1 /*
2 * Copyright (c) 1998, 2018, 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 "logging/log.hpp"
28 #include "jfr/jfrEvents.hpp"
29 #include "memory/allocation.inline.hpp"
30 #include "memory/metaspaceShared.hpp"
31 #include "memory/padded.hpp"
32 #include "memory/resourceArea.hpp"
33 #include "oops/markOop.hpp"
34 #include "oops/oop.inline.hpp"
35 #include "runtime/atomic.hpp"
36 #include "runtime/biasedLocking.hpp"
37 #include "runtime/handles.inline.hpp"
38 #include "runtime/interfaceSupport.inline.hpp"
39 #include "runtime/mutexLocker.hpp"
40 #include "runtime/objectMonitor.hpp"
41 #include "runtime/objectMonitor.inline.hpp"
42 #include "runtime/osThread.hpp"
43 #include "runtime/safepointVerifiers.hpp"
44 #include "runtime/sharedRuntime.hpp"
45 #include "runtime/stubRoutines.hpp"
46 #include "runtime/synchronizer.hpp"
47 #include "runtime/thread.inline.hpp"
48 #include "runtime/vframe.hpp"
49 #include "runtime/vmThread.hpp"
50 #include "utilities/align.hpp"
51 #include "utilities/dtrace.hpp"
52 #include "utilities/events.hpp"
53 #include "utilities/preserveException.hpp"
54
55 // The "core" versions of monitor enter and exit reside in this file.
56 // The interpreter and compilers contain specialized transliterated
57 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
58 // for instance. If you make changes here, make sure to modify the
59 // interpreter, and both C1 and C2 fast-path inline locking code emission.
60 //
61 // -----------------------------------------------------------------------------
62
63 #ifdef DTRACE_ENABLED
64
65 // Only bother with this argument setup if dtrace is available
66 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
67
68 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
69 char* bytes = NULL; \
70 int len = 0; \
71 jlong jtid = SharedRuntime::get_java_tid(thread); \
72 Symbol* klassname = ((oop)(obj))->klass()->name(); \
73 if (klassname != NULL) { \
74 bytes = (char*)klassname->bytes(); \
75 len = klassname->utf8_length(); \
76 }
77
78 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
79 { \
80 if (DTraceMonitorProbes) { \
81 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
82 HOTSPOT_MONITOR_WAIT(jtid, \
83 (uintptr_t)(monitor), bytes, len, (millis)); \
84 } \
85 }
86
87 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
88 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
89 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
90
91 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
92 { \
93 if (DTraceMonitorProbes) { \
94 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
95 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
96 (uintptr_t)(monitor), bytes, len); \
97 } \
98 }
99
100 #else // ndef DTRACE_ENABLED
101
102 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
103 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
104
105 #endif // ndef DTRACE_ENABLED
106
107 // This exists only as a workaround of dtrace bug 6254741
108 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
109 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
110 return 0;
111 }
112
113 #define NINFLATIONLOCKS 256
114 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
115
116 // global list of blocks of monitors
117 PaddedEnd<ObjectMonitor> * volatile ObjectSynchronizer::gBlockList = NULL;
118 // global monitor free list
119 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL;
120 // global monitor in-use list, for moribund threads,
121 // monitors they inflated need to be scanned for deflation
122 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL;
123 // count of entries in gOmInUseList
124 int ObjectSynchronizer::gOmInUseCount = 0;
125
126 static volatile intptr_t gListLock = 0; // protects global monitor lists
127 static volatile int gMonitorFreeCount = 0; // # on gFreeList
128 static volatile int gMonitorPopulation = 0; // # Extant -- in circulation
129
130 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
131
132
133 // =====================> Quick functions
134
135 // The quick_* forms are special fast-path variants used to improve
136 // performance. In the simplest case, a "quick_*" implementation could
137 // simply return false, in which case the caller will perform the necessary
138 // state transitions and call the slow-path form.
139 // The fast-path is designed to handle frequently arising cases in an efficient
140 // manner and is just a degenerate "optimistic" variant of the slow-path.
141 // returns true -- to indicate the call was satisfied.
142 // returns false -- to indicate the call needs the services of the slow-path.
143 // A no-loitering ordinance is in effect for code in the quick_* family
144 // operators: safepoints or indefinite blocking (blocking that might span a
145 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
146 // entry.
147 //
148 // Consider: An interesting optimization is to have the JIT recognize the
149 // following common idiom:
150 // synchronized (someobj) { .... ; notify(); }
151 // That is, we find a notify() or notifyAll() call that immediately precedes
152 // the monitorexit operation. In that case the JIT could fuse the operations
153 // into a single notifyAndExit() runtime primitive.
154
155 bool ObjectSynchronizer::quick_notify(oopDesc * obj, Thread * self, bool all) {
156 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
157 assert(self->is_Java_thread(), "invariant");
158 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
159 NoSafepointVerifier nsv;
160 if (obj == NULL) return false; // slow-path for invalid obj
161 const markOop mark = obj->mark();
162
163 if (mark->has_locker() && self->is_lock_owned((address)mark->locker())) {
164 // Degenerate notify
165 // stack-locked by caller so by definition the implied waitset is empty.
166 return true;
167 }
168
169 if (mark->has_monitor()) {
170 ObjectMonitor * const mon = mark->monitor();
171 assert(oopDesc::equals((oop) mon->object(), obj), "invariant");
172 if (mon->owner() != self) return false; // slow-path for IMS exception
173
174 if (mon->first_waiter() != NULL) {
175 // We have one or more waiters. Since this is an inflated monitor
176 // that we own, we can transfer one or more threads from the waitset
177 // to the entrylist here and now, avoiding the slow-path.
178 if (all) {
179 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
180 } else {
181 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
182 }
183 int tally = 0;
184 do {
185 mon->INotify(self);
186 ++tally;
187 } while (mon->first_waiter() != NULL && all);
188 OM_PERFDATA_OP(Notifications, inc(tally));
189 }
190 return true;
191 }
192
193 // biased locking and any other IMS exception states take the slow-path
194 return false;
195 }
196
197
198 // The LockNode emitted directly at the synchronization site would have
199 // been too big if it were to have included support for the cases of inflated
200 // recursive enter and exit, so they go here instead.
201 // Note that we can't safely call AsyncPrintJavaStack() from within
202 // quick_enter() as our thread state remains _in_Java.
203
204 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
205 BasicLock * lock) {
206 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
207 assert(Self->is_Java_thread(), "invariant");
208 assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
209 NoSafepointVerifier nsv;
210 if (obj == NULL) return false; // Need to throw NPE
211 const markOop mark = obj->mark();
212
213 if (mark->has_monitor()) {
214 ObjectMonitor * const m = mark->monitor();
215 assert(oopDesc::equals((oop) m->object(), obj), "invariant");
216 Thread * const owner = (Thread *) m->_owner;
217
218 // Lock contention and Transactional Lock Elision (TLE) diagnostics
219 // and observability
220 // Case: light contention possibly amenable to TLE
221 // Case: TLE inimical operations such as nested/recursive synchronization
222
223 if (owner == Self) {
224 m->_recursions++;
225 return true;
226 }
227
228 // This Java Monitor is inflated so obj's header will never be
229 // displaced to this thread's BasicLock. Make the displaced header
230 // non-NULL so this BasicLock is not seen as recursive nor as
231 // being locked. We do this unconditionally so that this thread's
232 // BasicLock cannot be mis-interpreted by any stack walkers. For
233 // performance reasons, stack walkers generally first check for
234 // Biased Locking in the object's header, the second check is for
235 // stack-locking in the object's header, the third check is for
236 // recursive stack-locking in the displaced header in the BasicLock,
237 // and last are the inflated Java Monitor (ObjectMonitor) checks.
238 lock->set_displaced_header(markOopDesc::unused_mark());
239
240 if (owner == NULL && Atomic::replace_if_null(Self, &(m->_owner))) {
241 assert(m->_recursions == 0, "invariant");
242 assert(m->_owner == Self, "invariant");
243 return true;
244 }
245 }
246
247 // Note that we could inflate in quick_enter.
248 // This is likely a useful optimization
249 // Critically, in quick_enter() we must not:
250 // -- perform bias revocation, or
251 // -- block indefinitely, or
252 // -- reach a safepoint
253
254 return false; // revert to slow-path
255 }
256
257 // -----------------------------------------------------------------------------
258 // Fast Monitor Enter/Exit
259 // This the fast monitor enter. The interpreter and compiler use
260 // some assembly copies of this code. Make sure update those code
261 // if the following function is changed. The implementation is
262 // extremely sensitive to race condition. Be careful.
