1 /*
2 * Copyright (c) 1998, 2014, 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/resourceArea.hpp"
28 #include "oops/markOop.hpp"
29 #include "oops/oop.inline.hpp"
30 #include "runtime/biasedLocking.hpp"
31 #include "runtime/handles.inline.hpp"
32 #include "runtime/interfaceSupport.hpp"
33 #include "runtime/mutexLocker.hpp"
34 #include "runtime/objectMonitor.hpp"
35 #include "runtime/objectMonitor.inline.hpp"
36 #include "runtime/osThread.hpp"
37 #include "runtime/stubRoutines.hpp"
38 #include "runtime/synchronizer.hpp"
39 #include "runtime/thread.inline.hpp"
40 #include "utilities/dtrace.hpp"
41 #include "utilities/events.hpp"
42 #include "utilities/preserveException.hpp"
43 #ifdef TARGET_OS_FAMILY_linux
44 # include "os_linux.inline.hpp"
45 #endif
46 #ifdef TARGET_OS_FAMILY_solaris
47 # include "os_solaris.inline.hpp"
48 #endif
49 #ifdef TARGET_OS_FAMILY_windows
50 # include "os_windows.inline.hpp"
51 #endif
52 #ifdef TARGET_OS_FAMILY_bsd
53 # include "os_bsd.inline.hpp"
54 #endif
55
56 #if defined(__GNUC__) && !defined(PPC64)
57 // Need to inhibit inlining for older versions of GCC to avoid build-time failures
58 #define ATTR __attribute__((noinline))
59 #else
60 #define ATTR
61 #endif
62
63 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
64
65 // The "core" versions of monitor enter and exit reside in this file.
66 // The interpreter and compilers contain specialized transliterated
67 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
68 // for instance. If you make changes here, make sure to modify the
69 // interpreter, and both C1 and C2 fast-path inline locking code emission.
70 //
71 //
72 // -----------------------------------------------------------------------------
73
74 #ifdef DTRACE_ENABLED
75
76 // Only bother with this argument setup if dtrace is available
77 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
78
79 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
80 char* bytes = NULL; \
81 int len = 0; \
82 jlong jtid = SharedRuntime::get_java_tid(thread); \
83 Symbol* klassname = ((oop)(obj))->klass()->name(); \
84 if (klassname != NULL) { \
85 bytes = (char*)klassname->bytes(); \
86 len = klassname->utf8_length(); \
87 }
88
89 #ifndef USDT2
90 HS_DTRACE_PROBE_DECL5(hotspot, monitor__wait,
91 jlong, uintptr_t, char*, int, long);
92 HS_DTRACE_PROBE_DECL4(hotspot, monitor__waited,
93 jlong, uintptr_t, char*, int);
94
95 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
96 { \
97 if (DTraceMonitorProbes) { \
98 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
99 HS_DTRACE_PROBE5(hotspot, monitor__wait, jtid, \
100 (monitor), bytes, len, (millis)); \
101 } \
102 }
103
104 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
105 { \
106 if (DTraceMonitorProbes) { \
107 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
108 HS_DTRACE_PROBE4(hotspot, monitor__##probe, jtid, \
109 (uintptr_t)(monitor), bytes, len); \
110 } \
111 }
112
113 #else /* USDT2 */
114
115 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
116 { \
117 if (DTraceMonitorProbes) { \
118 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
119 HOTSPOT_MONITOR_WAIT(jtid, \
120 (uintptr_t)(monitor), bytes, len, (millis)); \
121 } \
122 }
123
124 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
125
126 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
127 { \
128 if (DTraceMonitorProbes) { \
129 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
130 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
131 (uintptr_t)(monitor), bytes, len); \
132 } \
133 }
134
135 #endif /* USDT2 */
136 #else // ndef DTRACE_ENABLED
137
138 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
139 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
140
141 #endif // ndef DTRACE_ENABLED
142
143 // This exists only as a workaround of dtrace bug 6254741
144 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
145 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
146 return 0;
147 }
148
149 #define NINFLATIONLOCKS 256
150 static volatile intptr_t InflationLocks [NINFLATIONLOCKS] ;
151
152 ObjectMonitor * ObjectSynchronizer::gBlockList = NULL ;
153 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL ;
154 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL ;
155 int ObjectSynchronizer::gOmInUseCount = 0;
156 static volatile intptr_t ListLock = 0 ; // protects global monitor free-list cache
157 static volatile int MonitorFreeCount = 0 ; // # on gFreeList
158 static volatile int MonitorPopulation = 0 ; // # Extant -- in circulation
159 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
160
161 // -----------------------------------------------------------------------------
162 // Fast Monitor Enter/Exit
163 // This the fast monitor enter. The interpreter and compiler use
164 // some assembly copies of this code. Make sure update those code
165 // if the following function is changed. The implementation is
166 // extremely sensitive to race condition. Be careful.
167
168 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock, bool attempt_rebias, TRAPS) {
169 if (UseBiasedLocking) {
170 if (!SafepointSynchronize::is_at_safepoint()) {
171 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
172 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
173 return;
174 }
175 } else {
176 assert(!attempt_rebias, "can not rebias toward VM thread");
177 BiasedLocking::revoke_at_safepoint(obj);
178 }
179 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
180 }
181
182 slow_enter (obj, lock, THREAD) ;
183 }
184
185 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
186 assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here");
187 // if displaced header is null, the previous enter is recursive enter, no-op
188 markOop dhw = lock->displaced_header();
189 markOop mark ;
190 if (dhw == NULL) {
191 // Recursive stack-lock.
192 // Diagnostics -- Could be: stack-locked, inflating, inflated.
193 mark = object->mark() ;
194 assert (!mark->is_neutral(), "invariant") ;
195 if (mark->has_locker() && mark != markOopDesc::INFLATING()) {
196 assert(THREAD->is_lock_owned((address)mark->locker()), "invariant") ;
197 }
198 if (mark->has_monitor()) {
199 ObjectMonitor * m = mark->monitor() ;
200 assert(((oop)(m->object()))->mark() == mark, "invariant") ;
201 assert(m->is_entered(THREAD), "invariant") ;
202 }
203 return ;
204 }
205
206 mark = object->mark() ;
207
208 // If the object is stack-locked by the current thread, try to
209 // swing the displaced header from the box back to the mark.
210 if (mark == (markOop) lock) {
211 assert (dhw->is_neutral(), "invariant") ;
212 if (object->cas_set_mark(dhw, mark) == mark) {
213 TEVENT (fast_exit: release stacklock) ;
214 return;
215 }
216 }
217
218 ObjectSynchronizer::inflate(THREAD, object)->exit (true, THREAD) ;
219 }
220
221 // -----------------------------------------------------------------------------
222 // Interpreter/Compiler Slow Case
223 // This routine is used to handle interpreter/compiler slow case
224 // We don't need to use fast path here, because it must have been
225 // failed in the interpreter/compiler code.
226 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
227 markOop mark = obj->mark();
228 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
229
230 if (mark->is_neutral()) {
231 // Anticipate successful CAS -- the ST of the displaced mark must
232 // be visible <= the ST performed by the CAS.
233 lock->set_displaced_header(mark);
234 if (mark == obj()->cas_set_mark((markOop) lock, mark)) {
235 TEVENT (slow_enter: release stacklock) ;
236 return ;
237 }
238 // Fall through to inflate() ...
239 } else
240 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
241 assert(lock != mark->locker(), "must not re-lock the same lock");
242 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
243 lock->set_displaced_header(NULL);
244 return;
245 }
246
247 #if 0
248 // The following optimization isn't particularly useful.
249 if (mark->has_monitor() && mark->monitor()->is_entered(THREAD)) {
250 lock->set_displaced_header (NULL) ;
251 return ;
252 }
253 #endif
254
255 // The object header will never be displaced to this lock,
256 // so it does not matter what the value is, except that it
257 // must be non-zero to avoid looking like a re-entrant lock,
258 // and must not look locked either.
