1 /* 2 * Copyright (c) 1998, 2012, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "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" 39 #include "utilities/dtrace.hpp" 40 #include "utilities/events.hpp" 41 #include "utilities/preserveException.hpp" 42 #ifdef TARGET_OS_FAMILY_linux 43 # include "os_linux.inline.hpp" 44 # include "thread_linux.inline.hpp" 45 #endif 46 #ifdef TARGET_OS_FAMILY_solaris 47 # include "os_solaris.inline.hpp" 48 # include "thread_solaris.inline.hpp" 49 #endif 50 #ifdef TARGET_OS_FAMILY_windows 51 # include "os_windows.inline.hpp" 52 # include "thread_windows.inline.hpp" 53 #endif 54 #ifdef TARGET_OS_FAMILY_bsd 55 # include "os_bsd.inline.hpp" 56 # include "thread_bsd.inline.hpp" 57 #endif 58 59 #if defined(__GNUC__) && !defined(IA64) 60 // Need to inhibit inlining for older versions of GCC to avoid build-time failures 61 #define ATTR __attribute__((noinline)) 62 #else 63 #define ATTR 64 #endif 65 66 // The "core" versions of monitor enter and exit reside in this file. 67 // The interpreter and compilers contain specialized transliterated 68 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(), 69 // for instance. If you make changes here, make sure to modify the 70 // interpreter, and both C1 and C2 fast-path inline locking code emission. 71 // 72 // 73 // ----------------------------------------------------------------------------- 74 75 #ifdef DTRACE_ENABLED 76 77 // Only bother with this argument setup if dtrace is available 78 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly. 79 80 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \ 81 char* bytes = NULL; \ 82 int len = 0; \ 83 jlong jtid = SharedRuntime::get_java_tid(thread); \ 84 Symbol* klassname = ((oop)(obj))->klass()->name(); \ 85 if (klassname != NULL) { \ 86 bytes = (char*)klassname->bytes(); \ 87 len = klassname->utf8_length(); \ 88 } 89 90 #ifndef USDT2 91 HS_DTRACE_PROBE_DECL5(hotspot, monitor__wait, 92 jlong, uintptr_t, char*, int, long); 93 HS_DTRACE_PROBE_DECL4(hotspot, monitor__waited, 94 jlong, uintptr_t, char*, int); 95 96 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \ 97 { \ 98 if (DTraceMonitorProbes) { \ 99 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 100 HS_DTRACE_PROBE5(hotspot, monitor__wait, jtid, \ 101 (monitor), bytes, len, (millis)); \ 102 } \ 103 } 104 105 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \ 106 { \ 107 if (DTraceMonitorProbes) { \ 108 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 109 HS_DTRACE_PROBE4(hotspot, monitor__##probe, jtid, \ 110 (uintptr_t)(monitor), bytes, len); \ 111 } \ 112 } 113 114 #else /* USDT2 */ 115 116 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \ 117 { \ 118 if (DTraceMonitorProbes) { \ 119 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 120 HOTSPOT_MONITOR_WAIT(jtid, \ 121 (uintptr_t)(monitor), bytes, len, (millis)); \ 122 } \ 123 } 124 125 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_PROBE_WAITED 126 127 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \ 128 { \ 129 if (DTraceMonitorProbes) { \ 130 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 131 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \ 132 (uintptr_t)(monitor), bytes, len); \ 133 } \ 134 } 135 136 #endif /* USDT2 */ 137 #else // ndef DTRACE_ENABLED 138 139 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;} 140 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;} 141 142 #endif // ndef DTRACE_ENABLED 143 144 // This exists only as a workaround of dtrace bug 6254741 145 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) { 146 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr); 147 return 0; 148 } 149 150 #define NINFLATIONLOCKS 256 151 static volatile intptr_t InflationLocks [NINFLATIONLOCKS] ; 152 153 ObjectMonitor * ObjectSynchronizer::gBlockList = NULL ; 154 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL ; 155 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL ; 156 int ObjectSynchronizer::gOmInUseCount = 0; 157 static volatile intptr_t ListLock = 0 ; // protects global monitor free-list cache 158 static volatile int MonitorFreeCount = 0 ; // # on gFreeList 159 static volatile int MonitorPopulation = 0 ; // # Extant -- in circulation 160 #define CHAINMARKER ((oop)-1) 161 162 // ----------------------------------------------------------------------------- 163 // Fast Monitor Enter/Exit 164 // This the fast monitor enter. The interpreter and compiler use 165 // some assembly copies of this code. Make sure update those code 166 // if the following function is changed. The implementation is 167 // extremely sensitive to race condition. Be careful. 168 169 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock, bool attempt_rebias, TRAPS) { 170 if (UseBiasedLocking) { 171 if (!SafepointSynchronize::is_at_safepoint()) { 172 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD); 173 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) { 174 return; 175 } 176 } else { 177 assert(!attempt_rebias, "can not rebias toward VM thread"); 178 BiasedLocking::revoke_at_safepoint(obj); 179 } 180 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 181 } 182 183 slow_enter (obj, lock, THREAD) ; 184 } 185 186 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) { 187 assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here"); 188 // if displaced header is null, the previous enter is recursive enter, no-op 189 markOop dhw = lock->displaced_header(); 190 markOop mark ; 191 if (dhw == NULL) { 192 // Recursive stack-lock. 193 // Diagnostics -- Could be: stack-locked, inflating, inflated. 194 mark = object->mark() ; 195 assert (!mark->is_neutral(), "invariant") ; 196 if (mark->has_locker() && mark != markOopDesc::INFLATING()) { 197 assert(THREAD->is_lock_owned((address)mark->locker()), "invariant") ; 198 } 199 if (mark->has_monitor()) { 200 ObjectMonitor * m = mark->monitor() ; 201 assert(((oop)(m->object()))->mark() == mark, "invariant") ; 202 assert(m->is_entered(THREAD), "invariant") ; 203 } 204 return ; 205 } 206 207 mark = object->mark() ; 208 209 // If the object is stack-locked by the current thread, try to 210 // swing the displaced header from the box back to the mark. 211 if (mark == (markOop) lock) { 212 assert (dhw->is_neutral(), "invariant") ; 213 if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) { 214 TEVENT (fast_exit: release stacklock) ; 215 return; 216 } 217 } 218 219 ObjectSynchronizer::inflate(THREAD, object)->exit (THREAD) ; 220 } 221 222 // ----------------------------------------------------------------------------- 223 // Interpreter/Compiler Slow Case 224 // This routine is used to handle interpreter/compiler slow case 225 // We don't need to use fast path here, because it must have been 226 // failed in the interpreter/compiler code. 227 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) { 228 markOop mark = obj->mark(); 229 assert(!mark->has_bias_pattern(), "should not see bias pattern here"); 230 231 if (mark->is_neutral()) { 232 // Anticipate successful CAS -- the ST of the displaced mark must 233 // be visible <= the ST performed by the CAS. 234 lock->set_displaced_header(mark); 235 if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) { 236 TEVENT (slow_enter: release stacklock) ; 237 return ; 238 } 239 // Fall through to inflate() ... 240 } else 241 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { 242 assert(lock != mark->locker(), "must not re-lock the same lock"); 243 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock"); 244 lock->set_displaced_header(NULL); 245 return; 246 } 247 248 #if 0 249 // The following optimization isn't particularly useful. 250 if (mark->has_monitor() && mark->monitor()->is_entered(THREAD)) { 251 lock->set_displaced_header (NULL) ; 252 return ; 253 } 254 #endif 255 256 // The object header will never be displaced to this lock, 257 // so it does not matter what the value is, except that it 258 // must be non-zero to avoid looking like a re-entrant lock, 259 // and must not look locked either. 