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 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
125
126 struct ObjectMonitorListGlobals {
127 char _pad_prefix[OM_CACHE_LINE_SIZE];
128 // These are highly shared list related variables.
129 // To avoid false-sharing they need to be the sole occupants of a cache line.
130
131 // Global ObjectMonitor free list. Newly allocated and deflated
132 // ObjectMonitors are prepended here.
133 ObjectMonitor* _free_list;
134 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
135
136 // Global ObjectMonitor in-use list. When a JavaThread is exiting,
137 // ObjectMonitors on its per-thread in-use list are prepended here.
138 ObjectMonitor* _in_use_list;
139 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
140
141 // Global ObjectMonitor wait list. Deflated ObjectMonitors wait on
142 // this list until after a handshake or a safepoint for platforms
143 // that don't support handshakes. After the handshake or safepoint,
144 // the deflated ObjectMonitors are prepended to free_list.
145 ObjectMonitor* _wait_list;
146 DEFINE_PAD_MINUS_SIZE(3, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
147
148 int _free_count; // # on free_list
149 DEFINE_PAD_MINUS_SIZE(4, OM_CACHE_LINE_SIZE, sizeof(int));
150
151 int _in_use_count; // # on in_use_list
152 DEFINE_PAD_MINUS_SIZE(5, OM_CACHE_LINE_SIZE, sizeof(int));
153
154 int _population; // # Extant -- in circulation
155 DEFINE_PAD_MINUS_SIZE(6, OM_CACHE_LINE_SIZE, sizeof(int));
156
157 int _wait_count; // # on wait_list
158 DEFINE_PAD_MINUS_SIZE(7, OM_CACHE_LINE_SIZE, sizeof(int));
159 };
160 static ObjectMonitorListGlobals om_list_globals;
161
162 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
163
164
165 // =====================> Spin-lock functions
166
167 // ObjectMonitors are not lockable outside of this file. We use spin-locks
168 // implemented using a bit in the _next_om field instead of the heavier
169 // weight locking mechanisms for faster list management.
170
171 #define OM_LOCK_BIT 0x1
172
173 // Return true if the ObjectMonitor is locked.
174 // Otherwise returns false.
175 static bool is_locked(ObjectMonitor* om) {
176 return ((intptr_t)om->next_om() & OM_LOCK_BIT) == OM_LOCK_BIT;
177 }
178
179 // Mark an ObjectMonitor* with OM_LOCK_BIT and return it.
180 static ObjectMonitor* mark_om_ptr(ObjectMonitor* om) {
181 return (ObjectMonitor*)((intptr_t)om | OM_LOCK_BIT);
182 }
183
184 // Return the unmarked next field in an ObjectMonitor. Note: the next
185 // field may or may not have been marked with OM_LOCK_BIT originally.
186 static ObjectMonitor* unmarked_next(ObjectMonitor* om) {
187 return (ObjectMonitor*)((intptr_t)om->next_om() & ~OM_LOCK_BIT);
188 }
189
190 // Try to lock an ObjectMonitor. Returns true if locking was successful.
191 // Otherwise returns false.
192 static bool try_om_lock(ObjectMonitor* om) {
193 // Get current next field without any OM_LOCK_BIT value.
194 ObjectMonitor* next = unmarked_next(om);
195 if (om->try_set_next_om(next, mark_om_ptr(next)) != next) {
196 return false; // Cannot lock the ObjectMonitor.
197 }
198 return true;
199 }
200
201 // Lock an ObjectMonitor.
202 static void om_lock(ObjectMonitor* om) {
203 while (true) {
204 if (try_om_lock(om)) {
205 return;
206 }
207 }
208 }
209
210 // Unlock an ObjectMonitor.
211 static void om_unlock(ObjectMonitor* om) {
212 ObjectMonitor* next = om->next_om();
213 guarantee(((intptr_t)next & OM_LOCK_BIT) == OM_LOCK_BIT, "next=" INTPTR_FORMAT
214 " must have OM_LOCK_BIT=%x set.", p2i(next), OM_LOCK_BIT);
215
216 next = (ObjectMonitor*)((intptr_t)next & ~OM_LOCK_BIT); // Clear OM_LOCK_BIT.
217 om->set_next_om(next);
218 }
219
220 // Get the list head after locking it. Returns the list head or NULL
221 // if the list is empty.
222 static ObjectMonitor* get_list_head_locked(ObjectMonitor** list_p) {
223 while (true) {
224 ObjectMonitor* mid = Atomic::load(list_p);
225 if (mid == NULL) {
226 return NULL; // The list is empty.
227 }
228 if (try_om_lock(mid)) {
229 if (Atomic::load(list_p) != mid) {
230 // The list head changed before we could lock it so we have to retry.
231 om_unlock(mid);
232 continue;
233 }
234 return mid;
235 }
236 }
237 }
238
239 #undef OM_LOCK_BIT
240
241
242 // =====================> List Management functions
243
244 // Prepend a list of ObjectMonitors to the specified *list_p. 'tail' is
245 // the last ObjectMonitor in the list and there are 'count' on the list.
246 // Also updates the specified *count_p.
247 static void prepend_list_to_common(ObjectMonitor* list, ObjectMonitor* tail,
248 int count, ObjectMonitor** list_p,
249 int* count_p) {
250 while (true) {
251 ObjectMonitor* cur = Atomic::load(list_p);
252 // Prepend list to *list_p.
253 if (!try_om_lock(tail)) {
254 // Failed to lock tail due to a list walker so try it all again.
255 continue;
256 }
257 tail->set_next_om(cur); // tail now points to cur (and unlocks tail)
258 if (cur == NULL) {
259 // No potential race with takers or other prependers since
260 // *list_p is empty.
261 if (Atomic::cmpxchg(list_p, cur, list) == cur) {
262 // Successfully switched *list_p to the list value.
263 Atomic::add(count_p, count);
264 break;
265 }
266 // Implied else: try it all again
267 } else {
268 if (!try_om_lock(cur)) {
269 continue; // failed to lock cur so try it all again
270 }
271 // We locked cur so try to switch *list_p to the list value.
272 if (Atomic::cmpxchg(list_p, cur, list) != cur) {
273 // The list head has changed so unlock cur and try again:
274 om_unlock(cur);
275 continue;
276 }
277 Atomic::add(count_p, count);
278 om_unlock(cur);
279 break;
280 }
281 }
282 }
283
284 // Prepend a newly allocated block of ObjectMonitors to g_block_list and
285 // om_list_globals._free_list. Also updates om_list_globals._population
286 // and om_list_globals._free_count.
287 void ObjectSynchronizer::prepend_block_to_lists(PaddedObjectMonitor* new_blk) {
288 // First we handle g_block_list:
289 while (true) {
290 PaddedObjectMonitor* cur = Atomic::load(&g_block_list);
291 // Prepend new_blk to g_block_list. The first ObjectMonitor in
292 // a block is reserved for use as linkage to the next block.
293 new_blk[0].set_next_om(cur);
294 if (Atomic::cmpxchg(&g_block_list, cur, new_blk) == cur) {
295 // Successfully switched g_block_list to the new_blk value.
296 Atomic::add(&om_list_globals._population, _BLOCKSIZE - 1);
297 break;
298 }
299 // Implied else: try it all again
300 }
301
302 // Second we handle om_list_globals._free_list:
303 prepend_list_to_common(new_blk + 1, &new_blk[_BLOCKSIZE - 1], _BLOCKSIZE - 1,
304 &om_list_globals._free_list, &om_list_globals._free_count);
305 }
306
307 // Prepend a list of ObjectMonitors to om_list_globals._free_list.
308 // 'tail' is the last ObjectMonitor in the list and there are 'count'
309 // on the list. Also updates om_list_globals._free_count.
310 static void prepend_list_to_global_free_list(ObjectMonitor* list,
311 ObjectMonitor* tail, int count) {
312 prepend_list_to_common(list, tail, count, &om_list_globals._free_list,
313 &om_list_globals._free_count);
314 }
315
316 // Prepend a list of ObjectMonitors to om_list_globals._wait_list.
317 // 'tail' is the last ObjectMonitor in the list and there are 'count'
318 // on the list. Also updates om_list_globals._wait_count.
319 static void prepend_list_to_global_wait_list(ObjectMonitor* list,
320 ObjectMonitor* tail, int count) {
321 prepend_list_to_common(list, tail, count, &om_list_globals._wait_list,
322 &om_list_globals._wait_count);
323 }
324
325 // Prepend a list of ObjectMonitors to om_list_globals._in_use_list.
326 // 'tail' is the last ObjectMonitor in the list and there are 'count'
327 // on the list. Also updates om_list_globals._in_use_list.
328 static void prepend_list_to_global_in_use_list(ObjectMonitor* list,
329 ObjectMonitor* tail, int count) {
330 prepend_list_to_common(list, tail, count, &om_list_globals._in_use_list,
331 &om_list_globals._in_use_count);
332 }
333
334 // Prepend an ObjectMonitor to the specified list. Also updates
335 // the specified counter.
336 static void prepend_to_common(ObjectMonitor* m, ObjectMonitor** list_p,
337 int* count_p) {
338 while (true) {
339 om_lock(m); // Lock m so we can safely update its next field.
340 ObjectMonitor* cur = NULL;
341 // Lock the list head to guard against races with a list walker
342 // or async deflater thread (which only races in om_in_use_list):
343 if ((cur = get_list_head_locked(list_p)) != NULL) {
344 // List head is now locked so we can safely switch it.
345 m->set_next_om(cur); // m now points to cur (and unlocks m)
346 Atomic::store(list_p, m); // Switch list head to unlocked m.
347 om_unlock(cur);
348 break;
349 }
350 // The list is empty so try to set the list head.
351 assert(cur == NULL, "cur must be NULL: cur=" INTPTR_FORMAT, p2i(cur));
352 m->set_next_om(cur); // m now points to NULL (and unlocks m)
353 if (Atomic::cmpxchg(list_p, cur, m) == cur) {
354 // List head is now unlocked m.
355 break;
356 }
357 // Implied else: try it all again
358 }
359 Atomic::inc(count_p);
360 }
361
362 // Prepend an ObjectMonitor to a per-thread om_free_list.
363 // Also updates the per-thread om_free_count.
364 static void prepend_to_om_free_list(Thread* self, ObjectMonitor* m) {
365 prepend_to_common(m, &self->om_free_list, &self->om_free_count);
366 }
367
368 // Prepend an ObjectMonitor to a per-thread om_in_use_list.
369 // Also updates the per-thread om_in_use_count.
370 static void prepend_to_om_in_use_list(Thread* self, ObjectMonitor* m) {
371 prepend_to_common(m, &self->om_in_use_list, &self->om_in_use_count);
372 }
373
374 // Take an ObjectMonitor from the start of the specified list. Also
375 // decrements the specified counter. Returns NULL if none are available.
376 static ObjectMonitor* take_from_start_of_common(ObjectMonitor** list_p,
377 int* count_p) {
378 ObjectMonitor* take = NULL;
379 // Lock the list head to guard against races with a list walker
380 // or async deflater thread (which only races in om_list_globals._free_list):
381 if ((take = get_list_head_locked(list_p)) == NULL) {
382 return NULL; // None are available.
383 }
384 ObjectMonitor* next = unmarked_next(take);
385 // Switch locked list head to next (which unlocks the list head, but
386 // leaves take locked):
387 Atomic::store(list_p, next);
388 Atomic::dec(count_p);
389 // Unlock take, but leave the next value for any lagging list
390 // walkers. It will get cleaned up when take is prepended to
391 // the in-use list:
392 om_unlock(take);
393 return take;
394 }
395
396 // Take an ObjectMonitor from the start of the om_list_globals._free_list.
397 // Also updates om_list_globals._free_count. Returns NULL if none are
398 // available.
399 static ObjectMonitor* take_from_start_of_global_free_list() {
400 return take_from_start_of_common(&om_list_globals._free_list,
401 &om_list_globals._free_count);
402 }
403
404 // Take an ObjectMonitor from the start of a per-thread free-list.
405 // Also updates om_free_count. Returns NULL if none are available.
406 static ObjectMonitor* take_from_start_of_om_free_list(Thread* self) {
407 return take_from_start_of_common(&self->om_free_list, &self->om_free_count);
408 }
409
410
411 // =====================> Quick functions
412
413 // The quick_* forms are special fast-path variants used to improve
414 // performance. In the simplest case, a "quick_*" implementation could
415 // simply return false, in which case the caller will perform the necessary
416 // state transitions and call the slow-path form.
417 // The fast-path is designed to handle frequently arising cases in an efficient
418 // manner and is just a degenerate "optimistic" variant of the slow-path.
419 // returns true -- to indicate the call was satisfied.
420 // returns false -- to indicate the call needs the services of the slow-path.
421 // A no-loitering ordinance is in effect for code in the quick_* family
422 // operators: safepoints or indefinite blocking (blocking that might span a
423 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
424 // entry.
425 //
426 // Consider: An interesting optimization is to have the JIT recognize the
427 // following common idiom:
428 // synchronized (someobj) { .... ; notify(); }
429 // That is, we find a notify() or notifyAll() call that immediately precedes
430 // the monitorexit operation. In that case the JIT could fuse the operations
431 // into a single notifyAndExit() runtime primitive.
432
433 bool ObjectSynchronizer::quick_notify(oopDesc* obj, Thread* self, bool all) {
434 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
435 assert(self->is_Java_thread(), "invariant");
436 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
437 NoSafepointVerifier nsv;
438 if (obj == NULL) return false; // slow-path for invalid obj
439 const markWord mark = obj->mark();
440
441 if (mark.has_locker() && self->is_lock_owned((address)mark.locker())) {
442 // Degenerate notify
443 // stack-locked by caller so by definition the implied waitset is empty.
444 return true;
445 }
446
447 if (mark.has_monitor()) {
448 ObjectMonitor* const mon = mark.monitor();
449 assert(mon->object() == obj, "invariant");
450 if (mon->owner() != self) return false; // slow-path for IMS exception
451
452 if (mon->first_waiter() != NULL) {
453 // We have one or more waiters. Since this is an inflated monitor
454 // that we own, we can transfer one or more threads from the waitset
455 // to the entrylist here and now, avoiding the slow-path.
456 if (all) {
457 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
458 } else {
459 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
460 }
461 int free_count = 0;
462 do {
463 mon->INotify(self);
464 ++free_count;
465 } while (mon->first_waiter() != NULL && all);
466 OM_PERFDATA_OP(Notifications, inc(free_count));
467 }
468 return true;
469 }
470
471 // biased locking and any other IMS exception states take the slow-path
472 return false;
473 }
474
475
476 // The LockNode emitted directly at the synchronization site would have
477 // been too big if it were to have included support for the cases of inflated
478 // recursive enter and exit, so they go here instead.
479 // Note that we can't safely call AsyncPrintJavaStack() from within
480 // quick_enter() as our thread state remains _in_Java.
481
482 bool ObjectSynchronizer::quick_enter(oop obj, Thread* self,
483 BasicLock * lock) {
484 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
485 assert(self->is_Java_thread(), "invariant");
486 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
487 NoSafepointVerifier nsv;
488 if (obj == NULL) return false; // Need to throw NPE
489
490 const markWord mark = obj->mark();
491
492 if (mark.has_monitor()) {
493 ObjectMonitor* const m = mark.monitor();
494 if (AsyncDeflateIdleMonitors) {
495 // An async deflation can race us before we manage to make the
496 // ObjectMonitor busy by setting the owner below. If we detect
497 // that race we just bail out to the slow-path here.
