1 /*
2 * Copyright (c) 2005, 2017, 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.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 #include "trace/tracing.hpp"
39
40 static bool _biased_locking_enabled = false;
41 BiasedLockingCounters BiasedLocking::_counters;
42
43 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
44 static GrowableArray<markOop>* _preserved_mark_stack = NULL;
45
46 static void enable_biased_locking(InstanceKlass* k) {
47 k->set_prototype_header(markOopDesc::biased_locking_prototype());
48 }
49
50 class VM_EnableBiasedLocking: public VM_Operation {
51 private:
52 bool _is_cheap_allocated;
53 public:
54 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; }
55 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
56 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; }
57 bool is_cheap_allocated() const { return _is_cheap_allocated; }
58
59 void doit() {
60 // Iterate the class loader data dictionaries enabling biased locking for all
61 // currently loaded classes.
62 ClassLoaderDataGraph::dictionary_classes_do(enable_biased_locking);
63 // Indicate that future instances should enable it as well
64 _biased_locking_enabled = true;
65
66 log_info(biasedlocking)("Biased locking enabled");
67 }
68
69 bool allow_nested_vm_operations() const { return false; }
70 };
71
72
73 // One-shot PeriodicTask subclass for enabling biased locking
74 class EnableBiasedLockingTask : public PeriodicTask {
75 public:
76 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {}
77
78 virtual void task() {
79 // Use async VM operation to avoid blocking the Watcher thread.
80 // VM Thread will free C heap storage.
81 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true);
82 VMThread::execute(op);
83
84 // Reclaim our storage and disenroll ourself
85 delete this;
86 }
87 };
88
89
90 void BiasedLocking::init() {
91 // If biased locking is enabled, schedule a task to fire a few
92 // seconds into the run which turns on biased locking for all
93 // currently loaded classes as well as future ones. This is a
94 // workaround for startup time regressions due to a large number of
95 // safepoints being taken during VM startup for bias revocation.
96 // Ideally we would have a lower cost for individual bias revocation
97 // and not need a mechanism like this.
98 if (UseBiasedLocking) {
99 if (BiasedLockingStartupDelay > 0) {
100 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
101 task->enroll();
102 } else {
103 VM_EnableBiasedLocking op(false);
104 VMThread::execute(&op);
105 }
106 }
107 }
108
109
110 bool BiasedLocking::enabled() {
111 return _biased_locking_enabled;
112 }
113
114 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
115 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
116 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
117 if (info != NULL) {
118 return info;
119 }
120
121 info = new GrowableArray<MonitorInfo*>();
122
123 // It's possible for the thread to not have any Java frames on it,
124 // i.e., if it's the main thread and it's already returned from main()
125 if (thread->has_last_Java_frame()) {
126 RegisterMap rm(thread);
127 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
128 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
129 if (monitors != NULL) {
130 int len = monitors->length();
131 // Walk monitors youngest to oldest
132 for (int i = len - 1; i >= 0; i--) {
133 MonitorInfo* mon_info = monitors->at(i);
134 if (mon_info->eliminated()) continue;
135 oop owner = mon_info->owner();
136 if (owner != NULL) {
137 info->append(mon_info);
138 }
139 }
140 }
141 }
142 }
143
144 thread->set_cached_monitor_info(info);
145 return info;
146 }
147
148 // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL,
149 // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization).
150 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) {
151 markOop mark = obj->mark();
152 if (!mark->has_bias_pattern()) {
153 if (log_is_enabled(Info, biasedlocking)) {
154 ResourceMark rm;
155 log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT
156 ", mark " INTPTR_FORMAT ", type %s"
157 ", requesting thread " INTPTR_FORMAT
158 " because it's no longer biased)",
159 p2i((void *)obj), (intptr_t) mark,
160 obj->klass()->external_name(),
161 (intptr_t) requesting_thread);
162 }
163 return BiasedLocking::NOT_BIASED;
164 }
165
166 uint age = mark->age();
167 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
168 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
169
170 // Log at "info" level if not bulk, else "trace" level
171 if (!is_bulk) {
172 ResourceMark rm;
173 log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark "
174 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
175 ", allow rebias %d, requesting thread " INTPTR_FORMAT,
176 p2i((void *)obj),
177 (intptr_t) mark,
178 obj->klass()->external_name(),
179 (intptr_t) obj->klass()->prototype_header(),
180 (allow_rebias ? 1 : 0),
181 (intptr_t) requesting_thread);
182 } else {
183 ResourceMark rm;
184 log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark "
185 INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT
186 " , allow rebias %d , requesting thread " INTPTR_FORMAT,
187 p2i((void *)obj),
188 (intptr_t) mark,
189 obj->klass()->external_name(),
190 (intptr_t) obj->klass()->prototype_header(),
191 (allow_rebias ? 1 : 0),
192 (intptr_t) requesting_thread);
193 }
194
195 JavaThread* biased_thread = mark->biased_locker();
196 if (biased_thread == NULL) {
197 // Object is anonymously biased. We can get here if, for
198 // example, we revoke the bias due to an identity hash code
199 // being computed for an object.
