Releases all running calls when connection is shutdown.

        self._sock.close()

        # Release all running calls from this connection:

        for call in self._calls.values():

            if 'event' in call:

                call['error'] = {'exception': 'RpcError',

                                 'message': 'Connection reset by peer'}

                call['return'] = None

                call['event'].set()

        if callback is not None and not callable(callback):

            if self._handler is not None:

                try: