Composing Futures with a for-comprehension

Composing Futures

// Credit: http://blog.knoldus.com/2013/01/27/akka-futures-using-for-comprehensions/

import akka.actor.ActorSystem

import scala.concurrent.{future,  Future, Await }
import scala.concurrent.ExecutionContext.Implicits.global

object FutureComposingWithFor extends App {

    def longRunningFunction(number: Int) = {
    // Sleep for 3 seconds and return number
    Thread.sleep(3000)
    number
  }
    
  val system = ActorSystem("future")
  val startTime = System.currentTimeMillis
  val future1 = future { longRunningFunction(1) }
  val future2 = future { longRunningFunction(2) }
  val future3  = future { longRunningFunction(3) }

  val futuresum = for {
    a <- future1
    b <- future2
    c <- future3
  } yield (a + b + c)

  futuresum onSuccess {
    case sum =>
      val elapsedTime = ((System.currentTimeMillis - startTime) / 1000.0)
      println("Sum of 1, 2, and 3 is " + sum + " calculated in " + elapsedTime + " seconds")
  }

}