303 // This is a special case where the Java Monitor was inflated
304 // after this thread entered the stack-lock recursively. When a
305 // Java Monitor is inflated, we cannot safely walk the Java
306 // Monitor owner's stack and update the BasicLocks because a
307 // Java Monitor can be asynchronously inflated by a thread that
308 // does not own the Java Monitor.
309 ObjectMonitor * m = mark->monitor();
310 assert(((oop)(m->object()))->mark() == mark, "invariant");
311 assert(m->is_entered(THREAD), "invariant");
312 }
313 }
314 #endif
315 return;
316 }
317
318 if (mark == (markOop) lock) {
319 // If the object is stack-locked by the current thread, try to
320 // swing the displaced header from the BasicLock back to the mark.
321 assert(dhw->is_neutral(), "invariant");
322 if (object->cas_set_mark(dhw, mark) == mark) {
323 TEVENT(fast_exit: release stack-lock);
324 return;
325 }
326 }
327
328 // We have to take the slow-path of possible inflation and then exit.
329 ObjectSynchronizer::inflate(THREAD,
330 object,
331 inflate_cause_vm_internal)->exit(true, THREAD);
332 }
333
334 // -----------------------------------------------------------------------------
335 // Interpreter/Compiler Slow Case
336 // This routine is used to handle interpreter/compiler slow case
337 // We don't need to use fast path here, because it must have been
338 // failed in the interpreter/compiler code.
339 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
340 markOop mark = obj->mark();
341 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
342
343 if (mark->is_neutral()) {
344 // Anticipate successful CAS -- the ST of the displaced mark must
345 // be visible <= the ST performed by the CAS.
346 lock->set_displaced_header(mark);
347 if (mark == obj()->cas_set_mark((markOop) lock, mark)) {
348 TEVENT(slow_enter: release stacklock);
349 return;
350 }
351 // Fall through to inflate() ...
352 } else if (mark->has_locker() &&
353 THREAD->is_lock_owned((address)mark->locker())) {
354 assert(lock != mark->locker(), "must not re-lock the same lock");
355 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
356 lock->set_displaced_header(NULL);
357 return;
358 }
359
360 // The object header will never be displaced to this lock,
361 // so it does not matter what the value is, except that it
362 // must be non-zero to avoid looking like a re-entrant lock,
363 // and must not look locked either.
364 lock->set_displaced_header(markOopDesc::unused_mark());
365 ObjectSynchronizer::inflate(THREAD,
366 obj(),
367 inflate_cause_monitor_enter)->enter(THREAD);
368 }
371 // We don't need to use fast path here, because it must have
372 // failed in the interpreter/compiler code. Simply use the heavy
373 // weight monitor should be ok, unless someone find otherwise.
374 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
375 fast_exit(object, lock, THREAD);
376 }
377
378 // -----------------------------------------------------------------------------
379 // Class Loader support to workaround deadlocks on the class loader lock objects
380 // Also used by GC
381 // complete_exit()/reenter() are used to wait on a nested lock
382 // i.e. to give up an outer lock completely and then re-enter
383 // Used when holding nested locks - lock acquisition order: lock1 then lock2
384 // 1) complete_exit lock1 - saving recursion count
385 // 2) wait on lock2
386 // 3) when notified on lock2, unlock lock2
387 // 4) reenter lock1 with original recursion count
388 // 5) lock lock2
389 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
390 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
391 TEVENT(complete_exit);
392 if (UseBiasedLocking) {
393 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
394 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
395 }
396
397 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
398 obj(),
399 inflate_cause_vm_internal);
400
401 return monitor->complete_exit(THREAD);
402 }
403
404 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
405 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
406 TEVENT(reenter);
407 if (UseBiasedLocking) {
408 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
409 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
410 }
411
412 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
413 obj(),
414 inflate_cause_vm_internal);
415
416 monitor->reenter(recursion, THREAD);
417 }
418 // -----------------------------------------------------------------------------
419 // JNI locks on java objects
420 // NOTE: must use heavy weight monitor to handle jni monitor enter
421 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
422 // the current locking is from JNI instead of Java code
423 TEVENT(jni_enter);
424 if (UseBiasedLocking) {
425 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
426 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
427 }
428 THREAD->set_current_pending_monitor_is_from_java(false);
429 ObjectSynchronizer::inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);
430 THREAD->set_current_pending_monitor_is_from_java(true);
431 }
432
433 // NOTE: must use heavy weight monitor to handle jni monitor exit
434 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
435 TEVENT(jni_exit);
436 if (UseBiasedLocking) {
437 Handle h_obj(THREAD, obj);
438 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
439 obj = h_obj();
440 }
441 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
442
443 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
444 obj,
445 inflate_cause_jni_exit);
446 // If this thread has locked the object, exit the monitor. Note: can't use
447 // monitor->check(CHECK); must exit even if an exception is pending.
448 if (monitor->check(THREAD)) {
449 monitor->exit(true, THREAD);
450 }
451 }
452
453 // -----------------------------------------------------------------------------
454 // Internal VM locks on java objects
455 // standard constructor, allows locking failures
456 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
457 _dolock = doLock;
458 _thread = thread;
459 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
460 _obj = obj;
461
462 if (_dolock) {
463 TEVENT(ObjectLocker);
464
465 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
466 }
467 }
468
469 ObjectLocker::~ObjectLocker() {
470 if (_dolock) {
471 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
472 }
473 }
474
475
476 // -----------------------------------------------------------------------------
477 // Wait/Notify/NotifyAll
478 // NOTE: must use heavy weight monitor to handle wait()
479 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
480 if (UseBiasedLocking) {
481 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
482 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
483 }
484 if (millis < 0) {
485 TEVENT(wait - throw IAX);
486 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
487 }
488 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
489 obj(),
490 inflate_cause_wait);
491
492 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
493 monitor->wait(millis, true, THREAD);
494
495 // This dummy call is in place to get around dtrace bug 6254741. Once
496 // that's fixed we can uncomment the following line, remove the call
497 // and change this function back into a "void" func.
