1 /*
2 * Copyright (c) 1998, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/vmSymbols.hpp"
27 #include "memory/resourceArea.hpp"
28 #include "oops/markOop.hpp"
29 #include "oops/oop.inline.hpp"
30 #include "runtime/biasedLocking.hpp"
31 #include "runtime/handles.inline.hpp"
32 #include "runtime/interfaceSupport.hpp"
33 #include "runtime/mutexLocker.hpp"
34 #include "runtime/objectMonitor.hpp"
35 #include "runtime/objectMonitor.inline.hpp"
36 #include "runtime/osThread.hpp"
37 #include "runtime/stubRoutines.hpp"
38 #include "runtime/synchronizer.hpp"
39 #include "runtime/thread.inline.hpp"
40 #include "utilities/dtrace.hpp"
41 #include "utilities/events.hpp"
42 #include "utilities/preserveException.hpp"
43 #ifdef TARGET_OS_FAMILY_linux
44 # include "os_linux.inline.hpp"
45 #endif
46 #ifdef TARGET_OS_FAMILY_solaris
47 # include "os_solaris.inline.hpp"
48 #endif
49 #ifdef TARGET_OS_FAMILY_windows
50 # include "os_windows.inline.hpp"
51 #endif
52 #ifdef TARGET_OS_FAMILY_bsd
53 # include "os_bsd.inline.hpp"
54 #endif
55
56 #if defined(__GNUC__) && !defined(PPC64)
57 // Need to inhibit inlining for older versions of GCC to avoid build-time failures
58 #define ATTR __attribute__((noinline))
59 #else
60 #define ATTR
61 #endif
62
63 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
64
65 // The "core" versions of monitor enter and exit reside in this file.
66 // The interpreter and compilers contain specialized transliterated
67 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
68 // for instance. If you make changes here, make sure to modify the
69 // interpreter, and both C1 and C2 fast-path inline locking code emission.
70 //
71 //
72 // -----------------------------------------------------------------------------
73
74 #ifdef DTRACE_ENABLED
75
76 // Only bother with this argument setup if dtrace is available
77 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
78
79 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
80 char* bytes = NULL; \
81 int len = 0; \
82 jlong jtid = SharedRuntime::get_java_tid(thread); \
83 Symbol* klassname = ((oop)(obj))->klass()->name(); \
84 if (klassname != NULL) { \
85 bytes = (char*)klassname->bytes(); \
86 len = klassname->utf8_length(); \
87 }
88
89 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
90 { \
91 if (DTraceMonitorProbes) { \
92 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
93 HOTSPOT_MONITOR_WAIT(jtid, \
94 (uintptr_t)(monitor), bytes, len, (millis)); \
95 } \
96 }
97
98 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
99
100 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
101 { \
102 if (DTraceMonitorProbes) { \
103 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
104 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
105 (uintptr_t)(monitor), bytes, len); \
106 } \
107 }
108
109 #else // ndef DTRACE_ENABLED
110
111 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
112 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
113
114 #endif // ndef DTRACE_ENABLED
115
116 // This exists only as a workaround of dtrace bug 6254741
117 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
118 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
119 return 0;
120 }
121
122 #define NINFLATIONLOCKS 256
123 static volatile intptr_t InflationLocks [NINFLATIONLOCKS] ;
124
125 ObjectMonitor * ObjectSynchronizer::gBlockList = NULL ;
126 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL ;
127 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL ;
128 int ObjectSynchronizer::gOmInUseCount = 0;
129 static volatile intptr_t ListLock = 0 ; // protects global monitor free-list cache
130 static volatile int MonitorFreeCount = 0 ; // # on gFreeList
131 static volatile int MonitorPopulation = 0 ; // # Extant -- in circulation
132 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
133
134 // -----------------------------------------------------------------------------
135 // Fast Monitor Enter/Exit
136 // This the fast monitor enter. The interpreter and compiler use
137 // some assembly copies of this code. Make sure update those code
138 // if the following function is changed. The implementation is
139 // extremely sensitive to race condition. Be careful.
140
141 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock, bool attempt_rebias, TRAPS) {
142 if (UseBiasedLocking) {
143 if (!SafepointSynchronize::is_at_safepoint()) {
144 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
145 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
146 return;
147 }
148 } else {
149 assert(!attempt_rebias, "can not rebias toward VM thread");
150 BiasedLocking::revoke_at_safepoint(obj);
151 }
152 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
153 }
154
155 slow_enter (obj, lock, THREAD) ;
156 }
157
158 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
159 assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here");
160 // if displaced header is null, the previous enter is recursive enter, no-op
161 markOop dhw = lock->displaced_header();
162 markOop mark ;
163 if (dhw == NULL) {
164 // Recursive stack-lock.
165 // Diagnostics -- Could be: stack-locked, inflating, inflated.
166 mark = object->mark() ;
167 assert (!mark->is_neutral(), "invariant") ;
168 if (mark->has_locker() && mark != markOopDesc::INFLATING()) {
169 assert(THREAD->is_lock_owned((address)mark->locker()), "invariant") ;
170 }
171 if (mark->has_monitor()) {
172 ObjectMonitor * m = mark->monitor() ;
173 assert(((oop)(m->object()))->mark() == mark, "invariant") ;
174 assert(m->is_entered(THREAD), "invariant") ;
175 }
176 return ;
177 }
178
179 mark = object->mark() ;
180
181 // If the object is stack-locked by the current thread, try to
182 // swing the displaced header from the box back to the mark.
183 if (mark == (markOop) lock) {
184 assert (dhw->is_neutral(), "invariant") ;
185 if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) {
186 TEVENT (fast_exit: release stacklock) ;
187 return;
188 }
189 }
190
191 ObjectSynchronizer::inflate(THREAD, object)->exit (true, THREAD) ;
192 }
193
194 // -----------------------------------------------------------------------------
195 // Interpreter/Compiler Slow Case
196 // This routine is used to handle interpreter/compiler slow case
197 // We don't need to use fast path here, because it must have been
198 // failed in the interpreter/compiler code.
199 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
200 markOop mark = obj->mark();
201 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
202
203 if (mark->is_neutral()) {
204 // Anticipate successful CAS -- the ST of the displaced mark must
205 // be visible <= the ST performed by the CAS.
206 lock->set_displaced_header(mark);
207 if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) {
208 TEVENT (slow_enter: release stacklock) ;
209 return ;
210 }
211 // Fall through to inflate() ...
212 } else
213 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
214 assert(lock != mark->locker(), "must not re-lock the same lock");
215 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
216 lock->set_displaced_header(NULL);
217 return;
218 }
219
220 #if 0
221 // The following optimization isn't particularly useful.
222 if (mark->has_monitor() && mark->monitor()->is_entered(THREAD)) {
223 lock->set_displaced_header (NULL) ;
224 return ;
225 }
226 #endif
227
228 // The object header will never be displaced to this lock,
229 // so it does not matter what the value is, except that it
230 // must be non-zero to avoid looking like a re-entrant lock,
231 // and must not look locked either.
232 lock->set_displaced_header(markOopDesc::unused_mark());
233 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
234 }
235
236 // This routine is used to handle interpreter/compiler slow case
237 // We don't need to use fast path here, because it must have
238 // failed in the interpreter/compiler code. Simply use the heavy
239 // weight monitor should be ok, unless someone find otherwise.
