[Spice-devel] [PATCH spice 2/5] spicec-x11: Remove a race window in selection ownership release code

[Arnon Gilboa]

ack. and i always believed x11 is perfect.

Hans de Goede wrote:
> Well almost remove it, it was possible that another x11 app would acquire
> selection ownership, and we would receive a release message from the
> agent before having processed the xselection ownership change event.
>
> Then we would set the selection owner to none, overriding the new owner.
> As the comment in the patch indicates there still is a minute window left
> where something similar can happen after this patch. Nothing we can do
> about that (I blame the libX11 selection API).
> ---
>  client/x11/platform.cpp |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
>
> diff --git a/client/x11/platform.cpp b/client/x11/platform.cpp
> index 8f0665c..cb2431f 100644
> --- a/client/x11/platform.cpp
> +++ b/client/x11/platform.cpp
> @@ -3466,7 +3466,15 @@ void Platform::on_clipboard_release()
>  {
>      XEvent event;
>  
> +    if (XGetSelectionOwner(x_display, clipboard_prop) != platform_win) {
> +        LOG_INFO("Platform::on_clipboard_release() called while not selection owner");
> +        return;
> +    }
> +    /* Note there is a small race window here where another x11 app could
> +       acquire selection ownership and we kick it off again, nothing we
> +       can do about that :( */
>      XSetSelectionOwner(x_display, clipboard_prop, None, CurrentTime);
> +
>      /* Make sure we process the XFixesSetSelectionOwnerNotify event caused
>         by this, so we don't end up changing the clipboard owner to none, after
>         it has already been re-owned because this event is still pending. */
>