bug#24109: 24.5; Long lines in message mode make Emacs irresponsive

[Yuri D'Elia]

On Wed, Aug 31 2016, Eli Zaretskii <eliz@gnu.org> wrote:
> OK, thanks.  Next question: why does hscroll_windows returns non-zero
> when called repeatedly?  It is supposed to do that only once; the next
> call should return zero.
>
> For starters, in this line:
>
>             if (w->hscroll != hscroll)
>
> what are the values of those two, and do they change each time
> hscroll_windows is called in the infloop, for the selected window?

They swap the value at each iteration:

Thread 1 "emacs" hit Breakpoint 14, hscroll_window_tree (window=20142453) at 
xdisp.c:13086
$154 = 0
$155 = 487
Continuing.

Thread 1 "emacs" hit Breakpoint 14, hscroll_window_tree (window=20142453) at 
xdisp.c:13086
$156 = 487
$157 = 0
Continuing.

...