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 CHECK_THROW_VALUE_TYPE_IMSE(obj) \
132 if ((obj)->klass_is_value_type()) { \
133 ResourceMark rm(THREAD); \
134 THROW_MSG(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
135 }
136
137 #define CHECK_THROW_VALUE_TYPE_IMSE_0(obj) \
138 if ((obj)->klass_is_value_type()) { \
139 ResourceMark rm(THREAD); \
140 THROW_MSG_0(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
141 }
142
143
144 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
145
146
147 // =====================> Quick functions
148
149 // The quick_* forms are special fast-path variants used to improve
150 // performance. In the simplest case, a "quick_*" implementation could
151 // simply return false, in which case the caller will perform the necessary
152 // state transitions and call the slow-path form.
153 // The fast-path is designed to handle frequently arising cases in an efficient
154 // manner and is just a degenerate "optimistic" variant of the slow-path.
155 // returns true -- to indicate the call was satisfied.
156 // returns false -- to indicate the call needs the services of the slow-path.
157 // A no-loitering ordinance is in effect for code in the quick_* family
158 // operators: safepoints or indefinite blocking (blocking that might span a
159 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
160 // entry.
161 //
162 // Consider: An interesting optimization is to have the JIT recognize the
163 // following common idiom:
164 // synchronized (someobj) { .... ; notify(); }
165 // That is, we find a notify() or notifyAll() call that immediately precedes
166 // the monitorexit operation. In that case the JIT could fuse the operations
167 // into a single notifyAndExit() runtime primitive.
168
169 bool ObjectSynchronizer::quick_notify(oopDesc * obj, Thread * self, bool all) {
170 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
171 assert(self->is_Java_thread(), "invariant");
172 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
173 NoSafepointVerifier nsv;
174 if (obj == NULL) return false; // slow-path for invalid obj
175 assert(!obj->klass_is_value_type(), "monitor op on value type");
176 const markOop mark = obj->mark();
177
178 if (mark->has_locker() && self->is_lock_owned((address)mark->locker())) {
179 // Degenerate notify
180 // stack-locked by caller so by definition the implied waitset is empty.
181 return true;
182 }
183
184 if (mark->has_monitor()) {
185 ObjectMonitor * const mon = mark->monitor();
186 assert(mon->object() == obj, "invariant");
187 if (mon->owner() != self) return false; // slow-path for IMS exception
188
189 if (mon->first_waiter() != NULL) {
190 // We have one or more waiters. Since this is an inflated monitor
191 // that we own, we can transfer one or more threads from the waitset
192 // to the entrylist here and now, avoiding the slow-path.
193 if (all) {
194 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
195 } else {
196 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
197 }
198 int tally = 0;
199 do {
200 mon->INotify(self);
201 ++tally;
202 } while (mon->first_waiter() != NULL && all);
203 OM_PERFDATA_OP(Notifications, inc(tally));
204 }
205 return true;
206 }
207
208 // biased locking and any other IMS exception states take the slow-path
209 return false;
210 }
211
212
213 // The LockNode emitted directly at the synchronization site would have
214 // been too big if it were to have included support for the cases of inflated
215 // recursive enter and exit, so they go here instead.
216 // Note that we can't safely call AsyncPrintJavaStack() from within
217 // quick_enter() as our thread state remains _in_Java.
218
219 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
220 BasicLock * lock) {
221 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
222 assert(Self->is_Java_thread(), "invariant");
223 assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
224 NoSafepointVerifier nsv;
225 if (obj == NULL) return false; // Need to throw NPE
226 assert(!obj->klass_is_value_type(), "monitor op on value type");
227 const markOop mark = obj->mark();
228
229 if (mark->has_monitor()) {
230 ObjectMonitor * const m = mark->monitor();
231 assert(m->object() == obj, "invariant");
232 Thread * const owner = (Thread *) m->_owner;
233
234 // Lock contention and Transactional Lock Elision (TLE) diagnostics
235 // and observability
236 // Case: light contention possibly amenable to TLE
237 // Case: TLE inimical operations such as nested/recursive synchronization
238
239 if (owner == Self) {
240 m->_recursions++;
241 return true;
242 }
243
244 // This Java Monitor is inflated so obj's header will never be
245 // displaced to this thread's BasicLock. Make the displaced header
246 // non-NULL so this BasicLock is not seen as recursive nor as
247 // being locked. We do this unconditionally so that this thread's
248 // BasicLock cannot be mis-interpreted by any stack walkers. For
249 // performance reasons, stack walkers generally first check for
250 // Biased Locking in the object's header, the second check is for
251 // stack-locking in the object's header, the third check is for
252 // recursive stack-locking in the displaced header in the BasicLock,
253 // and last are the inflated Java Monitor (ObjectMonitor) checks.
254 lock->set_displaced_header(markOopDesc::unused_mark());
255
256 if (owner == NULL && Atomic::replace_if_null(Self, &(m->_owner))) {
257 assert(m->_recursions == 0, "invariant");
258 assert(m->_owner == Self, "invariant");
259 return true;
260 }
261 }
262
263 // Note that we could inflate in quick_enter.
264 // This is likely a useful optimization
265 // Critically, in quick_enter() we must not:
266 // -- perform bias revocation, or
267 // -- block indefinitely, or
268 // -- reach a safepoint
269
270 return false; // revert to slow-path
271 }
272
273 // -----------------------------------------------------------------------------
274 // Fast Monitor Enter/Exit
275 // This the fast monitor enter. The interpreter and compiler use
276 // some assembly copies of this code. Make sure update those code
277 // if the following function is changed. The implementation is
278 // extremely sensitive to race condition. Be careful.
279
280 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
281 bool attempt_rebias, TRAPS) {
282 assert(!obj->klass_is_value_type(), "monitor op on value type");
283 if (UseBiasedLocking) {
284 if (!SafepointSynchronize::is_at_safepoint()) {
285 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
286 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
287 return;
288 }
289 } else {
290 assert(!attempt_rebias, "can not rebias toward VM thread");
291 BiasedLocking::revoke_at_safepoint(obj);
292 }
293 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
294 }
295
296 slow_enter(obj, lock, THREAD);
297 }
298
299 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
300 markOop mark = object->mark();
301 assert(!object->klass_is_value_type(), "monitor op on value type");
302 // We cannot check for Biased Locking if we are racing an inflation.
303 assert(mark == markOopDesc::INFLATING() ||
304 !mark->has_bias_pattern(), "should not see bias pattern here");
305
306 markOop dhw = lock->displaced_header();
307 if (dhw == NULL) {
308 // If the displaced header is NULL, then this exit matches up with
309 // a recursive enter. No real work to do here except for diagnostics.
310 #ifndef PRODUCT
311 if (mark != markOopDesc::INFLATING()) {
312 // Only do diagnostics if we are not racing an inflation. Simply
313 // exiting a recursive enter of a Java Monitor that is being
314 // inflated is safe; see the has_monitor() comment below.
315 assert(!mark->is_neutral(), "invariant");
316 assert(!mark->has_locker() ||
317 THREAD->is_lock_owned((address)mark->locker()), "invariant");
318 if (mark->has_monitor()) {
319 // The BasicLock's displaced_header is marked as a recursive
320 // enter and we have an inflated Java Monitor (ObjectMonitor).
321 // This is a special case where the Java Monitor was inflated
322 // after this thread entered the stack-lock recursively. When a
323 // Java Monitor is inflated, we cannot safely walk the Java
324 // Monitor owner's stack and update the BasicLocks because a
325 // Java Monitor can be asynchronously inflated by a thread that
326 // does not own the Java Monitor.
327 ObjectMonitor * m = mark->monitor();
328 assert(((oop)(m->object()))->mark() == mark, "invariant");
329 assert(m->is_entered(THREAD), "invariant");
330 }
331 }
332 #endif
333 return;
334 }
335
336 if (mark == (markOop) lock) {
337 // If the object is stack-locked by the current thread, try to
338 // swing the displaced header from the BasicLock back to the mark.
339 assert(dhw->is_neutral(), "invariant");
340 if (object->cas_set_mark(dhw, mark) == mark) {
341 TEVENT(fast_exit: release stack-lock);
342 return;
343 }
344 }
345
346 // We have to take the slow-path of possible inflation and then exit.
347 ObjectSynchronizer::inflate(THREAD,
348 object,
349 inflate_cause_vm_internal)->exit(true, THREAD);
350 }
351
352 // -----------------------------------------------------------------------------
353 // Interpreter/Compiler Slow Case
354 // This routine is used to handle interpreter/compiler slow case
355 // We don't need to use fast path here, because it must have been
356 // failed in the interpreter/compiler code.
