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. However, we only ever bias Java instances and all
986 // of the call sites of identity_hash that might revoke biases have
987 // been checked to make sure they can handle a safepoint. The
988 // added check of the bias pattern is to avoid useless calls to
989 // thread-local storage.
990 if (obj->mark().has_bias_pattern()) {
991 // Handle for oop obj in case of STW safepoint
992 Handle hobj(self, obj);
993 // Relaxing assertion for bug 6320749.
994 assert(Universe::verify_in_progress() ||
995 !SafepointSynchronize::is_at_safepoint(),
996 "biases should not be seen by VM thread here");
997 BiasedLocking::revoke(hobj, JavaThread::current());
998 obj = hobj();
999 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
1000 }
1001 }
1002
1003 // hashCode() is a heap mutator ...
1004 // Relaxing assertion for bug 6320749.
1005 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
1006 !SafepointSynchronize::is_at_safepoint(), "invariant");
1007 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
1008 self->is_Java_thread() , "invariant");
1009 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
1010 ((JavaThread *)self)->thread_state() != _thread_blocked, "invariant");
1011
1012 while (true) {
1013 ObjectMonitor* monitor = NULL;
1014 markWord temp, test;
1015 intptr_t hash;
1016 markWord mark = read_stable_mark(obj);
1017
1018 // object should remain ineligible for biased locking
1019 assert(!mark.has_bias_pattern(), "invariant");
1020
1021 if (mark.is_neutral()) { // if this is a normal header
1022 hash = mark.hash();
1023 if (hash != 0) { // if it has a hash, just return it
1024 return hash;
1025 }
1026 hash = get_next_hash(self, obj); // get a new hash
1027 temp = mark.copy_set_hash(hash); // merge the hash into header
1028 // try to install the hash
1029 test = obj->cas_set_mark(temp, mark);
1030 if (test == mark) { // if the hash was installed, return it
1031 return hash;
1032 }
1033 // Failed to install the hash. It could be that another thread
1034 // installed the hash just before our attempt or inflation has
1035 // occurred or... so we fall thru to inflate the monitor for
1036 // stability and then install the hash.
1037 } else if (mark.has_monitor()) {
1038 monitor = mark.monitor();
1039 temp = monitor->header();
1040 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1041 hash = temp.hash();
1042 if (hash != 0) {
1043 // It has a hash.
1044
1045 // Separate load of dmw/header above from the loads in
1046 // is_being_async_deflated().
1047 if (support_IRIW_for_not_multiple_copy_atomic_cpu) {
1048 // A non-multiple copy atomic (nMCA) machine needs a bigger
1049 // hammer to separate the load above and the loads below.
1050 OrderAccess::fence();
1051 } else {
1052 OrderAccess::loadload();
1053 }
1054 if (monitor->is_being_async_deflated()) {
1055 // But we can't safely use the hash if we detect that async
1056 // deflation has occurred. So we attempt to restore the
1057 // header/dmw to the object's header so that we only retry
1058 // once if the deflater thread happens to be slow.
1059 monitor->install_displaced_markword_in_object(obj);
1060 continue;
1061 }
1062 return hash;
1063 }
1064 // Fall thru so we only have one place that installs the hash in
1065 // the ObjectMonitor.
1066 } else if (self->is_lock_owned((address)mark.locker())) {
1067 // This is a stack lock owned by the calling thread so fetch the
1068 // displaced markWord from the BasicLock on the stack.
1069 temp = mark.displaced_mark_helper();
1070 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1071 hash = temp.hash();
1072 if (hash != 0) { // if it has a hash, just return it
1073 return hash;
1074 }
1075 // WARNING:
1076 // The displaced header in the BasicLock on a thread's stack
1077 // is strictly immutable. It CANNOT be changed in ANY cases.
1078 // So we have to inflate the stack lock into an ObjectMonitor
1079 // even if the current thread owns the lock. The BasicLock on
1080 // a thread's stack can be asynchronously read by other threads
1081 // during an inflate() call so any change to that stack memory
1082 // may not propagate to other threads correctly.
1083 }
1084
1085 // Inflate the monitor to set the hash.
1086
1087 // An async deflation can race after the inflate() call and before we
1088 // can update the ObjectMonitor's header with the hash value below.
1089 monitor = inflate(self, obj, inflate_cause_hash_code);
1090 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1091 mark = monitor->header();
1092 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1093 hash = mark.hash();
1094 if (hash == 0) { // if it does not have a hash
1095 hash = get_next_hash(self, obj); // get a new hash
1096 temp = mark.copy_set_hash(hash); // merge the hash into header
1097 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1098 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1099 test = markWord(v);
1100 if (test != mark) {
1101 // The attempt to update the ObjectMonitor's header/dmw field
1102 // did not work. This can happen if another thread managed to
1103 // merge in the hash just before our cmpxchg().
1104 // If we add any new usages of the header/dmw field, this code
1105 // will need to be updated.
1106 hash = test.hash();
1107 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1108 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1109 }
1110 if (monitor->is_being_async_deflated()) {
1111 // If we detect that async deflation has occurred, then we
1112 // attempt to restore the header/dmw to the object's header
1113 // so that we only retry once if the deflater thread happens
1114 // to be slow.
1115 monitor->install_displaced_markword_in_object(obj);
1116 continue;
1117 }
1118 }
1119 // We finally get the hash.
1120 return hash;
1121 }
1122 }
1123
1124 // Deprecated -- use FastHashCode() instead.
1125
1126 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
1127 return FastHashCode(Thread::current(), obj());
1128 }
1129
1130
1131 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
1132 Handle h_obj) {
1133 if (UseBiasedLocking) {
1134 BiasedLocking::revoke(h_obj, thread);
1135 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1136 }
1137
1138 assert(thread == JavaThread::current(), "Can only be called on current thread");
1139 oop obj = h_obj();
1140
1141 markWord mark = read_stable_mark(obj);
1142
1143 // Uncontended case, header points to stack
1144 if (mark.has_locker()) {
1145 return thread->is_lock_owned((address)mark.locker());
1146 }
1147 // Contended case, header points to ObjectMonitor (tagged pointer)
1148 if (mark.has_monitor()) {
1149 // The first stage of async deflation does not affect any field
1150 // used by this comparison so the ObjectMonitor* is usable here.
1151 ObjectMonitor* monitor = mark.monitor();
1152 return monitor->is_entered(thread) != 0;
1153 }
1154 // Unlocked case, header in place
1155 assert(mark.is_neutral(), "sanity check");
1156 return false;
1157 }
1158
1159 // Be aware of this method could revoke bias of the lock object.
1160 // This method queries the ownership of the lock handle specified by 'h_obj'.
1161 // If the current thread owns the lock, it returns owner_self. If no
1162 // thread owns the lock, it returns owner_none. Otherwise, it will return
1163 // owner_other.
1164 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
1165 (JavaThread *self, Handle h_obj) {
1166 // The caller must beware this method can revoke bias, and
1167 // revocation can result in a safepoint.
1168 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
1169 assert(self->thread_state() != _thread_blocked, "invariant");
1170
1171 // Possible mark states: neutral, biased, stack-locked, inflated
1172
1173 if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) {
1174 // CASE: biased
1175 BiasedLocking::revoke(h_obj, self);
1176 assert(!h_obj->mark().has_bias_pattern(),
1177 "biases should be revoked by now");
1178 }
1179
1180 assert(self == JavaThread::current(), "Can only be called on current thread");
1181 oop obj = h_obj();
1182 markWord mark = read_stable_mark(obj);
1183
1184 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
1185 if (mark.has_locker()) {
1186 return self->is_lock_owned((address)mark.locker()) ?
1187 owner_self : owner_other;
1188 }
1189
1190 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
1191 if (mark.has_monitor()) {
1192 // The first stage of async deflation does not affect any field
1193 // used by this comparison so the ObjectMonitor* is usable here.
1194 ObjectMonitor* monitor = mark.monitor();
1195 void* owner = monitor->owner();
1196 if (owner == NULL) return owner_none;
1197 return (owner == self ||
1198 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
1199 }
1200
1201 // CASE: neutral
1202 assert(mark.is_neutral(), "sanity check");
1203 return owner_none; // it's unlocked
1204 }
1205
1206 // FIXME: jvmti should call this
1207 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1208 if (UseBiasedLocking) {
1209 if (SafepointSynchronize::is_at_safepoint()) {
1210 BiasedLocking::revoke_at_safepoint(h_obj);
1211 } else {
1212 BiasedLocking::revoke(h_obj, JavaThread::current());
1213 }
1214 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1215 }
1216
1217 oop obj = h_obj();
1218 address owner = NULL;
1219
1220 markWord mark = read_stable_mark(obj);
1221
1222 // Uncontended case, header points to stack
1223 if (mark.has_locker()) {
1224 owner = (address) mark.locker();
1225 }
1226
1227 // Contended case, header points to ObjectMonitor (tagged pointer)
1228 else if (mark.has_monitor()) {
1229 // The first stage of async deflation does not affect any field
1230 // used by this comparison so the ObjectMonitor* is usable here.
1231 ObjectMonitor* monitor = mark.monitor();
1232 assert(monitor != NULL, "monitor should be non-null");
1233 owner = (address) monitor->owner();
1234 }
1235
1236 if (owner != NULL) {
1237 // owning_thread_from_monitor_owner() may also return NULL here
1238 return Threads::owning_thread_from_monitor_owner(t_list, owner);
1239 }
1240
1241 // Unlocked case, header in place
1242 // Cannot have assertion since this object may have been
1243 // locked by another thread when reaching here.
1244 // assert(mark.is_neutral(), "sanity check");
1245
1246 return NULL;
1247 }
1248
1249 // Visitors ...
1250
1251 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
1252 PaddedObjectMonitor* block = Atomic::load(&g_block_list);
1253 while (block != NULL) {
1254 assert(block->object() == CHAINMARKER, "must be a block header");
1255 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
1256 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
1257 if (mid->object() != NULL) {
1258 // Only process with closure if the object is set.
1259
1260 // monitors_iterate() is only called at a safepoint or when the
1261 // target thread is suspended or when the target thread is
1262 // operating on itself. The current closures in use today are
1263 // only interested in an owned ObjectMonitor and ownership
1264 // cannot be dropped under the calling contexts so the
1265 // ObjectMonitor cannot be async deflated.
