Sat, 28 Mar 2009 15:47:29 -0700
6819891: ParNew: Fix work queue overflow code to deal correctly with +UseCompressedOops
Summary: When using compressed oops, rather than chaining the overflowed grey objects' pre-images through their klass words, we use GC-worker thread-local overflow stacks.
Reviewed-by: jcoomes, jmasa
1 /*
2 * Copyright 2005-2008 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions.
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23 */
25 # include "incls/_precompiled.incl"
26 # include "incls/_biasedLocking.cpp.incl"
28 static bool _biased_locking_enabled = false;
29 BiasedLockingCounters BiasedLocking::_counters;
31 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
32 static GrowableArray<markOop>* _preserved_mark_stack = NULL;
34 static void enable_biased_locking(klassOop k) {
35 Klass::cast(k)->set_prototype_header(markOopDesc::biased_locking_prototype());
36 }
38 class VM_EnableBiasedLocking: public VM_Operation {
39 private:
40 bool _is_cheap_allocated;
41 public:
42 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; }
43 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
44 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; }
45 bool is_cheap_allocated() const { return _is_cheap_allocated; }
47 void doit() {
48 // Iterate the system dictionary enabling biased locking for all
49 // currently loaded classes
50 SystemDictionary::classes_do(enable_biased_locking);
51 // Indicate that future instances should enable it as well
52 _biased_locking_enabled = true;
54 if (TraceBiasedLocking) {
55 tty->print_cr("Biased locking enabled");
56 }
57 }
59 bool allow_nested_vm_operations() const { return false; }
60 };
63 // One-shot PeriodicTask subclass for enabling biased locking
64 class EnableBiasedLockingTask : public PeriodicTask {
65 public:
66 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {}
68 virtual void task() {
69 // Use async VM operation to avoid blocking the Watcher thread.
70 // VM Thread will free C heap storage.
71 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true);
72 VMThread::execute(op);
74 // Reclaim our storage and disenroll ourself
75 delete this;
76 }
77 };
80 void BiasedLocking::init() {
81 // If biased locking is enabled, schedule a task to fire a few
82 // seconds into the run which turns on biased locking for all
83 // currently loaded classes as well as future ones. This is a
84 // workaround for startup time regressions due to a large number of
85 // safepoints being taken during VM startup for bias revocation.
86 // Ideally we would have a lower cost for individual bias revocation
87 // and not need a mechanism like this.
88 if (UseBiasedLocking) {
89 if (BiasedLockingStartupDelay > 0) {
90 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
91 task->enroll();
92 } else {
93 VM_EnableBiasedLocking op(false);
94 VMThread::execute(&op);
95 }
96 }
97 }
100 bool BiasedLocking::enabled() {
101 return _biased_locking_enabled;
102 }
104 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
105 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
106 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
107 if (info != NULL) {
108 return info;
109 }
111 info = new GrowableArray<MonitorInfo*>();
113 // It's possible for the thread to not have any Java frames on it,
114 // i.e., if it's the main thread and it's already returned from main()
115 if (thread->has_last_Java_frame()) {
116 RegisterMap rm(thread);
117 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
118 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
119 if (monitors != NULL) {
120 int len = monitors->length();
121 // Walk monitors youngest to oldest
122 for (int i = len - 1; i >= 0; i--) {
123 MonitorInfo* mon_info = monitors->at(i);
124 oop owner = mon_info->owner();
125 if (owner != NULL) {
126 info->append(mon_info);
127 }
128 }
129 }
130 }
131 }
133 thread->set_cached_monitor_info(info);
134 return info;
135 }
138 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) {
139 markOop mark = obj->mark();
140 if (!mark->has_bias_pattern()) {
141 if (TraceBiasedLocking) {
142 ResourceMark rm;
143 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)",
144 Klass::cast(obj->klass())->external_name());
145 }
146 return BiasedLocking::NOT_BIASED;
147 }
149 int age = mark->age();
150 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
151 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
153 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
154 ResourceMark rm;
155 tty->print_cr("Revoking bias of object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT " , allow rebias %d , requesting thread " INTPTR_FORMAT,
156 (intptr_t) obj, (intptr_t) mark, Klass::cast(obj->klass())->external_name(), (intptr_t) Klass::cast(obj->klass())->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread);
157 }
159 JavaThread* biased_thread = mark->biased_locker();
160 if (biased_thread == NULL) {
161 // Object is anonymously biased. We can get here if, for
162 // example, we revoke the bias due to an identity hash code
163 // being computed for an object.