357 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
358 CHECK_THROW_VALUE_TYPE_IMSE(obj);
359 markOop mark = obj->mark();
360 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
361
362 if (mark->is_neutral()) {
363 // Anticipate successful CAS -- the ST of the displaced mark must
364 // be visible <= the ST performed by the CAS.
365 lock->set_displaced_header(mark);
366 if (mark == obj()->cas_set_mark((markOop) lock, mark)) {
367 TEVENT(slow_enter: release stacklock);
368 return;
369 }
370 // Fall through to inflate() ...
371 } else if (mark->has_locker() &&
372 THREAD->is_lock_owned((address)mark->locker())) {
373 assert(lock != mark->locker(), "must not re-lock the same lock");
374 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
375 lock->set_displaced_header(NULL);
376 return;
377 }
378
379 // The object header will never be displaced to this lock,
380 // so it does not matter what the value is, except that it
381 // must be non-zero to avoid looking like a re-entrant lock,
382 // and must not look locked either.
383 lock->set_displaced_header(markOopDesc::unused_mark());
384 ObjectSynchronizer::inflate(THREAD,
385 obj(),
386 inflate_cause_monitor_enter)->enter(THREAD);
387 }
388
389 // This routine is used to handle interpreter/compiler slow case
390 // We don't need to use fast path here, because it must have
391 // failed in the interpreter/compiler code. Simply use the heavy
392 // weight monitor should be ok, unless someone find otherwise.
393 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
394 fast_exit(object, lock, THREAD);
395 }
396
397 // -----------------------------------------------------------------------------
398 // Class Loader support to workaround deadlocks on the class loader lock objects
399 // Also used by GC
400 // complete_exit()/reenter() are used to wait on a nested lock
401 // i.e. to give up an outer lock completely and then re-enter
402 // Used when holding nested locks - lock acquisition order: lock1 then lock2
403 // 1) complete_exit lock1 - saving recursion count
404 // 2) wait on lock2
405 // 3) when notified on lock2, unlock lock2
406 // 4) reenter lock1 with original recursion count
407 // 5) lock lock2
408 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
409 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
410 TEVENT(complete_exit);
411 assert(!obj->klass_is_value_type(), "monitor op on value type");
412 if (UseBiasedLocking) {
413 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
414 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
415 }
416
417 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
418 obj(),
419 inflate_cause_vm_internal);
420
421 return monitor->complete_exit(THREAD);
422 }
423
424 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
425 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
426 TEVENT(reenter);
427 assert(!obj->klass_is_value_type(), "monitor op on value type");
428 if (UseBiasedLocking) {
429 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
430 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
431 }
432
433 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
434 obj(),
435 inflate_cause_vm_internal);
436
437 monitor->reenter(recursion, THREAD);
438 }
439 // -----------------------------------------------------------------------------
440 // JNI locks on java objects
441 // NOTE: must use heavy weight monitor to handle jni monitor enter
442 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
443 // the current locking is from JNI instead of Java code
444 TEVENT(jni_enter);
445 CHECK_THROW_VALUE_TYPE_IMSE(obj);
446 if (UseBiasedLocking) {
447 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
448 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
449 }
450 THREAD->set_current_pending_monitor_is_from_java(false);
451 ObjectSynchronizer::inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);
452 THREAD->set_current_pending_monitor_is_from_java(true);
453 }
454
455 // NOTE: must use heavy weight monitor to handle jni monitor exit
456 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
457 TEVENT(jni_exit);
458 CHECK_THROW_VALUE_TYPE_IMSE(obj);
459 if (UseBiasedLocking) {
460 Handle h_obj(THREAD, obj);
461 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
462 obj = h_obj();
463 }
464 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
465
466 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
467 obj,
468 inflate_cause_jni_exit);
469 // If this thread has locked the object, exit the monitor. Note: can't use
470 // monitor->check(CHECK); must exit even if an exception is pending.
471 if (monitor->check(THREAD)) {
472 monitor->exit(true, THREAD);
473 }
474 }
475
476 // -----------------------------------------------------------------------------
477 // Internal VM locks on java objects
478 // standard constructor, allows locking failures
479 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
480 _dolock = doLock;
481 _thread = thread;
482 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
483 _obj = obj;
484
485 if (_dolock) {
486 TEVENT(ObjectLocker);
487
488 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
489 }
490 }
491
492 ObjectLocker::~ObjectLocker() {
493 if (_dolock) {
494 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
495 }
496 }
497
498
499 // -----------------------------------------------------------------------------
500 // Wait/Notify/NotifyAll
501 // NOTE: must use heavy weight monitor to handle wait()
502 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
503 CHECK_THROW_VALUE_TYPE_IMSE_0(obj);
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_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
511 }
512 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
513 obj(),
514 inflate_cause_wait);
515
516 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
517 monitor->wait(millis, true, THREAD);
518
519 // This dummy call is in place to get around dtrace bug 6254741. Once
520 // that's fixed we can uncomment the following line, remove the call
521 // and change this function back into a "void" func.
522 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
523 return dtrace_waited_probe(monitor, obj, THREAD);
524 }
525
526 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
527 CHECK_THROW_VALUE_TYPE_IMSE(obj);
528 if (UseBiasedLocking) {
529 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
530 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
531 }
532 if (millis < 0) {
533 TEVENT(wait - throw IAX);
534 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
535 }
536 ObjectSynchronizer::inflate(THREAD,
537 obj(),
538 inflate_cause_wait)->wait(millis, false, THREAD);
539 }
540
541 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
542 CHECK_THROW_VALUE_TYPE_IMSE(obj);
543 if (UseBiasedLocking) {
544 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
545 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
546 }
547
548 markOop mark = obj->mark();
549 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
550 return;
551 }
552 ObjectSynchronizer::inflate(THREAD,
553 obj(),
554 inflate_cause_notify)->notify(THREAD);
555 }
556
557 // NOTE: see comment of notify()
558 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
559 CHECK_THROW_VALUE_TYPE_IMSE(obj);
560 if (UseBiasedLocking) {
561 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
562 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
563 }
564
565 markOop mark = obj->mark();
566 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
567 return;
568 }
569 ObjectSynchronizer::inflate(THREAD,
570 obj(),
571 inflate_cause_notify)->notifyAll(THREAD);
572 }
573
574 // -----------------------------------------------------------------------------
575 // Hash Code handling
576 //
577 // Performance concern:
578 // OrderAccess::storestore() calls release() which at one time stored 0
579 // into the global volatile OrderAccess::dummy variable. This store was
580 // unnecessary for correctness. Many threads storing into a common location
581 // causes considerable cache migration or "sloshing" on large SMP systems.
582 // As such, I avoided using OrderAccess::storestore(). In some cases
583 // OrderAccess::fence() -- which incurs local latency on the executing
584 // processor -- is a better choice as it scales on SMP systems.
585 //
586 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
587 // a discussion of coherency costs. Note that all our current reference
588 // platforms provide strong ST-ST order, so the issue is moot on IA32,
589 // x64, and SPARC.
590 //
591 // As a general policy we use "volatile" to control compiler-based reordering
592 // and explicit fences (barriers) to control for architectural reordering
593 // performed by the CPU(s) or platform.
594
595 struct SharedGlobals {
596 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
597 // These are highly shared mostly-read variables.
598 // To avoid false-sharing they need to be the sole occupants of a cache line.
599 volatile int stwRandom;
600 volatile int stwCycle;
601 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
602 // Hot RW variable -- Sequester to avoid false-sharing
603 volatile int hcSequence;
604 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
605 };
606
607 static SharedGlobals GVars;
608 static int MonitorScavengeThreshold = 1000000;
609 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
610
611 static markOop ReadStableMark(oop obj) {
612 markOop mark = obj->mark();
613 if (!mark->is_being_inflated()) {
614 return mark; // normal fast-path return
615 }
616
617 int its = 0;
618 for (;;) {
619 markOop mark = obj->mark();
620 if (!mark->is_being_inflated()) {
621 return mark; // normal fast-path return
622 }
623
624 // The object is being inflated by some other thread.
625 // The caller of ReadStableMark() must wait for inflation to complete.
626 // Avoid live-lock
627 // TODO: consider calling SafepointSynchronize::do_call_back() while
628 // spinning to see if there's a safepoint pending. If so, immediately
629 // yielding or blocking would be appropriate. Avoid spinning while
630 // there is a safepoint pending.
631 // TODO: add inflation contention performance counters.
632 // TODO: restrict the aggregate number of spinners.
