java - 这段代码出现线程死锁了吗？如果有是什么原因？

问题描述

问 题

Film.java

package FilmTest;

public class Film {
    private String name;
    private boolean flag = true;

      public synchronized void play(String name) {
          if(!flag){
              try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
          }
          try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
          System.out.println("producer-1"+name);
          this.name = name;
         // System.out.println(name);
          this.notify();
          this.flag = false;
      }
      
      public synchronized void watch() {
          if(flag){
              try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
          }
          try {
            Thread.sleep(200);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
          
          System.out.println("watcher-2"+name);
         this.notify();
          this.flag = true;
      }
      }
      

Player.java

package FilmTest;

public class Player implements Runnable {
    private Film film;
    public Player(Film film) {
        // TODO Auto-generated constructor stub
     this.film = film;
    }
    @Override
    public void run() {
        // TODO Auto-generated method stub
        for(int i=0;i<20;i++){
            if(0==i%2){
                film.play("film-1-"+i);
            }else{
                film.play("film-2-"+i);
            }
            
        }
    }
}

Watcher.java

package FilmTest;

public class Watcher implements Runnable {
    private Film film;
    public Watcher(Film film) {
        super();
        this.film = film;
    }
    @Override
    public void run() {
        film.watch();
    }

}

MainTest.java

package FilmTest;

public class MainTest {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Film film = new Film();
        Player player = new Player(film);
        Watcher watcher = new Watcher(film);
        new Thread(player).start();
        new Thread(watcher).start();
    }

}

执行结果如下， 出现下面内容代码还是运行状态

producer-1film-1-0
watcher-2film-1-0
producer-1film-2-1

感觉出现了死锁 ，但不知道问题出在哪里，求指教

解决方案

这不是死锁啊，是你的代码有问题。
你打印了producer-1film-2-1之后，flag = false，那么在你下次执行play方法的时候会执行this.wait()，并且之后它不会被唤醒，一直处于wait状态。所以之后没有任何打印信息输出。

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