Hello,
I've been working on a way to turn a *Seq[Source[T]]* into *Source[Seq[T]]*
using Akka Streams 2.0. I believe I've succeeded, but I'd like people to
critique my code. Thanks in advance.
object StreamUtils {
def sequencedSource[T](sources: immutable.Seq[Source[T, Unit]]):
Source[immutable.Seq[T], Unit] =
Source.fromGraph(FlowGraph.create() { implicit builder =>
import FlowGraph.Implicits._
val sequenceGraphStage = builder.add(new
SequenceGraphStage[T](sources.size))
for ((source, index) <- sources.zipWithIndex) source ~>
sequenceGraphStage.in(index)
SourceShape(sequenceGraphStage.out)
})
}
class SequenceGraphStage[T](numInputs: Int) extends
GraphStage[UniformFanInShape[T, immutable.Seq[T]]] {
require(numInputs > 0, "1 or more inputs required")
val inputs = immutable.IndexedSeq.tabulate(numInputs)(num =>
Inlet[T]("Sequence.in" + num))
val output = Outlet[immutable.Seq[T]]("Sequence.out")
override val shape = UniformFanInShape(output, inputs: _*)
override def createLogic(inheritedAttributes: Attributes): GraphStageLogic =
new GraphStageLogic(shape) {
val elements = mutable.Buffer.empty[T]
setHandler(output, new OutHandler {
override def onPull(): Unit =
inputs.foreach { input =>
read(input) { element =>
elements += element
if (elements.size == inputs.size) {
push(output, elements.to[immutable.Seq])
elements.clear()
}
}
}
})
inputs.foreach(setHandler(_, eagerTerminateInput))
}
override val toString = "Sequence"
}
BTW, I did something similar in Streams 1.0 using FlexiMerge; the API and
boilerplate necessary was somewhat off-putting. I greatly appreciate the
cleanup in 2.0 so far.
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