498 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
499 return dtrace_waited_probe(monitor, obj, THREAD);
500 }
501
502 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
503 if (UseBiasedLocking) {
504 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
505 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
506 }
507 if (millis < 0) {
508 TEVENT(wait - throw IAX);
509 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
510 }
511 ObjectSynchronizer::inflate(THREAD,
512 obj(),
513 inflate_cause_wait)->wait(millis, false, THREAD);
514 }
515
516 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
517 if (UseBiasedLocking) {
518 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
519 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
520 }
521
522 markOop mark = obj->mark();
523 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
524 return;
525 }
526 ObjectSynchronizer::inflate(THREAD,
527 obj(),
528 inflate_cause_notify)->notify(THREAD);
591 for (;;) {
592 markOop mark = obj->mark();
593 if (!mark->is_being_inflated()) {
594 return mark; // normal fast-path return
595 }
596
597 // The object is being inflated by some other thread.
598 // The caller of ReadStableMark() must wait for inflation to complete.
599 // Avoid live-lock
600 // TODO: consider calling SafepointSynchronize::do_call_back() while
601 // spinning to see if there's a safepoint pending. If so, immediately
602 // yielding or blocking would be appropriate. Avoid spinning while
603 // there is a safepoint pending.
604 // TODO: add inflation contention performance counters.
605 // TODO: restrict the aggregate number of spinners.
606
607 ++its;
608 if (its > 10000 || !os::is_MP()) {
609 if (its & 1) {
610 os::naked_yield();
611 TEVENT(Inflate: INFLATING - yield);
612 } else {
613 // Note that the following code attenuates the livelock problem but is not
614 // a complete remedy. A more complete solution would require that the inflating
615 // thread hold the associated inflation lock. The following code simply restricts
616 // the number of spinners to at most one. We'll have N-2 threads blocked
617 // on the inflationlock, 1 thread holding the inflation lock and using
618 // a yield/park strategy, and 1 thread in the midst of inflation.
619 // A more refined approach would be to change the encoding of INFLATING
620 // to allow encapsulation of a native thread pointer. Threads waiting for
621 // inflation to complete would use CAS to push themselves onto a singly linked
622 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
623 // and calling park(). When inflation was complete the thread that accomplished inflation
624 // would detach the list and set the markword to inflated with a single CAS and
625 // then for each thread on the list, set the flag and unpark() the thread.
626 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
627 // wakes at most one thread whereas we need to wake the entire list.
628 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
629 int YieldThenBlock = 0;
630 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
631 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
632 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
633 while (obj->mark() == markOopDesc::INFLATING()) {
634 // Beware: NakedYield() is advisory and has almost no effect on some platforms
635 // so we periodically call Self->_ParkEvent->park(1).
636 // We use a mixed spin/yield/block mechanism.
637 if ((YieldThenBlock++) >= 16) {
638 Thread::current()->_ParkEvent->park(1);
639 } else {
640 os::naked_yield();
641 }
642 }
643 Thread::muxRelease(gInflationLocks + ix);
644 TEVENT(Inflate: INFLATING - yield/park);
645 }
646 } else {
647 SpinPause(); // SMP-polite spinning
648 }
649 }
650 }
651
652 // hashCode() generation :
653 //
654 // Possibilities:
655 // * MD5Digest of {obj,stwRandom}
656 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
657 // * A DES- or AES-style SBox[] mechanism
658 // * One of the Phi-based schemes, such as:
659 // 2654435761 = 2^32 * Phi (golden ratio)
660 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
661 // * A variation of Marsaglia's shift-xor RNG scheme.
662 // * (obj ^ stwRandom) is appealing, but can result
663 // in undesirable regularity in the hashCode values of adjacent objects
664 // (objects allocated back-to-back, in particular). This could potentially
686 } else if (hashCode == 4) {
687 value = cast_from_oop<intptr_t>(obj);
688 } else {
689 // Marsaglia's xor-shift scheme with thread-specific state
690 // This is probably the best overall implementation -- we'll
691 // likely make this the default in future releases.
692 unsigned t = Self->_hashStateX;
693 t ^= (t << 11);
694 Self->_hashStateX = Self->_hashStateY;
695 Self->_hashStateY = Self->_hashStateZ;
696 Self->_hashStateZ = Self->_hashStateW;
697 unsigned v = Self->_hashStateW;
698 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
699 Self->_hashStateW = v;
700 value = v;
701 }
702
703 value &= markOopDesc::hash_mask;
704 if (value == 0) value = 0xBAD;
705 assert(value != markOopDesc::no_hash, "invariant");
706 TEVENT(hashCode: GENERATE);
707 return value;
708 }
709
710 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
711 if (UseBiasedLocking) {
712 // NOTE: many places throughout the JVM do not expect a safepoint
713 // to be taken here, in particular most operations on perm gen
714 // objects. However, we only ever bias Java instances and all of
715 // the call sites of identity_hash that might revoke biases have
716 // been checked to make sure they can handle a safepoint. The
717 // added check of the bias pattern is to avoid useless calls to
718 // thread-local storage.
719 if (obj->mark()->has_bias_pattern()) {
720 // Handle for oop obj in case of STW safepoint
721 Handle hobj(Self, obj);
722 // Relaxing assertion for bug 6320749.
723 assert(Universe::verify_in_progress() ||
724 !SafepointSynchronize::is_at_safepoint(),
725 "biases should not be seen by VM thread here");
726 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
1137 // If the muxTry() fails then drop immediately into case 3.
1138 // If we're using thread-local free lists then try
1139 // to reprovision the caller's free list.
1140 if (gFreeList != NULL) {
1141 // Reprovision the thread's omFreeList.
1142 // Use bulk transfers to reduce the allocation rate and heat
1143 // on various locks.
1144 Thread::muxAcquire(&gListLock, "omAlloc");
1145 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1146 gMonitorFreeCount--;
1147 ObjectMonitor * take = gFreeList;
1148 gFreeList = take->FreeNext;
1149 guarantee(take->object() == NULL, "invariant");
1150 guarantee(!take->is_busy(), "invariant");
1151 take->Recycle();
1152 omRelease(Self, take, false);
1153 }
1154 Thread::muxRelease(&gListLock);
1155 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1156 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1157 TEVENT(omFirst - reprovision);
1158
1159 const int mx = MonitorBound;
1160 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1161 // We can't safely induce a STW safepoint from omAlloc() as our thread
1162 // state may not be appropriate for such activities and callers may hold
1163 // naked oops, so instead we defer the action.
1164 InduceScavenge(Self, "omAlloc");
1165 }
1166 continue;
1167 }
1168
1169 // 3: allocate a block of new ObjectMonitors
1170 // Both the local and global free lists are empty -- resort to malloc().