260 lock->set_displaced_header(markOopDesc::unused_mark()); 261 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD); 262 } 263 264 // This routine is used to handle interpreter/compiler slow case 265 // We don't need to use fast path here, because it must have 266 // failed in the interpreter/compiler code. Simply use the heavy 267 // weight monitor should be ok, unless someone find otherwise. 268 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) { 269 fast_exit (object, lock, THREAD) ; 270 } 271 272 // ----------------------------------------------------------------------------- 273 // Class Loader support to workaround deadlocks on the class loader lock objects 274 // Also used by GC 275 // complete_exit()/reenter() are used to wait on a nested lock 276 // i.e. to give up an outer lock completely and then re-enter 277 // Used when holding nested locks - lock acquisition order: lock1 then lock2 278 // 1) complete_exit lock1 - saving recursion count 279 // 2) wait on lock2 280 // 3) when notified on lock2, unlock lock2 281 // 4) reenter lock1 with original recursion count 282 // 5) lock lock2 283 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 284 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) { 285 TEVENT (complete_exit) ; 286 if (UseBiasedLocking) { 287 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 288 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 289 } 290 291 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); 292 293 return monitor->complete_exit(THREAD); 294 } 295 296 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 297 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) { 298 TEVENT (reenter) ; 299 if (UseBiasedLocking) { 300 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 301 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 302 } 303 304 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); 305 306 monitor->reenter(recursion, THREAD); 307 } 308 // ----------------------------------------------------------------------------- 309 // JNI locks on java objects 310 // NOTE: must use heavy weight monitor to handle jni monitor enter 311 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) { // possible entry from jni enter 312 // the current locking is from JNI instead of Java code 313 TEVENT (jni_enter) ; 314 if (UseBiasedLocking) { 315 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 316 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 317 } 318 THREAD->set_current_pending_monitor_is_from_java(false); 319 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD); 320 THREAD->set_current_pending_monitor_is_from_java(true); 321 } 322 323 // NOTE: must use heavy weight monitor to handle jni monitor enter 324 bool ObjectSynchronizer::jni_try_enter(Handle obj, Thread* THREAD) { 325 if (UseBiasedLocking) { 326 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 327 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 328 } 329 330 ObjectMonitor* monitor = ObjectSynchronizer::inflate_helper(obj()); 331 return monitor->try_enter(THREAD); 332 } 333 334 335 // NOTE: must use heavy weight monitor to handle jni monitor exit 336 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) { 337 TEVENT (jni_exit) ; 338 if (UseBiasedLocking) { 339 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 340 } 341 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 342 343 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj); 344 // If this thread has locked the object, exit the monitor. Note: can't use 345 // monitor->check(CHECK); must exit even if an exception is pending. 346 if (monitor->check(THREAD)) { 347 monitor->exit(THREAD); 348 } 349 } 350 351 // ----------------------------------------------------------------------------- 352 // Internal VM locks on java objects 353 // standard constructor, allows locking failures 354 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) { 355 _dolock = doLock; 356 _thread = thread; 357 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);) 358 _obj = obj; 359 360 if (_dolock) { 361 TEVENT (ObjectLocker) ; 362 363 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread); 364 } 365 } 366 367 ObjectLocker::~ObjectLocker() { 368 if (_dolock) { 369 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread); 370 } 371 } 372 373 374 // ----------------------------------------------------------------------------- 375 // Wait/Notify/NotifyAll 376 // NOTE: must use heavy weight monitor to handle wait() 377 void ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) { 378 if (UseBiasedLocking) { 379 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 380 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 381 } 382 if (millis < 0) { 383 TEVENT (wait - throw IAX) ; 384 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); 385 } 386 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); 387 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis); 388 monitor->wait(millis, true, THREAD); 389 390 /* This dummy call is in place to get around dtrace bug 6254741. Once 391 that's fixed we can uncomment the following line and remove the call */ 392 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD); 393 dtrace_waited_probe(monitor, obj, THREAD); 394 } 395 396 void ObjectSynchronizer::waitUninterruptibly (Handle obj, jlong millis, TRAPS) { 397 if (UseBiasedLocking) { 398 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 399 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 400 } 401 if (millis < 0) { 402 TEVENT (wait - throw IAX) ; 403 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); 404 } 405 ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD) ; 406 } 407 408 void ObjectSynchronizer::notify(Handle obj, TRAPS) { 409 if (UseBiasedLocking) { 410 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 411 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 412 } 413 414 markOop mark = obj->mark(); 415 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { 416 return; 417 } 418 ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD); 419 } 420 421 // NOTE: see comment of notify() 422 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) { 423 if (UseBiasedLocking) { 424 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 425 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 426 } 427 428 markOop mark = obj->mark(); 429 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { 430 return; 431 } 432 ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD); 433 } 434 435 // ----------------------------------------------------------------------------- 436 // Hash Code handling 437 // 438 // Performance concern: 439 // OrderAccess::storestore() calls release() which STs 0 into the global volatile 440 // OrderAccess::Dummy variable. This store is unnecessary for correctness. 441 // Many threads STing into a common location causes considerable cache migration 442 // or "sloshing" on large SMP system. As such, I avoid using OrderAccess::storestore() 443 // until it's repaired. In some cases OrderAccess::fence() -- which incurs local 444 // latency on the executing processor -- is a better choice as it scales on SMP 445 // systems. See http://blogs.sun.com/dave/entry/biased_locking_in_hotspot for a 446 // discussion of coherency costs. Note that all our current reference platforms 447 // provide strong ST-ST order, so the issue is moot on IA32, x64, and SPARC. 448 // 449 // As a general policy we use "volatile" to control compiler-based reordering 450 // and explicit fences (barriers) to control for architectural reordering performed 451 // by the CPU(s) or platform. 452 453 static int MBFence (int x) { OrderAccess::fence(); return x; } 454 455 struct SharedGlobals { 456 // These are highly shared mostly-read variables. 