1 /*
2 * Copyright (c) 1998, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/vmSymbols.hpp"
27 #include "memory/metaspaceShared.hpp"
28 #include "memory/padded.hpp"
29 #include "memory/resourceArea.hpp"
30 #include "oops/markOop.hpp"
31 #include "oops/oop.inline.hpp"
32 #include "runtime/atomic.inline.hpp"
33 #include "runtime/biasedLocking.hpp"
34 #include "runtime/handles.inline.hpp"
35 #include "runtime/interfaceSupport.hpp"
36 #include "runtime/mutexLocker.hpp"
37 #include "runtime/objectMonitor.hpp"
38 #include "runtime/objectMonitor.inline.hpp"
39 #include "runtime/osThread.hpp"
40 #include "runtime/stubRoutines.hpp"
41 #include "runtime/synchronizer.hpp"
42 #include "runtime/thread.inline.hpp"
43 #include "runtime/vframe.hpp"
44 #include "utilities/dtrace.hpp"
45 #include "utilities/events.hpp"
46 #include "utilities/preserveException.hpp"
47
48 #if defined(__GNUC__) && !defined(PPC64)
49 // Need to inhibit inlining for older versions of GCC to avoid build-time failures
50 #define NOINLINE __attribute__((noinline))
51 #else
52 #define NOINLINE
53 #endif
54
55 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
56
57 // The "core" versions of monitor enter and exit reside in this file.
58 // The interpreter and compilers contain specialized transliterated
59 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
60 // for instance. If you make changes here, make sure to modify the
61 // interpreter, and both C1 and C2 fast-path inline locking code emission.
62 //
63 // -----------------------------------------------------------------------------
64
65 #ifdef DTRACE_ENABLED
66
67 // Only bother with this argument setup if dtrace is available
68 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
69
70 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
71 char* bytes = NULL; \
72 int len = 0; \
73 jlong jtid = SharedRuntime::get_java_tid(thread); \
74 Symbol* klassname = ((oop)(obj))->klass()->name(); \
75 if (klassname != NULL) { \
76 bytes = (char*)klassname->bytes(); \
77 len = klassname->utf8_length(); \
78 }
79
80 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
81 { \
82 if (DTraceMonitorProbes) { \
83 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
84 HOTSPOT_MONITOR_WAIT(jtid, \
85 (uintptr_t)(monitor), bytes, len, (millis)); \
86 } \
87 }
88
89 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
90 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
91 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
92
93 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
94 { \
95 if (DTraceMonitorProbes) { \
96 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
97 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
98 (uintptr_t)(monitor), bytes, len); \
99 } \
100 }
101
102 #else // ndef DTRACE_ENABLED
103
104 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
105 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
106
107 #endif // ndef DTRACE_ENABLED
108
109 // This exists only as a workaround of dtrace bug 6254741
110 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
111 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
112 return 0;
113 }
114
115 #define NINFLATIONLOCKS 256
116 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
117
118 // global list of blocks of monitors
119 // gBlockList is really PaddedEnd<ObjectMonitor> *, but we don't
120 // want to expose the PaddedEnd template more than necessary.
121 ObjectMonitor * ObjectSynchronizer::gBlockList = NULL;
122 // global monitor free list
123 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL;
124 // global monitor in-use list, for moribund threads,
125 // monitors they inflated need to be scanned for deflation
126 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL;
127 // count of entries in gOmInUseList
128 int ObjectSynchronizer::gOmInUseCount = 0;
129
130 static volatile intptr_t gListLock = 0; // protects global monitor lists
131 static volatile int gMonitorFreeCount = 0; // # on gFreeList
132 static volatile int gMonitorPopulation = 0; // # Extant -- in circulation
133
134 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
135
136
137 // =====================> Quick functions
138
139 // The quick_* forms are special fast-path variants used to improve
140 // performance. In the simplest case, a "quick_*" implementation could
141 // simply return false, in which case the caller will perform the necessary
142 // state transitions and call the slow-path form.
143 // The fast-path is designed to handle frequently arising cases in an efficient
144 // manner and is just a degenerate "optimistic" variant of the slow-path.
145 // returns true -- to indicate the call was satisfied.
146 // returns false -- to indicate the call needs the services of the slow-path.
147 // A no-loitering ordinance is in effect for code in the quick_* family
148 // operators: safepoints or indefinite blocking (blocking that might span a
149 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
150 // entry.
151 //
152 // Consider: An interesting optimization is to have the JIT recognize the
153 // following common idiom:
154 // synchronized (someobj) { .... ; notify(); }
155 // That is, we find a notify() or notifyAll() call that immediately precedes
156 // the monitorexit operation. In that case the JIT could fuse the operations
157 // into a single notifyAndExit() runtime primitive.
158
159 bool ObjectSynchronizer::quick_notify(oopDesc * obj, Thread * self, bool all) {
160 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
161 assert(self->is_Java_thread(), "invariant");
162 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
163 assert(obj == oopDesc::bs()->write_barrier(obj), "expect to-space copy");
164 No_Safepoint_Verifier nsv;
165 if (obj == NULL) return false; // slow-path for invalid obj
166 const markOop mark = obj->mark();
167
168 if (mark->has_locker() && self->is_lock_owned((address)mark->locker())) {
169 // Degenerate notify
170 // stack-locked by caller so by definition the implied waitset is empty.
171 return true;
172 }
173
174 if (mark->has_monitor()) {
175 ObjectMonitor * const mon = mark->monitor();
176 assert(mon->object() == obj, "invariant");
177 if (mon->owner() != self) return false; // slow-path for IMS exception
178
179 if (mon->first_waiter() != NULL) {
180 // We have one or more waiters. Since this is an inflated monitor
181 // that we own, we can transfer one or more threads from the waitset
182 // to the entrylist here and now, avoiding the slow-path.
183 if (all) {
184 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
185 } else {
186 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
187 }
188 int tally = 0;
189 do {
190 mon->INotify(self);
191 ++tally;
192 } while (mon->first_waiter() != NULL && all);
193 OM_PERFDATA_OP(Notifications, inc(tally));
194 }
195 return true;
196 }
197
198 // biased locking and any other IMS exception states take the slow-path
199 return false;
200 }
201
202
203 // The LockNode emitted directly at the synchronization site would have
204 // been too big if it were to have included support for the cases of inflated
205 // recursive enter and exit, so they go here instead.
206 // Note that we can't safely call AsyncPrintJavaStack() from within
207 // quick_enter() as our thread state remains _in_Java.
208
209 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
210 BasicLock * Lock) {
211 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
212 assert(Self->is_Java_thread(), "invariant");
213 assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
214 assert(obj == oopDesc::bs()->write_barrier(obj), "expect to-space copy");
215 No_Safepoint_Verifier nsv;
216 if (obj == NULL) return false; // Need to throw NPE
217 const markOop mark = obj->mark();
218
219 if (mark->has_monitor()) {
220 ObjectMonitor * const m = mark->monitor();
221 assert(m->object() == obj, "invariant");
222 Thread * const owner = (Thread *) m->_owner;
223
224 // Lock contention and Transactional Lock Elision (TLE) diagnostics
225 // and observability
226 // Case: light contention possibly amenable to TLE
227 // Case: TLE inimical operations such as nested/recursive synchronization
228
229 if (owner == Self) {
230 m->_recursions++;
231 return true;
232 }
233
234 if (owner == NULL &&
235 Atomic::cmpxchg_ptr(Self, &(m->_owner), NULL) == NULL) {
236 assert(m->_recursions == 0, "invariant");
237 assert(m->_owner == Self, "invariant");
238 return true;
239 }
240 }
241
242 // Note that we could inflate in quick_enter.
243 // This is likely a useful optimization
244 // Critically, in quick_enter() we must not:
245 // -- perform bias revocation, or
246 // -- block indefinitely, or
247 // -- reach a safepoint
248
249 return false; // revert to slow-path
250 }
251
252 // -----------------------------------------------------------------------------
253 // Fast Monitor Enter/Exit
254 // This the fast monitor enter. The interpreter and compiler use
255 // some assembly copies of this code. Make sure update those code
256 // if the following function is changed. The implementation is
257 // extremely sensitive to race condition. Be careful.
