GNU bug report logs - #21313
25.0.50; Strange errors from dbus-handle-event

Previous Next

Full log

View this message in rfc822 format

From: Tassilo Horn <tsdh <at> gnu.org>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: michael.albinus <at> gmx.de, 21313 <at> debbugs.gnu.org
Subject: bug#21313: 25.0.50; Strange errors from dbus-handle-event
Date: Fri, 16 Oct 2015 09:45:08 +0200

Eli Zaretskii <eliz <at> gnu.org> writes:

>> > I think I found the problem: the call to Fformat eventually calls
>> > print_object, which calls QUIT, which resets quit-flag.
>> 
>> I've seen it now.  Well, that's not what I would have expected.
>
> You should expect any potentially prolonged operation to call QUIT
> somewhere in its loop.  That's standard Emacs coding practice, meant
> to make Emacs more responsive.

Ok, so QUIT; in C code basically means, here is a position where the
current lisp execution could be aborted.  If it weren't in
print_object(), then you couldn't for example abort printing a list with
gazillions of elements and emacs would get stuck while doing so.

Looking at QUIT, the difference between my original code and the new one
is just when process_quit_flag() is called.  process_quit_flag() always
signals quit.  So with the new code, the signal is handled by the right
recipient.  Who consumed (and discarded) it before?

Well, I think I just remember that I want to bind Qinhibit_quit to Qt
whenever I need to call Lisp functions from C.

>> > So you need to change the beginning of read_char like this:
>> >
>> >   ptrdiff_t count = SPECPDL_INDEX ();
>> >   specbind (Qinhibit_quit, Qt);
>> >   AUTO_STRING (format, "%S");
>> >   printf ("record_char: %s\n", SSDATA (CALLN (Fformat, format, c)));
>> >   unbind_to (count, Qnil);
>> 
>> Yes, that works.  So that's the C version of (let ((inhibit-quit t))
>> ...).  So specbind creates a dynamic binding, and with unbind_to you
>> pop entries up to a given index again, right?
>
> Yes.  See Flet (modulo the clutter) for a definitive evidence.
>
> (Btw, unwind-protect is implemented using the same mechanism in C.)

Seen that, thanks!

Bye,
Tassilo

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.