259 lock->set_displaced_header(markOopDesc::unused_mark());
260 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
261 }
262
263 // This routine is used to handle interpreter/compiler slow case
264 // We don't need to use fast path here, because it must have
265 // failed in the interpreter/compiler code. Simply use the heavy
266 // weight monitor should be ok, unless someone find otherwise.
267 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
268 fast_exit (object, lock, THREAD) ;
269 }
270
271 // -----------------------------------------------------------------------------
272 // Class Loader support to workaround deadlocks on the class loader lock objects
273 // Also used by GC
274 // complete_exit()/reenter() are used to wait on a nested lock
275 // i.e. to give up an outer lock completely and then re-enter
276 // Used when holding nested locks - lock acquisition order: lock1 then lock2
277 // 1) complete_exit lock1 - saving recursion count
278 // 2) wait on lock2
279 // 3) when notified on lock2, unlock lock2
280 // 4) reenter lock1 with original recursion count
281 // 5) lock lock2
282 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
283 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
284 TEVENT (complete_exit) ;
285 if (UseBiasedLocking) {
286 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
287 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
288 }
289
290 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
291
292 return monitor->complete_exit(THREAD);
293 }
294
295 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
296 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
297 TEVENT (reenter) ;
298 if (UseBiasedLocking) {
299 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
300 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
301 }
302
303 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
304
305 monitor->reenter(recursion, THREAD);
306 }
307 // -----------------------------------------------------------------------------
308 // JNI locks on java objects
309 // NOTE: must use heavy weight monitor to handle jni monitor enter
310 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) { // possible entry from jni enter
311 // the current locking is from JNI instead of Java code
312 TEVENT (jni_enter) ;
313 if (UseBiasedLocking) {
314 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
315 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
316 }
317 THREAD->set_current_pending_monitor_is_from_java(false);
318 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
319 THREAD->set_current_pending_monitor_is_from_java(true);
320 }
321
322 // NOTE: must use heavy weight monitor to handle jni monitor enter
323 bool ObjectSynchronizer::jni_try_enter(Handle obj, Thread* THREAD) {
324 if (UseBiasedLocking) {
325 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
326 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
327 }
328
329 ObjectMonitor* monitor = ObjectSynchronizer::inflate_helper(obj());
330 return monitor->try_enter(THREAD);
331 }
332
333
334 // NOTE: must use heavy weight monitor to handle jni monitor exit
335 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
336 TEVENT (jni_exit) ;
337 if (UseBiasedLocking) {
338 Handle h_obj(THREAD, obj);
339 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
340 obj = h_obj();
341 }
342 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
343
344 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj);
345 // If this thread has locked the object, exit the monitor. Note: can't use
346 // monitor->check(CHECK); must exit even if an exception is pending.
347 if (monitor->check(THREAD)) {
348 monitor->exit(true, THREAD);
349 }
350 }
351
352 // -----------------------------------------------------------------------------
353 // Internal VM locks on java objects
354 // standard constructor, allows locking failures
355 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
356 _dolock = doLock;
357 _thread = thread;
358 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
359 _obj = obj;
360
361 if (_dolock) {
362 TEVENT (ObjectLocker) ;
363
364 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
365 }
366 }
367
368 ObjectLocker::~ObjectLocker() {
369 if (_dolock) {
370 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
371 }
372 }
373
374
375 // -----------------------------------------------------------------------------
376 // Wait/Notify/NotifyAll
377 // NOTE: must use heavy weight monitor to handle wait()
378 void ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
379 if (UseBiasedLocking) {
380 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
381 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
382 }
383 if (millis < 0) {
384 TEVENT (wait - throw IAX) ;
385 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
386 }
387 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
388 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
389 monitor->wait(millis, true, THREAD);
390
391 /* This dummy call is in place to get around dtrace bug 6254741. Once
392 that's fixed we can uncomment the following line and remove the call */
393 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
394 dtrace_waited_probe(monitor, obj, THREAD);
395 }
396
397 void ObjectSynchronizer::waitUninterruptibly (Handle obj, jlong millis, TRAPS) {
398 if (UseBiasedLocking) {
399 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
400 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
401 }
402 if (millis < 0) {
403 TEVENT (wait - throw IAX) ;
404 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
405 }
406 ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD) ;
407 }
408
409 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
410 if (UseBiasedLocking) {
411 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
412 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
413 }
414
415 markOop mark = obj->mark();
416 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
417 return;
418 }
419 ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD);
420 }
421
422 // NOTE: see comment of notify()
423 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
424 if (UseBiasedLocking) {
425 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
426 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
427 }
428
429 markOop mark = obj->mark();
430 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
431 return;
432 }
433 ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD);
434 }
435
436 // -----------------------------------------------------------------------------
437 // Hash Code handling
438 //
439 // Performance concern:
440 // OrderAccess::storestore() calls release() which at one time stored 0
441 // into the global volatile OrderAccess::dummy variable. This store was
442 // unnecessary for correctness. Many threads storing into a common location
443 // causes considerable cache migration or "sloshing" on large SMP systems.
444 // As such, I avoided using OrderAccess::storestore(). In some cases
445 // OrderAccess::fence() -- which incurs local latency on the executing
446 // processor -- is a better choice as it scales on SMP systems.
447 //
448 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
449 // a discussion of coherency costs. Note that all our current reference
450 // platforms provide strong ST-ST order, so the issue is moot on IA32,
451 // x64, and SPARC.
452 //
453 // As a general policy we use "volatile" to control compiler-based reordering
454 // and explicit fences (barriers) to control for architectural reordering
455 // performed by the CPU(s) or platform.
456
457 struct SharedGlobals {
458 // These are highly shared mostly-read variables.
459 // To avoid false-sharing they need to be the sole occupants of a $ line.
460 double padPrefix [8];
461 volatile int stwRandom ;
462 volatile int stwCycle ;
463
464 // Hot RW variables -- Sequester to avoid false-sharing
465 double padSuffix [16];
466 volatile int hcSequence ;
467 double padFinal [8] ;
468 } ;
469
470 static SharedGlobals GVars ;
471 static int MonitorScavengeThreshold = 1000000 ;
472 static volatile int ForceMonitorScavenge = 0 ; // Scavenge required and pending
473
474 static markOop ReadStableMark (oop obj) {
475 markOop mark = obj->mark() ;
476 if (!mark->is_being_inflated()) {
477 return mark ; // normal fast-path return
478 }
479
480 int its = 0 ;
481 for (;;) {
482 markOop mark = obj->mark() ;
483 if (!mark->is_being_inflated()) {
484 return mark ; // normal fast-path return
485 }
486
487 // The object is being inflated by some other thread.
488 // The caller of ReadStableMark() must wait for inflation to complete.
489 // Avoid live-lock
490 // TODO: consider calling SafepointSynchronize::do_call_back() while
491 // spinning to see if there's a safepoint pending. If so, immediately
492 // yielding or blocking would be appropriate. Avoid spinning while
493 // there is a safepoint pending.
494 // TODO: add inflation contention performance counters.
495 // TODO: restrict the aggregate number of spinners.
496
497 ++its ;
498 if (its > 10000 || !os::is_MP()) {
499 if (its & 1) {
500 os::NakedYield() ;
501 TEVENT (Inflate: INFLATING - yield) ;
502 } else {
503 // Note that the following code attenuates the livelock problem but is not
504 // a complete remedy. A more complete solution would require that the inflating
505 // thread hold the associated inflation lock. The following code simply restricts
506 // the number of spinners to at most one. We'll have N-2 threads blocked
507 // on the inflationlock, 1 thread holding the inflation lock and using
508 // a yield/park strategy, and 1 thread in the midst of inflation.
509 // A more refined approach would be to change the encoding of INFLATING
510 // to allow encapsulation of a native thread pointer. Threads waiting for
511 // inflation to complete would use CAS to push themselves onto a singly linked
512 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
513 // and calling park(). When inflation was complete the thread that accomplished inflation
514 // would detach the list and set the markword to inflated with a single CAS and
515 // then for each thread on the list, set the flag and unpark() the thread.
