1 /*
2 * Copyright (c) 2005, 2014, 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
35 static bool _biased_locking_enabled = false;
36 BiasedLockingCounters BiasedLocking::_counters;
37
38 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
39 static GrowableArray<markOop>* _preserved_mark_stack = NULL;
40
41 static void enable_biased_locking(Klass* k) {
42 k->set_prototype_header(markOopDesc::biased_locking_prototype());
43 }
44
45 class VM_EnableBiasedLocking: public VM_Operation {
46 private:
47 bool _is_cheap_allocated;
48 public:
49 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; }
50 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
51 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; }
52 bool is_cheap_allocated() const { return _is_cheap_allocated; }
53
54 void doit() {
55 // Iterate the system dictionary enabling biased locking for all
56 // currently loaded classes
57 SystemDictionary::classes_do(enable_biased_locking);
58 // Indicate that future instances should enable it as well
59 _biased_locking_enabled = true;
60
61 if (TraceBiasedLocking) {
62 tty->print_cr("Biased locking enabled");
63 }
64 }
65
66 bool allow_nested_vm_operations() const { return false; }
67 };
68
69
70 // One-shot PeriodicTask subclass for enabling biased locking
71 class EnableBiasedLockingTask : public PeriodicTask {
72 public:
73 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {}
74
75 virtual void task() {
76 // Use async VM operation to avoid blocking the Watcher thread.
77 // VM Thread will free C heap storage.
78 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true);
79 VMThread::execute(op);
80
81 // Reclaim our storage and disenroll ourself
82 delete this;
83 }
84 };
85
86
87 void BiasedLocking::init() {
88 // If biased locking is enabled, schedule a task to fire a few
89 // seconds into the run which turns on biased locking for all
90 // currently loaded classes as well as future ones. This is a
91 // workaround for startup time regressions due to a large number of
92 // safepoints being taken during VM startup for bias revocation.
93 // Ideally we would have a lower cost for individual bias revocation
94 // and not need a mechanism like this.
95 if (UseBiasedLocking) {
96 if (BiasedLockingStartupDelay > 0) {
97 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
98 task->enroll();
99 } else {
100 VM_EnableBiasedLocking op(false);
101 VMThread::execute(&op);
102 }
103 }
104 }
105
106
107 bool BiasedLocking::enabled() {
108 return _biased_locking_enabled;
109 }
110
111 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
112 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
113 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
114 if (info != NULL) {
115 return info;
116 }
117
118 info = new GrowableArray<MonitorInfo*>();
119
120 // It's possible for the thread to not have any Java frames on it,
121 // i.e., if it's the main thread and it's already returned from main()
122 if (thread->has_last_Java_frame()) {
123 RegisterMap rm(thread);
124 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
125 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
126 if (monitors != NULL) {
127 int len = monitors->length();
128 // Walk monitors youngest to oldest
129 for (int i = len - 1; i >= 0; i--) {
130 MonitorInfo* mon_info = monitors->at(i);
131 if (mon_info->eliminated()) continue;
132 oop owner = mon_info->owner();
133 if (owner != NULL) {
134 info->append(mon_info);
135 }
136 }
137 }
138 }
139 }
140
141 thread->set_cached_monitor_info(info);
142 return info;
143 }
144
145
146 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) {
147 markOop mark = obj->mark();
148 if (!mark->has_bias_pattern()) {
149 if (TraceBiasedLocking) {
150 ResourceMark rm;
151 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)",
152 obj->klass()->external_name());
153 }
154 return BiasedLocking::NOT_BIASED;
155 }
156
157 uint age = mark->age();
158 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
159 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
160
161 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
162 ResourceMark rm;
163 tty->print_cr("Revoking bias of object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT " , allow rebias %d , requesting thread " INTPTR_FORMAT,
164 p2i((void *)obj), (intptr_t) mark, obj->klass()->external_name(), (intptr_t) obj->klass()->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread);
165 }
166
167 JavaThread* biased_thread = mark->biased_locker();
168 if (biased_thread == NULL) {
169 // Object is anonymously biased. We can get here if, for
170 // example, we revoke the bias due to an identity hash code
171 // being computed for an object.