164 if (!allow_rebias) {
165 obj->set_mark(unbiased_prototype);
166 }
167 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
168 tty->print_cr(" Revoked bias of anonymously-biased object");
169 }
170 return BiasedLocking::BIAS_REVOKED;
171 }
173 // Handle case where the thread toward which the object was biased has exited
174 bool thread_is_alive = false;
175 if (requesting_thread == biased_thread) {
176 thread_is_alive = true;
177 } else {
178 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) {
179 if (cur_thread == biased_thread) {
180 thread_is_alive = true;
181 break;
182 }
183 }
184 }
185 if (!thread_is_alive) {
186 if (allow_rebias) {
187 obj->set_mark(biased_prototype);
188 } else {
189 obj->set_mark(unbiased_prototype);
190 }
191 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
192 tty->print_cr(" Revoked bias of object biased toward dead thread");
193 }
194 return BiasedLocking::BIAS_REVOKED;
195 }
197 // Thread owning bias is alive.
198 // Check to see whether it currently owns the lock and, if so,
199 // write down the needed displaced headers to the thread's stack.
200 // Otherwise, restore the object's header either to the unlocked
201 // or unbiased state.
202 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
203 BasicLock* highest_lock = NULL;
204 for (int i = 0; i < cached_monitor_info->length(); i++) {
205 MonitorInfo* mon_info = cached_monitor_info->at(i);
206 if (mon_info->owner() == obj) {
207 if (TraceBiasedLocking && Verbose) {
208 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
209 (intptr_t) mon_info->owner(),
210 (intptr_t) obj);
211 }
212 // Assume recursive case and fix up highest lock later
213 markOop mark = markOopDesc::encode((BasicLock*) NULL);
214 highest_lock = mon_info->lock();
215 highest_lock->set_displaced_header(mark);
216 } else {
217 if (TraceBiasedLocking && Verbose) {
218 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
219 (intptr_t) mon_info->owner(),
220 (intptr_t) obj);
221 }
222 }
223 }
224 if (highest_lock != NULL) {
225 // Fix up highest lock to contain displaced header and point
226 // object at it
227 highest_lock->set_displaced_header(unbiased_prototype);
228 // Reset object header to point to displaced mark
229 obj->set_mark(markOopDesc::encode(highest_lock));
230 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
231 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
232 tty->print_cr(" Revoked bias of currently-locked object");
233 }
234 } else {
235 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
236 tty->print_cr(" Revoked bias of currently-unlocked object");
237 }
238 if (allow_rebias) {
239 obj->set_mark(biased_prototype);
240 } else {
241 // Store the unlocked value into the object's header.
242 obj->set_mark(unbiased_prototype);
243 }
244 }
246 return BiasedLocking::BIAS_REVOKED;
247 }
250 enum HeuristicsResult {
251 HR_NOT_BIASED = 1,
252 HR_SINGLE_REVOKE = 2,
253 HR_BULK_REBIAS = 3,
254 HR_BULK_REVOKE = 4
255 };
258 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
259 markOop mark = o->mark();
260 if (!mark->has_bias_pattern()) {
261 return HR_NOT_BIASED;
262 }
264 // Heuristics to attempt to throttle the number of revocations.
265 // Stages:
266 // 1. Revoke the biases of all objects in the heap of this type,
267 // but allow rebiasing of those objects if unlocked.
