Executor 执行两次

Question

我正在尝试同时运行 2 个线程以实现多线程，并且我的程序正在运行，但我怀疑为什么我的程序打印到标准输出两次。

这是我的代码库：

public class SimpleExec {
    public static void main(String[] args) {
        CountDownLatch countDownLatch = new CountDownLatch(5);
        CountDownLatch countDownLatch6 = new CountDownLatch(5);
        ExecutorService executorService = Executors.newFixedThreadPool(1);
        System.out.println("start" + LocalDateTime.now());
        executorService.execute(new MyThread("first ", countDownLatch));
        executorService.execute(new MyThread("Second", countDownLatch6));

        try {
            countDownLatch.await();
            countDownLatch6.await();
        } catch (InterruptedException e) {
            System.out.println(e);
        }
        System.out.println("end" + LocalDateTime.now());
        executorService.shutdown();

    }
}

class MyThread implements Runnable {
    String name;
    CountDownLatch cdl;

    public MyThread(String name, CountDownLatch cdl) {
        this.cdl = cdl;
        this.name = name;
        new Thread(this).start();
    }

    public void run() {
        for (int i = 0; i < 5; i++) {
            System.out.println(name + " " + i);
            cdl.countDown();
        }
    }
}

这是程序输出的示例：

start 2018-08-18T08:41:51.867
first  0 // first time thread labeled 'first' prints 0 through 4
first  1
first  2
first  3
first  4
Second 0
Second 1
Second 2
first  0   // second time thread labeled 'first' prints 0 through 4 - why does it print again here?
first  1
Second 3
first  2
Second 4
first  3
first  4
end2018-08-18T08:41:51.870
Second 0
Second 1
Second 2
Second 3
Second 4

Answer 1

因为您为构造函数中的每个 Runnables 启动了第二个线程 new Thread(this).start();

Runnables 是用 ExecutorService 启动的，不需要额外的Thread.start()删除它。