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