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Re: blink-cursor-end sometimes fails and disrupts pre-command-hook

From: Ken Manheimer
Subject: Re: blink-cursor-end sometimes fails and disrupts pre-command-hook
Date: Tue, 22 Aug 2006 17:12:35 -0400

On 8/21/06, Stuart D. Herring <address@hidden> wrote:
> that said, i had failed to find/realize that debug-on-signal would
> cause a debug session at the point of error within the condition case.
>  while not quite what i'm seeking, that will be helpful.  is there a
> reasonable way to substitute a function for the debug session, so it
> could stash a backtrace and proceed on, rather than invoking user
> intervention?

C-h v debugger

Does that help?

that was the final piece i needed.

i've just barely started using it, but my post-command-hook has this fragment:

  (condition-case failure
         (when allout-widgets-changes-record
           (let* ((debug-on-signal t)
                  (debug-on-error t)
                  (debugger 'allout-widgets-postcommand-hook-error-handler)
             [process the pending changes]
    (error (setq allout-widgets-changes-record nil))

and the handler looks like this:

(defun allout-widgets-postcommand-hook-error-handler (mode args)
 "Process errors which occurred within the extent of a command hook.

We store a backtrace of the error information in the variable,
`allout-widgets-last-hook-error', unset the error handlers, and
reraise the error, so that processing continues to the
encompassing condition-case."
 ;; first deconstruct special error environment so errors here propagate
 ;; to encompassing condition-case:
 (setq debugger 'debug
       debug-on-error nil
       debug-on-signal nil)
 (let* ((bt (with-output-to-string (backtrace)))
        (this "allout-widgets-postcommand-hook-error-handler")
         (format "allout-widgets-last-hook-error stored and posted, %s/%s %s"
                 this mode args
                 (format-time-string "%e-%b-%Y %r" (current-time)))))
   ;; post to *Messages* then immediately replace with more compact notice:
   (message (setq allout-widgets-last-hook-error
                  (format "%s:\n%s" header bt)))
   (message header) (sit-for allout-widgets-hook-error-post-time)
   ;; reraise the error, or one concerning this function if unexpected:
   (if (equal mode 'error)
       (apply 'signal args)
     (error "%s: unexpected mode, %s %s" this mode args))))

i expect this to be very helpful tracking down errors while making my
post-command-hook a "good citizen", unlikely to disrupt the hook due
to uncaught errors.

thanks all for pointing out what i needed to do to record backtraces
at the point of failure.

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