signal masks and garbage collection.

I have a problem with c_sigprocmask from the Posix library. This is supposed to set a signal mask for the process (but it appears it actually only sets it for the thread). I need some way of calling sigprocmask before the garbage collector thread is started so it inherits the same signal mask (or a way of setting the signal mask of the garbage collector whilst running). Any ideas? Regards, Keean Schupke.