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 * volatile 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 =
835 (ObjectMonitor*)OrderAccess::load_ptr_acquire(&gBlockList);
836 while (block != NULL) {
837 assert(block->object() == CHAINMARKER, "must be a block header");
838 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
839 ObjectMonitor* mid = (ObjectMonitor *)(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 ObjectMonitor* block =
861 (ObjectMonitor*)OrderAccess::load_ptr_acquire(&gBlockList);
862 for (; block != NULL; block = (ObjectMonitor *)next(block)) {
863 assert(block->object() == CHAINMARKER, "must be a block header");
864 for (int i = 1; i < _BLOCKSIZE; i++) {
865 ObjectMonitor* mid = &block[i];
866 if (mid->object() != NULL) {
867 f->do_oop((oop*)mid->object_addr());
868 }
869 }
870 }
871 }
872
873
874 // -----------------------------------------------------------------------------
875 // ObjectMonitor Lifecycle
876 // -----------------------
877 // Inflation unlinks monitors from the global gFreeList and
878 // associates them with objects. Deflation -- which occurs at
879 // STW-time -- disassociates idle monitors from objects. Such
880 // scavenged monitors are returned to the gFreeList.
881 //
882 // The global list is protected by ListLock. All the critical sections
883 // are short and operate in constant-time.
884 //
885 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
886 //
887 // Lifecycle:
888 // -- unassigned and on the global free list
889 // -- unassigned and on a thread's private omFreeList
890 // -- assigned to an object. The object is inflated and the mark refers
891 // to the objectmonitor.
892 //
893
894
895 // Constraining monitor pool growth via MonitorBound ...
896 //
897 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
898 // the rate of scavenging is driven primarily by GC. As such, we can find
899 // an inordinate number of monitors in circulation.
900 // To avoid that scenario we can artificially induce a STW safepoint
901 // if the pool appears to be growing past some reasonable bound.
902 // Generally we favor time in space-time tradeoffs, but as there's no
903 // natural back-pressure on the # of extant monitors we need to impose some
904 // type of limit. Beware that if MonitorBound is set to too low a value
905 // we could just loop. In addition, if MonitorBound is set to a low value
906 // we'll incur more safepoints, which are harmful to performance.
907 // See also: GuaranteedSafepointInterval
908 //
909 // The current implementation uses asynchronous VM operations.
910 //
911
912 static void InduceScavenge (Thread * Self, const char * Whence) {
913 // Induce STW safepoint to trim monitors
914 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
915 // More precisely, trigger an asynchronous STW safepoint as the number
916 // of active monitors passes the specified threshold.
917 // TODO: assert thread state is reasonable
918
919 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
920 if (ObjectMonitor::Knob_Verbose) {
921 ::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ;
922 ::fflush(stdout) ;
923 }
924 // Induce a 'null' safepoint to scavenge monitors
925 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
926 // to the VMthread and have a lifespan longer than that of this activation record.
927 // The VMThread will delete the op when completed.
928 VMThread::execute (new VM_ForceAsyncSafepoint()) ;
929
930 if (ObjectMonitor::Knob_Verbose) {
931 ::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ;
932 ::fflush(stdout) ;
933 }
934 }
935 }
936 /* Too slow for general assert or debug
937 void ObjectSynchronizer::verifyInUse (Thread *Self) {
938 ObjectMonitor* mid;
939 int inusetally = 0;
940 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) {
941 inusetally ++;
942 }
943 assert(inusetally == Self->omInUseCount, "inuse count off");
944
945 int freetally = 0;
946 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) {
947 freetally ++;
948 }
949 assert(freetally == Self->omFreeCount, "free count off");
950 }
951 */
952 ObjectMonitor * ATTR ObjectSynchronizer::omAlloc (Thread * Self) {
953 // A large MAXPRIVATE value reduces both list lock contention
954 // and list coherency traffic, but also tends to increase the
955 // number of objectMonitors in circulation as well as the STW
956 // scavenge costs. As usual, we lean toward time in space-time
957 // tradeoffs.
958 const int MAXPRIVATE = 1024 ;
959 for (;;) {
960 ObjectMonitor * m ;
961
962 // 1: try to allocate from the thread's local omFreeList.
963 // Threads will attempt to allocate first from their local list, then
964 // from the global list, and only after those attempts fail will the thread
965 // attempt to instantiate new monitors. Thread-local free lists take
966 // heat off the ListLock and improve allocation latency, as well as reducing
967 // coherency traffic on the shared global list.
