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 monitor = mark.monitor();
1045 temp = monitor->header();
1046 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1047 hash = temp.hash();
1048 if (hash != 0) {
1049 // It has a hash.
1050
1051 // Separate load of dmw/header above from the loads in
1052 // is_being_async_deflated().
1053 if (support_IRIW_for_not_multiple_copy_atomic_cpu) {
1054 // A non-multiple copy atomic (nMCA) machine needs a bigger
1055 // hammer to make sure that the load above and the loads
1056 // below all see non-stale memory values.
1057 OrderAccess::fence();
1058 } else {
1059 OrderAccess::loadload();
1060 }
1061 if (monitor->is_being_async_deflated()) {
1062 // But we can't safely use the hash if we detect that async
1063 // deflation has occurred. So we attempt to restore the
1064 // header/dmw to the object's header so that we only retry
1065 // once if the deflater thread happens to be slow.
1066 monitor->install_displaced_markword_in_object(obj);
1067 continue;
1068 }
1069 return hash;
1070 }
1071 // Fall thru so we only have one place that installs the hash in
1072 // the ObjectMonitor.
1073 } else if (self->is_lock_owned((address)mark.locker())) {
1074 // This is a stack lock owned by the calling thread so fetch the
1075 // displaced markWord from the BasicLock on the stack.
1076 temp = mark.displaced_mark_helper();
1077 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1078 hash = temp.hash();
1079 if (hash != 0) { // if it has a hash, just return it
1080 return hash;
1081 }
1082 // WARNING:
1083 // The displaced header in the BasicLock on a thread's stack
1084 // is strictly immutable. It CANNOT be changed in ANY cases.
1085 // So we have to inflate the stack lock into an ObjectMonitor
1086 // even if the current thread owns the lock. The BasicLock on
1087 // a thread's stack can be asynchronously read by other threads
1088 // during an inflate() call so any change to that stack memory
1089 // may not propagate to other threads correctly.
1090 }
1091
1092 // Inflate the monitor to set the hash.
1093
1094 // An async deflation can race after the inflate() call and before we
1095 // can update the ObjectMonitor's header with the hash value below.
1096 monitor = inflate(self, obj, inflate_cause_hash_code);
1097 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1098 mark = monitor->header();
1099 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1100 hash = mark.hash();
1101 if (hash == 0) { // if it does not have a hash
1102 hash = get_next_hash(self, obj); // get a new hash
1103 temp = mark.copy_set_hash(hash); // merge the hash into header
1104 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1105 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1106 test = markWord(v);
1107 if (test != mark) {
1108 // The attempt to update the ObjectMonitor's header/dmw field
1109 // did not work. This can happen if another thread managed to
1110 // merge in the hash just before our cmpxchg().
1111 // If we add any new usages of the header/dmw field, this code
1112 // will need to be updated.
1113 hash = test.hash();
1114 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1115 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1116 }
1117 if (monitor->is_being_async_deflated()) {
1118 // If we detect that async deflation has occurred, then we
1119 // attempt to restore the header/dmw to the object's header
1120 // so that we only retry once if the deflater thread happens
1121 // to be slow.
1122 monitor->install_displaced_markword_in_object(obj);
1123 continue;
1124 }
1125 }
1126 // We finally get the hash.
1127 return hash;
1128 }
1129 }
1130
1131 // Deprecated -- use FastHashCode() instead.
1132
1133 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
1134 return FastHashCode(Thread::current(), obj());
1135 }
1136
1137
1138 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
1139 Handle h_obj) {
1140 if (UseBiasedLocking) {
1141 BiasedLocking::revoke(h_obj, thread);
1142 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1143 }
1144
1145 assert(thread == JavaThread::current(), "Can only be called on current thread");
1146 oop obj = h_obj();
1147
1148 markWord mark = read_stable_mark(obj);
1149
1150 // Uncontended case, header points to stack
1151 if (mark.has_locker()) {
1152 return thread->is_lock_owned((address)mark.locker());
1153 }
1154 // Contended case, header points to ObjectMonitor (tagged pointer)
1155 if (mark.has_monitor()) {
1156 // The first stage of async deflation does not affect any field
1157 // used by this comparison so the ObjectMonitor* is usable here.
1158 ObjectMonitor* monitor = mark.monitor();
1159 return monitor->is_entered(thread) != 0;
1160 }
1161 // Unlocked case, header in place
1162 assert(mark.is_neutral(), "sanity check");
1163 return false;
1164 }
1165
1166 // Be aware of this method could revoke bias of the lock object.
1167 // This method queries the ownership of the lock handle specified by 'h_obj'.
1168 // If the current thread owns the lock, it returns owner_self. If no
1169 // thread owns the lock, it returns owner_none. Otherwise, it will return
1170 // owner_other.
1171 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
1172 (JavaThread *self, Handle h_obj) {
1173 // The caller must beware this method can revoke bias, and
1174 // revocation can result in a safepoint.
1175 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
1176 assert(self->thread_state() != _thread_blocked, "invariant");
1177
1178 // Possible mark states: neutral, biased, stack-locked, inflated
1179
1180 if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) {
1181 // CASE: biased
1182 BiasedLocking::revoke(h_obj, self);
1183 assert(!h_obj->mark().has_bias_pattern(),
1184 "biases should be revoked by now");
1185 }
1186
1187 assert(self == JavaThread::current(), "Can only be called on current thread");
1188 oop obj = h_obj();
1189 markWord mark = read_stable_mark(obj);
1190
1191 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
1192 if (mark.has_locker()) {
1193 return self->is_lock_owned((address)mark.locker()) ?
1194 owner_self : owner_other;
1195 }
1196
1197 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
1198 // The Object:ObjectMonitor relationship is stable as long as we're
1199 // not at a safepoint and AsyncDeflateIdleMonitors is false.
1200 if (mark.has_monitor()) {
1201 // The first stage of async deflation does not affect any field
1202 // used by this comparison so the ObjectMonitor* is usable here.
1203 ObjectMonitor* monitor = mark.monitor();
1204 void* owner = monitor->owner();
1205 if (owner == NULL) return owner_none;
1206 return (owner == self ||
1207 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
1208 }
1209
1210 // CASE: neutral
1211 assert(mark.is_neutral(), "sanity check");
1212 return owner_none; // it's unlocked
1213 }
1214
1215 // FIXME: jvmti should call this
1216 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1217 if (UseBiasedLocking) {
1218 if (SafepointSynchronize::is_at_safepoint()) {
1219 BiasedLocking::revoke_at_safepoint(h_obj);
1220 } else {
1221 BiasedLocking::revoke(h_obj, JavaThread::current());
1222 }
1223 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1224 }
1225
1226 oop obj = h_obj();
1227 address owner = NULL;
1228
1229 markWord mark = read_stable_mark(obj);
1230
1231 // Uncontended case, header points to stack
1232 if (mark.has_locker()) {
1233 owner = (address) mark.locker();
1234 }
1235
1236 // Contended case, header points to ObjectMonitor (tagged pointer)
1237 else if (mark.has_monitor()) {
1238 // The first stage of async deflation does not affect any field
1239 // used by this comparison so the ObjectMonitor* is usable here.
1240 ObjectMonitor* monitor = mark.monitor();
1241 assert(monitor != NULL, "monitor should be non-null");
1242 owner = (address) monitor->owner();
1243 }
1244
1245 if (owner != NULL) {
1246 // owning_thread_from_monitor_owner() may also return NULL here
1247 return Threads::owning_thread_from_monitor_owner(t_list, owner);
1248 }
1249
1250 // Unlocked case, header in place
1251 // Cannot have assertion since this object may have been
1252 // locked by another thread when reaching here.
1253 // assert(mark.is_neutral(), "sanity check");
1254
1255 return NULL;
1256 }
1257
1258 // Visitors ...
1259
1260 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
1261 PaddedObjectMonitor* block = Atomic::load(&g_block_list);
1262 while (block != NULL) {
1263 assert(block->object() == CHAINMARKER, "must be a block header");
1264 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
1265 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
1266 if (mid->object() != NULL) {
1267 // Only process with closure if the object is set.
1268
1269 // monitors_iterate() is only called at a safepoint or when the
1270 // target thread is suspended or when the target thread is
1271 // operating on itself. The current closures in use today are
1272 // only interested in an owned ObjectMonitor and ownership
1273 // cannot be dropped under the calling contexts so the
1274 // ObjectMonitor cannot be async deflated.
1275 closure->do_monitor(mid);
1276 }
1277 }
1278 // unmarked_next() is not needed with g_block_list (no locking
1279 // used with block linkage _next_om fields).
1280 block = (PaddedObjectMonitor*)block->next_om();
1281 }
1282 }
1283
1284 static bool monitors_used_above_threshold() {
1285 int population = Atomic::load(&om_list_globals._population);
1286 if (population == 0) {
1287 return false;
1288 }
1289 if (MonitorUsedDeflationThreshold > 0) {
1290 int monitors_used = population - Atomic::load(&om_list_globals._free_count) -
1291 Atomic::load(&om_list_globals._wait_count);
1292 int monitor_usage = (monitors_used * 100LL) / population;
1293 return monitor_usage > MonitorUsedDeflationThreshold;
1294 }
1295 return false;
1296 }
1297
1298 bool ObjectSynchronizer::is_async_deflation_needed() {
1299 if (!AsyncDeflateIdleMonitors) {
1300 return false;
1301 }
1302 if (is_async_deflation_requested()) {
1303 // Async deflation request.
1304 return true;
1305 }
1306 if (AsyncDeflationInterval > 0 &&
1307 time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1308 monitors_used_above_threshold()) {
1309 // It's been longer than our specified deflate interval and there
1310 // are too many monitors in use. We don't deflate more frequently
1311 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1312 // in order to not swamp the ServiceThread.
1313 _last_async_deflation_time_ns = os::javaTimeNanos();
1314 return true;
1315 }
1316 return false;
1317 }
1318
1319 bool ObjectSynchronizer::is_safepoint_deflation_needed() {
1320 if (!AsyncDeflateIdleMonitors) {
1321 if (monitors_used_above_threshold()) {
1322 // Too many monitors in use.
1323 return true;
1324 }
1325 return false;
1326 }
1327 if (is_special_deflation_requested()) {
1328 // For AsyncDeflateIdleMonitors only do a safepoint deflation
1329 // if there is a special deflation request.
1330 return true;
1331 }
1332 return false;
1333 }
1334
1335 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1336 return (os::javaTimeNanos() - _last_async_deflation_time_ns) / (NANOUNITS / MILLIUNITS);
1337 }
1338
1339 void ObjectSynchronizer::oops_do(OopClosure* f) {
1340 // We only scan the global used list here (for moribund threads), and
1341 // the thread-local monitors in Thread::oops_do().
1342 global_used_oops_do(f);
1343 }
1344
1345 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
1346 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1347 list_oops_do(Atomic::load(&om_list_globals._in_use_list), f);
1348 }
1349
1350 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
1351 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1352 list_oops_do(thread->om_in_use_list, f);
1353 }
1354
1355 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
1356 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1357 // The oops_do() phase does not overlap with monitor deflation
1358 // so no need to lock ObjectMonitors for the list traversal.
1359 for (ObjectMonitor* mid = list; mid != NULL; mid = unmarked_next(mid)) {
1360 if (mid->object() != NULL) {
1361 f->do_oop((oop*)mid->object_addr());
1362 }
1363 }
1364 }
1365
1366
1367 // -----------------------------------------------------------------------------
1368 // ObjectMonitor Lifecycle
1369 // -----------------------
1370 // Inflation unlinks monitors from om_list_globals._free_list or a per-thread
1371 // free list and associates them with objects. Deflation -- which occurs at
1372 // STW-time or asynchronously -- disassociates idle monitors from objects.
1373 // Such scavenged monitors are returned to the om_list_globals._free_list.
