1 /*
2 * Copyright (c) 1998, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/vmSymbols.hpp"
27 #include "memory/padded.hpp"
28 #include "memory/resourceArea.hpp"
29 #include "oops/markOop.hpp"
30 #include "oops/oop.inline.hpp"
31 #include "runtime/atomic.inline.hpp"
32 #include "runtime/biasedLocking.hpp"
33 #include "runtime/handles.inline.hpp"
34 #include "runtime/interfaceSupport.hpp"
35 #include "runtime/mutexLocker.hpp"
36 #include "runtime/objectMonitor.hpp"
37 #include "runtime/objectMonitor.inline.hpp"
38 #include "runtime/osThread.hpp"
39 #include "runtime/stubRoutines.hpp"
40 #include "runtime/synchronizer.hpp"
41 #include "runtime/thread.inline.hpp"
42 #include "utilities/dtrace.hpp"
43 #include "utilities/events.hpp"
44 #include "utilities/preserveException.hpp"
45
46 #if defined(__GNUC__) && !defined(PPC64)
47 // Need to inhibit inlining for older versions of GCC to avoid build-time failures
48 #define NOINLINE __attribute__((noinline))
49 #else
50 #define NOINLINE
51 #endif
52
53 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
54
55 // The "core" versions of monitor enter and exit reside in this file.
56 // The interpreter and compilers contain specialized transliterated
57 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
58 // for instance. If you make changes here, make sure to modify the
59 // interpreter, and both C1 and C2 fast-path inline locking code emission.
60 //
61 // -----------------------------------------------------------------------------
62
63 #ifdef DTRACE_ENABLED
64
65 // Only bother with this argument setup if dtrace is available
66 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
67
68 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
69 char* bytes = NULL; \
70 int len = 0; \
71 jlong jtid = SharedRuntime::get_java_tid(thread); \
72 Symbol* klassname = ((oop)(obj))->klass()->name(); \
73 if (klassname != NULL) { \
74 bytes = (char*)klassname->bytes(); \
75 len = klassname->utf8_length(); \
76 }
77
78 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
79 { \
80 if (DTraceMonitorProbes) { \
81 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
82 HOTSPOT_MONITOR_WAIT(jtid, \
83 (uintptr_t)(monitor), bytes, len, (millis)); \
84 } \
85 }
86
87 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
88
89 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
90 { \
91 if (DTraceMonitorProbes) { \
92 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
93 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
94 (uintptr_t)(monitor), bytes, len); \
95 } \
96 }
97
98 #else // ndef DTRACE_ENABLED
99
100 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
101 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
102
103 #endif // ndef DTRACE_ENABLED
104
105 // This exists only as a workaround of dtrace bug 6254741
106 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
107 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
108 return 0;
109 }
110
111 #define NINFLATIONLOCKS 256
112 static volatile intptr_t InflationLocks[NINFLATIONLOCKS];
113
114 // gBlockList is really PaddedEnd<ObjectMonitor> *, but we don't
115 // want to expose the PaddedEnd template more than necessary.
116 ObjectMonitor * ObjectSynchronizer::gBlockList = NULL;
117 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL;
118 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL;
119 int ObjectSynchronizer::gOmInUseCount = 0;
120 static volatile intptr_t ListLock = 0; // protects global monitor free-list cache
121 static volatile int MonitorFreeCount = 0; // # on gFreeList
122 static volatile int MonitorPopulation = 0; // # Extant -- in circulation
123 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
124
125
126 // =====================> Quick functions
127
128 // The quick_* forms are special fast-path variants used to improve
129 // performance. In the simplest case, a "quick_*" implementation could
130 // simply return false, in which case the caller will perform the necessary
131 // state transitions and call the slow-path form.
132 // The fast-path is designed to handle frequently arising cases in an efficient
133 // manner and is just a degenerate "optimistic" variant of the slow-path.
134 // returns true -- to indicate the call was satisfied.
135 // returns false -- to indicate the call needs the services of the slow-path.
136 // A no-loitering ordinance is in effect for code in the quick_* family
137 // operators: safepoints or indefinite blocking (blocking that might span a
138 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
139 // entry.
140
141 // The LockNode emitted directly at the synchronization site would have
142 // been too big if it were to have included support for the cases of inflated
143 // recursive enter and exit, so they go here instead.
144 // Note that we can't safely call AsyncPrintJavaStack() from within
145 // quick_enter() as our thread state remains _in_Java.
146
147 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
148 BasicLock * Lock) {
149 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
150 assert(Self->is_Java_thread(), "invariant");
151 assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
152 No_Safepoint_Verifier nsv;
153 if (obj == NULL) return false; // Need to throw NPE
154 const markOop mark = obj->mark();
155
156 if (mark->has_monitor()) {
157 ObjectMonitor * const m = mark->monitor();
158 assert(m->object() == obj, "invariant");
159 Thread * const owner = (Thread *) m->_owner;
160
161 // Lock contention and Transactional Lock Elision (TLE) diagnostics
162 // and observability
163 // Case: light contention possibly amenable to TLE
164 // Case: TLE inimical operations such as nested/recursive synchronization
165
166 if (owner == Self) {
167 m->_recursions++;
168 return true;
169 }
170
171 if (owner == NULL &&
172 Atomic::cmpxchg_ptr(Self, &(m->_owner), NULL) == NULL) {
173 assert(m->_recursions == 0, "invariant");
174 assert(m->_owner == Self, "invariant");
175 return true;
176 }
177 }
178
179 // Note that we could inflate in quick_enter.
180 // This is likely a useful optimization
181 // Critically, in quick_enter() we must not:
182 // -- perform bias revocation, or
183 // -- block indefinitely, or
184 // -- reach a safepoint
185
186 return false; // revert to slow-path
187 }
188
189 // -----------------------------------------------------------------------------
190 // Fast Monitor Enter/Exit
191 // This the fast monitor enter. The interpreter and compiler use
192 // some assembly copies of this code. Make sure update those code
193 // if the following function is changed. The implementation is
194 // extremely sensitive to race condition. Be careful.
195
196 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
197 bool attempt_rebias, TRAPS) {
198 if (UseBiasedLocking) {
199 if (!SafepointSynchronize::is_at_safepoint()) {
200 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
201 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
202 return;
203 }
204 } else {
205 assert(!attempt_rebias, "can not rebias toward VM thread");
206 BiasedLocking::revoke_at_safepoint(obj);
207 }
208 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
209 }
210
211 slow_enter(obj, lock, THREAD);
212 }
213
214 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
215 assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here");
216 // if displaced header is null, the previous enter is recursive enter, no-op
217 markOop dhw = lock->displaced_header();
218 markOop mark;
219 if (dhw == NULL) {
220 // Recursive stack-lock.
221 // Diagnostics -- Could be: stack-locked, inflating, inflated.
222 mark = object->mark();
223 assert(!mark->is_neutral(), "invariant");
224 if (mark->has_locker() && mark != markOopDesc::INFLATING()) {
225 assert(THREAD->is_lock_owned((address)mark->locker()), "invariant");
226 }
227 if (mark->has_monitor()) {
228 ObjectMonitor * m = mark->monitor();
229 assert(((oop)(m->object()))->mark() == mark, "invariant");
230 assert(m->is_entered(THREAD), "invariant");
231 }
232 return;
233 }
234
235 mark = object->mark();
236
237 // If the object is stack-locked by the current thread, try to
238 // swing the displaced header from the box back to the mark.
239 if (mark == (markOop) lock) {
240 assert(dhw->is_neutral(), "invariant");
241 if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) {
242 TEVENT(fast_exit: release stacklock);
243 return;
244 }
245 }
246
247 ObjectSynchronizer::inflate(THREAD, object)->exit(true, THREAD);
248 }
249
250 // -----------------------------------------------------------------------------
251 // Interpreter/Compiler Slow Case
252 // This routine is used to handle interpreter/compiler slow case
253 // We don't need to use fast path here, because it must have been
254 // failed in the interpreter/compiler code.
