1 /*
2 * Copyright (c) 1998, 2020, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/vmSymbols.hpp"
27 #include "logging/log.hpp"
28 #include "logging/logStream.hpp"
29 #include "jfr/jfrEvents.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "memory/metaspaceShared.hpp"
32 #include "memory/padded.hpp"
33 #include "memory/resourceArea.hpp"
34 #include "memory/universe.hpp"
35 #include "oops/markWord.hpp"
36 #include "oops/oop.inline.hpp"
37 #include "runtime/atomic.hpp"
38 #include "runtime/biasedLocking.hpp"
39 #include "runtime/handles.inline.hpp"
40 #include "runtime/handshake.hpp"
41 #include "runtime/interfaceSupport.inline.hpp"
42 #include "runtime/mutexLocker.hpp"
43 #include "runtime/objectMonitor.hpp"
44 #include "runtime/objectMonitor.inline.hpp"
45 #include "runtime/osThread.hpp"
46 #include "runtime/safepointMechanism.inline.hpp"
47 #include "runtime/safepointVerifiers.hpp"
48 #include "runtime/sharedRuntime.hpp"
49 #include "runtime/stubRoutines.hpp"
50 #include "runtime/synchronizer.hpp"
51 #include "runtime/thread.inline.hpp"
52 #include "runtime/timer.hpp"
53 #include "runtime/vframe.hpp"
54 #include "runtime/vmThread.hpp"
55 #include "utilities/align.hpp"
56 #include "utilities/dtrace.hpp"
57 #include "utilities/events.hpp"
58 #include "utilities/preserveException.hpp"
59
60 // The "core" versions of monitor enter and exit reside in this file.
61 // The interpreter and compilers contain specialized transliterated
62 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
63 // for instance. If you make changes here, make sure to modify the
64 // interpreter, and both C1 and C2 fast-path inline locking code emission.
65 //
66 // -----------------------------------------------------------------------------
67
68 #ifdef DTRACE_ENABLED
69
70 // Only bother with this argument setup if dtrace is available
71 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
72
73 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
74 char* bytes = NULL; \
75 int len = 0; \
76 jlong jtid = SharedRuntime::get_java_tid(thread); \
77 Symbol* klassname = ((oop)(obj))->klass()->name(); \
78 if (klassname != NULL) { \
79 bytes = (char*)klassname->bytes(); \
80 len = klassname->utf8_length(); \
81 }
82
83 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
84 { \
85 if (DTraceMonitorProbes) { \
86 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
87 HOTSPOT_MONITOR_WAIT(jtid, \
88 (uintptr_t)(monitor), bytes, len, (millis)); \
89 } \
90 }
91
92 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
93 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
94 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
95
96 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
97 { \
98 if (DTraceMonitorProbes) { \
99 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
100 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
101 (uintptr_t)(monitor), bytes, len); \
102 } \
103 }
104
105 #else // ndef DTRACE_ENABLED
106
107 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
108 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
109
110 #endif // ndef DTRACE_ENABLED
111
112 // This exists only as a workaround of dtrace bug 6254741
113 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
114 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
115 return 0;
116 }
117
118 #define NINFLATIONLOCKS 256
119 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
120
121 // global list of blocks of monitors
122 PaddedObjectMonitor* ObjectSynchronizer::g_block_list = NULL;
123 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
124 bool volatile ObjectSynchronizer::_is_special_deflation_requested = false;
125 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
126
127 struct ObjectMonitorListGlobals {
128 char _pad_prefix[OM_CACHE_LINE_SIZE];
129 // These are highly shared list related variables.
130 // To avoid false-sharing they need to be the sole occupants of a cache line.
131
132 // Global ObjectMonitor free list. Newly allocated and deflated
133 // ObjectMonitors are prepended here.
134 ObjectMonitor* _free_list;
135 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
136
137 // Global ObjectMonitor in-use list. When a JavaThread is exiting,
138 // ObjectMonitors on its per-thread in-use list are prepended here.
139 ObjectMonitor* _in_use_list;
140 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
141
142 // Global ObjectMonitor wait list. Deflated ObjectMonitors wait on
143 // this list until after a handshake or a safepoint for platforms
144 // that don't support handshakes. After the handshake or safepoint,
145 // the deflated ObjectMonitors are prepended to free_list.
146 ObjectMonitor* _wait_list;
147 DEFINE_PAD_MINUS_SIZE(3, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
148
149 int _free_count; // # on free_list
150 DEFINE_PAD_MINUS_SIZE(4, OM_CACHE_LINE_SIZE, sizeof(int));
151
152 int _in_use_count; // # on in_use_list
153 DEFINE_PAD_MINUS_SIZE(5, OM_CACHE_LINE_SIZE, sizeof(int));
154
155 int _population; // # Extant -- in circulation
156 DEFINE_PAD_MINUS_SIZE(6, OM_CACHE_LINE_SIZE, sizeof(int));
157
158 int _wait_count; // # on wait_list
159 DEFINE_PAD_MINUS_SIZE(7, OM_CACHE_LINE_SIZE, sizeof(int));
160 };
161 static ObjectMonitorListGlobals om_list_globals;
162
163 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
164
165
166 // =====================> Spin-lock functions
167
168 // ObjectMonitors are not lockable outside of this file. We use spin-locks
169 // implemented using a bit in the _next_om field instead of the heavier
170 // weight locking mechanisms for faster list management.
171
172 #define OM_LOCK_BIT 0x1
173
174 // Return true if the ObjectMonitor is locked.
175 // Otherwise returns false.
176 static bool is_locked(ObjectMonitor* om) {
177 return ((intptr_t)om->next_om() & OM_LOCK_BIT) == OM_LOCK_BIT;
178 }
179
180 // Mark an ObjectMonitor* with OM_LOCK_BIT and return it.
181 static ObjectMonitor* mark_om_ptr(ObjectMonitor* om) {
182 return (ObjectMonitor*)((intptr_t)om | OM_LOCK_BIT);
183 }
184
185 // Return the unmarked next field in an ObjectMonitor. Note: the next
186 // field may or may not have been marked with OM_LOCK_BIT originally.
187 static ObjectMonitor* unmarked_next(ObjectMonitor* om) {
188 return (ObjectMonitor*)((intptr_t)om->next_om() & ~OM_LOCK_BIT);
189 }
190
191 // Try to lock an ObjectMonitor. Returns true if locking was successful.
192 // Otherwise returns false.
193 static bool try_om_lock(ObjectMonitor* om) {
194 // Get current next field without any OM_LOCK_BIT value.
195 ObjectMonitor* next = unmarked_next(om);
196 if (om->try_set_next_om(next, mark_om_ptr(next)) != next) {
197 return false; // Cannot lock the ObjectMonitor.
198 }
199 return true;
200 }
201
202 // Lock an ObjectMonitor.
203 static void om_lock(ObjectMonitor* om) {
204 while (true) {
205 if (try_om_lock(om)) {
206 return;
207 }
208 }
209 }
210
211 // Unlock an ObjectMonitor.
212 static void om_unlock(ObjectMonitor* om) {
213 ObjectMonitor* next = om->next_om();
214 guarantee(((intptr_t)next & OM_LOCK_BIT) == OM_LOCK_BIT, "next=" INTPTR_FORMAT
215 " must have OM_LOCK_BIT=%x set.", p2i(next), OM_LOCK_BIT);
216
217 next = (ObjectMonitor*)((intptr_t)next & ~OM_LOCK_BIT); // Clear OM_LOCK_BIT.
218 om->set_next_om(next);
219 }
220
221 // Get the list head after locking it. Returns the list head or NULL
222 // if the list is empty.
223 static ObjectMonitor* get_list_head_locked(ObjectMonitor** list_p) {
224 while (true) {
225 ObjectMonitor* mid = Atomic::load(list_p);
226 if (mid == NULL) {
227 return NULL; // The list is empty.
228 }
229 if (try_om_lock(mid)) {
230 if (Atomic::load(list_p) != mid) {
231 // The list head changed before we could lock it so we have to retry.
232 om_unlock(mid);
233 continue;
234 }
235 return mid;
236 }
237 }
238 }
239
240 #undef OM_LOCK_BIT
241
242
243 // =====================> List Management functions
244
245 // Prepend a list of ObjectMonitors to the specified *list_p. 'tail' is
246 // the last ObjectMonitor in the list and there are 'count' on the list.
247 // Also updates the specified *count_p.
248 static void prepend_list_to_common(ObjectMonitor* list, ObjectMonitor* tail,
249 int count, ObjectMonitor** list_p,
250 int* count_p) {
251 while (true) {
252 ObjectMonitor* cur = Atomic::load(list_p);
253 // Prepend list to *list_p.
254 if (!try_om_lock(tail)) {
255 // Failed to lock tail due to a list walker so try it all again.
256 continue;
257 }
258 tail->set_next_om(cur); // tail now points to cur (and unlocks tail)
259 if (cur == NULL) {
260 // No potential race with takers or other prependers since
261 // *list_p is empty.
262 if (Atomic::cmpxchg(list_p, cur, list) == cur) {
263 // Successfully switched *list_p to the list value.
264 Atomic::add(count_p, count);
265 break;
266 }
267 // Implied else: try it all again
268 } else {
269 if (!try_om_lock(cur)) {
270 continue; // failed to lock cur so try it all again
271 }
272 // We locked cur so try to switch *list_p to the list value.
273 if (Atomic::cmpxchg(list_p, cur, list) != cur) {
274 // The list head has changed so unlock cur and try again:
275 om_unlock(cur);
276 continue;
277 }
278 Atomic::add(count_p, count);
279 om_unlock(cur);
280 break;
281 }
282 }
283 }
284
285 // Prepend a newly allocated block of ObjectMonitors to g_block_list and
286 // om_list_globals._free_list. Also updates om_list_globals._population
287 // and om_list_globals._free_count.
288 void ObjectSynchronizer::prepend_block_to_lists(PaddedObjectMonitor* new_blk) {
289 // First we handle g_block_list:
290 while (true) {
291 PaddedObjectMonitor* cur = Atomic::load(&g_block_list);
292 // Prepend new_blk to g_block_list. The first ObjectMonitor in
293 // a block is reserved for use as linkage to the next block.
294 new_blk[0].set_next_om(cur);
295 if (Atomic::cmpxchg(&g_block_list, cur, new_blk) == cur) {
296 // Successfully switched g_block_list to the new_blk value.
297 Atomic::add(&om_list_globals._population, _BLOCKSIZE - 1);
298 break;
299 }
300 // Implied else: try it all again
301 }
302
303 // Second we handle om_list_globals._free_list:
304 prepend_list_to_common(new_blk + 1, &new_blk[_BLOCKSIZE - 1], _BLOCKSIZE - 1,
305 &om_list_globals._free_list, &om_list_globals._free_count);
306 }
307
308 // Prepend a list of ObjectMonitors to om_list_globals._free_list.
309 // 'tail' is the last ObjectMonitor in the list and there are 'count'
310 // on the list. Also updates om_list_globals._free_count.
311 static void prepend_list_to_global_free_list(ObjectMonitor* list,
312 ObjectMonitor* tail, int count) {
313 prepend_list_to_common(list, tail, count, &om_list_globals._free_list,
314 &om_list_globals._free_count);
315 }
316
317 // Prepend a list of ObjectMonitors to om_list_globals._wait_list.
318 // 'tail' is the last ObjectMonitor in the list and there are 'count'
319 // on the list. Also updates om_list_globals._wait_count.
320 static void prepend_list_to_global_wait_list(ObjectMonitor* list,
321 ObjectMonitor* tail, int count) {
322 prepend_list_to_common(list, tail, count, &om_list_globals._wait_list,
323 &om_list_globals._wait_count);
324 }
325
326 // Prepend a list of ObjectMonitors to om_list_globals._in_use_list.
327 // 'tail' is the last ObjectMonitor in the list and there are 'count'
328 // on the list. Also updates om_list_globals._in_use_list.
329 static void prepend_list_to_global_in_use_list(ObjectMonitor* list,
330 ObjectMonitor* tail, int count) {
331 prepend_list_to_common(list, tail, count, &om_list_globals._in_use_list,
332 &om_list_globals._in_use_count);
333 }
334
335 // Prepend an ObjectMonitor to the specified list. Also updates
336 // the specified counter.
337 static void prepend_to_common(ObjectMonitor* m, ObjectMonitor** list_p,
338 int* count_p) {
339 while (true) {
340 om_lock(m); // Lock m so we can safely update its next field.
341 ObjectMonitor* cur = NULL;
342 // Lock the list head to guard against races with a list walker
343 // or async deflater thread (which only races in om_in_use_list):
344 if ((cur = get_list_head_locked(list_p)) != NULL) {
345 // List head is now locked so we can safely switch it.
346 m->set_next_om(cur); // m now points to cur (and unlocks m)
347 Atomic::store(list_p, m); // Switch list head to unlocked m.
348 om_unlock(cur);
349 break;
350 }
351 // The list is empty so try to set the list head.
352 assert(cur == NULL, "cur must be NULL: cur=" INTPTR_FORMAT, p2i(cur));
353 m->set_next_om(cur); // m now points to NULL (and unlocks m)
354 if (Atomic::cmpxchg(list_p, cur, m) == cur) {
355 // List head is now unlocked m.
356 break;
357 }
358 // Implied else: try it all again
359 }
360 Atomic::inc(count_p);
361 }
362
363 // Prepend an ObjectMonitor to a per-thread om_free_list.
364 // Also updates the per-thread om_free_count.
365 static void prepend_to_om_free_list(Thread* self, ObjectMonitor* m) {
366 prepend_to_common(m, &self->om_free_list, &self->om_free_count);
367 }
368
369 // Prepend an ObjectMonitor to a per-thread om_in_use_list.
370 // Also updates the per-thread om_in_use_count.
371 static void prepend_to_om_in_use_list(Thread* self, ObjectMonitor* m) {
372 prepend_to_common(m, &self->om_in_use_list, &self->om_in_use_count);
373 }
374
375 // Take an ObjectMonitor from the start of the specified list. Also
376 // decrements the specified counter. Returns NULL if none are available.
377 static ObjectMonitor* take_from_start_of_common(ObjectMonitor** list_p,
378 int* count_p) {
379 ObjectMonitor* take = NULL;
380 // Lock the list head to guard against races with a list walker
381 // or async deflater thread (which only races in om_list_globals._free_list):
382 if ((take = get_list_head_locked(list_p)) == NULL) {
383 return NULL; // None are available.
384 }
385 ObjectMonitor* next = unmarked_next(take);
386 // Switch locked list head to next (which unlocks the list head, but
387 // leaves take locked):
388 Atomic::store(list_p, next);
389 Atomic::dec(count_p);
390 // Unlock take, but leave the next value for any lagging list
391 // walkers. It will get cleaned up when take is prepended to
392 // the in-use list:
393 om_unlock(take);
394 return take;
395 }
396
397 // Take an ObjectMonitor from the start of the om_list_globals._free_list.
398 // Also updates om_list_globals._free_count. Returns NULL if none are
399 // available.
400 static ObjectMonitor* take_from_start_of_global_free_list() {
401 return take_from_start_of_common(&om_list_globals._free_list,
402 &om_list_globals._free_count);
403 }
404
405 // Take an ObjectMonitor from the start of a per-thread free-list.
406 // Also updates om_free_count. Returns NULL if none are available.
407 static ObjectMonitor* take_from_start_of_om_free_list(Thread* self) {
408 return take_from_start_of_common(&self->om_free_list, &self->om_free_count);
409 }
410
411
412 // =====================> Quick functions
413
414 // The quick_* forms are special fast-path variants used to improve
415 // performance. In the simplest case, a "quick_*" implementation could
416 // simply return false, in which case the caller will perform the necessary
417 // state transitions and call the slow-path form.
418 // The fast-path is designed to handle frequently arising cases in an efficient
419 // manner and is just a degenerate "optimistic" variant of the slow-path.
420 // returns true -- to indicate the call was satisfied.
421 // returns false -- to indicate the call needs the services of the slow-path.
422 // A no-loitering ordinance is in effect for code in the quick_* family
423 // operators: safepoints or indefinite blocking (blocking that might span a
424 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
425 // entry.
426 //
427 // Consider: An interesting optimization is to have the JIT recognize the
428 // following common idiom:
429 // synchronized (someobj) { .... ; notify(); }
430 // That is, we find a notify() or notifyAll() call that immediately precedes
431 // the monitorexit operation. In that case the JIT could fuse the operations
432 // into a single notifyAndExit() runtime primitive.
433
434 bool ObjectSynchronizer::quick_notify(oopDesc* obj, Thread* self, bool all) {
435 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
436 assert(self->is_Java_thread(), "invariant");
437 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
438 NoSafepointVerifier nsv;
439 if (obj == NULL) return false; // slow-path for invalid obj
440 const markWord mark = obj->mark();
441
442 if (mark.has_locker() && self->is_lock_owned((address)mark.locker())) {
443 // Degenerate notify
444 // stack-locked by caller so by definition the implied waitset is empty.
