| /* |
| * 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 "lock_word-inl.h" |
| #include "mirror/art_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 mirror::Object::monitor_ and the representation is described |
| * in the LockWord value type. |
| * |
| * 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. |
| */ |
| |
| 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* self, Thread* owner, mirror::Object* obj, int32_t hash_code) |
| : monitor_lock_("a monitor lock", kMonitorLock), |
| monitor_contenders_("monitor contenders", monitor_lock_), |
| num_waiters_(0), |
| owner_(owner), |
| lock_count_(0), |
| obj_(obj), |
| wait_set_(NULL), |
| hash_code_(hash_code), |
| locking_method_(NULL), |
| locking_dex_pc_(0), |
| monitor_id_(MonitorPool::CreateMonitorId(self, this)) { |
| // We should only inflate a lock if the owner is ourselves or suspended. This avoids a race |
| // with the owner unlocking the thin-lock. |
| CHECK(owner == nullptr || owner == self || owner->IsSuspended()); |
| // The identity hash code is set for the life time of the monitor. |
| } |
| |
| int32_t Monitor::GetHashCode() { |
| while (!HasHashCode()) { |
| if (hash_code_.CompareAndSwap(0, mirror::Object::GenerateIdentityHashCode())) { |
| break; |
| } |
| } |
| DCHECK(HasHashCode()); |
| return hash_code_.Load(); |
| } |
| |
| bool Monitor::Install(Thread* self) { |
| MutexLock mu(self, monitor_lock_); // Uncontended mutex acquisition as monitor isn't yet public. |
| CHECK(owner_ == nullptr || owner_ == self || owner_->IsSuspended()); |
| // Propagate the lock state. |
| LockWord lw(obj_->GetLockWord(false)); |
| switch (lw.GetState()) { |
| case LockWord::kThinLocked: { |
| CHECK_EQ(owner_->GetThreadId(), lw.ThinLockOwner()); |
| lock_count_ = lw.ThinLockCount(); |
| break; |
| } |
| case LockWord::kHashCode: { |
| CHECK_EQ(hash_code_, static_cast<int32_t>(lw.GetHashCode())); |
| break; |
| } |
| case LockWord::kFatLocked: { |
| // The owner_ is suspended but another thread beat us to install a monitor. |
| return false; |
| } |
| case LockWord::kUnlocked: { |
| LOG(FATAL) << "Inflating unlocked lock word"; |
| break; |
| } |
| default: { |
| LOG(FATAL) << "Invalid monitor state " << lw.GetState(); |
| return false; |
| } |
| } |
| LockWord fat(this); |
| // Publish the updated lock word, which may race with other threads. |
| bool success = obj_->CasLockWord(lw, fat); |
| // Lock profiling. |
| if (success && owner_ != nullptr && lock_profiling_threshold_ != 0) { |
| locking_method_ = owner_->GetCurrentMethod(&locking_dex_pc_); |
| } |
| return success; |
| } |
| |
| Monitor::~Monitor() { |
| MonitorPool::ReleaseMonitorId(monitor_id_); |
| // Deflated monitors have a null object. |
| } |
| |
| /* |
| * 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->GetWaitNext() == nullptr) << thread->GetWaitNext(); |
| if (wait_set_ == NULL) { |
| wait_set_ = thread; |
| return; |
| } |
| |
| // push_back. |
| Thread* t = wait_set_; |
| while (t->GetWaitNext() != nullptr) { |
| t = t->GetWaitNext(); |
| } |
| t->SetWaitNext(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->GetWaitNext(); |
| thread->SetWaitNext(nullptr); |
| return; |
| } |
| |
| Thread* t = wait_set_; |
| while (t->GetWaitNext() != NULL) { |
| if (t->GetWaitNext() == thread) { |
| t->SetWaitNext(thread->GetWaitNext()); |
| thread->SetWaitNext(nullptr); |
| return; |
| } |
| t = t->GetWaitNext(); |
| } |
| } |
| |