258
259 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
260 bool attempt_rebias, TRAPS) {
261 assert(obj() == oopDesc::bs()->write_barrier(obj()), "expect to-space copy");
262 if (UseBiasedLocking) {
263 if (!SafepointSynchronize::is_at_safepoint()) {
264 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
265 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
266 return;
267 }
268 } else {
269 assert(!attempt_rebias, "can not rebias toward VM thread");
270 BiasedLocking::revoke_at_safepoint(obj);
271 }
272 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
273 }
274
275 slow_enter(obj, lock, THREAD);
276 }
277
278 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
279 assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here");
280 // if displaced header is null, the previous enter is recursive enter, no-op
281 assert(object == oopDesc::bs()->write_barrier(object), "expect to-space copy");
282
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, object)->exit(true, THREAD);
314 }
315
316 // -----------------------------------------------------------------------------
317 // Interpreter/Compiler Slow Case
318 // This routine is used to handle interpreter/compiler slow case
319 // We don't need to use fast path here, because it must have been
320 // failed in the interpreter/compiler code.
321 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
322 assert(obj() == oopDesc::bs()->write_barrier(obj()), "expect to-space copy");
323 markOop mark = obj->mark();
324 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
325
326 if (mark->is_neutral()) {
327 // Anticipate successful CAS -- the ST of the displaced mark must
328 // be visible <= the ST performed by the CAS.
329 lock->set_displaced_header(mark);
330 if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) {
331 TEVENT(slow_enter: release stacklock);
332 return;
333 }
334 // Fall through to inflate() ...
335 } else if (mark->has_locker() &&
336 THREAD->is_lock_owned((address)mark->locker())) {
337 assert(lock != mark->locker(), "must not re-lock the same lock");
338 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
339 lock->set_displaced_header(NULL);
340 return;
341 }
342
343 // The object header will never be displaced to this lock,
344 // so it does not matter what the value is, except that it
345 // must be non-zero to avoid looking like a re-entrant lock,
346 // and must not look locked either.
347 lock->set_displaced_header(markOopDesc::unused_mark());
348 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
349 }
350
351 // This routine is used to handle interpreter/compiler slow case
352 // We don't need to use fast path here, because it must have
353 // failed in the interpreter/compiler code. Simply use the heavy
354 // weight monitor should be ok, unless someone find otherwise.
355 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
356 fast_exit(object, lock, THREAD);
357 }
358
359 // -----------------------------------------------------------------------------
360 // Class Loader support to workaround deadlocks on the class loader lock objects
361 // Also used by GC
362 // complete_exit()/reenter() are used to wait on a nested lock
363 // i.e. to give up an outer lock completely and then re-enter
364 // Used when holding nested locks - lock acquisition order: lock1 then lock2
365 // 1) complete_exit lock1 - saving recursion count
366 // 2) wait on lock2
367 // 3) when notified on lock2, unlock lock2
368 // 4) reenter lock1 with original recursion count
369 // 5) lock lock2
370 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
371 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
372 TEVENT(complete_exit);
373 assert(obj() == oopDesc::bs()->write_barrier(obj()), "expect to-space copy");
374 if (UseBiasedLocking) {
375 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
376 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
377 }
378
379 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
380
381 return monitor->complete_exit(THREAD);
382 }
383
384 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
385 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
386 TEVENT(reenter);
387 assert(obj() == oopDesc::bs()->write_barrier(obj()), "expect to-space copy");
388 if (UseBiasedLocking) {
389 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
390 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
391 }
392
393 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
394
395 monitor->reenter(recursion, THREAD);
396 }
397 // -----------------------------------------------------------------------------
398 // JNI locks on java objects
399 // NOTE: must use heavy weight monitor to handle jni monitor enter
400 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
401 // the current locking is from JNI instead of Java code
402 TEVENT(jni_enter);
403 assert(obj() == oopDesc::bs()->write_barrier(obj()), "expect to-space copy");
404 if (UseBiasedLocking) {
405 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
406 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
407 }
408 THREAD->set_current_pending_monitor_is_from_java(false);
409 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
410 THREAD->set_current_pending_monitor_is_from_java(true);
411 }
412
413 // NOTE: must use heavy weight monitor to handle jni monitor exit
414 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
415 TEVENT(jni_exit);
416 assert(obj == oopDesc::bs()->write_barrier(obj), "expect to-space copy");
417 if (UseBiasedLocking) {
418 Handle h_obj(THREAD, obj);
419 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
420 obj = h_obj();
421 }
422 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
423
424 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj);
425 // If this thread has locked the object, exit the monitor. Note: can't use
426 // monitor->check(CHECK); must exit even if an exception is pending.
427 if (monitor->check(THREAD)) {
428 monitor->exit(true, THREAD);
429 }
430 }
431
432 // -----------------------------------------------------------------------------
433 // Internal VM locks on java objects
434 // standard constructor, allows locking failures
435 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
436 _dolock = doLock;
437 _thread = thread;
438 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
439 _obj = obj;
440
441 if (_dolock) {
442 TEVENT(ObjectLocker);
443
444 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
445 }
446 }
447
448 ObjectLocker::~ObjectLocker() {
449 if (_dolock) {
450 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
451 }
452 }
453
454
455 // -----------------------------------------------------------------------------
456 // Wait/Notify/NotifyAll
457 // NOTE: must use heavy weight monitor to handle wait()
458 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
459 assert(obj() == oopDesc::bs()->write_barrier(obj()), "expect to-space copy");
460 if (UseBiasedLocking) {
461 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
462 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
463 }
464 if (millis < 0) {
465 TEVENT(wait - throw IAX);
466 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
467 }
468 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
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 assert(obj() == oopDesc::bs()->write_barrier(obj()), "expect to-space copy");
481 if (UseBiasedLocking) {
482 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
483 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
484 }
485 if (millis < 0) {
486 TEVENT(wait - throw IAX);
487 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
488 }
489 ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD);
490 }
491
492 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
493 assert(obj() == oopDesc::bs()->write_barrier(obj()), "expect to-space copy");
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, obj())->notify(THREAD);
504 }
505
506 // NOTE: see comment of notify()
507 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
508 assert(obj() == oopDesc::bs()->write_barrier(obj()), "expect to-space copy");
509 if (UseBiasedLocking) {
510 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
511 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
512 }
513
514 markOop mark = obj->mark();
515 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
516 return;
517 }
518 ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD);
519 }
520
521 // -----------------------------------------------------------------------------
522 // Hash Code handling
523 //
524 // Performance concern:
525 // OrderAccess::storestore() calls release() which at one time stored 0
526 // into the global volatile OrderAccess::dummy variable. This store was
527 // unnecessary for correctness. Many threads storing into a common location
528 // causes considerable cache migration or "sloshing" on large SMP systems.
529 // As such, I avoided using OrderAccess::storestore(). In some cases
530 // OrderAccess::fence() -- which incurs local latency on the executing
531 // processor -- is a better choice as it scales on SMP systems.
532 //
533 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
534 // a discussion of coherency costs. Note that all our current reference
535 // platforms provide strong ST-ST order, so the issue is moot on IA32,
536 // x64, and SPARC.
537 //
538 // As a general policy we use "volatile" to control compiler-based reordering
539 // and explicit fences (barriers) to control for architectural reordering
540 // performed by the CPU(s) or platform.
541
542 struct SharedGlobals {
543 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
544 // These are highly shared mostly-read variables.
545 // To avoid false-sharing they need to be the sole occupants of a cache line.
546 volatile int stwRandom;
547 volatile int stwCycle;
548 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
549 // Hot RW variable -- Sequester to avoid false-sharing
550 volatile int hcSequence;
551 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
552 };
553
554 static SharedGlobals GVars;
555 static int MonitorScavengeThreshold = 1000000;
556 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
557
558 static markOop ReadStableMark(oop obj) {
559 markOop mark = obj->mark();
560 if (!mark->is_being_inflated()) {
561 return mark; // normal fast-path return
562 }
563
564 int its = 0;
565 for (;;) {
566 markOop mark = obj->mark();
567 if (!mark->is_being_inflated()) {
568 return mark; // normal fast-path return
569 }
570
571 // The object is being inflated by some other thread.
