1 /*
2 * Copyright (c) 2005, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "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"
34 #include "trace/tracing.hpp"
35
36 static bool _biased_locking_enabled = false;
37 BiasedLockingCounters BiasedLocking::_counters;
38
39 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
40 static GrowableArray<markOop>* _preserved_mark_stack = NULL;
41
42 static void enable_biased_locking(Klass* k) {
43 k->set_prototype_header(markOopDesc::biased_locking_prototype());
44 }
45
46 class VM_EnableBiasedLocking: public VM_Operation {
47 private:
48 bool _is_cheap_allocated;
49 public:
50 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; }
51 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
52 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; }
53 bool is_cheap_allocated() const { return _is_cheap_allocated; }
54
55 void doit() {
56 // Iterate the system dictionary enabling biased locking for all
57 // currently loaded classes
58 SystemDictionary::classes_do(enable_biased_locking);
59 // Indicate that future instances should enable it as well
60 _biased_locking_enabled = true;
61
62 if (TraceBiasedLocking) {
63 tty->print_cr("Biased locking enabled");
64 }
65 }
66
67 bool allow_nested_vm_operations() const { return false; }
68 };
69
70
71 // One-shot PeriodicTask subclass for enabling biased locking
72 class EnableBiasedLockingTask : public PeriodicTask {
73 public:
74 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {}
75
76 virtual void task() {
77 // Use async VM operation to avoid blocking the Watcher thread.
78 // VM Thread will free C heap storage.
79 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true);
80 VMThread::execute(op);
81
82 // Reclaim our storage and disenroll ourself
83 delete this;
84 }
85 };
86
87
88 void BiasedLocking::init() {
89 // If biased locking is enabled, schedule a task to fire a few
90 // seconds into the run which turns on biased locking for all
91 // currently loaded classes as well as future ones. This is a
92 // workaround for startup time regressions due to a large number of
93 // safepoints being taken during VM startup for bias revocation.
94 // Ideally we would have a lower cost for individual bias revocation
95 // and not need a mechanism like this.
96 if (UseBiasedLocking) {
97 if (BiasedLockingStartupDelay > 0) {
98 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
99 task->enroll();
100 } else {
101 VM_EnableBiasedLocking op(false);
102 VMThread::execute(&op);
103 }
104 }
105 }
106
107
108 bool BiasedLocking::enabled() {
109 return _biased_locking_enabled;
110 }
111
112 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
113 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
114 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
115 if (info != NULL) {
116 return info;
117 }
118
119 info = new GrowableArray<MonitorInfo*>();
120
121 // It's possible for the thread to not have any Java frames on it,
122 // i.e., if it's the main thread and it's already returned from main()
123 if (thread->has_last_Java_frame()) {
124 RegisterMap rm(thread);
125 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
126 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
127 if (monitors != NULL) {
128 int len = monitors->length();
129 // Walk monitors youngest to oldest
130 for (int i = len - 1; i >= 0; i--) {
131 MonitorInfo* mon_info = monitors->at(i);
132 if (mon_info->eliminated()) continue;
133 oop owner = mon_info->owner();
134 if (owner != NULL) {
135 info->append(mon_info);
136 }
137 }
138 }
139 }
140 }
141
142 thread->set_cached_monitor_info(info);
143 return info;
144 }
145
146
147 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) {
148 markOop mark = obj->mark();
149 if (!mark->has_bias_pattern()) {
150 if (TraceBiasedLocking) {
151 ResourceMark rm;
152 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)",
153 obj->klass()->external_name());
154 }
155 return BiasedLocking::NOT_BIASED;
156 }
157
158 uint age = mark->age();
159 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
160 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
161
162 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
163 ResourceMark rm;
164 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,
165 p2i((void *)obj), (intptr_t) mark, obj->klass()->external_name(), (intptr_t) obj->klass()->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread);
166 }
167
168 JavaThread* biased_thread = mark->biased_locker();
169 if (biased_thread == NULL) {
170 // Object is anonymously biased. We can get here if, for
171 // example, we revoke the bias due to an identity hash code
172 // being computed for an object.