633
634 ++its;
635 if (its > 10000 || !os::is_MP()) {
636 if (its & 1) {
637 os::naked_yield();
638 TEVENT(Inflate: INFLATING - yield);
639 } else {
640 // Note that the following code attenuates the livelock problem but is not
641 // a complete remedy. A more complete solution would require that the inflating
642 // thread hold the associated inflation lock. The following code simply restricts
643 // the number of spinners to at most one. We'll have N-2 threads blocked
644 // on the inflationlock, 1 thread holding the inflation lock and using
645 // a yield/park strategy, and 1 thread in the midst of inflation.
646 // A more refined approach would be to change the encoding of INFLATING
647 // to allow encapsulation of a native thread pointer. Threads waiting for
648 // inflation to complete would use CAS to push themselves onto a singly linked
649 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
650 // and calling park(). When inflation was complete the thread that accomplished inflation
651 // would detach the list and set the markword to inflated with a single CAS and
652 // then for each thread on the list, set the flag and unpark() the thread.
653 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
654 // wakes at most one thread whereas we need to wake the entire list.
655 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
656 int YieldThenBlock = 0;
657 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
658 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
659 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
660 while (obj->mark() == markOopDesc::INFLATING()) {
661 // Beware: NakedYield() is advisory and has almost no effect on some platforms
662 // so we periodically call Self->_ParkEvent->park(1).
663 // We use a mixed spin/yield/block mechanism.
664 if ((YieldThenBlock++) >= 16) {
665 Thread::current()->_ParkEvent->park(1);
666 } else {
667 os::naked_yield();
668 }
669 }
670 Thread::muxRelease(gInflationLocks + ix);
671 TEVENT(Inflate: INFLATING - yield/park);
672 }
673 } else {
674 SpinPause(); // SMP-polite spinning
675 }
676 }
677 }
678
679 // hashCode() generation :
680 //
681 // Possibilities:
682 // * MD5Digest of {obj,stwRandom}
683 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
684 // * A DES- or AES-style SBox[] mechanism
685 // * One of the Phi-based schemes, such as:
686 // 2654435761 = 2^32 * Phi (golden ratio)
687 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
688 // * A variation of Marsaglia's shift-xor RNG scheme.
689 // * (obj ^ stwRandom) is appealing, but can result
690 // in undesirable regularity in the hashCode values of adjacent objects
691 // (objects allocated back-to-back, in particular). This could potentially
692 // result in hashtable collisions and reduced hashtable efficiency.
693 // There are simple ways to "diffuse" the middle address bits over the
694 // generated hashCode values:
695
696 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
697 intptr_t value = 0;
698 if (hashCode == 0) {
699 // This form uses global Park-Miller RNG.
700 // On MP system we'll have lots of RW access to a global, so the
701 // mechanism induces lots of coherency traffic.
702 value = os::random();
703 } else if (hashCode == 1) {
704 // This variation has the property of being stable (idempotent)
705 // between STW operations. This can be useful in some of the 1-0
706 // synchronization schemes.
707 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
708 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
709 } else if (hashCode == 2) {
710 value = 1; // for sensitivity testing
711 } else if (hashCode == 3) {
712 value = ++GVars.hcSequence;
713 } else if (hashCode == 4) {
714 value = cast_from_oop<intptr_t>(obj);
715 } else {
716 // Marsaglia's xor-shift scheme with thread-specific state
717 // This is probably the best overall implementation -- we'll
718 // likely make this the default in future releases.
719 unsigned t = Self->_hashStateX;
720 t ^= (t << 11);
721 Self->_hashStateX = Self->_hashStateY;
722 Self->_hashStateY = Self->_hashStateZ;
723 Self->_hashStateZ = Self->_hashStateW;
724 unsigned v = Self->_hashStateW;
725 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
726 Self->_hashStateW = v;
727 value = v;
728 }
729
730 value &= markOopDesc::hash_mask;
731 if (value == 0) value = 0xBAD;
732 assert(value != markOopDesc::no_hash, "invariant");
733 TEVENT(hashCode: GENERATE);
734 return value;
735 }
736
737 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
738 if (EnableValhalla && obj->klass_is_value_type()) {
739 // Expected tooling to override hashCode for value type, just don't crash
740 if (log_is_enabled(Debug, monitorinflation)) {
741 ResourceMark rm;
742 log_debug(monitorinflation)("FastHashCode for value type: %s", obj->klass()->external_name());
743 }
744 return 0;
745 }
746 if (UseBiasedLocking) {
747 // NOTE: many places throughout the JVM do not expect a safepoint
748 // to be taken here, in particular most operations on perm gen
749 // objects. However, we only ever bias Java instances and all of
750 // the call sites of identity_hash that might revoke biases have
751 // been checked to make sure they can handle a safepoint. The
752 // added check of the bias pattern is to avoid useless calls to
753 // thread-local storage.
754 if (obj->mark()->has_bias_pattern()) {
755 // Handle for oop obj in case of STW safepoint
756 Handle hobj(Self, obj);
757 // Relaxing assertion for bug 6320749.
758 assert(Universe::verify_in_progress() ||
759 !SafepointSynchronize::is_at_safepoint(),
760 "biases should not be seen by VM thread here");
761 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
762 obj = hobj();
763 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
764 }
765 }
766
767 // hashCode() is a heap mutator ...
768 // Relaxing assertion for bug 6320749.
769 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
770 !SafepointSynchronize::is_at_safepoint(), "invariant");
771 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
772 Self->is_Java_thread() , "invariant");
773 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
774 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
775
776 ObjectMonitor* monitor = NULL;
777 markOop temp, test;
778 intptr_t hash;
779 markOop mark = ReadStableMark(obj);
780
781 // object should remain ineligible for biased locking
782 assert(!mark->has_bias_pattern(), "invariant");
783
784 if (mark->is_neutral()) {
785 hash = mark->hash(); // this is a normal header
786 if (hash) { // if it has hash, just return it
787 return hash;
788 }
789 hash = get_next_hash(Self, obj); // allocate a new hash code
790 temp = mark->copy_set_hash(hash); // merge the hash code into header
791 // use (machine word version) atomic operation to install the hash
792 test = obj->cas_set_mark(temp, mark);
793 if (test == mark) {
794 return hash;
795 }
796 // If atomic operation failed, we must inflate the header
797 // into heavy weight monitor. We could add more code here
798 // for fast path, but it does not worth the complexity.
799 } else if (mark->has_monitor()) {
800 monitor = mark->monitor();
801 temp = monitor->header();
802 assert(temp->is_neutral(), "invariant");
803 hash = temp->hash();
804 if (hash) {
805 return hash;
806 }
807 // Skip to the following code to reduce code size
808 } else if (Self->is_lock_owned((address)mark->locker())) {
809 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
810 assert(temp->is_neutral(), "invariant");
811 hash = temp->hash(); // by current thread, check if the displaced
812 if (hash) { // header contains hash code
813 return hash;
814 }
815 // WARNING:
816 // The displaced header is strictly immutable.
817 // It can NOT be changed in ANY cases. So we have
818 // to inflate the header into heavyweight monitor
819 // even the current thread owns the lock. The reason
820 // is the BasicLock (stack slot) will be asynchronously
821 // read by other threads during the inflate() function.
822 // Any change to stack may not propagate to other threads
823 // correctly.
824 }
825
826 // Inflate the monitor to set hash code
827 monitor = ObjectSynchronizer::inflate(Self, obj, inflate_cause_hash_code);
828 // Load displaced header and check it has hash code
829 mark = monitor->header();
830 assert(mark->is_neutral(), "invariant");
831 hash = mark->hash();
832 if (hash == 0) {
833 hash = get_next_hash(Self, obj);
834 temp = mark->copy_set_hash(hash); // merge hash code into header
835 assert(temp->is_neutral(), "invariant");
836 test = Atomic::cmpxchg(temp, monitor->header_addr(), mark);
837 if (test != mark) {
838 // The only update to the header in the monitor (outside GC)
839 // is install the hash code. If someone add new usage of
840 // displaced header, please update this code
841 hash = test->hash();
842 assert(test->is_neutral(), "invariant");
843 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
844 }
845 }
846 // We finally get the hash
847 return hash;
848 }
849
850
851 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
852 Handle h_obj) {
853 if (UseBiasedLocking) {
854 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
855 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
856 }
857
858 assert(thread == JavaThread::current(), "Can only be called on current thread");
859 oop obj = h_obj();
860
861 markOop mark = ReadStableMark(obj);
862
863 // Uncontended case, header points to stack
864 if (mark->has_locker()) {
865 return thread->is_lock_owned((address)mark->locker());
866 }
867 // Contended case, header points to ObjectMonitor (tagged pointer)
868 if (mark->has_monitor()) {
869 ObjectMonitor* monitor = mark->monitor();
870 return monitor->is_entered(thread) != 0;
871 }
872 // Unlocked case, header in place
873 assert(mark->is_neutral(), "sanity check");
874 return false;
875 }
876
877 // Be aware of this method could revoke bias of the lock object.