572 // The caller of ReadStableMark() must wait for inflation to complete.
573 // Avoid live-lock
574 // TODO: consider calling SafepointSynchronize::do_call_back() while
575 // spinning to see if there's a safepoint pending. If so, immediately
576 // yielding or blocking would be appropriate. Avoid spinning while
577 // there is a safepoint pending.
578 // TODO: add inflation contention performance counters.
579 // TODO: restrict the aggregate number of spinners.
580
581 ++its;
582 if (its > 10000 || !os::is_MP()) {
583 if (its & 1) {
584 os::naked_yield();
585 TEVENT(Inflate: INFLATING - yield);
586 } else {
587 // Note that the following code attenuates the livelock problem but is not
588 // a complete remedy. A more complete solution would require that the inflating
589 // thread hold the associated inflation lock. The following code simply restricts
590 // the number of spinners to at most one. We'll have N-2 threads blocked
591 // on the inflationlock, 1 thread holding the inflation lock and using
592 // a yield/park strategy, and 1 thread in the midst of inflation.
593 // A more refined approach would be to change the encoding of INFLATING
594 // to allow encapsulation of a native thread pointer. Threads waiting for
595 // inflation to complete would use CAS to push themselves onto a singly linked
596 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
597 // and calling park(). When inflation was complete the thread that accomplished inflation
598 // would detach the list and set the markword to inflated with a single CAS and
599 // then for each thread on the list, set the flag and unpark() the thread.
600 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
601 // wakes at most one thread whereas we need to wake the entire list.
602 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
603 int YieldThenBlock = 0;
604 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
605 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
606 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
607 while (obj->mark() == markOopDesc::INFLATING()) {
608 // Beware: NakedYield() is advisory and has almost no effect on some platforms
609 // so we periodically call Self->_ParkEvent->park(1).
610 // We use a mixed spin/yield/block mechanism.
611 if ((YieldThenBlock++) >= 16) {
612 Thread::current()->_ParkEvent->park(1);
613 } else {
614 os::naked_yield();
615 }
616 }
617 Thread::muxRelease(gInflationLocks + ix);
618 TEVENT(Inflate: INFLATING - yield/park);
619 }
620 } else {
621 SpinPause(); // SMP-polite spinning
622 }
623 }
624 }
625
626 // hashCode() generation :
627 //
628 // Possibilities:
629 // * MD5Digest of {obj,stwRandom}
630 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
631 // * A DES- or AES-style SBox[] mechanism
632 // * One of the Phi-based schemes, such as:
633 // 2654435761 = 2^32 * Phi (golden ratio)
634 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
635 // * A variation of Marsaglia's shift-xor RNG scheme.
636 // * (obj ^ stwRandom) is appealing, but can result
637 // in undesirable regularity in the hashCode values of adjacent objects
638 // (objects allocated back-to-back, in particular). This could potentially
639 // result in hashtable collisions and reduced hashtable efficiency.
640 // There are simple ways to "diffuse" the middle address bits over the
641 // generated hashCode values:
642
643 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
644 intptr_t value = 0;
645 if (hashCode == 0) {
646 // This form uses an unguarded global Park-Miller RNG,
647 // so it's possible for two threads to race and generate the same RNG.
648 // On MP system we'll have lots of RW access to a global, so the
649 // mechanism induces lots of coherency traffic.
650 value = os::random();
651 } else if (hashCode == 1) {
652 // This variation has the property of being stable (idempotent)
653 // between STW operations. This can be useful in some of the 1-0
654 // synchronization schemes.
655 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
656 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
657 } else if (hashCode == 2) {
658 value = 1; // for sensitivity testing
659 } else if (hashCode == 3) {
660 value = ++GVars.hcSequence;
661 } else if (hashCode == 4) {
662 value = cast_from_oop<intptr_t>(obj);
663 } else {
664 // Marsaglia's xor-shift scheme with thread-specific state
665 // This is probably the best overall implementation -- we'll
666 // likely make this the default in future releases.
667 unsigned t = Self->_hashStateX;
668 t ^= (t << 11);
669 Self->_hashStateX = Self->_hashStateY;
670 Self->_hashStateY = Self->_hashStateZ;
671 Self->_hashStateZ = Self->_hashStateW;
672 unsigned v = Self->_hashStateW;
673 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
674 Self->_hashStateW = v;
675 value = v;
676 }
677
678 value &= markOopDesc::hash_mask;
679 if (value == 0) value = 0xBAD;
680 assert(value != markOopDesc::no_hash, "invariant");
681 TEVENT(hashCode: GENERATE);
682 return value;
683 }
684
685 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
686 assert(obj == oopDesc::bs()->write_barrier(obj), "expect to-space copy");
687 if (UseBiasedLocking) {
688 // NOTE: many places throughout the JVM do not expect a safepoint
689 // to be taken here, in particular most operations on perm gen
690 // objects. However, we only ever bias Java instances and all of
691 // the call sites of identity_hash that might revoke biases have
692 // been checked to make sure they can handle a safepoint. The
693 // added check of the bias pattern is to avoid useless calls to
694 // thread-local storage.
695 if (obj->mark()->has_bias_pattern()) {
696 // Handle for oop obj in case of STW safepoint
697 Handle hobj(Self, obj);
698 // Relaxing assertion for bug 6320749.
699 assert(Universe::verify_in_progress() ||
700 !SafepointSynchronize::is_at_safepoint(),
701 "biases should not be seen by VM thread here");
702 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
703 obj = hobj();
704 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
705 }
706 }
707
708 // hashCode() is a heap mutator ...
709 // Relaxing assertion for bug 6320749.
710 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
711 !SafepointSynchronize::is_at_safepoint(), "invariant");
712 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
713 Self->is_Java_thread() , "invariant");
714 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
715 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
716
717 ObjectMonitor* monitor = NULL;
718 markOop temp, test;
719 intptr_t hash;
720 markOop mark = ReadStableMark(obj);
721
722 // object should remain ineligible for biased locking
723 assert(!mark->has_bias_pattern(), "invariant");
724
725 if (mark->is_neutral()) {
726 hash = mark->hash(); // this is a normal header
727 if (hash) { // if it has hash, just return it
728 return hash;
729 }
730 hash = get_next_hash(Self, obj); // allocate a new hash code
731 temp = mark->copy_set_hash(hash); // merge the hash code into header
732 // use (machine word version) atomic operation to install the hash
733 test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark);
734 if (test == mark) {
735 return hash;
736 }
737 // If atomic operation failed, we must inflate the header
738 // into heavy weight monitor. We could add more code here
739 // for fast path, but it does not worth the complexity.
740 } else if (mark->has_monitor()) {
741 monitor = mark->monitor();
742 temp = monitor->header();
743 assert(temp->is_neutral(), "invariant");
744 hash = temp->hash();
745 if (hash) {
746 return hash;
747 }
748 // Skip to the following code to reduce code size
749 } else if (Self->is_lock_owned((address)mark->locker())) {
750 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
751 assert(temp->is_neutral(), "invariant");
752 hash = temp->hash(); // by current thread, check if the displaced
753 if (hash) { // header contains hash code
754 return hash;
755 }
756 // WARNING:
757 // The displaced header is strictly immutable.
758 // It can NOT be changed in ANY cases. So we have
759 // to inflate the header into heavyweight monitor
760 // even the current thread owns the lock. The reason
761 // is the BasicLock (stack slot) will be asynchronously
762 // read by other threads during the inflate() function.
763 // Any change to stack may not propagate to other threads
764 // correctly.
765 }
766
767 // Inflate the monitor to set hash code
768 monitor = ObjectSynchronizer::inflate(Self, obj);
769 // Load displaced header and check it has hash code
770 mark = monitor->header();
771 assert(mark->is_neutral(), "invariant");
772 hash = mark->hash();
773 if (hash == 0) {
774 hash = get_next_hash(Self, obj);
775 temp = mark->copy_set_hash(hash); // merge hash code into header
776 assert(temp->is_neutral(), "invariant");
777 test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark);
778 if (test != mark) {
779 // The only update to the header in the monitor (outside GC)
780 // is install the hash code. If someone add new usage of
781 // displaced header, please update this code
782 hash = test->hash();
783 assert(test->is_neutral(), "invariant");
784 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
785 }
786 }
787 // We finally get the hash
788 return hash;
789 }
790
791 // Deprecated -- use FastHashCode() instead.
