Hi guys, I’m experimenting exception handling insi...

# coroutines

[Andrea Giuliano]

Hi guys, I’m experimenting exception handling inside the launch, and I’ve created a very small test to do this

@Test
    fun testingScope() = runBlocking {
        myfun1()
    }

    suspend fun myfun1() = coroutineScope {
        val handler = CoroutineExceptionHandler { _, exception ->
            println("CoroutineExceptionHandler got $exception")
        }

        launch(handler) {
            throw Exception()
        }
    }

the test is failing because the exception gets bubbled up to the runblocking although I’m using an exception handler. Doing some debugging I’ve seen that the handler is set in the right child context, but still never called. Does anybody know why?

[sean]

CoroutineExceptionHandler only works when installed at the root coroutine (or direct child of a SupervisorJob)

https://kotlinlang.org/docs/reference/coroutines/exception-handling.html#coroutineexceptionhandler

[Andrea Giuliano]

ah! gotcha, thanks for pointing it out, didn’t know that. So in general when you are in an inner context it’s a good practice to use a try catch instead?

[sean]

If I'm planning on catching an exception I catch it on the await() call returned from async { } within a supervisorScope

[sean]

otherwise, you can try catch within the coroutine itself no problem

[Evan R.]

Alternatively coroutineScope rethrows exceptions from launched coroutines so you can wrap that in a try catch as well

[Andrea Giuliano]

for future reference, if you use supervisedScope then you can inject the errorHandler and it works as expected