Re: How to debug hang?

From: Perry Smith <pedz@easesoftware.com>
Cc: help-gnu-emacs@gnu.org, emacs-devel@gnu.org
Subject: Re: How to debug hang?
Date: Fri, 17 Nov 2006 22:13:33 -0600	[thread overview]
Message-ID: <F50DE345-5C80-4C46-8FA0-23C0E7CD328B@easesoftware.com> (raw)
In-Reply-To: <87irhdcvt8.fsf@pereiro.luannocracy.com>

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On Nov 17, 2006, at 8:50 PM, David Abrahams wrote:

>
> Hi,
>
> I'm trying to debug some kind of a hang that occurs when I try to use
> a font-lock mode I'm developing.  I can't get control back by hitting
> `C-g'.  I suspected it was a bad (combinatoric) regexp, but I added
> advice before and after re-search-forward that emitted enter/exit
> messages, and when the hang occurs I am seeing an exit message, so I'm
> guessing that's not it.  I'm quite stumped now; hoping someone can
> offer a clue.

Check out debug-on-quit.  If that doesn't work, try debug-on-signal  
and then kill the emacs from a separate window.  I'm not sure what  
that will do to your context.

There is also debug-on-entry if you have a routine that is called  
during the hang but it doesn't sounds like you do.

The other thing you might try is run emacs from a "terminal" (xterm  
or similar).  It use to be that emacs would hook the quit signal to  
control-g would actually generate a quit unix signal so it happened  
immediately (via the tty code that I so know and love :-) and not via  
some polling process.  Its been a long time since I've used it and I  
don't know if it is still hooked up that way or not.

But, while that might get you into the debugger, usually I'm too lost  
to figure out why it is hanging, what is looping, why is it not  
finishing, etc.

There is a message facility that might help too -- good ole printf  
debug technology.  (The function is called "message".)  It puts lines  
into the ever present *Messages* buffer.  So, if you ever do get  
control back, you can see what happened.

Good luck.

Perry Smith ( pedz@easesoftware.com )
Ease Software, Inc. ( http://www.easesoftware.com )

Low cost SATA Disk Systems for IBMs p5, pSeries, and RS/6000 AIX systems

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