878 // This method queries the ownership of the lock handle specified by 'h_obj'.
879 // If the current thread owns the lock, it returns owner_self. If no
880 // thread owns the lock, it returns owner_none. Otherwise, it will return
881 // owner_other.
882 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
883 (JavaThread *self, Handle h_obj) {
884 // The caller must beware this method can revoke bias, and
885 // revocation can result in a safepoint.
886 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
887 assert(self->thread_state() != _thread_blocked, "invariant");
888
889 // Possible mark states: neutral, biased, stack-locked, inflated
890
891 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
892 // CASE: biased
893 BiasedLocking::revoke_and_rebias(h_obj, false, self);
894 assert(!h_obj->mark()->has_bias_pattern(),
895 "biases should be revoked by now");
896 }
897
898 assert(self == JavaThread::current(), "Can only be called on current thread");
899 oop obj = h_obj();
900 markOop mark = ReadStableMark(obj);
901
902 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
903 if (mark->has_locker()) {
904 return self->is_lock_owned((address)mark->locker()) ?
905 owner_self : owner_other;
906 }
907
908 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
909 // The Object:ObjectMonitor relationship is stable as long as we're
910 // not at a safepoint.
911 if (mark->has_monitor()) {
912 void * owner = mark->monitor()->_owner;
913 if (owner == NULL) return owner_none;
914 return (owner == self ||
915 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
916 }
917
918 // CASE: neutral
919 assert(mark->is_neutral(), "sanity check");
920 return owner_none; // it's unlocked
921 }
922
923 // FIXME: jvmti should call this
924 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
925 if (UseBiasedLocking) {
926 if (SafepointSynchronize::is_at_safepoint()) {
927 BiasedLocking::revoke_at_safepoint(h_obj);
928 } else {
929 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
930 }
931 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
932 }
933
934 oop obj = h_obj();
935 address owner = NULL;
936
937 markOop mark = ReadStableMark(obj);
938
939 // Uncontended case, header points to stack
940 if (mark->has_locker()) {
941 owner = (address) mark->locker();
942 }
943
944 // Contended case, header points to ObjectMonitor (tagged pointer)
945 if (mark->has_monitor()) {
946 ObjectMonitor* monitor = mark->monitor();
947 assert(monitor != NULL, "monitor should be non-null");
948 owner = (address) monitor->owner();
949 }
950
951 if (owner != NULL) {
952 // owning_thread_from_monitor_owner() may also return NULL here
953 return Threads::owning_thread_from_monitor_owner(t_list, owner);
954 }
955
956 // Unlocked case, header in place
957 // Cannot have assertion since this object may have been
958 // locked by another thread when reaching here.
959 // assert(mark->is_neutral(), "sanity check");
960
961 return NULL;
962 }
963
964 // Visitors ...
965
966 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
967 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
968 while (block != NULL) {
969 assert(block->object() == CHAINMARKER, "must be a block header");
970 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
971 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
972 oop object = (oop)mid->object();
973 if (object != NULL) {
974 closure->do_monitor(mid);
975 }
976 }
977 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
978 }
979 }
980
981 // Get the next block in the block list.
982 static inline PaddedEnd<ObjectMonitor>* next(PaddedEnd<ObjectMonitor>* block) {
983 assert(block->object() == CHAINMARKER, "must be a block header");
984 block = (PaddedEnd<ObjectMonitor>*) block->FreeNext;
985 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
986 return block;
987 }
988
989 static bool monitors_used_above_threshold() {
990 if (gMonitorPopulation == 0) {
991 return false;
992 }
993 int monitors_used = gMonitorPopulation - gMonitorFreeCount;
994 int monitor_usage = (monitors_used * 100LL) / gMonitorPopulation;
995 return monitor_usage > MonitorUsedDeflationThreshold;
996 }
997
998 bool ObjectSynchronizer::is_cleanup_needed() {
999 if (MonitorUsedDeflationThreshold > 0) {
1000 return monitors_used_above_threshold();
1001 }
1002 return false;
1003 }
1004
1005 void ObjectSynchronizer::oops_do(OopClosure* f) {
1006 if (MonitorInUseLists) {
1007 // When using thread local monitor lists, we only scan the
1008 // global used list here (for moribund threads), and
1009 // the thread-local monitors in Thread::oops_do().
1010 global_used_oops_do(f);
1011 } else {
1012 global_oops_do(f);
1013 }
1014 }
1015
1016 void ObjectSynchronizer::global_oops_do(OopClosure* f) {
1017 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1018 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
1019 for (; block != NULL; block = next(block)) {
1020 assert(block->object() == CHAINMARKER, "must be a block header");
1021 for (int i = 1; i < _BLOCKSIZE; i++) {
1022 ObjectMonitor* mid = (ObjectMonitor *)&block[i];
1023 if (mid->object() != NULL) {
1024 f->do_oop((oop*)mid->object_addr());
1025 }
1026 }
1027 }
1028 }
1029
1030 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
1031 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1032 list_oops_do(gOmInUseList, f);
1033 }
1034
1035 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
1036 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1037 list_oops_do(thread->omInUseList, f);
1038 }
1039
1040 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
1041 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1042 ObjectMonitor* mid;
1043 for (mid = list; mid != NULL; mid = mid->FreeNext) {
1044 if (mid->object() != NULL) {
1045 f->do_oop((oop*)mid->object_addr());
1046 }
1047 }
1048 }
1049
1050
1051 // -----------------------------------------------------------------------------
1052 // ObjectMonitor Lifecycle
1053 // -----------------------
1054 // Inflation unlinks monitors from the global gFreeList and
1055 // associates them with objects. Deflation -- which occurs at
1056 // STW-time -- disassociates idle monitors from objects. Such
1057 // scavenged monitors are returned to the gFreeList.
1058 //
1059 // The global list is protected by gListLock. All the critical sections
1060 // are short and operate in constant-time.
1061 //
1062 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1063 //
1064 // Lifecycle:
1065 // -- unassigned and on the global free list
1066 // -- unassigned and on a thread's private omFreeList
1067 // -- assigned to an object. The object is inflated and the mark refers
1068 // to the objectmonitor.
1069
1070
1071 // Constraining monitor pool growth via MonitorBound ...
1072 //
1073 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
1074 // the rate of scavenging is driven primarily by GC. As such, we can find
1075 // an inordinate number of monitors in circulation.
1076 // To avoid that scenario we can artificially induce a STW safepoint
1077 // if the pool appears to be growing past some reasonable bound.
1078 // Generally we favor time in space-time tradeoffs, but as there's no
1079 // natural back-pressure on the # of extant monitors we need to impose some
1080 // type of limit. Beware that if MonitorBound is set to too low a value
1081 // we could just loop. In addition, if MonitorBound is set to a low value
1082 // we'll incur more safepoints, which are harmful to performance.
1083 // See also: GuaranteedSafepointInterval
1084 //
1085 // The current implementation uses asynchronous VM operations.
1086
1087 static void InduceScavenge(Thread * Self, const char * Whence) {
1088 // Induce STW safepoint to trim monitors
1089 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1090 // More precisely, trigger an asynchronous STW safepoint as the number
1091 // of active monitors passes the specified threshold.
1092 // TODO: assert thread state is reasonable
1093
1094 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1095 if (ObjectMonitor::Knob_Verbose) {
1096 tty->print_cr("INFO: Monitor scavenge - Induced STW @%s (%d)",
1097 Whence, ForceMonitorScavenge) ;
1098 tty->flush();
1099 }
1100 // Induce a 'null' safepoint to scavenge monitors
1101 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1102 // to the VMthread and have a lifespan longer than that of this activation record.
1103 // The VMThread will delete the op when completed.
1104 VMThread::execute(new VM_ScavengeMonitors());
1105
1106 if (ObjectMonitor::Knob_Verbose) {
1107 tty->print_cr("INFO: Monitor scavenge - STW posted @%s (%d)",
1108 Whence, ForceMonitorScavenge) ;
1109 tty->flush();
1110 }
1111 }
1112 }
1113
1114 void ObjectSynchronizer::verifyInUse(Thread *Self) {
1115 ObjectMonitor* mid;
1116 int in_use_tally = 0;
1117 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) {
1118 in_use_tally++;
1119 }
1120 assert(in_use_tally == Self->omInUseCount, "in-use count off");
1121
1122 int free_tally = 0;
1123 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) {
1124 free_tally++;
1125 }
1126 assert(free_tally == Self->omFreeCount, "free count off");
1127 }
1128
1129 ObjectMonitor* ObjectSynchronizer::omAlloc(Thread * Self) {
1130 // A large MAXPRIVATE value reduces both list lock contention
1131 // and list coherency traffic, but also tends to increase the
1132 // number of objectMonitors in circulation as well as the STW
1133 // scavenge costs. As usual, we lean toward time in space-time
1134 // tradeoffs.