457 // To avoid false-sharing they need to be the sole occupants of a $ line. 458 double padPrefix [8]; 459 volatile int stwRandom ; 460 volatile int stwCycle ; 461 462 // Hot RW variables -- Sequester to avoid false-sharing 463 double padSuffix [16]; 464 volatile int hcSequence ; 465 double padFinal [8] ; 466 } ; 467 468 static SharedGlobals GVars ; 469 static int MonitorScavengeThreshold = 1000000 ; 470 static volatile int ForceMonitorScavenge = 0 ; // Scavenge required and pending 471 472 static markOop ReadStableMark (oop obj) { 473 markOop mark = obj->mark() ; 474 if (!mark->is_being_inflated()) { 475 return mark ; // normal fast-path return 476 } 477 478 int its = 0 ; 479 for (;;) { 480 markOop mark = obj->mark() ; 481 if (!mark->is_being_inflated()) { 482 return mark ; // normal fast-path return 483 } 484 485 // The object is being inflated by some other thread. 486 // The caller of ReadStableMark() must wait for inflation to complete. 487 // Avoid live-lock 488 // TODO: consider calling SafepointSynchronize::do_call_back() while 489 // spinning to see if there's a safepoint pending. If so, immediately 490 // yielding or blocking would be appropriate. Avoid spinning while 491 // there is a safepoint pending. 492 // TODO: add inflation contention performance counters. 493 // TODO: restrict the aggregate number of spinners. 494 495 ++its ; 496 if (its > 10000 || !os::is_MP()) { 497 if (its & 1) { 498 os::NakedYield() ; 499 TEVENT (Inflate: INFLATING - yield) ; 500 } else { 501 // Note that the following code attenuates the livelock problem but is not 502 // a complete remedy. A more complete solution would require that the inflating 503 // thread hold the associated inflation lock. The following code simply restricts 504 // the number of spinners to at most one. We'll have N-2 threads blocked 505 // on the inflationlock, 1 thread holding the inflation lock and using 506 // a yield/park strategy, and 1 thread in the midst of inflation. 507 // A more refined approach would be to change the encoding of INFLATING 508 // to allow encapsulation of a native thread pointer. Threads waiting for 509 // inflation to complete would use CAS to push themselves onto a singly linked 510 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag 511 // and calling park(). When inflation was complete the thread that accomplished inflation 512 // would detach the list and set the markword to inflated with a single CAS and 513 // then for each thread on the list, set the flag and unpark() the thread. 514 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease 515 // wakes at most one thread whereas we need to wake the entire list. 516 int ix = (intptr_t(obj) >> 5) & (NINFLATIONLOCKS-1) ; 517 int YieldThenBlock = 0 ; 518 assert (ix >= 0 && ix < NINFLATIONLOCKS, "invariant") ; 519 assert ((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant") ; 520 Thread::muxAcquire (InflationLocks + ix, "InflationLock") ; 521 while (obj->mark() == markOopDesc::INFLATING()) { 522 // Beware: NakedYield() is advisory and has almost no effect on some platforms 523 // so we periodically call Self->_ParkEvent->park(1). 524 // We use a mixed spin/yield/block mechanism. 525 if ((YieldThenBlock++) >= 16) { 526 Thread::current()->_ParkEvent->park(1) ; 527 } else { 528 os::NakedYield() ; 529 } 530 } 531 Thread::muxRelease (InflationLocks + ix ) ; 532 TEVENT (Inflate: INFLATING - yield/park) ; 533 } 534 } else { 535 SpinPause() ; // SMP-polite spinning 536 } 537 } 538 } 539 540 // hashCode() generation : 541 // 542 // Possibilities: 543 // * MD5Digest of {obj,stwRandom} 544 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function. 545 // * A DES- or AES-style SBox[] mechanism 546 // * One of the Phi-based schemes, such as: 547 // 2654435761 = 2^32 * Phi (golden ratio) 548 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ; 549 // * A variation of Marsaglia's shift-xor RNG scheme. 550 // * (obj ^ stwRandom) is appealing, but can result 551 // in undesirable regularity in the hashCode values of adjacent objects 552 // (objects allocated back-to-back, in particular). This could potentially 553 // result in hashtable collisions and reduced hashtable efficiency. 554 // There are simple ways to "diffuse" the middle address bits over the 555 // generated hashCode values: 556 // 557 558 static inline intptr_t get_next_hash(Thread * Self, oop obj) { 559 intptr_t value = 0 ; 560 if (hashCode == 0) { 561 // This form uses an unguarded global Park-Miller RNG, 562 // so it's possible for two threads to race and generate the same RNG. 563 // On MP system we'll have lots of RW access to a global, so the 564 // mechanism induces lots of coherency traffic. 565 value = os::random() ; 566 } else 567 if (hashCode == 1) { 568 // This variation has the property of being stable (idempotent) 569 // between STW operations. This can be useful in some of the 1-0 570 // synchronization schemes. 571 intptr_t addrBits = intptr_t(obj) >> 3 ; 572 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom ; 573 } else 574 if (hashCode == 2) { 575 value = 1 ; // for sensitivity testing 576 } else 577 if (hashCode == 3) { 578 value = ++GVars.hcSequence ; 579 } else 580 if (hashCode == 4) { 581 value = intptr_t(obj) ; 582 } else { 583 // Marsaglia's xor-shift scheme with thread-specific state 584 // This is probably the best overall implementation -- we'll 585 // likely make this the default in future releases. 586 unsigned t = Self->_hashStateX ; 587 t ^= (t << 11) ; 588 Self->_hashStateX = Self->_hashStateY ; 589 Self->_hashStateY = Self->_hashStateZ ; 590 Self->_hashStateZ = Self->_hashStateW ; 591 unsigned v = Self->_hashStateW ; 592 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)) ; 593 Self->_hashStateW = v ; 594 value = v ; 595 } 596 597 value &= markOopDesc::hash_mask; 598 if (value == 0) value = 0xBAD ; 599 assert (value != markOopDesc::no_hash, "invariant") ; 600 TEVENT (hashCode: GENERATE) ; 601 return value; 602 } 603 // 604 intptr_t ObjectSynchronizer::FastHashCode (Thread * Self, oop obj) { 605 if (UseBiasedLocking) { 606 // NOTE: many places throughout the JVM do not expect a safepoint 607 // to be taken here, in particular most operations on perm gen 608 // objects. However, we only ever bias Java instances and all of 609 // the call sites of identity_hash that might revoke biases have 610 // been checked to make sure they can handle a safepoint. The 611 // added check of the bias pattern is to avoid useless calls to 612 // thread-local storage. 613 if (obj->mark()->has_bias_pattern()) { 614 // Box and unbox the raw reference just in case we cause a STW safepoint. 615 Handle hobj (Self, obj) ; 616 // Relaxing assertion for bug 6320749. 617 assert (Universe::verify_in_progress() || 618 !SafepointSynchronize::is_at_safepoint(), 619 "biases should not be seen by VM thread here"); 620 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current()); 621 obj = hobj() ; 622 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 623 } 624 } 625 626 // hashCode() is a heap mutator ... 627 // Relaxing assertion for bug 6320749. 628 assert (Universe::verify_in_progress() || 629 !SafepointSynchronize::is_at_safepoint(), "invariant") ; 630 assert (Universe::verify_in_progress() || 631 Self->is_Java_thread() , "invariant") ; 632 assert (Universe::verify_in_progress() || 633 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ; 634 635 ObjectMonitor* monitor = NULL; 636 markOop temp, test; 637 intptr_t hash; 638 markOop mark = ReadStableMark (obj); 639 640 // object should remain ineligible for biased locking 641 assert (!mark->has_bias_pattern(), "invariant") ; 642 643 if (mark->is_neutral()) { 644 hash = mark->hash(); // this is a normal header 645 if (hash) { // if it has hash, just return it 646 return hash; 647 } 648 hash = get_next_hash(Self, obj); // allocate a new hash code 649 temp = mark->copy_set_hash(hash); // merge the hash code into header 650 // use (machine word version) atomic operation to install the hash 651 test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark); 652 if (test == mark) { 653 return hash; 654 } 655 // If atomic operation failed, we must inflate the header 656 // into heavy weight monitor. We could add more code here 657 // for fast path, but it does not worth the complexity. 