Fix EventHandler subscriptions being registered several times

src/app/app.py

@@ -1,5 +1,4 @@
 import sys
-
 import tornado
 import zmq
 from tornado.web import Application

src/app/fsm_base.py

@@ -2,9 +2,10 @@ from transitions import Machine
 
 
 class FSMBase:
-    states, transitions, message_handlers = [], [], []
+    states, transitions = [], []
 
     def __init__(self, initial: str = None):
+        self.message_handlers = []
         self.machine = Machine(model=self,
                                states=self.states,
                                transitions=self.transitions,

src/app/handlers/zmq_websocket_handler.py

@@ -8,9 +8,11 @@ log = logging.getLogger(__name__)
 
 
 class ZMQWebSocketHandler(WebSocketHandler):
-    _event_handler_connector = EventHandlerConnector()  #<--------------------. TODO: how is __init__()
+    _event_handler_connector = EventHandlerConnector() #----.
-                                                        # fix: made it static | TODO: called more than once?
+    # TODO: investigate thread safety!    <-----------------'
-    def __init__(self, application, request, **kwargs): #---------------------'
+    # ZMQ sockets shared between several WebSocketHandler instances
+    # http://pyzmq.readthedocs.io/en/latest/morethanbindings.html#thread-safety
+    def __init__(self, application, request, **kwargs):
         super().__init__(application, request, **kwargs)
 
     def open(self, *args, **kwargs):