1 /*
2 * Copyright (c) 2005, 2017, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "logging/log.hpp"
27 #include "memory/resourceArea.hpp"
28 #include "oops/klass.inline.hpp"
29 #include "oops/markOop.hpp"
30 #include "oops/oop.inline.hpp"
31 #include "runtime/atomic.hpp"
32 #include "runtime/basicLock.hpp"
33 #include "runtime/biasedLocking.hpp"
34 #include "runtime/handles.inline.hpp"
35 #include "runtime/task.hpp"
36 #include "runtime/threadSMR.hpp"
37 #include "runtime/vframe.hpp"
38 #include "runtime/vmThread.hpp"
39 #include "runtime/vm_operations.hpp"
40 #include "trace/tracing.hpp"
41
42 static bool _biased_locking_enabled = false;
43 BiasedLockingCounters BiasedLocking::_counters;
44
45 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
46 static GrowableArray<markOop>* _preserved_mark_stack = NULL;
47
48 static void enable_biased_locking(InstanceKlass* k) {
49 k->set_prototype_header(markOopDesc::biased_locking_prototype());
50 }
51
52 class VM_EnableBiasedLocking: public VM_Operation {
53 private:
54 bool _is_cheap_allocated;
55 public:
56 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; }
57 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
58 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; }
59 bool is_cheap_allocated() const { return _is_cheap_allocated; }
60
61 void doit() {
62 // Iterate the class loader data dictionaries enabling biased locking for all
63 // currently loaded classes.
64 ClassLoaderDataGraph::dictionary_classes_do(enable_biased_locking);
65 // Indicate that future instances should enable it as well
66 _biased_locking_enabled = true;
67
68 log_info(biasedlocking)("Biased locking enabled");
69 }
70
71 bool allow_nested_vm_operations() const { return false; }
72 };
73
74
75 // One-shot PeriodicTask subclass for enabling biased locking
76 class EnableBiasedLockingTask : public PeriodicTask {
77 public:
78 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {}
79
80 virtual void task() {
81 // Use async VM operation to avoid blocking the Watcher thread.
82 // VM Thread will free C heap storage.
83 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true);
84 VMThread::execute(op);
85
86 // Reclaim our storage and disenroll ourself
87 delete this;
88 }
89 };
90
91
92 void BiasedLocking::init() {
93 // If biased locking is enabled, schedule a task to fire a few
94 // seconds into the run which turns on biased locking for all
95 // currently loaded classes as well as future ones. This is a
96 // workaround for startup time regressions due to a large number of
97 // safepoints being taken during VM startup for bias revocation.
98 // Ideally we would have a lower cost for individual bias revocation
99 // and not need a mechanism like this.
100 if (UseBiasedLocking) {
101 if (BiasedLockingStartupDelay > 0) {
102 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
103 task->enroll();
104 } else {
105 VM_EnableBiasedLocking op(false);
106 VMThread::execute(&op);
107 }
108 }
109 }
110
111
112 bool BiasedLocking::enabled() {
113 return _biased_locking_enabled;
114 }
115
116 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
117 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
118 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
119 if (info != NULL) {
120 return info;
121 }
122
123 info = new GrowableArray<MonitorInfo*>();
124
125 // It's possible for the thread to not have any Java frames on it,
126 // i.e., if it's the main thread and it's already returned from main()
127 if (thread->has_last_Java_frame()) {
128 RegisterMap rm(thread);
129 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
130 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
131 if (monitors != NULL) {
132 int len = monitors->length();
133 // Walk monitors youngest to oldest
134 for (int i = len - 1; i >= 0; i--) {
135 MonitorInfo* mon_info = monitors->at(i);
136 if (mon_info->eliminated()) continue;
137 oop owner = mon_info->owner();
138 if (owner != NULL) {
139 info->append(mon_info);
140 }
141 }
142 }
143 }
144 }
145
146 thread->set_cached_monitor_info(info);
147 return info;
148 }
149
150 // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL,
151 // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization).
