[xmonad] Visual hints for XMonad actions

[wagnerdm at seas.upenn.edu]

Quoting Mario Pastorelli <pastorelli.mario at gmail.com>:
>           forkIO $ do
>               threadDelay(1 * 1000000)
>               unmapWindow dpy win
>               destroyWindow dpy win
>               sync dpy False

Naively, this looks un-thread-safe to me. Only one thread is allowed  
to access a Display at a time; can you guarantee that the main  
xmonad-core thread won't be accessing dpy for some reason at the time  
this code runs? If not, you need to open a new display yourself in the  
forked thread.

You might be okay by accident -- I don't think xmonad is typically  
linked with GHC's threaded runtime -- but I'm not sure it's a good  
idea to rely on that staying true in the future.

~d