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/task.hpp"
35 #include "runtime/threadSMR.hpp"
36 #include "runtime/vframe.hpp"
37 #include "runtime/vmThread.hpp"
38 #include "runtime/vm_operations.hpp"
39 #include "trace/tracing.hpp"
40
41 static bool _biased_locking_enabled = false;
42 BiasedLockingCounters BiasedLocking::_counters;
43
44 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
45 static GrowableArray<markOop>* _preserved_mark_stack = NULL;
46
47 static void enable_biased_locking(InstanceKlass* k) {
48 k->set_prototype_header(markOopDesc::biased_locking_prototype());
49 }
50
51 class VM_EnableBiasedLocking: public VM_Operation {
52 private:
53 bool _is_cheap_allocated;
54 public:
55 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; }
56 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
57 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; }
58 bool is_cheap_allocated() const { return _is_cheap_allocated; }
59
60 void doit() {
61 // Iterate the class loader data dictionaries enabling biased locking for all
62 // currently loaded classes.
63 ClassLoaderDataGraph::dictionary_classes_do(enable_biased_locking);
64 // Indicate that future instances should enable it as well
65 _biased_locking_enabled = true;
66
67 log_info(biasedlocking)("Biased locking enabled");
68 }
69
70 bool allow_nested_vm_operations() const { return false; }
71 };
72
73
74 // One-shot PeriodicTask subclass for enabling biased locking
75 class EnableBiasedLockingTask : public PeriodicTask {
76 public:
77 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {}
78
79 virtual void task() {
80 // Use async VM operation to avoid blocking the Watcher thread.
81 // VM Thread will free C heap storage.
82 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true);
83 VMThread::execute(op);
84
85 // Reclaim our storage and disenroll ourself
86 delete this;
87 }
88 };
89
90
91 void BiasedLocking::init() {
92 // If biased locking is enabled, schedule a task to fire a few
93 // seconds into the run which turns on biased locking for all
94 // currently loaded classes as well as future ones. This is a
95 // workaround for startup time regressions due to a large number of
96 // safepoints being taken during VM startup for bias revocation.
97 // Ideally we would have a lower cost for individual bias revocation
98 // and not need a mechanism like this.
99 if (UseBiasedLocking) {
100 if (BiasedLockingStartupDelay > 0) {
101 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
102 task->enroll();
103 } else {
104 VM_EnableBiasedLocking op(false);
105 VMThread::execute(&op);
106 }
107 }
108 }
109
110
111 bool BiasedLocking::enabled() {
112 return _biased_locking_enabled;
113 }
114
115 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
116 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
117 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
118 if (info != NULL) {
119 return info;
120 }
121
122 info = new GrowableArray<MonitorInfo*>();
123
124 // It's possible for the thread to not have any Java frames on it,
125 // i.e., if it's the main thread and it's already returned from main()
126 if (thread->has_last_Java_frame()) {
127 RegisterMap rm(thread);
128 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
129 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
130 if (monitors != NULL) {
131 int len = monitors->length();
132 // Walk monitors youngest to oldest
133 for (int i = len - 1; i >= 0; i--) {
134 MonitorInfo* mon_info = monitors->at(i);
135 if (mon_info->eliminated()) continue;
136 oop owner = mon_info->owner();
137 if (owner != NULL) {
138 info->append(mon_info);
139 }
140 }
141 }
142 }
143 }
144
145 thread->set_cached_monitor_info(info);
146 return info;
147 }
148
149 // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL,
150 // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization).
151 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) {
152 markOop mark = obj->mark();
153 if (!mark->has_bias_pattern()) {
154 if (log_is_enabled(Info, biasedlocking)) {
155 ResourceMark rm;
156 log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT
157 ", mark " INTPTR_FORMAT ", type %s"
158 ", requesting thread " INTPTR_FORMAT
159 " because it's no longer biased)",
160 p2i((void *)obj), (intptr_t) mark,
161 obj->klass()->external_name(),
162 (intptr_t) requesting_thread);
163 }
164 return BiasedLocking::NOT_BIASED;
165 }
166
167 uint age = mark->age();
168 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
169 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
170
171 // Log at "info" level if not bulk, else "trace" level
172 if (!is_bulk) {
173 ResourceMark rm;
174 log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark "
175 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
176 ", allow rebias %d, requesting thread " INTPTR_FORMAT,
177 p2i((void *)obj),
178 (intptr_t) mark,
179 obj->klass()->external_name(),
180 (intptr_t) obj->klass()->prototype_header(),
181 (allow_rebias ? 1 : 0),
182 (intptr_t) requesting_thread);
183 } else {
184 ResourceMark rm;
185 log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark "
186 INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT
187 " , allow rebias %d , requesting thread " INTPTR_FORMAT,
188 p2i((void *)obj),
189 (intptr_t) mark,
190 obj->klass()->external_name(),
191 (intptr_t) obj->klass()->prototype_header(),
192 (allow_rebias ? 1 : 0),
193 (intptr_t) requesting_thread);
194 }
195
196 JavaThread* biased_thread = mark->biased_locker();
197 if (biased_thread == NULL) {
198 // Object is anonymously biased. We can get here if, for
199 // example, we revoke the bias due to an identity hash code
200 // being computed for an object.
