wait_readable

static VALUE
io_wait_readable(int argc, VALUE *argv, VALUE io)
{
    rb_io_t *fptr;
    int i;
    ioctl_arg n;
    VALUE timeout;
    struct timeval timerec;
    struct timeval *tv;

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

    if (rb_io_read_pending(fptr)) return Qtrue;
    if (!FIONREAD_POSSIBLE_P(fptr->fd)) return Qfalse;
    i = rb_wait_for_single_fd(fptr->fd, RB_WAITFD_IN, tv);
    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;
}