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 "jfr/jfrEvents.hpp"
28 #include "memory/resourceArea.hpp"
29 #include "oops/markOop.hpp"
30 #include "oops/oop.inline.hpp"
31 #include "runtime/biasedLocking.hpp"
32 #include "runtime/handles.inline.hpp"
33 #include "runtime/interfaceSupport.hpp"
34 #include "runtime/mutexLocker.hpp"
35 #include "runtime/objectMonitor.hpp"
36 #include "runtime/objectMonitor.inline.hpp"
37 #include "runtime/osThread.hpp"
38 #include "runtime/stubRoutines.hpp"
39 #include "runtime/synchronizer.hpp"
40 #include "runtime/thread.inline.hpp"
41 #include "utilities/dtrace.hpp"
42 #include "utilities/events.hpp"
43 #include "utilities/preserveException.hpp"
44 #ifdef TARGET_OS_FAMILY_linux
45 # include "os_linux.inline.hpp"
46 #endif
47 #ifdef TARGET_OS_FAMILY_solaris
48 # include "os_solaris.inline.hpp"
49 #endif
50 #ifdef TARGET_OS_FAMILY_windows
51 # include "os_windows.inline.hpp"
52 #endif
53 #ifdef TARGET_OS_FAMILY_bsd
54 # include "os_bsd.inline.hpp"
55 #endif
56
57 #if defined(__GNUC__) && !defined(PPC64)
58 // Need to inhibit inlining for older versions of GCC to avoid build-time failures
59 #define ATTR __attribute__((noinline))
60 #else
61 #define ATTR
62 #endif
63
64 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
65
66 // The "core" versions of monitor enter and exit reside in this file.
67 // The interpreter and compilers contain specialized transliterated
68 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
69 // for instance. If you make changes here, make sure to modify the
70 // interpreter, and both C1 and C2 fast-path inline locking code emission.
71 //
72 //
73 // -----------------------------------------------------------------------------
74
75 #ifdef DTRACE_ENABLED
76
77 // Only bother with this argument setup if dtrace is available
78 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
79
80 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
81 char* bytes = NULL; \
82 int len = 0; \
83 jlong jtid = SharedRuntime::get_java_tid(thread); \
84 Symbol* klassname = ((oop)(obj))->klass()->name(); \
85 if (klassname != NULL) { \
86 bytes = (char*)klassname->bytes(); \
87 len = klassname->utf8_length(); \
88 }
89
90 #ifndef USDT2
91 HS_DTRACE_PROBE_DECL5(hotspot, monitor__wait,
92 jlong, uintptr_t, char*, int, long);
93 HS_DTRACE_PROBE_DECL4(hotspot, monitor__waited,
94 jlong, uintptr_t, char*, int);
95
96 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
97 { \
98 if (DTraceMonitorProbes) { \
99 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
100 HS_DTRACE_PROBE5(hotspot, monitor__wait, jtid, \
101 (monitor), bytes, len, (millis)); \
102 } \
103 }
104
105 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
106 { \
107 if (DTraceMonitorProbes) { \
108 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
109 HS_DTRACE_PROBE4(hotspot, monitor__##probe, jtid, \
110 (uintptr_t)(monitor), bytes, len); \
111 } \
112 }
113
114 #else /* USDT2 */
115
116 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
117 { \
118 if (DTraceMonitorProbes) { \
119 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
120 HOTSPOT_MONITOR_WAIT(jtid, \
121 (uintptr_t)(monitor), bytes, len, (millis)); \
122 } \
123 }
124
125 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
126
127 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
128 { \
129 if (DTraceMonitorProbes) { \
130 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
131 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
132 (uintptr_t)(monitor), bytes, len); \
133 } \
134 }
135
136 #endif /* USDT2 */
137 #else // ndef DTRACE_ENABLED
138
139 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
140 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
141
142 #endif // ndef DTRACE_ENABLED
143
144 // This exists only as a workaround of dtrace bug 6254741
145 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
146 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
147 return 0;
148 }
149
150 #define NINFLATIONLOCKS 256
151 static volatile intptr_t InflationLocks [NINFLATIONLOCKS] ;
152
153 ObjectMonitor * ObjectSynchronizer::gBlockList = NULL ;
154 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL ;
155 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL ;
156 int ObjectSynchronizer::gOmInUseCount = 0;
157 static volatile intptr_t ListLock = 0 ; // protects global monitor free-list cache
158 static volatile int MonitorFreeCount = 0 ; // # on gFreeList
159 static volatile int MonitorPopulation = 0 ; // # Extant -- in circulation
160 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
161
162 // -----------------------------------------------------------------------------
163 // Fast Monitor Enter/Exit
164 // This the fast monitor enter. The interpreter and compiler use
165 // some assembly copies of this code. Make sure update those code
166 // if the following function is changed. The implementation is
167 // extremely sensitive to race condition. Be careful.
168
169 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock, bool attempt_rebias, TRAPS) {
170 if (UseBiasedLocking) {
171 if (!SafepointSynchronize::is_at_safepoint()) {
172 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
173 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
174 return;
175 }
176 } else {
177 assert(!attempt_rebias, "can not rebias toward VM thread");
178 BiasedLocking::revoke_at_safepoint(obj);
179 }
180 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
181 }
182
183 slow_enter (obj, lock, THREAD) ;
184 }
185
186 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
187 assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here");
188 // if displaced header is null, the previous enter is recursive enter, no-op
189 markOop dhw = lock->displaced_header();
190 markOop mark ;
191 if (dhw == NULL) {
192 // Recursive stack-lock.
193 // Diagnostics -- Could be: stack-locked, inflating, inflated.
194 mark = object->mark() ;
195 assert (!mark->is_neutral(), "invariant") ;
196 if (mark->has_locker() && mark != markOopDesc::INFLATING()) {
197 assert(THREAD->is_lock_owned((address)mark->locker()), "invariant") ;
198 }
199 if (mark->has_monitor()) {
200 ObjectMonitor * m = mark->monitor() ;
201 assert(((oop)(m->object()))->mark() == mark, "invariant") ;
202 assert(m->is_entered(THREAD), "invariant") ;
203 }
204 return ;
205 }
206
207 mark = object->mark() ;
208
209 // If the object is stack-locked by the current thread, try to
210 // swing the displaced header from the box back to the mark.
211 if (mark == (markOop) lock) {
212 assert (dhw->is_neutral(), "invariant") ;
213 if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) {
214 TEVENT (fast_exit: release stacklock) ;
215 return;
216 }
217 }
218
219 ObjectSynchronizer::inflate(THREAD, object)->exit (true, THREAD) ;
220 }
221
222 // -----------------------------------------------------------------------------
223 // Interpreter/Compiler Slow Case
224 // This routine is used to handle interpreter/compiler slow case
225 // We don't need to use fast path here, because it must have been
226 // failed in the interpreter/compiler code.
227 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
228 markOop mark = obj->mark();
229 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
230
231 if (mark->is_neutral()) {
232 // Anticipate successful CAS -- the ST of the displaced mark must
233 // be visible <= the ST performed by the CAS.
234 lock->set_displaced_header(mark);
235 if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) {
236 TEVENT (slow_enter: release stacklock) ;
237 return ;
238 }
239 // Fall through to inflate() ...
240 } else
241 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
242 assert(lock != mark->locker(), "must not re-lock the same lock");
243 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
244 lock->set_displaced_header(NULL);
245 return;
246 }
247
248 #if 0
249 // The following optimization isn't particularly useful.
250 if (mark->has_monitor() && mark->monitor()->is_entered(THREAD)) {
251 lock->set_displaced_header (NULL) ;
252 return ;
253 }
254 #endif
255
256 // The object header will never be displaced to this lock,
257 // so it does not matter what the value is, except that it
258 // must be non-zero to avoid looking like a re-entrant lock,
259 // and must not look locked either.
260 lock->set_displaced_header(markOopDesc::unused_mark());
261 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
262 }
263
264 // This routine is used to handle interpreter/compiler slow case
265 // We don't need to use fast path here, because it must have
266 // failed in the interpreter/compiler code. Simply use the heavy
267 // weight monitor should be ok, unless someone find otherwise.
