1 /*
2 * Copyright (c) 1998, 2017, 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 "memory/metaspaceShared.hpp"
29 #include "memory/padded.hpp"
30 #include "memory/resourceArea.hpp"
31 #include "oops/markOop.hpp"
32 #include "oops/oop.inline.hpp"
33 #include "runtime/atomic.hpp"
34 #include "runtime/biasedLocking.hpp"
35 #include "runtime/handles.inline.hpp"
36 #include "runtime/interfaceSupport.hpp"
37 #include "runtime/mutexLocker.hpp"
38 #include "runtime/objectMonitor.hpp"
39 #include "runtime/objectMonitor.inline.hpp"
40 #include "runtime/osThread.hpp"
41 #include "runtime/stubRoutines.hpp"
42 #include "runtime/synchronizer.hpp"
43 #include "runtime/thread.inline.hpp"
44 #include "runtime/vframe.hpp"
45 #include "trace/traceMacros.hpp"
46 #include "trace/tracing.hpp"
47 #include "utilities/align.hpp"
48 #include "utilities/dtrace.hpp"
49 #include "utilities/events.hpp"
50 #include "utilities/preserveException.hpp"
51
52 // The "core" versions of monitor enter and exit reside in this file.
53 // The interpreter and compilers contain specialized transliterated
54 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
55 // for instance. If you make changes here, make sure to modify the
56 // interpreter, and both C1 and C2 fast-path inline locking code emission.
57 //
58 // -----------------------------------------------------------------------------
59
60 #ifdef DTRACE_ENABLED
61
62 // Only bother with this argument setup if dtrace is available
63 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
64
65 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
66 char* bytes = NULL; \
67 int len = 0; \
68 jlong jtid = SharedRuntime::get_java_tid(thread); \
69 Symbol* klassname = ((oop)(obj))->klass()->name(); \
70 if (klassname != NULL) { \
71 bytes = (char*)klassname->bytes(); \
72 len = klassname->utf8_length(); \
73 }
74
75 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
76 { \
77 if (DTraceMonitorProbes) { \
78 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
79 HOTSPOT_MONITOR_WAIT(jtid, \
80 (uintptr_t)(monitor), bytes, len, (millis)); \
81 } \
82 }
83
84 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
85 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
86 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
87
88 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
89 { \
90 if (DTraceMonitorProbes) { \
91 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
92 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
93 (uintptr_t)(monitor), bytes, len); \
94 } \
95 }
96
97 #else // ndef DTRACE_ENABLED
98
99 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
100 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
101
102 #endif // ndef DTRACE_ENABLED
103
104 // This exists only as a workaround of dtrace bug 6254741
105 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
106 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
107 return 0;
108 }
109
110 #define NINFLATIONLOCKS 256
111 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
112
113 // global list of blocks of monitors
114 PaddedEnd<ObjectMonitor> * volatile ObjectSynchronizer::gBlockList = NULL;
115 // global monitor free list
116 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL;
117 // global monitor in-use list, for moribund threads,
118 // monitors they inflated need to be scanned for deflation
119 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL;
120 // count of entries in gOmInUseList
121 int ObjectSynchronizer::gOmInUseCount = 0;
122
123 static volatile intptr_t gListLock = 0; // protects global monitor lists
124 static volatile int gMonitorFreeCount = 0; // # on gFreeList
125 static volatile int gMonitorPopulation = 0; // # Extant -- in circulation
126
127 static void post_monitor_inflate_event(EventJavaMonitorInflate&,
128 const oop,
129 const ObjectSynchronizer::InflateCause);
130
131 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
132
133
134 // =====================> Quick functions
135
136 // The quick_* forms are special fast-path variants used to improve
137 // performance. In the simplest case, a "quick_*" implementation could
138 // simply return false, in which case the caller will perform the necessary
139 // state transitions and call the slow-path form.
140 // The fast-path is designed to handle frequently arising cases in an efficient
141 // manner and is just a degenerate "optimistic" variant of the slow-path.
142 // returns true -- to indicate the call was satisfied.
143 // returns false -- to indicate the call needs the services of the slow-path.
144 // A no-loitering ordinance is in effect for code in the quick_* family
145 // operators: safepoints or indefinite blocking (blocking that might span a
146 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
147 // entry.
148 //
149 // Consider: An interesting optimization is to have the JIT recognize the
150 // following common idiom:
151 // synchronized (someobj) { .... ; notify(); }
152 // That is, we find a notify() or notifyAll() call that immediately precedes
153 // the monitorexit operation. In that case the JIT could fuse the operations
154 // into a single notifyAndExit() runtime primitive.
155
156 bool ObjectSynchronizer::quick_notify(oopDesc * obj, Thread * self, bool all) {
157 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
158 assert(self->is_Java_thread(), "invariant");
159 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
160 NoSafepointVerifier nsv;
161 if (obj == NULL) return false; // slow-path for invalid obj
162 const markOop mark = obj->mark();
163
164 if (mark->has_locker() && self->is_lock_owned((address)mark->locker())) {
165 // Degenerate notify
166 // stack-locked by caller so by definition the implied waitset is empty.
167 return true;
168 }
169
170 if (mark->has_monitor()) {
171 ObjectMonitor * const mon = mark->monitor();
172 assert(mon->object() == obj, "invariant");
173 if (mon->owner() != self) return false; // slow-path for IMS exception
174
175 if (mon->first_waiter() != NULL) {
176 // We have one or more waiters. Since this is an inflated monitor
177 // that we own, we can transfer one or more threads from the waitset
178 // to the entrylist here and now, avoiding the slow-path.
179 if (all) {
180 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
181 } else {
182 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
183 }
184 int tally = 0;
185 do {
186 mon->INotify(self);
187 ++tally;
188 } while (mon->first_waiter() != NULL && all);
189 OM_PERFDATA_OP(Notifications, inc(tally));
190 }
191 return true;
192 }
193
194 // biased locking and any other IMS exception states take the slow-path
195 return false;
196 }
197
198
199 // The LockNode emitted directly at the synchronization site would have
200 // been too big if it were to have included support for the cases of inflated
201 // recursive enter and exit, so they go here instead.
202 // Note that we can't safely call AsyncPrintJavaStack() from within
203 // quick_enter() as our thread state remains _in_Java.
204
205 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
206 BasicLock * lock) {
207 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
208 assert(Self->is_Java_thread(), "invariant");
209 assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
210 NoSafepointVerifier nsv;
211 if (obj == NULL) return false; // Need to throw NPE
212 const markOop mark = obj->mark();
213
214 if (mark->has_monitor()) {
215 ObjectMonitor * const m = mark->monitor();
216 assert(m->object() == obj, "invariant");
217 Thread * const owner = (Thread *) m->_owner;
218
219 // Lock contention and Transactional Lock Elision (TLE) diagnostics
220 // and observability
221 // Case: light contention possibly amenable to TLE
222 // Case: TLE inimical operations such as nested/recursive synchronization
223
224 if (owner == Self) {
225 m->_recursions++;
226 return true;
227 }
228
229 // This Java Monitor is inflated so obj's header will never be
230 // displaced to this thread's BasicLock. Make the displaced header
231 // non-NULL so this BasicLock is not seen as recursive nor as
232 // being locked. We do this unconditionally so that this thread's
233 // BasicLock cannot be mis-interpreted by any stack walkers. For
234 // performance reasons, stack walkers generally first check for
235 // Biased Locking in the object's header, the second check is for
236 // stack-locking in the object's header, the third check is for
237 // recursive stack-locking in the displaced header in the BasicLock,
238 // and last are the inflated Java Monitor (ObjectMonitor) checks.
239 lock->set_displaced_header(markOopDesc::unused_mark());
240
241 if (owner == NULL && Atomic::replace_if_null(Self, &(m->_owner))) {
242 assert(m->_recursions == 0, "invariant");
243 assert(m->_owner == Self, "invariant");
244 return true;
245 }
246 }
247
248 // Note that we could inflate in quick_enter.
249 // This is likely a useful optimization
250 // Critically, in quick_enter() we must not:
251 // -- perform bias revocation, or
252 // -- block indefinitely, or
253 // -- reach a safepoint
254
255 return false; // revert to slow-path
256 }
257
258 // -----------------------------------------------------------------------------
259 // Fast Monitor Enter/Exit
260 // This the fast monitor enter. The interpreter and compiler use
261 // some assembly copies of this code. Make sure update those code
262 // if the following function is changed. The implementation is
263 // extremely sensitive to race condition. Be careful.
264
265 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
266 bool attempt_rebias, TRAPS) {
267 if (UseBiasedLocking) {
268 if (!SafepointSynchronize::is_at_safepoint()) {
269 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
270 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
271 return;
272 }
273 } else {
274 assert(!attempt_rebias, "can not rebias toward VM thread");
275 BiasedLocking::revoke_at_safepoint(obj);
276 }
277 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
278 }
279
280 slow_enter(obj, lock, THREAD);
281 }
282
283 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
284 markOop mark = object->mark();
285 // We cannot check for Biased Locking if we are racing an inflation.
