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 BiasedLocking::Condition BiasedLocking::single_revoke_at_safepoint(oop obj, bool allow_rebias, 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 NOT_BIASED;
177 }
178
179 uint age = mark.age();
180 markWord biased_prototype = markWord::biased_locking_prototype().set_age(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 ", allow rebias %d, requesting thread " INTPTR_FORMAT,
189 p2i((void *)obj),
190 mark.value(),
191 obj->klass()->external_name(),
192 obj->klass()->prototype_header().value(),
193 (allow_rebias ? 1 : 0),
194 (intptr_t) requesting_thread);
195 } else {
196 ResourceMark rm;
197 log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark "
198 INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT
199 " , allow rebias %d , requesting thread " INTPTR_FORMAT,
200 p2i((void *)obj),
201 mark.value(),
202 obj->klass()->external_name(),
203 obj->klass()->prototype_header().value(),
204 (allow_rebias ? 1 : 0),
205 (intptr_t) requesting_thread);
206 }
207
208 JavaThread* biased_thread = mark.biased_locker();
209 if (biased_thread == NULL) {
210 // Object is anonymously biased. We can get here if, for
211 // example, we revoke the bias due to an identity hash code
212 // being computed for an object.
213 if (!allow_rebias) {
214 obj->set_mark(unbiased_prototype);
215 }
216 // Log at "info" level if not bulk, else "trace" level
217 if (!is_bulk) {
218 log_info(biasedlocking)(" Revoked bias of anonymously-biased object");
219 } else {
220 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object");
221 }
222 return BIAS_REVOKED;
223 }
224
225 // Handle case where the thread toward which the object was biased has exited
226 bool thread_is_alive = false;
227 if (requesting_thread == biased_thread) {
228 thread_is_alive = true;
229 } else {
230 ThreadsListHandle tlh;
231 thread_is_alive = tlh.includes(biased_thread);
232 }
233 if (!thread_is_alive) {
234 if (allow_rebias) {
235 obj->set_mark(biased_prototype);
236 } else {
237 obj->set_mark(unbiased_prototype);
238 }
239 // Log at "info" level if not bulk, else "trace" level
240 if (!is_bulk) {
241 log_info(biasedlocking)(" Revoked bias of object biased toward dead thread ("
242 PTR_FORMAT ")", p2i(biased_thread));
243 } else {
244 log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread ("
245 PTR_FORMAT ")", p2i(biased_thread));
246 }
247 return BIAS_REVOKED;
248 }
249
250 // Log at "info" level if not bulk, else "trace" level
251 if (!is_bulk) {
252 log_info(biasedlocking)(" Revoked bias of object biased toward live thread ("
253 PTR_FORMAT ")", p2i(biased_thread));
254 } else {
255 log_trace(biasedlocking)(" Revoked bias of object biased toward live thread ("
256 PTR_FORMAT ")", p2i(biased_thread));
257 }
258
259 // Thread owning bias is alive.
260 // Check to see whether it currently owns the lock and, if so,
261 // write down the needed displaced headers to the thread's stack.
262 // Otherwise, restore the object's header either to the unlocked
263 // or unbiased state.
264 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
265 BasicLock* highest_lock = NULL;
266 for (int i = 0; i < cached_monitor_info->length(); i++) {
267 MonitorInfo* mon_info = cached_monitor_info->at(i);
268 if (oopDesc::equals(mon_info->owner(), obj)) {
269 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
270 p2i((void *) mon_info->owner()),
271 p2i((void *) obj));
272 // Assume recursive case and fix up highest lock below
273 markWord mark = markWord::encode((BasicLock*) NULL);
274 highest_lock = mon_info->lock();
275 highest_lock->set_displaced_header(mark);
276 } else {
277 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
278 p2i((void *) mon_info->owner()),
279 p2i((void *) obj));
280 }
281 }
282 if (highest_lock != NULL) {
283 // Fix up highest lock to contain displaced header and point
284 // object at it
285 highest_lock->set_displaced_header(unbiased_prototype);
286 // Reset object header to point to displaced mark.
