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/*
* 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_H_
#define ART_RUNTIME_BASE_MUTEX_H_
#include <limits.h> // for INT_MAX
#include <pthread.h>
#include <stdint.h>
#include <unistd.h> // for pid_t
#include <iosfwd>
#include <string>
#include <android-base/logging.h>
#include "base/aborting.h"
#include "base/atomic.h"
#include "runtime_globals.h"
#include "base/macros.h"
#include "locks.h"
#if defined(__linux__)
#define ART_USE_FUTEXES 1
#else
#define ART_USE_FUTEXES 0
#endif
// Currently Darwin doesn't support locks with timeouts.
#if !defined(__APPLE__)
#define HAVE_TIMED_RWLOCK 1
#else
#define HAVE_TIMED_RWLOCK 0
#endif
namespace art {
class SHARED_LOCKABLE ReaderWriterMutex;
class SHARED_LOCKABLE MutatorMutex;
class ScopedContentionRecorder;
class Thread;
class LOCKABLE Mutex;
constexpr bool kDebugLocking = kIsDebugBuild;
// Record Log contention information, dumpable via SIGQUIT.
#if ART_USE_FUTEXES
// To enable lock contention logging, set this to true.
constexpr bool kLogLockContentions = false;
// FUTEX_WAKE first argument:
constexpr int kWakeOne = 1;
constexpr int kWakeAll = INT_MAX;
#else
// Keep this false as lock contention logging is supported only with
// futex.
constexpr bool kLogLockContentions = false;
#endif
constexpr size_t kContentionLogSize = 4;
constexpr size_t kContentionLogDataSize = kLogLockContentions ? 1 : 0;
constexpr size_t kAllMutexDataSize = kLogLockContentions ? 1 : 0;
// Base class for all Mutex implementations
class BaseMutex {
public:
const char* GetName() const {
return name_;
}
virtual bool IsMutex() const { return false; }
virtual bool IsReaderWriterMutex() const { return false; }
virtual bool IsMutatorMutex() const { return false; }
virtual void Dump(std::ostream& os) const = 0;
static void DumpAll(std::ostream& os);
bool ShouldRespondToEmptyCheckpointRequest() const {
return should_respond_to_empty_checkpoint_request_;
}
void SetShouldRespondToEmptyCheckpointRequest(bool value) {
should_respond_to_empty_checkpoint_request_ = value;
}
virtual void WakeupToRespondToEmptyCheckpoint() = 0;
protected:
friend class ConditionVariable;
BaseMutex(const char* name, LockLevel level);
virtual ~BaseMutex();
// Add this mutex to those owned by self, and perform appropriate checking.
// For this call only, self may also be another suspended thread.
void RegisterAsLocked(Thread* self);
void RegisterAsUnlocked(Thread* self);
void CheckSafeToWait(Thread* self);
friend class ScopedContentionRecorder;
void RecordContention(uint64_t blocked_tid, uint64_t owner_tid, uint64_t nano_time_blocked);
void DumpContention(std::ostream& os) const;
const char* const name_;
// A log entry that records contention but makes no guarantee that either tid will be held live.
struct ContentionLogEntry {
ContentionLogEntry() : blocked_tid(0), owner_tid(0) {}
uint64_t blocked_tid;
uint64_t owner_tid;
AtomicInteger count;
};
struct ContentionLogData {
ContentionLogEntry contention_log[kContentionLogSize];
// The next entry in the contention log to be updated. Value ranges from 0 to
// kContentionLogSize - 1.
AtomicInteger cur_content_log_entry;
// Number of times the Mutex has been contended.
AtomicInteger contention_count;
// Sum of time waited by all contenders in ns.
Atomic<uint64_t> wait_time;
void AddToWaitTime(uint64_t value);
ContentionLogData() : wait_time(0) {}
};
ContentionLogData contention_log_data_[kContentionLogDataSize];
const LockLevel level_; // Support for lock hierarchy.
bool should_respond_to_empty_checkpoint_request_;
public:
bool HasEverContended() const {
if (kLogLockContentions) {
return contention_log_data_->contention_count.load(std::memory_order_seq_cst) > 0;
}
return false;
}
};
// A Mutex is used to achieve mutual exclusion between threads. A Mutex can be used to gain
// exclusive access to what it guards. A Mutex can be in one of two states:
// - Free - not owned by any thread,
// - Exclusive - owned by a single thread.
