Mercurial > hg > graal-compiler
annotate src/share/vm/runtime/synchronizer.cpp @ 14380:e6195383bcaf
8034080: Remove the USDT1 dtrace code from Hotspot
Reviewed-by: dholmes, coleenp
| author | sla |
|---|---|
| date | Tue, 18 Feb 2014 09:15:40 +0100 |
| parents | e7d8cbe4db3b |
| children | 28f281e8de1d |
| rev | line source |
|---|---|
| 0 | 1 /* |
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2 * Copyright (c) 1998, 2014, 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 "classfile/vmSymbols.hpp" | |
| 27 #include "memory/resourceArea.hpp" | |
| 28 #include "oops/markOop.hpp" | |
| 29 #include "oops/oop.inline.hpp" | |
| 30 #include "runtime/biasedLocking.hpp" | |
| 31 #include "runtime/handles.inline.hpp" | |
| 32 #include "runtime/interfaceSupport.hpp" | |
| 33 #include "runtime/mutexLocker.hpp" | |
| 34 #include "runtime/objectMonitor.hpp" | |
| 35 #include "runtime/objectMonitor.inline.hpp" | |
| 36 #include "runtime/osThread.hpp" | |
| 37 #include "runtime/stubRoutines.hpp" | |
| 38 #include "runtime/synchronizer.hpp" | |
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39 #include "runtime/thread.inline.hpp" |
| 1972 | 40 #include "utilities/dtrace.hpp" |
| 41 #include "utilities/events.hpp" | |
| 42 #include "utilities/preserveException.hpp" | |
| 43 #ifdef TARGET_OS_FAMILY_linux | |
| 44 # include "os_linux.inline.hpp" | |
| 45 #endif | |
| 46 #ifdef TARGET_OS_FAMILY_solaris | |
| 47 # include "os_solaris.inline.hpp" | |
| 48 #endif | |
| 49 #ifdef TARGET_OS_FAMILY_windows | |
| 50 # include "os_windows.inline.hpp" | |
| 51 #endif | |
| 3960 | 52 #ifdef TARGET_OS_FAMILY_bsd |
| 53 # include "os_bsd.inline.hpp" | |
| 54 #endif | |
| 0 | 55 |
| 7994 | 56 #if defined(__GNUC__) |
| 0 | 57 // Need to inhibit inlining for older versions of GCC to avoid build-time failures |
| 58 #define ATTR __attribute__((noinline)) | |
| 59 #else | |
| 60 #define ATTR | |
| 61 #endif | |
| 62 | |
| 63 // The "core" versions of monitor enter and exit reside in this file. | |
| 64 // The interpreter and compilers contain specialized transliterated | |
| 65 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(), | |
| 66 // for instance. If you make changes here, make sure to modify the | |
| 67 // interpreter, and both C1 and C2 fast-path inline locking code emission. | |
| 68 // | |
| 69 // | |
| 70 // ----------------------------------------------------------------------------- | |
| 71 | |
| 72 #ifdef DTRACE_ENABLED | |
| 73 | |
| 74 // Only bother with this argument setup if dtrace is available | |
| 75 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly. | |
| 76 | |
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77 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \ |
| 0 | 78 char* bytes = NULL; \ |
| 79 int len = 0; \ | |
| 80 jlong jtid = SharedRuntime::get_java_tid(thread); \ | |
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81 Symbol* klassname = ((oop)(obj))->klass()->name(); \ |
| 0 | 82 if (klassname != NULL) { \ |
| 83 bytes = (char*)klassname->bytes(); \ | |
| 84 len = klassname->utf8_length(); \ | |
| 85 } | |
| 86 | |
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87 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \ |
| 4006 | 88 { \ |
| 89 if (DTraceMonitorProbes) { \ | |
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90 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ |
| 4006 | 91 HOTSPOT_MONITOR_WAIT(jtid, \ |
| 92 (uintptr_t)(monitor), bytes, len, (millis)); \ | |
| 93 } \ | |
| 94 } | |
| 95 | |
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96 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED |
| 4006 | 97 |
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98 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \ |
| 4006 | 99 { \ |
| 100 if (DTraceMonitorProbes) { \ | |
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101 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ |
| 4006 | 102 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \ |
| 103 (uintptr_t)(monitor), bytes, len); \ | |
| 104 } \ | |
| 105 } | |
| 106 | |
| 0 | 107 #else // ndef DTRACE_ENABLED |
| 108 | |
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109 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;} |
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110 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;} |
| 0 | 111 |
| 112 #endif // ndef DTRACE_ENABLED | |
| 113 | |
| 1878 | 114 // This exists only as a workaround of dtrace bug 6254741 |
| 115 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) { | |
| 116 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr); | |
| 117 return 0; | |
| 118 } | |
| 119 | |
| 120 #define NINFLATIONLOCKS 256 | |
| 121 static volatile intptr_t InflationLocks [NINFLATIONLOCKS] ; | |
| 122 | |
| 123 ObjectMonitor * ObjectSynchronizer::gBlockList = NULL ; | |
| 124 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL ; | |
| 125 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL ; | |
| 126 int ObjectSynchronizer::gOmInUseCount = 0; | |
| 127 static volatile intptr_t ListLock = 0 ; // protects global monitor free-list cache | |
| 128 static volatile int MonitorFreeCount = 0 ; // # on gFreeList | |
| 129 static volatile int MonitorPopulation = 0 ; // # Extant -- in circulation | |
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130 #define CHAINMARKER (cast_to_oop<intptr_t>(-1)) |
| 1878 | 131 |
| 132 // ----------------------------------------------------------------------------- | |
| 133 // Fast Monitor Enter/Exit | |
| 134 // This the fast monitor enter. The interpreter and compiler use | |
| 135 // some assembly copies of this code. Make sure update those code | |
| 136 // if the following function is changed. The implementation is | |
| 137 // extremely sensitive to race condition. Be careful. | |
| 138 | |
| 139 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock, bool attempt_rebias, TRAPS) { | |
| 140 if (UseBiasedLocking) { | |
| 141 if (!SafepointSynchronize::is_at_safepoint()) { | |
| 142 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD); | |
| 143 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) { | |
| 144 return; | |
| 145 } | |
| 146 } else { | |
| 147 assert(!attempt_rebias, "can not rebias toward VM thread"); | |
| 148 BiasedLocking::revoke_at_safepoint(obj); | |
| 149 } | |
| 150 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
| 151 } | |
| 152 | |
| 153 slow_enter (obj, lock, THREAD) ; | |
| 154 } | |
| 155 | |
| 156 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) { | |
| 157 assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here"); | |
| 158 // if displaced header is null, the previous enter is recursive enter, no-op | |
| 159 markOop dhw = lock->displaced_header(); | |
| 160 markOop mark ; | |
| 161 if (dhw == NULL) { | |
| 162 // Recursive stack-lock. | |
| 163 // Diagnostics -- Could be: stack-locked, inflating, inflated. | |
| 164 mark = object->mark() ; | |
| 165 assert (!mark->is_neutral(), "invariant") ; | |
| 166 if (mark->has_locker() && mark != markOopDesc::INFLATING()) { | |
| 167 assert(THREAD->is_lock_owned((address)mark->locker()), "invariant") ; | |
| 168 } | |
| 169 if (mark->has_monitor()) { | |
| 170 ObjectMonitor * m = mark->monitor() ; | |
| 171 assert(((oop)(m->object()))->mark() == mark, "invariant") ; | |
| 172 assert(m->is_entered(THREAD), "invariant") ; | |
| 173 } | |
| 174 return ; | |
| 175 } | |
| 176 | |
| 177 mark = object->mark() ; | |
| 0 | 178 |
| 1878 | 179 // If the object is stack-locked by the current thread, try to |
| 180 // swing the displaced header from the box back to the mark. | |
| 181 if (mark == (markOop) lock) { | |
| 182 assert (dhw->is_neutral(), "invariant") ; | |
| 183 if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) { | |
| 184 TEVENT (fast_exit: release stacklock) ; | |
| 185 return; | |
| 186 } | |
| 187 } | |
| 188 | |
| 10405 | 189 ObjectSynchronizer::inflate(THREAD, object)->exit (true, THREAD) ; |
| 1878 | 190 } |
| 191 | |
| 192 // ----------------------------------------------------------------------------- | |
| 193 // Interpreter/Compiler Slow Case | |
| 194 // This routine is used to handle interpreter/compiler slow case | |
| 195 // We don't need to use fast path here, because it must have been | |
| 196 // failed in the interpreter/compiler code. | |
| 197 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) { | |
| 198 markOop mark = obj->mark(); | |
| 199 assert(!mark->has_bias_pattern(), "should not see bias pattern here"); | |
| 200 | |
| 201 if (mark->is_neutral()) { | |
| 202 // Anticipate successful CAS -- the ST of the displaced mark must | |
| 203 // be visible <= the ST performed by the CAS. | |
| 204 lock->set_displaced_header(mark); | |
| 205 if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) { | |
| 206 TEVENT (slow_enter: release stacklock) ; | |
| 207 return ; | |
| 208 } | |
| 209 // Fall through to inflate() ... | |
| 210 } else | |
| 211 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { | |
| 212 assert(lock != mark->locker(), "must not re-lock the same lock"); | |
| 213 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock"); | |
| 214 lock->set_displaced_header(NULL); | |
| 215 return; | |
| 216 } | |
| 217 | |
| 218 #if 0 | |
| 219 // The following optimization isn't particularly useful. | |
| 220 if (mark->has_monitor() && mark->monitor()->is_entered(THREAD)) { | |
| 221 lock->set_displaced_header (NULL) ; | |
| 222 return ; | |
| 223 } | |
| 224 #endif | |
| 225 | |
| 226 // The object header will never be displaced to this lock, | |
| 227 // so it does not matter what the value is, except that it | |
| 228 // must be non-zero to avoid looking like a re-entrant lock, | |
| 229 // and must not look locked either. | |
| 230 lock->set_displaced_header(markOopDesc::unused_mark()); | |
| 231 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD); | |
| 232 } | |
| 233 | |
| 234 // This routine is used to handle interpreter/compiler slow case | |
| 235 // We don't need to use fast path here, because it must have | |
| 236 // failed in the interpreter/compiler code. Simply use the heavy | |
| 237 // weight monitor should be ok, unless someone find otherwise. | |
| 238 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) { | |
| 239 fast_exit (object, lock, THREAD) ; | |
| 240 } | |
| 241 | |
| 242 // ----------------------------------------------------------------------------- | |
