monitor.cc revision 34e069606d6f1698cd3c33b39e72b79ae27e1c7b
1/* 2 * Copyright (C) 2008 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17#include "monitor.h" 18 19#include <errno.h> 20#include <fcntl.h> 21#include <pthread.h> 22#include <stdlib.h> 23#include <sys/time.h> 24#include <time.h> 25#include <unistd.h> 26 27#include "class_linker.h" 28#include "mutex.h" 29#include "object.h" 30#include "object_utils.h" 31#include "scoped_thread_list_lock.h" 32#include "stl_util.h" 33#include "thread.h" 34#include "thread_list.h" 35 36namespace art { 37 38/* 39 * Every Object has a monitor associated with it, but not every Object is 40 * actually locked. Even the ones that are locked do not need a 41 * full-fledged monitor until a) there is actual contention or b) wait() 42 * is called on the Object. 43 * 44 * For Android, we have implemented a scheme similar to the one described 45 * in Bacon et al.'s "Thin locks: featherweight synchronization for Java" 46 * (ACM 1998). Things are even easier for us, though, because we have 47 * a full 32 bits to work with. 48 * 49 * The two states of an Object's lock are referred to as "thin" and 50 * "fat". A lock may transition from the "thin" state to the "fat" 51 * state and this transition is referred to as inflation. Once a lock 52 * has been inflated it remains in the "fat" state indefinitely. 53 * 54 * The lock value itself is stored in Object.lock. The LSB of the 55 * lock encodes its state. When cleared, the lock is in the "thin" 56 * state and its bits are formatted as follows: 57 * 58 * [31 ---- 19] [18 ---- 3] [2 ---- 1] [0] 59 * lock count thread id hash state 0 60 * 61 * When set, the lock is in the "fat" state and its bits are formatted 62 * as follows: 63 * 64 * [31 ---- 3] [2 ---- 1] [0] 65 * pointer hash state 1 66 * 67 * For an in-depth description of the mechanics of thin-vs-fat locking, 68 * read the paper referred to above. 69 * 70 * Monitors provide: 71 * - mutually exclusive access to resources 72 * - a way for multiple threads to wait for notification 73 * 74 * In effect, they fill the role of both mutexes and condition variables. 75 * 76 * Only one thread can own the monitor at any time. There may be several 77 * threads waiting on it (the wait call unlocks it). One or more waiting 78 * threads may be getting interrupted or notified at any given time. 79 * 80 * TODO: the various members of monitor are not SMP-safe. 81 */ 82 83 84/* 85 * Monitor accessor. Extracts a monitor structure pointer from a fat 86 * lock. Performs no error checking. 87 */ 88#define LW_MONITOR(x) \ 89 (reinterpret_cast<Monitor*>((x) & ~((LW_HASH_STATE_MASK << LW_HASH_STATE_SHIFT) | LW_SHAPE_MASK))) 90 91/* 92 * Lock recursion count field. Contains a count of the number of times 93 * a lock has been recursively acquired. 94 */ 95#define LW_LOCK_COUNT_MASK 0x1fff 96#define LW_LOCK_COUNT_SHIFT 19 97#define LW_LOCK_COUNT(x) (((x) >> LW_LOCK_COUNT_SHIFT) & LW_LOCK_COUNT_MASK) 98 99bool (*Monitor::is_sensitive_thread_hook_)() = NULL; 100uint32_t Monitor::lock_profiling_threshold_ = 0; 101 102bool Monitor::IsSensitiveThread() { 103 if (is_sensitive_thread_hook_ != NULL) { 104 return (*is_sensitive_thread_hook_)(); 105 } 106 return false; 107} 108 109void Monitor::Init(uint32_t lock_profiling_threshold, bool (*is_sensitive_thread_hook)()) { 110 lock_profiling_threshold_ = lock_profiling_threshold; 111 is_sensitive_thread_hook_ = is_sensitive_thread_hook; 112} 113 114Monitor::Monitor(Object* obj) 115 : owner_(NULL), 116 lock_count_(0), 117 obj_(obj), 118 wait_set_(NULL), 119 lock_("a monitor lock"), 120 locking_method_(NULL), 121 locking_pc_(0) { 122} 123 124Monitor::~Monitor() { 125 DCHECK(obj_ != NULL); 126 DCHECK_EQ(LW_SHAPE(*obj_->GetRawLockWordAddress()), LW_SHAPE_FAT); 127} 128 129/* 130 * Links a thread into a monitor's wait set. The monitor lock must be 131 * held by the caller of this routine. 