498 if (m->object() == NULL) {
499 return false;
500 }
501 } else {
502 assert(m->object() == obj, "invariant");
503 }
504 Thread* const owner = (Thread *) m->_owner;
505
506 // Lock contention and Transactional Lock Elision (TLE) diagnostics
507 // and observability
508 // Case: light contention possibly amenable to TLE
509 // Case: TLE inimical operations such as nested/recursive synchronization
510
511 if (owner == self) {
512 m->_recursions++;
513 return true;
514 }
515
516 // This Java Monitor is inflated so obj's header will never be
517 // displaced to this thread's BasicLock. Make the displaced header
518 // non-NULL so this BasicLock is not seen as recursive nor as
519 // being locked. We do this unconditionally so that this thread's
520 // BasicLock cannot be mis-interpreted by any stack walkers. For
521 // performance reasons, stack walkers generally first check for
522 // Biased Locking in the object's header, the second check is for
523 // stack-locking in the object's header, the third check is for
524 // recursive stack-locking in the displaced header in the BasicLock,
525 // and last are the inflated Java Monitor (ObjectMonitor) checks.
526 lock->set_displaced_header(markWord::unused_mark());
527
528 if (owner == NULL && m->try_set_owner_from(NULL, self) == NULL) {
529 assert(m->_recursions == 0, "invariant");
530 return true;
531 }
532 }
533
534 // Note that we could inflate in quick_enter.
535 // This is likely a useful optimization
536 // Critically, in quick_enter() we must not:
537 // -- perform bias revocation, or
538 // -- block indefinitely, or
539 // -- reach a safepoint
540
541 return false; // revert to slow-path
542 }
543
544 // -----------------------------------------------------------------------------
545 // Monitor Enter/Exit
546 // The interpreter and compiler assembly code tries to lock using the fast path
547 // of this algorithm. Make sure to update that code if the following function is
548 // changed. The implementation is extremely sensitive to race condition. Be careful.
549
550 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, TRAPS) {
551 if (UseBiasedLocking) {
552 if (!SafepointSynchronize::is_at_safepoint()) {
553 BiasedLocking::revoke(obj, THREAD);
554 } else {
555 BiasedLocking::revoke_at_safepoint(obj);
556 }
557 }
558
559 markWord mark = obj->mark();
560 assert(!mark.has_bias_pattern(), "should not see bias pattern here");
561
562 if (mark.is_neutral()) {
563 // Anticipate successful CAS -- the ST of the displaced mark must
564 // be visible <= the ST performed by the CAS.
565 lock->set_displaced_header(mark);
566 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
567 return;
568 }
569 // Fall through to inflate() ...
570 } else if (mark.has_locker() &&
571 THREAD->is_lock_owned((address)mark.locker())) {
572 assert(lock != mark.locker(), "must not re-lock the same lock");
573 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
574 lock->set_displaced_header(markWord::from_pointer(NULL));
575 return;
576 }
577
578 // The object header will never be displaced to this lock,
579 // so it does not matter what the value is, except that it
580 // must be non-zero to avoid looking like a re-entrant lock,
581 // and must not look locked either.
582 lock->set_displaced_header(markWord::unused_mark());
583 // An async deflation can race after the inflate() call and before
584 // enter() can make the ObjectMonitor busy. enter() returns false if
585 // we have lost the race to async deflation and we simply try again.
586 while (true) {
587 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_monitor_enter);
588 if (monitor->enter(THREAD)) {
589 return;
590 }
591 }
592 }
593
594 void ObjectSynchronizer::exit(oop object, BasicLock* lock, TRAPS) {
595 markWord mark = object->mark();
596 // We cannot check for Biased Locking if we are racing an inflation.
597 assert(mark == markWord::INFLATING() ||
598 !mark.has_bias_pattern(), "should not see bias pattern here");
599
600 markWord dhw = lock->displaced_header();
601 if (dhw.value() == 0) {
602 // If the displaced header is NULL, then this exit matches up with
603 // a recursive enter. No real work to do here except for diagnostics.
604 #ifndef PRODUCT
605 if (mark != markWord::INFLATING()) {
606 // Only do diagnostics if we are not racing an inflation. Simply
607 // exiting a recursive enter of a Java Monitor that is being
608 // inflated is safe; see the has_monitor() comment below.
609 assert(!mark.is_neutral(), "invariant");
610 assert(!mark.has_locker() ||
611 THREAD->is_lock_owned((address)mark.locker()), "invariant");
612 if (mark.has_monitor()) {
613 // The BasicLock's displaced_header is marked as a recursive
614 // enter and we have an inflated Java Monitor (ObjectMonitor).
615 // This is a special case where the Java Monitor was inflated
616 // after this thread entered the stack-lock recursively. When a
617 // Java Monitor is inflated, we cannot safely walk the Java
618 // Monitor owner's stack and update the BasicLocks because a
619 // Java Monitor can be asynchronously inflated by a thread that
620 // does not own the Java Monitor.
621 ObjectMonitor* m = mark.monitor();
622 assert(((oop)(m->object()))->mark() == mark, "invariant");
623 assert(m->is_entered(THREAD), "invariant");
624 }
625 }
626 #endif
627 return;
628 }
629
630 if (mark == markWord::from_pointer(lock)) {
631 // If the object is stack-locked by the current thread, try to
632 // swing the displaced header from the BasicLock back to the mark.
633 assert(dhw.is_neutral(), "invariant");
634 if (object->cas_set_mark(dhw, mark) == mark) {
635 return;
636 }
637 }
638
639 // We have to take the slow-path of possible inflation and then exit.
640 // The ObjectMonitor* can't be async deflated until ownership is
641 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
642 ObjectMonitor* monitor = inflate(THREAD, object, inflate_cause_vm_internal);
643 monitor->exit(true, THREAD);
644 }
645
646 // -----------------------------------------------------------------------------
647 // Class Loader support to workaround deadlocks on the class loader lock objects
648 // Also used by GC
649 // complete_exit()/reenter() are used to wait on a nested lock
650 // i.e. to give up an outer lock completely and then re-enter
651 // Used when holding nested locks - lock acquisition order: lock1 then lock2
652 // 1) complete_exit lock1 - saving recursion count
653 // 2) wait on lock2
654 // 3) when notified on lock2, unlock lock2
655 // 4) reenter lock1 with original recursion count
656 // 5) lock lock2
657 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
658 intx ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
659 if (UseBiasedLocking) {
660 BiasedLocking::revoke(obj, THREAD);
661 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
662 }
663
664 // The ObjectMonitor* can't be async deflated until ownership is
665 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
666 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
667 intptr_t ret_code = monitor->complete_exit(THREAD);
668 return ret_code;
669 }
670
671 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
672 void ObjectSynchronizer::reenter(Handle obj, intx recursions, TRAPS) {
673 if (UseBiasedLocking) {
674 BiasedLocking::revoke(obj, THREAD);
675 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
676 }
677
678 // An async deflation can race after the inflate() call and before
679 // reenter() -> enter() can make the ObjectMonitor busy. reenter() ->
680 // enter() returns false if we have lost the race to async deflation
681 // and we simply try again.
682 while (true) {
683 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
684 if (monitor->reenter(recursions, THREAD)) {
685 return;
686 }
687 }
688 }
689
690 // -----------------------------------------------------------------------------
691 // JNI locks on java objects
692 // NOTE: must use heavy weight monitor to handle jni monitor enter
693 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
694 // the current locking is from JNI instead of Java code
695 if (UseBiasedLocking) {
696 BiasedLocking::revoke(obj, THREAD);
697 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
698 }
699 THREAD->set_current_pending_monitor_is_from_java(false);
700 // An async deflation can race after the inflate() call and before
701 // enter() can make the ObjectMonitor busy. enter() returns false if
702 // we have lost the race to async deflation and we simply try again.
703 while (true) {
704 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_jni_enter);
705 if (monitor->enter(THREAD)) {
706 break;
707 }
708 }
709 THREAD->set_current_pending_monitor_is_from_java(true);
710 }
711
712 // NOTE: must use heavy weight monitor to handle jni monitor exit
713 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
714 if (UseBiasedLocking) {
715 Handle h_obj(THREAD, obj);
716 BiasedLocking::revoke(h_obj, THREAD);
717 obj = h_obj();
718 }
719 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
720
721 // The ObjectMonitor* can't be async deflated until ownership is
722 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
723 ObjectMonitor* monitor = inflate(THREAD, obj, inflate_cause_jni_exit);
724 // If this thread has locked the object, exit the monitor. We
725 // intentionally do not use CHECK here because we must exit the
726 // monitor even if an exception is pending.
727 if (monitor->check_owner(THREAD)) {
728 monitor->exit(true, THREAD);
729 }
730 }
731
732 // -----------------------------------------------------------------------------
733 // Internal VM locks on java objects
734 // standard constructor, allows locking failures
735 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool do_lock) {
736 _dolock = do_lock;
737 _thread = thread;
738 _thread->check_for_valid_safepoint_state();
739 _obj = obj;
740
741 if (_dolock) {
742 ObjectSynchronizer::enter(_obj, &_lock, _thread);
743 }
744 }
745
746 ObjectLocker::~ObjectLocker() {
747 if (_dolock) {
748 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
749 }
750 }
751
752
753 // -----------------------------------------------------------------------------
754 // Wait/Notify/NotifyAll
755 // NOTE: must use heavy weight monitor to handle wait()
756 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
757 if (UseBiasedLocking) {
758 BiasedLocking::revoke(obj, THREAD);
759 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
760 }
761 if (millis < 0) {
762 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
763 }
764 // The ObjectMonitor* can't be async deflated because the _waiters
765 // field is incremented before ownership is dropped and decremented
766 // after ownership is regained.
767 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
768
769 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
770 monitor->wait(millis, true, THREAD);
771
772 // This dummy call is in place to get around dtrace bug 6254741. Once
773 // that's fixed we can uncomment the following line, remove the call
774 // and change this function back into a "void" func.
775 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
776 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
777 return ret_code;
778 }
779
780 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, jlong millis, TRAPS) {
781 if (UseBiasedLocking) {
782 BiasedLocking::revoke(obj, THREAD);
783 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
784 }
785 if (millis < 0) {
786 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
787 }
788 // The ObjectMonitor* can't be async deflated because the _waiters
789 // field is incremented before ownership is dropped and decremented
790 // after ownership is regained.
791 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
792 monitor->wait(millis, false, THREAD);
793 }
794
795 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
796 if (UseBiasedLocking) {
797 BiasedLocking::revoke(obj, THREAD);
798 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
799 }
800
801 markWord mark = obj->mark();
802 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
803 return;
804 }
805 // The ObjectMonitor* can't be async deflated until ownership is
806 // dropped by the calling thread.
807 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_notify);
808 monitor->notify(THREAD);
809 }
810
811 // NOTE: see comment of notify()
812 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
813 if (UseBiasedLocking) {
814 BiasedLocking::revoke(obj, THREAD);
815 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
816 }
817
818 markWord mark = obj->mark();
819 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
820 return;
821 }
822 // The ObjectMonitor* can't be async deflated until ownership is
823 // dropped by the calling thread.
824 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_notify);
825 monitor->notifyAll(THREAD);
826 }
827
828 // -----------------------------------------------------------------------------
829 // Hash Code handling
830 //
831 // Performance concern:
832 // OrderAccess::storestore() calls release() which at one time stored 0
833 // into the global volatile OrderAccess::dummy variable. This store was
834 // unnecessary for correctness. Many threads storing into a common location
835 // causes considerable cache migration or "sloshing" on large SMP systems.
836 // As such, I avoided using OrderAccess::storestore(). In some cases
837 // OrderAccess::fence() -- which incurs local latency on the executing
838 // processor -- is a better choice as it scales on SMP systems.
839 //
840 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
841 // a discussion of coherency costs. Note that all our current reference
842 // platforms provide strong ST-ST order, so the issue is moot on IA32,
843 // x64, and SPARC.
844 //
845 // As a general policy we use "volatile" to control compiler-based reordering
846 // and explicit fences (barriers) to control for architectural reordering
847 // performed by the CPU(s) or platform.
848
849 struct SharedGlobals {
850 char _pad_prefix[OM_CACHE_LINE_SIZE];
851 // These are highly shared mostly-read variables.
852 // To avoid false-sharing they need to be the sole occupants of a cache line.
853 volatile int stw_random;
854 volatile int stw_cycle;
855 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
856 // Hot RW variable -- Sequester to avoid false-sharing
857 volatile int hc_sequence;
858 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
859 };
860
861 static SharedGlobals GVars;
862
863 static markWord read_stable_mark(oop obj) {
864 markWord mark = obj->mark();
865 if (!mark.is_being_inflated()) {
866 return mark; // normal fast-path return
867 }
868
869 int its = 0;
870 for (;;) {
871 markWord mark = obj->mark();
872 if (!mark.is_being_inflated()) {
873 return mark; // normal fast-path return
874 }
875
876 // The object is being inflated by some other thread.
877 // The caller of read_stable_mark() must wait for inflation to complete.
878 // Avoid live-lock
879 // TODO: consider calling SafepointSynchronize::do_call_back() while
880 // spinning to see if there's a safepoint pending. If so, immediately
881 // yielding or blocking would be appropriate. Avoid spinning while
882 // there is a safepoint pending.
883 // TODO: add inflation contention performance counters.
884 // TODO: restrict the aggregate number of spinners.
885
886 ++its;
887 if (its > 10000 || !os::is_MP()) {
888 if (its & 1) {
889 os::naked_yield();
890 } else {
891 // Note that the following code attenuates the livelock problem but is not
892 // a complete remedy. A more complete solution would require that the inflating
893 // thread hold the associated inflation lock. The following code simply restricts
894 // the number of spinners to at most one. We'll have N-2 threads blocked
895 // on the inflationlock, 1 thread holding the inflation lock and using
896 // a yield/park strategy, and 1 thread in the midst of inflation.
897 // A more refined approach would be to change the encoding of INFLATING
898 // to allow encapsulation of a native thread pointer. Threads waiting for
899 // inflation to complete would use CAS to push themselves onto a singly linked
900 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
901 // and calling park(). When inflation was complete the thread that accomplished inflation
902 // would detach the list and set the markword to inflated with a single CAS and
903 // then for each thread on the list, set the flag and unpark() the thread.
904 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
905 // wakes at most one thread whereas we need to wake the entire list.
906 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
907 int YieldThenBlock = 0;
908 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
909 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
910 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
911 while (obj->mark() == markWord::INFLATING()) {
912 // Beware: NakedYield() is advisory and has almost no effect on some platforms
913 // so we periodically call self->_ParkEvent->park(1).
914 // We use a mixed spin/yield/block mechanism.
915 if ((YieldThenBlock++) >= 16) {
916 Thread::current()->_ParkEvent->park(1);
917 } else {
918 os::naked_yield();
919 }
920 }
921 Thread::muxRelease(gInflationLocks + ix);
922 }
923 } else {
924 SpinPause(); // SMP-polite spinning
925 }
926 }
927 }
928
929 // hashCode() generation :
930 //
931 // Possibilities:
932 // * MD5Digest of {obj,stw_random}
933 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
934 // * A DES- or AES-style SBox[] mechanism
935 // * One of the Phi-based schemes, such as:
936 // 2654435761 = 2^32 * Phi (golden ratio)
937 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
938 // * A variation of Marsaglia's shift-xor RNG scheme.
939 // * (obj ^ stw_random) is appealing, but can result
940 // in undesirable regularity in the hashCode values of adjacent objects
941 // (objects allocated back-to-back, in particular). This could potentially
942 // result in hashtable collisions and reduced hashtable efficiency.
943 // There are simple ways to "diffuse" the middle address bits over the
944 // generated hashCode values:
945
946 static inline intptr_t get_next_hash(Thread* self, oop obj) {
947 intptr_t value = 0;
948 if (hashCode == 0) {
949 // This form uses global Park-Miller RNG.
950 // On MP system we'll have lots of RW access to a global, so the
951 // mechanism induces lots of coherency traffic.
952 value = os::random();
953 } else if (hashCode == 1) {
954 // This variation has the property of being stable (idempotent)
955 // between STW operations. This can be useful in some of the 1-0
956 // synchronization schemes.
957 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
958 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
959 } else if (hashCode == 2) {
960 value = 1; // for sensitivity testing
961 } else if (hashCode == 3) {
962 value = ++GVars.hc_sequence;
963 } else if (hashCode == 4) {
964 value = cast_from_oop<intptr_t>(obj);
965 } else {
966 // Marsaglia's xor-shift scheme with thread-specific state
967 // This is probably the best overall implementation -- we'll
968 // likely make this the default in future releases.
969 unsigned t = self->_hashStateX;
970 t ^= (t << 11);
971 self->_hashStateX = self->_hashStateY;
972 self->_hashStateY = self->_hashStateZ;
973 self->_hashStateZ = self->_hashStateW;
974 unsigned v = self->_hashStateW;
975 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
976 self->_hashStateW = v;
977 value = v;
978 }
979
980 value &= markWord::hash_mask;
981 if (value == 0) value = 0xBAD;
982 assert(value != markWord::no_hash, "invariant");
983 return value;
984 }
985
986 intptr_t ObjectSynchronizer::FastHashCode(Thread* self, oop obj) {
987 if (UseBiasedLocking) {
988 // NOTE: many places throughout the JVM do not expect a safepoint
989 // to be taken here, in particular most operations on perm gen
990 // objects. However, we only ever bias Java instances and all of
991 // the call sites of identity_hash that might revoke biases have
992 // been checked to make sure they can handle a safepoint. The
993 // added check of the bias pattern is to avoid useless calls to
994 // thread-local storage.
995 if (obj->mark().has_bias_pattern()) {
996 // Handle for oop obj in case of STW safepoint
997 Handle hobj(self, obj);
998 // Relaxing assertion for bug 6320749.
999 assert(Universe::verify_in_progress() ||
1000 !SafepointSynchronize::is_at_safepoint(),
1001 "biases should not be seen by VM thread here");
1002 BiasedLocking::revoke(hobj, JavaThread::current());
1003 obj = hobj();
1004 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
1005 }
1006 }
1007
1008 // hashCode() is a heap mutator ...
1009 // Relaxing assertion for bug 6320749.
1010 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
1011 !SafepointSynchronize::is_at_safepoint(), "invariant");
1012 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
1013 self->is_Java_thread() , "invariant");
1014 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
1015 ((JavaThread *)self)->thread_state() != _thread_blocked, "invariant");
1016
1017 while (true) {
1018 ObjectMonitor* monitor = NULL;
1019 markWord temp, test;
1020 intptr_t hash;
1021 markWord mark = read_stable_mark(obj);
1022
1023 // object should remain ineligible for biased locking
1024 assert(!mark.has_bias_pattern(), "invariant");
1025
1026 if (mark.is_neutral()) { // if this is a normal header
1027 hash = mark.hash();
1028 if (hash != 0) { // if it has a hash, just return it
1029 return hash;
1030 }
1031 hash = get_next_hash(self, obj); // get a new hash
1032 temp = mark.copy_set_hash(hash); // merge the hash into header
1033 // try to install the hash
1034 test = obj->cas_set_mark(temp, mark);
1035 if (test == mark) { // if the hash was installed, return it
1036 return hash;
1037 }
1038 // Failed to install the hash. It could be that another thread
1039 // installed the hash just before our attempt or inflation has
1040 // occurred or... so we fall thru to inflate the monitor for
1041 // stability and then install the hash.
1042 } else if (mark.has_monitor()) {
1043 monitor = mark.monitor();
1044 temp = monitor->header();
1045 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1046 hash = temp.hash();
1047 if (hash != 0) {
1048 // It has a hash.
1049
1050 // Separate load of dmw/header above from the loads in
1051 // is_being_async_deflated().
1052 if (support_IRIW_for_not_multiple_copy_atomic_cpu) {
1053 // A non-multiple copy atomic (nMCA) machine needs a bigger
1054 // hammer to separate the load above and the loads below.
1055 OrderAccess::fence();
1056 } else {
1057 OrderAccess::loadload();
1058 }
1059 if (monitor->is_being_async_deflated()) {
1060 // But we can't safely use the hash if we detect that async
1061 // deflation has occurred. So we attempt to restore the
1062 // header/dmw to the object's header so that we only retry
1063 // once if the deflater thread happens to be slow.
1064 monitor->install_displaced_markword_in_object(obj);
1065 continue;
1066 }
1067 return hash;
1068 }
1069 // Fall thru so we only have one place that installs the hash in
1070 // the ObjectMonitor.
1071 } else if (self->is_lock_owned((address)mark.locker())) {
1072 // This is a stack lock owned by the calling thread so fetch the
1073 // displaced markWord from the BasicLock on the stack.
1074 temp = mark.displaced_mark_helper();
1075 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1076 hash = temp.hash();
1077 if (hash != 0) { // if it has a hash, just return it
1078 return hash;
1079 }
1080 // WARNING:
1081 // The displaced header in the BasicLock on a thread's stack
1082 // is strictly immutable. It CANNOT be changed in ANY cases.
1083 // So we have to inflate the stack lock into an ObjectMonitor
1084 // even if the current thread owns the lock. The BasicLock on
1085 // a thread's stack can be asynchronously read by other threads
1086 // during an inflate() call so any change to that stack memory
1087 // may not propagate to other threads correctly.
1088 }
1089
1090 // Inflate the monitor to set the hash.
1091
1092 // An async deflation can race after the inflate() call and before we
1093 // can update the ObjectMonitor's header with the hash value below.
1094 monitor = inflate(self, obj, inflate_cause_hash_code);
1095 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1096 mark = monitor->header();
1097 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1098 hash = mark.hash();
1099 if (hash == 0) { // if it does not have a hash
1100 hash = get_next_hash(self, obj); // get a new hash
1101 temp = mark.copy_set_hash(hash); // merge the hash into header
1102 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1103 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1104 test = markWord(v);
1105 if (test != mark) {
1106 // The attempt to update the ObjectMonitor's header/dmw field
1107 // did not work. This can happen if another thread managed to
1108 // merge in the hash just before our cmpxchg().
1109 // If we add any new usages of the header/dmw field, this code
1110 // will need to be updated.
1111 hash = test.hash();
1112 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1113 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1114 }
1115 if (monitor->is_being_async_deflated()) {
1116 // If we detect that async deflation has occurred, then we
1117 // attempt to restore the header/dmw to the object's header
1118 // so that we only retry once if the deflater thread happens
1119 // to be slow.
1120 monitor->install_displaced_markword_in_object(obj);
1121 continue;
1122 }
1123 }
1124 // We finally get the hash.
1125 return hash;
1126 }
1127 }
1128
1129 // Deprecated -- use FastHashCode() instead.
1130
1131 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
1132 return FastHashCode(Thread::current(), obj());
1133 }
1134
1135
1136 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
1137 Handle h_obj) {
1138 if (UseBiasedLocking) {
1139 BiasedLocking::revoke(h_obj, thread);
1140 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1141 }
1142
1143 assert(thread == JavaThread::current(), "Can only be called on current thread");
1144 oop obj = h_obj();
1145
1146 markWord mark = read_stable_mark(obj);
1147
1148 // Uncontended case, header points to stack
1149 if (mark.has_locker()) {
1150 return thread->is_lock_owned((address)mark.locker());
1151 }
1152 // Contended case, header points to ObjectMonitor (tagged pointer)
1153 if (mark.has_monitor()) {
1154 // The first stage of async deflation does not affect any field
1155 // used by this comparison so the ObjectMonitor* is usable here.
1156 ObjectMonitor* monitor = mark.monitor();
1157 return monitor->is_entered(thread) != 0;
1158 }
1159 // Unlocked case, header in place
1160 assert(mark.is_neutral(), "sanity check");
1161 return false;
1162 }
1163
1164 // Be aware of this method could revoke bias of the lock object.
1165 // This method queries the ownership of the lock handle specified by 'h_obj'.
1166 // If the current thread owns the lock, it returns owner_self. If no
1167 // thread owns the lock, it returns owner_none. Otherwise, it will return
1168 // owner_other.
1169 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
1170 (JavaThread *self, Handle h_obj) {
1171 // The caller must beware this method can revoke bias, and
1172 // revocation can result in a safepoint.
1173 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
1174 assert(self->thread_state() != _thread_blocked, "invariant");
1175
1176 // Possible mark states: neutral, biased, stack-locked, inflated
1177
1178 if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) {
1179 // CASE: biased
1180 BiasedLocking::revoke(h_obj, self);
1181 assert(!h_obj->mark().has_bias_pattern(),
1182 "biases should be revoked by now");
1183 }
1184
1185 assert(self == JavaThread::current(), "Can only be called on current thread");
1186 oop obj = h_obj();
1187 markWord mark = read_stable_mark(obj);
1188
1189 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
1190 if (mark.has_locker()) {
1191 return self->is_lock_owned((address)mark.locker()) ?
1192 owner_self : owner_other;
1193 }
1194
1195 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
1196 // The Object:ObjectMonitor relationship is stable as long as we're
1197 // not at a safepoint and AsyncDeflateIdleMonitors is false.
1198 if (mark.has_monitor()) {
1199 // The first stage of async deflation does not affect any field
1200 // used by this comparison so the ObjectMonitor* is usable here.
1201 ObjectMonitor* monitor = mark.monitor();
1202 void* owner = monitor->owner();
1203 if (owner == NULL) return owner_none;
1204 return (owner == self ||
1205 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
1206 }
1207
1208 // CASE: neutral
1209 assert(mark.is_neutral(), "sanity check");
1210 return owner_none; // it's unlocked
1211 }
1212
1213 // FIXME: jvmti should call this
1214 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1215 if (UseBiasedLocking) {
1216 if (SafepointSynchronize::is_at_safepoint()) {
1217 BiasedLocking::revoke_at_safepoint(h_obj);
1218 } else {
1219 BiasedLocking::revoke(h_obj, JavaThread::current());
1220 }
1221 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1222 }
1223
1224 oop obj = h_obj();
1225 address owner = NULL;
1226
1227 markWord mark = read_stable_mark(obj);
1228
1229 // Uncontended case, header points to stack
1230 if (mark.has_locker()) {
1231 owner = (address) mark.locker();
1232 }
1233
1234 // Contended case, header points to ObjectMonitor (tagged pointer)
1235 else if (mark.has_monitor()) {
1236 // The first stage of async deflation does not affect any field
1237 // used by this comparison so the ObjectMonitor* is usable here.
1238 ObjectMonitor* monitor = mark.monitor();
1239 assert(monitor != NULL, "monitor should be non-null");
1240 owner = (address) monitor->owner();
1241 }
1242
1243 if (owner != NULL) {
1244 // owning_thread_from_monitor_owner() may also return NULL here
1245 return Threads::owning_thread_from_monitor_owner(t_list, owner);
1246 }
1247
1248 // Unlocked case, header in place
1249 // Cannot have assertion since this object may have been
1250 // locked by another thread when reaching here.
1251 // assert(mark.is_neutral(), "sanity check");
1252
1253 return NULL;
1254 }
1255
1256 // Visitors ...
1257
1258 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
1259 PaddedObjectMonitor* block = Atomic::load(&g_block_list);
1260 while (block != NULL) {
1261 assert(block->object() == CHAINMARKER, "must be a block header");
1262 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
1263 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
1264 if (mid->object() != NULL) {
1265 // Only process with closure if the object is set.
1266
1267 // monitors_iterate() is only called at a safepoint or when the
1268 // target thread is suspended or when the target thread is
1269 // operating on itself. The current closures in use today are
1270 // only interested in an owned ObjectMonitor and ownership
1271 // cannot be dropped under the calling contexts so the
1272 // ObjectMonitor cannot be async deflated.
1273 closure->do_monitor(mid);
1274 }
1275 }
1276 // unmarked_next() is not needed with g_block_list (no locking
1277 // used with block linkage _next_om fields).
1278 block = (PaddedObjectMonitor*)block->next_om();
1279 }
1280 }
1281
1282 static bool monitors_used_above_threshold() {
1283 int population = Atomic::load(&om_list_globals._population);
1284 if (population == 0) {
1285 return false;
1286 }
1287 if (MonitorUsedDeflationThreshold > 0) {
1288 int monitors_used = population - Atomic::load(&om_list_globals._free_count) -
1289 Atomic::load(&om_list_globals._wait_count);
1290 int monitor_usage = (monitors_used * 100LL) / population;
1291 return monitor_usage > MonitorUsedDeflationThreshold;
1292 }
1293 return false;
1294 }
1295
1296 bool ObjectSynchronizer::is_async_deflation_needed() {
1297 if (!AsyncDeflateIdleMonitors) {
1298 return false;
1299 }
1300 if (is_async_deflation_requested()) {
1301 // Async deflation request.
1302 return true;
1303 }
1304 if (AsyncDeflationInterval > 0 &&
1305 time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1306 monitors_used_above_threshold()) {
1307 // It's been longer than our specified deflate interval and there
1308 // are too many monitors in use. We don't deflate more frequently
1309 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1310 // in order to not swamp the ServiceThread.
1311 return true;
1312 }
1313 return false;
1314 }
1315
1316 bool ObjectSynchronizer::is_safepoint_deflation_needed() {
1317 if (!AsyncDeflateIdleMonitors) {
1318 if (monitors_used_above_threshold()) {
1319 // Too many monitors in use.
1320 return true;
1321 }
1322 return false;
1323 }
1324 return false;
1325 }
1326
1327 bool ObjectSynchronizer::request_deflate_idle_monitors() {
1328 bool is_JavaThread = Thread::current()->is_Java_thread();
1329 bool ret_code = false;
1330
1331 if (AsyncDeflateIdleMonitors) {
1332 jlong last_time = last_async_deflation_time_ns();
1333 set_is_async_deflation_requested(true);
1334 {
1335 MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
1336 ml.notify_all();
1337 }
1338 const int N_CHECKS = 5;
1339 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1340 if (last_async_deflation_time_ns() > last_time) {
1341 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1342 ret_code = true;
1343 break;
1344 }
1345 if (is_JavaThread) {
1346 // JavaThread has to honor the blocking protocol.
1347 ThreadBlockInVM tbivm(JavaThread::current());
1348 os::naked_short_sleep(999); // sleep for almost 1 second
1349 } else {
1350 os::naked_short_sleep(999); // sleep for almost 1 second
1351 }
1352 }
1353 if (ret_code == false) {
1354 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1355 }
1356 } else if (!Thread::current()->is_VM_thread()) {
1357 // The VMThread only calls this at shutdown time before the final
1358 // safepoint so it should not need to force this safepoint.
1359 VM_ForceSafepoint force_safepoint_op;
1360 VMThread::execute(&force_safepoint_op);
1361 ret_code = true;
1362 }
1363
1364 return ret_code;
1365 }
1366
1367 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1368 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1369 }
1370
1371 void ObjectSynchronizer::oops_do(OopClosure* f) {
1372 // We only scan the global used list here (for moribund threads), and
1373 // the thread-local monitors in Thread::oops_do().
1374 global_used_oops_do(f);
1375 }
1376
1377 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
1378 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1379 list_oops_do(Atomic::load(&om_list_globals._in_use_list), f);
1380 }
1381
1382 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
1383 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1384 list_oops_do(thread->om_in_use_list, f);
1385 }
1386
1387 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
1388 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1389 // The oops_do() phase does not overlap with monitor deflation
1390 // so no need to lock ObjectMonitors for the list traversal.
1391 for (ObjectMonitor* mid = list; mid != NULL; mid = unmarked_next(mid)) {
1392 if (mid->object() != NULL) {
1393 f->do_oop((oop*)mid->object_addr());
1394 }
1395 }
1396 }
1397
1398
1399 // -----------------------------------------------------------------------------
1400 // ObjectMonitor Lifecycle
1401 // -----------------------
1402 // Inflation unlinks monitors from om_list_globals._free_list or a per-thread
1403 // free list and associates them with objects. Deflation -- which occurs at
1404 // STW-time or asynchronously -- disassociates idle monitors from objects.
1405 // Such scavenged monitors are returned to the om_list_globals._free_list.
1406 //
1407 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1408 //
1409 // Lifecycle:
1410 // -- unassigned and on the om_list_globals._free_list
1411 // -- unassigned and on a per-thread free list
1412 // -- assigned to an object. The object is inflated and the mark refers
1413 // to the ObjectMonitor.
