Mercurial > hg > truffle
annotate src/share/vm/runtime/synchronizer.cpp @ 1891:9de67bf4244d
6996136: VM crash in src/share/vm/runtime/virtualspace.cpp:424
Summary: Turn CDS off if compressed oops is on
Reviewed-by: ysr, kvn, jcoomes, phh
author | iveresov |
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date | Tue, 02 Nov 2010 16:02:46 -0700 |
parents | fa83ab460c54 |
children | 2d26b0046e0d f95d63e2154a |
rev | line source |
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0 | 1 /* |
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2 * Copyright (c) 1998, 2009, 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 | |
25 # include "incls/_precompiled.incl" | |
26 # include "incls/_synchronizer.cpp.incl" | |
27 | |
28 #if defined(__GNUC__) && !defined(IA64) | |
29 // Need to inhibit inlining for older versions of GCC to avoid build-time failures | |
30 #define ATTR __attribute__((noinline)) | |
31 #else | |
32 #define ATTR | |
33 #endif | |
34 | |
35 // The "core" versions of monitor enter and exit reside in this file. | |
36 // The interpreter and compilers contain specialized transliterated | |
37 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(), | |
38 // for instance. If you make changes here, make sure to modify the | |
39 // interpreter, and both C1 and C2 fast-path inline locking code emission. | |
40 // | |
41 // | |
42 // ----------------------------------------------------------------------------- | |
43 | |
44 #ifdef DTRACE_ENABLED | |
45 | |
46 // Only bother with this argument setup if dtrace is available | |
47 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly. | |
48 | |
49 HS_DTRACE_PROBE_DECL5(hotspot, monitor__wait, | |
50 jlong, uintptr_t, char*, int, long); | |
51 HS_DTRACE_PROBE_DECL4(hotspot, monitor__waited, | |
52 jlong, uintptr_t, char*, int); | |
53 | |
54 #define DTRACE_MONITOR_PROBE_COMMON(klassOop, thread) \ | |
55 char* bytes = NULL; \ | |
56 int len = 0; \ | |
57 jlong jtid = SharedRuntime::get_java_tid(thread); \ | |
58 symbolOop klassname = ((oop)(klassOop))->klass()->klass_part()->name(); \ | |
59 if (klassname != NULL) { \ | |
60 bytes = (char*)klassname->bytes(); \ | |
61 len = klassname->utf8_length(); \ | |
62 } | |
63 | |
64 #define DTRACE_MONITOR_WAIT_PROBE(monitor, klassOop, thread, millis) \ | |
65 { \ | |
66 if (DTraceMonitorProbes) { \ | |
67 DTRACE_MONITOR_PROBE_COMMON(klassOop, thread); \ | |
68 HS_DTRACE_PROBE5(hotspot, monitor__wait, jtid, \ | |
69 (monitor), bytes, len, (millis)); \ | |
70 } \ | |
71 } | |
72 | |
73 #define DTRACE_MONITOR_PROBE(probe, monitor, klassOop, thread) \ | |
74 { \ | |
75 if (DTraceMonitorProbes) { \ | |
76 DTRACE_MONITOR_PROBE_COMMON(klassOop, thread); \ | |
77 HS_DTRACE_PROBE4(hotspot, monitor__##probe, jtid, \ | |
78 (uintptr_t)(monitor), bytes, len); \ | |
79 } \ | |
80 } | |
81 | |
82 #else // ndef DTRACE_ENABLED | |
83 | |
84 #define DTRACE_MONITOR_WAIT_PROBE(klassOop, thread, millis, mon) {;} | |
85 #define DTRACE_MONITOR_PROBE(probe, klassOop, thread, mon) {;} | |
86 | |
87 #endif // ndef DTRACE_ENABLED | |
88 | |
1878 | 89 // This exists only as a workaround of dtrace bug 6254741 |
90 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) { | |
91 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr); | |
92 return 0; | |
93 } | |
94 | |
95 #define NINFLATIONLOCKS 256 | |
96 static volatile intptr_t InflationLocks [NINFLATIONLOCKS] ; | |
97 | |
98 ObjectMonitor * ObjectSynchronizer::gBlockList = NULL ; | |
99 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL ; | |
100 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL ; | |
101 int ObjectSynchronizer::gOmInUseCount = 0; | |
102 static volatile intptr_t ListLock = 0 ; // protects global monitor free-list cache | |
103 static volatile int MonitorFreeCount = 0 ; // # on gFreeList | |
104 static volatile int MonitorPopulation = 0 ; // # Extant -- in circulation | |
105 #define CHAINMARKER ((oop)-1) | |
106 | |
107 // ----------------------------------------------------------------------------- | |
108 // Fast Monitor Enter/Exit | |
109 // This the fast monitor enter. The interpreter and compiler use | |
110 // some assembly copies of this code. Make sure update those code | |
111 // if the following function is changed. The implementation is | |
112 // extremely sensitive to race condition. Be careful. | |
113 | |
114 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock, bool attempt_rebias, TRAPS) { | |
115 if (UseBiasedLocking) { | |
116 if (!SafepointSynchronize::is_at_safepoint()) { | |
117 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD); | |
118 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) { | |
119 return; | |
120 } | |
121 } else { | |
122 assert(!attempt_rebias, "can not rebias toward VM thread"); | |
123 BiasedLocking::revoke_at_safepoint(obj); | |
124 } | |
125 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
126 } | |
127 | |
128 slow_enter (obj, lock, THREAD) ; | |
129 } | |
130 | |
131 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) { | |
132 assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here"); | |
133 // if displaced header is null, the previous enter is recursive enter, no-op | |
134 markOop dhw = lock->displaced_header(); | |
135 markOop mark ; | |
136 if (dhw == NULL) { | |
137 // Recursive stack-lock. | |
138 // Diagnostics -- Could be: stack-locked, inflating, inflated. | |
139 mark = object->mark() ; | |
140 assert (!mark->is_neutral(), "invariant") ; | |
141 if (mark->has_locker() && mark != markOopDesc::INFLATING()) { | |
142 assert(THREAD->is_lock_owned((address)mark->locker()), "invariant") ; | |
143 } | |
144 if (mark->has_monitor()) { | |
145 ObjectMonitor * m = mark->monitor() ; | |
146 assert(((oop)(m->object()))->mark() == mark, "invariant") ; | |
147 assert(m->is_entered(THREAD), "invariant") ; | |
148 } | |
149 return ; | |
150 } | |
151 | |
152 mark = object->mark() ; | |
0 | 153 |
1878 | 154 // If the object is stack-locked by the current thread, try to |
155 // swing the displaced header from the box back to the mark. | |
156 if (mark == (markOop) lock) { | |
157 assert (dhw->is_neutral(), "invariant") ; | |
158 if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) { | |
159 TEVENT (fast_exit: release stacklock) ; | |
160 return; | |
161 } | |
162 } | |
163 | |
164 ObjectSynchronizer::inflate(THREAD, object)->exit (THREAD) ; | |
165 } | |
166 | |
167 // ----------------------------------------------------------------------------- | |
168 // Interpreter/Compiler Slow Case | |
169 // This routine is used to handle interpreter/compiler slow case | |
170 // We don't need to use fast path here, because it must have been | |
171 // failed in the interpreter/compiler code. | |
172 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) { | |
173 markOop mark = obj->mark(); | |
174 assert(!mark->has_bias_pattern(), "should not see bias pattern here"); | |
175 | |
176 if (mark->is_neutral()) { | |
177 // Anticipate successful CAS -- the ST of the displaced mark must | |
178 // be visible <= the ST performed by the CAS. | |
179 lock->set_displaced_header(mark); | |
180 if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) { | |
181 TEVENT (slow_enter: release stacklock) ; | |
182 return ; | |
183 } | |
184 // Fall through to inflate() ... | |
185 } else | |
186 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { | |
187 assert(lock != mark->locker(), "must not re-lock the same lock"); | |
188 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock"); | |
189 lock->set_displaced_header(NULL); | |
190 return; | |
191 } | |
192 | |
193 #if 0 | |
194 // The following optimization isn't particularly useful. | |
195 if (mark->has_monitor() && mark->monitor()->is_entered(THREAD)) { | |
196 lock->set_displaced_header (NULL) ; | |
197 return ; | |
198 } | |
199 #endif | |
200 | |
201 // The object header will never be displaced to this lock, | |
202 // so it does not matter what the value is, except that it | |
203 // must be non-zero to avoid looking like a re-entrant lock, | |
204 // and must not look locked either. | |
205 lock->set_displaced_header(markOopDesc::unused_mark()); | |
206 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD); | |
207 } | |
208 | |
209 // This routine is used to handle interpreter/compiler slow case | |
210 // We don't need to use fast path here, because it must have | |
211 // failed in the interpreter/compiler code. Simply use the heavy | |
212 // weight monitor should be ok, unless someone find otherwise. | |
213 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) { | |
214 fast_exit (object, lock, THREAD) ; | |
215 } | |
216 | |
217 // ----------------------------------------------------------------------------- | |
218 // Class Loader support to workaround deadlocks on the class loader lock objects | |
219 // Also used by GC | |
220 // complete_exit()/reenter() are used to wait on a nested lock | |
221 // i.e. to give up an outer lock completely and then re-enter | |
222 // Used when holding nested locks - lock acquisition order: lock1 then lock2 | |
223 // 1) complete_exit lock1 - saving recursion count | |
224 // 2) wait on lock2 | |
225 // 3) when notified on lock2, unlock lock2 | |
226 // 4) reenter lock1 with original recursion count | |
227 // 5) lock lock2 | |
228 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() | |
229 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) { | |
230 TEVENT (complete_exit) ; | |
231 if (UseBiasedLocking) { | |
232 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
233 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
0 | 234 } |
235 | |
1878 | 236 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); |
237 | |
238 return monitor->complete_exit(THREAD); | |
239 } | |