1171 // In the current implementation objectMonitors are TSM - immortal.
1172 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1173 // each ObjectMonitor to start at the beginning of a cache line,
1174 // so we use align_up().
1175 // A better solution would be to use C++ placement-new.
1176 // BEWARE: As it stands currently, we don't run the ctors!
1177 assert(_BLOCKSIZE > 1, "invariant");
1215 // list activity.
1216
1217 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1218 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1219 Thread::muxAcquire(&gListLock, "omAlloc [2]");
1220 gMonitorPopulation += _BLOCKSIZE-1;
1221 gMonitorFreeCount += _BLOCKSIZE-1;
1222
1223 // Add the new block to the list of extant blocks (gBlockList).
1224 // The very first objectMonitor in a block is reserved and dedicated.
1225 // It serves as blocklist "next" linkage.
1226 temp[0].FreeNext = gBlockList;
1227 // There are lock-free uses of gBlockList so make sure that
1228 // the previous stores happen before we update gBlockList.
1229 OrderAccess::release_store(&gBlockList, temp);
1230
1231 // Add the new string of objectMonitors to the global free list
1232 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1233 gFreeList = temp + 1;
1234 Thread::muxRelease(&gListLock);
1235 TEVENT(Allocate block of monitors);
1236 }
1237 }
1238
1239 // Place "m" on the caller's private per-thread omFreeList.
1240 // In practice there's no need to clamp or limit the number of
1241 // monitors on a thread's omFreeList as the only time we'll call
1242 // omRelease is to return a monitor to the free list after a CAS
1243 // attempt failed. This doesn't allow unbounded #s of monitors to
1244 // accumulate on a thread's free list.
1245 //
1246 // Key constraint: all ObjectMonitors on a thread's free list and the global
1247 // free list must have their object field set to null. This prevents the
1248 // scavenger -- deflate_idle_monitors -- from reclaiming them.
1249
1250 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1251 bool fromPerThreadAlloc) {
1252 guarantee(m->object() == NULL, "invariant");
1253 guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor");
1254 // Remove from omInUseList
1255 if (MonitorInUseLists && fromPerThreadAlloc) {
1300 // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's
1301 // monitors have been transferred to the global in-use list).
1302
1303 void ObjectSynchronizer::omFlush(Thread * Self) {
1304 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1305 Self->omFreeList = NULL;
1306 ObjectMonitor * tail = NULL;
1307 int tally = 0;
1308 if (list != NULL) {
1309 ObjectMonitor * s;
1310 // The thread is going away, the per-thread free monitors
1311 // are freed via set_owner(NULL)
1312 // Link them to tail, which will be linked into the global free list
1313 // gFreeList below, under the gListLock
1314 for (s = list; s != NULL; s = s->FreeNext) {
1315 tally++;
1316 tail = s;
1317 guarantee(s->object() == NULL, "invariant");
1318 guarantee(!s->is_busy(), "invariant");
1319 s->set_owner(NULL); // redundant but good hygiene
1320 TEVENT(omFlush - Move one);
1321 }
1322 guarantee(tail != NULL && list != NULL, "invariant");
1323 }
1324
1325 ObjectMonitor * inUseList = Self->omInUseList;
1326 ObjectMonitor * inUseTail = NULL;
1327 int inUseTally = 0;
1328 if (inUseList != NULL) {
1329 Self->omInUseList = NULL;
1330 ObjectMonitor *cur_om;
1331 // The thread is going away, however the omInUseList inflated
1332 // monitors may still be in-use by other threads.
1333 // Link them to inUseTail, which will be linked into the global in-use list
1334 // gOmInUseList below, under the gListLock
1335 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1336 inUseTail = cur_om;
1337 inUseTally++;
1338 }
1339 assert(Self->omInUseCount == inUseTally, "in-use count off");
1340 Self->omInUseCount = 0;
1341 guarantee(inUseTail != NULL && inUseList != NULL, "invariant");
1342 }
1343
1344 Thread::muxAcquire(&gListLock, "omFlush");
1345 if (tail != NULL) {
1346 tail->FreeNext = gFreeList;
1347 gFreeList = list;
1348 gMonitorFreeCount += tally;
1349 assert(Self->omFreeCount == tally, "free-count off");
1350 Self->omFreeCount = 0;
1351 }
1352
1353 if (inUseTail != NULL) {
1354 inUseTail->FreeNext = gOmInUseList;
1355 gOmInUseList = inUseList;
1356 gOmInUseCount += inUseTally;
1357 }
1358
1359 Thread::muxRelease(&gListLock);
1360 TEVENT(omFlush);
1361 }
1362
1363 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1364 const oop obj,
1365 ObjectSynchronizer::InflateCause cause) {
1366 assert(event != NULL, "invariant");
1367 assert(event->should_commit(), "invariant");
1368 event->set_monitorClass(obj->klass());
1369 event->set_address((uintptr_t)(void*)obj);
1370 event->set_cause((u1)cause);
1371 event->commit();
1372 }
1373
1374 // Fast path code shared by multiple functions
1375 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1376 markOop mark = obj->mark();
1377 if (mark->has_monitor()) {
1378 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1379 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1380 return mark->monitor();
1405 // * INFLATING - busy wait for conversion to complete
1406 // * Neutral - aggressively inflate the object.
1407 // * BIASED - Illegal. We should never see this
1408
1409 // CASE: inflated
1410 if (mark->has_monitor()) {
1411 ObjectMonitor * inf = mark->monitor();
1412 assert(inf->header()->is_neutral(), "invariant");
1413 assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1414 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1415 return inf;
1416 }
1417
1418 // CASE: inflation in progress - inflating over a stack-lock.
1419 // Some other thread is converting from stack-locked to inflated.
1420 // Only that thread can complete inflation -- other threads must wait.
1421 // The INFLATING value is transient.
1422 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1423 // We could always eliminate polling by parking the thread on some auxiliary list.
1424 if (mark == markOopDesc::INFLATING()) {
1425 TEVENT(Inflate: spin while INFLATING);
1426 ReadStableMark(object);
1427 continue;
1428 }
1429
1430 // CASE: stack-locked
1431 // Could be stack-locked either by this thread or by some other thread.
