pjfanning commented on code in PR #1701:
URL: https://github.com/apache/pekko/pull/1701#discussion_r1929188797
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stream/src/main/scala/org/apache/pekko/stream/impl/TraversalBuilder.scala:
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@@ -380,12 +380,53 @@ import pekko.util.unused
}
}
+ /**
+ * Try to find `SingleSource` or wrapped such. This is used as a
+ * performance optimization in FlattenConcat and possibly other places.
+ * @since 1.2.0
+ */
+ @InternalApi def getValuePresentedSource[A >: Null](
+ graph: Graph[SourceShape[A], _]): OptionVal[Graph[SourceShape[A], _]] = {
+ def isValuePresentedSource(graph: Graph[SourceShape[_ <: A], _]): Boolean
= graph match {
+ case _: SingleSource[_] | _: FutureSource[_] | _: IterableSource[_] | _:
JavaStreamSource[_, _] |
+ _: FailedSource[_] =>
+ true
+ case maybeEmpty if isEmptySource(maybeEmpty) => true
+ case _ => false
+ }
+ graph match {
+ case _ if isValuePresentedSource(graph) => OptionVal.Some(graph)
+ case _ =>
+ graph.traversalBuilder match {
+ case l: LinearTraversalBuilder =>
+ l.pendingBuilder match {
+ case OptionVal.Some(a: AtomicTraversalBuilder) =>
+ a.module match {
+ case m: GraphStageModule[_, _] =>
+ m.stage match {
+ case _ if
isValuePresentedSource(m.stage.asInstanceOf[Graph[SourceShape[A], _]]) =>
+ // It would be != EmptyTraversal if
mapMaterializedValue was used and then we can't optimize.
+ if ((l.traversalSoFar eq EmptyTraversal) &&
!l.attributes.isAsync)
+
OptionVal.Some(m.stage.asInstanceOf[Graph[SourceShape[A], _]])
+ else OptionVal.None
+ case _ => OptionVal.None
+ }
+ case _ => OptionVal.None
+ }
+ case _ => OptionVal.None
+ }
+ case _ => OptionVal.None
+ }
+ }
+ }
+
/**
* Test if a Graph is an empty Source.
*/
def isEmptySource(graph: Graph[SourceShape[_], _]): Boolean = graph match {
case source: scaladsl.Source[_, _] if source eq scaladsl.Source.empty =>
true
case source: javadsl.Source[_, _] if source eq javadsl.Source.empty() =>
true
+ case EmptySource =>
true
Review Comment:
I am lost. The only way this is an optimisation is if EmptySource appears
before one or more the existing cases.
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