1 /*
2 * Copyright (c) 1998, 2019, 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.
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23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/vmSymbols.hpp"
27 #include "logging/log.hpp"
28 #include "logging/logStream.hpp"
29 #include "jfr/jfrEvents.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "memory/metaspaceShared.hpp"
32 #include "memory/padded.hpp"
33 #include "memory/resourceArea.hpp"
34 #include "memory/universe.hpp"
35 #include "oops/markWord.hpp"
36 #include "oops/oop.inline.hpp"
37 #include "runtime/atomic.hpp"
38 #include "runtime/biasedLocking.hpp"
39 #include "runtime/handles.inline.hpp"
40 #include "runtime/interfaceSupport.inline.hpp"
41 #include "runtime/mutexLocker.hpp"
42 #include "runtime/objectMonitor.hpp"
43 #include "runtime/objectMonitor.inline.hpp"
44 #include "runtime/osThread.hpp"
45 #include "runtime/safepointVerifiers.hpp"
46 #include "runtime/sharedRuntime.hpp"
47 #include "runtime/stubRoutines.hpp"
48 #include "runtime/synchronizer.hpp"
49 #include "runtime/thread.inline.hpp"
50 #include "runtime/timer.hpp"
51 #include "runtime/vframe.hpp"
52 #include "runtime/vmThread.hpp"
53 #include "utilities/align.hpp"
54 #include "utilities/dtrace.hpp"
55 #include "utilities/events.hpp"
56 #include "utilities/preserveException.hpp"
57
58 // The "core" versions of monitor enter and exit reside in this file.
59 // The interpreter and compilers contain specialized transliterated
60 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
61 // for instance. If you make changes here, make sure to modify the
62 // interpreter, and both C1 and C2 fast-path inline locking code emission.
63 //
64 // -----------------------------------------------------------------------------
65
66 #ifdef DTRACE_ENABLED
67
68 // Only bother with this argument setup if dtrace is available
69 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
70
71 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
72 char* bytes = NULL; \
73 int len = 0; \
74 jlong jtid = SharedRuntime::get_java_tid(thread); \
75 Symbol* klassname = ((oop)(obj))->klass()->name(); \
76 if (klassname != NULL) { \
77 bytes = (char*)klassname->bytes(); \
78 len = klassname->utf8_length(); \
79 }
80
81 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
82 { \
83 if (DTraceMonitorProbes) { \
84 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
85 HOTSPOT_MONITOR_WAIT(jtid, \
86 (uintptr_t)(monitor), bytes, len, (millis)); \
87 } \
88 }
89
90 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
91 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
92 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
93
94 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
95 { \
96 if (DTraceMonitorProbes) { \
97 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
98 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
99 (uintptr_t)(monitor), bytes, len); \
100 } \
101 }
102
103 #else // ndef DTRACE_ENABLED
104
105 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
106 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
107
108 #endif // ndef DTRACE_ENABLED
109
110 // This exists only as a workaround of dtrace bug 6254741
111 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
112 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
113 return 0;
114 }
115
116 #define NINFLATIONLOCKS 256
117 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
118
119 // global list of blocks of monitors
120 PaddedObjectMonitor* volatile ObjectSynchronizer::g_block_list = NULL;
121 // Global ObjectMonitor free list. Newly allocated and deflated
122 // ObjectMonitors are prepended here.
123 ObjectMonitor* volatile ObjectSynchronizer::g_free_list = NULL;
124 // Global ObjectMonitor in-use list. When a JavaThread is exiting,
125 // ObjectMonitors on its per-thread in-use list are prepended here.
126 ObjectMonitor* volatile ObjectSynchronizer::g_om_in_use_list = NULL;
127 int ObjectSynchronizer::g_om_in_use_count = 0; // # on g_om_in_use_list
128 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
129 bool volatile ObjectSynchronizer::_is_special_deflation_requested = false;
130 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
131
132 static volatile intptr_t gListLock = 0; // protects global monitor lists
133 static volatile int g_om_free_count = 0; // # on g_free_list
134 static volatile int g_om_population = 0; // # Extant -- in circulation
135
136 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
137
138
139 // =====================> Quick functions
140
141 // The quick_* forms are special fast-path variants used to improve
142 // performance. In the simplest case, a "quick_*" implementation could
143 // simply return false, in which case the caller will perform the necessary
144 // state transitions and call the slow-path form.
145 // The fast-path is designed to handle frequently arising cases in an efficient
146 // manner and is just a degenerate "optimistic" variant of the slow-path.
147 // returns true -- to indicate the call was satisfied.
148 // returns false -- to indicate the call needs the services of the slow-path.
149 // A no-loitering ordinance is in effect for code in the quick_* family
150 // operators: safepoints or indefinite blocking (blocking that might span a
151 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
152 // entry.
153 //
154 // Consider: An interesting optimization is to have the JIT recognize the
155 // following common idiom:
156 // synchronized (someobj) { .... ; notify(); }
157 // That is, we find a notify() or notifyAll() call that immediately precedes
158 // the monitorexit operation. In that case the JIT could fuse the operations
159 // into a single notifyAndExit() runtime primitive.
160
161 bool ObjectSynchronizer::quick_notify(oopDesc* obj, Thread* self, bool all) {
162 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
163 assert(self->is_Java_thread(), "invariant");
164 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
165 NoSafepointVerifier nsv;
166 if (obj == NULL) return false; // slow-path for invalid obj
167 const markWord mark = obj->mark();
168
169 if (mark.has_locker() && self->is_lock_owned((address)mark.locker())) {
170 // Degenerate notify
171 // stack-locked by caller so by definition the implied waitset is empty.
172 return true;
173 }
174
175 if (mark.has_monitor()) {
176 ObjectMonitor* const mon = mark.monitor();
177 assert(oopDesc::equals((oop) mon->object(), obj), "invariant");
178 if (mon->owner() != self) return false; // slow-path for IMS exception
179
180 if (mon->first_waiter() != NULL) {
181 // We have one or more waiters. Since this is an inflated monitor
182 // that we own, we can transfer one or more threads from the waitset
183 // to the entrylist here and now, avoiding the slow-path.
184 if (all) {
185 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
186 } else {
187 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
188 }
189 int free_count = 0;
190 do {
191 mon->INotify(self);
192 ++free_count;
193 } while (mon->first_waiter() != NULL && all);
194 OM_PERFDATA_OP(Notifications, inc(free_count));
195 }
196 return true;
197 }
198
199 // biased locking and any other IMS exception states take the slow-path
200 return false;
201 }
202
203
204 // The LockNode emitted directly at the synchronization site would have
205 // been too big if it were to have included support for the cases of inflated
206 // recursive enter and exit, so they go here instead.
207 // Note that we can't safely call AsyncPrintJavaStack() from within
208 // quick_enter() as our thread state remains _in_Java.
209
210 bool ObjectSynchronizer::quick_enter(oop obj, Thread* self,
211 BasicLock * lock) {
212 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
213 assert(self->is_Java_thread(), "invariant");
214 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
215 NoSafepointVerifier nsv;
216 if (obj == NULL) return false; // Need to throw NPE
217
218 while (true) {
219 const markWord mark = obj->mark();
220
221 if (mark.has_monitor()) {
222 ObjectMonitorHandle omh;
223 if (!omh.save_om_ptr(obj, mark)) {
224 // Lost a race with async deflation so try again.
225 assert(AsyncDeflateIdleMonitors, "sanity check");
226 continue;
227 }
228 ObjectMonitor* const m = omh.om_ptr();
229 assert(oopDesc::equals((oop) m->object(), obj), "invariant");
230 Thread* const owner = (Thread *) m->_owner;
231
232 // Lock contention and Transactional Lock Elision (TLE) diagnostics
233 // and observability
234 // Case: light contention possibly amenable to TLE
235 // Case: TLE inimical operations such as nested/recursive synchronization
236
237 if (owner == self) {
238 m->_recursions++;
239 return true;
240 }
241
242 // This Java Monitor is inflated so obj's header will never be
243 // displaced to this thread's BasicLock. Make the displaced header
244 // non-NULL so this BasicLock is not seen as recursive nor as
245 // being locked. We do this unconditionally so that this thread's
246 // BasicLock cannot be mis-interpreted by any stack walkers. For
247 // performance reasons, stack walkers generally first check for
248 // Biased Locking in the object's header, the second check is for
249 // stack-locking in the object's header, the third check is for
250 // recursive stack-locking in the displaced header in the BasicLock,
251 // and last are the inflated Java Monitor (ObjectMonitor) checks.
252 lock->set_displaced_header(markWord::unused_mark());
253
254 if (owner == NULL && Atomic::replace_if_null(self, &(m->_owner))) {
255 assert(m->_recursions == 0, "invariant");
256 return true;
257 }
258
259 if (AsyncDeflateIdleMonitors &&
260 Atomic::cmpxchg(self, &m->_owner, DEFLATER_MARKER) == DEFLATER_MARKER) {
261 // The deflation protocol finished the first part (setting owner),
262 // but it failed the second part (making ref_count negative) and
263 // bailed. Or the ObjectMonitor was async deflated and reused.
264 // Acquired the monitor.
265 assert(m->_recursions == 0, "invariant");
266 return true;
267 }
268 }
269 break;
270 }
271
272 // Note that we could inflate in quick_enter.
273 // This is likely a useful optimization
274 // Critically, in quick_enter() we must not:
275 // -- perform bias revocation, or
276 // -- block indefinitely, or
277 // -- reach a safepoint
278
279 return false; // revert to slow-path
280 }
281
282 // -----------------------------------------------------------------------------
283 // Fast Monitor Enter/Exit
284 // This the fast monitor enter. The interpreter and compiler use
285 // some assembly copies of this code. Make sure update those code
286 // if the following function is changed. The implementation is
287 // extremely sensitive to race condition. Be careful.
288
289 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
290 bool attempt_rebias, TRAPS) {
291 if (UseBiasedLocking) {
292 if (!SafepointSynchronize::is_at_safepoint()) {
293 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
294 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
295 return;
296 }
297 } else {
298 assert(!attempt_rebias, "can not rebias toward VM thread");
299 BiasedLocking::revoke_at_safepoint(obj);
300 }
301 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
302 }
303
304 slow_enter(obj, lock, THREAD);
305 }
306
307 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
308 markWord mark = object->mark();
309 // We cannot check for Biased Locking if we are racing an inflation.
310 assert(mark == markWord::INFLATING() ||
311 !mark.has_bias_pattern(), "should not see bias pattern here");
312
313 markWord dhw = lock->displaced_header();
314 if (dhw.value() == 0) {
315 // If the displaced header is NULL, then this exit matches up with
316 // a recursive enter. No real work to do here except for diagnostics.
317 #ifndef PRODUCT
318 if (mark != markWord::INFLATING()) {
319 // Only do diagnostics if we are not racing an inflation. Simply
320 // exiting a recursive enter of a Java Monitor that is being
321 // inflated is safe; see the has_monitor() comment below.
322 assert(!mark.is_neutral(), "invariant");
323 assert(!mark.has_locker() ||
324 THREAD->is_lock_owned((address)mark.locker()), "invariant");
325 if (mark.has_monitor()) {
326 // The BasicLock's displaced_header is marked as a recursive
327 // enter and we have an inflated Java Monitor (ObjectMonitor).
328 // This is a special case where the Java Monitor was inflated
329 // after this thread entered the stack-lock recursively. When a
330 // Java Monitor is inflated, we cannot safely walk the Java
331 // Monitor owner's stack and update the BasicLocks because a
332 // Java Monitor can be asynchronously inflated by a thread that
333 // does not own the Java Monitor.
334 ObjectMonitor* m = mark.monitor();
335 assert(((oop)(m->object()))->mark() == mark, "invariant");
336 assert(m->is_entered(THREAD), "invariant");
337 }
338 }
339 #endif
340 return;
341 }
342
343 if (mark == markWord::from_pointer(lock)) {
344 // If the object is stack-locked by the current thread, try to
345 // swing the displaced header from the BasicLock back to the mark.
346 assert(dhw.is_neutral(), "invariant");
347 if (object->cas_set_mark(dhw, mark) == mark) {
348 return;
349 }
350 }
351
352 // We have to take the slow-path of possible inflation and then exit.
353 ObjectMonitorHandle omh;
354 inflate(&omh, THREAD, object, inflate_cause_vm_internal);
355 omh.om_ptr()->exit(true, THREAD);
356 }
357
358 // -----------------------------------------------------------------------------
359 // Interpreter/Compiler Slow Case
360 // This routine is used to handle interpreter/compiler slow case
361 // We don't need to use fast path here, because it must have been
362 // failed in the interpreter/compiler code.
363 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
364 markWord mark = obj->mark();
365 assert(!mark.has_bias_pattern(), "should not see bias pattern here");
366
367 if (mark.is_neutral()) {
368 // Anticipate successful CAS -- the ST of the displaced mark must
369 // be visible <= the ST performed by the CAS.
370 lock->set_displaced_header(mark);
371 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
372 return;
373 }
374 // Fall through to inflate() ...
375 } else if (mark.has_locker() &&
376 THREAD->is_lock_owned((address)mark.locker())) {
377 assert(lock != mark.locker(), "must not re-lock the same lock");
378 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
379 lock->set_displaced_header(markWord::from_pointer(NULL));
380 return;
381 }
382
383 // The object header will never be displaced to this lock,
384 // so it does not matter what the value is, except that it
385 // must be non-zero to avoid looking like a re-entrant lock,
386 // and must not look locked either.
387 lock->set_displaced_header(markWord::unused_mark());
388 ObjectMonitorHandle omh;
389 inflate(&omh, THREAD, obj(), inflate_cause_monitor_enter);
390 omh.om_ptr()->enter(THREAD);
391 }
392
393 // This routine is used to handle interpreter/compiler slow case
394 // We don't need to use fast path here, because it must have
395 // failed in the interpreter/compiler code. Simply use the heavy
396 // weight monitor should be ok, unless someone find otherwise.
