Tue, 09 Oct 2012 10:09:34 -0700
7197424: update copyright year to match last edit in jdk8 hotspot repository
Summary: Update copyright year to 2012 for relevant files
Reviewed-by: dholmes, coleenp
1 /*
2 * Copyright (c) 2005, 2012, 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 */
25 #include "precompiled.hpp"
26 #include "oops/klass.inline.hpp"
27 #include "oops/markOop.hpp"
28 #include "runtime/basicLock.hpp"
29 #include "runtime/biasedLocking.hpp"
30 #include "runtime/task.hpp"
31 #include "runtime/vframe.hpp"
32 #include "runtime/vmThread.hpp"
33 #include "runtime/vm_operations.hpp"
35 static bool _biased_locking_enabled = false;
36 BiasedLockingCounters BiasedLocking::_counters;
38 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
39 static GrowableArray<markOop>* _preserved_mark_stack = NULL;
41 static void enable_biased_locking(Klass* k) {
42 Klass::cast(k)->set_prototype_header(markOopDesc::biased_locking_prototype());
43 }
45 class VM_EnableBiasedLocking: public VM_Operation {
46 private:
47 bool _is_cheap_allocated;
48 public:
49 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; }
50 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
51 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; }
52 bool is_cheap_allocated() const { return _is_cheap_allocated; }
54 void doit() {
55 // Iterate the system dictionary enabling biased locking for all
56 // currently loaded classes
57 SystemDictionary::classes_do(enable_biased_locking);
58 // Indicate that future instances should enable it as well
59 _biased_locking_enabled = true;
61 if (TraceBiasedLocking) {
62 tty->print_cr("Biased locking enabled");
63 }
64 }
66 bool allow_nested_vm_operations() const { return false; }
67 };
70 // One-shot PeriodicTask subclass for enabling biased locking
71 class EnableBiasedLockingTask : public PeriodicTask {
72 public:
73 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {}
75 virtual void task() {
76 // Use async VM operation to avoid blocking the Watcher thread.
77 // VM Thread will free C heap storage.
78 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true);
79 VMThread::execute(op);
81 // Reclaim our storage and disenroll ourself
82 delete this;
83 }
84 };
87 void BiasedLocking::init() {
88 // If biased locking is enabled, schedule a task to fire a few
89 // seconds into the run which turns on biased locking for all
90 // currently loaded classes as well as future ones. This is a
91 // workaround for startup time regressions due to a large number of
92 // safepoints being taken during VM startup for bias revocation.
93 // Ideally we would have a lower cost for individual bias revocation
94 // and not need a mechanism like this.
95 if (UseBiasedLocking) {
96 if (BiasedLockingStartupDelay > 0) {
97 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
98 task->enroll();
99 } else {
100 VM_EnableBiasedLocking op(false);
101 VMThread::execute(&op);
102 }
103 }
104 }
107 bool BiasedLocking::enabled() {
108 return _biased_locking_enabled;
109 }
111 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
112 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
113 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
114 if (info != NULL) {
115 return info;
116 }
118 info = new GrowableArray<MonitorInfo*>();
120 // It's possible for the thread to not have any Java frames on it,
121 // i.e., if it's the main thread and it's already returned from main()
122 if (thread->has_last_Java_frame()) {
123 RegisterMap rm(thread);
124 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
125 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
126 if (monitors != NULL) {
127 int len = monitors->length();
128 // Walk monitors youngest to oldest
129 for (int i = len - 1; i >= 0; i--) {
130 MonitorInfo* mon_info = monitors->at(i);
131 if (mon_info->owner_is_scalar_replaced()) continue;
132 oop owner = mon_info->owner();
133 if (owner != NULL) {
134 info->append(mon_info);
135 }
136 }
137 }
138 }
139 }
141 thread->set_cached_monitor_info(info);
142 return info;
143 }
146 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) {
147 markOop mark = obj->mark();
148 if (!mark->has_bias_pattern()) {
149 if (TraceBiasedLocking) {
150 ResourceMark rm;
151 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)",
152 Klass::cast(obj->klass())->external_name());
153 }
154 return BiasedLocking::NOT_BIASED;
155 }
157 uint age = mark->age();
158 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
159 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
161 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
162 ResourceMark rm;
163 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,
164 (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);
165 }
167 JavaThread* biased_thread = mark->biased_locker();
168 if (biased_thread == NULL) {
169 // Object is anonymously biased. We can get here if, for
170 // example, we revoke the bias due to an identity hash code
171 // being computed for an object.
