Mercurial > hg > graal-compiler
annotate src/share/vm/runtime/biasedLocking.cpp @ 2874:d90bf514d647
Renamed packages.
author | Thomas Wuerthinger <thomas@wuerthinger.net> |
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date | Wed, 08 Jun 2011 08:59:54 +0200 |
parents | f95d63e2154a |
children | d2a62e0f25eb |
rev | line source |
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0 | 1 /* |
1972 | 2 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved. |
0 | 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 * | |
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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20 * or visit www.oracle.com if you need additional information or have any |
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21 * questions. |
0 | 22 * |
23 */ | |
24 | |
1972 | 25 #include "precompiled.hpp" |
26 #include "oops/klass.inline.hpp" | |
27 #include "oops/markOop.hpp" | |
28 #include "runtime/basicLock.hpp" | |
29 #include "runtime/biasedLocking.hpp" | |
30 #include "runtime/task.hpp" | |
31 #include "runtime/vframe.hpp" | |
32 #include "runtime/vmThread.hpp" | |
33 #include "runtime/vm_operations.hpp" | |
0 | 34 |
35 static bool _biased_locking_enabled = false; | |
36 BiasedLockingCounters BiasedLocking::_counters; | |
37 | |
38 static GrowableArray<Handle>* _preserved_oop_stack = NULL; | |
39 static GrowableArray<markOop>* _preserved_mark_stack = NULL; | |
40 | |
41 static void enable_biased_locking(klassOop k) { | |
42 Klass::cast(k)->set_prototype_header(markOopDesc::biased_locking_prototype()); | |
43 } | |
44 | |
45 class VM_EnableBiasedLocking: public VM_Operation { | |
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46 private: |
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47 bool _is_cheap_allocated; |
0 | 48 public: |
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49 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; } |
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50 VMOp_Type type() const { return VMOp_EnableBiasedLocking; } |
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51 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; } |
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52 bool is_cheap_allocated() const { return _is_cheap_allocated; } |
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53 |
0 | 54 void doit() { |
55 // Iterate the system dictionary enabling biased locking for all | |
56 // currently loaded classes | |
57 SystemDictionary::classes_do(enable_biased_locking); | |
58 // Indicate that future instances should enable it as well | |
59 _biased_locking_enabled = true; | |
60 | |
61 if (TraceBiasedLocking) { | |
62 tty->print_cr("Biased locking enabled"); | |
63 } | |
64 } | |
65 | |
66 bool allow_nested_vm_operations() const { return false; } | |
67 }; | |
68 | |
69 | |
70 // One-shot PeriodicTask subclass for enabling biased locking | |
71 class EnableBiasedLockingTask : public PeriodicTask { | |
72 public: | |
73 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {} | |
74 | |
75 virtual void task() { | |
58
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76 // Use async VM operation to avoid blocking the Watcher thread. |
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77 // VM Thread will free C heap storage. |
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78 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true); |
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79 VMThread::execute(op); |
0 | 80 |
81 // Reclaim our storage and disenroll ourself | |
82 delete this; | |
83 } | |
84 }; | |
85 | |
86 | |
87 void BiasedLocking::init() { | |
88 // If biased locking is enabled, schedule a task to fire a few | |
89 // seconds into the run which turns on biased locking for all | |
90 // currently loaded classes as well as future ones. This is a | |
91 // workaround for startup time regressions due to a large number of | |
92 // safepoints being taken during VM startup for bias revocation. | |
93 // Ideally we would have a lower cost for individual bias revocation | |
94 // and not need a mechanism like this. | |
95 if (UseBiasedLocking) { | |
96 if (BiasedLockingStartupDelay > 0) { | |
97 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay); | |
98 task->enroll(); | |
99 } else { | |
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100 VM_EnableBiasedLocking op(false); |
0 | 101 VMThread::execute(&op); |
102 } | |
103 } | |
104 } | |
105 | |
106 | |
107 bool BiasedLocking::enabled() { | |
108 return _biased_locking_enabled; | |