200 if (!allow_rebias) {
201 obj->set_mark(unbiased_prototype);
202 }
203 // Log at "info" level if not bulk, else "trace" level
204 if (!is_bulk) {
205 log_info(biasedlocking)(" Revoked bias of anonymously-biased object");
206 } else {
207 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object");
208 }
209 return BiasedLocking::BIAS_REVOKED;
210 }
211
212 // Handle case where the thread toward which the object was biased has exited
213 bool thread_is_alive = false;
214 if (requesting_thread == biased_thread) {
215 thread_is_alive = true;
216 } else {
217 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) {
218 if (cur_thread == biased_thread) {
219 thread_is_alive = true;
220 break;
221 }
222 }
223 }
224 if (!thread_is_alive) {
225 if (allow_rebias) {
226 obj->set_mark(biased_prototype);
227 } else {
228 obj->set_mark(unbiased_prototype);
229 }
230 // Log at "info" level if not bulk, else "trace" level
231 if (!is_bulk) {
232 log_info(biasedlocking)(" Revoked bias of object biased toward dead thread ("
233 PTR_FORMAT ")", p2i(biased_thread));
234 } else {
235 log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread ("
236 PTR_FORMAT ")", p2i(biased_thread));
237 }
238 return BiasedLocking::BIAS_REVOKED;
239 }
240
241 // Log at "info" level if not bulk, else "trace" level
242 if (!is_bulk) {
243 log_info(biasedlocking)(" Revoked bias of object biased toward live thread ("
244 PTR_FORMAT ")", p2i(biased_thread));
245 } else {
246 log_trace(biasedlocking)(" Revoked bias of object biased toward live thread ("
247 PTR_FORMAT ")", p2i(biased_thread));
248 }
249
250 // Thread owning bias is alive.
251 // Check to see whether it currently owns the lock and, if so,
252 // write down the needed displaced headers to the thread's stack.
253 // Otherwise, restore the object's header either to the unlocked
254 // or unbiased state.
255 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
256 BasicLock* highest_lock = NULL;
257 for (int i = 0; i < cached_monitor_info->length(); i++) {
258 MonitorInfo* mon_info = cached_monitor_info->at(i);
259 if (mon_info->owner() == obj) {
260 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
261 p2i((void *) mon_info->owner()),
262 p2i((void *) obj));
263 // Assume recursive case and fix up highest lock later
264 markOop mark = markOopDesc::encode((BasicLock*) NULL);
265 highest_lock = mon_info->lock();
266 highest_lock->set_displaced_header(mark);
267 } else {
268 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
269 p2i((void *) mon_info->owner()),
270 p2i((void *) obj));
271 }
272 }
273 if (highest_lock != NULL) {
274 // Fix up highest lock to contain displaced header and point
275 // object at it
276 highest_lock->set_displaced_header(unbiased_prototype);
277 // Reset object header to point to displaced mark.
278 // Must release storing the lock address for platforms without TSO
279 // ordering (e.g. ppc).
280 obj->release_set_mark(markOopDesc::encode(highest_lock));
281 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
282 // Log at "info" level if not bulk, else "trace" level
283 if (!is_bulk) {
284 log_info(biasedlocking)(" Revoked bias of currently-locked object");
285 } else {
286 log_trace(biasedlocking)(" Revoked bias of currently-locked object");
287 }
288 } else {
289 // Log at "info" level if not bulk, else "trace" level
290 if (!is_bulk) {
291 log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
292 } else {
293 log_trace(biasedlocking)(" Revoked bias of currently-unlocked object");
294 }
295 if (allow_rebias) {
296 obj->set_mark(biased_prototype);
297 } else {
298 // Store the unlocked value into the object's header.
