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Aaron Stannard
@Aaronontheweb
@pmbanka which page of the docs?
Paweł Bańka
@pmbanka
@Aaronontheweb the workflow was like that: 1) click http://getakka.net/articles/actors/receive-actor-api.html, start reading. It starts with actors, blah blah, then defining, props, all that jazz. Ok, but I see there is also another API. So I go to 2) http://getakka.net/articles/actors/untyped-actor-api.html, see the beginning is the same, scroll down, creating actors, props, etc. 3) realize that these APIs seem very similar, start hunting down what is the difference, notice OnReceive in one and pattern match in the other one 4) notice the info on top of UntypedActor API page about C# 7, confirming it is mostly about the switch (?)
I think it would be nice to put some section somewhere explainig why are there 2 different APIs, what is the difference and pros/cons
especially since googling akka.net receive actor vs untyped actor does not return anything about the why
Aaron Stannard
@Aaronontheweb
@pmbanka well then
I've been overdue for some technical blog posts on Petabridge's site
sounds like a good one lol
on the official website we mostly just try to give you an explanation for how things work
and what the different tools are meant to be used for
we don't editorialize them much
Stephen Newman
@goodisontoffee

Is there anyone out there that can help me get my head around the implications that leveraging persistence in an existing actor. I've changed the base class and am moving some "commands" over to the construct events, persist, process event pattern but am getting what "feels" like asynchronous processing of the event processing. Is it true to say that:

1) A message is received
2) Message is treated as a command and an event is created from the command
3) Persist is called supplying the event to persist and a handler to be invoked after successful persistence
4) Next message is pulled from the mailbox and processed
5) Persistence completes
6) Handler supplied in 3 is invoked with persisted event

That's how it feels, so I wonder if that is accurate, and is the fix to complete the moving over from messages to Commands/Events and it'll be okay.

Dave New
@davenewza
Question around async methods which return data (to an Ask) and PipeTo: would using ContinueWith on faulted tasks be a reasonable way to 'catch' and handle exceptions thrown. Example:
            Receive<SomeRequest>(request =>
            {
                GetSomethingAsync(request)
                    .ContinueWith(t => new FailedResponse(t.Exception), TaskContinuationOptions.OnlyOnFaulted)
                    .PipeTo(Sender);
            });
Dave New
@davenewza
if i try this, i get an empty Akka.Actor.Status.Failure message returned
Aaron Stannard
@Aaronontheweb
@davenewza ideally we should populate the exception into that Status.Failure message
part of the issue there though is that you'll never get anything on that PipeTo if the task succeeds normally I don't think
since PipeTo is continuing off of the OnlyOnFaulted Task
I have an example of what I usually do here...
// pipe the result of our markets to ourselves
            _exchangeFeedClient.HttpClient.Markets.GetProducts(cts.Token).ContinueWith<object>(tr =>
            {
                if (tr.IsCanceled || tr.IsFaulted)
                    return new Status.Failure(tr.Exception);
                return tr.Result;
            }).PipeTo(Self);
I have a catch-all continuation
that I use to handle any case
success or failure
and then my actor who receives this...
Receive<Status.Failure>(s =>
            {
                _currentRetryPolicy = _currentRetryPolicy.Retry(); // update the retry data
                _log.Warning(
                    "Request for list of exchange trade products timed out from {0}. Retrying in {1} seconds with {2} attempts remaining.",
                    _exchangeFeedClient.Endpoints.RestEndpointUri, _currentRetryPolicy.CurrentRetryInterval,
                    _currentRetryPolicy.RemainingAttempts);
                AcquireProductsFeed(_currentRetryPolicy.CurrentRetryInterval);
            }, failure => _currentRetryPolicy.CanRetry);

            Receive<Status.Failure>(s =>
            {
                _log.Error("ERROR: unable to contact exchange at {0} after {1} attempts. Aborting.",
                    _exchangeFeed.HttpClient.Endpoints.RestEndpointUri, _retryPolicyProvider.MaxNrOfAttempts);
                _currentRetryPolicy.Retry(); // throw a HopelessOperation exception on purpose
            }, failure => !_currentRetryPolicy.CanRetry);