287 // Must release store the lock address for platforms without TSO
288 // ordering (e.g. ppc).
289 obj->release_set_mark(markWord::encode(highest_lock));
290 assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit");
291 // Log at "info" level if not bulk, else "trace" level
292 if (!is_bulk) {
293 log_info(biasedlocking)(" Revoked bias of currently-locked object");
294 } else {
295 log_trace(biasedlocking)(" Revoked bias of currently-locked object");
296 }
297 } else {
298 // Log at "info" level if not bulk, else "trace" level
299 if (!is_bulk) {
300 log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
301 } else {
302 log_trace(biasedlocking)(" Revoked bias of currently-unlocked object");
303 }
304 if (allow_rebias) {
305 obj->set_mark(biased_prototype);
306 } else {
307 // Store the unlocked value into the object's header.
308 obj->set_mark(unbiased_prototype);
309 }
310 }
311
312 // If requested, return information on which thread held the bias
313 if (biased_locker != NULL) {
314 *biased_locker = biased_thread;
315 }
316
317 return BIAS_REVOKED;
318 }
319
320
321 enum HeuristicsResult {
322 HR_NOT_BIASED = 1,
323 HR_SINGLE_REVOKE = 2,
324 HR_BULK_REBIAS = 3,
325 HR_BULK_REVOKE = 4
326 };
327
328
329 static HeuristicsResult update_heuristics(oop o) {
330 markWord mark = o->mark();
331 if (!mark.has_bias_pattern()) {
332 return HR_NOT_BIASED;
333 }
334
335 // Heuristics to attempt to throttle the number of revocations.
336 // Stages:
337 // 1. Revoke the biases of all objects in the heap of this type,
338 // but allow rebiasing of those objects if unlocked.
339 // 2. Revoke the biases of all objects in the heap of this type
340 // and don't allow rebiasing of these objects. Disable
341 // allocation of objects of that type with the bias bit set.
342 Klass* k = o->klass();
343 jlong cur_time = os::javaTimeMillis();
344 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
345 int revocation_count = k->biased_lock_revocation_count();
346 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
347 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
348 (last_bulk_revocation_time != 0) &&
349 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
350 // This is the first revocation we've seen in a while of an
351 // object of this type since the last time we performed a bulk
352 // rebiasing operation. The application is allocating objects in
353 // bulk which are biased toward a thread and then handing them
354 // off to another thread. We can cope with this allocation
355 // pattern via the bulk rebiasing mechanism so we reset the
356 // klass's revocation count rather than allow it to increase
357 // monotonically. If we see the need to perform another bulk
358 // rebias operation later, we will, and if subsequently we see
359 // many more revocation operations in a short period of time we
360 // will completely disable biasing for this type.
361 k->set_biased_lock_revocation_count(0);
362 revocation_count = 0;
363 }
364
365 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
366 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
367 revocation_count = k->atomic_incr_biased_lock_revocation_count();
368 }
369
370 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
371 return HR_BULK_REVOKE;
372 }
373
374 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
375 return HR_BULK_REBIAS;
376 }
377
378 return HR_SINGLE_REVOKE;
379 }
380
381
382 BiasedLocking::Condition BiasedLocking::bulk_revoke_or_rebias_at_safepoint(oop o,
383 bool bulk_rebias,
384 bool attempt_rebias_of_object,
385 JavaThread* requesting_thread) {
386 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
387 assert(Thread::current()->is_VM_thread(), "must be VMThread");
388
389 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object "
390 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
391 (bulk_rebias ? "rebias" : "revoke"),
392 p2i((void *) o),
393 o->mark().value(),
394 o->klass()->external_name());
395
396 jlong cur_time = os::javaTimeMillis();
397 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
398
399 Klass* k_o = o->klass();
400 Klass* klass = k_o;
401
402 {
403 JavaThreadIteratorWithHandle jtiwh;
404
405 if (bulk_rebias) {
406 // Use the epoch in the klass of the object to implicitly revoke
407 // all biases of objects of this data type and force them to be
408 // reacquired. However, we also need to walk the stacks of all
409 // threads and update the headers of lightweight locked objects
410 // with biases to have the current epoch.
