1 /*
2 * Copyright (c) 2005, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderDataGraph.hpp"
27 #include "jfr/jfrEvents.hpp"
28 #include "jfr/support/jfrThreadId.hpp"
29 #include "logging/log.hpp"
30 #include "memory/resourceArea.hpp"
31 #include "oops/klass.inline.hpp"
32 #include "oops/markWord.hpp"
33 #include "oops/oop.inline.hpp"
34 #include "runtime/atomic.hpp"
35 #include "runtime/basicLock.hpp"
36 #include "runtime/biasedLocking.hpp"
37 #include "runtime/handles.inline.hpp"
38 #include "runtime/task.hpp"
39 #include "runtime/threadSMR.hpp"
40 #include "runtime/vframe.hpp"
41 #include "runtime/vmThread.hpp"
42 #include "runtime/vmOperations.hpp"
43
44
45 static bool _biased_locking_enabled = false;
46 BiasedLockingCounters BiasedLocking::_counters;
47
48 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
49 static GrowableArray<markWord>* _preserved_mark_stack = NULL;
50
51 static void enable_biased_locking(InstanceKlass* k) {
52 k->set_prototype_header(markWord::biased_locking_prototype());
53 }
54
55 static void enable_biased_locking() {
56 _biased_locking_enabled = true;
57 log_info(biasedlocking)("Biased locking enabled");
58 }
59
60 class VM_EnableBiasedLocking: public VM_Operation {
61 public:
62 VM_EnableBiasedLocking() {}
63 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
64 Mode evaluation_mode() const { return _async_safepoint; }
65 bool is_cheap_allocated() const { return true; }
66
67 void doit() {
68 // Iterate the class loader data dictionaries enabling biased locking for all
69 // currently loaded classes.
70 ClassLoaderDataGraph::dictionary_classes_do(enable_biased_locking);
71 // Indicate that future instances should enable it as well
72 enable_biased_locking();
73 }
74
75 bool allow_nested_vm_operations() const { return false; }
76 };
77
78
79 // One-shot PeriodicTask subclass for enabling biased locking
80 class EnableBiasedLockingTask : public PeriodicTask {
81 public:
82 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {}
83
84 virtual void task() {
85 // Use async VM operation to avoid blocking the Watcher thread.
86 // VM Thread will free C heap storage.
87 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking();
88 VMThread::execute(op);
89
90 // Reclaim our storage and disenroll ourself
91 delete this;
92 }
93 };
94
95
96 void BiasedLocking::init() {
97 // If biased locking is enabled and BiasedLockingStartupDelay is set,
98 // schedule a task to fire after the specified delay which turns on
99 // biased locking for all currently loaded classes as well as future
100 // ones. This could be a workaround for startup time regressions
101 // due to large number of safepoints being taken during VM startup for
102 // bias revocation.
103 if (UseBiasedLocking) {
104 if (BiasedLockingStartupDelay > 0) {
105 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
106 task->enroll();
107 } else {
108 enable_biased_locking();
109 }
110 }
111 }
112
113
114 bool BiasedLocking::enabled() {
115 assert(UseBiasedLocking, "precondition");
116 // We check "BiasedLockingStartupDelay == 0" here to cover the
117 // possibility of calls to BiasedLocking::enabled() before
118 // BiasedLocking::init().
119 return _biased_locking_enabled || BiasedLockingStartupDelay == 0;
120 }
121
122
123 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
124 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
125 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
126 if (info != NULL) {
127 return info;
128 }
129
130 info = new GrowableArray<MonitorInfo*>();
131
132 // It's possible for the thread to not have any Java frames on it,
133 // i.e., if it's the main thread and it's already returned from main()
134 if (thread->has_last_Java_frame()) {
135 RegisterMap rm(thread);
136 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
137 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
138 if (monitors != NULL) {
139 int len = monitors->length();
140 // Walk monitors youngest to oldest
141 for (int i = len - 1; i >= 0; i--) {
142 MonitorInfo* mon_info = monitors->at(i);
143 if (mon_info->eliminated()) continue;
144 oop owner = mon_info->owner();
145 if (owner != NULL) {
146 info->append(mon_info);
147 }
148 }
149 }
150 }
151 }
152
153 thread->set_cached_monitor_info(info);
154 return info;
155 }
156
157
158 // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL,
159 // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization).