1432 //
1433 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1434 // to install INFLATING into the mark word. We originally installed INFLATING,
1435 // allocated the objectmonitor, and then finally STed the address of the
1436 // objectmonitor into the mark. This was correct, but artificially lengthened
1437 // the interval in which INFLATED appeared in the mark, thus increasing
1438 // the odds of inflation contention.
1439 //
1440 // We now use per-thread private objectmonitor free lists.
1441 // These list are reprovisioned from the global free list outside the
1442 // critical INFLATING...ST interval. A thread can transfer
1443 // multiple objectmonitors en-mass from the global free list to its local free list.
1444 // This reduces coherency traffic and lock contention on the global free list.
1445 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1498 // Setup monitor fields to proper values -- prepare the monitor
1499 m->set_header(dmw);
1500
1501 // Optimization: if the mark->locker stack address is associated
1502 // with this thread we could simply set m->_owner = Self.
1503 // Note that a thread can inflate an object
1504 // that it has stack-locked -- as might happen in wait() -- directly
1505 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1506 m->set_owner(mark->locker());
1507 m->set_object(object);
1508 // TODO-FIXME: assert BasicLock->dhw != 0.
1509
1510 // Must preserve store ordering. The monitor state must
1511 // be stable at the time of publishing the monitor address.
1512 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1513 object->release_set_mark(markOopDesc::encode(m));
1514
1515 // Hopefully the performance counters are allocated on distinct cache lines
1516 // to avoid false sharing on MP systems ...
1517 OM_PERFDATA_OP(Inflations, inc());
1518 TEVENT(Inflate: overwrite stacklock);
1519 if (log_is_enabled(Debug, monitorinflation)) {
1520 if (object->is_instance()) {
1521 ResourceMark rm;
1522 log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1523 p2i(object), p2i(object->mark()),
1524 object->klass()->external_name());
1525 }
1526 }
1527 if (event.should_commit()) {
1528 post_monitor_inflate_event(&event, object, cause);
1529 }
1530 return m;
1531 }
1532
1533 // CASE: neutral
1534 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1535 // If we know we're inflating for entry it's better to inflate by swinging a
1536 // pre-locked objectMonitor pointer into the object header. A successful
1537 // CAS inflates the object *and* confers ownership to the inflating thread.
1538 // In the current implementation we use a 2-step mechanism where we CAS()
1549 m->set_object(object);
1550 m->_recursions = 0;
1551 m->_Responsible = NULL;
1552 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1553
1554 if (object->cas_set_mark(markOopDesc::encode(m), mark) != mark) {
1555 m->set_object(NULL);
1556 m->set_owner(NULL);
1557 m->Recycle();
1558 omRelease(Self, m, true);
1559 m = NULL;
1560 continue;
1561 // interference - the markword changed - just retry.
1562 // The state-transitions are one-way, so there's no chance of
1563 // live-lock -- "Inflated" is an absorbing state.
1564 }
1565
1566 // Hopefully the performance counters are allocated on distinct
1567 // cache lines to avoid false sharing on MP systems ...
1568 OM_PERFDATA_OP(Inflations, inc());
1569 TEVENT(Inflate: overwrite neutral);
1570 if (log_is_enabled(Debug, monitorinflation)) {
1571 if (object->is_instance()) {
1572 ResourceMark rm;
1573 log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1574 p2i(object), p2i(object->mark()),
1575 object->klass()->external_name());
1576 }
1577 }
1578 if (event.should_commit()) {
1579 post_monitor_inflate_event(&event, object, cause);
1580 }
1581 return m;
1582 }
1583 }
1584
1585
1586 // Deflate_idle_monitors() is called at all safepoints, immediately
1587 // after all mutators are stopped, but before any objects have moved.
1588 // It traverses the list of known monitors, deflating where possible.
1589 // The scavenged monitor are returned to the monitor free list.
1616 };
1617
1618 // Deflate a single monitor if not in-use
1619 // Return true if deflated, false if in-use
1620 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1621 ObjectMonitor** freeHeadp,
1622 ObjectMonitor** freeTailp) {
1623 bool deflated;
1624 // Normal case ... The monitor is associated with obj.
1625 guarantee(obj->mark() == markOopDesc::encode(mid), "invariant");
1626 guarantee(mid == obj->mark()->monitor(), "invariant");
1627 guarantee(mid->header()->is_neutral(), "invariant");
1628
1629 if (mid->is_busy()) {
1630 if (ClearResponsibleAtSTW) mid->_Responsible = NULL;
1631 deflated = false;
1632 } else {
1633 // Deflate the monitor if it is no longer being used
1634 // It's idle - scavenge and return to the global free list
1635 // plain old deflation ...
1636 TEVENT(deflate_idle_monitors - scavenge1);
1637 if (log_is_enabled(Debug, monitorinflation)) {
1638 if (obj->is_instance()) {
1639 ResourceMark rm;
1640 log_debug(monitorinflation)("Deflating object " INTPTR_FORMAT " , "
1641 "mark " INTPTR_FORMAT " , type %s",
1642 p2i(obj), p2i(obj->mark()),
1643 obj->klass()->external_name());
1644 }
1645 }
1646
1647 // Restore the header back to obj
1648 obj->release_set_mark(mid->header());
1649 mid->clear();
1650
1651 assert(mid->object() == NULL, "invariant");
1652
1653 // Move the object to the working free list defined by freeHeadp, freeTailp
1654 if (*freeHeadp == NULL) *freeHeadp = mid;
1655 if (*freeTailp != NULL) {
1656 ObjectMonitor * prevtail = *freeTailp;
1702 cur_mid_in_use = mid;
1703 mid = mid->FreeNext;
1704 }
1705 }
1706 return deflated_count;
1707 }
1708
1709 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1710 counters->nInuse = 0; // currently associated with objects
1711 counters->nInCirculation = 0; // extant
1712 counters->nScavenged = 0; // reclaimed
1713 }
1714
1715 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
1716 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1717 bool deflated = false;
1718
1719 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1720 ObjectMonitor * freeTailp = NULL;
1721
1722 TEVENT(deflate_idle_monitors);
1723 // Prevent omFlush from changing mids in Thread dtor's during deflation
1724 // And in case the vm thread is acquiring a lock during a safepoint
1725 // See e.g. 6320749
1726 Thread::muxAcquire(&gListLock, "scavenge - return");
1727
1728 if (MonitorInUseLists) {
1729 // Note: the thread-local monitors lists get deflated in
1730 // a separate pass. See deflate_thread_local_monitors().
