rb_fd_select      216 include/ruby/intern.h int rb_fd_select(int, rb_fdset_t *, rb_fdset_t *, rb_fdset_t *, struct timeval *);
rb_fd_select     7328 io.c               ret = rb_fd_select(rb_fd_max(&stp->fds), &stp->fds, NULL, NULL, NULL);
rb_fd_select     7343 io.c               ret = rb_fd_select(rb_fd_max(&stp->fds), NULL, &stp->fds, NULL, NULL);