516 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
517 // wakes at most one thread whereas we need to wake the entire list.
518 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1) ;
519 int YieldThenBlock = 0 ;
520 assert (ix >= 0 && ix < NINFLATIONLOCKS, "invariant") ;
521 assert ((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant") ;
522 Thread::muxAcquire (InflationLocks + ix, "InflationLock") ;
523 while (obj->mark() == markOopDesc::INFLATING()) {
524 // Beware: NakedYield() is advisory and has almost no effect on some platforms
525 // so we periodically call Self->_ParkEvent->park(1).
526 // We use a mixed spin/yield/block mechanism.
527 if ((YieldThenBlock++) >= 16) {
528 Thread::current()->_ParkEvent->park(1) ;
529 } else {
530 os::NakedYield() ;
531 }
532 }
533 Thread::muxRelease (InflationLocks + ix ) ;
534 TEVENT (Inflate: INFLATING - yield/park) ;
535 }
536 } else {
537 SpinPause() ; // SMP-polite spinning
538 }
539 }
540 }
541
542 // hashCode() generation :
543 //
544 // Possibilities:
545 // * MD5Digest of {obj,stwRandom}
546 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
547 // * A DES- or AES-style SBox[] mechanism
548 // * One of the Phi-based schemes, such as:
549 // 2654435761 = 2^32 * Phi (golden ratio)
550 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
551 // * A variation of Marsaglia's shift-xor RNG scheme.
552 // * (obj ^ stwRandom) is appealing, but can result
553 // in undesirable regularity in the hashCode values of adjacent objects
554 // (objects allocated back-to-back, in particular). This could potentially
555 // result in hashtable collisions and reduced hashtable efficiency.
556 // There are simple ways to "diffuse" the middle address bits over the
557 // generated hashCode values:
558 //
559
560 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
561 intptr_t value = 0 ;
562 if (hashCode == 0) {
563 // This form uses an unguarded global Park-Miller RNG,
564 // so it's possible for two threads to race and generate the same RNG.
565 // On MP system we'll have lots of RW access to a global, so the
566 // mechanism induces lots of coherency traffic.
567 value = os::random() ;
568 } else
569 if (hashCode == 1) {
570 // This variation has the property of being stable (idempotent)
571 // between STW operations. This can be useful in some of the 1-0
572 // synchronization schemes.
573 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3 ;
574 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom ;
575 } else
576 if (hashCode == 2) {
577 value = 1 ; // for sensitivity testing
578 } else
579 if (hashCode == 3) {
580 value = ++GVars.hcSequence ;
581 } else
582 if (hashCode == 4) {
583 value = cast_from_oop<intptr_t>(obj) ;
584 } else {
585 // Marsaglia's xor-shift scheme with thread-specific state
586 // This is probably the best overall implementation -- we'll
587 // likely make this the default in future releases.
588 unsigned t = Self->_hashStateX ;
589 t ^= (t << 11) ;
590 Self->_hashStateX = Self->_hashStateY ;
591 Self->_hashStateY = Self->_hashStateZ ;
592 Self->_hashStateZ = Self->_hashStateW ;
593 unsigned v = Self->_hashStateW ;
594 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)) ;
595 Self->_hashStateW = v ;
596 value = v ;
597 }
598
599 value &= markOopDesc::hash_mask;
600 if (value == 0) value = 0xBAD ;
601 assert (value != markOopDesc::no_hash, "invariant") ;
602 TEVENT (hashCode: GENERATE) ;
603 return value;
604 }
605 //
606 intptr_t ObjectSynchronizer::FastHashCode (Thread * Self, oop obj) {
607 if (UseBiasedLocking) {
608 // NOTE: many places throughout the JVM do not expect a safepoint
609 // to be taken here, in particular most operations on perm gen
610 // objects. However, we only ever bias Java instances and all of
611 // the call sites of identity_hash that might revoke biases have
612 // been checked to make sure they can handle a safepoint. The
613 // added check of the bias pattern is to avoid useless calls to
614 // thread-local storage.
615 if (obj->mark()->has_bias_pattern()) {
616 // Box and unbox the raw reference just in case we cause a STW safepoint.
617 Handle hobj (Self, obj) ;
618 // Relaxing assertion for bug 6320749.
619 assert (Universe::verify_in_progress() ||
620 !SafepointSynchronize::is_at_safepoint(),
621 "biases should not be seen by VM thread here");
622 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
623 obj = hobj() ;
624 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
625 }
626 }
627
628 // hashCode() is a heap mutator ...
629 // Relaxing assertion for bug 6320749.
630 assert (Universe::verify_in_progress() ||
631 !SafepointSynchronize::is_at_safepoint(), "invariant") ;
632 assert (Universe::verify_in_progress() ||
633 Self->is_Java_thread() , "invariant") ;
634 assert (Universe::verify_in_progress() ||
635 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ;
636
637 ObjectMonitor* monitor = NULL;
638 markOop temp, test;
639 intptr_t hash;
640 markOop mark = ReadStableMark (obj);
641
642 // object should remain ineligible for biased locking
643 assert (!mark->has_bias_pattern(), "invariant") ;
644
645 if (mark->is_neutral()) {
646 hash = mark->hash(); // this is a normal header
647 if (hash) { // if it has hash, just return it
648 return hash;
649 }
650 hash = get_next_hash(Self, obj); // allocate a new hash code
651 temp = mark->copy_set_hash(hash); // merge the hash code into header
652 // use (machine word version) atomic operation to install the hash
653 test = obj->cas_set_mark(temp, mark);
654 if (test == mark) {
655 return hash;
656 }
657 // If atomic operation failed, we must inflate the header
658 // into heavy weight monitor. We could add more code here
659 // for fast path, but it does not worth the complexity.
660 } else if (mark->has_monitor()) {
661 monitor = mark->monitor();
662 temp = monitor->header();
663 assert (temp->is_neutral(), "invariant") ;
664 hash = temp->hash();
665 if (hash) {
666 return hash;
667 }
668 // Skip to the following code to reduce code size
669 } else if (Self->is_lock_owned((address)mark->locker())) {
670 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
671 assert (temp->is_neutral(), "invariant") ;
672 hash = temp->hash(); // by current thread, check if the displaced
673 if (hash) { // header contains hash code
674 return hash;
675 }
676 // WARNING:
677 // The displaced header is strictly immutable.
678 // It can NOT be changed in ANY cases. So we have
679 // to inflate the header into heavyweight monitor
680 // even the current thread owns the lock. The reason
681 // is the BasicLock (stack slot) will be asynchronously
682 // read by other threads during the inflate() function.
683 // Any change to stack may not propagate to other threads
684 // correctly.
685 }
686
687 // Inflate the monitor to set hash code
688 monitor = ObjectSynchronizer::inflate(Self, obj);
689 // Load displaced header and check it has hash code
690 mark = monitor->header();
691 assert (mark->is_neutral(), "invariant") ;
692 hash = mark->hash();
693 if (hash == 0) {
694 hash = get_next_hash(Self, obj);
695 temp = mark->copy_set_hash(hash); // merge hash code into header
696 assert (temp->is_neutral(), "invariant") ;
697 test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark);
698 if (test != mark) {
699 // The only update to the header in the monitor (outside GC)
700 // is install the hash code. If someone add new usage of
701 // displaced header, please update this code
702 hash = test->hash();
703 assert (test->is_neutral(), "invariant") ;
704 assert (hash != 0, "Trivial unexpected object/monitor header usage.");
705 }
706 }
707 // We finally get the hash
708 return hash;
709 }
710
711 // Deprecated -- use FastHashCode() instead.
