Hi Peter,
Unfortunately this is one of the swampy areas where we have not good
support yet. This pattern is already implementable (Http client connection
pooling does something like this and more) but it is very error prone.
AsyncStage can work if you know what are you doing :) If you have something
that works (or almost work) share with us.
In the snippet you posted there is a problem, namely that you use
callback.invoke from foreach, and therefore you ignore any backpressure
signal from the downstream of AsyncStage. This can work, if the client Flow
does not create too much stuff for one input element, but for example if
the message you send to the client flow says "GIMME LARGE FILE", and then
you get several GB streamed back, then this will blow up memory.
-Endre
On Tue, Jun 2, 2015 at 8:35 PM, Peter Swift
wrote:
> Hello,
> I'm working on a client-side application atop tcp streams, and I'm
> curious what is the recommended approach for handling reconnects. I'm
> thinking to wrap the underlying transport flow in an AsyncStage, and then
> rematerialize the transport on completion. It would look something like
> this:
>
> class ReconnectionStage[In, Out](transport: Flow[In, Out, Any],
> maxInFlight: Int) extends AsyncStage[In, Out, Any] {
> private var inFlight = 0
> private val buffer = FixedSizeBuffer[Out](maxInFlight)
>
> private var fm: FlowMaterializer = _
> private var callback: AsyncCallback[Any] = _
> private var runnableFlow: RunnableFlow[(ActorRef, Future[Unit])] = _
>
> private var input: ActorRef = _
>
> private def connect() {
> val (ref, future) = runnableFlow.run()(fm)
> input = ref
> future.onComplete( _ =>
> callback.invoke(Reconnect))(fm.executionContext)
> }
>
> override def preStart(ctx: AsyncContext[Out, Any]) {
> fm = ctx.materializer
> callback = ctx.getAsyncCallback()
> runnableFlow = Source.actorRef(maxInFlight, OverflowStrategy.fail)
> .via(transport).toMat(Sink.foreach(callback.invoke))(Keep.both)
> }
> ...
> }
>
> It's a bit involved, and I haven't yet finished -- so I guess I'm just
> here to check if I'm even on the right track :)
>
> Cheers,
> Peter
>
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