| void Monitor::SetObject(mirror::Object* object) { |
| obj_ = object; |
| } |
| |
| void Monitor::Lock(Thread* self) { |
| MutexLock mu(self, monitor_lock_); |
| while (true) { |
| if (owner_ == nullptr) { // Unowned. |
| owner_ = self; |
| CHECK_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_); |
| } |
| return; |
| } else if (owner_ == self) { // Recursive. |
| lock_count_++; |
| return; |
| } |
| // Contended. |
| const bool log_contention = (lock_profiling_threshold_ != 0); |
| uint64_t wait_start_ms = log_contention ? 0 : MilliTime(); |
| mirror::ArtMethod* owners_method = locking_method_; |
| uint32_t owners_dex_pc = locking_dex_pc_; |
| // Do this before releasing the lock so that we don't get deflated. |
| ++num_waiters_; |
| monitor_lock_.Unlock(self); // Let go of locks in order. |
| { |
| ScopedThreadStateChange tsc(self, kBlocked); // Change to blocked and give up mutator_lock_. |
| self->SetMonitorEnterObject(obj_); |
| MutexLock mu2(self, monitor_lock_); // Reacquire monitor_lock_ without mutator_lock_ for Wait. |
| if (owner_ != NULL) { // Did the owner_ give the lock up? |
| monitor_contenders_.Wait(self); // Still contended so wait. |
| // Woken from contention. |
| if (log_contention) { |
| uint64_t wait_ms = MilliTime() - wait_start_ms; |
| uint32_t sample_percent; |
| if (wait_ms >= lock_profiling_threshold_) { |
| sample_percent = 100; |
| } else { |
| sample_percent = 100 * wait_ms / lock_profiling_threshold_; |
| } |
| if (sample_percent != 0 && (static_cast<uint32_t>(rand() % 100) < sample_percent)) { |
| const char* owners_filename; |
| uint32_t owners_line_number; |
| TranslateLocation(owners_method, owners_dex_pc, &owners_filename, &owners_line_number); |
| LogContentionEvent(self, wait_ms, sample_percent, owners_filename, owners_line_number); |
| } |
| } |
| } |
| self->SetMonitorEnterObject(nullptr); |
| } |
| monitor_lock_.Lock(self); // Reacquire locks in order. |
| --num_waiters_; |
| } |
| } |
| |
| 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() || VLOG_IS_ON(monitor)) { |
| std::ostringstream ss; |
| self->Dump(ss); |
| LOG(Runtime::Current()->IsStarted() ? INFO : ERROR) |
| << self->GetException(NULL)->Dump() << "\n" << ss.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->GetOwner() : 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) { |
| DCHECK(self != NULL); |
| MutexLock mu(self, monitor_lock_); |
| 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; |
| // Wake a contender. |
| monitor_contenders_.Signal(self); |
| } else { |
| --lock_count_; |
| } |
| } 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); |
| |
| monitor_lock_.Lock(self); |
| |
| // Make sure that we hold the lock. |
| if (owner_ != self) { |
| ThrowIllegalMonitorStateExceptionF("object not locked by thread before wait()"); |
| monitor_lock_.Unlock(self); |
| return; |
| } |
| |
| // 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; |
| } |
| |
| // 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=%" PRId64 " ns=%d", ms, ns); |
| monitor_lock_.Unlock(self); |
| 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); |
| ++num_waiters_; |
| int prev_lock_count = lock_count_; |
| lock_count_ = 0; |
| owner_ = NULL; |
| mirror::ArtMethod* 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->GetWaitMutex()); |
| |
| // 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->GetWaitMonitor() == nullptr); |
| self->SetWaitMonitor(this); |