152 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) {
153 markOop mark = obj->mark();
154 if (!mark->has_bias_pattern()) {
155 if (log_is_enabled(Info, biasedlocking)) {
156 ResourceMark rm;
157 log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT
158 ", mark " INTPTR_FORMAT ", type %s"
159 ", requesting thread " INTPTR_FORMAT
160 " because it's no longer biased)",
161 p2i((void *)obj), (intptr_t) mark,
162 obj->klass()->external_name(),
163 (intptr_t) requesting_thread);
164 }
165 return BiasedLocking::NOT_BIASED;
166 }
167
168 uint age = mark->age();
169 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
170 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
171
172 // Log at "info" level if not bulk, else "trace" level
173 if (!is_bulk) {
174 ResourceMark rm;
175 log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark "
176 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
177 ", allow rebias %d, requesting thread " INTPTR_FORMAT,
178 p2i((void *)obj),
179 (intptr_t) mark,
180 obj->klass()->external_name(),
181 (intptr_t) obj->klass()->prototype_header(),
182 (allow_rebias ? 1 : 0),
183 (intptr_t) requesting_thread);
184 } else {
185 ResourceMark rm;
186 log_trace(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 (intptr_t) mark,
191 obj->klass()->external_name(),
192 (intptr_t) obj->klass()->prototype_header(),
193 (allow_rebias ? 1 : 0),
194 (intptr_t) requesting_thread);
195 }
196
197 JavaThread* biased_thread = mark->biased_locker();
198 if (biased_thread == NULL) {
199 // Object is anonymously biased. We can get here if, for
200 // example, we revoke the bias due to an identity hash code
201 // being computed for an object.
202 if (!allow_rebias) {
203 obj->set_mark(unbiased_prototype);
204 }
205 // Log at "info" level if not bulk, else "trace" level
206 if (!is_bulk) {
207 log_info(biasedlocking)(" Revoked bias of anonymously-biased object");
208 } else {
209 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object");
210 }
211 return BiasedLocking::BIAS_REVOKED;
212 }
213
214 // Handle case where the thread toward which the object was biased has exited
215 bool thread_is_alive = false;
216 if (requesting_thread == biased_thread) {
217 thread_is_alive = true;
218 } else {
219 ThreadsListHandle tlh;
220 thread_is_alive = tlh.includes(biased_thread);
221 }
222 if (!thread_is_alive) {
223 if (allow_rebias) {
224 obj->set_mark(biased_prototype);
225 } else {
226 obj->set_mark(unbiased_prototype);
227 }
228 // Log at "info" level if not bulk, else "trace" level
229 if (!is_bulk) {
230 log_info(biasedlocking)(" Revoked bias of object biased toward dead thread ("
231 PTR_FORMAT ")", p2i(biased_thread));
232 } else {
233 log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread ("
234 PTR_FORMAT ")", p2i(biased_thread));
235 }
236 return BiasedLocking::BIAS_REVOKED;
237 }
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 live thread ("
242 PTR_FORMAT ")", p2i(biased_thread));
243 } else {
244 log_trace(biasedlocking)(" Revoked bias of object biased toward live thread ("
245 PTR_FORMAT ")", p2i(biased_thread));
246 }
247
248 // Thread owning bias is alive.
249 // Check to see whether it currently owns the lock and, if so,
250 // write down the needed displaced headers to the thread's stack.
251 // Otherwise, restore the object's header either to the unlocked
252 // or unbiased state.
253 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
254 BasicLock* highest_lock = NULL;
255 for (int i = 0; i < cached_monitor_info->length(); i++) {
256 MonitorInfo* mon_info = cached_monitor_info->at(i);
257 if (mon_info->owner() == obj) {
258 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
259 p2i((void *) mon_info->owner()),
260 p2i((void *) obj));
261 // Assume recursive case and fix up highest lock later
262 markOop mark = markOopDesc::encode((BasicLock*) NULL);
263 highest_lock = mon_info->lock();
264 highest_lock->set_displaced_header(mark);
265 } else {
266 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
267 p2i((void *) mon_info->owner()),
268 p2i((void *) obj));
269 }
270 }
271 if (highest_lock != NULL) {
272 // Fix up highest lock to contain displaced header and point
273 // object at it
274 highest_lock->set_displaced_header(unbiased_prototype);
275 // Reset object header to point to displaced mark.
276 // Must release storing the lock address for platforms without TSO
277 // ordering (e.g. ppc).
278 obj->release_set_mark(markOopDesc::encode(highest_lock));
279 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
280 // Log at "info" level if not bulk, else "trace" level
281 if (!is_bulk) {
282 log_info(biasedlocking)(" Revoked bias of currently-locked object");
283 } else {
284 log_trace(biasedlocking)(" Revoked bias of currently-locked object");
285 }
286 } else {
287 // Log at "info" level if not bulk, else "trace" level
288 if (!is_bulk) {
289 log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
290 } else {
291 log_trace(biasedlocking)(" Revoked bias of currently-unlocked object");
292 }
293 if (allow_rebias) {
294 obj->set_mark(biased_prototype);
295 } else {
296 // Store the unlocked value into the object's header.
