1 /* 2 * Copyright (c) 1998, 2021, 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 "jfr/jfrEvents.hpp" 28 #include "gc/shared/suspendibleThreadSet.hpp" 29 #include "logging/log.hpp" 30 #include "logging/logStream.hpp" 31 #include "memory/allocation.inline.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/handshake.hpp" 41 #include "runtime/interfaceSupport.inline.hpp" 42 #include "runtime/lockStack.inline.hpp" 43 #include "runtime/mutexLocker.hpp" 44 #include "runtime/objectMonitor.hpp" 45 #include "runtime/objectMonitor.inline.hpp" 46 #include "runtime/os.inline.hpp" 47 #include "runtime/osThread.hpp" 48 #include "runtime/perfData.hpp" 49 #include "runtime/safepointMechanism.inline.hpp" 50 #include "runtime/safepointVerifiers.hpp" 51 #include "runtime/sharedRuntime.hpp" 52 #include "runtime/stubRoutines.hpp" 53 #include "runtime/synchronizer.hpp" 54 #include "runtime/thread.inline.hpp" 55 #include "runtime/timer.hpp" 56 #include "runtime/vframe.hpp" 57 #include "runtime/vmThread.hpp" 58 #include "utilities/align.hpp" 59 #include "utilities/dtrace.hpp" 60 #include "utilities/events.hpp" 61 #include "utilities/preserveException.hpp" 62 63 void MonitorList::add(ObjectMonitor* m) { 64 ObjectMonitor* head; 65 do { 66 head = Atomic::load(&_head); 67 m->set_next_om(head); 68 } while (Atomic::cmpxchg(&_head, head, m) != head); 69 70 size_t count = Atomic::add(&_count, 1u); 71 if (count > max()) { 72 Atomic::inc(&_max); 73 } 74 } 75 76 size_t MonitorList::count() const { 77 return Atomic::load(&_count); 78 } 79 80 size_t MonitorList::max() const { 81 return Atomic::load(&_max); 82 } 83 84 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated 85 // ObjectMonitors. Returns the number of unlinked ObjectMonitors. 86 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls, 87 elapsedTimer* timer_p, 88 GrowableArray<ObjectMonitor*>* unlinked_list) { 89 size_t unlinked_count = 0; 90 ObjectMonitor* prev = NULL; 91 ObjectMonitor* head = Atomic::load_acquire(&_head); 92 ObjectMonitor* m = head; 93 // The in-use list head can be NULL during the final audit. 94 while (m != NULL) { 95 if (m->is_being_async_deflated()) { 96 // Find next live ObjectMonitor. 97 ObjectMonitor* next = m; 98 do { 99 ObjectMonitor* next_next = next->next_om(); 100 unlinked_count++; 101 unlinked_list->append(next); 102 next = next_next; 103 if (unlinked_count >= (size_t)MonitorDeflationMax) { 104 // Reached the max so bail out on the gathering loop. 105 break; 106 } 107 } while (next != NULL && next->is_being_async_deflated()); 108 if (prev == NULL) { 109 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next); 110 if (prev_head != head) { 111 // Find new prev ObjectMonitor that just got inserted. 112 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) { 113 prev = n; 114 } 115 prev->set_next_om(next); 116 } 117 } else { 118 prev->set_next_om(next); 119 } 120 if (unlinked_count >= (size_t)MonitorDeflationMax) { 121 // Reached the max so bail out on the searching loop. 122 break; 123 } 124 m = next; 125 } else { 126 prev = m; 127 m = m->next_om(); 128 } 129 130 if (current->is_Java_thread()) { 131 // A JavaThread must check for a safepoint/handshake and honor it. 132 ObjectSynchronizer::chk_for_block_req(current->as_Java_thread(), "unlinking", 133 "unlinked_count", unlinked_count, 134 ls, timer_p); 135 } 136 } 137 Atomic::sub(&_count, unlinked_count); 138 return unlinked_count; 139 } 140 141 MonitorList::Iterator MonitorList::iterator() const { 142 return Iterator(Atomic::load_acquire(&_head)); 143 } 144 145 ObjectMonitor* MonitorList::Iterator::next() { 146 ObjectMonitor* current = _current; 147 _current = current->next_om(); 148 return current; 149 } 150 151 // The "core" versions of monitor enter and exit reside in this file. 152 // The interpreter and compilers contain specialized transliterated 153 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp 154 // fast_lock(...) for instance. If you make changes here, make sure to modify the 155 // interpreter, and both C1 and C2 fast-path inline locking code emission. 156 // 157 // ----------------------------------------------------------------------------- 158 159 #ifdef DTRACE_ENABLED 160 161 // Only bother with this argument setup if dtrace is available 162 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly. 163 164 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \ 165 char* bytes = NULL; \ 166 int len = 0; \ 167 jlong jtid = SharedRuntime::get_java_tid(thread); \ 168 Symbol* klassname = obj->klass()->name(); \ 169 if (klassname != NULL) { \ 170 bytes = (char*)klassname->bytes(); \ 171 len = klassname->utf8_length(); \ 172 } 173 174 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \ 175 { \ 176 if (DTraceMonitorProbes) { \ 177 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 178 HOTSPOT_MONITOR_WAIT(jtid, \ 179 (uintptr_t)(monitor), bytes, len, (millis)); \ 180 } \ 181 } 182 183 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY 184 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL 185 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED 186 187 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \ 188 { \ 189 if (DTraceMonitorProbes) { \ 190 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 191 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \ 192 (uintptr_t)(monitor), bytes, len); \ 193 } \ 194 } 195 196 #else // ndef DTRACE_ENABLED 197 198 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;} 199 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;} 200 201 #endif // ndef DTRACE_ENABLED 202 203 // This exists only as a workaround of dtrace bug 6254741 204 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) { 205 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr); 206 return 0; 207 } 208 209 static const int NINFLATIONLOCKS = 256; 210 static os::PlatformMutex* gInflationLocks[NINFLATIONLOCKS]; 211 212 void ObjectSynchronizer::initialize() { 213 for (int i = 0; i < NINFLATIONLOCKS; i++) { 214 gInflationLocks[i] = new os::PlatformMutex(); 215 } 216 // Start the ceiling with the estimate for one thread. 217 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate); 218 } 219 220 MonitorList ObjectSynchronizer::_in_use_list; 221 // monitors_used_above_threshold() policy is as follows: 222 // 223 // The ratio of the current _in_use_list count to the ceiling is used 224 // to determine if we are above MonitorUsedDeflationThreshold and need 225 // to do an async monitor deflation cycle. The ceiling is increased by 226 // AvgMonitorsPerThreadEstimate when a thread is added to the system 227 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is 228 // removed from the system. 229 // 230 // Note: If the _in_use_list max exceeds the ceiling, then 231 // monitors_used_above_threshold() will use the in_use_list max instead 232 // of the thread count derived ceiling because we have used more 233 // ObjectMonitors than the estimated average. 234 // 235 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax 236 // no-progress async monitor deflation cycles in a row, then the ceiling 237 // is adjusted upwards by monitors_used_above_threshold(). 238 // 239 // Start the ceiling with the estimate for one thread in initialize() 240 // which is called after cmd line options are processed. 241 static size_t _in_use_list_ceiling = 0; 242 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false; 243 bool volatile ObjectSynchronizer::_is_final_audit = false; 244 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0; 245 static uintx _no_progress_cnt = 0; 246 247 // =====================> Quick functions 248 249 // The quick_* forms are special fast-path variants used to improve 250 // performance. In the simplest case, a "quick_*" implementation could 251 // simply return false, in which case the caller will perform the necessary 252 // state transitions and call the slow-path form. 253 // The fast-path is designed to handle frequently arising cases in an efficient 254 // manner and is just a degenerate "optimistic" variant of the slow-path. 255 // returns true -- to indicate the call was satisfied. 256 // returns false -- to indicate the call needs the services of the slow-path. 257 // A no-loitering ordinance is in effect for code in the quick_* family 258 // operators: safepoints or indefinite blocking (blocking that might span a 259 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon 260 // entry. 261 // 262 // Consider: An interesting optimization is to have the JIT recognize the 263 // following common idiom: 264 // synchronized (someobj) { .... ; notify(); } 265 // That is, we find a notify() or notifyAll() call that immediately precedes 266 // the monitorexit operation. In that case the JIT could fuse the operations 267 // into a single notifyAndExit() runtime primitive. 268 269 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) { 270 assert(current->thread_state() == _thread_in_Java, "invariant"); 271 NoSafepointVerifier nsv; 272 if (obj == NULL) return false; // slow-path for invalid obj 273 const markWord mark = obj->mark(); 274 275 if ((mark.is_fast_locked() && current->lock_stack().contains(oop(obj))) || 276 (mark.has_locker() && current->is_lock_owned((address)mark.locker()))) { 277 // Degenerate notify 278 // stack-locked by caller so by definition the implied waitset is empty. 