bug#39687: 26.3; Add customize-variable option for not locking keyboards

[Logan Perkins <logan@lp-programming.com>]

On Wed, 21 Jul 2021 08:57:44 -0700,
Lars Ingebrigtsen wrote:
> 
> Logan Perkins <logan@lp-programming.com> writes:
> 
> > I *think* I have a patch that still fixes the current behavior, and
> > does not reintroduce those two bugs, I've included it below.
> > Basically, the fix for Bug#5095 should only be applied if we are in
> > the right context.  If we're not, the if block above puts a
> > Qswitch_frame at the head of the side queue and triggers
> > replay_entire_sequence, so we just skip the second check.  It'll get
> > run again and catch the interruption on the next pass, but in the
> > right context.
> 
> I tried the various test cases, and the behaviour with your patch
> clearly seems better to me, so I've applied it to Emacs 28.

I assume you only applied the patch I supplied, which improves the fix
for Bug#5095, but does not address Bug#39687.  Hopefully, with that
sorted, we can discuss the issues around `temporarily_switch_to_single_kboard`.

> 
> But as Eli says, this is a ticklish area, so if this (re-)introduces
> other bugs, we'll have to revert.

Fair enough.  I am fairly confident that patch won't cause problems
(but it might allow latent problems to surface).  This is, indeed, a
tricky area: it took the better part of 2 hours last year to "wrap my
head around" the issue well enough to write the patch.  If any other
issues arise, I'm happy to address those.

> 
> This change was small enough to apply without assigning copyright to the
> FSF, but for future patches you want to submit, it might make sense to
> get the paperwork started now, so that subsequent patches can be applied
> speedily. Would you be willing to sign such paperwork?

I submitted my assignment paperwork 18 May 2020, signed via GPG.
Mr. Topham responded (on 4 Jun 2020) that he was having difficulty
verifying the signature (possibly due to it being an EDDSA key?), and
that he would try again.  I have heard nothing since, but did not
follow up as this thread was stalled, and last summer was a
bit... intense.  I still have the assignment document and can submit
it again if that would help.

Regards,
Logan