1 /*
2 * Copyright (c) 1998, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/vmSymbols.hpp"
27 #include "memory/resourceArea.hpp"
28 #include "oops/markOop.hpp"
29 #include "oops/oop.inline.hpp"
30 #include "runtime/atomic.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 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
91 { \
92 if (DTraceMonitorProbes) { \
93 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
94 HOTSPOT_MONITOR_WAIT(jtid, \
95 (uintptr_t)(monitor), bytes, len, (millis)); \
96 } \
97 }
98
99 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
100
101 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
102 { \
103 if (DTraceMonitorProbes) { \
104 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
105 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
106 (uintptr_t)(monitor), bytes, len); \
107 } \
108 }
109
110 #else // ndef DTRACE_ENABLED
111
112 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
113 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
114
115 #endif // ndef DTRACE_ENABLED
116
117 // This exists only as a workaround of dtrace bug 6254741
118 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
119 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
120 return 0;
121 }
122
123 #define NINFLATIONLOCKS 256
124 static volatile intptr_t InflationLocks [NINFLATIONLOCKS] ;
125
126 ObjectMonitor * ObjectSynchronizer::gBlockList = NULL ;
127 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL ;
128 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL ;
129 int ObjectSynchronizer::gOmInUseCount = 0;
130 static volatile intptr_t ListLock = 0 ; // protects global monitor free-list cache
131 static volatile int MonitorFreeCount = 0 ; // # on gFreeList
132 static volatile int MonitorPopulation = 0 ; // # Extant -- in circulation
133 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
134
135 // -----------------------------------------------------------------------------
136 // Fast Monitor Enter/Exit
137 // This the fast monitor enter. The interpreter and compiler use
138 // some assembly copies of this code. Make sure update those code
139 // if the following function is changed. The implementation is
140 // extremely sensitive to race condition. Be careful.
141
142 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock, bool attempt_rebias, TRAPS) {
143 if (UseBiasedLocking) {
144 if (!SafepointSynchronize::is_at_safepoint()) {
145 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
146 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
147 return;
148 }
149 } else {
150 assert(!attempt_rebias, "can not rebias toward VM thread");
151 BiasedLocking::revoke_at_safepoint(obj);
152 }
153 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
154 }
155
156 slow_enter (obj, lock, THREAD) ;
157 }
158
159 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
160 assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here");
161 // if displaced header is null, the previous enter is recursive enter, no-op
162 markOop dhw = lock->displaced_header();
163 markOop mark ;
164 if (dhw == NULL) {
165 // Recursive stack-lock.
166 // Diagnostics -- Could be: stack-locked, inflating, inflated.
167 mark = object->mark() ;
168 assert (!mark->is_neutral(), "invariant") ;
169 if (mark->has_locker() && mark != markOopDesc::INFLATING()) {
170 assert(THREAD->is_lock_owned((address)mark->locker()), "invariant") ;
171 }
172 if (mark->has_monitor()) {
173 ObjectMonitor * m = mark->monitor() ;
174 assert(((oop)(m->object()))->mark() == mark, "invariant") ;
175 assert(m->is_entered(THREAD), "invariant") ;
176 }
177 return ;
178 }
179
180 mark = object->mark() ;
181
182 // If the object is stack-locked by the current thread, try to
183 // swing the displaced header from the box back to the mark.
184 if (mark == (markOop) lock) {
185 assert (dhw->is_neutral(), "invariant") ;
186 if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) {
187 TEVENT (fast_exit: release stacklock) ;
188 return;
189 }
190 }
191
192 ObjectSynchronizer::inflate(THREAD, object)->exit (true, THREAD) ;
193 }
194
195 // -----------------------------------------------------------------------------
196 // Interpreter/Compiler Slow Case
197 // This routine is used to handle interpreter/compiler slow case
198 // We don't need to use fast path here, because it must have been
199 // failed in the interpreter/compiler code.
200 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
201 markOop mark = obj->mark();
202 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
203
204 if (mark->is_neutral()) {
205 // Anticipate successful CAS -- the ST of the displaced mark must
206 // be visible <= the ST performed by the CAS.
207 lock->set_displaced_header(mark);
208 if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) {
209 TEVENT (slow_enter: release stacklock) ;
210 return ;
211 }
212 // Fall through to inflate() ...
213 } else
214 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
215 assert(lock != mark->locker(), "must not re-lock the same lock");
216 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
217 lock->set_displaced_header(NULL);
218 return;
219 }
220
221 #if 0
222 // The following optimization isn't particularly useful.
223 if (mark->has_monitor() && mark->monitor()->is_entered(THREAD)) {
224 lock->set_displaced_header (NULL) ;
225 return ;
226 }
227 #endif
228
229 // The object header will never be displaced to this lock,
230 // so it does not matter what the value is, except that it
231 // must be non-zero to avoid looking like a re-entrant lock,
232 // and must not look locked either.
233 lock->set_displaced_header(markOopDesc::unused_mark());
234 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
235 }
236
237 // This routine is used to handle interpreter/compiler slow case
238 // We don't need to use fast path here, because it must have
239 // failed in the interpreter/compiler code. Simply use the heavy
240 // weight monitor should be ok, unless someone find otherwise.
241 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
242 fast_exit (object, lock, THREAD) ;
243 }
244
245 // -----------------------------------------------------------------------------
246 // Class Loader support to workaround deadlocks on the class loader lock objects
247 // Also used by GC
248 // complete_exit()/reenter() are used to wait on a nested lock
249 // i.e. to give up an outer lock completely and then re-enter
250 // Used when holding nested locks - lock acquisition order: lock1 then lock2
251 // 1) complete_exit lock1 - saving recursion count
252 // 2) wait on lock2
253 // 3) when notified on lock2, unlock lock2
254 // 4) reenter lock1 with original recursion count
255 // 5) lock lock2
256 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
257 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
258 TEVENT (complete_exit) ;
259 if (UseBiasedLocking) {
260 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
261 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
262 }
263
264 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
265
266 return monitor->complete_exit(THREAD);
267 }
268
269 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
270 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
271 TEVENT (reenter) ;
272 if (UseBiasedLocking) {
273 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
274 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
275 }
276
277 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
278
279 monitor->reenter(recursion, THREAD);
280 }
281 // -----------------------------------------------------------------------------
282 // JNI locks on java objects
283 // NOTE: must use heavy weight monitor to handle jni monitor enter
284 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) { // possible entry from jni enter
285 // the current locking is from JNI instead of Java code
286 TEVENT (jni_enter) ;
287 if (UseBiasedLocking) {
288 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
289 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
290 }
291 THREAD->set_current_pending_monitor_is_from_java(false);
292 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
293 THREAD->set_current_pending_monitor_is_from_java(true);
294 }
295
296 // NOTE: must use heavy weight monitor to handle jni monitor enter
297 bool ObjectSynchronizer::jni_try_enter(Handle obj, Thread* THREAD) {
298 if (UseBiasedLocking) {
299 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
300 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
301 }
302
303 ObjectMonitor* monitor = ObjectSynchronizer::inflate_helper(obj());
304 return monitor->try_enter(THREAD);
305 }
306
307
308 // NOTE: must use heavy weight monitor to handle jni monitor exit
309 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
310 TEVENT (jni_exit) ;
311 if (UseBiasedLocking) {
312 Handle h_obj(THREAD, obj);
313 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
314 obj = h_obj();
315 }
316 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
317
318 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj);
319 // If this thread has locked the object, exit the monitor. Note: can't use
320 // monitor->check(CHECK); must exit even if an exception is pending.
