1 /* 2 * Copyright (c) 1998, 2011, 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 55 #if defined(__GNUC__) && !defined(IA64) 56 // Need to inhibit inlining for older versions of GCC to avoid build-time failures 57 #define ATTR __attribute__((noinline)) 58 #else 59 #define ATTR 60 #endif 61 62 // The "core" versions of monitor enter and exit reside in this file. 63 // The interpreter and compilers contain specialized transliterated 64 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(), 65 // for instance. If you make changes here, make sure to modify the 66 // interpreter, and both C1 and C2 fast-path inline locking code emission. 67 // 68 // 69 // ----------------------------------------------------------------------------- 70 71 #ifdef DTRACE_ENABLED 72 73 // Only bother with this argument setup if dtrace is available 74 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly. 75 76 HS_DTRACE_PROBE_DECL5(hotspot, monitor__wait, 77 jlong, uintptr_t, char*, int, long); 78 HS_DTRACE_PROBE_DECL4(hotspot, monitor__waited, 79 jlong, uintptr_t, char*, int); 80 81 #define DTRACE_MONITOR_PROBE_COMMON(klassOop, thread) \ 82 char* bytes = NULL; \ 83 int len = 0; \ 84 jlong jtid = SharedRuntime::get_java_tid(thread); \ 85 Symbol* klassname = ((oop)(klassOop))->klass()->klass_part()->name(); \ 86 if (klassname != NULL) { \ 87 bytes = (char*)klassname->bytes(); \ 88 len = klassname->utf8_length(); \ 89 } 90 91 #define DTRACE_MONITOR_WAIT_PROBE(monitor, klassOop, thread, millis) \ 92 { \ 93 if (DTraceMonitorProbes) { \ 94 DTRACE_MONITOR_PROBE_COMMON(klassOop, thread); \ 95 HS_DTRACE_PROBE5(hotspot, monitor__wait, jtid, \ 96 (monitor), bytes, len, (millis)); \ 97 } \ 98 } 99 100 #define DTRACE_MONITOR_PROBE(probe, monitor, klassOop, thread) \ 101 { \ 102 if (DTraceMonitorProbes) { \ 103 DTRACE_MONITOR_PROBE_COMMON(klassOop, thread); \ 104 HS_DTRACE_PROBE4(hotspot, monitor__##probe, jtid, \ 105 (uintptr_t)(monitor), bytes, len); \ 106 } \ 107 } 108 109 #else // ndef DTRACE_ENABLED 110 111 #define DTRACE_MONITOR_WAIT_PROBE(klassOop, thread, millis, mon) {;} 112 #define DTRACE_MONITOR_PROBE(probe, klassOop, thread, mon) {;} 113 114 #endif // ndef DTRACE_ENABLED 115 116 // This exists only as a workaround of dtrace bug 6254741 117 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) { 118 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr); 119 return 0; 120 } 121 122 #define NINFLATIONLOCKS 256 123 static volatile intptr_t InflationLocks [NINFLATIONLOCKS] ; 124 125 ObjectMonitor * ObjectSynchronizer::gBlockList = NULL ; 126 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL ; 127 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL ; 128 int ObjectSynchronizer::gOmInUseCount = 0; 129 static volatile intptr_t ListLock = 0 ; // protects global monitor free-list cache 130 static volatile int MonitorFreeCount = 0 ; // # on gFreeList 131 static volatile int MonitorPopulation = 0 ; // # Extant -- in circulation 132 #define CHAINMARKER ((oop)-1) 133 134 // ----------------------------------------------------------------------------- 135 // Fast Monitor Enter/Exit 136 // This the fast monitor enter. The interpreter and compiler use 137 // some assembly copies of this code. Make sure update those code 138 // if the following function is changed. The implementation is 139 // extremely sensitive to race condition. Be careful. 140 141 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock, bool attempt_rebias, TRAPS) { 142 if (UseBiasedLocking) { 143 if (!SafepointSynchronize::is_at_safepoint()) { 144 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD); 145 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) { 146 return; 147 } 148 } else { 149 assert(!attempt_rebias, "can not rebias toward VM thread"); 150 BiasedLocking::revoke_at_safepoint(obj); 151 } 152 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 153 } 154 155 slow_enter (obj, lock, THREAD) ; 156 } 157 158 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) { 159 assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here"); 160 // if displaced header is null, the previous enter is recursive enter, no-op 161 markOop dhw = lock->displaced_header(); 162 markOop mark ; 163 if (dhw == NULL) { 164 // Recursive stack-lock. 165 // Diagnostics -- Could be: stack-locked, inflating, inflated. 166 mark = object->mark() ; 167 assert (!mark->is_neutral(), "invariant") ; 168 if (mark->has_locker() && mark != markOopDesc::INFLATING()) { 169 assert(THREAD->is_lock_owned((address)mark->locker()), "invariant") ; 170 } 171 if (mark->has_monitor()) { 172 ObjectMonitor * m = mark->monitor() ; 173 assert(((oop)(m->object()))->mark() == mark, "invariant") ; 174 assert(m->is_entered(THREAD), "invariant") ; 175 } 176 return ; 177 } 178 179 mark = object->mark() ; 180 181 // If the object is stack-locked by the current thread, try to 182 // swing the displaced header from the box back to the mark. 183 if (mark == (markOop) lock) { 184 assert (dhw->is_neutral(), "invariant") ; 185 if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) { 186 TEVENT (fast_exit: release stacklock) ; 187 return; 188 } 189 } 190 191 ObjectSynchronizer::inflate(THREAD, object)->exit (THREAD) ; 192 } 193 194 // ----------------------------------------------------------------------------- 195 // Interpreter/Compiler Slow Case 196 // This routine is used to handle interpreter/compiler slow case 197 // We don't need to use fast path here, because it must have been 198 // failed in the interpreter/compiler code. 199 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) { 200 markOop mark = obj->mark(); 201 assert(!mark->has_bias_pattern(), "should not see bias pattern here"); 202 203 if (mark->is_neutral()) { 204 // Anticipate successful CAS -- the ST of the displaced mark must 205 // be visible <= the ST performed by the CAS. 206 lock->set_displaced_header(mark); 207 if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) { 208 TEVENT (slow_enter: release stacklock) ; 209 return ; 210 } 211 // Fall through to inflate() ... 212 } else 213 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { 214 assert(lock != mark->locker(), "must not re-lock the same lock"); 215 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock"); 216 lock->set_displaced_header(NULL); 217 return; 218 } 219 220 #if 0 221 // The following optimization isn't particularly useful. 222 if (mark->has_monitor() && mark->monitor()->is_entered(THREAD)) { 223 lock->set_displaced_header (NULL) ; 224 return ; 225 } 226 #endif 227 228 // The object header will never be displaced to this lock, 229 // so it does not matter what the value is, except that it 230 // must be non-zero to avoid looking like a re-entrant lock, 231 // and must not look locked either. 232 lock->set_displaced_header(markOopDesc::unused_mark()); 233 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD); 234 } 235 236 // This routine is used to handle interpreter/compiler slow case 237 // We don't need to use fast path here, because it must have 238 // failed in the interpreter/compiler code. Simply use the heavy 239 // weight monitor should be ok, unless someone find otherwise. 