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.
22 *
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
129 static volatile intptr_t gListLock = 0; // protects global monitor lists
130 static volatile int g_om_free_count = 0; // # on g_free_list
131 static volatile int g_om_population = 0; // # Extant -- in circulation
132
133 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
134
135
136 // =====================> Quick functions
137
138 // The quick_* forms are special fast-path variants used to improve
139 // performance. In the simplest case, a "quick_*" implementation could
140 // simply return false, in which case the caller will perform the necessary
141 // state transitions and call the slow-path form.
142 // The fast-path is designed to handle frequently arising cases in an efficient
143 // manner and is just a degenerate "optimistic" variant of the slow-path.
144 // returns true -- to indicate the call was satisfied.
145 // returns false -- to indicate the call needs the services of the slow-path.
146 // A no-loitering ordinance is in effect for code in the quick_* family
147 // operators: safepoints or indefinite blocking (blocking that might span a
148 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
149 // entry.
150 //
151 // Consider: An interesting optimization is to have the JIT recognize the
152 // following common idiom:
153 // synchronized (someobj) { .... ; notify(); }
154 // That is, we find a notify() or notifyAll() call that immediately precedes
155 // the monitorexit operation. In that case the JIT could fuse the operations
156 // into a single notifyAndExit() runtime primitive.
157
158 bool ObjectSynchronizer::quick_notify(oopDesc* obj, Thread* self, bool all) {
159 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
160 assert(self->is_Java_thread(), "invariant");
161 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
162 NoSafepointVerifier nsv;
163 if (obj == NULL) return false; // slow-path for invalid obj
164 const markWord mark = obj->mark();
165
166 if (mark.has_locker() && self->is_lock_owned((address)mark.locker())) {
167 // Degenerate notify
168 // stack-locked by caller so by definition the implied waitset is empty.
169 return true;
170 }
171
172 if (mark.has_monitor()) {
173 ObjectMonitor* const mon = mark.monitor();
174 assert(oopDesc::equals((oop) mon->object(), obj), "invariant");
175 if (mon->owner() != self) return false; // slow-path for IMS exception
176
177 if (mon->first_waiter() != NULL) {
178 // We have one or more waiters. Since this is an inflated monitor
179 // that we own, we can transfer one or more threads from the waitset
180 // to the entrylist here and now, avoiding the slow-path.
181 if (all) {
182 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
183 } else {
184 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
185 }
186 int free_count = 0;
187 do {
188 mon->INotify(self);
189 ++free_count;
190 } while (mon->first_waiter() != NULL && all);
191 OM_PERFDATA_OP(Notifications, inc(free_count));
192 }
193 return true;
194 }
195
196 // biased locking and any other IMS exception states take the slow-path
197 return false;
198 }
199
200
201 // The LockNode emitted directly at the synchronization site would have
202 // been too big if it were to have included support for the cases of inflated
203 // recursive enter and exit, so they go here instead.
204 // Note that we can't safely call AsyncPrintJavaStack() from within
205 // quick_enter() as our thread state remains _in_Java.
206
207 bool ObjectSynchronizer::quick_enter(oop obj, Thread* self,
208 BasicLock * lock) {
209 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
210 assert(self->is_Java_thread(), "invariant");
211 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
212 NoSafepointVerifier nsv;
213 if (obj == NULL) return false; // Need to throw NPE
214 const markWord mark = obj->mark();
215
216 if (mark.has_monitor()) {
217 ObjectMonitor* const m = mark.monitor();
218 assert(oopDesc::equals((oop) m->object(), obj), "invariant");
219 Thread* const owner = (Thread *) m->_owner;
220
221 // Lock contention and Transactional Lock Elision (TLE) diagnostics
222 // and observability
223 // Case: light contention possibly amenable to TLE
224 // Case: TLE inimical operations such as nested/recursive synchronization
225
226 if (owner == self) {
227 m->_recursions++;
228 return true;
229 }
230
231 // This Java Monitor is inflated so obj's header will never be
232 // displaced to this thread's BasicLock. Make the displaced header
233 // non-NULL so this BasicLock is not seen as recursive nor as
234 // being locked. We do this unconditionally so that this thread's
235 // BasicLock cannot be mis-interpreted by any stack walkers. For
236 // performance reasons, stack walkers generally first check for
237 // Biased Locking in the object's header, the second check is for
238 // stack-locking in the object's header, the third check is for
239 // recursive stack-locking in the displaced header in the BasicLock,
240 // and last are the inflated Java Monitor (ObjectMonitor) checks.
241 lock->set_displaced_header(markWord::unused_mark());
242
243 if (owner == NULL && Atomic::replace_if_null(self, &(m->_owner))) {
244 assert(m->_recursions == 0, "invariant");
245 return true;
246 }
247 }
248
249 // Note that we could inflate in quick_enter.
250 // This is likely a useful optimization
251 // Critically, in quick_enter() we must not:
252 // -- perform bias revocation, or
253 // -- block indefinitely, or
254 // -- reach a safepoint
255
256 return false; // revert to slow-path
257 }
258
259 // -----------------------------------------------------------------------------
260 // Fast Monitor Enter/Exit
261 // This the fast monitor enter. The interpreter and compiler use
262 // some assembly copies of this code. Make sure update those code
263 // if the following function is changed. The implementation is
264 // extremely sensitive to race condition. Be careful.
265
266 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
267 bool attempt_rebias, TRAPS) {
268 if (UseBiasedLocking) {
269 if (!SafepointSynchronize::is_at_safepoint()) {
270 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
271 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
272 return;
273 }
274 } else {
275 assert(!attempt_rebias, "can not rebias toward VM thread");
276 BiasedLocking::revoke_at_safepoint(obj);
277 }
278 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
279 }
280
281 slow_enter(obj, lock, THREAD);
282 }
283
284 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
285 markWord mark = object->mark();
286 // We cannot check for Biased Locking if we are racing an inflation.
287 assert(mark == markWord::INFLATING() ||
288 !mark.has_bias_pattern(), "should not see bias pattern here");
289
290 markWord dhw = lock->displaced_header();
291 if (dhw.value() == 0) {
292 // If the displaced header is NULL, then this exit matches up with
293 // a recursive enter. No real work to do here except for diagnostics.
294 #ifndef PRODUCT
295 if (mark != markWord::INFLATING()) {
296 // Only do diagnostics if we are not racing an inflation. Simply
297 // exiting a recursive enter of a Java Monitor that is being
298 // inflated is safe; see the has_monitor() comment below.
299 assert(!mark.is_neutral(), "invariant");
300 assert(!mark.has_locker() ||
301 THREAD->is_lock_owned((address)mark.locker()), "invariant");
302 if (mark.has_monitor()) {
303 // The BasicLock's displaced_header is marked as a recursive
304 // enter and we have an inflated Java Monitor (ObjectMonitor).
305 // This is a special case where the Java Monitor was inflated
306 // after this thread entered the stack-lock recursively. When a
307 // Java Monitor is inflated, we cannot safely walk the Java
308 // Monitor owner's stack and update the BasicLocks because a
309 // Java Monitor can be asynchronously inflated by a thread that
310 // does not own the Java Monitor.
311 ObjectMonitor* m = mark.monitor();
312 assert(((oop)(m->object()))->mark() == mark, "invariant");
313 assert(m->is_entered(THREAD), "invariant");
314 }
315 }
316 #endif
317 return;
318 }
319
320 if (mark == markWord::from_pointer(lock)) {
321 // If the object is stack-locked by the current thread, try to
322 // swing the displaced header from the BasicLock back to the mark.
323 assert(dhw.is_neutral(), "invariant");
324 if (object->cas_set_mark(dhw, mark) == mark) {
325 return;
326 }
327 }
328
329 // We have to take the slow-path of possible inflation and then exit.
330 inflate(THREAD, object, inflate_cause_vm_internal)->exit(true, THREAD);
331 }
332
333 // -----------------------------------------------------------------------------
334 // Interpreter/Compiler Slow Case
335 // This routine is used to handle interpreter/compiler slow case
336 // We don't need to use fast path here, because it must have been
337 // failed in the interpreter/compiler code.
338 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
339 markWord mark = obj->mark();
340 assert(!mark.has_bias_pattern(), "should not see bias pattern here");
341
342 if (mark.is_neutral()) {
343 // Anticipate successful CAS -- the ST of the displaced mark must
344 // be visible <= the ST performed by the CAS.
345 lock->set_displaced_header(mark);
346 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
347 return;
348 }
349 // Fall through to inflate() ...
350 } else if (mark.has_locker() &&
351 THREAD->is_lock_owned((address)mark.locker())) {
352 assert(lock != mark.locker(), "must not re-lock the same lock");
353 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
354 lock->set_displaced_header(markWord::from_pointer(NULL));
355 return;
356 }
357
358 // The object header will never be displaced to this lock,
359 // so it does not matter what the value is, except that it
360 // must be non-zero to avoid looking like a re-entrant lock,
361 // and must not look locked either.
362 lock->set_displaced_header(markWord::unused_mark());
363 inflate(THREAD, obj(), inflate_cause_monitor_enter)->enter(THREAD);
364 }
365
366 // This routine is used to handle interpreter/compiler slow case
367 // We don't need to use fast path here, because it must have
368 // failed in the interpreter/compiler code. Simply use the heavy
369 // weight monitor should be ok, unless someone find otherwise.