201 if (!allow_rebias) {
202 obj->set_mark(unbiased_prototype);
203 }
204 // Log at "info" level if not bulk, else "trace" level
205 if (!is_bulk) {
206 log_info(biasedlocking)(" Revoked bias of anonymously-biased object");
207 } else {
208 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object");
209 }
210 return BiasedLocking::BIAS_REVOKED;
211 }
212
213 // Handle case where the thread toward which the object was biased has exited
214 bool thread_is_alive = false;
215 if (requesting_thread == biased_thread) {
216 thread_is_alive = true;
217 } else {
218 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
219 if (cur_thread == biased_thread) {
220 thread_is_alive = true;
221 break;
222 }
223 }
224 }
225 if (!thread_is_alive) {
226 if (allow_rebias) {
227 obj->set_mark(biased_prototype);
228 } else {
229 obj->set_mark(unbiased_prototype);
230 }
231 // Log at "info" level if not bulk, else "trace" level
232 if (!is_bulk) {
233 log_info(biasedlocking)(" Revoked bias of object biased toward dead thread ("
234 PTR_FORMAT ")", p2i(biased_thread));
235 } else {
236 log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread ("
237 PTR_FORMAT ")", p2i(biased_thread));
238 }
239 return BiasedLocking::BIAS_REVOKED;
240 }
241
242 // Log at "info" level if not bulk, else "trace" level
243 if (!is_bulk) {
244 log_info(biasedlocking)(" Revoked bias of object biased toward live thread ("
245 PTR_FORMAT ")", p2i(biased_thread));
246 } else {
247 log_trace(biasedlocking)(" Revoked bias of object biased toward live thread ("
248 PTR_FORMAT ")", p2i(biased_thread));
249 }
250
251 // Thread owning bias is alive.
252 // Check to see whether it currently owns the lock and, if so,
253 // write down the needed displaced headers to the thread's stack.
254 // Otherwise, restore the object's header either to the unlocked
255 // or unbiased state.
256 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
257 BasicLock* highest_lock = NULL;
258 for (int i = 0; i < cached_monitor_info->length(); i++) {
259 MonitorInfo* mon_info = cached_monitor_info->at(i);
260 if (mon_info->owner() == obj) {
261 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
262 p2i((void *) mon_info->owner()),
263 p2i((void *) obj));
264 // Assume recursive case and fix up highest lock later
265 markOop mark = markOopDesc::encode((BasicLock*) NULL);
266 highest_lock = mon_info->lock();
267 highest_lock->set_displaced_header(mark);
268 } else {
269 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
270 p2i((void *) mon_info->owner()),
271 p2i((void *) obj));
272 }
273 }
274 if (highest_lock != NULL) {
275 // Fix up highest lock to contain displaced header and point
276 // object at it
277 highest_lock->set_displaced_header(unbiased_prototype);
278 // Reset object header to point to displaced mark.
279 // Must release storing the lock address for platforms without TSO
280 // ordering (e.g. ppc).
281 obj->release_set_mark(markOopDesc::encode(highest_lock));
282 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
283 // Log at "info" level if not bulk, else "trace" level
284 if (!is_bulk) {
285 log_info(biasedlocking)(" Revoked bias of currently-locked object");
286 } else {
287 log_trace(biasedlocking)(" Revoked bias of currently-locked object");
288 }
289 } else {
290 // Log at "info" level if not bulk, else "trace" level
291 if (!is_bulk) {
292 log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
293 } else {
294 log_trace(biasedlocking)(" Revoked bias of currently-unlocked object");
295 }
296 if (allow_rebias) {
297 obj->set_mark(biased_prototype);
298 } else {
299 // Store the unlocked value into the object's header.
