From: Derek Upham <sand@blarg.net>
To: emacs-devel@gnu.org
Subject: Re: read_char() does not detect, handle special-event-map buffer changes
Date: Wed, 06 Feb 2013 22:33:38 -0800 [thread overview]
Message-ID: <87lib01vlp.fsf@priss.frightenedpiglet.com> (raw)
In-Reply-To: <87r4kwjx11.fsf@priss.frightenedpiglet.com>
Here's a small repro case for the problem. Start up two instances of
Emacs, and load this file into both. In the first, run
`bad-keymap-startup-server'. In the second, run `bad-keymap-send-signal',
and immediately switch back to the first Emacs.
The first Emacs will switch to a "*foo*" buffer with some dummy text.
That buffer will be in view mode. If you hit `q' after the buffer pops
up, Emacs will complain about "*foo*" being read-only. Hit `q' again and
the buffer disappears.
Kill the "*foo*" buffer and run the test again. This time, instead of
hitting `q', use `C-n' to move down a line. After that, when you hit
`q' you exit view mode immediately.
In the original code, I had theorized that the event was going to the
read-only temporary buffer, which had no binding for `q'. But if that
were the case, we would see different behavior when the "old" buffer is
the writable "bad-keymap.el". The "*foo*" buffer is getting the `q'
event, but it looks like read_char() has not started using the buffer's
new `view-mode' keymap, due to the way we are jumping to "retry:". The
proposed fix to exit read_char() after every special event gives the I/O
system a chance to see the new keymap.
Derek
------------------------- bad-keymap.el -------------------------
(require 'dbus)
(defun bad-keymap-switch-handler ()
(let* ((buf (get-buffer-create "*foo*")))
(with-current-buffer buf
(let ((inhibit-read-only t))
(erase-buffer)
(insert "foo foo foo\n")
(switch-to-buffer buf)
(goto-char (point-min)))
(view-mode))))
(defun bad-keymap-startup-server ()
(interactive)
(dbus-register-signal :session "bad-keymap" "/bad/keymap" "bad.keymap"
"Switch" 'bad-keymap-switch-handler))
(defun bad-keymap-send-signal ()
(interactive)
(sit-for 5)
(dbus-send-signal :session "bad-keymap" "/bad/keymap" "bad.keymap"
"Switch"))
-----------------------------------------------------------------
Derek Upham writes:
> There is an Emacs package that uses process buffers to communicate with a
> spawned worker process. Due to locking on underlying files, this limits
> me to one worker, and hence one Emacs. I'm trying to add D-Bus support
> to both sides, and have come across a bug in Emacs' support for special
> events.
>
> The package includes a chunk of code that:
>
> 1. Brings up a temporary buffer in a visible window.
> 2. Queries the worker through the process buffer channel.
> 3. Handles the worker's response in a process filter handler, putting
> the text into a new buffer and replacing the temporary buffer in the
> same window.
>
> The D-Bus code attempts to do the exact same steps, and appears to
> succeed. But the first event after displaying the response (usually a
> keystroke) goes to the /temporary buffer/, generating a "buffer
> read-only" error. After the error, the command loop resyncs the current
> buffer to the visible buffer and later events work normally.
>
> I ran Emacs 24.2.2 in GDB and found that the read_char() function has
> code that is supposed to detect this case:
>
> 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;
>
> However, `current_buffer' and `prev_buffer' are showing up as the same
> in the debugger. I think this is because we haven't gone through a
> display refresh at this point in the code; the Emacs window still shows
> the temporary buffer, for example. This specific error case affects
> D-Bus, but any similar activity by a special event handler should show
> the same bug.
>
> I have a fix that seems to work: remove the test and assume that any
> special event handler could have changed the keymaps.
>
> /* 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 potential optimization, as the code goes up to a higher
> level before restarting `read_char'. But looking at the list of
> special events (in `special-event-map'), those special events should be
> infrequent enough that this change won't cause a performance impact.
> Does anyone know of a reason not to make this change?
>
> Thanks,
>
> Derek
--
Derek Upham
sand@blarg.net
next prev parent reply other threads:[~2013-02-07 6:33 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 [this message]
2013-02-07 14:50 ` Derek Upham
2013-02-07 16:25 ` Stefan Monnier
2013-02-08 4:39 ` Derek Upham
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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