279 return true; 280 } 281 282 if (mark.has_monitor()) { 283 ObjectMonitor* const mon = mark.monitor(); 284 assert(mon->object() == oop(obj), "invariant"); 285 if (mon->owner() != current) return false; // slow-path for IMS exception 286 287 if (mon->first_waiter() != NULL) { 288 // We have one or more waiters. Since this is an inflated monitor 289 // that we own, we can transfer one or more threads from the waitset 290 // to the entrylist here and now, avoiding the slow-path. 291 if (all) { 292 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current); 293 } else { 294 DTRACE_MONITOR_PROBE(notify, mon, obj, current); 295 } 296 int free_count = 0; 297 do { 298 mon->INotify(current); 299 ++free_count; 300 } while (mon->first_waiter() != NULL && all); 301 OM_PERFDATA_OP(Notifications, inc(free_count)); 302 } 303 return true; 304 } 305 306 // biased locking and any other IMS exception states take the slow-path 307 return false; 308 } 309 310 311 // The LockNode emitted directly at the synchronization site would have 312 // been too big if it were to have included support for the cases of inflated 313 // recursive enter and exit, so they go here instead. 314 // Note that we can't safely call AsyncPrintJavaStack() from within 315 // quick_enter() as our thread state remains _in_Java. 316 317 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current, 318 BasicLock * lock) { 319 assert(current->thread_state() == _thread_in_Java, "invariant"); 320 NoSafepointVerifier nsv; 321 if (obj == NULL) return false; // Need to throw NPE 322 323 if (obj->klass()->is_value_based()) { 324 return false; 325 } 326 327 const markWord mark = obj->mark(); 328 329 if (mark.has_monitor()) { 330 ObjectMonitor* const m = mark.monitor(); 331 // An async deflation or GC can race us before we manage to make 332 // the ObjectMonitor busy by setting the owner below. If we detect 333 // that race we just bail out to the slow-path here. 334 if (m->object_peek() == NULL) { 335 return false; 336 } 337 JavaThread* const owner = (JavaThread*) m->owner_raw(); 338 339 // Lock contention and Transactional Lock Elision (TLE) diagnostics 340 // and observability 341 // Case: light contention possibly amenable to TLE 342 // Case: TLE inimical operations such as nested/recursive synchronization 343 344 if (owner == current) { 345 m->_recursions++; 346 return true; 347 } 348 349 // This Java Monitor is inflated so obj's header will never be 350 // displaced to this thread's BasicLock. Make the displaced header 351 // non-NULL so this BasicLock is not seen as recursive nor as 352 // being locked. We do this unconditionally so that this thread's 353 // BasicLock cannot be mis-interpreted by any stack walkers. For 354 // performance reasons, stack walkers generally first check for 355 // Biased Locking in the object's header, the second check is for 356 // stack-locking in the object's header, the third check is for 357 // recursive stack-locking in the displaced header in the BasicLock, 358 // and last are the inflated Java Monitor (ObjectMonitor) checks. 359 if (!UseFastLocking) { 360 lock->set_displaced_header(markWord::unused_mark()); 361 } 362 363 if (owner == NULL && m->try_set_owner_from(NULL, current) == NULL) { 364 assert(m->_recursions == 0, "invariant"); 365 return true; 366 } 367 } 368 369 // Note that we could inflate in quick_enter. 370 // This is likely a useful optimization 371 // Critically, in quick_enter() we must not: 372 // -- perform bias revocation, or 373 // -- block indefinitely, or 374 // -- reach a safepoint 375 376 return false; // revert to slow-path 377 } 378 379 // Handle notifications when synchronizing on value based classes 380 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) { 381 frame last_frame = current->last_frame(); 382 bool bcp_was_adjusted = false; 383 // Don't decrement bcp if it points to the frame's first instruction. This happens when 384 // handle_sync_on_value_based_class() is called because of a synchronized method. There 385 // is no actual monitorenter instruction in the byte code in this case. 386 if (last_frame.is_interpreted_frame() && 387 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) { 388 // adjust bcp to point back to monitorenter so that we print the correct line numbers 389 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1); 390 bcp_was_adjusted = true; 391 } 392 393 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) { 394 ResourceMark rm(current); 395 stringStream ss; 396 current->print_stack_on(&ss); 397 char* base = (char*)strstr(ss.base(), "at"); 398 char* newline = (char*)strchr(ss.base(), '\n'); 399 if (newline != NULL) { 400 *newline = '\0'; 401 } 402 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base); 403 } else { 404 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses"); 405 ResourceMark rm(current); 406 Log(valuebasedclasses) vblog; 407 408 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name()); 409 if (current->has_last_Java_frame()) { 410 LogStream info_stream(vblog.info()); 411 current->print_stack_on(&info_stream); 412 } else { 413 vblog.info("Cannot find the last Java frame"); 414 } 415 416 EventSyncOnValueBasedClass event; 417 if (event.should_commit()) { 418 event.set_valueBasedClass(obj->klass()); 419 event.commit(); 420 } 421 } 422 423 if (bcp_was_adjusted) { 424 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1); 425 } 426 } 427 428 // ----------------------------------------------------------------------------- 429 // Monitor Enter/Exit 430 // The interpreter and compiler assembly code tries to lock using the fast path 431 // of this algorithm. Make sure to update that code if the following function is 432 // changed. The implementation is extremely sensitive to race condition. Be careful. 433 434 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) { 435 if (obj->klass()->is_value_based()) { 436 handle_sync_on_value_based_class(obj, current); 437 } 438 439 if (UseFastLocking) { 440 LockStack& lock_stack = current->lock_stack(); 441 442 markWord header = obj()->mark_acquire(); 443 while (true) { 444 if (header.is_neutral()) { 445 assert(!lock_stack.contains(obj()), "thread must not already hold the lock"); 446 // Try to swing into 'fast-locked' state without inflating. 447 markWord locked_header = header.set_fast_locked(); 448 markWord witness = obj()->cas_set_mark(locked_header, header); 449 if (witness == header) { 450 // Successfully fast-locked, push object to lock-stack and return. 451 lock_stack.push(obj()); 452 return; 453 } 454 // Otherwise retry. 455 header = witness; 456 } else { 457 // Fall-through to inflate-enter. 458 break; 459 } 460 } 461 } else { 462 if (UseBiasedLocking) { 463 BiasedLocking::revoke(current, obj); 464 } 465 466 markWord mark = obj->mark(); 467 if (mark.is_neutral()) { 468 // Anticipate successful CAS -- the ST of the displaced mark must 469 // be visible <= the ST performed by the CAS. 470 lock->set_displaced_header(mark); 471 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) { 472 return; 473 } 474 // Fall through to inflate() ... 475 } else if (mark.has_locker() && 476 current->is_lock_owned((address) mark.locker())) { 477 assert(lock != mark.locker(), "must not re-lock the same lock"); 478 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock"); 479 lock->set_displaced_header(markWord::from_pointer(NULL)); 480 return; 481 } 482 483 // The object header will never be displaced to this lock, 484 // so it does not matter what the value is, except that it 485 // must be non-zero to avoid looking like a re-entrant lock, 486 // and must not look locked either. 487 lock->set_displaced_header(markWord::unused_mark()); 488 } 489 490 // An async deflation can race after the inflate() call and before 491 // enter() can make the ObjectMonitor busy. enter() returns false if 492 // we have lost the race to async deflation and we simply try again. 493 while (true) { 494 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter); 495 if (monitor->enter(current)) { 496 return; 497 } 498 } 499 } 500 501 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) { 502 markWord mark = object->mark(); 503 if (UseFastLocking) { 504 if (mark.is_fast_locked()) { 505 markWord unlocked_header = mark.set_unlocked(); 506 markWord witness = object->cas_set_mark(unlocked_header, mark); 507 if (witness != mark) { 508 // Another thread beat us, it can only have installed an anonymously locked monitor at this point. 509 // Fetch that monitor, set owner correctly to this thread, and exit it (allowing waiting threads to enter). 510 assert(witness.has_monitor(), "must have monitor"); 511 ObjectMonitor* monitor = witness.monitor(); 512 assert(monitor->is_owner_anonymous(), "must be anonymous owner"); 513 monitor->set_owner_from_anonymous(current); 514 monitor->exit(current); 515 } 516 LockStack& lock_stack = current->lock_stack(); 517 lock_stack.remove(object); 518 return; 519 } 520 } else { 521 markWord dhw = lock->displaced_header(); 522 if (dhw.value() == 0) { 523 // If the displaced header is NULL, then this exit matches up with 524 // a recursive enter. No real work to do here except for diagnostics. 