792
793 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
794 return FastHashCode(Thread::current(), obj());
795 }
796
797
798 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
799 Handle h_obj) {
800 assert(h_obj() == oopDesc::bs()->write_barrier(h_obj()), "expect to-space copy");
801 if (UseBiasedLocking) {
802 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
803 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
804 }
805
806 assert(thread == JavaThread::current(), "Can only be called on current thread");
807 oop obj = h_obj();
808
809 markOop mark = ReadStableMark(obj);
810
811 // Uncontended case, header points to stack
812 if (mark->has_locker()) {
813 return thread->is_lock_owned((address)mark->locker());
814 }
815 // Contended case, header points to ObjectMonitor (tagged pointer)
816 if (mark->has_monitor()) {
817 ObjectMonitor* monitor = mark->monitor();
818 return monitor->is_entered(thread) != 0;
819 }
820 // Unlocked case, header in place
821 assert(mark->is_neutral(), "sanity check");
822 return false;
823 }
824
825 // Be aware of this method could revoke bias of the lock object.
826 // This method queries the ownership of the lock handle specified by 'h_obj'.
827 // If the current thread owns the lock, it returns owner_self. If no
828 // thread owns the lock, it returns owner_none. Otherwise, it will return
829 // owner_other.
830 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
831 (JavaThread *self, Handle h_obj) {
832 // The caller must beware this method can revoke bias, and
833 // revocation can result in a safepoint.
834 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
835 assert(self->thread_state() != _thread_blocked, "invariant");
836
837 // Possible mark states: neutral, biased, stack-locked, inflated
838
839 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
840 // CASE: biased
841 BiasedLocking::revoke_and_rebias(h_obj, false, self);
842 assert(!h_obj->mark()->has_bias_pattern(),
843 "biases should be revoked by now");
844 }
845
846 assert(self == JavaThread::current(), "Can only be called on current thread");
847 oop obj = h_obj();
848 markOop mark = ReadStableMark(obj);
849
850 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
851 if (mark->has_locker()) {
852 return self->is_lock_owned((address)mark->locker()) ?
853 owner_self : owner_other;
854 }
855
856 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
857 // The Object:ObjectMonitor relationship is stable as long as we're
858 // not at a safepoint.
859 if (mark->has_monitor()) {
860 void * owner = mark->monitor()->_owner;
861 if (owner == NULL) return owner_none;
862 return (owner == self ||
863 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
864 }
865
866 // CASE: neutral
867 assert(mark->is_neutral(), "sanity check");
868 return owner_none; // it's unlocked
869 }
870
871 // FIXME: jvmti should call this
872 JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) {
873 assert(h_obj() == oopDesc::bs()->write_barrier(h_obj()), "expect to-space copy");
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 // Visitors ...
913
914 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
915 PaddedEnd<ObjectMonitor> * block = (PaddedEnd<ObjectMonitor> *)gBlockList;
916 ObjectMonitor* mid;
917 while (block) {
918 assert(block->object() == CHAINMARKER, "must be a block header");
919 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
920 mid = (ObjectMonitor *)(block + i);
921 oop object = (oop) mid->object();
922 if (object != NULL) {
923 closure->do_monitor(mid);
924 }
925 }
926 block = (PaddedEnd<ObjectMonitor> *) block->FreeNext;
927 }
928 }
929
930 // Get the next block in the block list.
931 static inline ObjectMonitor* next(ObjectMonitor* block) {
932 assert(block->object() == CHAINMARKER, "must be a block header");
933 block = block->FreeNext;
934 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
935 return block;
936 }
937
938
939 void ObjectSynchronizer::oops_do(OopClosure* f) {
940 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
941 for (PaddedEnd<ObjectMonitor> * block =
942 (PaddedEnd<ObjectMonitor> *)gBlockList; block != NULL;
943 block = (PaddedEnd<ObjectMonitor> *)next(block)) {
944 assert(block->object() == CHAINMARKER, "must be a block header");
945 for (int i = 1; i < _BLOCKSIZE; i++) {
946 ObjectMonitor* mid = (ObjectMonitor *)&block[i];
947 if (mid->object() != NULL) {
948 f->do_oop((oop*)mid->object_addr());
949 }
950 }
951 }
952 }
953
954
955 // -----------------------------------------------------------------------------
956 // ObjectMonitor Lifecycle
957 // -----------------------
958 // Inflation unlinks monitors from the global gFreeList and
959 // associates them with objects. Deflation -- which occurs at
960 // STW-time -- disassociates idle monitors from objects. Such
961 // scavenged monitors are returned to the gFreeList.
962 //
963 // The global list is protected by gListLock. All the critical sections
964 // are short and operate in constant-time.
965 //
966 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
967 //
968 // Lifecycle:
969 // -- unassigned and on the global free list
970 // -- unassigned and on a thread's private omFreeList
971 // -- assigned to an object. The object is inflated and the mark refers
972 // to the objectmonitor.
973
974
975 // Constraining monitor pool growth via MonitorBound ...
976 //
977 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
978 // the rate of scavenging is driven primarily by GC. As such, we can find
979 // an inordinate number of monitors in circulation.
980 // To avoid that scenario we can artificially induce a STW safepoint
981 // if the pool appears to be growing past some reasonable bound.
982 // Generally we favor time in space-time tradeoffs, but as there's no
983 // natural back-pressure on the # of extant monitors we need to impose some
984 // type of limit. Beware that if MonitorBound is set to too low a value
985 // we could just loop. In addition, if MonitorBound is set to a low value
986 // we'll incur more safepoints, which are harmful to performance.
987 // See also: GuaranteedSafepointInterval
988 //
989 // The current implementation uses asynchronous VM operations.
990
991 static void InduceScavenge(Thread * Self, const char * Whence) {
992 // Induce STW safepoint to trim monitors
993 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
994 // More precisely, trigger an asynchronous STW safepoint as the number
995 // of active monitors passes the specified threshold.
996 // TODO: assert thread state is reasonable
997
998 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
999 if (ObjectMonitor::Knob_Verbose) {
1000 tty->print_cr("INFO: Monitor scavenge - Induced STW @%s (%d)",
1001 Whence, ForceMonitorScavenge) ;
1002 tty->flush();
1003 }
1004 // Induce a 'null' safepoint to scavenge monitors
1005 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1006 // to the VMthread and have a lifespan longer than that of this activation record.
1007 // The VMThread will delete the op when completed.
1008 VMThread::execute(new VM_ForceAsyncSafepoint());
1009
1010 if (ObjectMonitor::Knob_Verbose) {
1011 tty->print_cr("INFO: Monitor scavenge - STW posted @%s (%d)",
1012 Whence, ForceMonitorScavenge) ;
1013 tty->flush();
1014 }
1015 }
1016 }
1017
1018 void ObjectSynchronizer::verifyInUse(Thread *Self) {
1019 ObjectMonitor* mid;
1020 int in_use_tally = 0;
1021 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) {
1022 in_use_tally++;
1023 }
1024 assert(in_use_tally == Self->omInUseCount, "in-use count off");
1025
1026 int free_tally = 0;
1027 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) {
1028 free_tally++;
1029 }
1030 assert(free_tally == Self->omFreeCount, "free count off");
1031 }
1032
1033 ObjectMonitor * NOINLINE ObjectSynchronizer::omAlloc(Thread * Self) {
1034 // A large MAXPRIVATE value reduces both list lock contention
1035 // and list coherency traffic, but also tends to increase the
1036 // number of objectMonitors in circulation as well as the STW
1037 // scavenge costs. As usual, we lean toward time in space-time
1038 // tradeoffs.
1039 const int MAXPRIVATE = 1024;
1040 for (;;) {
1041 ObjectMonitor * m;
1042
1043 // 1: try to allocate from the thread's local omFreeList.
