Re: Some experience with the igc branch

[Eli Zaretskii <eliz@gnu.org>]

> From: Helmut Eller <eller.helmut@gmail.com>
> Cc: gerd.moellmann@gmail.com,  pipcet@protonmail.com,  ofv@wanadoo.es,
>   emacs-devel@gnu.org,  acorallo@gnu.org
> Date: Thu, 26 Dec 2024 13:24:13 +0100
> 
> On Thu, Dec 26 2024, Eli Zaretskii wrote:
> 
> >> I quite like Pip's proposal of re-installing the SIGSEGV handler with an
> >> additional sa_mask argument to block other signals.  That would be nice
> >> because a) we can do that without changing MPS and b) it's likely more
> >> efficient than callbacks.
> >
> > Are we sure doing so will solve the problem?  AFAIU, MPS can take the
> > lock before SIGSEGV is delivered, or without its being delivered at
> > all, isn't that so?
> 
> Ahem.  I completely forgot that.
> 
> An alternative to callbacks would be to implement our own lock module as
> described here:
> 
>  https://memory-pool-system.readthedocs.io/en/latest/topic/porting.html
> 
> It would probably be a clean and efficient solution; but it would
> basically be our own fork of MPS.

Probably.  I still think we should talk to the MPS folks and hear what
they suggest.

> >> It would still be nice to simplify some signal handlers, like
> >> handle_interrupt_signal, but with other signals blocked for SIGSEGV, it
> >> would all be quite independent of MPS.
> >
> > Maybe.  What bothers me more is whether the signals are delivered only
> > to the main thread or to other threads.  AFAIU, this behavior is
> > system-dependent, and currently we seem to rely on the fact that the
> > signals is delivered to the main thread.  Given that we have other
> > threads, including the MPS thread, I'm not sure we have this figured
> > out.
> 
> I thought deliver_process_signal was there to forward signals to the
> main thread but you certainly know better what it does and doesn't.

Actually, we need Paul Eggert to chime in, because he knows much more
about this than I do.  We have arrangements for when a signal is
delivered to a thread, but I think Paul said this should rarely if
ever happen.  My bother is what if the signal is delivered when the
MPS thread runs.