268 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
269 fast_exit (object, lock, THREAD) ;
270 }
271
272 // -----------------------------------------------------------------------------
273 // Class Loader support to workaround deadlocks on the class loader lock objects
274 // Also used by GC
275 // complete_exit()/reenter() are used to wait on a nested lock
276 // i.e. to give up an outer lock completely and then re-enter
277 // Used when holding nested locks - lock acquisition order: lock1 then lock2
278 // 1) complete_exit lock1 - saving recursion count
279 // 2) wait on lock2
280 // 3) when notified on lock2, unlock lock2
281 // 4) reenter lock1 with original recursion count
282 // 5) lock lock2
283 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
284 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
285 TEVENT (complete_exit) ;
286 if (UseBiasedLocking) {
287 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
288 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
289 }
290
291 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
292
293 return monitor->complete_exit(THREAD);
294 }
295
296 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
297 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
298 TEVENT (reenter) ;
299 if (UseBiasedLocking) {
300 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
301 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
302 }
303
304 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
305
306 monitor->reenter(recursion, THREAD);
307 }
308 // -----------------------------------------------------------------------------
309 // JNI locks on java objects
310 // NOTE: must use heavy weight monitor to handle jni monitor enter
311 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) { // possible entry from jni enter
312 // the current locking is from JNI instead of Java code
313 TEVENT (jni_enter) ;
314 if (UseBiasedLocking) {
315 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
316 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
317 }
318 THREAD->set_current_pending_monitor_is_from_java(false);
319 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
320 THREAD->set_current_pending_monitor_is_from_java(true);
321 }
322
323 // NOTE: must use heavy weight monitor to handle jni monitor enter
324 bool ObjectSynchronizer::jni_try_enter(Handle obj, Thread* THREAD) {
325 if (UseBiasedLocking) {
326 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
327 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
328 }
329
330 ObjectMonitor* monitor = ObjectSynchronizer::inflate_helper(obj());
331 return monitor->try_enter(THREAD);
332 }
333
334
335 // NOTE: must use heavy weight monitor to handle jni monitor exit
336 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
337 TEVENT (jni_exit) ;
338 if (UseBiasedLocking) {
339 Handle h_obj(THREAD, obj);
340 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
341 obj = h_obj();
342 }
343 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
344
345 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj);
346 // If this thread has locked the object, exit the monitor. Note: can't use
347 // monitor->check(CHECK); must exit even if an exception is pending.
348 if (monitor->check(THREAD)) {
349 monitor->exit(true, THREAD);
350 }
351 }
352
353 // -----------------------------------------------------------------------------
354 // Internal VM locks on java objects
355 // standard constructor, allows locking failures
356 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
357 _dolock = doLock;
358 _thread = thread;
359 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
360 _obj = obj;
361
362 if (_dolock) {
363 TEVENT (ObjectLocker) ;
364
365 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
366 }
367 }
368
369 ObjectLocker::~ObjectLocker() {
370 if (_dolock) {
371 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
372 }
373 }
374
375
376 // -----------------------------------------------------------------------------
377 // Wait/Notify/NotifyAll
378 // NOTE: must use heavy weight monitor to handle wait()
379 void ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
380 if (UseBiasedLocking) {
381 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
382 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
383 }
384 if (millis < 0) {
385 TEVENT (wait - throw IAX) ;
386 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
387 }
388 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
389 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
390 monitor->wait(millis, true, THREAD);
391
392 /* This dummy call is in place to get around dtrace bug 6254741. Once
393 that's fixed we can uncomment the following line and remove the call */
394 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
395 dtrace_waited_probe(monitor, obj, THREAD);
396 }
397
398 void ObjectSynchronizer::waitUninterruptibly (Handle obj, jlong millis, TRAPS) {
399 if (UseBiasedLocking) {
400 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
401 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
402 }
403 if (millis < 0) {
404 TEVENT (wait - throw IAX) ;
405 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
406 }
407 ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD) ;
408 }
409
410 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
411 if (UseBiasedLocking) {
412 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
413 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
414 }
415
416 markOop mark = obj->mark();
417 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
418 return;
419 }
420 ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD);
421 }
422
423 // NOTE: see comment of notify()
424 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
425 if (UseBiasedLocking) {
426 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
427 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
428 }
429
430 markOop mark = obj->mark();
431 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
432 return;
433 }
434 ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD);
435 }
436
437 // -----------------------------------------------------------------------------
438 // Hash Code handling
439 //
440 // Performance concern:
441 // OrderAccess::storestore() calls release() which at one time stored 0
442 // into the global volatile OrderAccess::dummy variable. This store was
443 // unnecessary for correctness. Many threads storing into a common location
444 // causes considerable cache migration or "sloshing" on large SMP systems.
445 // As such, I avoided using OrderAccess::storestore(). In some cases
446 // OrderAccess::fence() -- which incurs local latency on the executing
447 // processor -- is a better choice as it scales on SMP systems.
448 //
449 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
450 // a discussion of coherency costs. Note that all our current reference
451 // platforms provide strong ST-ST order, so the issue is moot on IA32,
452 // x64, and SPARC.
453 //
454 // As a general policy we use "volatile" to control compiler-based reordering
455 // and explicit fences (barriers) to control for architectural reordering
456 // performed by the CPU(s) or platform.
457
458 struct SharedGlobals {
459 // These are highly shared mostly-read variables.
460 // To avoid false-sharing they need to be the sole occupants of a $ line.
461 double padPrefix [8];
462 volatile int stwRandom ;
463 volatile int stwCycle ;
464
465 // Hot RW variables -- Sequester to avoid false-sharing
466 double padSuffix [16];
467 volatile int hcSequence ;
468 double padFinal [8] ;
469 } ;
470
471 static SharedGlobals GVars ;
472 static int MonitorScavengeThreshold = 1000000 ;
473 static volatile int ForceMonitorScavenge = 0 ; // Scavenge required and pending
474
475 static markOop ReadStableMark (oop obj) {
476 markOop mark = obj->mark() ;
477 if (!mark->is_being_inflated()) {
478 return mark ; // normal fast-path return
479 }
480
481 int its = 0 ;
482 for (;;) {
483 markOop mark = obj->mark() ;
484 if (!mark->is_being_inflated()) {
485 return mark ; // normal fast-path return
486 }
487
488 // The object is being inflated by some other thread.
489 // The caller of ReadStableMark() must wait for inflation to complete.
490 // Avoid live-lock
491 // TODO: consider calling SafepointSynchronize::do_call_back() while
492 // spinning to see if there's a safepoint pending. If so, immediately
493 // yielding or blocking would be appropriate. Avoid spinning while
494 // there is a safepoint pending.
495 // TODO: add inflation contention performance counters.
496 // TODO: restrict the aggregate number of spinners.
497
498 ++its ;
499 if (its > 10000 || !os::is_MP()) {
500 if (its & 1) {
501 os::NakedYield() ;
502 TEVENT (Inflate: INFLATING - yield) ;
503 } else {
504 // Note that the following code attenuates the livelock problem but is not
505 // a complete remedy. A more complete solution would require that the inflating
506 // thread hold the associated inflation lock. The following code simply restricts
507 // the number of spinners to at most one. We'll have N-2 threads blocked
508 // on the inflationlock, 1 thread holding the inflation lock and using
509 // a yield/park strategy, and 1 thread in the midst of inflation.
510 // A more refined approach would be to change the encoding of INFLATING
511 // to allow encapsulation of a native thread pointer. Threads waiting for
512 // inflation to complete would use CAS to push themselves onto a singly linked
513 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
514 // and calling park(). When inflation was complete the thread that accomplished inflation
515 // would detach the list and set the markword to inflated with a single CAS and
516 // then for each thread on the list, set the flag and unpark() the thread.
517 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
518 // wakes at most one thread whereas we need to wake the entire list.
