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Re: Different behaviour while debugging?
From: |
Thorsten Jolitz |
Subject: |
Re: Different behaviour while debugging? |
Date: |
Wed, 20 Feb 2013 16:45:35 +0100 |
User-agent: |
Gnus/5.130002 (Ma Gnus v0.2) Emacs/24.2 (gnu/linux) |
"Drew Adams" <drew.adams@oracle.com> writes:
>> I have the very strange case that a program - in some special
>> situation
>> - does not work as expected, but when I instrument the relevant
>> function(s) for edebug and single-step through them, everythings works
>> as expected and the output is fine.
>>
>> There are no errors involved, so 'toggle-debug-on-error does not help.
>> Its just that the program should put a buffer temporarily into a given
>> major-mode and uncomment some comment-lines with 'uncomment-region'
>> before turning-on Org-mode.
>
> Yes, it can happen that using the debugger gives you different behavior,
> especially when there are changes of selected window or current buffer or
> frame
> focus, or there is interaction with a timer or some events. It's a case of
> the
> observer affecting the observation, in some sense.
>
> The debugger is pretty useful most of the time, but there are cases where you
> need to find another solution. Typically you can insert calls to `message' in
> the code to be debugged, perhaps with accompanying `sleep-for' or `sit-for'
> calls.
I inserted 'message calls in every condition-case of 'cond, and the
*Messages* buffer showed that the correct condition-cases are simply not
entered when run in normal mode, but are entered when in debugging mode.
> Before you do that, however, try the normal Emacs debugger, `debug', instead
> of
> `edebug'. You can use `M-x debug-on-entry' to do that. Or you can insert
> calls
> `(debug)' in the code itself. See the manual or `C-h f debug' for more info
> about using `debug'.
I tried `M-x debug-on-entry', and just like with edebug, everything
works fine as expected.
Here the relevant code part with the message calls:
,--------------------------------------------------------------------------------
| [...]
| (while (not (eobp))
| (message "Entering while-loop ...")
| (cond
| ;; empty line (do nothing)
| ((looking-at "^[[:space:]]*$"))
| ;; comment line after comment line or at
| ;; beginning of buffer
| ((and
| (message "Before sleep [comline after comline or bobp] ...")
| (progn (sleep-for 1)
| (message "After sleep [comline after comline or bobp] ..."))
| (message "Before checking condition [comline after comline or bobp]
...")
| (save-excursion
| (eq (comment-on-line-p) (point-at-bol)))
| (or (bobp) last-line-comment-p))
| (message "After checking condition [comline after comline or bobp] ...")
| (message "Entering comline after comline or bobp ...")
| (uncomment-region (point-at-bol) (point-at-eol))
| (setq last-line-comment-p t))
| [...]
`--------------------------------------------------------------------------------
Here the different - but only partly correct - output when using sleep
for 1 second:
,--------------------------------------------------------------
| Entering outorg-convert-to-org....
| html-mode
| Entering while-loop ...
| Before sleep [comline after comline or bobp] ...
| After sleep [comline after comline or bobp] ...
| Before checking condition [comline after comline or bobp] ...
| Entering codeline after codeline ....
| Entering while-loop ... [2 times]
| Before sleep [comline after comline or bobp] ...
| After sleep [comline after comline or bobp] ...
| Before checking condition [comline after comline or bobp] ...
| Entering comline after codeline ....
| Entering while-loop ... [2 times]
| Before sleep [comline after comline or bobp] ...
| After sleep [comline after comline or bobp] ...
| Before checking condition [comline after comline or bobp] ...
| Entering codeline after comline ....
`--------------------------------------------------------------
here again the entirely incorrect output after outcommenting
,-------------------------------------------------------------
| (progn (sleep-for 1)
| (message "After sleep [comline after comline or bobp] ..."))
`-------------------------------------------------------------
in the code example above:
,--------------------------------------------------------------
| Entering outorg-convert-to-org....
| html-mode
| Entering while-loop ...
| Before sleep [comline after comline or bobp] ...
| Before checking condition [comline after comline or bobp] ...
| Entering codeline after codeline ....
| Entering while-loop ... [2 times]
| Before sleep [comline after comline or bobp] ...
| Before checking condition [comline after comline or bobp] ...
| Entering codeline after codeline ....
| Entering while-loop ... [2 times]
| Before sleep [comline after comline or bobp] ...
| Before checking condition [comline after comline or bobp] ...
| Entering codeline after codeline ....
`--------------------------------------------------------------
from this evidence, I would conclude that slowing down the program by 1
second makes it partly behaving correct, but *really* slowing it down by
single-stepping in the debugger (no matter if debug or edebug) makes it
behave correctly.
Not really what I would expect...
--
cheers,
Thorsten
Re: Different behaviour while debugging?, Andreas Röhler, 2013/02/22