286 assert(mark == markOopDesc::INFLATING() ||
287 !mark->has_bias_pattern(), "should not see bias pattern here");
288
289 markOop dhw = lock->displaced_header();
290 if (dhw == NULL) {
291 // If the displaced header is NULL, then this exit matches up with
292 // a recursive enter. No real work to do here except for diagnostics.
293 #ifndef PRODUCT
294 if (mark != markOopDesc::INFLATING()) {
295 // Only do diagnostics if we are not racing an inflation. Simply
296 // exiting a recursive enter of a Java Monitor that is being
297 // inflated is safe; see the has_monitor() comment below.
298 assert(!mark->is_neutral(), "invariant");
299 assert(!mark->has_locker() ||
300 THREAD->is_lock_owned((address)mark->locker()), "invariant");
301 if (mark->has_monitor()) {
302 // The BasicLock's displaced_header is marked as a recursive
303 // enter and we have an inflated Java Monitor (ObjectMonitor).
304 // This is a special case where the Java Monitor was inflated
305 // after this thread entered the stack-lock recursively. When a
306 // Java Monitor is inflated, we cannot safely walk the Java
307 // Monitor owner's stack and update the BasicLocks because a
308 // Java Monitor can be asynchronously inflated by a thread that
309 // does not own the Java Monitor.
310 ObjectMonitor * m = mark->monitor();
311 assert(((oop)(m->object()))->mark() == mark, "invariant");
312 assert(m->is_entered(THREAD), "invariant");
313 }
314 }
315 #endif
316 return;
317 }
318
319 if (mark == (markOop) lock) {
320 // If the object is stack-locked by the current thread, try to
321 // swing the displaced header from the BasicLock back to the mark.
322 assert(dhw->is_neutral(), "invariant");
323 if (object->cas_set_mark(dhw, mark) == mark) {
324 TEVENT(fast_exit: release stack-lock);
325 return;
326 }
327 }
328
329 // We have to take the slow-path of possible inflation and then exit.
330 ObjectSynchronizer::inflate(THREAD,
331 object,
332 inflate_cause_vm_internal)->exit(true, THREAD);
333 }
334
335 // -----------------------------------------------------------------------------
336 // Interpreter/Compiler Slow Case
337 // This routine is used to handle interpreter/compiler slow case
338 // We don't need to use fast path here, because it must have been
339 // failed in the interpreter/compiler code.
340 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
341 markOop mark = obj->mark();
342 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
343
344 if (mark->is_neutral()) {
345 // Anticipate successful CAS -- the ST of the displaced mark must
346 // be visible <= the ST performed by the CAS.
347 lock->set_displaced_header(mark);
348 if (mark == obj()->cas_set_mark((markOop) lock, mark)) {
349 TEVENT(slow_enter: release stacklock);
350 return;
351 }
352 // Fall through to inflate() ...
353 } else if (mark->has_locker() &&
354 THREAD->is_lock_owned((address)mark->locker())) {
355 assert(lock != mark->locker(), "must not re-lock the same lock");
356 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
357 lock->set_displaced_header(NULL);
358 return;
359 }
360
361 // The object header will never be displaced to this lock,
362 // so it does not matter what the value is, except that it
363 // must be non-zero to avoid looking like a re-entrant lock,
364 // and must not look locked either.
365 lock->set_displaced_header(markOopDesc::unused_mark());
366 ObjectSynchronizer::inflate(THREAD,
367 obj(),
368 inflate_cause_monitor_enter)->enter(THREAD);
369 }
370
371 // This routine is used to handle interpreter/compiler slow case
372 // We don't need to use fast path here, because it must have
373 // failed in the interpreter/compiler code. Simply use the heavy
374 // weight monitor should be ok, unless someone find otherwise.
375 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
376 fast_exit(object, lock, THREAD);
377 }
378
379 // -----------------------------------------------------------------------------
380 // Class Loader support to workaround deadlocks on the class loader lock objects
381 // Also used by GC
382 // complete_exit()/reenter() are used to wait on a nested lock
383 // i.e. to give up an outer lock completely and then re-enter
384 // Used when holding nested locks - lock acquisition order: lock1 then lock2
385 // 1) complete_exit lock1 - saving recursion count
386 // 2) wait on lock2
387 // 3) when notified on lock2, unlock lock2
388 // 4) reenter lock1 with original recursion count
389 // 5) lock lock2
390 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
391 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
392 TEVENT(complete_exit);
393 if (UseBiasedLocking) {
394 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
395 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
396 }
397
398 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
399 obj(),
400 inflate_cause_vm_internal);
401
402 return monitor->complete_exit(THREAD);
403 }
404
405 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
406 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
407 TEVENT(reenter);
408 if (UseBiasedLocking) {
409 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
410 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
411 }
412
413 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
414 obj(),
415 inflate_cause_vm_internal);
416
417 monitor->reenter(recursion, THREAD);
418 }
419 // -----------------------------------------------------------------------------
420 // JNI locks on java objects
421 // NOTE: must use heavy weight monitor to handle jni monitor enter
422 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
423 // the current locking is from JNI instead of Java code
424 TEVENT(jni_enter);
425 if (UseBiasedLocking) {
426 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
427 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
428 }
429 THREAD->set_current_pending_monitor_is_from_java(false);
430 ObjectSynchronizer::inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);
431 THREAD->set_current_pending_monitor_is_from_java(true);
432 }
433
434 // NOTE: must use heavy weight monitor to handle jni monitor exit
435 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
436 TEVENT(jni_exit);
437 if (UseBiasedLocking) {
438 Handle h_obj(THREAD, obj);
439 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
440 obj = h_obj();
441 }
442 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
443
444 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
445 obj,
446 inflate_cause_jni_exit);
447 // If this thread has locked the object, exit the monitor. Note: can't use
448 // monitor->check(CHECK); must exit even if an exception is pending.
449 if (monitor->check(THREAD)) {
450 monitor->exit(true, THREAD);
451 }
452 }
453
454 // -----------------------------------------------------------------------------
455 // Internal VM locks on java objects
456 // standard constructor, allows locking failures
457 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
458 _dolock = doLock;
459 _thread = thread;
460 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
461 _obj = obj;
462
463 if (_dolock) {
464 TEVENT(ObjectLocker);
465
466 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
467 }
468 }
469
470 ObjectLocker::~ObjectLocker() {
471 if (_dolock) {
472 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
473 }
474 }
475
476
477 // -----------------------------------------------------------------------------
478 // Wait/Notify/NotifyAll
479 // NOTE: must use heavy weight monitor to handle wait()
480 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
481 if (UseBiasedLocking) {
482 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
483 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
484 }
485 if (millis < 0) {
486 TEVENT(wait - throw IAX);
487 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
488 }
489 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
490 obj(),
491 inflate_cause_wait);
492
493 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
494 monitor->wait(millis, true, THREAD);
495
496 // This dummy call is in place to get around dtrace bug 6254741. Once
497 // that's fixed we can uncomment the following line, remove the call
498 // and change this function back into a "void" func.
499 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
500 return dtrace_waited_probe(monitor, obj, THREAD);
501 }
502
503 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
504 if (UseBiasedLocking) {
505 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
506 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
507 }
508 if (millis < 0) {
509 TEVENT(wait - throw IAX);
510 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
511 }
512 ObjectSynchronizer::inflate(THREAD,
513 obj(),
514 inflate_cause_wait)->wait(millis, false, THREAD);
515 }
516
517 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
518 if (UseBiasedLocking) {
519 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
520 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
521 }
522
523 markOop mark = obj->mark();
524 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
525 return;
526 }
527 ObjectSynchronizer::inflate(THREAD,
528 obj(),
529 inflate_cause_notify)->notify(THREAD);
530 }
531
532 // NOTE: see comment of notify()
533 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
534 if (UseBiasedLocking) {
535 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
536 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
537 }
538
539 markOop mark = obj->mark();
540 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
541 return;
542 }
543 ObjectSynchronizer::inflate(THREAD,
544 obj(),
545 inflate_cause_notify)->notifyAll(THREAD);
546 }
547
548 // -----------------------------------------------------------------------------
549 // Hash Code handling
550 //
551 // Performance concern:
552 // OrderAccess::storestore() calls release() which at one time stored 0
553 // into the global volatile OrderAccess::dummy variable. This store was
554 // unnecessary for correctness. Many threads storing into a common location
555 // causes considerable cache migration or "sloshing" on large SMP systems.
556 // As such, I avoided using OrderAccess::storestore(). In some cases
557 // OrderAccess::fence() -- which incurs local latency on the executing
558 // processor -- is a better choice as it scales on SMP systems.
559 //
560 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
561 // a discussion of coherency costs. Note that all our current reference
562 // platforms provide strong ST-ST order, so the issue is moot on IA32,
563 // x64, and SPARC.