519 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1) ;
520 int YieldThenBlock = 0 ;
521 assert (ix >= 0 && ix < NINFLATIONLOCKS, "invariant") ;
522 assert ((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant") ;
523 Thread::muxAcquire (InflationLocks + ix, "InflationLock") ;
524 while (obj->mark() == markOopDesc::INFLATING()) {
525 // Beware: NakedYield() is advisory and has almost no effect on some platforms
526 // so we periodically call Self->_ParkEvent->park(1).
527 // We use a mixed spin/yield/block mechanism.
528 if ((YieldThenBlock++) >= 16) {
529 Thread::current()->_ParkEvent->park(1) ;
530 } else {
531 os::NakedYield() ;
532 }
533 }
534 Thread::muxRelease (InflationLocks + ix ) ;
535 TEVENT (Inflate: INFLATING - yield/park) ;
536 }
537 } else {
538 SpinPause() ; // SMP-polite spinning
539 }
540 }
541 }
542
543 // hashCode() generation :
544 //
545 // Possibilities:
546 // * MD5Digest of {obj,stwRandom}
547 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
548 // * A DES- or AES-style SBox[] mechanism
549 // * One of the Phi-based schemes, such as:
550 // 2654435761 = 2^32 * Phi (golden ratio)
551 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
552 // * A variation of Marsaglia's shift-xor RNG scheme.
553 // * (obj ^ stwRandom) is appealing, but can result
554 // in undesirable regularity in the hashCode values of adjacent objects
555 // (objects allocated back-to-back, in particular). This could potentially
556 // result in hashtable collisions and reduced hashtable efficiency.
557 // There are simple ways to "diffuse" the middle address bits over the
558 // generated hashCode values:
559 //
560
561 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
562 intptr_t value = 0 ;
563 if (hashCode == 0) {
564 // This form uses an unguarded global Park-Miller RNG,
565 // so it's possible for two threads to race and generate the same RNG.
566 // On MP system we'll have lots of RW access to a global, so the
567 // mechanism induces lots of coherency traffic.
568 value = os::random() ;
569 } else
570 if (hashCode == 1) {
571 // This variation has the property of being stable (idempotent)
572 // between STW operations. This can be useful in some of the 1-0
573 // synchronization schemes.
574 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3 ;
575 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom ;
576 } else
577 if (hashCode == 2) {
578 value = 1 ; // for sensitivity testing
579 } else
580 if (hashCode == 3) {
581 value = ++GVars.hcSequence ;
582 } else
583 if (hashCode == 4) {
584 value = cast_from_oop<intptr_t>(obj) ;
585 } else {
586 // Marsaglia's xor-shift scheme with thread-specific state
587 // This is probably the best overall implementation -- we'll
588 // likely make this the default in future releases.
589 unsigned t = Self->_hashStateX ;
590 t ^= (t << 11) ;
591 Self->_hashStateX = Self->_hashStateY ;
592 Self->_hashStateY = Self->_hashStateZ ;
593 Self->_hashStateZ = Self->_hashStateW ;
594 unsigned v = Self->_hashStateW ;
595 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)) ;
596 Self->_hashStateW = v ;
597 value = v ;
598 }
599
600 value &= markOopDesc::hash_mask;
601 if (value == 0) value = 0xBAD ;
602 assert (value != markOopDesc::no_hash, "invariant") ;
603 TEVENT (hashCode: GENERATE) ;
604 return value;
605 }
606 //
607 intptr_t ObjectSynchronizer::FastHashCode (Thread * Self, oop obj) {
608 if (UseBiasedLocking) {
609 // NOTE: many places throughout the JVM do not expect a safepoint
610 // to be taken here, in particular most operations on perm gen
611 // objects. However, we only ever bias Java instances and all of
612 // the call sites of identity_hash that might revoke biases have
613 // been checked to make sure they can handle a safepoint. The
614 // added check of the bias pattern is to avoid useless calls to
615 // thread-local storage.
616 if (obj->mark()->has_bias_pattern()) {
617 // Box and unbox the raw reference just in case we cause a STW safepoint.
618 Handle hobj (Self, obj) ;
619 // Relaxing assertion for bug 6320749.
620 assert (Universe::verify_in_progress() ||
621 !SafepointSynchronize::is_at_safepoint(),
622 "biases should not be seen by VM thread here");
623 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
624 obj = hobj() ;
625 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
626 }
627 }
628
629 // hashCode() is a heap mutator ...
630 // Relaxing assertion for bug 6320749.
631 assert (Universe::verify_in_progress() ||
632 !SafepointSynchronize::is_at_safepoint(), "invariant") ;
633 assert (Universe::verify_in_progress() ||
634 Self->is_Java_thread() , "invariant") ;
635 assert (Universe::verify_in_progress() ||
636 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ;
637
638 ObjectMonitor* monitor = NULL;
639 markOop temp, test;
640 intptr_t hash;
641 markOop mark = ReadStableMark (obj);
642
643 // object should remain ineligible for biased locking
644 assert (!mark->has_bias_pattern(), "invariant") ;
645
646 if (mark->is_neutral()) {
647 hash = mark->hash(); // this is a normal header
648 if (hash) { // if it has hash, just return it
649 return hash;
650 }
651 hash = get_next_hash(Self, obj); // allocate a new hash code
652 temp = mark->copy_set_hash(hash); // merge the hash code into header
653 // use (machine word version) atomic operation to install the hash
654 test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark);
655 if (test == mark) {
656 return hash;
657 }
658 // If atomic operation failed, we must inflate the header
659 // into heavy weight monitor. We could add more code here
660 // for fast path, but it does not worth the complexity.
661 } else if (mark->has_monitor()) {
662 monitor = mark->monitor();
663 temp = monitor->header();
664 assert (temp->is_neutral(), "invariant") ;
665 hash = temp->hash();
666 if (hash) {
667 return hash;
668 }
669 // Skip to the following code to reduce code size
670 } else if (Self->is_lock_owned((address)mark->locker())) {
671 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
672 assert (temp->is_neutral(), "invariant") ;
673 hash = temp->hash(); // by current thread, check if the displaced
674 if (hash) { // header contains hash code
675 return hash;
676 }
677 // WARNING:
678 // The displaced header is strictly immutable.
679 // It can NOT be changed in ANY cases. So we have
680 // to inflate the header into heavyweight monitor
681 // even the current thread owns the lock. The reason
682 // is the BasicLock (stack slot) will be asynchronously
683 // read by other threads during the inflate() function.
684 // Any change to stack may not propagate to other threads
685 // correctly.
686 }
687
688 // Inflate the monitor to set hash code
689 monitor = ObjectSynchronizer::inflate(Self, obj);
690 // Load displaced header and check it has hash code
691 mark = monitor->header();
692 assert (mark->is_neutral(), "invariant") ;
693 hash = mark->hash();
694 if (hash == 0) {
695 hash = get_next_hash(Self, obj);
696 temp = mark->copy_set_hash(hash); // merge hash code into header
697 assert (temp->is_neutral(), "invariant") ;
698 test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark);
699 if (test != mark) {
700 // The only update to the header in the monitor (outside GC)
701 // is install the hash code. If someone add new usage of
702 // displaced header, please update this code
703 hash = test->hash();
704 assert (test->is_neutral(), "invariant") ;
705 assert (hash != 0, "Trivial unexpected object/monitor header usage.");
706 }
707 }
708 // We finally get the hash
709 return hash;
710 }
711
712 // Deprecated -- use FastHashCode() instead.
713
714 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
715 return FastHashCode (Thread::current(), obj()) ;
716 }
717
718
719 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
720 Handle h_obj) {
721 if (UseBiasedLocking) {
722 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
723 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
724 }
725
726 assert(thread == JavaThread::current(), "Can only be called on current thread");
727 oop obj = h_obj();
728
729 markOop mark = ReadStableMark (obj) ;
730
731 // Uncontended case, header points to stack
732 if (mark->has_locker()) {
733 return thread->is_lock_owned((address)mark->locker());
734 }
735 // Contended case, header points to ObjectMonitor (tagged pointer)
736 if (mark->has_monitor()) {
737 ObjectMonitor* monitor = mark->monitor();
738 return monitor->is_entered(thread) != 0 ;
739 }
740 // Unlocked case, header in place
741 assert(mark->is_neutral(), "sanity check");
742 return false;
743 }
744
745 // Be aware of this method could revoke bias of the lock object.