321 if (monitor->check(THREAD)) {
322 monitor->exit(true, THREAD);
323 }
324 }
325
326 // -----------------------------------------------------------------------------
327 // Internal VM locks on java objects
328 // standard constructor, allows locking failures
329 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
330 _dolock = doLock;
331 _thread = thread;
332 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
333 _obj = obj;
334
335 if (_dolock) {
336 TEVENT (ObjectLocker) ;
337
338 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
339 }
340 }
341
342 ObjectLocker::~ObjectLocker() {
343 if (_dolock) {
344 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
345 }
346 }
347
348
349 // -----------------------------------------------------------------------------
350 // Wait/Notify/NotifyAll
351 // NOTE: must use heavy weight monitor to handle wait()
352 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
353 if (UseBiasedLocking) {
354 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
355 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
356 }
357 if (millis < 0) {
358 TEVENT (wait - throw IAX) ;
359 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
360 }
361 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
362 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
363 monitor->wait(millis, true, THREAD);
364
365 // This dummy call is in place to get around dtrace bug 6254741. Once
366 // that's fixed we can uncomment the following line, remove the call
367 // and change this function back into a "void" func.
368 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
369 return dtrace_waited_probe(monitor, obj, THREAD);
370 }
371
372 void ObjectSynchronizer::waitUninterruptibly (Handle obj, jlong millis, TRAPS) {
373 if (UseBiasedLocking) {
374 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
375 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
376 }
377 if (millis < 0) {
378 TEVENT (wait - throw IAX) ;
379 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
380 }
381 ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD) ;
382 }
383
384 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
385 if (UseBiasedLocking) {
386 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
387 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
388 }
389
390 markOop mark = obj->mark();
391 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
392 return;
393 }
394 ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD);
395 }
396
397 // NOTE: see comment of notify()
398 void ObjectSynchronizer::notifyall(Handle obj, 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
404 markOop mark = obj->mark();
405 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
406 return;
407 }
408 ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD);
409 }
410
411 // -----------------------------------------------------------------------------
412 // Hash Code handling
413 //
414 // Performance concern:
415 // OrderAccess::storestore() calls release() which STs 0 into the global volatile
416 // OrderAccess::Dummy variable. This store is unnecessary for correctness.
417 // Many threads STing into a common location causes considerable cache migration
418 // or "sloshing" on large SMP system. As such, I avoid using OrderAccess::storestore()
419 // until it's repaired. In some cases OrderAccess::fence() -- which incurs local
420 // latency on the executing processor -- is a better choice as it scales on SMP
421 // systems. See http://blogs.sun.com/dave/entry/biased_locking_in_hotspot for a
422 // discussion of coherency costs. Note that all our current reference platforms
423 // provide strong ST-ST order, so the issue is moot on IA32, x64, and SPARC.
424 //
425 // As a general policy we use "volatile" to control compiler-based reordering
426 // and explicit fences (barriers) to control for architectural reordering performed
427 // by the CPU(s) or platform.
428
429 struct SharedGlobals {
430 // These are highly shared mostly-read variables.
431 // To avoid false-sharing they need to be the sole occupants of a $ line.
432 double padPrefix [8];
433 volatile int stwRandom ;
434 volatile int stwCycle ;
435
436 // Hot RW variables -- Sequester to avoid false-sharing
437 double padSuffix [16];
438 volatile int hcSequence ;
439 double padFinal [8] ;
440 } ;
441
442 static SharedGlobals GVars ;
443 static int MonitorScavengeThreshold = 1000000 ;
444 static volatile int ForceMonitorScavenge = 0 ; // Scavenge required and pending
445
446 static markOop ReadStableMark (oop obj) {
447 markOop mark = obj->mark() ;
448 if (!mark->is_being_inflated()) {
449 return mark ; // normal fast-path return
450 }
451
452 int its = 0 ;
453 for (;;) {
454 markOop mark = obj->mark() ;
455 if (!mark->is_being_inflated()) {
456 return mark ; // normal fast-path return
457 }
458
459 // The object is being inflated by some other thread.
460 // The caller of ReadStableMark() must wait for inflation to complete.
461 // Avoid live-lock
462 // TODO: consider calling SafepointSynchronize::do_call_back() while
463 // spinning to see if there's a safepoint pending. If so, immediately
464 // yielding or blocking would be appropriate. Avoid spinning while
465 // there is a safepoint pending.
466 // TODO: add inflation contention performance counters.
467 // TODO: restrict the aggregate number of spinners.
468
469 ++its ;
470 if (its > 10000 || !os::is_MP()) {
471 if (its & 1) {
472 os::NakedYield() ;
473 TEVENT (Inflate: INFLATING - yield) ;
474 } else {
475 // Note that the following code attenuates the livelock problem but is not
476 // a complete remedy. A more complete solution would require that the inflating
477 // thread hold the associated inflation lock. The following code simply restricts
478 // the number of spinners to at most one. We'll have N-2 threads blocked
479 // on the inflationlock, 1 thread holding the inflation lock and using
480 // a yield/park strategy, and 1 thread in the midst of inflation.
481 // A more refined approach would be to change the encoding of INFLATING
482 // to allow encapsulation of a native thread pointer. Threads waiting for
483 // inflation to complete would use CAS to push themselves onto a singly linked
484 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
485 // and calling park(). When inflation was complete the thread that accomplished inflation
486 // would detach the list and set the markword to inflated with a single CAS and
487 // then for each thread on the list, set the flag and unpark() the thread.
488 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
489 // wakes at most one thread whereas we need to wake the entire list.
490 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1) ;
491 int YieldThenBlock = 0 ;
492 assert (ix >= 0 && ix < NINFLATIONLOCKS, "invariant") ;
493 assert ((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant") ;
494 Thread::muxAcquire (InflationLocks + ix, "InflationLock") ;
495 while (obj->mark() == markOopDesc::INFLATING()) {
496 // Beware: NakedYield() is advisory and has almost no effect on some platforms
497 // so we periodically call Self->_ParkEvent->park(1).
498 // We use a mixed spin/yield/block mechanism.
499 if ((YieldThenBlock++) >= 16) {
500 Thread::current()->_ParkEvent->park(1) ;
501 } else {
502 os::NakedYield() ;
503 }
504 }
505 Thread::muxRelease (InflationLocks + ix ) ;
506 TEVENT (Inflate: INFLATING - yield/park) ;
507 }
508 } else {
509 SpinPause() ; // SMP-polite spinning
510 }
511 }
512 }
513
514 // hashCode() generation :
515 //
516 // Possibilities:
517 // * MD5Digest of {obj,stwRandom}
518 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
519 // * A DES- or AES-style SBox[] mechanism
520 // * One of the Phi-based schemes, such as:
521 // 2654435761 = 2^32 * Phi (golden ratio)
522 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
523 // * A variation of Marsaglia's shift-xor RNG scheme.
524 // * (obj ^ stwRandom) is appealing, but can result
525 // in undesirable regularity in the hashCode values of adjacent objects
526 // (objects allocated back-to-back, in particular). This could potentially
527 // result in hashtable collisions and reduced hashtable efficiency.
