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 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false; 129 bool volatile ObjectSynchronizer::_is_special_deflation_requested = false; 130 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0; 131 132 static volatile intptr_t gListLock = 0; // protects global monitor lists 133 static volatile int g_om_free_count = 0; // # on g_free_list 134 static volatile int g_om_population = 0; // # Extant -- in circulation 135 136 #define CHAINMARKER (cast_to_oop<intptr_t>(-1)) 137 138 139 // =====================> Quick functions 140 141 // The quick_* forms are special fast-path variants used to improve 142 // performance. In the simplest case, a "quick_*" implementation could 143 // simply return false, in which case the caller will perform the necessary 144 // state transitions and call the slow-path form. 145 // The fast-path is designed to handle frequently arising cases in an efficient 146 // manner and is just a degenerate "optimistic" variant of the slow-path. 147 // returns true -- to indicate the call was satisfied. 148 // returns false -- to indicate the call needs the services of the slow-path. 149 // A no-loitering ordinance is in effect for code in the quick_* family 150 // operators: safepoints or indefinite blocking (blocking that might span a 151 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon 152 // entry. 153 // 154 // Consider: An interesting optimization is to have the JIT recognize the 155 // following common idiom: 156 // synchronized (someobj) { .... ; notify(); } 157 // That is, we find a notify() or notifyAll() call that immediately precedes 158 // the monitorexit operation. In that case the JIT could fuse the operations 159 // into a single notifyAndExit() runtime primitive. 160 161 bool ObjectSynchronizer::quick_notify(oopDesc* obj, Thread* self, bool all) { 162 assert(!SafepointSynchronize::is_at_safepoint(), "invariant"); 163 assert(self->is_Java_thread(), "invariant"); 164 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant"); 165 NoSafepointVerifier nsv; 166 if (obj == NULL) return false; // slow-path for invalid obj 167 const markWord mark = obj->mark(); 168 169 if (mark.has_locker() && self->is_lock_owned((address)mark.locker())) { 170 // Degenerate notify 171 // stack-locked by caller so by definition the implied waitset is empty. 172 return true; 173 } 174 175 if (mark.has_monitor()) { 176 ObjectMonitor* const mon = mark.monitor(); 177 assert(oopDesc::equals((oop) mon->object(), obj), "invariant"); 178 if (mon->owner() != self) return false; // slow-path for IMS exception 179 180 if (mon->first_waiter() != NULL) { 181 // We have one or more waiters. Since this is an inflated monitor 182 // that we own, we can transfer one or more threads from the waitset 183 // to the entrylist here and now, avoiding the slow-path. 184 if (all) { 185 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self); 186 } else { 187 DTRACE_MONITOR_PROBE(notify, mon, obj, self); 188 } 189 int free_count = 0; 190 do { 191 mon->INotify(self); 192 ++free_count; 193 } while (mon->first_waiter() != NULL && all); 194 OM_PERFDATA_OP(Notifications, inc(free_count)); 195 } 196 return true; 197 } 198 199 // biased locking and any other IMS exception states take the slow-path 200 return false; 201 } 202 203 204 // The LockNode emitted directly at the synchronization site would have 205 // been too big if it were to have included support for the cases of inflated 206 // recursive enter and exit, so they go here instead. 207 // Note that we can't safely call AsyncPrintJavaStack() from within 208 // quick_enter() as our thread state remains _in_Java. 209 210 bool ObjectSynchronizer::quick_enter(oop obj, Thread* self, 211 BasicLock * lock) { 212 assert(!SafepointSynchronize::is_at_safepoint(), "invariant"); 213 assert(self->is_Java_thread(), "invariant"); 214 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant"); 215 NoSafepointVerifier nsv; 216 if (obj == NULL) return false; // Need to throw NPE 217 218 while (true) { 219 const markWord mark = obj->mark(); 220 221 if (mark.has_monitor()) { 222 ObjectMonitorHandle omh; 223 if (!omh.save_om_ptr(obj, mark)) { 224 // Lost a race with async deflation so try again. 225 assert(AsyncDeflateIdleMonitors, "sanity check"); 226 continue; 227 } 228 ObjectMonitor* const m = omh.om_ptr(); 229 assert(oopDesc::equals((oop) m->object(), obj), "invariant"); 230 Thread* const owner = (Thread *) m->_owner; 231 232 // Lock contention and Transactional Lock Elision (TLE) diagnostics 233 // and observability 234 // Case: light contention possibly amenable to TLE 235 // Case: TLE inimical operations such as nested/recursive synchronization 236 237 if (owner == self) { 238 m->_recursions++; 239 return true; 240 } 241 242 // This Java Monitor is inflated so obj's header will never be 243 // displaced to this thread's BasicLock. Make the displaced header 244 // non-NULL so this BasicLock is not seen as recursive nor as 245 // being locked. We do this unconditionally so that this thread's 246 // BasicLock cannot be mis-interpreted by any stack walkers. For 247 // performance reasons, stack walkers generally first check for 248 // Biased Locking in the object's header, the second check is for 249 // stack-locking in the object's header, the third check is for 250 // recursive stack-locking in the displaced header in the BasicLock, 251 // and last are the inflated Java Monitor (ObjectMonitor) checks. 252 lock->set_displaced_header(markWord::unused_mark()); 253 254 if (owner == NULL && Atomic::replace_if_null(self, &(m->_owner))) { 255 assert(m->_recursions == 0, "invariant"); 256 return true; 257 } 258 259 if (AsyncDeflateIdleMonitors && 260 Atomic::cmpxchg(self, &m->_owner, DEFLATER_MARKER) == DEFLATER_MARKER) { 261 // The deflation protocol finished the first part (setting owner), 262 // but it failed the second part (making ref_count negative) and 263 // bailed. Or the ObjectMonitor was async deflated and reused. 264 // Acquired the monitor. 265 assert(m->_recursions == 0, "invariant"); 266 return true; 267 } 268 } 269 break; 270 } 271 272 // Note that we could inflate in quick_enter. 273 // This is likely a useful optimization 274 // Critically, in quick_enter() we must not: 275 // -- perform bias revocation, or 276 // -- block indefinitely, or 277 // -- reach a safepoint 278 279 return false; // revert to slow-path 280 } 281 282 // ----------------------------------------------------------------------------- 283 // Fast Monitor Enter/Exit 284 // This the fast monitor enter. The interpreter and compiler use 285 // some assembly copies of this code. Make sure update those code 286 // if the following function is changed. The implementation is 287 // extremely sensitive to race condition. Be careful. 288 289 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock, 290 bool attempt_rebias, TRAPS) { 291 if (UseBiasedLocking) { 292 if (!SafepointSynchronize::is_at_safepoint()) { 293 BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD); 294 if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) { 295 return; 296 } 297 } else { 298 assert(!attempt_rebias, "can not rebias toward VM thread"); 299 BiasedLocking::revoke_at_safepoint(obj); 300 } 301 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 302 } 303 304 slow_enter(obj, lock, THREAD); 305 } 306 307 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) { 308 markWord mark = object->mark(); 309 // We cannot check for Biased Locking if we are racing an inflation. 310 assert(mark == markWord::INFLATING() || 311 !mark.has_bias_pattern(), "should not see bias pattern here"); 312 313 markWord dhw = lock->displaced_header(); 314 if (dhw.value() == 0) { 315 // If the displaced header is NULL, then this exit matches up with 316 // a recursive enter. No real work to do here except for diagnostics. 317 #ifndef PRODUCT 318 if (mark != markWord::INFLATING()) { 319 // Only do diagnostics if we are not racing an inflation. Simply 320 // exiting a recursive enter of a Java Monitor that is being 321 // inflated is safe; see the has_monitor() comment below. 322 assert(!mark.is_neutral(), "invariant"); 323 assert(!mark.has_locker() || 324 THREAD->is_lock_owned((address)mark.locker()), "invariant"); 325 if (mark.has_monitor()) { 326 // The BasicLock's displaced_header is marked as a recursive 327 // enter and we have an inflated Java Monitor (ObjectMonitor). 328 // This is a special case where the Java Monitor was inflated 329 // after this thread entered the stack-lock recursively. When a 330 // Java Monitor is inflated, we cannot safely walk the Java 331 // Monitor owner's stack and update the BasicLocks because a 332 // Java Monitor can be asynchronously inflated by a thread that 333 // does not own the Java Monitor. 334 ObjectMonitor* m = mark.monitor(); 335 assert(((oop)(m->object()))->mark() == mark, "invariant"); 336 assert(m->is_entered(THREAD), "invariant"); 337 } 338 } 339 #endif 340 return; 341 } 342 343 if (mark == markWord::from_pointer(lock)) { 344 // If the object is stack-locked by the current thread, try to 345 // swing the displaced header from the BasicLock back to the mark. 346 assert(dhw.is_neutral(), "invariant"); 347 if (object->cas_set_mark(dhw, mark) == mark) { 348 return; 349 } 350 } 351 352 // We have to take the slow-path of possible inflation and then exit. 353 ObjectMonitorHandle omh; 354 inflate(&omh, THREAD, object, inflate_cause_vm_internal); 355 omh.om_ptr()->exit(true, THREAD); 356 } 357 358 // ----------------------------------------------------------------------------- 359 // Interpreter/Compiler Slow Case 360 // This routine is used to handle interpreter/compiler slow case 361 // We don't need to use fast path here, because it must have been 362 // failed in the interpreter/compiler code. 363 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) { 364 markWord mark = obj->mark(); 365 assert(!mark.has_bias_pattern(), "should not see bias pattern here"); 366 367 if (mark.is_neutral()) { 368 // Anticipate successful CAS -- the ST of the displaced mark must 369 // be visible <= the ST performed by the CAS. 370 lock->set_displaced_header(mark); 371 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) { 372 return; 373 } 374 // Fall through to inflate() ... 375 } else if (mark.has_locker() && 376 THREAD->is_lock_owned((address)mark.locker())) { 377 assert(lock != mark.locker(), "must not re-lock the same lock"); 378 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock"); 379 lock->set_displaced_header(markWord::from_pointer(NULL)); 380 return; 381 } 382 383 // The object header will never be displaced to this lock, 384 // so it does not matter what the value is, except that it 385 // must be non-zero to avoid looking like a re-entrant lock, 386 // and must not look locked either. 387 lock->set_displaced_header(markWord::unused_mark()); 388 ObjectMonitorHandle omh; 389 inflate(&omh, THREAD, obj(), inflate_cause_monitor_enter); 390 omh.om_ptr()->enter(THREAD); 391 } 392 393 // This routine is used to handle interpreter/compiler slow case 394 // We don't need to use fast path here, because it must have 395 // failed in the interpreter/compiler code. Simply use the heavy 396 // weight monitor should be ok, unless someone find otherwise. 397 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) { 398 fast_exit(object, lock, THREAD); 399 } 400 401 // ----------------------------------------------------------------------------- 402 // Class Loader support to workaround deadlocks on the class loader lock objects 403 // Also used by GC 404 // complete_exit()/reenter() are used to wait on a nested lock 405 // i.e. to give up an outer lock completely and then re-enter 406 // Used when holding nested locks - lock acquisition order: lock1 then lock2 407 // 1) complete_exit lock1 - saving recursion count 408 // 2) wait on lock2 409 // 3) when notified on lock2, unlock lock2 410 // 4) reenter lock1 with original recursion count 411 // 5) lock lock2 412 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 413 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) { 414 if (UseBiasedLocking) { 415 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 416 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 417 } 418 419 ObjectMonitorHandle omh; 420 inflate(&omh, THREAD, obj(), inflate_cause_vm_internal); 421 intptr_t ret_code = omh.om_ptr()->complete_exit(THREAD); 422 return ret_code; 423 } 424 425 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 426 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) { 427 if (UseBiasedLocking) { 428 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 429 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 430 } 431 432 ObjectMonitorHandle omh; 433 inflate(&omh, THREAD, obj(), inflate_cause_vm_internal); 434 omh.om_ptr()->reenter(recursion, THREAD); 435 } 436 // ----------------------------------------------------------------------------- 437 // JNI locks on java objects 438 // NOTE: must use heavy weight monitor to handle jni monitor enter 439 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) { 440 // the current locking is from JNI instead of Java code 441 if (UseBiasedLocking) { 442 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 443 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 444 } 445 THREAD->set_current_pending_monitor_is_from_java(false); 446 ObjectMonitorHandle omh; 447 inflate(&omh, THREAD, obj(), inflate_cause_jni_enter); 448 omh.om_ptr()->enter(THREAD); 449 THREAD->set_current_pending_monitor_is_from_java(true); 450 } 451 452 // NOTE: must use heavy weight monitor to handle jni monitor exit 453 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) { 454 if (UseBiasedLocking) { 455 Handle h_obj(THREAD, obj); 456 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD); 457 obj = h_obj(); 458 } 459 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 460 461 ObjectMonitorHandle omh; 462 inflate(&omh, THREAD, obj, inflate_cause_jni_exit); 463 ObjectMonitor* monitor = omh.om_ptr(); 464 // If this thread has locked the object, exit the monitor. We 465 // intentionally do not use CHECK here because we must exit the 466 // monitor even if an exception is pending. 