564 //
565 // As a general policy we use "volatile" to control compiler-based reordering
566 // and explicit fences (barriers) to control for architectural reordering
567 // performed by the CPU(s) or platform.
568
569 struct SharedGlobals {
570 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
571 // These are highly shared mostly-read variables.
572 // To avoid false-sharing they need to be the sole occupants of a cache line.
573 volatile int stwRandom;
574 volatile int stwCycle;
575 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
576 // Hot RW variable -- Sequester to avoid false-sharing
577 volatile int hcSequence;
578 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
579 };
580
581 static SharedGlobals GVars;
582 static int MonitorScavengeThreshold = 1000000;
583 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
584
585 static markOop ReadStableMark(oop obj) {
586 markOop mark = obj->mark();
587 if (!mark->is_being_inflated()) {
588 return mark; // normal fast-path return
589 }
590
591 int its = 0;
592 for (;;) {
593 markOop mark = obj->mark();
594 if (!mark->is_being_inflated()) {
595 return mark; // normal fast-path return
596 }
597
598 // The object is being inflated by some other thread.
599 // The caller of ReadStableMark() must wait for inflation to complete.
600 // Avoid live-lock
601 // TODO: consider calling SafepointSynchronize::do_call_back() while
602 // spinning to see if there's a safepoint pending. If so, immediately
603 // yielding or blocking would be appropriate. Avoid spinning while
604 // there is a safepoint pending.
605 // TODO: add inflation contention performance counters.
606 // TODO: restrict the aggregate number of spinners.
607
608 ++its;
609 if (its > 10000 || !os::is_MP()) {
610 if (its & 1) {
611 os::naked_yield();
612 TEVENT(Inflate: INFLATING - yield);
613 } else {
614 // Note that the following code attenuates the livelock problem but is not
615 // a complete remedy. A more complete solution would require that the inflating
616 // thread hold the associated inflation lock. The following code simply restricts
617 // the number of spinners to at most one. We'll have N-2 threads blocked
618 // on the inflationlock, 1 thread holding the inflation lock and using
619 // a yield/park strategy, and 1 thread in the midst of inflation.
620 // A more refined approach would be to change the encoding of INFLATING
621 // to allow encapsulation of a native thread pointer. Threads waiting for
622 // inflation to complete would use CAS to push themselves onto a singly linked
623 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
624 // and calling park(). When inflation was complete the thread that accomplished inflation
625 // would detach the list and set the markword to inflated with a single CAS and
626 // then for each thread on the list, set the flag and unpark() the thread.
627 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
628 // wakes at most one thread whereas we need to wake the entire list.
629 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
630 int YieldThenBlock = 0;
631 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
632 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
633 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
634 while (obj->mark() == markOopDesc::INFLATING()) {
635 // Beware: NakedYield() is advisory and has almost no effect on some platforms
636 // so we periodically call Self->_ParkEvent->park(1).
637 // We use a mixed spin/yield/block mechanism.
638 if ((YieldThenBlock++) >= 16) {
639 Thread::current()->_ParkEvent->park(1);
640 } else {
641 os::naked_yield();
642 }
643 }
644 Thread::muxRelease(gInflationLocks + ix);
645 TEVENT(Inflate: INFLATING - yield/park);
646 }
647 } else {
648 SpinPause(); // SMP-polite spinning
649 }
650 }
651 }
652
653 // hashCode() generation :
654 //
655 // Possibilities:
656 // * MD5Digest of {obj,stwRandom}
657 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
658 // * A DES- or AES-style SBox[] mechanism
659 // * One of the Phi-based schemes, such as:
660 // 2654435761 = 2^32 * Phi (golden ratio)
661 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
662 // * A variation of Marsaglia's shift-xor RNG scheme.
663 // * (obj ^ stwRandom) is appealing, but can result
664 // in undesirable regularity in the hashCode values of adjacent objects
665 // (objects allocated back-to-back, in particular). This could potentially
666 // result in hashtable collisions and reduced hashtable efficiency.
667 // There are simple ways to "diffuse" the middle address bits over the
668 // generated hashCode values:
669
670 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
671 intptr_t value = 0;
672 if (hashCode == 0) {
673 // This form uses global Park-Miller RNG.
674 // On MP system we'll have lots of RW access to a global, so the
675 // mechanism induces lots of coherency traffic.
676 value = os::random();
677 } else if (hashCode == 1) {
678 // This variation has the property of being stable (idempotent)
679 // between STW operations. This can be useful in some of the 1-0
680 // synchronization schemes.
681 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
682 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
683 } else if (hashCode == 2) {
684 value = 1; // for sensitivity testing
685 } else if (hashCode == 3) {
686 value = ++GVars.hcSequence;
687 } else if (hashCode == 4) {
688 value = cast_from_oop<intptr_t>(obj);
689 } else {
690 // Marsaglia's xor-shift scheme with thread-specific state
691 // This is probably the best overall implementation -- we'll
692 // likely make this the default in future releases.
693 unsigned t = Self->_hashStateX;
694 t ^= (t << 11);
695 Self->_hashStateX = Self->_hashStateY;
696 Self->_hashStateY = Self->_hashStateZ;
697 Self->_hashStateZ = Self->_hashStateW;
698 unsigned v = Self->_hashStateW;
699 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
700 Self->_hashStateW = v;
701 value = v;
702 }
703
704 value &= markOopDesc::hash_mask;
705 if (value == 0) value = 0xBAD;
706 assert(value != markOopDesc::no_hash, "invariant");
707 TEVENT(hashCode: GENERATE);
708 return value;
709 }
710
711 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
712 if (UseBiasedLocking) {
713 // NOTE: many places throughout the JVM do not expect a safepoint
714 // to be taken here, in particular most operations on perm gen
715 // objects. However, we only ever bias Java instances and all of
716 // the call sites of identity_hash that might revoke biases have
717 // been checked to make sure they can handle a safepoint. The
718 // added check of the bias pattern is to avoid useless calls to
719 // thread-local storage.
720 if (obj->mark()->has_bias_pattern()) {
721 // Handle for oop obj in case of STW safepoint
722 Handle hobj(Self, obj);
723 // Relaxing assertion for bug 6320749.
724 assert(Universe::verify_in_progress() ||
725 !SafepointSynchronize::is_at_safepoint(),
726 "biases should not be seen by VM thread here");
727 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
728 obj = hobj();
729 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
730 }
731 }
732
733 // hashCode() is a heap mutator ...
734 // Relaxing assertion for bug 6320749.
735 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
736 !SafepointSynchronize::is_at_safepoint(), "invariant");
737 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
738 Self->is_Java_thread() , "invariant");
739 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
740 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
741
742 ObjectMonitor* monitor = NULL;
743 markOop temp, test;
744 intptr_t hash;
745 markOop mark = ReadStableMark(obj);
746
747 // object should remain ineligible for biased locking
748 assert(!mark->has_bias_pattern(), "invariant");
749
750 if (mark->is_neutral()) {
751 hash = mark->hash(); // this is a normal header
752 if (hash) { // if it has hash, just return it
753 return hash;
754 }
755 hash = get_next_hash(Self, obj); // allocate a new hash code
756 temp = mark->copy_set_hash(hash); // merge the hash code into header
757 // use (machine word version) atomic operation to install the hash
758 test = obj->cas_set_mark(temp, mark);
759 if (test == mark) {
760 return hash;
761 }
762 // If atomic operation failed, we must inflate the header
763 // into heavy weight monitor. We could add more code here
764 // for fast path, but it does not worth the complexity.
765 } else if (mark->has_monitor()) {
766 monitor = mark->monitor();
767 temp = monitor->header();
768 assert(temp->is_neutral(), "invariant");
769 hash = temp->hash();
770 if (hash) {
771 return hash;
772 }
773 // Skip to the following code to reduce code size
774 } else if (Self->is_lock_owned((address)mark->locker())) {
775 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
776 assert(temp->is_neutral(), "invariant");
777 hash = temp->hash(); // by current thread, check if the displaced
778 if (hash) { // header contains hash code
779 return hash;
780 }
781 // WARNING:
782 // The displaced header is strictly immutable.
783 // It can NOT be changed in ANY cases. So we have
784 // to inflate the header into heavyweight monitor
785 // even the current thread owns the lock. The reason
786 // is the BasicLock (stack slot) will be asynchronously
787 // read by other threads during the inflate() function.
788 // Any change to stack may not propagate to other threads
789 // correctly.
