Thanks so much Roland. That makes sense. As a bonus, your comment about
addAttributes vs withAttributes might explain why I wasn't seeing .log
output :)
On Thu, Mar 3, 2016 at 12:04 AM, Roland Kuhn <goo...@rkuhn.info> wrote:
> Hi Richard,
>
> 3 mar 2016 kl. 00:24 skrev Richard Rodseth <rrods...@gmail.com>:
>
> This whole area of async boundaries in akka streams is still very
> confusing to me. I don't know what to suggest in terms of documentation,
> other than numerous examples of code, with corresponding diagrams showing
> the resultant boundaries and actor instances after materialization.
>
> As an example, I have a Sink which I use for console output. I'm sure you
> will tell me to use logging, but I didn't wish to deal with log levels and
> formatting for what is the real UI of the tool.
>
> So I have a Sink:
>
> def printSinkWithLabel[T](extractor: T => String): Sink[T,
> Future[akka.Done]]
> = Sink.foreach[T] { e => println(extractor(e)) }
>
> .withAttributes(ActorAttributes.dispatcher(
> "dispatcher-for-blocking-console"))
>
> .async // Should I have this?
>
> and a flow which uses it in an alsoTo()
>
> def progress[T](extractor: T => String) = {
>
> val flow = Flow[T]
>
> .alsoTo(Sinks.printSinkWithLabel(extractor) )
>
> .withAttributes(ActorAttributes.dispatcher(
> "dispatcher-for-blocking-console"))
>
> flow
>
> }
>
> WIth these I can do a via(progress(extractor)) as needed.
>
> Do I need the dispatcher attributes in both places?
>
>
> No, running the Sink on that dispatcher is sufficient, you don’t need (or
> want) to run the alsoTo on that dispatcher as well.
>
> Which is more appropriate?
>
>
> Running alsoTo on a different dispatcher slows down the “fast path” of
> your data through the progress indicator, so I wouldn’t recommend that.
>
> Is the .async on the Sink necessary/appropriate?
>
>
> Strictly speaking the .async is unnecessary if you know that the
> surrounding combinators (.alsoTo in this case) run on a different
> dispatcher, but I think it clearly spells out the intent to add this
> attribute explicitly.
>
> Does it make any difference if it's before or after the withAttributes?
>
>
> Yes, and that is something we should definitely put into the ScalaDoc as
> well as reference docs: .withAttributes replaces the attributes that were
> already on the Sink.foreach (which is just a .named("foreachSink") here,
> but it would include the .async if the order is swapped). If you use
> .addAttributes instead then the order does not matter.
>
> Regards,
>
> Roland
>
> Thanks in advance.
>
> --
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>
>
> *Dr. Roland Kuhn*
> *Akka Tech Lead*
> Typesafe <http://typesafe.com/> – Reactive apps on the JVM.
> twitter: @rolandkuhn
> <http://twitter.com/#!/rolandkuhn>
>
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>>>>>>>>>> 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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