1 /*
2 * Copyright (c) 1998, 2020, 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/handshake.hpp"
41 #include "runtime/interfaceSupport.inline.hpp"
42 #include "runtime/mutexLocker.hpp"
43 #include "runtime/objectMonitor.hpp"
44 #include "runtime/objectMonitor.inline.hpp"
45 #include "runtime/osThread.hpp"
46 #include "runtime/safepointMechanism.inline.hpp"
47 #include "runtime/safepointVerifiers.hpp"
48 #include "runtime/sharedRuntime.hpp"
49 #include "runtime/stubRoutines.hpp"
50 #include "runtime/synchronizer.hpp"
51 #include "runtime/thread.inline.hpp"
52 #include "runtime/timer.hpp"
53 #include "runtime/vframe.hpp"
54 #include "runtime/vmThread.hpp"
55 #include "utilities/align.hpp"
56 #include "utilities/dtrace.hpp"
57 #include "utilities/events.hpp"
58 #include "utilities/preserveException.hpp"
59
60 // The "core" versions of monitor enter and exit reside in this file.
61 // The interpreter and compilers contain specialized transliterated
62 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
63 // for instance. If you make changes here, make sure to modify the
64 // interpreter, and both C1 and C2 fast-path inline locking code emission.
65 //
66 // -----------------------------------------------------------------------------
67
68 #ifdef DTRACE_ENABLED
69
70 // Only bother with this argument setup if dtrace is available
71 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
72
73 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
74 char* bytes = NULL; \
75 int len = 0; \
76 jlong jtid = SharedRuntime::get_java_tid(thread); \
77 Symbol* klassname = ((oop)(obj))->klass()->name(); \
78 if (klassname != NULL) { \
79 bytes = (char*)klassname->bytes(); \
80 len = klassname->utf8_length(); \
81 }
82
83 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
84 { \
85 if (DTraceMonitorProbes) { \
86 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
87 HOTSPOT_MONITOR_WAIT(jtid, \
88 (uintptr_t)(monitor), bytes, len, (millis)); \
89 } \
90 }
91
92 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
93 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
94 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
95
96 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
97 { \
98 if (DTraceMonitorProbes) { \
99 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
100 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
101 (uintptr_t)(monitor), bytes, len); \
102 } \
103 }
104
105 #else // ndef DTRACE_ENABLED
106
107 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
108 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
109
110 #endif // ndef DTRACE_ENABLED
111
112 // This exists only as a workaround of dtrace bug 6254741
113 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
114 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
115 return 0;
116 }
117
118 #define NINFLATIONLOCKS 256
119 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
120
121 // global list of blocks of monitors
122 PaddedObjectMonitor* ObjectSynchronizer::g_block_list = NULL;
123 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
124 bool volatile ObjectSynchronizer::_is_special_deflation_requested = false;
125 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
126
127 struct ObjectMonitorListGlobals {
128 char _pad_prefix[OM_CACHE_LINE_SIZE];
129 // These are highly shared list related variables.
130 // To avoid false-sharing they need to be the sole occupants of a cache line.
131
132 // Global ObjectMonitor free list. Newly allocated and deflated
133 // ObjectMonitors are prepended here.
134 ObjectMonitor* _free_list;
135 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
136
137 // Global ObjectMonitor in-use list. When a JavaThread is exiting,
138 // ObjectMonitors on its per-thread in-use list are prepended here.
139 ObjectMonitor* _in_use_list;
140 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
141
142 // Global ObjectMonitor wait list. Deflated ObjectMonitors wait on
143 // this list until after a handshake or a safepoint for platforms
144 // that don't support handshakes. After the handshake or safepoint,
145 // the deflated ObjectMonitors are prepended to free_list.
146 ObjectMonitor* _wait_list;
147 DEFINE_PAD_MINUS_SIZE(3, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
148
149 int _free_count; // # on free_list
150 DEFINE_PAD_MINUS_SIZE(4, OM_CACHE_LINE_SIZE, sizeof(int));
151
152 int _in_use_count; // # on in_use_list
153 DEFINE_PAD_MINUS_SIZE(5, OM_CACHE_LINE_SIZE, sizeof(int));
154
155 int _population; // # Extant -- in circulation
156 DEFINE_PAD_MINUS_SIZE(6, OM_CACHE_LINE_SIZE, sizeof(int));
157
158 int _wait_count; // # on wait_list
159 DEFINE_PAD_MINUS_SIZE(7, OM_CACHE_LINE_SIZE, sizeof(int));
160 };
161 static ObjectMonitorListGlobals om_list_globals;
162
163 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
164
165
166 // =====================> Spin-lock functions
167
168 // ObjectMonitors are not lockable outside of this file. We use spin-locks
169 // implemented using a bit in the _next_om field instead of the heavier
170 // weight locking mechanisms for faster list management.
171
172 #define OM_LOCK_BIT 0x1
173
174 // Return true if the ObjectMonitor is locked.
175 // Otherwise returns false.
176 static bool is_locked(ObjectMonitor* om) {
177 return ((intptr_t)om->next_om() & OM_LOCK_BIT) == OM_LOCK_BIT;
178 }
179
180 // Mark an ObjectMonitor* with OM_LOCK_BIT and return it.
181 static ObjectMonitor* mark_om_ptr(ObjectMonitor* om) {
182 return (ObjectMonitor*)((intptr_t)om | OM_LOCK_BIT);
183 }
184
185 // Return the unmarked next field in an ObjectMonitor. Note: the next
186 // field may or may not have been marked with OM_LOCK_BIT originally.
187 static ObjectMonitor* unmarked_next(ObjectMonitor* om) {
188 return (ObjectMonitor*)((intptr_t)om->next_om() & ~OM_LOCK_BIT);
189 }
190
191 // Try to lock an ObjectMonitor. Returns true if locking was successful.
192 // Otherwise returns false.
193 static bool try_om_lock(ObjectMonitor* om) {
194 // Get current next field without any OM_LOCK_BIT value.
195 ObjectMonitor* next = unmarked_next(om);
196 if (om->try_set_next_om(next, mark_om_ptr(next)) != next) {
197 return false; // Cannot lock the ObjectMonitor.
198 }
199 return true;
200 }
201
202 // Lock an ObjectMonitor.
203 static void om_lock(ObjectMonitor* om) {
204 while (true) {
205 if (try_om_lock(om)) {
206 return;
207 }
208 }
209 }
210
211 // Unlock an ObjectMonitor.
212 static void om_unlock(ObjectMonitor* om) {
213 ObjectMonitor* next = om->next_om();
214 guarantee(((intptr_t)next & OM_LOCK_BIT) == OM_LOCK_BIT, "next=" INTPTR_FORMAT
215 " must have OM_LOCK_BIT=%x set.", p2i(next), OM_LOCK_BIT);
216
217 next = (ObjectMonitor*)((intptr_t)next & ~OM_LOCK_BIT); // Clear OM_LOCK_BIT.
218 om->set_next_om(next);
219 }
220
221 // Get the list head after locking it. Returns the list head or NULL
222 // if the list is empty.
223 static ObjectMonitor* get_list_head_locked(ObjectMonitor** list_p) {
224 while (true) {
225 ObjectMonitor* mid = Atomic::load(list_p);
226 if (mid == NULL) {
227 return NULL; // The list is empty.
228 }
229 if (try_om_lock(mid)) {
230 if (Atomic::load(list_p) != mid) {
231 // The list head changed before we could lock it so we have to retry.
232 om_unlock(mid);
233 continue;
234 }
235 return mid;
236 }
237 }
238 }
239
240 #undef OM_LOCK_BIT
241
242
243 // =====================> List Management functions
244
245 // Prepend a list of ObjectMonitors to the specified *list_p. 'tail' is
246 // the last ObjectMonitor in the list and there are 'count' on the list.
247 // Also updates the specified *count_p.
248 static void prepend_list_to_common(ObjectMonitor* list, ObjectMonitor* tail,
249 int count, ObjectMonitor** list_p,
250 int* count_p) {
251 while (true) {
252 ObjectMonitor* cur = Atomic::load(list_p);
253 // Prepend list to *list_p.
254 if (!try_om_lock(tail)) {
255 // Failed to lock tail due to a list walker so try it all again.
256 continue;
257 }
258 tail->set_next_om(cur); // tail now points to cur (and unlocks tail)
259 if (cur == NULL) {
260 // No potential race with takers or other prependers since
261 // *list_p is empty.
262 if (Atomic::cmpxchg(list_p, cur, list) == cur) {
263 // Successfully switched *list_p to the list value.
264 Atomic::add(count_p, count);
265 break;
266 }
267 // Implied else: try it all again
268 } else {
269 if (!try_om_lock(cur)) {
270 continue; // failed to lock cur so try it all again
271 }
272 // We locked cur so try to switch *list_p to the list value.
273 if (Atomic::cmpxchg(list_p, cur, list) != cur) {
274 // The list head has changed so unlock cur and try again:
275 om_unlock(cur);
276 continue;
277 }
278 Atomic::add(count_p, count);
279 om_unlock(cur);
280 break;
281 }
282 }
283 }
284
285 // Prepend a newly allocated block of ObjectMonitors to g_block_list and
286 // om_list_globals._free_list. Also updates om_list_globals._population
287 // and om_list_globals._free_count.
288 void ObjectSynchronizer::prepend_block_to_lists(PaddedObjectMonitor* new_blk) {
289 // First we handle g_block_list:
290 while (true) {
291 PaddedObjectMonitor* cur = Atomic::load(&g_block_list);
292 // Prepend new_blk to g_block_list. The first ObjectMonitor in
293 // a block is reserved for use as linkage to the next block.
294 new_blk[0].set_next_om(cur);
295 if (Atomic::cmpxchg(&g_block_list, cur, new_blk) == cur) {
296 // Successfully switched g_block_list to the new_blk value.
297 Atomic::add(&om_list_globals._population, _BLOCKSIZE - 1);
298 break;
299 }
300 // Implied else: try it all again
301 }
302
303 // Second we handle om_list_globals._free_list:
304 prepend_list_to_common(new_blk + 1, &new_blk[_BLOCKSIZE - 1], _BLOCKSIZE - 1,
305 &om_list_globals._free_list, &om_list_globals._free_count);
306 }
307
308 // Prepend a list of ObjectMonitors to om_list_globals._free_list.
309 // 'tail' is the last ObjectMonitor in the list and there are 'count'
310 // on the list. Also updates om_list_globals._free_count.
311 static void prepend_list_to_global_free_list(ObjectMonitor* list,
312 ObjectMonitor* tail, int count) {
313 prepend_list_to_common(list, tail, count, &om_list_globals._free_list,
314 &om_list_globals._free_count);
315 }
316
317 // Prepend a list of ObjectMonitors to om_list_globals._wait_list.
318 // 'tail' is the last ObjectMonitor in the list and there are 'count'
319 // on the list. Also updates om_list_globals._wait_count.
320 static void prepend_list_to_global_wait_list(ObjectMonitor* list,
321 ObjectMonitor* tail, int count) {
322 prepend_list_to_common(list, tail, count, &om_list_globals._wait_list,
323 &om_list_globals._wait_count);
324 }
325
326 // Prepend a list of ObjectMonitors to om_list_globals._in_use_list.
327 // 'tail' is the last ObjectMonitor in the list and there are 'count'
328 // on the list. Also updates om_list_globals._in_use_list.
329 static void prepend_list_to_global_in_use_list(ObjectMonitor* list,
330 ObjectMonitor* tail, int count) {
331 prepend_list_to_common(list, tail, count, &om_list_globals._in_use_list,
332 &om_list_globals._in_use_count);
333 }
334
335 // Prepend an ObjectMonitor to the specified list. Also updates
336 // the specified counter.
337 static void prepend_to_common(ObjectMonitor* m, ObjectMonitor** list_p,
338 int* count_p) {
339 while (true) {
340 om_lock(m); // Lock m so we can safely update its next field.
341 ObjectMonitor* cur = NULL;
342 // Lock the list head to guard against races with a list walker
343 // or async deflater thread (which only races in om_in_use_list):
344 if ((cur = get_list_head_locked(list_p)) != NULL) {
345 // List head is now locked so we can safely switch it.
346 m->set_next_om(cur); // m now points to cur (and unlocks m)
347 Atomic::store(list_p, m); // Switch list head to unlocked m.
348 om_unlock(cur);
349 break;
350 }
351 // The list is empty so try to set the list head.
352 assert(cur == NULL, "cur must be NULL: cur=" INTPTR_FORMAT, p2i(cur));
353 m->set_next_om(cur); // m now points to NULL (and unlocks m)
354 if (Atomic::cmpxchg(list_p, cur, m) == cur) {
355 // List head is now unlocked m.
356 break;
357 }
358 // Implied else: try it all again
359 }
360 Atomic::inc(count_p);
361 }
362
363 // Prepend an ObjectMonitor to a per-thread om_free_list.
364 // Also updates the per-thread om_free_count.
365 static void prepend_to_om_free_list(Thread* self, ObjectMonitor* m) {
366 prepend_to_common(m, &self->om_free_list, &self->om_free_count);
367 }
368
369 // Prepend an ObjectMonitor to a per-thread om_in_use_list.
370 // Also updates the per-thread om_in_use_count.
371 static void prepend_to_om_in_use_list(Thread* self, ObjectMonitor* m) {
372 prepend_to_common(m, &self->om_in_use_list, &self->om_in_use_count);
373 }
374
375 // Take an ObjectMonitor from the start of the specified list. Also
376 // decrements the specified counter. Returns NULL if none are available.
377 static ObjectMonitor* take_from_start_of_common(ObjectMonitor** list_p,
378 int* count_p) {
379 ObjectMonitor* take = NULL;
380 // Lock the list head to guard against races with a list walker
381 // or async deflater thread (which only races in om_list_globals._free_list):
382 if ((take = get_list_head_locked(list_p)) == NULL) {
383 return NULL; // None are available.
384 }
385 ObjectMonitor* next = unmarked_next(take);
386 // Switch locked list head to next (which unlocks the list head, but
387 // leaves take locked):
388 Atomic::store(list_p, next);
389 Atomic::dec(count_p);
390 // Unlock take, but leave the next value for any lagging list
391 // walkers. It will get cleaned up when take is prepended to
392 // the in-use list:
393 om_unlock(take);
394 return take;
395 }
396
397 // Take an ObjectMonitor from the start of the om_list_globals._free_list.
398 // Also updates om_list_globals._free_count. Returns NULL if none are
399 // available.
400 static ObjectMonitor* take_from_start_of_global_free_list() {
401 return take_from_start_of_common(&om_list_globals._free_list,
402 &om_list_globals._free_count);
403 }
404
405 // Take an ObjectMonitor from the start of a per-thread free-list.
406 // Also updates om_free_count. Returns NULL if none are available.
407 static ObjectMonitor* take_from_start_of_om_free_list(Thread* self) {
408 return take_from_start_of_common(&self->om_free_list, &self->om_free_count);
409 }
410
411
412 // =====================> Quick functions
413
414 // The quick_* forms are special fast-path variants used to improve
415 // performance. In the simplest case, a "quick_*" implementation could
416 // simply return false, in which case the caller will perform the necessary
417 // state transitions and call the slow-path form.
418 // The fast-path is designed to handle frequently arising cases in an efficient
419 // manner and is just a degenerate "optimistic" variant of the slow-path.
420 // returns true -- to indicate the call was satisfied.
421 // returns false -- to indicate the call needs the services of the slow-path.
422 // A no-loitering ordinance is in effect for code in the quick_* family
423 // operators: safepoints or indefinite blocking (blocking that might span a
424 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
425 // entry.
426 //
427 // Consider: An interesting optimization is to have the JIT recognize the
428 // following common idiom:
429 // synchronized (someobj) { .... ; notify(); }
430 // That is, we find a notify() or notifyAll() call that immediately precedes
431 // the monitorexit operation. In that case the JIT could fuse the operations
432 // into a single notifyAndExit() runtime primitive.
433
434 bool ObjectSynchronizer::quick_notify(oopDesc* obj, Thread* self, bool all) {
435 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
436 assert(self->is_Java_thread(), "invariant");
437 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
438 NoSafepointVerifier nsv;
439 if (obj == NULL) return false; // slow-path for invalid obj
440 const markWord mark = obj->mark();
441
442 if (mark.has_locker() && self->is_lock_owned((address)mark.locker())) {
443 // Degenerate notify
444 // stack-locked by caller so by definition the implied waitset is empty.
