132 lines
3.3 KiB
C++
132 lines
3.3 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#pragma once
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#include <assert.h>
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#include <atomic>
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#include <mutex>
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#include <thread>
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#include "port/port.h"
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namespace rocksdb {
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// Helper class that locks a mutex on construction and unlocks the mutex when
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// the destructor of the MutexLock object is invoked.
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//
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// Typical usage:
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//
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// void MyClass::MyMethod() {
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// MutexLock l(&mu_); // mu_ is an instance variable
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// ... some complex code, possibly with multiple return paths ...
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// }
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class MutexLock {
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public:
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explicit MutexLock(port::Mutex *mu) : mu_(mu) {
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this->mu_->Lock();
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}
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~MutexLock() { this->mu_->Unlock(); }
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private:
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port::Mutex *const mu_;
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// No copying allowed
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MutexLock(const MutexLock&);
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void operator=(const MutexLock&);
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};
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//
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// Acquire a ReadLock on the specified RWMutex.
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// The Lock will be automatically released then the
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// object goes out of scope.
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//
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class ReadLock {
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public:
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explicit ReadLock(port::RWMutex *mu) : mu_(mu) {
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this->mu_->ReadLock();
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}
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~ReadLock() { this->mu_->ReadUnlock(); }
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private:
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port::RWMutex *const mu_;
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// No copying allowed
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ReadLock(const ReadLock&);
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void operator=(const ReadLock&);
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};
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//
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// Automatically unlock a locked mutex when the object is destroyed
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//
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class ReadUnlock {
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public:
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explicit ReadUnlock(port::RWMutex *mu) : mu_(mu) { mu->AssertHeld(); }
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~ReadUnlock() { mu_->ReadUnlock(); }
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private:
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port::RWMutex *const mu_;
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// No copying allowed
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ReadUnlock(const ReadUnlock &) = delete;
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ReadUnlock &operator=(const ReadUnlock &) = delete;
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};
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//
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// Acquire a WriteLock on the specified RWMutex.
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// The Lock will be automatically released then the
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// object goes out of scope.
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//
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class WriteLock {
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public:
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explicit WriteLock(port::RWMutex *mu) : mu_(mu) {
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this->mu_->WriteLock();
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}
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~WriteLock() { this->mu_->WriteUnlock(); }
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private:
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port::RWMutex *const mu_;
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// No copying allowed
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WriteLock(const WriteLock&);
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void operator=(const WriteLock&);
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};
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//
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// SpinMutex has very low overhead for low-contention cases. Method names
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// are chosen so you can use std::unique_lock or std::lock_guard with it.
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//
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class SpinMutex {
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public:
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SpinMutex() : locked_(false) {}
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bool try_lock() {
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auto currently_locked = locked_.load(std::memory_order_relaxed);
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return !currently_locked &&
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locked_.compare_exchange_weak(currently_locked, true,
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std::memory_order_acquire,
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std::memory_order_relaxed);
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}
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void lock() {
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for (size_t tries = 0;; ++tries) {
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if (try_lock()) {
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// success
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break;
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}
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port::AsmVolatilePause();
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if (tries > 100) {
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std::this_thread::yield();
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}
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}
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}
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void unlock() { locked_.store(false, std::memory_order_release); }
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private:
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std::atomic<bool> locked_;
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};
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} // namespace rocksdb
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