You can achieve this by using Sink.last which will materialize into a
Future[T] that completes with the last element emitted.
It does however not complete the promise with the last element on failures,
this can be remedied by prepending it with a .recoverWithRetries(0, { case
_ => Source.empty }) making sure any upstream failure leads to a completion
of the stream.
--
Johan
Akka Team
On Sat, Jul 29, 2017 at 8:17 AM, Alexey Shuksto <[email protected]> wrote:
> Hello hAkkers,
>
> In our project we use some number of flows that follow same building logic:
> ```
> val input: Source[T, NotUsed] = ???
> val output = input.runWith(BroadcastHub.sink)
>
> output.runWith(Sink.ignore)
> ```
>
> Sink.ignore here used to prevent BroadcastHub inner buffer overflow and,
> also, to dump out old stream elements as they are usually do not matter.
>
> But in some rare cases we need to provide to clients of our source 'the
> last seen element' -- the last element which passed our flow before client
> materialization of BroadcastHub' Source.
>
> Currently it is done via some private volatile var:
>
> ```
> @volatile private var last: Option[T] = None
> _output.runForeach(e => last = Some(e))
>
> val output = _output.prepend(Source.lazily(() => last).collect { case
> Some(e} => e})
> ```
>
> I wonder maybe there is better way to do so, without mutable state and
> stuff?
>
> --
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>>>>>>>>>> Read the docs: http://akka.io/docs/
>>>>>>>>>> Check the FAQ:
>>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html
>>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user
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