445 return true;
446 }
447
448 if (mark.has_monitor()) {
449 ObjectMonitor* const mon = mark.monitor();
450 assert(mon->object() == obj, "invariant");
451 if (mon->owner() != self) return false; // slow-path for IMS exception
452
453 if (mon->first_waiter() != NULL) {
454 // We have one or more waiters. Since this is an inflated monitor
455 // that we own, we can transfer one or more threads from the waitset
456 // to the entrylist here and now, avoiding the slow-path.
457 if (all) {
458 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
459 } else {
460 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
461 }
462 int free_count = 0;
463 do {
464 mon->INotify(self);
465 ++free_count;
466 } while (mon->first_waiter() != NULL && all);
467 OM_PERFDATA_OP(Notifications, inc(free_count));
468 }
469 return true;
470 }
471
472 // biased locking and any other IMS exception states take the slow-path
473 return false;
474 }
475
476
477 // The LockNode emitted directly at the synchronization site would have
478 // been too big if it were to have included support for the cases of inflated
479 // recursive enter and exit, so they go here instead.
480 // Note that we can't safely call AsyncPrintJavaStack() from within
481 // quick_enter() as our thread state remains _in_Java.
482
483 bool ObjectSynchronizer::quick_enter(oop obj, Thread* self,
484 BasicLock * lock) {
485 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
486 assert(self->is_Java_thread(), "invariant");
487 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
488 NoSafepointVerifier nsv;
489 if (obj == NULL) return false; // Need to throw NPE
490
491 const markWord mark = obj->mark();
492
493 if (mark.has_monitor()) {
494 ObjectMonitor* const m = mark.monitor();
495 if (AsyncDeflateIdleMonitors) {
496 // An async deflation can race us before we manage to make the
497 // ObjectMonitor busy by setting the owner below. If we detect
498 // that race we just bail out to the slow-path here.
499 if (m->object() == NULL) {
500 return false;
501 }
502 } else {
503 assert(m->object() == obj, "invariant");
504 }
505 Thread* const owner = (Thread *) m->_owner;
506
507 // Lock contention and Transactional Lock Elision (TLE) diagnostics
508 // and observability
509 // Case: light contention possibly amenable to TLE
510 // Case: TLE inimical operations such as nested/recursive synchronization
511
512 if (owner == self) {
513 m->_recursions++;
514 return true;
515 }
516
517 // This Java Monitor is inflated so obj's header will never be
518 // displaced to this thread's BasicLock. Make the displaced header
519 // non-NULL so this BasicLock is not seen as recursive nor as
520 // being locked. We do this unconditionally so that this thread's
521 // BasicLock cannot be mis-interpreted by any stack walkers. For
522 // performance reasons, stack walkers generally first check for
523 // Biased Locking in the object's header, the second check is for
524 // stack-locking in the object's header, the third check is for
525 // recursive stack-locking in the displaced header in the BasicLock,
526 // and last are the inflated Java Monitor (ObjectMonitor) checks.
527 lock->set_displaced_header(markWord::unused_mark());
528
529 if (owner == NULL && m->try_set_owner_from(NULL, self) == NULL) {
530 assert(m->_recursions == 0, "invariant");
531 return true;
532 }
533 }
534
535 // Note that we could inflate in quick_enter.
536 // This is likely a useful optimization
537 // Critically, in quick_enter() we must not:
538 // -- perform bias revocation, or
539 // -- block indefinitely, or
540 // -- reach a safepoint
541
542 return false; // revert to slow-path
543 }
544
545 // -----------------------------------------------------------------------------
546 // Monitor Enter/Exit
547 // The interpreter and compiler assembly code tries to lock using the fast path
548 // of this algorithm. Make sure to update that code if the following function is
549 // changed. The implementation is extremely sensitive to race condition. Be careful.
550
551 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, TRAPS) {
552 if (UseBiasedLocking) {
553 if (!SafepointSynchronize::is_at_safepoint()) {
554 BiasedLocking::revoke(obj, THREAD);
555 } else {
556 BiasedLocking::revoke_at_safepoint(obj);
557 }
558 }
559
560 markWord mark = obj->mark();
561 assert(!mark.has_bias_pattern(), "should not see bias pattern here");
562
563 if (mark.is_neutral()) {
564 // Anticipate successful CAS -- the ST of the displaced mark must
565 // be visible <= the ST performed by the CAS.
566 lock->set_displaced_header(mark);
567 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
568 return;
569 }
570 // Fall through to inflate() ...
571 } else if (mark.has_locker() &&
572 THREAD->is_lock_owned((address)mark.locker())) {
573 assert(lock != mark.locker(), "must not re-lock the same lock");
574 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
575 lock->set_displaced_header(markWord::from_pointer(NULL));
576 return;
577 }
578
579 // The object header will never be displaced to this lock,
580 // so it does not matter what the value is, except that it
581 // must be non-zero to avoid looking like a re-entrant lock,
582 // and must not look locked either.
583 lock->set_displaced_header(markWord::unused_mark());
584 // An async deflation can race after the inflate() call and before
585 // enter() can make the ObjectMonitor busy. enter() returns false if
586 // we have lost the race to async deflation and we simply try again.
587 while (true) {
588 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_monitor_enter);
589 if (monitor->enter(THREAD)) {
590 return;
591 }
592 }
593 }
594
595 void ObjectSynchronizer::exit(oop object, BasicLock* lock, TRAPS) {
596 markWord mark = object->mark();
597 // We cannot check for Biased Locking if we are racing an inflation.
598 assert(mark == markWord::INFLATING() ||
599 !mark.has_bias_pattern(), "should not see bias pattern here");
600
601 markWord dhw = lock->displaced_header();
602 if (dhw.value() == 0) {
603 // If the displaced header is NULL, then this exit matches up with
604 // a recursive enter. No real work to do here except for diagnostics.
605 #ifndef PRODUCT
606 if (mark != markWord::INFLATING()) {
607 // Only do diagnostics if we are not racing an inflation. Simply
608 // exiting a recursive enter of a Java Monitor that is being
609 // inflated is safe; see the has_monitor() comment below.
610 assert(!mark.is_neutral(), "invariant");
611 assert(!mark.has_locker() ||
612 THREAD->is_lock_owned((address)mark.locker()), "invariant");
613 if (mark.has_monitor()) {
614 // The BasicLock's displaced_header is marked as a recursive
615 // enter and we have an inflated Java Monitor (ObjectMonitor).
616 // This is a special case where the Java Monitor was inflated
617 // after this thread entered the stack-lock recursively. When a
618 // Java Monitor is inflated, we cannot safely walk the Java
619 // Monitor owner's stack and update the BasicLocks because a
620 // Java Monitor can be asynchronously inflated by a thread that
621 // does not own the Java Monitor.
622 ObjectMonitor* m = mark.monitor();
623 assert(((oop)(m->object()))->mark() == mark, "invariant");
624 assert(m->is_entered(THREAD), "invariant");
625 }
626 }
627 #endif
628 return;
629 }
630
631 if (mark == markWord::from_pointer(lock)) {
632 // If the object is stack-locked by the current thread, try to
633 // swing the displaced header from the BasicLock back to the mark.
634 assert(dhw.is_neutral(), "invariant");
635 if (object->cas_set_mark(dhw, mark) == mark) {
636 return;
637 }
638 }
639
640 // We have to take the slow-path of possible inflation and then exit.
641 // The ObjectMonitor* can't be async deflated until ownership is
642 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
643 ObjectMonitor* monitor = inflate(THREAD, object, inflate_cause_vm_internal);
644 monitor->exit(true, THREAD);
645 }
646
647 // -----------------------------------------------------------------------------
648 // Class Loader support to workaround deadlocks on the class loader lock objects
649 // Also used by GC
650 // complete_exit()/reenter() are used to wait on a nested lock
651 // i.e. to give up an outer lock completely and then re-enter
652 // Used when holding nested locks - lock acquisition order: lock1 then lock2
653 // 1) complete_exit lock1 - saving recursion count
654 // 2) wait on lock2
655 // 3) when notified on lock2, unlock lock2
656 // 4) reenter lock1 with original recursion count
657 // 5) lock lock2
658 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
659 intx ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
660 if (UseBiasedLocking) {
661 BiasedLocking::revoke(obj, THREAD);
662 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
663 }
664
665 // The ObjectMonitor* can't be async deflated until ownership is
666 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
667 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
668 intptr_t ret_code = monitor->complete_exit(THREAD);
669 return ret_code;
670 }
671
672 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
673 void ObjectSynchronizer::reenter(Handle obj, intx recursions, TRAPS) {
674 if (UseBiasedLocking) {
675 BiasedLocking::revoke(obj, THREAD);
676 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
677 }
678
679 // An async deflation can race after the inflate() call and before
680 // reenter() -> enter() can make the ObjectMonitor busy. reenter() ->
681 // enter() returns false if we have lost the race to async deflation
682 // and we simply try again.
683 while (true) {
684 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
685 if (monitor->reenter(recursions, THREAD)) {
686 return;
687 }
688 }
689 }
690
691 // -----------------------------------------------------------------------------
692 // JNI locks on java objects
693 // NOTE: must use heavy weight monitor to handle jni monitor enter
694 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
695 // the current locking is from JNI instead of Java code
696 if (UseBiasedLocking) {
697 BiasedLocking::revoke(obj, THREAD);
698 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
699 }
700 THREAD->set_current_pending_monitor_is_from_java(false);
701 // An async deflation can race after the inflate() call and before
702 // enter() can make the ObjectMonitor busy. enter() returns false if
703 // we have lost the race to async deflation and we simply try again.
704 while (true) {
705 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_jni_enter);
706 if (monitor->enter(THREAD)) {
707 break;
708 }
709 }
710 THREAD->set_current_pending_monitor_is_from_java(true);
711 }
712
713 // NOTE: must use heavy weight monitor to handle jni monitor exit
714 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
715 if (UseBiasedLocking) {
716 Handle h_obj(THREAD, obj);
717 BiasedLocking::revoke(h_obj, THREAD);
718 obj = h_obj();
719 }
720 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
721
722 // The ObjectMonitor* can't be async deflated until ownership is
723 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
724 ObjectMonitor* monitor = inflate(THREAD, obj, inflate_cause_jni_exit);
725 // If this thread has locked the object, exit the monitor. We
726 // intentionally do not use CHECK here because we must exit the
727 // monitor even if an exception is pending.
728 if (monitor->check_owner(THREAD)) {
729 monitor->exit(true, THREAD);
730 }
731 }
732
733 // -----------------------------------------------------------------------------
734 // Internal VM locks on java objects
735 // standard constructor, allows locking failures
736 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool do_lock) {
737 _dolock = do_lock;
738 _thread = thread;
739 _thread->check_for_valid_safepoint_state();
740 _obj = obj;
741
742 if (_dolock) {
743 ObjectSynchronizer::enter(_obj, &_lock, _thread);
744 }
745 }
746
747 ObjectLocker::~ObjectLocker() {
748 if (_dolock) {
749 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
750 }
751 }
752
753
754 // -----------------------------------------------------------------------------
755 // Wait/Notify/NotifyAll
756 // NOTE: must use heavy weight monitor to handle wait()
757 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
758 if (UseBiasedLocking) {
759 BiasedLocking::revoke(obj, THREAD);
760 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
761 }
762 if (millis < 0) {
763 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
764 }
765 // The ObjectMonitor* can't be async deflated because the _waiters
766 // field is incremented before ownership is dropped and decremented
767 // after ownership is regained.
768 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
769
770 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
771 monitor->wait(millis, true, THREAD);
772
773 // This dummy call is in place to get around dtrace bug 6254741. Once
774 // that's fixed we can uncomment the following line, remove the call
775 // and change this function back into a "void" func.
776 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
777 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
778 return ret_code;
779 }
780
781 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, jlong millis, TRAPS) {
782 if (UseBiasedLocking) {
783 BiasedLocking::revoke(obj, THREAD);
784 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
785 }
786 if (millis < 0) {
787 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
788 }
789 // The ObjectMonitor* can't be async deflated because the _waiters
790 // field is incremented before ownership is dropped and decremented
791 // after ownership is regained.
792 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
793 monitor->wait(millis, false, THREAD);
794 }
795
796 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
797 if (UseBiasedLocking) {
798 BiasedLocking::revoke(obj, THREAD);
799 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
800 }
801
802 markWord mark = obj->mark();
803 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
804 return;
805 }
806 // The ObjectMonitor* can't be async deflated until ownership is
807 // dropped by the calling thread.
808 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_notify);
809 monitor->notify(THREAD);
810 }
811
812 // NOTE: see comment of notify()
813 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
814 if (UseBiasedLocking) {
815 BiasedLocking::revoke(obj, THREAD);
816 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
817 }
818
819 markWord mark = obj->mark();
820 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
821 return;
822 }
823 // The ObjectMonitor* can't be async deflated until ownership is
824 // dropped by the calling thread.
825 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_notify);
826 monitor->notifyAll(THREAD);
827 }
828
829 // -----------------------------------------------------------------------------
830 // Hash Code handling
831 //
832 // Performance concern:
833 // OrderAccess::storestore() calls release() which at one time stored 0
834 // into the global volatile OrderAccess::dummy variable. This store was
835 // unnecessary for correctness. Many threads storing into a common location
836 // causes considerable cache migration or "sloshing" on large SMP systems.
837 // As such, I avoided using OrderAccess::storestore(). In some cases
838 // OrderAccess::fence() -- which incurs local latency on the executing
839 // processor -- is a better choice as it scales on SMP systems.
840 //
841 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
842 // a discussion of coherency costs. Note that all our current reference
843 // platforms provide strong ST-ST order, so the issue is moot on IA32,
844 // x64, and SPARC.
845 //
846 // As a general policy we use "volatile" to control compiler-based reordering
847 // and explicit fences (barriers) to control for architectural reordering
848 // performed by the CPU(s) or platform.
849
850 struct SharedGlobals {
851 char _pad_prefix[OM_CACHE_LINE_SIZE];
852 // These are highly shared mostly-read variables.
853 // To avoid false-sharing they need to be the sole occupants of a cache line.
854 volatile int stw_random;
855 volatile int stw_cycle;
856 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
857 // Hot RW variable -- Sequester to avoid false-sharing
858 volatile int hc_sequence;
859 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
860 };
861
862 static SharedGlobals GVars;
863 static int _forceMonitorScavenge = 0; // Scavenge required and pending
864
865 static markWord read_stable_mark(oop obj) {
866 markWord mark = obj->mark();
867 if (!mark.is_being_inflated()) {
868 return mark; // normal fast-path return
869 }
870
871 int its = 0;
872 for (;;) {
873 markWord mark = obj->mark();
874 if (!mark.is_being_inflated()) {
875 return mark; // normal fast-path return
876 }
877
878 // The object is being inflated by some other thread.
879 // The caller of read_stable_mark() must wait for inflation to complete.
880 // Avoid live-lock
881 // TODO: consider calling SafepointSynchronize::do_call_back() while
882 // spinning to see if there's a safepoint pending. If so, immediately
883 // yielding or blocking would be appropriate. Avoid spinning while
884 // there is a safepoint pending.
885 // TODO: add inflation contention performance counters.
886 // TODO: restrict the aggregate number of spinners.
887
888 ++its;
889 if (its > 10000 || !os::is_MP()) {
890 if (its & 1) {
891 os::naked_yield();
892 } else {
893 // Note that the following code attenuates the livelock problem but is not
894 // a complete remedy. A more complete solution would require that the inflating
895 // thread hold the associated inflation lock. The following code simply restricts
896 // the number of spinners to at most one. We'll have N-2 threads blocked
897 // on the inflationlock, 1 thread holding the inflation lock and using
898 // a yield/park strategy, and 1 thread in the midst of inflation.
899 // A more refined approach would be to change the encoding of INFLATING
900 // to allow encapsulation of a native thread pointer. Threads waiting for
901 // inflation to complete would use CAS to push themselves onto a singly linked
902 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
903 // and calling park(). When inflation was complete the thread that accomplished inflation
904 // would detach the list and set the markword to inflated with a single CAS and
905 // then for each thread on the list, set the flag and unpark() the thread.
906 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
907 // wakes at most one thread whereas we need to wake the entire list.
908 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
909 int YieldThenBlock = 0;
910 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
911 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
912 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
913 while (obj->mark() == markWord::INFLATING()) {
914 // Beware: NakedYield() is advisory and has almost no effect on some platforms
915 // so we periodically call self->_ParkEvent->park(1).
916 // We use a mixed spin/yield/block mechanism.
