Schedule a job to run at multiple of 2 seconds i.e 2,4,8,16,32 seconds

Question

I want to Schedule a job to run at multiple of 2 seconds, which is 2,4,8,16,32 seconds. Second fire should happen after two seconds of completion of first fire, Third fire should happen after 4 seconds of completion of second fire and so on. The next fire is based on status we get from previous fire, based on which it will be decided whether we need to trigger next fire or not. Can somebody tell me how can I use quartz scheduler to achieve this?

If I use SimpleTrigger.withIntervalInSeconds(2) it runs a job after every 2 seconds where as I want time interval should be increased with multiple of 2 in every firing.

Answer 1

Perhaps you could forget trying to set up a single trigger, but use multiple triggers. My Java is not good in this area, so this is in pseudocode:

delay = 2
repeat
 TriggerOnceAfter(delay)
 delay <- delay * 2
 WaitUntilTriggered()
until (finished)

I am not sure how to implement the WaitUntilTriggered() method; you my need to add a signalling flag to the triggered code for WaitUntilTriggered() to look at.

That will give delays of 2, 4, 8, ...

Answer 2

This is a simplified implementation that will invoke a Runnable at the requested schedule:

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

public class Tasker {

    private int numberOfRuns; //how many times job executed 
    private int timeBetweenRuns;//seconds

    Tasker(int numberOfRuns){

        this.numberOfRuns = numberOfRuns;
        timeBetweenRuns = 2;
        execute();
    }


    private void execute() {

        for (int counter = 0; counter < numberOfRuns ; counter++) {
            CountDownLatch latch = new CountDownLatch(1);
            Job job = new Job(latch, timeBetweenRuns);
            job.run();

            try {
                latch.await();
                TimeUnit.SECONDS.sleep(timeBetweenRuns);
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
            timeBetweenRuns *=2;
        }
    }

    public static void main(String[] args){

        new Tasker(5);
    }
}

class Job implements Runnable {

    private int seconds;
    private CountDownLatch latch ;

    Job(CountDownLatch latch , int seconds){
        this.latch = latch;
        this.seconds = seconds;
    }

    @Override
    public void run() {

        System.out.println("Job runs "+ seconds +" after previous one");
        latch.countDown();
    }
}