172 if (!allow_rebias) {
173 obj->set_mark(unbiased_prototype);
174 }
175 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
176 tty->print_cr(" Revoked bias of anonymously-biased object");
177 }
178 return BiasedLocking::BIAS_REVOKED;
179 }
181 // Handle case where the thread toward which the object was biased has exited
182 bool thread_is_alive = false;
183 if (requesting_thread == biased_thread) {
184 thread_is_alive = true;
185 } else {
186 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) {
187 if (cur_thread == biased_thread) {
188 thread_is_alive = true;
189 break;
190 }
191 }
192 }
193 if (!thread_is_alive) {
194 if (allow_rebias) {
195 obj->set_mark(biased_prototype);
196 } else {
197 obj->set_mark(unbiased_prototype);
198 }
199 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
200 tty->print_cr(" Revoked bias of object biased toward dead thread");
201 }
202 return BiasedLocking::BIAS_REVOKED;
203 }
205 // Thread owning bias is alive.
206 // Check to see whether it currently owns the lock and, if so,
207 // write down the needed displaced headers to the thread's stack.
208 // Otherwise, restore the object's header either to the unlocked
209 // or unbiased state.
210 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
211 BasicLock* highest_lock = NULL;
212 for (int i = 0; i < cached_monitor_info->length(); i++) {
213 MonitorInfo* mon_info = cached_monitor_info->at(i);
214 if (mon_info->owner() == obj) {
215 if (TraceBiasedLocking && Verbose) {
216 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
217 (intptr_t) mon_info->owner(),
218 (intptr_t) obj);
219 }
220 // Assume recursive case and fix up highest lock later
221 markOop mark = markOopDesc::encode((BasicLock*) NULL);
222 highest_lock = mon_info->lock();
223 highest_lock->set_displaced_header(mark);
224 } else {
225 if (TraceBiasedLocking && Verbose) {
226 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
227 (intptr_t) mon_info->owner(),
228 (intptr_t) obj);
229 }
230 }
231 }
232 if (highest_lock != NULL) {
233 // Fix up highest lock to contain displaced header and point
234 // object at it
235 highest_lock->set_displaced_header(unbiased_prototype);
236 // Reset object header to point to displaced mark
237 obj->set_mark(markOopDesc::encode(highest_lock));
238 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
239 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
240 tty->print_cr(" Revoked bias of currently-locked object");
241 }
242 } else {
243 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
244 tty->print_cr(" Revoked bias of currently-unlocked object");
245 }
246 if (allow_rebias) {
247 obj->set_mark(biased_prototype);
248 } else {
249 // Store the unlocked value into the object's header.
250 obj->set_mark(unbiased_prototype);
251 }
252 }
254 return BiasedLocking::BIAS_REVOKED;
255 }
258 enum HeuristicsResult {
259 HR_NOT_BIASED = 1,
260 HR_SINGLE_REVOKE = 2,
261 HR_BULK_REBIAS = 3,
262 HR_BULK_REVOKE = 4
263 };
266 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
267 markOop mark = o->mark();
268 if (!mark->has_bias_pattern()) {
269 return HR_NOT_BIASED;
270 }
272 // Heuristics to attempt to throttle the number of revocations.