712
713 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
714 return FastHashCode (Thread::current(), obj()) ;
715 }
716
717
718 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
719 Handle h_obj) {
720 if (UseBiasedLocking) {
721 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
722 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
723 }
724
725 assert(thread == JavaThread::current(), "Can only be called on current thread");
726 oop obj = h_obj();
727
728 markOop mark = ReadStableMark (obj) ;
729
730 // Uncontended case, header points to stack
731 if (mark->has_locker()) {
732 return thread->is_lock_owned((address)mark->locker());
733 }
734 // Contended case, header points to ObjectMonitor (tagged pointer)
735 if (mark->has_monitor()) {
736 ObjectMonitor* monitor = mark->monitor();
737 return monitor->is_entered(thread) != 0 ;
738 }
739 // Unlocked case, header in place
740 assert(mark->is_neutral(), "sanity check");
741 return false;
742 }
743
744 // Be aware of this method could revoke bias of the lock object.
745 // This method querys the ownership of the lock handle specified by 'h_obj'.
746 // If the current thread owns the lock, it returns owner_self. If no
747 // thread owns the lock, it returns owner_none. Otherwise, it will return
748 // ower_other.
749 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
750 (JavaThread *self, Handle h_obj) {
751 // The caller must beware this method can revoke bias, and
752 // revocation can result in a safepoint.
753 assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ;
754 assert (self->thread_state() != _thread_blocked , "invariant") ;
755
756 // Possible mark states: neutral, biased, stack-locked, inflated
757
758 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
759 // CASE: biased
760 BiasedLocking::revoke_and_rebias(h_obj, false, self);
761 assert(!h_obj->mark()->has_bias_pattern(),
762 "biases should be revoked by now");
763 }
764
765 assert(self == JavaThread::current(), "Can only be called on current thread");
766 oop obj = h_obj();
767 markOop mark = ReadStableMark (obj) ;
768
769 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
770 if (mark->has_locker()) {
771 return self->is_lock_owned((address)mark->locker()) ?
772 owner_self : owner_other;
773 }
774
775 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
776 // The Object:ObjectMonitor relationship is stable as long as we're
777 // not at a safepoint.
778 if (mark->has_monitor()) {
779 void * owner = mark->monitor()->_owner ;
780 if (owner == NULL) return owner_none ;
781 return (owner == self ||
782 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
783 }
784
785 // CASE: neutral
786 assert(mark->is_neutral(), "sanity check");
787 return owner_none ; // it's unlocked
788 }
789
790 // FIXME: jvmti should call this
791 JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) {
792 if (UseBiasedLocking) {
793 if (SafepointSynchronize::is_at_safepoint()) {
794 BiasedLocking::revoke_at_safepoint(h_obj);
795 } else {
796 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
797 }
798 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
799 }
800
801 oop obj = h_obj();
802 address owner = NULL;
803
804 markOop mark = ReadStableMark (obj) ;
805
806 // Uncontended case, header points to stack
807 if (mark->has_locker()) {
808 owner = (address) mark->locker();
809 }
810
811 // Contended case, header points to ObjectMonitor (tagged pointer)
812 if (mark->has_monitor()) {
813 ObjectMonitor* monitor = mark->monitor();
814 assert(monitor != NULL, "monitor should be non-null");
815 owner = (address) monitor->owner();
816 }
817
818 if (owner != NULL) {
819 // owning_thread_from_monitor_owner() may also return NULL here
820 return Threads::owning_thread_from_monitor_owner(owner, doLock);
821 }
822
823 // Unlocked case, header in place
824 // Cannot have assertion since this object may have been
825 // locked by another thread when reaching here.
826 // assert(mark->is_neutral(), "sanity check");
827
828 return NULL;
829 }
830 // Visitors ...
831
832 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
833 ObjectMonitor* block = gBlockList;
834 ObjectMonitor* mid;
835 while (block) {
836 assert(block->object() == CHAINMARKER, "must be a block header");
837 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
838 mid = block + i;
839 oop object = (oop) mid->object();
840 if (object != NULL) {
841 closure->do_monitor(mid);
842 }
843 }
844 block = (ObjectMonitor*) block->FreeNext;
845 }
846 }
847
848 // Get the next block in the block list.
849 static inline ObjectMonitor* next(ObjectMonitor* block) {
850 assert(block->object() == CHAINMARKER, "must be a block header");
851 block = block->FreeNext ;
852 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
853 return block;
854 }
855
856
857 void ObjectSynchronizer::oops_do(OopClosure* f) {
858 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
859 for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) {
860 assert(block->object() == CHAINMARKER, "must be a block header");
861 for (int i = 1; i < _BLOCKSIZE; i++) {
862 ObjectMonitor* mid = &block[i];
863 if (mid->object() != NULL) {
864 f->do_oop((oop*)mid->object_addr());
865 }
866 }
867 }
868 }
869
870
871 // -----------------------------------------------------------------------------
872 // ObjectMonitor Lifecycle
873 // -----------------------
874 // Inflation unlinks monitors from the global gFreeList and
875 // associates them with objects. Deflation -- which occurs at
876 // STW-time -- disassociates idle monitors from objects. Such
877 // scavenged monitors are returned to the gFreeList.
878 //
879 // The global list is protected by ListLock. All the critical sections
880 // are short and operate in constant-time.
881 //
882 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
883 //
884 // Lifecycle:
885 // -- unassigned and on the global free list
886 // -- unassigned and on a thread's private omFreeList
887 // -- assigned to an object. The object is inflated and the mark refers
888 // to the objectmonitor.
889 //
890
891
892 // Constraining monitor pool growth via MonitorBound ...
893 //
894 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
895 // the rate of scavenging is driven primarily by GC. As such, we can find
896 // an inordinate number of monitors in circulation.
897 // To avoid that scenario we can artificially induce a STW safepoint
898 // if the pool appears to be growing past some reasonable bound.
899 // Generally we favor time in space-time tradeoffs, but as there's no
900 // natural back-pressure on the # of extant monitors we need to impose some
901 // type of limit. Beware that if MonitorBound is set to too low a value
902 // we could just loop. In addition, if MonitorBound is set to a low value
903 // we'll incur more safepoints, which are harmful to performance.
904 // See also: GuaranteedSafepointInterval
905 //
906 // The current implementation uses asynchronous VM operations.
907 //
908
909 static void InduceScavenge (Thread * Self, const char * Whence) {
910 // Induce STW safepoint to trim monitors
911 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
912 // More precisely, trigger an asynchronous STW safepoint as the number
913 // of active monitors passes the specified threshold.
914 // TODO: assert thread state is reasonable
915
916 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
917 if (ObjectMonitor::Knob_Verbose) {
918 ::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ;
919 ::fflush(stdout) ;
920 }
921 // Induce a 'null' safepoint to scavenge monitors
922 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
923 // to the VMthread and have a lifespan longer than that of this activation record.
924 // The VMThread will delete the op when completed.
925 VMThread::execute (new VM_ForceAsyncSafepoint()) ;
926
927 if (ObjectMonitor::Knob_Verbose) {
928 ::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ;
929 ::fflush(stdout) ;
930 }
931 }
932 }
933 /* Too slow for general assert or debug
934 void ObjectSynchronizer::verifyInUse (Thread *Self) {
935 ObjectMonitor* mid;
936 int inusetally = 0;
937 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) {
938 inusetally ++;
939 }
940 assert(inusetally == Self->omInUseCount, "inuse count off");
941
942 int freetally = 0;
943 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) {
944 freetally ++;
945 }
946 assert(freetally == Self->omFreeCount, "free count off");
947 }
948 */
949 ObjectMonitor * ATTR ObjectSynchronizer::omAlloc (Thread * Self) {
950 // A large MAXPRIVATE value reduces both list lock contention
951 // and list coherency traffic, but also tends to increase the
952 // number of objectMonitors in circulation as well as the STW
953 // scavenge costs. As usual, we lean toward time in space-time
954 // tradeoffs.
955 const int MAXPRIVATE = 1024 ;
956 for (;;) {
957 ObjectMonitor * m ;
958
959 // 1: try to allocate from the thread's local omFreeList.
960 // Threads will attempt to allocate first from their local list, then
961 // from the global list, and only after those attempts fail will the thread
962 // attempt to instantiate new monitors. Thread-local free lists take
963 // heat off the ListLock and improve allocation latency, as well as reducing
964 // coherency traffic on the shared global list.
