java语言进程通信学习

最近在看进程通信这块，觉得用wait、notify、notifiAll来做进程通信挺有意思的。

现把我写的一个小例子贴出来

package com.tsing.test1;

import java.util.LinkedList;

public class PrintQueue {
	
	private LinkedList<String> queue = new LinkedList<String>();
	
	public synchronized void add(String str){
		queue.add(str);
		System.out.println("already add str "+str+" and notify to remove");
		notifyAll();
	}
	
	public synchronized String remove() throws InterruptedException{
		while(queue.size() == 0){
			System.out.println(Thread.currentThread().getName()+" is waitting ...");
			wait();
		}
		return queue.remove();
	}
	
	public static void main(String[] args){
		PrintQueue queue = new PrintQueue();
		
		Printer p = new Printer(queue);
		new Thread(p).start();
		new Thread(p).start();
		
		for(int i = 0 ; i < 10 ; i++){
			queue.add("number : "+i);
		}
		try {
			Thread.sleep(3000);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		for(int i = 0 ; i < 10 ; i++){
			queue.add("number : "+i);
		}
	}
}

 

package com.tsing.test1;
/**
 * 用来打印
 * @author Administrator
 *
 */
public class Printer implements Runnable{

	private PrintQueue queue;
	
	public Printer(PrintQueue queue){
		this.queue = queue;
	}
	
	public void run() {
		while(true){
			try {
				System.out.println(Thread.currentThread().getName() +"try to remove : "+queue.remove());
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}

}

 

一、这上面有两个类：

1、PrintQueue

该类是打印队列类，用来添加打印字符串和打印字符串（实际是移除）。其中add方法和remove方法都是被synchronized修饰的：即对于同一个PrintQueue对象，add和remove方法是受同步保护的。

2、Printer

该类用来运行PrintQueue对象的remove方法的。

 

二、执行的结果（每次执行结果顺序可能会不一样）

already add str number : 0 and notify to remove
already add str number : 1 and notify to remove
Thread-1try to remove : number : 0
already add str number : 2 and notify to remove
Thread-0try to remove : number : 1
already add str number : 3 and notify to remove
already add str number : 4 and notify to remove
Thread-1try to remove : number : 2
already add str number : 5 and notify to remove
Thread-0try to remove : number : 3
already add str number : 6 and notify to remove
Thread-1try to remove : number : 4
already add str number : 7 and notify to remove
Thread-0try to remove : number : 5
already add str number : 8 and notify to remove
Thread-1try to remove : number : 6
already add str number : 9 and notify to remove
Thread-1try to remove : number : 7
Thread-1try to remove : number : 9
Thread-0try to remove : number : 8
Thread-1 is waitting ...
Thread-0 is waitting ...
already add str number : 0 and notify to remove
already add str number : 1 and notify to remove
already add str number : 2 and notify to remove
already add str number : 3 and notify to remove
already add str number : 4 and notify to remove
already add str number : 5 and notify to remove
already add str number : 6 and notify to remove
already add str number : 7 and notify to remove
already add str number : 8 and notify to remove
already add str number : 9 and notify to remove
Thread-0try to remove : number : 0
Thread-1try to remove : number : 1
Thread-1try to remove : number : 3
Thread-1try to remove : number : 4
Thread-1try to remove : number : 5
Thread-1try to remove : number : 6
Thread-1try to remove : number : 7
Thread-1try to remove : number : 8
Thread-1try to remove : number : 9
Thread-1 is waitting ...
Thread-0try to remove : number : 2
Thread-0 is waitting ...

三、分析

1、从执行结果可以看出来并不是每次执行notifyAll，wait进程就会被唤醒。

2、线程执行wait后就进入静默状态，直到notifyAll或者notify被执行

3、被synchronized修饰的方法，是已该对象实例为锁的

 

四、疑问

1、为啥不是每次执行notifyAll之后，wait就被唤醒？？？

还请知道的大牛指点一二