Question

I am using Play 2.0 and Akka to deploy a web application. I have separated actors based on responsibility, as such actors often need to communicate with each other during a single web request.

For example, given an actor that manages registered devices, it must query another actor that handles the associated user accounts:

class DeviceActor extends Actor {

  val accountActorRef = ...

  def receive = {
    case GetAccountByDeviceId(id:String) =>
      val accountId = getAccountIdAssociatedWithDevice(id)
      accountActorRef ? GetAccountById(accountId) map {
        case account: Account => sender ! account
      }
  }

}

When calling DeviceActor from my controller, I always get

akka.pattern.AskTimeoutException

Answer 1

When calling map on a Future or Promise you are actually registering a callback. The reference sender is caught in the callbacks closure, but sender is only appropriately set while the DeviceActor is handling the message.

You have to capture the senders reference before the receive method exists:

class DeviceActor extends Actor {

  val accountActorRef = ...

  def receive = {
    case GetAccountByDeviceId(id:String) =>
      val X = sender
      val accountId = getAccountIdAssociatedWithDevice(id)
      accountActorRef ? GetAccountById(accountId) map {
        case account: Account => X ! account
      }
  }

}