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/vframe.hpp"
36 #include "runtime/vmThread.hpp"
37 #include "runtime/vm_operations.hpp"
38 #include "trace/tracing.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 (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->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 if (bulk_rebias) {
387 // Use the epoch in the klass of the object to implicitly revoke
388 // all biases of objects of this data type and force them to be
389 // reacquired. However, we also need to walk the stacks of all
390 // threads and update the headers of lightweight locked objects
391 // with biases to have the current epoch.
392
393 // If the prototype header doesn't have the bias pattern, don't
394 // try to update the epoch -- assume another VM operation came in
395 // and reset the header to the unbiased state, which will
396 // implicitly cause all existing biases to be revoked
397 if (klass->prototype_header()->has_bias_pattern()) {
398 int prev_epoch = klass->prototype_header()->bias_epoch();
399 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
400 int cur_epoch = klass->prototype_header()->bias_epoch();
401
402 // Now walk all threads' stacks and adjust epochs of any biased
403 // and locked objects of this data type we encounter
404 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
405 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
406 for (int i = 0; i < cached_monitor_info->length(); i++) {
407 MonitorInfo* mon_info = cached_monitor_info->at(i);
408 oop owner = mon_info->owner();
409 markOop mark = owner->mark();
410 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
411 // We might have encountered this object already in the case of recursive locking
412 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
413 owner->set_mark(mark->set_bias_epoch(cur_epoch));
414 }
415 }
416 }
417 }
418
419 // At this point we're done. All we have to do is potentially
420 // adjust the header of the given object to revoke its bias.
421 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread);
422 } else {
423 if (log_is_enabled(Info, biasedlocking)) {
424 ResourceMark rm;
425 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name());
426 }
427
428 // Disable biased locking for this data type. Not only will this
429 // cause future instances to not be biased, but existing biased
430 // instances will notice that this implicitly caused their biases
431 // to be revoked.
432 klass->set_prototype_header(markOopDesc::prototype());
433
434 // Now walk all threads' stacks and forcibly revoke the biases of
435 // any locked and biased objects of this data type we encounter.
436 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
437 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
438 for (int i = 0; i < cached_monitor_info->length(); i++) {
439 MonitorInfo* mon_info = cached_monitor_info->at(i);
440 oop owner = mon_info->owner();
441 markOop mark = owner->mark();
442 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
443 revoke_bias(owner, false, true, requesting_thread);
444 }
445 }
446 }
447
448 // Must force the bias of the passed object to be forcibly revoked
449 // as well to ensure guarantees to callers
450 revoke_bias(o, false, true, requesting_thread);
451 }
452
453 log_info(biasedlocking)("* Ending bulk revocation");
454
455 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
456
457 if (attempt_rebias_of_object &&
458 o->mark()->has_bias_pattern() &&
459 klass->prototype_header()->has_bias_pattern()) {
460 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
461 klass->prototype_header()->bias_epoch());
462 o->set_mark(new_mark);
463 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
464 log_info(biasedlocking)(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
465 }
466
467 assert(!o->mark()->has_bias_pattern() ||
468 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
469 "bug in bulk bias revocation");
470
471 return status_code;
472 }
473
474
475 static void clean_up_cached_monitor_info() {
476 // Walk the thread list clearing out the cached monitors
477 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
478 thr->set_cached_monitor_info(NULL);
479 }
480 }
481
482
483 class VM_RevokeBias : public VM_Operation {
484 protected:
485 Handle* _obj;
486 GrowableArray<Handle>* _objs;
487 JavaThread* _requesting_thread;
488 BiasedLocking::Condition _status_code;
489
490 public:
491 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
492 : _obj(obj)
493 , _objs(NULL)
494 , _requesting_thread(requesting_thread)
495 , _status_code(BiasedLocking::NOT_BIASED) {}
496
497 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
498 : _obj(NULL)
499 , _objs(objs)
500 , _requesting_thread(requesting_thread)
501 , _status_code(BiasedLocking::NOT_BIASED) {}
502
503 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
504
505 virtual bool doit_prologue() {
506 // Verify that there is actual work to do since the callers just
507 // give us locked object(s). If we don't find any biased objects
508 // there is nothing to do and we avoid a safepoint.