255 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
256 markOop mark = obj->mark();
257 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
258
259 if (mark->is_neutral()) {
260 // Anticipate successful CAS -- the ST of the displaced mark must
261 // be visible <= the ST performed by the CAS.
262 lock->set_displaced_header(mark);
263 if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) {
264 TEVENT(slow_enter: release stacklock);
265 return;
266 }
267 // Fall through to inflate() ...
268 } else if (mark->has_locker() &&
269 THREAD->is_lock_owned((address)mark->locker())) {
270 assert(lock != mark->locker(), "must not re-lock the same lock");
271 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
272 lock->set_displaced_header(NULL);
273 return;
274 }
275
276 // The object header will never be displaced to this lock,
277 // so it does not matter what the value is, except that it
278 // must be non-zero to avoid looking like a re-entrant lock,
279 // and must not look locked either.
280 lock->set_displaced_header(markOopDesc::unused_mark());
281 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
282 }
283
284 // This routine is used to handle interpreter/compiler slow case
285 // We don't need to use fast path here, because it must have
286 // failed in the interpreter/compiler code. Simply use the heavy
287 // weight monitor should be ok, unless someone find otherwise.
288 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
289 fast_exit(object, lock, THREAD);
290 }
291
292 // -----------------------------------------------------------------------------
293 // Class Loader support to workaround deadlocks on the class loader lock objects
294 // Also used by GC
295 // complete_exit()/reenter() are used to wait on a nested lock
296 // i.e. to give up an outer lock completely and then re-enter
297 // Used when holding nested locks - lock acquisition order: lock1 then lock2
298 // 1) complete_exit lock1 - saving recursion count
299 // 2) wait on lock2
300 // 3) when notified on lock2, unlock lock2
301 // 4) reenter lock1 with original recursion count
302 // 5) lock lock2
303 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
304 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
305 TEVENT(complete_exit);
306 if (UseBiasedLocking) {
307 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
308 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
309 }
310
311 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
312
313 return monitor->complete_exit(THREAD);
314 }
315
316 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
317 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
318 TEVENT(reenter);
319 if (UseBiasedLocking) {
320 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
321 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
322 }
323
324 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
325
326 monitor->reenter(recursion, THREAD);
327 }
328 // -----------------------------------------------------------------------------
329 // JNI locks on java objects
330 // NOTE: must use heavy weight monitor to handle jni monitor enter
331 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
332 // the current locking is from JNI instead of Java code
333 TEVENT(jni_enter);
334 if (UseBiasedLocking) {
335 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
336 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
337 }
338 THREAD->set_current_pending_monitor_is_from_java(false);
339 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
340 THREAD->set_current_pending_monitor_is_from_java(true);
341 }
342
343 // NOTE: must use heavy weight monitor to handle jni monitor exit
344 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
345 TEVENT(jni_exit);
346 if (UseBiasedLocking) {
347 Handle h_obj(THREAD, obj);
348 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
349 obj = h_obj();
350 }
351 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
352
353 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj);
354 // If this thread has locked the object, exit the monitor. Note: can't use
355 // monitor->check(CHECK); must exit even if an exception is pending.
356 if (monitor->check(THREAD)) {
357 monitor->exit(true, THREAD);
358 }
359 }
360
361 // -----------------------------------------------------------------------------
362 // Internal VM locks on java objects
363 // standard constructor, allows locking failures
364 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
365 _dolock = doLock;
366 _thread = thread;
367 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
368 _obj = obj;
369
370 if (_dolock) {
371 TEVENT(ObjectLocker);
372
373 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
374 }
375 }
376
377 ObjectLocker::~ObjectLocker() {
378 if (_dolock) {
379 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
380 }
381 }
382
383
384 // -----------------------------------------------------------------------------
385 // Wait/Notify/NotifyAll
386 // NOTE: must use heavy weight monitor to handle wait()
387 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
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 if (millis < 0) {
393 TEVENT(wait - throw IAX);
394 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
395 }
396 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
397 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
398 monitor->wait(millis, true, THREAD);
399
400 // This dummy call is in place to get around dtrace bug 6254741. Once
401 // that's fixed we can uncomment the following line, remove the call
402 // and change this function back into a "void" func.
403 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
404 return dtrace_waited_probe(monitor, obj, THREAD);
405 }
406
407 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
408 if (UseBiasedLocking) {
409 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
410 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
411 }
412 if (millis < 0) {
413 TEVENT(wait - throw IAX);
414 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
415 }
416 ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD);
417 }
418
419 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
420 if (UseBiasedLocking) {
421 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
422 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
423 }
424
425 markOop mark = obj->mark();
426 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
427 return;
428 }
429 ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD);
430 }
431
432 // NOTE: see comment of notify()
433 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
434 if (UseBiasedLocking) {
435 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
436 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
437 }
438
439 markOop mark = obj->mark();
440 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
441 return;
442 }
443 ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD);
444 }
445
446 // -----------------------------------------------------------------------------
447 // Hash Code handling
448 //
449 // Performance concern:
450 // OrderAccess::storestore() calls release() which at one time stored 0
451 // into the global volatile OrderAccess::dummy variable. This store was
452 // unnecessary for correctness. Many threads storing into a common location
453 // causes considerable cache migration or "sloshing" on large SMP systems.
454 // As such, I avoided using OrderAccess::storestore(). In some cases
455 // OrderAccess::fence() -- which incurs local latency on the executing
456 // processor -- is a better choice as it scales on SMP systems.
457 //
458 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
459 // a discussion of coherency costs. Note that all our current reference
460 // platforms provide strong ST-ST order, so the issue is moot on IA32,
461 // x64, and SPARC.
462 //
463 // As a general policy we use "volatile" to control compiler-based reordering
464 // and explicit fences (barriers) to control for architectural reordering
465 // performed by the CPU(s) or platform.
466
467 struct SharedGlobals {
468 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
469 // These are highly shared mostly-read variables.
470 // To avoid false-sharing they need to be the sole occupants of a cache line.
471 volatile int stwRandom;
472 volatile int stwCycle;
473 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
474 // Hot RW variable -- Sequester to avoid false-sharing
475 volatile int hcSequence;
476 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
477 };
478
479 static SharedGlobals GVars;
480 static int MonitorScavengeThreshold = 1000000;
481 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
482
483 static markOop ReadStableMark(oop obj) {
484 markOop mark = obj->mark();
485 if (!mark->is_being_inflated()) {
486 return mark; // normal fast-path return
487 }
488
489 int its = 0;
490 for (;;) {
491 markOop mark = obj->mark();
492 if (!mark->is_being_inflated()) {
493 return mark; // normal fast-path return
494 }
495
496 // The object is being inflated by some other thread.
497 // The caller of ReadStableMark() must wait for inflation to complete.
498 // Avoid live-lock
499 // TODO: consider calling SafepointSynchronize::do_call_back() while
500 // spinning to see if there's a safepoint pending. If so, immediately
501 // yielding or blocking would be appropriate. Avoid spinning while
502 // there is a safepoint pending.
503 // TODO: add inflation contention performance counters.
504 // TODO: restrict the aggregate number of spinners.
505
506 ++its;
507 if (its > 10000 || !os::is_MP()) {
508 if (its & 1) {
509 os::naked_yield();
510 TEVENT(Inflate: INFLATING - yield);
511 } else {
512 // Note that the following code attenuates the livelock problem but is not
513 // a complete remedy. A more complete solution would require that the inflating
514 // thread hold the associated inflation lock. The following code simply restricts
515 // the number of spinners to at most one. We'll have N-2 threads blocked
516 // on the inflationlock, 1 thread holding the inflation lock and using
517 // a yield/park strategy, and 1 thread in the midst of inflation.