746 // This method querys the ownership of the lock handle specified by 'h_obj'.
747 // If the current thread owns the lock, it returns owner_self. If no
748 // thread owns the lock, it returns owner_none. Otherwise, it will return
749 // ower_other.
750 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
751 (JavaThread *self, Handle h_obj) {
752 // The caller must beware this method can revoke bias, and
753 // revocation can result in a safepoint.
754 assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ;
755 assert (self->thread_state() != _thread_blocked , "invariant") ;
756
757 // Possible mark states: neutral, biased, stack-locked, inflated
758
759 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
760 // CASE: biased
761 BiasedLocking::revoke_and_rebias(h_obj, false, self);
762 assert(!h_obj->mark()->has_bias_pattern(),
763 "biases should be revoked by now");
764 }
765
766 assert(self == JavaThread::current(), "Can only be called on current thread");
767 oop obj = h_obj();
768 markOop mark = ReadStableMark (obj) ;
769
770 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
771 if (mark->has_locker()) {
772 return self->is_lock_owned((address)mark->locker()) ?
773 owner_self : owner_other;
774 }
775
776 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
777 // The Object:ObjectMonitor relationship is stable as long as we're
778 // not at a safepoint.
779 if (mark->has_monitor()) {
780 void * owner = mark->monitor()->_owner ;
781 if (owner == NULL) return owner_none ;
782 return (owner == self ||
783 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
784 }
785
786 // CASE: neutral
787 assert(mark->is_neutral(), "sanity check");
788 return owner_none ; // it's unlocked
789 }
790
791 // FIXME: jvmti should call this
792 JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) {
793 if (UseBiasedLocking) {
794 if (SafepointSynchronize::is_at_safepoint()) {
795 BiasedLocking::revoke_at_safepoint(h_obj);
796 } else {
797 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
798 }
799 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
800 }
801
802 oop obj = h_obj();
803 address owner = NULL;
804
805 markOop mark = ReadStableMark (obj) ;
806
807 // Uncontended case, header points to stack
808 if (mark->has_locker()) {
809 owner = (address) mark->locker();
810 }
811
812 // Contended case, header points to ObjectMonitor (tagged pointer)
813 if (mark->has_monitor()) {
814 ObjectMonitor* monitor = mark->monitor();
815 assert(monitor != NULL, "monitor should be non-null");
816 owner = (address) monitor->owner();
817 }
818
819 if (owner != NULL) {
820 // owning_thread_from_monitor_owner() may also return NULL here
821 return Threads::owning_thread_from_monitor_owner(owner, doLock);
822 }
823
824 // Unlocked case, header in place
825 // Cannot have assertion since this object may have been
826 // locked by another thread when reaching here.
827 // assert(mark->is_neutral(), "sanity check");
828
829 return NULL;
830 }
831 // Visitors ...
832
833 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
834 ObjectMonitor* block = gBlockList;
835 ObjectMonitor* mid;
836 while (block) {
837 assert(block->object() == CHAINMARKER, "must be a block header");
838 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
839 mid = block + i;
840 oop object = (oop) mid->object();
841 if (object != NULL) {
842 closure->do_monitor(mid);
843 }
844 }
845 block = (ObjectMonitor*) block->FreeNext;
846 }
847 }
848
849 // Get the next block in the block list.
850 static inline ObjectMonitor* next(ObjectMonitor* block) {
851 assert(block->object() == CHAINMARKER, "must be a block header");
852 block = block->FreeNext ;
853 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
854 return block;
855 }
856
857
858 void ObjectSynchronizer::oops_do(OopClosure* f) {
859 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
860 for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) {
861 assert(block->object() == CHAINMARKER, "must be a block header");
862 for (int i = 1; i < _BLOCKSIZE; i++) {
863 ObjectMonitor* mid = &block[i];
864 if (mid->object() != NULL) {
865 f->do_oop((oop*)mid->object_addr());
866 }
867 }
868 }
869 }
870
871
872 // -----------------------------------------------------------------------------
873 // ObjectMonitor Lifecycle
874 // -----------------------
875 // Inflation unlinks monitors from the global gFreeList and
876 // associates them with objects. Deflation -- which occurs at
877 // STW-time -- disassociates idle monitors from objects. Such
878 // scavenged monitors are returned to the gFreeList.
879 //
880 // The global list is protected by ListLock. All the critical sections
881 // are short and operate in constant-time.
882 //
883 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
884 //
885 // Lifecycle:
886 // -- unassigned and on the global free list
887 // -- unassigned and on a thread's private omFreeList
888 // -- assigned to an object. The object is inflated and the mark refers
889 // to the objectmonitor.
890 //
891
892
893 // Constraining monitor pool growth via MonitorBound ...
894 //
895 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
896 // the rate of scavenging is driven primarily by GC. As such, we can find
897 // an inordinate number of monitors in circulation.
898 // To avoid that scenario we can artificially induce a STW safepoint
899 // if the pool appears to be growing past some reasonable bound.
900 // Generally we favor time in space-time tradeoffs, but as there's no
901 // natural back-pressure on the # of extant monitors we need to impose some
902 // type of limit. Beware that if MonitorBound is set to too low a value
903 // we could just loop. In addition, if MonitorBound is set to a low value
904 // we'll incur more safepoints, which are harmful to performance.
905 // See also: GuaranteedSafepointInterval
906 //
907 // The current implementation uses asynchronous VM operations.
908 //
909
910 static void InduceScavenge (Thread * Self, const char * Whence) {
911 // Induce STW safepoint to trim monitors
912 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
913 // More precisely, trigger an asynchronous STW safepoint as the number
914 // of active monitors passes the specified threshold.
915 // TODO: assert thread state is reasonable
916
917 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
918 if (ObjectMonitor::Knob_Verbose) {
919 ::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ;
920 ::fflush(stdout) ;
921 }
922 // Induce a 'null' safepoint to scavenge monitors
923 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
924 // to the VMthread and have a lifespan longer than that of this activation record.
925 // The VMThread will delete the op when completed.
926 VMThread::execute (new VM_ForceAsyncSafepoint()) ;
927
928 if (ObjectMonitor::Knob_Verbose) {
929 ::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ;
930 ::fflush(stdout) ;
931 }
932 }
933 }
934 /* Too slow for general assert or debug
935 void ObjectSynchronizer::verifyInUse (Thread *Self) {
936 ObjectMonitor* mid;
937 int inusetally = 0;
938 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) {
939 inusetally ++;
940 }
941 assert(inusetally == Self->omInUseCount, "inuse count off");
942
943 int freetally = 0;
944 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) {
945 freetally ++;
946 }
947 assert(freetally == Self->omFreeCount, "free count off");
948 }
949 */
950 ObjectMonitor * ATTR ObjectSynchronizer::omAlloc (Thread * Self) {
951 // A large MAXPRIVATE value reduces both list lock contention
952 // and list coherency traffic, but also tends to increase the
953 // number of objectMonitors in circulation as well as the STW
954 // scavenge costs. As usual, we lean toward time in space-time
955 // tradeoffs.
956 const int MAXPRIVATE = 1024 ;
957 for (;;) {
958 ObjectMonitor * m ;
959
960 // 1: try to allocate from the thread's local omFreeList.
961 // Threads will attempt to allocate first from their local list, then
962 // from the global list, and only after those attempts fail will the thread
963 // attempt to instantiate new monitors. Thread-local free lists take
964 // heat off the ListLock and improve allocation latency, as well as reducing
965 // coherency traffic on the shared global list.