263
264 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
265 bool attempt_rebias, TRAPS) {
266 if (UseBiasedLocking) {
267 if (!SafepointSynchronize::is_at_safepoint()) {
268 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
269 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
270 return;
271 }
272 } else {
273 assert(!attempt_rebias, "can not rebias toward VM thread");
274 BiasedLocking::revoke_at_safepoint(obj);
275 }
276 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
277 }
278
279 slow_enter(obj, lock, THREAD);
280 }
281
282 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
283 markOop mark = object->mark();
284 // We cannot check for Biased Locking if we are racing an inflation.
285 assert(mark == markOopDesc::INFLATING() ||
286 !mark->has_bias_pattern(), "should not see bias pattern here");
287
288 markOop dhw = lock->displaced_header();
289 if (dhw == NULL) {
290 // If the displaced header is NULL, then this exit matches up with
291 // a recursive enter. No real work to do here except for diagnostics.
292 #ifndef PRODUCT
293 if (mark != markOopDesc::INFLATING()) {
294 // Only do diagnostics if we are not racing an inflation. Simply
295 // exiting a recursive enter of a Java Monitor that is being
296 // inflated is safe; see the has_monitor() comment below.
297 assert(!mark->is_neutral(), "invariant");
298 assert(!mark->has_locker() ||
299 THREAD->is_lock_owned((address)mark->locker()), "invariant");
300 if (mark->has_monitor()) {
301 // The BasicLock's displaced_header is marked as a recursive
302 // enter and we have an inflated Java Monitor (ObjectMonitor).
303 // This is a special case where the Java Monitor was inflated
304 // after this thread entered the stack-lock recursively. When a
305 // Java Monitor is inflated, we cannot safely walk the Java
306 // Monitor owner's stack and update the BasicLocks because a
307 // Java Monitor can be asynchronously inflated by a thread that
308 // does not own the Java Monitor.
309 ObjectMonitor * m = mark->monitor();
310 assert(((oop)(m->object()))->mark() == mark, "invariant");
311 assert(m->is_entered(THREAD), "invariant");
312 }
313 }
314 #endif
315 return;
316 }
317
318 if (mark == (markOop) lock) {
319 // If the object is stack-locked by the current thread, try to
320 // swing the displaced header from the BasicLock back to the mark.
321 assert(dhw->is_neutral(), "invariant");
322 if (object->cas_set_mark(dhw, mark) == mark) {
323 return;
324 }
325 }
326
327 // We have to take the slow-path of possible inflation and then exit.
328 ObjectSynchronizer::inflate(THREAD,
329 object,
330 inflate_cause_vm_internal)->exit(true, THREAD);
331 }
332
333 // -----------------------------------------------------------------------------
334 // Interpreter/Compiler Slow Case
335 // This routine is used to handle interpreter/compiler slow case
336 // We don't need to use fast path here, because it must have been
337 // failed in the interpreter/compiler code.
338 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
339 markOop mark = obj->mark();
340 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
341
342 if (mark->is_neutral()) {
343 // Anticipate successful CAS -- the ST of the displaced mark must
344 // be visible <= the ST performed by the CAS.
345 lock->set_displaced_header(mark);
346 if (mark == obj()->cas_set_mark((markOop) lock, mark)) {
347 return;
348 }
349 // Fall through to inflate() ...
350 } else if (mark->has_locker() &&
351 THREAD->is_lock_owned((address)mark->locker())) {
352 assert(lock != mark->locker(), "must not re-lock the same lock");
353 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
354 lock->set_displaced_header(NULL);
355 return;
356 }
357
358 // The object header will never be displaced to this lock,
359 // so it does not matter what the value is, except that it
360 // must be non-zero to avoid looking like a re-entrant lock,
361 // and must not look locked either.
362 lock->set_displaced_header(markOopDesc::unused_mark());
363 ObjectSynchronizer::inflate(THREAD,
364 obj(),
365 inflate_cause_monitor_enter)->enter(THREAD);
366 }
367
368 // This routine is used to handle interpreter/compiler slow case
369 // We don't need to use fast path here, because it must have
370 // failed in the interpreter/compiler code. Simply use the heavy
371 // weight monitor should be ok, unless someone find otherwise.
372 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
373 fast_exit(object, lock, THREAD);
374 }
375
376 // -----------------------------------------------------------------------------
377 // Class Loader support to workaround deadlocks on the class loader lock objects
378 // Also used by GC
379 // complete_exit()/reenter() are used to wait on a nested lock
380 // i.e. to give up an outer lock completely and then re-enter
381 // Used when holding nested locks - lock acquisition order: lock1 then lock2
382 // 1) complete_exit lock1 - saving recursion count
383 // 2) wait on lock2
384 // 3) when notified on lock2, unlock lock2
385 // 4) reenter lock1 with original recursion count
386 // 5) lock lock2
387 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
388 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
389 if (UseBiasedLocking) {
390 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
391 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
392 }
393
394 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
395 obj(),
396 inflate_cause_vm_internal);
397
398 return monitor->complete_exit(THREAD);
399 }
400
401 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
402 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
403 if (UseBiasedLocking) {
404 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
405 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
406 }
407
408 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
409 obj(),
410 inflate_cause_vm_internal);
411
412 monitor->reenter(recursion, THREAD);
413 }
414 // -----------------------------------------------------------------------------
415 // JNI locks on java objects
416 // NOTE: must use heavy weight monitor to handle jni monitor enter
417 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
418 // the current locking is from JNI instead of Java code
419 if (UseBiasedLocking) {
420 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
421 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
422 }
423 THREAD->set_current_pending_monitor_is_from_java(false);
424 ObjectSynchronizer::inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);
425 THREAD->set_current_pending_monitor_is_from_java(true);
426 }
427
428 // NOTE: must use heavy weight monitor to handle jni monitor exit
429 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
430 if (UseBiasedLocking) {
431 Handle h_obj(THREAD, obj);
432 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
433 obj = h_obj();
434 }
435 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
436
437 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
438 obj,
439 inflate_cause_jni_exit);
440 // If this thread has locked the object, exit the monitor. Note: can't use
441 // monitor->check(CHECK); must exit even if an exception is pending.
442 if (monitor->check(THREAD)) {
443 monitor->exit(true, THREAD);
444 }
445 }
446
447 // -----------------------------------------------------------------------------
448 // Internal VM locks on java objects
449 // standard constructor, allows locking failures
450 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
451 _dolock = doLock;
452 _thread = thread;
453 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
454 _obj = obj;
455
456 if (_dolock) {
457 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
458 }
459 }
460
461 ObjectLocker::~ObjectLocker() {
462 if (_dolock) {
463 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
464 }
465 }
466
467
468 // -----------------------------------------------------------------------------
469 // Wait/Notify/NotifyAll
470 // NOTE: must use heavy weight monitor to handle wait()
471 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
472 if (UseBiasedLocking) {
473 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
474 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
475 }
476 if (millis < 0) {
477 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
478 }
479 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
480 obj(),
481 inflate_cause_wait);
482
483 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
484 monitor->wait(millis, true, THREAD);
485
486 // This dummy call is in place to get around dtrace bug 6254741. Once
487 // that's fixed we can uncomment the following line, remove the call
488 // and change this function back into a "void" func.
489 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
490 return dtrace_waited_probe(monitor, obj, THREAD);
491 }
492
493 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
494 if (UseBiasedLocking) {
495 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
496 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
497 }
498 if (millis < 0) {
499 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
500 }
501 ObjectSynchronizer::inflate(THREAD,
502 obj(),
503 inflate_cause_wait)->wait(millis, false, THREAD);
504 }
505
506 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
507 if (UseBiasedLocking) {
508 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
509 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
510 }
511
512 markOop mark = obj->mark();
513 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
514 return;
515 }
516 ObjectSynchronizer::inflate(THREAD,
517 obj(),
518 inflate_cause_notify)->notify(THREAD);
519 }
520
521 // NOTE: see comment of notify()
522 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
523 if (UseBiasedLocking) {
524 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
525 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
526 }
527
528 markOop mark = obj->mark();
529 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
530 return;
531 }
532 ObjectSynchronizer::inflate(THREAD,
533 obj(),
534 inflate_cause_notify)->notifyAll(THREAD);
535 }
536
537 // -----------------------------------------------------------------------------
538 // Hash Code handling
539 //
540 // Performance concern:
541 // OrderAccess::storestore() calls release() which at one time stored 0
542 // into the global volatile OrderAccess::dummy variable. This store was
543 // unnecessary for correctness. Many threads storing into a common location
544 // causes considerable cache migration or "sloshing" on large SMP systems.
