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