wait

static VALUE
io_wait(int argc, VALUE *argv, VALUE io)
{
    rb_io_t *fptr;
    struct wait_readable_arg arg;
    int fd, i;
    ioctl_arg n;
    VALUE timeout;
    struct timeval timerec;

    GetOpenFile(io, fptr);
    rb_io_check_readable(fptr);
    rb_scan_args(argc, argv, "01", &timeout);
    if (NIL_P(timeout)) {
        arg.timeout = 0;
    }
    else {
        timerec = rb_time_interval(timeout);
        arg.timeout = &timerec;
    }

    if (rb_io_read_pending(fptr)) return Qtrue;
    if (!FIONREAD_POSSIBLE_P(fptr->fd)) return Qfalse;
    fd = fptr->fd;
    rb_fd_init(&arg.fds);
    rb_fd_set(fd, &arg.fds);
#ifdef HAVE_RB_FD_INIT
    i = (int)rb_ensure(wait_readable, (VALUE)&arg,
                       (VALUE (*)_((VALUE)))rb_fd_term, (VALUE)&arg.fds);
#else
    i = rb_thread_select(fd + 1, rb_fd_ptr(&arg.fds), NULL, NULL, arg.timeout);
#endif
    if (i < 0)
        rb_sys_fail(0);
    rb_io_check_closed(fptr);
    if (ioctl(fptr->fd, FIONREAD, &n)) rb_sys_fail(0);
    if (n > 0) return io;
    return Qnil;
}