关于死锁

Question

老师你好，我在敲代码的时候发现static 修饰的Object o1= new Object();这样修饰的锁才能出现死锁，如果o1,o2去掉static之后 就没办法出现死锁了，想知道这是为什么

Answer 1

悟空 2021-10-31 22:28:44

去掉static的话，大家用的就不是同一个锁对象了，所以不会死锁

• 提问者 歌颂者T #1

  DeadLock deadLock = new DeadLock(0);
          Thread threadA = new Thread(deadLock);
          deadLock.flag = 1;
          Thread threadB = new Thread(deadLock);
          threadA.start();
          threadB.start();
  
  老师你好 我是这样创建的 并没有创建两个实例，因为我知道加了static之后，o1 o2属于类不属于实列对象的，是因为发生了指令重排导致的吗？因为在deadLock.flag = 1；这句代码好像被优化了

• 悟空 回复 提问者 歌颂者T #2

  麻烦你把所有代码都贴一下，我看一下

• 提问者 歌颂者T 回复 悟空 #3

  public class DeadLock implements Runnable {
      Object o1 = new Object();
      Object o2 = new Object();
      int flag = 0;
  
      public DeadLock(int flag) {
          this.flag = flag;
      }
  
      public static void main(String[] args) {
          DeadLock deadLock = new DeadLock(0);
          deadLock.flag = 0;
          Thread threadA = new Thread(deadLock);
          deadLock.flag = 1;
          Thread threadB = new Thread(deadLock);
          threadA.start();
          threadB.start();
      }
  
      @Override
      public void run() {
          System.out.println(flag);
          if (flag == 0) {
              synchronized (o1) {
                  System.out.println("I have got O1,then I will get o2");
                  synchronized (o2) {
                      System.out.println("i have get o2");
                  }
              }
          }
          if (flag == 1) {
              synchronized (o2) {
                  System.out.println("I have got O2,then I will get o1");
                  synchronized (o1) {
                      System.out.println("i have get o1");
                  }
              }
          }
  
      }
  }

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