268 // 2. Revoke the biases of all objects in the heap of this type
269 // and don't allow rebiasing of these objects. Disable
270 // allocation of objects of that type with the bias bit set.
271 Klass* k = o->blueprint();
272 jlong cur_time = os::javaTimeMillis();
273 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
274 int revocation_count = k->biased_lock_revocation_count();
275 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
276 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
277 (last_bulk_revocation_time != 0) &&
278 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
279 // This is the first revocation we've seen in a while of an
280 // object of this type since the last time we performed a bulk
281 // rebiasing operation. The application is allocating objects in
282 // bulk which are biased toward a thread and then handing them
283 // off to another thread. We can cope with this allocation
284 // pattern via the bulk rebiasing mechanism so we reset the
285 // klass's revocation count rather than allow it to increase
286 // monotonically. If we see the need to perform another bulk
287 // rebias operation later, we will, and if subsequently we see
288 // many more revocation operations in a short period of time we
289 // will completely disable biasing for this type.
290 k->set_biased_lock_revocation_count(0);
291 revocation_count = 0;
292 }
294 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
295 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
296 revocation_count = k->atomic_incr_biased_lock_revocation_count();
297 }
299 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
300 return HR_BULK_REVOKE;
301 }
303 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
304 return HR_BULK_REBIAS;
305 }
307 return HR_SINGLE_REVOKE;
308 }
311 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
312 bool bulk_rebias,
313 bool attempt_rebias_of_object,
314 JavaThread* requesting_thread) {
315 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
317 if (TraceBiasedLocking) {
318 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object "
319 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
320 (bulk_rebias ? "rebias" : "revoke"),
321 (intptr_t) o, (intptr_t) o->mark(), Klass::cast(o->klass())->external_name());
322 }
324 jlong cur_time = os::javaTimeMillis();
325 o->blueprint()->set_last_biased_lock_bulk_revocation_time(cur_time);
328 klassOop k_o = o->klass();
329 Klass* klass = Klass::cast(k_o);
331 if (bulk_rebias) {
332 // Use the epoch in the klass of the object to implicitly revoke
333 // all biases of objects of this data type and force them to be
334 // reacquired. However, we also need to walk the stacks of all
335 // threads and update the headers of lightweight locked objects
336 // with biases to have the current epoch.
338 // If the prototype header doesn't have the bias pattern, don't
339 // try to update the epoch -- assume another VM operation came in
340 // and reset the header to the unbiased state, which will
341 // implicitly cause all existing biases to be revoked
342 if (klass->prototype_header()->has_bias_pattern()) {
343 int prev_epoch = klass->prototype_header()->bias_epoch();
344 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
345 int cur_epoch = klass->prototype_header()->bias_epoch();
347 // Now walk all threads' stacks and adjust epochs of any biased
348 // and locked objects of this data type we encounter
349 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
350 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
351 for (int i = 0; i < cached_monitor_info->length(); i++) {
352 MonitorInfo* mon_info = cached_monitor_info->at(i);
353 oop owner = mon_info->owner();
354 markOop mark = owner->mark();
355 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
356 // We might have encountered this object already in the case of recursive locking
357 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
358 owner->set_mark(mark->set_bias_epoch(cur_epoch));
359 }
360 }
361 }
362 }
364 // At this point we're done. All we have to do is potentially
365 // adjust the header of the given object to revoke its bias.
366 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread);
367 } else {
368 if (TraceBiasedLocking) {
369 ResourceMark rm;
370 tty->print_cr("* Disabling biased locking for type %s", klass->external_name());
371 }
373 // Disable biased locking for this data type. Not only will this
374 // cause future instances to not be biased, but existing biased
375 // instances will notice that this implicitly caused their biases
376 // to be revoked.
377 klass->set_prototype_header(markOopDesc::prototype());
379 // Now walk all threads' stacks and forcibly revoke the biases of
380 // any locked and biased objects of this data type we encounter.
