1 /*
2 * Copyright (c) 2005, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "oops/klass.inline.hpp"
27 #include "oops/markOop.hpp"
28 #include "oops/oop.inline.hpp"
29 #include "runtime/atomic.inline.hpp"
30 #include "runtime/basicLock.hpp"
31 #include "runtime/biasedLocking.hpp"
32 #include "runtime/task.hpp"
33 #include "runtime/vframe.hpp"
34 #include "runtime/vmThread.hpp"
35 #include "runtime/vm_operations.hpp"
36
37 static bool _biased_locking_enabled = false;
38 BiasedLockingCounters BiasedLocking::_counters;
39
40 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
41 static GrowableArray<markOop>* _preserved_mark_stack = NULL;
42
43 static void enable_biased_locking(Klass* k) {
44 k->set_prototype_header(markOopDesc::biased_locking_prototype());
45 }
46
47 class VM_EnableBiasedLocking: public VM_Operation {
48 private:
49 bool _is_cheap_allocated;
50 public:
51 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; }
52 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
53 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; }
54 bool is_cheap_allocated() const { return _is_cheap_allocated; }
55
56 void doit() {
57 // Iterate the system dictionary enabling biased locking for all
58 // currently loaded classes
59 SystemDictionary::classes_do(enable_biased_locking);
60 // Indicate that future instances should enable it as well
61 _biased_locking_enabled = true;
62
63 if (TraceBiasedLocking) {
64 tty->print_cr("Biased locking enabled");
65 }
66 }
67
68 bool allow_nested_vm_operations() const { return false; }
69 };
70
71
72 // One-shot PeriodicTask subclass for enabling biased locking
73 class EnableBiasedLockingTask : public PeriodicTask {
74 public:
75 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {}
76
77 virtual void task() {
78 // Use async VM operation to avoid blocking the Watcher thread.
79 // VM Thread will free C heap storage.
80 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true);
81 VMThread::execute(op);
82
83 // Reclaim our storage and disenroll ourself
84 delete this;
85 }
86 };
87
88
89 void BiasedLocking::init() {
90 // If biased locking is enabled, schedule a task to fire a few
91 // seconds into the run which turns on biased locking for all
92 // currently loaded classes as well as future ones. This is a
93 // workaround for startup time regressions due to a large number of
94 // safepoints being taken during VM startup for bias revocation.
95 // Ideally we would have a lower cost for individual bias revocation
96 // and not need a mechanism like this.
97 if (UseBiasedLocking) {
98 if (BiasedLockingStartupDelay > 0) {
99 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
100 task->enroll();
101 } else {
102 VM_EnableBiasedLocking op(false);
103 VMThread::execute(&op);
104 }
105 }
106 }
107
108
109 bool BiasedLocking::enabled() {
110 return _biased_locking_enabled;
111 }
112
113 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
114 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
115 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
116 if (info != NULL) {
117 return info;
118 }
119
120 info = new GrowableArray<MonitorInfo*>();
121
122 // It's possible for the thread to not have any Java frames on it,
123 // i.e., if it's the main thread and it's already returned from main()
124 if (thread->has_last_Java_frame()) {
125 RegisterMap rm(thread);
126 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
127 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
128 if (monitors != NULL) {
129 int len = monitors->length();
130 // Walk monitors youngest to oldest
131 for (int i = len - 1; i >= 0; i--) {
132 MonitorInfo* mon_info = monitors->at(i);
133 if (mon_info->eliminated()) continue;
134 oop owner = mon_info->owner();
135 if (owner != NULL) {
136 info->append(mon_info);
137 }
138 }
139 }
140 }
141 }
142
143 thread->set_cached_monitor_info(info);
144 return info;
145 }
146
147
148 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) {
149 assert(obj == oopDesc::bs()->resolve_oop(obj), "expect to-space copy");
150 markOop mark = obj->mark();
151 if (!mark->has_bias_pattern()) {
152 if (TraceBiasedLocking) {
153 ResourceMark rm;
154 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)",
155 obj->klass()->external_name());
156 }
157 return BiasedLocking::NOT_BIASED;
158 }
159
160 uint age = mark->age();
161 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
162 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
163
164 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
165 ResourceMark rm;
166 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,
167 p2i((void *)obj), (intptr_t) mark, obj->klass()->external_name(), (intptr_t) obj->klass()->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread);
168 }
169
170 JavaThread* biased_thread = mark->biased_locker();
171 if (biased_thread == NULL) {
172 // Object is anonymously biased. We can get here if, for
173 // example, we revoke the bias due to an identity hash code
174 // being computed for an object.