518 // A more refined approach would be to change the encoding of INFLATING
519 // to allow encapsulation of a native thread pointer. Threads waiting for
520 // inflation to complete would use CAS to push themselves onto a singly linked
521 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
522 // and calling park(). When inflation was complete the thread that accomplished inflation
523 // would detach the list and set the markword to inflated with a single CAS and
524 // then for each thread on the list, set the flag and unpark() the thread.
525 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
526 // wakes at most one thread whereas we need to wake the entire list.
527 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
528 int YieldThenBlock = 0;
529 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
530 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
531 Thread::muxAcquire(InflationLocks + ix, "InflationLock");
532 while (obj->mark() == markOopDesc::INFLATING()) {
533 // Beware: NakedYield() is advisory and has almost no effect on some platforms
534 // so we periodically call Self->_ParkEvent->park(1).
535 // We use a mixed spin/yield/block mechanism.
536 if ((YieldThenBlock++) >= 16) {
537 Thread::current()->_ParkEvent->park(1);
538 } else {
539 os::naked_yield();
540 }
541 }
542 Thread::muxRelease(InflationLocks + ix);
543 TEVENT(Inflate: INFLATING - yield/park);
544 }
545 } else {
546 SpinPause(); // SMP-polite spinning
547 }
548 }
549 }
550
551 // hashCode() generation :
552 //
553 // Possibilities:
554 // * MD5Digest of {obj,stwRandom}
555 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
556 // * A DES- or AES-style SBox[] mechanism
557 // * One of the Phi-based schemes, such as:
558 // 2654435761 = 2^32 * Phi (golden ratio)
559 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
560 // * A variation of Marsaglia's shift-xor RNG scheme.
561 // * (obj ^ stwRandom) is appealing, but can result
562 // in undesirable regularity in the hashCode values of adjacent objects
563 // (objects allocated back-to-back, in particular). This could potentially
564 // result in hashtable collisions and reduced hashtable efficiency.
565 // There are simple ways to "diffuse" the middle address bits over the
566 // generated hashCode values:
567
568 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
569 intptr_t value = 0;
570 if (hashCode == 0) {
571 // This form uses an unguarded global Park-Miller RNG,
572 // so it's possible for two threads to race and generate the same RNG.
573 // On MP system we'll have lots of RW access to a global, so the
574 // mechanism induces lots of coherency traffic.
575 value = os::random();
576 } else if (hashCode == 1) {
577 // This variation has the property of being stable (idempotent)
578 // between STW operations. This can be useful in some of the 1-0
579 // synchronization schemes.
580 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
581 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
582 } else if (hashCode == 2) {
583 value = 1; // for sensitivity testing
584 } else if (hashCode == 3) {
585 value = ++GVars.hcSequence;
586 } else if (hashCode == 4) {
587 value = cast_from_oop<intptr_t>(obj);
588 } else {
589 // Marsaglia's xor-shift scheme with thread-specific state
590 // This is probably the best overall implementation -- we'll
591 // likely make this the default in future releases.
592 unsigned t = Self->_hashStateX;
593 t ^= (t << 11);
594 Self->_hashStateX = Self->_hashStateY;
595 Self->_hashStateY = Self->_hashStateZ;
596 Self->_hashStateZ = Self->_hashStateW;
597 unsigned v = Self->_hashStateW;
598 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
599 Self->_hashStateW = v;
600 value = v;
601 }
602
603 value &= markOopDesc::hash_mask;
604 if (value == 0) value = 0xBAD;
605 assert(value != markOopDesc::no_hash, "invariant");
606 TEVENT(hashCode: GENERATE);
607 return value;
608 }
609
610 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
611 if (UseBiasedLocking) {
612 // NOTE: many places throughout the JVM do not expect a safepoint
613 // to be taken here, in particular most operations on perm gen
614 // objects. However, we only ever bias Java instances and all of
615 // the call sites of identity_hash that might revoke biases have
616 // been checked to make sure they can handle a safepoint. The
617 // added check of the bias pattern is to avoid useless calls to
618 // thread-local storage.
619 if (obj->mark()->has_bias_pattern()) {
620 // Handle for oop obj in case of STW safepoint
621 Handle hobj(Self, obj);
622 // Relaxing assertion for bug 6320749.
623 assert(Universe::verify_in_progress() ||
624 !SafepointSynchronize::is_at_safepoint(),
625 "biases should not be seen by VM thread here");
626 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
627 obj = hobj();
628 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
629 }
630 }
631
632 // hashCode() is a heap mutator ...
633 // Relaxing assertion for bug 6320749.
634 assert(Universe::verify_in_progress() ||
635 !SafepointSynchronize::is_at_safepoint(), "invariant");
636 assert(Universe::verify_in_progress() ||
637 Self->is_Java_thread() , "invariant");
638 assert(Universe::verify_in_progress() ||
639 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
640
641 ObjectMonitor* monitor = NULL;
642 markOop temp, test;
643 intptr_t hash;
644 markOop mark = ReadStableMark(obj);
645
646 // object should remain ineligible for biased locking
647 assert(!mark->has_bias_pattern(), "invariant");
648
649 if (mark->is_neutral()) {
650 hash = mark->hash(); // this is a normal header
651 if (hash) { // if it has hash, just return it
652 return hash;
653 }
654 hash = get_next_hash(Self, obj); // allocate a new hash code
655 temp = mark->copy_set_hash(hash); // merge the hash code into header
656 // use (machine word version) atomic operation to install the hash
657 test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark);
658 if (test == mark) {
659 return hash;
660 }
661 // If atomic operation failed, we must inflate the header
662 // into heavy weight monitor. We could add more code here
663 // for fast path, but it does not worth the complexity.
664 } else if (mark->has_monitor()) {
665 monitor = mark->monitor();
666 temp = monitor->header();
667 assert(temp->is_neutral(), "invariant");
668 hash = temp->hash();
669 if (hash) {
670 return hash;
671 }
672 // Skip to the following code to reduce code size
673 } else if (Self->is_lock_owned((address)mark->locker())) {
674 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
675 assert(temp->is_neutral(), "invariant");
676 hash = temp->hash(); // by current thread, check if the displaced
677 if (hash) { // header contains hash code
678 return hash;
679 }
680 // WARNING:
681 // The displaced header is strictly immutable.
682 // It can NOT be changed in ANY cases. So we have
683 // to inflate the header into heavyweight monitor
684 // even the current thread owns the lock. The reason
685 // is the BasicLock (stack slot) will be asynchronously
686 // read by other threads during the inflate() function.
687 // Any change to stack may not propagate to other threads
688 // correctly.
689 }
690
691 // Inflate the monitor to set hash code
692 monitor = ObjectSynchronizer::inflate(Self, obj);
693 // Load displaced header and check it has hash code
694 mark = monitor->header();
695 assert(mark->is_neutral(), "invariant");
696 hash = mark->hash();
697 if (hash == 0) {
698 hash = get_next_hash(Self, obj);
699 temp = mark->copy_set_hash(hash); // merge hash code into header
700 assert(temp->is_neutral(), "invariant");
701 test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark);
702 if (test != mark) {
703 // The only update to the header in the monitor (outside GC)
704 // is install the hash code. If someone add new usage of
705 // displaced header, please update this code
706 hash = test->hash();
707 assert(test->is_neutral(), "invariant");
708 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
709 }
710 }
711 // We finally get the hash
712 return hash;
713 }
714
715 // Deprecated -- use FastHashCode() instead.
716
717 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
718 return FastHashCode(Thread::current(), obj());
719 }
720
721
722 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
723 Handle h_obj) {
724 if (UseBiasedLocking) {
725 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
726 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
727 }
728
729 assert(thread == JavaThread::current(), "Can only be called on current thread");
730 oop obj = h_obj();
731
732 markOop mark = ReadStableMark(obj);
733
734 // Uncontended case, header points to stack
735 if (mark->has_locker()) {
736 return thread->is_lock_owned((address)mark->locker());
737 }
738 // Contended case, header points to ObjectMonitor (tagged pointer)
739 if (mark->has_monitor()) {
740 ObjectMonitor* monitor = mark->monitor();
741 return monitor->is_entered(thread) != 0;
742 }
743 // Unlocked case, header in place
744 assert(mark->is_neutral(), "sanity check");
745 return false;
746 }
747
748 // Be aware of this method could revoke bias of the lock object.
