twitter/finagle

Hey all, I’m trying to have a background thread execute some task (task: => Future[A]) periodically. If it’s relevant,task calls some downstream under the hood and does some processing.

Initial approach was to do something like:

Future.sleep(initialDelay).flatMap { _ =>
  run()
}

…

def run() = task.onSuccess {
  Future.sleep(refreshInterval).map(_ => run())
}

This works fine for scheduling the futures properly (e.g, only when task is complete does the next one get scheduled), however it the task itself ends up running on the finagle netty threads rather than a background job. I tried to schedule the task execution on a FuturePool to try to get around that:

val pool: ExecutorServiceFuturePool = FuturePool.interruptible(
  Executors.newFixedThreadPool(5, new NamedPoolThreadFactory("BackgroundScheduler-ThreadPool", true))
)

pool { 
  logger.info(“Entered pool”)
  Future.sleep(initialDelay).flatMap { _ =>
    run()
  }
}

I noticed that altho “Entered pool” would run on the BackgroundScheduler-ThreadPool, we had thread switches once we entered a Future.sleep (to the Netty Timer thread) or any Future (to Netty finagle) in the task. I’m wondering if there’s any way to have these Futures run in the thread pool we ask for, rather than switching back on the Netty threads. I read in a few places (possibly old?) that this kind of thread scheduling is only possible at a global level, so we’d have to swap out the LocalScheduler with something else — but wanted to confirm. Thanks!