172 if (!allow_rebias) {
173 obj->set_mark(unbiased_prototype);
174 }
175 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
176 tty->print_cr(" Revoked bias of anonymously-biased object");
177 }
178 return BiasedLocking::BIAS_REVOKED;
179 }
180
181 // Handle case where the thread toward which the object was biased has exited
182 bool thread_is_alive = false;
183 if (requesting_thread == biased_thread) {
184 thread_is_alive = true;
185 } else {
186 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) {
187 if (cur_thread == biased_thread) {
188 thread_is_alive = true;
189 break;
190 }
191 }
192 }
193 if (!thread_is_alive) {
194 if (allow_rebias) {
195 obj->set_mark(biased_prototype);
196 } else {
197 obj->set_mark(unbiased_prototype);
198 }
199 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
200 tty->print_cr(" Revoked bias of object biased toward dead thread");
201 }
202 return BiasedLocking::BIAS_REVOKED;
203 }
204
205 // Thread owning bias is alive.
206 // Check to see whether it currently owns the lock and, if so,
207 // write down the needed displaced headers to the thread's stack.
208 // Otherwise, restore the object's header either to the unlocked
209 // or unbiased state.
210 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
211 BasicLock* highest_lock = NULL;
212 for (int i = 0; i < cached_monitor_info->length(); i++) {
213 MonitorInfo* mon_info = cached_monitor_info->at(i);
214 if (mon_info->owner() == obj) {
215 if (TraceBiasedLocking && Verbose) {
216 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
217 p2i((void *) mon_info->owner()),
218 p2i((void *) obj));
219 }
220 // Assume recursive case and fix up highest lock later
221 markOop mark = markOopDesc::encode((BasicLock*) NULL);
222 highest_lock = mon_info->lock();
223 highest_lock->set_displaced_header(mark);
224 } else {
225 if (TraceBiasedLocking && Verbose) {
226 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
227 p2i((void *) mon_info->owner()),
228 p2i((void *) obj));
229 }
230 }
231 }
232 if (highest_lock != NULL) {
233 // Fix up highest lock to contain displaced header and point
234 // object at it
235 highest_lock->set_displaced_header(unbiased_prototype);
236 // Reset object header to point to displaced mark.
237 // Must release storing the lock address for platforms without TSO
238 // ordering (e.g. ppc).
239 obj->release_set_mark(markOopDesc::encode(highest_lock));
240 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
241 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
242 tty->print_cr(" Revoked bias of currently-locked object");
243 }
244 } else {
245 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
246 tty->print_cr(" Revoked bias of currently-unlocked object");
247 }
248 if (allow_rebias) {
249 obj->set_mark(biased_prototype);
250 } else {
251 // Store the unlocked value into the object's header.
252 obj->set_mark(unbiased_prototype);
253 }
254 }
255
256 return BiasedLocking::BIAS_REVOKED;
257 }
258
259
260 enum HeuristicsResult {
261 HR_NOT_BIASED = 1,
262 HR_SINGLE_REVOKE = 2,
263 HR_BULK_REBIAS = 3,
264 HR_BULK_REVOKE = 4
265 };
266
267
268 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
269 markOop mark = o->mark();
270 if (!mark->has_bias_pattern()) {
271 return HR_NOT_BIASED;
272 }
273
274 // Heuristics to attempt to throttle the number of revocations.
275 // Stages:
276 // 1. Revoke the biases of all objects in the heap of this type,
277 // but allow rebiasing of those objects if unlocked.
278 // 2. Revoke the biases of all objects in the heap of this type
279 // and don't allow rebiasing of these objects. Disable
280 // allocation of objects of that type with the bias bit set.
