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Alexandru Nedelcu
@alexandru
@squadgazzz I don't know why that happens, from the look of it you're not doing anything incorrectly. This needs to be investigated. Let me think.
Glen Marchesani
@fizzy33
fwiw this does have the behaviour you expect

  val obs = Observable.fromIterable(1 to 2)
  val result =
    obs
      .publishSelector { o =>
        o ++ Observable.fromIterable(11 to 12)
      }
      .publishSelector(_ ++ Observable.fromIterable(101 to 102))
  result.toListL.executeAsync.runToFuture.foreach(l => println(l.mkString("[", ",", "]")))
  Thread.sleep(5000)
but that becomes untenable to anywhere you use the obs you have to use it inside of publishSelector
Alexandru Nedelcu
@alexandru
Yeah, well, if it's a bug, we'd have to fix it.
@squadgazzz can you please open an issue? I'll take a look.
Ilya
@squadgazzz
@alexandru monix/monix#1292 thank you
@fizzy33 yeah, this works if I know about previous publishSelector call.
Cyrill Sitnikov
@InfiniteDisorder
Hello guys, have you ever experienced migrating custom akka flow stages to monix, is it possible to do it without scheduler evidence? In the example below is it possible to emit batches from OutputStream to something observable-like
val buf = new OutputStream {
     override def write(b: Int): Unit = {
        /* previously bytes were emitted to the next stage of  the flow */
    }
}
Alexandru Nedelcu
@alexandru
@InfiniteDisorder in that write, you could write those bytes into a ConcurrentSubject.
ClementWee
@ClementWee
Does Observable cancel itself on encountering an error?
Piotr Gawryś
@Avasil
@ClementWee it completes with an error if you subscribe in Task (L methods, consumeWith) and stops upstream. So it cancels in some way and it's immediate but it's not the same as canceling a subscription
Alex Michael Berry
@almibe
Is there anything in Monix to help with nested Tasks that you want to run?
ClementWee
@ClementWee
@almibe what do you mean by "nested tasks"?
Alex Michael Berry
@almibe
I think I have it sorted out. I think I was just running to issues with mixing cats effect Resources, Monix Tasks, and Monix Observables in the same api w/ added intellij idea false negatives goodness.
Česlovas Lopan
@csk157

Hello, I'm using monix circuit breaker. All in all it works great, but I'd like to let some of the exceptions happen and still be thrown without counting towards failures. Does anyone have any hints on how to achieve that?

Currently it looks similar to:

circuitBreaker
  .protect { Task... }
  .toAsync(Async[M], eff)
  .recoverWith {
    case t: ErrIDontWantToCount => Effect[M].raiseError(t)
    case NonFatal(ex) if (n - 1) > 0 =>
      retry(n - 1)
    case t => Effect[M].raiseError(FailedLastRetry(t))
  }

and ErrIDontWantToCount is handled correctly, but counts towards failures

Glen Marchesani
@fizzy33
is there a way to have a Observable that gets completed / closed after a set period of time ?
Pau Alarcón
@paualarco
@fizzy33 you could use ob.lastL.timeout(finiteDuration) to wait either for the last emitted event or the end of the timeout
Glen Marchesani
@fizzy33
The use case is. I want to have the observable work for 30 seconds and then stop wherever it is at.
Pau Alarcón
@paualarco
yep so I think that would fit in your use case
Glen Marchesani
@fizzy33
if the source observable never finishes lastL would never happen
hang on I need to read the docs for timeout :-)
ah I see
nm
tx
Piotr Gawryś
@Avasil
There is takeByTimespan
Piotr Gawryś
@Avasil
@csk157 First idea that comes to my mind is exposing these failures in Either, for instance:
import cats.syntax.monadError._

circuitBreaker
  .protect { Task().map(Right(_).onErrorRecover { case e: YourError => Left(e) }}
  .rethrow
Česlovas Lopan
@csk157
Thanks! Let me give this a go
Česlovas Lopan
@csk157
@Avasil it seems to work. Thank you!
Glen Marchesani
@fizzy33
oh snap thanks @Avasil that is exactly it. I stared at the api docs a few times now how come I never found it :-/
Glen Marchesani
@fizzy33
so my next use case (previous one takeByTimespan worked great) is if the Observable emits no items for a period of time to close / complete it.
Glen Marchesani
@fizzy33
val messages: Observable[Message] = ...
I want that to close if no messages are seen for some FiniteDurection
Glen Marchesani
@fizzy33
staring at TakeLeftByTimespanObservable which backs takeByTimespan I think I can easily make my own
Piotr Gawryś
@Avasil
@fizzy33 I think you need timeoutOnSlowUpstream
Glen Marchesani
@fizzy33
yup tx
Glen Marchesani
@fizzy33
so fwiw I am working on server sent events server and client code for jvm and js... https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events
one more I have is error handling with state. Ideally I need to handle an error AND I need the most recent value as part of that error handling (the use case is lastEventId). If the server sent event connection drops then the re-connect needs to provide the Last-Event-ID head on the reconnect. All the error handling I see is orthogonal to the actual data. Any methods that let me see the last item with the error handling ?
should I just shift an Observable[A] -> Observable[Either[Throwable,A]]
then I can process things with mapAccumulate ?
sachin-rajwade
@sachin-rajwade
I need to called Observable on a List of objects and then based on some parameter of Object call a Datasource - mainly mongo or Cassandra. Am not able to do so
Jorge
@jvican
@aleczorab_twitter not yet, but I can open source them if you want
I'm planning to do that actually, I just haven't got to it yet
Piotr Gawryś
@Avasil

@sachin-rajwade

Could you be more specific?
If you want to create an Observable from a list of objects then you can call Observable.fromIterable(list)
And then you could call mapEval (if your mongo/cassandra connector returns Task ) or mapEvalF (if it's something else), or flatMap (if it's Observable)

9 replies
Piotr Gawryś
@Avasil

@fizzy33
In case you're still wondering about it, nothing built-in comes to my mind.

I think mapAccumulate / scan can work well.
Other option is keeping the last value in a shared variable (Ref / Atomic / volatile ) or modifying OnErrorRecoverWithObservable to keep track of the latest value.
I feel like the last option should work best if you want to restart Observable in case of an error and Observable[Either[Throwable, A]] is better if you want to have an option to handle the error without restart.

Glen Marchesani
@fizzy33
@Avasil thanks your input is appreciated as a sanity check... I have a large app in the wild and wonder sometimes if there is a purely FP to do this ;-)
I am doing the AtomicRef approach, plan to migrate that to a Ref someday but not in a rush
I did have it working with Either[] and mapAccumulate and scan but it was just too messy
and seemed to affect performance more than I wanted
where the AtomicRef just worked
I like the idea of a OnErrorRecoverWithObservable that tracks the last value... That has legs...
fwiw the move to Monix / Task / OBservable has been very smooth. We are moving a ton of our scala js stuff over to it. Fixed a pretty pathological issue with a very large model (1m rows) getting saved...