akkadotnet/akka.net

Port of Akka actors for .NET

Bartosz Sypytkowski

@Horusiath

you can use passivation mechanics to stop them, but passivation is not part of supervision chain and they will be recreated anyway if some message will arrive

Chris Ochs

@gamemachine

our use case is we want short term actors that have a globally unique id that we can reach from anywhere in a cluster.

we use a database to create and lookup the id's

so probably best to stick with the initial approach I had, which is just remote deploy

or actually probably simpler to have an actor that just creates them on demand, and it supervises them

Chris Ochs

@gamemachine

so cluster sharding docs say I need to specify an event journal. But node A can send a message to a sharded actor on node B (same computer) and I haven't configured any journal. What gives?

Bartosz Sypytkowski

@Horusiath

@gamemachine cluster sharding uses event journals to keep its internal state across the nodes. So i.e. if a node hosting so called shard coordinator dies, coordinator itself can be recreated on another node and it will still know which shards live on which nodes

(it's also useful to remember that cost of creating and communicating with sharded actors is higher than with standard ones)

you can read more technical details here: https://petabridge.com/blog/cluster-sharding-technical-overview-akkadotnet/

Weston

@ronnyek

so persistence wise, is there anything like the persistent state like azure service fabric has

(I think it works the same way in orleans)

Arjen Smits

@Danthar

using snapshots is basically the same

persistence has 2 types of storage methods, journal and snapshot

journal is eventsource based

so you save each event that mutates your state, as it comes in

when your actor restarts, all events are replayed, thus rebuilding your actor state

snapshotting stores the current state of your actor. Well, not the the actor state, but whatever state you tell it to

so if you store a list of whatevers in your actor, you can store that in one go with a snapshot

when your actor restarts, it gets the last snapshot you saved

journalling is often used in conjunction with snapshotting, to improve performance.

Boban Pavloski

@bobanco

@Aaronontheweb can you check if the overridden the GetHashCode() , Equals() is overridden too and you can provide == != operators too if somewhere == is used instead of Equals()

Aaron Stannard

@Aaronontheweb

@bobanco yeah resharper throws a warning about that

fixed it in my local branch

working on some more model based tests to get to the bottom of the issue

Boban Pavloski

@bobanco

it's odd how you are getting diffferent hash codes of the same object

the fileds used in the generation of the hash code are immutable?

Tomasz Jaskula

@tjaskula

Hi, I'm trying to create a child actor in F# (not using F# api but classes) and I have the following exception:

[ERROR][15/04/2017 09:07:26][Thread 0003][akka://MovieStreamingActorSystem/user/Playback/UserCoordinator/User42] Error while creating actor instance of type Actors+UserActor with 1 args: (System.Int32[])
Cause: [akka://MovieStreamingActorSystem/user/Playback/UserCoordinator/User42#197236877]: Akka.Actor.ActorInitializationException: Exception during creation ---> System.TypeLoadException: Error while creating actor instance of type Actors+UserActor with 1 args: (System.Int32[]) ---> System.MissingMethodException: Constructor on type 'Actors+UserActor' not found.
   at System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes, StackCrawlMark& stackMark)
   at System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
   at System.Activator.CreateInstance(Type type, Object[] args)
   at Akka.Actor.Props.ActivatorProducer.Produce()
   at Akka.Actor.Props.NewActor()
   --- End of inner exception stack trace ---
   at Akka.Actor.Props.NewActor()
   at Akka.Actor.ActorCell.CreateNewActorInstance()
   at Akka.Actor.ActorCell.<>c__DisplayClass115_0.<NewActor>b__0()
   at Akka.Actor.ActorCell.UseThreadContext(Action action)
   at Akka.Actor.ActorCell.NewActor()
   at Akka.Actor.ActorCell.Create(Exception failure)
   --- End of inner exception stack trace ---
   at Akka.Actor.ActorCell.Create(Exception failure)
   at Akka.Actor.ActorCell.SysMsgInvokeAll(EarliestFirstSystemMessageList messages, Int32 currentState)

Although my class is as follows:

type UserActor(userId : int) as this =
        inherit ReceiveActor()

        let userId = userId

And I try to create it like that:

let newChildActorRef = UserCoordinatorActor.Context.ActorOf(Props.Create(typeof<UserActor>, [|userId|]), "User" + userId.ToString())

Any hints?