1374 //
1375 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1376 //
1377 // Lifecycle:
1378 // -- unassigned and on the om_list_globals._free_list
1379 // -- unassigned and on a per-thread free list
1380 // -- assigned to an object. The object is inflated and the mark refers
1381 // to the ObjectMonitor.
1382
1383 ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self) {
1384 // A large MAXPRIVATE value reduces both list lock contention
1385 // and list coherency traffic, but also tends to increase the
1386 // number of ObjectMonitors in circulation as well as the STW
1387 // scavenge costs. As usual, we lean toward time in space-time
1388 // tradeoffs.
1389 const int MAXPRIVATE = 1024;
1390 NoSafepointVerifier nsv;
1391
1392 for (;;) {
1393 ObjectMonitor* m;
1394
1395 // 1: try to allocate from the thread's local om_free_list.
1396 // Threads will attempt to allocate first from their local list, then
1397 // from the global list, and only after those attempts fail will the
1398 // thread attempt to instantiate new monitors. Thread-local free lists
1399 // improve allocation latency, as well as reducing coherency traffic
1400 // on the shared global list.
1401 m = take_from_start_of_om_free_list(self);
1402 if (m != NULL) {
1403 guarantee(m->object() == NULL, "invariant");
1404 m->set_allocation_state(ObjectMonitor::New);
1405 prepend_to_om_in_use_list(self, m);
1406 return m;
1407 }
1408
1409 // 2: try to allocate from the global om_list_globals._free_list
1410 // If we're using thread-local free lists then try
1411 // to reprovision the caller's free list.
1412 if (Atomic::load(&om_list_globals._free_list) != NULL) {
1413 // Reprovision the thread's om_free_list.
1414 // Use bulk transfers to reduce the allocation rate and heat
1415 // on various locks.
1416 for (int i = self->om_free_provision; --i >= 0;) {
1417 ObjectMonitor* take = take_from_start_of_global_free_list();
1418 if (take == NULL) {
1419 break; // No more are available.
1420 }
1421 guarantee(take->object() == NULL, "invariant");
1422 if (AsyncDeflateIdleMonitors) {
1423 // We allowed 3 field values to linger during async deflation.
1424 // Clear or restore them as appropriate.
1425 take->set_header(markWord::zero());
1426 // DEFLATER_MARKER is the only non-NULL value we should see here.
1427 take->try_set_owner_from(DEFLATER_MARKER, NULL);
1428 if (take->contentions() < 0) {
1429 // Add back max_jint to restore the contentions field to its
1430 // proper value.
1431 take->add_to_contentions(max_jint);
1432
1433 #ifdef ASSERT
1434 jint l_contentions = take->contentions();
1435 #endif
1436 assert(l_contentions >= 0, "must not be negative: l_contentions=%d, contentions=%d",
1437 l_contentions, take->contentions());
1438 }
1439 }
1440 take->Recycle();
1441 // Since we're taking from the global free-list, take must be Free.
1442 // om_release() also sets the allocation state to Free because it
1443 // is called from other code paths.
1444 assert(take->is_free(), "invariant");
1445 om_release(self, take, false);
1446 }
1447 self->om_free_provision += 1 + (self->om_free_provision / 2);
1448 if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE;
1449 continue;
1450 }
1451
1452 // 3: allocate a block of new ObjectMonitors
1453 // Both the local and global free lists are empty -- resort to malloc().
1454 // In the current implementation ObjectMonitors are TSM - immortal.
1455 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1456 // each ObjectMonitor to start at the beginning of a cache line,
1457 // so we use align_up().
1458 // A better solution would be to use C++ placement-new.
1459 // BEWARE: As it stands currently, we don't run the ctors!
1460 assert(_BLOCKSIZE > 1, "invariant");
1461 size_t neededsize = sizeof(PaddedObjectMonitor) * _BLOCKSIZE;
1462 PaddedObjectMonitor* temp;
1463 size_t aligned_size = neededsize + (OM_CACHE_LINE_SIZE - 1);
1464 void* real_malloc_addr = NEW_C_HEAP_ARRAY(char, aligned_size, mtInternal);
1465 temp = (PaddedObjectMonitor*)align_up(real_malloc_addr, OM_CACHE_LINE_SIZE);
1466 (void)memset((void *) temp, 0, neededsize);
1467
1468 // Format the block.
1469 // initialize the linked list, each monitor points to its next
1470 // forming the single linked free list, the very first monitor
1471 // will points to next block, which forms the block list.
1472 // The trick of using the 1st element in the block as g_block_list
1473 // linkage should be reconsidered. A better implementation would
1474 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1475
1476 for (int i = 1; i < _BLOCKSIZE; i++) {
1477 temp[i].set_next_om((ObjectMonitor*)&temp[i + 1]);
1478 assert(temp[i].is_free(), "invariant");
1479 }
1480
1481 // terminate the last monitor as the end of list
1482 temp[_BLOCKSIZE - 1].set_next_om((ObjectMonitor*)NULL);
1483
1484 // Element [0] is reserved for global list linkage
1485 temp[0].set_object(CHAINMARKER);
1486
1487 // Consider carving out this thread's current request from the
1488 // block in hand. This avoids some lock traffic and redundant
1489 // list activity.
1490
1491 prepend_block_to_lists(temp);
1492 }
1493 }
1494
1495 // Place "m" on the caller's private per-thread om_free_list.
1496 // In practice there's no need to clamp or limit the number of
1497 // monitors on a thread's om_free_list as the only non-allocation time
1498 // we'll call om_release() is to return a monitor to the free list after
1499 // a CAS attempt failed. This doesn't allow unbounded #s of monitors to
1500 // accumulate on a thread's free list.
1501 //
1502 // Key constraint: all ObjectMonitors on a thread's free list and the global
1503 // free list must have their object field set to null. This prevents the
1504 // scavenger -- deflate_monitor_list() or deflate_monitor_list_using_JT()
1505 // -- from reclaiming them while we are trying to release them.
1506
1507 void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m,
1508 bool from_per_thread_alloc) {
1509 guarantee(m->header().value() == 0, "invariant");
1510 guarantee(m->object() == NULL, "invariant");
1511 NoSafepointVerifier nsv;
1512
1513 if ((m->is_busy() | m->_recursions) != 0) {
1514 stringStream ss;
1515 fatal("freeing in-use monitor: %s, recursions=" INTX_FORMAT,
1516 m->is_busy_to_string(&ss), m->_recursions);
1517 }
1518 m->set_allocation_state(ObjectMonitor::Free);
1519 // _next_om is used for both per-thread in-use and free lists so
1520 // we have to remove 'm' from the in-use list first (as needed).
1521 if (from_per_thread_alloc) {
1522 // Need to remove 'm' from om_in_use_list.
1523 ObjectMonitor* mid = NULL;
1524 ObjectMonitor* next = NULL;
1525
1526 // This list walk can race with another list walker or with async
1527 // deflation so we have to worry about an ObjectMonitor being
1528 // removed from this list while we are walking it.
1529
1530 // Lock the list head to avoid racing with another list walker
1531 // or with async deflation.
1532 if ((mid = get_list_head_locked(&self->om_in_use_list)) == NULL) {
1533 fatal("thread=" INTPTR_FORMAT " in-use list must not be empty.", p2i(self));
1534 }
1535 next = unmarked_next(mid);
1536 if (m == mid) {
1537 // First special case:
1538 // 'm' matches mid, is the list head and is locked. Switch the list
1539 // head to next which unlocks the list head, but leaves the extracted
1540 // mid locked:
1541 Atomic::store(&self->om_in_use_list, next);
1542 } else if (m == next) {
1543 // Second special case:
1544 // 'm' matches next after the list head and we already have the list
1545 // head locked so set mid to what we are extracting:
1546 mid = next;
1547 // Lock mid to prevent races with a list walker or an async
1548 // deflater thread that's ahead of us. The locked list head
1549 // prevents races from behind us.
1550 om_lock(mid);
1551 // Update next to what follows mid (if anything):
1552 next = unmarked_next(mid);
1553 // Switch next after the list head to new next which unlocks the
1554 // list head, but leaves the extracted mid locked:
1555 self->om_in_use_list->set_next_om(next);
1556 } else {
1557 // We have to search the list to find 'm'.
1558 guarantee(next != NULL, "thread=" INTPTR_FORMAT ": om_in_use_list=" INTPTR_FORMAT
1559 " is too short.", p2i(self), p2i(self->om_in_use_list));
1560 // Our starting anchor is next after the list head which is the
1561 // last ObjectMonitor we checked:
1562 ObjectMonitor* anchor = next;
1563 // Lock anchor to prevent races with a list walker or an async
1564 // deflater thread that's ahead of us. The locked list head
1565 // prevents races from behind us.
1566 om_lock(anchor);
1567 om_unlock(mid); // Unlock the list head now that anchor is locked.
1568 while ((mid = unmarked_next(anchor)) != NULL) {
1569 if (m == mid) {
1570 // We found 'm' on the per-thread in-use list so extract it.
1571 // Update next to what follows mid (if anything):
1572 next = unmarked_next(mid);
1573 // Switch next after the anchor to new next which unlocks the
1574 // anchor, but leaves the extracted mid locked:
1575 anchor->set_next_om(next);
1576 break;
1577 } else {
1578 // Lock the next anchor to prevent races with a list walker
1579 // or an async deflater thread that's ahead of us. The locked
1580 // current anchor prevents races from behind us.
1581 om_lock(mid);
1582 // Unlock current anchor now that next anchor is locked:
1583 om_unlock(anchor);
1584 anchor = mid; // Advance to new anchor and try again.
1585 }
1586 }
1587 }
1588
1589 if (mid == NULL) {
1590 // Reached end of the list and didn't find 'm' so:
1591 fatal("thread=" INTPTR_FORMAT " must find m=" INTPTR_FORMAT "on om_in_use_list="
1592 INTPTR_FORMAT, p2i(self), p2i(m), p2i(self->om_in_use_list));
1593 }
1594
1595 // At this point mid is disconnected from the in-use list so
1596 // its lock no longer has any effects on the in-use list.
1597 Atomic::dec(&self->om_in_use_count);
1598 // Unlock mid, but leave the next value for any lagging list
1599 // walkers. It will get cleaned up when mid is prepended to
1600 // the thread's free list:
1601 om_unlock(mid);
1602 }
1603
1604 prepend_to_om_free_list(self, m);
1605 guarantee(m->is_free(), "invariant");
1606 }
1607
1608 // Return ObjectMonitors on a moribund thread's free and in-use
1609 // lists to the appropriate global lists. The ObjectMonitors on the
1610 // per-thread in-use list may still be in use by other threads.
1611 //
1612 // We currently call om_flush() from Threads::remove() before the
1613 // thread has been excised from the thread list and is no longer a
1614 // mutator. This means that om_flush() cannot run concurrently with
1615 // a safepoint and interleave with deflate_idle_monitors(). In
1616 // particular, this ensures that the thread's in-use monitors are
1617 // scanned by a GC safepoint, either via Thread::oops_do() (before
1618 // om_flush() is called) or via ObjectSynchronizer::oops_do() (after
1619 // om_flush() is called).
1620 //
1621 // With AsyncDeflateIdleMonitors, deflate_global_idle_monitors_using_JT()
1622 // and deflate_per_thread_idle_monitors_using_JT() (in another thread) can
1623 // run at the same time as om_flush() so we have to follow a careful
1624 // protocol to prevent list corruption.
1625
1626 void ObjectSynchronizer::om_flush(Thread* self) {
1627 // Process the per-thread in-use list first to be consistent.
1628 int in_use_count = 0;
1629 ObjectMonitor* in_use_list = NULL;
1630 ObjectMonitor* in_use_tail = NULL;
1631 NoSafepointVerifier nsv;
1632
1633 // This function can race with a list walker or with an async
1634 // deflater thread so we lock the list head to prevent confusion.
