Reader Writer Problem

给定： http://www.1point3acres.com/bbs/thread-215980-1-1.html

Mutex:

void lock();

bool unlock();

SharedMutex:

void readerLock();.

void readerUnlock();

void writerLock();

void writerUnlock();

实现下面4个api，自己定义mutex和variable，不管starvation。

public class ReadWriteLock{ 
    private int readers       = 0;
    private int writers       = 0;
    private int writeRequests = 0;

    public void lockRead() throws InterruptedException{
        lock();
        while(writers > 0 || writeRequests > 0)    await();
        readers++;
        unlock();    
    }

    public void unlockRead(){
        lock();
        readers--;
        signal();
        unlock();
    }

    public void lockWrite() throws InterruptedException{
        lock();
        writeRequests++;
        while(readers > 0 || writers > 0)   await();
        writeRequests--;
        writers++;
        unlock();
    }

    public void unlockWrite() throws InterruptedException{
        lock();
        writers--;
        notifyAll();
        unlock();
    }
}