Modules: should_quit vs. process_input in Emacs 27

Modules: should_quit vs. process_input in Emacs 27

[Hans-Peter Deifel]

Hello Emacs hackers,

I'm writing a dynamic module in C that includes a long-running
computation. It uses `should_quit' as per the documentation to check
from time to time if the user wants to quit, in which case the
computation is immediately aborted. This works great on Emacs 26.2, but
doesn't on master: The computation just keeps on computing, no matter
how often the user presses C-g.

The git log and the info manual in master mention the new environment
function `process_inputs' that should be used instead of `should_quit'.
This does indeed work, but now the module is no longer compatible with
Emacs 26.

What should module authors in this case do to keep their modules
compatible with older Emacs versions? Conditional compilation?

Also, what's the purpose of the current `should_quit' in master, if it
doesn't work for the above use-case any more. Why doesn't it simply
behave like the following?

  process_input (env) == emacs_process_input_quit

Cheers,
HP

Re: Modules: should_quit vs. process_input in Emacs 27

[Eli Zaretskii]

> From: Hans-Peter Deifel <hpd@hpdeifel.de>
> Date: Mon, 22 Jul 2019 23:25:33 +0200
> 
> I'm writing a dynamic module in C that includes a long-running
> computation. It uses `should_quit' as per the documentation to check
> from time to time if the user wants to quit, in which case the
> computation is immediately aborted. This works great on Emacs 26.2, but
> doesn't on master: The computation just keeps on computing, no matter
> how often the user presses C-g.
> 
> The git log and the info manual in master mention the new environment
> function `process_inputs' that should be used instead of `should_quit'.
> This does indeed work, but now the module is no longer compatible with
> Emacs 26.
> 
> What should module authors in this case do to keep their modules
> compatible with older Emacs versions? Conditional compilation?

Not conditional compilation; dynamic discovery of the Emacs version in
which the module is running.  How to do that is described in the
"Module Initialization" node of the ELisp manual.

> Also, what's the purpose of the current `should_quit' in master, if it
> doesn't work for the above use-case any more. Why doesn't it simply
> behave like the following?
> 
>   process_input (env) == emacs_process_input_quit

AFAIR, because process_input processes pending input events.
Sometimes you may wish not to do that.