175 if (!allow_rebias) {
176 obj->set_mark(unbiased_prototype);
177 }
178 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
179 tty->print_cr(" Revoked bias of anonymously-biased object");
180 }
181 return BiasedLocking::BIAS_REVOKED;
182 }
183
184 // Handle case where the thread toward which the object was biased has exited
185 bool thread_is_alive = false;
186 if (requesting_thread == biased_thread) {
187 thread_is_alive = true;
188 } else {
189 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) {
190 if (cur_thread == biased_thread) {
191 thread_is_alive = true;
192 break;
193 }
194 }
195 }
196 if (!thread_is_alive) {
197 if (allow_rebias) {
198 obj->set_mark(biased_prototype);
199 } else {
200 obj->set_mark(unbiased_prototype);
201 }
202 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
203 tty->print_cr(" Revoked bias of object biased toward dead thread");
204 }
205 return BiasedLocking::BIAS_REVOKED;
206 }
207
208 // Thread owning bias is alive.
209 // Check to see whether it currently owns the lock and, if so,
210 // write down the needed displaced headers to the thread's stack.
211 // Otherwise, restore the object's header either to the unlocked
212 // or unbiased state.
213 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
214 BasicLock* highest_lock = NULL;
215 for (int i = 0; i < cached_monitor_info->length(); i++) {
216 MonitorInfo* mon_info = cached_monitor_info->at(i);
217 if (mon_info->owner() == obj) {
218 if (TraceBiasedLocking && Verbose) {
219 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
220 p2i((void *) mon_info->owner()),
221 p2i((void *) obj));
222 }
223 // Assume recursive case and fix up highest lock later
224 markOop mark = markOopDesc::encode((BasicLock*) NULL);
225 highest_lock = mon_info->lock();
226 highest_lock->set_displaced_header(mark);
227 } else {
228 if (TraceBiasedLocking && Verbose) {
229 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
230 p2i((void *) mon_info->owner()),
231 p2i((void *) obj));
232 }
233 }
234 }
235 if (highest_lock != NULL) {
236 // Fix up highest lock to contain displaced header and point
237 // object at it
238 highest_lock->set_displaced_header(unbiased_prototype);
239 // Reset object header to point to displaced mark.
240 // Must release storing the lock address for platforms without TSO
241 // ordering (e.g. ppc).
242 obj->release_set_mark(markOopDesc::encode(highest_lock));
243 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
244 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
245 tty->print_cr(" Revoked bias of currently-locked object");
246 }
247 } else {
248 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
249 tty->print_cr(" Revoked bias of currently-unlocked object");
250 }
251 if (allow_rebias) {
252 obj->set_mark(biased_prototype);
253 } else {
254 // Store the unlocked value into the object's header.
255 obj->set_mark(unbiased_prototype);
256 }
257 }
258
259 return BiasedLocking::BIAS_REVOKED;
260 }
261
262
263 enum HeuristicsResult {
264 HR_NOT_BIASED = 1,
265 HR_SINGLE_REVOKE = 2,
266 HR_BULK_REBIAS = 3,
267 HR_BULK_REVOKE = 4
268 };
269
270
271 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
272 markOop mark = o->mark();
273 if (!mark->has_bias_pattern()) {
274 return HR_NOT_BIASED;
275 }
276
277 // Heuristics to attempt to throttle the number of revocations.
278 // Stages:
279 // 1. Revoke the biases of all objects in the heap of this type,
280 // but allow rebiasing of those objects if unlocked.
