c++利用互斥锁实现读写锁

很简单就是在读的时候把写的锁锁住就好了

class readwrite_lock
{
public:
    readwrite_lock()
        : read_cnt(0)
    {
    }  

    void readLock()
    {
        read_mtx.lock();
        if (++read_cnt == 1)
            write_mtx.lock();  

        read_mtx.unlock();
    }  

    void readUnlock()
    {
        read_mtx.lock();
        if (--read_cnt == 0)
            write_mtx.unlock();  

        read_mtx.unlock();
    }  

    void writeLock()
    {
        write_mtx.lock();
    }  

    void writeUnlock()
    {
        write_mtx.unlock();
    }  

private:
    mutex read_mtx;
    mutex write_mtx;
    int read_cnt; // 已加读锁个数
};