Hello, some of my users are getting this crash in ...

# coroutines

[Thomas]

Hello, some of my users are getting this crash in my app:

Fatal Exception: kotlinx.coroutines.flow.internal.ChildCancelledException Child of the scoped flow was cancelled

For some reason this crash does not have a stack trace (on both Firebase and Google Play). This makes it very hard to find the cause. Could someone here help me out? I am using Kotlin 1.3.41 and Coroutines 1.3.0-M2.

[Dico]

Try putting a try/catch around your application's main

[Thomas]

@Dico Not sure where to put that as I have no idea where the crash occurs. I am using coroutines everywhere in my project. I’m also not able to reproduce the crash on demand so I think this would be difficult to fix. The crash occurs on app start and the second time it’s gone.

[Dico]

I said around your main, I.e. wrap all the code from the main thread in it then introspect any errors that make it there

[louiscad]

Are you using callbackFlow or channelFlow with APIs that might continue offering values after unregistering, or have non thread-safe unregistering which could lead to race conditions where a value is offered after unregistration?

[Vsevolod Tolstopyatov [JB]]

Hi, stacktraces of cancellation exceptions are missing in the release mode.

Could you please enable debug mode (https://github.com/Kotlin/kotlinx.coroutines/blob/master/docs/debugging.md) in your application and report where this exception came from?

[Thomas]

I tried making my own combineLatest operator (it was not added, see https://github.com/Kotlin/kotlinx.coroutines/issues/1262). You can find it in the same gist. My guess it I made a mistake somewhere.

[Thomas]

No, it’s not the combineLatest operator. Still getting the exception.

[Thomas]

I think something like this is throwing the exception:

someFlow
    .switchMap { transformTheFlow(it) }
    .collect {
        doSomethingWithTheResult(it)
    }

[Thomas]

Maybe this is related? It is a different exception but could be the same bug. https://github.com/Kotlin/kotlinx.coroutines/issues/1334

[Thomas]

Maybe this is related?...

Just built Kotlin coroutines myself with this fix. Unfortunately after some time I got the crash again. So this is a different issue.