FD_ZERO          2242 thread.c       #undef FD_ZERO
FD_ZERO          2247 thread.c       #define FD_ZERO(f)	rb_fd_zero(f)
FD_ZERO          2288 thread.c       #undef FD_ZERO
FD_ZERO          2293 thread.c       #define FD_ZERO(f)	rb_fd_zero(f)