545 // As such, I avoided using OrderAccess::storestore(). In some cases
546 // OrderAccess::fence() -- which incurs local latency on the executing
547 // processor -- is a better choice as it scales on SMP systems.
548 //
549 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
550 // a discussion of coherency costs. Note that all our current reference
551 // platforms provide strong ST-ST order, so the issue is moot on IA32,
552 // x64, and SPARC.
553 //
554 // As a general policy we use "volatile" to control compiler-based reordering
555 // and explicit fences (barriers) to control for architectural reordering
556 // performed by the CPU(s) or platform.
557
558 struct SharedGlobals {
559 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
560 // These are highly shared mostly-read variables.
561 // To avoid false-sharing they need to be the sole occupants of a cache line.
562 volatile int stwRandom;
563 volatile int stwCycle;
564 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
565 // Hot RW variable -- Sequester to avoid false-sharing
566 volatile int hcSequence;
567 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
568 };
569
570 static SharedGlobals GVars;
571 static int MonitorScavengeThreshold = 1000000;
572 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
573
574 static markOop ReadStableMark(oop obj) {
575 markOop mark = obj->mark();
576 if (!mark->is_being_inflated()) {
577 return mark; // normal fast-path return
578 }
579
580 int its = 0;
581 for (;;) {
582 markOop mark = obj->mark();
583 if (!mark->is_being_inflated()) {
584 return mark; // normal fast-path return
585 }
586
587 // The object is being inflated by some other thread.
588 // The caller of ReadStableMark() must wait for inflation to complete.
589 // Avoid live-lock
590 // TODO: consider calling SafepointSynchronize::do_call_back() while
591 // spinning to see if there's a safepoint pending. If so, immediately
592 // yielding or blocking would be appropriate. Avoid spinning while
593 // there is a safepoint pending.
594 // TODO: add inflation contention performance counters.
595 // TODO: restrict the aggregate number of spinners.
596
597 ++its;
598 if (its > 10000 || !os::is_MP()) {
599 if (its & 1) {
600 os::naked_yield();
601 } else {
602 // Note that the following code attenuates the livelock problem but is not
603 // a complete remedy. A more complete solution would require that the inflating
604 // thread hold the associated inflation lock. The following code simply restricts
605 // the number of spinners to at most one. We'll have N-2 threads blocked
606 // on the inflationlock, 1 thread holding the inflation lock and using
607 // a yield/park strategy, and 1 thread in the midst of inflation.
608 // A more refined approach would be to change the encoding of INFLATING
609 // to allow encapsulation of a native thread pointer. Threads waiting for
610 // inflation to complete would use CAS to push themselves onto a singly linked
611 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
612 // and calling park(). When inflation was complete the thread that accomplished inflation
613 // would detach the list and set the markword to inflated with a single CAS and
614 // then for each thread on the list, set the flag and unpark() the thread.
615 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
616 // wakes at most one thread whereas we need to wake the entire list.
617 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
618 int YieldThenBlock = 0;
619 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
620 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
621 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
622 while (obj->mark() == markOopDesc::INFLATING()) {
623 // Beware: NakedYield() is advisory and has almost no effect on some platforms
624 // so we periodically call Self->_ParkEvent->park(1).
625 // We use a mixed spin/yield/block mechanism.
626 if ((YieldThenBlock++) >= 16) {
627 Thread::current()->_ParkEvent->park(1);
628 } else {
629 os::naked_yield();
630 }
631 }
632 Thread::muxRelease(gInflationLocks + ix);
633 }
634 } else {
635 SpinPause(); // SMP-polite spinning
636 }
637 }
638 }
639
640 // hashCode() generation :
641 //
642 // Possibilities:
643 // * MD5Digest of {obj,stwRandom}
644 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
645 // * A DES- or AES-style SBox[] mechanism
646 // * One of the Phi-based schemes, such as:
647 // 2654435761 = 2^32 * Phi (golden ratio)
648 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
649 // * A variation of Marsaglia's shift-xor RNG scheme.
650 // * (obj ^ stwRandom) is appealing, but can result
651 // in undesirable regularity in the hashCode values of adjacent objects
652 // (objects allocated back-to-back, in particular). This could potentially
653 // result in hashtable collisions and reduced hashtable efficiency.
654 // There are simple ways to "diffuse" the middle address bits over the
655 // generated hashCode values:
656
657 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
658 intptr_t value = 0;
659 if (hashCode == 0) {
660 // This form uses global Park-Miller RNG.
661 // On MP system we'll have lots of RW access to a global, so the
662 // mechanism induces lots of coherency traffic.
663 value = os::random();
664 } else if (hashCode == 1) {
665 // This variation has the property of being stable (idempotent)
666 // between STW operations. This can be useful in some of the 1-0
667 // synchronization schemes.
668 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
669 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
670 } else if (hashCode == 2) {
671 value = 1; // for sensitivity testing
672 } else if (hashCode == 3) {
673 value = ++GVars.hcSequence;
674 } else if (hashCode == 4) {
675 value = cast_from_oop<intptr_t>(obj);
676 } else {
677 // Marsaglia's xor-shift scheme with thread-specific state
678 // This is probably the best overall implementation -- we'll
679 // likely make this the default in future releases.
680 unsigned t = Self->_hashStateX;
681 t ^= (t << 11);
682 Self->_hashStateX = Self->_hashStateY;
683 Self->_hashStateY = Self->_hashStateZ;
684 Self->_hashStateZ = Self->_hashStateW;
685 unsigned v = Self->_hashStateW;
686 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
687 Self->_hashStateW = v;
688 value = v;
689 }
690
691 value &= markOopDesc::hash_mask;
692 if (value == 0) value = 0xBAD;
693 assert(value != markOopDesc::no_hash, "invariant");
694 return value;
695 }
696
697 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
698 if (UseBiasedLocking) {
699 // NOTE: many places throughout the JVM do not expect a safepoint
700 // to be taken here, in particular most operations on perm gen
701 // objects. However, we only ever bias Java instances and all of
702 // the call sites of identity_hash that might revoke biases have
703 // been checked to make sure they can handle a safepoint. The
704 // added check of the bias pattern is to avoid useless calls to
705 // thread-local storage.
706 if (obj->mark()->has_bias_pattern()) {
707 // Handle for oop obj in case of STW safepoint
708 Handle hobj(Self, obj);
709 // Relaxing assertion for bug 6320749.
710 assert(Universe::verify_in_progress() ||
711 !SafepointSynchronize::is_at_safepoint(),
712 "biases should not be seen by VM thread here");
713 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
714 obj = hobj();
715 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
716 }
717 }
718
719 // hashCode() is a heap mutator ...
720 // Relaxing assertion for bug 6320749.
721 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
722 !SafepointSynchronize::is_at_safepoint(), "invariant");
723 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
724 Self->is_Java_thread() , "invariant");
725 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
726 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
727
728 ObjectMonitor* monitor = NULL;
729 markOop temp, test;
730 intptr_t hash;
731 markOop mark = ReadStableMark(obj);
732
733 // object should remain ineligible for biased locking
734 assert(!mark->has_bias_pattern(), "invariant");
735
736 if (mark->is_neutral()) {
737 hash = mark->hash(); // this is a normal header
738 if (hash) { // if it has hash, just return it
739 return hash;
740 }
741 hash = get_next_hash(Self, obj); // allocate a new hash code
742 temp = mark->copy_set_hash(hash); // merge the hash code into header
743 // use (machine word version) atomic operation to install the hash
744 test = obj->cas_set_mark(temp, mark);
745 if (test == mark) {
746 return hash;
747 }
748 // If atomic operation failed, we must inflate the header
749 // into heavy weight monitor. We could add more code here
750 // for fast path, but it does not worth the complexity.
751 } else if (mark->has_monitor()) {
752 monitor = mark->monitor();
753 temp = monitor->header();
754 assert(temp->is_neutral(), "invariant");
755 hash = temp->hash();
756 if (hash) {
757 return hash;
758 }
759 // Skip to the following code to reduce code size
760 } else if (Self->is_lock_owned((address)mark->locker())) {
761 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
762 assert(temp->is_neutral(), "invariant");
763 hash = temp->hash(); // by current thread, check if the displaced
764 if (hash) { // header contains hash code
765 return hash;
766 }
767 // WARNING:
768 // The displaced header is strictly immutable.
769 // It can NOT be changed in ANY cases. So we have
770 // to inflate the header into heavyweight monitor
771 // even the current thread owns the lock. The reason
772 // is the BasicLock (stack slot) will be asynchronously
773 // read by other threads during the inflate() function.
