Re: MPS: weak hash tables

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 06 Jul 2024 09:23:27 +0000
> From: Pip Cet <pipcet@protonmail.com>
> Cc: gerd.moellmann@gmail.com, eller.helmut@gmail.com, emacs-devel@gnu.org
> 
> On Saturday, July 6th, 2024 at 06:46, Eli Zaretskii <eliz@gnu.org> wrote:
> > Thanks, but why is this important or interesting? We are not going to
> > add native threads to Emacs.
> 
> We do want other threads to be able to access MPS-managed memory, don't we?

We do?  Do you mean Lisp threads (created via make-thread)?  Those run
via a different machinery, and should be registered with MPS.

> And the bugs it has caught so far were actual bugs. I believe this is true even for the specpdl thing, though we could avoid that by trusting our thread data more.

You could easily be led astray with this code, since AFAIU it doesn't
work like Emacs should be working.

> > Also, AFAIU, MPS docs says to register each thread with it, and your
> > code doesn't, AFAICT.
> 
> It needs to be registered as a root if it is one. This one isn't. It also needs to be able to be suspended, but on pthreads that's handled automatically.

I have no idea what that means and why it is true, but then I don't
understand MPS well enough.

> You're correct, though, that it's possible this will crash on code that can't actually crash without the extra thread. We need to look at each crash and decide whether it is.

Why not try first the code that will definitely run in Emacs and
should work correctly?  Once that is solved, we can later go to more
exotic test cases.