1 /*
2 * Copyright (c) 2005, 2016, 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 "logging/log.hpp"
27 #include "memory/resourceArea.hpp"
28 #include "oops/klass.inline.hpp"
29 #include "oops/markOop.hpp"
30 #include "oops/oop.inline.hpp"
31 #include "runtime/atomic.inline.hpp"
32 #include "runtime/basicLock.hpp"
33 #include "runtime/biasedLocking.hpp"
34 #include "runtime/task.hpp"
35 #include "runtime/vframe.hpp"
36 #include "runtime/vmThread.hpp"
37 #include "runtime/vm_operations.hpp"
38
39 static bool _biased_locking_enabled = false;
40 BiasedLockingCounters BiasedLocking::_counters;
41
42 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
43 static GrowableArray<markOop>* _preserved_mark_stack = NULL;
44
45 static void enable_biased_locking(Klass* k) {
46 k->set_prototype_header(markOopDesc::biased_locking_prototype());
47 }
48
49 class VM_EnableBiasedLocking: public VM_Operation {
50 private:
51 bool _is_cheap_allocated;
52 public:
53 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; }
54 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
55 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; }
56 bool is_cheap_allocated() const { return _is_cheap_allocated; }
57
58 void doit() {
59 // Iterate the system dictionary enabling biased locking for all
60 // currently loaded classes
61 SystemDictionary::classes_do(enable_biased_locking);
62 // Indicate that future instances should enable it as well
63 _biased_locking_enabled = true;
64
65 log_info(biasedlocking)("Biased locking enabled");
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 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) {
148 markOop mark = obj->mark();
149 if (!mark->has_bias_pattern()) {
150 if (log_is_enabled(Info, biasedlocking)) {
151 ResourceMark rm;
152 log_info(biasedlocking)(" (Skipping revocation of object of type %s "
153 "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 // Log at "info" level if not bulk, else "trace" level
164 if (!is_bulk) {
165 ResourceMark rm;
166 log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark "
167 INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT
168 " , allow rebias %d , requesting thread " INTPTR_FORMAT,
169 p2i((void *)obj),
170 (intptr_t) mark,
171 obj->klass()->external_name(),
172 (intptr_t) obj->klass()->prototype_header(),
173 (allow_rebias ? 1 : 0),
174 (intptr_t) requesting_thread);
175 } else {
176 ResourceMark rm;
177 log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark "
178 INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT
179 " , allow rebias %d , requesting thread " INTPTR_FORMAT,
180 p2i((void *)obj),
181 (intptr_t) mark,
182 obj->klass()->external_name(),
183 (intptr_t) obj->klass()->prototype_header(),
184 (allow_rebias ? 1 : 0),
185 (intptr_t) requesting_thread);
186 }
187
188 JavaThread* biased_thread = mark->biased_locker();
189 if (biased_thread == NULL) {
190 // Object is anonymously biased. We can get here if, for
191 // example, we revoke the bias due to an identity hash code
192 // being computed for an object.
193 if (!allow_rebias) {
194 obj->set_mark(unbiased_prototype);
195 }
196 if (!is_bulk) {
197 log_info(biasedlocking)(" Revoked bias of anonymously-biased object");
198 } else {
199 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object");
200 }
201 return BiasedLocking::BIAS_REVOKED;
202 }
203
204 // Handle case where the thread toward which the object was biased has exited
205 bool thread_is_alive = false;
206 if (requesting_thread == biased_thread) {
207 thread_is_alive = true;
208 } else {
209 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) {
210 if (cur_thread == biased_thread) {
211 thread_is_alive = true;
212 break;
213 }
214 }
215 }
216 if (!thread_is_alive) {
217 if (allow_rebias) {
218 obj->set_mark(biased_prototype);
219 } else {
220 obj->set_mark(unbiased_prototype);
221 }
222 // Log at "info" level if not bulk, else "trace" level
223 if (!is_bulk) {
224 log_info(biasedlocking)(" Revoked bias of object biased toward dead thread");
225 } else {
226 log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread");
227 }
228 return BiasedLocking::BIAS_REVOKED;
229 }
230
231 // Thread owning bias is alive.
232 // Check to see whether it currently owns the lock and, if so,
233 // write down the needed displaced headers to the thread's stack.
234 // Otherwise, restore the object's header either to the unlocked
235 // or unbiased state.