1731
1732 // For moribund threads, scan gOmInUseList
1733 if (gOmInUseList) {
1734 counters->nInCirculation += gOmInUseCount;
1735 int deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
1736 gOmInUseCount -= deflated_count;
1737 counters->nScavenged += deflated_count;
1738 counters->nInuse += gOmInUseCount;
1739 }
1740
1741 } else {
1742 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
|
303 // This is a special case where the Java Monitor was inflated
304 // after this thread entered the stack-lock recursively. When a
305 // Java Monitor is inflated, we cannot safely walk the Java
306 // Monitor owner's stack and update the BasicLocks because a
307 // Java Monitor can be asynchronously inflated by a thread that
308 // does not own the Java Monitor.
309 ObjectMonitor * m = mark->monitor();
310 assert(((oop)(m->object()))->mark() == mark, "invariant");
311 assert(m->is_entered(THREAD), "invariant");
312 }
313 }
314 #endif
315 return;
316 }
317
318 if (mark == (markOop) lock) {
319 // If the object is stack-locked by the current thread, try to
320 // swing the displaced header from the BasicLock back to the mark.
321 assert(dhw->is_neutral(), "invariant");
322 if (object->cas_set_mark(dhw, mark) == mark) {
323 return;
324 }
325 }
326
327 // We have to take the slow-path of possible inflation and then exit.
328 ObjectSynchronizer::inflate(THREAD,
329 object,
330 inflate_cause_vm_internal)->exit(true, THREAD);
331 }
332
333 // -----------------------------------------------------------------------------
334 // Interpreter/Compiler Slow Case
335 // This routine is used to handle interpreter/compiler slow case
336 // We don't need to use fast path here, because it must have been
337 // failed in the interpreter/compiler code.
338 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
339 markOop mark = obj->mark();
340 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
341
342 if (mark->is_neutral()) {
343 // Anticipate successful CAS -- the ST of the displaced mark must
344 // be visible <= the ST performed by the CAS.
345 lock->set_displaced_header(mark);
346 if (mark == obj()->cas_set_mark((markOop) lock, mark)) {
347 return;
348 }
349 // Fall through to inflate() ...
350 } else if (mark->has_locker() &&
351 THREAD->is_lock_owned((address)mark->locker())) {
352 assert(lock != mark->locker(), "must not re-lock the same lock");
353 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
354 lock->set_displaced_header(NULL);
355 return;
356 }
357
358 // The object header will never be displaced to this lock,
359 // so it does not matter what the value is, except that it
360 // must be non-zero to avoid looking like a re-entrant lock,
361 // and must not look locked either.
362 lock->set_displaced_header(markOopDesc::unused_mark());
363 ObjectSynchronizer::inflate(THREAD,
364 obj(),
365 inflate_cause_monitor_enter)->enter(THREAD);
366 }
369 // We don't need to use fast path here, because it must have
370 // failed in the interpreter/compiler code. Simply use the heavy
371 // weight monitor should be ok, unless someone find otherwise.
372 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
373 fast_exit(object, lock, THREAD);
374 }
375
376 // -----------------------------------------------------------------------------
377 // Class Loader support to workaround deadlocks on the class loader lock objects
378 // Also used by GC
379 // complete_exit()/reenter() are used to wait on a nested lock
380 // i.e. to give up an outer lock completely and then re-enter
381 // Used when holding nested locks - lock acquisition order: lock1 then lock2
382 // 1) complete_exit lock1 - saving recursion count
383 // 2) wait on lock2
384 // 3) when notified on lock2, unlock lock2
385 // 4) reenter lock1 with original recursion count
386 // 5) lock lock2
387 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
388 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
389 if (UseBiasedLocking) {
390 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
391 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
392 }
393
394 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
395 obj(),
396 inflate_cause_vm_internal);
397
398 return monitor->complete_exit(THREAD);
399 }
400
401 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
402 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
403 if (UseBiasedLocking) {
404 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
405 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
406 }
407
408 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
409 obj(),
410 inflate_cause_vm_internal);
411
412 monitor->reenter(recursion, THREAD);
413 }
414 // -----------------------------------------------------------------------------
415 // JNI locks on java objects
416 // NOTE: must use heavy weight monitor to handle jni monitor enter
417 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
418 // the current locking is from JNI instead of Java code
419 if (UseBiasedLocking) {
420 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
421 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
422 }
423 THREAD->set_current_pending_monitor_is_from_java(false);
424 ObjectSynchronizer::inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);
425 THREAD->set_current_pending_monitor_is_from_java(true);
426 }
427
428 // NOTE: must use heavy weight monitor to handle jni monitor exit
429 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
430 if (UseBiasedLocking) {
431 Handle h_obj(THREAD, obj);
432 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
433 obj = h_obj();
434 }
435 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
436
437 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
438 obj,
439 inflate_cause_jni_exit);
440 // If this thread has locked the object, exit the monitor. Note: can't use
441 // monitor->check(CHECK); must exit even if an exception is pending.
442 if (monitor->check(THREAD)) {
443 monitor->exit(true, THREAD);
444 }
445 }
446
447 // -----------------------------------------------------------------------------
448 // Internal VM locks on java objects
449 // standard constructor, allows locking failures
450 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
451 _dolock = doLock;
452 _thread = thread;
453 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
454 _obj = obj;
455
456 if (_dolock) {
457 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
458 }
459 }
460
461 ObjectLocker::~ObjectLocker() {
462 if (_dolock) {
463 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
464 }
465 }
466
467
468 // -----------------------------------------------------------------------------
469 // Wait/Notify/NotifyAll
470 // NOTE: must use heavy weight monitor to handle wait()
471 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
472 if (UseBiasedLocking) {
473 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
474 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
475 }
476 if (millis < 0) {
477 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
478 }
479 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD,
480 obj(),
481 inflate_cause_wait);
482
483 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
484 monitor->wait(millis, true, THREAD);
485
486 // This dummy call is in place to get around dtrace bug 6254741. Once
487 // that's fixed we can uncomment the following line, remove the call
488 // and change this function back into a "void" func.
