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/handshake.hpp"
39 #include "runtime/task.hpp"
40 #include "runtime/threadSMR.hpp"
41 #include "runtime/vframe.hpp"
42 #include "runtime/vmThread.hpp"
43 #include "runtime/vmOperations.hpp"
44
45
46 static bool _biased_locking_enabled = false;
47 BiasedLockingCounters BiasedLocking::_counters;
48
49 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
50 static GrowableArray<markWord>* _preserved_mark_stack = NULL;
51
52 static void enable_biased_locking(InstanceKlass* k) {
53 k->set_prototype_header(markWord::biased_locking_prototype());
54 }
55
56 static void enable_biased_locking() {
57 _biased_locking_enabled = true;
58 log_info(biasedlocking)("Biased locking enabled");
59 }
60
61 class VM_EnableBiasedLocking: public VM_Operation {
62 public:
63 VM_EnableBiasedLocking() {}
64 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
65 Mode evaluation_mode() const { return _async_safepoint; }
66 bool is_cheap_allocated() const { return true; }
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 // Use async VM operation to avoid blocking the Watcher thread.
87 // VM Thread will free C heap storage.
88 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking();
89 VMThread::execute(op);
90
91 // Reclaim our storage and disenroll ourself
92 delete this;
93 }
94 };
95
96
97 void BiasedLocking::init() {
98 // If biased locking is enabled and BiasedLockingStartupDelay is set,
99 // schedule a task to fire after the specified delay which turns on
100 // biased locking for all currently loaded classes as well as future
101 // ones. This could be a workaround for startup time regressions
102 // due to large number of safepoints being taken during VM startup for
103 // bias revocation.
104 if (UseBiasedLocking) {
105 if (BiasedLockingStartupDelay > 0) {
106 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
107 task->enroll();
108 } else {
109 enable_biased_locking();
110 }
111 }
112 }
113
114
115 bool BiasedLocking::enabled() {
116 assert(UseBiasedLocking, "precondition");
117 // We check "BiasedLockingStartupDelay == 0" here to cover the
118 // possibility of calls to BiasedLocking::enabled() before
119 // BiasedLocking::init().
120 return _biased_locking_enabled || BiasedLockingStartupDelay == 0;
121 }
122
123
124 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
125 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
126 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
127 if (info != NULL) {
128 return info;
129 }
130
131 info = new GrowableArray<MonitorInfo*>();
132
133 // It's possible for the thread to not have any Java frames on it,
134 // i.e., if it's the main thread and it's already returned from main()
135 if (thread->has_last_Java_frame()) {
136 RegisterMap rm(thread);
137 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
138 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
139 if (monitors != NULL) {
140 int len = monitors->length();
141 // Walk monitors youngest to oldest
142 for (int i = len - 1; i >= 0; i--) {
143 MonitorInfo* mon_info = monitors->at(i);
144 if (mon_info->eliminated()) continue;
145 oop owner = mon_info->owner();
146 if (owner != NULL) {
147 info->append(mon_info);
148 }
149 }
150 }
151 }
152 }
153
154 thread->set_cached_monitor_info(info);
155 return info;
156 }
157
158
159 // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL,
160 // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization).
161 void BiasedLocking::single_revoke_at_safepoint(oop obj, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) {
162 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
163 assert(Thread::current()->is_VM_thread(), "must be VMThread");
164
165 markWord mark = obj->mark();
166 if (!mark.has_bias_pattern()) {
167 if (log_is_enabled(Info, biasedlocking)) {
168 ResourceMark rm;
169 log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT
170 ", mark " INTPTR_FORMAT ", type %s"
171 ", requesting thread " INTPTR_FORMAT
172 " because it's no longer biased)",
173 p2i((void *)obj), mark.value(),
174 obj->klass()->external_name(),
175 (intptr_t) requesting_thread);
176 }
177 return;
178 }
179
180 uint age = mark.age();
181 markWord unbiased_prototype = markWord::prototype().set_age(age);
182
183 // Log at "info" level if not bulk, else "trace" level
184 if (!is_bulk) {
185 ResourceMark rm;
186 log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark "
187 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
188 ", requesting thread " INTPTR_FORMAT,
189 p2i((void *)obj),
190 mark.value(),
191 obj->klass()->external_name(),
192 obj->klass()->prototype_header().value(),
193 (intptr_t) requesting_thread);
194 } else {
195 ResourceMark rm;
196 log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark "
197 INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT
198 " , requesting thread " INTPTR_FORMAT,
199 p2i((void *)obj),
200 mark.value(),
201 obj->klass()->external_name(),
202 obj->klass()->prototype_header().value(),
203 (intptr_t) requesting_thread);
204 }
205
206 JavaThread* biased_thread = mark.biased_locker();
207 if (biased_thread == NULL) {
208 // Object is anonymously biased. We can get here if, for
209 // example, we revoke the bias due to an identity hash code
210 // being computed for an object.