173 if (!allow_rebias) {
174 obj->set_mark(unbiased_prototype);
175 }
176 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
177 tty->print_cr(" Revoked bias of anonymously-biased object");
178 }
179 return BiasedLocking::BIAS_REVOKED;
180 }
181
182 // Handle case where the thread toward which the object was biased has exited
183 bool thread_is_alive = false;
184 if (requesting_thread == biased_thread) {
185 thread_is_alive = true;
186 } else {
187 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) {
188 if (cur_thread == biased_thread) {
189 thread_is_alive = true;
190 break;
191 }
192 }
193 }
194 if (!thread_is_alive) {
195 if (allow_rebias) {
196 obj->set_mark(biased_prototype);
197 } else {
198 obj->set_mark(unbiased_prototype);
199 }
200 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
201 tty->print_cr(" Revoked bias of object biased toward dead thread");
202 }
203 return BiasedLocking::BIAS_REVOKED;
204 }
205
206 // Thread owning bias is alive.
207 // Check to see whether it currently owns the lock and, if so,
208 // write down the needed displaced headers to the thread's stack.
209 // Otherwise, restore the object's header either to the unlocked
210 // or unbiased state.
211 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
212 BasicLock* highest_lock = NULL;
213 for (int i = 0; i < cached_monitor_info->length(); i++) {
214 MonitorInfo* mon_info = cached_monitor_info->at(i);
215 if (mon_info->owner() == obj) {
216 if (TraceBiasedLocking && Verbose) {
217 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
218 p2i((void *) mon_info->owner()),
219 p2i((void *) obj));
220 }
221 // Assume recursive case and fix up highest lock later
222 markOop mark = markOopDesc::encode((BasicLock*) NULL);
223 highest_lock = mon_info->lock();
224 highest_lock->set_displaced_header(mark);
225 } else {
226 if (TraceBiasedLocking && Verbose) {
227 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
228 p2i((void *) mon_info->owner()),
229 p2i((void *) obj));
230 }
231 }
232 }
233 if (highest_lock != NULL) {
234 // Fix up highest lock to contain displaced header and point
235 // object at it
236 highest_lock->set_displaced_header(unbiased_prototype);
237 // Reset object header to point to displaced mark.
238 // Must release storing the lock address for platforms without TSO
239 // ordering (e.g. ppc).
240 obj->release_set_mark(markOopDesc::encode(highest_lock));
241 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
242 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
243 tty->print_cr(" Revoked bias of currently-locked object");
244 }
245 } else {
246 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
247 tty->print_cr(" Revoked bias of currently-unlocked object");
248 }
249 if (allow_rebias) {
250 obj->set_mark(biased_prototype);
251 } else {
252 // Store the unlocked value into the object's header.
253 obj->set_mark(unbiased_prototype);
254 }
255 }
256
257 // If requested, return information on which thread held the bias
258 if (EnableJFR && biased_locker != NULL) {
259 *biased_locker = biased_thread;
260 }
261
262 return BiasedLocking::BIAS_REVOKED;
263 }
264
265
266 enum HeuristicsResult {
267 HR_NOT_BIASED = 1,
268 HR_SINGLE_REVOKE = 2,
269 HR_BULK_REBIAS = 3,
270 HR_BULK_REVOKE = 4
271 };
272
273
274 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
275 markOop mark = o->mark();
276 if (!mark->has_bias_pattern()) {
277 return HR_NOT_BIASED;
278 }
279
280 // Heuristics to attempt to throttle the number of revocations.
281 // Stages:
282 // 1. Revoke the biases of all objects in the heap of this type,
283 // but allow rebiasing of those objects if unlocked.
284 // 2. Revoke the biases of all objects in the heap of this type
285 // and don't allow rebiasing of these objects. Disable
286 // allocation of objects of that type with the bias bit set.