528 // There are simple ways to "diffuse" the middle address bits over the
529 // generated hashCode values:
530 //
531
532 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
533 intptr_t value = 0 ;
534 if (hashCode == 0) {
535 // This form uses an unguarded global Park-Miller RNG,
536 // so it's possible for two threads to race and generate the same RNG.
537 // On MP system we'll have lots of RW access to a global, so the
538 // mechanism induces lots of coherency traffic.
539 value = os::random() ;
540 } else
541 if (hashCode == 1) {
542 // This variation has the property of being stable (idempotent)
543 // between STW operations. This can be useful in some of the 1-0
544 // synchronization schemes.
545 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3 ;
546 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom ;
547 } else
548 if (hashCode == 2) {
549 value = 1 ; // for sensitivity testing
550 } else
551 if (hashCode == 3) {
552 value = ++GVars.hcSequence ;
553 } else
554 if (hashCode == 4) {
555 value = cast_from_oop<intptr_t>(obj) ;
556 } else {
557 // Marsaglia's xor-shift scheme with thread-specific state
558 // This is probably the best overall implementation -- we'll
559 // likely make this the default in future releases.
560 unsigned t = Self->_hashStateX ;
561 t ^= (t << 11) ;
562 Self->_hashStateX = Self->_hashStateY ;
563 Self->_hashStateY = Self->_hashStateZ ;
564 Self->_hashStateZ = Self->_hashStateW ;
565 unsigned v = Self->_hashStateW ;
566 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)) ;
567 Self->_hashStateW = v ;
568 value = v ;
569 }
570
571 value &= markOopDesc::hash_mask;
572 if (value == 0) value = 0xBAD ;
573 assert (value != markOopDesc::no_hash, "invariant") ;
574 TEVENT (hashCode: GENERATE) ;
575 return value;
576 }
577 //
578 intptr_t ObjectSynchronizer::FastHashCode (Thread * Self, oop obj) {
579 if (UseBiasedLocking) {
580 // NOTE: many places throughout the JVM do not expect a safepoint
581 // to be taken here, in particular most operations on perm gen
582 // objects. However, we only ever bias Java instances and all of
583 // the call sites of identity_hash that might revoke biases have
584 // been checked to make sure they can handle a safepoint. The
585 // added check of the bias pattern is to avoid useless calls to
586 // thread-local storage.
587 if (obj->mark()->has_bias_pattern()) {
588 // Box and unbox the raw reference just in case we cause a STW safepoint.
589 Handle hobj (Self, obj) ;
590 // Relaxing assertion for bug 6320749.
591 assert (Universe::verify_in_progress() ||
592 !SafepointSynchronize::is_at_safepoint(),
593 "biases should not be seen by VM thread here");
594 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
595 obj = hobj() ;
596 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
597 }
598 }
599
600 // hashCode() is a heap mutator ...
601 // Relaxing assertion for bug 6320749.
602 assert (Universe::verify_in_progress() ||
603 !SafepointSynchronize::is_at_safepoint(), "invariant") ;
604 assert (Universe::verify_in_progress() ||
605 Self->is_Java_thread() , "invariant") ;
606 assert (Universe::verify_in_progress() ||
607 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ;
608
609 ObjectMonitor* monitor = NULL;
610 markOop temp, test;
611 intptr_t hash;
612 markOop mark = ReadStableMark (obj);
613
614 // object should remain ineligible for biased locking
615 assert (!mark->has_bias_pattern(), "invariant") ;
616
617 if (mark->is_neutral()) {
618 hash = mark->hash(); // this is a normal header
619 if (hash) { // if it has hash, just return it
620 return hash;
621 }
622 hash = get_next_hash(Self, obj); // allocate a new hash code
623 temp = mark->copy_set_hash(hash); // merge the hash code into header
624 // use (machine word version) atomic operation to install the hash
625 test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark);
626 if (test == mark) {
627 return hash;
628 }
629 // If atomic operation failed, we must inflate the header
630 // into heavy weight monitor. We could add more code here
631 // for fast path, but it does not worth the complexity.
632 } else if (mark->has_monitor()) {
633 monitor = mark->monitor();
634 temp = monitor->header();
635 assert (temp->is_neutral(), "invariant") ;
636 hash = temp->hash();
637 if (hash) {
638 return hash;
639 }
640 // Skip to the following code to reduce code size
641 } else if (Self->is_lock_owned((address)mark->locker())) {
642 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
643 assert (temp->is_neutral(), "invariant") ;
644 hash = temp->hash(); // by current thread, check if the displaced
645 if (hash) { // header contains hash code
646 return hash;
647 }
648 // WARNING:
649 // The displaced header is strictly immutable.
650 // It can NOT be changed in ANY cases. So we have
651 // to inflate the header into heavyweight monitor
652 // even the current thread owns the lock. The reason
653 // is the BasicLock (stack slot) will be asynchronously
654 // read by other threads during the inflate() function.
655 // Any change to stack may not propagate to other threads
656 // correctly.
657 }
658
659 // Inflate the monitor to set hash code
660 monitor = ObjectSynchronizer::inflate(Self, obj);
661 // Load displaced header and check it has hash code
662 mark = monitor->header();
663 assert (mark->is_neutral(), "invariant") ;
664 hash = mark->hash();
665 if (hash == 0) {
666 hash = get_next_hash(Self, obj);
667 temp = mark->copy_set_hash(hash); // merge hash code into header
668 assert (temp->is_neutral(), "invariant") ;
669 test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark);
670 if (test != mark) {
671 // The only update to the header in the monitor (outside GC)
672 // is install the hash code. If someone add new usage of
673 // displaced header, please update this code
674 hash = test->hash();
675 assert (test->is_neutral(), "invariant") ;
676 assert (hash != 0, "Trivial unexpected object/monitor header usage.");
677 }
678 }
679 // We finally get the hash
680 return hash;
681 }
682
683 // Deprecated -- use FastHashCode() instead.
684
685 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
686 return FastHashCode (Thread::current(), obj()) ;
687 }
688
689
690 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
691 Handle h_obj) {
692 if (UseBiasedLocking) {
693 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
694 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
695 }
696
697 assert(thread == JavaThread::current(), "Can only be called on current thread");
698 oop obj = h_obj();
699
700 markOop mark = ReadStableMark (obj) ;
701
702 // Uncontended case, header points to stack
703 if (mark->has_locker()) {
704 return thread->is_lock_owned((address)mark->locker());
705 }
706 // Contended case, header points to ObjectMonitor (tagged pointer)
707 if (mark->has_monitor()) {
708 ObjectMonitor* monitor = mark->monitor();
709 return monitor->is_entered(thread) != 0 ;
710 }
711 // Unlocked case, header in place
712 assert(mark->is_neutral(), "sanity check");
713 return false;
714 }
715
716 // Be aware of this method could revoke bias of the lock object.
717 // This method queries the ownership of the lock handle specified by 'h_obj'.
718 // If the current thread owns the lock, it returns owner_self. If no
719 // thread owns the lock, it returns owner_none. Otherwise, it will return
720 // owner_other.
721 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
722 (JavaThread *self, Handle h_obj) {
723 // The caller must beware this method can revoke bias, and
724 // revocation can result in a safepoint.