240 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) { 241 fast_exit (object, lock, THREAD) ; 242 } 243 244 // ----------------------------------------------------------------------------- 245 // Class Loader support to workaround deadlocks on the class loader lock objects 246 // Also used by GC 247 // complete_exit()/reenter() are used to wait on a nested lock 248 // i.e. to give up an outer lock completely and then re-enter 249 // Used when holding nested locks - lock acquisition order: lock1 then lock2 250 // 1) complete_exit lock1 - saving recursion count 251 // 2) wait on lock2 252 // 3) when notified on lock2, unlock lock2 253 // 4) reenter lock1 with original recursion count 254 // 5) lock lock2 255 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 256 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) { 257 TEVENT (complete_exit) ; 258 if (UseBiasedLocking) { 259 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 260 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 261 } 262 263 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); 264 265 return monitor->complete_exit(THREAD); 266 } 267 268 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 269 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) { 270 TEVENT (reenter) ; 271 if (UseBiasedLocking) { 272 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 273 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 274 } 275 276 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); 277 278 monitor->reenter(recursion, THREAD); 279 } 280 // ----------------------------------------------------------------------------- 281 // JNI locks on java objects 282 // NOTE: must use heavy weight monitor to handle jni monitor enter 283 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) { // possible entry from jni enter 284 // the current locking is from JNI instead of Java code 285 TEVENT (jni_enter) ; 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 THREAD->set_current_pending_monitor_is_from_java(false); 291 ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD); 292 THREAD->set_current_pending_monitor_is_from_java(true); 293 } 294 295 // NOTE: must use heavy weight monitor to handle jni monitor enter 296 bool ObjectSynchronizer::jni_try_enter(Handle obj, Thread* THREAD) { 297 if (UseBiasedLocking) { 298 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 299 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 300 } 301 302 ObjectMonitor* monitor = ObjectSynchronizer::inflate_helper(obj()); 303 return monitor->try_enter(THREAD); 304 } 305 306 307 // NOTE: must use heavy weight monitor to handle jni monitor exit 308 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) { 309 TEVENT (jni_exit) ; 310 if (UseBiasedLocking) { 311 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 312 } 313 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 314 315 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj); 316 // If this thread has locked the object, exit the monitor. Note: can't use 317 // monitor->check(CHECK); must exit even if an exception is pending. 318 if (monitor->check(THREAD)) { 319 monitor->exit(THREAD); 320 } 321 } 322 323 // ----------------------------------------------------------------------------- 324 // Internal VM locks on java objects 325 // standard constructor, allows locking failures 326 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) { 327 _dolock = doLock; 328 _thread = thread; 329 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);) 330 _obj = obj; 331 332 if (_dolock) { 333 TEVENT (ObjectLocker) ; 334 335 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread); 336 } 337 } 338 339 ObjectLocker::~ObjectLocker() { 340 if (_dolock) { 341 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread); 342 } 343 } 344 345 346 // ----------------------------------------------------------------------------- 347 // Wait/Notify/NotifyAll 348 // NOTE: must use heavy weight monitor to handle wait() 349 void ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) { 350 if (UseBiasedLocking) { 351 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 352 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 353 } 354 if (millis < 0) { 355 TEVENT (wait - throw IAX) ; 356 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); 357 } 358 ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); 359 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis); 360 monitor->wait(millis, true, THREAD); 361 362 /* This dummy call is in place to get around dtrace bug 6254741. Once 363 that's fixed we can uncomment the following line and remove the call */ 364 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD); 365 dtrace_waited_probe(monitor, obj, THREAD); 366 } 367 368 void ObjectSynchronizer::waitUninterruptibly (Handle obj, jlong millis, TRAPS) { 369 if (UseBiasedLocking) { 370 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 371 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 372 } 373 if (millis < 0) { 374 TEVENT (wait - throw IAX) ; 375 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); 376 } 377 ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD) ; 378 } 379 380 void ObjectSynchronizer::notify(Handle obj, TRAPS) { 381 if (UseBiasedLocking) { 382 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 383 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 384 } 385 386 markOop mark = obj->mark(); 387 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { 388 return; 389 } 390 ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD); 391 } 392 393 // NOTE: see comment of notify() 394 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) { 395 if (UseBiasedLocking) { 396 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 397 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 398 } 399 400 markOop mark = obj->mark(); 401 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { 402 return; 403 } 404 ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD); 405 } 406 407 // ----------------------------------------------------------------------------- 408 // Hash Code handling 409 // 410 // Performance concern: 411 // OrderAccess::storestore() calls release() which STs 0 into the global volatile 412 // OrderAccess::Dummy variable. This store is unnecessary for correctness. 413 // Many threads STing into a common location causes considerable cache migration 414 // or "sloshing" on large SMP system. As such, I avoid using OrderAccess::storestore() 415 // until it's repaired. In some cases OrderAccess::fence() -- which incurs local 416 // latency on the executing processor -- is a better choice as it scales on SMP 417 // systems. See http://blogs.sun.com/dave/entry/biased_locking_in_hotspot for a 418 // discussion of coherency costs. Note that all our current reference platforms 419 // provide strong ST-ST order, so the issue is moot on IA32, x64, and SPARC. 420 // 421 // As a general policy we use "volatile" to control compiler-based reordering 422 // and explicit fences (barriers) to control for architectural reordering performed 423 // by the CPU(s) or platform. 424 425 static int MBFence (int x) { OrderAccess::fence(); return x; } 426 427 struct SharedGlobals { 428 // These are highly shared mostly-read variables. 429 // To avoid false-sharing they need to be the sole occupants of a $ line. 430 double padPrefix [8]; 431 volatile int stwRandom ; 432 volatile int stwCycle ; 433 434 // Hot RW variables -- Sequester to avoid false-sharing 435 double padSuffix [16]; 436 volatile int hcSequence ; 437 double padFinal [8] ; 438 } ; 439 440 static SharedGlobals GVars ; 441 static int MonitorScavengeThreshold = 1000000 ; 442 static volatile int ForceMonitorScavenge = 0 ; // Scavenge required and pending 443 444 static markOop ReadStableMark (oop obj) { 445 markOop mark = obj->mark() ; 446 if (!mark->is_being_inflated()) { 447 return mark ; // normal fast-path return 448 } 449 450 int its = 0 ; 451 for (;;) { 452 markOop mark = obj->mark() ; 453 if (!mark->is_being_inflated()) { 454 return mark ; // normal fast-path return 455 } 456 457 // The object is being inflated by some other thread. 458 // The caller of ReadStableMark() must wait for inflation to complete. 459 // Avoid live-lock 460 // TODO: consider calling SafepointSynchronize::do_call_back() while 461 // spinning to see if there's a safepoint pending. If so, immediately 462 // yielding or blocking would be appropriate. Avoid spinning while 463 // there is a safepoint pending. 464 // TODO: add inflation contention performance counters. 465 // TODO: restrict the aggregate number of spinners. 