IllegalMonitorStateException当共享对象

Question

我想创建单个变量生产者消费者解决方案，但我在Producer的notifyAll（）方法中获取IllegalMonitorStateException。 我正在获取同步块中的锁，可能出现了什么问题？

/** 
* Write a description of class SingleProducerConsumer here. 
* 
* @author (your name) 
* @version (a version number or a date) 
*/ 
public class SingleProdCons 
{ 

    public static void main(String args[]) 
    { 
     Integer x = 0; 
     Thread producer = new Thread(new Producer(x),"Producer"); 
     Thread consumer = new Thread(new Consumer(x),"Consumer"); 
     producer.start(); 
     consumer.start(); 
    }  
} 

    class Producer implements Runnable 
    { 
     private Integer x; 

     Producer(Integer x) 
     { 
      this.x = x; 
     } 

     @Override 
     public void run() 
     { 
      synchronized(x) 
      { 
      while(x.equals(0)==false){ 

       //The value of the variable has not been consumed yet , we should wait here till it gets consumed 
       try{ 
       x.wait(); 
       }catch(InterruptedException ie) 
       { 
        System.out.println("Caught Exception : "+ie.getMessage()); 
       } 

      } 

      //Else initialze the variable and let it get used by the Consumer then 
      synchronized(x) 
      { 
       x=10; 
       x.notifyAll(); 

      } 
     } 

     } 

    } 

    class Consumer implements Runnable 
    { 
     private Integer x; 

     Consumer(Integer x) 
     { 
      this.x = x; 
     } 

     @Override 
     public void run() 
     { 
      synchronized(x) 
      { 
      while(x.equals(0)==true) 
      { 
       //The value has not been put by the Producer thread yet hence we should wait here 
       System.out.println("We are before the method call of the wait on the x object"); 
       try{ 
       x.wait(); 
       }catch(InterruptedException ie) 
       { 
        System.out.println("Caught the exception : "+ie.getMessage()); 
       } 
      } 
      } 

      synchronized(x) 
      { 
       System.out.println("Consuming : "+x); 
       x.notifyAll(); 
      } 

     } 

    } 

Exception in thread "Producer" java.lang.IllegalMonitorStateException 
    at java.lang.Object.notifyAll(Native Method) 
    at Producer.run(SingleProdCons.java:55) 
    at java.lang.Thread.run(Thread.java:745) 
Exception in thread "Producer" java.lang.IllegalMonitorStateException 
    at java.lang.Object.notifyAll(Native Method) 
    at Producer.run(SingleProdCons.java:55) 
    at java.lang.Thread.run(Thread.java:745) 
Exception in thread "Producer" java.lang.IllegalMonitorStateException 
    at java.lang.Object.notifyAll(Native Method) 
    at Producer.run(SingleProdCons.java:55) 
    at java.lang.Thread.run(Thread.java:745) 
Exception in thread "Producer" java.lang.IllegalMonitorStateException 
    at java.lang.Object.notifyAll(Native Method) 
    at Producer.run(SingleProdCons.java:55) 
    at java.lang.Thread.run(Thread.java:745) 

Answer 1

这就是问题所在：

synchronized(x) 
{ 
    x=10; 
    x.notifyAll(); 
} 

明白，你不上变量同步是很重要的 - 你的对象上同步。因此，您将x的值修改为指向一个不同的Integer对象，然后您将对该不同对象调用notifyAll ...来自不拥有该对象的显示器的线程。

我强烈建议您不要使用Integer对象进行同步。理想情况下，使用不用于其他目的的任何对象 - 这使得更易于推理。

你仍然可以拥有你的x变量，并且记录它不应该被修改，除非线程持有合适的锁 - 但是使它独立于锁本身。