411
412 // If the prototype header doesn't have the bias pattern, don't
413 // try to update the epoch -- assume another VM operation came in
414 // and reset the header to the unbiased state, which will
415 // implicitly cause all existing biases to be revoked
416 if (klass->prototype_header().has_bias_pattern()) {
417 int prev_epoch = klass->prototype_header().bias_epoch();
418 klass->set_prototype_header(klass->prototype_header().incr_bias_epoch());
419 int cur_epoch = klass->prototype_header().bias_epoch();
420
421 // Now walk all threads' stacks and adjust epochs of any biased
422 // and locked objects of this data type we encounter
423 for (; JavaThread *thr = jtiwh.next(); ) {
424 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
425 for (int i = 0; i < cached_monitor_info->length(); i++) {
426 MonitorInfo* mon_info = cached_monitor_info->at(i);
427 oop owner = mon_info->owner();
428 markWord mark = owner->mark();
429 if ((owner->klass() == k_o) && mark.has_bias_pattern()) {
430 // We might have encountered this object already in the case of recursive locking
431 assert(mark.bias_epoch() == prev_epoch || mark.bias_epoch() == cur_epoch, "error in bias epoch adjustment");
432 owner->set_mark(mark.set_bias_epoch(cur_epoch));
433 }
434 }
435 }
436 }
437
438 // At this point we're done. All we have to do is potentially
439 // adjust the header of the given object to revoke its bias.
440 single_revoke_at_safepoint(o, attempt_rebias_of_object && klass->prototype_header().has_bias_pattern(), true, requesting_thread, NULL);
441 } else {
442 if (log_is_enabled(Info, biasedlocking)) {
443 ResourceMark rm;
444 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name());
445 }
446
447 // Disable biased locking for this data type. Not only will this
448 // cause future instances to not be biased, but existing biased
449 // instances will notice that this implicitly caused their biases
450 // to be revoked.
451 klass->set_prototype_header(markWord::prototype());
452
453 // Now walk all threads' stacks and forcibly revoke the biases of
454 // any locked and biased objects of this data type we encounter.
455 for (; JavaThread *thr = jtiwh.next(); ) {
456 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
457 for (int i = 0; i < cached_monitor_info->length(); i++) {
458 MonitorInfo* mon_info = cached_monitor_info->at(i);
459 oop owner = mon_info->owner();
460 markWord mark = owner->mark();
461 if ((owner->klass() == k_o) && mark.has_bias_pattern()) {
462 single_revoke_at_safepoint(owner, false, true, requesting_thread, NULL);
463 }
464 }
465 }
466
467 // Must force the bias of the passed object to be forcibly revoked
468 // as well to ensure guarantees to callers
469 single_revoke_at_safepoint(o, false, true, requesting_thread, NULL);
470 }
471 } // ThreadsListHandle is destroyed here.
472
473 log_info(biasedlocking)("* Ending bulk revocation");
474
475 BiasedLocking::Condition status_code = BIAS_REVOKED;
476
477 if (attempt_rebias_of_object &&
478 o->mark().has_bias_pattern() &&
479 klass->prototype_header().has_bias_pattern()) {
480 markWord new_mark = markWord::encode(requesting_thread, o->mark().age(),
481 klass->prototype_header().bias_epoch());
482 o->set_mark(new_mark);
483 status_code = BIAS_REVOKED_AND_REBIASED;
484 log_info(biasedlocking)(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
485 }
486
487 assert(!o->mark().has_bias_pattern() ||
488 (attempt_rebias_of_object && (o->mark().biased_locker() == requesting_thread)),
489 "bug in bulk bias revocation");
490
491 return status_code;
492 }
493
494
495 static void clean_up_cached_monitor_info(JavaThread* thread = NULL) {
496 if (thread != NULL) {
497 thread->set_cached_monitor_info(NULL);
498 } else {
499 // Walk the thread list clearing out the cached monitors
500 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
501 thr->set_cached_monitor_info(NULL);
502 }
503 }
504 }
505
506
507 class VM_BulkRevokeBias : public VM_Operation {
508 private:
