From: Eli Zaretskii <eliz@gnu.org>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: emacs-devel@gnu.org, phillip.lord@russet.org.uk
Subject: Re: Calling Lisp from undo.c's record_* functions
Date: Tue, 17 Nov 2015 20:00:56 +0200 [thread overview]
Message-ID: <8337w4bj53.fsf@gnu.org> (raw)
In-Reply-To: <jwv4mgk1qmo.fsf-monnier+emacs@gnu.org>
> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: phillip.lord@russet.org.uk, emacs-devel@gnu.org
> Date: Tue, 17 Nov 2015 12:34:08 -0500
>
> >> When would it not be called?
> > E.g., in insert_from_gap. Also, in many insdel.c functions when they
> > are called with the PREPARE argument false.
>
> AFAIK these are cases where prepare_to_modify_buffer has already been
> called earlier.
That's what the comments say, yes. How deep do we believe them?
> >> You mean there are cases where we'd add stuff to the undo list but
> >> we don't run before-change-functions?
> > I don't know. I don't think we have such bugs, but thinking is one
> > thing and convincing yourself it's true by looking at the callers is
> > something entirely different...
>
> That's OK, then: I believe that failing to call run_undoable_change is
> not more serious than failing to run before-change-functions.
>
> So I think moving the call to run_undoable_change into
> prepare_to_modify_buffer is n attractive solution to this problem, since
> it preserves the use of Elisp, and it probably also simplifies the code
> (since we can remove most/all other calls to run_undoable_change).
Did you take a look at subst-char-in-region? It calls
prepare_to_modify_buffer from within a loop which seems to assume that
(a) gap position doesn't move, and (b) that pointer into buffer text
is valid across the call to prepare_to_modify_buffer. GC could
invalidate both assumptions, no?
transpose-regions also does something funky, but it looks safe.
zlib-decompress-region, OTOH, seems to call insert_from_gap, and
doesn't call prepare_to_modify_buffer at all, except at its very end,
when it deletes the uncompressed data.
Bottom line: I think all the functions that manipulate the gap should
be carefully audited to identify any potential problem with this
approach.
next prev parent reply other threads:[~2015-11-17 18:00 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-16 16:46 Calling Lisp from undo.c's record_* functions Eli Zaretskii
2015-11-16 21:51 ` Phillip Lord
2015-11-16 22:51 ` Stefan Monnier
2015-11-17 12:14 ` Phillip Lord
2015-11-17 13:46 ` Stefan Monnier
2015-11-17 14:42 ` Phillip Lord
2015-11-17 15:40 ` Stefan Monnier
2015-11-17 16:24 ` Eli Zaretskii
2015-11-17 16:49 ` Stefan Monnier
2015-11-17 17:05 ` Eli Zaretskii
2015-11-17 17:34 ` Stefan Monnier
2015-11-17 18:00 ` Eli Zaretskii [this message]
2015-11-17 19:09 ` Stefan Monnier
2015-11-17 19:22 ` Eli Zaretskii
2015-11-17 21:05 ` Phillip Lord
2015-11-17 21:02 ` Phillip Lord
2015-11-18 2:55 ` Stefan Monnier
2015-11-18 12:26 ` Phillip Lord
2015-11-17 16:35 ` Eli Zaretskii
2015-11-17 20:52 ` Phillip Lord
2015-11-18 3:38 ` Eli Zaretskii
2015-11-18 9:56 ` Phillip Lord
2015-11-18 10:49 ` David Kastrup
2015-11-18 17:30 ` Eli Zaretskii
2015-11-17 16:40 ` Eli Zaretskii
2015-11-17 16:51 ` Stefan Monnier
2015-11-17 19:44 ` Eli Zaretskii
2015-11-17 21:35 ` Phillip Lord
2015-11-18 2:52 ` Stefan Monnier
2015-11-18 3:49 ` Eli Zaretskii
2015-11-18 12:31 ` Phillip Lord
2015-11-18 17:49 ` Eli Zaretskii
2015-11-19 1:49 ` Stefan Monnier
2015-11-19 10:16 ` Phillip Lord
2015-11-19 15:53 ` Eli Zaretskii
2015-11-19 17:49 ` Stefan Monnier
2015-11-19 17:58 ` Eli Zaretskii
2015-11-19 18:17 ` Stefan Monnier
2015-11-22 21:44 ` Phillip Lord
2015-11-22 22:41 ` John Wiegley
2015-11-23 17:29 ` Phillip Lord
2015-11-23 3:37 ` Eli Zaretskii
2015-11-23 17:28 ` Phillip Lord
2015-11-25 17:43 ` Eli Zaretskii
2015-11-25 22:51 ` Richard Stallman
2015-11-26 10:27 ` Phillip Lord
2015-11-17 21:13 ` Phillip Lord
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