966 m = Self->omFreeList ;
967 if (m != NULL) {
968 Self->omFreeList = m->FreeNext ;
969 Self->omFreeCount -- ;
970 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene
971 guarantee (m->object() == NULL, "invariant") ;
972 if (MonitorInUseLists) {
973 m->FreeNext = Self->omInUseList;
974 Self->omInUseList = m;
975 Self->omInUseCount ++;
976 // verifyInUse(Self);
977 } else {
978 m->FreeNext = NULL;
979 }
980 return m ;
981 }
982
983 // 2: try to allocate from the global gFreeList
984 // CONSIDER: use muxTry() instead of muxAcquire().
985 // If the muxTry() fails then drop immediately into case 3.
986 // If we're using thread-local free lists then try
987 // to reprovision the caller's free list.
988 if (gFreeList != NULL) {
989 // Reprovision the thread's omFreeList.
990 // Use bulk transfers to reduce the allocation rate and heat
991 // on various locks.
992 Thread::muxAcquire (&ListLock, "omAlloc") ;
993 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL; ) {
994 MonitorFreeCount --;
995 ObjectMonitor * take = gFreeList ;
996 gFreeList = take->FreeNext ;
997 guarantee (take->object() == NULL, "invariant") ;
998 guarantee (!take->is_busy(), "invariant") ;
999 take->Recycle() ;
1000 omRelease (Self, take, false) ;
1001 }
1002 Thread::muxRelease (&ListLock) ;
1003 Self->omFreeProvision += 1 + (Self->omFreeProvision/2) ;
1004 if (Self->omFreeProvision > MAXPRIVATE ) Self->omFreeProvision = MAXPRIVATE ;
1005 TEVENT (omFirst - reprovision) ;
1006
1007 const int mx = MonitorBound ;
1008 if (mx > 0 && (MonitorPopulation-MonitorFreeCount) > mx) {
1009 // We can't safely induce a STW safepoint from omAlloc() as our thread
1010 // state may not be appropriate for such activities and callers may hold
1011 // naked oops, so instead we defer the action.
1012 InduceScavenge (Self, "omAlloc") ;
1013 }
1014 continue;
1015 }
1016
1017 // 3: allocate a block of new ObjectMonitors
1018 // Both the local and global free lists are empty -- resort to malloc().
1019 // In the current implementation objectMonitors are TSM - immortal.
1020 assert (_BLOCKSIZE > 1, "invariant") ;
1021 ObjectMonitor * temp = new ObjectMonitor[_BLOCKSIZE];
1022
1023 // NOTE: (almost) no way to recover if allocation failed.
1024 // We might be able to induce a STW safepoint and scavenge enough
1025 // objectMonitors to permit progress.
1026 if (temp == NULL) {
1027 vm_exit_out_of_memory (sizeof (ObjectMonitor[_BLOCKSIZE]), OOM_MALLOC_ERROR,
1028 "Allocate ObjectMonitors");
1029 }
1030
1031 // Format the block.
1032 // initialize the linked list, each monitor points to its next
1033 // forming the single linked free list, the very first monitor
1034 // will points to next block, which forms the block list.
1035 // The trick of using the 1st element in the block as gBlockList
1036 // linkage should be reconsidered. A better implementation would
1037 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1038
1039 for (int i = 1; i < _BLOCKSIZE ; i++) {
1040 temp[i].FreeNext = &temp[i+1];
1041 }
1042
1043 // terminate the last monitor as the end of list
1044 temp[_BLOCKSIZE - 1].FreeNext = NULL ;
1045
1046 // Element [0] is reserved for global list linkage
1047 temp[0].set_object(CHAINMARKER);
1048
1049 // Consider carving out this thread's current request from the
1050 // block in hand. This avoids some lock traffic and redundant
1051 // list activity.
1052
1053 // Acquire the ListLock to manipulate BlockList and FreeList.
1054 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1055 Thread::muxAcquire (&ListLock, "omAlloc [2]") ;
1056 MonitorPopulation += _BLOCKSIZE-1;
1057 MonitorFreeCount += _BLOCKSIZE-1;
1058
1059 // Add the new block to the list of extant blocks (gBlockList).
1060 // The very first objectMonitor in a block is reserved and dedicated.
1061 // It serves as blocklist "next" linkage.
1062 temp[0].FreeNext = gBlockList;
1063 gBlockList = temp;
1064
1065 // Add the new string of objectMonitors to the global free list
1066 temp[_BLOCKSIZE - 1].FreeNext = gFreeList ;
1067 gFreeList = temp + 1;
1068 Thread::muxRelease (&ListLock) ;
1069 TEVENT (Allocate block of monitors) ;
1070 }
1071 }
1072
1073 // Place "m" on the caller's private per-thread omFreeList.
1074 // In practice there's no need to clamp or limit the number of
1075 // monitors on a thread's omFreeList as the only time we'll call
1076 // omRelease is to return a monitor to the free list after a CAS
1077 // attempt failed. This doesn't allow unbounded #s of monitors to
1078 // accumulate on a thread's free list.
1079 //
1080
1081 void ObjectSynchronizer::omRelease (Thread * Self, ObjectMonitor * m, bool fromPerThreadAlloc) {
1082 guarantee (m->object() == NULL, "invariant") ;
1083
1084 // Remove from omInUseList
1085 if (MonitorInUseLists && fromPerThreadAlloc) {
1086 ObjectMonitor* curmidinuse = NULL;
1087 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; ) {
1088 if (m == mid) {
1089 // extract from per-thread in-use-list
1090 if (mid == Self->omInUseList) {
1091 Self->omInUseList = mid->FreeNext;
1092 } else if (curmidinuse != NULL) {
1093 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1094 }
1095 Self->omInUseCount --;
1096 // verifyInUse(Self);
1097 break;
1098 } else {
1099 curmidinuse = mid;
1100 mid = mid->FreeNext;
1101 }
1102 }
1103 }
1104
1105 // FreeNext is used for both onInUseList and omFreeList, so clear old before setting new
1106 m->FreeNext = Self->omFreeList ;
1107 Self->omFreeList = m ;
1108 Self->omFreeCount ++ ;
1109 }
1110
1111 // Return the monitors of a moribund thread's local free list to
1112 // the global free list. Typically a thread calls omFlush() when
1113 // it's dying. We could also consider having the VM thread steal
1114 // monitors from threads that have not run java code over a few
1115 // consecutive STW safepoints. Relatedly, we might decay
1116 // omFreeProvision at STW safepoints.
1117 //
1118 // Also return the monitors of a moribund thread"s omInUseList to
1119 // a global gOmInUseList under the global list lock so these
1120 // will continue to be scanned.
1121 //
1122 // We currently call omFlush() from the Thread:: dtor _after the thread
1123 // has been excised from the thread list and is no longer a mutator.
1124 // That means that omFlush() can run concurrently with a safepoint and
1125 // the scavenge operator. Calling omFlush() from JavaThread::exit() might
1126 // be a better choice as we could safely reason that that the JVM is
1127 // not at a safepoint at the time of the call, and thus there could
1128 // be not inopportune interleavings between omFlush() and the scavenge
1129 // operator.