160 void BiasedLocking::single_revoke_at_safepoint(oop obj, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) {
161 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
162 assert(Thread::current()->is_VM_thread(), "must be VMThread");
163
164 markWord mark = obj->mark();
165 if (!mark.has_bias_pattern()) {
166 if (log_is_enabled(Info, biasedlocking)) {
167 ResourceMark rm;
168 log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT
169 ", mark " INTPTR_FORMAT ", type %s"
170 ", requesting thread " INTPTR_FORMAT
171 " because it's no longer biased)",
172 p2i((void *)obj), mark.value(),
173 obj->klass()->external_name(),
174 (intptr_t) requesting_thread);
175 }
176 return;
177 }
178
179 uint age = mark.age();
180 markWord unbiased_prototype = markWord::prototype().set_age(age);
181
182 // Log at "info" level if not bulk, else "trace" level
183 if (!is_bulk) {
184 ResourceMark rm;
185 log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark "
186 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
187 ", requesting thread " INTPTR_FORMAT,
188 p2i((void *)obj),
189 mark.value(),
190 obj->klass()->external_name(),
191 obj->klass()->prototype_header().value(),
192 (intptr_t) requesting_thread);
193 } else {
194 ResourceMark rm;
195 log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark "
196 INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT
197 " , requesting thread " INTPTR_FORMAT,
198 p2i((void *)obj),
199 mark.value(),
200 obj->klass()->external_name(),
201 obj->klass()->prototype_header().value(),
202 (intptr_t) requesting_thread);
203 }
204
205 JavaThread* biased_thread = mark.biased_locker();
206 if (biased_thread == NULL) {
207 // Object is anonymously biased. We can get here if, for
208 // example, we revoke the bias due to an identity hash code
209 // being computed for an object.
210 obj->set_mark(unbiased_prototype);
211
212 // Log at "info" level if not bulk, else "trace" level
213 if (!is_bulk) {
214 log_info(biasedlocking)(" Revoked bias of anonymously-biased object");
215 } else {
216 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object");
217 }
218 return;
219 }
220
221 // Handle case where the thread toward which the object was biased has exited
222 bool thread_is_alive = false;
223 if (requesting_thread == biased_thread) {
224 thread_is_alive = true;
225 } else {
226 ThreadsListHandle tlh;
227 thread_is_alive = tlh.includes(biased_thread);
228 }
229 if (!thread_is_alive) {
230 obj->set_mark(unbiased_prototype);
231 // Log at "info" level if not bulk, else "trace" level
232 if (!is_bulk) {
233 log_info(biasedlocking)(" Revoked bias of object biased toward dead thread ("
234 PTR_FORMAT ")", p2i(biased_thread));
235 } else {
236 log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread ("
237 PTR_FORMAT ")", p2i(biased_thread));
238 }
239 return;
240 }
241
242 // Log at "info" level if not bulk, else "trace" level
243 if (!is_bulk) {
244 log_info(biasedlocking)(" Revoked bias of object biased toward live thread ("
245 PTR_FORMAT ")", p2i(biased_thread));
246 } else {
247 log_trace(biasedlocking)(" Revoked bias of object biased toward live thread ("
248 PTR_FORMAT ")", p2i(biased_thread));
249 }
250
251 // Thread owning bias is alive.
252 // Check to see whether it currently owns the lock and, if so,
253 // write down the needed displaced headers to the thread's stack.
254 // Otherwise, restore the object's header either to the unlocked
255 // or unbiased state.
256 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
257 BasicLock* highest_lock = NULL;
258 for (int i = 0; i < cached_monitor_info->length(); i++) {
259 MonitorInfo* mon_info = cached_monitor_info->at(i);
260 if (mon_info->owner() == obj) {
261 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
262 p2i((void *) mon_info->owner()),
263 p2i((void *) obj));
264 // Assume recursive case and fix up highest lock below
265 markWord mark = markWord::encode((BasicLock*) NULL);
266 highest_lock = mon_info->lock();
267 highest_lock->set_displaced_header(mark);
268 } else {
269 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
270 p2i((void *) mon_info->owner()),
271 p2i((void *) obj));
272 }
273 }
274 if (highest_lock != NULL) {
275 // Fix up highest lock to contain displaced header and point
276 // object at it
277 highest_lock->set_displaced_header(unbiased_prototype);
278 // Reset object header to point to displaced mark.
279 // Must release store the lock address for platforms without TSO
280 // ordering (e.g. ppc).
