FD_SET            119 ext/readline/readline.c     FD_SET(fileno(rl_instream), &rset);
FD_SET            243 include/ruby/intern.h #define rb_fd_set(n, f)	FD_SET(n, f)
FD_SET           2195 thread.c           FD_SET(n, fds->fdset);
FD_SET           2441 thread.c       	FD_SET(fd, &set);