1 /*
2 * Copyright (c) 2005, 2020, 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/handshake.hpp"
39 #include "runtime/monitorInfo.inline.hpp"
40 #include "runtime/safepointMechanism.hpp"
41 #include "runtime/task.hpp"
42 #include "runtime/threadSMR.hpp"
43 #include "runtime/vframe.hpp"
44 #include "runtime/vmThread.hpp"
45 #include "runtime/vmOperations.hpp"
46
47
48 static bool _biased_locking_enabled = false;
49 BiasedLockingCounters BiasedLocking::_counters;
50
51 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
52 static GrowableArray<markWord>* _preserved_mark_stack = NULL;
53
54 static void enable_biased_locking(InstanceKlass* k) {
55 k->set_prototype_header(markWord::biased_locking_prototype());
56 }
57
58 static void enable_biased_locking() {
59 _biased_locking_enabled = true;
60 log_info(biasedlocking)("Biased locking enabled");
61 }
62
63 class VM_EnableBiasedLocking: public VM_Operation {
64 public:
65 VM_EnableBiasedLocking() {}
66 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
67
68 void doit() {
69 // Iterate the class loader data dictionaries enabling biased locking for all
70 // currently loaded classes.
71 ClassLoaderDataGraph::dictionary_classes_do(enable_biased_locking);
72 // Indicate that future instances should enable it as well
73 enable_biased_locking();
74 }
75
76 bool allow_nested_vm_operations() const { return false; }
77 };
78
79
80 // One-shot PeriodicTask subclass for enabling biased locking
81 class EnableBiasedLockingTask : public PeriodicTask {
82 public:
83 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {}
84
85 virtual void task() {
86 VM_EnableBiasedLocking op;
87 VMThread::execute(&op);
88
89 // Reclaim our storage and disenroll ourself
90 delete this;
91 }
92 };
93
94
95 void BiasedLocking::init() {
96 // If biased locking is enabled and BiasedLockingStartupDelay is set,
97 // schedule a task to fire after the specified delay which turns on
98 // biased locking for all currently loaded classes as well as future
99 // ones. This could be a workaround for startup time regressions
100 // due to large number of safepoints being taken during VM startup for
101 // bias revocation.
102 if (UseBiasedLocking) {
103 if (BiasedLockingStartupDelay > 0) {
104 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
105 task->enroll();
106 } else {
107 enable_biased_locking();
108 }
109 }
110 }
111
112
113 bool BiasedLocking::enabled() {
114 assert(UseBiasedLocking, "precondition");
115 // We check "BiasedLockingStartupDelay == 0" here to cover the
116 // possibility of calls to BiasedLocking::enabled() before
117 // BiasedLocking::init().
118 return _biased_locking_enabled || BiasedLockingStartupDelay == 0;
119 }
120
121
122 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
123 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
124 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
125 if (info != NULL) {
126 return info;
127 }
128
129 info = new GrowableArray<MonitorInfo*>();
130
131 // It's possible for the thread to not have any Java frames on it,
132 // i.e., if it's the main thread and it's already returned from main()
133 if (thread->has_last_Java_frame()) {
134 RegisterMap rm(thread);
135 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
136 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
137 if (monitors != NULL) {
138 int len = monitors->length();
139 // Walk monitors youngest to oldest
140 for (int i = len - 1; i >= 0; i--) {
141 MonitorInfo* mon_info = monitors->at(i);
142 if (mon_info->eliminated()) continue;
143 Handle owner_h = mon_info->owner_h();
144 if (owner_h.not_null()) {
145 info->append(mon_info);
146 }
147 }
148 }
149 }
150 }
151
152 thread->set_cached_monitor_info(info);
153 return info;
154 }
155
156
157 // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL,
158 // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization).
