Re: scratch/igc: Implications of MPS being asynchronous

[Eli Zaretskii]

> From: Stefan Kangas <stefankangas@gmail.com>
> Date: Sun, 12 Jan 2025 21:59:28 +0000
> Cc: pipcet@protonmail.com, emacs-devel@gnu.org, gerd@gnu.org, 
>       eller.helmut@gmail.com
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: Stefan Kangas <stefankangas@gmail.com>
> >> Date: Sun, 12 Jan 2025 16:55:54 +0000
> >> Cc: pipcet@protonmail.com, emacs-devel@gnu.org, gerd@gnu.org,
> >>    eller.helmut@gmail.com
> >>
> >> (IMHO, the code organization is a bit funny here, because
> >> garbage_collect() doesn't do what it says on the tin.  I don't think
> >> it's worth addressing that right now though.  Maybe it's worth taking a
> >> second look after merging.)
> >
> > If we want to add igc_collect somewhere which is called by
> > garbage-collect, we should add it to garbage_collect, because what you
> > call "funny" here is quite confusing.  Are there any good reasons not
> > to call igc_collect from garbage_collect?
> 
> AFAIU, MPS should decide when to GC, not maybe_gc.

OK, but then the non-mark-and-sweep part should be factored out of
garbage_collect into a separate function, which should be called from
garbage-collect.

IOW, the fact that with MPS we want to do some part of
garbage_collect, but not the other, doesn't mean a function called
"garbage_collect" should not collect garbage when MPS is used, because
that's very confusing and unclean, IMO.

Btw, which control path triggers calls to garbage_collect in the MPS
build?  The various memory-related cleanups we do in garbage_collect,
like compacting buffer text, font caches, and buffer-undo-lists, are
important to be done, so they should not be called only from
garbage-collect.  I seem to be unable to make Emacs enter
garbage_collect without invoking garbage-collect from Lisp or
manually.  If that means we never compact all those memory resources,
it's not good, I think?

Or what am I missing?