774 // Any change to stack may not propagate to other threads
775 // correctly.
776 }
777
778 // Inflate the monitor to set hash code
779 monitor = ObjectSynchronizer::inflate(Self, obj, inflate_cause_hash_code);
780 // Load displaced header and check it has hash code
781 mark = monitor->header();
782 assert(mark->is_neutral(), "invariant");
783 hash = mark->hash();
784 if (hash == 0) {
785 hash = get_next_hash(Self, obj);
786 temp = mark->copy_set_hash(hash); // merge hash code into header
787 assert(temp->is_neutral(), "invariant");
788 test = Atomic::cmpxchg(temp, monitor->header_addr(), mark);
789 if (test != mark) {
790 // The only update to the header in the monitor (outside GC)
791 // is install the hash code. If someone add new usage of
792 // displaced header, please update this code
793 hash = test->hash();
794 assert(test->is_neutral(), "invariant");
795 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
796 }
797 }
798 // We finally get the hash
799 return hash;
800 }
801
802 // Deprecated -- use FastHashCode() instead.
803
804 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
805 return FastHashCode(Thread::current(), obj());
806 }
807
808
809 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
810 Handle h_obj) {
811 if (UseBiasedLocking) {
812 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
813 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
814 }
815
816 assert(thread == JavaThread::current(), "Can only be called on current thread");
817 oop obj = h_obj();
818
819 markOop mark = ReadStableMark(obj);
820
821 // Uncontended case, header points to stack
822 if (mark->has_locker()) {
823 return thread->is_lock_owned((address)mark->locker());
824 }
825 // Contended case, header points to ObjectMonitor (tagged pointer)
826 if (mark->has_monitor()) {
827 ObjectMonitor* monitor = mark->monitor();
828 return monitor->is_entered(thread) != 0;
829 }
830 // Unlocked case, header in place
831 assert(mark->is_neutral(), "sanity check");
832 return false;
833 }
834
835 // Be aware of this method could revoke bias of the lock object.
836 // This method queries the ownership of the lock handle specified by 'h_obj'.
837 // If the current thread owns the lock, it returns owner_self. If no
838 // thread owns the lock, it returns owner_none. Otherwise, it will return
839 // owner_other.
840 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
841 (JavaThread *self, Handle h_obj) {
842 // The caller must beware this method can revoke bias, and
843 // revocation can result in a safepoint.
844 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
845 assert(self->thread_state() != _thread_blocked, "invariant");
846
847 // Possible mark states: neutral, biased, stack-locked, inflated
848
849 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
850 // CASE: biased
851 BiasedLocking::revoke_and_rebias(h_obj, false, self);
852 assert(!h_obj->mark()->has_bias_pattern(),
853 "biases should be revoked by now");
854 }
855
856 assert(self == JavaThread::current(), "Can only be called on current thread");
857 oop obj = h_obj();
858 markOop mark = ReadStableMark(obj);
859
860 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
861 if (mark->has_locker()) {
862 return self->is_lock_owned((address)mark->locker()) ?
863 owner_self : owner_other;
864 }
865
866 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
867 // The Object:ObjectMonitor relationship is stable as long as we're
868 // not at a safepoint.
869 if (mark->has_monitor()) {
870 void * owner = mark->monitor()->_owner;
871 if (owner == NULL) return owner_none;
872 return (owner == self ||
873 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
874 }
875
876 // CASE: neutral
877 assert(mark->is_neutral(), "sanity check");
878 return owner_none; // it's unlocked
879 }
880
881 // FIXME: jvmti should call this
882 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
883 if (UseBiasedLocking) {
884 if (SafepointSynchronize::is_at_safepoint()) {
885 BiasedLocking::revoke_at_safepoint(h_obj);
886 } else {
887 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
888 }
889 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
890 }
891
892 oop obj = h_obj();
893 address owner = NULL;
894
895 markOop mark = ReadStableMark(obj);
896
897 // Uncontended case, header points to stack
898 if (mark->has_locker()) {
899 owner = (address) mark->locker();
900 }
901
902 // Contended case, header points to ObjectMonitor (tagged pointer)
903 if (mark->has_monitor()) {
904 ObjectMonitor* monitor = mark->monitor();
905 assert(monitor != NULL, "monitor should be non-null");
906 owner = (address) monitor->owner();
907 }
908
909 if (owner != NULL) {
910 // owning_thread_from_monitor_owner() may also return NULL here
911 return Threads::owning_thread_from_monitor_owner(t_list, owner);
912 }
913
914 // Unlocked case, header in place
915 // Cannot have assertion since this object may have been
916 // locked by another thread when reaching here.
917 // assert(mark->is_neutral(), "sanity check");
918
919 return NULL;
920 }
921
922 // Visitors ...
923
924 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
925 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
926 while (block != NULL) {
927 assert(block->object() == CHAINMARKER, "must be a block header");
928 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
929 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
930 oop object = (oop)mid->object();
931 if (object != NULL) {
932 closure->do_monitor(mid);
933 }
934 }
935 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
936 }
937 }
938
939 // Get the next block in the block list.
940 static inline PaddedEnd<ObjectMonitor>* next(PaddedEnd<ObjectMonitor>* block) {
941 assert(block->object() == CHAINMARKER, "must be a block header");
942 block = (PaddedEnd<ObjectMonitor>*) block->FreeNext;
943 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
944 return block;
945 }
946
947 static bool monitors_used_above_threshold() {
948 if (gMonitorPopulation == 0) {
949 return false;
950 }
951 int monitors_used = gMonitorPopulation - gMonitorFreeCount;
952 int monitor_usage = (monitors_used * 100LL) / gMonitorPopulation;
953 return monitor_usage > MonitorUsedDeflationThreshold;
954 }
955
956 bool ObjectSynchronizer::is_cleanup_needed() {
957 if (MonitorUsedDeflationThreshold > 0) {
958 return monitors_used_above_threshold();
959 }
960 return false;
961 }
962
963 void ObjectSynchronizer::oops_do(OopClosure* f) {
964 if (MonitorInUseLists) {
965 // When using thread local monitor lists, we only scan the
966 // global used list here (for moribund threads), and
967 // the thread-local monitors in Thread::oops_do().
968 global_used_oops_do(f);
969 } else {
970 global_oops_do(f);
971 }
972 }
973
974 void ObjectSynchronizer::global_oops_do(OopClosure* f) {
975 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
976 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
977 for (; block != NULL; block = next(block)) {
978 assert(block->object() == CHAINMARKER, "must be a block header");
979 for (int i = 1; i < _BLOCKSIZE; i++) {
980 ObjectMonitor* mid = (ObjectMonitor *)&block[i];
981 if (mid->object() != NULL) {
982 f->do_oop((oop*)mid->object_addr());
983 }
984 }
985 }
986 }
987
988 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
989 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
990 list_oops_do(gOmInUseList, f);
991 }
992
993 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
994 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
995 list_oops_do(thread->omInUseList, f);
996 }
997
998 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
999 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1000 ObjectMonitor* mid;
1001 for (mid = list; mid != NULL; mid = mid->FreeNext) {
1002 if (mid->object() != NULL) {
1003 f->do_oop((oop*)mid->object_addr());
1004 }
1005 }
1006 }
1007
1008
1009 // -----------------------------------------------------------------------------
1010 // ObjectMonitor Lifecycle
1011 // -----------------------
1012 // Inflation unlinks monitors from the global gFreeList and
1013 // associates them with objects. Deflation -- which occurs at
1014 // STW-time -- disassociates idle monitors from objects. Such
1015 // scavenged monitors are returned to the gFreeList.
1016 //
1017 // The global list is protected by gListLock. All the critical sections
1018 // are short and operate in constant-time.
1019 //
1020 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1021 //
1022 // Lifecycle:
1023 // -- unassigned and on the global free list
1024 // -- unassigned and on a thread's private omFreeList
1025 // -- assigned to an object. The object is inflated and the mark refers
1026 // to the objectmonitor.
1027
1028
1029 // Constraining monitor pool growth via MonitorBound ...
1030 //
1031 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
1032 // the rate of scavenging is driven primarily by GC. As such, we can find
1033 // an inordinate number of monitors in circulation.
1034 // To avoid that scenario we can artificially induce a STW safepoint
1035 // if the pool appears to be growing past some reasonable bound.
1036 // Generally we favor time in space-time tradeoffs, but as there's no
1037 // natural back-pressure on the # of extant monitors we need to impose some
1038 // type of limit. Beware that if MonitorBound is set to too low a value
1039 // we could just loop. In addition, if MonitorBound is set to a low value
1040 // we'll incur more safepoints, which are harmful to performance.