159 void BiasedLocking::single_revoke_at_safepoint(oop obj, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) {
160 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
161 assert(Thread::current()->is_VM_thread(), "must be VMThread");
162
163 markWord mark = obj->mark();
164 if (!mark.has_bias_pattern()) {
165 if (log_is_enabled(Info, biasedlocking)) {
166 ResourceMark rm;
167 log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT
168 ", mark " INTPTR_FORMAT ", type %s"
169 ", requesting thread " INTPTR_FORMAT
170 " because it's no longer biased)",
171 p2i((void *)obj), mark.value(),
172 obj->klass()->external_name(),
173 (intptr_t) requesting_thread);
174 }
175 return;
176 }
177
178 uint age = mark.age();
179 markWord unbiased_prototype = markWord::prototype().set_age(age);
180
181 // Log at "info" level if not bulk, else "trace" level
182 if (!is_bulk) {
183 ResourceMark rm;
184 log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark "
185 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
186 ", requesting thread " INTPTR_FORMAT,
187 p2i((void *)obj),
188 mark.value(),
189 obj->klass()->external_name(),
190 obj->klass()->prototype_header().value(),
191 (intptr_t) requesting_thread);
192 } else {
193 ResourceMark rm;
194 log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark "
195 INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT
196 " , requesting thread " INTPTR_FORMAT,
197 p2i((void *)obj),
198 mark.value(),
199 obj->klass()->external_name(),
200 obj->klass()->prototype_header().value(),
201 (intptr_t) requesting_thread);
202 }
203
204 JavaThread* biased_thread = mark.biased_locker();
205 if (biased_thread == NULL) {
206 // Object is anonymously biased. We can get here if, for
207 // example, we revoke the bias due to an identity hash code
208 // being computed for an object.
209 obj->set_mark(unbiased_prototype);
210
211 // Log at "info" level if not bulk, else "trace" level
212 if (!is_bulk) {
213 log_info(biasedlocking)(" Revoked bias of anonymously-biased object");
214 } else {
215 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object");
216 }
217 return;
218 }
219
220 // Handle case where the thread toward which the object was biased has exited
221 bool thread_is_alive = false;
222 if (requesting_thread == biased_thread) {
223 thread_is_alive = true;
224 } else {
225 ThreadsListHandle tlh;
226 thread_is_alive = tlh.includes(biased_thread);
227 }
228 if (!thread_is_alive) {
229 obj->set_mark(unbiased_prototype);
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;
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 below
264 markWord mark = markWord::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 store the lock address for platforms without TSO
279 // ordering (e.g. ppc).
280 obj->release_set_mark(markWord::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 // Store the unlocked value into the object's header.
296 obj->set_mark(unbiased_prototype);
297 }
298
299 // If requested, return information on which thread held the bias
300 if (biased_locker != NULL) {
301 *biased_locker = biased_thread;
302 }
303 }
304
305
306 enum HeuristicsResult {
307 HR_NOT_BIASED = 1,
308 HR_SINGLE_REVOKE = 2,
309 HR_BULK_REBIAS = 3,
310 HR_BULK_REVOKE = 4
311 };
312
313
314 static HeuristicsResult update_heuristics(oop o) {
315 markWord mark = o->mark();
316 if (!mark.has_bias_pattern()) {
317 return HR_NOT_BIASED;
318 }
319
320 // Heuristics to attempt to throttle the number of revocations.
321 // Stages:
322 // 1. Revoke the biases of all objects in the heap of this type,
323 // but allow rebiasing of those objects if unlocked.
324 // 2. Revoke the biases of all objects in the heap of this type
325 // and don't allow rebiasing of these objects. Disable
326 // allocation of objects of that type with the bias bit set.
327 Klass* k = o->klass();
328 jlong cur_time = nanos_to_millis(os::javaTimeNanos());
329 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
330 int revocation_count = k->biased_lock_revocation_count();
331 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
332 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
333 (last_bulk_revocation_time != 0) &&
334 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
335 // This is the first revocation we've seen in a while of an
336 // object of this type since the last time we performed a bulk
337 // rebiasing operation. The application is allocating objects in
338 // bulk which are biased toward a thread and then handing them
339 // off to another thread. We can cope with this allocation
340 // pattern via the bulk rebiasing mechanism so we reset the
341 // klass's revocation count rather than allow it to increase
342 // monotonically. If we see the need to perform another bulk
343 // rebias operation later, we will, and if subsequently we see
344 // many more revocation operations in a short period of time we
345 // will completely disable biasing for this type.