467 if (monitor->check_owner(THREAD)) { 468 monitor->exit(true, THREAD); 469 } 470 } 471 472 // ----------------------------------------------------------------------------- 473 // Internal VM locks on java objects 474 // standard constructor, allows locking failures 475 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool do_lock) { 476 _dolock = do_lock; 477 _thread = thread; 478 _thread->check_for_valid_safepoint_state(false); 479 _obj = obj; 480 481 if (_dolock) { 482 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread); 483 } 484 } 485 486 ObjectLocker::~ObjectLocker() { 487 if (_dolock) { 488 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread); 489 } 490 } 491 492 493 // ----------------------------------------------------------------------------- 494 // Wait/Notify/NotifyAll 495 // NOTE: must use heavy weight monitor to handle wait() 496 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) { 497 if (UseBiasedLocking) { 498 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 499 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 500 } 501 if (millis < 0) { 502 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); 503 } 504 ObjectMonitorHandle omh; 505 inflate(&omh, THREAD, obj(), inflate_cause_wait); 506 ObjectMonitor* monitor = omh.om_ptr(); 507 508 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis); 509 monitor->wait(millis, true, THREAD); 510 511 // This dummy call is in place to get around dtrace bug 6254741. Once 512 // that's fixed we can uncomment the following line, remove the call 513 // and change this function back into a "void" func. 514 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD); 515 int ret_code = dtrace_waited_probe(monitor, obj, THREAD); 516 return ret_code; 517 } 518 519 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, jlong millis, TRAPS) { 520 if (UseBiasedLocking) { 521 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 522 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 523 } 524 if (millis < 0) { 525 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); 526 } 527 ObjectMonitorHandle omh; 528 inflate(&omh, THREAD, obj(), inflate_cause_wait); 529 omh.om_ptr()->wait(millis, false, THREAD); 530 } 531 532 void ObjectSynchronizer::notify(Handle obj, TRAPS) { 533 if (UseBiasedLocking) { 534 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 535 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 536 } 537 538 markWord mark = obj->mark(); 539 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) { 540 return; 541 } 542 ObjectMonitorHandle omh; 543 inflate(&omh, THREAD, obj(), inflate_cause_notify); 544 omh.om_ptr()->notify(THREAD); 545 } 546 547 // NOTE: see comment of notify() 548 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) { 549 if (UseBiasedLocking) { 550 BiasedLocking::revoke_and_rebias(obj, false, THREAD); 551 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 552 } 553 554 markWord mark = obj->mark(); 555 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) { 556 return; 557 } 558 ObjectMonitorHandle omh; 559 inflate(&omh, THREAD, obj(), inflate_cause_notify); 560 omh.om_ptr()->notifyAll(THREAD); 561 } 562 563 // ----------------------------------------------------------------------------- 564 // Hash Code handling 565 // 566 // Performance concern: 567 // OrderAccess::storestore() calls release() which at one time stored 0 568 // into the global volatile OrderAccess::dummy variable. This store was 569 // unnecessary for correctness. Many threads storing into a common location 570 // causes considerable cache migration or "sloshing" on large SMP systems. 571 // As such, I avoided using OrderAccess::storestore(). In some cases 572 // OrderAccess::fence() -- which incurs local latency on the executing 573 // processor -- is a better choice as it scales on SMP systems. 574 // 575 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for 576 // a discussion of coherency costs. Note that all our current reference 577 // platforms provide strong ST-ST order, so the issue is moot on IA32, 578 // x64, and SPARC. 579 // 580 // As a general policy we use "volatile" to control compiler-based reordering 581 // and explicit fences (barriers) to control for architectural reordering 582 // performed by the CPU(s) or platform. 583 584 struct SharedGlobals { 585 char _pad_prefix[DEFAULT_CACHE_LINE_SIZE]; 586 // These are highly shared mostly-read variables. 587 // To avoid false-sharing they need to be the sole occupants of a cache line. 588 volatile int stw_random; 589 volatile int stw_cycle; 590 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2); 591 // Hot RW variable -- Sequester to avoid false-sharing 592 volatile int hc_sequence; 593 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int)); 594 }; 595 596 static SharedGlobals GVars; 597 static int MonitorScavengeThreshold = 1000000; 598 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending 599 600 static markWord read_stable_mark(oop obj) { 601 markWord mark = obj->mark(); 602 if (!mark.is_being_inflated()) { 603 return mark; // normal fast-path return 604 } 605 606 int its = 0; 607 for (;;) { 608 markWord mark = obj->mark(); 609 if (!mark.is_being_inflated()) { 610 return mark; // normal fast-path return 611 } 612 613 // The object is being inflated by some other thread. 614 // The caller of read_stable_mark() must wait for inflation to complete. 615 // Avoid live-lock 616 // TODO: consider calling SafepointSynchronize::do_call_back() while 617 // spinning to see if there's a safepoint pending. If so, immediately 618 // yielding or blocking would be appropriate. Avoid spinning while 619 // there is a safepoint pending. 620 // TODO: add inflation contention performance counters. 621 // TODO: restrict the aggregate number of spinners. 622 623 ++its; 624 if (its > 10000 || !os::is_MP()) { 625 if (its & 1) { 626 os::naked_yield(); 627 } else { 628 // Note that the following code attenuates the livelock problem but is not 629 // a complete remedy. A more complete solution would require that the inflating 630 // thread hold the associated inflation lock. The following code simply restricts 631 // the number of spinners to at most one. We'll have N-2 threads blocked 632 // on the inflationlock, 1 thread holding the inflation lock and using 633 // a yield/park strategy, and 1 thread in the midst of inflation. 634 // A more refined approach would be to change the encoding of INFLATING 635 // to allow encapsulation of a native thread pointer. Threads waiting for 636 // inflation to complete would use CAS to push themselves onto a singly linked 637 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag 638 // and calling park(). When inflation was complete the thread that accomplished inflation 639 // would detach the list and set the markword to inflated with a single CAS and 640 // then for each thread on the list, set the flag and unpark() the thread. 641 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease 642 // wakes at most one thread whereas we need to wake the entire list. 643 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1); 644 int YieldThenBlock = 0; 645 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant"); 646 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant"); 647 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock"); 648 while (obj->mark() == markWord::INFLATING()) { 649 // Beware: NakedYield() is advisory and has almost no effect on some platforms 650 // so we periodically call self->_ParkEvent->park(1). 651 // We use a mixed spin/yield/block mechanism. 652 if ((YieldThenBlock++) >= 16) { 653 Thread::current()->_ParkEvent->park(1); 654 } else { 655 os::naked_yield(); 656 } 657 } 658 Thread::muxRelease(gInflationLocks + ix); 659 } 660 } else { 661 SpinPause(); // SMP-polite spinning 662 } 663 } 664 } 665 666 // hashCode() generation : 667 // 668 // Possibilities: 669 // * MD5Digest of {obj,stw_random} 670 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function. 671 // * A DES- or AES-style SBox[] mechanism 672 // * One of the Phi-based schemes, such as: 673 // 2654435761 = 2^32 * Phi (golden ratio) 674 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ; 675 // * A variation of Marsaglia's shift-xor RNG scheme. 676 // * (obj ^ stw_random) is appealing, but can result 677 // in undesirable regularity in the hashCode values of adjacent objects 678 // (objects allocated back-to-back, in particular). This could potentially 679 // result in hashtable collisions and reduced hashtable efficiency. 680 // There are simple ways to "diffuse" the middle address bits over the 681 // generated hashCode values: 682 683 static inline intptr_t get_next_hash(Thread* self, oop obj) { 684 intptr_t value = 0; 685 if (hashCode == 0) { 686 // This form uses global Park-Miller RNG. 687 // On MP system we'll have lots of RW access to a global, so the 688 // mechanism induces lots of coherency traffic. 689 value = os::random(); 690 } else if (hashCode == 1) { 691 // This variation has the property of being stable (idempotent) 692 // between STW operations. This can be useful in some of the 1-0 693 // synchronization schemes. 694 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3; 695 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random; 696 } else if (hashCode == 2) { 697 value = 1; // for sensitivity testing 698 } else if (hashCode == 3) { 699 value = ++GVars.hc_sequence; 700 } else if (hashCode == 4) { 701 value = cast_from_oop<intptr_t>(obj); 702 } else { 703 // Marsaglia's xor-shift scheme with thread-specific state 704 // This is probably the best overall implementation -- we'll 705 // likely make this the default in future releases. 706 unsigned t = self->_hashStateX; 707 t ^= (t << 11); 708 self->_hashStateX = self->_hashStateY; 709 self->_hashStateY = self->_hashStateZ; 710 self->_hashStateZ = self->_hashStateW; 711 unsigned v = self->_hashStateW; 712 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)); 713 self->_hashStateW = v; 714 value = v; 715 } 716 717 value &= markWord::hash_mask; 718 if (value == 0) value = 0xBAD; 719 assert(value != markWord::no_hash, "invariant"); 720 return value; 721 } 722 723 intptr_t ObjectSynchronizer::FastHashCode(Thread* self, oop obj) { 724 if (UseBiasedLocking) { 725 // NOTE: many places throughout the JVM do not expect a safepoint 726 // to be taken here, in particular most operations on perm gen 727 // objects. However, we only ever bias Java instances and all of 728 // the call sites of identity_hash that might revoke biases have 729 // been checked to make sure they can handle a safepoint. The 730 // added check of the bias pattern is to avoid useless calls to 731 // thread-local storage. 732 if (obj->mark().has_bias_pattern()) { 733 // Handle for oop obj in case of STW safepoint 734 Handle hobj(self, obj); 735 // Relaxing assertion for bug 6320749. 736 assert(Universe::verify_in_progress() || 737 !SafepointSynchronize::is_at_safepoint(), 738 "biases should not be seen by VM thread here"); 739 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current()); 740 obj = hobj(); 741 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 742 } 743 } 744 745 // hashCode() is a heap mutator ... 746 // Relaxing assertion for bug 6320749. 747 assert(Universe::verify_in_progress() || DumpSharedSpaces || 748 !SafepointSynchronize::is_at_safepoint(), "invariant"); 749 assert(Universe::verify_in_progress() || DumpSharedSpaces || 750 self->is_Java_thread() , "invariant"); 751 assert(Universe::verify_in_progress() || DumpSharedSpaces || 752 ((JavaThread *)self)->thread_state() != _thread_blocked, "invariant"); 753 754 while (true) { 755 ObjectMonitor* monitor = NULL; 756 markWord temp, test; 757 intptr_t hash; 758 markWord mark = read_stable_mark(obj); 759 760 // object should remain ineligible for biased locking 761 assert(!mark.has_bias_pattern(), "invariant"); 762 763 if (mark.is_neutral()) { 764 hash = mark.hash(); // this is a normal header 765 if (hash != 0) { // if it has hash, just return it 766 return hash; 767 } 768 hash = get_next_hash(self, obj); // allocate a new hash code 769 temp = mark.copy_set_hash(hash); // merge the hash code into header 770 // use (machine word version) atomic operation to install the hash 771 test = obj->cas_set_mark(temp, mark); 772 if (test == mark) { 773 return hash; 774 } 775 // If atomic operation failed, we must inflate the header 776 // into heavy weight monitor. We could add more code here 777 // for fast path, but it does not worth the complexity. 778 } else if (mark.has_monitor()) { 779 ObjectMonitorHandle omh; 780 if (!omh.save_om_ptr(obj, mark)) { 781 // Lost a race with async deflation so try again. 782 assert(AsyncDeflateIdleMonitors, "sanity check"); 783 continue; 784 } 785 monitor = omh.om_ptr(); 786 temp = monitor->header(); 787 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 788 hash = temp.hash(); 789 if (hash != 0) { 790 return hash; 791 } 792 // Skip to the following code to reduce code size 793 } else if (self->is_lock_owned((address)mark.locker())) { 794 temp = mark.displaced_mark_helper(); // this is a lightweight monitor owned 795 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 796 hash = temp.hash(); // by current thread, check if the displaced 797 if (hash != 0) { // header contains hash code 798 return hash; 799 } 800 // WARNING: 801 // The displaced header in the BasicLock on a thread's stack 802 // is strictly immutable. It CANNOT be changed in ANY cases. 