749 // This method queries the ownership of the lock handle specified by 'h_obj'.
750 // If the current thread owns the lock, it returns owner_self. If no
751 // thread owns the lock, it returns owner_none. Otherwise, it will return
752 // owner_other.
753 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
754 (JavaThread *self, Handle h_obj) {
755 // The caller must beware this method can revoke bias, and
756 // revocation can result in a safepoint.
757 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
758 assert(self->thread_state() != _thread_blocked, "invariant");
759
760 // Possible mark states: neutral, biased, stack-locked, inflated
761
762 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
763 // CASE: biased
764 BiasedLocking::revoke_and_rebias(h_obj, false, self);
765 assert(!h_obj->mark()->has_bias_pattern(),
766 "biases should be revoked by now");
767 }
768
769 assert(self == JavaThread::current(), "Can only be called on current thread");
770 oop obj = h_obj();
771 markOop mark = ReadStableMark(obj);
772
773 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
774 if (mark->has_locker()) {
775 return self->is_lock_owned((address)mark->locker()) ?
776 owner_self : owner_other;
777 }
778
779 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
780 // The Object:ObjectMonitor relationship is stable as long as we're
781 // not at a safepoint.
782 if (mark->has_monitor()) {
783 void * owner = mark->monitor()->_owner;
784 if (owner == NULL) return owner_none;
785 return (owner == self ||
786 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
787 }
788
789 // CASE: neutral
790 assert(mark->is_neutral(), "sanity check");
791 return owner_none; // it's unlocked
792 }
793
794 // FIXME: jvmti should call this
795 JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) {
796 if (UseBiasedLocking) {
797 if (SafepointSynchronize::is_at_safepoint()) {
798 BiasedLocking::revoke_at_safepoint(h_obj);
799 } else {
800 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
801 }
802 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
803 }
804
805 oop obj = h_obj();
806 address owner = NULL;
807
808 markOop mark = ReadStableMark(obj);
809
810 // Uncontended case, header points to stack
811 if (mark->has_locker()) {
812 owner = (address) mark->locker();
813 }
814
815 // Contended case, header points to ObjectMonitor (tagged pointer)
816 if (mark->has_monitor()) {
817 ObjectMonitor* monitor = mark->monitor();
818 assert(monitor != NULL, "monitor should be non-null");
819 owner = (address) monitor->owner();
820 }
821
822 if (owner != NULL) {
823 // owning_thread_from_monitor_owner() may also return NULL here
824 return Threads::owning_thread_from_monitor_owner(owner, doLock);
825 }
826
827 // Unlocked case, header in place
828 // Cannot have assertion since this object may have been
829 // locked by another thread when reaching here.
830 // assert(mark->is_neutral(), "sanity check");
831
832 return NULL;
833 }
834 // Visitors ...
835
836 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
837 PaddedEnd<ObjectMonitor> * block = (PaddedEnd<ObjectMonitor> *)gBlockList;
838 ObjectMonitor* mid;
839 while (block) {
840 assert(block->object() == CHAINMARKER, "must be a block header");
841 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
842 mid = (ObjectMonitor *)(block + i);
843 oop object = (oop) mid->object();
844 if (object != NULL) {
845 closure->do_monitor(mid);
846 }
847 }
848 block = (PaddedEnd<ObjectMonitor> *) block->FreeNext;
849 }
850 }
851
852 // Get the next block in the block list.
853 static inline ObjectMonitor* next(ObjectMonitor* block) {
854 assert(block->object() == CHAINMARKER, "must be a block header");
855 block = block->FreeNext;
856 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
857 return block;
858 }
859
860
861 void ObjectSynchronizer::oops_do(OopClosure* f) {
862 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
863 for (PaddedEnd<ObjectMonitor> * block =
864 (PaddedEnd<ObjectMonitor> *)gBlockList; block != NULL;
865 block = (PaddedEnd<ObjectMonitor> *)next(block)) {
866 assert(block->object() == CHAINMARKER, "must be a block header");
867 for (int i = 1; i < _BLOCKSIZE; i++) {
868 ObjectMonitor* mid = (ObjectMonitor *)&block[i];
869 if (mid->object() != NULL) {
870 f->do_oop((oop*)mid->object_addr());
871 }
872 }
873 }
874 }
875
876
877 // -----------------------------------------------------------------------------
878 // ObjectMonitor Lifecycle
879 // -----------------------
880 // Inflation unlinks monitors from the global gFreeList and
881 // associates them with objects. Deflation -- which occurs at
882 // STW-time -- disassociates idle monitors from objects. Such
883 // scavenged monitors are returned to the gFreeList.
884 //
885 // The global list is protected by ListLock. All the critical sections
886 // are short and operate in constant-time.
887 //
888 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
889 //
890 // Lifecycle:
891 // -- unassigned and on the global free list
892 // -- unassigned and on a thread's private omFreeList
893 // -- assigned to an object. The object is inflated and the mark refers
894 // to the objectmonitor.
895
896
897 // Constraining monitor pool growth via MonitorBound ...
898 //
899 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
900 // the rate of scavenging is driven primarily by GC. As such, we can find
901 // an inordinate number of monitors in circulation.
902 // To avoid that scenario we can artificially induce a STW safepoint
903 // if the pool appears to be growing past some reasonable bound.
904 // Generally we favor time in space-time tradeoffs, but as there's no
905 // natural back-pressure on the # of extant monitors we need to impose some
906 // type of limit. Beware that if MonitorBound is set to too low a value
907 // we could just loop. In addition, if MonitorBound is set to a low value
908 // we'll incur more safepoints, which are harmful to performance.
909 // See also: GuaranteedSafepointInterval
910 //
911 // The current implementation uses asynchronous VM operations.
912
913 static void InduceScavenge(Thread * Self, const char * Whence) {
914 // Induce STW safepoint to trim monitors
915 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
916 // More precisely, trigger an asynchronous STW safepoint as the number
917 // of active monitors passes the specified threshold.
918 // TODO: assert thread state is reasonable
919
920 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
921 if (ObjectMonitor::Knob_Verbose) {
922 ::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ;
923 ::fflush(stdout);
924 }
925 // Induce a 'null' safepoint to scavenge monitors
926 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
927 // to the VMthread and have a lifespan longer than that of this activation record.
928 // The VMThread will delete the op when completed.
929 VMThread::execute(new VM_ForceAsyncSafepoint());
930
931 if (ObjectMonitor::Knob_Verbose) {
932 ::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ;
933 ::fflush(stdout);
934 }
935 }
936 }
937
938 void ObjectSynchronizer::verifyInUse(Thread *Self) {
939 ObjectMonitor* mid;
940 int inusetally = 0;
941 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) {
942 inusetally++;
943 }
944 assert(inusetally == Self->omInUseCount, "inuse count off");
945
946 int freetally = 0;
947 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) {
948 freetally++;
949 }
950 assert(freetally == Self->omFreeCount, "free count off");
951 }
952
953 ObjectMonitor * NOINLINE ObjectSynchronizer::omAlloc(Thread * Self) {
954 // A large MAXPRIVATE value reduces both list lock contention
955 // and list coherency traffic, but also tends to increase the
956 // number of objectMonitors in circulation as well as the STW
957 // scavenge costs. As usual, we lean toward time in space-time
958 // tradeoffs.
959 const int MAXPRIVATE = 1024;
960 for (;;) {
961 ObjectMonitor * m;
962
963 // 1: try to allocate from the thread's local omFreeList.