346 k->set_biased_lock_revocation_count(0);
347 revocation_count = 0;
348 }
349
350 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
351 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
352 revocation_count = k->atomic_incr_biased_lock_revocation_count();
353 }
354
355 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
356 return HR_BULK_REVOKE;
357 }
358
359 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
360 return HR_BULK_REBIAS;
361 }
362
363 return HR_SINGLE_REVOKE;
364 }
365
366
367 void BiasedLocking::bulk_revoke_at_safepoint(oop o, bool bulk_rebias, JavaThread* requesting_thread) {
368 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
369 assert(Thread::current()->is_VM_thread(), "must be VMThread");
370
371 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object "
372 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
373 (bulk_rebias ? "rebias" : "revoke"),
374 p2i((void *) o),
375 o->mark().value(),
376 o->klass()->external_name());
377
378 jlong cur_time = nanos_to_millis(os::javaTimeNanos());
379 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
380
381 Klass* k_o = o->klass();
382 Klass* klass = k_o;
383
384 {
385 JavaThreadIteratorWithHandle jtiwh;
386
387 if (bulk_rebias) {
388 // Use the epoch in the klass of the object to implicitly revoke
389 // all biases of objects of this data type and force them to be
390 // reacquired. However, we also need to walk the stacks of all
391 // threads and update the headers of lightweight locked objects
392 // with biases to have the current epoch.
393
394 // If the prototype header doesn't have the bias pattern, don't
395 // try to update the epoch -- assume another VM operation came in
396 // and reset the header to the unbiased state, which will
397 // implicitly cause all existing biases to be revoked
398 if (klass->prototype_header().has_bias_pattern()) {
399 int prev_epoch = klass->prototype_header().bias_epoch();
400 klass->set_prototype_header(klass->prototype_header().incr_bias_epoch());
401 int cur_epoch = klass->prototype_header().bias_epoch();
402
403 // Now walk all threads' stacks and adjust epochs of any biased
404 // and locked objects of this data type we encounter
405 for (; JavaThread *thr = jtiwh.next(); ) {
406 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
407 for (int i = 0; i < cached_monitor_info->length(); i++) {
408 MonitorInfo* mon_info = cached_monitor_info->at(i);
409 Handle owner_h = mon_info->owner_h();
410 markWord mark = owner_h->mark();
411 if ((owner_h->klass() == k_o) && mark.has_bias_pattern()) {
412 // We might have encountered this object already in the case of recursive locking
413 assert(mark.bias_epoch() == prev_epoch || mark.bias_epoch() == cur_epoch, "error in bias epoch adjustment");
414 owner_h->set_mark(mark.set_bias_epoch(cur_epoch));
415 }
416 }
417 }
418 }
419
420 // At this point we're done. All we have to do is potentially
421 // adjust the header of the given object to revoke its bias.
422 single_revoke_at_safepoint(o, true, requesting_thread, NULL);
423 } else {
424 if (log_is_enabled(Info, biasedlocking)) {
425 ResourceMark rm;
426 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name());
427 }
428
429 // Disable biased locking for this data type. Not only will this
430 // cause future instances to not be biased, but existing biased
431 // instances will notice that this implicitly caused their biases
432 // to be revoked.
433 klass->set_prototype_header(markWord::prototype());
434
435 // Now walk all threads' stacks and forcibly revoke the biases of
436 // any locked and biased objects of this data type we encounter.
437 for (; JavaThread *thr = jtiwh.next(); ) {
438 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
439 for (int i = 0; i < cached_monitor_info->length(); i++) {
440 MonitorInfo* mon_info = cached_monitor_info->at(i);
441 Handle owner_h = mon_info->owner_h();
442 markWord mark = owner_h->mark();
443 if ((owner_h->klass() == k_o) && mark.has_bias_pattern()) {
444 single_revoke_at_safepoint(owner_h(), true, requesting_thread, NULL);
445 }
446 }
447 }
448
449 // Must force the bias of the passed object to be forcibly revoked
450 // as well to ensure guarantees to callers
451 single_revoke_at_safepoint(o, true, requesting_thread, NULL);
452 }
453 } // ThreadsListHandle is destroyed here.