211 obj->set_mark(unbiased_prototype);
212
213 // Log at "info" level if not bulk, else "trace" level
214 if (!is_bulk) {
215 log_info(biasedlocking)(" Revoked bias of anonymously-biased object");
216 } else {
217 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object");
218 }
219 return;
220 }
221
222 // Handle case where the thread toward which the object was biased has exited
223 bool thread_is_alive = false;
224 if (requesting_thread == biased_thread) {
225 thread_is_alive = true;
226 } else {
227 ThreadsListHandle tlh;
228 thread_is_alive = tlh.includes(biased_thread);
229 }
230 if (!thread_is_alive) {
231 obj->set_mark(unbiased_prototype);
232 // Log at "info" level if not bulk, else "trace" level
233 if (!is_bulk) {
234 log_info(biasedlocking)(" Revoked bias of object biased toward dead thread ("
235 PTR_FORMAT ")", p2i(biased_thread));
236 } else {
237 log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread ("
238 PTR_FORMAT ")", p2i(biased_thread));
239 }
240 return;
241 }
242
243 // Log at "info" level if not bulk, else "trace" level
244 if (!is_bulk) {
245 log_info(biasedlocking)(" Revoked bias of object biased toward live thread ("
246 PTR_FORMAT ")", p2i(biased_thread));
247 } else {
248 log_trace(biasedlocking)(" Revoked bias of object biased toward live thread ("
249 PTR_FORMAT ")", p2i(biased_thread));
250 }
251
252 // Thread owning bias is alive.
253 // Check to see whether it currently owns the lock and, if so,
254 // write down the needed displaced headers to the thread's stack.
255 // Otherwise, restore the object's header either to the unlocked
256 // or unbiased state.
257 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
258 BasicLock* highest_lock = NULL;
259 for (int i = 0; i < cached_monitor_info->length(); i++) {
260 MonitorInfo* mon_info = cached_monitor_info->at(i);
261 if (mon_info->owner() == obj) {
262 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
263 p2i((void *) mon_info->owner()),
264 p2i((void *) obj));
265 // Assume recursive case and fix up highest lock below
266 markWord mark = markWord::encode((BasicLock*) NULL);
267 highest_lock = mon_info->lock();
268 highest_lock->set_displaced_header(mark);
269 } else {
270 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
271 p2i((void *) mon_info->owner()),
272 p2i((void *) obj));
273 }
274 }
275 if (highest_lock != NULL) {
276 // Fix up highest lock to contain displaced header and point
277 // object at it
278 highest_lock->set_displaced_header(unbiased_prototype);
279 // Reset object header to point to displaced mark.
280 // Must release store the lock address for platforms without TSO
281 // ordering (e.g. ppc).
282 obj->release_set_mark(markWord::encode(highest_lock));
283 assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit");
284 // Log at "info" level if not bulk, else "trace" level
285 if (!is_bulk) {
286 log_info(biasedlocking)(" Revoked bias of currently-locked object");
287 } else {
288 log_trace(biasedlocking)(" Revoked bias of currently-locked object");
289 }
290 } else {
291 // Log at "info" level if not bulk, else "trace" level
292 if (!is_bulk) {
293 log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
294 } else {
295 log_trace(biasedlocking)(" Revoked bias of currently-unlocked object");
296 }
297 // Store the unlocked value into the object's header.
298 obj->set_mark(unbiased_prototype);
299 }
300
301 // If requested, return information on which thread held the bias
302 if (biased_locker != NULL) {
303 *biased_locker = biased_thread;
304 }
305 }
306
307
308 enum HeuristicsResult {
309 HR_NOT_BIASED = 1,
310 HR_SINGLE_REVOKE = 2,
311 HR_BULK_REBIAS = 3,
312 HR_BULK_REVOKE = 4
313 };
314
315
316 static HeuristicsResult update_heuristics(oop o) {
317 markWord mark = o->mark();
318 if (!mark.has_bias_pattern()) {
319 return HR_NOT_BIASED;
320 }
321
322 // Heuristics to attempt to throttle the number of revocations.