917 if ((YieldThenBlock++) >= 16) {
918 Thread::current()->_ParkEvent->park(1);
919 } else {
920 os::naked_yield();
921 }
922 }
923 Thread::muxRelease(gInflationLocks + ix);
924 }
925 } else {
926 SpinPause(); // SMP-polite spinning
927 }
928 }
929 }
930
931 // hashCode() generation :
932 //
933 // Possibilities:
934 // * MD5Digest of {obj,stw_random}
935 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
936 // * A DES- or AES-style SBox[] mechanism
937 // * One of the Phi-based schemes, such as:
938 // 2654435761 = 2^32 * Phi (golden ratio)
939 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
940 // * A variation of Marsaglia's shift-xor RNG scheme.
941 // * (obj ^ stw_random) is appealing, but can result
942 // in undesirable regularity in the hashCode values of adjacent objects
943 // (objects allocated back-to-back, in particular). This could potentially
944 // result in hashtable collisions and reduced hashtable efficiency.
945 // There are simple ways to "diffuse" the middle address bits over the
946 // generated hashCode values:
947
948 static inline intptr_t get_next_hash(Thread* self, oop obj) {
949 intptr_t value = 0;
950 if (hashCode == 0) {
951 // This form uses global Park-Miller RNG.
952 // On MP system we'll have lots of RW access to a global, so the
953 // mechanism induces lots of coherency traffic.
954 value = os::random();
955 } else if (hashCode == 1) {
956 // This variation has the property of being stable (idempotent)
957 // between STW operations. This can be useful in some of the 1-0
958 // synchronization schemes.
959 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
960 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
961 } else if (hashCode == 2) {
962 value = 1; // for sensitivity testing
963 } else if (hashCode == 3) {
964 value = ++GVars.hc_sequence;
965 } else if (hashCode == 4) {
966 value = cast_from_oop<intptr_t>(obj);
967 } else {
968 // Marsaglia's xor-shift scheme with thread-specific state
969 // This is probably the best overall implementation -- we'll
970 // likely make this the default in future releases.
971 unsigned t = self->_hashStateX;
972 t ^= (t << 11);
973 self->_hashStateX = self->_hashStateY;
974 self->_hashStateY = self->_hashStateZ;
975 self->_hashStateZ = self->_hashStateW;
976 unsigned v = self->_hashStateW;
977 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
978 self->_hashStateW = v;
979 value = v;
980 }
981
982 value &= markWord::hash_mask;
983 if (value == 0) value = 0xBAD;
984 assert(value != markWord::no_hash, "invariant");
985 return value;
986 }
987
988 intptr_t ObjectSynchronizer::FastHashCode(Thread* self, oop obj) {
989 if (UseBiasedLocking) {
990 // NOTE: many places throughout the JVM do not expect a safepoint
991 // to be taken here, in particular most operations on perm gen
992 // objects. However, we only ever bias Java instances and all of
993 // the call sites of identity_hash that might revoke biases have
994 // been checked to make sure they can handle a safepoint. The
995 // added check of the bias pattern is to avoid useless calls to
996 // thread-local storage.
997 if (obj->mark().has_bias_pattern()) {
998 // Handle for oop obj in case of STW safepoint
999 Handle hobj(self, obj);
1000 // Relaxing assertion for bug 6320749.
1001 assert(Universe::verify_in_progress() ||
1002 !SafepointSynchronize::is_at_safepoint(),
1003 "biases should not be seen by VM thread here");
1004 BiasedLocking::revoke(hobj, JavaThread::current());
1005 obj = hobj();
1006 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
1007 }
1008 }
1009
1010 // hashCode() is a heap mutator ...
1011 // Relaxing assertion for bug 6320749.
1012 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
1013 !SafepointSynchronize::is_at_safepoint(), "invariant");
1014 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
1015 self->is_Java_thread() , "invariant");
1016 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
1017 ((JavaThread *)self)->thread_state() != _thread_blocked, "invariant");
1018
1019 while (true) {
1020 ObjectMonitor* monitor = NULL;
1021 markWord temp, test;
1022 intptr_t hash;
1023 markWord mark = read_stable_mark(obj);
1024
1025 // object should remain ineligible for biased locking
1026 assert(!mark.has_bias_pattern(), "invariant");
1027
1028 if (mark.is_neutral()) { // if this is a normal header
1029 hash = mark.hash();
1030 if (hash != 0) { // if it has a hash, just return it
1031 return hash;
1032 }
1033 hash = get_next_hash(self, obj); // get a new hash
1034 temp = mark.copy_set_hash(hash); // merge the hash into header
1035 // try to install the hash
1036 test = obj->cas_set_mark(temp, mark);
1037 if (test == mark) { // if the hash was installed, return it
1038 return hash;
1039 }
1040 // Failed to install the hash. It could be that another thread
1041 // installed the hash just before our attempt or inflation has
1042 // occurred or... so we fall thru to inflate the monitor for
1043 // stability and then install the hash.
1044 } else if (mark.has_monitor()) {
1045 // The first stage of a racing async deflation won't affect the
1046 // hash value if this ObjectMonitor happens to already have one.
1047 monitor = mark.monitor();
1048 temp = monitor->header();
1049 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1050 hash = temp.hash();
1051 if (hash != 0) { // if it has a hash, just return it
1052 return hash;
1053 }
1054 // Fall thru so we only have one place that installs the hash in
1055 // the ObjectMonitor.
1056 } else if (self->is_lock_owned((address)mark.locker())) {
1057 // This is a stack lock owned by the calling thread so fetch the
1058 // displaced markWord from the BasicLock on the stack.
1059 temp = mark.displaced_mark_helper();
1060 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1061 hash = temp.hash();
1062 if (hash != 0) { // if it has a hash, just return it
1063 return hash;
1064 }
1065 // WARNING:
1066 // The displaced header in the BasicLock on a thread's stack
1067 // is strictly immutable. It CANNOT be changed in ANY cases.
1068 // So we have to inflate the stack lock into an ObjectMonitor
1069 // even if the current thread owns the lock. The BasicLock on
1070 // a thread's stack can be asynchronously read by other threads
1071 // during an inflate() call so any change to that stack memory
1072 // may not propagate to other threads correctly.
1073 }
1074
1075 // Inflate the monitor to set the hash.
1076
1077 // An async deflation can race after the inflate() call and before we
1078 // can update the ObjectMonitor's header with the hash value below.
1079 monitor = inflate(self, obj, inflate_cause_hash_code);
1080 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1081 mark = monitor->header();
1082 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1083 hash = mark.hash();
1084 if (hash == 0) { // if it does not have a hash
1085 hash = get_next_hash(self, obj); // get a new hash
1086 temp = mark.copy_set_hash(hash); // merge the hash into header
1087 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1088 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1089 test = markWord(v);
1090 if (test != mark) {
1091 // The attempt to update the ObjectMonitor's header/dmw field
1092 // did not work. This can happen if another thread managed to
1093 // merge in the hash just before our cmpxchg().
1094 // If we add any new usages of the header/dmw field, this code
1095 // will need to be updated.
1096 hash = test.hash();
1097 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1098 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1099 }
1100 if (monitor->is_being_async_deflated()) {
1101 // If we detect that async deflation has occurred, then we
1102 // simply retry so that the hash value can be stored in either
1103 // the object's header or in the re-inflated ObjectMonitor's
1104 // header as appropriate.
1105 continue;
1106 }
1107 }
1108 // We finally get the hash.
1109 return hash;
1110 }
1111 }
1112
1113 // Deprecated -- use FastHashCode() instead.
1114
1115 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
1116 return FastHashCode(Thread::current(), obj());
1117 }
1118
1119
1120 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
1121 Handle h_obj) {
1122 if (UseBiasedLocking) {
1123 BiasedLocking::revoke(h_obj, thread);
1124 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1125 }
1126
1127 assert(thread == JavaThread::current(), "Can only be called on current thread");
1128 oop obj = h_obj();
1129
1130 markWord mark = read_stable_mark(obj);
1131
1132 // Uncontended case, header points to stack
1133 if (mark.has_locker()) {
1134 return thread->is_lock_owned((address)mark.locker());
1135 }
1136 // Contended case, header points to ObjectMonitor (tagged pointer)
1137 if (mark.has_monitor()) {
1138 // The first stage of async deflation does not affect any field
1139 // used by this comparison so the ObjectMonitor* is usable here.
1140 ObjectMonitor* monitor = mark.monitor();
1141 return monitor->is_entered(thread) != 0;
1142 }
1143 // Unlocked case, header in place
1144 assert(mark.is_neutral(), "sanity check");
1145 return false;
1146 }
1147
1148 // Be aware of this method could revoke bias of the lock object.
1149 // This method queries the ownership of the lock handle specified by 'h_obj'.
1150 // If the current thread owns the lock, it returns owner_self. If no
1151 // thread owns the lock, it returns owner_none. Otherwise, it will return
1152 // owner_other.
1153 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
1154 (JavaThread *self, Handle h_obj) {
1155 // The caller must beware this method can revoke bias, and
1156 // revocation can result in a safepoint.
1157 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
1158 assert(self->thread_state() != _thread_blocked, "invariant");
1159
1160 // Possible mark states: neutral, biased, stack-locked, inflated
1161
1162 if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) {
1163 // CASE: biased
1164 BiasedLocking::revoke(h_obj, self);
1165 assert(!h_obj->mark().has_bias_pattern(),
1166 "biases should be revoked by now");
1167 }
1168
1169 assert(self == JavaThread::current(), "Can only be called on current thread");
1170 oop obj = h_obj();
1171 markWord mark = read_stable_mark(obj);
1172
1173 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
1174 if (mark.has_locker()) {
1175 return self->is_lock_owned((address)mark.locker()) ?
1176 owner_self : owner_other;
1177 }
1178
1179 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
1180 // The Object:ObjectMonitor relationship is stable as long as we're
1181 // not at a safepoint and AsyncDeflateIdleMonitors is false.
1182 if (mark.has_monitor()) {
1183 // The first stage of async deflation does not affect any field
1184 // used by this comparison so the ObjectMonitor* is usable here.
1185 ObjectMonitor* monitor = mark.monitor();
1186 void* owner = monitor->owner();
1187 if (owner == NULL) return owner_none;
1188 return (owner == self ||
1189 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
1190 }
1191
1192 // CASE: neutral
1193 assert(mark.is_neutral(), "sanity check");
1194 return owner_none; // it's unlocked
1195 }
1196
1197 // FIXME: jvmti should call this
1198 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1199 if (UseBiasedLocking) {
1200 if (SafepointSynchronize::is_at_safepoint()) {
1201 BiasedLocking::revoke_at_safepoint(h_obj);
1202 } else {
1203 BiasedLocking::revoke(h_obj, JavaThread::current());
1204 }
1205 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1206 }
1207
1208 oop obj = h_obj();
1209 address owner = NULL;
1210
1211 markWord mark = read_stable_mark(obj);
1212
1213 // Uncontended case, header points to stack
1214 if (mark.has_locker()) {
1215 owner = (address) mark.locker();
1216 }
1217
1218 // Contended case, header points to ObjectMonitor (tagged pointer)
1219 else if (mark.has_monitor()) {
1220 // The first stage of async deflation does not affect any field
1221 // used by this comparison so the ObjectMonitor* is usable here.
1222 ObjectMonitor* monitor = mark.monitor();
1223 assert(monitor != NULL, "monitor should be non-null");
1224 owner = (address) monitor->owner();
1225 }
1226
1227 if (owner != NULL) {
1228 // owning_thread_from_monitor_owner() may also return NULL here
1229 return Threads::owning_thread_from_monitor_owner(t_list, owner);
1230 }
1231
1232 // Unlocked case, header in place
1233 // Cannot have assertion since this object may have been
1234 // locked by another thread when reaching here.
1235 // assert(mark.is_neutral(), "sanity check");
1236
1237 return NULL;
1238 }
1239
1240 // Visitors ...
1241
1242 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
1243 PaddedObjectMonitor* block = Atomic::load(&g_block_list);
1244 while (block != NULL) {
1245 assert(block->object() == CHAINMARKER, "must be a block header");
1246 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
1247 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
1248 if (!mid->is_free() && mid->object() != NULL) {
1249 // Only process with closure if the object is set.
1250
1251 // monitors_iterate() is only called at a safepoint or when the
1252 // target thread is suspended or when the target thread is
1253 // operating on itself. The closures are only interested in an
1254 // owned ObjectMonitor and ownership cannot be dropped under the
1255 // calling contexts so the ObjectMonitor cannot be async deflated.
1256 closure->do_monitor(mid);
1257 }
1258 }
1259 // unmarked_next() is not needed with g_block_list (no locking
1260 // used with block linkage _next_om fields).
1261 block = (PaddedObjectMonitor*)block->next_om();
1262 }
1263 }
1264
1265 static bool monitors_used_above_threshold() {
1266 int population = Atomic::load(&om_list_globals._population);
1267 if (population == 0) {
1268 return false;
1269 }
1270 if (MonitorUsedDeflationThreshold > 0) {
1271 int monitors_used = population - Atomic::load(&om_list_globals._free_count) -
1272 Atomic::load(&om_list_globals._wait_count);
1273 int monitor_usage = (monitors_used * 100LL) / population;
1274 return monitor_usage > MonitorUsedDeflationThreshold;
1275 }
1276 return false;
1277 }
1278
1279 // Returns true if MonitorBound is set (> 0) and if the specified
1280 // cnt is > MonitorBound. Otherwise returns false.
1281 static bool is_MonitorBound_exceeded(const int cnt) {
1282 const int mx = MonitorBound;
1283 return mx > 0 && cnt > mx;
1284 }
1285
1286 bool ObjectSynchronizer::is_async_deflation_needed() {
1287 if (!AsyncDeflateIdleMonitors) {
1288 return false;
1289 }
1290 if (is_async_deflation_requested()) {
1291 // Async deflation request.
1292 return true;
1293 }
1294 if (AsyncDeflationInterval > 0 &&
1295 time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1296 monitors_used_above_threshold()) {
1297 // It's been longer than our specified deflate interval and there
1298 // are too many monitors in use. We don't deflate more frequently
1299 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1300 // in order to not swamp the ServiceThread.
1301 _last_async_deflation_time_ns = os::javaTimeNanos();
1302 return true;
1303 }
1304 int monitors_used = Atomic::load(&om_list_globals._population) -
1305 Atomic::load(&om_list_globals._free_count) -
1306 Atomic::load(&om_list_globals._wait_count);
1307 if (is_MonitorBound_exceeded(monitors_used)) {
1308 // Not enough ObjectMonitors on the global free list.
1309 return true;
1310 }
1311 return false;
1312 }
1313
1314 bool ObjectSynchronizer::needs_monitor_scavenge() {
1315 if (Atomic::load(&_forceMonitorScavenge) == 1) {
1316 log_info(monitorinflation)("Monitor scavenge needed, triggering safepoint cleanup.");
1317 return true;
1318 }
1319 return false;
1320 }
1321
1322 bool ObjectSynchronizer::is_safepoint_deflation_needed() {
1323 if (!AsyncDeflateIdleMonitors) {
1324 if (monitors_used_above_threshold()) {
1325 // Too many monitors in use.
1326 return true;
1327 }
1328 return needs_monitor_scavenge();
1329 }
1330 if (is_special_deflation_requested()) {
1331 // For AsyncDeflateIdleMonitors only do a safepoint deflation
1332 // if there is a special deflation request.
1333 return true;
1334 }
1335 return false;
1336 }
1337
1338 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1339 return (os::javaTimeNanos() - _last_async_deflation_time_ns) / (NANOUNITS / MILLIUNITS);
1340 }
1341
1342 void ObjectSynchronizer::oops_do(OopClosure* f) {
1343 // We only scan the global used list here (for moribund threads), and
1344 // the thread-local monitors in Thread::oops_do().
1345 global_used_oops_do(f);
1346 }
1347
1348 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
1349 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1350 list_oops_do(Atomic::load(&om_list_globals._in_use_list), f);
1351 }
1352
1353 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
1354 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1355 list_oops_do(thread->om_in_use_list, f);
1356 }
1357
1358 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
1359 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1360 // The oops_do() phase does not overlap with monitor deflation
1361 // so no need to lock ObjectMonitors for the list traversal.
1362 for (ObjectMonitor* mid = list; mid != NULL; mid = unmarked_next(mid)) {
1363 if (mid->object() != NULL) {
1364 f->do_oop((oop*)mid->object_addr());
1365 }
1366 }
1367 }
1368
1369
1370 // -----------------------------------------------------------------------------
1371 // ObjectMonitor Lifecycle
1372 // -----------------------
1373 // Inflation unlinks monitors from om_list_globals._free_list or a per-thread
1374 // free list and associates them with objects. Deflation -- which occurs at
1375 // STW-time or asynchronously -- disassociates idle monitors from objects.
1376 // Such scavenged monitors are returned to the om_list_globals._free_list.
1377 //
1378 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1379 //
1380 // Lifecycle:
1381 // -- unassigned and on the om_list_globals._free_list
1382 // -- unassigned and on a per-thread free list
1383 // -- assigned to an object. The object is inflated and the mark refers
1384 // to the ObjectMonitor.