273 // Stages:
274 // 1. Revoke the biases of all objects in the heap of this type,
275 // but allow rebiasing of those objects if unlocked.
276 // 2. Revoke the biases of all objects in the heap of this type
277 // and don't allow rebiasing of these objects. Disable
278 // allocation of objects of that type with the bias bit set.
279 Klass* k = o->klass();
280 jlong cur_time = os::javaTimeMillis();
281 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
282 int revocation_count = k->biased_lock_revocation_count();
283 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
284 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
285 (last_bulk_revocation_time != 0) &&
286 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
287 // This is the first revocation we've seen in a while of an
288 // object of this type since the last time we performed a bulk
289 // rebiasing operation. The application is allocating objects in
290 // bulk which are biased toward a thread and then handing them
291 // off to another thread. We can cope with this allocation
292 // pattern via the bulk rebiasing mechanism so we reset the
293 // klass's revocation count rather than allow it to increase
294 // monotonically. If we see the need to perform another bulk
295 // rebias operation later, we will, and if subsequently we see
296 // many more revocation operations in a short period of time we
297 // will completely disable biasing for this type.
298 k->set_biased_lock_revocation_count(0);
299 revocation_count = 0;
300 }
302 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
303 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
304 revocation_count = k->atomic_incr_biased_lock_revocation_count();
305 }
307 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
308 return HR_BULK_REVOKE;
309 }
311 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
312 return HR_BULK_REBIAS;
313 }
315 return HR_SINGLE_REVOKE;
316 }
319 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
320 bool bulk_rebias,
321 bool attempt_rebias_of_object,
322 JavaThread* requesting_thread) {
323 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
325 if (TraceBiasedLocking) {
326 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object "
327 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
328 (bulk_rebias ? "rebias" : "revoke"),
329 (intptr_t) o, (intptr_t) o->mark(), Klass::cast(o->klass())->external_name());
330 }
332 jlong cur_time = os::javaTimeMillis();
333 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
336 Klass* k_o = o->klass();
337 Klass* klass = Klass::cast(k_o);
339 if (bulk_rebias) {
340 // Use the epoch in the klass of the object to implicitly revoke
341 // all biases of objects of this data type and force them to be
342 // reacquired. However, we also need to walk the stacks of all
343 // threads and update the headers of lightweight locked objects
344 // with biases to have the current epoch.
346 // If the prototype header doesn't have the bias pattern, don't
347 // try to update the epoch -- assume another VM operation came in
348 // and reset the header to the unbiased state, which will
349 // implicitly cause all existing biases to be revoked
350 if (klass->prototype_header()->has_bias_pattern()) {
351 int prev_epoch = klass->prototype_header()->bias_epoch();
352 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
353 int cur_epoch = klass->prototype_header()->bias_epoch();
355 // Now walk all threads' stacks and adjust epochs of any biased
356 // and locked objects of this data type we encounter
357 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
358 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
359 for (int i = 0; i < cached_monitor_info->length(); i++) {
360 MonitorInfo* mon_info = cached_monitor_info->at(i);
361 oop owner = mon_info->owner();
362 markOop mark = owner->mark();
363 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
364 // We might have encountered this object already in the case of recursive locking
365 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
366 owner->set_mark(mark->set_bias_epoch(cur_epoch));
367 }
368 }
369 }
370 }
372 // At this point we're done. All we have to do is potentially
373 // adjust the header of the given object to revoke its bias.
374 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread);
375 } else {
376 if (TraceBiasedLocking) {
377 ResourceMark rm;
378 tty->print_cr("* Disabling biased locking for type %s", klass->external_name());
379 }
381 // Disable biased locking for this data type. Not only will this
382 // cause future instances to not be biased, but existing biased
383 // instances will notice that this implicitly caused their biases
384 // to be revoked.
385 klass->set_prototype_header(markOopDesc::prototype());
387 // Now walk all threads' stacks and forcibly revoke the biases of
388 // any locked and biased objects of this data type we encounter.