725 assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ;
726 assert (self->thread_state() != _thread_blocked , "invariant") ;
727
728 // Possible mark states: neutral, biased, stack-locked, inflated
729
730 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
731 // CASE: biased
732 BiasedLocking::revoke_and_rebias(h_obj, false, self);
733 assert(!h_obj->mark()->has_bias_pattern(),
734 "biases should be revoked by now");
735 }
736
737 assert(self == JavaThread::current(), "Can only be called on current thread");
738 oop obj = h_obj();
739 markOop mark = ReadStableMark (obj) ;
740
741 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
742 if (mark->has_locker()) {
743 return self->is_lock_owned((address)mark->locker()) ?
744 owner_self : owner_other;
745 }
746
747 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
748 // The Object:ObjectMonitor relationship is stable as long as we're
749 // not at a safepoint.
750 if (mark->has_monitor()) {
751 void * owner = mark->monitor()->_owner ;
752 if (owner == NULL) return owner_none ;
753 return (owner == self ||
754 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
755 }
756
757 // CASE: neutral
758 assert(mark->is_neutral(), "sanity check");
759 return owner_none ; // it's unlocked
760 }
761
762 // FIXME: jvmti should call this
763 JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) {
764 if (UseBiasedLocking) {
765 if (SafepointSynchronize::is_at_safepoint()) {
766 BiasedLocking::revoke_at_safepoint(h_obj);
767 } else {
768 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
769 }
770 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
771 }
772
773 oop obj = h_obj();
774 address owner = NULL;
775
776 markOop mark = ReadStableMark (obj) ;
777
778 // Uncontended case, header points to stack
779 if (mark->has_locker()) {
780 owner = (address) mark->locker();
781 }
782
783 // Contended case, header points to ObjectMonitor (tagged pointer)
784 if (mark->has_monitor()) {
785 ObjectMonitor* monitor = mark->monitor();
786 assert(monitor != NULL, "monitor should be non-null");
787 owner = (address) monitor->owner();
788 }
789
790 if (owner != NULL) {
791 // owning_thread_from_monitor_owner() may also return NULL here
792 return Threads::owning_thread_from_monitor_owner(owner, doLock);
793 }
794
795 // Unlocked case, header in place
796 // Cannot have assertion since this object may have been
797 // locked by another thread when reaching here.
798 // assert(mark->is_neutral(), "sanity check");
799
800 return NULL;
801 }
802 // Visitors ...
803
804 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
805 ObjectMonitor* block = gBlockList;
806 ObjectMonitor* mid;
807 while (block) {
808 assert(block->object() == CHAINMARKER, "must be a block header");
809 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
810 mid = block + i;
811 oop object = (oop) mid->object();
812 if (object != NULL) {
813 closure->do_monitor(mid);
814 }
815 }
816 block = (ObjectMonitor*) block->FreeNext;
817 }
818 }
819
820 // Get the next block in the block list.
821 static inline ObjectMonitor* next(ObjectMonitor* block) {
822 assert(block->object() == CHAINMARKER, "must be a block header");
823 block = block->FreeNext ;
824 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
825 return block;
826 }
827
828
829 void ObjectSynchronizer::oops_do(OopClosure* f) {
830 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
831 for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) {
832 assert(block->object() == CHAINMARKER, "must be a block header");
833 for (int i = 1; i < _BLOCKSIZE; i++) {
834 ObjectMonitor* mid = &block[i];
835 if (mid->object() != NULL) {
836 f->do_oop((oop*)mid->object_addr());
837 }
838 }
839 }
840 }
841
842
843 // -----------------------------------------------------------------------------
844 // ObjectMonitor Lifecycle
845 // -----------------------
846 // Inflation unlinks monitors from the global gFreeList and
847 // associates them with objects. Deflation -- which occurs at
848 // STW-time -- disassociates idle monitors from objects. Such
849 // scavenged monitors are returned to the gFreeList.
850 //
851 // The global list is protected by ListLock. All the critical sections
852 // are short and operate in constant-time.
853 //
854 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
855 //
856 // Lifecycle:
857 // -- unassigned and on the global free list
858 // -- unassigned and on a thread's private omFreeList
859 // -- assigned to an object. The object is inflated and the mark refers
860 // to the objectmonitor.
861 //
862
863
864 // Constraining monitor pool growth via MonitorBound ...
865 //
866 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
867 // the rate of scavenging is driven primarily by GC. As such, we can find
868 // an inordinate number of monitors in circulation.
869 // To avoid that scenario we can artificially induce a STW safepoint
870 // if the pool appears to be growing past some reasonable bound.
871 // Generally we favor time in space-time tradeoffs, but as there's no
872 // natural back-pressure on the # of extant monitors we need to impose some
873 // type of limit. Beware that if MonitorBound is set to too low a value
874 // we could just loop. In addition, if MonitorBound is set to a low value
875 // we'll incur more safepoints, which are harmful to performance.
876 // See also: GuaranteedSafepointInterval
877 //
878 // The current implementation uses asynchronous VM operations.
879 //
880
881 static void InduceScavenge (Thread * Self, const char * Whence) {
882 // Induce STW safepoint to trim monitors
883 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
884 // More precisely, trigger an asynchronous STW safepoint as the number
885 // of active monitors passes the specified threshold.
886 // TODO: assert thread state is reasonable
887
888 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
889 if (ObjectMonitor::Knob_Verbose) {
890 ::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ;
891 ::fflush(stdout) ;
892 }
893 // Induce a 'null' safepoint to scavenge monitors
894 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
895 // to the VMthread and have a lifespan longer than that of this activation record.
896 // The VMThread will delete the op when completed.
897 VMThread::execute (new VM_ForceAsyncSafepoint()) ;
898
899 if (ObjectMonitor::Knob_Verbose) {
900 ::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ;
901 ::fflush(stdout) ;
902 }
903 }
904 }
905 /* Too slow for general assert or debug
906 void ObjectSynchronizer::verifyInUse (Thread *Self) {
907 ObjectMonitor* mid;
908 int inusetally = 0;
909 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) {
910 inusetally ++;
911 }
912 assert(inusetally == Self->omInUseCount, "inuse count off");
913
914 int freetally = 0;
915 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) {
916 freetally ++;
917 }
918 assert(freetally == Self->omFreeCount, "free count off");
919 }
920 */
921 ObjectMonitor * ATTR ObjectSynchronizer::omAlloc (Thread * Self) {
922 // A large MAXPRIVATE value reduces both list lock contention
923 // and list coherency traffic, but also tends to increase the
924 // number of objectMonitors in circulation as well as the STW
925 // scavenge costs. As usual, we lean toward time in space-time
926 // tradeoffs.
927 const int MAXPRIVATE = 1024 ;
928 for (;;) {
929 ObjectMonitor * m ;
930
931 // 1: try to allocate from the thread's local omFreeList.
932 // Threads will attempt to allocate first from their local list, then
933 // from the global list, and only after those attempts fail will the thread
934 // attempt to instantiate new monitors. Thread-local free lists take
935 // heat off the ListLock and improve allocation latency, as well as reducing
936 // coherency traffic on the shared global list.