1385
1386
1387 // Constraining monitor pool growth via MonitorBound ...
1388 //
1389 // If MonitorBound is not set (<= 0), MonitorBound checks are disabled.
1390 //
1391 // When safepoint deflation is being used (!AsyncDeflateIdleMonitors):
1392 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
1393 // the rate of scavenging is driven primarily by GC. As such, we can find
1394 // an inordinate number of monitors in circulation.
1395 // To avoid that scenario we can artificially induce a STW safepoint
1396 // if the pool appears to be growing past some reasonable bound.
1397 // Generally we favor time in space-time tradeoffs, but as there's no
1398 // natural back-pressure on the # of extant monitors we need to impose some
1399 // type of limit. Beware that if MonitorBound is set to too low a value
1400 // we could just loop. In addition, if MonitorBound is set to a low value
1401 // we'll incur more safepoints, which are harmful to performance.
1402 // See also: GuaranteedSafepointInterval
1403 //
1404 // When safepoint deflation is being used and MonitorBound is set, the
1405 // boundry applies to
1406 // (om_list_globals._population - om_list_globals._free_count)
1407 // i.e., if there are not enough ObjectMonitors on the global free list,
1408 // then a safepoint deflation is induced. Picking a good MonitorBound value
1409 // is non-trivial.
1410 //
1411 // When async deflation is being used:
1412 // The monitor pool is still grow-only. Async deflation is requested
1413 // by a safepoint's cleanup phase or by the ServiceThread at periodic
1414 // intervals when is_async_deflation_needed() returns true. In
1415 // addition to other policies that are checked, if there are not
1416 // enough ObjectMonitors on the global free list, then
1417 // is_async_deflation_needed() will return true. The ServiceThread
1418 // calls deflate_global_idle_monitors_using_JT() and also calls
1419 // deflate_per_thread_idle_monitors_using_JT() as needed.
1420
1421 static void InduceScavenge(Thread* self, const char * Whence) {
1422 assert(!AsyncDeflateIdleMonitors, "is not used by async deflation");
1423
1424 // Induce STW safepoint to trim monitors
1425 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1426 // More precisely, trigger a cleanup safepoint as the number
1427 // of active monitors passes the specified threshold.
1428 // TODO: assert thread state is reasonable
1429
1430 if (Atomic::xchg(&_forceMonitorScavenge, 1) == 0) {
1431 VMThread::check_for_forced_cleanup();
1432 }
1433 }
1434
1435 ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self) {
1436 // A large MAXPRIVATE value reduces both list lock contention
1437 // and list coherency traffic, but also tends to increase the
1438 // number of ObjectMonitors in circulation as well as the STW
1439 // scavenge costs. As usual, we lean toward time in space-time
1440 // tradeoffs.
1441 const int MAXPRIVATE = 1024;
1442 NoSafepointVerifier nsv;
1443
1444 for (;;) {
1445 ObjectMonitor* m;
1446
1447 // 1: try to allocate from the thread's local om_free_list.
1448 // Threads will attempt to allocate first from their local list, then
1449 // from the global list, and only after those attempts fail will the
1450 // thread attempt to instantiate new monitors. Thread-local free lists
1451 // improve allocation latency, as well as reducing coherency traffic
1452 // on the shared global list.
1453 m = take_from_start_of_om_free_list(self);
1454 if (m != NULL) {
1455 guarantee(m->object() == NULL, "invariant");
1456 m->set_allocation_state(ObjectMonitor::New);
1457 prepend_to_om_in_use_list(self, m);
1458 return m;
1459 }
1460
1461 // 2: try to allocate from the global om_list_globals._free_list
1462 // If we're using thread-local free lists then try
1463 // to reprovision the caller's free list.
1464 if (Atomic::load(&om_list_globals._free_list) != NULL) {
1465 // Reprovision the thread's om_free_list.
1466 // Use bulk transfers to reduce the allocation rate and heat
1467 // on various locks.
1468 for (int i = self->om_free_provision; --i >= 0;) {
1469 ObjectMonitor* take = take_from_start_of_global_free_list();
1470 if (take == NULL) {
1471 break; // No more are available.
1472 }
1473 guarantee(take->object() == NULL, "invariant");
1474 if (AsyncDeflateIdleMonitors) {
1475 // We allowed 3 field values to linger during async deflation.
1476 // Clear or restore them as appropriate.
1477 take->set_header(markWord::zero());
1478 // DEFLATER_MARKER is the only non-NULL value we should see here.
1479 take->try_set_owner_from(DEFLATER_MARKER, NULL);
1480 if (take->contentions() < 0) {
1481 // Add back max_jint to restore the contentions field to its
1482 // proper value.
1483 Atomic::add(&take->_contentions, max_jint);
1484
1485 #ifdef ASSERT
1486 jint l_contentions = take->contentions();
1487 #endif
1488 assert(l_contentions >= 0, "must not be negative: l_contentions=%d, contentions=%d",
1489 l_contentions, take->contentions());
1490 }
1491 }
1492 take->Recycle();
1493 // Since we're taking from the global free-list, take must be Free.
1494 // om_release() also sets the allocation state to Free because it
1495 // is called from other code paths.
1496 assert(take->is_free(), "invariant");
1497 om_release(self, take, false);
1498 }
1499 self->om_free_provision += 1 + (self->om_free_provision / 2);
1500 if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE;
1501
1502 if (!AsyncDeflateIdleMonitors &&
1503 is_MonitorBound_exceeded(Atomic::load(&om_list_globals._population) -
1504 Atomic::load(&om_list_globals._free_count))) {
1505 // Not enough ObjectMonitors on the global free list.
1506 // We can't safely induce a STW safepoint from om_alloc() as our thread
1507 // state may not be appropriate for such activities and callers may hold
1508 // naked oops, so instead we defer the action.
1509 InduceScavenge(self, "om_alloc");
1510 }
1511 continue;
1512 }
1513
1514 // 3: allocate a block of new ObjectMonitors
1515 // Both the local and global free lists are empty -- resort to malloc().
1516 // In the current implementation ObjectMonitors are TSM - immortal.
1517 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1518 // each ObjectMonitor to start at the beginning of a cache line,
1519 // so we use align_up().
1520 // A better solution would be to use C++ placement-new.
1521 // BEWARE: As it stands currently, we don't run the ctors!
1522 assert(_BLOCKSIZE > 1, "invariant");
1523 size_t neededsize = sizeof(PaddedObjectMonitor) * _BLOCKSIZE;
1524 PaddedObjectMonitor* temp;
1525 size_t aligned_size = neededsize + (OM_CACHE_LINE_SIZE - 1);
1526 void* real_malloc_addr = NEW_C_HEAP_ARRAY(char, aligned_size, mtInternal);
1527 temp = (PaddedObjectMonitor*)align_up(real_malloc_addr, OM_CACHE_LINE_SIZE);
1528 (void)memset((void *) temp, 0, neededsize);
1529
1530 // Format the block.
1531 // initialize the linked list, each monitor points to its next
1532 // forming the single linked free list, the very first monitor
1533 // will points to next block, which forms the block list.
1534 // The trick of using the 1st element in the block as g_block_list
1535 // linkage should be reconsidered. A better implementation would
1536 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1537
1538 for (int i = 1; i < _BLOCKSIZE; i++) {
1539 temp[i].set_next_om((ObjectMonitor*)&temp[i + 1]);
1540 assert(temp[i].is_free(), "invariant");
1541 }
1542
1543 // terminate the last monitor as the end of list
1544 temp[_BLOCKSIZE - 1].set_next_om((ObjectMonitor*)NULL);
1545
1546 // Element [0] is reserved for global list linkage
1547 temp[0].set_object(CHAINMARKER);
1548
1549 // Consider carving out this thread's current request from the
1550 // block in hand. This avoids some lock traffic and redundant
1551 // list activity.
1552
1553 prepend_block_to_lists(temp);
1554 }
1555 }
1556
1557 // Place "m" on the caller's private per-thread om_free_list.
1558 // In practice there's no need to clamp or limit the number of
1559 // monitors on a thread's om_free_list as the only non-allocation time
1560 // we'll call om_release() is to return a monitor to the free list after
1561 // a CAS attempt failed. This doesn't allow unbounded #s of monitors to
1562 // accumulate on a thread's free list.
1563 //
1564 // Key constraint: all ObjectMonitors on a thread's free list and the global
1565 // free list must have their object field set to null. This prevents the
1566 // scavenger -- deflate_monitor_list() or deflate_monitor_list_using_JT()
1567 // -- from reclaiming them while we are trying to release them.
1568
1569 void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m,
1570 bool from_per_thread_alloc) {
1571 guarantee(m->header().value() == 0, "invariant");
1572 guarantee(m->object() == NULL, "invariant");
1573 NoSafepointVerifier nsv;
1574
1575 if ((m->is_busy() | m->_recursions) != 0) {
1576 stringStream ss;
1577 fatal("freeing in-use monitor: %s, recursions=" INTX_FORMAT,
1578 m->is_busy_to_string(&ss), m->_recursions);
1579 }
1580 m->set_allocation_state(ObjectMonitor::Free);
1581 // _next_om is used for both per-thread in-use and free lists so
1582 // we have to remove 'm' from the in-use list first (as needed).
1583 if (from_per_thread_alloc) {
1584 // Need to remove 'm' from om_in_use_list.
1585 ObjectMonitor* mid = NULL;
1586 ObjectMonitor* next = NULL;
1587
1588 // This list walk can race with another list walker or with async
1589 // deflation so we have to worry about an ObjectMonitor being
1590 // removed from this list while we are walking it.
1591
1592 // Lock the list head to avoid racing with another list walker
1593 // or with async deflation.
1594 if ((mid = get_list_head_locked(&self->om_in_use_list)) == NULL) {
1595 fatal("thread=" INTPTR_FORMAT " in-use list must not be empty.", p2i(self));
1596 }
1597 next = unmarked_next(mid);
1598 if (m == mid) {
1599 // First special case:
1600 // 'm' matches mid, is the list head and is locked. Switch the list
1601 // head to next which unlocks the list head, but leaves the extracted
1602 // mid locked:
1603 Atomic::store(&self->om_in_use_list, next);
1604 } else if (m == next) {
1605 // Second special case:
1606 // 'm' matches next after the list head and we already have the list
1607 // head locked so set mid to what we are extracting:
1608 mid = next;
1609 // Lock mid to prevent races with a list walker or an async
1610 // deflater thread that's ahead of us. The locked list head
1611 // prevents races from behind us.
1612 om_lock(mid);
1613 // Update next to what follows mid (if anything):
1614 next = unmarked_next(mid);
1615 // Switch next after the list head to new next which unlocks the
1616 // list head, but leaves the extracted mid locked:
1617 self->om_in_use_list->set_next_om(next);
1618 } else {
1619 // We have to search the list to find 'm'.
1620 guarantee(next != NULL, "thread=" INTPTR_FORMAT ": om_in_use_list=" INTPTR_FORMAT
1621 " is too short.", p2i(self), p2i(self->om_in_use_list));
1622 // Our starting anchor is next after the list head which is the
1623 // last ObjectMonitor we checked:
1624 ObjectMonitor* anchor = next;
1625 // Lock anchor to prevent races with a list walker or an async
1626 // deflater thread that's ahead of us. The locked list head
1627 // prevents races from behind us.
1628 om_lock(anchor);
1629 om_unlock(mid); // Unlock the list head now that anchor is locked.
1630 while ((mid = unmarked_next(anchor)) != NULL) {
1631 if (m == mid) {
1632 // We found 'm' on the per-thread in-use list so extract it.
1633 // Update next to what follows mid (if anything):
1634 next = unmarked_next(mid);
1635 // Switch next after the anchor to new next which unlocks the
1636 // anchor, but leaves the extracted mid locked:
1637 anchor->set_next_om(next);
1638 break;
1639 } else {
1640 // Lock the next anchor to prevent races with a list walker
1641 // or an async deflater thread that's ahead of us. The locked
1642 // current anchor prevents races from behind us.
1643 om_lock(mid);
1644 // Unlock current anchor now that next anchor is locked:
1645 om_unlock(anchor);
1646 anchor = mid; // Advance to new anchor and try again.
1647 }
1648 }
1649 }
1650
1651 if (mid == NULL) {
1652 // Reached end of the list and didn't find 'm' so:
1653 fatal("thread=" INTPTR_FORMAT " must find m=" INTPTR_FORMAT "on om_in_use_list="
1654 INTPTR_FORMAT, p2i(self), p2i(m), p2i(self->om_in_use_list));
1655 }
1656
1657 // At this point mid is disconnected from the in-use list so
1658 // its lock no longer has any effects on the in-use list.
1659 Atomic::dec(&self->om_in_use_count);
1660 // Unlock mid, but leave the next value for any lagging list
1661 // walkers. It will get cleaned up when mid is prepended to
1662 // the thread's free list:
1663 om_unlock(mid);
1664 }
1665
1666 prepend_to_om_free_list(self, m);
1667 guarantee(m->is_free(), "invariant");
1668 }
1669
1670 // Return ObjectMonitors on a moribund thread's free and in-use
1671 // lists to the appropriate global lists. The ObjectMonitors on the
1672 // per-thread in-use list may still be in use by other threads.
1673 //
1674 // We currently call om_flush() from Threads::remove() before the
1675 // thread has been excised from the thread list and is no longer a
1676 // mutator. This means that om_flush() cannot run concurrently with
1677 // a safepoint and interleave with deflate_idle_monitors(). In
1678 // particular, this ensures that the thread's in-use monitors are
1679 // scanned by a GC safepoint, either via Thread::oops_do() (before
1680 // om_flush() is called) or via ObjectSynchronizer::oops_do() (after
1681 // om_flush() is called).
1682 //
1683 // With AsyncDeflateIdleMonitors, deflate_global_idle_monitors_using_JT()
1684 // and deflate_per_thread_idle_monitors_using_JT() (in another thread) can
1685 // run at the same time as om_flush() so we have to follow a careful
1686 // protocol to prevent list corruption.
1687
1688 void ObjectSynchronizer::om_flush(Thread* self) {
1689 // Process the per-thread in-use list first to be consistent.
1690 int in_use_count = 0;
1691 ObjectMonitor* in_use_list = NULL;
1692 ObjectMonitor* in_use_tail = NULL;
1693 NoSafepointVerifier nsv;
1694
1695 // This function can race with a list walker or with an async
1696 // deflater thread so we lock the list head to prevent confusion.
1697 // An async deflater thread checks to see if the target thread
1698 // is exiting, but if it has made it past that check before we
1699 // started exiting, then it is racing to get to the in-use list.
1700 if ((in_use_list = get_list_head_locked(&self->om_in_use_list)) != NULL) {
1701 // At this point, we have locked the in-use list head so a racing
1702 // thread cannot come in after us. However, a racing thread could
1703 // be ahead of us; we'll detect that and delay to let it finish.
1704 //
1705 // The thread is going away, however the ObjectMonitors on the
1706 // om_in_use_list may still be in-use by other threads. Link
1707 // them to in_use_tail, which will be linked into the global
1708 // in-use list (om_list_globals._in_use_list) below.
1709 //
1710 // Account for the in-use list head before the loop since it is
1711 // already locked (by this thread):
1712 in_use_tail = in_use_list;
1713 in_use_count++;
1714 for (ObjectMonitor* cur_om = unmarked_next(in_use_list); cur_om != NULL;) {
1715 if (is_locked(cur_om)) {
1716 // cur_om is locked so there must be a racing walker or async
1717 // deflater thread ahead of us so we'll give it a chance to finish.
1718 while (is_locked(cur_om)) {
1719 os::naked_short_sleep(1);
1720 }
1721 // Refetch the possibly changed next field and try again.
1722 cur_om = unmarked_next(in_use_tail);
1723 continue;
1724 }
1725 if (cur_om->is_free()) {
1726 // cur_om was deflated and the allocation state was changed
1727 // to Free while it was locked. We happened to see it just
1728 // after it was unlocked (and added to the free list).
1729 // Refetch the possibly changed next field and try again.
1730 cur_om = unmarked_next(in_use_tail);
1731 continue;
1732 }
1733 in_use_tail = cur_om;
1734 in_use_count++;
1735 cur_om = unmarked_next(cur_om);
1736 }
1737 guarantee(in_use_tail != NULL, "invariant");
1738 int l_om_in_use_count = Atomic::load(&self->om_in_use_count);
1739 ADIM_guarantee(l_om_in_use_count == in_use_count, "in-use counts don't match: "
1740 "l_om_in_use_count=%d, in_use_count=%d", l_om_in_use_count, in_use_count);
1741 Atomic::store(&self->om_in_use_count, 0);
1742 // Clear the in-use list head (which also unlocks it):
1743 Atomic::store(&self->om_in_use_list, (ObjectMonitor*)NULL);
1744 om_unlock(in_use_list);
1745 }
1746
1747 int free_count = 0;
1748 ObjectMonitor* free_list = NULL;
1749 ObjectMonitor* free_tail = NULL;
1750 // This function can race with a list walker thread so we lock the
1751 // list head to prevent confusion.