389 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
390 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
391 for (int i = 0; i < cached_monitor_info->length(); i++) {
392 MonitorInfo* mon_info = cached_monitor_info->at(i);
393 oop owner = mon_info->owner();
394 markOop mark = owner->mark();
395 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
396 revoke_bias(owner, false, true, requesting_thread);
397 }
398 }
399 }
401 // Must force the bias of the passed object to be forcibly revoked
402 // as well to ensure guarantees to callers
403 revoke_bias(o, false, true, requesting_thread);
404 }
406 if (TraceBiasedLocking) {
407 tty->print_cr("* Ending bulk revocation");
408 }
410 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
412 if (attempt_rebias_of_object &&
413 o->mark()->has_bias_pattern() &&
414 klass->prototype_header()->has_bias_pattern()) {
415 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
416 klass->prototype_header()->bias_epoch());
417 o->set_mark(new_mark);
418 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
419 if (TraceBiasedLocking) {
420 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
421 }
422 }
424 assert(!o->mark()->has_bias_pattern() ||
425 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
426 "bug in bulk bias revocation");
428 return status_code;
429 }
432 static void clean_up_cached_monitor_info() {
433 // Walk the thread list clearing out the cached monitors
434 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
435 thr->set_cached_monitor_info(NULL);
436 }
437 }
440 class VM_RevokeBias : public VM_Operation {
441 protected:
442 Handle* _obj;
443 GrowableArray<Handle>* _objs;
444 JavaThread* _requesting_thread;
445 BiasedLocking::Condition _status_code;
447 public:
448 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
449 : _obj(obj)
450 , _objs(NULL)
451 , _requesting_thread(requesting_thread)
452 , _status_code(BiasedLocking::NOT_BIASED) {}
454 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
455 : _obj(NULL)
456 , _objs(objs)
457 , _requesting_thread(requesting_thread)
458 , _status_code(BiasedLocking::NOT_BIASED) {}
460 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
462 virtual bool doit_prologue() {
463 // Verify that there is actual work to do since the callers just
464 // give us locked object(s). If we don't find any biased objects
465 // there is nothing to do and we avoid a safepoint.
466 if (_obj != NULL) {
467 markOop mark = (*_obj)()->mark();
468 if (mark->has_bias_pattern()) {
469 return true;
470 }
471 } else {
472 for ( int i = 0 ; i < _objs->length(); i++ ) {
473 markOop mark = (_objs->at(i))()->mark();
474 if (mark->has_bias_pattern()) {
475 return true;
476 }
477 }
478 }
479 return false;
480 }
482 virtual void doit() {
483 if (_obj != NULL) {
484 if (TraceBiasedLocking) {
485 tty->print_cr("Revoking bias with potentially per-thread safepoint:");
486 }
487 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread);
488 clean_up_cached_monitor_info();
489 return;
490 } else {
491 if (TraceBiasedLocking) {
492 tty->print_cr("Revoking bias with global safepoint:");
493 }
494 BiasedLocking::revoke_at_safepoint(_objs);
495 }
496 }
498 BiasedLocking::Condition status_code() const {
499 return _status_code;
500 }
501 };
504 class VM_BulkRevokeBias : public VM_RevokeBias {
505 private:
506 bool _bulk_rebias;
507 bool _attempt_rebias_of_object;
509 public:
510 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
511 bool bulk_rebias,
512 bool attempt_rebias_of_object)
513 : VM_RevokeBias(obj, requesting_thread)
514 , _bulk_rebias(bulk_rebias)
515 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
517 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
518 virtual bool doit_prologue() { return true; }
520 virtual void doit() {
521 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
522 clean_up_cached_monitor_info();
523 }
524 };
527 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
528 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
530 // We can revoke the biases of anonymously-biased objects
531 // efficiently enough that we should not cause these revocations to
532 // update the heuristics because doing so may cause unwanted bulk
533 // revocations (which are expensive) to occur.