968 m = Self->omFreeList ;
969 if (m != NULL) {
970 Self->omFreeList = m->FreeNext ;
971 Self->omFreeCount -- ;
972 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene
973 guarantee (m->object() == NULL, "invariant") ;
974 if (MonitorInUseLists) {
975 m->FreeNext = Self->omInUseList;
976 Self->omInUseList = m;
977 Self->omInUseCount ++;
978 // verifyInUse(Self);
979 } else {
980 m->FreeNext = NULL;
981 }
982 return m ;
983 }
984
985 // 2: try to allocate from the global gFreeList
986 // CONSIDER: use muxTry() instead of muxAcquire().
987 // If the muxTry() fails then drop immediately into case 3.
988 // If we're using thread-local free lists then try
989 // to reprovision the caller's free list.
990 if (gFreeList != NULL) {
991 // Reprovision the thread's omFreeList.
992 // Use bulk transfers to reduce the allocation rate and heat
993 // on various locks.
994 Thread::muxAcquire (&ListLock, "omAlloc") ;
995 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL; ) {
996 MonitorFreeCount --;
997 ObjectMonitor * take = gFreeList ;
998 gFreeList = take->FreeNext ;
999 guarantee (take->object() == NULL, "invariant") ;
1000 guarantee (!take->is_busy(), "invariant") ;
1001 take->Recycle() ;
1002 omRelease (Self, take, false) ;
1003 }
1004 Thread::muxRelease (&ListLock) ;
1005 Self->omFreeProvision += 1 + (Self->omFreeProvision/2) ;
1006 if (Self->omFreeProvision > MAXPRIVATE ) Self->omFreeProvision = MAXPRIVATE ;
1007 TEVENT (omFirst - reprovision) ;
1008
1009 const int mx = MonitorBound ;
1010 if (mx > 0 && (MonitorPopulation-MonitorFreeCount) > mx) {
1011 // We can't safely induce a STW safepoint from omAlloc() as our thread
1012 // state may not be appropriate for such activities and callers may hold
1013 // naked oops, so instead we defer the action.
1014 InduceScavenge (Self, "omAlloc") ;
1015 }
1016 continue;
1017 }
1018
1019 // 3: allocate a block of new ObjectMonitors
1020 // Both the local and global free lists are empty -- resort to malloc().
1021 // In the current implementation objectMonitors are TSM - immortal.
1022 assert (_BLOCKSIZE > 1, "invariant") ;
1023 ObjectMonitor * temp = new ObjectMonitor[_BLOCKSIZE];
1024
1025 // NOTE: (almost) no way to recover if allocation failed.
1026 // We might be able to induce a STW safepoint and scavenge enough
1027 // objectMonitors to permit progress.
1028 if (temp == NULL) {
1029 vm_exit_out_of_memory (sizeof (ObjectMonitor[_BLOCKSIZE]), OOM_MALLOC_ERROR,
1030 "Allocate ObjectMonitors");
1031 }
1032
1033 // Format the block.
1034 // initialize the linked list, each monitor points to its next
1035 // forming the single linked free list, the very first monitor
1036 // will points to next block, which forms the block list.
1037 // The trick of using the 1st element in the block as gBlockList
1038 // linkage should be reconsidered. A better implementation would
1039 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1040
1041 for (int i = 1; i < _BLOCKSIZE ; i++) {
1042 temp[i].FreeNext = &temp[i+1];
1043 }
1044
1045 // terminate the last monitor as the end of list
1046 temp[_BLOCKSIZE - 1].FreeNext = NULL ;
1047
1048 // Element [0] is reserved for global list linkage
1049 temp[0].set_object(CHAINMARKER);
1050
1051 // Consider carving out this thread's current request from the
1052 // block in hand. This avoids some lock traffic and redundant
1053 // list activity.
1054
1055 // Acquire the ListLock to manipulate BlockList and FreeList.
1056 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1057 Thread::muxAcquire (&ListLock, "omAlloc [2]") ;
1058 MonitorPopulation += _BLOCKSIZE-1;
1059 MonitorFreeCount += _BLOCKSIZE-1;
1060
1061 // Add the new block to the list of extant blocks (gBlockList).
1062 // The very first objectMonitor in a block is reserved and dedicated.
1063 // It serves as blocklist "next" linkage.
1064 temp[0].FreeNext = gBlockList;
1065 // There are lock-free uses of gBlockList so make sure that
1066 // the previous stores happen before we update gBlockList.
1067 OrderAccess::release_store_ptr(&gBlockList, temp);
1068
1069 // Add the new string of objectMonitors to the global free list
1070 temp[_BLOCKSIZE - 1].FreeNext = gFreeList ;
1071 gFreeList = temp + 1;
1072 Thread::muxRelease (&ListLock) ;
1073 TEVENT (Allocate block of monitors) ;
1074 }
1075 }
1076
1077 // Place "m" on the caller's private per-thread omFreeList.