1414
1415 ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self) {
1416 // A large MAXPRIVATE value reduces both list lock contention
1417 // and list coherency traffic, but also tends to increase the
1418 // number of ObjectMonitors in circulation as well as the STW
1419 // scavenge costs. As usual, we lean toward time in space-time
1420 // tradeoffs.
1421 const int MAXPRIVATE = 1024;
1422 NoSafepointVerifier nsv;
1423
1424 for (;;) {
1425 ObjectMonitor* m;
1426
1427 // 1: try to allocate from the thread's local om_free_list.
1428 // Threads will attempt to allocate first from their local list, then
1429 // from the global list, and only after those attempts fail will the
1430 // thread attempt to instantiate new monitors. Thread-local free lists
1431 // improve allocation latency, as well as reducing coherency traffic
1432 // on the shared global list.
1433 m = take_from_start_of_om_free_list(self);
1434 if (m != NULL) {
1435 guarantee(m->object() == NULL, "invariant");
1436 m->set_allocation_state(ObjectMonitor::New);
1437 prepend_to_om_in_use_list(self, m);
1438 return m;
1439 }
1440
1441 // 2: try to allocate from the global om_list_globals._free_list
1442 // If we're using thread-local free lists then try
1443 // to reprovision the caller's free list.
1444 if (Atomic::load(&om_list_globals._free_list) != NULL) {
1445 // Reprovision the thread's om_free_list.
1446 // Use bulk transfers to reduce the allocation rate and heat
1447 // on various locks.
1448 for (int i = self->om_free_provision; --i >= 0;) {
1449 ObjectMonitor* take = take_from_start_of_global_free_list();
1450 if (take == NULL) {
1451 break; // No more are available.
1452 }
1453 guarantee(take->object() == NULL, "invariant");
1454 if (AsyncDeflateIdleMonitors) {
1455 // We allowed 3 field values to linger during async deflation.
1456 // Clear or restore them as appropriate.
1457 take->set_header(markWord::zero());
1458 // DEFLATER_MARKER is the only non-NULL value we should see here.
1459 take->try_set_owner_from(DEFLATER_MARKER, NULL);
1460 if (take->contentions() < 0) {
1461 // Add back max_jint to restore the contentions field to its
1462 // proper value.
1463 take->add_to_contentions(max_jint);
1464
1465 #ifdef ASSERT
1466 jint l_contentions = take->contentions();
1467 #endif
1468 assert(l_contentions >= 0, "must not be negative: l_contentions=%d, contentions=%d",
1469 l_contentions, take->contentions());
1470 }
1471 }
1472 take->Recycle();
1473 // Since we're taking from the global free-list, take must be Free.
1474 // om_release() also sets the allocation state to Free because it
1475 // is called from other code paths.
1476 assert(take->is_free(), "invariant");
1477 om_release(self, take, false);
1478 }
1479 self->om_free_provision += 1 + (self->om_free_provision / 2);
1480 if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE;
1481 continue;
1482 }
1483
1484 // 3: allocate a block of new ObjectMonitors
1485 // Both the local and global free lists are empty -- resort to malloc().
1486 // In the current implementation ObjectMonitors are TSM - immortal.
1487 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1488 // each ObjectMonitor to start at the beginning of a cache line,
1489 // so we use align_up().
1490 // A better solution would be to use C++ placement-new.
1491 // BEWARE: As it stands currently, we don't run the ctors!
1492 assert(_BLOCKSIZE > 1, "invariant");
1493 size_t neededsize = sizeof(PaddedObjectMonitor) * _BLOCKSIZE;
1494 PaddedObjectMonitor* temp;
1495 size_t aligned_size = neededsize + (OM_CACHE_LINE_SIZE - 1);
1496 void* real_malloc_addr = NEW_C_HEAP_ARRAY(char, aligned_size, mtInternal);
1497 temp = (PaddedObjectMonitor*)align_up(real_malloc_addr, OM_CACHE_LINE_SIZE);
1498 (void)memset((void *) temp, 0, neededsize);
1499
1500 // Format the block.
1501 // initialize the linked list, each monitor points to its next
1502 // forming the single linked free list, the very first monitor
1503 // will points to next block, which forms the block list.
1504 // The trick of using the 1st element in the block as g_block_list
1505 // linkage should be reconsidered. A better implementation would
1506 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1507
1508 for (int i = 1; i < _BLOCKSIZE; i++) {
1509 temp[i].set_next_om((ObjectMonitor*)&temp[i + 1]);
1510 assert(temp[i].is_free(), "invariant");
1511 }
1512
1513 // terminate the last monitor as the end of list
1514 temp[_BLOCKSIZE - 1].set_next_om((ObjectMonitor*)NULL);
1515
1516 // Element [0] is reserved for global list linkage
1517 temp[0].set_object(CHAINMARKER);
1518
1519 // Consider carving out this thread's current request from the
1520 // block in hand. This avoids some lock traffic and redundant
1521 // list activity.
1522
1523 prepend_block_to_lists(temp);
1524 }
1525 }
1526
1527 // Place "m" on the caller's private per-thread om_free_list.
1528 // In practice there's no need to clamp or limit the number of
1529 // monitors on a thread's om_free_list as the only non-allocation time
1530 // we'll call om_release() is to return a monitor to the free list after
1531 // a CAS attempt failed. This doesn't allow unbounded #s of monitors to
1532 // accumulate on a thread's free list.
1533 //
1534 // Key constraint: all ObjectMonitors on a thread's free list and the global
1535 // free list must have their object field set to null. This prevents the
1536 // scavenger -- deflate_monitor_list() or deflate_monitor_list_using_JT()
1537 // -- from reclaiming them while we are trying to release them.
1538
1539 void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m,
1540 bool from_per_thread_alloc) {
1541 guarantee(m->header().value() == 0, "invariant");
1542 guarantee(m->object() == NULL, "invariant");
1543 NoSafepointVerifier nsv;
1544
1545 if ((m->is_busy() | m->_recursions) != 0) {
1546 stringStream ss;
1547 fatal("freeing in-use monitor: %s, recursions=" INTX_FORMAT,
1548 m->is_busy_to_string(&ss), m->_recursions);
1549 }
1550 m->set_allocation_state(ObjectMonitor::Free);
1551 // _next_om is used for both per-thread in-use and free lists so
1552 // we have to remove 'm' from the in-use list first (as needed).
1553 if (from_per_thread_alloc) {
1554 // Need to remove 'm' from om_in_use_list.
1555 ObjectMonitor* mid = NULL;
1556 ObjectMonitor* next = NULL;
1557
1558 // This list walk can race with another list walker or with async
1559 // deflation so we have to worry about an ObjectMonitor being
1560 // removed from this list while we are walking it.
1561
1562 // Lock the list head to avoid racing with another list walker
1563 // or with async deflation.
1564 if ((mid = get_list_head_locked(&self->om_in_use_list)) == NULL) {
1565 fatal("thread=" INTPTR_FORMAT " in-use list must not be empty.", p2i(self));
1566 }
1567 next = unmarked_next(mid);
1568 if (m == mid) {
1569 // First special case:
1570 // 'm' matches mid, is the list head and is locked. Switch the list
1571 // head to next which unlocks the list head, but leaves the extracted
1572 // mid locked:
1573 Atomic::store(&self->om_in_use_list, next);
1574 } else if (m == next) {
1575 // Second special case:
1576 // 'm' matches next after the list head and we already have the list
1577 // head locked so set mid to what we are extracting:
1578 mid = next;
1579 // Lock mid to prevent races with a list walker or an async
1580 // deflater thread that's ahead of us. The locked list head
1581 // prevents races from behind us.
1582 om_lock(mid);
1583 // Update next to what follows mid (if anything):
1584 next = unmarked_next(mid);
1585 // Switch next after the list head to new next which unlocks the
1586 // list head, but leaves the extracted mid locked:
1587 self->om_in_use_list->set_next_om(next);
1588 } else {
1589 // We have to search the list to find 'm'.
1590 guarantee(next != NULL, "thread=" INTPTR_FORMAT ": om_in_use_list=" INTPTR_FORMAT
1591 " is too short.", p2i(self), p2i(self->om_in_use_list));
1592 // Our starting anchor is next after the list head which is the
1593 // last ObjectMonitor we checked:
1594 ObjectMonitor* anchor = next;
1595 // Lock anchor to prevent races with a list walker or an async
1596 // deflater thread that's ahead of us. The locked list head
1597 // prevents races from behind us.
1598 om_lock(anchor);
1599 om_unlock(mid); // Unlock the list head now that anchor is locked.
1600 while ((mid = unmarked_next(anchor)) != NULL) {
1601 if (m == mid) {
1602 // We found 'm' on the per-thread in-use list so extract it.
1603 // Update next to what follows mid (if anything):
1604 next = unmarked_next(mid);
1605 // Switch next after the anchor to new next which unlocks the
1606 // anchor, but leaves the extracted mid locked:
1607 anchor->set_next_om(next);
1608 break;
1609 } else {
1610 // Lock the next anchor to prevent races with a list walker
1611 // or an async deflater thread that's ahead of us. The locked
1612 // current anchor prevents races from behind us.
1613 om_lock(mid);
1614 // Unlock current anchor now that next anchor is locked:
1615 om_unlock(anchor);
1616 anchor = mid; // Advance to new anchor and try again.
1617 }
1618 }
1619 }
1620
1621 if (mid == NULL) {
1622 // Reached end of the list and didn't find 'm' so:
1623 fatal("thread=" INTPTR_FORMAT " must find m=" INTPTR_FORMAT "on om_in_use_list="
1624 INTPTR_FORMAT, p2i(self), p2i(m), p2i(self->om_in_use_list));
1625 }
1626
1627 // At this point mid is disconnected from the in-use list so
1628 // its lock no longer has any effects on the in-use list.
1629 Atomic::dec(&self->om_in_use_count);
1630 // Unlock mid, but leave the next value for any lagging list
1631 // walkers. It will get cleaned up when mid is prepended to
1632 // the thread's free list:
1633 om_unlock(mid);
1634 }
1635
1636 prepend_to_om_free_list(self, m);
1637 guarantee(m->is_free(), "invariant");
1638 }
1639
1640 // Return ObjectMonitors on a moribund thread's free and in-use
1641 // lists to the appropriate global lists. The ObjectMonitors on the
1642 // per-thread in-use list may still be in use by other threads.
1643 //
1644 // We currently call om_flush() from Threads::remove() before the
1645 // thread has been excised from the thread list and is no longer a
1646 // mutator. This means that om_flush() cannot run concurrently with
1647 // a safepoint and interleave with deflate_idle_monitors(). In
1648 // particular, this ensures that the thread's in-use monitors are
1649 // scanned by a GC safepoint, either via Thread::oops_do() (before
1650 // om_flush() is called) or via ObjectSynchronizer::oops_do() (after
1651 // om_flush() is called).
1652 //
1653 // With AsyncDeflateIdleMonitors, deflate_global_idle_monitors_using_JT()
1654 // and deflate_per_thread_idle_monitors_using_JT() (in another thread) can
1655 // run at the same time as om_flush() so we have to follow a careful
1656 // protocol to prevent list corruption.
1657
1658 void ObjectSynchronizer::om_flush(Thread* self) {
1659 // Process the per-thread in-use list first to be consistent.
1660 int in_use_count = 0;
1661 ObjectMonitor* in_use_list = NULL;
1662 ObjectMonitor* in_use_tail = NULL;
1663 NoSafepointVerifier nsv;
1664
1665 // This function can race with a list walker or with an async
1666 // deflater thread so we lock the list head to prevent confusion.
1667 // An async deflater thread checks to see if the target thread
1668 // is exiting, but if it has made it past that check before we
1669 // started exiting, then it is racing to get to the in-use list.
1670 if ((in_use_list = get_list_head_locked(&self->om_in_use_list)) != NULL) {
1671 // At this point, we have locked the in-use list head so a racing
1672 // thread cannot come in after us. However, a racing thread could
1673 // be ahead of us; we'll detect that and delay to let it finish.
1674 //
1675 // The thread is going away, however the ObjectMonitors on the
1676 // om_in_use_list may still be in-use by other threads. Link
1677 // them to in_use_tail, which will be linked into the global
1678 // in-use list (om_list_globals._in_use_list) below.
1679 //
1680 // Account for the in-use list head before the loop since it is
1681 // already locked (by this thread):
1682 in_use_tail = in_use_list;
1683 in_use_count++;
1684 for (ObjectMonitor* cur_om = unmarked_next(in_use_list); cur_om != NULL;) {
1685 if (is_locked(cur_om)) {
1686 // cur_om is locked so there must be a racing walker or async
1687 // deflater thread ahead of us so we'll give it a chance to finish.
1688 while (is_locked(cur_om)) {
1689 os::naked_short_sleep(1);
1690 }
1691 // Refetch the possibly changed next field and try again.
1692 cur_om = unmarked_next(in_use_tail);
1693 continue;
1694 }
1695 if (cur_om->object() == NULL) {
1696 // cur_om was deflated and the object ref was cleared while it
1697 // was locked. We happened to see it just after it was unlocked
1698 // (and added to the free list). Refetch the possibly changed
1699 // next field and try again.
1700 cur_om = unmarked_next(in_use_tail);
1701 continue;
1702 }
1703 in_use_tail = cur_om;
1704 in_use_count++;
1705 cur_om = unmarked_next(cur_om);
1706 }
1707 guarantee(in_use_tail != NULL, "invariant");
1708 int l_om_in_use_count = Atomic::load(&self->om_in_use_count);
1709 ADIM_guarantee(l_om_in_use_count == in_use_count, "in-use counts don't match: "
1710 "l_om_in_use_count=%d, in_use_count=%d", l_om_in_use_count, in_use_count);
1711 Atomic::store(&self->om_in_use_count, 0);
1712 // Clear the in-use list head (which also unlocks it):
1713 Atomic::store(&self->om_in_use_list, (ObjectMonitor*)NULL);
1714 om_unlock(in_use_list);
1715 }
1716
1717 int free_count = 0;
1718 ObjectMonitor* free_list = NULL;
1719 ObjectMonitor* free_tail = NULL;
1720 // This function can race with a list walker thread so we lock the
1721 // list head to prevent confusion.
1722 if ((free_list = get_list_head_locked(&self->om_free_list)) != NULL) {
1723 // At this point, we have locked the free list head so a racing
1724 // thread cannot come in after us. However, a racing thread could
1725 // be ahead of us; we'll detect that and delay to let it finish.
1726 //
1727 // The thread is going away. Set 'free_tail' to the last per-thread free
1728 // monitor which will be linked to om_list_globals._free_list below.
1729 //
1730 // Account for the free list head before the loop since it is
1731 // already locked (by this thread):
1732 free_tail = free_list;
1733 free_count++;
1734 for (ObjectMonitor* s = unmarked_next(free_list); s != NULL; s = unmarked_next(s)) {
1735 if (is_locked(s)) {
1736 // s is locked so there must be a racing walker thread ahead
1737 // of us so we'll give it a chance to finish.