Ismael Hamed

@ismaelhamed

@alexvaluyskiy there're still some bad references:

Unable to find a version of 'Akka.Streams.TestKit' that is compatible with 'Akka.Persistence.Sql.TestKit 1.2.0.36-beta constraint: Akka.Streams.TestKit (>= 1.2.0.36-beta)'.

Tomasz Jaskula

@tjaskula

Found the issue, I have to pass args without the array

let newChildActorRef = UserCoordinatorActor.Context.ActorOf(Props.Create(typeof<UserActor>, userId), "User" + userId.ToString())

Michael Tissen

@rubiktubik

Hello, i'am using Akka.Persistence for a event-sourced application and i was wondering if one of the Akka.Persistence Plugins Support Persistence.Query?

Lev Lehn

@llehn

Regarding DI (autofac) integration. The docs say: The basic functionality is provided by a DependencyResolver class, that can create Props using the DI container. with example ending with this IDependencyResolver resolver = new XyzDependencyResolver(someContainer, system);

then there's When creating actorRefs straight off your ActorSystem instance, you can use the DI() Extension..

I don't understand that - in the example the resolver isn't used anywhere. And where does the system.DI() method know which DI container to use?

mwardm

@mwardm

5th

Chris Ochs

@gamemachine

so a comment on the akka documention style. I see this pattern a lot. Some part of the doc will go into all sorts of detail on stuff most people don't need to know, but then fail to document the basics, the stuff you have to know. http://getakka.net/docs/working-with-actors/identifying-actors-via-actor-selection is a good example. It never actually say's where you get the actor identity from. Sender? ActorIdentity .Subject?

Weston

@ronnyek

so if I want to build a console app, and have it connect or share an actorsystem with a webapp

is that clustering and requiring lighthouse?

Chris Ochs

@gamemachine

if both have static ip's and can reach each other, I don't see a reason for lighthouse really. just put the addresses of both as the seed nodes in both apps

or same address different ports that works also

Arjen Smits

@Danthar

@ronnyek at the very least that you would need akka.remote. You can create an server/client or peer to peer connection with akka.remote manually

akka.clustering layers on top of akka.remote and adds service discoverability and reliability things that would expect from a full blown cluster

Weston

@ronnyek

Ok...

I think I'll do that and add clustering later... Need to simplify this project for experimentation

Remove variables until I am familiar with and comfortable with Akka.net

Tomasz Jaskula

@tjaskula

Is this the only way defining parent/child relationship with FSharp API ? cc: @Horusiath

let playback = 
        spawn system "Playback"
        <| fun parentMailbox ->
            let child = 
                spawn parentMailbox "child" 
                    <| fun childMailbox ->
                        childMailbox.Defer (fun () -> printfn "Child stopping")
                        printfn "Child started"
                        let rec childLoop() = actor {
                            let! msg = childMailbox.Receive()
                            return! childLoop()
                        }
                        childLoop()
            cprintfn ConsoleColor.Gray "Creating parent actor..."
            // define parent behavior
            let rec loop() = actor {
                let! msg = parentMailbox.Receive()
                child.Forward(msg)  // forward all messages through
                return! loop ()
            }
            loop ()

Bartosz Sypytkowski

@Horusiath

@tjaskula using Akka.FSharp? Yes. But in normal conditions you'd probably move child behavior to separate function

Arsene Tochemey Gandote

@Tochemey

@ronnyek you can build a full blown reactive Web applications using Akka without clustering and Akka remote. It is sth I have done.

Weston

@ronnyek

Basically shooting for say a web application and another worker service

Seems like good have remote or something for that

You'd need

Arsene Tochemey Gandote

@Tochemey

Weston

@ronnyek

You'd know more than I would... I am just saying from my minimal experience... That seems like that would be the case

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