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