489 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
490 return dtrace_waited_probe(monitor, obj, THREAD);
491 }
492
493 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
494 if (UseBiasedLocking) {
495 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
496 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
497 }
498 if (millis < 0) {
499 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
500 }
501 ObjectSynchronizer::inflate(THREAD,
502 obj(),
503 inflate_cause_wait)->wait(millis, false, THREAD);
504 }
505
506 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
507 if (UseBiasedLocking) {
508 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
509 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
510 }
511
512 markOop mark = obj->mark();
513 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
514 return;
515 }
516 ObjectSynchronizer::inflate(THREAD,
517 obj(),
518 inflate_cause_notify)->notify(THREAD);
581 for (;;) {
582 markOop mark = obj->mark();
583 if (!mark->is_being_inflated()) {
584 return mark; // normal fast-path return
585 }
586
587 // The object is being inflated by some other thread.
588 // The caller of ReadStableMark() must wait for inflation to complete.
589 // Avoid live-lock
590 // TODO: consider calling SafepointSynchronize::do_call_back() while
591 // spinning to see if there's a safepoint pending. If so, immediately
592 // yielding or blocking would be appropriate. Avoid spinning while
593 // there is a safepoint pending.
594 // TODO: add inflation contention performance counters.
595 // TODO: restrict the aggregate number of spinners.
596
597 ++its;
598 if (its > 10000 || !os::is_MP()) {
599 if (its & 1) {
600 os::naked_yield();
601 } else {
602 // Note that the following code attenuates the livelock problem but is not
603 // a complete remedy. A more complete solution would require that the inflating
604 // thread hold the associated inflation lock. The following code simply restricts
605 // the number of spinners to at most one. We'll have N-2 threads blocked
606 // on the inflationlock, 1 thread holding the inflation lock and using
607 // a yield/park strategy, and 1 thread in the midst of inflation.
608 // A more refined approach would be to change the encoding of INFLATING
609 // to allow encapsulation of a native thread pointer. Threads waiting for
610 // inflation to complete would use CAS to push themselves onto a singly linked
611 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
612 // and calling park(). When inflation was complete the thread that accomplished inflation
613 // would detach the list and set the markword to inflated with a single CAS and
614 // then for each thread on the list, set the flag and unpark() the thread.
615 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
616 // wakes at most one thread whereas we need to wake the entire list.
617 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
618 int YieldThenBlock = 0;
619 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
620 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
621 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
622 while (obj->mark() == markOopDesc::INFLATING()) {
623 // Beware: NakedYield() is advisory and has almost no effect on some platforms
624 // so we periodically call Self->_ParkEvent->park(1).
625 // We use a mixed spin/yield/block mechanism.
626 if ((YieldThenBlock++) >= 16) {
627 Thread::current()->_ParkEvent->park(1);
628 } else {
629 os::naked_yield();
630 }
631 }
632 Thread::muxRelease(gInflationLocks + ix);
633 }
634 } else {
635 SpinPause(); // SMP-polite spinning
636 }
637 }
638 }
639
640 // hashCode() generation :
641 //
642 // Possibilities:
643 // * MD5Digest of {obj,stwRandom}
644 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
645 // * A DES- or AES-style SBox[] mechanism
646 // * One of the Phi-based schemes, such as:
647 // 2654435761 = 2^32 * Phi (golden ratio)
648 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
649 // * A variation of Marsaglia's shift-xor RNG scheme.
650 // * (obj ^ stwRandom) is appealing, but can result
651 // in undesirable regularity in the hashCode values of adjacent objects
652 // (objects allocated back-to-back, in particular). This could potentially
674 } else if (hashCode == 4) {
675 value = cast_from_oop<intptr_t>(obj);
676 } else {
677 // Marsaglia's xor-shift scheme with thread-specific state
678 // This is probably the best overall implementation -- we'll
679 // likely make this the default in future releases.
680 unsigned t = Self->_hashStateX;
681 t ^= (t << 11);
682 Self->_hashStateX = Self->_hashStateY;
683 Self->_hashStateY = Self->_hashStateZ;
684 Self->_hashStateZ = Self->_hashStateW;
685 unsigned v = Self->_hashStateW;
686 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
687 Self->_hashStateW = v;
688 value = v;
689 }
690
691 value &= markOopDesc::hash_mask;
692 if (value == 0) value = 0xBAD;
693 assert(value != markOopDesc::no_hash, "invariant");
694 return value;
695 }
696
697 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
698 if (UseBiasedLocking) {
699 // NOTE: many places throughout the JVM do not expect a safepoint
700 // to be taken here, in particular most operations on perm gen
701 // objects. However, we only ever bias Java instances and all of
702 // the call sites of identity_hash that might revoke biases have
703 // been checked to make sure they can handle a safepoint. The
704 // added check of the bias pattern is to avoid useless calls to
705 // thread-local storage.
706 if (obj->mark()->has_bias_pattern()) {
707 // Handle for oop obj in case of STW safepoint
708 Handle hobj(Self, obj);
709 // Relaxing assertion for bug 6320749.
710 assert(Universe::verify_in_progress() ||
711 !SafepointSynchronize::is_at_safepoint(),
712 "biases should not be seen by VM thread here");
713 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
1124 // If the muxTry() fails then drop immediately into case 3.
1125 // If we're using thread-local free lists then try
1126 // to reprovision the caller's free list.
1127 if (gFreeList != NULL) {
1128 // Reprovision the thread's omFreeList.
1129 // Use bulk transfers to reduce the allocation rate and heat
1130 // on various locks.
1131 Thread::muxAcquire(&gListLock, "omAlloc");
1132 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1133 gMonitorFreeCount--;
1134 ObjectMonitor * take = gFreeList;
1135 gFreeList = take->FreeNext;
1136 guarantee(take->object() == NULL, "invariant");
1137 guarantee(!take->is_busy(), "invariant");
1138 take->Recycle();
1139 omRelease(Self, take, false);
1140 }
1141 Thread::muxRelease(&gListLock);
1142 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1143 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1144
1145 const int mx = MonitorBound;
1146 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1147 // We can't safely induce a STW safepoint from omAlloc() as our thread
1148 // state may not be appropriate for such activities and callers may hold
1149 // naked oops, so instead we defer the action.
1150 InduceScavenge(Self, "omAlloc");
1151 }
1152 continue;
1153 }
1154
1155 // 3: allocate a block of new ObjectMonitors
1156 // Both the local and global free lists are empty -- resort to malloc().
