wait_writable

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

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

    i = rb_wait_for_single_fd(fptr->fd, RB_WAITFD_OUT, tv);
    if (i < 0)
        rb_sys_fail(0);
    rb_io_check_closed(fptr);
    if (i & RB_WAITFD_OUT)
        return io;
    return Qnil;
}