一个简答的生产者-消费者多线程模型

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生产者消费者模型

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同一段代码，分别设置produce和consumer的频率(通过sleep的长短控制)。

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第一种情况produce后，sleep(500),consumer后，sleep(100),也就是取消息快，生产消息慢。这种情况正常。代码如下

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packagetest;
 
importjava.util.Vector;
 
publicclass Producer extendsThread
{
    staticfinal int MAXQUEUE =5;
    privateVector messages =newVector();
  
    @Override
    publicvoid run()
    {
        try
        {
            while(true)
            {
                putMessage();//
                sleep(500);
            }
        }catch(InterruptedException e)
        {
        }
    }
  
    publicsynchronized void putMessage()throwsInterruptedException
    {
        while(messages.size()== MAXQUEUE)
        {
            System.out.println("messages full,wait......");
            wait();
        }
        String element = newjava.util.Date().toString();
        messages.addElement(element);
        System.out.println("put message: "+element+";size:"+messages.size());
        notify();//Later, when the necessary event happens, the thread that is running it calls notify() from a block synchronized on the same object.
    }
  
        // Called by Consumer 
    publicsynchronized String getMessage() throwsInterruptedException
    {
       String message = null;
       while(messages.size()==0)
        {
           System.out.println("messages empty,wait......");
           wait();
        }
        //By executing wait() from a synchronized block, a thread gives up its hold on the lock and goes to sleep.}
        message =(String) messages.firstElement();
        messages.removeElement(message);
        System.out.println("get message: "+message+";size:"+messages.size());
        returnmessage;
      }
     
    publicstatic void main(String args[])
    {
        Producer producer =newProducer();
        producer.start();
        newConsumer (producer).start(); 
    }
  
}
classConsumer  extendsThread
{
    Producer producer;
    Consumer (Producer p)
    {
        producer = p;
    }
  
    @Override
    publicvoid run()
    {
        try
        {
            while(true)
            {
                String message = producer.getMessage();
                //System.out.println("get message: "+ message);
                sleep(100);
            }
        }catch(InterruptedException e)
        {
            e.printStackTrace();
        }
    }
}

运行结果：

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put message: Wed Feb 1714:24:19CST 2016;size:1
get message: Wed Feb 1714:24:19CST 2016;size:0
messages empty,wait......
put message: Wed Feb 1714:24:19CST 2016;size:1
get message: Wed Feb 1714:24:19CST 2016;size:0
messages empty,wait......
put message: Wed Feb 1714:24:20CST 2016;size:1
get message: Wed Feb 1714:24:20CST 2016;size:0
messages empty,wait......
put message: Wed Feb 1714:24:20CST 2016;size:1
get message: Wed Feb 1714:24:20CST 2016;size:0
messages empty,wait......
put message: Wed Feb 1714:24:21CST 2016;size:1
get message: Wed Feb 1714:24:21CST 2016;size:0
messages empty,wait......
put message: Wed Feb 1714:24:21CST 2016;size:1
get message: Wed Feb 1714:24:21CST 2016;size:0
messages empty,wait......
put message: Wed Feb 1714:24:22CST 2016;size:1
get message: Wed Feb 1714:24:22CST 2016;size:0
messages empty,wait......
put message: Wed Feb 1714:24:22CST 2016;size:1
get message: Wed Feb 1714:24:22CST 2016;size:0
messages empty,wait......
put message: Wed Feb 1714:24:23CST 2016;size:1
get message: Wed Feb 1714:24:23CST 2016;size:0
messages empty,wait......
put message: Wed Feb 1714:24:23CST 2016;size:1
get message: Wed Feb 1714:24:23CST 2016;size:0
messages empty,wait......
put message: Wed Feb 1714:24:24CST 2016;size:1
get message: Wed Feb 1714:24:24CST 2016;size:0
messages empty,wait......
put message: Wed Feb 1714:24:24CST 2016;size:1
get message: Wed Feb 1714:24:24CST 2016;size:0
messages empty,wait......

2、第二种情况，把两个sleep的时间调换下，也就是produce后，sleep(100),consumer后，sleep(500),也就是取消息慢，生产消息快。这种情况就出现了问题，如果队列满了，produce线程等待，consumer线程取完消息就hang住了，线程全部挂住了。运行结果如下：

put message: Wed Feb 17 14:27:00 CST 2016;size:1
get message: Wed Feb 17 14:27:00 CST 2016;size:0
put message: Wed Feb 17 14:27:00 CST 2016;size:1
put message: Wed Feb 17 14:27:00 CST 2016;size:2
put message: Wed Feb 17 14:27:00 CST 2016;size:3
put message: Wed Feb 17 14:27:00 CST 2016;size:4
get message: Wed Feb 17 14:27:00 CST 2016;size:3
put message: Wed Feb 17 14:27:01 CST 2016;size:4
put message: Wed Feb 17 14:27:01 CST 2016;size:5
messages full,wait......
get message: Wed Feb 17 14:27:00 CST 2016;size:4
get message: Wed Feb 17 14:27:00 CST 2016;size:3
get message: Wed Feb 17 14:27:00 CST 2016;size:2
get message: Wed Feb 17 14:27:01 CST 2016;size:1
get message: Wed Feb 17 14:27:01 CST 2016;size:0
messages empty,wait......
运行到这里就结束了，后面没有输出了

分析后，感觉应该和wait、notify有关系。

第二种情况下，生产消息快，队列慢了后就wait(),consumer线程取消息，直到队列空了之后，consumer线程只有一个wait(),并没有类似于notify的机制去通知produce线程，导致一直挂起；

而第一种情况下，取消息快，放消息慢，不存在队列满，队列只会空。队列空了后，consumer线程就wait()，等produce线程放入消息后，就会notify

还没想到解决办法，有哪个大神看出问题来就给个解答吧。

问题解决了，getMessage()函数改为如下：

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publicsynchronized String getMessage() throwsInterruptedException
   {
      String message = null;
      while(messages.size()==0)
       {
          System.out.println("messages empty,wait......");
          notify();
          returnnull;
       }
       //By executing wait() from a synchronized block, a thread gives up its hold on the lock and goes to sleep.}
       message =(String) messages.firstElement();
       messages.removeElement(message);
       System.out.println("get message: "+message+";size:"+messages.size());
       returnmessage;
     }

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