1078 // In practice there's no need to clamp or limit the number of
1079 // monitors on a thread's omFreeList as the only time we'll call
1080 // omRelease is to return a monitor to the free list after a CAS
1081 // attempt failed. This doesn't allow unbounded #s of monitors to
1082 // accumulate on a thread's free list.
1083 //
1084
1085 void ObjectSynchronizer::omRelease (Thread * Self, ObjectMonitor * m, bool fromPerThreadAlloc) {
1086 guarantee (m->object() == NULL, "invariant") ;
1087
1088 // Remove from omInUseList
1089 if (MonitorInUseLists && fromPerThreadAlloc) {
1090 ObjectMonitor* curmidinuse = NULL;
1091 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; ) {
1092 if (m == mid) {
1093 // extract from per-thread in-use-list
1094 if (mid == Self->omInUseList) {
1095 Self->omInUseList = mid->FreeNext;
1096 } else if (curmidinuse != NULL) {
1097 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1098 }
1099 Self->omInUseCount --;
1100 // verifyInUse(Self);
1101 break;
1102 } else {
1103 curmidinuse = mid;
1104 mid = mid->FreeNext;
1105 }
1106 }
1107 }
1108
1109 // FreeNext is used for both onInUseList and omFreeList, so clear old before setting new
1110 m->FreeNext = Self->omFreeList ;
1111 Self->omFreeList = m ;
1112 Self->omFreeCount ++ ;
1113 }
1114
1115 // Return the monitors of a moribund thread's local free list to
1116 // the global free list. Typically a thread calls omFlush() when
1117 // it's dying. We could also consider having the VM thread steal
1118 // monitors from threads that have not run java code over a few
1119 // consecutive STW safepoints. Relatedly, we might decay
1120 // omFreeProvision at STW safepoints.
1121 //
1122 // Also return the monitors of a moribund thread"s omInUseList to
1123 // a global gOmInUseList under the global list lock so these
1124 // will continue to be scanned.
1125 //
1126 // We currently call omFlush() from the Thread:: dtor _after the thread
1127 // has been excised from the thread list and is no longer a mutator.
1128 // That means that omFlush() can run concurrently with a safepoint and
1129 // the scavenge operator. Calling omFlush() from JavaThread::exit() might
1130 // be a better choice as we could safely reason that that the JVM is
1131 // not at a safepoint at the time of the call, and thus there could
1132 // be not inopportune interleavings between omFlush() and the scavenge
1133 // operator.
1134
1135 void ObjectSynchronizer::omFlush (Thread * Self) {
1136 ObjectMonitor * List = Self->omFreeList ; // Null-terminated SLL
1137 Self->omFreeList = NULL ;
1138 ObjectMonitor * Tail = NULL ;
1139 int Tally = 0;
1140 if (List != NULL) {
1141 ObjectMonitor * s ;
1142 for (s = List ; s != NULL ; s = s->FreeNext) {
1143 Tally ++ ;
1144 Tail = s ;
1145 guarantee (s->object() == NULL, "invariant") ;
1146 guarantee (!s->is_busy(), "invariant") ;
1147 s->set_owner (NULL) ; // redundant but good hygiene
1148 TEVENT (omFlush - Move one) ;
1149 }
1150 guarantee (Tail != NULL && List != NULL, "invariant") ;
1151 }
1152
1153 ObjectMonitor * InUseList = Self->omInUseList;
1154 ObjectMonitor * InUseTail = NULL ;
1155 int InUseTally = 0;
1156 if (InUseList != NULL) {
1157 Self->omInUseList = NULL;
1158 ObjectMonitor *curom;
1159 for (curom = InUseList; curom != NULL; curom = curom->FreeNext) {
1160 InUseTail = curom;
1161 InUseTally++;
1162 }
1163 // TODO debug
1164 assert(Self->omInUseCount == InUseTally, "inuse count off");
1165 Self->omInUseCount = 0;
1166 guarantee (InUseTail != NULL && InUseList != NULL, "invariant");
1167 }
1168
1169 Thread::muxAcquire (&ListLock, "omFlush") ;
1170 if (Tail != NULL) {
1171 Tail->FreeNext = gFreeList ;
1172 gFreeList = List ;
1173 MonitorFreeCount += Tally;
1174 }
1175
1176 if (InUseTail != NULL) {
1177 InUseTail->FreeNext = gOmInUseList;
1178 gOmInUseList = InUseList;
1179 gOmInUseCount += InUseTally;
1180 }
1181
1182 Thread::muxRelease (&ListLock) ;
1183 TEVENT (omFlush) ;
1184 }
1185
1186 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1187 const oop obj) {
1188 assert(event != NULL, "invariant");
1189 assert(event->should_commit(), "invariant");
1190 event->set_monitorClass(obj->klass());
1191 event->set_address((uintptr_t)(void*)obj);
1192 event->commit();
1193 }
1194
1195 // Fast path code shared by multiple functions
1196 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1197 markOop mark = obj->mark();
1198 if (mark->has_monitor()) {
1199 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1200 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1201 return mark->monitor();
1202 }
1203 return ObjectSynchronizer::inflate(Thread::current(), obj);
1204 }
1205
1206
1207 // Note that we could encounter some performance loss through false-sharing as
1208 // multiple locks occupy the same $ line. Padding might be appropriate.