381 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
382 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
383 for (int i = 0; i < cached_monitor_info->length(); i++) {
384 MonitorInfo* mon_info = cached_monitor_info->at(i);
385 oop owner = mon_info->owner();
386 markOop mark = owner->mark();
387 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
388 revoke_bias(owner, false, true, requesting_thread);
389 }
390 }
391 }
393 // Must force the bias of the passed object to be forcibly revoked
394 // as well to ensure guarantees to callers
395 revoke_bias(o, false, true, requesting_thread);
396 }
398 if (TraceBiasedLocking) {
399 tty->print_cr("* Ending bulk revocation");
400 }
402 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
404 if (attempt_rebias_of_object &&
405 o->mark()->has_bias_pattern() &&
406 klass->prototype_header()->has_bias_pattern()) {
407 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
408 klass->prototype_header()->bias_epoch());
409 o->set_mark(new_mark);
410 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
411 if (TraceBiasedLocking) {
412 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
413 }
414 }
416 assert(!o->mark()->has_bias_pattern() ||
417 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
418 "bug in bulk bias revocation");
420 return status_code;
421 }
424 static void clean_up_cached_monitor_info() {
425 // Walk the thread list clearing out the cached monitors
426 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
427 thr->set_cached_monitor_info(NULL);
428 }
429 }
432 class VM_RevokeBias : public VM_Operation {
433 protected:
434 Handle* _obj;
435 GrowableArray<Handle>* _objs;
436 JavaThread* _requesting_thread;
437 BiasedLocking::Condition _status_code;
439 public:
440 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
441 : _obj(obj)
442 , _objs(NULL)
443 , _requesting_thread(requesting_thread)
444 , _status_code(BiasedLocking::NOT_BIASED) {}
446 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
447 : _obj(NULL)
448 , _objs(objs)
449 , _requesting_thread(requesting_thread)
450 , _status_code(BiasedLocking::NOT_BIASED) {}
452 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
454 virtual bool doit_prologue() {
455 // Verify that there is actual work to do since the callers just
456 // give us locked object(s). If we don't find any biased objects
457 // there is nothing to do and we avoid a safepoint.
458 if (_obj != NULL) {
459 markOop mark = (*_obj)()->mark();
460 if (mark->has_bias_pattern()) {
461 return true;
462 }
463 } else {
464 for ( int i = 0 ; i < _objs->length(); i++ ) {
465 markOop mark = (_objs->at(i))()->mark();
466 if (mark->has_bias_pattern()) {
467 return true;
468 }
469 }
470 }
471 return false;
472 }
474 virtual void doit() {
475 if (_obj != NULL) {
476 if (TraceBiasedLocking) {
477 tty->print_cr("Revoking bias with potentially per-thread safepoint:");
478 }
479 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread);
480 clean_up_cached_monitor_info();
481 return;
482 } else {
483 if (TraceBiasedLocking) {
484 tty->print_cr("Revoking bias with global safepoint:");
485 }
486 BiasedLocking::revoke_at_safepoint(_objs);
487 }
488 }
490 BiasedLocking::Condition status_code() const {
491 return _status_code;
492 }
493 };
496 class VM_BulkRevokeBias : public VM_RevokeBias {
497 private:
498 bool _bulk_rebias;
499 bool _attempt_rebias_of_object;
501 public:
502 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
503 bool bulk_rebias,
504 bool attempt_rebias_of_object)
505 : VM_RevokeBias(obj, requesting_thread)
506 , _bulk_rebias(bulk_rebias)
507 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
509 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
510 virtual bool doit_prologue() { return true; }
512 virtual void doit() {
513 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
514 clean_up_cached_monitor_info();
515 }
516 };
519 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
520 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
522 // We can revoke the biases of anonymously-biased objects
523 // efficiently enough that we should not cause these revocations to
524 // update the heuristics because doing so may cause unwanted bulk
525 // revocations (which are expensive) to occur.