1738 while (is_locked(s)) {
1739 os::naked_short_sleep(1);
1740 }
1741 }
1742 free_tail = s;
1743 free_count++;
1744 guarantee(s->object() == NULL, "invariant");
1745 if (s->is_busy()) {
1746 stringStream ss;
1747 fatal("must be !is_busy: %s", s->is_busy_to_string(&ss));
1748 }
1749 }
1750 guarantee(free_tail != NULL, "invariant");
1751 int l_om_free_count = Atomic::load(&self->om_free_count);
1752 ADIM_guarantee(l_om_free_count == free_count, "free counts don't match: "
1753 "l_om_free_count=%d, free_count=%d", l_om_free_count, free_count);
1754 Atomic::store(&self->om_free_count, 0);
1755 Atomic::store(&self->om_free_list, (ObjectMonitor*)NULL);
1756 om_unlock(free_list);
1757 }
1758
1759 if (free_tail != NULL) {
1760 prepend_list_to_global_free_list(free_list, free_tail, free_count);
1761 }
1762
1763 if (in_use_tail != NULL) {
1764 prepend_list_to_global_in_use_list(in_use_list, in_use_tail, in_use_count);
1765 }
1766
1767 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1768 LogStreamHandle(Info, monitorinflation) lsh_info;
1769 LogStream* ls = NULL;
1770 if (log_is_enabled(Debug, monitorinflation)) {
1771 ls = &lsh_debug;
1772 } else if ((free_count != 0 || in_use_count != 0) &&
1773 log_is_enabled(Info, monitorinflation)) {
1774 ls = &lsh_info;
1775 }
1776 if (ls != NULL) {
1777 ls->print_cr("om_flush: jt=" INTPTR_FORMAT ", free_count=%d"
1778 ", in_use_count=%d" ", om_free_provision=%d",
1779 p2i(self), free_count, in_use_count, self->om_free_provision);
1780 }
1781 }
1782
1783 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1784 const oop obj,
1785 ObjectSynchronizer::InflateCause cause) {
1786 assert(event != NULL, "invariant");
1787 assert(event->should_commit(), "invariant");
1788 event->set_monitorClass(obj->klass());
1789 event->set_address((uintptr_t)(void*)obj);
1790 event->set_cause((u1)cause);
1791 event->commit();
1792 }
1793
1794 // Fast path code shared by multiple functions
1795 void ObjectSynchronizer::inflate_helper(oop obj) {
1796 markWord mark = obj->mark();
1797 if (mark.has_monitor()) {
1798 ObjectMonitor* monitor = mark.monitor();
1799 assert(ObjectSynchronizer::verify_objmon_isinpool(monitor), "monitor=" INTPTR_FORMAT " is invalid", p2i(monitor));
1800 markWord dmw = monitor->header();
1801 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1802 return;
1803 }
1804 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1805 }
1806
1807 ObjectMonitor* ObjectSynchronizer::inflate(Thread* self, oop object,
1808 const InflateCause cause) {
1809 // Inflate mutates the heap ...
1810 // Relaxing assertion for bug 6320749.
1811 assert(Universe::verify_in_progress() ||
1812 !SafepointSynchronize::is_at_safepoint(), "invariant");
1813
1814 EventJavaMonitorInflate event;
1815
1816 for (;;) {
1817 const markWord mark = object->mark();
1818 assert(!mark.has_bias_pattern(), "invariant");
1819
1820 // The mark can be in one of the following states:
1821 // * Inflated - just return
1822 // * Stack-locked - coerce it to inflated
1823 // * INFLATING - busy wait for conversion to complete
1824 // * Neutral - aggressively inflate the object.
1825 // * BIASED - Illegal. We should never see this
1826
1827 // CASE: inflated
1828 if (mark.has_monitor()) {
1829 ObjectMonitor* inf = mark.monitor();
1830 markWord dmw = inf->header();
1831 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1832 assert(AsyncDeflateIdleMonitors || inf->object() == object, "invariant");
1833 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1834 return inf;
1835 }
1836
1837 // CASE: inflation in progress - inflating over a stack-lock.
1838 // Some other thread is converting from stack-locked to inflated.
1839 // Only that thread can complete inflation -- other threads must wait.
1840 // The INFLATING value is transient.
1841 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1842 // We could always eliminate polling by parking the thread on some auxiliary list.
1843 if (mark == markWord::INFLATING()) {
1844 read_stable_mark(object);
1845 continue;
1846 }
1847
1848 // CASE: stack-locked
1849 // Could be stack-locked either by this thread or by some other thread.
1850 //
1851 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1852 // to install INFLATING into the mark word. We originally installed INFLATING,
1853 // allocated the objectmonitor, and then finally STed the address of the
1854 // objectmonitor into the mark. This was correct, but artificially lengthened
1855 // the interval in which INFLATED appeared in the mark, thus increasing
1856 // the odds of inflation contention.
1857 //
1858 // We now use per-thread private objectmonitor free lists.
1859 // These list are reprovisioned from the global free list outside the
1860 // critical INFLATING...ST interval. A thread can transfer
1861 // multiple objectmonitors en-mass from the global free list to its local free list.
1862 // This reduces coherency traffic and lock contention on the global free list.
1863 // Using such local free lists, it doesn't matter if the om_alloc() call appears
1864 // before or after the CAS(INFLATING) operation.
1865 // See the comments in om_alloc().
1866
1867 LogStreamHandle(Trace, monitorinflation) lsh;
1868
1869 if (mark.has_locker()) {
1870 ObjectMonitor* m = om_alloc(self);
1871 // Optimistically prepare the objectmonitor - anticipate successful CAS
1872 // We do this before the CAS in order to minimize the length of time
1873 // in which INFLATING appears in the mark.
1874 m->Recycle();
1875 m->_Responsible = NULL;
1876 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1877
1878 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1879 if (cmp != mark) {
1880 // om_release() will reset the allocation state from New to Free.
1881 om_release(self, m, true);
1882 continue; // Interference -- just retry
1883 }
1884
1885 // We've successfully installed INFLATING (0) into the mark-word.
1886 // This is the only case where 0 will appear in a mark-word.
1887 // Only the singular thread that successfully swings the mark-word
1888 // to 0 can perform (or more precisely, complete) inflation.
1889 //
1890 // Why do we CAS a 0 into the mark-word instead of just CASing the
1891 // mark-word from the stack-locked value directly to the new inflated state?
1892 // Consider what happens when a thread unlocks a stack-locked object.
1893 // It attempts to use CAS to swing the displaced header value from the
1894 // on-stack BasicLock back into the object header. Recall also that the
1895 // header value (hash code, etc) can reside in (a) the object header, or
1896 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1897 // header in an ObjectMonitor. The inflate() routine must copy the header
1898 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1899 // the while preserving the hashCode stability invariants. If the owner
1900 // decides to release the lock while the value is 0, the unlock will fail
1901 // and control will eventually pass from slow_exit() to inflate. The owner
1902 // will then spin, waiting for the 0 value to disappear. Put another way,
1903 // the 0 causes the owner to stall if the owner happens to try to
1904 // drop the lock (restoring the header from the BasicLock to the object)
1905 // while inflation is in-progress. This protocol avoids races that might
1906 // would otherwise permit hashCode values to change or "flicker" for an object.
1907 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1908 // 0 serves as a "BUSY" inflate-in-progress indicator.
1909
1910
1911 // fetch the displaced mark from the owner's stack.
1912 // The owner can't die or unwind past the lock while our INFLATING
1913 // object is in the mark. Furthermore the owner can't complete
1914 // an unlock on the object, either.
1915 markWord dmw = mark.displaced_mark_helper();
1916 // Catch if the object's header is not neutral (not locked and
1917 // not marked is what we care about here).
1918 ADIM_guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1919
1920 // Setup monitor fields to proper values -- prepare the monitor
1921 m->set_header(dmw);
1922
1923 // Optimization: if the mark.locker stack address is associated
1924 // with this thread we could simply set m->_owner = self.
1925 // Note that a thread can inflate an object
1926 // that it has stack-locked -- as might happen in wait() -- directly
1927 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1928 if (AsyncDeflateIdleMonitors) {
1929 m->set_owner_from(NULL, DEFLATER_MARKER, mark.locker());
1930 } else {
1931 m->set_owner_from(NULL, mark.locker());
1932 }
1933 m->set_object(object);
1934 // TODO-FIXME: assert BasicLock->dhw != 0.
1935
1936 // Must preserve store ordering. The monitor state must
1937 // be stable at the time of publishing the monitor address.
1938 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1939 object->release_set_mark(markWord::encode(m));
1940
1941 // Once ObjectMonitor is configured and the object is associated
1942 // with the ObjectMonitor, it is safe to allow async deflation:
1943 assert(m->is_new(), "freshly allocated monitor must be new");
1944 m->set_allocation_state(ObjectMonitor::Old);
1945
1946 // Hopefully the performance counters are allocated on distinct cache lines
1947 // to avoid false sharing on MP systems ...
1948 OM_PERFDATA_OP(Inflations, inc());
1949 if (log_is_enabled(Trace, monitorinflation)) {
1950 ResourceMark rm(self);
1951 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1952 INTPTR_FORMAT ", type='%s'", p2i(object),
1953 object->mark().value(), object->klass()->external_name());
1954 }
1955 if (event.should_commit()) {
1956 post_monitor_inflate_event(&event, object, cause);
1957 }
1958 return m;
1959 }
1960
1961 // CASE: neutral
1962 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1963 // If we know we're inflating for entry it's better to inflate by swinging a
1964 // pre-locked ObjectMonitor pointer into the object header. A successful
1965 // CAS inflates the object *and* confers ownership to the inflating thread.
1966 // In the current implementation we use a 2-step mechanism where we CAS()
1967 // to inflate and then CAS() again to try to swing _owner from NULL to self.
1968 // An inflateTry() method that we could call from enter() would be useful.
1969
1970 // Catch if the object's header is not neutral (not locked and
1971 // not marked is what we care about here).
1972 ADIM_guarantee(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1973 ObjectMonitor* m = om_alloc(self);
1974 // prepare m for installation - set monitor to initial state
1975 m->Recycle();
1976 m->set_header(mark);
1977 if (AsyncDeflateIdleMonitors) {
1978 // DEFLATER_MARKER is the only non-NULL value we should see here.
1979 m->try_set_owner_from(DEFLATER_MARKER, NULL);
1980 }
1981 m->set_object(object);
1982 m->_Responsible = NULL;
1983 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1984
1985 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1986 m->set_header(markWord::zero());
1987 m->set_object(NULL);
1988 m->Recycle();
1989 // om_release() will reset the allocation state from New to Free.
1990 om_release(self, m, true);
1991 m = NULL;
1992 continue;
1993 // interference - the markword changed - just retry.
1994 // The state-transitions are one-way, so there's no chance of
1995 // live-lock -- "Inflated" is an absorbing state.
1996 }
1997
1998 // Once the ObjectMonitor is configured and object is associated
1999 // with the ObjectMonitor, it is safe to allow async deflation:
2000 assert(m->is_new(), "freshly allocated monitor must be new");
2001 m->set_allocation_state(ObjectMonitor::Old);
2002
2003 // Hopefully the performance counters are allocated on distinct
2004 // cache lines to avoid false sharing on MP systems ...
2005 OM_PERFDATA_OP(Inflations, inc());
2006 if (log_is_enabled(Trace, monitorinflation)) {
2007 ResourceMark rm(self);
2008 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
2009 INTPTR_FORMAT ", type='%s'", p2i(object),
2010 object->mark().value(), object->klass()->external_name());
2011 }
2012 if (event.should_commit()) {
2013 post_monitor_inflate_event(&event, object, cause);
2014 }
2015 return m;
2016 }
2017 }
2018
2019
2020 // We maintain a list of in-use monitors for each thread.
2021 //
2022 // For safepoint based deflation:
2023 // deflate_thread_local_monitors() scans a single thread's in-use list, while
2024 // deflate_idle_monitors() scans only a global list of in-use monitors which
2025 // is populated only as a thread dies (see om_flush()).
2026 //
2027 // These operations are called at all safepoints, immediately after mutators
2028 // are stopped, but before any objects have moved. Collectively they traverse
2029 // the population of in-use monitors, deflating where possible. The scavenged
2030 // monitors are returned to the global monitor free list.
2031 //
2032 // Beware that we scavenge at *every* stop-the-world point. Having a large
2033 // number of monitors in-use could negatively impact performance. We also want
2034 // to minimize the total # of monitors in circulation, as they incur a small
2035 // footprint penalty.
2036 //
2037 // Perversely, the heap size -- and thus the STW safepoint rate --
2038 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
2039 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
2040 // This is an unfortunate aspect of this design.
2041 //
2042 // For async deflation:
2043 // If a special deflation request is made, then the safepoint based
2044 // deflation mechanism is used. Otherwise, an async deflation request
2045 // is registered with the ServiceThread and it is notified.
2046
2047 void ObjectSynchronizer::do_safepoint_work(DeflateMonitorCounters* counters) {
2048 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2049
2050 // The per-thread in-use lists are handled in
2051 // ParallelSPCleanupThreadClosure::do_thread().
2052
2053 if (!AsyncDeflateIdleMonitors) {
2054 // Use the older mechanism for the global in-use list.
2055 ObjectSynchronizer::deflate_idle_monitors(counters);
2056 return;
2057 }
2058
2059 log_debug(monitorinflation)("requesting async deflation of idle monitors.");
2060 // Request deflation of idle monitors by the ServiceThread:
2061 set_is_async_deflation_requested(true);
2062 MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
2063 ml.notify_all();
2064
2065 if (log_is_enabled(Debug, monitorinflation)) {
2066 // exit_globals()'s call to audit_and_print_stats() is done
2067 // at the Info level and not at a safepoint.
2068 // For safepoint based deflation, audit_and_print_stats() is called
2069 // in ObjectSynchronizer::finish_deflate_idle_monitors() at the
2070 // Debug level at a safepoint.
2071 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2072 }
2073 }
2074
2075 // Deflate a single monitor if not in-use
2076 // Return true if deflated, false if in-use
2077 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
2078 ObjectMonitor** free_head_p,
2079 ObjectMonitor** free_tail_p) {
2080 bool deflated;
2081 // Normal case ... The monitor is associated with obj.
2082 const markWord mark = obj->mark();
2083 guarantee(mark == markWord::encode(mid), "should match: mark="
2084 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(),
2085 markWord::encode(mid).value());
2086 // Make sure that mark.monitor() and markWord::encode() agree:
2087 guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
2088 ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid));
2089 const markWord dmw = mid->header();
2090 guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
2091
2092 if (mid->is_busy()) {
2093 // Easy checks are first - the ObjectMonitor is busy so no deflation.
2094 deflated = false;
2095 } else {
2096 // Deflate the monitor if it is no longer being used
2097 // It's idle - scavenge and return to the global free list
2098 // plain old deflation ...
2099 if (log_is_enabled(Trace, monitorinflation)) {
2100 ResourceMark rm;
2101 log_trace(monitorinflation)("deflate_monitor: "
2102 "object=" INTPTR_FORMAT ", mark="
2103 INTPTR_FORMAT ", type='%s'", p2i(obj),
2104 mark.value(), obj->klass()->external_name());
2105 }
2106
2107 // Restore the header back to obj
2108 obj->release_set_mark(dmw);
2109 if (AsyncDeflateIdleMonitors) {
2110 // clear() expects the owner field to be NULL.
2111 // DEFLATER_MARKER is the only non-NULL value we should see here.
2112 mid->try_set_owner_from(DEFLATER_MARKER, NULL);
2113 }
2114 mid->clear();
2115
2116 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
2117 p2i(mid->object()));
2118 assert(mid->is_free(), "invariant");
2119
2120 // Move the deflated ObjectMonitor to the working free list
2121 // defined by free_head_p and free_tail_p.
2122 if (*free_head_p == NULL) *free_head_p = mid;
2123 if (*free_tail_p != NULL) {
2124 // We append to the list so the caller can use mid->_next_om
2125 // to fix the linkages in its context.
2126 ObjectMonitor* prevtail = *free_tail_p;
2127 // Should have been cleaned up by the caller:
2128 // Note: Should not have to lock prevtail here since we're at a
2129 // safepoint and ObjectMonitors on the local free list should
2130 // not be accessed in parallel.
2131 #ifdef ASSERT
2132 ObjectMonitor* l_next_om = prevtail->next_om();
2133 #endif
2134 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2135 prevtail->set_next_om(mid);
2136 }
2137 *free_tail_p = mid;
2138 // At this point, mid->_next_om still refers to its current
2139 // value and another ObjectMonitor's _next_om field still
2140 // refers to this ObjectMonitor. Those linkages have to be
2141 // cleaned up by the caller who has the complete context.
2142 deflated = true;
2143 }
2144 return deflated;
2145 }
2146
2147 // Deflate the specified ObjectMonitor if not in-use using a JavaThread.
2148 // Returns true if it was deflated and false otherwise.
2149 //
2150 // The async deflation protocol sets owner to DEFLATER_MARKER and
2151 // makes contentions negative as signals to contending threads that
2152 // an async deflation is in progress. There are a number of checks
2153 // as part of the protocol to make sure that the calling thread has
2154 // not lost the race to a contending thread.
