Wait until all Future.onComplete callbacks are executed

Question

I am using the Future API from Scala 2.10.X.

Here is my use case:

object Class1 {

  def apply(f: (Int) => Future[String])(i: Int): F         


        

Answer 1

With 1 Future and 3 onComplete

I think you're going to have to go the route of either composing your functions into a single onComplete call or else you'll have to do exactly what you said, use map:

 val fut1 = myFut map func1 // yes, a Future[Unit]
 val fut2 = myFut map func2
 val fut3 = myFut map func3

Follow the next section to find out when they all finish.

With 3 different Futures

It's very possible to know when all three Futures will complete. In fact, in Scala Future composes!

 def threeFutures(one: Future[Int], two: Future[Int], three: Future[Int]) {
   val fourth = for {
     _ <- one
     _ <- two
     _ <- three
   } yield 0

   fourth onComplete {
     case _ => println("all done")
   }
 }

Now what does this mean? It means that fourth is a Future which does not care about the inputs of the three arguments but that, when they all are complete, it will complete itself. This is pre-packaged and made ready just for you.

(Side note: In the example I'm also assuming you have all your implicits in scope.)