ScheduledExecutorService with variable delay

java concurrency executorservice blockingqueue
parkr picture parkr · Oct 5, 2009 · Viewed 15.7k times · Source

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

public void scheduleTask(int delay, TimeUnit timeUnit)
{
    scheduledExecutorService.scheduleWithFixedDelay(new Task(queue), 0, delay, timeUnit);
}

How can I schedule / reschedule the task if the frequency can be changed dynamically?

  • The idea is to take a stream of data updates and propagate them in batch to a GUI
  • The user should be able to vary the frequency of updates

Answer

Adamski picture Adamski · Oct 5, 2009

Use schedule(Callable<V>, 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<Void> c = new Callable<Void>() {
  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.

Related questions

producer/consumer work queues

I'm wrestling with the best way to implement my processing pipeline. My producers feed work to a BlockingQueue. On the consumer side, I poll the queue, wrap what I get in a Runnable task, and submit it to an ExecutorService. …

Read More
Is adding tasks to BlockingQueue of ThreadPoolExecutor advisable?

The JavaDoc for ThreadPoolExecutor is unclear on whether it is acceptable to add tasks directly to the BlockingQueue backing the executor. The docs say calling executor.getQueue() is "intended primarily for debugging and monitoring". I'm constructing a ThreadPoolExecutor with my …

Read More
How to wait for all threads to finish, using ExecutorService?

I need to execute some amount of tasks 4 at a time, something like this: ExecutorService taskExecutor = Executors.newFixedThreadPool(4); while(...) { taskExecutor.execute(new MyTask()); } //...wait for completion somehow How can I get notified once all of them are complete? For now …

Read More