1 /*
2 * Copyright (c) 1998, 2019, 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/interfaceSupport.inline.hpp"
41 #include "runtime/mutexLocker.hpp"
42 #include "runtime/objectMonitor.hpp"
43 #include "runtime/objectMonitor.inline.hpp"
44 #include "runtime/osThread.hpp"
45 #include "runtime/safepointVerifiers.hpp"
46 #include "runtime/sharedRuntime.hpp"
47 #include "runtime/stubRoutines.hpp"
48 #include "runtime/synchronizer.hpp"
49 #include "runtime/thread.inline.hpp"
50 #include "runtime/timer.hpp"
51 #include "runtime/vframe.hpp"
52 #include "runtime/vmThread.hpp"
53 #include "utilities/align.hpp"
54 #include "utilities/dtrace.hpp"
55 #include "utilities/events.hpp"
56 #include "utilities/preserveException.hpp"
57
58 // The "core" versions of monitor enter and exit reside in this file.
59 // The interpreter and compilers contain specialized transliterated
60 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
61 // for instance. If you make changes here, make sure to modify the
62 // interpreter, and both C1 and C2 fast-path inline locking code emission.
63 //
64 // -----------------------------------------------------------------------------
65
66 #ifdef DTRACE_ENABLED
67
68 // Only bother with this argument setup if dtrace is available
69 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
70
71 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
72 char* bytes = NULL; \
73 int len = 0; \
74 jlong jtid = SharedRuntime::get_java_tid(thread); \
75 Symbol* klassname = ((oop)(obj))->klass()->name(); \
76 if (klassname != NULL) { \
77 bytes = (char*)klassname->bytes(); \
78 len = klassname->utf8_length(); \
79 }
80
81 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
82 { \
83 if (DTraceMonitorProbes) { \
84 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
85 HOTSPOT_MONITOR_WAIT(jtid, \
86 (uintptr_t)(monitor), bytes, len, (millis)); \
87 } \
88 }
89
90 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
91 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
92 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
93
94 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
95 { \
96 if (DTraceMonitorProbes) { \
97 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
98 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
99 (uintptr_t)(monitor), bytes, len); \
100 } \
101 }
102
103 #else // ndef DTRACE_ENABLED
104
105 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
106 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
107
108 #endif // ndef DTRACE_ENABLED
109
110 // This exists only as a workaround of dtrace bug 6254741
111 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
112 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
113 return 0;
114 }
115
116 #define NINFLATIONLOCKS 256
117 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
118
119 // global list of blocks of monitors
120 PaddedObjectMonitor* ObjectSynchronizer::g_block_list = NULL;
121
122 struct ObjectMonitorListGlobals {
123 char _pad_prefix[OM_CACHE_LINE_SIZE];
124 // These are highly shared list related variables.
125 // To avoid false-sharing they need to be the sole occupants of a cache line.
126
127 // Global ObjectMonitor free list. Newly allocated and deflated
128 // ObjectMonitors are prepended here.
129 ObjectMonitor* _free_list;
130 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
131
132 // Global ObjectMonitor in-use list. When a JavaThread is exiting,
133 // ObjectMonitors on its per-thread in-use list are prepended here.
134 ObjectMonitor* _in_use_list;
135 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
136
137 int _free_count; // # on free_list
138 DEFINE_PAD_MINUS_SIZE(3, OM_CACHE_LINE_SIZE, sizeof(int));
139
140 int _in_use_count; // # on in_use_list
141 DEFINE_PAD_MINUS_SIZE(4, OM_CACHE_LINE_SIZE, sizeof(int));
142
143 int _population; // # Extant -- in circulation
144 DEFINE_PAD_MINUS_SIZE(5, OM_CACHE_LINE_SIZE, sizeof(int));
145 };
146 static ObjectMonitorListGlobals om_list_globals;
147
148 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
149
150
151 // =====================> Spin-lock functions
152
153 // ObjectMonitors are not lockable outside of this file. We use spin-locks
154 // implemented using a bit in the _next_om field instead of the heavier
155 // weight locking mechanisms for faster list management.
156
157 #define OM_LOCK_BIT 0x1
158
159 // Return true if the ObjectMonitor is locked.
160 // Otherwise returns false.
161 static bool is_locked(ObjectMonitor* om) {
162 return ((intptr_t)om->next_om() & OM_LOCK_BIT) == OM_LOCK_BIT;
163 }
164
165 // Mark an ObjectMonitor* with OM_LOCK_BIT and return it.
166 static ObjectMonitor* mark_om_ptr(ObjectMonitor* om) {
167 return (ObjectMonitor*)((intptr_t)om | OM_LOCK_BIT);
168 }
169
170 // Return the unmarked next field in an ObjectMonitor. Note: the next
171 // field may or may not have been marked with OM_LOCK_BIT originally.
172 static ObjectMonitor* unmarked_next(ObjectMonitor* om) {
173 return (ObjectMonitor*)((intptr_t)om->next_om() & ~OM_LOCK_BIT);
174 }
175
176 // Try to lock an ObjectMonitor. Returns true if locking was successful.
177 // Otherwise returns false.
178 static bool try_om_lock(ObjectMonitor* om) {
179 // Get current next field without any OM_LOCK_BIT value.
180 ObjectMonitor* next = unmarked_next(om);
181 if (om->try_set_next_om(next, mark_om_ptr(next)) != next) {
182 return false; // Cannot lock the ObjectMonitor.
183 }
184 return true;
185 }
186
187 // Lock an ObjectMonitor.
188 static void om_lock(ObjectMonitor* om) {
189 while (true) {
190 if (try_om_lock(om)) {
191 return;
192 }
193 }
194 }
195
196 // Unlock an ObjectMonitor.
197 static void om_unlock(ObjectMonitor* om) {
198 ObjectMonitor* next = om->next_om();
199 guarantee(((intptr_t)next & OM_LOCK_BIT) == OM_LOCK_BIT, "next=" INTPTR_FORMAT
200 " must have OM_LOCK_BIT=%x set.", p2i(next), OM_LOCK_BIT);
201
202 next = (ObjectMonitor*)((intptr_t)next & ~OM_LOCK_BIT); // Clear OM_LOCK_BIT.
203 om->set_next_om(next);
204 }
205
206 // Get the list head after locking it. Returns the list head or NULL
207 // if the list is empty.
208 static ObjectMonitor* get_list_head_locked(ObjectMonitor** list_p) {
209 while (true) {
210 ObjectMonitor* mid = Atomic::load(list_p);
211 if (mid == NULL) {
212 return NULL; // The list is empty.
213 }
214 if (try_om_lock(mid)) {
215 if (Atomic::load(list_p) != mid) {
216 // The list head changed before we could lock it so we have to retry.
217 om_unlock(mid);
218 continue;
219 }
220 return mid;
221 }
222 }
223 }
224
225 #undef OM_LOCK_BIT
226
227
228 // =====================> List Management functions
229
230 // Prepend a list of ObjectMonitors to the specified *list_p. 'tail' is
231 // the last ObjectMonitor in the list and there are 'count' on the list.
232 // Also updates the specified *count_p.
233 static void prepend_list_to_common(ObjectMonitor* list, ObjectMonitor* tail,
234 int count, ObjectMonitor** list_p,
235 int* count_p) {
236 while (true) {
237 ObjectMonitor* cur = Atomic::load(list_p);
238 // Prepend list to *list_p.
239 if (!try_om_lock(tail)) {
240 // Failed to lock tail due to a list walker so try it all again.
241 continue;
242 }
243 tail->set_next_om(cur); // tail now points to cur (and unlocks tail)
244 if (cur == NULL) {
245 // No potential race with takers or other prependers since
246 // *list_p is empty.
247 if (Atomic::cmpxchg(list_p, cur, list) == cur) {
248 // Successfully switched *list_p to the list value.
249 Atomic::add(count_p, count);
250 break;
251 }
252 // Implied else: try it all again
253 } else {
254 if (!try_om_lock(cur)) {
255 continue; // failed to lock cur so try it all again
256 }
257 // We locked cur so try to switch *list_p to the list value.
258 if (Atomic::cmpxchg(list_p, cur, list) != cur) {
259 // The list head has changed so unlock cur and try again:
260 om_unlock(cur);
261 continue;
262 }
263 Atomic::add(count_p, count);
264 om_unlock(cur);
265 break;
266 }
267 }
268 }
269
270 // Prepend a newly allocated block of ObjectMonitors to g_block_list and
271 // om_list_globals._free_list. Also updates om_list_globals._population
272 // and om_list_globals._free_count.
273 void ObjectSynchronizer::prepend_block_to_lists(PaddedObjectMonitor* new_blk) {
274 // First we handle g_block_list:
275 while (true) {
276 PaddedObjectMonitor* cur = Atomic::load(&g_block_list);
277 // Prepend new_blk to g_block_list. The first ObjectMonitor in
278 // a block is reserved for use as linkage to the next block.
279 new_blk[0].set_next_om(cur);
280 if (Atomic::cmpxchg(&g_block_list, cur, new_blk) == cur) {
281 // Successfully switched g_block_list to the new_blk value.
282 Atomic::add(&om_list_globals._population, _BLOCKSIZE - 1);
283 break;
284 }
285 // Implied else: try it all again
286 }
287
288 // Second we handle om_list_globals._free_list:
289 prepend_list_to_common(new_blk + 1, &new_blk[_BLOCKSIZE - 1], _BLOCKSIZE - 1,
290 &om_list_globals._free_list, &om_list_globals._free_count);
291 }
292
293 // Prepend a list of ObjectMonitors to om_list_globals._free_list.
294 // 'tail' is the last ObjectMonitor in the list and there are 'count'
295 // on the list. Also updates om_list_globals._free_count.
296 static void prepend_list_to_global_free_list(ObjectMonitor* list,
297 ObjectMonitor* tail, int count) {
298 prepend_list_to_common(list, tail, count, &om_list_globals._free_list,
299 &om_list_globals._free_count);
300 }
301
302 // Prepend a list of ObjectMonitors to om_list_globals._in_use_list.
303 // 'tail' is the last ObjectMonitor in the list and there are 'count'
304 // on the list. Also updates om_list_globals._in_use_list.
305 static void prepend_list_to_global_in_use_list(ObjectMonitor* list,
306 ObjectMonitor* tail, int count) {
307 prepend_list_to_common(list, tail, count, &om_list_globals._in_use_list,
308 &om_list_globals._in_use_count);
309 }
310
311 // Prepend an ObjectMonitor to the specified list. Also updates
312 // the specified counter.
313 static void prepend_to_common(ObjectMonitor* m, ObjectMonitor** list_p,
314 int* count_p) {
315 while (true) {
316 om_lock(m); // Lock m so we can safely update its next field.
317 ObjectMonitor* cur = NULL;
318 // Lock the list head to guard against races with a list walker
319 // thread:
320 if ((cur = get_list_head_locked(list_p)) != NULL) {
321 // List head is now locked so we can safely switch it.
322 m->set_next_om(cur); // m now points to cur (and unlocks m)
323 Atomic::store(list_p, m); // Switch list head to unlocked m.
324 om_unlock(cur);
325 break;
326 }
327 // The list is empty so try to set the list head.
328 assert(cur == NULL, "cur must be NULL: cur=" INTPTR_FORMAT, p2i(cur));
329 m->set_next_om(cur); // m now points to NULL (and unlocks m)
330 if (Atomic::cmpxchg(list_p, cur, m) == cur) {
331 // List head is now unlocked m.
332 break;
333 }
334 // Implied else: try it all again
335 }
336 Atomic::inc(count_p);
337 }
338
339 // Prepend an ObjectMonitor to a per-thread om_free_list.
340 // Also updates the per-thread om_free_count.
341 static void prepend_to_om_free_list(Thread* self, ObjectMonitor* m) {
342 prepend_to_common(m, &self->om_free_list, &self->om_free_count);
343 }
344
345 // Prepend an ObjectMonitor to a per-thread om_in_use_list.
346 // Also updates the per-thread om_in_use_count.
347 static void prepend_to_om_in_use_list(Thread* self, ObjectMonitor* m) {
348 prepend_to_common(m, &self->om_in_use_list, &self->om_in_use_count);
349 }
350
351 // Take an ObjectMonitor from the start of the specified list. Also
352 // decrements the specified counter. Returns NULL if none are available.