240 | |
241 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() | |
242 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) { | |
243 TEVENT (reenter) ; | |
244 if (UseBiasedLocking) { | |
245 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
246 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
247 } | |
248 | |
249 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); | |
250 | |
251 monitor->reenter(recursion, THREAD); | |
252 } | |
253 // ----------------------------------------------------------------------------- | |
254 // JNI locks on java objects | |
255 // NOTE: must use heavy weight monitor to handle jni monitor enter | |
256 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) { // possible entry from jni enter | |
257 // the current locking is from JNI instead of Java code | |
258 TEVENT (jni_enter) ; | |
259 if (UseBiasedLocking) { | |
260 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
261 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
262 } | |
263 THREAD->set_current_pending_monitor_is_from_java(false); | |
264 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD); | |
265 THREAD->set_current_pending_monitor_is_from_java(true); | |
266 } | |
267 | |
268 // NOTE: must use heavy weight monitor to handle jni monitor enter | |
269 bool ObjectSynchronizer::jni_try_enter(Handle obj, Thread* THREAD) { | |
270 if (UseBiasedLocking) { | |
271 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
272 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
0 | 273 } |
274 | |
1878 | 275 ObjectMonitor* monitor = ObjectSynchronizer::inflate_helper(obj()); |
276 return monitor->try_enter(THREAD); | |
277 } | |
278 | |
279 | |
280 // NOTE: must use heavy weight monitor to handle jni monitor exit | |
281 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) { | |
282 TEVENT (jni_exit) ; | |
283 if (UseBiasedLocking) { | |
284 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
285 } | |
286 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
287 | |
288 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj); | |
289 // If this thread has locked the object, exit the monitor. Note: can't use | |
290 // monitor->check(CHECK); must exit even if an exception is pending. | |
291 if (monitor->check(THREAD)) { | |
292 monitor->exit(THREAD); | |
0 | 293 } |
1878 | 294 } |
295 | |
296 // ----------------------------------------------------------------------------- | |
297 // Internal VM locks on java objects | |
298 // standard constructor, allows locking failures | |
299 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) { | |
300 _dolock = doLock; | |
301 _thread = thread; | |
302 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);) | |
303 _obj = obj; | |
0 | 304 |
1878 | 305 if (_dolock) { |
306 TEVENT (ObjectLocker) ; | |
307 | |
308 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread); | |
309 } | |
310 } | |
311 | |
312 ObjectLocker::~ObjectLocker() { | |
313 if (_dolock) { | |
314 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread); | |
315 } | |
316 } | |
0 | 317 |
318 | |
1878 | 319 // ----------------------------------------------------------------------------- |
320 // Wait/Notify/NotifyAll | |
321 // NOTE: must use heavy weight monitor to handle wait() | |
322 void ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) { | |
323 if (UseBiasedLocking) { | |
324 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
325 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
326 } | |
327 if (millis < 0) { | |
328 TEVENT (wait - throw IAX) ; | |
329 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); | |
330 } | |
331 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); | |
332 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis); | |
333 monitor->wait(millis, true, THREAD); | |
334 | |
335 /* This dummy call is in place to get around dtrace bug 6254741. Once | |
336 that's fixed we can uncomment the following line and remove the call */ | |
337 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD); | |
338 dtrace_waited_probe(monitor, obj, THREAD); | |
339 } | |
0 | 340 |
1878 | 341 void ObjectSynchronizer::waitUninterruptibly (Handle obj, jlong millis, TRAPS) { |
342 if (UseBiasedLocking) { | |
343 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
344 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
345 } | |
346 if (millis < 0) { | |
347 TEVENT (wait - throw IAX) ; | |
348 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); | |
349 } | |
350 ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD) ; | |
351 } | |
352 | |
353 void ObjectSynchronizer::notify(Handle obj, TRAPS) { | |
354 if (UseBiasedLocking) { | |
355 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
356 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
357 } | |
0 | 358 |
1878 | 359 markOop mark = obj->mark(); |
360 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { | |
361 return; | |
362 } | |
363 ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD); | |
364 } | |
0 | 365 |
1878 | 366 // NOTE: see comment of notify() |
367 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) { | |
368 if (UseBiasedLocking) { | |
369 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
370 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
371 } | |
372 | |
373 markOop mark = obj->mark(); | |
374 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { | |
375 return; | |
376 } | |
377 ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD); | |
378 } | |
379 | |
380 // ----------------------------------------------------------------------------- | |
381 // Hash Code handling | |
382 // | |
0 | 383 // Performance concern: |
384 // OrderAccess::storestore() calls release() which STs 0 into the global volatile | |
385 // OrderAccess::Dummy variable. This store is unnecessary for correctness. | |
386 // Many threads STing into a common location causes considerable cache migration | |
387 // or "sloshing" on large SMP system. As such, I avoid using OrderAccess::storestore() | |
388 // until it's repaired. In some cases OrderAccess::fence() -- which incurs local | |
389 // latency on the executing processor -- is a better choice as it scales on SMP | |
390 // systems. See http://blogs.sun.com/dave/entry/biased_locking_in_hotspot for a | |
391 // discussion of coherency costs. Note that all our current reference platforms | |
392 // provide strong ST-ST order, so the issue is moot on IA32, x64, and SPARC. | |
393 // | |
394 // As a general policy we use "volatile" to control compiler-based reordering | |
395 // and explicit fences (barriers) to control for architectural reordering performed | |
396 // by the CPU(s) or platform. | |
397 | |
398 static int MBFence (int x) { OrderAccess::fence(); return x; } | |
399 | |
400 struct SharedGlobals { | |
401 // These are highly shared mostly-read variables. | |
402 // To avoid false-sharing they need to be the sole occupants of a $ line. | |
403 double padPrefix [8]; | |
404 volatile int stwRandom ; | |
405 volatile int stwCycle ; | |
406 | |
407 // Hot RW variables -- Sequester to avoid false-sharing | |
408 double padSuffix [16]; | |
409 volatile int hcSequence ; | |
410 double padFinal [8] ; | |
411 } ; | |
412 | |
413 static SharedGlobals GVars ; | |
1587 | 414 static int MonitorScavengeThreshold = 1000000 ; |
415 static volatile int ForceMonitorScavenge = 0 ; // Scavenge required and pending | |
0 | 416 |
1878 | 417 static markOop ReadStableMark (oop obj) { |
418 markOop mark = obj->mark() ; | |
419 if (!mark->is_being_inflated()) { | |
420 return mark ; // normal fast-path return | |
421 } | |
0 | 422 |
1878 | 423 int its = 0 ; |
424 for (;;) { | |
425 markOop mark = obj->mark() ; | |
426 if (!mark->is_being_inflated()) { | |
427 return mark ; // normal fast-path return | |
428 } | |
429 | |
430 // The object is being inflated by some other thread. | |
431 // The caller of ReadStableMark() must wait for inflation to complete. | |
432 // Avoid live-lock | |
433 // TODO: consider calling SafepointSynchronize::do_call_back() while | |
434 // spinning to see if there's a safepoint pending. If so, immediately | |
435 // yielding or blocking would be appropriate. Avoid spinning while | |
436 // there is a safepoint pending. | |
437 // TODO: add inflation contention performance counters. | |
438 // TODO: restrict the aggregate number of spinners. | |
0 | 439 |
1878 | 440 ++its ; |
441 if (its > 10000 || !os::is_MP()) { | |
442 if (its & 1) { | |
443 os::NakedYield() ; | |
444 TEVENT (Inflate: INFLATING - yield) ; | |
445 } else { | |
446 // Note that the following code attenuates the livelock problem but is not | |
447 // a complete remedy. A more complete solution would require that the inflating | |
448 // thread hold the associated inflation lock. The following code simply restricts | |
449 // the number of spinners to at most one. We'll have N-2 threads blocked | |
450 // on the inflationlock, 1 thread holding the inflation lock and using | |
451 // a yield/park strategy, and 1 thread in the midst of inflation. | |
452 // A more refined approach would be to change the encoding of INFLATING | |
453 // to allow encapsulation of a native thread pointer. Threads waiting for | |
454 // inflation to complete would use CAS to push themselves onto a singly linked | |
455 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag | |
456 // and calling park(). When inflation was complete the thread that accomplished inflation | |
457 // would detach the list and set the markword to inflated with a single CAS and | |
458 // then for each thread on the list, set the flag and unpark() the thread. | |
459 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease | |
460 // wakes at most one thread whereas we need to wake the entire list. | |
