From: Kalle Olavi Niemitalo <kon@iki.fi>
To: Emacs developers <emacs-devel@gnu.org>
Subject: Re: Why is `after-change-functions' reset?
Date: Tue, 18 Feb 2014 00:11:49 +0200 [thread overview]
Message-ID: <87bny58k4a.fsf@Niukka.kon.iki.fi> (raw)
In-Reply-To: <878ut9r3ik.fsf@web.de> (Michael Heerdegen's message of "Mon, 17 Feb 2014 19:35:31 +0100")
Michael Heerdegen <michael_heerdegen@web.de> writes:
> Evaluate it and hit tab (for completion) and C-g C-g in succession.
> When you repeat this a few times, you get "Why does this happen?".
I debugged this a bit, with my custom Emacs 23.0.51. I don't
know how much this machinery has changed in later versions.
Emacs set Vquit_flag at:
handle_interrupt
tty_read_avail_input
read_avail_input
handle_async_input
input_available_signal
<signal handler called>
mark_object
Fgarbage_collect
Ffuncall
run_hook_list_with_args
signal_after_change
Fadd_text_properties
Fput_text_property
Fdisplay_completion_list
internal_with_output_to_temp_buffer
Fminibuffer_completion_help
do_completion
Fminibuffer_complete
Ffuncall
Fcall_interactively
After Fgarbage_collect returned, Ffuncall called funcall_lambda,
in which the QUIT macro detected the non-nil value of Vquit_flag
and called Fsignal (Qquit, Qnil). Because the quit was signaled
within signal_after_change, after-change-functions were not
restored.
I don't see any reasonable way to prevent after-change-functions
from being reset like this.
> In my original situation, quitting was not involved, the above
> recipe was just the first reproducible program I had discovered.
Perhaps you could change your Emacs to break when the reset
happens, and always run it in a debugger. Make
signal_before_change and signal_after_change maintain some kind
of flag or nesting counter, and set conditional breakpoints in
Fthrow and Fsignal. That will get a false positive if the error
is caught within the hook; but I don't think it happens often.
next prev parent reply other threads:[~2014-02-17 22:11 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-17 18:35 Why is `after-change-functions' reset? Michael Heerdegen
2014-02-17 22:11 ` Kalle Olavi Niemitalo [this message]
2014-02-18 17:50 ` Michael Heerdegen
2014-02-17 23:49 ` Stefan Monnier
2014-02-17 23:57 ` Michael Heerdegen
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