353 static ObjectMonitor* take_from_start_of_common(ObjectMonitor** list_p,
354 int* count_p) {
355 ObjectMonitor* take = NULL;
356 // Lock the list head to guard against races with a list walker
357 // thread:
358 if ((take = get_list_head_locked(list_p)) == NULL) {
359 return NULL; // None are available.
360 }
361 ObjectMonitor* next = unmarked_next(take);
362 // Switch locked list head to next (which unlocks the list head, but
363 // leaves take locked):
364 Atomic::store(list_p, next);
365 Atomic::dec(count_p);
366 // Unlock take, but leave the next value for any lagging list
367 // walkers. It will get cleaned up when take is prepended to
368 // the in-use list:
369 om_unlock(take);
370 return take;
371 }
372
373 // Take an ObjectMonitor from the start of the om_list_globals._free_list.
374 // Also updates om_list_globals._free_count. Returns NULL if none are
375 // available.
376 static ObjectMonitor* take_from_start_of_global_free_list() {
377 return take_from_start_of_common(&om_list_globals._free_list,
378 &om_list_globals._free_count);
379 }
380
381 // Take an ObjectMonitor from the start of a per-thread free-list.
382 // Also updates om_free_count. Returns NULL if none are available.
383 static ObjectMonitor* take_from_start_of_om_free_list(Thread* self) {
384 return take_from_start_of_common(&self->om_free_list, &self->om_free_count);
385 }
386
387
388 // =====================> Quick functions
389
390 // The quick_* forms are special fast-path variants used to improve
391 // performance. In the simplest case, a "quick_*" implementation could
392 // simply return false, in which case the caller will perform the necessary
393 // state transitions and call the slow-path form.
394 // The fast-path is designed to handle frequently arising cases in an efficient
395 // manner and is just a degenerate "optimistic" variant of the slow-path.
396 // returns true -- to indicate the call was satisfied.
397 // returns false -- to indicate the call needs the services of the slow-path.
398 // A no-loitering ordinance is in effect for code in the quick_* family
399 // operators: safepoints or indefinite blocking (blocking that might span a
400 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
401 // entry.
402 //
403 // Consider: An interesting optimization is to have the JIT recognize the
404 // following common idiom:
405 // synchronized (someobj) { .... ; notify(); }
406 // That is, we find a notify() or notifyAll() call that immediately precedes
407 // the monitorexit operation. In that case the JIT could fuse the operations
408 // into a single notifyAndExit() runtime primitive.
409
410 bool ObjectSynchronizer::quick_notify(oopDesc* obj, Thread* self, bool all) {
411 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
412 assert(self->is_Java_thread(), "invariant");
413 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
414 NoSafepointVerifier nsv;
415 if (obj == NULL) return false; // slow-path for invalid obj
416 const markWord mark = obj->mark();
417
418 if (mark.has_locker() && self->is_lock_owned((address)mark.locker())) {
419 // Degenerate notify
420 // stack-locked by caller so by definition the implied waitset is empty.
421 return true;
422 }
423
424 if (mark.has_monitor()) {
425 ObjectMonitor* const mon = mark.monitor();
426 assert(mon->object() == obj, "invariant");
427 if (mon->owner() != self) return false; // slow-path for IMS exception
428
429 if (mon->first_waiter() != NULL) {
430 // We have one or more waiters. Since this is an inflated monitor
431 // that we own, we can transfer one or more threads from the waitset
432 // to the entrylist here and now, avoiding the slow-path.
433 if (all) {
434 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
435 } else {
436 DTRACE_MONITOR_PROBE(notify, mon, obj, self);
437 }
438 int free_count = 0;
439 do {
440 mon->INotify(self);
441 ++free_count;
442 } while (mon->first_waiter() != NULL && all);
443 OM_PERFDATA_OP(Notifications, inc(free_count));
444 }
445 return true;
446 }
447
448 // biased locking and any other IMS exception states take the slow-path
449 return false;
450 }
451
452
453 // The LockNode emitted directly at the synchronization site would have
454 // been too big if it were to have included support for the cases of inflated
455 // recursive enter and exit, so they go here instead.
456 // Note that we can't safely call AsyncPrintJavaStack() from within
457 // quick_enter() as our thread state remains _in_Java.
458
459 bool ObjectSynchronizer::quick_enter(oop obj, Thread* self,
460 BasicLock * lock) {
461 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
462 assert(self->is_Java_thread(), "invariant");
463 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
464 NoSafepointVerifier nsv;
465 if (obj == NULL) return false; // Need to throw NPE
466 const markWord mark = obj->mark();
467
468 if (mark.has_monitor()) {
469 ObjectMonitor* const m = mark.monitor();
470 assert(m->object() == obj, "invariant");
471 Thread* const owner = (Thread *) m->_owner;
472
473 // Lock contention and Transactional Lock Elision (TLE) diagnostics
474 // and observability
475 // Case: light contention possibly amenable to TLE
476 // Case: TLE inimical operations such as nested/recursive synchronization
477
478 if (owner == self) {
479 m->_recursions++;
480 return true;
481 }
482
483 // This Java Monitor is inflated so obj's header will never be
484 // displaced to this thread's BasicLock. Make the displaced header
485 // non-NULL so this BasicLock is not seen as recursive nor as
486 // being locked. We do this unconditionally so that this thread's
487 // BasicLock cannot be mis-interpreted by any stack walkers. For
488 // performance reasons, stack walkers generally first check for
489 // Biased Locking in the object's header, the second check is for
490 // stack-locking in the object's header, the third check is for
491 // recursive stack-locking in the displaced header in the BasicLock,
492 // and last are the inflated Java Monitor (ObjectMonitor) checks.
493 lock->set_displaced_header(markWord::unused_mark());
494
495 if (owner == NULL && m->try_set_owner_from(NULL, self) == NULL) {
496 assert(m->_recursions == 0, "invariant");
497 return true;
498 }
499 }
500
501 // Note that we could inflate in quick_enter.
502 // This is likely a useful optimization
503 // Critically, in quick_enter() we must not:
504 // -- perform bias revocation, or
505 // -- block indefinitely, or
506 // -- reach a safepoint
507
508 return false; // revert to slow-path
509 }
510
511 // -----------------------------------------------------------------------------
512 // Monitor Enter/Exit
513 // The interpreter and compiler assembly code tries to lock using the fast path
514 // of this algorithm. Make sure to update that code if the following function is
515 // changed. The implementation is extremely sensitive to race condition. Be careful.
516
517 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, TRAPS) {
518 if (UseBiasedLocking) {
519 if (!SafepointSynchronize::is_at_safepoint()) {
520 BiasedLocking::revoke(obj, THREAD);
521 } else {
522 BiasedLocking::revoke_at_safepoint(obj);
523 }
524 }
525
526 markWord mark = obj->mark();
527 assert(!mark.has_bias_pattern(), "should not see bias pattern here");
528
529 if (mark.is_neutral()) {
530 // Anticipate successful CAS -- the ST of the displaced mark must
531 // be visible <= the ST performed by the CAS.
532 lock->set_displaced_header(mark);
533 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
534 return;
535 }
536 // Fall through to inflate() ...
537 } else if (mark.has_locker() &&
538 THREAD->is_lock_owned((address)mark.locker())) {
539 assert(lock != mark.locker(), "must not re-lock the same lock");
540 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
541 lock->set_displaced_header(markWord::from_pointer(NULL));
542 return;
543 }
544
545 // The object header will never be displaced to this lock,
546 // so it does not matter what the value is, except that it
547 // must be non-zero to avoid looking like a re-entrant lock,
548 // and must not look locked either.
549 lock->set_displaced_header(markWord::unused_mark());
550 inflate(THREAD, obj(), inflate_cause_monitor_enter)->enter(THREAD);
551 }
552
553 void ObjectSynchronizer::exit(oop object, BasicLock* lock, TRAPS) {
554 markWord mark = object->mark();
555 // We cannot check for Biased Locking if we are racing an inflation.
556 assert(mark == markWord::INFLATING() ||
557 !mark.has_bias_pattern(), "should not see bias pattern here");
558
559 markWord dhw = lock->displaced_header();
560 if (dhw.value() == 0) {
561 // If the displaced header is NULL, then this exit matches up with
562 // a recursive enter. No real work to do here except for diagnostics.
563 #ifndef PRODUCT
564 if (mark != markWord::INFLATING()) {
565 // Only do diagnostics if we are not racing an inflation. Simply
566 // exiting a recursive enter of a Java Monitor that is being
567 // inflated is safe; see the has_monitor() comment below.
568 assert(!mark.is_neutral(), "invariant");
569 assert(!mark.has_locker() ||
570 THREAD->is_lock_owned((address)mark.locker()), "invariant");
571 if (mark.has_monitor()) {
572 // The BasicLock's displaced_header is marked as a recursive
573 // enter and we have an inflated Java Monitor (ObjectMonitor).
574 // This is a special case where the Java Monitor was inflated
575 // after this thread entered the stack-lock recursively. When a
576 // Java Monitor is inflated, we cannot safely walk the Java
577 // Monitor owner's stack and update the BasicLocks because a
578 // Java Monitor can be asynchronously inflated by a thread that
579 // does not own the Java Monitor.
580 ObjectMonitor* m = mark.monitor();
581 assert(((oop)(m->object()))->mark() == mark, "invariant");
582 assert(m->is_entered(THREAD), "invariant");
583 }
584 }
585 #endif
586 return;
587 }
588
589 if (mark == markWord::from_pointer(lock)) {
590 // If the object is stack-locked by the current thread, try to
591 // swing the displaced header from the BasicLock back to the mark.
592 assert(dhw.is_neutral(), "invariant");
593 if (object->cas_set_mark(dhw, mark) == mark) {
594 return;
595 }
596 }
597
598 // We have to take the slow-path of possible inflation and then exit.
599 inflate(THREAD, object, inflate_cause_vm_internal)->exit(true, THREAD);
600 }
601
602 // -----------------------------------------------------------------------------
603 // Class Loader support to workaround deadlocks on the class loader lock objects
604 // Also used by GC
605 // complete_exit()/reenter() are used to wait on a nested lock
606 // i.e. to give up an outer lock completely and then re-enter
607 // Used when holding nested locks - lock acquisition order: lock1 then lock2
608 // 1) complete_exit lock1 - saving recursion count
609 // 2) wait on lock2
610 // 3) when notified on lock2, unlock lock2
611 // 4) reenter lock1 with original recursion count
612 // 5) lock lock2
613 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
614 intx ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
615 if (UseBiasedLocking) {
616 BiasedLocking::revoke(obj, THREAD);
617 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
618 }
619
620 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
621
622 return monitor->complete_exit(THREAD);
623 }
624
625 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
626 void ObjectSynchronizer::reenter(Handle obj, intx recursions, TRAPS) {
627 if (UseBiasedLocking) {
628 BiasedLocking::revoke(obj, THREAD);
629 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
630 }
631
632 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
633
634 monitor->reenter(recursions, THREAD);
635 }
636 // -----------------------------------------------------------------------------
637 // JNI locks on java objects
638 // NOTE: must use heavy weight monitor to handle jni monitor enter
639 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
640 // the current locking is from JNI instead of Java code
641 if (UseBiasedLocking) {
642 BiasedLocking::revoke(obj, THREAD);
643 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
644 }
645 THREAD->set_current_pending_monitor_is_from_java(false);
646 inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);
647 THREAD->set_current_pending_monitor_is_from_java(true);
648 }
649
650 // NOTE: must use heavy weight monitor to handle jni monitor exit
651 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
652 if (UseBiasedLocking) {
653 Handle h_obj(THREAD, obj);
654 BiasedLocking::revoke(h_obj, THREAD);
655 obj = h_obj();
656 }
657 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
658
659 ObjectMonitor* monitor = inflate(THREAD, obj, inflate_cause_jni_exit);
660 // If this thread has locked the object, exit the monitor. We
661 // intentionally do not use CHECK here because we must exit the
662 // monitor even if an exception is pending.
