Question

In Scala 2.10, along with the new Future/Promise API, they introduced a Duration and Deadline utilities (as described here). I looked around but couldn’t find anything that comes with the scala standard library, to do something like:

val deadline = 5 seconds fromNow
After(deadline){
  //do stuff
}

//or

val deadlineFuture: Future[Nothing] = (5 seconds fromNow).asFuture
deadlineFuture onComplete {
  //do stuff
}

Is there anything like that available that I’ve missed, or will I have to implement this kind of behavior myself?

Answer 1

Not quite built in, but they provide just enough rope.

The gist is to wait on an empty promise that must disappoint (i.e., time out).

import scala.concurrent._
import scala.concurrent.duration._
import scala.util._
import ExecutionContext.Implicits.global

object Test extends App {
  val v = new SyncVar[Boolean]()
  val deadline = 5 seconds fromNow
  future(Await.ready(Promise().future, deadline.timeLeft)) onComplete { _ =>
    println("Bye, now.")
    v.put(true)
  }
  v.take()
  // or
  val w = new SyncVar[Boolean]()
  val dropdeadline = 5 seconds fromNow
  val p = Promise[Boolean]()
  p.future onComplete {_ =>
    println("Bye, now.")
    w.put(true)
  }
  Try(Await.ready(Promise().future, dropdeadline.timeLeft))
  p trySuccess true
  w.take()
  // rolling it
  implicit class Expiry(val d: Deadline) extends AnyVal {
    def expiring(f: =>Unit) {
      future(Await.ready(Promise().future, d.timeLeft)) onComplete { _ =>
        f
      }
    }
  }
  val x = new SyncVar[Boolean]()
  5 seconds fromNow expiring {
    println("That's all, folks.")
    x.put(true)
  }
  x.take() // wait for it
}