937 m = Self->omFreeList ;
938 if (m != NULL) {
939 Self->omFreeList = m->FreeNext ;
940 Self->omFreeCount -- ;
941 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene
942 guarantee (m->object() == NULL, "invariant") ;
943 if (MonitorInUseLists) {
944 m->FreeNext = Self->omInUseList;
945 Self->omInUseList = m;
946 Self->omInUseCount ++;
947 // verifyInUse(Self);
948 } else {
949 m->FreeNext = NULL;
950 }
951 return m ;
952 }
953
954 // 2: try to allocate from the global gFreeList
955 // CONSIDER: use muxTry() instead of muxAcquire().
956 // If the muxTry() fails then drop immediately into case 3.
957 // If we're using thread-local free lists then try
958 // to reprovision the caller's free list.
959 if (gFreeList != NULL) {
960 // Reprovision the thread's omFreeList.
961 // Use bulk transfers to reduce the allocation rate and heat
962 // on various locks.
963 Thread::muxAcquire (&ListLock, "omAlloc") ;
964 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL; ) {
965 MonitorFreeCount --;
966 ObjectMonitor * take = gFreeList ;
967 gFreeList = take->FreeNext ;
968 guarantee (take->object() == NULL, "invariant") ;
969 guarantee (!take->is_busy(), "invariant") ;
970 take->Recycle() ;
971 omRelease (Self, take, false) ;
972 }
973 Thread::muxRelease (&ListLock) ;
974 Self->omFreeProvision += 1 + (Self->omFreeProvision/2) ;
975 if (Self->omFreeProvision > MAXPRIVATE ) Self->omFreeProvision = MAXPRIVATE ;
976 TEVENT (omFirst - reprovision) ;
977
978 const int mx = MonitorBound ;
979 if (mx > 0 && (MonitorPopulation-MonitorFreeCount) > mx) {
980 // We can't safely induce a STW safepoint from omAlloc() as our thread
981 // state may not be appropriate for such activities and callers may hold
982 // naked oops, so instead we defer the action.
983 InduceScavenge (Self, "omAlloc") ;
984 }
985 continue;
986 }
987
988 // 3: allocate a block of new ObjectMonitors
989 // Both the local and global free lists are empty -- resort to malloc().
990 // In the current implementation objectMonitors are TSM - immortal.
991 assert (_BLOCKSIZE > 1, "invariant") ;
992 ObjectMonitor * temp = new ObjectMonitor[_BLOCKSIZE];
993
994 // NOTE: (almost) no way to recover if allocation failed.
995 // We might be able to induce a STW safepoint and scavenge enough
996 // objectMonitors to permit progress.
997 if (temp == NULL) {
998 vm_exit_out_of_memory (sizeof (ObjectMonitor[_BLOCKSIZE]), OOM_MALLOC_ERROR,
999 "Allocate ObjectMonitors");
1000 }
1001
1002 // Format the block.
1003 // initialize the linked list, each monitor points to its next
1004 // forming the single linked free list, the very first monitor
1005 // will points to next block, which forms the block list.
1006 // The trick of using the 1st element in the block as gBlockList
1007 // linkage should be reconsidered. A better implementation would
1008 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1009
1010 for (int i = 1; i < _BLOCKSIZE ; i++) {
1011 temp[i].FreeNext = &temp[i+1];
1012 }
1013
1014 // terminate the last monitor as the end of list
1015 temp[_BLOCKSIZE - 1].FreeNext = NULL ;
1016
1017 // Element [0] is reserved for global list linkage
1018 temp[0].set_object(CHAINMARKER);
1019
1020 // Consider carving out this thread's current request from the
1021 // block in hand. This avoids some lock traffic and redundant
1022 // list activity.
1023
1024 // Acquire the ListLock to manipulate BlockList and FreeList.
1025 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1026 Thread::muxAcquire (&ListLock, "omAlloc [2]") ;
1027 MonitorPopulation += _BLOCKSIZE-1;
1028 MonitorFreeCount += _BLOCKSIZE-1;
1029
1030 // Add the new block to the list of extant blocks (gBlockList).
1031 // The very first objectMonitor in a block is reserved and dedicated.
1032 // It serves as blocklist "next" linkage.
1033 temp[0].FreeNext = gBlockList;
1034 gBlockList = temp;
1035
1036 // Add the new string of objectMonitors to the global free list
1037 temp[_BLOCKSIZE - 1].FreeNext = gFreeList ;
1038 gFreeList = temp + 1;
1039 Thread::muxRelease (&ListLock) ;
1040 TEVENT (Allocate block of monitors) ;
1041 }
1042 }
1043
1044 // Place "m" on the caller's private per-thread omFreeList.
1045 // In practice there's no need to clamp or limit the number of
1046 // monitors on a thread's omFreeList as the only time we'll call
1047 // omRelease is to return a monitor to the free list after a CAS
1048 // attempt failed. This doesn't allow unbounded #s of monitors to
1049 // accumulate on a thread's free list.
1050 //
1051
1052 void ObjectSynchronizer::omRelease (Thread * Self, ObjectMonitor * m, bool fromPerThreadAlloc) {
1053 guarantee (m->object() == NULL, "invariant") ;
1054
1055 // Remove from omInUseList
1056 if (MonitorInUseLists && fromPerThreadAlloc) {
1057 ObjectMonitor* curmidinuse = NULL;
1058 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; ) {
1059 if (m == mid) {
1060 // extract from per-thread in-use-list
1061 if (mid == Self->omInUseList) {
1062 Self->omInUseList = mid->FreeNext;
1063 } else if (curmidinuse != NULL) {
1064 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1065 }
1066 Self->omInUseCount --;
1067 // verifyInUse(Self);
1068 break;
1069 } else {
1070 curmidinuse = mid;
1071 mid = mid->FreeNext;
1072 }
1073 }
1074 }
1075
1076 // FreeNext is used for both onInUseList and omFreeList, so clear old before setting new
1077 m->FreeNext = Self->omFreeList ;
1078 Self->omFreeList = m ;
1079 Self->omFreeCount ++ ;
1080 }
1081
1082 // Return the monitors of a moribund thread's local free list to
1083 // the global free list. Typically a thread calls omFlush() when
1084 // it's dying. We could also consider having the VM thread steal
1085 // monitors from threads that have not run java code over a few
1086 // consecutive STW safepoints. Relatedly, we might decay
1087 // omFreeProvision at STW safepoints.
1088 //
1089 // Also return the monitors of a moribund thread"s omInUseList to
1090 // a global gOmInUseList under the global list lock so these
1091 // will continue to be scanned.
1092 //
1093 // We currently call omFlush() from the Thread:: dtor _after the thread
1094 // has been excised from the thread list and is no longer a mutator.
1095 // That means that omFlush() can run concurrently with a safepoint and
1096 // the scavenge operator. Calling omFlush() from JavaThread::exit() might
1097 // be a better choice as we could safely reason that that the JVM is
1098 // not at a safepoint at the time of the call, and thus there could
1099 // be not inopportune interleavings between omFlush() and the scavenge
1100 // operator.