461 int ix = (intptr_t(obj) >> 5) & (NINFLATIONLOCKS-1) ; | |
462 int YieldThenBlock = 0 ; | |
463 assert (ix >= 0 && ix < NINFLATIONLOCKS, "invariant") ; | |
464 assert ((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant") ; | |
465 Thread::muxAcquire (InflationLocks + ix, "InflationLock") ; | |
466 while (obj->mark() == markOopDesc::INFLATING()) { | |
467 // Beware: NakedYield() is advisory and has almost no effect on some platforms | |
468 // so we periodically call Self->_ParkEvent->park(1). | |
469 // We use a mixed spin/yield/block mechanism. | |
470 if ((YieldThenBlock++) >= 16) { | |
471 Thread::current()->_ParkEvent->park(1) ; | |
472 } else { | |
473 os::NakedYield() ; | |
474 } | |
475 } | |
476 Thread::muxRelease (InflationLocks + ix ) ; | |
477 TEVENT (Inflate: INFLATING - yield/park) ; | |
478 } | |
479 } else { | |
480 SpinPause() ; // SMP-polite spinning | |
481 } | |
482 } | |
483 } | |
0 | 484 |
485 // hashCode() generation : | |
486 // | |
487 // Possibilities: | |
488 // * MD5Digest of {obj,stwRandom} | |
489 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function. | |
490 // * A DES- or AES-style SBox[] mechanism | |
491 // * One of the Phi-based schemes, such as: | |
492 // 2654435761 = 2^32 * Phi (golden ratio) | |
493 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ; | |
494 // * A variation of Marsaglia's shift-xor RNG scheme. | |
495 // * (obj ^ stwRandom) is appealing, but can result | |
496 // in undesirable regularity in the hashCode values of adjacent objects | |
497 // (objects allocated back-to-back, in particular). This could potentially | |
498 // result in hashtable collisions and reduced hashtable efficiency. | |
499 // There are simple ways to "diffuse" the middle address bits over the | |
500 // generated hashCode values: | |
501 // | |
502 | |
503 static inline intptr_t get_next_hash(Thread * Self, oop obj) { | |
504 intptr_t value = 0 ; | |
505 if (hashCode == 0) { | |
506 // This form uses an unguarded global Park-Miller RNG, | |
507 // so it's possible for two threads to race and generate the same RNG. | |
508 // On MP system we'll have lots of RW access to a global, so the | |
509 // mechanism induces lots of coherency traffic. | |
510 value = os::random() ; | |
511 } else | |
512 if (hashCode == 1) { | |
513 // This variation has the property of being stable (idempotent) | |
514 // between STW operations. This can be useful in some of the 1-0 | |
515 // synchronization schemes. | |
516 intptr_t addrBits = intptr_t(obj) >> 3 ; | |
517 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom ; | |
518 } else | |
519 if (hashCode == 2) { | |
520 value = 1 ; // for sensitivity testing | |
521 } else | |
522 if (hashCode == 3) { | |
523 value = ++GVars.hcSequence ; | |
524 } else | |
525 if (hashCode == 4) { | |
526 value = intptr_t(obj) ; | |
527 } else { | |
528 // Marsaglia's xor-shift scheme with thread-specific state | |
529 // This is probably the best overall implementation -- we'll | |
530 // likely make this the default in future releases. | |
531 unsigned t = Self->_hashStateX ; | |
532 t ^= (t << 11) ; | |
533 Self->_hashStateX = Self->_hashStateY ; | |
534 Self->_hashStateY = Self->_hashStateZ ; | |
535 Self->_hashStateZ = Self->_hashStateW ; | |
536 unsigned v = Self->_hashStateW ; | |
537 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)) ; | |
538 Self->_hashStateW = v ; | |
539 value = v ; | |
540 } | |
541 | |
542 value &= markOopDesc::hash_mask; | |
543 if (value == 0) value = 0xBAD ; | |
544 assert (value != markOopDesc::no_hash, "invariant") ; | |
545 TEVENT (hashCode: GENERATE) ; | |
546 return value; | |
547 } | |
1878 | 548 // |
549 intptr_t ObjectSynchronizer::FastHashCode (Thread * Self, oop obj) { | |
550 if (UseBiasedLocking) { | |
551 // NOTE: many places throughout the JVM do not expect a safepoint | |
552 // to be taken here, in particular most operations on perm gen | |
553 // objects. However, we only ever bias Java instances and all of | |
554 // the call sites of identity_hash that might revoke biases have | |
555 // been checked to make sure they can handle a safepoint. The | |
556 // added check of the bias pattern is to avoid useless calls to | |
557 // thread-local storage. | |
558 if (obj->mark()->has_bias_pattern()) { | |
559 // Box and unbox the raw reference just in case we cause a STW safepoint. | |
560 Handle hobj (Self, obj) ; | |
561 // Relaxing assertion for bug 6320749. | |
562 assert (Universe::verify_in_progress() || | |
563 !SafepointSynchronize::is_at_safepoint(), | |
564 "biases should not be seen by VM thread here"); | |
565 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current()); | |
566 obj = hobj() ; | |
567 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
568 } | |
569 } | |
0 | 570 |
1878 | 571 // hashCode() is a heap mutator ... |
572 // Relaxing assertion for bug 6320749. | |
573 assert (Universe::verify_in_progress() || | |
574 !SafepointSynchronize::is_at_safepoint(), "invariant") ; | |
575 assert (Universe::verify_in_progress() || | |
576 Self->is_Java_thread() , "invariant") ; | |
577 assert (Universe::verify_in_progress() || | |
578 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ; | |
579 | |
580 ObjectMonitor* monitor = NULL; | |
581 markOop temp, test; | |
582 intptr_t hash; | |
583 markOop mark = ReadStableMark (obj); | |
584 | |
585 // object should remain ineligible for biased locking | |
586 assert (!mark->has_bias_pattern(), "invariant") ; | |
587 | |
588 if (mark->is_neutral()) { | |
589 hash = mark->hash(); // this is a normal header | |
590 if (hash) { // if it has hash, just return it | |
591 return hash; | |
592 } | |
593 hash = get_next_hash(Self, obj); // allocate a new hash code | |
594 temp = mark->copy_set_hash(hash); // merge the hash code into header | |
595 // use (machine word version) atomic operation to install the hash | |
596 test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark); | |
597 if (test == mark) { | |
598 return hash; | |
599 } | |
600 // If atomic operation failed, we must inflate the header | |
601 // into heavy weight monitor. We could add more code here | |
602 // for fast path, but it does not worth the complexity. | |
603 } else if (mark->has_monitor()) { | |
604 monitor = mark->monitor(); | |
605 temp = monitor->header(); | |
606 assert (temp->is_neutral(), "invariant") ; | |
607 hash = temp->hash(); | |
608 if (hash) { | |
609 return hash; | |
610 } | |
611 // Skip to the following code to reduce code size | |
612 } else if (Self->is_lock_owned((address)mark->locker())) { | |
613 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned | |
614 assert (temp->is_neutral(), "invariant") ; | |
615 hash = temp->hash(); // by current thread, check if the displaced | |
616 if (hash) { // header contains hash code | |
617 return hash; | |
618 } | |
619 // WARNING: | |
620 // The displaced header is strictly immutable. | |
621 // It can NOT be changed in ANY cases. So we have | |
622 // to inflate the header into heavyweight monitor | |
623 // even the current thread owns the lock. The reason | |
624 // is the BasicLock (stack slot) will be asynchronously | |
625 // read by other threads during the inflate() function. | |
626 // Any change to stack may not propagate to other threads | |
627 // correctly. | |
628 } | |
629 | |
630 // Inflate the monitor to set hash code | |
631 monitor = ObjectSynchronizer::inflate(Self, obj); | |
632 // Load displaced header and check it has hash code | |
633 mark = monitor->header(); | |
634 assert (mark->is_neutral(), "invariant") ; | |
635 hash = mark->hash(); | |
636 if (hash == 0) { | |
637 hash = get_next_hash(Self, obj); | |
638 temp = mark->copy_set_hash(hash); // merge hash code into header | |
639 assert (temp->is_neutral(), "invariant") ; | |
640 test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark); | |
641 if (test != mark) { | |
642 // The only update to the header in the monitor (outside GC) | |
643 // is install the hash code. If someone add new usage of | |
644 // displaced header, please update this code | |
645 hash = test->hash(); | |
646 assert (test->is_neutral(), "invariant") ; | |
647 assert (hash != 0, "Trivial unexpected object/monitor header usage."); | |
648 } | |
649 } | |
650 // We finally get the hash | |
651 return hash; | |
0 | 652 } |
653 | |
1878 | 654 // Deprecated -- use FastHashCode() instead. |
0 | 655 |
1878 | 656 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) { |
657 return FastHashCode (Thread::current(), obj()) ; | |
0 | 658 } |
659 | |
660 | |
1878 | 661 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread, |
662 Handle h_obj) { | |
663 if (UseBiasedLocking) { | |
664 BiasedLocking::revoke_and_rebias(h_obj, false, thread); | |
665 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
666 } | |
667 | |
668 assert(thread == JavaThread::current(), "Can only be called on current thread"); | |
669 oop obj = h_obj(); | |
670 | |
671 markOop mark = ReadStableMark (obj) ; | |
0 | 672 |
1878 | 673 // Uncontended case, header points to stack |
674 if (mark->has_locker()) { | |
675 return thread->is_lock_owned((address)mark->locker()); | |
0 | 676 } |
1878 | 677 // Contended case, header points to ObjectMonitor (tagged pointer) |
678 if (mark->has_monitor()) { | |
679 ObjectMonitor* monitor = mark->monitor(); | |
680 return monitor->is_entered(thread) != 0 ; | |
0 | 681 } |
1878 | 682 // Unlocked case, header in place |
683 assert(mark->is_neutral(), "sanity check"); | |
684 return false; | |
0 | 685 } |
686 | |
1878 | 687 // Be aware of this method could revoke bias of the lock object. |
688 // This method querys the ownership of the lock handle specified by 'h_obj'. | |
