How do I make a custom CoroutineExceptionHandler t...

# coroutines

[martmists]

How do I make a custom CoroutineExceptionHandler that re-throws the exception that caused a job to cancel?
e.g.

coroutineScope {
    launch {
        throw NotImplementedError()  // Currently somehow deadlocks
    }

    launch {
        // ...
    }
}  
// Ideally coroutineScope exits early and also (re-)throw the NotImplementedError

[Sam]

In principle this should already work the way you described

[Sam]

If it's not, something else is going on

[martmists]

Is there any way to debug? I tried running it in the IntelliJ debugger but that doesn't help much; Most if not all of the RUNNING threads are in wait

[martmists]

I added this catch clause, which does log the error, but after rethrowing it, there doesn't seem to be anything that happens.

coroutineScope {
            for (field in operation.fields) {
                launch {
                    wrapper {
                        try {
                            map[field.alias ?: field.name] = execute(operation, defMap[field.name] ?: throw GraphQLException("Cannot query field \"${field.name}\" on type \"${operation.type}\".", field.loc), field)
                        } catch (e: GraphQLException) {
                            errors += e.errors.map { it.withParent(field.alias ?: field.name) }
                        } catch (e: Exception) {  // Added catch clause
                            e.printStackTrace()
                            throw e
                        }
                    }
                }
            }
        }

[martmists]

I figured out the issue, turns out there's some strange behavior when catching exceptions in Ktor monitoring. Will investigate more over there.

[Don Mitchell]

if you're using supervisorScope it swallows everything except CancellationException I think; so, you need to wrap your error in a throw CancellationException(e). I'm not clear on the scoping of CoroutineExceptionHandler, I know it can't "ignore" the error to allow progression bc the stack's already unwound.