| |
| // Release the monitor lock. |
| monitor_contenders_.Signal(self); |
| monitor_lock_.Unlock(self); |
| |
| // Handle the case where the thread was interrupted before we called wait(). |
| if (self->IsInterruptedLocked()) { |
| was_interrupted = true; |
| } else { |
| // Wait for a notification or a timeout to occur. |
| if (why == kWaiting) { |
| self->GetWaitConditionVariable()->Wait(self); |
| } else { |
| DCHECK(why == kTimedWaiting || why == kSleeping) << why; |
| self->GetWaitConditionVariable()->TimedWait(self, ms, ns); |
| } |
| if (self->IsInterruptedLocked()) { |
| was_interrupted = true; |
| } |
| self->SetInterruptedLocked(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->GetWaitMutex()); |
| DCHECK(self->GetWaitMonitor() != nullptr); |
| self->SetWaitMonitor(nullptr); |
| } |
| |
| // Re-acquire the monitor and lock. |
| Lock(self); |
| monitor_lock_.Lock(self); |
| self->GetWaitMutex()->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; |
| --num_waiters_; |
| 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->GetWaitMutex()); |
| self->SetInterruptedLocked(false); |
| } |
| if (interruptShouldThrow) { |
| ThrowLocation throw_location = self->GetCurrentLocationForThrow(); |
| self->ThrowNewException(throw_location, "Ljava/lang/InterruptedException;", NULL); |
| } |
| } |
| monitor_lock_.Unlock(self); |
| } |
| |
| void Monitor::Notify(Thread* self) { |
| DCHECK(self != NULL); |
| MutexLock mu(self, monitor_lock_); |
| // Make sure that we hold the lock. |
| if (owner_ != self) { |
| ThrowIllegalMonitorStateExceptionF("object not locked by thread before notify()"); |
| return; |
| } |
| // Signal the first waiting thread in the wait set. |
| while (wait_set_ != NULL) { |
| Thread* thread = wait_set_; |
| wait_set_ = thread->GetWaitNext(); |
| thread->SetWaitNext(nullptr); |
| |
| // Check to see if the thread is still waiting. |
| MutexLock mu(self, *thread->GetWaitMutex()); |
| if (thread->GetWaitMonitor() != nullptr) { |
| thread->GetWaitConditionVariable()->Signal(self); |
| return; |
| } |
| } |
| } |
| |
| void Monitor::NotifyAll(Thread* self) { |
| DCHECK(self != NULL); |
| MutexLock mu(self, monitor_lock_); |
| // Make sure that we hold the lock. |
| if (owner_ != self) { |
| ThrowIllegalMonitorStateExceptionF("object not locked by thread before notifyAll()"); |
| return; |
| } |
| // Signal all threads in the wait set. |
| while (wait_set_ != NULL) { |
| Thread* thread = wait_set_; |
| wait_set_ = thread->GetWaitNext(); |
| thread->SetWaitNext(nullptr); |
| thread->Notify(); |
| } |
| } |
| |
| bool Monitor::Deflate(Thread* self, mirror::Object* obj) { |
| DCHECK(obj != nullptr); |
| // Don't need volatile since we only deflate with mutators suspended. |
| LockWord lw(obj->GetLockWord(false)); |
| // If the lock isn't an inflated monitor, then we don't need to deflate anything. |
| if (lw.GetState() == LockWord::kFatLocked) { |
| Monitor* monitor = lw.FatLockMonitor(); |
| DCHECK(monitor != nullptr); |
| MutexLock mu(self, monitor->monitor_lock_); |
| // Can't deflate if we have anybody waiting on the CV. |
| if (monitor->num_waiters_ > 0) { |
| return false; |
| } |
| Thread* owner = monitor->owner_; |
| if (owner != nullptr) { |
| // Can't deflate if we are locked and have a hash code. |
| if (monitor->HasHashCode()) { |
| return false; |
| } |
| // Can't deflate if our lock count is too high. |