109 } | |
110 | |
111 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order | |
112 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) { | |
113 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info(); | |
114 if (info != NULL) { | |
115 return info; | |
116 } | |
117 | |
118 info = new GrowableArray<MonitorInfo*>(); | |
119 | |
120 // It's possible for the thread to not have any Java frames on it, | |
121 // i.e., if it's the main thread and it's already returned from main() | |
122 if (thread->has_last_Java_frame()) { | |
123 RegisterMap rm(thread); | |
124 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { | |
125 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); | |
126 if (monitors != NULL) { | |
127 int len = monitors->length(); | |
128 // Walk monitors youngest to oldest | |
129 for (int i = len - 1; i >= 0; i--) { | |
130 MonitorInfo* mon_info = monitors->at(i); | |
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131 if (mon_info->owner_is_scalar_replaced()) continue; |
0 | 132 oop owner = mon_info->owner(); |
133 if (owner != NULL) { | |
134 info->append(mon_info); | |
135 } | |
136 } | |
137 } | |
138 } | |
139 } | |
140 | |
141 thread->set_cached_monitor_info(info); | |
142 return info; | |
143 } | |
144 | |
145 | |
146 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) { | |
147 markOop mark = obj->mark(); | |
148 if (!mark->has_bias_pattern()) { | |
149 if (TraceBiasedLocking) { | |
150 ResourceMark rm; | |
151 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)", | |
152 Klass::cast(obj->klass())->external_name()); | |
153 } | |
154 return BiasedLocking::NOT_BIASED; | |
155 } | |
156 | |
157 int age = mark->age(); | |
158 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age); | |
159 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age); | |
160 | |
161 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
162 ResourceMark rm; | |
163 tty->print_cr("Revoking bias of object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT " , allow rebias %d , requesting thread " INTPTR_FORMAT, | |
164 (intptr_t) obj, (intptr_t) mark, Klass::cast(obj->klass())->external_name(), (intptr_t) Klass::cast(obj->klass())->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread); | |
165 } | |
166 | |
167 JavaThread* biased_thread = mark->biased_locker(); | |
168 if (biased_thread == NULL) { | |
169 // Object is anonymously biased. We can get here if, for | |
170 // example, we revoke the bias due to an identity hash code | |
171 // being computed for an object. | |
172 if (!allow_rebias) { | |
173 obj->set_mark(unbiased_prototype); | |
174 } | |
175 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
176 tty->print_cr(" Revoked bias of anonymously-biased object"); | |
177 } | |
178 return BiasedLocking::BIAS_REVOKED; | |
179 } | |
180 | |
181 // Handle case where the thread toward which the object was biased has exited | |
182 bool thread_is_alive = false; | |
183 if (requesting_thread == biased_thread) { | |
184 thread_is_alive = true; | |
185 } else { | |
186 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) { | |
187 if (cur_thread == biased_thread) { | |
188 thread_is_alive = true; | |
189 break; | |
190 } | |
191 } | |
192 } | |
193 if (!thread_is_alive) { | |
194 if (allow_rebias) { | |
195 obj->set_mark(biased_prototype); | |
196 } else { | |
197 obj->set_mark(unbiased_prototype); | |
198 } | |
199 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
200 tty->print_cr(" Revoked bias of object biased toward dead thread"); | |
201 } | |
202 return BiasedLocking::BIAS_REVOKED; | |
203 } | |
204 | |
205 // Thread owning bias is alive. | |
206 // Check to see whether it currently owns the lock and, if so, | |
207 // write down the needed displaced headers to the thread's stack. | |
208 // Otherwise, restore the object's header either to the unlocked | |
209 // or unbiased state. | |
210 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread); | |
211 BasicLock* highest_lock = NULL; | |
212 for (int i = 0; i < cached_monitor_info->length(); i++) { | |
213 MonitorInfo* mon_info = cached_monitor_info->at(i); | |
214 if (mon_info->owner() == obj) { | |
215 if (TraceBiasedLocking && Verbose) { | |
216 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", | |
217 (intptr_t) mon_info->owner(), | |
218 (intptr_t) obj); | |
219 } | |
220 // Assume recursive case and fix up highest lock later | |
221 markOop mark = markOopDesc::encode((BasicLock*) NULL); | |
222 highest_lock = mon_info->lock(); | |
223 highest_lock->set_displaced_header(mark); | |