1635 // An async deflater thread checks to see if the target thread
1636 // is exiting, but if it has made it past that check before we
1637 // started exiting, then it is racing to get to the in-use list.
1638 if ((in_use_list = get_list_head_locked(&self->om_in_use_list)) != NULL) {
1639 // At this point, we have locked the in-use list head so a racing
1640 // thread cannot come in after us. However, a racing thread could
1641 // be ahead of us; we'll detect that and delay to let it finish.
1642 //
1643 // The thread is going away, however the ObjectMonitors on the
1644 // om_in_use_list may still be in-use by other threads. Link
1645 // them to in_use_tail, which will be linked into the global
1646 // in-use list (om_list_globals._in_use_list) below.
1647 //
1648 // Account for the in-use list head before the loop since it is
1649 // already locked (by this thread):
1650 in_use_tail = in_use_list;
1651 in_use_count++;
1652 for (ObjectMonitor* cur_om = unmarked_next(in_use_list); cur_om != NULL;) {
1653 if (is_locked(cur_om)) {
1654 // cur_om is locked so there must be a racing walker or async
1655 // deflater thread ahead of us so we'll give it a chance to finish.
1656 while (is_locked(cur_om)) {
1657 os::naked_short_sleep(1);
1658 }
1659 // Refetch the possibly changed next field and try again.
1660 cur_om = unmarked_next(in_use_tail);
1661 continue;
1662 }
1663 if (cur_om->object() == NULL) {
1664 // cur_om was deflated and the object ref was cleared while it
1665 // was locked. We happened to see it just after it was unlocked
1666 // (and added to the free list). Refetch the possibly changed
1667 // next field and try again.
1668 cur_om = unmarked_next(in_use_tail);
1669 continue;
1670 }
1671 in_use_tail = cur_om;
1672 in_use_count++;
1673 cur_om = unmarked_next(cur_om);
1674 }
1675 guarantee(in_use_tail != NULL, "invariant");
1676 int l_om_in_use_count = Atomic::load(&self->om_in_use_count);
1677 ADIM_guarantee(l_om_in_use_count == in_use_count, "in-use counts don't match: "
1678 "l_om_in_use_count=%d, in_use_count=%d", l_om_in_use_count, in_use_count);
1679 Atomic::store(&self->om_in_use_count, 0);
1680 // Clear the in-use list head (which also unlocks it):
1681 Atomic::store(&self->om_in_use_list, (ObjectMonitor*)NULL);
1682 om_unlock(in_use_list);
1683 }
1684
1685 int free_count = 0;
1686 ObjectMonitor* free_list = NULL;
1687 ObjectMonitor* free_tail = NULL;
1688 // This function can race with a list walker thread so we lock the
1689 // list head to prevent confusion.
1690 if ((free_list = get_list_head_locked(&self->om_free_list)) != NULL) {
1691 // At this point, we have locked the free list head so a racing
1692 // thread cannot come in after us. However, a racing thread could
1693 // be ahead of us; we'll detect that and delay to let it finish.
1694 //
1695 // The thread is going away. Set 'free_tail' to the last per-thread free
1696 // monitor which will be linked to om_list_globals._free_list below.
1697 //
1698 // Account for the free list head before the loop since it is
1699 // already locked (by this thread):
1700 free_tail = free_list;
1701 free_count++;
1702 for (ObjectMonitor* s = unmarked_next(free_list); s != NULL; s = unmarked_next(s)) {
1703 if (is_locked(s)) {
1704 // s is locked so there must be a racing walker thread ahead
1705 // of us so we'll give it a chance to finish.
1706 while (is_locked(s)) {
1707 os::naked_short_sleep(1);
1708 }
1709 }
1710 free_tail = s;
1711 free_count++;
1712 guarantee(s->object() == NULL, "invariant");
1713 if (s->is_busy()) {
1714 stringStream ss;
1715 fatal("must be !is_busy: %s", s->is_busy_to_string(&ss));
1716 }
1717 }
1718 guarantee(free_tail != NULL, "invariant");
1719 int l_om_free_count = Atomic::load(&self->om_free_count);
1720 ADIM_guarantee(l_om_free_count == free_count, "free counts don't match: "
1721 "l_om_free_count=%d, free_count=%d", l_om_free_count, free_count);
1722 Atomic::store(&self->om_free_count, 0);
1723 Atomic::store(&self->om_free_list, (ObjectMonitor*)NULL);
1724 om_unlock(free_list);
1725 }
1726
1727 if (free_tail != NULL) {
1728 prepend_list_to_global_free_list(free_list, free_tail, free_count);
1729 }
1730
1731 if (in_use_tail != NULL) {
1732 prepend_list_to_global_in_use_list(in_use_list, in_use_tail, in_use_count);
1733 }
1734
1735 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1736 LogStreamHandle(Info, monitorinflation) lsh_info;
1737 LogStream* ls = NULL;
1738 if (log_is_enabled(Debug, monitorinflation)) {
1739 ls = &lsh_debug;
1740 } else if ((free_count != 0 || in_use_count != 0) &&
1741 log_is_enabled(Info, monitorinflation)) {
1742 ls = &lsh_info;
1743 }
1744 if (ls != NULL) {
1745 ls->print_cr("om_flush: jt=" INTPTR_FORMAT ", free_count=%d"
1746 ", in_use_count=%d" ", om_free_provision=%d",
1747 p2i(self), free_count, in_use_count, self->om_free_provision);
1748 }
1749 }
1750
1751 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1752 const oop obj,
1753 ObjectSynchronizer::InflateCause cause) {
1754 assert(event != NULL, "invariant");
1755 assert(event->should_commit(), "invariant");
1756 event->set_monitorClass(obj->klass());
1757 event->set_address((uintptr_t)(void*)obj);
1758 event->set_cause((u1)cause);
1759 event->commit();
1760 }
1761
1762 // Fast path code shared by multiple functions
1763 void ObjectSynchronizer::inflate_helper(oop obj) {
1764 markWord mark = obj->mark();
1765 if (mark.has_monitor()) {
1766 ObjectMonitor* monitor = mark.monitor();
1767 assert(ObjectSynchronizer::verify_objmon_isinpool(monitor), "monitor=" INTPTR_FORMAT " is invalid", p2i(monitor));
1768 markWord dmw = monitor->header();
1769 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1770 return;
1771 }
1772 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1773 }
1774
1775 ObjectMonitor* ObjectSynchronizer::inflate(Thread* self, oop object,
1776 const InflateCause cause) {
1777 // Inflate mutates the heap ...
1778 // Relaxing assertion for bug 6320749.
1779 assert(Universe::verify_in_progress() ||
1780 !SafepointSynchronize::is_at_safepoint(), "invariant");
1781
1782 EventJavaMonitorInflate event;
1783
1784 for (;;) {
1785 const markWord mark = object->mark();
1786 assert(!mark.has_bias_pattern(), "invariant");
1787
1788 // The mark can be in one of the following states:
1789 // * Inflated - just return
1790 // * Stack-locked - coerce it to inflated
1791 // * INFLATING - busy wait for conversion to complete
1792 // * Neutral - aggressively inflate the object.
1793 // * BIASED - Illegal. We should never see this
1794
1795 // CASE: inflated
1796 if (mark.has_monitor()) {
1797 ObjectMonitor* inf = mark.monitor();
1798 markWord dmw = inf->header();
1799 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1800 assert(AsyncDeflateIdleMonitors || inf->object() == object, "invariant");
1801 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1802 return inf;
1803 }
1804
1805 // CASE: inflation in progress - inflating over a stack-lock.
1806 // Some other thread is converting from stack-locked to inflated.
1807 // Only that thread can complete inflation -- other threads must wait.
1808 // The INFLATING value is transient.
1809 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1810 // We could always eliminate polling by parking the thread on some auxiliary list.
1811 if (mark == markWord::INFLATING()) {
1812 read_stable_mark(object);
1813 continue;
1814 }
1815
1816 // CASE: stack-locked
1817 // Could be stack-locked either by this thread or by some other thread.
1818 //
1819 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1820 // to install INFLATING into the mark word. We originally installed INFLATING,
1821 // allocated the objectmonitor, and then finally STed the address of the
1822 // objectmonitor into the mark. This was correct, but artificially lengthened
1823 // the interval in which INFLATED appeared in the mark, thus increasing
1824 // the odds of inflation contention.
1825 //
1826 // We now use per-thread private objectmonitor free lists.
1827 // These list are reprovisioned from the global free list outside the
1828 // critical INFLATING...ST interval. A thread can transfer
1829 // multiple objectmonitors en-mass from the global free list to its local free list.
1830 // This reduces coherency traffic and lock contention on the global free list.
1831 // Using such local free lists, it doesn't matter if the om_alloc() call appears
1832 // before or after the CAS(INFLATING) operation.
1833 // See the comments in om_alloc().
1834
1835 LogStreamHandle(Trace, monitorinflation) lsh;
1836
1837 if (mark.has_locker()) {
1838 ObjectMonitor* m = om_alloc(self);
1839 // Optimistically prepare the objectmonitor - anticipate successful CAS
1840 // We do this before the CAS in order to minimize the length of time
1841 // in which INFLATING appears in the mark.
1842 m->Recycle();
1843 m->_Responsible = NULL;
1844 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1845
1846 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1847 if (cmp != mark) {
1848 // om_release() will reset the allocation state from New to Free.
1849 om_release(self, m, true);
1850 continue; // Interference -- just retry
1851 }
1852
1853 // We've successfully installed INFLATING (0) into the mark-word.
1854 // This is the only case where 0 will appear in a mark-word.
1855 // Only the singular thread that successfully swings the mark-word
1856 // to 0 can perform (or more precisely, complete) inflation.
1857 //
1858 // Why do we CAS a 0 into the mark-word instead of just CASing the
1859 // mark-word from the stack-locked value directly to the new inflated state?
1860 // Consider what happens when a thread unlocks a stack-locked object.
1861 // It attempts to use CAS to swing the displaced header value from the
1862 // on-stack BasicLock back into the object header. Recall also that the
1863 // header value (hash code, etc) can reside in (a) the object header, or
1864 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1865 // header in an ObjectMonitor. The inflate() routine must copy the header
1866 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1867 // the while preserving the hashCode stability invariants. If the owner
1868 // decides to release the lock while the value is 0, the unlock will fail
1869 // and control will eventually pass from slow_exit() to inflate. The owner
1870 // will then spin, waiting for the 0 value to disappear. Put another way,
1871 // the 0 causes the owner to stall if the owner happens to try to
1872 // drop the lock (restoring the header from the BasicLock to the object)
1873 // while inflation is in-progress. This protocol avoids races that might
1874 // would otherwise permit hashCode values to change or "flicker" for an object.
1875 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1876 // 0 serves as a "BUSY" inflate-in-progress indicator.
1877
1878
1879 // fetch the displaced mark from the owner's stack.
1880 // The owner can't die or unwind past the lock while our INFLATING
1881 // object is in the mark. Furthermore the owner can't complete
1882 // an unlock on the object, either.
1883 markWord dmw = mark.displaced_mark_helper();
1884 // Catch if the object's header is not neutral (not locked and
1885 // not marked is what we care about here).
1886 ADIM_guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1887
1888 // Setup monitor fields to proper values -- prepare the monitor
1889 m->set_header(dmw);
1890
1891 // Optimization: if the mark.locker stack address is associated
1892 // with this thread we could simply set m->_owner = self.
1893 // Note that a thread can inflate an object
1894 // that it has stack-locked -- as might happen in wait() -- directly
1895 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1896 if (AsyncDeflateIdleMonitors) {
1897 m->set_owner_from(NULL, DEFLATER_MARKER, mark.locker());
1898 } else {
1899 m->set_owner_from(NULL, mark.locker());
1900 }
1901 m->set_object(object);
1902 // TODO-FIXME: assert BasicLock->dhw != 0.