526 markOop mark = obj->mark();
527 if (mark->is_biased_anonymously() && !attempt_rebias) {
528 // We are probably trying to revoke the bias of this object due to
529 // an identity hash code computation. Try to revoke the bias
530 // without a safepoint. This is possible if we can successfully
531 // compare-and-exchange an unbiased header into the mark word of
532 // the object, meaning that no other thread has raced to acquire
533 // the bias of the object.
534 markOop biased_value = mark;
535 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
536 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
537 if (res_mark == biased_value) {
538 return BIAS_REVOKED;
539 }
540 } else if (mark->has_bias_pattern()) {
541 Klass* k = Klass::cast(obj->klass());
542 markOop prototype_header = k->prototype_header();
543 if (!prototype_header->has_bias_pattern()) {
544 // This object has a stale bias from before the bulk revocation
545 // for this data type occurred. It's pointless to update the
546 // heuristics at this point so simply update the header with a
547 // CAS. If we fail this race, the object's bias has been revoked
548 // by another thread so we simply return and let the caller deal
549 // with it.
550 markOop biased_value = mark;
551 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark);
552 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked");
553 return BIAS_REVOKED;
554 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
555 // The epoch of this biasing has expired indicating that the
556 // object is effectively unbiased. Depending on whether we need
557 // to rebias or revoke the bias of this object we can do it
558 // efficiently enough with a CAS that we shouldn't update the
559 // heuristics. This is normally done in the assembly code but we
560 // can reach this point due to various points in the runtime
561 // needing to revoke biases.
562 if (attempt_rebias) {
563 assert(THREAD->is_Java_thread(), "");
564 markOop biased_value = mark;
565 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
566 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark);
567 if (res_mark == biased_value) {
568 return BIAS_REVOKED_AND_REBIASED;
569 }
570 } else {
571 markOop biased_value = mark;
572 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
573 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
574 if (res_mark == biased_value) {
575 return BIAS_REVOKED;
576 }
577 }
578 }
579 }
581 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
582 if (heuristics == HR_NOT_BIASED) {
583 return NOT_BIASED;
584 } else if (heuristics == HR_SINGLE_REVOKE) {
585 Klass *k = Klass::cast(obj->klass());
586 markOop prototype_header = k->prototype_header();
587 if (mark->biased_locker() == THREAD &&
588 prototype_header->bias_epoch() == mark->bias_epoch()) {
589 // A thread is trying to revoke the bias of an object biased
590 // toward it, again likely due to an identity hash code
591 // computation. We can again avoid a safepoint in this case
592 // since we are only going to walk our own stack. There are no
593 // races with revocations occurring in other threads because we
594 // reach no safepoints in the revocation path.
595 // Also check the epoch because even if threads match, another thread
596 // can come in with a CAS to steal the bias of an object that has a
597 // stale epoch.