803 // So we have to inflate the stack lock into an ObjectMonitor 804 // even if the current thread owns the lock. The BasicLock on 805 // a thread's stack can be asynchronously read by other threads 806 // during an inflate() call so any change to that stack memory 807 // may not propagate to other threads correctly. 808 } 809 810 // Inflate the monitor to set hash code 811 ObjectMonitorHandle omh; 812 inflate(&omh, self, obj, inflate_cause_hash_code); 813 monitor = omh.om_ptr(); 814 // Load displaced header and check it has hash code 815 mark = monitor->header(); 816 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value()); 817 hash = mark.hash(); 818 if (hash == 0) { 819 hash = get_next_hash(self, obj); 820 temp = mark.copy_set_hash(hash); // merge hash code into header 821 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 822 uintptr_t v = Atomic::cmpxchg(temp.value(), (volatile uintptr_t*)monitor->header_addr(), mark.value()); 823 test = markWord(v); 824 if (test != mark) { 825 // The only non-deflation update to the ObjectMonitor's 826 // header/dmw field is to merge in the hash code. If someone 827 // adds a new usage of the header/dmw field, please update 828 // this code. 829 // ObjectMonitor::install_displaced_markword_in_object() 830 // does mark the header/dmw field as part of async deflation, 831 // but that protocol cannot happen now due to the 832 // ObjectMonitorHandle above. 833 hash = test.hash(); 834 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value()); 835 assert(hash != 0, "Trivial unexpected object/monitor header usage."); 836 } 837 } 838 // We finally get the hash 839 return hash; 840 } 841 } 842 843 // Deprecated -- use FastHashCode() instead. 844 845 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) { 846 return FastHashCode(Thread::current(), obj()); 847 } 848 849 850 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread, 851 Handle h_obj) { 852 if (UseBiasedLocking) { 853 BiasedLocking::revoke_and_rebias(h_obj, false, thread); 854 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now"); 855 } 856 857 assert(thread == JavaThread::current(), "Can only be called on current thread"); 858 oop obj = h_obj(); 859 860 while (true) { 861 markWord mark = read_stable_mark(obj); 862 863 // Uncontended case, header points to stack 864 if (mark.has_locker()) { 865 return thread->is_lock_owned((address)mark.locker()); 866 } 867 // Contended case, header points to ObjectMonitor (tagged pointer) 868 if (mark.has_monitor()) { 869 ObjectMonitorHandle omh; 870 if (!omh.save_om_ptr(obj, mark)) { 871 // Lost a race with async deflation so try again. 872 assert(AsyncDeflateIdleMonitors, "sanity check"); 873 continue; 874 } 875 bool ret_code = omh.om_ptr()->is_entered(thread) != 0; 876 return ret_code; 877 } 878 // Unlocked case, header in place 879 assert(mark.is_neutral(), "sanity check"); 880 return false; 881 } 882 } 883 884 // Be aware of this method could revoke bias of the lock object. 885 // This method queries the ownership of the lock handle specified by 'h_obj'. 886 // If the current thread owns the lock, it returns owner_self. If no 887 // thread owns the lock, it returns owner_none. Otherwise, it will return 888 // owner_other. 889 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership 890 (JavaThread *self, Handle h_obj) { 891 // The caller must beware this method can revoke bias, and 892 // revocation can result in a safepoint. 893 assert(!SafepointSynchronize::is_at_safepoint(), "invariant"); 894 assert(self->thread_state() != _thread_blocked, "invariant"); 895 896 // Possible mark states: neutral, biased, stack-locked, inflated 897 898 if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) { 899 // CASE: biased 900 BiasedLocking::revoke_and_rebias(h_obj, false, self); 901 assert(!h_obj->mark().has_bias_pattern(), 902 "biases should be revoked by now"); 903 } 904 905 assert(self == JavaThread::current(), "Can only be called on current thread"); 906 oop obj = h_obj(); 907 908 while (true) { 909 markWord mark = read_stable_mark(obj); 910 911 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack. 912 if (mark.has_locker()) { 913 return self->is_lock_owned((address)mark.locker()) ? 914 owner_self : owner_other; 915 } 916 917 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor. 918 // The Object:ObjectMonitor relationship is stable as long as we're 919 // not at a safepoint and AsyncDeflateIdleMonitors is false. 920 if (mark.has_monitor()) { 921 ObjectMonitorHandle omh; 922 if (!omh.save_om_ptr(obj, mark)) { 923 // Lost a race with async deflation so try again. 924 assert(AsyncDeflateIdleMonitors, "sanity check"); 925 continue; 926 } 927 ObjectMonitor* monitor = omh.om_ptr(); 928 void* owner = monitor->_owner; 929 if (owner == NULL) return owner_none; 930 return (owner == self || 931 self->is_lock_owned((address)owner)) ? owner_self : owner_other; 932 } 933 934 // CASE: neutral 935 assert(mark.is_neutral(), "sanity check"); 936 return owner_none; // it's unlocked 937 } 938 } 939 940 // FIXME: jvmti should call this 941 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) { 942 if (UseBiasedLocking) { 943 if (SafepointSynchronize::is_at_safepoint()) { 944 BiasedLocking::revoke_at_safepoint(h_obj); 945 } else { 946 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current()); 947 } 948 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now"); 949 } 950 951 oop obj = h_obj(); 952 953 while (true) { 954 address owner = NULL; 955 markWord mark = read_stable_mark(obj); 956 957 // Uncontended case, header points to stack 958 if (mark.has_locker()) { 959 owner = (address) mark.locker(); 960 } 961 962 // Contended case, header points to ObjectMonitor (tagged pointer) 963 else if (mark.has_monitor()) { 964 ObjectMonitorHandle omh; 965 if (!omh.save_om_ptr(obj, mark)) { 966 // Lost a race with async deflation so try again. 967 assert(AsyncDeflateIdleMonitors, "sanity check"); 968 continue; 969 } 970 ObjectMonitor* monitor = omh.om_ptr(); 971 assert(monitor != NULL, "monitor should be non-null"); 972 owner = (address) monitor->owner(); 973 } 974 975 if (owner != NULL) { 976 // owning_thread_from_monitor_owner() may also return NULL here 977 return Threads::owning_thread_from_monitor_owner(t_list, owner); 978 } 979 980 // Unlocked case, header in place 981 // Cannot have assertion since this object may have been 982 // locked by another thread when reaching here. 983 // assert(mark.is_neutral(), "sanity check"); 984 985 return NULL; 986 } 987 } 988 989 // Visitors ... 990 991 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) { 992 PaddedObjectMonitor* block = OrderAccess::load_acquire(&g_block_list); 993 while (block != NULL) { 994 assert(block->object() == CHAINMARKER, "must be a block header"); 995 for (int i = _BLOCKSIZE - 1; i > 0; i--) { 996 ObjectMonitor* mid = (ObjectMonitor *)(block + i); 997 if (mid->is_active()) { 998 ObjectMonitorHandle omh(mid); 999 1000 if (mid->object() == NULL || 1001 (AsyncDeflateIdleMonitors && mid->_owner == DEFLATER_MARKER)) { 1002 // Only process with closure if the object is set. 1003 // For async deflation, race here if monitor is not owned! 1004 // The above ref_count bump (in ObjectMonitorHandle ctr) 1005 // will cause subsequent async deflation to skip it. 1006 // However, previous or concurrent async deflation is a race. 1007 continue; 1008 } 1009 closure->do_monitor(mid); 1010 } 1011 } 1012 block = (PaddedObjectMonitor*)block->_next_om; 1013 } 1014 } 1015 1016 static bool monitors_used_above_threshold() { 1017 if (g_om_population == 0) { 1018 return false; 1019 } 1020 if (MonitorUsedDeflationThreshold > 0) { 1021 int monitors_used = g_om_population - g_om_free_count; 1022 int monitor_usage = (monitors_used * 100LL) / g_om_population; 1023 return monitor_usage > MonitorUsedDeflationThreshold; 1024 } 1025 return false; 1026 } 1027 1028 // Returns true if MonitorBound is set (> 0) and if the specified 1029 // cnt is > MonitorBound. Otherwise returns false. 1030 static bool is_MonitorBound_exceeded(const int cnt) { 1031 const int mx = MonitorBound; 1032 return mx > 0 && cnt > mx; 1033 } 1034 1035 bool ObjectSynchronizer::is_async_deflation_needed() { 1036 if (!AsyncDeflateIdleMonitors) { 1037 return false; 1038 } 1039 if (is_async_deflation_requested()) { 1040 // Async deflation request. 1041 return true; 1042 } 1043 if (AsyncDeflationInterval > 0 && 1044 time_since_last_async_deflation_ms() > AsyncDeflationInterval && 1045 monitors_used_above_threshold()) { 1046 // It's been longer than our specified deflate interval and there 1047 // are too many monitors in use. We don't deflate more frequently 1048 // than AsyncDeflationInterval (unless is_async_deflation_requested) 1049 // in order to not swamp the ServiceThread. 1050 _last_async_deflation_time_ns = os::javaTimeNanos(); 1051 return true; 1052 } 1053 if (is_MonitorBound_exceeded(g_om_population - g_om_free_count)) { 1054 // Not enough ObjectMonitors on the global free list. 1055 return true; 1056 } 1057 return false; 1058 } 1059 1060 bool ObjectSynchronizer::is_safepoint_deflation_needed() { 1061 if (!AsyncDeflateIdleMonitors) { 1062 if (monitors_used_above_threshold()) { 1063 // Too many monitors in use. 1064 return true; 1065 } 1066 return false; 1067 } 1068 if (is_special_deflation_requested()) { 1069 // For AsyncDeflateIdleMonitors only do a safepoint deflation 1070 // if there is a special deflation request. 1071 return true; 1072 } 1073 return false; 1074 } 1075 1076 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() { 1077 return (os::javaTimeNanos() - _last_async_deflation_time_ns) / (NANOUNITS / MILLIUNITS); 1078 } 1079 1080 void ObjectSynchronizer::oops_do(OopClosure* f) { 1081 // We only scan the global used list here (for moribund threads), and 1082 // the thread-local monitors in Thread::oops_do(). 1083 global_used_oops_do(f); 1084 } 1085 1086 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) { 1087 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 1088 list_oops_do(g_om_in_use_list, f); 1089 } 1090 1091 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) { 1092 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 1093 list_oops_do(thread->om_in_use_list, f); 1094 } 1095 1096 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) { 1097 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 1098 ObjectMonitor* mid; 1099 for (mid = list; mid != NULL; mid = mid->_next_om) { 1100 if (mid->object() != NULL) { 1101 f->do_oop((oop*)mid->object_addr()); 1102 } 1103 } 1104 } 1105 1106 1107 // ----------------------------------------------------------------------------- 1108 // ObjectMonitor Lifecycle 1109 // ----------------------- 1110 // Inflation unlinks monitors from the global g_free_list and 1111 // associates them with objects. Deflation -- which occurs at 1112 // STW-time -- disassociates idle monitors from objects. Such 1113 // scavenged monitors are returned to the g_free_list. 1114 // 1115 // The global list is protected by gListLock. All the critical sections 1116 // are short and operate in constant-time. 1117 // 1118 // ObjectMonitors reside in type-stable memory (TSM) and are immortal. 1119 // 1120 // Lifecycle: 1121 // -- unassigned and on the global free list 1122 // -- unassigned and on a thread's private om_free_list 1123 // -- assigned to an object. The object is inflated and the mark refers 1124 // to the objectmonitor. 1125 1126 1127 // Constraining monitor pool growth via MonitorBound ... 1128 // 1129 // If MonitorBound is not set (<= 0), MonitorBound checks are disabled. 1130 // 1131 // When safepoint deflation is being used (!AsyncDeflateIdleMonitors): 1132 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the 1133 // the rate of scavenging is driven primarily by GC. As such, we can find 1134 // an inordinate number of monitors in circulation. 1135 // To avoid that scenario we can artificially induce a STW safepoint 1136 // if the pool appears to be growing past some reasonable bound. 1137 // Generally we favor time in space-time tradeoffs, but as there's no 1138 // natural back-pressure on the # of extant monitors we need to impose some 1139 // type of limit. Beware that if MonitorBound is set to too low a value 1140 // we could just loop. In addition, if MonitorBound is set to a low value 1141 // we'll incur more safepoints, which are harmful to performance. 1142 // See also: GuaranteedSafepointInterval 1143 // 1144 // The current implementation uses asynchronous VM operations. 1145 // 1146 // When safepoint deflation is being used and MonitorBound is set, the 1147 // boundry applies to 1148 // (g_om_population - g_om_free_count) 1149 // i.e., if there are not enough ObjectMonitors on the global free list, 1150 // then a safepoint deflation is induced. Picking a good MonitorBound value 1151 // is non-trivial. 1152 // 1153 // When async deflation is being used: 1154 // The monitor pool is still grow-only. Async deflation is requested 1155 // by a safepoint's cleanup phase or by the ServiceThread at periodic 1156 // intervals when is_async_deflation_needed() returns true. In 1157 // addition to other policies that are checked, if there are not 1158 // enough ObjectMonitors on the global free list, then 1159 // is_async_deflation_needed() will return true. The ServiceThread 1160 // calls deflate_global_idle_monitors_using_JT() and also sets the 1161 // per-thread om_request_deflation flag as needed. 1162 1163 static void InduceScavenge(Thread* self, const char * Whence) { 1164 assert(!AsyncDeflateIdleMonitors, "is not used by async deflation"); 1165 1166 // Induce STW safepoint to trim monitors 1167 // Ultimately, this results in a call to deflate_idle_monitors() in the near future. 1168 // More precisely, trigger an asynchronous STW safepoint as the number 1169 // of active monitors passes the specified threshold. 