323 // Stages:
324 // 1. Revoke the biases of all objects in the heap of this type,
325 // but allow rebiasing of those objects if unlocked.
326 // 2. Revoke the biases of all objects in the heap of this type
327 // and don't allow rebiasing of these objects. Disable
328 // allocation of objects of that type with the bias bit set.
329 Klass* k = o->klass();
330 jlong cur_time = os::javaTimeMillis();
331 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
332 int revocation_count = k->biased_lock_revocation_count();
333 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
334 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
335 (last_bulk_revocation_time != 0) &&
336 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
337 // This is the first revocation we've seen in a while of an
338 // object of this type since the last time we performed a bulk
339 // rebiasing operation. The application is allocating objects in
340 // bulk which are biased toward a thread and then handing them
341 // off to another thread. We can cope with this allocation
342 // pattern via the bulk rebiasing mechanism so we reset the
343 // klass's revocation count rather than allow it to increase
344 // monotonically. If we see the need to perform another bulk
345 // rebias operation later, we will, and if subsequently we see
346 // many more revocation operations in a short period of time we
347 // will completely disable biasing for this type.
348 k->set_biased_lock_revocation_count(0);
349 revocation_count = 0;
350 }
351
352 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
353 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
354 revocation_count = k->atomic_incr_biased_lock_revocation_count();
355 }
356
357 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
358 return HR_BULK_REVOKE;
359 }
360
361 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
362 return HR_BULK_REBIAS;
363 }
364
365 return HR_SINGLE_REVOKE;
366 }
367
368
369 void BiasedLocking::bulk_revoke_at_safepoint(oop o, bool bulk_rebias, JavaThread* requesting_thread) {
370 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
371 assert(Thread::current()->is_VM_thread(), "must be VMThread");
372
373 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object "
374 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
375 (bulk_rebias ? "rebias" : "revoke"),
376 p2i((void *) o),
377 o->mark().value(),
378 o->klass()->external_name());
379
380 jlong cur_time = os::javaTimeMillis();
381 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
382
383 Klass* k_o = o->klass();
384 Klass* klass = k_o;
385
386 {
387 JavaThreadIteratorWithHandle jtiwh;
388
389 if (bulk_rebias) {
390 // Use the epoch in the klass of the object to implicitly revoke
391 // all biases of objects of this data type and force them to be
392 // reacquired. However, we also need to walk the stacks of all
393 // threads and update the headers of lightweight locked objects
394 // with biases to have the current epoch.
395
396 // If the prototype header doesn't have the bias pattern, don't
397 // try to update the epoch -- assume another VM operation came in
398 // and reset the header to the unbiased state, which will
399 // implicitly cause all existing biases to be revoked
400 if (klass->prototype_header().has_bias_pattern()) {
401 int prev_epoch = klass->prototype_header().bias_epoch();
402 klass->set_prototype_header(klass->prototype_header().incr_bias_epoch());
403 int cur_epoch = klass->prototype_header().bias_epoch();
404
405 // Now walk all threads' stacks and adjust epochs of any biased
406 // and locked objects of this data type we encounter
407 for (; JavaThread *thr = jtiwh.next(); ) {
408 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
409 for (int i = 0; i < cached_monitor_info->length(); i++) {
410 MonitorInfo* mon_info = cached_monitor_info->at(i);
411 oop owner = mon_info->owner();
412 markWord mark = owner->mark();
413 if ((owner->klass() == k_o) && mark.has_bias_pattern()) {
414 // We might have encountered this object already in the case of recursive locking
415 assert(mark.bias_epoch() == prev_epoch || mark.bias_epoch() == cur_epoch, "error in bias epoch adjustment");
416 owner->set_mark(mark.set_bias_epoch(cur_epoch));
417 }
418 }
419 }
420 }
421
422 // At this point we're done. All we have to do is potentially
423 // adjust the header of the given object to revoke its bias.
424 single_revoke_at_safepoint(o, true, requesting_thread, NULL);
425 } else {
426 if (log_is_enabled(Info, biasedlocking)) {
427 ResourceMark rm;
428 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name());
429 }
430
431 // Disable biased locking for this data type. Not only will this
432 // cause future instances to not be biased, but existing biased
433 // instances will notice that this implicitly caused their biases
434 // to be revoked.