240 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
241 fast_exit (object, lock, THREAD) ;
242 }
243
244 // -----------------------------------------------------------------------------
245 // Class Loader support to workaround deadlocks on the class loader lock objects
246 // Also used by GC
247 // complete_exit()/reenter() are used to wait on a nested lock
248 // i.e. to give up an outer lock completely and then re-enter
249 // Used when holding nested locks - lock acquisition order: lock1 then lock2
250 // 1) complete_exit lock1 - saving recursion count
251 // 2) wait on lock2
252 // 3) when notified on lock2, unlock lock2
253 // 4) reenter lock1 with original recursion count
254 // 5) lock lock2
255 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
256 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
257 TEVENT (complete_exit) ;
258 if (UseBiasedLocking) {
259 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
260 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
261 }
262
263 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
264
265 return monitor->complete_exit(THREAD);
266 }
267
268 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
269 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
270 TEVENT (reenter) ;
271 if (UseBiasedLocking) {
272 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
273 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
274 }
275
276 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
277
278 monitor->reenter(recursion, THREAD);
279 }
280 // -----------------------------------------------------------------------------
281 // JNI locks on java objects
282 // NOTE: must use heavy weight monitor to handle jni monitor enter
283 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) { // possible entry from jni enter
284 // the current locking is from JNI instead of Java code
285 TEVENT (jni_enter) ;
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 THREAD->set_current_pending_monitor_is_from_java(false);
291 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
292 THREAD->set_current_pending_monitor_is_from_java(true);
293 }
294
295 // NOTE: must use heavy weight monitor to handle jni monitor enter
296 bool ObjectSynchronizer::jni_try_enter(Handle obj, Thread* THREAD) {
297 if (UseBiasedLocking) {
298 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
299 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
300 }
301
302 ObjectMonitor* monitor = ObjectSynchronizer::inflate_helper(obj());
303 return monitor->try_enter(THREAD);
304 }
305
306
307 // NOTE: must use heavy weight monitor to handle jni monitor exit
308 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
309 TEVENT (jni_exit) ;
310 if (UseBiasedLocking) {
311 Handle h_obj(THREAD, obj);
312 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
313 obj = h_obj();
314 }
315 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
316
317 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj);
318 // If this thread has locked the object, exit the monitor. Note: can't use
319 // monitor->check(CHECK); must exit even if an exception is pending.
320 if (monitor->check(THREAD)) {
321 monitor->exit(true, THREAD);
322 }
323 }
324
325 // -----------------------------------------------------------------------------
326 // Internal VM locks on java objects
327 // standard constructor, allows locking failures
328 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
329 _dolock = doLock;
330 _thread = thread;
331 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
332 _obj = obj;
333
334 if (_dolock) {
335 TEVENT (ObjectLocker) ;
336
337 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
338 }
339 }
340
341 ObjectLocker::~ObjectLocker() {
342 if (_dolock) {
343 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
344 }
345 }
346
347
348 // -----------------------------------------------------------------------------
349 // Wait/Notify/NotifyAll
350 // NOTE: must use heavy weight monitor to handle wait()
351 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
352 if (UseBiasedLocking) {
353 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
354 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
355 }
356 if (millis < 0) {
357 TEVENT (wait - throw IAX) ;
358 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
359 }
360 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
361 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
362 monitor->wait(millis, true, THREAD);
363
364 // This dummy call is in place to get around dtrace bug 6254741. Once
365 // that's fixed we can uncomment the following line, remove the call
366 // and change this function back into a "void" func.
367 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
368 return dtrace_waited_probe(monitor, obj, THREAD);
369 }
370
371 void ObjectSynchronizer::waitUninterruptibly (Handle obj, jlong millis, TRAPS) {
372 if (UseBiasedLocking) {
373 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
374 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
375 }
376 if (millis < 0) {
377 TEVENT (wait - throw IAX) ;
378 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
379 }
380 ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD) ;
381 }
382
383 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
384 if (UseBiasedLocking) {
385 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
386 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
387 }
388
389 markOop mark = obj->mark();
390 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
391 return;
392 }
393 ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD);
394 }
395
396 // NOTE: see comment of notify()
397 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
398 if (UseBiasedLocking) {
399 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
400 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
401 }
402
403 markOop mark = obj->mark();
404 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
405 return;
406 }
407 ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD);
408 }
409
410 // -----------------------------------------------------------------------------
411 // Hash Code handling
412 //
413 // Performance concern:
414 // OrderAccess::storestore() calls release() which STs 0 into the global volatile
415 // OrderAccess::Dummy variable. This store is unnecessary for correctness.
416 // Many threads STing into a common location causes considerable cache migration
417 // or "sloshing" on large SMP system. As such, I avoid using OrderAccess::storestore()
418 // until it's repaired. In some cases OrderAccess::fence() -- which incurs local
419 // latency on the executing processor -- is a better choice as it scales on SMP
420 // systems. See http://blogs.sun.com/dave/entry/biased_locking_in_hotspot for a
421 // discussion of coherency costs. Note that all our current reference platforms
422 // provide strong ST-ST order, so the issue is moot on IA32, x64, and SPARC.
423 //
424 // As a general policy we use "volatile" to control compiler-based reordering
425 // and explicit fences (barriers) to control for architectural reordering performed
426 // by the CPU(s) or platform.
427
428 struct SharedGlobals {
429 // These are highly shared mostly-read variables.
430 // To avoid false-sharing they need to be the sole occupants of a $ line.
431 double padPrefix [8];
432 volatile int stwRandom ;
433 volatile int stwCycle ;
434
435 // Hot RW variables -- Sequester to avoid false-sharing
436 double padSuffix [16];
437 volatile int hcSequence ;
438 double padFinal [8] ;
439 } ;
440
441 static SharedGlobals GVars ;
442 static int MonitorScavengeThreshold = 1000000 ;
443 static volatile int ForceMonitorScavenge = 0 ; // Scavenge required and pending
444
445 static markOop ReadStableMark (oop obj) {
446 markOop mark = obj->mark() ;
447 if (!mark->is_being_inflated()) {
448 return mark ; // normal fast-path return
449 }
450
451 int its = 0 ;
452 for (;;) {
453 markOop mark = obj->mark() ;
454 if (!mark->is_being_inflated()) {
455 return mark ; // normal fast-path return
456 }
457
458 // The object is being inflated by some other thread.
459 // The caller of ReadStableMark() must wait for inflation to complete.
460 // Avoid live-lock
461 // TODO: consider calling SafepointSynchronize::do_call_back() while
462 // spinning to see if there's a safepoint pending. If so, immediately
463 // yielding or blocking would be appropriate. Avoid spinning while
464 // there is a safepoint pending.
465 // TODO: add inflation contention performance counters.
466 // TODO: restrict the aggregate number of spinners.
467
468 ++its ;
469 if (its > 10000 || !os::is_MP()) {
470 if (its & 1) {
471 os::NakedYield() ;
472 TEVENT (Inflate: INFLATING - yield) ;
473 } else {
474 // Note that the following code attenuates the livelock problem but is not
475 // a complete remedy. A more complete solution would require that the inflating
476 // thread hold the associated inflation lock. The following code simply restricts
477 // the number of spinners to at most one. We'll have N-2 threads blocked
478 // on the inflationlock, 1 thread holding the inflation lock and using
479 // a yield/park strategy, and 1 thread in the midst of inflation.
480 // A more refined approach would be to change the encoding of INFLATING
481 // to allow encapsulation of a native thread pointer. Threads waiting for
482 // inflation to complete would use CAS to push themselves onto a singly linked
483 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
484 // and calling park(). When inflation was complete the thread that accomplished inflation
485 // would detach the list and set the markword to inflated with a single CAS and
486 // then for each thread on the list, set the flag and unpark() the thread.
487 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
488 // wakes at most one thread whereas we need to wake the entire list.
489 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1) ;
490 int YieldThenBlock = 0 ;
491 assert (ix >= 0 && ix < NINFLATIONLOCKS, "invariant") ;
492 assert ((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant") ;
493 Thread::muxAcquire (InflationLocks + ix, "InflationLock") ;
494 while (obj->mark() == markOopDesc::INFLATING()) {
495 // Beware: NakedYield() is advisory and has almost no effect on some platforms
496 // so we periodically call Self->_ParkEvent->park(1).
497 // We use a mixed spin/yield/block mechanism.
498 if ((YieldThenBlock++) >= 16) {
499 Thread::current()->_ParkEvent->park(1) ;
500 } else {
501 os::NakedYield() ;
502 }
503 }
504 Thread::muxRelease (InflationLocks + ix ) ;
505 TEVENT (Inflate: INFLATING - yield/park) ;
506 }
507 } else {
508 SpinPause() ; // SMP-polite spinning
509 }
510 }
511 }
512
513 // hashCode() generation :
514 //
515 // Possibilities:
516 // * MD5Digest of {obj,stwRandom}
517 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
518 // * A DES- or AES-style SBox[] mechanism
519 // * One of the Phi-based schemes, such as:
520 // 2654435761 = 2^32 * Phi (golden ratio)
521 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
522 // * A variation of Marsaglia's shift-xor RNG scheme.
523 // * (obj ^ stwRandom) is appealing, but can result
524 // in undesirable regularity in the hashCode values of adjacent objects
525 // (objects allocated back-to-back, in particular). This could potentially
526 // result in hashtable collisions and reduced hashtable efficiency.
527 // There are simple ways to "diffuse" the middle address bits over the
528 // generated hashCode values:
529 //
530
531 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
532 intptr_t value = 0 ;
533 if (hashCode == 0) {
534 // This form uses an unguarded global Park-Miller RNG,
535 // so it's possible for two threads to race and generate the same RNG.
536 // On MP system we'll have lots of RW access to a global, so the
537 // mechanism induces lots of coherency traffic.
538 value = os::random() ;
539 } else
540 if (hashCode == 1) {
541 // This variation has the property of being stable (idempotent)
542 // between STW operations. This can be useful in some of the 1-0
543 // synchronization schemes.
544 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3 ;
545 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom ;
546 } else
547 if (hashCode == 2) {
548 value = 1 ; // for sensitivity testing
549 } else
550 if (hashCode == 3) {
551 value = ++GVars.hcSequence ;
552 } else
553 if (hashCode == 4) {
554 value = cast_from_oop<intptr_t>(obj) ;
555 } else {
556 // Marsaglia's xor-shift scheme with thread-specific state
557 // This is probably the best overall implementation -- we'll
558 // likely make this the default in future releases.
559 unsigned t = Self->_hashStateX ;
560 t ^= (t << 11) ;
561 Self->_hashStateX = Self->_hashStateY ;
562 Self->_hashStateY = Self->_hashStateZ ;
563 Self->_hashStateZ = Self->_hashStateW ;
564 unsigned v = Self->_hashStateW ;
565 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)) ;
566 Self->_hashStateW = v ;
567 value = v ;
568 }
569
570 value &= markOopDesc::hash_mask;
571 if (value == 0) value = 0xBAD ;
572 assert (value != markOopDesc::no_hash, "invariant") ;
573 TEVENT (hashCode: GENERATE) ;
574 return value;
575 }
576 //
577 intptr_t ObjectSynchronizer::FastHashCode (Thread * Self, oop obj) {
578 if (UseBiasedLocking) {
579 // NOTE: many places throughout the JVM do not expect a safepoint
580 // to be taken here, in particular most operations on perm gen
581 // objects. However, we only ever bias Java instances and all of
582 // the call sites of identity_hash that might revoke biases have
583 // been checked to make sure they can handle a safepoint. The
584 // added check of the bias pattern is to avoid useless calls to
585 // thread-local storage.
586 if (obj->mark()->has_bias_pattern()) {
587 // Box and unbox the raw reference just in case we cause a STW safepoint.
588 Handle hobj (Self, obj) ;
589 // Relaxing assertion for bug 6320749.
590 assert (Universe::verify_in_progress() ||
591 !SafepointSynchronize::is_at_safepoint(),
592 "biases should not be seen by VM thread here");
593 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
594 obj = hobj() ;
595 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
596 }
597 }
598
599 // hashCode() is a heap mutator ...
600 // Relaxing assertion for bug 6320749.
601 assert (Universe::verify_in_progress() ||
602 !SafepointSynchronize::is_at_safepoint(), "invariant") ;
603 assert (Universe::verify_in_progress() ||
604 Self->is_Java_thread() , "invariant") ;
605 assert (Universe::verify_in_progress() ||
606 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ;
607
608 ObjectMonitor* monitor = NULL;
609 markOop temp, test;
610 intptr_t hash;
611 markOop mark = ReadStableMark (obj);
612
613 // object should remain ineligible for biased locking
614 assert (!mark->has_bias_pattern(), "invariant") ;
615
616 if (mark->is_neutral()) {
617 hash = mark->hash(); // this is a normal header
618 if (hash) { // if it has hash, just return it
619 return hash;
620 }
621 hash = get_next_hash(Self, obj); // allocate a new hash code
622 temp = mark->copy_set_hash(hash); // merge the hash code into header
623 // use (machine word version) atomic operation to install the hash
624 test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark);
625 if (test == mark) {
626 return hash;
627 }
628 // If atomic operation failed, we must inflate the header
629 // into heavy weight monitor. We could add more code here
630 // for fast path, but it does not worth the complexity.
631 } else if (mark->has_monitor()) {
632 monitor = mark->monitor();
633 temp = monitor->header();
634 assert (temp->is_neutral(), "invariant") ;
635 hash = temp->hash();
636 if (hash) {
637 return hash;
638 }
639 // Skip to the following code to reduce code size
640 } else if (Self->is_lock_owned((address)mark->locker())) {
641 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
642 assert (temp->is_neutral(), "invariant") ;
643 hash = temp->hash(); // by current thread, check if the displaced
644 if (hash) { // header contains hash code
645 return hash;
646 }
647 // WARNING:
648 // The displaced header is strictly immutable.
649 // It can NOT be changed in ANY cases. So we have
650 // to inflate the header into heavyweight monitor
651 // even the current thread owns the lock. The reason
652 // is the BasicLock (stack slot) will be asynchronously
653 // read by other threads during the inflate() function.
654 // Any change to stack may not propagate to other threads
655 // correctly.
656 }
657
658 // Inflate the monitor to set hash code
659 monitor = ObjectSynchronizer::inflate(Self, obj);
660 // Load displaced header and check it has hash code
661 mark = monitor->header();
662 assert (mark->is_neutral(), "invariant") ;
663 hash = mark->hash();
664 if (hash == 0) {
665 hash = get_next_hash(Self, obj);
666 temp = mark->copy_set_hash(hash); // merge hash code into header
667 assert (temp->is_neutral(), "invariant") ;
668 test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark);
669 if (test != mark) {
670 // The only update to the header in the monitor (outside GC)
671 // is install the hash code. If someone add new usage of
672 // displaced header, please update this code
673 hash = test->hash();
674 assert (test->is_neutral(), "invariant") ;
675 assert (hash != 0, "Trivial unexpected object/monitor header usage.");
676 }
677 }
678 // We finally get the hash
679 return hash;
680 }
681
682 // Deprecated -- use FastHashCode() instead.