964 // Threads will attempt to allocate first from their local list, then
965 // from the global list, and only after those attempts fail will the thread
966 // attempt to instantiate new monitors. Thread-local free lists take
967 // heat off the ListLock and improve allocation latency, as well as reducing
968 // coherency traffic on the shared global list.
969 m = Self->omFreeList;
970 if (m != NULL) {
971 Self->omFreeList = m->FreeNext;
972 Self->omFreeCount--;
973 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene
974 guarantee(m->object() == NULL, "invariant");
975 if (MonitorInUseLists) {
976 m->FreeNext = Self->omInUseList;
977 Self->omInUseList = m;
978 Self->omInUseCount++;
979 if (ObjectMonitor::Knob_VerifyInUse) {
980 verifyInUse(Self);
981 }
982 } else {
983 m->FreeNext = NULL;
984 }
985 return m;
986 }
987
988 // 2: try to allocate from the global gFreeList
989 // CONSIDER: use muxTry() instead of muxAcquire().
990 // If the muxTry() fails then drop immediately into case 3.
991 // If we're using thread-local free lists then try
992 // to reprovision the caller's free list.
993 if (gFreeList != NULL) {
994 // Reprovision the thread's omFreeList.
995 // Use bulk transfers to reduce the allocation rate and heat
996 // on various locks.
997 Thread::muxAcquire(&ListLock, "omAlloc");
998 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
999 MonitorFreeCount--;
1000 ObjectMonitor * take = gFreeList;
1001 gFreeList = take->FreeNext;
1002 guarantee(take->object() == NULL, "invariant");
1003 guarantee(!take->is_busy(), "invariant");
1004 take->Recycle();
1005 omRelease(Self, take, false);
1006 }
1007 Thread::muxRelease(&ListLock);
1008 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1009 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1010 TEVENT(omFirst - reprovision);
1011
1012 const int mx = MonitorBound;
1013 if (mx > 0 && (MonitorPopulation-MonitorFreeCount) > mx) {
1014 // We can't safely induce a STW safepoint from omAlloc() as our thread
1015 // state may not be appropriate for such activities and callers may hold
1016 // naked oops, so instead we defer the action.
1017 InduceScavenge(Self, "omAlloc");
1018 }
1019 continue;
1020 }
1021
1022 // 3: allocate a block of new ObjectMonitors
1023 // Both the local and global free lists are empty -- resort to malloc().
1024 // In the current implementation objectMonitors are TSM - immortal.
1025 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1026 // each ObjectMonitor to start at the beginning of a cache line,
1027 // so we use align_size_up().
1028 // A better solution would be to use C++ placement-new.
1029 // BEWARE: As it stands currently, we don't run the ctors!
1030 assert(_BLOCKSIZE > 1, "invariant");
1031 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
1032 PaddedEnd<ObjectMonitor> * temp;
1033 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1034 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
1035 mtInternal);
1036 temp = (PaddedEnd<ObjectMonitor> *)
1037 align_size_up((intptr_t)real_malloc_addr,
1038 DEFAULT_CACHE_LINE_SIZE);
1039
1040 // NOTE: (almost) no way to recover if allocation failed.
1041 // We might be able to induce a STW safepoint and scavenge enough
1042 // objectMonitors to permit progress.
1043 if (temp == NULL) {
1044 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1045 "Allocate ObjectMonitors");
1046 }
1047 (void)memset((void *) temp, 0, neededsize);
1048
1049 // Format the block.
1050 // initialize the linked list, each monitor points to its next
1051 // forming the single linked free list, the very first monitor
1052 // will points to next block, which forms the block list.
1053 // The trick of using the 1st element in the block as gBlockList
1054 // linkage should be reconsidered. A better implementation would
1055 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1056
1057 for (int i = 1; i < _BLOCKSIZE; i++) {
1058 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1059 }
1060
1061 // terminate the last monitor as the end of list
1062 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1063
1064 // Element [0] is reserved for global list linkage
1065 temp[0].set_object(CHAINMARKER);
1066
1067 // Consider carving out this thread's current request from the
1068 // block in hand. This avoids some lock traffic and redundant
1069 // list activity.
1070
1071 // Acquire the ListLock to manipulate BlockList and FreeList.
1072 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1073 Thread::muxAcquire(&ListLock, "omAlloc [2]");
1074 MonitorPopulation += _BLOCKSIZE-1;
1075 MonitorFreeCount += _BLOCKSIZE-1;
1076
1077 // Add the new block to the list of extant blocks (gBlockList).
1078 // The very first objectMonitor in a block is reserved and dedicated.
1079 // It serves as blocklist "next" linkage.
1080 temp[0].FreeNext = gBlockList;
1081 gBlockList = temp;
1082
1083 // Add the new string of objectMonitors to the global free list
1084 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1085 gFreeList = temp + 1;
1086 Thread::muxRelease(&ListLock);
1087 TEVENT(Allocate block of monitors);
1088 }
1089 }
1090
1091 // Place "m" on the caller's private per-thread omFreeList.
1092 // In practice there's no need to clamp or limit the number of
1093 // monitors on a thread's omFreeList as the only time we'll call
1094 // omRelease is to return a monitor to the free list after a CAS
1095 // attempt failed. This doesn't allow unbounded #s of monitors to
1096 // accumulate on a thread's free list.
1097
1098 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1099 bool fromPerThreadAlloc) {
1100 guarantee(m->object() == NULL, "invariant");
1101
1102 // Remove from omInUseList
1103 if (MonitorInUseLists && fromPerThreadAlloc) {
1104 ObjectMonitor* curmidinuse = NULL;
1105 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL;) {
1106 if (m == mid) {
1107 // extract from per-thread in-use-list
1108 if (mid == Self->omInUseList) {
1109 Self->omInUseList = mid->FreeNext;
1110 } else if (curmidinuse != NULL) {
1111 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1112 }
1113 Self->omInUseCount--;
1114 if (ObjectMonitor::Knob_VerifyInUse) {
1115 verifyInUse(Self);
1116 }
1117 break;
1118 } else {
1119 curmidinuse = mid;
1120 mid = mid->FreeNext;
1121 }
1122 }
1123 }
1124
1125 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1126 m->FreeNext = Self->omFreeList;
1127 Self->omFreeList = m;
1128 Self->omFreeCount++;
1129 }
1130
1131 // Return the monitors of a moribund thread's local free list to
1132 // the global free list. Typically a thread calls omFlush() when
1133 // it's dying. We could also consider having the VM thread steal
1134 // monitors from threads that have not run java code over a few
1135 // consecutive STW safepoints. Relatedly, we might decay
1136 // omFreeProvision at STW safepoints.
1137 //
1138 // Also return the monitors of a moribund thread's omInUseList to
1139 // a global gOmInUseList under the global list lock so these
1140 // will continue to be scanned.
1141 //
1142 // We currently call omFlush() from the Thread:: dtor _after the thread
1143 // has been excised from the thread list and is no longer a mutator.
1144 // That means that omFlush() can run concurrently with a safepoint and
1145 // the scavenge operator. Calling omFlush() from JavaThread::exit() might
1146 // be a better choice as we could safely reason that that the JVM is
1147 // not at a safepoint at the time of the call, and thus there could
1148 // be not inopportune interleavings between omFlush() and the scavenge
1149 // operator.