435 klass->set_prototype_header(markWord::prototype());
436
437 // Now walk all threads' stacks and forcibly revoke the biases of
438 // any locked and biased objects of this data type we encounter.
439 for (; JavaThread *thr = jtiwh.next(); ) {
440 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
441 for (int i = 0; i < cached_monitor_info->length(); i++) {
442 MonitorInfo* mon_info = cached_monitor_info->at(i);
443 oop owner = mon_info->owner();
444 markWord mark = owner->mark();
445 if ((owner->klass() == k_o) && mark.has_bias_pattern()) {
446 single_revoke_at_safepoint(owner, true, requesting_thread, NULL);
447 }
448 }
449 }
450
451 // Must force the bias of the passed object to be forcibly revoked
452 // as well to ensure guarantees to callers
453 single_revoke_at_safepoint(o, true, requesting_thread, NULL);
454 }
455 } // ThreadsListHandle is destroyed here.
456
457 log_info(biasedlocking)("* Ending bulk revocation");
458
459 assert(!o->mark().has_bias_pattern(), "bug in bulk bias revocation");
460 }
461
462
463 static void clean_up_cached_monitor_info(JavaThread* thread = NULL) {
464 if (thread != NULL) {
465 thread->set_cached_monitor_info(NULL);
466 } else {
467 // Walk the thread list clearing out the cached monitors
468 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
469 thr->set_cached_monitor_info(NULL);
470 }
471 }
472 }
473
474
475 class VM_BulkRevokeBias : public VM_Operation {
476 private:
477 Handle* _obj;
478 JavaThread* _requesting_thread;
479 bool _bulk_rebias;
480 uint64_t _safepoint_id;
481
482 public:
483 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
484 bool bulk_rebias)
485 : _obj(obj)
486 , _requesting_thread(requesting_thread)
487 , _bulk_rebias(bulk_rebias)
488 , _safepoint_id(0) {}
489
490 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
491
492 virtual void doit() {
493 BiasedLocking::bulk_revoke_at_safepoint((*_obj)(), _bulk_rebias, _requesting_thread);
494 _safepoint_id = SafepointSynchronize::safepoint_id();
495 clean_up_cached_monitor_info();
496 }
497
498 bool is_bulk_rebias() const {
499 return _bulk_rebias;
500 }
501
502 uint64_t safepoint_id() const {
503 return _safepoint_id;
504 }
505 };
506
507
508 class RevokeOneBias : public HandshakeClosure {
509 protected:
510 Handle _obj;
511 JavaThread* _requesting_thread;
512 JavaThread* _biased_locker;
513 BiasedLocking::Condition _status_code;
514 traceid _biased_locker_id;
515
516 public:
517 RevokeOneBias(Handle obj, JavaThread* requesting_thread, JavaThread* biased_locker)
518 : HandshakeClosure("RevokeOneBias")
519 , _obj(obj)
520 , _requesting_thread(requesting_thread)
521 , _biased_locker(biased_locker)
522 , _status_code(BiasedLocking::NOT_BIASED)
523 , _biased_locker_id(0) {}
524
525 void do_thread(Thread* target) {
526 assert(target == _biased_locker, "Wrong thread");
527
528 oop o = _obj();
529 markWord mark = o->mark();
530
531 if (!mark.has_bias_pattern()) {
532 return;
533 }
534
535 markWord prototype = o->klass()->prototype_header();
536 if (!prototype.has_bias_pattern()) {
537 // This object has a stale bias from before the handshake
538 // was requested. If we fail this race, the object's bias
539 // has been revoked by another thread so we simply return.
540 markWord biased_value = mark;
541 mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark);
542 assert(!o->mark().has_bias_pattern(), "even if we raced, should still be revoked");
543 if (biased_value == mark) {
544 _status_code = BiasedLocking::BIAS_REVOKED;
545 }
546 return;
547 }
548
549 if (_biased_locker == mark.biased_locker()) {
550 if (mark.bias_epoch() == prototype.bias_epoch()) {
551 // Epoch is still valid. This means biaser could be currently
552 // synchronized on this object. We must walk its stack looking
553 // for monitor records associated with this object and change
554 // them to be stack locks if any are found.