1266 closure->do_monitor(mid);
1267 }
1268 }
1269 // unmarked_next() is not needed with g_block_list (no locking
1270 // used with block linkage _next_om fields).
1271 block = (PaddedObjectMonitor*)block->next_om();
1272 }
1273 }
1274
1275 static bool monitors_used_above_threshold() {
1276 int population = Atomic::load(&om_list_globals._population);
1277 if (population == 0) {
1278 return false;
1279 }
1280 if (MonitorUsedDeflationThreshold > 0) {
1281 int monitors_used = population - Atomic::load(&om_list_globals._free_count) -
1282 Atomic::load(&om_list_globals._wait_count);
1283 int monitor_usage = (monitors_used * 100LL) / population;
1284 return monitor_usage > MonitorUsedDeflationThreshold;
1285 }
1286 return false;
1287 }
1288
1289 bool ObjectSynchronizer::is_async_deflation_needed() {
1290 if (is_async_deflation_requested()) {
1291 // Async deflation request.
1292 return true;
1293 }
1294 if (AsyncDeflationInterval > 0 &&
1295 time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1296 monitors_used_above_threshold()) {
1297 // It's been longer than our specified deflate interval and there
1298 // are too many monitors in use. We don't deflate more frequently
1299 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1300 // in order to not swamp the ServiceThread.
1301 return true;
1302 }
1303 return false;
1304 }
1305
1306 bool ObjectSynchronizer::request_deflate_idle_monitors() {
1307 bool is_JavaThread = Thread::current()->is_Java_thread();
1308 bool ret_code = false;
1309
1310 jlong last_time = last_async_deflation_time_ns();
1311 set_is_async_deflation_requested(true);
1312 {
1313 MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
1314 ml.notify_all();
1315 }
1316 const int N_CHECKS = 5;
1317 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1318 if (last_async_deflation_time_ns() > last_time) {
1319 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1320 ret_code = true;
1321 break;
1322 }
1323 if (is_JavaThread) {
1324 // JavaThread has to honor the blocking protocol.
1325 ThreadBlockInVM tbivm(JavaThread::current());
1326 os::naked_short_sleep(999); // sleep for almost 1 second
1327 } else {
1328 os::naked_short_sleep(999); // sleep for almost 1 second
1329 }
1330 }
1331 if (!ret_code) {
1332 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1333 }
1334
1335 return ret_code;
1336 }
1337
1338 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1339 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1340 }
1341
1342 void ObjectSynchronizer::oops_do(OopClosure* f) {
1343 // We only scan the global used list here (for moribund threads), and
1344 // the thread-local monitors in Thread::oops_do().
1345 global_used_oops_do(f);
1346 }
1347
1348 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
1349 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1350 list_oops_do(Atomic::load(&om_list_globals._in_use_list), f);
1351 }
1352
1353 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
1354 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1355 list_oops_do(thread->om_in_use_list, f);
1356 }
1357
1358 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
1359 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1360 // The oops_do() phase does not overlap with monitor deflation
1361 // so no need to lock ObjectMonitors for the list traversal.
1362 for (ObjectMonitor* mid = list; mid != NULL; mid = unmarked_next(mid)) {
1363 if (mid->object() != NULL) {
1364 f->do_oop((oop*)mid->object_addr());
1365 }
1366 }
1367 }
1368
1369
1370 // -----------------------------------------------------------------------------
1371 // ObjectMonitor Lifecycle
1372 // -----------------------
1373 // Inflation unlinks monitors from om_list_globals._free_list or a per-thread
1374 // free list and associates them with objects. Async deflation disassociates
1375 // idle monitors from objects. Such scavenged monitors are returned to the
1376 // om_list_globals._free_list.
1377 //
1378 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1379 //
1380 // Lifecycle:
1381 // -- unassigned and on the om_list_globals._free_list
1382 // -- unassigned and on a per-thread free list
1383 // -- assigned to an object. The object is inflated and the mark refers
1384 // to the ObjectMonitor.
1385
1386 ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self) {
1387 // A large MAXPRIVATE value reduces both list lock contention
1388 // and list coherency traffic, but also tends to increase the
1389 // number of ObjectMonitors in circulation as well as the
1390 // scavenge costs. As usual, we lean toward time in space-time
1391 // tradeoffs.
1392 const int MAXPRIVATE = 1024;
1393 NoSafepointVerifier nsv;
1394
1395 for (;;) {
1396 ObjectMonitor* m;
1397
1398 // 1: try to allocate from the thread's local om_free_list.
1399 // Threads will attempt to allocate first from their local list, then
1400 // from the global list, and only after those attempts fail will the
1401 // thread attempt to instantiate new monitors. Thread-local free lists
1402 // improve allocation latency, as well as reducing coherency traffic
1403 // on the shared global list.
1404 m = take_from_start_of_om_free_list(self);
1405 if (m != NULL) {
1406 guarantee(m->object() == NULL, "invariant");
1407 m->set_allocation_state(ObjectMonitor::New);
1408 prepend_to_om_in_use_list(self, m);
1409 return m;
1410 }
1411
1412 // 2: try to allocate from the global om_list_globals._free_list
1413 // If we're using thread-local free lists then try
1414 // to reprovision the caller's free list.
1415 if (Atomic::load(&om_list_globals._free_list) != NULL) {
1416 // Reprovision the thread's om_free_list.
1417 // Use bulk transfers to reduce the allocation rate and heat
1418 // on various locks.
1419 for (int i = self->om_free_provision; --i >= 0;) {
1420 ObjectMonitor* take = take_from_start_of_global_free_list();
1421 if (take == NULL) {
1422 break; // No more are available.
1423 }
1424 guarantee(take->object() == NULL, "invariant");
1425 // We allowed 3 field values to linger during async deflation.
1426 // Clear or restore them as appropriate.
1427 take->set_header(markWord::zero());
1428 // DEFLATER_MARKER is the only non-NULL value we should see here.
1429 take->try_set_owner_from(DEFLATER_MARKER, NULL);
1430 if (take->contentions() < 0) {
1431 // Add back max_jint to restore the contentions field to its
1432 // proper value.
1433 take->add_to_contentions(max_jint);
1434
1435 #ifdef ASSERT
1436 jint l_contentions = take->contentions();
1437 assert(l_contentions >= 0, "must not be negative: l_contentions=%d, contentions=%d",
1438 l_contentions, take->contentions());
1439 #endif
1440 }
1441 take->Recycle();
1442 // Since we're taking from the global free-list, take must be Free.
1443 // om_release() also sets the allocation state to Free because it
1444 // is called from other code paths.
1445 assert(take->is_free(), "invariant");
1446 om_release(self, take, false);
1447 }
1448 self->om_free_provision += 1 + (self->om_free_provision / 2);
1449 if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE;
1450 continue;
1451 }
1452
1453 // 3: allocate a block of new ObjectMonitors
1454 // Both the local and global free lists are empty -- resort to malloc().
1455 // In the current implementation ObjectMonitors are TSM - immortal.
1456 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1457 // each ObjectMonitor to start at the beginning of a cache line,
1458 // so we use align_up().
1459 // A better solution would be to use C++ placement-new.
1460 // BEWARE: As it stands currently, we don't run the ctors!
1461 assert(_BLOCKSIZE > 1, "invariant");
1462 size_t neededsize = sizeof(PaddedObjectMonitor) * _BLOCKSIZE;
1463 PaddedObjectMonitor* temp;
1464 size_t aligned_size = neededsize + (OM_CACHE_LINE_SIZE - 1);
1465 void* real_malloc_addr = NEW_C_HEAP_ARRAY(char, aligned_size, mtInternal);
1466 temp = (PaddedObjectMonitor*)align_up(real_malloc_addr, OM_CACHE_LINE_SIZE);
1467 (void)memset((void *) temp, 0, neededsize);
1468
1469 // Format the block.
1470 // initialize the linked list, each monitor points to its next
1471 // forming the single linked free list, the very first monitor
1472 // will points to next block, which forms the block list.
1473 // The trick of using the 1st element in the block as g_block_list
1474 // linkage should be reconsidered. A better implementation would
1475 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1476
1477 for (int i = 1; i < _BLOCKSIZE; i++) {
1478 temp[i].set_next_om((ObjectMonitor*)&temp[i + 1]);
1479 assert(temp[i].is_free(), "invariant");
1480 }
1481
1482 // terminate the last monitor as the end of list
1483 temp[_BLOCKSIZE - 1].set_next_om((ObjectMonitor*)NULL);
1484
1485 // Element [0] is reserved for global list linkage
1486 temp[0].set_object(CHAINMARKER);
1487
1488 // Consider carving out this thread's current request from the
1489 // block in hand. This avoids some lock traffic and redundant
1490 // list activity.
1491
1492 prepend_block_to_lists(temp);
1493 }
1494 }
1495
1496 // Place "m" on the caller's private per-thread om_free_list.
1497 // In practice there's no need to clamp or limit the number of
1498 // monitors on a thread's om_free_list as the only non-allocation time
1499 // we'll call om_release() is to return a monitor to the free list after
1500 // a CAS attempt failed. This doesn't allow unbounded #s of monitors to
1501 // accumulate on a thread's free list.
1502 //
1503 // Key constraint: all ObjectMonitors on a thread's free list and the global
1504 // free list must have their object field set to null. This prevents the
1505 // scavenger -- deflate_monitor_list_using_JT() -- from reclaiming them
1506 // while we are trying to release them.
1507
1508 void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m,
1509 bool from_per_thread_alloc) {
1510 guarantee(m->header().value() == 0, "invariant");
1511 guarantee(m->object() == NULL, "invariant");
1512 NoSafepointVerifier nsv;
1513
1514 if ((m->is_busy() | m->_recursions) != 0) {
1515 stringStream ss;
1516 fatal("freeing in-use monitor: %s, recursions=" INTX_FORMAT,
1517 m->is_busy_to_string(&ss), m->_recursions);
1518 }
1519 m->set_allocation_state(ObjectMonitor::Free);
1520 // _next_om is used for both per-thread in-use and free lists so
1521 // we have to remove 'm' from the in-use list first (as needed).