1209
1210
1211 ObjectMonitor * ATTR ObjectSynchronizer::inflate (Thread * Self, oop object) {
1212 // Inflate mutates the heap ...
1213 // Relaxing assertion for bug 6320749.
1214 assert (Universe::verify_in_progress() ||
1215 !SafepointSynchronize::is_at_safepoint(), "invariant") ;
1216
1217 EventJavaMonitorInflate event;
1218
1219 for (;;) {
1220 const markOop mark = object->mark() ;
1221 assert (!mark->has_bias_pattern(), "invariant") ;
1222
1223 // The mark can be in one of the following states:
1224 // * Inflated - just return
1225 // * Stack-locked - coerce it to inflated
1226 // * INFLATING - busy wait for conversion to complete
1227 // * Neutral - aggressively inflate the object.
1228 // * BIASED - Illegal. We should never see this
1229
1230 // CASE: inflated
1231 if (mark->has_monitor()) {
1232 ObjectMonitor * inf = mark->monitor() ;
1233 assert (inf->header()->is_neutral(), "invariant");
1234 assert (inf->object() == object, "invariant") ;
1235 assert (ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1236 return inf ;
1237 }
1238
1239 // CASE: inflation in progress - inflating over a stack-lock.
1240 // Some other thread is converting from stack-locked to inflated.
1241 // Only that thread can complete inflation -- other threads must wait.
1242 // The INFLATING value is transient.
1243 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1244 // We could always eliminate polling by parking the thread on some auxiliary list.
1245 if (mark == markOopDesc::INFLATING()) {
1246 TEVENT (Inflate: spin while INFLATING) ;
1247 ReadStableMark(object) ;
1248 continue ;
1249 }
1250
1251 // CASE: stack-locked
1252 // Could be stack-locked either by this thread or by some other thread.
1253 //
1254 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1255 // to install INFLATING into the mark word. We originally installed INFLATING,
1256 // allocated the objectmonitor, and then finally STed the address of the
1257 // objectmonitor into the mark. This was correct, but artificially lengthened
1258 // the interval in which INFLATED appeared in the mark, thus increasing
1259 // the odds of inflation contention.
1260 //
1261 // We now use per-thread private objectmonitor free lists.
1262 // These list are reprovisioned from the global free list outside the
1263 // critical INFLATING...ST interval. A thread can transfer
1264 // multiple objectmonitors en-mass from the global free list to its local free list.
1265 // This reduces coherency traffic and lock contention on the global free list.
1266 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1267 // before or after the CAS(INFLATING) operation.
1268 // See the comments in omAlloc().
1269
1270 if (mark->has_locker()) {
1271 ObjectMonitor * m = omAlloc (Self) ;
1272 // Optimistically prepare the objectmonitor - anticipate successful CAS
1273 // We do this before the CAS in order to minimize the length of time
1274 // in which INFLATING appears in the mark.
1275 m->Recycle();
1276 m->_Responsible = NULL ;
1277 m->OwnerIsThread = 0 ;
1278 m->_recursions = 0 ;
1279 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // Consider: maintain by type/class
1280
1281 markOop cmp = (markOop) Atomic::cmpxchg_ptr (markOopDesc::INFLATING(), object->mark_addr(), mark) ;
1282 if (cmp != mark) {
1283 omRelease (Self, m, true) ;
1284 continue ; // Interference -- just retry
1285 }
1286
1287 // We've successfully installed INFLATING (0) into the mark-word.
1288 // This is the only case where 0 will appear in a mark-work.
1289 // Only the singular thread that successfully swings the mark-word
1290 // to 0 can perform (or more precisely, complete) inflation.
1291 //
1292 // Why do we CAS a 0 into the mark-word instead of just CASing the
1293 // mark-word from the stack-locked value directly to the new inflated state?
1294 // Consider what happens when a thread unlocks a stack-locked object.
