Deny callbacks while connecting

__init__.py

 import logging
 import paho.mqtt.client as paho
 import socket
+import time
 
 try:
     from config import APP_NAME as ROOT_LOGGER_NAME
 
 class mqtt_client(object):
     def __init__(self, name, host, port=1883, username=None, password=None):
+        self.__block_add_callbacks__ = False
         logger.info("Initiating mqtt client instance")
         self.__callbacks__ = {}
         self.__client__ = paho.Client(name)                                     # create client object
         self.__client__.loop_start()                                            # start the loop
 
     def add_callback(self, topic, callback):
+        while self.__block_add_callbacks__:
+            time.sleep(.1)
+        logger.debug("Adding callback for topic %s", topic)
         self.__callbacks__[topic] = callback
         self.__client__.subscribe(topic)
 
     def __on_connect__(self, client, userdata, flags, rc):
         logger.debug("Connect with rc=%d", rc)
         if rc == 0:
+            self.__block_add_callbacks__ = True
             logger.debug("Registering topics...")
             for topic in self.__callbacks__:
                 self.__client__.subscribe(topic)
+            self.__block_add_callbacks__ = False
  
     def __on_disconnect__(self, client, flags, rc):
         logger.warning("Disconnect with rc=%d", rc)