1150
1151 void ObjectSynchronizer::omFlush(Thread * Self) {
1152 ObjectMonitor * List = Self->omFreeList; // Null-terminated SLL
1153 Self->omFreeList = NULL;
1154 ObjectMonitor * Tail = NULL;
1155 int Tally = 0;
1156 if (List != NULL) {
1157 ObjectMonitor * s;
1158 for (s = List; s != NULL; s = s->FreeNext) {
1159 Tally++;
1160 Tail = s;
1161 guarantee(s->object() == NULL, "invariant");
1162 guarantee(!s->is_busy(), "invariant");
1163 s->set_owner(NULL); // redundant but good hygiene
1164 TEVENT(omFlush - Move one);
1165 }
1166 guarantee(Tail != NULL && List != NULL, "invariant");
1167 }
1168
1169 ObjectMonitor * InUseList = Self->omInUseList;
1170 ObjectMonitor * InUseTail = NULL;
1171 int InUseTally = 0;
1172 if (InUseList != NULL) {
1173 Self->omInUseList = NULL;
1174 ObjectMonitor *curom;
1175 for (curom = InUseList; curom != NULL; curom = curom->FreeNext) {
1176 InUseTail = curom;
1177 InUseTally++;
1178 }
1179 assert(Self->omInUseCount == InUseTally, "inuse count off");
1180 Self->omInUseCount = 0;
1181 guarantee(InUseTail != NULL && InUseList != NULL, "invariant");
1182 }
1183
1184 Thread::muxAcquire(&ListLock, "omFlush");
1185 if (Tail != NULL) {
1186 Tail->FreeNext = gFreeList;
1187 gFreeList = List;
1188 MonitorFreeCount += Tally;
1189 }
1190
1191 if (InUseTail != NULL) {
1192 InUseTail->FreeNext = gOmInUseList;
1193 gOmInUseList = InUseList;
1194 gOmInUseCount += InUseTally;
1195 }
1196
1197 Thread::muxRelease(&ListLock);
1198 TEVENT(omFlush);
1199 }
1200
1201 // Fast path code shared by multiple functions
1202 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1203 markOop mark = obj->mark();
1204 if (mark->has_monitor()) {
1205 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1206 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1207 return mark->monitor();
1208 }
1209 return ObjectSynchronizer::inflate(Thread::current(), obj);
1210 }
1211
1212
1213 ObjectMonitor * NOINLINE ObjectSynchronizer::inflate(Thread * Self,
1214 oop object) {
1215 // Inflate mutates the heap ...
1216 // Relaxing assertion for bug 6320749.
1217 assert(Universe::verify_in_progress() ||
1218 !SafepointSynchronize::is_at_safepoint(), "invariant");
1219
1220 for (;;) {
1221 const markOop mark = object->mark();
1222 assert(!mark->has_bias_pattern(), "invariant");
1223
1224 // The mark can be in one of the following states:
1225 // * Inflated - just return
1226 // * Stack-locked - coerce it to inflated
1227 // * INFLATING - busy wait for conversion to complete
1228 // * Neutral - aggressively inflate the object.
1229 // * BIASED - Illegal. We should never see this
1230
1231 // CASE: inflated
1232 if (mark->has_monitor()) {
1233 ObjectMonitor * inf = mark->monitor();
1234 assert(inf->header()->is_neutral(), "invariant");
1235 assert(inf->object() == object, "invariant");
1236 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1237 return inf;
1238 }
1239
1240 // CASE: inflation in progress - inflating over a stack-lock.
1241 // Some other thread is converting from stack-locked to inflated.
1242 // Only that thread can complete inflation -- other threads must wait.
1243 // The INFLATING value is transient.
1244 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1245 // We could always eliminate polling by parking the thread on some auxiliary list.
1246 if (mark == markOopDesc::INFLATING()) {
1247 TEVENT(Inflate: spin while INFLATING);
1248 ReadStableMark(object);
1249 continue;
1250 }
1251
1252 // CASE: stack-locked
1253 // Could be stack-locked either by this thread or by some other thread.
1254 //
1255 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1256 // to install INFLATING into the mark word. We originally installed INFLATING,
1257 // allocated the objectmonitor, and then finally STed the address of the
1258 // objectmonitor into the mark. This was correct, but artificially lengthened
1259 // the interval in which INFLATED appeared in the mark, thus increasing
1260 // the odds of inflation contention.
1261 //
1262 // We now use per-thread private objectmonitor free lists.
1263 // These list are reprovisioned from the global free list outside the
1264 // critical INFLATING...ST interval. A thread can transfer
1265 // multiple objectmonitors en-mass from the global free list to its local free list.
1266 // This reduces coherency traffic and lock contention on the global free list.
1267 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1268 // before or after the CAS(INFLATING) operation.
1269 // See the comments in omAlloc().
1270
1271 if (mark->has_locker()) {
1272 ObjectMonitor * m = omAlloc(Self);
1273 // Optimistically prepare the objectmonitor - anticipate successful CAS
1274 // We do this before the CAS in order to minimize the length of time
1275 // in which INFLATING appears in the mark.
1276 m->Recycle();
1277 m->_Responsible = NULL;
1278 m->_recursions = 0;
1279 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1280
1281 markOop cmp = (markOop) Atomic::cmpxchg_ptr(markOopDesc::INFLATING(), object->mark_addr(), mark);
1282 if (cmp != mark) {
1283 omRelease(Self, m, true);
1284 continue; // Interference -- just retry
1285 }
1286
1287 // We've successfully installed INFLATING (0) into the mark-word.
1288 // This is the only case where 0 will appear in a mark-work.
1289 // Only the singular thread that successfully swings the mark-word
1290 // to 0 can perform (or more precisely, complete) inflation.
1291 //
1292 // Why do we CAS a 0 into the mark-word instead of just CASing the
1293 // mark-word from the stack-locked value directly to the new inflated state?
1294 // Consider what happens when a thread unlocks a stack-locked object.
1295 // It attempts to use CAS to swing the displaced header value from the
1296 // on-stack basiclock back into the object header. Recall also that the
1297 // header value (hashcode, etc) can reside in (a) the object header, or
1298 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1299 // header in an objectMonitor. The inflate() routine must copy the header
1300 // value from the basiclock on the owner's stack to the objectMonitor, all
1301 // the while preserving the hashCode stability invariants. If the owner
1302 // decides to release the lock while the value is 0, the unlock will fail
1303 // and control will eventually pass from slow_exit() to inflate. The owner
1304 // will then spin, waiting for the 0 value to disappear. Put another way,
1305 // the 0 causes the owner to stall if the owner happens to try to
1306 // drop the lock (restoring the header from the basiclock to the object)
1307 // while inflation is in-progress. This protocol avoids races that might
1308 // would otherwise permit hashCode values to change or "flicker" for an object.
1309 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1310 // 0 serves as a "BUSY" inflate-in-progress indicator.
1311
1312
1313 // fetch the displaced mark from the owner's stack.
1314 // The owner can't die or unwind past the lock while our INFLATING
1315 // object is in the mark. Furthermore the owner can't complete
1316 // an unlock on the object, either.
1317 markOop dmw = mark->displaced_mark_helper();
1318 assert(dmw->is_neutral(), "invariant");
1319
1320 // Setup monitor fields to proper values -- prepare the monitor
1321 m->set_header(dmw);
1322
1323 // Optimization: if the mark->locker stack address is associated
1324 // with this thread we could simply set m->_owner = Self.
1325 // Note that a thread can inflate an object
1326 // that it has stack-locked -- as might happen in wait() -- directly
1327 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1328 m->set_owner(mark->locker());
1329 m->set_object(object);
1330 // TODO-FIXME: assert BasicLock->dhw != 0.
1331
1332 // Must preserve store ordering. The monitor state must
1333 // be stable at the time of publishing the monitor address.
1334 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1335 object->release_set_mark(markOopDesc::encode(m));
1336
1337 // Hopefully the performance counters are allocated on distinct cache lines
1338 // to avoid false sharing on MP systems ...
1339 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc();
1340 TEVENT(Inflate: overwrite stacklock);
1341 if (TraceMonitorInflation) {
1342 if (object->is_instance()) {
1343 ResourceMark rm;
1344 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1345 (void *) object, (intptr_t) object->mark(),
1346 object->klass()->external_name());
1347 }
1348 }
1349 return m;
1350 }
1351
1352 // CASE: neutral
1353 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1354 // If we know we're inflating for entry it's better to inflate by swinging a
1355 // pre-locked objectMonitor pointer into the object header. A successful
1356 // CAS inflates the object *and* confers ownership to the inflating thread.