1903
1904 // Must preserve store ordering. The monitor state must
1905 // be stable at the time of publishing the monitor address.
1906 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1907 object->release_set_mark(markWord::encode(m));
1908
1909 // Once ObjectMonitor is configured and the object is associated
1910 // with the ObjectMonitor, it is safe to allow async deflation:
1911 assert(m->is_new(), "freshly allocated monitor must be new");
1912 m->set_allocation_state(ObjectMonitor::Old);
1913
1914 // Hopefully the performance counters are allocated on distinct cache lines
1915 // to avoid false sharing on MP systems ...
1916 OM_PERFDATA_OP(Inflations, inc());
1917 if (log_is_enabled(Trace, monitorinflation)) {
1918 ResourceMark rm(self);
1919 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1920 INTPTR_FORMAT ", type='%s'", p2i(object),
1921 object->mark().value(), object->klass()->external_name());
1922 }
1923 if (event.should_commit()) {
1924 post_monitor_inflate_event(&event, object, cause);
1925 }
1926 return m;
1927 }
1928
1929 // CASE: neutral
1930 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1931 // If we know we're inflating for entry it's better to inflate by swinging a
1932 // pre-locked ObjectMonitor pointer into the object header. A successful
1933 // CAS inflates the object *and* confers ownership to the inflating thread.
1934 // In the current implementation we use a 2-step mechanism where we CAS()
1935 // to inflate and then CAS() again to try to swing _owner from NULL to self.
1936 // An inflateTry() method that we could call from enter() would be useful.
1937
1938 // Catch if the object's header is not neutral (not locked and
1939 // not marked is what we care about here).
1940 ADIM_guarantee(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1941 ObjectMonitor* m = om_alloc(self);
1942 // prepare m for installation - set monitor to initial state
1943 m->Recycle();
1944 m->set_header(mark);
1945 if (AsyncDeflateIdleMonitors) {
1946 // DEFLATER_MARKER is the only non-NULL value we should see here.
1947 m->try_set_owner_from(DEFLATER_MARKER, NULL);
1948 }
1949 m->set_object(object);
1950 m->_Responsible = NULL;
1951 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1952
1953 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1954 m->set_header(markWord::zero());
1955 m->set_object(NULL);
1956 m->Recycle();
1957 // om_release() will reset the allocation state from New to Free.
1958 om_release(self, m, true);
1959 m = NULL;
1960 continue;
1961 // interference - the markword changed - just retry.
1962 // The state-transitions are one-way, so there's no chance of
1963 // live-lock -- "Inflated" is an absorbing state.
1964 }
1965
1966 // Once the ObjectMonitor is configured and object is associated
1967 // with the ObjectMonitor, it is safe to allow async deflation:
1968 assert(m->is_new(), "freshly allocated monitor must be new");
1969 m->set_allocation_state(ObjectMonitor::Old);
1970
1971 // Hopefully the performance counters are allocated on distinct
1972 // cache lines to avoid false sharing on MP systems ...
1973 OM_PERFDATA_OP(Inflations, inc());
1974 if (log_is_enabled(Trace, monitorinflation)) {
1975 ResourceMark rm(self);
1976 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1977 INTPTR_FORMAT ", type='%s'", p2i(object),
1978 object->mark().value(), object->klass()->external_name());
1979 }
1980 if (event.should_commit()) {
1981 post_monitor_inflate_event(&event, object, cause);
1982 }
1983 return m;
1984 }
1985 }
1986
1987
1988 // We maintain a list of in-use monitors for each thread.
1989 //
1990 // For safepoint based deflation:
1991 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1992 // deflate_idle_monitors() scans only a global list of in-use monitors which
1993 // is populated only as a thread dies (see om_flush()).
1994 //
1995 // These operations are called at all safepoints, immediately after mutators
1996 // are stopped, but before any objects have moved. Collectively they traverse
1997 // the population of in-use monitors, deflating where possible. The scavenged
1998 // monitors are returned to the global monitor free list.
1999 //
2000 // Beware that we scavenge at *every* stop-the-world point. Having a large
2001 // number of monitors in-use could negatively impact performance. We also want
2002 // to minimize the total # of monitors in circulation, as they incur a small
2003 // footprint penalty.
2004 //
2005 // Perversely, the heap size -- and thus the STW safepoint rate --
2006 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
2007 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
2008 // This is an unfortunate aspect of this design.
2009 //
2010 // For async deflation:
2011 // If a special deflation request is made, then the safepoint based
2012 // deflation mechanism is used. Otherwise, an async deflation request
2013 // is registered with the ServiceThread and it is notified.
2014
2015 void ObjectSynchronizer::do_safepoint_work(DeflateMonitorCounters* counters) {
2016 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2017
2018 // The per-thread in-use lists are handled in
2019 // ParallelSPCleanupThreadClosure::do_thread().
2020
2021 if (!AsyncDeflateIdleMonitors || is_special_deflation_requested()) {
2022 // Use the older mechanism for the global in-use list or if a
2023 // special deflation has been requested before the safepoint.
2024 ObjectSynchronizer::deflate_idle_monitors(counters);
2025 return;
2026 }
2027
2028 log_debug(monitorinflation)("requesting async deflation of idle monitors.");
2029 // Request deflation of idle monitors by the ServiceThread:
2030 set_is_async_deflation_requested(true);
2031 MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
2032 ml.notify_all();
2033
2034 if (log_is_enabled(Debug, monitorinflation)) {
2035 // exit_globals()'s call to audit_and_print_stats() is done
2036 // at the Info level and not at a safepoint.
2037 // For safepoint based deflation, audit_and_print_stats() is called
2038 // in ObjectSynchronizer::finish_deflate_idle_monitors() at the
2039 // Debug level at a safepoint.
2040 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2041 }
2042 }
2043
2044 // Deflate a single monitor if not in-use
2045 // Return true if deflated, false if in-use
2046 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
2047 ObjectMonitor** free_head_p,
2048 ObjectMonitor** free_tail_p) {
2049 bool deflated;
2050 // Normal case ... The monitor is associated with obj.
2051 const markWord mark = obj->mark();
2052 guarantee(mark == markWord::encode(mid), "should match: mark="
2053 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(),
2054 markWord::encode(mid).value());
2055 // Make sure that mark.monitor() and markWord::encode() agree:
2056 guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
2057 ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid));
2058 const markWord dmw = mid->header();
2059 guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
2060
2061 if (mid->is_busy()) {
2062 // Easy checks are first - the ObjectMonitor is busy so no deflation.
2063 deflated = false;
2064 } else {
2065 // Deflate the monitor if it is no longer being used
2066 // It's idle - scavenge and return to the global free list
2067 // plain old deflation ...
2068 if (log_is_enabled(Trace, monitorinflation)) {
2069 ResourceMark rm;
2070 log_trace(monitorinflation)("deflate_monitor: "
2071 "object=" INTPTR_FORMAT ", mark="
2072 INTPTR_FORMAT ", type='%s'", p2i(obj),
2073 mark.value(), obj->klass()->external_name());
2074 }
2075
2076 // Restore the header back to obj
2077 obj->release_set_mark(dmw);
2078 if (AsyncDeflateIdleMonitors) {
2079 // clear() expects the owner field to be NULL.
2080 // DEFLATER_MARKER is the only non-NULL value we should see here.
2081 mid->try_set_owner_from(DEFLATER_MARKER, NULL);
2082 }
2083 mid->clear();
2084
2085 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
2086 p2i(mid->object()));
2087 assert(mid->is_free(), "invariant");
2088
2089 // Move the deflated ObjectMonitor to the working free list
2090 // defined by free_head_p and free_tail_p.
2091 if (*free_head_p == NULL) *free_head_p = mid;
2092 if (*free_tail_p != NULL) {
2093 // We append to the list so the caller can use mid->_next_om
2094 // to fix the linkages in its context.
2095 ObjectMonitor* prevtail = *free_tail_p;
2096 // Should have been cleaned up by the caller:
2097 // Note: Should not have to lock prevtail here since we're at a
2098 // safepoint and ObjectMonitors on the local free list should
2099 // not be accessed in parallel.
2100 #ifdef ASSERT
2101 ObjectMonitor* l_next_om = prevtail->next_om();
2102 #endif
2103 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2104 prevtail->set_next_om(mid);
2105 }
2106 *free_tail_p = mid;
2107 // At this point, mid->_next_om still refers to its current
2108 // value and another ObjectMonitor's _next_om field still
2109 // refers to this ObjectMonitor. Those linkages have to be
2110 // cleaned up by the caller who has the complete context.
2111 deflated = true;
2112 }
2113 return deflated;
2114 }
2115
2116 // Deflate the specified ObjectMonitor if not in-use using a JavaThread.
2117 // Returns true if it was deflated and false otherwise.
2118 //
2119 // The async deflation protocol sets owner to DEFLATER_MARKER and
2120 // makes contentions negative as signals to contending threads that
2121 // an async deflation is in progress. There are a number of checks
2122 // as part of the protocol to make sure that the calling thread has
2123 // not lost the race to a contending thread.
2124 //
2125 // The ObjectMonitor has been successfully async deflated when:
2126 // (owner == DEFLATER_MARKER && contentions < 0)
2127 // Contending threads that see those values know to retry their operation.
2128 //
2129 bool ObjectSynchronizer::deflate_monitor_using_JT(ObjectMonitor* mid,
2130 ObjectMonitor** free_head_p,
2131 ObjectMonitor** free_tail_p) {
2132 assert(AsyncDeflateIdleMonitors, "sanity check");
2133 assert(Thread::current()->is_Java_thread(), "precondition");
2134 // A newly allocated ObjectMonitor should not be seen here so we
2135 // avoid an endless inflate/deflate cycle.
2136 assert(mid->is_old(), "must be old: allocation_state=%d",
2137 (int) mid->allocation_state());
2138
2139 if (mid->is_busy()) {
2140 // Easy checks are first - the ObjectMonitor is busy so no deflation.
2141 return false;
2142 }
2143
2144 // Set a NULL owner to DEFLATER_MARKER to force any contending thread
2145 // through the slow path. This is just the first part of the async
2146 // deflation dance.
2147 if (mid->try_set_owner_from(NULL, DEFLATER_MARKER) != NULL) {
2148 // The owner field is no longer NULL so we lost the race since the
2149 // ObjectMonitor is now busy.
2150 return false;
2151 }
2152
2153 if (mid->contentions() > 0 || mid->_waiters != 0) {
2154 // Another thread has raced to enter the ObjectMonitor after
2155 // mid->is_busy() above or has already entered and waited on
2156 // it which makes it busy so no deflation. Restore owner to
2157 // NULL if it is still DEFLATER_MARKER.
2158 mid->try_set_owner_from(DEFLATER_MARKER, NULL);
2159 return false;
2160 }
2161
2162 // Make a zero contentions field negative to force any contending threads
2163 // to retry. This is the second part of the async deflation dance.
2164 if (Atomic::cmpxchg(&mid->_contentions, (jint)0, -max_jint) != 0) {
2165 // Contentions was no longer 0 so we lost the race since the
2166 // ObjectMonitor is now busy. Restore owner to NULL if it is
2167 // still DEFLATER_MARKER:
2168 mid->try_set_owner_from(DEFLATER_MARKER, NULL);
2169 return false;
2170 }
2171
2172 // If owner is still DEFLATER_MARKER, then we have successfully
2173 // signaled any contending threads to retry.
2174 if (!mid->owner_is_DEFLATER_MARKER()) {
2175 // If it is not, then we have lost the race to an entering thread
2176 // and the ObjectMonitor is now busy. This is the third and final
2177 // part of the async deflation dance.