663 if (monitor->check_owner(THREAD)) {
664 monitor->exit(true, THREAD);
665 }
666 }
667
668 // -----------------------------------------------------------------------------
669 // Internal VM locks on java objects
670 // standard constructor, allows locking failures
671 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool do_lock) {
672 _dolock = do_lock;
673 _thread = thread;
674 _thread->check_for_valid_safepoint_state();
675 _obj = obj;
676
677 if (_dolock) {
678 ObjectSynchronizer::enter(_obj, &_lock, _thread);
679 }
680 }
681
682 ObjectLocker::~ObjectLocker() {
683 if (_dolock) {
684 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
685 }
686 }
687
688
689 // -----------------------------------------------------------------------------
690 // Wait/Notify/NotifyAll
691 // NOTE: must use heavy weight monitor to handle wait()
692 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
693 if (UseBiasedLocking) {
694 BiasedLocking::revoke(obj, THREAD);
695 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
696 }
697 if (millis < 0) {
698 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
699 }
700 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
701
702 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
703 monitor->wait(millis, true, THREAD);
704
705 // This dummy call is in place to get around dtrace bug 6254741. Once
706 // that's fixed we can uncomment the following line, remove the call
707 // and change this function back into a "void" func.
708 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
709 return dtrace_waited_probe(monitor, obj, THREAD);
710 }
711
712 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, jlong millis, TRAPS) {
713 if (UseBiasedLocking) {
714 BiasedLocking::revoke(obj, THREAD);
715 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
716 }
717 if (millis < 0) {
718 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
719 }
720 inflate(THREAD, obj(), inflate_cause_wait)->wait(millis, false, THREAD);
721 }
722
723 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
724 if (UseBiasedLocking) {
725 BiasedLocking::revoke(obj, THREAD);
726 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
727 }
728
729 markWord mark = obj->mark();
730 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
731 return;
732 }
733 inflate(THREAD, obj(), inflate_cause_notify)->notify(THREAD);
734 }
735
736 // NOTE: see comment of notify()
737 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
738 if (UseBiasedLocking) {
739 BiasedLocking::revoke(obj, THREAD);
740 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
741 }
742
743 markWord mark = obj->mark();
744 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
745 return;
746 }
747 inflate(THREAD, obj(), inflate_cause_notify)->notifyAll(THREAD);
748 }
749
750 // -----------------------------------------------------------------------------
751 // Hash Code handling
752 //
753 // Performance concern:
754 // OrderAccess::storestore() calls release() which at one time stored 0
755 // into the global volatile OrderAccess::dummy variable. This store was
756 // unnecessary for correctness. Many threads storing into a common location
757 // causes considerable cache migration or "sloshing" on large SMP systems.
758 // As such, I avoided using OrderAccess::storestore(). In some cases
759 // OrderAccess::fence() -- which incurs local latency on the executing
760 // processor -- is a better choice as it scales on SMP systems.
761 //
762 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
763 // a discussion of coherency costs. Note that all our current reference
764 // platforms provide strong ST-ST order, so the issue is moot on IA32,
765 // x64, and SPARC.
766 //
767 // As a general policy we use "volatile" to control compiler-based reordering
768 // and explicit fences (barriers) to control for architectural reordering
769 // performed by the CPU(s) or platform.
770
771 struct SharedGlobals {
772 char _pad_prefix[OM_CACHE_LINE_SIZE];
773 // These are highly shared mostly-read variables.
774 // To avoid false-sharing they need to be the sole occupants of a cache line.
775 volatile int stw_random;
776 volatile int stw_cycle;
777 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
778 // Hot RW variable -- Sequester to avoid false-sharing
779 volatile int hc_sequence;
780 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
781 };
782
783 static SharedGlobals GVars;
784 static int _forceMonitorScavenge = 0; // Scavenge required and pending
785
786 static markWord read_stable_mark(oop obj) {
787 markWord mark = obj->mark();
788 if (!mark.is_being_inflated()) {
789 return mark; // normal fast-path return
790 }
791
792 int its = 0;
793 for (;;) {
794 markWord mark = obj->mark();
795 if (!mark.is_being_inflated()) {
796 return mark; // normal fast-path return
797 }
798
799 // The object is being inflated by some other thread.
800 // The caller of read_stable_mark() must wait for inflation to complete.
801 // Avoid live-lock
802 // TODO: consider calling SafepointSynchronize::do_call_back() while
803 // spinning to see if there's a safepoint pending. If so, immediately
804 // yielding or blocking would be appropriate. Avoid spinning while
805 // there is a safepoint pending.
806 // TODO: add inflation contention performance counters.
807 // TODO: restrict the aggregate number of spinners.
808
809 ++its;
810 if (its > 10000 || !os::is_MP()) {
811 if (its & 1) {
812 os::naked_yield();
813 } else {
814 // Note that the following code attenuates the livelock problem but is not
815 // a complete remedy. A more complete solution would require that the inflating
816 // thread hold the associated inflation lock. The following code simply restricts
817 // the number of spinners to at most one. We'll have N-2 threads blocked
818 // on the inflationlock, 1 thread holding the inflation lock and using
819 // a yield/park strategy, and 1 thread in the midst of inflation.
820 // A more refined approach would be to change the encoding of INFLATING
821 // to allow encapsulation of a native thread pointer. Threads waiting for
822 // inflation to complete would use CAS to push themselves onto a singly linked
823 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
824 // and calling park(). When inflation was complete the thread that accomplished inflation
825 // would detach the list and set the markword to inflated with a single CAS and
826 // then for each thread on the list, set the flag and unpark() the thread.
827 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
828 // wakes at most one thread whereas we need to wake the entire list.
829 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
830 int YieldThenBlock = 0;
831 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
832 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
833 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
834 while (obj->mark() == markWord::INFLATING()) {
835 // Beware: NakedYield() is advisory and has almost no effect on some platforms
836 // so we periodically call self->_ParkEvent->park(1).
837 // We use a mixed spin/yield/block mechanism.
838 if ((YieldThenBlock++) >= 16) {
839 Thread::current()->_ParkEvent->park(1);
840 } else {
841 os::naked_yield();
842 }
843 }
844 Thread::muxRelease(gInflationLocks + ix);
845 }
846 } else {
847 SpinPause(); // SMP-polite spinning
848 }
849 }
850 }
851
852 // hashCode() generation :
853 //
854 // Possibilities:
855 // * MD5Digest of {obj,stw_random}
856 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
857 // * A DES- or AES-style SBox[] mechanism
858 // * One of the Phi-based schemes, such as:
859 // 2654435761 = 2^32 * Phi (golden ratio)
860 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
861 // * A variation of Marsaglia's shift-xor RNG scheme.
862 // * (obj ^ stw_random) is appealing, but can result
863 // in undesirable regularity in the hashCode values of adjacent objects
864 // (objects allocated back-to-back, in particular). This could potentially
865 // result in hashtable collisions and reduced hashtable efficiency.
866 // There are simple ways to "diffuse" the middle address bits over the
867 // generated hashCode values:
868
869 static inline intptr_t get_next_hash(Thread* self, oop obj) {
870 intptr_t value = 0;
871 if (hashCode == 0) {
872 // This form uses global Park-Miller RNG.
873 // On MP system we'll have lots of RW access to a global, so the
874 // mechanism induces lots of coherency traffic.
875 value = os::random();
876 } else if (hashCode == 1) {
877 // This variation has the property of being stable (idempotent)
878 // between STW operations. This can be useful in some of the 1-0
879 // synchronization schemes.
880 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
881 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
882 } else if (hashCode == 2) {
883 value = 1; // for sensitivity testing
884 } else if (hashCode == 3) {
885 value = ++GVars.hc_sequence;
886 } else if (hashCode == 4) {
887 value = cast_from_oop<intptr_t>(obj);
888 } else {
889 // Marsaglia's xor-shift scheme with thread-specific state
890 // This is probably the best overall implementation -- we'll
891 // likely make this the default in future releases.
892 unsigned t = self->_hashStateX;
893 t ^= (t << 11);
894 self->_hashStateX = self->_hashStateY;
895 self->_hashStateY = self->_hashStateZ;
896 self->_hashStateZ = self->_hashStateW;
897 unsigned v = self->_hashStateW;
898 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
899 self->_hashStateW = v;
900 value = v;
901 }
902
903 value &= markWord::hash_mask;
904 if (value == 0) value = 0xBAD;
905 assert(value != markWord::no_hash, "invariant");
906 return value;
907 }
908
909 intptr_t ObjectSynchronizer::FastHashCode(Thread* self, oop obj) {
910 if (UseBiasedLocking) {
911 // NOTE: many places throughout the JVM do not expect a safepoint
912 // to be taken here, in particular most operations on perm gen
913 // objects. However, we only ever bias Java instances and all of
914 // the call sites of identity_hash that might revoke biases have
915 // been checked to make sure they can handle a safepoint. The
916 // added check of the bias pattern is to avoid useless calls to
917 // thread-local storage.
918 if (obj->mark().has_bias_pattern()) {
919 // Handle for oop obj in case of STW safepoint
920 Handle hobj(self, obj);
921 // Relaxing assertion for bug 6320749.
922 assert(Universe::verify_in_progress() ||
923 !SafepointSynchronize::is_at_safepoint(),
924 "biases should not be seen by VM thread here");
925 BiasedLocking::revoke(hobj, JavaThread::current());
926 obj = hobj();
927 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
928 }
929 }
930
931 // hashCode() is a heap mutator ...
932 // Relaxing assertion for bug 6320749.
933 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
934 !SafepointSynchronize::is_at_safepoint(), "invariant");
935 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
936 self->is_Java_thread() , "invariant");
937 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
938 ((JavaThread *)self)->thread_state() != _thread_blocked, "invariant");
939
940 ObjectMonitor* monitor = NULL;
941 markWord temp, test;
942 intptr_t hash;
943 markWord mark = read_stable_mark(obj);
944
945 // object should remain ineligible for biased locking
946 assert(!mark.has_bias_pattern(), "invariant");
947
948 if (mark.is_neutral()) { // if this is a normal header
949 hash = mark.hash();
950 if (hash != 0) { // if it has a hash, just return it
951 return hash;
952 }
953 hash = get_next_hash(self, obj); // get a new hash
954 temp = mark.copy_set_hash(hash); // merge the hash into header
955 // try to install the hash
956 test = obj->cas_set_mark(temp, mark);
957 if (test == mark) { // if the hash was installed, return it
958 return hash;
959 }
960 // Failed to install the hash. It could be that another thread
961 // installed the hash just before our attempt or inflation has
962 // occurred or... so we fall thru to inflate the monitor for
963 // stability and then install the hash.
964 } else if (mark.has_monitor()) {
965 monitor = mark.monitor();
966 temp = monitor->header();
967 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
968 hash = temp.hash();
969 if (hash != 0) { // if it has a hash, just return it
970 return hash;
971 }
972 // Fall thru so we only have one place that installs the hash in
973 // the ObjectMonitor.
974 } else if (self->is_lock_owned((address)mark.locker())) {
975 // This is a stack lock owned by the calling thread so fetch the
976 // displaced markWord from the BasicLock on the stack.
977 temp = mark.displaced_mark_helper();
978 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
979 hash = temp.hash();
980 if (hash != 0) { // if it has a hash, just return it
981 return hash;
982 }
983 // WARNING:
984 // The displaced header in the BasicLock on a thread's stack
985 // is strictly immutable. It CANNOT be changed in ANY cases.
986 // So we have to inflate the stack lock into an ObjectMonitor
987 // even if the current thread owns the lock. The BasicLock on
988 // a thread's stack can be asynchronously read by other threads
989 // during an inflate() call so any change to that stack memory
990 // may not propagate to other threads correctly.
991 }
992
993 // Inflate the monitor to set the hash.
994 monitor = inflate(self, obj, inflate_cause_hash_code);
995 // Load ObjectMonitor's header/dmw field and see if it has a hash.
996 mark = monitor->header();
997 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
998 hash = mark.hash();
999 if (hash == 0) { // if it does not have a hash
1000 hash = get_next_hash(self, obj); // get a new hash
1001 temp = mark.copy_set_hash(hash); // merge the hash into header
1002 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1003 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1004 test = markWord(v);
1005 if (test != mark) {
1006 // The attempt to update the ObjectMonitor's header/dmw field
1007 // did not work. This can happen if another thread managed to
1008 // merge in the hash just before our cmpxchg().
1009 // If we add any new usages of the header/dmw field, this code
1010 // will need to be updated.
1011 hash = test.hash();
1012 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1013 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1014 }
1015 }
1016 // We finally get the hash.
1017 return hash;
1018 }
1019
1020 // Deprecated -- use FastHashCode() instead.