1295 // It attempts to use CAS to swing the displaced header value from the
1296 // on-stack basiclock back into the object header. Recall also that the
1297 // header value (hashcode, etc) can reside in (a) the object header, or
1298 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1299 // header in an objectMonitor. The inflate() routine must copy the header
1300 // value from the basiclock on the owner's stack to the objectMonitor, all
1301 // the while preserving the hashCode stability invariants. If the owner
1302 // decides to release the lock while the value is 0, the unlock will fail
1303 // and control will eventually pass from slow_exit() to inflate. The owner
1304 // will then spin, waiting for the 0 value to disappear. Put another way,
1305 // the 0 causes the owner to stall if the owner happens to try to
1306 // drop the lock (restoring the header from the basiclock to the object)
1307 // while inflation is in-progress. This protocol avoids races that might
1308 // would otherwise permit hashCode values to change or "flicker" for an object.
1309 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1310 // 0 serves as a "BUSY" inflate-in-progress indicator.
1311
1312
1313 // fetch the displaced mark from the owner's stack.
1314 // The owner can't die or unwind past the lock while our INFLATING
1315 // object is in the mark. Furthermore the owner can't complete
1316 // an unlock on the object, either.
1317 markOop dmw = mark->displaced_mark_helper() ;
1318 assert (dmw->is_neutral(), "invariant") ;
1319
1320 // Setup monitor fields to proper values -- prepare the monitor
1321 m->set_header(dmw) ;
1322
1323 // Optimization: if the mark->locker stack address is associated
1324 // with this thread we could simply set m->_owner = Self and
1325 // m->OwnerIsThread = 1. Note that a thread can inflate an object
1326 // that it has stack-locked -- as might happen in wait() -- directly
1327 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1328 m->set_owner(mark->locker());
1329 m->set_object(object);
1330 // TODO-FIXME: assert BasicLock->dhw != 0.
1331
1332 // Must preserve store ordering. The monitor state must
1333 // be stable at the time of publishing the monitor address.
1334 guarantee (object->mark() == markOopDesc::INFLATING(), "invariant") ;
1335 object->release_set_mark(markOopDesc::encode(m));
1336
1337 // Hopefully the performance counters are allocated on distinct cache lines
1338 // to avoid false sharing on MP systems ...
1339 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ;
1340 TEVENT(Inflate: overwrite stacklock) ;
1341 if (TraceMonitorInflation) {
1342 if (object->is_instance()) {
1343 ResourceMark rm;
1344 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1345 (void *) object, (intptr_t) object->mark(),
1346 object->klass()->external_name());
1347 }
1348 }
1349 if (event.should_commit()) {
1350 post_monitor_inflate_event(&event, object);
1351 }
1352 return m ;
1353 }
1354
1355 // CASE: neutral
1356 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1357 // If we know we're inflating for entry it's better to inflate by swinging a
1358 // pre-locked objectMonitor pointer into the object header. A successful
1359 // CAS inflates the object *and* confers ownership to the inflating thread.
1360 // In the current implementation we use a 2-step mechanism where we CAS()
1361 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1362 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1363 // would be useful.
1364
1365 assert (mark->is_neutral(), "invariant");
1366 ObjectMonitor * m = omAlloc (Self) ;
1367 // prepare m for installation - set monitor to initial state
1368 m->Recycle();
1369 m->set_header(mark);
1370 m->set_owner(NULL);
1371 m->set_object(object);
1372 m->OwnerIsThread = 1 ;
1373 m->_recursions = 0 ;
1374 m->_Responsible = NULL ;
1375 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // consider: keep metastats by type/class
1376
1377 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) {
1378 m->set_object (NULL) ;
1379 m->set_owner (NULL) ;
1380 m->OwnerIsThread = 0 ;
1381 m->Recycle() ;
1382 omRelease (Self, m, true) ;
1383 m = NULL ;
1384 continue ;
1385 // interference - the markword changed - just retry.
1386 // The state-transitions are one-way, so there's no chance of
1387 // live-lock -- "Inflated" is an absorbing state.
1388 }
1389
1390 // Hopefully the performance counters are allocated on distinct
1391 // cache lines to avoid false sharing on MP systems ...
1392 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ;
1393 TEVENT(Inflate: overwrite neutral) ;
1394 if (TraceMonitorInflation) {
1395 if (object->is_instance()) {
1396 ResourceMark rm;
1397 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1398 (void *) object, (intptr_t) object->mark(),
1399 object->klass()->external_name());
1400 }
1401 }
1402 if (event.should_commit()) {
1403 post_monitor_inflate_event(&event, object);
1404 }
1405 return m ;
1406 }
1407 }
1408
1409 // Note that we could encounter some performance loss through false-sharing as
1410 // multiple locks occupy the same $ line. Padding might be appropriate.
1411
1412
1413 // Deflate_idle_monitors() is called at all safepoints, immediately
1414 // after all mutators are stopped, but before any objects have moved.
1415 // It traverses the list of known monitors, deflating where possible.
