java - 如何序列化正在同步的代码？

Question

这个问题已经有答案了:

Should you synchronize the run method? Why or why not? (6 个回答)

已关闭 7 年前。

我需要创建 2 个类，Class Player和Class Referee其中implement Runnable接口(interface)(基本上，创建线程)。

线程执行的顺序是

裁判玩家 1 或 2裁判玩家 1 或 2等等..

这是我想出的解决方案，但是，订单似乎没有发生。在裁判完成检查之前，选手们仍在继续比赛。

``

public class a {

      public static synchronized void main(String[] args) throws InterruptedException {

         ready = false;
         finish = false;

         ExecutorService executorService = Executors.newCachedThreadPool();

         executorService.execute(new Referee());
         executorService.execute(new Player(1));
         executorService.execute(new Player(2));

         Thread.sleep(1000);
         executorService.shutdown();
         executorService.awaitTermination(1, TimeUnit.MINUTES);
    }

   /*....FOLLOWED BY GETTER AND SETTER METHODS
   *
   *
   */

}

class Player implements Runnable{

    public synchronized void play() throws InterruptedException{

        //continue playing unless game is over
        while(true)
        {

                 while( (a.getReady()) != true){

                     wait();
                 }
              /***
              *
              *
              *
              execute some code to play
              **/

              //Change the value of the condition variable for the referee to start executing
                a.putReady(false);

        }
    }       



    @Override
    public void run() {

        try {
            play();
        } catch (InterruptedException ex) {
            Logger.getLogger(Player.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}

class Referee implements Runnable{

    public synchronized void check() throws InterruptedException {

            while(true)
            {
                /****INITIALIZING THE GAME***/

                while(a.getReady())
                    wait();


                 //If some player has won, releasing locks and exiting the threads                             
                   if(winner != 0)
                   {

                       a.putReady(true);
                       a.putFinish(true);
                       return;
                   }


                   //If the boards are full and ends in a draw
                   else if(count_plays >= 42)
                   {
                       System.out.print("\n Board is full. Its a draw!!\n");
                       a.putReady(true);
                       a.putFinish(true);
                       return;
                   }

                   //If there is more space on the board to play
                   else 
                   {
                       System.out.print("\nNo player has won, let the play resume!!\n");
                      //Thread.sleep((long)100);  
                   }


                   /* Code for checking if there has been a winner

                   *
                   *
                   */


                 a.putReady(true);
                 notify();
                }
            }

    @Override
    public void run(){
        try {
            check();
        } 
        catch (InterruptedException ex) {
            Logger.getLogger(Player.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}
`

我知道不同对象的线程无法同步，并且序列化同步下的代码是没有意义的。这是我被分配的任务。在上面的代码中，即使提供了一组条件变量，玩家也会同时进行比赛，并且不允许裁判线程在每次比赛时检查获胜者。

请给我一个使用同步方法、notify() 和 wait() 提供此类输出的代码概要。

Answer 1

这是允许的，但很少有意义，并且在您的情况下没有意义。两个线程将在不同的对象上同步，这不会产生任何影响。同步方法的目的是防止两个线程同时访问同一个对象。如果两个玩家需要访问某个公共(public)对象，但您不希望访问重叠，则应该在该对象上同步或同步该对象的方法之一。您应该只在同步块(synchronized block)或方法中停留尽可能短的时间。不必要的同步可能会导致性能不佳或死锁。

对我来说最有意义的是:

一个

public static class a {

    static boolean finish = false;

    public static void main(String[] args) throws InterruptedException {

        finish = false;

        ExecutorService executorService = Executors.newCachedThreadPool();

        executorService.execute(new Referee());
        executorService.execute(new Player(1));
        executorService.execute(new Player(2));

        // wait for user to press enter, just for testing
        new Scanner(System.in).nextLine();
        executorService.shutdown();
        executorService.awaitTermination(1, TimeUnit.MINUTES);
    }
}

玩家

public class Player implements Runnable {

    final int playernum;

    public Player(int playernum) {
        this.playernum = playernum;
    }

    @Override
    public void run() {
        try {
            while (!a.finish) {

                synchronized (a.class) {
                    for (int i = 0; i < 5; i++) {
                        Thread.sleep(1000);
                        System.out.println("player " + playernum + " does step " + i);
                    }
                }
                Thread.sleep(1000);
            }
        } catch (InterruptedException interruptedException) {
        }
    }
}

裁判

public class Referee implements Runnable {

    @Override
    public void run() {
        try {
            while (!a.finish) {
                synchronized (a.class) {
                    System.out.println("Check for winner.");
                }
                Thread.sleep(1000);
            }
        } catch (InterruptedException interruptedException) {
        }
    }
}

请注意，仅在内部 block 期间，它在整个运行期间不同步。

它应该产生这样的结果:

Check for winner.
player 1 does step 0
player 1 does step 1
player 1 does step 2
player 1 does step 3
player 1 does step 4
Check for winner.
player 2 does step 0
player 2 does step 1
player 2 does step 2
player 2 does step 3
player 2 does step 4

如果没有同步，您将无法看到每个玩家的全部 5 个步骤，而没有其他玩家的干预检查或步骤。