525 #ifndef PRODUCT 526 if (mark != markWord::INFLATING()) { 527 // Only do diagnostics if we are not racing an inflation. Simply 528 // exiting a recursive enter of a Java Monitor that is being 529 // inflated is safe; see the has_monitor() comment below. 530 assert(!mark.is_neutral(), "invariant"); 531 assert(!mark.has_locker() || 532 current->is_lock_owned((address)mark.locker()), "invariant"); 533 if (mark.has_monitor()) { 534 // The BasicLock's displaced_header is marked as a recursive 535 // enter and we have an inflated Java Monitor (ObjectMonitor). 536 // This is a special case where the Java Monitor was inflated 537 // after this thread entered the stack-lock recursively. When a 538 // Java Monitor is inflated, we cannot safely walk the Java 539 // Monitor owner's stack and update the BasicLocks because a 540 // Java Monitor can be asynchronously inflated by a thread that 541 // does not own the Java Monitor. 542 ObjectMonitor* m = mark.monitor(); 543 assert(m->object()->mark() == mark, "invariant"); 544 assert(m->is_entered(current), "invariant"); 545 } 546 } 547 #endif 548 return; 549 } 550 551 if (mark == markWord::from_pointer(lock)) { 552 // If the object is stack-locked by the current thread, try to 553 // swing the displaced header from the BasicLock back to the mark. 554 assert(dhw.is_neutral(), "invariant"); 555 if (object->cas_set_mark(dhw, mark) == mark) { 556 return; 557 } 558 } 559 } 560 561 // We have to take the slow-path of possible inflation and then exit. 562 // The ObjectMonitor* can't be async deflated until ownership is 563 // dropped inside exit() and the ObjectMonitor* must be !is_busy(). 564 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal); 565 if (UseFastLocking && monitor->is_owner_anonymous()) { 566 // It must be us. Pop lock object from lock stack. 567 LockStack& lock_stack = current->lock_stack(); 568 oop popped = lock_stack.pop(); 569 assert(popped == object, "must be owned by this thread"); 570 monitor->set_owner_from_anonymous(current); 571 } 572 monitor->exit(current); 573 } 574 575 // ----------------------------------------------------------------------------- 576 // Class Loader support to workaround deadlocks on the class loader lock objects 577 // Also used by GC 578 // complete_exit()/reenter() are used to wait on a nested lock 579 // i.e. to give up an outer lock completely and then re-enter 580 // Used when holding nested locks - lock acquisition order: lock1 then lock2 581 // 1) complete_exit lock1 - saving recursion count 582 // 2) wait on lock2 583 // 3) when notified on lock2, unlock lock2 584 // 4) reenter lock1 with original recursion count 585 // 5) lock lock2 586 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 587 intx ObjectSynchronizer::complete_exit(Handle obj, JavaThread* current) { 588 if (UseBiasedLocking) { 589 BiasedLocking::revoke(current, obj); 590 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 591 } 592 593 // The ObjectMonitor* can't be async deflated until ownership is 594 // dropped inside exit() and the ObjectMonitor* must be !is_busy(). 595 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal); 596 intptr_t ret_code = monitor->complete_exit(current); 597 return ret_code; 598 } 599 600 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 601 void ObjectSynchronizer::reenter(Handle obj, intx recursions, JavaThread* current) { 602 if (UseBiasedLocking) { 603 BiasedLocking::revoke(current, obj); 604 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 605 } 606 607 // An async deflation can race after the inflate() call and before 608 // reenter() -> enter() can make the ObjectMonitor busy. reenter() -> 609 // enter() returns false if we have lost the race to async deflation 610 // and we simply try again. 611 while (true) { 612 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal); 613 if (monitor->reenter(recursions, current)) { 614 return; 615 } 616 } 617 } 618 619 // ----------------------------------------------------------------------------- 620 // JNI locks on java objects 621 // NOTE: must use heavy weight monitor to handle jni monitor enter 622 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) { 623 if (obj->klass()->is_value_based()) { 624 handle_sync_on_value_based_class(obj, current); 625 } 626 627 // the current locking is from JNI instead of Java code 628 if (UseBiasedLocking) { 629 BiasedLocking::revoke(current, obj); 630 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 631 } 632 current->set_current_pending_monitor_is_from_java(false); 633 // An async deflation can race after the inflate() call and before 634 // enter() can make the ObjectMonitor busy. enter() returns false if 635 // we have lost the race to async deflation and we simply try again. 636 while (true) { 637 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter); 638 if (monitor->enter(current)) { 639 break; 640 } 641 } 642 current->set_current_pending_monitor_is_from_java(true); 643 } 644 645 // NOTE: must use heavy weight monitor to handle jni monitor exit 646 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) { 647 JavaThread* current = THREAD; 648 if (UseBiasedLocking) { 649 Handle h_obj(current, obj); 650 BiasedLocking::revoke(current, h_obj); 651 obj = h_obj(); 652 } 653 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 654 655 // The ObjectMonitor* can't be async deflated until ownership is 656 // dropped inside exit() and the ObjectMonitor* must be !is_busy(). 657 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit); 658 // If this thread has locked the object, exit the monitor. We 659 // intentionally do not use CHECK on check_owner because we must exit the 660 // monitor even if an exception was already pending. 661 if (monitor->check_owner(THREAD)) { 662 monitor->exit(current); 663 } 664 } 665 666 // ----------------------------------------------------------------------------- 667 // Internal VM locks on java objects 668 // standard constructor, allows locking failures 669 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) { 670 _thread = thread; 671 _thread->check_for_valid_safepoint_state(); 672 _obj = obj; 673 674 if (_obj() != NULL) { 675 ObjectSynchronizer::enter(_obj, &_lock, _thread); 676 } 677 } 678 679 ObjectLocker::~ObjectLocker() { 680 if (_obj() != NULL) { 681 ObjectSynchronizer::exit(_obj(), &_lock, _thread); 682 } 683 } 684 685 686 // ----------------------------------------------------------------------------- 687 // Wait/Notify/NotifyAll 688 // NOTE: must use heavy weight monitor to handle wait() 689 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) { 690 JavaThread* current = THREAD; 691 if (UseBiasedLocking) { 692 BiasedLocking::revoke(current, obj); 693 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 694 } 695 if (millis < 0) { 696 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); 697 } 698 // The ObjectMonitor* can't be async deflated because the _waiters 699 // field is incremented before ownership is dropped and decremented 700 // after ownership is regained. 701 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait); 702 703 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis); 704 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code 705 706 // This dummy call is in place to get around dtrace bug 6254741. Once 707 // that's fixed we can uncomment the following line, remove the call 708 // and change this function back into a "void" func. 709 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD); 710 int ret_code = dtrace_waited_probe(monitor, obj, THREAD); 711 return ret_code; 712 } 713 714 // No exception are possible in this case as we only use this internally when locking is 715 // correct and we have to wait until notified - so no interrupts or timeouts. 716 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, JavaThread* current) { 717 if (UseBiasedLocking) { 718 BiasedLocking::revoke(current, obj); 719 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 720 } 721 // The ObjectMonitor* can't be async deflated because the _waiters 722 // field is incremented before ownership is dropped and decremented 723 // after ownership is regained. 724 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait); 725 monitor->wait(0 /* wait-forever */, false /* not interruptible */, current); 726 } 727 728 void ObjectSynchronizer::notify(Handle obj, TRAPS) { 729 JavaThread* current = THREAD; 730 if (UseBiasedLocking) { 731 BiasedLocking::revoke(current, obj); 732 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 733 } 734 735 markWord mark = obj->mark(); 736 if ((mark.is_fast_locked() && current->lock_stack().contains(obj())) || 737 (mark.has_locker() && current->is_lock_owned((address)mark.locker()))) { 738 // Not inflated so there can't be any waiters to notify. 739 return; 740 } 741 // The ObjectMonitor* can't be async deflated until ownership is 742 // dropped by the calling thread. 