281 // 2. Revoke the biases of all objects in the heap of this type
282 // and don't allow rebiasing of these objects. Disable
283 // allocation of objects of that type with the bias bit set.
284 Klass* k = o->klass();
285 jlong cur_time = os::javaTimeMillis();
286 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
287 int revocation_count = k->biased_lock_revocation_count();
288 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
289 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
290 (last_bulk_revocation_time != 0) &&
291 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
292 // This is the first revocation we've seen in a while of an
293 // object of this type since the last time we performed a bulk
294 // rebiasing operation. The application is allocating objects in
295 // bulk which are biased toward a thread and then handing them
296 // off to another thread. We can cope with this allocation
297 // pattern via the bulk rebiasing mechanism so we reset the
298 // klass's revocation count rather than allow it to increase
299 // monotonically. If we see the need to perform another bulk
300 // rebias operation later, we will, and if subsequently we see
301 // many more revocation operations in a short period of time we
302 // will completely disable biasing for this type.
303 k->set_biased_lock_revocation_count(0);
304 revocation_count = 0;
305 }
306
307 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
308 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
309 revocation_count = k->atomic_incr_biased_lock_revocation_count();
310 }
311
312 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
313 return HR_BULK_REVOKE;
314 }
315
316 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
317 return HR_BULK_REBIAS;
318 }
319
320 return HR_SINGLE_REVOKE;
321 }
322
323
324 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
325 bool bulk_rebias,
326 bool attempt_rebias_of_object,
327 JavaThread* requesting_thread) {
328 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
329 assert(o == oopDesc::bs()->resolve_oop(o), "expect to-space copy");
330 if (TraceBiasedLocking) {
331 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object "
332 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
333 (bulk_rebias ? "rebias" : "revoke"),
334 p2i((void *) o), (intptr_t) o->mark(), o->klass()->external_name());
335 }
336
337 jlong cur_time = os::javaTimeMillis();
338 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
339
340
341 Klass* k_o = o->klass();
342 Klass* klass = k_o;
343
344 if (bulk_rebias) {
345 // Use the epoch in the klass of the object to implicitly revoke
346 // all biases of objects of this data type and force them to be
347 // reacquired. However, we also need to walk the stacks of all
348 // threads and update the headers of lightweight locked objects
349 // with biases to have the current epoch.
350
351 // If the prototype header doesn't have the bias pattern, don't
352 // try to update the epoch -- assume another VM operation came in
353 // and reset the header to the unbiased state, which will
354 // implicitly cause all existing biases to be revoked
355 if (klass->prototype_header()->has_bias_pattern()) {
356 int prev_epoch = klass->prototype_header()->bias_epoch();
357 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
358 int cur_epoch = klass->prototype_header()->bias_epoch();
359
360 // Now walk all threads' stacks and adjust epochs of any biased
361 // and locked objects of this data type we encounter
362 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
363 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
364 for (int i = 0; i < cached_monitor_info->length(); i++) {
365 MonitorInfo* mon_info = cached_monitor_info->at(i);
366 oop owner = mon_info->owner();
367 markOop mark = owner->mark();
368 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
369 // We might have encountered this object already in the case of recursive locking
370 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
371 assert(owner == oopDesc::bs()->resolve_oop(owner), "expect to-space copy");
372 owner->set_mark(mark->set_bias_epoch(cur_epoch));
373 }
374 }
375 }
376 }
377
378 // At this point we're done. All we have to do is potentially
379 // adjust the header of the given object to revoke its bias.
380 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread);
381 } else {
382 if (TraceBiasedLocking) {
383 ResourceMark rm;
384 tty->print_cr("* Disabling biased locking for type %s", klass->external_name());
385 }
386
387 // Disable biased locking for this data type. Not only will this
388 // cause future instances to not be biased, but existing biased
389 // instances will notice that this implicitly caused their biases
390 // to be revoked.
391 klass->set_prototype_header(markOopDesc::prototype());
392
393 // Now walk all threads' stacks and forcibly revoke the biases of
394 // any locked and biased objects of this data type we encounter.
