ExecutorService 机制问题记录

最新推荐文章于 2024-08-23 21:00:00 发布

cw_hstx

最新推荐文章于 2024-08-23 21:00:00 发布

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分类专栏： java

本文链接：https://blog.youkuaiyun.com/cw_hstx/article/details/87997843

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本文记录了在使用ExecutorService时遇到的一个关于任务执行顺序的异常现象。通过两个不同的运行示例，展示了任务执行顺序的不同，尤其是join方法的影响。目前作者尚未深入研究源码找出原因，但计划后续进行分析，以此作为问题记录。

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写了一个关于 join 的小程序，发现了一个问题如下

package concurrent;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class Joining2
{
    public static void main(String[] args)
    {
        //ExecutorService exec = Executors.newCachedThreadPool();
        Thread t2 = new Thread(new MusicPlay2());
        Thread t1 = new Thread(new MusicPlay1(t2));
        //exec.execute(t1);
        //exec.execute(t2);
        //exec.shutdown();
        t1.start();
        t2.start();
    }
}

class MusicPlay1 implements Runnable
{
    private int countDown = 10;
    private Thread thread;
    public MusicPlay1(Thread thread)
    {
        this.thread = thread;
    }
    @Override
    public void run()
    {
        while(true)
        {
            try
            {
                //TimeUnit.MICROSECONDS.sleep(1000);
                System.out.println(--countDown);
                if(countDown == 5)
                {
                    thread.join();
                }
                if(countDown == 0)
                {
                    return;
                }
            } catch (InterruptedException e)
            {
                e.printStackTrace();
            }
        }
    }
}

class MusicPlay2 implements Runnable
{

    @Override
    public void run()
    {

        try
        {
            TimeUnit.MICROSECONDS.sleep(2000);
            for (int i = 15; i < 20; i++)
            {
                System.out.println(i);
            }
        } catch (InterruptedException e)
        {
            e.printStackTrace();
        }

    }
}

运行结果：
9
8
7
6
5
15
16
17
18
19
4
3
2
1
0

如果使用 ExecutorService 运行如下：

package concurrent;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class Joining2
{
    public static void main(String[] args)
    {
        ExecutorService exec = Executors.newCachedThreadPool();
        Thread t2 = new Thread(new MusicPlay2());
        Thread t1 = new Thread(new MusicPlay1(t2));
        exec.execute(t1);
        exec.execute(t2);
        exec.shutdown();
        //t1.start();
        //t2.start();
    }
}

class MusicPlay1 implements Runnable
{
    private int countDown = 10;
    private Thread thread;
    public MusicPlay1(Thread thread)
    {
        this.thread = thread;
    }
    @Override
    public void run()
    {
        while(true)
        {
            try
            {
                //TimeUnit.MICROSECONDS.sleep(1000);
                System.out.println(--countDown);
                if(countDown == 5)
                {
                    thread.join();
                }
                if(countDown == 0)
                {
                    return;
                }
            } catch (InterruptedException e)
            {
                e.printStackTrace();
            }
        }
    }
}

class MusicPlay2 implements Runnable
{

    @Override
    public void run()
    {

        try
        {
            TimeUnit.MICROSECONDS.sleep(2000);
            for (int i = 15; i < 20; i++)
            {
                System.out.println(i);
            }
        } catch (InterruptedException e)
        {
            e.printStackTrace();
        }

    }
}

运行结果：

9
8
7
6
5
4
3
2
1
0
15
16
17
18
19

目前还不知道原因，以后看看源码。就此记录