300 obj->set_mark(unbiased_prototype);
301 }
302 }
303
304 // If requested, return information on which thread held the bias
305 if (biased_locker != NULL) {
306 *biased_locker = biased_thread;
307 }
308
309 return BiasedLocking::BIAS_REVOKED;
310 }
311
312
313 enum HeuristicsResult {
314 HR_NOT_BIASED = 1,
315 HR_SINGLE_REVOKE = 2,
316 HR_BULK_REBIAS = 3,
317 HR_BULK_REVOKE = 4
318 };
319
320
321 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
322 markOop mark = o->mark();
323 if (!mark->has_bias_pattern()) {
324 return HR_NOT_BIASED;
325 }
326
327 // Heuristics to attempt to throttle the number of revocations.
328 // Stages:
329 // 1. Revoke the biases of all objects in the heap of this type,
330 // but allow rebiasing of those objects if unlocked.
331 // 2. Revoke the biases of all objects in the heap of this type
332 // and don't allow rebiasing of these objects. Disable
333 // allocation of objects of that type with the bias bit set.
334 Klass* k = o->klass();
335 jlong cur_time = os::javaTimeMillis();
336 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
337 int revocation_count = k->biased_lock_revocation_count();
338 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
339 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
340 (last_bulk_revocation_time != 0) &&
341 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
342 // This is the first revocation we've seen in a while of an
343 // object of this type since the last time we performed a bulk
344 // rebiasing operation. The application is allocating objects in
345 // bulk which are biased toward a thread and then handing them
346 // off to another thread. We can cope with this allocation
347 // pattern via the bulk rebiasing mechanism so we reset the
348 // klass's revocation count rather than allow it to increase
349 // monotonically. If we see the need to perform another bulk
350 // rebias operation later, we will, and if subsequently we see
351 // many more revocation operations in a short period of time we
352 // will completely disable biasing for this type.
353 k->set_biased_lock_revocation_count(0);
354 revocation_count = 0;
355 }
356
357 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
358 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
359 revocation_count = k->atomic_incr_biased_lock_revocation_count();
360 }
361
362 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
363 return HR_BULK_REVOKE;
364 }
365
366 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
367 return HR_BULK_REBIAS;
368 }
369
370 return HR_SINGLE_REVOKE;
371 }
372
373
374 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
375 bool bulk_rebias,
376 bool attempt_rebias_of_object,
377 JavaThread* requesting_thread) {
378 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
379
380 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object "
381 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
382 (bulk_rebias ? "rebias" : "revoke"),
383 p2i((void *) o),
384 (intptr_t) o->mark(),
385 o->klass()->external_name());
386
387 jlong cur_time = os::javaTimeMillis();
388 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
389
390
391 Klass* k_o = o->klass();
392 Klass* klass = k_o;
393
394 {
395 JavaThreadIteratorWithHandle jtiwh;
396
397 if (bulk_rebias) {
398 // Use the epoch in the klass of the object to implicitly revoke
399 // all biases of objects of this data type and force them to be
400 // reacquired. However, we also need to walk the stacks of all
401 // threads and update the headers of lightweight locked objects
402 // with biases to have the current epoch.
403
404 // If the prototype header doesn't have the bias pattern, don't
405 // try to update the epoch -- assume another VM operation came in
406 // and reset the header to the unbiased state, which will
407 // implicitly cause all existing biases to be revoked
408 if (klass->prototype_header()->has_bias_pattern()) {
409 int prev_epoch = klass->prototype_header()->bias_epoch();
410 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
411 int cur_epoch = klass->prototype_header()->bias_epoch();
412
413 // Now walk all threads' stacks and adjust epochs of any biased
414 // and locked objects of this data type we encounter
415 for (; JavaThread *thr = jtiwh.next(); ) {
416 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
417 for (int i = 0; i < cached_monitor_info->length(); i++) {
418 MonitorInfo* mon_info = cached_monitor_info->at(i);
419 oop owner = mon_info->owner();
420 markOop mark = owner->mark();
421 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
422 // We might have encountered this object already in the case of recursive locking
423 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
424 owner->set_mark(mark->set_bias_epoch(cur_epoch));
425 }
426 }
427 }
428 }
429
430 // At this point we're done. All we have to do is potentially
431 // adjust the header of the given object to revoke its bias.
