Future with Timeout in Scala

Question

Suppose I have a function, which invokes a blocking interruptible operation. I would like to run it asynchronously with a timeout. That is, I would like to interrupt the function when the timeout is expired.

So I am trying to do something like that:

 import scala.util.Try import scala.concurrent.Future  def launch(f: () => Unit, timeout: Int): Future[Try[Unit]] = {    val aref = new java.util.concurrent.atomic.AtomicReference[Thread]()     import ExecutionContext.Implicits.global   Future {Thread.sleep(timeout); aref.get().interrupt} // 1   Future {aref.set(Thread.currentThread); Try(f())}    // 2 } 

The problem is that aref in (1) can be null because (2) has not set it to the current thread yet. In this case I would like to wait until aref is set. What is the best way to do that ?

Answer 1

You can go for a slightly easier approach using Await. The Await.result method takes timeout duration as a second parameter and throws a TimeoutException on timeout.

try {   import scala.concurrent.duration._   Await.result(aref, 10 seconds); } catch {     case e: TimeoutException => // whatever you want to do. } 

Answer 2

I needed the same behavior as well, so this is how I solved it. I basically created an object that creates a timer and fails the promise with a TimeoutException if the future hasn't completed in the specified duration.

package mypackage  import scala.concurrent.{Promise, Future} import scala.concurrent.duration.FiniteDuration import akka.actor.ActorSystem import scala.concurrent.ExecutionContext.Implicits.global  object TimeoutFuture {    val actorSystem = ActorSystem("myActorSystem")   def apply[A](timeout: FiniteDuration)(block: => A): Future[A] = {     val promise = Promise[A]()     actorSystem.scheduler.scheduleOnce(timeout) {       promise tryFailure new java.util.concurrent.TimeoutException     }      Future {       try {         promise success block       }       catch {         case e:Throwable => promise failure e       }      }      promise.future   } }