1752 if ((free_list = get_list_head_locked(&self->om_free_list)) != NULL) {
1753 // At this point, we have locked the free list head so a racing
1754 // thread cannot come in after us. However, a racing thread could
1755 // be ahead of us; we'll detect that and delay to let it finish.
1756 //
1757 // The thread is going away. Set 'free_tail' to the last per-thread free
1758 // monitor which will be linked to om_list_globals._free_list below.
1759 //
1760 // Account for the free list head before the loop since it is
1761 // already locked (by this thread):
1762 free_tail = free_list;
1763 free_count++;
1764 for (ObjectMonitor* s = unmarked_next(free_list); s != NULL; s = unmarked_next(s)) {
1765 if (is_locked(s)) {
1766 // s is locked so there must be a racing walker thread ahead
1767 // of us so we'll give it a chance to finish.
1768 while (is_locked(s)) {
1769 os::naked_short_sleep(1);
1770 }
1771 }
1772 free_tail = s;
1773 free_count++;
1774 guarantee(s->object() == NULL, "invariant");
1775 if (s->is_busy()) {
1776 stringStream ss;
1777 fatal("must be !is_busy: %s", s->is_busy_to_string(&ss));
1778 }
1779 }
1780 guarantee(free_tail != NULL, "invariant");
1781 int l_om_free_count = Atomic::load(&self->om_free_count);
1782 ADIM_guarantee(l_om_free_count == free_count, "free counts don't match: "
1783 "l_om_free_count=%d, free_count=%d", l_om_free_count, free_count);
1784 Atomic::store(&self->om_free_count, 0);
1785 Atomic::store(&self->om_free_list, (ObjectMonitor*)NULL);
1786 om_unlock(free_list);
1787 }
1788
1789 if (free_tail != NULL) {
1790 prepend_list_to_global_free_list(free_list, free_tail, free_count);
1791 }
1792
1793 if (in_use_tail != NULL) {
1794 prepend_list_to_global_in_use_list(in_use_list, in_use_tail, in_use_count);
1795 }
1796
1797 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1798 LogStreamHandle(Info, monitorinflation) lsh_info;
1799 LogStream* ls = NULL;
1800 if (log_is_enabled(Debug, monitorinflation)) {
1801 ls = &lsh_debug;
1802 } else if ((free_count != 0 || in_use_count != 0) &&
1803 log_is_enabled(Info, monitorinflation)) {
1804 ls = &lsh_info;
1805 }
1806 if (ls != NULL) {
1807 ls->print_cr("om_flush: jt=" INTPTR_FORMAT ", free_count=%d"
1808 ", in_use_count=%d" ", om_free_provision=%d",
1809 p2i(self), free_count, in_use_count, self->om_free_provision);
1810 }
1811 }
1812
1813 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1814 const oop obj,
1815 ObjectSynchronizer::InflateCause cause) {
1816 assert(event != NULL, "invariant");
1817 assert(event->should_commit(), "invariant");
1818 event->set_monitorClass(obj->klass());
1819 event->set_address((uintptr_t)(void*)obj);
1820 event->set_cause((u1)cause);
1821 event->commit();
1822 }
1823
1824 // Fast path code shared by multiple functions
1825 void ObjectSynchronizer::inflate_helper(oop obj) {
1826 markWord mark = obj->mark();
1827 if (mark.has_monitor()) {
1828 ObjectMonitor* monitor = mark.monitor();
1829 assert(ObjectSynchronizer::verify_objmon_isinpool(monitor), "monitor=" INTPTR_FORMAT " is invalid", p2i(monitor));
1830 markWord dmw = monitor->header();
1831 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1832 return;
1833 }
1834 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1835 }
1836
1837 ObjectMonitor* ObjectSynchronizer::inflate(Thread* self, oop object,
1838 const InflateCause cause) {
1839 // Inflate mutates the heap ...
1840 // Relaxing assertion for bug 6320749.
1841 assert(Universe::verify_in_progress() ||
1842 !SafepointSynchronize::is_at_safepoint(), "invariant");
1843
1844 EventJavaMonitorInflate event;
1845
1846 for (;;) {
1847 const markWord mark = object->mark();
1848 assert(!mark.has_bias_pattern(), "invariant");
1849
1850 // The mark can be in one of the following states:
1851 // * Inflated - just return
1852 // * Stack-locked - coerce it to inflated
1853 // * INFLATING - busy wait for conversion to complete
1854 // * Neutral - aggressively inflate the object.
1855 // * BIASED - Illegal. We should never see this
1856
1857 // CASE: inflated
1858 if (mark.has_monitor()) {
1859 ObjectMonitor* inf = mark.monitor();
1860 markWord dmw = inf->header();
1861 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1862 assert(AsyncDeflateIdleMonitors || inf->object() == object, "invariant");
1863 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1864 return inf;
1865 }
1866
1867 // CASE: inflation in progress - inflating over a stack-lock.
1868 // Some other thread is converting from stack-locked to inflated.
1869 // Only that thread can complete inflation -- other threads must wait.
1870 // The INFLATING value is transient.
1871 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1872 // We could always eliminate polling by parking the thread on some auxiliary list.
1873 if (mark == markWord::INFLATING()) {
1874 read_stable_mark(object);
1875 continue;
1876 }
1877
1878 // CASE: stack-locked
1879 // Could be stack-locked either by this thread or by some other thread.
1880 //
1881 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1882 // to install INFLATING into the mark word. We originally installed INFLATING,
1883 // allocated the objectmonitor, and then finally STed the address of the
1884 // objectmonitor into the mark. This was correct, but artificially lengthened
1885 // the interval in which INFLATED appeared in the mark, thus increasing
1886 // the odds of inflation contention.
1887 //
1888 // We now use per-thread private objectmonitor free lists.
1889 // These list are reprovisioned from the global free list outside the
1890 // critical INFLATING...ST interval. A thread can transfer
1891 // multiple objectmonitors en-mass from the global free list to its local free list.
1892 // This reduces coherency traffic and lock contention on the global free list.
1893 // Using such local free lists, it doesn't matter if the om_alloc() call appears
1894 // before or after the CAS(INFLATING) operation.
1895 // See the comments in om_alloc().
1896
1897 LogStreamHandle(Trace, monitorinflation) lsh;
1898
1899 if (mark.has_locker()) {
1900 ObjectMonitor* m = om_alloc(self);
1901 // Optimistically prepare the objectmonitor - anticipate successful CAS
1902 // We do this before the CAS in order to minimize the length of time
1903 // in which INFLATING appears in the mark.
1904 m->Recycle();
1905 m->_Responsible = NULL;
1906 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1907
1908 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1909 if (cmp != mark) {
1910 // om_release() will reset the allocation state from New to Free.
1911 om_release(self, m, true);
1912 continue; // Interference -- just retry
1913 }
1914
1915 // We've successfully installed INFLATING (0) into the mark-word.
1916 // This is the only case where 0 will appear in a mark-word.
1917 // Only the singular thread that successfully swings the mark-word
1918 // to 0 can perform (or more precisely, complete) inflation.
1919 //
1920 // Why do we CAS a 0 into the mark-word instead of just CASing the
1921 // mark-word from the stack-locked value directly to the new inflated state?
1922 // Consider what happens when a thread unlocks a stack-locked object.
1923 // It attempts to use CAS to swing the displaced header value from the
1924 // on-stack BasicLock back into the object header. Recall also that the
1925 // header value (hash code, etc) can reside in (a) the object header, or
1926 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1927 // header in an ObjectMonitor. The inflate() routine must copy the header
1928 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1929 // the while preserving the hashCode stability invariants. If the owner
1930 // decides to release the lock while the value is 0, the unlock will fail
1931 // and control will eventually pass from slow_exit() to inflate. The owner
1932 // will then spin, waiting for the 0 value to disappear. Put another way,
1933 // the 0 causes the owner to stall if the owner happens to try to
1934 // drop the lock (restoring the header from the BasicLock to the object)
1935 // while inflation is in-progress. This protocol avoids races that might
1936 // would otherwise permit hashCode values to change or "flicker" for an object.
1937 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1938 // 0 serves as a "BUSY" inflate-in-progress indicator.
1939
1940
1941 // fetch the displaced mark from the owner's stack.
1942 // The owner can't die or unwind past the lock while our INFLATING
1943 // object is in the mark. Furthermore the owner can't complete
1944 // an unlock on the object, either.
1945 markWord dmw = mark.displaced_mark_helper();
1946 // Catch if the object's header is not neutral (not locked and
1947 // not marked is what we care about here).
1948 ADIM_guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1949
1950 // Setup monitor fields to proper values -- prepare the monitor
1951 m->set_header(dmw);
1952
1953 // Optimization: if the mark.locker stack address is associated
1954 // with this thread we could simply set m->_owner = self.
1955 // Note that a thread can inflate an object
1956 // that it has stack-locked -- as might happen in wait() -- directly
1957 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1958 if (AsyncDeflateIdleMonitors) {
1959 m->set_owner_from(NULL, DEFLATER_MARKER, mark.locker());
1960 } else {
1961 m->set_owner_from(NULL, mark.locker());
1962 }
1963 m->set_object(object);
1964 // TODO-FIXME: assert BasicLock->dhw != 0.
1965
1966 // Must preserve store ordering. The monitor state must
1967 // be stable at the time of publishing the monitor address.
1968 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1969 object->release_set_mark(markWord::encode(m));
1970
1971 // Once ObjectMonitor is configured and the object is associated
1972 // with the ObjectMonitor, it is safe to allow async deflation:
1973 assert(m->is_new(), "freshly allocated monitor must be new");
1974 m->set_allocation_state(ObjectMonitor::Old);
1975
1976 // Hopefully the performance counters are allocated on distinct cache lines
1977 // to avoid false sharing on MP systems ...
1978 OM_PERFDATA_OP(Inflations, inc());
1979 if (log_is_enabled(Trace, monitorinflation)) {
1980 ResourceMark rm(self);
1981 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1982 INTPTR_FORMAT ", type='%s'", p2i(object),
1983 object->mark().value(), object->klass()->external_name());
1984 }
1985 if (event.should_commit()) {
1986 post_monitor_inflate_event(&event, object, cause);
1987 }
1988 return m;
1989 }
1990
1991 // CASE: neutral
1992 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1993 // If we know we're inflating for entry it's better to inflate by swinging a
1994 // pre-locked ObjectMonitor pointer into the object header. A successful
1995 // CAS inflates the object *and* confers ownership to the inflating thread.
1996 // In the current implementation we use a 2-step mechanism where we CAS()
1997 // to inflate and then CAS() again to try to swing _owner from NULL to self.
1998 // An inflateTry() method that we could call from enter() would be useful.
1999
2000 // Catch if the object's header is not neutral (not locked and
2001 // not marked is what we care about here).
2002 ADIM_guarantee(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
2003 ObjectMonitor* m = om_alloc(self);
2004 // prepare m for installation - set monitor to initial state
2005 m->Recycle();
2006 m->set_header(mark);
2007 if (AsyncDeflateIdleMonitors) {
2008 // DEFLATER_MARKER is the only non-NULL value we should see here.
2009 m->try_set_owner_from(DEFLATER_MARKER, NULL);
2010 }
2011 m->set_object(object);
2012 m->_Responsible = NULL;
2013 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
2014
2015 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
2016 m->set_header(markWord::zero());
2017 m->set_object(NULL);
2018 m->Recycle();
2019 // om_release() will reset the allocation state from New to Free.
2020 om_release(self, m, true);
2021 m = NULL;
2022 continue;
2023 // interference - the markword changed - just retry.
2024 // The state-transitions are one-way, so there's no chance of
2025 // live-lock -- "Inflated" is an absorbing state.
2026 }
2027
2028 // Once the ObjectMonitor is configured and object is associated
2029 // with the ObjectMonitor, it is safe to allow async deflation:
2030 assert(m->is_new(), "freshly allocated monitor must be new");
2031 m->set_allocation_state(ObjectMonitor::Old);
2032
2033 // Hopefully the performance counters are allocated on distinct
2034 // cache lines to avoid false sharing on MP systems ...
2035 OM_PERFDATA_OP(Inflations, inc());
2036 if (log_is_enabled(Trace, monitorinflation)) {
2037 ResourceMark rm(self);
2038 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
2039 INTPTR_FORMAT ", type='%s'", p2i(object),
2040 object->mark().value(), object->klass()->external_name());
2041 }
2042 if (event.should_commit()) {
2043 post_monitor_inflate_event(&event, object, cause);
2044 }
2045 return m;
2046 }
2047 }
2048
2049
2050 // We maintain a list of in-use monitors for each thread.
2051 //
2052 // For safepoint based deflation:
2053 // deflate_thread_local_monitors() scans a single thread's in-use list, while
2054 // deflate_idle_monitors() scans only a global list of in-use monitors which
2055 // is populated only as a thread dies (see om_flush()).
2056 //
2057 // These operations are called at all safepoints, immediately after mutators
2058 // are stopped, but before any objects have moved. Collectively they traverse
2059 // the population of in-use monitors, deflating where possible. The scavenged
2060 // monitors are returned to the global monitor free list.
2061 //
2062 // Beware that we scavenge at *every* stop-the-world point. Having a large
2063 // number of monitors in-use could negatively impact performance. We also want
2064 // to minimize the total # of monitors in circulation, as they incur a small
2065 // footprint penalty.
2066 //
2067 // Perversely, the heap size -- and thus the STW safepoint rate --
2068 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
2069 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
2070 // This is an unfortunate aspect of this design.
2071 //
2072 // For async deflation:
2073 // If a special deflation request is made, then the safepoint based
2074 // deflation mechanism is used. Otherwise, an async deflation request
2075 // is registered with the ServiceThread and it is notified.
2076
2077 void ObjectSynchronizer::do_safepoint_work(DeflateMonitorCounters* counters) {
2078 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2079
2080 // The per-thread in-use lists are handled in
2081 // ParallelSPCleanupThreadClosure::do_thread().
2082
2083 if (!AsyncDeflateIdleMonitors || is_special_deflation_requested()) {
2084 // Use the older mechanism for the global in-use list or if a
2085 // special deflation has been requested before the safepoint.
2086 ObjectSynchronizer::deflate_idle_monitors(counters);
2087 return;
2088 }
2089
2090 log_debug(monitorinflation)("requesting async deflation of idle monitors.");
2091 // Request deflation of idle monitors by the ServiceThread:
2092 set_is_async_deflation_requested(true);
2093 MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
2094 ml.notify_all();
2095
2096 if (log_is_enabled(Debug, monitorinflation)) {
2097 // exit_globals()'s call to audit_and_print_stats() is done
2098 // at the Info level and not at a safepoint.
2099 // For safepoint based deflation, audit_and_print_stats() is called
2100 // in ObjectSynchronizer::finish_deflate_idle_monitors() at the
2101 // Debug level at a safepoint.
2102 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2103 }
2104 }
2105
2106 // Deflate a single monitor if not in-use
2107 // Return true if deflated, false if in-use
2108 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
2109 ObjectMonitor** free_head_p,
2110 ObjectMonitor** free_tail_p) {
2111 bool deflated;
2112 // Normal case ... The monitor is associated with obj.
2113 const markWord mark = obj->mark();
2114 guarantee(mark == markWord::encode(mid), "should match: mark="
2115 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(),
2116 markWord::encode(mid).value());
2117 // Make sure that mark.monitor() and markWord::encode() agree:
2118 guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
2119 ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid));
2120 const markWord dmw = mid->header();
2121 guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
2122
2123 if (mid->is_busy()) {
2124 // Easy checks are first - the ObjectMonitor is busy so no deflation.
2125 deflated = false;
2126 } else {
2127 // Deflate the monitor if it is no longer being used
2128 // It's idle - scavenge and return to the global free list
2129 // plain old deflation ...
2130 if (log_is_enabled(Trace, monitorinflation)) {
2131 ResourceMark rm;
2132 log_trace(monitorinflation)("deflate_monitor: "
2133 "object=" INTPTR_FORMAT ", mark="
2134 INTPTR_FORMAT ", type='%s'", p2i(obj),
2135 mark.value(), obj->klass()->external_name());
2136 }
2137
2138 // Restore the header back to obj
2139 obj->release_set_mark(dmw);
2140 if (AsyncDeflateIdleMonitors) {
2141 // clear() expects the owner field to be NULL.
2142 // DEFLATER_MARKER is the only non-NULL value we should see here.
2143 mid->try_set_owner_from(DEFLATER_MARKER, NULL);
2144 }
2145 mid->clear();
2146
2147 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
2148 p2i(mid->object()));
2149 assert(mid->is_free(), "invariant");
2150
2151 // Move the deflated ObjectMonitor to the working free list
2152 // defined by free_head_p and free_tail_p.