965 m = Self->omFreeList ;
966 if (m != NULL) {
967 Self->omFreeList = m->FreeNext ;
968 Self->omFreeCount -- ;
969 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene
970 guarantee (m->object() == NULL, "invariant") ;
971 if (MonitorInUseLists) {
972 m->FreeNext = Self->omInUseList;
973 Self->omInUseList = m;
974 Self->omInUseCount ++;
975 // verifyInUse(Self);
976 } else {
977 m->FreeNext = NULL;
978 }
979 return m ;
980 }
981
982 // 2: try to allocate from the global gFreeList
983 // CONSIDER: use muxTry() instead of muxAcquire().
984 // If the muxTry() fails then drop immediately into case 3.
985 // If we're using thread-local free lists then try
986 // to reprovision the caller's free list.
987 if (gFreeList != NULL) {
988 // Reprovision the thread's omFreeList.
989 // Use bulk transfers to reduce the allocation rate and heat
990 // on various locks.
991 Thread::muxAcquire (&ListLock, "omAlloc") ;
992 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL; ) {
993 MonitorFreeCount --;
994 ObjectMonitor * take = gFreeList ;
995 gFreeList = take->FreeNext ;
996 guarantee (take->object() == NULL, "invariant") ;
997 guarantee (!take->is_busy(), "invariant") ;
998 take->Recycle() ;
999 omRelease (Self, take, false) ;
1000 }
1001 Thread::muxRelease (&ListLock) ;
1002 Self->omFreeProvision += 1 + (Self->omFreeProvision/2) ;
1003 if (Self->omFreeProvision > MAXPRIVATE ) Self->omFreeProvision = MAXPRIVATE ;
1004 TEVENT (omFirst - reprovision) ;
1005
1006 const int mx = MonitorBound ;
1007 if (mx > 0 && (MonitorPopulation-MonitorFreeCount) > mx) {
1008 // We can't safely induce a STW safepoint from omAlloc() as our thread
1009 // state may not be appropriate for such activities and callers may hold
1010 // naked oops, so instead we defer the action.
1011 InduceScavenge (Self, "omAlloc") ;
1012 }
1013 continue;
1014 }
1015
1016 // 3: allocate a block of new ObjectMonitors
1017 // Both the local and global free lists are empty -- resort to malloc().
1018 // In the current implementation objectMonitors are TSM - immortal.
1019 assert (_BLOCKSIZE > 1, "invariant") ;
1020 ObjectMonitor * temp = new ObjectMonitor[_BLOCKSIZE];
1021
1022 // NOTE: (almost) no way to recover if allocation failed.
1023 // We might be able to induce a STW safepoint and scavenge enough
1024 // objectMonitors to permit progress.
1025 if (temp == NULL) {
1026 vm_exit_out_of_memory (sizeof (ObjectMonitor[_BLOCKSIZE]), OOM_MALLOC_ERROR,
1027 "Allocate ObjectMonitors");
1028 }
1029
1030 // Format the block.
1031 // initialize the linked list, each monitor points to its next
1032 // forming the single linked free list, the very first monitor
1033 // will points to next block, which forms the block list.
1034 // The trick of using the 1st element in the block as gBlockList
1035 // linkage should be reconsidered. A better implementation would
1036 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1037
1038 for (int i = 1; i < _BLOCKSIZE ; i++) {
1039 temp[i].FreeNext = &temp[i+1];
1040 }
1041
1042 // terminate the last monitor as the end of list
1043 temp[_BLOCKSIZE - 1].FreeNext = NULL ;
1044
1045 // Element [0] is reserved for global list linkage
1046 temp[0].set_object(CHAINMARKER);
1047
1048 // Consider carving out this thread's current request from the
1049 // block in hand. This avoids some lock traffic and redundant
1050 // list activity.
1051
1052 // Acquire the ListLock to manipulate BlockList and FreeList.
1053 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1054 Thread::muxAcquire (&ListLock, "omAlloc [2]") ;
1055 MonitorPopulation += _BLOCKSIZE-1;
1056 MonitorFreeCount += _BLOCKSIZE-1;
1057
1058 // Add the new block to the list of extant blocks (gBlockList).
1059 // The very first objectMonitor in a block is reserved and dedicated.
1060 // It serves as blocklist "next" linkage.
1061 temp[0].FreeNext = gBlockList;
1062 gBlockList = temp;
1063
1064 // Add the new string of objectMonitors to the global free list
1065 temp[_BLOCKSIZE - 1].FreeNext = gFreeList ;
1066 gFreeList = temp + 1;
1067 Thread::muxRelease (&ListLock) ;
1068 TEVENT (Allocate block of monitors) ;
1069 }
1070 }
1071
1072 // Place "m" on the caller's private per-thread omFreeList.
1073 // In practice there's no need to clamp or limit the number of
1074 // monitors on a thread's omFreeList as the only time we'll call
1075 // omRelease is to return a monitor to the free list after a CAS
1076 // attempt failed. This doesn't allow unbounded #s of monitors to
1077 // accumulate on a thread's free list.
1078 //
1079
1080 void ObjectSynchronizer::omRelease (Thread * Self, ObjectMonitor * m, bool fromPerThreadAlloc) {
1081 guarantee (m->object() == NULL, "invariant") ;
1082
1083 // Remove from omInUseList
1084 if (MonitorInUseLists && fromPerThreadAlloc) {
1085 ObjectMonitor* curmidinuse = NULL;
1086 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; ) {
1087 if (m == mid) {
1088 // extract from per-thread in-use-list
1089 if (mid == Self->omInUseList) {
1090 Self->omInUseList = mid->FreeNext;
1091 } else if (curmidinuse != NULL) {
1092 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1093 }
1094 Self->omInUseCount --;
1095 // verifyInUse(Self);
1096 break;
1097 } else {
1098 curmidinuse = mid;
1099 mid = mid->FreeNext;
1100 }
1101 }
1102 }
1103
1104 // FreeNext is used for both onInUseList and omFreeList, so clear old before setting new
1105 m->FreeNext = Self->omFreeList ;
1106 Self->omFreeList = m ;
1107 Self->omFreeCount ++ ;
1108 }
1109
1110 // Return the monitors of a moribund thread's local free list to
1111 // the global free list. Typically a thread calls omFlush() when
1112 // it's dying. We could also consider having the VM thread steal
1113 // monitors from threads that have not run java code over a few
1114 // consecutive STW safepoints. Relatedly, we might decay
1115 // omFreeProvision at STW safepoints.
1116 //
1117 // Also return the monitors of a moribund thread"s omInUseList to
1118 // a global gOmInUseList under the global list lock so these
1119 // will continue to be scanned.
1120 //
1121 // We currently call omFlush() from the Thread:: dtor _after the thread
1122 // has been excised from the thread list and is no longer a mutator.
1123 // That means that omFlush() can run concurrently with a safepoint and
1124 // the scavenge operator. Calling omFlush() from JavaThread::exit() might
1125 // be a better choice as we could safely reason that that the JVM is
1126 // not at a safepoint at the time of the call, and thus there could
1127 // be not inopportune interleavings between omFlush() and the scavenge
1128 // operator.
