private static void _onSent(IAsyncResult ar)
        {
            AsyncResult     result = (AsyncResult)ar;
            AsyncSendMethod caller = (AsyncSendMethod)result.AsyncDelegate;

            caller.EndInvoke(ar);
        }
        protected static void _onSent(IAsyncResult ar)
        {
            AsyncSendMethod caller = (AsyncSendMethod)ar.AsyncState;

            caller.EndInvoke(ar);
        }