297 obj->set_mark(unbiased_prototype);
298 }
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 return BiasedLocking::BIAS_REVOKED;
307 }
308
309
310 enum HeuristicsResult {
311 HR_NOT_BIASED = 1,
312 HR_SINGLE_REVOKE = 2,
313 HR_BULK_REBIAS = 3,
314 HR_BULK_REVOKE = 4
315 };
316
317
318 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
319 markOop mark = o->mark();
320 if (!mark->has_bias_pattern()) {
321 return HR_NOT_BIASED;
322 }
323
324 // Heuristics to attempt to throttle the number of revocations.
325 // Stages:
326 // 1. Revoke the biases of all objects in the heap of this type,
327 // but allow rebiasing of those objects if unlocked.
328 // 2. Revoke the biases of all objects in the heap of this type
329 // and don't allow rebiasing of these objects. Disable
330 // allocation of objects of that type with the bias bit set.
331 Klass* k = o->klass();
332 jlong cur_time = os::javaTimeMillis();
333 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
334 int revocation_count = k->biased_lock_revocation_count();
335 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
336 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
337 (last_bulk_revocation_time != 0) &&
338 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
339 // This is the first revocation we've seen in a while of an
340 // object of this type since the last time we performed a bulk
341 // rebiasing operation. The application is allocating objects in
342 // bulk which are biased toward a thread and then handing them
343 // off to another thread. We can cope with this allocation
344 // pattern via the bulk rebiasing mechanism so we reset the
345 // klass's revocation count rather than allow it to increase
346 // monotonically. If we see the need to perform another bulk
347 // rebias operation later, we will, and if subsequently we see
348 // many more revocation operations in a short period of time we
349 // will completely disable biasing for this type.
350 k->set_biased_lock_revocation_count(0);
351 revocation_count = 0;
352 }
353
354 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
355 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
356 revocation_count = k->atomic_incr_biased_lock_revocation_count();
357 }
358
359 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
360 return HR_BULK_REVOKE;
361 }
362
363 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
364 return HR_BULK_REBIAS;
365 }
366
367 return HR_SINGLE_REVOKE;
368 }
369
370
371 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
372 bool bulk_rebias,
373 bool attempt_rebias_of_object,
374 JavaThread* requesting_thread) {
375 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
376
377 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object "
378 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
379 (bulk_rebias ? "rebias" : "revoke"),
380 p2i((void *) o),
381 (intptr_t) o->mark(),
382 o->klass()->external_name());
383
384 jlong cur_time = os::javaTimeMillis();
385 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
386
387
388 Klass* k_o = o->klass();
389 Klass* klass = k_o;
390
391 {
392 JavaThreadIteratorWithHandle jtiwh;
393
394 if (bulk_rebias) {
395 // Use the epoch in the klass of the object to implicitly revoke
396 // all biases of objects of this data type and force them to be
397 // reacquired. However, we also need to walk the stacks of all
398 // threads and update the headers of lightweight locked objects
399 // with biases to have the current epoch.
400
401 // If the prototype header doesn't have the bias pattern, don't
402 // try to update the epoch -- assume another VM operation came in
403 // and reset the header to the unbiased state, which will
404 // implicitly cause all existing biases to be revoked
405 if (klass->prototype_header()->has_bias_pattern()) {
406 int prev_epoch = klass->prototype_header()->bias_epoch();
407 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
408 int cur_epoch = klass->prototype_header()->bias_epoch();
409
410 // Now walk all threads' stacks and adjust epochs of any biased
411 // and locked objects of this data type we encounter
412 for (; JavaThread *thr = jtiwh.next(); ) {
413 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
414 for (int i = 0; i < cached_monitor_info->length(); i++) {
415 MonitorInfo* mon_info = cached_monitor_info->at(i);
416 oop owner = mon_info->owner();
417 markOop mark = owner->mark();
418 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
419 // We might have encountered this object already in the case of recursive locking
420 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
421 owner->set_mark(mark->set_bias_epoch(cur_epoch));
422 }
423 }
424 }
425 }
426
427 // At this point we're done. All we have to do is potentially
428 // adjust the header of the given object to revoke its bias.