445 return true;
446 }
447
448 if (mark.has_monitor()) {
449 ObjectMonitor* const mon = mark.monitor();
450 assert(mon->object() == obj, "invariant");
451 if (mon->owner() != self) return false; // slow-path for IMS exception
452
453 if (mon->first_waiter() != NULL) {
454 // We have one or more waiters. Since this is an inflated monitor
455 // that we own, we can transfer one or more threads from the waitset
456 // to the entrylist here and now, avoiding the slow-path.
457 if (all) {
458 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
459 } else {
460 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
461 }
462 int free_count = 0;
463 do {
464 mon->INotify(self);
465 ++free_count;
466 } while (mon->first_waiter() != NULL && all);
467 OM_PERFDATA_OP(Notifications, inc(free_count));
468 }
469 return true;
470 }
471
472 // biased locking and any other IMS exception states take the slow-path
473 return false;
474 }
475
476
477 // The LockNode emitted directly at the synchronization site would have
478 // been too big if it were to have included support for the cases of inflated
479 // recursive enter and exit, so they go here instead.
480 // Note that we can't safely call AsyncPrintJavaStack() from within
481 // quick_enter() as our thread state remains _in_Java.
482
483 bool ObjectSynchronizer::quick_enter(oop obj, Thread* self,
484 BasicLock * lock) {
485 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
486 assert(self->is_Java_thread(), "invariant");
487 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
488 NoSafepointVerifier nsv;
489 if (obj == NULL) return false; // Need to throw NPE
490
491 const markWord mark = obj->mark();
492
493 if (mark.has_monitor()) {
494 ObjectMonitor* const m = mark.monitor();
495 if (AsyncDeflateIdleMonitors) {
496 // An async deflation can race us before we manage to make the
497 // ObjectMonitor busy by setting the owner below. If we detect
498 // that race we just bail out to the slow-path here.
499 if (m->object() == NULL) {
500 return false;
501 }
502 } else {
503 assert(m->object() == obj, "invariant");
504 }
505 Thread* const owner = (Thread *) m->_owner;
506
507 // Lock contention and Transactional Lock Elision (TLE) diagnostics
508 // and observability
509 // Case: light contention possibly amenable to TLE
510 // Case: TLE inimical operations such as nested/recursive synchronization
511
512 if (owner == self) {
513 m->_recursions++;
514 return true;
515 }
516
517 // This Java Monitor is inflated so obj's header will never be
518 // displaced to this thread's BasicLock. Make the displaced header
519 // non-NULL so this BasicLock is not seen as recursive nor as
520 // being locked. We do this unconditionally so that this thread's
521 // BasicLock cannot be mis-interpreted by any stack walkers. For
522 // performance reasons, stack walkers generally first check for
523 // Biased Locking in the object's header, the second check is for
524 // stack-locking in the object's header, the third check is for
525 // recursive stack-locking in the displaced header in the BasicLock,
526 // and last are the inflated Java Monitor (ObjectMonitor) checks.
527 lock->set_displaced_header(markWord::unused_mark());
528
529 if (owner == NULL && m->try_set_owner_from(NULL, self) == NULL) {
530 assert(m->_recursions == 0, "invariant");
531 return true;
532 }
533 }
534
535 // Note that we could inflate in quick_enter.
536 // This is likely a useful optimization
537 // Critically, in quick_enter() we must not:
538 // -- perform bias revocation, or
539 // -- block indefinitely, or
540 // -- reach a safepoint
541
542 return false; // revert to slow-path
543 }
544
545 // -----------------------------------------------------------------------------
546 // Monitor Enter/Exit
547 // The interpreter and compiler assembly code tries to lock using the fast path
548 // of this algorithm. Make sure to update that code if the following function is
549 // changed. The implementation is extremely sensitive to race condition. Be careful.
550
551 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, TRAPS) {
552 if (UseBiasedLocking) {
553 if (!SafepointSynchronize::is_at_safepoint()) {
554 BiasedLocking::revoke(obj, THREAD);
555 } else {
556 BiasedLocking::revoke_at_safepoint(obj);
557 }
558 }
559
560 markWord mark = obj->mark();
561 assert(!mark.has_bias_pattern(), "should not see bias pattern here");
562
563 if (mark.is_neutral()) {
564 // Anticipate successful CAS -- the ST of the displaced mark must
565 // be visible <= the ST performed by the CAS.
566 lock->set_displaced_header(mark);
567 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
568 return;
569 }
570 // Fall through to inflate() ...
571 } else if (mark.has_locker() &&
572 THREAD->is_lock_owned((address)mark.locker())) {
573 assert(lock != mark.locker(), "must not re-lock the same lock");
574 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
575 lock->set_displaced_header(markWord::from_pointer(NULL));
576 return;
577 }
578
579 // The object header will never be displaced to this lock,
580 // so it does not matter what the value is, except that it
581 // must be non-zero to avoid looking like a re-entrant lock,
582 // and must not look locked either.
583 lock->set_displaced_header(markWord::unused_mark());
584 // An async deflation can race after the inflate() call and before
585 // enter() can make the ObjectMonitor busy. enter() returns false if
586 // we have lost the race to async deflation and we simply try again.
587 while (true) {
588 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_monitor_enter);
589 if (monitor->enter(THREAD)) {
590 return;
591 }
592 }
593 }
594
595 void ObjectSynchronizer::exit(oop object, BasicLock* lock, TRAPS) {
596 markWord mark = object->mark();
597 // We cannot check for Biased Locking if we are racing an inflation.
598 assert(mark == markWord::INFLATING() ||
599 !mark.has_bias_pattern(), "should not see bias pattern here");
600
601 markWord dhw = lock->displaced_header();
602 if (dhw.value() == 0) {
603 // If the displaced header is NULL, then this exit matches up with
604 // a recursive enter. No real work to do here except for diagnostics.
605 #ifndef PRODUCT
606 if (mark != markWord::INFLATING()) {
607 // Only do diagnostics if we are not racing an inflation. Simply
608 // exiting a recursive enter of a Java Monitor that is being
609 // inflated is safe; see the has_monitor() comment below.
610 assert(!mark.is_neutral(), "invariant");
611 assert(!mark.has_locker() ||
612 THREAD->is_lock_owned((address)mark.locker()), "invariant");
613 if (mark.has_monitor()) {
614 // The BasicLock's displaced_header is marked as a recursive
615 // enter and we have an inflated Java Monitor (ObjectMonitor).
616 // This is a special case where the Java Monitor was inflated
617 // after this thread entered the stack-lock recursively. When a
618 // Java Monitor is inflated, we cannot safely walk the Java
619 // Monitor owner's stack and update the BasicLocks because a
620 // Java Monitor can be asynchronously inflated by a thread that
621 // does not own the Java Monitor.
622 ObjectMonitor* m = mark.monitor();
623 assert(((oop)(m->object()))->mark() == mark, "invariant");
624 assert(m->is_entered(THREAD), "invariant");
625 }
626 }
627 #endif
628 return;
629 }
630
631 if (mark == markWord::from_pointer(lock)) {
632 // If the object is stack-locked by the current thread, try to
633 // swing the displaced header from the BasicLock back to the mark.
634 assert(dhw.is_neutral(), "invariant");
635 if (object->cas_set_mark(dhw, mark) == mark) {
636 return;
637 }
638 }
639
640 // We have to take the slow-path of possible inflation and then exit.
641 // The ObjectMonitor* can't be async deflated until ownership is
642 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
643 ObjectMonitor* monitor = inflate(THREAD, object, inflate_cause_vm_internal);
644 monitor->exit(true, THREAD);
645 }
646
647 // -----------------------------------------------------------------------------
648 // Class Loader support to workaround deadlocks on the class loader lock objects
649 // Also used by GC
650 // complete_exit()/reenter() are used to wait on a nested lock
651 // i.e. to give up an outer lock completely and then re-enter
652 // Used when holding nested locks - lock acquisition order: lock1 then lock2
653 // 1) complete_exit lock1 - saving recursion count
654 // 2) wait on lock2
655 // 3) when notified on lock2, unlock lock2
656 // 4) reenter lock1 with original recursion count
657 // 5) lock lock2
658 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
659 intx ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
660 if (UseBiasedLocking) {
661 BiasedLocking::revoke(obj, THREAD);
662 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
663 }
664
665 // The ObjectMonitor* can't be async deflated until ownership is
666 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
667 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
668 intptr_t ret_code = monitor->complete_exit(THREAD);
669 return ret_code;
670 }
671
672 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
673 void ObjectSynchronizer::reenter(Handle obj, intx recursions, TRAPS) {
674 if (UseBiasedLocking) {
675 BiasedLocking::revoke(obj, THREAD);
676 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
677 }
678
679 // An async deflation can race after the inflate() call and before
680 // reenter() -> enter() can make the ObjectMonitor busy. reenter() ->
681 // enter() returns false if we have lost the race to async deflation
682 // and we simply try again.
683 while (true) {
684 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
685 if (monitor->reenter(recursions, THREAD)) {
686 return;
687 }
688 }
689 }
690
691 // -----------------------------------------------------------------------------
692 // JNI locks on java objects
693 // NOTE: must use heavy weight monitor to handle jni monitor enter
694 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
695 // the current locking is from JNI instead of Java code
696 if (UseBiasedLocking) {
697 BiasedLocking::revoke(obj, THREAD);
698 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
699 }
700 THREAD->set_current_pending_monitor_is_from_java(false);
701 // An async deflation can race after the inflate() call and before
702 // enter() can make the ObjectMonitor busy. enter() returns false if
703 // we have lost the race to async deflation and we simply try again.
704 while (true) {
705 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_jni_enter);
706 if (monitor->enter(THREAD)) {
707 break;
708 }
709 }
710 THREAD->set_current_pending_monitor_is_from_java(true);
711 }
712
713 // NOTE: must use heavy weight monitor to handle jni monitor exit
714 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
715 if (UseBiasedLocking) {
716 Handle h_obj(THREAD, obj);
717 BiasedLocking::revoke(h_obj, THREAD);
718 obj = h_obj();
719 }
720 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
721
722 // The ObjectMonitor* can't be async deflated until ownership is
723 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
724 ObjectMonitor* monitor = inflate(THREAD, obj, inflate_cause_jni_exit);
725 // If this thread has locked the object, exit the monitor. We
726 // intentionally do not use CHECK here because we must exit the
727 // monitor even if an exception is pending.
728 if (monitor->check_owner(THREAD)) {
729 monitor->exit(true, THREAD);
730 }
731 }
732
733 // -----------------------------------------------------------------------------
734 // Internal VM locks on java objects
735 // standard constructor, allows locking failures
736 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool do_lock) {
737 _dolock = do_lock;
738 _thread = thread;
739 _thread->check_for_valid_safepoint_state();
740 _obj = obj;
741
742 if (_dolock) {
743 ObjectSynchronizer::enter(_obj, &_lock, _thread);
744 }
745 }
746
747 ObjectLocker::~ObjectLocker() {
748 if (_dolock) {
749 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
750 }
751 }
752
753
754 // -----------------------------------------------------------------------------
755 // Wait/Notify/NotifyAll
756 // NOTE: must use heavy weight monitor to handle wait()
757 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
758 if (UseBiasedLocking) {
759 BiasedLocking::revoke(obj, THREAD);
760 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
761 }
762 if (millis < 0) {
763 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
764 }
765 // The ObjectMonitor* can't be async deflated because the _waiters
766 // field is incremented before ownership is dropped and decremented
767 // after ownership is regained.
768 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
769
770 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
771 monitor->wait(millis, true, THREAD);
772
773 // This dummy call is in place to get around dtrace bug 6254741. Once
774 // that's fixed we can uncomment the following line, remove the call
775 // and change this function back into a "void" func.
776 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
777 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
778 return ret_code;
779 }
780
781 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, jlong millis, TRAPS) {
782 if (UseBiasedLocking) {
783 BiasedLocking::revoke(obj, THREAD);
784 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
785 }
786 if (millis < 0) {
787 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
788 }
789 // The ObjectMonitor* can't be async deflated because the _waiters
790 // field is incremented before ownership is dropped and decremented
791 // after ownership is regained.
792 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
793 monitor->wait(millis, false, THREAD);
794 }
795
796 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
797 if (UseBiasedLocking) {
798 BiasedLocking::revoke(obj, THREAD);
799 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
800 }
801
802 markWord mark = obj->mark();
803 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
804 return;
805 }
806 // The ObjectMonitor* can't be async deflated until ownership is
807 // dropped by the calling thread.
808 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_notify);
809 monitor->notify(THREAD);
810 }
811
812 // NOTE: see comment of notify()
813 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
814 if (UseBiasedLocking) {
815 BiasedLocking::revoke(obj, THREAD);
816 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
817 }
818
819 markWord mark = obj->mark();
820 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
821 return;
822 }
823 // The ObjectMonitor* can't be async deflated until ownership is
824 // dropped by the calling thread.
825 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_notify);
826 monitor->notifyAll(THREAD);
827 }
828
829 // -----------------------------------------------------------------------------
830 // Hash Code handling
831 //
832 // Performance concern:
833 // OrderAccess::storestore() calls release() which at one time stored 0
834 // into the global volatile OrderAccess::dummy variable. This store was
835 // unnecessary for correctness. Many threads storing into a common location
836 // causes considerable cache migration or "sloshing" on large SMP systems.
837 // As such, I avoided using OrderAccess::storestore(). In some cases
838 // OrderAccess::fence() -- which incurs local latency on the executing
839 // processor -- is a better choice as it scales on SMP systems.
840 //
841 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
842 // a discussion of coherency costs. Note that all our current reference
843 // platforms provide strong ST-ST order, so the issue is moot on IA32,
844 // x64, and SPARC.
845 //
846 // As a general policy we use "volatile" to control compiler-based reordering
847 // and explicit fences (barriers) to control for architectural reordering
848 // performed by the CPU(s) or platform.
849
850 struct SharedGlobals {
851 char _pad_prefix[OM_CACHE_LINE_SIZE];
852 // These are highly shared mostly-read variables.
853 // To avoid false-sharing they need to be the sole occupants of a cache line.
854 volatile int stw_random;
855 volatile int stw_cycle;
856 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
857 // Hot RW variable -- Sequester to avoid false-sharing
858 volatile int hc_sequence;
859 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
860 };
861
862 static SharedGlobals GVars;
863
864 static markWord read_stable_mark(oop obj) {
865 markWord mark = obj->mark();
866 if (!mark.is_being_inflated()) {
867 return mark; // normal fast-path return
868 }
869
870 int its = 0;
871 for (;;) {
872 markWord mark = obj->mark();
873 if (!mark.is_being_inflated()) {
874 return mark; // normal fast-path return
875 }
876
877 // The object is being inflated by some other thread.
878 // The caller of read_stable_mark() must wait for inflation to complete.
879 // Avoid live-lock
880 // TODO: consider calling SafepointSynchronize::do_call_back() while
881 // spinning to see if there's a safepoint pending. If so, immediately
882 // yielding or blocking would be appropriate. Avoid spinning while
883 // there is a safepoint pending.
884 // TODO: add inflation contention performance counters.
885 // TODO: restrict the aggregate number of spinners.
886
887 ++its;
888 if (its > 10000 || !os::is_MP()) {
889 if (its & 1) {
890 os::naked_yield();
891 } else {
892 // Note that the following code attenuates the livelock problem but is not
893 // a complete remedy. A more complete solution would require that the inflating
894 // thread hold the associated inflation lock. The following code simply restricts
895 // the number of spinners to at most one. We'll have N-2 threads blocked
896 // on the inflationlock, 1 thread holding the inflation lock and using
897 // a yield/park strategy, and 1 thread in the midst of inflation.
898 // A more refined approach would be to change the encoding of INFLATING
899 // to allow encapsulation of a native thread pointer. Threads waiting for
900 // inflation to complete would use CAS to push themselves onto a singly linked
901 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
902 // and calling park(). When inflation was complete the thread that accomplished inflation
903 // would detach the list and set the markword to inflated with a single CAS and
904 // then for each thread on the list, set the flag and unpark() the thread.
905 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
906 // wakes at most one thread whereas we need to wake the entire list.