1170 // TODO: assert thread state is reasonable 1171 1172 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) { 1173 // Induce a 'null' safepoint to scavenge monitors 1174 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted 1175 // to the VMthread and have a lifespan longer than that of this activation record. 1176 // The VMThread will delete the op when completed. 1177 VMThread::execute(new VM_ScavengeMonitors()); 1178 } 1179 } 1180 1181 ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self, 1182 const InflateCause cause) { 1183 // A large MAXPRIVATE value reduces both list lock contention 1184 // and list coherency traffic, but also tends to increase the 1185 // number of ObjectMonitors in circulation as well as the STW 1186 // scavenge costs. As usual, we lean toward time in space-time 1187 // tradeoffs. 1188 const int MAXPRIVATE = 1024; 1189 1190 if (AsyncDeflateIdleMonitors) { 1191 JavaThread* jt = (JavaThread *)self; 1192 if (jt->om_request_deflation && jt->om_in_use_count > 0 && 1193 cause != inflate_cause_vm_internal) { 1194 // Deflate any per-thread idle monitors for this JavaThread if 1195 // this is not an internal inflation; internal inflations can 1196 // occur in places where it is not safe to pause for a safepoint. 1197 // Clean up your own mess (Gibbs Rule 45). Otherwise, skip this 1198 // deflation. deflate_global_idle_monitors_using_JT() is called 1199 // by the ServiceThread. Per-thread async deflation is triggered 1200 // by the ServiceThread via om_request_deflation. 1201 debug_only(jt->check_for_valid_safepoint_state(false);) 1202 ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT(); 1203 } 1204 } 1205 1206 stringStream ss; 1207 for (;;) { 1208 ObjectMonitor* m; 1209 1210 // 1: try to allocate from the thread's local om_free_list. 1211 // Threads will attempt to allocate first from their local list, then 1212 // from the global list, and only after those attempts fail will the thread 1213 // attempt to instantiate new monitors. Thread-local free lists take 1214 // heat off the gListLock and improve allocation latency, as well as reducing 1215 // coherency traffic on the shared global list. 1216 m = self->om_free_list; 1217 if (m != NULL) { 1218 self->om_free_list = m->_next_om; 1219 self->om_free_count--; 1220 guarantee(m->object() == NULL, "invariant"); 1221 m->set_allocation_state(ObjectMonitor::New); 1222 m->_next_om = self->om_in_use_list; 1223 self->om_in_use_list = m; 1224 self->om_in_use_count++; 1225 return m; 1226 } 1227 1228 // 2: try to allocate from the global g_free_list 1229 // CONSIDER: use muxTry() instead of muxAcquire(). 1230 // If the muxTry() fails then drop immediately into case 3. 1231 // If we're using thread-local free lists then try 1232 // to reprovision the caller's free list. 1233 if (g_free_list != NULL) { 1234 // Reprovision the thread's om_free_list. 1235 // Use bulk transfers to reduce the allocation rate and heat 1236 // on various locks. 1237 Thread::muxAcquire(&gListLock, "om_alloc(1)"); 1238 for (int i = self->om_free_provision; --i >= 0 && g_free_list != NULL;) { 1239 g_om_free_count--; 1240 ObjectMonitor* take = g_free_list; 1241 g_free_list = take->_next_om; 1242 guarantee(take->object() == NULL, "invariant"); 1243 if (AsyncDeflateIdleMonitors) { 1244 // We allowed 3 field values to linger during async deflation. 1245 // We clear header and restore ref_count here, but we leave 1246 // owner == DEFLATER_MARKER so the simple C2 ObjectMonitor 1247 // enter optimization can no longer race with async deflation 1248 // and reuse. 1249 take->set_header(markWord::zero()); 1250 if (take->ref_count() < 0) { 1251 // Add back max_jint to restore the ref_count field to its 1252 // proper value. 1253 Atomic::add(max_jint, &take->_ref_count); 1254 1255 assert(take->ref_count() >= 0, "must not be negative: ref_count=%d", 1256 take->ref_count()); 1257 } 1258 } 1259 take->Recycle(); 1260 assert(take->is_free(), "invariant"); 1261 om_release(self, take, false); 1262 } 1263 Thread::muxRelease(&gListLock); 1264 self->om_free_provision += 1 + (self->om_free_provision/2); 1265 if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE; 1266 1267 if (!AsyncDeflateIdleMonitors && 1268 is_MonitorBound_exceeded(g_om_population - g_om_free_count)) { 1269 // Not enough ObjectMonitors on the global free list. 1270 // We can't safely induce a STW safepoint from om_alloc() as our thread 1271 // state may not be appropriate for such activities and callers may hold 1272 // naked oops, so instead we defer the action. 1273 InduceScavenge(self, "om_alloc"); 1274 } 1275 continue; 1276 } 1277 1278 // 3: allocate a block of new ObjectMonitors 1279 // Both the local and global free lists are empty -- resort to malloc(). 1280 // In the current implementation ObjectMonitors are TSM - immortal. 1281 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want 1282 // each ObjectMonitor to start at the beginning of a cache line, 1283 // so we use align_up(). 1284 // A better solution would be to use C++ placement-new. 1285 // BEWARE: As it stands currently, we don't run the ctors! 1286 assert(_BLOCKSIZE > 1, "invariant"); 1287 size_t neededsize = sizeof(PaddedObjectMonitor) * _BLOCKSIZE; 1288 PaddedObjectMonitor* temp; 1289 size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1); 1290 void* real_malloc_addr = (void*)NEW_C_HEAP_ARRAY(char, aligned_size, 1291 mtInternal); 1292 temp = (PaddedObjectMonitor*)align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE); 1293 1294 // NOTE: (almost) no way to recover if allocation failed. 1295 // We might be able to induce a STW safepoint and scavenge enough 1296 // ObjectMonitors to permit progress. 1297 if (temp == NULL) { 1298 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR, 1299 "Allocate ObjectMonitors"); 1300 } 1301 (void)memset((void *) temp, 0, neededsize); 1302 1303 // Format the block. 1304 // initialize the linked list, each monitor points to its next 1305 // forming the single linked free list, the very first monitor 1306 // will points to next block, which forms the block list. 1307 // The trick of using the 1st element in the block as g_block_list 1308 // linkage should be reconsidered. A better implementation would 1309 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; } 1310 1311 for (int i = 1; i < _BLOCKSIZE; i++) { 1312 temp[i]._next_om = (ObjectMonitor *)&temp[i+1]; 1313 assert(temp[i].is_free(), "invariant"); 1314 } 1315 1316 // terminate the last monitor as the end of list 1317 temp[_BLOCKSIZE - 1]._next_om = NULL; 1318 1319 // Element [0] is reserved for global list linkage 1320 temp[0].set_object(CHAINMARKER); 1321 1322 // Consider carving out this thread's current request from the 1323 // block in hand. This avoids some lock traffic and redundant 1324 // list activity. 1325 1326 // Acquire the gListLock to manipulate g_block_list and g_free_list. 1327 // An Oyama-Taura-Yonezawa scheme might be more efficient. 1328 Thread::muxAcquire(&gListLock, "om_alloc(2)"); 1329 g_om_population += _BLOCKSIZE-1; 1330 g_om_free_count += _BLOCKSIZE-1; 1331 1332 // Add the new block to the list of extant blocks (g_block_list). 1333 // The very first ObjectMonitor in a block is reserved and dedicated. 1334 // It serves as blocklist "next" linkage. 1335 temp[0]._next_om = g_block_list; 1336 // There are lock-free uses of g_block_list so make sure that 1337 // the previous stores happen before we update g_block_list. 1338 OrderAccess::release_store(&g_block_list, temp); 1339 1340 // Add the new string of ObjectMonitors to the global free list 1341 temp[_BLOCKSIZE - 1]._next_om = g_free_list; 1342 g_free_list = temp + 1; 1343 Thread::muxRelease(&gListLock); 1344 } 1345 } 1346 1347 // Place "m" on the caller's private per-thread om_free_list. 1348 // In practice there's no need to clamp or limit the number of 1349 // monitors on a thread's om_free_list as the only non-allocation time 1350 // we'll call om_release() is to return a monitor to the free list after 1351 // a CAS attempt failed. This doesn't allow unbounded #s of monitors to 1352 // accumulate on a thread's free list. 1353 // 1354 // Key constraint: all ObjectMonitors on a thread's free list and the global 1355 // free list must have their object field set to null. This prevents the 1356 // scavenger -- deflate_monitor_list() or deflate_monitor_list_using_JT() 1357 // -- from reclaiming them while we are trying to release them. 1358 1359 void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m, 1360 bool from_per_thread_alloc) { 1361 guarantee(m->header().value() == 0, "invariant"); 1362 guarantee(m->object() == NULL, "invariant"); 1363 stringStream ss; 1364 guarantee((m->is_busy() | m->_recursions) == 0, "freeing in-use monitor: " 1365 "%s, recursions=" INTPTR_FORMAT, m->is_busy_to_string(&ss), 1366 m->_recursions); 1367 m->set_allocation_state(ObjectMonitor::Free); 1368 // _next_om is used for both per-thread in-use and free lists so 1369 // we have to remove 'm' from the in-use list first (as needed). 1370 if (from_per_thread_alloc) { 1371 // Need to remove 'm' from om_in_use_list. 1372 ObjectMonitor* cur_mid_in_use = NULL; 1373 bool extracted = false; 1374 for (ObjectMonitor* mid = self->om_in_use_list; mid != NULL; cur_mid_in_use = mid, mid = mid->_next_om) { 1375 if (m == mid) { 1376 // extract from per-thread in-use list 1377 if (mid == self->om_in_use_list) { 1378 self->om_in_use_list = mid->_next_om; 1379 } else if (cur_mid_in_use != NULL) { 1380 cur_mid_in_use->_next_om = mid->_next_om; // maintain the current thread in-use list 1381 } 1382 extracted = true; 1383 self->om_in_use_count--; 1384 break; 1385 } 1386 } 1387 assert(extracted, "Should have extracted from in-use list"); 1388 } 1389 1390 m->_next_om = self->om_free_list; 1391 guarantee(m->is_free(), "invariant"); 1392 self->om_free_list = m; 1393 self->om_free_count++; 1394 } 1395 1396 // Return ObjectMonitors on a moribund thread's free and in-use 1397 // lists to the appropriate global lists. The ObjectMonitors on the 1398 // per-thread in-use list may still be in use by other threads. 1399 // 1400 // We currently call om_flush() from Threads::remove() before the 1401 // thread has been excised from the thread list and is no longer a 1402 // mutator. This means that om_flush() cannot run concurrently with 1403 // a safepoint and interleave with deflate_idle_monitors(). In 1404 // particular, this ensures that the thread's in-use monitors are 1405 // scanned by a GC safepoint, either via Thread::oops_do() (before 1406 // om_flush() is called) or via ObjectSynchronizer::oops_do() (after 1407 // om_flush() is called). 1408 // 1409 // With AsyncDeflateIdleMonitors, deflate_global_idle_monitors_using_JT() 1410 // and deflate_per_thread_idle_monitors_using_JT() (in another thread) can 1411 // run at the same time as om_flush() so we have to be careful. 1412 1413 void ObjectSynchronizer::om_flush(Thread* self) { 1414 ObjectMonitor* free_list = self->om_free_list; 1415 ObjectMonitor* free_tail = NULL; 1416 int free_count = 0; 1417 if (free_list != NULL) { 1418 ObjectMonitor* s; 1419 // The thread is going away. Set 'free_tail' to the last per-thread free 1420 // monitor which will be linked to g_free_list below under the gListLock. 1421 stringStream ss; 1422 for (s = free_list; s != NULL; s = s->_next_om) { 1423 free_count++; 1424 free_tail = s; 1425 guarantee(s->object() == NULL, "invariant"); 1426 guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss)); 1427 } 1428 guarantee(free_tail != NULL, "invariant"); 1429 ADIM_guarantee(self->om_free_count == free_count, "free-count off"); 1430 self->om_free_list = NULL; 1431 self->om_free_count = 0; 1432 } 1433 1434 ObjectMonitor* in_use_list = self->om_in_use_list; 1435 ObjectMonitor* in_use_tail = NULL; 1436 int in_use_count = 0; 1437 if (in_use_list != NULL) { 1438 // The thread is going away, however the ObjectMonitors on the 1439 // om_in_use_list may still be in-use by other threads. Link 1440 // them to in_use_tail, which will be linked into the global 1441 // in-use list g_om_in_use_list below, under the gListLock. 1442 ObjectMonitor *cur_om; 1443 for (cur_om = in_use_list; cur_om != NULL; cur_om = cur_om->_next_om) { 1444 in_use_tail = cur_om; 1445 in_use_count++; 1446 ADIM_guarantee(cur_om->is_active(), "invariant"); 1447 } 1448 guarantee(in_use_tail != NULL, "invariant"); 1449 ADIM_guarantee(self->om_in_use_count == in_use_count, "in-use count off"); 1450 self->om_in_use_list = NULL; 1451 self->om_in_use_count = 0; 1452 } 1453 1454 Thread::muxAcquire(&gListLock, "om_flush"); 1455 if (free_tail != NULL) { 1456 free_tail->_next_om = g_free_list; 1457 g_free_list = free_list; 1458 g_om_free_count += free_count; 1459 } 1460 1461 if (in_use_tail != NULL) { 1462 in_use_tail->_next_om = g_om_in_use_list; 1463 g_om_in_use_list = in_use_list; 1464 g_om_in_use_count += in_use_count; 1465 } 1466 1467 Thread::muxRelease(&gListLock); 1468 1469 LogStreamHandle(Debug, monitorinflation) lsh_debug; 1470 LogStreamHandle(Info, monitorinflation) lsh_info; 1471 LogStream* ls = NULL; 1472 if (log_is_enabled(Debug, monitorinflation)) { 1473 ls = &lsh_debug; 1474 } else if ((free_count != 0 || in_use_count != 0) && 1475 log_is_enabled(Info, monitorinflation)) { 1476 ls = &lsh_info; 1477 } 1478 if (ls != NULL) { 1479 ls->print_cr("om_flush: jt=" INTPTR_FORMAT ", free_count=%d" 1480 ", in_use_count=%d" ", om_free_provision=%d", 1481 p2i(self), free_count, in_use_count, self->om_free_provision); 1482 } 1483 } 1484 1485 static void post_monitor_inflate_event(EventJavaMonitorInflate* event, 1486 const oop obj, 1487 ObjectSynchronizer::InflateCause cause) { 1488 assert(event != NULL, "invariant"); 1489 assert(event->should_commit(), "invariant"); 1490 event->set_monitorClass(obj->klass()); 1491 event->set_address((uintptr_t)(void*)obj); 1492 event->set_cause((u1)cause); 1493 event->commit(); 1494 } 1495 1496 // Fast path code shared by multiple functions 1497 void ObjectSynchronizer::inflate_helper(ObjectMonitorHandle* omh_p, oop obj) { 1498 while (true) { 1499 markWord mark = obj->mark(); 1500 if (mark.has_monitor()) { 1501 if (!omh_p->save_om_ptr(obj, mark)) { 1502 // Lost a race with async deflation so try again. 