java - 可限时运行

Question

尝试构造一个必须在给定时间限制内结束的Runnable。

目前我正在使用 java.util.Timer 来中断 Runnable 线程。

Timer 在 Runnable 启动后立即启动。

import java.util.Timer;
import java.util.TimerTask;

public class test {
    Thread task;
    Timer  timer;

    public void start(){

        task = new Thread(new worker());
        timer = new Timer("timer",true);

        task.start();
        timer.schedule(new Terminator(),1000*2);
    }


    class worker implements Runnable{
        @Override
        public void run() {

            for (int i = 0 ; i < 2; i++){
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    System.out.println("Test Interrupted !!");
                    return;
                }
            }

            System.out.println("Test Finished !!");
            timer.cancel();
        }
    }

    class Terminator extends TimerTask{
        @Override
        public void run() {
            task.interrupt();
            System.out.println("Test Terminated !!");
        }
    }
}

但我怀疑这会导致 Timer 和 Runnable 线程之间出现竞争条件:Runnable 即将完成，Timer 也在触发。

这会导致同时打印Finished !! 和Terminated !! 吗？如果是，如何避免？

更新:

它发生了:

11-09 21:14:40.741: INFO/System.out(31442): Test Finished !! 18
11-09 21:14:40.751: INFO/System.out(31442): Test Terminated !! 18
11-09 21:14:40.751: INFO/System.out(31442): Test Finished !! 19
11-09 21:14:40.751: INFO/System.out(31442): Test Terminated !! 19

Answer 1

Can this ever result in both Finished !! and Terminated !! being printed ?

是的。当打印“完成”消息时，计时器可能会在取消之前触发。

System.out.println("Finished !!");
// The timer can fire here.
timer.cancel(); 

如果发生这种情况，两条消息都将被打印出来。

---

要避免此问题，您可以使用同步。

synchronized (someObject) {
    if (!finished) {
        finished = true;
        System.out.println("Finished !!");
        timer.cancel(); 
    }
}

在终结符中:

synchronized (someObject) {
    if (!finished) {
        finished = true;
        task.interrupt();
        System.out.println("Test Terminated !!");
    }
}

这会阻止打印这两条消息。