'Send a single message.'

@inlineCallbacks
def send_message(self, exchange, routing_key, msg):

    log.msg(('%s    (%s):    %s' % (exchange, routing_key, repr(msg))), system='Pika:=>')
    (yield self.channel.exchange_declare(exchange=exchange, type='topic', durable=True, auto_delete=False))
    prop = spec.BasicProperties(delivery_mode=2)
    try:
        (yield self.channel.basic_publish(exchange=exchange, routing_key=routing_key, body=msg, properties=prop))
    except Exception as error:
        log.msg(('Error    while    sending    message:    %s' % error), system=self.name)