658 } else if (mark->has_monitor()) { 659 monitor = mark->monitor(); 660 temp = monitor->header(); 661 assert (temp->is_neutral(), "invariant") ; 662 hash = temp->hash(); 663 if (hash) { 664 return hash; 665 } 666 // Skip to the following code to reduce code size 667 } else if (Self->is_lock_owned((address)mark->locker())) { 668 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned 669 assert (temp->is_neutral(), "invariant") ; 670 hash = temp->hash(); // by current thread, check if the displaced 671 if (hash) { // header contains hash code 672 return hash; 673 } 674 // WARNING: 675 // The displaced header is strictly immutable. 676 // It can NOT be changed in ANY cases. So we have 677 // to inflate the header into heavyweight monitor 678 // even the current thread owns the lock. The reason 679 // is the BasicLock (stack slot) will be asynchronously 680 // read by other threads during the inflate() function. 681 // Any change to stack may not propagate to other threads 682 // correctly. 683 } 684 685 // Inflate the monitor to set hash code 686 monitor = ObjectSynchronizer::inflate(Self, obj); 687 // Load displaced header and check it has hash code 688 mark = monitor->header(); 689 assert (mark->is_neutral(), "invariant") ; 690 hash = mark->hash(); 691 if (hash == 0) { 692 hash = get_next_hash(Self, obj); 693 temp = mark->copy_set_hash(hash); // merge hash code into header 694 assert (temp->is_neutral(), "invariant") ; 695 test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark); 696 if (test != mark) { 697 // The only update to the header in the monitor (outside GC) 698 // is install the hash code. If someone add new usage of 699 // displaced header, please update this code 700 hash = test->hash(); 701 assert (test->is_neutral(), "invariant") ; 702 assert (hash != 0, "Trivial unexpected object/monitor header usage."); 703 } 704 } 705 // We finally get the hash 706 return hash; 707 } 708 709 // Deprecated -- use FastHashCode() instead. 710 711 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) { 712 return FastHashCode (Thread::current(), obj()) ; 713 } 714 715 716 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread, 717 Handle h_obj) { 718 if (UseBiasedLocking) { 719 BiasedLocking::revoke_and_rebias(h_obj, false, thread); 720 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 721 } 722 723 assert(thread == JavaThread::current(), "Can only be called on current thread"); 724 oop obj = h_obj(); 725 726 markOop mark = ReadStableMark (obj) ; 727 728 // Uncontended case, header points to stack 729 if (mark->has_locker()) { 730 return thread->is_lock_owned((address)mark->locker()); 731 } 732 // Contended case, header points to ObjectMonitor (tagged pointer) 733 if (mark->has_monitor()) { 734 ObjectMonitor* monitor = mark->monitor(); 735 return monitor->is_entered(thread) != 0 ; 736 } 737 // Unlocked case, header in place 738 assert(mark->is_neutral(), "sanity check"); 739 return false; 740 } 741 742 // Be aware of this method could revoke bias of the lock object. 743 // This method querys the ownership of the lock handle specified by 'h_obj'. 744 // If the current thread owns the lock, it returns owner_self. If no 745 // thread owns the lock, it returns owner_none. Otherwise, it will return 746 // ower_other. 747 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership 748 (JavaThread *self, Handle h_obj) { 749 // The caller must beware this method can revoke bias, and 750 // revocation can result in a safepoint. 751 assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ; 752 assert (self->thread_state() != _thread_blocked , "invariant") ; 753 754 // Possible mark states: neutral, biased, stack-locked, inflated 755 756 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) { 757 // CASE: biased 758 BiasedLocking::revoke_and_rebias(h_obj, false, self); 759 assert(!h_obj->mark()->has_bias_pattern(), 760 "biases should be revoked by now"); 761 } 762 763 assert(self == JavaThread::current(), "Can only be called on current thread"); 764 oop obj = h_obj(); 765 markOop mark = ReadStableMark (obj) ; 766 767 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack. 768 if (mark->has_locker()) { 769 return self->is_lock_owned((address)mark->locker()) ? 770 owner_self : owner_other; 771 } 772 773 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor. 774 // The Object:ObjectMonitor relationship is stable as long as we're 775 // not at a safepoint. 776 if (mark->has_monitor()) { 777 void * owner = mark->monitor()->_owner ; 778 if (owner == NULL) return owner_none ; 779 return (owner == self || 780 self->is_lock_owned((address)owner)) ? owner_self : owner_other; 781 } 782 783 // CASE: neutral 784 assert(mark->is_neutral(), "sanity check"); 785 return owner_none ; // it's unlocked 786 } 787 788 // FIXME: jvmti should call this 789 JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) { 790 if (UseBiasedLocking) { 791 if (SafepointSynchronize::is_at_safepoint()) { 792 BiasedLocking::revoke_at_safepoint(h_obj); 793 } else { 794 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current()); 795 } 796 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 797 } 798 799 oop obj = h_obj(); 800 address owner = NULL; 801 802 markOop mark = ReadStableMark (obj) ; 803 804 // Uncontended case, header points to stack 805 if (mark->has_locker()) { 806 owner = (address) mark->locker(); 807 } 808 809 // Contended case, header points to ObjectMonitor (tagged pointer) 810 if (mark->has_monitor()) { 811 ObjectMonitor* monitor = mark->monitor(); 812 assert(monitor != NULL, "monitor should be non-null"); 813 owner = (address) monitor->owner(); 814 } 815 816 if (owner != NULL) { 817 return Threads::owning_thread_from_monitor_owner(owner, doLock); 818 } 819 820 // Unlocked case, header in place 821 // Cannot have assertion since this object may have been 822 // locked by another thread when reaching here. 823 // assert(mark->is_neutral(), "sanity check"); 824 825 return NULL; 826 } 827 // Visitors ... 828 829 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) { 830 ObjectMonitor* block = gBlockList; 831 ObjectMonitor* mid; 832 while (block) { 833 assert(block->object() == CHAINMARKER, "must be a block header"); 834 for (int i = _BLOCKSIZE - 1; i > 0; i--) { 835 mid = block + i; 836 oop object = (oop) mid->object(); 837 if (object != NULL) { 838 closure->do_monitor(mid); 839 } 840 } 841 block = (ObjectMonitor*) block->FreeNext; 842 } 843 } 844 845 // Get the next block in the block list. 846 static inline ObjectMonitor* next(ObjectMonitor* block) { 847 assert(block->object() == CHAINMARKER, "must be a block header"); 848 block = block->FreeNext ; 849 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header"); 850 return block; 851 } 852 853 854 void ObjectSynchronizer::oops_do(OopClosure* f) { 855 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 856 for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) { 857 assert(block->object() == CHAINMARKER, "must be a block header"); 858 for (int i = 1; i < _BLOCKSIZE; i++) { 859 ObjectMonitor* mid = &block[i]; 860 if (mid->object() != NULL) { 861 f->do_oop((oop*)mid->object_addr()); 862 } 863 } 864 } 865 } 866 867 868 // ----------------------------------------------------------------------------- 869 // ObjectMonitor Lifecycle 870 // ----------------------- 871 // Inflation unlinks monitors from the global gFreeList and 872 // associates them with objects. Deflation -- which occurs at 873 // STW-time -- disassociates idle monitors from objects. Such 874 // scavenged monitors are returned to the gFreeList. 875 // 876 // The global list is protected by ListLock. All the critical sections 877 // are short and operate in constant-time. 878 // 879 // ObjectMonitors reside in type-stable memory (TSM) and are immortal. 880 // 881 // Lifecycle: 882 // -- unassigned and on the global free list 883 // -- unassigned and on a thread's private omFreeList 884 // -- assigned to an object. The object is inflated and the mark refers 885 // to the objectmonitor. 886 // 887 888 889 // Constraining monitor pool growth via MonitorBound ... 