689 // If the current thread owns the lock, it returns owner_self. If no | |
690 // thread owns the lock, it returns owner_none. Otherwise, it will return | |
691 // ower_other. | |
692 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership | |
693 (JavaThread *self, Handle h_obj) { | |
694 // The caller must beware this method can revoke bias, and | |
695 // revocation can result in a safepoint. | |
696 assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ; | |
697 assert (self->thread_state() != _thread_blocked , "invariant") ; | |
0 | 698 |
1878 | 699 // Possible mark states: neutral, biased, stack-locked, inflated |
700 | |
701 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) { | |
702 // CASE: biased | |
703 BiasedLocking::revoke_and_rebias(h_obj, false, self); | |
704 assert(!h_obj->mark()->has_bias_pattern(), | |
705 "biases should be revoked by now"); | |
706 } | |
0 | 707 |
1878 | 708 assert(self == JavaThread::current(), "Can only be called on current thread"); |
709 oop obj = h_obj(); | |
710 markOop mark = ReadStableMark (obj) ; | |
711 | |
712 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack. | |
713 if (mark->has_locker()) { | |
714 return self->is_lock_owned((address)mark->locker()) ? | |
715 owner_self : owner_other; | |
716 } | |
0 | 717 |
1878 | 718 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor. |
719 // The Object:ObjectMonitor relationship is stable as long as we're | |
720 // not at a safepoint. | |
721 if (mark->has_monitor()) { | |
722 void * owner = mark->monitor()->_owner ; | |
723 if (owner == NULL) return owner_none ; | |
724 return (owner == self || | |
725 self->is_lock_owned((address)owner)) ? owner_self : owner_other; | |
726 } | |
727 | |
728 // CASE: neutral | |
729 assert(mark->is_neutral(), "sanity check"); | |
730 return owner_none ; // it's unlocked | |
731 } | |
0 | 732 |
1878 | 733 // FIXME: jvmti should call this |
734 JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) { | |
735 if (UseBiasedLocking) { | |
736 if (SafepointSynchronize::is_at_safepoint()) { | |
737 BiasedLocking::revoke_at_safepoint(h_obj); | |
738 } else { | |
739 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current()); | |
740 } | |
741 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
742 } | |
743 | |
744 oop obj = h_obj(); | |
745 address owner = NULL; | |
746 | |
747 markOop mark = ReadStableMark (obj) ; | |
748 | |
749 // Uncontended case, header points to stack | |
750 if (mark->has_locker()) { | |
751 owner = (address) mark->locker(); | |
752 } | |
753 | |
754 // Contended case, header points to ObjectMonitor (tagged pointer) | |
755 if (mark->has_monitor()) { | |
756 ObjectMonitor* monitor = mark->monitor(); | |
757 assert(monitor != NULL, "monitor should be non-null"); | |
758 owner = (address) monitor->owner(); | |
759 } | |
760 | |
761 if (owner != NULL) { | |
762 return Threads::owning_thread_from_monitor_owner(owner, doLock); | |
763 } | |
764 | |
765 // Unlocked case, header in place | |
766 // Cannot have assertion since this object may have been | |
767 // locked by another thread when reaching here. | |
768 // assert(mark->is_neutral(), "sanity check"); | |
769 | |
770 return NULL; | |
771 } | |
772 // Visitors ... | |
773 | |
774 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) { | |
775 ObjectMonitor* block = gBlockList; | |
776 ObjectMonitor* mid; | |
777 while (block) { | |
778 assert(block->object() == CHAINMARKER, "must be a block header"); | |
779 for (int i = _BLOCKSIZE - 1; i > 0; i--) { | |
780 mid = block + i; | |
781 oop object = (oop) mid->object(); | |
782 if (object != NULL) { | |
783 closure->do_monitor(mid); | |
784 } | |
785 } | |
786 block = (ObjectMonitor*) block->FreeNext; | |
0 | 787 } |
788 } | |
789 | |
1878 | 790 // Get the next block in the block list. |
791 static inline ObjectMonitor* next(ObjectMonitor* block) { | |
792 assert(block->object() == CHAINMARKER, "must be a block header"); | |
793 block = block->FreeNext ; | |
794 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header"); | |
795 return block; | |
0 | 796 } |
797 | |
798 | |
1878 | 799 void ObjectSynchronizer::oops_do(OopClosure* f) { |
800 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); | |
801 for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) { | |
802 assert(block->object() == CHAINMARKER, "must be a block header"); | |
803 for (int i = 1; i < _BLOCKSIZE; i++) { | |
804 ObjectMonitor* mid = &block[i]; | |
805 if (mid->object() != NULL) { | |
806 f->do_oop((oop*)mid->object_addr()); | |
0 | 807 } |
808 } | |
809 } | |
810 } | |
811 | |
812 | |
1878 | 813 // ----------------------------------------------------------------------------- |
0 | 814 // ObjectMonitor Lifecycle |
815 // ----------------------- | |
816 // Inflation unlinks monitors from the global gFreeList and | |
817 // associates them with objects. Deflation -- which occurs at | |
818 // STW-time -- disassociates idle monitors from objects. Such | |
819 // scavenged monitors are returned to the gFreeList. | |
820 // | |
821 // The global list is protected by ListLock. All the critical sections | |
822 // are short and operate in constant-time. | |
823 // | |
824 // ObjectMonitors reside in type-stable memory (TSM) and are immortal. | |
825 // | |
826 // Lifecycle: | |
827 // -- unassigned and on the global free list | |
828 // -- unassigned and on a thread's private omFreeList | |
829 // -- assigned to an object. The object is inflated and the mark refers | |
830 // to the objectmonitor. | |
831 // | |
832 | |
833 | |
1587 | 834 // Constraining monitor pool growth via MonitorBound ... |
835 // | |
836 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the | |
837 // the rate of scavenging is driven primarily by GC. As such, we can find | |
838 // an inordinate number of monitors in circulation. | |
839 // To avoid that scenario we can artificially induce a STW safepoint | |
840 // if the pool appears to be growing past some reasonable bound. | |
841 // Generally we favor time in space-time tradeoffs, but as there's no | |
842 // natural back-pressure on the # of extant monitors we need to impose some | |
843 // type of limit. Beware that if MonitorBound is set to too low a value | |
844 // we could just loop. In addition, if MonitorBound is set to a low value | |
845 // we'll incur more safepoints, which are harmful to performance. | |
846 // See also: GuaranteedSafepointInterval | |
847 // | |
848 // The current implementation uses asynchronous VM operations. | |
849 // | |
850 | |
851 static void InduceScavenge (Thread * Self, const char * Whence) { | |
852 // Induce STW safepoint to trim monitors | |
853 // Ultimately, this results in a call to deflate_idle_monitors() in the near future. | |
854 // More precisely, trigger an asynchronous STW safepoint as the number | |
855 // of active monitors passes the specified threshold. | |
856 // TODO: assert thread state is reasonable | |
857 | |
858 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) { | |
1878 | 859 if (ObjectMonitor::Knob_Verbose) { |
1587 | 860 ::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ; |
861 ::fflush(stdout) ; | |
862 } | |
863 // Induce a 'null' safepoint to scavenge monitors | |
864 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted | |
865 // to the VMthread and have a lifespan longer than that of this activation record. | |
866 // The VMThread will delete the op when completed. | |
867 VMThread::execute (new VM_ForceAsyncSafepoint()) ; | |
868 | |
1878 | 869 if (ObjectMonitor::Knob_Verbose) { |
1587 | 870 ::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ; |
871 ::fflush(stdout) ; | |
872 } | |
873 } | |
874 } | |
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875 /* Too slow for general assert or debug |
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876 void ObjectSynchronizer::verifyInUse (Thread *Self) { |
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877 ObjectMonitor* mid; |
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878 int inusetally = 0; |
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879 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) { |
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880 inusetally ++; |
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881 } |
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882 assert(inusetally == Self->omInUseCount, "inuse count off"); |
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883 |
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884 int freetally = 0; |
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885 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) { |
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886 freetally ++; |
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887 } |
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888 assert(freetally == Self->omFreeCount, "free count off"); |
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889 } |
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890 */ |
0 | 891 ObjectMonitor * ATTR ObjectSynchronizer::omAlloc (Thread * Self) { |
892 // A large MAXPRIVATE value reduces both list lock contention | |
893 // and list coherency traffic, but also tends to increase the | |
894 // number of objectMonitors in circulation as well as the STW | |
895 // scavenge costs. As usual, we lean toward time in space-time | |
896 // tradeoffs. | |
897 const int MAXPRIVATE = 1024 ; | |
898 for (;;) { | |
899 ObjectMonitor * m ; | |
900 | |
901 // 1: try to allocate from the thread's local omFreeList. | |
902 // Threads will attempt to allocate first from their local list, then | |
903 // from the global list, and only after those attempts fail will the thread | |
904 // attempt to instantiate new monitors. Thread-local free lists take | |
