runtime/base/mutex-inl.h - platform/art - Git at Google

 /*
  * Copyright (C) 2011 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.
  */

 #ifndef ART_RUNTIME_BASE_MUTEX_INL_H_
 #define ART_RUNTIME_BASE_MUTEX_INL_H_

 #include <inttypes.h>

 #include "mutex.h"

 #include "base/utils.h"
 #include "base/value_object.h"
 #include "thread.h"

 #if ART_USE_FUTEXES
 #include "linux/futex.h"
 #include "sys/syscall.h"
 #ifndef SYS_futex
 #define SYS_futex __NR_futex
 #endif
 #endif  // ART_USE_FUTEXES

 #define CHECK_MUTEX_CALL(call, args) CHECK_PTHREAD_CALL(call, args, name_)

 namespace art {

 #if ART_USE_FUTEXES
 static inline int futex(volatile int *uaddr, int op, int val, const struct timespec *timeout,
                         volatile int *uaddr2, int val3) {
   return syscall(SYS_futex, uaddr, op, val, timeout, uaddr2, val3);
 }
 #endif  // ART_USE_FUTEXES

 // The following isn't strictly necessary, but we want updates on Atomic<pid_t> to be lock-free.
 // TODO: Use std::atomic::is_always_lock_free after switching to C++17 atomics.
 static_assert(sizeof(pid_t) <= sizeof(int32_t), "pid_t should fit in 32 bits");

 static inline pid_t SafeGetTid(const Thread* self) {
   if (self != nullptr) {
     return self->GetTid();
   } else {
     return GetTid();
   }
 }

 static inline void CheckUnattachedThread(LockLevel level) NO_THREAD_SAFETY_ANALYSIS {
   // The check below enumerates the cases where we expect not to be able to sanity check locks
   // on a thread. Lock checking is disabled to avoid deadlock when checking shutdown lock.
   // TODO: tighten this check.
   if (kDebugLocking) {
     CHECK(!Locks::IsSafeToCallAbortRacy() ||
           // Used during thread creation to avoid races with runtime shutdown. Thread::Current not
           // yet established.
           level == kRuntimeShutdownLock ||
           // Thread Ids are allocated/released before threads are established.
           level == kAllocatedThreadIdsLock ||
           // Thread LDT's are initialized without Thread::Current established.
           level == kModifyLdtLock ||
           // Threads are unregistered while holding the thread list lock, during this process they
           // no longer exist and so we expect an unlock with no self.
           level == kThreadListLock ||
           // Ignore logging which may or may not have set up thread data structures.
           level == kLoggingLock ||
           // When transitioning from suspended to runnable, a daemon thread might be in
           // a situation where the runtime is shutting down. To not crash our debug locking
           // mechanism we just pass null Thread* to the MutexLock during that transition
           // (see Thread::TransitionFromSuspendedToRunnable).
           level == kThreadSuspendCountLock ||
           // Avoid recursive death.
           level == kAbortLock ||
           // Locks at the absolute top of the stack can be locked at any time.
           level == kTopLockLevel) << level;
   }
 }