890 // 891 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the 892 // the rate of scavenging is driven primarily by GC. As such, we can find 893 // an inordinate number of monitors in circulation. 894 // To avoid that scenario we can artificially induce a STW safepoint 895 // if the pool appears to be growing past some reasonable bound. 896 // Generally we favor time in space-time tradeoffs, but as there's no 897 // natural back-pressure on the # of extant monitors we need to impose some 898 // type of limit. Beware that if MonitorBound is set to too low a value 899 // we could just loop. In addition, if MonitorBound is set to a low value 900 // we'll incur more safepoints, which are harmful to performance. 901 // See also: GuaranteedSafepointInterval 902 // 903 // The current implementation uses asynchronous VM operations. 904 // 905 906 static void InduceScavenge (Thread * Self, const char * Whence) { 907 // Induce STW safepoint to trim monitors 908 // Ultimately, this results in a call to deflate_idle_monitors() in the near future. 909 // More precisely, trigger an asynchronous STW safepoint as the number 910 // of active monitors passes the specified threshold. 911 // TODO: assert thread state is reasonable 912 913 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) { 914 if (ObjectMonitor::Knob_Verbose) { 915 ::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ; 916 ::fflush(stdout) ; 917 } 918 // Induce a 'null' safepoint to scavenge monitors 919 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted 920 // to the VMthread and have a lifespan longer than that of this activation record. 921 // The VMThread will delete the op when completed. 922 VMThread::execute (new VM_ForceAsyncSafepoint()) ; 923 924 if (ObjectMonitor::Knob_Verbose) { 925 ::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ; 926 ::fflush(stdout) ; 927 } 928 } 929 } 930 /* Too slow for general assert or debug 931 void ObjectSynchronizer::verifyInUse (Thread *Self) { 932 ObjectMonitor* mid; 933 int inusetally = 0; 934 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) { 935 inusetally ++; 936 } 937 assert(inusetally == Self->omInUseCount, "inuse count off"); 938 939 int freetally = 0; 940 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) { 941 freetally ++; 942 } 943 assert(freetally == Self->omFreeCount, "free count off"); 944 } 945 */ 946 ObjectMonitor * ATTR ObjectSynchronizer::omAlloc (Thread * Self) { 947 // A large MAXPRIVATE value reduces both list lock contention 948 // and list coherency traffic, but also tends to increase the 949 // number of objectMonitors in circulation as well as the STW 950 // scavenge costs. As usual, we lean toward time in space-time 951 // tradeoffs. 952 const int MAXPRIVATE = 1024 ; 953 for (;;) { 954 ObjectMonitor * m ; 955 956 // 1: try to allocate from the thread's local omFreeList. 957 // Threads will attempt to allocate first from their local list, then 958 // from the global list, and only after those attempts fail will the thread 959 // attempt to instantiate new monitors. Thread-local free lists take 960 // heat off the ListLock and improve allocation latency, as well as reducing 961 // coherency traffic on the shared global list. 962 m = Self->omFreeList ; 963 if (m != NULL) { 964 Self->omFreeList = m->FreeNext ; 965 Self->omFreeCount -- ; 966 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene 967 guarantee (m->object() == NULL, "invariant") ; 968 if (MonitorInUseLists) { 969 m->FreeNext = Self->omInUseList; 970 Self->omInUseList = m; 971 Self->omInUseCount ++; 972 // verifyInUse(Self); 973 } else { 974 m->FreeNext = NULL; 975 } 976 return m ; 977 } 978 979 // 2: try to allocate from the global gFreeList 980 // CONSIDER: use muxTry() instead of muxAcquire(). 981 // If the muxTry() fails then drop immediately into case 3. 982 // If we're using thread-local free lists then try 983 // to reprovision the caller's free list. 984 if (gFreeList != NULL) { 985 // Reprovision the thread's omFreeList. 986 // Use bulk transfers to reduce the allocation rate and heat 987 // on various locks. 988 Thread::muxAcquire (&ListLock, "omAlloc") ; 989 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL; ) { 990 MonitorFreeCount --; 991 ObjectMonitor * take = gFreeList ; 992 gFreeList = take->FreeNext ; 993 guarantee (take->object() == NULL, "invariant") ; 994 guarantee (!take->is_busy(), "invariant") ; 995 take->Recycle() ; 996 omRelease (Self, take, false) ; 997 } 998 Thread::muxRelease (&ListLock) ; 999 Self->omFreeProvision += 1 + (Self->omFreeProvision/2) ; 1000 if (Self->omFreeProvision > MAXPRIVATE ) Self->omFreeProvision = MAXPRIVATE ; 1001 TEVENT (omFirst - reprovision) ; 1002 1003 const int mx = MonitorBound ; 1004 if (mx > 0 && (MonitorPopulation-MonitorFreeCount) > mx) { 1005 // We can't safely induce a STW safepoint from omAlloc() as our thread 1006 // state may not be appropriate for such activities and callers may hold 1007 // naked oops, so instead we defer the action. 1008 InduceScavenge (Self, "omAlloc") ; 1009 } 1010 continue; 1011 } 1012 1013 // 3: allocate a block of new ObjectMonitors 1014 // Both the local and global free lists are empty -- resort to malloc(). 1015 // In the current implementation objectMonitors are TSM - immortal. 1016 assert (_BLOCKSIZE > 1, "invariant") ; 1017 ObjectMonitor * temp = new ObjectMonitor[_BLOCKSIZE]; 1018 1019 // NOTE: (almost) no way to recover if allocation failed. 1020 // We might be able to induce a STW safepoint and scavenge enough 1021 // objectMonitors to permit progress. 1022 if (temp == NULL) { 1023 vm_exit_out_of_memory (sizeof (ObjectMonitor[_BLOCKSIZE]), "Allocate ObjectMonitors") ; 1024 } 1025 1026 // Format the block. 1027 // initialize the linked list, each monitor points to its next 1028 // forming the single linked free list, the very first monitor 1029 // will points to next block, which forms the block list. 1030 // The trick of using the 1st element in the block as gBlockList 1031 // linkage should be reconsidered. A better implementation would 1032 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; } 1033 1034 for (int i = 1; i < _BLOCKSIZE ; i++) { 1035 temp[i].FreeNext = &temp[i+1]; 1036 } 1037 1038 // terminate the last monitor as the end of list 1039 temp[_BLOCKSIZE - 1].FreeNext = NULL ; 1040 1041 // Element [0] is reserved for global list linkage 1042 temp[0].set_object(CHAINMARKER); 1043 1044 // Consider carving out this thread's current request from the 1045 // block in hand. This avoids some lock traffic and redundant 1046 // list activity. 1047 1048 // Acquire the ListLock to manipulate BlockList and FreeList. 1049 // An Oyama-Taura-Yonezawa scheme might be more efficient. 1050 Thread::muxAcquire (&ListLock, "omAlloc [2]") ; 1051 MonitorPopulation += _BLOCKSIZE-1; 1052 MonitorFreeCount += _BLOCKSIZE-1; 1053 1054 // Add the new block to the list of extant blocks (gBlockList). 1055 // The very first objectMonitor in a block is reserved and dedicated. 1056 // It serves as blocklist "next" linkage. 1057 temp[0].FreeNext = gBlockList; 1058 gBlockList = temp; 1059 1060 // Add the new string of objectMonitors to the global free list 1061 temp[_BLOCKSIZE - 1].FreeNext = gFreeList ; 1062 gFreeList = temp + 1; 1063 Thread::muxRelease (&ListLock) ; 1064 TEVENT (Allocate block of monitors) ; 1065 } 1066 } 1067 1068 // Place "m" on the caller's private per-thread omFreeList. 