132 */ 133void Monitor::AppendToWaitSet(Thread* thread) { 134 DCHECK(owner_ == Thread::Current()); 135 DCHECK(thread != NULL); 136 DCHECK(thread->wait_next_ == NULL) << thread->wait_next_; 137 if (wait_set_ == NULL) { 138 wait_set_ = thread; 139 return; 140 } 141 142 // push_back. 143 Thread* t = wait_set_; 144 while (t->wait_next_ != NULL) { 145 t = t->wait_next_; 146 } 147 t->wait_next_ = thread; 148} 149 150/* 151 * Unlinks a thread from a monitor's wait set. The monitor lock must 152 * be held by the caller of this routine. 153 */ 154void Monitor::RemoveFromWaitSet(Thread *thread) { 155 DCHECK(owner_ == Thread::Current()); 156 DCHECK(thread != NULL); 157 if (wait_set_ == NULL) { 158 return; 159 } 160 if (wait_set_ == thread) { 161 wait_set_ = thread->wait_next_; 162 thread->wait_next_ = NULL; 163 return; 164 } 165 166 Thread* t = wait_set_; 167 while (t->wait_next_ != NULL) { 168 if (t->wait_next_ == thread) { 169 t->wait_next_ = thread->wait_next_; 170 thread->wait_next_ = NULL; 171 return; 172 } 173 t = t->wait_next_; 174 } 175} 176 177Object* Monitor::GetObject() { 178 return obj_; 179} 180 181void Monitor::Lock(Thread* self) { 182 if (owner_ == self) { 183 lock_count_++; 184 return; 185 } 186 187 uint64_t waitStart, waitEnd; 188 if (!lock_.TryLock()) { 189 uint32_t wait_threshold = lock_profiling_threshold_; 190 const Method* current_locking_method = NULL; 191 uintptr_t current_locking_pc = 0; 192 { 193 ScopedThreadStateChange tsc(self, kBlocked); 194 if (wait_threshold != 0) { 195 waitStart = NanoTime() / 1000; 196 } 197 current_locking_method = locking_method_; 198 current_locking_pc = locking_pc_; 199 200 lock_.Lock(); 201 if (wait_threshold != 0) { 202 waitEnd = NanoTime() / 1000; 203 } 204 } 205 206 if (wait_threshold != 0) { 207 uint64_t wait_ms = (waitEnd - waitStart) / 1000; 208 uint32_t sample_percent; 209 if (wait_ms >= wait_threshold) { 210 sample_percent = 100; 211 } else { 212 sample_percent = 100 * wait_ms / wait_threshold; 213 } 214 if (sample_percent != 0 && (static_cast<uint32_t>(rand() % 100) < sample_percent)) { 215 const char* current_locking_filename; 216 uint32_t current_locking_line_number; 217 TranslateLocation(current_locking_method, current_locking_pc, 218 current_locking_filename, current_locking_line_number); 219 LogContentionEvent(self, wait_ms, sample_percent, current_locking_filename, current_locking_line_number); 220 } 221 } 222 } 223 owner_ = self; 224 DCHECK_EQ(lock_count_, 0); 225 226 // When debugging, save the current monitor holder for future 227 // acquisition failures to use in sampled logging. 228 if (lock_profiling_threshold_ != 0) { 229 locking_method_ = self->GetCurrentMethod(&locking_pc_); 230 } 231} 232 233static void ThrowIllegalMonitorStateExceptionF(const char* fmt, ...) 234 __attribute__((format(printf, 1, 2))); 235 236static void ThrowIllegalMonitorStateExceptionF(const char* fmt, ...) { 237 va_list args; 238 va_start(args, fmt); 239 Thread::Current()->ThrowNewExceptionV("Ljava/lang/IllegalMonitorStateException;", fmt, args); 240 if (!Runtime::Current()->IsStarted()) { 241 std::ostringstream ss; 242 Thread::Current()->Dump(ss); 243 std::string str(ss.str()); 244 LOG(ERROR) << "IllegalMonitorStateException: " << str; 245 } 246 va_end(args); 247} 248 249static std::string ThreadToString(Thread* thread) { 250 if (thread == NULL) { 251 return "NULL"; 252 } 253 std::ostringstream oss; 254 // TODO: alternatively, we could just return the thread's name. 255 oss << *thread; 256 return oss.str(); 257} 258 259void Monitor::FailedUnlock(Object* o, Thread* expected_owner, Thread* found_owner, 260 Monitor* monitor) { 261 Thread* current_owner = NULL; 262 std::string current_owner_string; 263 std::string expected_owner_string; 264 std::string found_owner_string; 265 { 266 // TODO: isn't this too late to prevent threads from disappearing? 