905 // heat off the ListLock and improve allocation latency, as well as reducing | |
906 // coherency traffic on the shared global list. | |
907 m = Self->omFreeList ; | |
908 if (m != NULL) { | |
909 Self->omFreeList = m->FreeNext ; | |
910 Self->omFreeCount -- ; | |
911 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene | |
912 guarantee (m->object() == NULL, "invariant") ; | |
1587 | 913 if (MonitorInUseLists) { |
914 m->FreeNext = Self->omInUseList; | |
915 Self->omInUseList = m; | |
916 Self->omInUseCount ++; | |
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917 // verifyInUse(Self); |
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918 } else { |
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919 m->FreeNext = NULL; |
1587 | 920 } |
0 | 921 return m ; |
922 } | |
923 | |
924 // 2: try to allocate from the global gFreeList | |
925 // CONSIDER: use muxTry() instead of muxAcquire(). | |
926 // If the muxTry() fails then drop immediately into case 3. | |
927 // If we're using thread-local free lists then try | |
928 // to reprovision the caller's free list. | |
929 if (gFreeList != NULL) { | |
930 // Reprovision the thread's omFreeList. | |
931 // Use bulk transfers to reduce the allocation rate and heat | |
932 // on various locks. | |
933 Thread::muxAcquire (&ListLock, "omAlloc") ; | |
934 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL; ) { | |
1587 | 935 MonitorFreeCount --; |
0 | 936 ObjectMonitor * take = gFreeList ; |
937 gFreeList = take->FreeNext ; | |
938 guarantee (take->object() == NULL, "invariant") ; | |
939 guarantee (!take->is_busy(), "invariant") ; | |
940 take->Recycle() ; | |
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941 omRelease (Self, take, false) ; |
0 | 942 } |
943 Thread::muxRelease (&ListLock) ; | |
944 Self->omFreeProvision += 1 + (Self->omFreeProvision/2) ; | |
945 if (Self->omFreeProvision > MAXPRIVATE ) Self->omFreeProvision = MAXPRIVATE ; | |
946 TEVENT (omFirst - reprovision) ; | |
1587 | 947 |
948 const int mx = MonitorBound ; | |
949 if (mx > 0 && (MonitorPopulation-MonitorFreeCount) > mx) { | |
950 // We can't safely induce a STW safepoint from omAlloc() as our thread | |
951 // state may not be appropriate for such activities and callers may hold | |
952 // naked oops, so instead we defer the action. | |
953 InduceScavenge (Self, "omAlloc") ; | |
954 } | |
955 continue; | |
0 | 956 } |
957 | |
958 // 3: allocate a block of new ObjectMonitors | |
959 // Both the local and global free lists are empty -- resort to malloc(). | |
960 // In the current implementation objectMonitors are TSM - immortal. | |
961 assert (_BLOCKSIZE > 1, "invariant") ; | |
962 ObjectMonitor * temp = new ObjectMonitor[_BLOCKSIZE]; | |
963 | |
964 // NOTE: (almost) no way to recover if allocation failed. | |
965 // We might be able to induce a STW safepoint and scavenge enough | |
966 // objectMonitors to permit progress. | |
967 if (temp == NULL) { | |
968 vm_exit_out_of_memory (sizeof (ObjectMonitor[_BLOCKSIZE]), "Allocate ObjectMonitors") ; | |
969 } | |
970 | |
971 // Format the block. | |
972 // initialize the linked list, each monitor points to its next | |
973 // forming the single linked free list, the very first monitor | |
974 // will points to next block, which forms the block list. | |
975 // The trick of using the 1st element in the block as gBlockList | |
976 // linkage should be reconsidered. A better implementation would | |
977 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; } | |
978 | |
979 for (int i = 1; i < _BLOCKSIZE ; i++) { | |
980 temp[i].FreeNext = &temp[i+1]; | |
981 } | |
982 | |
983 // terminate the last monitor as the end of list | |
984 temp[_BLOCKSIZE - 1].FreeNext = NULL ; | |
985 | |
986 // Element [0] is reserved for global list linkage | |
987 temp[0].set_object(CHAINMARKER); | |
988 | |
989 // Consider carving out this thread's current request from the | |
990 // block in hand. This avoids some lock traffic and redundant | |
991 // list activity. | |
992 | |
993 // Acquire the ListLock to manipulate BlockList and FreeList. | |
994 // An Oyama-Taura-Yonezawa scheme might be more efficient. | |
995 Thread::muxAcquire (&ListLock, "omAlloc [2]") ; | |
1587 | 996 MonitorPopulation += _BLOCKSIZE-1; |
997 MonitorFreeCount += _BLOCKSIZE-1; | |
0 | 998 |
999 // Add the new block to the list of extant blocks (gBlockList). | |
1000 // The very first objectMonitor in a block is reserved and dedicated. | |
1001 // It serves as blocklist "next" linkage. | |
1002 temp[0].FreeNext = gBlockList; | |
1003 gBlockList = temp; | |
1004 | |
1005 // Add the new string of objectMonitors to the global free list | |
1006 temp[_BLOCKSIZE - 1].FreeNext = gFreeList ; | |
1007 gFreeList = temp + 1; | |
1008 Thread::muxRelease (&ListLock) ; | |
1009 TEVENT (Allocate block of monitors) ; | |
1010 } | |
1011 } | |
1012 | |
1013 // Place "m" on the caller's private per-thread omFreeList. | |
1014 // In practice there's no need to clamp or limit the number of | |
1015 // monitors on a thread's omFreeList as the only time we'll call | |
1016 // omRelease is to return a monitor to the free list after a CAS | |
1017 // attempt failed. This doesn't allow unbounded #s of monitors to | |
1018 // accumulate on a thread's free list. | |
1019 // | |
1020 | |
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1021 void ObjectSynchronizer::omRelease (Thread * Self, ObjectMonitor * m, bool fromPerThreadAlloc) { |
0 | 1022 guarantee (m->object() == NULL, "invariant") ; |
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1023 |
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1024 // Remove from omInUseList |
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1025 if (MonitorInUseLists && fromPerThreadAlloc) { |
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1026 ObjectMonitor* curmidinuse = NULL; |
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1027 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; ) { |
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1028 if (m == mid) { |
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1029 // extract from per-thread in-use-list |
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1030 if (mid == Self->omInUseList) { |
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1031 Self->omInUseList = mid->FreeNext; |
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1032 } else if (curmidinuse != NULL) { |
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1033 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist |
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1034 } |
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1035 Self->omInUseCount --; |
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1036 // verifyInUse(Self); |
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1037 break; |
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1038 } else { |
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1039 curmidinuse = mid; |
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1040 mid = mid->FreeNext; |
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1041 } |
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1042 } |
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1043 } |
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1044 |
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1045 // FreeNext is used for both onInUseList and omFreeList, so clear old before setting new |
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1046 m->FreeNext = Self->omFreeList ; |
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1047 Self->omFreeList = m ; |
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1048 Self->omFreeCount ++ ; |
0 | 1049 } |
1050 | |
1051 // Return the monitors of a moribund thread's local free list to | |
1052 // the global free list. Typically a thread calls omFlush() when | |
1053 // it's dying. We could also consider having the VM thread steal | |
1054 // monitors from threads that have not run java code over a few | |
1055 // consecutive STW safepoints. Relatedly, we might decay | |
1056 // omFreeProvision at STW safepoints. | |
1057 // | |
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1058 // Also return the monitors of a moribund thread"s omInUseList to |
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1059 // a global gOmInUseList under the global list lock so these |
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1060 // will continue to be scanned. |
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1061 // |
0 | 1062 // We currently call omFlush() from the Thread:: dtor _after the thread |
1063 // has been excised from the thread list and is no longer a mutator. | |
1064 // That means that omFlush() can run concurrently with a safepoint and | |
1065 // the scavenge operator. Calling omFlush() from JavaThread::exit() might | |
1066 // be a better choice as we could safely reason that that the JVM is | |
1067 // not at a safepoint at the time of the call, and thus there could | |
1068 // be not inopportune interleavings between omFlush() and the scavenge | |
1069 // operator. | |
1070 | |
1071 void ObjectSynchronizer::omFlush (Thread * Self) { | |
1072 ObjectMonitor * List = Self->omFreeList ; // Null-terminated SLL | |
1073 Self->omFreeList = NULL ; | |
1074 ObjectMonitor * Tail = NULL ; | |
1587 | 1075 int Tally = 0; |
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1076 if (List != NULL) { |
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1077 ObjectMonitor * s ; |
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1078 for (s = List ; s != NULL ; s = s->FreeNext) { |
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1079 Tally ++ ; |
