[writing a compositor] wl_display_add_socket_auto fails

[adlo]

I am attempting to write a test compositor using libweston. I want to
run it in a window on GNOME Shell, so I am using the Wayland backend.

When I call wl_display_add_socket_auto, it fails with the error
message: unable to lock lockfile /run/user/1000/wayland-0.lock, maybe
another compositor is running

How can I resolve this?

Regards

adlo