bug#10149: Emacs 24 hangs for several minutes with very large c++ files

[Stefan Kangas <stefan@marxist.se>]

suvayu ali <fatkasuvayu+linux@gmail.com> writes:

> Hi Emacs devs,
>
> I am seeing a weird problem. I have an automatically generated C++ class
> for some ntupled data for quick (but dirty) analysis. It has lots of
> (~1k) data members. Every time I try to navigate in that file and I
> reach the large block of text where the data members are declared[1],
> Emacs takes a long time to move the cursor (e.g. with commands like
> forward-paragraph or backward-paragraph) and the CPU usage on my
> Thinkpad X201 maxes out on one of the 4 logical cores. If I wait long
> enough (several minutes), Emacs 24 does manage to move the cursor to the
> end of the paragraph. However I don't see this problem with Emacs 23.3.1
> (or vim).
>
> I can replicate this behaviour with `emacs -Q'. The file that causes the
> issue is attached with this email. I am using Emacs from the repo.or.cz
> git mirror.
>
> commit aecaa1ffa122258c0fbc580ccbfad268ea46b89d
> Author: Andreas Schwab <schwab@linux-m68k.org>
> Date:   Sat Nov 26 10:10:36 2011 +0100
>
>     * grammars/bovine-grammar.el (bovine--grammar-newstyle-unquote):
>     Avoid warning about old-style backquote.
>
> This is how I compile emacs:
>
> In GNU Emacs 24.0.91.1 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.7)
>  of 2011-11-27 on mylaptop.example.com
> configured using `configure  '--prefix=/opt/emacs-lisp'
> '--with-selinux' '--with-imagemagick''
>
> Important settings:
>   value of $LC_ALL: nil
>   value of $LC_COLLATE: nil
>   value of $LC_CTYPE: nil
>   value of $LC_MESSAGES: nil
>   value of $LC_MONETARY: nil
>   value of $LC_NUMERIC: nil
>   value of $LC_TIME: nil
>   value of $LANG: en_IN.UTF-8
>   value of $XMODIFIERS: @im=ibus
>   locale-coding-system: utf-8-unix
>   default enable-multibyte-characters: t
>
> Since I don't actually get a backtrace, I am not sure what else I can
> provide. Please feel free to ask me if you need more information.
>
> Hope this helps.
>
> Footnotes:
>
> [1] The large chunk of commented text in the attached file

I do see a significant slowdown in navigating the file once I comment
out the block of code.  It doesn't hang for several minutes for me,
but it takes 5-10 seconds for C-v, M-v depending on where point is.

Alan, any comments on this?

Best regards,
Stefan Kangas