267 // Acquire thread list lock so threads won't disappear from under us. 268 ScopedThreadListLock thread_list_lock; 269 // Re-read owner now that we hold lock. 270 current_owner = (monitor != NULL) ? monitor->owner_ : NULL; 271 // Get short descriptions of the threads involved. 272 current_owner_string = ThreadToString(current_owner); 273 expected_owner_string = ThreadToString(expected_owner); 274 found_owner_string = ThreadToString(found_owner); 275 } 276 if (current_owner == NULL) { 277 if (found_owner == NULL) { 278 ThrowIllegalMonitorStateExceptionF("unlock of unowned monitor on object of type '%s'" 279 " on thread '%s'", 280 PrettyTypeOf(o).c_str(), 281 expected_owner_string.c_str()); 282 } else { 283 // Race: the original read found an owner but now there is none 284 ThrowIllegalMonitorStateExceptionF("unlock of monitor owned by '%s' on object of type '%s'" 285 " (where now the monitor appears unowned) on thread '%s'", 286 found_owner_string.c_str(), 287 PrettyTypeOf(o).c_str(), 288 expected_owner_string.c_str()); 289 } 290 } else { 291 if (found_owner == NULL) { 292 // Race: originally there was no owner, there is now 293 ThrowIllegalMonitorStateExceptionF("unlock of monitor owned by '%s' on object of type '%s'" 294 " (originally believed to be unowned) on thread '%s'", 295 current_owner_string.c_str(), 296 PrettyTypeOf(o).c_str(), 297 expected_owner_string.c_str()); 298 } else { 299 if (found_owner != current_owner) { 300 // Race: originally found and current owner have changed 301 ThrowIllegalMonitorStateExceptionF("unlock of monitor originally owned by '%s' (now" 302 " owned by '%s') on object of type '%s' on thread '%s'", 303 found_owner_string.c_str(), 304 current_owner_string.c_str(), 305 PrettyTypeOf(o).c_str(), 306 expected_owner_string.c_str()); 307 } else { 308 ThrowIllegalMonitorStateExceptionF("unlock of monitor owned by '%s' on object of type '%s'" 309 " on thread '%s", 310 current_owner_string.c_str(), 311 PrettyTypeOf(o).c_str(), 312 expected_owner_string.c_str()); 313 } 314 } 315 } 316} 317 318bool Monitor::Unlock(Thread* self) { 319 DCHECK(self != NULL); 320 Thread* owner = owner_; 321 if (owner == self) { 322 // We own the monitor, so nobody else can be in here. 323 if (lock_count_ == 0) { 324 owner_ = NULL; 325 locking_method_ = NULL; 326 locking_pc_ = 0; 327 lock_.Unlock(); 328 } else { 329 --lock_count_; 330 } 331 } else { 332 // We don't own this, so we're not allowed to unlock it. 333 // The JNI spec says that we should throw IllegalMonitorStateException 334 // in this case. 335 FailedUnlock(obj_, self, owner, this); 336 return false; 337 } 338 return true; 339} 340 341/* 342 * Converts the given relative waiting time into an absolute time. 343 */ 344static void ToAbsoluteTime(int64_t ms, int32_t ns, struct timespec *ts) { 345 int64_t endSec; 346 347#ifdef HAVE_TIMEDWAIT_MONOTONIC 348 clock_gettime(CLOCK_MONOTONIC, ts); 349#else 350 { 351 struct timeval tv; 352 gettimeofday(&tv, NULL); 353 ts->tv_sec = tv.tv_sec; 354 ts->tv_nsec = tv.tv_usec * 1000; 355 } 356#endif 357 endSec = ts->tv_sec + ms / 1000; 358 if (endSec >= 0x7fffffff) { 359 LOG(INFO) << "Note: end time exceeds epoch"; 360 endSec = 0x7ffffffe; 361 } 362 ts->tv_sec = endSec; 363 ts->tv_nsec = (ts->tv_nsec + (ms % 1000) * 1000000) + ns; 364 365 // Catch rollover. 