287 Klass* k = o->klass();
288 jlong cur_time = os::javaTimeMillis();
289 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
290 int revocation_count = k->biased_lock_revocation_count();
291 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
292 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
293 (last_bulk_revocation_time != 0) &&
294 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
295 // This is the first revocation we've seen in a while of an
296 // object of this type since the last time we performed a bulk
297 // rebiasing operation. The application is allocating objects in
298 // bulk which are biased toward a thread and then handing them
299 // off to another thread. We can cope with this allocation
300 // pattern via the bulk rebiasing mechanism so we reset the
301 // klass's revocation count rather than allow it to increase
302 // monotonically. If we see the need to perform another bulk
303 // rebias operation later, we will, and if subsequently we see
304 // many more revocation operations in a short period of time we
305 // will completely disable biasing for this type.
306 k->set_biased_lock_revocation_count(0);
307 revocation_count = 0;
308 }
309
310 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
311 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
312 revocation_count = k->atomic_incr_biased_lock_revocation_count();
313 }
314
315 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
316 return HR_BULK_REVOKE;
317 }
318
319 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
320 return HR_BULK_REBIAS;
321 }
322
323 return HR_SINGLE_REVOKE;
324 }
325
326
327 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
328 bool bulk_rebias,
329 bool attempt_rebias_of_object,
330 JavaThread* requesting_thread) {
331 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
332
333 if (TraceBiasedLocking) {
334 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object "
335 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
336 (bulk_rebias ? "rebias" : "revoke"),
337 p2i((void *) o), (intptr_t) o->mark(), o->klass()->external_name());
338 }
339
340 jlong cur_time = os::javaTimeMillis();
341 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
342
343
344 Klass* k_o = o->klass();
345 Klass* klass = k_o;
346
347 if (bulk_rebias) {
348 // Use the epoch in the klass of the object to implicitly revoke
349 // all biases of objects of this data type and force them to be
350 // reacquired. However, we also need to walk the stacks of all
351 // threads and update the headers of lightweight locked objects
352 // with biases to have the current epoch.
353
354 // If the prototype header doesn't have the bias pattern, don't
355 // try to update the epoch -- assume another VM operation came in
356 // and reset the header to the unbiased state, which will
357 // implicitly cause all existing biases to be revoked
358 if (klass->prototype_header()->has_bias_pattern()) {
359 int prev_epoch = klass->prototype_header()->bias_epoch();
360 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
361 int cur_epoch = klass->prototype_header()->bias_epoch();
362
363 // Now walk all threads' stacks and adjust epochs of any biased
364 // and locked objects of this data type we encounter
365 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
366 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
367 for (int i = 0; i < cached_monitor_info->length(); i++) {
368 MonitorInfo* mon_info = cached_monitor_info->at(i);
369 oop owner = mon_info->owner();
370 markOop mark = owner->mark();
371 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
372 // We might have encountered this object already in the case of recursive locking
373 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
374 owner->set_mark(mark->set_bias_epoch(cur_epoch));
375 }
376 }
377 }
378 }
379
380 // At this point we're done. All we have to do is potentially
381 // adjust the header of the given object to revoke its bias.
382 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread, NULL);
383 } else {
384 if (TraceBiasedLocking) {
385 ResourceMark rm;
386 tty->print_cr("* Disabling biased locking for type %s", klass->external_name());
387 }
388
389 // Disable biased locking for this data type. Not only will this
390 // cause future instances to not be biased, but existing biased
391 // instances will notice that this implicitly caused their biases
392 // to be revoked.
393 klass->set_prototype_header(markOopDesc::prototype());
394
395 // Now walk all threads' stacks and forcibly revoke the biases of
396 // any locked and biased objects of this data type we encounter.