743 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify); 744 monitor->notify(CHECK); 745 } 746 747 // NOTE: see comment of notify() 748 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) { 749 JavaThread* current = THREAD; 750 if (UseBiasedLocking) { 751 BiasedLocking::revoke(current, obj); 752 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 753 } 754 755 markWord mark = obj->mark(); 756 if ((mark.is_fast_locked() && current->lock_stack().contains(obj())) || 757 (mark.has_locker() && current->is_lock_owned((address)mark.locker()))) { 758 // Not inflated so there can't be any waiters to notify. 759 return; 760 } 761 // The ObjectMonitor* can't be async deflated until ownership is 762 // dropped by the calling thread. 763 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify); 764 monitor->notifyAll(CHECK); 765 } 766 767 // ----------------------------------------------------------------------------- 768 // Hash Code handling 769 770 struct SharedGlobals { 771 char _pad_prefix[OM_CACHE_LINE_SIZE]; 772 // This is a highly shared mostly-read variable. 773 // To avoid false-sharing it needs to be the sole occupant of a cache line. 774 volatile int stw_random; 775 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int)); 776 // Hot RW variable -- Sequester to avoid false-sharing 777 volatile int hc_sequence; 778 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int)); 779 }; 780 781 static SharedGlobals GVars; 782 783 static markWord read_stable_mark(oop obj) { 784 markWord mark = obj->mark(); 785 if (!mark.is_being_inflated() || UseFastLocking) { 786 return mark; // normal fast-path return 787 } 788 789 int its = 0; 790 for (;;) { 791 markWord mark = obj->mark(); 792 if (!mark.is_being_inflated()) { 793 return mark; // normal fast-path return 794 } 795 796 // The object is being inflated by some other thread. 797 // The caller of read_stable_mark() must wait for inflation to complete. 798 // Avoid live-lock. 799 800 ++its; 801 if (its > 10000 || !os::is_MP()) { 802 if (its & 1) { 803 os::naked_yield(); 804 } else { 805 // Note that the following code attenuates the livelock problem but is not 806 // a complete remedy. A more complete solution would require that the inflating 807 // thread hold the associated inflation lock. The following code simply restricts 808 // the number of spinners to at most one. We'll have N-2 threads blocked 809 // on the inflationlock, 1 thread holding the inflation lock and using 810 // a yield/park strategy, and 1 thread in the midst of inflation. 811 // A more refined approach would be to change the encoding of INFLATING 812 // to allow encapsulation of a native thread pointer. Threads waiting for 813 // inflation to complete would use CAS to push themselves onto a singly linked 814 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag 815 // and calling park(). When inflation was complete the thread that accomplished inflation 816 // would detach the list and set the markword to inflated with a single CAS and 817 // then for each thread on the list, set the flag and unpark() the thread. 818 819 // Index into the lock array based on the current object address. 820 static_assert(is_power_of_2(NINFLATIONLOCKS), "must be"); 821 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1); 822 int YieldThenBlock = 0; 823 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant"); 824 gInflationLocks[ix]->lock(); 825 while (obj->mark() == markWord::INFLATING()) { 826 // Beware: naked_yield() is advisory and has almost no effect on some platforms 827 // so we periodically call current->_ParkEvent->park(1). 828 // We use a mixed spin/yield/block mechanism. 829 if ((YieldThenBlock++) >= 16) { 830 Thread::current()->_ParkEvent->park(1); 831 } else { 832 os::naked_yield(); 833 } 834 } 835 gInflationLocks[ix]->unlock(); 836 } 837 } else { 838 SpinPause(); // SMP-polite spinning 839 } 840 } 841 } 842 843 // hashCode() generation : 844 // 845 // Possibilities: 846 // * MD5Digest of {obj,stw_random} 847 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function. 848 // * A DES- or AES-style SBox[] mechanism 849 // * One of the Phi-based schemes, such as: 850 // 2654435761 = 2^32 * Phi (golden ratio) 851 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ; 852 // * A variation of Marsaglia's shift-xor RNG scheme. 853 // * (obj ^ stw_random) is appealing, but can result 854 // in undesirable regularity in the hashCode values of adjacent objects 855 // (objects allocated back-to-back, in particular). This could potentially 856 // result in hashtable collisions and reduced hashtable efficiency. 857 // There are simple ways to "diffuse" the middle address bits over the 858 // generated hashCode values: 859 860 static inline intptr_t get_next_hash(Thread* current, oop obj) { 861 intptr_t value = 0; 862 if (hashCode == 0) { 863 // This form uses global Park-Miller RNG. 864 // On MP system we'll have lots of RW access to a global, so the 865 // mechanism induces lots of coherency traffic. 866 value = os::random(); 867 } else if (hashCode == 1) { 868 // This variation has the property of being stable (idempotent) 869 // between STW operations. This can be useful in some of the 1-0 870 // synchronization schemes. 871 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3; 872 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random; 873 } else if (hashCode == 2) { 874 value = 1; // for sensitivity testing 875 } else if (hashCode == 3) { 876 value = ++GVars.hc_sequence; 877 } else if (hashCode == 4) { 878 value = cast_from_oop<intptr_t>(obj); 879 } else { 880 // Marsaglia's xor-shift scheme with thread-specific state 881 // This is probably the best overall implementation -- we'll 882 // likely make this the default in future releases. 883 unsigned t = current->_hashStateX; 884 t ^= (t << 11); 885 current->_hashStateX = current->_hashStateY; 886 current->_hashStateY = current->_hashStateZ; 887 current->_hashStateZ = current->_hashStateW; 888 unsigned v = current->_hashStateW; 889 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)); 890 current->_hashStateW = v; 891 value = v; 892 } 893 894 value &= markWord::hash_mask; 895 if (value == 0) value = 0xBAD; 896 assert(value != markWord::no_hash, "invariant"); 897 return value; 898 } 899 900 static bool is_lock_owned(Thread* thread, oop obj) { 901 assert(UseFastLocking, "only call this with fast-locking enabled"); 902 return thread->is_Java_thread() ? reinterpret_cast<JavaThread*>(thread)->lock_stack().contains(obj) : false; 903 } 904 905 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) { 906 if (UseBiasedLocking) { 907 // NOTE: many places throughout the JVM do not expect a safepoint 908 // to be taken here. However, we only ever bias Java instances and all 909 // of the call sites of identity_hash that might revoke biases have 910 // been checked to make sure they can handle a safepoint. The 911 // added check of the bias pattern is to avoid useless calls to 912 // thread-local storage. 913 if (obj->mark().has_bias_pattern()) { 914 // Handle for oop obj in case of STW safepoint 915 Handle hobj(current, obj); 916 if (SafepointSynchronize::is_at_safepoint()) { 917 BiasedLocking::revoke_at_safepoint(hobj); 918 } else { 919 BiasedLocking::revoke(current->as_Java_thread(), hobj); 920 } 921 obj = hobj(); 922 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 923 } 924 } 925 926 while (true) { 927 ObjectMonitor* monitor = NULL; 928 markWord temp, test; 929 intptr_t hash; 930 markWord mark = read_stable_mark(obj); 931 932 // object should remain ineligible for biased locking 933 assert(!mark.has_bias_pattern(), "invariant"); 934 935 if (mark.is_neutral()) { // if this is a normal header 936 hash = mark.hash(); 937 if (hash != 0) { // if it has a hash, just return it 938 return hash; 939 } 940 hash = get_next_hash(current, obj); // get a new hash 941 temp = mark.copy_set_hash(hash); // merge the hash into header 942 // try to install the hash 943 test = obj->cas_set_mark(temp, mark); 944 if (test == mark) { // if the hash was installed, return it 945 return hash; 946 } 947 // Failed to install the hash. It could be that another thread 948 // installed the hash just before our attempt or inflation has 949 // occurred or... so we fall thru to inflate the monitor for 950 // stability and then install the hash. 951 } else if (mark.has_monitor()) { 952 monitor = mark.monitor(); 953 temp = monitor->header(); 954 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 955 hash = temp.hash(); 956 if (hash != 0) { 957 // It has a hash. 958 959 // Separate load of dmw/header above from the loads in 960 // is_being_async_deflated(). 961 962 // dmw/header and _contentions may get written by different threads. 963 // Make sure to observe them in the same order when having several observers. 964 OrderAccess::loadload_for_IRIW(); 965 966 if (monitor->is_being_async_deflated()) { 967 // But we can't safely use the hash if we detect that async 968 // deflation has occurred. So we attempt to restore the 969 // header/dmw to the object's header so that we only retry 970 // once if the deflater thread happens to be slow. 971 monitor->install_displaced_markword_in_object(obj); 972 continue; 973 } 974 return hash; 975 } 976 // Fall thru so we only have one place that installs the hash in 977 // the ObjectMonitor. 