了解synchronized关键字的工作原理

Question

在下面的代码中,我只希望两个线程中的一个进入该halt()函数,然后暂停程序.但似乎两个线程都进入了synchronizedhalt()函数.为什么会发生这种情况？

package practice;

class NewThread implements Runnable {
  String name; // name of thread
  Thread t;
  boolean suspendFlag;

  NewThread(String threadname) {
    name = threadname;
    t = new Thread(this, name);
    System.out.println("New thread: " + t);
    suspendFlag = false;
    t.start(); // Start the thread
  }

  // This is the entry point for thread.
  public void run() {
    try {
      for(int i = 15; i > 0; i--) {
        System.out.println(name + ": " + i);
        Thread.sleep(200);
        Runtime r = Runtime.getRuntime();
        halt();
      }
    } catch (InterruptedException e) {
      System.out.println(name + " interrupted.");
    }
    System.out.println(name + " exiting.");
  }

  synchronized void halt() throws InterruptedException
  {
      System.out.println(name + " entered synchronized halt");
      Runtime r = Runtime.getRuntime();
      Thread.sleep(1000);
      r.halt(9);
      System.out.println(name + " exiting synchronized halt"); // This should never execute
  }
}

class Practice{
  public static void main(String args[]) {
    NewThread ob1 = new NewThread("One");
    NewThread ob2 = new NewThread("Two");

    // wait for threads to finish
    try {
      System.out.println("Waiting for threads to finish.");
      ob1.t.join();
      ob2.t.join();
    } catch (InterruptedException e) {
      System.out.println("Main thread Interrupted");
    }

    System.out.println("Main thread exiting."); // This should never execute
  }
}

Answer 1

synchronized不锁定方法,它锁定一个对象.

你有一个方法,但有两个对象.每个线程都锁定自己的对象并调用halt().