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Re: Random idea: Debugging `quit'

From: Lars Magne Ingebrigtsen
Subject: Re: Random idea: Debugging `quit'
Date: Sun, 11 Sep 2011 23:01:12 +0200
User-agent: Gnus/5.110018 (No Gnus v0.18) Emacs/24.0.50 (gnu/linux)

Helmut Eller <address@hidden> writes:

> Not so nice, but  kill -SIGUSR2 <emacs-pid>  in shell tells Emacs to
> enter the debugger.

I didn't know that.  That sounds useful.

> Another possibility would be to set debug-on-quit permanently to t
> and at the same time set the variable debugger to some function
> that is smart enough to look at the queued events:
> (require 'cl)
> (require 'debug) ; load it now to avoid resetting debugger
> (setq debug-on-quit t)
> (setq debugger 'my-debug)
> (defun my-debug (&rest args)
>   (cond ((equal args '(error (quit)))
>        (let ((unread-events (loop while (input-pending-p)
>                                   collect (read-event nil nil 0.1))))
>          (cond ((equal (subseq unread-events -4)
>                        '(21 54 54 54)) ;  C-u 6 6 6
>                 (debug nil 'my-break))
>                (t
>                 (discard-input)
>                 (let ((debug-on-quit nil))
>                   (signal 'quit nil))))))
>       (t
>        (apply #'debug args))))

That works great!  Thanks!  It's now in my .emacs.

I think Emacs 24.2 should have something along these lines switched on
by default.  I think it would make a lot of bug reporting easier, since
it would enable users to get a backtrace on hangs very easily.

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

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