397 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
398 fast_exit(object, lock, THREAD);
399 }
400
401 // -----------------------------------------------------------------------------
402 // Class Loader support to workaround deadlocks on the class loader lock objects
403 // Also used by GC
404 // complete_exit()/reenter() are used to wait on a nested lock
405 // i.e. to give up an outer lock completely and then re-enter
406 // Used when holding nested locks - lock acquisition order: lock1 then lock2
407 // 1) complete_exit lock1 - saving recursion count
408 // 2) wait on lock2
409 // 3) when notified on lock2, unlock lock2
410 // 4) reenter lock1 with original recursion count
411 // 5) lock lock2
412 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
413 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
414 if (UseBiasedLocking) {
415 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
416 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
417 }
418
419 ObjectMonitorHandle omh;
420 inflate(&omh, THREAD, obj(), inflate_cause_vm_internal);
421 intptr_t ret_code = omh.om_ptr()->complete_exit(THREAD);
422 return ret_code;
423 }
424
425 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
426 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
427 if (UseBiasedLocking) {
428 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
429 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
430 }
431
432 ObjectMonitorHandle omh;
433 inflate(&omh, THREAD, obj(), inflate_cause_vm_internal);
434 omh.om_ptr()->reenter(recursion, THREAD);
435 }
436 // -----------------------------------------------------------------------------
437 // JNI locks on java objects
438 // NOTE: must use heavy weight monitor to handle jni monitor enter
439 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
440 // the current locking is from JNI instead of Java code
441 if (UseBiasedLocking) {
442 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
443 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
444 }
445 THREAD->set_current_pending_monitor_is_from_java(false);
446 ObjectMonitorHandle omh;
447 inflate(&omh, THREAD, obj(), inflate_cause_jni_enter);
448 omh.om_ptr()->enter(THREAD);
449 THREAD->set_current_pending_monitor_is_from_java(true);
450 }
451
452 // NOTE: must use heavy weight monitor to handle jni monitor exit
453 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
454 if (UseBiasedLocking) {
455 Handle h_obj(THREAD, obj);
456 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
457 obj = h_obj();
458 }
459 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
460
461 ObjectMonitorHandle omh;
462 inflate(&omh, THREAD, obj, inflate_cause_jni_exit);
463 ObjectMonitor* monitor = omh.om_ptr();
464 // If this thread has locked the object, exit the monitor. We
465 // intentionally do not use CHECK here because we must exit the
466 // monitor even if an exception is pending.
467 if (monitor->check_owner(THREAD)) {
468 monitor->exit(true, THREAD);
469 }
470 }
471
472 // -----------------------------------------------------------------------------
473 // Internal VM locks on java objects
474 // standard constructor, allows locking failures
475 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool do_lock) {
476 _dolock = do_lock;
477 _thread = thread;
478 _thread->check_for_valid_safepoint_state(false);
479 _obj = obj;
480
481 if (_dolock) {
482 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
483 }
484 }
485
486 ObjectLocker::~ObjectLocker() {
487 if (_dolock) {
488 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
489 }
490 }
491
492
493 // -----------------------------------------------------------------------------
494 // Wait/Notify/NotifyAll
495 // NOTE: must use heavy weight monitor to handle wait()
496 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
497 if (UseBiasedLocking) {
498 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
499 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
500 }
501 if (millis < 0) {
502 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
503 }
504 ObjectMonitorHandle omh;
505 inflate(&omh, THREAD, obj(), inflate_cause_wait);
506 ObjectMonitor* monitor = omh.om_ptr();
507
508 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
509 monitor->wait(millis, true, THREAD);
510
511 // This dummy call is in place to get around dtrace bug 6254741. Once
512 // that's fixed we can uncomment the following line, remove the call
513 // and change this function back into a "void" func.
514 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
515 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
516 return ret_code;
517 }
518
519 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, jlong millis, TRAPS) {
520 if (UseBiasedLocking) {
521 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
522 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
523 }
524 if (millis < 0) {
525 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
526 }
527 ObjectMonitorHandle omh;
528 inflate(&omh, THREAD, obj(), inflate_cause_wait);
529 omh.om_ptr()->wait(millis, false, THREAD);
530 }
531
532 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
533 if (UseBiasedLocking) {
534 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
535 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
536 }
537
538 markWord mark = obj->mark();
539 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
540 return;
541 }
542 ObjectMonitorHandle omh;
543 inflate(&omh, THREAD, obj(), inflate_cause_notify);
544 omh.om_ptr()->notify(THREAD);
545 }
546
547 // NOTE: see comment of notify()
548 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
549 if (UseBiasedLocking) {
550 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
551 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
552 }
553
554 markWord mark = obj->mark();
555 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
556 return;
557 }
558 ObjectMonitorHandle omh;
559 inflate(&omh, THREAD, obj(), inflate_cause_notify);
560 omh.om_ptr()->notifyAll(THREAD);
561 }
562
563 // -----------------------------------------------------------------------------
564 // Hash Code handling
565 //
566 // Performance concern:
567 // OrderAccess::storestore() calls release() which at one time stored 0
568 // into the global volatile OrderAccess::dummy variable. This store was
569 // unnecessary for correctness. Many threads storing into a common location
570 // causes considerable cache migration or "sloshing" on large SMP systems.
571 // As such, I avoided using OrderAccess::storestore(). In some cases
572 // OrderAccess::fence() -- which incurs local latency on the executing
573 // processor -- is a better choice as it scales on SMP systems.
574 //
575 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
576 // a discussion of coherency costs. Note that all our current reference
577 // platforms provide strong ST-ST order, so the issue is moot on IA32,
578 // x64, and SPARC.
579 //
580 // As a general policy we use "volatile" to control compiler-based reordering
581 // and explicit fences (barriers) to control for architectural reordering
582 // performed by the CPU(s) or platform.
583
584 struct SharedGlobals {
585 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
586 // These are highly shared mostly-read variables.
587 // To avoid false-sharing they need to be the sole occupants of a cache line.
588 volatile int stw_random;
589 volatile int stw_cycle;
590 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
591 // Hot RW variable -- Sequester to avoid false-sharing
592 volatile int hc_sequence;
593 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
594 };
595
596 static SharedGlobals GVars;
597 static int MonitorScavengeThreshold = 1000000;
598 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
599
600 static markWord read_stable_mark(oop obj) {
601 markWord mark = obj->mark();
602 if (!mark.is_being_inflated()) {
603 return mark; // normal fast-path return
604 }
605
606 int its = 0;
607 for (;;) {
608 markWord mark = obj->mark();
609 if (!mark.is_being_inflated()) {
610 return mark; // normal fast-path return
611 }
612
613 // The object is being inflated by some other thread.
614 // The caller of read_stable_mark() must wait for inflation to complete.
615 // Avoid live-lock
616 // TODO: consider calling SafepointSynchronize::do_call_back() while
617 // spinning to see if there's a safepoint pending. If so, immediately
618 // yielding or blocking would be appropriate. Avoid spinning while
619 // there is a safepoint pending.
620 // TODO: add inflation contention performance counters.
621 // TODO: restrict the aggregate number of spinners.
622
623 ++its;
624 if (its > 10000 || !os::is_MP()) {
625 if (its & 1) {
626 os::naked_yield();
627 } else {
628 // Note that the following code attenuates the livelock problem but is not
629 // a complete remedy. A more complete solution would require that the inflating
630 // thread hold the associated inflation lock. The following code simply restricts
631 // the number of spinners to at most one. We'll have N-2 threads blocked
632 // on the inflationlock, 1 thread holding the inflation lock and using
633 // a yield/park strategy, and 1 thread in the midst of inflation.
634 // A more refined approach would be to change the encoding of INFLATING
635 // to allow encapsulation of a native thread pointer. Threads waiting for
636 // inflation to complete would use CAS to push themselves onto a singly linked
637 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
638 // and calling park(). When inflation was complete the thread that accomplished inflation
639 // would detach the list and set the markword to inflated with a single CAS and
640 // then for each thread on the list, set the flag and unpark() the thread.
641 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
642 // wakes at most one thread whereas we need to wake the entire list.
643 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
644 int YieldThenBlock = 0;
645 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
646 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
647 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
648 while (obj->mark() == markWord::INFLATING()) {
649 // Beware: NakedYield() is advisory and has almost no effect on some platforms
650 // so we periodically call self->_ParkEvent->park(1).
651 // We use a mixed spin/yield/block mechanism.
652 if ((YieldThenBlock++) >= 16) {
653 Thread::current()->_ParkEvent->park(1);
654 } else {
655 os::naked_yield();
656 }
657 }
658 Thread::muxRelease(gInflationLocks + ix);
659 }
660 } else {
661 SpinPause(); // SMP-polite spinning
662 }
663 }
664 }
665
666 // hashCode() generation :
667 //
668 // Possibilities:
669 // * MD5Digest of {obj,stw_random}
670 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
671 // * A DES- or AES-style SBox[] mechanism
672 // * One of the Phi-based schemes, such as:
673 // 2654435761 = 2^32 * Phi (golden ratio)
674 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
675 // * A variation of Marsaglia's shift-xor RNG scheme.
676 // * (obj ^ stw_random) is appealing, but can result
677 // in undesirable regularity in the hashCode values of adjacent objects
678 // (objects allocated back-to-back, in particular). This could potentially
679 // result in hashtable collisions and reduced hashtable efficiency.
680 // There are simple ways to "diffuse" the middle address bits over the
681 // generated hashCode values:
682
683 static inline intptr_t get_next_hash(Thread* self, oop obj) {
684 intptr_t value = 0;
685 if (hashCode == 0) {
686 // This form uses global Park-Miller RNG.
687 // On MP system we'll have lots of RW access to a global, so the
688 // mechanism induces lots of coherency traffic.
689 value = os::random();
690 } else if (hashCode == 1) {
691 // This variation has the property of being stable (idempotent)
692 // between STW operations. This can be useful in some of the 1-0
693 // synchronization schemes.
694 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
695 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
696 } else if (hashCode == 2) {
697 value = 1; // for sensitivity testing
698 } else if (hashCode == 3) {
699 value = ++GVars.hc_sequence;
700 } else if (hashCode == 4) {
701 value = cast_from_oop<intptr_t>(obj);
702 } else {
703 // Marsaglia's xor-shift scheme with thread-specific state
704 // This is probably the best overall implementation -- we'll
705 // likely make this the default in future releases.
706 unsigned t = self->_hashStateX;
707 t ^= (t << 11);
708 self->_hashStateX = self->_hashStateY;
709 self->_hashStateY = self->_hashStateZ;
710 self->_hashStateZ = self->_hashStateW;
711 unsigned v = self->_hashStateW;
712 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
713 self->_hashStateW = v;
714 value = v;
715 }
716
717 value &= markWord::hash_mask;
718 if (value == 0) value = 0xBAD;
719 assert(value != markWord::no_hash, "invariant");
720 return value;
721 }
722
723 intptr_t ObjectSynchronizer::FastHashCode(Thread* self, oop obj) {
724 if (UseBiasedLocking) {
725 // NOTE: many places throughout the JVM do not expect a safepoint
726 // to be taken here, in particular most operations on perm gen
727 // objects. However, we only ever bias Java instances and all of
728 // the call sites of identity_hash that might revoke biases have
729 // been checked to make sure they can handle a safepoint. The
730 // added check of the bias pattern is to avoid useless calls to
731 // thread-local storage.
732 if (obj->mark().has_bias_pattern()) {
733 // Handle for oop obj in case of STW safepoint
734 Handle hobj(self, obj);
735 // Relaxing assertion for bug 6320749.
736 assert(Universe::verify_in_progress() ||
737 !SafepointSynchronize::is_at_safepoint(),
738 "biases should not be seen by VM thread here");
739 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
740 obj = hobj();
741 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
742 }
743 }
744
745 // hashCode() is a heap mutator ...
746 // Relaxing assertion for bug 6320749.
747 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
748 !SafepointSynchronize::is_at_safepoint(), "invariant");
749 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
750 self->is_Java_thread() , "invariant");
751 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
752 ((JavaThread *)self)->thread_state() != _thread_blocked, "invariant");
753
754 while (true) {
755 ObjectMonitor* monitor = NULL;
756 markWord temp, test;
757 intptr_t hash;
758 markWord mark = read_stable_mark(obj);
759
760 // object should remain ineligible for biased locking
761 assert(!mark.has_bias_pattern(), "invariant");
762
763 if (mark.is_neutral()) {
764 hash = mark.hash(); // this is a normal header
765 if (hash != 0) { // if it has hash, just return it
766 return hash;
767 }
768 hash = get_next_hash(self, obj); // allocate a new hash code
769 temp = mark.copy_set_hash(hash); // merge the hash code into header
770 // use (machine word version) atomic operation to install the hash
771 test = obj->cas_set_mark(temp, mark);
772 if (test == mark) {
773 return hash;
774 }
775 // If atomic operation failed, we must inflate the header
776 // into heavy weight monitor. We could add more code here
777 // for fast path, but it does not worth the complexity.
778 } else if (mark.has_monitor()) {
779 ObjectMonitorHandle omh;
780 if (!omh.save_om_ptr(obj, mark)) {
781 // Lost a race with async deflation so try again.
782 assert(AsyncDeflateIdleMonitors, "sanity check");
783 continue;
784 }
785 monitor = omh.om_ptr();
786 temp = monitor->header();
787 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
788 hash = temp.hash();
789 if (hash != 0) {
790 return hash;
791 }
792 // Skip to the following code to reduce code size
793 } else if (self->is_lock_owned((address)mark.locker())) {
794 temp = mark.displaced_mark_helper(); // this is a lightweight monitor owned
795 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
796 hash = temp.hash(); // by current thread, check if the displaced
797 if (hash != 0) { // header contains hash code
798 return hash;
799 }
800 // WARNING:
801 // The displaced header in the BasicLock on a thread's stack
802 // is strictly immutable. It CANNOT be changed in ANY cases.