395 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
396 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
397 for (int i = 0; i < cached_monitor_info->length(); i++) {
398 MonitorInfo* mon_info = cached_monitor_info->at(i);
399 oop owner = mon_info->owner();
400 markOop mark = owner->mark();
401 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
402 revoke_bias(owner, false, true, requesting_thread);
403 }
404 }
405 }
406
407 // Must force the bias of the passed object to be forcibly revoked
408 // as well to ensure guarantees to callers
409 revoke_bias(o, false, true, requesting_thread);
410 }
411
412 if (TraceBiasedLocking) {
413 tty->print_cr("* Ending bulk revocation");
414 }
415
416 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
417
418 if (attempt_rebias_of_object &&
419 o->mark()->has_bias_pattern() &&
420 klass->prototype_header()->has_bias_pattern()) {
421 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
422 klass->prototype_header()->bias_epoch());
423 o->set_mark(new_mark);
424 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
425 if (TraceBiasedLocking) {
426 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
427 }
428 }
429
430 assert(!o->mark()->has_bias_pattern() ||
431 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
432 "bug in bulk bias revocation");
433
434 return status_code;
435 }
436
437
438 static void clean_up_cached_monitor_info() {
439 // Walk the thread list clearing out the cached monitors
440 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
441 thr->set_cached_monitor_info(NULL);
442 }
443 }
444
445
446 class VM_RevokeBias : public VM_Operation {
447 protected:
448 Handle* _obj;
449 GrowableArray<Handle>* _objs;
450 JavaThread* _requesting_thread;
451 BiasedLocking::Condition _status_code;
452
453 public:
454 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
455 : _obj(obj)
456 , _objs(NULL)
457 , _requesting_thread(requesting_thread)
458 , _status_code(BiasedLocking::NOT_BIASED) {}
459
460 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
461 : _obj(NULL)
462 , _objs(objs)
463 , _requesting_thread(requesting_thread)
464 , _status_code(BiasedLocking::NOT_BIASED) {}
465
466 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
467
468 virtual bool doit_prologue() {
469 // Verify that there is actual work to do since the callers just
470 // give us locked object(s). If we don't find any biased objects
471 // there is nothing to do and we avoid a safepoint.
472 if (_obj != NULL) {
473 markOop mark = (*_obj)()->mark();
474 if (mark->has_bias_pattern()) {
475 return true;
476 }
477 } else {
478 for ( int i = 0 ; i < _objs->length(); i++ ) {
479 markOop mark = (_objs->at(i))()->mark();
480 if (mark->has_bias_pattern()) {
481 return true;
482 }
483 }
484 }
485 return false;
486 }
487
488 virtual void doit() {
489 if (_obj != NULL) {
490 if (TraceBiasedLocking) {
491 tty->print_cr("Revoking bias with potentially per-thread safepoint:");
492 }
493 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread);
494 clean_up_cached_monitor_info();
495 return;
496 } else {
497 if (TraceBiasedLocking) {
498 tty->print_cr("Revoking bias with global safepoint:");
499 }
500 BiasedLocking::revoke_at_safepoint(_objs);
501 }
502 }
503
504 BiasedLocking::Condition status_code() const {
505 return _status_code;
506 }
507 };
508
509
510 class VM_BulkRevokeBias : public VM_RevokeBias {
511 private:
512 bool _bulk_rebias;
513 bool _attempt_rebias_of_object;
514
515 public:
516 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
517 bool bulk_rebias,
518 bool attempt_rebias_of_object)
519 : VM_RevokeBias(obj, requesting_thread)
520 , _bulk_rebias(bulk_rebias)
521 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
522
523 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
524 virtual bool doit_prologue() { return true; }
525
526 virtual void doit() {
527 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
528 clean_up_cached_monitor_info();
529 }
530 };
531
532
533 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
534 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
535
536 assert(obj() == oopDesc::bs()->resolve_oop(obj()), "must be to-space copy");
537
538 // We can revoke the biases of anonymously-biased objects
539 // efficiently enough that we should not cause these revocations to
540 // update the heuristics because doing so may cause unwanted bulk
541 // revocations (which are expensive) to occur.