1157 // In the current implementation objectMonitors are TSM - immortal.
1158 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1159 // each ObjectMonitor to start at the beginning of a cache line,
1160 // so we use align_up().
1161 // A better solution would be to use C++ placement-new.
1162 // BEWARE: As it stands currently, we don't run the ctors!
1163 assert(_BLOCKSIZE > 1, "invariant");
1201 // list activity.
1202
1203 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1204 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1205 Thread::muxAcquire(&gListLock, "omAlloc [2]");
1206 gMonitorPopulation += _BLOCKSIZE-1;
1207 gMonitorFreeCount += _BLOCKSIZE-1;
1208
1209 // Add the new block to the list of extant blocks (gBlockList).
1210 // The very first objectMonitor in a block is reserved and dedicated.
1211 // It serves as blocklist "next" linkage.
1212 temp[0].FreeNext = gBlockList;
1213 // There are lock-free uses of gBlockList so make sure that
1214 // the previous stores happen before we update gBlockList.
1215 OrderAccess::release_store(&gBlockList, temp);
1216
1217 // Add the new string of objectMonitors to the global free list
1218 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1219 gFreeList = temp + 1;
1220 Thread::muxRelease(&gListLock);
1221 }
1222 }
1223
1224 // Place "m" on the caller's private per-thread omFreeList.
1225 // In practice there's no need to clamp or limit the number of
1226 // monitors on a thread's omFreeList as the only time we'll call
1227 // omRelease is to return a monitor to the free list after a CAS
1228 // attempt failed. This doesn't allow unbounded #s of monitors to
1229 // accumulate on a thread's free list.
1230 //
1231 // Key constraint: all ObjectMonitors on a thread's free list and the global
1232 // free list must have their object field set to null. This prevents the
1233 // scavenger -- deflate_idle_monitors -- from reclaiming them.
1234
1235 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1236 bool fromPerThreadAlloc) {
1237 guarantee(m->object() == NULL, "invariant");
1238 guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor");
1239 // Remove from omInUseList
1240 if (MonitorInUseLists && fromPerThreadAlloc) {
1285 // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's
1286 // monitors have been transferred to the global in-use list).
1287
1288 void ObjectSynchronizer::omFlush(Thread * Self) {
1289 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1290 Self->omFreeList = NULL;
1291 ObjectMonitor * tail = NULL;
1292 int tally = 0;
1293 if (list != NULL) {
1294 ObjectMonitor * s;
1295 // The thread is going away, the per-thread free monitors
1296 // are freed via set_owner(NULL)
1297 // Link them to tail, which will be linked into the global free list
1298 // gFreeList below, under the gListLock
1299 for (s = list; s != NULL; s = s->FreeNext) {
1300 tally++;
1301 tail = s;
1302 guarantee(s->object() == NULL, "invariant");
1303 guarantee(!s->is_busy(), "invariant");
1304 s->set_owner(NULL); // redundant but good hygiene
1305 }
1306 guarantee(tail != NULL && list != NULL, "invariant");
1307 }
1308
1309 ObjectMonitor * inUseList = Self->omInUseList;
1310 ObjectMonitor * inUseTail = NULL;
1311 int inUseTally = 0;
1312 if (inUseList != NULL) {
1313 Self->omInUseList = NULL;
1314 ObjectMonitor *cur_om;
1315 // The thread is going away, however the omInUseList inflated
1316 // monitors may still be in-use by other threads.
1317 // Link them to inUseTail, which will be linked into the global in-use list
1318 // gOmInUseList below, under the gListLock
1319 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1320 inUseTail = cur_om;
1321 inUseTally++;
1322 }
1323 assert(Self->omInUseCount == inUseTally, "in-use count off");
1324 Self->omInUseCount = 0;
1325 guarantee(inUseTail != NULL && inUseList != NULL, "invariant");
1326 }
1327
1328 Thread::muxAcquire(&gListLock, "omFlush");
1329 if (tail != NULL) {
1330 tail->FreeNext = gFreeList;
1331 gFreeList = list;
1332 gMonitorFreeCount += tally;
1333 assert(Self->omFreeCount == tally, "free-count off");
1334 Self->omFreeCount = 0;
1335 }
1336
1337 if (inUseTail != NULL) {
1338 inUseTail->FreeNext = gOmInUseList;
1339 gOmInUseList = inUseList;
1340 gOmInUseCount += inUseTally;
1341 }
1342
1343 Thread::muxRelease(&gListLock);
1344 }
1345
1346 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1347 const oop obj,
1348 ObjectSynchronizer::InflateCause cause) {
1349 assert(event != NULL, "invariant");
1350 assert(event->should_commit(), "invariant");
1351 event->set_monitorClass(obj->klass());
1352 event->set_address((uintptr_t)(void*)obj);
1353 event->set_cause((u1)cause);
1354 event->commit();
1355 }
1356
1357 // Fast path code shared by multiple functions
1358 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1359 markOop mark = obj->mark();
1360 if (mark->has_monitor()) {
1361 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1362 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1363 return mark->monitor();
1388 // * INFLATING - busy wait for conversion to complete
1389 // * Neutral - aggressively inflate the object.
1390 // * BIASED - Illegal. We should never see this
1391
1392 // CASE: inflated
1393 if (mark->has_monitor()) {
1394 ObjectMonitor * inf = mark->monitor();
1395 assert(inf->header()->is_neutral(), "invariant");
1396 assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1397 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1398 return inf;
1399 }
1400
1401 // CASE: inflation in progress - inflating over a stack-lock.
1402 // Some other thread is converting from stack-locked to inflated.
1403 // Only that thread can complete inflation -- other threads must wait.
1404 // The INFLATING value is transient.
1405 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1406 // We could always eliminate polling by parking the thread on some auxiliary list.
1407 if (mark == markOopDesc::INFLATING()) {
1408 ReadStableMark(object);
1409 continue;
1410 }
1411
1412 // CASE: stack-locked
1413 // Could be stack-locked either by this thread or by some other thread.
1414 //
1415 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1416 // to install INFLATING into the mark word. We originally installed INFLATING,
1417 // allocated the objectmonitor, and then finally STed the address of the
1418 // objectmonitor into the mark. This was correct, but artificially lengthened
1419 // the interval in which INFLATED appeared in the mark, thus increasing
1420 // the odds of inflation contention.