907 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
908 int YieldThenBlock = 0;
909 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
910 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
911 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
912 while (obj->mark() == markWord::INFLATING()) {
913 // Beware: NakedYield() is advisory and has almost no effect on some platforms
914 // so we periodically call self->_ParkEvent->park(1).
915 // We use a mixed spin/yield/block mechanism.
916 if ((YieldThenBlock++) >= 16) {
917 Thread::current()->_ParkEvent->park(1);
918 } else {
919 os::naked_yield();
920 }
921 }
922 Thread::muxRelease(gInflationLocks + ix);
923 }
924 } else {
925 SpinPause(); // SMP-polite spinning
926 }
927 }
928 }
929
930 // hashCode() generation :
931 //
932 // Possibilities:
933 // * MD5Digest of {obj,stw_random}
934 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
935 // * A DES- or AES-style SBox[] mechanism
936 // * One of the Phi-based schemes, such as:
937 // 2654435761 = 2^32 * Phi (golden ratio)
938 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
939 // * A variation of Marsaglia's shift-xor RNG scheme.
940 // * (obj ^ stw_random) is appealing, but can result
941 // in undesirable regularity in the hashCode values of adjacent objects
942 // (objects allocated back-to-back, in particular). This could potentially
943 // result in hashtable collisions and reduced hashtable efficiency.
944 // There are simple ways to "diffuse" the middle address bits over the
945 // generated hashCode values:
946
947 static inline intptr_t get_next_hash(Thread* self, oop obj) {
948 intptr_t value = 0;
949 if (hashCode == 0) {
950 // This form uses global Park-Miller RNG.
951 // On MP system we'll have lots of RW access to a global, so the
952 // mechanism induces lots of coherency traffic.
953 value = os::random();
954 } else if (hashCode == 1) {
955 // This variation has the property of being stable (idempotent)
956 // between STW operations. This can be useful in some of the 1-0
957 // synchronization schemes.
958 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
959 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
960 } else if (hashCode == 2) {
961 value = 1; // for sensitivity testing
962 } else if (hashCode == 3) {
963 value = ++GVars.hc_sequence;
964 } else if (hashCode == 4) {
965 value = cast_from_oop<intptr_t>(obj);
966 } else {
967 // Marsaglia's xor-shift scheme with thread-specific state
968 // This is probably the best overall implementation -- we'll
969 // likely make this the default in future releases.
970 unsigned t = self->_hashStateX;
971 t ^= (t << 11);
972 self->_hashStateX = self->_hashStateY;
973 self->_hashStateY = self->_hashStateZ;
974 self->_hashStateZ = self->_hashStateW;
975 unsigned v = self->_hashStateW;
976 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
977 self->_hashStateW = v;
978 value = v;
979 }
980
981 value &= markWord::hash_mask;
982 if (value == 0) value = 0xBAD;
983 assert(value != markWord::no_hash, "invariant");
984 return value;
985 }
986
987 intptr_t ObjectSynchronizer::FastHashCode(Thread* self, oop obj) {
988 if (UseBiasedLocking) {
989 // NOTE: many places throughout the JVM do not expect a safepoint
990 // to be taken here, in particular most operations on perm gen
991 // objects. However, we only ever bias Java instances and all of
992 // the call sites of identity_hash that might revoke biases have
993 // been checked to make sure they can handle a safepoint. The
994 // added check of the bias pattern is to avoid useless calls to
995 // thread-local storage.
996 if (obj->mark().has_bias_pattern()) {
997 // Handle for oop obj in case of STW safepoint
998 Handle hobj(self, obj);
999 // Relaxing assertion for bug 6320749.
1000 assert(Universe::verify_in_progress() ||
1001 !SafepointSynchronize::is_at_safepoint(),
1002 "biases should not be seen by VM thread here");
1003 BiasedLocking::revoke(hobj, JavaThread::current());
1004 obj = hobj();
1005 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
1006 }
1007 }
1008
1009 // hashCode() is a heap mutator ...
1010 // Relaxing assertion for bug 6320749.
1011 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
1012 !SafepointSynchronize::is_at_safepoint(), "invariant");
1013 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
1014 self->is_Java_thread() , "invariant");
1015 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
1016 ((JavaThread *)self)->thread_state() != _thread_blocked, "invariant");
1017
1018 while (true) {
1019 ObjectMonitor* monitor = NULL;
1020 markWord temp, test;
1021 intptr_t hash;
1022 markWord mark = read_stable_mark(obj);
1023
1024 // object should remain ineligible for biased locking
1025 assert(!mark.has_bias_pattern(), "invariant");
1026
1027 if (mark.is_neutral()) { // if this is a normal header
1028 hash = mark.hash();
1029 if (hash != 0) { // if it has a hash, just return it
1030 return hash;
1031 }
1032 hash = get_next_hash(self, obj); // get a new hash
1033 temp = mark.copy_set_hash(hash); // merge the hash into header
1034 // try to install the hash
1035 test = obj->cas_set_mark(temp, mark);
1036 if (test == mark) { // if the hash was installed, return it
1037 return hash;
1038 }
1039 // Failed to install the hash. It could be that another thread
1040 // installed the hash just before our attempt or inflation has
1041 // occurred or... so we fall thru to inflate the monitor for
1042 // stability and then install the hash.
1043 } else if (mark.has_monitor()) {
1044 // The first stage of a racing async deflation won't affect the
1045 // hash value if this ObjectMonitor happens to already have one.
1046 monitor = mark.monitor();
1047 temp = monitor->header();
1048 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1049 hash = temp.hash();
1050 if (hash != 0) { // if it has a hash, just return it
1051 return hash;
1052 }
1053 // Fall thru so we only have one place that installs the hash in
1054 // the ObjectMonitor.
1055 } else if (self->is_lock_owned((address)mark.locker())) {
1056 // This is a stack lock owned by the calling thread so fetch the
1057 // displaced markWord from the BasicLock on the stack.
1058 temp = mark.displaced_mark_helper();
1059 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1060 hash = temp.hash();
1061 if (hash != 0) { // if it has a hash, just return it
1062 return hash;
1063 }
1064 // WARNING:
1065 // The displaced header in the BasicLock on a thread's stack
1066 // is strictly immutable. It CANNOT be changed in ANY cases.
1067 // So we have to inflate the stack lock into an ObjectMonitor
1068 // even if the current thread owns the lock. The BasicLock on
1069 // a thread's stack can be asynchronously read by other threads
1070 // during an inflate() call so any change to that stack memory
1071 // may not propagate to other threads correctly.
1072 }
1073
1074 // Inflate the monitor to set the hash.
1075
1076 // An async deflation can race after the inflate() call and before we
1077 // can update the ObjectMonitor's header with the hash value below.
1078 monitor = inflate(self, obj, inflate_cause_hash_code);
1079 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1080 mark = monitor->header();
1081 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1082 hash = mark.hash();
1083 if (hash == 0) { // if it does not have a hash
1084 hash = get_next_hash(self, obj); // get a new hash
1085 temp = mark.copy_set_hash(hash); // merge the hash into header
1086 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1087 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1088 test = markWord(v);
1089 if (test != mark) {
1090 // The attempt to update the ObjectMonitor's header/dmw field
1091 // did not work. This can happen if another thread managed to
1092 // merge in the hash just before our cmpxchg().
1093 // If we add any new usages of the header/dmw field, this code
1094 // will need to be updated.
1095 hash = test.hash();
1096 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1097 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1098 }
1099 if (monitor->is_being_async_deflated()) {
1100 // If we detect that async deflation has occurred, then we
1101 // simply retry so that the hash value can be stored in either
1102 // the object's header or in the re-inflated ObjectMonitor's
1103 // header as appropriate.
1104 continue;
1105 }
1106 }
1107 // We finally get the hash.
1108 return hash;
1109 }
1110 }
1111
1112 // Deprecated -- use FastHashCode() instead.
1113
1114 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
1115 return FastHashCode(Thread::current(), obj());
1116 }
1117
1118
1119 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
1120 Handle h_obj) {
1121 if (UseBiasedLocking) {
1122 BiasedLocking::revoke(h_obj, thread);
1123 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1124 }
1125
1126 assert(thread == JavaThread::current(), "Can only be called on current thread");
1127 oop obj = h_obj();
1128
1129 markWord mark = read_stable_mark(obj);
1130
1131 // Uncontended case, header points to stack
1132 if (mark.has_locker()) {
1133 return thread->is_lock_owned((address)mark.locker());
1134 }
1135 // Contended case, header points to ObjectMonitor (tagged pointer)
1136 if (mark.has_monitor()) {
1137 // The first stage of async deflation does not affect any field
1138 // used by this comparison so the ObjectMonitor* is usable here.
1139 ObjectMonitor* monitor = mark.monitor();
1140 return monitor->is_entered(thread) != 0;
1141 }
1142 // Unlocked case, header in place
1143 assert(mark.is_neutral(), "sanity check");
1144 return false;
1145 }
1146
1147 // Be aware of this method could revoke bias of the lock object.
1148 // This method queries the ownership of the lock handle specified by 'h_obj'.
1149 // If the current thread owns the lock, it returns owner_self. If no
1150 // thread owns the lock, it returns owner_none. Otherwise, it will return
1151 // owner_other.
1152 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
1153 (JavaThread *self, Handle h_obj) {
1154 // The caller must beware this method can revoke bias, and
1155 // revocation can result in a safepoint.
1156 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
1157 assert(self->thread_state() != _thread_blocked, "invariant");
1158
1159 // Possible mark states: neutral, biased, stack-locked, inflated
1160
1161 if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) {
1162 // CASE: biased
1163 BiasedLocking::revoke(h_obj, self);
1164 assert(!h_obj->mark().has_bias_pattern(),
1165 "biases should be revoked by now");
1166 }
1167
1168 assert(self == JavaThread::current(), "Can only be called on current thread");
1169 oop obj = h_obj();
1170 markWord mark = read_stable_mark(obj);
1171
1172 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
1173 if (mark.has_locker()) {
1174 return self->is_lock_owned((address)mark.locker()) ?
1175 owner_self : owner_other;
1176 }
1177
1178 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
1179 // The Object:ObjectMonitor relationship is stable as long as we're
1180 // not at a safepoint and AsyncDeflateIdleMonitors is false.
1181 if (mark.has_monitor()) {
1182 // The first stage of async deflation does not affect any field
1183 // used by this comparison so the ObjectMonitor* is usable here.
1184 ObjectMonitor* monitor = mark.monitor();
1185 void* owner = monitor->owner();
1186 if (owner == NULL) return owner_none;
1187 return (owner == self ||
1188 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
1189 }
1190
1191 // CASE: neutral
1192 assert(mark.is_neutral(), "sanity check");
1193 return owner_none; // it's unlocked
1194 }
1195
1196 // FIXME: jvmti should call this
1197 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1198 if (UseBiasedLocking) {
1199 if (SafepointSynchronize::is_at_safepoint()) {
1200 BiasedLocking::revoke_at_safepoint(h_obj);
1201 } else {
1202 BiasedLocking::revoke(h_obj, JavaThread::current());
1203 }
1204 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1205 }
1206
1207 oop obj = h_obj();
1208 address owner = NULL;
1209
1210 markWord mark = read_stable_mark(obj);
1211
1212 // Uncontended case, header points to stack
1213 if (mark.has_locker()) {
1214 owner = (address) mark.locker();
1215 }
1216
1217 // Contended case, header points to ObjectMonitor (tagged pointer)
1218 else if (mark.has_monitor()) {
1219 // The first stage of async deflation does not affect any field
1220 // used by this comparison so the ObjectMonitor* is usable here.
1221 ObjectMonitor* monitor = mark.monitor();
1222 assert(monitor != NULL, "monitor should be non-null");
1223 owner = (address) monitor->owner();
1224 }
1225
1226 if (owner != NULL) {
1227 // owning_thread_from_monitor_owner() may also return NULL here
1228 return Threads::owning_thread_from_monitor_owner(t_list, owner);
1229 }
1230
1231 // Unlocked case, header in place
1232 // Cannot have assertion since this object may have been
1233 // locked by another thread when reaching here.
1234 // assert(mark.is_neutral(), "sanity check");
1235
1236 return NULL;
1237 }
1238
1239 // Visitors ...
1240
1241 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
1242 PaddedObjectMonitor* block = Atomic::load(&g_block_list);
1243 while (block != NULL) {
1244 assert(block->object() == CHAINMARKER, "must be a block header");
1245 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
1246 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
1247 if (!mid->is_free() && mid->object() != NULL) {
1248 // Only process with closure if the object is set.
1249
1250 // monitors_iterate() is only called at a safepoint or when the
1251 // target thread is suspended or when the target thread is
1252 // operating on itself. The closures are only interested in an
1253 // owned ObjectMonitor and ownership cannot be dropped under the
1254 // calling contexts so the ObjectMonitor cannot be async deflated.
1255 closure->do_monitor(mid);
1256 }
1257 }
1258 // unmarked_next() is not needed with g_block_list (no locking
1259 // used with block linkage _next_om fields).
1260 block = (PaddedObjectMonitor*)block->next_om();
1261 }
1262 }
1263
1264 static bool monitors_used_above_threshold() {
1265 int population = Atomic::load(&om_list_globals._population);
1266 if (population == 0) {
1267 return false;
1268 }
1269 if (MonitorUsedDeflationThreshold > 0) {
1270 int monitors_used = population - Atomic::load(&om_list_globals._free_count) -
1271 Atomic::load(&om_list_globals._wait_count);
1272 int monitor_usage = (monitors_used * 100LL) / population;
1273 return monitor_usage > MonitorUsedDeflationThreshold;
1274 }
1275 return false;
1276 }
1277
1278 bool ObjectSynchronizer::is_async_deflation_needed() {
1279 if (!AsyncDeflateIdleMonitors) {
1280 return false;
1281 }
1282 if (is_async_deflation_requested()) {
1283 // Async deflation request.
1284 return true;
1285 }
1286 if (AsyncDeflationInterval > 0 &&
1287 time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1288 monitors_used_above_threshold()) {
1289 // It's been longer than our specified deflate interval and there
1290 // are too many monitors in use. We don't deflate more frequently
1291 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1292 // in order to not swamp the ServiceThread.
1293 _last_async_deflation_time_ns = os::javaTimeNanos();
1294 return true;
1295 }
1296 return false;
1297 }
1298
1299 bool ObjectSynchronizer::is_safepoint_deflation_needed() {
1300 if (!AsyncDeflateIdleMonitors) {
1301 if (monitors_used_above_threshold()) {
1302 // Too many monitors in use.
1303 return true;
1304 }
1305 return false;
1306 }
1307 if (is_special_deflation_requested()) {
1308 // For AsyncDeflateIdleMonitors only do a safepoint deflation
1309 // if there is a special deflation request.
1310 return true;
1311 }
1312 return false;
1313 }
1314
1315 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1316 return (os::javaTimeNanos() - _last_async_deflation_time_ns) / (NANOUNITS / MILLIUNITS);
1317 }
1318
1319 void ObjectSynchronizer::oops_do(OopClosure* f) {
1320 // We only scan the global used list here (for moribund threads), and
1321 // the thread-local monitors in Thread::oops_do().
1322 global_used_oops_do(f);
1323 }
1324
1325 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
1326 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1327 list_oops_do(Atomic::load(&om_list_globals._in_use_list), f);
1328 }
1329
1330 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
1331 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1332 list_oops_do(thread->om_in_use_list, f);
1333 }
1334
1335 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
1336 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1337 // The oops_do() phase does not overlap with monitor deflation
1338 // so no need to lock ObjectMonitors for the list traversal.
1339 for (ObjectMonitor* mid = list; mid != NULL; mid = unmarked_next(mid)) {
1340 if (mid->object() != NULL) {
1341 f->do_oop((oop*)mid->object_addr());
1342 }
1343 }
1344 }
1345
1346
1347 // -----------------------------------------------------------------------------
1348 // ObjectMonitor Lifecycle
1349 // -----------------------
1350 // Inflation unlinks monitors from om_list_globals._free_list or a per-thread
1351 // free list and associates them with objects. Deflation -- which occurs at
1352 // STW-time or asynchronously -- disassociates idle monitors from objects.
1353 // Such scavenged monitors are returned to the om_list_globals._free_list.
1354 //
1355 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1356 //
1357 // Lifecycle:
1358 // -- unassigned and on the om_list_globals._free_list
1359 // -- unassigned and on a per-thread free list
1360 // -- assigned to an object. The object is inflated and the mark refers
1361 // to the ObjectMonitor.