1041 // See also: GuaranteedSafepointInterval
1042 //
1043 // The current implementation uses asynchronous VM operations.
1044
1045 static void InduceScavenge(Thread * Self, const char * Whence) {
1046 // Induce STW safepoint to trim monitors
1047 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1048 // More precisely, trigger an asynchronous STW safepoint as the number
1049 // of active monitors passes the specified threshold.
1050 // TODO: assert thread state is reasonable
1051
1052 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1053 if (ObjectMonitor::Knob_Verbose) {
1054 tty->print_cr("INFO: Monitor scavenge - Induced STW @%s (%d)",
1055 Whence, ForceMonitorScavenge) ;
1056 tty->flush();
1057 }
1058 // Induce a 'null' safepoint to scavenge monitors
1059 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1060 // to the VMthread and have a lifespan longer than that of this activation record.
1061 // The VMThread will delete the op when completed.
1062 VMThread::execute(new VM_ScavengeMonitors());
1063
1064 if (ObjectMonitor::Knob_Verbose) {
1065 tty->print_cr("INFO: Monitor scavenge - STW posted @%s (%d)",
1066 Whence, ForceMonitorScavenge) ;
1067 tty->flush();
1068 }
1069 }
1070 }
1071
1072 void ObjectSynchronizer::verifyInUse(Thread *Self) {
1073 ObjectMonitor* mid;
1074 int in_use_tally = 0;
1075 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) {
1076 in_use_tally++;
1077 }
1078 assert(in_use_tally == Self->omInUseCount, "in-use count off");
1079
1080 int free_tally = 0;
1081 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) {
1082 free_tally++;
1083 }
1084 assert(free_tally == Self->omFreeCount, "free count off");
1085 }
1086
1087 ObjectMonitor* ObjectSynchronizer::omAlloc(Thread * Self) {
1088 // A large MAXPRIVATE value reduces both list lock contention
1089 // and list coherency traffic, but also tends to increase the
1090 // number of objectMonitors in circulation as well as the STW
1091 // scavenge costs. As usual, we lean toward time in space-time
1092 // tradeoffs.
1093 const int MAXPRIVATE = 1024;
1094 for (;;) {
1095 ObjectMonitor * m;
1096
1097 // 1: try to allocate from the thread's local omFreeList.
1098 // Threads will attempt to allocate first from their local list, then
1099 // from the global list, and only after those attempts fail will the thread
1100 // attempt to instantiate new monitors. Thread-local free lists take
1101 // heat off the gListLock and improve allocation latency, as well as reducing
1102 // coherency traffic on the shared global list.
1103 m = Self->omFreeList;
1104 if (m != NULL) {
1105 Self->omFreeList = m->FreeNext;
1106 Self->omFreeCount--;
1107 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene
1108 guarantee(m->object() == NULL, "invariant");
1109 if (MonitorInUseLists) {
1110 m->FreeNext = Self->omInUseList;
1111 Self->omInUseList = m;
1112 Self->omInUseCount++;
1113 if (ObjectMonitor::Knob_VerifyInUse) {
1114 verifyInUse(Self);
1115 }
1116 } else {
1117 m->FreeNext = NULL;
1118 }
1119 return m;
1120 }
1121
1122 // 2: try to allocate from the global gFreeList
1123 // CONSIDER: use muxTry() instead of muxAcquire().
1124 // If the muxTry() fails then drop immediately into case 3.
1125 // If we're using thread-local free lists then try
1126 // to reprovision the caller's free list.
1127 if (gFreeList != NULL) {
1128 // Reprovision the thread's omFreeList.
1129 // Use bulk transfers to reduce the allocation rate and heat
1130 // on various locks.
1131 Thread::muxAcquire(&gListLock, "omAlloc");
1132 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1133 gMonitorFreeCount--;
1134 ObjectMonitor * take = gFreeList;
1135 gFreeList = take->FreeNext;
1136 guarantee(take->object() == NULL, "invariant");
1137 guarantee(!take->is_busy(), "invariant");
1138 take->Recycle();
1139 omRelease(Self, take, false);
1140 }
1141 Thread::muxRelease(&gListLock);
1142 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1143 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1144
1145 const int mx = MonitorBound;
1146 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1147 // We can't safely induce a STW safepoint from omAlloc() as our thread
1148 // state may not be appropriate for such activities and callers may hold
1149 // naked oops, so instead we defer the action.
1150 InduceScavenge(Self, "omAlloc");
1151 }
1152 continue;
1153 }
1154
1155 // 3: allocate a block of new ObjectMonitors
1156 // Both the local and global free lists are empty -- resort to malloc().
1157 // In the current implementation objectMonitors are TSM - immortal.
1158 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1159 // each ObjectMonitor to start at the beginning of a cache line,
1160 // so we use align_up().
1161 // A better solution would be to use C++ placement-new.
1162 // BEWARE: As it stands currently, we don't run the ctors!
1163 assert(_BLOCKSIZE > 1, "invariant");
1164 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
1165 PaddedEnd<ObjectMonitor> * temp;
1166 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1167 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
1168 mtInternal);
1169 temp = (PaddedEnd<ObjectMonitor> *)
1170 align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE);
1171
1172 // NOTE: (almost) no way to recover if allocation failed.
1173 // We might be able to induce a STW safepoint and scavenge enough
1174 // objectMonitors to permit progress.
1175 if (temp == NULL) {
1176 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1177 "Allocate ObjectMonitors");
1178 }
1179 (void)memset((void *) temp, 0, neededsize);
1180
1181 // Format the block.
1182 // initialize the linked list, each monitor points to its next
1183 // forming the single linked free list, the very first monitor
1184 // will points to next block, which forms the block list.
1185 // The trick of using the 1st element in the block as gBlockList
1186 // linkage should be reconsidered. A better implementation would
1187 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1188
1189 for (int i = 1; i < _BLOCKSIZE; i++) {
1190 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1191 }
1192
1193 // terminate the last monitor as the end of list
1194 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1195
1196 // Element [0] is reserved for global list linkage
1197 temp[0].set_object(CHAINMARKER);
1198
1199 // Consider carving out this thread's current request from the
1200 // block in hand. This avoids some lock traffic and redundant
1201 // list activity.
1202
1203 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1204 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1205 Thread::muxAcquire(&gListLock, "omAlloc [2]");
1206 gMonitorPopulation += _BLOCKSIZE-1;
1207 gMonitorFreeCount += _BLOCKSIZE-1;
1208
1209 // Add the new block to the list of extant blocks (gBlockList).
1210 // The very first objectMonitor in a block is reserved and dedicated.
1211 // It serves as blocklist "next" linkage.
1212 temp[0].FreeNext = gBlockList;
1213 // There are lock-free uses of gBlockList so make sure that
1214 // the previous stores happen before we update gBlockList.
1215 OrderAccess::release_store(&gBlockList, temp);
1216
1217 // Add the new string of objectMonitors to the global free list
1218 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1219 gFreeList = temp + 1;
1220 Thread::muxRelease(&gListLock);
1221 }
1222 }
1223
1224 // Place "m" on the caller's private per-thread omFreeList.
1225 // In practice there's no need to clamp or limit the number of
1226 // monitors on a thread's omFreeList as the only time we'll call
1227 // omRelease is to return a monitor to the free list after a CAS
1228 // attempt failed. This doesn't allow unbounded #s of monitors to
1229 // accumulate on a thread's free list.
1230 //
1231 // Key constraint: all ObjectMonitors on a thread's free list and the global
1232 // free list must have their object field set to null. This prevents the
1233 // scavenger -- deflate_idle_monitors -- from reclaiming them.
1234
1235 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1236 bool fromPerThreadAlloc) {
1237 guarantee(m->object() == NULL, "invariant");
1238 guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor");
1239 // Remove from omInUseList
1240 if (MonitorInUseLists && fromPerThreadAlloc) {
1241 ObjectMonitor* cur_mid_in_use = NULL;
1242 bool extracted = false;
1243 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1244 if (m == mid) {
1245 // extract from per-thread in-use list
1246 if (mid == Self->omInUseList) {
1247 Self->omInUseList = mid->FreeNext;
1248 } else if (cur_mid_in_use != NULL) {
1249 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1250 }
1251 extracted = true;
1252 Self->omInUseCount--;
1253 if (ObjectMonitor::Knob_VerifyInUse) {
1254 verifyInUse(Self);
1255 }
1256 break;
1257 }
1258 }
1259 assert(extracted, "Should have extracted from in-use list");
1260 }
1261
1262 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1263 m->FreeNext = Self->omFreeList;
1264 Self->omFreeList = m;
1265 Self->omFreeCount++;
1266 }
1267
1268 // Return the monitors of a moribund thread's local free list to
1269 // the global free list. Typically a thread calls omFlush() when
1270 // it's dying. We could also consider having the VM thread steal
1271 // monitors from threads that have not run java code over a few
1272 // consecutive STW safepoints. Relatedly, we might decay
1273 // omFreeProvision at STW safepoints.
