race condition in __wait_for_db_init() ?

[jipanyang]

Based on the description in https://redis.io/topics/notifications:
"
Because Redis Pub/Sub is fire and forget currently there is no way to use this feature if your application demands reliable notification of events, that is, if your Pub/Sub client disconnects, and reconnects later, all the events delivered during the time the client was disconnected are lost.
"
It looks to me there is possibility the INIT_INDICATOR is set between client.get() and pubsub.psubscribe(pattern), the notification might get missed and pubsub.listen() will be blocked there, unless client buffers all notification from the moment of client.pubsub()

def __wait_for_db_init(self):
    client = self.redis_clients[self.CONFIG_DB]
    pubsub = client.pubsub()
    initialized = client.get(self.INIT_INDICATOR)
    if not initialized:
        pattern = "__keyspace@{}__:{}".format(self.db_map[self.CONFIG_DB]['db'], self.INIT_INDICATOR)
        pubsub.psubscribe(pattern)
        for item in pubsub.listen():