683
684 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
685 return FastHashCode (Thread::current(), obj()) ;
686 }
687
688
689 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
690 Handle h_obj) {
691 if (UseBiasedLocking) {
692 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
693 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
694 }
695
696 assert(thread == JavaThread::current(), "Can only be called on current thread");
697 oop obj = h_obj();
698
699 markOop mark = ReadStableMark (obj) ;
700
701 // Uncontended case, header points to stack
702 if (mark->has_locker()) {
703 return thread->is_lock_owned((address)mark->locker());
704 }
705 // Contended case, header points to ObjectMonitor (tagged pointer)
706 if (mark->has_monitor()) {
707 ObjectMonitor* monitor = mark->monitor();
708 return monitor->is_entered(thread) != 0 ;
709 }
710 // Unlocked case, header in place
711 assert(mark->is_neutral(), "sanity check");
712 return false;
713 }
714
715 // Be aware of this method could revoke bias of the lock object.
716 // This method queries the ownership of the lock handle specified by 'h_obj'.
717 // If the current thread owns the lock, it returns owner_self. If no
718 // thread owns the lock, it returns owner_none. Otherwise, it will return
719 // owner_other.
720 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
721 (JavaThread *self, Handle h_obj) {
722 // The caller must beware this method can revoke bias, and
723 // revocation can result in a safepoint.
724 assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ;
725 assert (self->thread_state() != _thread_blocked , "invariant") ;
726
727 // Possible mark states: neutral, biased, stack-locked, inflated
728
729 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
730 // CASE: biased
731 BiasedLocking::revoke_and_rebias(h_obj, false, self);
732 assert(!h_obj->mark()->has_bias_pattern(),
733 "biases should be revoked by now");
734 }
735
736 assert(self == JavaThread::current(), "Can only be called on current thread");
737 oop obj = h_obj();
738 markOop mark = ReadStableMark (obj) ;
739
740 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
741 if (mark->has_locker()) {
742 return self->is_lock_owned((address)mark->locker()) ?
743 owner_self : owner_other;
744 }
745
746 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
747 // The Object:ObjectMonitor relationship is stable as long as we're
748 // not at a safepoint.
749 if (mark->has_monitor()) {
750 void * owner = mark->monitor()->_owner ;
751 if (owner == NULL) return owner_none ;
752 return (owner == self ||
753 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
754 }
755
756 // CASE: neutral
757 assert(mark->is_neutral(), "sanity check");
758 return owner_none ; // it's unlocked
759 }
760
761 // FIXME: jvmti should call this
762 JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) {
763 if (UseBiasedLocking) {
764 if (SafepointSynchronize::is_at_safepoint()) {
765 BiasedLocking::revoke_at_safepoint(h_obj);
766 } else {
767 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
768 }
769 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
770 }
771
772 oop obj = h_obj();
773 address owner = NULL;
774
775 markOop mark = ReadStableMark (obj) ;
776
777 // Uncontended case, header points to stack
778 if (mark->has_locker()) {
779 owner = (address) mark->locker();
780 }
781
782 // Contended case, header points to ObjectMonitor (tagged pointer)
783 if (mark->has_monitor()) {
784 ObjectMonitor* monitor = mark->monitor();
785 assert(monitor != NULL, "monitor should be non-null");
786 owner = (address) monitor->owner();
787 }
788
789 if (owner != NULL) {
790 // owning_thread_from_monitor_owner() may also return NULL here
791 return Threads::owning_thread_from_monitor_owner(owner, doLock);
792 }
793
794 // Unlocked case, header in place
795 // Cannot have assertion since this object may have been
796 // locked by another thread when reaching here.
797 // assert(mark->is_neutral(), "sanity check");
798
799 return NULL;
800 }
801 // Visitors ...
802
803 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
804 ObjectMonitor* block = gBlockList;
805 ObjectMonitor* mid;
806 while (block) {
807 assert(block->object() == CHAINMARKER, "must be a block header");
808 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
809 mid = block + i;
810 oop object = (oop) mid->object();
811 if (object != NULL) {
812 closure->do_monitor(mid);
813 }
814 }
815 block = (ObjectMonitor*) block->FreeNext;
816 }
817 }
818
819 // Get the next block in the block list.
820 static inline ObjectMonitor* next(ObjectMonitor* block) {
821 assert(block->object() == CHAINMARKER, "must be a block header");
822 block = block->FreeNext ;
823 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
824 return block;
825 }
826
827
828 void ObjectSynchronizer::oops_do(OopClosure* f) {
829 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
830 for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) {
831 assert(block->object() == CHAINMARKER, "must be a block header");
832 for (int i = 1; i < _BLOCKSIZE; i++) {
833 ObjectMonitor* mid = &block[i];
834 if (mid->object() != NULL) {
835 f->do_oop((oop*)mid->object_addr());
836 }
837 }
838 }
839 }
840
841
842 // -----------------------------------------------------------------------------
843 // ObjectMonitor Lifecycle
844 // -----------------------
845 // Inflation unlinks monitors from the global gFreeList and
846 // associates them with objects. Deflation -- which occurs at
847 // STW-time -- disassociates idle monitors from objects. Such
848 // scavenged monitors are returned to the gFreeList.
849 //
850 // The global list is protected by ListLock. All the critical sections
851 // are short and operate in constant-time.
852 //
853 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
854 //
855 // Lifecycle:
856 // -- unassigned and on the global free list
857 // -- unassigned and on a thread's private omFreeList
858 // -- assigned to an object. The object is inflated and the mark refers
859 // to the objectmonitor.
860 //
861
862
863 // Constraining monitor pool growth via MonitorBound ...
864 //
865 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
866 // the rate of scavenging is driven primarily by GC. As such, we can find
867 // an inordinate number of monitors in circulation.
868 // To avoid that scenario we can artificially induce a STW safepoint
869 // if the pool appears to be growing past some reasonable bound.
870 // Generally we favor time in space-time tradeoffs, but as there's no
871 // natural back-pressure on the # of extant monitors we need to impose some
872 // type of limit. Beware that if MonitorBound is set to too low a value
873 // we could just loop. In addition, if MonitorBound is set to a low value
874 // we'll incur more safepoints, which are harmful to performance.
875 // See also: GuaranteedSafepointInterval
876 //
877 // The current implementation uses asynchronous VM operations.
878 //
879
880 static void InduceScavenge (Thread * Self, const char * Whence) {
881 // Induce STW safepoint to trim monitors
882 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
883 // More precisely, trigger an asynchronous STW safepoint as the number
884 // of active monitors passes the specified threshold.
885 // TODO: assert thread state is reasonable
886
887 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
888 if (ObjectMonitor::Knob_Verbose) {
889 ::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ;
890 ::fflush(stdout) ;
891 }
892 // Induce a 'null' safepoint to scavenge monitors
893 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
894 // to the VMthread and have a lifespan longer than that of this activation record.
895 // The VMThread will delete the op when completed.
896 VMThread::execute (new VM_ForceAsyncSafepoint()) ;
897
898 if (ObjectMonitor::Knob_Verbose) {
899 ::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ;
900 ::fflush(stdout) ;
901 }
902 }
903 }
904 /* Too slow for general assert or debug
905 void ObjectSynchronizer::verifyInUse (Thread *Self) {
906 ObjectMonitor* mid;
907 int inusetally = 0;
908 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) {
909 inusetally ++;
910 }
911 assert(inusetally == Self->omInUseCount, "inuse count off");
912
913 int freetally = 0;
914 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) {
915 freetally ++;
916 }
917 assert(freetally == Self->omFreeCount, "free count off");
918 }
919 */
920 ObjectMonitor * ATTR ObjectSynchronizer::omAlloc (Thread * Self) {
921 // A large MAXPRIVATE value reduces both list lock contention
922 // and list coherency traffic, but also tends to increase the
923 // number of objectMonitors in circulation as well as the STW
924 // scavenge costs. As usual, we lean toward time in space-time
925 // tradeoffs.
