1 /* 2 * Copyright (c) 1998, 2019, 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 "logging/log.hpp" 28 #include "logging/logStream.hpp" 29 #include "jfr/jfrEvents.hpp" 30 #include "memory/allocation.inline.hpp" 31 #include "memory/metaspaceShared.hpp" 32 #include "memory/padded.hpp" 33 #include "memory/resourceArea.hpp" 34 #include "memory/universe.hpp" 35 #include "oops/markWord.hpp" 36 #include "oops/oop.inline.hpp" 37 #include "runtime/atomic.hpp" 38 #include "runtime/biasedLocking.hpp" 39 #include "runtime/handles.inline.hpp" 40 #include "runtime/interfaceSupport.inline.hpp" 41 #include "runtime/mutexLocker.hpp" 42 #include "runtime/objectMonitor.hpp" 43 #include "runtime/objectMonitor.inline.hpp" 44 #include "runtime/osThread.hpp" 45 #include "runtime/safepointVerifiers.hpp" 46 #include "runtime/sharedRuntime.hpp" 47 #include "runtime/stubRoutines.hpp" 48 #include "runtime/synchronizer.hpp" 49 #include "runtime/thread.inline.hpp" 50 #include "runtime/timer.hpp" 51 #include "runtime/vframe.hpp" 52 #include "runtime/vmThread.hpp" 53 #include "utilities/align.hpp" 54 #include "utilities/dtrace.hpp" 55 #include "utilities/events.hpp" 56 #include "utilities/preserveException.hpp" 57 58 // The "core" versions of monitor enter and exit reside in this file. 59 // The interpreter and compilers contain specialized transliterated 60 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(), 61 // for instance. If you make changes here, make sure to modify the 62 // interpreter, and both C1 and C2 fast-path inline locking code emission. 63 // 64 // ----------------------------------------------------------------------------- 65 66 #ifdef DTRACE_ENABLED 67 68 // Only bother with this argument setup if dtrace is available 69 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly. 70 71 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \ 72 char* bytes = NULL; \ 73 int len = 0; \ 74 jlong jtid = SharedRuntime::get_java_tid(thread); \ 75 Symbol* klassname = ((oop)(obj))->klass()->name(); \ 76 if (klassname != NULL) { \ 77 bytes = (char*)klassname->bytes(); \ 78 len = klassname->utf8_length(); \ 79 } 80 81 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \ 82 { \ 83 if (DTraceMonitorProbes) { \ 84 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 85 HOTSPOT_MONITOR_WAIT(jtid, \ 86 (uintptr_t)(monitor), bytes, len, (millis)); \ 87 } \ 88 } 89 90 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY 91 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL 92 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED 93 94 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \ 95 { \ 96 if (DTraceMonitorProbes) { \ 97 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 98 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \ 99 (uintptr_t)(monitor), bytes, len); \ 100 } \ 101 } 102 103 #else // ndef DTRACE_ENABLED 104 105 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;} 106 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;} 107 108 #endif // ndef DTRACE_ENABLED 109 110 // This exists only as a workaround of dtrace bug 6254741 111 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) { 112 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr); 113 return 0; 114 } 115 116 #define NINFLATIONLOCKS 256 117 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS]; 118 119 // global list of blocks of monitors 120 PaddedEnd<ObjectMonitor> * volatile ObjectSynchronizer::gBlockList = NULL; 121 // global monitor free list 122 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL; 123 // global monitor in-use list, for moribund threads, 124 // monitors they inflated need to be scanned for deflation 125 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL; 126 // count of entries in gOmInUseList 127 int ObjectSynchronizer::gOmInUseCount = 0; 128 129 static volatile intptr_t gListLock = 0; // protects global monitor lists 130 static volatile int gMonitorFreeCount = 0; // # on gFreeList 131 static volatile int gMonitorPopulation = 0; // # Extant -- in circulation 132 133 #define CHAINMARKER (cast_to_oop<intptr_t>(-1)) 134 135 136 // =====================> Quick functions 137 138 // The quick_* forms are special fast-path variants used to improve 139 // performance. In the simplest case, a "quick_*" implementation could 140 // simply return false, in which case the caller will perform the necessary 141 // state transitions and call the slow-path form. 142 // The fast-path is designed to handle frequently arising cases in an efficient 143 // manner and is just a degenerate "optimistic" variant of the slow-path. 144 // returns true -- to indicate the call was satisfied. 145 // returns false -- to indicate the call needs the services of the slow-path. 146 // A no-loitering ordinance is in effect for code in the quick_* family 147 // operators: safepoints or indefinite blocking (blocking that might span a 148 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon 149 // entry. 150 // 151 // Consider: An interesting optimization is to have the JIT recognize the 152 // following common idiom: 153 // synchronized (someobj) { .... ; notify(); } 154 // That is, we find a notify() or notifyAll() call that immediately precedes 155 // the monitorexit operation. In that case the JIT could fuse the operations 156 // into a single notifyAndExit() runtime primitive. 157 158 bool ObjectSynchronizer::quick_notify(oopDesc * obj, Thread * self, bool all) { 159 assert(!SafepointSynchronize::is_at_safepoint(), "invariant"); 160 assert(self->is_Java_thread(), "invariant"); 161 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant"); 162 NoSafepointVerifier nsv; 163 if (obj == NULL) return false; // slow-path for invalid obj 164 const markWord mark = obj->mark(); 165 166 if (mark.has_locker() && self->is_lock_owned((address)mark.locker())) { 167 // Degenerate notify 168 // stack-locked by caller so by definition the implied waitset is empty. 169 return true; 170 } 171 172 if (mark.has_monitor()) { 173 ObjectMonitor * const mon = mark.monitor(); 174 assert(oopDesc::equals((oop) mon->object(), obj), "invariant"); 175 if (mon->owner() != self) return false; // slow-path for IMS exception 176 177 if (mon->first_waiter() != NULL) { 178 // We have one or more waiters. Since this is an inflated monitor 179 // that we own, we can transfer one or more threads from the waitset 180 // to the entrylist here and now, avoiding the slow-path. 181 if (all) { 182 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self); 183 } else { 184 DTRACE_MONITOR_PROBE(notify, mon, obj, self); 185 } 186 int tally = 0; 187 do { 188 mon->INotify(self); 189 ++tally; 190 } while (mon->first_waiter() != NULL && all); 191 OM_PERFDATA_OP(Notifications, inc(tally)); 192 } 193 return true; 194 } 195 196 // biased locking and any other IMS exception states take the slow-path 197 return false; 198 } 199 200 201 // The LockNode emitted directly at the synchronization site would have 202 // been too big if it were to have included support for the cases of inflated 203 // recursive enter and exit, so they go here instead. 204 // Note that we can't safely call AsyncPrintJavaStack() from within 205 // quick_enter() as our thread state remains _in_Java. 206 207 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self, 208 BasicLock * lock) { 209 assert(!SafepointSynchronize::is_at_safepoint(), "invariant"); 210 assert(Self->is_Java_thread(), "invariant"); 211 assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant"); 212 NoSafepointVerifier nsv; 213 if (obj == NULL) return false; // Need to throw NPE 214 const markWord mark = obj->mark(); 215 216 if (mark.has_monitor()) { 217 ObjectMonitor * const m = mark.monitor(); 218 assert(oopDesc::equals((oop) m->object(), obj), "invariant"); 219 Thread * const owner = (Thread *) m->_owner; 220 221 // Lock contention and Transactional Lock Elision (TLE) diagnostics 222 // and observability 223 // Case: light contention possibly amenable to TLE 224 // Case: TLE inimical operations such as nested/recursive synchronization 225 226 if (owner == Self) { 227 m->_recursions++; 228 return true; 229 } 230 231 // This Java Monitor is inflated so obj's header will never be 232 // displaced to this thread's BasicLock. Make the displaced header 233 // non-NULL so this BasicLock is not seen as recursive nor as 234 // being locked. We do this unconditionally so that this thread's 235 // BasicLock cannot be mis-interpreted by any stack walkers. For 236 // performance reasons, stack walkers generally first check for 237 // Biased Locking in the object's header, the second check is for 238 // stack-locking in the object's header, the third check is for 239 // recursive stack-locking in the displaced header in the BasicLock, 240 // and last are the inflated Java Monitor (ObjectMonitor) checks. 241 lock->set_displaced_header(markWord::unused_mark()); 242 243 if (owner == NULL && Atomic::replace_if_null(Self, &(m->_owner))) { 244 assert(m->_recursions == 0, "invariant"); 245 return true; 246 } 247 } 248 249 // Note that we could inflate in quick_enter. 250 // This is likely a useful optimization 251 // Critically, in quick_enter() we must not: 252 // -- perform bias revocation, or 253 // -- block indefinitely, or 254 // -- reach a safepoint 255 256 return false; // revert to slow-path 257 } 258 259 // ----------------------------------------------------------------------------- 260 // Fast Monitor Enter/Exit 261 // This the fast monitor enter. The interpreter and compiler use 262 // some assembly copies of this code. Make sure update those code 263 // if the following function is changed. The implementation is 264 // extremely sensitive to race condition. Be careful. 265 266 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock, 267 bool attempt_rebias, TRAPS) { 268 if (UseBiasedLocking) { 269 if (!SafepointSynchronize::is_at_safepoint()) { 270 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD); 271 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) { 272 return; 273 } 274 } else { 275 assert(!attempt_rebias, "can not rebias toward VM thread"); 276 BiasedLocking::revoke_at_safepoint(obj); 277 } 278 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 279 } 280 281 slow_enter(obj, lock, THREAD); 282 } 283 284 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) { 285 markWord mark = object->mark(); 286 // We cannot check for Biased Locking if we are racing an inflation. 287 assert(mark == markWord::INFLATING() || 288 !mark.has_bias_pattern(), "should not see bias pattern here"); 289 290 markWord dhw = lock->displaced_header(); 291 if (dhw.value() == 0) { 292 // If the displaced header is NULL, then this exit matches up with 293 // a recursive enter. No real work to do here except for diagnostics. 294 #ifndef PRODUCT 295 if (mark != markWord::INFLATING()) { 296 // Only do diagnostics if we are not racing an inflation. Simply 297 // exiting a recursive enter of a Java Monitor that is being 298 // inflated is safe; see the has_monitor() comment below. 