1044 // Threads will attempt to allocate first from their local list, then
1045 // from the global list, and only after those attempts fail will the thread
1046 // attempt to instantiate new monitors. Thread-local free lists take
1047 // heat off the gListLock and improve allocation latency, as well as reducing
1048 // coherency traffic on the shared global list.
1049 m = Self->omFreeList;
1050 if (m != NULL) {
1051 Self->omFreeList = m->FreeNext;
1052 Self->omFreeCount--;
1053 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene
1054 guarantee(m->object() == NULL, "invariant");
1055 if (MonitorInUseLists) {
1056 m->FreeNext = Self->omInUseList;
1057 Self->omInUseList = m;
1058 Self->omInUseCount++;
1059 if (ObjectMonitor::Knob_VerifyInUse) {
1060 verifyInUse(Self);
1061 }
1062 } else {
1063 m->FreeNext = NULL;
1064 }
1065 return m;
1066 }
1067
1068 // 2: try to allocate from the global gFreeList
1069 // CONSIDER: use muxTry() instead of muxAcquire().
1070 // If the muxTry() fails then drop immediately into case 3.
1071 // If we're using thread-local free lists then try
1072 // to reprovision the caller's free list.
1073 if (gFreeList != NULL) {
1074 // Reprovision the thread's omFreeList.
1075 // Use bulk transfers to reduce the allocation rate and heat
1076 // on various locks.
1077 Thread::muxAcquire(&gListLock, "omAlloc");
1078 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1079 gMonitorFreeCount--;
1080 ObjectMonitor * take = gFreeList;
1081 gFreeList = take->FreeNext;
1082 guarantee(take->object() == NULL, "invariant");
1083 guarantee(!take->is_busy(), "invariant");
1084 take->Recycle();
1085 omRelease(Self, take, false);
1086 }
1087 Thread::muxRelease(&gListLock);
1088 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1089 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1090 TEVENT(omFirst - reprovision);
1091
1092 const int mx = MonitorBound;
1093 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1094 // We can't safely induce a STW safepoint from omAlloc() as our thread
1095 // state may not be appropriate for such activities and callers may hold
1096 // naked oops, so instead we defer the action.
1097 InduceScavenge(Self, "omAlloc");
1098 }
1099 continue;
1100 }
1101
1102 // 3: allocate a block of new ObjectMonitors
1103 // Both the local and global free lists are empty -- resort to malloc().
1104 // In the current implementation objectMonitors are TSM - immortal.
1105 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1106 // each ObjectMonitor to start at the beginning of a cache line,
1107 // so we use align_size_up().
1108 // A better solution would be to use C++ placement-new.
1109 // BEWARE: As it stands currently, we don't run the ctors!
1110 assert(_BLOCKSIZE > 1, "invariant");
1111 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
1112 PaddedEnd<ObjectMonitor> * temp;
1113 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1114 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
1115 mtInternal);
1116 temp = (PaddedEnd<ObjectMonitor> *)
1117 align_size_up((intptr_t)real_malloc_addr,
1118 DEFAULT_CACHE_LINE_SIZE);
1119
1120 // NOTE: (almost) no way to recover if allocation failed.
1121 // We might be able to induce a STW safepoint and scavenge enough
1122 // objectMonitors to permit progress.
1123 if (temp == NULL) {
1124 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1125 "Allocate ObjectMonitors");
1126 }
1127 (void)memset((void *) temp, 0, neededsize);
1128
1129 // Format the block.
1130 // initialize the linked list, each monitor points to its next
1131 // forming the single linked free list, the very first monitor
1132 // will points to next block, which forms the block list.
1133 // The trick of using the 1st element in the block as gBlockList
1134 // linkage should be reconsidered. A better implementation would
1135 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1136
1137 for (int i = 1; i < _BLOCKSIZE; i++) {
1138 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1139 }
1140
1141 // terminate the last monitor as the end of list
1142 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1143
1144 // Element [0] is reserved for global list linkage
1145 temp[0].set_object(CHAINMARKER);
1146
1147 // Consider carving out this thread's current request from the
1148 // block in hand. This avoids some lock traffic and redundant
1149 // list activity.
1150
1151 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1152 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1153 Thread::muxAcquire(&gListLock, "omAlloc [2]");
1154 gMonitorPopulation += _BLOCKSIZE-1;
1155 gMonitorFreeCount += _BLOCKSIZE-1;
1156
1157 // Add the new block to the list of extant blocks (gBlockList).
1158 // The very first objectMonitor in a block is reserved and dedicated.
1159 // It serves as blocklist "next" linkage.
1160 temp[0].FreeNext = gBlockList;
1161 gBlockList = temp;
1162
1163 // Add the new string of objectMonitors to the global free list
1164 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1165 gFreeList = temp + 1;
1166 Thread::muxRelease(&gListLock);
1167 TEVENT(Allocate block of monitors);
1168 }
1169 }
1170
1171 // Place "m" on the caller's private per-thread omFreeList.
1172 // In practice there's no need to clamp or limit the number of
1173 // monitors on a thread's omFreeList as the only time we'll call
1174 // omRelease is to return a monitor to the free list after a CAS
1175 // attempt failed. This doesn't allow unbounded #s of monitors to
1176 // accumulate on a thread's free list.
1177 //
1178 // Key constraint: all ObjectMonitors on a thread's free list and the global
1179 // free list must have their object field set to null. This prevents the
1180 // scavenger -- deflate_idle_monitors -- from reclaiming them.
1181
1182 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1183 bool fromPerThreadAlloc) {
1184 guarantee(m->object() == NULL, "invariant");
1185 guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor");
1186 // Remove from omInUseList
1187 if (MonitorInUseLists && fromPerThreadAlloc) {
1188 ObjectMonitor* cur_mid_in_use = NULL;
1189 bool extracted = false;
1190 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1191 if (m == mid) {
1192 // extract from per-thread in-use list
1193 if (mid == Self->omInUseList) {
1194 Self->omInUseList = mid->FreeNext;
1195 } else if (cur_mid_in_use != NULL) {
1196 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1197 }
1198 extracted = true;
1199 Self->omInUseCount--;
1200 if (ObjectMonitor::Knob_VerifyInUse) {
1201 verifyInUse(Self);
1202 }
1203 break;
1204 }
1205 }
1206 assert(extracted, "Should have extracted from in-use list");
1207 }
1208
1209 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1210 m->FreeNext = Self->omFreeList;
1211 Self->omFreeList = m;
1212 Self->omFreeCount++;
1213 }
1214
1215 // Return the monitors of a moribund thread's local free list to
1216 // the global free list. Typically a thread calls omFlush() when
1217 // it's dying. We could also consider having the VM thread steal
1218 // monitors from threads that have not run java code over a few
1219 // consecutive STW safepoints. Relatedly, we might decay
1220 // omFreeProvision at STW safepoints.
1221 //
1222 // Also return the monitors of a moribund thread's omInUseList to
1223 // a global gOmInUseList under the global list lock so these
1224 // will continue to be scanned.
1225 //
1226 // We currently call omFlush() from the Thread:: dtor _after the thread
1227 // has been excised from the thread list and is no longer a mutator.
1228 // That means that omFlush() can run concurrently with a safepoint and
1229 // the scavenge operator. Calling omFlush() from JavaThread::exit() might
1230 // be a better choice as we could safely reason that that the JVM is
1231 // not at a safepoint at the time of the call, and thus there could
1232 // be not inopportune interleavings between omFlush() and the scavenge
1233 // operator.
1234
1235 void ObjectSynchronizer::omFlush(Thread * Self) {
1236 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1237 Self->omFreeList = NULL;
1238 ObjectMonitor * tail = NULL;
1239 int tally = 0;
1240 if (list != NULL) {
1241 ObjectMonitor * s;
1242 // The thread is going away, the per-thread free monitors
1243 // are freed via set_owner(NULL)
1244 // Link them to tail, which will be linked into the global free list
1245 // gFreeList below, under the gListLock
1246 for (s = list; s != NULL; s = s->FreeNext) {
1247 tally++;
1248 tail = s;
1249 guarantee(s->object() == NULL, "invariant");
1250 guarantee(!s->is_busy(), "invariant");
1251 s->set_owner(NULL); // redundant but good hygiene
1252 TEVENT(omFlush - Move one);
1253 }
1254 guarantee(tail != NULL && list != NULL, "invariant");
1255 }
1256
1257 ObjectMonitor * inUseList = Self->omInUseList;
1258 ObjectMonitor * inUseTail = NULL;
1259 int inUseTally = 0;
1260 if (inUseList != NULL) {
1261 Self->omInUseList = NULL;
1262 ObjectMonitor *cur_om;
1263 // The thread is going away, however the omInUseList inflated
1264 // monitors may still be in-use by other threads.