1362
1363 ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self) {
1364 // A large MAXPRIVATE value reduces both list lock contention
1365 // and list coherency traffic, but also tends to increase the
1366 // number of ObjectMonitors in circulation as well as the STW
1367 // scavenge costs. As usual, we lean toward time in space-time
1368 // tradeoffs.
1369 const int MAXPRIVATE = 1024;
1370 NoSafepointVerifier nsv;
1371
1372 for (;;) {
1373 ObjectMonitor* m;
1374
1375 // 1: try to allocate from the thread's local om_free_list.
1376 // Threads will attempt to allocate first from their local list, then
1377 // from the global list, and only after those attempts fail will the
1378 // thread attempt to instantiate new monitors. Thread-local free lists
1379 // improve allocation latency, as well as reducing coherency traffic
1380 // on the shared global list.
1381 m = take_from_start_of_om_free_list(self);
1382 if (m != NULL) {
1383 guarantee(m->object() == NULL, "invariant");
1384 m->set_allocation_state(ObjectMonitor::New);
1385 prepend_to_om_in_use_list(self, m);
1386 return m;
1387 }
1388
1389 // 2: try to allocate from the global om_list_globals._free_list
1390 // If we're using thread-local free lists then try
1391 // to reprovision the caller's free list.
1392 if (Atomic::load(&om_list_globals._free_list) != NULL) {
1393 // Reprovision the thread's om_free_list.
1394 // Use bulk transfers to reduce the allocation rate and heat
1395 // on various locks.
1396 for (int i = self->om_free_provision; --i >= 0;) {
1397 ObjectMonitor* take = take_from_start_of_global_free_list();
1398 if (take == NULL) {
1399 break; // No more are available.
1400 }
1401 guarantee(take->object() == NULL, "invariant");
1402 if (AsyncDeflateIdleMonitors) {
1403 // We allowed 3 field values to linger during async deflation.
1404 // Clear or restore them as appropriate.
1405 take->set_header(markWord::zero());
1406 // DEFLATER_MARKER is the only non-NULL value we should see here.
1407 take->try_set_owner_from(DEFLATER_MARKER, NULL);
1408 if (take->contentions() < 0) {
1409 // Add back max_jint to restore the contentions field to its
1410 // proper value.
1411 Atomic::add(&take->_contentions, max_jint);
1412
1413 #ifdef ASSERT
1414 jint l_contentions = take->contentions();
1415 #endif
1416 assert(l_contentions >= 0, "must not be negative: l_contentions=%d, contentions=%d",
1417 l_contentions, take->contentions());
1418 }
1419 }
1420 take->Recycle();
1421 // Since we're taking from the global free-list, take must be Free.
1422 // om_release() also sets the allocation state to Free because it
1423 // is called from other code paths.
1424 assert(take->is_free(), "invariant");
1425 om_release(self, take, false);
1426 }
1427 self->om_free_provision += 1 + (self->om_free_provision / 2);
1428 if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE;
1429 continue;
1430 }
1431
1432 // 3: allocate a block of new ObjectMonitors
1433 // Both the local and global free lists are empty -- resort to malloc().
1434 // In the current implementation ObjectMonitors are TSM - immortal.
1435 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1436 // each ObjectMonitor to start at the beginning of a cache line,
1437 // so we use align_up().
1438 // A better solution would be to use C++ placement-new.
1439 // BEWARE: As it stands currently, we don't run the ctors!
1440 assert(_BLOCKSIZE > 1, "invariant");
1441 size_t neededsize = sizeof(PaddedObjectMonitor) * _BLOCKSIZE;
1442 PaddedObjectMonitor* temp;
1443 size_t aligned_size = neededsize + (OM_CACHE_LINE_SIZE - 1);
1444 void* real_malloc_addr = NEW_C_HEAP_ARRAY(char, aligned_size, mtInternal);
1445 temp = (PaddedObjectMonitor*)align_up(real_malloc_addr, OM_CACHE_LINE_SIZE);
1446 (void)memset((void *) temp, 0, neededsize);
1447
1448 // Format the block.
1449 // initialize the linked list, each monitor points to its next
1450 // forming the single linked free list, the very first monitor
1451 // will points to next block, which forms the block list.
1452 // The trick of using the 1st element in the block as g_block_list
1453 // linkage should be reconsidered. A better implementation would
1454 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1455
1456 for (int i = 1; i < _BLOCKSIZE; i++) {
1457 temp[i].set_next_om((ObjectMonitor*)&temp[i + 1]);
1458 assert(temp[i].is_free(), "invariant");
1459 }
1460
1461 // terminate the last monitor as the end of list
1462 temp[_BLOCKSIZE - 1].set_next_om((ObjectMonitor*)NULL);
1463
1464 // Element [0] is reserved for global list linkage
1465 temp[0].set_object(CHAINMARKER);
1466
1467 // Consider carving out this thread's current request from the
1468 // block in hand. This avoids some lock traffic and redundant
1469 // list activity.
1470
1471 prepend_block_to_lists(temp);
1472 }
1473 }
1474
1475 // Place "m" on the caller's private per-thread om_free_list.
1476 // In practice there's no need to clamp or limit the number of
1477 // monitors on a thread's om_free_list as the only non-allocation time
1478 // we'll call om_release() is to return a monitor to the free list after
1479 // a CAS attempt failed. This doesn't allow unbounded #s of monitors to
1480 // accumulate on a thread's free list.
1481 //
1482 // Key constraint: all ObjectMonitors on a thread's free list and the global
1483 // free list must have their object field set to null. This prevents the
1484 // scavenger -- deflate_monitor_list() or deflate_monitor_list_using_JT()
1485 // -- from reclaiming them while we are trying to release them.
1486
1487 void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m,
1488 bool from_per_thread_alloc) {
1489 guarantee(m->header().value() == 0, "invariant");
1490 guarantee(m->object() == NULL, "invariant");
1491 NoSafepointVerifier nsv;
1492
1493 if ((m->is_busy() | m->_recursions) != 0) {
1494 stringStream ss;
1495 fatal("freeing in-use monitor: %s, recursions=" INTX_FORMAT,
1496 m->is_busy_to_string(&ss), m->_recursions);
1497 }
1498 m->set_allocation_state(ObjectMonitor::Free);
1499 // _next_om is used for both per-thread in-use and free lists so
1500 // we have to remove 'm' from the in-use list first (as needed).
1501 if (from_per_thread_alloc) {
1502 // Need to remove 'm' from om_in_use_list.
1503 ObjectMonitor* mid = NULL;
1504 ObjectMonitor* next = NULL;
1505
1506 // This list walk can race with another list walker or with async
1507 // deflation so we have to worry about an ObjectMonitor being
1508 // removed from this list while we are walking it.
1509
1510 // Lock the list head to avoid racing with another list walker
1511 // or with async deflation.
1512 if ((mid = get_list_head_locked(&self->om_in_use_list)) == NULL) {
1513 fatal("thread=" INTPTR_FORMAT " in-use list must not be empty.", p2i(self));
1514 }
1515 next = unmarked_next(mid);
1516 if (m == mid) {
1517 // First special case:
1518 // 'm' matches mid, is the list head and is locked. Switch the list
1519 // head to next which unlocks the list head, but leaves the extracted
1520 // mid locked:
1521 Atomic::store(&self->om_in_use_list, next);
1522 } else if (m == next) {
1523 // Second special case:
1524 // 'm' matches next after the list head and we already have the list
1525 // head locked so set mid to what we are extracting:
1526 mid = next;
1527 // Lock mid to prevent races with a list walker or an async
1528 // deflater thread that's ahead of us. The locked list head
1529 // prevents races from behind us.
1530 om_lock(mid);
1531 // Update next to what follows mid (if anything):
1532 next = unmarked_next(mid);
1533 // Switch next after the list head to new next which unlocks the
1534 // list head, but leaves the extracted mid locked:
1535 self->om_in_use_list->set_next_om(next);
1536 } else {
1537 // We have to search the list to find 'm'.
1538 guarantee(next != NULL, "thread=" INTPTR_FORMAT ": om_in_use_list=" INTPTR_FORMAT
1539 " is too short.", p2i(self), p2i(self->om_in_use_list));
1540 // Our starting anchor is next after the list head which is the
1541 // last ObjectMonitor we checked:
1542 ObjectMonitor* anchor = next;
1543 // Lock anchor to prevent races with a list walker or an async
1544 // deflater thread that's ahead of us. The locked list head
1545 // prevents races from behind us.
1546 om_lock(anchor);
1547 om_unlock(mid); // Unlock the list head now that anchor is locked.
1548 while ((mid = unmarked_next(anchor)) != NULL) {
1549 if (m == mid) {
1550 // We found 'm' on the per-thread in-use list so extract it.
1551 // Update next to what follows mid (if anything):
1552 next = unmarked_next(mid);
1553 // Switch next after the anchor to new next which unlocks the
1554 // anchor, but leaves the extracted mid locked:
1555 anchor->set_next_om(next);
1556 break;
1557 } else {
1558 // Lock the next anchor to prevent races with a list walker
1559 // or an async deflater thread that's ahead of us. The locked
1560 // current anchor prevents races from behind us.
1561 om_lock(mid);
1562 // Unlock current anchor now that next anchor is locked:
1563 om_unlock(anchor);
1564 anchor = mid; // Advance to new anchor and try again.
1565 }
1566 }
1567 }
1568
1569 if (mid == NULL) {
1570 // Reached end of the list and didn't find 'm' so:
1571 fatal("thread=" INTPTR_FORMAT " must find m=" INTPTR_FORMAT "on om_in_use_list="
1572 INTPTR_FORMAT, p2i(self), p2i(m), p2i(self->om_in_use_list));
1573 }
1574
1575 // At this point mid is disconnected from the in-use list so
1576 // its lock no longer has any effects on the in-use list.
1577 Atomic::dec(&self->om_in_use_count);
1578 // Unlock mid, but leave the next value for any lagging list
1579 // walkers. It will get cleaned up when mid is prepended to
1580 // the thread's free list:
1581 om_unlock(mid);
1582 }
1583
1584 prepend_to_om_free_list(self, m);
1585 guarantee(m->is_free(), "invariant");
1586 }
1587
1588 // Return ObjectMonitors on a moribund thread's free and in-use
1589 // lists to the appropriate global lists. The ObjectMonitors on the
1590 // per-thread in-use list may still be in use by other threads.
1591 //
1592 // We currently call om_flush() from Threads::remove() before the
1593 // thread has been excised from the thread list and is no longer a
1594 // mutator. This means that om_flush() cannot run concurrently with
1595 // a safepoint and interleave with deflate_idle_monitors(). In
1596 // particular, this ensures that the thread's in-use monitors are
1597 // scanned by a GC safepoint, either via Thread::oops_do() (before
1598 // om_flush() is called) or via ObjectSynchronizer::oops_do() (after
1599 // om_flush() is called).
1600 //
1601 // With AsyncDeflateIdleMonitors, deflate_global_idle_monitors_using_JT()
1602 // and deflate_per_thread_idle_monitors_using_JT() (in another thread) can
1603 // run at the same time as om_flush() so we have to follow a careful
1604 // protocol to prevent list corruption.
1605
1606 void ObjectSynchronizer::om_flush(Thread* self) {
1607 // Process the per-thread in-use list first to be consistent.
1608 int in_use_count = 0;
1609 ObjectMonitor* in_use_list = NULL;
1610 ObjectMonitor* in_use_tail = NULL;
1611 NoSafepointVerifier nsv;
1612
1613 // This function can race with a list walker or with an async
1614 // deflater thread so we lock the list head to prevent confusion.
1615 // An async deflater thread checks to see if the target thread
1616 // is exiting, but if it has made it past that check before we
1617 // started exiting, then it is racing to get to the in-use list.
1618 if ((in_use_list = get_list_head_locked(&self->om_in_use_list)) != NULL) {
1619 // At this point, we have locked the in-use list head so a racing
1620 // thread cannot come in after us. However, a racing thread could
1621 // be ahead of us; we'll detect that and delay to let it finish.
1622 //
1623 // The thread is going away, however the ObjectMonitors on the
1624 // om_in_use_list may still be in-use by other threads. Link
1625 // them to in_use_tail, which will be linked into the global
1626 // in-use list (om_list_globals._in_use_list) below.
1627 //
1628 // Account for the in-use list head before the loop since it is
1629 // already locked (by this thread):
1630 in_use_tail = in_use_list;
1631 in_use_count++;
1632 for (ObjectMonitor* cur_om = unmarked_next(in_use_list); cur_om != NULL;) {
1633 if (is_locked(cur_om)) {
1634 // cur_om is locked so there must be a racing walker or async
1635 // deflater thread ahead of us so we'll give it a chance to finish.
1636 while (is_locked(cur_om)) {
1637 os::naked_short_sleep(1);
1638 }
1639 // Refetch the possibly changed next field and try again.
1640 cur_om = unmarked_next(in_use_tail);
1641 continue;
1642 }
1643 if (cur_om->is_free()) {
1644 // cur_om was deflated and the allocation state was changed
1645 // to Free while it was locked. We happened to see it just
1646 // after it was unlocked (and added to the free list).
1647 // Refetch the possibly changed next field and try again.
1648 cur_om = unmarked_next(in_use_tail);
1649 continue;
1650 }
1651 in_use_tail = cur_om;
1652 in_use_count++;
1653 cur_om = unmarked_next(cur_om);
1654 }
1655 guarantee(in_use_tail != NULL, "invariant");
1656 int l_om_in_use_count = Atomic::load(&self->om_in_use_count);
1657 ADIM_guarantee(l_om_in_use_count == in_use_count, "in-use counts don't match: "
1658 "l_om_in_use_count=%d, in_use_count=%d", l_om_in_use_count, in_use_count);
1659 Atomic::store(&self->om_in_use_count, 0);
1660 // Clear the in-use list head (which also unlocks it):
1661 Atomic::store(&self->om_in_use_list, (ObjectMonitor*)NULL);
1662 om_unlock(in_use_list);
1663 }
1664
1665 int free_count = 0;
1666 ObjectMonitor* free_list = NULL;
1667 ObjectMonitor* free_tail = NULL;
1668 // This function can race with a list walker thread so we lock the
1669 // list head to prevent confusion.
1670 if ((free_list = get_list_head_locked(&self->om_free_list)) != NULL) {
1671 // At this point, we have locked the free list head so a racing
1672 // thread cannot come in after us. However, a racing thread could
1673 // be ahead of us; we'll detect that and delay to let it finish.
1674 //
1675 // The thread is going away. Set 'free_tail' to the last per-thread free
1676 // monitor which will be linked to om_list_globals._free_list below.
1677 //
1678 // Account for the free list head before the loop since it is
1679 // already locked (by this thread):
1680 free_tail = free_list;
1681 free_count++;
1682 for (ObjectMonitor* s = unmarked_next(free_list); s != NULL; s = unmarked_next(s)) {
1683 if (is_locked(s)) {
1684 // s is locked so there must be a racing walker thread ahead
1685 // of us so we'll give it a chance to finish.