1522 if (from_per_thread_alloc) {
1523 // Need to remove 'm' from om_in_use_list.
1524 ObjectMonitor* mid = NULL;
1525 ObjectMonitor* next = NULL;
1526
1527 // This list walk can race with another list walker or with async
1528 // deflation so we have to worry about an ObjectMonitor being
1529 // removed from this list while we are walking it.
1530
1531 // Lock the list head to avoid racing with another list walker
1532 // or with async deflation.
1533 if ((mid = get_list_head_locked(&self->om_in_use_list)) == NULL) {
1534 fatal("thread=" INTPTR_FORMAT " in-use list must not be empty.", p2i(self));
1535 }
1536 next = unmarked_next(mid);
1537 if (m == mid) {
1538 // First special case:
1539 // 'm' matches mid, is the list head and is locked. Switch the list
1540 // head to next which unlocks the list head, but leaves the extracted
1541 // mid locked:
1542 Atomic::store(&self->om_in_use_list, next);
1543 } else if (m == next) {
1544 // Second special case:
1545 // 'm' matches next after the list head and we already have the list
1546 // head locked so set mid to what we are extracting:
1547 mid = next;
1548 // Lock mid to prevent races with a list walker or an async
1549 // deflater thread that's ahead of us. The locked list head
1550 // prevents races from behind us.
1551 om_lock(mid);
1552 // Update next to what follows mid (if anything):
1553 next = unmarked_next(mid);
1554 // Switch next after the list head to new next which unlocks the
1555 // list head, but leaves the extracted mid locked:
1556 self->om_in_use_list->set_next_om(next);
1557 } else {
1558 // We have to search the list to find 'm'.
1559 guarantee(next != NULL, "thread=" INTPTR_FORMAT ": om_in_use_list=" INTPTR_FORMAT
1560 " is too short.", p2i(self), p2i(self->om_in_use_list));
1561 // Our starting anchor is next after the list head which is the
1562 // last ObjectMonitor we checked:
1563 ObjectMonitor* anchor = next;
1564 // Lock anchor to prevent races with a list walker or an async
1565 // deflater thread that's ahead of us. The locked list head
1566 // prevents races from behind us.
1567 om_lock(anchor);
1568 om_unlock(mid); // Unlock the list head now that anchor is locked.
1569 while ((mid = unmarked_next(anchor)) != NULL) {
1570 if (m == mid) {
1571 // We found 'm' on the per-thread in-use list so extract it.
1572 // Update next to what follows mid (if anything):
1573 next = unmarked_next(mid);
1574 // Switch next after the anchor to new next which unlocks the
1575 // anchor, but leaves the extracted mid locked:
1576 anchor->set_next_om(next);
1577 break;
1578 } else {
1579 // Lock the next anchor to prevent races with a list walker
1580 // or an async deflater thread that's ahead of us. The locked
1581 // current anchor prevents races from behind us.
1582 om_lock(mid);
1583 // Unlock current anchor now that next anchor is locked:
1584 om_unlock(anchor);
1585 anchor = mid; // Advance to new anchor and try again.
1586 }
1587 }
1588 }
1589
1590 if (mid == NULL) {
1591 // Reached end of the list and didn't find 'm' so:
1592 fatal("thread=" INTPTR_FORMAT " must find m=" INTPTR_FORMAT "on om_in_use_list="
1593 INTPTR_FORMAT, p2i(self), p2i(m), p2i(self->om_in_use_list));
1594 }
1595
1596 // At this point mid is disconnected from the in-use list so
1597 // its lock no longer has any effects on the in-use list.
1598 Atomic::dec(&self->om_in_use_count);
1599 // Unlock mid, but leave the next value for any lagging list
1600 // walkers. It will get cleaned up when mid is prepended to
1601 // the thread's free list:
1602 om_unlock(mid);
1603 }
1604
1605 prepend_to_om_free_list(self, m);
1606 guarantee(m->is_free(), "invariant");
1607 }
1608
1609 // Return ObjectMonitors on a moribund thread's free and in-use
1610 // lists to the appropriate global lists. The ObjectMonitors on the
1611 // per-thread in-use list may still be in use by other threads.
1612 //
1613 // We currently call om_flush() from Threads::remove() before the
1614 // thread has been excised from the thread list and is no longer a
1615 // mutator. In particular, this ensures that the thread's in-use
1616 // monitors are scanned by a GC safepoint, either via Thread::oops_do()
1617 // (before om_flush() is called) or via ObjectSynchronizer::oops_do()
1618 // (after om_flush() is called).
1619 //
1620 // deflate_global_idle_monitors_using_JT() and
1621 // deflate_per_thread_idle_monitors_using_JT() (in another thread) can
1622 // run at the same time as om_flush() so we have to follow a careful
1623 // protocol to prevent list corruption.
1624
1625 void ObjectSynchronizer::om_flush(Thread* self) {
1626 // Process the per-thread in-use list first to be consistent.
1627 int in_use_count = 0;
1628 ObjectMonitor* in_use_list = NULL;
1629 ObjectMonitor* in_use_tail = NULL;
1630 NoSafepointVerifier nsv;
1631
1632 // This function can race with a list walker or with an async
1633 // deflater thread so we lock the list head to prevent confusion.
1634 // An async deflater thread checks to see if the target thread
1635 // is exiting, but if it has made it past that check before we
1636 // started exiting, then it is racing to get to the in-use list.
1637 if ((in_use_list = get_list_head_locked(&self->om_in_use_list)) != NULL) {
1638 // At this point, we have locked the in-use list head so a racing
1639 // thread cannot come in after us. However, a racing thread could
1640 // be ahead of us; we'll detect that and delay to let it finish.
1641 //
1642 // The thread is going away, however the ObjectMonitors on the
1643 // om_in_use_list may still be in-use by other threads. Link
1644 // them to in_use_tail, which will be linked into the global
1645 // in-use list (om_list_globals._in_use_list) below.
1646 //
1647 // Account for the in-use list head before the loop since it is
1648 // already locked (by this thread):
1649 in_use_tail = in_use_list;
1650 in_use_count++;
1651 for (ObjectMonitor* cur_om = unmarked_next(in_use_list); cur_om != NULL;) {
1652 if (is_locked(cur_om)) {
1653 // cur_om is locked so there must be a racing walker or async
1654 // deflater thread ahead of us so we'll give it a chance to finish.
1655 while (is_locked(cur_om)) {
1656 os::naked_short_sleep(1);
1657 }
1658 // Refetch the possibly changed next field and try again.
1659 cur_om = unmarked_next(in_use_tail);
1660 continue;
1661 }
1662 if (cur_om->object() == NULL) {
1663 // cur_om was deflated and the object ref was cleared while it
1664 // was locked. We happened to see it just after it was unlocked
1665 // (and added to the free list). Refetch the possibly changed
1666 // next field and try again.
1667 cur_om = unmarked_next(in_use_tail);
1668 continue;
1669 }
1670 in_use_tail = cur_om;
1671 in_use_count++;
1672 cur_om = unmarked_next(cur_om);
1673 }
1674 guarantee(in_use_tail != NULL, "invariant");
1675 #ifdef ASSERT
1676 int l_om_in_use_count = Atomic::load(&self->om_in_use_count);
1677 assert(l_om_in_use_count == in_use_count, "in-use counts don't match: "
1678 "l_om_in_use_count=%d, in_use_count=%d", l_om_in_use_count, in_use_count);
1679 #endif
1680 Atomic::store(&self->om_in_use_count, 0);
1681 // Clear the in-use list head (which also unlocks it):
1682 Atomic::store(&self->om_in_use_list, (ObjectMonitor*)NULL);
1683 om_unlock(in_use_list);
1684 }
1685
1686 int free_count = 0;
1687 ObjectMonitor* free_list = NULL;
1688 ObjectMonitor* free_tail = NULL;
1689 // This function can race with a list walker thread so we lock the
1690 // list head to prevent confusion.
1691 if ((free_list = get_list_head_locked(&self->om_free_list)) != NULL) {
1692 // At this point, we have locked the free list head so a racing
1693 // thread cannot come in after us. However, a racing thread could
1694 // be ahead of us; we'll detect that and delay to let it finish.
1695 //
1696 // The thread is going away. Set 'free_tail' to the last per-thread free
1697 // monitor which will be linked to om_list_globals._free_list below.
1698 //
1699 // Account for the free list head before the loop since it is
1700 // already locked (by this thread):
1701 free_tail = free_list;
1702 free_count++;
1703 for (ObjectMonitor* s = unmarked_next(free_list); s != NULL; s = unmarked_next(s)) {
1704 if (is_locked(s)) {
1705 // s is locked so there must be a racing walker thread ahead
1706 // of us so we'll give it a chance to finish.
1707 while (is_locked(s)) {
1708 os::naked_short_sleep(1);
1709 }
1710 }
1711 free_tail = s;
1712 free_count++;
1713 guarantee(s->object() == NULL, "invariant");
1714 if (s->is_busy()) {
1715 stringStream ss;
1716 fatal("must be !is_busy: %s", s->is_busy_to_string(&ss));
1717 }
1718 }
1719 guarantee(free_tail != NULL, "invariant");
1720 #ifdef ASSERT
1721 int l_om_free_count = Atomic::load(&self->om_free_count);
1722 assert(l_om_free_count == free_count, "free counts don't match: "
1723 "l_om_free_count=%d, free_count=%d", l_om_free_count, free_count);
1724 #endif
1725 Atomic::store(&self->om_free_count, 0);
1726 Atomic::store(&self->om_free_list, (ObjectMonitor*)NULL);
1727 om_unlock(free_list);
1728 }
1729
1730 if (free_tail != NULL) {
1731 prepend_list_to_global_free_list(free_list, free_tail, free_count);
1732 }
1733
1734 if (in_use_tail != NULL) {
1735 prepend_list_to_global_in_use_list(in_use_list, in_use_tail, in_use_count);
1736 }
1737
1738 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1739 LogStreamHandle(Info, monitorinflation) lsh_info;
1740 LogStream* ls = NULL;
1741 if (log_is_enabled(Debug, monitorinflation)) {
1742 ls = &lsh_debug;
1743 } else if ((free_count != 0 || in_use_count != 0) &&
1744 log_is_enabled(Info, monitorinflation)) {
1745 ls = &lsh_info;
1746 }
1747 if (ls != NULL) {
1748 ls->print_cr("om_flush: jt=" INTPTR_FORMAT ", free_count=%d"
1749 ", in_use_count=%d" ", om_free_provision=%d",
1750 p2i(self), free_count, in_use_count, self->om_free_provision);
1751 }
1752 }
1753
1754 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1755 const oop obj,
1756 ObjectSynchronizer::InflateCause cause) {
1757 assert(event != NULL, "invariant");
1758 assert(event->should_commit(), "invariant");
1759 event->set_monitorClass(obj->klass());
1760 event->set_address((uintptr_t)(void*)obj);
1761 event->set_cause((u1)cause);
1762 event->commit();
1763 }
1764
1765 // Fast path code shared by multiple functions
1766 void ObjectSynchronizer::inflate_helper(oop obj) {
1767 markWord mark = obj->mark();
1768 if (mark.has_monitor()) {
1769 ObjectMonitor* monitor = mark.monitor();
1770 assert(ObjectSynchronizer::verify_objmon_isinpool(monitor), "monitor=" INTPTR_FORMAT " is invalid", p2i(monitor));
1771 markWord dmw = monitor->header();
1772 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1773 return;
1774 }
1775 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1776 }
1777
1778 ObjectMonitor* ObjectSynchronizer::inflate(Thread* self, oop object,
1779 const InflateCause cause) {
1780 // Inflate mutates the heap ...