 inline void BaseMutex::RegisterAsLocked(Thread* self) {
   if (UNLIKELY(self == nullptr)) {
     CheckUnattachedThread(level_);
     return;
   }
   LockLevel level = level_;
   // It would be nice to avoid this condition checking in the non-debug case,
   // but that would make the various methods that check if a mutex is held not
   // work properly for thread wait locks. Since the vast majority of lock
   // acquisitions are not thread wait locks, this check should not be too
   // expensive.
   if (UNLIKELY(level == kThreadWaitLock) && self->GetHeldMutex(kThreadWaitLock) != nullptr) {
     level = kThreadWaitWakeLock;
   }
   if (kDebugLocking) {
     // Check if a bad Mutex of this level or lower is held.
     bool bad_mutexes_held = false;
     // Specifically allow a kTopLockLevel lock to be gained when the current thread holds the
     // mutator_lock_ exclusive. This is because we suspending when holding locks at this level is
     // not allowed and if we hold the mutator_lock_ exclusive we must unsuspend stuff eventually
     // so there are no deadlocks.
     if (level == kTopLockLevel &&
         Locks::mutator_lock_->IsSharedHeld(self) &&
         !Locks::mutator_lock_->IsExclusiveHeld(self)) {
       LOG(ERROR) << "Lock level violation: holding \"" << Locks::mutator_lock_->name_ << "\" "
                   << "(level " << kMutatorLock << " - " << static_cast<int>(kMutatorLock)
                   << ") non-exclusive while locking \"" << name_ << "\" "
                   << "(level " << level << " - " << static_cast<int>(level) << ") a top level"
                   << "mutex. This is not allowed.";
       bad_mutexes_held = true;
     } else if (this == Locks::mutator_lock_ && self->GetHeldMutex(kTopLockLevel) != nullptr) {
       LOG(ERROR) << "Lock level violation. Locking mutator_lock_ while already having a "
                  << "kTopLevelLock (" << self->GetHeldMutex(kTopLockLevel)->name_ << "held is "
                  << "not allowed.";
       bad_mutexes_held = true;
     }
     for (int i = level; i >= 0; --i) {
       LockLevel lock_level_i = static_cast<LockLevel>(i);
       BaseMutex* held_mutex = self->GetHeldMutex(lock_level_i);
       if (level == kTopLockLevel &&
           lock_level_i == kMutatorLock &&
           Locks::mutator_lock_->IsExclusiveHeld(self)) {
         // This is checked above.
         continue;
       } else if (UNLIKELY(held_mutex != nullptr) && lock_level_i != kAbortLock) {
         LOG(ERROR) << "Lock level violation: holding \"" << held_mutex->name_ << "\" "
                    << "(level " << lock_level_i << " - " << i
                    << ") while locking \"" << name_ << "\" "
                    << "(level " << level << " - " << static_cast<int>(level) << ")";
         if (lock_level_i > kAbortLock) {
           // Only abort in the check below if this is more than abort level lock.
           bad_mutexes_held = true;
         }
       }
     }
     if (gAborting == 0) {  // Avoid recursive aborts.
       CHECK(!bad_mutexes_held);
     }
   }
   // Don't record monitors as they are outside the scope of analysis. They may be inspected off of
   // the monitor list.
   if (level != kMonitorLock) {
     self->SetHeldMutex(level, this);
   }
 }

 inline void BaseMutex::RegisterAsUnlocked(Thread* self) {
   if (UNLIKELY(self == nullptr)) {
     CheckUnattachedThread(level_);
     return;
   }
   if (level_ != kMonitorLock) {
     auto level = level_;
     if (UNLIKELY(level == kThreadWaitLock) && self->GetHeldMutex(kThreadWaitWakeLock) == this) {
       level = kThreadWaitWakeLock;
     }
     if (kDebugLocking && gAborting == 0) {  // Avoid recursive aborts.
       if (level == kThreadWaitWakeLock) {
         CHECK(self->GetHeldMutex(kThreadWaitLock) != nullptr) << "Held " << kThreadWaitWakeLock << " without " << kThreadWaitLock;;
       }
       CHECK(self->GetHeldMutex(level) == this) << "Unlocking on unacquired mutex: " << name_;
     }
     self->SetHeldMutex(level, nullptr);
   }
 }

 inline void ReaderWriterMutex::SharedLock(Thread* self) {
   DCHECK(self == nullptr || self == Thread::Current());
 #if ART_USE_FUTEXES
   bool done = false;
   do {
     int32_t cur_state = state_.load(std::memory_order_relaxed);
     if (LIKELY(cur_state >= 0)) {
       // Add as an extra reader.
       done = state_.CompareAndSetWeakAcquire(cur_state, cur_state + 1);
     } else {
       HandleSharedLockContention(self, cur_state);
     }
   } while (!done);
 #else
   CHECK_MUTEX_CALL(pthread_rwlock_rdlock, (&rwlock_));
 #endif
   DCHECK(GetExclusiveOwnerTid() == 0 || GetExclusiveOwnerTid() == -1);
   RegisterAsLocked(self);
   AssertSharedHeld(self);
 }

