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 markOop mark = obj->mark();
150 if (!mark->has_bias_pattern()) {
151 if (TraceBiasedLocking) {
152 ResourceMark rm;
153 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)",
154 obj->klass()->external_name());
155 }
156 return BiasedLocking::NOT_BIASED;
157 }
158
159 uint age = mark->age();
160 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
161 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
162
163 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
164 ResourceMark rm;
165 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,
166 p2i((void *)obj), (intptr_t) mark, obj->klass()->external_name(), (intptr_t) obj->klass()->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread);
167 }
168
169 JavaThread* biased_thread = mark->biased_locker();
170 if (biased_thread == NULL) {
171 // Object is anonymously biased. We can get here if, for
172 // example, we revoke the bias due to an identity hash code
173 // being computed for an object.
174 if (!allow_rebias) {
175 obj->set_mark(unbiased_prototype);
176 }
177 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
178 tty->print_cr(" Revoked bias of anonymously-biased object");
179 }
180 return BiasedLocking::BIAS_REVOKED;
181 }
182
183 // Handle case where the thread toward which the object was biased has exited
184 bool thread_is_alive = false;
185 if (requesting_thread == biased_thread) {
186 thread_is_alive = true;
187 } else {
188 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) {
189 if (cur_thread == biased_thread) {
190 thread_is_alive = true;
191 break;
192 }
193 }
194 }
195 if (!thread_is_alive) {
196 if (allow_rebias) {
197 obj->set_mark(biased_prototype);
198 } else {
199 obj->set_mark(unbiased_prototype);
200 }
201 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
202 tty->print_cr(" Revoked bias of object biased toward dead thread");
203 }
204 return BiasedLocking::BIAS_REVOKED;
205 }
206
207 // Thread owning bias is alive.
208 // Check to see whether it currently owns the lock and, if so,
209 // write down the needed displaced headers to the thread's stack.
210 // Otherwise, restore the object's header either to the unlocked
211 // or unbiased state.
212 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
213 BasicLock* highest_lock = NULL;
214 for (int i = 0; i < cached_monitor_info->length(); i++) {
215 MonitorInfo* mon_info = cached_monitor_info->at(i);
216 if (mon_info->owner() == obj) {
217 if (TraceBiasedLocking && Verbose) {
218 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
219 p2i((void *) mon_info->owner()),
220 p2i((void *) obj));
221 }
222 // Assume recursive case and fix up highest lock later
223 markOop mark = markOopDesc::encode((BasicLock*) NULL);
224 highest_lock = mon_info->lock();
225 highest_lock->set_displaced_header(mark);
226 } else {
227 if (TraceBiasedLocking && Verbose) {
228 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
229 p2i((void *) mon_info->owner()),
230 p2i((void *) obj));
231 }
232 }
233 }
234 if (highest_lock != NULL) {
235 // Fix up highest lock to contain displaced header and point
236 // object at it
237 highest_lock->set_displaced_header(unbiased_prototype);
238 // Reset object header to point to displaced mark.
239 // Must release storing the lock address for platforms without TSO
240 // ordering (e.g. ppc).
241 obj->release_set_mark(markOopDesc::encode(highest_lock));
242 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
243 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
244 tty->print_cr(" Revoked bias of currently-locked object");
245 }
246 } else {
247 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
248 tty->print_cr(" Revoked bias of currently-unlocked object");
249 }
250 if (allow_rebias) {
251 obj->set_mark(biased_prototype);
252 } else {
253 // Store the unlocked value into the object's header.
254 obj->set_mark(unbiased_prototype);
255 }
256 }
257
258 return BiasedLocking::BIAS_REVOKED;
259 }
260
261
262 enum HeuristicsResult {
263 HR_NOT_BIASED = 1,
264 HR_SINGLE_REVOKE = 2,
265 HR_BULK_REBIAS = 3,
266 HR_BULK_REVOKE = 4
267 };
268
269
270 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
271 markOop mark = o->mark();
272 if (!mark->has_bias_pattern()) {
273 return HR_NOT_BIASED;
274 }
275
276 // Heuristics to attempt to throttle the number of revocations.
