Using futures and Thread.sleep

Question

By executing this scala code, I don't have any output in the console. (I don't really understand what is happening)

If I remove Console.println("Console.println OK!") => everything seems fine.

If I remove Thread.sleep(2000) => everything seems fine.

Do you have any ideas about this ? Thank you very much!

Clément

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

object ScalaFuture {

  def main(args: Array[String]) {

    val f: Future[String] = Future {
      Thread.sleep(2000)
      "future value"
    }

    f.onSuccess {
      case s => {
        Console.println("Console.println OK!")
        System.out.println("System.out.println OK!")
      }
    }

    Await.ready(f, 60 seconds)
  }

}

Answer 1

Your await is waiting for future to complete, which is done after 2 seconds, but it doesn't wait for onSuccess handler, which executes in another thread (similar to future), but after Await.ready(f, 60 seconds), so process exits earlier than you print something. To process it correctly - create new future for onComplete:

val f: Future[String] = Future {
  Thread.sleep(2000)
  "future value"
}

val f2 = f map { s => 
    println("OK!")
    println("OK!")    
}

Await.ready(f2, 60 seconds)
println("exit")

Results for Await.ready(f, ...):

exit
OK!
OK!

Results for Await.ready(f2, ...):

OK!
OK!
exit