1069 // In practice there's no need to clamp or limit the number of 1070 // monitors on a thread's omFreeList as the only time we'll call 1071 // omRelease is to return a monitor to the free list after a CAS 1072 // attempt failed. This doesn't allow unbounded #s of monitors to 1073 // accumulate on a thread's free list. 1074 // 1075 1076 void ObjectSynchronizer::omRelease (Thread * Self, ObjectMonitor * m, bool fromPerThreadAlloc) { 1077 guarantee (m->object() == NULL, "invariant") ; 1078 1079 // Remove from omInUseList 1080 if (MonitorInUseLists && fromPerThreadAlloc) { 1081 ObjectMonitor* curmidinuse = NULL; 1082 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; ) { 1083 if (m == mid) { 1084 // extract from per-thread in-use-list 1085 if (mid == Self->omInUseList) { 1086 Self->omInUseList = mid->FreeNext; 1087 } else if (curmidinuse != NULL) { 1088 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist 1089 } 1090 Self->omInUseCount --; 1091 // verifyInUse(Self); 1092 break; 1093 } else { 1094 curmidinuse = mid; 1095 mid = mid->FreeNext; 1096 } 1097 } 1098 } 1099 1100 // FreeNext is used for both onInUseList and omFreeList, so clear old before setting new 1101 m->FreeNext = Self->omFreeList ; 1102 Self->omFreeList = m ; 1103 Self->omFreeCount ++ ; 1104 } 1105 1106 // Return the monitors of a moribund thread's local free list to 1107 // the global free list. Typically a thread calls omFlush() when 1108 // it's dying. We could also consider having the VM thread steal 1109 // monitors from threads that have not run java code over a few 1110 // consecutive STW safepoints. Relatedly, we might decay 1111 // omFreeProvision at STW safepoints. 1112 // 1113 // Also return the monitors of a moribund thread"s omInUseList to 1114 // a global gOmInUseList under the global list lock so these 1115 // will continue to be scanned. 1116 // 1117 // We currently call omFlush() from the Thread:: dtor _after the thread 1118 // has been excised from the thread list and is no longer a mutator. 1119 // That means that omFlush() can run concurrently with a safepoint and 1120 // the scavenge operator. Calling omFlush() from JavaThread::exit() might 1121 // be a better choice as we could safely reason that that the JVM is 1122 // not at a safepoint at the time of the call, and thus there could 1123 // be not inopportune interleavings between omFlush() and the scavenge 1124 // operator. 1125 1126 void ObjectSynchronizer::omFlush (Thread * Self) { 1127 ObjectMonitor * List = Self->omFreeList ; // Null-terminated SLL 1128 Self->omFreeList = NULL ; 1129 ObjectMonitor * Tail = NULL ; 1130 int Tally = 0; 1131 if (List != NULL) { 1132 ObjectMonitor * s ; 1133 for (s = List ; s != NULL ; s = s->FreeNext) { 1134 Tally ++ ; 1135 Tail = s ; 1136 guarantee (s->object() == NULL, "invariant") ; 1137 guarantee (!s->is_busy(), "invariant") ; 1138 s->set_owner (NULL) ; // redundant but good hygiene 1139 TEVENT (omFlush - Move one) ; 1140 } 1141 guarantee (Tail != NULL && List != NULL, "invariant") ; 1142 } 1143 1144 ObjectMonitor * InUseList = Self->omInUseList; 1145 ObjectMonitor * InUseTail = NULL ; 1146 int InUseTally = 0; 1147 if (InUseList != NULL) { 1148 Self->omInUseList = NULL; 1149 ObjectMonitor *curom; 1150 for (curom = InUseList; curom != NULL; curom = curom->FreeNext) { 1151 InUseTail = curom; 1152 InUseTally++; 1153 } 1154 // TODO debug 1155 assert(Self->omInUseCount == InUseTally, "inuse count off"); 1156 Self->omInUseCount = 0; 1157 guarantee (InUseTail != NULL && InUseList != NULL, "invariant"); 1158 } 1159 1160 Thread::muxAcquire (&ListLock, "omFlush") ; 1161 if (Tail != NULL) { 1162 Tail->FreeNext = gFreeList ; 1163 gFreeList = List ; 1164 MonitorFreeCount += Tally; 1165 } 1166 1167 if (InUseTail != NULL) { 1168 InUseTail->FreeNext = gOmInUseList; 1169 gOmInUseList = InUseList; 1170 gOmInUseCount += InUseTally; 1171 } 1172 1173 Thread::muxRelease (&ListLock) ; 1174 TEVENT (omFlush) ; 1175 } 1176 1177 // Fast path code shared by multiple functions 1178 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) { 1179 markOop mark = obj->mark(); 1180 if (mark->has_monitor()) { 1181 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid"); 1182 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header"); 1183 return mark->monitor(); 1184 } 1185 return ObjectSynchronizer::inflate(Thread::current(), obj); 1186 } 1187 1188 1189 // Note that we could encounter some performance loss through false-sharing as 1190 // multiple locks occupy the same $ line. Padding might be appropriate. 1191 1192 1193 ObjectMonitor * ATTR ObjectSynchronizer::inflate (Thread * Self, oop object) { 1194 // Inflate mutates the heap ... 1195 // Relaxing assertion for bug 6320749. 1196 assert (Universe::verify_in_progress() || 1197 !SafepointSynchronize::is_at_safepoint(), "invariant") ; 1198 1199 for (;;) { 1200 const markOop mark = object->mark() ; 1201 assert (!mark->has_bias_pattern(), "invariant") ; 1202 1203 // The mark can be in one of the following states: 1204 // * Inflated - just return 1205 // * Stack-locked - coerce it to inflated 1206 // * INFLATING - busy wait for conversion to complete 1207 // * Neutral - aggressively inflate the object. 1208 // * BIASED - Illegal. We should never see this 1209 1210 // CASE: inflated 1211 if (mark->has_monitor()) { 1212 ObjectMonitor * inf = mark->monitor() ; 1213 assert (inf->header()->is_neutral(), "invariant"); 1214 assert (inf->object() == object, "invariant") ; 1215 assert (ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid"); 1216 return inf ; 1217 } 1218 1219 // CASE: inflation in progress - inflating over a stack-lock. 1220 // Some other thread is converting from stack-locked to inflated. 1221 // Only that thread can complete inflation -- other threads must wait. 1222 // The INFLATING value is transient. 1223 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish. 1224 // We could always eliminate polling by parking the thread on some auxiliary list. 1225 if (mark == markOopDesc::INFLATING()) { 1226 TEVENT (Inflate: spin while INFLATING) ; 1227 ReadStableMark(object) ; 1228 continue ; 1229 } 1230 1231 // CASE: stack-locked 1232 // Could be stack-locked either by this thread or by some other thread. 1233 // 1234 // Note that we allocate the objectmonitor speculatively, _before_ attempting 1235 // to install INFLATING into the mark word. We originally installed INFLATING, 1236 // allocated the objectmonitor, and then finally STed the address of the 1237 // objectmonitor into the mark. This was correct, but artificially lengthened 1238 // the interval in which INFLATED appeared in the mark, thus increasing 1239 // the odds of inflation contention. 1240 // 1241 // We now use per-thread private objectmonitor free lists. 1242 // These list are reprovisioned from the global free list outside the 1243 // critical INFLATING...ST interval. A thread can transfer 1244 // multiple objectmonitors en-mass from the global free list to its local free list. 1245 // This reduces coherency traffic and lock contention on the global free list. 1246 // Using such local free lists, it doesn't matter if the omAlloc() call appears 1247 // before or after the CAS(INFLATING) operation. 1248 // See the comments in omAlloc(). 1249 1250 if (mark->has_locker()) { 1251 ObjectMonitor * m = omAlloc (Self) ; 1252 // Optimistically prepare the objectmonitor - anticipate successful CAS 1253 // We do this before the CAS in order to minimize the length of time 1254 // in which INFLATING appears in the mark. 1255 m->Recycle(); 1256 m->_Responsible = NULL ; 1257 m->OwnerIsThread = 0 ; 1258 m->_recursions = 0 ; 1259 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // Consider: maintain by type/class 1260 1261 markOop cmp = (markOop) Atomic::cmpxchg_ptr (markOopDesc::INFLATING(), object->mark_addr(), mark) ; 1262 if (cmp != mark) { 1263 omRelease (Self, m, true) ; 1264 continue ; // Interference -- just retry 1265 } 1266 1267 // We've successfully installed INFLATING (0) into the mark-word. 1268 // This is the only case where 0 will appear in a mark-work. 1269 // Only the singular thread that successfully swings the mark-word 1270 // to 0 can perform (or more precisely, complete) inflation. 1271 // 1272 // Why do we CAS a 0 into the mark-word instead of just CASing the 1273 // mark-word from the stack-locked value directly to the new inflated state? 1274 // Consider what happens when a thread unlocks a stack-locked object. 