466 467 ++its ; 468 if (its > 10000 || !os::is_MP()) { 469 if (its & 1) { 470 os::NakedYield() ; 471 TEVENT (Inflate: INFLATING - yield) ; 472 } else { 473 // Note that the following code attenuates the livelock problem but is not 474 // a complete remedy. A more complete solution would require that the inflating 475 // thread hold the associated inflation lock. The following code simply restricts 476 // the number of spinners to at most one. We'll have N-2 threads blocked 477 // on the inflationlock, 1 thread holding the inflation lock and using 478 // a yield/park strategy, and 1 thread in the midst of inflation. 479 // A more refined approach would be to change the encoding of INFLATING 480 // to allow encapsulation of a native thread pointer. Threads waiting for 481 // inflation to complete would use CAS to push themselves onto a singly linked 482 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag 483 // and calling park(). When inflation was complete the thread that accomplished inflation 484 // would detach the list and set the markword to inflated with a single CAS and 485 // then for each thread on the list, set the flag and unpark() the thread. 486 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease 487 // wakes at most one thread whereas we need to wake the entire list. 488 int ix = (intptr_t(obj) >> 5) & (NINFLATIONLOCKS-1) ; 489 int YieldThenBlock = 0 ; 490 assert (ix >= 0 && ix < NINFLATIONLOCKS, "invariant") ; 491 assert ((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant") ; 492 Thread::muxAcquire (InflationLocks + ix, "InflationLock") ; 493 while (obj->mark() == markOopDesc::INFLATING()) { 494 // Beware: NakedYield() is advisory and has almost no effect on some platforms 495 // so we periodically call Self->_ParkEvent->park(1). 496 // We use a mixed spin/yield/block mechanism. 497 if ((YieldThenBlock++) >= 16) { 498 Thread::current()->_ParkEvent->park(1) ; 499 } else { 500 os::NakedYield() ; 501 } 502 } 503 Thread::muxRelease (InflationLocks + ix ) ; 504 TEVENT (Inflate: INFLATING - yield/park) ; 505 } 506 } else { 507 SpinPause() ; // SMP-polite spinning 508 } 509 } 510 } 511 512 // hashCode() generation : 513 // 514 // Possibilities: 515 // * MD5Digest of {obj,stwRandom} 516 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function. 517 // * A DES- or AES-style SBox[] mechanism 518 // * One of the Phi-based schemes, such as: 519 // 2654435761 = 2^32 * Phi (golden ratio) 520 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ; 521 // * A variation of Marsaglia's shift-xor RNG scheme. 522 // * (obj ^ stwRandom) is appealing, but can result 523 // in undesirable regularity in the hashCode values of adjacent objects 524 // (objects allocated back-to-back, in particular). This could potentially 525 // result in hashtable collisions and reduced hashtable efficiency. 526 // There are simple ways to "diffuse" the middle address bits over the 527 // generated hashCode values: 528 // 529 530 static inline intptr_t get_next_hash(Thread * Self, oop obj) { 531 intptr_t value = 0 ; 532 if (hashCode == 0) { 533 // This form uses an unguarded global Park-Miller RNG, 534 // so it's possible for two threads to race and generate the same RNG. 535 // On MP system we'll have lots of RW access to a global, so the 536 // mechanism induces lots of coherency traffic. 537 value = os::random() ; 538 } else 539 if (hashCode == 1) { 540 // This variation has the property of being stable (idempotent) 541 // between STW operations. This can be useful in some of the 1-0 542 // synchronization schemes. 543 intptr_t addrBits = intptr_t(obj) >> 3 ; 544 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom ; 545 } else 546 if (hashCode == 2) { 547 value = 1 ; // for sensitivity testing 548 } else 549 if (hashCode == 3) { 550 value = ++GVars.hcSequence ; 551 } else 552 if (hashCode == 4) { 553 value = intptr_t(obj) ; 554 } else { 555 // Marsaglia's xor-shift scheme with thread-specific state 556 // This is probably the best overall implementation -- we'll 557 // likely make this the default in future releases. 558 unsigned t = Self->_hashStateX ; 559 t ^= (t << 11) ; 560 Self->_hashStateX = Self->_hashStateY ; 561 Self->_hashStateY = Self->_hashStateZ ; 562 Self->_hashStateZ = Self->_hashStateW ; 563 unsigned v = Self->_hashStateW ; 564 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)) ; 565 Self->_hashStateW = v ; 566 value = v ; 567 } 568 569 value &= markOopDesc::hash_mask; 570 if (value == 0) value = 0xBAD ; 571 assert (value != markOopDesc::no_hash, "invariant") ; 572 TEVENT (hashCode: GENERATE) ; 573 return value; 574 } 575 // 576 intptr_t ObjectSynchronizer::FastHashCode (Thread * Self, oop obj) { 577 if (UseBiasedLocking) { 578 // NOTE: many places throughout the JVM do not expect a safepoint 579 // to be taken here, in particular most operations on perm gen 580 // objects. However, we only ever bias Java instances and all of 581 // the call sites of identity_hash that might revoke biases have 582 // been checked to make sure they can handle a safepoint. The 583 // added check of the bias pattern is to avoid useless calls to 584 // thread-local storage. 585 if (obj->mark()->has_bias_pattern()) { 586 // Box and unbox the raw reference just in case we cause a STW safepoint. 587 Handle hobj (Self, obj) ; 588 // Relaxing assertion for bug 6320749. 589 assert (Universe::verify_in_progress() || 590 !SafepointSynchronize::is_at_safepoint(), 591 "biases should not be seen by VM thread here"); 592 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current()); 593 obj = hobj() ; 594 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 595 } 596 } 597 598 // hashCode() is a heap mutator ... 599 // Relaxing assertion for bug 6320749. 600 assert (Universe::verify_in_progress() || 601 !SafepointSynchronize::is_at_safepoint(), "invariant") ; 602 assert (Universe::verify_in_progress() || 603 Self->is_Java_thread() , "invariant") ; 604 assert (Universe::verify_in_progress() || 605 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ; 606 607 ObjectMonitor* monitor = NULL; 608 markOop temp, test; 609 intptr_t hash; 610 markOop mark = ReadStableMark (obj); 611 612 // object should remain ineligible for biased locking 613 assert (!mark->has_bias_pattern(), "invariant") ; 614 615 if (mark->is_neutral()) { 616 hash = mark->hash(); // this is a normal header 617 if (hash) { // if it has hash, just return it 618 return hash; 619 } 620 hash = get_next_hash(Self, obj); // allocate a new hash code 621 temp = mark->copy_set_hash(hash); // merge the hash code into header 622 // use (machine word version) atomic operation to install the hash 623 test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark); 624 if (test == mark) { 625 return hash; 626 } 627 // If atomic operation failed, we must inflate the header 628 // into heavy weight monitor. We could add more code here 629 // for fast path, but it does not worth the complexity. 630 } else if (mark->has_monitor()) { 631 monitor = mark->monitor(); 632 temp = monitor->header(); 633 assert (temp->is_neutral(), "invariant") ; 634 hash = temp->hash(); 635 if (hash) { 636 return hash; 637 } 638 // Skip to the following code to reduce code size 639 } else if (Self->is_lock_owned((address)mark->locker())) { 640 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned 641 assert (temp->is_neutral(), "invariant") ; 642 hash = temp->hash(); // by current thread, check if the displaced 643 if (hash) { // header contains hash code 644 return hash; 645 } 646 // WARNING: 647 // The displaced header is strictly immutable. 648 // It can NOT be changed in ANY cases. So we have 649 // to inflate the header into heavyweight monitor 650 // even the current thread owns the lock. The reason 651 // is the BasicLock (stack slot) will be asynchronously 652 // read by other threads during the inflate() function. 