555 ResourceMark rm;
556 BiasedLocking::walk_stack_and_revoke(o, _biased_locker);
557 _biased_locker->set_cached_monitor_info(NULL);
558 assert(!o->mark().has_bias_pattern(), "invariant");
559 _biased_locker_id = JFR_THREAD_ID(_biased_locker);
560 _status_code = BiasedLocking::BIAS_REVOKED;
561 return;
562 } else {
563 markWord biased_value = mark;
564 mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark);
565 if (mark == biased_value || !mark.has_bias_pattern()) {
566 assert(!o->mark().has_bias_pattern(), "should be revoked");
567 _status_code = (biased_value == mark) ? BiasedLocking::BIAS_REVOKED : BiasedLocking::NOT_BIASED;
568 return;
569 }
570 }
571 }
572
573 _status_code = BiasedLocking::NOT_REVOKED;
574 }
575
576 BiasedLocking::Condition status_code() const {
577 return _status_code;
578 }
579
580 traceid biased_locker() const {
581 return _biased_locker_id;
582 }
583 };
584
585
586 static void post_self_revocation_event(EventBiasedLockSelfRevocation* event, Klass* k) {
587 assert(event != NULL, "invariant");
588 assert(k != NULL, "invariant");
589 assert(event->should_commit(), "invariant");
590 event->set_lockClass(k);
591 event->commit();
592 }
593
594 static void post_revocation_event(EventBiasedLockRevocation* event, Klass* k, RevokeOneBias* op) {
595 assert(event != NULL, "invariant");
596 assert(k != NULL, "invariant");
597 assert(op != NULL, "invariant");
598 assert(event->should_commit(), "invariant");
599 event->set_lockClass(k);
600 event->set_safepointId(0);
601 event->set_previousOwner(op->biased_locker());
602 event->commit();
603 }
604
605 static void post_class_revocation_event(EventBiasedLockClassRevocation* event, Klass* k, VM_BulkRevokeBias* op) {
606 assert(event != NULL, "invariant");
607 assert(k != NULL, "invariant");
608 assert(op != NULL, "invariant");
609 assert(event->should_commit(), "invariant");
610 event->set_revokedClass(k);
611 event->set_disableBiasing(!op->is_bulk_rebias());
612 event->set_safepointId(op->safepoint_id());
613 event->commit();
614 }
615
616
617 BiasedLocking::Condition BiasedLocking::single_revoke_with_handshake(Handle obj, JavaThread *requester, JavaThread *biaser) {
618
619 EventBiasedLockRevocation event;
620 if (PrintBiasedLockingStatistics) {
621 Atomic::inc(handshakes_count_addr());
622 }
623 log_info(biasedlocking, handshake)("JavaThread " INTPTR_FORMAT " handshaking JavaThread "
624 INTPTR_FORMAT " to revoke object " INTPTR_FORMAT, p2i(requester),
625 p2i(biaser), p2i(obj()));
626
627 RevokeOneBias revoke(obj, requester, biaser);
628 bool executed = Handshake::execute(&revoke, biaser);
629 if (revoke.status_code() == NOT_REVOKED) {
630 return NOT_REVOKED;
631 }
632 if (executed) {
633 log_info(biasedlocking, handshake)("Handshake revocation for object " INTPTR_FORMAT " succeeded. Bias was %srevoked",
634 p2i(obj()), (revoke.status_code() == BIAS_REVOKED ? "" : "already "));
635 if (event.should_commit() && revoke.status_code() == BIAS_REVOKED) {
636 post_revocation_event(&event, obj->klass(), &revoke);
637 }
638 assert(!obj->mark().has_bias_pattern(), "invariant");
639 return revoke.status_code();
640 } else {
641 // Thread was not alive.
642 // Grab Threads_lock before manually trying to revoke bias. This avoids race with a newly
643 // created JavaThread (that happens to get the same memory address as biaser) synchronizing
644 // on this object.
645 {
646 MutexLocker ml(Threads_lock);
647 markWord mark = obj->mark();
648 // Check if somebody else was able to revoke it before biased thread exited.