790 }
791
792 // Inflate the monitor to set hash code
793 monitor = ObjectSynchronizer::inflate(Self, obj, inflate_cause_hash_code);
794 // Load displaced header and check it has hash code
795 mark = monitor->header();
796 assert(mark->is_neutral(), "invariant");
797 hash = mark->hash();
798 if (hash == 0) {
799 hash = get_next_hash(Self, obj);
800 temp = mark->copy_set_hash(hash); // merge hash code into header
801 assert(temp->is_neutral(), "invariant");
802 test = Atomic::cmpxchg(temp, monitor->header_addr(), mark);
803 if (test != mark) {
804 // The only update to the header in the monitor (outside GC)
805 // is install the hash code. If someone add new usage of
806 // displaced header, please update this code
807 hash = test->hash();
808 assert(test->is_neutral(), "invariant");
809 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
810 }
811 }
812 // We finally get the hash
813 return hash;
814 }
815
816 // Deprecated -- use FastHashCode() instead.
817
818 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
819 return FastHashCode(Thread::current(), obj());
820 }
821
822
823 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
824 Handle h_obj) {
825 if (UseBiasedLocking) {
826 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
827 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
828 }
829
830 assert(thread == JavaThread::current(), "Can only be called on current thread");
831 oop obj = h_obj();
832
833 markOop mark = ReadStableMark(obj);
834
835 // Uncontended case, header points to stack
836 if (mark->has_locker()) {
837 return thread->is_lock_owned((address)mark->locker());
838 }
839 // Contended case, header points to ObjectMonitor (tagged pointer)
840 if (mark->has_monitor()) {
841 ObjectMonitor* monitor = mark->monitor();
842 return monitor->is_entered(thread) != 0;
843 }
844 // Unlocked case, header in place
845 assert(mark->is_neutral(), "sanity check");
846 return false;
847 }
848
849 // Be aware of this method could revoke bias of the lock object.
850 // This method queries the ownership of the lock handle specified by 'h_obj'.
851 // If the current thread owns the lock, it returns owner_self. If no
852 // thread owns the lock, it returns owner_none. Otherwise, it will return
853 // owner_other.
854 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
855 (JavaThread *self, Handle h_obj) {
856 // The caller must beware this method can revoke bias, and
857 // revocation can result in a safepoint.
858 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
859 assert(self->thread_state() != _thread_blocked, "invariant");
860
861 // Possible mark states: neutral, biased, stack-locked, inflated
862
863 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
864 // CASE: biased
865 BiasedLocking::revoke_and_rebias(h_obj, false, self);
866 assert(!h_obj->mark()->has_bias_pattern(),
867 "biases should be revoked by now");
868 }
869
870 assert(self == JavaThread::current(), "Can only be called on current thread");
871 oop obj = h_obj();
872 markOop mark = ReadStableMark(obj);
873
874 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
875 if (mark->has_locker()) {
876 return self->is_lock_owned((address)mark->locker()) ?
877 owner_self : owner_other;
878 }
879
880 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
881 // The Object:ObjectMonitor relationship is stable as long as we're
882 // not at a safepoint.
883 if (mark->has_monitor()) {
884 void * owner = mark->monitor()->_owner;
885 if (owner == NULL) return owner_none;
886 return (owner == self ||
887 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
888 }
889
890 // CASE: neutral
891 assert(mark->is_neutral(), "sanity check");
892 return owner_none; // it's unlocked
893 }
894
895 // FIXME: jvmti should call this
896 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
897 if (UseBiasedLocking) {
898 if (SafepointSynchronize::is_at_safepoint()) {
899 BiasedLocking::revoke_at_safepoint(h_obj);
900 } else {
901 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
902 }
903 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
904 }
905
906 oop obj = h_obj();
907 address owner = NULL;
908
909 markOop mark = ReadStableMark(obj);
910
911 // Uncontended case, header points to stack
912 if (mark->has_locker()) {
913 owner = (address) mark->locker();
914 }
915
916 // Contended case, header points to ObjectMonitor (tagged pointer)
917 if (mark->has_monitor()) {
918 ObjectMonitor* monitor = mark->monitor();
919 assert(monitor != NULL, "monitor should be non-null");
920 owner = (address) monitor->owner();
921 }
922
923 if (owner != NULL) {
924 // owning_thread_from_monitor_owner() may also return NULL here
925 return Threads::owning_thread_from_monitor_owner(t_list, owner);
926 }
927
928 // Unlocked case, header in place
929 // Cannot have assertion since this object may have been
930 // locked by another thread when reaching here.
931 // assert(mark->is_neutral(), "sanity check");
932
933 return NULL;
934 }
935
936 // Visitors ...
937
938 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
939 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
940 while (block != NULL) {
941 assert(block->object() == CHAINMARKER, "must be a block header");
942 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
943 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
944 oop object = (oop)mid->object();
945 if (object != NULL) {
946 closure->do_monitor(mid);
947 }
948 }
949 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
950 }
951 }
952
953 // Get the next block in the block list.
954 static inline PaddedEnd<ObjectMonitor>* next(PaddedEnd<ObjectMonitor>* block) {
955 assert(block->object() == CHAINMARKER, "must be a block header");
956 block = (PaddedEnd<ObjectMonitor>*) block->FreeNext;
957 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
958 return block;
959 }
960
961 static bool monitors_used_above_threshold() {
962 if (gMonitorPopulation == 0) {
963 return false;
964 }
965 int monitors_used = gMonitorPopulation - gMonitorFreeCount;
966 int monitor_usage = (monitors_used * 100LL) / gMonitorPopulation;
967 return monitor_usage > MonitorUsedDeflationThreshold;
968 }
969
970 bool ObjectSynchronizer::is_cleanup_needed() {
971 if (MonitorUsedDeflationThreshold > 0) {
972 return monitors_used_above_threshold();
973 }
974 return false;
975 }
976
977 void ObjectSynchronizer::oops_do(OopClosure* f) {
978 if (MonitorInUseLists) {
979 // When using thread local monitor lists, we only scan the
980 // global used list here (for moribund threads), and
981 // the thread-local monitors in Thread::oops_do().
982 global_used_oops_do(f);
983 } else {
984 global_oops_do(f);
985 }
986 }
987
988 void ObjectSynchronizer::global_oops_do(OopClosure* f) {
989 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
990 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
991 for (; block != NULL; block = next(block)) {
992 assert(block->object() == CHAINMARKER, "must be a block header");
993 for (int i = 1; i < _BLOCKSIZE; i++) {
994 ObjectMonitor* mid = (ObjectMonitor *)&block[i];
995 if (mid->object() != NULL) {
996 f->do_oop((oop*)mid->object_addr());
997 }
998 }
999 }
1000 }
1001
1002 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
1003 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1004 list_oops_do(gOmInUseList, f);
1005 }
1006
1007 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
1008 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1009 list_oops_do(thread->omInUseList, f);
1010 }
1011
1012 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
1013 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1014 ObjectMonitor* mid;
1015 for (mid = list; mid != NULL; mid = mid->FreeNext) {
1016 if (mid->object() != NULL) {
1017 f->do_oop((oop*)mid->object_addr());
1018 }
1019 }
1020 }
1021
1022
1023 // -----------------------------------------------------------------------------
1024 // ObjectMonitor Lifecycle
1025 // -----------------------
1026 // Inflation unlinks monitors from the global gFreeList and
1027 // associates them with objects. Deflation -- which occurs at
1028 // STW-time -- disassociates idle monitors from objects. Such
1029 // scavenged monitors are returned to the gFreeList.
1030 //
1031 // The global list is protected by gListLock. All the critical sections
1032 // are short and operate in constant-time.
1033 //
1034 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1035 //
1036 // Lifecycle:
1037 // -- unassigned and on the global free list
1038 // -- unassigned and on a thread's private omFreeList
1039 // -- assigned to an object. The object is inflated and the mark refers
1040 // to the objectmonitor.
1041
1042
1043 // Constraining monitor pool growth via MonitorBound ...
1044 //
1045 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
1046 // the rate of scavenging is driven primarily by GC. As such, we can find
1047 // an inordinate number of monitors in circulation.
1048 // To avoid that scenario we can artificially induce a STW safepoint
1049 // if the pool appears to be growing past some reasonable bound.
1050 // Generally we favor time in space-time tradeoffs, but as there's no
1051 // natural back-pressure on the # of extant monitors we need to impose some
1052 // type of limit. Beware that if MonitorBound is set to too low a value
1053 // we could just loop. In addition, if MonitorBound is set to a low value
1054 // we'll incur more safepoints, which are harmful to performance.
1055 // See also: GuaranteedSafepointInterval
1056 //
1057 // The current implementation uses asynchronous VM operations.
1058
1059 static void InduceScavenge(Thread * Self, const char * Whence) {
1060 // Induce STW safepoint to trim monitors
1061 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1062 // More precisely, trigger an asynchronous STW safepoint as the number
1063 // of active monitors passes the specified threshold.
1064 // TODO: assert thread state is reasonable
1065
1066 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1067 if (ObjectMonitor::Knob_Verbose) {
1068 tty->print_cr("INFO: Monitor scavenge - Induced STW @%s (%d)",
1069 Whence, ForceMonitorScavenge) ;
1070 tty->flush();
1071 }
1072 // Induce a 'null' safepoint to scavenge monitors
1073 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1074 // to the VMthread and have a lifespan longer than that of this activation record.