803 // So we have to inflate the stack lock into an ObjectMonitor
804 // even if the current thread owns the lock. The BasicLock on
805 // a thread's stack can be asynchronously read by other threads
806 // during an inflate() call so any change to that stack memory
807 // may not propagate to other threads correctly.
808 }
809
810 // Inflate the monitor to set hash code
811 ObjectMonitorHandle omh;
812 inflate(&omh, self, obj, inflate_cause_hash_code);
813 monitor = omh.om_ptr();
814 // Load displaced header and check it has hash code
815 mark = monitor->header();
816 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
817 hash = mark.hash();
818 if (hash == 0) {
819 hash = get_next_hash(self, obj);
820 temp = mark.copy_set_hash(hash); // merge hash code into header
821 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
822 uintptr_t v = Atomic::cmpxchg(temp.value(), (volatile uintptr_t*)monitor->header_addr(), mark.value());
823 test = markWord(v);
824 if (test != mark) {
825 // The only non-deflation update to the ObjectMonitor's
826 // header/dmw field is to merge in the hash code. If someone
827 // adds a new usage of the header/dmw field, please update
828 // this code.
829 // ObjectMonitor::install_displaced_markword_in_object()
830 // does mark the header/dmw field as part of async deflation,
831 // but that protocol cannot happen now due to the
832 // ObjectMonitorHandle above.
833 hash = test.hash();
834 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
835 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
836 }
837 }
838 // We finally get the hash
839 return hash;
840 }
841 }
842
843 // Deprecated -- use FastHashCode() instead.
844
845 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
846 return FastHashCode(Thread::current(), obj());
847 }
848
849
850 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
851 Handle h_obj) {
852 if (UseBiasedLocking) {
853 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
854 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
855 }
856
857 assert(thread == JavaThread::current(), "Can only be called on current thread");
858 oop obj = h_obj();
859
860 while (true) {
861 markWord mark = read_stable_mark(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 ObjectMonitorHandle omh;
870 if (!omh.save_om_ptr(obj, mark)) {
871 // Lost a race with async deflation so try again.
872 assert(AsyncDeflateIdleMonitors, "sanity check");
873 continue;
874 }
875 bool ret_code = omh.om_ptr()->is_entered(thread) != 0;
876 return ret_code;
877 }
878 // Unlocked case, header in place
879 assert(mark.is_neutral(), "sanity check");
880 return false;
881 }
882 }
883
884 // Be aware of this method could revoke bias of the lock object.
885 // This method queries the ownership of the lock handle specified by 'h_obj'.
886 // If the current thread owns the lock, it returns owner_self. If no
887 // thread owns the lock, it returns owner_none. Otherwise, it will return
888 // owner_other.
889 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
890 (JavaThread *self, Handle h_obj) {
891 // The caller must beware this method can revoke bias, and
892 // revocation can result in a safepoint.
893 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
894 assert(self->thread_state() != _thread_blocked, "invariant");
895
896 // Possible mark states: neutral, biased, stack-locked, inflated
897
898 if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) {
899 // CASE: biased
900 BiasedLocking::revoke_and_rebias(h_obj, false, self);
901 assert(!h_obj->mark().has_bias_pattern(),
902 "biases should be revoked by now");
903 }
904
905 assert(self == JavaThread::current(), "Can only be called on current thread");
906 oop obj = h_obj();
907
908 while (true) {
909 markWord mark = read_stable_mark(obj);
910
911 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
912 if (mark.has_locker()) {
913 return self->is_lock_owned((address)mark.locker()) ?
914 owner_self : owner_other;
915 }
916
917 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
918 // The Object:ObjectMonitor relationship is stable as long as we're
919 // not at a safepoint and AsyncDeflateIdleMonitors is false.
920 if (mark.has_monitor()) {
921 ObjectMonitorHandle omh;
922 if (!omh.save_om_ptr(obj, mark)) {
923 // Lost a race with async deflation so try again.
924 assert(AsyncDeflateIdleMonitors, "sanity check");
925 continue;
926 }
927 ObjectMonitor* monitor = omh.om_ptr();
928 void* owner = monitor->_owner;
929 if (owner == NULL) return owner_none;
930 return (owner == self ||
931 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
932 }
933
934 // CASE: neutral
935 assert(mark.is_neutral(), "sanity check");
936 return owner_none; // it's unlocked
937 }
938 }
939
940 // FIXME: jvmti should call this
941 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
942 if (UseBiasedLocking) {
943 if (SafepointSynchronize::is_at_safepoint()) {
944 BiasedLocking::revoke_at_safepoint(h_obj);
945 } else {
946 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
947 }
948 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
949 }
950
951 oop obj = h_obj();
952
953 while (true) {
954 address owner = NULL;
955 markWord mark = read_stable_mark(obj);
956
957 // Uncontended case, header points to stack
958 if (mark.has_locker()) {
959 owner = (address) mark.locker();
960 }
961
962 // Contended case, header points to ObjectMonitor (tagged pointer)
963 else if (mark.has_monitor()) {
964 ObjectMonitorHandle omh;
965 if (!omh.save_om_ptr(obj, mark)) {
966 // Lost a race with async deflation so try again.
967 assert(AsyncDeflateIdleMonitors, "sanity check");
968 continue;
969 }
970 ObjectMonitor* monitor = omh.om_ptr();
971 assert(monitor != NULL, "monitor should be non-null");
972 owner = (address) monitor->owner();
973 }
974
975 if (owner != NULL) {
976 // owning_thread_from_monitor_owner() may also return NULL here
977 return Threads::owning_thread_from_monitor_owner(t_list, owner);
978 }
979
980 // Unlocked case, header in place
981 // Cannot have assertion since this object may have been
982 // locked by another thread when reaching here.
983 // assert(mark.is_neutral(), "sanity check");
984
985 return NULL;
986 }
987 }
988
989 // Visitors ...
990
991 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
992 PaddedObjectMonitor* block = OrderAccess::load_acquire(&g_block_list);
993 while (block != NULL) {
994 assert(block->object() == CHAINMARKER, "must be a block header");
995 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
996 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
997 if (mid->is_active()) {
998 ObjectMonitorHandle omh(mid);
999
1000 if (mid->object() == NULL ||
1001 (AsyncDeflateIdleMonitors && mid->_owner == DEFLATER_MARKER)) {
1002 // Only process with closure if the object is set.
1003 // For async deflation, race here if monitor is not owned!
1004 // The above ref_count bump (in ObjectMonitorHandle ctr)
1005 // will cause subsequent async deflation to skip it.
1006 // However, previous or concurrent async deflation is a race.
1007 continue;
1008 }
1009 closure->do_monitor(mid);
1010 }
1011 }
1012 block = (PaddedObjectMonitor*)block->_next_om;
1013 }
1014 }
1015
1016 static bool monitors_used_above_threshold() {
1017 if (g_om_population == 0) {
1018 return false;
1019 }
1020 if (MonitorUsedDeflationThreshold > 0) {
1021 int monitors_used = g_om_population - g_om_free_count;
1022 int monitor_usage = (monitors_used * 100LL) / g_om_population;
1023 return monitor_usage > MonitorUsedDeflationThreshold;
1024 }
1025 return false;
1026 }
1027
1028 // Returns true if MonitorBound is set (> 0) and if the specified
1029 // cnt is > MonitorBound. Otherwise returns false.
1030 static bool is_MonitorBound_exceeded(const int cnt) {
1031 const int mx = MonitorBound;
1032 return mx > 0 && cnt > mx;
1033 }
1034
1035 bool ObjectSynchronizer::is_async_deflation_needed() {
1036 if (!AsyncDeflateIdleMonitors) {
1037 return false;
1038 }
1039 if (is_async_deflation_requested()) {
1040 // Async deflation request.
1041 return true;
1042 }
1043 if (AsyncDeflationInterval > 0 &&
1044 time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1045 monitors_used_above_threshold()) {
1046 // It's been longer than our specified deflate interval and there
1047 // are too many monitors in use. We don't deflate more frequently
1048 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1049 // in order to not swamp the ServiceThread.
1050 _last_async_deflation_time_ns = os::javaTimeNanos();
1051 return true;
1052 }
1053 if (is_MonitorBound_exceeded(g_om_population - g_om_free_count)) {
1054 // Not enough ObjectMonitors on the global free list.
1055 return true;
1056 }
1057 return false;
1058 }
1059
1060 bool ObjectSynchronizer::is_safepoint_deflation_needed() {
1061 if (!AsyncDeflateIdleMonitors) {
1062 if (monitors_used_above_threshold()) {
1063 // Too many monitors in use.
1064 return true;
1065 }
1066 return false;
1067 }
1068 if (is_special_deflation_requested()) {
1069 // For AsyncDeflateIdleMonitors only do a safepoint deflation
1070 // if there is a special deflation request.
1071 return true;
1072 }
1073 return false;
1074 }
1075
1076 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1077 return (os::javaTimeNanos() - _last_async_deflation_time_ns) / (NANOUNITS / MILLIUNITS);
1078 }
1079
1080 void ObjectSynchronizer::oops_do(OopClosure* f) {
1081 // We only scan the global used list here (for moribund threads), and
1082 // the thread-local monitors in Thread::oops_do().
1083 global_used_oops_do(f);
1084 }
1085
1086 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
1087 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1088 list_oops_do(g_om_in_use_list, f);
1089 }
1090
1091 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
1092 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1093 list_oops_do(thread->om_in_use_list, f);
1094 }
1095
1096 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
1097 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1098 // The oops_do() phase does not overlap with monitor deflation
1099 // so no need to update the ObjectMonitor's ref_count for this
1100 // ObjectMonitor* use.
1101 ObjectMonitor* mid;
1102 for (mid = list; mid != NULL; mid = mid->_next_om) {
1103 if (mid->object() != NULL) {
1104 f->do_oop((oop*)mid->object_addr());
1105 }
1106 }
1107 }
1108
1109
1110 // -----------------------------------------------------------------------------
1111 // ObjectMonitor Lifecycle
1112 // -----------------------
1113 // Inflation unlinks monitors from the global g_free_list and
1114 // associates them with objects. Deflation -- which occurs at
1115 // STW-time -- disassociates idle monitors from objects. Such
1116 // scavenged monitors are returned to the g_free_list.
1117 //
1118 // The global list is protected by gListLock. All the critical sections
1119 // are short and operate in constant-time.
1120 //
1121 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1122 //
1123 // Lifecycle:
1124 // -- unassigned and on the global free list
1125 // -- unassigned and on a thread's private om_free_list
1126 // -- assigned to an object. The object is inflated and the mark refers
1127 // to the objectmonitor.
1128
1129
1130 // Constraining monitor pool growth via MonitorBound ...
1131 //
1132 // If MonitorBound is not set (<= 0), MonitorBound checks are disabled.
1133 //
1134 // When safepoint deflation is being used (!AsyncDeflateIdleMonitors):
1135 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
1136 // the rate of scavenging is driven primarily by GC. As such, we can find
1137 // an inordinate number of monitors in circulation.
1138 // To avoid that scenario we can artificially induce a STW safepoint
1139 // if the pool appears to be growing past some reasonable bound.
1140 // Generally we favor time in space-time tradeoffs, but as there's no
1141 // natural back-pressure on the # of extant monitors we need to impose some
1142 // type of limit. Beware that if MonitorBound is set to too low a value
1143 // we could just loop. In addition, if MonitorBound is set to a low value
1144 // we'll incur more safepoints, which are harmful to performance.
1145 // See also: GuaranteedSafepointInterval
1146 //
1147 // The current implementation uses asynchronous VM operations.
1148 //
1149 // When safepoint deflation is being used and MonitorBound is set, the
1150 // boundry applies to
1151 // (g_om_population - g_om_free_count)
1152 // i.e., if there are not enough ObjectMonitors on the global free list,
1153 // then a safepoint deflation is induced. Picking a good MonitorBound value
1154 // is non-trivial.
1155 //
1156 // When async deflation is being used:
1157 // The monitor pool is still grow-only. Async deflation is requested
1158 // by a safepoint's cleanup phase or by the ServiceThread at periodic
1159 // intervals when is_async_deflation_needed() returns true. In
1160 // addition to other policies that are checked, if there are not
1161 // enough ObjectMonitors on the global free list, then
1162 // is_async_deflation_needed() will return true. The ServiceThread
1163 // calls deflate_global_idle_monitors_using_JT() and also sets the
1164 // per-thread om_request_deflation flag as needed.
1165
1166 static void InduceScavenge(Thread* self, const char * Whence) {
1167 assert(!AsyncDeflateIdleMonitors, "is not used by async deflation");
1168
1169 // Induce STW safepoint to trim monitors
1170 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1171 // More precisely, trigger an asynchronous STW safepoint as the number
1172 // of active monitors passes the specified threshold.
1173 // TODO: assert thread state is reasonable
1174
1175 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1176 // Induce a 'null' safepoint to scavenge monitors
1177 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1178 // to the VMthread and have a lifespan longer than that of this activation record.
1179 // The VMThread will delete the op when completed.
1180 VMThread::execute(new VM_ScavengeMonitors());
1181 }
1182 }
1183
1184 ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self,
1185 const InflateCause cause) {
1186 // A large MAXPRIVATE value reduces both list lock contention
1187 // and list coherency traffic, but also tends to increase the
1188 // number of ObjectMonitors in circulation as well as the STW
1189 // scavenge costs. As usual, we lean toward time in space-time
1190 // tradeoffs.
1191 const int MAXPRIVATE = 1024;
1192
1193 if (AsyncDeflateIdleMonitors) {
1194 JavaThread* jt = (JavaThread *)self;
1195 if (jt->om_request_deflation && jt->om_in_use_count > 0 &&
1196 cause != inflate_cause_vm_internal) {
1197 // Deflate any per-thread idle monitors for this JavaThread if
1198 // this is not an internal inflation; internal inflations can
1199 // occur in places where it is not safe to pause for a safepoint.
