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Re: Opportunistic GC

From: Pip Cet
Subject: Re: Opportunistic GC
Date: Thu, 11 Mar 2021 07:55:30 +0000

On Wed, Mar 10, 2021 at 8:48 PM Eli Zaretskii <eliz@gnu.org> wrote:
> > From: Pip Cet <pipcet@gmail.com>
> > Date: Wed, 10 Mar 2021 20:25:04 +0000
> > Cc: Stefan Monnier <monnier@iro.umontreal.ca>, Andrea Corallo 
> > <akrl@sdf.org>, emacs-devel@gnu.org
> >
> > > There are other potential complications with this, related to
> > > threads.  Posix says 'fork' only copies a single thread, the one that
> > > called it, but what if that single thread is not the main thread?
> >
> > Why would that be a problem?
> Well, I mentioned one aspect that should be considered below.  There
> are probably others, as we never intended for one of these threads to
> be left alone.  E.g., what about error handling? non-main threads have
> a very simplistic one.

GC doesn't throw, though, and we're in a non-returning function.

> > > In
> > > Emacs nowadays a non-main Lisp thread can trigger GC.  What happens to
> > > the mutexes we use in the threads machinery when we fork like that?
> >
> > In the child, they're irrelevant
> They are?  Don't you intend to send the results to the parent process?

I do intend to do that. I'm currently using write synchronously, and I
don't see a problem with that.

> or read some stuff from the parent?

Not right now, no.

> Doesn't that mean you'd need to
> call pselect?

Not at present, no. But even if I did, how would that make mutexes relevant?

> > Everything should be fine...
> Famous last words ;-)



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