1135 const int MAXPRIVATE = 1024;
1136 for (;;) {
1137 ObjectMonitor * m;
1138
1139 // 1: try to allocate from the thread's local omFreeList.
1140 // Threads will attempt to allocate first from their local list, then
1141 // from the global list, and only after those attempts fail will the thread
1142 // attempt to instantiate new monitors. Thread-local free lists take
1143 // heat off the gListLock and improve allocation latency, as well as reducing
1144 // coherency traffic on the shared global list.
1145 m = Self->omFreeList;
1146 if (m != NULL) {
1147 Self->omFreeList = m->FreeNext;
1148 Self->omFreeCount--;
1149 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene
1150 guarantee(m->object() == NULL, "invariant");
1151 if (MonitorInUseLists) {
1152 m->FreeNext = Self->omInUseList;
1153 Self->omInUseList = m;
1154 Self->omInUseCount++;
1155 if (ObjectMonitor::Knob_VerifyInUse) {
1156 verifyInUse(Self);
1157 }
1158 } else {
1159 m->FreeNext = NULL;
1160 }
1161 return m;
1162 }
1163
1164 // 2: try to allocate from the global gFreeList
1165 // CONSIDER: use muxTry() instead of muxAcquire().
1166 // If the muxTry() fails then drop immediately into case 3.
1167 // If we're using thread-local free lists then try
1168 // to reprovision the caller's free list.
1169 if (gFreeList != NULL) {
1170 // Reprovision the thread's omFreeList.
1171 // Use bulk transfers to reduce the allocation rate and heat
1172 // on various locks.
1173 Thread::muxAcquire(&gListLock, "omAlloc");
1174 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1175 gMonitorFreeCount--;
1176 ObjectMonitor * take = gFreeList;
1177 gFreeList = take->FreeNext;
1178 guarantee(take->object() == NULL, "invariant");
1179 guarantee(!take->is_busy(), "invariant");
1180 take->Recycle();
1181 omRelease(Self, take, false);
1182 }
1183 Thread::muxRelease(&gListLock);
1184 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1185 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1186 TEVENT(omFirst - reprovision);
1187
1188 const int mx = MonitorBound;
1189 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1190 // We can't safely induce a STW safepoint from omAlloc() as our thread
1191 // state may not be appropriate for such activities and callers may hold
1192 // naked oops, so instead we defer the action.
1193 InduceScavenge(Self, "omAlloc");
1194 }
1195 continue;
1196 }
1197
1198 // 3: allocate a block of new ObjectMonitors
1199 // Both the local and global free lists are empty -- resort to malloc().
1200 // In the current implementation objectMonitors are TSM - immortal.
1201 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1202 // each ObjectMonitor to start at the beginning of a cache line,
1203 // so we use align_up().
1204 // A better solution would be to use C++ placement-new.
1205 // BEWARE: As it stands currently, we don't run the ctors!
1206 assert(_BLOCKSIZE > 1, "invariant");
1207 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
1208 PaddedEnd<ObjectMonitor> * temp;
1209 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1210 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
1211 mtInternal);
1212 temp = (PaddedEnd<ObjectMonitor> *)
1213 align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE);
1214
1215 // NOTE: (almost) no way to recover if allocation failed.
1216 // We might be able to induce a STW safepoint and scavenge enough
1217 // objectMonitors to permit progress.
1218 if (temp == NULL) {
1219 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1220 "Allocate ObjectMonitors");
1221 }
1222 (void)memset((void *) temp, 0, neededsize);
1223
1224 // Format the block.
1225 // initialize the linked list, each monitor points to its next
1226 // forming the single linked free list, the very first monitor
1227 // will points to next block, which forms the block list.
1228 // The trick of using the 1st element in the block as gBlockList
1229 // linkage should be reconsidered. A better implementation would
1230 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1231
1232 for (int i = 1; i < _BLOCKSIZE; i++) {
1233 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1234 }
1235
1236 // terminate the last monitor as the end of list
1237 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1238
1239 // Element [0] is reserved for global list linkage
1240 temp[0].set_object(CHAINMARKER);
1241
1242 // Consider carving out this thread's current request from the
1243 // block in hand. This avoids some lock traffic and redundant
1244 // list activity.
1245
1246 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1247 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1248 Thread::muxAcquire(&gListLock, "omAlloc [2]");
1249 gMonitorPopulation += _BLOCKSIZE-1;
1250 gMonitorFreeCount += _BLOCKSIZE-1;
1251
1252 // Add the new block to the list of extant blocks (gBlockList).
1253 // The very first objectMonitor in a block is reserved and dedicated.
1254 // It serves as blocklist "next" linkage.
1255 temp[0].FreeNext = gBlockList;
1256 // There are lock-free uses of gBlockList so make sure that
1257 // the previous stores happen before we update gBlockList.
1258 OrderAccess::release_store(&gBlockList, temp);
1259
1260 // Add the new string of objectMonitors to the global free list
1261 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1262 gFreeList = temp + 1;
1263 Thread::muxRelease(&gListLock);
1264 TEVENT(Allocate block of monitors);
1265 }
1266 }
1267
1268 // Place "m" on the caller's private per-thread omFreeList.
1269 // In practice there's no need to clamp or limit the number of
1270 // monitors on a thread's omFreeList as the only time we'll call
1271 // omRelease is to return a monitor to the free list after a CAS
1272 // attempt failed. This doesn't allow unbounded #s of monitors to
1273 // accumulate on a thread's free list.
1274 //
1275 // Key constraint: all ObjectMonitors on a thread's free list and the global
1276 // free list must have their object field set to null. This prevents the
1277 // scavenger -- deflate_idle_monitors -- from reclaiming them.
1278
1279 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1280 bool fromPerThreadAlloc) {
1281 guarantee(m->object() == NULL, "invariant");
1282 guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor");
1283 // Remove from omInUseList
1284 if (MonitorInUseLists && fromPerThreadAlloc) {
1285 ObjectMonitor* cur_mid_in_use = NULL;
1286 bool extracted = false;
1287 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1288 if (m == mid) {
1289 // extract from per-thread in-use list
1290 if (mid == Self->omInUseList) {
1291 Self->omInUseList = mid->FreeNext;
1292 } else if (cur_mid_in_use != NULL) {
1293 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1294 }
1295 extracted = true;
1296 Self->omInUseCount--;
1297 if (ObjectMonitor::Knob_VerifyInUse) {
1298 verifyInUse(Self);
1299 }
1300 break;
1301 }
1302 }
1303 assert(extracted, "Should have extracted from in-use list");
1304 }
1305
1306 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1307 m->FreeNext = Self->omFreeList;
1308 Self->omFreeList = m;
1309 Self->omFreeCount++;
1310 }
1311
1312 // Return the monitors of a moribund thread's local free list to
1313 // the global free list. Typically a thread calls omFlush() when
1314 // it's dying. We could also consider having the VM thread steal
1315 // monitors from threads that have not run java code over a few
1316 // consecutive STW safepoints. Relatedly, we might decay
1317 // omFreeProvision at STW safepoints.
1318 //
1319 // Also return the monitors of a moribund thread's omInUseList to
1320 // a global gOmInUseList under the global list lock so these
1321 // will continue to be scanned.
1322 //
1323 // We currently call omFlush() from Threads::remove() _before the thread
1324 // has been excised from the thread list and is no longer a mutator.
1325 // This means that omFlush() can not run concurrently with a safepoint and
1326 // interleave with the scavenge operator. In particular, this ensures that
1327 // the thread's monitors are scanned by a GC safepoint, either via
1328 // Thread::oops_do() (if safepoint happens before omFlush()) or via
1329 // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's
1330 // monitors have been transferred to the global in-use list).
1331
1332 void ObjectSynchronizer::omFlush(Thread * Self) {
1333 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1334 Self->omFreeList = NULL;
1335 ObjectMonitor * tail = NULL;
1336 int tally = 0;
1337 if (list != NULL) {
1338 ObjectMonitor * s;
1339 // The thread is going away, the per-thread free monitors
1340 // are freed via set_owner(NULL)
1341 // Link them to tail, which will be linked into the global free list
1342 // gFreeList below, under the gListLock
1343 for (s = list; s != NULL; s = s->FreeNext) {
1344 tally++;
1345 tail = s;
1346 guarantee(s->object() == NULL, "invariant");
1347 guarantee(!s->is_busy(), "invariant");
1348 s->set_owner(NULL); // redundant but good hygiene
1349 TEVENT(omFlush - Move one);
1350 }
1351 guarantee(tail != NULL && list != NULL, "invariant");
1352 }
1353
1354 ObjectMonitor * inUseList = Self->omInUseList;
1355 ObjectMonitor * inUseTail = NULL;
1356 int inUseTally = 0;
1357 if (inUseList != NULL) {
1358 Self->omInUseList = NULL;
1359 ObjectMonitor *cur_om;
1360 // The thread is going away, however the omInUseList inflated
1361 // monitors may still be in-use by other threads.
