From: Derek Upham <sand@blarg.net>
To: "Stefan Monnier" <monnier@IRO.UMontreal.CA>
Cc: emacs-devel@gnu.org
Subject: Re: read_char() does not detect, handle special-event-map buffer changes
Date: Thu, 07 Feb 2013 20:39:42 -0800 [thread overview]
Message-ID: <87haln1ks1.fsf@priss.frightenedpiglet.com> (raw)
In-Reply-To: <jwvsj58cd2l.fsf-monnier+emacs@gnu.org>
Stefan Monnier writes:
>> in a separate terminal. Move focus back to Emacs before the signal goes
>> out. Hit `q' in the new buffer and Emacs will complain about "*foo*"
>> being read-only. The second time you hit `q', Emacs will exit view mode
>> and bury the buffer.
>
> I think this is a known problem: the set of active keymaps is determined
> at the end of the previous command, so any change performed via
> something like a special-event-map binding or a process-filter will bump
> into this problem (you don't even need to switch-to-buffer, just
> enabling view-mode is sufficient).
>
> It's a bug: we should instead wait until the first key is pressed
> before figuring out the active keymaps.
> Problem is, this bug is in read_key_sequence, which is a pretty
> scary function.
>
> In the mean time, you can work around the bug by adding to
> unread-command-event (from your sigusr1-handler) a dummy event that is
> bound in global-map to something like `ignore'.
>
>
> Stefan
Did you see my comment in the original email? read_char() is already
trying to detect changed keymaps.
if (current_buffer != prev_buffer)
{
/* The command may have changed the keymaps. Pretend there
is input in another keyboard and return. This will
recalculate keymaps. */
c = make_number (-2);
goto exit;
}
else
goto retry;
The bug is happening because the test is flawed: current_buffer and
prev_buffer are the same, so Emacs doesn't think it needs to recalculate
anything. It loops back to the top of read_char() and reads another
character with the same keymap.
Removing the retry case and exiting every time fixes the problem:
/* The command may have changed the keymaps. Pretend there
is input in another keyboard and return. This will
recalculate keymaps. */
c = make_number (-2);
goto exit;
This removes a flawed optimization and returns a documented value. It
doesn't touch read_key_sequence, so that risk goes away. If we were
getting special events at a high rate of speed this /might/ cause a
slowdown, but nothing in the special events table seems to be used that
way---and I expect that the extra time spent popping back up to
read_key_sequence for the retry will still be very fast compared to the
time spent in the Emacs Lisp callback.
Derek
--
Derek Upham
sand@blarg.net
next prev parent reply other threads:[~2013-02-08 4:39 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-04 8:36 read_char() does not detect, handle special-event-map buffer changes Derek Upham
2013-02-07 6:33 ` Derek Upham
2013-02-07 14:50 ` Derek Upham
2013-02-07 16:25 ` Stefan Monnier
2013-02-08 4:39 ` Derek Upham [this message]
2013-02-08 7:35 ` Michael Albinus
2013-02-08 15:32 ` Derek Upham
2013-02-08 16:11 ` Michael Albinus
2013-02-09 5:31 ` Derek Upham
2013-02-11 19:22 ` Stefan Monnier
2013-02-12 5:29 ` Derek Upham
2013-02-12 14:02 ` Stefan Monnier
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