GNU bug report logs - #79228
30.1.90; native--compile-async sentinel can error if threads are running

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#79228: closed (30.1.90; native--compile-async sentinel can
 error if threads are running)
Date: Tue, 02 Sep 2025 15:09:01 +0000

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Your message dated Tue, 02 Sep 2025 18:07:33 +0300
with message-id <86plc8lwp6.fsf <at> gnu.org>
and subject line Re: bug#79228: 30.1.90; native--compile-async sentinel can error if threads are running
has caused the debbugs.gnu.org bug report #79228,
regarding 30.1.90; native--compile-async sentinel can error if threads are running
to be marked as done.

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From: Spencer Baugh <sbaugh <at> janestreet.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 30.1.90; native--compile-async sentinel can error if threads are
 running
Date: Tue, 12 Aug 2025 17:56:29 -0400

Other threads can run pending_funcalls if they call
accept-process-output.  This should probably not be allowed.

A specific bug is that the C core calls native--compile-async using
pending_funcalls.  If that runs on another thread, then the processes
created in native--compile-async are locked to that other thread.  Then
the sentinels for those processes error when they call
accept-process-output on the processes while on yet another thrad.  Or
something like that; the sentinels were definitely erroring with the
"Attempt to accept output from process %s locked to thread %s" error.

This can be reproduced somewhat reliably by causing the C code to start
async native compilation while there are other threads running.  Sorry
for not making a full reproduction, but I think it's fairly
self-explanatory, and having pending_funcalls run on other threads is
clearly wrong.

[Message part 3 (message/rfc822, inline)]

From: Eli Zaretskii <eliz <at> gnu.org>
To: Spencer Baugh <sbaugh <at> janestreet.com>
Cc: dmitry <at> gutov.dev, acorallo <at> gnu.org, johnw <at> gnu.org,
 79228-done <at> debbugs.gnu.org
Subject: Re: bug#79228: 30.1.90; native--compile-async sentinel can error if
 threads are running
Date: Tue, 02 Sep 2025 18:07:33 +0300

> From: Spencer Baugh <sbaugh <at> janestreet.com>
> Cc: dmitry <at> gutov.dev,  acorallo <at> gnu.org,  johnw <at> gnu.org,  79228 <at> debbugs.gnu.org
> Date: Tue, 02 Sep 2025 10:40:53 -0400
> 
> Eli Zaretskii <eliz <at> gnu.org> writes:
> 
> >> From: Spencer Baugh <sbaugh <at> janestreet.com>
> >> Cc: dmitry <at> gutov.dev,  acorallo <at> gnu.org,  johnw <at> gnu.org,  79228 <at> debbugs.gnu.org
> >> Date: Tue, 02 Sep 2025 09:18:12 -0400
> >> 
> >> > And it's unjustified, since if worse comes to worst, we can simply
> >> > unlock the process that performs async compilation.  No need to reach
> >> > far-fetched conclusions about processes in general because of this
> >> > specific case.
> >> 
> >> Okay, then this patch should fix the bug.
> >
> > But does it?  You've brought up the issue, so presumably you have a
> > way of recreating the problem.
> 
> Not easily, but fine, I did some more work to figure out a reliable
> reproduction:
> 
> 1. Delete eln-cache
> 2. emacs -Q --eval '(dotimes (_ 5) (make-thread (lambda () (while t (sit-for 1)))))'
> 3. Observe errors in *Messages* from native compilation
> 
> > Then please try this patch and tell whether it indeed solves the
> > problem.
> 
> Yes, it does.

Thanks, installed on master, and closing the bug.

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