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Diffstat (limited to 'runtime/monitor.cc')
| -rw-r--r-- | runtime/monitor.cc | 1016 |
1 files changed, 1016 insertions, 0 deletions
diff --git a/runtime/monitor.cc b/runtime/monitor.cc new file mode 100644 index 0000000..11790e5 --- /dev/null +++ b/runtime/monitor.cc @@ -0,0 +1,1016 @@ +/* + * Copyright (C) 2008 The Android Open Source Project + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +#include "monitor.h" + +#include <vector> + +#include "base/mutex.h" +#include "base/stl_util.h" +#include "class_linker.h" +#include "dex_file-inl.h" +#include "dex_instruction.h" +#include "mirror/abstract_method-inl.h" +#include "mirror/class-inl.h" +#include "mirror/object-inl.h" +#include "mirror/object_array-inl.h" +#include "object_utils.h" +#include "scoped_thread_state_change.h" +#include "thread.h" +#include "thread_list.h" +#include "verifier/method_verifier.h" +#include "well_known_classes.h" + +namespace art { + +/* + * Every Object has a monitor associated with it, but not every Object is + * actually locked. Even the ones that are locked do not need a + * full-fledged monitor until a) there is actual contention or b) wait() + * is called on the Object. + * + * For Android, we have implemented a scheme similar to the one described + * in Bacon et al.'s "Thin locks: featherweight synchronization for Java" + * (ACM 1998). Things are even easier for us, though, because we have + * a full 32 bits to work with. + * + * The two states of an Object's lock are referred to as "thin" and + * "fat". A lock may transition from the "thin" state to the "fat" + * state and this transition is referred to as inflation. Once a lock + * has been inflated it remains in the "fat" state indefinitely. + * + * The lock value itself is stored in Object.lock. The LSB of the + * lock encodes its state. When cleared, the lock is in the "thin" + * state and its bits are formatted as follows: + * + * [31 ---- 19] [18 ---- 3] [2 ---- 1] [0] + * lock count thread id hash state 0 + * + * When set, the lock is in the "fat" state and its bits are formatted + * as follows: + * + * [31 ---- 3] [2 ---- 1] [0] + * pointer hash state 1 + * + * For an in-depth description of the mechanics of thin-vs-fat locking, + * read the paper referred to above. + * + * Monitors provide: + * - mutually exclusive access to resources + * - a way for multiple threads to wait for notification + * + * In effect, they fill the role of both mutexes and condition variables. + * + * Only one thread can own the monitor at any time. There may be several + * threads waiting on it (the wait call unlocks it). One or more waiting + * threads may be getting interrupted or notified at any given time. + * + * TODO: the various members of monitor are not SMP-safe. + */ + +// The shape is the bottom bit; either LW_SHAPE_THIN or LW_SHAPE_FAT. +#define LW_SHAPE_MASK 0x1 +#define LW_SHAPE(x) static_cast<int>((x) & LW_SHAPE_MASK) + +/* + * Monitor accessor. Extracts a monitor structure pointer from a fat + * lock. Performs no error checking. + */ +#define LW_MONITOR(x) \ + (reinterpret_cast<Monitor*>((x) & ~((LW_HASH_STATE_MASK << LW_HASH_STATE_SHIFT) | LW_SHAPE_MASK))) + +/* + * Lock recursion count field. Contains a count of the number of times + * a lock has been recursively acquired. + */ +#define LW_LOCK_COUNT_MASK 0x1fff +#define LW_LOCK_COUNT_SHIFT 19 +#define LW_LOCK_COUNT(x) (((x) >> LW_LOCK_COUNT_SHIFT) & LW_LOCK_COUNT_MASK) + +bool (*Monitor::is_sensitive_thread_hook_)() = NULL; +uint32_t Monitor::lock_profiling_threshold_ = 0; + +bool Monitor::IsSensitiveThread() { + if (is_sensitive_thread_hook_ != NULL) { + return (*is_sensitive_thread_hook_)(); + } + return false; +} + +void Monitor::Init(uint32_t lock_profiling_threshold, bool (*is_sensitive_thread_hook)()) { + lock_profiling_threshold_ = lock_profiling_threshold; + is_sensitive_thread_hook_ = is_sensitive_thread_hook; +} + +Monitor::Monitor(Thread* owner, mirror::Object* obj) + : monitor_lock_("a monitor lock", kMonitorLock), + owner_(owner), + lock_count_(0), + obj_(obj), + wait_set_(NULL), + locking_method_(NULL), + locking_dex_pc_(0) { + monitor_lock_.Lock(owner); + // Propagate