1362 // Link them to inUseTail, which will be linked into the global in-use list
1363 // gOmInUseList below, under the gListLock
1364 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1365 inUseTail = cur_om;
1366 inUseTally++;
1367 }
1368 assert(Self->omInUseCount == inUseTally, "in-use count off");
1369 Self->omInUseCount = 0;
1370 guarantee(inUseTail != NULL && inUseList != NULL, "invariant");
1371 }
1372
1373 Thread::muxAcquire(&gListLock, "omFlush");
1374 if (tail != NULL) {
1375 tail->FreeNext = gFreeList;
1376 gFreeList = list;
1377 gMonitorFreeCount += tally;
1378 assert(Self->omFreeCount == tally, "free-count off");
1379 Self->omFreeCount = 0;
1380 }
1381
1382 if (inUseTail != NULL) {
1383 inUseTail->FreeNext = gOmInUseList;
1384 gOmInUseList = inUseList;
1385 gOmInUseCount += inUseTally;
1386 }
1387
1388 Thread::muxRelease(&gListLock);
1389 TEVENT(omFlush);
1390 }
1391
1392 // Fast path code shared by multiple functions
1393 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1394 markOop mark = obj->mark();
1395 if (mark->has_monitor()) {
1396 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1397 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1398 return mark->monitor();
1399 }
1400 return ObjectSynchronizer::inflate(Thread::current(),
1401 obj,
1402 inflate_cause_vm_internal);
1403 }
1404
1405 ObjectMonitor* ObjectSynchronizer::inflate(Thread * Self,
1406 oop object,
1407 const InflateCause cause) {
1408
1409 // Inflate mutates the heap ...
1410 // Relaxing assertion for bug 6320749.
1411 assert(Universe::verify_in_progress() ||
1412 !SafepointSynchronize::is_at_safepoint(), "invariant");
1413
1414 if (EnableValhalla) {
1415 guarantee(!object->klass_is_value_type(), "Attempt to inflate value type");
1416 }
1417
1418 EventJavaMonitorInflate event;
1419
1420 for (;;) {
1421 const markOop mark = object->mark();
1422 assert(!mark->has_bias_pattern(), "invariant");
1423
1424 // The mark can be in one of the following states:
1425 // * Inflated - just return
1426 // * Stack-locked - coerce it to inflated
1427 // * INFLATING - busy wait for conversion to complete
1428 // * Neutral - aggressively inflate the object.
1429 // * BIASED - Illegal. We should never see this
1430
1431 // CASE: inflated
1432 if (mark->has_monitor()) {
1433 ObjectMonitor * inf = mark->monitor();
1434 assert(inf->header()->is_neutral(), "invariant");
1435 assert(inf->object() == object, "invariant");
1436 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1437 return inf;
1438 }
1439
1440 // CASE: inflation in progress - inflating over a stack-lock.
1441 // Some other thread is converting from stack-locked to inflated.
1442 // Only that thread can complete inflation -- other threads must wait.
1443 // The INFLATING value is transient.
1444 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1445 // We could always eliminate polling by parking the thread on some auxiliary list.
1446 if (mark == markOopDesc::INFLATING()) {
1447 TEVENT(Inflate: spin while INFLATING);
1448 ReadStableMark(object);
1449 continue;
1450 }
1451
1452 // CASE: stack-locked
1453 // Could be stack-locked either by this thread or by some other thread.
1454 //
1455 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1456 // to install INFLATING into the mark word. We originally installed INFLATING,
1457 // allocated the objectmonitor, and then finally STed the address of the
1458 // objectmonitor into the mark. This was correct, but artificially lengthened
1459 // the interval in which INFLATED appeared in the mark, thus increasing
1460 // the odds of inflation contention.
1461 //
1462 // We now use per-thread private objectmonitor free lists.
1463 // These list are reprovisioned from the global free list outside the
1464 // critical INFLATING...ST interval. A thread can transfer
1465 // multiple objectmonitors en-mass from the global free list to its local free list.
1466 // This reduces coherency traffic and lock contention on the global free list.
1467 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1468 // before or after the CAS(INFLATING) operation.
1469 // See the comments in omAlloc().
1470
1471 if (mark->has_locker()) {
1472 ObjectMonitor * m = omAlloc(Self);
1473 // Optimistically prepare the objectmonitor - anticipate successful CAS
1474 // We do this before the CAS in order to minimize the length of time
1475 // in which INFLATING appears in the mark.
1476 m->Recycle();
1477 m->_Responsible = NULL;
1478 m->_recursions = 0;
1479 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1480
1481 markOop cmp = object->cas_set_mark(markOopDesc::INFLATING(), mark);
1482 if (cmp != mark) {
1483 omRelease(Self, m, true);
1484 continue; // Interference -- just retry
1485 }
1486
1487 // We've successfully installed INFLATING (0) into the mark-word.
1488 // This is the only case where 0 will appear in a mark-word.
1489 // Only the singular thread that successfully swings the mark-word
1490 // to 0 can perform (or more precisely, complete) inflation.
1491 //
1492 // Why do we CAS a 0 into the mark-word instead of just CASing the
1493 // mark-word from the stack-locked value directly to the new inflated state?
1494 // Consider what happens when a thread unlocks a stack-locked object.
1495 // It attempts to use CAS to swing the displaced header value from the
1496 // on-stack basiclock back into the object header. Recall also that the
1497 // header value (hashcode, etc) can reside in (a) the object header, or
1498 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1499 // header in an objectMonitor. The inflate() routine must copy the header
1500 // value from the basiclock on the owner's stack to the objectMonitor, all
1501 // the while preserving the hashCode stability invariants. If the owner
1502 // decides to release the lock while the value is 0, the unlock will fail
1503 // and control will eventually pass from slow_exit() to inflate. The owner
1504 // will then spin, waiting for the 0 value to disappear. Put another way,
1505 // the 0 causes the owner to stall if the owner happens to try to
1506 // drop the lock (restoring the header from the basiclock to the object)
1507 // while inflation is in-progress. This protocol avoids races that might
1508 // would otherwise permit hashCode values to change or "flicker" for an object.
1509 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1510 // 0 serves as a "BUSY" inflate-in-progress indicator.
1511
1512
1513 // fetch the displaced mark from the owner's stack.
1514 // The owner can't die or unwind past the lock while our INFLATING
1515 // object is in the mark. Furthermore the owner can't complete
1516 // an unlock on the object, either.
1517 markOop dmw = mark->displaced_mark_helper();
1518 assert(dmw->is_neutral(), "invariant");
1519
1520 // Setup monitor fields to proper values -- prepare the monitor
1521 m->set_header(dmw);
1522
1523 // Optimization: if the mark->locker stack address is associated
1524 // with this thread we could simply set m->_owner = Self.
1525 // Note that a thread can inflate an object
1526 // that it has stack-locked -- as might happen in wait() -- directly
1527 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1528 m->set_owner(mark->locker());
1529 m->set_object(object);
1530 // TODO-FIXME: assert BasicLock->dhw != 0.
1531
1532 // Must preserve store ordering. The monitor state must
1533 // be stable at the time of publishing the monitor address.
1534 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1535 object->release_set_mark(markOopDesc::encode(m));
1536
1537 // Hopefully the performance counters are allocated on distinct cache lines
1538 // to avoid false sharing on MP systems ...
1539 OM_PERFDATA_OP(Inflations, inc());
1540 TEVENT(Inflate: overwrite stacklock);
1541 if (log_is_enabled(Debug, monitorinflation)) {
1542 if (object->is_instance()) {
1543 ResourceMark rm;
1544 log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1545 p2i(object), p2i(object->mark()),
1546 object->klass()->external_name());
1547 }
1548 }
1549 if (event.should_commit()) {
1550 post_monitor_inflate_event(event, object, cause);
1551 }
1552 return m;
1553 }
1554
1555 // CASE: neutral
1556 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1557 // If we know we're inflating for entry it's better to inflate by swinging a
1558 // pre-locked objectMonitor pointer into the object header. A successful
1559 // CAS inflates the object *and* confers ownership to the inflating thread.
1560 // In the current implementation we use a 2-step mechanism where we CAS()
1561 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1562 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1563 // would be useful.