653 // Any change to stack may not propagate to other threads 654 // correctly. 655 } 656 657 // Inflate the monitor to set hash code 658 monitor = ObjectSynchronizer::inflate(Self, obj); 659 // Load displaced header and check it has hash code 660 mark = monitor->header(); 661 assert (mark->is_neutral(), "invariant") ; 662 hash = mark->hash(); 663 if (hash == 0) { 664 hash = get_next_hash(Self, obj); 665 temp = mark->copy_set_hash(hash); // merge hash code into header 666 assert (temp->is_neutral(), "invariant") ; 667 test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark); 668 if (test != mark) { 669 // The only update to the header in the monitor (outside GC) 670 // is install the hash code. If someone add new usage of 671 // displaced header, please update this code 672 hash = test->hash(); 673 assert (test->is_neutral(), "invariant") ; 674 assert (hash != 0, "Trivial unexpected object/monitor header usage."); 675 } 676 } 677 // We finally get the hash 678 return hash; 679 } 680 681 // Deprecated -- use FastHashCode() instead. 682 683 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) { 684 return FastHashCode (Thread::current(), obj()) ; 685 } 686 687 688 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread, 689 Handle h_obj) { 690 if (UseBiasedLocking) { 691 BiasedLocking::revoke_and_rebias(h_obj, false, thread); 692 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 693 } 694 695 assert(thread == JavaThread::current(), "Can only be called on current thread"); 696 oop obj = h_obj(); 697 698 markOop mark = ReadStableMark (obj) ; 699 700 // Uncontended case, header points to stack 701 if (mark->has_locker()) { 702 return thread->is_lock_owned((address)mark->locker()); 703 } 704 // Contended case, header points to ObjectMonitor (tagged pointer) 705 if (mark->has_monitor()) { 706 ObjectMonitor* monitor = mark->monitor(); 707 return monitor->is_entered(thread) != 0 ; 708 } 709 // Unlocked case, header in place 710 assert(mark->is_neutral(), "sanity check"); 711 return false; 712 } 713 714 // Be aware of this method could revoke bias of the lock object. 715 // This method querys the ownership of the lock handle specified by 'h_obj'. 716 // If the current thread owns the lock, it returns owner_self. If no 717 // thread owns the lock, it returns owner_none. Otherwise, it will return 718 // ower_other. 719 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership 720 (JavaThread *self, Handle h_obj) { 721 // The caller must beware this method can revoke bias, and 722 // revocation can result in a safepoint. 723 assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ; 724 assert (self->thread_state() != _thread_blocked , "invariant") ; 725 726 // Possible mark states: neutral, biased, stack-locked, inflated 727 728 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) { 729 // CASE: biased 730 BiasedLocking::revoke_and_rebias(h_obj, false, self); 731 assert(!h_obj->mark()->has_bias_pattern(), 732 "biases should be revoked by now"); 733 } 734 735 assert(self == JavaThread::current(), "Can only be called on current thread"); 736 oop obj = h_obj(); 737 markOop mark = ReadStableMark (obj) ; 738 739 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack. 740 if (mark->has_locker()) { 741 return self->is_lock_owned((address)mark->locker()) ? 742 owner_self : owner_other; 743 } 744 745 // CASE: inflated. Mark (tagged pointer) points to an objectMonitor. 746 // The Object:ObjectMonitor relationship is stable as long as we're 747 // not at a safepoint. 748 if (mark->has_monitor()) { 749 void * owner = mark->monitor()->_owner ; 750 if (owner == NULL) return owner_none ; 751 return (owner == self || 752 self->is_lock_owned((address)owner)) ? owner_self : owner_other; 753 } 754 755 // CASE: neutral 756 assert(mark->is_neutral(), "sanity check"); 757 return owner_none ; // it's unlocked 758 } 759 760 // FIXME: jvmti should call this 761 JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) { 762 if (UseBiasedLocking) { 763 if (SafepointSynchronize::is_at_safepoint()) { 764 BiasedLocking::revoke_at_safepoint(h_obj); 765 } else { 766 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current()); 767 } 768 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now"); 769 } 770 771 oop obj = h_obj(); 772 address owner = NULL; 773 774 markOop mark = ReadStableMark (obj) ; 775 776 // Uncontended case, header points to stack 777 if (mark->has_locker()) { 778 owner = (address) mark->locker(); 779 } 780 781 // Contended case, header points to ObjectMonitor (tagged pointer) 782 if (mark->has_monitor()) { 783 ObjectMonitor* monitor = mark->monitor(); 784 assert(monitor != NULL, "monitor should be non-null"); 785 owner = (address) monitor->owner(); 786 } 787 788 if (owner != NULL) { 789 return Threads::owning_thread_from_monitor_owner(owner, doLock); 790 } 791 792 // Unlocked case, header in place 793 // Cannot have assertion since this object may have been 794 // locked by another thread when reaching here. 795 // assert(mark->is_neutral(), "sanity check"); 796 797 return NULL; 798 } 799 // Visitors ... 800 801 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) { 802 ObjectMonitor* block = gBlockList; 803 ObjectMonitor* mid; 804 while (block) { 805 assert(block->object() == CHAINMARKER, "must be a block header"); 806 for (int i = _BLOCKSIZE - 1; i > 0; i--) { 807 mid = block + i; 808 oop object = (oop) mid->object(); 809 if (object != NULL) { 810 closure->do_monitor(mid); 811 } 812 } 813 block = (ObjectMonitor*) block->FreeNext; 814 } 815 } 816 817 // Get the next block in the block list. 818 static inline ObjectMonitor* next(ObjectMonitor* block) { 819 assert(block->object() == CHAINMARKER, "must be a block header"); 820 block = block->FreeNext ; 821 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header"); 822 return block; 823 } 824 825 826 void ObjectSynchronizer::oops_do(OopClosure* f) { 827 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 828 for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) { 829 assert(block->object() == CHAINMARKER, "must be a block header"); 830 for (int i = 1; i < _BLOCKSIZE; i++) { 831 ObjectMonitor* mid = &block[i]; 832 if (mid->object() != NULL) { 833 f->do_oop((oop*)mid->object_addr()); 834 } 835 } 836 } 837 } 838 839 840 // ----------------------------------------------------------------------------- 841 // ObjectMonitor Lifecycle 842 // ----------------------- 843 // Inflation unlinks monitors from the global gFreeList and 844 // associates them with objects. Deflation -- which occurs at 845 // STW-time -- disassociates idle monitors from objects. Such 846 // scavenged monitors are returned to the gFreeList. 847 // 848 // The global list is protected by ListLock. All the critical sections 849 // are short and operate in constant-time. 850 // 851 // ObjectMonitors reside in type-stable memory (TSM) and are immortal. 852 // 853 // Lifecycle: 854 // -- unassigned and on the global free list 855 // -- unassigned and on a thread's private omFreeList 856 // -- assigned to an object. The object is inflated and the mark refers 857 // to the objectmonitor. 858 // 859 860 861 // Constraining monitor pool growth via MonitorBound ... 862 // 863 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the 864 // the rate of scavenging is driven primarily by GC. As such, we can find 865 // an inordinate number of monitors in circulation. 866 // To avoid that scenario we can artificially induce a STW safepoint 867 // if the pool appears to be growing past some reasonable bound. 868 // Generally we favor time in space-time tradeoffs, but as there's no 869 // natural back-pressure on the # of extant monitors we need to impose some 870 // type of limit. Beware that if MonitorBound is set to too low a value 871 // we could just loop. In addition, if MonitorBound is set to a low value 872 // we'll incur more safepoints, which are harmful to performance. 