370 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
371 fast_exit(object, lock, THREAD);
372 }
373
374 // -----------------------------------------------------------------------------
375 // Class Loader support to workaround deadlocks on the class loader lock objects
376 // Also used by GC
377 // complete_exit()/reenter() are used to wait on a nested lock
378 // i.e. to give up an outer lock completely and then re-enter
379 // Used when holding nested locks - lock acquisition order: lock1 then lock2
380 // 1) complete_exit lock1 - saving recursion count
381 // 2) wait on lock2
382 // 3) when notified on lock2, unlock lock2
383 // 4) reenter lock1 with original recursion count
384 // 5) lock lock2
385 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
386 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
387 if (UseBiasedLocking) {
388 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
389 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
390 }
391
392 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
393
394 return monitor->complete_exit(THREAD);
395 }
396
397 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
398 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
399 if (UseBiasedLocking) {
400 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
401 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
402 }
403
404 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
405
406 monitor->reenter(recursion, THREAD);
407 }
408 // -----------------------------------------------------------------------------
409 // JNI locks on java objects
410 // NOTE: must use heavy weight monitor to handle jni monitor enter
411 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
412 // the current locking is from JNI instead of Java code
413 if (UseBiasedLocking) {
414 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
415 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
416 }
417 THREAD->set_current_pending_monitor_is_from_java(false);
418 inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);
419 THREAD->set_current_pending_monitor_is_from_java(true);
420 }
421
422 // NOTE: must use heavy weight monitor to handle jni monitor exit
423 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
424 if (UseBiasedLocking) {
425 Handle h_obj(THREAD, obj);
426 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
427 obj = h_obj();
428 }
429 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
430
431 ObjectMonitor* monitor = inflate(THREAD, obj, inflate_cause_jni_exit);
432 // If this thread has locked the object, exit the monitor. We
433 // intentionally do not use CHECK here because we must exit the
434 // monitor even if an exception is pending.
435 if (monitor->check_owner(THREAD)) {
436 monitor->exit(true, THREAD);
437 }
438 }
439
440 // -----------------------------------------------------------------------------
441 // Internal VM locks on java objects
442 // standard constructor, allows locking failures
443 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool do_lock) {
444 _dolock = do_lock;
445 _thread = thread;
446 _thread->check_for_valid_safepoint_state(false);
447 _obj = obj;
448
449 if (_dolock) {
450 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
451 }
452 }
453
454 ObjectLocker::~ObjectLocker() {
455 if (_dolock) {
456 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
457 }
458 }
459
460
461 // -----------------------------------------------------------------------------
462 // Wait/Notify/NotifyAll
463 // NOTE: must use heavy weight monitor to handle wait()
464 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
465 if (UseBiasedLocking) {
466 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
467 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
468 }
469 if (millis < 0) {
470 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
471 }
472 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
473
474 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
475 monitor->wait(millis, true, THREAD);
476
477 // This dummy call is in place to get around dtrace bug 6254741. Once
478 // that's fixed we can uncomment the following line, remove the call
479 // and change this function back into a "void" func.
480 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
481 return dtrace_waited_probe(monitor, obj, THREAD);
482 }
483
484 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, jlong millis, TRAPS) {
485 if (UseBiasedLocking) {
486 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
487 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
488 }
489 if (millis < 0) {
490 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
491 }
492 inflate(THREAD, obj(), inflate_cause_wait)->wait(millis, false, THREAD);
493 }
494
495 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
496 if (UseBiasedLocking) {
497 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
498 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
499 }
500
501 markWord mark = obj->mark();
502 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
503 return;
504 }
505 inflate(THREAD, obj(), inflate_cause_notify)->notify(THREAD);
506 }
507
508 // NOTE: see comment of notify()
509 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
510 if (UseBiasedLocking) {
511 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
512 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
513 }
514
515 markWord mark = obj->mark();
516 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
517 return;
518 }
519 inflate(THREAD, obj(), inflate_cause_notify)->notifyAll(THREAD);
520 }
521
522 // -----------------------------------------------------------------------------
523 // Hash Code handling
524 //
525 // Performance concern:
526 // OrderAccess::storestore() calls release() which at one time stored 0
527 // into the global volatile OrderAccess::dummy variable. This store was
528 // unnecessary for correctness. Many threads storing into a common location
529 // causes considerable cache migration or "sloshing" on large SMP systems.
530 // As such, I avoided using OrderAccess::storestore(). In some cases
531 // OrderAccess::fence() -- which incurs local latency on the executing
532 // processor -- is a better choice as it scales on SMP systems.
533 //
534 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
535 // a discussion of coherency costs. Note that all our current reference
536 // platforms provide strong ST-ST order, so the issue is moot on IA32,
537 // x64, and SPARC.
538 //
539 // As a general policy we use "volatile" to control compiler-based reordering
540 // and explicit fences (barriers) to control for architectural reordering
541 // performed by the CPU(s) or platform.
542
543 struct SharedGlobals {
544 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
545 // These are highly shared mostly-read variables.
546 // To avoid false-sharing they need to be the sole occupants of a cache line.
547 volatile int stw_random;
548 volatile int stw_cycle;
549 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
550 // Hot RW variable -- Sequester to avoid false-sharing
551 volatile int hc_sequence;
552 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
553 };
554
555 static SharedGlobals GVars;
556 static int MonitorScavengeThreshold = 1000000;
557 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
558
559 static markWord read_stable_mark(oop obj) {
560 markWord mark = obj->mark();
561 if (!mark.is_being_inflated()) {
562 return mark; // normal fast-path return
563 }
564
565 int its = 0;
566 for (;;) {
567 markWord mark = obj->mark();
568 if (!mark.is_being_inflated()) {
569 return mark; // normal fast-path return
570 }
571
572 // The object is being inflated by some other thread.
573 // The caller of read_stable_mark() must wait for inflation to complete.
574 // Avoid live-lock
575 // TODO: consider calling SafepointSynchronize::do_call_back() while
576 // spinning to see if there's a safepoint pending. If so, immediately
577 // yielding or blocking would be appropriate. Avoid spinning while
578 // there is a safepoint pending.
579 // TODO: add inflation contention performance counters.
580 // TODO: restrict the aggregate number of spinners.
581
582 ++its;
583 if (its > 10000 || !os::is_MP()) {
584 if (its & 1) {
585 os::naked_yield();
586 } else {
587 // Note that the following code attenuates the livelock problem but is not
588 // a complete remedy. A more complete solution would require that the inflating
589 // thread hold the associated inflation lock. The following code simply restricts
590 // the number of spinners to at most one. We'll have N-2 threads blocked
591 // on the inflationlock, 1 thread holding the inflation lock and using
592 // a yield/park strategy, and 1 thread in the midst of inflation.
593 // A more refined approach would be to change the encoding of INFLATING
594 // to allow encapsulation of a native thread pointer. Threads waiting for
595 // inflation to complete would use CAS to push themselves onto a singly linked
596 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
597 // and calling park(). When inflation was complete the thread that accomplished inflation
598 // would detach the list and set the markword to inflated with a single CAS and
599 // then for each thread on the list, set the flag and unpark() the thread.
600 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
601 // wakes at most one thread whereas we need to wake the entire list.
602 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
603 int YieldThenBlock = 0;
604 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
605 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
606 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
607 while (obj->mark() == markWord::INFLATING()) {
608 // Beware: NakedYield() is advisory and has almost no effect on some platforms
609 // so we periodically call self->_ParkEvent->park(1).
610 // We use a mixed spin/yield/block mechanism.
611 if ((YieldThenBlock++) >= 16) {
612 Thread::current()->_ParkEvent->park(1);
613 } else {
614 os::naked_yield();
615 }
616 }
617 Thread::muxRelease(gInflationLocks + ix);
618 }
619 } else {
620 SpinPause(); // SMP-polite spinning
621 }
622 }
623 }
624
625 // hashCode() generation :
626 //
627 // Possibilities:
628 // * MD5Digest of {obj,stw_random}
629 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
630 // * A DES- or AES-style SBox[] mechanism
631 // * One of the Phi-based schemes, such as:
632 // 2654435761 = 2^32 * Phi (golden ratio)
633 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
634 // * A variation of Marsaglia's shift-xor RNG scheme.
635 // * (obj ^ stw_random) is appealing, but can result
636 // in undesirable regularity in the hashCode values of adjacent objects
637 // (objects allocated back-to-back, in particular). This could potentially
638 // result in hashtable collisions and reduced hashtable efficiency.
639 // There are simple ways to "diffuse" the middle address bits over the
640 // generated hashCode values:
641
642 static inline intptr_t get_next_hash(Thread* self, oop obj) {
643 intptr_t value = 0;
644 if (hashCode == 0) {
645 // This form uses global Park-Miller RNG.
646 // On MP system we'll have lots of RW access to a global, so the
647 // mechanism induces lots of coherency traffic.
648 value = os::random();
649 } else if (hashCode == 1) {
650 // This variation has the property of being stable (idempotent)
651 // between STW operations. This can be useful in some of the 1-0
652 // synchronization schemes.
653 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
654 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
655 } else if (hashCode == 2) {
656 value = 1; // for sensitivity testing
657 } else if (hashCode == 3) {
658 value = ++GVars.hc_sequence;
659 } else if (hashCode == 4) {
660 value = cast_from_oop<intptr_t>(obj);
661 } else {
662 // Marsaglia's xor-shift scheme with thread-specific state
663 // This is probably the best overall implementation -- we'll
664 // likely make this the default in future releases.
665 unsigned t = self->_hashStateX;
666 t ^= (t << 11);
667 self->_hashStateX = self->_hashStateY;
668 self->_hashStateY = self->_hashStateZ;
669 self->_hashStateZ = self->_hashStateW;
670 unsigned v = self->_hashStateW;
671 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
672 self->_hashStateW = v;
673 value = v;
674 }
675
676 value &= markWord::hash_mask;
677 if (value == 0) value = 0xBAD;
678 assert(value != markWord::no_hash, "invariant");
679 return value;
680 }
681
682 intptr_t ObjectSynchronizer::FastHashCode(Thread* self, oop obj) {
683 if (UseBiasedLocking) {
684 // NOTE: many places throughout the JVM do not expect a safepoint
685 // to be taken here, in particular most operations on perm gen
686 // objects. However, we only ever bias Java instances and all of
687 // the call sites of identity_hash that might revoke biases have
688 // been checked to make sure they can handle a safepoint. The
689 // added check of the bias pattern is to avoid useless calls to
690 // thread-local storage.