1021
1022 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
1023 return FastHashCode(Thread::current(), obj());
1024 }
1025
1026
1027 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
1028 Handle h_obj) {
1029 if (UseBiasedLocking) {
1030 BiasedLocking::revoke(h_obj, thread);
1031 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1032 }
1033
1034 assert(thread == JavaThread::current(), "Can only be called on current thread");
1035 oop obj = h_obj();
1036
1037 markWord mark = read_stable_mark(obj);
1038
1039 // Uncontended case, header points to stack
1040 if (mark.has_locker()) {
1041 return thread->is_lock_owned((address)mark.locker());
1042 }
1043 // Contended case, header points to ObjectMonitor (tagged pointer)
1044 if (mark.has_monitor()) {
1045 ObjectMonitor* monitor = mark.monitor();
1046 return monitor->is_entered(thread) != 0;
1047 }
1048 // Unlocked case, header in place
1049 assert(mark.is_neutral(), "sanity check");
1050 return false;
1051 }
1052
1053 // Be aware of this method could revoke bias of the lock object.
1054 // This method queries the ownership of the lock handle specified by 'h_obj'.
1055 // If the current thread owns the lock, it returns owner_self. If no
1056 // thread owns the lock, it returns owner_none. Otherwise, it will return
1057 // owner_other.
1058 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
1059 (JavaThread *self, Handle h_obj) {
1060 // The caller must beware this method can revoke bias, and
1061 // revocation can result in a safepoint.
1062 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
1063 assert(self->thread_state() != _thread_blocked, "invariant");
1064
1065 // Possible mark states: neutral, biased, stack-locked, inflated
1066
1067 if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) {
1068 // CASE: biased
1069 BiasedLocking::revoke(h_obj, self);
1070 assert(!h_obj->mark().has_bias_pattern(),
1071 "biases should be revoked by now");
1072 }
1073
1074 assert(self == JavaThread::current(), "Can only be called on current thread");
1075 oop obj = h_obj();
1076 markWord mark = read_stable_mark(obj);
1077
1078 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
1079 if (mark.has_locker()) {
1080 return self->is_lock_owned((address)mark.locker()) ?
1081 owner_self : owner_other;
1082 }
1083
1084 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
1085 // The Object:ObjectMonitor relationship is stable as long as we're
1086 // not at a safepoint.
1087 if (mark.has_monitor()) {
1088 void* owner = mark.monitor()->_owner;
1089 if (owner == NULL) return owner_none;
1090 return (owner == self ||
1091 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
1092 }
1093
1094 // CASE: neutral
1095 assert(mark.is_neutral(), "sanity check");
1096 return owner_none; // it's unlocked
1097 }
1098
1099 // FIXME: jvmti should call this
1100 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1101 if (UseBiasedLocking) {
1102 if (SafepointSynchronize::is_at_safepoint()) {
1103 BiasedLocking::revoke_at_safepoint(h_obj);
1104 } else {
1105 BiasedLocking::revoke(h_obj, JavaThread::current());
1106 }
1107 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1108 }
1109
1110 oop obj = h_obj();
1111 address owner = NULL;
1112
1113 markWord mark = read_stable_mark(obj);
1114
1115 // Uncontended case, header points to stack
1116 if (mark.has_locker()) {
1117 owner = (address) mark.locker();
1118 }
1119
1120 // Contended case, header points to ObjectMonitor (tagged pointer)
1121 else if (mark.has_monitor()) {
1122 ObjectMonitor* monitor = mark.monitor();
1123 assert(monitor != NULL, "monitor should be non-null");
1124 owner = (address) monitor->owner();
1125 }
1126
1127 if (owner != NULL) {
1128 // owning_thread_from_monitor_owner() may also return NULL here
1129 return Threads::owning_thread_from_monitor_owner(t_list, owner);
1130 }
1131
1132 // Unlocked case, header in place
1133 // Cannot have assertion since this object may have been
1134 // locked by another thread when reaching here.
1135 // assert(mark.is_neutral(), "sanity check");
1136
1137 return NULL;
1138 }
1139
1140 // Visitors ...
1141
1142 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
1143 PaddedObjectMonitor* block = Atomic::load(&g_block_list);
1144 while (block != NULL) {
1145 assert(block->object() == CHAINMARKER, "must be a block header");
1146 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
1147 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
1148 oop object = (oop)mid->object();
1149 if (object != NULL) {
1150 // Only process with closure if the object is set.
1151 closure->do_monitor(mid);
1152 }
1153 }
1154 // unmarked_next() is not needed with g_block_list (no locking
1155 // used with block linkage _next_om fields).
1156 block = (PaddedObjectMonitor*)block->next_om();
1157 }
1158 }
1159
1160 static bool monitors_used_above_threshold() {
1161 int population = Atomic::load(&om_list_globals._population);
1162 if (population == 0) {
1163 return false;
1164 }
1165 if (MonitorUsedDeflationThreshold > 0) {
1166 int monitors_used = population - Atomic::load(&om_list_globals._free_count);
1167 int monitor_usage = (monitors_used * 100LL) / population;
1168 return monitor_usage > MonitorUsedDeflationThreshold;
1169 }
1170 return false;
1171 }
1172
1173 // Returns true if MonitorBound is set (> 0) and if the specified
1174 // cnt is > MonitorBound. Otherwise returns false.
1175 static bool is_MonitorBound_exceeded(const int cnt) {
1176 const int mx = MonitorBound;
1177 return mx > 0 && cnt > mx;
1178 }
1179
1180 bool ObjectSynchronizer::is_cleanup_needed() {
1181 if (monitors_used_above_threshold()) {
1182 // Too many monitors in use.
1183 return true;
1184 }
1185 return needs_monitor_scavenge();
1186 }
1187
1188 bool ObjectSynchronizer::needs_monitor_scavenge() {
1189 if (Atomic::load(&_forceMonitorScavenge) == 1) {
1190 log_info(monitorinflation)("Monitor scavenge needed, triggering safepoint cleanup.");
1191 return true;
1192 }
1193 return false;
1194 }
1195
1196 void ObjectSynchronizer::oops_do(OopClosure* f) {
1197 // We only scan the global used list here (for moribund threads), and
1198 // the thread-local monitors in Thread::oops_do().
1199 global_used_oops_do(f);
1200 }
1201
1202 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
1203 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1204 list_oops_do(Atomic::load(&om_list_globals._in_use_list), f);
1205 }
1206
1207 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
1208 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1209 list_oops_do(thread->om_in_use_list, f);
1210 }
1211
1212 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
1213 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1214 // The oops_do() phase does not overlap with monitor deflation
1215 // so no need to lock ObjectMonitors for the list traversal.
1216 for (ObjectMonitor* mid = list; mid != NULL; mid = unmarked_next(mid)) {
1217 if (mid->object() != NULL) {
1218 f->do_oop((oop*)mid->object_addr());
1219 }
1220 }
1221 }
1222
1223
1224 // -----------------------------------------------------------------------------
1225 // ObjectMonitor Lifecycle
1226 // -----------------------
1227 // Inflation unlinks monitors from om_list_globals._free_list or a per-thread
1228 // free list and associates them with objects. Deflation -- which occurs at
1229 // STW-time -- disassociates idle monitors from objects.
1230 // Such scavenged monitors are returned to the om_list_globals._free_list.
1231 //
1232 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1233 //
1234 // Lifecycle:
1235 // -- unassigned and on the om_list_globals._free_list
1236 // -- unassigned and on a per-thread free list
1237 // -- assigned to an object. The object is inflated and the mark refers
1238 // to the ObjectMonitor.
1239
1240
1241 // Constraining monitor pool growth via MonitorBound ...
1242 //
1243 // If MonitorBound is not set (<= 0), MonitorBound checks are disabled.
1244 //
1245 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the
1246 // the rate of scavenging is driven primarily by GC. As such, we can find
1247 // an inordinate number of monitors in circulation.
1248 // To avoid that scenario we can artificially induce a STW safepoint
1249 // if the pool appears to be growing past some reasonable bound.
1250 // Generally we favor time in space-time tradeoffs, but as there's no
1251 // natural back-pressure on the # of extant monitors we need to impose some
1252 // type of limit. Beware that if MonitorBound is set to too low a value
1253 // we could just loop. In addition, if MonitorBound is set to a low value
1254 // we'll incur more safepoints, which are harmful to performance.
1255 // See also: GuaranteedSafepointInterval
1256 //
1257 // If MonitorBound is set, the boundry applies to
1258 // (om_list_globals._population - om_list_globals._free_count)
1259 // i.e., if there are not enough ObjectMonitors on the global free list,
1260 // then a safepoint deflation is induced. Picking a good MonitorBound value
1261 // is non-trivial.
1262
1263 static void InduceScavenge(Thread* self, const char * Whence) {
1264 // Induce STW safepoint to trim monitors
1265 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1266 // More precisely, trigger a cleanup safepoint as the number
1267 // of active monitors passes the specified threshold.
1268 // TODO: assert thread state is reasonable
1269
1270 if (Atomic::xchg(&_forceMonitorScavenge, 1) == 0) {
1271 VMThread::check_for_forced_cleanup();
1272 }
1273 }
1274
1275 ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self) {
1276 // A large MAXPRIVATE value reduces both list lock contention
1277 // and list coherency traffic, but also tends to increase the
1278 // number of ObjectMonitors in circulation as well as the STW
1279 // scavenge costs. As usual, we lean toward time in space-time
1280 // tradeoffs.
1281 const int MAXPRIVATE = 1024;
1282 NoSafepointVerifier nsv;
1283
1284 stringStream ss;
1285 for (;;) {
1286 ObjectMonitor* m;
1287
1288 // 1: try to allocate from the thread's local om_free_list.
1289 // Threads will attempt to allocate first from their local list, then
1290 // from the global list, and only after those attempts fail will the
1291 // thread attempt to instantiate new monitors. Thread-local free lists
1292 // improve allocation latency, as well as reducing coherency traffic
1293 // on the shared global list.
1294 m = take_from_start_of_om_free_list(self);
1295 if (m != NULL) {
1296 guarantee(m->object() == NULL, "invariant");
1297 prepend_to_om_in_use_list(self, m);
1298 return m;
1299 }
1300
1301 // 2: try to allocate from the global om_list_globals._free_list
1302 // If we're using thread-local free lists then try
1303 // to reprovision the caller's free list.
1304 if (Atomic::load(&om_list_globals._free_list) != NULL) {
1305 // Reprovision the thread's om_free_list.
1306 // Use bulk transfers to reduce the allocation rate and heat
1307 // on various locks.
1308 for (int i = self->om_free_provision; --i >= 0;) {
1309 ObjectMonitor* take = take_from_start_of_global_free_list();
1310 if (take == NULL) {
1311 break; // No more are available.
1312 }
1313 guarantee(take->object() == NULL, "invariant");
1314 take->Recycle();
1315 om_release(self, take, false);
1316 }
1317 self->om_free_provision += 1 + (self->om_free_provision / 2);
1318 if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE;
1319
1320 if (is_MonitorBound_exceeded(Atomic::load(&om_list_globals._population) -
1321 Atomic::load(&om_list_globals._free_count))) {
1322 // Not enough ObjectMonitors on the global free list.
1323 // We can't safely induce a STW safepoint from om_alloc() as our thread
1324 // state may not be appropriate for such activities and callers may hold
1325 // naked oops, so instead we defer the action.
1326 InduceScavenge(self, "om_alloc");
1327 }
1328 continue;
1329 }
1330
1331 // 3: allocate a block of new ObjectMonitors
1332 // Both the local and global free lists are empty -- resort to malloc().
1333 // In the current implementation ObjectMonitors are TSM - immortal.
1334 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1335 // each ObjectMonitor to start at the beginning of a cache line,
1336 // so we use align_up().
1337 // A better solution would be to use C++ placement-new.
1338 // BEWARE: As it stands currently, we don't run the ctors!
1339 assert(_BLOCKSIZE > 1, "invariant");
1340 size_t neededsize = sizeof(PaddedObjectMonitor) * _BLOCKSIZE;
1341 PaddedObjectMonitor* temp;
1342 size_t aligned_size = neededsize + (OM_CACHE_LINE_SIZE - 1);
1343 void* real_malloc_addr = NEW_C_HEAP_ARRAY(char, aligned_size, mtInternal);
1344 temp = (PaddedObjectMonitor*)align_up(real_malloc_addr, OM_CACHE_LINE_SIZE);
1345 (void)memset((void *) temp, 0, neededsize);
1346
1347 // Format the block.
