Thanks for the detailed reply on SO! We're almost certainly going with your recommended method of tagging requests and responses with an id field, but I thought a wider discussion could be interesting.
On Tuesday, July 22, 2014 10:59:41 AM UTC-4, Konrad Malawski wrote: > > You're welcome :-) > > Happy hakking! > > > On Tue, Jul 22, 2014 at 4:53 PM, Paul Kinsky <pki...@gmail.com > <javascript:>> wrote: > >> I recently posted this question on Stack Overflow, as Waiting on >> multiple Akka FSM messages >> <https://stackoverflow.com/questions/24872342/waiting-on-multiple-akka-fsm-messages>. >> >> I got one great answer (reproduced below) from Konrad 'ktoso' Malawski. I'm >> reposting it on this list just in case there are any other methods for >> distinguishing between responses. >> >> My question: >> >>> I have an Akka FSM actor that runs the following pseudocode after >>> receiving a message while in ReadyState >>> lookupA ! Wrapper(Lookup("A")) >>> lookupB ! Wrapper(Lookup("B")) >>> lookupC ! Wrapper(Lookup("C")) >>> goto(LookingUpDataState) using DataFound(a = None, b = None, c = None) >>> The actor then waits for responses which can be either FullResult[T] >>> (extending ServiceResult[T]) or Empty (extending ServiceResult[Nothing]). >>> Successful lookup results are used to populate the DataFound instance's >>> fields and Empty lookup results result in a logged error message and the >>> termination of the actor. >>> My question is this: how can I determine which lookup failed, so that I >>> can log the failure or fallback to a default value? All I can think of is >>> examining the sender's ActorRef (hacky) or adding a unique ID field to all >>> messages (high overhead). >>> This is a simple problem to solve using Ask's and Futures. Does an >>> idiomatic Akka solution exist? >> >> >> >> Konrad's answer: >> >>> There's a few patterns you could use here. You will have to resort to >>> one of these options listed below. They all have some trade off (and >>> benchmarking is king anyway), but I've listed them in order of "bad to >>> good", >>> >>> - performing the queries in-order, so send A, wait for A response, >>> send B ... But that's *horrible* - as in needlessly sequential. >>> >>> >>> - use the ask pattern, so you'll spin up (internally that's how ask >>> works) 3 actors, and they'll complete "their own" future. So this also >>> has >>> some cost on the sender because it has to start these special purpose >>> actors (smaller than a normal actor, but still). >>> >>> >>> - Yes, you'll need to tag these messages somehow. So you'd send some >>> ID and the response must contain the same ID, then you know it's "oh >>> it's >>> the response for A" etc. I would argue that this is the recommended way >>> to >>> go here. >>> >>> >>> - there's a *contrib* pattern available in Akka called the >>> Aggregator, which is designed for this use case, so you might want to >>> check >>> it out: >>> http://doc.akka.io/docs/akka/2.3.4/contrib/aggregator.htmlHowever >>> if you like it or not is very much a matter of personal taste I guess. >>> >>> My personal favourite (we tend to avoid ask in general) would be >>> tagging the requests in an Envelope(id, payload) so the responses can >>> also be wrapped in such Envelope(id, response). If you decide to call >>> these simply envelope or more with domain terminology is up to you. >>> Hope this helps. >> >> -- >> >>>>>>>>>> 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 >> --- >> You received this message because you are subscribed to the Google Groups >> "Akka User List" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to akka-user+...@googlegroups.com <javascript:>. >> To post to this group, send email to akka...@googlegroups.com >> <javascript:>. >> Visit this group at http://groups.google.com/group/akka-user. >> For more options, visit https://groups.google.com/d/optout. >> > > > > -- > Cheers, > Konrad 'ktoso' Malawski > hAkker @ Typesafe > > <http://typesafe.com> > -- >>>>>>>>>> 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 --- You received this message because you are subscribed to the Google Groups "Akka User List" group. To unsubscribe from this group and stop receiving emails from it, send an email to akka-user+unsubscr...@googlegroups.com. To post to this group, send email to akka-user@googlegroups.com. Visit this group at http://groups.google.com/group/akka-user. For more options, visit https://groups.google.com/d/optout.