509 if (_obj != NULL) {
510 markOop mark = (*_obj)()->mark();
511 if (mark->has_bias_pattern()) {
512 return true;
513 }
514 } else {
515 for ( int i = 0 ; i < _objs->length(); i++ ) {
516 markOop mark = (_objs->at(i))()->mark();
517 if (mark->has_bias_pattern()) {
518 return true;
519 }
520 }
521 }
522 return false;
523 }
524
525 virtual void doit() {
526 if (_obj != NULL) {
527 log_info(biasedlocking)("Revoking bias with potentially per-thread safepoint:");
528 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread);
529 clean_up_cached_monitor_info();
530 return;
531 } else {
532 log_info(biasedlocking)("Revoking bias with global safepoint:");
533 BiasedLocking::revoke_at_safepoint(_objs);
534 }
535 }
536
537 BiasedLocking::Condition status_code() const {
538 return _status_code;
539 }
540 };
541
542
543 class VM_BulkRevokeBias : public VM_RevokeBias {
544 private:
545 bool _bulk_rebias;
546 bool _attempt_rebias_of_object;
547
548 public:
549 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
550 bool bulk_rebias,
551 bool attempt_rebias_of_object)
552 : VM_RevokeBias(obj, requesting_thread)
553 , _bulk_rebias(bulk_rebias)
554 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
555
556 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
557 virtual bool doit_prologue() { return true; }
558
559 virtual void doit() {
560 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
561 clean_up_cached_monitor_info();
562 }
563 };
564
565
566 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
567 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
568
569 // We can revoke the biases of anonymously-biased objects
570 // efficiently enough that we should not cause these revocations to
571 // update the heuristics because doing so may cause unwanted bulk
572 // revocations (which are expensive) to occur.
573 markOop mark = obj->mark();
574 if (mark->is_biased_anonymously() && !attempt_rebias) {
575 // We are probably trying to revoke the bias of this object due to
576 // an identity hash code computation. Try to revoke the bias
577 // without a safepoint. This is possible if we can successfully
578 // compare-and-exchange an unbiased header into the mark word of
579 // the object, meaning that no other thread has raced to acquire
580 // the bias of the object.
581 markOop biased_value = mark;
582 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
583 markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
584 if (res_mark == biased_value) {
585 return BIAS_REVOKED;
586 }
587 } else if (mark->has_bias_pattern()) {
588 Klass* k = obj->klass();
589 markOop prototype_header = k->prototype_header();
590 if (!prototype_header->has_bias_pattern()) {
591 // This object has a stale bias from before the bulk revocation
592 // for this data type occurred. It's pointless to update the
593 // heuristics at this point so simply update the header with a
594 // CAS. If we fail this race, the object's bias has been revoked
595 // by another thread so we simply return and let the caller deal
596 // with it.
597 markOop biased_value = mark;
598 markOop res_mark = obj->cas_set_mark(prototype_header, mark);
599 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked");
600 return BIAS_REVOKED;
601 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
602 // The epoch of this biasing has expired indicating that the
603 // object is effectively unbiased. Depending on whether we need
604 // to rebias or revoke the bias of this object we can do it
605 // efficiently enough with a CAS that we shouldn't update the
606 // heuristics. This is normally done in the assembly code but we
607 // can reach this point due to various points in the runtime
608 // needing to revoke biases.
609 if (attempt_rebias) {
610 assert(THREAD->is_Java_thread(), "");
611 markOop biased_value = mark;
612 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
613 markOop res_mark = obj->cas_set_mark(rebiased_prototype, mark);
614 if (res_mark == biased_value) {
615 return BIAS_REVOKED_AND_REBIASED;
616 }
617 } else {
618 markOop biased_value = mark;
619 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
620 markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
621 if (res_mark == biased_value) {
622 return BIAS_REVOKED;
623 }
624 }
625 }
626 }
627
628 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
629 if (heuristics == HR_NOT_BIASED) {
630 return NOT_BIASED;
631 } else if (heuristics == HR_SINGLE_REVOKE) {
632 Klass *k = obj->klass();
633 markOop prototype_header = k->prototype_header();
634 if (mark->biased_locker() == THREAD &&
635 prototype_header->bias_epoch() == mark->bias_epoch()) {
636 // A thread is trying to revoke the bias of an object biased
637 // toward it, again likely due to an identity hash code
638 // computation. We can again avoid a safepoint in this case
639 // since we are only going to walk our own stack. There are no
640 // races with revocations occurring in other threads because we
641 // reach no safepoints in the revocation path.
642 // Also check the epoch because even if threads match, another thread
643 // can come in with a CAS to steal the bias of an object that has a
644 // stale epoch.
