1、RAII简介

RAII（Resource Acquisition Is Initialization），也称为“资源获取就是初始化”，是C++语言的一种管理资源、避免泄漏的惯用法。C++标准保证任何情况下，已构造的对象最终会销毁，即它的析构函数最终会被调用。简单的说，RAII的做法是使用一个对象，在其构造时获取资源，在对象生命期控制对资源的访问使之始终保持有效，最后在对象析构的时候释放资源。

2、RAII分类

根据RAII对资源的所有权可分为常性类型和变性类型，代表者分别是std::shared_ptr和std::auto_ptr，从所管资源的初始化位置上可分为外部初始化类型和内部初始化类型。

常性类型是指获取资源的地点是构造函数，释放点是析构函数，并且在这两点之间的一段时间里，任何对该RAII类型实例的操纵都不应该从它手里夺走资源的所有权。

变性类型是指可以中途被设置为接管另一个资源，或者干脆被置为不拥有任何资源。

外部初始化类型是指资源在外部被创建，并被传给RAII实例的构造函数，后者进而接管了其所有权。std::shared_ptr和std::auto_ptr都是此类型。

内部初始化类型与外部初始化类型则正好相反。

3、基于RAII对锁进行封装

源代码如下，需要在支持C++11的环境下编译

#ifndef __LOCK_H
#define __LOCK_H

#include <thread>
#include <memory>
#include <pthread.h>
#include <semaphore.h>
#include <atomic>

struct Noncopyable
{ 
   
    Noncopyable() = default;

    ~Noncopyable() = default;

    Noncopyable(const Noncopyable&) = delete;

    Noncopyable& operator=(const Noncopyable&) = delete;
};

/** * brief: 信号量 */
class Semaphore : Noncopyable
{ 
   
public:
    Semaphore(uint32_t count = 0)
    { 
   
        sem_init(&m_sem, 0, count);
    }

    ~Semaphore()
    { 
   
        sem_destroy(&m_sem);
    }

    void wait()
    { 
   
        sem_wait(&m_sem);
    }

    void notify()
    { 
   
        sem_post(&m_sem);
    }

private:
    sem_t m_sem;
};

/** * brief: 局部锁模板 */
template<typename T>
class ScopedLock
{ 
   
public:
    ScopedLock(T &m)
        :m_mutex(m)
    { 
   
        lock();
    }

    ~ScopedLock()
    { 
   
        unlock();
    }

    void lock()
    { 
   
        if (!m_lock)
        { 
   
            m_mutex.lock();
            m_lock = true;
        }
    }

    void unlock()
    { 
   
        if (m_lock)
        { 
   
            m_mutex.unlock();
            m_lock = false;
        }
    }

private:
    T &m_mutex;
    bool m_lock = false;
};

/** * brief: 局部写锁 */
template<typename T>
class WriteScopedLock
{ 
   
public:
    WriteScopedLock(T &m)
        :m_mutex(m)
    { 
   
        lock();
    }

    ~WriteScopedLock()
    { 
   
        unlock();
    }

    void lock()
    { 
   
        if (!m_lock)
        { 
   
            m_mutex.wrlock();
            m_lock = true;
        }
    }

    void unlock()
    { 
   
        if (m_lock)
        { 
   
            m_mutex.unlock();
            m_lock = false;
        }
    }

private:
    T& m_mutex;
    bool m_lock = false;
};

/** * brief: 局部读锁 */
template<typename T>
class ReadScopedLock
{ 
   
public:
    ReadScopedLock(T &m)
        :m_mutex(m)
    { 
   
        lock();
    }

    ~ReadScopedLock()
    { 
   
        unlock();
    }

    void lock()
    { 
   
        if (!m_lock)
        { 
   
            m_mutex.rdlock();
            m_lock = true;
        }
    }

    void unlock()
    { 
   
        if (m_lock)
        { 
   
            m_mutex.unlock();
            m_lock = false;
        }
    }

private:
    T& m_mutex;
    bool m_lock = false;
};

/** * brief: 互斥量 */
class Mutex : Noncopyable
{ 
   
public:
    typedef ScopedLock<Mutex> Lock;

    Mutex()
    { 
   
        pthread_mutex_init(&m_mutex, nullptr);
    }

    ~Mutex()
    { 
   
        pthread_mutex_destroy(&m_mutex);
    }

    void lock()
    { 
   
        pthread_mutex_lock(&m_mutex);
    }
    
    int trylock()
    { 
   
        pthread_mutex_trylock(&m_mutex);
    }

    void unlock()
    { 
   
        pthread_mutex_unlock(&m_mutex);
    }

private:
    pthread_mutex_t m_mutex;
};

/** * brief: 读写互斥量 */
class RWMutex : Noncopyable
{ 
   
public:
    typedef WriteScopedLock<RWMutex> WriteLock;
    typedef ReadScopedLock<RWMutex> ReadLock;

    RWMutex()
    { 
   
        pthread_rwlock_init(&m_lock, nullptr);
    }

    ~RWMutex()
    { 
   
        pthread_rwlock_destroy(&m_lock);
    }

    void rdlock()
    { 
   
        pthread_rwlock_rdlock(&m_lock);
    }

    void wrlock()
    { 
   
        pthread_rwlock_wrlock(&m_lock);
    }

    void unlock()
    { 
   
        pthread_rwlock_unlock(&m_lock);
    }

private:
    pthread_rwlock_t m_lock;
};

/** * brief: 自旋锁 */
class SpinLock : Noncopyable
{ 
   
public:
    typedef ScopedLock<SpinLock> Lock;

    SpinLock()
    { 
   
        pthread_spin_init(&m_mutex, 0);
    }

    ~SpinLock()
    { 
   
        pthread_spin_destroy(&m_mutex);
    }

    void lock()
    { 
   
        pthread_spin_lock(&m_mutex);
    }

    int trylock()
    { 
   
        pthread_spin_trylock(&m_mutex);
    }

    void unlock()
    { 
   
        pthread_spin_unlock(&m_mutex);
    }

private:
    pthread_spinlock_t m_mutex;
};

/** * brief: 原子锁 */
class CASLock : Noncopyable
{ 
   
public:
    typedef ScopedLock<CASLock> Lock;

    CASLock()
    { 
   
        m_mutex.clear();
    }

    ~CASLock()
    { 
   
    }

    void lock()
    { 
   
        while (std::atomic_flag_test_and_set_explicit(&m_mutex, std::memory_order_acquire));
    }

    void unlock()
    { 
   
        std::atomic_flag_clear_explicit(&m_mutex, std::memory_order_release);
    }

private:
    volatile std::atomic_flag m_mutex;
};

#endif /*__LOCK_H*/