1686 while (is_locked(s)) {
1687 os::naked_short_sleep(1);
1688 }
1689 }
1690 free_tail = s;
1691 free_count++;
1692 guarantee(s->object() == NULL, "invariant");
1693 if (s->is_busy()) {
1694 stringStream ss;
1695 fatal("must be !is_busy: %s", s->is_busy_to_string(&ss));
1696 }
1697 }
1698 guarantee(free_tail != NULL, "invariant");
1699 int l_om_free_count = Atomic::load(&self->om_free_count);
1700 ADIM_guarantee(l_om_free_count == free_count, "free counts don't match: "
1701 "l_om_free_count=%d, free_count=%d", l_om_free_count, free_count);
1702 Atomic::store(&self->om_free_count, 0);
1703 Atomic::store(&self->om_free_list, (ObjectMonitor*)NULL);
1704 om_unlock(free_list);
1705 }
1706
1707 if (free_tail != NULL) {
1708 prepend_list_to_global_free_list(free_list, free_tail, free_count);
1709 }
1710
1711 if (in_use_tail != NULL) {
1712 prepend_list_to_global_in_use_list(in_use_list, in_use_tail, in_use_count);
1713 }
1714
1715 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1716 LogStreamHandle(Info, monitorinflation) lsh_info;
1717 LogStream* ls = NULL;
1718 if (log_is_enabled(Debug, monitorinflation)) {
1719 ls = &lsh_debug;
1720 } else if ((free_count != 0 || in_use_count != 0) &&
1721 log_is_enabled(Info, monitorinflation)) {
1722 ls = &lsh_info;
1723 }
1724 if (ls != NULL) {
1725 ls->print_cr("om_flush: jt=" INTPTR_FORMAT ", free_count=%d"
1726 ", in_use_count=%d" ", om_free_provision=%d",
1727 p2i(self), free_count, in_use_count, self->om_free_provision);
1728 }
1729 }
1730
1731 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1732 const oop obj,
1733 ObjectSynchronizer::InflateCause cause) {
1734 assert(event != NULL, "invariant");
1735 assert(event->should_commit(), "invariant");
1736 event->set_monitorClass(obj->klass());
1737 event->set_address((uintptr_t)(void*)obj);
1738 event->set_cause((u1)cause);
1739 event->commit();
1740 }
1741
1742 // Fast path code shared by multiple functions
1743 void ObjectSynchronizer::inflate_helper(oop obj) {
1744 markWord mark = obj->mark();
1745 if (mark.has_monitor()) {
1746 ObjectMonitor* monitor = mark.monitor();
1747 assert(ObjectSynchronizer::verify_objmon_isinpool(monitor), "monitor=" INTPTR_FORMAT " is invalid", p2i(monitor));
1748 markWord dmw = monitor->header();
1749 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1750 return;
1751 }
1752 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1753 }
1754
1755 ObjectMonitor* ObjectSynchronizer::inflate(Thread* self, oop object,
1756 const InflateCause cause) {
1757 // Inflate mutates the heap ...
1758 // Relaxing assertion for bug 6320749.
1759 assert(Universe::verify_in_progress() ||
1760 !SafepointSynchronize::is_at_safepoint(), "invariant");
1761
1762 EventJavaMonitorInflate event;
1763
1764 for (;;) {
1765 const markWord mark = object->mark();
1766 assert(!mark.has_bias_pattern(), "invariant");
1767
1768 // The mark can be in one of the following states:
1769 // * Inflated - just return
1770 // * Stack-locked - coerce it to inflated
1771 // * INFLATING - busy wait for conversion to complete
1772 // * Neutral - aggressively inflate the object.
1773 // * BIASED - Illegal. We should never see this
1774
1775 // CASE: inflated
1776 if (mark.has_monitor()) {
1777 ObjectMonitor* inf = mark.monitor();
1778 markWord dmw = inf->header();
1779 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1780 assert(AsyncDeflateIdleMonitors || inf->object() == object, "invariant");
1781 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1782 return inf;
1783 }
1784
1785 // CASE: inflation in progress - inflating over a stack-lock.
1786 // Some other thread is converting from stack-locked to inflated.
1787 // Only that thread can complete inflation -- other threads must wait.
1788 // The INFLATING value is transient.
1789 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1790 // We could always eliminate polling by parking the thread on some auxiliary list.
1791 if (mark == markWord::INFLATING()) {
1792 read_stable_mark(object);
1793 continue;
1794 }
1795
1796 // CASE: stack-locked
1797 // Could be stack-locked either by this thread or by some other thread.
1798 //
1799 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1800 // to install INFLATING into the mark word. We originally installed INFLATING,
1801 // allocated the objectmonitor, and then finally STed the address of the
1802 // objectmonitor into the mark. This was correct, but artificially lengthened
1803 // the interval in which INFLATED appeared in the mark, thus increasing
1804 // the odds of inflation contention.
1805 //
1806 // We now use per-thread private objectmonitor free lists.
1807 // These list are reprovisioned from the global free list outside the
1808 // critical INFLATING...ST interval. A thread can transfer
1809 // multiple objectmonitors en-mass from the global free list to its local free list.
1810 // This reduces coherency traffic and lock contention on the global free list.
1811 // Using such local free lists, it doesn't matter if the om_alloc() call appears
1812 // before or after the CAS(INFLATING) operation.
1813 // See the comments in om_alloc().
1814
1815 LogStreamHandle(Trace, monitorinflation) lsh;
1816
1817 if (mark.has_locker()) {
1818 ObjectMonitor* m = om_alloc(self);
1819 // Optimistically prepare the objectmonitor - anticipate successful CAS
1820 // We do this before the CAS in order to minimize the length of time
1821 // in which INFLATING appears in the mark.
1822 m->Recycle();
1823 m->_Responsible = NULL;
1824 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1825
1826 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1827 if (cmp != mark) {
1828 // om_release() will reset the allocation state from New to Free.
1829 om_release(self, m, true);
1830 continue; // Interference -- just retry
1831 }
1832
1833 // We've successfully installed INFLATING (0) into the mark-word.
1834 // This is the only case where 0 will appear in a mark-word.
1835 // Only the singular thread that successfully swings the mark-word
1836 // to 0 can perform (or more precisely, complete) inflation.
1837 //
1838 // Why do we CAS a 0 into the mark-word instead of just CASing the
1839 // mark-word from the stack-locked value directly to the new inflated state?
1840 // Consider what happens when a thread unlocks a stack-locked object.
1841 // It attempts to use CAS to swing the displaced header value from the
1842 // on-stack BasicLock back into the object header. Recall also that the
1843 // header value (hash code, etc) can reside in (a) the object header, or
1844 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1845 // header in an ObjectMonitor. The inflate() routine must copy the header
1846 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1847 // the while preserving the hashCode stability invariants. If the owner
1848 // decides to release the lock while the value is 0, the unlock will fail
1849 // and control will eventually pass from slow_exit() to inflate. The owner
1850 // will then spin, waiting for the 0 value to disappear. Put another way,
1851 // the 0 causes the owner to stall if the owner happens to try to
1852 // drop the lock (restoring the header from the BasicLock to the object)
1853 // while inflation is in-progress. This protocol avoids races that might
1854 // would otherwise permit hashCode values to change or "flicker" for an object.
1855 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1856 // 0 serves as a "BUSY" inflate-in-progress indicator.
1857
1858
1859 // fetch the displaced mark from the owner's stack.
1860 // The owner can't die or unwind past the lock while our INFLATING
1861 // object is in the mark. Furthermore the owner can't complete
1862 // an unlock on the object, either.
1863 markWord dmw = mark.displaced_mark_helper();
1864 // Catch if the object's header is not neutral (not locked and
1865 // not marked is what we care about here).
1866 ADIM_guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1867
1868 // Setup monitor fields to proper values -- prepare the monitor
1869 m->set_header(dmw);
1870
1871 // Optimization: if the mark.locker stack address is associated
1872 // with this thread we could simply set m->_owner = self.
1873 // Note that a thread can inflate an object
1874 // that it has stack-locked -- as might happen in wait() -- directly
1875 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1876 if (AsyncDeflateIdleMonitors) {
1877 m->set_owner_from(NULL, DEFLATER_MARKER, mark.locker());
1878 } else {
1879 m->set_owner_from(NULL, mark.locker());
1880 }
1881 m->set_object(object);
1882 // TODO-FIXME: assert BasicLock->dhw != 0.
1883
1884 // Must preserve store ordering. The monitor state must
1885 // be stable at the time of publishing the monitor address.
1886 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1887 object->release_set_mark(markWord::encode(m));
1888
1889 // Once ObjectMonitor is configured and the object is associated
1890 // with the ObjectMonitor, it is safe to allow async deflation:
1891 assert(m->is_new(), "freshly allocated monitor must be new");
1892 m->set_allocation_state(ObjectMonitor::Old);
1893
1894 // Hopefully the performance counters are allocated on distinct cache lines
1895 // to avoid false sharing on MP systems ...
1896 OM_PERFDATA_OP(Inflations, inc());
1897 if (log_is_enabled(Trace, monitorinflation)) {
1898 ResourceMark rm(self);
1899 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1900 INTPTR_FORMAT ", type='%s'", p2i(object),
1901 object->mark().value(), object->klass()->external_name());
1902 }
1903 if (event.should_commit()) {
1904 post_monitor_inflate_event(&event, object, cause);
1905 }
1906 return m;
1907 }
1908
1909 // CASE: neutral
1910 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1911 // If we know we're inflating for entry it's better to inflate by swinging a
1912 // pre-locked ObjectMonitor pointer into the object header. A successful
1913 // CAS inflates the object *and* confers ownership to the inflating thread.
1914 // In the current implementation we use a 2-step mechanism where we CAS()
1915 // to inflate and then CAS() again to try to swing _owner from NULL to self.
1916 // An inflateTry() method that we could call from enter() would be useful.
1917
1918 // Catch if the object's header is not neutral (not locked and
1919 // not marked is what we care about here).
1920 ADIM_guarantee(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1921 ObjectMonitor* m = om_alloc(self);
1922 // prepare m for installation - set monitor to initial state
1923 m->Recycle();
1924 m->set_header(mark);
1925 if (AsyncDeflateIdleMonitors) {
1926 // DEFLATER_MARKER is the only non-NULL value we should see here.
1927 m->try_set_owner_from(DEFLATER_MARKER, NULL);
1928 }
1929 m->set_object(object);
1930 m->_Responsible = NULL;
1931 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1932
1933 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1934 m->set_header(markWord::zero());
1935 m->set_object(NULL);
1936 m->Recycle();
1937 // om_release() will reset the allocation state from New to Free.
1938 om_release(self, m, true);
1939 m = NULL;
1940 continue;
1941 // interference - the markword changed - just retry.
1942 // The state-transitions are one-way, so there's no chance of
1943 // live-lock -- "Inflated" is an absorbing state.
1944 }
1945
1946 // Once the ObjectMonitor is configured and object is associated
1947 // with the ObjectMonitor, it is safe to allow async deflation:
1948 assert(m->is_new(), "freshly allocated monitor must be new");
1949 m->set_allocation_state(ObjectMonitor::Old);
1950
1951 // Hopefully the performance counters are allocated on distinct
1952 // cache lines to avoid false sharing on MP systems ...
1953 OM_PERFDATA_OP(Inflations, inc());
1954 if (log_is_enabled(Trace, monitorinflation)) {
1955 ResourceMark rm(self);
1956 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1957 INTPTR_FORMAT ", type='%s'", p2i(object),
1958 object->mark().value(), object->klass()->external_name());
1959 }
1960 if (event.should_commit()) {
1961 post_monitor_inflate_event(&event, object, cause);
1962 }
1963 return m;
1964 }
1965 }
1966
1967
1968 // We maintain a list of in-use monitors for each thread.
1969 //
1970 // For safepoint based deflation:
1971 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1972 // deflate_idle_monitors() scans only a global list of in-use monitors which
1973 // is populated only as a thread dies (see om_flush()).
1974 //
1975 // These operations are called at all safepoints, immediately after mutators
1976 // are stopped, but before any objects have moved. Collectively they traverse
1977 // the population of in-use monitors, deflating where possible. The scavenged
1978 // monitors are returned to the global monitor free list.
1979 //
1980 // Beware that we scavenge at *every* stop-the-world point. Having a large
1981 // number of monitors in-use could negatively impact performance. We also want
1982 // to minimize the total # of monitors in circulation, as they incur a small
1983 // footprint penalty.
1984 //
1985 // Perversely, the heap size -- and thus the STW safepoint rate --
1986 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1987 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1988 // This is an unfortunate aspect of this design.
1989 //
1990 // For async deflation:
1991 // If a special deflation request is made, then the safepoint based
1992 // deflation mechanism is used. Otherwise, an async deflation request
1993 // is registered with the ServiceThread and it is notified.
1994
1995 void ObjectSynchronizer::do_safepoint_work(DeflateMonitorCounters* counters) {
1996 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1997
1998 // The per-thread in-use lists are handled in
1999 // ParallelSPCleanupThreadClosure::do_thread().
2000
2001 if (!AsyncDeflateIdleMonitors || is_special_deflation_requested()) {
2002 // Use the older mechanism for the global in-use list or if a
2003 // special deflation has been requested before the safepoint.
2004 ObjectSynchronizer::deflate_idle_monitors(counters);
2005 return;
2006 }
2007
2008 log_debug(monitorinflation)("requesting async deflation of idle monitors.");
2009 // Request deflation of idle monitors by the ServiceThread:
2010 set_is_async_deflation_requested(true);
2011 MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
2012 ml.notify_all();
2013
2014 if (log_is_enabled(Debug, monitorinflation)) {
2015 // exit_globals()'s call to audit_and_print_stats() is done
2016 // at the Info level and not at a safepoint.
2017 // For safepoint based deflation, audit_and_print_stats() is called
2018 // in ObjectSynchronizer::finish_deflate_idle_monitors() at the
2019 // Debug level at a safepoint.
2020 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2021 }
2022 }
2023
2024 // Deflate a single monitor if not in-use
2025 // Return true if deflated, false if in-use
2026 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
2027 ObjectMonitor** free_head_p,
2028 ObjectMonitor** free_tail_p) {
2029 bool deflated;
2030 // Normal case ... The monitor is associated with obj.
2031 const markWord mark = obj->mark();
2032 guarantee(mark == markWord::encode(mid), "should match: mark="
2033 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(),
2034 markWord::encode(mid).value());
2035 // Make sure that mark.monitor() and markWord::encode() agree:
2036 guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
2037 ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid));
2038 const markWord dmw = mid->header();
2039 guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
2040
2041 if (mid->is_busy()) {
2042 // Easy checks are first - the ObjectMonitor is busy so no deflation.
2043 deflated = false;
2044 } else {
2045 // Deflate the monitor if it is no longer being used
2046 // It's idle - scavenge and return to the global free list
2047 // plain old deflation ...
2048 if (log_is_enabled(Trace, monitorinflation)) {
2049 ResourceMark rm;
2050 log_trace(monitorinflation)("deflate_monitor: "
2051 "object=" INTPTR_FORMAT ", mark="
2052 INTPTR_FORMAT ", type='%s'", p2i(obj),
2053 mark.value(), obj->klass()->external_name());
2054 }
2055
2056 // Restore the header back to obj
2057 obj->release_set_mark(dmw);
2058 if (AsyncDeflateIdleMonitors) {
2059 // clear() expects the owner field to be NULL.
2060 // DEFLATER_MARKER is the only non-NULL value we should see here.
2061 mid->try_set_owner_from(DEFLATER_MARKER, NULL);
2062 }
2063 mid->clear();
2064
2065 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
2066 p2i(mid->object()));
2067 assert(mid->is_free(), "invariant");
2068
2069 // Move the deflated ObjectMonitor to the working free list
2070 // defined by free_head_p and free_tail_p.
2071 if (*free_head_p == NULL) *free_head_p = mid;
2072 if (*free_tail_p != NULL) {
2073 // We append to the list so the caller can use mid->_next_om
2074 // to fix the linkages in its context.
2075 ObjectMonitor* prevtail = *free_tail_p;
2076 // Should have been cleaned up by the caller:
2077 // Note: Should not have to lock prevtail here since we're at a
2078 // safepoint and ObjectMonitors on the local free list should
2079 // not be accessed in parallel.
2080 #ifdef ASSERT
2081 ObjectMonitor* l_next_om = prevtail->next_om();
2082 #endif
2083 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2084 prevtail->set_next_om(mid);
2085 }
2086 *free_tail_p = mid;
2087 // At this point, mid->_next_om still refers to its current
2088 // value and another ObjectMonitor's _next_om field still
2089 // refers to this ObjectMonitor. Those linkages have to be
2090 // cleaned up by the caller who has the complete context.
2091 deflated = true;
2092 }
2093 return deflated;
2094 }
2095
2096 // Deflate the specified ObjectMonitor if not in-use using a JavaThread.
2097 // Returns true if it was deflated and false otherwise.
2098 //
2099 // The async deflation protocol sets owner to DEFLATER_MARKER and
2100 // makes contentions negative as signals to contending threads that
2101 // an async deflation is in progress. There are a number of checks
2102 // as part of the protocol to make sure that the calling thread has
2103 // not lost the race to a contending thread.
2104 //
2105 // The ObjectMonitor has been successfully async deflated when:
2106 // (owner == DEFLATER_MARKER && contentions < 0)
2107 // Contending threads that see those values know to retry their operation.