926 const int MAXPRIVATE = 1024 ;
927 for (;;) {
928 ObjectMonitor * m ;
929
930 // 1: try to allocate from the thread's local omFreeList.
931 // Threads will attempt to allocate first from their local list, then
932 // from the global list, and only after those attempts fail will the thread
933 // attempt to instantiate new monitors. Thread-local free lists take
934 // heat off the ListLock and improve allocation latency, as well as reducing
935 // coherency traffic on the shared global list.
936 m = Self->omFreeList ;
937 if (m != NULL) {
938 Self->omFreeList = m->FreeNext ;
939 Self->omFreeCount -- ;
940 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene
941 guarantee (m->object() == NULL, "invariant") ;
942 if (MonitorInUseLists) {
943 m->FreeNext = Self->omInUseList;
944 Self->omInUseList = m;
945 Self->omInUseCount ++;
946 // verifyInUse(Self);
947 } else {
948 m->FreeNext = NULL;
949 }
950 return m ;
951 }
952
953 // 2: try to allocate from the global gFreeList
954 // CONSIDER: use muxTry() instead of muxAcquire().
955 // If the muxTry() fails then drop immediately into case 3.
956 // If we're using thread-local free lists then try
957 // to reprovision the caller's free list.
958 if (gFreeList != NULL) {
959 // Reprovision the thread's omFreeList.
960 // Use bulk transfers to reduce the allocation rate and heat
961 // on various locks.
962 Thread::muxAcquire (&ListLock, "omAlloc") ;
963 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL; ) {
964 MonitorFreeCount --;
965 ObjectMonitor * take = gFreeList ;
966 gFreeList = take->FreeNext ;
967 guarantee (take->object() == NULL, "invariant") ;
968 guarantee (!take->is_busy(), "invariant") ;
969 take->Recycle() ;
970 omRelease (Self, take, false) ;
971 }
972 Thread::muxRelease (&ListLock) ;
973 Self->omFreeProvision += 1 + (Self->omFreeProvision/2) ;
974 if (Self->omFreeProvision > MAXPRIVATE ) Self->omFreeProvision = MAXPRIVATE ;
975 TEVENT (omFirst - reprovision) ;
976
977 const int mx = MonitorBound ;
978 if (mx > 0 && (MonitorPopulation-MonitorFreeCount) > mx) {
979 // We can't safely induce a STW safepoint from omAlloc() as our thread
980 // state may not be appropriate for such activities and callers may hold
981 // naked oops, so instead we defer the action.
982 InduceScavenge (Self, "omAlloc") ;
983 }
984 continue;
985 }
986
987 // 3: allocate a block of new ObjectMonitors
988 // Both the local and global free lists are empty -- resort to malloc().
989 // In the current implementation objectMonitors are TSM - immortal.
990 assert (_BLOCKSIZE > 1, "invariant") ;
991 ObjectMonitor * temp = new ObjectMonitor[_BLOCKSIZE];
992
993 // NOTE: (almost) no way to recover if allocation failed.
994 // We might be able to induce a STW safepoint and scavenge enough
995 // objectMonitors to permit progress.
996 if (temp == NULL) {
997 vm_exit_out_of_memory (sizeof (ObjectMonitor[_BLOCKSIZE]), OOM_MALLOC_ERROR,
998 "Allocate ObjectMonitors");
999 }
1000
1001 // Format the block.
1002 // initialize the linked list, each monitor points to its next
1003 // forming the single linked free list, the very first monitor
1004 // will points to next block, which forms the block list.
1005 // The trick of using the 1st element in the block as gBlockList
1006 // linkage should be reconsidered. A better implementation would
1007 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1008
1009 for (int i = 1; i < _BLOCKSIZE ; i++) {
1010 temp[i].FreeNext = &temp[i+1];
1011 }
1012
1013 // terminate the last monitor as the end of list
1014 temp[_BLOCKSIZE - 1].FreeNext = NULL ;
1015
1016 // Element [0] is reserved for global list linkage
1017 temp[0].set_object(CHAINMARKER);
1018
1019 // Consider carving out this thread's current request from the
1020 // block in hand. This avoids some lock traffic and redundant
1021 // list activity.
1022
1023 // Acquire the ListLock to manipulate BlockList and FreeList.
1024 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1025 Thread::muxAcquire (&ListLock, "omAlloc [2]") ;
1026 MonitorPopulation += _BLOCKSIZE-1;
1027 MonitorFreeCount += _BLOCKSIZE-1;
1028
1029 // Add the new block to the list of extant blocks (gBlockList).
1030 // The very first objectMonitor in a block is reserved and dedicated.
1031 // It serves as blocklist "next" linkage.
1032 temp[0].FreeNext = gBlockList;
1033 gBlockList = temp;
1034
1035 // Add the new string of objectMonitors to the global free list
1036 temp[_BLOCKSIZE - 1].FreeNext = gFreeList ;
1037 gFreeList = temp + 1;
1038 Thread::muxRelease (&ListLock) ;
1039 TEVENT (Allocate block of monitors) ;
1040 }
1041 }
1042
1043 // Place "m" on the caller's private per-thread omFreeList.
1044 // In practice there's no need to clamp or limit the number of
1045 // monitors on a thread's omFreeList as the only time we'll call
1046 // omRelease is to return a monitor to the free list after a CAS
1047 // attempt failed. This doesn't allow unbounded #s of monitors to
1048 // accumulate on a thread's free list.
1049 //
1050
1051 void ObjectSynchronizer::omRelease (Thread * Self, ObjectMonitor * m, bool fromPerThreadAlloc) {
1052 guarantee (m->object() == NULL, "invariant") ;
1053
1054 // Remove from omInUseList
1055 if (MonitorInUseLists && fromPerThreadAlloc) {
1056 ObjectMonitor* curmidinuse = NULL;
1057 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; ) {
1058 if (m == mid) {
1059 // extract from per-thread in-use-list
1060 if (mid == Self->omInUseList) {
1061 Self->omInUseList = mid->FreeNext;
1062 } else if (curmidinuse != NULL) {
1063 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1064 }
1065 Self->omInUseCount --;
1066 // verifyInUse(Self);
1067 break;
1068 } else {
1069 curmidinuse = mid;
1070 mid = mid->FreeNext;
1071 }
1072 }
1073 }
1074
1075 // FreeNext is used for both onInUseList and omFreeList, so clear old before setting new
1076 m->FreeNext = Self->omFreeList ;
1077 Self->omFreeList = m ;
1078 Self->omFreeCount ++ ;
1079 }
1080
1081 // Return the monitors of a moribund thread's local free list to
1082 // the global free list. Typically a thread calls omFlush() when
1083 // it's dying. We could also consider having the VM thread steal
1084 // monitors from threads that have not run java code over a few
1085 // consecutive STW safepoints. Relatedly, we might decay
1086 // omFreeProvision at STW safepoints.
1087 //
1088 // Also return the monitors of a moribund thread"s omInUseList to
1089 // a global gOmInUseList under the global list lock so these
1090 // will continue to be scanned.
1091 //
1092 // We currently call omFlush() from the Thread:: dtor _after the thread
1093 // has been excised from the thread list and is no longer a mutator.