1348 // initialize the linked list, each monitor points to its next
1349 // forming the single linked free list, the very first monitor
1350 // will points to next block, which forms the block list.
1351 // The trick of using the 1st element in the block as g_block_list
1352 // linkage should be reconsidered. A better implementation would
1353 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1354
1355 for (int i = 1; i < _BLOCKSIZE; i++) {
1356 temp[i].set_next_om((ObjectMonitor*)&temp[i + 1]);
1357 }
1358
1359 // terminate the last monitor as the end of list
1360 temp[_BLOCKSIZE - 1].set_next_om((ObjectMonitor*)NULL);
1361
1362 // Element [0] is reserved for global list linkage
1363 temp[0].set_object(CHAINMARKER);
1364
1365 // Consider carving out this thread's current request from the
1366 // block in hand. This avoids some lock traffic and redundant
1367 // list activity.
1368
1369 prepend_block_to_lists(temp);
1370 }
1371 }
1372
1373 // Place "m" on the caller's private per-thread om_free_list.
1374 // In practice there's no need to clamp or limit the number of
1375 // monitors on a thread's om_free_list as the only non-allocation time
1376 // we'll call om_release() is to return a monitor to the free list after
1377 // a CAS attempt failed. This doesn't allow unbounded #s of monitors to
1378 // accumulate on a thread's free list.
1379 //
1380 // Key constraint: all ObjectMonitors on a thread's free list and the global
1381 // free list must have their object field set to null. This prevents the
1382 // scavenger -- deflate_monitor_list() -- from reclaiming them while we
1383 // are trying to release them.
1384
1385 void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m,
1386 bool from_per_thread_alloc) {
1387 guarantee(m->header().value() == 0, "invariant");
1388 guarantee(m->object() == NULL, "invariant");
1389 NoSafepointVerifier nsv;
1390
1391 stringStream ss;
1392 guarantee((m->is_busy() | m->_recursions) == 0, "freeing in-use monitor: "
1393 "%s, recursions=" INTX_FORMAT, m->is_busy_to_string(&ss),
1394 m->_recursions);
1395 // _next_om is used for both per-thread in-use and free lists so
1396 // we have to remove 'm' from the in-use list first (as needed).
1397 if (from_per_thread_alloc) {
1398 // Need to remove 'm' from om_in_use_list.
1399 ObjectMonitor* mid = NULL;
1400 ObjectMonitor* next = NULL;
1401
1402 // This list walk can only race with another list walker since
1403 // deflation can only happen at a safepoint so we don't have to
1404 // worry about an ObjectMonitor being removed from this list
1405 // while we are walking it.
1406
1407 // Lock the list head to avoid racing with another list walker.
1408 if ((mid = get_list_head_locked(&self->om_in_use_list)) == NULL) {
1409 fatal("thread=" INTPTR_FORMAT " in-use list must not be empty.", p2i(self));
1410 }
1411 next = unmarked_next(mid);
1412 if (m == mid) {
1413 // First special case:
1414 // 'm' matches mid, is the list head and is locked. Switch the list
1415 // head to next which unlocks the list head, but leaves the extracted
1416 // mid locked:
1417 Atomic::store(&self->om_in_use_list, next);
1418 } else if (m == next) {
1419 // Second special case:
1420 // 'm' matches next after the list head and we already have the list
1421 // head locked so set mid to what we are extracting:
1422 mid = next;
1423 // Lock mid to prevent races with a list walker:
1424 om_lock(mid);
1425 // Update next to what follows mid (if anything):
1426 next = unmarked_next(mid);
1427 // Switch next after the list head to new next which unlocks the
1428 // list head, but leaves the extracted mid locked:
1429 self->om_in_use_list->set_next_om(next);
1430 } else {
1431 // We have to search the list to find 'm'.
1432 om_unlock(mid); // unlock the list head
1433 guarantee(next != NULL, "thread=" INTPTR_FORMAT ": om_in_use_list=" INTPTR_FORMAT
1434 " is too short.", p2i(self), p2i(self->om_in_use_list));
1435 // Our starting anchor is next after the list head which is the
1436 // last ObjectMonitor we checked:
1437 ObjectMonitor* anchor = next;
1438 while ((mid = unmarked_next(anchor)) != NULL) {
1439 if (m == mid) {
1440 // We found 'm' on the per-thread in-use list so extract it.
1441 om_lock(anchor); // Lock the anchor so we can safely modify it.
1442 // Update next to what follows mid (if anything):
1443 next = unmarked_next(mid);
1444 // Switch next after the anchor to new next which unlocks the
1445 // anchor, but leaves the extracted mid locked:
1446 anchor->set_next_om(next);
1447 break;
1448 } else {
1449 anchor = mid;
1450 }
1451 }
1452 }
1453
1454 if (mid == NULL) {
1455 // Reached end of the list and didn't find 'm' so:
1456 fatal("thread=" INTPTR_FORMAT " must find m=" INTPTR_FORMAT "on om_in_use_list="
1457 INTPTR_FORMAT, p2i(self), p2i(m), p2i(self->om_in_use_list));
1458 }
1459
1460 // At this point mid is disconnected from the in-use list so
1461 // its lock no longer has any effects on the in-use list.
1462 Atomic::dec(&self->om_in_use_count);
1463 // Unlock mid, but leave the next value for any lagging list
1464 // walkers. It will get cleaned up when mid is prepended to
1465 // the thread's free list:
1466 om_unlock(mid);
1467 }
1468
1469 prepend_to_om_free_list(self, m);
1470 }
1471
1472 // Return ObjectMonitors on a moribund thread's free and in-use
1473 // lists to the appropriate global lists. The ObjectMonitors on the
1474 // per-thread in-use list may still be in use by other threads.
1475 //
1476 // We currently call om_flush() from Threads::remove() before the
1477 // thread has been excised from the thread list and is no longer a
1478 // mutator. This means that om_flush() cannot run concurrently with
1479 // a safepoint and interleave with deflate_idle_monitors(). In
1480 // particular, this ensures that the thread's in-use monitors are
1481 // scanned by a GC safepoint, either via Thread::oops_do() (before
1482 // om_flush() is called) or via ObjectSynchronizer::oops_do() (after
1483 // om_flush() is called).
1484
1485 void ObjectSynchronizer::om_flush(Thread* self) {
1486 // Process the per-thread in-use list first to be consistent.
1487 int in_use_count = 0;
1488 ObjectMonitor* in_use_list = NULL;
1489 ObjectMonitor* in_use_tail = NULL;
1490 NoSafepointVerifier nsv;
1491
1492 // This function can race with a list walker thread so we lock the
1493 // list head to prevent confusion.
1494 if ((in_use_list = get_list_head_locked(&self->om_in_use_list)) != NULL) {
1495 // At this point, we have locked the in-use list head so a racing
1496 // thread cannot come in after us. However, a racing thread could
1497 // be ahead of us; we'll detect that and delay to let it finish.
1498 //
1499 // The thread is going away, however the ObjectMonitors on the
1500 // om_in_use_list may still be in-use by other threads. Link
1501 // them to in_use_tail, which will be linked into the global
1502 // in-use list (om_list_globals._in_use_list) below.
1503 //
1504 // Account for the in-use list head before the loop since it is
1505 // already locked (by this thread):
1506 in_use_tail = in_use_list;
1507 in_use_count++;
1508 for (ObjectMonitor* cur_om = unmarked_next(in_use_list); cur_om != NULL; cur_om = unmarked_next(cur_om)) {
1509 if (is_locked(cur_om)) {
1510 // cur_om is locked so there must be a racing walker thread ahead
1511 // of us so we'll give it a chance to finish.
1512 while (is_locked(cur_om)) {
1513 os::naked_short_sleep(1);
1514 }
1515 }
1516 in_use_tail = cur_om;
1517 in_use_count++;
1518 }
1519 guarantee(in_use_tail != NULL, "invariant");
1520 int l_om_in_use_count = Atomic::load(&self->om_in_use_count);
1521 assert(l_om_in_use_count == in_use_count, "in-use counts don't match: "
1522 "l_om_in_use_count=%d, in_use_count=%d", l_om_in_use_count, in_use_count);
1523 Atomic::store(&self->om_in_use_count, 0);
1524 // Clear the in-use list head (which also unlocks it):
1525 Atomic::store(&self->om_in_use_list, (ObjectMonitor*)NULL);
1526 om_unlock(in_use_list);
1527 }
1528
1529 int free_count = 0;
1530 ObjectMonitor* free_list = NULL;
1531 ObjectMonitor* free_tail = NULL;
1532 // This function can race with a list walker thread so we lock the
1533 // list head to prevent confusion.
1534 if ((free_list = get_list_head_locked(&self->om_free_list)) != NULL) {
1535 // At this point, we have locked the free list head so a racing
1536 // thread cannot come in after us. However, a racing thread could
1537 // be ahead of us; we'll detect that and delay to let it finish.
1538 //
1539 // The thread is going away. Set 'free_tail' to the last per-thread free
1540 // monitor which will be linked to om_list_globals._free_list below.
1541 //
1542 // Account for the free list head before the loop since it is
1543 // already locked (by this thread):
1544 free_tail = free_list;
1545 free_count++;
1546 for (ObjectMonitor* s = unmarked_next(free_list); s != NULL; s = unmarked_next(s)) {
1547 if (is_locked(s)) {
1548 // s is locked so there must be a racing walker thread ahead
1549 // of us so we'll give it a chance to finish.
1550 while (is_locked(s)) {
1551 os::naked_short_sleep(1);
1552 }
1553 }
1554 free_tail = s;
1555 free_count++;
1556 guarantee(s->object() == NULL, "invariant");
1557 stringStream ss;
1558 guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss));
1559 }
1560 guarantee(free_tail != NULL, "invariant");
1561 int l_om_free_count = Atomic::load(&self->om_free_count);
1562 assert(l_om_free_count == free_count, "free counts don't match: "
1563 "l_om_free_count=%d, free_count=%d", l_om_free_count, free_count);
1564 Atomic::store(&self->om_free_count, 0);
1565 Atomic::store(&self->om_free_list, (ObjectMonitor*)NULL);
1566 om_unlock(free_list);
1567 }
1568
1569 if (free_tail != NULL) {
1570 prepend_list_to_global_free_list(free_list, free_tail, free_count);
1571 }
1572
1573 if (in_use_tail != NULL) {
1574 prepend_list_to_global_in_use_list(in_use_list, in_use_tail, in_use_count);
1575 }
1576
1577 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1578 LogStreamHandle(Info, monitorinflation) lsh_info;
1579 LogStream* ls = NULL;
1580 if (log_is_enabled(Debug, monitorinflation)) {
1581 ls = &lsh_debug;
1582 } else if ((free_count != 0 || in_use_count != 0) &&
1583 log_is_enabled(Info, monitorinflation)) {
1584 ls = &lsh_info;
1585 }
1586 if (ls != NULL) {
1587 ls->print_cr("om_flush: jt=" INTPTR_FORMAT ", free_count=%d"
1588 ", in_use_count=%d" ", om_free_provision=%d",
1589 p2i(self), free_count, in_use_count, self->om_free_provision);
1590 }
1591 }
1592
1593 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1594 const oop obj,
1595 ObjectSynchronizer::InflateCause cause) {
1596 assert(event != NULL, "invariant");
1597 assert(event->should_commit(), "invariant");
1598 event->set_monitorClass(obj->klass());
1599 event->set_address((uintptr_t)(void*)obj);
1600 event->set_cause((u1)cause);
1601 event->commit();
1602 }
1603
1604 // Fast path code shared by multiple functions
1605 void ObjectSynchronizer::inflate_helper(oop obj) {
1606 markWord mark = obj->mark();
1607 if (mark.has_monitor()) {
1608 assert(ObjectSynchronizer::verify_objmon_isinpool(mark.monitor()), "monitor is invalid");
1609 assert(mark.monitor()->header().is_neutral(), "monitor must record a good object header");
1610 return;
1611 }
1612 inflate(Thread::current(), obj, inflate_cause_vm_internal);
1613 }
1614
1615 ObjectMonitor* ObjectSynchronizer::inflate(Thread* self,
1616 oop object, const InflateCause cause) {
1617 // Inflate mutates the heap ...
1618 // Relaxing assertion for bug 6320749.