| if (monitor->lock_count_ > LockWord::kThinLockMaxCount) { |
| return false; |
| } |
| // Deflate to a thin lock. |
| obj->SetLockWord(LockWord::FromThinLockId(owner->GetThreadId(), monitor->lock_count_), false); |
| VLOG(monitor) << "Deflated " << obj << " to thin lock " << owner->GetTid() << " / " |
| << monitor->lock_count_; |
| } else if (monitor->HasHashCode()) { |
| obj->SetLockWord(LockWord::FromHashCode(monitor->GetHashCode()), false); |
| VLOG(monitor) << "Deflated " << obj << " to hash monitor " << monitor->GetHashCode(); |
| } else { |
| // No lock and no hash, just put an empty lock word inside the object. |
| obj->SetLockWord(LockWord(), false); |
| VLOG(monitor) << "Deflated" << obj << " to empty lock word"; |
| } |
| // The monitor is deflated, mark the object as nullptr so that we know to delete it during the |
| // next GC. |
| monitor->obj_ = nullptr; |
| } |
| return true; |
| } |
| |
| /* |
| * Changes the shape of a monitor from thin to fat, preserving the internal lock state. The calling |
| * thread must own the lock or the owner must be suspended. There's a race with other threads |
| * inflating the lock and so the caller should read the monitor following the call. |
| */ |
| void Monitor::Inflate(Thread* self, Thread* owner, mirror::Object* obj, int32_t hash_code) { |
| DCHECK(self != NULL); |
| DCHECK(obj != NULL); |
| // Allocate and acquire a new monitor. |
| UniquePtr<Monitor> m(new Monitor(self, owner, obj, hash_code)); |
| if (m->Install(self)) { |
| VLOG(monitor) << "monitor: thread " << owner->GetThreadId() |
| << " created monitor " << m.get() << " for object " << obj; |
| Runtime::Current()->GetMonitorList()->Add(m.release()); |
| CHECK_EQ(obj->GetLockWord(true).GetState(), LockWord::kFatLocked); |
| } |
| } |
| |
| void Monitor::InflateThinLocked(Thread* self, SirtRef<mirror::Object>& obj, LockWord lock_word, |
| uint32_t hash_code) { |
| DCHECK_EQ(lock_word.GetState(), LockWord::kThinLocked); |
| uint32_t owner_thread_id = lock_word.ThinLockOwner(); |
| if (owner_thread_id == self->GetThreadId()) { |
| // We own the monitor, we can easily inflate it. |
| Inflate(self, self, obj.get(), hash_code); |
| } else { |
| ThreadList* thread_list = Runtime::Current()->GetThreadList(); |
| // Suspend the owner, inflate. First change to blocked and give up mutator_lock_. |
| ScopedThreadStateChange tsc(self, kBlocked); |
| self->SetMonitorEnterObject(obj.get()); |
| if (lock_word == obj->GetLockWord(true)) { // If lock word hasn't changed. |
| bool timed_out; |
| Thread* owner = thread_list->SuspendThreadByThreadId(owner_thread_id, false, &timed_out); |
| if (owner != nullptr) { |
| // We succeeded in suspending the thread, check the lock's status didn't change. |
| lock_word = obj->GetLockWord(true); |
| if (lock_word.GetState() == LockWord::kThinLocked && |
| lock_word.ThinLockOwner() == owner_thread_id) { |
| // Go ahead and inflate the lock. |
| Inflate(self, owner, obj.get(), hash_code); |
| } |
| thread_list->Resume(owner, false); |
| } |
| } |
| self->SetMonitorEnterObject(nullptr); |
| } |
| } |
| |
| // Fool annotalysis into thinking that the lock on obj is acquired. |
| static mirror::Object* FakeLock(mirror::Object* obj) |
| EXCLUSIVE_LOCK_FUNCTION(obj) NO_THREAD_SAFETY_ANALYSIS { |
| return obj; |
| } |
| |
| // Fool annotalysis into thinking that the lock on obj is release. |
| static mirror::Object* FakeUnlock(mirror::Object* obj) |