224 } else { | |
225 if (TraceBiasedLocking && Verbose) { | |
226 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", | |
227 (intptr_t) mon_info->owner(), | |
228 (intptr_t) obj); | |
229 } | |
230 } | |
231 } | |
232 if (highest_lock != NULL) { | |
233 // Fix up highest lock to contain displaced header and point | |
234 // object at it | |
235 highest_lock->set_displaced_header(unbiased_prototype); | |
236 // Reset object header to point to displaced mark | |
237 obj->set_mark(markOopDesc::encode(highest_lock)); | |
238 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit"); | |
239 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
240 tty->print_cr(" Revoked bias of currently-locked object"); | |
241 } | |
242 } else { | |
243 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
244 tty->print_cr(" Revoked bias of currently-unlocked object"); | |
245 } | |
246 if (allow_rebias) { | |
247 obj->set_mark(biased_prototype); | |
248 } else { | |
249 // Store the unlocked value into the object's header. | |
250 obj->set_mark(unbiased_prototype); | |
251 } | |
252 } | |
253 | |
254 return BiasedLocking::BIAS_REVOKED; | |
255 } | |
256 | |
257 | |
258 enum HeuristicsResult { | |
259 HR_NOT_BIASED = 1, | |
260 HR_SINGLE_REVOKE = 2, | |
261 HR_BULK_REBIAS = 3, | |
262 HR_BULK_REVOKE = 4 | |
263 }; | |
264 | |
265 | |
266 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) { | |
267 markOop mark = o->mark(); | |
268 if (!mark->has_bias_pattern()) { | |
269 return HR_NOT_BIASED; | |
270 } | |
271 | |
272 // Heuristics to attempt to throttle the number of revocations. | |
273 // Stages: | |
274 // 1. Revoke the biases of all objects in the heap of this type, | |
275 // but allow rebiasing of those objects if unlocked. | |
276 // 2. Revoke the biases of all objects in the heap of this type | |
277 // and don't allow rebiasing of these objects. Disable | |
278 // allocation of objects of that type with the bias bit set. | |
279 Klass* k = o->blueprint(); | |
280 jlong cur_time = os::javaTimeMillis(); | |
281 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time(); | |
282 int revocation_count = k->biased_lock_revocation_count(); | |
283 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) && | |
284 (revocation_count < BiasedLockingBulkRevokeThreshold) && | |
285 (last_bulk_revocation_time != 0) && | |
286 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) { | |
287 // This is the first revocation we've seen in a while of an | |
288 // object of this type since the last time we performed a bulk | |
289 // rebiasing operation. The application is allocating objects in | |
290 // bulk which are biased toward a thread and then handing them | |
291 // off to another thread. We can cope with this allocation | |
292 // pattern via the bulk rebiasing mechanism so we reset the | |
293 // klass's revocation count rather than allow it to increase | |
294 // monotonically. If we see the need to perform another bulk | |
295 // rebias operation later, we will, and if subsequently we see | |
296 // many more revocation operations in a short period of time we | |
297 // will completely disable biasing for this type. | |
298 k->set_biased_lock_revocation_count(0); | |
299 revocation_count = 0; | |
300 } | |
301 | |
302 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold | |
303 if (revocation_count <= BiasedLockingBulkRevokeThreshold) { | |
304 revocation_count = k->atomic_incr_biased_lock_revocation_count(); | |
305 } | |
306 | |
307 if (revocation_count == BiasedLockingBulkRevokeThreshold) { | |
308 return HR_BULK_REVOKE; | |
309 } | |
310 | |
311 if (revocation_count == BiasedLockingBulkRebiasThreshold) { | |
312 return HR_BULK_REBIAS; | |
313 } | |
314 | |
315 return HR_SINGLE_REVOKE; | |
316 } | |
317 | |
318 | |
319 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o, | |
320 bool bulk_rebias, | |
321 bool attempt_rebias_of_object, | |
322 JavaThread* requesting_thread) { | |
323 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); | |
324 | |
325 if (TraceBiasedLocking) { | |
326 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object " | |
327 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", | |
328 (bulk_rebias ? "rebias" : "revoke"), | |
329 (intptr_t) o, (intptr_t) o->mark(), Klass::cast(o->klass())->external_name()); | |
330 } | |
331 | |
332 jlong cur_time = os::javaTimeMillis(); | |
333 o->blueprint()->set_last_biased_lock_bulk_revocation_time(cur_time); | |
334 | |
335 | |
336 klassOop k_o = o->klass(); | |
337 Klass* klass = Klass::cast(k_o); | |