1781 // Relaxing assertion for bug 6320749.
1782 assert(Universe::verify_in_progress() ||
1783 !SafepointSynchronize::is_at_safepoint(), "invariant");
1784
1785 EventJavaMonitorInflate event;
1786
1787 for (;;) {
1788 const markWord mark = object->mark();
1789 assert(!mark.has_bias_pattern(), "invariant");
1790
1791 // The mark can be in one of the following states:
1792 // * Inflated - just return
1793 // * Stack-locked - coerce it to inflated
1794 // * INFLATING - busy wait for conversion to complete
1795 // * Neutral - aggressively inflate the object.
1796 // * BIASED - Illegal. We should never see this
1797
1798 // CASE: inflated
1799 if (mark.has_monitor()) {
1800 ObjectMonitor* inf = mark.monitor();
1801 markWord dmw = inf->header();
1802 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1803 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1804 return inf;
1805 }
1806
1807 // CASE: inflation in progress - inflating over a stack-lock.
1808 // Some other thread is converting from stack-locked to inflated.
1809 // Only that thread can complete inflation -- other threads must wait.
1810 // The INFLATING value is transient.
1811 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1812 // We could always eliminate polling by parking the thread on some auxiliary list.
1813 if (mark == markWord::INFLATING()) {
1814 read_stable_mark(object);
1815 continue;
1816 }
1817
1818 // CASE: stack-locked
1819 // Could be stack-locked either by this thread or by some other thread.
1820 //
1821 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1822 // to install INFLATING into the mark word. We originally installed INFLATING,
1823 // allocated the objectmonitor, and then finally STed the address of the
1824 // objectmonitor into the mark. This was correct, but artificially lengthened
1825 // the interval in which INFLATED appeared in the mark, thus increasing
1826 // the odds of inflation contention.
1827 //
1828 // We now use per-thread private objectmonitor free lists.
1829 // These list are reprovisioned from the global free list outside the
1830 // critical INFLATING...ST interval. A thread can transfer
1831 // multiple objectmonitors en-mass from the global free list to its local free list.
1832 // This reduces coherency traffic and lock contention on the global free list.
1833 // Using such local free lists, it doesn't matter if the om_alloc() call appears
1834 // before or after the CAS(INFLATING) operation.
1835 // See the comments in om_alloc().
1836
1837 LogStreamHandle(Trace, monitorinflation) lsh;
1838
1839 if (mark.has_locker()) {
1840 ObjectMonitor* m = om_alloc(self);
1841 // Optimistically prepare the objectmonitor - anticipate successful CAS
1842 // We do this before the CAS in order to minimize the length of time
1843 // in which INFLATING appears in the mark.
1844 m->Recycle();
1845 m->_Responsible = NULL;
1846 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1847
1848 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1849 if (cmp != mark) {
1850 // om_release() will reset the allocation state from New to Free.
1851 om_release(self, m, true);
1852 continue; // Interference -- just retry
1853 }
1854
1855 // We've successfully installed INFLATING (0) into the mark-word.
1856 // This is the only case where 0 will appear in a mark-word.
1857 // Only the singular thread that successfully swings the mark-word
1858 // to 0 can perform (or more precisely, complete) inflation.
1859 //
1860 // Why do we CAS a 0 into the mark-word instead of just CASing the
1861 // mark-word from the stack-locked value directly to the new inflated state?
1862 // Consider what happens when a thread unlocks a stack-locked object.
1863 // It attempts to use CAS to swing the displaced header value from the
1864 // on-stack BasicLock back into the object header. Recall also that the
1865 // header value (hash code, etc) can reside in (a) the object header, or
1866 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1867 // header in an ObjectMonitor. The inflate() routine must copy the header
1868 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1869 // the while preserving the hashCode stability invariants. If the owner
1870 // decides to release the lock while the value is 0, the unlock will fail
1871 // and control will eventually pass from slow_exit() to inflate. The owner
1872 // will then spin, waiting for the 0 value to disappear. Put another way,
1873 // the 0 causes the owner to stall if the owner happens to try to
1874 // drop the lock (restoring the header from the BasicLock to the object)
1875 // while inflation is in-progress. This protocol avoids races that might
1876 // would otherwise permit hashCode values to change or "flicker" for an object.
1877 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1878 // 0 serves as a "BUSY" inflate-in-progress indicator.
1879
1880
1881 // fetch the displaced mark from the owner's stack.
1882 // The owner can't die or unwind past the lock while our INFLATING
1883 // object is in the mark. Furthermore the owner can't complete
1884 // an unlock on the object, either.
1885 markWord dmw = mark.displaced_mark_helper();
1886 // Catch if the object's header is not neutral (not locked and
1887 // not marked is what we care about here).
1888 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1889
1890 // Setup monitor fields to proper values -- prepare the monitor
1891 m->set_header(dmw);
1892
1893 // Optimization: if the mark.locker stack address is associated
1894 // with this thread we could simply set m->_owner = self.
1895 // Note that a thread can inflate an object
1896 // that it has stack-locked -- as might happen in wait() -- directly
1897 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1898 m->set_owner_from(NULL, DEFLATER_MARKER, mark.locker());
1899 m->set_object(object);
1900 // TODO-FIXME: assert BasicLock->dhw != 0.
1901
1902 // Must preserve store ordering. The monitor state must
1903 // be stable at the time of publishing the monitor address.
1904 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1905 object->release_set_mark(markWord::encode(m));
1906
1907 // Once ObjectMonitor is configured and the object is associated
1908 // with the ObjectMonitor, it is safe to allow async deflation:
1909 assert(m->is_new(), "freshly allocated monitor must be new");
1910 m->set_allocation_state(ObjectMonitor::Old);
1911
1912 // Hopefully the performance counters are allocated on distinct cache lines
1913 // to avoid false sharing on MP systems ...
1914 OM_PERFDATA_OP(Inflations, inc());
1915 if (log_is_enabled(Trace, monitorinflation)) {
1916 ResourceMark rm(self);
1917 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1918 INTPTR_FORMAT ", type='%s'", p2i(object),
1919 object->mark().value(), object->klass()->external_name());
1920 }
1921 if (event.should_commit()) {
1922 post_monitor_inflate_event(&event, object, cause);
1923 }
1924 return m;
1925 }
1926
1927 // CASE: neutral
1928 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1929 // If we know we're inflating for entry it's better to inflate by swinging a
1930 // pre-locked ObjectMonitor pointer into the object header. A successful
1931 // CAS inflates the object *and* confers ownership to the inflating thread.
1932 // In the current implementation we use a 2-step mechanism where we CAS()
1933 // to inflate and then CAS() again to try to swing _owner from NULL to self.
1934 // An inflateTry() method that we could call from enter() would be useful.
1935
1936 // Catch if the object's header is not neutral (not locked and
1937 // not marked is what we care about here).
1938 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1939 ObjectMonitor* m = om_alloc(self);
1940 // prepare m for installation - set monitor to initial state
1941 m->Recycle();
1942 m->set_header(mark);
1943 // DEFLATER_MARKER is the only non-NULL value we should see here.
1944 m->try_set_owner_from(DEFLATER_MARKER, NULL);
1945 m->set_object(object);
1946 m->_Responsible = NULL;
1947 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1948
1949 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1950 m->set_header(markWord::zero());
1951 m->set_object(NULL);
1952 m->Recycle();
1953 // om_release() will reset the allocation state from New to Free.
1954 om_release(self, m, true);
1955 m = NULL;
1956 continue;
1957 // interference - the markword changed - just retry.
1958 // The state-transitions are one-way, so there's no chance of
1959 // live-lock -- "Inflated" is an absorbing state.
1960 }
1961
1962 // Once the ObjectMonitor is configured and object is associated
1963 // with the ObjectMonitor, it is safe to allow async deflation:
1964 assert(m->is_new(), "freshly allocated monitor must be new");
1965 m->set_allocation_state(ObjectMonitor::Old);
1966
1967 // Hopefully the performance counters are allocated on distinct
1968 // cache lines to avoid false sharing on MP systems ...
1969 OM_PERFDATA_OP(Inflations, inc());
1970 if (log_is_enabled(Trace, monitorinflation)) {
1971 ResourceMark rm(self);
1972 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1973 INTPTR_FORMAT ", type='%s'", p2i(object),
1974 object->mark().value(), object->klass()->external_name());
1975 }
1976 if (event.should_commit()) {
1977 post_monitor_inflate_event(&event, object, cause);
1978 }
1979 return m;
1980 }
1981 }
1982
1983
1984 // An async deflation request is registered with the ServiceThread
1985 // and it is notified.
1986 void ObjectSynchronizer::do_safepoint_work() {
1987 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1988
1989 log_debug(monitorinflation)("requesting async deflation of idle monitors.");
1990 // Request deflation of idle monitors by the ServiceThread:
1991 set_is_async_deflation_requested(true);
1992 MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
1993 ml.notify_all();
1994
1995 if (log_is_enabled(Debug, monitorinflation)) {
1996 // exit_globals()'s call to audit_and_print_stats() is done
1997 // at the Info level and not at a safepoint.