281 Klass* k = o->klass();
282 jlong cur_time = os::javaTimeMillis();
283 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
284 int revocation_count = k->biased_lock_revocation_count();
285 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
286 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
287 (last_bulk_revocation_time != 0) &&
288 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
289 // This is the first revocation we've seen in a while of an
290 // object of this type since the last time we performed a bulk
291 // rebiasing operation. The application is allocating objects in
292 // bulk which are biased toward a thread and then handing them
293 // off to another thread. We can cope with this allocation
294 // pattern via the bulk rebiasing mechanism so we reset the
295 // klass's revocation count rather than allow it to increase
296 // monotonically. If we see the need to perform another bulk
297 // rebias operation later, we will, and if subsequently we see
298 // many more revocation operations in a short period of time we
299 // will completely disable biasing for this type.
300 k->set_biased_lock_revocation_count(0);
301 revocation_count = 0;
302 }
303
304 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
305 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
306 revocation_count = k->atomic_incr_biased_lock_revocation_count();
307 }
308
309 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
310 return HR_BULK_REVOKE;
311 }
312
313 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
314 return HR_BULK_REBIAS;
315 }
316
317 return HR_SINGLE_REVOKE;
318 }
319
320
321 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
322 bool bulk_rebias,
323 bool attempt_rebias_of_object,
324 JavaThread* requesting_thread) {
325 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
326
327 if (TraceBiasedLocking) {
328 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object "
329 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
330 (bulk_rebias ? "rebias" : "revoke"),
331 p2i((void *) o), (intptr_t) o->mark(), o->klass()->external_name());
332 }
333
334 jlong cur_time = os::javaTimeMillis();
335 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
336
337
338 Klass* k_o = o->klass();
339 Klass* klass = k_o;
340
341 if (bulk_rebias) {
342 // Use the epoch in the klass of the object to implicitly revoke
343 // all biases of objects of this data type and force them to be
344 // reacquired. However, we also need to walk the stacks of all
345 // threads and update the headers of lightweight locked objects
346 // with biases to have the current epoch.
347
348 // If the prototype header doesn't have the bias pattern, don't
349 // try to update the epoch -- assume another VM operation came in
350 // and reset the header to the unbiased state, which will
351 // implicitly cause all existing biases to be revoked
352 if (klass->prototype_header()->has_bias_pattern()) {
353 int prev_epoch = klass->prototype_header()->bias_epoch();
354 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
355 int cur_epoch = klass->prototype_header()->bias_epoch();
356
357 // Now walk all threads' stacks and adjust epochs of any biased
358 // and locked objects of this data type we encounter
359 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
360 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
361 for (int i = 0; i < cached_monitor_info->length(); i++) {
362 MonitorInfo* mon_info = cached_monitor_info->at(i);
363 oop owner = mon_info->owner();
364 markOop mark = owner->mark();
365 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
366 // We might have encountered this object already in the case of recursive locking
367 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
368 owner->set_mark(mark->set_bias_epoch(cur_epoch));
369 }
370 }
371 }
372 }
373
374 // At this point we're done. All we have to do is potentially
375 // adjust the header of the given object to revoke its bias.
376 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread);
377 } else {
378 if (TraceBiasedLocking) {
379 ResourceMark rm;
380 tty->print_cr("* Disabling biased locking for type %s", klass->external_name());
381 }
382
383 // Disable biased locking for this data type. Not only will this
384 // cause future instances to not be biased, but existing biased
385 // instances will notice that this implicitly caused their biases
386 // to be revoked.
387 klass->set_prototype_header(markOopDesc::prototype());
388
389 // Now walk all threads' stacks and forcibly revoke the biases of
390 // any locked and biased objects of this data type we encounter.
