public void SendRequest(PendingResRequest pendingRequest)
        {
            var requestId = Guid.NewGuid();

            try
            {
                var callback = pendingRequest.Send(_socket, requestId);
                _callbacks[requestId] = new InflightEntry(requestId, pendingRequest, callback);
            }
            catch (NetMQException)
            {
                _socket = connect();
            }
        }