236 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
237 BasicLock* highest_lock = NULL;
238 for (int i = 0; i < cached_monitor_info->length(); i++) {
239 MonitorInfo* mon_info = cached_monitor_info->at(i);
240 if (mon_info->owner() == obj) {
241 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
242 p2i((void *) mon_info->owner()),
243 p2i((void *) obj));
244 // Assume recursive case and fix up highest lock later
245 markOop mark = markOopDesc::encode((BasicLock*) NULL);
246 highest_lock = mon_info->lock();
247 highest_lock->set_displaced_header(mark);
248 } else {
249 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
250 p2i((void *) mon_info->owner()),
251 p2i((void *) obj));
252 }
253 }
254 if (highest_lock != NULL) {
255 // Fix up highest lock to contain displaced header and point
256 // object at it
257 highest_lock->set_displaced_header(unbiased_prototype);
258 // Reset object header to point to displaced mark.
259 // Must release storing the lock address for platforms without TSO
260 // ordering (e.g. ppc).
261 obj->release_set_mark(markOopDesc::encode(highest_lock));
262 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
263 // Log at "info" level if not bulk, else "trace" level
264 if (!is_bulk) {
265 log_info(biasedlocking)(" Revoked bias of currently-locked object");
266 } else {
267 log_trace(biasedlocking)(" Revoked bias of currently-locked object");
268 }
269 } else {
270 // Log at "info" level if not bulk, else "trace" level
271 if (!is_bulk) {
272 log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
273 } else {
274 log_trace(biasedlocking)(" Revoked bias of currently-unlocked object");
275 }
276 if (allow_rebias) {
277 obj->set_mark(biased_prototype);
278 } else {
279 // Store the unlocked value into the object's header.
280 obj->set_mark(unbiased_prototype);
281 }
282 }
283
284 return BiasedLocking::BIAS_REVOKED;
285 }
286
287
288 enum HeuristicsResult {
289 HR_NOT_BIASED = 1,
290 HR_SINGLE_REVOKE = 2,
291 HR_BULK_REBIAS = 3,
292 HR_BULK_REVOKE = 4
293 };
294
295
296 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
297 markOop mark = o->mark();
298 if (!mark->has_bias_pattern()) {
299 return HR_NOT_BIASED;
300 }
301
302 // Heuristics to attempt to throttle the number of revocations.
303 // Stages:
304 // 1. Revoke the biases of all objects in the heap of this type,
305 // but allow rebiasing of those objects if unlocked.
306 // 2. Revoke the biases of all objects in the heap of this type
307 // and don't allow rebiasing of these objects. Disable
308 // allocation of objects of that type with the bias bit set.
309 Klass* k = o->klass();
310 jlong cur_time = os::javaTimeMillis();
311 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
312 int revocation_count = k->biased_lock_revocation_count();
313 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
314 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
315 (last_bulk_revocation_time != 0) &&
316 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
317 // This is the first revocation we've seen in a while of an
318 // object of this type since the last time we performed a bulk
319 // rebiasing operation. The application is allocating objects in
320 // bulk which are biased toward a thread and then handing them
321 // off to another thread. We can cope with this allocation
322 // pattern via the bulk rebiasing mechanism so we reset the
323 // klass's revocation count rather than allow it to increase
324 // monotonically. If we see the need to perform another bulk
325 // rebias operation later, we will, and if subsequently we see
326 // many more revocation operations in a short period of time we
327 // will completely disable biasing for this type.
328 k->set_biased_lock_revocation_count(0);
329 revocation_count = 0;
330 }
331
332 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
333 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
334 revocation_count = k->atomic_incr_biased_lock_revocation_count();
335 }
336
337 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
338 return HR_BULK_REVOKE;
339 }
340
341 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
342 return HR_BULK_REBIAS;
343 }
344
345 return HR_SINGLE_REVOKE;
346 }
347
348
349 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
350 bool bulk_rebias,
351 bool attempt_rebias_of_object,
352 JavaThread* requesting_thread) {
353 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
354
355 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object "
356 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
357 (bulk_rebias ? "rebias" : "revoke"),
358 p2i((void *) o),
359 (intptr_t) o->mark(),
360 o->klass()->external_name());
361
362 jlong cur_time = os::javaTimeMillis();
363 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
364
365
366 Klass* k_o = o->klass();
367 Klass* klass = k_o;
368
369 if (bulk_rebias) {
370 // Use the epoch in the klass of the object to implicitly revoke
371 // all biases of objects of this data type and force them to be
372 // reacquired. However, we also need to walk the stacks of all
373 // threads and update the headers of lightweight locked objects
374 // with biases to have the current epoch.