| UNLOCK_FUNCTION(obj) NO_THREAD_SAFETY_ANALYSIS { |
| return obj; |
| } |
| |
| mirror::Object* Monitor::MonitorEnter(Thread* self, mirror::Object* obj) { |
| DCHECK(self != NULL); |
| DCHECK(obj != NULL); |
| obj = FakeLock(obj); |
| uint32_t thread_id = self->GetThreadId(); |
| size_t contention_count = 0; |
| SirtRef<mirror::Object> sirt_obj(self, obj); |
| while (true) { |
| LockWord lock_word = sirt_obj->GetLockWord(true); |
| switch (lock_word.GetState()) { |
| case LockWord::kUnlocked: { |
| LockWord thin_locked(LockWord::FromThinLockId(thread_id, 0)); |
| if (sirt_obj->CasLockWord(lock_word, thin_locked)) { |
| QuasiAtomic::MembarLoadLoad(); |
| return sirt_obj.get(); // Success! |
| } |
| continue; // Go again. |
| } |
| case LockWord::kThinLocked: { |
| uint32_t owner_thread_id = lock_word.ThinLockOwner(); |
| if (owner_thread_id == thread_id) { |
| // We own the lock, increase the recursion count. |
| uint32_t new_count = lock_word.ThinLockCount() + 1; |
| if (LIKELY(new_count <= LockWord::kThinLockMaxCount)) { |
| LockWord thin_locked(LockWord::FromThinLockId(thread_id, new_count)); |
| sirt_obj->SetLockWord(thin_locked, true); |
| return sirt_obj.get(); // Success! |
| } else { |
| // We'd overflow the recursion count, so inflate the monitor. |
| InflateThinLocked(self, sirt_obj, lock_word, 0); |
| } |
| } else { |
| // Contention. |
| contention_count++; |
| Runtime* runtime = Runtime::Current(); |
| if (contention_count <= runtime->GetMaxSpinsBeforeThinkLockInflation()) { |
| NanoSleep(1000); // Sleep for 1us and re-attempt. |
| } else { |
| contention_count = 0; |
| InflateThinLocked(self, sirt_obj, lock_word, 0); |
| } |
| } |
| continue; // Start from the beginning. |
| } |
| case LockWord::kFatLocked: { |
| Monitor* mon = lock_word.FatLockMonitor(); |
| mon->Lock(self); |
| return sirt_obj.get(); // Success! |
| } |
| case LockWord::kHashCode: |
| // Inflate with the existing hashcode. |
| Inflate(self, nullptr, sirt_obj.get(), lock_word.GetHashCode()); |
| continue; // Start from the beginning. |
| default: { |
| LOG(FATAL) << "Invalid monitor state " << lock_word.GetState(); |
| return sirt_obj.get(); |
| } |
| } |
| } |
| } |
| |
| bool Monitor::MonitorExit(Thread* self, mirror::Object* obj) { |
| DCHECK(self != NULL); |
| DCHECK(obj != NULL); |
| obj = FakeUnlock(obj); |
| LockWord lock_word = obj->GetLockWord(true); |
| SirtRef<mirror::Object> sirt_obj(self, obj); |
| switch (lock_word.GetState()) { |
| case LockWord::kHashCode: |
| // Fall-through. |
| case LockWord::kUnlocked: |
| FailedUnlock(sirt_obj.get(), self, nullptr, nullptr); |
| return false; // Failure. |
| case LockWord::kThinLocked: { |
| uint32_t thread_id = self->GetThreadId(); |
| uint32_t owner_thread_id = lock_word.ThinLockOwner(); |
| if (owner_thread_id != thread_id) { |
| // TODO: there's a race here with the owner dying while we unlock. |
| Thread* owner = |
| Runtime::Current()->GetThreadList()->FindThreadByThreadId(lock_word.ThinLockOwner()); |
| FailedUnlock(sirt_obj.get(), self, owner, nullptr); |
| return false; // Failure. |
| } else { |
| // We own the lock, decrease the recursion count. |
| if (lock_word.ThinLockCount() != 0) { |
| uint32_t new_count = lock_word.ThinLockCount() - 1; |
| LockWord thin_locked(LockWord::FromThinLockId(thread_id, new_count)); |
| sirt_obj->SetLockWord(thin_locked, true); |
| } else { |
| sirt_obj->SetLockWord(LockWord(), true); |
| } |
| return true; // Success! |
