On Mon, 6 Jan 2020, 00:10 Stefan Monnier, <monnier@iro.umontreal.ca> wrote:

>
> The question is how quickly this stops the parsing: any delay here
> is very costly because the Elisp execution will have to sit idly waiting
> for the parser to stop before it can continue its own execution.
>

Without looking into the implementation I bet that it checks for
cancellations on each char. This means that we do not need to wait it to
stop, we just have to ensure that if it reads one more char it is from the
original content which could be achieved by caching one char ahead.

>