I have a Akka streams application, and I would like to emulate the
following behaviour: a node should emit the last n elements from upstream.
It should never backpressure, but instead drop the oldest elements.
The situation is as follows: there is an incoming stream of elements
`source`. A few computations are to be ran on `source`, each of which will
take some time. The results of the computations will be then zipped
together. Downstream one is interested in having the freshest results, at
the cost of skipping some elements.
An example application would be like this:
val source: Source[Double] = ???
val n: Int = ???
def computation1(xs: Seq[Double]): Double = ???
def computation2(xs: Seq[Double]): Double = ???
val g = RunnableGraph.fromGraph(FlowGraph.create() { implicit builder =>
import FlowGraph.Implicits._
val broadcast = builder.add(Broadcast[Double](3))
val merge = builder.add(ZipWith[A, B, C, (A, B, C)](Tuple3.apply))
val comp1 = Flow[Double]
.nonBlockingSliding(n)
.map(computation1)
val comp2 = Flow[Double]
.nonBlockingSliding(n)
.map(computation2)
source ~> broadcast ~> merge.in0
broadcast ~> comp1 ~> merge.in1
broadcast ~> comp2 ~> merge.in2
merge.out ~> Sink.foreach(println)
ClosedShape
})
The problem here is how to write the `.nonBlockingSliding` operation.
I have tried to use the `sliding` method, but it backpressures, so for
large values of n, the `merge` node never emits.
What would be the best way to write this? I could use `transform` using a
custom Stage, but I have the impression that some combination of `conflate`
and `sliding` would be enough
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