1129
1130 void ObjectSynchronizer::omFlush (Thread * Self) {
1131 ObjectMonitor * List = Self->omFreeList ; // Null-terminated SLL
1132 Self->omFreeList = NULL ;
1133 ObjectMonitor * Tail = NULL ;
1134 int Tally = 0;
1135 if (List != NULL) {
1136 ObjectMonitor * s ;
1137 for (s = List ; s != NULL ; s = s->FreeNext) {
1138 Tally ++ ;
1139 Tail = s ;
1140 guarantee (s->object() == NULL, "invariant") ;
1141 guarantee (!s->is_busy(), "invariant") ;
1142 s->set_owner (NULL) ; // redundant but good hygiene
1143 TEVENT (omFlush - Move one) ;
1144 }
1145 guarantee (Tail != NULL && List != NULL, "invariant") ;
1146 }
1147
1148 ObjectMonitor * InUseList = Self->omInUseList;
1149 ObjectMonitor * InUseTail = NULL ;
1150 int InUseTally = 0;
1151 if (InUseList != NULL) {
1152 Self->omInUseList = NULL;
1153 ObjectMonitor *curom;
1154 for (curom = InUseList; curom != NULL; curom = curom->FreeNext) {
1155 InUseTail = curom;
1156 InUseTally++;
1157 }
1158 // TODO debug
1159 assert(Self->omInUseCount == InUseTally, "inuse count off");
1160 Self->omInUseCount = 0;
1161 guarantee (InUseTail != NULL && InUseList != NULL, "invariant");
1162 }
1163
1164 Thread::muxAcquire (&ListLock, "omFlush") ;
1165 if (Tail != NULL) {
1166 Tail->FreeNext = gFreeList ;
1167 gFreeList = List ;
1168 MonitorFreeCount += Tally;
1169 }
1170
1171 if (InUseTail != NULL) {
1172 InUseTail->FreeNext = gOmInUseList;
1173 gOmInUseList = InUseList;
1174 gOmInUseCount += InUseTally;
1175 }
1176
1177 Thread::muxRelease (&ListLock) ;
1178 TEVENT (omFlush) ;
1179 }
1180
1181 // Fast path code shared by multiple functions
1182 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1183 markOop mark = obj->mark();
1184 if (mark->has_monitor()) {
1185 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1186 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1187 return mark->monitor();
1188 }
1189 return ObjectSynchronizer::inflate(Thread::current(), obj);
1190 }
1191
1192
1193 // Note that we could encounter some performance loss through false-sharing as
1194 // multiple locks occupy the same $ line. Padding might be appropriate.
1195
1196
1197 ObjectMonitor * ATTR ObjectSynchronizer::inflate (Thread * Self, oop object) {
1198 // Inflate mutates the heap ...
1199 // Relaxing assertion for bug 6320749.
1200 assert (Universe::verify_in_progress() ||
1201 !SafepointSynchronize::is_at_safepoint(), "invariant") ;
1202
1203 for (;;) {
1204 const markOop mark = object->mark() ;
1205 assert (!mark->has_bias_pattern(), "invariant") ;
1206
1207 // The mark can be in one of the following states:
1208 // * Inflated - just return
1209 // * Stack-locked - coerce it to inflated
1210 // * INFLATING - busy wait for conversion to complete
1211 // * Neutral - aggressively inflate the object.
1212 // * BIASED - Illegal. We should never see this
1213
1214 // CASE: inflated
1215 if (mark->has_monitor()) {
1216 ObjectMonitor * inf = mark->monitor() ;
1217 assert (inf->header()->is_neutral(), "invariant");
1218 assert ((oop) inf->object() == object, "invariant") ;
1219 assert (ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1220 return inf ;
1221 }
1222
1223 // CASE: inflation in progress - inflating over a stack-lock.
1224 // Some other thread is converting from stack-locked to inflated.
1225 // Only that thread can complete inflation -- other threads must wait.
1226 // The INFLATING value is transient.
1227 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1228 // We could always eliminate polling by parking the thread on some auxiliary list.
1229 if (mark == markOopDesc::INFLATING()) {
1230 TEVENT (Inflate: spin while INFLATING) ;
1231 ReadStableMark(object) ;
1232 continue ;
1233 }
1234
1235 // CASE: stack-locked
1236 // Could be stack-locked either by this thread or by some other thread.
1237 //
1238 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1239 // to install INFLATING into the mark word. We originally installed INFLATING,
1240 // allocated the objectmonitor, and then finally STed the address of the
1241 // objectmonitor into the mark. This was correct, but artificially lengthened
1242 // the interval in which INFLATED appeared in the mark, thus increasing
1243 // the odds of inflation contention.
1244 //
1245 // We now use per-thread private objectmonitor free lists.
1246 // These list are reprovisioned from the global free list outside the
1247 // critical INFLATING...ST interval. A thread can transfer
1248 // multiple objectmonitors en-mass from the global free list to its local free list.
1249 // This reduces coherency traffic and lock contention on the global free list.
1250 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1251 // before or after the CAS(INFLATING) operation.
1252 // See the comments in omAlloc().
1253
1254 if (mark->has_locker()) {
1255 ObjectMonitor * m = omAlloc (Self) ;
1256 // Optimistically prepare the objectmonitor - anticipate successful CAS
1257 // We do this before the CAS in order to minimize the length of time
1258 // in which INFLATING appears in the mark.
1259 m->Recycle();
1260 m->_Responsible = NULL ;
1261 m->OwnerIsThread = 0 ;
1262 m->_recursions = 0 ;
1263 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // Consider: maintain by type/class
1264
1265 markOop cmp = object->cas_set_mark(markOopDesc::INFLATING(), mark);
1266 if (cmp != mark) {
1267 omRelease (Self, m, true) ;
1268 continue ; // Interference -- just retry
1269 }
1270
1271 // We've successfully installed INFLATING (0) into the mark-word.
1272 // This is the only case where 0 will appear in a mark-work.
1273 // Only the singular thread that successfully swings the mark-word
1274 // to 0 can perform (or more precisely, complete) inflation.
1275 //
1276 // Why do we CAS a 0 into the mark-word instead of just CASing the
1277 // mark-word from the stack-locked value directly to the new inflated state?
1278 // Consider what happens when a thread unlocks a stack-locked object.
1279 // It attempts to use CAS to swing the displaced header value from the
1280 // on-stack basiclock back into the object header. Recall also that the
1281 // header value (hashcode, etc) can reside in (a) the object header, or
1282 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1283 // header in an objectMonitor. The inflate() routine must copy the header
1284 // value from the basiclock on the owner's stack to the objectMonitor, all
1285 // the while preserving the hashCode stability invariants. If the owner
1286 // decides to release the lock while the value is 0, the unlock will fail
1287 // and control will eventually pass from slow_exit() to inflate. The owner
1288 // will then spin, waiting for the 0 value to disappear. Put another way,
1289 // the 0 causes the owner to stall if the owner happens to try to
1290 // drop the lock (restoring the header from the basiclock to the object)
1291 // while inflation is in-progress. This protocol avoids races that might
1292 // would otherwise permit hashCode values to change or "flicker" for an object.
1293 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1294 // 0 serves as a "BUSY" inflate-in-progress indicator.
1295
1296
1297 // fetch the displaced mark from the owner's stack.
1298 // The owner can't die or unwind past the lock while our INFLATING
1299 // object is in the mark. Furthermore the owner can't complete
1300 // an unlock on the object, either.
1301 markOop dmw = mark->displaced_mark_helper() ;
1302 assert (dmw->is_neutral(), "invariant") ;
1303
1304 // Setup monitor fields to proper values -- prepare the monitor
1305 m->set_header(dmw) ;
1306
1307 // Optimization: if the mark->locker stack address is associated
1308 // with this thread we could simply set m->_owner = Self and
1309 // m->OwnerIsThread = 1. Note that a thread can inflate an object
1310 // that it has stack-locked -- as might happen in wait() -- directly
1311 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1312 m->set_owner(mark->locker());
1313 m->set_object(object);
1314 // TODO-FIXME: assert BasicLock->dhw != 0.
1315
1316 // Must preserve store ordering. The monitor state must
1317 // be stable at the time of publishing the monitor address.
1318 guarantee (object->mark() == markOopDesc::INFLATING(), "invariant") ;
1319 object->release_set_mark(markOopDesc::encode(m));
1320
1321 // Hopefully the performance counters are allocated on distinct cache lines
1322 // to avoid false sharing on MP systems ...