 inline void ReaderWriterMutex::SharedUnlock(Thread* self) {
   DCHECK(self == nullptr || self == Thread::Current());
   DCHECK(GetExclusiveOwnerTid() == 0 || GetExclusiveOwnerTid() == -1);
   AssertSharedHeld(self);
   RegisterAsUnlocked(self);
 #if ART_USE_FUTEXES
   bool done = false;
   do {
     int32_t cur_state = state_.load(std::memory_order_relaxed);
     if (LIKELY(cur_state > 0)) {
       // Reduce state by 1 and impose lock release load/store ordering.
       // Note, the relaxed loads below musn't reorder before the CompareAndSet.
       // TODO: the ordering here is non-trivial as state is split across 3 fields, fix by placing
       // a status bit into the state on contention.
       done = state_.CompareAndSetWeakSequentiallyConsistent(cur_state, cur_state - 1);
       if (done && (cur_state - 1) == 0) {  // Weak CAS may fail spuriously.
         if (num_pending_writers_.load(std::memory_order_seq_cst) > 0 ||
             num_pending_readers_.load(std::memory_order_seq_cst) > 0) {
           // Wake any exclusive waiters as there are now no readers.
           futex(state_.Address(), FUTEX_WAKE_PRIVATE, -1, nullptr, nullptr, 0);
         }
       }
     } else {
       LOG(FATAL) << "Unexpected state_:" << cur_state << " for " << name_;
     }
   } while (!done);
 #else
   CHECK_MUTEX_CALL(pthread_rwlock_unlock, (&rwlock_));
 #endif
 }

 inline bool Mutex::IsExclusiveHeld(const Thread* self) const {
   DCHECK(self == nullptr || self == Thread::Current());
   bool result = (GetExclusiveOwnerTid() == SafeGetTid(self));
   if (kDebugLocking) {
     // Sanity debug check that if we think it is locked we have it in our held mutexes.
     if (result && self != nullptr && level_ != kMonitorLock && !gAborting) {
       if (level_ == kThreadWaitLock && self->GetHeldMutex(kThreadWaitLock) != this) {
         CHECK_EQ(self->GetHeldMutex(kThreadWaitWakeLock), this);
       } else {
         CHECK_EQ(self->GetHeldMutex(level_), this);
       }
     }
   }
   return result;
 }

 inline pid_t Mutex::GetExclusiveOwnerTid() const {
   return exclusive_owner_.load(std::memory_order_relaxed);
 }

 inline void Mutex::AssertExclusiveHeld(const Thread* self) const {
   if (kDebugLocking && (gAborting == 0)) {
     CHECK(IsExclusiveHeld(self)) << *this;
   }
 }

 inline void Mutex::AssertHeld(const Thread* self) const {
   AssertExclusiveHeld(self);
 }

 inline bool ReaderWriterMutex::IsExclusiveHeld(const Thread* self) const {
   DCHECK(self == nullptr || self == Thread::Current());
   bool result = (GetExclusiveOwnerTid() == SafeGetTid(self));
   if (kDebugLocking) {
     // Sanity that if the pthread thinks we own the lock the Thread agrees.
     if (self != nullptr && result)  {
       CHECK_EQ(self->GetHeldMutex(level_), this);
     }
   }
   return result;
 }

 inline pid_t ReaderWriterMutex::GetExclusiveOwnerTid() const {
 #if ART_USE_FUTEXES
   int32_t state = state_.load(std::memory_order_relaxed);
   if (state == 0) {
     return 0;  // No owner.
   } else if (state > 0) {
     return -1;  // Shared.
   } else {
     return exclusive_owner_.load(std::memory_order_relaxed);
   }
 #else
   return exclusive_owner_.load(std::memory_order_relaxed);
 #endif
 }

 inline void ReaderWriterMutex::AssertExclusiveHeld(const Thread* self) const {
   if (kDebugLocking && (gAborting == 0)) {
     CHECK(IsExclusiveHeld(self)) << *this;
   }
 }

 inline void ReaderWriterMutex::AssertWriterHeld(const Thread* self) const {
   AssertExclusiveHeld(self);
 }

 inline void MutatorMutex::TransitionFromRunnableToSuspended(Thread* self) {
   AssertSharedHeld(self);
   RegisterAsUnlocked(self);
 }

 inline void MutatorMutex::TransitionFromSuspendedToRunnable(Thread* self) {
   RegisterAsLocked(self);
   AssertSharedHeld(self);
 }

 inline ReaderMutexLock::ReaderMutexLock(Thread* self, ReaderWriterMutex& mu)
     : self_(self), mu_(mu) {
   mu_.SharedLock(self_);
 }

 inline ReaderMutexLock::~ReaderMutexLock() {
   mu_.SharedUnlock(self_);
 }

 }  // namespace art

 #endif  // ART_RUNTIME_BASE_MUTEX_INL_H_
	/*
	* Copyright (C) 2011 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.
	*/

