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OrElse stage for fallback when no elements emitted #21024

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Johan Andrén 2016-08-30 13:35:59 +02:00 • committed by GitHub
parent fbfc8b4c58
commit 012919fdb3
12 changed files with 465 additions and 7 deletions
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59
akka-stream/src/main/scala/akka/stream/scaladsl/Flow.scala
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@ -1793,6 +1793,40 @@ trait FlowOps[+Out, +Mat] {
FlowShape(merge.in(1), merge.out)
}
/**
* Provides a secondary source that will be consumed if this stream completes without any
* elements passing by. As soon as the first element comes through this stream, the alternative
* will be cancelled.
*
* Note that this Flow will be materialized together with the [[Source]] and just kept
* from producing elements by asserting back-pressure until its time comes or it gets
* cancelled.
*
* On errors the stage is failed regardless of source of the error.
*
* '''Emits when''' element is available from first stream or first stream closed without emitting any elements and an element
* is available from the second stream
*
* '''Backpressures when''' downstream backpressures
*
* '''Completes when''' the primary stream completes after emitting at least one element, when the primary stream completes
* without emitting and the secondary stream already has completed or when the secondary stream completes
*
* '''Cancels when''' downstream cancels and additionally the alternative is cancelled as soon as an element passes
* by from this stream.
*/
def orElse[U >: Out, Mat2](secondary: Graph[SourceShape[U], Mat2]): Repr[U] =
via(orElseGraph(secondary))
protected def orElseGraph[U >: Out, Mat2](secondary: Graph[SourceShape[U], Mat2]): Graph[FlowShape[Out @uncheckedVariance, U], Mat2] =
GraphDSL.create(secondary) { implicit b ⇒ secondary ⇒
val orElse = b.add(OrElse[U]())
secondary ~> orElse.in(1)
FlowShape(orElse.in(0), orElse.out)
}
/**
* Concatenates this [[Flow]] with the given [[Source]] so the first element
* emitted by that source is emitted after the last element of this
@ -2031,6 +2065,31 @@ trait FlowOpsMat[+Out, +Mat] extends FlowOps[Out, Mat] {
def prependMat[U >: Out, Mat2, Mat3](that: Graph[SourceShape[U], Mat2])(matF: (Mat, Mat2) ⇒ Mat3): ReprMat[U, Mat3] =
viaMat(prependGraph(that))(matF)
/**
* Provides a secondary source that will be consumed if this stream completes without any
* elements passing by. As soon as the first element comes through this stream, the alternative
* will be cancelled.
*
* Note that this Flow will be materialized together with the [[Source]] and just kept
* from producing elements by asserting back-pressure until its time comes or it gets
* cancelled.
*
* On errors the stage is failed regardless of source of the error.
*
* '''Emits when''' element is available from first stream or first stream closed without emitting any elements and an element
* is available from the second stream
*
* '''Backpressures when''' downstream backpressures
*
* '''Completes when''' the primary stream completes after emitting at least one element, when the primary stream completes
* without emitting and the secondary stream already has completed or when the secondary stream completes
*
* '''Cancels when''' downstream cancels and additionally the alternative is cancelled as soon as an element passes
* by from this stream.
*/
def orElseMat[U >: Out, Mat2, Mat3](secondary: Graph[SourceShape[U], Mat2])(matF: (Mat, Mat2) ⇒ Mat3): ReprMat[U, Mat3] =
viaMat(orElseGraph(secondary))(matF)
/**
* Attaches the given [[Sink]] to this [[Flow]], meaning that elements that passes
* through will also be sent to the [[Sink]].