1265 // Link them to inUseTail, which will be linked into the global in-use list
1266 // gOmInUseList below, under the gListLock
1267 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1268 inUseTail = cur_om;
1269 inUseTally++;
1270 }
1271 assert(Self->omInUseCount == inUseTally, "in-use count off");
1272 Self->omInUseCount = 0;
1273 guarantee(inUseTail != NULL && inUseList != NULL, "invariant");
1274 }
1275
1276 Thread::muxAcquire(&gListLock, "omFlush");
1277 if (tail != NULL) {
1278 tail->FreeNext = gFreeList;
1279 gFreeList = list;
1280 gMonitorFreeCount += tally;
1281 }
1282
1283 if (inUseTail != NULL) {
1284 inUseTail->FreeNext = gOmInUseList;
1285 gOmInUseList = inUseList;
1286 gOmInUseCount += inUseTally;
1287 }
1288
1289 Thread::muxRelease(&gListLock);
1290 TEVENT(omFlush);
1291 }
1292
1293 // Fast path code shared by multiple functions
1294 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1295 assert(obj == oopDesc::bs()->write_barrier(obj), "expect to-space copy");
1296 markOop mark = obj->mark();
1297 if (mark->has_monitor()) {
1298 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1299 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1300 return mark->monitor();
1301 }
1302 return ObjectSynchronizer::inflate(Thread::current(), obj);
1303 }
1304
1305
1306 ObjectMonitor * NOINLINE ObjectSynchronizer::inflate(Thread * Self,
1307 oop object) {
1308 // Inflate mutates the heap ...
1309 // Relaxing assertion for bug 6320749.
1310 assert(object == oopDesc::bs()->write_barrier(object), "expect to-space copy");
1311 assert(Universe::verify_in_progress() ||
1312 !SafepointSynchronize::is_at_safepoint(), "invariant");
1313
1314 for (;;) {
1315 const markOop mark = object->mark();
1316 assert(!mark->has_bias_pattern(), "invariant");
1317
1318 // The mark can be in one of the following states:
1319 // * Inflated - just return
1320 // * Stack-locked - coerce it to inflated
1321 // * INFLATING - busy wait for conversion to complete
1322 // * Neutral - aggressively inflate the object.
1323 // * BIASED - Illegal. We should never see this
1324
1325 // CASE: inflated
1326 if (mark->has_monitor()) {
1327 ObjectMonitor * inf = mark->monitor();
1328 assert(inf->header()->is_neutral(), "invariant");
1329 assert((oop) inf->object() == object, "invariant");
1330 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1331 return inf;
1332 }
1333
1334 // CASE: inflation in progress - inflating over a stack-lock.
1335 // Some other thread is converting from stack-locked to inflated.
1336 // Only that thread can complete inflation -- other threads must wait.
1337 // The INFLATING value is transient.
1338 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1339 // We could always eliminate polling by parking the thread on some auxiliary list.
1340 if (mark == markOopDesc::INFLATING()) {
1341 TEVENT(Inflate: spin while INFLATING);
1342 ReadStableMark(object);
1343 continue;
1344 }
1345
1346 // CASE: stack-locked
1347 // Could be stack-locked either by this thread or by some other thread.
1348 //
1349 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1350 // to install INFLATING into the mark word. We originally installed INFLATING,
1351 // allocated the objectmonitor, and then finally STed the address of the
1352 // objectmonitor into the mark. This was correct, but artificially lengthened
1353 // the interval in which INFLATED appeared in the mark, thus increasing
1354 // the odds of inflation contention.
1355 //
1356 // We now use per-thread private objectmonitor free lists.
1357 // These list are reprovisioned from the global free list outside the
1358 // critical INFLATING...ST interval. A thread can transfer
1359 // multiple objectmonitors en-mass from the global free list to its local free list.
1360 // This reduces coherency traffic and lock contention on the global free list.
1361 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1362 // before or after the CAS(INFLATING) operation.
1363 // See the comments in omAlloc().
1364
1365 if (mark->has_locker()) {
1366 ObjectMonitor * m = omAlloc(Self);
1367 // Optimistically prepare the objectmonitor - anticipate successful CAS
1368 // We do this before the CAS in order to minimize the length of time
1369 // in which INFLATING appears in the mark.
1370 m->Recycle();
1371 m->_Responsible = NULL;
1372 m->_recursions = 0;
1373 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1374
1375 markOop cmp = (markOop) Atomic::cmpxchg_ptr(markOopDesc::INFLATING(), object->mark_addr(), mark);
1376 if (cmp != mark) {
1377 omRelease(Self, m, true);
1378 continue; // Interference -- just retry
1379 }
1380
1381 // We've successfully installed INFLATING (0) into the mark-word.
1382 // This is the only case where 0 will appear in a mark-word.
1383 // Only the singular thread that successfully swings the mark-word
1384 // to 0 can perform (or more precisely, complete) inflation.
1385 //
1386 // Why do we CAS a 0 into the mark-word instead of just CASing the
1387 // mark-word from the stack-locked value directly to the new inflated state?
1388 // Consider what happens when a thread unlocks a stack-locked object.
1389 // It attempts to use CAS to swing the displaced header value from the
1390 // on-stack basiclock back into the object header. Recall also that the
1391 // header value (hashcode, etc) can reside in (a) the object header, or
1392 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1393 // header in an objectMonitor. The inflate() routine must copy the header
1394 // value from the basiclock on the owner's stack to the objectMonitor, all
1395 // the while preserving the hashCode stability invariants. If the owner
1396 // decides to release the lock while the value is 0, the unlock will fail
1397 // and control will eventually pass from slow_exit() to inflate. The owner
1398 // will then spin, waiting for the 0 value to disappear. Put another way,
1399 // the 0 causes the owner to stall if the owner happens to try to
1400 // drop the lock (restoring the header from the basiclock to the object)
1401 // while inflation is in-progress. This protocol avoids races that might
1402 // would otherwise permit hashCode values to change or "flicker" for an object.
1403 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1404 // 0 serves as a "BUSY" inflate-in-progress indicator.
1405
1406
1407 // fetch the displaced mark from the owner's stack.
1408 // The owner can't die or unwind past the lock while our INFLATING
1409 // object is in the mark. Furthermore the owner can't complete
1410 // an unlock on the object, either.
1411 markOop dmw = mark->displaced_mark_helper();
1412 assert(dmw->is_neutral(), "invariant");
1413
1414 // Setup monitor fields to proper values -- prepare the monitor
1415 m->set_header(dmw);
1416
1417 // Optimization: if the mark->locker stack address is associated
1418 // with this thread we could simply set m->_owner = Self.
1419 // Note that a thread can inflate an object
1420 // that it has stack-locked -- as might happen in wait() -- directly
1421 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1422 m->set_owner(mark->locker());
1423 m->set_object(object);
1424 // TODO-FIXME: assert BasicLock->dhw != 0.
1425
1426 // Must preserve store ordering. The monitor state must
1427 // be stable at the time of publishing the monitor address.
1428 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1429 object->release_set_mark(markOopDesc::encode(m));
1430
1431 // Hopefully the performance counters are allocated on distinct cache lines
1432 // to avoid false sharing on MP systems ...
1433 OM_PERFDATA_OP(Inflations, inc());
1434 TEVENT(Inflate: overwrite stacklock);
1435 if (TraceMonitorInflation) {
1436 if (object->is_instance()) {
1437 ResourceMark rm;
1438 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1439 (void *) object, (intptr_t) object->mark(),
1440 object->klass()->external_name());
1441 }
1442 }
1443 return m;
1444 }
1445
1446 // CASE: neutral
1447 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1448 // If we know we're inflating for entry it's better to inflate by swinging a
1449 // pre-locked objectMonitor pointer into the object header. A successful
1450 // CAS inflates the object *and* confers ownership to the inflating thread.