432 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread, NULL);
433 } else {
434 if (log_is_enabled(Info, biasedlocking)) {
435 ResourceMark rm;
436 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name());
437 }
438
439 // Disable biased locking for this data type. Not only will this
440 // cause future instances to not be biased, but existing biased
441 // instances will notice that this implicitly caused their biases
442 // to be revoked.
443 klass->set_prototype_header(markOopDesc::prototype());
444
445 // Now walk all threads' stacks and forcibly revoke the biases of
446 // any locked and biased objects of this data type we encounter.
447 for (; JavaThread *thr = jtiwh.next(); ) {
448 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
449 for (int i = 0; i < cached_monitor_info->length(); i++) {
450 MonitorInfo* mon_info = cached_monitor_info->at(i);
451 oop owner = mon_info->owner();
452 markOop mark = owner->mark();
453 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
454 revoke_bias(owner, false, true, requesting_thread, NULL);
455 }
456 }
457 }
458
459 // Must force the bias of the passed object to be forcibly revoked
460 // as well to ensure guarantees to callers
461 revoke_bias(o, false, true, requesting_thread, NULL);
462 }
463 } // ThreadsListHandle is destroyed here.
464
465 log_info(biasedlocking)("* Ending bulk revocation");
466
467 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
468
469 if (attempt_rebias_of_object &&
470 o->mark()->has_bias_pattern() &&
471 klass->prototype_header()->has_bias_pattern()) {
472 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
473 klass->prototype_header()->bias_epoch());
474 o->set_mark(new_mark);
475 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
476 log_info(biasedlocking)(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
477 }
478
479 assert(!o->mark()->has_bias_pattern() ||
480 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
481 "bug in bulk bias revocation");
482
483 return status_code;
484 }
485
486
487 static void clean_up_cached_monitor_info() {
488 // Walk the thread list clearing out the cached monitors
489 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
490 thr->set_cached_monitor_info(NULL);
491 }
492 }
493
494
495 class VM_RevokeBias : public VM_Operation {
496 protected:
497 Handle* _obj;
498 GrowableArray<Handle>* _objs;
499 JavaThread* _requesting_thread;
500 BiasedLocking::Condition _status_code;
501 traceid _biased_locker_id;
502
503 public:
504 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
505 : _obj(obj)
506 , _objs(NULL)
507 , _requesting_thread(requesting_thread)
508 , _status_code(BiasedLocking::NOT_BIASED)
509 , _biased_locker_id(0) {}
510
511 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
512 : _obj(NULL)
513 , _objs(objs)
514 , _requesting_thread(requesting_thread)
515 , _status_code(BiasedLocking::NOT_BIASED)
516 , _biased_locker_id(0) {}
517
518 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
519
520 virtual bool doit_prologue() {
521 // Verify that there is actual work to do since the callers just
522 // give us locked object(s). If we don't find any biased objects
523 // there is nothing to do and we avoid a safepoint.
524 if (_obj != NULL) {
525 markOop mark = (*_obj)()->mark();
526 if (mark->has_bias_pattern()) {
527 return true;
528 }
529 } else {
530 for ( int i = 0 ; i < _objs->length(); i++ ) {
531 markOop mark = (_objs->at(i))()->mark();
532 if (mark->has_bias_pattern()) {
533 return true;
534 }
535 }
536 }
537 return false;
538 }
539
540 virtual void doit() {
541 if (_obj != NULL) {
542 log_info(biasedlocking)("Revoking bias with potentially per-thread safepoint:");
543 JavaThread* biased_locker = NULL;
544 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread, &biased_locker);
545 if (biased_locker != NULL) {
546 _biased_locker_id = THREAD_TRACE_ID(biased_locker);
547 }
548 clean_up_cached_monitor_info();
549 return;
550 } else {
551 log_info(biasedlocking)("Revoking bias with global safepoint:");
552 BiasedLocking::revoke_at_safepoint(_objs);
553 }
554 }
555
556 BiasedLocking::Condition status_code() const {
557 return _status_code;
558 }
559
560 traceid biased_locker() const {
561 return _biased_locker_id;
562 }
563 };
564
565
566 class VM_BulkRevokeBias : public VM_RevokeBias {
567 private:
568 bool _bulk_rebias;
569 bool _attempt_rebias_of_object;
570
571 public:
572 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
573 bool bulk_rebias,
574 bool attempt_rebias_of_object)
575 : VM_RevokeBias(obj, requesting_thread)
576 , _bulk_rebias(bulk_rebias)
577 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
578
579 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
580 virtual bool doit_prologue() { return true; }
581
582 virtual void doit() {
583 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
584 clean_up_cached_monitor_info();
585 }
586 };
587
588
589 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
590 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
591
592 // We can revoke the biases of anonymously-biased objects
593 // efficiently enough that we should not cause these revocations to
594 // update the heuristics because doing so may cause unwanted bulk
595 // revocations (which are expensive) to occur.