1075 // The VMThread will delete the op when completed.
1076 VMThread::execute(new VM_ScavengeMonitors());
1077
1078 if (ObjectMonitor::Knob_Verbose) {
1079 tty->print_cr("INFO: Monitor scavenge - STW posted @%s (%d)",
1080 Whence, ForceMonitorScavenge) ;
1081 tty->flush();
1082 }
1083 }
1084 }
1085
1086 void ObjectSynchronizer::verifyInUse(Thread *Self) {
1087 ObjectMonitor* mid;
1088 int in_use_tally = 0;
1089 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) {
1090 in_use_tally++;
1091 }
1092 assert(in_use_tally == Self->omInUseCount, "in-use count off");
1093
1094 int free_tally = 0;
1095 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) {
1096 free_tally++;
1097 }
1098 assert(free_tally == Self->omFreeCount, "free count off");
1099 }
1100
1101 ObjectMonitor* ObjectSynchronizer::omAlloc(Thread * Self) {
1102 // A large MAXPRIVATE value reduces both list lock contention
1103 // and list coherency traffic, but also tends to increase the
1104 // number of objectMonitors in circulation as well as the STW
1105 // scavenge costs. As usual, we lean toward time in space-time
1106 // tradeoffs.
1107 const int MAXPRIVATE = 1024;
1108 for (;;) {
1109 ObjectMonitor * m;
1110
1111 // 1: try to allocate from the thread's local omFreeList.
1112 // Threads will attempt to allocate first from their local list, then
1113 // from the global list, and only after those attempts fail will the thread
1114 // attempt to instantiate new monitors. Thread-local free lists take
1115 // heat off the gListLock and improve allocation latency, as well as reducing
1116 // coherency traffic on the shared global list.
1117 m = Self->omFreeList;
1118 if (m != NULL) {
1119 Self->omFreeList = m->FreeNext;
1120 Self->omFreeCount--;
1121 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene
1122 guarantee(m->object() == NULL, "invariant");
1123 if (MonitorInUseLists) {
1124 m->FreeNext = Self->omInUseList;
1125 Self->omInUseList = m;
1126 Self->omInUseCount++;
1127 if (ObjectMonitor::Knob_VerifyInUse) {
1128 verifyInUse(Self);
1129 }
1130 } else {
1131 m->FreeNext = NULL;
1132 }
1133 return m;
1134 }
1135
1136 // 2: try to allocate from the global gFreeList
1137 // CONSIDER: use muxTry() instead of muxAcquire().
1138 // If the muxTry() fails then drop immediately into case 3.
1139 // If we're using thread-local free lists then try
1140 // to reprovision the caller's free list.
1141 if (gFreeList != NULL) {
1142 // Reprovision the thread's omFreeList.
1143 // Use bulk transfers to reduce the allocation rate and heat
1144 // on various locks.
1145 Thread::muxAcquire(&gListLock, "omAlloc");
1146 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1147 gMonitorFreeCount--;
1148 ObjectMonitor * take = gFreeList;
1149 gFreeList = take->FreeNext;
1150 guarantee(take->object() == NULL, "invariant");
1151 guarantee(!take->is_busy(), "invariant");
1152 take->Recycle();
1153 omRelease(Self, take, false);
1154 }
1155 Thread::muxRelease(&gListLock);
1156 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1157 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1158 TEVENT(omFirst - reprovision);
1159
1160 const int mx = MonitorBound;
1161 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1162 // We can't safely induce a STW safepoint from omAlloc() as our thread
1163 // state may not be appropriate for such activities and callers may hold
1164 // naked oops, so instead we defer the action.
1165 InduceScavenge(Self, "omAlloc");
1166 }
1167 continue;
1168 }
1169
1170 // 3: allocate a block of new ObjectMonitors
1171 // Both the local and global free lists are empty -- resort to malloc().
1172 // In the current implementation objectMonitors are TSM - immortal.
1173 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1174 // each ObjectMonitor to start at the beginning of a cache line,
1175 // so we use align_up().
1176 // A better solution would be to use C++ placement-new.
1177 // BEWARE: As it stands currently, we don't run the ctors!
1178 assert(_BLOCKSIZE > 1, "invariant");
1179 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
1180 PaddedEnd<ObjectMonitor> * temp;
1181 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1182 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
1183 mtInternal);
1184 temp = (PaddedEnd<ObjectMonitor> *)
1185 align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE);
1186
1187 // NOTE: (almost) no way to recover if allocation failed.
1188 // We might be able to induce a STW safepoint and scavenge enough
1189 // objectMonitors to permit progress.
1190 if (temp == NULL) {
1191 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1192 "Allocate ObjectMonitors");
1193 }
1194 (void)memset((void *) temp, 0, neededsize);
1195
1196 // Format the block.
1197 // initialize the linked list, each monitor points to its next
1198 // forming the single linked free list, the very first monitor
1199 // will points to next block, which forms the block list.
1200 // The trick of using the 1st element in the block as gBlockList
1201 // linkage should be reconsidered. A better implementation would
1202 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1203
1204 for (int i = 1; i < _BLOCKSIZE; i++) {
1205 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1206 }
1207
1208 // terminate the last monitor as the end of list
1209 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1210
1211 // Element [0] is reserved for global list linkage
1212 temp[0].set_object(CHAINMARKER);
1213
1214 // Consider carving out this thread's current request from the
1215 // block in hand. This avoids some lock traffic and redundant
1216 // list activity.
1217
1218 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1219 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1220 Thread::muxAcquire(&gListLock, "omAlloc [2]");
1221 gMonitorPopulation += _BLOCKSIZE-1;
1222 gMonitorFreeCount += _BLOCKSIZE-1;
1223
1224 // Add the new block to the list of extant blocks (gBlockList).
1225 // The very first objectMonitor in a block is reserved and dedicated.
1226 // It serves as blocklist "next" linkage.
1227 temp[0].FreeNext = gBlockList;
1228 // There are lock-free uses of gBlockList so make sure that
1229 // the previous stores happen before we update gBlockList.
1230 OrderAccess::release_store(&gBlockList, temp);
1231
1232 // Add the new string of objectMonitors to the global free list
1233 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1234 gFreeList = temp + 1;
1235 Thread::muxRelease(&gListLock);
1236 TEVENT(Allocate block of monitors);
1237 }
1238 }
1239
1240 // Place "m" on the caller's private per-thread omFreeList.
1241 // In practice there's no need to clamp or limit the number of
1242 // monitors on a thread's omFreeList as the only time we'll call
1243 // omRelease is to return a monitor to the free list after a CAS
1244 // attempt failed. This doesn't allow unbounded #s of monitors to
1245 // accumulate on a thread's free list.
1246 //
1247 // Key constraint: all ObjectMonitors on a thread's free list and the global
1248 // free list must have their object field set to null. This prevents the
1249 // scavenger -- deflate_idle_monitors -- from reclaiming them.
1250
1251 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1252 bool fromPerThreadAlloc) {
1253 guarantee(m->object() == NULL, "invariant");
1254 guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor");
1255 // Remove from omInUseList
1256 if (MonitorInUseLists && fromPerThreadAlloc) {
1257 ObjectMonitor* cur_mid_in_use = NULL;
1258 bool extracted = false;
1259 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1260 if (m == mid) {
1261 // extract from per-thread in-use list
1262 if (mid == Self->omInUseList) {
1263 Self->omInUseList = mid->FreeNext;
1264 } else if (cur_mid_in_use != NULL) {
1265 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1266 }
1267 extracted = true;
1268 Self->omInUseCount--;
1269 if (ObjectMonitor::Knob_VerifyInUse) {
1270 verifyInUse(Self);
1271 }
1272 break;
1273 }
1274 }
1275 assert(extracted, "Should have extracted from in-use list");
1276 }
1277
1278 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1279 m->FreeNext = Self->omFreeList;
1280 Self->omFreeList = m;
1281 Self->omFreeCount++;
1282 }
1283
1284 // Return the monitors of a moribund thread's local free list to
1285 // the global free list. Typically a thread calls omFlush() when
1286 // it's dying. We could also consider having the VM thread steal
1287 // monitors from threads that have not run java code over a few
1288 // consecutive STW safepoints. Relatedly, we might decay
1289 // omFreeProvision at STW safepoints.
1290 //
1291 // Also return the monitors of a moribund thread's omInUseList to
1292 // a global gOmInUseList under the global list lock so these
1293 // will continue to be scanned.
1294 //
1295 // We currently call omFlush() from Threads::remove() _before the thread
1296 // has been excised from the thread list and is no longer a mutator.
1297 // This means that omFlush() can not run concurrently with a safepoint and
1298 // interleave with the scavenge operator. In particular, this ensures that
1299 // the thread's monitors are scanned by a GC safepoint, either via
1300 // Thread::oops_do() (if safepoint happens before omFlush()) or via
1301 // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's
1302 // monitors have been transferred to the global in-use list).
