ScheduledExecutorService with variable delay

Question

Suppose I have a task that is pulling elements from a java.util.concurrent.BlockingQueue and processing them.

public void scheduleTask(int delay, TimeUnit ti         


        

Answer 1

Use schedule(Callable, long, TimeUnit) rather than scheduleAtFixedRate or scheduleWithFixedDelay. Then ensure that your Callable reschedules itself or a new Callable instance at some point in the future. For example:

// Create Callable instance to schedule.
Callable c = new Callable() {
  public Void call() {
   try { 
     // Do work.
   } finally {
     // Reschedule in new Callable, typically with a delay based on the result
     // of this Callable.  In this example the Callable is stateless so we
     // simply reschedule passing a reference to this.
     service.schedule(this, 5000L, TimeUnit.MILLISECONDS);
   }  
   return null;
  }
}

service.schedule(c);

This approach avoids the need to shut down and recreate the ScheduledExecutorService.