1274 //
1275 // Also return the monitors of a moribund thread's omInUseList to
1276 // a global gOmInUseList under the global list lock so these
1277 // will continue to be scanned.
1278 //
1279 // We currently call omFlush() from Threads::remove() _before the thread
1280 // has been excised from the thread list and is no longer a mutator.
1281 // This means that omFlush() can not run concurrently with a safepoint and
1282 // interleave with the scavenge operator. In particular, this ensures that
1283 // the thread's monitors are scanned by a GC safepoint, either via
1284 // Thread::oops_do() (if safepoint happens before omFlush()) or via
1285 // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's
1286 // monitors have been transferred to the global in-use list).
1287
1288 void ObjectSynchronizer::omFlush(Thread * Self) {
1289 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1290 Self->omFreeList = NULL;
1291 ObjectMonitor * tail = NULL;
1292 int tally = 0;
1293 if (list != NULL) {
1294 ObjectMonitor * s;
1295 // The thread is going away, the per-thread free monitors
1296 // are freed via set_owner(NULL)
1297 // Link them to tail, which will be linked into the global free list
1298 // gFreeList below, under the gListLock
1299 for (s = list; s != NULL; s = s->FreeNext) {
1300 tally++;
1301 tail = s;
1302 guarantee(s->object() == NULL, "invariant");
1303 guarantee(!s->is_busy(), "invariant");
1304 s->set_owner(NULL); // redundant but good hygiene
1305 }
1306 guarantee(tail != NULL && list != NULL, "invariant");
1307 }
1308
1309 ObjectMonitor * inUseList = Self->omInUseList;
1310 ObjectMonitor * inUseTail = NULL;
1311 int inUseTally = 0;
1312 if (inUseList != NULL) {
1313 Self->omInUseList = NULL;
1314 ObjectMonitor *cur_om;
1315 // The thread is going away, however the omInUseList inflated
1316 // monitors may still be in-use by other threads.
1317 // Link them to inUseTail, which will be linked into the global in-use list
1318 // gOmInUseList below, under the gListLock
1319 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1320 inUseTail = cur_om;
1321 inUseTally++;
1322 }
1323 assert(Self->omInUseCount == inUseTally, "in-use count off");
1324 Self->omInUseCount = 0;
1325 guarantee(inUseTail != NULL && inUseList != NULL, "invariant");
1326 }
1327
1328 Thread::muxAcquire(&gListLock, "omFlush");
1329 if (tail != NULL) {
1330 tail->FreeNext = gFreeList;
1331 gFreeList = list;
1332 gMonitorFreeCount += tally;
1333 assert(Self->omFreeCount == tally, "free-count off");
1334 Self->omFreeCount = 0;
1335 }
1336
1337 if (inUseTail != NULL) {
1338 inUseTail->FreeNext = gOmInUseList;
1339 gOmInUseList = inUseList;
1340 gOmInUseCount += inUseTally;
1341 }
1342
1343 Thread::muxRelease(&gListLock);
1344 }
1345
1346 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1347 const oop obj,
1348 ObjectSynchronizer::InflateCause cause) {
1349 assert(event != NULL, "invariant");
1350 assert(event->should_commit(), "invariant");
1351 event->set_monitorClass(obj->klass());
1352 event->set_address((uintptr_t)(void*)obj);
1353 event->set_cause((u1)cause);
1354 event->commit();
1355 }
1356
1357 // Fast path code shared by multiple functions
1358 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1359 markOop mark = obj->mark();
1360 if (mark->has_monitor()) {
1361 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1362 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1363 return mark->monitor();
1364 }
1365 return ObjectSynchronizer::inflate(Thread::current(),
1366 obj,
1367 inflate_cause_vm_internal);
1368 }
1369
1370 ObjectMonitor* ObjectSynchronizer::inflate(Thread * Self,
1371 oop object,
1372 const InflateCause cause) {
1373
1374 // Inflate mutates the heap ...
1375 // Relaxing assertion for bug 6320749.
1376 assert(Universe::verify_in_progress() ||
1377 !SafepointSynchronize::is_at_safepoint(), "invariant");
1378
1379 EventJavaMonitorInflate event;
1380
1381 for (;;) {
1382 const markOop mark = object->mark();
1383 assert(!mark->has_bias_pattern(), "invariant");
1384
1385 // The mark can be in one of the following states:
1386 // * Inflated - just return
1387 // * Stack-locked - coerce it to inflated
1388 // * INFLATING - busy wait for conversion to complete
1389 // * Neutral - aggressively inflate the object.
1390 // * BIASED - Illegal. We should never see this
1391
1392 // CASE: inflated
1393 if (mark->has_monitor()) {
1394 ObjectMonitor * inf = mark->monitor();
1395 assert(inf->header()->is_neutral(), "invariant");
1396 assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1397 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1398 return inf;
1399 }
1400
1401 // CASE: inflation in progress - inflating over a stack-lock.
1402 // Some other thread is converting from stack-locked to inflated.
1403 // Only that thread can complete inflation -- other threads must wait.
1404 // The INFLATING value is transient.
1405 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1406 // We could always eliminate polling by parking the thread on some auxiliary list.
1407 if (mark == markOopDesc::INFLATING()) {
1408 ReadStableMark(object);
1409 continue;
1410 }
1411
1412 // CASE: stack-locked
1413 // Could be stack-locked either by this thread or by some other thread.
1414 //
1415 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1416 // to install INFLATING into the mark word. We originally installed INFLATING,
1417 // allocated the objectmonitor, and then finally STed the address of the
1418 // objectmonitor into the mark. This was correct, but artificially lengthened
1419 // the interval in which INFLATED appeared in the mark, thus increasing
1420 // the odds of inflation contention.
1421 //
1422 // We now use per-thread private objectmonitor free lists.
1423 // These list are reprovisioned from the global free list outside the
1424 // critical INFLATING...ST interval. A thread can transfer
1425 // multiple objectmonitors en-mass from the global free list to its local free list.
1426 // This reduces coherency traffic and lock contention on the global free list.
1427 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1428 // before or after the CAS(INFLATING) operation.
1429 // See the comments in omAlloc().
1430
1431 if (mark->has_locker()) {
1432 ObjectMonitor * m = omAlloc(Self);
1433 // Optimistically prepare the objectmonitor - anticipate successful CAS
1434 // We do this before the CAS in order to minimize the length of time
1435 // in which INFLATING appears in the mark.
1436 m->Recycle();
1437 m->_Responsible = NULL;
1438 m->_recursions = 0;
1439 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1440
1441 markOop cmp = object->cas_set_mark(markOopDesc::INFLATING(), mark);
1442 if (cmp != mark) {
1443 omRelease(Self, m, true);
1444 continue; // Interference -- just retry
1445 }
1446
1447 // We've successfully installed INFLATING (0) into the mark-word.
1448 // This is the only case where 0 will appear in a mark-word.
1449 // Only the singular thread that successfully swings the mark-word
1450 // to 0 can perform (or more precisely, complete) inflation.
1451 //
1452 // Why do we CAS a 0 into the mark-word instead of just CASing the
1453 // mark-word from the stack-locked value directly to the new inflated state?
1454 // Consider what happens when a thread unlocks a stack-locked object.
1455 // It attempts to use CAS to swing the displaced header value from the
1456 // on-stack basiclock back into the object header. Recall also that the
1457 // header value (hashcode, etc) can reside in (a) the object header, or
1458 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1459 // header in an objectMonitor. The inflate() routine must copy the header
1460 // value from the basiclock on the owner's stack to the objectMonitor, all
1461 // the while preserving the hashCode stability invariants. If the owner
1462 // decides to release the lock while the value is 0, the unlock will fail
1463 // and control will eventually pass from slow_exit() to inflate. The owner
1464 // will then spin, waiting for the 0 value to disappear. Put another way,
1465 // the 0 causes the owner to stall if the owner happens to try to
1466 // drop the lock (restoring the header from the basiclock to the object)
1467 // while inflation is in-progress. This protocol avoids races that might
1468 // would otherwise permit hashCode values to change or "flicker" for an object.
1469 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1470 // 0 serves as a "BUSY" inflate-in-progress indicator.