the lock state. + uint32_t thin = *obj->GetRawLockWordAddress(); + lock_count_ = LW_LOCK_COUNT(thin); + thin &= LW_HASH_STATE_MASK << LW_HASH_STATE_SHIFT; + thin |= reinterpret_cast<uint32_t>(this) | LW_SHAPE_FAT; + // Publish the updated lock word. + android_atomic_release_store(thin, obj->GetRawLockWordAddress()); + // Lock profiling. + if (lock_profiling_threshold_ != 0) { + locking_method_ = owner->GetCurrentMethod(&locking_dex_pc_); + } +} + +Monitor::~Monitor() { + DCHECK(obj_ != NULL); + DCHECK_EQ(LW_SHAPE(*obj_->GetRawLockWordAddress()), LW_SHAPE_FAT); +} + +/* + * Links a thread into a monitor's wait set. The monitor lock must be + * held by the caller of this routine. + */ +void Monitor::AppendToWaitSet(Thread* thread) { + DCHECK(owner_ == Thread::Current()); + DCHECK(thread != NULL); + DCHECK(thread->wait_next_ == NULL) << thread->wait_next_; + if (wait_set_ == NULL) { + wait_set_ = thread; + return; + } + + // push_back. + Thread* t = wait_set_; + while (t->wait_next_ != NULL) { + t = t->wait_next_; + } + t->wait_next_ = thread; +} + +/* + * Unlinks a thread from a monitor's wait set. The monitor lock must + * be held by the caller of this routine. + */ +void Monitor::RemoveFromWaitSet(Thread *thread) { + DCHECK(owner_ == Thread::Current()); + DCHECK(thread != NULL); + if (wait_set_ == NULL) { + return; + } + if (wait_set_ == thread) { + wait_set_ = thread->wait_next_; + thread->wait_next_ = NULL; + return; + } + + Thread* t = wait_set_; + while (t->wait_next_ != NULL) { + if (t->wait_next_ == thread) { + t->wait_next_ = thread->wait_next_; + thread->wait_next_ = NULL; + return; + } + t = t->wait_next_; + } +} + +mirror::Object* Monitor::GetObject() { + return obj_; +} + +void Monitor::Lock(Thread* self) { + if (owner_ == self) { + lock_count_++; + return; + } + + if (!monitor_lock_.TryLock(self)) { + uint64_t waitStart = 0; + uint64_t waitEnd = 0; + uint32_t wait_threshold = lock_profiling_threshold_; + const mirror::AbstractMethod* current_locking_method = NULL; + uint32_t current_locking_dex_pc = 0; + { + ScopedThreadStateChange tsc(self, kBlocked); + if (wait_threshold != 0) { + waitStart = NanoTime() / 1000; + } + current_locking_method = locking_method_; + current_locking_dex_pc = locking_dex_pc_; + + monitor_lock_.Lock(self); + if (wait_threshold != 0) { + waitEnd = NanoTime() / 1000; + } + } + + if (wait_threshold != 0) { + uint64_t wait_ms = (waitEnd - waitStart) / 1000; + uint32_t sample_percent; + if (wait_ms >= wait_threshold) { + sample_percent = 100; + } else { + sample_percent = 100 * wait_ms / wait_threshold; + } + if (sample_percent != 0 && (static_cast<uint32_t>(rand() % 100) < sample_percent)) { + const char* current_locking_filename; + uint32_t current_locking_line_number; + TranslateLocation(current_locking_method, current_locking_dex_pc, + current_locking_filename, current_locking_line_number); + LogContentionEvent(self, wait_ms, sample_percent, current_locking_filename, current_locking_line_number); + } + } + } + owner_ = self; + DCHECK_EQ(lock_count_, 0); + + // When debugging, save the current monitor holder for future + // acquisition failures to use in sampled logging. + if (lock_profiling_threshold_ != 0) { + locking_method_ = self->GetCurrentMethod(&locking_dex_pc_); + } +} + +static void ThrowIllegalMonitorStateExceptionF(const char* fmt, ...) + __attribute__((format(printf, 1, 2))); + +static void ThrowIllegalMonitorStateExceptionF(const char* fmt, ...) + SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) { + va_list args; + va_start(args, fmt); + Thread* self = Thread::Current(); + ThrowLocation throw_location = self->GetCurrentLocationForThrow(); + self->ThrowNewExceptionV(throw_location, "Ljava/lang/IllegalMonitorStateException;", fmt, args); + if (!Runtime::Current()->IsStarted()) { + std::ostringstream ss; + self->Dump(ss); + std::string str(ss.str()); + LOG(ERROR) << "IllegalMonitorStateException: " << str; + } + va_end(args); +} + +static std::string ThreadToString(Thread* thread) { + if (thread == NULL) { + return "NULL"; + } + std::ostringstream oss; + // TODO: alternatively, we could just return the thread's name. + oss << *thread; + return oss.str(); +} + +void Monitor::FailedUnlock(mirror::Object* o, Thread* expected_owner, Thread* found_owner, + Monitor* monitor) { + Thread* current_owner = NULL; + std::string current_owner_string; + std::string expected_owner_string; + std::string found_owner_string; + { + // TODO: isn't this too late to prevent threads from disappearing? + // Acquire thread list lock so threads won't disappear from under us. + MutexLock mu(Thread::Current(), *Locks::thread_list_lock_); + // Re-read owner now that we hold lock. + current_owner = (monitor != NULL) ? monitor->owner_ : NULL; + // Get short descriptions of the threads involved. + current_owner_string = ThreadToString(current_owner); + expected_owner_string = ThreadToString(expected_owner); + found_owner_string = ThreadToString(found_owner); + } + if (current_owner == NULL) { + if (found_owner == NULL) { + ThrowIllegalMonitorStateExceptionF("unlock of unowned monitor on object of type '%s'" + " on thread '%s'", + PrettyTypeOf(o).c_str(), + expected_owner_string.c_str()); + } else { + // Race: the original read found an owner but now there is none + ThrowIllegalMonitorStateExceptionF("unlock of monitor owned by '%s' on object of type '%s'" + " (where now the monitor appears unowned) on thread '%s'", + found_owner_string.c_str(), + PrettyTypeOf(o).c_str(), + expected_owner_string.c_str()); + } + } else { + if (found_owner == NULL) { + // Race: originally there was no owner, there is now + ThrowIllegalMonitorStateExceptionF("unlock of monitor owned by '%s' on object of type '%s'" + " (originally believed to be unowned) on thread '%s'", + current_owner_string.c_str(), + PrettyTypeOf(o).c_str(), + expected_owner_string.c_str()); + } else { + if (found_owner != current_owner) { + // Race: originally found and current owner have changed + ThrowIllegalMonitorStateExceptionF("unlock of monitor originally owned by '%s' (now" + " owned by '%s') on object of type '%s' on thread '%s'", + found_owner_string.c_str(), + current_owner_string.c_str(), + PrettyTypeOf(o).c_str(), + expected_owner_string.c_str()); + } else { + ThrowIllegalMonitorStateExceptionF("unlock of monitor owned by '%s' on object of type '%s'" + " on thread '%s", + current_owner_string.c_str(), + PrettyTypeOf(o).c_str(), + expected_owner_string.c_str()); + } + } + } +} + +bool Monitor::Unlock(Thread* self, bool for_wait) { + DCHECK(self != NULL); + Thread* owner = owner_; + if (owner == self) { + // We own the monitor, so nobody else can be in here. + if (lock_count_ == 0) { + owner_ = NULL; + locking_method_ = NULL; + locking_dex_pc_ = 0; + monitor_lock_.Unlock(self); + } else { + --lock_count_; + } + } else if (for_wait) { + // Wait should have already cleared the fields. + DCHECK_EQ(lock_count_, 0); + DCHECK(owner == NULL); + DCHECK(locking_method_ == NULL); + DCHECK_EQ(locking_dex_pc_, 0u); + monitor_lock_.Unlock(self); + } else { + // We don't own this, so we're not allowed to unlock it. + // The JNI spec says that we should throw IllegalMonitorStateException + // in this case. + FailedUnlock(obj_, self, owner, this); + return false; + } + return true; +} + +/* + * Wait on a monitor until timeout, interrupt, or notification. Used for + * Object.wait() and (somewhat indirectly) Thread.sleep() and Thread.join(). + * + * If another thread calls Thread.interrupt(), we throw InterruptedException + * and return immediately if one of the following are true: + * - blocked in wait(), wait(long), or wait(long, int) methods of Object + * - blocked in join(), join(long), or join(long, int) methods of Thread + * - blocked in sleep(long), or sleep(long, int) methods of Thread + * Otherwise, we set the "interrupted" flag. + * + * Checks to make sure that "ns" is in the range 0-999999 + * (i.e. fractions of a millisecond) and throws the appropriate + * exception if it isn't. + * + * The spec allows "spurious wakeups", and recommends that all code using + * Object.wait() do so in a loop. This appears to derive from concerns + * about pthread_cond_wait() on multiprocessor systems. Some commentary + * on the web casts doubt on whether these can/should occur. + * + * Since we're allowed to wake up "early", we clamp extremely long durations + * to return at the end of the 32-bit time epoch. + */ +void Monitor::Wait(Thread* self, int64_t ms, int32_t ns, + bool interruptShouldThrow, ThreadState why) { + DCHECK(self != NULL); + DCHECK(why == kTimedWaiting || why == kWaiting || why == kSleeping); + + // Make sure that we hold the lock. + if (owner_ != self) { + ThrowIllegalMonitorStateExceptionF("object not locked by thread before wait()"); + return; + } + monitor_lock_.AssertHeld(self); + + // We need to turn a zero-length timed wait into a regular wait because + // Object.wait(0, 0) is defined as Object.wait(0), which is defined as Object.wait(). + if (why == kTimedWaiting && (ms == 0 && ns == 0)) { + why = kWaiting; + } + + WaitWithLock(self, ms, ns, interruptShouldThrow, why); +} + +void Monitor::WaitWithLock(Thread* self, int64_t ms, int32_t ns, + bool interruptShouldThrow, ThreadState why) { + // Enforce the timeout range. + if (ms < 0 || ns < 0 || ns > 999999) { + ThrowLocation throw_location = self->GetCurrentLocationForThrow(); + self->ThrowNewExceptionF(throw_location, "Ljava/lang/IllegalArgumentException;", + "timeout arguments out of range: ms=%lld ns=%d", ms, ns); + return; + } + + /* + * Add ourselves to the set of threads waiting on this monitor, and + * release our hold. We need to let it go even if we're a few levels + * deep in a recursive lock, and we need to restore that later. + * + * We append to the wait set ahead of clearing the count and owner + * fields so the subroutine can check that the calling thread owns + * the monitor. Aside from that, the order of member updates is + * not order sensitive as we hold the pthread mutex. + */ + AppendToWaitSet(self); + int prev_lock_count = lock_count_; + lock_count_ = 0; + owner_ = NULL; + const mirror::AbstractMethod* saved_method = locking_method_; + locking_method_ = NULL; + uintptr_t saved_dex_pc = locking_dex_pc_; + locking_dex_pc_ = 0; + + /* + * Update thread state. If the GC wakes up, it'll ignore us, knowing + * that we won't touch any references in this state, and we'll check + * our suspend mode before we transition out. + */ + self->TransitionFromRunnableToSuspended(why); + + bool was_interrupted = false; + { + // Pseudo-atomically wait on self's wait_cond_ and release the monitor lock. + MutexLock mu(self, *self->wait_mutex_); + + // Set wait_monitor_ to the monitor object we will be waiting on. When wait_monitor_ is + // non-NULL a notifying or interrupting thread must signal the thread's wait_cond_ to wake it + // up. + DCHECK(self->wait_monitor_ == NULL); + self->wait_monitor_ = this; + + // Release the monitor lock. + Unlock(self, true); + + // Handle the case where the thread was interrupted before we called wait(). + if (self->interrupted_) { + was_interrupted = true; + } else { + // Wait for a notification or a timeout to occur. + if (why == kWaiting) { + self->wait_cond_->Wait(self); + } else { + DCHECK(why == kTimedWaiting || why == kSleeping) << why; + self->wait_cond_->TimedWait(self, ms, ns); + } + if (self->interrupted_) { + was_interrupted = true; + } + self->interrupted_ = false; + } + } + + // Set self->status back to kRunnable, and self-suspend if needed. + self->TransitionFromSuspendedToRunnable(); + + { + // We reset the thread's wait_monitor_ field after transitioning back to runnable so + // that a thread in a waiting/sleeping state has a non-null wait_monitor_ for debugging + // and diagnostic purposes. (If you reset this earlier, stack dumps will claim that threads + // are waiting on "null".) + MutexLock mu(self, *self->wait_mutex_); + DCHECK(self->wait_monitor_ != NULL); + self->wait_monitor_ = NULL; + } + + // Re-acquire the monitor lock. + Lock(self); + + self->wait_mutex_->AssertNotHeld(self); + + /* + * We remove our thread from wait set after restoring the count + * and owner fields so the subroutine can check that the calling + * thread owns the monitor. Aside from that, the order of member + * updates is not order sensitive as we hold the pthread mutex. + */ + owner_ = self; + lock_count_ = prev_lock_count; + locking_method_ = saved_method; + locking_dex_pc_ = saved_dex_pc; + RemoveFromWaitSet(self); + + if (was_interrupted) { + /* + * We were interrupted while waiting, or somebody interrupted an + * un-interruptible thread earlier and we're bailing out immediately. + * + * The doc sayeth: "The interrupted status of the current thread is + * cleared when this exception is thrown." + */ + { + MutexLock mu(self, *self->wait_mutex_); + self->interrupted_ = false; + } + if (interruptShouldThrow) { + ThrowLocation throw_location = self->GetCurrentLocationForThrow(); + self->ThrowNewException(throw_location, "Ljava/lang/InterruptedException;", NULL); + } + } +} + +void Monitor::Notify(Thread* self) { + DCHECK(self != NULL); + // Make sure that we hold the lock. + if (owner_ != self) { + ThrowIllegalMonitorStateExceptionF("object not locked by thread before notify()"); + return; + } + monitor_lock_.AssertHeld(self); + NotifyWithLock(self); +} + +void Monitor::NotifyWithLock(Thread* self) { + // Signal the first waiting thread in the wait set. + while (wait_set_ != NULL) { + Thread* thread = wait_set_; + wait_set_ = thread->wait_next_; + thread->wait_next_ = NULL; + + // Check to see if the thread is still waiting. + MutexLock mu(self, *thread->wait_mutex_); + if (thread->wait_monitor_ != NULL) { + thread->wait_cond_->Signal(self); + return; + } + } +} + +void Monitor::NotifyAll(Thread* self) { + DCHECK(self != NULL); + // Make sure that we hold the lock. + if (owner_ != self) { + ThrowIllegalMonitorStateExceptionF("object not locked by thread before notifyAll()"); + return; + } + monitor_lock_.AssertHeld(self); + NotifyAllWithLock(); +} + +void Monitor::NotifyAllWithLock() { + // Signal all threads in the wait set. + while (wait_set_ != NULL) { + Thread* thread = wait_set_; + wait_set_ = thread->wait_next_; + thread->wait_next_ = NULL; + thread->Notify(); + } +} + +/* + * Changes the shape of a monitor from thin to fat, preserving the + * internal lock state. The calling thread must own the lock. + */ +void Monitor::Inflate(Thread* self, mirror::Object* obj) { + DCHECK(self != NULL); + DCHECK(obj != NULL); + DCHECK_EQ(LW_SHAPE(*obj->GetRawLockWordAddress()), LW_SHAPE_THIN); + DCHECK_EQ(LW_LOCK_OWNER(*obj->GetRawLockWordAddress()), static_cast<int32_t>(self->GetThinLockId())); + + // Allocate and acquire a new monitor. + Monitor* m = new Monitor(self, obj); + VLOG(monitor) << "monitor: thread " << self->GetThinLockId() + << " created monitor " << m << " for object " << obj; + Runtime::Current()->GetMonitorList()->Add(m); +} + +void Monitor::MonitorEnter(Thread* self, mirror::Object* obj) { + volatile int32_t* thinp = obj->GetRawLockWordAddress(); + uint32_t sleepDelayNs; + uint32_t minSleepDelayNs = 1000000; /* 1 millisecond */ + uint32_t maxSleepDelayNs = 1000000000; /* 1 second */ + uint32_t thin, newThin; + + DCHECK(self != NULL); + DCHECK(obj != NULL); + uint32_t threadId = self->GetThinLockId(); + retry: + thin = *thinp; + if (LW_SHAPE(thin) == LW_SHAPE_THIN) { + /* + * The lock is a thin lock. The owner field is used to + * determine the acquire method, ordered by cost. + */ + if (LW_LOCK_OWNER(thin) == threadId) { + /* + * The calling thread owns the lock. Increment the + * value of the recursion count field. + */ + *thinp += 1 << LW_LOCK_COUNT_SHIFT; + if (LW_LOCK_COUNT(*thinp) == LW_LOCK_COUNT_MASK) { + /* + * The reacquisition limit has been reached. Inflate + * the lock so the next acquire will not overflow the + * recursion count field. + */ + Inflate(self, obj); + } + } else if (LW_LOCK_OWNER(thin) == 0) { + // The lock is unowned. Install the thread id of the calling thread into the owner field. + // This is the common case: compiled code will have tried this before calling back into + // the runtime. + newThin = thin | (threadId << LW_LOCK_OWNER_SHIFT); + if (android_atomic_acquire_cas(thin, newThin, thinp) != 0) { + // The acquire failed. Try again. + goto retry; + } + } else { + VLOG(monitor) << StringPrintf("monitor: thread %d spin on lock %p (a %s) owned by %d", + threadId, thinp, PrettyTypeOf(obj).c_str(), LW_LOCK_OWNER(thin)); + // The