338 | |
339 if (bulk_rebias) { | |
340 // Use the epoch in the klass of the object to implicitly revoke | |
341 // all biases of objects of this data type and force them to be | |
342 // reacquired. However, we also need to walk the stacks of all | |
343 // threads and update the headers of lightweight locked objects | |
344 // with biases to have the current epoch. | |
345 | |
346 // If the prototype header doesn't have the bias pattern, don't | |
347 // try to update the epoch -- assume another VM operation came in | |
348 // and reset the header to the unbiased state, which will | |
349 // implicitly cause all existing biases to be revoked | |
350 if (klass->prototype_header()->has_bias_pattern()) { | |
351 int prev_epoch = klass->prototype_header()->bias_epoch(); | |
352 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch()); | |
353 int cur_epoch = klass->prototype_header()->bias_epoch(); | |
354 | |
355 // Now walk all threads' stacks and adjust epochs of any biased | |
356 // and locked objects of this data type we encounter | |
357 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { | |
358 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); | |
359 for (int i = 0; i < cached_monitor_info->length(); i++) { | |
360 MonitorInfo* mon_info = cached_monitor_info->at(i); | |
361 oop owner = mon_info->owner(); | |
362 markOop mark = owner->mark(); | |
363 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { | |
364 // We might have encountered this object already in the case of recursive locking | |
365 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment"); | |
366 owner->set_mark(mark->set_bias_epoch(cur_epoch)); | |
367 } | |
368 } | |
369 } | |
370 } | |
371 | |
372 // At this point we're done. All we have to do is potentially | |
373 // adjust the header of the given object to revoke its bias. | |
374 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread); | |
375 } else { | |
376 if (TraceBiasedLocking) { | |
377 ResourceMark rm; | |
378 tty->print_cr("* Disabling biased locking for type %s", klass->external_name()); | |
379 } | |
380 | |
381 // Disable biased locking for this data type. Not only will this | |
382 // cause future instances to not be biased, but existing biased | |
383 // instances will notice that this implicitly caused their biases | |
384 // to be revoked. | |
385 klass->set_prototype_header(markOopDesc::prototype()); | |
386 | |
387 // Now walk all threads' stacks and forcibly revoke the biases of | |
388 // any locked and biased objects of this data type we encounter. | |
389 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { | |
390 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); | |
391 for (int i = 0; i < cached_monitor_info->length(); i++) { | |
392 MonitorInfo* mon_info = cached_monitor_info->at(i); | |
393 oop owner = mon_info->owner(); | |
394 markOop mark = owner->mark(); | |
395 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { | |
396 revoke_bias(owner, false, true, requesting_thread); | |
397 } | |
398 } | |
399 } | |
400 | |
401 // Must force the bias of the passed object to be forcibly revoked | |
402 // as well to ensure guarantees to callers | |
403 revoke_bias(o, false, true, requesting_thread); | |
404 } | |
405 | |
406 if (TraceBiasedLocking) { | |
407 tty->print_cr("* Ending bulk revocation"); | |
408 } | |
409 | |
410 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED; | |
411 | |
412 if (attempt_rebias_of_object && | |
413 o->mark()->has_bias_pattern() && | |
414 klass->prototype_header()->has_bias_pattern()) { | |
415 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(), | |
416 klass->prototype_header()->bias_epoch()); | |
417 o->set_mark(new_mark); | |
418 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED; | |
419 if (TraceBiasedLocking) { | |
420 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread); | |
421 } | |
422 } | |
423 | |
424 assert(!o->mark()->has_bias_pattern() || | |
425 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)), | |
426 "bug in bulk bias revocation"); | |
427 | |
428 return status_code; | |
429 } | |
430 | |
431 | |
432 static void clean_up_cached_monitor_info() { | |
433 // Walk the thread list clearing out the cached monitors | |
434 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { | |
435 thr->set_cached_monitor_info(NULL); | |
436 } | |
437 } | |
438 | |
439 | |
440 class VM_RevokeBias : public VM_Operation { | |
441 protected: | |
442 Handle* _obj; | |
443 GrowableArray<Handle>* _objs; | |
444 JavaThread* _requesting_thread; | |
