10a12b2a6f
Summary: Closes https://github.com/facebook/rocksdb/pull/2226 Differential Revision: D4967547 Pulled By: siying fbshipit-source-id: dd3b58ae1e7a106ab6bb6f37ab5c88575b125ab4
134 lines
3.4 KiB
C++
134 lines
3.4 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
|
|
// This source code is licensed under the BSD-style license found in the
|
|
// LICENSE file in the root directory of this source tree. An additional grant
|
|
// of patent rights can be found in the PATENTS file in the same directory.
|
|
// This source code is also licensed under the GPLv2 license found in the
|
|
// COPYING file in the root directory of this source tree.
|
|
//
|
|
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style license that can be
|
|
// found in the LICENSE file. See the AUTHORS file for names of contributors.
|
|
|
|
#pragma once
|
|
#include <assert.h>
|
|
#include <atomic>
|
|
#include <mutex>
|
|
#include <thread>
|
|
#include "port/port.h"
|
|
|
|
namespace rocksdb {
|
|
|
|
// Helper class that locks a mutex on construction and unlocks the mutex when
|
|
// the destructor of the MutexLock object is invoked.
|
|
//
|
|
// Typical usage:
|
|
//
|
|
// void MyClass::MyMethod() {
|
|
// MutexLock l(&mu_); // mu_ is an instance variable
|
|
// ... some complex code, possibly with multiple return paths ...
|
|
// }
|
|
|
|
class MutexLock {
|
|
public:
|
|
explicit MutexLock(port::Mutex *mu) : mu_(mu) {
|
|
this->mu_->Lock();
|
|
}
|
|
~MutexLock() { this->mu_->Unlock(); }
|
|
|
|
private:
|
|
port::Mutex *const mu_;
|
|
// No copying allowed
|
|
MutexLock(const MutexLock&);
|
|
void operator=(const MutexLock&);
|
|
};
|
|
|
|
//
|
|
// Acquire a ReadLock on the specified RWMutex.
|
|
// The Lock will be automatically released then the
|
|
// object goes out of scope.
|
|
//
|
|
class ReadLock {
|
|
public:
|
|
explicit ReadLock(port::RWMutex *mu) : mu_(mu) {
|
|
this->mu_->ReadLock();
|
|
}
|
|
~ReadLock() { this->mu_->ReadUnlock(); }
|
|
|
|
private:
|
|
port::RWMutex *const mu_;
|
|
// No copying allowed
|
|
ReadLock(const ReadLock&);
|
|
void operator=(const ReadLock&);
|
|
};
|
|
|
|
//
|
|
// Automatically unlock a locked mutex when the object is destroyed
|
|
//
|
|
class ReadUnlock {
|
|
public:
|
|
explicit ReadUnlock(port::RWMutex *mu) : mu_(mu) { mu->AssertHeld(); }
|
|
~ReadUnlock() { mu_->ReadUnlock(); }
|
|
|
|
private:
|
|
port::RWMutex *const mu_;
|
|
// No copying allowed
|
|
ReadUnlock(const ReadUnlock &) = delete;
|
|
ReadUnlock &operator=(const ReadUnlock &) = delete;
|
|
};
|
|
|
|
//
|
|
// Acquire a WriteLock on the specified RWMutex.
|
|
// The Lock will be automatically released then the
|
|
// object goes out of scope.
|
|
//
|
|
class WriteLock {
|
|
public:
|
|
explicit WriteLock(port::RWMutex *mu) : mu_(mu) {
|
|
this->mu_->WriteLock();
|
|
}
|
|
~WriteLock() { this->mu_->WriteUnlock(); }
|
|
|
|
private:
|
|
port::RWMutex *const mu_;
|
|
// No copying allowed
|
|
WriteLock(const WriteLock&);
|
|
void operator=(const WriteLock&);
|
|
};
|
|
|
|
//
|
|
// SpinMutex has very low overhead for low-contention cases. Method names
|
|
// are chosen so you can use std::unique_lock or std::lock_guard with it.
|
|
//
|
|
class SpinMutex {
|
|
public:
|
|
SpinMutex() : locked_(false) {}
|
|
|
|
bool try_lock() {
|
|
auto currently_locked = locked_.load(std::memory_order_relaxed);
|
|
return !currently_locked &&
|
|
locked_.compare_exchange_weak(currently_locked, true,
|
|
std::memory_order_acquire,
|
|
std::memory_order_relaxed);
|
|
}
|
|
|
|
void lock() {
|
|
for (size_t tries = 0;; ++tries) {
|
|
if (try_lock()) {
|
|
// success
|
|
break;
|
|
}
|
|
port::AsmVolatilePause();
|
|
if (tries > 100) {
|
|
std::this_thread::yield();
|
|
}
|
|
}
|
|
}
|
|
|
|
void unlock() { locked_.store(false, std::memory_order_release); }
|
|
|
|
private:
|
|
std::atomic<bool> locked_;
|
|
};
|
|
|
|
} // namespace rocksdb
|