| } |
| } |
| case LockWord::kFatLocked: { |
| Monitor* mon = lock_word.FatLockMonitor(); |
| return mon->Unlock(self); |
| } |
| default: { |
| LOG(FATAL) << "Invalid monitor state " << lock_word.GetState(); |
| return false; |
| } |
| } |
| } |
| |
| /* |
| * 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) { |
| DCHECK(self != nullptr); |
| DCHECK(obj != nullptr); |
| LockWord lock_word = obj->GetLockWord(true); |
| switch (lock_word.GetState()) { |
| case LockWord::kHashCode: |
| // Fall-through. |
| case LockWord::kUnlocked: |
| ThrowIllegalMonitorStateExceptionF("object not locked by thread before wait()"); |
| return; // Failure. |
| case LockWord::kThinLocked: { |
| uint32_t thread_id = self->GetThreadId(); |
| uint32_t owner_thread_id = lock_word.ThinLockOwner(); |
| if (owner_thread_id != thread_id) { |
| ThrowIllegalMonitorStateExceptionF("object not locked by thread before wait()"); |
| return; // Failure. |
| } else { |
| // We own the lock, inflate to enqueue ourself on the Monitor. |
| Inflate(self, self, obj, 0); |
| lock_word = obj->GetLockWord(true); |
| } |
| break; |
| } |
| case LockWord::kFatLocked: |
| break; // Already set for a wait. |
| default: { |
| LOG(FATAL) << "Invalid monitor state " << lock_word.GetState(); |
| return; |
| } |
| } |
| Monitor* mon = lock_word.FatLockMonitor(); |
| mon->Wait(self, ms, ns, interruptShouldThrow, why); |
| } |
| |
| void Monitor::DoNotify(Thread* self, mirror::Object* obj, bool notify_all) { |
| DCHECK(self != nullptr); |
| DCHECK(obj != nullptr); |
| LockWord lock_word = obj->GetLockWord(true); |
| switch (lock_word.GetState()) { |
| case LockWord::kHashCode: |
| // Fall-through. |
| case LockWord::kUnlocked: |
| ThrowIllegalMonitorStateExceptionF("object not locked by thread before notify()"); |
| return; // Failure. |
| case LockWord::kThinLocked: { |
| uint32_t thread_id = self->GetThreadId(); |
| uint32_t owner_thread_id = lock_word.ThinLockOwner(); |
| if (owner_thread_id != thread_id) { |
| ThrowIllegalMonitorStateExceptionF("object not locked by thread before notify()"); |
| return; // Failure. |
| } else { |
| // We own the lock but there's no Monitor and therefore no waiters. |
| return; // Success. |
| } |
| } |
| case LockWord::kFatLocked: { |
| Monitor* mon = lock_word.FatLockMonitor(); |
| if (notify_all) { |
| mon->NotifyAll(self); |
| } else { |
| mon->Notify(self); |
| } |
| return; // Success. |
| } |
| default: { |
| LOG(FATAL) << "Invalid monitor state " << lock_word.GetState(); |
| return; |
| } |
| } |
| } |
| |
| uint32_t Monitor::GetLockOwnerThreadId(mirror::Object* obj) { |
| DCHECK(obj != nullptr); |
| LockWord lock_word = obj->GetLockWord(true); |
| switch (lock_word.GetState()) { |
| case LockWord::kHashCode: |
| // Fall-through. |
| case LockWord::kUnlocked: |
| return ThreadList::kInvalidThreadId; |
| case LockWord::kThinLocked: |
| return lock_word.ThinLockOwner(); |
| case LockWord::kFatLocked: { |
| Monitor* mon = lock_word.FatLockMonitor(); |
| return mon->GetOwnerThreadId(); |
| } |
| default: { |
| LOG(FATAL) << "Unreachable"; |
| return ThreadList::kInvalidThreadId; |
| } |
| } |
| } |
| |
| void Monitor::DescribeWait(std::ostream& os, const Thread* thread) { |
| // Determine the wait message and object we're waiting or blocked upon. |
| mirror::Object* pretty_object = nullptr; |
| const char* wait_message = nullptr; |
| uint32_t lock_owner = ThreadList::kInvalidThreadId; |