2178 // Note: This owner check solves the ABA problem with contentions
2179 // where another thread acquired the ObjectMonitor, finished
2180 // using it and restored contentions to zero.
2181
2182 // Add back max_jint to restore the contentions field to its
2183 // proper value (which may not be what we saw above):
2184 mid->add_to_contentions(max_jint);
2185
2186 #ifdef ASSERT
2187 jint l_contentions = mid->contentions();
2188 #endif
2189 assert(l_contentions >= 0, "must not be negative: l_contentions=%d, contentions=%d",
2190 l_contentions, mid->contentions());
2191 return false;
2192 }
2193
2194 // Sanity checks for the races:
2195 guarantee(mid->contentions() < 0, "must be negative: contentions=%d",
2196 mid->contentions());
2197 guarantee(mid->_waiters == 0, "must be 0: waiters=%d", mid->_waiters);
2198 guarantee(mid->_cxq == NULL, "must be no contending threads: cxq="
2199 INTPTR_FORMAT, p2i(mid->_cxq));
2200 guarantee(mid->_EntryList == NULL,
2201 "must be no entering threads: EntryList=" INTPTR_FORMAT,
2202 p2i(mid->_EntryList));
2203
2204 const oop obj = (oop) mid->object();
2205 if (log_is_enabled(Trace, monitorinflation)) {
2206 ResourceMark rm;
2207 log_trace(monitorinflation)("deflate_monitor_using_JT: "
2208 "object=" INTPTR_FORMAT ", mark="
2209 INTPTR_FORMAT ", type='%s'",
2210 p2i(obj), obj->mark().value(),
2211 obj->klass()->external_name());
2212 }
2213
2214 // Install the old mark word if nobody else has already done it.
2215 mid->install_displaced_markword_in_object(obj);
2216 mid->clear_common();
2217
2218 assert(mid->object() == NULL, "must be NULL: object=" INTPTR_FORMAT,
2219 p2i(mid->object()));
2220 assert(mid->is_free(), "must be free: allocation_state=%d",
2221 (int)mid->allocation_state());
2222
2223 // Move the deflated ObjectMonitor to the working free list
2224 // defined by free_head_p and free_tail_p.
2225 if (*free_head_p == NULL) {
2226 // First one on the list.
2227 *free_head_p = mid;
2228 }
2229 if (*free_tail_p != NULL) {
2230 // We append to the list so the caller can use mid->_next_om
2231 // to fix the linkages in its context.
2232 ObjectMonitor* prevtail = *free_tail_p;
2233 // prevtail should have been cleaned up by the caller:
2234 #ifdef ASSERT
2235 ObjectMonitor* l_next_om = unmarked_next(prevtail);
2236 #endif
2237 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2238 om_lock(prevtail);
2239 prevtail->set_next_om(mid); // prevtail now points to mid (and is unlocked)
2240 }
2241 *free_tail_p = mid;
2242
2243 // At this point, mid->_next_om still refers to its current
2244 // value and another ObjectMonitor's _next_om field still
2245 // refers to this ObjectMonitor. Those linkages have to be
2246 // cleaned up by the caller who has the complete context.
2247
2248 // We leave owner == DEFLATER_MARKER and contentions < 0
2249 // to force any racing threads to retry.
2250 return true; // Success, ObjectMonitor has been deflated.
2251 }
2252
2253 // Walk a given monitor list, and deflate idle monitors.
2254 // The given list could be a per-thread list or a global list.
2255 //
2256 // In the case of parallel processing of thread local monitor lists,
2257 // work is done by Threads::parallel_threads_do() which ensures that
2258 // each Java thread is processed by exactly one worker thread, and
2259 // thus avoid conflicts that would arise when worker threads would
2260 // process the same monitor lists concurrently.
2261 //
2262 // See also ParallelSPCleanupTask and
2263 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
2264 // Threads::parallel_java_threads_do() in thread.cpp.
2265 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** list_p,
2266 int* count_p,
2267 ObjectMonitor** free_head_p,
2268 ObjectMonitor** free_tail_p) {
2269 ObjectMonitor* cur_mid_in_use = NULL;
2270 ObjectMonitor* mid = NULL;
2271 ObjectMonitor* next = NULL;
2272 int deflated_count = 0;
2273
2274 // This list walk executes at a safepoint and does not race with any
2275 // other list walkers.
2276
2277 for (mid = Atomic::load(list_p); mid != NULL; mid = next) {
2278 next = unmarked_next(mid);
2279 oop obj = (oop) mid->object();
2280 if (obj != NULL && deflate_monitor(mid, obj, free_head_p, free_tail_p)) {
2281 // Deflation succeeded and already updated free_head_p and
2282 // free_tail_p as needed. Finish the move to the local free list
2283 // by unlinking mid from the global or per-thread in-use list.
2284 if (cur_mid_in_use == NULL) {
2285 // mid is the list head so switch the list head to next:
2286 Atomic::store(list_p, next);
2287 } else {
2288 // Switch cur_mid_in_use's next field to next:
2289 cur_mid_in_use->set_next_om(next);
2290 }
2291 // At this point mid is disconnected from the in-use list.
2292 deflated_count++;
2293 Atomic::dec(count_p);
2294 // mid is current tail in the free_head_p list so NULL terminate it:
2295 mid->set_next_om(NULL);
2296 } else {
2297 cur_mid_in_use = mid;
2298 }
2299 }
2300 return deflated_count;
2301 }
2302
2303 // Walk a given ObjectMonitor list and deflate idle ObjectMonitors using
2304 // a JavaThread. Returns the number of deflated ObjectMonitors. The given
2305 // list could be a per-thread in-use list or the global in-use list.
2306 // If a safepoint has started, then we save state via saved_mid_in_use_p
2307 // and return to the caller to honor the safepoint.
2308 //
2309 int ObjectSynchronizer::deflate_monitor_list_using_JT(ObjectMonitor** list_p,
2310 int* count_p,
2311 ObjectMonitor** free_head_p,
2312 ObjectMonitor** free_tail_p,
2313 ObjectMonitor** saved_mid_in_use_p) {
2314 assert(AsyncDeflateIdleMonitors, "sanity check");
2315 JavaThread* self = JavaThread::current();
2316
2317 ObjectMonitor* cur_mid_in_use = NULL;
2318 ObjectMonitor* mid = NULL;
2319 ObjectMonitor* next = NULL;
2320 ObjectMonitor* next_next = NULL;
2321 int deflated_count = 0;
2322 NoSafepointVerifier nsv;
2323
2324 // We use the more complicated lock-cur_mid_in_use-and-mid-as-we-go
2325 // protocol because om_release() can do list deletions in parallel;
2326 // this also prevents races with a list walker thread. We also
2327 // lock-next-next-as-we-go to prevent an om_flush() that is behind
2328 // this thread from passing us.
2329 if (*saved_mid_in_use_p == NULL) {
2330 // No saved state so start at the beginning.
2331 // Lock the list head so we can possibly deflate it:
2332 if ((mid = get_list_head_locked(list_p)) == NULL) {
2333 return 0; // The list is empty so nothing to deflate.
2334 }
2335 next = unmarked_next(mid);
2336 } else {
2337 // We're restarting after a safepoint so restore the necessary state
2338 // before we resume.
2339 cur_mid_in_use = *saved_mid_in_use_p;
2340 // Lock cur_mid_in_use so we can possibly update its
2341 // next field to extract a deflated ObjectMonitor.
2342 om_lock(cur_mid_in_use);
2343 mid = unmarked_next(cur_mid_in_use);
2344 if (mid == NULL) {
2345 om_unlock(cur_mid_in_use);
2346 *saved_mid_in_use_p = NULL;
2347 return 0; // The remainder is empty so nothing more to deflate.
2348 }
2349 // Lock mid so we can possibly deflate it:
2350 om_lock(mid);
2351 next = unmarked_next(mid);
2352 }
2353
2354 while (true) {
2355 // The current mid is locked at this point. If we have a
2356 // cur_mid_in_use, then it is also locked at this point.
2357
2358 if (next != NULL) {
2359 // We lock next so that an om_flush() thread that is behind us
2360 // cannot pass us when we unlock the current mid.
2361 om_lock(next);
2362 next_next = unmarked_next(next);
2363 }
2364
2365 // Only try to deflate if there is an associated Java object and if
2366 // mid is old (is not newly allocated and is not newly freed).
2367 if (mid->object() != NULL && mid->is_old() &&
2368 deflate_monitor_using_JT(mid, free_head_p, free_tail_p)) {
2369 // Deflation succeeded and already updated free_head_p and
2370 // free_tail_p as needed. Finish the move to the local free list
2371 // by unlinking mid from the global or per-thread in-use list.
2372 if (cur_mid_in_use == NULL) {
2373 // mid is the list head and it is locked. Switch the list head
2374 // to next which is also locked (if not NULL) and also leave
2375 // mid locked:
2376 Atomic::store(list_p, next);
2377 } else {
2378 ObjectMonitor* locked_next = mark_om_ptr(next);
2379 // mid and cur_mid_in_use are locked. Switch cur_mid_in_use's
2380 // next field to locked_next and also leave mid locked:
2381 cur_mid_in_use->set_next_om(locked_next);
2382 }
2383 // At this point mid is disconnected from the in-use list so
2384 // its lock longer has any effects on in-use list.
2385 deflated_count++;
2386 Atomic::dec(count_p);
2387 // mid is current tail in the free_head_p list so NULL terminate it
2388 // (which also unlocks it):
2389 mid->set_next_om(NULL);
2390
2391 // All the list management is done so move on to the next one:
2392 mid = next; // mid keeps non-NULL next's locked state
2393 next = next_next;
2394 } else {
2395 // mid is considered in-use if it does not have an associated
2396 // Java object or mid is not old or deflation did not succeed.
2397 // A mid->is_new() node can be seen here when it is freshly
2398 // returned by om_alloc() (and skips the deflation code path).
2399 // A mid->is_old() node can be seen here when deflation failed.
2400 // A mid->is_free() node can be seen here when a fresh node from
2401 // om_alloc() is released by om_release() due to losing the race
2402 // in inflate().
2403
2404 // All the list management is done so move on to the next one:
2405 if (cur_mid_in_use != NULL) {
2406 om_unlock(cur_mid_in_use);
2407 }
2408 // The next cur_mid_in_use keeps mid's lock state so
2409 // that it is stable for a possible next field change. It
2410 // cannot be modified by om_release() while it is locked.
2411 cur_mid_in_use = mid;
2412 mid = next; // mid keeps non-NULL next's locked state
2413 next = next_next;
2414
2415 if (SafepointMechanism::should_block(self) &&
2416 cur_mid_in_use != Atomic::load(list_p) && cur_mid_in_use->is_old()) {
2417 // If a safepoint has started and cur_mid_in_use is not the list
2418 // head and is old, then it is safe to use as saved state. Return
2419 // to the caller before blocking.
2420 *saved_mid_in_use_p = cur_mid_in_use;
2421 om_unlock(cur_mid_in_use);
2422 if (mid != NULL) {
2423 om_unlock(mid);
2424 }
2425 return deflated_count;
2426 }
2427 }
2428 if (mid == NULL) {
2429 if (cur_mid_in_use != NULL) {
2430 om_unlock(cur_mid_in_use);
2431 }
2432 break; // Reached end of the list so nothing more to deflate.
2433 }
2434
2435 // The current mid's next field is locked at this point. If we have
2436 // a cur_mid_in_use, then it is also locked at this point.
2437 }
2438 // We finished the list without a safepoint starting so there's
2439 // no need to save state.