299 obj->set_mark(unbiased_prototype);
300 }
301 }
302
303 // If requested, return information on which thread held the bias
304 if (biased_locker != NULL) {
305 *biased_locker = biased_thread;
306 }
307
308 return BiasedLocking::BIAS_REVOKED;
309 }
310
311
312 enum HeuristicsResult {
313 HR_NOT_BIASED = 1,
314 HR_SINGLE_REVOKE = 2,
315 HR_BULK_REBIAS = 3,
316 HR_BULK_REVOKE = 4
317 };
318
319
320 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
321 markOop mark = o->mark();
322 if (!mark->has_bias_pattern()) {
323 return HR_NOT_BIASED;
324 }
325
326 // Heuristics to attempt to throttle the number of revocations.
327 // Stages:
328 // 1. Revoke the biases of all objects in the heap of this type,
329 // but allow rebiasing of those objects if unlocked.
330 // 2. Revoke the biases of all objects in the heap of this type
331 // and don't allow rebiasing of these objects. Disable
332 // allocation of objects of that type with the bias bit set.
333 Klass* k = o->klass();
334 jlong cur_time = os::javaTimeMillis();
335 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
336 int revocation_count = k->biased_lock_revocation_count();
337 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
338 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
339 (last_bulk_revocation_time != 0) &&
340 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
341 // This is the first revocation we've seen in a while of an
342 // object of this type since the last time we performed a bulk
343 // rebiasing operation. The application is allocating objects in
344 // bulk which are biased toward a thread and then handing them
345 // off to another thread. We can cope with this allocation
346 // pattern via the bulk rebiasing mechanism so we reset the
347 // klass's revocation count rather than allow it to increase
348 // monotonically. If we see the need to perform another bulk
349 // rebias operation later, we will, and if subsequently we see
350 // many more revocation operations in a short period of time we
351 // will completely disable biasing for this type.
352 k->set_biased_lock_revocation_count(0);
353 revocation_count = 0;
354 }
355
356 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
357 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
358 revocation_count = k->atomic_incr_biased_lock_revocation_count();
359 }
360
361 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
362 return HR_BULK_REVOKE;
363 }
364
365 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
366 return HR_BULK_REBIAS;
367 }
368
369 return HR_SINGLE_REVOKE;
370 }
371
372
373 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
374 bool bulk_rebias,
375 bool attempt_rebias_of_object,
376 JavaThread* requesting_thread) {
377 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
378
379 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object "
380 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
381 (bulk_rebias ? "rebias" : "revoke"),
382 p2i((void *) o),
383 (intptr_t) o->mark(),
384 o->klass()->external_name());
385
386 jlong cur_time = os::javaTimeMillis();
387 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
388
389
390 Klass* k_o = o->klass();
391 Klass* klass = k_o;
392
393 if (bulk_rebias) {
394 // Use the epoch in the klass of the object to implicitly revoke
395 // all biases of objects of this data type and force them to be
396 // reacquired. However, we also need to walk the stacks of all
397 // threads and update the headers of lightweight locked objects
398 // with biases to have the current epoch.
399
400 // If the prototype header doesn't have the bias pattern, don't
401 // try to update the epoch -- assume another VM operation came in
402 // and reset the header to the unbiased state, which will
403 // implicitly cause all existing biases to be revoked
404 if (klass->prototype_header()->has_bias_pattern()) {
405 int prev_epoch = klass->prototype_header()->bias_epoch();
406 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
407 int cur_epoch = klass->prototype_header()->bias_epoch();
408
409 // Now walk all threads' stacks and adjust epochs of any biased
410 // and locked objects of this data type we encounter
411 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
412 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
413 for (int i = 0; i < cached_monitor_info->length(); i++) {
414 MonitorInfo* mon_info = cached_monitor_info->at(i);
415 oop owner = mon_info->owner();
416 markOop mark = owner->mark();
417 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
418 // We might have encountered this object already in the case of recursive locking
419 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
420 owner->set_mark(mark->set_bias_epoch(cur_epoch));
421 }
422 }
423 }
424 }
425
426 // At this point we're done. All we have to do is potentially
427 // adjust the header of the given object to revoke its bias.
428 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread, NULL);
429 } else {
430 if (log_is_enabled(Info, biasedlocking)) {
431 ResourceMark rm;
432 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name());
433 }
434
435 // Disable biased locking for this data type. Not only will this
436 // cause future instances to not be biased, but existing biased
437 // instances will notice that this implicitly caused their biases
438 // to be revoked.
