bug#29789: 25.1; Emacs blocks user input when using visual-fill-column in wide terminals

[Eli Zaretskii]

> From: Luis Gerhorst <privat@luisgerhorst.de>
> Date: Wed, 20 Dec 2017 20:28:27 +0100
> 
> 
> 1. Run Emacs in a wide terminal (about 150 characters, 100 isn't
> enough): emacs -nw -Q
> 
> 2. Load a arbitrary theme: M-x load-theme adwaita
> 
> 3. Load visual-fill-column. E.g. by copying
> https://raw.githubusercontent.com/joostkremers/visual-fill-column/c0e5ec8f88a7598f7afdee565978410bee0de2a0/visual-fill-column.el
> into the scratch buffer and typing M-x eval-buffer.
> 
> There is nothing suspicious about the code, regular lisp code should not
> be able to block Emacs (I believe). It does not seem to contain any loops 
> that block the main thread. The maintainer knows about the issue but say's it 
> may be an issue with low-level code. In GUI Emacs it works.
> 
> 4. Open a buffer and enable visual-fill-column-mode: M-x
> visual-fill-column-mode
> 
> 5. Your Emacs is now blocked.

I tried to reproduce this on GNU/Linux and on MS-Windows, but failed
both times, both with Emacs 25.1 and the current emacs-26 release
branch.

What I see is that after enabling the mode, Emacs becomes somewhat
sluggish in cursor motion (hardly surprising, given what the mode
does), but it certainly doesn't hang.

I wonder what's different on your system, or on that of those who
confirmed the problem.