691 if (obj->mark().has_bias_pattern()) {
692 // Handle for oop obj in case of STW safepoint
693 Handle hobj(self, obj);
694 // Relaxing assertion for bug 6320749.
695 assert(Universe::verify_in_progress() ||
696 !SafepointSynchronize::is_at_safepoint(),
697 "biases should not be seen by VM thread here");
698 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
699 obj = hobj();
700 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
701 }
702 }
703
704 // hashCode() is a heap mutator ...
705 // Relaxing assertion for bug 6320749.
706 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
707 !SafepointSynchronize::is_at_safepoint(), "invariant");
708 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
709 self->is_Java_thread() , "invariant");
710 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
711 ((JavaThread *)self)->thread_state() != _thread_blocked, "invariant");
712
713 ObjectMonitor* monitor = NULL;
714 markWord temp, test;
715 intptr_t hash;
716 markWord mark = read_stable_mark(obj);
717
718 // object should remain ineligible for biased locking
719 assert(!mark.has_bias_pattern(), "invariant");
720
721 if (mark.is_neutral()) {
722 hash = mark.hash(); // this is a normal header
723 if (hash != 0) { // if it has hash, just return it
724 return hash;
725 }
726 hash = get_next_hash(self, obj); // allocate a new hash code
727 temp = mark.copy_set_hash(hash); // merge the hash code into header
728 // use (machine word version) atomic operation to install the hash
729 test = obj->cas_set_mark(temp, mark);
730 if (test == mark) {
731 return hash;
732 }
733 // If atomic operation failed, we must inflate the header
734 // into heavy weight monitor. We could add more code here
735 // for fast path, but it does not worth the complexity.
736 } else if (mark.has_monitor()) {
737 monitor = mark.monitor();
738 temp = monitor->header();
739 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
740 hash = temp.hash();
741 if (hash != 0) {
742 return hash;
743 }
744 // Skip to the following code to reduce code size
745 } else if (self->is_lock_owned((address)mark.locker())) {
746 temp = mark.displaced_mark_helper(); // this is a lightweight monitor owned
747 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
748 hash = temp.hash(); // by current thread, check if the displaced
749 if (hash != 0) { // header contains hash code
750 return hash;
751 }
752 // WARNING:
753 // The displaced header in the BasicLock on a thread's stack
754 // is strictly immutable. It CANNOT be changed in ANY cases.
755 // So we have to inflate the stack lock into an ObjectMonitor
756 // even if the current thread owns the lock. The BasicLock on
757 // a thread's stack can be asynchronously read by other threads
758 // during an inflate() call so any change to that stack memory
759 // may not propagate to other threads correctly.
760 }
761
762 // Inflate the monitor to set hash code
763 monitor = inflate(self, obj, inflate_cause_hash_code);
764 // Load displaced header and check it has hash code
765 mark = monitor->header();
766 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
767 hash = mark.hash();
768 if (hash == 0) {
769 hash = get_next_hash(self, obj);
770 temp = mark.copy_set_hash(hash); // merge hash code into header
771 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
772 uintptr_t v = Atomic::cmpxchg(temp.value(), (volatile uintptr_t*)monitor->header_addr(), mark.value());
773 test = markWord(v);
774 if (test != mark) {
775 // The only non-deflation update to the ObjectMonitor's
776 // header/dmw field is to merge in the hash code. If someone
777 // adds a new usage of the header/dmw field, please update
778 // this code.
779 hash = test.hash();
780 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
781 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
782 }
783 }
784 // We finally get the hash
785 return hash;
786 }
787
788 // Deprecated -- use FastHashCode() instead.
789
790 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
791 return FastHashCode(Thread::current(), obj());
792 }
793
794
795 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
796 Handle h_obj) {
797 if (UseBiasedLocking) {
798 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
799 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
800 }
801
802 assert(thread == JavaThread::current(), "Can only be called on current thread");
803 oop obj = h_obj();
804
805 markWord mark = read_stable_mark(obj);
806
807 // Uncontended case, header points to stack
808 if (mark.has_locker()) {
809 return thread->is_lock_owned((address)mark.locker());
810 }
811 // Contended case, header points to ObjectMonitor (tagged pointer)
812 if (mark.has_monitor()) {
813 ObjectMonitor* monitor = mark.monitor();
814 return monitor->is_entered(thread) != 0;
815 }
816 // Unlocked case, header in place
817 assert(mark.is_neutral(), "sanity check");
818 return false;
819 }
820
821 // Be aware of this method could revoke bias of the lock object.
822 // This method queries the ownership of the lock handle specified by 'h_obj'.
823 // If the current thread owns the lock, it returns owner_self. If no
824 // thread owns the lock, it returns owner_none. Otherwise, it will return
825 // owner_other.
826 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
827 (JavaThread *self, Handle h_obj) {
828 // The caller must beware this method can revoke bias, and
829 // revocation can result in a safepoint.
830 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
831 assert(self->thread_state() != _thread_blocked, "invariant");
832
833 // Possible mark states: neutral, biased, stack-locked, inflated
834
835 if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) {
836 // CASE: biased
837 BiasedLocking::revoke_and_rebias(h_obj, false, self);
838 assert(!h_obj->mark().has_bias_pattern(),
839 "biases should be revoked by now");
840 }
841
842 assert(self == JavaThread::current(), "Can only be called on current thread");
843 oop obj = h_obj();
844 markWord mark = read_stable_mark(obj);
845
846 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
847 if (mark.has_locker()) {
848 return self->is_lock_owned((address)mark.locker()) ?
849 owner_self : owner_other;
850 }
851
852 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
853 // The Object:ObjectMonitor relationship is stable as long as we're
854 // not at a safepoint.
855 if (mark.has_monitor()) {
856 void* owner = mark.monitor()->_owner;
857 if (owner == NULL) return owner_none;
858 return (owner == self ||
859 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
860 }
861
862 // CASE: neutral
863 assert(mark.is_neutral(), "sanity check");
864 return owner_none; // it's unlocked
865 }
866
867 // FIXME: jvmti should call this
868 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
869 if (UseBiasedLocking) {
870 if (SafepointSynchronize::is_at_safepoint()) {
871 BiasedLocking::revoke_at_safepoint(h_obj);
872 } else {
873 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
874 }
875 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
876 }
877
878 oop obj = h_obj();
879 address owner = NULL;
880
881 markWord mark = read_stable_mark(obj);
882
883 // Uncontended case, header points to stack
884 if (mark.has_locker()) {
885 owner = (address) mark.locker();
886 }
887
888 // Contended case, header points to ObjectMonitor (tagged pointer)
889 else if (mark.has_monitor()) {
890 ObjectMonitor* monitor = mark.monitor();
891 assert(monitor != NULL, "monitor should be non-null");
892 owner = (address) monitor->owner();
893 }
894
895 if (owner != NULL) {
896 // owning_thread_from_monitor_owner() may also return NULL here
897 return Threads::owning_thread_from_monitor_owner(t_list, owner);
898 }
899
900 // Unlocked case, header in place
901 // Cannot have assertion since this object may have been
902 // locked by another thread when reaching here.
903 // assert(mark.is_neutral(), "sanity check");
904
905 return NULL;
906 }
907
908 // Visitors ...
909
910 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
911 PaddedObjectMonitor* block = OrderAccess::load_acquire(&g_block_list);
912 while (block != NULL) {
913 assert(block->object() == CHAINMARKER, "must be a block header");
914 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
915 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
916 oop object = (oop)mid->object();
917 if (object != NULL) {
918 // Only process with closure if the object is set.
919 closure->do_monitor(mid);
920 }
921 }
922 block = (PaddedObjectMonitor*)block->_next_om;
923 }
924 }
925
926 static bool monitors_used_above_threshold() {
927 if (g_om_population == 0) {
928 return false;
929 }
930 int monitors_used = g_om_population - g_om_free_count;
931 int monitor_usage = (monitors_used * 100LL) / g_om_population;
932 return monitor_usage > MonitorUsedDeflationThreshold;
933 }
934
935 bool ObjectSynchronizer::is_cleanup_needed() {
936 if (MonitorUsedDeflationThreshold > 0) {
937 return monitors_used_above_threshold();
938 }
939 return false;
940 }
941
942 void ObjectSynchronizer::oops_do(OopClosure* f) {
943 // We only scan the global used list here (for moribund threads), and
944 // the thread-local monitors in Thread::oops_do().
945 global_used_oops_do(f);
946 }
947
948 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
949 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
950 list_oops_do(g_om_in_use_list, f);
951 }
952
953 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
954 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
955 list_oops_do(thread->om_in_use_list, f);
956 }
957
958 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
959 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
960 ObjectMonitor* mid;
961 for (mid = list; mid != NULL; mid = mid->_next_om) {
962 if (mid->object() != NULL) {
963 f->do_oop((oop*)mid->object_addr());
964 }
965 }
966 }
967
968
969 // -----------------------------------------------------------------------------
970 // ObjectMonitor Lifecycle
971 // -----------------------
972 // Inflation unlinks monitors from the global g_free_list and
973 // associates them with objects. Deflation -- which occurs at
974 // STW-time -- disassociates idle monitors from objects. Such
975 // scavenged monitors are returned to the g_free_list.
976 //
977 // The global list is protected by gListLock. All the critical sections
978 // are short and operate in constant-time.