391 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
392 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
393 for (int i = 0; i < cached_monitor_info->length(); i++) {
394 MonitorInfo* mon_info = cached_monitor_info->at(i);
395 oop owner = mon_info->owner();
396 markOop mark = owner->mark();
397 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
398 revoke_bias(owner, false, true, requesting_thread);
399 }
400 }
401 }
402
403 // Must force the bias of the passed object to be forcibly revoked
404 // as well to ensure guarantees to callers
405 revoke_bias(o, false, true, requesting_thread);
406 }
407
408 if (TraceBiasedLocking) {
409 tty->print_cr("* Ending bulk revocation");
410 }
411
412 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
413
414 if (attempt_rebias_of_object &&
415 o->mark()->has_bias_pattern() &&
416 klass->prototype_header()->has_bias_pattern()) {
417 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
418 klass->prototype_header()->bias_epoch());
419 o->set_mark(new_mark);
420 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
421 if (TraceBiasedLocking) {
422 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
423 }
424 }
425
426 assert(!o->mark()->has_bias_pattern() ||
427 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
428 "bug in bulk bias revocation");
429
430 return status_code;
431 }
432
433
434 static void clean_up_cached_monitor_info() {
435 // Walk the thread list clearing out the cached monitors
436 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
437 thr->set_cached_monitor_info(NULL);
438 }
439 }
440
441
442 class VM_RevokeBias : public VM_Operation {
443 protected:
444 Handle* _obj;
445 GrowableArray<Handle>* _objs;
446 JavaThread* _requesting_thread;
447 BiasedLocking::Condition _status_code;
448
449 public:
450 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
451 : _obj(obj)
452 , _objs(NULL)
453 , _requesting_thread(requesting_thread)
454 , _status_code(BiasedLocking::NOT_BIASED) {}
455
456 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
457 : _obj(NULL)
458 , _objs(objs)
459 , _requesting_thread(requesting_thread)
460 , _status_code(BiasedLocking::NOT_BIASED) {}
461
462 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
463
464 virtual bool doit_prologue() {
465 // Verify that there is actual work to do since the callers just
466 // give us locked object(s). If we don't find any biased objects
467 // there is nothing to do and we avoid a safepoint.
468 if (_obj != NULL) {
469 markOop mark = (*_obj)()->mark();
470 if (mark->has_bias_pattern()) {
471 return true;
472 }
473 } else {
474 for ( int i = 0 ; i < _objs->length(); i++ ) {
475 markOop mark = (_objs->at(i))()->mark();
476 if (mark->has_bias_pattern()) {
477 return true;
478 }
479 }
480 }
481 return false;
482 }
483
484 virtual void doit() {
485 if (_obj != NULL) {
486 if (TraceBiasedLocking) {
487 tty->print_cr("Revoking bias with potentially per-thread safepoint:");
488 }
489 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread);
490 clean_up_cached_monitor_info();
491 return;
492 } else {
493 if (TraceBiasedLocking) {
494 tty->print_cr("Revoking bias with global safepoint:");
495 }
496 BiasedLocking::revoke_at_safepoint(_objs);
497 }
498 }
499
500 BiasedLocking::Condition status_code() const {
501 return _status_code;
502 }
503 };
504
505
506 class VM_BulkRevokeBias : public VM_RevokeBias {
507 private:
508 bool _bulk_rebias;
509 bool _attempt_rebias_of_object;
510
511 public:
512 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
513 bool bulk_rebias,
514 bool attempt_rebias_of_object)
515 : VM_RevokeBias(obj, requesting_thread)
516 , _bulk_rebias(bulk_rebias)
517 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
518
519 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
520 virtual bool doit_prologue() { return true; }
521
522 virtual void doit() {
523 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
524 clean_up_cached_monitor_info();
525 }
526 };
527
528
529 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
530 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
531
532 // We can revoke the biases of anonymously-biased objects
533 // efficiently enough that we should not cause these revocations to
534 // update the heuristics because doing so may cause unwanted bulk
535 // revocations (which are expensive) to occur.
