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