1619 assert(Universe::verify_in_progress() ||
1620 !SafepointSynchronize::is_at_safepoint(), "invariant");
1621
1622 EventJavaMonitorInflate event;
1623
1624 for (;;) {
1625 const markWord mark = object->mark();
1626 assert(!mark.has_bias_pattern(), "invariant");
1627
1628 // The mark can be in one of the following states:
1629 // * Inflated - just return
1630 // * Stack-locked - coerce it to inflated
1631 // * INFLATING - busy wait for conversion to complete
1632 // * Neutral - aggressively inflate the object.
1633 // * BIASED - Illegal. We should never see this
1634
1635 // CASE: inflated
1636 if (mark.has_monitor()) {
1637 ObjectMonitor* inf = mark.monitor();
1638 markWord dmw = inf->header();
1639 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1640 assert(inf->object() == object, "invariant");
1641 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1642 return inf;
1643 }
1644
1645 // CASE: inflation in progress - inflating over a stack-lock.
1646 // Some other thread is converting from stack-locked to inflated.
1647 // Only that thread can complete inflation -- other threads must wait.
1648 // The INFLATING value is transient.
1649 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1650 // We could always eliminate polling by parking the thread on some auxiliary list.
1651 if (mark == markWord::INFLATING()) {
1652 read_stable_mark(object);
1653 continue;
1654 }
1655
1656 // CASE: stack-locked
1657 // Could be stack-locked either by this thread or by some other thread.
1658 //
1659 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1660 // to install INFLATING into the mark word. We originally installed INFLATING,
1661 // allocated the objectmonitor, and then finally STed the address of the
1662 // objectmonitor into the mark. This was correct, but artificially lengthened
1663 // the interval in which INFLATED appeared in the mark, thus increasing
1664 // the odds of inflation contention.
1665 //
1666 // We now use per-thread private objectmonitor free lists.
1667 // These list are reprovisioned from the global free list outside the
1668 // critical INFLATING...ST interval. A thread can transfer
1669 // multiple objectmonitors en-mass from the global free list to its local free list.
1670 // This reduces coherency traffic and lock contention on the global free list.
1671 // Using such local free lists, it doesn't matter if the om_alloc() call appears
1672 // before or after the CAS(INFLATING) operation.
1673 // See the comments in om_alloc().
1674
1675 LogStreamHandle(Trace, monitorinflation) lsh;
1676
1677 if (mark.has_locker()) {
1678 ObjectMonitor* m = om_alloc(self);
1679 // Optimistically prepare the objectmonitor - anticipate successful CAS
1680 // We do this before the CAS in order to minimize the length of time
1681 // in which INFLATING appears in the mark.
1682 m->Recycle();
1683 m->_Responsible = NULL;
1684 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1685
1686 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1687 if (cmp != mark) {
1688 om_release(self, m, true);
1689 continue; // Interference -- just retry
1690 }
1691
1692 // We've successfully installed INFLATING (0) into the mark-word.
1693 // This is the only case where 0 will appear in a mark-word.
1694 // Only the singular thread that successfully swings the mark-word
1695 // to 0 can perform (or more precisely, complete) inflation.
1696 //
1697 // Why do we CAS a 0 into the mark-word instead of just CASing the
1698 // mark-word from the stack-locked value directly to the new inflated state?
1699 // Consider what happens when a thread unlocks a stack-locked object.
1700 // It attempts to use CAS to swing the displaced header value from the
1701 // on-stack BasicLock back into the object header. Recall also that the
1702 // header value (hash code, etc) can reside in (a) the object header, or
1703 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1704 // header in an ObjectMonitor. The inflate() routine must copy the header
1705 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1706 // the while preserving the hashCode stability invariants. If the owner
1707 // decides to release the lock while the value is 0, the unlock will fail
1708 // and control will eventually pass from slow_exit() to inflate. The owner
1709 // will then spin, waiting for the 0 value to disappear. Put another way,
1710 // the 0 causes the owner to stall if the owner happens to try to
1711 // drop the lock (restoring the header from the BasicLock to the object)
1712 // while inflation is in-progress. This protocol avoids races that might
1713 // would otherwise permit hashCode values to change or "flicker" for an object.
1714 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1715 // 0 serves as a "BUSY" inflate-in-progress indicator.
1716
1717
1718 // fetch the displaced mark from the owner's stack.
1719 // The owner can't die or unwind past the lock while our INFLATING
1720 // object is in the mark. Furthermore the owner can't complete
1721 // an unlock on the object, either.
1722 markWord dmw = mark.displaced_mark_helper();
1723 // Catch if the object's header is not neutral (not locked and
1724 // not marked is what we care about here).
1725 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1726
1727 // Setup monitor fields to proper values -- prepare the monitor
1728 m->set_header(dmw);
1729
1730 // Optimization: if the mark.locker stack address is associated
1731 // with this thread we could simply set m->_owner = self.
1732 // Note that a thread can inflate an object
1733 // that it has stack-locked -- as might happen in wait() -- directly
1734 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1735 m->set_owner_from(NULL, mark.locker());
1736 m->set_object(object);
1737 // TODO-FIXME: assert BasicLock->dhw != 0.
1738
1739 // Must preserve store ordering. The monitor state must
1740 // be stable at the time of publishing the monitor address.
1741 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1742 object->release_set_mark(markWord::encode(m));
1743
1744 // Hopefully the performance counters are allocated on distinct cache lines
1745 // to avoid false sharing on MP systems ...
1746 OM_PERFDATA_OP(Inflations, inc());
1747 if (log_is_enabled(Trace, monitorinflation)) {
1748 ResourceMark rm(self);
1749 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1750 INTPTR_FORMAT ", type='%s'", p2i(object),
1751 object->mark().value(), object->klass()->external_name());
1752 }
1753 if (event.should_commit()) {
1754 post_monitor_inflate_event(&event, object, cause);
1755 }
1756 return m;
1757 }
1758
1759 // CASE: neutral
1760 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1761 // If we know we're inflating for entry it's better to inflate by swinging a
1762 // pre-locked ObjectMonitor pointer into the object header. A successful
1763 // CAS inflates the object *and* confers ownership to the inflating thread.
1764 // In the current implementation we use a 2-step mechanism where we CAS()
1765 // to inflate and then CAS() again to try to swing _owner from NULL to self.
1766 // An inflateTry() method that we could call from enter() would be useful.
1767
1768 // Catch if the object's header is not neutral (not locked and
1769 // not marked is what we care about here).
1770 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1771 ObjectMonitor* m = om_alloc(self);
1772 // prepare m for installation - set monitor to initial state
1773 m->Recycle();
1774 m->set_header(mark);
1775 m->set_object(object);
1776 m->_Responsible = NULL;
1777 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1778
1779 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1780 m->set_header(markWord::zero());
1781 m->set_object(NULL);
1782 m->Recycle();
1783 om_release(self, m, true);
1784 m = NULL;
1785 continue;
1786 // interference - the markword changed - just retry.
1787 // The state-transitions are one-way, so there's no chance of
1788 // live-lock -- "Inflated" is an absorbing state.
1789 }
1790
1791 // Hopefully the performance counters are allocated on distinct
1792 // cache lines to avoid false sharing on MP systems ...
1793 OM_PERFDATA_OP(Inflations, inc());
1794 if (log_is_enabled(Trace, monitorinflation)) {
1795 ResourceMark rm(self);
1796 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1797 INTPTR_FORMAT ", type='%s'", p2i(object),
1798 object->mark().value(), object->klass()->external_name());
1799 }
1800 if (event.should_commit()) {
1801 post_monitor_inflate_event(&event, object, cause);
1802 }
1803 return m;
1804 }
1805 }
1806
1807
1808 // We maintain a list of in-use monitors for each thread.
1809 //
1810 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1811 // deflate_idle_monitors() scans only a global list of in-use monitors which
1812 // is populated only as a thread dies (see om_flush()).
1813 //
1814 // These operations are called at all safepoints, immediately after mutators
1815 // are stopped, but before any objects have moved. Collectively they traverse
1816 // the population of in-use monitors, deflating where possible. The scavenged
1817 // monitors are returned to the global monitor free list.
1818 //
1819 // Beware that we scavenge at *every* stop-the-world point. Having a large
1820 // number of monitors in-use could negatively impact performance. We also want
1821 // to minimize the total # of monitors in circulation, as they incur a small
1822 // footprint penalty.
1823 //
1824 // Perversely, the heap size -- and thus the STW safepoint rate --
1825 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1826 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1827 // This is an unfortunate aspect of this design.
1828
1829 // Deflate a single monitor if not in-use
1830 // Return true if deflated, false if in-use
1831 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1832 ObjectMonitor** free_head_p,
1833 ObjectMonitor** free_tail_p) {
1834 bool deflated;
1835 // Normal case ... The monitor is associated with obj.
1836 const markWord mark = obj->mark();
1837 guarantee(mark == markWord::encode(mid), "should match: mark="
1838 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(),
1839 markWord::encode(mid).value());
1840 // Make sure that mark.monitor() and markWord::encode() agree:
1841 guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
1842 ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid));
1843 const markWord dmw = mid->header();
1844 guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1845
1846 if (mid->is_busy()) {
1847 // Easy checks are first - the ObjectMonitor is busy so no deflation.
1848 deflated = false;
1849 } else {
1850 // Deflate the monitor if it is no longer being used
1851 // It's idle - scavenge and return to the global free list
1852 // plain old deflation ...
1853 if (log_is_enabled(Trace, monitorinflation)) {
1854 ResourceMark rm;
1855 log_trace(monitorinflation)("deflate_monitor: "
1856 "object=" INTPTR_FORMAT ", mark="
1857 INTPTR_FORMAT ", type='%s'", p2i(obj),
1858 mark.value(), obj->klass()->external_name());
1859 }
1860
1861 // Restore the header back to obj
1862 obj->release_set_mark(dmw);
1863 mid->clear();
1864
1865 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
1866 p2i(mid->object()));
1867
1868 // Move the deflated ObjectMonitor to the working free list
1869 // defined by free_head_p and free_tail_p.
1870 if (*free_head_p == NULL) *free_head_p = mid;
1871 if (*free_tail_p != NULL) {
1872 // We append to the list so the caller can use mid->_next_om
1873 // to fix the linkages in its context.
1874 ObjectMonitor* prevtail = *free_tail_p;
1875 // Should have been cleaned up by the caller:
1876 // Note: Should not have to lock prevtail here since we're at a
1877 // safepoint and ObjectMonitors on the local free list should
1878 // not be accessed in parallel.
1879 #ifdef ASSERT
1880 ObjectMonitor* l_next_om = prevtail->next_om();
1881 #endif
1882 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
1883 prevtail->set_next_om(mid);
1884 }
1885 *free_tail_p = mid;
1886 // At this point, mid->_next_om still refers to its current
1887 // value and another ObjectMonitor's _next_om field still
1888 // refers to this ObjectMonitor. Those linkages have to be
1889 // cleaned up by the caller who has the complete context.
1890 deflated = true;
1891 }
1892 return deflated;
1893 }
1894
1895 // Walk a given monitor list, and deflate idle monitors.
1896 // The given list could be a per-thread list or a global list.
1897 //
1898 // In the case of parallel processing of thread local monitor lists,
1899 // work is done by Threads::parallel_threads_do() which ensures that
1900 // each Java thread is processed by exactly one worker thread, and
1901 // thus avoid conflicts that would arise when worker threads would
1902 // process the same monitor lists concurrently.
1903 //
1904 // See also ParallelSPCleanupTask and
1905 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1906 // Threads::parallel_java_threads_do() in thread.cpp.
1907 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** list_p,
1908 int* count_p,
1909 ObjectMonitor** free_head_p,
1910 ObjectMonitor** free_tail_p) {
1911 ObjectMonitor* cur_mid_in_use = NULL;
1912 ObjectMonitor* mid = NULL;
1913 ObjectMonitor* next = NULL;
1914 int deflated_count = 0;
1915
1916 // This list walk executes at a safepoint and does not race with any
1917 // other list walkers.
1918
1919 for (mid = Atomic::load(list_p); mid != NULL; mid = next) {
1920 next = unmarked_next(mid);
1921 oop obj = (oop) mid->object();
1922 if (obj != NULL && deflate_monitor(mid, obj, free_head_p, free_tail_p)) {
1923 // Deflation succeeded and already updated free_head_p and
1924 // free_tail_p as needed. Finish the move to the local free list
1925 // by unlinking mid from the global or per-thread in-use list.