542 markOop mark = obj->mark();
543 if (mark->is_biased_anonymously() && !attempt_rebias) {
544 // We are probably trying to revoke the bias of this object due to
545 // an identity hash code computation. Try to revoke the bias
546 // without a safepoint. This is possible if we can successfully
547 // compare-and-exchange an unbiased header into the mark word of
548 // the object, meaning that no other thread has raced to acquire
549 // the bias of the object.
550 markOop biased_value = mark;
551 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
552 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
553 if (res_mark == biased_value) {
554 return BIAS_REVOKED;
555 }
556 } else if (mark->has_bias_pattern()) {
557 Klass* k = obj->klass();
558 markOop prototype_header = k->prototype_header();
559 if (!prototype_header->has_bias_pattern()) {
560 // This object has a stale bias from before the bulk revocation
561 // for this data type occurred. It's pointless to update the
562 // heuristics at this point so simply update the header with a
563 // CAS. If we fail this race, the object's bias has been revoked
564 // by another thread so we simply return and let the caller deal
565 // with it.
566 markOop biased_value = mark;
567 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark);
568 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked");
569 return BIAS_REVOKED;
570 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
571 // The epoch of this biasing has expired indicating that the
572 // object is effectively unbiased. Depending on whether we need
573 // to rebias or revoke the bias of this object we can do it
574 // efficiently enough with a CAS that we shouldn't update the
575 // heuristics. This is normally done in the assembly code but we
576 // can reach this point due to various points in the runtime
577 // needing to revoke biases.
578 if (attempt_rebias) {
579 assert(THREAD->is_Java_thread(), "");
580 markOop biased_value = mark;
581 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
582 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark);
583 if (res_mark == biased_value) {
584 return BIAS_REVOKED_AND_REBIASED;
585 }
586 } else {
587 markOop biased_value = mark;
588 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
589 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
590 if (res_mark == biased_value) {
591 return BIAS_REVOKED;
592 }
593 }
594 }
595 }
596
597 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
598 if (heuristics == HR_NOT_BIASED) {
599 return NOT_BIASED;
600 } else if (heuristics == HR_SINGLE_REVOKE) {
601 Klass *k = obj->klass();
602 markOop prototype_header = k->prototype_header();
603 if (mark->biased_locker() == THREAD &&
604 prototype_header->bias_epoch() == mark->bias_epoch()) {
605 // A thread is trying to revoke the bias of an object biased
606 // toward it, again likely due to an identity hash code
607 // computation. We can again avoid a safepoint in this case
608 // since we are only going to walk our own stack. There are no
609 // races with revocations occurring in other threads because we
610 // reach no safepoints in the revocation path.
611 // Also check the epoch because even if threads match, another thread
612 // can come in with a CAS to steal the bias of an object that has a
613 // stale epoch.