1998 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
1999 }
2000 }
2001
2002 // Deflate the specified ObjectMonitor if not in-use using a JavaThread.
2003 // Returns true if it was deflated and false otherwise.
2004 //
2005 // The async deflation protocol sets owner to DEFLATER_MARKER and
2006 // makes contentions negative as signals to contending threads that
2007 // an async deflation is in progress. There are a number of checks
2008 // as part of the protocol to make sure that the calling thread has
2009 // not lost the race to a contending thread.
2010 //
2011 // The ObjectMonitor has been successfully async deflated when:
2012 // (contentions < 0)
2013 // Contending threads that see that condition know to retry their operation.
2014 //
2015 bool ObjectSynchronizer::deflate_monitor_using_JT(ObjectMonitor* mid,
2016 ObjectMonitor** free_head_p,
2017 ObjectMonitor** free_tail_p) {
2018 assert(Thread::current()->is_Java_thread(), "precondition");
2019 // A newly allocated ObjectMonitor should not be seen here so we
2020 // avoid an endless inflate/deflate cycle.
2021 assert(mid->is_old(), "must be old: allocation_state=%d",
2022 (int) mid->allocation_state());
2023
2024 if (mid->is_busy()) {
2025 // Easy checks are first - the ObjectMonitor is busy so no deflation.
2026 return false;
2027 }
2028
2029 // Set a NULL owner to DEFLATER_MARKER to force any contending thread
2030 // through the slow path. This is just the first part of the async
2031 // deflation dance.
2032 if (mid->try_set_owner_from(NULL, DEFLATER_MARKER) != NULL) {
2033 // The owner field is no longer NULL so we lost the race since the
2034 // ObjectMonitor is now busy.
2035 return false;
2036 }
2037
2038 if (mid->contentions() > 0 || mid->_waiters != 0) {
2039 // Another thread has raced to enter the ObjectMonitor after
2040 // mid->is_busy() above or has already entered and waited on
2041 // it which makes it busy so no deflation. Restore owner to
2042 // NULL if it is still DEFLATER_MARKER.
2043 if (mid->try_set_owner_from(DEFLATER_MARKER, NULL) != DEFLATER_MARKER) {
2044 // Deferred decrement for the JT EnterI() that cancelled the async deflation.
2045 mid->add_to_contentions(-1);
2046 }
2047 return false;
2048 }
2049
2050 // Make a zero contentions field negative to force any contending threads
2051 // to retry. This is the second part of the async deflation dance.
2052 if (Atomic::cmpxchg(&mid->_contentions, (jint)0, -max_jint) != 0) {
2053 // Contentions was no longer 0 so we lost the race since the
2054 // ObjectMonitor is now busy. Restore owner to NULL if it is
2055 // still DEFLATER_MARKER:
2056 if (mid->try_set_owner_from(DEFLATER_MARKER, NULL) != DEFLATER_MARKER) {
2057 // Deferred decrement for the JT EnterI() that cancelled the async deflation.
2058 mid->add_to_contentions(-1);
2059 }
2060 return false;
2061 }
2062
2063 // Sanity checks for the races:
2064 guarantee(mid->owner_is_DEFLATER_MARKER(), "must be deflater marker");
2065 guarantee(mid->contentions() < 0, "must be negative: contentions=%d",
2066 mid->contentions());
2067 guarantee(mid->_waiters == 0, "must be 0: waiters=%d", mid->_waiters);
2068 guarantee(mid->_cxq == NULL, "must be no contending threads: cxq="
2069 INTPTR_FORMAT, p2i(mid->_cxq));
2070 guarantee(mid->_EntryList == NULL,
2071 "must be no entering threads: EntryList=" INTPTR_FORMAT,
2072 p2i(mid->_EntryList));
2073
2074 const oop obj = (oop) mid->object();
2075 if (log_is_enabled(Trace, monitorinflation)) {
2076 ResourceMark rm;
2077 log_trace(monitorinflation)("deflate_monitor_using_JT: "
2078 "object=" INTPTR_FORMAT ", mark="
2079 INTPTR_FORMAT ", type='%s'",
2080 p2i(obj), obj->mark().value(),
2081 obj->klass()->external_name());
2082 }
2083
2084 // Install the old mark word if nobody else has already done it.
2085 mid->install_displaced_markword_in_object(obj);
2086 mid->clear_common();
2087
2088 assert(mid->object() == NULL, "must be NULL: object=" INTPTR_FORMAT,
2089 p2i(mid->object()));
2090 assert(mid->is_free(), "must be free: allocation_state=%d",
2091 (int)mid->allocation_state());
2092
2093 // Move the deflated ObjectMonitor to the working free list
2094 // defined by free_head_p and free_tail_p.
2095 if (*free_head_p == NULL) {
2096 // First one on the list.
2097 *free_head_p = mid;
2098 }
2099 if (*free_tail_p != NULL) {
2100 // We append to the list so the caller can use mid->_next_om
2101 // to fix the linkages in its context.
2102 ObjectMonitor* prevtail = *free_tail_p;
2103 // prevtail should have been cleaned up by the caller:
2104 #ifdef ASSERT
2105 ObjectMonitor* l_next_om = unmarked_next(prevtail);
2106 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2107 #endif
2108 om_lock(prevtail);
2109 prevtail->set_next_om(mid); // prevtail now points to mid (and is unlocked)
2110 }
2111 *free_tail_p = mid;
2112
2113 // At this point, mid->_next_om still refers to its current
2114 // value and another ObjectMonitor's _next_om field still
2115 // refers to this ObjectMonitor. Those linkages have to be
2116 // cleaned up by the caller who has the complete context.
2117
2118 // We leave owner == DEFLATER_MARKER and contentions < 0
2119 // to force any racing threads to retry.
2120 return true; // Success, ObjectMonitor has been deflated.
2121 }
2122
2123 // Walk a given ObjectMonitor list and deflate idle ObjectMonitors using
2124 // a JavaThread. Returns the number of deflated ObjectMonitors. The given
2125 // list could be a per-thread in-use list or the global in-use list.
2126 // If a safepoint has started, then we save state via saved_mid_in_use_p
2127 // and return to the caller to honor the safepoint.
2128 //
2129 int ObjectSynchronizer::deflate_monitor_list_using_JT(ObjectMonitor** list_p,
2130 int* count_p,
2131 ObjectMonitor** free_head_p,
2132 ObjectMonitor** free_tail_p,
2133 ObjectMonitor** saved_mid_in_use_p) {
2134 JavaThread* self = JavaThread::current();
2135
2136 ObjectMonitor* cur_mid_in_use = NULL;
2137 ObjectMonitor* mid = NULL;
2138 ObjectMonitor* next = NULL;
2139 ObjectMonitor* next_next = NULL;
2140 int deflated_count = 0;
2141 NoSafepointVerifier nsv;
2142
2143 // We use the more complicated lock-cur_mid_in_use-and-mid-as-we-go
2144 // protocol because om_release() can do list deletions in parallel;
2145 // this also prevents races with a list walker thread. We also
2146 // lock-next-next-as-we-go to prevent an om_flush() that is behind
2147 // this thread from passing us.
2148 if (*saved_mid_in_use_p == NULL) {
2149 // No saved state so start at the beginning.
2150 // Lock the list head so we can possibly deflate it:
2151 if ((mid = get_list_head_locked(list_p)) == NULL) {
2152 return 0; // The list is empty so nothing to deflate.
2153 }
2154 next = unmarked_next(mid);
2155 } else {
2156 // We're restarting after a safepoint so restore the necessary state
2157 // before we resume.
2158 cur_mid_in_use = *saved_mid_in_use_p;
2159 // Lock cur_mid_in_use so we can possibly update its
2160 // next field to extract a deflated ObjectMonitor.
2161 om_lock(cur_mid_in_use);
2162 mid = unmarked_next(cur_mid_in_use);
2163 if (mid == NULL) {
2164 om_unlock(cur_mid_in_use);
2165 *saved_mid_in_use_p = NULL;
2166 return 0; // The remainder is empty so nothing more to deflate.
2167 }
2168 // Lock mid so we can possibly deflate it:
2169 om_lock(mid);
2170 next = unmarked_next(mid);
2171 }
2172
2173 while (true) {
2174 // The current mid is locked at this point. If we have a
2175 // cur_mid_in_use, then it is also locked at this point.
2176
2177 if (next != NULL) {
2178 // We lock next so that an om_flush() thread that is behind us
2179 // cannot pass us when we unlock the current mid.
2180 om_lock(next);
2181 next_next = unmarked_next(next);
2182 }
2183
2184 // Only try to deflate if there is an associated Java object and if
2185 // mid is old (is not newly allocated and is not newly freed).
2186 if (mid->object() != NULL && mid->is_old() &&
2187 deflate_monitor_using_JT(mid, free_head_p, free_tail_p)) {
2188 // Deflation succeeded and already updated free_head_p and
2189 // free_tail_p as needed. Finish the move to the local free list
2190 // by unlinking mid from the global or per-thread in-use list.
2191 if (cur_mid_in_use == NULL) {
2192 // mid is the list head and it is locked. Switch the list head
2193 // to next which is also locked (if not NULL) and also leave
2194 // mid locked:
2195 Atomic::store(list_p, next);
2196 } else {
2197 ObjectMonitor* locked_next = mark_om_ptr(next);
2198 // mid and cur_mid_in_use are locked. Switch cur_mid_in_use's
2199 // next field to locked_next and also leave mid locked:
2200 cur_mid_in_use->set_next_om(locked_next);
2201 }
2202 // At this point mid is disconnected from the in-use list so
2203 // its lock longer has any effects on in-use list.
2204 deflated_count++;
2205 Atomic::dec(count_p);
2206 // mid is current tail in the free_head_p list so NULL terminate it
2207 // (which also unlocks it):
2208 mid->set_next_om(NULL);
2209
2210 // All the list management is done so move on to the next one:
2211 mid = next; // mid keeps non-NULL next's locked state
2212 next = next_next;
2213 } else {
2214 // mid is considered in-use if it does not have an associated
2215 // Java object or mid is not old or deflation did not succeed.