2108 //
2109 bool ObjectSynchronizer::deflate_monitor_using_JT(ObjectMonitor* mid,
2110 ObjectMonitor** free_head_p,
2111 ObjectMonitor** free_tail_p) {
2112 assert(AsyncDeflateIdleMonitors, "sanity check");
2113 assert(Thread::current()->is_Java_thread(), "precondition");
2114 // A newly allocated ObjectMonitor should not be seen here so we
2115 // avoid an endless inflate/deflate cycle.
2116 assert(mid->is_old(), "must be old: allocation_state=%d",
2117 (int) mid->allocation_state());
2118
2119 if (mid->is_busy()) {
2120 // Easy checks are first - the ObjectMonitor is busy so no deflation.
2121 return false;
2122 }
2123
2124 // Set a NULL owner to DEFLATER_MARKER to force any contending thread
2125 // through the slow path. This is just the first part of the async
2126 // deflation dance.
2127 if (mid->try_set_owner_from(NULL, DEFLATER_MARKER) != NULL) {
2128 // The owner field is no longer NULL so we lost the race since the
2129 // ObjectMonitor is now busy.
2130 return false;
2131 }
2132
2133 if (mid->contentions() > 0 || mid->_waiters != 0) {
2134 // Another thread has raced to enter the ObjectMonitor after
2135 // mid->is_busy() above or has already entered and waited on
2136 // it which makes it busy so no deflation. Restore owner to
2137 // NULL if it is still DEFLATER_MARKER.
2138 mid->try_set_owner_from(DEFLATER_MARKER, NULL);
2139 return false;
2140 }
2141
2142 // Make contentions negative to force any contending threads to
2143 // retry. This is the second part of the async deflation dance.
2144 if (Atomic::cmpxchg(&mid->_contentions, (jint)0, -max_jint) != 0) {
2145 // The contentions was no longer 0 so we lost the race since the
2146 // ObjectMonitor is now busy. Restore owner to NULL if it is
2147 // still DEFLATER_MARKER:
2148 mid->try_set_owner_from(DEFLATER_MARKER, NULL);
2149 return false;
2150 }
2151
2152 // If owner is still DEFLATER_MARKER, then we have successfully
2153 // signaled any contending threads to retry.
2154 if (!mid->owner_is_DEFLATER_MARKER()) {
2155 // If it is not, then we have lost the race to an entering thread
2156 // and the ObjectMonitor is now busy. This is the third and final
2157 // part of the async deflation dance.
2158 // Note: This owner check solves the ABA problem with contentions
2159 // where another thread acquired the ObjectMonitor, finished
2160 // using it and restored contentions to zero.
2161
2162 // Add back max_jint to restore the contentions field to its
2163 // proper value (which may not be what we saw above):
2164 Atomic::add(&mid->_contentions, max_jint);
2165
2166 #ifdef ASSERT
2167 jint l_contentions = mid->contentions();
2168 #endif
2169 assert(l_contentions >= 0, "must not be negative: l_contentions=%d, contentions=%d",
2170 l_contentions, mid->contentions());
2171 return false;
2172 }
2173
2174 // Sanity checks for the races:
2175 guarantee(mid->contentions() < 0, "must be negative: contentions=%d",
2176 mid->contentions());
2177 guarantee(mid->_waiters == 0, "must be 0: waiters=%d", mid->_waiters);
2178 guarantee(mid->_cxq == NULL, "must be no contending threads: cxq="
2179 INTPTR_FORMAT, p2i(mid->_cxq));
2180 guarantee(mid->_EntryList == NULL,
2181 "must be no entering threads: EntryList=" INTPTR_FORMAT,
2182 p2i(mid->_EntryList));
2183
2184 const oop obj = (oop) mid->object();
2185 if (log_is_enabled(Trace, monitorinflation)) {
2186 ResourceMark rm;
2187 log_trace(monitorinflation)("deflate_monitor_using_JT: "
2188 "object=" INTPTR_FORMAT ", mark="
2189 INTPTR_FORMAT ", type='%s'",
2190 p2i(obj), obj->mark().value(),
2191 obj->klass()->external_name());
2192 }
2193
2194 // Install the old mark word if nobody else has already done it.
2195 mid->install_displaced_markword_in_object(obj);
2196 mid->clear_using_JT();
2197
2198 assert(mid->object() == NULL, "must be NULL: object=" INTPTR_FORMAT,
2199 p2i(mid->object()));
2200 assert(mid->is_free(), "must be free: allocation_state=%d",
2201 (int)mid->allocation_state());
2202
2203 // Move the deflated ObjectMonitor to the working free list
2204 // defined by free_head_p and free_tail_p.
2205 if (*free_head_p == NULL) {
2206 // First one on the list.
2207 *free_head_p = mid;
2208 }
2209 if (*free_tail_p != NULL) {
2210 // We append to the list so the caller can use mid->_next_om
2211 // to fix the linkages in its context.
2212 ObjectMonitor* prevtail = *free_tail_p;
2213 // prevtail should have been cleaned up by the caller:
2214 #ifdef ASSERT
2215 ObjectMonitor* l_next_om = unmarked_next(prevtail);
2216 #endif
2217 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2218 om_lock(prevtail);
2219 prevtail->set_next_om(mid); // prevtail now points to mid (and is unlocked)
2220 }
2221 *free_tail_p = mid;
2222
2223 // At this point, mid->_next_om still refers to its current
2224 // value and another ObjectMonitor's _next_om field still
2225 // refers to this ObjectMonitor. Those linkages have to be
2226 // cleaned up by the caller who has the complete context.
2227
2228 // We leave owner == DEFLATER_MARKER and contentions < 0
2229 // to force any racing threads to retry.
2230 return true; // Success, ObjectMonitor has been deflated.
2231 }
2232
2233 // Walk a given monitor list, and deflate idle monitors.
2234 // The given list could be a per-thread list or a global list.
2235 //
2236 // In the case of parallel processing of thread local monitor lists,
2237 // work is done by Threads::parallel_threads_do() which ensures that
2238 // each Java thread is processed by exactly one worker thread, and
2239 // thus avoid conflicts that would arise when worker threads would
2240 // process the same monitor lists concurrently.
2241 //
2242 // See also ParallelSPCleanupTask and
2243 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
2244 // Threads::parallel_java_threads_do() in thread.cpp.
2245 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** list_p,
2246 int* count_p,
2247 ObjectMonitor** free_head_p,
2248 ObjectMonitor** free_tail_p) {
2249 ObjectMonitor* cur_mid_in_use = NULL;
2250 ObjectMonitor* mid = NULL;
2251 ObjectMonitor* next = NULL;
2252 int deflated_count = 0;
2253
2254 // This list walk executes at a safepoint and does not race with any
2255 // other list walkers.
2256
2257 for (mid = Atomic::load(list_p); mid != NULL; mid = next) {
2258 next = unmarked_next(mid);
2259 oop obj = (oop) mid->object();
2260 if (obj != NULL && deflate_monitor(mid, obj, free_head_p, free_tail_p)) {
2261 // Deflation succeeded and already updated free_head_p and
2262 // free_tail_p as needed. Finish the move to the local free list
2263 // by unlinking mid from the global or per-thread in-use list.
2264 if (cur_mid_in_use == NULL) {
2265 // mid is the list head so switch the list head to next:
2266 Atomic::store(list_p, next);
2267 } else {
2268 // Switch cur_mid_in_use's next field to next:
2269 cur_mid_in_use->set_next_om(next);
2270 }
2271 // At this point mid is disconnected from the in-use list.
2272 deflated_count++;
2273 Atomic::dec(count_p);
2274 // mid is current tail in the free_head_p list so NULL terminate it:
2275 mid->set_next_om(NULL);
2276 } else {
2277 cur_mid_in_use = mid;
2278 }
2279 }
2280 return deflated_count;
2281 }
2282
2283 // Walk a given ObjectMonitor list and deflate idle ObjectMonitors using
2284 // a JavaThread. Returns the number of deflated ObjectMonitors. The given
2285 // list could be a per-thread in-use list or the global in-use list.
2286 // If a safepoint has started, then we save state via saved_mid_in_use_p
2287 // and return to the caller to honor the safepoint.
2288 //
2289 int ObjectSynchronizer::deflate_monitor_list_using_JT(ObjectMonitor** list_p,
2290 int* count_p,
2291 ObjectMonitor** free_head_p,
2292 ObjectMonitor** free_tail_p,
2293 ObjectMonitor** saved_mid_in_use_p) {
2294 assert(AsyncDeflateIdleMonitors, "sanity check");
2295 JavaThread* self = JavaThread::current();
2296
2297 ObjectMonitor* cur_mid_in_use = NULL;
2298 ObjectMonitor* mid = NULL;
2299 ObjectMonitor* next = NULL;
2300 ObjectMonitor* next_next = NULL;
2301 int deflated_count = 0;
2302 NoSafepointVerifier nsv;
2303
2304 // We use the more complicated lock-cur_mid_in_use-and-mid-as-we-go
2305 // protocol because om_release() can do list deletions in parallel;
2306 // this also prevents races with a list walker thread. We also
2307 // lock-next-next-as-we-go to prevent an om_flush() that is behind
2308 // this thread from passing us.
2309 if (*saved_mid_in_use_p == NULL) {
2310 // No saved state so start at the beginning.
2311 // Lock the list head so we can possibly deflate it:
2312 if ((mid = get_list_head_locked(list_p)) == NULL) {
2313 return 0; // The list is empty so nothing to deflate.
2314 }
2315 next = unmarked_next(mid);
2316 } else {
2317 // We're restarting after a safepoint so restore the necessary state
2318 // before we resume.
2319 cur_mid_in_use = *saved_mid_in_use_p;
2320 // Lock cur_mid_in_use so we can possibly update its
2321 // next field to extract a deflated ObjectMonitor.
2322 om_lock(cur_mid_in_use);
2323 mid = unmarked_next(cur_mid_in_use);
2324 if (mid == NULL) {
2325 om_unlock(cur_mid_in_use);
2326 *saved_mid_in_use_p = NULL;
2327 return 0; // The remainder is empty so nothing more to deflate.
2328 }
2329 // Lock mid so we can possibly deflate it:
2330 om_lock(mid);
2331 next = unmarked_next(mid);
2332 }
2333
2334 while (true) {
2335 // The current mid is locked at this point. If we have a
2336 // cur_mid_in_use, then it is also locked at this point.
2337
2338 if (next != NULL) {
2339 // We lock next so that an om_flush() thread that is behind us
2340 // cannot pass us when we unlock the current mid.
2341 om_lock(next);
2342 next_next = unmarked_next(next);
2343 }
2344
2345 // Only try to deflate if there is an associated Java object and if
2346 // mid is old (is not newly allocated and is not newly freed).
2347 if (mid->object() != NULL && mid->is_old() &&
2348 deflate_monitor_using_JT(mid, free_head_p, free_tail_p)) {
2349 // Deflation succeeded and already updated free_head_p and
2350 // free_tail_p as needed. Finish the move to the local free list
2351 // by unlinking mid from the global or per-thread in-use list.
2352 if (cur_mid_in_use == NULL) {
2353 // mid is the list head and it is locked. Switch the list head
2354 // to next which is also locked (if not NULL) and also leave
2355 // mid locked:
2356 Atomic::store(list_p, next);
2357 } else {
2358 ObjectMonitor* locked_next = mark_om_ptr(next);
2359 // mid and cur_mid_in_use are locked. Switch cur_mid_in_use's
2360 // next field to locked_next and also leave mid locked:
2361 cur_mid_in_use->set_next_om(locked_next);
2362 }
2363 // At this point mid is disconnected from the in-use list so
2364 // its lock longer has any effects on in-use list.
2365 deflated_count++;
2366 Atomic::dec(count_p);
2367 // mid is current tail in the free_head_p list so NULL terminate it
2368 // (which also unlocks it):
2369 mid->set_next_om(NULL);
2370
2371 // All the list management is done so move on to the next one:
2372 mid = next; // mid keeps non-NULL next's locked state
2373 next = next_next;
2374 } else {
2375 // mid is considered in-use if it does not have an associated
2376 // Java object or mid is not old or deflation did not succeed.
2377 // A mid->is_new() node can be seen here when it is freshly
2378 // returned by om_alloc() (and skips the deflation code path).
2379 // A mid->is_old() node can be seen here when deflation failed.
2380 // A mid->is_free() node can be seen here when a fresh node from
2381 // om_alloc() is released by om_release() due to losing the race
2382 // in inflate().
2383
2384 // All the list management is done so move on to the next one:
2385 if (cur_mid_in_use != NULL) {
2386 om_unlock(cur_mid_in_use);
2387 }
2388 // The next cur_mid_in_use keeps mid's lock state so
2389 // that it is stable for a possible next field change. It
2390 // cannot be modified by om_release() while it is locked.
2391 cur_mid_in_use = mid;
2392 mid = next; // mid keeps non-NULL next's locked state
2393 next = next_next;
2394
2395 if (SafepointMechanism::should_block(self) &&
2396 cur_mid_in_use != Atomic::load(list_p) && cur_mid_in_use->is_old()) {
2397 // If a safepoint has started and cur_mid_in_use is not the list
2398 // head and is old, then it is safe to use as saved state. Return
2399 // to the caller before blocking.
2400 *saved_mid_in_use_p = cur_mid_in_use;
2401 om_unlock(cur_mid_in_use);
2402 if (mid != NULL) {
2403 om_unlock(mid);
2404 }
2405 return deflated_count;
2406 }
2407 }
2408 if (mid == NULL) {
2409 if (cur_mid_in_use != NULL) {
2410 om_unlock(cur_mid_in_use);
2411 }
2412 break; // Reached end of the list so nothing more to deflate.
2413 }
2414
2415 // The current mid's next field is locked at this point. If we have
2416 // a cur_mid_in_use, then it is also locked at this point.
2417 }
2418 // We finished the list without a safepoint starting so there's
2419 // no need to save state.
2420 *saved_mid_in_use_p = NULL;
2421 return deflated_count;
2422 }
2423
2424 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2425 counters->n_in_use = 0; // currently associated with objects
2426 counters->n_in_circulation = 0; // extant
2427 counters->n_scavenged = 0; // reclaimed (global and per-thread)
2428 counters->per_thread_scavenged = 0; // per-thread scavenge total
2429 counters->per_thread_times = 0.0; // per-thread scavenge times
2430 }
2431
2432 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
2433 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2434
2435 if (AsyncDeflateIdleMonitors) {
2436 // Nothing to do when global idle ObjectMonitors are deflated using
2437 // a JavaThread unless a special deflation has been requested.
2438 if (!is_special_deflation_requested()) {
2439 return;
2440 }
2441 }
2442
2443 bool deflated = false;
2444
2445 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
2446 ObjectMonitor* free_tail_p = NULL;
2447 elapsedTimer timer;
2448
2449 if (log_is_enabled(Info, monitorinflation)) {
2450 timer.start();
2451 }
2452
2453 // Note: the thread-local monitors lists get deflated in
2454 // a separate pass. See deflate_thread_local_monitors().
2455
2456 // For moribund threads, scan om_list_globals._in_use_list
2457 int deflated_count = 0;
2458 if (Atomic::load(&om_list_globals._in_use_list) != NULL) {
2459 // Update n_in_circulation before om_list_globals._in_use_count is
2460 // updated by deflation.
2461 Atomic::add(&counters->n_in_circulation,
2462 Atomic::load(&om_list_globals._in_use_count));
2463
2464 deflated_count = deflate_monitor_list(&om_list_globals._in_use_list,
2465 &om_list_globals._in_use_count,
2466 &free_head_p, &free_tail_p);
2467 Atomic::add(&counters->n_in_use, Atomic::load(&om_list_globals._in_use_count));
2468 }
2469
2470 if (free_head_p != NULL) {
2471 // Move the deflated ObjectMonitors back to the global free list.
2472 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
2473 #ifdef ASSERT
2474 ObjectMonitor* l_next_om = free_tail_p->next_om();
2475 #endif
2476 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2477 prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count);
2478 Atomic::add(&counters->n_scavenged, deflated_count);
2479 }
2480 timer.stop();
2481
2482 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2483 LogStreamHandle(Info, monitorinflation) lsh_info;
2484 LogStream* ls = NULL;
2485 if (log_is_enabled(Debug, monitorinflation)) {
2486 ls = &lsh_debug;
2487 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2488 ls = &lsh_info;
2489 }
2490 if (ls != NULL) {
2491 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2492 }
2493 }
2494
2495 class HandshakeForDeflation : public HandshakeClosure {
2496 public:
2497 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
2498
2499 void do_thread(Thread* thread) {
2500 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
2501 INTPTR_FORMAT, p2i(thread));
2502 }
2503 };
2504
2505 void ObjectSynchronizer::deflate_idle_monitors_using_JT() {
2506 assert(AsyncDeflateIdleMonitors, "sanity check");
2507
2508 // Deflate any global idle monitors.
