bug#65700: time when gcs-done is updated needs to be clarified

[Eli Zaretskii <eliz@gnu.org>]

> From: Shynur Xie <one.last.kiss@outlook.com>
> CC: "65700@debbugs.gnu.org" <65700@debbugs.gnu.org>
> Date: Thu, 7 Sep 2023 14:35:32 +0000
> msip_labels:
> 
> > Stefan:
> > I'd be curious to know how it affects your code.
> 
> My Emacs displays its runtime information like this:
>   <github.com/shynur/.emacs.d/issues/1#issuecomment-1671815270>
> Since it's mainly related to GC, I have it updated after each GC.

That's just causes off-by-one count of GC cycles, no?  Easy enough to
fix.

> > Stefan:
> > "Philosophically", both choices make sense (either consider
> > `post-gc-hook` as being part of the GC or consider it as external to
> > the GC).
> 
> I'm not a native English speaker.  Does the POST in `post-gc-hook'
> mean the functions will run when GC is DONE?

Its being "done" doesn't necessarily have to include updating the
count of GCs.  The main job of GC is already done by the time the hook
is called.

This is what Stefan meant when he said that philosophically it is not
clear-cut whether updating the count should be done before or after
calling the hook.

> > shynur:
> > Is this an intended behavior?  If so, I think the docstring of these
> > variables (such as `gcs-done', `gc-elapsed', ...) need to clarify
> > when the variable is updated.
> 
> And `garbage-collection-messages'.

What about it?