1303
1304 void ObjectSynchronizer::omFlush(Thread * Self) {
1305 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1306 Self->omFreeList = NULL;
1307 ObjectMonitor * tail = NULL;
1308 int tally = 0;
1309 if (list != NULL) {
1310 ObjectMonitor * s;
1311 // The thread is going away, the per-thread free monitors
1312 // are freed via set_owner(NULL)
1313 // Link them to tail, which will be linked into the global free list
1314 // gFreeList below, under the gListLock
1315 for (s = list; s != NULL; s = s->FreeNext) {
1316 tally++;
1317 tail = s;
1318 guarantee(s->object() == NULL, "invariant");
1319 guarantee(!s->is_busy(), "invariant");
1320 s->set_owner(NULL); // redundant but good hygiene
1321 TEVENT(omFlush - Move one);
1322 }
1323 guarantee(tail != NULL && list != NULL, "invariant");
1324 }
1325
1326 ObjectMonitor * inUseList = Self->omInUseList;
1327 ObjectMonitor * inUseTail = NULL;
1328 int inUseTally = 0;
1329 if (inUseList != NULL) {
1330 Self->omInUseList = NULL;
1331 ObjectMonitor *cur_om;
1332 // The thread is going away, however the omInUseList inflated
1333 // monitors may still be in-use by other threads.
1334 // Link them to inUseTail, which will be linked into the global in-use list
1335 // gOmInUseList below, under the gListLock
1336 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1337 inUseTail = cur_om;
1338 inUseTally++;
1339 }
1340 assert(Self->omInUseCount == inUseTally, "in-use count off");
1341 Self->omInUseCount = 0;
1342 guarantee(inUseTail != NULL && inUseList != NULL, "invariant");
1343 }
1344
1345 Thread::muxAcquire(&gListLock, "omFlush");
1346 if (tail != NULL) {
1347 tail->FreeNext = gFreeList;
1348 gFreeList = list;
1349 gMonitorFreeCount += tally;
1350 assert(Self->omFreeCount == tally, "free-count off");
1351 Self->omFreeCount = 0;
1352 }
1353
1354 if (inUseTail != NULL) {
1355 inUseTail->FreeNext = gOmInUseList;
1356 gOmInUseList = inUseList;
1357 gOmInUseCount += inUseTally;
1358 }
1359
1360 Thread::muxRelease(&gListLock);
1361 TEVENT(omFlush);
1362 }
1363
1364 // Fast path code shared by multiple functions
1365 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1366 markOop mark = obj->mark();
1367 if (mark->has_monitor()) {
1368 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1369 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1370 return mark->monitor();
1371 }
1372 return ObjectSynchronizer::inflate(Thread::current(),
1373 obj,
1374 inflate_cause_vm_internal);
1375 }
1376
1377 ObjectMonitor* ObjectSynchronizer::inflate(Thread * Self,
1378 oop object,
1379 const InflateCause cause) {
1380
1381 // Inflate mutates the heap ...
1382 // Relaxing assertion for bug 6320749.
1383 assert(Universe::verify_in_progress() ||
1384 !SafepointSynchronize::is_at_safepoint(), "invariant");
1385
1386 EventJavaMonitorInflate event;
1387
1388 for (;;) {
1389 const markOop mark = object->mark();
1390 assert(!mark->has_bias_pattern(), "invariant");
1391
1392 // The mark can be in one of the following states:
1393 // * Inflated - just return
1394 // * Stack-locked - coerce it to inflated
1395 // * INFLATING - busy wait for conversion to complete
1396 // * Neutral - aggressively inflate the object.
1397 // * BIASED - Illegal. We should never see this
1398
1399 // CASE: inflated
1400 if (mark->has_monitor()) {
1401 ObjectMonitor * inf = mark->monitor();
1402 assert(inf->header()->is_neutral(), "invariant");
1403 assert(inf->object() == object, "invariant");
1404 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1405 return inf;
1406 }
1407
1408 // CASE: inflation in progress - inflating over a stack-lock.
1409 // Some other thread is converting from stack-locked to inflated.
1410 // Only that thread can complete inflation -- other threads must wait.
1411 // The INFLATING value is transient.
1412 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1413 // We could always eliminate polling by parking the thread on some auxiliary list.
1414 if (mark == markOopDesc::INFLATING()) {
1415 TEVENT(Inflate: spin while INFLATING);
1416 ReadStableMark(object);
1417 continue;
1418 }
1419
1420 // CASE: stack-locked
1421 // Could be stack-locked either by this thread or by some other thread.
1422 //
1423 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1424 // to install INFLATING into the mark word. We originally installed INFLATING,
1425 // allocated the objectmonitor, and then finally STed the address of the
1426 // objectmonitor into the mark. This was correct, but artificially lengthened
1427 // the interval in which INFLATED appeared in the mark, thus increasing
1428 // the odds of inflation contention.
1429 //
1430 // We now use per-thread private objectmonitor free lists.
1431 // These list are reprovisioned from the global free list outside the
1432 // critical INFLATING...ST interval. A thread can transfer
1433 // multiple objectmonitors en-mass from the global free list to its local free list.
1434 // This reduces coherency traffic and lock contention on the global free list.
1435 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1436 // before or after the CAS(INFLATING) operation.
1437 // See the comments in omAlloc().
1438
1439 if (mark->has_locker()) {
1440 ObjectMonitor * m = omAlloc(Self);
1441 // Optimistically prepare the objectmonitor - anticipate successful CAS
1442 // We do this before the CAS in order to minimize the length of time
1443 // in which INFLATING appears in the mark.
1444 m->Recycle();
1445 m->_Responsible = NULL;
1446 m->_recursions = 0;
1447 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1448
1449 markOop cmp = object->cas_set_mark(markOopDesc::INFLATING(), mark);
1450 if (cmp != mark) {
1451 omRelease(Self, m, true);
1452 continue; // Interference -- just retry
1453 }
1454
1455 // We've successfully installed INFLATING (0) into the mark-word.
1456 // This is the only case where 0 will appear in a mark-word.
1457 // Only the singular thread that successfully swings the mark-word
1458 // to 0 can perform (or more precisely, complete) inflation.
1459 //
1460 // Why do we CAS a 0 into the mark-word instead of just CASing the
1461 // mark-word from the stack-locked value directly to the new inflated state?
1462 // Consider what happens when a thread unlocks a stack-locked object.
1463 // It attempts to use CAS to swing the displaced header value from the
1464 // on-stack basiclock back into the object header. Recall also that the
1465 // header value (hashcode, etc) can reside in (a) the object header, or
1466 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1467 // header in an objectMonitor. The inflate() routine must copy the header
1468 // value from the basiclock on the owner's stack to the objectMonitor, all
1469 // the while preserving the hashCode stability invariants. If the owner
1470 // decides to release the lock while the value is 0, the unlock will fail
1471 // and control will eventually pass from slow_exit() to inflate. The owner
1472 // will then spin, waiting for the 0 value to disappear. Put another way,
1473 // the 0 causes the owner to stall if the owner happens to try to
1474 // drop the lock (restoring the header from the basiclock to the object)
1475 // while inflation is in-progress. This protocol avoids races that might
1476 // would otherwise permit hashCode values to change or "flicker" for an object.
1477 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1478 // 0 serves as a "BUSY" inflate-in-progress indicator.
1479
1480
1481 // fetch the displaced mark from the owner's stack.
1482 // The owner can't die or unwind past the lock while our INFLATING
1483 // object is in the mark. Furthermore the owner can't complete
1484 // an unlock on the object, either.
1485 markOop dmw = mark->displaced_mark_helper();
1486 assert(dmw->is_neutral(), "invariant");
1487
1488 // Setup monitor fields to proper values -- prepare the monitor
1489 m->set_header(dmw);
1490
1491 // Optimization: if the mark->locker stack address is associated
1492 // with this thread we could simply set m->_owner = Self.
1493 // Note that a thread can inflate an object
1494 // that it has stack-locked -- as might happen in wait() -- directly
1495 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1496 m->set_owner(mark->locker());
1497 m->set_object(object);
1498 // TODO-FIXME: assert BasicLock->dhw != 0.
1499
1500 // Must preserve store ordering. The monitor state must
1501 // be stable at the time of publishing the monitor address.
1502 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1503 object->release_set_mark(markOopDesc::encode(m));
1504
1505 // Hopefully the performance counters are allocated on distinct cache lines
1506 // to avoid false sharing on MP systems ...
1507 OM_PERFDATA_OP(Inflations, inc());
1508 TEVENT(Inflate: overwrite stacklock);
1509 if (log_is_enabled(Debug, monitorinflation)) {
1510 if (object->is_instance()) {
1511 ResourceMark rm;
1512 log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1513 p2i(object), p2i(object->mark()),
1514 object->klass()->external_name());
1515 }
1516 }
1517 if (event.should_commit()) {
1518 post_monitor_inflate_event(event, object, cause);
1519 }
1520 return m;
1521 }
1522
1523 // CASE: neutral
1524 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1525 // If we know we're inflating for entry it's better to inflate by swinging a
1526 // pre-locked objectMonitor pointer into the object header. A successful
1527 // CAS inflates the object *and* confers ownership to the inflating thread.