397 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
398 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
399 for (int i = 0; i < cached_monitor_info->length(); i++) {
400 MonitorInfo* mon_info = cached_monitor_info->at(i);
401 oop owner = mon_info->owner();
402 markOop mark = owner->mark();
403 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
404 revoke_bias(owner, false, true, requesting_thread, NULL);
405 }
406 }
407 }
408
409 // Must force the bias of the passed object to be forcibly revoked
410 // as well to ensure guarantees to callers
411 revoke_bias(o, false, true, requesting_thread, NULL);
412 }
413
414 if (TraceBiasedLocking) {
415 tty->print_cr("* Ending bulk revocation");
416 }
417
418 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
419
420 if (attempt_rebias_of_object &&
421 o->mark()->has_bias_pattern() &&
422 klass->prototype_header()->has_bias_pattern()) {
423 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
424 klass->prototype_header()->bias_epoch());
425 o->set_mark(new_mark);
426 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
427 if (TraceBiasedLocking) {
428 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
429 }
430 }
431
432 assert(!o->mark()->has_bias_pattern() ||
433 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
434 "bug in bulk bias revocation");
435
436 return status_code;
437 }
438
439
440 static void clean_up_cached_monitor_info() {
441 // Walk the thread list clearing out the cached monitors
442 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
443 thr->set_cached_monitor_info(NULL);
444 }
445 }
446
447
448 class VM_RevokeBias : public VM_Operation {
449 protected:
450 Handle* _obj;
451 GrowableArray<Handle>* _objs;
452 JavaThread* _requesting_thread;
453 BiasedLocking::Condition _status_code;
454 traceid _biased_locker_id;
455
456 public:
457 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
458 : _obj(obj)
459 , _objs(NULL)
460 , _requesting_thread(requesting_thread)
461 , _status_code(BiasedLocking::NOT_BIASED)
462 , _biased_locker_id(0) {}
463
464 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
465 : _obj(NULL)
466 , _objs(objs)
467 , _requesting_thread(requesting_thread)
468 , _status_code(BiasedLocking::NOT_BIASED)
469 , _biased_locker_id(0) {}
470
471 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
472
473 virtual bool doit_prologue() {
474 // Verify that there is actual work to do since the callers just
475 // give us locked object(s). If we don't find any biased objects
476 // there is nothing to do and we avoid a safepoint.
477 if (_obj != NULL) {
478 markOop mark = (*_obj)()->mark();
479 if (mark->has_bias_pattern()) {
480 return true;
481 }
482 } else {
483 for ( int i = 0 ; i < _objs->length(); i++ ) {
484 markOop mark = (_objs->at(i))()->mark();
485 if (mark->has_bias_pattern()) {
486 return true;
487 }
488 }
489 }
490 return false;
491 }
492
493 virtual void doit() {
494 if (_obj != NULL) {
495 if (TraceBiasedLocking) {
496 tty->print_cr("Revoking bias with potentially per-thread safepoint:");
497 }
498 JavaThread* biased_locker = NULL;
499 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread, &biased_locker);
500 if (biased_locker != NULL) {
501 _biased_locker_id = THREAD_TRACE_ID(biased_locker);
502 }
503 clean_up_cached_monitor_info();
504 return;
505 } else {
506 if (TraceBiasedLocking) {
507 tty->print_cr("Revoking bias with global safepoint:");
508 }
509 BiasedLocking::revoke_at_safepoint(_objs);
510 }
511 }
512
513 BiasedLocking::Condition status_code() const {
514 return _status_code;
515 }
516
517 traceid biased_locker() const {
518 return _biased_locker_id;
519 }
520 };
521
522
523 class VM_BulkRevokeBias : public VM_RevokeBias {
524 private:
525 bool _bulk_rebias;
526 bool _attempt_rebias_of_object;
527
528 public:
529 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
530 bool bulk_rebias,
531 bool attempt_rebias_of_object)
532 : VM_RevokeBias(obj, requesting_thread)
533 , _bulk_rebias(bulk_rebias)
534 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
535
536 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
537 virtual bool doit_prologue() { return true; }
538
539 virtual void doit() {
540 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
541 clean_up_cached_monitor_info();
542 }
543 };
544
545
546 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
547 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
548
549 // We can revoke the biases of anonymously-biased objects
550 // efficiently enough that we should not cause these revocations to
551 // update the heuristics because doing so may cause unwanted bulk
552 // revocations (which are expensive) to occur.
553 markOop mark = obj->mark();
554 if (mark->is_biased_anonymously() && !attempt_rebias) {
555 // We are probably trying to revoke the bias of this object due to
556 // an identity hash code computation. Try to revoke the bias
557 // without a safepoint. This is possible if we can successfully
558 // compare-and-exchange an unbiased header into the mark word of
559 // the object, meaning that no other thread has raced to acquire
560 // the bias of the object.
