Java 读者写者问题

实验存档。

允许好几个人同时读，但是不允许在有人读的时候写，以及同一时间只能有一个人在写。

读者.java：

package operating.entity.readerwriter;

import operating.method.Semaphore;

public class Reader implements Runnable {
    private static int total = 0;
    private int id;
    private Semaphore rmutex, wmutex;
    private static int readCount = 0;

    public Reader(Semaphore rmutex, Semaphore wmutex) {
        id = ++total;
        this.rmutex = rmutex;
        this.wmutex = wmutex;
    }

    @Override
    public void run() {
        while (true) {
            rmutex.p();
            // 只有第一个读者进程需要执行 wmutex.p()
            if (readCount == 0) wmutex.p();
            readCount++;
            rmutex.v();

            // 执行读操作
            try {
                Thread.sleep(30);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            rmutex.p();
            readCount--;
            System.out.println(id + " 号读者结束阅读：当前还剩 " + readCount + " 位读者在读");
            if (readCount == 0) wmutex.v();
            rmutex.v();
        }
    }
}

写者.java：

package operating.entity.readerwriter;

import operating.method.Semaphore;

public class Writer implements Runnable {
    private static int total = 0;
    private int id;
    private Semaphore wmutex;

    public Writer(Semaphore wmutex) {
        id = ++total;
        this.wmutex = wmutex;
    }

    @Override
    public void run() {
        while (true) {
            wmutex.p();
            // 执行写操作
            System.out.println(id + " 号写者正在写");

            wmutex.v();
        }
    }
}

主函数.java：

package operating.test;

import operating.entity.readerwriter.Reader;
import operating.entity.readerwriter.Writer;
import operating.method.Semaphore;

public class ReaderWriterTest {
    public static void main(String[] args) {
        // 实现写者与写者间、读者与写者间互斥
        Semaphore wmutex = new Semaphore(1);
        // 用于改变 readCount 变量时实现互斥
        Semaphore rmutex = new Semaphore(1);

        for (int i = 0; i != 5; ++i) {
            new Thread(new Writer(wmutex)).start();
            new Thread(new Reader(rmutex, wmutex)).start();
        }
    }
}

/

Semaphore.java