//
// The effect of locking and unlocking operations on the state is:
// State | ExclusiveLock | ExclusiveUnlock
// -------------------------------------------
// Free | Exclusive | error
// Exclusive | Block* | Free
// * Mutex is not reentrant unless recursive is true. An attempt to ExclusiveLock on a
// recursive=false Mutex on a thread already owning the Mutex results in an error.
//
// TODO(b/140590186): Remove support for recursive == true.
//
// Some mutexes, including those associated with Java monitors may be accessed (in particular
// acquired) by a thread in suspended state. Suspending all threads does NOT prevent mutex state
// from changing.
std::ostream& operator<<(std::ostream& os, const Mutex& mu);
class LOCKABLE Mutex : public BaseMutex {
public:
explicit Mutex(const char* name, LockLevel level = kDefaultMutexLevel, bool recursive = false);
~Mutex();
bool IsMutex() const override { return true; }
// Block until mutex is free then acquire exclusive access.
void ExclusiveLock(Thread* self) ACQUIRE();
void Lock(Thread* self) ACQUIRE() { ExclusiveLock(self); }
// Returns true if acquires exclusive access, false otherwise.
bool ExclusiveTryLock(Thread* self) TRY_ACQUIRE(true);
bool TryLock(Thread* self) TRY_ACQUIRE(true) { return ExclusiveTryLock(self); }
// Equivalent to ExclusiveTryLock, but retry for a short period before giving up.
bool ExclusiveTryLockWithSpinning(Thread* self) TRY_ACQUIRE(true);
// Release exclusive access.
void ExclusiveUnlock(Thread* self) RELEASE();
void Unlock(Thread* self) RELEASE() { ExclusiveUnlock(self); }
// Is the current thread the exclusive holder of the Mutex.
ALWAYS_INLINE bool IsExclusiveHeld(const Thread* self) const;
// Assert that the Mutex is exclusively held by the current thread.
ALWAYS_INLINE void AssertExclusiveHeld(const Thread* self) const ASSERT_CAPABILITY(this);
ALWAYS_INLINE void AssertHeld(const Thread* self) const ASSERT_CAPABILITY(this);
// Assert that the Mutex is not held by the current thread.
void AssertNotHeldExclusive(const Thread* self) ASSERT_CAPABILITY(!*this) {
if (kDebugLocking && (gAborting == 0)) {
CHECK(!IsExclusiveHeld(self)) << *this;
}
}
void AssertNotHeld(const Thread* self) ASSERT_CAPABILITY(!*this) {
AssertNotHeldExclusive(self);
}
// Id associated with exclusive owner. No memory ordering semantics if called from a thread
// other than the owner. GetTid() == GetExclusiveOwnerTid() is a reliable way to determine
// whether we hold the lock; any other information may be invalidated before we return.
pid_t GetExclusiveOwnerTid() const;
// Returns how many times this Mutex has been locked, it is typically better to use
// AssertHeld/NotHeld. For a simply held mutex this method returns 1. Should only be called
// while holding the mutex or threads are suspended.
unsigned int GetDepth() const {
return recursion_count_;
}
void Dump(std::ostream& os) const override;
// For negative capabilities in clang annotations.
const Mutex& operator!() const { return *this; }
void WakeupToRespondToEmptyCheckpoint() override;
#if ART_USE_FUTEXES
// Acquire the mutex, possibly on behalf of another thread. Acquisition must be
// uncontended. New_owner must be current thread or suspended.
// Mutex must be at level kMonitorLock.
// Not implementable for the pthreads version, so we must avoid calling it there.
void ExclusiveLockUncontendedFor(Thread* new_owner);
// Undo the effect of the previous calling, setting the mutex back to unheld.
// Still assumes no concurrent access.
void ExclusiveUnlockUncontended();
#endif // ART_USE_FUTEXES
private:
#if ART_USE_FUTEXES
// Low order bit: 0 is unheld, 1 is held.
// High order bits: Number of waiting contenders.