1926 if (cur_mid_in_use == NULL) {
1927 // mid is the list head so switch the list head to next:
1928 Atomic::store(list_p, next);
1929 } else {
1930 // Switch cur_mid_in_use's next field to next:
1931 cur_mid_in_use->set_next_om(next);
1932 }
1933 // At this point mid is disconnected from the in-use list.
1934 deflated_count++;
1935 Atomic::dec(count_p);
1936 // mid is current tail in the free_head_p list so NULL terminate it:
1937 mid->set_next_om(NULL);
1938 } else {
1939 cur_mid_in_use = mid;
1940 }
1941 }
1942 return deflated_count;
1943 }
1944
1945 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1946 counters->n_in_use = 0; // currently associated with objects
1947 counters->n_in_circulation = 0; // extant
1948 counters->n_scavenged = 0; // reclaimed (global and per-thread)
1949 counters->per_thread_scavenged = 0; // per-thread scavenge total
1950 counters->per_thread_times = 0.0; // per-thread scavenge times
1951 }
1952
1953 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
1954 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1955 bool deflated = false;
1956
1957 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
1958 ObjectMonitor* free_tail_p = NULL;
1959 elapsedTimer timer;
1960
1961 if (log_is_enabled(Info, monitorinflation)) {
1962 timer.start();
1963 }
1964
1965 // Note: the thread-local monitors lists get deflated in
1966 // a separate pass. See deflate_thread_local_monitors().
1967
1968 // For moribund threads, scan om_list_globals._in_use_list
1969 int deflated_count = 0;
1970 if (Atomic::load(&om_list_globals._in_use_list) != NULL) {
1971 // Update n_in_circulation before om_list_globals._in_use_count is
1972 // updated by deflation.
1973 Atomic::add(&counters->n_in_circulation,
1974 Atomic::load(&om_list_globals._in_use_count));
1975
1976 deflated_count = deflate_monitor_list(&om_list_globals._in_use_list,
1977 &om_list_globals._in_use_count,
1978 &free_head_p, &free_tail_p);
1979 Atomic::add(&counters->n_in_use, Atomic::load(&om_list_globals._in_use_count));
1980 }
1981
1982 if (free_head_p != NULL) {
1983 // Move the deflated ObjectMonitors back to the global free list.
1984 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
1985 #ifdef ASSERT
1986 ObjectMonitor* l_next_om = free_tail_p->next_om();
1987 #endif
1988 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
1989 prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count);
1990 Atomic::add(&counters->n_scavenged, deflated_count);
1991 }
1992 timer.stop();
1993
1994 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1995 LogStreamHandle(Info, monitorinflation) lsh_info;
1996 LogStream* ls = NULL;
1997 if (log_is_enabled(Debug, monitorinflation)) {
1998 ls = &lsh_debug;
1999 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2000 ls = &lsh_info;
2001 }
2002 if (ls != NULL) {
2003 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2004 }
2005 }
2006
2007 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2008 // Report the cumulative time for deflating each thread's idle
2009 // monitors. Note: if the work is split among more than one
2010 // worker thread, then the reported time will likely be more
2011 // than a beginning to end measurement of the phase.
2012 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged);
2013
2014 if (log_is_enabled(Debug, monitorinflation)) {
2015 // exit_globals()'s call to audit_and_print_stats() is done
2016 // at the Info level and not at a safepoint.
2017 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2018 } else if (log_is_enabled(Info, monitorinflation)) {
2019 log_info(monitorinflation)("global_population=%d, global_in_use_count=%d, "
2020 "global_free_count=%d",
2021 Atomic::load(&om_list_globals._population),
2022 Atomic::load(&om_list_globals._in_use_count),
2023 Atomic::load(&om_list_globals._free_count));
2024 }
2025
2026 Atomic::store(&_forceMonitorScavenge, 0); // Reset
2027
2028 OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged));
2029 OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation));
2030
2031 GVars.stw_random = os::random();
2032 GVars.stw_cycle++;
2033 }
2034
2035 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
2036 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2037
2038 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
2039 ObjectMonitor* free_tail_p = NULL;
2040 elapsedTimer timer;
2041
2042 if (log_is_enabled(Info, safepoint, cleanup) ||
2043 log_is_enabled(Info, monitorinflation)) {
2044 timer.start();
2045 }
2046
2047 // Update n_in_circulation before om_in_use_count is updated by deflation.
2048 Atomic::add(&counters->n_in_circulation, Atomic::load(&thread->om_in_use_count));
2049
2050 int deflated_count = deflate_monitor_list(&thread->om_in_use_list, &thread->om_in_use_count, &free_head_p, &free_tail_p);
2051 Atomic::add(&counters->n_in_use, Atomic::load(&thread->om_in_use_count));
2052
2053 if (free_head_p != NULL) {
2054 // Move the deflated ObjectMonitors back to the global free list.
2055 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
2056 #ifdef ASSERT
2057 ObjectMonitor* l_next_om = free_tail_p->next_om();
2058 #endif
2059 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2060 prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count);
2061 Atomic::add(&counters->n_scavenged, deflated_count);
2062 Atomic::add(&counters->per_thread_scavenged, deflated_count);
2063 }
2064
2065 timer.stop();
2066 counters->per_thread_times += timer.seconds();
2067
2068 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2069 LogStreamHandle(Info, monitorinflation) lsh_info;
2070 LogStream* ls = NULL;
2071 if (log_is_enabled(Debug, monitorinflation)) {
2072 ls = &lsh_debug;
2073 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2074 ls = &lsh_info;
2075 }
2076 if (ls != NULL) {
2077 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
2078 }
2079 }
2080
2081 // Monitor cleanup on JavaThread::exit
2082
2083 // Iterate through monitor cache and attempt to release thread's monitors
2084 // Gives up on a particular monitor if an exception occurs, but continues
2085 // the overall iteration, swallowing the exception.
2086 class ReleaseJavaMonitorsClosure: public MonitorClosure {
2087 private:
2088 TRAPS;
2089
2090 public:
2091 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
2092 void do_monitor(ObjectMonitor* mid) {
2093 if (mid->owner() == THREAD) {
2094 (void)mid->complete_exit(CHECK);
2095 }
2096 }
2097 };
2098
2099 // Release all inflated monitors owned by THREAD. Lightweight monitors are
2100 // ignored. This is meant to be called during JNI thread detach which assumes
2101 // all remaining monitors are heavyweight. All exceptions are swallowed.
2102 // Scanning the extant monitor list can be time consuming.
2103 // A simple optimization is to add a per-thread flag that indicates a thread
2104 // called jni_monitorenter() during its lifetime.
2105 //
2106 // Instead of No_Savepoint_Verifier it might be cheaper to
2107 // use an idiom of the form:
2108 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
2109 // <code that must not run at safepoint>
2110 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
2111 // Since the tests are extremely cheap we could leave them enabled
2112 // for normal product builds.
2113
2114 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
2115 assert(THREAD == JavaThread::current(), "must be current Java thread");
2116 NoSafepointVerifier nsv;
2117 ReleaseJavaMonitorsClosure rjmc(THREAD);
2118 ObjectSynchronizer::monitors_iterate(&rjmc);
2119 THREAD->clear_pending_exception();
2120 }
2121
2122 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
2123 switch (cause) {
2124 case inflate_cause_vm_internal: return "VM Internal";
2125 case inflate_cause_monitor_enter: return "Monitor Enter";
2126 case inflate_cause_wait: return "Monitor Wait";
2127 case inflate_cause_notify: return "Monitor Notify";
2128 case inflate_cause_hash_code: return "Monitor Hash Code";
2129 case inflate_cause_jni_enter: return "JNI Monitor Enter";
2130 case inflate_cause_jni_exit: return "JNI Monitor Exit";
2131 default:
2132 ShouldNotReachHere();
2133 }
2134 return "Unknown";
2135 }
2136
2137 //------------------------------------------------------------------------------
2138 // Debugging code
2139
2140 u_char* ObjectSynchronizer::get_gvars_addr() {
2141 return (u_char*)&GVars;
2142 }
2143
2144 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
2145 return (u_char*)&GVars.hc_sequence;
2146 }
2147
2148 size_t ObjectSynchronizer::get_gvars_size() {
2149 return sizeof(SharedGlobals);
2150 }
2151
2152 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
2153 return (u_char*)&GVars.stw_random;
2154 }
2155
2156 // This function can be called at a safepoint or it can be called when
2157 // we are trying to exit the VM. When we are trying to exit the VM, the
2158 // list walker functions can run in parallel with the other list
2159 // operations so spin-locking is used for safety.
2160 //
2161 // Calls to this function can be added in various places as a debugging
2162 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
2163 // details logged at the Info level and 'false' for the 'on_exit'
2164 // parameter to have in-use monitor details logged at the Trace level.
2165 //
2166 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
2167 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
2168
2169 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2170 LogStreamHandle(Info, monitorinflation) lsh_info;
2171 LogStreamHandle(Trace, monitorinflation) lsh_trace;
2172 LogStream* ls = NULL;
2173 if (log_is_enabled(Trace, monitorinflation)) {
2174 ls = &lsh_trace;
2175 } else if (log_is_enabled(Debug, monitorinflation)) {
2176 ls = &lsh_debug;
2177 } else if (log_is_enabled(Info, monitorinflation)) {
2178 ls = &lsh_info;
2179 }
2180 assert(ls != NULL, "sanity check");
2181
2182 // Log counts for the global and per-thread monitor lists:
2183 int chk_om_population = log_monitor_list_counts(ls);
2184 int error_cnt = 0;
2185
2186 ls->print_cr("Checking global lists:");
2187
2188 // Check om_list_globals._population:
2189 if (Atomic::load(&om_list_globals._population) == chk_om_population) {
2190 ls->print_cr("global_population=%d equals chk_om_population=%d",
2191 Atomic::load(&om_list_globals._population), chk_om_population);
2192 } else {
2193 // With fine grained locks on the monitor lists, it is possible for
2194 // log_monitor_list_counts() to return a value that doesn't match
2195 // om_list_globals._population. So far a higher value has been
2196 // seen in testing so something is being double counted by
2197 // log_monitor_list_counts().
2198 ls->print_cr("WARNING: global_population=%d is not equal to "
2199 "chk_om_population=%d",
2200 Atomic::load(&om_list_globals._population), chk_om_population);
2201 }
2202
2203 // Check om_list_globals._in_use_list and om_list_globals._in_use_count:
2204 chk_global_in_use_list_and_count(ls, &error_cnt);
2205
2206 // Check om_list_globals._free_list and om_list_globals._free_count:
2207 chk_global_free_list_and_count(ls, &error_cnt);
2208
2209 ls->print_cr("Checking per-thread lists:");
2210
2211 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2212 // Check om_in_use_list and om_in_use_count:
2213 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
2214
2215 // Check om_free_list and om_free_count:
2216 chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
2217 }
2218
2219 if (error_cnt == 0) {
2220 ls->print_cr("No errors found in monitor list checks.");
2221 } else {
2222 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
2223 }
2224
2225 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
2226 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
2227 // When exiting this log output is at the Info level. When called
2228 // at a safepoint, this log output is at the Trace level since
2229 // there can be a lot of it.
2230 log_in_use_monitor_details(ls);
2231 }
2232
2233 ls->flush();
2234
2235 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2236 }
2237
2238 // Check a free monitor entry; log any errors.
2239 void ObjectSynchronizer::chk_free_entry(JavaThread* jt, ObjectMonitor* n,
2240 outputStream * out, int *error_cnt_p) {
2241 stringStream ss;
2242 if (n->is_busy()) {
2243 if (jt != NULL) {
2244 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2245 ": free per-thread monitor must not be busy: %s", p2i(jt),
2246 p2i(n), n->is_busy_to_string(&ss));
2247 } else {
2248 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2249 "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
2250 }
2251 *error_cnt_p = *error_cnt_p + 1;
2252 }
2253 if (n->header().value() != 0) {
2254 if (jt != NULL) {
2255 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2256 ": free per-thread monitor must have NULL _header "
2257 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
2258 n->header().value());
2259 } else {
2260 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2261 "must have NULL _header field: _header=" INTPTR_FORMAT,
2262 p2i(n), n->header().value());
2263 }
2264 *error_cnt_p = *error_cnt_p + 1;
2265 }
2266 if (n->object() != NULL) {
2267 if (jt != NULL) {
2268 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2269 ": free per-thread monitor must have NULL _object "
2270 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
2271 p2i(n->object()));
2272 } else {
2273 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2274 "must have NULL _object field: _object=" INTPTR_FORMAT,
2275 p2i(n), p2i(n->object()));
2276 }
2277 *error_cnt_p = *error_cnt_p + 1;
2278 }
2279 }
2280
2281 // Lock the next ObjectMonitor for traversal and unlock the current
2282 // ObjectMonitor. Returns the next ObjectMonitor if there is one.