| 243 // Class Loader support to workaround deadlocks on the class loader lock objects | |
| 244 // Also used by GC | |
| 245 // complete_exit()/reenter() are used to wait on a nested lock | |
| 246 // i.e. to give up an outer lock completely and then re-enter | |
| 247 // Used when holding nested locks - lock acquisition order: lock1 then lock2 | |
| 248 // 1) complete_exit lock1 - saving recursion count | |
| 249 // 2) wait on lock2 | |
| 250 // 3) when notified on lock2, unlock lock2 | |
| 251 // 4) reenter lock1 with original recursion count | |
| 252 // 5) lock lock2 | |
| 253 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() | |
| 254 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) { | |
| 255 TEVENT (complete_exit) ; | |
| 256 if (UseBiasedLocking) { | |
| 257 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
| 258 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
| 0 | 259 } |
| 260 | |
| 1878 | 261 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); |
| 262 | |
| 263 return monitor->complete_exit(THREAD); | |
| 264 } | |
| 265 | |
| 266 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() | |
| 267 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) { | |
| 268 TEVENT (reenter) ; | |
| 269 if (UseBiasedLocking) { | |
| 270 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
| 271 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
| 272 } | |
| 273 | |
| 274 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); | |
| 275 | |
| 276 monitor->reenter(recursion, THREAD); | |
| 277 } | |
| 278 // ----------------------------------------------------------------------------- | |
| 279 // JNI locks on java objects | |
| 280 // NOTE: must use heavy weight monitor to handle jni monitor enter | |
| 281 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) { // possible entry from jni enter | |
| 282 // the current locking is from JNI instead of Java code | |
| 283 TEVENT (jni_enter) ; | |
| 284 if (UseBiasedLocking) { | |
| 285 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
| 286 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
| 287 } | |
| 288 THREAD->set_current_pending_monitor_is_from_java(false); | |
| 289 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD); | |
| 290 THREAD->set_current_pending_monitor_is_from_java(true); | |
| 291 } | |
| 292 | |
| 293 // NOTE: must use heavy weight monitor to handle jni monitor enter | |
| 294 bool ObjectSynchronizer::jni_try_enter(Handle obj, Thread* THREAD) { | |
| 295 if (UseBiasedLocking) { | |
| 296 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
| 297 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
| 0 | 298 } |
| 299 | |
| 1878 | 300 ObjectMonitor* monitor = ObjectSynchronizer::inflate_helper(obj()); |
| 301 return monitor->try_enter(THREAD); | |
| 302 } | |
| 303 | |
| 304 | |
| 305 // NOTE: must use heavy weight monitor to handle jni monitor exit | |
| 306 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) { | |
| 307 TEVENT (jni_exit) ; | |
| 308 if (UseBiasedLocking) { | |
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309 Handle h_obj(THREAD, obj); |
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310 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD); |
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311 obj = h_obj(); |
| 1878 | 312 } |
| 313 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
| 314 | |
| 315 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj); | |
| 316 // If this thread has locked the object, exit the monitor. Note: can't use | |
| 317 // monitor->check(CHECK); must exit even if an exception is pending. | |
| 318 if (monitor->check(THREAD)) { | |
| 10405 | 319 monitor->exit(true, THREAD); |
| 0 | 320 } |
| 1878 | 321 } |
| 322 | |
| 323 // ----------------------------------------------------------------------------- | |
| 324 // Internal VM locks on java objects | |
| 325 // standard constructor, allows locking failures | |
| 326 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) { | |
| 327 _dolock = doLock; | |
| 328 _thread = thread; | |
| 329 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);) | |
| 330 _obj = obj; | |
| 0 | 331 |
| 1878 | 332 if (_dolock) { |
| 333 TEVENT (ObjectLocker) ; | |
| 334 | |
| 335 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread); | |
| 336 } | |
| 337 } | |
| 338 | |
| 339 ObjectLocker::~ObjectLocker() { | |
| 340 if (_dolock) { | |
| 341 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread); | |
| 342 } | |
| 343 } | |
| 0 | 344 |
| 345 | |
| 1878 | 346 // ----------------------------------------------------------------------------- |
| 347 // Wait/Notify/NotifyAll | |
| 348 // NOTE: must use heavy weight monitor to handle wait() | |
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349 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) { |
| 1878 | 350 if (UseBiasedLocking) { |
| 351 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
| 352 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
| 353 } | |
| 354 if (millis < 0) { | |
| 355 TEVENT (wait - throw IAX) ; | |
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356 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); |
| 1878 | 357 } |
| 358 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); | |
| 359 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis); | |
| 360 monitor->wait(millis, true, THREAD); | |
| 361 | |
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362 // This dummy call is in place to get around dtrace bug 6254741. Once |
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363 // that's fixed we can uncomment the following line, remove the call |
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364 // and change this function back into a "void" func. |
| 1878 | 365 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD); |
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366 return dtrace_waited_probe(monitor, obj, THREAD); |
| 1878 | 367 } |
| 0 | 368 |
| 1878 | 369 void ObjectSynchronizer::waitUninterruptibly (Handle obj, jlong millis, TRAPS) { |
| 370 if (UseBiasedLocking) { | |
| 371 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
| 372 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
| 373 } | |
| 374 if (millis < 0) { | |
| 375 TEVENT (wait - throw IAX) ; | |
| 376 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); | |
| 377 } | |
| 378 ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD) ; | |
| 379 } | |
| 380 | |
| 381 void ObjectSynchronizer::notify(Handle obj, TRAPS) { | |
| 382 if (UseBiasedLocking) { | |
| 383 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
| 384 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
| 385 } | |
| 0 | 386 |
| 1878 | 387 markOop mark = obj->mark(); |
| 388 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { | |
| 389 return; | |
| 390 } | |
| 391 ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD); | |
| 392 } | |
| 0 | 393 |
| 1878 | 394 // NOTE: see comment of notify() |
| 395 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) { | |
| 396 if (UseBiasedLocking) { | |
| 397 BiasedLocking::revoke_and_rebias(obj, false, THREAD); | |
| 398 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
| 399 } | |
| 400 | |
| 401 markOop mark = obj->mark(); | |
| 402 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { | |
| 403 return; | |
| 404 } | |
| 405 ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD); | |
| 406 } | |
| 407 | |
| 408 // ----------------------------------------------------------------------------- | |
| 409 // Hash Code handling | |
| 410 // | |
| 0 | 411 // Performance concern: |
| 412 // OrderAccess::storestore() calls release() which STs 0 into the global volatile | |
| 413 // OrderAccess::Dummy variable. This store is unnecessary for correctness. | |
| 414 // Many threads STing into a common location causes considerable cache migration | |
| 415 // or "sloshing" on large SMP system. As such, I avoid using OrderAccess::storestore() | |
| 416 // until it's repaired. In some cases OrderAccess::fence() -- which incurs local | |
| 417 // latency on the executing processor -- is a better choice as it scales on SMP | |
| 418 // systems. See http://blogs.sun.com/dave/entry/biased_locking_in_hotspot for a | |
| 419 // discussion of coherency costs. Note that all our current reference platforms | |
| 420 // provide strong ST-ST order, so the issue is moot on IA32, x64, and SPARC. | |
| 421 // | |
| 422 // As a general policy we use "volatile" to control compiler-based reordering | |
| 423 // and explicit fences (barriers) to control for architectural reordering performed | |
| 424 // by the CPU(s) or platform. | |
| 425 | |
| 426 struct SharedGlobals { | |
| 427 // These are highly shared mostly-read variables. | |
| 428 // To avoid false-sharing they need to be the sole occupants of a $ line. | |
| 429 double padPrefix [8]; | |
| 430 volatile int stwRandom ; | |
| 431 volatile int stwCycle ; | |
| 432 | |
| 433 // Hot RW variables -- Sequester to avoid false-sharing | |
| 434 double padSuffix [16]; | |
| 435 volatile int hcSequence ; | |
| 436 double padFinal [8] ; | |
| 437 } ; | |
| 438 | |
| 439 static SharedGlobals GVars ; | |
| 1587 | 440 static int MonitorScavengeThreshold = 1000000 ; |
| 441 static volatile int ForceMonitorScavenge = 0 ; // Scavenge required and pending | |
| 0 | 442 |
| 1878 | 443 static markOop ReadStableMark (oop obj) { |
| 444 markOop mark = obj->mark() ; | |
| 445 if (!mark->is_being_inflated()) { | |
| 446 return mark ; // normal fast-path return | |
| 447 } | |
| 0 | 448 |
| 1878 | 449 int its = 0 ; |
| 450 for (;;) { | |
| 451 markOop mark = obj->mark() ; | |
| 452 if (!mark->is_being_inflated()) { | |
| 453 return mark ; // normal fast-path return | |
| 454 } | |
| 455 | |
| 456 // The object is being inflated by some other thread. | |
| 457 // The caller of ReadStableMark() must wait for inflation to complete. | |
| 458 // Avoid live-lock | |
| 459 // TODO: consider calling SafepointSynchronize::do_call_back() while | |
| 460 // spinning to see if there's a safepoint pending. If so, immediately | |
| 461 // yielding or blocking would be appropriate. Avoid spinning while | |
| 462 // there is a safepoint pending. | |
| 463 // TODO: add inflation contention performance counters. | |
| 464 // TODO: restrict the aggregate number of spinners. | |
