用JAVA實現的第二類讀者寫者問題

//--Semaphore.java

package rw;

public class Semaphore {
	private int value;//記錄希望訪問臨界資源的線程的計數器個數
	
	public Semaphore(int i)
	{
		this.value=i;
	}
	
	public synchronized void P()
	{
		value--;
		if(value<0)
			try {
				wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
				Thread.currentThread().interrupt();
			}
	}

	public synchronized void V()
	{
		value++;
		if(value<=0)
		{
			notifyAll();
		}
	}
}

//------------------------------文件2  ReaderWriter.java------------------------------------------------
package rw;

import java.io.FileNotFoundException;
import java.io.PrintStream;

public class ReaderWriter extends Thread{

	String msg;
	int NO;
	final int N=100;
	static public int num=0;
	static public int readers=0;
	static public int writers=0;
	final static public String base="Last Writer:";
	static public String resource=base+"0";
	static Semaphore mutexr=new Semaphore(1);
	static Semaphore mutexw=new Semaphore(1);
	
	static Semaphore mutex=new Semaphore(1);
	
	static Semaphore mutexWrite=new Semaphore(1);
	
	public ReaderWriter()
	{
		NO=num++;
		if(NO%N!=1)
		    msg="I am reader @"+NO;
		else 
			msg="I am writer @"+NO;
	}
	
	public void read()
	{
		if(writers!=0)//如果有寫者，阻塞，並且後續的讀者不許進來
			mutex.P();
		mutexr.P();
		readers++;
		if(readers==1)//保證當讀的時候，對寫互斥，寫者等待
			mutexWrite.P();
		mutexr.V();
		
		//.............................................讀開始...
		System.out.println("      "+NO+" is reading, resource=" +resource);
		//.............................................讀結束...
		
		mutexr.P();
		readers--;
		if(readers==0)
			mutexWrite.V();
		mutexr.V();
		if(writers!=0)//如果有寫者，阻塞，並且後續的讀者不許進來
			mutex.V();
	}
	
	public void write()
	{
		
		mutexw.P();
		writers++;
		if(writers==1)
			mutex.P();
		mutexw.V();
		
		//.....................................................寫開始
        mutexWrite.P();
		resource="base"+NO;
		System.out.println(NO+" IS WRITING, resource=" +resource);
		mutexWrite.V();
		//.....................................................寫結束
		
		mutexw.P();
		writers--;
		if(writers==0)
			mutex.V();
		mutexw.V();
	}
	
	public void run()
	{
		int n=1000;
		while(n-->0)
		{
			if(NO%N!=1)
			{/*
				try {
					Thread.sleep(1);
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
				*/
				read();
			}
			else 
			{
				write();
				/*
				try {
					Thread.sleep(100);
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
				*/
			}
		}
	}
	
	public static void main(String args[])
	{
		PrintStream ps;
		try {
			ps = new PrintStream("D:\\readerWriter.txt");
			System.setOut(ps);
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		}
		for(int i=0;i<1000;i++)
		{
			new ReaderWriter().start();
		}
	}
}