Akka actor dispatcher and nested futures

akka_actors_and_nested_futures

import akka.actor._
import scala.concurrent.duration._
import scala.concurrent.Future

object MyApp extends App {
  val actorSystem = ActorSystem()
  val myActor = actorSystem.actorOf(Props[MyActor])
  myActor ! "Hello!"
}

class MyActor extends Actor with ActorLogging {
  import context.dispatcher // This causes the second future to fail during intialization with NPE because dispatcher is a 'def' inside of an actor
  //implicit val ctx = context.dispatcher // This works as we "capture" execution context by eagerly evaluating it while actor is still alive

  context.setReceiveTimeout(2.seconds)

  def receive = {
    case ReceiveTimeout =>
      println("Receive timeout! Stopping...")
      context.stop(self)

    case msg: String    =>
      println(s"Received a message: $msg")
      Future {
        Thread.sleep(3000) // 3 seconds
      } onComplete {
        case _ =>
          println("First future is done.")
          Future { // a nested future. Initialization may fail with NPE: ERROR [Dispatcher]: java.lang.NullPointerException: null            
            Thread.sleep(1000)
          } onComplete {
            case _ =>
              println("Second future is done.")
          }
      }
  }
}