1451 // In the current implementation we use a 2-step mechanism where we CAS()
1452 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1453 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1454 // would be useful.
1455
1456 assert(mark->is_neutral(), "invariant");
1457 ObjectMonitor * m = omAlloc(Self);
1458 // prepare m for installation - set monitor to initial state
1459 m->Recycle();
1460 m->set_header(mark);
1461 m->set_owner(NULL);
1462 m->set_object(object);
1463 m->_recursions = 0;
1464 m->_Responsible = NULL;
1465 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1466
1467 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) {
1468 m->set_object(NULL);
1469 m->set_owner(NULL);
1470 m->Recycle();
1471 omRelease(Self, m, true);
1472 m = NULL;
1473 continue;
1474 // interference - the markword changed - just retry.
1475 // The state-transitions are one-way, so there's no chance of
1476 // live-lock -- "Inflated" is an absorbing state.
1477 }
1478
1479 // Hopefully the performance counters are allocated on distinct
1480 // cache lines to avoid false sharing on MP systems ...
1481 OM_PERFDATA_OP(Inflations, inc());
1482 TEVENT(Inflate: overwrite neutral);
1483 if (TraceMonitorInflation) {
1484 if (object->is_instance()) {
1485 ResourceMark rm;
1486 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1487 (void *) object, (intptr_t) object->mark(),
1488 object->klass()->external_name());
1489 }
1490 }
1491 return m;
1492 }
1493 }
1494
1495
1496 // Deflate_idle_monitors() is called at all safepoints, immediately
1497 // after all mutators are stopped, but before any objects have moved.
1498 // It traverses the list of known monitors, deflating where possible.
1499 // The scavenged monitor are returned to the monitor free list.
1500 //
1501 // Beware that we scavenge at *every* stop-the-world point.
1502 // Having a large number of monitors in-circulation negatively
1503 // impacts the performance of some applications (e.g., PointBase).
1504 // Broadly, we want to minimize the # of monitors in circulation.
1505 //
1506 // We have added a flag, MonitorInUseLists, which creates a list
1507 // of active monitors for each thread. deflate_idle_monitors()
1508 // only scans the per-thread in-use lists. omAlloc() puts all
1509 // assigned monitors on the per-thread list. deflate_idle_monitors()
1510 // returns the non-busy monitors to the global free list.
1511 // When a thread dies, omFlush() adds the list of active monitors for
1512 // that thread to a global gOmInUseList acquiring the
1513 // global list lock. deflate_idle_monitors() acquires the global
1514 // list lock to scan for non-busy monitors to the global free list.
1515 // An alternative could have used a single global in-use list. The
1516 // downside would have been the additional cost of acquiring the global list lock
1517 // for every omAlloc().
1518 //
1519 // Perversely, the heap size -- and thus the STW safepoint rate --
1520 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1521 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1522 // This is an unfortunate aspect of this design.
1523
1524 enum ManifestConstants {
1525 ClearResponsibleAtSTW = 0
1526 };
1527
1528 // Deflate a single monitor if not in-use
1529 // Return true if deflated, false if in-use
1530 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1531 ObjectMonitor** freeHeadp,
1532 ObjectMonitor** freeTailp) {
1533 bool deflated;
1534 // Normal case ... The monitor is associated with obj.
1535 assert(obj == oopDesc::bs()->write_barrier(obj), "expect to-space copy");
1536 guarantee(obj->mark() == markOopDesc::encode(mid), "invariant");
1537 guarantee(mid == obj->mark()->monitor(), "invariant");
1538 guarantee(mid->header()->is_neutral(), "invariant");
1539
1540 if (mid->is_busy()) {
1541 if (ClearResponsibleAtSTW) mid->_Responsible = NULL;
1542 deflated = false;
1543 } else {
1544 // Deflate the monitor if it is no longer being used
1545 // It's idle - scavenge and return to the global free list
1546 // plain old deflation ...
1547 TEVENT(deflate_idle_monitors - scavenge1);
1548 if (TraceMonitorInflation) {
1549 if (obj->is_instance()) {
1550 ResourceMark rm;
1551 tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1552 (void *) obj, (intptr_t) obj->mark(), obj->klass()->external_name());
1553 }
1554 }
1555
1556 // Restore the header back to obj
1557 obj->release_set_mark(mid->header());
1558 mid->clear();
1559
1560 assert(mid->object() == NULL, "invariant");
1561
1562 // Move the object to the working free list defined by freeHeadp, freeTailp
1563 if (*freeHeadp == NULL) *freeHeadp = mid;
1564 if (*freeTailp != NULL) {
1565 ObjectMonitor * prevtail = *freeTailp;
1566 assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1567 prevtail->FreeNext = mid;
1568 }
1569 *freeTailp = mid;
1570 deflated = true;
1571 }
1572 return deflated;
1573 }
1574
1575 // Walk a given monitor list, and deflate idle monitors
1576 // The given list could be a per-thread list or a global list
1577 // Caller acquires gListLock
1578 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1579 ObjectMonitor** freeHeadp,
1580 ObjectMonitor** freeTailp) {
1581 ObjectMonitor* mid;
1582 ObjectMonitor* next;
1583 ObjectMonitor* cur_mid_in_use = NULL;
1584 int deflated_count = 0;
1585
1586 for (mid = *listHeadp; mid != NULL;) {
1587 oop obj = (oop) mid->object();
1588 if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1589 // if deflate_monitor succeeded,
1590 // extract from per-thread in-use list
1591 if (mid == *listHeadp) {
1592 *listHeadp = mid->FreeNext;
1593 } else if (cur_mid_in_use != NULL) {
1594 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1595 }
1596 next = mid->FreeNext;
1597 mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list
1598 mid = next;
1599 deflated_count++;
1600 } else {
1601 cur_mid_in_use = mid;
1602 mid = mid->FreeNext;
1603 }
1604 }
1605 return deflated_count;
1606 }
1607
1608 void ObjectSynchronizer::deflate_idle_monitors() {
1609 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1610 int nInuse = 0; // currently associated with objects
1611 int nInCirculation = 0; // extant
1612 int nScavenged = 0; // reclaimed
1613 bool deflated = false;
1614
1615 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1616 ObjectMonitor * freeTailp = NULL;
1617
1618 TEVENT(deflate_idle_monitors);
1619 // Prevent omFlush from changing mids in Thread dtor's during deflation
1620 // And in case the vm thread is acquiring a lock during a safepoint
1621 // See e.g. 6320749
1622 Thread::muxAcquire(&gListLock, "scavenge - return");
1623
1624 if (MonitorInUseLists) {
1625 int inUse = 0;
1626 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) {
1627 nInCirculation+= cur->omInUseCount;
1628 int deflated_count = deflate_monitor_list(cur->omInUseList_addr(), &freeHeadp, &freeTailp);
1629 cur->omInUseCount-= deflated_count;
1630 if (ObjectMonitor::Knob_VerifyInUse) {
1631 verifyInUse(cur);
1632 }
1633 nScavenged += deflated_count;
1634 nInuse += cur->omInUseCount;
1635 }
1636
1637 // For moribund threads, scan gOmInUseList
1638 if (gOmInUseList) {
1639 nInCirculation += gOmInUseCount;
1640 int deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
1641 gOmInUseCount-= deflated_count;
1642 nScavenged += deflated_count;
1643 nInuse += gOmInUseCount;
1644 }
1645
1646 } else for (PaddedEnd<ObjectMonitor> * block =
1647 (PaddedEnd<ObjectMonitor> *)gBlockList; block != NULL;
1648 block = (PaddedEnd<ObjectMonitor> *)next(block)) {
1649 // Iterate over all extant monitors - Scavenge all idle monitors.