979 //
980 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
981 //
982 // Lifecycle:
983 // -- unassigned and on the global free list
984 // -- unassigned and on a thread's private om_free_list
985 // -- assigned to an object. The object is inflated and the mark refers
986 // to the objectmonitor.
987
988
989 // Constraining monitor pool growth via MonitorBound ...
990 //
991 // If MonitorBound is not set (<= 0), MonitorBound checks are disabled.
992 //
993 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
994 // the rate of scavenging is driven primarily by GC. As such, we can find
995 // an inordinate number of monitors in circulation.
996 // To avoid that scenario we can artificially induce a STW safepoint
997 // if the pool appears to be growing past some reasonable bound.
998 // Generally we favor time in space-time tradeoffs, but as there's no
999 // natural back-pressure on the # of extant monitors we need to impose some
1000 // type of limit. Beware that if MonitorBound is set to too low a value
1001 // we could just loop. In addition, if MonitorBound is set to a low value
1002 // we'll incur more safepoints, which are harmful to performance.
1003 // See also: GuaranteedSafepointInterval
1004 //
1005 // The current implementation uses asynchronous VM operations.
1006 //
1007 // If MonitorBound is set, the boundry applies to
1008 // (g_om_population - g_om_free_count)
1009 // i.e., if there are not enough ObjectMonitors on the global free list,
1010 // then a safepoint deflation is induced. Picking a good MonitorBound value
1011 // is non-trivial.
1012
1013 static void InduceScavenge(Thread* self, const char * Whence) {
1014 // Induce STW safepoint to trim monitors
1015 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1016 // More precisely, trigger an asynchronous STW safepoint as the number
1017 // of active monitors passes the specified threshold.
1018 // TODO: assert thread state is reasonable
1019
1020 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1021 // Induce a 'null' safepoint to scavenge monitors
1022 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1023 // to the VMthread and have a lifespan longer than that of this activation record.
1024 // The VMThread will delete the op when completed.
1025 VMThread::execute(new VM_ScavengeMonitors());
1026 }
1027 }
1028
1029 ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self) {
1030 // A large MAXPRIVATE value reduces both list lock contention
1031 // and list coherency traffic, but also tends to increase the
1032 // number of ObjectMonitors in circulation as well as the STW
1033 // scavenge costs. As usual, we lean toward time in space-time
1034 // tradeoffs.
1035 const int MAXPRIVATE = 1024;
1036 stringStream ss;
1037 for (;;) {
1038 ObjectMonitor* m;
1039
1040 // 1: try to allocate from the thread's local om_free_list.
1041 // Threads will attempt to allocate first from their local list, then
1042 // from the global list, and only after those attempts fail will the thread
1043 // attempt to instantiate new monitors. Thread-local free lists take
1044 // heat off the gListLock and improve allocation latency, as well as reducing
1045 // coherency traffic on the shared global list.
1046 m = self->om_free_list;
1047 if (m != NULL) {
1048 self->om_free_list = m->_next_om;
1049 self->om_free_count--;
1050 guarantee(m->object() == NULL, "invariant");
1051 m->_next_om = self->om_in_use_list;
1052 self->om_in_use_list = m;
1053 self->om_in_use_count++;
1054 return m;
1055 }
1056
1057 // 2: try to allocate from the global g_free_list
1058 // CONSIDER: use muxTry() instead of muxAcquire().
1059 // If the muxTry() fails then drop immediately into case 3.
1060 // If we're using thread-local free lists then try
1061 // to reprovision the caller's free list.
1062 if (g_free_list != NULL) {
1063 // Reprovision the thread's om_free_list.
1064 // Use bulk transfers to reduce the allocation rate and heat
1065 // on various locks.
1066 Thread::muxAcquire(&gListLock, "om_alloc(1)");
1067 for (int i = self->om_free_provision; --i >= 0 && g_free_list != NULL;) {
1068 g_om_free_count--;
1069 ObjectMonitor* take = g_free_list;
1070 g_free_list = take->_next_om;
1071 guarantee(take->object() == NULL, "invariant");
1072 take->Recycle();
1073 om_release(self, take, false);
1074 }
1075 Thread::muxRelease(&gListLock);
1076 self->om_free_provision += 1 + (self->om_free_provision/2);
1077 if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE;
1078
1079 const int mx = MonitorBound;
1080 if (mx > 0 && (g_om_population-g_om_free_count) > mx) {
1081 // Not enough ObjectMonitors on the global free list.
1082 // We can't safely induce a STW safepoint from om_alloc() as our thread
1083 // state may not be appropriate for such activities and callers may hold
1084 // naked oops, so instead we defer the action.
1085 InduceScavenge(self, "om_alloc");
1086 }
1087 continue;
1088 }
1089
1090 // 3: allocate a block of new ObjectMonitors
1091 // Both the local and global free lists are empty -- resort to malloc().
1092 // In the current implementation ObjectMonitors are TSM - immortal.
1093 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1094 // each ObjectMonitor to start at the beginning of a cache line,
1095 // so we use align_up().
1096 // A better solution would be to use C++ placement-new.
1097 // BEWARE: As it stands currently, we don't run the ctors!
1098 assert(_BLOCKSIZE > 1, "invariant");
1099 size_t neededsize = sizeof(PaddedObjectMonitor) * _BLOCKSIZE;
1100 PaddedObjectMonitor* temp;
1101 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1102 void* real_malloc_addr = (void*)NEW_C_HEAP_ARRAY(char, aligned_size,
1103 mtInternal);
1104 temp = (PaddedObjectMonitor*)align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE);
1105
1106 // NOTE: (almost) no way to recover if allocation failed.
1107 // We might be able to induce a STW safepoint and scavenge enough
1108 // ObjectMonitors to permit progress.
1109 if (temp == NULL) {
1110 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1111 "Allocate ObjectMonitors");
1112 }
1113 (void)memset((void *) temp, 0, neededsize);
1114
1115 // Format the block.
1116 // initialize the linked list, each monitor points to its next
1117 // forming the single linked free list, the very first monitor
1118 // will points to next block, which forms the block list.
1119 // The trick of using the 1st element in the block as g_block_list
1120 // linkage should be reconsidered. A better implementation would
1121 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1122
1123 for (int i = 1; i < _BLOCKSIZE; i++) {
1124 temp[i]._next_om = (ObjectMonitor *)&temp[i+1];
1125 }
1126
1127 // terminate the last monitor as the end of list
1128 temp[_BLOCKSIZE - 1]._next_om = NULL;
1129
1130 // Element [0] is reserved for global list linkage
1131 temp[0].set_object(CHAINMARKER);
1132
1133 // Consider carving out this thread's current request from the
1134 // block in hand. This avoids some lock traffic and redundant
1135 // list activity.
1136
1137 // Acquire the gListLock to manipulate g_block_list and g_free_list.
1138 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1139 Thread::muxAcquire(&gListLock, "om_alloc(2)");
1140 g_om_population += _BLOCKSIZE-1;
1141 g_om_free_count += _BLOCKSIZE-1;
1142
1143 // Add the new block to the list of extant blocks (g_block_list).
1144 // The very first ObjectMonitor in a block is reserved and dedicated.
1145 // It serves as blocklist "next" linkage.
1146 temp[0]._next_om = g_block_list;
1147 // There are lock-free uses of g_block_list so make sure that
1148 // the previous stores happen before we update g_block_list.
1149 OrderAccess::release_store(&g_block_list, temp);
1150
1151 // Add the new string of ObjectMonitors to the global free list
1152 temp[_BLOCKSIZE - 1]._next_om = g_free_list;
1153 g_free_list = temp + 1;
1154 Thread::muxRelease(&gListLock);
1155 }
1156 }
1157
1158 // Place "m" on the caller's private per-thread om_free_list.
1159 // In practice there's no need to clamp or limit the number of
1160 // monitors on a thread's om_free_list as the only non-allocation time
1161 // we'll call om_release() is to return a monitor to the free list after
1162 // a CAS attempt failed. This doesn't allow unbounded #s of monitors to
1163 // accumulate on a thread's free list.
1164 //
1165 // Key constraint: all ObjectMonitors on a thread's free list and the global
1166 // free list must have their object field set to null. This prevents the
1167 // scavenger -- deflate_monitor_list() -- from reclaiming them while we
1168 // are trying to release them.
1169
1170 void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m,
1171 bool from_per_thread_alloc) {
1172 guarantee(m->header().value() == 0, "invariant");
1173 guarantee(m->object() == NULL, "invariant");
1174 stringStream ss;
1175 guarantee((m->is_busy() | m->_recursions) == 0, "freeing in-use monitor: "
1176 "%s, recursions=" INTPTR_FORMAT, m->is_busy_to_string(&ss),
1177 m->_recursions);
1178 // _next_om is used for both per-thread in-use and free lists so
1179 // we have to remove 'm' from the in-use list first (as needed).
1180 if (from_per_thread_alloc) {
1181 // Need to remove 'm' from om_in_use_list.
1182 ObjectMonitor* cur_mid_in_use = NULL;
1183 bool extracted = false;
1184 for (ObjectMonitor* mid = self->om_in_use_list; mid != NULL; cur_mid_in_use = mid, mid = mid->_next_om) {
1185 if (m == mid) {
1186 // extract from per-thread in-use list
1187 if (mid == self->om_in_use_list) {
1188 self->om_in_use_list = mid->_next_om;
1189 } else if (cur_mid_in_use != NULL) {
1190 cur_mid_in_use->_next_om = mid->_next_om; // maintain the current thread in-use list
1191 }
1192 extracted = true;
1193 self->om_in_use_count--;
1194 break;
1195 }
1196 }
1197 assert(extracted, "Should have extracted from in-use list");
1198 }
1199
1200 m->_next_om = self->om_free_list;
1201 self->om_free_list = m;
1202 self->om_free_count++;
1203 }
1204
1205 // Return ObjectMonitors on a moribund thread's free and in-use
1206 // lists to the appropriate global lists. The ObjectMonitors on the
1207 // per-thread in-use list may still be in use by other threads.