281 obj->release_set_mark(markWord::encode(highest_lock));
282 assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit");
283 // Log at "info" level if not bulk, else "trace" level
284 if (!is_bulk) {
285 log_info(biasedlocking)(" Revoked bias of currently-locked object");
286 } else {
287 log_trace(biasedlocking)(" Revoked bias of currently-locked object");
288 }
289 } else {
290 // Log at "info" level if not bulk, else "trace" level
291 if (!is_bulk) {
292 log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
293 } else {
294 log_trace(biasedlocking)(" Revoked bias of currently-unlocked object");
295 }
296 // Store the unlocked value into the object's header.
297 obj->set_mark(unbiased_prototype);
298 }
299
300 // If requested, return information on which thread held the bias
301 if (biased_locker != NULL) {
302 *biased_locker = biased_thread;
303 }
304 }
305
306
307 enum HeuristicsResult {
308 HR_NOT_BIASED = 1,
309 HR_SINGLE_REVOKE = 2,
310 HR_BULK_REBIAS = 3,
311 HR_BULK_REVOKE = 4
312 };
313
314
315 static HeuristicsResult update_heuristics(oop o) {
316 markWord mark = o->mark();
317 if (!mark.has_bias_pattern()) {
318 return HR_NOT_BIASED;
319 }
320
321 // Heuristics to attempt to throttle the number of revocations.
322 // Stages:
323 // 1. Revoke the biases of all objects in the heap of this type,
324 // but allow rebiasing of those objects if unlocked.
325 // 2. Revoke the biases of all objects in the heap of this type
326 // and don't allow rebiasing of these objects. Disable
327 // allocation of objects of that type with the bias bit set.
328 Klass* k = o->klass();
329 jlong cur_time = os::javaTimeMillis();
330 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
331 int revocation_count = k->biased_lock_revocation_count();
332 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
333 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
334 (last_bulk_revocation_time != 0) &&
335 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
336 // This is the first revocation we've seen in a while of an
337 // object of this type since the last time we performed a bulk
338 // rebiasing operation. The application is allocating objects in
339 // bulk which are biased toward a thread and then handing them
340 // off to another thread. We can cope with this allocation
341 // pattern via the bulk rebiasing mechanism so we reset the
342 // klass's revocation count rather than allow it to increase
343 // monotonically. If we see the need to perform another bulk
344 // rebias operation later, we will, and if subsequently we see
345 // many more revocation operations in a short period of time we
346 // will completely disable biasing for this type.
347 k->set_biased_lock_revocation_count(0);
348 revocation_count = 0;
349 }
350
351 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
352 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
353 revocation_count = k->atomic_incr_biased_lock_revocation_count();
354 }
355
356 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
357 return HR_BULK_REVOKE;
358 }
359
360 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
361 return HR_BULK_REBIAS;
362 }
363
364 return HR_SINGLE_REVOKE;
365 }
366
367
368 void BiasedLocking::bulk_revoke_at_safepoint(oop o, bool bulk_rebias, JavaThread* requesting_thread) {
369 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
370 assert(Thread::current()->is_VM_thread(), "must be VMThread");
371
372 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object "
373 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
374 (bulk_rebias ? "rebias" : "revoke"),
375 p2i((void *) o),
376 o->mark().value(),
377 o->klass()->external_name());
378
379 jlong cur_time = os::javaTimeMillis();
380 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
381
382 Klass* k_o = o->klass();
383 Klass* klass = k_o;
384
385 {
386 JavaThreadIteratorWithHandle jtiwh;
387
388 if (bulk_rebias) {
389 // Use the epoch in the klass of the object to implicitly revoke
390 // all biases of objects of this data type and force them to be
391 // reacquired. However, we also need to walk the stacks of all
392 // threads and update the headers of lightweight locked objects
393 // with biases to have the current epoch.
394
395 // If the prototype header doesn't have the bias pattern, don't
396 // try to update the epoch -- assume another VM operation came in
397 // and reset the header to the unbiased state, which will
398 // implicitly cause all existing biases to be revoked
399 if (klass->prototype_header().has_bias_pattern()) {
400 int prev_epoch = klass->prototype_header().bias_epoch();
401 klass->set_prototype_header(klass->prototype_header().incr_bias_epoch());
402 int cur_epoch = klass->prototype_header().bias_epoch();
403
404 // Now walk all threads' stacks and adjust epochs of any biased
405 // and locked objects of this data type we encounter
406 for (; JavaThread *thr = jtiwh.next(); ) {
407 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
408 for (int i = 0; i < cached_monitor_info->length(); i++) {
409 MonitorInfo* mon_info = cached_monitor_info->at(i);
410 oop owner = mon_info->owner();
411 markWord mark = owner->mark();
412 if ((owner->klass() == k_o) && mark.has_bias_pattern()) {
413 // We might have encountered this object already in the case of recursive locking
414 assert(mark.bias_epoch() == prev_epoch || mark.bias_epoch() == cur_epoch, "error in bias epoch adjustment");
415 owner->set_mark(mark.set_bias_epoch(cur_epoch));
416 }
417 }
418 }
419 }
420
421 // At this point we're done. All we have to do is potentially
422 // adjust the header of the given object to revoke its bias.
