等待並通知Java中的死鎖情況

Question

1. 線程t1在wait()被命中後進入死鎖。即使 在t2中有notify()。代碼正陷入僵局。 沒有得到打印聲明 - 「等待釋放後::::」

2. 我可以看到兩個線程競爭獲取顯示器counterAdd()。所以，我假設通知會起作用。

   package com.java.thread.practice; 
   
       public class WaitAndNotify4 { 
   
        int counter = 0; 
   
        /* 
         CounterAdd() is to be accessed by both t1 and t2. 
         If not synchronized not giving consistent output. 
        */ 
        synchronized int counterAdd(){ 
         return counter++; 
        } 
   
        public static void main(String[] args) throws InterruptedException{ 
   
         // Creating method to call the threads. 
         WaitAndNotify4 andNotify4 = new WaitAndNotify4(); 
         andNotify4.testRaceCondition(); 
   
        } 
   
        private void testRaceCondition() throws InterruptedException { 
   
         // Thread t1 created and launched. 
   
         Thread t1 = new Thread(new Runnable(){ 
          @Override 
          public void run() { 
   
           for(int i=0; i<5; i++){ 
            synchronized(this){ 
            if(i== 1){ 
             System.out.println("Calling wait after count 1"); 
             try { 
             // Assuming that this wait will be resumed by notify in t2. 
   
              wait(); 
              System.out.println("After wait is released :::: "); 
             } catch (InterruptedException e) { 
              // TODO Auto-generated catch block 
              e.printStackTrace(); 
             } 
   
            } 
            } 
            counterAdd(); 
           } 
          } 
         }); 
   
   
         Thread t2 = new Thread(new Runnable(){ 
          @Override 
          public void run() { 
           // TODO Auto-generated method stub 
   
           for(int i=0; i<5; i++){ 
            if(i==2){ 
   
             synchronized(this){ 
              System.out.println("Before releasing the counter :::::"); 
              notify(); 
              System.out.println("After releasing the counter :::::"); 
             } 
   
            } 
            counterAdd(); 
           } 
   
          } 
         }); 
   
   
   
         t1.start(); 
         t2.start(); 
   
         t1.join(); 
         t2.join(); 
   
         System.out.println(" Sum value is found as ::::: "+counter); 
   
        } 
       } 
   

Answer 1

正在同步於不同的對象。在對象t1的第一種情況下，在t2的第二種情況下，在方法counterAdd的andNotify4中。爲了永久鎖定andNotify4，你需要做這樣的事情。

public class Main { 
    private int counter = 0; 

    synchronized int counterAdd() { 
     return counter++; 
    } 

    public static void main(String[] args) throws InterruptedException { 
     Main andNotify4 = new Main(); 
     andNotify4.testRaceCondition(); 
    } 

    private void testRaceCondition() throws InterruptedException { 
     Thread t1 = new Thread(new Runnable() { 
      @Override 
      public void run() { 
       for (int i = 0; i < 5; i++) { 
        synchronized (Main.this) { 
         if (i == 1) { 
          System.out.println("Calling wait after count 1"); 
          try { 
           Main.this.wait(); 
           System.out.println("After wait is released :::: "); 
          } catch (InterruptedException e) { 
           e.printStackTrace(); 
          } 
         } 
        } 
        counterAdd(); 
       } 
      } 
     }); 

     Thread t2 = new Thread(new Runnable() { 
      @Override 
      public void run() { 
       for (int i = 0; i < 5; i++) { 
        if (i == 2) { 
         synchronized (Main.this) { 
          System.out.println("Before releasing the counter :::::"); 
          Main.this.notify(); 
          System.out.println("After releasing the counter :::::"); 
         } 
        } 
        counterAdd(); 
       } 
      } 
     }); 

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

     t1.join(); 
     t2.join(); 

     System.out.println(" Sum value is found as ::::: " + counter); 
    } 
}