1503 assert(AsyncDeflateIdleMonitors, "sanity check"); 1504 continue; 1505 } 1506 ObjectMonitor* monitor = omh_p->om_ptr(); 1507 assert(ObjectSynchronizer::verify_objmon_isinpool(monitor), "monitor is invalid"); 1508 markWord dmw = monitor->header(); 1509 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value()); 1510 return; 1511 } 1512 inflate(omh_p, Thread::current(), obj, inflate_cause_vm_internal); 1513 return; 1514 } 1515 } 1516 1517 void ObjectSynchronizer::inflate(ObjectMonitorHandle* omh_p, Thread* self, 1518 oop object, const InflateCause cause) { 1519 // Inflate mutates the heap ... 1520 // Relaxing assertion for bug 6320749. 1521 assert(Universe::verify_in_progress() || 1522 !SafepointSynchronize::is_at_safepoint(), "invariant"); 1523 1524 EventJavaMonitorInflate event; 1525 1526 for (;;) { 1527 const markWord mark = object->mark(); 1528 assert(!mark.has_bias_pattern(), "invariant"); 1529 1530 // The mark can be in one of the following states: 1531 // * Inflated - just return 1532 // * Stack-locked - coerce it to inflated 1533 // * INFLATING - busy wait for conversion to complete 1534 // * Neutral - aggressively inflate the object. 1535 // * BIASED - Illegal. We should never see this 1536 1537 // CASE: inflated 1538 if (mark.has_monitor()) { 1539 if (!omh_p->save_om_ptr(object, mark)) { 1540 // Lost a race with async deflation so try again. 1541 assert(AsyncDeflateIdleMonitors, "sanity check"); 1542 continue; 1543 } 1544 ObjectMonitor* inf = omh_p->om_ptr(); 1545 markWord dmw = inf->header(); 1546 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1547 assert(oopDesc::equals((oop) inf->object(), object), "invariant"); 1548 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid"); 1549 return; 1550 } 1551 1552 // CASE: inflation in progress - inflating over a stack-lock. 1553 // Some other thread is converting from stack-locked to inflated. 1554 // Only that thread can complete inflation -- other threads must wait. 1555 // The INFLATING value is transient. 1556 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish. 1557 // We could always eliminate polling by parking the thread on some auxiliary list. 1558 if (mark == markWord::INFLATING()) { 1559 read_stable_mark(object); 1560 continue; 1561 } 1562 1563 // CASE: stack-locked 1564 // Could be stack-locked either by this thread or by some other thread. 1565 // 1566 // Note that we allocate the objectmonitor speculatively, _before_ attempting 1567 // to install INFLATING into the mark word. We originally installed INFLATING, 1568 // allocated the objectmonitor, and then finally STed the address of the 1569 // objectmonitor into the mark. This was correct, but artificially lengthened 1570 // the interval in which INFLATED appeared in the mark, thus increasing 1571 // the odds of inflation contention. 1572 // 1573 // We now use per-thread private objectmonitor free lists. 1574 // These list are reprovisioned from the global free list outside the 1575 // critical INFLATING...ST interval. A thread can transfer 1576 // multiple objectmonitors en-mass from the global free list to its local free list. 1577 // This reduces coherency traffic and lock contention on the global free list. 1578 // Using such local free lists, it doesn't matter if the om_alloc() call appears 1579 // before or after the CAS(INFLATING) operation. 1580 // See the comments in om_alloc(). 1581 1582 LogStreamHandle(Trace, monitorinflation) lsh; 1583 1584 if (mark.has_locker()) { 1585 ObjectMonitor* m; 1586 if (!AsyncDeflateIdleMonitors || cause == inflate_cause_vm_internal) { 1587 // If !AsyncDeflateIdleMonitors or if an internal inflation, then 1588 // we won't stop for a potential safepoint in om_alloc. 1589 m = om_alloc(self, cause); 1590 } else { 1591 // If AsyncDeflateIdleMonitors and not an internal inflation, then 1592 // we may stop for a safepoint in om_alloc() so protect object. 1593 Handle h_obj(self, object); 1594 m = om_alloc(self, cause); 1595 object = h_obj(); // Refresh object. 1596 } 1597 // Optimistically prepare the objectmonitor - anticipate successful CAS 1598 // We do this before the CAS in order to minimize the length of time 1599 // in which INFLATING appears in the mark. 1600 m->Recycle(); 1601 m->_Responsible = NULL; 1602 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class 1603 1604 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark); 1605 if (cmp != mark) { 1606 om_release(self, m, true); 1607 continue; // Interference -- just retry 1608 } 1609 1610 // We've successfully installed INFLATING (0) into the mark-word. 1611 // This is the only case where 0 will appear in a mark-word. 1612 // Only the singular thread that successfully swings the mark-word 1613 // to 0 can perform (or more precisely, complete) inflation. 1614 // 1615 // Why do we CAS a 0 into the mark-word instead of just CASing the 1616 // mark-word from the stack-locked value directly to the new inflated state? 1617 // Consider what happens when a thread unlocks a stack-locked object. 1618 // It attempts to use CAS to swing the displaced header value from the 1619 // on-stack BasicLock back into the object header. Recall also that the 1620 // header value (hash code, etc) can reside in (a) the object header, or 1621 // (b) a displaced header associated with the stack-lock, or (c) a displaced 1622 // header in an ObjectMonitor. The inflate() routine must copy the header 1623 // value from the BasicLock on the owner's stack to the ObjectMonitor, all 1624 // the while preserving the hashCode stability invariants. If the owner 1625 // decides to release the lock while the value is 0, the unlock will fail 1626 // and control will eventually pass from slow_exit() to inflate. The owner 1627 // will then spin, waiting for the 0 value to disappear. Put another way, 1628 // the 0 causes the owner to stall if the owner happens to try to 1629 // drop the lock (restoring the header from the BasicLock to the object) 1630 // while inflation is in-progress. This protocol avoids races that might 1631 // would otherwise permit hashCode values to change or "flicker" for an object. 1632 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable. 1633 // 0 serves as a "BUSY" inflate-in-progress indicator. 1634 1635 1636 // fetch the displaced mark from the owner's stack. 1637 // The owner can't die or unwind past the lock while our INFLATING 1638 // object is in the mark. Furthermore the owner can't complete 1639 // an unlock on the object, either. 1640 markWord dmw = mark.displaced_mark_helper(); 1641 // Catch if the object's header is not neutral (not locked and 1642 // not marked is what we care about here). 1643 ADIM_guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1644 1645 // Setup monitor fields to proper values -- prepare the monitor 1646 m->set_header(dmw); 1647 1648 // Optimization: if the mark.locker stack address is associated 1649 // with this thread we could simply set m->_owner = self. 1650 // Note that a thread can inflate an object 1651 // that it has stack-locked -- as might happen in wait() -- directly 1652 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom. 1653 m->set_owner(mark.locker()); 1654 m->set_object(object); 1655 // TODO-FIXME: assert BasicLock->dhw != 0. 1656 1657 omh_p->set_om_ptr(m); 1658 assert(m->is_new(), "freshly allocated monitor must be new"); 1659 m->set_allocation_state(ObjectMonitor::Old); 1660 1661 // Must preserve store ordering. The monitor state must 1662 // be stable at the time of publishing the monitor address. 1663 guarantee(object->mark() == markWord::INFLATING(), "invariant"); 1664 object->release_set_mark(markWord::encode(m)); 1665 1666 // Hopefully the performance counters are allocated on distinct cache lines 1667 // to avoid false sharing on MP systems ... 1668 OM_PERFDATA_OP(Inflations, inc()); 1669 if (log_is_enabled(Trace, monitorinflation)) { 1670 ResourceMark rm(self); 1671 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark=" 1672 INTPTR_FORMAT ", type='%s'", p2i(object), 1673 object->mark().value(), object->klass()->external_name()); 1674 } 1675 if (event.should_commit()) { 1676 post_monitor_inflate_event(&event, object, cause); 1677 } 1678 ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free"); 1679 return; 1680 } 1681 1682 // CASE: neutral 1683 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner. 1684 // If we know we're inflating for entry it's better to inflate by swinging a 1685 // pre-locked ObjectMonitor pointer into the object header. A successful 1686 // CAS inflates the object *and* confers ownership to the inflating thread. 1687 // In the current implementation we use a 2-step mechanism where we CAS() 1688 // to inflate and then CAS() again to try to swing _owner from NULL to self. 1689 // An inflateTry() method that we could call from fast_enter() and slow_enter() 1690 // would be useful. 1691 1692 // Catch if the object's header is not neutral (not locked and 1693 // not marked is what we care about here). 1694 ADIM_guarantee(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value()); 1695 ObjectMonitor* m; 1696 if (!AsyncDeflateIdleMonitors || cause == inflate_cause_vm_internal) { 1697 // If !AsyncDeflateIdleMonitors or if an internal inflation, then 1698 // we won't stop for a potential safepoint in om_alloc. 1699 m = om_alloc(self, cause); 1700 } else { 1701 // If AsyncDeflateIdleMonitors and not an internal inflation, then 1702 // we may stop for a safepoint in om_alloc() so protect object. 1703 Handle h_obj(self, object); 1704 m = om_alloc(self, cause); 1705 object = h_obj(); // Refresh object. 1706 } 1707 // prepare m for installation - set monitor to initial state 1708 m->Recycle(); 1709 m->set_header(mark); 1710 // If we leave _owner == DEFLATER_MARKER here, then the simple C2 1711 // ObjectMonitor enter optimization can no longer race with async 1712 // deflation and reuse. 1713 m->set_object(object); 1714 m->_Responsible = NULL; 1715 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class 1716 1717 omh_p->set_om_ptr(m); 1718 assert(m->is_new(), "freshly allocated monitor must be new"); 1719 m->set_allocation_state(ObjectMonitor::Old); 1720 1721 if (object->cas_set_mark(markWord::encode(m), mark) != mark) { 1722 m->set_header(markWord::zero()); 1723 m->set_object(NULL); 1724 m->Recycle(); 1725 omh_p->set_om_ptr(NULL); 1726 // om_release() will reset the allocation state 1727 om_release(self, m, true); 1728 m = NULL; 1729 continue; 1730 // interference - the markword changed - just retry. 1731 // The state-transitions are one-way, so there's no chance of 1732 // live-lock -- "Inflated" is an absorbing state. 1733 } 1734 1735 // Hopefully the performance counters are allocated on distinct 1736 // cache lines to avoid false sharing on MP systems ... 1737 OM_PERFDATA_OP(Inflations, inc()); 1738 if (log_is_enabled(Trace, monitorinflation)) { 1739 ResourceMark rm(self); 1740 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark=" 1741 INTPTR_FORMAT ", type='%s'", p2i(object), 1742 object->mark().value(), object->klass()->external_name()); 1743 } 1744 if (event.should_commit()) { 1745 post_monitor_inflate_event(&event, object, cause); 1746 } 1747 ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free"); 1748 return; 1749 } 1750 } 1751 1752 1753 // We maintain a list of in-use monitors for each thread. 1754 // 1755 // For safepoint based deflation: 1756 // deflate_thread_local_monitors() scans a single thread's in-use list, while 1757 // deflate_idle_monitors() scans only a global list of in-use monitors which 1758 // is populated only as a thread dies (see om_flush()). 1759 // 1760 // These operations are called at all safepoints, immediately after mutators 1761 // are stopped, but before any objects have moved. Collectively they traverse 1762 // the population of in-use monitors, deflating where possible. The scavenged 1763 // monitors are returned to the global monitor free list. 1764 // 1765 // Beware that we scavenge at *every* stop-the-world point. Having a large 1766 // number of monitors in-use could negatively impact performance. We also want 1767 // to minimize the total # of monitors in circulation, as they incur a small 1768 // footprint penalty. 1769 // 1770 // Perversely, the heap size -- and thus the STW safepoint rate -- 1771 // typically drives the scavenge rate. Large heaps can mean infrequent GC, 1772 // which in turn can mean large(r) numbers of ObjectMonitors in circulation. 1773 // This is an unfortunate aspect of this design. 1774 // 1775 // For async deflation: 1776 // If a special deflation request is made, then the safepoint based 1777 // deflation mechanism is used. Otherwise, an async deflation request 1778 // is registered with the ServiceThread and it is notified. 1779 1780 void ObjectSynchronizer::do_safepoint_work(DeflateMonitorCounters* _counters) { 1781 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 1782 1783 // The per-thread in-use lists are handled in 1784 // ParallelSPCleanupThreadClosure::do_thread(). 1785 1786 if (!AsyncDeflateIdleMonitors || is_special_deflation_requested()) { 1787 // Use the older mechanism for the global in-use list or if a 1788 // special deflation has been requested before the safepoint. 