| ThreadState state = thread->GetState(); |
| if (state == kWaiting || state == kTimedWaiting || state == kSleeping) { |
| wait_message = (state == kSleeping) ? " - sleeping on " : " - waiting on "; |
| Thread* self = Thread::Current(); |
| MutexLock mu(self, *thread->GetWaitMutex()); |
| Monitor* monitor = thread->GetWaitMonitor(); |
| if (monitor != nullptr) { |
| pretty_object = monitor->obj_; |
| } |
| } else if (state == kBlocked) { |
| wait_message = " - waiting to lock "; |
| pretty_object = thread->GetMonitorEnterObject(); |
| if (pretty_object != nullptr) { |
| lock_owner = pretty_object->GetLockOwnerThreadId(); |
| } |
| } |
| |
| if (wait_message != nullptr) { |
| if (pretty_object == nullptr) { |
| os << wait_message << "an unknown object"; |
| } else { |
| if ((pretty_object->GetLockWord(true).GetState() == LockWord::kThinLocked) && |
| Locks::mutator_lock_->IsExclusiveHeld(Thread::Current())) { |
| // Getting the identity hashcode here would result in lock inflation and suspension of the |
| // current thread, which isn't safe if this is the only runnable thread. |
| os << wait_message << StringPrintf("<@addr=0x%" PRIxPTR "> (a %s)", |
| reinterpret_cast<intptr_t>(pretty_object), |
| PrettyTypeOf(pretty_object).c_str()); |
| } else { |
| // - waiting on <0x6008c468> (a java.lang.Class<java.lang.ref.ReferenceQueue>) |
| os << wait_message << StringPrintf("<0x%08x> (a %s)", pretty_object->IdentityHashCode(), |
| PrettyTypeOf(pretty_object).c_str()); |
| } |
| } |
| // - waiting to lock <0x613f83d8> (a java.lang.Object) held by thread 5 |
| if (lock_owner != ThreadList::kInvalidThreadId) { |
| 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->GetMonitorEnterObject(); |
| if (result == NULL) { |
| // ...but also a monitor that the thread is waiting on. |
| MutexLock mu(Thread::Current(), *thread->GetWaitMutex()); |
| Monitor* monitor = thread->GetWaitMonitor(); |
| if (monitor != NULL) { |
| result = monitor->GetObject(); |
| } |
| } |
| return result; |
| } |
| |
| void Monitor::VisitLocks(StackVisitor* stack_visitor, void (*callback)(mirror::Object*, void*), |
| void* callback_context) { |
| mirror::ArtMethod* 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); |
| } |
| } |
| |
| bool Monitor::IsValidLockWord(LockWord lock_word) { |
| switch (lock_word.GetState()) { |
| case LockWord::kUnlocked: |
| // Nothing to check. |
| return true; |
| case LockWord::kThinLocked: |
| // Basic sanity check of owner. |
| return lock_word.ThinLockOwner() != ThreadList::kInvalidThreadId; |
| case LockWord::kFatLocked: { |
| // Check the monitor appears in the monitor list. |
| Monitor* mon = lock_word.FatLockMonitor(); |
| MonitorList* list = Runtime::Current()->GetMonitorList(); |
| MutexLock mu(Thread::Current(), list->monitor_list_lock_); |
| for (Monitor* list_mon : list->list_) { |
| if (mon == list_mon) { |
| return true; // Found our monitor. |
| } |
| } |
| return false; // Fail - unowned monitor in an object. |
| } |
| case LockWord::kHashCode: |
| return true; |
| default: |
| LOG(FATAL) << "Unreachable"; |
| return false; |
| } |
| } |
| |
| bool Monitor::IsLocked() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) { |
| MutexLock mu(Thread::Current(), monitor_lock_); |
| return owner_ != nullptr; |
| } |
| |
| void Monitor::TranslateLocation(mirror::ArtMethod* 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); |
| } |
| |