1416 // The scavenged monitor are returned to the monitor free list.
1417 //
1418 // Beware that we scavenge at *every* stop-the-world point.
1419 // Having a large number of monitors in-circulation negatively
1420 // impacts the performance of some applications (e.g., PointBase).
1421 // Broadly, we want to minimize the # of monitors in circulation.
1422 //
1423 // We have added a flag, MonitorInUseLists, which creates a list
1424 // of active monitors for each thread. deflate_idle_monitors()
1425 // only scans the per-thread inuse lists. omAlloc() puts all
1426 // assigned monitors on the per-thread list. deflate_idle_monitors()
1427 // returns the non-busy monitors to the global free list.
1428 // When a thread dies, omFlush() adds the list of active monitors for
1429 // that thread to a global gOmInUseList acquiring the
1430 // global list lock. deflate_idle_monitors() acquires the global
1431 // list lock to scan for non-busy monitors to the global free list.
1432 // An alternative could have used a single global inuse list. The
1433 // downside would have been the additional cost of acquiring the global list lock
1434 // for every omAlloc().
1435 //
1436 // Perversely, the heap size -- and thus the STW safepoint rate --
1437 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1438 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1439 // This is an unfortunate aspect of this design.
1440 //
1441
1442 enum ManifestConstants {
1443 ClearResponsibleAtSTW = 0,
1444 MaximumRecheckInterval = 1000
1445 } ;
1446
1447 // Deflate a single monitor if not in use
1448 // Return true if deflated, false if in use
1449 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1450 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) {
1451 bool deflated;
1452 // Normal case ... The monitor is associated with obj.
1453 guarantee (obj->mark() == markOopDesc::encode(mid), "invariant") ;
1454 guarantee (mid == obj->mark()->monitor(), "invariant");
1455 guarantee (mid->header()->is_neutral(), "invariant");
1456
1457 if (mid->is_busy()) {
1458 if (ClearResponsibleAtSTW) mid->_Responsible = NULL ;
1459 deflated = false;
1460 } else {
1461 // Deflate the monitor if it is no longer being used
1462 // It's idle - scavenge and return to the global free list
1463 // plain old deflation ...
1464 TEVENT (deflate_idle_monitors - scavenge1) ;
1465 if (TraceMonitorInflation) {
1466 if (obj->is_instance()) {
1467 ResourceMark rm;
1468 tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1469 (void *) obj, (intptr_t) obj->mark(), obj->klass()->external_name());
1470 }
1471 }
1472
1473 // Restore the header back to obj
1474 obj->release_set_mark(mid->header());
1475 mid->clear();
1476
1477 assert (mid->object() == NULL, "invariant") ;
1478
1479 // Move the object to the working free list defined by FreeHead,FreeTail.
1480 if (*FreeHeadp == NULL) *FreeHeadp = mid;
1481 if (*FreeTailp != NULL) {
1482 ObjectMonitor * prevtail = *FreeTailp;
1483 assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); // TODO KK
1484 prevtail->FreeNext = mid;
1485 }
1486 *FreeTailp = mid;
1487 deflated = true;
1488 }
1489 return deflated;
1490 }
1491
1492 // Caller acquires ListLock
1493 int ObjectSynchronizer::walk_monitor_list(ObjectMonitor** listheadp,
1494 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) {
1495 ObjectMonitor* mid;
1496 ObjectMonitor* next;
1497 ObjectMonitor* curmidinuse = NULL;
1498 int deflatedcount = 0;
1499
1500 for (mid = *listheadp; mid != NULL; ) {
1501 oop obj = (oop) mid->object();
1502 bool deflated = false;
1503 if (obj != NULL) {
1504 deflated = deflate_monitor(mid, obj, FreeHeadp, FreeTailp);
1505 }
1506 if (deflated) {
1507 // extract from per-thread in-use-list
1508 if (mid == *listheadp) {
1509 *listheadp = mid->FreeNext;
1510 } else if (curmidinuse != NULL) {
1511 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1512 }
1513 next = mid->FreeNext;
1514 mid->FreeNext = NULL; // This mid is current tail in the FreeHead list
1515 mid = next;
1516 deflatedcount++;
1517 } else {
1518 curmidinuse = mid;
1519 mid = mid->FreeNext;
1520 }
1521 }
1522 return deflatedcount;
1523 }
1524
1525 void ObjectSynchronizer::deflate_idle_monitors() {
1526 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1527 int nInuse = 0 ; // currently associated with objects