299 assert(!mark.is_neutral(), "invariant"); 300 assert(!mark.has_locker() || 301 THREAD->is_lock_owned((address)mark.locker()), "invariant"); 302 if (mark.has_monitor()) { 303 // The BasicLock's displaced_header is marked as a recursive 304 // enter and we have an inflated Java Monitor (ObjectMonitor). 305 // This is a special case where the Java Monitor was inflated 306 // after this thread entered the stack-lock recursively. When a 307 // Java Monitor is inflated, we cannot safely walk the Java 308 // Monitor owner's stack and update the BasicLocks because a 309 // Java Monitor can be asynchronously inflated by a thread that 310 // does not own the Java Monitor. 311 ObjectMonitor * m = mark.monitor(); 312 assert(((oop)(m->object()))->mark() == mark, "invariant"); 313 assert(m->is_entered(THREAD), "invariant"); 314 } 315 } 316 #endif 317 return; 318 } 319 320 if (mark == markWord::from_pointer(lock)) { 321 // If the object is stack-locked by the current thread, try to 322 // swing the displaced header from the BasicLock back to the mark. 323 assert(dhw.is_neutral(), "invariant"); 324 if (object->cas_set_mark(dhw, mark) == mark) { 325 return; 326 } 327 } 328 329 // We have to take the slow-path of possible inflation and then exit. 330 inflate(THREAD, object, inflate_cause_vm_internal)->exit(true, THREAD); 331 } 332 333 // ----------------------------------------------------------------------------- 334 // Interpreter/Compiler Slow Case 335 // This routine is used to handle interpreter/compiler slow case 336 // We don't need to use fast path here, because it must have been 337 // failed in the interpreter/compiler code. 338 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) { 339 markWord mark = obj->mark(); 340 assert(!mark.has_bias_pattern(), "should not see bias pattern here"); 341 342 if (mark.is_neutral()) { 343 // Anticipate successful CAS -- the ST of the displaced mark must 344 // be visible <= the ST performed by the CAS. 345 lock->set_displaced_header(mark); 346 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) { 347 return; 348 } 349 // Fall through to inflate() ... 350 } else if (mark.has_locker() && 351 THREAD->is_lock_owned((address)mark.locker())) { 352 assert(lock != mark.locker(), "must not re-lock the same lock"); 353 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock"); 354 lock->set_displaced_header(markWord::from_pointer(NULL)); 355 return; 356 } 357 358 // The object header will never be displaced to this lock, 359 // so it does not matter what the value is, except that it 360 // must be non-zero to avoid looking like a re-entrant lock, 361 // and must not look locked either. 362 lock->set_displaced_header(markWord::unused_mark()); 363 inflate(THREAD, obj(), inflate_cause_monitor_enter)->enter(THREAD); 364 } 365 366 // This routine is used to handle interpreter/compiler slow case 367 // We don't need to use fast path here, because it must have 368 // failed in the interpreter/compiler code. Simply use the heavy 369 // weight monitor should be ok, unless someone find otherwise. 370 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) { 371 fast_exit(object, lock, THREAD); 372 } 373 374 // ----------------------------------------------------------------------------- 375 // Class Loader support to workaround deadlocks on the class loader lock objects 376 // Also used by GC 377 // complete_exit()/reenter() are used to wait on a nested lock 378 // i.e. to give up an outer lock completely and then re-enter 379 // Used when holding nested locks - lock acquisition order: lock1 then lock2 380 // 1) complete_exit lock1 - saving recursion count 381 // 2) wait on lock2 382 // 3) when notified on lock2, unlock lock2 383 // 4) reenter lock1 with original recursion count 384 // 5) lock lock2 385 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 386 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) { 387 if (UseBiasedLocking) { 388 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 389 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 390 } 391 392 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal); 393 394 return monitor->complete_exit(THREAD); 395 } 396 397 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 398 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) { 399 if (UseBiasedLocking) { 400 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 401 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 402 } 403 404 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal); 405 406 monitor->reenter(recursion, THREAD); 407 } 408 // ----------------------------------------------------------------------------- 409 // JNI locks on java objects 410 // NOTE: must use heavy weight monitor to handle jni monitor enter 411 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) { 412 // the current locking is from JNI instead of Java code 413 if (UseBiasedLocking) { 414 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 415 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 416 } 417 THREAD->set_current_pending_monitor_is_from_java(false); 418 inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD); 419 THREAD->set_current_pending_monitor_is_from_java(true); 420 } 421 422 // NOTE: must use heavy weight monitor to handle jni monitor exit 423 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) { 424 if (UseBiasedLocking) { 425 Handle h_obj(THREAD, obj); 426 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD); 427 obj = h_obj(); 428 } 429 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 430 431 ObjectMonitor* monitor = inflate(THREAD, obj, inflate_cause_jni_exit); 432 // If this thread has locked the object, exit the monitor. We 433 // intentionally do not use CHECK here because we must exit the 434 // monitor even if an exception is pending. 435 if (monitor->check_owner(THREAD)) { 436 monitor->exit(true, THREAD); 437 } 438 } 439 440 // ----------------------------------------------------------------------------- 441 // Internal VM locks on java objects 442 // standard constructor, allows locking failures 443 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) { 444 _dolock = doLock; 445 _thread = thread; 446 _thread->check_for_valid_safepoint_state(false); 447 _obj = obj; 448 449 if (_dolock) { 450 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread); 451 } 452 } 453 454 ObjectLocker::~ObjectLocker() { 455 if (_dolock) { 456 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread); 457 } 458 } 459 460 461 // ----------------------------------------------------------------------------- 462 // Wait/Notify/NotifyAll 463 // NOTE: must use heavy weight monitor to handle wait() 464 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) { 465 if (UseBiasedLocking) { 466 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 467 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 468 } 469 if (millis < 0) { 470 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); 471 } 472 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait); 473 474 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis); 475 monitor->wait(millis, true, THREAD); 476 477 // This dummy call is in place to get around dtrace bug 6254741. Once 478 // that's fixed we can uncomment the following line, remove the call 479 // and change this function back into a "void" func. 480 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD); 481 return dtrace_waited_probe(monitor, obj, THREAD); 482 } 483 484 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) { 485 if (UseBiasedLocking) { 486 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 487 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 488 } 489 if (millis < 0) { 490 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); 491 } 492 inflate(THREAD, obj(), inflate_cause_wait)->wait(millis, false, THREAD); 493 } 494 495 void ObjectSynchronizer::notify(Handle obj, TRAPS) { 496 if (UseBiasedLocking) { 497 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 498 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 499 } 500 501 markWord mark = obj->mark(); 502 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) { 503 return; 504 } 505 inflate(THREAD, obj(), inflate_cause_notify)->notify(THREAD); 506 } 507 508 // NOTE: see comment of notify() 509 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) { 510 if (UseBiasedLocking) { 511 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 512 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 513 } 514 515 markWord mark = obj->mark(); 516 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) { 517 return; 518 } 519 inflate(THREAD, obj(), inflate_cause_notify)->notifyAll(THREAD); 520 } 521 522 // ----------------------------------------------------------------------------- 523 // Hash Code handling 524 // 525 // Performance concern: 526 // OrderAccess::storestore() calls release() which at one time stored 0 527 // into the global volatile OrderAccess::dummy variable. This store was 528 // unnecessary for correctness. Many threads storing into a common location 529 // causes considerable cache migration or "sloshing" on large SMP systems. 530 // As such, I avoided using OrderAccess::storestore(). In some cases 531 // OrderAccess::fence() -- which incurs local latency on the executing 532 // processor -- is a better choice as it scales on SMP systems. 533 // 534 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for 535 // a discussion of coherency costs. Note that all our current reference 536 // platforms provide strong ST-ST order, so the issue is moot on IA32, 537 // x64, and SPARC. 538 // 539 // As a general policy we use "volatile" to control compiler-based reordering 540 // and explicit fences (barriers) to control for architectural reordering 541 // performed by the CPU(s) or platform. 542 543 struct SharedGlobals { 544 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE]; 545 // These are highly shared mostly-read variables. 546 // To avoid false-sharing they need to be the sole occupants of a cache line. 547 volatile int stwRandom; 548 volatile int stwCycle; 549 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2); 550 // Hot RW variable -- Sequester to avoid false-sharing 551 volatile int hcSequence; 552 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int)); 553 }; 554 555 static SharedGlobals GVars; 556 static int MonitorScavengeThreshold = 1000000; 557 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending 558 559 static markWord ReadStableMark(oop obj) { 560 markWord mark = obj->mark(); 561 if (!mark.is_being_inflated()) { 562 return mark; // normal fast-path return 563 } 564 565 int its = 0; 566 for (;;) { 567 markWord mark = obj->mark(); 568 if (!mark.is_being_inflated()) { 569 return mark; // normal fast-path return 570 } 571 572 // The object is being inflated by some other thread. 