Hello, I have a hot flow (MutableSharedFlow) and w...

# coroutines

[Christopher Porto]

Hello, I have a hot flow (MutableSharedFlow) and was wondering why I'm required to launch a new coroutine from a new scope when calling collect for the logic to continue? e.g

suspend fun func1() = CoroutineScope(Dispatchers.Default).launch {
    func2()
    println("Not called")
}
suspend fun func2() = coroutineScope {
    launch {
        someFlow.collect { logic.invoke(it) }
    }
}

[Eric Chee]

Because MutableSharedFlow is hot, it "never" closes. Collect is like an infinite for loop that will keep collecting until the last item is emitted. In a Cold Flow of 1,2,3 it will collect 3 times and then close and Not Called will be printed. But in a hot flow (shared or state flow), it stays active even after emitting N objs. So your collect function is waiting for the next item to be emitted

See: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/-shared-flow/

Shared flow never completes. A call to Flow.collect on a shared flow never completes normally, and neither does a coroutine started by the Flow.launchIn function. An active collector of a shared flow is called a subscriber.

[Christopher Porto]

I get that, I just assumed since I launched it in new coroutine it would handle collection on the new coroutine and allow existing one to continue but seems not.
Is this because with the way I'm launching new coroutine, it's using context that has previous coroutine?

[Casey Brooks]

coroutineScope { } will suspend as long as there are any other coroutines still running it in. Since the MutableSharedFlow never completes as mentioned above, the launch { } will continue to run forever, and thus the coroutineScope { } will also suspend indefinitely

[Christopher Porto]

Ah ok yeah makes sense, guess I'll launch in new scope or pass scope, thank you

[Casey Brooks]

What you probably meant to do instead is: fun CoroutineScope.func2() = launch { }. a function marked suspend implies that it will run until whatever inside it is finished. In contrast, by removing suspend and requiring a CoroutineScope receiver, you’re implying that the method is a “fire-and-forget” that will not suspend execution of the other stuff in the spot where it is called

[Christopher Porto]

Ah well that's an easy way to pass the scope lol, thank you 👍