2283 // Otherwise returns NULL (after unlocking the current ObjectMonitor).
2284 // This function is used by the various list walker functions to
2285 // safely walk a list without allowing an ObjectMonitor to be moved
2286 // to another list in the middle of a walk.
2287 static ObjectMonitor* lock_next_for_traversal(ObjectMonitor* cur) {
2288 assert(is_locked(cur), "cur=" INTPTR_FORMAT " must be locked", p2i(cur));
2289 ObjectMonitor* next = unmarked_next(cur);
2290 if (next == NULL) { // Reached the end of the list.
2291 om_unlock(cur);
2292 return NULL;
2293 }
2294 om_lock(next); // Lock next before unlocking current to keep
2295 om_unlock(cur); // from being by-passed by another thread.
2296 return next;
2297 }
2298
2299 // Check the global free list and count; log the results of the checks.
2300 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
2301 int *error_cnt_p) {
2302 int chk_om_free_count = 0;
2303 ObjectMonitor* cur = NULL;
2304 if ((cur = get_list_head_locked(&om_list_globals._free_list)) != NULL) {
2305 // Marked the global free list head so process the list.
2306 while (true) {
2307 chk_free_entry(NULL /* jt */, cur, out, error_cnt_p);
2308 chk_om_free_count++;
2309
2310 cur = lock_next_for_traversal(cur);
2311 if (cur == NULL) {
2312 break;
2313 }
2314 }
2315 }
2316 int l_free_count = Atomic::load(&om_list_globals._free_count);
2317 if (l_free_count == chk_om_free_count) {
2318 out->print_cr("global_free_count=%d equals chk_om_free_count=%d",
2319 l_free_count, chk_om_free_count);
2320 } else {
2321 // With fine grained locks on om_list_globals._free_list, it
2322 // is possible for an ObjectMonitor to be prepended to
2323 // om_list_globals._free_list after we started calculating
2324 // chk_om_free_count so om_list_globals._free_count may not
2325 // match anymore.
2326 out->print_cr("WARNING: global_free_count=%d is not equal to "
2327 "chk_om_free_count=%d", l_free_count, chk_om_free_count);
2328 }
2329 }
2330
2331 // Check the global in-use list and count; log the results of the checks.
2332 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
2333 int *error_cnt_p) {
2334 int chk_om_in_use_count = 0;
2335 ObjectMonitor* cur = NULL;
2336 if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) {
2337 // Marked the global in-use list head so process the list.
2338 while (true) {
2339 chk_in_use_entry(NULL /* jt */, cur, out, error_cnt_p);
2340 chk_om_in_use_count++;
2341
2342 cur = lock_next_for_traversal(cur);
2343 if (cur == NULL) {
2344 break;
2345 }
2346 }
2347 }
2348 int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
2349 if (l_in_use_count == chk_om_in_use_count) {
2350 out->print_cr("global_in_use_count=%d equals chk_om_in_use_count=%d",
2351 l_in_use_count, chk_om_in_use_count);
2352 } else {
2353 // With fine grained locks on the monitor lists, it is possible for
2354 // an exiting JavaThread to put its in-use ObjectMonitors on the
2355 // global in-use list after chk_om_in_use_count is calculated above.
2356 out->print_cr("WARNING: global_in_use_count=%d is not equal to chk_om_in_use_count=%d",
2357 l_in_use_count, chk_om_in_use_count);
2358 }
2359 }
2360
2361 // Check an in-use monitor entry; log any errors.
2362 void ObjectSynchronizer::chk_in_use_entry(JavaThread* jt, ObjectMonitor* n,
2363 outputStream * out, int *error_cnt_p) {
2364 if (n->header().value() == 0) {
2365 if (jt != NULL) {
2366 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2367 ": in-use per-thread monitor must have non-NULL _header "
2368 "field.", p2i(jt), p2i(n));
2369 } else {
2370 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2371 "must have non-NULL _header field.", p2i(n));
2372 }
2373 *error_cnt_p = *error_cnt_p + 1;
2374 }
2375 if (n->object() == NULL) {
2376 if (jt != NULL) {
2377 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2378 ": in-use per-thread monitor must have non-NULL _object "
2379 "field.", p2i(jt), p2i(n));
2380 } else {
2381 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2382 "must have non-NULL _object field.", p2i(n));
2383 }
2384 *error_cnt_p = *error_cnt_p + 1;
2385 }
2386 const oop obj = (oop)n->object();
2387 const markWord mark = obj->mark();
2388 if (!mark.has_monitor()) {
2389 if (jt != NULL) {
2390 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2391 ": in-use per-thread monitor's object does not think "
2392 "it has a monitor: obj=" INTPTR_FORMAT ", mark="
2393 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), mark.value());
2394 } else {
2395 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2396 "monitor's object does not think it has a monitor: obj="
2397 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2398 p2i(obj), mark.value());
2399 }
2400 *error_cnt_p = *error_cnt_p + 1;
2401 }
2402 ObjectMonitor* const obj_mon = mark.monitor();
2403 if (n != obj_mon) {
2404 if (jt != NULL) {
2405 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2406 ": in-use per-thread monitor's object does not refer "
2407 "to the same monitor: obj=" INTPTR_FORMAT ", mark="
2408 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
2409 p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2410 } else {
2411 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2412 "monitor's object does not refer to the same monitor: obj="
2413 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2414 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2415 }
2416 *error_cnt_p = *error_cnt_p + 1;
2417 }
2418 }
2419
2420 // Check the thread's free list and count; log the results of the checks.
2421 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
2422 outputStream * out,
2423 int *error_cnt_p) {
2424 int chk_om_free_count = 0;
2425 ObjectMonitor* cur = NULL;
2426 if ((cur = get_list_head_locked(&jt->om_free_list)) != NULL) {
2427 // Marked the per-thread free list head so process the list.
2428 while (true) {
2429 chk_free_entry(jt, cur, out, error_cnt_p);
2430 chk_om_free_count++;
2431
2432 cur = lock_next_for_traversal(cur);
2433 if (cur == NULL) {
2434 break;
2435 }
2436 }
2437 }
2438 int l_om_free_count = Atomic::load(&jt->om_free_count);
2439 if (l_om_free_count == chk_om_free_count) {
2440 out->print_cr("jt=" INTPTR_FORMAT ": om_free_count=%d equals "
2441 "chk_om_free_count=%d", p2i(jt), l_om_free_count, chk_om_free_count);
2442 } else {
2443 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_free_count=%d is not "
2444 "equal to chk_om_free_count=%d", p2i(jt), l_om_free_count,
2445 chk_om_free_count);
2446 *error_cnt_p = *error_cnt_p + 1;
2447 }
2448 }
2449
2450 // Check the thread's in-use list and count; log the results of the checks.
2451 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
2452 outputStream * out,
2453 int *error_cnt_p) {
2454 int chk_om_in_use_count = 0;
2455 ObjectMonitor* cur = NULL;
2456 if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
2457 // Marked the per-thread in-use list head so process the list.
2458 while (true) {
2459 chk_in_use_entry(jt, cur, out, error_cnt_p);
2460 chk_om_in_use_count++;
2461
2462 cur = lock_next_for_traversal(cur);
2463 if (cur == NULL) {
2464 break;
2465 }
2466 }
2467 }
2468 int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
2469 if (l_om_in_use_count == chk_om_in_use_count) {
2470 out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals "
2471 "chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
2472 chk_om_in_use_count);
2473 } else {
2474 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not "
2475 "equal to chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
2476 chk_om_in_use_count);
2477 *error_cnt_p = *error_cnt_p + 1;
2478 }
2479 }
2480
2481 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2482 // flags indicate why the entry is in-use, 'object' and 'object type'
2483 // indicate the associated object and its type.
2484 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out) {
2485 stringStream ss;
2486 if (Atomic::load(&om_list_globals._in_use_count) > 0) {
2487 out->print_cr("In-use global monitor info:");
2488 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2489 out->print_cr("%18s %s %18s %18s",
2490 "monitor", "BHL", "object", "object type");
2491 out->print_cr("================== === ================== ==================");
2492 ObjectMonitor* cur = NULL;
2493 if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) {
2494 // Marked the global in-use list head so process the list.
2495 while (true) {
2496 const oop obj = (oop) cur->object();
2497 const markWord mark = cur->header();
2498 ResourceMark rm;
2499 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(cur),
2500 cur->is_busy() != 0, mark.hash() != 0, cur->owner() != NULL,
2501 p2i(obj), obj->klass()->external_name());
2502 if (cur->is_busy() != 0) {
2503 out->print(" (%s)", cur->is_busy_to_string(&ss));
2504 ss.reset();
2505 }
2506 out->cr();
2507
2508 cur = lock_next_for_traversal(cur);
2509 if (cur == NULL) {
2510 break;
2511 }
2512 }
2513 }
2514 }
2515
2516 out->print_cr("In-use per-thread monitor info:");
2517 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2518 out->print_cr("%18s %18s %s %18s %18s",
2519 "jt", "monitor", "BHL", "object", "object type");
2520 out->print_cr("================== ================== === ================== ==================");
2521 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2522 ObjectMonitor* cur = NULL;
2523 if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
2524 // Marked the global in-use list head so process the list.
2525 while (true) {
2526 const oop obj = (oop) cur->object();
2527 const markWord mark = cur->header();
2528 ResourceMark rm;
2529 out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT
2530 " %s", p2i(jt), p2i(cur), cur->is_busy() != 0,
2531 mark.hash() != 0, cur->owner() != NULL, p2i(obj),
2532 obj->klass()->external_name());
2533 if (cur->is_busy() != 0) {
2534 out->print(" (%s)", cur->is_busy_to_string(&ss));
2535 ss.reset();
2536 }
2537 out->cr();
2538
2539 cur = lock_next_for_traversal(cur);
2540 if (cur == NULL) {
2541 break;
2542 }
2543 }
2544 }
2545 }
2546
2547 out->flush();
2548 }
2549
2550 // Log counts for the global and per-thread monitor lists and return
2551 // the population count.
2552 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2553 int pop_count = 0;
2554 out->print_cr("%18s %10s %10s %10s",
2555 "Global Lists:", "InUse", "Free", "Total");
2556 out->print_cr("================== ========== ========== ==========");
2557 int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
2558 int l_free_count = Atomic::load(&om_list_globals._free_count);
2559 out->print_cr("%18s %10d %10d %10d", "", l_in_use_count,
2560 l_free_count, Atomic::load(&om_list_globals._population));
2561 pop_count += l_in_use_count + l_free_count;
2562
2563 out->print_cr("%18s %10s %10s %10s",
2564 "Per-Thread Lists:", "InUse", "Free", "Provision");
2565 out->print_cr("================== ========== ========== ==========");
2566
2567 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2568 int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
2569 int l_om_free_count = Atomic::load(&jt->om_free_count);
2570 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
2571 l_om_in_use_count, l_om_free_count, jt->om_free_provision);
2572 pop_count += l_om_in_use_count + l_om_free_count;
2573 }
2574 return pop_count;
2575 }
2576
2577 #ifndef PRODUCT
2578
2579 // Check if monitor belongs to the monitor cache
2580 // The list is grow-only so it's *relatively* safe to traverse
2581 // the list of extant blocks without taking a lock.
2582
2583 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
2584 PaddedObjectMonitor* block = Atomic::load(&g_block_list);
2585 while (block != NULL) {
2586 assert(block->object() == CHAINMARKER, "must be a block header");
2587 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
2588 address mon = (address)monitor;
2589 address blk = (address)block;
2590 size_t diff = mon - blk;
2591 assert((diff % sizeof(PaddedObjectMonitor)) == 0, "must be aligned");
2592 return 1;
2593 }
2594 // unmarked_next() is not needed with g_block_list (no locking
2595 // used with block linkage _next_om fields).
2596 block = (PaddedObjectMonitor*)block->next_om();
2597 }
2598 return 0;
2599 }
2600
2601 #endif