Is it possible to start a Coroutine in a flow operator so th kotlinlang #coroutines

Is it possible to start a Coroutine in a flow operator, so that when the flow completes, the Coroutine is cancelled as well? I somehow need access to the scope of the flow, right?

simon.vergauwen

08/12/2022, 10:01 AM

You can do

flow { coroutineScope { } }

. The only thing that is forbidden is

emit

from a different Coroutine, but following is valid.

flow {
  coroutineScope {
    launch { /** do something */ }
    while(true) {
      currentCoroutineContext().ensureActive()
      emit(1)
    }
  }
}

Joffrey

08/12/2022, 10:07 AM

What is your use case, actually? You might better be served by

callbackFlow

(or maybe

channelFlow

) depending on what you're trying to do

Lukas Lechner

08/12/2022, 10:16 AM

@simon.vergauwen Oh, its actually that simple 🙂 Thanks

Okay, with

coroutineScope

, the flow suspends until the launched Coroutine has completed. How can I create a Coroutine that runs concurrently with the flow?

@Joffrey My use case is that whenever someone collects from a flow that is exposed from a repository, I want to start a Coroutine that fetches data from the network and stores it in the database. The flow of the repository should emit the items that the database flow (Android Room Database) emits. So it basically should just forward the emissions from the database and also start/stop the process of updating the database on subscription/unsubscription.

Nick Allen

08/15/2022, 7:21 PM

Snippet above should work for your use case. Maybe you are emitting after the

coroutineScope

instead of inside it?

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