445 BiasedLocking::Condition _status_code; | |
446 | |
447 public: | |
448 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread) | |
449 : _obj(obj) | |
450 , _objs(NULL) | |
451 , _requesting_thread(requesting_thread) | |
452 , _status_code(BiasedLocking::NOT_BIASED) {} | |
453 | |
454 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread) | |
455 : _obj(NULL) | |
456 , _objs(objs) | |
457 , _requesting_thread(requesting_thread) | |
458 , _status_code(BiasedLocking::NOT_BIASED) {} | |
459 | |
460 virtual VMOp_Type type() const { return VMOp_RevokeBias; } | |
461 | |
462 virtual bool doit_prologue() { | |
463 // Verify that there is actual work to do since the callers just | |
464 // give us locked object(s). If we don't find any biased objects | |
465 // there is nothing to do and we avoid a safepoint. | |
466 if (_obj != NULL) { | |
467 markOop mark = (*_obj)()->mark(); | |
468 if (mark->has_bias_pattern()) { | |
469 return true; | |
470 } | |
471 } else { | |
472 for ( int i = 0 ; i < _objs->length(); i++ ) { | |
473 markOop mark = (_objs->at(i))()->mark(); | |
474 if (mark->has_bias_pattern()) { | |
475 return true; | |
476 } | |
477 } | |
478 } | |
479 return false; | |
480 } | |
481 | |
482 virtual void doit() { | |
483 if (_obj != NULL) { | |
484 if (TraceBiasedLocking) { | |
485 tty->print_cr("Revoking bias with potentially per-thread safepoint:"); | |
486 } | |
487 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread); | |
488 clean_up_cached_monitor_info(); | |
489 return; | |
490 } else { | |
491 if (TraceBiasedLocking) { | |
492 tty->print_cr("Revoking bias with global safepoint:"); | |
493 } | |
494 BiasedLocking::revoke_at_safepoint(_objs); | |
495 } | |
496 } | |
497 | |
498 BiasedLocking::Condition status_code() const { | |
499 return _status_code; | |
500 } | |
501 }; | |
502 | |
503 | |
504 class VM_BulkRevokeBias : public VM_RevokeBias { | |
505 private: | |
506 bool _bulk_rebias; | |
507 bool _attempt_rebias_of_object; | |
508 | |
509 public: | |
510 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, | |
511 bool bulk_rebias, | |
512 bool attempt_rebias_of_object) | |
513 : VM_RevokeBias(obj, requesting_thread) | |
514 , _bulk_rebias(bulk_rebias) | |
515 , _attempt_rebias_of_object(attempt_rebias_of_object) {} | |
516 | |
517 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } | |
518 virtual bool doit_prologue() { return true; } | |
519 | |
520 virtual void doit() { | |
521 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread); | |
522 clean_up_cached_monitor_info(); | |
523 } | |
524 }; | |
525 | |
526 | |
527 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) { | |
528 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); | |
529 | |
530 // We can revoke the biases of anonymously-biased objects | |
531 // efficiently enough that we should not cause these revocations to | |
532 // update the heuristics because doing so may cause unwanted bulk | |
533 // revocations (which are expensive) to occur. | |
534 markOop mark = obj->mark(); | |
535 if (mark->is_biased_anonymously() && !attempt_rebias) { | |
536 // We are probably trying to revoke the bias of this object due to | |
537 // an identity hash code computation. Try to revoke the bias | |
538 // without a safepoint. This is possible if we can successfully | |
539 // compare-and-exchange an unbiased header into the mark word of | |
540 // the object, meaning that no other thread has raced to acquire | |
541 // the bias of the object. | |
542 markOop biased_value = mark; | |
543 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); | |
544 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); | |
545 if (res_mark == biased_value) { | |
546 return BIAS_REVOKED; | |
547 } | |
548 } else if (mark->has_bias_pattern()) { | |
549 Klass* k = Klass::cast(obj->klass()); | |
550 markOop prototype_header = k->prototype_header(); | |
551 if (!prototype_header->has_bias_pattern()) { | |
552 // This object has a stale bias from before the bulk revocation | |
553 // for this data type occurred. It's pointless to update the | |
554 // heuristics at this point so simply update the header with a | |
555 // CAS. If we fail this race, the object's bias has been revoked | |
556 // by another thread so we simply return and let the caller deal | |
557 // with it. | |
558 markOop biased_value = mark; | |
559 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark); | |
560 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked"); | |
561 return BIAS_REVOKED; | |
