I m trying to track down the source of a `JobCancellationExc

Question

I m trying to track down the source of a `JobCancellationException` My crash reporting tool isn t offering any useful information and I don t quite understand this exception

Tim Malseed · Answer

```kotlinx coroutines JobCancellationException Job was cancelled unknown fileunknown method```

Tim Malseed · Answer

Looking at the breadcrumbs it looks like this occurs after `MainActivity onDestroy ` is called in my Android app So presumably someone is swiping the app away from recents potentially killing the app process

Tim Malseed · Answer

There s a coroutine that runs when the app is launched which I suspect is the source The scope used to launch this coroutine is ```CoroutineScope Dispatchers Main + job + coroutineExceptionHandler ``` Where `job` is a `SupervisorJob` and `coroutineExceptionHandler` is an instance of `CoroutineExceptionHandler` that logs errors

Tim Malseed · Answer

I m not sure if I m looking in the wrong place or the app is throwing an exception that is swallowed by coroutines or the crash is simply that the job is being cancelled Any insight would be great I m still wrapping my head around JobCancellationExceptions and CoroutineExceptionHandlers

elizarov · Answer

Turning on debug mode should help because it enables stacktrace in JCE

Tim Malseed · Answer

Thanks for the quick reply The issue here is I m not able to reproduce this crash myself

Tim Malseed · Answer

~Oh I wonder if I can ship the app it s only in alpha with debug mode on Would that be crazy ~ Just had a read of <https github com Kotlin kotlinx coroutines blob master docs debugging md> Thanks

louiscad · Answer

< Tim Malseed> Are you using `Channel` and the `offer` function

Tim Malseed · Answer

I am in some places yes

louiscad · Answer

< Tim Malseed> Then it s quite likely you have these exceptions thrown here either because you re using `consume` `consumeEach` or `consumeAsFlow ` when respectively you should not when you should use a plain `for` loop or `receive ` or when you should use `receiveAsFlow ` because you have a race condition for example in `callbackFlow` `channelFlow` or elsewhere which is this issue because you `close` or `cancel` the channel in a way or another where a `JobCancellationException` is passed as a cause

Tim Malseed · Answer

Thanks for the info