I think I've moved one step closer: I think I know how to weld a flow
breaker into my graph:
def watch(key: String, waitIndex: Option[Int] = None, recursive:
Option[Boolean] = None, quorum: Option[Boolean] = None):
Source[EtcdResponse, Cancellable] = {
case class WatchRequest(key: String, waitIndex: Option[Int], recursive:
Option[Boolean], quorum: Option[Boolean])
val init = WatchRequest(key, waitIndex, recursive, quorum)
val breaker: Graph[FlowShape[WatchRequest, WatchRequest], Cancellable]
= ???
Source[EtcdResponse, Cancellable](breaker) { implicit b =>
import FlowGraph.Implicits._
val initReq = b.add(Source.single(init))
val reqMerge = b.add(Merge[WatchRequest](2))
val runWait = b.add(Flow[WatchRequest].mapAsync { req =>
this.wait(req.key, req.waitIndex, req.recursive, req.quorum).map {
resp =>
(req.copy(waitIndex = Some(resp.node.modifiedIndex + 1)), resp)
}
})
val respUnzip = b.add(Unzip[WatchRequest, EtcdResponse]())
initReq ~> reqMerge.in(0)
reqMerge ~> runWait
runWait ~> respUnzip.in
breaker => {
respUnzip.out0 ~> breaker.inlet
breaker.outlet ~> reqMerge.in(1)
respUnzip.out1
}
}
}
The question now remains, how do I fabricate a Graph[FlowShape[T, T],
Cancellable] that will generate an instance of Cancellable on each
materialization connected to a PushPullStage, in such way that cancel()
would "blow the fuse" and terminate the stream?
Cheers,
Rafał
W dniu piątek, 24 kwietnia 2015 11:53:31 UTC+2 użytkownik Rafał Krzewski
napisał:
>
> Hi,
>
> I've decided to dive into the streams ;) and implemented a client for
> etcd[1] using akka http client. It worked really well, and was a lot of fun!
>
> However, I'm missing one final piece that I wasn't able to figure out: The
> client offers a watch function that returns a stream of EtcdResponses [2]
> Right now the actual returned type is Source[EtcdResponse, Unit], but
> actually I'd like the materialized value to be akka.actor.Cancellable
> that would allow the client to shut down the updates stream and release
> it's resources. I think a custom PushPullStage exposing Cancellable
> interface, inserted into the flow's feedback loop could do the job of
> shutting down the stream, but I couldn't find a way to expose the
> materialized value
> from the FlowGraph construction block. I was looking at TCP streams and
> TickSource that do return interesting materialized values, but they use
> low level private [stream] APIs so I couldn't adapt any of that to my
> high-level client code. Hints will be appreciated :)
>
> Cheers,
> Rafał
>
> [1] https://github.com/coreos/etcd
> [2]
> https://github.com/rkrzewski/akka-cluster-etcd/blob/master/etcd-client/src/main/scala/pl/caltha/akka/etcd/EtcdClient.scala#L57
>
>
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