1528 // In the current implementation we use a 2-step mechanism where we CAS()
1529 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1530 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1531 // would be useful.
1532
1533 assert(mark->is_neutral(), "invariant");
1534 ObjectMonitor * m = omAlloc(Self);
1535 // prepare m for installation - set monitor to initial state
1536 m->Recycle();
1537 m->set_header(mark);
1538 m->set_owner(NULL);
1539 m->set_object(object);
1540 m->_recursions = 0;
1541 m->_Responsible = NULL;
1542 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1543
1544 if (object->cas_set_mark(markOopDesc::encode(m), mark) != mark) {
1545 m->set_object(NULL);
1546 m->set_owner(NULL);
1547 m->Recycle();
1548 omRelease(Self, m, true);
1549 m = NULL;
1550 continue;
1551 // interference - the markword changed - just retry.
1552 // The state-transitions are one-way, so there's no chance of
1553 // live-lock -- "Inflated" is an absorbing state.
1554 }
1555
1556 // Hopefully the performance counters are allocated on distinct
1557 // cache lines to avoid false sharing on MP systems ...
1558 OM_PERFDATA_OP(Inflations, inc());
1559 TEVENT(Inflate: overwrite neutral);
1560 if (log_is_enabled(Debug, monitorinflation)) {
1561 if (object->is_instance()) {
1562 ResourceMark rm;
1563 log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1564 p2i(object), p2i(object->mark()),
1565 object->klass()->external_name());
1566 }
1567 }
1568 if (event.should_commit()) {
1569 post_monitor_inflate_event(event, object, cause);
1570 }
1571 return m;
1572 }
1573 }
1574
1575
1576 // Deflate_idle_monitors() is called at all safepoints, immediately
1577 // after all mutators are stopped, but before any objects have moved.
1578 // It traverses the list of known monitors, deflating where possible.
1579 // The scavenged monitor are returned to the monitor free list.
1580 //
1581 // Beware that we scavenge at *every* stop-the-world point.
1582 // Having a large number of monitors in-circulation negatively
1583 // impacts the performance of some applications (e.g., PointBase).
1584 // Broadly, we want to minimize the # of monitors in circulation.
1585 //
1586 // We have added a flag, MonitorInUseLists, which creates a list
1587 // of active monitors for each thread. deflate_idle_monitors()
1588 // only scans the per-thread in-use lists. omAlloc() puts all
1589 // assigned monitors on the per-thread list. deflate_idle_monitors()
1590 // returns the non-busy monitors to the global free list.
1591 // When a thread dies, omFlush() adds the list of active monitors for
1592 // that thread to a global gOmInUseList acquiring the
1593 // global list lock. deflate_idle_monitors() acquires the global
1594 // list lock to scan for non-busy monitors to the global free list.
1595 // An alternative could have used a single global in-use list. The
1596 // downside would have been the additional cost of acquiring the global list lock
1597 // for every omAlloc().
1598 //
1599 // Perversely, the heap size -- and thus the STW safepoint rate --
1600 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1601 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1602 // This is an unfortunate aspect of this design.
1603
1604 enum ManifestConstants {
1605 ClearResponsibleAtSTW = 0
1606 };
1607
1608 // Deflate a single monitor if not in-use
1609 // Return true if deflated, false if in-use
1610 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1611 ObjectMonitor** freeHeadp,
1612 ObjectMonitor** freeTailp) {
1613 bool deflated;
1614 // Normal case ... The monitor is associated with obj.
1615 guarantee(obj->mark() == markOopDesc::encode(mid), "invariant");
1616 guarantee(mid == obj->mark()->monitor(), "invariant");
1617 guarantee(mid->header()->is_neutral(), "invariant");
1618
1619 if (mid->is_busy()) {
1620 if (ClearResponsibleAtSTW) mid->_Responsible = NULL;
1621 deflated = false;
1622 } else {
1623 // Deflate the monitor if it is no longer being used
1624 // It's idle - scavenge and return to the global free list
1625 // plain old deflation ...
1626 TEVENT(deflate_idle_monitors - scavenge1);
1627 if (log_is_enabled(Debug, monitorinflation)) {
1628 if (obj->is_instance()) {
1629 ResourceMark rm;
1630 log_debug(monitorinflation)("Deflating object " INTPTR_FORMAT " , "
1631 "mark " INTPTR_FORMAT " , type %s",
1632 p2i(obj), p2i(obj->mark()),
1633 obj->klass()->external_name());
1634 }
1635 }
1636
1637 // Restore the header back to obj
1638 obj->release_set_mark(mid->header());
1639 mid->clear();
1640
1641 assert(mid->object() == NULL, "invariant");
1642
1643 // Move the object to the working free list defined by freeHeadp, freeTailp
1644 if (*freeHeadp == NULL) *freeHeadp = mid;
1645 if (*freeTailp != NULL) {
1646 ObjectMonitor * prevtail = *freeTailp;
1647 assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1648 prevtail->FreeNext = mid;
1649 }
1650 *freeTailp = mid;
1651 deflated = true;
1652 }
1653 return deflated;
1654 }
1655
1656 // Walk a given monitor list, and deflate idle monitors
1657 // The given list could be a per-thread list or a global list
1658 // Caller acquires gListLock.
1659 //
1660 // In the case of parallel processing of thread local monitor lists,
1661 // work is done by Threads::parallel_threads_do() which ensures that
1662 // each Java thread is processed by exactly one worker thread, and
1663 // thus avoid conflicts that would arise when worker threads would
1664 // process the same monitor lists concurrently.
1665 //
1666 // See also ParallelSPCleanupTask and
1667 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1668 // Threads::parallel_java_threads_do() in thread.cpp.
1669 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1670 ObjectMonitor** freeHeadp,
1671 ObjectMonitor** freeTailp) {
1672 ObjectMonitor* mid;
1673 ObjectMonitor* next;
1674 ObjectMonitor* cur_mid_in_use = NULL;
1675 int deflated_count = 0;
1676
1677 for (mid = *listHeadp; mid != NULL;) {
1678 oop obj = (oop) mid->object();
1679 if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1680 // if deflate_monitor succeeded,
1681 // extract from per-thread in-use list
1682 if (mid == *listHeadp) {
1683 *listHeadp = mid->FreeNext;
1684 } else if (cur_mid_in_use != NULL) {
1685 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1686 }
1687 next = mid->FreeNext;
1688 mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list
1689 mid = next;
1690 deflated_count++;
1691 } else {
1692 cur_mid_in_use = mid;
1693 mid = mid->FreeNext;
1694 }
1695 }
1696 return deflated_count;
1697 }
1698
1699 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1700 counters->nInuse = 0; // currently associated with objects
1701 counters->nInCirculation = 0; // extant
1702 counters->nScavenged = 0; // reclaimed
1703 }
1704
1705 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
1706 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1707 bool deflated = false;
1708
1709 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1710 ObjectMonitor * freeTailp = NULL;
1711
1712 TEVENT(deflate_idle_monitors);
1713 // Prevent omFlush from changing mids in Thread dtor's during deflation
1714 // And in case the vm thread is acquiring a lock during a safepoint
1715 // See e.g. 6320749
1716 Thread::muxAcquire(&gListLock, "scavenge - return");
1717
1718 if (MonitorInUseLists) {
1719 // Note: the thread-local monitors lists get deflated in
1720 // a separate pass. See deflate_thread_local_monitors().
1721
1722 // For moribund threads, scan gOmInUseList
1723 if (gOmInUseList) {
1724 counters->nInCirculation += gOmInUseCount;
1725 int deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
1726 gOmInUseCount -= deflated_count;
1727 counters->nScavenged += deflated_count;
1728 counters->nInuse += gOmInUseCount;
1729 }
1730
1731 } else {
1732 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
1733 for (; block != NULL; block = next(block)) {
1734 // Iterate over all extant monitors - Scavenge all idle monitors.
1735 assert(block->object() == CHAINMARKER, "must be a block header");
1736 counters->nInCirculation += _BLOCKSIZE;
1737 for (int i = 1; i < _BLOCKSIZE; i++) {
1738 ObjectMonitor* mid = (ObjectMonitor*)&block[i];
1739 oop obj = (oop)mid->object();
1740
1741 if (obj == NULL) {
1742 // The monitor is not associated with an object.
1743 // The monitor should either be a thread-specific private
1744 // free list or the global free list.
1745 // obj == NULL IMPLIES mid->is_busy() == 0
1746 guarantee(!mid->is_busy(), "invariant");
1747 continue;
1748 }
1749 deflated = deflate_monitor(mid, obj, &freeHeadp, &freeTailp);
1750
1751 if (deflated) {
1752 mid->FreeNext = NULL;
1753 counters->nScavenged++;
1754 } else {
1755 counters->nInuse++;
1756 }
1757 }
1758 }
1759 }
1760
1761 // Move the scavenged monitors back to the global free list.