1564
1565 assert(mark->is_neutral(), "invariant");
1566 ObjectMonitor * m = omAlloc(Self);
1567 // prepare m for installation - set monitor to initial state
1568 m->Recycle();
1569 m->set_header(mark);
1570 m->set_owner(NULL);
1571 m->set_object(object);
1572 m->_recursions = 0;
1573 m->_Responsible = NULL;
1574 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1575
1576 if (object->cas_set_mark(markOopDesc::encode(m), mark) != mark) {
1577 m->set_object(NULL);
1578 m->set_owner(NULL);
1579 m->Recycle();
1580 omRelease(Self, m, true);
1581 m = NULL;
1582 continue;
1583 // interference - the markword changed - just retry.
1584 // The state-transitions are one-way, so there's no chance of
1585 // live-lock -- "Inflated" is an absorbing state.
1586 }
1587
1588 // Hopefully the performance counters are allocated on distinct
1589 // cache lines to avoid false sharing on MP systems ...
1590 OM_PERFDATA_OP(Inflations, inc());
1591 TEVENT(Inflate: overwrite neutral);
1592 if (log_is_enabled(Debug, monitorinflation)) {
1593 if (object->is_instance()) {
1594 ResourceMark rm;
1595 log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1596 p2i(object), p2i(object->mark()),
1597 object->klass()->external_name());
1598 }
1599 }
1600 if (event.should_commit()) {
1601 post_monitor_inflate_event(event, object, cause);
1602 }
1603 return m;
1604 }
1605 }
1606
1607
1608 // Deflate_idle_monitors() is called at all safepoints, immediately
1609 // after all mutators are stopped, but before any objects have moved.
1610 // It traverses the list of known monitors, deflating where possible.
1611 // The scavenged monitor are returned to the monitor free list.
1612 //
1613 // Beware that we scavenge at *every* stop-the-world point.
1614 // Having a large number of monitors in-circulation negatively
1615 // impacts the performance of some applications (e.g., PointBase).
1616 // Broadly, we want to minimize the # of monitors in circulation.
1617 //
1618 // We have added a flag, MonitorInUseLists, which creates a list
1619 // of active monitors for each thread. deflate_idle_monitors()
1620 // only scans the per-thread in-use lists. omAlloc() puts all
1621 // assigned monitors on the per-thread list. deflate_idle_monitors()
1622 // returns the non-busy monitors to the global free list.
1623 // When a thread dies, omFlush() adds the list of active monitors for
1624 // that thread to a global gOmInUseList acquiring the
1625 // global list lock. deflate_idle_monitors() acquires the global
1626 // list lock to scan for non-busy monitors to the global free list.
1627 // An alternative could have used a single global in-use list. The
1628 // downside would have been the additional cost of acquiring the global list lock
1629 // for every omAlloc().
1630 //
1631 // Perversely, the heap size -- and thus the STW safepoint rate --
1632 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1633 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1634 // This is an unfortunate aspect of this design.
1635
1636 enum ManifestConstants {
1637 ClearResponsibleAtSTW = 0
1638 };
1639
1640 // Deflate a single monitor if not in-use
1641 // Return true if deflated, false if in-use
1642 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1643 ObjectMonitor** freeHeadp,
1644 ObjectMonitor** freeTailp) {
1645 bool deflated;
1646 // Normal case ... The monitor is associated with obj.
1647 guarantee(obj->mark() == markOopDesc::encode(mid), "invariant");
1648 guarantee(mid == obj->mark()->monitor(), "invariant");
1649 guarantee(mid->header()->is_neutral(), "invariant");
1650
1651 if (mid->is_busy()) {
1652 if (ClearResponsibleAtSTW) mid->_Responsible = NULL;
1653 deflated = false;
1654 } else {
1655 // Deflate the monitor if it is no longer being used
1656 // It's idle - scavenge and return to the global free list
1657 // plain old deflation ...
1658 TEVENT(deflate_idle_monitors - scavenge1);
1659 if (log_is_enabled(Debug, monitorinflation)) {
1660 if (obj->is_instance()) {
1661 ResourceMark rm;
1662 log_debug(monitorinflation)("Deflating object " INTPTR_FORMAT " , "
1663 "mark " INTPTR_FORMAT " , type %s",
1664 p2i(obj), p2i(obj->mark()),
1665 obj->klass()->external_name());
1666 }
1667 }
1668
1669 // Restore the header back to obj
1670 obj->release_set_mark(mid->header());
1671 mid->clear();
1672
1673 assert(mid->object() == NULL, "invariant");
1674
1675 // Move the object to the working free list defined by freeHeadp, freeTailp
1676 if (*freeHeadp == NULL) *freeHeadp = mid;
1677 if (*freeTailp != NULL) {
1678 ObjectMonitor * prevtail = *freeTailp;
1679 assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1680 prevtail->FreeNext = mid;
1681 }
1682 *freeTailp = mid;
1683 deflated = true;
1684 }
1685 return deflated;
1686 }
1687
1688 // Walk a given monitor list, and deflate idle monitors
1689 // The given list could be a per-thread list or a global list
1690 // Caller acquires gListLock.
1691 //
1692 // In the case of parallel processing of thread local monitor lists,
1693 // work is done by Threads::parallel_threads_do() which ensures that
1694 // each Java thread is processed by exactly one worker thread, and
1695 // thus avoid conflicts that would arise when worker threads would
1696 // process the same monitor lists concurrently.
1697 //
1698 // See also ParallelSPCleanupTask and
1699 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1700 // Threads::parallel_java_threads_do() in thread.cpp.
1701 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1702 ObjectMonitor** freeHeadp,
1703 ObjectMonitor** freeTailp) {
1704 ObjectMonitor* mid;
1705 ObjectMonitor* next;
1706 ObjectMonitor* cur_mid_in_use = NULL;
1707 int deflated_count = 0;
1708
1709 for (mid = *listHeadp; mid != NULL;) {
1710 oop obj = (oop) mid->object();
1711 if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1712 // if deflate_monitor succeeded,
1713 // extract from per-thread in-use list
1714 if (mid == *listHeadp) {
1715 *listHeadp = mid->FreeNext;
1716 } else if (cur_mid_in_use != NULL) {
1717 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1718 }
1719 next = mid->FreeNext;
1720 mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list
1721 mid = next;
1722 deflated_count++;
1723 } else {
1724 cur_mid_in_use = mid;
1725 mid = mid->FreeNext;
1726 }
1727 }
1728 return deflated_count;
1729 }
1730
1731 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1732 counters->nInuse = 0; // currently associated with objects
1733 counters->nInCirculation = 0; // extant
1734 counters->nScavenged = 0; // reclaimed
1735 }
1736
1737 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
1738 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1739 bool deflated = false;
1740
1741 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1742 ObjectMonitor * freeTailp = NULL;
1743
1744 TEVENT(deflate_idle_monitors);
1745 // Prevent omFlush from changing mids in Thread dtor's during deflation
1746 // And in case the vm thread is acquiring a lock during a safepoint
1747 // See e.g. 6320749
1748 Thread::muxAcquire(&gListLock, "scavenge - return");
1749
1750 if (MonitorInUseLists) {
1751 // Note: the thread-local monitors lists get deflated in
1752 // a separate pass. See deflate_thread_local_monitors().
1753
1754 // For moribund threads, scan gOmInUseList
1755 if (gOmInUseList) {
1756 counters->nInCirculation += gOmInUseCount;
1757 int deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
1758 gOmInUseCount -= deflated_count;
1759 counters->nScavenged += deflated_count;
1760 counters->nInuse += gOmInUseCount;
1761 }
1762
1763 } else {
1764 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
1765 for (; block != NULL; block = next(block)) {
1766 // Iterate over all extant monitors - Scavenge all idle monitors.
1767 assert(block->object() == CHAINMARKER, "must be a block header");
1768 counters->nInCirculation += _BLOCKSIZE;
1769 for (int i = 1; i < _BLOCKSIZE; i++) {
1770 ObjectMonitor* mid = (ObjectMonitor*)&block[i];
1771 oop obj = (oop)mid->object();
1772
1773 if (obj == NULL) {
1774 // The monitor is not associated with an object.
1775 // The monitor should either be a thread-specific private
1776 // free list or the global free list.
1777 // obj == NULL IMPLIES mid->is_busy() == 0
1778 guarantee(!mid->is_busy(), "invariant");
1779 continue;
1780 }
1781 deflated = deflate_monitor(mid, obj, &freeHeadp, &freeTailp);
1782
1783 if (deflated) {
1784 mid->FreeNext = NULL;
1785 counters->nScavenged++;
1786 } else {
1787 counters->nInuse++;
1788 }
1789 }
1790 }
1791 }
1792
1793 // Move the scavenged monitors back to the global free list.