366 if (ts->tv_nsec >= 1000000000L) { 367 ts->tv_sec++; 368 ts->tv_nsec -= 1000000000L; 369 } 370} 371 372/* 373 * Wait on a monitor until timeout, interrupt, or notification. Used for 374 * Object.wait() and (somewhat indirectly) Thread.sleep() and Thread.join(). 375 * 376 * If another thread calls Thread.interrupt(), we throw InterruptedException 377 * and return immediately if one of the following are true: 378 * - blocked in wait(), wait(long), or wait(long, int) methods of Object 379 * - blocked in join(), join(long), or join(long, int) methods of Thread 380 * - blocked in sleep(long), or sleep(long, int) methods of Thread 381 * Otherwise, we set the "interrupted" flag. 382 * 383 * Checks to make sure that "ns" is in the range 0-999999 384 * (i.e. fractions of a millisecond) and throws the appropriate 385 * exception if it isn't. 386 * 387 * The spec allows "spurious wakeups", and recommends that all code using 388 * Object.wait() do so in a loop. This appears to derive from concerns 389 * about pthread_cond_wait() on multiprocessor systems. Some commentary 390 * on the web casts doubt on whether these can/should occur. 391 * 392 * Since we're allowed to wake up "early", we clamp extremely long durations 393 * to return at the end of the 32-bit time epoch. 394 */ 395void Monitor::Wait(Thread* self, int64_t ms, int32_t ns, bool interruptShouldThrow) { 396 DCHECK(self != NULL); 397 398 // Make sure that we hold the lock. 399 if (owner_ != self) { 400 ThrowIllegalMonitorStateExceptionF("object not locked by thread before wait()"); 401 return; 402 } 403 404 // Enforce the timeout range. 405 if (ms < 0 || ns < 0 || ns > 999999) { 406 Thread::Current()->ThrowNewExceptionF("Ljava/lang/IllegalArgumentException;", 407 "timeout arguments out of range: ms=%lld ns=%d", ms, ns); 408 return; 409 } 410 411 // Compute absolute wakeup time, if necessary. 412 struct timespec ts; 413 bool timed = false; 414 if (ms != 0 || ns != 0) { 415 ToAbsoluteTime(ms, ns, &ts); 416 timed = true; 417 } 418 419 /* 420 * Add ourselves to the set of threads waiting on this monitor, and 421 * release our hold. We need to let it go even if we're a few levels 422 * deep in a recursive lock, and we need to restore that later. 423 * 424 * We append to the wait set ahead of clearing the count and owner 425 * fields so the subroutine can check that the calling thread owns 426 * the monitor. Aside from that, the order of member updates is 427 * not order sensitive as we hold the pthread mutex. 428 */ 429 AppendToWaitSet(self); 430 int prevLockCount = lock_count_; 431 lock_count_ = 0; 432 owner_ = NULL; 433 const Method* savedMethod = locking_method_; 434 locking_method_ = NULL; 435 uintptr_t savedPc = locking_pc_; 436 locking_pc_ = 0; 437 438 /* 439 * Update thread status. If the GC wakes up, it'll ignore us, knowing 440 * that we won't touch any references in this state, and we'll check 441 * our suspend mode before we transition out. 442 */ 443 if (timed) { 444 self->SetState(kTimedWaiting); 445 } else { 446 self->SetState(kWaiting); 447 } 448 449 self->wait_mutex_->Lock(); 450 451 /* 452 * Set wait_monitor_ to the monitor object we will be waiting on. 453 * When wait_monitor_ is non-NULL a notifying or interrupting thread 454 * must signal the thread's wait_cond_ to wake it up. 455 */ 456 DCHECK(self->wait_monitor_ == NULL); 457 self->wait_monitor_ = this; 458 459 /* 460 * Handle the case where the thread was interrupted before we called 461 * wait(). 