1421 //
1422 // We now use per-thread private objectmonitor free lists.
1423 // These list are reprovisioned from the global free list outside the
1424 // critical INFLATING...ST interval. A thread can transfer
1425 // multiple objectmonitors en-mass from the global free list to its local free list.
1426 // This reduces coherency traffic and lock contention on the global free list.
1427 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1480 // Setup monitor fields to proper values -- prepare the monitor
1481 m->set_header(dmw);
1482
1483 // Optimization: if the mark->locker stack address is associated
1484 // with this thread we could simply set m->_owner = Self.
1485 // Note that a thread can inflate an object
1486 // that it has stack-locked -- as might happen in wait() -- directly
1487 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1488 m->set_owner(mark->locker());
1489 m->set_object(object);
1490 // TODO-FIXME: assert BasicLock->dhw != 0.
1491
1492 // Must preserve store ordering. The monitor state must
1493 // be stable at the time of publishing the monitor address.
1494 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1495 object->release_set_mark(markOopDesc::encode(m));
1496
1497 // Hopefully the performance counters are allocated on distinct cache lines
1498 // to avoid false sharing on MP systems ...
1499 OM_PERFDATA_OP(Inflations, inc());
1500 if (log_is_enabled(Debug, monitorinflation)) {
1501 if (object->is_instance()) {
1502 ResourceMark rm;
1503 log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1504 p2i(object), p2i(object->mark()),
1505 object->klass()->external_name());
1506 }
1507 }
1508 if (event.should_commit()) {
1509 post_monitor_inflate_event(&event, object, cause);
1510 }
1511 return m;
1512 }
1513
1514 // CASE: neutral
1515 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1516 // If we know we're inflating for entry it's better to inflate by swinging a
1517 // pre-locked objectMonitor pointer into the object header. A successful
1518 // CAS inflates the object *and* confers ownership to the inflating thread.
1519 // In the current implementation we use a 2-step mechanism where we CAS()
1530 m->set_object(object);
1531 m->_recursions = 0;
1532 m->_Responsible = NULL;
1533 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1534
1535 if (object->cas_set_mark(markOopDesc::encode(m), mark) != mark) {
1536 m->set_object(NULL);
1537 m->set_owner(NULL);
1538 m->Recycle();
1539 omRelease(Self, m, true);
1540 m = NULL;
1541 continue;
1542 // interference - the markword changed - just retry.
1543 // The state-transitions are one-way, so there's no chance of
1544 // live-lock -- "Inflated" is an absorbing state.
1545 }
1546
1547 // Hopefully the performance counters are allocated on distinct
1548 // cache lines to avoid false sharing on MP systems ...
1549 OM_PERFDATA_OP(Inflations, inc());
1550 if (log_is_enabled(Debug, monitorinflation)) {
1551 if (object->is_instance()) {
1552 ResourceMark rm;
1553 log_debug(monitorinflation)("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
1554 p2i(object), p2i(object->mark()),
1555 object->klass()->external_name());
1556 }
1557 }
1558 if (event.should_commit()) {
1559 post_monitor_inflate_event(&event, object, cause);
1560 }
1561 return m;
1562 }
1563 }
1564
1565
1566 // Deflate_idle_monitors() is called at all safepoints, immediately
1567 // after all mutators are stopped, but before any objects have moved.
1568 // It traverses the list of known monitors, deflating where possible.
1569 // The scavenged monitor are returned to the monitor free list.
1596 };
1597
1598 // Deflate a single monitor if not in-use
1599 // Return true if deflated, false if in-use
1600 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1601 ObjectMonitor** freeHeadp,
1602 ObjectMonitor** freeTailp) {
1603 bool deflated;
1604 // Normal case ... The monitor is associated with obj.
1605 guarantee(obj->mark() == markOopDesc::encode(mid), "invariant");
1606 guarantee(mid == obj->mark()->monitor(), "invariant");
1607 guarantee(mid->header()->is_neutral(), "invariant");
1608
1609 if (mid->is_busy()) {
1610 if (ClearResponsibleAtSTW) mid->_Responsible = NULL;
1611 deflated = false;
1612 } else {
1613 // Deflate the monitor if it is no longer being used
1614 // It's idle - scavenge and return to the global free list
1615 // plain old deflation ...
1616 if (log_is_enabled(Debug, monitorinflation)) {
1617 if (obj->is_instance()) {
1618 ResourceMark rm;
1619 log_debug(monitorinflation)("Deflating object " INTPTR_FORMAT " , "
1620 "mark " INTPTR_FORMAT " , type %s",
1621 p2i(obj), p2i(obj->mark()),
1622 obj->klass()->external_name());
1623 }
1624 }
1625
1626 // Restore the header back to obj
1627 obj->release_set_mark(mid->header());
1628 mid->clear();
1629
1630 assert(mid->object() == NULL, "invariant");
1631
1632 // Move the object to the working free list defined by freeHeadp, freeTailp
1633 if (*freeHeadp == NULL) *freeHeadp = mid;
1634 if (*freeTailp != NULL) {
1635 ObjectMonitor * prevtail = *freeTailp;
1681 cur_mid_in_use = mid;
1682 mid = mid->FreeNext;
1683 }
1684 }
1685 return deflated_count;
1686 }
1687
1688 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1689 counters->nInuse = 0; // currently associated with objects
1690 counters->nInCirculation = 0; // extant
1691 counters->nScavenged = 0; // reclaimed
1692 }
1693
1694 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
1695 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1696 bool deflated = false;
1697
1698 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1699 ObjectMonitor * freeTailp = NULL;
1700
1701 // Prevent omFlush from changing mids in Thread dtor's during deflation
1702 // And in case the vm thread is acquiring a lock during a safepoint
1703 // See e.g. 6320749
1704 Thread::muxAcquire(&gListLock, "scavenge - return");
1705
1706 if (MonitorInUseLists) {
1707 // Note: the thread-local monitors lists get deflated in
1708 // a separate pass. See deflate_thread_local_monitors().
1709
1710 // For moribund threads, scan gOmInUseList
1711 if (gOmInUseList) {
1712 counters->nInCirculation += gOmInUseCount;
1713 int deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
1714 gOmInUseCount -= deflated_count;
1715 counters->nScavenged += deflated_count;
1716 counters->nInuse += gOmInUseCount;
1717 }
1718
1719 } else {
1720 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
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