Example of ask pattern in akka typed

user_1743843 0
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I am trying to figure out, how the ask pattern works. In the documentation, it says:

Perform a single request-response message interaction with another actor, and transform the messages back to the protocol of this actor.

The interaction has a timeout (to avoid a resource leak). If the timeout hits without any response it will be passed as a Failure(java.util.concurrent.TimeoutException) to the mapResponse function (this is the only "normal" way a Failure is passed to the function).

For other messaging patterns with other actors, see ActorContext#messageAdapter.

This method is thread-safe and can be called from other threads than the ordinary actor message processing thread, such as scala.concurrent.Future callbacks.

Could someone please provide an example to get a better understanding of ask pattern.

akka scala
3 Answers

'Ask pattern' is used in the code outside of actors to communicate with actors. Akka will create an actor for you behind the scenes, send a message and wait for reply within timeout. None of this will block your thread because a Future result will be returned immediately which is expected to contain response later on. This is needed because actors can only communicate by sending messages and if you are not within an actor you can't receive a message. It's recommended to use 'tell' ! instead of 'ask' ? because it's more efficient but sometimes there is no choice so you have to bridge two worlds together with 'ask'.

Look for examples on internet or try to call actors from main method to get a feel of it.

user_12729500

When you need interact with another actor and also depend on its response you might use the tell method to send a message and wait for a new response message (fire-and-forget).
Due to the fact that Akka does not have guaranteed delivery, you might wait infinitely if the receiving actor is down.
Ask returns a Future[Response] that is either completed with a successful response or failed with a TimeoutException if there was no response within the specified timeout.
Please see the the example

user_4914970

The question you asked is related to akka typed and ask pattern API is slightly different to the standard (untyped) akka.

The examples can be found on akka docs and it is replicated here

trait CookieCommand {}
case class GiveMeCookies(replyTo: ActorRef[Cookies]) extends CookieCommand
case class Cookies(count: Int)

import akka.actor.typed.scaladsl.AskPattern._

// asking someone requires a timeout and a scheduler, if the timeout hits without response
// the ask is failed with a TimeoutException
implicit val timeout: Timeout = 3.seconds
implicit val scheduler = system.scheduler

val result: Future[Cookies] = cookieActorRef.ask(ref => GiveMeCookies(ref))

// the response callback will be executed on this execution context
implicit val ec = system.executionContext

result.onComplete {
  case Success(cookies) => println("Yay, cookies!")
  case Failure(ex)      => println("Boo! didn't get cookies in time.")
}
user_48038420
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