1789 ObjectSynchronizer::deflate_idle_monitors(_counters); 1790 return; 1791 } 1792 1793 log_debug(monitorinflation)("requesting async deflation of idle monitors."); 1794 // Request deflation of idle monitors by the ServiceThread: 1795 set_is_async_deflation_requested(true); 1796 MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag); 1797 ml.notify_all(); 1798 } 1799 1800 // Deflate a single monitor if not in-use 1801 // Return true if deflated, false if in-use 1802 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj, 1803 ObjectMonitor** free_head_p, 1804 ObjectMonitor** free_tail_p) { 1805 bool deflated; 1806 // Normal case ... The monitor is associated with obj. 1807 const markWord mark = obj->mark(); 1808 guarantee(mark == markWord::encode(mid), "should match: mark=" 1809 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(), 1810 markWord::encode(mid).value()); 1811 // Make sure that mark.monitor() and markWord::encode() agree: 1812 guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT 1813 ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid)); 1814 const markWord dmw = mid->header(); 1815 guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1816 1817 if (mid->is_busy() || mid->ref_count() != 0) { 1818 // Easy checks are first - the ObjectMonitor is busy or ObjectMonitor* 1819 // is in use so no deflation. 1820 deflated = false; 1821 } else { 1822 // Deflate the monitor if it is no longer being used 1823 // It's idle - scavenge and return to the global free list 1824 // plain old deflation ... 1825 if (log_is_enabled(Trace, monitorinflation)) { 1826 ResourceMark rm; 1827 log_trace(monitorinflation)("deflate_monitor: " 1828 "object=" INTPTR_FORMAT ", mark=" 1829 INTPTR_FORMAT ", type='%s'", p2i(obj), 1830 mark.value(), obj->klass()->external_name()); 1831 } 1832 1833 // Restore the header back to obj 1834 obj->release_set_mark(dmw); 1835 if (AsyncDeflateIdleMonitors) { 1836 // clear() expects the owner field to be NULL and we won't race 1837 // with the simple C2 ObjectMonitor enter optimization since 1838 // we're at a safepoint. 1839 mid->set_owner(NULL); 1840 } 1841 mid->clear(); 1842 1843 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT, 1844 p2i(mid->object())); 1845 assert(mid->is_free(), "invariant"); 1846 1847 // Move the deflated ObjectMonitor to the working free list 1848 // defined by free_head_p and free_tail_p. 1849 if (*free_head_p == NULL) *free_head_p = mid; 1850 if (*free_tail_p != NULL) { 1851 // We append to the list so the caller can use mid->_next_om 1852 // to fix the linkages in its context. 1853 ObjectMonitor* prevtail = *free_tail_p; 1854 // Should have been cleaned up by the caller: 1855 assert(prevtail->_next_om == NULL, "cleaned up deflated?"); 1856 prevtail->_next_om = mid; 1857 } 1858 *free_tail_p = mid; 1859 // At this point, mid->_next_om still refers to its current 1860 // value and another ObjectMonitor's _next_om field still 1861 // refers to this ObjectMonitor. Those linkages have to be 1862 // cleaned up by the caller who has the complete context. 1863 deflated = true; 1864 } 1865 return deflated; 1866 } 1867 1868 // Deflate the specified ObjectMonitor if not in-use using a JavaThread. 1869 // Returns true if it was deflated and false otherwise. 1870 // 1871 // The async deflation protocol sets owner to DEFLATER_MARKER and 1872 // makes ref_count negative as signals to contending threads that 1873 // an async deflation is in progress. There are a number of checks 1874 // as part of the protocol to make sure that the calling thread has 1875 // not lost the race to a contending thread or to a thread that just 1876 // wants to use the ObjectMonitor*. 1877 // 1878 // The ObjectMonitor has been successfully async deflated when: 1879 // (owner == DEFLATER_MARKER && ref_count < 0) 1880 // Contending threads or ObjectMonitor* using threads that see those 1881 // values know to retry their operation. 1882 // 1883 bool ObjectSynchronizer::deflate_monitor_using_JT(ObjectMonitor* mid, 1884 ObjectMonitor** free_head_p, 1885 ObjectMonitor** free_tail_p) { 1886 assert(AsyncDeflateIdleMonitors, "sanity check"); 1887 assert(Thread::current()->is_Java_thread(), "precondition"); 1888 // A newly allocated ObjectMonitor should not be seen here so we 1889 // avoid an endless inflate/deflate cycle. 1890 assert(mid->is_old(), "must be old: allocation_state=%d", 1891 (int) mid->allocation_state()); 1892 1893 if (mid->is_busy() || mid->ref_count() != 0) { 1894 // Easy checks are first - the ObjectMonitor is busy or ObjectMonitor* 1895 // is in use so no deflation. 1896 return false; 1897 } 1898 1899 if (Atomic::replace_if_null(DEFLATER_MARKER, &(mid->_owner))) { 1900 // ObjectMonitor is not owned by another thread. Our setting 1901 // owner to DEFLATER_MARKER forces any contending thread through 1902 // the slow path. This is just the first part of the async 1903 // deflation dance. 1904 1905 if (mid->_contentions != 0 || mid->_waiters != 0) { 1906 // Another thread has raced to enter the ObjectMonitor after 1907 // mid->is_busy() above or has already entered and waited on 1908 // it which makes it busy so no deflation. Restore owner to 1909 // NULL if it is still DEFLATER_MARKER. 1910 Atomic::cmpxchg((void*)NULL, &mid->_owner, DEFLATER_MARKER); 1911 return false; 1912 } 1913 1914 if (Atomic::cmpxchg(-max_jint, &mid->_ref_count, (jint)0) == 0) { 1915 // Make ref_count negative to force any contending threads or 1916 // ObjectMonitor* using threads to retry. This is the second 1917 // part of the async deflation dance. 1918 1919 if (mid->owner_is_DEFLATER_MARKER()) { 1920 // If owner is still DEFLATER_MARKER, then we have successfully 1921 // signaled any contending threads to retry. If it is not, then we 1922 // have lost the race to an entering thread and the ObjectMonitor 1923 // is now busy. This is the third and final part of the async 1924 // deflation dance. 1925 // Note: This owner check solves the ABA problem with ref_count 1926 // where another thread acquired the ObjectMonitor, finished 1927 // using it and restored the ref_count to zero. 1928 1929 // Sanity checks for the races: 1930 guarantee(mid->_contentions == 0, "must be 0: contentions=%d", 1931 mid->_contentions); 1932 guarantee(mid->_waiters == 0, "must be 0: waiters=%d", mid->_waiters); 1933 guarantee(mid->_cxq == NULL, "must be no contending threads: cxq=" 1934 INTPTR_FORMAT, p2i(mid->_cxq)); 1935 guarantee(mid->_EntryList == NULL, 1936 "must be no entering threads: EntryList=" INTPTR_FORMAT, 1937 p2i(mid->_EntryList)); 1938 1939 const oop obj = (oop) mid->object(); 1940 if (log_is_enabled(Trace, monitorinflation)) { 1941 ResourceMark rm; 1942 log_trace(monitorinflation)("deflate_monitor_using_JT: " 1943 "object=" INTPTR_FORMAT ", mark=" 1944 INTPTR_FORMAT ", type='%s'", 1945 p2i(obj), obj->mark().value(), 1946 obj->klass()->external_name()); 1947 } 1948 1949 // Install the old mark word if nobody else has already done it. 1950 mid->install_displaced_markword_in_object(obj); 1951 mid->clear_using_JT(); 1952 1953 assert(mid->object() == NULL, "must be NULL: object=" INTPTR_FORMAT, 1954 p2i(mid->object())); 1955 assert(mid->is_free(), "must be free: allocation_state=%d", 1956 (int) mid->allocation_state()); 1957 1958 // Move the deflated ObjectMonitor to the working free list 1959 // defined by free_head_p and free_tail_p. 1960 if (*free_head_p == NULL) { 1961 // First one on the list. 1962 *free_head_p = mid; 1963 } 1964 if (*free_tail_p != NULL) { 1965 // We append to the list so the caller can use mid->_next_om 1966 // to fix the linkages in its context. 1967 ObjectMonitor* prevtail = *free_tail_p; 1968 // Should have been cleaned up by the caller: 1969 assert(prevtail->_next_om == NULL, "must be NULL: _next_om=" 1970 INTPTR_FORMAT, p2i(prevtail->_next_om)); 1971 prevtail->_next_om = mid; 1972 } 1973 *free_tail_p = mid; 1974 1975 // At this point, mid->_next_om still refers to its current 1976 // value and another ObjectMonitor's _next_om field still 1977 // refers to this ObjectMonitor. Those linkages have to be 1978 // cleaned up by the caller who has the complete context. 1979 1980 // We leave owner == DEFLATER_MARKER and ref_count < 0 1981 // to force any racing threads to retry. 1982 return true; // Success, ObjectMonitor has been deflated. 1983 } 1984 1985 // The owner was changed from DEFLATER_MARKER so we lost the 1986 // race since the ObjectMonitor is now busy. 1987 1988 // Add back max_jint to restore the ref_count field to its 1989 // proper value (which may not be what we saw above): 1990 Atomic::add(max_jint, &mid->_ref_count); 1991 1992 assert(mid->ref_count() >= 0, "must not be negative: ref_count=%d", 1993 mid->ref_count()); 1994 return false; 1995 } 1996 1997 // The ref_count was no longer 0 so we lost the race since the 1998 // ObjectMonitor is now busy or the ObjectMonitor* is now is use. 1999 // Restore owner to NULL if it is still DEFLATER_MARKER: 2000 Atomic::cmpxchg((void*)NULL, &mid->_owner, DEFLATER_MARKER); 2001 } 2002 2003 // The owner field is no longer NULL so we lost the race since the 2004 // ObjectMonitor is now busy. 2005 return false; 2006 } 2007 2008 // Walk a given monitor list, and deflate idle monitors 2009 // The given list could be a per-thread list or a global list 2010 // Caller acquires gListLock as needed. 2011 // 2012 // In the case of parallel processing of thread local monitor lists, 2013 // work is done by Threads::parallel_threads_do() which ensures that 2014 // each Java thread is processed by exactly one worker thread, and 2015 // thus avoid conflicts that would arise when worker threads would 2016 // process the same monitor lists concurrently. 2017 // 2018 // See also ParallelSPCleanupTask and 2019 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and 2020 // Threads::parallel_java_threads_do() in thread.cpp. 2021 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** list_p, 2022 ObjectMonitor** free_head_p, 2023 ObjectMonitor** free_tail_p) { 2024 ObjectMonitor* mid; 2025 ObjectMonitor* next; 2026 ObjectMonitor* cur_mid_in_use = NULL; 2027 int deflated_count = 0; 2028 2029 for (mid = *list_p; mid != NULL;) { 2030 oop obj = (oop) mid->object(); 2031 if (obj != NULL && deflate_monitor(mid, obj, free_head_p, free_tail_p)) { 2032 // Deflation succeeded and already updated free_head_p and 2033 // free_tail_p as needed. Finish the move to the local free list 2034 // by unlinking mid from the global or per-thread in-use list. 2035 if (mid == *list_p) { 2036 *list_p = mid->_next_om; 2037 } else if (cur_mid_in_use != NULL) { 2038 cur_mid_in_use->_next_om = mid->_next_om; // maintain the current thread in-use list 2039 } 2040 next = mid->_next_om; 2041 mid->_next_om = NULL; // This mid is current tail in the free_head_p list 2042 mid = next; 2043 deflated_count++; 2044 } else { 2045 cur_mid_in_use = mid; 2046 mid = mid->_next_om; 2047 } 2048 } 2049 return deflated_count; 2050 } 2051 2052 // Walk a given ObjectMonitor list and deflate idle ObjectMonitors using 2053 // a JavaThread. Returns the number of deflated ObjectMonitors. The given 2054 // list could be a per-thread in-use list or the global in-use list. 2055 // Caller acquires gListLock as appropriate. If a safepoint has started, 2056 // then we save state via saved_mid_in_use_p and return to the caller to 2057 // honor the safepoint. 2058 // 2059 int ObjectSynchronizer::deflate_monitor_list_using_JT(ObjectMonitor** list_p, 2060 ObjectMonitor** free_head_p, 2061 ObjectMonitor** free_tail_p, 2062 ObjectMonitor** saved_mid_in_use_p) { 2063 assert(AsyncDeflateIdleMonitors, "sanity check"); 2064 assert(Thread::current()->is_Java_thread(), "precondition"); 2065 2066 ObjectMonitor* mid; 2067 ObjectMonitor* next; 2068 ObjectMonitor* cur_mid_in_use = NULL; 2069 int deflated_count = 0; 2070 2071 if (*saved_mid_in_use_p == NULL) { 2072 // No saved state so start at the beginning. 2073 mid = *list_p; 2074 } else { 2075 // We're restarting after a safepoint so restore the necessary state 2076 // before we resume. 2077 cur_mid_in_use = *saved_mid_in_use_p; 2078 mid = cur_mid_in_use->_next_om; 2079 } 2080 while (mid != NULL) { 2081 // Only try to deflate if there is an associated Java object and if 2082 // mid is old (is not newly allocated and is not newly freed). 2083 if (mid->object() != NULL && mid->is_old() && 2084 deflate_monitor_using_JT(mid, free_head_p, free_tail_p)) { 2085 // Deflation succeeded so update the in-use list. 2086 if (mid == *list_p) { 2087 *list_p = mid->_next_om; 2088 } else if (cur_mid_in_use != NULL) { 2089 // Maintain the current in-use list. 2090 cur_mid_in_use->_next_om = mid->_next_om; 2091 } 2092 next = mid->_next_om; 2093 mid->_next_om = NULL; 2094 // At this point mid is disconnected from the in-use list 2095 // and is the current tail in the free_head_p list. 2096 mid = next; 2097 deflated_count++; 2098 } else { 2099 // mid is considered in-use if it does not have an associated 2100 // Java object or mid is not old or deflation did not succeed. 2101 // A mid->is_new() node can be seen here when it is freshly 2102 // returned by om_alloc() (and skips the deflation code path). 2103 // A mid->is_old() node can be seen here when deflation failed. 2104 // A mid->is_free() node can be seen here when a fresh node from 2105 // om_alloc() is released by om_release() due to losing the race 2106 // in inflate(). 2107 2108 cur_mid_in_use = mid; 2109 mid = mid->_next_om; 2110 2111 if (SafepointSynchronize::is_synchronizing() && 2112 cur_mid_in_use != *list_p && cur_mid_in_use->is_old()) { 2113 // If a safepoint has started and cur_mid_in_use is not the list 2114 // head and is old, then it is safe to use as saved state. Return 2115 // to the caller so gListLock can be dropped as appropriate 2116 // before blocking. 2117 *saved_mid_in_use_p = cur_mid_in_use; 2118 return deflated_count; 2119 } 2120 } 2121 } 2122 // We finished the list without a safepoint starting so there's 2123 // no need to save state. 2124 *saved_mid_in_use_p = NULL; 2125 return deflated_count; 2126 } 2127 2128 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) { 2129 counters->n_in_use = 0; // currently associated with objects 2130 counters->n_in_circulation = 0; // extant 2131 counters->n_scavenged = 0; // reclaimed (global and per-thread) 2132 counters->per_thread_scavenged = 0; // per-thread scavenge total 2133 counters->per_thread_times = 0.0; // per-thread scavenge times 2134 } 2135 2136 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) { 2137 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 2138 2139 if (AsyncDeflateIdleMonitors) { 2140 // Nothing to do when global idle ObjectMonitors are deflated using 2141 // a JavaThread unless a special deflation has been requested. 