423 single_revoke_at_safepoint(o, true, requesting_thread, NULL);
424 } else {
425 if (log_is_enabled(Info, biasedlocking)) {
426 ResourceMark rm;
427 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name());
428 }
429
430 // Disable biased locking for this data type. Not only will this
431 // cause future instances to not be biased, but existing biased
432 // instances will notice that this implicitly caused their biases
433 // to be revoked.
434 klass->set_prototype_header(markWord::prototype());
435
436 // Now walk all threads' stacks and forcibly revoke the biases of
437 // any locked and biased objects of this data type we encounter.
438 for (; JavaThread *thr = jtiwh.next(); ) {
439 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
440 for (int i = 0; i < cached_monitor_info->length(); i++) {
441 MonitorInfo* mon_info = cached_monitor_info->at(i);
442 oop owner = mon_info->owner();
443 markWord mark = owner->mark();
444 if ((owner->klass() == k_o) && mark.has_bias_pattern()) {
445 single_revoke_at_safepoint(owner, true, requesting_thread, NULL);
446 }
447 }
448 }
449
450 // Must force the bias of the passed object to be forcibly revoked
451 // as well to ensure guarantees to callers
452 single_revoke_at_safepoint(o, true, requesting_thread, NULL);
453 }
454 } // ThreadsListHandle is destroyed here.
455
456 log_info(biasedlocking)("* Ending bulk revocation");
457
458 assert(!o->mark().has_bias_pattern(), "bug in bulk bias revocation");
459 }
460
461
462 static void clean_up_cached_monitor_info(JavaThread* thread = NULL) {
463 if (thread != NULL) {
464 thread->set_cached_monitor_info(NULL);
465 } else {
466 // Walk the thread list clearing out the cached monitors
467 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
468 thr->set_cached_monitor_info(NULL);
469 }
470 }
471 }
472
473
474 class VM_BulkRevokeBias : public VM_Operation {
475 private:
476 Handle* _obj;
477 JavaThread* _requesting_thread;
478 bool _bulk_rebias;
479 uint64_t _safepoint_id;
480
481 public:
482 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
483 bool bulk_rebias)
484 : _obj(obj)
485 , _requesting_thread(requesting_thread)
486 , _bulk_rebias(bulk_rebias)
487 , _safepoint_id(0) {}
488
489 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
490
491 virtual void doit() {
492 BiasedLocking::bulk_revoke_at_safepoint((*_obj)(), _bulk_rebias, _requesting_thread);
493 _safepoint_id = SafepointSynchronize::safepoint_id();
494 clean_up_cached_monitor_info();
495 }
496
497 bool is_bulk_rebias() const {
498 return _bulk_rebias;
499 }
500
501 uint64_t safepoint_id() const {
502 return _safepoint_id;
503 }
504 };
505
506
507 class RevokeOneBias : public ThreadClosure {
508 protected:
509 Handle _obj;
510 JavaThread* _requesting_thread;
511 JavaThread* _biased_locker;
512 BiasedLocking::Condition _status_code;
513 traceid _biased_locker_id;
514
515 public:
516 RevokeOneBias(Handle obj, JavaThread* requesting_thread, JavaThread* biased_locker)
517 : _obj(obj)
518 , _requesting_thread(requesting_thread)
519 , _biased_locker(biased_locker)
520 , _status_code(BiasedLocking::NOT_BIASED)
521 , _biased_locker_id(0) {}
522
523 void do_thread(Thread* target) {
524 assert(target == _biased_locker, "Wrong thread");
525
526 oop o = _obj();
527 markWord mark = o->mark();
528
529 if (!mark.has_bias_pattern()) {
530 return;
531 }
532
533 markWord prototype = o->klass()->prototype_header();
534 if (!prototype.has_bias_pattern()) {
535 // This object has a stale bias from before the handshake
536 // was requested. If we fail this race, the object's bias
537 // has been revoked by another thread so we simply return.