873 // See also: GuaranteedSafepointInterval 874 // 875 // The current implementation uses asynchronous VM operations. 876 // 877 878 static void InduceScavenge (Thread * Self, const char * Whence) { 879 // Induce STW safepoint to trim monitors 880 // Ultimately, this results in a call to deflate_idle_monitors() in the near future. 881 // More precisely, trigger an asynchronous STW safepoint as the number 882 // of active monitors passes the specified threshold. 883 // TODO: assert thread state is reasonable 884 885 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) { 886 if (ObjectMonitor::Knob_Verbose) { 887 ::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ; 888 ::fflush(stdout) ; 889 } 890 // Induce a 'null' safepoint to scavenge monitors 891 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted 892 // to the VMthread and have a lifespan longer than that of this activation record. 893 // The VMThread will delete the op when completed. 894 VMThread::execute (new VM_ForceAsyncSafepoint()) ; 895 896 if (ObjectMonitor::Knob_Verbose) { 897 ::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ; 898 ::fflush(stdout) ; 899 } 900 } 901 } 902 /* Too slow for general assert or debug 903 void ObjectSynchronizer::verifyInUse (Thread *Self) { 904 ObjectMonitor* mid; 905 int inusetally = 0; 906 for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) { 907 inusetally ++; 908 } 909 assert(inusetally == Self->omInUseCount, "inuse count off"); 910 911 int freetally = 0; 912 for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) { 913 freetally ++; 914 } 915 assert(freetally == Self->omFreeCount, "free count off"); 916 } 917 */ 918 ObjectMonitor * ATTR ObjectSynchronizer::omAlloc (Thread * Self) { 919 // A large MAXPRIVATE value reduces both list lock contention 920 // and list coherency traffic, but also tends to increase the 921 // number of objectMonitors in circulation as well as the STW 922 // scavenge costs. As usual, we lean toward time in space-time 923 // tradeoffs. 924 const int MAXPRIVATE = 1024 ; 925 for (;;) { 926 ObjectMonitor * m ; 927 928 // 1: try to allocate from the thread's local omFreeList. 929 // Threads will attempt to allocate first from their local list, then 930 // from the global list, and only after those attempts fail will the thread 931 // attempt to instantiate new monitors. Thread-local free lists take 932 // heat off the ListLock and improve allocation latency, as well as reducing 933 // coherency traffic on the shared global list. 934 m = Self->omFreeList ; 935 if (m != NULL) { 936 Self->omFreeList = m->FreeNext ; 937 Self->omFreeCount -- ; 938 // CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene 939 guarantee (m->object() == NULL, "invariant") ; 940 if (MonitorInUseLists) { 941 m->FreeNext = Self->omInUseList; 942 Self->omInUseList = m; 943 Self->omInUseCount ++; 944 // verifyInUse(Self); 945 } else { 946 m->FreeNext = NULL; 947 } 948 return m ; 949 } 950 951 // 2: try to allocate from the global gFreeList 952 // CONSIDER: use muxTry() instead of muxAcquire(). 953 // If the muxTry() fails then drop immediately into case 3. 954 // If we're using thread-local free lists then try 955 // to reprovision the caller's free list. 956 if (gFreeList != NULL) { 957 // Reprovision the thread's omFreeList. 958 // Use bulk transfers to reduce the allocation rate and heat 959 // on various locks. 960 Thread::muxAcquire (&ListLock, "omAlloc") ; 961 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL; ) { 962 MonitorFreeCount --; 963 ObjectMonitor * take = gFreeList ; 964 gFreeList = take->FreeNext ; 965 guarantee (take->object() == NULL, "invariant") ; 966 guarantee (!take->is_busy(), "invariant") ; 967 take->Recycle() ; 968 omRelease (Self, take, false) ; 969 } 970 Thread::muxRelease (&ListLock) ; 971 Self->omFreeProvision += 1 + (Self->omFreeProvision/2) ; 972 if (Self->omFreeProvision > MAXPRIVATE ) Self->omFreeProvision = MAXPRIVATE ; 973 TEVENT (omFirst - reprovision) ; 974 975 const int mx = MonitorBound ; 976 if (mx > 0 && (MonitorPopulation-MonitorFreeCount) > mx) { 977 // We can't safely induce a STW safepoint from omAlloc() as our thread 978 // state may not be appropriate for such activities and callers may hold 979 // naked oops, so instead we defer the action. 980 InduceScavenge (Self, "omAlloc") ; 981 } 982 continue; 983 } 984 985 // 3: allocate a block of new ObjectMonitors 986 // Both the local and global free lists are empty -- resort to malloc(). 987 // In the current implementation objectMonitors are TSM - immortal. 988 assert (_BLOCKSIZE > 1, "invariant") ; 989 ObjectMonitor * temp = new ObjectMonitor[_BLOCKSIZE]; 990 991 // NOTE: (almost) no way to recover if allocation failed. 992 // We might be able to induce a STW safepoint and scavenge enough 993 // objectMonitors to permit progress. 994 if (temp == NULL) { 995 vm_exit_out_of_memory (sizeof (ObjectMonitor[_BLOCKSIZE]), "Allocate ObjectMonitors") ; 996 } 997 998 // Format the block. 999 // initialize the linked list, each monitor points to its next 1000 // forming the single linked free list, the very first monitor 1001 // will points to next block, which forms the block list. 1002 // The trick of using the 1st element in the block as gBlockList 1003 // linkage should be reconsidered. A better implementation would 1004 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; } 1005 1006 for (int i = 1; i < _BLOCKSIZE ; i++) { 1007 temp[i].FreeNext = &temp[i+1]; 1008 } 1009 1010 // terminate the last monitor as the end of list 1011 temp[_BLOCKSIZE - 1].FreeNext = NULL ; 1012 1013 // Element [0] is reserved for global list linkage 1014 temp[0].set_object(CHAINMARKER); 1015 1016 // Consider carving out this thread's current request from the 1017 // block in hand. This avoids some lock traffic and redundant 1018 // list activity. 1019 1020 // Acquire the ListLock to manipulate BlockList and FreeList. 1021 // An Oyama-Taura-Yonezawa scheme might be more efficient. 1022 Thread::muxAcquire (&ListLock, "omAlloc [2]") ; 1023 MonitorPopulation += _BLOCKSIZE-1; 1024 MonitorFreeCount += _BLOCKSIZE-1; 1025 1026 // Add the new block to the list of extant blocks (gBlockList). 1027 // The very first objectMonitor in a block is reserved and dedicated. 1028 // It serves as blocklist "next" linkage. 1029 temp[0].FreeNext = gBlockList; 1030 gBlockList = temp; 1031 1032 // Add the new string of objectMonitors to the global free list 1033 temp[_BLOCKSIZE - 1].FreeNext = gFreeList ; 1034 gFreeList = temp + 1; 1035 Thread::muxRelease (&ListLock) ; 1036 TEVENT (Allocate block of monitors) ; 1037 } 1038 } 1039 1040 // Place "m" on the caller's private per-thread omFreeList. 1041 // In practice there's no need to clamp or limit the number of 1042 // monitors on a thread's omFreeList as the only time we'll call 1043 // omRelease is to return a monitor to the free list after a CAS 1044 // attempt failed. This doesn't allow unbounded #s of monitors to 1045 // accumulate on a thread's free list. 1046 // 1047 1048 void ObjectSynchronizer::omRelease (Thread * Self, ObjectMonitor * m, bool fromPerThreadAlloc) { 1049 guarantee (m->object() == NULL, "invariant") ; 1050 1051 // Remove from omInUseList 1052 if (MonitorInUseLists && fromPerThreadAlloc) { 1053 ObjectMonitor* curmidinuse = NULL; 1054 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; ) { 1055 if (m == mid) { 1056 // extract from per-thread in-use-list 1057 if (mid == Self->omInUseList) { 1058 Self->omInUseList = mid->FreeNext; 1059 } else if (curmidinuse != NULL) { 1060 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist 1061 } 1062 Self->omInUseCount --; 1063 // verifyInUse(Self); 1064 break; 1065 } else { 1066 curmidinuse = mid; 1067 mid = mid->FreeNext; 1068 } 1069 } 1070 } 1071 1072 // FreeNext is used for both onInUseList and omFreeList, so clear old before setting new 1073 m->FreeNext = Self->omFreeList ; 1074 Self->omFreeList = m ; 1075 Self->omFreeCount ++ ; 1076 } 1077 1078 // Return the monitors of a moribund thread's local free list to 1079 // the global free list. Typically a thread calls omFlush() when 1080 // it's dying. We could also consider having the VM thread steal 1081 // monitors from threads that have not run java code over a few 1082 // consecutive STW safepoints. Relatedly, we might decay 1083 // omFreeProvision at STW safepoints. 