| 0 | 465 |
| 1878 | 466 ++its ; |
| 467 if (its > 10000 || !os::is_MP()) { | |
| 468 if (its & 1) { | |
| 469 os::NakedYield() ; | |
| 470 TEVENT (Inflate: INFLATING - yield) ; | |
| 471 } else { | |
| 472 // Note that the following code attenuates the livelock problem but is not | |
| 473 // a complete remedy. A more complete solution would require that the inflating | |
| 474 // thread hold the associated inflation lock. The following code simply restricts | |
| 475 // the number of spinners to at most one. We'll have N-2 threads blocked | |
| 476 // on the inflationlock, 1 thread holding the inflation lock and using | |
| 477 // a yield/park strategy, and 1 thread in the midst of inflation. | |
| 478 // A more refined approach would be to change the encoding of INFLATING | |
| 479 // to allow encapsulation of a native thread pointer. Threads waiting for | |
| 480 // inflation to complete would use CAS to push themselves onto a singly linked | |
| 481 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag | |
| 482 // and calling park(). When inflation was complete the thread that accomplished inflation | |
| 483 // would detach the list and set the markword to inflated with a single CAS and | |
| 484 // then for each thread on the list, set the flag and unpark() the thread. | |
| 485 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease | |
| 486 // wakes at most one thread whereas we need to wake the entire list. | |
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487 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1) ; |
| 1878 | 488 int YieldThenBlock = 0 ; |
| 489 assert (ix >= 0 && ix < NINFLATIONLOCKS, "invariant") ; | |
| 490 assert ((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant") ; | |
| 491 Thread::muxAcquire (InflationLocks + ix, "InflationLock") ; | |
| 492 while (obj->mark() == markOopDesc::INFLATING()) { | |
| 493 // Beware: NakedYield() is advisory and has almost no effect on some platforms | |
| 494 // so we periodically call Self->_ParkEvent->park(1). | |
| 495 // We use a mixed spin/yield/block mechanism. | |
| 496 if ((YieldThenBlock++) >= 16) { | |
| 497 Thread::current()->_ParkEvent->park(1) ; | |
| 498 } else { | |
| 499 os::NakedYield() ; | |
| 500 } | |
| 501 } | |
| 502 Thread::muxRelease (InflationLocks + ix ) ; | |
| 503 TEVENT (Inflate: INFLATING - yield/park) ; | |
| 504 } | |
| 505 } else { | |
| 506 SpinPause() ; // SMP-polite spinning | |
| 507 } | |
| 508 } | |
| 509 } | |
| 0 | 510 |
| 511 // hashCode() generation : | |
| 512 // | |
| 513 // Possibilities: | |
| 514 // * MD5Digest of {obj,stwRandom} | |
| 515 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function. | |
| 516 // * A DES- or AES-style SBox[] mechanism | |
| 517 // * One of the Phi-based schemes, such as: | |
| 518 // 2654435761 = 2^32 * Phi (golden ratio) | |
| 519 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ; | |
| 520 // * A variation of Marsaglia's shift-xor RNG scheme. | |
| 521 // * (obj ^ stwRandom) is appealing, but can result | |
| 522 // in undesirable regularity in the hashCode values of adjacent objects | |
| 523 // (objects allocated back-to-back, in particular). This could potentially | |
| 524 // result in hashtable collisions and reduced hashtable efficiency. | |
| 525 // There are simple ways to "diffuse" the middle address bits over the | |
| 526 // generated hashCode values: | |
| 527 // | |
| 528 | |
| 529 static inline intptr_t get_next_hash(Thread * Self, oop obj) { | |
| 530 intptr_t value = 0 ; | |
| 531 if (hashCode == 0) { | |
| 532 // This form uses an unguarded global Park-Miller RNG, | |
| 533 // so it's possible for two threads to race and generate the same RNG. | |
| 534 // On MP system we'll have lots of RW access to a global, so the | |
| 535 // mechanism induces lots of coherency traffic. | |
| 536 value = os::random() ; | |
| 537 } else | |
| 538 if (hashCode == 1) { | |
| 539 // This variation has the property of being stable (idempotent) | |
| 540 // between STW operations. This can be useful in some of the 1-0 | |
| 541 // synchronization schemes. | |
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542 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3 ; |
| 0 | 543 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom ; |
| 544 } else | |
| 545 if (hashCode == 2) { | |
| 546 value = 1 ; // for sensitivity testing | |
| 547 } else | |
| 548 if (hashCode == 3) { | |
| 549 value = ++GVars.hcSequence ; | |
| 550 } else | |
| 551 if (hashCode == 4) { | |
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552 value = cast_from_oop<intptr_t>(obj) ; |
| 0 | 553 } else { |
| 554 // Marsaglia's xor-shift scheme with thread-specific state | |
| 555 // This is probably the best overall implementation -- we'll | |
| 556 // likely make this the default in future releases. | |
| 557 unsigned t = Self->_hashStateX ; | |
| 558 t ^= (t << 11) ; | |
| 559 Self->_hashStateX = Self->_hashStateY ; | |
| 560 Self->_hashStateY = Self->_hashStateZ ; | |
| 561 Self->_hashStateZ = Self->_hashStateW ; | |
| 562 unsigned v = Self->_hashStateW ; | |
| 563 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)) ; | |
| 564 Self->_hashStateW = v ; | |
| 565 value = v ; | |
| 566 } | |
| 567 | |
| 568 value &= markOopDesc::hash_mask; | |
| 569 if (value == 0) value = 0xBAD ; | |
| 570 assert (value != markOopDesc::no_hash, "invariant") ; | |
| 571 TEVENT (hashCode: GENERATE) ; | |
| 572 return value; | |
| 573 } | |
| 1878 | 574 // |
| 575 intptr_t ObjectSynchronizer::FastHashCode (Thread * Self, oop obj) { | |
| 576 if (UseBiasedLocking) { | |
| 577 // NOTE: many places throughout the JVM do not expect a safepoint | |
| 578 // to be taken here, in particular most operations on perm gen | |
| 579 // objects. However, we only ever bias Java instances and all of | |
| 580 // the call sites of identity_hash that might revoke biases have | |
| 581 // been checked to make sure they can handle a safepoint. The | |
| 582 // added check of the bias pattern is to avoid useless calls to | |
| 583 // thread-local storage. | |
| 584 if (obj->mark()->has_bias_pattern()) { | |
| 585 // Box and unbox the raw reference just in case we cause a STW safepoint. | |
| 586 Handle hobj (Self, obj) ; | |
| 587 // Relaxing assertion for bug 6320749. | |
| 588 assert (Universe::verify_in_progress() || | |
| 589 !SafepointSynchronize::is_at_safepoint(), | |
| 590 "biases should not be seen by VM thread here"); | |
| 591 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current()); | |
| 592 obj = hobj() ; | |
| 593 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
| 594 } | |
| 595 } | |
| 0 | 596 |
| 1878 | 597 // hashCode() is a heap mutator ... |
| 598 // Relaxing assertion for bug 6320749. | |
| 599 assert (Universe::verify_in_progress() || | |
| 600 !SafepointSynchronize::is_at_safepoint(), "invariant") ; | |
| 601 assert (Universe::verify_in_progress() || | |
| 602 Self->is_Java_thread() , "invariant") ; | |
| 603 assert (Universe::verify_in_progress() || | |
| 604 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ; | |
| 605 | |
| 606 ObjectMonitor* monitor = NULL; | |
| 607 markOop temp, test; | |
| 608 intptr_t hash; | |
| 609 markOop mark = ReadStableMark (obj); | |
| 610 | |
| 611 // object should remain ineligible for biased locking | |
| 612 assert (!mark->has_bias_pattern(), "invariant") ; | |
| 613 | |
| 614 if (mark->is_neutral()) { | |
| 615 hash = mark->hash(); // this is a normal header | |
| 616 if (hash) { // if it has hash, just return it | |
| 617 return hash; | |
| 618 } | |
| 619 hash = get_next_hash(Self, obj); // allocate a new hash code | |
| 620 temp = mark->copy_set_hash(hash); // merge the hash code into header | |
| 621 // use (machine word version) atomic operation to install the hash | |
| 622 test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark); | |
| 623 if (test == mark) { | |
| 624 return hash; | |
| 625 } | |
| 626 // If atomic operation failed, we must inflate the header | |
| 627 // into heavy weight monitor. We could add more code here | |
| 628 // for fast path, but it does not worth the complexity. | |
| 629 } else if (mark->has_monitor()) { | |
| 630 monitor = mark->monitor(); | |
| 631 temp = monitor->header(); | |
| 632 assert (temp->is_neutral(), "invariant") ; | |
| 633 hash = temp->hash(); | |
| 634 if (hash) { | |
| 635 return hash; | |
| 636 } | |
| 637 // Skip to the following code to reduce code size | |
| 638 } else if (Self->is_lock_owned((address)mark->locker())) { | |
| 639 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned | |
| 640 assert (temp->is_neutral(), "invariant") ; | |
| 641 hash = temp->hash(); // by current thread, check if the displaced | |
| 642 if (hash) { // header contains hash code | |
| 643 return hash; | |
| 644 } | |
| 645 // WARNING: | |
| 646 // The displaced header is strictly immutable. | |
| 647 // It can NOT be changed in ANY cases. So we have | |
| 648 // to inflate the header into heavyweight monitor | |
| 649 // even the current thread owns the lock. The reason | |
| 650 // is the BasicLock (stack slot) will be asynchronously | |
| 651 // read by other threads during the inflate() function. | |
| 652 // Any change to stack may not propagate to other threads | |
| 653 // correctly. | |
| 654 } | |
| 655 | |
| 656 // Inflate the monitor to set hash code | |
| 657 monitor = ObjectSynchronizer::inflate(Self, obj); | |
| 658 // Load displaced header and check it has hash code | |
| 659 mark = monitor->header(); | |
| 660 assert (mark->is_neutral(), "invariant") ; | |
| 661 hash = mark->hash(); | |
| 662 if (hash == 0) { | |
| 663 hash = get_next_hash(Self, obj); | |
| 664 temp = mark->copy_set_hash(hash); // merge hash code into header | |
| 665 assert (temp->is_neutral(), "invariant") ; | |
| 666 test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark); | |
| 667 if (test != mark) { | |
| 668 // The only update to the header in the monitor (outside GC) | |
| 669 // is install the hash code. If someone add new usage of | |
| 670 // displaced header, please update this code | |
| 671 hash = test->hash(); | |
| 672 assert (test->is_neutral(), "invariant") ; | |
| 673 assert (hash != 0, "Trivial unexpected object/monitor header usage."); | |
| 674 } | |
| 675 } | |
| 676 // We finally get the hash | |
| 677 return hash; | |
| 0 | 678 } |
| 679 | |
| 1878 | 680 // Deprecated -- use FastHashCode() instead. |