1094 // That means that omFlush() can run concurrently with a safepoint and
1095 // the scavenge operator. Calling omFlush() from JavaThread::exit() might
1096 // be a better choice as we could safely reason that that the JVM is
1097 // not at a safepoint at the time of the call, and thus there could
1098 // be not inopportune interleavings between omFlush() and the scavenge
1099 // operator.
1100
1101 void ObjectSynchronizer::omFlush (Thread * Self) {
1102 ObjectMonitor * List = Self->omFreeList ; // Null-terminated SLL
1103 Self->omFreeList = NULL ;
1104 ObjectMonitor * Tail = NULL ;
1105 int Tally = 0;
1106 if (List != NULL) {
1107 ObjectMonitor * s ;
1108 for (s = List ; s != NULL ; s = s->FreeNext) {
1109 Tally ++ ;
1110 Tail = s ;
1111 guarantee (s->object() == NULL, "invariant") ;
1112 guarantee (!s->is_busy(), "invariant") ;
1113 s->set_owner (NULL) ; // redundant but good hygiene
1114 TEVENT (omFlush - Move one) ;
1115 }
1116 guarantee (Tail != NULL && List != NULL, "invariant") ;
1117 }
1118
1119 ObjectMonitor * InUseList = Self->omInUseList;
1120 ObjectMonitor * InUseTail = NULL ;
1121 int InUseTally = 0;
1122 if (InUseList != NULL) {
1123 Self->omInUseList = NULL;
1124 ObjectMonitor *curom;
1125 for (curom = InUseList; curom != NULL; curom = curom->FreeNext) {
1126 InUseTail = curom;
1127 InUseTally++;
1128 }
1129 // TODO debug
1130 assert(Self->omInUseCount == InUseTally, "inuse count off");
1131 Self->omInUseCount = 0;
1132 guarantee (InUseTail != NULL && InUseList != NULL, "invariant");
1133 }
1134
1135 Thread::muxAcquire (&ListLock, "omFlush") ;
1136 if (Tail != NULL) {
1137 Tail->FreeNext = gFreeList ;
1138 gFreeList = List ;
1139 MonitorFreeCount += Tally;
1140 }
1141
1142 if (InUseTail != NULL) {
1143 InUseTail->FreeNext = gOmInUseList;
1144 gOmInUseList = InUseList;
1145 gOmInUseCount += InUseTally;
1146 }
1147
1148 Thread::muxRelease (&ListLock) ;
1149 TEVENT (omFlush) ;
1150 }
1151
1152 // Fast path code shared by multiple functions
1153 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1154 markOop mark = obj->mark();
1155 if (mark->has_monitor()) {
1156 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1157 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1158 return mark->monitor();
1159 }
1160 return ObjectSynchronizer::inflate(Thread::current(), obj);
1161 }
1162
1163
1164 // Note that we could encounter some performance loss through false-sharing as
1165 // multiple locks occupy the same $ line. Padding might be appropriate.
1166
1167
1168 ObjectMonitor * ATTR ObjectSynchronizer::inflate (Thread * Self, oop object) {
1169 // Inflate mutates the heap ...
1170 // Relaxing assertion for bug 6320749.
1171 assert (Universe::verify_in_progress() ||
1172 !SafepointSynchronize::is_at_safepoint(), "invariant") ;
1173
1174 for (;;) {
1175 const markOop mark = object->mark() ;
1176 assert (!mark->has_bias_pattern(), "invariant") ;
1177
1178 // The mark can be in one of the following states:
1179 // * Inflated - just return
1180 // * Stack-locked - coerce it to inflated
1181 // * INFLATING - busy wait for conversion to complete
1182 // * Neutral - aggressively inflate the object.
1183 // * BIASED - Illegal. We should never see this
1184
1185 // CASE: inflated
1186 if (mark->has_monitor()) {
1187 ObjectMonitor * inf = mark->monitor() ;
1188 assert (inf->header()->is_neutral(), "invariant");
1189 assert (inf->object() == object, "invariant") ;
1190 assert (ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1191 return inf ;
1192 }
1193
1194 // CASE: inflation in progress - inflating over a stack-lock.
1195 // Some other thread is converting from stack-locked to inflated.
1196 // Only that thread can complete inflation -- other threads must wait.
1197 // The INFLATING value is transient.
1198 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1199 // We could always eliminate polling by parking the thread on some auxiliary list.
1200 if (mark == markOopDesc::INFLATING()) {
1201 TEVENT (Inflate: spin while INFLATING) ;
1202 ReadStableMark(object) ;
1203 continue ;
1204 }
1205
1206 // CASE: stack-locked
1207 // Could be stack-locked either by this thread or by some other thread.
1208 //
1209 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1210 // to install INFLATING into the mark word. We originally installed INFLATING,
1211 // allocated the objectmonitor, and then finally STed the address of the
1212 // objectmonitor into the mark. This was correct, but artificially lengthened
1213 // the interval in which INFLATED appeared in the mark, thus increasing
1214 // the odds of inflation contention.
1215 //
1216 // We now use per-thread private objectmonitor free lists.
1217 // These list are reprovisioned from the global free list outside the
1218 // critical INFLATING...ST interval. A thread can transfer
1219 // multiple objectmonitors en-mass from the global free list to its local free list.
1220 // This reduces coherency traffic and lock contention on the global free list.
1221 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1222 // before or after the CAS(INFLATING) operation.
1223 // See the comments in omAlloc().
1224
1225 if (mark->has_locker()) {
1226 ObjectMonitor * m = omAlloc (Self) ;
1227 // Optimistically prepare the objectmonitor - anticipate successful CAS
1228 // We do this before the CAS in order to minimize the length of time
1229 // in which INFLATING appears in the mark.
1230 m->Recycle();
1231 m->_Responsible = NULL ;
1232 m->OwnerIsThread = 0 ;
1233 m->_recursions = 0 ;
1234 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // Consider: maintain by type/class
1235
1236 markOop cmp = (markOop) Atomic::cmpxchg_ptr (markOopDesc::INFLATING(), object->mark_addr(), mark) ;
1237 if (cmp != mark) {
1238 omRelease (Self, m, true) ;
1239 continue ; // Interference -- just retry
1240 }
1241
1242 // We've successfully installed INFLATING (0) into the mark-word.
1243 // This is the only case where 0 will appear in a mark-work.
1244 // Only the singular thread that successfully swings the mark-word
1245 // to 0 can perform (or more precisely, complete) inflation.
1246 //
1247 // Why do we CAS a 0 into the mark-word instead of just CASing the
1248 // mark-word from the stack-locked value directly to the new inflated state?
1249 // Consider what happens when a thread unlocks a stack-locked object.
1250 // It attempts to use CAS to swing the displaced header value from the
1251 // on-stack basiclock back into the object header. Recall also that the
1252 // header value (hashcode, etc) can reside in (a) the object header, or
1253 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1254 // header in an objectMonitor. The inflate() routine must copy the header
1255 // value from the basiclock on the owner's stack to the objectMonitor, all
1256 // the while preserving the hashCode stability invariants. If the owner
1257 // decides to release the lock while the value is 0, the unlock will fail
1258 // and control will eventually pass from slow_exit() to inflate. The owner
1259 // will then spin, waiting for the 0 value to disappear. Put another way,
1260 // the 0 causes the owner to stall if the owner happens to try to
1261 // drop the lock (restoring the header from the basiclock to the object)
1262 // while inflation is in-progress. This protocol avoids races that might
1263 // would otherwise permit hashCode values to change or "flicker" for an object.
1264 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1265 // 0 serves as a "BUSY" inflate-in-progress indicator.