562 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) { | |
563 // The epoch of this biasing has expired indicating that the | |
564 // object is effectively unbiased. Depending on whether we need | |
565 // to rebias or revoke the bias of this object we can do it | |
566 // efficiently enough with a CAS that we shouldn't update the | |
567 // heuristics. This is normally done in the assembly code but we | |
568 // can reach this point due to various points in the runtime | |
569 // needing to revoke biases. | |
570 if (attempt_rebias) { | |
571 assert(THREAD->is_Java_thread(), ""); | |
572 markOop biased_value = mark; | |
573 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch()); | |
574 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark); | |
575 if (res_mark == biased_value) { | |
576 return BIAS_REVOKED_AND_REBIASED; | |
577 } | |
578 } else { | |
579 markOop biased_value = mark; | |
580 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); | |
581 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); | |
582 if (res_mark == biased_value) { | |
583 return BIAS_REVOKED; | |
584 } | |
585 } | |
586 } | |
587 } | |
588 | |
589 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias); | |
590 if (heuristics == HR_NOT_BIASED) { | |
591 return NOT_BIASED; | |
592 } else if (heuristics == HR_SINGLE_REVOKE) { | |
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593 Klass *k = Klass::cast(obj->klass()); |
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594 markOop prototype_header = k->prototype_header(); |
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595 if (mark->biased_locker() == THREAD && |
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596 prototype_header->bias_epoch() == mark->bias_epoch()) { |
0 | 597 // A thread is trying to revoke the bias of an object biased |
598 // toward it, again likely due to an identity hash code | |
599 // computation. We can again avoid a safepoint in this case | |
600 // since we are only going to walk our own stack. There are no | |
601 // races with revocations occurring in other threads because we | |
602 // reach no safepoints in the revocation path. | |
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603 // Also check the epoch because even if threads match, another thread |
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604 // can come in with a CAS to steal the bias of an object that has a |
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605 // stale epoch. |
0 | 606 ResourceMark rm; |
607 if (TraceBiasedLocking) { | |
608 tty->print_cr("Revoking bias by walking my own stack:"); | |
609 } | |
610 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD); | |
611 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL); | |
612 assert(cond == BIAS_REVOKED, "why not?"); | |
613 return cond; | |
614 } else { | |
615 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD); | |
616 VMThread::execute(&revoke); | |
617 return revoke.status_code(); | |
618 } | |
619 } | |
620 | |
621 assert((heuristics == HR_BULK_REVOKE) || | |
622 (heuristics == HR_BULK_REBIAS), "?"); | |
623 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD, | |
624 (heuristics == HR_BULK_REBIAS), | |
625 attempt_rebias); | |
626 VMThread::execute(&bulk_revoke); | |
627 return bulk_revoke.status_code(); | |
628 } | |
629 | |
630 | |
631 void BiasedLocking::revoke(GrowableArray<Handle>* objs) { | |
632 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); | |
633 if (objs->length() == 0) { | |
634 return; | |
635 } | |
636 VM_RevokeBias revoke(objs, JavaThread::current()); | |
637 VMThread::execute(&revoke); | |
638 } | |
639 | |
640 | |
641 void BiasedLocking::revoke_at_safepoint(Handle h_obj) { | |
642 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); | |
643 oop obj = h_obj(); | |
644 HeuristicsResult heuristics = update_heuristics(obj, false); | |
645 if (heuristics == HR_SINGLE_REVOKE) { | |
646 revoke_bias(obj, false, false, NULL); | |
647 } else if ((heuristics == HR_BULK_REBIAS) || | |
648 (heuristics == HR_BULK_REVOKE)) { | |
649 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); | |
650 } | |
651 clean_up_cached_monitor_info(); | |
652 } | |
653 | |
654 | |
655 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) { | |
656 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); | |
657 int len = objs->length(); | |
658 for (int i = 0; i < len; i++) { | |
659 oop obj = (objs->at(i))(); | |
660 HeuristicsResult heuristics = update_heuristics(obj, false); | |
661 if (heuristics == HR_SINGLE_REVOKE) { | |