978 } else if (mark.is_fast_locked() && is_lock_owned(current, obj)) { 979 // This is a fast lock owned by the calling thread so use the 980 // markWord from the object. 981 hash = mark.hash(); 982 if (hash != 0) { // if it has a hash, just return it 983 return hash; 984 } 985 } else if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) { 986 // This is a stack lock owned by the calling thread so fetch the 987 // displaced markWord from the BasicLock on the stack. 988 temp = mark.displaced_mark_helper(); 989 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 990 hash = temp.hash(); 991 if (hash != 0) { // if it has a hash, just return it 992 return hash; 993 } 994 // WARNING: 995 // The displaced header in the BasicLock on a thread's stack 996 // is strictly immutable. It CANNOT be changed in ANY cases. 997 // So we have to inflate the stack lock into an ObjectMonitor 998 // even if the current thread owns the lock. The BasicLock on 999 // a thread's stack can be asynchronously read by other threads 1000 // during an inflate() call so any change to that stack memory 1001 // may not propagate to other threads correctly. 1002 } 1003 1004 // Inflate the monitor to set the hash. 1005 1006 // An async deflation can race after the inflate() call and before we 1007 // can update the ObjectMonitor's header with the hash value below. 1008 monitor = inflate(current, obj, inflate_cause_hash_code); 1009 // Load ObjectMonitor's header/dmw field and see if it has a hash. 1010 mark = monitor->header(); 1011 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value()); 1012 hash = mark.hash(); 1013 if (hash == 0) { // if it does not have a hash 1014 hash = get_next_hash(current, obj); // get a new hash 1015 temp = mark.copy_set_hash(hash) ; // merge the hash into header 1016 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 1017 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value()); 1018 test = markWord(v); 1019 if (test != mark) { 1020 // The attempt to update the ObjectMonitor's header/dmw field 1021 // did not work. This can happen if another thread managed to 1022 // merge in the hash just before our cmpxchg(). 1023 // If we add any new usages of the header/dmw field, this code 1024 // will need to be updated. 1025 hash = test.hash(); 1026 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value()); 1027 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash"); 1028 } 1029 if (monitor->is_being_async_deflated()) { 1030 // If we detect that async deflation has occurred, then we 1031 // attempt to restore the header/dmw to the object's header 1032 // so that we only retry once if the deflater thread happens 1033 // to be slow. 1034 monitor->install_displaced_markword_in_object(obj); 1035 continue; 1036 } 1037 } 1038 // We finally get the hash. 1039 return hash; 1040 } 1041 } 1042 1043 // Deprecated -- use FastHashCode() instead. 1044 1045 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) { 1046 return FastHashCode(Thread::current(), obj()); 1047 } 1048 1049 1050 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current, 1051 Handle h_obj) { 1052 if (UseBiasedLocking) { 1053 BiasedLocking::revoke(current, h_obj); 1054 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now"); 1055 } 1056 1057 assert(current == JavaThread::current(), "Can only be called on current thread"); 1058 oop obj = h_obj(); 1059 1060 markWord mark = read_stable_mark(obj); 1061 1062 // Uncontended case, header points to stack 1063 if (mark.has_locker()) { 1064 return current->is_lock_owned((address)mark.locker()); 1065 } 1066 1067 // Fast-locking case. 1068 if (mark.is_fast_locked()) { 1069 return current->lock_stack().contains(h_obj()); 1070 } 1071 1072 // Contended case, header points to ObjectMonitor (tagged pointer) 1073 if (mark.has_monitor()) { 1074 // The first stage of async deflation does not affect any field 1075 // used by this comparison so the ObjectMonitor* is usable here. 1076 ObjectMonitor* monitor = mark.monitor(); 1077 return monitor->is_entered(current) != 0; 1078 } 1079 // Unlocked case, header in place 1080 assert(mark.is_neutral(), "sanity check"); 1081 return false; 1082 } 1083 1084 // FIXME: jvmti should call this 1085 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) { 1086 if (UseBiasedLocking) { 1087 if (SafepointSynchronize::is_at_safepoint()) { 1088 BiasedLocking::revoke_at_safepoint(h_obj); 1089 } else { 1090 BiasedLocking::revoke(JavaThread::current(), h_obj); 1091 } 1092 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now"); 1093 } 1094 1095 oop obj = h_obj(); 1096 markWord mark = read_stable_mark(obj); 1097 1098 // Uncontended case, header points to stack 1099 if (mark.has_locker()) { 1100 return Threads::owning_thread_from_monitor_owner(t_list, (address) mark.locker()); 1101 } 1102 1103 if (mark.is_fast_locked()) { 1104 return Threads::owning_thread_from_object(t_list, h_obj()); 1105 } 1106 1107 // Contended case, header points to ObjectMonitor (tagged pointer) 1108 if (mark.has_monitor()) { 1109 // The first stage of async deflation does not affect any field 1110 // used by this comparison so the ObjectMonitor* is usable here. 1111 ObjectMonitor* monitor = mark.monitor(); 1112 assert(monitor != NULL, "monitor should be non-null"); 1113 return Threads::owning_thread_from_monitor(t_list, monitor); 1114 } 1115 1116 return NULL; 1117 } 1118 1119 // Visitors ... 1120 1121 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) { 1122 MonitorList::Iterator iter = _in_use_list.iterator(); 1123 while (iter.has_next()) { 1124 ObjectMonitor* mid = iter.next(); 1125 if (mid->owner() != thread) { 1126 continue; 1127 } 1128 if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) { 1129 // Only process with closure if the object is set. 1130 1131 // monitors_iterate() is only called at a safepoint or when the 1132 // target thread is suspended or when the target thread is 1133 // operating on itself. The current closures in use today are 1134 // only interested in an owned ObjectMonitor and ownership 1135 // cannot be dropped under the calling contexts so the 1136 // ObjectMonitor cannot be async deflated. 1137 closure->do_monitor(mid); 1138 } 1139 } 1140 } 1141 1142 static bool monitors_used_above_threshold(MonitorList* list) { 1143 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy 1144 return false; 1145 } 1146 // Start with ceiling based on a per-thread estimate: 1147 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling(); 1148 size_t old_ceiling = ceiling; 1149 if (ceiling < list->max()) { 1150 // The max used by the system has exceeded the ceiling so use that: 1151 ceiling = list->max(); 1152 } 1153 size_t monitors_used = list->count(); 1154 if (monitors_used == 0) { // empty list is easy 1155 return false; 1156 } 1157 if (NoAsyncDeflationProgressMax != 0 && 1158 _no_progress_cnt >= NoAsyncDeflationProgressMax) { 1159 float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0; 1160 size_t new_ceiling = ceiling + (ceiling * remainder) + 1; 1161 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling); 1162 log_info(monitorinflation)("Too many deflations without progress; " 1163 "bumping in_use_list_ceiling from " SIZE_FORMAT 1164 " to " SIZE_FORMAT, old_ceiling, new_ceiling); 1165 _no_progress_cnt = 0; 1166 ceiling = new_ceiling; 1167 } 1168 1169 // Check if our monitor usage is above the threshold: 1170 size_t monitor_usage = (monitors_used * 100LL) / ceiling; 1171 return int(monitor_usage) > MonitorUsedDeflationThreshold; 1172 } 1173 1174 size_t ObjectSynchronizer::in_use_list_ceiling() { 1175 return _in_use_list_ceiling; 1176 } 1177 1178 void ObjectSynchronizer::dec_in_use_list_ceiling() { 1179 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate); 1180 } 1181 1182 void ObjectSynchronizer::inc_in_use_list_ceiling() { 1183 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate); 1184 } 1185 1186 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) { 1187 _in_use_list_ceiling = new_value; 1188 } 1189 1190 bool ObjectSynchronizer::is_async_deflation_needed() { 1191 if (is_async_deflation_requested()) { 1192 // Async deflation request. 1193 return true; 1194 } 1195 if (AsyncDeflationInterval > 0 && 1196 time_since_last_async_deflation_ms() > AsyncDeflationInterval && 1197 monitors_used_above_threshold(&_in_use_list)) { 1198 // It's been longer than our specified deflate interval and there 1199 // are too many monitors in use. We don't deflate more frequently 1200 // than AsyncDeflationInterval (unless is_async_deflation_requested) 1201 // in order to not swamp the MonitorDeflationThread. 1202 return true; 1203 } 1204 return false; 1205 } 1206 1207 bool ObjectSynchronizer::request_deflate_idle_monitors() { 1208 JavaThread* current = JavaThread::current(); 1209 bool ret_code = false; 1210 1211 jlong last_time = last_async_deflation_time_ns(); 1212 set_is_async_deflation_requested(true); 1213 { 1214 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag); 1215 ml.notify_all(); 1216 } 1217 const int N_CHECKS = 5; 1218 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds 1219 if (last_async_deflation_time_ns() > last_time) { 1220 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i); 1221 ret_code = true; 1222 break; 1223 } 1224 { 1225 // JavaThread has to honor the blocking protocol. 