1528 int nInCirculation = 0 ; // extant
1529 int nScavenged = 0 ; // reclaimed
1530 bool deflated = false;
1531
1532 ObjectMonitor * FreeHead = NULL ; // Local SLL of scavenged monitors
1533 ObjectMonitor * FreeTail = NULL ;
1534
1535 TEVENT (deflate_idle_monitors) ;
1536 // Prevent omFlush from changing mids in Thread dtor's during deflation
1537 // And in case the vm thread is acquiring a lock during a safepoint
1538 // See e.g. 6320749
1539 Thread::muxAcquire (&ListLock, "scavenge - return") ;
1540
1541 if (MonitorInUseLists) {
1542 int inUse = 0;
1543 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) {
1544 nInCirculation+= cur->omInUseCount;
1545 int deflatedcount = walk_monitor_list(cur->omInUseList_addr(), &FreeHead, &FreeTail);
1546 cur->omInUseCount-= deflatedcount;
1547 // verifyInUse(cur);
1548 nScavenged += deflatedcount;
1549 nInuse += cur->omInUseCount;
1550 }
1551
1552 // For moribund threads, scan gOmInUseList
1553 if (gOmInUseList) {
1554 nInCirculation += gOmInUseCount;
1555 int deflatedcount = walk_monitor_list((ObjectMonitor **)&gOmInUseList, &FreeHead, &FreeTail);
1556 gOmInUseCount-= deflatedcount;
1557 nScavenged += deflatedcount;
1558 nInuse += gOmInUseCount;
1559 }
1560
1561 } else {
1562 ObjectMonitor* block =
1563 (ObjectMonitor*)OrderAccess::load_ptr_acquire(&gBlockList);
1564 for (; block != NULL; block = (ObjectMonitor*)next(block)) {
1565 // Iterate over all extant monitors - Scavenge all idle monitors.
1566 assert(block->object() == CHAINMARKER, "must be a block header");
1567 nInCirculation += _BLOCKSIZE;
1568 for (int i = 1; i < _BLOCKSIZE; i++) {
1569 ObjectMonitor* mid = (ObjectMonitor*)&block[i];
1570 oop obj = (oop)mid->object();
1571
1572 if (obj == NULL) {
1573 // The monitor is not associated with an object.
1574 // The monitor should either be a thread-specific private
1575 // free list or the global free list.
1576 // obj == NULL IMPLIES mid->is_busy() == 0
1577 guarantee(!mid->is_busy(), "invariant");
1578 continue;
1579 }
1580 deflated = deflate_monitor(mid, obj, &FreeHead, &FreeTail);
1581
1582 if (deflated) {
1583 mid->FreeNext = NULL;
1584 nScavenged++;
1585 } else {
1586 nInuse++;
1587 }
1588 }
1589 }
1590 }
1591
1592 MonitorFreeCount += nScavenged;
1593
1594 // Consider: audit gFreeList to ensure that MonitorFreeCount and list agree.
1595
1596 if (ObjectMonitor::Knob_Verbose) {
1597 ::printf ("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n",
1598 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge,
1599 MonitorPopulation, MonitorFreeCount) ;
1600 ::fflush(stdout) ;
1601 }
1602
1603 ForceMonitorScavenge = 0; // Reset
1604
1605 // Move the scavenged monitors back to the global free list.
1606 if (FreeHead != NULL) {
1607 guarantee (FreeTail != NULL && nScavenged > 0, "invariant") ;
1608 assert (FreeTail->FreeNext == NULL, "invariant") ;
1609 // constant-time list splice - prepend scavenged segment to gFreeList
1610 FreeTail->FreeNext = gFreeList ;
1611 gFreeList = FreeHead ;
1612 }
1613 Thread::muxRelease (&ListLock) ;
1614
1615 if (ObjectMonitor::_sync_Deflations != NULL) ObjectMonitor::_sync_Deflations->inc(nScavenged) ;
1616 if (ObjectMonitor::_sync_MonExtant != NULL) ObjectMonitor::_sync_MonExtant ->set_value(nInCirculation);
1617
1618 // TODO: Add objectMonitor leak detection.
1619 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1620 GVars.stwRandom = os::random() ;
1621 GVars.stwCycle ++ ;
1622 }
1623
1624 // Monitor cleanup on JavaThread::exit
1625
1626 // Iterate through monitor cache and attempt to release thread's monitors
1627 // Gives up on a particular monitor if an exception occurs, but continues
1628 // the overall iteration, swallowing the exception.
1629 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1630 private:
1631 TRAPS;
1632
1633 public:
1634 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1635 void do_monitor(ObjectMonitor* mid) {
1636 if (mid->owner() == THREAD) {
1637 (void)mid->complete_exit(CHECK);
1638 }
1639 }
1640 };
1641
1642 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1643 // ignored. This is meant to be called during JNI thread detach which assumes
1644 // all remaining monitors are heavyweight. All exceptions are swallowed.