454
455 log_info(biasedlocking)("* Ending bulk revocation");
456
457 assert(!o->mark().has_bias_pattern(), "bug in bulk bias revocation");
458 }
459
460
461 static void clean_up_cached_monitor_info(JavaThread* thread = NULL) {
462 if (thread != NULL) {
463 thread->set_cached_monitor_info(NULL);
464 } else {
465 // Walk the thread list clearing out the cached monitors
466 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
467 thr->set_cached_monitor_info(NULL);
468 }
469 }
470 }
471
472
473 class VM_BulkRevokeBias : public VM_Operation {
474 private:
475 Handle* _obj;
476 JavaThread* _requesting_thread;
477 bool _bulk_rebias;
478 uint64_t _safepoint_id;
479
480 public:
481 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
482 bool bulk_rebias)
483 : _obj(obj)
484 , _requesting_thread(requesting_thread)
485 , _bulk_rebias(bulk_rebias)
486 , _safepoint_id(0) {}
487
488 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
489
490 virtual void doit() {
491 BiasedLocking::bulk_revoke_at_safepoint((*_obj)(), _bulk_rebias, _requesting_thread);
492 _safepoint_id = SafepointSynchronize::safepoint_id();
493 clean_up_cached_monitor_info();
494 }
495
496 bool is_bulk_rebias() const {
497 return _bulk_rebias;
498 }
499
500 uint64_t safepoint_id() const {
501 return _safepoint_id;
502 }
503 };
504
505
506 class RevokeOneBias : public HandshakeClosure {
507 protected:
508 Handle _obj;
509 JavaThread* _requesting_thread;
510 JavaThread* _biased_locker;
511 BiasedLocking::Condition _status_code;
512 traceid _biased_locker_id;
513
514 public:
515 RevokeOneBias(Handle obj, JavaThread* requesting_thread, JavaThread* biased_locker)
516 : HandshakeClosure("RevokeOneBias")
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_direct(&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 Thread* cur = Thread::current();
671 assert(!SafepointSynchronize::is_at_safepoint(), "this should always be executed outside safepoints");
672 assert(cur == biased_locker || cur == biased_locker->active_handshaker(), "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)("JavaThread(" INTPTR_FORMAT ") revoking object " INTPTR_FORMAT ", mark "
679 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
680 ", biaser " INTPTR_FORMAT " %s",
681 p2i(cur),
682 p2i(obj),
683 mark.value(),
684 obj->klass()->external_name(),
685 obj->klass()->prototype_header().value(),
686 p2i(biased_locker),
687 cur != biased_locker ? "" : "(walking own stack)");
688
689 markWord unbiased_prototype = markWord::prototype().set_age(obj->mark().age());
690
691 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_locker);
692 BasicLock* highest_lock = NULL;
693 for (int i = 0; i < cached_monitor_info->length(); i++) {
694 MonitorInfo* mon_info = cached_monitor_info->at(i);
695 if (mon_info->owner() == obj) {
696 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
697 p2i(mon_info->owner()),
698 p2i(obj));
699 // Assume recursive case and fix up highest lock below
700 markWord mark = markWord::encode((BasicLock*) NULL);
701 highest_lock = mon_info->lock();
702 highest_lock->set_displaced_header(mark);
703 } else {
704 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
705 p2i(mon_info->owner()),
706 p2i(obj));
707 }
708 }
709 if (highest_lock != NULL) {
710 // Fix up highest lock to contain displaced header and point
711 // object at it
712 highest_lock->set_displaced_header(unbiased_prototype);
713 // Reset object header to point to displaced mark.
714 // Must release store the lock address for platforms without TSO
715 // ordering (e.g. ppc).
716 obj->release_set_mark(markWord::encode(highest_lock));
717 assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit");
718 log_info(biasedlocking)(" Revoked bias of currently-locked object");
719 } else {
720 log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
721 // Store the unlocked value into the object's header.
722 obj->set_mark(unbiased_prototype);
723 }
724
725 assert(!obj->mark().has_bias_pattern(), "must not be biased");
726 }
727
728 void BiasedLocking::revoke_own_lock(Handle obj, TRAPS) {
729 assert(THREAD->is_Java_thread(), "must be called by a JavaThread");
730 JavaThread* thread = (JavaThread*)THREAD;
731
732 markWord mark = obj->mark();
733
734 if (!mark.has_bias_pattern()) {
735 return;
736 }
737
738 Klass *k = obj->klass();
739 assert(mark.biased_locker() == thread &&
740 k->prototype_header().bias_epoch() == mark.bias_epoch(), "Revoke failed, unhandled biased lock state");
741 ResourceMark rm;
742 log_info(biasedlocking)("Revoking bias by walking my own stack:");
743 EventBiasedLockSelfRevocation event;
744 BiasedLocking::walk_stack_and_revoke(obj(), (JavaThread*) thread);
745 thread->set_cached_monitor_info(NULL);
746 assert(!obj->mark().has_bias_pattern(), "invariant");
747 if (event.should_commit()) {
748 post_self_revocation_event(&event, k);
749 }
750 }
751
752 void BiasedLocking::revoke(Handle obj, TRAPS) {
753 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
754
755 while (true) {
756 // We can revoke the biases of anonymously-biased objects
757 // efficiently enough that we should not cause these revocations to
758 // update the heuristics because doing so may cause unwanted bulk
759 // revocations (which are expensive) to occur.
