``` val xHandlerParent = CoroutineExceptionHandler...

# coroutines

[streetsofboston]

val xHandlerParent = CoroutineExceptionHandler { c, e ->
    println("Parent Handled Crash")
}

val xHandlerLeaf = CoroutineExceptionHandler { c, e ->
    println("Leaf Handled Crash")
}

fun main() {
    CoroutineScope(xHandlerParent).launch(xHandlerLeaf) {
        delay(1000)
        throw Exception("Some Exception 1")
    }

    Thread.sleep(2000)
}

prints out Leaf Handled Crash.

However, I expected the output to be Parent Handled Crash, because an exception bubbles up to the top-most parent and CoroutineExceptionHandler of that top-most parent should be used.

If I replace CoroutineScope(xHandlerParent). ... with runBlocking { ... }, the xHandlerLeaf is not used, as I expected, because the top-most parent is used and that is a scoped-parent that just throws the exception up the call-stack.

I’m not sure if this is a bug or if I don’t understand how exceptions are handled 🙂

[yousefa2]

Your xHandlerLeaf handles the exception which stops it from propagating to it's parent. That's why you don't get it in the parent.

[streetsofboston]

But if I do:

fun main() {
    runBlocking{ 
        launch(xHandlerLeaf) {
            delay(1000)
            throw Exception("Some Exception 1")
        }
    }
    Thread.sleep(2000)
}

the xHandlerLeaf is not used.

[streetsofboston]

According to Roman:
https://kotlinlang.slack.com/archives/C1CFAFJSK/p1556289120231200?thread_ts=1556225617.217800&cid=C1CFAFJSK

and

https://kotlinlang.slack.com/archives/C1CFAFJSK/p1556289713232000?thread_ts=1556225617.217800&cid=C1CFAFJSK

It bubbles up to the top-most parent and the CoroutineExceptionHandler of that parent is used.

[streetsofboston]

When I change the example to this, the xHandlerParent does handle the exception, as I expect:

fun main() {
    CoroutineScope(Dispatchers.Default).launch(xHandlerParent) {
        launch(xHandlerLeaf) {
            delay(1000)
            throw Exception("Some Exception 1")
        }
    }

    Thread.sleep(2000)
}

[Martín Ickowicz]

as far I know the CoroutineExceptionHandler consumes the exception and does not propagates it
in your last example you are throwing a new exception, which is caught by the parent scope

[streetsofboston]

I created an issue for this 🙂
https://github.com/Kotlin/kotlinx.coroutines/issues/1157

[Martín Ickowicz]

👍