Re: scratch/igc: Implications of MPS being asynchronous

[Eli Zaretskii]

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Cc: stefankangas@gmail.com,  pipcet@protonmail.com,  emacs-devel@gnu.org,
>   gerd@gnu.org,  eller.helmut@gmail.com
> Date: Mon, 13 Jan 2025 14:21:49 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Your opinion is that Emacs will never want to intentionally trigger GC
> > from Lisp?  Can you explain why not?  We do this with the current GC
> > quite a lot.
> 
> Here's what MPS says about mps_arena_collect in a note
> 
>   It is not normally necessary to call this function: in the unclamped
>   state, collections start automatically. However, it may be useful during
>   development and debugging: the more frequently the collector runs, the
>   sooner and more reliably errors are discovered. See General debugging
>   advice.
> 
> There are only rare situations in which I'd use igc--collect from Lisp,
> igc-stats being an example.

With the old GC, we used to call it during loadup, for example, to
make sure we don't dump garbage.  And there are other situations where
we might need that.  E.g., you added igc_on_idle for a reason, I
suppose.

> Secondly I think offering garbage-collect gives the false impression
> that it has the same semantics in old and new GC. How would one make
> sure that existing calls to garbage-collect made for the old gC are
> the right thing for igc?

Why could they not be?  I'm probably missing something.