462 */ 463 bool wasInterrupted = false; 464 if (self->interrupted_) { 465 wasInterrupted = true; 466 self->wait_monitor_ = NULL; 467 self->wait_mutex_->Unlock(); 468 goto done; 469 } 470 471 /* 472 * Release the monitor lock and wait for a notification or 473 * a timeout to occur. 474 */ 475 lock_.Unlock(); 476 477 if (!timed) { 478 self->wait_cond_->Wait(*self->wait_mutex_); 479 } else { 480 self->wait_cond_->TimedWait(*self->wait_mutex_, ts); 481 } 482 if (self->interrupted_) { 483 wasInterrupted = true; 484 } 485 486 self->interrupted_ = false; 487 self->wait_monitor_ = NULL; 488 self->wait_mutex_->Unlock(); 489 490 // Reacquire the monitor lock. 491 Lock(self); 492 493done: 494 /* 495 * We remove our thread from wait set after restoring the count 496 * and owner fields so the subroutine can check that the calling 497 * thread owns the monitor. Aside from that, the order of member 498 * updates is not order sensitive as we hold the pthread mutex. 499 */ 500 owner_ = self; 501 lock_count_ = prevLockCount; 502 locking_method_ = savedMethod; 503 locking_pc_ = savedPc; 504 RemoveFromWaitSet(self); 505 506 /* set self->status back to kRunnable, and self-suspend if needed */ 507 self->SetState(kRunnable); 508 509 if (wasInterrupted) { 510 /* 511 * We were interrupted while waiting, or somebody interrupted an 512 * un-interruptible thread earlier and we're bailing out immediately. 513 * 514 * The doc sayeth: "The interrupted status of the current thread is 515 * cleared when this exception is thrown." 516 */ 517 self->interrupted_ = false; 518 if (interruptShouldThrow) { 519 Thread::Current()->ThrowNewException("Ljava/lang/InterruptedException;", NULL); 520 } 521 } 522} 523 524void Monitor::Notify(Thread* self) { 525 DCHECK(self != NULL); 526 527 // Make sure that we hold the lock. 528 if (owner_ != self) { 529 ThrowIllegalMonitorStateExceptionF("object not locked by thread before notify()"); 530 return; 531 } 532 // Signal the first waiting thread in the wait set. 533 while (wait_set_ != NULL) { 534 Thread* thread = wait_set_; 535 wait_set_ = thread->wait_next_; 536 thread->wait_next_ = NULL; 537 538 // Check to see if the thread is still waiting. 539 MutexLock mu(*thread->wait_mutex_); 540 if (thread->wait_monitor_ != NULL) { 541 thread->wait_cond_->Signal(); 542 return; 543 } 544 } 545} 546 547void Monitor::NotifyAll(Thread* self) { 548 DCHECK(self != NULL); 549 550 // Make sure that we hold the lock. 551 if (owner_ != self) { 552 ThrowIllegalMonitorStateExceptionF("object not locked by thread before notifyAll()"); 553 return; 554 } 555 // Signal all threads in the wait set. 556 while (wait_set_ != NULL) { 557 Thread* thread = wait_set_; 558 wait_set_ = thread->wait_next_; 559 thread->wait_next_ = NULL; 560 thread->Notify(); 561 } 562} 563 564/* 565 * Changes the shape of a monitor from thin to fat, preserving the 566 * internal lock state. The calling thread must own the lock. 567 */ 568void Monitor::Inflate(Thread* self, Object* obj) { 569 DCHECK(self != NULL); 570 DCHECK(obj != NULL); 571 DCHECK_EQ(LW_SHAPE(*obj->GetRawLockWordAddress()), LW_SHAPE_THIN); 572 DCHECK_EQ(LW_LOCK_OWNER(*obj->GetRawLockWordAddress()), static_cast<int32_t>(self->GetThinLockId())); 573 574 // Allocate and acquire a new monitor. 575 Monitor* m = new Monitor(obj); 576 VLOG(monitor) << "monitor: thread " << self->GetThinLockId() 577 << " created monitor " << m << " for object " << obj; 578 Runtime::Current()->GetMonitorList()->Add(m); 579 m->Lock(self); 580 // Propagate the lock state. 