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