
1831 tty->print_cr("WARNING: the SharedGlobals.stwRandom field is closer "
1832 "to the struct beginning than a cache line which permits "
1833 "false sharing.");
1834 (*warning_cnt_ptr)++;
1835 }
1836
1837 if ((offset_hcSequence - offset_stwRandom) < cache_line_size) {
1838 tty->print_cr("WARNING: the SharedGlobals.stwRandom and "
1839 "SharedGlobals.hcSequence fields are closer than a cache "
1840 "line which permits false sharing.");
1841 (*warning_cnt_ptr)++;
1842 }
1843
1844 if ((sizeof(SharedGlobals) - offset_hcSequence) < cache_line_size) {
1845 tty->print_cr("WARNING: the SharedGlobals.hcSequence field is closer "
1846 "to the struct end than a cache line which permits false "
1847 "sharing.");
1848 (*warning_cnt_ptr)++;
1849 }
1850 }
1851 }
1852
1853 #ifndef PRODUCT
1854
1855 // Verify all monitors in the monitor cache, the verification is weak.
1856 void ObjectSynchronizer::verify() {
1857 PaddedEnd<ObjectMonitor> * block =
1858 (PaddedEnd<ObjectMonitor> *)OrderAccess::load_ptr_acquire(&gBlockList);
1859 while (block != NULL) {
1860 assert(block->object() == CHAINMARKER, "must be a block header");
1861 for (int i = 1; i < _BLOCKSIZE; i++) {
1862 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
1863 oop object = (oop)mid->object();
1864 if (object != NULL) {
1865 mid->verify();
1866 }
1867 }
1868 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
1869 }
1870 }
1871
1872 // Check if monitor belongs to the monitor cache
1873 // The list is grow-only so it's *relatively* safe to traverse
1874 // the list of extant blocks without taking a lock.
1875
1876 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
1877 PaddedEnd<ObjectMonitor> * block =
1878 (PaddedEnd<ObjectMonitor> *)OrderAccess::load_ptr_acquire(&gBlockList);
1879 while (block != NULL) {
1880 assert(block->object() == CHAINMARKER, "must be a block header");
1881 if (monitor > (ObjectMonitor *)&block[0] &&
1882 monitor < (ObjectMonitor *)&block[_BLOCKSIZE]) {
1883 address mon = (address)monitor;
1884 address blk = (address)block;
1885 size_t diff = mon - blk;
1886 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "must be aligned");
1887 return 1;
1888 }
1889 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
1890 }
1891 return 0;
1892 }
1893
1894 #endif