2155 //
2156 // The ObjectMonitor has been successfully async deflated when:
2157 // (contentions < 0)
2158 // Contending threads that see that condition know to retry their operation.
2159 //
2160 bool ObjectSynchronizer::deflate_monitor_using_JT(ObjectMonitor* mid,
2161 ObjectMonitor** free_head_p,
2162 ObjectMonitor** free_tail_p) {
2163 assert(AsyncDeflateIdleMonitors, "sanity check");
2164 assert(Thread::current()->is_Java_thread(), "precondition");
2165 // A newly allocated ObjectMonitor should not be seen here so we
2166 // avoid an endless inflate/deflate cycle.
2167 assert(mid->is_old(), "must be old: allocation_state=%d",
2168 (int) mid->allocation_state());
2169
2170 if (mid->is_busy()) {
2171 // Easy checks are first - the ObjectMonitor is busy so no deflation.
2172 return false;
2173 }
2174
2175 // Set a NULL owner to DEFLATER_MARKER to force any contending thread
2176 // through the slow path. This is just the first part of the async
2177 // deflation dance.
2178 if (mid->try_set_owner_from(NULL, DEFLATER_MARKER) != NULL) {
2179 // The owner field is no longer NULL so we lost the race since the
2180 // ObjectMonitor is now busy.
2181 return false;
2182 }
2183
2184 if (mid->contentions() > 0 || mid->_waiters != 0) {
2185 // Another thread has raced to enter the ObjectMonitor after
2186 // mid->is_busy() above or has already entered and waited on
2187 // it which makes it busy so no deflation. Restore owner to
2188 // NULL if it is still DEFLATER_MARKER.
2189 if (mid->try_set_owner_from(DEFLATER_MARKER, NULL) != DEFLATER_MARKER) {
2190 // Deferred decrement for the JT EnterI() that cancelled the async deflation.
2191 mid->add_to_contentions(-1);
2192 }
2193 return false;
2194 }
2195
2196 // Make a zero contentions field negative to force any contending threads
2197 // to retry. This is the second part of the async deflation dance.
2198 if (Atomic::cmpxchg(&mid->_contentions, (jint)0, -max_jint) != 0) {
2199 // Contentions was no longer 0 so we lost the race since the
2200 // ObjectMonitor is now busy. Restore owner to NULL if it is
2201 // still DEFLATER_MARKER:
2202 if (mid->try_set_owner_from(DEFLATER_MARKER, NULL) != DEFLATER_MARKER) {
2203 // Deferred decrement for the JT EnterI() that cancelled the async deflation.
2204 mid->add_to_contentions(-1);
2205 }
2206 return false;
2207 }
2208
2209 // Sanity checks for the races:
2210 guarantee(mid->owner_is_DEFLATER_MARKER(), "must be deflater marker");
2211 guarantee(mid->contentions() < 0, "must be negative: contentions=%d",
2212 mid->contentions());
2213 guarantee(mid->_waiters == 0, "must be 0: waiters=%d", mid->_waiters);
2214 guarantee(mid->_cxq == NULL, "must be no contending threads: cxq="
2215 INTPTR_FORMAT, p2i(mid->_cxq));
2216 guarantee(mid->_EntryList == NULL,
2217 "must be no entering threads: EntryList=" INTPTR_FORMAT,
2218 p2i(mid->_EntryList));
2219
2220 const oop obj = (oop) mid->object();
2221 if (log_is_enabled(Trace, monitorinflation)) {
2222 ResourceMark rm;
2223 log_trace(monitorinflation)("deflate_monitor_using_JT: "
2224 "object=" INTPTR_FORMAT ", mark="
2225 INTPTR_FORMAT ", type='%s'",
2226 p2i(obj), obj->mark().value(),
2227 obj->klass()->external_name());
2228 }
2229
2230 // Install the old mark word if nobody else has already done it.
2231 mid->install_displaced_markword_in_object(obj);
2232 mid->clear_common();
2233
2234 assert(mid->object() == NULL, "must be NULL: object=" INTPTR_FORMAT,
2235 p2i(mid->object()));
2236 assert(mid->is_free(), "must be free: allocation_state=%d",
2237 (int)mid->allocation_state());
2238
2239 // Move the deflated ObjectMonitor to the working free list
2240 // defined by free_head_p and free_tail_p.
2241 if (*free_head_p == NULL) {
2242 // First one on the list.
2243 *free_head_p = mid;
2244 }
2245 if (*free_tail_p != NULL) {
2246 // We append to the list so the caller can use mid->_next_om
2247 // to fix the linkages in its context.
2248 ObjectMonitor* prevtail = *free_tail_p;
2249 // prevtail should have been cleaned up by the caller:
2250 #ifdef ASSERT
2251 ObjectMonitor* l_next_om = unmarked_next(prevtail);
2252 #endif
2253 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2254 om_lock(prevtail);
2255 prevtail->set_next_om(mid); // prevtail now points to mid (and is unlocked)
2256 }
2257 *free_tail_p = mid;
2258
2259 // At this point, mid->_next_om still refers to its current
2260 // value and another ObjectMonitor's _next_om field still
2261 // refers to this ObjectMonitor. Those linkages have to be
2262 // cleaned up by the caller who has the complete context.
2263
2264 // We leave owner == DEFLATER_MARKER and contentions < 0
2265 // to force any racing threads to retry.
2266 return true; // Success, ObjectMonitor has been deflated.
2267 }
2268
2269 // Walk a given monitor list, and deflate idle monitors.
2270 // The given list could be a per-thread list or a global list.
2271 //
2272 // In the case of parallel processing of thread local monitor lists,
2273 // work is done by Threads::parallel_threads_do() which ensures that
2274 // each Java thread is processed by exactly one worker thread, and
2275 // thus avoid conflicts that would arise when worker threads would
2276 // process the same monitor lists concurrently.
2277 //
2278 // See also ParallelSPCleanupTask and
2279 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
2280 // Threads::parallel_java_threads_do() in thread.cpp.
2281 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** list_p,
2282 int* count_p,
2283 ObjectMonitor** free_head_p,
2284 ObjectMonitor** free_tail_p) {
2285 ObjectMonitor* cur_mid_in_use = NULL;
2286 ObjectMonitor* mid = NULL;
2287 ObjectMonitor* next = NULL;
2288 int deflated_count = 0;
2289
2290 // This list walk executes at a safepoint and does not race with any
2291 // other list walkers.
2292
2293 for (mid = Atomic::load(list_p); mid != NULL; mid = next) {
2294 next = unmarked_next(mid);
2295 oop obj = (oop) mid->object();
2296 if (obj != NULL && deflate_monitor(mid, obj, free_head_p, free_tail_p)) {
2297 // Deflation succeeded and already updated free_head_p and
2298 // free_tail_p as needed. Finish the move to the local free list
2299 // by unlinking mid from the global or per-thread in-use list.
2300 if (cur_mid_in_use == NULL) {
2301 // mid is the list head so switch the list head to next:
2302 Atomic::store(list_p, next);
2303 } else {
2304 // Switch cur_mid_in_use's next field to next:
2305 cur_mid_in_use->set_next_om(next);
2306 }
2307 // At this point mid is disconnected from the in-use list.
2308 deflated_count++;
2309 Atomic::dec(count_p);
2310 // mid is current tail in the free_head_p list so NULL terminate it:
2311 mid->set_next_om(NULL);
2312 } else {
2313 cur_mid_in_use = mid;
2314 }
2315 }
2316 return deflated_count;
2317 }
2318
2319 // Walk a given ObjectMonitor list and deflate idle ObjectMonitors using
2320 // a JavaThread. Returns the number of deflated ObjectMonitors. The given
2321 // list could be a per-thread in-use list or the global in-use list.
2322 // If a safepoint has started, then we save state via saved_mid_in_use_p
2323 // and return to the caller to honor the safepoint.
2324 //
2325 int ObjectSynchronizer::deflate_monitor_list_using_JT(ObjectMonitor** list_p,
2326 int* count_p,
2327 ObjectMonitor** free_head_p,
2328 ObjectMonitor** free_tail_p,
2329 ObjectMonitor** saved_mid_in_use_p) {
2330 assert(AsyncDeflateIdleMonitors, "sanity check");
2331 JavaThread* self = JavaThread::current();
2332
2333 ObjectMonitor* cur_mid_in_use = NULL;
2334 ObjectMonitor* mid = NULL;
2335 ObjectMonitor* next = NULL;
2336 ObjectMonitor* next_next = NULL;
2337 int deflated_count = 0;
2338 NoSafepointVerifier nsv;
2339
2340 // We use the more complicated lock-cur_mid_in_use-and-mid-as-we-go
2341 // protocol because om_release() can do list deletions in parallel;
2342 // this also prevents races with a list walker thread. We also
2343 // lock-next-next-as-we-go to prevent an om_flush() that is behind
2344 // this thread from passing us.
2345 if (*saved_mid_in_use_p == NULL) {
2346 // No saved state so start at the beginning.
2347 // Lock the list head so we can possibly deflate it:
2348 if ((mid = get_list_head_locked(list_p)) == NULL) {
2349 return 0; // The list is empty so nothing to deflate.
2350 }
2351 next = unmarked_next(mid);
2352 } else {
2353 // We're restarting after a safepoint so restore the necessary state
2354 // before we resume.
2355 cur_mid_in_use = *saved_mid_in_use_p;
2356 // Lock cur_mid_in_use so we can possibly update its
2357 // next field to extract a deflated ObjectMonitor.
2358 om_lock(cur_mid_in_use);
2359 mid = unmarked_next(cur_mid_in_use);
2360 if (mid == NULL) {
2361 om_unlock(cur_mid_in_use);
2362 *saved_mid_in_use_p = NULL;
2363 return 0; // The remainder is empty so nothing more to deflate.
2364 }
2365 // Lock mid so we can possibly deflate it:
2366 om_lock(mid);
2367 next = unmarked_next(mid);
2368 }
2369
2370 while (true) {
2371 // The current mid is locked at this point. If we have a
2372 // cur_mid_in_use, then it is also locked at this point.
2373
2374 if (next != NULL) {
2375 // We lock next so that an om_flush() thread that is behind us
2376 // cannot pass us when we unlock the current mid.
2377 om_lock(next);
2378 next_next = unmarked_next(next);
2379 }
2380
2381 // Only try to deflate if there is an associated Java object and if
2382 // mid is old (is not newly allocated and is not newly freed).
2383 if (mid->object() != NULL && mid->is_old() &&
2384 deflate_monitor_using_JT(mid, free_head_p, free_tail_p)) {
2385 // Deflation succeeded and already updated free_head_p and
2386 // free_tail_p as needed. Finish the move to the local free list
2387 // by unlinking mid from the global or per-thread in-use list.
2388 if (cur_mid_in_use == NULL) {
2389 // mid is the list head and it is locked. Switch the list head
2390 // to next which is also locked (if not NULL) and also leave
2391 // mid locked:
2392 Atomic::store(list_p, next);
2393 } else {
2394 ObjectMonitor* locked_next = mark_om_ptr(next);
2395 // mid and cur_mid_in_use are locked. Switch cur_mid_in_use's
2396 // next field to locked_next and also leave mid locked:
2397 cur_mid_in_use->set_next_om(locked_next);
2398 }
2399 // At this point mid is disconnected from the in-use list so
2400 // its lock longer has any effects on in-use list.
2401 deflated_count++;
2402 Atomic::dec(count_p);
2403 // mid is current tail in the free_head_p list so NULL terminate it
2404 // (which also unlocks it):
2405 mid->set_next_om(NULL);
2406
2407 // All the list management is done so move on to the next one:
2408 mid = next; // mid keeps non-NULL next's locked state
2409 next = next_next;
2410 } else {
2411 // mid is considered in-use if it does not have an associated
2412 // Java object or mid is not old or deflation did not succeed.
2413 // A mid->is_new() node can be seen here when it is freshly
2414 // returned by om_alloc() (and skips the deflation code path).
2415 // A mid->is_old() node can be seen here when deflation failed.
2416 // A mid->is_free() node can be seen here when a fresh node from
2417 // om_alloc() is released by om_release() due to losing the race
2418 // in inflate().
2419
2420 // All the list management is done so move on to the next one:
2421 if (cur_mid_in_use != NULL) {
2422 om_unlock(cur_mid_in_use);
2423 }
2424 // The next cur_mid_in_use keeps mid's lock state so
2425 // that it is stable for a possible next field change. It
2426 // cannot be modified by om_release() while it is locked.
2427 cur_mid_in_use = mid;
2428 mid = next; // mid keeps non-NULL next's locked state
2429 next = next_next;
2430
2431 if (SafepointMechanism::should_block(self) &&
2432 cur_mid_in_use != Atomic::load(list_p) && cur_mid_in_use->is_old()) {
2433 // If a safepoint has started and cur_mid_in_use is not the list
2434 // head and is old, then it is safe to use as saved state. Return
2435 // to the caller before blocking.
2436 *saved_mid_in_use_p = cur_mid_in_use;
2437 om_unlock(cur_mid_in_use);
2438 if (mid != NULL) {
2439 om_unlock(mid);
2440 }
2441 return deflated_count;
2442 }
2443 }
2444 if (mid == NULL) {
2445 if (cur_mid_in_use != NULL) {
2446 om_unlock(cur_mid_in_use);
2447 }
2448 break; // Reached end of the list so nothing more to deflate.
2449 }
2450
2451 // The current mid's next field is locked at this point. If we have
2452 // a cur_mid_in_use, then it is also locked at this point.
2453 }
2454 // We finished the list without a safepoint starting so there's
2455 // no need to save state.
2456 *saved_mid_in_use_p = NULL;
2457 return deflated_count;
2458 }
2459
2460 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2461 counters->n_in_use = 0; // currently associated with objects
2462 counters->n_in_circulation = 0; // extant
2463 counters->n_scavenged = 0; // reclaimed (global and per-thread)
2464 counters->per_thread_scavenged = 0; // per-thread scavenge total
2465 counters->per_thread_times = 0.0; // per-thread scavenge times
2466 }
2467
2468 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
2469 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2470
2471 if (AsyncDeflateIdleMonitors) {
2472 // Nothing to do when global idle ObjectMonitors are deflated using
2473 // a JavaThread.
2474 return;
2475 }
2476
2477 bool deflated = false;
2478
2479 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
2480 ObjectMonitor* free_tail_p = NULL;
2481 elapsedTimer timer;
2482
2483 if (log_is_enabled(Info, monitorinflation)) {
2484 timer.start();
2485 }
2486
2487 // Note: the thread-local monitors lists get deflated in
2488 // a separate pass. See deflate_thread_local_monitors().
2489
2490 // For moribund threads, scan om_list_globals._in_use_list
2491 int deflated_count = 0;
2492 if (Atomic::load(&om_list_globals._in_use_list) != NULL) {
2493 // Update n_in_circulation before om_list_globals._in_use_count is
2494 // updated by deflation.
2495 Atomic::add(&counters->n_in_circulation,
2496 Atomic::load(&om_list_globals._in_use_count));
2497
2498 deflated_count = deflate_monitor_list(&om_list_globals._in_use_list,
2499 &om_list_globals._in_use_count,
2500 &free_head_p, &free_tail_p);
2501 Atomic::add(&counters->n_in_use, Atomic::load(&om_list_globals._in_use_count));
2502 }
2503
2504 if (free_head_p != NULL) {
2505 // Move the deflated ObjectMonitors back to the global free list.
2506 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
2507 #ifdef ASSERT
2508 ObjectMonitor* l_next_om = free_tail_p->next_om();
2509 #endif
2510 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2511 prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count);
2512 Atomic::add(&counters->n_scavenged, deflated_count);
2513 }
2514 timer.stop();
2515
2516 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2517 LogStreamHandle(Info, monitorinflation) lsh_info;
2518 LogStream* ls = NULL;
2519 if (log_is_enabled(Debug, monitorinflation)) {
2520 ls = &lsh_debug;
2521 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2522 ls = &lsh_info;
2523 }
2524 if (ls != NULL) {
2525 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2526 }
2527 }
2528
2529 class HandshakeForDeflation : public HandshakeClosure {
2530 public:
2531 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
2532
2533 void do_thread(Thread* thread) {
2534 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
2535 INTPTR_FORMAT, p2i(thread));
2536 }
2537 };
2538
2539 void ObjectSynchronizer::deflate_idle_monitors_using_JT() {
2540 assert(AsyncDeflateIdleMonitors, "sanity check");
2541
2542 // Deflate any global idle monitors.