lock is owned by another thread. Notify the runtime that we are about to wait. + self->monitor_enter_object_ = obj; + self->TransitionFromRunnableToSuspended(kBlocked); + // Spin until the thin lock is released or inflated. + sleepDelayNs = 0; + for (;;) { + thin = *thinp; + // Check the shape of the lock word. Another thread + // may have inflated the lock while we were waiting. + if (LW_SHAPE(thin) == LW_SHAPE_THIN) { + if (LW_LOCK_OWNER(thin) == 0) { + // The lock has been released. Install the thread id of the + // calling thread into the owner field. + newThin = thin | (threadId << LW_LOCK_OWNER_SHIFT); + if (android_atomic_acquire_cas(thin, newThin, thinp) == 0) { + // The acquire succeed. Break out of the loop and proceed to inflate the lock. + break; + } + } else { + // The lock has not been released. Yield so the owning thread can run. + if (sleepDelayNs == 0) { + sched_yield(); + sleepDelayNs = minSleepDelayNs; + } else { + NanoSleep(sleepDelayNs); + // Prepare the next delay value. Wrap to avoid once a second polls for eternity. + if (sleepDelayNs < maxSleepDelayNs / 2) { + sleepDelayNs *= 2; + } else { + sleepDelayNs = minSleepDelayNs; + } + } + } + } else { + // The thin lock was inflated by another thread. Let the runtime know we are no longer + // waiting and try again. + VLOG(monitor) << StringPrintf("monitor: thread %d found lock %p surprise-fattened by another thread", threadId, thinp); + self->monitor_enter_object_ = NULL; + self->TransitionFromSuspendedToRunnable(); + goto retry; + } + } + VLOG(monitor) << StringPrintf("monitor: thread %d spin on lock %p done", threadId, thinp); + // We have acquired the thin lock. Let the runtime know that we are no longer waiting. + self->monitor_enter_object_ = NULL; + self->TransitionFromSuspendedToRunnable(); + // Fatten the lock. + Inflate(self, obj); + VLOG(monitor) << StringPrintf("monitor: thread %d fattened lock %p", threadId, thinp); + } + } else { + // The lock is a fat lock. + VLOG(monitor) << StringPrintf("monitor: thread %d locking fat lock %p (%p) %p on a %s", + threadId, thinp, LW_MONITOR(*thinp), + reinterpret_cast<void*>(*thinp), PrettyTypeOf(obj).c_str()); + DCHECK(LW_MONITOR(*thinp) != NULL); + LW_MONITOR(*thinp)->Lock(self); + } +} + +bool Monitor::MonitorExit(Thread* self, mirror::Object* obj) { + volatile int32_t* thinp = obj->GetRawLockWordAddress(); + + DCHECK(self != NULL); + //DCHECK_EQ(self->GetState(), kRunnable); + DCHECK(obj != NULL); + + /* + * Cache the lock word as its value can change while we are + * examining its state. + */ + uint32_t thin = *thinp; + if (LW_SHAPE(thin) == LW_SHAPE_THIN) { + /* + * The lock is thin. We must ensure that the lock is owned + * by the given thread before unlocking it. + */ + if (LW_LOCK_OWNER(thin) == self->GetThinLockId()) { + /* + * We are the lock owner. It is safe to update the lock + * without CAS as lock ownership guards the lock itself. + */ + if (LW_LOCK_COUNT(thin) == 0) { + /* + * The lock was not recursively acquired, the common + * case. Unlock by clearing all bits except for the + * hash state. + */ + thin &= (LW_HASH_STATE_MASK << LW_HASH_STATE_SHIFT); + android_atomic_release_store(thin, thinp); + } else { + /* + * The object was recursively acquired. Decrement the + * lock recursion count field. + */ + *thinp -= 1 << LW_LOCK_COUNT_SHIFT; + } + } else { + /* + * We do not own the lock. The JVM spec requires that we + * throw an exception in this case. + */ + FailedUnlock(obj, self, NULL, NULL); + return false; + } + } else { + /* + * The lock is fat. We must check to see if Unlock has + * raised any exceptions before continuing. + */ + DCHECK(LW_MONITOR(*thinp) != NULL); + if (!LW_MONITOR(*thinp)->Unlock(self, false)) { + // An exception has been raised. Do not fall through. + return false; + } + } + return true; +} + +/* + * Object.wait(). Also called for class init. + */ +void Monitor::Wait(Thread* self, mirror::Object *obj, int64_t ms, int32_t ns, + bool interruptShouldThrow, ThreadState why) { + volatile int32_t* thinp = obj->GetRawLockWordAddress(); + + // If the lock is still thin, we need to fatten