581 uint32_t thin = *obj->GetRawLockWordAddress(); 582 m->lock_count_ = LW_LOCK_COUNT(thin); 583 thin &= LW_HASH_STATE_MASK << LW_HASH_STATE_SHIFT; 584 thin |= reinterpret_cast<uint32_t>(m) | LW_SHAPE_FAT; 585 // Publish the updated lock word. 586 android_atomic_release_store(thin, obj->GetRawLockWordAddress()); 587} 588 589void Monitor::MonitorEnter(Thread* self, Object* obj) { 590 volatile int32_t* thinp = obj->GetRawLockWordAddress(); 591 struct timespec tm; 592 uint32_t sleepDelayNs; 593 uint32_t minSleepDelayNs = 1000000; /* 1 millisecond */ 594 uint32_t maxSleepDelayNs = 1000000000; /* 1 second */ 595 uint32_t thin, newThin; 596 597 DCHECK(self != NULL); 598 DCHECK(obj != NULL); 599 uint32_t threadId = self->GetThinLockId(); 600retry: 601 thin = *thinp; 602 if (LW_SHAPE(thin) == LW_SHAPE_THIN) { 603 /* 604 * The lock is a thin lock. The owner field is used to 605 * determine the acquire method, ordered by cost. 606 */ 607 if (LW_LOCK_OWNER(thin) == threadId) { 608 /* 609 * The calling thread owns the lock. Increment the 610 * value of the recursion count field. 611 */ 612 *thinp += 1 << LW_LOCK_COUNT_SHIFT; 613 if (LW_LOCK_COUNT(*thinp) == LW_LOCK_COUNT_MASK) { 614 /* 615 * The reacquisition limit has been reached. Inflate 616 * the lock so the next acquire will not overflow the 617 * recursion count field. 618 */ 619 Inflate(self, obj); 620 } 621 } else if (LW_LOCK_OWNER(thin) == 0) { 622 // The lock is unowned. Install the thread id of the calling thread into the owner field. 623 // This is the common case: compiled code will have tried this before calling back into 624 // the runtime. 625 newThin = thin | (threadId << LW_LOCK_OWNER_SHIFT); 626 if (android_atomic_acquire_cas(thin, newThin, thinp) != 0) { 627 // The acquire failed. Try again. 628 goto retry; 629 } 630 } else { 631 VLOG(monitor) << StringPrintf("monitor: thread %d spin on lock %p (a %s) owned by %d", 632 threadId, thinp, PrettyTypeOf(obj).c_str(), LW_LOCK_OWNER(thin)); 633 // The lock is owned by another thread. Notify the runtime that we are about to wait. 634 self->monitor_enter_object_ = obj; 635 ThreadState oldStatus = self->SetState(kBlocked); 636 // Spin until the thin lock is released or inflated. 637 sleepDelayNs = 0; 638 for (;;) { 639 thin = *thinp; 640 // Check the shape of the lock word. Another thread 641 // may have inflated the lock while we were waiting. 642 if (LW_SHAPE(thin) == LW_SHAPE_THIN) { 643 if (LW_LOCK_OWNER(thin) == 0) { 644 // The lock has been released. Install the thread id of the 645 // calling thread into the owner field. 646 newThin = thin | (threadId << LW_LOCK_OWNER_SHIFT); 647 if (android_atomic_acquire_cas(thin, newThin, thinp) == 0) { 648 // The acquire succeed. Break out of the loop and proceed to inflate the lock. 649 break; 650 } 651 } else { 652 // The lock has not been released. Yield so the owning thread can run. 653 if (sleepDelayNs == 0) { 654 sched_yield(); 655 sleepDelayNs = minSleepDelayNs; 656 } else { 657 tm.tv_sec = 0; 658 tm.tv_nsec = sleepDelayNs; 659 nanosleep(&tm, NULL); 660 // Prepare the next delay value. Wrap to avoid once a second polls for eternity. 661 if (sleepDelayNs < maxSleepDelayNs / 2) { 662 sleepDelayNs *= 2; 663 } else { 664 sleepDelayNs = minSleepDelayNs; 665 } 666 } 667 } 668 } else { 669 // The thin lock was inflated by another thread. Let the runtime know we are no longer 670 // waiting and try again. 671 VLOG(monitor) << StringPrintf("monitor: thread %d found lock %p surprise-fattened by another thread", threadId, thinp); 672 self->monitor_enter_object_ = NULL; 673 self->SetState(oldStatus); 674 goto retry; 675 } 676 } 677 VLOG(monitor) << StringPrintf("monitor: thread %d spin on lock %p done", threadId, thinp); 678 // We have acquired the thin lock. Let the runtime know that we are no longer waiting. 