538 markWord biased_value = mark;
539 mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark);
540 assert(!o->mark().has_bias_pattern(), "even if we raced, should still be revoked");
541 if (biased_value == mark) {
542 _status_code = BiasedLocking::BIAS_REVOKED;
543 }
544 return;
545 }
546
547 if (_biased_locker == mark.biased_locker()) {
548 if (mark.bias_epoch() == prototype.bias_epoch()) {
549 // Epoch is still valid. This means biaser could be currently
550 // synchronized on this object. We must walk its stack looking
551 // for monitor records associated with this object and change
552 // them to be stack locks if any are found.
553 ResourceMark rm;
554 BiasedLocking::walk_stack_and_revoke(o, _biased_locker);
555 _biased_locker->set_cached_monitor_info(NULL);
556 assert(!o->mark().has_bias_pattern(), "invariant");
557 _biased_locker_id = JFR_THREAD_ID(_biased_locker);
558 _status_code = BiasedLocking::BIAS_REVOKED;
559 return;
560 } else {
561 markWord biased_value = mark;
562 mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark);
563 if (mark == biased_value || !mark.has_bias_pattern()) {
564 assert(!o->mark().has_bias_pattern(), "should be revoked");
565 _status_code = (biased_value == mark) ? BiasedLocking::BIAS_REVOKED : BiasedLocking::NOT_BIASED;
566 return;
567 }
568 }
569 }
570
571 _status_code = BiasedLocking::NOT_REVOKED;
572 }
573
574 BiasedLocking::Condition status_code() const {
575 return _status_code;
576 }
577
578 traceid biased_locker() const {
579 return _biased_locker_id;
580 }
581 };
582
583
584 static void post_self_revocation_event(EventBiasedLockSelfRevocation* event, Klass* k) {
585 assert(event != NULL, "invariant");
586 assert(k != NULL, "invariant");
587 assert(event->should_commit(), "invariant");
588 event->set_lockClass(k);
589 event->commit();
590 }
591
592 static void post_revocation_event(EventBiasedLockRevocation* event, Klass* k, RevokeOneBias* op) {
593 assert(event != NULL, "invariant");
594 assert(k != NULL, "invariant");
595 assert(op != NULL, "invariant");
596 assert(event->should_commit(), "invariant");
597 event->set_lockClass(k);
598 event->set_safepointId(0);
599 event->set_previousOwner(op->biased_locker());
600 event->commit();
601 }
602
603 static void post_class_revocation_event(EventBiasedLockClassRevocation* event, Klass* k, VM_BulkRevokeBias* op) {
604 assert(event != NULL, "invariant");
605 assert(k != NULL, "invariant");
606 assert(op != NULL, "invariant");
607 assert(event->should_commit(), "invariant");
608 event->set_revokedClass(k);
609 event->set_disableBiasing(!op->is_bulk_rebias());
610 event->set_safepointId(op->safepoint_id());
611 event->commit();
612 }
613
614
615 BiasedLocking::Condition BiasedLocking::single_revoke_with_handshake(Handle obj, JavaThread *requester, JavaThread *biaser) {
616
617 EventBiasedLockRevocation event;
618 if (PrintBiasedLockingStatistics) {
619 Atomic::inc(handshakes_count_addr());
620 }
621 log_info(biasedlocking, handshake)("JavaThread " INTPTR_FORMAT " handshaking JavaThread "
622 INTPTR_FORMAT " to revoke object " INTPTR_FORMAT, p2i(requester),
623 p2i(biaser), p2i(obj()));
624
625 RevokeOneBias revoke(obj, requester, biaser);
626 bool executed = Handshake::execute(&revoke, biaser);
627 if (revoke.status_code() == NOT_REVOKED) {
628 return NOT_REVOKED;
629 }
630 if (executed) {
631 log_info(biasedlocking, handshake)("Handshake revocation for object " INTPTR_FORMAT " succeeded. Bias was %srevoked",
632 p2i(obj()), (revoke.status_code() == BIAS_REVOKED ? "" : "already "));
633 if (event.should_commit() && revoke.status_code() == BIAS_REVOKED) {
634 post_revocation_event(&event, obj->klass(), &revoke);
635 }
636 assert(!obj->mark().has_bias_pattern(), "invariant");
637 return revoke.status_code();
638 } else {
639 // Thread was not alive.
640 // Grab Threads_lock before manually trying to revoke bias. This avoids race with a newly
641 // created JavaThread (that happens to get the same memory address as biaser) synchronizing
642 // on this object.
