GM - how to get out of blocked gm_unknow() when exiting?

When gm_unknown() is sleeping, is there any sort of event that I can
generate so that
I can cleanly exit? My event loop is running in a thread and I would like to
be able to
re-join the thread when exiting. I can't do this right now, as gm is
sleeping and
there is no activity so it will not wake up. Any ideas?

 - Richard