439 klass->set_prototype_header(markOopDesc::prototype());
440
441 // Now walk all threads' stacks and forcibly revoke the biases of
442 // any locked and biased objects of this data type we encounter.
443 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
444 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
445 for (int i = 0; i < cached_monitor_info->length(); i++) {
446 MonitorInfo* mon_info = cached_monitor_info->at(i);
447 oop owner = mon_info->owner();
448 markOop mark = owner->mark();
449 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
450 revoke_bias(owner, false, true, requesting_thread, NULL);
451 }
452 }
453 }
454
455 // Must force the bias of the passed object to be forcibly revoked
456 // as well to ensure guarantees to callers
457 revoke_bias(o, false, true, requesting_thread, NULL);
458 }
459
460 log_info(biasedlocking)("* Ending bulk revocation");
461
462 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
463
464 if (attempt_rebias_of_object &&
465 o->mark()->has_bias_pattern() &&
466 klass->prototype_header()->has_bias_pattern()) {
467 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
468 klass->prototype_header()->bias_epoch());
469 o->set_mark(new_mark);
470 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
471 log_info(biasedlocking)(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
472 }
473
474 assert(!o->mark()->has_bias_pattern() ||
475 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
476 "bug in bulk bias revocation");
477
478 return status_code;
479 }
480
481
482 static void clean_up_cached_monitor_info() {
483 // Walk the thread list clearing out the cached monitors
484 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
485 thr->set_cached_monitor_info(NULL);
486 }
487 }
488
489
490 class VM_RevokeBias : public VM_Operation {
491 protected:
492 Handle* _obj;
493 GrowableArray<Handle>* _objs;
494 JavaThread* _requesting_thread;
495 BiasedLocking::Condition _status_code;
496 traceid _biased_locker_id;
497
498 public:
499 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
500 : _obj(obj)
501 , _objs(NULL)
502 , _requesting_thread(requesting_thread)
503 , _status_code(BiasedLocking::NOT_BIASED)
504 , _biased_locker_id(0) {}
505
506 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
507 : _obj(NULL)
508 , _objs(objs)
509 , _requesting_thread(requesting_thread)
510 , _status_code(BiasedLocking::NOT_BIASED)
511 , _biased_locker_id(0) {}
512
513 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
514
515 virtual bool doit_prologue() {
516 // Verify that there is actual work to do since the callers just
517 // give us locked object(s). If we don't find any biased objects
518 // there is nothing to do and we avoid a safepoint.
519 if (_obj != NULL) {
520 markOop mark = (*_obj)()->mark();
521 if (mark->has_bias_pattern()) {
522 return true;
523 }
524 } else {
525 for ( int i = 0 ; i < _objs->length(); i++ ) {
526 markOop mark = (_objs->at(i))()->mark();
527 if (mark->has_bias_pattern()) {
528 return true;
529 }
530 }
531 }
532 return false;
533 }
534
535 virtual void doit() {
536 if (_obj != NULL) {
537 log_info(biasedlocking)("Revoking bias with potentially per-thread safepoint:");
538 JavaThread* biased_locker = NULL;
539 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread, &biased_locker);
540 if (biased_locker != NULL) {
541 _biased_locker_id = THREAD_TRACE_ID(biased_locker);
542 }
543 clean_up_cached_monitor_info();
544 return;
545 } else {
546 log_info(biasedlocking)("Revoking bias with global safepoint:");
547 BiasedLocking::revoke_at_safepoint(_objs);
548 }
549 }
550
551 BiasedLocking::Condition status_code() const {
552 return _status_code;
553 }
554
555 traceid biased_locker() const {
556 return _biased_locker_id;
557 }
558 };
559
560
561 class VM_BulkRevokeBias : public VM_RevokeBias {
562 private:
563 bool _bulk_rebias;
564 bool _attempt_rebias_of_object;
565
566 public:
567 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
568 bool bulk_rebias,
569 bool attempt_rebias_of_object)
570 : VM_RevokeBias(obj, requesting_thread)
571 , _bulk_rebias(bulk_rebias)
572 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
573
574 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
575 virtual bool doit_prologue() { return true; }
576
577 virtual void doit() {
578 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
579 clean_up_cached_monitor_info();
580 }
581 };
582
583
584 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
585 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
586
587 // We can revoke the biases of anonymously-biased objects
588 // efficiently enough that we should not cause these revocations to
589 // update the heuristics because doing so may cause unwanted bulk
590 // revocations (which are expensive) to occur.