375
376 // If the prototype header doesn't have the bias pattern, don't
377 // try to update the epoch -- assume another VM operation came in
378 // and reset the header to the unbiased state, which will
379 // implicitly cause all existing biases to be revoked
380 if (klass->prototype_header()->has_bias_pattern()) {
381 int prev_epoch = klass->prototype_header()->bias_epoch();
382 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
383 int cur_epoch = klass->prototype_header()->bias_epoch();
384
385 // Now walk all threads' stacks and adjust epochs of any biased
386 // and locked objects of this data type we encounter
387 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
388 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
389 for (int i = 0; i < cached_monitor_info->length(); i++) {
390 MonitorInfo* mon_info = cached_monitor_info->at(i);
391 oop owner = mon_info->owner();
392 markOop mark = owner->mark();
393 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
394 // We might have encountered this object already in the case of recursive locking
395 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
396 owner->set_mark(mark->set_bias_epoch(cur_epoch));
397 }
398 }
399 }
400 }
401
402 // At this point we're done. All we have to do is potentially
403 // adjust the header of the given object to revoke its bias.
404 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread);
405 } else {
406 if (log_is_enabled(Info, biasedlocking)) {
407 ResourceMark rm;
408 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name());
409 }
410
411 // Disable biased locking for this data type. Not only will this
412 // cause future instances to not be biased, but existing biased
413 // instances will notice that this implicitly caused their biases
414 // to be revoked.
415 klass->set_prototype_header(markOopDesc::prototype());
416
417 // Now walk all threads' stacks and forcibly revoke the biases of
418 // any locked and biased objects of this data type we encounter.
419 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
420 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
421 for (int i = 0; i < cached_monitor_info->length(); i++) {
422 MonitorInfo* mon_info = cached_monitor_info->at(i);
423 oop owner = mon_info->owner();
424 markOop mark = owner->mark();
425 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
426 revoke_bias(owner, false, true, requesting_thread);
427 }
428 }
429 }
430
431 // Must force the bias of the passed object to be forcibly revoked
432 // as well to ensure guarantees to callers
433 revoke_bias(o, false, true, requesting_thread);
434 }
435
436 log_info(biasedlocking)("* Ending bulk revocation");
437
438 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
439
440 if (attempt_rebias_of_object &&
441 o->mark()->has_bias_pattern() &&
442 klass->prototype_header()->has_bias_pattern()) {
443 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
444 klass->prototype_header()->bias_epoch());
445 o->set_mark(new_mark);
446 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
447 log_info(biasedlocking)(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
448 }
449
450 assert(!o->mark()->has_bias_pattern() ||
451 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
452 "bug in bulk bias revocation");
453
454 return status_code;
455 }
456
457
458 static void clean_up_cached_monitor_info() {
459 // Walk the thread list clearing out the cached monitors
460 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
461 thr->set_cached_monitor_info(NULL);
462 }
463 }
464
465
466 class VM_RevokeBias : public VM_Operation {
467 protected:
468 Handle* _obj;
469 GrowableArray<Handle>* _objs;
470 JavaThread* _requesting_thread;
471 BiasedLocking::Condition _status_code;
472
473 public:
474 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
475 : _obj(obj)
476 , _objs(NULL)
477 , _requesting_thread(requesting_thread)
478 , _status_code(BiasedLocking::NOT_BIASED) {}
479
480 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
481 : _obj(NULL)
482 , _objs(objs)
483 , _requesting_thread(requesting_thread)
484 , _status_code(BiasedLocking::NOT_BIASED) {}
485
486 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
487
488 virtual bool doit_prologue() {
489 // Verify that there is actual work to do since the callers just
490 // give us locked object(s). If we don't find any biased objects
491 // there is nothing to do and we avoid a safepoint.