649 if (!mark.has_bias_pattern()) {
650 return NOT_BIASED;
651 }
652 ThreadsListHandle tlh;
653 markWord prototype = obj->klass()->prototype_header();
654 if (!prototype.has_bias_pattern() || (!tlh.includes(biaser) && biaser == mark.biased_locker() &&
655 prototype.bias_epoch() == mark.bias_epoch())) {
656 obj->cas_set_mark(markWord::prototype().set_age(mark.age()), mark);
657 if (event.should_commit()) {
658 post_revocation_event(&event, obj->klass(), &revoke);
659 }
660 assert(!obj->mark().has_bias_pattern(), "bias should be revoked by now");
661 return BIAS_REVOKED;
662 }
663 }
664 }
665
666 return NOT_REVOKED;
667 }
668
669
670 // Caller should have instantiated a ResourceMark object before calling this method
671 void BiasedLocking::walk_stack_and_revoke(oop obj, JavaThread* biased_locker) {
672 assert(!SafepointSynchronize::is_at_safepoint() || !ThreadLocalHandshakes,
673 "if ThreadLocalHandshakes is enabled this should always be executed outside safepoints");
674 assert(Thread::current() == biased_locker || Thread::current()->is_VM_thread(), "wrong thread");
675
676 markWord mark = obj->mark();
677 assert(mark.biased_locker() == biased_locker &&
678 obj->klass()->prototype_header().bias_epoch() == mark.bias_epoch(), "invariant");
679
680 log_trace(biasedlocking)("%s(" INTPTR_FORMAT ") revoking object " INTPTR_FORMAT ", mark "
681 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
682 ", biaser " INTPTR_FORMAT " %s",
683 Thread::current()->is_VM_thread() ? "VMThread" : "JavaThread",
684 p2i(Thread::current()),
685 p2i(obj),
686 mark.value(),
687 obj->klass()->external_name(),
688 obj->klass()->prototype_header().value(),
689 p2i(biased_locker),
690 Thread::current()->is_VM_thread() ? "" : "(walking own stack)");
691
692 markWord unbiased_prototype = markWord::prototype().set_age(obj->mark().age());
693
694 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_locker);
695 BasicLock* highest_lock = NULL;
696 for (int i = 0; i < cached_monitor_info->length(); i++) {
697 MonitorInfo* mon_info = cached_monitor_info->at(i);
698 if (mon_info->owner() == obj) {
699 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
700 p2i(mon_info->owner()),
701 p2i(obj));
702 // Assume recursive case and fix up highest lock below
703 markWord mark = markWord::encode((BasicLock*) NULL);
704 highest_lock = mon_info->lock();
705 highest_lock->set_displaced_header(mark);
706 } else {
707 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
708 p2i(mon_info->owner()),
709 p2i(obj));
710 }
711 }
712 if (highest_lock != NULL) {
713 // Fix up highest lock to contain displaced header and point
714 // object at it
715 highest_lock->set_displaced_header(unbiased_prototype);
716 // Reset object header to point to displaced mark.
717 // Must release store the lock address for platforms without TSO
718 // ordering (e.g. ppc).
719 obj->release_set_mark(markWord::encode(highest_lock));
720 assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit");
721 log_info(biasedlocking)(" Revoked bias of currently-locked object");
722 } else {
723 log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
724 // Store the unlocked value into the object's header.
725 obj->set_mark(unbiased_prototype);
726 }
727
728 assert(!obj->mark().has_bias_pattern(), "must not be biased");
729 }
730
731 void BiasedLocking::revoke_own_lock(Handle obj, TRAPS) {
732 assert(THREAD->is_Java_thread(), "must be called by a JavaThread");
733 JavaThread* thread = (JavaThread*)THREAD;
734
735 markWord mark = obj->mark();
736
737 if (!mark.has_bias_pattern()) {
738 return;
739 }
740
741 Klass *k = obj->klass();
742 assert(mark.biased_locker() == thread &&
743 k->prototype_header().bias_epoch() == mark.bias_epoch(), "Revoke failed, unhandled biased lock state");
744 ResourceMark rm;
745 log_info(biasedlocking)("Revoking bias by walking my own stack:");
746 EventBiasedLockSelfRevocation event;
747 BiasedLocking::walk_stack_and_revoke(obj(), (JavaThread*) thread);
748 thread->set_cached_monitor_info(NULL);
749 assert(!obj->mark().has_bias_pattern(), "invariant");
750 if (event.should_commit()) {
751 post_self_revocation_event(&event, k);
752 }
753 }
754
755 void BiasedLocking::revoke(Handle obj, TRAPS) {
756 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
757
758 while (true) {
759 // We can revoke the biases of anonymously-biased objects
760 // efficiently enough that we should not cause these revocations to
761 // update the heuristics because doing so may cause unwanted bulk
762 // revocations (which are expensive) to occur.