561 markOop biased_value = mark;
562 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
563 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
564 if (res_mark == biased_value) {
565 return BIAS_REVOKED;
566 }
567 } else if (mark->has_bias_pattern()) {
568 Klass* k = obj->klass();
569 markOop prototype_header = k->prototype_header();
570 if (!prototype_header->has_bias_pattern()) {
571 // This object has a stale bias from before the bulk revocation
572 // for this data type occurred. It's pointless to update the
573 // heuristics at this point so simply update the header with a
574 // CAS. If we fail this race, the object's bias has been revoked
575 // by another thread so we simply return and let the caller deal
576 // with it.
577 markOop biased_value = mark;
578 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark);
579 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked");
580 return BIAS_REVOKED;
581 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
582 // The epoch of this biasing has expired indicating that the
583 // object is effectively unbiased. Depending on whether we need
584 // to rebias or revoke the bias of this object we can do it
585 // efficiently enough with a CAS that we shouldn't update the
586 // heuristics. This is normally done in the assembly code but we
587 // can reach this point due to various points in the runtime
588 // needing to revoke biases.
589 if (attempt_rebias) {
590 assert(THREAD->is_Java_thread(), "");
591 markOop biased_value = mark;
592 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
593 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark);
594 if (res_mark == biased_value) {
595 return BIAS_REVOKED_AND_REBIASED;
596 }
597 } else {
598 markOop biased_value = mark;
599 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
600 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
601 if (res_mark == biased_value) {
602 return BIAS_REVOKED;
603 }
604 }
605 }
606 }
607
608 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
609 if (heuristics == HR_NOT_BIASED) {
610 return NOT_BIASED;
611 } else if (heuristics == HR_SINGLE_REVOKE) {
612 Klass *k = obj->klass();
613 markOop prototype_header = k->prototype_header();
614 if (mark->biased_locker() == THREAD &&
615 prototype_header->bias_epoch() == mark->bias_epoch()) {
616 // A thread is trying to revoke the bias of an object biased
617 // toward it, again likely due to an identity hash code
618 // computation. We can again avoid a safepoint in this case
619 // since we are only going to walk our own stack. There are no
620 // races with revocations occurring in other threads because we
621 // reach no safepoints in the revocation path.
622 // Also check the epoch because even if threads match, another thread
623 // can come in with a CAS to steal the bias of an object that has a
624 // stale epoch.
625 ResourceMark rm;
626 if (TraceBiasedLocking) {
627 tty->print_cr("Revoking bias by walking my own stack:");
628 }
629 EventBiasedLockSelfRevocation event;
630 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD, NULL);
631 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
632 assert(cond == BIAS_REVOKED, "why not?");
633 if (event.should_commit()) {
634 event.set_lockClass(k);
635 event.commit();
636 }
637 return cond;
638 } else {
639 EventBiasedLockRevocation event;
640 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
641 VMThread::execute(&revoke);
642 if (event.should_commit() && (revoke.status_code() != NOT_BIASED)) {
643 event.set_lockClass(k);
644 // Subtract 1 to match the id of events committed inside the safepoint
645 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1);
646 event.set_previousOwner(revoke.biased_locker());
647 event.commit();
648 }
649 return revoke.status_code();
650 }
651 }
652
653 assert((heuristics == HR_BULK_REVOKE) ||
654 (heuristics == HR_BULK_REBIAS), "?");
655 EventBiasedLockClassRevocation event;
656 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
657 (heuristics == HR_BULK_REBIAS),
658 attempt_rebias);
659 VMThread::execute(&bulk_revoke);
660 if (event.should_commit()) {
661 event.set_revokedClass(obj->klass());
662 event.set_disableBiasing((heuristics != HR_BULK_REBIAS));
663 // Subtract 1 to match the id of events committed inside the safepoint
664 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1);
665 event.commit();
666 }
667 return bulk_revoke.status_code();
668 }
669
670
671 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
672 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
673 if (objs->length() == 0) {
674 return;
675 }
676 VM_RevokeBias revoke(objs, JavaThread::current());
677 VMThread::execute(&revoke);
678 }
679
680
681 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