AtomicInteger state_and_contenders_;
static constexpr int32_t kHeldMask = 1;
static constexpr int32_t kContenderShift = 1;
static constexpr int32_t kContenderIncrement = 1 << kContenderShift;
void increment_contenders() {
state_and_contenders_.fetch_add(kContenderIncrement);
}
void decrement_contenders() {
state_and_contenders_.fetch_sub(kContenderIncrement);
}
int32_t get_contenders() {
// Result is guaranteed to include any contention added by this thread; otherwise approximate.
// Treat contenders as unsigned because we're paranoid about overflow; should never matter.
return static_cast<uint32_t>(state_and_contenders_.load(std::memory_order_relaxed))
>> kContenderShift;
}
// Exclusive owner.
Atomic<pid_t> exclusive_owner_;
#else
pthread_mutex_t mutex_;
Atomic<pid_t> exclusive_owner_; // Guarded by mutex_. Asynchronous reads are OK.
#endif
unsigned int recursion_count_;
const bool recursive_; // Can the lock be recursively held?
friend class ConditionVariable;
DISALLOW_COPY_AND_ASSIGN(Mutex);
};
// A ReaderWriterMutex is used to achieve mutual exclusion between threads, similar to a Mutex.
// Unlike a Mutex a ReaderWriterMutex can be used to gain exclusive (writer) or shared (reader)
// access to what it guards. A flaw in relation to a Mutex is that it cannot be used with a
// condition variable. A ReaderWriterMutex can be in one of three states:
// - Free - not owned by any thread,
// - Exclusive - owned by a single thread,
// - Shared(n) - shared amongst n threads.
//
// The effect of locking and unlocking operations on the state is:
//
// State | ExclusiveLock | ExclusiveUnlock | SharedLock | SharedUnlock
// ----------------------------------------------------------------------------
// Free | Exclusive | error | SharedLock(1) | error
// Exclusive | Block | Free | Block | error
// Shared(n) | Block | error | SharedLock(n+1)* | Shared(n-1) or Free
// * for large values of n the SharedLock may block.
std::ostream& operator<<(std::ostream& os, const ReaderWriterMutex& mu);
class SHARED_LOCKABLE ReaderWriterMutex : public BaseMutex {
public:
explicit ReaderWriterMutex(const char* name, LockLevel level = kDefaultMutexLevel);
~ReaderWriterMutex();
bool IsReaderWriterMutex() const override { return true; }
// Block until ReaderWriterMutex is free then acquire exclusive access.
void ExclusiveLock(Thread* self) ACQUIRE();
void WriterLock(Thread* self) ACQUIRE() { ExclusiveLock(self); }
// Release exclusive access.
void ExclusiveUnlock(Thread* self) RELEASE();
void WriterUnlock(Thread* self) RELEASE() { ExclusiveUnlock(self); }
// Block until ReaderWriterMutex is free and acquire exclusive access. Returns true on success
// or false if timeout is reached.
#if HAVE_TIMED_RWLOCK
bool ExclusiveLockWithTimeout(Thread* self, int64_t ms, int32_t ns)
EXCLUSIVE_TRYLOCK_FUNCTION(true);
#endif
// Block until ReaderWriterMutex is shared or free then acquire a share on the access.
void SharedLock(Thread* self) ACQUIRE_SHARED() ALWAYS_INLINE;
void ReaderLock(Thread* self) ACQUIRE_SHARED() { SharedLock(self); }
// Try to acquire share of ReaderWriterMutex.
bool SharedTryLock(Thread* self) SHARED_TRYLOCK_FUNCTION(true);
// Release a share of the access.
void SharedUnlock(Thread* self) RELEASE_SHARED() ALWAYS_INLINE;
void ReaderUnlock(Thread* self) RELEASE_SHARED() { SharedUnlock(self); }
// Is the current thread the exclusive holder of the ReaderWriterMutex.
ALWAYS_INLINE bool IsExclusiveHeld(const Thread* self) const;
// Assert the current thread has exclusive access to the ReaderWriterMutex.