1101
1102 void ObjectSynchronizer::omFlush (Thread * Self) {
1103 ObjectMonitor * List = Self->omFreeList ; // Null-terminated SLL
1104 Self->omFreeList = NULL ;
1105 ObjectMonitor * Tail = NULL ;
1106 int Tally = 0;
1107 if (List != NULL) {
1108 ObjectMonitor * s ;
1109 for (s = List ; s != NULL ; s = s->FreeNext) {
1110 Tally ++ ;
1111 Tail = s ;
1112 guarantee (s->object() == NULL, "invariant") ;
1113 guarantee (!s->is_busy(), "invariant") ;
1114 s->set_owner (NULL) ; // redundant but good hygiene
1115 TEVENT (omFlush - Move one) ;
1116 }
1117 guarantee (Tail != NULL && List != NULL, "invariant") ;
1118 }
1119
1120 ObjectMonitor * InUseList = Self->omInUseList;
1121 ObjectMonitor * InUseTail = NULL ;
1122 int InUseTally = 0;
1123 if (InUseList != NULL) {
1124 Self->omInUseList = NULL;
1125 ObjectMonitor *curom;
1126 for (curom = InUseList; curom != NULL; curom = curom->FreeNext) {
1127 InUseTail = curom;
1128 InUseTally++;
1129 }
1130 // TODO debug
1131 assert(Self->omInUseCount == InUseTally, "inuse count off");
1132 Self->omInUseCount = 0;
1133 guarantee (InUseTail != NULL && InUseList != NULL, "invariant");
1134 }
1135
1136 Thread::muxAcquire (&ListLock, "omFlush") ;
1137 if (Tail != NULL) {
1138 Tail->FreeNext = gFreeList ;
1139 gFreeList = List ;
1140 MonitorFreeCount += Tally;
1141 }
1142
1143 if (InUseTail != NULL) {
1144 InUseTail->FreeNext = gOmInUseList;
1145 gOmInUseList = InUseList;
1146 gOmInUseCount += InUseTally;
1147 }
1148
1149 Thread::muxRelease (&ListLock) ;
1150 TEVENT (omFlush) ;
1151 }
1152
1153 // Fast path code shared by multiple functions
1154 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1155 markOop mark = obj->mark();
1156 if (mark->has_monitor()) {
1157 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1158 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1159 return mark->monitor();
1160 }
1161 return ObjectSynchronizer::inflate(Thread::current(), obj);
1162 }
1163
1164
1165 // Note that we could encounter some performance loss through false-sharing as
1166 // multiple locks occupy the same $ line. Padding might be appropriate.
1167
1168
1169 ObjectMonitor * ATTR ObjectSynchronizer::inflate (Thread * Self, oop object) {
1170 // Inflate mutates the heap ...
1171 // Relaxing assertion for bug 6320749.
1172 assert (Universe::verify_in_progress() ||
1173 !SafepointSynchronize::is_at_safepoint(), "invariant") ;
1174
1175 for (;;) {
1176 const markOop mark = object->mark() ;
1177 assert (!mark->has_bias_pattern(), "invariant") ;
1178
1179 // The mark can be in one of the following states:
1180 // * Inflated - just return
1181 // * Stack-locked - coerce it to inflated
1182 // * INFLATING - busy wait for conversion to complete
1183 // * Neutral - aggressively inflate the object.
1184 // * BIASED - Illegal. We should never see this
1185
1186 // CASE: inflated
1187 if (mark->has_monitor()) {
1188 ObjectMonitor * inf = mark->monitor() ;
1189 assert (inf->header()->is_neutral(), "invariant");
1190 assert (inf->object() == object, "invariant") ;
1191 assert (ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1192 return inf ;
1193 }
1194
1195 // CASE: inflation in progress - inflating over a stack-lock.
1196 // Some other thread is converting from stack-locked to inflated.
1197 // Only that thread can complete inflation -- other threads must wait.
1198 // The INFLATING value is transient.
1199 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1200 // We could always eliminate polling by parking the thread on some auxiliary list.
1201 if (mark == markOopDesc::INFLATING()) {
1202 TEVENT (Inflate: spin while INFLATING) ;
1203 ReadStableMark(object) ;
1204 continue ;
1205 }
1206
1207 // CASE: stack-locked
1208 // Could be stack-locked either by this thread or by some other thread.
1209 //
1210 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1211 // to install INFLATING into the mark word. We originally installed INFLATING,
1212 // allocated the objectmonitor, and then finally STed the address of the
1213 // objectmonitor into the mark. This was correct, but artificially lengthened
1214 // the interval in which INFLATED appeared in the mark, thus increasing
1215 // the odds of inflation contention.
1216 //
1217 // We now use per-thread private objectmonitor free lists.
1218 // These list are reprovisioned from the global free list outside the
1219 // critical INFLATING...ST interval. A thread can transfer
1220 // multiple objectmonitors en-mass from the global free list to its local free list.
1221 // This reduces coherency traffic and lock contention on the global free list.
1222 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1223 // before or after the CAS(INFLATING) operation.
1224 // See the comments in omAlloc().
1225
1226 if (mark->has_locker()) {
1227 ObjectMonitor * m = omAlloc (Self) ;
1228 // Optimistically prepare the objectmonitor - anticipate successful CAS
1229 // We do this before the CAS in order to minimize the length of time
1230 // in which INFLATING appears in the mark.
1231 m->Recycle();
1232 m->_Responsible = NULL ;
1233 m->OwnerIsThread = 0 ;
1234 m->_recursions = 0 ;
1235 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // Consider: maintain by type/class
1236
1237 markOop cmp = (markOop) Atomic::cmpxchg_ptr (markOopDesc::INFLATING(), object->mark_addr(), mark) ;
1238 if (cmp != mark) {
1239 omRelease (Self, m, true) ;
1240 continue ; // Interference -- just retry
1241 }
1242
1243 // We've successfully installed INFLATING (0) into the mark-word.
1244 // This is the only case where 0 will appear in a mark-work.
1245 // Only the singular thread that successfully swings the mark-word
1246 // to 0 can perform (or more precisely, complete) inflation.
1247 //
1248 // Why do we CAS a 0 into the mark-word instead of just CASing the
1249 // mark-word from the stack-locked value directly to the new inflated state?
1250 // Consider what happens when a thread unlocks a stack-locked object.
1251 // It attempts to use CAS to swing the displaced header value from the
1252 // on-stack basiclock back into the object header. Recall also that the
1253 // header value (hashcode, etc) can reside in (a) the object header, or
1254 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1255 // header in an objectMonitor. The inflate() routine must copy the header
1256 // value from the basiclock on the owner's stack to the objectMonitor, all
1257 // the while preserving the hashCode stability invariants. If the owner
1258 // decides to release the lock while the value is 0, the unlock will fail
1259 // and control will eventually pass from slow_exit() to inflate. The owner
1260 // will then spin, waiting for the 0 value to disappear. Put another way,
1261 // the 0 causes the owner to stall if the owner happens to try to
1262 // drop the lock (restoring the header from the basiclock to the object)
1263 // while inflation is in-progress. This protocol avoids races that might
1264 // would otherwise permit hashCode values to change or "flicker" for an object.
1265 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1266 // 0 serves as a "BUSY" inflate-in-progress indicator.
1267
1268
1269 // fetch the displaced mark from the owner's stack.
1270 // The owner can't die or unwind past the lock while our INFLATING
1271 // object is in the mark. Furthermore the owner can't complete
1272 // an unlock on the object, either.
