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  • Sep 05 2019 14:43
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    codecov-io commented #460
Gabriel Volpe
@gvolpe
:+1: :)
Ryan Peters
@sloshy
I need to slow down I'm answering questions faster than my brain works this morning
vimalaguti
@vimalaguti
thanks!
Rolando Manrique
@rolandomanrique
Hi, I'm trying to use tuple parMapN syntax but I can't make it work with parameterized effect, this is a very simple representation of what I'm trying to do:
scala> :paste
// Entering paste mode (ctrl-D to finish)

  import cats.effect._
  import cats.implicits._
  import cats.effect.implicits._
  import scala.concurrent.ExecutionContext
  val cs = IO.contextShift(ExecutionContext.global)

  def parMapIO(implicit cs: ContextShift[IO]) = {
    val ioA = IO("A")
    val ioB = IO(10)
    val ioC = IO(false)
    (ioA, ioB, ioC).parMapN { (a, b, c) => println(s"done: $a $b $c") }
  }

scala> parMapIO(cs).unsafeRunSync
done: A 10 false

scala> :paste
// Entering paste mode (ctrl-D to finish)


  def parMapF[F[_]](implicit F: ConcurrentEffect[F], cs: ContextShift[F]) = {
    val ioA = F.delay("A")
    val ioB = F.delay(10)
    val ioC = F.delay(false)
    (ioA, ioB, ioC).parMapN { (a, b, c) => println(s"$a > $b > $c") }
  }

// Exiting paste mode, now interpreting.

<pastie>:25: error: could not find implicit value for parameter p: cats.NonEmptyParallel[F,F]
    (ioA, ioB, ioC).parMapN { (a, b, c) => println(s"$a > $b > $c") }
                            ^
<pastie>:21: warning: parameter value F in method parMapF is never used
def parMapF[F[_]](implicit F: ConcurrentEffect[F], cs: ContextShift[F]) = {
                           ^
<pastie>:21: warning: parameter value cs in method parMapF is never used
def parMapF[F[_]](implicit F: ConcurrentEffect[F], cs: ContextShift[F]) = {
                                                   ^
Oleg Pyzhcov
@oleg-py
@rolandomanrique you need Parallel constraint on your F to use .par methods
Loránd Szakács
@lorandszakacs
did someone write a cats-effect wrapper over better-files? :smile:
while I love fs2-io, sometimes I need more :sweat:
Piotr Gawryś
@Avasil
haha, the same topic just came up in few different places
Fabio Labella
@SystemFw
Piotr Gawryś
@Avasil
it would be nice to have common files library on top of cats-effect and then specialized modules for streaming
Wojtek Pituła
@Krever
totally agree with Piotr as much as it matters :D
Piotr Gawryś
@Avasil
Having it in fs2 is not that bad considering it's easy to have this dependency because of doobie/http4s but it can be harder to discover/use for Monix/ZIO users. Also many utilities are not related to streaming at all. I would be happy to contribute to something like it and bring fresh contributors but I would count on someone else (TM) to kickstart it :D
Fabio Labella
@SystemFw
the same could be said for monix-catnap though
Piotr Gawryś
@Avasil
monix-catnap doesn't have a dependency on Task / Observable / Iterant but that's still a good point
Loránd Szakács
@lorandszakacs
@SystemFw nice, thanks :D
Fabio Labella
@SystemFw

monix-catnap doesn't have a dependency on Task...

