```private suspend fun connectAndStartListening() ...

# coroutines

[ursus]

private suspend fun connectAndStartListening() = coroutineScope {
    val webSocketSession = ktorClient.webSocketSession("<ws://10.0.2.2:8765>")

    launch {
        for (frame in webSocketSession.incoming) {
            Log.d("Default", "frame=$frame")
        }
    }
    ... stuff
}

I want to add graceful closing when this coroutine gets cancelled. How do I listen for cancellation of this function?

launch {
   awaitCancellation()
   webSocketSession.close()
}

like this?

[Zach Klippenstein (he/him) [MOD]]

private suspend fun connectAndStartListening() {
    val webSocketSession = ktorClient.webSocketSession("<ws://10.0.2.2:8765>")

    // Assuming the session implements AutoCloseable
    webSocketSession.use {
        coroutineScope {
            launch {
                for (frame in webSocketSession.incoming) {
                    Log.d("Default", "frame=$frame")
                }
            }
            ... stuff
        }
    }
}

[ursus]

public interface WebSocketSession : CoroutineScope

so.. I dont think so?

also now im noticing, close is a suspend function

public suspend fun WebSocketSession.close(reason: CloseReason = CloseReason(CloseReason.Codes.NORMAL, ""))

[Zach Klippenstein (he/him) [MOD]]

then replace use with try/finally

[ursus]

but, which part exactly will throw? I was expecting some sort of callback api

[Zach Klippenstein (he/him) [MOD]]

Presumably whatever suspends? I’m guessing incoming? I don’t know this api so maybe I’m totally wrong

[ursus]

btw if I run a suspend function in finally; doesnt that break the structured concurrency?

[Zach Klippenstein (he/him) [MOD]]

Nope that’s fine

[Zach Klippenstein (he/him) [MOD]]

The coroutine will be in a “canceling” state while finally blocks run and join calls won’t resume until all finally blocks are done.

[ursus]

alrighty, thanks !

[ursus]

private suspend fun listenAndSend(webSocketSession: DefaultClientWebSocketSession) = coroutineScope {
    val channel = Channel<ByteArray>(capacity = Channel.BUFFERED)
    launch {
        while (isActive) {
            val bytes = queryMicrophone()
            channel.send(bytes)
        }
        channel.close()
    }

    for (bytes in channel) { <-------
        webSocketSession.send(bytes)
    }
}

If I may follow up

would you wrap this loop in launch or not?

[Zach Klippenstein (he/him) [MOD]]

No

[ursus]

@Zach Klippenstein (he/him) [MOD] sorry to resurect this but I don't think I understand what you meant.
Running a suspend function in finally seems to do nothing once the coroutine was cancelled? it hits first suspension point, which throws cancellation exception and rest is a no-op then. So basically it doesnt do anything (?)

[Zach Klippenstein (he/him) [MOD]]

Yes, anything that would normally check for cancellation and throw will continue to do so in a finally. That is extremely not “doesn’t do anything”. There are an infinite number of things you can do that don’t check coroutine cancellation, and if you do need to call something that checks you can wrap in a NonCancellable context. Closing resources is a very common use case.

[ursus]

yes but if it's a normal high level suspend function, it does nothing - so an odd choice on the ktor part