2440 *saved_mid_in_use_p = NULL;
2441 return deflated_count;
2442 }
2443
2444 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2445 counters->n_in_use = 0; // currently associated with objects
2446 counters->n_in_circulation = 0; // extant
2447 counters->n_scavenged = 0; // reclaimed (global and per-thread)
2448 counters->per_thread_scavenged = 0; // per-thread scavenge total
2449 counters->per_thread_times = 0.0; // per-thread scavenge times
2450 }
2451
2452 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
2453 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2454
2455 if (AsyncDeflateIdleMonitors) {
2456 // Nothing to do when global idle ObjectMonitors are deflated using
2457 // a JavaThread unless a special deflation has been requested.
2458 if (!is_special_deflation_requested()) {
2459 return;
2460 }
2461 }
2462
2463 bool deflated = false;
2464
2465 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
2466 ObjectMonitor* free_tail_p = NULL;
2467 elapsedTimer timer;
2468
2469 if (log_is_enabled(Info, monitorinflation)) {
2470 timer.start();
2471 }
2472
2473 // Note: the thread-local monitors lists get deflated in
2474 // a separate pass. See deflate_thread_local_monitors().
2475
2476 // For moribund threads, scan om_list_globals._in_use_list
2477 int deflated_count = 0;
2478 if (Atomic::load(&om_list_globals._in_use_list) != NULL) {
2479 // Update n_in_circulation before om_list_globals._in_use_count is
2480 // updated by deflation.
2481 Atomic::add(&counters->n_in_circulation,
2482 Atomic::load(&om_list_globals._in_use_count));
2483
2484 deflated_count = deflate_monitor_list(&om_list_globals._in_use_list,
2485 &om_list_globals._in_use_count,
2486 &free_head_p, &free_tail_p);
2487 Atomic::add(&counters->n_in_use, Atomic::load(&om_list_globals._in_use_count));
2488 }
2489
2490 if (free_head_p != NULL) {
2491 // Move the deflated ObjectMonitors back to the global free list.
2492 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
2493 #ifdef ASSERT
2494 ObjectMonitor* l_next_om = free_tail_p->next_om();
2495 #endif
2496 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2497 prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count);
2498 Atomic::add(&counters->n_scavenged, deflated_count);
2499 }
2500 timer.stop();
2501
2502 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2503 LogStreamHandle(Info, monitorinflation) lsh_info;
2504 LogStream* ls = NULL;
2505 if (log_is_enabled(Debug, monitorinflation)) {
2506 ls = &lsh_debug;
2507 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2508 ls = &lsh_info;
2509 }
2510 if (ls != NULL) {
2511 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2512 }
2513 }
2514
2515 class HandshakeForDeflation : public HandshakeClosure {
2516 public:
2517 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
2518
2519 void do_thread(Thread* thread) {
2520 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
2521 INTPTR_FORMAT, p2i(thread));
2522 }
2523 };
2524
2525 void ObjectSynchronizer::deflate_idle_monitors_using_JT() {
2526 assert(AsyncDeflateIdleMonitors, "sanity check");
2527
2528 // Deflate any global idle monitors.
2529 deflate_global_idle_monitors_using_JT();
2530
2531 int count = 0;
2532 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2533 if (Atomic::load(&jt->om_in_use_count) > 0 && !jt->is_exiting()) {
2534 // This JavaThread is using ObjectMonitors so deflate any that
2535 // are idle unless this JavaThread is exiting; do not race with
2536 // ObjectSynchronizer::om_flush().
2537 deflate_per_thread_idle_monitors_using_JT(jt);
2538 count++;
2539 }
2540 }
2541 if (count > 0) {
2542 log_debug(monitorinflation)("did async deflation of idle monitors for %d thread(s).", count);
2543 }
2544
2545 log_info(monitorinflation)("async global_population=%d, global_in_use_count=%d, "
2546 "global_free_count=%d, global_wait_count=%d",
2547 Atomic::load(&om_list_globals._population),
2548 Atomic::load(&om_list_globals._in_use_count),
2549 Atomic::load(&om_list_globals._free_count),
2550 Atomic::load(&om_list_globals._wait_count));
2551
2552 // The ServiceThread's async deflation request has been processed.
2553 set_is_async_deflation_requested(false);
2554
2555 if (Atomic::load(&om_list_globals._wait_count) > 0) {
2556 // There are deflated ObjectMonitors waiting for a handshake
2557 // (or a safepoint) for safety.
2558
2559 ObjectMonitor* list = Atomic::load(&om_list_globals._wait_list);
2560 ADIM_guarantee(list != NULL, "om_list_globals._wait_list must not be NULL");
2561 int count = Atomic::load(&om_list_globals._wait_count);
2562 Atomic::store(&om_list_globals._wait_count, 0);
2563 Atomic::store(&om_list_globals._wait_list, (ObjectMonitor*)NULL);
2564
2565 // Find the tail for prepend_list_to_common(). No need to mark
2566 // ObjectMonitors for this list walk since only the deflater
2567 // thread manages the wait list.
2568 int l_count = 0;
2569 ObjectMonitor* tail = NULL;
2570 for (ObjectMonitor* n = list; n != NULL; n = unmarked_next(n)) {
2571 tail = n;
2572 l_count++;
2573 }
2574 ADIM_guarantee(count == l_count, "count=%d != l_count=%d", count, l_count);
2575
2576 // Will execute a safepoint if !ThreadLocalHandshakes:
2577 HandshakeForDeflation hfd_hc;
2578 Handshake::execute(&hfd_hc);
2579
2580 prepend_list_to_common(list, tail, count, &om_list_globals._free_list,
2581 &om_list_globals._free_count);
2582
2583 log_info(monitorinflation)("moved %d idle monitors from global waiting list to global free list", count);
2584 }
2585 }
2586
2587 // Deflate global idle ObjectMonitors using a JavaThread.
2588 //
2589 void ObjectSynchronizer::deflate_global_idle_monitors_using_JT() {
2590 assert(AsyncDeflateIdleMonitors, "sanity check");
2591 assert(Thread::current()->is_Java_thread(), "precondition");
2592 JavaThread* self = JavaThread::current();
2593
2594 deflate_common_idle_monitors_using_JT(true /* is_global */, self);
2595 }
2596
2597 // Deflate the specified JavaThread's idle ObjectMonitors using a JavaThread.
2598 //
2599 void ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT(JavaThread* target) {
2600 assert(AsyncDeflateIdleMonitors, "sanity check");
2601 assert(Thread::current()->is_Java_thread(), "precondition");
2602
2603 deflate_common_idle_monitors_using_JT(false /* !is_global */, target);
2604 }
2605
2606 // Deflate global or per-thread idle ObjectMonitors using a JavaThread.
2607 //
2608 void ObjectSynchronizer::deflate_common_idle_monitors_using_JT(bool is_global, JavaThread* target) {
2609 JavaThread* self = JavaThread::current();
2610
2611 int deflated_count = 0;
2612 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged ObjectMonitors
2613 ObjectMonitor* free_tail_p = NULL;
2614 ObjectMonitor* saved_mid_in_use_p = NULL;
2615 elapsedTimer timer;
2616
2617 if (log_is_enabled(Info, monitorinflation)) {
2618 timer.start();
2619 }
2620
2621 if (is_global) {
2622 OM_PERFDATA_OP(MonExtant, set_value(Atomic::load(&om_list_globals._in_use_count)));
2623 } else {
2624 OM_PERFDATA_OP(MonExtant, inc(Atomic::load(&target->om_in_use_count)));
2625 }
2626
2627 do {
2628 if (saved_mid_in_use_p != NULL) {
2629 // We looped around because deflate_monitor_list_using_JT()
2630 // detected a pending safepoint. Honoring the safepoint is good,
2631 // but as long as is_special_deflation_requested() is supported,
2632 // we can't safely restart using saved_mid_in_use_p. That saved
2633 // ObjectMonitor could have been deflated by safepoint based
2634 // deflation and would no longer be on the in-use list where we
2635 // originally found it.
2636 saved_mid_in_use_p = NULL;
2637 }
2638 int local_deflated_count;
2639 if (is_global) {
2640 local_deflated_count =
2641 deflate_monitor_list_using_JT(&om_list_globals._in_use_list,
2642 &om_list_globals._in_use_count,
2643 &free_head_p, &free_tail_p,
2644 &saved_mid_in_use_p);
2645 } else {
2646 local_deflated_count =
2647 deflate_monitor_list_using_JT(&target->om_in_use_list,
2648 &target->om_in_use_count, &free_head_p,
2649 &free_tail_p, &saved_mid_in_use_p);
2650 }
2651 deflated_count += local_deflated_count;
2652
2653 if (free_head_p != NULL) {
2654 // Move the deflated ObjectMonitors to the global free list.
2655 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);
2656 // Note: The target thread can be doing an om_alloc() that
2657 // is trying to prepend an ObjectMonitor on its in-use list
2658 // at the same time that we have deflated the current in-use
2659 // list head and put it on the local free list. prepend_to_common()
2660 // will detect the race and retry which avoids list corruption,
2661 // but the next field in free_tail_p can flicker to marked
2662 // and then unmarked while prepend_to_common() is sorting it
2663 // all out.
2664 #ifdef ASSERT
2665 ObjectMonitor* l_next_om = unmarked_next(free_tail_p);
2666 #endif
2667 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2668
2669 prepend_list_to_global_wait_list(free_head_p, free_tail_p, local_deflated_count);
2670
2671 OM_PERFDATA_OP(Deflations, inc(local_deflated_count));
2672 }
2673
2674 if (saved_mid_in_use_p != NULL) {
2675 // deflate_monitor_list_using_JT() detected a safepoint starting.
2676 timer.stop();
2677 {
2678 if (is_global) {
2679 log_debug(monitorinflation)("pausing deflation of global idle monitors for a safepoint.");
2680 } else {
2681 log_debug(monitorinflation)("jt=" INTPTR_FORMAT ": pausing deflation of per-thread idle monitors for a safepoint.", p2i(target));
2682 }
2683 assert(SafepointMechanism::should_block(self), "sanity check");
2684 ThreadBlockInVM blocker(self);
2685 }
2686 // Prepare for another loop after the safepoint.
2687 free_head_p = NULL;
2688 free_tail_p = NULL;
2689 if (log_is_enabled(Info, monitorinflation)) {
2690 timer.start();
2691 }
2692 }
2693 } while (saved_mid_in_use_p != NULL);
2694 timer.stop();
2695
2696 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2697 LogStreamHandle(Info, monitorinflation) lsh_info;
2698 LogStream* ls = NULL;
2699 if (log_is_enabled(Debug, monitorinflation)) {
2700 ls = &lsh_debug;
2701 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2702 ls = &lsh_info;
2703 }
2704 if (ls != NULL) {
2705 if (is_global) {
2706 ls->print_cr("async-deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2707 } else {
2708 ls->print_cr("jt=" INTPTR_FORMAT ": async-deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(target), timer.seconds(), deflated_count);
2709 }
2710 }
2711 }
2712
2713 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2714 // Report the cumulative time for deflating each thread's idle
2715 // monitors. Note: if the work is split among more than one
2716 // worker thread, then the reported time will likely be more
2717 // than a beginning to end measurement of the phase.
2718 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged);
2719
2720 bool needs_special_deflation = is_special_deflation_requested();
2721 if (AsyncDeflateIdleMonitors && !needs_special_deflation) {
2722 // Nothing to do when idle ObjectMonitors are deflated using
2723 // a JavaThread unless a special deflation has been requested.
2724 return;
2725 }
2726
2727 if (log_is_enabled(Debug, monitorinflation)) {
2728 // exit_globals()'s call to audit_and_print_stats() is done
2729 // at the Info level and not at a safepoint.
2730 // For async deflation, audit_and_print_stats() is called in
2731 // ObjectSynchronizer::do_safepoint_work() at the Debug level
2732 // at a safepoint.
