[PATCH xserver 0/2] RFC: Sync key repeat with Wayland compositor

[Hans de Goede]

Hi,

On 07-03-16 18:44, Olivier Fourdan wrote:
> Key repeat is handled by the X server, but for Wayland, the key
> press/release events need to be processed and forwarded by the Wayland
> compositor first.
>
> If the Wayland compositor get stuck for whatever reason and does not
> process the key release event fast enough, this may cause the Xwayland
> server to generate spurious key repeat events.
>
> That actually can lead to a complete hang of both the Wayland compositor
> and Xwayland as seen in the following GNOME bug:
>
>    https://bugzilla.gnome.org/show_bug.cgi?id=762618
>
> Basically, what happens here is that the Wayland compositor takes longer
> to actually process the fullscreen/unfullscreen transition than the
> repeat delay.
>
> As a result, while the user has released the F11 key that triggers the
> fullscreen/unfullscreen transition, the Wayland compositor is stuck
> is a graphical operation and cannot process the key release events, which
> triggers the auto-repeat in Xwayland, and therefore cause even more
> fullscreen transitions. Only way out here is to kill the Xwayland
> application and wait for the queued up event to clear out...
>
> While this is arguably a bug in the Wayland compositor, there is no
> way that I can think of to guarantee that this cannot happen.
>
> One possiblity to mitigate the problem is to block the key repeat until
> we are sure the Wayland compositor is actually processing events.
>
> The idea comes from a similar patch for gtk+ by Ray Strode here:
>
>    https://bug757942.bugzilla-attachments.gnome.org/attachment.cgi?id=322876
>
> from bug https://bugzilla.gnome.org/show_bug.cgi?id=757942
>
> While the following patches do fix the issue in my case, they are not
> perfect and only a mitigation of the problem (e.g. they could easily be
> defeated by a Wayland compositor that would have different priority for
> Wayland protocol and input processing), that's why I send these couple
> of patches as an RFC for now.

Why not simply rely on the keyrepeat of the compositor and forward repeat
events from it ? That way xwayland will also end up using the compositors
keyrepeat settings which would mean the user does not need to worry
about configuring this in multiple places ?

Or is keyrepeat left to the toolkit under wayland ? In that case please
ignore my comment :)

Regards,

Hans