1200 // Clean up your own mess (Gibbs Rule 45). Otherwise, skip this
1201 // deflation. deflate_global_idle_monitors_using_JT() is called
1202 // by the ServiceThread. Per-thread async deflation is triggered
1203 // by the ServiceThread via om_request_deflation.
1204 debug_only(jt->check_for_valid_safepoint_state(false);)
1205 ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT();
1206 }
1207 }
1208
1209 stringStream ss;
1210 for (;;) {
1211 ObjectMonitor* m;
1212
1213 // 1: try to allocate from the thread's local om_free_list.
1214 // Threads will attempt to allocate first from their local list, then
1215 // from the global list, and only after those attempts fail will the thread
1216 // attempt to instantiate new monitors. Thread-local free lists take
1217 // heat off the gListLock and improve allocation latency, as well as reducing
1218 // coherency traffic on the shared global list.
1219 m = self->om_free_list;
1220 if (m != NULL) {
1221 self->om_free_list = m->_next_om;
1222 self->om_free_count--;
1223 guarantee(m->object() == NULL, "invariant");
1224 m->set_allocation_state(ObjectMonitor::New);
1225 m->_next_om = self->om_in_use_list;
1226 self->om_in_use_list = m;
1227 self->om_in_use_count++;
1228 return m;
1229 }
1230
1231 // 2: try to allocate from the global g_free_list
1232 // CONSIDER: use muxTry() instead of muxAcquire().
1233 // If the muxTry() fails then drop immediately into case 3.
1234 // If we're using thread-local free lists then try
1235 // to reprovision the caller's free list.
1236 if (g_free_list != NULL) {
1237 // Reprovision the thread's om_free_list.
1238 // Use bulk transfers to reduce the allocation rate and heat
1239 // on various locks.
1240 Thread::muxAcquire(&gListLock, "om_alloc(1)");
1241 for (int i = self->om_free_provision; --i >= 0 && g_free_list != NULL;) {
1242 g_om_free_count--;
1243 ObjectMonitor* take = g_free_list;
1244 g_free_list = take->_next_om;
1245 guarantee(take->object() == NULL, "invariant");
1246 if (AsyncDeflateIdleMonitors) {
1247 // We allowed 3 field values to linger during async deflation.
1248 // We clear header and restore ref_count here, but we leave
1249 // owner == DEFLATER_MARKER so the simple C2 ObjectMonitor
1250 // enter optimization can no longer race with async deflation
1251 // and reuse.
1252 take->set_header(markWord::zero());
1253 if (take->ref_count() < 0) {
1254 // Add back max_jint to restore the ref_count field to its
1255 // proper value.
1256 Atomic::add(max_jint, &take->_ref_count);
1257
1258 assert(take->ref_count() >= 0, "must not be negative: ref_count=%d",
1259 take->ref_count());
1260 }
1261 }
1262 take->Recycle();
1263 assert(take->is_free(), "invariant");
1264 om_release(self, take, false);
1265 }
1266 Thread::muxRelease(&gListLock);
1267 self->om_free_provision += 1 + (self->om_free_provision/2);
1268 if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE;
1269
1270 if (!AsyncDeflateIdleMonitors &&
1271 is_MonitorBound_exceeded(g_om_population - g_om_free_count)) {
1272 // Not enough ObjectMonitors on the global free list.
1273 // We can't safely induce a STW safepoint from om_alloc() as our thread
1274 // state may not be appropriate for such activities and callers may hold
1275 // naked oops, so instead we defer the action.
1276 InduceScavenge(self, "om_alloc");
1277 }
1278 continue;
1279 }
1280
1281 // 3: allocate a block of new ObjectMonitors
1282 // Both the local and global free lists are empty -- resort to malloc().
1283 // In the current implementation ObjectMonitors are TSM - immortal.
1284 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1285 // each ObjectMonitor to start at the beginning of a cache line,
1286 // so we use align_up().
1287 // A better solution would be to use C++ placement-new.
1288 // BEWARE: As it stands currently, we don't run the ctors!
1289 assert(_BLOCKSIZE > 1, "invariant");
1290 size_t neededsize = sizeof(PaddedObjectMonitor) * _BLOCKSIZE;
1291 PaddedObjectMonitor* temp;
1292 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1293 void* real_malloc_addr = (void*)NEW_C_HEAP_ARRAY(char, aligned_size,
1294 mtInternal);
1295 temp = (PaddedObjectMonitor*)align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE);
1296
1297 // NOTE: (almost) no way to recover if allocation failed.
1298 // We might be able to induce a STW safepoint and scavenge enough
1299 // ObjectMonitors to permit progress.
1300 if (temp == NULL) {
1301 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1302 "Allocate ObjectMonitors");
1303 }
1304 (void)memset((void *) temp, 0, neededsize);
1305
1306 // Format the block.
1307 // initialize the linked list, each monitor points to its next
1308 // forming the single linked free list, the very first monitor
1309 // will points to next block, which forms the block list.
1310 // The trick of using the 1st element in the block as g_block_list
1311 // linkage should be reconsidered. A better implementation would
1312 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1313
1314 for (int i = 1; i < _BLOCKSIZE; i++) {
1315 temp[i]._next_om = (ObjectMonitor *)&temp[i+1];
1316 assert(temp[i].is_free(), "invariant");
1317 }
1318
1319 // terminate the last monitor as the end of list
1320 temp[_BLOCKSIZE - 1]._next_om = NULL;
1321
1322 // Element [0] is reserved for global list linkage
1323 temp[0].set_object(CHAINMARKER);
1324
1325 // Consider carving out this thread's current request from the
1326 // block in hand. This avoids some lock traffic and redundant
1327 // list activity.
1328
1329 // Acquire the gListLock to manipulate g_block_list and g_free_list.
1330 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1331 Thread::muxAcquire(&gListLock, "om_alloc(2)");
1332 g_om_population += _BLOCKSIZE-1;
1333 g_om_free_count += _BLOCKSIZE-1;
1334
1335 // Add the new block to the list of extant blocks (g_block_list).
1336 // The very first ObjectMonitor in a block is reserved and dedicated.
1337 // It serves as blocklist "next" linkage.
1338 temp[0]._next_om = g_block_list;
1339 // There are lock-free uses of g_block_list so make sure that
1340 // the previous stores happen before we update g_block_list.
1341 OrderAccess::release_store(&g_block_list, temp);
1342
1343 // Add the new string of ObjectMonitors to the global free list
1344 temp[_BLOCKSIZE - 1]._next_om = g_free_list;
1345 g_free_list = temp + 1;
1346 Thread::muxRelease(&gListLock);
1347 }
1348 }
1349
1350 // Place "m" on the caller's private per-thread om_free_list.
1351 // In practice there's no need to clamp or limit the number of
1352 // monitors on a thread's om_free_list as the only non-allocation time
1353 // we'll call om_release() is to return a monitor to the free list after
1354 // a CAS attempt failed. This doesn't allow unbounded #s of monitors to
1355 // accumulate on a thread's free list.
1356 //
1357 // Key constraint: all ObjectMonitors on a thread's free list and the global
1358 // free list must have their object field set to null. This prevents the
1359 // scavenger -- deflate_monitor_list() or deflate_monitor_list_using_JT()
1360 // -- from reclaiming them while we are trying to release them.
1361
1362 void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m,
1363 bool from_per_thread_alloc) {
1364 guarantee(m->header().value() == 0, "invariant");
1365 guarantee(m->object() == NULL, "invariant");
1366 stringStream ss;
1367 guarantee((m->is_busy() | m->_recursions) == 0, "freeing in-use monitor: "
1368 "%s, recursions=" INTPTR_FORMAT, m->is_busy_to_string(&ss),
1369 m->_recursions);
1370 m->set_allocation_state(ObjectMonitor::Free);
1371 // _next_om is used for both per-thread in-use and free lists so
1372 // we have to remove 'm' from the in-use list first (as needed).
1373 if (from_per_thread_alloc) {
1374 // Need to remove 'm' from om_in_use_list.
1375 ObjectMonitor* cur_mid_in_use = NULL;
1376 bool extracted = false;
1377 for (ObjectMonitor* mid = self->om_in_use_list; mid != NULL; cur_mid_in_use = mid, mid = mid->_next_om) {
1378 if (m == mid) {
1379 // extract from per-thread in-use list
1380 if (mid == self->om_in_use_list) {
1381 self->om_in_use_list = mid->_next_om;
1382 } else if (cur_mid_in_use != NULL) {
1383 cur_mid_in_use->_next_om = mid->_next_om; // maintain the current thread in-use list
1384 }
1385 extracted = true;
1386 self->om_in_use_count--;
1387 break;
1388 }
1389 }
1390 assert(extracted, "Should have extracted from in-use list");
1391 }
1392
1393 m->_next_om = self->om_free_list;
1394 guarantee(m->is_free(), "invariant");
1395 self->om_free_list = m;
1396 self->om_free_count++;
1397 }
1398
1399 // Return ObjectMonitors on a moribund thread's free and in-use
1400 // lists to the appropriate global lists. The ObjectMonitors on the
1401 // per-thread in-use list may still be in use by other threads.
1402 //
1403 // We currently call om_flush() from Threads::remove() before the
1404 // thread has been excised from the thread list and is no longer a
1405 // mutator. This means that om_flush() cannot run concurrently with
1406 // a safepoint and interleave with deflate_idle_monitors(). In
1407 // particular, this ensures that the thread's in-use monitors are
1408 // scanned by a GC safepoint, either via Thread::oops_do() (before
1409 // om_flush() is called) or via ObjectSynchronizer::oops_do() (after
1410 // om_flush() is called).
1411 //
1412 // With AsyncDeflateIdleMonitors, deflate_global_idle_monitors_using_JT()
1413 // and deflate_per_thread_idle_monitors_using_JT() (in another thread) can
1414 // run at the same time as om_flush() so we have to be careful.
1415
1416 void ObjectSynchronizer::om_flush(Thread* self) {
1417 ObjectMonitor* free_list = self->om_free_list;
1418 ObjectMonitor* free_tail = NULL;
1419 int free_count = 0;
1420 if (free_list != NULL) {
1421 ObjectMonitor* s;
1422 // The thread is going away. Set 'free_tail' to the last per-thread free
1423 // monitor which will be linked to g_free_list below under the gListLock.
1424 stringStream ss;
1425 for (s = free_list; s != NULL; s = s->_next_om) {
1426 free_count++;
1427 free_tail = s;
1428 guarantee(s->object() == NULL, "invariant");
1429 guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss));
1430 }
1431 guarantee(free_tail != NULL, "invariant");
1432 ADIM_guarantee(self->om_free_count == free_count, "free-count off");
1433 self->om_free_list = NULL;
1434 self->om_free_count = 0;
1435 }
1436
1437 ObjectMonitor* in_use_list = self->om_in_use_list;
1438 ObjectMonitor* in_use_tail = NULL;
1439 int in_use_count = 0;
1440 if (in_use_list != NULL) {
1441 // The thread is going away, however the ObjectMonitors on the
1442 // om_in_use_list may still be in-use by other threads. Link
1443 // them to in_use_tail, which will be linked into the global
1444 // in-use list g_om_in_use_list below, under the gListLock.
1445 ObjectMonitor *cur_om;
1446 for (cur_om = in_use_list; cur_om != NULL; cur_om = cur_om->_next_om) {
1447 in_use_tail = cur_om;
1448 in_use_count++;
1449 ADIM_guarantee(cur_om->is_active(), "invariant");
1450 }
1451 guarantee(in_use_tail != NULL, "invariant");
1452 ADIM_guarantee(self->om_in_use_count == in_use_count, "in-use count off");
1453 self->om_in_use_list = NULL;
1454 self->om_in_use_count = 0;
1455 }
1456
1457 Thread::muxAcquire(&gListLock, "om_flush");
1458 if (free_tail != NULL) {
1459 free_tail->_next_om = g_free_list;
1460 g_free_list = free_list;
1461 g_om_free_count += free_count;
1462 }
1463
1464 if (in_use_tail != NULL) {
1465 in_use_tail->_next_om = g_om_in_use_list;
1466 g_om_in_use_list = in_use_list;
1467 g_om_in_use_count += in_use_count;
1468 }
1469
1470 Thread::muxRelease(&gListLock);
1471
1472 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1473 LogStreamHandle(Info, monitorinflation) lsh_info;
1474 LogStream* ls = NULL;
1475 if (log_is_enabled(Debug, monitorinflation)) {
1476 ls = &lsh_debug;
1477 } else if ((free_count != 0 || in_use_count != 0) &&
1478 log_is_enabled(Info, monitorinflation)) {
1479 ls = &lsh_info;
1480 }
1481 if (ls != NULL) {
1482 ls->print_cr("om_flush: jt=" INTPTR_FORMAT ", free_count=%d"
1483 ", in_use_count=%d" ", om_free_provision=%d",
1484 p2i(self), free_count, in_use_count, self->om_free_provision);
1485 }
1486 }
1487
1488 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1489 const oop obj,
1490 ObjectSynchronizer::InflateCause cause) {
1491 assert(event != NULL, "invariant");
1492 assert(event->should_commit(), "invariant");
1493 event->set_monitorClass(obj->klass());
1494 event->set_address((uintptr_t)(void*)obj);
1495 event->set_cause((u1)cause);
1496 event->commit();
1497 }
1498
1499 // Fast path code shared by multiple functions
1500 void ObjectSynchronizer::inflate_helper(ObjectMonitorHandle* omh_p, oop obj) {
1501 while (true) {
1502 markWord mark = obj->mark();
1503 if (mark.has_monitor()) {
1504 if (!omh_p->save_om_ptr(obj, mark)) {
1505 // Lost a race with async deflation so try again.
