GNU bug report logs - #76969
kill-buffer fails silently when a thread exists where it's current

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Dmitry Gutov <dmitry <at> gutov.dev>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#76969: closed (kill-buffer fails silently when a thread
 exists where it's current)
Date: Sat, 09 Aug 2025 20:13:02 +0000

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Your message dated Sat, 9 Aug 2025 23:11:51 +0300
with message-id <50a5a35b-c229-4c1f-b86d-a321676f4bb4 <at> gutov.dev>
and subject line Re: bug#76969: kill-buffer fails silently when a thread exists where it's current
has caused the debbugs.gnu.org bug report #76969,
regarding kill-buffer fails silently when a thread exists where it's current
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


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76969: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=76969
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From: Dmitry Gutov <dmitry <at> gutov.dev>
To: bug-gnu-emacs <at> gnu.org
Subject: kill-buffer fails silently when a thread exists where it's current
Date: Wed, 12 Mar 2025 03:16:08 +0200

This stems from a private bug report about diff-hl when it uses a thread 
to update the fringe highlights.

To reproduce:

  1. Install, enable diff-hl-mode.
  2. (setq diff-hl-update-async t)
  3. Visit a code buffer in a (e.g.) Git repo, save it.
  4. Make an edit, don't save.
  5. Evaluate this:

  (progn
    (save-buffer)
    (kill-buffer))

Current:

The result is that the buffer is not killed. And that happens silently, 
no errors or anything. Only further examination and reading the sources 
led to understanding the reason.

Expected:

It probably should be killed. After the thread is signaled some error 
(perhaps) and is aborted. And if the buffer can't be killed, 
'kill-buffer' itself should exit with an error.

As I understand the behavior is old (2013) and comes from the 
'thread_check_current_buffer' call in Fkill_buffer. But it's not 
mentioned in kill-buffer's docstring or the manual.

Alternative repro:

If you don't have diff-hl installed, you could replace 1 and 2 with:

  (defun foo ()
    (make-thread (lambda () (sleep-for 0.1))))

  (add-hook 'after-save-hook #'foo)

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From: Dmitry Gutov <dmitry <at> gutov.dev>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: sbaugh <at> janestreet.com, 76969-done <at> debbugs.gnu.org
Subject: Re: bug#76969: kill-buffer fails silently when a thread exists where
 it's current
Date: Sat, 9 Aug 2025 23:11:51 +0300

On 09/08/2025 15:20, Eli Zaretskii wrote:
>> Date: Fri, 1 Aug 2025 03:01:11 +0300
>> Cc:sbaugh <at> janestreet.com,76969 <at> debbugs.gnu.org
>> From: Dmitry Gutov<dmitry <at> gutov.dev>
>>
>> +@var{buffer-disposition} indicates what happens if the thread's current
>> +buffer is about to be killed.  If the value is @code{t}, it's not
>> +allowed.
> I'd say "killing the buffer is not allowed", because "it" might be
> ambiguous.
> 
>>             Any other value, including nil (which is the default), means
>                                          ^^^
> @code{nil}
> 
>> --- a/src/thread.h
>> +++ b/src/thread.h
>> @@ -143,6 +143,9 @@ #define lisp_eval_depth (current_thread->m_lisp_eval_depth)
>>     struct buffer *m_current_buffer;
>>   #define current_buffer (current_thread->m_current_buffer)
>>   
>> +  /* Decides whether the thread's current buffer can be killed.  */
>> +  Lisp_Object buffer_disposition;
> I think this change means ABI_VERSION in comp.c should be bumped.
> 
> Also, please move this member to before event_object, because the
> comment there says:
> 
>    /* event_object must be the last Lisp field.  */
> 
> which is consistent with how we allocate thread objects:
> 
>    struct thread_state *new_thread
>      = ALLOCATE_ZEROED_PSEUDOVECTOR (struct thread_state, event_object,
> 				    PVEC_THREAD);
> 
> Finally, this needs a NEWS entry.
> 
> With the above nits fixed, please feel free to install, and thanks.

Thanks! Done all that and pushed to master:

https://cgit.git.savannah.gnu.org/cgit/emacs.git/commit/?id=07eb39f1132ceb15e80e7912445890faa8f5b78c

Now closing, and let's be on lookout for user feedback.

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