534 markOop mark = obj->mark();
535 if (mark->is_biased_anonymously() && !attempt_rebias) {
536 // We are probably trying to revoke the bias of this object due to
537 // an identity hash code computation. Try to revoke the bias
538 // without a safepoint. This is possible if we can successfully
539 // compare-and-exchange an unbiased header into the mark word of
540 // the object, meaning that no other thread has raced to acquire
541 // the bias of the object.
542 markOop biased_value = mark;
543 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
544 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
545 if (res_mark == biased_value) {
546 return BIAS_REVOKED;
547 }
548 } else if (mark->has_bias_pattern()) {
549 Klass* k = Klass::cast(obj->klass());
550 markOop prototype_header = k->prototype_header();
551 if (!prototype_header->has_bias_pattern()) {
552 // This object has a stale bias from before the bulk revocation
553 // for this data type occurred. It's pointless to update the
554 // heuristics at this point so simply update the header with a
555 // CAS. If we fail this race, the object's bias has been revoked
556 // by another thread so we simply return and let the caller deal
557 // with it.
558 markOop biased_value = mark;
559 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark);
560 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked");
561 return BIAS_REVOKED;
562 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
563 // The epoch of this biasing has expired indicating that the
564 // object is effectively unbiased. Depending on whether we need
565 // to rebias or revoke the bias of this object we can do it
566 // efficiently enough with a CAS that we shouldn't update the
567 // heuristics. This is normally done in the assembly code but we
568 // can reach this point due to various points in the runtime
569 // needing to revoke biases.
570 if (attempt_rebias) {
571 assert(THREAD->is_Java_thread(), "");
572 markOop biased_value = mark;
573 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
574 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark);
575 if (res_mark == biased_value) {
576 return BIAS_REVOKED_AND_REBIASED;
577 }
578 } else {
579 markOop biased_value = mark;
580 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
581 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
582 if (res_mark == biased_value) {
583 return BIAS_REVOKED;
584 }
585 }
586 }
587 }
589 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
590 if (heuristics == HR_NOT_BIASED) {
591 return NOT_BIASED;
592 } else if (heuristics == HR_SINGLE_REVOKE) {
593 Klass *k = Klass::cast(obj->klass());
594 markOop prototype_header = k->prototype_header();
595 if (mark->biased_locker() == THREAD &&
596 prototype_header->bias_epoch() == mark->bias_epoch()) {
597 // A thread is trying to revoke the bias of an object biased
598 // toward it, again likely due to an identity hash code
599 // computation. We can again avoid a safepoint in this case
600 // since we are only going to walk our own stack. There are no
601 // races with revocations occurring in other threads because we
602 // reach no safepoints in the revocation path.
603 // Also check the epoch because even if threads match, another thread
604 // can come in with a CAS to steal the bias of an object that has a
605 // stale epoch.