536 markOop mark = obj->mark();
537 if (mark->is_biased_anonymously() && !attempt_rebias) {
538 // We are probably trying to revoke the bias of this object due to
539 // an identity hash code computation. Try to revoke the bias
540 // without a safepoint. This is possible if we can successfully
541 // compare-and-exchange an unbiased header into the mark word of
542 // the object, meaning that no other thread has raced to acquire
543 // the bias of the object.
544 markOop biased_value = mark;
545 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
546 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
547 if (res_mark == biased_value) {
548 return BIAS_REVOKED;
549 }
550 } else if (mark->has_bias_pattern()) {
551 Klass* k = obj->klass();
552 markOop prototype_header = k->prototype_header();
553 if (!prototype_header->has_bias_pattern()) {
554 // This object has a stale bias from before the bulk revocation
555 // for this data type occurred. It's pointless to update the
556 // heuristics at this point so simply update the header with a
557 // CAS. If we fail this race, the object's bias has been revoked
558 // by another thread so we simply return and let the caller deal
559 // with it.
560 markOop biased_value = mark;
561 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark);
562 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked");
563 return BIAS_REVOKED;
564 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
565 // The epoch of this biasing has expired indicating that the
566 // object is effectively unbiased. Depending on whether we need
567 // to rebias or revoke the bias of this object we can do it
568 // efficiently enough with a CAS that we shouldn't update the
569 // heuristics. This is normally done in the assembly code but we
570 // can reach this point due to various points in the runtime
571 // needing to revoke biases.
572 if (attempt_rebias) {
573 assert(THREAD->is_Java_thread(), "");
574 markOop biased_value = mark;
575 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
576 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark);
577 if (res_mark == biased_value) {
578 return BIAS_REVOKED_AND_REBIASED;
579 }
580 } else {
581 markOop biased_value = mark;
582 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
583 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
584 if (res_mark == biased_value) {
585 return BIAS_REVOKED;
586 }
587 }
588 }
589 }
590
591 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
592 if (heuristics == HR_NOT_BIASED) {
593 return NOT_BIASED;
594 } else if (heuristics == HR_SINGLE_REVOKE) {
595 Klass *k = obj->klass();
596 markOop prototype_header = k->prototype_header();
597 if (mark->biased_locker() == THREAD &&
598 prototype_header->bias_epoch() == mark->bias_epoch()) {
599 // A thread is trying to revoke the bias of an object biased
600 // toward it, again likely due to an identity hash code
601 // computation. We can again avoid a safepoint in this case
602 // since we are only going to walk our own stack. There are no
603 // races with revocations occurring in other threads because we
604 // reach no safepoints in the revocation path.
605 // Also check the epoch because even if threads match, another thread
606 // can come in with a CAS to steal the bias of an object that has a
607 // stale epoch.