573 // The caller of ReadStableMark() must wait for inflation to complete. 574 // Avoid live-lock 575 // TODO: consider calling SafepointSynchronize::do_call_back() while 576 // spinning to see if there's a safepoint pending. If so, immediately 577 // yielding or blocking would be appropriate. Avoid spinning while 578 // there is a safepoint pending. 579 // TODO: add inflation contention performance counters. 580 // TODO: restrict the aggregate number of spinners. 581 582 ++its; 583 if (its > 10000 || !os::is_MP()) { 584 if (its & 1) { 585 os::naked_yield(); 586 } else { 587 // Note that the following code attenuates the livelock problem but is not 588 // a complete remedy. A more complete solution would require that the inflating 589 // thread hold the associated inflation lock. The following code simply restricts 590 // the number of spinners to at most one. We'll have N-2 threads blocked 591 // on the inflationlock, 1 thread holding the inflation lock and using 592 // a yield/park strategy, and 1 thread in the midst of inflation. 593 // A more refined approach would be to change the encoding of INFLATING 594 // to allow encapsulation of a native thread pointer. Threads waiting for 595 // inflation to complete would use CAS to push themselves onto a singly linked 596 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag 597 // and calling park(). When inflation was complete the thread that accomplished inflation 598 // would detach the list and set the markword to inflated with a single CAS and 599 // then for each thread on the list, set the flag and unpark() the thread. 600 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease 601 // wakes at most one thread whereas we need to wake the entire list. 602 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1); 603 int YieldThenBlock = 0; 604 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant"); 605 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant"); 606 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock"); 607 while (obj->mark() == markWord::INFLATING()) { 608 // Beware: NakedYield() is advisory and has almost no effect on some platforms 609 // so we periodically call Self->_ParkEvent->park(1). 610 // We use a mixed spin/yield/block mechanism. 611 if ((YieldThenBlock++) >= 16) { 612 Thread::current()->_ParkEvent->park(1); 613 } else { 614 os::naked_yield(); 615 } 616 } 617 Thread::muxRelease(gInflationLocks + ix); 618 } 619 } else { 620 SpinPause(); // SMP-polite spinning 621 } 622 } 623 } 624 625 // hashCode() generation : 626 // 627 // Possibilities: 628 // * MD5Digest of {obj,stwRandom} 629 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function. 630 // * A DES- or AES-style SBox[] mechanism 631 // * One of the Phi-based schemes, such as: 632 // 2654435761 = 2^32 * Phi (golden ratio) 633 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ; 634 // * A variation of Marsaglia's shift-xor RNG scheme. 635 // * (obj ^ stwRandom) is appealing, but can result 636 // in undesirable regularity in the hashCode values of adjacent objects 637 // (objects allocated back-to-back, in particular). This could potentially 638 // result in hashtable collisions and reduced hashtable efficiency. 639 // There are simple ways to "diffuse" the middle address bits over the 640 // generated hashCode values: 641 642 static inline intptr_t get_next_hash(Thread * Self, oop obj) { 643 intptr_t value = 0; 644 if (hashCode == 0) { 645 // This form uses global Park-Miller RNG. 646 // On MP system we'll have lots of RW access to a global, so the 647 // mechanism induces lots of coherency traffic. 648 value = os::random(); 649 } else if (hashCode == 1) { 650 // This variation has the property of being stable (idempotent) 651 // between STW operations. This can be useful in some of the 1-0 652 // synchronization schemes. 653 intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3; 654 value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom; 655 } else if (hashCode == 2) { 656 value = 1; // for sensitivity testing 657 } else if (hashCode == 3) { 658 value = ++GVars.hcSequence; 659 } else if (hashCode == 4) { 660 value = cast_from_oop<intptr_t>(obj); 661 } else { 662 // Marsaglia's xor-shift scheme with thread-specific state 663 // This is probably the best overall implementation -- we'll 664 // likely make this the default in future releases. 665 unsigned t = Self->_hashStateX; 666 t ^= (t << 11); 667 Self->_hashStateX = Self->_hashStateY; 668 Self->_hashStateY = Self->_hashStateZ; 669 Self->_hashStateZ = Self->_hashStateW; 670 unsigned v = Self->_hashStateW; 671 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)); 672 Self->_hashStateW = v; 673 value = v; 674 } 675 676 value &= markWord::hash_mask; 677 if (value == 0) value = 0xBAD; 678 assert(value != markWord::no_hash, "invariant"); 679 return value; 680 } 681 682 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) { 683 if (UseBiasedLocking) { 684 // NOTE: many places throughout the JVM do not expect a safepoint 685 // to be taken here, in particular most operations on perm gen 686 // objects. However, we only ever bias Java instances and all of 687 // the call sites of identity_hash that might revoke biases have 688 // been checked to make sure they can handle a safepoint. The 689 // added check of the bias pattern is to avoid useless calls to 690 // thread-local storage. 691 if (obj->mark().has_bias_pattern()) { 692 // Handle for oop obj in case of STW safepoint 693 Handle hobj(Self, obj); 694 // Relaxing assertion for bug 6320749. 695 assert(Universe::verify_in_progress() || 696 !SafepointSynchronize::is_at_safepoint(), 697 "biases should not be seen by VM thread here"); 698 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current()); 699 obj = hobj(); 700 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 701 } 702 } 703 704 // hashCode() is a heap mutator ... 705 // Relaxing assertion for bug 6320749. 706 assert(Universe::verify_in_progress() || DumpSharedSpaces || 707 !SafepointSynchronize::is_at_safepoint(), "invariant"); 708 assert(Universe::verify_in_progress() || DumpSharedSpaces || 709 Self->is_Java_thread() , "invariant"); 710 assert(Universe::verify_in_progress() || DumpSharedSpaces || 711 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant"); 712 713 ObjectMonitor* monitor = NULL; 714 markWord temp, test; 715 intptr_t hash; 716 markWord mark = ReadStableMark(obj); 717 718 // object should remain ineligible for biased locking 719 assert(!mark.has_bias_pattern(), "invariant"); 720 721 if (mark.is_neutral()) { 722 hash = mark.hash(); // this is a normal header 723 if (hash != 0) { // if it has hash, just return it 724 return hash; 725 } 726 hash = get_next_hash(Self, obj); // allocate a new hash code 727 temp = mark.copy_set_hash(hash); // merge the hash code into header 728 // use (machine word version) atomic operation to install the hash 729 test = obj->cas_set_mark(temp, mark); 730 if (test == mark) { 731 return hash; 732 } 733 // If atomic operation failed, we must inflate the header 734 // into heavy weight monitor. We could add more code here 735 // for fast path, but it does not worth the complexity. 736 } else if (mark.has_monitor()) { 737 monitor = mark.monitor(); 738 temp = monitor->header(); 739 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 740 hash = temp.hash(); 741 if (hash != 0) { 742 return hash; 743 } 744 // Skip to the following code to reduce code size 745 } else if (Self->is_lock_owned((address)mark.locker())) { 746 temp = mark.displaced_mark_helper(); // this is a lightweight monitor owned 747 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 748 hash = temp.hash(); // by current thread, check if the displaced 749 if (hash != 0) { // header contains hash code 750 return hash; 751 } 752 // WARNING: 753 // The displaced header in the BasicLock on a thread's stack 754 // is strictly immutable. It CANNOT be changed in ANY cases. 755 // So we have to inflate the stack lock into an ObjectMonitor 756 // even if the current thread owns the lock. The BasicLock on 757 // a thread's stack can be asynchronously read by other threads 758 // during an inflate() call so any change to that stack memory 759 // may not propagate to other threads correctly. 760 } 761 762 // Inflate the monitor to set hash code 763 monitor = inflate(Self, obj, inflate_cause_hash_code); 764 // Load displaced header and check it has hash code 765 mark = monitor->header(); 766 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value()); 767 hash = mark.hash(); 768 if (hash == 0) { 769 hash = get_next_hash(Self, obj); 770 temp = mark.copy_set_hash(hash); // merge hash code into header 771 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 772 uintptr_t v = Atomic::cmpxchg(temp.value(), (volatile uintptr_t*)monitor->header_addr(), mark.value()); 773 test = markWord(v); 774 if (test != mark) { 775 // The only update to the ObjectMonitor's header/dmw field 776 // is to merge in the hash code. If someone adds a new usage 777 // of the header/dmw field, please update this code. 778 hash = test.hash(); 779 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value()); 780 assert(hash != 0, "Trivial unexpected object/monitor header usage."); 781 } 782 } 783 // We finally get the hash 784 return hash; 785 } 786 787 // Deprecated -- use FastHashCode() instead. 788 789 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) { 790 return FastHashCode(Thread::current(), obj()); 791 } 792 793 794 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread, 795 Handle h_obj) { 796 if (UseBiasedLocking) { 797 BiasedLocking::revoke_and_rebias(h_obj, false, thread); 798 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now"); 799 } 800 801 assert(thread == JavaThread::current(), "Can only be called on current thread"); 802 oop obj = h_obj(); 803 804 markWord mark = ReadStableMark(obj); 805 806 // Uncontended case, header points to stack 807 if (mark.has_locker()) { 808 return thread->is_lock_owned((address)mark.locker()); 809 } 810 // Contended case, header points to ObjectMonitor (tagged pointer) 811 if (mark.has_monitor()) { 812 ObjectMonitor* monitor = mark.monitor(); 813 return monitor->is_entered(thread) != 0; 814 } 815 // Unlocked case, header in place 816 assert(mark.is_neutral(), "sanity check"); 817 return false; 818 } 819 820 // Be aware of this method could revoke bias of the lock object. 821 // This method queries the ownership of the lock handle specified by 'h_obj'. 822 // If the current thread owns the lock, it returns owner_self. If no 823 // thread owns the lock, it returns owner_none. Otherwise, it will return 824 // owner_other. 825 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership 826 (JavaThread *self, Handle h_obj) { 827 // The caller must beware this method can revoke bias, and 828 // revocation can result in a safepoint. 