1208 //
1209 // We currently call om_flush() from Threads::remove() before the
1210 // thread has been excised from the thread list and is no longer a
1211 // mutator. This means that om_flush() cannot run concurrently with
1212 // a safepoint and interleave with deflate_idle_monitors(). In
1213 // particular, this ensures that the thread's in-use monitors are
1214 // scanned by a GC safepoint, either via Thread::oops_do() (before
1215 // om_flush() is called) or via ObjectSynchronizer::oops_do() (after
1216 // om_flush() is called).
1217
1218 void ObjectSynchronizer::om_flush(Thread* self) {
1219 ObjectMonitor* free_list = self->om_free_list;
1220 ObjectMonitor* free_tail = NULL;
1221 int free_count = 0;
1222 if (free_list != NULL) {
1223 ObjectMonitor* s;
1224 // The thread is going away. Set 'free_tail' to the last per-thread free
1225 // monitor which will be linked to g_free_list below under the gListLock.
1226 stringStream ss;
1227 for (s = free_list; s != NULL; s = s->_next_om) {
1228 free_count++;
1229 free_tail = s;
1230 guarantee(s->object() == NULL, "invariant");
1231 guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss));
1232 }
1233 guarantee(free_tail != NULL, "invariant");
1234 assert(self->om_free_count == free_count, "free-count off");
1235 self->om_free_list = NULL;
1236 self->om_free_count = 0;
1237 }
1238
1239 ObjectMonitor* in_use_list = self->om_in_use_list;
1240 ObjectMonitor* in_use_tail = NULL;
1241 int in_use_count = 0;
1242 if (in_use_list != NULL) {
1243 // The thread is going away, however the ObjectMonitors on the
1244 // om_in_use_list may still be in-use by other threads. Link
1245 // them to in_use_tail, which will be linked into the global
1246 // in-use list g_om_in_use_list below, under the gListLock.
1247 ObjectMonitor *cur_om;
1248 for (cur_om = in_use_list; cur_om != NULL; cur_om = cur_om->_next_om) {
1249 in_use_tail = cur_om;
1250 in_use_count++;
1251 }
1252 guarantee(in_use_tail != NULL, "invariant");
1253 assert(self->om_in_use_count == in_use_count, "in-use count off");
1254 self->om_in_use_list = NULL;
1255 self->om_in_use_count = 0;
1256 }
1257
1258 Thread::muxAcquire(&gListLock, "om_flush");
1259 if (free_tail != NULL) {
1260 free_tail->_next_om = g_free_list;
1261 g_free_list = free_list;
1262 g_om_free_count += free_count;
1263 }
1264
1265 if (in_use_tail != NULL) {
1266 in_use_tail->_next_om = g_om_in_use_list;
1267 g_om_in_use_list = in_use_list;
1268 g_om_in_use_count += in_use_count;
1269 }
1270
1271 Thread::muxRelease(&gListLock);
1272
1273 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1274 LogStreamHandle(Info, monitorinflation) lsh_info;
1275 LogStream* ls = NULL;
1276 if (log_is_enabled(Debug, monitorinflation)) {
1277 ls = &lsh_debug;
1278 } else if ((free_count != 0 || in_use_count != 0) &&
1279 log_is_enabled(Info, monitorinflation)) {
1280 ls = &lsh_info;
1281 }
1282 if (ls != NULL) {
1283 ls->print_cr("om_flush: jt=" INTPTR_FORMAT ", free_count=%d"
1284 ", in_use_count=%d" ", om_free_provision=%d",
1285 p2i(self), free_count, in_use_count, self->om_free_provision);
1286 }
1287 }
1288
1289 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1290 const oop obj,
1291 ObjectSynchronizer::InflateCause cause) {
1292 assert(event != NULL, "invariant");
1293 assert(event->should_commit(), "invariant");
1294 event->set_monitorClass(obj->klass());
1295 event->set_address((uintptr_t)(void*)obj);
1296 event->set_cause((u1)cause);
1297 event->commit();
1298 }
1299
1300 // Fast path code shared by multiple functions
1301 void ObjectSynchronizer::inflate_helper(oop obj) {
1302 markWord mark = obj->mark();
1303 if (mark.has_monitor()) {
1304 assert(ObjectSynchronizer::verify_objmon_isinpool(mark.monitor()), "monitor is invalid");
1305 assert(mark.monitor()->header().is_neutral(), "monitor must record a good object header");
1306 return;
1307 }
1308 inflate(Thread::current(), obj, inflate_cause_vm_internal);
1309 }
1310
1311 ObjectMonitor* ObjectSynchronizer::inflate(Thread* self,
1312 oop object,
1313 const InflateCause cause) {
1314 // Inflate mutates the heap ...
1315 // Relaxing assertion for bug 6320749.
1316 assert(Universe::verify_in_progress() ||
1317 !SafepointSynchronize::is_at_safepoint(), "invariant");
1318
1319 EventJavaMonitorInflate event;
1320
1321 for (;;) {
1322 const markWord mark = object->mark();
1323 assert(!mark.has_bias_pattern(), "invariant");
1324
1325 // The mark can be in one of the following states:
1326 // * Inflated - just return
1327 // * Stack-locked - coerce it to inflated
1328 // * INFLATING - busy wait for conversion to complete
1329 // * Neutral - aggressively inflate the object.
1330 // * BIASED - Illegal. We should never see this
1331
1332 // CASE: inflated
1333 if (mark.has_monitor()) {
1334 ObjectMonitor* inf = mark.monitor();
1335 markWord dmw = inf->header();
1336 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1337 assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1338 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1339 return inf;
1340 }
1341
1342 // CASE: inflation in progress - inflating over a stack-lock.
1343 // Some other thread is converting from stack-locked to inflated.
1344 // Only that thread can complete inflation -- other threads must wait.
1345 // The INFLATING value is transient.
1346 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1347 // We could always eliminate polling by parking the thread on some auxiliary list.
1348 if (mark == markWord::INFLATING()) {
1349 read_stable_mark(object);
1350 continue;
1351 }
1352
1353 // CASE: stack-locked
1354 // Could be stack-locked either by this thread or by some other thread.
1355 //
1356 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1357 // to install INFLATING into the mark word. We originally installed INFLATING,
1358 // allocated the objectmonitor, and then finally STed the address of the
1359 // objectmonitor into the mark. This was correct, but artificially lengthened
1360 // the interval in which INFLATED appeared in the mark, thus increasing
1361 // the odds of inflation contention.
1362 //
1363 // We now use per-thread private objectmonitor free lists.
1364 // These list are reprovisioned from the global free list outside the
1365 // critical INFLATING...ST interval. A thread can transfer
1366 // multiple objectmonitors en-mass from the global free list to its local free list.
1367 // This reduces coherency traffic and lock contention on the global free list.
1368 // Using such local free lists, it doesn't matter if the om_alloc() call appears
1369 // before or after the CAS(INFLATING) operation.
1370 // See the comments in om_alloc().
1371
1372 LogStreamHandle(Trace, monitorinflation) lsh;
1373
1374 if (mark.has_locker()) {
1375 ObjectMonitor* m = om_alloc(self);
1376 // Optimistically prepare the objectmonitor - anticipate successful CAS
1377 // We do this before the CAS in order to minimize the length of time
1378 // in which INFLATING appears in the mark.
1379 m->Recycle();
1380 m->_Responsible = NULL;
1381 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1382
1383 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1384 if (cmp != mark) {
1385 om_release(self, m, true);
1386 continue; // Interference -- just retry
1387 }
1388
1389 // We've successfully installed INFLATING (0) into the mark-word.
1390 // This is the only case where 0 will appear in a mark-word.
1391 // Only the singular thread that successfully swings the mark-word
1392 // to 0 can perform (or more precisely, complete) inflation.
1393 //
1394 // Why do we CAS a 0 into the mark-word instead of just CASing the
1395 // mark-word from the stack-locked value directly to the new inflated state?
1396 // Consider what happens when a thread unlocks a stack-locked object.
1397 // It attempts to use CAS to swing the displaced header value from the
1398 // on-stack BasicLock back into the object header. Recall also that the
1399 // header value (hash code, etc) can reside in (a) the object header, or
1400 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1401 // header in an ObjectMonitor. The inflate() routine must copy the header
1402 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1403 // the while preserving the hashCode stability invariants. If the owner
1404 // decides to release the lock while the value is 0, the unlock will fail
1405 // and control will eventually pass from slow_exit() to inflate. The owner
1406 // will then spin, waiting for the 0 value to disappear. Put another way,
1407 // the 0 causes the owner to stall if the owner happens to try to
1408 // drop the lock (restoring the header from the BasicLock to the object)
1409 // while inflation is in-progress. This protocol avoids races that might
1410 // would otherwise permit hashCode values to change or "flicker" for an object.
1411 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1412 // 0 serves as a "BUSY" inflate-in-progress indicator.
1413
1414
1415 // fetch the displaced mark from the owner's stack.
1416 // The owner can't die or unwind past the lock while our INFLATING
1417 // object is in the mark. Furthermore the owner can't complete
1418 // an unlock on the object, either.
1419 markWord dmw = mark.displaced_mark_helper();
1420 // Catch if the object's header is not neutral (not locked and
1421 // not marked is what we care about here).
1422 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1423
1424 // Setup monitor fields to proper values -- prepare the monitor
1425 m->set_header(dmw);
1426
1427 // Optimization: if the mark.locker stack address is associated
1428 // with this thread we could simply set m->_owner = self.