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1080 Tail = s ; |
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1081 guarantee (s->object() == NULL, "invariant") ; |
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1082 guarantee (!s->is_busy(), "invariant") ; |
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1083 s->set_owner (NULL) ; // redundant but good hygiene |
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1084 TEVENT (omFlush - Move one) ; |
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1085 } |
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1086 guarantee (Tail != NULL && List != NULL, "invariant") ; |
0 | 1087 } |
1088 | |
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1089 ObjectMonitor * InUseList = Self->omInUseList; |
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1090 ObjectMonitor * InUseTail = NULL ; |
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1091 int InUseTally = 0; |
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1092 if (InUseList != NULL) { |
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1093 Self->omInUseList = NULL; |
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1094 ObjectMonitor *curom; |
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1095 for (curom = InUseList; curom != NULL; curom = curom->FreeNext) { |
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1096 InUseTail = curom; |
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1097 InUseTally++; |
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1098 } |
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1099 // TODO debug |
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1100 assert(Self->omInUseCount == InUseTally, "inuse count off"); |
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1101 Self->omInUseCount = 0; |
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1102 guarantee (InUseTail != NULL && InUseList != NULL, "invariant"); |
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1103 } |
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1104 |
0 | 1105 Thread::muxAcquire (&ListLock, "omFlush") ; |
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1106 if (Tail != NULL) { |
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1107 Tail->FreeNext = gFreeList ; |
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1108 gFreeList = List ; |
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1109 MonitorFreeCount += Tally; |
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1110 } |
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1111 |
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1112 if (InUseTail != NULL) { |
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1113 InUseTail->FreeNext = gOmInUseList; |
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1114 gOmInUseList = InUseList; |
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1115 gOmInUseCount += InUseTally; |
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1116 } |
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1117 |
0 | 1118 Thread::muxRelease (&ListLock) ; |
1119 TEVENT (omFlush) ; | |
1120 } | |
1121 | |
1122 // Fast path code shared by multiple functions | |
1123 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) { | |
1124 markOop mark = obj->mark(); | |
1125 if (mark->has_monitor()) { | |
1126 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid"); | |
1127 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header"); | |
1128 return mark->monitor(); | |
1129 } | |
1130 return ObjectSynchronizer::inflate(Thread::current(), obj); | |
1131 } | |
1132 | |
1878 | 1133 |
0 | 1134 // Note that we could encounter some performance loss through false-sharing as |
1135 // multiple locks occupy the same $ line. Padding might be appropriate. | |
1136 | |
1137 | |
1138 ObjectMonitor * ATTR ObjectSynchronizer::inflate (Thread * Self, oop object) { | |
1139 // Inflate mutates the heap ... | |
1140 // Relaxing assertion for bug 6320749. | |
1141 assert (Universe::verify_in_progress() || | |
1142 !SafepointSynchronize::is_at_safepoint(), "invariant") ; | |
1143 | |
1144 for (;;) { | |
1145 const markOop mark = object->mark() ; | |
1146 assert (!mark->has_bias_pattern(), "invariant") ; | |
1147 | |
1148 // The mark can be in one of the following states: | |
1149 // * Inflated - just return | |
1150 // * Stack-locked - coerce it to inflated | |
1151 // * INFLATING - busy wait for conversion to complete | |
1152 // * Neutral - aggressively inflate the object. | |
1153 // * BIASED - Illegal. We should never see this | |
1154 | |
1155 // CASE: inflated | |
1156 if (mark->has_monitor()) { | |
1157 ObjectMonitor * inf = mark->monitor() ; | |
1158 assert (inf->header()->is_neutral(), "invariant"); | |
1159 assert (inf->object() == object, "invariant") ; | |
1160 assert (ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid"); | |
1161 return inf ; | |
1162 } | |
1163 | |
1164 // CASE: inflation in progress - inflating over a stack-lock. | |
1165 // Some other thread is converting from stack-locked to inflated. | |
1166 // Only that thread can complete inflation -- other threads must wait. | |
1167 // The INFLATING value is transient. | |
1168 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish. | |
1169 // We could always eliminate polling by parking the thread on some auxiliary list. | |
1170 if (mark == markOopDesc::INFLATING()) { | |
1171 TEVENT (Inflate: spin while INFLATING) ; | |
1172 ReadStableMark(object) ; | |
1173 continue ; | |
1174 } | |
1175 | |
1176 // CASE: stack-locked | |
1177 // Could be stack-locked either by this thread or by some other thread. | |
1178 // | |
1179 // Note that we allocate the objectmonitor speculatively, _before_ attempting | |
1180 // to install INFLATING into the mark word. We originally installed INFLATING, | |
1181 // allocated the objectmonitor, and then finally STed the address of the | |
1182 // objectmonitor into the mark. This was correct, but artificially lengthened | |
1183 // the interval in which INFLATED appeared in the mark, thus increasing | |
1184 // the odds of inflation contention. | |
1185 // | |
1186 // We now use per-thread private objectmonitor free lists. | |
1187 // These list are reprovisioned from the global free list outside the | |
1188 // critical INFLATING...ST interval. A thread can transfer | |
1189 // multiple objectmonitors en-mass from the global free list to its local free list. | |
1190 // This reduces coherency traffic and lock contention on the global free list. | |
1191 // Using such local free lists, it doesn't matter if the omAlloc() call appears | |
1192 // before or after the CAS(INFLATING) operation. | |
1193 // See the comments in omAlloc(). | |
1194 | |
1195 if (mark->has_locker()) { | |
1196 ObjectMonitor * m = omAlloc (Self) ; | |
1197 // Optimistically prepare the objectmonitor - anticipate successful CAS | |
1198 // We do this before the CAS in order to minimize the length of time | |
1199 // in which INFLATING appears in the mark. | |
1200 m->Recycle(); | |
1201 m->_Responsible = NULL ; | |
1202 m->OwnerIsThread = 0 ; | |
1203 m->_recursions = 0 ; | |
1878 | 1204 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // Consider: maintain by type/class |
0 | 1205 |
1206 markOop cmp = (markOop) Atomic::cmpxchg_ptr (markOopDesc::INFLATING(), object->mark_addr(), mark) ; | |
1207 if (cmp != mark) { | |
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1208 omRelease (Self, m, true) ; |
0 | 1209 continue ; // Interference -- just retry |
1210 } | |
1211 | |
1212 // We've successfully installed INFLATING (0) into the mark-word. | |
1213 // This is the only case where 0 will appear in a mark-work. | |
1214 // Only the singular thread that successfully swings the mark-word | |
1215 // to 0 can perform (or more precisely, complete) inflation. | |
1216 // | |
1217 // Why do we CAS a 0 into the mark-word instead of just CASing the | |
1218 // mark-word from the stack-locked value directly to the new inflated state? | |
1219 // Consider what happens when a thread unlocks a stack-locked object. | |
1220 // It attempts to use CAS to swing the displaced header value from the | |
1221 // on-stack basiclock back into the object header. Recall also that the | |
1222 // header value (hashcode, etc) can reside in (a) the object header, or | |
1223 // (b) a displaced header associated with the stack-lock, or (c) a displaced | |
1224 // header in an objectMonitor. The inflate() routine must copy the header | |
1225 // value from the basiclock on the owner's stack to the objectMonitor, all | |
1226 // the while preserving the hashCode stability invariants. If the owner | |
1227 // decides to release the lock while the value is 0, the unlock will fail | |
1228 // and control will eventually pass from slow_exit() to inflate. The owner | |
1229 // will then spin, waiting for the 0 value to disappear. Put another way, | |
1230 // the 0 causes the owner to stall if the owner happens to try to | |
1231 // drop the lock (restoring the header from the basiclock to the object) | |
1232 // while inflation is in-progress. This protocol avoids races that might | |
1233 // would otherwise permit hashCode values to change or "flicker" for an object. | |
1234 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable. | |
1235 // 0 serves as a "BUSY" inflate-in-progress indicator. | |
1236 | |
1237 | |
1238 // fetch the displaced mark from the owner's stack. | |
1239 // The owner can't die or unwind past the lock while our INFLATING | |
1240 // object is in the mark. Furthermore the owner can't complete | |
1241 // an unlock on the object, either. | |
1242 markOop dmw = mark->displaced_mark_helper() ; | |
1243 assert (dmw->is_neutral(), "invariant") ; | |
