程序输出完成后返回命令行

Question

写了一个多线程程序，依次打印出奇偶数，直到序列达到30。

import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicInteger;

public class NumPrintTX
{
public static void main(String[] args)
{
    final int max = 31;
    final AtomicInteger i = new AtomicInteger(0);
    Executor dd = Executors.newFixedThreadPool(2);

    final Object lock = new Object();

    dd.execute(new Runnable()
    {
        @Override
        public void run()
        {
            while (i.get() < max)
            {
                if (i.get() % 2 == 0)
                {
                    System.out.print(" " + i.getAndAdd(1));

                    synchronized(lock)
                    {
                        lock.notify();
                    }
                }
                else
                {
                    synchronized(lock)
                    {
                        try
                        {
                            lock.wait();
                        }
                        catch (InterruptedException e)
                        {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                    }
                }
            }
        }
    });
    dd.execute(new Runnable()
    {
        @Override
        public void run()
        {
            while (i.get() < max)
            {
                if (i.get() % 2 != 0)
                {
                    System.out.print(" " + i.getAndAdd(1));

                    synchronized(lock)
                    {
                        lock.notify();
                    }
                }
                else
                {
                    synchronized(lock)
                    {
                        try
                        {
                            lock.wait();
                        }
                        catch (InterruptedException e)
                        {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                    }
                }
            }
        }
    });
    do
    {
        try 
        {
            Thread.currentThread().sleep(1000);
            }
        catch (InterruptedException e)
        {
            e.printStackTrace();
        }
    }
    while (i.get() != max);
}
}

当程序运行时，结果很好，但它不会转到下一行，所以我可以输入另一个命令来执行我接下来想做的任何事情。任何想法为什么会这样以及我可以做些什么来解决它？

修改代码： 导入 java.util.concurrent.Executor； 导入 java.util.concurrent.Executors； 导入 java.util.concurrent.atomic.AtomicInteger;

public class NumPrintTX
{
public static void main(String[] args)
{
    final int max = 31;
    final AtomicInteger i = new AtomicInteger(0);
    Executor dd = Executors.newFixedThreadPool(2);

    final Object lock = new Object();

    dd.execute(new Runnable()
    {
        @Override
        public void run()
        {
            while (i.get() < max)
            {
                if (i.get() % 2 == 0)
                {
                    System.out.print(" " + i.getAndAdd(1));

                    synchronized(lock)
                    {
                        lock.notify();
                    }
                }
                else
                {
                    synchronized(lock)
                    {
                        try
                        {
                            lock.wait();
                        }
                        catch (InterruptedException e)
                        {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                    }
                }
            }
        }
    });
    dd.execute(new Runnable()
    {
        @Override
        public void run()
        {
            while (i.get() < max)
            {
                if (i.get() % 2 != 0)
                {
                    System.out.print(" " + i.getAndAdd(1));

                    synchronized(lock)
                    {
                        lock.notify();
                    }
                }
                else
                {
                    synchronized(lock)
                    {
                        try
                        {
                            lock.wait();
                        }
                        catch (InterruptedException e)
                        {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                    }
                }
            }
        }
    });
    do
    {
        try 
        {
            Thread.currentThread().sleep(1000);
            }
        catch (InterruptedException e)
        {
            e.printStackTrace();
        }
    }
    while (i.get() != max);
}
public void close()
{
System.exit(0);
}
}

Answer 1

你没有停止你的线程池，所以它不会让你的主程序结束。

考虑以下代码：

import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.atomic.AtomicInteger;

class Worker implements Runnable {
    private AtomicInteger i;
    private Object lock;
    private int max;
    private int mod;

    Worker(AtomicInteger i_, Object lock_, int max_, int mod_){ 
        this.i   = i_;
        this.lock = lock_;
        this.max  = max_;
        this.mod  = mod_; 
    }

    @Override
    public void run(){
        while (i.get() < max)
        {
            if(i.get() % 2 == mod)
            {
                System.out.print(" " + i.getAndAdd(1));

                synchronized(lock){ lock.notify(); }
            }
            else
            {
                synchronized(lock)
                {
                    try { lock.wait(); }
                    catch (InterruptedException e) { e.printStackTrace(); }
                }
            }
        }
    }
}

public class NumPrintTX
{
   public static void main(String[] args)
    {
        final int max = 31;
        final AtomicInteger i = new AtomicInteger(0);
        ExecutorService dd = Executors.newFixedThreadPool(2);

        final Object lock = new Object();

        dd.execute(new Worker(i, lock, max, 0));
        dd.execute(new Worker(i, lock, max, 1));

        dd.shutdown();
    }    
}

如果没有dd.shutdown()，您的程序将在结束时挂起。

主 do-while 循环和System.exit(0) 可以工作，但似乎有点“蛮力”。

此外，此代码简化了您的线程代码，并使其更具可读性，而无需更改底层逻辑。

Answer 2

您需要通过调用System.exit(0); 来退出程序，其中0 是“正常”退出的退出状态代码。应该在打印出数字的循环完成后进行调用。

Java Docs for System.exit(int status)

Answer 3

您需要明确关闭您的程序。所以，是这样的：

public void close() {
    // Put any closing code here, like joining Threads or whatever
    System.exit(0); // 0 means it is a normal exit, i.e. there are no errors
}