ALWAYS_INLINE void AssertExclusiveHeld(const Thread* self) const ASSERT_CAPABILITY(this);
ALWAYS_INLINE void AssertWriterHeld(const Thread* self) const ASSERT_CAPABILITY(this);
// Assert the current thread doesn't have exclusive access to the ReaderWriterMutex.
void AssertNotExclusiveHeld(const Thread* self) ASSERT_CAPABILITY(!this) {
if (kDebugLocking && (gAborting == 0)) {
CHECK(!IsExclusiveHeld(self)) << *this;
}
}
void AssertNotWriterHeld(const Thread* self) ASSERT_CAPABILITY(!this) {
AssertNotExclusiveHeld(self);
}
// Is the current thread a shared holder of the ReaderWriterMutex.
bool IsSharedHeld(const Thread* self) const;
// Assert the current thread has shared access to the ReaderWriterMutex.
ALWAYS_INLINE void AssertSharedHeld(const Thread* self) ASSERT_SHARED_CAPABILITY(this) {
if (kDebugLocking && (gAborting == 0)) {
// TODO: we can only assert this well when self != null.
CHECK(IsSharedHeld(self) || self == nullptr) << *this;
}
}
ALWAYS_INLINE void AssertReaderHeld(const Thread* self) ASSERT_SHARED_CAPABILITY(this) {
AssertSharedHeld(self);
}
// Assert the current thread doesn't hold this ReaderWriterMutex either in shared or exclusive
// mode.
ALWAYS_INLINE void AssertNotHeld(const Thread* self) ASSERT_CAPABILITY(!this) {
if (kDebugLocking && (gAborting == 0)) {
CHECK(!IsExclusiveHeld(self)) << *this;
CHECK(!IsSharedHeld(self)) << *this;
}
}
// Id associated with exclusive owner. No memory ordering semantics if called from a thread other
// than the owner. Returns 0 if the lock is not held. Returns either 0 or -1 if it is held by
// one or more readers.
pid_t GetExclusiveOwnerTid() const;
void Dump(std::ostream& os) const override;
// For negative capabilities in clang annotations.
const ReaderWriterMutex& operator!() const { return *this; }
void WakeupToRespondToEmptyCheckpoint() override;
private:
#if ART_USE_FUTEXES
// Out-of-inline path for handling contention for a SharedLock.
void HandleSharedLockContention(Thread* self, int32_t cur_state);
// -1 implies held exclusive, >= 0: shared held by state_ many owners.
AtomicInteger state_;
// Exclusive owner. Modification guarded by this mutex.
Atomic<pid_t> exclusive_owner_;
// Number of contenders waiting for either a reader share or exclusive access. We only maintain
// the sum, since we would otherwise need to read both in all unlock operations.
// We keep this separate from the state, since futexes are limited to 32 bits, and obvious
// approaches to combining with state_ risk overflow.
AtomicInteger num_contenders_;
#else
pthread_rwlock_t rwlock_;
Atomic<pid_t> exclusive_owner_; // Writes guarded by rwlock_. Asynchronous reads are OK.
#endif
DISALLOW_COPY_AND_ASSIGN(ReaderWriterMutex);
};
// MutatorMutex is a special kind of ReaderWriterMutex created specifically for the
// Locks::mutator_lock_ mutex. The behaviour is identical to the ReaderWriterMutex except that
// thread state changes also play a part in lock ownership. The mutator_lock_ will not be truly
// held by any mutator threads. However, a thread in the kRunnable state is considered to have
// shared ownership of the mutator lock and therefore transitions in and out of the kRunnable
// state have associated implications on lock ownership. Extra methods to handle the state
// transitions have been added to the interface but are only accessible to the methods dealing
// with state transitions. The thread state and flags attributes are used to ensure thread state
// transitions are consistent with the permitted behaviour of the mutex.
//
// *) The most important consequence of this behaviour is that all threads must be in one of the
// suspended states before exclusive ownership of the mutator mutex is sought.
