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

["Ken Manheimer" <ken.manheimer@gmail.com>]

On 8/21/06, Stuart D. Herring <herring@lanl.gov> 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")
         (header
          (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.
-- 
ken
ken.manheimer@gmail.com
http://myriadicity.net