[racket] Queuing calls to printf

> Since printf requires another thread to run, adding calls to printf in
> on-subwindow-event, or anything on-subwindow-event calls directly, will
> cause a GUI to break.

How about the logging functions such as log-debug?  Do they suffer
from the same problems?

    http://docs.racket-lang.org/reference/logging.html(form._((lib._racket/private/more-scheme..rkt)._log-debug))


Their output can be conditionally silenced by setting the system log
level appropriately (running with "racket ... -L debug", for example)