如何在Java中找到第一个成功完成的线程的结果？

Question

public class WorkerThread implements Runnable {
    @Override
    public void run() {
        // some long task here, returns int value
    }
}

public class Main {
    public static void main(String[] args){
         // initialize multiple worker threads here
         // then get result from the thread that completes first
    }
}

我查看了文档并找到了invokeAny ExecutorService，但这将返回任何已成功完成的线程的结果，而不一定是第一个线程。

Answer 1

您还可以使用CountDownLatch和ExecutorService来实现这一点。

创建count=1的CountDownLatch对象。

CountDownLatch latch = new CountDownLatch(1);

使用ExecutorService池执行线程并在所有线程中传递锁存器。

workerThreadPool.execute(new WorkerThread(latch));

latch.await();

latch.countDown();

workerThreadPool.shutdownNow();

import static java.lang.Thread.sleep;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

class WorkerThread implements Runnable
{

    CountDownLatch _latch;

    public WorkerThread(CountDownLatch latch)
    {
        _latch = latch;
    }

    @Override
    public void run()
    {
        try
        {
            // some long task here, returns int value
            System.out.println("In thread1 " + this.toString());
            sleep(5000);
        }
        catch (InterruptedException ex)
        {
            System.out.println("thread1 interupted");
        }
        finally
        {

            System.out.println("Finished1 " + this.toString());
            _latch.countDown();
        }
    }
}

class WorkerThread2 implements Runnable
{

    CountDownLatch _latch;

    public WorkerThread2(CountDownLatch latch)
    {
        _latch = latch;
    }

    @Override
    public void run()
    {
        try
        {
            // some long task here, returns int value
            System.out.println("In thread2 " + this.toString());
            sleep(10000);
        }
        catch (InterruptedException ex)
        {
            System.out.println("thread2 interupted");
        }
        finally
        {

            System.out.println("Finished2 " + this.toString());
            _latch.countDown();
        }
    }
}

public class Main
{

    public static void main(String[] args) throws InterruptedException
    {
        ExecutorService workerThreadPool = Executors.newFixedThreadPool(2);

        CountDownLatch latch = new CountDownLatch(1);

        workerThreadPool.execute(new WorkerThread(latch));
        workerThreadPool.execute(new WorkerThread2(latch));

        latch.await();

        workerThreadPool.shutdownNow();
    }
}