1084 // 1085 // Also return the monitors of a moribund thread"s omInUseList to 1086 // a global gOmInUseList under the global list lock so these 1087 // will continue to be scanned. 1088 // 1089 // We currently call omFlush() from the Thread:: dtor _after the thread 1090 // has been excised from the thread list and is no longer a mutator. 1091 // That means that omFlush() can run concurrently with a safepoint and 1092 // the scavenge operator. Calling omFlush() from JavaThread::exit() might 1093 // be a better choice as we could safely reason that that the JVM is 1094 // not at a safepoint at the time of the call, and thus there could 1095 // be not inopportune interleavings between omFlush() and the scavenge 1096 // operator. 1097 1098 void ObjectSynchronizer::omFlush (Thread * Self) { 1099 ObjectMonitor * List = Self->omFreeList ; // Null-terminated SLL 1100 Self->omFreeList = NULL ; 1101 ObjectMonitor * Tail = NULL ; 1102 int Tally = 0; 1103 if (List != NULL) { 1104 ObjectMonitor * s ; 1105 for (s = List ; s != NULL ; s = s->FreeNext) { 1106 Tally ++ ; 1107 Tail = s ; 1108 guarantee (s->object() == NULL, "invariant") ; 1109 guarantee (!s->is_busy(), "invariant") ; 1110 s->set_owner (NULL) ; // redundant but good hygiene 1111 TEVENT (omFlush - Move one) ; 1112 } 1113 guarantee (Tail != NULL && List != NULL, "invariant") ; 1114 } 1115 1116 ObjectMonitor * InUseList = Self->omInUseList; 1117 ObjectMonitor * InUseTail = NULL ; 1118 int InUseTally = 0; 1119 if (InUseList != NULL) { 1120 Self->omInUseList = NULL; 1121 ObjectMonitor *curom; 1122 for (curom = InUseList; curom != NULL; curom = curom->FreeNext) { 1123 InUseTail = curom; 1124 InUseTally++; 1125 } 1126 // TODO debug 1127 assert(Self->omInUseCount == InUseTally, "inuse count off"); 1128 Self->omInUseCount = 0; 1129 guarantee (InUseTail != NULL && InUseList != NULL, "invariant"); 1130 } 1131 1132 Thread::muxAcquire (&ListLock, "omFlush") ; 1133 if (Tail != NULL) { 1134 Tail->FreeNext = gFreeList ; 1135 gFreeList = List ; 1136 MonitorFreeCount += Tally; 1137 } 1138 1139 if (InUseTail != NULL) { 1140 InUseTail->FreeNext = gOmInUseList; 1141 gOmInUseList = InUseList; 1142 gOmInUseCount += InUseTally; 1143 } 1144 1145 Thread::muxRelease (&ListLock) ; 1146 TEVENT (omFlush) ; 1147 } 1148 1149 // Fast path code shared by multiple functions 1150 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) { 1151 markOop mark = obj->mark(); 1152 if (mark->has_monitor()) { 1153 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid"); 1154 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header"); 1155 return mark->monitor(); 1156 } 1157 return ObjectSynchronizer::inflate(Thread::current(), obj); 1158 } 1159 1160 1161 // Note that we could encounter some performance loss through false-sharing as 1162 // multiple locks occupy the same $ line. Padding might be appropriate. 1163 1164 1165 ObjectMonitor * ATTR ObjectSynchronizer::inflate (Thread * Self, oop object) { 1166 // Inflate mutates the heap ... 1167 // Relaxing assertion for bug 6320749. 1168 assert (Universe::verify_in_progress() || 1169 !SafepointSynchronize::is_at_safepoint(), "invariant") ; 1170 1171 for (;;) { 1172 const markOop mark = object->mark() ; 1173 assert (!mark->has_bias_pattern(), "invariant") ; 1174 1175 // The mark can be in one of the following states: 1176 // * Inflated - just return 1177 // * Stack-locked - coerce it to inflated 1178 // * INFLATING - busy wait for conversion to complete 1179 // * Neutral - aggressively inflate the object. 1180 // * BIASED - Illegal. We should never see this 1181 1182 // CASE: inflated 1183 if (mark->has_monitor()) { 1184 ObjectMonitor * inf = mark->monitor() ; 1185 assert (inf->header()->is_neutral(), "invariant"); 1186 assert (inf->object() == object, "invariant") ; 1187 assert (ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid"); 1188 return inf ; 1189 } 1190 1191 // CASE: inflation in progress - inflating over a stack-lock. 1192 // Some other thread is converting from stack-locked to inflated. 1193 // Only that thread can complete inflation -- other threads must wait. 1194 // The INFLATING value is transient. 1195 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish. 1196 // We could always eliminate polling by parking the thread on some auxiliary list. 1197 if (mark == markOopDesc::INFLATING()) { 1198 TEVENT (Inflate: spin while INFLATING) ; 1199 ReadStableMark(object) ; 1200 continue ; 1201 } 1202 1203 // CASE: stack-locked 1204 // Could be stack-locked either by this thread or by some other thread. 1205 // 1206 // Note that we allocate the objectmonitor speculatively, _before_ attempting 1207 // to install INFLATING into the mark word. We originally installed INFLATING, 1208 // allocated the objectmonitor, and then finally STed the address of the 1209 // objectmonitor into the mark. This was correct, but artificially lengthened 1210 // the interval in which INFLATED appeared in the mark, thus increasing 1211 // the odds of inflation contention. 1212 // 1213 // We now use per-thread private objectmonitor free lists. 1214 // These list are reprovisioned from the global free list outside the 1215 // critical INFLATING...ST interval. A thread can transfer 1216 // multiple objectmonitors en-mass from the global free list to its local free list. 1217 // This reduces coherency traffic and lock contention on the global free list. 1218 // Using such local free lists, it doesn't matter if the omAlloc() call appears 1219 // before or after the CAS(INFLATING) operation. 1220 // See the comments in omAlloc(). 1221 1222 if (mark->has_locker()) { 1223 ObjectMonitor * m = omAlloc (Self) ; 1224 // Optimistically prepare the objectmonitor - anticipate successful CAS 1225 // We do this before the CAS in order to minimize the length of time 1226 // in which INFLATING appears in the mark. 1227 m->Recycle(); 1228 m->_Responsible = NULL ; 1229 m->OwnerIsThread = 0 ; 1230 m->_recursions = 0 ; 1231 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // Consider: maintain by type/class 1232 1233 markOop cmp = (markOop) Atomic::cmpxchg_ptr (markOopDesc::INFLATING(), object->mark_addr(), mark) ; 1234 if (cmp != mark) { 1235 omRelease (Self, m, true) ; 1236 continue ; // Interference -- just retry 1237 } 1238 1239 // We've successfully installed INFLATING (0) into the mark-word. 1240 // This is the only case where 0 will appear in a mark-work. 1241 // Only the singular thread that successfully swings the mark-word 1242 // to 0 can perform (or more precisely, complete) inflation. 1243 // 1244 // Why do we CAS a 0 into the mark-word instead of just CASing the 1245 // mark-word from the stack-locked value directly to the new inflated state? 1246 // Consider what happens when a thread unlocks a stack-locked object. 1247 // It attempts to use CAS to swing the displaced header value from the 1248 // on-stack basiclock back into the object header. Recall also that the 1249 // header value (hashcode, etc) can reside in (a) the object header, or 1250 // (b) a displaced header associated with the stack-lock, or (c) a displaced 1251 // header in an objectMonitor. The inflate() routine must copy the header 1252 // value from the basiclock on the owner's stack to the objectMonitor, all 1253 // the while preserving the hashCode stability invariants. If the owner 1254 // decides to release the lock while the value is 0, the unlock will fail 1255 // and control will eventually pass from slow_exit() to inflate. The owner 1256 // will then spin, waiting for the 0 value to disappear. Put another way, 1257 // the 0 causes the owner to stall if the owner happens to try to 1258 // drop the lock (restoring the header from the basiclock to the object) 1259 // while inflation is in-progress. This protocol avoids races that might 1260 // would otherwise permit hashCode values to change or "flicker" for an object. 