Java---19---多线程：生产者和消费者

生产者和消费者问题是多线程通信的经典问题。这类问题描述了这样一种情况：假设有一个仓库，用来存储产品，有生产者负责生产产品，有消费者负责消费。生产者生产的产品存放在仓库之中，消费者从仓库之中取出产品。显然这是一个同步问题，生产者和消费者共享同一资源，并且生产者和消费者之间彼此依赖，互为条件向前推进。那么，该如何编写代码来实现呢？

class Resource {
	private String name;
	private String sex;
	private boolean flag = false;

	public synchronized void set(String name, String sex) {
		if (flag == true) {
			try {
				wait();
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		this.name = name + "--" + sex;
		System.out.println(Thread.currentThread().getName() + "--生产者--"
				+ this.name);
		flag = true;
		notify();
	}

	public synchronized void out() {
		if (flag == false) {
			try {
				wait();
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		System.out.println(Thread.currentThread().getName() + "---消费者---"
				+ this.name);
		flag = false;
		notify();
	}
}

class Producer implements Runnable {
	private Resource resource;
	private int num = 0;

	Producer(Resource resource) {
		this.resource = resource;
	}

	public void run() {
		while (true) {
			if (num == 1) {

				resource.set("丽丽", "女女女");
			} else {
				resource.set("mike", "man");
			}
			num = ++num % 2;
		}
	}
}

class Consumer implements Runnable {
	private Resource resource;

	Consumer(Resource resource) {
		this.resource = resource;
	}

	public void run() {
		while (true) {
			resource.out();
		}
	}
}

class Communicate {
	public static void main(String[] args) {
		Resource resource = new Resource();
		Producer pro = new Producer(resource);
		Consumer con = new Consumer(resource);
		Thread t1 = new Thread(pro);
		Thread t2 = new Thread(con);

		t1.start();
		t2.start();

	}
}

这个例子已经实现了生产一个就消费一个，其实这个例子就是上一篇文章中的例子，只是将代码略作优化。

但是还有一个问题，这个例子只是一个线程用来生产，一个线程用来消费，那如果多加几个线程呢？

那我们多加上几个线程试试。

class Resource {
	private String name;
	private String sex;
	private boolean flag = false;

	public synchronized void set(String name, String sex) {
		if (flag == true) {
			try {
				wait();
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		this.name = name + "--" + sex;
		System.out.println(Thread.currentThread().getName() + "--生产者--"
				+ this.name);
		flag = true;
		notify();
	}

	public synchronized void out() {
		if (flag == false) {
			try {
				wait();
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		System.out.println(Thread.currentThread().getName() + "---消费者---"
				+ this.name);
		flag = false;
		notify();
	}
}

class Producer implements Runnable {
	private Resource resource;
	private int num = 0;

	Producer(Resource resource) {
		this.resource = resource;
	}

	public void run() {
		while (true) {
			if (num == 1) {

				resource.set("丽丽", "女女女");
			} else {
				resource.set("mike", "man");
			}
			num = ++num % 2;
		}
	}
}

class Consumer implements Runnable {
	private Resource resource;

	Consumer(Resource resource) {
		this.resource = resource;
	}

	public void run() {
		while (true) {
			resource.out();
		}
	}
}

class Communicate {
	public static void main(String[] args) {
		Resource resource = new Resource();
		Producer pro = new Producer(resource);
		Consumer con = new Consumer(resource);
		Thread t1 = new Thread(pro);
		Thread t2 = new Thread(pro);

		Thread t3 = new Thread(con);
		Thread t4 = new Thread(con);

		t1.start();
		t2.start();
		t3.start();
		t4.start();
	}
}

在打印结果中我们发现会有这种情况：

Thread-1--生产者--mike--man

Thread-0--生产者--mike--man

Thread-2---消费者---mike--man

还可能会发生生产一个而消费两个的情况。出现的原因在 wait()这，就不过多的解释了。

只需要将判断flag 的if 改为while 同时将notify改为notifyAll() 就ok。

修改完如下：

class Resource {
	private String name;
	private String sex;
	private boolean flag = false;

	public synchronized void set(String name, String sex) {
		while (flag == true) {
			try {
				wait();
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		this.name = name + "--" + sex;
		System.out.println(Thread.currentThread().getName() + "--生产者--"
				+ this.name);
		flag = true;
		notifyAll();
	}

	public synchronized void out() {
		while (flag == false) {
			try {
				wait();
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		System.out.println(Thread.currentThread().getName() + "---消费者---"
				+ this.name);
		flag = false;
		notifyAll();
	}
}

class Producer implements Runnable {
	private Resource resource;
	private int num = 0;

	Producer(Resource resource) {
		this.resource = resource;
	}

	public void run() {
		while (true) {
			if (num == 1) {

				resource.set("丽丽", "女女女");
			} else {
				resource.set("mike", "man");
			}
			num = ++num % 2;
		}
	}
}

class Consumer implements Runnable {
	private Resource resource;

	Consumer(Resource resource) {
		this.resource = resource;
	}

	public void run() {
		while (true) {
			resource.out();
		}
	}
}

class Communicate {
	public static void main(String[] args) {
		Resource resource = new Resource();
		Producer pro = new Producer(resource);
		Consumer con = new Consumer(resource);
		Thread t1 = new Thread(pro);
		Thread t2 = new Thread(pro);

		Thread t3 = new Thread(con);
		Thread t4 = new Thread(con);

		t1.start();
		t2.start();
		t3.start();
		t4.start();
	}
}