643 {
644 MutexLocker ml(Threads_lock);
645 markWord mark = obj->mark();
646 // Check if somebody else was able to revoke it before biased thread exited.
647 if (!mark.has_bias_pattern()) {
648 return NOT_BIASED;
649 }
650 ThreadsListHandle tlh;
651 markWord prototype = obj->klass()->prototype_header();
652 if (!prototype.has_bias_pattern() || (!tlh.includes(biaser) && biaser == mark.biased_locker() &&
653 prototype.bias_epoch() == mark.bias_epoch())) {
654 obj->cas_set_mark(markWord::prototype().set_age(mark.age()), mark);
655 if (event.should_commit()) {
656 post_revocation_event(&event, obj->klass(), &revoke);
657 }
658 assert(!obj->mark().has_bias_pattern(), "bias should be revoked by now");
659 return BIAS_REVOKED;
660 }
661 }
662 }
663
664 return NOT_REVOKED;
665 }
666
667
668 // Caller should have instantiated a ResourceMark object before calling this method
669 void BiasedLocking::walk_stack_and_revoke(oop obj, JavaThread* biased_locker) {
670 assert(!SafepointSynchronize::is_at_safepoint() || !ThreadLocalHandshakes,
671 "if ThreadLocalHandshakes is enabled this should always be executed outside safepoints");
672 assert(Thread::current() == biased_locker || Thread::current()->is_VM_thread(), "wrong thread");
673
674 markWord mark = obj->mark();
675 assert(mark.biased_locker() == biased_locker &&
676 obj->klass()->prototype_header().bias_epoch() == mark.bias_epoch(), "invariant");
677
678 log_trace(biasedlocking)("%s(" INTPTR_FORMAT ") revoking object " INTPTR_FORMAT ", mark "
679 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
680 ", biaser " INTPTR_FORMAT " %s",
681 Thread::current()->is_VM_thread() ? "VMThread" : "JavaThread",
682 p2i(Thread::current()),
683 p2i(obj),
684 mark.value(),
685 obj->klass()->external_name(),
686 obj->klass()->prototype_header().value(),
687 p2i(biased_locker),
688 Thread::current()->is_VM_thread() ? "" : "(walking own stack)");
689
690 markWord unbiased_prototype = markWord::prototype().set_age(obj->mark().age());
691
692 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_locker);
693 BasicLock* highest_lock = NULL;
694 for (int i = 0; i < cached_monitor_info->length(); i++) {
695 MonitorInfo* mon_info = cached_monitor_info->at(i);
696 if (mon_info->owner() == obj) {
697 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
698 p2i(mon_info->owner()),
699 p2i(obj));
700 // Assume recursive case and fix up highest lock below
701 markWord mark = markWord::encode((BasicLock*) NULL);
702 highest_lock = mon_info->lock();
703 highest_lock->set_displaced_header(mark);
704 } else {
705 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
706 p2i(mon_info->owner()),
707 p2i(obj));
708 }
709 }
710 if (highest_lock != NULL) {
711 // Fix up highest lock to contain displaced header and point
712 // object at it
713 highest_lock->set_displaced_header(unbiased_prototype);
714 // Reset object header to point to displaced mark.
715 // Must release store the lock address for platforms without TSO
716 // ordering (e.g. ppc).
717 obj->release_set_mark(markWord::encode(highest_lock));
718 assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit");
719 log_info(biasedlocking)(" Revoked bias of currently-locked object");
720 } else {
721 log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
722 // Store the unlocked value into the object's header.
723 obj->set_mark(unbiased_prototype);
724 }
725
726 assert(!obj->mark().has_bias_pattern(), "must not be biased");
727 }
728
729 void BiasedLocking::revoke_own_lock(Handle obj, TRAPS) {
730 assert(THREAD->is_Java_thread(), "must be called by a JavaThread");
731 JavaThread* thread = (JavaThread*)THREAD;
732
733 markWord mark = obj->mark();
734
735 if (!mark.has_bias_pattern()) {
736 return;
737 }
738
739 Klass *k = obj->klass();
740 assert(mark.biased_locker() == thread &&
741 k->prototype_header().bias_epoch() == mark.bias_epoch(), "Revoke failed, unhandled biased lock state");
742 ResourceMark rm;
743 log_info(biasedlocking)("Revoking bias by walking my own stack:");
744 EventBiasedLockSelfRevocation event;
745 BiasedLocking::walk_stack_and_revoke(obj(), (JavaThread*) thread);
746 thread->set_cached_monitor_info(NULL);
747 assert(!obj->mark().has_bias_pattern(), "invariant");
748 if (event.should_commit()) {
749 post_self_revocation_event(&event, k);
750 }
751 }
752
753 void BiasedLocking::revoke(Handle obj, TRAPS) {
754 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
755
756 while (true) {
757 // We can revoke the biases of anonymously-biased objects
758 // efficiently enough that we should not cause these revocations to
759 // update the heuristics because doing so may cause unwanted bulk
760 // revocations (which are expensive) to occur.
