akka/akka-core

Convenience for attributes on Sink

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#30,199 opened on Apr 22, 2021

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 (5 comments) (0 reactions) (0 assignees)Scala (13,277 stars) (3,547 forks)batch import
1 - triagedhelp wantedt:stream

Description

When working on https://github.com/akka/akka-persistence-cassandra/pull/888 I realized that it wasn't obvious how to set a dispatcher all the way to the Sink (and not introduce async boundary).

My first thought, when I didn't realize that the Sink is also involved, was:

.map(stuff)
.withAttributes(ActorAttributes.dispatcher(theDispatcher))
.runWith(Sink.ignore)

but it should be:

.map(stuff)
.toMat(Sink.ignore)(Keep.right)
.withAttributes(ActorAttributes.dispatcher(theDispatcher))
.run()

Contributor guide

Tech stack
scala
Domain
backend
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
basic Akka Streams knowledge
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
The issue requests adding a convenience method for applying attributes directly on `Sink`, similar to how `Flow` already supports `withAttributes`. The main work involves adding a method to `Sink` in the Scala and Java DSL (e.g., `akka stream/src/main/scala/akka/stream/scaladsl/Sink.scala` and the Java counterpart). The linked PR #888 provides context for the use case. Review existing attribute handling in `Flow` and ensure the new method returns a `Sink` with the specified attributes without introducing an async boundary.
Convenience for attributes on Sink · akka/akka-core#30199 | Good First Issue