1471
1472
1473 // fetch the displaced mark from the owner's stack.
1474 // The owner can't die or unwind past the lock while our INFLATING
1475 // object is in the mark. Furthermore the owner can't complete
1476 // an unlock on the object, either.
1477 markOop dmw = mark->displaced_mark_helper();
1478 assert(dmw->is_neutral(), "invariant");
1479
1480 // Setup monitor fields to proper values -- prepare the monitor
1481 m->set_header(dmw);
1482
1483 // Optimization: if the mark->locker stack address is associated
1484 // with this thread we could simply set m->_owner = Self.
1485 // Note that a thread can inflate an object
1486 // that it has stack-locked -- as might happen in wait() -- directly
1487 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1488 m->set_owner(mark->locker());
1489 m->set_object(object);
1490 // TODO-FIXME: assert BasicLock->dhw != 0.
1491
1492 // Must preserve store ordering. The monitor state must
1493 // be stable at the time of publishing the monitor address.
1494 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1495 object->release_set_mark(markOopDesc::encode(m));
1496
1497 // Hopefully the performance counters are allocated on distinct cache lines
1498 // to avoid false sharing on MP systems ...
1499 OM_PERFDATA_OP(Inflations, inc());
1500 if (log_is_enabled(Debug, monitorinflation)) {
1501 if (object->is_instance()) {
1502 ResourceMark rm;
1503 log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1504 p2i(object), p2i(object->mark()),
1505 object->klass()->external_name());
1506 }
1507 }
1508 if (event.should_commit()) {
1509 post_monitor_inflate_event(&event, object, cause);
1510 }
1511 return m;
1512 }
1513
1514 // CASE: neutral
1515 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1516 // If we know we're inflating for entry it's better to inflate by swinging a
1517 // pre-locked objectMonitor pointer into the object header. A successful
1518 // CAS inflates the object *and* confers ownership to the inflating thread.
1519 // In the current implementation we use a 2-step mechanism where we CAS()
1520 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1521 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1522 // would be useful.
1523
1524 assert(mark->is_neutral(), "invariant");
1525 ObjectMonitor * m = omAlloc(Self);
1526 // prepare m for installation - set monitor to initial state
1527 m->Recycle();
1528 m->set_header(mark);
1529 m->set_owner(NULL);
1530 m->set_object(object);
1531 m->_recursions = 0;
1532 m->_Responsible = NULL;
1533 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1534
1535 if (object->cas_set_mark(markOopDesc::encode(m), mark) != mark) {
1536 m->set_object(NULL);
1537 m->set_owner(NULL);
1538 m->Recycle();
1539 omRelease(Self, m, true);
1540 m = NULL;
1541 continue;
1542 // interference - the markword changed - just retry.
1543 // The state-transitions are one-way, so there's no chance of
1544 // live-lock -- "Inflated" is an absorbing state.
1545 }
1546
1547 // Hopefully the performance counters are allocated on distinct
1548 // cache lines to avoid false sharing on MP systems ...
1549 OM_PERFDATA_OP(Inflations, inc());
1550 if (log_is_enabled(Debug, monitorinflation)) {
1551 if (object->is_instance()) {
1552 ResourceMark rm;
1553 log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1554 p2i(object), p2i(object->mark()),
1555 object->klass()->external_name());
1556 }
1557 }
1558 if (event.should_commit()) {
1559 post_monitor_inflate_event(&event, object, cause);
1560 }
1561 return m;
1562 }
1563 }
1564
1565
1566 // Deflate_idle_monitors() is called at all safepoints, immediately
1567 // after all mutators are stopped, but before any objects have moved.
1568 // It traverses the list of known monitors, deflating where possible.
1569 // The scavenged monitor are returned to the monitor free list.
1570 //
1571 // Beware that we scavenge at *every* stop-the-world point.
1572 // Having a large number of monitors in-circulation negatively
1573 // impacts the performance of some applications (e.g., PointBase).
1574 // Broadly, we want to minimize the # of monitors in circulation.
1575 //
1576 // We have added a flag, MonitorInUseLists, which creates a list
1577 // of active monitors for each thread. deflate_idle_monitors()
1578 // only scans the per-thread in-use lists. omAlloc() puts all
1579 // assigned monitors on the per-thread list. deflate_idle_monitors()
1580 // returns the non-busy monitors to the global free list.
1581 // When a thread dies, omFlush() adds the list of active monitors for
1582 // that thread to a global gOmInUseList acquiring the
1583 // global list lock. deflate_idle_monitors() acquires the global
1584 // list lock to scan for non-busy monitors to the global free list.
1585 // An alternative could have used a single global in-use list. The
1586 // downside would have been the additional cost of acquiring the global list lock
1587 // for every omAlloc().
1588 //
1589 // Perversely, the heap size -- and thus the STW safepoint rate --
1590 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1591 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1592 // This is an unfortunate aspect of this design.
1593
1594 enum ManifestConstants {
1595 ClearResponsibleAtSTW = 0
1596 };
1597
1598 // Deflate a single monitor if not in-use
1599 // Return true if deflated, false if in-use
1600 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1601 ObjectMonitor** freeHeadp,
1602 ObjectMonitor** freeTailp) {
1603 bool deflated;
1604 // Normal case ... The monitor is associated with obj.
1605 guarantee(obj->mark() == markOopDesc::encode(mid), "invariant");
1606 guarantee(mid == obj->mark()->monitor(), "invariant");
1607 guarantee(mid->header()->is_neutral(), "invariant");
1608
1609 if (mid->is_busy()) {
1610 if (ClearResponsibleAtSTW) mid->_Responsible = NULL;
1611 deflated = false;
1612 } else {
1613 // Deflate the monitor if it is no longer being used
1614 // It's idle - scavenge and return to the global free list
1615 // plain old deflation ...
1616 if (log_is_enabled(Debug, monitorinflation)) {
1617 if (obj->is_instance()) {
1618 ResourceMark rm;
1619 log_debug(monitorinflation)("Deflating object " INTPTR_FORMAT " , "
1620 "mark " INTPTR_FORMAT " , type %s",
1621 p2i(obj), p2i(obj->mark()),
1622 obj->klass()->external_name());
1623 }
1624 }
1625
1626 // Restore the header back to obj
1627 obj->release_set_mark(mid->header());
1628 mid->clear();
1629
1630 assert(mid->object() == NULL, "invariant");
1631
1632 // Move the object to the working free list defined by freeHeadp, freeTailp
1633 if (*freeHeadp == NULL) *freeHeadp = mid;
1634 if (*freeTailp != NULL) {
1635 ObjectMonitor * prevtail = *freeTailp;
1636 assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1637 prevtail->FreeNext = mid;
1638 }
1639 *freeTailp = mid;
1640 deflated = true;
1641 }
1642 return deflated;
1643 }
1644
1645 // Walk a given monitor list, and deflate idle monitors
1646 // The given list could be a per-thread list or a global list
1647 // Caller acquires gListLock.
1648 //
1649 // In the case of parallel processing of thread local monitor lists,
1650 // work is done by Threads::parallel_threads_do() which ensures that
1651 // each Java thread is processed by exactly one worker thread, and
1652 // thus avoid conflicts that would arise when worker threads would
1653 // process the same monitor lists concurrently.
1654 //
1655 // See also ParallelSPCleanupTask and
1656 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1657 // Threads::parallel_java_threads_do() in thread.cpp.
1658 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1659 ObjectMonitor** freeHeadp,
1660 ObjectMonitor** freeTailp) {
1661 ObjectMonitor* mid;
1662 ObjectMonitor* next;
1663 ObjectMonitor* cur_mid_in_use = NULL;
1664 int deflated_count = 0;
1665
1666 for (mid = *listHeadp; mid != NULL;) {
1667 oop obj = (oop) mid->object();
1668 if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1669 // if deflate_monitor succeeded,
1670 // extract from per-thread in-use list
1671 if (mid == *listHeadp) {
1672 *listHeadp = mid->FreeNext;
1673 } else if (cur_mid_in_use != NULL) {
1674 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1675 }
1676 next = mid->FreeNext;
1677 mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list
1678 mid = next;
1679 deflated_count++;
1680 } else {
1681 cur_mid_in_use = mid;
1682 mid = mid->FreeNext;
1683 }
1684 }
1685 return deflated_count;
1686 }
1687
1688 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1689 counters->nInuse = 0; // currently associated with objects
1690 counters->nInCirculation = 0; // extant
1691 counters->nScavenged = 0; // reclaimed
1692 }
1693
1694 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
1695 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1696 bool deflated = false;
1697
1698 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1699 ObjectMonitor * freeTailp = NULL;
1700
1701 // Prevent omFlush from changing mids in Thread dtor's during deflation
1702 // And in case the vm thread is acquiring a lock during a safepoint
1703 // See e.g. 6320749
1704 Thread::muxAcquire(&gListLock, "scavenge - return");
1705
1706 if (MonitorInUseLists) {
1707 // Note: the thread-local monitors lists get deflated in
1708 // a separate pass. See deflate_thread_local_monitors().