429 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread, NULL);
430 } else {
431 if (log_is_enabled(Info, biasedlocking)) {
432 ResourceMark rm;
433 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name());
434 }
435
436 // Disable biased locking for this data type. Not only will this
437 // cause future instances to not be biased, but existing biased
438 // instances will notice that this implicitly caused their biases
439 // to be revoked.
440 klass->set_prototype_header(markOopDesc::prototype());
441
442 // Now walk all threads' stacks and forcibly revoke the biases of
443 // any locked and biased objects of this data type we encounter.
444 for (; JavaThread *thr = jtiwh.next(); ) {
445 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
446 for (int i = 0; i < cached_monitor_info->length(); i++) {
447 MonitorInfo* mon_info = cached_monitor_info->at(i);
448 oop owner = mon_info->owner();
449 markOop mark = owner->mark();
450 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
451 revoke_bias(owner, false, true, requesting_thread, NULL);
452 }
453 }
454 }
455
456 // Must force the bias of the passed object to be forcibly revoked
457 // as well to ensure guarantees to callers
458 revoke_bias(o, false, true, requesting_thread, NULL);
459 }
460 } // ThreadsListHandle is destroyed here.
461
462 log_info(biasedlocking)("* Ending bulk revocation");
463
464 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
465
466 if (attempt_rebias_of_object &&
467 o->mark()->has_bias_pattern() &&
468 klass->prototype_header()->has_bias_pattern()) {
469 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
470 klass->prototype_header()->bias_epoch());
471 o->set_mark(new_mark);
472 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
473 log_info(biasedlocking)(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
474 }
475
476 assert(!o->mark()->has_bias_pattern() ||
477 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
478 "bug in bulk bias revocation");
479
480 return status_code;
481 }
482
483
484 static void clean_up_cached_monitor_info() {
485 // Walk the thread list clearing out the cached monitors
486 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
487 thr->set_cached_monitor_info(NULL);
488 }
489 }
490
491
492 class VM_RevokeBias : public VM_Operation {
493 protected:
494 Handle* _obj;
495 GrowableArray<Handle>* _objs;
496 JavaThread* _requesting_thread;
497 BiasedLocking::Condition _status_code;
498 traceid _biased_locker_id;
499
500 public:
501 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
502 : _obj(obj)
503 , _objs(NULL)
504 , _requesting_thread(requesting_thread)
505 , _status_code(BiasedLocking::NOT_BIASED)
506 , _biased_locker_id(0) {}
507
508 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
509 : _obj(NULL)
510 , _objs(objs)
511 , _requesting_thread(requesting_thread)
512 , _status_code(BiasedLocking::NOT_BIASED)
513 , _biased_locker_id(0) {}
514
515 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
516
517 virtual bool doit_prologue() {
518 // Verify that there is actual work to do since the callers just
519 // give us locked object(s). If we don't find any biased objects
520 // there is nothing to do and we avoid a safepoint.
521 if (_obj != NULL) {
522 markOop mark = (*_obj)()->mark();
523 if (mark->has_bias_pattern()) {
524 return true;
525 }
526 } else {
527 for ( int i = 0 ; i < _objs->length(); i++ ) {
528 markOop mark = (_objs->at(i))()->mark();
529 if (mark->has_bias_pattern()) {
530 return true;
531 }
532 }
533 }
534 return false;
535 }
536
537 virtual void doit() {
538 if (_obj != NULL) {
539 log_info(biasedlocking)("Revoking bias with potentially per-thread safepoint:");
540 JavaThread* biased_locker = NULL;
541 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread, &biased_locker);
542 if (biased_locker != NULL) {
543 _biased_locker_id = THREAD_TRACE_ID(biased_locker);
544 }
545 clean_up_cached_monitor_info();
546 return;
547 } else {
548 log_info(biasedlocking)("Revoking bias with global safepoint:");
549 BiasedLocking::revoke_at_safepoint(_objs);
550 }
551 }
552
553 BiasedLocking::Condition status_code() const {
554 return _status_code;
555 }
556
557 traceid biased_locker() const {
558 return _biased_locker_id;
559 }
560 };
561
562
563 class VM_BulkRevokeBias : public VM_RevokeBias {
564 private:
565 bool _bulk_rebias;
566 bool _attempt_rebias_of_object;
567
568 public:
569 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
570 bool bulk_rebias,
571 bool attempt_rebias_of_object)
572 : VM_RevokeBias(obj, requesting_thread)
573 , _bulk_rebias(bulk_rebias)
574 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
575
576 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
577 virtual bool doit_prologue() { return true; }
578
579 virtual void doit() {
580 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
581 clean_up_cached_monitor_info();
582 }
583 };
584
585
586 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
587 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
588
589 // We can revoke the biases of anonymously-biased objects
590 // efficiently enough that we should not cause these revocations to
591 // update the heuristics because doing so may cause unwanted bulk
592 // revocations (which are expensive) to occur.