2733 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2734 } else if (log_is_enabled(Info, monitorinflation)) {
2735 log_info(monitorinflation)("global_population=%d, global_in_use_count=%d, "
2736 "global_free_count=%d, global_wait_count=%d",
2737 Atomic::load(&om_list_globals._population),
2738 Atomic::load(&om_list_globals._in_use_count),
2739 Atomic::load(&om_list_globals._free_count),
2740 Atomic::load(&om_list_globals._wait_count));
2741 }
2742
2743 OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged));
2744 OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation));
2745
2746 GVars.stw_random = os::random();
2747 GVars.stw_cycle++;
2748
2749 if (needs_special_deflation) {
2750 set_is_special_deflation_requested(false); // special deflation is done
2751 }
2752 }
2753
2754 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
2755 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2756
2757 if (AsyncDeflateIdleMonitors && !is_special_deflation_requested()) {
2758 // Nothing to do if a special deflation has NOT been requested.
2759 return;
2760 }
2761
2762 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
2763 ObjectMonitor* free_tail_p = NULL;
2764 elapsedTimer timer;
2765
2766 if (log_is_enabled(Info, safepoint, cleanup) ||
2767 log_is_enabled(Info, monitorinflation)) {
2768 timer.start();
2769 }
2770
2771 // Update n_in_circulation before om_in_use_count is updated by deflation.
2772 Atomic::add(&counters->n_in_circulation, Atomic::load(&thread->om_in_use_count));
2773
2774 int deflated_count = deflate_monitor_list(&thread->om_in_use_list, &thread->om_in_use_count, &free_head_p, &free_tail_p);
2775 Atomic::add(&counters->n_in_use, Atomic::load(&thread->om_in_use_count));
2776
2777 if (free_head_p != NULL) {
2778 // Move the deflated ObjectMonitors back to the global free list.
2779 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
2780 #ifdef ASSERT
2781 ObjectMonitor* l_next_om = free_tail_p->next_om();
2782 #endif
2783 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2784 prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count);
2785 Atomic::add(&counters->n_scavenged, deflated_count);
2786 Atomic::add(&counters->per_thread_scavenged, deflated_count);
2787 }
2788
2789 timer.stop();
2790 counters->per_thread_times += timer.seconds();
2791
2792 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2793 LogStreamHandle(Info, monitorinflation) lsh_info;
2794 LogStream* ls = NULL;
2795 if (log_is_enabled(Debug, monitorinflation)) {
2796 ls = &lsh_debug;
2797 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2798 ls = &lsh_info;
2799 }
2800 if (ls != NULL) {
2801 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
2802 }
2803 }
2804
2805 // Monitor cleanup on JavaThread::exit
2806
2807 // Iterate through monitor cache and attempt to release thread's monitors
2808 // Gives up on a particular monitor if an exception occurs, but continues
2809 // the overall iteration, swallowing the exception.
2810 class ReleaseJavaMonitorsClosure: public MonitorClosure {
2811 private:
2812 TRAPS;
2813
2814 public:
2815 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
2816 void do_monitor(ObjectMonitor* mid) {
2817 if (mid->owner() == THREAD) {
2818 (void)mid->complete_exit(CHECK);
2819 }
2820 }
2821 };
2822
2823 // Release all inflated monitors owned by THREAD. Lightweight monitors are
2824 // ignored. This is meant to be called during JNI thread detach which assumes
2825 // all remaining monitors are heavyweight. All exceptions are swallowed.
2826 // Scanning the extant monitor list can be time consuming.
2827 // A simple optimization is to add a per-thread flag that indicates a thread
2828 // called jni_monitorenter() during its lifetime.
2829 //
2830 // Instead of No_Savepoint_Verifier it might be cheaper to
2831 // use an idiom of the form:
2832 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
2833 // <code that must not run at safepoint>
2834 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
2835 // Since the tests are extremely cheap we could leave them enabled
2836 // for normal product builds.
2837
2838 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
2839 assert(THREAD == JavaThread::current(), "must be current Java thread");
2840 NoSafepointVerifier nsv;
2841 ReleaseJavaMonitorsClosure rjmc(THREAD);
2842 ObjectSynchronizer::monitors_iterate(&rjmc);
2843 THREAD->clear_pending_exception();
2844 }
2845
2846 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
2847 switch (cause) {
2848 case inflate_cause_vm_internal: return "VM Internal";
2849 case inflate_cause_monitor_enter: return "Monitor Enter";
2850 case inflate_cause_wait: return "Monitor Wait";
2851 case inflate_cause_notify: return "Monitor Notify";
2852 case inflate_cause_hash_code: return "Monitor Hash Code";
2853 case inflate_cause_jni_enter: return "JNI Monitor Enter";
2854 case inflate_cause_jni_exit: return "JNI Monitor Exit";
2855 default:
2856 ShouldNotReachHere();
2857 }
2858 return "Unknown";
2859 }
2860
2861 //------------------------------------------------------------------------------
2862 // Debugging code
2863
2864 u_char* ObjectSynchronizer::get_gvars_addr() {
2865 return (u_char*)&GVars;
2866 }
2867
2868 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
2869 return (u_char*)&GVars.hc_sequence;
2870 }
2871
2872 size_t ObjectSynchronizer::get_gvars_size() {
2873 return sizeof(SharedGlobals);
2874 }
2875
2876 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
2877 return (u_char*)&GVars.stw_random;
2878 }
2879
2880 // This function can be called at a safepoint or it can be called when
2881 // we are trying to exit the VM. When we are trying to exit the VM, the
2882 // list walker functions can run in parallel with the other list
2883 // operations so spin-locking is used for safety.
2884 //
2885 // Calls to this function can be added in various places as a debugging
2886 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
2887 // details logged at the Info level and 'false' for the 'on_exit'
2888 // parameter to have in-use monitor details logged at the Trace level.
2889 // deflate_monitor_list() no longer uses spin-locking so be careful
2890 // when adding audit_and_print_stats() calls at a safepoint.
2891 //
2892 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
2893 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
2894
2895 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2896 LogStreamHandle(Info, monitorinflation) lsh_info;
2897 LogStreamHandle(Trace, monitorinflation) lsh_trace;
2898 LogStream* ls = NULL;
2899 if (log_is_enabled(Trace, monitorinflation)) {
2900 ls = &lsh_trace;
2901 } else if (log_is_enabled(Debug, monitorinflation)) {
2902 ls = &lsh_debug;
2903 } else if (log_is_enabled(Info, monitorinflation)) {
2904 ls = &lsh_info;
2905 }
2906 assert(ls != NULL, "sanity check");
2907
2908 // Log counts for the global and per-thread monitor lists:
2909 int chk_om_population = log_monitor_list_counts(ls);
2910 int error_cnt = 0;
2911
2912 ls->print_cr("Checking global lists:");
2913
2914 // Check om_list_globals._population:
2915 if (Atomic::load(&om_list_globals._population) == chk_om_population) {
2916 ls->print_cr("global_population=%d equals chk_om_population=%d",
2917 Atomic::load(&om_list_globals._population), chk_om_population);
2918 } else {
2919 // With fine grained locks on the monitor lists, it is possible for
2920 // log_monitor_list_counts() to return a value that doesn't match
2921 // om_list_globals._population. So far a higher value has been
2922 // seen in testing so something is being double counted by
2923 // log_monitor_list_counts().
2924 ls->print_cr("WARNING: global_population=%d is not equal to "
2925 "chk_om_population=%d",
2926 Atomic::load(&om_list_globals._population), chk_om_population);
2927 }
2928
2929 // Check om_list_globals._in_use_list and om_list_globals._in_use_count:
2930 chk_global_in_use_list_and_count(ls, &error_cnt);
2931
2932 // Check om_list_globals._free_list and om_list_globals._free_count:
2933 chk_global_free_list_and_count(ls, &error_cnt);
2934
2935 // Check om_list_globals._wait_list and om_list_globals._wait_count:
2936 chk_global_wait_list_and_count(ls, &error_cnt);
2937
2938 ls->print_cr("Checking per-thread lists:");
2939
2940 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2941 // Check om_in_use_list and om_in_use_count:
2942 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
2943
2944 // Check om_free_list and om_free_count:
2945 chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
2946 }
2947
2948 if (error_cnt == 0) {
2949 ls->print_cr("No errors found in monitor list checks.");
2950 } else {
2951 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
2952 }
2953
2954 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
2955 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
2956 // When exiting this log output is at the Info level. When called
2957 // at a safepoint, this log output is at the Trace level since
2958 // there can be a lot of it.
2959 log_in_use_monitor_details(ls);
2960 }
2961
2962 ls->flush();
2963
2964 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2965 }
2966
2967 // Check a free monitor entry; log any errors.
2968 void ObjectSynchronizer::chk_free_entry(JavaThread* jt, ObjectMonitor* n,
2969 outputStream * out, int *error_cnt_p) {
2970 stringStream ss;
2971 if (n->is_busy()) {
2972 if (jt != NULL) {
2973 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2974 ": free per-thread monitor must not be busy: %s", p2i(jt),
2975 p2i(n), n->is_busy_to_string(&ss));
2976 } else {
2977 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2978 "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
2979 }
2980 *error_cnt_p = *error_cnt_p + 1;
2981 }
2982 if (n->header().value() != 0) {
2983 if (jt != NULL) {
2984 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2985 ": free per-thread monitor must have NULL _header "
2986 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
2987 n->header().value());
2988 *error_cnt_p = *error_cnt_p + 1;
2989 } else if (!AsyncDeflateIdleMonitors) {
2990 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2991 "must have NULL _header field: _header=" INTPTR_FORMAT,
2992 p2i(n), n->header().value());
2993 *error_cnt_p = *error_cnt_p + 1;
2994 }
2995 }
2996 if (n->object() != NULL) {
2997 if (jt != NULL) {
2998 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2999 ": free per-thread monitor must have NULL _object "
3000 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
3001 p2i(n->object()));
3002 } else {
3003 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
3004 "must have NULL _object field: _object=" INTPTR_FORMAT,
3005 p2i(n), p2i(n->object()));
3006 }
3007 *error_cnt_p = *error_cnt_p + 1;
3008 }
3009 }
3010
3011 // Lock the next ObjectMonitor for traversal and unlock the current
3012 // ObjectMonitor. Returns the next ObjectMonitor if there is one.
3013 // Otherwise returns NULL (after unlocking the current ObjectMonitor).
3014 // This function is used by the various list walker functions to
3015 // safely walk a list without allowing an ObjectMonitor to be moved
3016 // to another list in the middle of a walk.
3017 static ObjectMonitor* lock_next_for_traversal(ObjectMonitor* cur) {
3018 assert(is_locked(cur), "cur=" INTPTR_FORMAT " must be locked", p2i(cur));
3019 ObjectMonitor* next = unmarked_next(cur);
3020 if (next == NULL) { // Reached the end of the list.
3021 om_unlock(cur);
3022 return NULL;
3023 }
3024 om_lock(next); // Lock next before unlocking current to keep
3025 om_unlock(cur); // from being by-passed by another thread.
3026 return next;
3027 }
3028
3029 // Check the global free list and count; log the results of the checks.
3030 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
3031 int *error_cnt_p) {
3032 int chk_om_free_count = 0;
3033 ObjectMonitor* cur = NULL;
3034 if ((cur = get_list_head_locked(&om_list_globals._free_list)) != NULL) {
3035 // Marked the global free list head so process the list.
3036 while (true) {
3037 chk_free_entry(NULL /* jt */, cur, out, error_cnt_p);
3038 chk_om_free_count++;
3039
3040 cur = lock_next_for_traversal(cur);
3041 if (cur == NULL) {
3042 break;
3043 }
3044 }
3045 }
3046 int l_free_count = Atomic::load(&om_list_globals._free_count);
3047 if (l_free_count == chk_om_free_count) {
3048 out->print_cr("global_free_count=%d equals chk_om_free_count=%d",
3049 l_free_count, chk_om_free_count);
3050 } else {
3051 // With fine grained locks on om_list_globals._free_list, it
3052 // is possible for an ObjectMonitor to be prepended to
3053 // om_list_globals._free_list after we started calculating
3054 // chk_om_free_count so om_list_globals._free_count may not
3055 // match anymore.