662 revoke_bias(obj, false, false, NULL); | |
663 } else if ((heuristics == HR_BULK_REBIAS) || | |
664 (heuristics == HR_BULK_REVOKE)) { | |
665 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); | |
666 } | |
667 } | |
668 clean_up_cached_monitor_info(); | |
669 } | |
670 | |
671 | |
672 void BiasedLocking::preserve_marks() { | |
673 if (!UseBiasedLocking) | |
674 return; | |
675 | |
676 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); | |
677 | |
678 assert(_preserved_oop_stack == NULL, "double initialization"); | |
679 assert(_preserved_mark_stack == NULL, "double initialization"); | |
680 | |
681 // In order to reduce the number of mark words preserved during GC | |
682 // due to the presence of biased locking, we reinitialize most mark | |
683 // words to the class's prototype during GC -- even those which have | |
684 // a currently valid bias owner. One important situation where we | |
685 // must not clobber a bias is when a biased object is currently | |
686 // locked. To handle this case we iterate over the currently-locked | |
687 // monitors in a prepass and, if they are biased, preserve their | |
688 // mark words here. This should be a relatively small set of objects | |
689 // especially compared to the number of objects in the heap. | |
690 _preserved_mark_stack = new (ResourceObj::C_HEAP) GrowableArray<markOop>(10, true); | |
691 _preserved_oop_stack = new (ResourceObj::C_HEAP) GrowableArray<Handle>(10, true); | |
692 | |
693 ResourceMark rm; | |
694 Thread* cur = Thread::current(); | |
695 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) { | |
696 if (thread->has_last_Java_frame()) { | |
697 RegisterMap rm(thread); | |
698 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { | |
699 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); | |
700 if (monitors != NULL) { | |
701 int len = monitors->length(); | |
702 // Walk monitors youngest to oldest | |
703 for (int i = len - 1; i >= 0; i--) { | |
704 MonitorInfo* mon_info = monitors->at(i); | |
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705 if (mon_info->owner_is_scalar_replaced()) continue; |
0 | 706 oop owner = mon_info->owner(); |
707 if (owner != NULL) { | |
708 markOop mark = owner->mark(); | |
709 if (mark->has_bias_pattern()) { | |
710 _preserved_oop_stack->push(Handle(cur, owner)); | |
711 _preserved_mark_stack->push(mark); | |
712 } | |
713 } | |
714 } | |
715 } | |
716 } | |
717 } | |
718 } | |
719 } | |
720 | |
721 | |
722 void BiasedLocking::restore_marks() { | |
723 if (!UseBiasedLocking) | |
724 return; | |
725 | |
726 assert(_preserved_oop_stack != NULL, "double free"); | |
727 assert(_preserved_mark_stack != NULL, "double free"); | |
728 | |
729 int len = _preserved_oop_stack->length(); | |
730 for (int i = 0; i < len; i++) { | |
731 Handle owner = _preserved_oop_stack->at(i); | |
732 markOop mark = _preserved_mark_stack->at(i); | |
733 owner->set_mark(mark); | |
734 } | |
735 | |
736 delete _preserved_oop_stack; | |
737 _preserved_oop_stack = NULL; | |
738 delete _preserved_mark_stack; | |
739 _preserved_mark_stack = NULL; | |
740 } | |
741 | |
742 | |
743 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); } | |
744 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); } | |
745 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); } | |
746 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); } | |
747 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); } | |
748 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); } | |
749 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); } | |
750 | |
751 | |
752 // BiasedLockingCounters | |
753 | |
754 int BiasedLockingCounters::slow_path_entry_count() { | |
755 if (_slow_path_entry_count != 0) { | |
756 return _slow_path_entry_count; | |
757 } | |
758 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count + | |
759 _rebiased_lock_entry_count + _revoked_lock_entry_count + | |
760 _fast_path_entry_count; | |
761 | |
762 return _total_entry_count - sum; | |
763 } | |
764 | |
765 void BiasedLockingCounters::print_on(outputStream* st) { | |
766 tty->print_cr("# total entries: %d", _total_entry_count); | |
767 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count); | |
768 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count); | |
769 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count); | |
770 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count); | |
771 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count); | |
772 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count()); | |
773 } |