Java生产者与消费者（下）

本文来自http://blog.csdn.net/liuxian13183/ ，引用必须注明出处！

上一讲我们让消费者和生产者都各停1毫秒，实际上大多并不是这样的。第二讲，我们讲一个极端的例子和一个正常的例子，假设您已经看过上一讲，我们只改变Consumer和Producer，来看结果。

Java生产者与消费者（上）

名词解释

wait:当前线程不运行，处理等待状态，等待notify；所以也不会往下执行。

您可能会有疑问前例中的为什么要用while循环而非if语句？

主要是防止多线程操作时，例桌子已经占满，两个生产线程均处理等待状态，但消费线程通过notifyAll打开其等待状态，就造成生产过量的蛋糕，而导致生产消费模式失败，所以不能用if语句。

sleep:暂停当前线程若干时间，之后继续运行

Special Sample：生产者和消费者均不加sleep

Result：

Produce1 produce:1
Produce2 produce:2
Produce1 produce:3
Produce1 produce:4
Produce1 produce:5
Produce1 begin to wait !
Consumer1 consume:5
Consumer1 consume:4
Consumer1 consume:3
Consumer1 consume:2
Consumer1 consume:1
Consumer1 begin to wait !
Produce1 stop waiting !
Produce1 produce:1

Produce1 produce:2
Produce2 produce:3
Produce2 produce:4
Produce2 produce:5
Produce2 begin to wait !
Consumer2 consume:5
Consumer2 consume:4
Consumer2 consume:3
Consumer2 consume:2
Consumer2 consume:1
Consumer2 begin to wait !
Produce2 stop waiting !
Produce2 produce:1
Produce2 produce:2
Produce2 produce:3
Produce2 produce:4
Produce2 produce:5
Produce2 begin to wait !
Produce1 begin to wait !
Consumer1 stop waiting !
Consumer1 consume:5
Consumer1 consume:4
Consumer1 consume:3
Consumer1 consume:2
Consumer1 consume:1
Consumer1 begin to wait !
Produce1 stop waiting !
Produce1 produce:1
Produce1 produce:2
Produce1 produce:3
Produce1 produce:4
Produce1 produce:5
Produce1 begin to wait !
Produce2 stop waiting !
Produce2 begin to wait !
Consumer2 stop waiting !
Consumer2 consume:5
Consumer2 consume:4
Consumer2 consume:3
Consumer2 consume:2
Consumer2 consume:1
Consumer2 begin to wait !
Produce2 stop waiting !
Produce2 produce:1
Produce2 produce:2
Produce2 produce:3
Produce2 produce:4
Produce2 produce:5
Produce2 begin to wait !
Produce1 stop waiting !
Produce1 begin to wait !
Consumer1 stop waiting !
Consumer1 consume:5
Consumer1 consume:4
Consumer1 consume:3
Consumer1 consume:2
Consumer1 consume:1
Consumer1 begin to wait !
Produce1 stop waiting !
Produce1 produce:1
Produce1 stop at last !

解析：例子很极端，生产和消费均两个线程，A线程在工作时B在等待；

A生产线程生产，B生产线程等待直到A生产完；

A消费线程消费，B消费线程等待直到A消费完；

B生产线程生产，A生产线程等待直到A生产完；

B消费线程消费，A消费线程等待直到A消费完；

……

这样一个循环，失去多线程的意义所在（变成了单线程）！

正常的例子：生产可能只需要1毫秒，消费需要2毫秒

Produce1 produce:1
Consumer1 consume:1
Consumer2 begin to wait !//此时Consumer2检测到count为0，所以等待
Produce2 produce:1
Consumer2 stop waiting !//此时Consumer2检测到count已经大于0，所以打开
Consumer2 consume:1
Produce1 produce:1//看，生产与消费是无序的。两者分开，不管你在不在生产，我都要消费，只要蛋糕还有；
Produce2 produce:2//不管你消费不消费，只要桌子还有空的；它们两个均对一种情况负责：桌子和蛋糕形成的映射关系！
Consumer2 consume:2
Consumer1 consume:1
Produce2 produce:1
Produce1 produce:2
Produce2 produce:3
Produce1 produce:4
Consumer1 consume:4
Consumer2 consume:3
Produce1 produce:3
Produce2 produce:4
Produce2 produce:5
Produce1 begin to wait !
Consumer1 consume:5
Produce1 stop waiting !
Produce1 produce:5
Produce2 begin to wait !
Consumer2 consume:5
Produce2 stop waiting !
Produce2 produce:5
Produce2 begin to wait !
Produce1 begin to wait !
Consumer2 consume:5
Produce1 stop waiting !
Produce1 produce:5
Produce2 stop waiting !
Produce2 begin to wait !
Consumer1 consume:5
Produce2 stop waiting !
Produce2 produce:5
Produce1 begin to wait !
Produce2 begin to wait !
Consumer1 consume:5
Consumer1 stop at last !

解析：这次我让执行25次即退出虚拟机。

大家可以看到，本次两个生产线程和两个消费线程，在生产和消费的时候都是无序的，无论你要不要停，我都要工作，不能让一个线程一直抓住锁不放，其实这才是多线程本质。

代码如下：

Producer：

public class Producer extends Thread {
	Table table;
	String threadName;

	public Producer(String string, Table table) {
		// TODO Auto-generated constructor stub
		this.table = table;
		this.threadName = string;
		this.setName(threadName);
	}

	@Override
	public void run() {
		// TODO Auto-generated method stub
		super.run();
		try {
			while (true) {
				table.produce(threadName);
				sleep(1);
			}
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

消费者：

public class Consumer extends Thread {
	Table table;
	String threadName;

	public Consumer(String string, Table table) {
		// TODO Auto-generated constructor stub
		this.table = table;
		this.threadName = string;
		this.setName(threadName);
	}

	@Override
	public void run() {
		// TODO Auto-generated method stub
		super.run();
		try {
			while (true) {
				table.consume(threadName);
				sleep(2);
			}
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}