509 Handle* _obj;
510 JavaThread* _requesting_thread;
511 bool _bulk_rebias;
512 bool _attempt_rebias_of_object;
513 BiasedLocking::Condition _status_code;
514 uint64_t _safepoint_id;
515
516 public:
517 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
518 bool bulk_rebias,
519 bool attempt_rebias_of_object)
520 : _obj(obj)
521 , _requesting_thread(requesting_thread)
522 , _bulk_rebias(bulk_rebias)
523 , _attempt_rebias_of_object(attempt_rebias_of_object)
524 , _status_code(BiasedLocking::NOT_BIASED)
525 , _safepoint_id(0) {}
526
527 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
528
529 virtual void doit() {
530 _status_code = BiasedLocking::bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
531 _safepoint_id = SafepointSynchronize::safepoint_id();
532 clean_up_cached_monitor_info();
533 }
534
535 bool is_bulk_rebias() const {
536 return _bulk_rebias;
537 }
538
539 BiasedLocking::Condition status_code() const {
540 return _status_code;
541 }
542
543 uint64_t safepoint_id() const {
544 return _safepoint_id;
545 }
546 };
547
548
549 class RevokeOneBias : public ThreadClosure {
550 protected:
551 Handle _obj;
552 JavaThread* _requesting_thread;
553 JavaThread* _biased_locker;
554 BiasedLocking::Condition _status_code;
555 traceid _biased_locker_id;
556
557 public:
558 RevokeOneBias(Handle obj, JavaThread* requesting_thread, JavaThread* biased_locker)
559 : _obj(obj)
560 , _requesting_thread(requesting_thread)
561 , _biased_locker(biased_locker)
562 , _status_code(BiasedLocking::NOT_BIASED)
563 , _biased_locker_id(0) {}
564
565 void do_thread(Thread* target) {
566 assert(target == _biased_locker, "Wrong thread");
567
568 oop o = _obj();
569 markWord mark = o->mark();
570
571 if (!mark.has_bias_pattern()) {
572 return;
573 }
574
575 markWord prototype = o->klass()->prototype_header();
576 if (!prototype.has_bias_pattern()) {
577 // This object has a stale bias from before the handshake
578 // was requested. If we fail this race, the object's bias
579 // has been revoked by another thread so we simply return.
580 markWord biased_value = mark;
581 mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark);
582 assert(!o->mark().has_bias_pattern(), "even if we raced, should still be revoked");
583 if (biased_value == mark) {
584 _status_code = BiasedLocking::BIAS_REVOKED;
585 }
586 return;
587 }
588
589 if (_biased_locker == mark.biased_locker()) {
590 if (mark.bias_epoch() == prototype.bias_epoch()) {
591 // Epoch is still valid. This means biaser could be currently
592 // synchronized on this object. We must walk its stack looking
593 // for monitor records associated with this object and change
594 // them to be stack locks if any are found.
595 ResourceMark rm;
596 BiasedLocking::walk_stack_and_revoke(o, _biased_locker);
597 _biased_locker->set_cached_monitor_info(NULL);
598 assert(!o->mark().has_bias_pattern(), "invariant");
599 _biased_locker_id = JFR_THREAD_ID(_biased_locker);
600 _status_code = BiasedLocking::BIAS_REVOKED;
601 return;
602 } else {
603 markWord biased_value = mark;
604 mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark);
605 if (mark == biased_value || !mark.has_bias_pattern()) {
606 assert(!o->mark().has_bias_pattern(), "should be revoked");
607 _status_code = (biased_value == mark) ? BiasedLocking::BIAS_REVOKED : BiasedLocking::NOT_BIASED;
608 return;
609 }
610 }
611 }
612
613 _status_code = BiasedLocking::NOT_REVOKED;
614 }
615
616 BiasedLocking::Condition status_code() const {
617 return _status_code;
618 }
619
620 traceid biased_locker() const {
621 return _biased_locker_id;
622 }
623 };
624
625
626 static void post_self_revocation_event(EventBiasedLockSelfRevocation* event, Klass* k) {
627 assert(event != NULL, "invariant");
628 assert(k != NULL, "invariant");
629 assert(event->should_commit(), "invariant");
630 event->set_lockClass(k);
631 event->commit();
632 }
633
634 static void post_revocation_event(EventBiasedLockRevocation* event, Klass* k, RevokeOneBias* op) {