277 // Stages:
278 // 1. Revoke the biases of all objects in the heap of this type,
279 // but allow rebiasing of those objects if unlocked.
280 // 2. Revoke the biases of all objects in the heap of this type
281 // and don't allow rebiasing of these objects. Disable
282 // allocation of objects of that type with the bias bit set.
283 Klass* k = o->klass();
284 jlong cur_time = os::javaTimeMillis();
285 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
286 int revocation_count = k->biased_lock_revocation_count();
287 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
288 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
289 (last_bulk_revocation_time != 0) &&
290 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
291 // This is the first revocation we've seen in a while of an
292 // object of this type since the last time we performed a bulk
293 // rebiasing operation. The application is allocating objects in
294 // bulk which are biased toward a thread and then handing them
295 // off to another thread. We can cope with this allocation
296 // pattern via the bulk rebiasing mechanism so we reset the
297 // klass's revocation count rather than allow it to increase
298 // monotonically. If we see the need to perform another bulk
299 // rebias operation later, we will, and if subsequently we see
300 // many more revocation operations in a short period of time we
301 // will completely disable biasing for this type.
302 k->set_biased_lock_revocation_count(0);
303 revocation_count = 0;
304 }
305
306 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
307 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
308 revocation_count = k->atomic_incr_biased_lock_revocation_count();
309 }
310
311 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
312 return HR_BULK_REVOKE;
313 }
314
315 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
316 return HR_BULK_REBIAS;
317 }
318
319 return HR_SINGLE_REVOKE;
320 }
321
322
323 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
324 bool bulk_rebias,
325 bool attempt_rebias_of_object,
326 JavaThread* requesting_thread) {
327 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
328
329 if (TraceBiasedLocking) {
330 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object "
331 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
332 (bulk_rebias ? "rebias" : "revoke"),
333 p2i((void *) o), (intptr_t) o->mark(), o->klass()->external_name());
334 }
335
336 jlong cur_time = os::javaTimeMillis();
337 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
338
339
340 Klass* k_o = o->klass();
341 Klass* klass = k_o;
342
343 if (bulk_rebias) {
344 // Use the epoch in the klass of the object to implicitly revoke
345 // all biases of objects of this data type and force them to be
346 // reacquired. However, we also need to walk the stacks of all
347 // threads and update the headers of lightweight locked objects
348 // with biases to have the current epoch.
349
350 // If the prototype header doesn't have the bias pattern, don't
351 // try to update the epoch -- assume another VM operation came in
352 // and reset the header to the unbiased state, which will
353 // implicitly cause all existing biases to be revoked
354 if (klass->prototype_header()->has_bias_pattern()) {
355 int prev_epoch = klass->prototype_header()->bias_epoch();
356 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
357 int cur_epoch = klass->prototype_header()->bias_epoch();
358
359 // Now walk all threads' stacks and adjust epochs of any biased
360 // and locked objects of this data type we encounter
361 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
362 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
363 for (int i = 0; i < cached_monitor_info->length(); i++) {
364 MonitorInfo* mon_info = cached_monitor_info->at(i);
365 oop owner = mon_info->owner();
366 markOop mark = owner->mark();
367 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
368 // We might have encountered this object already in the case of recursive locking
369 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
370 owner->set_mark(mark->set_bias_epoch(cur_epoch));
371 }
372 }
373 }
374 }
375
376 // At this point we're done. All we have to do is potentially
377 // adjust the header of the given object to revoke its bias.
378 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread);
379 } else {
380 if (TraceBiasedLocking) {
381 ResourceMark rm;
382 tty->print_cr("* Disabling biased locking for type %s", klass->external_name());
383 }
384
385 // Disable biased locking for this data type. Not only will this
386 // cause future instances to not be biased, but existing biased
387 // instances will notice that this implicitly caused their biases
388 // to be revoked.