| 0 | 681 |
| 1878 | 682 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) { |
| 683 return FastHashCode (Thread::current(), obj()) ; | |
| 0 | 684 } |
| 685 | |
| 686 | |
| 1878 | 687 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread, |
| 688 Handle h_obj) { | |
| 689 if (UseBiasedLocking) { | |
| 690 BiasedLocking::revoke_and_rebias(h_obj, false, thread); | |
| 691 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
| 692 } | |
| 693 | |
| 694 assert(thread == JavaThread::current(), "Can only be called on current thread"); | |
| 695 oop obj = h_obj(); | |
| 696 | |
| 697 markOop mark = ReadStableMark (obj) ; | |
| 0 | 698 |
| 1878 | 699 // Uncontended case, header points to stack |
| 700 if (mark->has_locker()) { | |
| 701 return thread->is_lock_owned((address)mark->locker()); | |
| 0 | 702 } |
| 1878 | 703 // Contended case, header points to ObjectMonitor (tagged pointer) |
| 704 if (mark->has_monitor()) { | |
| 705 ObjectMonitor* monitor = mark->monitor(); | |
| 706 return monitor->is_entered(thread) != 0 ; | |
| 0 | 707 } |
| 1878 | 708 // Unlocked case, header in place |
| 709 assert(mark->is_neutral(), "sanity check"); | |
| 710 return false; | |
| 0 | 711 } |
| 712 | |
| 1878 | 713 // Be aware of this method could revoke bias of the lock object. |
| 14309 | 714 // This method queries the ownership of the lock handle specified by 'h_obj'. |
| 1878 | 715 // If the current thread owns the lock, it returns owner_self. If no |
| 716 // thread owns the lock, it returns owner_none. Otherwise, it will return | |
| 14309 | 717 // owner_other. |
| 1878 | 718 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership |
| 719 (JavaThread *self, Handle h_obj) { | |
| 720 // The caller must beware this method can revoke bias, and | |
| 721 // revocation can result in a safepoint. | |
| 722 assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ; | |
| 723 assert (self->thread_state() != _thread_blocked , "invariant") ; | |
| 0 | 724 |
| 1878 | 725 // Possible mark states: neutral, biased, stack-locked, inflated |
| 726 | |
| 727 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) { | |
| 728 // CASE: biased | |
| 729 BiasedLocking::revoke_and_rebias(h_obj, false, self); | |
| 730 assert(!h_obj->mark()->has_bias_pattern(), | |
| 731 "biases should be revoked by now"); | |
| 732 } | |
| 0 | 733 |
| 1878 | 734 assert(self == JavaThread::current(), "Can only be called on current thread"); |
| 735 oop obj = h_obj(); | |
| 736 markOop mark = ReadStableMark (obj) ; | |
| 737 | |
| 738 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack. | |
| 739 if (mark->has_locker()) { | |
| 740 return self->is_lock_owned((address)mark->locker()) ? | |
| 741 owner_self : owner_other; | |
| 742 } | |
| 0 | 743 |
| 1878 | 744 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor. |
| 745 // The Object:ObjectMonitor relationship is stable as long as we're | |
| 746 // not at a safepoint. | |
| 747 if (mark->has_monitor()) { | |
| 748 void * owner = mark->monitor()->_owner ; | |
| 749 if (owner == NULL) return owner_none ; | |
| 750 return (owner == self || | |
| 751 self->is_lock_owned((address)owner)) ? owner_self : owner_other; | |
| 752 } | |
| 753 | |
| 754 // CASE: neutral | |
| 755 assert(mark->is_neutral(), "sanity check"); | |
| 756 return owner_none ; // it's unlocked | |
| 757 } | |
| 0 | 758 |
| 1878 | 759 // FIXME: jvmti should call this |
| 760 JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) { | |
| 761 if (UseBiasedLocking) { | |
| 762 if (SafepointSynchronize::is_at_safepoint()) { | |
| 763 BiasedLocking::revoke_at_safepoint(h_obj); | |
| 764 } else { | |
| 765 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current()); | |
| 766 } | |
| 767 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now"); | |
| 768 } | |
| 769 | |
| 770 oop obj = h_obj(); | |
| 771 address owner = NULL; | |
| 772 | |
| 773 markOop mark = ReadStableMark (obj) ; | |
| 774 | |
| 775 // Uncontended case, header points to stack | |
| 776 if (mark->has_locker()) { | |
| 777 owner = (address) mark->locker(); | |
| 778 } | |
| 779 | |
| 780 // Contended case, header points to ObjectMonitor (tagged pointer) | |
| 781 if (mark->has_monitor()) { | |
| 782 ObjectMonitor* monitor = mark->monitor(); | |
| 783 assert(monitor != NULL, "monitor should be non-null"); | |
| 784 owner = (address) monitor->owner(); | |
| 785 } | |
| 786 | |
| 787 if (owner != NULL) { | |
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788 // owning_thread_from_monitor_owner() may also return NULL here |
| 1878 | 789 return Threads::owning_thread_from_monitor_owner(owner, doLock); |
| 790 } | |
| 791 | |
| 792 // Unlocked case, header in place | |
| 793 // Cannot have assertion since this object may have been | |
| 794 // locked by another thread when reaching here. | |
| 795 // assert(mark->is_neutral(), "sanity check"); | |
| 796 | |
| 797 return NULL; | |
| 798 } | |
| 799 // Visitors ... | |
| 800 | |
| 801 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) { | |
| 802 ObjectMonitor* block = gBlockList; | |
| 803 ObjectMonitor* mid; | |
| 804 while (block) { | |
| 805 assert(block->object() == CHAINMARKER, "must be a block header"); | |
| 806 for (int i = _BLOCKSIZE - 1; i > 0; i--) { | |
| 807 mid = block + i; | |
| 808 oop object = (oop) mid->object(); | |
| 809 if (object != NULL) { | |
| 810 closure->do_monitor(mid); | |
| 811 } | |
| 812 } | |
| 813 block = (ObjectMonitor*) block->FreeNext; | |
| 0 | 814 } |
| 815 } | |
| 816 | |
| 1878 | 817 // Get the next block in the block list. |
| 818 static inline ObjectMonitor* next(ObjectMonitor* block) { | |
| 819 assert(block->object() == CHAINMARKER, "must be a block header"); | |
| 820 block = block->FreeNext ; | |
| 821 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header"); | |
| 822 return block; | |
| 0 | 823 } |
| 824 | |
| 825 | |
| 1878 | 826 void ObjectSynchronizer::oops_do(OopClosure* f) { |
| 827 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); | |
| 828 for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) { | |
| 829 assert(block->object() == CHAINMARKER, "must be a block header"); | |
| 830 for (int i = 1; i < _BLOCKSIZE; i++) { | |
| 831 ObjectMonitor* mid = &block[i]; | |
| 832 if (mid->object() != NULL) { | |
| 833 f->do_oop((oop*)mid->object_addr()); | |
| 0 | 834 } |
| 835 } | |
| 836 } | |
| 837 } | |
| 838 | |
| 839 | |
| 1878 | 840 // ----------------------------------------------------------------------------- |
| 0 | 841 // ObjectMonitor Lifecycle |
| 842 // ----------------------- | |
| 843 // Inflation unlinks monitors from the global gFreeList and | |
| 844 // associates them with objects. Deflation -- which occurs at | |
| 845 // STW-time -- disassociates idle monitors from objects. Such | |
| 846 // scavenged monitors are returned to the gFreeList. | |
| 847 // | |
| 848 // The global list is protected by ListLock. All the critical sections | |
| 849 // are short and operate in constant-time. | |
| 850 // | |
| 851 // ObjectMonitors reside in type-stable memory (TSM) and are immortal. | |
| 852 // | |
| 853 // Lifecycle: | |
| 854 // -- unassigned and on the global free list | |
| 855 // -- unassigned and on a thread's private omFreeList | |
| 856 // -- assigned to an object. The object is inflated and the mark refers | |
| 857 // to the objectmonitor. | |
| 858 // | |
| 859 | |
| 860 | |
| 1587 | 861 // Constraining monitor pool growth via MonitorBound ... |
| 862 // | |
| 863 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the | |
| 864 // the rate of scavenging is driven primarily by GC. As such, we can find | |
| 865 // an inordinate number of monitors in circulation. | |
| 866 // To avoid that scenario we can artificially induce a STW safepoint | |
| 867 // if the pool appears to be growing past some reasonable bound. | |
| 868 // Generally we favor time in space-time tradeoffs, but as there's no | |
| 869 // natural back-pressure on the # of extant monitors we need to impose some | |
| 870 // type of limit. Beware that if MonitorBound is set to too low a value | |
| 871 // we could just loop. In addition, if MonitorBound is set to a low value | |
| 872 // we'll incur more safepoints, which are harmful to performance. | |
| 873 // See also: GuaranteedSafepointInterval | |
| 874 // | |
| 875 // The current implementation uses asynchronous VM operations. | |
| 876 // | |
| 877 | |
| 878 static void InduceScavenge (Thread * Self, const char * Whence) { | |
| 879 // Induce STW safepoint to trim monitors | |
| 880 // Ultimately, this results in a call to deflate_idle_monitors() in the near future. | |
| 881 // More precisely, trigger an asynchronous STW safepoint as the number | |
| 882 // of active monitors passes the specified threshold. | |
| 883 // TODO: assert thread state is reasonable | |
| 884 | |
| 885 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) { | |
| 1878 | 886 if (ObjectMonitor::Knob_Verbose) { |
| 1587 | 887 ::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ; |
| 888 ::fflush(stdout) ; | |
| 889 } | |
| 890 // Induce a 'null' safepoint to scavenge monitors | |
| 891 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted | |
| 892 // to the VMthread and have a lifespan longer than that of this activation record. | |
| 893 // The VMThread will delete the op when completed. | |
| 894 VMThread::execute (new VM_ForceAsyncSafepoint()) ; | |
| 895 | |
| 1878 | 896 if (ObjectMonitor::Knob_Verbose) { |
| 1587 | 897 ::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ; |
| 898 ::fflush(stdout) ; | |
| 899 } | |
| 900 } | |
| 901 } | |
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902 /* Too slow for general assert or debug |
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903 void ObjectSynchronizer::verifyInUse (Thread *Self) { |
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904 ObjectMonitor* mid; |
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905 int inusetally = 0; |
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906 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) { |
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907 inusetally ++; |
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908 } |
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909 assert(inusetally == Self->omInUseCount, "inuse count off"); |
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910 |