591 markOop mark = obj->mark();
592 if (mark->is_biased_anonymously() && !attempt_rebias) {
593 // We are probably trying to revoke the bias of this object due to
594 // an identity hash code computation. Try to revoke the bias
595 // without a safepoint. This is possible if we can successfully
596 // compare-and-exchange an unbiased header into the mark word of
597 // the object, meaning that no other thread has raced to acquire
598 // the bias of the object.
599 markOop biased_value = mark;
600 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
601 markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
602 if (res_mark == biased_value) {
603 return BIAS_REVOKED;
604 }
605 } else if (mark->has_bias_pattern()) {
606 Klass* k = obj->klass();
607 markOop prototype_header = k->prototype_header();
608 if (!prototype_header->has_bias_pattern()) {
609 // This object has a stale bias from before the bulk revocation
610 // for this data type occurred. It's pointless to update the
611 // heuristics at this point so simply update the header with a
612 // CAS. If we fail this race, the object's bias has been revoked
613 // by another thread so we simply return and let the caller deal
614 // with it.
615 markOop biased_value = mark;
616 markOop res_mark = obj->cas_set_mark(prototype_header, mark);
617 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked");
618 return BIAS_REVOKED;
619 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
620 // The epoch of this biasing has expired indicating that the
621 // object is effectively unbiased. Depending on whether we need
622 // to rebias or revoke the bias of this object we can do it
623 // efficiently enough with a CAS that we shouldn't update the
624 // heuristics. This is normally done in the assembly code but we
625 // can reach this point due to various points in the runtime
626 // needing to revoke biases.
627 if (attempt_rebias) {
628 assert(THREAD->is_Java_thread(), "");
629 markOop biased_value = mark;
630 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
631 markOop res_mark = obj->cas_set_mark(rebiased_prototype, mark);
632 if (res_mark == biased_value) {
633 return BIAS_REVOKED_AND_REBIASED;
634 }
635 } else {
636 markOop biased_value = mark;
637 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
638 markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
639 if (res_mark == biased_value) {
640 return BIAS_REVOKED;
641 }
642 }
643 }
644 }
645
646 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
647 if (heuristics == HR_NOT_BIASED) {
648 return NOT_BIASED;
649 } else if (heuristics == HR_SINGLE_REVOKE) {
650 Klass *k = obj->klass();
651 markOop prototype_header = k->prototype_header();
652 if (mark->biased_locker() == THREAD &&
653 prototype_header->bias_epoch() == mark->bias_epoch()) {
654 // A thread is trying to revoke the bias of an object biased
655 // toward it, again likely due to an identity hash code
656 // computation. We can again avoid a safepoint in this case
657 // since we are only going to walk our own stack. There are no
658 // races with revocations occurring in other threads because we
659 // reach no safepoints in the revocation path.
660 // Also check the epoch because even if threads match, another thread
661 // can come in with a CAS to steal the bias of an object that has a
662 // stale epoch.
