d_yield_proc - Invisible dialog procedure that yields CPU time slices. Allegro
game programming library.
int d_yield_proc(int msg, DIALOG *d, int c);
An invisible helper object that yields time slices for the scheduler (if the
system supports it) when the GUI has nothing to do but waiting for user
actions. You should put one instance of this object in each dialog array
because it may be needed on systems with an unusual scheduling algorithm (for
instance QNX) in order to make the GUI fully responsive.