9eb3e1f77d
Summary: Use delete to disable automatic generated methods instead of private, and put the constructor together for more clear.This modification cause the unused field warning, so add unused attribute to disable this warning. Pull Request resolved: https://github.com/facebook/rocksdb/pull/5009 Differential Revision: D17288733 fbshipit-source-id: 8a767ce096f185f1db01bd28fc88fef1cdd921f3
136 lines
3.3 KiB
C++
136 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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// No copying allowed
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MutexLock(const MutexLock&) = delete;
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void operator=(const MutexLock&) = delete;
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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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};
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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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// No copying allowed
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ReadLock(const ReadLock&) = delete;
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void operator=(const ReadLock&) = delete;
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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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};
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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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// No copying allowed
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ReadUnlock(const ReadUnlock &) = delete;
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ReadUnlock &operator=(const ReadUnlock &) = delete;
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~ReadUnlock() { mu_->ReadUnlock(); }
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private:
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port::RWMutex *const mu_;
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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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// No copying allowed
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WriteLock(const WriteLock&) = delete;
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void operator=(const WriteLock&) = delete;
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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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};
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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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