760 markWord mark = obj->mark();
761
762 if (!mark.has_bias_pattern()) {
763 return;
764 }
765
766 if (mark.is_biased_anonymously()) {
767 // We are probably trying to revoke the bias of this object due to
768 // an identity hash code computation. Try to revoke the bias
769 // without a safepoint. This is possible if we can successfully
770 // compare-and-exchange an unbiased header into the mark word of
771 // the object, meaning that no other thread has raced to acquire
772 // the bias of the object.
773 markWord biased_value = mark;
774 markWord unbiased_prototype = markWord::prototype().set_age(mark.age());
775 markWord res_mark = obj->cas_set_mark(unbiased_prototype, mark);
776 if (res_mark == biased_value) {
777 return;
778 }
779 mark = res_mark; // Refresh mark with the latest value.
780 } else {
781 Klass* k = obj->klass();
782 markWord prototype_header = k->prototype_header();
783 if (!prototype_header.has_bias_pattern()) {
784 // This object has a stale bias from before the bulk revocation
785 // for this data type occurred. It's pointless to update the
786 // heuristics at this point so simply update the header with a
787 // CAS. If we fail this race, the object's bias has been revoked
788 // by another thread so we simply return and let the caller deal
789 // with it.
790 obj->cas_set_mark(prototype_header.set_age(mark.age()), mark);
791 assert(!obj->mark().has_bias_pattern(), "even if we raced, should still be revoked");
792 return;
793 } else if (prototype_header.bias_epoch() != mark.bias_epoch()) {
794 // The epoch of this biasing has expired indicating that the
795 // object is effectively unbiased. We can revoke the bias of this
796 // object efficiently enough with a CAS that we shouldn't update the
797 // heuristics. This is normally done in the assembly code but we
798 // can reach this point due to various points in the runtime
799 // needing to revoke biases.
800 markWord res_mark;
801 markWord biased_value = mark;
802 markWord unbiased_prototype = markWord::prototype().set_age(mark.age());
803 res_mark = obj->cas_set_mark(unbiased_prototype, mark);
804 if (res_mark == biased_value) {
805 return;
806 }
807 mark = res_mark; // Refresh mark with the latest value.
808 }
809 }
810
811 HeuristicsResult heuristics = update_heuristics(obj());
812 if (heuristics == HR_NOT_BIASED) {
813 return;
814 } else if (heuristics == HR_SINGLE_REVOKE) {
815 JavaThread *blt = mark.biased_locker();
816 assert(blt != NULL, "invariant");
817 if (blt == THREAD) {
818 // A thread is trying to revoke the bias of an object biased
819 // toward it, again likely due to an identity hash code
820 // computation. We can again avoid a safepoint/handshake in this case
821 // since we are only going to walk our own stack. There are no
822 // races with revocations occurring in other threads because we
823 // reach no safepoints in the revocation path.