1273 markOop dmw = mark->displaced_mark_helper() ;
1274 assert (dmw->is_neutral(), "invariant") ;
1275
1276 // Setup monitor fields to proper values -- prepare the monitor
1277 m->set_header(dmw) ;
1278
1279 // Optimization: if the mark->locker stack address is associated
1280 // with this thread we could simply set m->_owner = Self and
1281 // m->OwnerIsThread = 1. Note that a thread can inflate an object
1282 // that it has stack-locked -- as might happen in wait() -- directly
1283 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1284 m->set_owner(mark->locker());
1285 m->set_object(object);
1286 // TODO-FIXME: assert BasicLock->dhw != 0.
1287
1288 // Must preserve store ordering. The monitor state must
1289 // be stable at the time of publishing the monitor address.
1290 guarantee (object->mark() == markOopDesc::INFLATING(), "invariant") ;
1291 object->release_set_mark(markOopDesc::encode(m));
1292
1293 // Hopefully the performance counters are allocated on distinct cache lines
1294 // to avoid false sharing on MP systems ...
1295 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ;
1296 TEVENT(Inflate: overwrite stacklock) ;
1297 if (TraceMonitorInflation) {
1298 if (object->is_instance()) {
1299 ResourceMark rm;
1300 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1301 (void *) object, (intptr_t) object->mark(),
1302 object->klass()->external_name());
1303 }
1304 }
1305 return m ;
1306 }
1307
1308 // CASE: neutral
1309 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1310 // If we know we're inflating for entry it's better to inflate by swinging a
1311 // pre-locked objectMonitor pointer into the object header. A successful
1312 // CAS inflates the object *and* confers ownership to the inflating thread.
1313 // In the current implementation we use a 2-step mechanism where we CAS()
1314 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1315 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1316 // would be useful.
1317
1318 assert (mark->is_neutral(), "invariant");
1319 ObjectMonitor * m = omAlloc (Self) ;
1320 // prepare m for installation - set monitor to initial state
1321 m->Recycle();
1322 m->set_header(mark);
1323 m->set_owner(NULL);
1324 m->set_object(object);
1325 m->OwnerIsThread = 1 ;
1326 m->_recursions = 0 ;
1327 m->_Responsible = NULL ;
1328 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // consider: keep metastats by type/class
1329
1330 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) {
1331 m->set_object (NULL) ;
1332 m->set_owner (NULL) ;
1333 m->OwnerIsThread = 0 ;
1334 m->Recycle() ;
1335 omRelease (Self, m, true) ;
1336 m = NULL ;
1337 continue ;
1338 // interference - the markword changed - just retry.
1339 // The state-transitions are one-way, so there's no chance of
1340 // live-lock -- "Inflated" is an absorbing state.
1341 }
1342
1343 // Hopefully the performance counters are allocated on distinct
1344 // cache lines to avoid false sharing on MP systems ...
1345 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ;
1346 TEVENT(Inflate: overwrite neutral) ;
1347 if (TraceMonitorInflation) {
1348 if (object->is_instance()) {
1349 ResourceMark rm;
1350 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1351 (void *) object, (intptr_t) object->mark(),
1352 object->klass()->external_name());
1353 }
1354 }
1355 return m ;
1356 }
1357 }
1358
1359 // Note that we could encounter some performance loss through false-sharing as
1360 // multiple locks occupy the same $ line. Padding might be appropriate.
1361
1362
1363 // Deflate_idle_monitors() is called at all safepoints, immediately
1364 // after all mutators are stopped, but before any objects have moved.
1365 // It traverses the list of known monitors, deflating where possible.
1366 // The scavenged monitor are returned to the monitor free list.
1367 //
1368 // Beware that we scavenge at *every* stop-the-world point.
1369 // Having a large number of monitors in-circulation negatively
1370 // impacts the performance of some applications (e.g., PointBase).
1371 // Broadly, we want to minimize the # of monitors in circulation.
1372 //
1373 // We have added a flag, MonitorInUseLists, which creates a list
1374 // of active monitors for each thread. deflate_idle_monitors()
1375 // only scans the per-thread inuse lists. omAlloc() puts all
1376 // assigned monitors on the per-thread list. deflate_idle_monitors()
1377 // returns the non-busy monitors to the global free list.
1378 // When a thread dies, omFlush() adds the list of active monitors for
1379 // that thread to a global gOmInUseList acquiring the
1380 // global list lock. deflate_idle_monitors() acquires the global
1381 // list lock to scan for non-busy monitors to the global free list.
1382 // An alternative could have used a single global inuse list. The
1383 // downside would have been the additional cost of acquiring the global list lock
1384 // for every omAlloc().
1385 //
1386 // Perversely, the heap size -- and thus the STW safepoint rate --
1387 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1388 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1389 // This is an unfortunate aspect of this design.
1390 //
1391
1392 enum ManifestConstants {
1393 ClearResponsibleAtSTW = 0,
1394 MaximumRecheckInterval = 1000
1395 } ;
1396
1397 // Deflate a single monitor if not in use
1398 // Return true if deflated, false if in use
1399 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1400 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) {
1401 bool deflated;
1402 // Normal case ... The monitor is associated with obj.
1403 guarantee (obj->mark() == markOopDesc::encode(mid), "invariant") ;
1404 guarantee (mid == obj->mark()->monitor(), "invariant");
1405 guarantee (mid->header()->is_neutral(), "invariant");
1406
1407 if (mid->is_busy()) {
1408 if (ClearResponsibleAtSTW) mid->_Responsible = NULL ;
1409 deflated = false;
1410 } else {
1411 // Deflate the monitor if it is no longer being used
1412 // It's idle - scavenge and return to the global free list
1413 // plain old deflation ...
1414 TEVENT (deflate_idle_monitors - scavenge1) ;
1415 if (TraceMonitorInflation) {
1416 if (obj->is_instance()) {
1417 ResourceMark rm;
1418 tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1419 (void *) obj, (intptr_t) obj->mark(), obj->klass()->external_name());
1420 }
1421 }
1422
1423 // Restore the header back to obj
1424 obj->release_set_mark(mid->header());
1425 mid->clear();
1426
1427 assert (mid->object() == NULL, "invariant") ;
1428
1429 // Move the object to the working free list defined by FreeHead,FreeTail.