| uint32_t Monitor::GetOwnerThreadId() { |
| MutexLock mu(Thread::Current(), monitor_lock_); |
| Thread* owner = owner_; |
| if (owner != NULL) { |
| return owner->GetThreadId(); |
| } else { |
| return ThreadList::kInvalidThreadId; |
| } |
| } |
| |
| MonitorList::MonitorList() |
| : allow_new_monitors_(true), monitor_list_lock_("MonitorList lock", kMonitorListLock), |
| monitor_add_condition_("MonitorList disallow condition", monitor_list_lock_) { |
| } |
| |
| MonitorList::~MonitorList() { |
| MutexLock mu(Thread::Current(), monitor_list_lock_); |
| STLDeleteElements(&list_); |
| } |
| |
| void MonitorList::DisallowNewMonitors() { |
| MutexLock mu(Thread::Current(), monitor_list_lock_); |
| allow_new_monitors_ = false; |
| } |
| |
| void MonitorList::AllowNewMonitors() { |
| Thread* self = Thread::Current(); |
| MutexLock mu(self, monitor_list_lock_); |
| allow_new_monitors_ = true; |
| monitor_add_condition_.Broadcast(self); |
| } |
| |
| void MonitorList::Add(Monitor* m) { |
| Thread* self = Thread::Current(); |
| MutexLock mu(self, monitor_list_lock_); |
| while (UNLIKELY(!allow_new_monitors_)) { |
| monitor_add_condition_.WaitHoldingLocks(self); |
| } |
| list_.push_front(m); |
| } |
| |
| void MonitorList::SweepMonitorList(IsMarkedCallback* callback, void* arg) { |
| MutexLock mu(Thread::Current(), monitor_list_lock_); |
| for (auto it = list_.begin(); it != list_.end(); ) { |
| Monitor* m = *it; |
| mirror::Object* obj = m->GetObject(); |
| // The object of a monitor can be null if we have deflated it. |
| mirror::Object* new_obj = obj != nullptr ? callback(obj, arg) : nullptr; |
| if (new_obj == nullptr) { |
| VLOG(monitor) << "freeing monitor " << m << " belonging to unmarked object " |
| << m->GetObject(); |
| delete m; |
| it = list_.erase(it); |
| } else { |
| m->SetObject(new_obj); |
| ++it; |
| } |
| } |
| } |
| |
| static mirror::Object* MonitorDeflateCallback(mirror::Object* object, void* arg) |
| SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) { |
| if (Monitor::Deflate(reinterpret_cast<Thread*>(arg), object)) { |
| DCHECK_NE(object->GetLockWord(true).GetState(), LockWord::kFatLocked); |
| // If we deflated, return nullptr so that the monitor gets removed from the array. |
| return nullptr; |
| } |
| return object; // Monitor was not deflated. |
| } |
| |
| void MonitorList::DeflateMonitors() { |
| Thread* self = Thread::Current(); |
| Locks::mutator_lock_->AssertExclusiveHeld(self); |
| SweepMonitorList(MonitorDeflateCallback, reinterpret_cast<Thread*>(self)); |
| } |
| |
| MonitorInfo::MonitorInfo(mirror::Object* obj) : owner_(NULL), entry_count_(0) { |
| DCHECK(obj != nullptr); |
| LockWord lock_word = obj->GetLockWord(true); |
| switch (lock_word.GetState()) { |
| case LockWord::kUnlocked: |
| // Fall-through. |
| case LockWord::kForwardingAddress: |
| // Fall-through. |
| case LockWord::kHashCode: |
| break; |
| case LockWord::kThinLocked: |
| owner_ = Runtime::Current()->GetThreadList()->FindThreadByThreadId(lock_word.ThinLockOwner()); |
| entry_count_ = 1 + lock_word.ThinLockCount(); |
| // Thin locks have no waiters. |
| break; |
| case LockWord::kFatLocked: { |
| Monitor* mon = lock_word.FatLockMonitor(); |
| owner_ = mon->owner_; |
| entry_count_ = 1 + mon->lock_count_; |
| for (Thread* waiter = mon->wait_set_; waiter != NULL; waiter = waiter->GetWaitNext()) { |
| waiters_.push_back(waiter); |
| } |
| break; |
| } |
| } |
| } |
| |
| } // namespace art |