598 ResourceMark rm;
599 if (TraceBiasedLocking) {
600 tty->print_cr("Revoking bias by walking my own stack:");
601 }
602 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD);
603 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
604 assert(cond == BIAS_REVOKED, "why not?");
605 return cond;
606 } else {
607 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
608 VMThread::execute(&revoke);
609 return revoke.status_code();
610 }
611 }
613 assert((heuristics == HR_BULK_REVOKE) ||
614 (heuristics == HR_BULK_REBIAS), "?");
615 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
616 (heuristics == HR_BULK_REBIAS),
617 attempt_rebias);
618 VMThread::execute(&bulk_revoke);
619 return bulk_revoke.status_code();
620 }
623 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
624 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
625 if (objs->length() == 0) {
626 return;
627 }
628 VM_RevokeBias revoke(objs, JavaThread::current());
629 VMThread::execute(&revoke);
630 }
633 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
634 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
635 oop obj = h_obj();
636 HeuristicsResult heuristics = update_heuristics(obj, false);
637 if (heuristics == HR_SINGLE_REVOKE) {
638 revoke_bias(obj, false, false, NULL);
639 } else if ((heuristics == HR_BULK_REBIAS) ||
640 (heuristics == HR_BULK_REVOKE)) {
641 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
642 }
643 clean_up_cached_monitor_info();
644 }
647 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
648 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
649 int len = objs->length();
650 for (int i = 0; i < len; i++) {
651 oop obj = (objs->at(i))();
652 HeuristicsResult heuristics = update_heuristics(obj, false);
653 if (heuristics == HR_SINGLE_REVOKE) {
654 revoke_bias(obj, false, false, NULL);
655 } else if ((heuristics == HR_BULK_REBIAS) ||
656 (heuristics == HR_BULK_REVOKE)) {
657 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
658 }
659 }
660 clean_up_cached_monitor_info();
661 }
664 void BiasedLocking::preserve_marks() {
665 if (!UseBiasedLocking)
666 return;
668 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
670 assert(_preserved_oop_stack == NULL, "double initialization");
671 assert(_preserved_mark_stack == NULL, "double initialization");
673 // In order to reduce the number of mark words preserved during GC
674 // due to the presence of biased locking, we reinitialize most mark
675 // words to the class's prototype during GC -- even those which have
676 // a currently valid bias owner. One important situation where we
677 // must not clobber a bias is when a biased object is currently
678 // locked. To handle this case we iterate over the currently-locked
679 // monitors in a prepass and, if they are biased, preserve their
680 // mark words here. This should be a relatively small set of objects
681 // especially compared to the number of objects in the heap.
682 _preserved_mark_stack = new (ResourceObj::C_HEAP) GrowableArray<markOop>(10, true);
683 _preserved_oop_stack = new (ResourceObj::C_HEAP) GrowableArray<Handle>(10, true);
685 ResourceMark rm;
686 Thread* cur = Thread::current();
687 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) {
688 if (thread->has_last_Java_frame()) {
689 RegisterMap rm(thread);
690 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
691 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
692 if (monitors != NULL) {
693 int len = monitors->length();
694 // Walk monitors youngest to oldest
695 for (int i = len - 1; i >= 0; i--) {
696 MonitorInfo* mon_info = monitors->at(i);
697 oop owner = mon_info->owner();
698 if (owner != NULL) {
699 markOop mark = owner->mark();
700 if (mark->has_bias_pattern()) {
701 _preserved_oop_stack->push(Handle(cur, owner));
702 _preserved_mark_stack->push(mark);
703 }
704 }
705 }
706 }
707 }
708 }
709 }
710 }
713 void BiasedLocking::restore_marks() {
714 if (!UseBiasedLocking)
715 return;
717 assert(_preserved_oop_stack != NULL, "double free");
718 assert(_preserved_mark_stack != NULL, "double free");
720 int len = _preserved_oop_stack->length();
721 for (int i = 0; i < len; i++) {
722 Handle owner = _preserved_oop_stack->at(i);
723 markOop mark = _preserved_mark_stack->at(i);
724 owner->set_mark(mark);
725 }
727 delete _preserved_oop_stack;
728 _preserved_oop_stack = NULL;
729 delete _preserved_mark_stack;
730 _preserved_mark_stack = NULL;
731 }
734 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
735 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
736 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
737 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
738 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
739 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
740 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
743 // BiasedLockingCounters
745 int BiasedLockingCounters::slow_path_entry_count() {
746 if (_slow_path_entry_count != 0) {
747 return _slow_path_entry_count;
748 }
749 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
750 _rebiased_lock_entry_count + _revoked_lock_entry_count +
751 _fast_path_entry_count;
753 return _total_entry_count - sum;
754 }
756 void BiasedLockingCounters::print_on(outputStream* st) {
757 tty->print_cr("# total entries: %d", _total_entry_count);
758 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
759 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
760 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
761 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
762 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
763 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
764 }