Hello there,
In general always perfer tell (!) instead of ask (?), unless you have a
compelling reason not to. It has less overhead, and I also find things nicer to
model using plain actor tell's instead of ask's - which mix up styles a little
bit (actors in general "fire and forget").
But let's also look at your example, because I think you may have mixed up what
Future[_] gets completed when. The futures don't automatically get composed,
but by chanining of reactions to a futures completion, actors can "cascade"
completing their corresponding futures.
In the bellow example we use ask twice. The a actor completes the fa future,
but only once the fb future completes successfuly. Completing an "ask created
Future", happens when an actor replies to the message sent by ask - so in the
end => b completes the fb future, which then triggers the map in a, which
completes the fa future.
import akka.pattern.ask
val b = context.system.actorOf(Props(new Actor {
def receive = {
case s => sender() ! s // this response completes the `fb` future
}
}))
val a = context.system.actorOf(Props(new Actor {
def receive = {
case s =>
val replyTo = sender()
val fb = b ? (s + "!")
fb map { bResponse =>
// this runs when the b actor replies - thus, completing the `fb`
future
replyTo ! bResponse // this completes the `fa` future
}
}
}))
val fa: Future[Any] = a ? "wat" // this future will be completed by the `a`
actor replying to the "wat" message
--
Konrad Malawski
geecon.org / java.pl / krakowscala.pl / gdgkrakow.pl
From: glidester [email protected]
Reply: [email protected] [email protected]
Date: 21 March 2014 at 11:49:05
To: [email protected] [email protected]
Subject: [akka-user] Chaining actor ask calls
Hi,
I'm in the process of learning Akka and I wondered if anyone could clarify
something for me.
If I have 2 actors. I 'ask' Actor A which in turn 'asks' Actor B.
This means I get returned a Future from ActorB wrapped in a Future from Actor A
(correct?)
Is this good practice? Should I be using "tell" instead to avoid the nested
Futures?
Any pointers gratefully received!
G
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>>>>>>>>>> Read the docs: http://akka.io/docs/
>>>>>>>>>> Check the FAQ:
>>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html
>>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user
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