761 markWord mark = obj->mark();
762
763 if (!mark.has_bias_pattern()) {
764 return;
765 }
766
767 if (mark.is_biased_anonymously()) {
768 // We are probably trying to revoke the bias of this object due to
769 // an identity hash code computation. Try to revoke the bias
770 // without a safepoint. This is possible if we can successfully
771 // compare-and-exchange an unbiased header into the mark word of
772 // the object, meaning that no other thread has raced to acquire
773 // the bias of the object.
774 markWord biased_value = mark;
775 markWord unbiased_prototype = markWord::prototype().set_age(mark.age());
776 markWord res_mark = obj->cas_set_mark(unbiased_prototype, mark);
777 if (res_mark == biased_value) {
778 return;
779 }
780 mark = res_mark; // Refresh mark with the latest value.
781 } else {
782 Klass* k = obj->klass();
783 markWord prototype_header = k->prototype_header();
784 if (!prototype_header.has_bias_pattern()) {
785 // This object has a stale bias from before the bulk revocation
786 // for this data type occurred. It's pointless to update the
787 // heuristics at this point so simply update the header with a
788 // CAS. If we fail this race, the object's bias has been revoked
789 // by another thread so we simply return and let the caller deal
790 // with it.
791 obj->cas_set_mark(prototype_header.set_age(mark.age()), mark);
792 assert(!obj->mark().has_bias_pattern(), "even if we raced, should still be revoked");
793 return;
794 } else if (prototype_header.bias_epoch() != mark.bias_epoch()) {
795 // The epoch of this biasing has expired indicating that the
796 // object is effectively unbiased. We can revoke the bias of this
797 // object efficiently enough with a CAS that we shouldn't update the
798 // heuristics. This is normally done in the assembly code but we
799 // can reach this point due to various points in the runtime
800 // needing to revoke biases.
801 markWord res_mark;
802 markWord biased_value = mark;
803 markWord unbiased_prototype = markWord::prototype().set_age(mark.age());
804 res_mark = obj->cas_set_mark(unbiased_prototype, mark);
805 if (res_mark == biased_value) {
806 return;
807 }
808 mark = res_mark; // Refresh mark with the latest value.
809 }
810 }
811
812 HeuristicsResult heuristics = update_heuristics(obj());
813 if (heuristics == HR_NOT_BIASED) {
814 return;
815 } else if (heuristics == HR_SINGLE_REVOKE) {
816 JavaThread *blt = mark.biased_locker();
817 assert(blt != NULL, "invariant");
818 if (blt == THREAD) {
819 // A thread is trying to revoke the bias of an object biased
820 // toward it, again likely due to an identity hash code
821 // computation. We can again avoid a safepoint/handshake in this case
822 // since we are only going to walk our own stack. There are no
823 // races with revocations occurring in other threads because we
824 // reach no safepoints in the revocation path.