1130
1131 void ObjectSynchronizer::omFlush (Thread * Self) {
1132 ObjectMonitor * List = Self->omFreeList ; // Null-terminated SLL
1133 Self->omFreeList = NULL ;
1134 ObjectMonitor * Tail = NULL ;
1135 int Tally = 0;
1136 if (List != NULL) {
1137 ObjectMonitor * s ;
1138 for (s = List ; s != NULL ; s = s->FreeNext) {
1139 Tally ++ ;
1140 Tail = s ;
1141 guarantee (s->object() == NULL, "invariant") ;
1142 guarantee (!s->is_busy(), "invariant") ;
1143 s->set_owner (NULL) ; // redundant but good hygiene
1144 TEVENT (omFlush - Move one) ;
1145 }
1146 guarantee (Tail != NULL && List != NULL, "invariant") ;
1147 }
1148
1149 ObjectMonitor * InUseList = Self->omInUseList;
1150 ObjectMonitor * InUseTail = NULL ;
1151 int InUseTally = 0;
1152 if (InUseList != NULL) {
1153 Self->omInUseList = NULL;
1154 ObjectMonitor *curom;
1155 for (curom = InUseList; curom != NULL; curom = curom->FreeNext) {
1156 InUseTail = curom;
1157 InUseTally++;
1158 }
1159 // TODO debug
1160 assert(Self->omInUseCount == InUseTally, "inuse count off");
1161 Self->omInUseCount = 0;
1162 guarantee (InUseTail != NULL && InUseList != NULL, "invariant");
1163 }
1164
1165 Thread::muxAcquire (&ListLock, "omFlush") ;
1166 if (Tail != NULL) {
1167 Tail->FreeNext = gFreeList ;
1168 gFreeList = List ;
1169 MonitorFreeCount += Tally;
1170 }
1171
1172 if (InUseTail != NULL) {
1173 InUseTail->FreeNext = gOmInUseList;
1174 gOmInUseList = InUseList;
1175 gOmInUseCount += InUseTally;
1176 }
1177
1178 Thread::muxRelease (&ListLock) ;
1179 TEVENT (omFlush) ;
1180 }
1181
1182 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1183 const oop obj) {
1184 assert(event != NULL, "invariant");
1185 assert(event->should_commit(), "invariant");
1186 event->set_monitorClass(obj->klass());
1187 event->set_address((uintptr_t)(void*)obj);
1188 // XXX no such counters. implement?
1189 // event->set_cause((u1)cause);
1190 event->commit();
1191 }
1192
1193 // Fast path code shared by multiple functions
1194 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1195 markOop mark = obj->mark();
1196 if (mark->has_monitor()) {
1197 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1198 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1199 return mark->monitor();
1200 }
1201 return ObjectSynchronizer::inflate(Thread::current(), obj);
1202 }
1203
1204
1205 // Note that we could encounter some performance loss through false-sharing as
1206 // multiple locks occupy the same $ line. Padding might be appropriate.
1207
1208
1209 ObjectMonitor * ATTR ObjectSynchronizer::inflate (Thread * Self, oop object) {
1210 // Inflate mutates the heap ...
1211 // Relaxing assertion for bug 6320749.
1212 assert (Universe::verify_in_progress() ||
1213 !SafepointSynchronize::is_at_safepoint(), "invariant") ;
1214
1215 EventJavaMonitorInflate event;
1216
1217 for (;;) {
1218 const markOop mark = object->mark() ;
1219 assert (!mark->has_bias_pattern(), "invariant") ;
1220
1221 // The mark can be in one of the following states:
1222 // * Inflated - just return
1223 // * Stack-locked - coerce it to inflated
1224 // * INFLATING - busy wait for conversion to complete
1225 // * Neutral - aggressively inflate the object.
1226 // * BIASED - Illegal. We should never see this
1227
1228 // CASE: inflated
1229 if (mark->has_monitor()) {
1230 ObjectMonitor * inf = mark->monitor() ;
1231 assert (inf->header()->is_neutral(), "invariant");
1232 assert (inf->object() == object, "invariant") ;
1233 assert (ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1234 return inf ;
1235 }
1236
1237 // CASE: inflation in progress - inflating over a stack-lock.
1238 // Some other thread is converting from stack-locked to inflated.
1239 // Only that thread can complete inflation -- other threads must wait.
1240 // The INFLATING value is transient.
1241 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1242 // We could always eliminate polling by parking the thread on some auxiliary list.
1243 if (mark == markOopDesc::INFLATING()) {
1244 TEVENT (Inflate: spin while INFLATING) ;
1245 ReadStableMark(object) ;
1246 continue ;
1247 }
1248
1249 // CASE: stack-locked
1250 // Could be stack-locked either by this thread or by some other thread.
1251 //
1252 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1253 // to install INFLATING into the mark word. We originally installed INFLATING,
1254 // allocated the objectmonitor, and then finally STed the address of the
1255 // objectmonitor into the mark. This was correct, but artificially lengthened
1256 // the interval in which INFLATED appeared in the mark, thus increasing
1257 // the odds of inflation contention.
1258 //
1259 // We now use per-thread private objectmonitor free lists.
1260 // These list are reprovisioned from the global free list outside the
1261 // critical INFLATING...ST interval. A thread can transfer
1262 // multiple objectmonitors en-mass from the global free list to its local free list.
1263 // This reduces coherency traffic and lock contention on the global free list.
1264 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1265 // before or after the CAS(INFLATING) operation.
1266 // See the comments in omAlloc().
1267
1268 if (mark->has_locker()) {
1269 ObjectMonitor * m = omAlloc (Self) ;
1270 // Optimistically prepare the objectmonitor - anticipate successful CAS
1271 // We do this before the CAS in order to minimize the length of time
1272 // in which INFLATING appears in the mark.
1273 m->Recycle();
1274 m->_Responsible = NULL ;
1275 m->OwnerIsThread = 0 ;
1276 m->_recursions = 0 ;
1277 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // Consider: maintain by type/class
1278
1279 markOop cmp = (markOop) Atomic::cmpxchg_ptr (markOopDesc::INFLATING(), object->mark_addr(), mark) ;
1280 if (cmp != mark) {
1281 omRelease (Self, m, true) ;
1282 continue ; // Interference -- just retry
1283 }
1284
1285 // We've successfully installed INFLATING (0) into the mark-word.
1286 // This is the only case where 0 will appear in a mark-work.
1287 // Only the singular thread that successfully swings the mark-word
1288 // to 0 can perform (or more precisely, complete) inflation.
1289 //
1290 // Why do we CAS a 0 into the mark-word instead of just CASing the
1291 // mark-word from the stack-locked value directly to the new inflated state?
1292 // Consider what happens when a thread unlocks a stack-locked object.
1293 // It attempts to use CAS to swing the displaced header value from the
1294 // on-stack basiclock back into the object header. Recall also that the
1295 // header value (hashcode, etc) can reside in (a) the object header, or
1296 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1297 // header in an objectMonitor. The inflate() routine must copy the header
1298 // value from the basiclock on the owner's stack to the objectMonitor, all
1299 // the while preserving the hashCode stability invariants. If the owner
1300 // decides to release the lock while the value is 0, the unlock will fail
1301 // and control will eventually pass from slow_exit() to inflate. The owner
1302 // will then spin, waiting for the 0 value to disappear. Put another way,
1303 // the 0 causes the owner to stall if the owner happens to try to
1304 // drop the lock (restoring the header from the basiclock to the object)
1305 // while inflation is in-progress. This protocol avoids races that might
1306 // would otherwise permit hashCode values to change or "flicker" for an object.
1307 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1308 // 0 serves as a "BUSY" inflate-in-progress indicator.
1309
1310
1311 // fetch the displaced mark from the owner's stack.
1312 // The owner can't die or unwind past the lock while our INFLATING
1313 // object is in the mark. Furthermore the owner can't complete
1314 // an unlock on the object, either.
1315 markOop dmw = mark->displaced_mark_helper() ;
1316 assert (dmw->is_neutral(), "invariant") ;
1317
1318 // Setup monitor fields to proper values -- prepare the monitor
1319 m->set_header(dmw) ;
1320
1321 // Optimization: if the mark->locker stack address is associated
1322 // with this thread we could simply set m->_owner = Self and
1323 // m->OwnerIsThread = 1. Note that a thread can inflate an object
1324 // that it has stack-locked -- as might happen in wait() -- directly
1325 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1326 m->set_owner(mark->locker());
1327 m->set_object(object);
1328 // TODO-FIXME: assert BasicLock->dhw != 0.
1329
1330 // Must preserve store ordering. The monitor state must
1331 // be stable at the time of publishing the monitor address.
1332 guarantee (object->mark() == markOopDesc::INFLATING(), "invariant") ;
1333 object->release_set_mark(markOopDesc::encode(m));
1334
1335 // Hopefully the performance counters are allocated on distinct cache lines
1336 // to avoid false sharing on MP systems ...