1261 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable. 1262 // 0 serves as a "BUSY" inflate-in-progress indicator. 1263 1264 1265 // fetch the displaced mark from the owner's stack. 1266 // The owner can't die or unwind past the lock while our INFLATING 1267 // object is in the mark. Furthermore the owner can't complete 1268 // an unlock on the object, either. 1269 markOop dmw = mark->displaced_mark_helper() ; 1270 assert (dmw->is_neutral(), "invariant") ; 1271 1272 // Setup monitor fields to proper values -- prepare the monitor 1273 m->set_header(dmw) ; 1274 1275 // Optimization: if the mark->locker stack address is associated 1276 // with this thread we could simply set m->_owner = Self and 1277 // m->OwnerIsThread = 1. Note that a thread can inflate an object 1278 // that it has stack-locked -- as might happen in wait() -- directly 1279 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom. 1280 m->set_owner(mark->locker()); 1281 m->set_object(object); 1282 // TODO-FIXME: assert BasicLock->dhw != 0. 1283 1284 // Must preserve store ordering. The monitor state must 1285 // be stable at the time of publishing the monitor address. 1286 guarantee (object->mark() == markOopDesc::INFLATING(), "invariant") ; 1287 object->release_set_mark(markOopDesc::encode(m)); 1288 1289 // Hopefully the performance counters are allocated on distinct cache lines 1290 // to avoid false sharing on MP systems ... 1291 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ; 1292 TEVENT(Inflate: overwrite stacklock) ; 1293 if (TraceMonitorInflation) { 1294 if (object->is_instance()) { 1295 ResourceMark rm; 1296 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 1297 (intptr_t) object, (intptr_t) object->mark(), 1298 Klass::cast(object->klass())->external_name()); 1299 } 1300 } 1301 return m ; 1302 } 1303 1304 // CASE: neutral 1305 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner. 1306 // If we know we're inflating for entry it's better to inflate by swinging a 1307 // pre-locked objectMonitor pointer into the object header. A successful 1308 // CAS inflates the object *and* confers ownership to the inflating thread. 1309 // In the current implementation we use a 2-step mechanism where we CAS() 1310 // to inflate and then CAS() again to try to swing _owner from NULL to Self. 1311 // An inflateTry() method that we could call from fast_enter() and slow_enter() 1312 // would be useful. 1313 1314 assert (mark->is_neutral(), "invariant"); 1315 ObjectMonitor * m = omAlloc (Self) ; 1316 // prepare m for installation - set monitor to initial state 1317 m->Recycle(); 1318 m->set_header(mark); 1319 m->set_owner(NULL); 1320 m->set_object(object); 1321 m->OwnerIsThread = 1 ; 1322 m->_recursions = 0 ; 1323 m->_Responsible = NULL ; 1324 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // consider: keep metastats by type/class 1325 1326 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) { 1327 m->set_object (NULL) ; 1328 m->set_owner (NULL) ; 1329 m->OwnerIsThread = 0 ; 1330 m->Recycle() ; 1331 omRelease (Self, m, true) ; 1332 m = NULL ; 1333 continue ; 1334 // interference - the markword changed - just retry. 1335 // The state-transitions are one-way, so there's no chance of 1336 // live-lock -- "Inflated" is an absorbing state. 1337 } 1338 1339 // Hopefully the performance counters are allocated on distinct 1340 // cache lines to avoid false sharing on MP systems ... 1341 if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ; 1342 TEVENT(Inflate: overwrite neutral) ; 1343 if (TraceMonitorInflation) { 1344 if (object->is_instance()) { 1345 ResourceMark rm; 1346 tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 1347 (intptr_t) object, (intptr_t) object->mark(), 1348 Klass::cast(object->klass())->external_name()); 1349 } 1350 } 1351 return m ; 1352 } 1353 } 1354 1355 // Note that we could encounter some performance loss through false-sharing as 1356 // multiple locks occupy the same $ line. Padding might be appropriate. 1357 1358 1359 // Deflate_idle_monitors() is called at all safepoints, immediately 1360 // after all mutators are stopped, but before any objects have moved. 1361 // It traverses the list of known monitors, deflating where possible. 1362 // The scavenged monitor are returned to the monitor free list. 1363 // 1364 // Beware that we scavenge at *every* stop-the-world point. 1365 // Having a large number of monitors in-circulation negatively 1366 // impacts the performance of some applications (e.g., PointBase). 1367 // Broadly, we want to minimize the # of monitors in circulation. 1368 // 1369 // We have added a flag, MonitorInUseLists, which creates a list 1370 // of active monitors for each thread. deflate_idle_monitors() 1371 // only scans the per-thread inuse lists. omAlloc() puts all 1372 // assigned monitors on the per-thread list. deflate_idle_monitors() 1373 // returns the non-busy monitors to the global free list. 1374 // When a thread dies, omFlush() adds the list of active monitors for 1375 // that thread to a global gOmInUseList acquiring the 1376 // global list lock. deflate_idle_monitors() acquires the global 1377 // list lock to scan for non-busy monitors to the global free list. 1378 // An alternative could have used a single global inuse list. The 1379 // downside would have been the additional cost of acquiring the global list lock 1380 // for every omAlloc(). 1381 // 1382 // Perversely, the heap size -- and thus the STW safepoint rate -- 1383 // typically drives the scavenge rate. Large heaps can mean infrequent GC, 1384 // which in turn can mean large(r) numbers of objectmonitors in circulation. 1385 // This is an unfortunate aspect of this design. 1386 // 1387 1388 enum ManifestConstants { 1389 ClearResponsibleAtSTW = 0, 1390 MaximumRecheckInterval = 1000 1391 } ; 1392 1393 // Deflate a single monitor if not in use 1394 // Return true if deflated, false if in use 1395 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj, 1396 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) { 1397 bool deflated; 1398 // Normal case ... The monitor is associated with obj. 1399 guarantee (obj->mark() == markOopDesc::encode(mid), "invariant") ; 1400 guarantee (mid == obj->mark()->monitor(), "invariant"); 1401 guarantee (mid->header()->is_neutral(), "invariant"); 1402 1403 if (mid->is_busy()) { 1404 if (ClearResponsibleAtSTW) mid->_Responsible = NULL ; 1405 deflated = false; 1406 } else { 1407 // Deflate the monitor if it is no longer being used 1408 // It's idle - scavenge and return to the global free list 1409 // plain old deflation ... 1410 TEVENT (deflate_idle_monitors - scavenge1) ; 1411 if (TraceMonitorInflation) { 1412 if (obj->is_instance()) { 1413 ResourceMark rm; 1414 tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 1415 (intptr_t) obj, (intptr_t) obj->mark(), Klass::cast(obj->klass())->external_name()); 1416 } 1417 } 1418 1419 // Restore the header back to obj 1420 obj->release_set_mark(mid->header()); 1421 mid->clear(); 1422 1423 assert (mid->object() == NULL, "invariant") ; 1424 1425 // Move the object to the working free list defined by FreeHead,FreeTail. 