1709
1710 // For moribund threads, scan gOmInUseList
1711 if (gOmInUseList) {
1712 counters->nInCirculation += gOmInUseCount;
1713 int deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
1714 gOmInUseCount -= deflated_count;
1715 counters->nScavenged += deflated_count;
1716 counters->nInuse += gOmInUseCount;
1717 }
1718
1719 } else {
1720 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
1721 for (; block != NULL; block = next(block)) {
1722 // Iterate over all extant monitors - Scavenge all idle monitors.
1723 assert(block->object() == CHAINMARKER, "must be a block header");
1724 counters->nInCirculation += _BLOCKSIZE;
1725 for (int i = 1; i < _BLOCKSIZE; i++) {
1726 ObjectMonitor* mid = (ObjectMonitor*)&block[i];
1727 oop obj = (oop)mid->object();
1728
1729 if (obj == NULL) {
1730 // The monitor is not associated with an object.
1731 // The monitor should either be a thread-specific private
1732 // free list or the global free list.
1733 // obj == NULL IMPLIES mid->is_busy() == 0
1734 guarantee(!mid->is_busy(), "invariant");
1735 continue;
1736 }
1737 deflated = deflate_monitor(mid, obj, &freeHeadp, &freeTailp);
1738
1739 if (deflated) {
1740 mid->FreeNext = NULL;
1741 counters->nScavenged++;
1742 } else {
1743 counters->nInuse++;
1744 }
1745 }
1746 }
1747 }
1748
1749 // Move the scavenged monitors back to the global free list.
1750 if (freeHeadp != NULL) {
1751 guarantee(freeTailp != NULL && counters->nScavenged > 0, "invariant");
1752 assert(freeTailp->FreeNext == NULL, "invariant");
1753 // constant-time list splice - prepend scavenged segment to gFreeList
1754 freeTailp->FreeNext = gFreeList;
1755 gFreeList = freeHeadp;
1756 }
1757 Thread::muxRelease(&gListLock);
1758
1759 }
1760
1761 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1762 gMonitorFreeCount += counters->nScavenged;
1763
1764 // Consider: audit gFreeList to ensure that gMonitorFreeCount and list agree.
1765
1766 if (ObjectMonitor::Knob_Verbose) {
1767 tty->print_cr("INFO: Deflate: InCirc=%d InUse=%d Scavenged=%d "
1768 "ForceMonitorScavenge=%d : pop=%d free=%d",
1769 counters->nInCirculation, counters->nInuse, counters->nScavenged, ForceMonitorScavenge,
1770 gMonitorPopulation, gMonitorFreeCount);
1771 tty->flush();
1772 }
1773
1774 ForceMonitorScavenge = 0; // Reset
1775
1776 OM_PERFDATA_OP(Deflations, inc(counters->nScavenged));
1777 OM_PERFDATA_OP(MonExtant, set_value(counters->nInCirculation));
1778
1779 // TODO: Add objectMonitor leak detection.
1780 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1781 GVars.stwRandom = os::random();
1782 GVars.stwCycle++;
1783 }
1784
1785 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
1786 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1787 if (!MonitorInUseLists) return;
1788
1789 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1790 ObjectMonitor * freeTailp = NULL;
1791
1792 int deflated_count = deflate_monitor_list(thread->omInUseList_addr(), &freeHeadp, &freeTailp);
1793
1794 Thread::muxAcquire(&gListLock, "scavenge - return");
1795
1796 // Adjust counters
1797 counters->nInCirculation += thread->omInUseCount;
1798 thread->omInUseCount -= deflated_count;
1799 if (ObjectMonitor::Knob_VerifyInUse) {
1800 verifyInUse(thread);
1801 }
1802 counters->nScavenged += deflated_count;
1803 counters->nInuse += thread->omInUseCount;
1804
1805 // Move the scavenged monitors back to the global free list.
1806 if (freeHeadp != NULL) {
1807 guarantee(freeTailp != NULL && deflated_count > 0, "invariant");
1808 assert(freeTailp->FreeNext == NULL, "invariant");
1809
1810 // constant-time list splice - prepend scavenged segment to gFreeList
1811 freeTailp->FreeNext = gFreeList;
1812 gFreeList = freeHeadp;
1813 }
1814 Thread::muxRelease(&gListLock);
1815 }
1816
1817 // Monitor cleanup on JavaThread::exit
1818
1819 // Iterate through monitor cache and attempt to release thread's monitors
1820 // Gives up on a particular monitor if an exception occurs, but continues
1821 // the overall iteration, swallowing the exception.
1822 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1823 private:
1824 TRAPS;
1825
1826 public:
1827 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1828 void do_monitor(ObjectMonitor* mid) {
1829 if (mid->owner() == THREAD) {
1830 if (ObjectMonitor::Knob_VerifyMatch != 0) {
1831 ResourceMark rm;
1832 Handle obj(THREAD, (oop) mid->object());
1833 tty->print("INFO: unexpected locked object:");
1834 javaVFrame::print_locked_object_class_name(tty, obj, "locked");
1835 fatal("exiting JavaThread=" INTPTR_FORMAT
1836 " unexpectedly owns ObjectMonitor=" INTPTR_FORMAT,
1837 p2i(THREAD), p2i(mid));
1838 }
1839 (void)mid->complete_exit(CHECK);
1840 }
1841 }
1842 };
1843
1844 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1845 // ignored. This is meant to be called during JNI thread detach which assumes
1846 // all remaining monitors are heavyweight. All exceptions are swallowed.
1847 // Scanning the extant monitor list can be time consuming.
1848 // A simple optimization is to add a per-thread flag that indicates a thread
1849 // called jni_monitorenter() during its lifetime.
1850 //
1851 // Instead of No_Savepoint_Verifier it might be cheaper to
1852 // use an idiom of the form:
1853 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1854 // <code that must not run at safepoint>
1855 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1856 // Since the tests are extremely cheap we could leave them enabled
1857 // for normal product builds.
1858
1859 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1860 assert(THREAD == JavaThread::current(), "must be current Java thread");
1861 NoSafepointVerifier nsv;
1862 ReleaseJavaMonitorsClosure rjmc(THREAD);
1863 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
1864 ObjectSynchronizer::monitors_iterate(&rjmc);
1865 Thread::muxRelease(&gListLock);
1866 THREAD->clear_pending_exception();
1867 }
1868
1869 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1870 switch (cause) {
1871 case inflate_cause_vm_internal: return "VM Internal";
1872 case inflate_cause_monitor_enter: return "Monitor Enter";
1873 case inflate_cause_wait: return "Monitor Wait";
1874 case inflate_cause_notify: return "Monitor Notify";
1875 case inflate_cause_hash_code: return "Monitor Hash Code";
1876 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1877 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1878 default:
1879 ShouldNotReachHere();
1880 }
1881 return "Unknown";
1882 }
1883
1884 //------------------------------------------------------------------------------
1885 // Debugging code
1886
1887 u_char* ObjectSynchronizer::get_gvars_addr() {
1888 return (u_char*)&GVars;
1889 }
1890
1891 u_char* ObjectSynchronizer::get_gvars_hcSequence_addr() {
1892 return (u_char*)&GVars.hcSequence;
1893 }
1894
1895 size_t ObjectSynchronizer::get_gvars_size() {
1896 return sizeof(SharedGlobals);
1897 }
1898
1899 u_char* ObjectSynchronizer::get_gvars_stwRandom_addr() {
1900 return (u_char*)&GVars.stwRandom;
1901 }
1902
1903 #ifndef PRODUCT
1904
1905 // Check if monitor belongs to the monitor cache
1906 // The list is grow-only so it's *relatively* safe to traverse
1907 // the list of extant blocks without taking a lock.
1908
1909 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
1910 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
1911 while (block != NULL) {
1912 assert(block->object() == CHAINMARKER, "must be a block header");
1913 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
1914 address mon = (address)monitor;
1915 address blk = (address)block;
1916 size_t diff = mon - blk;
1917 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "must be aligned");
1918 return 1;
1919 }
1920 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
1921 }
1922 return 0;
1923 }
1924
1925 #endif