[racket] SIgnal-catching in Racket

Hi all,

If I wanted to catch a Unix signal (say, SIGUSR1) within my Racket
program, how should I go about it?

My current best guess is:
 - load a C extension, which
 - creates a semaphore and
 - hooks the signal with a handler (MZ_SIGSET looks relevant), which
 - posts to the semaphore when the signal arrives.

However this seems like a recipe for problems. Is it even permitted to
post to a semaphore from a signal handler? Will the runtime be upset
about unscheduled intrusions into its demesne? Is it possible for a C
extension to allocate a global value like a semaphore and make it
available to Racket code?

Is there a better way?

 - Perhaps a self-pipe would be better than a semaphore?
 - A thread from 2006 [1] points at scheme_signal_received() but
   I don't understand why creating an event type is the right thing
   to do.

Tony

[1] http://lists.racket-lang.org/users/archive/2006-July/013999.html