GNU bug report logs - #56682
Fix the long lines font locking related slowdowns

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From: Eli Zaretskii <eliz <at> gnu.org>
To: Gregory Heytings <gregory <at> heytings.org>
Cc: 56682 <at> debbugs.gnu.org, monnier <at> iro.umontreal.ca, akrl <at> sdf.org
Subject: bug#56682: feature/improved-locked-narrowing 9dee6df39c: Reworked locked narrowing.
Date: Tue, 14 Feb 2023 18:55:29 +0200

> Date: Tue, 14 Feb 2023 14:59:22 +0000
> From: Gregory Heytings <gregory <at> heytings.org>
> cc: 56682 <at> debbugs.gnu.org, monnier <at> iro.umontreal.ca, akrl <at> sdf.org
> 
> 
> >> 1. There are three places (indent.c:line_number_display_width, 
> >> xdisp.c:display_count_lines_logically, fileio.c:write_region) where we 
> >> currently use
> >>
> >> record_unwind_protect (save_restriction_restore, save_restriction_save ());
> >> Fwiden ();
> >
> > I'm not sure these should be subject to locked narrowing.  They don't 
> > present performance problems with very long lines, AFAIK.
> >
> >> 2. In another place (process.c:Finternal_default_process_filter) we 
> >> currently have:
> >>
> >> /* If the output marker is outside of the visible region, save
> >>     the restriction and widen.  */
> >> if (! (BEGV <= PT && PT <= ZV))
> >>    Fwiden ();
> >>
> >> (without the "save the restriction" mentioned in the comment).
> >
> > This should be fixed to use unwind-protect of some kind, I think, and 
> > that's orthogonal to locked narrowing.
> >
> >> 3. Also, in Ferase_buffer, we do Fwiden to "delete the entire contents 
> >> of the current buffer".
> >>
> >> These five places probably need to be adapted to handle labeled 
> >> narrowings correctly.  If you agree with that, I'll write a patch to 
> >> that effect.
> >
> > I'm not sure what you mean by "adapt to".  Please tell more.
> >
> 
> Fwiden in the functions above (which are AFAICS the only places in Emacs 
> where Fwiden is called) is not prepared to the possibility of them being 
> called inside a labeled narrowing, either one installed by the long lines 
> code, or another one.  Basically we need to use a variant of 
> reset_outermost_narrowings (for the current buffer only) where we use
> 
> record_unwind_protect (save_restriction_restore, save_restriction_save ());

Ah, okay.  Please do, and thanks.

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