763 markWord mark = obj->mark();
764
765 if (!mark.has_bias_pattern()) {
766 return;
767 }
768
769 if (mark.is_biased_anonymously()) {
770 // We are probably trying to revoke the bias of this object due to
771 // an identity hash code computation. Try to revoke the bias
772 // without a safepoint. This is possible if we can successfully
773 // compare-and-exchange an unbiased header into the mark word of
774 // the object, meaning that no other thread has raced to acquire
775 // the bias of the object.
776 markWord biased_value = mark;
777 markWord unbiased_prototype = markWord::prototype().set_age(mark.age());
778 markWord res_mark = obj->cas_set_mark(unbiased_prototype, mark);
779 if (res_mark == biased_value) {
780 return;
781 }
782 mark = res_mark; // Refresh mark with the latest value.
783 } else {
784 Klass* k = obj->klass();
785 markWord prototype_header = k->prototype_header();
786 if (!prototype_header.has_bias_pattern()) {
787 // This object has a stale bias from before the bulk revocation
788 // for this data type occurred. It's pointless to update the
789 // heuristics at this point so simply update the header with a
790 // CAS. If we fail this race, the object's bias has been revoked
791 // by another thread so we simply return and let the caller deal
792 // with it.
793 obj->cas_set_mark(prototype_header.set_age(mark.age()), mark);
794 assert(!obj->mark().has_bias_pattern(), "even if we raced, should still be revoked");
795 return;
796 } else if (prototype_header.bias_epoch() != mark.bias_epoch()) {
797 // The epoch of this biasing has expired indicating that the
798 // object is effectively unbiased. We can revoke the bias of this
799 // object efficiently enough with a CAS that we shouldn't update the
800 // heuristics. This is normally done in the assembly code but we
801 // can reach this point due to various points in the runtime
802 // needing to revoke biases.
803 markWord res_mark;
804 markWord biased_value = mark;
805 markWord unbiased_prototype = markWord::prototype().set_age(mark.age());
806 res_mark = obj->cas_set_mark(unbiased_prototype, mark);
807 if (res_mark == biased_value) {
808 return;
809 }
810 mark = res_mark; // Refresh mark with the latest value.
811 }
812 }
813
814 HeuristicsResult heuristics = update_heuristics(obj());
815 if (heuristics == HR_NOT_BIASED) {
816 return;
817 } else if (heuristics == HR_SINGLE_REVOKE) {
818 JavaThread *blt = mark.biased_locker();
819 assert(blt != NULL, "invariant");
820 if (blt == THREAD) {
821 // A thread is trying to revoke the bias of an object biased
822 // toward it, again likely due to an identity hash code
823 // computation. We can again avoid a safepoint/handshake in this case
824 // since we are only going to walk our own stack. There are no
825 // races with revocations occurring in other threads because we
826 // reach no safepoints in the revocation path.
