A source that will subscribe to a TopicTopic and stream messages published to the topic.

Actor interop operators

The source can be materialized multiple times, each materialized stream will stream messages published to the topic after the stream has started.

Note that it is not possible to propagate the backpressure from the running stream to the pub sub topic, if the stream is backpressuring published messages are buffered up to a limit and if the limit is hit the configurable OverflowStrategy decides what happens. It is not possible to use the Backpressure strategy.


This operator is included in:

val AkkaVersion = "2.6.19"
libraryDependencies += "com.typesafe.akka" %% "akka-stream-typed" % AkkaVersion
def versions = [
  ScalaBinary: "2.13"
dependencies {
  implementation platform("com.typesafe.akka:akka-bom_${versions.ScalaBinary}:2.6.19")

  implementation "com.typesafe.akka:akka-stream-typed_${versions.ScalaBinary}"



Reactive Streams semantics

emits a message published to the topic is emitted as soon as there is demand from downstream

completes when the topic actor terminates

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