it. + uint32_t thin = *thinp; + if (LW_SHAPE(thin) == LW_SHAPE_THIN) { + // Make sure that 'self' holds the lock. + if (LW_LOCK_OWNER(thin) != self->GetThinLockId()) { + ThrowIllegalMonitorStateExceptionF("object not locked by thread before wait()"); + return; + } + + /* This thread holds the lock. We need to fatten the lock + * so 'self' can block on it. Don't update the object lock + * field yet, because 'self' needs to acquire the lock before + * any other thread gets a chance. + */ + Inflate(self, obj); + VLOG(monitor) << StringPrintf("monitor: thread %d fattened lock %p by wait()", self->GetThinLockId(), thinp); + } + LW_MONITOR(*thinp)->Wait(self, ms, ns, interruptShouldThrow, why); +} + +void Monitor::Notify(Thread* self, mirror::Object *obj) { + uint32_t thin = *obj->GetRawLockWordAddress(); + + // If the lock is still thin, there aren't any waiters; + // waiting on an object forces lock fattening. + if (LW_SHAPE(thin) == LW_SHAPE_THIN) { + // Make sure that 'self' holds the lock. + if (LW_LOCK_OWNER(thin) != self->GetThinLockId()) { + ThrowIllegalMonitorStateExceptionF("object not locked by thread before notify()"); + return; + } + // no-op; there are no waiters to notify. + Inflate(self, obj); + } else { + // It's a fat lock. + LW_MONITOR(thin)->Notify(self); + } +} + +void Monitor::NotifyAll(Thread* self, mirror::Object *obj) { + uint32_t thin = *obj->GetRawLockWordAddress(); + + // If the lock is still thin, there aren't any waiters; + // waiting on an object forces lock fattening. + if (LW_SHAPE(thin) == LW_SHAPE_THIN) { + // Make sure that 'self' holds the lock. + if (LW_LOCK_OWNER(thin) != self->GetThinLockId()) { + ThrowIllegalMonitorStateExceptionF("object not locked by thread before notifyAll()"); + return; + } + // no-op; there are no waiters to notify. + Inflate(self, obj); + } else { + // It's a fat lock. + LW_MONITOR(thin)->NotifyAll(self); + } +} + +uint32_t Monitor::GetThinLockId(uint32_t raw_lock_word) { + if (LW_SHAPE(raw_lock_word) == LW_SHAPE_THIN) { + return LW_LOCK_OWNER(raw_lock_word); + } else { + Thread* owner = LW_MONITOR(raw_lock_word)->owner_; + return owner ? owner->GetThinLockId() : 0; + } +} + +void Monitor::DescribeWait(std::ostream& os, const Thread* thread) { + ThreadState state = thread->GetState(); + + mirror::Object* object = NULL; + uint32_t lock_owner = ThreadList::kInvalidId; + if (state == kWaiting || state == kTimedWaiting || state == kSleeping) { + if (state == kSleeping) { + os << " - sleeping on "; + } else { + os << " - waiting on "; + } + { + Thread* self = Thread::Current(); + MutexLock mu(self, *thread->wait_mutex_); + Monitor* monitor = thread->wait_monitor_; + if (monitor != NULL) { + object = monitor->obj_; + } + } + } else if (state == kBlocked) { + os << " - waiting to lock "; + object = thread->monitor_enter_object_; + if (object != NULL) { + lock_owner = object->GetThinLockId(); + } + } else { + // We're not waiting on anything. + return; + } + + // - waiting on <0x6008c468> (a java.lang.Class<java.lang.ref.ReferenceQueue>) + os << "<" << object << "> (a " << PrettyTypeOf(object) << ")"; + + // - waiting to lock <0x613f83d8> (a java.lang.Object) held by thread 5 + if (lock_owner != ThreadList::kInvalidId) { + os << " held by thread " << lock_owner; + } + + os << "\n"; +} + +mirror::Object* Monitor::GetContendedMonitor(Thread* thread) { + // This is used to implement JDWP's ThreadReference.CurrentContendedMonitor, and has a bizarre + // definition of contended that includes a monitor a thread is trying to enter... + mirror::Object* result = thread->monitor_enter_object_; + if (result != NULL) { + return result; + } + // ...but also a monitor that the thread is waiting on. + { + MutexLock mu(Thread::Current(), *thread->wait_mutex_); + Monitor* monitor = thread->wait_monitor_; + if (monitor != NULL) { + return monitor->obj_; + } + } + return NULL; +} + +void Monitor::VisitLocks(StackVisitor* stack_visitor, void (*callback)(mirror::Object*, void*), + void* callback_context) { + mirror::AbstractMethod* m = stack_visitor->GetMethod(); + CHECK(m != NULL); + + // Native methods are an easy special case. + // TODO: use the