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911 int freetally = 0; |
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912 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) { |
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913 freetally ++; |
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914 } |
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915 assert(freetally == Self->omFreeCount, "free count off"); |
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916 } |
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917 */ |
| 0 | 918 ObjectMonitor * ATTR ObjectSynchronizer::omAlloc (Thread * Self) { |
| 919 // A large MAXPRIVATE value reduces both list lock contention | |
| 920 // and list coherency traffic, but also tends to increase the | |
| 921 // number of objectMonitors in circulation as well as the STW | |
| 922 // scavenge costs. As usual, we lean toward time in space-time | |
| 923 // tradeoffs. | |
| 924 const int MAXPRIVATE = 1024 ; | |
| 925 for (;;) { | |
| 926 ObjectMonitor * m ; | |
| 927 | |
| 928 // 1: try to allocate from the thread's local omFreeList. | |
| 929 // Threads will attempt to allocate first from their local list, then | |
| 930 // from the global list, and only after those attempts fail will the thread | |
| 931 // attempt to instantiate new monitors. Thread-local free lists take | |
| 932 // heat off the ListLock and improve allocation latency, as well as reducing | |
| 933 // coherency traffic on the shared global list. | |
| 934 m = Self->omFreeList ; | |
| 935 if (m != NULL) { | |
| 936 Self->omFreeList = m->FreeNext ; | |
| 937 Self->omFreeCount -- ; | |
| 938 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene | |
| 939 guarantee (m->object() == NULL, "invariant") ; | |
| 1587 | 940 if (MonitorInUseLists) { |
| 941 m->FreeNext = Self->omInUseList; | |
| 942 Self->omInUseList = m; | |
| 943 Self->omInUseCount ++; | |
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944 // verifyInUse(Self); |
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945 } else { |
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946 m->FreeNext = NULL; |
| 1587 | 947 } |
| 0 | 948 return m ; |
| 949 } | |
| 950 | |
| 951 // 2: try to allocate from the global gFreeList | |
| 952 // CONSIDER: use muxTry() instead of muxAcquire(). | |
| 953 // If the muxTry() fails then drop immediately into case 3. | |
| 954 // If we're using thread-local free lists then try | |
| 955 // to reprovision the caller's free list. | |
| 956 if (gFreeList != NULL) { | |
| 957 // Reprovision the thread's omFreeList. | |
| 958 // Use bulk transfers to reduce the allocation rate and heat | |
| 959 // on various locks. | |
| 960 Thread::muxAcquire (&ListLock, "omAlloc") ; | |
| 961 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL; ) { | |
| 1587 | 962 MonitorFreeCount --; |
| 0 | 963 ObjectMonitor * take = gFreeList ; |
| 964 gFreeList = take->FreeNext ; | |
| 965 guarantee (take->object() == NULL, "invariant") ; | |
| 966 guarantee (!take->is_busy(), "invariant") ; | |
| 967 take->Recycle() ; | |
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968 omRelease (Self, take, false) ; |
| 0 | 969 } |
| 970 Thread::muxRelease (&ListLock) ; | |
| 971 Self->omFreeProvision += 1 + (Self->omFreeProvision/2) ; | |
| 972 if (Self->omFreeProvision > MAXPRIVATE ) Self->omFreeProvision = MAXPRIVATE ; | |
| 973 TEVENT (omFirst - reprovision) ; | |
| 1587 | 974 |
| 975 const int mx = MonitorBound ; | |
| 976 if (mx > 0 && (MonitorPopulation-MonitorFreeCount) > mx) { | |
| 977 // We can't safely induce a STW safepoint from omAlloc() as our thread | |
| 978 // state may not be appropriate for such activities and callers may hold | |
| 979 // naked oops, so instead we defer the action. | |
| 980 InduceScavenge (Self, "omAlloc") ; | |
| 981 } | |
| 982 continue; | |
| 0 | 983 } |
| 984 | |
| 985 // 3: allocate a block of new ObjectMonitors | |
| 986 // Both the local and global free lists are empty -- resort to malloc(). | |
| 987 // In the current implementation objectMonitors are TSM - immortal. | |
| 988 assert (_BLOCKSIZE > 1, "invariant") ; | |
| 10135 | 989 ObjectMonitor * temp = new ObjectMonitor[_BLOCKSIZE]; |
| 0 | 990 |
| 991 // NOTE: (almost) no way to recover if allocation failed. | |
| 992 // We might be able to induce a STW safepoint and scavenge enough | |
| 993 // objectMonitors to permit progress. | |
| 994 if (temp == NULL) { | |
|
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995 vm_exit_out_of_memory (sizeof (ObjectMonitor[_BLOCKSIZE]), OOM_MALLOC_ERROR, |
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996 "Allocate ObjectMonitors"); |
| 0 | 997 } |
| 998 | |
| 999 // Format the block. | |
| 1000 // initialize the linked list, each monitor points to its next | |
| 1001 // forming the single linked free list, the very first monitor | |
| 1002 // will points to next block, which forms the block list. | |
| 1003 // The trick of using the 1st element in the block as gBlockList | |
| 1004 // linkage should be reconsidered. A better implementation would | |
| 1005 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; } | |
| 1006 | |
| 1007 for (int i = 1; i < _BLOCKSIZE ; i++) { | |
| 1008 temp[i].FreeNext = &temp[i+1]; | |
| 1009 } | |
| 1010 | |
| 1011 // terminate the last monitor as the end of list | |
| 1012 temp[_BLOCKSIZE - 1].FreeNext = NULL ; | |
| 1013 | |
| 1014 // Element [0] is reserved for global list linkage | |
| 1015 temp[0].set_object(CHAINMARKER); | |
| 1016 | |
| 1017 // Consider carving out this thread's current request from the | |
| 1018 // block in hand. This avoids some lock traffic and redundant | |
| 1019 // list activity. | |
| 1020 | |
| 1021 // Acquire the ListLock to manipulate BlockList and FreeList. | |
| 1022 // An Oyama-Taura-Yonezawa scheme might be more efficient. | |
| 1023 Thread::muxAcquire (&ListLock, "omAlloc [2]") ; | |
| 1587 | 1024 MonitorPopulation += _BLOCKSIZE-1; |
| 1025 MonitorFreeCount += _BLOCKSIZE-1; | |
| 0 | 1026 |
| 1027 // Add the new block to the list of extant blocks (gBlockList). | |
| 1028 // The very first objectMonitor in a block is reserved and dedicated. | |
| 1029 // It serves as blocklist "next" linkage. | |
| 1030 temp[0].FreeNext = gBlockList; | |
| 1031 gBlockList = temp; | |
| 1032 | |
| 1033 // Add the new string of objectMonitors to the global free list | |
| 1034 temp[_BLOCKSIZE - 1].FreeNext = gFreeList ; | |
| 1035 gFreeList = temp + 1; | |
| 1036 Thread::muxRelease (&ListLock) ; | |
| 1037 TEVENT (Allocate block of monitors) ; | |
| 1038 } | |
| 1039 } | |
| 1040 | |
| 1041 // Place "m" on the caller's private per-thread omFreeList. | |
| 1042 // In practice there's no need to clamp or limit the number of | |
| 1043 // monitors on a thread's omFreeList as the only time we'll call | |
| 1044 // omRelease is to return a monitor to the free list after a CAS | |
| 1045 // attempt failed. This doesn't allow unbounded #s of monitors to | |
| 1046 // accumulate on a thread's free list. | |
| 1047 // | |
| 1048 | |
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1049 void ObjectSynchronizer::omRelease (Thread * Self, ObjectMonitor * m, bool fromPerThreadAlloc) { |
| 0 | 1050 guarantee (m->object() == NULL, "invariant") ; |
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1051 |
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1052 // Remove from omInUseList |
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1053 if (MonitorInUseLists && fromPerThreadAlloc) { |
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1054 ObjectMonitor* curmidinuse = NULL; |
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1055 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; ) { |
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1056 if (m == mid) { |
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1057 // extract from per-thread in-use-list |
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1058 if (mid == Self->omInUseList) { |
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1059 Self->omInUseList = mid->FreeNext; |
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1060 } else if (curmidinuse != NULL) { |
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1061 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist |
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1062 } |
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1063 Self->omInUseCount --; |
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1064 // verifyInUse(Self); |
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1065 break; |
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1066 } else { |
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1067 curmidinuse = mid; |
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1068 mid = mid->FreeNext; |
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1069 } |
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1070 } |
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1071 } |
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1072 |
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1073 // FreeNext is used for both onInUseList and omFreeList, so clear old before setting new |
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1074 m->FreeNext = Self->omFreeList ; |
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1075 Self->omFreeList = m ; |
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1076 Self->omFreeCount ++ ; |
| 0 | 1077 } |
| 1078 | |
| 1079 // Return the monitors of a moribund thread's local free list to | |
| 1080 // the global free list. Typically a thread calls omFlush() when | |
| 1081 // it's dying. We could also consider having the VM thread steal | |
| 1082 // monitors from threads that have not run java code over a few | |
| 1083 // consecutive STW safepoints. Relatedly, we might decay | |
| 1084 // omFreeProvision at STW safepoints. | |
| 1085 // | |
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1086 // Also return the monitors of a moribund thread"s omInUseList to |
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1087 // a global gOmInUseList under the global list lock so these |
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1088 // will continue to be scanned. |
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1089 // |
| 0 | 1090 // We currently call omFlush() from the Thread:: dtor _after the thread |