	#ifndef ART_RUNTIME_BASE_MUTEX_INL_H_
	#define ART_RUNTIME_BASE_MUTEX_INL_H_

	#include <inttypes.h>

	#include "mutex.h"

	#include "base/utils.h"
	#include "base/value_object.h"
	#include "thread.h"

	#if ART_USE_FUTEXES
	#include "linux/futex.h"
	#include "sys/syscall.h"
	#ifndef SYS_futex
	#define SYS_futex __NR_futex
	#endif
	#endif // ART_USE_FUTEXES

	#define CHECK_MUTEX_CALL(call, args) CHECK_PTHREAD_CALL(call, args, name_)

	namespace art {

	#if ART_USE_FUTEXES
	static inline int futex(volatile int uaddr, int op, int val, const struct timespec timeout,
	volatile int *uaddr2, int val3) {
	return syscall(SYS_futex, uaddr, op, val, timeout, uaddr2, val3);
	}
	#endif // ART_USE_FUTEXES

	// The following isn't strictly necessary, but we want updates on Atomic<pid_t> to be lock-free.
	// TODO: Use std::atomic::is_always_lock_free after switching to C++17 atomics.
	static_assert(sizeof(pid_t) <= sizeof(int32_t), "pid_t should fit in 32 bits");

	static inline pid_t SafeGetTid(const Thread* self) {
	if (self != nullptr) {
	return self->GetTid();
	} else {
	return GetTid();
	}
	}

	static inline void CheckUnattachedThread(LockLevel level) NO_THREAD_SAFETY_ANALYSIS {
	// The check below enumerates the cases where we expect not to be able to sanity check locks
	// on a thread. Lock checking is disabled to avoid deadlock when checking shutdown lock.
	// TODO: tighten this check.
	if (kDebugLocking) {
	CHECK(!Locks::IsSafeToCallAbortRacy() \|\|
	// Used during thread creation to avoid races with runtime shutdown. Thread::Current not
	// yet established.
	level == kRuntimeShutdownLock \|\|
	// Thread Ids are allocated/released before threads are established.
	level == kAllocatedThreadIdsLock \|\|
	// Thread LDT's are initialized without Thread::Current established.
	level == kModifyLdtLock \|\|
	// Threads are unregistered while holding the thread list lock, during this process they
	// no longer exist and so we expect an unlock with no self.
	level == kThreadListLock \|\|
	// Ignore logging which may or may not have set up thread data structures.
	level == kLoggingLock \|\|
	// When transitioning from suspended to runnable, a daemon thread might be in
	// a situation where the runtime is shutting down. To not crash our debug locking
	// mechanism we just pass null Thread* to the MutexLock during that transition
	// (see Thread::TransitionFromSuspendedToRunnable).
	level == kThreadSuspendCountLock \|\|
	// Avoid recursive death.
	level == kAbortLock \|\|
	// Locks at the absolute top of the stack can be locked at any time.
	level == kTopLockLevel) << level;
	}
	}

