rb_fd_dup         318 include/ruby/intern.h void rb_fd_dup(rb_fdset_t *dst, const rb_fdset_t *src);
rb_fd_dup        3583 thread.c           rb_fd_dup(dst, src);
rb_fd_dup        3639 thread.c           ((fds1) ? rb_fd_dup(fds1, fds2) : (void)0)