1426 if (*FreeHeadp == NULL) *FreeHeadp = mid; 1427 if (*FreeTailp != NULL) { 1428 ObjectMonitor * prevtail = *FreeTailp; 1429 assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); // TODO KK 1430 prevtail->FreeNext = mid; 1431 } 1432 *FreeTailp = mid; 1433 deflated = true; 1434 } 1435 return deflated; 1436 } 1437 1438 // Caller acquires ListLock 1439 int ObjectSynchronizer::walk_monitor_list(ObjectMonitor** listheadp, 1440 ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) { 1441 ObjectMonitor* mid; 1442 ObjectMonitor* next; 1443 ObjectMonitor* curmidinuse = NULL; 1444 int deflatedcount = 0; 1445 1446 for (mid = *listheadp; mid != NULL; ) { 1447 oop obj = (oop) mid->object(); 1448 bool deflated = false; 1449 if (obj != NULL) { 1450 deflated = deflate_monitor(mid, obj, FreeHeadp, FreeTailp); 1451 } 1452 if (deflated) { 1453 // extract from per-thread in-use-list 1454 if (mid == *listheadp) { 1455 *listheadp = mid->FreeNext; 1456 } else if (curmidinuse != NULL) { 1457 curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist 1458 } 1459 next = mid->FreeNext; 1460 mid->FreeNext = NULL; // This mid is current tail in the FreeHead list 1461 mid = next; 1462 deflatedcount++; 1463 } else { 1464 curmidinuse = mid; 1465 mid = mid->FreeNext; 1466 } 1467 } 1468 return deflatedcount; 1469 } 1470 1471 void ObjectSynchronizer::deflate_idle_monitors() { 1472 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 1473 int nInuse = 0 ; // currently associated with objects 1474 int nInCirculation = 0 ; // extant 1475 int nScavenged = 0 ; // reclaimed 1476 bool deflated = false; 1477 1478 ObjectMonitor * FreeHead = NULL ; // Local SLL of scavenged monitors 1479 ObjectMonitor * FreeTail = NULL ; 1480 1481 TEVENT (deflate_idle_monitors) ; 1482 // Prevent omFlush from changing mids in Thread dtor's during deflation 1483 // And in case the vm thread is acquiring a lock during a safepoint 1484 // See e.g. 6320749 1485 Thread::muxAcquire (&ListLock, "scavenge - return") ; 1486 1487 if (MonitorInUseLists) { 1488 int inUse = 0; 1489 for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) { 1490 nInCirculation+= cur->omInUseCount; 1491 int deflatedcount = walk_monitor_list(cur->omInUseList_addr(), &FreeHead, &FreeTail); 1492 cur->omInUseCount-= deflatedcount; 1493 // verifyInUse(cur); 1494 nScavenged += deflatedcount; 1495 nInuse += cur->omInUseCount; 1496 } 1497 1498 // For moribund threads, scan gOmInUseList 1499 if (gOmInUseList) { 1500 nInCirculation += gOmInUseCount; 1501 int deflatedcount = walk_monitor_list((ObjectMonitor **)&gOmInUseList, &FreeHead, &FreeTail); 1502 gOmInUseCount-= deflatedcount; 1503 nScavenged += deflatedcount; 1504 nInuse += gOmInUseCount; 1505 } 1506 1507 } else for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) { 1508 // Iterate over all extant monitors - Scavenge all idle monitors. 1509 assert(block->object() == CHAINMARKER, "must be a block header"); 1510 nInCirculation += _BLOCKSIZE ; 1511 for (int i = 1 ; i < _BLOCKSIZE; i++) { 1512 ObjectMonitor* mid = &block[i]; 1513 oop obj = (oop) mid->object(); 1514 1515 if (obj == NULL) { 1516 // The monitor is not associated with an object. 1517 // The monitor should either be a thread-specific private 1518 // free list or the global free list. 1519 // obj == NULL IMPLIES mid->is_busy() == 0 1520 guarantee (!mid->is_busy(), "invariant") ; 1521 continue ; 1522 } 1523 deflated = deflate_monitor(mid, obj, &FreeHead, &FreeTail); 1524 1525 if (deflated) { 1526 mid->FreeNext = NULL ; 1527 nScavenged ++ ; 1528 } else { 1529 nInuse ++; 1530 } 1531 } 1532 } 1533 1534 MonitorFreeCount += nScavenged; 1535 1536 // Consider: audit gFreeList to ensure that MonitorFreeCount and list agree. 1537 1538 if (ObjectMonitor::Knob_Verbose) { 1539 ::printf ("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n", 1540 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge, 1541 MonitorPopulation, MonitorFreeCount) ; 1542 ::fflush(stdout) ; 1543 } 1544 1545 ForceMonitorScavenge = 0; // Reset 1546 1547 // Move the scavenged monitors back to the global free list. 1548 if (FreeHead != NULL) { 1549 guarantee (FreeTail != NULL && nScavenged > 0, "invariant") ; 1550 assert (FreeTail->FreeNext == NULL, "invariant") ; 1551 // constant-time list splice - prepend scavenged segment to gFreeList 1552 FreeTail->FreeNext = gFreeList ; 1553 gFreeList = FreeHead ; 1554 } 1555 Thread::muxRelease (&ListLock) ; 1556 1557 if (ObjectMonitor::_sync_Deflations != NULL) ObjectMonitor::_sync_Deflations->inc(nScavenged) ; 1558 if (ObjectMonitor::_sync_MonExtant != NULL) ObjectMonitor::_sync_MonExtant ->set_value(nInCirculation); 1559 1560 // TODO: Add objectMonitor leak detection. 1561 // Audit/inventory the objectMonitors -- make sure they're all accounted for. 1562 GVars.stwRandom = os::random() ; 1563 GVars.stwCycle ++ ; 1564 } 1565 1566 // Monitor cleanup on JavaThread::exit 1567 1568 // Iterate through monitor cache and attempt to release thread's monitors 1569 // Gives up on a particular monitor if an exception occurs, but continues 1570 // the overall iteration, swallowing the exception. 1571 class ReleaseJavaMonitorsClosure: public MonitorClosure { 1572 private: 1573 TRAPS; 1574 1575 public: 1576 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {} 1577 void do_monitor(ObjectMonitor* mid) { 1578 if (mid->owner() == THREAD) { 1579 (void)mid->complete_exit(CHECK); 1580 } 1581 } 1582 }; 1583 1584 // Release all inflated monitors owned by THREAD. Lightweight monitors are 1585 // ignored. This is meant to be called during JNI thread detach which assumes 1586 // all remaining monitors are heavyweight. All exceptions are swallowed. 1587 // Scanning the extant monitor list can be time consuming. 1588 // A simple optimization is to add a per-thread flag that indicates a thread 1589 // called jni_monitorenter() during its lifetime. 1590 // 1591 // Instead of No_Savepoint_Verifier it might be cheaper to 1592 // use an idiom of the form: 1593 // auto int tmp = SafepointSynchronize::_safepoint_counter ; 1594 // <code that must not run at safepoint> 1595 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ; 1596 // Since the tests are extremely cheap we could leave them enabled 1597 // for normal product builds. 1598 1599 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) { 1600 assert(THREAD == JavaThread::current(), "must be current Java thread"); 1601 No_Safepoint_Verifier nsv ; 1602 ReleaseJavaMonitorsClosure rjmc(THREAD); 1603 Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread"); 1604 ObjectSynchronizer::monitors_iterate(&rjmc); 1605 Thread::muxRelease(&ListLock); 1606 THREAD->clear_pending_exception(); 1607 } 1608 1609 //------------------------------------------------------------------------------ 1610 // Non-product code 1611 1612 #ifndef PRODUCT 1613 1614 void ObjectSynchronizer::trace_locking(Handle locking_obj, bool is_compiled, 1615 bool is_method, bool is_locking) { 1616 // Don't know what to do here 1617 } 1618 1619 // Verify all monitors in the monitor cache, the verification is weak. 1620 void ObjectSynchronizer::verify() { 1621 ObjectMonitor* block = gBlockList; 1622 ObjectMonitor* mid; 1623 while (block) { 1624 assert(block->object() == CHAINMARKER, "must be a block header"); 1625 for (int i = 1; i < _BLOCKSIZE; i++) { 1626 mid = block + i; 1627 oop object = (oop) mid->object(); 1628 if (object != NULL) { 1629 mid->verify(); 1630 } 1631 } 1632 block = (ObjectMonitor*) block->FreeNext; 1633 } 1634 } 1635 1636 // Check if monitor belongs to the monitor cache 1637 // The list is grow-only so it's *relatively* safe to traverse 1638 // the list of extant blocks without taking a lock. 1639 1640 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) { 1641 ObjectMonitor* block = gBlockList; 1642 1643 while (block) { 1644 assert(block->object() == CHAINMARKER, "must be a block header"); 1645 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) { 1646 address mon = (address) monitor; 1647 address blk = (address) block; 1648 size_t diff = mon - blk; 1649 assert((diff % sizeof(ObjectMonitor)) == 0, "check"); 1650 return 1; 1651 } 1652 block = (ObjectMonitor*) block->FreeNext; 1653 } 1654 return 0; 1655 } 1656 1657 #endif