1275 // It attempts to use CAS to swing the displaced header value from the 1276 // on-stack basiclock back into the object header. Recall also that the 1277 // header value (hashcode, etc) can reside in (a) the object header, or 1278 // (b) a displaced header associated with the stack-lock, or (c) a displaced 1279 // header in an objectMonitor. The inflate() routine must copy the header 1280 // value from the basiclock on the owner's stack to the objectMonitor, all 1281 // the while preserving the hashCode stability invariants. If the owner 1282 // decides to release the lock while the value is 0, the unlock will fail 1283 // and control will eventually pass from slow_exit() to inflate. The owner 1284 // will then spin, waiting for the 0 value to disappear. Put another way, 1285 // the 0 causes the owner to stall if the owner happens to try to 1286 // drop the lock (restoring the header from the basiclock to the object) 1287 // while inflation is in-progress. This protocol avoids races that might 1288 // would otherwise permit hashCode values to change or "flicker" for an object. 1289 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable. 1290 // 0 serves as a "BUSY" inflate-in-progress indicator. 1291 1292 1293 // fetch the displaced mark from the owner's stack. 1294 // The owner can't die or unwind past the lock while our INFLATING 1295 // object is in the mark. Furthermore the owner can't complete 1296 // an unlock on the object, either. 1297 markOop dmw = mark->displaced_mark_helper() ; 1298 assert (dmw->is_neutral(), "invariant") ; 1299 1300 // Setup monitor fields to proper values -- prepare the monitor 1301 m->set_header(dmw) ; 1302 1303 // Optimization: if the mark->locker stack address is associated 1304 // with this thread we could simply set m->_owner = Self and 1305 // m->OwnerIsThread = 1. Note that a thread can inflate an object 1306 // that it has stack-locked -- as might happen in wait() -- directly 1307 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom. 1308 m->set_owner(mark->locker()); 1309 m->set_object(object); 1310 // TODO-FIXME: assert BasicLock->dhw != 0. 1311 1312 // Must preserve store ordering. The monitor state must 1313 // be stable at the time of publishing the monitor address. 1314 guarantee (object->mark() == markOopDesc::INFLATING(), "invariant") ; 1315 object->release_set_mark(markOopDesc::encode(m)); 1316 1317 // Hopefully the performance counters are allocated on distinct cache lines 1318 // to avoid false sharing on MP systems ... 1319 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ; 1320 TEVENT(Inflate: overwrite stacklock) ; 1321 if (TraceMonitorInflation) { 1322 if (object->is_instance()) { 1323 ResourceMark rm; 1324 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 1325 (intptr_t) object, (intptr_t) object->mark(), 1326 object->klass()->external_name()); 1327 } 1328 } 1329 return m ; 1330 } 1331 1332 // CASE: neutral 1333 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner. 1334 // If we know we're inflating for entry it's better to inflate by swinging a 1335 // pre-locked objectMonitor pointer into the object header. A successful 1336 // CAS inflates the object *and* confers ownership to the inflating thread. 1337 // In the current implementation we use a 2-step mechanism where we CAS() 1338 // to inflate and then CAS() again to try to swing _owner from NULL to Self. 1339 // An inflateTry() method that we could call from fast_enter() and slow_enter() 1340 // would be useful. 1341 1342 assert (mark->is_neutral(), "invariant"); 1343 ObjectMonitor * m = omAlloc (Self) ; 1344 // prepare m for installation - set monitor to initial state 1345 m->Recycle(); 1346 m->set_header(mark); 1347 m->set_owner(NULL); 1348 m->set_object(object); 1349 m->OwnerIsThread = 1 ; 1350 m->_recursions = 0 ; 1351 m->_Responsible = NULL ; 1352 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // consider: keep metastats by type/class 1353 1354 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) { 1355 m->set_object (NULL) ; 1356 m->set_owner (NULL) ; 1357 m->OwnerIsThread = 0 ; 1358 m->Recycle() ; 1359 omRelease (Self, m, true) ; 1360 m = NULL ; 1361 continue ; 1362 // interference - the markword changed - just retry. 1363 // The state-transitions are one-way, so there's no chance of 1364 // live-lock -- "Inflated" is an absorbing state. 1365 } 1366 1367 // Hopefully the performance counters are allocated on distinct 1368 // cache lines to avoid false sharing on MP systems ... 1369 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ; 1370 TEVENT(Inflate: overwrite neutral) ; 1371 if (TraceMonitorInflation) { 1372 if (object->is_instance()) { 1373 ResourceMark rm; 1374 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 1375 (intptr_t) object, (intptr_t) object->mark(), 1376 object->klass()->external_name()); 1377 } 1378 } 1379 return m ; 1380 } 1381 } 1382 1383 // Note that we could encounter some performance loss through false-sharing as 1384 // multiple locks occupy the same $ line. Padding might be appropriate. 1385 1386 1387 // Deflate_idle_monitors() is called at all safepoints, immediately 1388 // after all mutators are stopped, but before any objects have moved. 1389 // It traverses the list of known monitors, deflating where possible. 1390 // The scavenged monitor are returned to the monitor free list. 1391 // 1392 // Beware that we scavenge at *every* stop-the-world point. 1393 // Having a large number of monitors in-circulation negatively 1394 // impacts the performance of some applications (e.g., PointBase). 1395 // Broadly, we want to minimize the # of monitors in circulation. 1396 // 1397 // We have added a flag, MonitorInUseLists, which creates a list 1398 // of active monitors for each thread. deflate_idle_monitors() 1399 // only scans the per-thread inuse lists. omAlloc() puts all 1400 // assigned monitors on the per-thread list. deflate_idle_monitors() 1401 // returns the non-busy monitors to the global free list. 1402 // When a thread dies, omFlush() adds the list of active monitors for 1403 // that thread to a global gOmInUseList acquiring the 1404 // global list lock. deflate_idle_monitors() acquires the global 1405 // list lock to scan for non-busy monitors to the global free list. 1406 // An alternative could have used a single global inuse list. The 1407 // downside would have been the additional cost of acquiring the global list lock 1408 // for every omAlloc(). 1409 // 1410 // Perversely, the heap size -- and thus the STW safepoint rate -- 1411 // typically drives the scavenge rate. Large heaps can mean infrequent GC, 1412 // which in turn can mean large(r) numbers of objectmonitors in circulation. 1413 // This is an unfortunate aspect of this design. 1414 // 1415 1416 enum ManifestConstants { 1417 ClearResponsibleAtSTW = 0, 1418 MaximumRecheckInterval = 1000 1419 } ; 1420 1421 // Deflate a single monitor if not in use 1422 // Return true if deflated, false if in use 1423 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj, 1424 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) { 1425 bool deflated; 1426 // Normal case ... The monitor is associated with obj. 1427 guarantee (obj->mark() == markOopDesc::encode(mid), "invariant") ; 1428 guarantee (mid == obj->mark()->monitor(), "invariant"); 1429 guarantee (mid->header()->is_neutral(), "invariant"); 1430 1431 if (mid->is_busy()) { 1432 if (ClearResponsibleAtSTW) mid->_Responsible = NULL ; 1433 deflated = false; 1434 } else { 1435 // Deflate the monitor if it is no longer being used 1436 // It's idle - scavenge and return to the global free list 1437 // plain old deflation ... 1438 TEVENT (deflate_idle_monitors - scavenge1) ; 1439 if (TraceMonitorInflation) { 1440 if (obj->is_instance()) { 1441 ResourceMark rm; 1442 tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 1443 (intptr_t) obj, (intptr_t) obj->mark(), obj->klass()->external_name()); 1444 } 1445 } 1446 1447 // Restore the header back to obj 1448 obj->release_set_mark(mid->header()); 1449 mid->clear(); 1450 1451 assert (mid->object() == NULL, "invariant") ; 1452 1453 // Move the object to the working free list defined by FreeHead,FreeTail. 