These are chat archives for akkadotnet/akka.net

11th
Oct 2017
Stijn Herreman
@stijnherreman
Oct 11 2017 14:11
I have an actor that needs to handle one type of message only, RetrieveFoo, to retrieve a resource from a REST API. Once the resource is retrieved, it is cached indefinitely. Is this a good case for using async/await (and thus blocking the actor), or should I still attempt to use PipeTo and keep track in some way of RetrieveFoo messages that need to be responded to?
I want to avoid multiple requests to retrieve the resource.
Stijn Herreman
@stijnherreman
Oct 11 2017 14:43
After thinking about this some more, I think I can just store a task in a variable when receiving the first message and use PipeTo, and then for all subsequent messages skip creating the task and just use PipeTo on the existing task. That should work even when the task is completed already.
Stijn Herreman
@stijnherreman
Oct 11 2017 15:18
I came up with the following (initial) implementation. It feels a bit awkward to use ContinueWith but maybe that's of my habit to use async/await.
    public sealed class Specification
        : ReceiveActor
    {
        private readonly IClient specsDataServiceClient;

        private Task<Messages.Models.Specification> modelTask;

        public Specification(IClient specsDataServiceClient)
        {
            this.specsDataServiceClient = specsDataServiceClient ?? throw new ArgumentNullException(nameof(specsDataServiceClient));

            this.Receive<GetSpecification>(message => this.GetSpecification(message));
        }

        private void GetSpecification(GetSpecification message)
        {
            if (modelTask == null)
            {
                var getSpecificationTask = this.specsDataServiceClient.Specification_GetSpecificationAsync(message.SpecificationId);
                var getOperationsTask = this.specsDataServiceClient.Operations_GetOperationsForSpecIdAsync(message.SpecificationId);
                var getTestsTask = this.specsDataServiceClient.Test_GetTestsForSpecIdAsync(message.SpecificationId);

                var modelTask = Task.WhenAll(getSpecificationTask, getOperationsTask, getTestsTask)
                    .ContinueWith(_ =>
                    {
                        return new Messages.Models.Specification(getSpecificationTask.Result, getOperationsTask.Result, getTestsTask.Result);
                    });
            }

            var senderClosure = this.Sender;
            modelTask.PipeTo(senderClosure);
        }
    }
Arsene Tochemey GANDOTE
@Tochemey
Oct 11 2017 15:20
@stijnherreman Since you are using Actor if it is possible simply use the synchronous version of your function call.
@stijnherreman Also if you can explain in details what you want to do I can be of a help.
Stijn Herreman
@stijnherreman
Oct 11 2017 15:21
@Tochemey no sync versions available unfortunately. The IClient implementation code is generated by a third-party tool, from an OpenAPI (Swagger) spec.
Arsene Tochemey GANDOTE
@Tochemey
Oct 11 2017 15:21
@stijnherreman Okay
Stijn Herreman
@stijnherreman
Oct 11 2017 15:22
I was reading http://gigi.nullneuron.net/gigilabs/asynchronous-and-concurrent-processing-in-akka-net-actors/ (and the previous article), about using ReceiveAsync or using PipeTo.
Arsene Tochemey GANDOTE
@Tochemey
Oct 11 2017 15:22
@stijnherreman That is cool
Stijn Herreman
@stijnherreman
Oct 11 2017 15:24
Basically, the actor is responsible for retrieving a REST resource and supplying it back to whoever asked for it. But it should only ever retrieve the resource once, and then respond with the cached resource.
Arsene Tochemey GANDOTE
@Tochemey
Oct 11 2017 15:25
@stijnherreman From the Rest API controller use Ask<> to send the message to the Actor.
Stijn Herreman
@stijnherreman
Oct 11 2017 15:26
@Tochemey ok, I'll take a look at that. I had previously read that Ask<> should be avoided, but to be honest I haven't taken a proper look at it yet.
Thank you :)
Arsene Tochemey GANDOTE
@Tochemey
Oct 11 2017 15:26
Then within the Actor where you are doing async stuff use:
CheckAsync().ContinueWith(task =>
                                {
                                    var response = task.Result;
                                    return response;
                                },
                                TaskContinuationOptions.AttachedToParent &
                                TaskContinuationOptions.ExecuteSynchronously).PipeTo(
                                closure);
@stijnherreman I have a production app using Rest API and Akka.NET
@stijnherreman CheckAsync() is a function that is running asynchronously.
@stijnherreman closure = Sender
Stijn Herreman
@stijnherreman
Oct 11 2017 15:29
I'll read the article, it looks like a good resource.
Arsene Tochemey GANDOTE
@Tochemey
Oct 11 2017 15:30
@stijnherreman These articles have helped to be grounded in the Ask/PipeTo pattern
Arjen Smits
@Danthar
Oct 11 2017 15:37
@stijnherreman avoid ask if you can. In your scenario. Why not use the Become feature.
So you receive a request for your REST data. You detect that you dont have it in cache
Arsene Tochemey GANDOTE
@Tochemey
Oct 11 2017 15:38
@Danthar from REST API controller I think Ask is the best bet.
Arjen Smits
@Danthar
Oct 11 2017 15:38
then perform your async -> pipeto stuff. At the end, switch behaviors with the Become feature
where you wait for your response message
and stash everything else
once you receive your response message
unstash all. And serve all the other stuff from your cache
that way you dont have to block your actor's execution. And you are sure you only pay the hit once
From your REST API Controller, ask is the only way to do request -> response style communication with an actor. So yes. Then you should use Ask
But then your communicating from outside your actor system. So you don't have much options there :)
Stijn Herreman
@stijnherreman
Oct 11 2017 15:50
@Danthar thank you for the insight, it sounds like a viable path. I'll try out some things tomorrow, end of the (work) day for me here.
Jack Wild
@jackowild
Oct 11 2017 17:43
Hi all, just submitted a PR to upgrade the Akka.Persistence.MongoDB plugin to 1.3.1. If somebody could review this it would be much appreciated.
Here's the link: AkkaNetContrib/Akka.Persistence.MongoDB#30