Async call with callback

            if 'event' in call:

                # Release the call if its synchronous:

                call['event'].set()

            elif 'async_cb' in call:

                call['async_cb'](call_id=message['id'],

                                 response=call.get('return'),

                                 error=call.get('error'))

            else:

                # Else, it's an asynchonous call, we need to push the answer

                # on the queue:

        self._calls[msg_id] = {'id': msg_id, 'async': True, 

                               'data': data, 'queue': queue}

        return msg_id

    def async_call_cb(self, callback, method_name, *args, **kwargs):

        '''Make an asynchronous call on the peer and callback when call is done.

        :param callable callback: callback must have the following named

            arguments:

            * **call_id** (*int*) - unique identifier for the async call made

            * **response** - response as returned by the remote function

            * **error** (*dict*) - error indicator in case remote call throwed exception

        :param str method_name: the method to call on the peer

        :param \*args: the arguments for the call

        :param \*\*kwargs: the keyword arguments for the call

        :return: the message id of the call

        '''

        msg_id = self._send_call(method_name, *args, **kwargs)

        self._calls[msg_id] = {'id': msg_id, 'async_cb': callback}

        return msg_id