Futures.scala

package com.samstarling.futures

import com.twitter.util.{Future, Await}
import com.samstarling.util.time

object ConcurrentComposition extends App {

  def slowTask(time: Int): Future[String] = Future {
    Thread.sleep(time)
    "Hello"
  }

  time("collect", {
    Await.result(Future.collect(List(slowTask(1000), slowTask(2000))))
  })

  time("join", {
    Await.result(Future.join(slowTask(1000), slowTask(2000)))
  })

  time("for", {
    for {
      r1 <- slowTask(1000)
      r2 <- slowTask(2000)
    } yield (r1, r2)
  })
}

Why do all of these take 3 seconds to complete?