829 assert(!SafepointSynchronize::is_at_safepoint(), "invariant"); 830 assert(self->thread_state() != _thread_blocked, "invariant"); 831 832 // Possible mark states: neutral, biased, stack-locked, inflated 833 834 if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) { 835 // CASE: biased 836 BiasedLocking::revoke_and_rebias(h_obj, false, self); 837 assert(!h_obj->mark().has_bias_pattern(), 838 "biases should be revoked by now"); 839 } 840 841 assert(self == JavaThread::current(), "Can only be called on current thread"); 842 oop obj = h_obj(); 843 markWord mark = ReadStableMark(obj); 844 845 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack. 846 if (mark.has_locker()) { 847 return self->is_lock_owned((address)mark.locker()) ? 848 owner_self : owner_other; 849 } 850 851 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor. 852 // The Object:ObjectMonitor relationship is stable as long as we're 853 // not at a safepoint. 854 if (mark.has_monitor()) { 855 void * owner = mark.monitor()->_owner; 856 if (owner == NULL) return owner_none; 857 return (owner == self || 858 self->is_lock_owned((address)owner)) ? owner_self : owner_other; 859 } 860 861 // CASE: neutral 862 assert(mark.is_neutral(), "sanity check"); 863 return owner_none; // it's unlocked 864 } 865 866 // FIXME: jvmti should call this 867 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) { 868 if (UseBiasedLocking) { 869 if (SafepointSynchronize::is_at_safepoint()) { 870 BiasedLocking::revoke_at_safepoint(h_obj); 871 } else { 872 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current()); 873 } 874 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now"); 875 } 876 877 oop obj = h_obj(); 878 address owner = NULL; 879 880 markWord mark = ReadStableMark(obj); 881 882 // Uncontended case, header points to stack 883 if (mark.has_locker()) { 884 owner = (address) mark.locker(); 885 } 886 887 // Contended case, header points to ObjectMonitor (tagged pointer) 888 else if (mark.has_monitor()) { 889 ObjectMonitor* monitor = mark.monitor(); 890 assert(monitor != NULL, "monitor should be non-null"); 891 owner = (address) monitor->owner(); 892 } 893 894 if (owner != NULL) { 895 // owning_thread_from_monitor_owner() may also return NULL here 896 return Threads::owning_thread_from_monitor_owner(t_list, owner); 897 } 898 899 // Unlocked case, header in place 900 // Cannot have assertion since this object may have been 901 // locked by another thread when reaching here. 902 // assert(mark.is_neutral(), "sanity check"); 903 904 return NULL; 905 } 906 907 // Visitors ... 908 909 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) { 910 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList); 911 while (block != NULL) { 912 assert(block->object() == CHAINMARKER, "must be a block header"); 913 for (int i = _BLOCKSIZE - 1; i > 0; i--) { 914 ObjectMonitor* mid = (ObjectMonitor *)(block + i); 915 oop object = (oop)mid->object(); 916 if (object != NULL) { 917 closure->do_monitor(mid); 918 } 919 } 920 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext; 921 } 922 } 923 924 // Get the next block in the block list. 925 static inline PaddedEnd<ObjectMonitor>* next(PaddedEnd<ObjectMonitor>* block) { 926 assert(block->object() == CHAINMARKER, "must be a block header"); 927 block = (PaddedEnd<ObjectMonitor>*) block->FreeNext; 928 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header"); 929 return block; 930 } 931 932 static bool monitors_used_above_threshold() { 933 if (gMonitorPopulation == 0) { 934 return false; 935 } 936 int monitors_used = gMonitorPopulation - gMonitorFreeCount; 937 int monitor_usage = (monitors_used * 100LL) / gMonitorPopulation; 938 return monitor_usage > MonitorUsedDeflationThreshold; 939 } 940 941 bool ObjectSynchronizer::is_cleanup_needed() { 942 if (MonitorUsedDeflationThreshold > 0) { 943 return monitors_used_above_threshold(); 944 } 945 return false; 946 } 947 948 void ObjectSynchronizer::oops_do(OopClosure* f) { 949 // We only scan the global used list here (for moribund threads), and 950 // the thread-local monitors in Thread::oops_do(). 951 global_used_oops_do(f); 952 } 953 954 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) { 955 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 956 list_oops_do(gOmInUseList, f); 957 } 958 959 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) { 960 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 961 list_oops_do(thread->omInUseList, f); 962 } 963 964 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) { 965 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 966 ObjectMonitor* mid; 967 for (mid = list; mid != NULL; mid = mid->FreeNext) { 968 if (mid->object() != NULL) { 969 f->do_oop((oop*)mid->object_addr()); 970 } 971 } 972 } 973 974 975 // ----------------------------------------------------------------------------- 976 // ObjectMonitor Lifecycle 977 // ----------------------- 978 // Inflation unlinks monitors from the global gFreeList and 979 // associates them with objects. Deflation -- which occurs at 980 // STW-time -- disassociates idle monitors from objects. Such 981 // scavenged monitors are returned to the gFreeList. 982 // 983 // The global list is protected by gListLock. All the critical sections 984 // are short and operate in constant-time. 985 // 986 // ObjectMonitors reside in type-stable memory (TSM) and are immortal. 987 // 988 // Lifecycle: 989 // -- unassigned and on the global free list 990 // -- unassigned and on a thread's private omFreeList 991 // -- assigned to an object. The object is inflated and the mark refers 992 // to the objectmonitor. 993 994 995 // Constraining monitor pool growth via MonitorBound ... 996 // 997 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the 998 // the rate of scavenging is driven primarily by GC. As such, we can find 999 // an inordinate number of monitors in circulation. 1000 // To avoid that scenario we can artificially induce a STW safepoint 1001 // if the pool appears to be growing past some reasonable bound. 1002 // Generally we favor time in space-time tradeoffs, but as there's no 1003 // natural back-pressure on the # of extant monitors we need to impose some 1004 // type of limit. Beware that if MonitorBound is set to too low a value 1005 // we could just loop. In addition, if MonitorBound is set to a low value 1006 // we'll incur more safepoints, which are harmful to performance. 1007 // See also: GuaranteedSafepointInterval 1008 // 1009 // The current implementation uses asynchronous VM operations. 1010 1011 static void InduceScavenge(Thread * Self, const char * Whence) { 1012 // Induce STW safepoint to trim monitors 1013 // Ultimately, this results in a call to deflate_idle_monitors() in the near future. 1014 // More precisely, trigger an asynchronous STW safepoint as the number 1015 // of active monitors passes the specified threshold. 1016 // TODO: assert thread state is reasonable 1017 1018 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) { 1019 // Induce a 'null' safepoint to scavenge monitors 1020 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted 1021 // to the VMthread and have a lifespan longer than that of this activation record. 1022 // The VMThread will delete the op when completed. 1023 VMThread::execute(new VM_ScavengeMonitors()); 1024 } 1025 } 1026 1027 ObjectMonitor* ObjectSynchronizer::omAlloc(Thread * Self) { 1028 // A large MAXPRIVATE value reduces both list lock contention 1029 // and list coherency traffic, but also tends to increase the 1030 // number of objectMonitors in circulation as well as the STW 1031 // scavenge costs. As usual, we lean toward time in space-time 1032 // tradeoffs. 1033 const int MAXPRIVATE = 1024; 1034 stringStream ss; 1035 for (;;) { 1036 ObjectMonitor * m; 1037 1038 // 1: try to allocate from the thread's local omFreeList. 1039 // Threads will attempt to allocate first from their local list, then 1040 // from the global list, and only after those attempts fail will the thread 1041 // attempt to instantiate new monitors. Thread-local free lists take 1042 // heat off the gListLock and improve allocation latency, as well as reducing 1043 // coherency traffic on the shared global list. 1044 m = Self->omFreeList; 1045 if (m != NULL) { 1046 Self->omFreeList = m->FreeNext; 1047 Self->omFreeCount--; 1048 guarantee(m->object() == NULL, "invariant"); 1049 m->FreeNext = Self->omInUseList; 1050 Self->omInUseList = m; 1051 Self->omInUseCount++; 1052 return m; 1053 } 1054 1055 // 2: try to allocate from the global gFreeList 1056 // CONSIDER: use muxTry() instead of muxAcquire(). 1057 // If the muxTry() fails then drop immediately into case 3. 1058 // If we're using thread-local free lists then try 1059 // to reprovision the caller's free list. 1060 if (gFreeList != NULL) { 1061 // Reprovision the thread's omFreeList. 1062 // Use bulk transfers to reduce the allocation rate and heat 1063 // on various locks. 1064 Thread::muxAcquire(&gListLock, "omAlloc(1)"); 1065 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) { 1066 gMonitorFreeCount--; 1067 ObjectMonitor * take = gFreeList; 1068 gFreeList = take->FreeNext; 1069 guarantee(take->object() == NULL, "invariant"); 1070 take->Recycle(); 1071 omRelease(Self, take, false); 1072 } 1073 Thread::muxRelease(&gListLock); 1074 Self->omFreeProvision += 1 + (Self->omFreeProvision/2); 1075 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE; 1076 1077 const int mx = MonitorBound; 1078 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) { 1079 // We can't safely induce a STW safepoint from omAlloc() as our thread 1080 // state may not be appropriate for such activities and callers may hold 1081 // naked oops, so instead we defer the action. 1082 InduceScavenge(Self, "omAlloc"); 1083 } 1084 continue; 1085 } 1086 1087 // 3: allocate a block of new ObjectMonitors 1088 // Both the local and global free lists are empty -- resort to malloc(). 1089 // In the current implementation objectMonitors are TSM - immortal. 1090 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want 1091 // each ObjectMonitor to start at the beginning of a cache line, 1092 // so we use align_up(). 1093 // A better solution would be to use C++ placement-new. 1094 // BEWARE: As it stands currently, we don't run the ctors! 1095 assert(_BLOCKSIZE > 1, "invariant"); 1096 size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE; 1097 PaddedEnd<ObjectMonitor> * temp; 1098 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1); 1099 void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size, 1100 mtInternal); 1101 temp = (PaddedEnd<ObjectMonitor> *) 1102 align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE); 1103 1104 // NOTE: (almost) no way to recover if allocation failed. 1105 // We might be able to induce a STW safepoint and scavenge enough 1106 // objectMonitors to permit progress. 1107 if (temp == NULL) { 1108 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR, 1109 "Allocate ObjectMonitors"); 1110 } 1111 (void)memset((void *) temp, 0, neededsize); 1112 1113 // Format the block. 