如何在变化的时间后执行任务

Question

Class A 
{
 long x;
 method1()
  {
   x = current time in millisecs;
  }
 task()//want to run this after (x+30) time
}

I need to run task() after (x+30) . x could be varying. if method1 is called, then task is scheduled to run after 30 from current time, but within that 30 timeperiod if method1 is called again then i want to cancel the previous task call and want to schedule a new call to task after 30 sec from current time. How should i create a scheduler or task of this type?

Went through the scheduledthreadpoolexecutor API but didn't find a scheduler of this type.

Answer 1

You're asking 2 questions:

1. How can I schedule a task with an arbitrary delay?

You can use one of the schedule methods on a java.util.concurrent.ScheduledThreadPoolExecutor

int delay = System.currentTimeMillis + 30;
myScheduledExecutor.schedule(myTask, delay, TimeUnit.MILLISECONDS);

2. How can I cancel an already running task?

You cancel a task by calling cancel on the Future that is returned from the schedule method you called.

if (!future.isDone()){
    future.cancel(true);
}
future = myScheduledExecutor.schedule(myTask, delay, TimeUnit.MILLISECONDS);

Answer 2

I would record the time method1 is called and I would check every second whether the method was called 30 seconds ago. This way it will only perform the task when there has been no call for 30 seconds.

Answer 3

Use java.util.Timer and pass a callback into the TimerTask to schedule the next run. TimerTask can be cancelled with cancel method if needed. eg

package test;

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

public class TimerTaskDemo {
    private Timer timer = new Timer();
    private MyTimerTask nextTask = null;

    private interface Callback {
        public void scheduleNext(long delay);
    }

    Callback callback = new Callback() {
        @Override
        public void scheduleNext(long delay) {
            nextTask = new MyTimerTask(this);
            timer.schedule(nextTask, delay);
        }
    };

    public static class MyTimerTask extends TimerTask {
        Callback callback;

        public MyTimerTask(Callback callback) {
            this.callback = callback;
        }

        @Override
        public void run() {
            // You task code
            int delay = 1000;
            callback.scheduleNext(delay);
        };
    }

    public void start() {
        nextTask = new MyTimerTask(callback);
        timer.schedule(nextTask, 1000);
    }

    public static void main(String[] args) {
        new TimerTaskDemo().start();
    }
}

Answer 4

Why don't you model your requirement using the Timer class of the JDK. Based on your requirements you will be scheduling the task in the timer as required.

Answer 5

I think the easiest way to do what you need is the following. Class B is the calling class.

class A {

    public void runAfterDelay(long timeToWait) throws InterruptedException {
        Thread.sleep(timeToWait);

        task();
    }
}

class B {
    public static void main(String[] args) throws InterruptedException {
        A a = new A();
        // run after 30 seconds
        a.runAfterDelay(30000);
    }
}

Answer 6

Class A 
{
 $x;
 function method1()
  {
   $time = microtime(true);
  }
 sleep($time + 30);
 task()//want to run this after (x+30) time
}