	inline void BaseMutex::RegisterAsLocked(Thread* self) {
	if (UNLIKELY(self == nullptr)) {
	CheckUnattachedThread(level_);
	return;
	}
	LockLevel level = level_;
	// It would be nice to avoid this condition checking in the non-debug case,
	// but that would make the various methods that check if a mutex is held not
	// work properly for thread wait locks. Since the vast majority of lock
	// acquisitions are not thread wait locks, this check should not be too
	// expensive.
	if (UNLIKELY(level == kThreadWaitLock) && self->GetHeldMutex(kThreadWaitLock) != nullptr) {
	level = kThreadWaitWakeLock;
	}
	if (kDebugLocking) {
	// Check if a bad Mutex of this level or lower is held.
	bool bad_mutexes_held = false;
	// Specifically allow a kTopLockLevel lock to be gained when the current thread holds the
	// mutator_lock_ exclusive. This is because we suspending when holding locks at this level is
	// not allowed and if we hold the mutator_lock_ exclusive we must unsuspend stuff eventually
	// so there are no deadlocks.
	if (level == kTopLockLevel &&
	Locks::mutator_lock_->IsSharedHeld(self) &&
	!Locks::mutator_lock_->IsExclusiveHeld(self)) {
	LOG(ERROR) << "Lock level violation: holding \"" << Locks::mutator_lock_->name_ << "\" "
	<< "(level " << kMutatorLock << " - " << static_cast<int>(kMutatorLock)
	<< ") non-exclusive while locking \"" << name_ << "\" "
	<< "(level " << level << " - " << static_cast<int>(level) << ") a top level"
	<< "mutex. This is not allowed.";
	bad_mutexes_held = true;
	} else if (this == Locks::mutator_lock_ && self->GetHeldMutex(kTopLockLevel) != nullptr) {
	LOG(ERROR) << "Lock level violation. Locking mutator_lock_ while already having a "
	<< "kTopLevelLock (" << self->GetHeldMutex(kTopLockLevel)->name_ << "held is "
	<< "not allowed.";
	bad_mutexes_held = true;
	}
	for (int i = level; i >= 0; --i) {
	LockLevel lock_level_i = static_cast<LockLevel>(i);
	BaseMutex* held_mutex = self->GetHeldMutex(lock_level_i);
	if (level == kTopLockLevel &&
	lock_level_i == kMutatorLock &&
	Locks::mutator_lock_->IsExclusiveHeld(self)) {
	// This is checked above.
	continue;
	} else if (UNLIKELY(held_mutex != nullptr) && lock_level_i != kAbortLock) {
	LOG(ERROR) << "Lock level violation: holding \"" << held_mutex->name_ << "\" "
	<< "(level " << lock_level_i << " - " << i
	<< ") while locking \"" << name_ << "\" "
	<< "(level " << level << " - " << static_cast<int>(level) << ")";
	if (lock_level_i > kAbortLock) {
	// Only abort in the check below if this is more than abort level lock.
	bad_mutexes_held = true;
	}
	}
	}
	if (gAborting == 0) { // Avoid recursive aborts.
	CHECK(!bad_mutexes_held);
	}
	}
	// Don't record monitors as they are outside the scope of analysis. They may be inspected off of
	// the monitor list.
	if (level != kMonitorLock) {
	self->SetHeldMutex(level, this);
	}
	}

	inline void BaseMutex::RegisterAsUnlocked(Thread* self) {
	if (UNLIKELY(self == nullptr)) {
	CheckUnattachedThread(level_);
	return;
	}
	if (level_ != kMonitorLock) {
	auto level = level_;
	if (UNLIKELY(level == kThreadWaitLock) && self->GetHeldMutex(kThreadWaitWakeLock) == this) {
	level = kThreadWaitWakeLock;
	}
	if (kDebugLocking && gAborting == 0) { // Avoid recursive aborts.
	if (level == kThreadWaitWakeLock) {
	CHECK(self->GetHeldMutex(kThreadWaitLock) != nullptr) << "Held " << kThreadWaitWakeLock << " without " << kThreadWaitLock;;
	}
	CHECK(self->GetHeldMutex(level) == this) << "Unlocking on unacquired mutex: " << name_;
	}
	self->SetHeldMutex(level, nullptr);
	}
	}

	inline void ReaderWriterMutex::SharedLock(Thread* self) {
	DCHECK(self == nullptr \|\| self == Thread::Current());
	#if ART_USE_FUTEXES
	bool done = false;
	do {
	int32_t cur_state = state_.load(std::memory_order_relaxed);
	if (LIKELY(cur_state >= 0)) {
	// Add as an extra reader.
	done = state_.CompareAndSetWeakAcquire(cur_state, cur_state + 1);
	} else {
	HandleSharedLockContention(self, cur_state);
	}
	} while (!done);
	#else
	CHECK_MUTEX_CALL(pthread_rwlock_rdlock, (&rwlock_));
	#endif
	DCHECK(GetExclusiveOwnerTid() == 0 \|\| GetExclusiveOwnerTid() == -1);
	RegisterAsLocked(self);
	AssertSharedHeld(self);
	}