824 EventBiasedLockSelfRevocation event;
825 ResourceMark rm;
826 walk_stack_and_revoke(obj(), blt);
827 blt->set_cached_monitor_info(NULL);
828 assert(!obj->mark().has_bias_pattern(), "invariant");
829 if (event.should_commit()) {
830 post_self_revocation_event(&event, obj->klass());
831 }
832 return;
833 } else {
834 BiasedLocking::Condition cond = single_revoke_with_handshake(obj, (JavaThread*)THREAD, blt);
835 if (cond != NOT_REVOKED) {
836 return;
837 }
838 }
839 } else {
840 assert((heuristics == HR_BULK_REVOKE) ||
841 (heuristics == HR_BULK_REBIAS), "?");
842 EventBiasedLockClassRevocation event;
843 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*)THREAD,
844 (heuristics == HR_BULK_REBIAS));
845 VMThread::execute(&bulk_revoke);
846 if (event.should_commit()) {
847 post_class_revocation_event(&event, obj->klass(), &bulk_revoke);
848 }
849 return;
850 }
851 }
852 }
853
854 // All objects in objs should be locked by biaser
855 void BiasedLocking::revoke(GrowableArray<Handle>* objs, JavaThread *biaser) {
856 bool clean_my_cache = false;
857 for (int i = 0; i < objs->length(); i++) {
858 oop obj = (objs->at(i))();
859 markWord mark = obj->mark();
860 if (mark.has_bias_pattern()) {
861 walk_stack_and_revoke(obj, biaser);
862 clean_my_cache = true;
863 }
864 }
865 if (clean_my_cache) {
866 clean_up_cached_monitor_info(biaser);
867 }
868 }
869
870
871 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
872 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
873 oop obj = h_obj();
874 HeuristicsResult heuristics = update_heuristics(obj);
875 if (heuristics == HR_SINGLE_REVOKE) {
876 JavaThread* biased_locker = NULL;
877 single_revoke_at_safepoint(obj, false, NULL, &biased_locker);
878 if (biased_locker) {
879 clean_up_cached_monitor_info(biased_locker);
880 }
881 } else if ((heuristics == HR_BULK_REBIAS) ||
882 (heuristics == HR_BULK_REVOKE)) {
883 bulk_revoke_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), NULL);
884 clean_up_cached_monitor_info();
885 }
886 }
887
888
889 void BiasedLocking::preserve_marks() {
890 if (!UseBiasedLocking)
891 return;
892
893 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
894
895 assert(_preserved_oop_stack == NULL, "double initialization");
896 assert(_preserved_mark_stack == NULL, "double initialization");
897
898 // In order to reduce the number of mark words preserved during GC
899 // due to the presence of biased locking, we reinitialize most mark
900 // words to the class's prototype during GC -- even those which have
901 // a currently valid bias owner. One important situation where we
902 // must not clobber a bias is when a biased object is currently
903 // locked. To handle this case we iterate over the currently-locked
904 // monitors in a prepass and, if they are biased, preserve their
905 // mark words here. This should be a relatively small set of objects
906 // especially compared to the number of objects in the heap.
907 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtGC) GrowableArray<markWord>(10, mtGC);
908 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtGC) GrowableArray<Handle>(10, mtGC);
909
910 ResourceMark rm;
911 HandleMark hm;
912 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
913 if (thread->has_last_Java_frame()) {
914 RegisterMap rm(thread);
915 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
916 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
917 if (monitors != NULL) {
918 int len = monitors->length();
919 // Walk monitors youngest to oldest
920 for (int i = len - 1; i >= 0; i--) {
921 MonitorInfo* mon_info = monitors->at(i);
922 if (mon_info->owner_is_scalar_replaced()) continue;
923 Handle owner_h = mon_info->owner_h();
924 if (owner_h.not_null()) {
925 markWord mark = owner_h->mark();
926 if (mark.has_bias_pattern()) {
927 _preserved_oop_stack->push(owner_h);
928 _preserved_mark_stack->push(mark);
929 }
930 }
931 }
932 }
933 }
934 }
935 }
936 }
937
938
939 void BiasedLocking::restore_marks() {
940 if (!UseBiasedLocking)
941 return;
942
943 assert(_preserved_oop_stack != NULL, "double free");
944 assert(_preserved_mark_stack != NULL, "double free");
945
946 int len = _preserved_oop_stack->length();
947 for (int i = 0; i < len; i++) {
948 Handle owner = _preserved_oop_stack->at(i);
949 markWord mark = _preserved_mark_stack->at(i);
950 owner->set_mark(mark);
951 }
952
953 delete _preserved_oop_stack;
954 _preserved_oop_stack = NULL;
955 delete _preserved_mark_stack;
956 _preserved_mark_stack = NULL;
957 }
958
959
960 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
961 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
962 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
963 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
964 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
965 int* BiasedLocking::handshakes_count_addr() { return _counters.handshakes_count_addr(); }
966 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
967 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
968
969
970 // BiasedLockingCounters
971
972 int BiasedLockingCounters::slow_path_entry_count() const {
973 if (_slow_path_entry_count != 0) {
974 return _slow_path_entry_count;
975 }
976 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
977 _rebiased_lock_entry_count + _revoked_lock_entry_count +
978 _fast_path_entry_count;
979
980 return _total_entry_count - sum;
981 }
982
983 void BiasedLockingCounters::print_on(outputStream* st) const {
984 tty->print_cr("# total entries: %d", _total_entry_count);
985 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
986 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
987 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
988 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
989 tty->print_cr("# handshakes entries: %d", _handshakes_count);
990 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
991 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
992 }
993
994 void BiasedLockingCounters::print() const { print_on(tty); }