1357 // In the current implementation we use a 2-step mechanism where we CAS()
1358 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1359 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1360 // would be useful.
1361
1362 assert(mark->is_neutral(), "invariant");
1363 ObjectMonitor * m = omAlloc(Self);
1364 // prepare m for installation - set monitor to initial state
1365 m->Recycle();
1366 m->set_header(mark);
1367 m->set_owner(NULL);
1368 m->set_object(object);
1369 m->_recursions = 0;
1370 m->_Responsible = NULL;
1371 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1372
1373 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) {
1374 m->set_object(NULL);
1375 m->set_owner(NULL);
1376 m->Recycle();
1377 omRelease(Self, m, true);
1378 m = NULL;
1379 continue;
1380 // interference - the markword changed - just retry.
1381 // The state-transitions are one-way, so there's no chance of
1382 // live-lock -- "Inflated" is an absorbing state.
1383 }
1384
1385 // Hopefully the performance counters are allocated on distinct
1386 // cache lines to avoid false sharing on MP systems ...
1387 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc();
1388 TEVENT(Inflate: overwrite neutral);
1389 if (TraceMonitorInflation) {
1390 if (object->is_instance()) {
1391 ResourceMark rm;
1392 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1393 (void *) object, (intptr_t) object->mark(),
1394 object->klass()->external_name());
1395 }
1396 }
1397 return m;
1398 }
1399 }
1400
1401
1402 // Deflate_idle_monitors() is called at all safepoints, immediately
1403 // after all mutators are stopped, but before any objects have moved.
1404 // It traverses the list of known monitors, deflating where possible.
1405 // The scavenged monitor are returned to the monitor free list.
1406 //
1407 // Beware that we scavenge at *every* stop-the-world point.
1408 // Having a large number of monitors in-circulation negatively
1409 // impacts the performance of some applications (e.g., PointBase).
1410 // Broadly, we want to minimize the # of monitors in circulation.
1411 //
1412 // We have added a flag, MonitorInUseLists, which creates a list
1413 // of active monitors for each thread. deflate_idle_monitors()
1414 // only scans the per-thread inuse lists. omAlloc() puts all
1415 // assigned monitors on the per-thread list. deflate_idle_monitors()
1416 // returns the non-busy monitors to the global free list.
1417 // When a thread dies, omFlush() adds the list of active monitors for
1418 // that thread to a global gOmInUseList acquiring the
1419 // global list lock. deflate_idle_monitors() acquires the global
1420 // list lock to scan for non-busy monitors to the global free list.
1421 // An alternative could have used a single global inuse list. The
1422 // downside would have been the additional cost of acquiring the global list lock
1423 // for every omAlloc().
1424 //
1425 // Perversely, the heap size -- and thus the STW safepoint rate --
1426 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1427 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1428 // This is an unfortunate aspect of this design.
1429
1430 enum ManifestConstants {
1431 ClearResponsibleAtSTW = 0,
1432 MaximumRecheckInterval = 1000
1433 };
1434
1435 // Deflate a single monitor if not in use
1436 // Return true if deflated, false if in use
1437 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1438 ObjectMonitor** freeHeadp,
1439 ObjectMonitor** freeTailp) {
1440 bool deflated;
1441 // Normal case ... The monitor is associated with obj.
1442 guarantee(obj->mark() == markOopDesc::encode(mid), "invariant");
1443 guarantee(mid == obj->mark()->monitor(), "invariant");
1444 guarantee(mid->header()->is_neutral(), "invariant");
1445
1446 if (mid->is_busy()) {
1447 if (ClearResponsibleAtSTW) mid->_Responsible = NULL;
1448 deflated = false;
1449 } else {
1450 // Deflate the monitor if it is no longer being used
1451 // It's idle - scavenge and return to the global free list
1452 // plain old deflation ...
1453 TEVENT(deflate_idle_monitors - scavenge1);
1454 if (TraceMonitorInflation) {
1455 if (obj->is_instance()) {
1456 ResourceMark rm;
1457 tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1458 (void *) obj, (intptr_t) obj->mark(), obj->klass()->external_name());
1459 }
1460 }
1461
1462 // Restore the header back to obj
1463 obj->release_set_mark(mid->header());
1464 mid->clear();
1465
1466 assert(mid->object() == NULL, "invariant");
1467
1468 // Move the object to the working free list defined by FreeHead,FreeTail.
1469 if (*freeHeadp == NULL) *freeHeadp = mid;
1470 if (*freeTailp != NULL) {
1471 ObjectMonitor * prevtail = *freeTailp;
1472 assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); // TODO KK
1473 prevtail->FreeNext = mid;
1474 }
1475 *freeTailp = mid;
1476 deflated = true;
1477 }
1478 return deflated;
1479 }
1480
1481 // Caller acquires ListLock
1482 int ObjectSynchronizer::walk_monitor_list(ObjectMonitor** listheadp,
1483 ObjectMonitor** freeHeadp,
1484 ObjectMonitor** freeTailp) {
1485 ObjectMonitor* mid;
1486 ObjectMonitor* next;
1487 ObjectMonitor* curmidinuse = NULL;
1488 int deflatedcount = 0;
1489
1490 for (mid = *listheadp; mid != NULL;) {
1491 oop obj = (oop) mid->object();
1492 bool deflated = false;
1493 if (obj != NULL) {
1494 deflated = deflate_monitor(mid, obj, freeHeadp, freeTailp);
1495 }
1496 if (deflated) {
1497 // extract from per-thread in-use-list
1498 if (mid == *listheadp) {
1499 *listheadp = mid->FreeNext;
1500 } else if (curmidinuse != NULL) {
1501 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1502 }
1503 next = mid->FreeNext;
1504 mid->FreeNext = NULL; // This mid is current tail in the FreeHead list
1505 mid = next;
1506 deflatedcount++;
1507 } else {
1508 curmidinuse = mid;
1509 mid = mid->FreeNext;
1510 }
1511 }
1512 return deflatedcount;
1513 }
1514
1515 void ObjectSynchronizer::deflate_idle_monitors() {
1516 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1517 int nInuse = 0; // currently associated with objects
1518 int nInCirculation = 0; // extant
1519 int nScavenged = 0; // reclaimed
1520 bool deflated = false;
1521
1522 ObjectMonitor * FreeHead = NULL; // Local SLL of scavenged monitors
1523 ObjectMonitor * FreeTail = NULL;
1524
1525 TEVENT(deflate_idle_monitors);
1526 // Prevent omFlush from changing mids in Thread dtor's during deflation
1527 // And in case the vm thread is acquiring a lock during a safepoint
1528 // See e.g. 6320749
1529 Thread::muxAcquire(&ListLock, "scavenge - return");
1530
1531 if (MonitorInUseLists) {
1532 int inUse = 0;
1533 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) {
1534 nInCirculation+= cur->omInUseCount;
1535 int deflatedcount = walk_monitor_list(cur->omInUseList_addr(), &FreeHead, &FreeTail);
1536 cur->omInUseCount-= deflatedcount;
1537 if (ObjectMonitor::Knob_VerifyInUse) {
1538 verifyInUse(cur);
1539 }
1540 nScavenged += deflatedcount;
1541 nInuse += cur->omInUseCount;
1542 }
1543
1544 // For moribund threads, scan gOmInUseList
1545 if (gOmInUseList) {
1546 nInCirculation += gOmInUseCount;
1547 int deflatedcount = walk_monitor_list((ObjectMonitor **)&gOmInUseList, &FreeHead, &FreeTail);
1548 gOmInUseCount-= deflatedcount;
1549 nScavenged += deflatedcount;
1550 nInuse += gOmInUseCount;
1551 }
1552
1553 } else for (PaddedEnd<ObjectMonitor> * block =
1554 (PaddedEnd<ObjectMonitor> *)gBlockList; block != NULL;
1555 block = (PaddedEnd<ObjectMonitor> *)next(block)) {
1556 // Iterate over all extant monitors - Scavenge all idle monitors.