	inline void ReaderWriterMutex::SharedUnlock(Thread* self) {
	DCHECK(self == nullptr \|\| self == Thread::Current());
	DCHECK(GetExclusiveOwnerTid() == 0 \|\| GetExclusiveOwnerTid() == -1);
	AssertSharedHeld(self);
	RegisterAsUnlocked(self);
	#if ART_USE_FUTEXES
	bool done = false;
	do {
	int32_t cur_state = state_.load(std::memory_order_relaxed);
	if (LIKELY(cur_state > 0)) {
	// Reduce state by 1 and impose lock release load/store ordering.
	// Note, the relaxed loads below musn't reorder before the CompareAndSet.
	// TODO: the ordering here is non-trivial as state is split across 3 fields, fix by placing
	// a status bit into the state on contention.
	done = state_.CompareAndSetWeakSequentiallyConsistent(cur_state, cur_state - 1);
	if (done && (cur_state - 1) == 0) { // Weak CAS may fail spuriously.
	if (num_pending_writers_.load(std::memory_order_seq_cst) > 0 \|\|
	num_pending_readers_.load(std::memory_order_seq_cst) > 0) {
	// Wake any exclusive waiters as there are now no readers.
	futex(state_.Address(), FUTEX_WAKE_PRIVATE, -1, nullptr, nullptr, 0);
	}
	}
	} else {
	LOG(FATAL) << "Unexpected state_:" << cur_state << " for " << name_;
	}
	} while (!done);
	#else
	CHECK_MUTEX_CALL(pthread_rwlock_unlock, (&rwlock_));
	#endif
	}

	inline bool Mutex::IsExclusiveHeld(const Thread* self) const {
	DCHECK(self == nullptr \|\| self == Thread::Current());
	bool result = (GetExclusiveOwnerTid() == SafeGetTid(self));
	if (kDebugLocking) {
	// Sanity debug check that if we think it is locked we have it in our held mutexes.
	if (result && self != nullptr && level_ != kMonitorLock && !gAborting) {
	if (level_ == kThreadWaitLock && self->GetHeldMutex(kThreadWaitLock) != this) {
	CHECK_EQ(self->GetHeldMutex(kThreadWaitWakeLock), this);
	} else {
	CHECK_EQ(self->GetHeldMutex(level_), this);
	}
	}
	}
	return result;
	}

	inline pid_t Mutex::GetExclusiveOwnerTid() const {
	return exclusive_owner_.load(std::memory_order_relaxed);
	}

	inline void Mutex::AssertExclusiveHeld(const Thread* self) const {
	if (kDebugLocking && (gAborting == 0)) {
	CHECK(IsExclusiveHeld(self)) << *this;
	}
	}

	inline void Mutex::AssertHeld(const Thread* self) const {
	AssertExclusiveHeld(self);
	}

	inline bool ReaderWriterMutex::IsExclusiveHeld(const Thread* self) const {
	DCHECK(self == nullptr \|\| self == Thread::Current());
	bool result = (GetExclusiveOwnerTid() == SafeGetTid(self));
	if (kDebugLocking) {
	// Sanity that if the pthread thinks we own the lock the Thread agrees.
	if (self != nullptr && result) {
	CHECK_EQ(self->GetHeldMutex(level_), this);
	}
	}
	return result;
	}

	inline pid_t ReaderWriterMutex::GetExclusiveOwnerTid() const {
	#if ART_USE_FUTEXES
	int32_t state = state_.load(std::memory_order_relaxed);
	if (state == 0) {
	return 0; // No owner.
	} else if (state > 0) {
	return -1; // Shared.
	} else {
	return exclusive_owner_.load(std::memory_order_relaxed);
	}
	#else
	return exclusive_owner_.load(std::memory_order_relaxed);
	#endif
	}

	inline void ReaderWriterMutex::AssertExclusiveHeld(const Thread* self) const {
	if (kDebugLocking && (gAborting == 0)) {
	CHECK(IsExclusiveHeld(self)) << *this;
	}
	}

	inline void ReaderWriterMutex::AssertWriterHeld(const Thread* self) const {
	AssertExclusiveHeld(self);
	}

	inline void MutatorMutex::TransitionFromRunnableToSuspended(Thread* self) {
	AssertSharedHeld(self);
	RegisterAsUnlocked(self);
	}

	inline void MutatorMutex::TransitionFromSuspendedToRunnable(Thread* self) {
	RegisterAsLocked(self);
	AssertSharedHeld(self);
	}

	inline ReaderMutexLock::ReaderMutexLock(Thread* self, ReaderWriterMutex& mu)
	: self_(self), mu_(mu) {
	mu_.SharedLock(self_);
	}

	inline ReaderMutexLock::~ReaderMutexLock() {
	mu_.SharedUnlock(self_);
	}

	} // namespace art

	#endif // ART_RUNTIME_BASE_MUTEX_INL_H_