596 markOop mark = obj->mark();
597 if (mark->is_biased_anonymously() && !attempt_rebias) {
598 // We are probably trying to revoke the bias of this object due to
599 // an identity hash code computation. Try to revoke the bias
600 // without a safepoint. This is possible if we can successfully
601 // compare-and-exchange an unbiased header into the mark word of
602 // the object, meaning that no other thread has raced to acquire
603 // the bias of the object.
604 markOop biased_value = mark;
605 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
606 markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
607 if (res_mark == biased_value) {
608 return BIAS_REVOKED;
609 }
610 } else if (mark->has_bias_pattern()) {
611 Klass* k = obj->klass();
612 markOop prototype_header = k->prototype_header();
613 if (!prototype_header->has_bias_pattern()) {
614 // This object has a stale bias from before the bulk revocation
615 // for this data type occurred. It's pointless to update the
616 // heuristics at this point so simply update the header with a
617 // CAS. If we fail this race, the object's bias has been revoked
618 // by another thread so we simply return and let the caller deal
619 // with it.
620 markOop biased_value = mark;
621 markOop res_mark = obj->cas_set_mark(prototype_header, mark);
622 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked");
623 return BIAS_REVOKED;
624 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
625 // The epoch of this biasing has expired indicating that the
626 // object is effectively unbiased. Depending on whether we need
627 // to rebias or revoke the bias of this object we can do it
628 // efficiently enough with a CAS that we shouldn't update the
629 // heuristics. This is normally done in the assembly code but we
630 // can reach this point due to various points in the runtime
631 // needing to revoke biases.
632 if (attempt_rebias) {
633 assert(THREAD->is_Java_thread(), "");
634 markOop biased_value = mark;
635 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
636 markOop res_mark = obj->cas_set_mark(rebiased_prototype, mark);
637 if (res_mark == biased_value) {
638 return BIAS_REVOKED_AND_REBIASED;
639 }
640 } else {
641 markOop biased_value = mark;
642 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
643 markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
644 if (res_mark == biased_value) {
645 return BIAS_REVOKED;
646 }
647 }
648 }
649 }
650
651 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
652 if (heuristics == HR_NOT_BIASED) {
653 return NOT_BIASED;
654 } else if (heuristics == HR_SINGLE_REVOKE) {
655 Klass *k = obj->klass();
656 markOop prototype_header = k->prototype_header();
657 if (mark->biased_locker() == THREAD &&
658 prototype_header->bias_epoch() == mark->bias_epoch()) {
659 // A thread is trying to revoke the bias of an object biased
660 // toward it, again likely due to an identity hash code
661 // computation. We can again avoid a safepoint in this case
662 // since we are only going to walk our own stack. There are no
663 // races with revocations occurring in other threads because we
664 // reach no safepoints in the revocation path.
665 // Also check the epoch because even if threads match, another thread
666 // can come in with a CAS to steal the bias of an object that has a
667 // stale epoch.