1430 if (*FreeHeadp == NULL) *FreeHeadp = mid;
1431 if (*FreeTailp != NULL) {
1432 ObjectMonitor * prevtail = *FreeTailp;
1433 assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); // TODO KK
1434 prevtail->FreeNext = mid;
1435 }
1436 *FreeTailp = mid;
1437 deflated = true;
1438 }
1439 return deflated;
1440 }
1441
1442 // Caller acquires ListLock
1443 int ObjectSynchronizer::walk_monitor_list(ObjectMonitor** listheadp,
1444 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) {
1445 ObjectMonitor* mid;
1446 ObjectMonitor* next;
1447 ObjectMonitor* curmidinuse = NULL;
1448 int deflatedcount = 0;
1449
1450 for (mid = *listheadp; mid != NULL; ) {
1451 oop obj = (oop) mid->object();
1452 bool deflated = false;
1453 if (obj != NULL) {
1454 deflated = deflate_monitor(mid, obj, FreeHeadp, FreeTailp);
1455 }
1456 if (deflated) {
1457 // extract from per-thread in-use-list
1458 if (mid == *listheadp) {
1459 *listheadp = mid->FreeNext;
1460 } else if (curmidinuse != NULL) {
1461 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1462 }
1463 next = mid->FreeNext;
1464 mid->FreeNext = NULL; // This mid is current tail in the FreeHead list
1465 mid = next;
1466 deflatedcount++;
1467 } else {
1468 curmidinuse = mid;
1469 mid = mid->FreeNext;
1470 }
1471 }
1472 return deflatedcount;
1473 }
1474
1475 void ObjectSynchronizer::deflate_idle_monitors() {
1476 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1477 int nInuse = 0 ; // currently associated with objects
1478 int nInCirculation = 0 ; // extant
1479 int nScavenged = 0 ; // reclaimed
1480 bool deflated = false;
1481
1482 ObjectMonitor * FreeHead = NULL ; // Local SLL of scavenged monitors
1483 ObjectMonitor * FreeTail = NULL ;
1484
1485 TEVENT (deflate_idle_monitors) ;
1486 // Prevent omFlush from changing mids in Thread dtor's during deflation
1487 // And in case the vm thread is acquiring a lock during a safepoint
1488 // See e.g. 6320749
1489 Thread::muxAcquire (&ListLock, "scavenge - return") ;
1490
1491 if (MonitorInUseLists) {
1492 int inUse = 0;
1493 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) {
1494 nInCirculation+= cur->omInUseCount;
1495 int deflatedcount = walk_monitor_list(cur->omInUseList_addr(), &FreeHead, &FreeTail);
1496 cur->omInUseCount-= deflatedcount;
1497 // verifyInUse(cur);
1498 nScavenged += deflatedcount;
1499 nInuse += cur->omInUseCount;
1500 }
1501
1502 // For moribund threads, scan gOmInUseList
1503 if (gOmInUseList) {
1504 nInCirculation += gOmInUseCount;
1505 int deflatedcount = walk_monitor_list((ObjectMonitor **)&gOmInUseList, &FreeHead, &FreeTail);
1506 gOmInUseCount-= deflatedcount;
1507 nScavenged += deflatedcount;
1508 nInuse += gOmInUseCount;
1509 }
1510
1511 } else for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) {
1512 // Iterate over all extant monitors - Scavenge all idle monitors.
1513 assert(block->object() == CHAINMARKER, "must be a block header");
1514 nInCirculation += _BLOCKSIZE ;
1515 for (int i = 1 ; i < _BLOCKSIZE; i++) {
1516 ObjectMonitor* mid = &block[i];
1517 oop obj = (oop) mid->object();
1518
1519 if (obj == NULL) {
1520 // The monitor is not associated with an object.
1521 // The monitor should either be a thread-specific private
1522 // free list or the global free list.
1523 // obj == NULL IMPLIES mid->is_busy() == 0
1524 guarantee (!mid->is_busy(), "invariant") ;
1525 continue ;
1526 }
1527 deflated = deflate_monitor(mid, obj, &FreeHead, &FreeTail);
1528
1529 if (deflated) {
1530 mid->FreeNext = NULL ;
1531 nScavenged ++ ;
1532 } else {
1533 nInuse ++;
1534 }
1535 }
1536 }
1537
1538 MonitorFreeCount += nScavenged;
1539
1540 // Consider: audit gFreeList to ensure that MonitorFreeCount and list agree.
1541
1542 if (ObjectMonitor::Knob_Verbose) {
1543 ::printf ("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n",
1544 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge,
1545 MonitorPopulation, MonitorFreeCount) ;
1546 ::fflush(stdout) ;
1547 }
1548
1549 ForceMonitorScavenge = 0; // Reset
1550
1551 // Move the scavenged monitors back to the global free list.
1552 if (FreeHead != NULL) {
1553 guarantee (FreeTail != NULL && nScavenged > 0, "invariant") ;
1554 assert (FreeTail->FreeNext == NULL, "invariant") ;
1555 // constant-time list splice - prepend scavenged segment to gFreeList
1556 FreeTail->FreeNext = gFreeList ;
1557 gFreeList = FreeHead ;
1558 }
1559 Thread::muxRelease (&ListLock) ;
1560
1561 if (ObjectMonitor::_sync_Deflations != NULL) ObjectMonitor::_sync_Deflations->inc(nScavenged) ;
1562 if (ObjectMonitor::_sync_MonExtant != NULL) ObjectMonitor::_sync_MonExtant ->set_value(nInCirculation);
1563
1564 // TODO: Add objectMonitor leak detection.
1565 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1566 GVars.stwRandom = os::random() ;
1567 GVars.stwCycle ++ ;
1568 }
1569
1570 // Monitor cleanup on JavaThread::exit
1571
1572 // Iterate through monitor cache and attempt to release thread's monitors
1573 // Gives up on a particular monitor if an exception occurs, but continues
1574 // the overall iteration, swallowing the exception.
1575 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1576 private:
1577 TRAPS;
1578
1579 public:
1580 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1581 void do_monitor(ObjectMonitor* mid) {
1582 if (mid->owner() == THREAD) {
1583 (void)mid->complete_exit(CHECK);
1584 }
1585 }
1586 };
1587
1588 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1589 // ignored. This is meant to be called during JNI thread detach which assumes
1590 // all remaining monitors are heavyweight. All exceptions are swallowed.
1591 // Scanning the extant monitor list can be time consuming.
1592 // A simple optimization is to add a per-thread flag that indicates a thread
1593 // called jni_monitorenter() during its lifetime.
1594 //
1595 // Instead of No_Savepoint_Verifier it might be cheaper to
1596 // use an idiom of the form:
1597 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1598 // <code that must not run at safepoint>
1599 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1600 // Since the tests are extremely cheap we could leave them enabled
1601 // for normal product builds.
1602
1603 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1604 assert(THREAD == JavaThread::current(), "must be current Java thread");
1605 No_Safepoint_Verifier nsv ;
1606 ReleaseJavaMonitorsClosure rjmc(THREAD);
1607 Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread");
1608 ObjectSynchronizer::monitors_iterate(&rjmc);
1609 Thread::muxRelease(&ListLock);
1610 THREAD->clear_pending_exception();
1611 }
1612
1613 //------------------------------------------------------------------------------
1614 // Non-product code
1615
1616 #ifndef PRODUCT
1617
1618 // Verify all monitors in the monitor cache, the verification is weak.
1619 void ObjectSynchronizer::verify() {
1620 ObjectMonitor* block = gBlockList;
1621 ObjectMonitor* mid;
1622 while (block) {
1623 assert(block->object() == CHAINMARKER, "must be a block header");
1624 for (int i = 1; i < _BLOCKSIZE; i++) {
1625 mid = block + i;
1626 oop object = (oop) mid->object();
1627 if (object != NULL) {
1628 mid->verify();
1629 }
1630 }
1631 block = (ObjectMonitor*) block->FreeNext;
1632 }
1633 }
1634
1635 // Check if monitor belongs to the monitor cache
1636 // The list is grow-only so it's *relatively* safe to traverse
1637 // the list of extant blocks without taking a lock.
1638
1639 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
1640 ObjectMonitor* block = gBlockList;
1641
1642 while (block) {
1643 assert(block->object() == CHAINMARKER, "must be a block header");
1644 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
1645 address mon = (address) monitor;
1646 address blk = (address) block;
1647 size_t diff = mon - blk;
1648 assert((diff % sizeof(ObjectMonitor)) == 0, "check");
1649 return 1;
1650 }
1651 block = (ObjectMonitor*) block->FreeNext;
1652 }
1653 return 0;
1654 }
1655
1656 #endif