1114 // initialize the linked list, each monitor points to its next 1115 // forming the single linked free list, the very first monitor 1116 // will points to next block, which forms the block list. 1117 // The trick of using the 1st element in the block as gBlockList 1118 // linkage should be reconsidered. A better implementation would 1119 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; } 1120 1121 for (int i = 1; i < _BLOCKSIZE; i++) { 1122 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1]; 1123 } 1124 1125 // terminate the last monitor as the end of list 1126 temp[_BLOCKSIZE - 1].FreeNext = NULL; 1127 1128 // Element [0] is reserved for global list linkage 1129 temp[0].set_object(CHAINMARKER); 1130 1131 // Consider carving out this thread's current request from the 1132 // block in hand. This avoids some lock traffic and redundant 1133 // list activity. 1134 1135 // Acquire the gListLock to manipulate gBlockList and gFreeList. 1136 // An Oyama-Taura-Yonezawa scheme might be more efficient. 1137 Thread::muxAcquire(&gListLock, "omAlloc(2)"); 1138 gMonitorPopulation += _BLOCKSIZE-1; 1139 gMonitorFreeCount += _BLOCKSIZE-1; 1140 1141 // Add the new block to the list of extant blocks (gBlockList). 1142 // The very first objectMonitor in a block is reserved and dedicated. 1143 // It serves as blocklist "next" linkage. 1144 temp[0].FreeNext = gBlockList; 1145 // There are lock-free uses of gBlockList so make sure that 1146 // the previous stores happen before we update gBlockList. 1147 OrderAccess::release_store(&gBlockList, temp); 1148 1149 // Add the new string of objectMonitors to the global free list 1150 temp[_BLOCKSIZE - 1].FreeNext = gFreeList; 1151 gFreeList = temp + 1; 1152 Thread::muxRelease(&gListLock); 1153 } 1154 } 1155 1156 // Place "m" on the caller's private per-thread omFreeList. 1157 // In practice there's no need to clamp or limit the number of 1158 // monitors on a thread's omFreeList as the only time we'll call 1159 // omRelease is to return a monitor to the free list after a CAS 1160 // attempt failed. This doesn't allow unbounded #s of monitors to 1161 // accumulate on a thread's free list. 1162 // 1163 // Key constraint: all ObjectMonitors on a thread's free list and the global 1164 // free list must have their object field set to null. This prevents the 1165 // scavenger -- deflate_monitor_list() -- from reclaiming them. 1166 1167 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m, 1168 bool fromPerThreadAlloc) { 1169 guarantee(m->header().value() == 0, "invariant"); 1170 guarantee(m->object() == NULL, "invariant"); 1171 stringStream ss; 1172 guarantee((m->is_busy() | m->_recursions) == 0, "freeing in-use monitor: " 1173 "%s, recursions=" INTPTR_FORMAT, m->is_busy_to_string(&ss), 1174 m->_recursions); 1175 // Remove from omInUseList 1176 if (fromPerThreadAlloc) { 1177 ObjectMonitor* cur_mid_in_use = NULL; 1178 bool extracted = false; 1179 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) { 1180 if (m == mid) { 1181 // extract from per-thread in-use list 1182 if (mid == Self->omInUseList) { 1183 Self->omInUseList = mid->FreeNext; 1184 } else if (cur_mid_in_use != NULL) { 1185 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list 1186 } 1187 extracted = true; 1188 Self->omInUseCount--; 1189 break; 1190 } 1191 } 1192 assert(extracted, "Should have extracted from in-use list"); 1193 } 1194 1195 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new 1196 m->FreeNext = Self->omFreeList; 1197 Self->omFreeList = m; 1198 Self->omFreeCount++; 1199 } 1200 1201 // Return the monitors of a moribund thread's local free list to 1202 // the global free list. Typically a thread calls omFlush() when 1203 // it's dying. We could also consider having the VM thread steal 1204 // monitors from threads that have not run java code over a few 1205 // consecutive STW safepoints. Relatedly, we might decay 1206 // omFreeProvision at STW safepoints. 1207 // 1208 // Also return the monitors of a moribund thread's omInUseList to 1209 // a global gOmInUseList under the global list lock so these 1210 // will continue to be scanned. 1211 // 1212 // We currently call omFlush() from Threads::remove() _before the thread 1213 // has been excised from the thread list and is no longer a mutator. 1214 // This means that omFlush() cannot run concurrently with a safepoint and 1215 // interleave with the deflate_idle_monitors scavenge operator. In particular, 1216 // this ensures that the thread's monitors are scanned by a GC safepoint, 1217 // either via Thread::oops_do() (if safepoint happens before omFlush()) or via 1218 // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's 1219 // monitors have been transferred to the global in-use list). 1220 1221 void ObjectSynchronizer::omFlush(Thread * Self) { 1222 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL 1223 ObjectMonitor * tail = NULL; 1224 int tally = 0; 1225 if (list != NULL) { 1226 ObjectMonitor * s; 1227 // The thread is going away. Set 'tail' to the last per-thread free 1228 // monitor which will be linked to gFreeList below under the gListLock. 1229 stringStream ss; 1230 for (s = list; s != NULL; s = s->FreeNext) { 1231 tally++; 1232 tail = s; 1233 guarantee(s->object() == NULL, "invariant"); 1234 guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss)); 1235 } 1236 guarantee(tail != NULL, "invariant"); 1237 assert(Self->omFreeCount == tally, "free-count off"); 1238 Self->omFreeList = NULL; 1239 Self->omFreeCount = 0; 1240 } 1241 1242 ObjectMonitor * inUseList = Self->omInUseList; 1243 ObjectMonitor * inUseTail = NULL; 1244 int inUseTally = 0; 1245 if (inUseList != NULL) { 1246 ObjectMonitor *cur_om; 1247 // The thread is going away, however the omInUseList inflated 1248 // monitors may still be in-use by other threads. 1249 // Link them to inUseTail, which will be linked into the global in-use list 1250 // gOmInUseList below, under the gListLock 1251 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) { 1252 inUseTail = cur_om; 1253 inUseTally++; 1254 } 1255 guarantee(inUseTail != NULL, "invariant"); 1256 assert(Self->omInUseCount == inUseTally, "in-use count off"); 1257 Self->omInUseList = NULL; 1258 Self->omInUseCount = 0; 1259 } 1260 1261 Thread::muxAcquire(&gListLock, "omFlush"); 1262 if (tail != NULL) { 1263 tail->FreeNext = gFreeList; 1264 gFreeList = list; 1265 gMonitorFreeCount += tally; 1266 } 1267 1268 if (inUseTail != NULL) { 1269 inUseTail->FreeNext = gOmInUseList; 1270 gOmInUseList = inUseList; 1271 gOmInUseCount += inUseTally; 1272 } 1273 1274 Thread::muxRelease(&gListLock); 1275 1276 LogStreamHandle(Debug, monitorinflation) lsh_debug; 1277 LogStreamHandle(Info, monitorinflation) lsh_info; 1278 LogStream * ls = NULL; 1279 if (log_is_enabled(Debug, monitorinflation)) { 1280 ls = &lsh_debug; 1281 } else if ((tally != 0 || inUseTally != 0) && 1282 log_is_enabled(Info, monitorinflation)) { 1283 ls = &lsh_info; 1284 } 1285 if (ls != NULL) { 1286 ls->print_cr("omFlush: jt=" INTPTR_FORMAT ", free_monitor_tally=%d" 1287 ", in_use_monitor_tally=%d" ", omFreeProvision=%d", 1288 p2i(Self), tally, inUseTally, Self->omFreeProvision); 1289 } 1290 } 1291 1292 static void post_monitor_inflate_event(EventJavaMonitorInflate* event, 1293 const oop obj, 1294 ObjectSynchronizer::InflateCause cause) { 1295 assert(event != NULL, "invariant"); 1296 assert(event->should_commit(), "invariant"); 1297 event->set_monitorClass(obj->klass()); 1298 event->set_address((uintptr_t)(void*)obj); 1299 event->set_cause((u1)cause); 1300 event->commit(); 1301 } 1302 1303 // Fast path code shared by multiple functions 1304 void ObjectSynchronizer::inflate_helper(oop obj) { 1305 markWord mark = obj->mark(); 1306 if (mark.has_monitor()) { 1307 assert(ObjectSynchronizer::verify_objmon_isinpool(mark.monitor()), "monitor is invalid"); 1308 assert(mark.monitor()->header().is_neutral(), "monitor must record a good object header"); 1309 return; 1310 } 1311 inflate(Thread::current(), obj, inflate_cause_vm_internal); 1312 } 1313 1314 ObjectMonitor* ObjectSynchronizer::inflate(Thread * Self, 1315 oop object, 1316 const InflateCause cause) { 1317 // Inflate mutates the heap ... 1318 // Relaxing assertion for bug 6320749. 1319 assert(Universe::verify_in_progress() || 1320 !SafepointSynchronize::is_at_safepoint(), "invariant"); 1321 1322 EventJavaMonitorInflate event; 1323 1324 for (;;) { 1325 const markWord mark = object->mark(); 1326 assert(!mark.has_bias_pattern(), "invariant"); 1327 1328 // The mark can be in one of the following states: 1329 // * Inflated - just return 1330 // * Stack-locked - coerce it to inflated 1331 // * INFLATING - busy wait for conversion to complete 1332 // * Neutral - aggressively inflate the object. 1333 // * BIASED - Illegal. We should never see this 1334 1335 // CASE: inflated 1336 if (mark.has_monitor()) { 1337 ObjectMonitor * inf = mark.monitor(); 1338 markWord dmw = inf->header(); 1339 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1340 assert(oopDesc::equals((oop) inf->object(), object), "invariant"); 1341 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid"); 1342 return inf; 1343 } 1344 1345 // CASE: inflation in progress - inflating over a stack-lock. 1346 // Some other thread is converting from stack-locked to inflated. 1347 // Only that thread can complete inflation -- other threads must wait. 1348 // The INFLATING value is transient. 1349 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish. 1350 // We could always eliminate polling by parking the thread on some auxiliary list. 1351 if (mark == markWord::INFLATING()) { 1352 ReadStableMark(object); 1353 continue; 1354 } 1355 1356 // CASE: stack-locked 1357 // Could be stack-locked either by this thread or by some other thread. 1358 // 1359 // Note that we allocate the objectmonitor speculatively, _before_ attempting 1360 // to install INFLATING into the mark word. We originally installed INFLATING, 1361 // allocated the objectmonitor, and then finally STed the address of the 1362 // objectmonitor into the mark. This was correct, but artificially lengthened 1363 // the interval in which INFLATED appeared in the mark, thus increasing 1364 // the odds of inflation contention. 1365 // 1366 // We now use per-thread private objectmonitor free lists. 1367 // These list are reprovisioned from the global free list outside the 1368 // critical INFLATING...ST interval. A thread can transfer 1369 // multiple objectmonitors en-mass from the global free list to its local free list. 1370 // This reduces coherency traffic and lock contention on the global free list. 1371 // Using such local free lists, it doesn't matter if the omAlloc() call appears 1372 // before or after the CAS(INFLATING) operation. 1373 // See the comments in omAlloc(). 