825 EventBiasedLockSelfRevocation event;
826 ResourceMark rm;
827 walk_stack_and_revoke(obj(), blt);
828 blt->set_cached_monitor_info(NULL);
829 assert(!obj->mark().has_bias_pattern(), "invariant");
830 if (event.should_commit()) {
831 post_self_revocation_event(&event, obj->klass());
832 }
833 return;
834 } else {
835 BiasedLocking::Condition cond = single_revoke_with_handshake(obj, (JavaThread*)THREAD, blt);
836 if (cond != NOT_REVOKED) {
837 return;
838 }
839 }
840 } else {
841 assert((heuristics == HR_BULK_REVOKE) ||
842 (heuristics == HR_BULK_REBIAS), "?");
843 EventBiasedLockClassRevocation event;
844 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*)THREAD,
845 (heuristics == HR_BULK_REBIAS));
846 VMThread::execute(&bulk_revoke);
847 if (event.should_commit()) {
848 post_class_revocation_event(&event, obj->klass(), &bulk_revoke);
849 }
850 return;
851 }
852 }
853 }
854
855 // All objects in objs should be locked by biaser
856 void BiasedLocking::revoke(GrowableArray<Handle>* objs, JavaThread *biaser) {
857 bool clean_my_cache = false;
858 for (int i = 0; i < objs->length(); i++) {
859 oop obj = (objs->at(i))();
860 markWord mark = obj->mark();
861 if (mark.has_bias_pattern()) {
862 walk_stack_and_revoke(obj, biaser);
863 clean_my_cache = true;
864 }
865 }
866 if (clean_my_cache) {
867 clean_up_cached_monitor_info(biaser);
868 }
869 }
870
871
872 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
873 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
874 oop obj = h_obj();
875 HeuristicsResult heuristics = update_heuristics(obj);
876 if (heuristics == HR_SINGLE_REVOKE) {
877 JavaThread* biased_locker = NULL;
878 single_revoke_at_safepoint(obj, false, NULL, &biased_locker);
879 if (biased_locker) {
880 clean_up_cached_monitor_info(biased_locker);
881 }
882 } else if ((heuristics == HR_BULK_REBIAS) ||
883 (heuristics == HR_BULK_REVOKE)) {
884 bulk_revoke_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), NULL);
885 clean_up_cached_monitor_info();
886 }
887 }
888
889
890 void BiasedLocking::preserve_marks() {
891 if (!UseBiasedLocking)
892 return;
893
894 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
895
896 assert(_preserved_oop_stack == NULL, "double initialization");
897 assert(_preserved_mark_stack == NULL, "double initialization");
898
899 // In order to reduce the number of mark words preserved during GC
900 // due to the presence of biased locking, we reinitialize most mark
901 // words to the class's prototype during GC -- even those which have
902 // a currently valid bias owner. One important situation where we
903 // must not clobber a bias is when a biased object is currently
904 // locked. To handle this case we iterate over the currently-locked
905 // monitors in a prepass and, if they are biased, preserve their
906 // mark words here. This should be a relatively small set of objects
907 // especially compared to the number of objects in the heap.
908 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markWord>(10, true);
909 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
910
911 ResourceMark rm;
912 Thread* cur = Thread::current();
913 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
914 if (thread->has_last_Java_frame()) {
915 RegisterMap rm(thread);
916 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
917 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
918 if (monitors != NULL) {
919 int len = monitors->length();
920 // Walk monitors youngest to oldest
921 for (int i = len - 1; i >= 0; i--) {
922 MonitorInfo* mon_info = monitors->at(i);
923 if (mon_info->owner_is_scalar_replaced()) continue;
924 oop owner = mon_info->owner();
925 if (owner != NULL) {
926 markWord mark = owner->mark();
927 if (mark.has_bias_pattern()) {
928 _preserved_oop_stack->push(Handle(cur, owner));
929 _preserved_mark_stack->push(mark);
930 }
931 }
932 }
933 }
934 }
935 }
936 }
937 }
938
939
940 void BiasedLocking::restore_marks() {
941 if (!UseBiasedLocking)
942 return;
943
944 assert(_preserved_oop_stack != NULL, "double free");
945 assert(_preserved_mark_stack != NULL, "double free");
946
947 int len = _preserved_oop_stack->length();
948 for (int i = 0; i < len; i++) {
949 Handle owner = _preserved_oop_stack->at(i);
950 markWord mark = _preserved_mark_stack->at(i);
951 owner->set_mark(mark);
952 }
953
954 delete _preserved_oop_stack;
955 _preserved_oop_stack = NULL;
956 delete _preserved_mark_stack;
957 _preserved_mark_stack = NULL;
958 }
959
960
961 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
962 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
963 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
964 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
965 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
966 int* BiasedLocking::handshakes_count_addr() { return _counters.handshakes_count_addr(); }
967 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
968 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
969
970
971 // BiasedLockingCounters
972
973 int BiasedLockingCounters::slow_path_entry_count() const {
974 if (_slow_path_entry_count != 0) {
975 return _slow_path_entry_count;
976 }
977 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
978 _rebiased_lock_entry_count + _revoked_lock_entry_count +
979 _fast_path_entry_count;
980
981 return _total_entry_count - sum;
982 }
983
984 void BiasedLockingCounters::print_on(outputStream* st) const {
985 tty->print_cr("# total entries: %d", _total_entry_count);
986 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
987 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
988 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
989 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
990 tty->print_cr("# handshakes entries: %d", _handshakes_count);
991 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
992 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
993 }
994
995 void BiasedLockingCounters::print() const { print_on(tty); }