679 self->monitor_enter_object_ = NULL; 680 self->SetState(oldStatus); 681 // Fatten the lock. 682 Inflate(self, obj); 683 VLOG(monitor) << StringPrintf("monitor: thread %d fattened lock %p", threadId, thinp); 684 } 685 } else { 686 // The lock is a fat lock. 687 VLOG(monitor) << StringPrintf("monitor: thread %d locking fat lock %p (%p) %p on a %s", 688 threadId, thinp, LW_MONITOR(*thinp), 689 reinterpret_cast<void*>(*thinp), PrettyTypeOf(obj).c_str()); 690 DCHECK(LW_MONITOR(*thinp) != NULL); 691 LW_MONITOR(*thinp)->Lock(self); 692 } 693} 694 695bool Monitor::MonitorExit(Thread* self, Object* obj) { 696 volatile int32_t* thinp = obj->GetRawLockWordAddress(); 697 698 DCHECK(self != NULL); 699 //DCHECK_EQ(self->GetState(), kRunnable); 700 DCHECK(obj != NULL); 701 702 /* 703 * Cache the lock word as its value can change while we are 704 * examining its state. 705 */ 706 uint32_t thin = *thinp; 707 if (LW_SHAPE(thin) == LW_SHAPE_THIN) { 708 /* 709 * The lock is thin. We must ensure that the lock is owned 710 * by the given thread before unlocking it. 711 */ 712 if (LW_LOCK_OWNER(thin) == self->GetThinLockId()) { 713 /* 714 * We are the lock owner. It is safe to update the lock 715 * without CAS as lock ownership guards the lock itself. 716 */ 717 if (LW_LOCK_COUNT(thin) == 0) { 718 /* 719 * The lock was not recursively acquired, the common 720 * case. Unlock by clearing all bits except for the 721 * hash state. 722 */ 723 thin &= (LW_HASH_STATE_MASK << LW_HASH_STATE_SHIFT); 724 android_atomic_release_store(thin, thinp); 725 } else { 726 /* 727 * The object was recursively acquired. Decrement the 728 * lock recursion count field. 729 */ 730 *thinp -= 1 << LW_LOCK_COUNT_SHIFT; 731 } 732 } else { 733 /* 734 * We do not own the lock. The JVM spec requires that we 735 * throw an exception in this case. 736 */ 737 FailedUnlock(obj, self, NULL, NULL); 738 return false; 739 } 740 } else { 741 /* 742 * The lock is fat. We must check to see if Unlock has 743 * raised any exceptions before continuing. 744 */ 745 DCHECK(LW_MONITOR(*thinp) != NULL); 746 if (!LW_MONITOR(*thinp)->Unlock(self)) { 747 // An exception has been raised. Do not fall through. 748 return false; 749 } 750 } 751 return true; 752} 753 754/* 755 * Object.wait(). Also called for class init. 756 */ 757void Monitor::Wait(Thread* self, Object *obj, int64_t ms, int32_t ns, bool interruptShouldThrow) { 758 volatile int32_t* thinp = obj->GetRawLockWordAddress(); 759 760 // If the lock is still thin, we need to fatten it. 761 uint32_t thin = *thinp; 762 if (LW_SHAPE(thin) == LW_SHAPE_THIN) { 763 // Make sure that 'self' holds the lock. 764 if (LW_LOCK_OWNER(thin) != self->GetThinLockId()) { 765 ThrowIllegalMonitorStateExceptionF("object not locked by thread before wait()"); 766 return; 767 } 768 769 /* This thread holds the lock. We need to fatten the lock 770 * so 'self' can block on it. Don't update the object lock 771 * field yet, because 'self' needs to acquire the lock before 772 * any other thread gets a chance. 773 */ 774 Inflate(self, obj); 775 VLOG(monitor) << StringPrintf("monitor: thread %d fattened lock %p by wait()", self->GetThinLockId(), thinp); 776 } 777 LW_MONITOR(*thinp)->Wait(self, ms, ns, interruptShouldThrow); 778} 779 780void Monitor::Notify(Thread* self, Object *obj) { 781 uint32_t thin = *obj->GetRawLockWordAddress(); 782 783 // If the lock is still thin, there aren't any waiters; 784 // waiting on an object forces lock fattening. 