1645 // Scanning the extant monitor list can be time consuming.
1646 // A simple optimization is to add a per-thread flag that indicates a thread
1647 // called jni_monitorenter() during its lifetime.
1648 //
1649 // Instead of No_Savepoint_Verifier it might be cheaper to
1650 // use an idiom of the form:
1651 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1652 // <code that must not run at safepoint>
1653 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1654 // Since the tests are extremely cheap we could leave them enabled
1655 // for normal product builds.
1656
1657 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1658 assert(THREAD == JavaThread::current(), "must be current Java thread");
1659 No_Safepoint_Verifier nsv ;
1660 ReleaseJavaMonitorsClosure rjmc(THREAD);
1661 Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread");
1662 ObjectSynchronizer::monitors_iterate(&rjmc);
1663 Thread::muxRelease(&ListLock);
1664 THREAD->clear_pending_exception();
1665 }
1666
1667 //------------------------------------------------------------------------------
1668 // Debugging code
1669
1670 void ObjectSynchronizer::sanity_checks(const bool verbose,
1671 const uint cache_line_size,
1672 int *error_cnt_ptr,
1673 int *warning_cnt_ptr) {
1674 u_char *addr_begin = (u_char*)&GVars;
1675 u_char *addr_stwRandom = (u_char*)&GVars.stwRandom;
1676 u_char *addr_hcSequence = (u_char*)&GVars.hcSequence;
1677
1678 if (verbose) {
1679 tty->print_cr("INFO: sizeof(SharedGlobals)=" SIZE_FORMAT,
1680 sizeof(SharedGlobals));
1681 }
1682
1683 uint offset_stwRandom = (uint)(addr_stwRandom - addr_begin);
1684 if (verbose) tty->print_cr("INFO: offset(stwRandom)=%u", offset_stwRandom);
1685
1686 uint offset_hcSequence = (uint)(addr_hcSequence - addr_begin);
1687 if (verbose) {
1688 tty->print_cr("INFO: offset(_hcSequence)=%u", offset_hcSequence);
1689 }
1690
1691 if (cache_line_size != 0) {
1692 // We were able to determine the L1 data cache line size so
1693 // do some cache line specific sanity checks
1694
1695 if (offset_stwRandom < cache_line_size) {
1696 tty->print_cr("WARNING: the SharedGlobals.stwRandom field is closer "
1697 "to the struct beginning than a cache line which permits "
1698 "false sharing.");
1699 (*warning_cnt_ptr)++;
1700 }
1701
1702 if ((offset_hcSequence - offset_stwRandom) < cache_line_size) {
1703 tty->print_cr("WARNING: the SharedGlobals.stwRandom and "
1704 "SharedGlobals.hcSequence fields are closer than a cache "
1705 "line which permits false sharing.");
1706 (*warning_cnt_ptr)++;
1707 }
1708
1709 if ((sizeof(SharedGlobals) - offset_hcSequence) < cache_line_size) {
1710 tty->print_cr("WARNING: the SharedGlobals.hcSequence field is closer "
1711 "to the struct end than a cache line which permits false "
1712 "sharing.");
1713 (*warning_cnt_ptr)++;
1714 }
1715 }
1716 }
1717
1718 #ifndef PRODUCT
1719
1720 // Verify all monitors in the monitor cache, the verification is weak.
1721 void ObjectSynchronizer::verify() {
1722 ObjectMonitor* block =
1723 (ObjectMonitor *)OrderAccess::load_ptr_acquire(&gBlockList);
1724 while (block != NULL) {
1725 assert(block->object() == CHAINMARKER, "must be a block header");
1726 for (int i = 1; i < _BLOCKSIZE; i++) {
1727 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
1728 oop object = (oop)mid->object();
1729 if (object != NULL) {
1730 mid->verify();
1731 }
1732 }
1733 block = (ObjectMonitor*) block->FreeNext;
1734 }
1735 }
1736
1737 // Check if monitor belongs to the monitor cache
1738 // The list is grow-only so it's *relatively* safe to traverse
1739 // the list of extant blocks without taking a lock.
1740
1741 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
1742 ObjectMonitor* block =
1743 (ObjectMonitor*)OrderAccess::load_ptr_acquire(&gBlockList);
1744 while (block != NULL) {
1745 assert(block->object() == CHAINMARKER, "must be a block header");
1746 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
1747 address mon = (address)monitor;
1748 address blk = (address)block;
1749 size_t diff = mon - blk;
1750 assert((diff % sizeof(ObjectMonitor)) == 0, "must be aligned");
1751 return 1;
1752 }
1753 block = (ObjectMonitor*)block->FreeNext;
1754 }
1755 return 0;
1756 }
1757
1758 #endif