1226 ThreadBlockInVM tbivm(current); 1227 os::naked_short_sleep(999); // sleep for almost 1 second 1228 } 1229 } 1230 if (!ret_code) { 1231 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS); 1232 } 1233 1234 return ret_code; 1235 } 1236 1237 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() { 1238 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS); 1239 } 1240 1241 static void post_monitor_inflate_event(EventJavaMonitorInflate* event, 1242 const oop obj, 1243 ObjectSynchronizer::InflateCause cause) { 1244 assert(event != NULL, "invariant"); 1245 assert(event->should_commit(), "invariant"); 1246 event->set_monitorClass(obj->klass()); 1247 event->set_address((uintptr_t)(void*)obj); 1248 event->set_cause((u1)cause); 1249 event->commit(); 1250 } 1251 1252 // Fast path code shared by multiple functions 1253 void ObjectSynchronizer::inflate_helper(oop obj) { 1254 markWord mark = obj->mark(); 1255 if (mark.has_monitor()) { 1256 ObjectMonitor* monitor = mark.monitor(); 1257 markWord dmw = monitor->header(); 1258 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value()); 1259 return; 1260 } 1261 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal); 1262 } 1263 1264 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object, 1265 const InflateCause cause) { 1266 EventJavaMonitorInflate event; 1267 1268 for (;;) { 1269 const markWord mark = object->mark(); 1270 assert(!mark.has_bias_pattern(), "invariant"); 1271 1272 // The mark can be in one of the following states: 1273 // * Inflated - just return 1274 // * Stack-locked - coerce it to inflated 1275 // * INFLATING - busy wait for conversion to complete 1276 // * Neutral - aggressively inflate the object. 1277 // * BIASED - Illegal. We should never see this 1278 1279 // CASE: inflated 1280 if (mark.has_monitor()) { 1281 ObjectMonitor* inf = mark.monitor(); 1282 markWord dmw = inf->header(); 1283 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1284 if (UseFastLocking && inf->is_owner_anonymous() && is_lock_owned(current, object)) { 1285 inf->set_owner_from_anonymous(current); 1286 assert(current->is_Java_thread(), "must be Java thread"); 1287 reinterpret_cast<JavaThread*>(current)->lock_stack().remove(object); 1288 } 1289 return inf; 1290 } 1291 1292 // CASE: inflation in progress - inflating over a stack-lock. 1293 // Some other thread is converting from stack-locked to inflated. 1294 // Only that thread can complete inflation -- other threads must wait. 1295 // The INFLATING value is transient. 1296 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish. 1297 // We could always eliminate polling by parking the thread on some auxiliary list. 1298 // NOTE: We need to check UseFastLocking here, because with fast-locking, the header 1299 // may legitimately be zero: cleared lock-bits and all upper header bits zero. 1300 // With fast-locking, the INFLATING protocol is not used. 1301 if (mark == markWord::INFLATING() && !UseFastLocking) { 1302 read_stable_mark(object); 1303 continue; 1304 } 1305 1306 // CASE: stack-locked 1307 // Could be stack-locked either by this thread or by some other thread. 1308 // 1309 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting 1310 // to install INFLATING into the mark word. We originally installed INFLATING, 1311 // allocated the ObjectMonitor, and then finally STed the address of the 1312 // ObjectMonitor into the mark. This was correct, but artificially lengthened 1313 // the interval in which INFLATING appeared in the mark, thus increasing 1314 // the odds of inflation contention. 1315 1316 LogStreamHandle(Trace, monitorinflation) lsh; 1317 if (mark.is_fast_locked()) { 1318 assert(UseFastLocking, "can only happen with fast-locking"); 1319 ObjectMonitor* monitor = new ObjectMonitor(object); 1320 monitor->set_header(mark.set_unlocked()); 1321 bool own = is_lock_owned(current, object); 1322 if (own) { 1323 // Owned by us. 1324 monitor->set_owner_from(NULL, current); 1325 } else { 1326 // Owned by somebody else. 1327 monitor->set_owner_anonymous(); 1328 } 1329 markWord monitor_mark = markWord::encode(monitor); 1330 markWord witness = object->cas_set_mark(monitor_mark, mark); 1331 if (witness == mark) { 1332 // Success! Return inflated monitor. 1333 if (own) { 1334 assert(current->is_Java_thread(), "must be: checked in is_lock_owned()"); 1335 reinterpret_cast<JavaThread*>(current)->lock_stack().remove(object); 1336 } 1337 // Once the ObjectMonitor is configured and object is associated 1338 // with the ObjectMonitor, it is safe to allow async deflation: 1339 _in_use_list.add(monitor); 1340 1341 // Hopefully the performance counters are allocated on distinct 1342 // cache lines to avoid false sharing on MP systems ... 1343 OM_PERFDATA_OP(Inflations, inc()); 1344 if (log_is_enabled(Trace, monitorinflation)) { 1345 ResourceMark rm(current); 1346 lsh.print_cr("inflate(locked): object=" INTPTR_FORMAT ", mark=" 1347 INTPTR_FORMAT ", type='%s'", p2i(object), 1348 object->mark().value(), object->klass()->external_name()); 1349 } 1350 if (event.should_commit()) { 1351 post_monitor_inflate_event(&event, object, cause); 1352 } 1353 return monitor; 1354 } else { 1355 delete monitor; 1356 continue; 1357 } 1358 } 1359 1360 if (mark.has_locker()) { 1361 assert(!UseFastLocking, "can not happen with fast-locking"); 1362 ObjectMonitor* m = new ObjectMonitor(object); 1363 // Optimistically prepare the ObjectMonitor - anticipate successful CAS 1364 // We do this before the CAS in order to minimize the length of time 1365 // in which INFLATING appears in the mark. 1366 1367 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark); 1368 if (cmp != mark) { 1369 delete m; 1370 continue; // Interference -- just retry 1371 } 1372 1373 // We've successfully installed INFLATING (0) into the mark-word. 1374 // This is the only case where 0 will appear in a mark-word. 1375 // Only the singular thread that successfully swings the mark-word 1376 // to 0 can perform (or more precisely, complete) inflation. 1377 // 1378 // Why do we CAS a 0 into the mark-word instead of just CASing the 1379 // mark-word from the stack-locked value directly to the new inflated state? 1380 // Consider what happens when a thread unlocks a stack-locked object. 1381 // It attempts to use CAS to swing the displaced header value from the 1382 // on-stack BasicLock back into the object header. Recall also that the 1383 // header value (hash code, etc) can reside in (a) the object header, or 1384 // (b) a displaced header associated with the stack-lock, or (c) a displaced 1385 // header in an ObjectMonitor. The inflate() routine must copy the header 1386 // value from the BasicLock on the owner's stack to the ObjectMonitor, all 1387 // the while preserving the hashCode stability invariants. If the owner 1388 // decides to release the lock while the value is 0, the unlock will fail 1389 // and control will eventually pass from slow_exit() to inflate. The owner 1390 // will then spin, waiting for the 0 value to disappear. Put another way, 1391 // the 0 causes the owner to stall if the owner happens to try to 1392 // drop the lock (restoring the header from the BasicLock to the object) 1393 // while inflation is in-progress. This protocol avoids races that might 1394 // would otherwise permit hashCode values to change or "flicker" for an object. 1395 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable. 1396 // 0 serves as a "BUSY" inflate-in-progress indicator. 1397 1398 1399 // fetch the displaced mark from the owner's stack. 1400 // The owner can't die or unwind past the lock while our INFLATING 1401 // object is in the mark. Furthermore the owner can't complete 1402 // an unlock on the object, either. 1403 markWord dmw = mark.displaced_mark_helper(); 1404 // Catch if the object's header is not neutral (not locked and 1405 // not marked is what we care about here). 1406 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1407 1408 // Setup monitor fields to proper values -- prepare the monitor 1409 m->set_header(dmw); 1410 1411 // Optimization: if the mark.locker stack address is associated 1412 // with this thread we could simply set m->_owner = current. 1413 // Note that a thread can inflate an object 1414 // that it has stack-locked -- as might happen in wait() -- directly 1415 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom. 1416 m->set_owner_from(NULL, mark.locker()); 1417 // TODO-FIXME: assert BasicLock->dhw != 0. 1418 1419 // Must preserve store ordering. The monitor state must 1420 // be stable at the time of publishing the monitor address. 1421 guarantee(object->mark() == markWord::INFLATING(), "invariant"); 1422 // Release semantics so that above set_object() is seen first. 