606 ResourceMark rm;
607 if (TraceBiasedLocking) {
608 tty->print_cr("Revoking bias by walking my own stack:");
609 }
610 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD);
611 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
612 assert(cond == BIAS_REVOKED, "why not?");
613 return cond;
614 } else {
615 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
616 VMThread::execute(&revoke);
617 return revoke.status_code();
618 }
619 }
621 assert((heuristics == HR_BULK_REVOKE) ||
622 (heuristics == HR_BULK_REBIAS), "?");
623 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
624 (heuristics == HR_BULK_REBIAS),
625 attempt_rebias);
626 VMThread::execute(&bulk_revoke);
627 return bulk_revoke.status_code();
628 }
631 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
632 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
633 if (objs->length() == 0) {
634 return;
635 }
636 VM_RevokeBias revoke(objs, JavaThread::current());
637 VMThread::execute(&revoke);
638 }
641 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
642 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
643 oop obj = h_obj();
644 HeuristicsResult heuristics = update_heuristics(obj, false);
645 if (heuristics == HR_SINGLE_REVOKE) {
646 revoke_bias(obj, false, false, NULL);
647 } else if ((heuristics == HR_BULK_REBIAS) ||
648 (heuristics == HR_BULK_REVOKE)) {
649 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
650 }
651 clean_up_cached_monitor_info();
652 }
655 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
656 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
657 int len = objs->length();
658 for (int i = 0; i < len; i++) {
659 oop obj = (objs->at(i))();
660 HeuristicsResult heuristics = update_heuristics(obj, false);
661 if (heuristics == HR_SINGLE_REVOKE) {
662 revoke_bias(obj, false, false, NULL);
663 } else if ((heuristics == HR_BULK_REBIAS) ||
664 (heuristics == HR_BULK_REVOKE)) {
665 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
666 }
667 }
668 clean_up_cached_monitor_info();
669 }
672 void BiasedLocking::preserve_marks() {
673 if (!UseBiasedLocking)
674 return;
676 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
678 assert(_preserved_oop_stack == NULL, "double initialization");
679 assert(_preserved_mark_stack == NULL, "double initialization");
681 // In order to reduce the number of mark words preserved during GC
682 // due to the presence of biased locking, we reinitialize most mark
683 // words to the class's prototype during GC -- even those which have
684 // a currently valid bias owner. One important situation where we
685 // must not clobber a bias is when a biased object is currently
686 // locked. To handle this case we iterate over the currently-locked
687 // monitors in a prepass and, if they are biased, preserve their
688 // mark words here. This should be a relatively small set of objects
689 // especially compared to the number of objects in the heap.
690 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true);
691 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
693 ResourceMark rm;
694 Thread* cur = Thread::current();
695 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) {
696 if (thread->has_last_Java_frame()) {
697 RegisterMap rm(thread);
698 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
699 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
700 if (monitors != NULL) {
701 int len = monitors->length();
702 // Walk monitors youngest to oldest
703 for (int i = len - 1; i >= 0; i--) {
704 MonitorInfo* mon_info = monitors->at(i);
705 if (mon_info->owner_is_scalar_replaced()) continue;
706 oop owner = mon_info->owner();
707 if (owner != NULL) {
708 markOop mark = owner->mark();
709 if (mark->has_bias_pattern()) {
710 _preserved_oop_stack->push(Handle(cur, owner));
711 _preserved_mark_stack->push(mark);
712 }
713 }
714 }
715 }
716 }
717 }
718 }
719 }
722 void BiasedLocking::restore_marks() {
723 if (!UseBiasedLocking)
724 return;
726 assert(_preserved_oop_stack != NULL, "double free");
727 assert(_preserved_mark_stack != NULL, "double free");
729 int len = _preserved_oop_stack->length();
730 for (int i = 0; i < len; i++) {
731 Handle owner = _preserved_oop_stack->at(i);
732 markOop mark = _preserved_mark_stack->at(i);
733 owner->set_mark(mark);
734 }
736 delete _preserved_oop_stack;
737 _preserved_oop_stack = NULL;
738 delete _preserved_mark_stack;
739 _preserved_mark_stack = NULL;
740 }
743 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
744 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
745 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
746 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
747 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
748 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
749 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
752 // BiasedLockingCounters
754 int BiasedLockingCounters::slow_path_entry_count() {
755 if (_slow_path_entry_count != 0) {
756 return _slow_path_entry_count;
757 }
758 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
759 _rebiased_lock_entry_count + _revoked_lock_entry_count +
760 _fast_path_entry_count;
762 return _total_entry_count - sum;
763 }
765 void BiasedLockingCounters::print_on(outputStream* st) {
766 tty->print_cr("# total entries: %d", _total_entry_count);
767 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
768 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
769 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
770 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
771 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
772 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
773 }