2153 if (*free_head_p == NULL) *free_head_p = mid;
2154 if (*free_tail_p != NULL) {
2155 // We append to the list so the caller can use mid->_next_om
2156 // to fix the linkages in its context.
2157 ObjectMonitor* prevtail = *free_tail_p;
2158 // Should have been cleaned up by the caller:
2159 // Note: Should not have to lock prevtail here since we're at a
2160 // safepoint and ObjectMonitors on the local free list should
2161 // not be accessed in parallel.
2162 #ifdef ASSERT
2163 ObjectMonitor* l_next_om = prevtail->next_om();
2164 #endif
2165 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2166 prevtail->set_next_om(mid);
2167 }
2168 *free_tail_p = mid;
2169 // At this point, mid->_next_om still refers to its current
2170 // value and another ObjectMonitor's _next_om field still
2171 // refers to this ObjectMonitor. Those linkages have to be
2172 // cleaned up by the caller who has the complete context.
2173 deflated = true;
2174 }
2175 return deflated;
2176 }
2177
2178 // Deflate the specified ObjectMonitor if not in-use using a JavaThread.
2179 // Returns true if it was deflated and false otherwise.
2180 //
2181 // The async deflation protocol sets owner to DEFLATER_MARKER and
2182 // makes contentions negative as signals to contending threads that
2183 // an async deflation is in progress. There are a number of checks
2184 // as part of the protocol to make sure that the calling thread has
2185 // not lost the race to a contending thread.
2186 //
2187 // The ObjectMonitor has been successfully async deflated when:
2188 // (owner == DEFLATER_MARKER && contentions < 0)
2189 // Contending threads that see those values know to retry their operation.
2190 //
2191 bool ObjectSynchronizer::deflate_monitor_using_JT(ObjectMonitor* mid,
2192 ObjectMonitor** free_head_p,
2193 ObjectMonitor** free_tail_p) {
2194 assert(AsyncDeflateIdleMonitors, "sanity check");
2195 assert(Thread::current()->is_Java_thread(), "precondition");
2196 // A newly allocated ObjectMonitor should not be seen here so we
2197 // avoid an endless inflate/deflate cycle.
2198 assert(mid->is_old(), "must be old: allocation_state=%d",
2199 (int) mid->allocation_state());
2200
2201 if (mid->is_busy()) {
2202 // Easy checks are first - the ObjectMonitor is busy so no deflation.
2203 return false;
2204 }
2205
2206 // Set a NULL owner to DEFLATER_MARKER to force any contending thread
2207 // through the slow path. This is just the first part of the async
2208 // deflation dance.
2209 if (mid->try_set_owner_from(NULL, DEFLATER_MARKER) != NULL) {
2210 // The owner field is no longer NULL so we lost the race since the
2211 // ObjectMonitor is now busy.
2212 return false;
2213 }
2214
2215 if (mid->contentions() > 0 || mid->_waiters != 0) {
2216 // Another thread has raced to enter the ObjectMonitor after
2217 // mid->is_busy() above or has already entered and waited on
2218 // it which makes it busy so no deflation. Restore owner to
2219 // NULL if it is still DEFLATER_MARKER.
2220 mid->try_set_owner_from(DEFLATER_MARKER, NULL);
2221 return false;
2222 }
2223
2224 // Make contentions negative to force any contending threads to
2225 // retry. This is the second part of the async deflation dance.
2226 if (Atomic::cmpxchg(&mid->_contentions, (jint)0, -max_jint) != 0) {
2227 // The contentions was no longer 0 so we lost the race since the
2228 // ObjectMonitor is now busy. Restore owner to NULL if it is
2229 // still DEFLATER_MARKER:
2230 mid->try_set_owner_from(DEFLATER_MARKER, NULL);
2231 return false;
2232 }
2233
2234 // If owner is still DEFLATER_MARKER, then we have successfully
2235 // signaled any contending threads to retry.
2236 if (!mid->owner_is_DEFLATER_MARKER()) {
2237 // If it is not, then we have lost the race to an entering thread
2238 // and the ObjectMonitor is now busy. This is the third and final
2239 // part of the async deflation dance.
2240 // Note: This owner check solves the ABA problem with contentions
2241 // where another thread acquired the ObjectMonitor, finished
2242 // using it and restored contentions to zero.
2243
2244 // Add back max_jint to restore the contentions field to its
2245 // proper value (which may not be what we saw above):
2246 Atomic::add(&mid->_contentions, max_jint);
2247
2248 #ifdef ASSERT
2249 jint l_contentions = mid->contentions();
2250 #endif
2251 assert(l_contentions >= 0, "must not be negative: l_contentions=%d, contentions=%d",
2252 l_contentions, mid->contentions());
2253 return false;
2254 }
2255
2256 // Sanity checks for the races:
2257 guarantee(mid->contentions() < 0, "must be negative: contentions=%d",
2258 mid->contentions());
2259 guarantee(mid->_waiters == 0, "must be 0: waiters=%d", mid->_waiters);
2260 guarantee(mid->_cxq == NULL, "must be no contending threads: cxq="
2261 INTPTR_FORMAT, p2i(mid->_cxq));
2262 guarantee(mid->_EntryList == NULL,
2263 "must be no entering threads: EntryList=" INTPTR_FORMAT,
2264 p2i(mid->_EntryList));
2265
2266 const oop obj = (oop) mid->object();
2267 if (log_is_enabled(Trace, monitorinflation)) {
2268 ResourceMark rm;
2269 log_trace(monitorinflation)("deflate_monitor_using_JT: "
2270 "object=" INTPTR_FORMAT ", mark="
2271 INTPTR_FORMAT ", type='%s'",
2272 p2i(obj), obj->mark().value(),
2273 obj->klass()->external_name());
2274 }
2275
2276 // Install the old mark word if nobody else has already done it.
2277 mid->install_displaced_markword_in_object(obj);
2278 mid->clear_using_JT();
2279
2280 assert(mid->object() == NULL, "must be NULL: object=" INTPTR_FORMAT,
2281 p2i(mid->object()));
2282 assert(mid->is_free(), "must be free: allocation_state=%d",
2283 (int)mid->allocation_state());
2284
2285 // Move the deflated ObjectMonitor to the working free list
2286 // defined by free_head_p and free_tail_p.
2287 if (*free_head_p == NULL) {
2288 // First one on the list.
2289 *free_head_p = mid;
2290 }
2291 if (*free_tail_p != NULL) {
2292 // We append to the list so the caller can use mid->_next_om
2293 // to fix the linkages in its context.
2294 ObjectMonitor* prevtail = *free_tail_p;
2295 // prevtail should have been cleaned up by the caller:
2296 #ifdef ASSERT
2297 ObjectMonitor* l_next_om = unmarked_next(prevtail);
2298 #endif
2299 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2300 om_lock(prevtail);
2301 prevtail->set_next_om(mid); // prevtail now points to mid (and is unlocked)
2302 }
2303 *free_tail_p = mid;
2304
2305 // At this point, mid->_next_om still refers to its current
2306 // value and another ObjectMonitor's _next_om field still
2307 // refers to this ObjectMonitor. Those linkages have to be
2308 // cleaned up by the caller who has the complete context.
2309
2310 // We leave owner == DEFLATER_MARKER and contentions < 0
2311 // to force any racing threads to retry.
2312 return true; // Success, ObjectMonitor has been deflated.
2313 }
2314
2315 // Walk a given monitor list, and deflate idle monitors.
2316 // The given list could be a per-thread list or a global list.
2317 //
2318 // In the case of parallel processing of thread local monitor lists,
2319 // work is done by Threads::parallel_threads_do() which ensures that
2320 // each Java thread is processed by exactly one worker thread, and
2321 // thus avoid conflicts that would arise when worker threads would
2322 // process the same monitor lists concurrently.
2323 //
2324 // See also ParallelSPCleanupTask and
2325 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
2326 // Threads::parallel_java_threads_do() in thread.cpp.
2327 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** list_p,
2328 int* count_p,
2329 ObjectMonitor** free_head_p,
2330 ObjectMonitor** free_tail_p) {
2331 ObjectMonitor* cur_mid_in_use = NULL;
2332 ObjectMonitor* mid = NULL;
2333 ObjectMonitor* next = NULL;
2334 int deflated_count = 0;
2335
2336 // This list walk executes at a safepoint and does not race with any
2337 // other list walkers.
2338
2339 for (mid = Atomic::load(list_p); mid != NULL; mid = next) {
2340 next = unmarked_next(mid);
2341 oop obj = (oop) mid->object();
2342 if (obj != NULL && deflate_monitor(mid, obj, free_head_p, free_tail_p)) {
2343 // Deflation succeeded and already updated free_head_p and
2344 // free_tail_p as needed. Finish the move to the local free list
2345 // by unlinking mid from the global or per-thread in-use list.
2346 if (cur_mid_in_use == NULL) {
2347 // mid is the list head so switch the list head to next:
2348 Atomic::store(list_p, next);
2349 } else {
2350 // Switch cur_mid_in_use's next field to next:
2351 cur_mid_in_use->set_next_om(next);
2352 }
2353 // At this point mid is disconnected from the in-use list.
2354 deflated_count++;
2355 Atomic::dec(count_p);
2356 // mid is current tail in the free_head_p list so NULL terminate it:
2357 mid->set_next_om(NULL);
2358 } else {
2359 cur_mid_in_use = mid;
2360 }
2361 }
2362 return deflated_count;
2363 }
2364
2365 // Walk a given ObjectMonitor list and deflate idle ObjectMonitors using
2366 // a JavaThread. Returns the number of deflated ObjectMonitors. The given
2367 // list could be a per-thread in-use list or the global in-use list.
2368 // If a safepoint has started, then we save state via saved_mid_in_use_p
2369 // and return to the caller to honor the safepoint.
2370 //
2371 int ObjectSynchronizer::deflate_monitor_list_using_JT(ObjectMonitor** list_p,
2372 int* count_p,
2373 ObjectMonitor** free_head_p,
2374 ObjectMonitor** free_tail_p,
2375 ObjectMonitor** saved_mid_in_use_p) {
2376 assert(AsyncDeflateIdleMonitors, "sanity check");
2377 JavaThread* self = JavaThread::current();
2378
2379 ObjectMonitor* cur_mid_in_use = NULL;
2380 ObjectMonitor* mid = NULL;
2381 ObjectMonitor* next = NULL;
2382 ObjectMonitor* next_next = NULL;
2383 int deflated_count = 0;
2384 NoSafepointVerifier nsv;
2385
2386 // We use the more complicated lock-cur_mid_in_use-and-mid-as-we-go
2387 // protocol because om_release() can do list deletions in parallel;
2388 // this also prevents races with a list walker thread. We also
2389 // lock-next-next-as-we-go to prevent an om_flush() that is behind
2390 // this thread from passing us.
2391 if (*saved_mid_in_use_p == NULL) {
2392 // No saved state so start at the beginning.
2393 // Lock the list head so we can possibly deflate it:
2394 if ((mid = get_list_head_locked(list_p)) == NULL) {
2395 return 0; // The list is empty so nothing to deflate.
2396 }
2397 next = unmarked_next(mid);
2398 } else {
2399 // We're restarting after a safepoint so restore the necessary state
2400 // before we resume.
2401 cur_mid_in_use = *saved_mid_in_use_p;
2402 // Lock cur_mid_in_use so we can possibly update its
2403 // next field to extract a deflated ObjectMonitor.
2404 om_lock(cur_mid_in_use);
2405 mid = unmarked_next(cur_mid_in_use);
2406 if (mid == NULL) {
2407 om_unlock(cur_mid_in_use);
2408 *saved_mid_in_use_p = NULL;
2409 return 0; // The remainder is empty so nothing more to deflate.
2410 }
2411 // Lock mid so we can possibly deflate it:
2412 om_lock(mid);
2413 next = unmarked_next(mid);
2414 }
2415
2416 while (true) {
2417 // The current mid is locked at this point. If we have a
2418 // cur_mid_in_use, then it is also locked at this point.
2419
2420 if (next != NULL) {
2421 // We lock next so that an om_flush() thread that is behind us
2422 // cannot pass us when we unlock the current mid.
2423 om_lock(next);
2424 next_next = unmarked_next(next);
2425 }
2426
2427 // Only try to deflate if there is an associated Java object and if
2428 // mid is old (is not newly allocated and is not newly freed).
2429 if (mid->object() != NULL && mid->is_old() &&
2430 deflate_monitor_using_JT(mid, free_head_p, free_tail_p)) {
2431 // Deflation succeeded and already updated free_head_p and
2432 // free_tail_p as needed. Finish the move to the local free list
2433 // by unlinking mid from the global or per-thread in-use list.
2434 if (cur_mid_in_use == NULL) {
2435 // mid is the list head and it is locked. Switch the list head
2436 // to next which is also locked (if not NULL) and also leave
2437 // mid locked:
2438 Atomic::store(list_p, next);
2439 } else {
2440 ObjectMonitor* locked_next = mark_om_ptr(next);
2441 // mid and cur_mid_in_use are locked. Switch cur_mid_in_use's
2442 // next field to locked_next and also leave mid locked:
2443 cur_mid_in_use->set_next_om(locked_next);
2444 }
2445 // At this point mid is disconnected from the in-use list so
2446 // its lock longer has any effects on in-use list.
2447 deflated_count++;
2448 Atomic::dec(count_p);
2449 // mid is current tail in the free_head_p list so NULL terminate it
2450 // (which also unlocks it):
2451 mid->set_next_om(NULL);
2452
2453 // All the list management is done so move on to the next one:
2454 mid = next; // mid keeps non-NULL next's locked state
2455 next = next_next;
2456 } else {
2457 // mid is considered in-use if it does not have an associated
2458 // Java object or mid is not old or deflation did not succeed.
2459 // A mid->is_new() node can be seen here when it is freshly
2460 // returned by om_alloc() (and skips the deflation code path).
2461 // A mid->is_old() node can be seen here when deflation failed.
2462 // A mid->is_free() node can be seen here when a fresh node from
2463 // om_alloc() is released by om_release() due to losing the race
2464 // in inflate().
2465
2466 // All the list management is done so move on to the next one:
2467 if (cur_mid_in_use != NULL) {
2468 om_unlock(cur_mid_in_use);
2469 }
2470 // The next cur_mid_in_use keeps mid's lock state so
2471 // that it is stable for a possible next field change. It
2472 // cannot be modified by om_release() while it is locked.
2473 cur_mid_in_use = mid;
2474 mid = next; // mid keeps non-NULL next's locked state
2475 next = next_next;
2476
2477 if (SafepointMechanism::should_block(self) &&
2478 cur_mid_in_use != Atomic::load(list_p) && cur_mid_in_use->is_old()) {
2479 // If a safepoint has started and cur_mid_in_use is not the list
2480 // head and is old, then it is safe to use as saved state. Return
2481 // to the caller before blocking.
2482 *saved_mid_in_use_p = cur_mid_in_use;
2483 om_unlock(cur_mid_in_use);
2484 if (mid != NULL) {
2485 om_unlock(mid);
2486 }
2487 return deflated_count;
2488 }
2489 }
2490 if (mid == NULL) {
2491 if (cur_mid_in_use != NULL) {
2492 om_unlock(cur_mid_in_use);
2493 }
2494 break; // Reached end of the list so nothing more to deflate.
2495 }
2496
2497 // The current mid's next field is locked at this point. If we have
2498 // a cur_mid_in_use, then it is also locked at this point.
2499 }
2500 // We finished the list without a safepoint starting so there's
2501 // no need to save state.
2502 *saved_mid_in_use_p = NULL;
2503 return deflated_count;
2504 }
2505
2506 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2507 counters->n_in_use = 0; // currently associated with objects
2508 counters->n_in_circulation = 0; // extant
2509 counters->n_scavenged = 0; // reclaimed (global and per-thread)
2510 counters->per_thread_scavenged = 0; // per-thread scavenge total
2511 counters->per_thread_times = 0.0; // per-thread scavenge times
2512 }
2513
2514 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
2515 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2516
2517 if (AsyncDeflateIdleMonitors) {
2518 // Nothing to do when global idle ObjectMonitors are deflated using
2519 // a JavaThread unless a special deflation has been requested.
2520 if (!is_special_deflation_requested()) {
2521 return;
2522 }
2523 }
2524
2525 bool deflated = false;
2526
2527 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
2528 ObjectMonitor* free_tail_p = NULL;
2529 elapsedTimer timer;
2530
2531 if (log_is_enabled(Info, monitorinflation)) {
2532 timer.start();
2533 }
2534
2535 // Note: the thread-local monitors lists get deflated in
2536 // a separate pass. See deflate_thread_local_monitors().
2537
2538 // For moribund threads, scan om_list_globals._in_use_list
2539 int deflated_count = 0;
2540 if (Atomic::load(&om_list_globals._in_use_list) != NULL) {
2541 // Update n_in_circulation before om_list_globals._in_use_count is
2542 // updated by deflation.