2216 // A mid->is_new() node can be seen here when it is freshly
2217 // returned by om_alloc() (and skips the deflation code path).
2218 // A mid->is_old() node can be seen here when deflation failed.
2219 // A mid->is_free() node can be seen here when a fresh node from
2220 // om_alloc() is released by om_release() due to losing the race
2221 // in inflate().
2222
2223 // All the list management is done so move on to the next one:
2224 if (cur_mid_in_use != NULL) {
2225 om_unlock(cur_mid_in_use);
2226 }
2227 // The next cur_mid_in_use keeps mid's lock state so
2228 // that it is stable for a possible next field change. It
2229 // cannot be modified by om_release() while it is locked.
2230 cur_mid_in_use = mid;
2231 mid = next; // mid keeps non-NULL next's locked state
2232 next = next_next;
2233
2234 if (SafepointMechanism::should_block(self) &&
2235 cur_mid_in_use != Atomic::load(list_p) && cur_mid_in_use->is_old()) {
2236 // If a safepoint has started and cur_mid_in_use is not the list
2237 // head and is old, then it is safe to use as saved state. Return
2238 // to the caller before blocking.
2239 *saved_mid_in_use_p = cur_mid_in_use;
2240 om_unlock(cur_mid_in_use);
2241 if (mid != NULL) {
2242 om_unlock(mid);
2243 }
2244 return deflated_count;
2245 }
2246 }
2247 if (mid == NULL) {
2248 if (cur_mid_in_use != NULL) {
2249 om_unlock(cur_mid_in_use);
2250 }
2251 break; // Reached end of the list so nothing more to deflate.
2252 }
2253
2254 // The current mid's next field is locked at this point. If we have
2255 // a cur_mid_in_use, then it is also locked at this point.
2256 }
2257 // We finished the list without a safepoint starting so there's
2258 // no need to save state.
2259 *saved_mid_in_use_p = NULL;
2260 return deflated_count;
2261 }
2262
2263 class HandshakeForDeflation : public HandshakeClosure {
2264 public:
2265 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
2266
2267 void do_thread(Thread* thread) {
2268 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
2269 INTPTR_FORMAT, p2i(thread));
2270 }
2271 };
2272
2273 void ObjectSynchronizer::deflate_idle_monitors_using_JT() {
2274 // Deflate any global idle monitors.
2275 deflate_global_idle_monitors_using_JT();
2276
2277 int count = 0;
2278 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2279 if (Atomic::load(&jt->om_in_use_count) > 0 && !jt->is_exiting()) {
2280 // This JavaThread is using ObjectMonitors so deflate any that
2281 // are idle unless this JavaThread is exiting; do not race with
2282 // ObjectSynchronizer::om_flush().
2283 deflate_per_thread_idle_monitors_using_JT(jt);
2284 count++;
2285 }
2286 }
2287 if (count > 0) {
2288 log_debug(monitorinflation)("did async deflation of idle monitors for %d thread(s).", count);
2289 }
2290
2291 log_info(monitorinflation)("async global_population=%d, global_in_use_count=%d, "
2292 "global_free_count=%d, global_wait_count=%d",
2293 Atomic::load(&om_list_globals._population),
2294 Atomic::load(&om_list_globals._in_use_count),
2295 Atomic::load(&om_list_globals._free_count),
2296 Atomic::load(&om_list_globals._wait_count));
2297
2298 // The ServiceThread's async deflation request has been processed.
2299 _last_async_deflation_time_ns = os::javaTimeNanos();
2300 set_is_async_deflation_requested(false);
2301
2302 if (Atomic::load(&om_list_globals._wait_count) > 0) {
2303 // There are deflated ObjectMonitors waiting for a handshake
2304 // (or a safepoint) for safety.
2305
2306 ObjectMonitor* list = Atomic::load(&om_list_globals._wait_list);
2307 assert(list != NULL, "om_list_globals._wait_list must not be NULL");
2308 int count = Atomic::load(&om_list_globals._wait_count);
2309 Atomic::store(&om_list_globals._wait_count, 0);
2310 Atomic::store(&om_list_globals._wait_list, (ObjectMonitor*)NULL);
2311
2312 // Find the tail for prepend_list_to_common(). No need to mark
2313 // ObjectMonitors for this list walk since only the deflater
2314 // thread manages the wait list.
2315 #ifdef ASSERT
2316 int l_count = 0;
2317 #endif
2318 ObjectMonitor* tail = NULL;
2319 for (ObjectMonitor* n = list; n != NULL; n = unmarked_next(n)) {
2320 tail = n;
2321 #ifdef ASSERT
2322 l_count++;
2323 #endif
2324 }
2325 assert(count == l_count, "count=%d != l_count=%d", count, l_count);
2326
2327 // Will execute a safepoint if !ThreadLocalHandshakes:
2328 HandshakeForDeflation hfd_hc;
2329 Handshake::execute(&hfd_hc);
2330
2331 prepend_list_to_common(list, tail, count, &om_list_globals._free_list,
2332 &om_list_globals._free_count);
2333
2334 log_info(monitorinflation)("moved %d idle monitors from global waiting list to global free list", count);
2335 }
2336 }
2337
2338 // Deflate global idle ObjectMonitors using a JavaThread.
2339 //
2340 void ObjectSynchronizer::deflate_global_idle_monitors_using_JT() {
2341 assert(Thread::current()->is_Java_thread(), "precondition");
2342 JavaThread* self = JavaThread::current();
2343
2344 deflate_common_idle_monitors_using_JT(true /* is_global */, self);
2345 }
2346
2347 // Deflate the specified JavaThread's idle ObjectMonitors using a JavaThread.
2348 //
2349 void ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT(JavaThread* target) {
2350 assert(Thread::current()->is_Java_thread(), "precondition");
2351
2352 deflate_common_idle_monitors_using_JT(false /* !is_global */, target);
2353 }
2354
2355 // Deflate global or per-thread idle ObjectMonitors using a JavaThread.
2356 //
2357 void ObjectSynchronizer::deflate_common_idle_monitors_using_JT(bool is_global, JavaThread* target) {
2358 JavaThread* self = JavaThread::current();
2359
2360 int deflated_count = 0;
2361 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged ObjectMonitors
2362 ObjectMonitor* free_tail_p = NULL;
2363 ObjectMonitor* saved_mid_in_use_p = NULL;
2364 elapsedTimer timer;
2365
2366 if (log_is_enabled(Info, monitorinflation)) {
2367 timer.start();
2368 }
2369
2370 if (is_global) {
2371 OM_PERFDATA_OP(MonExtant, set_value(Atomic::load(&om_list_globals._in_use_count)));
2372 } else {
2373 OM_PERFDATA_OP(MonExtant, inc(Atomic::load(&target->om_in_use_count)));
2374 }
2375
2376 do {
2377 int local_deflated_count;
2378 if (is_global) {
2379 local_deflated_count =
2380 deflate_monitor_list_using_JT(&om_list_globals._in_use_list,
2381 &om_list_globals._in_use_count,
2382 &free_head_p, &free_tail_p,
2383 &saved_mid_in_use_p);
2384 } else {
2385 local_deflated_count =
2386 deflate_monitor_list_using_JT(&target->om_in_use_list,
2387 &target->om_in_use_count, &free_head_p,
2388 &free_tail_p, &saved_mid_in_use_p);
2389 }
2390 deflated_count += local_deflated_count;
2391
2392 if (free_head_p != NULL) {
2393 // Move the deflated ObjectMonitors to the global free list.
2394 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);
2395 // Note: The target thread can be doing an om_alloc() that
2396 // is trying to prepend an ObjectMonitor on its in-use list
2397 // at the same time that we have deflated the current in-use
2398 // list head and put it on the local free list. prepend_to_common()
2399 // will detect the race and retry which avoids list corruption,
2400 // but the next field in free_tail_p can flicker to marked
2401 // and then unmarked while prepend_to_common() is sorting it
2402 // all out.
2403 #ifdef ASSERT
2404 ObjectMonitor* l_next_om = unmarked_next(free_tail_p);
2405 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2406 #endif
2407
2408 prepend_list_to_global_wait_list(free_head_p, free_tail_p, local_deflated_count);
2409
2410 OM_PERFDATA_OP(Deflations, inc(local_deflated_count));
2411 }
2412
2413 if (saved_mid_in_use_p != NULL) {
2414 // deflate_monitor_list_using_JT() detected a safepoint starting.
2415 timer.stop();
2416 {
2417 if (is_global) {
2418 log_debug(monitorinflation)("pausing deflation of global idle monitors for a safepoint.");
2419 } else {
2420 log_debug(monitorinflation)("jt=" INTPTR_FORMAT ": pausing deflation of per-thread idle monitors for a safepoint.", p2i(target));
2421 }
2422 assert(SafepointMechanism::should_block(self), "sanity check");
2423 ThreadBlockInVM blocker(self);
2424 }
2425 // Prepare for another loop after the safepoint.
2426 free_head_p = NULL;
2427 free_tail_p = NULL;
2428 if (log_is_enabled(Info, monitorinflation)) {
2429 timer.start();
2430 }
2431 }
2432 } while (saved_mid_in_use_p != NULL);
2433 timer.stop();
2434
2435 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2436 LogStreamHandle(Info, monitorinflation) lsh_info;
2437 LogStream* ls = NULL;
2438 if (log_is_enabled(Debug, monitorinflation)) {
2439 ls = &lsh_debug;
2440 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2441 ls = &lsh_info;
2442 }
2443 if (ls != NULL) {
2444 if (is_global) {
2445 ls->print_cr("async-deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2446 } else {
2447 ls->print_cr("jt=" INTPTR_FORMAT ": async-deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(target), timer.seconds(), deflated_count);
2448 }
2449 }
2450 }
2451
2452 // Monitor cleanup on JavaThread::exit
2453
2454 // Iterate through monitor cache and attempt to release thread's monitors
2455 // Gives up on a particular monitor if an exception occurs, but continues
2456 // the overall iteration, swallowing the exception.