682 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
683 oop obj = h_obj();
684 HeuristicsResult heuristics = update_heuristics(obj, false);
685 if (heuristics == HR_SINGLE_REVOKE) {
686 revoke_bias(obj, false, false, NULL, NULL);
687 } else if ((heuristics == HR_BULK_REBIAS) ||
688 (heuristics == HR_BULK_REVOKE)) {
689 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
690 }
691 clean_up_cached_monitor_info();
692 }
693
694
695 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
696 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
697 int len = objs->length();
698 for (int i = 0; i < len; i++) {
699 oop obj = (objs->at(i))();
700 HeuristicsResult heuristics = update_heuristics(obj, false);
701 if (heuristics == HR_SINGLE_REVOKE) {
702 revoke_bias(obj, false, false, NULL, NULL);
703 } else if ((heuristics == HR_BULK_REBIAS) ||
704 (heuristics == HR_BULK_REVOKE)) {
705 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
706 }
707 }
708 clean_up_cached_monitor_info();
709 }
710
711
712 void BiasedLocking::preserve_marks() {
713 if (!UseBiasedLocking)
714 return;
715
716 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
717
718 assert(_preserved_oop_stack == NULL, "double initialization");
719 assert(_preserved_mark_stack == NULL, "double initialization");
720
721 // In order to reduce the number of mark words preserved during GC
722 // due to the presence of biased locking, we reinitialize most mark
723 // words to the class's prototype during GC -- even those which have
724 // a currently valid bias owner. One important situation where we
725 // must not clobber a bias is when a biased object is currently
726 // locked. To handle this case we iterate over the currently-locked
727 // monitors in a prepass and, if they are biased, preserve their
728 // mark words here. This should be a relatively small set of objects
729 // especially compared to the number of objects in the heap.
730 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true);
731 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
732
733 ResourceMark rm;
734 Thread* cur = Thread::current();
735 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) {
736 if (thread->has_last_Java_frame()) {
737 RegisterMap rm(thread);
738 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
739 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
740 if (monitors != NULL) {
741 int len = monitors->length();
742 // Walk monitors youngest to oldest
743 for (int i = len - 1; i >= 0; i--) {
744 MonitorInfo* mon_info = monitors->at(i);
745 if (mon_info->owner_is_scalar_replaced()) continue;
746 oop owner = mon_info->owner();
747 if (owner != NULL) {
748 markOop mark = owner->mark();
749 if (mark->has_bias_pattern()) {
750 _preserved_oop_stack->push(Handle(cur, owner));
751 _preserved_mark_stack->push(mark);
752 }
753 }
754 }
755 }
756 }
757 }
758 }
759 }
760
761
762 void BiasedLocking::restore_marks() {
763 if (!UseBiasedLocking)
764 return;
765
766 assert(_preserved_oop_stack != NULL, "double free");
767 assert(_preserved_mark_stack != NULL, "double free");
768
769 int len = _preserved_oop_stack->length();
770 for (int i = 0; i < len; i++) {
771 Handle owner = _preserved_oop_stack->at(i);
772 markOop mark = _preserved_mark_stack->at(i);
773 owner->set_mark(mark);
774 }
775
776 delete _preserved_oop_stack;
777 _preserved_oop_stack = NULL;
778 delete _preserved_mark_stack;
779 _preserved_mark_stack = NULL;
780 }
781
782
783 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
784 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
785 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
786 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
787 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
788 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
789 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
790
791
792 // BiasedLockingCounters
793
794 int BiasedLockingCounters::slow_path_entry_count() {
795 if (_slow_path_entry_count != 0) {
796 return _slow_path_entry_count;
797 }
798 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
799 _rebiased_lock_entry_count + _revoked_lock_entry_count +
800 _fast_path_entry_count;
801
802 return _total_entry_count - sum;
803 }
804
805 void BiasedLockingCounters::print_on(outputStream* st) {
806 tty->print_cr("# total entries: %d", _total_entry_count);
807 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
808 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
809 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
810 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
811 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
812 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
813 }