1374 1375 LogStreamHandle(Trace, monitorinflation) lsh; 1376 1377 if (mark.has_locker()) { 1378 ObjectMonitor * m = omAlloc(Self); 1379 // Optimistically prepare the objectmonitor - anticipate successful CAS 1380 // We do this before the CAS in order to minimize the length of time 1381 // in which INFLATING appears in the mark. 1382 m->Recycle(); 1383 m->_Responsible = NULL; 1384 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class 1385 1386 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark); 1387 if (cmp != mark) { 1388 omRelease(Self, m, true); 1389 continue; // Interference -- just retry 1390 } 1391 1392 // We've successfully installed INFLATING (0) into the mark-word. 1393 // This is the only case where 0 will appear in a mark-word. 1394 // Only the singular thread that successfully swings the mark-word 1395 // to 0 can perform (or more precisely, complete) inflation. 1396 // 1397 // Why do we CAS a 0 into the mark-word instead of just CASing the 1398 // mark-word from the stack-locked value directly to the new inflated state? 1399 // Consider what happens when a thread unlocks a stack-locked object. 1400 // It attempts to use CAS to swing the displaced header value from the 1401 // on-stack basiclock back into the object header. Recall also that the 1402 // header value (hash code, etc) can reside in (a) the object header, or 1403 // (b) a displaced header associated with the stack-lock, or (c) a displaced 1404 // header in an objectMonitor. The inflate() routine must copy the header 1405 // value from the basiclock on the owner's stack to the objectMonitor, all 1406 // the while preserving the hashCode stability invariants. If the owner 1407 // decides to release the lock while the value is 0, the unlock will fail 1408 // and control will eventually pass from slow_exit() to inflate. The owner 1409 // will then spin, waiting for the 0 value to disappear. Put another way, 1410 // the 0 causes the owner to stall if the owner happens to try to 1411 // drop the lock (restoring the header from the basiclock to the object) 1412 // while inflation is in-progress. This protocol avoids races that might 1413 // would otherwise permit hashCode values to change or "flicker" for an object. 1414 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable. 1415 // 0 serves as a "BUSY" inflate-in-progress indicator. 1416 1417 1418 // fetch the displaced mark from the owner's stack. 1419 // The owner can't die or unwind past the lock while our INFLATING 1420 // object is in the mark. Furthermore the owner can't complete 1421 // an unlock on the object, either. 1422 markWord dmw = mark.displaced_mark_helper(); 1423 // Catch if the object's header is not neutral (not locked and 1424 // not marked is what we care about here). 1425 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1426 1427 // Setup monitor fields to proper values -- prepare the monitor 1428 m->set_header(dmw); 1429 1430 // Optimization: if the mark.locker stack address is associated 1431 // with this thread we could simply set m->_owner = Self. 1432 // Note that a thread can inflate an object 1433 // that it has stack-locked -- as might happen in wait() -- directly 1434 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom. 1435 m->set_owner(mark.locker()); 1436 m->set_object(object); 1437 // TODO-FIXME: assert BasicLock->dhw != 0. 1438 1439 // Must preserve store ordering. The monitor state must 1440 // be stable at the time of publishing the monitor address. 1441 guarantee(object->mark() == markWord::INFLATING(), "invariant"); 1442 object->release_set_mark(markWord::encode(m)); 1443 1444 // Hopefully the performance counters are allocated on distinct cache lines 1445 // to avoid false sharing on MP systems ... 1446 OM_PERFDATA_OP(Inflations, inc()); 1447 if (log_is_enabled(Trace, monitorinflation)) { 1448 ResourceMark rm(Self); 1449 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark=" 1450 INTPTR_FORMAT ", type='%s'", p2i(object), 1451 object->mark().value(), object->klass()->external_name()); 1452 } 1453 if (event.should_commit()) { 1454 post_monitor_inflate_event(&event, object, cause); 1455 } 1456 return m; 1457 } 1458 1459 // CASE: neutral 1460 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner. 1461 // If we know we're inflating for entry it's better to inflate by swinging a 1462 // pre-locked objectMonitor pointer into the object header. A successful 1463 // CAS inflates the object *and* confers ownership to the inflating thread. 1464 // In the current implementation we use a 2-step mechanism where we CAS() 1465 // to inflate and then CAS() again to try to swing _owner from NULL to Self. 1466 // An inflateTry() method that we could call from fast_enter() and slow_enter() 1467 // would be useful. 1468 1469 // Catch if the object's header is not neutral (not locked and 1470 // not marked is what we care about here). 1471 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value()); 1472 ObjectMonitor * m = omAlloc(Self); 1473 // prepare m for installation - set monitor to initial state 1474 m->Recycle(); 1475 m->set_header(mark); 1476 m->set_object(object); 1477 m->_Responsible = NULL; 1478 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class 1479 1480 if (object->cas_set_mark(markWord::encode(m), mark) != mark) { 1481 m->set_header(markWord::zero()); 1482 m->set_object(NULL); 1483 m->Recycle(); 1484 omRelease(Self, m, true); 1485 m = NULL; 1486 continue; 1487 // interference - the markword changed - just retry. 1488 // The state-transitions are one-way, so there's no chance of 1489 // live-lock -- "Inflated" is an absorbing state. 1490 } 1491 1492 // Hopefully the performance counters are allocated on distinct 1493 // cache lines to avoid false sharing on MP systems ... 1494 OM_PERFDATA_OP(Inflations, inc()); 1495 if (log_is_enabled(Trace, monitorinflation)) { 1496 ResourceMark rm(Self); 1497 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark=" 1498 INTPTR_FORMAT ", type='%s'", p2i(object), 1499 object->mark().value(), object->klass()->external_name()); 1500 } 1501 if (event.should_commit()) { 1502 post_monitor_inflate_event(&event, object, cause); 1503 } 1504 return m; 1505 } 1506 } 1507 1508 1509 // We maintain a list of in-use monitors for each thread. 1510 // 1511 // deflate_thread_local_monitors() scans a single thread's in-use list, while 1512 // deflate_idle_monitors() scans only a global list of in-use monitors which 1513 // is populated only as a thread dies (see omFlush()). 1514 // 1515 // These operations are called at all safepoints, immediately after mutators 1516 // are stopped, but before any objects have moved. Collectively they traverse 1517 // the population of in-use monitors, deflating where possible. The scavenged 1518 // monitors are returned to the global monitor free list. 1519 // 1520 // Beware that we scavenge at *every* stop-the-world point. Having a large 1521 // number of monitors in-use could negatively impact performance. We also want 1522 // to minimize the total # of monitors in circulation, as they incur a small 1523 // footprint penalty. 1524 // 1525 // Perversely, the heap size -- and thus the STW safepoint rate -- 1526 // typically drives the scavenge rate. Large heaps can mean infrequent GC, 1527 // which in turn can mean large(r) numbers of ObjectMonitors in circulation. 1528 // This is an unfortunate aspect of this design. 1529 1530 // Deflate a single monitor if not in-use 1531 // Return true if deflated, false if in-use 1532 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj, 1533 ObjectMonitor** freeHeadp, 1534 ObjectMonitor** freeTailp) { 1535 bool deflated; 1536 // Normal case ... The monitor is associated with obj. 1537 const markWord mark = obj->mark(); 1538 guarantee(mark == markWord::encode(mid), "should match: mark=" 1539 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(), 1540 markWord::encode(mid).value()); 1541 // Make sure that mark.monitor() and markWord::encode() agree: 1542 guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT 1543 ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid)); 1544 const markWord dmw = mid->header(); 1545 guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1546 1547 if (mid->is_busy()) { 1548 deflated = false; 1549 } else { 1550 // Deflate the monitor if it is no longer being used 1551 // It's idle - scavenge and return to the global free list 1552 // plain old deflation ... 1553 if (log_is_enabled(Trace, monitorinflation)) { 1554 ResourceMark rm; 1555 log_trace(monitorinflation)("deflate_monitor: " 1556 "object=" INTPTR_FORMAT ", mark=" 1557 INTPTR_FORMAT ", type='%s'", p2i(obj), 1558 mark.value(), obj->klass()->external_name()); 1559 } 1560 1561 // Restore the header back to obj 1562 obj->release_set_mark(dmw); 1563 mid->clear(); 1564 1565 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT, 1566 p2i(mid->object())); 1567 1568 // Move the object to the working free list defined by freeHeadp, freeTailp 1569 if (*freeHeadp == NULL) *freeHeadp = mid; 1570 if (*freeTailp != NULL) { 1571 ObjectMonitor * prevtail = *freeTailp; 1572 assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); 1573 prevtail->FreeNext = mid; 1574 } 1575 *freeTailp = mid; 1576 deflated = true; 1577 } 1578 return deflated; 1579 } 1580 1581 // Walk a given monitor list, and deflate idle monitors 1582 // The given list could be a per-thread list or a global list 1583 // Caller acquires gListLock as needed. 1584 // 1585 // In the case of parallel processing of thread local monitor lists, 1586 // work is done by Threads::parallel_threads_do() which ensures that 1587 // each Java thread is processed by exactly one worker thread, and 1588 // thus avoid conflicts that would arise when worker threads would 1589 // process the same monitor lists concurrently. 1590 // 1591 // See also ParallelSPCleanupTask and 1592 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and 1593 // Threads::parallel_java_threads_do() in thread.cpp. 1594 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp, 1595 ObjectMonitor** freeHeadp, 1596 ObjectMonitor** freeTailp) { 1597 ObjectMonitor* mid; 1598 ObjectMonitor* next; 1599 ObjectMonitor* cur_mid_in_use = NULL; 1600 int deflated_count = 0; 1601 1602 for (mid = *listHeadp; mid != NULL;) { 1603 oop obj = (oop) mid->object(); 1604 if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) { 1605 // if deflate_monitor succeeded, 1606 // extract from per-thread in-use list 1607 if (mid == *listHeadp) { 1608 *listHeadp = mid->FreeNext; 1609 } else if (cur_mid_in_use != NULL) { 1610 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list 1611 } 1612 next = mid->FreeNext; 1613 mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list 1614 mid = next; 1615 deflated_count++; 1616 } else { 1617 cur_mid_in_use = mid; 1618 mid = mid->FreeNext; 1619 } 1620 } 1621 return deflated_count; 1622 } 1623 1624 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) { 1625 counters->nInuse = 0; // currently associated with objects 1626 counters->nInCirculation = 0; // extant 1627 counters->nScavenged = 0; // reclaimed (global and per-thread) 1628 counters->perThreadScavenged = 0; // per-thread scavenge total 1629 counters->perThreadTimes = 0.0; // per-thread scavenge times 1630 } 1631 1632 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) { 1633 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 1634 bool deflated = false; 1635 1636 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors 1637 ObjectMonitor * freeTailp = NULL; 1638 elapsedTimer timer; 1639 1640 if (log_is_enabled(Info, monitorinflation)) { 1641 timer.start(); 1642 } 1643 1644 // Prevent omFlush from changing mids in Thread dtor's during deflation 1645 // And in case the vm thread is acquiring a lock during a safepoint 1646 // See e.g. 6320749 1647 Thread::muxAcquire(&gListLock, "deflate_idle_monitors"); 1648 1649 // Note: the thread-local monitors lists get deflated in 1650 // a separate pass. See deflate_thread_local_monitors(). 