389 klass->set_prototype_header(markOopDesc::prototype());
390
391 // Now walk all threads' stacks and forcibly revoke the biases of
392 // any locked and biased objects of this data type we encounter.
393 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
394 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
395 for (int i = 0; i < cached_monitor_info->length(); i++) {
396 MonitorInfo* mon_info = cached_monitor_info->at(i);
397 oop owner = mon_info->owner();
398 markOop mark = owner->mark();
399 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
400 revoke_bias(owner, false, true, requesting_thread);
401 }
402 }
403 }
404
405 // Must force the bias of the passed object to be forcibly revoked
406 // as well to ensure guarantees to callers
407 revoke_bias(o, false, true, requesting_thread);
408 }
409
410 if (TraceBiasedLocking) {
411 tty->print_cr("* Ending bulk revocation");
412 }
413
414 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
415
416 if (attempt_rebias_of_object &&
417 o->mark()->has_bias_pattern() &&
418 klass->prototype_header()->has_bias_pattern()) {
419 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
420 klass->prototype_header()->bias_epoch());
421 o->set_mark(new_mark);
422 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
423 if (TraceBiasedLocking) {
424 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
425 }
426 }
427
428 assert(!o->mark()->has_bias_pattern() ||
429 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
430 "bug in bulk bias revocation");
431
432 return status_code;
433 }
434
435
436 static void clean_up_cached_monitor_info() {
437 // Walk the thread list clearing out the cached monitors
438 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
439 thr->set_cached_monitor_info(NULL);
440 }
441 }
442
443
444 class VM_RevokeBias : public VM_Operation {
445 protected:
446 Handle* _obj;
447 GrowableArray<Handle>* _objs;
448 JavaThread* _requesting_thread;
449 BiasedLocking::Condition _status_code;
450
451 public:
452 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
453 : _obj(obj)
454 , _objs(NULL)
455 , _requesting_thread(requesting_thread)
456 , _status_code(BiasedLocking::NOT_BIASED) {}
457
458 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
459 : _obj(NULL)
460 , _objs(objs)
461 , _requesting_thread(requesting_thread)
462 , _status_code(BiasedLocking::NOT_BIASED) {}
463
464 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
465
466 virtual bool doit_prologue() {
467 // Verify that there is actual work to do since the callers just
468 // give us locked object(s). If we don't find any biased objects
469 // there is nothing to do and we avoid a safepoint.
470 if (_obj != NULL) {
471 markOop mark = (*_obj)()->mark();
472 if (mark->has_bias_pattern()) {
473 return true;
474 }
475 } else {
476 for ( int i = 0 ; i < _objs->length(); i++ ) {
477 markOop mark = (_objs->at(i))()->mark();
478 if (mark->has_bias_pattern()) {
479 return true;
480 }
481 }
482 }
483 return false;
484 }
485
486 virtual void doit() {
487 if (_obj != NULL) {
488 if (TraceBiasedLocking) {
489 tty->print_cr("Revoking bias with potentially per-thread safepoint:");
490 }
491 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread);
492 clean_up_cached_monitor_info();
493 return;
494 } else {
495 if (TraceBiasedLocking) {
496 tty->print_cr("Revoking bias with global safepoint:");
497 }
498 BiasedLocking::revoke_at_safepoint(_objs);
499 }
500 }
501
502 BiasedLocking::Condition status_code() const {
503 return _status_code;
504 }
505 };
506
507
508 class VM_BulkRevokeBias : public VM_RevokeBias {
509 private:
510 bool _bulk_rebias;
511 bool _attempt_rebias_of_object;
512
513 public:
514 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
515 bool bulk_rebias,
516 bool attempt_rebias_of_object)
517 : VM_RevokeBias(obj, requesting_thread)
518 , _bulk_rebias(bulk_rebias)
519 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
520
521 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
522 virtual bool doit_prologue() { return true; }
523
524 virtual void doit() {
525 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
526 clean_up_cached_monitor_info();
527 }
528 };
529
530
531 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
532 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
533
534 // We can revoke the biases of anonymously-biased objects
535 // efficiently enough that we should not cause these revocations to
536 // update the heuristics because doing so may cause unwanted bulk
537 // revocations (which are expensive) to occur.
