GNU bug report logs - #32426
27.0.50; Losing key bindings in threads

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Michael Albinus <michael.albinus <at> gmx.de>
To: bug-gnu-emacs <at> gnu.org
Subject: 27.0.50; Loosing key bindings in threads
Date: Mon, 13 Aug 2018 10:40:06 +0200

This is about the feature/tramp-thread-safe branch. The bug seems to be
related to the threads implementation in general; that branch is used
only because it is simpler to demonstrate.

I have two files, a.test and b.test. Both files have the same contents

--8<---------------cut here---------------start------------->8---
Local Variables:
risky-variable: nil
End:
--8<---------------cut here---------------end--------------->8---

I open both files asynchronously via "C-x & C-x C-f *.test". The buffer
*Local Variables* is displayed, and in the minibuffer I'm asked "Please
type y, n, or !, or C-v to scroll:". Whatever key I type, I get "y is
undefined".

I have no idea how to debug this.


In GNU Emacs 27.0.50 (build 18, x86_64-pc-linux-gnu, GTK+ Version 3.22.30)
 of 2018-07-18 built on detlef
Repository revision: ba6cc1d04cef8e25534a72e90a8f0f8db0026c9f
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Ubuntu 18.04.1 LTS

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Message #8 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: bug-gnu-emacs <at> gnu.org, Michael Albinus <michael.albinus <at> gmx.de>,
 32426 <at> debbugs.gnu.org
Subject: Re: bug#32426: 27.0.50; Loosing key bindings in threads
Date: Mon, 13 Aug 2018 12:39:30 +0300

On August 13, 2018 11:40:06 AM GMT+03:00, Michael Albinus <michael.albinus <at> gmx.de> wrote:
> 
> This is about the feature/tramp-thread-safe branch. The bug seems to
> be
> related to the threads implementation in general; that branch is used
> only because it is simpler to demonstrate.
> 
> I have two files, a.test and b.test. Both files have the same contents
> 
> --8<---------------cut here---------------start------------->8---
> Local Variables:
> risky-variable: nil
> End:
> --8<---------------cut here---------------end--------------->8---
> 
> I open both files asynchronously via "C-x & C-x C-f *.test". The
> buffer
> *Local Variables* is displayed, and in the minibuffer I'm asked
> "Please
> type y, n, or !, or C-v to scroll:". Whatever key I type, I get "y is
> undefined".
> 
> I have no idea how to debug this.


See bug#25214.

Message #16 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Michael Albinus <michael.albinus <at> gmx.de>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: bug-gnu-emacs <at> gnu.org, 32426 <at> debbugs.gnu.org
Subject: Re: bug#32426: 27.0.50; Loosing key bindings in threads
Date: Mon, 13 Aug 2018 14:17:12 +0200

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

Hi Eli,

> See bug#25214.

Thanks, I've merged both bugs. Bug#25214 has the analysis, but I don't
know which direction we want to continue. Using a message pump, as
proposed by Clément?

Best regards, Michael.

Message #22 received at 32426 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Michael Albinus <michael.albinus <at> gmx.de>
Cc: 32426 <at> debbugs.gnu.org
Subject: Re: bug#32426: 27.0.50; Loosing key bindings in threads
Date: Mon, 13 Aug 2018 17:38:42 +0300

> From: Michael Albinus <michael.albinus <at> gmx.de>
> Cc: bug-gnu-emacs <at> gnu.org, 32426 <at> debbugs.gnu.org
> Date: Mon, 13 Aug 2018 14:17:12 +0200
> 
> > See bug#25214.
> 
> Thanks, I've merged both bugs. Bug#25214 has the analysis, but I don't
> know which direction we want to continue. Using a message pump, as
> proposed by Clément?

I don't know, the discussion never reached any concrete conclusions.
(And the more I think about that, the less I understand how a message
pump could help: after all, keyboard input is already a kind of
"message pump", on the OS level.  It seems we'd eventually have the
same problem: how to allow multiple threads to read from the message
pump.)

Some additional discussion was in this thread:

  http://lists.gnu.org/archive/html/emacs-devel/2016-12/msg00607.html

Maybe we need to start a new discussion on emacs-devel, once you read
that.

Message #25 received at 32426 <at> debbugs.gnu.org (full text, mbox):

From: Michael Albinus <michael.albinus <at> gmx.de>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 32426 <at> debbugs.gnu.org
Subject: Re: bug#32426: 27.0.50; Loosing key bindings in threads
Date: Tue, 14 Aug 2018 12:05:12 +0200

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

Hi Eli,

> I don't know, the discussion never reached any concrete conclusions.
> (And the more I think about that, the less I understand how a message
> pump could help: after all, keyboard input is already a kind of
> "message pump", on the OS level.  It seems we'd eventually have the
> same problem: how to allow multiple threads to read from the message
> pump.)
>
> Some additional discussion was in this thread:
>
>   http://lists.gnu.org/archive/html/emacs-devel/2016-12/msg00607.html
>
> Maybe we need to start a new discussion on emacs-devel, once you read
> that.

Yes, that's needed. I have also no idea how to fix. But I know that the
proposal to disable keyboard reading for all threads but the main one is
not working; see my example in bug#32426.

Perhaps we need this also for other events, D-Bus and file notifications
come to mind.

I fear I'm not the best one to reanimate this discussion. Keyboard
handling in Emacs is terra incognita for me.

Best regards, Michael.

Message #28 received at 32426 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Michael Albinus <michael.albinus <at> gmx.de>
Cc: 32426 <at> debbugs.gnu.org
Subject: Re: bug#32426: 27.0.50; Loosing key bindings in threads
Date: Tue, 14 Aug 2018 18:16:00 +0300

> From: Michael Albinus <michael.albinus <at> gmx.de>
> Cc: 32426 <at> debbugs.gnu.org
> Date: Tue, 14 Aug 2018 12:05:12 +0200
> 
> > Maybe we need to start a new discussion on emacs-devel, once you read
> > that.
> 
> Yes, that's needed.

Started a discussion on emacs-devel.

> But I know that the proposal to disable keyboard reading for all
> threads but the main one is not working; see my example in
> bug#32426.

I'm not surprised.

> Perhaps we need this also for other events, D-Bus and file notifications
> come to mind.

Possibly, but those seem like an easier nut to crack: AFAIU, each time
we need to watch for D-Bus events, we register a file descriptor for
that, and deregister it when we no longer need it, is that right?  If
so, we could easily make these descriptors watched only by the thread
that registered the watch, the infrastructure for that already exists.

By contrast, there's only one keyboard descriptor.

Message #31 received at 32426 <at> debbugs.gnu.org (full text, mbox):

From: Michael Albinus <michael.albinus <at> gmx.de>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 32426 <at> debbugs.gnu.org
Subject: Re: bug#32426: 27.0.50; Loosing key bindings in threads
Date: Tue, 14 Aug 2018 17:48:22 +0200

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

Hi Eli,

>> Perhaps we need this also for other events, D-Bus and file notifications
>> come to mind.
>
> Possibly, but those seem like an easier nut to crack: AFAIU, each time
> we need to watch for D-Bus events, we register a file descriptor for
> that, and deregister it when we no longer need it, is that right?  If
> so, we could easily make these descriptors watched only by the thread
> that registered the watch, the infrastructure for that already exists.

We need a file descriptor per D-Bus bus (system and session). But
applications register for (asynchronous) method calls and signals on the
buses. This could happen in several threads, so we need a mechanism how
to distribute incoming events to those threads.

But I would postpone this discussion until after we have resolved the
keyboard issue.

Best regards, Michael.

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