JNI implementation's table of explicit MonitorEnter calls and dump those too. + if (m->IsNative()) { + if (m->IsSynchronized()) { + mirror::Object* jni_this = stack_visitor->GetCurrentSirt()->GetReference(0); + callback(jni_this, callback_context); + } + return; + } + + // Proxy methods should not be synchronized. + if (m->IsProxyMethod()) { + CHECK(!m->IsSynchronized()); + return; + } + + // <clinit> is another special case. The runtime holds the class lock while calling <clinit>. + MethodHelper mh(m); + if (mh.IsClassInitializer()) { + callback(m->GetDeclaringClass(), callback_context); + // Fall through because there might be synchronization in the user code too. + } + + // Is there any reason to believe there's any synchronization in this method? + const DexFile::CodeItem* code_item = mh.GetCodeItem(); + CHECK(code_item != NULL) << PrettyMethod(m); + if (code_item->tries_size_ == 0) { + return; // No "tries" implies no synchronization, so no held locks to report. + } + + // Ask the verifier for the dex pcs of all the monitor-enter instructions corresponding to + // the locks held in this stack frame. + std::vector<uint32_t> monitor_enter_dex_pcs; + verifier::MethodVerifier::FindLocksAtDexPc(m, stack_visitor->GetDexPc(), monitor_enter_dex_pcs); + if (monitor_enter_dex_pcs.empty()) { + return; + } + + for (size_t i = 0; i < monitor_enter_dex_pcs.size(); ++i) { + // The verifier works in terms of the dex pcs of the monitor-enter instructions. + // We want the registers used by those instructions (so we can read the values out of them). + uint32_t dex_pc = monitor_enter_dex_pcs[i]; + uint16_t monitor_enter_instruction = code_item->insns_[dex_pc]; + + // Quick sanity check. + if ((monitor_enter_instruction & 0xff) != Instruction::MONITOR_ENTER) { + LOG(FATAL) << "expected monitor-enter @" << dex_pc << "; was " + << reinterpret_cast<void*>(monitor_enter_instruction); + } + + uint16_t monitor_register = ((monitor_enter_instruction >> 8) & 0xff); + mirror::Object* o = reinterpret_cast<mirror::Object*>(stack_visitor->GetVReg(m, monitor_register, + kReferenceVReg)); + callback(o, callback_context); + } +} + +void Monitor::TranslateLocation(const mirror::AbstractMethod* method, uint32_t dex_pc, + const char*& source_file, uint32_t& line_number) const { + // If method is null, location is unknown + if (method == NULL) { + source_file = ""; + line_number = 0; + return; + } + MethodHelper mh(method); + source_file = mh.GetDeclaringClassSourceFile(); + if (source_file == NULL) { + source_file = ""; + } + line_number = mh.GetLineNumFromDexPC(dex_pc); +} + +MonitorList::MonitorList() : monitor_list_lock_("MonitorList lock") { +} + +MonitorList::~MonitorList() { + MutexLock mu(Thread::Current(), monitor_list_lock_); + STLDeleteElements(&list_); +} + +void MonitorList::Add(Monitor* m) { + MutexLock mu(Thread::Current(), monitor_list_lock_); + list_.push_front(m); +} + +void MonitorList::SweepMonitorList(IsMarkedTester is_marked, void* arg) { + MutexLock mu(Thread::Current(), monitor_list_lock_); + typedef std::list<Monitor*>::iterator It; // TODO: C++0x auto + It it = list_.begin(); + while (it != list_.end()) { + Monitor* m = *it; + if (!is_marked(m->GetObject(), arg)) { + VLOG(monitor) << "freeing monitor " << m << " belonging to unmarked object " << m->GetObject(); + delete m; + it = list_.erase(it); + } else { + ++it; + } + } +} + +MonitorInfo::MonitorInfo(mirror::Object* o) : owner(NULL), entry_count(0) { + uint32_t lock_word = *o->GetRawLockWordAddress(); + if (LW_SHAPE(lock_word) == LW_SHAPE_THIN) { + uint32_t owner_thin_lock_id = LW_LOCK_OWNER(lock_word); + if (owner_thin_lock_id != 0) { + owner = Runtime::Current()->GetThreadList()->FindThreadByThinLockId(owner_thin_lock_id); + entry_count = 1 + LW_LOCK_COUNT(lock_word); + } + // Thin locks have no waiters. + } else { + CHECK_EQ(LW_SHAPE(lock_word), LW_SHAPE_FAT); + Monitor* monitor = LW_MONITOR(lock_word); + owner = monitor->owner_; + entry_count = 1 + monitor->lock_count_; + for (Thread* waiter = monitor->wait_set_; waiter != NULL; waiter = waiter->wait_next_) { + waiters.push_back(waiter); + } + } +} + +} // namespace art |