2457 class ReleaseJavaMonitorsClosure: public MonitorClosure {
2458 private:
2459 TRAPS;
2460
2461 public:
2462 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
2463 void do_monitor(ObjectMonitor* mid) {
2464 if (mid->owner() == THREAD) {
2465 (void)mid->complete_exit(CHECK);
2466 }
2467 }
2468 };
2469
2470 // Release all inflated monitors owned by THREAD. Lightweight monitors are
2471 // ignored. This is meant to be called during JNI thread detach which assumes
2472 // all remaining monitors are heavyweight. All exceptions are swallowed.
2473 // Scanning the extant monitor list can be time consuming.
2474 // A simple optimization is to add a per-thread flag that indicates a thread
2475 // called jni_monitorenter() during its lifetime.
2476 //
2477 // Instead of NoSafepointVerifier it might be cheaper to
2478 // use an idiom of the form:
2479 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
2480 // <code that must not run at safepoint>
2481 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
2482 // Since the tests are extremely cheap we could leave them enabled
2483 // for normal product builds.
2484
2485 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
2486 assert(THREAD == JavaThread::current(), "must be current Java thread");
2487 NoSafepointVerifier nsv;
2488 ReleaseJavaMonitorsClosure rjmc(THREAD);
2489 ObjectSynchronizer::monitors_iterate(&rjmc);
2490 THREAD->clear_pending_exception();
2491 }
2492
2493 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
2494 switch (cause) {
2495 case inflate_cause_vm_internal: return "VM Internal";
2496 case inflate_cause_monitor_enter: return "Monitor Enter";
2497 case inflate_cause_wait: return "Monitor Wait";
2498 case inflate_cause_notify: return "Monitor Notify";
2499 case inflate_cause_hash_code: return "Monitor Hash Code";
2500 case inflate_cause_jni_enter: return "JNI Monitor Enter";
2501 case inflate_cause_jni_exit: return "JNI Monitor Exit";
2502 default:
2503 ShouldNotReachHere();
2504 }
2505 return "Unknown";
2506 }
2507
2508 //------------------------------------------------------------------------------
2509 // Debugging code
2510
2511 u_char* ObjectSynchronizer::get_gvars_addr() {
2512 return (u_char*)&GVars;
2513 }
2514
2515 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
2516 return (u_char*)&GVars.hc_sequence;
2517 }
2518
2519 size_t ObjectSynchronizer::get_gvars_size() {
2520 return sizeof(SharedGlobals);
2521 }
2522
2523 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
2524 return (u_char*)&GVars.stw_random;
2525 }
2526
2527 // This function can be called at a safepoint or it can be called when
2528 // we are trying to exit the VM. When we are trying to exit the VM, the
2529 // list walker functions can run in parallel with the other list
2530 // operations so spin-locking is used for safety.
2531 //
2532 // Calls to this function can be added in various places as a debugging
2533 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
2534 // details logged at the Info level and 'false' for the 'on_exit'
2535 // parameter to have in-use monitor details logged at the Trace level.
2536 //
2537 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
2538 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
2539
2540 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2541 LogStreamHandle(Info, monitorinflation) lsh_info;
2542 LogStreamHandle(Trace, monitorinflation) lsh_trace;
2543 LogStream* ls = NULL;
2544 if (log_is_enabled(Trace, monitorinflation)) {
2545 ls = &lsh_trace;
2546 } else if (log_is_enabled(Debug, monitorinflation)) {
2547 ls = &lsh_debug;
2548 } else if (log_is_enabled(Info, monitorinflation)) {
2549 ls = &lsh_info;
2550 }
2551 assert(ls != NULL, "sanity check");
2552
2553 // Log counts for the global and per-thread monitor lists:
2554 int chk_om_population = log_monitor_list_counts(ls);
2555 int error_cnt = 0;
2556
2557 ls->print_cr("Checking global lists:");
2558
2559 // Check om_list_globals._population:
2560 if (Atomic::load(&om_list_globals._population) == chk_om_population) {
2561 ls->print_cr("global_population=%d equals chk_om_population=%d",
2562 Atomic::load(&om_list_globals._population), chk_om_population);
2563 } else {
2564 // With fine grained locks on the monitor lists, it is possible for
2565 // log_monitor_list_counts() to return a value that doesn't match
2566 // om_list_globals._population. So far a higher value has been
2567 // seen in testing so something is being double counted by
2568 // log_monitor_list_counts().
2569 ls->print_cr("WARNING: global_population=%d is not equal to "
2570 "chk_om_population=%d",
2571 Atomic::load(&om_list_globals._population), chk_om_population);
2572 }
2573
2574 // Check om_list_globals._in_use_list and om_list_globals._in_use_count:
2575 chk_global_in_use_list_and_count(ls, &error_cnt);
2576
2577 // Check om_list_globals._free_list and om_list_globals._free_count:
2578 chk_global_free_list_and_count(ls, &error_cnt);
2579
2580 // Check om_list_globals._wait_list and om_list_globals._wait_count:
2581 chk_global_wait_list_and_count(ls, &error_cnt);
2582
2583 ls->print_cr("Checking per-thread lists:");
2584
2585 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2586 // Check om_in_use_list and om_in_use_count:
2587 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
2588
2589 // Check om_free_list and om_free_count:
2590 chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
2591 }
2592
2593 if (error_cnt == 0) {
2594 ls->print_cr("No errors found in monitor list checks.");
2595 } else {
2596 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
2597 }
2598
2599 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
2600 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
2601 // When exiting this log output is at the Info level. When called
2602 // at a safepoint, this log output is at the Trace level since
2603 // there can be a lot of it.
2604 log_in_use_monitor_details(ls);
2605 }
2606
2607 ls->flush();
2608
2609 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2610 }
2611
2612 // Check a free monitor entry; log any errors.
2613 void ObjectSynchronizer::chk_free_entry(JavaThread* jt, ObjectMonitor* n,
2614 outputStream * out, int *error_cnt_p) {
2615 stringStream ss;
2616 if (n->is_busy()) {
2617 if (jt != NULL) {
2618 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2619 ": free per-thread monitor must not be busy: %s", p2i(jt),
2620 p2i(n), n->is_busy_to_string(&ss));
2621 } else {
2622 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2623 "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
2624 }
2625 *error_cnt_p = *error_cnt_p + 1;
2626 }
2627 if (n->header().value() != 0) {
2628 if (jt != NULL) {
2629 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2630 ": free per-thread monitor must have NULL _header "
2631 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
2632 n->header().value());
2633 *error_cnt_p = *error_cnt_p + 1;
2634 }
2635 }
2636 if (n->object() != NULL) {
2637 if (jt != NULL) {
2638 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2639 ": free per-thread monitor must have NULL _object "
2640 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
2641 p2i(n->object()));
2642 } else {
2643 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2644 "must have NULL _object field: _object=" INTPTR_FORMAT,
2645 p2i(n), p2i(n->object()));
2646 }
2647 *error_cnt_p = *error_cnt_p + 1;
2648 }
2649 }
2650
2651 // Lock the next ObjectMonitor for traversal and unlock the current
2652 // ObjectMonitor. Returns the next ObjectMonitor if there is one.
2653 // Otherwise returns NULL (after unlocking the current ObjectMonitor).
2654 // This function is used by the various list walker functions to
2655 // safely walk a list without allowing an ObjectMonitor to be moved
2656 // to another list in the middle of a walk.
2657 static ObjectMonitor* lock_next_for_traversal(ObjectMonitor* cur) {
2658 assert(is_locked(cur), "cur=" INTPTR_FORMAT " must be locked", p2i(cur));
2659 ObjectMonitor* next = unmarked_next(cur);
2660 if (next == NULL) { // Reached the end of the list.
2661 om_unlock(cur);
2662 return NULL;
2663 }
2664 om_lock(next); // Lock next before unlocking current to keep
2665 om_unlock(cur); // from being by-passed by another thread.
2666 return next;
2667 }
2668
2669 // Check the global free list and count; log the results of the checks.
2670 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
2671 int *error_cnt_p) {
2672 int chk_om_free_count = 0;
2673 ObjectMonitor* cur = NULL;
2674 if ((cur = get_list_head_locked(&om_list_globals._free_list)) != NULL) {
2675 // Marked the global free list head so process the list.
2676 while (true) {
2677 chk_free_entry(NULL /* jt */, cur, out, error_cnt_p);
2678 chk_om_free_count++;
2679
2680 cur = lock_next_for_traversal(cur);
2681 if (cur == NULL) {
2682 break;
2683 }
2684 }
2685 }
2686 int l_free_count = Atomic::load(&om_list_globals._free_count);
2687 if (l_free_count == chk_om_free_count) {
2688 out->print_cr("global_free_count=%d equals chk_om_free_count=%d",
2689 l_free_count, chk_om_free_count);
2690 } else {
2691 // With fine grained locks on om_list_globals._free_list, it
2692 // is possible for an ObjectMonitor to be prepended to
2693 // om_list_globals._free_list after we started calculating
2694 // chk_om_free_count so om_list_globals._free_count may not
2695 // match anymore.
2696 out->print_cr("WARNING: global_free_count=%d is not equal to "
2697 "chk_om_free_count=%d", l_free_count, chk_om_free_count);
2698 }
2699 }
2700
2701 // Check the global wait list and count; log the results of the checks.
2702 void ObjectSynchronizer::chk_global_wait_list_and_count(outputStream * out,
2703 int *error_cnt_p) {
2704 int chk_om_wait_count = 0;
2705 ObjectMonitor* cur = NULL;
2706 if ((cur = get_list_head_locked(&om_list_globals._wait_list)) != NULL) {
2707 // Marked the global wait list head so process the list.
2708 while (true) {
2709 // Rules for om_list_globals._wait_list are the same as for
2710 // om_list_globals._free_list:
2711 chk_free_entry(NULL /* jt */, cur, out, error_cnt_p);
2712 chk_om_wait_count++;
2713
2714 cur = lock_next_for_traversal(cur);
2715 if (cur == NULL) {
2716 break;
2717 }
2718 }
2719 }
2720 if (Atomic::load(&om_list_globals._wait_count) == chk_om_wait_count) {
2721 out->print_cr("global_wait_count=%d equals chk_om_wait_count=%d",
2722 Atomic::load(&om_list_globals._wait_count), chk_om_wait_count);
2723 } else {
2724 out->print_cr("ERROR: global_wait_count=%d is not equal to "
2725 "chk_om_wait_count=%d",
2726 Atomic::load(&om_list_globals._wait_count), chk_om_wait_count);
2727 *error_cnt_p = *error_cnt_p + 1;
2728 }
2729 }
2730
2731 // Check the global in-use list and count; log the results of the checks.