1266
1267
1268 // fetch the displaced mark from the owner's stack.
1269 // The owner can't die or unwind past the lock while our INFLATING
1270 // object is in the mark. Furthermore the owner can't complete
1271 // an unlock on the object, either.
1272 markOop dmw = mark->displaced_mark_helper() ;
1273 assert (dmw->is_neutral(), "invariant") ;
1274
1275 // Setup monitor fields to proper values -- prepare the monitor
1276 m->set_header(dmw) ;
1277
1278 // Optimization: if the mark->locker stack address is associated
1279 // with this thread we could simply set m->_owner = Self and
1280 // m->OwnerIsThread = 1. Note that a thread can inflate an object
1281 // that it has stack-locked -- as might happen in wait() -- directly
1282 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1283 m->set_owner(mark->locker());
1284 m->set_object(object);
1285 // TODO-FIXME: assert BasicLock->dhw != 0.
1286
1287 // Must preserve store ordering. The monitor state must
1288 // be stable at the time of publishing the monitor address.
1289 guarantee (object->mark() == markOopDesc::INFLATING(), "invariant") ;
1290 object->release_set_mark(markOopDesc::encode(m));
1291
1292 // Hopefully the performance counters are allocated on distinct cache lines
1293 // to avoid false sharing on MP systems ...
1294 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ;
1295 TEVENT(Inflate: overwrite stacklock) ;
1296 if (TraceMonitorInflation) {
1297 if (object->is_instance()) {
1298 ResourceMark rm;
1299 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1300 (void *) object, (intptr_t) object->mark(),
1301 object->klass()->external_name());
1302 }
1303 }
1304 return m ;
1305 }
1306
1307 // CASE: neutral
1308 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1309 // If we know we're inflating for entry it's better to inflate by swinging a
1310 // pre-locked objectMonitor pointer into the object header. A successful
1311 // CAS inflates the object *and* confers ownership to the inflating thread.
1312 // In the current implementation we use a 2-step mechanism where we CAS()
1313 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1314 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1315 // would be useful.
1316
1317 assert (mark->is_neutral(), "invariant");
1318 ObjectMonitor * m = omAlloc (Self) ;
1319 // prepare m for installation - set monitor to initial state
1320 m->Recycle();
1321 m->set_header(mark);
1322 m->set_owner(NULL);
1323 m->set_object(object);
1324 m->OwnerIsThread = 1 ;
1325 m->_recursions = 0 ;
1326 m->_Responsible = NULL ;
1327 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // consider: keep metastats by type/class
1328
1329 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) {
1330 m->set_object (NULL) ;
1331 m->set_owner (NULL) ;
1332 m->OwnerIsThread = 0 ;
1333 m->Recycle() ;
1334 omRelease (Self, m, true) ;
1335 m = NULL ;
1336 continue ;
1337 // interference - the markword changed - just retry.
1338 // The state-transitions are one-way, so there's no chance of
1339 // live-lock -- "Inflated" is an absorbing state.
1340 }
1341
1342 // Hopefully the performance counters are allocated on distinct
1343 // cache lines to avoid false sharing on MP systems ...
1344 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ;
1345 TEVENT(Inflate: overwrite neutral) ;
1346 if (TraceMonitorInflation) {
1347 if (object->is_instance()) {
1348 ResourceMark rm;
1349 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1350 (void *) object, (intptr_t) object->mark(),
1351 object->klass()->external_name());
1352 }
1353 }
1354 return m ;
1355 }
1356 }
1357
1358 // Note that we could encounter some performance loss through false-sharing as
1359 // multiple locks occupy the same $ line. Padding might be appropriate.
1360
1361
1362 // Deflate_idle_monitors() is called at all safepoints, immediately
1363 // after all mutators are stopped, but before any objects have moved.
1364 // It traverses the list of known monitors, deflating where possible.
1365 // The scavenged monitor are returned to the monitor free list.
1366 //
1367 // Beware that we scavenge at *every* stop-the-world point.
1368 // Having a large number of monitors in-circulation negatively
1369 // impacts the performance of some applications (e.g., PointBase).
1370 // Broadly, we want to minimize the # of monitors in circulation.
1371 //
1372 // We have added a flag, MonitorInUseLists, which creates a list
1373 // of active monitors for each thread. deflate_idle_monitors()
1374 // only scans the per-thread inuse lists. omAlloc() puts all
1375 // assigned monitors on the per-thread list. deflate_idle_monitors()
1376 // returns the non-busy monitors to the global free list.
1377 // When a thread dies, omFlush() adds the list of active monitors for
1378 // that thread to a global gOmInUseList acquiring the
1379 // global list lock. deflate_idle_monitors() acquires the global
1380 // list lock to scan for non-busy monitors to the global free list.
1381 // An alternative could have used a single global inuse list. The
1382 // downside would have been the additional cost of acquiring the global list lock
1383 // for every omAlloc().
1384 //
1385 // Perversely, the heap size -- and thus the STW safepoint rate --
1386 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1387 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1388 // This is an unfortunate aspect of this design.
1389 //
1390
1391 enum ManifestConstants {
1392 ClearResponsibleAtSTW = 0,
1393 MaximumRecheckInterval = 1000
1394 } ;
1395
1396 // Deflate a single monitor if not in use
1397 // Return true if deflated, false if in use
1398 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1399 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) {
1400 bool deflated;
1401 // Normal case ... The monitor is associated with obj.
1402 guarantee (obj->mark() == markOopDesc::encode(mid), "invariant") ;
1403 guarantee (mid == obj->mark()->monitor(), "invariant");
1404 guarantee (mid->header()->is_neutral(), "invariant");
1405
1406 if (mid->is_busy()) {
1407 if (ClearResponsibleAtSTW) mid->_Responsible = NULL ;
1408 deflated = false;
1409 } else {
1410 // Deflate the monitor if it is no longer being used
1411 // It's idle - scavenge and return to the global free list
1412 // plain old deflation ...
1413 TEVENT (deflate_idle_monitors - scavenge1) ;
1414 if (TraceMonitorInflation) {
1415 if (obj->is_instance()) {
1416 ResourceMark rm;
1417 tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1418 (void *) obj, (intptr_t) obj->mark(), obj->klass()->external_name());
1419 }
1420 }
1421
1422 // Restore the header back to obj
1423 obj->release_set_mark(mid->header());
1424 mid->clear();
1425
1426 assert (mid->object() == NULL, "invariant") ;
1427
1428 // Move the object to the working free list defined by FreeHead,FreeTail.