608 ResourceMark rm;
609 if (TraceBiasedLocking) {
610 tty->print_cr("Revoking bias by walking my own stack:");
611 }
612 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD);
613 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
614 assert(cond == BIAS_REVOKED, "why not?");
615 return cond;
616 } else {
617 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
618 VMThread::execute(&revoke);
619 return revoke.status_code();
620 }
621 }
622
623 assert((heuristics == HR_BULK_REVOKE) ||
624 (heuristics == HR_BULK_REBIAS), "?");
625 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
626 (heuristics == HR_BULK_REBIAS),
627 attempt_rebias);
628 VMThread::execute(&bulk_revoke);
629 return bulk_revoke.status_code();
630 }
631
632
633 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
634 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
635 if (objs->length() == 0) {
636 return;
637 }
638 VM_RevokeBias revoke(objs, JavaThread::current());
639 VMThread::execute(&revoke);
640 }
641
642
643 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
644 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
645 oop obj = h_obj();
646 HeuristicsResult heuristics = update_heuristics(obj, false);
647 if (heuristics == HR_SINGLE_REVOKE) {
648 revoke_bias(obj, false, false, NULL);
649 } else if ((heuristics == HR_BULK_REBIAS) ||
650 (heuristics == HR_BULK_REVOKE)) {
651 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
652 }
653 clean_up_cached_monitor_info();
654 }
655
656
657 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
658 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
659 int len = objs->length();
660 for (int i = 0; i < len; i++) {
661 oop obj = (objs->at(i))();
662 HeuristicsResult heuristics = update_heuristics(obj, false);
663 if (heuristics == HR_SINGLE_REVOKE) {
664 revoke_bias(obj, false, false, NULL);
665 } else if ((heuristics == HR_BULK_REBIAS) ||
666 (heuristics == HR_BULK_REVOKE)) {
667 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
668 }
669 }
670 clean_up_cached_monitor_info();
671 }
672
673
674 void BiasedLocking::preserve_marks() {
675 if (!UseBiasedLocking)
676 return;
677
678 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
679
680 assert(_preserved_oop_stack == NULL, "double initialization");
681 assert(_preserved_mark_stack == NULL, "double initialization");
682
683 // In order to reduce the number of mark words preserved during GC
684 // due to the presence of biased locking, we reinitialize most mark
685 // words to the class's prototype during GC -- even those which have
686 // a currently valid bias owner. One important situation where we
687 // must not clobber a bias is when a biased object is currently
688 // locked. To handle this case we iterate over the currently-locked
689 // monitors in a prepass and, if they are biased, preserve their
690 // mark words here. This should be a relatively small set of objects
691 // especially compared to the number of objects in the heap.
692 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true);
693 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
694
695 ResourceMark rm;
696 Thread* cur = Thread::current();
697 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) {
698 if (thread->has_last_Java_frame()) {
699 RegisterMap rm(thread);
700 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
701 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
702 if (monitors != NULL) {
703 int len = monitors->length();
704 // Walk monitors youngest to oldest
705 for (int i = len - 1; i >= 0; i--) {
706 MonitorInfo* mon_info = monitors->at(i);
707 if (mon_info->owner_is_scalar_replaced()) continue;
708 oop owner = mon_info->owner();
709 if (owner != NULL) {
710 markOop mark = owner->mark();
711 if (mark->has_bias_pattern()) {
712 _preserved_oop_stack->push(Handle(cur, owner));
713 _preserved_mark_stack->push(mark);
714 }
715 }
716 }
717 }
718 }
719 }
720 }
721 }
722
723
724 void BiasedLocking::restore_marks() {
725 if (!UseBiasedLocking)
726 return;
727
728 assert(_preserved_oop_stack != NULL, "double free");
729 assert(_preserved_mark_stack != NULL, "double free");
730
731 int len = _preserved_oop_stack->length();
732 for (int i = 0; i < len; i++) {
733 Handle owner = _preserved_oop_stack->at(i);
734 markOop mark = _preserved_mark_stack->at(i);
735 owner->set_mark(mark);
736 }
737
738 delete _preserved_oop_stack;
739 _preserved_oop_stack = NULL;
740 delete _preserved_mark_stack;
741 _preserved_mark_stack = NULL;
742 }
743
744
745 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
746 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
747 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
748 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
749 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
750 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
751 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
752
753
754 // BiasedLockingCounters
755
756 int BiasedLockingCounters::slow_path_entry_count() {
757 if (_slow_path_entry_count != 0) {
758 return _slow_path_entry_count;
759 }
760 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
761 _rebiased_lock_entry_count + _revoked_lock_entry_count +
762 _fast_path_entry_count;
763
764 return _total_entry_count - sum;
765 }
766
767 void BiasedLockingCounters::print_on(outputStream* st) {
768 tty->print_cr("# total entries: %d", _total_entry_count);
769 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
770 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
771 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
772 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
773 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
774 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
775 }