1429 // Note that a thread can inflate an object
1430 // that it has stack-locked -- as might happen in wait() -- directly
1431 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1432 m->set_owner(mark.locker());
1433 m->set_object(object);
1434 // TODO-FIXME: assert BasicLock->dhw != 0.
1435
1436 // Must preserve store ordering. The monitor state must
1437 // be stable at the time of publishing the monitor address.
1438 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1439 object->release_set_mark(markWord::encode(m));
1440
1441 // Hopefully the performance counters are allocated on distinct cache lines
1442 // to avoid false sharing on MP systems ...
1443 OM_PERFDATA_OP(Inflations, inc());
1444 if (log_is_enabled(Trace, monitorinflation)) {
1445 ResourceMark rm(self);
1446 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1447 INTPTR_FORMAT ", type='%s'", p2i(object),
1448 object->mark().value(), object->klass()->external_name());
1449 }
1450 if (event.should_commit()) {
1451 post_monitor_inflate_event(&event, object, cause);
1452 }
1453 return m;
1454 }
1455
1456 // CASE: neutral
1457 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1458 // If we know we're inflating for entry it's better to inflate by swinging a
1459 // pre-locked ObjectMonitor pointer into the object header. A successful
1460 // CAS inflates the object *and* confers ownership to the inflating thread.
1461 // In the current implementation we use a 2-step mechanism where we CAS()
1462 // to inflate and then CAS() again to try to swing _owner from NULL to self.
1463 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1464 // would be useful.
1465
1466 // Catch if the object's header is not neutral (not locked and
1467 // not marked is what we care about here).
1468 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1469 ObjectMonitor* m = om_alloc(self);
1470 // prepare m for installation - set monitor to initial state
1471 m->Recycle();
1472 m->set_header(mark);
1473 m->set_object(object);
1474 m->_Responsible = NULL;
1475 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1476
1477 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1478 m->set_header(markWord::zero());
1479 m->set_object(NULL);
1480 m->Recycle();
1481 om_release(self, m, true);
1482 m = NULL;
1483 continue;
1484 // interference - the markword changed - just retry.
1485 // The state-transitions are one-way, so there's no chance of
1486 // live-lock -- "Inflated" is an absorbing state.
1487 }
1488
1489 // Hopefully the performance counters are allocated on distinct
1490 // cache lines to avoid false sharing on MP systems ...
1491 OM_PERFDATA_OP(Inflations, inc());
1492 if (log_is_enabled(Trace, monitorinflation)) {
1493 ResourceMark rm(self);
1494 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1495 INTPTR_FORMAT ", type='%s'", p2i(object),
1496 object->mark().value(), object->klass()->external_name());
1497 }
1498 if (event.should_commit()) {
1499 post_monitor_inflate_event(&event, object, cause);
1500 }
1501 return m;
1502 }
1503 }
1504
1505
1506 // We maintain a list of in-use monitors for each thread.
1507 //
1508 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1509 // deflate_idle_monitors() scans only a global list of in-use monitors which
1510 // is populated only as a thread dies (see om_flush()).
1511 //
1512 // These operations are called at all safepoints, immediately after mutators
1513 // are stopped, but before any objects have moved. Collectively they traverse
1514 // the population of in-use monitors, deflating where possible. The scavenged
1515 // monitors are returned to the global monitor free list.
1516 //
1517 // Beware that we scavenge at *every* stop-the-world point. Having a large
1518 // number of monitors in-use could negatively impact performance. We also want
1519 // to minimize the total # of monitors in circulation, as they incur a small
1520 // footprint penalty.
1521 //
1522 // Perversely, the heap size -- and thus the STW safepoint rate --
1523 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1524 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1525 // This is an unfortunate aspect of this design.
1526
1527 // Deflate a single monitor if not in-use
1528 // Return true if deflated, false if in-use
1529 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1530 ObjectMonitor** free_head_p,
1531 ObjectMonitor** free_tail_p) {
1532 bool deflated;
1533 // Normal case ... The monitor is associated with obj.
1534 const markWord mark = obj->mark();
1535 guarantee(mark == markWord::encode(mid), "should match: mark="
1536 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(),
1537 markWord::encode(mid).value());
1538 // Make sure that mark.monitor() and markWord::encode() agree:
1539 guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
1540 ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid));
1541 const markWord dmw = mid->header();
1542 guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1543
1544 if (mid->is_busy()) {
1545 deflated = false;
1546 } else {
1547 // Deflate the monitor if it is no longer being used
1548 // It's idle - scavenge and return to the global free list
1549 // plain old deflation ...
1550 if (log_is_enabled(Trace, monitorinflation)) {
1551 ResourceMark rm;
1552 log_trace(monitorinflation)("deflate_monitor: "
1553 "object=" INTPTR_FORMAT ", mark="
1554 INTPTR_FORMAT ", type='%s'", p2i(obj),
1555 mark.value(), obj->klass()->external_name());
1556 }
1557
1558 // Restore the header back to obj
1559 obj->release_set_mark(dmw);
1560 mid->clear();
1561
1562 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
1563 p2i(mid->object()));
1564
1565 // Move the deflated ObjectMonitor to the working free list
1566 // defined by free_head_p and free_tail_p.
1567 if (*free_head_p == NULL) *free_head_p = mid;
1568 if (*free_tail_p != NULL) {
1569 // We append to the list so the caller can use mid->_next_om
1570 // to fix the linkages in its context.
1571 ObjectMonitor* prevtail = *free_tail_p;
1572 // Should have been cleaned up by the caller:
1573 assert(prevtail->_next_om == NULL, "cleaned up deflated?");
1574 prevtail->_next_om = mid;
1575 }
1576 *free_tail_p = mid;
1577 // At this point, mid->_next_om still refers to its current
1578 // value and another ObjectMonitor's _next_om field still
1579 // refers to this ObjectMonitor. Those linkages have to be
1580 // cleaned up by the caller who has the complete context.
1581 deflated = true;
1582 }
1583 return deflated;
1584 }
1585
1586 // Walk a given monitor list, and deflate idle monitors
1587 // The given list could be a per-thread list or a global list
1588 // Caller acquires gListLock as needed.
1589 //
1590 // In the case of parallel processing of thread local monitor lists,
1591 // work is done by Threads::parallel_threads_do() which ensures that
1592 // each Java thread is processed by exactly one worker thread, and
1593 // thus avoid conflicts that would arise when worker threads would
1594 // process the same monitor lists concurrently.
1595 //
1596 // See also ParallelSPCleanupTask and
1597 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1598 // Threads::parallel_java_threads_do() in thread.cpp.
1599 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** list_p,
1600 ObjectMonitor** free_head_p,
1601 ObjectMonitor** free_tail_p) {
1602 ObjectMonitor* mid;
1603 ObjectMonitor* next;
1604 ObjectMonitor* cur_mid_in_use = NULL;
1605 int deflated_count = 0;
1606
1607 for (mid = *list_p; mid != NULL;) {
1608 oop obj = (oop) mid->object();
1609 if (obj != NULL && deflate_monitor(mid, obj, free_head_p, free_tail_p)) {
1610 // Deflation succeeded and already updated free_head_p and
1611 // free_tail_p as needed. Finish the move to the local free list
1612 // by unlinking mid from the global or per-thread in-use list.
1613 if (mid == *list_p) {
1614 *list_p = mid->_next_om;
1615 } else if (cur_mid_in_use != NULL) {
1616 cur_mid_in_use->_next_om = mid->_next_om; // maintain the current thread in-use list
1617 }
1618 next = mid->_next_om;
1619 mid->_next_om = NULL; // This mid is current tail in the free_head_p list
1620 mid = next;
1621 deflated_count++;
1622 } else {
1623 cur_mid_in_use = mid;
1624 mid = mid->_next_om;
1625 }
1626 }
1627 return deflated_count;
1628 }
1629
1630 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1631 counters->n_in_use = 0; // currently associated with objects
1632 counters->n_in_circulation = 0; // extant
1633 counters->n_scavenged = 0; // reclaimed (global and per-thread)
1634 counters->per_thread_scavenged = 0; // per-thread scavenge total
1635 counters->per_thread_times = 0.0; // per-thread scavenge times
1636 }
1637
1638 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
1639 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1640 bool deflated = false;
1641
1642 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
1643 ObjectMonitor* free_tail_p = NULL;
1644 elapsedTimer timer;
1645
1646 if (log_is_enabled(Info, monitorinflation)) {
1647 timer.start();
1648 }
1649
1650 // Prevent om_flush from changing mids in Thread dtor's during deflation
1651 // And in case the vm thread is acquiring a lock during a safepoint
1652 // See e.g. 6320749
1653 Thread::muxAcquire(&gListLock, "deflate_idle_monitors");
1654
1655 // Note: the thread-local monitors lists get deflated in
1656 // a separate pass. See deflate_thread_local_monitors().
1657
1658 // For moribund threads, scan g_om_in_use_list
1659 int deflated_count = 0;
1660 if (g_om_in_use_list) {
1661 counters->n_in_circulation += g_om_in_use_count;
1662 deflated_count = deflate_monitor_list((ObjectMonitor **)&g_om_in_use_list, &free_head_p, &free_tail_p);
1663 g_om_in_use_count -= deflated_count;
1664 counters->n_scavenged += deflated_count;
1665 counters->n_in_use += g_om_in_use_count;
1666 }
1667
1668 if (free_head_p != NULL) {
1669 // Move the deflated ObjectMonitors back to the global free list.