785 if (LW_SHAPE(thin) == LW_SHAPE_THIN) { 786 // Make sure that 'self' holds the lock. 787 if (LW_LOCK_OWNER(thin) != self->GetThinLockId()) { 788 ThrowIllegalMonitorStateExceptionF("object not locked by thread before notify()"); 789 return; 790 } 791 // no-op; there are no waiters to notify. 792 } else { 793 // It's a fat lock. 794 LW_MONITOR(thin)->Notify(self); 795 } 796} 797 798void Monitor::NotifyAll(Thread* self, Object *obj) { 799 uint32_t thin = *obj->GetRawLockWordAddress(); 800 801 // If the lock is still thin, there aren't any waiters; 802 // waiting on an object forces lock fattening. 803 if (LW_SHAPE(thin) == LW_SHAPE_THIN) { 804 // Make sure that 'self' holds the lock. 805 if (LW_LOCK_OWNER(thin) != self->GetThinLockId()) { 806 ThrowIllegalMonitorStateExceptionF("object not locked by thread before notifyAll()"); 807 return; 808 } 809 // no-op; there are no waiters to notify. 810 } else { 811 // It's a fat lock. 812 LW_MONITOR(thin)->NotifyAll(self); 813 } 814} 815 816uint32_t Monitor::GetThinLockId(uint32_t raw_lock_word) { 817 if (LW_SHAPE(raw_lock_word) == LW_SHAPE_THIN) { 818 return LW_LOCK_OWNER(raw_lock_word); 819 } else { 820 Thread* owner = LW_MONITOR(raw_lock_word)->owner_; 821 return owner ? owner->GetThinLockId() : 0; 822 } 823} 824 825void Monitor::DescribeWait(std::ostream& os, const Thread* thread) { 826 ThreadState state = thread->GetState(); 827 828 Object* object = NULL; 829 uint32_t lock_owner = ThreadList::kInvalidId; 830 if (state == kWaiting || state == kTimedWaiting) { 831 os << " - waiting on "; 832 Monitor* monitor = thread->wait_monitor_; 833 if (monitor != NULL) { 834 object = monitor->obj_; 835 } 836 lock_owner = Thread::LockOwnerFromThreadLock(object); 837 } else if (state == kBlocked) { 838 os << " - waiting to lock "; 839 object = thread->monitor_enter_object_; 840 if (object != NULL) { 841 lock_owner = object->GetThinLockId(); 842 } 843 } else { 844 // We're not waiting on anything. 845 return; 846 } 847 os << "<" << object << ">"; 848 849 // - waiting on <0x613f83d8> (a java.lang.ThreadLock) held by thread 5 850 // - waiting on <0x6008c468> (a java.lang.Class<java.lang.ref.ReferenceQueue>) 851 os << " (a " << PrettyTypeOf(object) << ")"; 852 853 if (lock_owner != ThreadList::kInvalidId) { 854 os << " held by thread " << lock_owner; 855 } 856 857 os << "\n"; 858} 859 860void Monitor::TranslateLocation(const Method* method, uint32_t pc, 861 const char*& source_file, uint32_t& line_number) const { 862 // If method is null, location is unknown 863 if (method == NULL) { 864 source_file = ""; 865 line_number = 0; 866 return; 867 } 868 MethodHelper mh(method); 869 source_file = mh.GetDeclaringClassSourceFile(); 870 if (source_file == NULL) { 871 source_file = ""; 872 } 873 line_number = mh.GetLineNumFromNativePC(pc); 874} 875 876MonitorList::MonitorList() : lock_("MonitorList lock") { 877} 878 879MonitorList::~MonitorList() { 880 MutexLock mu(lock_); 881 STLDeleteElements(&list_); 882} 883 884void MonitorList::Add(Monitor* m) { 885 MutexLock mu(lock_); 886 list_.push_front(m); 887} 888 889void MonitorList::SweepMonitorList(Heap::IsMarkedTester is_marked, void* arg) { 890 MutexLock mu(lock_); 891 typedef std::list<Monitor*>::iterator It; // TODO: C++0x auto 892 It it = list_.begin(); 893 while (it != list_.end()) { 894 Monitor* m = *it; 895 if (!is_marked(m->GetObject(), arg)) { 896 VLOG(monitor) << "freeing monitor " << m << " belonging to unmarked object " << m->GetObject(); 897 delete m; 898 it = list_.erase(it); 899 } else { 900 ++it; 901 } 902 } 903} 904 905} // namespace art 906