1423 object->release_set_mark(markWord::encode(m)); 1424 1425 // Once ObjectMonitor is configured and the object is associated 1426 // with the ObjectMonitor, it is safe to allow async deflation: 1427 _in_use_list.add(m); 1428 1429 // Hopefully the performance counters are allocated on distinct cache lines 1430 // to avoid false sharing on MP systems ... 1431 OM_PERFDATA_OP(Inflations, inc()); 1432 if (log_is_enabled(Trace, monitorinflation)) { 1433 ResourceMark rm(current); 1434 lsh.print_cr("inflate(locked): object=" INTPTR_FORMAT ", mark=" 1435 INTPTR_FORMAT ", type='%s'", p2i(object), 1436 object->mark().value(), object->klass()->external_name()); 1437 } 1438 if (event.should_commit()) { 1439 post_monitor_inflate_event(&event, object, cause); 1440 } 1441 return m; 1442 } 1443 1444 // CASE: neutral 1445 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner. 1446 // If we know we're inflating for entry it's better to inflate by swinging a 1447 // pre-locked ObjectMonitor pointer into the object header. A successful 1448 // CAS inflates the object *and* confers ownership to the inflating thread. 1449 // In the current implementation we use a 2-step mechanism where we CAS() 1450 // to inflate and then CAS() again to try to swing _owner from NULL to current. 1451 // An inflateTry() method that we could call from enter() would be useful. 1452 1453 // Catch if the object's header is not neutral (not locked and 1454 // not marked is what we care about here). 1455 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value()); 1456 ObjectMonitor* m = new ObjectMonitor(object); 1457 // prepare m for installation - set monitor to initial state 1458 m->set_header(mark); 1459 1460 if (object->cas_set_mark(markWord::encode(m), mark) != mark) { 1461 delete m; 1462 m = NULL; 1463 continue; 1464 // interference - the markword changed - just retry. 1465 // The state-transitions are one-way, so there's no chance of 1466 // live-lock -- "Inflated" is an absorbing state. 1467 } 1468 1469 // Once the ObjectMonitor is configured and object is associated 1470 // with the ObjectMonitor, it is safe to allow async deflation: 1471 _in_use_list.add(m); 1472 1473 // Hopefully the performance counters are allocated on distinct 1474 // cache lines to avoid false sharing on MP systems ... 1475 OM_PERFDATA_OP(Inflations, inc()); 1476 if (log_is_enabled(Trace, monitorinflation)) { 1477 ResourceMark rm(current); 1478 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark=" 1479 INTPTR_FORMAT ", type='%s'", p2i(object), 1480 object->mark().value(), object->klass()->external_name()); 1481 } 1482 if (event.should_commit()) { 1483 post_monitor_inflate_event(&event, object, cause); 1484 } 1485 return m; 1486 } 1487 } 1488 1489 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name, 1490 const char* cnt_name, size_t cnt, 1491 LogStream* ls, elapsedTimer* timer_p) { 1492 if (!SafepointMechanism::should_process(current)) { 1493 return; 1494 } 1495 1496 // A safepoint/handshake has started. 1497 if (ls != NULL) { 1498 timer_p->stop(); 1499 ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling=" 1500 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1501 op_name, cnt_name, cnt, in_use_list_ceiling(), 1502 _in_use_list.count(), _in_use_list.max()); 1503 } 1504 1505 { 1506 // Honor block request. 1507 ThreadBlockInVM tbivm(current); 1508 } 1509 1510 if (ls != NULL) { 1511 ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT 1512 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name, 1513 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1514 timer_p->start(); 1515 } 1516 } 1517 1518 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle 1519 // ObjectMonitors. Returns the number of deflated ObjectMonitors. 1520 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls, 1521 elapsedTimer* timer_p) { 1522 MonitorList::Iterator iter = _in_use_list.iterator(); 1523 size_t deflated_count = 0; 1524 1525 while (iter.has_next()) { 1526 if (deflated_count >= (size_t)MonitorDeflationMax) { 1527 break; 1528 } 1529 ObjectMonitor* mid = iter.next(); 1530 if (mid->deflate_monitor()) { 1531 deflated_count++; 1532 } 1533 1534 if (current->is_Java_thread()) { 1535 // A JavaThread must check for a safepoint/handshake and honor it. 1536 chk_for_block_req(current->as_Java_thread(), "deflation", "deflated_count", 1537 deflated_count, ls, timer_p); 1538 } 1539 } 1540 1541 return deflated_count; 1542 } 1543 1544 class HandshakeForDeflation : public HandshakeClosure { 1545 public: 1546 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {} 1547 1548 void do_thread(Thread* thread) { 1549 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread=" 1550 INTPTR_FORMAT, p2i(thread)); 1551 } 1552 }; 1553 1554 class VM_RendezvousGCThreads : public VM_Operation { 1555 public: 1556 bool evaluate_at_safepoint() const override { return false; } 1557 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; } 1558 void doit() override { 1559 SuspendibleThreadSet::synchronize(); 1560 SuspendibleThreadSet::desynchronize(); 1561 }; 1562 }; 1563 1564 // This function is called by the MonitorDeflationThread to deflate 1565 // ObjectMonitors. It is also called via do_final_audit_and_print_stats() 1566 // by the VMThread. 1567 size_t ObjectSynchronizer::deflate_idle_monitors() { 1568 Thread* current = Thread::current(); 1569 if (current->is_Java_thread()) { 1570 // The async deflation request has been processed. 1571 _last_async_deflation_time_ns = os::javaTimeNanos(); 1572 set_is_async_deflation_requested(false); 1573 } 1574 1575 LogStreamHandle(Debug, monitorinflation) lsh_debug; 1576 LogStreamHandle(Info, monitorinflation) lsh_info; 1577 LogStream* ls = NULL; 1578 if (log_is_enabled(Debug, monitorinflation)) { 1579 ls = &lsh_debug; 1580 } else if (log_is_enabled(Info, monitorinflation)) { 1581 ls = &lsh_info; 1582 } 1583 1584 elapsedTimer timer; 1585 if (ls != NULL) { 1586 ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1587 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1588 timer.start(); 1589 } 1590 1591 // Deflate some idle ObjectMonitors. 1592 size_t deflated_count = deflate_monitor_list(current, ls, &timer); 1593 if (deflated_count > 0 || is_final_audit()) { 1594 // There are ObjectMonitors that have been deflated or this is the 1595 // final audit and all the remaining ObjectMonitors have been 1596 // deflated, BUT the MonitorDeflationThread blocked for the final 1597 // safepoint during unlinking. 1598 1599 // Unlink deflated ObjectMonitors from the in-use list. 1600 ResourceMark rm; 1601 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count); 1602 size_t unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer, 1603 &delete_list); 1604 if (current->is_Java_thread()) { 1605 if (ls != NULL) { 1606 timer.stop(); 1607 ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT 1608 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count=" 1609 SIZE_FORMAT ", max=" SIZE_FORMAT, 1610 unlinked_count, in_use_list_ceiling(), 1611 _in_use_list.count(), _in_use_list.max()); 1612 } 1613 1614 // A JavaThread needs to handshake in order to safely free the 1615 // ObjectMonitors that were deflated in this cycle. 1616 // Also, we sync and desync GC threads around the handshake, so that they can 1617 // safely read the mark-word and look-through to the object-monitor, without 1618 // being afraid that the object-monitor is going away. 1619 HandshakeForDeflation hfd_hc; 1620 Handshake::execute(&hfd_hc); 1621 VM_RendezvousGCThreads sync_gc; 1622 VMThread::execute(&sync_gc); 1623 1624 if (ls != NULL) { 1625 ls->print_cr("after handshaking: in_use_list stats: ceiling=" 1626 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1627 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1628 timer.start(); 1629 } 1630 } 1631 1632 // After the handshake, safely free the ObjectMonitors that were 1633 // deflated in this cycle. 1634 size_t deleted_count = 0; 1635 for (ObjectMonitor* monitor: delete_list) { 1636 delete monitor; 1637 deleted_count++; 1638 1639 if (current->is_Java_thread()) { 1640 // A JavaThread must check for a safepoint/handshake and honor it. 1641 chk_for_block_req(current->as_Java_thread(), "deletion", "deleted_count", 1642 deleted_count, ls, &timer); 1643 } 1644 } 1645 } 1646 1647 if (ls != NULL) { 1648 timer.stop(); 1649 if (deflated_count != 0 || log_is_enabled(Debug, monitorinflation)) { 1650 ls->print_cr("deflated " SIZE_FORMAT " monitors in %3.7f secs", 1651 deflated_count, timer.seconds()); 1652 } 1653 ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1654 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1655 } 1656 1657 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count())); 1658 OM_PERFDATA_OP(Deflations, inc(deflated_count)); 1659 1660 GVars.stw_random = os::random(); 1661 1662 if (deflated_count != 0) { 1663 _no_progress_cnt = 0; 1664 } else { 1665 _no_progress_cnt++; 1666 } 1667 1668 return deflated_count; 1669 } 1670 1671 // Monitor cleanup on JavaThread::exit 1672 1673 // Iterate through monitor cache and attempt to release thread's monitors 1674 class ReleaseJavaMonitorsClosure: public MonitorClosure { 1675 private: 1676 JavaThread* _thread; 1677 1678 public: 1679 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {} 1680 void do_monitor(ObjectMonitor* mid) { 1681 (void)mid->complete_exit(_thread); 1682 } 1683 }; 1684 1685 // Release all inflated monitors owned by current thread. Lightweight monitors are 1686 // ignored. This is meant to be called during JNI thread detach which assumes 1687 // all remaining monitors are heavyweight. All exceptions are swallowed. 