1506 assert(AsyncDeflateIdleMonitors, "sanity check");
1507 continue;
1508 }
1509 ObjectMonitor* monitor = omh_p->om_ptr();
1510 assert(ObjectSynchronizer::verify_objmon_isinpool(monitor), "monitor is invalid");
1511 markWord dmw = monitor->header();
1512 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1513 return;
1514 }
1515 inflate(omh_p, Thread::current(), obj, inflate_cause_vm_internal);
1516 return;
1517 }
1518 }
1519
1520 void ObjectSynchronizer::inflate(ObjectMonitorHandle* omh_p, Thread* self,
1521 oop object, const InflateCause cause) {
1522 // Inflate mutates the heap ...
1523 // Relaxing assertion for bug 6320749.
1524 assert(Universe::verify_in_progress() ||
1525 !SafepointSynchronize::is_at_safepoint(), "invariant");
1526
1527 EventJavaMonitorInflate event;
1528
1529 for (;;) {
1530 const markWord mark = object->mark();
1531 assert(!mark.has_bias_pattern(), "invariant");
1532
1533 // The mark can be in one of the following states:
1534 // * Inflated - just return
1535 // * Stack-locked - coerce it to inflated
1536 // * INFLATING - busy wait for conversion to complete
1537 // * Neutral - aggressively inflate the object.
1538 // * BIASED - Illegal. We should never see this
1539
1540 // CASE: inflated
1541 if (mark.has_monitor()) {
1542 if (!omh_p->save_om_ptr(object, mark)) {
1543 // Lost a race with async deflation so try again.
1544 assert(AsyncDeflateIdleMonitors, "sanity check");
1545 continue;
1546 }
1547 ObjectMonitor* inf = omh_p->om_ptr();
1548 markWord dmw = inf->header();
1549 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1550 assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1551 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1552 return;
1553 }
1554
1555 // CASE: inflation in progress - inflating over a stack-lock.
1556 // Some other thread is converting from stack-locked to inflated.
1557 // Only that thread can complete inflation -- other threads must wait.
1558 // The INFLATING value is transient.
1559 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1560 // We could always eliminate polling by parking the thread on some auxiliary list.
1561 if (mark == markWord::INFLATING()) {
1562 read_stable_mark(object);
1563 continue;
1564 }
1565
1566 // CASE: stack-locked
1567 // Could be stack-locked either by this thread or by some other thread.
1568 //
1569 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1570 // to install INFLATING into the mark word. We originally installed INFLATING,
1571 // allocated the objectmonitor, and then finally STed the address of the
1572 // objectmonitor into the mark. This was correct, but artificially lengthened
1573 // the interval in which INFLATED appeared in the mark, thus increasing
1574 // the odds of inflation contention.
1575 //
1576 // We now use per-thread private objectmonitor free lists.
1577 // These list are reprovisioned from the global free list outside the
1578 // critical INFLATING...ST interval. A thread can transfer
1579 // multiple objectmonitors en-mass from the global free list to its local free list.
1580 // This reduces coherency traffic and lock contention on the global free list.
1581 // Using such local free lists, it doesn't matter if the om_alloc() call appears
1582 // before or after the CAS(INFLATING) operation.
1583 // See the comments in om_alloc().
1584
1585 LogStreamHandle(Trace, monitorinflation) lsh;
1586
1587 if (mark.has_locker()) {
1588 ObjectMonitor* m;
1589 if (!AsyncDeflateIdleMonitors || cause == inflate_cause_vm_internal) {
1590 // If !AsyncDeflateIdleMonitors or if an internal inflation, then
1591 // we won't stop for a potential safepoint in om_alloc.
1592 m = om_alloc(self, cause);
1593 } else {
1594 // If AsyncDeflateIdleMonitors and not an internal inflation, then
1595 // we may stop for a safepoint in om_alloc() so protect object.
1596 Handle h_obj(self, object);
1597 m = om_alloc(self, cause);
1598 object = h_obj(); // Refresh object.
1599 }
1600 // Optimistically prepare the objectmonitor - anticipate successful CAS
1601 // We do this before the CAS in order to minimize the length of time
1602 // in which INFLATING appears in the mark.
1603 m->Recycle();
1604 m->_Responsible = NULL;
1605 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1606
1607 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1608 if (cmp != mark) {
1609 om_release(self, m, true);
1610 continue; // Interference -- just retry
1611 }
1612
1613 // We've successfully installed INFLATING (0) into the mark-word.
1614 // This is the only case where 0 will appear in a mark-word.
1615 // Only the singular thread that successfully swings the mark-word
1616 // to 0 can perform (or more precisely, complete) inflation.
1617 //
1618 // Why do we CAS a 0 into the mark-word instead of just CASing the
1619 // mark-word from the stack-locked value directly to the new inflated state?
1620 // Consider what happens when a thread unlocks a stack-locked object.
1621 // It attempts to use CAS to swing the displaced header value from the
1622 // on-stack BasicLock back into the object header. Recall also that the
1623 // header value (hash code, etc) can reside in (a) the object header, or
1624 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1625 // header in an ObjectMonitor. The inflate() routine must copy the header
1626 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1627 // the while preserving the hashCode stability invariants. If the owner
1628 // decides to release the lock while the value is 0, the unlock will fail
1629 // and control will eventually pass from slow_exit() to inflate. The owner
1630 // will then spin, waiting for the 0 value to disappear. Put another way,
1631 // the 0 causes the owner to stall if the owner happens to try to
1632 // drop the lock (restoring the header from the BasicLock to the object)
1633 // while inflation is in-progress. This protocol avoids races that might
1634 // would otherwise permit hashCode values to change or "flicker" for an object.
1635 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1636 // 0 serves as a "BUSY" inflate-in-progress indicator.
1637
1638
1639 // fetch the displaced mark from the owner's stack.
1640 // The owner can't die or unwind past the lock while our INFLATING
1641 // object is in the mark. Furthermore the owner can't complete
1642 // an unlock on the object, either.
1643 markWord dmw = mark.displaced_mark_helper();
1644 // Catch if the object's header is not neutral (not locked and
1645 // not marked is what we care about here).
1646 ADIM_guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1647
1648 // Setup monitor fields to proper values -- prepare the monitor
1649 m->set_header(dmw);
1650
1651 // Optimization: if the mark.locker stack address is associated
1652 // with this thread we could simply set m->_owner = self.
1653 // Note that a thread can inflate an object
1654 // that it has stack-locked -- as might happen in wait() -- directly
1655 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1656 m->set_owner(mark.locker());
1657 m->set_object(object);
1658 // TODO-FIXME: assert BasicLock->dhw != 0.
1659
1660 omh_p->set_om_ptr(m);
1661 assert(m->is_new(), "freshly allocated monitor must be new");
1662 m->set_allocation_state(ObjectMonitor::Old);
1663
1664 // Must preserve store ordering. The monitor state must
1665 // be stable at the time of publishing the monitor address.
1666 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1667 object->release_set_mark(markWord::encode(m));
1668
1669 // Hopefully the performance counters are allocated on distinct cache lines
1670 // to avoid false sharing on MP systems ...
1671 OM_PERFDATA_OP(Inflations, inc());
1672 if (log_is_enabled(Trace, monitorinflation)) {
1673 ResourceMark rm(self);
1674 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1675 INTPTR_FORMAT ", type='%s'", p2i(object),
1676 object->mark().value(), object->klass()->external_name());
1677 }
1678 if (event.should_commit()) {
1679 post_monitor_inflate_event(&event, object, cause);
1680 }
1681 ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free");
1682 return;
1683 }
1684
1685 // CASE: neutral
1686 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1687 // If we know we're inflating for entry it's better to inflate by swinging a
1688 // pre-locked ObjectMonitor pointer into the object header. A successful
1689 // CAS inflates the object *and* confers ownership to the inflating thread.
1690 // In the current implementation we use a 2-step mechanism where we CAS()
1691 // to inflate and then CAS() again to try to swing _owner from NULL to self.
1692 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1693 // would be useful.
1694
1695 // Catch if the object's header is not neutral (not locked and
1696 // not marked is what we care about here).
1697 ADIM_guarantee(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1698 ObjectMonitor* m;
1699 if (!AsyncDeflateIdleMonitors || cause == inflate_cause_vm_internal) {
1700 // If !AsyncDeflateIdleMonitors or if an internal inflation, then
1701 // we won't stop for a potential safepoint in om_alloc.
1702 m = om_alloc(self, cause);
1703 } else {
1704 // If AsyncDeflateIdleMonitors and not an internal inflation, then
1705 // we may stop for a safepoint in om_alloc() so protect object.
1706 Handle h_obj(self, object);
1707 m = om_alloc(self, cause);
1708 object = h_obj(); // Refresh object.
1709 }
1710 // prepare m for installation - set monitor to initial state
1711 m->Recycle();
1712 m->set_header(mark);
1713 // If we leave _owner == DEFLATER_MARKER here, then the simple C2
1714 // ObjectMonitor enter optimization can no longer race with async
1715 // deflation and reuse.
1716 m->set_object(object);
1717 m->_Responsible = NULL;
1718 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1719
1720 omh_p->set_om_ptr(m);
1721 assert(m->is_new(), "freshly allocated monitor must be new");
1722 m->set_allocation_state(ObjectMonitor::Old);
1723
1724 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1725 m->set_header(markWord::zero());
1726 m->set_object(NULL);
1727 m->Recycle();
1728 omh_p->set_om_ptr(NULL);
1729 // om_release() will reset the allocation state
1730 om_release(self, m, true);
1731 m = NULL;
1732 continue;
1733 // interference - the markword changed - just retry.
1734 // The state-transitions are one-way, so there's no chance of
1735 // live-lock -- "Inflated" is an absorbing state.
1736 }
1737
1738 // Hopefully the performance counters are allocated on distinct
1739 // cache lines to avoid false sharing on MP systems ...
1740 OM_PERFDATA_OP(Inflations, inc());
1741 if (log_is_enabled(Trace, monitorinflation)) {
1742 ResourceMark rm(self);
1743 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1744 INTPTR_FORMAT ", type='%s'", p2i(object),
1745 object->mark().value(), object->klass()->external_name());
1746 }
1747 if (event.should_commit()) {
1748 post_monitor_inflate_event(&event, object, cause);
1749 }
1750 ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free");
1751 return;
1752 }
1753 }
1754
1755
1756 // We maintain a list of in-use monitors for each thread.
1757 //
1758 // For safepoint based deflation:
1759 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1760 // deflate_idle_monitors() scans only a global list of in-use monitors which
1761 // is populated only as a thread dies (see om_flush()).
1762 //
1763 // These operations are called at all safepoints, immediately after mutators
1764 // are stopped, but before any objects have moved. Collectively they traverse
1765 // the population of in-use monitors, deflating where possible. The scavenged
1766 // monitors are returned to the global monitor free list.
1767 //
1768 // Beware that we scavenge at *every* stop-the-world point. Having a large
1769 // number of monitors in-use could negatively impact performance. We also want
1770 // to minimize the total # of monitors in circulation, as they incur a small
1771 // footprint penalty.
1772 //
1773 // Perversely, the heap size -- and thus the STW safepoint rate --
1774 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1775 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1776 // This is an unfortunate aspect of this design.
1777 //
1778 // For async deflation:
1779 // If a special deflation request is made, then the safepoint based
1780 // deflation mechanism is used. Otherwise, an async deflation request
1781 // is registered with the ServiceThread and it is notified.
1782
1783 void ObjectSynchronizer::do_safepoint_work(DeflateMonitorCounters* _counters) {
1784 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1785
1786 // The per-thread in-use lists are handled in
1787 // ParallelSPCleanupThreadClosure::do_thread().
1788
1789 if (!AsyncDeflateIdleMonitors || is_special_deflation_requested()) {
1790 // Use the older mechanism for the global in-use list or if a
1791 // special deflation has been requested before the safepoint.
1792 ObjectSynchronizer::deflate_idle_monitors(_counters);
1793 return;
1794 }
1795
1796 log_debug(monitorinflation)("requesting async deflation of idle monitors.");
1797 // Request deflation of idle monitors by the ServiceThread:
1798 set_is_async_deflation_requested(true);
1799 MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
1800 ml.notify_all();
1801 }
1802
1803 // Deflate a single monitor if not in-use
1804 // Return true if deflated, false if in-use
1805 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1806 ObjectMonitor** free_head_p,
1807 ObjectMonitor** free_tail_p) {
1808 bool deflated;
1809 // Normal case ... The monitor is associated with obj.
1810 const markWord mark = obj->mark();
1811 guarantee(mark == markWord::encode(mid), "should match: mark="
1812 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(),
1813 markWord::encode(mid).value());
1814 // Make sure that mark.monitor() and markWord::encode() agree:
1815 guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
1816 ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid));
1817 const markWord dmw = mid->header();
1818 guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1819
1820 if (mid->is_busy() || mid->ref_count() != 0) {
1821 // Easy checks are first - the ObjectMonitor is busy or ObjectMonitor*
1822 // is in use so no deflation.
1823 deflated = false;
1824 } else {
1825 // Deflate the monitor if it is no longer being used
1826 // It's idle - scavenge and return to the global free list
1827 // plain old deflation ...
1828 if (log_is_enabled(Trace, monitorinflation)) {
1829 ResourceMark rm;
1830 log_trace(monitorinflation)("deflate_monitor: "
1831 "object=" INTPTR_FORMAT ", mark="
1832 INTPTR_FORMAT ", type='%s'", p2i(obj),
1833 mark.value(), obj->klass()->external_name());
1834 }
1835
1836 // Restore the header back to obj
1837 obj->release_set_mark(dmw);
1838 if (AsyncDeflateIdleMonitors) {
1839 // clear() expects the owner field to be NULL and we won't race
1840 // with the simple C2 ObjectMonitor enter optimization since
1841 // we're at a safepoint.