2543 deflate_global_idle_monitors_using_JT();
2544
2545 int count = 0;
2546 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2547 if (Atomic::load(&jt->om_in_use_count) > 0 && !jt->is_exiting()) {
2548 // This JavaThread is using ObjectMonitors so deflate any that
2549 // are idle unless this JavaThread is exiting; do not race with
2550 // ObjectSynchronizer::om_flush().
2551 deflate_per_thread_idle_monitors_using_JT(jt);
2552 count++;
2553 }
2554 }
2555 if (count > 0) {
2556 log_debug(monitorinflation)("did async deflation of idle monitors for %d thread(s).", count);
2557 }
2558
2559 log_info(monitorinflation)("async global_population=%d, global_in_use_count=%d, "
2560 "global_free_count=%d, global_wait_count=%d",
2561 Atomic::load(&om_list_globals._population),
2562 Atomic::load(&om_list_globals._in_use_count),
2563 Atomic::load(&om_list_globals._free_count),
2564 Atomic::load(&om_list_globals._wait_count));
2565
2566 // The ServiceThread's async deflation request has been processed.
2567 _last_async_deflation_time_ns = os::javaTimeNanos();
2568 set_is_async_deflation_requested(false);
2569
2570 if (Atomic::load(&om_list_globals._wait_count) > 0) {
2571 // There are deflated ObjectMonitors waiting for a handshake
2572 // (or a safepoint) for safety.
2573
2574 ObjectMonitor* list = Atomic::load(&om_list_globals._wait_list);
2575 ADIM_guarantee(list != NULL, "om_list_globals._wait_list must not be NULL");
2576 int count = Atomic::load(&om_list_globals._wait_count);
2577 Atomic::store(&om_list_globals._wait_count, 0);
2578 Atomic::store(&om_list_globals._wait_list, (ObjectMonitor*)NULL);
2579
2580 // Find the tail for prepend_list_to_common(). No need to mark
2581 // ObjectMonitors for this list walk since only the deflater
2582 // thread manages the wait list.
2583 int l_count = 0;
2584 ObjectMonitor* tail = NULL;
2585 for (ObjectMonitor* n = list; n != NULL; n = unmarked_next(n)) {
2586 tail = n;
2587 l_count++;
2588 }
2589 ADIM_guarantee(count == l_count, "count=%d != l_count=%d", count, l_count);
2590
2591 // Will execute a safepoint if !ThreadLocalHandshakes:
2592 HandshakeForDeflation hfd_hc;
2593 Handshake::execute(&hfd_hc);
2594
2595 prepend_list_to_common(list, tail, count, &om_list_globals._free_list,
2596 &om_list_globals._free_count);
2597
2598 log_info(monitorinflation)("moved %d idle monitors from global waiting list to global free list", count);
2599 }
2600 }
2601
2602 // Deflate global idle ObjectMonitors using a JavaThread.
2603 //
2604 void ObjectSynchronizer::deflate_global_idle_monitors_using_JT() {
2605 assert(AsyncDeflateIdleMonitors, "sanity check");
2606 assert(Thread::current()->is_Java_thread(), "precondition");
2607 JavaThread* self = JavaThread::current();
2608
2609 deflate_common_idle_monitors_using_JT(true /* is_global */, self);
2610 }
2611
2612 // Deflate the specified JavaThread's idle ObjectMonitors using a JavaThread.
2613 //
2614 void ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT(JavaThread* target) {
2615 assert(AsyncDeflateIdleMonitors, "sanity check");
2616 assert(Thread::current()->is_Java_thread(), "precondition");
2617
2618 deflate_common_idle_monitors_using_JT(false /* !is_global */, target);
2619 }
2620
2621 // Deflate global or per-thread idle ObjectMonitors using a JavaThread.
2622 //
2623 void ObjectSynchronizer::deflate_common_idle_monitors_using_JT(bool is_global, JavaThread* target) {
2624 JavaThread* self = JavaThread::current();
2625
2626 int deflated_count = 0;
2627 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged ObjectMonitors
2628 ObjectMonitor* free_tail_p = NULL;
2629 ObjectMonitor* saved_mid_in_use_p = NULL;
2630 elapsedTimer timer;
2631
2632 if (log_is_enabled(Info, monitorinflation)) {
2633 timer.start();
2634 }
2635
2636 if (is_global) {
2637 OM_PERFDATA_OP(MonExtant, set_value(Atomic::load(&om_list_globals._in_use_count)));
2638 } else {
2639 OM_PERFDATA_OP(MonExtant, inc(Atomic::load(&target->om_in_use_count)));
2640 }
2641
2642 do {
2643 int local_deflated_count;
2644 if (is_global) {
2645 local_deflated_count =
2646 deflate_monitor_list_using_JT(&om_list_globals._in_use_list,
2647 &om_list_globals._in_use_count,
2648 &free_head_p, &free_tail_p,
2649 &saved_mid_in_use_p);
2650 } else {
2651 local_deflated_count =
2652 deflate_monitor_list_using_JT(&target->om_in_use_list,
2653 &target->om_in_use_count, &free_head_p,
2654 &free_tail_p, &saved_mid_in_use_p);
2655 }
2656 deflated_count += local_deflated_count;
2657
2658 if (free_head_p != NULL) {
2659 // Move the deflated ObjectMonitors to the global free list.
2660 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);
2661 // Note: The target thread can be doing an om_alloc() that
2662 // is trying to prepend an ObjectMonitor on its in-use list
2663 // at the same time that we have deflated the current in-use
2664 // list head and put it on the local free list. prepend_to_common()
2665 // will detect the race and retry which avoids list corruption,
2666 // but the next field in free_tail_p can flicker to marked
2667 // and then unmarked while prepend_to_common() is sorting it
2668 // all out.
2669 #ifdef ASSERT
2670 ObjectMonitor* l_next_om = unmarked_next(free_tail_p);
2671 #endif
2672 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2673
2674 prepend_list_to_global_wait_list(free_head_p, free_tail_p, local_deflated_count);
2675
2676 OM_PERFDATA_OP(Deflations, inc(local_deflated_count));
2677 }
2678
2679 if (saved_mid_in_use_p != NULL) {
2680 // deflate_monitor_list_using_JT() detected a safepoint starting.
2681 timer.stop();
2682 {
2683 if (is_global) {
2684 log_debug(monitorinflation)("pausing deflation of global idle monitors for a safepoint.");
2685 } else {
2686 log_debug(monitorinflation)("jt=" INTPTR_FORMAT ": pausing deflation of per-thread idle monitors for a safepoint.", p2i(target));
2687 }
2688 assert(SafepointMechanism::should_block(self), "sanity check");
2689 ThreadBlockInVM blocker(self);
2690 }
2691 // Prepare for another loop after the safepoint.
2692 free_head_p = NULL;
2693 free_tail_p = NULL;
2694 if (log_is_enabled(Info, monitorinflation)) {
2695 timer.start();
2696 }
2697 }
2698 } while (saved_mid_in_use_p != NULL);
2699 timer.stop();
2700
2701 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2702 LogStreamHandle(Info, monitorinflation) lsh_info;
2703 LogStream* ls = NULL;
2704 if (log_is_enabled(Debug, monitorinflation)) {
2705 ls = &lsh_debug;
2706 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2707 ls = &lsh_info;
2708 }
2709 if (ls != NULL) {
2710 if (is_global) {
2711 ls->print_cr("async-deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2712 } else {
2713 ls->print_cr("jt=" INTPTR_FORMAT ": async-deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(target), timer.seconds(), deflated_count);
2714 }
2715 }
2716 }
2717
2718 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2719 // Report the cumulative time for deflating each thread's idle
2720 // monitors. Note: if the work is split among more than one
2721 // worker thread, then the reported time will likely be more
2722 // than a beginning to end measurement of the phase.
2723 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged);
2724
2725 if (AsyncDeflateIdleMonitors) {
2726 // Nothing to do when idle ObjectMonitors are deflated using
2727 // a JavaThread.
2728 return;
2729 }
2730
2731 if (log_is_enabled(Debug, monitorinflation)) {
2732 // exit_globals()'s call to audit_and_print_stats() is done
2733 // at the Info level and not at a safepoint.
2734 // For async deflation, audit_and_print_stats() is called in
2735 // ObjectSynchronizer::do_safepoint_work() at the Debug level
2736 // at a safepoint.
2737 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2738 } else if (log_is_enabled(Info, monitorinflation)) {
2739 log_info(monitorinflation)("global_population=%d, global_in_use_count=%d, "
2740 "global_free_count=%d, global_wait_count=%d",
2741 Atomic::load(&om_list_globals._population),
2742 Atomic::load(&om_list_globals._in_use_count),
2743 Atomic::load(&om_list_globals._free_count),
2744 Atomic::load(&om_list_globals._wait_count));
2745 }
2746
2747 OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged));
2748 OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation));
2749
2750 GVars.stw_random = os::random();
2751 GVars.stw_cycle++;
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) {
2758 // Nothing to do when per-thread idle ObjectMonitors are deflated
2759 // using a JavaThread.
2760 return;
2761 }
2762
2763 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
2764 ObjectMonitor* free_tail_p = NULL;
2765 elapsedTimer timer;
2766
2767 if (log_is_enabled(Info, safepoint, cleanup) ||
2768 log_is_enabled(Info, monitorinflation)) {
2769 timer.start();
2770 }
2771
2772 // Update n_in_circulation before om_in_use_count is updated by deflation.
2773 Atomic::add(&counters->n_in_circulation, Atomic::load(&thread->om_in_use_count));
2774
2775 int deflated_count = deflate_monitor_list(&thread->om_in_use_list, &thread->om_in_use_count, &free_head_p, &free_tail_p);
2776 Atomic::add(&counters->n_in_use, Atomic::load(&thread->om_in_use_count));
2777
2778 if (free_head_p != NULL) {
2779 // Move the deflated ObjectMonitors back to the global free list.
2780 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
2781 #ifdef ASSERT
2782 ObjectMonitor* l_next_om = free_tail_p->next_om();
2783 #endif
2784 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2785 prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count);
2786 Atomic::add(&counters->n_scavenged, deflated_count);
2787 Atomic::add(&counters->per_thread_scavenged, deflated_count);
2788 }
2789
2790 timer.stop();
2791 counters->per_thread_times += timer.seconds();
2792
2793 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2794 LogStreamHandle(Info, monitorinflation) lsh_info;
2795 LogStream* ls = NULL;
2796 if (log_is_enabled(Debug, monitorinflation)) {
2797 ls = &lsh_debug;
2798 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2799 ls = &lsh_info;
2800 }
2801 if (ls != NULL) {
2802 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
2803 }
2804 }
2805
2806 // Monitor cleanup on JavaThread::exit
2807
2808 // Iterate through monitor cache and attempt to release thread's monitors
2809 // Gives up on a particular monitor if an exception occurs, but continues
2810 // the overall iteration, swallowing the exception.
2811 class ReleaseJavaMonitorsClosure: public MonitorClosure {
2812 private:
2813 TRAPS;
2814
2815 public:
2816 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
2817 void do_monitor(ObjectMonitor* mid) {
2818 if (mid->owner() == THREAD) {
2819 (void)mid->complete_exit(CHECK);
2820 }
2821 }
2822 };
2823
2824 // Release all inflated monitors owned by THREAD. Lightweight monitors are
2825 // ignored. This is meant to be called during JNI thread detach which assumes
2826 // all remaining monitors are heavyweight. All exceptions are swallowed.
2827 // Scanning the extant monitor list can be time consuming.
2828 // A simple optimization is to add a per-thread flag that indicates a thread
2829 // called jni_monitorenter() during its lifetime.
2830 //
2831 // Instead of No_Savepoint_Verifier it might be cheaper to
2832 // use an idiom of the form:
2833 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
2834 // <code that must not run at safepoint>
2835 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
2836 // Since the tests are extremely cheap we could leave them enabled
2837 // for normal product builds.
2838
2839 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
2840 assert(THREAD == JavaThread::current(), "must be current Java thread");
2841 NoSafepointVerifier nsv;
2842 ReleaseJavaMonitorsClosure rjmc(THREAD);
2843 ObjectSynchronizer::monitors_iterate(&rjmc);
2844 THREAD->clear_pending_exception();
2845 }
2846
2847 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
2848 switch (cause) {
2849 case inflate_cause_vm_internal: return "VM Internal";
2850 case inflate_cause_monitor_enter: return "Monitor Enter";
2851 case inflate_cause_wait: return "Monitor Wait";
2852 case inflate_cause_notify: return "Monitor Notify";
2853 case inflate_cause_hash_code: return "Monitor Hash Code";
2854 case inflate_cause_jni_enter: return "JNI Monitor Enter";
2855 case inflate_cause_jni_exit: return "JNI Monitor Exit";
2856 default:
2857 ShouldNotReachHere();
2858 }
2859 return "Unknown";
2860 }
2861
2862 //------------------------------------------------------------------------------
2863 // Debugging code
2864
2865 u_char* ObjectSynchronizer::get_gvars_addr() {
2866 return (u_char*)&GVars;
2867 }
2868
2869 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
2870 return (u_char*)&GVars.hc_sequence;
2871 }
2872
2873 size_t ObjectSynchronizer::get_gvars_size() {
2874 return sizeof(SharedGlobals);
2875 }
2876
2877 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
2878 return (u_char*)&GVars.stw_random;
2879 }
2880
2881 // This function can be called at a safepoint or it can be called when
2882 // we are trying to exit the VM. When we are trying to exit the VM, the
2883 // list walker functions can run in parallel with the other list
2884 // operations so spin-locking is used for safety.
2885 //
2886 // Calls to this function can be added in various places as a debugging
2887 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
2888 // details logged at the Info level and 'false' for the 'on_exit'
2889 // parameter to have in-use monitor details logged at the Trace level.
2890 // deflate_monitor_list() no longer uses spin-locking so be careful
2891 // when adding audit_and_print_stats() calls at a safepoint.
2892 //
2893 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
2894 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
2895
2896 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2897 LogStreamHandle(Info, monitorinflation) lsh_info;
2898 LogStreamHandle(Trace, monitorinflation) lsh_trace;
2899 LogStream* ls = NULL;
2900 if (log_is_enabled(Trace, monitorinflation)) {
2901 ls = &lsh_trace;
2902 } else if (log_is_enabled(Debug, monitorinflation)) {
2903 ls = &lsh_debug;
2904 } else if (log_is_enabled(Info, monitorinflation)) {
2905 ls = &lsh_info;
2906 }
2907 assert(ls != NULL, "sanity check");
2908
2909 // Log counts for the global and per-thread monitor lists:
2910 int chk_om_population = log_monitor_list_counts(ls);
2911 int error_cnt = 0;
2912
2913 ls->print_cr("Checking global lists:");
2914
2915 // Check om_list_globals._population:
2916 if (Atomic::load(&om_list_globals._population) == chk_om_population) {
2917 ls->print_cr("global_population=%d equals chk_om_population=%d",
2918 Atomic::load(&om_list_globals._population), chk_om_population);
2919 } else {
2920 // With fine grained locks on the monitor lists, it is possible for
2921 // log_monitor_list_counts() to return a value that doesn't match
2922 // om_list_globals._population. So far a higher value has been
2923 // seen in testing so something is being double counted by
2924 // log_monitor_list_counts().