2142 if (!is_special_deflation_requested()) { 2143 return; 2144 } 2145 } 2146 2147 bool deflated = false; 2148 2149 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors 2150 ObjectMonitor* free_tail_p = NULL; 2151 elapsedTimer timer; 2152 2153 if (log_is_enabled(Info, monitorinflation)) { 2154 timer.start(); 2155 } 2156 2157 // Prevent om_flush from changing mids in Thread dtor's during deflation 2158 // And in case the vm thread is acquiring a lock during a safepoint 2159 // See e.g. 6320749 2160 Thread::muxAcquire(&gListLock, "deflate_idle_monitors"); 2161 2162 // Note: the thread-local monitors lists get deflated in 2163 // a separate pass. See deflate_thread_local_monitors(). 2164 2165 // For moribund threads, scan g_om_in_use_list 2166 int deflated_count = 0; 2167 if (g_om_in_use_list) { 2168 counters->n_in_circulation += g_om_in_use_count; 2169 deflated_count = deflate_monitor_list((ObjectMonitor **)&g_om_in_use_list, &free_head_p, &free_tail_p); 2170 g_om_in_use_count -= deflated_count; 2171 counters->n_scavenged += deflated_count; 2172 counters->n_in_use += g_om_in_use_count; 2173 } 2174 2175 if (free_head_p != NULL) { 2176 // Move the deflated ObjectMonitors back to the global free list. 2177 guarantee(free_tail_p != NULL && counters->n_scavenged > 0, "invariant"); 2178 assert(free_tail_p->_next_om == NULL, "invariant"); 2179 // constant-time list splice - prepend scavenged segment to g_free_list 2180 free_tail_p->_next_om = g_free_list; 2181 g_free_list = free_head_p; 2182 } 2183 Thread::muxRelease(&gListLock); 2184 timer.stop(); 2185 2186 LogStreamHandle(Debug, monitorinflation) lsh_debug; 2187 LogStreamHandle(Info, monitorinflation) lsh_info; 2188 LogStream* ls = NULL; 2189 if (log_is_enabled(Debug, monitorinflation)) { 2190 ls = &lsh_debug; 2191 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) { 2192 ls = &lsh_info; 2193 } 2194 if (ls != NULL) { 2195 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count); 2196 } 2197 } 2198 2199 // Deflate global idle ObjectMonitors using a JavaThread. 2200 // 2201 void ObjectSynchronizer::deflate_global_idle_monitors_using_JT() { 2202 assert(AsyncDeflateIdleMonitors, "sanity check"); 2203 assert(Thread::current()->is_Java_thread(), "precondition"); 2204 JavaThread* self = JavaThread::current(); 2205 2206 deflate_common_idle_monitors_using_JT(true /* is_global */, self); 2207 } 2208 2209 // Deflate per-thread idle ObjectMonitors using a JavaThread. 2210 // 2211 void ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT() { 2212 assert(AsyncDeflateIdleMonitors, "sanity check"); 2213 assert(Thread::current()->is_Java_thread(), "precondition"); 2214 JavaThread* self = JavaThread::current(); 2215 2216 self->om_request_deflation = false; 2217 2218 deflate_common_idle_monitors_using_JT(false /* !is_global */, self); 2219 } 2220 2221 // Deflate global or per-thread idle ObjectMonitors using a JavaThread. 2222 // 2223 void ObjectSynchronizer::deflate_common_idle_monitors_using_JT(bool is_global, JavaThread* self) { 2224 int deflated_count = 0; 2225 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged ObjectMonitors 2226 ObjectMonitor* free_tail_p = NULL; 2227 ObjectMonitor* saved_mid_in_use_p = NULL; 2228 elapsedTimer timer; 2229 2230 if (log_is_enabled(Info, monitorinflation)) { 2231 timer.start(); 2232 } 2233 2234 if (is_global) { 2235 Thread::muxAcquire(&gListLock, "deflate_global_idle_monitors_using_JT(1)"); 2236 OM_PERFDATA_OP(MonExtant, set_value(g_om_in_use_count)); 2237 } else { 2238 OM_PERFDATA_OP(MonExtant, inc(self->om_in_use_count)); 2239 } 2240 2241 do { 2242 int local_deflated_count; 2243 if (is_global) { 2244 local_deflated_count = deflate_monitor_list_using_JT((ObjectMonitor **)&g_om_in_use_list, &free_head_p, &free_tail_p, &saved_mid_in_use_p); 2245 g_om_in_use_count -= local_deflated_count; 2246 } else { 2247 local_deflated_count = deflate_monitor_list_using_JT(self->om_in_use_list_addr(), &free_head_p, &free_tail_p, &saved_mid_in_use_p); 2248 self->om_in_use_count -= local_deflated_count; 2249 } 2250 deflated_count += local_deflated_count; 2251 2252 if (free_head_p != NULL) { 2253 // Move the scavenged ObjectMonitors to the global free list. 2254 guarantee(free_tail_p != NULL && local_deflated_count > 0, "free_tail_p=" INTPTR_FORMAT ", local_deflated_count=%d", p2i(free_tail_p), local_deflated_count); 2255 assert(free_tail_p->_next_om == NULL, "invariant"); 2256 2257 if (!is_global) { 2258 Thread::muxAcquire(&gListLock, "deflate_per_thread_idle_monitors_using_JT(2)"); 2259 } 2260 // Constant-time list splice - prepend scavenged segment to g_free_list. 2261 free_tail_p->_next_om = g_free_list; 2262 g_free_list = free_head_p; 2263 2264 g_om_free_count += local_deflated_count; 2265 OM_PERFDATA_OP(Deflations, inc(local_deflated_count)); 2266 if (!is_global) { 2267 Thread::muxRelease(&gListLock); 2268 } 2269 } 2270 2271 if (saved_mid_in_use_p != NULL) { 2272 // deflate_monitor_list_using_JT() detected a safepoint starting. 2273 if (is_global) { 2274 Thread::muxRelease(&gListLock); 2275 } 2276 timer.stop(); 2277 { 2278 if (is_global) { 2279 log_debug(monitorinflation)("pausing deflation of global idle monitors for a safepoint."); 2280 } else { 2281 log_debug(monitorinflation)("jt=" INTPTR_FORMAT ": pausing deflation of per-thread idle monitors for a safepoint.", p2i(self)); 2282 } 2283 assert(SafepointSynchronize::is_synchronizing(), "sanity check"); 2284 ThreadBlockInVM blocker(self); 2285 } 2286 // Prepare for another loop after the safepoint. 2287 free_head_p = NULL; 2288 free_tail_p = NULL; 2289 if (log_is_enabled(Info, monitorinflation)) { 2290 timer.start(); 2291 } 2292 if (is_global) { 2293 Thread::muxAcquire(&gListLock, "deflate_global_idle_monitors_using_JT(3)"); 2294 } 2295 } 2296 } while (saved_mid_in_use_p != NULL); 2297 if (is_global) { 2298 Thread::muxRelease(&gListLock); 2299 } 2300 timer.stop(); 2301 2302 LogStreamHandle(Debug, monitorinflation) lsh_debug; 2303 LogStreamHandle(Info, monitorinflation) lsh_info; 2304 LogStream* ls = NULL; 2305 if (log_is_enabled(Debug, monitorinflation)) { 2306 ls = &lsh_debug; 2307 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) { 2308 ls = &lsh_info; 2309 } 2310 if (ls != NULL) { 2311 if (is_global) { 2312 ls->print_cr("async-deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count); 2313 } else { 2314 ls->print_cr("jt=" INTPTR_FORMAT ": async-deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(self), timer.seconds(), deflated_count); 2315 } 2316 } 2317 } 2318 2319 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) { 2320 // Report the cumulative time for deflating each thread's idle 2321 // monitors. Note: if the work is split among more than one 2322 // worker thread, then the reported time will likely be more 2323 // than a beginning to end measurement of the phase. 2324 // Note: AsyncDeflateIdleMonitors only deflates per-thread idle 2325 // monitors at a safepoint when a special deflation has been requested. 2326 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged); 2327 2328 bool needs_special_deflation = is_special_deflation_requested(); 2329 if (!AsyncDeflateIdleMonitors || needs_special_deflation) { 2330 // AsyncDeflateIdleMonitors does not use these counters unless 2331 // there is a special deflation request. 2332 2333 g_om_free_count += counters->n_scavenged; 2334 2335 OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged)); 2336 OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation)); 2337 } 2338 2339 if (log_is_enabled(Debug, monitorinflation)) { 2340 // exit_globals()'s call to audit_and_print_stats() is done 2341 // at the Info level. 2342 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */); 2343 } else if (log_is_enabled(Info, monitorinflation)) { 2344 Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors"); 2345 log_info(monitorinflation)("g_om_population=%d, g_om_in_use_count=%d, " 2346 "g_om_free_count=%d", g_om_population, 2347 g_om_in_use_count, g_om_free_count); 2348 Thread::muxRelease(&gListLock); 2349 } 2350 2351 ForceMonitorScavenge = 0; // Reset 2352 GVars.stw_random = os::random(); 2353 GVars.stw_cycle++; 2354 if (needs_special_deflation) { 2355 set_is_special_deflation_requested(false); // special deflation is done 2356 } 2357 } 2358 2359 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) { 2360 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 2361 2362 if (AsyncDeflateIdleMonitors) { 2363 if (!is_special_deflation_requested()) { 2364 // Mark the JavaThread for idle monitor deflation if a special 2365 // deflation has NOT been requested. 2366 if (thread->om_in_use_count > 0) { 2367 // This JavaThread is using monitors so mark it. 2368 thread->om_request_deflation = true; 2369 } 2370 return; 2371 } 2372 } 2373 2374 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors 2375 ObjectMonitor* free_tail_p = NULL; 2376 elapsedTimer timer; 2377 2378 if (log_is_enabled(Info, safepoint, cleanup) || 2379 log_is_enabled(Info, monitorinflation)) { 2380 timer.start(); 2381 } 2382 2383 int deflated_count = deflate_monitor_list(thread->om_in_use_list_addr(), &free_head_p, &free_tail_p); 2384 2385 Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors"); 2386 2387 // Adjust counters 2388 counters->n_in_circulation += thread->om_in_use_count; 2389 thread->om_in_use_count -= deflated_count; 2390 counters->n_scavenged += deflated_count; 2391 counters->n_in_use += thread->om_in_use_count; 2392 counters->per_thread_scavenged += deflated_count; 2393 2394 if (free_head_p != NULL) { 2395 // Move the deflated ObjectMonitors back to the global free list. 2396 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant"); 2397 assert(free_tail_p->_next_om == NULL, "invariant"); 2398 2399 // constant-time list splice - prepend scavenged segment to g_free_list 2400 free_tail_p->_next_om = g_free_list; 2401 g_free_list = free_head_p; 2402 } 2403 2404 timer.stop(); 2405 // Safepoint logging cares about cumulative per_thread_times and 2406 // we'll capture most of the cost, but not the muxRelease() which 2407 // should be cheap. 2408 counters->per_thread_times += timer.seconds(); 2409 2410 Thread::muxRelease(&gListLock); 2411 2412 LogStreamHandle(Debug, monitorinflation) lsh_debug; 2413 LogStreamHandle(Info, monitorinflation) lsh_info; 2414 LogStream* ls = NULL; 2415 if (log_is_enabled(Debug, monitorinflation)) { 2416 ls = &lsh_debug; 2417 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) { 2418 ls = &lsh_info; 2419 } 2420 if (ls != NULL) { 2421 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count); 2422 } 2423 } 2424 2425 // Monitor cleanup on JavaThread::exit 2426 2427 // Iterate through monitor cache and attempt to release thread's monitors 2428 // Gives up on a particular monitor if an exception occurs, but continues 2429 // the overall iteration, swallowing the exception. 2430 class ReleaseJavaMonitorsClosure: public MonitorClosure { 2431 private: 2432 TRAPS; 2433 2434 public: 2435 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {} 2436 void do_monitor(ObjectMonitor* mid) { 2437 if (mid->owner() == THREAD) { 2438 (void)mid->complete_exit(CHECK); 2439 } 2440 } 2441 }; 2442 2443 // Release all inflated monitors owned by THREAD. Lightweight monitors are 2444 // ignored. This is meant to be called during JNI thread detach which assumes 2445 // all remaining monitors are heavyweight. All exceptions are swallowed. 2446 // Scanning the extant monitor list can be time consuming. 2447 // A simple optimization is to add a per-thread flag that indicates a thread 2448 // called jni_monitorenter() during its lifetime. 2449 // 2450 // Instead of No_Savepoint_Verifier it might be cheaper to 2451 // use an idiom of the form: 2452 // auto int tmp = SafepointSynchronize::_safepoint_counter ; 2453 // <code that must not run at safepoint> 2454 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ; 2455 // Since the tests are extremely cheap we could leave them enabled 2456 // for normal product builds. 