1670 guarantee(free_tail_p != NULL && counters->n_scavenged > 0, "invariant");
1671 assert(free_tail_p->_next_om == NULL, "invariant");
1672 // constant-time list splice - prepend scavenged segment to g_free_list
1673 free_tail_p->_next_om = g_free_list;
1674 g_free_list = free_head_p;
1675 }
1676 Thread::muxRelease(&gListLock);
1677 timer.stop();
1678
1679 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1680 LogStreamHandle(Info, monitorinflation) lsh_info;
1681 LogStream* ls = NULL;
1682 if (log_is_enabled(Debug, monitorinflation)) {
1683 ls = &lsh_debug;
1684 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
1685 ls = &lsh_info;
1686 }
1687 if (ls != NULL) {
1688 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
1689 }
1690 }
1691
1692 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1693 // Report the cumulative time for deflating each thread's idle
1694 // monitors. Note: if the work is split among more than one
1695 // worker thread, then the reported time will likely be more
1696 // than a beginning to end measurement of the phase.
1697 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged);
1698
1699 g_om_free_count += counters->n_scavenged;
1700
1701 if (log_is_enabled(Debug, monitorinflation)) {
1702 // exit_globals()'s call to audit_and_print_stats() is done
1703 // at the Info level.
1704 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
1705 } else if (log_is_enabled(Info, monitorinflation)) {
1706 Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors");
1707 log_info(monitorinflation)("g_om_population=%d, g_om_in_use_count=%d, "
1708 "g_om_free_count=%d", g_om_population,
1709 g_om_in_use_count, g_om_free_count);
1710 Thread::muxRelease(&gListLock);
1711 }
1712
1713 ForceMonitorScavenge = 0; // Reset
1714
1715 OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged));
1716 OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation));
1717
1718 GVars.stw_random = os::random();
1719 GVars.stw_cycle++;
1720 }
1721
1722 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
1723 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1724
1725 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
1726 ObjectMonitor* free_tail_p = NULL;
1727 elapsedTimer timer;
1728
1729 if (log_is_enabled(Info, safepoint, cleanup) ||
1730 log_is_enabled(Info, monitorinflation)) {
1731 timer.start();
1732 }
1733
1734 int deflated_count = deflate_monitor_list(thread->om_in_use_list_addr(), &free_head_p, &free_tail_p);
1735
1736 Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors");
1737
1738 // Adjust counters
1739 counters->n_in_circulation += thread->om_in_use_count;
1740 thread->om_in_use_count -= deflated_count;
1741 counters->n_scavenged += deflated_count;
1742 counters->n_in_use += thread->om_in_use_count;
1743 counters->per_thread_scavenged += deflated_count;
1744
1745 if (free_head_p != NULL) {
1746 // Move the deflated ObjectMonitors back to the global free list.
1747 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
1748 assert(free_tail_p->_next_om == NULL, "invariant");
1749
1750 // constant-time list splice - prepend scavenged segment to g_free_list
1751 free_tail_p->_next_om = g_free_list;
1752 g_free_list = free_head_p;
1753 }
1754
1755 timer.stop();
1756 // Safepoint logging cares about cumulative per_thread_times and
1757 // we'll capture most of the cost, but not the muxRelease() which
1758 // should be cheap.
1759 counters->per_thread_times += timer.seconds();
1760
1761 Thread::muxRelease(&gListLock);
1762
1763 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1764 LogStreamHandle(Info, monitorinflation) lsh_info;
1765 LogStream* ls = NULL;
1766 if (log_is_enabled(Debug, monitorinflation)) {
1767 ls = &lsh_debug;
1768 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
1769 ls = &lsh_info;
1770 }
1771 if (ls != NULL) {
1772 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
1773 }
1774 }
1775
1776 // Monitor cleanup on JavaThread::exit
1777
1778 // Iterate through monitor cache and attempt to release thread's monitors
1779 // Gives up on a particular monitor if an exception occurs, but continues
1780 // the overall iteration, swallowing the exception.
1781 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1782 private:
1783 TRAPS;
1784
1785 public:
1786 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1787 void do_monitor(ObjectMonitor* mid) {
1788 if (mid->owner() == THREAD) {
1789 (void)mid->complete_exit(CHECK);
1790 }
1791 }
1792 };
1793
1794 // Release all inflated monitors owned by THREAD. Lightweight monitors are
1795 // ignored. This is meant to be called during JNI thread detach which assumes
1796 // all remaining monitors are heavyweight. All exceptions are swallowed.
1797 // Scanning the extant monitor list can be time consuming.
1798 // A simple optimization is to add a per-thread flag that indicates a thread
1799 // called jni_monitorenter() during its lifetime.
1800 //
1801 // Instead of No_Savepoint_Verifier it might be cheaper to
1802 // use an idiom of the form:
1803 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1804 // <code that must not run at safepoint>
1805 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1806 // Since the tests are extremely cheap we could leave them enabled
1807 // for normal product builds.
1808
1809 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1810 assert(THREAD == JavaThread::current(), "must be current Java thread");
1811 NoSafepointVerifier nsv;
1812 ReleaseJavaMonitorsClosure rjmc(THREAD);
1813 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
1814 ObjectSynchronizer::monitors_iterate(&rjmc);
1815 Thread::muxRelease(&gListLock);
1816 THREAD->clear_pending_exception();
1817 }
1818
1819 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1820 switch (cause) {
1821 case inflate_cause_vm_internal: return "VM Internal";
1822 case inflate_cause_monitor_enter: return "Monitor Enter";
1823 case inflate_cause_wait: return "Monitor Wait";
1824 case inflate_cause_notify: return "Monitor Notify";
1825 case inflate_cause_hash_code: return "Monitor Hash Code";
1826 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1827 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1828 default:
1829 ShouldNotReachHere();
1830 }
1831 return "Unknown";
1832 }
1833
1834 //------------------------------------------------------------------------------
1835 // Debugging code
1836
1837 u_char* ObjectSynchronizer::get_gvars_addr() {
1838 return (u_char*)&GVars;
1839 }
1840
1841 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1842 return (u_char*)&GVars.hc_sequence;
1843 }
1844
1845 size_t ObjectSynchronizer::get_gvars_size() {
1846 return sizeof(SharedGlobals);
1847 }
1848
1849 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1850 return (u_char*)&GVars.stw_random;
1851 }
1852
1853 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1854 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1855
1856 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1857 LogStreamHandle(Info, monitorinflation) lsh_info;
1858 LogStreamHandle(Trace, monitorinflation) lsh_trace;
1859 LogStream* ls = NULL;
1860 if (log_is_enabled(Trace, monitorinflation)) {
1861 ls = &lsh_trace;
1862 } else if (log_is_enabled(Debug, monitorinflation)) {
1863 ls = &lsh_debug;
1864 } else if (log_is_enabled(Info, monitorinflation)) {
1865 ls = &lsh_info;
1866 }
1867 assert(ls != NULL, "sanity check");
1868
1869 if (!on_exit) {
1870 // Not at VM exit so grab the global list lock.
1871 Thread::muxAcquire(&gListLock, "audit_and_print_stats");
1872 }
1873
1874 // Log counts for the global and per-thread monitor lists:
1875 int chk_om_population = log_monitor_list_counts(ls);
1876 int error_cnt = 0;
1877
1878 ls->print_cr("Checking global lists:");
1879
1880 // Check g_om_population:
1881 if (g_om_population == chk_om_population) {
1882 ls->print_cr("g_om_population=%d equals chk_om_population=%d",
1883 g_om_population, chk_om_population);
1884 } else {
1885 ls->print_cr("ERROR: g_om_population=%d is not equal to "
1886 "chk_om_population=%d", g_om_population,
1887 chk_om_population);
1888 error_cnt++;
1889 }
1890
1891 // Check g_om_in_use_list and g_om_in_use_count:
1892 chk_global_in_use_list_and_count(ls, &error_cnt);
1893
1894 // Check g_free_list and g_om_free_count:
1895 chk_global_free_list_and_count(ls, &error_cnt);
1896
1897 if (!on_exit) {
1898 Thread::muxRelease(&gListLock);
1899 }
1900
1901 ls->print_cr("Checking per-thread lists:");
1902
1903 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
1904 // Check om_in_use_list and om_in_use_count:
1905 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
1906
1907 // Check om_free_list and om_free_count:
1908 chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
1909 }
1910
1911 if (error_cnt == 0) {
1912 ls->print_cr("No errors found in monitor list checks.");
1913 } else {
1914 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
1915 }
1916
1917 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1918 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1919 // When exiting this log output is at the Info level. When called
1920 // at a safepoint, this log output is at the Trace level since
1921 // there can be a lot of it.
1922 log_in_use_monitor_details(ls, on_exit);
1923 }
1924
1925 ls->flush();
1926
1927 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1928 }
1929
1930 // Check a free monitor entry; log any errors.
1931 void ObjectSynchronizer::chk_free_entry(JavaThread* jt, ObjectMonitor* n,
1932 outputStream * out, int *error_cnt_p) {
1933 stringStream ss;
1934 if (n->is_busy()) {
1935 if (jt != NULL) {
1936 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1937 ": free per-thread monitor must not be busy: %s", p2i(jt),
1938 p2i(n), n->is_busy_to_string(&ss));
1939 } else {
1940 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1941 "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
1942 }
1943 *error_cnt_p = *error_cnt_p + 1;
1944 }
1945 if (n->header().value() != 0) {
1946 if (jt != NULL) {
1947 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1948 ": free per-thread monitor must have NULL _header "
1949 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
1950 n->header().value());
1951 } else {
1952 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1953 "must have NULL _header field: _header=" INTPTR_FORMAT,
1954 p2i(n), n->header().value());
1955 }
1956 *error_cnt_p = *error_cnt_p + 1;
1957 }
1958 if (n->object() != NULL) {
1959 if (jt != NULL) {
1960 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1961 ": free per-thread monitor must have NULL _object "
1962 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
1963 p2i(n->object()));
1964 } else {
1965 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1966 "must have NULL _object field: _object=" INTPTR_FORMAT,
1967 p2i(n), p2i(n->object()));
1968 }
1969 *error_cnt_p = *error_cnt_p + 1;
1970 }
1971 }
1972
1973 // Check the global free list and count; log the results of the checks.