614 ResourceMark rm;
615 if (TraceBiasedLocking) {
616 tty->print_cr("Revoking bias by walking my own stack:");
617 }
618 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD);
619 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
620 assert(cond == BIAS_REVOKED, "why not?");
621 return cond;
622 } else {
623 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
624 VMThread::execute(&revoke);
625 return revoke.status_code();
626 }
627 }
628
629 assert((heuristics == HR_BULK_REVOKE) ||
630 (heuristics == HR_BULK_REBIAS), "?");
631 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
632 (heuristics == HR_BULK_REBIAS),
633 attempt_rebias);
634 VMThread::execute(&bulk_revoke);
635 return bulk_revoke.status_code();
636 }
637
638
639 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
640 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
641 if (objs->length() == 0) {
642 return;
643 }
644 VM_RevokeBias revoke(objs, JavaThread::current());
645 VMThread::execute(&revoke);
646 }
647
648
649 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
650 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
651 oop obj = h_obj();
652 assert(obj == oopDesc::bs()->resolve_oop(obj), "expect to-space copy");
653 HeuristicsResult heuristics = update_heuristics(obj, false);
654 if (heuristics == HR_SINGLE_REVOKE) {
655 revoke_bias(obj, false, false, NULL);
656 } else if ((heuristics == HR_BULK_REBIAS) ||
657 (heuristics == HR_BULK_REVOKE)) {
658 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
659 }
660 clean_up_cached_monitor_info();
661 }
662
663
664 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
665 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
666 int len = objs->length();
667 for (int i = 0; i < len; i++) {
668 oop obj = (objs->at(i))();
669 HeuristicsResult heuristics = update_heuristics(obj, false);
670 if (heuristics == HR_SINGLE_REVOKE) {
671 revoke_bias(obj, false, false, NULL);
672 } else if ((heuristics == HR_BULK_REBIAS) ||
673 (heuristics == HR_BULK_REVOKE)) {
674 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
675 }
676 }
677 clean_up_cached_monitor_info();
678 }
679
680
681 void BiasedLocking::preserve_marks() {
682 if (!UseBiasedLocking)
683 return;
684
685 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
686
687 assert(_preserved_oop_stack == NULL, "double initialization");
688 assert(_preserved_mark_stack == NULL, "double initialization");
689
690 // In order to reduce the number of mark words preserved during GC
691 // due to the presence of biased locking, we reinitialize most mark
692 // words to the class's prototype during GC -- even those which have
693 // a currently valid bias owner. One important situation where we
694 // must not clobber a bias is when a biased object is currently
695 // locked. To handle this case we iterate over the currently-locked
696 // monitors in a prepass and, if they are biased, preserve their
697 // mark words here. This should be a relatively small set of objects
698 // especially compared to the number of objects in the heap.
699 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true);
700 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
701
702 ResourceMark rm;
703 Thread* cur = Thread::current();
704 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) {
705 if (thread->has_last_Java_frame()) {
706 RegisterMap rm(thread);
707 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
708 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
709 if (monitors != NULL) {
710 int len = monitors->length();
711 // Walk monitors youngest to oldest
712 for (int i = len - 1; i >= 0; i--) {
713 MonitorInfo* mon_info = monitors->at(i);
714 if (mon_info->owner_is_scalar_replaced()) continue;
715 oop owner = mon_info->owner();
716 assert(owner == oopDesc::bs()->resolve_oop(owner), "expect to-space copy");
717 if (owner != NULL) {
718 markOop mark = owner->mark();
719 if (mark->has_bias_pattern()) {
720 _preserved_oop_stack->push(Handle(cur, owner));
721 _preserved_mark_stack->push(mark);
722 }
723 }
724 }
725 }
726 }
727 }
728 }
729 }
730
731
732 void BiasedLocking::restore_marks() {
733 if (!UseBiasedLocking)
734 return;
735
736 assert(_preserved_oop_stack != NULL, "double free");
737 assert(_preserved_mark_stack != NULL, "double free");
738
739 int len = _preserved_oop_stack->length();
740 for (int i = 0; i < len; i++) {
741 Handle owner = _preserved_oop_stack->at(i);
742 markOop mark = _preserved_mark_stack->at(i);
743 owner->set_mark(mark);
744 }
745
746 delete _preserved_oop_stack;
747 _preserved_oop_stack = NULL;
748 delete _preserved_mark_stack;
749 _preserved_mark_stack = NULL;
750 }
751
752
753 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
754 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
755 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
756 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
757 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
758 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
759 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
760
761
762 // BiasedLockingCounters
763
764 int BiasedLockingCounters::slow_path_entry_count() {
765 if (_slow_path_entry_count != 0) {
766 return _slow_path_entry_count;
767 }
768 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
769 _rebiased_lock_entry_count + _revoked_lock_entry_count +
770 _fast_path_entry_count;
771
772 return _total_entry_count - sum;
773 }
774
775 void BiasedLockingCounters::print_on(outputStream* st) {
776 tty->print_cr("# total entries: %d", _total_entry_count);
777 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
778 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
779 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
780 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
781 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
782 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
783 }