1323 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ;
1324 TEVENT(Inflate: overwrite stacklock) ;
1325 if (TraceMonitorInflation) {
1326 if (object->is_instance()) {
1327 ResourceMark rm;
1328 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1329 (void *) object, (intptr_t) object->mark(),
1330 object->klass()->external_name());
1331 }
1332 }
1333 return m ;
1334 }
1335
1336 // CASE: neutral
1337 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1338 // If we know we're inflating for entry it's better to inflate by swinging a
1339 // pre-locked objectMonitor pointer into the object header. A successful
1340 // CAS inflates the object *and* confers ownership to the inflating thread.
1341 // In the current implementation we use a 2-step mechanism where we CAS()
1342 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1343 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1344 // would be useful.
1345
1346 assert (mark->is_neutral(), "invariant");
1347 ObjectMonitor * m = omAlloc (Self) ;
1348 // prepare m for installation - set monitor to initial state
1349 m->Recycle();
1350 m->set_header(mark);
1351 m->set_owner(NULL);
1352 m->set_object(object);
1353 m->OwnerIsThread = 1 ;
1354 m->_recursions = 0 ;
1355 m->_Responsible = NULL ;
1356 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // consider: keep metastats by type/class
1357
1358 if (object->cas_set_mark(markOopDesc::encode(m), mark) != mark) {
1359 m->set_object (NULL) ;
1360 m->set_owner (NULL) ;
1361 m->OwnerIsThread = 0 ;
1362 m->Recycle() ;
1363 omRelease (Self, m, true) ;
1364 m = NULL ;
1365 continue ;
1366 // interference - the markword changed - just retry.
1367 // The state-transitions are one-way, so there's no chance of
1368 // live-lock -- "Inflated" is an absorbing state.
1369 }
1370
1371 // Hopefully the performance counters are allocated on distinct
1372 // cache lines to avoid false sharing on MP systems ...
1373 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ;
1374 TEVENT(Inflate: overwrite neutral) ;
1375 if (TraceMonitorInflation) {
1376 if (object->is_instance()) {
1377 ResourceMark rm;
1378 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1379 (void *) object, (intptr_t) object->mark(),
1380 object->klass()->external_name());
1381 }
1382 }
1383 return m ;
1384 }
1385 }
1386
1387 // Note that we could encounter some performance loss through false-sharing as
1388 // multiple locks occupy the same $ line. Padding might be appropriate.
1389
1390
1391 // Deflate_idle_monitors() is called at all safepoints, immediately
1392 // after all mutators are stopped, but before any objects have moved.
1393 // It traverses the list of known monitors, deflating where possible.
1394 // The scavenged monitor are returned to the monitor free list.
1395 //
1396 // Beware that we scavenge at *every* stop-the-world point.
1397 // Having a large number of monitors in-circulation negatively
1398 // impacts the performance of some applications (e.g., PointBase).
1399 // Broadly, we want to minimize the # of monitors in circulation.
1400 //
1401 // We have added a flag, MonitorInUseLists, which creates a list
1402 // of active monitors for each thread. deflate_idle_monitors()
1403 // only scans the per-thread inuse lists. omAlloc() puts all
1404 // assigned monitors on the per-thread list. deflate_idle_monitors()
1405 // returns the non-busy monitors to the global free list.
1406 // When a thread dies, omFlush() adds the list of active monitors for
1407 // that thread to a global gOmInUseList acquiring the
1408 // global list lock. deflate_idle_monitors() acquires the global
1409 // list lock to scan for non-busy monitors to the global free list.
1410 // An alternative could have used a single global inuse list. The
1411 // downside would have been the additional cost of acquiring the global list lock
1412 // for every omAlloc().
1413 //
1414 // Perversely, the heap size -- and thus the STW safepoint rate --
1415 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1416 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1417 // This is an unfortunate aspect of this design.
1418 //
1419
1420 enum ManifestConstants {
1421 ClearResponsibleAtSTW = 0,
1422 MaximumRecheckInterval = 1000
1423 } ;
1424
1425 // Deflate a single monitor if not in use
1426 // Return true if deflated, false if in use
1427 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1428 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) {
1429 bool deflated;
1430 // Normal case ... The monitor is associated with obj.
1431 guarantee (obj->mark() == markOopDesc::encode(mid), "invariant") ;
1432 guarantee (mid == obj->mark()->monitor(), "invariant");
1433 guarantee (mid->header()->is_neutral(), "invariant");
1434
1435 if (mid->is_busy()) {
1436 if (ClearResponsibleAtSTW) mid->_Responsible = NULL ;
1437 deflated = false;
1438 } else {
1439 // Deflate the monitor if it is no longer being used
1440 // It's idle - scavenge and return to the global free list
1441 // plain old deflation ...
1442 TEVENT (deflate_idle_monitors - scavenge1) ;
1443 if (TraceMonitorInflation) {
1444 if (obj->is_instance()) {
1445 ResourceMark rm;
1446 tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1447 (void *) obj, (intptr_t) obj->mark(), obj->klass()->external_name());
1448 }
1449 }
1450
1451 // Restore the header back to obj
1452 obj->release_set_mark(mid->header());
1453 mid->clear();
1454
1455 assert (mid->object() == NULL, "invariant") ;
1456
1457 // Move the object to the working free list defined by FreeHead,FreeTail.
1458 if (*FreeHeadp == NULL) *FreeHeadp = mid;
1459 if (*FreeTailp != NULL) {
1460 ObjectMonitor * prevtail = *FreeTailp;
1461 assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); // TODO KK
1462 prevtail->FreeNext = mid;
1463 }
1464 *FreeTailp = mid;
1465 deflated = true;
1466 }
1467 return deflated;
1468 }
1469
1470 // Caller acquires ListLock
1471 int ObjectSynchronizer::walk_monitor_list(ObjectMonitor** listheadp,
1472 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) {
1473 ObjectMonitor* mid;
1474 ObjectMonitor* next;
1475 ObjectMonitor* curmidinuse = NULL;
1476 int deflatedcount = 0;
1477
1478 for (mid = *listheadp; mid != NULL; ) {
1479 oop obj = (oop) mid->object();
1480 bool deflated = false;
1481 if (obj != NULL) {
1482 deflated = deflate_monitor(mid, obj, FreeHeadp, FreeTailp);
1483 }
1484 if (deflated) {
1485 // extract from per-thread in-use-list
1486 if (mid == *listheadp) {
1487 *listheadp = mid->FreeNext;
1488 } else if (curmidinuse != NULL) {
1489 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1490 }
1491 next = mid->FreeNext;
1492 mid->FreeNext = NULL; // This mid is current tail in the FreeHead list
1493 mid = next;
1494 deflatedcount++;
1495 } else {
1496 curmidinuse = mid;
1497 mid = mid->FreeNext;
1498 }
1499 }
1500 return deflatedcount;
1501 }
1502
1503 void ObjectSynchronizer::deflate_idle_monitors() {
1504 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1505 int nInuse = 0 ; // currently associated with objects
1506 int nInCirculation = 0 ; // extant
1507 int nScavenged = 0 ; // reclaimed
1508 bool deflated = false;
1509
1510 ObjectMonitor * FreeHead = NULL ; // Local SLL of scavenged monitors
1511 ObjectMonitor * FreeTail = NULL ;
1512
1513 TEVENT (deflate_idle_monitors) ;
1514 // Prevent omFlush from changing mids in Thread dtor's during deflation
1515 // And in case the vm thread is acquiring a lock during a safepoint
1516 // See e.g. 6320749
1517 Thread::muxAcquire (&ListLock, "scavenge - return") ;
1518
1519 if (MonitorInUseLists) {
1520 int inUse = 0;
1521 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) {
1522 nInCirculation+= cur->omInUseCount;
1523 int deflatedcount = walk_monitor_list(cur->omInUseList_addr(), &FreeHead, &FreeTail);
1524 cur->omInUseCount-= deflatedcount;
1525 // verifyInUse(cur);
1526 nScavenged += deflatedcount;
1527 nInuse += cur->omInUseCount;
1528 }
1529
1530 // For moribund threads, scan gOmInUseList
1531 if (gOmInUseList) {
1532 nInCirculation += gOmInUseCount;
1533 int deflatedcount = walk_monitor_list((ObjectMonitor **)&gOmInUseList, &FreeHead, &FreeTail);
1534 gOmInUseCount-= deflatedcount;
1535 nScavenged += deflatedcount;
1536 nInuse += gOmInUseCount;
1537 }
1538
1539 } else for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) {
1540 // Iterate over all extant monitors - Scavenge all idle monitors.