1651 1652 // For moribund threads, scan gOmInUseList 1653 int deflated_count = 0; 1654 if (gOmInUseList) { 1655 counters->nInCirculation += gOmInUseCount; 1656 deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp); 1657 gOmInUseCount -= deflated_count; 1658 counters->nScavenged += deflated_count; 1659 counters->nInuse += gOmInUseCount; 1660 } 1661 1662 // Move the scavenged monitors back to the global free list. 1663 if (freeHeadp != NULL) { 1664 guarantee(freeTailp != NULL && counters->nScavenged > 0, "invariant"); 1665 assert(freeTailp->FreeNext == NULL, "invariant"); 1666 // constant-time list splice - prepend scavenged segment to gFreeList 1667 freeTailp->FreeNext = gFreeList; 1668 gFreeList = freeHeadp; 1669 } 1670 Thread::muxRelease(&gListLock); 1671 timer.stop(); 1672 1673 LogStreamHandle(Debug, monitorinflation) lsh_debug; 1674 LogStreamHandle(Info, monitorinflation) lsh_info; 1675 LogStream * ls = NULL; 1676 if (log_is_enabled(Debug, monitorinflation)) { 1677 ls = &lsh_debug; 1678 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) { 1679 ls = &lsh_info; 1680 } 1681 if (ls != NULL) { 1682 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count); 1683 } 1684 } 1685 1686 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) { 1687 // Report the cumulative time for deflating each thread's idle 1688 // monitors. Note: if the work is split among more than one 1689 // worker thread, then the reported time will likely be more 1690 // than a beginning to end measurement of the phase. 1691 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->perThreadTimes, counters->perThreadScavenged); 1692 1693 gMonitorFreeCount += counters->nScavenged; 1694 1695 if (log_is_enabled(Debug, monitorinflation)) { 1696 // exit_globals()'s call to audit_and_print_stats() is done 1697 // at the Info level. 1698 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */); 1699 } else if (log_is_enabled(Info, monitorinflation)) { 1700 Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors"); 1701 log_info(monitorinflation)("gMonitorPopulation=%d, gOmInUseCount=%d, " 1702 "gMonitorFreeCount=%d", gMonitorPopulation, 1703 gOmInUseCount, gMonitorFreeCount); 1704 Thread::muxRelease(&gListLock); 1705 } 1706 1707 ForceMonitorScavenge = 0; // Reset 1708 1709 OM_PERFDATA_OP(Deflations, inc(counters->nScavenged)); 1710 OM_PERFDATA_OP(MonExtant, set_value(counters->nInCirculation)); 1711 1712 GVars.stwRandom = os::random(); 1713 GVars.stwCycle++; 1714 } 1715 1716 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) { 1717 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 1718 1719 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors 1720 ObjectMonitor * freeTailp = NULL; 1721 elapsedTimer timer; 1722 1723 if (log_is_enabled(Info, safepoint, cleanup) || 1724 log_is_enabled(Info, monitorinflation)) { 1725 timer.start(); 1726 } 1727 1728 int deflated_count = deflate_monitor_list(thread->omInUseList_addr(), &freeHeadp, &freeTailp); 1729 1730 Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors"); 1731 1732 // Adjust counters 1733 counters->nInCirculation += thread->omInUseCount; 1734 thread->omInUseCount -= deflated_count; 1735 counters->nScavenged += deflated_count; 1736 counters->nInuse += thread->omInUseCount; 1737 counters->perThreadScavenged += deflated_count; 1738 1739 // Move the scavenged monitors back to the global free list. 1740 if (freeHeadp != NULL) { 1741 guarantee(freeTailp != NULL && deflated_count > 0, "invariant"); 1742 assert(freeTailp->FreeNext == NULL, "invariant"); 1743 1744 // constant-time list splice - prepend scavenged segment to gFreeList 1745 freeTailp->FreeNext = gFreeList; 1746 gFreeList = freeHeadp; 1747 } 1748 1749 timer.stop(); 1750 // Safepoint logging cares about cumulative perThreadTimes and 1751 // we'll capture most of the cost, but not the muxRelease() which 1752 // should be cheap. 1753 counters->perThreadTimes += timer.seconds(); 1754 1755 Thread::muxRelease(&gListLock); 1756 1757 LogStreamHandle(Debug, monitorinflation) lsh_debug; 1758 LogStreamHandle(Info, monitorinflation) lsh_info; 1759 LogStream * ls = NULL; 1760 if (log_is_enabled(Debug, monitorinflation)) { 1761 ls = &lsh_debug; 1762 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) { 1763 ls = &lsh_info; 1764 } 1765 if (ls != NULL) { 1766 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count); 1767 } 1768 } 1769 1770 // Monitor cleanup on JavaThread::exit 1771 1772 // Iterate through monitor cache and attempt to release thread's monitors 1773 // Gives up on a particular monitor if an exception occurs, but continues 1774 // the overall iteration, swallowing the exception. 1775 class ReleaseJavaMonitorsClosure: public MonitorClosure { 1776 private: 1777 TRAPS; 1778 1779 public: 1780 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {} 1781 void do_monitor(ObjectMonitor* mid) { 1782 if (mid->owner() == THREAD) { 1783 (void)mid->complete_exit(CHECK); 1784 } 1785 } 1786 }; 1787 1788 // Release all inflated monitors owned by THREAD. Lightweight monitors are 1789 // ignored. This is meant to be called during JNI thread detach which assumes 1790 // all remaining monitors are heavyweight. All exceptions are swallowed. 1791 // Scanning the extant monitor list can be time consuming. 1792 // A simple optimization is to add a per-thread flag that indicates a thread 1793 // called jni_monitorenter() during its lifetime. 1794 // 1795 // Instead of No_Savepoint_Verifier it might be cheaper to 1796 // use an idiom of the form: 1797 // auto int tmp = SafepointSynchronize::_safepoint_counter ; 1798 // <code that must not run at safepoint> 1799 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ; 1800 // Since the tests are extremely cheap we could leave them enabled 1801 // for normal product builds. 1802 1803 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) { 1804 assert(THREAD == JavaThread::current(), "must be current Java thread"); 1805 NoSafepointVerifier nsv; 1806 ReleaseJavaMonitorsClosure rjmc(THREAD); 1807 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread"); 1808 ObjectSynchronizer::monitors_iterate(&rjmc); 1809 Thread::muxRelease(&gListLock); 1810 THREAD->clear_pending_exception(); 1811 } 1812 1813 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) { 1814 switch (cause) { 1815 case inflate_cause_vm_internal: return "VM Internal"; 1816 case inflate_cause_monitor_enter: return "Monitor Enter"; 1817 case inflate_cause_wait: return "Monitor Wait"; 1818 case inflate_cause_notify: return "Monitor Notify"; 1819 case inflate_cause_hash_code: return "Monitor Hash Code"; 1820 case inflate_cause_jni_enter: return "JNI Monitor Enter"; 1821 case inflate_cause_jni_exit: return "JNI Monitor Exit"; 1822 default: 1823 ShouldNotReachHere(); 1824 } 1825 return "Unknown"; 1826 } 1827 1828 //------------------------------------------------------------------------------ 1829 // Debugging code 1830 1831 u_char* ObjectSynchronizer::get_gvars_addr() { 1832 return (u_char*)&GVars; 1833 } 1834 1835 u_char* ObjectSynchronizer::get_gvars_hcSequence_addr() { 1836 return (u_char*)&GVars.hcSequence; 1837 } 1838 1839 size_t ObjectSynchronizer::get_gvars_size() { 1840 return sizeof(SharedGlobals); 1841 } 1842 1843 u_char* ObjectSynchronizer::get_gvars_stwRandom_addr() { 1844 return (u_char*)&GVars.stwRandom; 1845 } 1846 1847 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) { 1848 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant"); 1849 1850 LogStreamHandle(Debug, monitorinflation) lsh_debug; 1851 LogStreamHandle(Info, monitorinflation) lsh_info; 1852 LogStreamHandle(Trace, monitorinflation) lsh_trace; 1853 LogStream * ls = NULL; 1854 if (log_is_enabled(Trace, monitorinflation)) { 1855 ls = &lsh_trace; 1856 } else if (log_is_enabled(Debug, monitorinflation)) { 1857 ls = &lsh_debug; 1858 } else if (log_is_enabled(Info, monitorinflation)) { 1859 ls = &lsh_info; 1860 } 1861 assert(ls != NULL, "sanity check"); 1862 1863 if (!on_exit) { 1864 // Not at VM exit so grab the global list lock. 1865 Thread::muxAcquire(&gListLock, "audit_and_print_stats"); 1866 } 1867 1868 // Log counts for the global and per-thread monitor lists: 1869 int chkMonitorPopulation = log_monitor_list_counts(ls); 1870 int error_cnt = 0; 1871 1872 ls->print_cr("Checking global lists:"); 1873 1874 // Check gMonitorPopulation: 1875 if (gMonitorPopulation == chkMonitorPopulation) { 1876 ls->print_cr("gMonitorPopulation=%d equals chkMonitorPopulation=%d", 1877 gMonitorPopulation, chkMonitorPopulation); 1878 } else { 1879 ls->print_cr("ERROR: gMonitorPopulation=%d is not equal to " 1880 "chkMonitorPopulation=%d", gMonitorPopulation, 1881 chkMonitorPopulation); 1882 error_cnt++; 1883 } 1884 1885 // Check gOmInUseList and gOmInUseCount: 1886 chk_global_in_use_list_and_count(ls, &error_cnt); 1887 1888 // Check gFreeList and gMonitorFreeCount: 1889 chk_global_free_list_and_count(ls, &error_cnt); 1890 1891 if (!on_exit) { 1892 Thread::muxRelease(&gListLock); 1893 } 1894 1895 ls->print_cr("Checking per-thread lists:"); 1896 1897 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) { 1898 // Check omInUseList and omInUseCount: 1899 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt); 1900 1901 // Check omFreeList and omFreeCount: 1902 chk_per_thread_free_list_and_count(jt, ls, &error_cnt); 1903 } 1904 1905 if (error_cnt == 0) { 1906 ls->print_cr("No errors found in monitor list checks."); 1907 } else { 1908 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt); 1909 } 1910 1911 if ((on_exit && log_is_enabled(Info, monitorinflation)) || 1912 (!on_exit && log_is_enabled(Trace, monitorinflation))) { 1913 // When exiting this log output is at the Info level. When called 1914 // at a safepoint, this log output is at the Trace level since 1915 // there can be a lot of it. 1916 log_in_use_monitor_details(ls, on_exit); 1917 } 1918 1919 ls->flush(); 1920 1921 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt); 1922 } 1923 1924 // Check a free monitor entry; log any errors. 