1762 if (freeHeadp != NULL) {
1763 guarantee(freeTailp != NULL && counters->nScavenged > 0, "invariant");
1764 assert(freeTailp->FreeNext == NULL, "invariant");
1765 // constant-time list splice - prepend scavenged segment to gFreeList
1766 freeTailp->FreeNext = gFreeList;
1767 gFreeList = freeHeadp;
1768 }
1769 Thread::muxRelease(&gListLock);
1770
1771 }
1772
1773 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1774 gMonitorFreeCount += counters->nScavenged;
1775
1776 // Consider: audit gFreeList to ensure that gMonitorFreeCount and list agree.
1777
1778 if (ObjectMonitor::Knob_Verbose) {
1779 tty->print_cr("INFO: Deflate: InCirc=%d InUse=%d Scavenged=%d "
1780 "ForceMonitorScavenge=%d : pop=%d free=%d",
1781 counters->nInCirculation, counters->nInuse, counters->nScavenged, ForceMonitorScavenge,
1782 gMonitorPopulation, gMonitorFreeCount);
1783 tty->flush();
1784 }
1785
1786 ForceMonitorScavenge = 0; // Reset
1787
1788 OM_PERFDATA_OP(Deflations, inc(counters->nScavenged));
1789 OM_PERFDATA_OP(MonExtant, set_value(counters->nInCirculation));
1790
1791 // TODO: Add objectMonitor leak detection.
1792 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1793 GVars.stwRandom = os::random();
1794 GVars.stwCycle++;
1795 }
1796
1797 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
1798 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1799 if (!MonitorInUseLists) return;
1800
1801 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1802 ObjectMonitor * freeTailp = NULL;
1803
1804 int deflated_count = deflate_monitor_list(thread->omInUseList_addr(), &freeHeadp, &freeTailp);
1805
1806 Thread::muxAcquire(&gListLock, "scavenge - return");
1807
1808 // Adjust counters
1809 counters->nInCirculation += thread->omInUseCount;
1810 thread->omInUseCount -= deflated_count;
1811 if (ObjectMonitor::Knob_VerifyInUse) {
1812 verifyInUse(thread);
1813 }
1814 counters->nScavenged += deflated_count;
1815 counters->nInuse += thread->omInUseCount;
1816
1817 // Move the scavenged monitors back to the global free list.
1818 if (freeHeadp != NULL) {
1819 guarantee(freeTailp != NULL && deflated_count > 0, "invariant");
1820 assert(freeTailp->FreeNext == NULL, "invariant");
1821
1822 // constant-time list splice - prepend scavenged segment to gFreeList
1823 freeTailp->FreeNext = gFreeList;
1824 gFreeList = freeHeadp;
1825 }
1826 Thread::muxRelease(&gListLock);
1827 }
1828
1829 // Monitor cleanup on JavaThread::exit
1830
1831 // Iterate through monitor cache and attempt to release thread's monitors
1832 // Gives up on a particular monitor if an exception occurs, but continues
1833 // the overall iteration, swallowing the exception.
1834 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1835 private:
1836 TRAPS;
1837
1838 public:
1839 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1840 void do_monitor(ObjectMonitor* mid) {
1841 if (mid->owner() == THREAD) {
1842 if (ObjectMonitor::Knob_VerifyMatch != 0) {
1843 ResourceMark rm;
1844 Handle obj(THREAD, (oop) mid->object());
1845 tty->print("INFO: unexpected locked object:");
1846 javaVFrame::print_locked_object_class_name(tty, obj, "locked");
1847 fatal("exiting JavaThread=" INTPTR_FORMAT
1848 " unexpectedly owns ObjectMonitor=" INTPTR_FORMAT,
1849 p2i(THREAD), p2i(mid));
1850 }
1851 (void)mid->complete_exit(CHECK);
1852 }
1853 }
1854 };
1855
1856 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1857 // ignored. This is meant to be called during JNI thread detach which assumes
1858 // all remaining monitors are heavyweight. All exceptions are swallowed.
1859 // Scanning the extant monitor list can be time consuming.
1860 // A simple optimization is to add a per-thread flag that indicates a thread
1861 // called jni_monitorenter() during its lifetime.
1862 //
1863 // Instead of No_Savepoint_Verifier it might be cheaper to
1864 // use an idiom of the form:
1865 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1866 // <code that must not run at safepoint>
1867 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1868 // Since the tests are extremely cheap we could leave them enabled
1869 // for normal product builds.
1870
1871 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1872 assert(THREAD == JavaThread::current(), "must be current Java thread");
1873 NoSafepointVerifier nsv;
1874 ReleaseJavaMonitorsClosure rjmc(THREAD);
1875 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
1876 ObjectSynchronizer::monitors_iterate(&rjmc);
1877 Thread::muxRelease(&gListLock);
1878 THREAD->clear_pending_exception();
1879 }
1880
1881 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1882 switch (cause) {
1883 case inflate_cause_vm_internal: return "VM Internal";
1884 case inflate_cause_monitor_enter: return "Monitor Enter";
1885 case inflate_cause_wait: return "Monitor Wait";
1886 case inflate_cause_notify: return "Monitor Notify";
1887 case inflate_cause_hash_code: return "Monitor Hash Code";
1888 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1889 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1890 default:
1891 ShouldNotReachHere();
1892 }
1893 return "Unknown";
1894 }
1895
1896 static void post_monitor_inflate_event(EventJavaMonitorInflate& event,
1897 const oop obj,
1898 const ObjectSynchronizer::InflateCause cause) {
1899 #if INCLUDE_TRACE
1900 assert(event.should_commit(), "check outside");
1901 event.set_monitorClass(obj->klass());
1902 event.set_address((TYPE_ADDRESS)(uintptr_t)(void*)obj);
1903 event.set_cause((u1)cause);
1904 event.commit();
1905 #endif
1906 }
1907
1908 //------------------------------------------------------------------------------
1909 // Debugging code
1910
1911 void ObjectSynchronizer::sanity_checks(const bool verbose,
1912 const uint cache_line_size,
1913 int *error_cnt_ptr,
1914 int *warning_cnt_ptr) {
1915 u_char *addr_begin = (u_char*)&GVars;
1916 u_char *addr_stwRandom = (u_char*)&GVars.stwRandom;
1917 u_char *addr_hcSequence = (u_char*)&GVars.hcSequence;
1918
1919 if (verbose) {
1920 tty->print_cr("INFO: sizeof(SharedGlobals)=" SIZE_FORMAT,
1921 sizeof(SharedGlobals));
1922 }
1923
1924 uint offset_stwRandom = (uint)(addr_stwRandom - addr_begin);
1925 if (verbose) tty->print_cr("INFO: offset(stwRandom)=%u", offset_stwRandom);
1926
1927 uint offset_hcSequence = (uint)(addr_hcSequence - addr_begin);
1928 if (verbose) {
1929 tty->print_cr("INFO: offset(_hcSequence)=%u", offset_hcSequence);
1930 }
1931
1932 if (cache_line_size != 0) {
1933 // We were able to determine the L1 data cache line size so
1934 // do some cache line specific sanity checks
1935
1936 if (offset_stwRandom < cache_line_size) {
1937 tty->print_cr("WARNING: the SharedGlobals.stwRandom field is closer "
1938 "to the struct beginning than a cache line which permits "
1939 "false sharing.");
1940 (*warning_cnt_ptr)++;
1941 }
1942
1943 if ((offset_hcSequence - offset_stwRandom) < cache_line_size) {
1944 tty->print_cr("WARNING: the SharedGlobals.stwRandom and "
1945 "SharedGlobals.hcSequence fields are closer than a cache "
1946 "line which permits false sharing.");
1947 (*warning_cnt_ptr)++;
1948 }
1949
1950 if ((sizeof(SharedGlobals) - offset_hcSequence) < cache_line_size) {
1951 tty->print_cr("WARNING: the SharedGlobals.hcSequence field is closer "
1952 "to the struct end than a cache line which permits false "
1953 "sharing.");
1954 (*warning_cnt_ptr)++;
1955 }
1956 }
1957 }
1958
1959 #ifndef PRODUCT
1960
1961 // Check if monitor belongs to the monitor cache
1962 // The list is grow-only so it's *relatively* safe to traverse
1963 // the list of extant blocks without taking a lock.
1964
1965 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
1966 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
1967 while (block != NULL) {
1968 assert(block->object() == CHAINMARKER, "must be a block header");
1969 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
1970 address mon = (address)monitor;
1971 address blk = (address)block;
1972 size_t diff = mon - blk;
1973 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "must be aligned");
1974 return 1;
1975 }
1976 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
1977 }
1978 return 0;
1979 }
1980
1981 #endif