1650 assert(block->object() == CHAINMARKER, "must be a block header");
1651 nInCirculation += _BLOCKSIZE;
1652 for (int i = 1; i < _BLOCKSIZE; i++) {
1653 ObjectMonitor* mid = (ObjectMonitor*)&block[i];
1654 oop obj = (oop) mid->object();
1655
1656 if (obj == NULL) {
1657 // The monitor is not associated with an object.
1658 // The monitor should either be a thread-specific private
1659 // free list or the global free list.
1660 // obj == NULL IMPLIES mid->is_busy() == 0
1661 guarantee(!mid->is_busy(), "invariant");
1662 continue;
1663 }
1664 deflated = deflate_monitor(mid, obj, &freeHeadp, &freeTailp);
1665
1666 if (deflated) {
1667 mid->FreeNext = NULL;
1668 nScavenged++;
1669 } else {
1670 nInuse++;
1671 }
1672 }
1673 }
1674
1675 gMonitorFreeCount += nScavenged;
1676
1677 // Consider: audit gFreeList to ensure that gMonitorFreeCount and list agree.
1678
1679 if (ObjectMonitor::Knob_Verbose) {
1680 tty->print_cr("INFO: Deflate: InCirc=%d InUse=%d Scavenged=%d "
1681 "ForceMonitorScavenge=%d : pop=%d free=%d",
1682 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge,
1683 gMonitorPopulation, gMonitorFreeCount);
1684 tty->flush();
1685 }
1686
1687 ForceMonitorScavenge = 0; // Reset
1688
1689 // Move the scavenged monitors back to the global free list.
1690 if (freeHeadp != NULL) {
1691 guarantee(freeTailp != NULL && nScavenged > 0, "invariant");
1692 assert(freeTailp->FreeNext == NULL, "invariant");
1693 // constant-time list splice - prepend scavenged segment to gFreeList
1694 freeTailp->FreeNext = gFreeList;
1695 gFreeList = freeHeadp;
1696 }
1697 Thread::muxRelease(&gListLock);
1698
1699 OM_PERFDATA_OP(Deflations, inc(nScavenged));
1700 OM_PERFDATA_OP(MonExtant, set_value(nInCirculation));
1701
1702 // TODO: Add objectMonitor leak detection.
1703 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1704 GVars.stwRandom = os::random();
1705 GVars.stwCycle++;
1706 }
1707
1708 // Monitor cleanup on JavaThread::exit
1709
1710 // Iterate through monitor cache and attempt to release thread's monitors
1711 // Gives up on a particular monitor if an exception occurs, but continues
1712 // the overall iteration, swallowing the exception.
1713 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1714 private:
1715 TRAPS;
1716
1717 public:
1718 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1719 void do_monitor(ObjectMonitor* mid) {
1720 if (mid->owner() == THREAD) {
1721 if (ObjectMonitor::Knob_VerifyMatch != 0) {
1722 Handle obj((oop) mid->object());
1723 tty->print("INFO: unexpected locked object:");
1724 javaVFrame::print_locked_object_class_name(tty, obj, "locked");
1725 fatal(err_msg("exiting JavaThread=" INTPTR_FORMAT
1726 " unexpectedly owns ObjectMonitor=" INTPTR_FORMAT,
1727 THREAD, mid));
1728 }
1729 (void)mid->complete_exit(CHECK);
1730 }
1731 }
1732 };
1733
1734 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1735 // ignored. This is meant to be called during JNI thread detach which assumes
1736 // all remaining monitors are heavyweight. All exceptions are swallowed.
1737 // Scanning the extant monitor list can be time consuming.
1738 // A simple optimization is to add a per-thread flag that indicates a thread
1739 // called jni_monitorenter() during its lifetime.
1740 //
1741 // Instead of No_Savepoint_Verifier it might be cheaper to
1742 // use an idiom of the form:
1743 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1744 // <code that must not run at safepoint>
1745 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1746 // Since the tests are extremely cheap we could leave them enabled
1747 // for normal product builds.
1748
1749 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1750 assert(THREAD == JavaThread::current(), "must be current Java thread");
1751 No_Safepoint_Verifier nsv;
1752 ReleaseJavaMonitorsClosure rjmc(THREAD);
1753 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
1754 ObjectSynchronizer::monitors_iterate(&rjmc);
1755 Thread::muxRelease(&gListLock);
1756 THREAD->clear_pending_exception();
1757 }
1758
1759 //------------------------------------------------------------------------------
1760 // Debugging code
1761
1762 void ObjectSynchronizer::sanity_checks(const bool verbose,
1763 const uint cache_line_size,
1764 int *error_cnt_ptr,
1765 int *warning_cnt_ptr) {
1766 u_char *addr_begin = (u_char*)&GVars;
1767 u_char *addr_stwRandom = (u_char*)&GVars.stwRandom;
1768 u_char *addr_hcSequence = (u_char*)&GVars.hcSequence;
1769
1770 if (verbose) {
1771 tty->print_cr("INFO: sizeof(SharedGlobals)=" SIZE_FORMAT,
1772 sizeof(SharedGlobals));
1773 }
1774
1775 uint offset_stwRandom = (uint)(addr_stwRandom - addr_begin);
1776 if (verbose) tty->print_cr("INFO: offset(stwRandom)=%u", offset_stwRandom);
1777
1778 uint offset_hcSequence = (uint)(addr_hcSequence - addr_begin);
1779 if (verbose) {
1780 tty->print_cr("INFO: offset(_hcSequence)=%u", offset_hcSequence);
1781 }
1782
1783 if (cache_line_size != 0) {
1784 // We were able to determine the L1 data cache line size so
1785 // do some cache line specific sanity checks
1786
1787 if (offset_stwRandom < cache_line_size) {
1788 tty->print_cr("WARNING: the SharedGlobals.stwRandom field is closer "
1789 "to the struct beginning than a cache line which permits "
1790 "false sharing.");
1791 (*warning_cnt_ptr)++;
1792 }
1793
1794 if ((offset_hcSequence - offset_stwRandom) < cache_line_size) {
1795 tty->print_cr("WARNING: the SharedGlobals.stwRandom and "
1796 "SharedGlobals.hcSequence fields are closer than a cache "
1797 "line which permits false sharing.");
1798 (*warning_cnt_ptr)++;
1799 }
1800
1801 if ((sizeof(SharedGlobals) - offset_hcSequence) < cache_line_size) {
1802 tty->print_cr("WARNING: the SharedGlobals.hcSequence field is closer "
1803 "to the struct end than a cache line which permits false "
1804 "sharing.");
1805 (*warning_cnt_ptr)++;
1806 }
1807 }
1808 }
1809
1810 #ifndef PRODUCT
1811
1812 // Verify all monitors in the monitor cache, the verification is weak.
1813 void ObjectSynchronizer::verify() {
1814 PaddedEnd<ObjectMonitor> * block = (PaddedEnd<ObjectMonitor> *)gBlockList;
1815 ObjectMonitor* mid;
1816 while (block) {
1817 assert(block->object() == CHAINMARKER, "must be a block header");
1818 for (int i = 1; i < _BLOCKSIZE; i++) {
1819 mid = (ObjectMonitor *)(block + i);
1820 oop object = (oop) mid->object();
1821
1822 if (object != NULL) {
1823 mid->verify();
1824 }
1825 }
1826 block = (PaddedEnd<ObjectMonitor> *) block->FreeNext;
1827 }
1828 }
1829
1830 // Check if monitor belongs to the monitor cache
1831 // The list is grow-only so it's *relatively* safe to traverse
1832 // the list of extant blocks without taking a lock.
1833
1834 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
1835 PaddedEnd<ObjectMonitor> * block = (PaddedEnd<ObjectMonitor> *)gBlockList;
1836
1837 while (block) {
1838 assert(block->object() == CHAINMARKER, "must be a block header");
1839 if (monitor > (ObjectMonitor *)&block[0] &&
1840 monitor < (ObjectMonitor *)&block[_BLOCKSIZE]) {
1841 address mon = (address) monitor;
1842 address blk = (address) block;
1843 size_t diff = mon - blk;
1844 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "check");
1845 return 1;
1846 }
1847 block = (PaddedEnd<ObjectMonitor> *) block->FreeNext;
1848 }
1849 return 0;
1850 }
1851
1852 #endif