Question

As the name suggests, we have a daemon framework which uses Executor service to schedule daemons.

java.util.concurrent.ScheduledThreadPoolExecutor.scheduleWithFixedDelay(Runnable 
     command, long initialDelay, long delay, TimeUnit unit)

At runtime, I want to change the delay between two runs of the Runnable class, without terminating our application.

Is it possible? If yes, how?

Answer 1

I don’t know the minimum granularity in advance

In that case you need to cancel the schedule and add it again.

private Future future = null;
private long periodMS = 0;

public void setPeriod(long periodMS) {
   if (future != null && this.periodMS == periodMS) return;
   if (future != null) future.cancel(false);
   scheduledExecutorService.scheduleWithFixedDelay(task, periodMS/2, periodMS, TimeUnit.MILLI_SECONDS);
}

or you can make the task reschedule itself.

private long periodMS;

public void start() {
  scheduledExecutorService.schedule(this, periodMS, TimeUnit.MILLI_SECONDS);
}

public void run() {
   try {
       task.run();
   } catch(Exception e) {
       // handle e
   }
   start();
}

This way the period can change every time it is run.