Example of running futures in parallel

ParallelFuture.scala

import scala.concurrent.duration._
import scala.concurrent.duration.FiniteDuration
import scala.concurrent.{Await, Future}
import scala.language.postfixOps
import scala.concurrent.ExecutionContext.Implicits.global

object ParallelFuture {

  def printWithTimeAndThreadID(s : String): Unit = println(s"${System.currentTimeMillis()} thread id ${Thread.currentThread().getId} : $s")

  // A simple example future which takes configurable time and returns the thread ID it ran on
  // The label is so we can identify the job in the output ...
  def timedFuture(finiteDuration: FiniteDuration, label: String): Future[Long] = Future {

    if(label.startsWith("job 2")) throw new Exception("oh dead")

    printWithTimeAndThreadID(s"starting $label")

    Thread.sleep(finiteDuration.toMillis)

    printWithTimeAndThreadID(s"completing $label")
    Thread.currentThread().getId
  }

  def main(args: Array[String]): Unit = {

    // This function shows how to run futures in parallel using Future.sequence
    // which takes a List[Future[A]] and returns a Future[List[A]]
    def threeAtOnce(a: Long) = Future.sequence((1 to 3).map {
      n => timedFuture(5 seconds, s"job $n $a")
    })

    // Simple demo where we run the first job then run three jobs
    // in parallel with the result
    val exampleF = for (
      a <- timedFuture(3 seconds, "first job");
      b <- threeAtOnce(a)
    ) yield (a,b)

    val runMe = exampleF

    Await.ready(exampleF, 10 seconds)

  }

}