1842 mid->set_owner(NULL);
1843 }
1844 mid->clear();
1845
1846 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
1847 p2i(mid->object()));
1848 assert(mid->is_free(), "invariant");
1849
1850 // Move the deflated ObjectMonitor to the working free list
1851 // defined by free_head_p and free_tail_p.
1852 if (*free_head_p == NULL) *free_head_p = mid;
1853 if (*free_tail_p != NULL) {
1854 // We append to the list so the caller can use mid->_next_om
1855 // to fix the linkages in its context.
1856 ObjectMonitor* prevtail = *free_tail_p;
1857 // Should have been cleaned up by the caller:
1858 assert(prevtail->_next_om == NULL, "cleaned up deflated?");
1859 prevtail->_next_om = mid;
1860 }
1861 *free_tail_p = mid;
1862 // At this point, mid->_next_om still refers to its current
1863 // value and another ObjectMonitor's _next_om field still
1864 // refers to this ObjectMonitor. Those linkages have to be
1865 // cleaned up by the caller who has the complete context.
1866 deflated = true;
1867 }
1868 return deflated;
1869 }
1870
1871 // Deflate the specified ObjectMonitor if not in-use using a JavaThread.
1872 // Returns true if it was deflated and false otherwise.
1873 //
1874 // The async deflation protocol sets owner to DEFLATER_MARKER and
1875 // makes ref_count negative as signals to contending threads that
1876 // an async deflation is in progress. There are a number of checks
1877 // as part of the protocol to make sure that the calling thread has
1878 // not lost the race to a contending thread or to a thread that just
1879 // wants to use the ObjectMonitor*.
1880 //
1881 // The ObjectMonitor has been successfully async deflated when:
1882 // (owner == DEFLATER_MARKER && ref_count < 0)
1883 // Contending threads or ObjectMonitor* using threads that see those
1884 // values know to retry their operation.
1885 //
1886 bool ObjectSynchronizer::deflate_monitor_using_JT(ObjectMonitor* mid,
1887 ObjectMonitor** free_head_p,
1888 ObjectMonitor** free_tail_p) {
1889 assert(AsyncDeflateIdleMonitors, "sanity check");
1890 assert(Thread::current()->is_Java_thread(), "precondition");
1891 // A newly allocated ObjectMonitor should not be seen here so we
1892 // avoid an endless inflate/deflate cycle.
1893 assert(mid->is_old(), "must be old: allocation_state=%d",
1894 (int) mid->allocation_state());
1895
1896 if (mid->is_busy() || mid->ref_count() != 0) {
1897 // Easy checks are first - the ObjectMonitor is busy or ObjectMonitor*
1898 // is in use so no deflation.
1899 return false;
1900 }
1901
1902 if (Atomic::replace_if_null(DEFLATER_MARKER, &(mid->_owner))) {
1903 // ObjectMonitor is not owned by another thread. Our setting
1904 // owner to DEFLATER_MARKER forces any contending thread through
1905 // the slow path. This is just the first part of the async
1906 // deflation dance.
1907
1908 if (mid->_contentions != 0 || mid->_waiters != 0) {
1909 // Another thread has raced to enter the ObjectMonitor after
1910 // mid->is_busy() above or has already entered and waited on
1911 // it which makes it busy so no deflation. Restore owner to
1912 // NULL if it is still DEFLATER_MARKER.
1913 Atomic::cmpxchg((void*)NULL, &mid->_owner, DEFLATER_MARKER);
1914 return false;
1915 }
1916
1917 if (Atomic::cmpxchg(-max_jint, &mid->_ref_count, (jint)0) == 0) {
1918 // Make ref_count negative to force any contending threads or
1919 // ObjectMonitor* using threads to retry. This is the second
1920 // part of the async deflation dance.
1921
1922 if (mid->owner_is_DEFLATER_MARKER()) {
1923 // If owner is still DEFLATER_MARKER, then we have successfully
1924 // signaled any contending threads to retry. If it is not, then we
1925 // have lost the race to an entering thread and the ObjectMonitor
1926 // is now busy. This is the third and final part of the async
1927 // deflation dance.
1928 // Note: This owner check solves the ABA problem with ref_count
1929 // where another thread acquired the ObjectMonitor, finished
1930 // using it and restored the ref_count to zero.
1931
1932 // Sanity checks for the races:
1933 guarantee(mid->_contentions == 0, "must be 0: contentions=%d",
1934 mid->_contentions);
1935 guarantee(mid->_waiters == 0, "must be 0: waiters=%d", mid->_waiters);
1936 guarantee(mid->_cxq == NULL, "must be no contending threads: cxq="
1937 INTPTR_FORMAT, p2i(mid->_cxq));
1938 guarantee(mid->_EntryList == NULL,
1939 "must be no entering threads: EntryList=" INTPTR_FORMAT,
1940 p2i(mid->_EntryList));
1941
1942 const oop obj = (oop) mid->object();
1943 if (log_is_enabled(Trace, monitorinflation)) {
1944 ResourceMark rm;
1945 log_trace(monitorinflation)("deflate_monitor_using_JT: "
1946 "object=" INTPTR_FORMAT ", mark="
1947 INTPTR_FORMAT ", type='%s'",
1948 p2i(obj), obj->mark().value(),
1949 obj->klass()->external_name());
1950 }
1951
1952 // Install the old mark word if nobody else has already done it.
1953 mid->install_displaced_markword_in_object(obj);
1954 mid->clear_using_JT();
1955
1956 assert(mid->object() == NULL, "must be NULL: object=" INTPTR_FORMAT,
1957 p2i(mid->object()));
1958 assert(mid->is_free(), "must be free: allocation_state=%d",
1959 (int) mid->allocation_state());
1960
1961 // Move the deflated ObjectMonitor to the working free list
1962 // defined by free_head_p and free_tail_p.
1963 if (*free_head_p == NULL) {
1964 // First one on the list.
1965 *free_head_p = mid;
1966 }
1967 if (*free_tail_p != NULL) {
1968 // We append to the list so the caller can use mid->_next_om
1969 // to fix the linkages in its context.
1970 ObjectMonitor* prevtail = *free_tail_p;
1971 // Should have been cleaned up by the caller:
1972 assert(prevtail->_next_om == NULL, "must be NULL: _next_om="
1973 INTPTR_FORMAT, p2i(prevtail->_next_om));
1974 prevtail->_next_om = mid;
1975 }
1976 *free_tail_p = mid;
1977
1978 // At this point, mid->_next_om still refers to its current
1979 // value and another ObjectMonitor's _next_om field still
1980 // refers to this ObjectMonitor. Those linkages have to be
1981 // cleaned up by the caller who has the complete context.
1982
1983 // We leave owner == DEFLATER_MARKER and ref_count < 0
1984 // to force any racing threads to retry.
1985 return true; // Success, ObjectMonitor has been deflated.
1986 }
1987
1988 // The owner was changed from DEFLATER_MARKER so we lost the
1989 // race since the ObjectMonitor is now busy.
1990
1991 // Add back max_jint to restore the ref_count field to its
1992 // proper value (which may not be what we saw above):
1993 Atomic::add(max_jint, &mid->_ref_count);
1994
1995 assert(mid->ref_count() >= 0, "must not be negative: ref_count=%d",
1996 mid->ref_count());
1997 return false;
1998 }
1999
2000 // The ref_count was no longer 0 so we lost the race since the
2001 // ObjectMonitor is now busy or the ObjectMonitor* is now is use.
2002 // Restore owner to NULL if it is still DEFLATER_MARKER:
2003 Atomic::cmpxchg((void*)NULL, &mid->_owner, DEFLATER_MARKER);
2004 }
2005
2006 // The owner field is no longer NULL so we lost the race since the
2007 // ObjectMonitor is now busy.
2008 return false;
2009 }
2010
2011 // Walk a given monitor list, and deflate idle monitors
2012 // The given list could be a per-thread list or a global list
2013 // Caller acquires gListLock as needed.
2014 //
2015 // In the case of parallel processing of thread local monitor lists,
2016 // work is done by Threads::parallel_threads_do() which ensures that
2017 // each Java thread is processed by exactly one worker thread, and
2018 // thus avoid conflicts that would arise when worker threads would
2019 // process the same monitor lists concurrently.
2020 //
2021 // See also ParallelSPCleanupTask and
2022 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
2023 // Threads::parallel_java_threads_do() in thread.cpp.
2024 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** list_p,
2025 ObjectMonitor** free_head_p,
2026 ObjectMonitor** free_tail_p) {
2027 ObjectMonitor* mid;
2028 ObjectMonitor* next;
2029 ObjectMonitor* cur_mid_in_use = NULL;
2030 int deflated_count = 0;
2031
2032 for (mid = *list_p; mid != NULL;) {
2033 oop obj = (oop) mid->object();
2034 if (obj != NULL && deflate_monitor(mid, obj, free_head_p, free_tail_p)) {
2035 // Deflation succeeded and already updated free_head_p and
2036 // free_tail_p as needed. Finish the move to the local free list
2037 // by unlinking mid from the global or per-thread in-use list.
2038 if (mid == *list_p) {
2039 *list_p = mid->_next_om;
2040 } else if (cur_mid_in_use != NULL) {
2041 cur_mid_in_use->_next_om = mid->_next_om; // maintain the current thread in-use list
2042 }
2043 next = mid->_next_om;
2044 mid->_next_om = NULL; // This mid is current tail in the free_head_p list
2045 mid = next;
2046 deflated_count++;
2047 } else {
2048 cur_mid_in_use = mid;
2049 mid = mid->_next_om;
2050 }
2051 }
2052 return deflated_count;
2053 }
2054
2055 // Walk a given ObjectMonitor list and deflate idle ObjectMonitors using
2056 // a JavaThread. Returns the number of deflated ObjectMonitors. The given
2057 // list could be a per-thread in-use list or the global in-use list.
2058 // Caller acquires gListLock as appropriate. If a safepoint has started,
2059 // then we save state via saved_mid_in_use_p and return to the caller to
2060 // honor the safepoint.
2061 //
2062 int ObjectSynchronizer::deflate_monitor_list_using_JT(ObjectMonitor** list_p,
2063 ObjectMonitor** free_head_p,
2064 ObjectMonitor** free_tail_p,
2065 ObjectMonitor** saved_mid_in_use_p) {
2066 assert(AsyncDeflateIdleMonitors, "sanity check");
2067 assert(Thread::current()->is_Java_thread(), "precondition");
2068
2069 ObjectMonitor* mid;
2070 ObjectMonitor* next;
2071 ObjectMonitor* cur_mid_in_use = NULL;
2072 int deflated_count = 0;
2073
2074 if (*saved_mid_in_use_p == NULL) {
2075 // No saved state so start at the beginning.
2076 mid = *list_p;
2077 } else {
2078 // We're restarting after a safepoint so restore the necessary state
2079 // before we resume.
2080 cur_mid_in_use = *saved_mid_in_use_p;
2081 mid = cur_mid_in_use->_next_om;
2082 }
2083 while (mid != NULL) {
2084 // Only try to deflate if there is an associated Java object and if
2085 // mid is old (is not newly allocated and is not newly freed).
2086 if (mid->object() != NULL && mid->is_old() &&
2087 deflate_monitor_using_JT(mid, free_head_p, free_tail_p)) {
2088 // Deflation succeeded and already updated free_head_p and
2089 // free_tail_p as needed. Finish the move to the local free list
2090 // by unlinking mid from the global or per-thread in-use list.
2091 if (mid == *list_p) {
2092 *list_p = mid->_next_om;
2093 } else if (cur_mid_in_use != NULL) {
2094 // Maintain the current in-use list.
2095 cur_mid_in_use->_next_om = mid->_next_om;
2096 }
2097 next = mid->_next_om;
2098 mid->_next_om = NULL;
2099 // At this point mid is disconnected from the in-use list
2100 // and is the current tail in the free_head_p list.
2101 mid = next;
2102 deflated_count++;
2103 } else {
2104 // mid is considered in-use if it does not have an associated
2105 // Java object or mid is not old or deflation did not succeed.
2106 // A mid->is_new() node can be seen here when it is freshly
2107 // returned by om_alloc() (and skips the deflation code path).
2108 // A mid->is_old() node can be seen here when deflation failed.
2109 // A mid->is_free() node can be seen here when a fresh node from
2110 // om_alloc() is released by om_release() due to losing the race
2111 // in inflate().
2112
2113 cur_mid_in_use = mid;
2114 mid = mid->_next_om;
2115
2116 if (SafepointSynchronize::is_synchronizing() &&
2117 cur_mid_in_use != *list_p && cur_mid_in_use->is_old()) {
2118 // If a safepoint has started and cur_mid_in_use is not the list
2119 // head and is old, then it is safe to use as saved state. Return
2120 // to the caller so gListLock can be dropped as appropriate
2121 // before blocking.
2122 *saved_mid_in_use_p = cur_mid_in_use;
2123 return deflated_count;
2124 }
2125 }
2126 }
2127 // We finished the list without a safepoint starting so there's
2128 // no need to save state.
2129 *saved_mid_in_use_p = NULL;
2130 return deflated_count;
2131 }
2132
2133 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2134 counters->n_in_use = 0; // currently associated with objects
2135 counters->n_in_circulation = 0; // extant
2136 counters->n_scavenged = 0; // reclaimed (global and per-thread)
2137 counters->per_thread_scavenged = 0; // per-thread scavenge total
2138 counters->per_thread_times = 0.0; // per-thread scavenge times
2139 }
2140
2141 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
2142 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2143
2144 if (AsyncDeflateIdleMonitors) {
2145 // Nothing to do when global idle ObjectMonitors are deflated using
2146 // a JavaThread unless a special deflation has been requested.