635 assert(event != NULL, "invariant");
636 assert(k != NULL, "invariant");
637 assert(op != NULL, "invariant");
638 assert(event->should_commit(), "invariant");
639 event->set_lockClass(k);
640 event->set_safepointId(0);
641 event->set_previousOwner(op->biased_locker());
642 event->commit();
643 }
644
645 static void post_class_revocation_event(EventBiasedLockClassRevocation* event, Klass* k, VM_BulkRevokeBias* op) {
646 assert(event != NULL, "invariant");
647 assert(k != NULL, "invariant");
648 assert(op != NULL, "invariant");
649 assert(event->should_commit(), "invariant");
650 event->set_revokedClass(k);
651 event->set_disableBiasing(!op->is_bulk_rebias());
652 event->set_safepointId(op->safepoint_id());
653 event->commit();
654 }
655
656
657 BiasedLocking::Condition BiasedLocking::single_revoke_with_handshake(Handle obj, JavaThread *requester, JavaThread *biaser) {
658
659 EventBiasedLockRevocation event;
660 if (PrintBiasedLockingStatistics) {
661 Atomic::inc(handshakes_count_addr());
662 }
663 log_info(biasedlocking, handshake)("JavaThread " INTPTR_FORMAT " handshaking JavaThread "
664 INTPTR_FORMAT " to revoke object " INTPTR_FORMAT, p2i(requester),
665 p2i(biaser), p2i(obj()));
666
667 RevokeOneBias revoke(obj, requester, biaser);
668 bool executed = Handshake::execute(&revoke, biaser);
669 if (revoke.status_code() == NOT_REVOKED) {
670 return NOT_REVOKED;
671 }
672 if (executed) {
673 log_info(biasedlocking, handshake)("Handshake revocation for object " INTPTR_FORMAT " succeeded. Bias was %srevoked",
674 p2i(obj()), (revoke.status_code() == BIAS_REVOKED ? "" : "already "));
675 if (event.should_commit() && revoke.status_code() == BIAS_REVOKED) {
676 post_revocation_event(&event, obj->klass(), &revoke);
677 }
678 assert(!obj->mark().has_bias_pattern(), "invariant");
679 return revoke.status_code();
680 } else {
681 // Thread was not alive.
682 // Grab Threads_lock before manually trying to revoke bias. This avoids race with a newly
683 // created JavaThread (that happens to get the same memory address as biaser) synchronizing
684 // on this object.
685 {
686 MutexLocker ml(Threads_lock);
687 markWord mark = obj->mark();
688 // Check if somebody else was able to revoke it before biased thread exited.
689 if (!mark.has_bias_pattern()) {
690 return NOT_BIASED;
691 }
692 ThreadsListHandle tlh;
693 markWord prototype = obj->klass()->prototype_header();
694 if (!prototype.has_bias_pattern() || (!tlh.includes(biaser) && biaser == mark.biased_locker() &&
695 prototype.bias_epoch() == mark.bias_epoch())) {
696 obj->cas_set_mark(markWord::prototype().set_age(mark.age()), mark);
697 if (event.should_commit()) {
698 post_revocation_event(&event, obj->klass(), &revoke);
699 }
700 assert(!obj->mark().has_bias_pattern(), "bias should be revoked by now");
701 return BIAS_REVOKED;
702 }
703 }
704 }
705
706 return NOT_REVOKED;
707 }
708
709
710 // Caller should have instantiated a ResourceMark object before calling this method
711 void BiasedLocking::walk_stack_and_revoke(oop obj, JavaThread* biased_locker) {
712 assert(!SafepointSynchronize::is_at_safepoint() || !ThreadLocalHandshakes,
713 "if ThreadLocalHandshakes is enabled this should always be executed outside safepoints");
714 assert(Thread::current() == biased_locker || Thread::current()->is_VM_thread(), "wrong thread");
715
716 markWord mark = obj->mark();
717 assert(mark.biased_locker() == biased_locker &&
718 obj->klass()->prototype_header().bias_epoch() == mark.bias_epoch(), "invariant");
719
720 log_trace(biasedlocking)("%s(" INTPTR_FORMAT ") revoking object " INTPTR_FORMAT ", mark "
721 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
722 ", biaser " INTPTR_FORMAT " %s",
723 Thread::current()->is_VM_thread() ? "VMThread" : "JavaThread",
724 p2i(Thread::current()),
725 p2i(obj),
726 mark.value(),
727 obj->klass()->external_name(),
728 obj->klass()->prototype_header().value(),
729 p2i(biased_locker),
730 Thread::current()->is_VM_thread() ? "" : "(walking own stack)");