663 ResourceMark rm;
664 log_info(biasedlocking)("Revoking bias by walking my own stack:");
665 EventBiasedLockSelfRevocation event;
666 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD, NULL);
667 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
668 assert(cond == BIAS_REVOKED, "why not?");
669 if (event.should_commit()) {
670 event.set_lockClass(k);
671 event.commit();
672 }
673 return cond;
674 } else {
675 EventBiasedLockRevocation event;
676 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
677 VMThread::execute(&revoke);
678 if (event.should_commit() && (revoke.status_code() != NOT_BIASED)) {
679 event.set_lockClass(k);
680 // Subtract 1 to match the id of events committed inside the safepoint
681 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1);
682 event.set_previousOwner(revoke.biased_locker());
683 event.commit();
684 }
685 return revoke.status_code();
686 }
687 }
688
689 assert((heuristics == HR_BULK_REVOKE) ||
690 (heuristics == HR_BULK_REBIAS), "?");
691 EventBiasedLockClassRevocation event;
692 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
693 (heuristics == HR_BULK_REBIAS),
694 attempt_rebias);
695 VMThread::execute(&bulk_revoke);
696 if (event.should_commit()) {
697 event.set_revokedClass(obj->klass());
698 event.set_disableBiasing((heuristics != HR_BULK_REBIAS));
699 // Subtract 1 to match the id of events committed inside the safepoint
700 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1);
701 event.commit();
702 }
703 return bulk_revoke.status_code();
704 }
705
706
707 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
708 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
709 if (objs->length() == 0) {
710 return;
711 }
712 VM_RevokeBias revoke(objs, JavaThread::current());
713 VMThread::execute(&revoke);
714 }
715
716
717 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
718 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
719 oop obj = h_obj();
720 HeuristicsResult heuristics = update_heuristics(obj, false);
721 if (heuristics == HR_SINGLE_REVOKE) {
722 revoke_bias(obj, false, false, NULL, NULL);
723 } else if ((heuristics == HR_BULK_REBIAS) ||
724 (heuristics == HR_BULK_REVOKE)) {
725 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
726 }
727 clean_up_cached_monitor_info();
728 }
729
730
731 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
732 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
733 int len = objs->length();
734 for (int i = 0; i < len; i++) {
735 oop obj = (objs->at(i))();
736 HeuristicsResult heuristics = update_heuristics(obj, false);
737 if (heuristics == HR_SINGLE_REVOKE) {
738 revoke_bias(obj, false, false, NULL, NULL);
739 } else if ((heuristics == HR_BULK_REBIAS) ||
740 (heuristics == HR_BULK_REVOKE)) {
741 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
742 }
743 }
744 clean_up_cached_monitor_info();
745 }
746
747
748 void BiasedLocking::preserve_marks() {
749 if (!UseBiasedLocking)
750 return;
751
752 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
753
754 assert(_preserved_oop_stack == NULL, "double initialization");
755 assert(_preserved_mark_stack == NULL, "double initialization");
756
757 // In order to reduce the number of mark words preserved during GC
758 // due to the presence of biased locking, we reinitialize most mark
759 // words to the class's prototype during GC -- even those which have
760 // a currently valid bias owner. One important situation where we
761 // must not clobber a bias is when a biased object is currently
762 // locked. To handle this case we iterate over the currently-locked
763 // monitors in a prepass and, if they are biased, preserve their
764 // mark words here. This should be a relatively small set of objects
765 // especially compared to the number of objects in the heap.
766 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true);
767 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
768
769 ResourceMark rm;
770 Thread* cur = Thread::current();
771 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) {
772 if (thread->has_last_Java_frame()) {
773 RegisterMap rm(thread);
774 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
775 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
776 if (monitors != NULL) {
777 int len = monitors->length();
778 // Walk monitors youngest to oldest
779 for (int i = len - 1; i >= 0; i--) {
780 MonitorInfo* mon_info = monitors->at(i);
781 if (mon_info->owner_is_scalar_replaced()) continue;
782 oop owner = mon_info->owner();
783 if (owner != NULL) {
784 markOop mark = owner->mark();
785 if (mark->has_bias_pattern()) {
786 _preserved_oop_stack->push(Handle(cur, owner));
787 _preserved_mark_stack->push(mark);
788 }
789 }
790 }
791 }
792 }
793 }
794 }
795 }
796
797
798 void BiasedLocking::restore_marks() {
799 if (!UseBiasedLocking)
800 return;
801
802 assert(_preserved_oop_stack != NULL, "double free");
803 assert(_preserved_mark_stack != NULL, "double free");
804
805 int len = _preserved_oop_stack->length();
806 for (int i = 0; i < len; i++) {
807 Handle owner = _preserved_oop_stack->at(i);
808 markOop mark = _preserved_mark_stack->at(i);
809 owner->set_mark(mark);
810 }
811
812 delete _preserved_oop_stack;
813 _preserved_oop_stack = NULL;
814 delete _preserved_mark_stack;
815 _preserved_mark_stack = NULL;
816 }
817
818
819 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
820 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
821 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
822 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
823 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
824 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
825 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
826
827
828 // BiasedLockingCounters
829
830 int BiasedLockingCounters::slow_path_entry_count() {
831 if (_slow_path_entry_count != 0) {
832 return _slow_path_entry_count;
833 }
834 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
835 _rebiased_lock_entry_count + _revoked_lock_entry_count +
836 _fast_path_entry_count;
837
838 return _total_entry_count - sum;
839 }
840
841 void BiasedLockingCounters::print_on(outputStream* st) {
842 tty->print_cr("# total entries: %d", _total_entry_count);
843 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
844 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
845 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
846 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
847 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
848 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
849 }