2147 if (!is_special_deflation_requested()) {
2148 return;
2149 }
2150 }
2151
2152 bool deflated = false;
2153
2154 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
2155 ObjectMonitor* free_tail_p = NULL;
2156 elapsedTimer timer;
2157
2158 if (log_is_enabled(Info, monitorinflation)) {
2159 timer.start();
2160 }
2161
2162 // Prevent om_flush from changing mids in Thread dtor's during deflation
2163 // And in case the vm thread is acquiring a lock during a safepoint
2164 // See e.g. 6320749
2165 Thread::muxAcquire(&gListLock, "deflate_idle_monitors");
2166
2167 // Note: the thread-local monitors lists get deflated in
2168 // a separate pass. See deflate_thread_local_monitors().
2169
2170 // For moribund threads, scan g_om_in_use_list
2171 int deflated_count = 0;
2172 if (g_om_in_use_list) {
2173 counters->n_in_circulation += g_om_in_use_count;
2174 deflated_count = deflate_monitor_list((ObjectMonitor **)&g_om_in_use_list, &free_head_p, &free_tail_p);
2175 g_om_in_use_count -= deflated_count;
2176 counters->n_scavenged += deflated_count;
2177 counters->n_in_use += g_om_in_use_count;
2178 }
2179
2180 if (free_head_p != NULL) {
2181 // Move the deflated ObjectMonitors back to the global free list.
2182 guarantee(free_tail_p != NULL && counters->n_scavenged > 0, "invariant");
2183 assert(free_tail_p->_next_om == NULL, "invariant");
2184 // constant-time list splice - prepend scavenged segment to g_free_list
2185 free_tail_p->_next_om = g_free_list;
2186 g_free_list = free_head_p;
2187 }
2188 Thread::muxRelease(&gListLock);
2189 timer.stop();
2190
2191 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2192 LogStreamHandle(Info, monitorinflation) lsh_info;
2193 LogStream* ls = NULL;
2194 if (log_is_enabled(Debug, monitorinflation)) {
2195 ls = &lsh_debug;
2196 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2197 ls = &lsh_info;
2198 }
2199 if (ls != NULL) {
2200 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2201 }
2202 }
2203
2204 // Deflate global idle ObjectMonitors using a JavaThread.
2205 //
2206 void ObjectSynchronizer::deflate_global_idle_monitors_using_JT() {
2207 assert(AsyncDeflateIdleMonitors, "sanity check");
2208 assert(Thread::current()->is_Java_thread(), "precondition");
2209 JavaThread* self = JavaThread::current();
2210
2211 deflate_common_idle_monitors_using_JT(true /* is_global */, self);
2212 }
2213
2214 // Deflate per-thread idle ObjectMonitors using a JavaThread.
2215 //
2216 void ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT() {
2217 assert(AsyncDeflateIdleMonitors, "sanity check");
2218 assert(Thread::current()->is_Java_thread(), "precondition");
2219 JavaThread* self = JavaThread::current();
2220
2221 self->om_request_deflation = false;
2222
2223 deflate_common_idle_monitors_using_JT(false /* !is_global */, self);
2224 }
2225
2226 // Deflate global or per-thread idle ObjectMonitors using a JavaThread.
2227 //
2228 void ObjectSynchronizer::deflate_common_idle_monitors_using_JT(bool is_global, JavaThread* self) {
2229 int deflated_count = 0;
2230 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged ObjectMonitors
2231 ObjectMonitor* free_tail_p = NULL;
2232 ObjectMonitor* saved_mid_in_use_p = NULL;
2233 elapsedTimer timer;
2234
2235 if (log_is_enabled(Info, monitorinflation)) {
2236 timer.start();
2237 }
2238
2239 if (is_global) {
2240 Thread::muxAcquire(&gListLock, "deflate_global_idle_monitors_using_JT(1)");
2241 OM_PERFDATA_OP(MonExtant, set_value(g_om_in_use_count));
2242 } else {
2243 OM_PERFDATA_OP(MonExtant, inc(self->om_in_use_count));
2244 }
2245
2246 do {
2247 int local_deflated_count;
2248 if (is_global) {
2249 local_deflated_count = deflate_monitor_list_using_JT((ObjectMonitor **)&g_om_in_use_list, &free_head_p, &free_tail_p, &saved_mid_in_use_p);
2250 g_om_in_use_count -= local_deflated_count;
2251 } else {
2252 local_deflated_count = deflate_monitor_list_using_JT(self->om_in_use_list_addr(), &free_head_p, &free_tail_p, &saved_mid_in_use_p);
2253 self->om_in_use_count -= local_deflated_count;
2254 }
2255 deflated_count += local_deflated_count;
2256
2257 if (free_head_p != NULL) {
2258 // Move the deflated ObjectMonitors to the global free list.
2259 guarantee(free_tail_p != NULL && local_deflated_count > 0, "free_tail_p=" INTPTR_FORMAT ", local_deflated_count=%d", p2i(free_tail_p), local_deflated_count);
2260 assert(free_tail_p->_next_om == NULL, "invariant");
2261
2262 if (!is_global) {
2263 Thread::muxAcquire(&gListLock, "deflate_per_thread_idle_monitors_using_JT(2)");
2264 }
2265 // Constant-time list splice - prepend scavenged segment to g_free_list.
2266 free_tail_p->_next_om = g_free_list;
2267 g_free_list = free_head_p;
2268
2269 g_om_free_count += local_deflated_count;
2270 OM_PERFDATA_OP(Deflations, inc(local_deflated_count));
2271 if (!is_global) {
2272 Thread::muxRelease(&gListLock);
2273 }
2274 }
2275
2276 if (saved_mid_in_use_p != NULL) {
2277 // deflate_monitor_list_using_JT() detected a safepoint starting.
2278 if (is_global) {
2279 Thread::muxRelease(&gListLock);
2280 }
2281 timer.stop();
2282 {
2283 if (is_global) {
2284 log_debug(monitorinflation)("pausing deflation of global idle monitors for a safepoint.");
2285 } else {
2286 log_debug(monitorinflation)("jt=" INTPTR_FORMAT ": pausing deflation of per-thread idle monitors for a safepoint.", p2i(self));
2287 }
2288 assert(SafepointSynchronize::is_synchronizing(), "sanity check");
2289 ThreadBlockInVM blocker(self);
2290 }
2291 // Prepare for another loop after the safepoint.
2292 free_head_p = NULL;
2293 free_tail_p = NULL;
2294 if (log_is_enabled(Info, monitorinflation)) {
2295 timer.start();
2296 }
2297 if (is_global) {
2298 Thread::muxAcquire(&gListLock, "deflate_global_idle_monitors_using_JT(3)");
2299 }
2300 }
2301 } while (saved_mid_in_use_p != NULL);
2302 if (is_global) {
2303 Thread::muxRelease(&gListLock);
2304 }
2305 timer.stop();
2306
2307 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2308 LogStreamHandle(Info, monitorinflation) lsh_info;
2309 LogStream* ls = NULL;
2310 if (log_is_enabled(Debug, monitorinflation)) {
2311 ls = &lsh_debug;
2312 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2313 ls = &lsh_info;
2314 }
2315 if (ls != NULL) {
2316 if (is_global) {
2317 ls->print_cr("async-deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2318 } else {
2319 ls->print_cr("jt=" INTPTR_FORMAT ": async-deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(self), timer.seconds(), deflated_count);
2320 }
2321 }
2322 }
2323
2324 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2325 // Report the cumulative time for deflating each thread's idle
2326 // monitors. Note: if the work is split among more than one
2327 // worker thread, then the reported time will likely be more
2328 // than a beginning to end measurement of the phase.
2329 // Note: AsyncDeflateIdleMonitors only deflates per-thread idle
2330 // monitors at a safepoint when a special deflation has been requested.
2331 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged);
2332
2333 bool needs_special_deflation = is_special_deflation_requested();
2334 if (!AsyncDeflateIdleMonitors || needs_special_deflation) {
2335 // AsyncDeflateIdleMonitors does not use these counters unless
2336 // there is a special deflation request.
2337
2338 g_om_free_count += counters->n_scavenged;
2339
2340 OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged));
2341 OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation));
2342 }
2343
2344 if (log_is_enabled(Debug, monitorinflation)) {
2345 // exit_globals()'s call to audit_and_print_stats() is done
2346 // at the Info level.
2347 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2348 } else if (log_is_enabled(Info, monitorinflation)) {
2349 Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors");
2350 log_info(monitorinflation)("g_om_population=%d, g_om_in_use_count=%d, "
2351 "g_om_free_count=%d", g_om_population,
2352 g_om_in_use_count, g_om_free_count);
2353 Thread::muxRelease(&gListLock);
2354 }
2355
2356 ForceMonitorScavenge = 0; // Reset
2357 GVars.stw_random = os::random();
2358 GVars.stw_cycle++;
2359 if (needs_special_deflation) {
2360 set_is_special_deflation_requested(false); // special deflation is done
2361 }
2362 }
2363
2364 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
2365 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2366
2367 if (AsyncDeflateIdleMonitors) {
2368 if (!is_special_deflation_requested()) {
2369 // Mark the JavaThread for idle monitor deflation if a special
2370 // deflation has NOT been requested.
2371 if (thread->om_in_use_count > 0) {
2372 // This JavaThread is using monitors so mark it.
2373 thread->om_request_deflation = true;
2374 }
2375 return;
2376 }
2377 }
2378
2379 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
2380 ObjectMonitor* free_tail_p = NULL;
2381 elapsedTimer timer;
2382
2383 if (log_is_enabled(Info, safepoint, cleanup) ||
2384 log_is_enabled(Info, monitorinflation)) {
2385 timer.start();
2386 }
2387
2388 int deflated_count = deflate_monitor_list(thread->om_in_use_list_addr(), &free_head_p, &free_tail_p);
2389
2390 Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors");
2391
2392 // Adjust counters
2393 counters->n_in_circulation += thread->om_in_use_count;
2394 thread->om_in_use_count -= deflated_count;
2395 counters->n_scavenged += deflated_count;
2396 counters->n_in_use += thread->om_in_use_count;
2397 counters->per_thread_scavenged += deflated_count;
2398
2399 if (free_head_p != NULL) {
2400 // Move the deflated ObjectMonitors back to the global free list.
2401 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
2402 assert(free_tail_p->_next_om == NULL, "invariant");
2403
2404 // constant-time list splice - prepend scavenged segment to g_free_list
2405 free_tail_p->_next_om = g_free_list;
2406 g_free_list = free_head_p;
2407 }
2408
2409 timer.stop();
2410 // Safepoint logging cares about cumulative per_thread_times and
2411 // we'll capture most of the cost, but not the muxRelease() which
2412 // should be cheap.
2413 counters->per_thread_times += timer.seconds();
2414
2415 Thread::muxRelease(&gListLock);
2416
2417 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2418 LogStreamHandle(Info, monitorinflation) lsh_info;
2419 LogStream* ls = NULL;
2420 if (log_is_enabled(Debug, monitorinflation)) {
2421 ls = &lsh_debug;
2422 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2423 ls = &lsh_info;
2424 }
2425 if (ls != NULL) {
2426 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
2427 }
2428 }
2429
2430 // Monitor cleanup on JavaThread::exit
2431
2432 // Iterate through monitor cache and attempt to release thread's monitors
2433 // Gives up on a particular monitor if an exception occurs, but continues
2434 // the overall iteration, swallowing the exception.
2435 class ReleaseJavaMonitorsClosure: public MonitorClosure {
2436 private:
2437 TRAPS;
2438
2439 public:
2440 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
2441 void do_monitor(ObjectMonitor* mid) {
2442 if (mid->owner() == THREAD) {
2443 (void)mid->complete_exit(CHECK);
2444 }
2445 }
2446 };
2447
2448 // Release all inflated monitors owned by THREAD. Lightweight monitors are
2449 // ignored. This is meant to be called during JNI thread detach which assumes
2450 // all remaining monitors are heavyweight. All exceptions are swallowed.
2451 // Scanning the extant monitor list can be time consuming.
2452 // A simple optimization is to add a per-thread flag that indicates a thread
2453 // called jni_monitorenter() during its lifetime.
2454 //
2455 // Instead of No_Savepoint_Verifier it might be cheaper to
2456 // use an idiom of the form:
2457 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
2458 // <code that must not run at safepoint>
2459 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
2460 // Since the tests are extremely cheap we could leave them enabled
2461 // for normal product builds.
2462
2463 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
2464 assert(THREAD == JavaThread::current(), "must be current Java thread");
2465 NoSafepointVerifier nsv;
2466 ReleaseJavaMonitorsClosure rjmc(THREAD);
2467 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
2468 ObjectSynchronizer::monitors_iterate(&rjmc);
2469 Thread::muxRelease(&gListLock);
2470 THREAD->clear_pending_exception();
2471 }
2472
2473 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
2474 switch (cause) {
2475 case inflate_cause_vm_internal: return "VM Internal";
2476 case inflate_cause_monitor_enter: return "Monitor Enter";
2477 case inflate_cause_wait: return "Monitor Wait";
2478 case inflate_cause_notify: return "Monitor Notify";
2479 case inflate_cause_hash_code: return "Monitor Hash Code";
2480 case inflate_cause_jni_enter: return "JNI Monitor Enter";
2481 case inflate_cause_jni_exit: return "JNI Monitor Exit";
2482 default:
2483 ShouldNotReachHere();
2484 }
2485 return "Unknown";
2486 }
2487
2488 //------------------------------------------------------------------------------
2489 // Debugging code
2490
2491 u_char* ObjectSynchronizer::get_gvars_addr() {
2492 return (u_char*)&GVars;
2493 }
2494
2495 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
2496 return (u_char*)&GVars.hc_sequence;
2497 }
2498
2499 size_t ObjectSynchronizer::get_gvars_size() {
2500 return sizeof(SharedGlobals);
2501 }
2502
2503 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
2504 return (u_char*)&GVars.stw_random;
2505 }
2506
2507 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
2508 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
2509
2510 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2511 LogStreamHandle(Info, monitorinflation) lsh_info;
2512 LogStreamHandle(Trace, monitorinflation) lsh_trace;
2513 LogStream* ls = NULL;
2514 if (log_is_enabled(Trace, monitorinflation)) {
2515 ls = &lsh_trace;
2516 } else if (log_is_enabled(Debug, monitorinflation)) {
2517 ls = &lsh_debug;
2518 } else if (log_is_enabled(Info, monitorinflation)) {
2519 ls = &lsh_info;
2520 }
2521 assert(ls != NULL, "sanity check");
2522
2523 if (!on_exit) {
2524 // Not at VM exit so grab the global list lock.