1429 if (*FreeHeadp == NULL) *FreeHeadp = mid;
1430 if (*FreeTailp != NULL) {
1431 ObjectMonitor * prevtail = *FreeTailp;
1432 assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); // TODO KK
1433 prevtail->FreeNext = mid;
1434 }
1435 *FreeTailp = mid;
1436 deflated = true;
1437 }
1438 return deflated;
1439 }
1440
1441 // Caller acquires ListLock
1442 int ObjectSynchronizer::walk_monitor_list(ObjectMonitor** listheadp,
1443 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) {
1444 ObjectMonitor* mid;
1445 ObjectMonitor* next;
1446 ObjectMonitor* curmidinuse = NULL;
1447 int deflatedcount = 0;
1448
1449 for (mid = *listheadp; mid != NULL; ) {
1450 oop obj = (oop) mid->object();
1451 bool deflated = false;
1452 if (obj != NULL) {
1453 deflated = deflate_monitor(mid, obj, FreeHeadp, FreeTailp);
1454 }
1455 if (deflated) {
1456 // extract from per-thread in-use-list
1457 if (mid == *listheadp) {
1458 *listheadp = mid->FreeNext;
1459 } else if (curmidinuse != NULL) {
1460 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist
1461 }
1462 next = mid->FreeNext;
1463 mid->FreeNext = NULL; // This mid is current tail in the FreeHead list
1464 mid = next;
1465 deflatedcount++;
1466 } else {
1467 curmidinuse = mid;
1468 mid = mid->FreeNext;
1469 }
1470 }
1471 return deflatedcount;
1472 }
1473
1474 void ObjectSynchronizer::deflate_idle_monitors() {
1475 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1476 int nInuse = 0 ; // currently associated with objects
1477 int nInCirculation = 0 ; // extant
1478 int nScavenged = 0 ; // reclaimed
1479 bool deflated = false;
1480
1481 ObjectMonitor * FreeHead = NULL ; // Local SLL of scavenged monitors
1482 ObjectMonitor * FreeTail = NULL ;
1483
1484 TEVENT (deflate_idle_monitors) ;
1485 // Prevent omFlush from changing mids in Thread dtor's during deflation
1486 // And in case the vm thread is acquiring a lock during a safepoint
1487 // See e.g. 6320749
1488 Thread::muxAcquire (&ListLock, "scavenge - return") ;
1489
1490 if (MonitorInUseLists) {
1491 int inUse = 0;
1492 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) {
1493 nInCirculation+= cur->omInUseCount;
1494 int deflatedcount = walk_monitor_list(cur->omInUseList_addr(), &FreeHead, &FreeTail);
1495 cur->omInUseCount-= deflatedcount;
1496 // verifyInUse(cur);
1497 nScavenged += deflatedcount;
1498 nInuse += cur->omInUseCount;
1499 }
1500
1501 // For moribund threads, scan gOmInUseList
1502 if (gOmInUseList) {
1503 nInCirculation += gOmInUseCount;
1504 int deflatedcount = walk_monitor_list((ObjectMonitor **)&gOmInUseList, &FreeHead, &FreeTail);
1505 gOmInUseCount-= deflatedcount;
1506 nScavenged += deflatedcount;
1507 nInuse += gOmInUseCount;
1508 }
1509
1510 } else for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) {
1511 // Iterate over all extant monitors - Scavenge all idle monitors.
1512 assert(block->object() == CHAINMARKER, "must be a block header");
1513 nInCirculation += _BLOCKSIZE ;
1514 for (int i = 1 ; i < _BLOCKSIZE; i++) {
1515 ObjectMonitor* mid = &block[i];
1516 oop obj = (oop) mid->object();
1517
1518 if (obj == NULL) {
1519 // The monitor is not associated with an object.
1520 // The monitor should either be a thread-specific private
1521 // free list or the global free list.
1522 // obj == NULL IMPLIES mid->is_busy() == 0
1523 guarantee (!mid->is_busy(), "invariant") ;
1524 continue ;
1525 }
1526 deflated = deflate_monitor(mid, obj, &FreeHead, &FreeTail);
1527
1528 if (deflated) {
1529 mid->FreeNext = NULL ;
1530 nScavenged ++ ;
1531 } else {
1532 nInuse ++;
1533 }
1534 }
1535 }
1536
1537 MonitorFreeCount += nScavenged;
1538
1539 // Consider: audit gFreeList to ensure that MonitorFreeCount and list agree.
1540
1541 if (ObjectMonitor::Knob_Verbose) {
1542 ::printf ("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n",
1543 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge,
1544 MonitorPopulation, MonitorFreeCount) ;
1545 ::fflush(stdout) ;
1546 }
1547
1548 ForceMonitorScavenge = 0; // Reset
1549
1550 // Move the scavenged monitors back to the global free list.
1551 if (FreeHead != NULL) {
1552 guarantee (FreeTail != NULL && nScavenged > 0, "invariant") ;
1553 assert (FreeTail->FreeNext == NULL, "invariant") ;
1554 // constant-time list splice - prepend scavenged segment to gFreeList
1555 FreeTail->FreeNext = gFreeList ;
1556 gFreeList = FreeHead ;
1557 }
1558 Thread::muxRelease (&ListLock) ;
1559
1560 if (ObjectMonitor::_sync_Deflations != NULL) ObjectMonitor::_sync_Deflations->inc(nScavenged) ;
1561 if (ObjectMonitor::_sync_MonExtant != NULL) ObjectMonitor::_sync_MonExtant ->set_value(nInCirculation);
1562
1563 // TODO: Add objectMonitor leak detection.
1564 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1565 GVars.stwRandom = os::random() ;
1566 GVars.stwCycle ++ ;
1567 }
1568
1569 // Monitor cleanup on JavaThread::exit
1570
1571 // Iterate through monitor cache and attempt to release thread's monitors
1572 // Gives up on a particular monitor if an exception occurs, but continues
1573 // the overall iteration, swallowing the exception.
1574 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1575 private:
1576 TRAPS;
1577
1578 public:
1579 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1580 void do_monitor(ObjectMonitor* mid) {
1581 if (mid->owner() == THREAD) {
1582 (void)mid->complete_exit(CHECK);
1583 }
1584 }
1585 };
1586
1587 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1588 // ignored. This is meant to be called during JNI thread detach which assumes
1589 // all remaining monitors are heavyweight. All exceptions are swallowed.
1590 // Scanning the extant monitor list can be time consuming.
1591 // A simple optimization is to add a per-thread flag that indicates a thread
1592 // called jni_monitorenter() during its lifetime.
1593 //
1594 // Instead of No_Savepoint_Verifier it might be cheaper to
1595 // use an idiom of the form:
1596 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1597 // <code that must not run at safepoint>
1598 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1599 // Since the tests are extremely cheap we could leave them enabled
1600 // for normal product builds.
1601
1602 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1603 assert(THREAD == JavaThread::current(), "must be current Java thread");
1604 No_Safepoint_Verifier nsv ;
1605 ReleaseJavaMonitorsClosure rjmc(THREAD);
1606 Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread");
1607 ObjectSynchronizer::monitors_iterate(&rjmc);
1608 Thread::muxRelease(&ListLock);
1609 THREAD->clear_pending_exception();
1610 }
1611
1612 //------------------------------------------------------------------------------
1613 // Non-product code
1614
1615 #ifndef PRODUCT
1616
1617 // Verify all monitors in the monitor cache, the verification is weak.
1618 void ObjectSynchronizer::verify() {
1619 ObjectMonitor* block = gBlockList;
1620 ObjectMonitor* mid;
1621 while (block) {
1622 assert(block->object() == CHAINMARKER, "must be a block header");
1623 for (int i = 1; i < _BLOCKSIZE; i++) {
1624 mid = block + i;
1625 oop object = (oop) mid->object();
1626 if (object != NULL) {
1627 mid->verify();
1628 }
1629 }
1630 block = (ObjectMonitor*) block->FreeNext;
1631 }
1632 }
1633
1634 // Check if monitor belongs to the monitor cache
1635 // The list is grow-only so it's *relatively* safe to traverse
1636 // the list of extant blocks without taking a lock.
1637
1638 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
1639 ObjectMonitor* block = gBlockList;
1640
1641 while (block) {
1642 assert(block->object() == CHAINMARKER, "must be a block header");
1643 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
1644 address mon = (address) monitor;
1645 address blk = (address) block;
1646 size_t diff = mon - blk;
1647 assert((diff % sizeof(ObjectMonitor)) == 0, "check");
1648 return 1;
1649 }
1650 block = (ObjectMonitor*) block->FreeNext;
1651 }
1652 return 0;
1653 }
1654
1655 #endif