2732 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
2733 int *error_cnt_p) {
2734 int chk_om_in_use_count = 0;
2735 ObjectMonitor* cur = NULL;
2736 if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) {
2737 // Marked the global in-use list head so process the list.
2738 while (true) {
2739 chk_in_use_entry(NULL /* jt */, cur, out, error_cnt_p);
2740 chk_om_in_use_count++;
2741
2742 cur = lock_next_for_traversal(cur);
2743 if (cur == NULL) {
2744 break;
2745 }
2746 }
2747 }
2748 int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
2749 if (l_in_use_count == chk_om_in_use_count) {
2750 out->print_cr("global_in_use_count=%d equals chk_om_in_use_count=%d",
2751 l_in_use_count, chk_om_in_use_count);
2752 } else {
2753 // With fine grained locks on the monitor lists, it is possible for
2754 // an exiting JavaThread to put its in-use ObjectMonitors on the
2755 // global in-use list after chk_om_in_use_count is calculated above.
2756 out->print_cr("WARNING: global_in_use_count=%d is not equal to chk_om_in_use_count=%d",
2757 l_in_use_count, chk_om_in_use_count);
2758 }
2759 }
2760
2761 // Check an in-use monitor entry; log any errors.
2762 void ObjectSynchronizer::chk_in_use_entry(JavaThread* jt, ObjectMonitor* n,
2763 outputStream * out, int *error_cnt_p) {
2764 if (n->header().value() == 0) {
2765 if (jt != NULL) {
2766 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2767 ": in-use per-thread monitor must have non-NULL _header "
2768 "field.", p2i(jt), p2i(n));
2769 } else {
2770 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2771 "must have non-NULL _header field.", p2i(n));
2772 }
2773 *error_cnt_p = *error_cnt_p + 1;
2774 }
2775 if (n->object() == NULL) {
2776 if (jt != NULL) {
2777 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2778 ": in-use per-thread monitor must have non-NULL _object "
2779 "field.", p2i(jt), p2i(n));
2780 } else {
2781 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2782 "must have non-NULL _object field.", p2i(n));
2783 }
2784 *error_cnt_p = *error_cnt_p + 1;
2785 }
2786 const oop obj = (oop)n->object();
2787 const markWord mark = obj->mark();
2788 if (!mark.has_monitor()) {
2789 if (jt != NULL) {
2790 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2791 ": in-use per-thread monitor's object does not think "
2792 "it has a monitor: obj=" INTPTR_FORMAT ", mark="
2793 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), mark.value());
2794 } else {
2795 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2796 "monitor's object does not think it has a monitor: obj="
2797 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2798 p2i(obj), mark.value());
2799 }
2800 *error_cnt_p = *error_cnt_p + 1;
2801 }
2802 ObjectMonitor* const obj_mon = mark.monitor();
2803 if (n != obj_mon) {
2804 if (jt != NULL) {
2805 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2806 ": in-use per-thread monitor's object does not refer "
2807 "to the same monitor: obj=" INTPTR_FORMAT ", mark="
2808 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
2809 p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2810 } else {
2811 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2812 "monitor's object does not refer to the same monitor: obj="
2813 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2814 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2815 }
2816 *error_cnt_p = *error_cnt_p + 1;
2817 }
2818 }
2819
2820 // Check the thread's free list and count; log the results of the checks.
2821 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
2822 outputStream * out,
2823 int *error_cnt_p) {
2824 int chk_om_free_count = 0;
2825 ObjectMonitor* cur = NULL;
2826 if ((cur = get_list_head_locked(&jt->om_free_list)) != NULL) {
2827 // Marked the per-thread free list head so process the list.
2828 while (true) {
2829 chk_free_entry(jt, cur, out, error_cnt_p);
2830 chk_om_free_count++;
2831
2832 cur = lock_next_for_traversal(cur);
2833 if (cur == NULL) {
2834 break;
2835 }
2836 }
2837 }
2838 int l_om_free_count = Atomic::load(&jt->om_free_count);
2839 if (l_om_free_count == chk_om_free_count) {
2840 out->print_cr("jt=" INTPTR_FORMAT ": om_free_count=%d equals "
2841 "chk_om_free_count=%d", p2i(jt), l_om_free_count, chk_om_free_count);
2842 } else {
2843 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_free_count=%d is not "
2844 "equal to chk_om_free_count=%d", p2i(jt), l_om_free_count,
2845 chk_om_free_count);
2846 *error_cnt_p = *error_cnt_p + 1;
2847 }
2848 }
2849
2850 // Check the thread's in-use list and count; log the results of the checks.
2851 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
2852 outputStream * out,
2853 int *error_cnt_p) {
2854 int chk_om_in_use_count = 0;
2855 ObjectMonitor* cur = NULL;
2856 if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
2857 // Marked the per-thread in-use list head so process the list.
2858 while (true) {
2859 chk_in_use_entry(jt, cur, out, error_cnt_p);
2860 chk_om_in_use_count++;
2861
2862 cur = lock_next_for_traversal(cur);
2863 if (cur == NULL) {
2864 break;
2865 }
2866 }
2867 }
2868 int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
2869 if (l_om_in_use_count == chk_om_in_use_count) {
2870 out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals "
2871 "chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
2872 chk_om_in_use_count);
2873 } else {
2874 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not "
2875 "equal to chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
2876 chk_om_in_use_count);
2877 *error_cnt_p = *error_cnt_p + 1;
2878 }
2879 }
2880
2881 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2882 // flags indicate why the entry is in-use, 'object' and 'object type'
2883 // indicate the associated object and its type.
2884 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out) {
2885 stringStream ss;
2886 if (Atomic::load(&om_list_globals._in_use_count) > 0) {
2887 out->print_cr("In-use global monitor info:");
2888 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2889 out->print_cr("%18s %s %18s %18s",
2890 "monitor", "BHL", "object", "object type");
2891 out->print_cr("================== === ================== ==================");
2892 ObjectMonitor* cur = NULL;
2893 if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) {
2894 // Marked the global in-use list head so process the list.
2895 while (true) {
2896 const oop obj = (oop) cur->object();
2897 const markWord mark = cur->header();
2898 ResourceMark rm;
2899 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(cur),
2900 cur->is_busy() != 0, mark.hash() != 0, cur->owner() != NULL,
2901 p2i(obj), obj->klass()->external_name());
2902 if (cur->is_busy() != 0) {
2903 out->print(" (%s)", cur->is_busy_to_string(&ss));
2904 ss.reset();
2905 }
2906 out->cr();
2907
2908 cur = lock_next_for_traversal(cur);
2909 if (cur == NULL) {
2910 break;
2911 }
2912 }
2913 }
2914 }
2915
2916 out->print_cr("In-use per-thread monitor info:");
2917 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2918 out->print_cr("%18s %18s %s %18s %18s",
2919 "jt", "monitor", "BHL", "object", "object type");
2920 out->print_cr("================== ================== === ================== ==================");
2921 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2922 ObjectMonitor* cur = NULL;
2923 if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
2924 // Marked the global in-use list head so process the list.
2925 while (true) {
2926 const oop obj = (oop) cur->object();
2927 const markWord mark = cur->header();
2928 ResourceMark rm;
2929 out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT
2930 " %s", p2i(jt), p2i(cur), cur->is_busy() != 0,
2931 mark.hash() != 0, cur->owner() != NULL, p2i(obj),
2932 obj->klass()->external_name());
2933 if (cur->is_busy() != 0) {
2934 out->print(" (%s)", cur->is_busy_to_string(&ss));
2935 ss.reset();
2936 }
2937 out->cr();
2938
2939 cur = lock_next_for_traversal(cur);
2940 if (cur == NULL) {
2941 break;
2942 }
2943 }
2944 }
2945 }
2946
2947 out->flush();
2948 }
2949
2950 // Log counts for the global and per-thread monitor lists and return
2951 // the population count.
2952 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2953 int pop_count = 0;
2954 out->print_cr("%18s %10s %10s %10s %10s",
2955 "Global Lists:", "InUse", "Free", "Wait", "Total");
2956 out->print_cr("================== ========== ========== ========== ==========");
2957 int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
2958 int l_free_count = Atomic::load(&om_list_globals._free_count);
2959 int l_wait_count = Atomic::load(&om_list_globals._wait_count);
2960 out->print_cr("%18s %10d %10d %10d %10d", "", l_in_use_count,
2961 l_free_count, l_wait_count,
2962 Atomic::load(&om_list_globals._population));
2963 pop_count += l_in_use_count + l_free_count + l_wait_count;
2964
2965 out->print_cr("%18s %10s %10s %10s",
2966 "Per-Thread Lists:", "InUse", "Free", "Provision");
2967 out->print_cr("================== ========== ========== ==========");
2968
2969 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2970 int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
2971 int l_om_free_count = Atomic::load(&jt->om_free_count);
2972 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
2973 l_om_in_use_count, l_om_free_count, jt->om_free_provision);
2974 pop_count += l_om_in_use_count + l_om_free_count;
2975 }
2976 return pop_count;
2977 }
2978
2979 #ifndef PRODUCT
2980
2981 // Check if monitor belongs to the monitor cache
2982 // The list is grow-only so it's *relatively* safe to traverse
2983 // the list of extant blocks without taking a lock.
2984
2985 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
2986 PaddedObjectMonitor* block = Atomic::load(&g_block_list);
2987 while (block != NULL) {
2988 assert(block->object() == CHAINMARKER, "must be a block header");
2989 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
2990 address mon = (address)monitor;
2991 address blk = (address)block;
2992 size_t diff = mon - blk;
2993 assert((diff % sizeof(PaddedObjectMonitor)) == 0, "must be aligned");
2994 return 1;
2995 }
2996 // unmarked_next() is not needed with g_block_list (no locking
2997 // used with block linkage _next_om fields).
2998 block = (PaddedObjectMonitor*)block->next_om();
2999 }
3000 return 0;
3001 }
3002
3003 #endif