2525 Thread::muxAcquire(&gListLock, "audit_and_print_stats");
2526 }
2527
2528 // Log counts for the global and per-thread monitor lists:
2529 int chk_om_population = log_monitor_list_counts(ls);
2530 int error_cnt = 0;
2531
2532 ls->print_cr("Checking global lists:");
2533
2534 // Check g_om_population:
2535 if (g_om_population == chk_om_population) {
2536 ls->print_cr("g_om_population=%d equals chk_om_population=%d",
2537 g_om_population, chk_om_population);
2538 } else {
2539 ls->print_cr("ERROR: g_om_population=%d is not equal to "
2540 "chk_om_population=%d", g_om_population,
2541 chk_om_population);
2542 error_cnt++;
2543 }
2544
2545 // Check g_om_in_use_list and g_om_in_use_count:
2546 chk_global_in_use_list_and_count(ls, &error_cnt);
2547
2548 // Check g_free_list and g_om_free_count:
2549 chk_global_free_list_and_count(ls, &error_cnt);
2550
2551 if (!on_exit) {
2552 Thread::muxRelease(&gListLock);
2553 }
2554
2555 ls->print_cr("Checking per-thread lists:");
2556
2557 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2558 // Check om_in_use_list and om_in_use_count:
2559 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
2560
2561 // Check om_free_list and om_free_count:
2562 chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
2563 }
2564
2565 if (error_cnt == 0) {
2566 ls->print_cr("No errors found in monitor list checks.");
2567 } else {
2568 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
2569 }
2570
2571 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
2572 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
2573 // When exiting this log output is at the Info level. When called
2574 // at a safepoint, this log output is at the Trace level since
2575 // there can be a lot of it.
2576 log_in_use_monitor_details(ls, on_exit);
2577 }
2578
2579 ls->flush();
2580
2581 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2582 }
2583
2584 // Check a free monitor entry; log any errors.
2585 void ObjectSynchronizer::chk_free_entry(JavaThread* jt, ObjectMonitor* n,
2586 outputStream * out, int *error_cnt_p) {
2587 stringStream ss;
2588 if (n->is_busy()) {
2589 if (jt != NULL) {
2590 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2591 ": free per-thread monitor must not be busy: %s", p2i(jt),
2592 p2i(n), n->is_busy_to_string(&ss));
2593 } else {
2594 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2595 "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
2596 }
2597 *error_cnt_p = *error_cnt_p + 1;
2598 }
2599 if (n->header().value() != 0) {
2600 if (jt != NULL) {
2601 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2602 ": free per-thread monitor must have NULL _header "
2603 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
2604 n->header().value());
2605 *error_cnt_p = *error_cnt_p + 1;
2606 } else if (!AsyncDeflateIdleMonitors) {
2607 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2608 "must have NULL _header field: _header=" INTPTR_FORMAT,
2609 p2i(n), n->header().value());
2610 *error_cnt_p = *error_cnt_p + 1;
2611 }
2612 }
2613 if (n->object() != NULL) {
2614 if (jt != NULL) {
2615 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2616 ": free per-thread monitor must have NULL _object "
2617 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
2618 p2i(n->object()));
2619 } else {
2620 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2621 "must have NULL _object field: _object=" INTPTR_FORMAT,
2622 p2i(n), p2i(n->object()));
2623 }
2624 *error_cnt_p = *error_cnt_p + 1;
2625 }
2626 }
2627
2628 // Check the global free list and count; log the results of the checks.
2629 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
2630 int *error_cnt_p) {
2631 int chk_om_free_count = 0;
2632 for (ObjectMonitor* n = g_free_list; n != NULL; n = n->_next_om) {
2633 chk_free_entry(NULL /* jt */, n, out, error_cnt_p);
2634 chk_om_free_count++;
2635 }
2636 if (g_om_free_count == chk_om_free_count) {
2637 out->print_cr("g_om_free_count=%d equals chk_om_free_count=%d",
2638 g_om_free_count, chk_om_free_count);
2639 } else {
2640 out->print_cr("ERROR: g_om_free_count=%d is not equal to "
2641 "chk_om_free_count=%d", g_om_free_count,
2642 chk_om_free_count);
2643 *error_cnt_p = *error_cnt_p + 1;
2644 }
2645 }
2646
2647 // Check the global in-use list and count; log the results of the checks.
2648 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
2649 int *error_cnt_p) {
2650 int chk_om_in_use_count = 0;
2651 for (ObjectMonitor* n = g_om_in_use_list; n != NULL; n = n->_next_om) {
2652 chk_in_use_entry(NULL /* jt */, n, out, error_cnt_p);
2653 chk_om_in_use_count++;
2654 }
2655 if (g_om_in_use_count == chk_om_in_use_count) {
2656 out->print_cr("g_om_in_use_count=%d equals chk_om_in_use_count=%d", g_om_in_use_count,
2657 chk_om_in_use_count);
2658 } else {
2659 out->print_cr("ERROR: g_om_in_use_count=%d is not equal to chk_om_in_use_count=%d",
2660 g_om_in_use_count, chk_om_in_use_count);
2661 *error_cnt_p = *error_cnt_p + 1;
2662 }
2663 }
2664
2665 // Check an in-use monitor entry; log any errors.
2666 void ObjectSynchronizer::chk_in_use_entry(JavaThread* jt, ObjectMonitor* n,
2667 outputStream * out, int *error_cnt_p) {
2668 if (n->header().value() == 0) {
2669 if (jt != NULL) {
2670 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2671 ": in-use per-thread monitor must have non-NULL _header "
2672 "field.", p2i(jt), p2i(n));
2673 } else {
2674 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2675 "must have non-NULL _header field.", p2i(n));
2676 }
2677 *error_cnt_p = *error_cnt_p + 1;
2678 }
2679 if (n->object() == NULL) {
2680 if (jt != NULL) {
2681 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2682 ": in-use per-thread monitor must have non-NULL _object "
2683 "field.", p2i(jt), p2i(n));
2684 } else {
2685 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2686 "must have non-NULL _object field.", p2i(n));
2687 }
2688 *error_cnt_p = *error_cnt_p + 1;
2689 }
2690 const oop obj = (oop)n->object();
2691 const markWord mark = obj->mark();
2692 if (!mark.has_monitor()) {
2693 if (jt != NULL) {
2694 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2695 ": in-use per-thread monitor's object does not think "
2696 "it has a monitor: obj=" INTPTR_FORMAT ", mark="
2697 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), mark.value());
2698 } else {
2699 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2700 "monitor's object does not think it has a monitor: obj="
2701 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2702 p2i(obj), mark.value());
2703 }
2704 *error_cnt_p = *error_cnt_p + 1;
2705 }
2706 ObjectMonitor* const obj_mon = mark.monitor();
2707 if (n != obj_mon) {
2708 if (jt != NULL) {
2709 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2710 ": in-use per-thread monitor's object does not refer "
2711 "to the same monitor: obj=" INTPTR_FORMAT ", mark="
2712 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
2713 p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2714 } else {
2715 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2716 "monitor's object does not refer to the same monitor: obj="
2717 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2718 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2719 }
2720 *error_cnt_p = *error_cnt_p + 1;
2721 }
2722 }
2723
2724 // Check the thread's free list and count; log the results of the checks.
2725 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
2726 outputStream * out,
2727 int *error_cnt_p) {
2728 int chk_om_free_count = 0;
2729 for (ObjectMonitor* n = jt->om_free_list; n != NULL; n = n->_next_om) {
2730 chk_free_entry(jt, n, out, error_cnt_p);
2731 chk_om_free_count++;
2732 }
2733 if (jt->om_free_count == chk_om_free_count) {
2734 out->print_cr("jt=" INTPTR_FORMAT ": om_free_count=%d equals "
2735 "chk_om_free_count=%d", p2i(jt), jt->om_free_count, chk_om_free_count);
2736 } else {
2737 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_free_count=%d is not "
2738 "equal to chk_om_free_count=%d", p2i(jt), jt->om_free_count,
2739 chk_om_free_count);
2740 *error_cnt_p = *error_cnt_p + 1;
2741 }
2742 }
2743
2744 // Check the thread's in-use list and count; log the results of the checks.
2745 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
2746 outputStream * out,
2747 int *error_cnt_p) {
2748 int chk_om_in_use_count = 0;
2749 for (ObjectMonitor* n = jt->om_in_use_list; n != NULL; n = n->_next_om) {
2750 chk_in_use_entry(jt, n, out, error_cnt_p);
2751 chk_om_in_use_count++;
2752 }
2753 if (jt->om_in_use_count == chk_om_in_use_count) {
2754 out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals "
2755 "chk_om_in_use_count=%d", p2i(jt), jt->om_in_use_count,
2756 chk_om_in_use_count);
2757 } else {
2758 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not "
2759 "equal to chk_om_in_use_count=%d", p2i(jt), jt->om_in_use_count,
2760 chk_om_in_use_count);
2761 *error_cnt_p = *error_cnt_p + 1;
2762 }
2763 }
2764
2765 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2766 // flags indicate why the entry is in-use, 'object' and 'object type'
2767 // indicate the associated object and its type.
2768 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out,
2769 bool on_exit) {
2770 if (!on_exit) {
2771 // Not at VM exit so grab the global list lock.
2772 Thread::muxAcquire(&gListLock, "log_in_use_monitor_details");
2773 }
2774
2775 stringStream ss;
2776 if (g_om_in_use_count > 0) {
2777 out->print_cr("In-use global monitor info:");
2778 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2779 out->print_cr("%18s %s %7s %18s %18s",
2780 "monitor", "BHL", "ref_cnt", "object", "object type");
2781 out->print_cr("================== === ======= ================== ==================");
2782 for (ObjectMonitor* n = g_om_in_use_list; n != NULL; n = n->_next_om) {
2783 const oop obj = (oop) n->object();
2784 const markWord mark = n->header();
2785 ResourceMark rm;
2786 out->print(INTPTR_FORMAT " %d%d%d %7d " INTPTR_FORMAT " %s",
2787 p2i(n), n->is_busy() != 0, mark.hash() != 0,
2788 n->owner() != NULL, (int)n->ref_count(), p2i(obj),
2789 obj->klass()->external_name());
2790 if (n->is_busy() != 0) {
2791 out->print(" (%s)", n->is_busy_to_string(&ss));
2792 ss.reset();
2793 }
2794 out->cr();
2795 }
2796 }
2797
2798 if (!on_exit) {
2799 Thread::muxRelease(&gListLock);
2800 }
2801
2802 out->print_cr("In-use per-thread monitor info:");
2803 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2804 out->print_cr("%18s %18s %s %7s %18s %18s",
2805 "jt", "monitor", "BHL", "ref_cnt", "object", "object type");
2806 out->print_cr("================== ================== === ======= ================== ==================");
2807 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2808 for (ObjectMonitor* n = jt->om_in_use_list; n != NULL; n = n->_next_om) {
2809 const oop obj = (oop) n->object();
2810 const markWord mark = n->header();
2811 ResourceMark rm;
2812 out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d %7d "
2813 INTPTR_FORMAT " %s", p2i(jt), p2i(n), n->is_busy() != 0,
2814 mark.hash() != 0, n->owner() != NULL, (int)n->ref_count(),
2815 p2i(obj), obj->klass()->external_name());
2816 if (n->is_busy() != 0) {
2817 out->print(" (%s)", n->is_busy_to_string(&ss));
2818 ss.reset();
2819 }
2820 out->cr();
2821 }
2822 }
2823
2824 out->flush();
2825 }
2826
2827 // Log counts for the global and per-thread monitor lists and return
2828 // the population count.
2829 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2830 int pop_count = 0;
2831 out->print_cr("%18s %10s %10s %10s",
2832 "Global Lists:", "InUse", "Free", "Total");
2833 out->print_cr("================== ========== ========== ==========");
2834 out->print_cr("%18s %10d %10d %10d", "",
2835 g_om_in_use_count, g_om_free_count, g_om_population);
2836 pop_count += g_om_in_use_count + g_om_free_count;
2837
2838 out->print_cr("%18s %10s %10s %10s",
2839 "Per-Thread Lists:", "InUse", "Free", "Provision");
2840 out->print_cr("================== ========== ========== ==========");
2841
2842 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2843 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
2844 jt->om_in_use_count, jt->om_free_count, jt->om_free_provision);
2845 pop_count += jt->om_in_use_count + jt->om_free_count;
2846 }
2847 return pop_count;
2848 }
2849
2850 #ifndef PRODUCT
2851
2852 // Check if monitor belongs to the monitor cache
2853 // The list is grow-only so it's *relatively* safe to traverse
2854 // the list of extant blocks without taking a lock.
2855
2856 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
2857 PaddedObjectMonitor* block = OrderAccess::load_acquire(&g_block_list);
2858 while (block != NULL) {
2859 assert(block->object() == CHAINMARKER, "must be a block header");
2860 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
2861 address mon = (address)monitor;
2862 address blk = (address)block;
2863 size_t diff = mon - blk;
2864 assert((diff % sizeof(PaddedObjectMonitor)) == 0, "must be aligned");
2865 return 1;
2866 }
2867 block = (PaddedObjectMonitor*)block->_next_om;
2868 }
2869 return 0;
2870 }
2871
2872 #endif