1794 if (freeHeadp != NULL) {
1795 guarantee(freeTailp != NULL && counters->nScavenged > 0, "invariant");
1796 assert(freeTailp->FreeNext == NULL, "invariant");
1797 // constant-time list splice - prepend scavenged segment to gFreeList
1798 freeTailp->FreeNext = gFreeList;
1799 gFreeList = freeHeadp;
1800 }
1801 Thread::muxRelease(&gListLock);
1802
1803 }
1804
1805 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1806 gMonitorFreeCount += counters->nScavenged;
1807
1808 // Consider: audit gFreeList to ensure that gMonitorFreeCount and list agree.
1809
1810 if (ObjectMonitor::Knob_Verbose) {
1811 tty->print_cr("INFO: Deflate: InCirc=%d InUse=%d Scavenged=%d "
1812 "ForceMonitorScavenge=%d : pop=%d free=%d",
1813 counters->nInCirculation, counters->nInuse, counters->nScavenged, ForceMonitorScavenge,
1814 gMonitorPopulation, gMonitorFreeCount);
1815 tty->flush();
1816 }
1817
1818 ForceMonitorScavenge = 0; // Reset
1819
1820 OM_PERFDATA_OP(Deflations, inc(counters->nScavenged));
1821 OM_PERFDATA_OP(MonExtant, set_value(counters->nInCirculation));
1822
1823 // TODO: Add objectMonitor leak detection.
1824 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1825 GVars.stwRandom = os::random();
1826 GVars.stwCycle++;
1827 }
1828
1829 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
1830 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1831 if (!MonitorInUseLists) return;
1832
1833 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1834 ObjectMonitor * freeTailp = NULL;
1835
1836 int deflated_count = deflate_monitor_list(thread->omInUseList_addr(), &freeHeadp, &freeTailp);
1837
1838 Thread::muxAcquire(&gListLock, "scavenge - return");
1839
1840 // Adjust counters
1841 counters->nInCirculation += thread->omInUseCount;
1842 thread->omInUseCount -= deflated_count;
1843 if (ObjectMonitor::Knob_VerifyInUse) {
1844 verifyInUse(thread);
1845 }
1846 counters->nScavenged += deflated_count;
1847 counters->nInuse += thread->omInUseCount;
1848
1849 // Move the scavenged monitors back to the global free list.
1850 if (freeHeadp != NULL) {
1851 guarantee(freeTailp != NULL && deflated_count > 0, "invariant");
1852 assert(freeTailp->FreeNext == NULL, "invariant");
1853
1854 // constant-time list splice - prepend scavenged segment to gFreeList
1855 freeTailp->FreeNext = gFreeList;
1856 gFreeList = freeHeadp;
1857 }
1858 Thread::muxRelease(&gListLock);
1859 }
1860
1861 // Monitor cleanup on JavaThread::exit
1862
1863 // Iterate through monitor cache and attempt to release thread's monitors
1864 // Gives up on a particular monitor if an exception occurs, but continues
1865 // the overall iteration, swallowing the exception.
1866 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1867 private:
1868 TRAPS;
1869
1870 public:
1871 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1872 void do_monitor(ObjectMonitor* mid) {
1873 if (mid->owner() == THREAD) {
1874 if (ObjectMonitor::Knob_VerifyMatch != 0) {
1875 ResourceMark rm;
1876 Handle obj(THREAD, (oop) mid->object());
1877 tty->print("INFO: unexpected locked object:");
1878 javaVFrame::print_locked_object_class_name(tty, obj, "locked");
1879 fatal("exiting JavaThread=" INTPTR_FORMAT
1880 " unexpectedly owns ObjectMonitor=" INTPTR_FORMAT,
1881 p2i(THREAD), p2i(mid));
1882 }
1883 (void)mid->complete_exit(CHECK);
1884 }
1885 }
1886 };
1887
1888 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1889 // ignored. This is meant to be called during JNI thread detach which assumes
1890 // all remaining monitors are heavyweight. All exceptions are swallowed.
1891 // Scanning the extant monitor list can be time consuming.
1892 // A simple optimization is to add a per-thread flag that indicates a thread
1893 // called jni_monitorenter() during its lifetime.
1894 //
1895 // Instead of No_Savepoint_Verifier it might be cheaper to
1896 // use an idiom of the form:
1897 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1898 // <code that must not run at safepoint>
1899 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1900 // Since the tests are extremely cheap we could leave them enabled
1901 // for normal product builds.
1902
1903 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1904 assert(THREAD == JavaThread::current(), "must be current Java thread");
1905 NoSafepointVerifier nsv;
1906 ReleaseJavaMonitorsClosure rjmc(THREAD);
1907 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
1908 ObjectSynchronizer::monitors_iterate(&rjmc);
1909 Thread::muxRelease(&gListLock);
1910 THREAD->clear_pending_exception();
1911 }
1912
1913 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1914 switch (cause) {
1915 case inflate_cause_vm_internal: return "VM Internal";
1916 case inflate_cause_monitor_enter: return "Monitor Enter";
1917 case inflate_cause_wait: return "Monitor Wait";
1918 case inflate_cause_notify: return "Monitor Notify";
1919 case inflate_cause_hash_code: return "Monitor Hash Code";
1920 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1921 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1922 default:
1923 ShouldNotReachHere();
1924 }
1925 return "Unknown";
1926 }
1927
1928 static void post_monitor_inflate_event(EventJavaMonitorInflate& event,
1929 const oop obj,
1930 const ObjectSynchronizer::InflateCause cause) {
1931 #if INCLUDE_TRACE
1932 assert(event.should_commit(), "check outside");
1933 event.set_monitorClass(obj->klass());
1934 event.set_address((TYPE_ADDRESS)(uintptr_t)(void*)obj);
1935 event.set_cause((u1)cause);
1936 event.commit();
1937 #endif
1938 }
1939
1940 //------------------------------------------------------------------------------
1941 // Debugging code
1942
1943 void ObjectSynchronizer::sanity_checks(const bool verbose,
1944 const uint cache_line_size,
1945 int *error_cnt_ptr,
1946 int *warning_cnt_ptr) {
1947 u_char *addr_begin = (u_char*)&GVars;
1948 u_char *addr_stwRandom = (u_char*)&GVars.stwRandom;
1949 u_char *addr_hcSequence = (u_char*)&GVars.hcSequence;
1950
1951 if (verbose) {
1952 tty->print_cr("INFO: sizeof(SharedGlobals)=" SIZE_FORMAT,
1953 sizeof(SharedGlobals));
1954 }
1955
1956 uint offset_stwRandom = (uint)(addr_stwRandom - addr_begin);
1957 if (verbose) tty->print_cr("INFO: offset(stwRandom)=%u", offset_stwRandom);
1958
1959 uint offset_hcSequence = (uint)(addr_hcSequence - addr_begin);
1960 if (verbose) {
1961 tty->print_cr("INFO: offset(_hcSequence)=%u", offset_hcSequence);
1962 }
1963
1964 if (cache_line_size != 0) {
1965 // We were able to determine the L1 data cache line size so
1966 // do some cache line specific sanity checks
1967
1968 if (offset_stwRandom < cache_line_size) {
1969 tty->print_cr("WARNING: the SharedGlobals.stwRandom field is closer "
1970 "to the struct beginning than a cache line which permits "
1971 "false sharing.");
1972 (*warning_cnt_ptr)++;
1973 }
1974
1975 if ((offset_hcSequence - offset_stwRandom) < cache_line_size) {
1976 tty->print_cr("WARNING: the SharedGlobals.stwRandom and "
1977 "SharedGlobals.hcSequence fields are closer than a cache "
1978 "line which permits false sharing.");
1979 (*warning_cnt_ptr)++;
1980 }
1981
1982 if ((sizeof(SharedGlobals) - offset_hcSequence) < cache_line_size) {
1983 tty->print_cr("WARNING: the SharedGlobals.hcSequence field is closer "
1984 "to the struct end than a cache line which permits false "
1985 "sharing.");
1986 (*warning_cnt_ptr)++;
1987 }
1988 }
1989 }
1990
1991 #ifndef PRODUCT
1992
1993 // Check if monitor belongs to the monitor cache
1994 // The list is grow-only so it's *relatively* safe to traverse
1995 // the list of extant blocks without taking a lock.
1996
1997 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
1998 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
1999 while (block != NULL) {
2000 assert(block->object() == CHAINMARKER, "must be a block header");
2001 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
2002 address mon = (address)monitor;
2003 address blk = (address)block;
2004 size_t diff = mon - blk;
2005 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "must be aligned");
2006 return 1;
2007 }
2008 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
2009 }
2010 return 0;
2011 }
2012
2013 #endif