731
732 markWord unbiased_prototype = markWord::prototype().set_age(obj->mark().age());
733
734 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_locker);
735 BasicLock* highest_lock = NULL;
736 for (int i = 0; i < cached_monitor_info->length(); i++) {
737 MonitorInfo* mon_info = cached_monitor_info->at(i);
738 if (oopDesc::equals(mon_info->owner(), obj)) {
739 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
740 p2i(mon_info->owner()),
741 p2i(obj));
742 // Assume recursive case and fix up highest lock below
743 markWord mark = markWord::encode((BasicLock*) NULL);
744 highest_lock = mon_info->lock();
745 highest_lock->set_displaced_header(mark);
746 } else {
747 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
748 p2i(mon_info->owner()),
749 p2i(obj));
750 }
751 }
752 if (highest_lock != NULL) {
753 // Fix up highest lock to contain displaced header and point
754 // object at it
755 highest_lock->set_displaced_header(unbiased_prototype);
756 // Reset object header to point to displaced mark.
757 // Must release store the lock address for platforms without TSO
758 // ordering (e.g. ppc).
759 obj->release_set_mark(markWord::encode(highest_lock));
760 assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit");
761 log_info(biasedlocking)(" Revoked bias of currently-locked object");
762 } else {
763 log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
764 // Store the unlocked value into the object's header.
765 obj->set_mark(unbiased_prototype);
766 }
767
768 assert(!obj->mark().has_bias_pattern(), "must not be biased");
769 }
770
771
772 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
773 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
774
775 while (true) {
776 // We can revoke the biases of anonymously-biased objects
777 // efficiently enough that we should not cause these revocations to
778 // update the heuristics because doing so may cause unwanted bulk
779 // revocations (which are expensive) to occur.
780 markWord mark = obj->mark();
781 if (mark.is_biased_anonymously() && !attempt_rebias) {
782 // We are probably trying to revoke the bias of this object due to
783 // an identity hash code computation. Try to revoke the bias
784 // without a safepoint. This is possible if we can successfully
785 // compare-and-exchange an unbiased header into the mark word of
786 // the object, meaning that no other thread has raced to acquire
787 // the bias of the object.
788 markWord biased_value = mark;
789 markWord unbiased_prototype = markWord::prototype().set_age(mark.age());
790 markWord res_mark = obj->cas_set_mark(unbiased_prototype, mark);
791 if (res_mark == biased_value) {
792 return BIAS_REVOKED;
793 }
794 mark = res_mark; // Refresh mark with the latest value.
795 } else if (mark.has_bias_pattern()) {
796 Klass* k = obj->klass();
797 markWord prototype_header = k->prototype_header();
798 if (!prototype_header.has_bias_pattern()) {
799 // This object has a stale bias from before the bulk revocation
800 // for this data type occurred. It's pointless to update the
801 // heuristics at this point so simply update the header with a
802 // CAS. If we fail this race, the object's bias has been revoked
803 // by another thread so we simply return and let the caller deal
804 // with it.
805 obj->cas_set_mark(prototype_header.set_age(mark.age()), mark);
806 assert(!obj->mark().has_bias_pattern(), "even if we raced, should still be revoked");
807 return BIAS_REVOKED;
808 } else if (prototype_header.bias_epoch() != mark.bias_epoch()) {
809 // The epoch of this biasing has expired indicating that the
810 // object is effectively unbiased. Depending on whether we need
811 // to rebias or revoke the bias of this object we can do it
812 // efficiently enough with a CAS that we shouldn't update the
813 // heuristics. This is normally done in the assembly code but we
814 // can reach this point due to various points in the runtime
815 // needing to revoke biases.