1454 if (*FreeHeadp == NULL) *FreeHeadp = mid; 1455 if (*FreeTailp != NULL) { 1456 ObjectMonitor * prevtail = *FreeTailp; 1457 assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); // TODO KK 1458 prevtail->FreeNext = mid; 1459 } 1460 *FreeTailp = mid; 1461 deflated = true; 1462 } 1463 return deflated; 1464 } 1465 1466 // Caller acquires ListLock 1467 int ObjectSynchronizer::walk_monitor_list(ObjectMonitor** listheadp, 1468 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) { 1469 ObjectMonitor* mid; 1470 ObjectMonitor* next; 1471 ObjectMonitor* curmidinuse = NULL; 1472 int deflatedcount = 0; 1473 1474 for (mid = *listheadp; mid != NULL; ) { 1475 oop obj = (oop) mid->object(); 1476 bool deflated = false; 1477 if (obj != NULL) { 1478 deflated = deflate_monitor(mid, obj, FreeHeadp, FreeTailp); 1479 } 1480 if (deflated) { 1481 // extract from per-thread in-use-list 1482 if (mid == *listheadp) { 1483 *listheadp = mid->FreeNext; 1484 } else if (curmidinuse != NULL) { 1485 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist 1486 } 1487 next = mid->FreeNext; 1488 mid->FreeNext = NULL; // This mid is current tail in the FreeHead list 1489 mid = next; 1490 deflatedcount++; 1491 } else { 1492 curmidinuse = mid; 1493 mid = mid->FreeNext; 1494 } 1495 } 1496 return deflatedcount; 1497 } 1498 1499 void ObjectSynchronizer::deflate_idle_monitors() { 1500 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 1501 int nInuse = 0 ; // currently associated with objects 1502 int nInCirculation = 0 ; // extant 1503 int nScavenged = 0 ; // reclaimed 1504 bool deflated = false; 1505 1506 ObjectMonitor * FreeHead = NULL ; // Local SLL of scavenged monitors 1507 ObjectMonitor * FreeTail = NULL ; 1508 1509 TEVENT (deflate_idle_monitors) ; 1510 // Prevent omFlush from changing mids in Thread dtor's during deflation 1511 // And in case the vm thread is acquiring a lock during a safepoint 1512 // See e.g. 6320749 1513 Thread::muxAcquire (&ListLock, "scavenge - return") ; 1514 1515 if (MonitorInUseLists) { 1516 int inUse = 0; 1517 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) { 1518 nInCirculation+= cur->omInUseCount; 1519 int deflatedcount = walk_monitor_list(cur->omInUseList_addr(), &FreeHead, &FreeTail); 1520 cur->omInUseCount-= deflatedcount; 1521 // verifyInUse(cur); 1522 nScavenged += deflatedcount; 1523 nInuse += cur->omInUseCount; 1524 } 1525 1526 // For moribund threads, scan gOmInUseList 1527 if (gOmInUseList) { 1528 nInCirculation += gOmInUseCount; 1529 int deflatedcount = walk_monitor_list((ObjectMonitor **)&gOmInUseList, &FreeHead, &FreeTail); 1530 gOmInUseCount-= deflatedcount; 1531 nScavenged += deflatedcount; 1532 nInuse += gOmInUseCount; 1533 } 1534 1535 } else for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) { 1536 // Iterate over all extant monitors - Scavenge all idle monitors. 1537 assert(block->object() == CHAINMARKER, "must be a block header"); 1538 nInCirculation += _BLOCKSIZE ; 1539 for (int i = 1 ; i < _BLOCKSIZE; i++) { 1540 ObjectMonitor* mid = &block[i]; 1541 oop obj = (oop) mid->object(); 1542 1543 if (obj == NULL) { 1544 // The monitor is not associated with an object. 1545 // The monitor should either be a thread-specific private 1546 // free list or the global free list. 1547 // obj == NULL IMPLIES mid->is_busy() == 0 1548 guarantee (!mid->is_busy(), "invariant") ; 1549 continue ; 1550 } 1551 deflated = deflate_monitor(mid, obj, &FreeHead, &FreeTail); 1552 1553 if (deflated) { 1554 mid->FreeNext = NULL ; 1555 nScavenged ++ ; 1556 } else { 1557 nInuse ++; 1558 } 1559 } 1560 } 1561 1562 MonitorFreeCount += nScavenged; 1563 1564 // Consider: audit gFreeList to ensure that MonitorFreeCount and list agree. 1565 1566 if (ObjectMonitor::Knob_Verbose) { 1567 ::printf ("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n", 1568 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge, 1569 MonitorPopulation, MonitorFreeCount) ; 1570 ::fflush(stdout) ; 1571 } 1572 1573 ForceMonitorScavenge = 0; // Reset 1574 1575 // Move the scavenged monitors back to the global free list. 1576 if (FreeHead != NULL) { 1577 guarantee (FreeTail != NULL && nScavenged > 0, "invariant") ; 1578 assert (FreeTail->FreeNext == NULL, "invariant") ; 1579 // constant-time list splice - prepend scavenged segment to gFreeList 1580 FreeTail->FreeNext = gFreeList ; 1581 gFreeList = FreeHead ; 1582 } 1583 Thread::muxRelease (&ListLock) ; 1584 1585 if (ObjectMonitor::_sync_Deflations != NULL) ObjectMonitor::_sync_Deflations->inc(nScavenged) ; 1586 if (ObjectMonitor::_sync_MonExtant != NULL) ObjectMonitor::_sync_MonExtant ->set_value(nInCirculation); 1587 1588 // TODO: Add objectMonitor leak detection. 1589 // Audit/inventory the objectMonitors -- make sure they're all accounted for. 1590 GVars.stwRandom = os::random() ; 1591 GVars.stwCycle ++ ; 1592 } 1593 1594 // Monitor cleanup on JavaThread::exit 1595 1596 // Iterate through monitor cache and attempt to release thread's monitors 1597 // Gives up on a particular monitor if an exception occurs, but continues 1598 // the overall iteration, swallowing the exception. 1599 class ReleaseJavaMonitorsClosure: public MonitorClosure { 1600 private: 1601 TRAPS; 1602 1603 public: 1604 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {} 1605 void do_monitor(ObjectMonitor* mid) { 1606 if (mid->owner() == THREAD) { 1607 (void)mid->complete_exit(CHECK); 1608 } 1609 } 1610 }; 1611 1612 // Release all inflated monitors owned by THREAD. Lightweight monitors are 1613 // ignored. This is meant to be called during JNI thread detach which assumes 1614 // all remaining monitors are heavyweight. All exceptions are swallowed. 1615 // Scanning the extant monitor list can be time consuming. 1616 // A simple optimization is to add a per-thread flag that indicates a thread 1617 // called jni_monitorenter() during its lifetime. 1618 // 1619 // Instead of No_Savepoint_Verifier it might be cheaper to 1620 // use an idiom of the form: 1621 // auto int tmp = SafepointSynchronize::_safepoint_counter ; 1622 // <code that must not run at safepoint> 1623 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ; 1624 // Since the tests are extremely cheap we could leave them enabled 1625 // for normal product builds. 1626 1627 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) { 1628 assert(THREAD == JavaThread::current(), "must be current Java thread"); 1629 No_Safepoint_Verifier nsv ; 1630 ReleaseJavaMonitorsClosure rjmc(THREAD); 1631 Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread"); 1632 ObjectSynchronizer::monitors_iterate(&rjmc); 1633 Thread::muxRelease(&ListLock); 1634 THREAD->clear_pending_exception(); 1635 } 1636 1637 //------------------------------------------------------------------------------ 1638 // Non-product code 1639 1640 #ifndef PRODUCT 1641 1642 void ObjectSynchronizer::trace_locking(Handle locking_obj, bool is_compiled, 1643 bool is_method, bool is_locking) { 1644 // Don't know what to do here 1645 } 1646 1647 // Verify all monitors in the monitor cache, the verification is weak. 1648 void ObjectSynchronizer::verify() { 1649 ObjectMonitor* block = gBlockList; 1650 ObjectMonitor* mid; 1651 while (block) { 1652 assert(block->object() == CHAINMARKER, "must be a block header"); 1653 for (int i = 1; i < _BLOCKSIZE; i++) { 1654 mid = block + i; 1655 oop object = (oop) mid->object(); 1656 if (object != NULL) { 1657 mid->verify(); 1658 } 1659 } 1660 block = (ObjectMonitor*) block->FreeNext; 1661 } 1662 } 1663 1664 // Check if monitor belongs to the monitor cache 1665 // The list is grow-only so it's *relatively* safe to traverse 1666 // the list of extant blocks without taking a lock. 1667 1668 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) { 1669 ObjectMonitor* block = gBlockList; 1670 1671 while (block) { 1672 assert(block->object() == CHAINMARKER, "must be a block header"); 1673 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) { 1674 address mon = (address) monitor; 1675 address blk = (address) block; 1676 size_t diff = mon - blk; 1677 assert((diff % sizeof(ObjectMonitor)) == 0, "check"); 1678 return 1; 1679 } 1680 block = (ObjectMonitor*) block->FreeNext; 1681 } 1682 return 0; 1683 } 1684 1685 #endif