ah, that's true

Daniel Spiewak
@djspiewak
I’ve often thought about doing something like a cats-effect-jvm and cats-effect-js library
Maybe even merging them together into a cats-effect-platform
Like, there isn’t much point in having a file read or write function without streaming effects, but other things like moving, copying, listing, etc, not to mention more basic stuff like println and exit hooks, not to mention browser things, all could be nicely wrapped
Ryan Peters
@sloshy
I'm trying to build a concurrent variable like structure that resets itself after nobody is using it for some period of time. So multiple subscribers can "acquire" it, and when all have released I set off a timer that, when finished, resets the variable to an initial value provided nobody subscribes during that window. I have the timer part handled with https://christopherdavenport.github.io/agitation/, and I'm thinking semaphore would be good for figuring out when the number of users that have acquired the variable is 0. Semaphore does not have an "unbounded" variant, and I'm wondering whether or not such a thing would even be useful, or if there is a simpler way of expressing what it is I'm going for (that may or may not need semaphore). Maybe Long.MaxValue as the number of permits is a fine way of getting what I need. What are your thoughts?
Fabio Labella
@SystemFw

and I'm thinking semaphore would be good for figuring out when the number of users that have acquired the variable is 0

if you don't need any semantic blocking, just a Ref should be enough

Ryan Peters
@sloshy
I'll try doing it with just Ref then, I think that should work fine. Thanks for the suggestion @SystemFw
Gavin Bisesi
@Daenyth
@sloshy you might also consider chris d's agitation, it has things like resettable timeouts
Ryan Peters
@sloshy
Way ahead of you @Daenyth :D
Gavin Bisesi
@Daenyth
oh wow
yeah you linked to it
haha
excuse me while I go have more coffee :grin:
Ryan Peters
@sloshy
TBF it was a hyperlink, easy to skim right over
And not to the github but to the microsite since it's what I had open at the moment
Fabio Labella
@SystemFw
agitate seems leaky rn (if you cancel agitate your reset is still happening)
also I think there is a race between oldFiber.cancel and buzzer.complete but it's very very likely innocuous
bifunctor
@bifunctor
Hi all
Is there a way to integrate cats effect into akka streams in the sink position?
For example:
    implicit val system = ActorSystem("QuickStart")
    implicit val materializer = ActorMaterializer()
    implicit val executor = system.getDispatcher

    val ticker = Source.tick(0.second, 1.second, "H")
      .runWith(Sink.foreach(println))
the type ticker of the ticker is Future[Done]
Ryan Peters
@sloshy
@bifunctor Are you asking about running IO inside Sink.foreach or are you looking at making the type of ticker be IO[Done]?
bifunctor
@bifunctor
I am looking the run inside the foreach
I think, I have to create Graphstage
Daniel Spiewak
@djspiewak
@bifunctor I think that fs2-reactive-streams is one answer to this. at least it seems like it should be. I don't know much about akka streams.
Ryan Peters
@sloshy
fs2-reactive-streams will get you a stream where multiple libraries form the connecting pieces of it, which might be what you want. Another alternative is to just do an unsafeRunSync inside of the foreach (not my first choice but it should "work"). Personally if it were me I would defer to fs2 as much as possible as it has direct support for cats effect .
I think there's value in not necessarily having to deal with multiple streaming libraries. Mixing and matching them changes semantics and performance expectations. If you get something from Akka Streams in another lib but would prefer to use fs2, that's a good time to use fs2-reactive-streams. If your application is already mostly Akka Streams and you just want to run some isolated pure code in there, just running the IO is also an option (albeit a compromise)
Daniel Spiewak
@djspiewak
a strong point
streaming is really complicated and each library has its own take on it
multiplying those complexities by throwing them together isn't good
Ryan Peters
@sloshy
In one app I worked on I just wrote the akka streams code as "normal Scala" and converted the resulting Future to IO for the rest of the app which was mostly pure. It feels gross, doesn't exactly compose well, but sometimes it's the way you get stuff done.
Paul Snively
@paul-snively
That said: fromPublisher(...runWith(Sink.asPublisher(fanout = false)))
bifunctor
@bifunctor
@sloshy Could you please explain, how did you do that the akka streams code as "normal Scala" and converted ....
Paul Snively
@paul-snively
@bifunctor: When you run an Akka stream, you get a Future[T]. You can put that expression in IO.fromFuture.
tl;dr Don't run the Akka stream, since Futures start immediately. Put the run expression in IO.fromFuture.