1688 // Scanning the extant monitor list can be time consuming. 1689 // A simple optimization is to add a per-thread flag that indicates a thread 1690 // called jni_monitorenter() during its lifetime. 1691 // 1692 // Instead of NoSafepointVerifier it might be cheaper to 1693 // use an idiom of the form: 1694 // auto int tmp = SafepointSynchronize::_safepoint_counter ; 1695 // <code that must not run at safepoint> 1696 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ; 1697 // Since the tests are extremely cheap we could leave them enabled 1698 // for normal product builds. 1699 1700 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) { 1701 assert(current == JavaThread::current(), "must be current Java thread"); 1702 NoSafepointVerifier nsv; 1703 ReleaseJavaMonitorsClosure rjmc(current); 1704 ObjectSynchronizer::monitors_iterate(&rjmc, current); 1705 assert(!current->has_pending_exception(), "Should not be possible"); 1706 current->clear_pending_exception(); 1707 } 1708 1709 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) { 1710 switch (cause) { 1711 case inflate_cause_vm_internal: return "VM Internal"; 1712 case inflate_cause_monitor_enter: return "Monitor Enter"; 1713 case inflate_cause_wait: return "Monitor Wait"; 1714 case inflate_cause_notify: return "Monitor Notify"; 1715 case inflate_cause_hash_code: return "Monitor Hash Code"; 1716 case inflate_cause_jni_enter: return "JNI Monitor Enter"; 1717 case inflate_cause_jni_exit: return "JNI Monitor Exit"; 1718 default: 1719 ShouldNotReachHere(); 1720 } 1721 return "Unknown"; 1722 } 1723 1724 //------------------------------------------------------------------------------ 1725 // Debugging code 1726 1727 u_char* ObjectSynchronizer::get_gvars_addr() { 1728 return (u_char*)&GVars; 1729 } 1730 1731 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() { 1732 return (u_char*)&GVars.hc_sequence; 1733 } 1734 1735 size_t ObjectSynchronizer::get_gvars_size() { 1736 return sizeof(SharedGlobals); 1737 } 1738 1739 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() { 1740 return (u_char*)&GVars.stw_random; 1741 } 1742 1743 // Do the final audit and print of ObjectMonitor stats; must be done 1744 // by the VMThread at VM exit time. 1745 void ObjectSynchronizer::do_final_audit_and_print_stats() { 1746 assert(Thread::current()->is_VM_thread(), "sanity check"); 1747 1748 if (is_final_audit()) { // Only do the audit once. 1749 return; 1750 } 1751 set_is_final_audit(); 1752 1753 if (log_is_enabled(Info, monitorinflation)) { 1754 // Do a deflation in order to reduce the in-use monitor population 1755 // that is reported by ObjectSynchronizer::log_in_use_monitor_details() 1756 // which is called by ObjectSynchronizer::audit_and_print_stats(). 1757 while (ObjectSynchronizer::deflate_idle_monitors() != 0) { 1758 ; // empty 1759 } 1760 // The other audit_and_print_stats() call is done at the Debug 1761 // level at a safepoint in ObjectSynchronizer::do_safepoint_work(). 1762 ObjectSynchronizer::audit_and_print_stats(true /* on_exit */); 1763 } 1764 } 1765 1766 // This function can be called at a safepoint or it can be called when 1767 // we are trying to exit the VM. When we are trying to exit the VM, the 1768 // list walker functions can run in parallel with the other list 1769 // operations so spin-locking is used for safety. 1770 // 1771 // Calls to this function can be added in various places as a debugging 1772 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor 1773 // details logged at the Info level and 'false' for the 'on_exit' 1774 // parameter to have in-use monitor details logged at the Trace level. 1775 // 1776 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) { 1777 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant"); 1778 1779 LogStreamHandle(Debug, monitorinflation) lsh_debug; 1780 LogStreamHandle(Info, monitorinflation) lsh_info; 1781 LogStreamHandle(Trace, monitorinflation) lsh_trace; 1782 LogStream* ls = NULL; 1783 if (log_is_enabled(Trace, monitorinflation)) { 1784 ls = &lsh_trace; 1785 } else if (log_is_enabled(Debug, monitorinflation)) { 1786 ls = &lsh_debug; 1787 } else if (log_is_enabled(Info, monitorinflation)) { 1788 ls = &lsh_info; 1789 } 1790 assert(ls != NULL, "sanity check"); 1791 1792 int error_cnt = 0; 1793 1794 ls->print_cr("Checking in_use_list:"); 1795 chk_in_use_list(ls, &error_cnt); 1796 1797 if (error_cnt == 0) { 1798 ls->print_cr("No errors found in in_use_list checks."); 1799 } else { 1800 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt); 1801 } 1802 1803 if ((on_exit && log_is_enabled(Info, monitorinflation)) || 1804 (!on_exit && log_is_enabled(Trace, monitorinflation))) { 1805 // When exiting this log output is at the Info level. When called 1806 // at a safepoint, this log output is at the Trace level since 1807 // there can be a lot of it. 1808 log_in_use_monitor_details(ls); 1809 } 1810 1811 ls->flush(); 1812 1813 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt); 1814 } 1815 1816 // Check the in_use_list; log the results of the checks. 1817 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) { 1818 size_t l_in_use_count = _in_use_list.count(); 1819 size_t l_in_use_max = _in_use_list.max(); 1820 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count, 1821 l_in_use_max); 1822 1823 size_t ck_in_use_count = 0; 1824 MonitorList::Iterator iter = _in_use_list.iterator(); 1825 while (iter.has_next()) { 1826 ObjectMonitor* mid = iter.next(); 1827 chk_in_use_entry(mid, out, error_cnt_p); 1828 ck_in_use_count++; 1829 } 1830 1831 if (l_in_use_count == ck_in_use_count) { 1832 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count=" 1833 SIZE_FORMAT, l_in_use_count, ck_in_use_count); 1834 } else { 1835 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to " 1836 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count, 1837 ck_in_use_count); 1838 } 1839 1840 size_t ck_in_use_max = _in_use_list.max(); 1841 if (l_in_use_max == ck_in_use_max) { 1842 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max=" 1843 SIZE_FORMAT, l_in_use_max, ck_in_use_max); 1844 } else { 1845 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to " 1846 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max); 1847 } 1848 } 1849 1850 // Check an in-use monitor entry; log any errors. 1851 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out, 1852 int* error_cnt_p) { 1853 if (n->owner_is_DEFLATER_MARKER()) { 1854 // This should not happen, but if it does, it is not fatal. 1855 out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is " 1856 "deflated.", p2i(n)); 1857 return; 1858 } 1859 if (n->header().value() == 0) { 1860 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must " 1861 "have non-NULL _header field.", p2i(n)); 1862 *error_cnt_p = *error_cnt_p + 1; 1863 } 1864 const oop obj = n->object_peek(); 1865 if (obj != NULL) { 1866 const markWord mark = obj->mark(); 1867 if (!mark.has_monitor()) { 1868 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's " 1869 "object does not think it has a monitor: obj=" 1870 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n), 1871 p2i(obj), mark.value()); 1872 *error_cnt_p = *error_cnt_p + 1; 1873 } 1874 ObjectMonitor* const obj_mon = mark.monitor(); 1875 if (n != obj_mon) { 1876 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's " 1877 "object does not refer to the same monitor: obj=" 1878 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon=" 1879 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon)); 1880 *error_cnt_p = *error_cnt_p + 1; 1881 } 1882 } 1883 } 1884 1885 // Log details about ObjectMonitors on the in_use_list. The 'BHL' 1886 // flags indicate why the entry is in-use, 'object' and 'object type' 1887 // indicate the associated object and its type. 1888 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) { 1889 stringStream ss; 1890 if (_in_use_list.count() > 0) { 1891 out->print_cr("In-use monitor info:"); 1892 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)"); 1893 out->print_cr("%18s %s %18s %18s", 1894 "monitor", "BHL", "object", "object type"); 1895 out->print_cr("================== === ================== =================="); 1896 MonitorList::Iterator iter = _in_use_list.iterator(); 1897 while (iter.has_next()) { 1898 ObjectMonitor* mid = iter.next(); 1899 const oop obj = mid->object_peek(); 1900 const markWord mark = mid->header(); 1901 ResourceMark rm; 1902 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(mid), 1903 mid->is_busy(), mark.hash() != 0, mid->owner() != NULL, 1904 p2i(obj), obj == NULL ? "" : obj->klass()->external_name()); 1905 if (mid->is_busy()) { 1906 out->print(" (%s)", mid->is_busy_to_string(&ss)); 1907 ss.reset(); 1908 } 1909 out->cr(); 1910 } 1911 } 1912 1913 out->flush(); 1914 }