HowScalaFutureWorks.scala

gistfile1.scala

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


val is = 1 to 10 toList
def db = s"${Thread.currentThread}"
def f(i: Int) = Future {
  println(db + s" -> \t I'm ${i} -> \t I start to sleep")
  Thread.sleep(1*1000)
  println(db + s" -> \t I'm ${i} -> \t I wake from sleep")
  i * 100
}.map {
  x =>
    println(db + s" => \t I'm ${x} => \t I start to sleep")
    Thread.sleep(1*1000)
    println(db + s" => \t I'm ${x} => \t I wake from sleep")
    i
}

val theFuture = Future.traverse(is)(f _)
Await.result(theFuture, 100.seconds)

This is the output on my computer

Thread[ForkJoinPool-1-worker-5,5,main] ->        I'm 1 ->        I start to sleep
Thread[ForkJoinPool-1-worker-1,5,main] ->        I'm 2 ->        I start to sleep
Thread[ForkJoinPool-1-worker-7,5,main] ->        I'm 4 ->        I start to sleep
Thread[ForkJoinPool-1-worker-3,5,main] ->        I'm 3 ->        I start to sleep
Thread[ForkJoinPool-1-worker-5,5,main] ->        I'm 1 ->        I wake from sleep
Thread[ForkJoinPool-1-worker-5,5,main] =>        I'm 100 =>      I start to sleep
Thread[ForkJoinPool-1-worker-1,5,main] ->        I'm 2 ->        I wake from sleep
Thread[ForkJoinPool-1-worker-3,5,main] ->        I'm 3 ->        I wake from sleep
Thread[ForkJoinPool-1-worker-7,5,main] ->        I'm 4 ->        I wake from sleep
Thread[ForkJoinPool-1-worker-3,5,main] =>        I'm 300 =>      I start to sleep
Thread[ForkJoinPool-1-worker-7,5,main] =>        I'm 400 =>      I start to sleep
Thread[ForkJoinPool-1-worker-1,5,main] =>        I'm 200 =>      I start to sleep
Thread[ForkJoinPool-1-worker-5,5,main] =>        I'm 100 =>      I wake from sleep
Thread[ForkJoinPool-1-worker-1,5,main] =>        I'm 200 =>      I wake from sleep
Thread[ForkJoinPool-1-worker-7,5,main] =>        I'm 400 =>      I wake from sleep
Thread[ForkJoinPool-1-worker-5,5,main] ->        I'm 6 ->        I start to sleep
Thread[ForkJoinPool-1-worker-7,5,main] ->        I'm 7 ->        I start to sleep
Thread[ForkJoinPool-1-worker-3,5,main] =>        I'm 300 =>      I wake from sleep
Thread[ForkJoinPool-1-worker-1,5,main] ->        I'm 5 ->        I start to sleep
Thread[ForkJoinPool-1-worker-3,5,main] ->        I'm 8 ->        I start to sleep
Thread[ForkJoinPool-1-worker-5,5,main] ->        I'm 6 ->        I wake from sleep
Thread[ForkJoinPool-1-worker-7,5,main] ->        I'm 7 ->        I wake from sleep
Thread[ForkJoinPool-1-worker-1,5,main] ->        I'm 5 ->        I wake from sleep
Thread[ForkJoinPool-1-worker-3,5,main] ->        I'm 8 ->        I wake from sleep
Thread[ForkJoinPool-1-worker-5,5,main] =>        I'm 600 =>      I start to sleep
Thread[ForkJoinPool-1-worker-3,5,main] =>        I'm 800 =>      I start to sleep
Thread[ForkJoinPool-1-worker-1,5,main] =>        I'm 500 =>      I start to sleep
Thread[ForkJoinPool-1-worker-7,5,main] =>        I'm 700 =>      I start to sleep
Thread[ForkJoinPool-1-worker-3,5,main] =>        I'm 800 =>      I wake from sleep
Thread[ForkJoinPool-1-worker-7,5,main] =>        I'm 700 =>      I wake from sleep
Thread[ForkJoinPool-1-worker-1,5,main] =>        I'm 500 =>      I wake from sleep
Thread[ForkJoinPool-1-worker-5,5,main] =>        I'm 600 =>      I wake from sleep
Thread[ForkJoinPool-1-worker-7,5,main] ->        I'm 10 ->       I start to sleep
Thread[ForkJoinPool-1-worker-3,5,main] ->        I'm 9 ->        I start to sleep
Thread[ForkJoinPool-1-worker-3,5,main] ->        I'm 9 ->        I wake from sleep
Thread[ForkJoinPool-1-worker-7,5,main] ->        I'm 10 ->       I wake from sleep
Thread[ForkJoinPool-1-worker-5,5,main] =>        I'm 1000 =>     I start to sleep
Thread[ForkJoinPool-1-worker-3,5,main] =>        I'm 900 =>      I start to sleep
Thread[ForkJoinPool-1-worker-5,5,main] =>        I'm 1000 =>     I wake from sleep
Thread[ForkJoinPool-1-worker-3,5,main] =>        I'm 900 =>      I wake from sleep

An advanced version can be viewed at https://gist.github.com/hanfeisun/9f2a486f0c7f75d67ac3