2457 2458 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) { 2459 assert(THREAD == JavaThread::current(), "must be current Java thread"); 2460 NoSafepointVerifier nsv; 2461 ReleaseJavaMonitorsClosure rjmc(THREAD); 2462 Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread"); 2463 ObjectSynchronizer::monitors_iterate(&rjmc); 2464 Thread::muxRelease(&gListLock); 2465 THREAD->clear_pending_exception(); 2466 } 2467 2468 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) { 2469 switch (cause) { 2470 case inflate_cause_vm_internal: return "VM Internal"; 2471 case inflate_cause_monitor_enter: return "Monitor Enter"; 2472 case inflate_cause_wait: return "Monitor Wait"; 2473 case inflate_cause_notify: return "Monitor Notify"; 2474 case inflate_cause_hash_code: return "Monitor Hash Code"; 2475 case inflate_cause_jni_enter: return "JNI Monitor Enter"; 2476 case inflate_cause_jni_exit: return "JNI Monitor Exit"; 2477 default: 2478 ShouldNotReachHere(); 2479 } 2480 return "Unknown"; 2481 } 2482 2483 //------------------------------------------------------------------------------ 2484 // Debugging code 2485 2486 u_char* ObjectSynchronizer::get_gvars_addr() { 2487 return (u_char*)&GVars; 2488 } 2489 2490 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() { 2491 return (u_char*)&GVars.hc_sequence; 2492 } 2493 2494 size_t ObjectSynchronizer::get_gvars_size() { 2495 return sizeof(SharedGlobals); 2496 } 2497 2498 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() { 2499 return (u_char*)&GVars.stw_random; 2500 } 2501 2502 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) { 2503 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant"); 2504 2505 LogStreamHandle(Debug, monitorinflation) lsh_debug; 2506 LogStreamHandle(Info, monitorinflation) lsh_info; 2507 LogStreamHandle(Trace, monitorinflation) lsh_trace; 2508 LogStream* ls = NULL; 2509 if (log_is_enabled(Trace, monitorinflation)) { 2510 ls = &lsh_trace; 2511 } else if (log_is_enabled(Debug, monitorinflation)) { 2512 ls = &lsh_debug; 2513 } else if (log_is_enabled(Info, monitorinflation)) { 2514 ls = &lsh_info; 2515 } 2516 assert(ls != NULL, "sanity check"); 2517 2518 if (!on_exit) { 2519 // Not at VM exit so grab the global list lock. 2520 Thread::muxAcquire(&gListLock, "audit_and_print_stats"); 2521 } 2522 2523 // Log counts for the global and per-thread monitor lists: 2524 int chk_om_population = log_monitor_list_counts(ls); 2525 int error_cnt = 0; 2526 2527 ls->print_cr("Checking global lists:"); 2528 2529 // Check g_om_population: 2530 if (g_om_population == chk_om_population) { 2531 ls->print_cr("g_om_population=%d equals chk_om_population=%d", 2532 g_om_population, chk_om_population); 2533 } else { 2534 ls->print_cr("ERROR: g_om_population=%d is not equal to " 2535 "chk_om_population=%d", g_om_population, 2536 chk_om_population); 2537 error_cnt++; 2538 } 2539 2540 // Check g_om_in_use_list and g_om_in_use_count: 2541 chk_global_in_use_list_and_count(ls, &error_cnt); 2542 2543 // Check g_free_list and g_om_free_count: 2544 chk_global_free_list_and_count(ls, &error_cnt); 2545 2546 if (!on_exit) { 2547 Thread::muxRelease(&gListLock); 2548 } 2549 2550 ls->print_cr("Checking per-thread lists:"); 2551 2552 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) { 2553 // Check om_in_use_list and om_in_use_count: 2554 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt); 2555 2556 // Check om_free_list and om_free_count: 2557 chk_per_thread_free_list_and_count(jt, ls, &error_cnt); 2558 } 2559 2560 if (error_cnt == 0) { 2561 ls->print_cr("No errors found in monitor list checks."); 2562 } else { 2563 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt); 2564 } 2565 2566 if ((on_exit && log_is_enabled(Info, monitorinflation)) || 2567 (!on_exit && log_is_enabled(Trace, monitorinflation))) { 2568 // When exiting this log output is at the Info level. When called 2569 // at a safepoint, this log output is at the Trace level since 2570 // there can be a lot of it. 2571 log_in_use_monitor_details(ls, on_exit); 2572 } 2573 2574 ls->flush(); 2575 2576 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt); 2577 } 2578 2579 // Check a free monitor entry; log any errors. 2580 void ObjectSynchronizer::chk_free_entry(JavaThread* jt, ObjectMonitor* n, 2581 outputStream * out, int *error_cnt_p) { 2582 stringStream ss; 2583 if (n->is_busy()) { 2584 if (jt != NULL) { 2585 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 2586 ": free per-thread monitor must not be busy: %s", p2i(jt), 2587 p2i(n), n->is_busy_to_string(&ss)); 2588 } else { 2589 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor " 2590 "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss)); 2591 } 2592 *error_cnt_p = *error_cnt_p + 1; 2593 } 2594 if (n->header().value() != 0) { 2595 if (jt != NULL) { 2596 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 2597 ": free per-thread monitor must have NULL _header " 2598 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n), 2599 n->header().value()); 2600 *error_cnt_p = *error_cnt_p + 1; 2601 } else if (!AsyncDeflateIdleMonitors) { 2602 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor " 2603 "must have NULL _header field: _header=" INTPTR_FORMAT, 2604 p2i(n), n->header().value()); 2605 *error_cnt_p = *error_cnt_p + 1; 2606 } 2607 } 2608 if (n->object() != NULL) { 2609 if (jt != NULL) { 2610 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 2611 ": free per-thread monitor must have NULL _object " 2612 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n), 2613 p2i(n->object())); 2614 } else { 2615 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor " 2616 "must have NULL _object field: _object=" INTPTR_FORMAT, 2617 p2i(n), p2i(n->object())); 2618 } 2619 *error_cnt_p = *error_cnt_p + 1; 2620 } 2621 } 2622 2623 // Check the global free list and count; log the results of the checks. 2624 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out, 2625 int *error_cnt_p) { 2626 int chk_om_free_count = 0; 2627 for (ObjectMonitor* n = g_free_list; n != NULL; n = n->_next_om) { 2628 chk_free_entry(NULL /* jt */, n, out, error_cnt_p); 2629 chk_om_free_count++; 2630 } 2631 if (g_om_free_count == chk_om_free_count) { 2632 out->print_cr("g_om_free_count=%d equals chk_om_free_count=%d", 2633 g_om_free_count, chk_om_free_count); 2634 } else { 2635 out->print_cr("ERROR: g_om_free_count=%d is not equal to " 2636 "chk_om_free_count=%d", g_om_free_count, 2637 chk_om_free_count); 2638 *error_cnt_p = *error_cnt_p + 1; 2639 } 2640 } 2641 2642 // Check the global in-use list and count; log the results of the checks. 2643 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out, 2644 int *error_cnt_p) { 2645 int chk_om_in_use_count = 0; 2646 for (ObjectMonitor* n = g_om_in_use_list; n != NULL; n = n->_next_om) { 2647 chk_in_use_entry(NULL /* jt */, n, out, error_cnt_p); 2648 chk_om_in_use_count++; 2649 } 2650 if (g_om_in_use_count == chk_om_in_use_count) { 2651 out->print_cr("g_om_in_use_count=%d equals chk_om_in_use_count=%d", g_om_in_use_count, 2652 chk_om_in_use_count); 2653 } else { 2654 out->print_cr("ERROR: g_om_in_use_count=%d is not equal to chk_om_in_use_count=%d", 2655 g_om_in_use_count, chk_om_in_use_count); 2656 *error_cnt_p = *error_cnt_p + 1; 2657 } 2658 } 2659 2660 // Check an in-use monitor entry; log any errors. 2661 void ObjectSynchronizer::chk_in_use_entry(JavaThread* jt, ObjectMonitor* n, 2662 outputStream * out, int *error_cnt_p) { 2663 if (n->header().value() == 0) { 2664 if (jt != NULL) { 2665 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 2666 ": in-use per-thread monitor must have non-NULL _header " 2667 "field.", p2i(jt), p2i(n)); 2668 } else { 2669 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor " 2670 "must have non-NULL _header field.", p2i(n)); 2671 } 2672 *error_cnt_p = *error_cnt_p + 1; 2673 } 2674 if (n->object() == NULL) { 2675 if (jt != NULL) { 2676 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 2677 ": in-use per-thread monitor must have non-NULL _object " 2678 "field.", p2i(jt), p2i(n)); 2679 } else { 2680 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor " 2681 "must have non-NULL _object field.", p2i(n)); 2682 } 2683 *error_cnt_p = *error_cnt_p + 1; 2684 } 2685 const oop obj = (oop)n->object(); 2686 const markWord mark = obj->mark(); 2687 if (!mark.has_monitor()) { 2688 if (jt != NULL) { 2689 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 2690 ": in-use per-thread monitor's object does not think " 2691 "it has a monitor: obj=" INTPTR_FORMAT ", mark=" 2692 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), mark.value()); 2693 } else { 2694 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global " 2695 "monitor's object does not think it has a monitor: obj=" 2696 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n), 2697 p2i(obj), mark.value()); 2698 } 2699 *error_cnt_p = *error_cnt_p + 1; 2700 } 2701 ObjectMonitor* const obj_mon = mark.monitor(); 2702 if (n != obj_mon) { 2703 if (jt != NULL) { 2704 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 2705 ": in-use per-thread monitor's object does not refer " 2706 "to the same monitor: obj=" INTPTR_FORMAT ", mark=" 2707 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt), 2708 p2i(n), p2i(obj), mark.value(), p2i(obj_mon)); 2709 } else { 2710 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global " 2711 "monitor's object does not refer to the same monitor: obj=" 2712 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon=" 2713 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon)); 2714 } 2715 *error_cnt_p = *error_cnt_p + 1; 2716 } 2717 } 2718 2719 // Check the thread's free list and count; log the results of the checks. 2720 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt, 2721 outputStream * out, 2722 int *error_cnt_p) { 2723 int chk_om_free_count = 0; 2724 for (ObjectMonitor* n = jt->om_free_list; n != NULL; n = n->_next_om) { 2725 chk_free_entry(jt, n, out, error_cnt_p); 2726 chk_om_free_count++; 2727 } 2728 if (jt->om_free_count == chk_om_free_count) { 2729 out->print_cr("jt=" INTPTR_FORMAT ": om_free_count=%d equals " 2730 "chk_om_free_count=%d", p2i(jt), jt->om_free_count, chk_om_free_count); 2731 } else { 2732 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_free_count=%d is not " 2733 "equal to chk_om_free_count=%d", p2i(jt), jt->om_free_count, 2734 chk_om_free_count); 2735 *error_cnt_p = *error_cnt_p + 1; 2736 } 2737 } 2738 2739 // Check the thread's in-use list and count; log the results of the checks. 2740 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt, 2741 outputStream * out, 2742 int *error_cnt_p) { 2743 int chk_om_in_use_count = 0; 2744 for (ObjectMonitor* n = jt->om_in_use_list; n != NULL; n = n->_next_om) { 2745 chk_in_use_entry(jt, n, out, error_cnt_p); 2746 chk_om_in_use_count++; 2747 } 2748 if (jt->om_in_use_count == chk_om_in_use_count) { 2749 out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals " 2750 "chk_om_in_use_count=%d", p2i(jt), jt->om_in_use_count, 2751 chk_om_in_use_count); 2752 } else { 2753 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not " 2754 "equal to chk_om_in_use_count=%d", p2i(jt), jt->om_in_use_count, 2755 chk_om_in_use_count); 2756 *error_cnt_p = *error_cnt_p + 1; 2757 } 2758 } 2759 2760 // Log details about ObjectMonitors on the in-use lists. The 'BHL' 2761 // flags indicate why the entry is in-use, 'object' and 'object type' 2762 // indicate the associated object and its type. 2763 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out, 2764 bool on_exit) { 2765 if (!on_exit) { 2766 // Not at VM exit so grab the global list lock. 2767 Thread::muxAcquire(&gListLock, "log_in_use_monitor_details"); 2768 } 2769 2770 stringStream ss; 2771 if (g_om_in_use_count > 0) { 2772 out->print_cr("In-use global monitor info:"); 2773 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)"); 2774 out->print_cr("%18s %s %7s %18s %18s", 2775 "monitor", "BHL", "ref_cnt", "object", "object type"); 2776 out->print_cr("================== === ======= ================== =================="); 2777 for (ObjectMonitor* n = g_om_in_use_list; n != NULL; n = n->_next_om) { 2778 const oop obj = (oop) n->object(); 2779 const markWord mark = n->header(); 2780 ResourceMark rm; 2781 out->print(INTPTR_FORMAT " %d%d%d %7d " INTPTR_FORMAT " %s", 2782 p2i(n), n->is_busy() != 0, mark.hash() != 0, 2783 n->owner() != NULL, (int)n->ref_count(), p2i(obj), 2784 obj->klass()->external_name()); 2785 if (n->is_busy() != 0) { 2786 out->print(" (%s)", n->is_busy_to_string(&ss)); 2787 ss.reset(); 2788 } 2789 out->cr(); 2790 } 2791 } 2792 2793 if (!on_exit) { 2794 Thread::muxRelease(&gListLock); 2795 } 2796 2797 out->print_cr("In-use per-thread monitor info:"); 2798 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)"); 2799 out->print_cr("%18s %18s %s %7s %18s %18s", 2800 "jt", "monitor", "BHL", "ref_cnt", "object", "object type"); 2801 out->print_cr("================== ================== === ======= ================== =================="); 2802 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) { 2803 for (ObjectMonitor* n = jt->om_in_use_list; n != NULL; n = n->_next_om) { 2804 const oop obj = (oop) n->object(); 2805 const markWord mark = n->header(); 2806 ResourceMark rm; 2807 out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d %7d " 2808 INTPTR_FORMAT " %s", p2i(jt), p2i(n), n->is_busy() != 0, 2809 mark.hash() != 0, n->owner() != NULL, (int)n->ref_count(), 2810 p2i(obj), obj->klass()->external_name()); 2811 if (n->is_busy() != 0) { 2812 out->print(" (%s)", n->is_busy_to_string(&ss)); 2813 ss.reset(); 2814 } 2815 out->cr(); 2816 } 2817 } 2818 2819 out->flush(); 2820 } 2821 2822 // Log counts for the global and per-thread monitor lists and return 2823 // the population count. 2824 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) { 2825 int pop_count = 0; 2826 out->print_cr("%18s %10s %10s %10s", 2827 "Global Lists:", "InUse", "Free", "Total"); 2828 out->print_cr("================== ========== ========== =========="); 2829 out->print_cr("%18s %10d %10d %10d", "", 2830 g_om_in_use_count, g_om_free_count, g_om_population); 2831 pop_count += g_om_in_use_count + g_om_free_count; 2832 2833 out->print_cr("%18s %10s %10s %10s", 2834 "Per-Thread Lists:", "InUse", "Free", "Provision"); 2835 out->print_cr("================== ========== ========== =========="); 2836 2837 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) { 2838 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt), 2839 jt->om_in_use_count, jt->om_free_count, jt->om_free_provision); 2840 pop_count += jt->om_in_use_count + jt->om_free_count; 2841 } 2842 return pop_count; 2843 } 2844 2845 #ifndef PRODUCT 2846 2847 // Check if monitor belongs to the monitor cache 2848 // The list is grow-only so it's *relatively* safe to traverse 2849 // the list of extant blocks without taking a lock. 2850 2851 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) { 2852 PaddedObjectMonitor* block = OrderAccess::load_acquire(&g_block_list); 2853 while (block != NULL) { 2854 assert(block->object() == CHAINMARKER, "must be a block header"); 2855 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) { 2856 address mon = (address)monitor; 2857 address blk = (address)block; 2858 size_t diff = mon - blk; 2859 assert((diff % sizeof(PaddedObjectMonitor)) == 0, "must be aligned"); 2860 return 1; 2861 } 2862 block = (PaddedObjectMonitor*)block->_next_om; 2863 } 2864 return 0; 2865 } 2866 2867 #endif