645 ResourceMark rm;
646 log_info(biasedlocking)("Revoking bias by walking my own stack:");
647 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD);
648 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
649 assert(cond == BIAS_REVOKED, "why not?");
650 return cond;
651 } else {
652 EventBiasedLockRevocation event;
653 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
654 VMThread::execute(&revoke);
655 if (event.should_commit() && (revoke.status_code() != NOT_BIASED)) {
656 event.set_lockClass(k);
657 // Subtract 1 to match the id of events committed inside the safepoint
658 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1);
659 event.commit();
660 }
661 return revoke.status_code();
662 }
663 }
664
665 assert((heuristics == HR_BULK_REVOKE) ||
666 (heuristics == HR_BULK_REBIAS), "?");
667 EventBiasedLockClassRevocation event;
668 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
669 (heuristics == HR_BULK_REBIAS),
670 attempt_rebias);
671 VMThread::execute(&bulk_revoke);
672 if (event.should_commit()) {
673 event.set_revokedClass(obj->klass());
674 event.set_disableBiasing((heuristics != HR_BULK_REBIAS));
675 // Subtract 1 to match the id of events committed inside the safepoint
676 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1);
677 event.commit();
678 }
679 return bulk_revoke.status_code();
680 }
681
682
683 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
684 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
685 if (objs->length() == 0) {
686 return;
687 }
688 VM_RevokeBias revoke(objs, JavaThread::current());
689 VMThread::execute(&revoke);
690 }
691
692
693 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
694 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
695 oop obj = h_obj();
696 HeuristicsResult heuristics = update_heuristics(obj, false);
697 if (heuristics == HR_SINGLE_REVOKE) {
698 revoke_bias(obj, false, false, NULL);
699 } else if ((heuristics == HR_BULK_REBIAS) ||
700 (heuristics == HR_BULK_REVOKE)) {
701 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
702 }
703 clean_up_cached_monitor_info();
704 }
705
706
707 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
708 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
709 int len = objs->length();
710 for (int i = 0; i < len; i++) {
711 oop obj = (objs->at(i))();
712 HeuristicsResult heuristics = update_heuristics(obj, false);
713 if (heuristics == HR_SINGLE_REVOKE) {
714 revoke_bias(obj, false, false, NULL);
715 } else if ((heuristics == HR_BULK_REBIAS) ||
716 (heuristics == HR_BULK_REVOKE)) {
717 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
718 }
719 }
720 clean_up_cached_monitor_info();
721 }
722
723
724 void BiasedLocking::preserve_marks() {
725 if (!UseBiasedLocking)
726 return;
727
728 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
729
730 assert(_preserved_oop_stack == NULL, "double initialization");
731 assert(_preserved_mark_stack == NULL, "double initialization");
732
733 // In order to reduce the number of mark words preserved during GC
734 // due to the presence of biased locking, we reinitialize most mark
735 // words to the class's prototype during GC -- even those which have
736 // a currently valid bias owner. One important situation where we
737 // must not clobber a bias is when a biased object is currently
738 // locked. To handle this case we iterate over the currently-locked
739 // monitors in a prepass and, if they are biased, preserve their
740 // mark words here. This should be a relatively small set of objects
741 // especially compared to the number of objects in the heap.
742 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true);
743 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
744
745 ResourceMark rm;
746 Thread* cur = Thread::current();
747 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) {
748 if (thread->has_last_Java_frame()) {
749 RegisterMap rm(thread);
750 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
751 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
752 if (monitors != NULL) {
753 int len = monitors->length();
754 // Walk monitors youngest to oldest
755 for (int i = len - 1; i >= 0; i--) {
756 MonitorInfo* mon_info = monitors->at(i);
757 if (mon_info->owner_is_scalar_replaced()) continue;
758 oop owner = mon_info->owner();
759 if (owner != NULL) {
760 markOop mark = owner->mark();
761 if (mark->has_bias_pattern()) {
762 _preserved_oop_stack->push(Handle(cur, owner));
763 _preserved_mark_stack->push(mark);
764 }
765 }
766 }
767 }
768 }
769 }
770 }
771 }
772
773
774 void BiasedLocking::restore_marks() {
775 if (!UseBiasedLocking)
776 return;
777
778 assert(_preserved_oop_stack != NULL, "double free");
779 assert(_preserved_mark_stack != NULL, "double free");
780
781 int len = _preserved_oop_stack->length();
782 for (int i = 0; i < len; i++) {
783 Handle owner = _preserved_oop_stack->at(i);
784 markOop mark = _preserved_mark_stack->at(i);
785 owner->set_mark(mark);
786 }
787
788 delete _preserved_oop_stack;
789 _preserved_oop_stack = NULL;
790 delete _preserved_mark_stack;
791 _preserved_mark_stack = NULL;
792 }
793
794
795 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
796 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
797 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
798 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
799 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
800 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
801 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
802
803
804 // BiasedLockingCounters
805
806 int BiasedLockingCounters::slow_path_entry_count() {
807 if (_slow_path_entry_count != 0) {
808 return _slow_path_entry_count;
809 }
810 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
811 _rebiased_lock_entry_count + _revoked_lock_entry_count +
812 _fast_path_entry_count;
813
814 return _total_entry_count - sum;
815 }
816
817 void BiasedLockingCounters::print_on(outputStream* st) {
818 tty->print_cr("# total entries: %d", _total_entry_count);
819 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
820 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
821 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
822 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
823 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
824 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
825 }