bug#18696: Emacs freezes for a while visitin Conf (.ini)) buffers

bug#18696: Emacs freezes for a while visitin Conf (.ini)) buffers

[Angelo Graziosi]

I have see this trying to visit Cygwin setup.ini files [*], for example:

   ftp://mirrors.kernel.org/sourceware/cygwin/x86_64/setup.ini


(it is a file of about 2.5 MiB).

After C-x C-f setup.ini, Emacs freezes (or hangs, if you prefer) and 
does not respond for a while (> 1 minute), CPU is at 80-100%. Then it 
works fine. Maybe it is processing the file but I wonder if this 
'freezing' is to be expected.

I have experimented this with Cygwin and MSYS2-MinGW64 builds.


Ciao,
  Angelo.

---
[*] Mode line shows it is in Config[Colon] mode

bug#18696: Emacs freezes for a while visitin Conf (.ini)) buffers

[Eli Zaretskii]

> Date: Sun, 12 Oct 2014 10:24:18 +0200
> From: Angelo Graziosi <angelo.graziosi@alice.it>
> 
> I have see this trying to visit Cygwin setup.ini files [*], for example:
> 
>    ftp://mirrors.kernel.org/sourceware/cygwin/x86_64/setup.ini
> 
> 
> (it is a file of about 2.5 MiB).
> 
> After C-x C-f setup.ini, Emacs freezes (or hangs, if you prefer) and 
> does not respond for a while (> 1 minute), CPU is at 80-100%. Then it 
> works fine. Maybe it is processing the file but I wonder if this 
> 'freezing' is to be expected.

If this is in "emacs -Q", then I cannot reproduce this in a MinGW
build.  (You didn't say which version, so I tried the 24.3.94 pretest
and a recent trunk.)

If this is not in "emacs -Q", there's likely some optional feature
that causes that.

In any case, attaching a debugger during the freeze and looking what
does the main thread do should shed some light on this.

bug#18696: Emacs freezes for a while visitin Conf (.ini)) buffers

[Angelo Graziosi]

Il 12/10/2014 10:36, Eli Zaretskii ha scritto:
>
> If this is not in "emacs -Q", there's likely some optional feature
> that causes that.

Indeed.. it is this in my initialization file:

   (which-function-mode t)


and, considering the structure of that setup.ini file, this 'freezing' 
could be expected..


Thanks,
  Angelo.

bug#18696: Emacs freezes for a while visitin Conf (.ini)) buffers

[Stefan Monnier]

> Indeed.. it is this in my initialization file:
>   (which-function-mode t)
> and, considering the structure of that setup.ini file, this 'freezing' could
> be expected..

Actually IIUC which-function-mode shouldn't cause such a slow down.
If it does, it's probably because the major mode doesn't have special
support for which-function-mode, so it falls back on using imenu's
support, i.e. it needs to scan the whole buffer.

This said, scanning the whole buffer shouldn't be that sow, unless you
really have very many sections.  So it might also simply be a bug in the
way the major mode supports imenu (e.g. the regexp used is inefficient).


        Stefan

bug#18696: Emacs freezes for a while visitin Conf (.ini)) buffers

[Lars Ingebrigtsen]

Stefan Monnier <monnier@IRO.UMontreal.CA> writes:

> Actually IIUC which-function-mode shouldn't cause such a slow down.
> If it does, it's probably because the major mode doesn't have special
> support for which-function-mode, so it falls back on using imenu's
> support, i.e. it needs to scan the whole buffer.
>
> This said, scanning the whole buffer shouldn't be that sow, unless you
> really have very many sections.  So it might also simply be a bug in the
> way the major mode supports imenu (e.g. the regexp used is inefficient).

I can reproduce this problem in Emacs 28:

curl https://mirrors.kernel.org/sourceware/cygwin/x86_64/setup.ini > /tmp/setup.ini
./src/emacs -f which-function-mode -Q /tmp/setup.ini
y

Emacs hangs completely, and even `C-g' doesn't help.

The major mode here is conf-colon-mode, which does:

  (setq-local imenu-generic-expression
	      `(("Parameters" "^[ \t]*\\(.+?\\)[ \t]*:" 1)
	        ,@(cdr imenu-generic-expression))))

And, indeed, removing that make the file open in a couple of seconds
instead of taking forever (where "forever" is defined as "longer than I
had patience to wait").

Hm...  That regexp does have some backtracking in it, but this is
an 18MB file where 99.997% of the lines match the regexp:

sdesc: "Debug info for 2048-cli"
ldesc: "This package contains files necessary for debugging the
2048-cli package with gdb."
category: Debug
requires: cygwin-debuginfo
version: 0.9.1-1

etc.

So no matter how efficient the regexp is, it's gonna hang here.

Perhaps `imenu-default-create-index-function' should just give up after
spending more than x seconds?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#18696: Emacs freezes for a while visitin Conf (.ini)) buffers

[Andreas Schwab]

On Aug 19 2021, Lars Ingebrigtsen wrote:

> 	      `(("Parameters" "^[ \t]*\\(.+?\\)[ \t]*:" 1)

Does that work better?

                              "^[ \t]*\\([^ \t].*?\\)[ \t]*:"

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

bug#18696: Emacs freezes for a while visitin Conf (.ini)) buffers

[Lars Ingebrigtsen]

Andreas Schwab <schwab@linux-m68k.org> writes:

> On Aug 19 2021, Lars Ingebrigtsen wrote:
>
>> 	      `(("Parameters" "^[ \t]*\\(.+?\\)[ \t]*:" 1)
>
> Does that work better?
>
>                               "^[ \t]*\\([^ \t].*?\\)[ \t]*:"

It's probably an improvement, but it's still very slow.  (I.e., I
stopped it after half a minute, and it was still going.)

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#18696: Emacs freezes for a while visitin Conf (.ini)) buffers

[Lars Ingebrigtsen]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> Perhaps `imenu-default-create-index-function' should just give up after
> spending more than x seconds?

I've now done this in Emacs 28.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no