algos: use mutex to implement read-write lock

MyRWLock.cpp

extern "C"
{
    #include <pthread.h>
}

class MyRWLock
{
    public:
        MyRWLock();
        ~MyRWLock();
        void r_lock();
        void r_unlock();
        void w_lock();
        void w_unlock();

    private:
        int key;
        pthread_mutex_t mutex_r_lock;
        pthread_mutex_t mutex_w_lock;
};

MyRWLock::MyRWLock()
{
    key = 0;
    pthread_mutex_init(&mutex_r_lock, 0);
    pthread_mutex_init(&mutex_w_lock, 0);
}

MyRWLock::~MyRWLock()
{
    pthread_mutex_destroy(&mutex_r_lock);
    pthread_mutex_destroy(&mutex_w_lock);
}

void MyRWLock::r_lock()
{
    pthread_mutex_lock(&mutex_r_lock);
    key++;
    if (1 == key)
    {
        pthread_mutex_lock(&mutex_w_lock);
    }
    pthread_mutex_unlock(&mutex_r_lock);
}

void MyRWLock::r_unlock()
{
    pthread_mutex_lock(&mutex_r_lock);
    key--;
    if (0 == key)
    {
        pthread_mutex_unlock(&mutex_w_lock);
    }
    pthread_mutex_unlock(&mutex_r_lock);
}

void MyRWLock::w_lock()
{
    pthread_mutex_lock(&mutex_w_lock);
}

void MyRWLock::w_unlock()
{
    pthread_mutex_unlock(&mutex_w_lock);
}

int main()
{
    MyRWLock t;
    return 0;
}