How to tell if the response has already been sent in an exception handler?

[ojii]

If background tasks raise exceptions, these get caught by exception handlers. Normally, we can return a response in exception handlers, but if they're triggered from background tasks, the response is already sent so we get a RuntimeError: Caught handled exception, but response already started.. How can I determine whether the response has already been sent in the exception handler?

[Kludex]

A fix for this was already merged on master. See #761

[ojii]

from what I understand, that simply throws away the response, but I still can't detect if that's gonna happen or not.