3056 out->print_cr("WARNING: global_free_count=%d is not equal to "
3057 "chk_om_free_count=%d", l_free_count, chk_om_free_count);
3058 }
3059 }
3060
3061 // Check the global wait list and count; log the results of the checks.
3062 void ObjectSynchronizer::chk_global_wait_list_and_count(outputStream * out,
3063 int *error_cnt_p) {
3064 int chk_om_wait_count = 0;
3065 ObjectMonitor* cur = NULL;
3066 if ((cur = get_list_head_locked(&om_list_globals._wait_list)) != NULL) {
3067 // Marked the global wait list head so process the list.
3068 while (true) {
3069 // Rules for om_list_globals._wait_list are the same as for
3070 // om_list_globals._free_list:
3071 chk_free_entry(NULL /* jt */, cur, out, error_cnt_p);
3072 chk_om_wait_count++;
3073
3074 cur = lock_next_for_traversal(cur);
3075 if (cur == NULL) {
3076 break;
3077 }
3078 }
3079 }
3080 if (Atomic::load(&om_list_globals._wait_count) == chk_om_wait_count) {
3081 out->print_cr("global_wait_count=%d equals chk_om_wait_count=%d",
3082 Atomic::load(&om_list_globals._wait_count), chk_om_wait_count);
3083 } else {
3084 out->print_cr("ERROR: global_wait_count=%d is not equal to "
3085 "chk_om_wait_count=%d",
3086 Atomic::load(&om_list_globals._wait_count), chk_om_wait_count);
3087 *error_cnt_p = *error_cnt_p + 1;
3088 }
3089 }
3090
3091 // Check the global in-use list and count; log the results of the checks.
3092 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
3093 int *error_cnt_p) {
3094 int chk_om_in_use_count = 0;
3095 ObjectMonitor* cur = NULL;
3096 if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) {
3097 // Marked the global in-use list head so process the list.
3098 while (true) {
3099 chk_in_use_entry(NULL /* jt */, cur, out, error_cnt_p);
3100 chk_om_in_use_count++;
3101
3102 cur = lock_next_for_traversal(cur);
3103 if (cur == NULL) {
3104 break;
3105 }
3106 }
3107 }
3108 int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
3109 if (l_in_use_count == chk_om_in_use_count) {
3110 out->print_cr("global_in_use_count=%d equals chk_om_in_use_count=%d",
3111 l_in_use_count, chk_om_in_use_count);
3112 } else {
3113 // With fine grained locks on the monitor lists, it is possible for
3114 // an exiting JavaThread to put its in-use ObjectMonitors on the
3115 // global in-use list after chk_om_in_use_count is calculated above.
3116 out->print_cr("WARNING: global_in_use_count=%d is not equal to chk_om_in_use_count=%d",
3117 l_in_use_count, chk_om_in_use_count);
3118 }
3119 }
3120
3121 // Check an in-use monitor entry; log any errors.
3122 void ObjectSynchronizer::chk_in_use_entry(JavaThread* jt, ObjectMonitor* n,
3123 outputStream * out, int *error_cnt_p) {
3124 if (n->header().value() == 0) {
3125 if (jt != NULL) {
3126 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3127 ": in-use per-thread monitor must have non-NULL _header "
3128 "field.", p2i(jt), p2i(n));
3129 } else {
3130 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
3131 "must have non-NULL _header field.", p2i(n));
3132 }
3133 *error_cnt_p = *error_cnt_p + 1;
3134 }
3135 if (n->object() == NULL) {
3136 if (jt != NULL) {
3137 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3138 ": in-use per-thread monitor must have non-NULL _object "
3139 "field.", p2i(jt), p2i(n));
3140 } else {
3141 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
3142 "must have non-NULL _object field.", p2i(n));
3143 }
3144 *error_cnt_p = *error_cnt_p + 1;
3145 }
3146 const oop obj = (oop)n->object();
3147 const markWord mark = obj->mark();
3148 if (!mark.has_monitor()) {
3149 if (jt != NULL) {
3150 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3151 ": in-use per-thread monitor's object does not think "
3152 "it has a monitor: obj=" INTPTR_FORMAT ", mark="
3153 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), mark.value());
3154 } else {
3155 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
3156 "monitor's object does not think it has a monitor: obj="
3157 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
3158 p2i(obj), mark.value());
3159 }
3160 *error_cnt_p = *error_cnt_p + 1;
3161 }
3162 ObjectMonitor* const obj_mon = mark.monitor();
3163 if (n != obj_mon) {
3164 if (jt != NULL) {
3165 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3166 ": in-use per-thread monitor's object does not refer "
3167 "to the same monitor: obj=" INTPTR_FORMAT ", mark="
3168 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
3169 p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
3170 } else {
3171 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
3172 "monitor's object does not refer to the same monitor: obj="
3173 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
3174 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
3175 }
3176 *error_cnt_p = *error_cnt_p + 1;
3177 }
3178 }
3179
3180 // Check the thread's free list and count; log the results of the checks.
3181 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
3182 outputStream * out,
3183 int *error_cnt_p) {
3184 int chk_om_free_count = 0;
3185 ObjectMonitor* cur = NULL;
3186 if ((cur = get_list_head_locked(&jt->om_free_list)) != NULL) {
3187 // Marked the per-thread free list head so process the list.
3188 while (true) {
3189 chk_free_entry(jt, cur, out, error_cnt_p);
3190 chk_om_free_count++;
3191
3192 cur = lock_next_for_traversal(cur);
3193 if (cur == NULL) {
3194 break;
3195 }
3196 }
3197 }
3198 int l_om_free_count = Atomic::load(&jt->om_free_count);
3199 if (l_om_free_count == chk_om_free_count) {
3200 out->print_cr("jt=" INTPTR_FORMAT ": om_free_count=%d equals "
3201 "chk_om_free_count=%d", p2i(jt), l_om_free_count, chk_om_free_count);
3202 } else {
3203 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_free_count=%d is not "
3204 "equal to chk_om_free_count=%d", p2i(jt), l_om_free_count,
3205 chk_om_free_count);
3206 *error_cnt_p = *error_cnt_p + 1;
3207 }
3208 }
3209
3210 // Check the thread's in-use list and count; log the results of the checks.
3211 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
3212 outputStream * out,
3213 int *error_cnt_p) {
3214 int chk_om_in_use_count = 0;
3215 ObjectMonitor* cur = NULL;
3216 if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
3217 // Marked the per-thread in-use list head so process the list.
3218 while (true) {
3219 chk_in_use_entry(jt, cur, out, error_cnt_p);
3220 chk_om_in_use_count++;
3221
3222 cur = lock_next_for_traversal(cur);
3223 if (cur == NULL) {
3224 break;
3225 }
3226 }
3227 }
3228 int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
3229 if (l_om_in_use_count == chk_om_in_use_count) {
3230 out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals "
3231 "chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
3232 chk_om_in_use_count);
3233 } else {
3234 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not "
3235 "equal to chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
3236 chk_om_in_use_count);
3237 *error_cnt_p = *error_cnt_p + 1;
3238 }
3239 }
3240
3241 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
3242 // flags indicate why the entry is in-use, 'object' and 'object type'
3243 // indicate the associated object and its type.
3244 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out) {
3245 stringStream ss;
3246 if (Atomic::load(&om_list_globals._in_use_count) > 0) {
3247 out->print_cr("In-use global monitor info:");
3248 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
3249 out->print_cr("%18s %s %18s %18s",
3250 "monitor", "BHL", "object", "object type");
3251 out->print_cr("================== === ================== ==================");
3252 ObjectMonitor* cur = NULL;
3253 if ((cur = get_list_head_locked(&om_list_globals._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 " %d%d%d " INTPTR_FORMAT " %s", p2i(cur),
3260 cur->is_busy() != 0, mark.hash() != 0, cur->owner() != NULL,
3261 p2i(obj), obj->klass()->external_name());
3262 if (cur->is_busy() != 0) {
3263 out->print(" (%s)", cur->is_busy_to_string(&ss));
3264 ss.reset();
3265 }
3266 out->cr();
3267
3268 cur = lock_next_for_traversal(cur);
3269 if (cur == NULL) {
3270 break;
3271 }
3272 }
3273 }
3274 }
3275
3276 out->print_cr("In-use per-thread monitor info:");
3277 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
3278 out->print_cr("%18s %18s %s %18s %18s",
3279 "jt", "monitor", "BHL", "object", "object type");
3280 out->print_cr("================== ================== === ================== ==================");
3281 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
3282 ObjectMonitor* cur = NULL;
3283 if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
3284 // Marked the global in-use list head so process the list.
3285 while (true) {
3286 const oop obj = (oop) cur->object();
3287 const markWord mark = cur->header();
3288 ResourceMark rm;
3289 out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT
3290 " %s", p2i(jt), p2i(cur), cur->is_busy() != 0,
3291 mark.hash() != 0, cur->owner() != NULL, p2i(obj),
3292 obj->klass()->external_name());
3293 if (cur->is_busy() != 0) {
3294 out->print(" (%s)", cur->is_busy_to_string(&ss));
3295 ss.reset();
3296 }
3297 out->cr();
3298
3299 cur = lock_next_for_traversal(cur);
3300 if (cur == NULL) {
3301 break;
3302 }
3303 }
3304 }
3305 }
3306
3307 out->flush();
3308 }
3309
3310 // Log counts for the global and per-thread monitor lists and return
3311 // the population count.
3312 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
3313 int pop_count = 0;
3314 out->print_cr("%18s %10s %10s %10s %10s",
3315 "Global Lists:", "InUse", "Free", "Wait", "Total");
3316 out->print_cr("================== ========== ========== ========== ==========");
3317 int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
3318 int l_free_count = Atomic::load(&om_list_globals._free_count);
3319 int l_wait_count = Atomic::load(&om_list_globals._wait_count);
3320 out->print_cr("%18s %10d %10d %10d %10d", "", l_in_use_count,
3321 l_free_count, l_wait_count,
3322 Atomic::load(&om_list_globals._population));
3323 pop_count += l_in_use_count + l_free_count + l_wait_count;
3324
3325 out->print_cr("%18s %10s %10s %10s",
3326 "Per-Thread Lists:", "InUse", "Free", "Provision");
3327 out->print_cr("================== ========== ========== ==========");
3328
3329 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
3330 int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
3331 int l_om_free_count = Atomic::load(&jt->om_free_count);
3332 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
3333 l_om_in_use_count, l_om_free_count, jt->om_free_provision);
3334 pop_count += l_om_in_use_count + l_om_free_count;
3335 }
3336 return pop_count;
3337 }
3338
3339 #ifndef PRODUCT
3340
3341 // Check if monitor belongs to the monitor cache
3342 // The list is grow-only so it's *relatively* safe to traverse
3343 // the list of extant blocks without taking a lock.
3344
3345 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
3346 PaddedObjectMonitor* block = Atomic::load(&g_block_list);
3347 while (block != NULL) {
3348 assert(block->object() == CHAINMARKER, "must be a block header");
3349 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
3350 address mon = (address)monitor;
3351 address blk = (address)block;
3352 size_t diff = mon - blk;
3353 assert((diff % sizeof(PaddedObjectMonitor)) == 0, "must be aligned");
3354 return 1;
3355 }
3356 // unmarked_next() is not needed with g_block_list (no locking
3357 // used with block linkage _next_om fields).
3358 block = (PaddedObjectMonitor*)block->next_om();
3359 }
3360 return 0;
3361 }
3362
3363 #endif