concurrent-futures-in-for-comprehensions

FutureTestApp.scala

package com.hiya.h4b.cpas.futuretest

import akka.actor.ActorSystem
import scala.concurrent.{Await, Future}
import scala.concurrent.duration._

object FutureTestApp extends App {

  private val sys         = ActorSystem.apply("future-test-app")
  implicit private val ec = sys.dispatcher

  val t1 = System.currentTimeMillis()

  val joinedFuture = for {
    _ <- Future(Thread.sleep(5000))
    _ <- Future(Thread.sleep(5000))
  } yield ()
  Await.ready(joinedFuture, 15 seconds)
  val t2 = System.currentTimeMillis()
  println(s"Waited ${t2 - t1}ms")

  val f1 = Future(Thread.sleep(5000))
  val f2 = Future(Thread.sleep(5000))

  val joinedFuture2 = for {
    _ <- f1
    _ <- f2
  } yield ()
  Await.ready(joinedFuture2, 15 seconds)
  val t3 = System.currentTimeMillis()
  println(s"Waited ${t3 - t2}ms")

  Await.ready(sys.terminate(), 10 seconds)
  println(s"Shut down")
}

/* output:
[info] Waited 10008ms
[info] Waited 5009ms
[info] Shut down
*/