2543 Atomic::add(&counters->n_in_circulation,
2544 Atomic::load(&om_list_globals._in_use_count));
2545
2546 deflated_count = deflate_monitor_list(&om_list_globals._in_use_list,
2547 &om_list_globals._in_use_count,
2548 &free_head_p, &free_tail_p);
2549 Atomic::add(&counters->n_in_use, Atomic::load(&om_list_globals._in_use_count));
2550 }
2551
2552 if (free_head_p != NULL) {
2553 // Move the deflated ObjectMonitors back to the global free list.
2554 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
2555 #ifdef ASSERT
2556 ObjectMonitor* l_next_om = free_tail_p->next_om();
2557 #endif
2558 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2559 prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count);
2560 Atomic::add(&counters->n_scavenged, deflated_count);
2561 }
2562 timer.stop();
2563
2564 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2565 LogStreamHandle(Info, monitorinflation) lsh_info;
2566 LogStream* ls = NULL;
2567 if (log_is_enabled(Debug, monitorinflation)) {
2568 ls = &lsh_debug;
2569 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2570 ls = &lsh_info;
2571 }
2572 if (ls != NULL) {
2573 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2574 }
2575 }
2576
2577 class HandshakeForDeflation : public HandshakeClosure {
2578 public:
2579 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
2580
2581 void do_thread(Thread* thread) {
2582 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
2583 INTPTR_FORMAT, p2i(thread));
2584 }
2585 };
2586
2587 void ObjectSynchronizer::deflate_idle_monitors_using_JT() {
2588 assert(AsyncDeflateIdleMonitors, "sanity check");
2589
2590 // Deflate any global idle monitors.
2591 deflate_global_idle_monitors_using_JT();
2592
2593 int count = 0;
2594 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2595 if (Atomic::load(&jt->om_in_use_count) > 0 && !jt->is_exiting()) {
2596 // This JavaThread is using ObjectMonitors so deflate any that
2597 // are idle unless this JavaThread is exiting; do not race with
2598 // ObjectSynchronizer::om_flush().
2599 deflate_per_thread_idle_monitors_using_JT(jt);
2600 count++;
2601 }
2602 }
2603 if (count > 0) {
2604 log_debug(monitorinflation)("did async deflation of idle monitors for %d thread(s).", count);
2605 }
2606
2607 log_info(monitorinflation)("async global_population=%d, global_in_use_count=%d, "
2608 "global_free_count=%d, global_wait_count=%d",
2609 Atomic::load(&om_list_globals._population),
2610 Atomic::load(&om_list_globals._in_use_count),
2611 Atomic::load(&om_list_globals._free_count),
2612 Atomic::load(&om_list_globals._wait_count));
2613
2614 // The ServiceThread's async deflation request has been processed.
2615 set_is_async_deflation_requested(false);
2616
2617 if (Atomic::load(&om_list_globals._wait_count) > 0) {
2618 // There are deflated ObjectMonitors waiting for a handshake
2619 // (or a safepoint) for safety.
2620
2621 ObjectMonitor* list = Atomic::load(&om_list_globals._wait_list);
2622 ADIM_guarantee(list != NULL, "om_list_globals._wait_list must not be NULL");
2623 int count = Atomic::load(&om_list_globals._wait_count);
2624 Atomic::store(&om_list_globals._wait_count, 0);
2625 Atomic::store(&om_list_globals._wait_list, (ObjectMonitor*)NULL);
2626
2627 // Find the tail for prepend_list_to_common(). No need to mark
2628 // ObjectMonitors for this list walk since only the deflater
2629 // thread manages the wait list.
2630 int l_count = 0;
2631 ObjectMonitor* tail = NULL;
2632 for (ObjectMonitor* n = list; n != NULL; n = unmarked_next(n)) {
2633 tail = n;
2634 l_count++;
2635 }
2636 ADIM_guarantee(count == l_count, "count=%d != l_count=%d", count, l_count);
2637
2638 // Will execute a safepoint if !ThreadLocalHandshakes:
2639 HandshakeForDeflation hfd_hc;
2640 Handshake::execute(&hfd_hc);
2641
2642 prepend_list_to_common(list, tail, count, &om_list_globals._free_list,
2643 &om_list_globals._free_count);
2644
2645 log_info(monitorinflation)("moved %d idle monitors from global waiting list to global free list", count);
2646 }
2647 }
2648
2649 // Deflate global idle ObjectMonitors using a JavaThread.
2650 //
2651 void ObjectSynchronizer::deflate_global_idle_monitors_using_JT() {
2652 assert(AsyncDeflateIdleMonitors, "sanity check");
2653 assert(Thread::current()->is_Java_thread(), "precondition");
2654 JavaThread* self = JavaThread::current();
2655
2656 deflate_common_idle_monitors_using_JT(true /* is_global */, self);
2657 }
2658
2659 // Deflate the specified JavaThread's idle ObjectMonitors using a JavaThread.
2660 //
2661 void ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT(JavaThread* target) {
2662 assert(AsyncDeflateIdleMonitors, "sanity check");
2663 assert(Thread::current()->is_Java_thread(), "precondition");
2664
2665 deflate_common_idle_monitors_using_JT(false /* !is_global */, target);
2666 }
2667
2668 // Deflate global or per-thread idle ObjectMonitors using a JavaThread.
2669 //
2670 void ObjectSynchronizer::deflate_common_idle_monitors_using_JT(bool is_global, JavaThread* target) {
2671 JavaThread* self = JavaThread::current();
2672
2673 int deflated_count = 0;
2674 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged ObjectMonitors
2675 ObjectMonitor* free_tail_p = NULL;
2676 ObjectMonitor* saved_mid_in_use_p = NULL;
2677 elapsedTimer timer;
2678
2679 if (log_is_enabled(Info, monitorinflation)) {
2680 timer.start();
2681 }
2682
2683 if (is_global) {
2684 OM_PERFDATA_OP(MonExtant, set_value(Atomic::load(&om_list_globals._in_use_count)));
2685 } else {
2686 OM_PERFDATA_OP(MonExtant, inc(Atomic::load(&target->om_in_use_count)));
2687 }
2688
2689 do {
2690 int local_deflated_count;
2691 if (is_global) {
2692 local_deflated_count =
2693 deflate_monitor_list_using_JT(&om_list_globals._in_use_list,
2694 &om_list_globals._in_use_count,
2695 &free_head_p, &free_tail_p,
2696 &saved_mid_in_use_p);
2697 } else {
2698 local_deflated_count =
2699 deflate_monitor_list_using_JT(&target->om_in_use_list,
2700 &target->om_in_use_count, &free_head_p,
2701 &free_tail_p, &saved_mid_in_use_p);
2702 }
2703 deflated_count += local_deflated_count;
2704
2705 if (free_head_p != NULL) {
2706 // Move the deflated ObjectMonitors to the global free list.
2707 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);
2708 // Note: The target thread can be doing an om_alloc() that
2709 // is trying to prepend an ObjectMonitor on its in-use list
2710 // at the same time that we have deflated the current in-use
2711 // list head and put it on the local free list. prepend_to_common()
2712 // will detect the race and retry which avoids list corruption,
2713 // but the next field in free_tail_p can flicker to marked
2714 // and then unmarked while prepend_to_common() is sorting it
2715 // all out.
2716 #ifdef ASSERT
2717 ObjectMonitor* l_next_om = unmarked_next(free_tail_p);
2718 #endif
2719 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2720
2721 prepend_list_to_global_wait_list(free_head_p, free_tail_p, local_deflated_count);
2722
2723 OM_PERFDATA_OP(Deflations, inc(local_deflated_count));
2724 }
2725
2726 if (saved_mid_in_use_p != NULL) {
2727 // deflate_monitor_list_using_JT() detected a safepoint starting.
2728 timer.stop();
2729 {
2730 if (is_global) {
2731 log_debug(monitorinflation)("pausing deflation of global idle monitors for a safepoint.");
2732 } else {
2733 log_debug(monitorinflation)("jt=" INTPTR_FORMAT ": pausing deflation of per-thread idle monitors for a safepoint.", p2i(target));
2734 }
2735 assert(SafepointMechanism::should_block(self), "sanity check");
2736 ThreadBlockInVM blocker(self);
2737 }
2738 // Prepare for another loop after the safepoint.
2739 free_head_p = NULL;
2740 free_tail_p = NULL;
2741 if (log_is_enabled(Info, monitorinflation)) {
2742 timer.start();
2743 }
2744 }
2745 } while (saved_mid_in_use_p != NULL);
2746 timer.stop();
2747
2748 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2749 LogStreamHandle(Info, monitorinflation) lsh_info;
2750 LogStream* ls = NULL;
2751 if (log_is_enabled(Debug, monitorinflation)) {
2752 ls = &lsh_debug;
2753 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2754 ls = &lsh_info;
2755 }
2756 if (ls != NULL) {
2757 if (is_global) {
2758 ls->print_cr("async-deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2759 } else {
2760 ls->print_cr("jt=" INTPTR_FORMAT ": async-deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(target), timer.seconds(), deflated_count);
2761 }
2762 }
2763 }
2764
2765 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2766 // Report the cumulative time for deflating each thread's idle
2767 // monitors. Note: if the work is split among more than one
2768 // worker thread, then the reported time will likely be more
2769 // than a beginning to end measurement of the phase.
2770 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged);
2771
2772 bool needs_special_deflation = is_special_deflation_requested();
2773 if (AsyncDeflateIdleMonitors && !needs_special_deflation) {
2774 // Nothing to do when idle ObjectMonitors are deflated using
2775 // a JavaThread unless a special deflation has been requested.
2776 return;
2777 }
2778
2779 if (log_is_enabled(Debug, monitorinflation)) {
2780 // exit_globals()'s call to audit_and_print_stats() is done
2781 // at the Info level and not at a safepoint.
2782 // For async deflation, audit_and_print_stats() is called in
2783 // ObjectSynchronizer::do_safepoint_work() at the Debug level
2784 // at a safepoint.
2785 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2786 } else if (log_is_enabled(Info, monitorinflation)) {
2787 log_info(monitorinflation)("global_population=%d, global_in_use_count=%d, "
2788 "global_free_count=%d, global_wait_count=%d",
2789 Atomic::load(&om_list_globals._population),
2790 Atomic::load(&om_list_globals._in_use_count),
2791 Atomic::load(&om_list_globals._free_count),
2792 Atomic::load(&om_list_globals._wait_count));
2793 }
2794
2795 Atomic::store(&_forceMonitorScavenge, 0); // Reset
2796
2797 OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged));
2798 OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation));
2799
2800 GVars.stw_random = os::random();
2801 GVars.stw_cycle++;
2802
2803 if (needs_special_deflation) {
2804 set_is_special_deflation_requested(false); // special deflation is done
2805 }
2806 }
2807
2808 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
2809 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2810
2811 if (AsyncDeflateIdleMonitors && !is_special_deflation_requested()) {
2812 // Nothing to do if a special deflation has NOT been requested.
2813 return;
2814 }
2815
2816 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
2817 ObjectMonitor* free_tail_p = NULL;
2818 elapsedTimer timer;
2819
2820 if (log_is_enabled(Info, safepoint, cleanup) ||
2821 log_is_enabled(Info, monitorinflation)) {
2822 timer.start();
2823 }
2824
2825 // Update n_in_circulation before om_in_use_count is updated by deflation.
2826 Atomic::add(&counters->n_in_circulation, Atomic::load(&thread->om_in_use_count));
2827
2828 int deflated_count = deflate_monitor_list(&thread->om_in_use_list, &thread->om_in_use_count, &free_head_p, &free_tail_p);
2829 Atomic::add(&counters->n_in_use, Atomic::load(&thread->om_in_use_count));
2830
2831 if (free_head_p != NULL) {
2832 // Move the deflated ObjectMonitors back to the global free list.
2833 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
2834 #ifdef ASSERT
2835 ObjectMonitor* l_next_om = free_tail_p->next_om();
2836 #endif
2837 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2838 prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count);
2839 Atomic::add(&counters->n_scavenged, deflated_count);
2840 Atomic::add(&counters->per_thread_scavenged, deflated_count);
2841 }
2842
2843 timer.stop();
2844 counters->per_thread_times += timer.seconds();
2845
2846 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2847 LogStreamHandle(Info, monitorinflation) lsh_info;
2848 LogStream* ls = NULL;
2849 if (log_is_enabled(Debug, monitorinflation)) {
2850 ls = &lsh_debug;
2851 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2852 ls = &lsh_info;
2853 }
2854 if (ls != NULL) {
2855 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
2856 }
2857 }
2858
2859 // Monitor cleanup on JavaThread::exit
2860
2861 // Iterate through monitor cache and attempt to release thread's monitors
2862 // Gives up on a particular monitor if an exception occurs, but continues
2863 // the overall iteration, swallowing the exception.
2864 class ReleaseJavaMonitorsClosure: public MonitorClosure {
2865 private:
2866 TRAPS;
2867
2868 public:
2869 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
2870 void do_monitor(ObjectMonitor* mid) {
2871 if (mid->owner() == THREAD) {
2872 (void)mid->complete_exit(CHECK);
2873 }
2874 }
2875 };
2876
2877 // Release all inflated monitors owned by THREAD. Lightweight monitors are
2878 // ignored. This is meant to be called during JNI thread detach which assumes
2879 // all remaining monitors are heavyweight. All exceptions are swallowed.
2880 // Scanning the extant monitor list can be time consuming.
2881 // A simple optimization is to add a per-thread flag that indicates a thread
2882 // called jni_monitorenter() during its lifetime.
2883 //
2884 // Instead of No_Savepoint_Verifier it might be cheaper to
2885 // use an idiom of the form:
2886 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
2887 // <code that must not run at safepoint>
2888 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
2889 // Since the tests are extremely cheap we could leave them enabled
2890 // for normal product builds.
2891
2892 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
2893 assert(THREAD == JavaThread::current(), "must be current Java thread");
2894 NoSafepointVerifier nsv;
2895 ReleaseJavaMonitorsClosure rjmc(THREAD);
2896 ObjectSynchronizer::monitors_iterate(&rjmc);
2897 THREAD->clear_pending_exception();
2898 }
2899
2900 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
2901 switch (cause) {
2902 case inflate_cause_vm_internal: return "VM Internal";
2903 case inflate_cause_monitor_enter: return "Monitor Enter";
2904 case inflate_cause_wait: return "Monitor Wait";
2905 case inflate_cause_notify: return "Monitor Notify";
2906 case inflate_cause_hash_code: return "Monitor Hash Code";
2907 case inflate_cause_jni_enter: return "JNI Monitor Enter";
2908 case inflate_cause_jni_exit: return "JNI Monitor Exit";
2909 default:
2910 ShouldNotReachHere();
2911 }
2912 return "Unknown";
2913 }
2914
2915 //------------------------------------------------------------------------------
2916 // Debugging code
2917
2918 u_char* ObjectSynchronizer::get_gvars_addr() {
2919 return (u_char*)&GVars;
2920 }
2921
2922 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
2923 return (u_char*)&GVars.hc_sequence;
2924 }
2925
2926 size_t ObjectSynchronizer::get_gvars_size() {
2927 return sizeof(SharedGlobals);
2928 }
2929
2930 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
2931 return (u_char*)&GVars.stw_random;
2932 }
2933
2934 // This function can be called at a safepoint or it can be called when
2935 // we are trying to exit the VM. When we are trying to exit the VM, the
2936 // list walker functions can run in parallel with the other list
2937 // operations so spin-locking is used for safety.
2938 //
2939 // Calls to this function can be added in various places as a debugging
2940 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
2941 // details logged at the Info level and 'false' for the 'on_exit'
2942 // parameter to have in-use monitor details logged at the Trace level.
2943 // deflate_monitor_list() no longer uses spin-locking so be careful
2944 // when adding audit_and_print_stats() calls at a safepoint.
2945 //
2946 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
2947 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
2948
2949 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2950 LogStreamHandle(Info, monitorinflation) lsh_info;
2951 LogStreamHandle(Trace, monitorinflation) lsh_trace;
2952 LogStream* ls = NULL;
2953 if (log_is_enabled(Trace, monitorinflation)) {
2954 ls = &lsh_trace;
2955 } else if (log_is_enabled(Debug, monitorinflation)) {
2956 ls = &lsh_debug;
2957 } else if (log_is_enabled(Info, monitorinflation)) {
2958 ls = &lsh_info;
2959 }
2960 assert(ls != NULL, "sanity check");
2961
2962 // Log counts for the global and per-thread monitor lists:
2963 int chk_om_population = log_monitor_list_counts(ls);
2964 int error_cnt = 0;
2965
2966 ls->print_cr("Checking global lists:");
2967
2968 // Check om_list_globals._population:
2969 if (Atomic::load(&om_list_globals._population) == chk_om_population) {
2970 ls->print_cr("global_population=%d equals chk_om_population=%d",
2971 Atomic::load(&om_list_globals._population), chk_om_population);
2972 } else {
2973 // With fine grained locks on the monitor lists, it is possible for
2974 // log_monitor_list_counts() to return a value that doesn't match
2975 // om_list_globals._population. So far a higher value has been
2976 // seen in testing so something is being double counted by
2977 // log_monitor_list_counts().