538 markOop mark = obj->mark();
539 if (mark->is_biased_anonymously() && !attempt_rebias) {
540 // We are probably trying to revoke the bias of this object due to
541 // an identity hash code computation. Try to revoke the bias
542 // without a safepoint. This is possible if we can successfully
543 // compare-and-exchange an unbiased header into the mark word of
544 // the object, meaning that no other thread has raced to acquire
545 // the bias of the object.
546 markOop biased_value = mark;
547 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
548 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
549 if (res_mark == biased_value) {
550 return BIAS_REVOKED;
551 }
552 } else if (mark->has_bias_pattern()) {
553 Klass* k = obj->klass();
554 markOop prototype_header = k->prototype_header();
555 if (!prototype_header->has_bias_pattern()) {
556 // This object has a stale bias from before the bulk revocation
557 // for this data type occurred. It's pointless to update the
558 // heuristics at this point so simply update the header with a
559 // CAS. If we fail this race, the object's bias has been revoked
560 // by another thread so we simply return and let the caller deal
561 // with it.
562 markOop biased_value = mark;
563 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark);
564 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked");
565 return BIAS_REVOKED;
566 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
567 // The epoch of this biasing has expired indicating that the
568 // object is effectively unbiased. Depending on whether we need
569 // to rebias or revoke the bias of this object we can do it
570 // efficiently enough with a CAS that we shouldn't update the
571 // heuristics. This is normally done in the assembly code but we
572 // can reach this point due to various points in the runtime
573 // needing to revoke biases.
574 if (attempt_rebias) {
575 assert(THREAD->is_Java_thread(), "");
576 markOop biased_value = mark;
577 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
578 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark);
579 if (res_mark == biased_value) {
580 return BIAS_REVOKED_AND_REBIASED;
581 }
582 } else {
583 markOop biased_value = mark;
584 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
585 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
586 if (res_mark == biased_value) {
587 return BIAS_REVOKED;
588 }
589 }
590 }
591 }
592
593 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
594 if (heuristics == HR_NOT_BIASED) {
595 return NOT_BIASED;
596 } else if (heuristics == HR_SINGLE_REVOKE) {
597 Klass *k = obj->klass();
598 markOop prototype_header = k->prototype_header();
599 if (mark->biased_locker() == THREAD &&
600 prototype_header->bias_epoch() == mark->bias_epoch()) {
601 // A thread is trying to revoke the bias of an object biased
602 // toward it, again likely due to an identity hash code
603 // computation. We can again avoid a safepoint in this case
604 // since we are only going to walk our own stack. There are no
605 // races with revocations occurring in other threads because we
606 // reach no safepoints in the revocation path.
607 // Also check the epoch because even if threads match, another thread
608 // can come in with a CAS to steal the bias of an object that has a
609 // stale epoch.