1541 assert(block->object() == CHAINMARKER, "must be a block header");
1542 nInCirculation += _BLOCKSIZE ;
1543 for (int i = 1 ; i < _BLOCKSIZE; i++) {
1544 ObjectMonitor* mid = &block[i];
1545 oop obj = (oop) mid->object();
1546
1547 if (obj == NULL) {
1548 // The monitor is not associated with an object.
1549 // The monitor should either be a thread-specific private
1550 // free list or the global free list.
1551 // obj == NULL IMPLIES mid->is_busy() == 0
1552 guarantee (!mid->is_busy(), "invariant") ;
1553 continue ;
1554 }
1555 deflated = deflate_monitor(mid, obj, &FreeHead, &FreeTail);
1556
1557 if (deflated) {
1558 mid->FreeNext = NULL ;
1559 nScavenged ++ ;
1560 } else {
1561 nInuse ++;
1562 }
1563 }
1564 }
1565
1566 MonitorFreeCount += nScavenged;
1567
1568 // Consider: audit gFreeList to ensure that MonitorFreeCount and list agree.
1569
1570 if (ObjectMonitor::Knob_Verbose) {
1571 ::printf ("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n",
1572 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge,
1573 MonitorPopulation, MonitorFreeCount) ;
1574 ::fflush(stdout) ;
1575 }
1576
1577 ForceMonitorScavenge = 0; // Reset
1578
1579 // Move the scavenged monitors back to the global free list.
1580 if (FreeHead != NULL) {
1581 guarantee (FreeTail != NULL && nScavenged > 0, "invariant") ;
1582 assert (FreeTail->FreeNext == NULL, "invariant") ;
1583 // constant-time list splice - prepend scavenged segment to gFreeList
1584 FreeTail->FreeNext = gFreeList ;
1585 gFreeList = FreeHead ;
1586 }
1587 Thread::muxRelease (&ListLock) ;
1588
1589 if (ObjectMonitor::_sync_Deflations != NULL) ObjectMonitor::_sync_Deflations->inc(nScavenged) ;
1590 if (ObjectMonitor::_sync_MonExtant != NULL) ObjectMonitor::_sync_MonExtant ->set_value(nInCirculation);
1591
1592 // TODO: Add objectMonitor leak detection.
1593 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1594 GVars.stwRandom = os::random() ;
1595 GVars.stwCycle ++ ;
1596 }
1597
1598 // Monitor cleanup on JavaThread::exit
1599
1600 // Iterate through monitor cache and attempt to release thread's monitors
1601 // Gives up on a particular monitor if an exception occurs, but continues
1602 // the overall iteration, swallowing the exception.
1603 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1604 private:
1605 TRAPS;
1606
1607 public:
1608 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1609 void do_monitor(ObjectMonitor* mid) {
1610 if (mid->owner() == THREAD) {
1611 (void)mid->complete_exit(CHECK);
1612 }
1613 }
1614 };
1615
1616 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1617 // ignored. This is meant to be called during JNI thread detach which assumes
1618 // all remaining monitors are heavyweight. All exceptions are swallowed.
1619 // Scanning the extant monitor list can be time consuming.
1620 // A simple optimization is to add a per-thread flag that indicates a thread
1621 // called jni_monitorenter() during its lifetime.
1622 //
1623 // Instead of No_Savepoint_Verifier it might be cheaper to
1624 // use an idiom of the form:
1625 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1626 // <code that must not run at safepoint>
1627 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1628 // Since the tests are extremely cheap we could leave them enabled
1629 // for normal product builds.
1630
1631 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1632 assert(THREAD == JavaThread::current(), "must be current Java thread");
1633 No_Safepoint_Verifier nsv ;
1634 ReleaseJavaMonitorsClosure rjmc(THREAD);
1635 Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread");
1636 ObjectSynchronizer::monitors_iterate(&rjmc);
1637 Thread::muxRelease(&ListLock);
1638 THREAD->clear_pending_exception();
1639 }
1640
1641 //------------------------------------------------------------------------------
1642 // Debugging code
1643
1644 void ObjectSynchronizer::sanity_checks(const bool verbose,
1645 const uint cache_line_size,
1646 int *error_cnt_ptr,
1647 int *warning_cnt_ptr) {
1648 u_char *addr_begin = (u_char*)&GVars;
1649 u_char *addr_stwRandom = (u_char*)&GVars.stwRandom;
1650 u_char *addr_hcSequence = (u_char*)&GVars.hcSequence;
1651
1652 if (verbose) {
1653 tty->print_cr("INFO: sizeof(SharedGlobals)=" SIZE_FORMAT,
1654 sizeof(SharedGlobals));
1655 }
1656
1657 uint offset_stwRandom = (uint)(addr_stwRandom - addr_begin);
1658 if (verbose) tty->print_cr("INFO: offset(stwRandom)=%u", offset_stwRandom);
1659
1660 uint offset_hcSequence = (uint)(addr_hcSequence - addr_begin);
1661 if (verbose) {
1662 tty->print_cr("INFO: offset(_hcSequence)=%u", offset_hcSequence);
1663 }
1664
1665 if (cache_line_size != 0) {
1666 // We were able to determine the L1 data cache line size so
1667 // do some cache line specific sanity checks
1668
1669 if (offset_stwRandom < cache_line_size) {
1670 tty->print_cr("WARNING: the SharedGlobals.stwRandom field is closer "
1671 "to the struct beginning than a cache line which permits "
1672 "false sharing.");
1673 (*warning_cnt_ptr)++;
1674 }
1675
1676 if ((offset_hcSequence - offset_stwRandom) < cache_line_size) {
1677 tty->print_cr("WARNING: the SharedGlobals.stwRandom and "
1678 "SharedGlobals.hcSequence fields are closer than a cache "
1679 "line which permits false sharing.");
1680 (*warning_cnt_ptr)++;
1681 }
1682
1683 if ((sizeof(SharedGlobals) - offset_hcSequence) < cache_line_size) {
1684 tty->print_cr("WARNING: the SharedGlobals.hcSequence field is closer "
1685 "to the struct end than a cache line which permits false "
1686 "sharing.");
1687 (*warning_cnt_ptr)++;
1688 }
1689 }
1690 }
1691
1692 #ifndef PRODUCT
1693
1694 // Verify all monitors in the monitor cache, the verification is weak.
1695 void ObjectSynchronizer::verify() {
1696 ObjectMonitor* block = gBlockList;
1697 ObjectMonitor* mid;
1698 while (block) {
1699 assert(block->object() == CHAINMARKER, "must be a block header");
1700 for (int i = 1; i < _BLOCKSIZE; i++) {
1701 mid = block + i;
1702 oop object = (oop) mid->object();
1703 if (object != NULL) {
1704 mid->verify();
1705 }
1706 }
1707 block = (ObjectMonitor*) block->FreeNext;
1708 }
1709 }
1710
1711 // Check if monitor belongs to the monitor cache
1712 // The list is grow-only so it's *relatively* safe to traverse
1713 // the list of extant blocks without taking a lock.
1714
1715 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
1716 ObjectMonitor* block = gBlockList;
1717
1718 while (block) {
1719 assert(block->object() == CHAINMARKER, "must be a block header");
1720 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
1721 address mon = (address) monitor;
1722 address blk = (address) block;
1723 size_t diff = mon - blk;
1724 assert((diff % sizeof(ObjectMonitor)) == 0, "check");
1725 return 1;
1726 }
1727 block = (ObjectMonitor*) block->FreeNext;
1728 }
1729 return 0;
1730 }
1731
1732 #endif