1974 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
1975 int *error_cnt_p) {
1976 int chk_om_free_count = 0;
1977 for (ObjectMonitor* n = g_free_list; n != NULL; n = n->_next_om) {
1978 chk_free_entry(NULL /* jt */, n, out, error_cnt_p);
1979 chk_om_free_count++;
1980 }
1981 if (g_om_free_count == chk_om_free_count) {
1982 out->print_cr("g_om_free_count=%d equals chk_om_free_count=%d",
1983 g_om_free_count, chk_om_free_count);
1984 } else {
1985 out->print_cr("ERROR: g_om_free_count=%d is not equal to "
1986 "chk_om_free_count=%d", g_om_free_count,
1987 chk_om_free_count);
1988 *error_cnt_p = *error_cnt_p + 1;
1989 }
1990 }
1991
1992 // Check the global in-use list and count; log the results of the checks.
1993 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
1994 int *error_cnt_p) {
1995 int chk_om_in_use_count = 0;
1996 for (ObjectMonitor* n = g_om_in_use_list; n != NULL; n = n->_next_om) {
1997 chk_in_use_entry(NULL /* jt */, n, out, error_cnt_p);
1998 chk_om_in_use_count++;
1999 }
2000 if (g_om_in_use_count == chk_om_in_use_count) {
2001 out->print_cr("g_om_in_use_count=%d equals chk_om_in_use_count=%d", g_om_in_use_count,
2002 chk_om_in_use_count);
2003 } else {
2004 out->print_cr("ERROR: g_om_in_use_count=%d is not equal to chk_om_in_use_count=%d",
2005 g_om_in_use_count, chk_om_in_use_count);
2006 *error_cnt_p = *error_cnt_p + 1;
2007 }
2008 }
2009
2010 // Check an in-use monitor entry; log any errors.
2011 void ObjectSynchronizer::chk_in_use_entry(JavaThread* jt, ObjectMonitor* n,
2012 outputStream * out, int *error_cnt_p) {
2013 if (n->header().value() == 0) {
2014 if (jt != NULL) {
2015 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2016 ": in-use per-thread monitor must have non-NULL _header "
2017 "field.", p2i(jt), p2i(n));
2018 } else {
2019 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2020 "must have non-NULL _header field.", p2i(n));
2021 }
2022 *error_cnt_p = *error_cnt_p + 1;
2023 }
2024 if (n->object() == NULL) {
2025 if (jt != NULL) {
2026 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2027 ": in-use per-thread monitor must have non-NULL _object "
2028 "field.", p2i(jt), p2i(n));
2029 } else {
2030 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2031 "must have non-NULL _object field.", p2i(n));
2032 }
2033 *error_cnt_p = *error_cnt_p + 1;
2034 }
2035 const oop obj = (oop)n->object();
2036 const markWord mark = obj->mark();
2037 if (!mark.has_monitor()) {
2038 if (jt != NULL) {
2039 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2040 ": in-use per-thread monitor's object does not think "
2041 "it has a monitor: obj=" INTPTR_FORMAT ", mark="
2042 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), mark.value());
2043 } else {
2044 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2045 "monitor's object does not think it has a monitor: obj="
2046 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2047 p2i(obj), mark.value());
2048 }
2049 *error_cnt_p = *error_cnt_p + 1;
2050 }
2051 ObjectMonitor* const obj_mon = mark.monitor();
2052 if (n != obj_mon) {
2053 if (jt != NULL) {
2054 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2055 ": in-use per-thread monitor's object does not refer "
2056 "to the same monitor: obj=" INTPTR_FORMAT ", mark="
2057 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
2058 p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2059 } else {
2060 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2061 "monitor's object does not refer to the same monitor: obj="
2062 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2063 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2064 }
2065 *error_cnt_p = *error_cnt_p + 1;
2066 }
2067 }
2068
2069 // Check the thread's free list and count; log the results of the checks.
2070 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
2071 outputStream * out,
2072 int *error_cnt_p) {
2073 int chk_om_free_count = 0;
2074 for (ObjectMonitor* n = jt->om_free_list; n != NULL; n = n->_next_om) {
2075 chk_free_entry(jt, n, out, error_cnt_p);
2076 chk_om_free_count++;
2077 }
2078 if (jt->om_free_count == chk_om_free_count) {
2079 out->print_cr("jt=" INTPTR_FORMAT ": om_free_count=%d equals "
2080 "chk_om_free_count=%d", p2i(jt), jt->om_free_count, chk_om_free_count);
2081 } else {
2082 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_free_count=%d is not "
2083 "equal to chk_om_free_count=%d", p2i(jt), jt->om_free_count,
2084 chk_om_free_count);
2085 *error_cnt_p = *error_cnt_p + 1;
2086 }
2087 }
2088
2089 // Check the thread's in-use list and count; log the results of the checks.
2090 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
2091 outputStream * out,
2092 int *error_cnt_p) {
2093 int chk_om_in_use_count = 0;
2094 for (ObjectMonitor* n = jt->om_in_use_list; n != NULL; n = n->_next_om) {
2095 chk_in_use_entry(jt, n, out, error_cnt_p);
2096 chk_om_in_use_count++;
2097 }
2098 if (jt->om_in_use_count == chk_om_in_use_count) {
2099 out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals "
2100 "chk_om_in_use_count=%d", p2i(jt), jt->om_in_use_count,
2101 chk_om_in_use_count);
2102 } else {
2103 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not "
2104 "equal to chk_om_in_use_count=%d", p2i(jt), jt->om_in_use_count,
2105 chk_om_in_use_count);
2106 *error_cnt_p = *error_cnt_p + 1;
2107 }
2108 }
2109
2110 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2111 // flags indicate why the entry is in-use, 'object' and 'object type'
2112 // indicate the associated object and its type.
2113 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out,
2114 bool on_exit) {
2115 if (!on_exit) {
2116 // Not at VM exit so grab the global list lock.
2117 Thread::muxAcquire(&gListLock, "log_in_use_monitor_details");
2118 }
2119
2120 stringStream ss;
2121 if (g_om_in_use_count > 0) {
2122 out->print_cr("In-use global monitor info:");
2123 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2124 out->print_cr("%18s %s %18s %18s",
2125 "monitor", "BHL", "object", "object type");
2126 out->print_cr("================== === ================== ==================");
2127 for (ObjectMonitor* n = g_om_in_use_list; n != NULL; n = n->_next_om) {
2128 const oop obj = (oop) n->object();
2129 const markWord mark = n->header();
2130 ResourceMark rm;
2131 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(n),
2132 n->is_busy() != 0, mark.hash() != 0, n->owner() != NULL,
2133 p2i(obj), obj->klass()->external_name());
2134 if (n->is_busy() != 0) {
2135 out->print(" (%s)", n->is_busy_to_string(&ss));
2136 ss.reset();
2137 }
2138 out->cr();
2139 }
2140 }
2141
2142 if (!on_exit) {
2143 Thread::muxRelease(&gListLock);
2144 }
2145
2146 out->print_cr("In-use per-thread monitor info:");
2147 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2148 out->print_cr("%18s %18s %s %18s %18s",
2149 "jt", "monitor", "BHL", "object", "object type");
2150 out->print_cr("================== ================== === ================== ==================");
2151 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2152 for (ObjectMonitor* n = jt->om_in_use_list; n != NULL; n = n->_next_om) {
2153 const oop obj = (oop) n->object();
2154 const markWord mark = n->header();
2155 ResourceMark rm;
2156 out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT
2157 " %s", p2i(jt), p2i(n), n->is_busy() != 0,
2158 mark.hash() != 0, n->owner() != NULL, p2i(obj),
2159 obj->klass()->external_name());
2160 if (n->is_busy() != 0) {
2161 out->print(" (%s)", n->is_busy_to_string(&ss));
2162 ss.reset();
2163 }
2164 out->cr();
2165 }
2166 }
2167
2168 out->flush();
2169 }
2170
2171 // Log counts for the global and per-thread monitor lists and return
2172 // the population count.
2173 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2174 int pop_count = 0;
2175 out->print_cr("%18s %10s %10s %10s",
2176 "Global Lists:", "InUse", "Free", "Total");
2177 out->print_cr("================== ========== ========== ==========");
2178 out->print_cr("%18s %10d %10d %10d", "",
2179 g_om_in_use_count, g_om_free_count, g_om_population);
2180 pop_count += g_om_in_use_count + g_om_free_count;
2181
2182 out->print_cr("%18s %10s %10s %10s",
2183 "Per-Thread Lists:", "InUse", "Free", "Provision");
2184 out->print_cr("================== ========== ========== ==========");
2185
2186 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2187 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
2188 jt->om_in_use_count, jt->om_free_count, jt->om_free_provision);
2189 pop_count += jt->om_in_use_count + jt->om_free_count;
2190 }
2191 return pop_count;
2192 }
2193
2194 #ifndef PRODUCT
2195
2196 // Check if monitor belongs to the monitor cache
2197 // The list is grow-only so it's *relatively* safe to traverse
2198 // the list of extant blocks without taking a lock.
2199
2200 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
2201 PaddedObjectMonitor* block = OrderAccess::load_acquire(&g_block_list);
2202 while (block != NULL) {
2203 assert(block->object() == CHAINMARKER, "must be a block header");
2204 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
2205 address mon = (address)monitor;
2206 address blk = (address)block;
2207 size_t diff = mon - blk;
2208 assert((diff % sizeof(PaddedObjectMonitor)) == 0, "must be aligned");
2209 return 1;
2210 }
2211 block = (PaddedObjectMonitor*)block->_next_om;
2212 }
2213 return 0;
2214 }
2215
2216 #endif