610 ResourceMark rm;
611 if (TraceBiasedLocking) {
612 tty->print_cr("Revoking bias by walking my own stack:");
613 }
614 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD);
615 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
616 assert(cond == BIAS_REVOKED, "why not?");
617 return cond;
618 } else {
619 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
620 VMThread::execute(&revoke);
621 return revoke.status_code();
622 }
623 }
624
625 assert((heuristics == HR_BULK_REVOKE) ||
626 (heuristics == HR_BULK_REBIAS), "?");
627 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
628 (heuristics == HR_BULK_REBIAS),
629 attempt_rebias);
630 VMThread::execute(&bulk_revoke);
631 return bulk_revoke.status_code();
632 }
633
634
635 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
636 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
637 if (objs->length() == 0) {
638 return;
639 }
640 VM_RevokeBias revoke(objs, JavaThread::current());
641 VMThread::execute(&revoke);
642 }
643
644
645 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
646 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
647 oop obj = h_obj();
648 HeuristicsResult heuristics = update_heuristics(obj, false);
649 if (heuristics == HR_SINGLE_REVOKE) {
650 revoke_bias(obj, false, false, NULL);
651 } else if ((heuristics == HR_BULK_REBIAS) ||
652 (heuristics == HR_BULK_REVOKE)) {
653 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
654 }
655 clean_up_cached_monitor_info();
656 }
657
658
659 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
660 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
661 int len = objs->length();
662 for (int i = 0; i < len; i++) {
663 oop obj = (objs->at(i))();
664 HeuristicsResult heuristics = update_heuristics(obj, false);
665 if (heuristics == HR_SINGLE_REVOKE) {
666 revoke_bias(obj, false, false, NULL);
667 } else if ((heuristics == HR_BULK_REBIAS) ||
668 (heuristics == HR_BULK_REVOKE)) {
669 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
670 }
671 }
672 clean_up_cached_monitor_info();
673 }
674
675
676 void BiasedLocking::preserve_marks() {
677 if (!UseBiasedLocking)
678 return;
679
680 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
681
682 assert(_preserved_oop_stack == NULL, "double initialization");
683 assert(_preserved_mark_stack == NULL, "double initialization");
684
685 // In order to reduce the number of mark words preserved during GC
686 // due to the presence of biased locking, we reinitialize most mark
687 // words to the class's prototype during GC -- even those which have
688 // a currently valid bias owner. One important situation where we
689 // must not clobber a bias is when a biased object is currently
690 // locked. To handle this case we iterate over the currently-locked
691 // monitors in a prepass and, if they are biased, preserve their
692 // mark words here. This should be a relatively small set of objects
693 // especially compared to the number of objects in the heap.
694 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true);
695 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
696
697 ResourceMark rm;
698 Thread* cur = Thread::current();
699 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) {
700 if (thread->has_last_Java_frame()) {
701 RegisterMap rm(thread);
702 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
703 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
704 if (monitors != NULL) {
705 int len = monitors->length();
706 // Walk monitors youngest to oldest
707 for (int i = len - 1; i >= 0; i--) {
708 MonitorInfo* mon_info = monitors->at(i);
709 if (mon_info->owner_is_scalar_replaced()) continue;
710 oop owner = mon_info->owner();
711 if (owner != NULL) {
712 markOop mark = owner->mark();
713 if (mark->has_bias_pattern()) {
714 _preserved_oop_stack->push(Handle(cur, owner));
715 _preserved_mark_stack->push(mark);
716 }
717 }
718 }
719 }
720 }
721 }
722 }
723 }
724
725
726 void BiasedLocking::restore_marks() {
727 if (!UseBiasedLocking)
728 return;
729
730 assert(_preserved_oop_stack != NULL, "double free");
731 assert(_preserved_mark_stack != NULL, "double free");
732
733 int len = _preserved_oop_stack->length();
734 for (int i = 0; i < len; i++) {
735 Handle owner = _preserved_oop_stack->at(i);
736 markOop mark = _preserved_mark_stack->at(i);
737 owner->set_mark(mark);
738 }
739
740 delete _preserved_oop_stack;
741 _preserved_oop_stack = NULL;
742 delete _preserved_mark_stack;
743 _preserved_mark_stack = NULL;
744 }
745
746
747 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
748 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
749 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
750 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
751 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
752 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
753 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
754
755
756 // BiasedLockingCounters
757
758 int BiasedLockingCounters::slow_path_entry_count() {
759 if (_slow_path_entry_count != 0) {
760 return _slow_path_entry_count;
761 }
762 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
763 _rebiased_lock_entry_count + _revoked_lock_entry_count +
764 _fast_path_entry_count;
765
766 return _total_entry_count - sum;
767 }
768
769 void BiasedLockingCounters::print_on(outputStream* st) {
770 tty->print_cr("# total entries: %d", _total_entry_count);
771 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
772 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
773 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
774 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
775 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
776 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
777 }