593 markOop mark = obj->mark();
594 if (mark->is_biased_anonymously() && !attempt_rebias) {
595 // We are probably trying to revoke the bias of this object due to
596 // an identity hash code computation. Try to revoke the bias
597 // without a safepoint. This is possible if we can successfully
598 // compare-and-exchange an unbiased header into the mark word of
599 // the object, meaning that no other thread has raced to acquire
600 // the bias of the object.
601 markOop biased_value = mark;
602 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
603 markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
604 if (res_mark == biased_value) {
605 return BIAS_REVOKED;
606 }
607 } else if (mark->has_bias_pattern()) {
608 Klass* k = obj->klass();
609 markOop prototype_header = k->prototype_header();
610 if (!prototype_header->has_bias_pattern()) {
611 // This object has a stale bias from before the bulk revocation
612 // for this data type occurred. It's pointless to update the
613 // heuristics at this point so simply update the header with a
614 // CAS. If we fail this race, the object's bias has been revoked
615 // by another thread so we simply return and let the caller deal
616 // with it.
617 markOop biased_value = mark;
618 markOop res_mark = obj->cas_set_mark(prototype_header, mark);
619 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked");
620 return BIAS_REVOKED;
621 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
622 // The epoch of this biasing has expired indicating that the
623 // object is effectively unbiased. Depending on whether we need
624 // to rebias or revoke the bias of this object we can do it
625 // efficiently enough with a CAS that we shouldn't update the
626 // heuristics. This is normally done in the assembly code but we
627 // can reach this point due to various points in the runtime
628 // needing to revoke biases.
629 if (attempt_rebias) {
630 assert(THREAD->is_Java_thread(), "");
631 markOop biased_value = mark;
632 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
633 markOop res_mark = obj->cas_set_mark(rebiased_prototype, mark);
634 if (res_mark == biased_value) {
635 return BIAS_REVOKED_AND_REBIASED;
636 }
637 } else {
638 markOop biased_value = mark;
639 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
640 markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
641 if (res_mark == biased_value) {
642 return BIAS_REVOKED;
643 }
644 }
645 }
646 }
647
648 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
649 if (heuristics == HR_NOT_BIASED) {
650 return NOT_BIASED;
651 } else if (heuristics == HR_SINGLE_REVOKE) {
652 Klass *k = obj->klass();
653 markOop prototype_header = k->prototype_header();
654 if (mark->biased_locker() == THREAD &&
655 prototype_header->bias_epoch() == mark->bias_epoch()) {
656 // A thread is trying to revoke the bias of an object biased
657 // toward it, again likely due to an identity hash code
658 // computation. We can again avoid a safepoint in this case
659 // since we are only going to walk our own stack. There are no
660 // races with revocations occurring in other threads because we
661 // reach no safepoints in the revocation path.
662 // Also check the epoch because even if threads match, another thread
663 // can come in with a CAS to steal the bias of an object that has a
664 // stale epoch.