2509 deflate_global_idle_monitors_using_JT();
2510
2511 int count = 0;
2512 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2513 if (Atomic::load(&jt->om_in_use_count) > 0 && !jt->is_exiting()) {
2514 // This JavaThread is using ObjectMonitors so deflate any that
2515 // are idle unless this JavaThread is exiting; do not race with
2516 // ObjectSynchronizer::om_flush().
2517 deflate_per_thread_idle_monitors_using_JT(jt);
2518 count++;
2519 }
2520 }
2521 if (count > 0) {
2522 log_debug(monitorinflation)("did async deflation of idle monitors for %d thread(s).", count);
2523 }
2524
2525 log_info(monitorinflation)("async global_population=%d, global_in_use_count=%d, "
2526 "global_free_count=%d, global_wait_count=%d",
2527 Atomic::load(&om_list_globals._population),
2528 Atomic::load(&om_list_globals._in_use_count),
2529 Atomic::load(&om_list_globals._free_count),
2530 Atomic::load(&om_list_globals._wait_count));
2531
2532 // The ServiceThread's async deflation request has been processed.
2533 set_is_async_deflation_requested(false);
2534
2535 if (Atomic::load(&om_list_globals._wait_count) > 0) {
2536 // There are deflated ObjectMonitors waiting for a handshake
2537 // (or a safepoint) for safety.
2538
2539 ObjectMonitor* list = Atomic::load(&om_list_globals._wait_list);
2540 ADIM_guarantee(list != NULL, "om_list_globals._wait_list must not be NULL");
2541 int count = Atomic::load(&om_list_globals._wait_count);
2542 Atomic::store(&om_list_globals._wait_count, 0);
2543 Atomic::store(&om_list_globals._wait_list, (ObjectMonitor*)NULL);
2544
2545 // Find the tail for prepend_list_to_common(). No need to mark
2546 // ObjectMonitors for this list walk since only the deflater
2547 // thread manages the wait list.
2548 int l_count = 0;
2549 ObjectMonitor* tail = NULL;
2550 for (ObjectMonitor* n = list; n != NULL; n = unmarked_next(n)) {
2551 tail = n;
2552 l_count++;
2553 }
2554 ADIM_guarantee(count == l_count, "count=%d != l_count=%d", count, l_count);
2555
2556 // Will execute a safepoint if !ThreadLocalHandshakes:
2557 HandshakeForDeflation hfd_hc;
2558 Handshake::execute(&hfd_hc);
2559
2560 prepend_list_to_common(list, tail, count, &om_list_globals._free_list,
2561 &om_list_globals._free_count);
2562
2563 log_info(monitorinflation)("moved %d idle monitors from global waiting list to global free list", count);
2564 }
2565 }
2566
2567 // Deflate global idle ObjectMonitors using a JavaThread.
2568 //
2569 void ObjectSynchronizer::deflate_global_idle_monitors_using_JT() {
2570 assert(AsyncDeflateIdleMonitors, "sanity check");
2571 assert(Thread::current()->is_Java_thread(), "precondition");
2572 JavaThread* self = JavaThread::current();
2573
2574 deflate_common_idle_monitors_using_JT(true /* is_global */, self);
2575 }
2576
2577 // Deflate the specified JavaThread's idle ObjectMonitors using a JavaThread.
2578 //
2579 void ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT(JavaThread* target) {
2580 assert(AsyncDeflateIdleMonitors, "sanity check");
2581 assert(Thread::current()->is_Java_thread(), "precondition");
2582
2583 deflate_common_idle_monitors_using_JT(false /* !is_global */, target);
2584 }
2585
2586 // Deflate global or per-thread idle ObjectMonitors using a JavaThread.
2587 //
2588 void ObjectSynchronizer::deflate_common_idle_monitors_using_JT(bool is_global, JavaThread* target) {
2589 JavaThread* self = JavaThread::current();
2590
2591 int deflated_count = 0;
2592 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged ObjectMonitors
2593 ObjectMonitor* free_tail_p = NULL;
2594 ObjectMonitor* saved_mid_in_use_p = NULL;
2595 elapsedTimer timer;
2596
2597 if (log_is_enabled(Info, monitorinflation)) {
2598 timer.start();
2599 }
2600
2601 if (is_global) {
2602 OM_PERFDATA_OP(MonExtant, set_value(Atomic::load(&om_list_globals._in_use_count)));
2603 } else {
2604 OM_PERFDATA_OP(MonExtant, inc(Atomic::load(&target->om_in_use_count)));
2605 }
2606
2607 do {
2608 int local_deflated_count;
2609 if (is_global) {
2610 local_deflated_count =
2611 deflate_monitor_list_using_JT(&om_list_globals._in_use_list,
2612 &om_list_globals._in_use_count,
2613 &free_head_p, &free_tail_p,
2614 &saved_mid_in_use_p);
2615 } else {
2616 local_deflated_count =
2617 deflate_monitor_list_using_JT(&target->om_in_use_list,
2618 &target->om_in_use_count, &free_head_p,
2619 &free_tail_p, &saved_mid_in_use_p);
2620 }
2621 deflated_count += local_deflated_count;
2622
2623 if (free_head_p != NULL) {
2624 // Move the deflated ObjectMonitors to the global free list.
2625 guarantee(free_tail_p != NULL && local_deflated_count > 0, "free_tail_p=" INTPTR_FORMAT ", local_deflated_count=%d", p2i(free_tail_p), local_deflated_count);
2626 // Note: The target thread can be doing an om_alloc() that
2627 // is trying to prepend an ObjectMonitor on its in-use list
2628 // at the same time that we have deflated the current in-use
2629 // list head and put it on the local free list. prepend_to_common()
2630 // will detect the race and retry which avoids list corruption,
2631 // but the next field in free_tail_p can flicker to marked
2632 // and then unmarked while prepend_to_common() is sorting it
2633 // all out.
2634 #ifdef ASSERT
2635 ObjectMonitor* l_next_om = unmarked_next(free_tail_p);
2636 #endif
2637 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2638
2639 prepend_list_to_global_wait_list(free_head_p, free_tail_p, local_deflated_count);
2640
2641 OM_PERFDATA_OP(Deflations, inc(local_deflated_count));
2642 }
2643
2644 if (saved_mid_in_use_p != NULL) {
2645 // deflate_monitor_list_using_JT() detected a safepoint starting.
2646 timer.stop();
2647 {
2648 if (is_global) {
2649 log_debug(monitorinflation)("pausing deflation of global idle monitors for a safepoint.");
2650 } else {
2651 log_debug(monitorinflation)("jt=" INTPTR_FORMAT ": pausing deflation of per-thread idle monitors for a safepoint.", p2i(target));
2652 }
2653 assert(SafepointMechanism::should_block(self), "sanity check");
2654 ThreadBlockInVM blocker(self);
2655 }
2656 // Prepare for another loop after the safepoint.
2657 free_head_p = NULL;
2658 free_tail_p = NULL;
2659 if (log_is_enabled(Info, monitorinflation)) {
2660 timer.start();
2661 }
2662 }
2663 } while (saved_mid_in_use_p != NULL);
2664 timer.stop();
2665
2666 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2667 LogStreamHandle(Info, monitorinflation) lsh_info;
2668 LogStream* ls = NULL;
2669 if (log_is_enabled(Debug, monitorinflation)) {
2670 ls = &lsh_debug;
2671 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2672 ls = &lsh_info;
2673 }
2674 if (ls != NULL) {
2675 if (is_global) {
2676 ls->print_cr("async-deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2677 } else {
2678 ls->print_cr("jt=" INTPTR_FORMAT ": async-deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(target), timer.seconds(), deflated_count);
2679 }
2680 }
2681 }
2682
2683 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2684 // Report the cumulative time for deflating each thread's idle
2685 // monitors. Note: if the work is split among more than one
2686 // worker thread, then the reported time will likely be more
2687 // than a beginning to end measurement of the phase.
2688 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged);
2689
2690 bool needs_special_deflation = is_special_deflation_requested();
2691 if (AsyncDeflateIdleMonitors && !needs_special_deflation) {
2692 // Nothing to do when idle ObjectMonitors are deflated using
2693 // a JavaThread unless a special deflation has been requested.
2694 return;
2695 }
2696
2697 if (log_is_enabled(Debug, monitorinflation)) {
2698 // exit_globals()'s call to audit_and_print_stats() is done
2699 // at the Info level and not at a safepoint.
2700 // For async deflation, audit_and_print_stats() is called in
2701 // ObjectSynchronizer::do_safepoint_work() at the Debug level
2702 // at a safepoint.
2703 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2704 } else if (log_is_enabled(Info, monitorinflation)) {
2705 log_info(monitorinflation)("global_population=%d, global_in_use_count=%d, "
2706 "global_free_count=%d, global_wait_count=%d",
2707 Atomic::load(&om_list_globals._population),
2708 Atomic::load(&om_list_globals._in_use_count),
2709 Atomic::load(&om_list_globals._free_count),
2710 Atomic::load(&om_list_globals._wait_count));
2711 }
2712
2713 OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged));
2714 OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation));
2715
2716 GVars.stw_random = os::random();
2717 GVars.stw_cycle++;
2718
2719 if (needs_special_deflation) {
2720 set_is_special_deflation_requested(false); // special deflation is done
2721 }
2722 }
2723
2724 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
2725 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2726
2727 if (AsyncDeflateIdleMonitors && !is_special_deflation_requested()) {
2728 // Nothing to do if a special deflation has NOT been requested.
2729 return;
2730 }
2731
2732 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
2733 ObjectMonitor* free_tail_p = NULL;
2734 elapsedTimer timer;
2735
2736 if (log_is_enabled(Info, safepoint, cleanup) ||
2737 log_is_enabled(Info, monitorinflation)) {
2738 timer.start();
2739 }
2740
2741 // Update n_in_circulation before om_in_use_count is updated by deflation.
2742 Atomic::add(&counters->n_in_circulation, Atomic::load(&thread->om_in_use_count));
2743
2744 int deflated_count = deflate_monitor_list(&thread->om_in_use_list, &thread->om_in_use_count, &free_head_p, &free_tail_p);
2745 Atomic::add(&counters->n_in_use, Atomic::load(&thread->om_in_use_count));
2746
2747 if (free_head_p != NULL) {
2748 // Move the deflated ObjectMonitors back to the global free list.
2749 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
2750 #ifdef ASSERT
2751 ObjectMonitor* l_next_om = free_tail_p->next_om();
2752 #endif
2753 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2754 prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count);
2755 Atomic::add(&counters->n_scavenged, deflated_count);
2756 Atomic::add(&counters->per_thread_scavenged, deflated_count);
2757 }
2758
2759 timer.stop();
2760 counters->per_thread_times += timer.seconds();
2761
2762 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2763 LogStreamHandle(Info, monitorinflation) lsh_info;
2764 LogStream* ls = NULL;
2765 if (log_is_enabled(Debug, monitorinflation)) {
2766 ls = &lsh_debug;
2767 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2768 ls = &lsh_info;
2769 }
2770 if (ls != NULL) {
2771 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
2772 }
2773 }
2774
2775 // Monitor cleanup on JavaThread::exit
2776
2777 // Iterate through monitor cache and attempt to release thread's monitors
2778 // Gives up on a particular monitor if an exception occurs, but continues
2779 // the overall iteration, swallowing the exception.
2780 class ReleaseJavaMonitorsClosure: public MonitorClosure {
2781 private:
2782 TRAPS;
2783
2784 public:
2785 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
2786 void do_monitor(ObjectMonitor* mid) {
2787 if (mid->owner() == THREAD) {
2788 (void)mid->complete_exit(CHECK);
2789 }
2790 }
2791 };
2792
2793 // Release all inflated monitors owned by THREAD. Lightweight monitors are
2794 // ignored. This is meant to be called during JNI thread detach which assumes
2795 // all remaining monitors are heavyweight. All exceptions are swallowed.
2796 // Scanning the extant monitor list can be time consuming.
2797 // A simple optimization is to add a per-thread flag that indicates a thread
2798 // called jni_monitorenter() during its lifetime.
2799 //
2800 // Instead of No_Savepoint_Verifier it might be cheaper to
2801 // use an idiom of the form:
2802 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
2803 // <code that must not run at safepoint>
2804 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
2805 // Since the tests are extremely cheap we could leave them enabled
2806 // for normal product builds.
2807
2808 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
2809 assert(THREAD == JavaThread::current(), "must be current Java thread");
2810 NoSafepointVerifier nsv;
2811 ReleaseJavaMonitorsClosure rjmc(THREAD);
2812 ObjectSynchronizer::monitors_iterate(&rjmc);
2813 THREAD->clear_pending_exception();
2814 }
2815
2816 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
2817 switch (cause) {
2818 case inflate_cause_vm_internal: return "VM Internal";
2819 case inflate_cause_monitor_enter: return "Monitor Enter";
2820 case inflate_cause_wait: return "Monitor Wait";
2821 case inflate_cause_notify: return "Monitor Notify";
2822 case inflate_cause_hash_code: return "Monitor Hash Code";
2823 case inflate_cause_jni_enter: return "JNI Monitor Enter";
2824 case inflate_cause_jni_exit: return "JNI Monitor Exit";
2825 default:
2826 ShouldNotReachHere();
2827 }
2828 return "Unknown";
2829 }
2830
2831 //------------------------------------------------------------------------------
2832 // Debugging code
2833
2834 u_char* ObjectSynchronizer::get_gvars_addr() {
2835 return (u_char*)&GVars;
2836 }
2837
2838 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
2839 return (u_char*)&GVars.hc_sequence;
2840 }
2841
2842 size_t ObjectSynchronizer::get_gvars_size() {
2843 return sizeof(SharedGlobals);
2844 }
2845
2846 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
2847 return (u_char*)&GVars.stw_random;
2848 }
2849
2850 // This function can be called at a safepoint or it can be called when
2851 // we are trying to exit the VM. When we are trying to exit the VM, the
2852 // list walker functions can run in parallel with the other list
2853 // operations so spin-locking is used for safety.
2854 //
2855 // Calls to this function can be added in various places as a debugging
2856 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
2857 // details logged at the Info level and 'false' for the 'on_exit'
2858 // parameter to have in-use monitor details logged at the Trace level.
2859 // deflate_monitor_list() no longer uses spin-locking so be careful
2860 // when adding audit_and_print_stats() calls at a safepoint.
2861 //
2862 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
2863 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
2864
2865 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2866 LogStreamHandle(Info, monitorinflation) lsh_info;
2867 LogStreamHandle(Trace, monitorinflation) lsh_trace;
2868 LogStream* ls = NULL;
2869 if (log_is_enabled(Trace, monitorinflation)) {
2870 ls = &lsh_trace;
2871 } else if (log_is_enabled(Debug, monitorinflation)) {
2872 ls = &lsh_debug;
2873 } else if (log_is_enabled(Info, monitorinflation)) {
2874 ls = &lsh_info;
2875 }
2876 assert(ls != NULL, "sanity check");
2877
2878 // Log counts for the global and per-thread monitor lists:
2879 int chk_om_population = log_monitor_list_counts(ls);
2880 int error_cnt = 0;
2881
2882 ls->print_cr("Checking global lists:");
2883
2884 // Check om_list_globals._population:
2885 if (Atomic::load(&om_list_globals._population) == chk_om_population) {
2886 ls->print_cr("global_population=%d equals chk_om_population=%d",
2887 Atomic::load(&om_list_globals._population), chk_om_population);
2888 } else {
2889 // With fine grained locks on the monitor lists, it is possible for
2890 // log_monitor_list_counts() to return a value that doesn't match
2891 // om_list_globals._population. So far a higher value has been
2892 // seen in testing so something is being double counted by
2893 // log_monitor_list_counts().