816 markWord res_mark;
817 if (attempt_rebias) {
818 assert(THREAD->is_Java_thread(), "");
819 markWord biased_value = mark;
820 markWord rebiased_prototype = markWord::encode((JavaThread*) THREAD, mark.age(), prototype_header.bias_epoch());
821 res_mark = obj->cas_set_mark(rebiased_prototype, mark);
822 if (res_mark == biased_value) {
823 return BIAS_REVOKED_AND_REBIASED;
824 }
825 } else {
826 markWord biased_value = mark;
827 markWord unbiased_prototype = markWord::prototype().set_age(mark.age());
828 res_mark = obj->cas_set_mark(unbiased_prototype, mark);
829 if (res_mark == biased_value) {
830 return BIAS_REVOKED;
831 }
832 }
833 mark = res_mark; // Refresh mark with the latest value.
834 }
835 }
836
837 HeuristicsResult heuristics = update_heuristics(obj());
838 if (heuristics == HR_NOT_BIASED) {
839 return NOT_BIASED;
840 } else if (heuristics == HR_SINGLE_REVOKE) {
841 JavaThread *blt = mark.biased_locker();
842 assert(blt != NULL, "invariant");
843 if (blt == THREAD) {
844 // A thread is trying to revoke the bias of an object biased
845 // toward it, again likely due to an identity hash code
846 // computation. We can again avoid a safepoint/handshake in this case
847 // since we are only going to walk our own stack. There are no
848 // races with revocations occurring in other threads because we
849 // reach no safepoints in the revocation path.
850 EventBiasedLockSelfRevocation event;
851 ResourceMark rm;
852 walk_stack_and_revoke(obj(), blt);
853 blt->set_cached_monitor_info(NULL);
854 assert(!obj->mark().has_bias_pattern(), "invariant");
855 if (event.should_commit()) {
856 post_self_revocation_event(&event, obj->klass());
857 }
858 return BIAS_REVOKED;
859 } else {
860 BiasedLocking::Condition cond = single_revoke_with_handshake(obj, (JavaThread*)THREAD, blt);
861 if (cond != NOT_REVOKED) {
862 return cond;
863 }
864 }
865 } else {
866 assert((heuristics == HR_BULK_REVOKE) ||
867 (heuristics == HR_BULK_REBIAS), "?");
868 EventBiasedLockClassRevocation event;
869 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*)THREAD,
870 (heuristics == HR_BULK_REBIAS),
871 attempt_rebias);
872 VMThread::execute(&bulk_revoke);
873 if (event.should_commit()) {
874 post_class_revocation_event(&event, obj->klass(), &bulk_revoke);
875 }
876 return bulk_revoke.status_code();
877 }
878 }
879 }
880
881 // All objects in objs should be locked by biaser
882 void BiasedLocking::revoke(GrowableArray<Handle>* objs, JavaThread *biaser) {
883 bool clean_my_cache = false;
884 for (int i = 0; i < objs->length(); i++) {
885 oop obj = (objs->at(i))();
886 markWord mark = obj->mark();
887 if (mark.has_bias_pattern()) {
888 walk_stack_and_revoke(obj, biaser);
889 clean_my_cache = true;
890 }
891 }
892 if (clean_my_cache) {
893 clean_up_cached_monitor_info(biaser);
894 }
895 }
896
897
898 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
899 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
900 oop obj = h_obj();
901 HeuristicsResult heuristics = update_heuristics(obj);
902 if (heuristics == HR_SINGLE_REVOKE) {
903 JavaThread* biased_locker = NULL;
904 single_revoke_at_safepoint(obj, false, false, NULL, &biased_locker);
905 if (biased_locker) {
906 clean_up_cached_monitor_info(biased_locker);
907 }
908 } else if ((heuristics == HR_BULK_REBIAS) ||
909 (heuristics == HR_BULK_REVOKE)) {
910 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
911 clean_up_cached_monitor_info();
912 }
913 }
914
915
916 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
917 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
918 int len = objs->length();
919 for (int i = 0; i < len; i++) {
920 oop obj = (objs->at(i))();
921 HeuristicsResult heuristics = update_heuristics(obj);
922 if (heuristics == HR_SINGLE_REVOKE) {
923 single_revoke_at_safepoint(obj, false, false, NULL, NULL);
924 } else if ((heuristics == HR_BULK_REBIAS) ||
925 (heuristics == HR_BULK_REVOKE)) {
926 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
927 }
928 }
929 clean_up_cached_monitor_info();