| 1091 // has been excised from the thread list and is no longer a mutator. | |
| 1092 // That means that omFlush() can run concurrently with a safepoint and | |
| 1093 // the scavenge operator. Calling omFlush() from JavaThread::exit() might | |
| 1094 // be a better choice as we could safely reason that that the JVM is | |
| 1095 // not at a safepoint at the time of the call, and thus there could | |
| 1096 // be not inopportune interleavings between omFlush() and the scavenge | |
| 1097 // operator. | |
| 1098 | |
| 1099 void ObjectSynchronizer::omFlush (Thread * Self) { | |
| 1100 ObjectMonitor * List = Self->omFreeList ; // Null-terminated SLL | |
| 1101 Self->omFreeList = NULL ; | |
| 1102 ObjectMonitor * Tail = NULL ; | |
| 1587 | 1103 int Tally = 0; |
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1104 if (List != NULL) { |
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1105 ObjectMonitor * s ; |
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1106 for (s = List ; s != NULL ; s = s->FreeNext) { |
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1107 Tally ++ ; |
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1108 Tail = s ; |
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1109 guarantee (s->object() == NULL, "invariant") ; |
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1110 guarantee (!s->is_busy(), "invariant") ; |
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1111 s->set_owner (NULL) ; // redundant but good hygiene |
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1112 TEVENT (omFlush - Move one) ; |
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1113 } |
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1114 guarantee (Tail != NULL && List != NULL, "invariant") ; |
| 0 | 1115 } |
| 1116 | |
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1117 ObjectMonitor * InUseList = Self->omInUseList; |
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1118 ObjectMonitor * InUseTail = NULL ; |
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1119 int InUseTally = 0; |
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1120 if (InUseList != NULL) { |
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1121 Self->omInUseList = NULL; |
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1122 ObjectMonitor *curom; |
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1123 for (curom = InUseList; curom != NULL; curom = curom->FreeNext) { |
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1124 InUseTail = curom; |
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1125 InUseTally++; |
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1126 } |
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1127 // TODO debug |
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1128 assert(Self->omInUseCount == InUseTally, "inuse count off"); |
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1129 Self->omInUseCount = 0; |
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1130 guarantee (InUseTail != NULL && InUseList != NULL, "invariant"); |
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1131 } |
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1132 |
| 0 | 1133 Thread::muxAcquire (&ListLock, "omFlush") ; |
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1134 if (Tail != NULL) { |
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1135 Tail->FreeNext = gFreeList ; |
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1136 gFreeList = List ; |
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1137 MonitorFreeCount += Tally; |
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1138 } |
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1139 |
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1140 if (InUseTail != NULL) { |
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1141 InUseTail->FreeNext = gOmInUseList; |
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1142 gOmInUseList = InUseList; |
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1143 gOmInUseCount += InUseTally; |
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1144 } |
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1145 |
| 0 | 1146 Thread::muxRelease (&ListLock) ; |
| 1147 TEVENT (omFlush) ; | |
| 1148 } | |
| 1149 | |
| 1150 // Fast path code shared by multiple functions | |
| 1151 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) { | |
| 1152 markOop mark = obj->mark(); | |
| 1153 if (mark->has_monitor()) { | |
| 1154 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid"); | |
| 1155 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header"); | |
| 1156 return mark->monitor(); | |
| 1157 } | |
| 1158 return ObjectSynchronizer::inflate(Thread::current(), obj); | |
| 1159 } | |
| 1160 | |
| 1878 | 1161 |
| 0 | 1162 // Note that we could encounter some performance loss through false-sharing as |
| 1163 // multiple locks occupy the same $ line. Padding might be appropriate. | |
| 1164 | |
| 1165 | |
| 1166 ObjectMonitor * ATTR ObjectSynchronizer::inflate (Thread * Self, oop object) { | |
| 1167 // Inflate mutates the heap ... | |
| 1168 // Relaxing assertion for bug 6320749. | |
| 1169 assert (Universe::verify_in_progress() || | |
| 1170 !SafepointSynchronize::is_at_safepoint(), "invariant") ; | |
| 1171 | |
| 1172 for (;;) { | |
| 1173 const markOop mark = object->mark() ; | |
| 1174 assert (!mark->has_bias_pattern(), "invariant") ; | |
| 1175 | |
| 1176 // The mark can be in one of the following states: | |
| 1177 // * Inflated - just return | |
| 1178 // * Stack-locked - coerce it to inflated | |
| 1179 // * INFLATING - busy wait for conversion to complete | |
| 1180 // * Neutral - aggressively inflate the object. | |
| 1181 // * BIASED - Illegal. We should never see this | |
| 1182 | |
| 1183 // CASE: inflated | |
| 1184 if (mark->has_monitor()) { | |
| 1185 ObjectMonitor * inf = mark->monitor() ; | |
| 1186 assert (inf->header()->is_neutral(), "invariant"); | |
| 1187 assert (inf->object() == object, "invariant") ; | |
| 1188 assert (ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid"); | |
| 1189 return inf ; | |
| 1190 } | |
| 1191 | |
| 1192 // CASE: inflation in progress - inflating over a stack-lock. | |
| 1193 // Some other thread is converting from stack-locked to inflated. | |
| 1194 // Only that thread can complete inflation -- other threads must wait. | |
| 1195 // The INFLATING value is transient. | |
| 1196 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish. | |
| 1197 // We could always eliminate polling by parking the thread on some auxiliary list. | |
| 1198 if (mark == markOopDesc::INFLATING()) { | |
| 1199 TEVENT (Inflate: spin while INFLATING) ; | |
| 1200 ReadStableMark(object) ; | |
| 1201 continue ; | |
| 1202 } | |
| 1203 | |
| 1204 // CASE: stack-locked | |
| 1205 // Could be stack-locked either by this thread or by some other thread. | |
| 1206 // | |
| 1207 // Note that we allocate the objectmonitor speculatively, _before_ attempting | |
| 1208 // to install INFLATING into the mark word. We originally installed INFLATING, | |
| 1209 // allocated the objectmonitor, and then finally STed the address of the | |
| 1210 // objectmonitor into the mark. This was correct, but artificially lengthened | |
| 1211 // the interval in which INFLATED appeared in the mark, thus increasing | |
| 1212 // the odds of inflation contention. | |
| 1213 // | |
| 1214 // We now use per-thread private objectmonitor free lists. | |
| 1215 // These list are reprovisioned from the global free list outside the | |
| 1216 // critical INFLATING...ST interval. A thread can transfer | |
| 1217 // multiple objectmonitors en-mass from the global free list to its local free list. | |
| 1218 // This reduces coherency traffic and lock contention on the global free list. | |
| 1219 // Using such local free lists, it doesn't matter if the omAlloc() call appears | |
| 1220 // before or after the CAS(INFLATING) operation. | |
| 1221 // See the comments in omAlloc(). | |
| 1222 | |
| 1223 if (mark->has_locker()) { | |
| 1224 ObjectMonitor * m = omAlloc (Self) ; | |
| 1225 // Optimistically prepare the objectmonitor - anticipate successful CAS | |
| 1226 // We do this before the CAS in order to minimize the length of time | |
| 1227 // in which INFLATING appears in the mark. | |
| 1228 m->Recycle(); | |
| 1229 m->_Responsible = NULL ; | |
| 1230 m->OwnerIsThread = 0 ; | |
| 1231 m->_recursions = 0 ; | |
| 1878 | 1232 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // Consider: maintain by type/class |
| 0 | 1233 |
| 1234 markOop cmp = (markOop) Atomic::cmpxchg_ptr (markOopDesc::INFLATING(), object->mark_addr(), mark) ; | |
| 1235 if (cmp != mark) { | |
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1236 omRelease (Self, m, true) ; |
| 0 | 1237 continue ; // Interference -- just retry |
| 1238 } | |
| 1239 | |
| 1240 // We've successfully installed INFLATING (0) into the mark-word. | |
| 1241 // This is the only case where 0 will appear in a mark-work. | |
| 1242 // Only the singular thread that successfully swings the mark-word | |
| 1243 // to 0 can perform (or more precisely, complete) inflation. | |
| 1244 // | |
| 1245 // Why do we CAS a 0 into the mark-word instead of just CASing the | |
| 1246 // mark-word from the stack-locked value directly to the new inflated state? | |
| 1247 // Consider what happens when a thread unlocks a stack-locked object. | |
| 1248 // It attempts to use CAS to swing the displaced header value from the | |
| 1249 // on-stack basiclock back into the object header. Recall also that the | |
| 1250 // header value (hashcode, etc) can reside in (a) the object header, or | |
| 1251 // (b) a displaced header associated with the stack-lock, or (c) a displaced | |
| 1252 // header in an objectMonitor. The inflate() routine must copy the header | |
| 1253 // value from the basiclock on the owner's stack to the objectMonitor, all | |
| 1254 // the while preserving the hashCode stability invariants. If the owner | |
| 1255 // decides to release the lock while the value is 0, the unlock will fail | |
| 1256 // and control will eventually pass from slow_exit() to inflate. The owner | |
| 1257 // will then spin, waiting for the 0 value to disappear. Put another way, | |
| 1258 // the 0 causes the owner to stall if the owner happens to try to | |
| 1259 // drop the lock (restoring the header from the basiclock to the object) | |