492 if (_obj != NULL) {
493 markOop mark = (*_obj)()->mark();
494 if (mark->has_bias_pattern()) {
495 return true;
496 }
497 } else {
498 for ( int i = 0 ; i < _objs->length(); i++ ) {
499 markOop mark = (_objs->at(i))()->mark();
500 if (mark->has_bias_pattern()) {
501 return true;
502 }
503 }
504 }
505 return false;
506 }
507
508 virtual void doit() {
509 if (_obj != NULL) {
510 log_info(biasedlocking)("Revoking bias with potentially per-thread safepoint:");
511 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread);
512 clean_up_cached_monitor_info();
513 return;
514 } else {
515 log_info(biasedlocking)("Revoking bias with global safepoint:");
516 BiasedLocking::revoke_at_safepoint(_objs);
517 }
518 }
519
520 BiasedLocking::Condition status_code() const {
521 return _status_code;
522 }
523 };
524
525
526 class VM_BulkRevokeBias : public VM_RevokeBias {
527 private:
528 bool _bulk_rebias;
529 bool _attempt_rebias_of_object;
530
531 public:
532 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
533 bool bulk_rebias,
534 bool attempt_rebias_of_object)
535 : VM_RevokeBias(obj, requesting_thread)
536 , _bulk_rebias(bulk_rebias)
537 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
538
539 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
540 virtual bool doit_prologue() { return true; }
541
542 virtual void doit() {
543 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
544 clean_up_cached_monitor_info();
545 }
546 };
547
548
549 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
550 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
551
552 // We can revoke the biases of anonymously-biased objects
553 // efficiently enough that we should not cause these revocations to
554 // update the heuristics because doing so may cause unwanted bulk
555 // revocations (which are expensive) to occur.
556 markOop mark = obj->mark();
557 if (mark->is_biased_anonymously() && !attempt_rebias) {
558 // We are probably trying to revoke the bias of this object due to
559 // an identity hash code computation. Try to revoke the bias
560 // without a safepoint. This is possible if we can successfully
561 // compare-and-exchange an unbiased header into the mark word of
562 // the object, meaning that no other thread has raced to acquire
563 // the bias of the object.
564 markOop biased_value = mark;
565 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
566 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
567 if (res_mark == biased_value) {
568 return BIAS_REVOKED;
569 }
570 } else if (mark->has_bias_pattern()) {
571 Klass* k = obj->klass();
572 markOop prototype_header = k->prototype_header();
573 if (!prototype_header->has_bias_pattern()) {
574 // This object has a stale bias from before the bulk revocation
575 // for this data type occurred. It's pointless to update the
576 // heuristics at this point so simply update the header with a
577 // CAS. If we fail this race, the object's bias has been revoked
578 // by another thread so we simply return and let the caller deal
579 // with it.
580 markOop biased_value = mark;
581 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark);
582 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked");
583 return BIAS_REVOKED;
584 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
585 // The epoch of this biasing has expired indicating that the
586 // object is effectively unbiased. Depending on whether we need
587 // to rebias or revoke the bias of this object we can do it
588 // efficiently enough with a CAS that we shouldn't update the
589 // heuristics. This is normally done in the assembly code but we
590 // can reach this point due to various points in the runtime
591 // needing to revoke biases.
592 if (attempt_rebias) {
593 assert(THREAD->is_Java_thread(), "");
594 markOop biased_value = mark;
595 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
596 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark);
597 if (res_mark == biased_value) {
598 return BIAS_REVOKED_AND_REBIASED;
599 }
600 } else {
601 markOop biased_value = mark;
602 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
603 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
604 if (res_mark == biased_value) {
605 return BIAS_REVOKED;
606 }
607 }
608 }
609 }
610
611 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
612 if (heuristics == HR_NOT_BIASED) {
613 return NOT_BIASED;
614 } else if (heuristics == HR_SINGLE_REVOKE) {
615 Klass *k = obj->klass();
616 markOop prototype_header = k->prototype_header();
617 if (mark->biased_locker() == THREAD &&
618 prototype_header->bias_epoch() == mark->bias_epoch()) {
619 // A thread is trying to revoke the bias of an object biased
620 // toward it, again likely due to an identity hash code
621 // computation. We can again avoid a safepoint in this case
622 // since we are only going to walk our own stack. There are no
623 // races with revocations occurring in other threads because we
624 // reach no safepoints in the revocation path.
625 // Also check the epoch because even if threads match, another thread
626 // can come in with a CAS to steal the bias of an object that has a
627 // stale epoch.