2925 ls->print_cr("WARNING: global_population=%d is not equal to "
2926 "chk_om_population=%d",
2927 Atomic::load(&om_list_globals._population), chk_om_population);
2928 }
2929
2930 // Check om_list_globals._in_use_list and om_list_globals._in_use_count:
2931 chk_global_in_use_list_and_count(ls, &error_cnt);
2932
2933 // Check om_list_globals._free_list and om_list_globals._free_count:
2934 chk_global_free_list_and_count(ls, &error_cnt);
2935
2936 // Check om_list_globals._wait_list and om_list_globals._wait_count:
2937 chk_global_wait_list_and_count(ls, &error_cnt);
2938
2939 ls->print_cr("Checking per-thread lists:");
2940
2941 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2942 // Check om_in_use_list and om_in_use_count:
2943 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
2944
2945 // Check om_free_list and om_free_count:
2946 chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
2947 }
2948
2949 if (error_cnt == 0) {
2950 ls->print_cr("No errors found in monitor list checks.");
2951 } else {
2952 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
2953 }
2954
2955 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
2956 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
2957 // When exiting this log output is at the Info level. When called
2958 // at a safepoint, this log output is at the Trace level since
2959 // there can be a lot of it.
2960 log_in_use_monitor_details(ls);
2961 }
2962
2963 ls->flush();
2964
2965 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2966 }
2967
2968 // Check a free monitor entry; log any errors.
2969 void ObjectSynchronizer::chk_free_entry(JavaThread* jt, ObjectMonitor* n,
2970 outputStream * out, int *error_cnt_p) {
2971 stringStream ss;
2972 if (n->is_busy()) {
2973 if (jt != NULL) {
2974 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2975 ": free per-thread monitor must not be busy: %s", p2i(jt),
2976 p2i(n), n->is_busy_to_string(&ss));
2977 } else {
2978 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2979 "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
2980 }
2981 *error_cnt_p = *error_cnt_p + 1;
2982 }
2983 if (n->header().value() != 0) {
2984 if (jt != NULL) {
2985 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2986 ": free per-thread monitor must have NULL _header "
2987 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
2988 n->header().value());
2989 *error_cnt_p = *error_cnt_p + 1;
2990 } else if (!AsyncDeflateIdleMonitors) {
2991 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2992 "must have NULL _header field: _header=" INTPTR_FORMAT,
2993 p2i(n), n->header().value());
2994 *error_cnt_p = *error_cnt_p + 1;
2995 }
2996 }
2997 if (n->object() != NULL) {
2998 if (jt != NULL) {
2999 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3000 ": free per-thread monitor must have NULL _object "
3001 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
3002 p2i(n->object()));
3003 } else {
3004 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
3005 "must have NULL _object field: _object=" INTPTR_FORMAT,
3006 p2i(n), p2i(n->object()));
3007 }
3008 *error_cnt_p = *error_cnt_p + 1;
3009 }
3010 }
3011
3012 // Lock the next ObjectMonitor for traversal and unlock the current
3013 // ObjectMonitor. Returns the next ObjectMonitor if there is one.
3014 // Otherwise returns NULL (after unlocking the current ObjectMonitor).
3015 // This function is used by the various list walker functions to
3016 // safely walk a list without allowing an ObjectMonitor to be moved
3017 // to another list in the middle of a walk.
3018 static ObjectMonitor* lock_next_for_traversal(ObjectMonitor* cur) {
3019 assert(is_locked(cur), "cur=" INTPTR_FORMAT " must be locked", p2i(cur));
3020 ObjectMonitor* next = unmarked_next(cur);
3021 if (next == NULL) { // Reached the end of the list.
3022 om_unlock(cur);
3023 return NULL;
3024 }
3025 om_lock(next); // Lock next before unlocking current to keep
3026 om_unlock(cur); // from being by-passed by another thread.
3027 return next;
3028 }
3029
3030 // Check the global free list and count; log the results of the checks.
3031 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
3032 int *error_cnt_p) {
3033 int chk_om_free_count = 0;
3034 ObjectMonitor* cur = NULL;
3035 if ((cur = get_list_head_locked(&om_list_globals._free_list)) != NULL) {
3036 // Marked the global free list head so process the list.
3037 while (true) {
3038 chk_free_entry(NULL /* jt */, cur, out, error_cnt_p);
3039 chk_om_free_count++;
3040
3041 cur = lock_next_for_traversal(cur);
3042 if (cur == NULL) {
3043 break;
3044 }
3045 }
3046 }
3047 int l_free_count = Atomic::load(&om_list_globals._free_count);
3048 if (l_free_count == chk_om_free_count) {
3049 out->print_cr("global_free_count=%d equals chk_om_free_count=%d",
3050 l_free_count, chk_om_free_count);
3051 } else {
3052 // With fine grained locks on om_list_globals._free_list, it
3053 // is possible for an ObjectMonitor to be prepended to
3054 // om_list_globals._free_list after we started calculating
3055 // chk_om_free_count so om_list_globals._free_count may not
3056 // match anymore.
3057 out->print_cr("WARNING: global_free_count=%d is not equal to "
3058 "chk_om_free_count=%d", l_free_count, chk_om_free_count);
3059 }
3060 }
3061
3062 // Check the global wait list and count; log the results of the checks.
3063 void ObjectSynchronizer::chk_global_wait_list_and_count(outputStream * out,
3064 int *error_cnt_p) {
3065 int chk_om_wait_count = 0;
3066 ObjectMonitor* cur = NULL;
3067 if ((cur = get_list_head_locked(&om_list_globals._wait_list)) != NULL) {
3068 // Marked the global wait list head so process the list.
3069 while (true) {
3070 // Rules for om_list_globals._wait_list are the same as for
3071 // om_list_globals._free_list:
3072 chk_free_entry(NULL /* jt */, cur, out, error_cnt_p);
3073 chk_om_wait_count++;
3074
3075 cur = lock_next_for_traversal(cur);
3076 if (cur == NULL) {
3077 break;
3078 }
3079 }
3080 }
3081 if (Atomic::load(&om_list_globals._wait_count) == chk_om_wait_count) {
3082 out->print_cr("global_wait_count=%d equals chk_om_wait_count=%d",
3083 Atomic::load(&om_list_globals._wait_count), chk_om_wait_count);
3084 } else {
3085 out->print_cr("ERROR: global_wait_count=%d is not equal to "
3086 "chk_om_wait_count=%d",
3087 Atomic::load(&om_list_globals._wait_count), chk_om_wait_count);
3088 *error_cnt_p = *error_cnt_p + 1;
3089 }
3090 }
3091
3092 // Check the global in-use list and count; log the results of the checks.
3093 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
3094 int *error_cnt_p) {
3095 int chk_om_in_use_count = 0;
3096 ObjectMonitor* cur = NULL;
3097 if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) {
3098 // Marked the global in-use list head so process the list.
3099 while (true) {
3100 chk_in_use_entry(NULL /* jt */, cur, out, error_cnt_p);
3101 chk_om_in_use_count++;
3102
3103 cur = lock_next_for_traversal(cur);
3104 if (cur == NULL) {
3105 break;
3106 }
3107 }
3108 }
3109 int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
3110 if (l_in_use_count == chk_om_in_use_count) {
3111 out->print_cr("global_in_use_count=%d equals chk_om_in_use_count=%d",
3112 l_in_use_count, chk_om_in_use_count);
3113 } else {
3114 // With fine grained locks on the monitor lists, it is possible for
3115 // an exiting JavaThread to put its in-use ObjectMonitors on the
3116 // global in-use list after chk_om_in_use_count is calculated above.
3117 out->print_cr("WARNING: global_in_use_count=%d is not equal to chk_om_in_use_count=%d",
3118 l_in_use_count, chk_om_in_use_count);
3119 }
3120 }
3121
3122 // Check an in-use monitor entry; log any errors.
3123 void ObjectSynchronizer::chk_in_use_entry(JavaThread* jt, ObjectMonitor* n,
3124 outputStream * out, int *error_cnt_p) {
3125 if (n->header().value() == 0) {
3126 if (jt != NULL) {
3127 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3128 ": in-use per-thread monitor must have non-NULL _header "
3129 "field.", p2i(jt), p2i(n));
3130 } else {
3131 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
3132 "must have non-NULL _header field.", p2i(n));
3133 }
3134 *error_cnt_p = *error_cnt_p + 1;
3135 }
3136 if (n->object() == NULL) {
3137 if (jt != NULL) {
3138 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3139 ": in-use per-thread monitor must have non-NULL _object "
3140 "field.", p2i(jt), p2i(n));
3141 } else {
3142 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
3143 "must have non-NULL _object field.", p2i(n));
3144 }
3145 *error_cnt_p = *error_cnt_p + 1;
3146 }
3147 const oop obj = (oop)n->object();
3148 const markWord mark = obj->mark();
3149 if (!mark.has_monitor()) {
3150 if (jt != NULL) {
3151 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3152 ": in-use per-thread monitor's object does not think "
3153 "it has a monitor: obj=" INTPTR_FORMAT ", mark="
3154 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), mark.value());
3155 } else {
3156 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
3157 "monitor's object does not think it has a monitor: obj="
3158 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
3159 p2i(obj), mark.value());
3160 }
3161 *error_cnt_p = *error_cnt_p + 1;
3162 }
3163 ObjectMonitor* const obj_mon = mark.monitor();
3164 if (n != obj_mon) {
3165 if (jt != NULL) {
3166 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3167 ": in-use per-thread monitor's object does not refer "
3168 "to the same monitor: obj=" INTPTR_FORMAT ", mark="
3169 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
3170 p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
3171 } else {
3172 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
3173 "monitor's object does not refer to the same monitor: obj="
3174 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
3175 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
3176 }
3177 *error_cnt_p = *error_cnt_p + 1;
3178 }
3179 }
3180
3181 // Check the thread's free list and count; log the results of the checks.
3182 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
3183 outputStream * out,
3184 int *error_cnt_p) {
3185 int chk_om_free_count = 0;
3186 ObjectMonitor* cur = NULL;
3187 if ((cur = get_list_head_locked(&jt->om_free_list)) != NULL) {
3188 // Marked the per-thread free list head so process the list.
3189 while (true) {
3190 chk_free_entry(jt, cur, out, error_cnt_p);
3191 chk_om_free_count++;
3192
3193 cur = lock_next_for_traversal(cur);
3194 if (cur == NULL) {
3195 break;
3196 }
3197 }
3198 }
3199 int l_om_free_count = Atomic::load(&jt->om_free_count);
3200 if (l_om_free_count == chk_om_free_count) {
3201 out->print_cr("jt=" INTPTR_FORMAT ": om_free_count=%d equals "
3202 "chk_om_free_count=%d", p2i(jt), l_om_free_count, chk_om_free_count);
3203 } else {
3204 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_free_count=%d is not "
3205 "equal to chk_om_free_count=%d", p2i(jt), l_om_free_count,
3206 chk_om_free_count);
3207 *error_cnt_p = *error_cnt_p + 1;
3208 }
3209 }
3210
3211 // Check the thread's in-use list and count; log the results of the checks.
3212 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
3213 outputStream * out,
3214 int *error_cnt_p) {
3215 int chk_om_in_use_count = 0;
3216 ObjectMonitor* cur = NULL;
3217 if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
3218 // Marked the per-thread in-use list head so process the list.
3219 while (true) {
3220 chk_in_use_entry(jt, cur, out, error_cnt_p);
3221 chk_om_in_use_count++;
3222
3223 cur = lock_next_for_traversal(cur);
3224 if (cur == NULL) {
3225 break;
3226 }
3227 }
3228 }
3229 int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
3230 if (l_om_in_use_count == chk_om_in_use_count) {
3231 out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals "
3232 "chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
3233 chk_om_in_use_count);
3234 } else {
3235 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not "
3236 "equal to chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
3237 chk_om_in_use_count);
3238 *error_cnt_p = *error_cnt_p + 1;
3239 }
3240 }
3241
3242 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
3243 // flags indicate why the entry is in-use, 'object' and 'object type'
3244 // indicate the associated object and its type.
3245 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out) {
3246 stringStream ss;
3247 if (Atomic::load(&om_list_globals._in_use_count) > 0) {
3248 out->print_cr("In-use global monitor info:");
3249 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
3250 out->print_cr("%18s %s %18s %18s",
3251 "monitor", "BHL", "object", "object type");
3252 out->print_cr("================== === ================== ==================");
3253 ObjectMonitor* cur = NULL;
3254 if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) {
3255 // Marked the global in-use list head so process the list.
3256 while (true) {
3257 const oop obj = (oop) cur->object();
3258 const markWord mark = cur->header();
3259 ResourceMark rm;
3260 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(cur),
3261 cur->is_busy() != 0, mark.hash() != 0, cur->owner() != NULL,
3262 p2i(obj), obj->klass()->external_name());
3263 if (cur->is_busy() != 0) {
3264 out->print(" (%s)", cur->is_busy_to_string(&ss));
3265 ss.reset();
3266 }
3267 out->cr();
3268
3269 cur = lock_next_for_traversal(cur);
3270 if (cur == NULL) {
3271 break;
3272 }
3273 }
3274 }
3275 }
3276
3277 out->print_cr("In-use per-thread monitor info:");
3278 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
3279 out->print_cr("%18s %18s %s %18s %18s",
3280 "jt", "monitor", "BHL", "object", "object type");
3281 out->print_cr("================== ================== === ================== ==================");
3282 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
3283 ObjectMonitor* cur = NULL;
3284 if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
3285 // Marked the global in-use list head so process the list.
3286 while (true) {
3287 const oop obj = (oop) cur->object();
3288 const markWord mark = cur->header();
3289 ResourceMark rm;
3290 out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT
3291 " %s", p2i(jt), p2i(cur), cur->is_busy() != 0,
3292 mark.hash() != 0, cur->owner() != NULL, p2i(obj),
3293 obj->klass()->external_name());
3294 if (cur->is_busy() != 0) {
3295 out->print(" (%s)", cur->is_busy_to_string(&ss));
3296 ss.reset();
3297 }
3298 out->cr();
3299
3300 cur = lock_next_for_traversal(cur);
3301 if (cur == NULL) {
3302 break;
3303 }
3304 }
3305 }
3306 }
3307
3308 out->flush();
3309 }
3310
3311 // Log counts for the global and per-thread monitor lists and return
3312 // the population count.
3313 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
3314 int pop_count = 0;
3315 out->print_cr("%18s %10s %10s %10s %10s",
3316 "Global Lists:", "InUse", "Free", "Wait", "Total");
3317 out->print_cr("================== ========== ========== ========== ==========");
3318 int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
3319 int l_free_count = Atomic::load(&om_list_globals._free_count);
3320 int l_wait_count = Atomic::load(&om_list_globals._wait_count);
3321 out->print_cr("%18s %10d %10d %10d %10d", "", l_in_use_count,
3322 l_free_count, l_wait_count,
3323 Atomic::load(&om_list_globals._population));
3324 pop_count += l_in_use_count + l_free_count + l_wait_count;
3325
3326 out->print_cr("%18s %10s %10s %10s",
3327 "Per-Thread Lists:", "InUse", "Free", "Provision");
3328 out->print_cr("================== ========== ========== ==========");
3329
3330 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
3331 int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
3332 int l_om_free_count = Atomic::load(&jt->om_free_count);
3333 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
3334 l_om_in_use_count, l_om_free_count, jt->om_free_provision);
3335 pop_count += l_om_in_use_count + l_om_free_count;
3336 }
3337 return pop_count;
3338 }
3339
3340 #ifndef PRODUCT
3341
3342 // Check if monitor belongs to the monitor cache
3343 // The list is grow-only so it's *relatively* safe to traverse
3344 // the list of extant blocks without taking a lock.
3345
3346 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
3347 PaddedObjectMonitor* block = Atomic::load(&g_block_list);
3348 while (block != NULL) {
3349 assert(block->object() == CHAINMARKER, "must be a block header");
3350 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
3351 address mon = (address)monitor;
3352 address blk = (address)block;
3353 size_t diff = mon - blk;
3354 assert((diff % sizeof(PaddedObjectMonitor)) == 0, "must be aligned");
3355 return 1;
3356 }
3357 // unmarked_next() is not needed with g_block_list (no locking
3358 // used with block linkage _next_om fields).
3359 block = (PaddedObjectMonitor*)block->next_om();
3360 }
3361 return 0;
3362 }
3363
3364 #endif