| 1260 // while inflation is in-progress. This protocol avoids races that might | |
| 1261 // would otherwise permit hashCode values to change or "flicker" for an object. | |
| 1262 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable. | |
| 1263 // 0 serves as a "BUSY" inflate-in-progress indicator. | |
| 1264 | |
| 1265 | |
| 1266 // fetch the displaced mark from the owner's stack. | |
| 1267 // The owner can't die or unwind past the lock while our INFLATING | |
| 1268 // object is in the mark. Furthermore the owner can't complete | |
| 1269 // an unlock on the object, either. | |
| 1270 markOop dmw = mark->displaced_mark_helper() ; | |
| 1271 assert (dmw->is_neutral(), "invariant") ; | |
| 1272 | |
| 1273 // Setup monitor fields to proper values -- prepare the monitor | |
| 1274 m->set_header(dmw) ; | |
| 1275 | |
| 1276 // Optimization: if the mark->locker stack address is associated | |
| 1277 // with this thread we could simply set m->_owner = Self and | |
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1278 // m->OwnerIsThread = 1. Note that a thread can inflate an object |
| 0 | 1279 // that it has stack-locked -- as might happen in wait() -- directly |
| 1280 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom. | |
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1281 m->set_owner(mark->locker()); |
| 0 | 1282 m->set_object(object); |
| 1283 // TODO-FIXME: assert BasicLock->dhw != 0. | |
| 1284 | |
| 1285 // Must preserve store ordering. The monitor state must | |
| 1286 // be stable at the time of publishing the monitor address. | |
| 1287 guarantee (object->mark() == markOopDesc::INFLATING(), "invariant") ; | |
| 1288 object->release_set_mark(markOopDesc::encode(m)); | |
| 1289 | |
| 1290 // Hopefully the performance counters are allocated on distinct cache lines | |
| 1291 // to avoid false sharing on MP systems ... | |
| 1878 | 1292 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ; |
| 0 | 1293 TEVENT(Inflate: overwrite stacklock) ; |
| 1294 if (TraceMonitorInflation) { | |
| 1295 if (object->is_instance()) { | |
| 1296 ResourceMark rm; | |
| 1297 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", | |
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1298 (void *) object, (intptr_t) object->mark(), |
| 6983 | 1299 object->klass()->external_name()); |
| 0 | 1300 } |
| 1301 } | |
| 1302 return m ; | |
| 1303 } | |
| 1304 | |
| 1305 // CASE: neutral | |
| 1306 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner. | |
| 1307 // If we know we're inflating for entry it's better to inflate by swinging a | |
| 1308 // pre-locked objectMonitor pointer into the object header. A successful | |
| 1309 // CAS inflates the object *and* confers ownership to the inflating thread. | |
| 1310 // In the current implementation we use a 2-step mechanism where we CAS() | |
| 1311 // to inflate and then CAS() again to try to swing _owner from NULL to Self. | |
| 1312 // An inflateTry() method that we could call from fast_enter() and slow_enter() | |
| 1313 // would be useful. | |
| 1314 | |
| 1315 assert (mark->is_neutral(), "invariant"); | |
| 1316 ObjectMonitor * m = omAlloc (Self) ; | |
| 1317 // prepare m for installation - set monitor to initial state | |
| 1318 m->Recycle(); | |
| 1319 m->set_header(mark); | |
| 1320 m->set_owner(NULL); | |
| 1321 m->set_object(object); | |
| 1322 m->OwnerIsThread = 1 ; | |
| 1323 m->_recursions = 0 ; | |
| 1324 m->_Responsible = NULL ; | |
| 1878 | 1325 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // consider: keep metastats by type/class |
| 0 | 1326 |
| 1327 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) { | |
| 1328 m->set_object (NULL) ; | |
| 1329 m->set_owner (NULL) ; | |
| 1330 m->OwnerIsThread = 0 ; | |
| 1331 m->Recycle() ; | |
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1332 omRelease (Self, m, true) ; |
| 0 | 1333 m = NULL ; |
| 1334 continue ; | |
| 1335 // interference - the markword changed - just retry. | |
| 1336 // The state-transitions are one-way, so there's no chance of | |
| 1337 // live-lock -- "Inflated" is an absorbing state. | |
| 1338 } | |
| 1339 | |
| 1340 // Hopefully the performance counters are allocated on distinct | |
| 1341 // cache lines to avoid false sharing on MP systems ... | |
| 1878 | 1342 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ; |
| 0 | 1343 TEVENT(Inflate: overwrite neutral) ; |
| 1344 if (TraceMonitorInflation) { | |
| 1345 if (object->is_instance()) { | |
| 1346 ResourceMark rm; | |
| 1347 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", | |
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1348 (void *) object, (intptr_t) object->mark(), |
| 6983 | 1349 object->klass()->external_name()); |
| 0 | 1350 } |
| 1351 } | |
| 1352 return m ; | |
| 1353 } | |
| 1354 } | |
| 1355 | |
| 1878 | 1356 // Note that we could encounter some performance loss through false-sharing as |
| 1357 // multiple locks occupy the same $ line. Padding might be appropriate. | |
| 0 | 1358 |
| 1359 | |
| 1360 // Deflate_idle_monitors() is called at all safepoints, immediately | |
| 1361 // after all mutators are stopped, but before any objects have moved. | |
| 1362 // It traverses the list of known monitors, deflating where possible. | |
| 1363 // The scavenged monitor are returned to the monitor free list. | |
| 1364 // | |
| 1365 // Beware that we scavenge at *every* stop-the-world point. | |
| 1366 // Having a large number of monitors in-circulation negatively | |
| 1367 // impacts the performance of some applications (e.g., PointBase). | |
| 1368 // Broadly, we want to minimize the # of monitors in circulation. | |
| 1587 | 1369 // |
| 1370 // We have added a flag, MonitorInUseLists, which creates a list | |
| 1371 // of active monitors for each thread. deflate_idle_monitors() | |
| 1372 // only scans the per-thread inuse lists. omAlloc() puts all | |
| 1373 // assigned monitors on the per-thread list. deflate_idle_monitors() | |
| 1374 // returns the non-busy monitors to the global free list. | |
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1375 // When a thread dies, omFlush() adds the list of active monitors for |
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1376 // that thread to a global gOmInUseList acquiring the |
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1377 // global list lock. deflate_idle_monitors() acquires the global |
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1378 // list lock to scan for non-busy monitors to the global free list. |
| 1587 | 1379 // An alternative could have used a single global inuse list. The |
| 1380 // downside would have been the additional cost of acquiring the global list lock | |
| 1381 // for every omAlloc(). | |
| 0 | 1382 // |
| 1383 // Perversely, the heap size -- and thus the STW safepoint rate -- | |
| 1384 // typically drives the scavenge rate. Large heaps can mean infrequent GC, | |
| 1385 // which in turn can mean large(r) numbers of objectmonitors in circulation. | |
| 1386 // This is an unfortunate aspect of this design. | |
| 1387 // | |
| 1388 | |
| 1878 | 1389 enum ManifestConstants { |
| 1390 ClearResponsibleAtSTW = 0, | |
| 1391 MaximumRecheckInterval = 1000 | |
| 1392 } ; | |
| 1587 | 1393 |
| 1394 // Deflate a single monitor if not in use | |
| 1395 // Return true if deflated, false if in use | |
| 1396 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj, | |
| 1397 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) { | |
| 1398 bool deflated; | |
| 1399 // Normal case ... The monitor is associated with obj. | |
| 1400 guarantee (obj->mark() == markOopDesc::encode(mid), "invariant") ; | |
| 1401 guarantee (mid == obj->mark()->monitor(), "invariant"); | |
| 1402 guarantee (mid->header()->is_neutral(), "invariant"); | |
| 1403 | |
| 1404 if (mid->is_busy()) { | |
| 1405 if (ClearResponsibleAtSTW) mid->_Responsible = NULL ; | |
| 1406 deflated = false; | |
| 1407 } else { | |
| 1408 // Deflate the monitor if it is no longer being used | |
| 1409 // It's idle - scavenge and return to the global free list | |
| 1410 // plain old deflation ... | |
| 1411 TEVENT (deflate_idle_monitors - scavenge1) ; | |
| 1412 if (TraceMonitorInflation) { | |
| 1413 if (obj->is_instance()) { | |
| 1414 ResourceMark rm; | |
| 1415 tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", | |
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1416 (void *) obj, (intptr_t) obj->mark(), obj->klass()->external_name()); |
| 1587 | 1417 } |
| 1418 } | |
| 1419 | |
| 1420 // Restore the header back to obj | |
| 1421 obj->release_set_mark(mid->header()); | |
| 1422 mid->clear(); | |
| 1423 | |
| 1424 assert (mid->object() == NULL, "invariant") ; | |
| 1425 | |
| 1426 // Move the object to the working free list defined by FreeHead,FreeTail. | |
| 1427 if (*FreeHeadp == NULL) *FreeHeadp = mid; | |
| 1428 if (*FreeTailp != NULL) { | |
| 1429 ObjectMonitor * prevtail = *FreeTailp; | |
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1430 assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); // TODO KK |
| 1587 | 1431 prevtail->FreeNext = mid; |
| 1432 } | |
| 1433 *FreeTailp = mid; | |
| 1434 deflated = true; | |
| 1435 } | |
| 1436 return deflated; | |
| 1437 } | |
| 1438 | |
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1439 // Caller acquires ListLock |
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1440 int ObjectSynchronizer::walk_monitor_list(ObjectMonitor** listheadp, |
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1441 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) { |
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1442 ObjectMonitor* mid; |
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1443 ObjectMonitor* next; |
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1444 ObjectMonitor* curmidinuse = NULL; |
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1445 int deflatedcount = 0; |
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1446 |
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1447 for (mid = *listheadp; mid != NULL; ) { |
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1448 oop obj = (oop) mid->object(); |
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1449 bool deflated = false; |
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1450 if (obj != NULL) { |