2894 ls->print_cr("WARNING: global_population=%d is not equal to "
2895 "chk_om_population=%d",
2896 Atomic::load(&om_list_globals._population), chk_om_population);
2897 }
2898
2899 // Check om_list_globals._in_use_list and om_list_globals._in_use_count:
2900 chk_global_in_use_list_and_count(ls, &error_cnt);
2901
2902 // Check om_list_globals._free_list and om_list_globals._free_count:
2903 chk_global_free_list_and_count(ls, &error_cnt);
2904
2905 // Check om_list_globals._wait_list and om_list_globals._wait_count:
2906 chk_global_wait_list_and_count(ls, &error_cnt);
2907
2908 ls->print_cr("Checking per-thread lists:");
2909
2910 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2911 // Check om_in_use_list and om_in_use_count:
2912 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
2913
2914 // Check om_free_list and om_free_count:
2915 chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
2916 }
2917
2918 if (error_cnt == 0) {
2919 ls->print_cr("No errors found in monitor list checks.");
2920 } else {
2921 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
2922 }
2923
2924 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
2925 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
2926 // When exiting this log output is at the Info level. When called
2927 // at a safepoint, this log output is at the Trace level since
2928 // there can be a lot of it.
2929 log_in_use_monitor_details(ls);
2930 }
2931
2932 ls->flush();
2933
2934 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2935 }
2936
2937 // Check a free monitor entry; log any errors.
2938 void ObjectSynchronizer::chk_free_entry(JavaThread* jt, ObjectMonitor* n,
2939 outputStream * out, int *error_cnt_p) {
2940 stringStream ss;
2941 if (n->is_busy()) {
2942 if (jt != NULL) {
2943 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2944 ": free per-thread monitor must not be busy: %s", p2i(jt),
2945 p2i(n), n->is_busy_to_string(&ss));
2946 } else {
2947 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2948 "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
2949 }
2950 *error_cnt_p = *error_cnt_p + 1;
2951 }
2952 if (n->header().value() != 0) {
2953 if (jt != NULL) {
2954 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2955 ": free per-thread monitor must have NULL _header "
2956 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
2957 n->header().value());
2958 *error_cnt_p = *error_cnt_p + 1;
2959 } else if (!AsyncDeflateIdleMonitors) {
2960 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2961 "must have NULL _header field: _header=" INTPTR_FORMAT,
2962 p2i(n), n->header().value());
2963 *error_cnt_p = *error_cnt_p + 1;
2964 }
2965 }
2966 if (n->object() != NULL) {
2967 if (jt != NULL) {
2968 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2969 ": free per-thread monitor must have NULL _object "
2970 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
2971 p2i(n->object()));
2972 } else {
2973 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2974 "must have NULL _object field: _object=" INTPTR_FORMAT,
2975 p2i(n), p2i(n->object()));
2976 }
2977 *error_cnt_p = *error_cnt_p + 1;
2978 }
2979 }
2980
2981 // Lock the next ObjectMonitor for traversal and unlock the current
2982 // ObjectMonitor. Returns the next ObjectMonitor if there is one.
2983 // Otherwise returns NULL (after unlocking the current ObjectMonitor).
2984 // This function is used by the various list walker functions to
2985 // safely walk a list without allowing an ObjectMonitor to be moved
2986 // to another list in the middle of a walk.
2987 static ObjectMonitor* lock_next_for_traversal(ObjectMonitor* cur) {
2988 assert(is_locked(cur), "cur=" INTPTR_FORMAT " must be locked", p2i(cur));
2989 ObjectMonitor* next = unmarked_next(cur);
2990 if (next == NULL) { // Reached the end of the list.
2991 om_unlock(cur);
2992 return NULL;
2993 }
2994 om_lock(next); // Lock next before unlocking current to keep
2995 om_unlock(cur); // from being by-passed by another thread.
2996 return next;
2997 }
2998
2999 // Check the global free list and count; log the results of the checks.
3000 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
3001 int *error_cnt_p) {
3002 int chk_om_free_count = 0;
3003 ObjectMonitor* cur = NULL;
3004 if ((cur = get_list_head_locked(&om_list_globals._free_list)) != NULL) {
3005 // Marked the global free list head so process the list.
3006 while (true) {
3007 chk_free_entry(NULL /* jt */, cur, out, error_cnt_p);
3008 chk_om_free_count++;
3009
3010 cur = lock_next_for_traversal(cur);
3011 if (cur == NULL) {
3012 break;
3013 }
3014 }
3015 }
3016 int l_free_count = Atomic::load(&om_list_globals._free_count);
3017 if (l_free_count == chk_om_free_count) {
3018 out->print_cr("global_free_count=%d equals chk_om_free_count=%d",
3019 l_free_count, chk_om_free_count);
3020 } else {
3021 // With fine grained locks on om_list_globals._free_list, it
3022 // is possible for an ObjectMonitor to be prepended to
3023 // om_list_globals._free_list after we started calculating
3024 // chk_om_free_count so om_list_globals._free_count may not
3025 // match anymore.
3026 out->print_cr("WARNING: global_free_count=%d is not equal to "
3027 "chk_om_free_count=%d", l_free_count, chk_om_free_count);
3028 }
3029 }
3030
3031 // Check the global wait list and count; log the results of the checks.
3032 void ObjectSynchronizer::chk_global_wait_list_and_count(outputStream * out,
3033 int *error_cnt_p) {
3034 int chk_om_wait_count = 0;
3035 ObjectMonitor* cur = NULL;
3036 if ((cur = get_list_head_locked(&om_list_globals._wait_list)) != NULL) {
3037 // Marked the global wait list head so process the list.
3038 while (true) {
3039 // Rules for om_list_globals._wait_list are the same as for
3040 // om_list_globals._free_list:
3041 chk_free_entry(NULL /* jt */, cur, out, error_cnt_p);
3042 chk_om_wait_count++;
3043
3044 cur = lock_next_for_traversal(cur);
3045 if (cur == NULL) {
3046 break;
3047 }
3048 }
3049 }
3050 if (Atomic::load(&om_list_globals._wait_count) == chk_om_wait_count) {
3051 out->print_cr("global_wait_count=%d equals chk_om_wait_count=%d",
3052 Atomic::load(&om_list_globals._wait_count), chk_om_wait_count);
3053 } else {
3054 out->print_cr("ERROR: global_wait_count=%d is not equal to "
3055 "chk_om_wait_count=%d",
3056 Atomic::load(&om_list_globals._wait_count), chk_om_wait_count);
3057 *error_cnt_p = *error_cnt_p + 1;
3058 }
3059 }
3060
3061 // Check the global in-use list and count; log the results of the checks.
3062 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
3063 int *error_cnt_p) {
3064 int chk_om_in_use_count = 0;
3065 ObjectMonitor* cur = NULL;
3066 if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) {
3067 // Marked the global in-use list head so process the list.
3068 while (true) {
3069 chk_in_use_entry(NULL /* jt */, cur, out, error_cnt_p);
3070 chk_om_in_use_count++;
3071
3072 cur = lock_next_for_traversal(cur);
3073 if (cur == NULL) {
3074 break;
3075 }
3076 }
3077 }
3078 int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
3079 if (l_in_use_count == chk_om_in_use_count) {
3080 out->print_cr("global_in_use_count=%d equals chk_om_in_use_count=%d",
3081 l_in_use_count, chk_om_in_use_count);
3082 } else {
3083 // With fine grained locks on the monitor lists, it is possible for
3084 // an exiting JavaThread to put its in-use ObjectMonitors on the
3085 // global in-use list after chk_om_in_use_count is calculated above.
3086 out->print_cr("WARNING: global_in_use_count=%d is not equal to chk_om_in_use_count=%d",
3087 l_in_use_count, chk_om_in_use_count);
3088 }
3089 }
3090
3091 // Check an in-use monitor entry; log any errors.
3092 void ObjectSynchronizer::chk_in_use_entry(JavaThread* jt, ObjectMonitor* n,
3093 outputStream * out, int *error_cnt_p) {
3094 if (n->header().value() == 0) {
3095 if (jt != NULL) {
3096 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3097 ": in-use per-thread monitor must have non-NULL _header "
3098 "field.", p2i(jt), p2i(n));
3099 } else {
3100 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
3101 "must have non-NULL _header field.", p2i(n));
3102 }
3103 *error_cnt_p = *error_cnt_p + 1;
3104 }
3105 if (n->object() == NULL) {
3106 if (jt != NULL) {
3107 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3108 ": in-use per-thread monitor must have non-NULL _object "
3109 "field.", p2i(jt), p2i(n));
3110 } else {
3111 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
3112 "must have non-NULL _object field.", p2i(n));
3113 }
3114 *error_cnt_p = *error_cnt_p + 1;
3115 }
3116 const oop obj = (oop)n->object();
3117 const markWord mark = obj->mark();
3118 if (!mark.has_monitor()) {
3119 if (jt != NULL) {
3120 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3121 ": in-use per-thread monitor's object does not think "
3122 "it has a monitor: obj=" INTPTR_FORMAT ", mark="
3123 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), mark.value());
3124 } else {
3125 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
3126 "monitor's object does not think it has a monitor: obj="
3127 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
3128 p2i(obj), mark.value());
3129 }
3130 *error_cnt_p = *error_cnt_p + 1;
3131 }
3132 ObjectMonitor* const obj_mon = mark.monitor();
3133 if (n != obj_mon) {
3134 if (jt != NULL) {
3135 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3136 ": in-use per-thread monitor's object does not refer "
3137 "to the same monitor: obj=" INTPTR_FORMAT ", mark="
3138 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
3139 p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
3140 } else {
3141 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
3142 "monitor's object does not refer to the same monitor: obj="
3143 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
3144 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
3145 }
3146 *error_cnt_p = *error_cnt_p + 1;
3147 }
3148 }
3149
3150 // Check the thread's free list and count; log the results of the checks.
3151 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
3152 outputStream * out,
3153 int *error_cnt_p) {
3154 int chk_om_free_count = 0;
3155 ObjectMonitor* cur = NULL;
3156 if ((cur = get_list_head_locked(&jt->om_free_list)) != NULL) {
3157 // Marked the per-thread free list head so process the list.
3158 while (true) {
3159 chk_free_entry(jt, cur, out, error_cnt_p);
3160 chk_om_free_count++;
3161
3162 cur = lock_next_for_traversal(cur);
3163 if (cur == NULL) {
3164 break;
3165 }
3166 }
3167 }
3168 int l_om_free_count = Atomic::load(&jt->om_free_count);
3169 if (l_om_free_count == chk_om_free_count) {
3170 out->print_cr("jt=" INTPTR_FORMAT ": om_free_count=%d equals "
3171 "chk_om_free_count=%d", p2i(jt), l_om_free_count, chk_om_free_count);
3172 } else {
3173 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_free_count=%d is not "
3174 "equal to chk_om_free_count=%d", p2i(jt), l_om_free_count,
3175 chk_om_free_count);
3176 *error_cnt_p = *error_cnt_p + 1;
3177 }
3178 }
3179
3180 // Check the thread's in-use list and count; log the results of the checks.
3181 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
3182 outputStream * out,
3183 int *error_cnt_p) {
3184 int chk_om_in_use_count = 0;
3185 ObjectMonitor* cur = NULL;
3186 if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
3187 // Marked the per-thread in-use list head so process the list.
3188 while (true) {
3189 chk_in_use_entry(jt, cur, out, error_cnt_p);
3190 chk_om_in_use_count++;
3191
3192 cur = lock_next_for_traversal(cur);
3193 if (cur == NULL) {
3194 break;
3195 }
3196 }
3197 }
3198 int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
3199 if (l_om_in_use_count == chk_om_in_use_count) {
3200 out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals "
3201 "chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
3202 chk_om_in_use_count);
3203 } else {
3204 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not "
3205 "equal to chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
3206 chk_om_in_use_count);
3207 *error_cnt_p = *error_cnt_p + 1;
3208 }
3209 }
3210
3211 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
3212 // flags indicate why the entry is in-use, 'object' and 'object type'
3213 // indicate the associated object and its type.
3214 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out) {
3215 stringStream ss;
3216 if (Atomic::load(&om_list_globals._in_use_count) > 0) {
3217 out->print_cr("In-use global monitor info:");
3218 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
3219 out->print_cr("%18s %s %18s %18s",
3220 "monitor", "BHL", "object", "object type");
3221 out->print_cr("================== === ================== ==================");
3222 ObjectMonitor* cur = NULL;
3223 if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) {
3224 // Marked the global in-use list head so process the list.
3225 while (true) {
3226 const oop obj = (oop) cur->object();
3227 const markWord mark = cur->header();
3228 ResourceMark rm;
3229 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(cur),
3230 cur->is_busy() != 0, mark.hash() != 0, cur->owner() != NULL,
3231 p2i(obj), obj->klass()->external_name());
3232 if (cur->is_busy() != 0) {
3233 out->print(" (%s)", cur->is_busy_to_string(&ss));
3234 ss.reset();
3235 }
3236 out->cr();
3237
3238 cur = lock_next_for_traversal(cur);
3239 if (cur == NULL) {
3240 break;
3241 }
3242 }
3243 }
3244 }
3245
3246 out->print_cr("In-use per-thread monitor info:");
3247 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
3248 out->print_cr("%18s %18s %s %18s %18s",
3249 "jt", "monitor", "BHL", "object", "object type");
3250 out->print_cr("================== ================== === ================== ==================");
3251 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
3252 ObjectMonitor* cur = NULL;
3253 if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
3254 // Marked the global in-use list head so process the list.
3255 while (true) {
3256 const oop obj = (oop) cur->object();
3257 const markWord mark = cur->header();
3258 ResourceMark rm;
3259 out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT
3260 " %s", p2i(jt), p2i(cur), cur->is_busy() != 0,
3261 mark.hash() != 0, cur->owner() != NULL, p2i(obj),
3262 obj->klass()->external_name());
3263 if (cur->is_busy() != 0) {
3264 out->print(" (%s)", cur->is_busy_to_string(&ss));
3265 ss.reset();
3266 }
3267 out->cr();
3268
3269 cur = lock_next_for_traversal(cur);
3270 if (cur == NULL) {
3271 break;
3272 }
3273 }
3274 }
3275 }
3276
3277 out->flush();
3278 }
3279
3280 // Log counts for the global and per-thread monitor lists and return
3281 // the population count.
3282 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
3283 int pop_count = 0;
3284 out->print_cr("%18s %10s %10s %10s %10s",
3285 "Global Lists:", "InUse", "Free", "Wait", "Total");
3286 out->print_cr("================== ========== ========== ========== ==========");
3287 int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
3288 int l_free_count = Atomic::load(&om_list_globals._free_count);
3289 int l_wait_count = Atomic::load(&om_list_globals._wait_count);
3290 out->print_cr("%18s %10d %10d %10d %10d", "", l_in_use_count,
3291 l_free_count, l_wait_count,
3292 Atomic::load(&om_list_globals._population));
3293 pop_count += l_in_use_count + l_free_count + l_wait_count;
3294
3295 out->print_cr("%18s %10s %10s %10s",
3296 "Per-Thread Lists:", "InUse", "Free", "Provision");
3297 out->print_cr("================== ========== ========== ==========");
3298
3299 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
3300 int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
3301 int l_om_free_count = Atomic::load(&jt->om_free_count);
3302 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
3303 l_om_in_use_count, l_om_free_count, jt->om_free_provision);
3304 pop_count += l_om_in_use_count + l_om_free_count;
3305 }
3306 return pop_count;
3307 }
3308
3309 #ifndef PRODUCT
3310
3311 // Check if monitor belongs to the monitor cache
3312 // The list is grow-only so it's *relatively* safe to traverse
3313 // the list of extant blocks without taking a lock.
3314
3315 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
3316 PaddedObjectMonitor* block = Atomic::load(&g_block_list);
3317 while (block != NULL) {
3318 assert(block->object() == CHAINMARKER, "must be a block header");
3319 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
3320 address mon = (address)monitor;
3321 address blk = (address)block;
3322 size_t diff = mon - blk;
3323 assert((diff % sizeof(PaddedObjectMonitor)) == 0, "must be aligned");
3324 return 1;
3325 }
3326 // unmarked_next() is not needed with g_block_list (no locking
3327 // used with block linkage _next_om fields).
3328 block = (PaddedObjectMonitor*)block->next_om();
3329 }
3330 return 0;
3331 }
3332
3333 #endif