1244 | |
1245 // Setup monitor fields to proper values -- prepare the monitor | |
1246 m->set_header(dmw) ; | |
1247 | |
1248 // Optimization: if the mark->locker stack address is associated | |
1249 // with this thread we could simply set m->_owner = Self and | |
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1250 // m->OwnerIsThread = 1. Note that a thread can inflate an object |
0 | 1251 // that it has stack-locked -- as might happen in wait() -- directly |
1252 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom. | |
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1253 m->set_owner(mark->locker()); |
0 | 1254 m->set_object(object); |
1255 // TODO-FIXME: assert BasicLock->dhw != 0. | |
1256 | |
1257 // Must preserve store ordering. The monitor state must | |
1258 // be stable at the time of publishing the monitor address. | |
1259 guarantee (object->mark() == markOopDesc::INFLATING(), "invariant") ; | |
1260 object->release_set_mark(markOopDesc::encode(m)); | |
1261 | |
1262 // Hopefully the performance counters are allocated on distinct cache lines | |
1263 // to avoid false sharing on MP systems ... | |
1878 | 1264 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ; |
0 | 1265 TEVENT(Inflate: overwrite stacklock) ; |
1266 if (TraceMonitorInflation) { | |
1267 if (object->is_instance()) { | |
1268 ResourceMark rm; | |
1269 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", | |
1270 (intptr_t) object, (intptr_t) object->mark(), | |
1271 Klass::cast(object->klass())->external_name()); | |
1272 } | |
1273 } | |
1274 return m ; | |
1275 } | |
1276 | |
1277 // CASE: neutral | |
1278 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner. | |
1279 // If we know we're inflating for entry it's better to inflate by swinging a | |
1280 // pre-locked objectMonitor pointer into the object header. A successful | |
1281 // CAS inflates the object *and* confers ownership to the inflating thread. | |
1282 // In the current implementation we use a 2-step mechanism where we CAS() | |
1283 // to inflate and then CAS() again to try to swing _owner from NULL to Self. | |
1284 // An inflateTry() method that we could call from fast_enter() and slow_enter() | |
1285 // would be useful. | |
1286 | |
1287 assert (mark->is_neutral(), "invariant"); | |
1288 ObjectMonitor * m = omAlloc (Self) ; | |
1289 // prepare m for installation - set monitor to initial state | |
1290 m->Recycle(); | |
1291 m->set_header(mark); | |
1292 m->set_owner(NULL); | |
1293 m->set_object(object); | |
1294 m->OwnerIsThread = 1 ; | |
1295 m->_recursions = 0 ; | |
1296 m->_Responsible = NULL ; | |
1878 | 1297 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // consider: keep metastats by type/class |
0 | 1298 |
1299 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) { | |
1300 m->set_object (NULL) ; | |
1301 m->set_owner (NULL) ; | |
1302 m->OwnerIsThread = 0 ; | |
1303 m->Recycle() ; | |
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1304 omRelease (Self, m, true) ; |
0 | 1305 m = NULL ; |
1306 continue ; | |
1307 // interference - the markword changed - just retry. | |
1308 // The state-transitions are one-way, so there's no chance of | |
1309 // live-lock -- "Inflated" is an absorbing state. | |
1310 } | |
1311 | |
1312 // Hopefully the performance counters are allocated on distinct | |
1313 // cache lines to avoid false sharing on MP systems ... | |
1878 | 1314 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ; |
0 | 1315 TEVENT(Inflate: overwrite neutral) ; |
1316 if (TraceMonitorInflation) { | |
1317 if (object->is_instance()) { | |
1318 ResourceMark rm; | |
1319 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", | |
1320 (intptr_t) object, (intptr_t) object->mark(), | |
1321 Klass::cast(object->klass())->external_name()); | |
1322 } | |
1323 } | |
1324 return m ; | |
1325 } | |
1326 } | |
1327 | |
1878 | 1328 // Note that we could encounter some performance loss through false-sharing as |
1329 // multiple locks occupy the same $ line. Padding might be appropriate. | |
0 | 1330 |
1331 | |
1332 // Deflate_idle_monitors() is called at all safepoints, immediately | |
1333 // after all mutators are stopped, but before any objects have moved. | |
1334 // It traverses the list of known monitors, deflating where possible. | |
1335 // The scavenged monitor are returned to the monitor free list. | |
1336 // | |
1337 // Beware that we scavenge at *every* stop-the-world point. | |
1338 // Having a large number of monitors in-circulation negatively | |
1339 // impacts the performance of some applications (e.g., PointBase). | |
1340 // Broadly, we want to minimize the # of monitors in circulation. | |
1587 | 1341 // |
1342 // We have added a flag, MonitorInUseLists, which creates a list | |
1343 // of active monitors for each thread. deflate_idle_monitors() | |
1344 // only scans the per-thread inuse lists. omAlloc() puts all | |
1345 // assigned monitors on the per-thread list. deflate_idle_monitors() | |
1346 // returns the non-busy monitors to the global free list. | |
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1347 // When a thread dies, omFlush() adds the list of active monitors for |
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1348 // that thread to a global gOmInUseList acquiring the |
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1349 // global list lock. deflate_idle_monitors() acquires the global |
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1350 // list lock to scan for non-busy monitors to the global free list. |
1587 | 1351 // An alternative could have used a single global inuse list. The |
1352 // downside would have been the additional cost of acquiring the global list lock | |
1353 // for every omAlloc(). | |
0 | 1354 // |
1355 // Perversely, the heap size -- and thus the STW safepoint rate -- | |
1356 // typically drives the scavenge rate. Large heaps can mean infrequent GC, | |
1357 // which in turn can mean large(r) numbers of objectmonitors in circulation. | |
1358 // This is an unfortunate aspect of this design. | |
1359 // | |
1360 | |
1878 | 1361 enum ManifestConstants { |
1362 ClearResponsibleAtSTW = 0, | |
1363 MaximumRecheckInterval = 1000 | |
1364 } ; | |
1587 | 1365 |
1366 // Deflate a single monitor if not in use | |
1367 // Return true if deflated, false if in use | |
1368 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj, | |
1369 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) { | |
1370 bool deflated; | |
1371 // Normal case ... The monitor is associated with obj. | |
1372 guarantee (obj->mark() == markOopDesc::encode(mid), "invariant") ; | |
1373 guarantee (mid == obj->mark()->monitor(), "invariant"); | |
1374 guarantee (mid->header()->is_neutral(), "invariant"); | |
1375 | |
1376 if (mid->is_busy()) { | |
1377 if (ClearResponsibleAtSTW) mid->_Responsible = NULL ; | |
1378 deflated = false; | |
1379 } else { | |
1380 // Deflate the monitor if it is no longer being used | |
1381 // It's idle - scavenge and return to the global free list | |
1382 // plain old deflation ... | |
1383 TEVENT (deflate_idle_monitors - scavenge1) ; | |
1384 if (TraceMonitorInflation) { | |
1385 if (obj->is_instance()) { | |
1386 ResourceMark rm; | |
1387 tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", | |
1388 (intptr_t) obj, (intptr_t) obj->mark(), Klass::cast(obj->klass())->external_name()); | |
1389 } | |
1390 } | |
1391 | |
1392 // Restore the header back to obj | |
1393 obj->release_set_mark(mid->header()); | |
1394 mid->clear(); | |
1395 | |
1396 assert (mid->object() == NULL, "invariant") ; | |
1397 | |
1398 // Move the object to the working free list defined by FreeHead,FreeTail. | |
1399 if (*FreeHeadp == NULL) *FreeHeadp = mid; | |
1400 if (*FreeTailp != NULL) { | |
1401 ObjectMonitor * prevtail = *FreeTailp; | |
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1402 assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); // TODO KK |
1587 | 1403 prevtail->FreeNext = mid; |
1404 } | |
1405 *FreeTailp = mid; | |
1406 deflated = true; | |
1407 } | |
1408 return deflated; | |
1409 } | |
1410 | |
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1411 // Caller acquires ListLock |
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1412 int ObjectSynchronizer::walk_monitor_list(ObjectMonitor** listheadp, |
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1413 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) { |
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1414 ObjectMonitor* mid; |
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1415 ObjectMonitor* next; |
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1416 ObjectMonitor* curmidinuse = NULL; |
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1417 int deflatedcount = 0; |
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1418 |
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1419 for (mid = *listheadp; mid != NULL; ) { |
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1420 oop obj = (oop) mid->object(); |
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1421 bool deflated = false; |
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1422 if (obj != NULL) { |
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1423 deflated = deflate_monitor(mid, obj, FreeHeadp, FreeTailp); |
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1424 } |
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1425 if (deflated) { |
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1426 // extract from per-thread in-use-list |
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1427 if (mid == *listheadp) { |
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1428 *listheadp = mid->FreeNext; |
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1429 } else if (curmidinuse != NULL) { |
