Hi everyone,
we are currently integrating Akka-Streams in an application.
Looking at the current Flow DSL/API, I can see that Transformers
(Flow#transform) allow to *synchronously* produce a number of
output-messages from 1 message.
abstract class Transformer[-T, +U] {
* /***
* * Invoked for each element to produce a (possibly empty) sequence of*
* * output elements.*
* */*
def onNext(element: T): *immutable.Seq[U]*
Semantically, the Flow remains a Flow[U] - not a Flow[Seq[U]] - despite
multiplying the incoming message. (Great!)
Is there also a way to achieve the same thing *asynchronously *in a Flow
(i.e. transform a single message into multiples)?
>From what I've seen, the FlowDSL supports mapFuture which allows async
computation of a single output message:
* /***
* * Transform this stream by applying the given function to each of the
elements*
* * as they pass through this processing step. The function returns a
`Future` of the*
* * element that will be emitted downstream. As many futures as requested
elements by*
* * downstream may run in parallel and may complete in any order, but the
elements that*
* * are emitted downstream are in the same order as from upstream.*
* */*
def mapFuture[U](f: T ⇒ Future[U]): Flow[U]
Again, the Flow remains a Flow[U] - despite the async computation of the
output element.
Naturally mapFuture follows the semantics of the map operation and converts
1 input msg into 1 output message.
Using MapFuture to produce a Seq[U] would alter the Flow from Flow[U] to
Flow[Seq[U]].
Following processors in that Flow would have to deal with Sequences instead
of single messages.
This somewhat defies the purpose of backpressure.
Maybe I am missing another function of the Flow DSL, but I haven't found
it...
Thanks for any help,
-Thomas
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