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1451 deflated = deflate_monitor(mid, obj, FreeHeadp, FreeTailp); |
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1452 } |
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1453 if (deflated) { |
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1454 // extract from per-thread in-use-list |
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1455 if (mid == *listheadp) { |
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1456 *listheadp = mid->FreeNext; |
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1457 } else if (curmidinuse != NULL) { |
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1458 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist |
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1459 } |
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1460 next = mid->FreeNext; |
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1461 mid->FreeNext = NULL; // This mid is current tail in the FreeHead list |
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1462 mid = next; |
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1463 deflatedcount++; |
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1464 } else { |
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1465 curmidinuse = mid; |
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1466 mid = mid->FreeNext; |
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1467 } |
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1468 } |
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1469 return deflatedcount; |
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1470 } |
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1471 |
| 0 | 1472 void ObjectSynchronizer::deflate_idle_monitors() { |
| 1473 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); | |
| 1474 int nInuse = 0 ; // currently associated with objects | |
| 1475 int nInCirculation = 0 ; // extant | |
| 1476 int nScavenged = 0 ; // reclaimed | |
| 1587 | 1477 bool deflated = false; |
| 0 | 1478 |
| 1479 ObjectMonitor * FreeHead = NULL ; // Local SLL of scavenged monitors | |
| 1480 ObjectMonitor * FreeTail = NULL ; | |
| 1481 | |
| 1587 | 1482 TEVENT (deflate_idle_monitors) ; |
| 1483 // Prevent omFlush from changing mids in Thread dtor's during deflation | |
| 1484 // And in case the vm thread is acquiring a lock during a safepoint | |
| 1485 // See e.g. 6320749 | |
| 1486 Thread::muxAcquire (&ListLock, "scavenge - return") ; | |
| 1487 | |
| 1488 if (MonitorInUseLists) { | |
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1489 int inUse = 0; |
| 1587 | 1490 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) { |
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1491 nInCirculation+= cur->omInUseCount; |
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1492 int deflatedcount = walk_monitor_list(cur->omInUseList_addr(), &FreeHead, &FreeTail); |
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1493 cur->omInUseCount-= deflatedcount; |
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1494 // verifyInUse(cur); |
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1495 nScavenged += deflatedcount; |
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1496 nInuse += cur->omInUseCount; |
| 1587 | 1497 } |
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1498 |
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1499 // For moribund threads, scan gOmInUseList |
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1500 if (gOmInUseList) { |
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1501 nInCirculation += gOmInUseCount; |
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1502 int deflatedcount = walk_monitor_list((ObjectMonitor **)&gOmInUseList, &FreeHead, &FreeTail); |
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1503 gOmInUseCount-= deflatedcount; |
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1504 nScavenged += deflatedcount; |
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1505 nInuse += gOmInUseCount; |
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1506 } |
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1507 |
| 1587 | 1508 } else for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) { |
| 0 | 1509 // Iterate over all extant monitors - Scavenge all idle monitors. |
| 1510 assert(block->object() == CHAINMARKER, "must be a block header"); | |
| 1511 nInCirculation += _BLOCKSIZE ; | |
| 1512 for (int i = 1 ; i < _BLOCKSIZE; i++) { | |
| 1513 ObjectMonitor* mid = &block[i]; | |
| 1514 oop obj = (oop) mid->object(); | |
| 1515 | |
| 1516 if (obj == NULL) { | |
| 1517 // The monitor is not associated with an object. | |
| 1518 // The monitor should either be a thread-specific private | |
| 1519 // free list or the global free list. | |
| 1520 // obj == NULL IMPLIES mid->is_busy() == 0 | |
| 1521 guarantee (!mid->is_busy(), "invariant") ; | |
| 1522 continue ; | |
| 1523 } | |
| 1587 | 1524 deflated = deflate_monitor(mid, obj, &FreeHead, &FreeTail); |
| 1525 | |
| 1526 if (deflated) { | |
| 1527 mid->FreeNext = NULL ; | |
| 1528 nScavenged ++ ; | |
| 0 | 1529 } else { |
| 1587 | 1530 nInuse ++; |
| 0 | 1531 } |
| 1532 } | |
| 1533 } | |
| 1534 | |
| 1587 | 1535 MonitorFreeCount += nScavenged; |
| 1536 | |
| 1537 // Consider: audit gFreeList to ensure that MonitorFreeCount and list agree. | |
| 1538 | |
| 1878 | 1539 if (ObjectMonitor::Knob_Verbose) { |
| 1587 | 1540 ::printf ("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n", |
| 1541 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge, | |
| 1542 MonitorPopulation, MonitorFreeCount) ; | |
| 1543 ::fflush(stdout) ; | |
| 1544 } | |
| 1545 | |
| 1546 ForceMonitorScavenge = 0; // Reset | |
| 1547 | |
| 0 | 1548 // Move the scavenged monitors back to the global free list. |
| 1549 if (FreeHead != NULL) { | |
| 1550 guarantee (FreeTail != NULL && nScavenged > 0, "invariant") ; | |
| 1551 assert (FreeTail->FreeNext == NULL, "invariant") ; | |
| 1552 // constant-time list splice - prepend scavenged segment to gFreeList | |
| 1553 FreeTail->FreeNext = gFreeList ; | |
| 1554 gFreeList = FreeHead ; | |
| 1555 } | |
| 1587 | 1556 Thread::muxRelease (&ListLock) ; |
| 0 | 1557 |
| 1878 | 1558 if (ObjectMonitor::_sync_Deflations != NULL) ObjectMonitor::_sync_Deflations->inc(nScavenged) ; |
| 1559 if (ObjectMonitor::_sync_MonExtant != NULL) ObjectMonitor::_sync_MonExtant ->set_value(nInCirculation); | |
| 0 | 1560 |
| 1561 // TODO: Add objectMonitor leak detection. | |
| 1562 // Audit/inventory the objectMonitors -- make sure they're all accounted for. | |
| 1563 GVars.stwRandom = os::random() ; | |
| 1564 GVars.stwCycle ++ ; | |
| 1565 } | |
| 1566 | |
| 1878 | 1567 // Monitor cleanup on JavaThread::exit |
| 0 | 1568 |
| 1878 | 1569 // Iterate through monitor cache and attempt to release thread's monitors |
| 1570 // Gives up on a particular monitor if an exception occurs, but continues | |
| 1571 // the overall iteration, swallowing the exception. | |
| 1572 class ReleaseJavaMonitorsClosure: public MonitorClosure { | |
| 1573 private: | |
| 1574 TRAPS; | |
| 0 | 1575 |
| 1878 | 1576 public: |
| 1577 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {} | |
| 1578 void do_monitor(ObjectMonitor* mid) { | |
| 1579 if (mid->owner() == THREAD) { | |
| 1580 (void)mid->complete_exit(CHECK); | |
| 0 | 1581 } |
| 1582 } | |
| 1878 | 1583 }; |
| 0 | 1584 |
| 1878 | 1585 // Release all inflated monitors owned by THREAD. Lightweight monitors are |
| 1586 // ignored. This is meant to be called during JNI thread detach which assumes | |
| 1587 // all remaining monitors are heavyweight. All exceptions are swallowed. | |
| 1588 // Scanning the extant monitor list can be time consuming. | |
| 1589 // A simple optimization is to add a per-thread flag that indicates a thread | |
| 1590 // called jni_monitorenter() during its lifetime. | |
| 0 | 1591 // |
| 1878 | 1592 // Instead of No_Savepoint_Verifier it might be cheaper to |
| 1593 // use an idiom of the form: | |
| 1594 // auto int tmp = SafepointSynchronize::_safepoint_counter ; | |
| 1595 // <code that must not run at safepoint> | |
| 1596 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ; | |
| 1597 // Since the tests are extremely cheap we could leave them enabled | |
| 1598 // for normal product builds. | |
| 0 | 1599 |
| 1878 | 1600 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) { |
| 1601 assert(THREAD == JavaThread::current(), "must be current Java thread"); | |
| 1602 No_Safepoint_Verifier nsv ; | |
| 1603 ReleaseJavaMonitorsClosure rjmc(THREAD); | |
| 1604 Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread"); | |
| 1605 ObjectSynchronizer::monitors_iterate(&rjmc); | |
| 1606 Thread::muxRelease(&ListLock); | |
| 1607 THREAD->clear_pending_exception(); | |
| 0 | 1608 } |
| 1609 | |
| 1610 //------------------------------------------------------------------------------ | |
| 1611 // Non-product code | |
| 1612 | |
| 1613 #ifndef PRODUCT | |
| 1614 | |
| 1615 // Verify all monitors in the monitor cache, the verification is weak. | |
| 1616 void ObjectSynchronizer::verify() { | |
| 1617 ObjectMonitor* block = gBlockList; | |
| 1618 ObjectMonitor* mid; | |
| 1619 while (block) { | |
| 1620 assert(block->object() == CHAINMARKER, "must be a block header"); | |
| 1621 for (int i = 1; i < _BLOCKSIZE; i++) { | |
| 1622 mid = block + i; | |
| 1623 oop object = (oop) mid->object(); | |
| 1624 if (object != NULL) { | |
| 1625 mid->verify(); | |
| 1626 } | |
| 1627 } | |
| 1628 block = (ObjectMonitor*) block->FreeNext; | |
| 1629 } | |
| 1630 } | |
| 1631 | |
| 1632 // Check if monitor belongs to the monitor cache | |
| 1633 // The list is grow-only so it's *relatively* safe to traverse | |
| 1634 // the list of extant blocks without taking a lock. | |
| 1635 | |
| 1636 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) { | |
| 1637 ObjectMonitor* block = gBlockList; | |
| 1638 | |
| 1639 while (block) { | |
| 1640 assert(block->object() == CHAINMARKER, "must be a block header"); | |
| 1641 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) { | |
| 1642 address mon = (address) monitor; | |
| 1643 address blk = (address) block; | |
| 1644 size_t diff = mon - blk; | |
| 1645 assert((diff % sizeof(ObjectMonitor)) == 0, "check"); | |
| 1646 return 1; | |
| 1647 } | |
| 1648 block = (ObjectMonitor*) block->FreeNext; | |
| 1649 } | |
| 1650 return 0; | |
| 1651 } | |
| 1652 | |
| 1653 #endif |