665 ResourceMark rm;
666 log_info(biasedlocking)("Revoking bias by walking my own stack:");
667 EventBiasedLockSelfRevocation event;
668 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD, NULL);
669 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
670 assert(cond == BIAS_REVOKED, "why not?");
671 if (event.should_commit()) {
672 event.set_lockClass(k);
673 event.commit();
674 }
675 return cond;
676 } else {
677 EventBiasedLockRevocation event;
678 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
679 VMThread::execute(&revoke);
680 if (event.should_commit() && (revoke.status_code() != NOT_BIASED)) {
681 event.set_lockClass(k);
682 // Subtract 1 to match the id of events committed inside the safepoint
683 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1);
684 event.set_previousOwner(revoke.biased_locker());
685 event.commit();
686 }
687 return revoke.status_code();
688 }
689 }
690
691 assert((heuristics == HR_BULK_REVOKE) ||
692 (heuristics == HR_BULK_REBIAS), "?");
693 EventBiasedLockClassRevocation event;
694 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
695 (heuristics == HR_BULK_REBIAS),
696 attempt_rebias);
697 VMThread::execute(&bulk_revoke);
698 if (event.should_commit()) {
699 event.set_revokedClass(obj->klass());
700 event.set_disableBiasing((heuristics != HR_BULK_REBIAS));
701 // Subtract 1 to match the id of events committed inside the safepoint
702 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1);
703 event.commit();
704 }
705 return bulk_revoke.status_code();
706 }
707
708
709 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
710 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
711 if (objs->length() == 0) {
712 return;
713 }
714 VM_RevokeBias revoke(objs, JavaThread::current());
715 VMThread::execute(&revoke);
716 }
717
718
719 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
720 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
721 oop obj = h_obj();
722 HeuristicsResult heuristics = update_heuristics(obj, false);
723 if (heuristics == HR_SINGLE_REVOKE) {
724 revoke_bias(obj, false, false, NULL, NULL);
725 } else if ((heuristics == HR_BULK_REBIAS) ||
726 (heuristics == HR_BULK_REVOKE)) {
727 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
728 }
729 clean_up_cached_monitor_info();
730 }
731
732
733 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
734 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
735 int len = objs->length();
736 for (int i = 0; i < len; i++) {
737 oop obj = (objs->at(i))();
738 HeuristicsResult heuristics = update_heuristics(obj, false);
739 if (heuristics == HR_SINGLE_REVOKE) {
740 revoke_bias(obj, false, false, NULL, NULL);
741 } else if ((heuristics == HR_BULK_REBIAS) ||
742 (heuristics == HR_BULK_REVOKE)) {
743 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
744 }
745 }
746 clean_up_cached_monitor_info();
747 }
748
749
750 void BiasedLocking::preserve_marks() {
751 if (!UseBiasedLocking)
752 return;
753
754 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
755
756 assert(_preserved_oop_stack == NULL, "double initialization");
757 assert(_preserved_mark_stack == NULL, "double initialization");
758
759 // In order to reduce the number of mark words preserved during GC
760 // due to the presence of biased locking, we reinitialize most mark
761 // words to the class's prototype during GC -- even those which have
762 // a currently valid bias owner. One important situation where we
763 // must not clobber a bias is when a biased object is currently
764 // locked. To handle this case we iterate over the currently-locked
765 // monitors in a prepass and, if they are biased, preserve their
766 // mark words here. This should be a relatively small set of objects
767 // especially compared to the number of objects in the heap.
768 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true);
769 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
770
771 ResourceMark rm;
772 Thread* cur = Thread::current();
773 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
774 if (thread->has_last_Java_frame()) {
775 RegisterMap rm(thread);
776 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
777 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
778 if (monitors != NULL) {
779 int len = monitors->length();
780 // Walk monitors youngest to oldest
781 for (int i = len - 1; i >= 0; i--) {
782 MonitorInfo* mon_info = monitors->at(i);
783 if (mon_info->owner_is_scalar_replaced()) continue;
784 oop owner = mon_info->owner();
785 if (owner != NULL) {
786 markOop mark = owner->mark();
787 if (mark->has_bias_pattern()) {
788 _preserved_oop_stack->push(Handle(cur, owner));
789 _preserved_mark_stack->push(mark);
790 }
791 }
792 }
793 }
794 }
795 }
796 }
797 }
798
799
800 void BiasedLocking::restore_marks() {
801 if (!UseBiasedLocking)
802 return;
803
804 assert(_preserved_oop_stack != NULL, "double free");
805 assert(_preserved_mark_stack != NULL, "double free");
806
807 int len = _preserved_oop_stack->length();
808 for (int i = 0; i < len; i++) {
809 Handle owner = _preserved_oop_stack->at(i);
810 markOop mark = _preserved_mark_stack->at(i);
811 owner->set_mark(mark);
812 }
813
814 delete _preserved_oop_stack;
815 _preserved_oop_stack = NULL;
816 delete _preserved_mark_stack;
817 _preserved_mark_stack = NULL;
818 }
819
820
821 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
822 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
823 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
824 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
825 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
826 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
827 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
828
829
830 // BiasedLockingCounters
831
832 int BiasedLockingCounters::slow_path_entry_count() {
833 if (_slow_path_entry_count != 0) {
834 return _slow_path_entry_count;
835 }
836 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
837 _rebiased_lock_entry_count + _revoked_lock_entry_count +
838 _fast_path_entry_count;
839
840 return _total_entry_count - sum;
841 }
842
843 void BiasedLockingCounters::print_on(outputStream* st) {
844 tty->print_cr("# total entries: %d", _total_entry_count);
845 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
846 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
847 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
848 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
849 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
850 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
851 }