//
std::ostream& operator<<(std::ostream& os, const MutatorMutex& mu);
class SHARED_LOCKABLE MutatorMutex : public ReaderWriterMutex {
public:
explicit MutatorMutex(const char* name, LockLevel level = kDefaultMutexLevel)
: ReaderWriterMutex(name, level) {}
~MutatorMutex() {}
virtual bool IsMutatorMutex() const { return true; }
// For negative capabilities in clang annotations.
const MutatorMutex& operator!() const { return *this; }
private:
friend class Thread;
void TransitionFromRunnableToSuspended(Thread* self) UNLOCK_FUNCTION() ALWAYS_INLINE;
void TransitionFromSuspendedToRunnable(Thread* self) SHARED_LOCK_FUNCTION() ALWAYS_INLINE;
DISALLOW_COPY_AND_ASSIGN(MutatorMutex);
};
// ConditionVariables allow threads to queue and sleep. Threads may then be resumed individually
// (Signal) or all at once (Broadcast).
class ConditionVariable {
public:
ConditionVariable(const char* name, Mutex& mutex);
~ConditionVariable();
// Requires the mutex to be held.
void Broadcast(Thread* self);
// Requires the mutex to be held.
void Signal(Thread* self);
// TODO: No thread safety analysis on Wait and TimedWait as they call mutex operations via their
// pointer copy, thereby defeating annotalysis.
void Wait(Thread* self) NO_THREAD_SAFETY_ANALYSIS;
bool TimedWait(Thread* self, int64_t ms, int32_t ns) NO_THREAD_SAFETY_ANALYSIS;
// Variant of Wait that should be used with caution. Doesn't validate that no mutexes are held
// when waiting.
// TODO: remove this.
void WaitHoldingLocks(Thread* self) NO_THREAD_SAFETY_ANALYSIS;
void CheckSafeToWait(Thread* self) NO_THREAD_SAFETY_ANALYSIS {
if (kDebugLocking) {
guard_.CheckSafeToWait(self);
}
}
private:
const char* const name_;
// The Mutex being used by waiters. It is an error to mix condition variables between different
// Mutexes.
Mutex& guard_;
#if ART_USE_FUTEXES
// A counter that is modified by signals and broadcasts. This ensures that when a waiter gives up
// their Mutex and another thread takes it and signals, the waiting thread observes that sequence_
// changed and doesn't enter the wait. Modified while holding guard_, but is read by futex wait
// without guard_ held.
AtomicInteger sequence_;
// Number of threads that have come into to wait, not the length of the waiters on the futex as
// waiters may have been requeued onto guard_. Guarded by guard_.
int32_t num_waiters_;
void RequeueWaiters(int32_t count);
#else
pthread_cond_t cond_;
#endif
DISALLOW_COPY_AND_ASSIGN(ConditionVariable);
};
// Scoped locker/unlocker for a regular Mutex that acquires mu upon construction and releases it
// upon destruction.
class SCOPED_CAPABILITY MutexLock {
public:
MutexLock(Thread* self, Mutex& mu) ACQUIRE(mu) : self_(self), mu_(mu) {
mu_.ExclusiveLock(self_);
}
~MutexLock() RELEASE() {
mu_.ExclusiveUnlock(self_);
}
private:
Thread* const self_;
Mutex& mu_;
DISALLOW_COPY_AND_ASSIGN(MutexLock);
};
// Scoped locker/unlocker for a ReaderWriterMutex that acquires read access to mu upon
// construction and releases it upon destruction.
class SCOPED_CAPABILITY ReaderMutexLock {
public:
ALWAYS_INLINE ReaderMutexLock(Thread* self, ReaderWriterMutex& mu) ACQUIRE(mu);
ALWAYS_INLINE ~ReaderMutexLock() RELEASE();
private:
Thread* const self_;
ReaderWriterMutex& mu_;
DISALLOW_COPY_AND_ASSIGN(ReaderMutexLock);
};
// Scoped locker/unlocker for a ReaderWriterMutex that acquires write access to mu upon
// construction and releases it upon destruction.
class SCOPED_CAPABILITY WriterMutexLock {
public:
WriterMutexLock(Thread* self, ReaderWriterMutex& mu) EXCLUSIVE_LOCK_FUNCTION(mu) :
self_(self), mu_(mu) {
mu_.ExclusiveLock(self_);
}
~WriterMutexLock() UNLOCK_FUNCTION() {
mu_.ExclusiveUnlock(self_);
}
private:
Thread* const self_;
ReaderWriterMutex& mu_;
DISALLOW_COPY_AND_ASSIGN(WriterMutexLock);
};
} // namespace art
#endif // ART_RUNTIME_BASE_MUTEX_H_