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emacs hangs in c++ font-lock-modeo

From: Alan Mackenzie
Subject: emacs hangs in c++ font-lock-modeo
Date: Sat, 16 Apr 2005 16:50:18 +0000 (GMT)

[cc to address@hidden added.]

>From address@hidden Fri Apr 15 20:33:22 2005

> Hi,

> I have got a C++ source file that causes "GNU Emacs 21.4.1" (current Debian
> testing) to hang with 100% cpu. To reproduce the bug, load the attached
> source file and turn font-lock-mode on in C++ mode. If you move the cursor
> down, at some position, emacs will hang and accept no more keyboard inputs.

Outch!  That's nasty.  I had that happen to me a couple of years ago.

I know that everything will still be set up to their defaults, but could
you perhaps give us some more details just the same:

How powerful is your computer?  (Processor speed in MHz or GHz).

What version of CC Mode have you got?  (M-x c-version)

Did you start your session with "emacs -q --no-site-file"?  (I.e. without
your .emacs and any site-lisp.el loaded.)  If not, do you still get the
problem when you do?

Does Emacs _always_ hang up, _usually_ hang up or _sometimes_ hang up?
How long does it take after loading the file before it hangs?  Does it
free up if you leave it running 8 or 12 hours or more?

How many other buffers have you got loaded at the same time, how big are
they (a few kilobytes, or a few hundred kilobytes), what modes are they
(other C++, perhaps)?

What support mode are you using in font lock?  (C-h v
font-lock-support-mode).  Probably jit-lock-mode, the default.  Does the
problem go away if you use lazy lock instead?  (Do M-: (setq
font-lock-support-mode 'lazy-lock-mode) before loading the buffer (or put
the setq in your .emacs, or do the same thing in the pertinent customize


[OT good news:  My city council has just decided to use Debian as the
replacement for MS-Windows on its several thousand desktop PCs.  They're
hoping to start rolling it out at the end of this year.  :-]

Alan Mackenzie (Munich, Germany)

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