            // Received data from the exchange API.
            Receive<ApiResult<IEnumerable<Product>>>(products =>
            {
                if (products.Status == HttpStatusCode.OK)
                {
                    _tradeProducts.AddRange(products.Result);
                    _log.Info("Received products from exchange: {0}", string.Join(",", _tradeProducts.Select(x => x.id)));
                    BecomePublishing();
                }
                else if (_currentRetryPolicy.CanRetry
                ) // something went wrong with our web request, but we have retry attempts remaining
                {
                    _currentRetryPolicy = _currentRetryPolicy.Retry(); // update the retry data
                    _log.Warning(
                        "Received error with our HTTP request ({0}): {1}. Retrying in {2} with {3} attempts left.",
                        products.Status, products.Message,
                        _currentRetryPolicy.CurrentRetryInterval, _currentRetryPolicy.RemainingAttempts);
                    AcquireProductsFeed(_currentRetryPolicy.CurrentRetryInterval);
                }
                else // web request failed, no retry attempts remaining
                {
                    _log.Error(
                        "ERROR: unable to contact exchange at {0} after {1} attempts. HTTP Status: {2}, Message: {3}. Aborting.",
                        _exchangeFeed.HttpClient.Endpoints.RestEndpointUri,
                        _retryPolicyProvider.MaxNrOfAttempts, products.Status, products.Message);
                    _currentRetryPolicy.Retry(); // throw a HopelessOperation exception on purpose
                }
            });
AcquireProductsFeed(_currentRetryPolicy.CurrentRetryInterval); causes me to re-run the task that failed
Aaron Stannard
@Aaronontheweb
and the _currentRetryPolicy thing is just a strategy class I wrote that implements various retry strategies
the implementation I'm using here is an exponential-backoff type approach
I wrote that stuff by hand but you can use a library like Polly to get that for free
@goodisontoffee if you call the normal Persist method
the actor will complete its persistence operation before the next message from the mailbox can be processed
if you call PersistAsync
it will behave as you've described
Dave New
@davenewza
@Aaronontheweb thank you. checking it out
Aaron Stannard
@Aaronontheweb
but even if you call multiple PersistAsync calls in a row
all of your events will still be persisted in order
because the journal itself is implemented as an actor
and it will receive the messages in its own mailbox in that order
Stephen Newman
@goodisontoffee
Just Persist being called, I'll try to confirm but I can't share the code so I'll have to make something that also exhibits what I'm seeing. At which point the example will work properly ;)
So Persist blocks new message consumption until the persistence is complete.
Aaron Stannard
@Aaronontheweb
under the covers
the actor is just stashing messages until it gets an acknowledgement that the persist operation has completed
and then it invokes the callback
so it's not literally blocking a thread
Andrey Leskov
@andreyleskov

Hi all, trying to build client to remote akka system using association. Using test:

public class AssociationErrorTest
    {
        public class EchoActor : ReceiveActor
        {
            public EchoActor(){Receive<object>(m => Sender.Tell(m));}
        }

        [Fact]
        public async Task Test_association()
        {
            var server = ActorSystem.Create("server", @"akka { actor.provider = ""Akka.Remote.RemoteActorRefProvider, Akka.Remote""
                                                               remote.dot-netty.tcp { port = 10001 
                                                                                      hostname = localhost}}");
            var serverActor = server.ActorOf<EchoActor>(nameof(EchoActor));
            var client = ActorSystem.Create("client", @"akka{ actor.provider = ""Akka.Remote.RemoteActorRefProvider, Akka.Remote""
                                                                remote.dot-netty.tcp { port = 0
                                                                                       hostname = localhost}}");
            var remoteActorRef = await client.ActorSelection(@"akka.tcp://server@localhost:10001/user/EchoActor").ResolveOne(TimeSpan.FromSeconds(5));
            await remoteActorRef.Ask<string>("Hello");
        }
    }

if I run it as single test, all is OK . But if I run it with bunch of test, actor selection hangs. Got error from internals:

17-10-05 17:50:08.366 [DBG TH193] Src:[remoting
 "Associated [akka.tcp://server@localhost:10001] <- akka.tcp://client@localhost:5703"

17-10-05 17:50:08.375 [DBG TH201] Src:[endpointWriter#116268940]
 "Associated [akka.tcp://client@localhost:5703] -> akka.tcp://server@localhost:10001"

17-10-05 17:50:08.375 [DBG TH201] Src:[endpointWriter#116268940]
 Drained buffer with maxWriteCount: 50, fullBackoffCount: 1,smallBackoffCount: 0, noBackoffCount: 0,adaptiveBackoff: 1000

17-10-05 17:50:08.388 [DBG TH201] Src:[client)
 Resolve of path sequence [/"temp/N"] failed

looks like client system cannot locate temp actor during Ask()
Can anybody suggest reasons? May be I need some additional configuration ?

Aaron Stannard
@Aaronontheweb
@andreyleskov dollars to donuts
issue is either going to be a static variable that is shared among the actor system instances and this test is running with AppDomains turned off
or one of the remote actor systems is replying to an actor who has since terminated
Andrey Leskov
@andreyleskov
sounds reasonable, but in test above I don't use anything static
may be something inside akka system itself?
Aaron Stannard
@Aaronontheweb
yeah that's what I meant
the name counter we use for naming temporary actors