1337 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ;
1338 TEVENT(Inflate: overwrite stacklock) ;
1339 if (TraceMonitorInflation) {
1340 if (object->is_instance()) {
1341 ResourceMark rm;
1342 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1343 (void *) object, (intptr_t) object->mark(),
1344 object->klass()->external_name());
1345 }
1346 }
1347 if (event.should_commit()) {
1348 post_monitor_inflate_event(&event, object);
1349 }
1350 return m ;
1351 }
1352
1353 // CASE: neutral
1354 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1355 // If we know we're inflating for entry it's better to inflate by swinging a
1356 // pre-locked objectMonitor pointer into the object header. A successful
1357 // CAS inflates the object *and* confers ownership to the inflating thread.
1358 // In the current implementation we use a 2-step mechanism where we CAS()
1359 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1360 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1361 // would be useful.
1362
1363 assert (mark->is_neutral(), "invariant");
1364 ObjectMonitor * m = omAlloc (Self) ;
1365 // prepare m for installation - set monitor to initial state
1366 m->Recycle();
1367 m->set_header(mark);
1368 m->set_owner(NULL);
1369 m->set_object(object);
1370 m->OwnerIsThread = 1 ;
1371 m->_recursions = 0 ;
1372 m->_Responsible = NULL ;
1373 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // consider: keep metastats by type/class
1374
1375 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) {
1376 m->set_object (NULL) ;
1377 m->set_owner (NULL) ;
1378 m->OwnerIsThread = 0 ;
1379 m->Recycle() ;
1380 omRelease (Self, m, true) ;
1381 m = NULL ;
1382 continue ;
1383 // interference - the markword changed - just retry.
1384 // The state-transitions are one-way, so there's no chance of
1385 // live-lock -- "Inflated" is an absorbing state.
1386 }
1387
1388 // Hopefully the performance counters are allocated on distinct
1389 // cache lines to avoid false sharing on MP systems ...
1390 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ;
1391 TEVENT(Inflate: overwrite neutral) ;
1392 if (TraceMonitorInflation) {
1393 if (object->is_instance()) {
1394 ResourceMark rm;
1395 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1396 (void *) object, (intptr_t) object->mark(),
1397 object->klass()->external_name());
1398 }
1399 }
1400 if (event.should_commit()) {
1401 post_monitor_inflate_event(&event, object);
1402 }
1403 return m ;
1404 }
1405 }
1406
1407 // Note that we could encounter some performance loss through false-sharing as
1408 // multiple locks occupy the same $ line. Padding might be appropriate.
1409
1410
1411 // Deflate_idle_monitors() is called at all safepoints, immediately
1412 // after all mutators are stopped, but before any objects have moved.
1413 // It traverses the list of known monitors, deflating where possible.
1414 // The scavenged monitor are returned to the monitor free list.
1415 //
1416 // Beware that we scavenge at *every* stop-the-world point.
1417 // Having a large number of monitors in-circulation negatively
1418 // impacts the performance of some applications (e.g., PointBase).
1419 // Broadly, we want to minimize the # of monitors in circulation.
1420 //
1421 // We have added a flag, MonitorInUseLists, which creates a list
1422 // of active monitors for each thread. deflate_idle_monitors()
1423 // only scans the per-thread inuse lists. omAlloc() puts all
1424 // assigned monitors on the per-thread list. deflate_idle_monitors()
1425 // returns the non-busy monitors to the global free list.
1426 // When a thread dies, omFlush() adds the list of active monitors for
1427 // that thread to a global gOmInUseList acquiring the
1428 // global list lock. deflate_idle_monitors() acquires the global
1429 // list lock to scan for non-busy monitors to the global free list.
1430 // An alternative could have used a single global inuse list. The
1431 // downside would have been the additional cost of acquiring the global list lock
1432 // for every omAlloc().
1433 //
1434 // Perversely, the heap size -- and thus the STW safepoint rate --
1435 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1436 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1437 // This is an unfortunate aspect of this design.
1438 //
1439
1440 enum ManifestConstants {
1441 ClearResponsibleAtSTW = 0,
1442 MaximumRecheckInterval = 1000
1443 } ;
1444
1445 // Deflate a single monitor if not in use
1446 // Return true if deflated, false if in use
1447 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1448 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) {
1449 bool deflated;
1450 // Normal case ... The monitor is associated with obj.
1451 guarantee (obj->mark() == markOopDesc::encode(mid), "invariant") ;
1452 guarantee (mid == obj->mark()->monitor(), "invariant");
1453 guarantee (mid->header()->is_neutral(), "invariant");
1454
1455 if (mid->is_busy()) {
1456 if (ClearResponsibleAtSTW) mid->_Responsible = NULL ;
1457 deflated = false;
1458 } else {
1459 // Deflate the monitor if it is no longer being used
1460 // It's idle - scavenge and return to the global free list
1461 // plain old deflation ...
1462 TEVENT (deflate_idle_monitors - scavenge1) ;
1463 if (TraceMonitorInflation) {
1464 if (obj->is_instance()) {
1465 ResourceMark rm;
1466 tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1467 (void *) obj, (intptr_t) obj->mark(), obj->klass()->external_name());
1468 }
1469 }
1470
1471 // Restore the header back to obj
1472 obj->release_set_mark(mid->header());
1473 mid->clear();
1474
1475 assert (mid->object() == NULL, "invariant") ;
1476
1477 // Move the object to the working free list defined by FreeHead,FreeTail.
1478 if (*FreeHeadp == NULL) *FreeHeadp = mid;
1479 if (*FreeTailp != NULL) {
1480 ObjectMonitor * prevtail = *FreeTailp;
1481 assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); // TODO KK
1482 prevtail->FreeNext = mid;
1483 }
1484 *FreeTailp = mid;
1485 deflated = true;
1486 }
1487 return deflated;
1488 }
1489
1490 // Caller acquires ListLock
1491 int ObjectSynchronizer::walk_monitor_list(ObjectMonitor** listheadp,
1492 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) {
1493 ObjectMonitor* mid;
1494 ObjectMonitor* next;
1495 ObjectMonitor* curmidinuse = NULL;
1496 int deflatedcount = 0;
1497
1498 for (mid = *listheadp; mid != NULL; ) {
1499 oop obj = (oop) mid->object();
1500 bool deflated = false;
1501 if (obj != NULL) {
1502 deflated = deflate_monitor(mid, obj, FreeHeadp, FreeTailp);
1503 }
1504 if (deflated) {
1505 // extract from per-thread in-use-list
1506 if (mid == *listheadp) {
1507 *listheadp = mid->FreeNext;
1508 } else if (curmidinuse != NULL) {
1509 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1510 }
1511 next = mid->FreeNext;
1512 mid->FreeNext = NULL; // This mid is current tail in the FreeHead list
1513 mid = next;
1514 deflatedcount++;
1515 } else {
1516 curmidinuse = mid;
1517 mid = mid->FreeNext;
1518 }
1519 }
1520 return deflatedcount;
1521 }
1522
1523 void ObjectSynchronizer::deflate_idle_monitors() {
1524 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1525 int nInuse = 0 ; // currently associated with objects
1526 int nInCirculation = 0 ; // extant
1527 int nScavenged = 0 ; // reclaimed
1528 bool deflated = false;
1529
1530 ObjectMonitor * FreeHead = NULL ; // Local SLL of scavenged monitors
1531 ObjectMonitor * FreeTail = NULL ;
1532
1533 TEVENT (deflate_idle_monitors) ;
1534 // Prevent omFlush from changing mids in Thread dtor's during deflation
1535 // And in case the vm thread is acquiring a lock during a safepoint
1536 // See e.g. 6320749
1537 Thread::muxAcquire (&ListLock, "scavenge - return") ;
1538
1539 if (MonitorInUseLists) {
1540 int inUse = 0;
1541 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) {
1542 nInCirculation+= cur->omInUseCount;
1543 int deflatedcount = walk_monitor_list(cur->omInUseList_addr(), &FreeHead, &FreeTail);
1544 cur->omInUseCount-= deflatedcount;
1545 // verifyInUse(cur);
1546 nScavenged += deflatedcount;
1547 nInuse += cur->omInUseCount;
1548 }
1549
1550 // For moribund threads, scan gOmInUseList
1551 if (gOmInUseList) {
1552 nInCirculation += gOmInUseCount;
1553 int deflatedcount = walk_monitor_list((ObjectMonitor **)&gOmInUseList, &FreeHead, &FreeTail);
1554 gOmInUseCount-= deflatedcount;
1555 nScavenged += deflatedcount;
1556 nInuse += gOmInUseCount;
1557 }
1558
1559 } else for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) {
1560 // Iterate over all extant monitors - Scavenge all idle monitors.