668 ResourceMark rm;
669 log_info(biasedlocking)("Revoking bias by walking my own stack:");
670 EventBiasedLockSelfRevocation event;
671 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD, NULL);
672 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
673 assert(cond == BIAS_REVOKED, "why not?");
674 if (event.should_commit()) {
675 event.set_lockClass(k);
676 event.commit();
677 }
678 return cond;
679 } else {
680 EventBiasedLockRevocation event;
681 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
682 VMThread::execute(&revoke);
683 if (event.should_commit() && (revoke.status_code() != NOT_BIASED)) {
684 event.set_lockClass(k);
685 // Subtract 1 to match the id of events committed inside the safepoint
686 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1);
687 event.set_previousOwner(revoke.biased_locker());
688 event.commit();
689 }
690 return revoke.status_code();
691 }
692 }
693
694 assert((heuristics == HR_BULK_REVOKE) ||
695 (heuristics == HR_BULK_REBIAS), "?");
696 EventBiasedLockClassRevocation event;
697 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
698 (heuristics == HR_BULK_REBIAS),
699 attempt_rebias);
700 VMThread::execute(&bulk_revoke);
701 if (event.should_commit()) {
702 event.set_revokedClass(obj->klass());
703 event.set_disableBiasing((heuristics != HR_BULK_REBIAS));
704 // Subtract 1 to match the id of events committed inside the safepoint
705 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1);
706 event.commit();
707 }
708 return bulk_revoke.status_code();
709 }
710
711
712 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
713 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
714 if (objs->length() == 0) {
715 return;
716 }
717 VM_RevokeBias revoke(objs, JavaThread::current());
718 VMThread::execute(&revoke);
719 }
720
721
722 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
723 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
724 oop obj = h_obj();
725 HeuristicsResult heuristics = update_heuristics(obj, false);
726 if (heuristics == HR_SINGLE_REVOKE) {
727 revoke_bias(obj, false, false, NULL, NULL);
728 } else if ((heuristics == HR_BULK_REBIAS) ||
729 (heuristics == HR_BULK_REVOKE)) {
730 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
731 }
732 clean_up_cached_monitor_info();
733 }
734
735
736 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
737 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
738 int len = objs->length();
739 for (int i = 0; i < len; i++) {
740 oop obj = (objs->at(i))();
741 HeuristicsResult heuristics = update_heuristics(obj, false);
742 if (heuristics == HR_SINGLE_REVOKE) {
743 revoke_bias(obj, false, false, NULL, NULL);
744 } else if ((heuristics == HR_BULK_REBIAS) ||
745 (heuristics == HR_BULK_REVOKE)) {
746 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
747 }
748 }
749 clean_up_cached_monitor_info();
750 }
751
752
753 void BiasedLocking::preserve_marks() {
754 if (!UseBiasedLocking)
755 return;
756
757 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
758
759 assert(_preserved_oop_stack == NULL, "double initialization");
760 assert(_preserved_mark_stack == NULL, "double initialization");
761
762 // In order to reduce the number of mark words preserved during GC
763 // due to the presence of biased locking, we reinitialize most mark
764 // words to the class's prototype during GC -- even those which have
765 // a currently valid bias owner. One important situation where we
766 // must not clobber a bias is when a biased object is currently
767 // locked. To handle this case we iterate over the currently-locked
768 // monitors in a prepass and, if they are biased, preserve their
769 // mark words here. This should be a relatively small set of objects
770 // especially compared to the number of objects in the heap.
771 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true);
772 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
773
774 ResourceMark rm;
775 Thread* cur = Thread::current();
776 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
777 if (thread->has_last_Java_frame()) {
778 RegisterMap rm(thread);
779 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
780 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
781 if (monitors != NULL) {
782 int len = monitors->length();
783 // Walk monitors youngest to oldest
784 for (int i = len - 1; i >= 0; i--) {
785 MonitorInfo* mon_info = monitors->at(i);
786 if (mon_info->owner_is_scalar_replaced()) continue;
787 oop owner = mon_info->owner();
788 if (owner != NULL) {
789 markOop mark = owner->mark();
790 if (mark->has_bias_pattern()) {
791 _preserved_oop_stack->push(Handle(cur, owner));
792 _preserved_mark_stack->push(mark);
793 }
794 }
795 }
796 }
797 }
798 }
799 }
800 }
801
802
803 void BiasedLocking::restore_marks() {
804 if (!UseBiasedLocking)
805 return;
806
807 assert(_preserved_oop_stack != NULL, "double free");
808 assert(_preserved_mark_stack != NULL, "double free");
809
810 int len = _preserved_oop_stack->length();
811 for (int i = 0; i < len; i++) {
812 Handle owner = _preserved_oop_stack->at(i);
813 markOop mark = _preserved_mark_stack->at(i);
814 owner->set_mark(mark);
815 }
816
817 delete _preserved_oop_stack;
818 _preserved_oop_stack = NULL;
819 delete _preserved_mark_stack;
820 _preserved_mark_stack = NULL;
821 }
822
823
824 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
825 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
826 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
827 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
828 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
829 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
830 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
831
832
833 // BiasedLockingCounters
834
835 int BiasedLockingCounters::slow_path_entry_count() {
836 if (_slow_path_entry_count != 0) {
837 return _slow_path_entry_count;
838 }
839 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
840 _rebiased_lock_entry_count + _revoked_lock_entry_count +
841 _fast_path_entry_count;
842
843 return _total_entry_count - sum;
844 }
845
846 void BiasedLockingCounters::print_on(outputStream* st) {
847 tty->print_cr("# total entries: %d", _total_entry_count);
848 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
849 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
850 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
851 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
852 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
853 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
854 }