1557 assert(block->object() == CHAINMARKER, "must be a block header");
1558 nInCirculation += _BLOCKSIZE;
1559 for (int i = 1; i < _BLOCKSIZE; i++) {
1560 ObjectMonitor* mid = (ObjectMonitor*)&block[i];
1561 oop obj = (oop) mid->object();
1562
1563 if (obj == NULL) {
1564 // The monitor is not associated with an object.
1565 // The monitor should either be a thread-specific private
1566 // free list or the global free list.
1567 // obj == NULL IMPLIES mid->is_busy() == 0
1568 guarantee(!mid->is_busy(), "invariant");
1569 continue;
1570 }
1571 deflated = deflate_monitor(mid, obj, &FreeHead, &FreeTail);
1572
1573 if (deflated) {
1574 mid->FreeNext = NULL;
1575 nScavenged++;
1576 } else {
1577 nInuse++;
1578 }
1579 }
1580 }
1581
1582 MonitorFreeCount += nScavenged;
1583
1584 // Consider: audit gFreeList to ensure that MonitorFreeCount and list agree.
1585
1586 if (ObjectMonitor::Knob_Verbose) {
1587 ::printf("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n",
1588 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge,
1589 MonitorPopulation, MonitorFreeCount);
1590 ::fflush(stdout);
1591 }
1592
1593 ForceMonitorScavenge = 0; // Reset
1594
1595 // Move the scavenged monitors back to the global free list.
1596 if (FreeHead != NULL) {
1597 guarantee(FreeTail != NULL && nScavenged > 0, "invariant");
1598 assert(FreeTail->FreeNext == NULL, "invariant");
1599 // constant-time list splice - prepend scavenged segment to gFreeList
1600 FreeTail->FreeNext = gFreeList;
1601 gFreeList = FreeHead;
1602 }
1603 Thread::muxRelease(&ListLock);
1604
1605 if (ObjectMonitor::_sync_Deflations != NULL) ObjectMonitor::_sync_Deflations->inc(nScavenged);
1606 if (ObjectMonitor::_sync_MonExtant != NULL) ObjectMonitor::_sync_MonExtant ->set_value(nInCirculation);
1607
1608 // TODO: Add objectMonitor leak detection.
1609 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1610 GVars.stwRandom = os::random();
1611 GVars.stwCycle++;
1612 }
1613
1614 // Monitor cleanup on JavaThread::exit
1615
1616 // Iterate through monitor cache and attempt to release thread's monitors
1617 // Gives up on a particular monitor if an exception occurs, but continues
1618 // the overall iteration, swallowing the exception.
1619 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1620 private:
1621 TRAPS;
1622
1623 public:
1624 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1625 void do_monitor(ObjectMonitor* mid) {
1626 if (mid->owner() == THREAD) {
1627 (void)mid->complete_exit(CHECK);
1628 }
1629 }
1630 };
1631
1632 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1633 // ignored. This is meant to be called during JNI thread detach which assumes
1634 // all remaining monitors are heavyweight. All exceptions are swallowed.
1635 // Scanning the extant monitor list can be time consuming.
1636 // A simple optimization is to add a per-thread flag that indicates a thread
1637 // called jni_monitorenter() during its lifetime.
1638 //
1639 // Instead of No_Savepoint_Verifier it might be cheaper to
1640 // use an idiom of the form:
1641 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1642 // <code that must not run at safepoint>
1643 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1644 // Since the tests are extremely cheap we could leave them enabled
1645 // for normal product builds.
1646
1647 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1648 assert(THREAD == JavaThread::current(), "must be current Java thread");
1649 No_Safepoint_Verifier nsv;
1650 ReleaseJavaMonitorsClosure rjmc(THREAD);
1651 Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread");
1652 ObjectSynchronizer::monitors_iterate(&rjmc);
1653 Thread::muxRelease(&ListLock);
1654 THREAD->clear_pending_exception();
1655 }
1656
1657 //------------------------------------------------------------------------------
1658 // Debugging code
1659
1660 void ObjectSynchronizer::sanity_checks(const bool verbose,
1661 const uint cache_line_size,
1662 int *error_cnt_ptr,
1663 int *warning_cnt_ptr) {
1664 u_char *addr_begin = (u_char*)&GVars;
1665 u_char *addr_stwRandom = (u_char*)&GVars.stwRandom;
1666 u_char *addr_hcSequence = (u_char*)&GVars.hcSequence;
1667
1668 if (verbose) {
1669 tty->print_cr("INFO: sizeof(SharedGlobals)=" SIZE_FORMAT,
1670 sizeof(SharedGlobals));
1671 }
1672
1673 uint offset_stwRandom = (uint)(addr_stwRandom - addr_begin);
1674 if (verbose) tty->print_cr("INFO: offset(stwRandom)=%u", offset_stwRandom);
1675
1676 uint offset_hcSequence = (uint)(addr_hcSequence - addr_begin);
1677 if (verbose) {
1678 tty->print_cr("INFO: offset(_hcSequence)=%u", offset_hcSequence);
1679 }
1680
1681 if (cache_line_size != 0) {
1682 // We were able to determine the L1 data cache line size so
1683 // do some cache line specific sanity checks
1684
1685 if (offset_stwRandom < cache_line_size) {
1686 tty->print_cr("WARNING: the SharedGlobals.stwRandom field is closer "
1687 "to the struct beginning than a cache line which permits "
1688 "false sharing.");
1689 (*warning_cnt_ptr)++;
1690 }
1691
1692 if ((offset_hcSequence - offset_stwRandom) < cache_line_size) {
1693 tty->print_cr("WARNING: the SharedGlobals.stwRandom and "
1694 "SharedGlobals.hcSequence fields are closer than a cache "
1695 "line which permits false sharing.");
1696 (*warning_cnt_ptr)++;
1697 }
1698
1699 if ((sizeof(SharedGlobals) - offset_hcSequence) < cache_line_size) {
1700 tty->print_cr("WARNING: the SharedGlobals.hcSequence field is closer "
1701 "to the struct end than a cache line which permits false "
1702 "sharing.");
1703 (*warning_cnt_ptr)++;
1704 }
1705 }
1706 }
1707
1708 #ifndef PRODUCT
1709
1710 // Verify all monitors in the monitor cache, the verification is weak.
1711 void ObjectSynchronizer::verify() {
1712 PaddedEnd<ObjectMonitor> * block = (PaddedEnd<ObjectMonitor> *)gBlockList;
1713 ObjectMonitor* mid;
1714 while (block) {
1715 assert(block->object() == CHAINMARKER, "must be a block header");
1716 for (int i = 1; i < _BLOCKSIZE; i++) {
1717 mid = (ObjectMonitor *)(block + i);
1718 oop object = (oop) mid->object();
1719 if (object != NULL) {
1720 mid->verify();
1721 }
1722 }
1723 block = (PaddedEnd<ObjectMonitor> *) block->FreeNext;
1724 }
1725 }
1726
1727 // Check if monitor belongs to the monitor cache
1728 // The list is grow-only so it's *relatively* safe to traverse
1729 // the list of extant blocks without taking a lock.
1730
1731 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
1732 PaddedEnd<ObjectMonitor> * block = (PaddedEnd<ObjectMonitor> *)gBlockList;
1733
1734 while (block) {
1735 assert(block->object() == CHAINMARKER, "must be a block header");
1736 if (monitor > (ObjectMonitor *)&block[0] &&
1737 monitor < (ObjectMonitor *)&block[_BLOCKSIZE]) {
1738 address mon = (address) monitor;
1739 address blk = (address) block;
1740 size_t diff = mon - blk;
1741 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "check");
1742 return 1;
1743 }
1744 block = (PaddedEnd<ObjectMonitor> *) block->FreeNext;
1745 }
1746 return 0;
1747 }
1748
1749 #endif