930 }
931
932
933 void BiasedLocking::preserve_marks() {
934 if (!UseBiasedLocking)
935 return;
936
937 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
938
939 assert(_preserved_oop_stack == NULL, "double initialization");
940 assert(_preserved_mark_stack == NULL, "double initialization");
941
942 // In order to reduce the number of mark words preserved during GC
943 // due to the presence of biased locking, we reinitialize most mark
944 // words to the class's prototype during GC -- even those which have
945 // a currently valid bias owner. One important situation where we
946 // must not clobber a bias is when a biased object is currently
947 // locked. To handle this case we iterate over the currently-locked
948 // monitors in a prepass and, if they are biased, preserve their
949 // mark words here. This should be a relatively small set of objects
950 // especially compared to the number of objects in the heap.
951 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markWord>(10, true);
952 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
953
954 ResourceMark rm;
955 Thread* cur = Thread::current();
956 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
957 if (thread->has_last_Java_frame()) {
958 RegisterMap rm(thread);
959 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
960 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
961 if (monitors != NULL) {
962 int len = monitors->length();
963 // Walk monitors youngest to oldest
964 for (int i = len - 1; i >= 0; i--) {
965 MonitorInfo* mon_info = monitors->at(i);
966 if (mon_info->owner_is_scalar_replaced()) continue;
967 oop owner = mon_info->owner();
968 if (owner != NULL) {
969 markWord mark = owner->mark();
970 if (mark.has_bias_pattern()) {
971 _preserved_oop_stack->push(Handle(cur, owner));
972 _preserved_mark_stack->push(mark);
973 }
974 }
975 }
976 }
977 }
978 }
979 }
980 }
981
982
983 void BiasedLocking::restore_marks() {
984 if (!UseBiasedLocking)
985 return;
986
987 assert(_preserved_oop_stack != NULL, "double free");
988 assert(_preserved_mark_stack != NULL, "double free");
989
990 int len = _preserved_oop_stack->length();
991 for (int i = 0; i < len; i++) {
992 Handle owner = _preserved_oop_stack->at(i);
993 markWord mark = _preserved_mark_stack->at(i);
994 owner->set_mark(mark);
995 }
996
997 delete _preserved_oop_stack;
998 _preserved_oop_stack = NULL;
999 delete _preserved_mark_stack;
1000 _preserved_mark_stack = NULL;
1001 }
1002
1003
1004 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
1005 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
1006 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
1007 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
1008 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
1009 int* BiasedLocking::handshakes_count_addr() { return _counters.handshakes_count_addr(); }
1010 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
1011 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
1012
1013
1014 // BiasedLockingCounters
1015
1016 int BiasedLockingCounters::slow_path_entry_count() const {
1017 if (_slow_path_entry_count != 0) {
1018 return _slow_path_entry_count;
1019 }
1020 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
1021 _rebiased_lock_entry_count + _revoked_lock_entry_count +
1022 _fast_path_entry_count;
1023
1024 return _total_entry_count - sum;
1025 }
1026
1027 void BiasedLockingCounters::print_on(outputStream* st) const {
1028 tty->print_cr("# total entries: %d", _total_entry_count);
1029 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
1030 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
1031 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
1032 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
1033 tty->print_cr("# handshakes entries: %d", _handshakes_count);
1034 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
1035 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
1036 }
1037
1038 void BiasedLockingCounters::print() const { print_on(tty); }