628 ResourceMark rm;
629 log_info(biasedlocking)("Revoking bias by walking my own stack:");
630 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD);
631 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
632 assert(cond == BIAS_REVOKED, "why not?");
633 return cond;
634 } else {
635 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
636 VMThread::execute(&revoke);
637 return revoke.status_code();
638 }
639 }
640
641 assert((heuristics == HR_BULK_REVOKE) ||
642 (heuristics == HR_BULK_REBIAS), "?");
643 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
644 (heuristics == HR_BULK_REBIAS),
645 attempt_rebias);
646 VMThread::execute(&bulk_revoke);
647 return bulk_revoke.status_code();
648 }
649
650
651 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
652 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
653 if (objs->length() == 0) {
654 return;
655 }
656 VM_RevokeBias revoke(objs, JavaThread::current());
657 VMThread::execute(&revoke);
658 }
659
660
661 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
662 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
663 oop obj = h_obj();
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 clean_up_cached_monitor_info();
672 }
673
674
675 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
676 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
677 int len = objs->length();
678 for (int i = 0; i < len; i++) {
679 oop obj = (objs->at(i))();
680 HeuristicsResult heuristics = update_heuristics(obj, false);
681 if (heuristics == HR_SINGLE_REVOKE) {
682 revoke_bias(obj, false, false, NULL);
683 } else if ((heuristics == HR_BULK_REBIAS) ||
684 (heuristics == HR_BULK_REVOKE)) {
685 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
686 }
687 }
688 clean_up_cached_monitor_info();
689 }
690
691
692 void BiasedLocking::preserve_marks() {
693 if (!UseBiasedLocking)
694 return;
695
696 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
697
698 assert(_preserved_oop_stack == NULL, "double initialization");
699 assert(_preserved_mark_stack == NULL, "double initialization");
700
701 // In order to reduce the number of mark words preserved during GC
702 // due to the presence of biased locking, we reinitialize most mark
703 // words to the class's prototype during GC -- even those which have
704 // a currently valid bias owner. One important situation where we
705 // must not clobber a bias is when a biased object is currently
706 // locked. To handle this case we iterate over the currently-locked
707 // monitors in a prepass and, if they are biased, preserve their
708 // mark words here. This should be a relatively small set of objects
709 // especially compared to the number of objects in the heap.
710 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true);
711 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
712
713 ResourceMark rm;
714 Thread* cur = Thread::current();
715 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) {
716 if (thread->has_last_Java_frame()) {
717 RegisterMap rm(thread);
718 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
719 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
720 if (monitors != NULL) {
721 int len = monitors->length();
722 // Walk monitors youngest to oldest
723 for (int i = len - 1; i >= 0; i--) {
724 MonitorInfo* mon_info = monitors->at(i);
725 if (mon_info->owner_is_scalar_replaced()) continue;
726 oop owner = mon_info->owner();
727 if (owner != NULL) {
728 markOop mark = owner->mark();
729 if (mark->has_bias_pattern()) {
730 _preserved_oop_stack->push(Handle(cur, owner));
731 _preserved_mark_stack->push(mark);
732 }
733 }
734 }
735 }
736 }
737 }
738 }
739 }
740
741
742 void BiasedLocking::restore_marks() {
743 if (!UseBiasedLocking)
744 return;
745
746 assert(_preserved_oop_stack != NULL, "double free");
747 assert(_preserved_mark_stack != NULL, "double free");
748
749 int len = _preserved_oop_stack->length();
750 for (int i = 0; i < len; i++) {
751 Handle owner = _preserved_oop_stack->at(i);
752 markOop mark = _preserved_mark_stack->at(i);
753 owner->set_mark(mark);
754 }
755
756 delete _preserved_oop_stack;
757 _preserved_oop_stack = NULL;
758 delete _preserved_mark_stack;
759 _preserved_mark_stack = NULL;
760 }
761
762
763 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
764 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
765 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
766 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
767 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
768 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
769 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
770
771
772 // BiasedLockingCounters
773
774 int BiasedLockingCounters::slow_path_entry_count() {
775 if (_slow_path_entry_count != 0) {
776 return _slow_path_entry_count;
777 }
778 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
779 _rebiased_lock_entry_count + _revoked_lock_entry_count +
780 _fast_path_entry_count;
781
782 return _total_entry_count - sum;
783 }
784
785 void BiasedLockingCounters::print_on(outputStream* st) {
786 tty->print_cr("# total entries: %d", _total_entry_count);
787 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
788 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
789 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
790 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
791 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
792 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
793 }