/*
* 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;
}
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) {
if (kDebugLocking && gAborting == 0) { // Avoid recursive aborts.
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_.LoadRelaxed();
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_.LoadRelaxed();
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_.LoadRelaxed() > 0 ||
num_pending_readers_.LoadRelaxed() > 0) {
// Wake any exclusive waiters as there are now no readers.
futex(state_.Address(), FUTEX_WAKE, -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) {
CHECK_EQ(self->GetHeldMutex(level_), this);
}
}
return result;
}
inline pid_t Mutex::GetExclusiveOwnerTid() const {
return exclusive_owner_.LoadRelaxed();
}
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_.LoadRelaxed();
if (state == 0) {
return 0; // No owner.
} else if (state > 0) {
return -1; // Shared.
} else {
return exclusive_owner_.LoadRelaxed();
}
#else
return exclusive_owner_.LoadRelaxed();
#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_);
}
// Catch bug where variable name is omitted. "ReaderMutexLock (lock);" instead of
// "ReaderMutexLock mu(lock)".
#define ReaderMutexLock(x) static_assert(0, "ReaderMutexLock declaration missing variable name")
} // namespace art
#endif // ART_RUNTIME_BASE_MUTEX_INL_H_