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 🙂

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.

But if I do:

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

the

xHandlerLeaf

is not used.

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

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

👍