What about callbacks? You can pass a Lisp closure to module and call the
closure from module. You may also want something like "Promise" in
JavaScript to make it sweet

Emacs Lisp Promise/A+ Implementation: https://github.com/chuntaro/emacs-promise 

Akira Kyle writes:

> I'm trying to use Emacs' Dynamic Modules in an asynchronous setting where C
> module functions run in a separate thread from Emacs' main thread which is
> responsible for calling into the module functions. The natural problem then is
> how to notify Emacs when one wants to retrieve the result of the asynchronous 
> operation from some lisp. Since the module docs explicitly say that module
> functions "may only interact with Emacs from Lisp interpreter threads (including
> the main thread) created by Emacs", it is not possible then for a separate
> module thread to interact with Emacs in an unprompted way through the module
> interface [1].
>
> This blog post [2] has a solution to this problem by sending SIGUSR1 to Emacs,
> but that feels a bit hackish and forces one to do more work to manage all the
> different possible module threads and events that one may want to signal to
> Emacs. I suppose one could also conceivably also use Emacs' dbus support but
> that still feels clunky. Maybe its possible it's possible to use Emacs lisp's 
> threads [2] to solve this but it's not clear to me how to go about doing so and
> I haven't found anyone that has done so.
>
> Does anyone know of the best way to handle this? Perhaps the module interface
> should be expanded to handle this situation?
>
> [1]
> https://www.gnu.org/software/emacs/manual/html_node/elisp/Module-Functions.html#Module-Functions
> [2]
> https://www.gnu.org/software/emacs/manual/html_node/elisp/Threads.html#Threads
> [3] https://nullprogram.com/blog/2017/02/14/


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Zihao