827 EventBiasedLockSelfRevocation event;
828 ResourceMark rm;
829 walk_stack_and_revoke(obj(), blt);
830 blt->set_cached_monitor_info(NULL);
831 assert(!obj->mark().has_bias_pattern(), "invariant");
832 if (event.should_commit()) {
833 post_self_revocation_event(&event, obj->klass());
834 }
835 return;
836 } else {
837 BiasedLocking::Condition cond = single_revoke_with_handshake(obj, (JavaThread*)THREAD, blt);
838 if (cond != NOT_REVOKED) {
839 return;
840 }
841 }
842 } else {
843 assert((heuristics == HR_BULK_REVOKE) ||
844 (heuristics == HR_BULK_REBIAS), "?");
845 EventBiasedLockClassRevocation event;
846 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*)THREAD,
847 (heuristics == HR_BULK_REBIAS));
848 VMThread::execute(&bulk_revoke);
849 if (event.should_commit()) {
850 post_class_revocation_event(&event, obj->klass(), &bulk_revoke);
851 }
852 return;
853 }
854 }
855 }
856
857 // All objects in objs should be locked by biaser
858 void BiasedLocking::revoke(GrowableArray<Handle>* objs, JavaThread *biaser) {
859 bool clean_my_cache = false;
860 for (int i = 0; i < objs->length(); i++) {
861 oop obj = (objs->at(i))();
862 markWord mark = obj->mark();
863 if (mark.has_bias_pattern()) {
864 walk_stack_and_revoke(obj, biaser);
865 clean_my_cache = true;
866 }
867 }
868 if (clean_my_cache) {
869 clean_up_cached_monitor_info(biaser);
870 }
871 }
872
873
874 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
875 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
876 oop obj = h_obj();
877 HeuristicsResult heuristics = update_heuristics(obj);
878 if (heuristics == HR_SINGLE_REVOKE) {
879 JavaThread* biased_locker = NULL;
880 single_revoke_at_safepoint(obj, false, NULL, &biased_locker);
881 if (biased_locker) {
882 clean_up_cached_monitor_info(biased_locker);
883 }
884 } else if ((heuristics == HR_BULK_REBIAS) ||
885 (heuristics == HR_BULK_REVOKE)) {
886 bulk_revoke_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), NULL);
887 clean_up_cached_monitor_info();
888 }
889 }
890
891
892 void BiasedLocking::preserve_marks() {
893 if (!UseBiasedLocking)
894 return;
895
896 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
897
898 assert(_preserved_oop_stack == NULL, "double initialization");
899 assert(_preserved_mark_stack == NULL, "double initialization");
900
901 // In order to reduce the number of mark words preserved during GC
902 // due to the presence of biased locking, we reinitialize most mark
903 // words to the class's prototype during GC -- even those which have
904 // a currently valid bias owner. One important situation where we
905 // must not clobber a bias is when a biased object is currently
906 // locked. To handle this case we iterate over the currently-locked
907 // monitors in a prepass and, if they are biased, preserve their
908 // mark words here. This should be a relatively small set of objects
909 // especially compared to the number of objects in the heap.
910 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markWord>(10, true);
911 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
912
913 ResourceMark rm;
914 Thread* cur = Thread::current();
915 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
916 if (thread->has_last_Java_frame()) {
917 RegisterMap rm(thread);
918 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
919 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
920 if (monitors != NULL) {
921 int len = monitors->length();
922 // Walk monitors youngest to oldest
923 for (int i = len - 1; i >= 0; i--) {
924 MonitorInfo* mon_info = monitors->at(i);
925 if (mon_info->owner_is_scalar_replaced()) continue;
926 oop owner = mon_info->owner();
927 if (owner != NULL) {
928 markWord mark = owner->mark();
929 if (mark.has_bias_pattern()) {
930 _preserved_oop_stack->push(Handle(cur, owner));
931 _preserved_mark_stack->push(mark);
932 }
933 }
934 }
935 }
936 }
937 }
938 }
939 }
940
941
942 void BiasedLocking::restore_marks() {
943 if (!UseBiasedLocking)
944 return;
945
946 assert(_preserved_oop_stack != NULL, "double free");
947 assert(_preserved_mark_stack != NULL, "double free");
948
949 int len = _preserved_oop_stack->length();
950 for (int i = 0; i < len; i++) {
951 Handle owner = _preserved_oop_stack->at(i);
952 markWord mark = _preserved_mark_stack->at(i);
953 owner->set_mark(mark);
954 }
955
956 delete _preserved_oop_stack;
957 _preserved_oop_stack = NULL;
958 delete _preserved_mark_stack;
959 _preserved_mark_stack = NULL;
960 }
961
962
963 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
964 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
965 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
966 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
967 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
968 int* BiasedLocking::handshakes_count_addr() { return _counters.handshakes_count_addr(); }
969 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
970 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
971
972
973 // BiasedLockingCounters
974
975 int BiasedLockingCounters::slow_path_entry_count() const {
976 if (_slow_path_entry_count != 0) {
977 return _slow_path_entry_count;
978 }
979 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
980 _rebiased_lock_entry_count + _revoked_lock_entry_count +
981 _fast_path_entry_count;
982
983 return _total_entry_count - sum;
984 }
985
986 void BiasedLockingCounters::print_on(outputStream* st) const {
987 tty->print_cr("# total entries: %d", _total_entry_count);
988 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
989 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
990 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
991 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
992 tty->print_cr("# handshakes entries: %d", _handshakes_count);
993 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
994 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
995 }
996
997 void BiasedLockingCounters::print() const { print_on(tty); }