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1430 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist |
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1431 } |
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1432 next = mid->FreeNext; |
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1433 mid->FreeNext = NULL; // This mid is current tail in the FreeHead list |
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1434 mid = next; |
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1435 deflatedcount++; |
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1436 } else { |
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1437 curmidinuse = mid; |
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1438 mid = mid->FreeNext; |
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1439 } |
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1440 } |
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1441 return deflatedcount; |
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1442 } |
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1443 |
0 | 1444 void ObjectSynchronizer::deflate_idle_monitors() { |
1445 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); | |
1446 int nInuse = 0 ; // currently associated with objects | |
1447 int nInCirculation = 0 ; // extant | |
1448 int nScavenged = 0 ; // reclaimed | |
1587 | 1449 bool deflated = false; |
0 | 1450 |
1451 ObjectMonitor * FreeHead = NULL ; // Local SLL of scavenged monitors | |
1452 ObjectMonitor * FreeTail = NULL ; | |
1453 | |
1587 | 1454 TEVENT (deflate_idle_monitors) ; |
1455 // Prevent omFlush from changing mids in Thread dtor's during deflation | |
1456 // And in case the vm thread is acquiring a lock during a safepoint | |
1457 // See e.g. 6320749 | |
1458 Thread::muxAcquire (&ListLock, "scavenge - return") ; | |
1459 | |
1460 if (MonitorInUseLists) { | |
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1461 int inUse = 0; |
1587 | 1462 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) { |
1640
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1463 nInCirculation+= cur->omInUseCount; |
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1464 int deflatedcount = walk_monitor_list(cur->omInUseList_addr(), &FreeHead, &FreeTail); |
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1465 cur->omInUseCount-= deflatedcount; |
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1466 // verifyInUse(cur); |
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1467 nScavenged += deflatedcount; |
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1468 nInuse += cur->omInUseCount; |
1587 | 1469 } |
1640
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1470 |
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1471 // For moribund threads, scan gOmInUseList |
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1472 if (gOmInUseList) { |
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1473 nInCirculation += gOmInUseCount; |
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1474 int deflatedcount = walk_monitor_list((ObjectMonitor **)&gOmInUseList, &FreeHead, &FreeTail); |
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1475 gOmInUseCount-= deflatedcount; |
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1476 nScavenged += deflatedcount; |
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1477 nInuse += gOmInUseCount; |
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1478 } |
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1479 |
1587 | 1480 } else for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) { |
0 | 1481 // Iterate over all extant monitors - Scavenge all idle monitors. |
1482 assert(block->object() == CHAINMARKER, "must be a block header"); | |
1483 nInCirculation += _BLOCKSIZE ; | |
1484 for (int i = 1 ; i < _BLOCKSIZE; i++) { | |
1485 ObjectMonitor* mid = &block[i]; | |
1486 oop obj = (oop) mid->object(); | |
1487 | |
1488 if (obj == NULL) { | |
1489 // The monitor is not associated with an object. | |
1490 // The monitor should either be a thread-specific private | |
1491 // free list or the global free list. | |
1492 // obj == NULL IMPLIES mid->is_busy() == 0 | |
1493 guarantee (!mid->is_busy(), "invariant") ; | |
1494 continue ; | |
1495 } | |
1587 | 1496 deflated = deflate_monitor(mid, obj, &FreeHead, &FreeTail); |
1497 | |
1498 if (deflated) { | |
1499 mid->FreeNext = NULL ; | |
1500 nScavenged ++ ; | |
0 | 1501 } else { |
1587 | 1502 nInuse ++; |
0 | 1503 } |
1504 } | |
1505 } | |
1506 | |
1587 | 1507 MonitorFreeCount += nScavenged; |
1508 | |
1509 // Consider: audit gFreeList to ensure that MonitorFreeCount and list agree. | |
1510 | |
1878 | 1511 if (ObjectMonitor::Knob_Verbose) { |
1587 | 1512 ::printf ("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n", |
1513 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge, | |
1514 MonitorPopulation, MonitorFreeCount) ; | |
1515 ::fflush(stdout) ; | |
1516 } | |
1517 | |
1518 ForceMonitorScavenge = 0; // Reset | |
1519 | |
0 | 1520 // Move the scavenged monitors back to the global free list. |
1521 if (FreeHead != NULL) { | |
1522 guarantee (FreeTail != NULL && nScavenged > 0, "invariant") ; | |
1523 assert (FreeTail->FreeNext == NULL, "invariant") ; | |
1524 // constant-time list splice - prepend scavenged segment to gFreeList | |
1525 FreeTail->FreeNext = gFreeList ; | |
1526 gFreeList = FreeHead ; | |
1527 } | |
1587 | 1528 Thread::muxRelease (&ListLock) ; |
0 | 1529 |
1878 | 1530 if (ObjectMonitor::_sync_Deflations != NULL) ObjectMonitor::_sync_Deflations->inc(nScavenged) ; |
1531 if (ObjectMonitor::_sync_MonExtant != NULL) ObjectMonitor::_sync_MonExtant ->set_value(nInCirculation); | |
0 | 1532 |
1533 // TODO: Add objectMonitor leak detection. | |
1534 // Audit/inventory the objectMonitors -- make sure they're all accounted for. | |
1535 GVars.stwRandom = os::random() ; | |
1536 GVars.stwCycle ++ ; | |
1537 } | |
1538 | |
1878 | 1539 // Monitor cleanup on JavaThread::exit |
0 | 1540 |
1878 | 1541 // Iterate through monitor cache and attempt to release thread's monitors |
1542 // Gives up on a particular monitor if an exception occurs, but continues | |
1543 // the overall iteration, swallowing the exception. | |
1544 class ReleaseJavaMonitorsClosure: public MonitorClosure { | |
1545 private: | |
1546 TRAPS; | |
0 | 1547 |
1878 | 1548 public: |
1549 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {} | |
1550 void do_monitor(ObjectMonitor* mid) { | |
1551 if (mid->owner() == THREAD) { | |
1552 (void)mid->complete_exit(CHECK); | |
0 | 1553 } |
1554 } | |
1878 | 1555 }; |
0 | 1556 |
1878 | 1557 // Release all inflated monitors owned by THREAD. Lightweight monitors are |
1558 // ignored. This is meant to be called during JNI thread detach which assumes | |
1559 // all remaining monitors are heavyweight. All exceptions are swallowed. | |
1560 // Scanning the extant monitor list can be time consuming. | |
1561 // A simple optimization is to add a per-thread flag that indicates a thread | |
1562 // called jni_monitorenter() during its lifetime. | |
0 | 1563 // |
1878 | 1564 // Instead of No_Savepoint_Verifier it might be cheaper to |
1565 // use an idiom of the form: | |
1566 // auto int tmp = SafepointSynchronize::_safepoint_counter ; | |
1567 // <code that must not run at safepoint> | |
1568 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ; | |
1569 // Since the tests are extremely cheap we could leave them enabled | |
1570 // for normal product builds. | |
0 | 1571 |
1878 | 1572 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) { |
1573 assert(THREAD == JavaThread::current(), "must be current Java thread"); | |
1574 No_Safepoint_Verifier nsv ; | |
1575 ReleaseJavaMonitorsClosure rjmc(THREAD); | |
1576 Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread"); | |
1577 ObjectSynchronizer::monitors_iterate(&rjmc); | |
1578 Thread::muxRelease(&ListLock); | |
1579 THREAD->clear_pending_exception(); | |
0 | 1580 } |
1581 | |
1582 //------------------------------------------------------------------------------ | |
1583 // Non-product code | |
1584 | |
1585 #ifndef PRODUCT | |
1586 | |
1587 void ObjectSynchronizer::trace_locking(Handle locking_obj, bool is_compiled, | |
1588 bool is_method, bool is_locking) { | |
1589 // Don't know what to do here | |
1590 } | |
1591 | |
1592 // Verify all monitors in the monitor cache, the verification is weak. | |
1593 void ObjectSynchronizer::verify() { | |
1594 ObjectMonitor* block = gBlockList; | |
1595 ObjectMonitor* mid; | |
1596 while (block) { | |
1597 assert(block->object() == CHAINMARKER, "must be a block header"); | |
1598 for (int i = 1; i < _BLOCKSIZE; i++) { | |
1599 mid = block + i; | |
1600 oop object = (oop) mid->object(); | |
1601 if (object != NULL) { | |
1602 mid->verify(); | |
1603 } | |
1604 } | |
1605 block = (ObjectMonitor*) block->FreeNext; | |
1606 } | |
1607 } | |
1608 | |
1609 // Check if monitor belongs to the monitor cache | |
1610 // The list is grow-only so it's *relatively* safe to traverse | |
1611 // the list of extant blocks without taking a lock. | |
1612 | |
1613 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) { | |
1614 ObjectMonitor* block = gBlockList; | |
1615 | |
1616 while (block) { | |
1617 assert(block->object() == CHAINMARKER, "must be a block header"); | |
1618 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) { | |
1619 address mon = (address) monitor; | |
1620 address blk = (address) block; | |
1621 size_t diff = mon - blk; | |
1622 assert((diff % sizeof(ObjectMonitor)) == 0, "check"); | |
1623 return 1; | |
1624 } | |
1625 block = (ObjectMonitor*) block->FreeNext; | |
1626 } | |
1627 return 0; | |
1628 } | |
1629 | |
1630 #endif |