1561 assert(block->object() == CHAINMARKER, "must be a block header");
1562 nInCirculation += _BLOCKSIZE ;
1563 for (int i = 1 ; i < _BLOCKSIZE; i++) {
1564 ObjectMonitor* mid = &block[i];
1565 oop obj = (oop) mid->object();
1566
1567 if (obj == NULL) {
1568 // The monitor is not associated with an object.
1569 // The monitor should either be a thread-specific private
1570 // free list or the global free list.
1571 // obj == NULL IMPLIES mid->is_busy() == 0
1572 guarantee (!mid->is_busy(), "invariant") ;
1573 continue ;
1574 }
1575 deflated = deflate_monitor(mid, obj, &FreeHead, &FreeTail);
1576
1577 if (deflated) {
1578 mid->FreeNext = NULL ;
1579 nScavenged ++ ;
1580 } else {
1581 nInuse ++;
1582 }
1583 }
1584 }
1585
1586 MonitorFreeCount += nScavenged;
1587
1588 // Consider: audit gFreeList to ensure that MonitorFreeCount and list agree.
1589
1590 if (ObjectMonitor::Knob_Verbose) {
1591 ::printf ("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n",
1592 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge,
1593 MonitorPopulation, MonitorFreeCount) ;
1594 ::fflush(stdout) ;
1595 }
1596
1597 ForceMonitorScavenge = 0; // Reset
1598
1599 // Move the scavenged monitors back to the global free list.
1600 if (FreeHead != NULL) {
1601 guarantee (FreeTail != NULL && nScavenged > 0, "invariant") ;
1602 assert (FreeTail->FreeNext == NULL, "invariant") ;
1603 // constant-time list splice - prepend scavenged segment to gFreeList
1604 FreeTail->FreeNext = gFreeList ;
1605 gFreeList = FreeHead ;
1606 }
1607 Thread::muxRelease (&ListLock) ;
1608
1609 if (ObjectMonitor::_sync_Deflations != NULL) ObjectMonitor::_sync_Deflations->inc(nScavenged) ;
1610 if (ObjectMonitor::_sync_MonExtant != NULL) ObjectMonitor::_sync_MonExtant ->set_value(nInCirculation);
1611
1612 // TODO: Add objectMonitor leak detection.
1613 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1614 GVars.stwRandom = os::random() ;
1615 GVars.stwCycle ++ ;
1616 }
1617
1618 // Monitor cleanup on JavaThread::exit
1619
1620 // Iterate through monitor cache and attempt to release thread's monitors
1621 // Gives up on a particular monitor if an exception occurs, but continues
1622 // the overall iteration, swallowing the exception.
1623 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1624 private:
1625 TRAPS;
1626
1627 public:
1628 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1629 void do_monitor(ObjectMonitor* mid) {
1630 if (mid->owner() == THREAD) {
1631 (void)mid->complete_exit(CHECK);
1632 }
1633 }
1634 };
1635
1636 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1637 // ignored. This is meant to be called during JNI thread detach which assumes
1638 // all remaining monitors are heavyweight. All exceptions are swallowed.
1639 // Scanning the extant monitor list can be time consuming.
1640 // A simple optimization is to add a per-thread flag that indicates a thread
1641 // called jni_monitorenter() during its lifetime.
1642 //
1643 // Instead of No_Savepoint_Verifier it might be cheaper to
1644 // use an idiom of the form:
1645 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1646 // <code that must not run at safepoint>
1647 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1648 // Since the tests are extremely cheap we could leave them enabled
1649 // for normal product builds.
1650
1651 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1652 assert(THREAD == JavaThread::current(), "must be current Java thread");
1653 No_Safepoint_Verifier nsv ;
1654 ReleaseJavaMonitorsClosure rjmc(THREAD);
1655 Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread");
1656 ObjectSynchronizer::monitors_iterate(&rjmc);
1657 Thread::muxRelease(&ListLock);
1658 THREAD->clear_pending_exception();
1659 }
1660
1661 //------------------------------------------------------------------------------
1662 // Debugging code
1663
1664 void ObjectSynchronizer::sanity_checks(const bool verbose,
1665 const uint cache_line_size,
1666 int *error_cnt_ptr,
1667 int *warning_cnt_ptr) {
1668 u_char *addr_begin = (u_char*)&GVars;
1669 u_char *addr_stwRandom = (u_char*)&GVars.stwRandom;
1670 u_char *addr_hcSequence = (u_char*)&GVars.hcSequence;
1671
1672 if (verbose) {
1673 tty->print_cr("INFO: sizeof(SharedGlobals)=" SIZE_FORMAT,
1674 sizeof(SharedGlobals));
1675 }
1676
1677 uint offset_stwRandom = (uint)(addr_stwRandom - addr_begin);
1678 if (verbose) tty->print_cr("INFO: offset(stwRandom)=%u", offset_stwRandom);
1679
1680 uint offset_hcSequence = (uint)(addr_hcSequence - addr_begin);
1681 if (verbose) {
1682 tty->print_cr("INFO: offset(_hcSequence)=%u", offset_hcSequence);
1683 }
1684
1685 if (cache_line_size != 0) {
1686 // We were able to determine the L1 data cache line size so
1687 // do some cache line specific sanity checks
1688
1689 if (offset_stwRandom < cache_line_size) {
1690 tty->print_cr("WARNING: the SharedGlobals.stwRandom field is closer "
1691 "to the struct beginning than a cache line which permits "
1692 "false sharing.");
1693 (*warning_cnt_ptr)++;
1694 }
1695
1696 if ((offset_hcSequence - offset_stwRandom) < cache_line_size) {
1697 tty->print_cr("WARNING: the SharedGlobals.stwRandom and "
1698 "SharedGlobals.hcSequence fields are closer than a cache "
1699 "line which permits false sharing.");
1700 (*warning_cnt_ptr)++;
1701 }
1702
1703 if ((sizeof(SharedGlobals) - offset_hcSequence) < cache_line_size) {
1704 tty->print_cr("WARNING: the SharedGlobals.hcSequence field is closer "
1705 "to the struct end than a cache line which permits false "
1706 "sharing.");
1707 (*warning_cnt_ptr)++;
1708 }
1709 }
1710 }
1711
1712 #ifndef PRODUCT
1713
1714 // Verify all monitors in the monitor cache, the verification is weak.
1715 void ObjectSynchronizer::verify() {
1716 ObjectMonitor* block = gBlockList;
1717 ObjectMonitor* mid;
1718 while (block) {
1719 assert(block->object() == CHAINMARKER, "must be a block header");
1720 for (int i = 1; i < _BLOCKSIZE; i++) {
1721 mid = block + i;
1722 oop object = (oop) mid->object();
1723 if (object != NULL) {
1724 mid->verify();
1725 }
1726 }
1727 block = (ObjectMonitor*) block->FreeNext;
1728 }
1729 }
1730
1731 // Check if monitor belongs to the monitor cache
1732 // The list is grow-only so it's *relatively* safe to traverse
1733 // the list of extant blocks without taking a lock.
1734
1735 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
1736 ObjectMonitor* block = gBlockList;
1737
1738 while (block) {
1739 assert(block->object() == CHAINMARKER, "must be a block header");
1740 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
1741 address mon = (address) monitor;
1742 address blk = (address) block;
1743 size_t diff = mon - blk;
1744 assert((diff % sizeof(ObjectMonitor)) == 0, "check");
1745 return 1;
1746 }
1747 block = (ObjectMonitor*) block->FreeNext;
1748 }
1749 return 0;
1750 }
1751
1752 #endif