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