Is there a way to add a task to do when a coroutine scope is cancelled? e.g. ```scope.onCancellatio...

# coroutines

[CLOVIS]

Is there a way to add a task to do when a coroutine scope is cancelled?

e.g.

scope.onCancellation {
    disposeSomeStuff()
}

[Sam]

scope.launch {
    try {
        awaitCancellation()
    } finally {
        disposeSomeStuff()
    }
}

[Sam]

(But it won’t work if the scope was already cancelled)

[CLOVIS]

Thanks, do you think it's good practice?

[Sam]

It’s what I would do 😄

[jw]

You can also grab the Job and add a completion listener

https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/-job/invoke-on-completion.html

it will be invoked synchronously if the job is already canceled

[jw]

this callback is invoked on more cases so if you only care about cancelation you need to check for that

[CLOVIS]

Oh, that's great, thanks

[bezrukov]

Note invokeOnCompletion is slightly different. It will be invoked only when the job's children are completed. If any of them are not cooperative for cancellation it may be invoked with a delay (or not invoked at all). If you need a callback as soon as scope gets cancelled use the first answer (I would add atomic/undispatched launch to it to handle an already cancelled scope).

[bezrukov]

we have this ext fun (essentially the first answer):

fun CoroutineScope.invokeOnCancellation(block: () -> Unit) {
    launch(start = CoroutineStart.ATOMIC) {
        try {
            awaitCancellation()
        } finally {
            block()
        }
    }
}