1925 void ObjectSynchronizer::chk_free_entry(JavaThread * jt, ObjectMonitor * n, 1926 outputStream * out, int *error_cnt_p) { 1927 stringStream ss; 1928 if (n->is_busy()) { 1929 if (jt != NULL) { 1930 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 1931 ": free per-thread monitor must not be busy: %s", p2i(jt), 1932 p2i(n), n->is_busy_to_string(&ss)); 1933 } else { 1934 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor " 1935 "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss)); 1936 } 1937 *error_cnt_p = *error_cnt_p + 1; 1938 } 1939 if (n->header().value() != 0) { 1940 if (jt != NULL) { 1941 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 1942 ": free per-thread monitor must have NULL _header " 1943 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n), 1944 n->header().value()); 1945 } else { 1946 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor " 1947 "must have NULL _header field: _header=" INTPTR_FORMAT, 1948 p2i(n), n->header().value()); 1949 } 1950 *error_cnt_p = *error_cnt_p + 1; 1951 } 1952 if (n->object() != NULL) { 1953 if (jt != NULL) { 1954 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 1955 ": free per-thread monitor must have NULL _object " 1956 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n), 1957 p2i(n->object())); 1958 } else { 1959 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor " 1960 "must have NULL _object field: _object=" INTPTR_FORMAT, 1961 p2i(n), p2i(n->object())); 1962 } 1963 *error_cnt_p = *error_cnt_p + 1; 1964 } 1965 } 1966 1967 // Check the global free list and count; log the results of the checks. 1968 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out, 1969 int *error_cnt_p) { 1970 int chkMonitorFreeCount = 0; 1971 for (ObjectMonitor * n = gFreeList; n != NULL; n = n->FreeNext) { 1972 chk_free_entry(NULL /* jt */, n, out, error_cnt_p); 1973 chkMonitorFreeCount++; 1974 } 1975 if (gMonitorFreeCount == chkMonitorFreeCount) { 1976 out->print_cr("gMonitorFreeCount=%d equals chkMonitorFreeCount=%d", 1977 gMonitorFreeCount, chkMonitorFreeCount); 1978 } else { 1979 out->print_cr("ERROR: gMonitorFreeCount=%d is not equal to " 1980 "chkMonitorFreeCount=%d", gMonitorFreeCount, 1981 chkMonitorFreeCount); 1982 *error_cnt_p = *error_cnt_p + 1; 1983 } 1984 } 1985 1986 // Check the global in-use list and count; log the results of the checks. 1987 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out, 1988 int *error_cnt_p) { 1989 int chkOmInUseCount = 0; 1990 for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) { 1991 chk_in_use_entry(NULL /* jt */, n, out, error_cnt_p); 1992 chkOmInUseCount++; 1993 } 1994 if (gOmInUseCount == chkOmInUseCount) { 1995 out->print_cr("gOmInUseCount=%d equals chkOmInUseCount=%d", gOmInUseCount, 1996 chkOmInUseCount); 1997 } else { 1998 out->print_cr("ERROR: gOmInUseCount=%d is not equal to chkOmInUseCount=%d", 1999 gOmInUseCount, chkOmInUseCount); 2000 *error_cnt_p = *error_cnt_p + 1; 2001 } 2002 } 2003 2004 // Check an in-use monitor entry; log any errors. 2005 void ObjectSynchronizer::chk_in_use_entry(JavaThread * jt, ObjectMonitor * n, 2006 outputStream * out, int *error_cnt_p) { 2007 if (n->header().value() == 0) { 2008 if (jt != NULL) { 2009 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 2010 ": in-use per-thread monitor must have non-NULL _header " 2011 "field.", p2i(jt), p2i(n)); 2012 } else { 2013 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor " 2014 "must have non-NULL _header field.", p2i(n)); 2015 } 2016 *error_cnt_p = *error_cnt_p + 1; 2017 } 2018 if (n->object() == NULL) { 2019 if (jt != NULL) { 2020 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 2021 ": in-use per-thread monitor must have non-NULL _object " 2022 "field.", p2i(jt), p2i(n)); 2023 } else { 2024 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor " 2025 "must have non-NULL _object field.", p2i(n)); 2026 } 2027 *error_cnt_p = *error_cnt_p + 1; 2028 } 2029 const oop obj = (oop)n->object(); 2030 const markWord mark = obj->mark(); 2031 if (!mark.has_monitor()) { 2032 if (jt != NULL) { 2033 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 2034 ": in-use per-thread monitor's object does not think " 2035 "it has a monitor: obj=" INTPTR_FORMAT ", mark=" 2036 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), mark.value()); 2037 } else { 2038 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global " 2039 "monitor's object does not think it has a monitor: obj=" 2040 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n), 2041 p2i(obj), mark.value()); 2042 } 2043 *error_cnt_p = *error_cnt_p + 1; 2044 } 2045 ObjectMonitor * const obj_mon = mark.monitor(); 2046 if (n != obj_mon) { 2047 if (jt != NULL) { 2048 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 2049 ": in-use per-thread monitor's object does not refer " 2050 "to the same monitor: obj=" INTPTR_FORMAT ", mark=" 2051 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt), 2052 p2i(n), p2i(obj), mark.value(), p2i(obj_mon)); 2053 } else { 2054 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global " 2055 "monitor's object does not refer to the same monitor: obj=" 2056 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon=" 2057 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon)); 2058 } 2059 *error_cnt_p = *error_cnt_p + 1; 2060 } 2061 } 2062 2063 // Check the thread's free list and count; log the results of the checks. 2064 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt, 2065 outputStream * out, 2066 int *error_cnt_p) { 2067 int chkOmFreeCount = 0; 2068 for (ObjectMonitor * n = jt->omFreeList; n != NULL; n = n->FreeNext) { 2069 chk_free_entry(jt, n, out, error_cnt_p); 2070 chkOmFreeCount++; 2071 } 2072 if (jt->omFreeCount == chkOmFreeCount) { 2073 out->print_cr("jt=" INTPTR_FORMAT ": omFreeCount=%d equals " 2074 "chkOmFreeCount=%d", p2i(jt), jt->omFreeCount, chkOmFreeCount); 2075 } else { 2076 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omFreeCount=%d is not " 2077 "equal to chkOmFreeCount=%d", p2i(jt), jt->omFreeCount, 2078 chkOmFreeCount); 2079 *error_cnt_p = *error_cnt_p + 1; 2080 } 2081 } 2082 2083 // Check the thread's in-use list and count; log the results of the checks. 2084 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt, 2085 outputStream * out, 2086 int *error_cnt_p) { 2087 int chkOmInUseCount = 0; 2088 for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) { 2089 chk_in_use_entry(jt, n, out, error_cnt_p); 2090 chkOmInUseCount++; 2091 } 2092 if (jt->omInUseCount == chkOmInUseCount) { 2093 out->print_cr("jt=" INTPTR_FORMAT ": omInUseCount=%d equals " 2094 "chkOmInUseCount=%d", p2i(jt), jt->omInUseCount, 2095 chkOmInUseCount); 2096 } else { 2097 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omInUseCount=%d is not " 2098 "equal to chkOmInUseCount=%d", p2i(jt), jt->omInUseCount, 2099 chkOmInUseCount); 2100 *error_cnt_p = *error_cnt_p + 1; 2101 } 2102 } 2103 2104 // Log details about ObjectMonitors on the in-use lists. The 'BHL' 2105 // flags indicate why the entry is in-use, 'object' and 'object type' 2106 // indicate the associated object and its type. 2107 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out, 2108 bool on_exit) { 2109 if (!on_exit) { 2110 // Not at VM exit so grab the global list lock. 2111 Thread::muxAcquire(&gListLock, "log_in_use_monitor_details"); 2112 } 2113 2114 stringStream ss; 2115 if (gOmInUseCount > 0) { 2116 out->print_cr("In-use global monitor info:"); 2117 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)"); 2118 out->print_cr("%18s %s %18s %18s", 2119 "monitor", "BHL", "object", "object type"); 2120 out->print_cr("================== === ================== =================="); 2121 for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) { 2122 const oop obj = (oop) n->object(); 2123 const markWord mark = n->header(); 2124 ResourceMark rm; 2125 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(n), 2126 n->is_busy() != 0, mark.hash() != 0, n->owner() != NULL, 2127 p2i(obj), obj->klass()->external_name()); 2128 if (n->is_busy() != 0) { 2129 out->print(" (%s)", n->is_busy_to_string(&ss)); 2130 ss.reset(); 2131 } 2132 out->cr(); 2133 } 2134 } 2135 2136 if (!on_exit) { 2137 Thread::muxRelease(&gListLock); 2138 } 2139 2140 out->print_cr("In-use per-thread monitor info:"); 2141 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)"); 2142 out->print_cr("%18s %18s %s %18s %18s", 2143 "jt", "monitor", "BHL", "object", "object type"); 2144 out->print_cr("================== ================== === ================== =================="); 2145 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) { 2146 for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) { 2147 const oop obj = (oop) n->object(); 2148 const markWord mark = n->header(); 2149 ResourceMark rm; 2150 out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT 2151 " %s", p2i(jt), p2i(n), n->is_busy() != 0, 2152 mark.hash() != 0, n->owner() != NULL, p2i(obj), 2153 obj->klass()->external_name()); 2154 if (n->is_busy() != 0) { 2155 out->print(" (%s)", n->is_busy_to_string(&ss)); 2156 ss.reset(); 2157 } 2158 out->cr(); 2159 } 2160 } 2161 2162 out->flush(); 2163 } 2164 2165 // Log counts for the global and per-thread monitor lists and return 2166 // the population count. 2167 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) { 2168 int popCount = 0; 2169 out->print_cr("%18s %10s %10s %10s", 2170 "Global Lists:", "InUse", "Free", "Total"); 2171 out->print_cr("================== ========== ========== =========="); 2172 out->print_cr("%18s %10d %10d %10d", "", 2173 gOmInUseCount, gMonitorFreeCount, gMonitorPopulation); 2174 popCount += gOmInUseCount + gMonitorFreeCount; 2175 2176 out->print_cr("%18s %10s %10s %10s", 2177 "Per-Thread Lists:", "InUse", "Free", "Provision"); 2178 out->print_cr("================== ========== ========== =========="); 2179 2180 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) { 2181 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt), 2182 jt->omInUseCount, jt->omFreeCount, jt->omFreeProvision); 2183 popCount += jt->omInUseCount + jt->omFreeCount; 2184 } 2185 return popCount; 2186 } 2187 2188 #ifndef PRODUCT 2189 2190 // Check if monitor belongs to the monitor cache 2191 // The list is grow-only so it's *relatively* safe to traverse 2192 // the list of extant blocks without taking a lock. 2193 2194 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) { 2195 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList); 2196 while (block != NULL) { 2197 assert(block->object() == CHAINMARKER, "must be a block header"); 2198 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) { 2199 address mon = (address)monitor; 2200 address blk = (address)block; 2201 size_t diff = mon - blk; 2202 assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "must be aligned"); 2203 return 1; 2204 } 2205 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext; 2206 } 2207 return 0; 2208 } 2209 2210 #endif