IllegalMonitorStateException當共享對象

Question

我想創建單個變量生產者消費者解決方案，但我在Producer的notifyAll（）方法中獲取IllegalMonitorStateException。 我正在獲取同步塊中的鎖，可能出現了什麼問題？

/** 
* 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

這就是問題所在：

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

明白，你不上變量同步是很重要的 - 你的對象上同步。因此，您將x的值修改爲指向一個不同的Integer對象，然後您將對該不同對象調用notifyAll ...來自不擁有該對象的顯示器的線程。

我強烈建議您不要使用Integer對象進行同步。理想情況下，使用不用於其他目的的任何對象 - 這使得更易於推理。

你仍然可以擁有你的x變量，並且記錄它不應該被修改，除非線程持有合適的鎖 - 但是使它獨立於鎖本身。