生产者消费者模型——wait/notify/notifyAll使用

告警系统架构如下

1、 数据处理系统处理完原始数据并入库后，发送消息到kafka系统；

2、 告警生产者从kafka系统查询消息存入告警消息队列；

3、 告警消费者从告警消息队列查询消息进行处理。

这显然是生产者消费者模型，一个告警消息生产者，多个告警消息消费者。生产者生产消息过快会产生消息积压，生产者生产消息过慢不能充分利用硬件资源。所以必须要生产者和消费者协同处理，使得系统充分利用。具体做法是消息队列为空时，消费者通知生产者生产消息，生产者生产好消息后，通知消费者处理消息。Java中我们使用的对象锁以及wait/notify方法进行线程通信，原理如下：

生产者——循环（获取锁synchronized，释放锁wait（等待被唤醒），生产消息）

消费者——循环（获取锁，消息空则notify/消息不空则消费消息）

消息队列代码：

package com.coshaho.threadpool;

import java.util.ArrayList;
import java.util.List;

/**
 * 消息队列
 * @author coshaho
 */
public class MessageQueue
{
	List<String> messageList = new ArrayList<String>();

	public boolean isEmpty()
	{
		return messageList.isEmpty();
	}

	/**
	 * 消费消息
	 * @return
	 */
	public String consumeMessage()
	{
		return messageList.remove(0);
	}

	/**
	 * 生产消息
	 * @param msg
	 */
	public void produceMessage(String msg)
	{
		messageList.add(msg);
	}
}

消费者代码：

package com.coshaho.threadpool;

/**
 * 消费者，消息队列为空则唤醒生产者
 * @author h00219638
 *
 */
public class Customer implements Runnable
{
	String name;
	MessageQueue msgQueue;
	public Customer(String name, MessageQueue msgQueue)
	{
		this.name = name;
		this.msgQueue = msgQueue;
	}

	@Override
	public void run()
	{
		while(true)
		{
			// 消费消息
			synchronized(msgQueue)
			{
				// 如果消息队列为空，唤醒生产者生产消息
				if(msgQueue.isEmpty())
				{
					msgQueue.notify();
				}
				// 消息队列不为空，则消费消息
				else
				{
					String msg = msgQueue.consumeMessage();
					System.out.println("Customer " + name + " consumed message: " + msg + ".");
				}
			}
			try
			{
				Thread.sleep(1000);
			}
			catch (InterruptedException e)
			{
				e.printStackTrace();
			}
		}
	}
}

生产者代码：

package com.coshaho.threadpool;

/**
 * 生产者，消息队列为空时，消费者会唤醒生产者生产消息
 * @author coshaho
 */
public class Producer implements Runnable
{
	String name;
	MessageQueue msgQueue;
	public Producer(String name, MessageQueue msgQueue)
	{
		this.name = name;
		this.msgQueue = msgQueue;
	}

	@Override
	public void run()
	{
		int i = 0;
		while(true)
		{
			synchronized(msgQueue)
			{
				try
				{
					// 释放msgQueue的锁，等待消费者唤醒
					msgQueue.wait();
				}
				catch (InterruptedException e)
				{
					e.printStackTrace();
				}
				// 唤醒后生产消息
				for(int j = 0; j < 5; j++)
				{
					msgQueue.produceMessage("message_" + i + "_" + j);
				}
			}
			System.out.println("Producer " + name + " produced 5 messages.");
		}
	}

}

消息处理进程代码：

package com.coshaho.threadpool;

/**
 * 消息处理中心
 * @author coshaho
 */
public class MessageProcessCenter
{
	public static void main(String[] args)
	{
		// 初始化消息队列
		MessageQueue msgQueue = new MessageQueue();
		// 运行1个生产者
		new Thread(new Producer("Producer", msgQueue)).start();

		// 运行3个消费者
		new Thread(new Customer("Customer1", msgQueue)).start();
		new Thread(new Customer("Customer2", msgQueue)).start();
		new Thread(new Customer("Customer3", msgQueue)).start();
	}
}

运行结果：

Producer Producer produced 5 messages.
Customer Customer2 consumed message: message_0_0.
Customer Customer3 consumed message: message_0_1.
Customer Customer2 consumed message: message_0_2.
Customer Customer1 consumed message: message_0_3.
Customer Customer3 consumed message: message_0_4.
Producer Producer produced 5 messages.
Customer Customer3 consumed message: message_0_0.
Customer Customer1 consumed message: message_0_1.
Customer Customer2 consumed message: message_0_2.
Customer Customer1 consumed message: message_0_3.
Customer Customer3 consumed message: message_0_4.
Producer Producer produced 5 messages.
Customer Customer3 consumed message: message_0_0.
Customer Customer1 consumed message: message_0_1.
Customer Customer2 consumed message: message_0_2.
Customer Customer3 consumed message: message_0_3.
Customer Customer1 consumed message: message_0_4.