2978 ls->print_cr("WARNING: global_population=%d is not equal to "
2979 "chk_om_population=%d",
2980 Atomic::load(&om_list_globals._population), chk_om_population);
2981 }
2982
2983 // Check om_list_globals._in_use_list and om_list_globals._in_use_count:
2984 chk_global_in_use_list_and_count(ls, &error_cnt);
2985
2986 // Check om_list_globals._free_list and om_list_globals._free_count:
2987 chk_global_free_list_and_count(ls, &error_cnt);
2988
2989 // Check om_list_globals._wait_list and om_list_globals._wait_count:
2990 chk_global_wait_list_and_count(ls, &error_cnt);
2991
2992 ls->print_cr("Checking per-thread lists:");
2993
2994 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2995 // Check om_in_use_list and om_in_use_count:
2996 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
2997
2998 // Check om_free_list and om_free_count:
2999 chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
3000 }
3001
3002 if (error_cnt == 0) {
3003 ls->print_cr("No errors found in monitor list checks.");
3004 } else {
3005 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
3006 }
3007
3008 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
3009 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
3010 // When exiting this log output is at the Info level. When called
3011 // at a safepoint, this log output is at the Trace level since
3012 // there can be a lot of it.
3013 log_in_use_monitor_details(ls);
3014 }
3015
3016 ls->flush();
3017
3018 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
3019 }
3020
3021 // Check a free monitor entry; log any errors.
3022 void ObjectSynchronizer::chk_free_entry(JavaThread* jt, ObjectMonitor* n,
3023 outputStream * out, int *error_cnt_p) {
3024 stringStream ss;
3025 if (n->is_busy()) {
3026 if (jt != NULL) {
3027 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3028 ": free per-thread monitor must not be busy: %s", p2i(jt),
3029 p2i(n), n->is_busy_to_string(&ss));
3030 } else {
3031 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
3032 "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
3033 }
3034 *error_cnt_p = *error_cnt_p + 1;
3035 }
3036 if (n->header().value() != 0) {
3037 if (jt != NULL) {
3038 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3039 ": free per-thread monitor must have NULL _header "
3040 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
3041 n->header().value());
3042 *error_cnt_p = *error_cnt_p + 1;
3043 } else if (!AsyncDeflateIdleMonitors) {
3044 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
3045 "must have NULL _header field: _header=" INTPTR_FORMAT,
3046 p2i(n), n->header().value());
3047 *error_cnt_p = *error_cnt_p + 1;
3048 }
3049 }
3050 if (n->object() != NULL) {
3051 if (jt != NULL) {
3052 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3053 ": free per-thread monitor must have NULL _object "
3054 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
3055 p2i(n->object()));
3056 } else {
3057 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
3058 "must have NULL _object field: _object=" INTPTR_FORMAT,
3059 p2i(n), p2i(n->object()));
3060 }
3061 *error_cnt_p = *error_cnt_p + 1;
3062 }
3063 }
3064
3065 // Lock the next ObjectMonitor for traversal and unlock the current
3066 // ObjectMonitor. Returns the next ObjectMonitor if there is one.
3067 // Otherwise returns NULL (after unlocking the current ObjectMonitor).
3068 // This function is used by the various list walker functions to
3069 // safely walk a list without allowing an ObjectMonitor to be moved
3070 // to another list in the middle of a walk.
3071 static ObjectMonitor* lock_next_for_traversal(ObjectMonitor* cur) {
3072 assert(is_locked(cur), "cur=" INTPTR_FORMAT " must be locked", p2i(cur));
3073 ObjectMonitor* next = unmarked_next(cur);
3074 if (next == NULL) { // Reached the end of the list.
3075 om_unlock(cur);
3076 return NULL;
3077 }
3078 om_lock(next); // Lock next before unlocking current to keep
3079 om_unlock(cur); // from being by-passed by another thread.
3080 return next;
3081 }
3082
3083 // Check the global free list and count; log the results of the checks.
3084 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
3085 int *error_cnt_p) {
3086 int chk_om_free_count = 0;
3087 ObjectMonitor* cur = NULL;
3088 if ((cur = get_list_head_locked(&om_list_globals._free_list)) != NULL) {
3089 // Marked the global free list head so process the list.
3090 while (true) {
3091 chk_free_entry(NULL /* jt */, cur, out, error_cnt_p);
3092 chk_om_free_count++;
3093
3094 cur = lock_next_for_traversal(cur);
3095 if (cur == NULL) {
3096 break;
3097 }
3098 }
3099 }
3100 int l_free_count = Atomic::load(&om_list_globals._free_count);
3101 if (l_free_count == chk_om_free_count) {
3102 out->print_cr("global_free_count=%d equals chk_om_free_count=%d",
3103 l_free_count, chk_om_free_count);
3104 } else {
3105 // With fine grained locks on om_list_globals._free_list, it
3106 // is possible for an ObjectMonitor to be prepended to
3107 // om_list_globals._free_list after we started calculating
3108 // chk_om_free_count so om_list_globals._free_count may not
3109 // match anymore.
3110 out->print_cr("WARNING: global_free_count=%d is not equal to "
3111 "chk_om_free_count=%d", l_free_count, chk_om_free_count);
3112 }
3113 }
3114
3115 // Check the global wait list and count; log the results of the checks.
3116 void ObjectSynchronizer::chk_global_wait_list_and_count(outputStream * out,
3117 int *error_cnt_p) {
3118 int chk_om_wait_count = 0;
3119 ObjectMonitor* cur = NULL;
3120 if ((cur = get_list_head_locked(&om_list_globals._wait_list)) != NULL) {
3121 // Marked the global wait list head so process the list.
3122 while (true) {
3123 // Rules for om_list_globals._wait_list are the same as for
3124 // om_list_globals._free_list:
3125 chk_free_entry(NULL /* jt */, cur, out, error_cnt_p);
3126 chk_om_wait_count++;
3127
3128 cur = lock_next_for_traversal(cur);
3129 if (cur == NULL) {
3130 break;
3131 }
3132 }
3133 }
3134 if (Atomic::load(&om_list_globals._wait_count) == chk_om_wait_count) {
3135 out->print_cr("global_wait_count=%d equals chk_om_wait_count=%d",
3136 Atomic::load(&om_list_globals._wait_count), chk_om_wait_count);
3137 } else {
3138 out->print_cr("ERROR: global_wait_count=%d is not equal to "
3139 "chk_om_wait_count=%d",
3140 Atomic::load(&om_list_globals._wait_count), chk_om_wait_count);
3141 *error_cnt_p = *error_cnt_p + 1;
3142 }
3143 }
3144
3145 // Check the global in-use list and count; log the results of the checks.
3146 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
3147 int *error_cnt_p) {
3148 int chk_om_in_use_count = 0;
3149 ObjectMonitor* cur = NULL;
3150 if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) {
3151 // Marked the global in-use list head so process the list.
3152 while (true) {
3153 chk_in_use_entry(NULL /* jt */, cur, out, error_cnt_p);
3154 chk_om_in_use_count++;
3155
3156 cur = lock_next_for_traversal(cur);
3157 if (cur == NULL) {
3158 break;
3159 }
3160 }
3161 }
3162 int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
3163 if (l_in_use_count == chk_om_in_use_count) {
3164 out->print_cr("global_in_use_count=%d equals chk_om_in_use_count=%d",
3165 l_in_use_count, chk_om_in_use_count);
3166 } else {
3167 // With fine grained locks on the monitor lists, it is possible for
3168 // an exiting JavaThread to put its in-use ObjectMonitors on the
3169 // global in-use list after chk_om_in_use_count is calculated above.
3170 out->print_cr("WARNING: global_in_use_count=%d is not equal to chk_om_in_use_count=%d",
3171 l_in_use_count, chk_om_in_use_count);
3172 }
3173 }
3174
3175 // Check an in-use monitor entry; log any errors.
3176 void ObjectSynchronizer::chk_in_use_entry(JavaThread* jt, ObjectMonitor* n,
3177 outputStream * out, int *error_cnt_p) {
3178 if (n->header().value() == 0) {
3179 if (jt != NULL) {
3180 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3181 ": in-use per-thread monitor must have non-NULL _header "
3182 "field.", p2i(jt), p2i(n));
3183 } else {
3184 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
3185 "must have non-NULL _header field.", p2i(n));
3186 }
3187 *error_cnt_p = *error_cnt_p + 1;
3188 }
3189 if (n->object() == NULL) {
3190 if (jt != NULL) {
3191 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3192 ": in-use per-thread monitor must have non-NULL _object "
3193 "field.", p2i(jt), p2i(n));
3194 } else {
3195 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
3196 "must have non-NULL _object field.", p2i(n));
3197 }
3198 *error_cnt_p = *error_cnt_p + 1;
3199 }
3200 const oop obj = (oop)n->object();
3201 const markWord mark = obj->mark();
3202 if (!mark.has_monitor()) {
3203 if (jt != NULL) {
3204 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3205 ": in-use per-thread monitor's object does not think "
3206 "it has a monitor: obj=" INTPTR_FORMAT ", mark="
3207 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), mark.value());
3208 } else {
3209 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
3210 "monitor's object does not think it has a monitor: obj="
3211 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
3212 p2i(obj), mark.value());
3213 }
3214 *error_cnt_p = *error_cnt_p + 1;
3215 }
3216 ObjectMonitor* const obj_mon = mark.monitor();
3217 if (n != obj_mon) {
3218 if (jt != NULL) {
3219 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3220 ": in-use per-thread monitor's object does not refer "
3221 "to the same monitor: obj=" INTPTR_FORMAT ", mark="
3222 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
3223 p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
3224 } else {
3225 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
3226 "monitor's object does not refer to the same monitor: obj="
3227 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
3228 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
3229 }
3230 *error_cnt_p = *error_cnt_p + 1;
3231 }
3232 }
3233
3234 // Check the thread's free list and count; log the results of the checks.
3235 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
3236 outputStream * out,
3237 int *error_cnt_p) {
3238 int chk_om_free_count = 0;
3239 ObjectMonitor* cur = NULL;
3240 if ((cur = get_list_head_locked(&jt->om_free_list)) != NULL) {
3241 // Marked the per-thread free list head so process the list.
3242 while (true) {
3243 chk_free_entry(jt, cur, out, error_cnt_p);
3244 chk_om_free_count++;
3245
3246 cur = lock_next_for_traversal(cur);
3247 if (cur == NULL) {
3248 break;
3249 }
3250 }
3251 }
3252 int l_om_free_count = Atomic::load(&jt->om_free_count);
3253 if (l_om_free_count == chk_om_free_count) {
3254 out->print_cr("jt=" INTPTR_FORMAT ": om_free_count=%d equals "
3255 "chk_om_free_count=%d", p2i(jt), l_om_free_count, chk_om_free_count);
3256 } else {
3257 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_free_count=%d is not "
3258 "equal to chk_om_free_count=%d", p2i(jt), l_om_free_count,
3259 chk_om_free_count);
3260 *error_cnt_p = *error_cnt_p + 1;
3261 }
3262 }
3263
3264 // Check the thread's in-use list and count; log the results of the checks.
3265 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
3266 outputStream * out,
3267 int *error_cnt_p) {
3268 int chk_om_in_use_count = 0;
3269 ObjectMonitor* cur = NULL;
3270 if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
3271 // Marked the per-thread in-use list head so process the list.
3272 while (true) {
3273 chk_in_use_entry(jt, cur, out, error_cnt_p);
3274 chk_om_in_use_count++;
3275
3276 cur = lock_next_for_traversal(cur);
3277 if (cur == NULL) {
3278 break;
3279 }
3280 }
3281 }
3282 int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
3283 if (l_om_in_use_count == chk_om_in_use_count) {
3284 out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals "
3285 "chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
3286 chk_om_in_use_count);
3287 } else {
3288 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not "
3289 "equal to chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
3290 chk_om_in_use_count);
3291 *error_cnt_p = *error_cnt_p + 1;
3292 }
3293 }
3294
3295 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
3296 // flags indicate why the entry is in-use, 'object' and 'object type'
3297 // indicate the associated object and its type.
3298 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out) {
3299 stringStream ss;
3300 if (Atomic::load(&om_list_globals._in_use_count) > 0) {
3301 out->print_cr("In-use global monitor info:");
3302 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
3303 out->print_cr("%18s %s %18s %18s",
3304 "monitor", "BHL", "object", "object type");
3305 out->print_cr("================== === ================== ==================");
3306 ObjectMonitor* cur = NULL;
3307 if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) {
3308 // Marked the global in-use list head so process the list.
3309 while (true) {
3310 const oop obj = (oop) cur->object();
3311 const markWord mark = cur->header();
3312 ResourceMark rm;
3313 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(cur),
3314 cur->is_busy() != 0, mark.hash() != 0, cur->owner() != NULL,
3315 p2i(obj), obj->klass()->external_name());
3316 if (cur->is_busy() != 0) {
3317 out->print(" (%s)", cur->is_busy_to_string(&ss));
3318 ss.reset();
3319 }
3320 out->cr();
3321
3322 cur = lock_next_for_traversal(cur);
3323 if (cur == NULL) {
3324 break;
3325 }
3326 }
3327 }
3328 }
3329
3330 out->print_cr("In-use per-thread monitor info:");
3331 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
3332 out->print_cr("%18s %18s %s %18s %18s",
3333 "jt", "monitor", "BHL", "object", "object type");
3334 out->print_cr("================== ================== === ================== ==================");
3335 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
3336 ObjectMonitor* cur = NULL;
3337 if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
3338 // Marked the global in-use list head so process the list.
3339 while (true) {
3340 const oop obj = (oop) cur->object();
3341 const markWord mark = cur->header();
3342 ResourceMark rm;
3343 out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT
3344 " %s", p2i(jt), p2i(cur), cur->is_busy() != 0,
3345 mark.hash() != 0, cur->owner() != NULL, p2i(obj),
3346 obj->klass()->external_name());
3347 if (cur->is_busy() != 0) {
3348 out->print(" (%s)", cur->is_busy_to_string(&ss));
3349 ss.reset();
3350 }
3351 out->cr();
3352
3353 cur = lock_next_for_traversal(cur);
3354 if (cur == NULL) {
3355 break;
3356 }
3357 }
3358 }
3359 }
3360
3361 out->flush();
3362 }
3363
3364 // Log counts for the global and per-thread monitor lists and return
3365 // the population count.
3366 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
3367 int pop_count = 0;
3368 out->print_cr("%18s %10s %10s %10s %10s",
3369 "Global Lists:", "InUse", "Free", "Wait", "Total");
3370 out->print_cr("================== ========== ========== ========== ==========");
3371 int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
3372 int l_free_count = Atomic::load(&om_list_globals._free_count);
3373 int l_wait_count = Atomic::load(&om_list_globals._wait_count);
3374 out->print_cr("%18s %10d %10d %10d %10d", "", l_in_use_count,
3375 l_free_count, l_wait_count,
3376 Atomic::load(&om_list_globals._population));
3377 pop_count += l_in_use_count + l_free_count + l_wait_count;
3378
3379 out->print_cr("%18s %10s %10s %10s",
3380 "Per-Thread Lists:", "InUse", "Free", "Provision");
3381 out->print_cr("================== ========== ========== ==========");
3382
3383 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
3384 int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
3385 int l_om_free_count = Atomic::load(&jt->om_free_count);
3386 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
3387 l_om_in_use_count, l_om_free_count, jt->om_free_provision);
3388 pop_count += l_om_in_use_count + l_om_free_count;
3389 }
3390 return pop_count;
3391 }
3392
3393 #ifndef PRODUCT
3394
3395 // Check if monitor belongs to the monitor cache
3396 // The list is grow-only so it's *relatively* safe to traverse
3397 // the list of extant blocks without taking a lock.
3398
3399 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
3400 PaddedObjectMonitor* block = Atomic::load(&g_block_list);
3401 while (block != NULL) {
3402 assert(block->object() == CHAINMARKER, "must be a block header");
3403 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
3404 address mon = (address)monitor;
3405 address blk = (address)block;
3406 size_t diff = mon - blk;
3407 assert((diff % sizeof(PaddedObjectMonitor)) == 0, "must be aligned");
3408 return 1;
3409 }
3410 // unmarked_next() is not needed with g_block_list (no locking
3411 // used with block linkage _next_om fields).
3412 block = (PaddedObjectMonitor*)block->next_om();
3413 }
3414 return 0;
3415 }
3416
3417 #endif