gitter: Maintain a list of threads and create only one thread per room (

#20)

Closes #19

gitter.py

@@ -247,6 +247,9 @@ def __init__(self, config):
                              'Accept': 'application/json'}
         self.bot_identifier = self._get_bot_identifier()
 
+        self._joined_rooms_lock = threading.Lock()
+        self._joined_rooms = []
+
     def _get_bot_identifier(self):
         """
         Query the API for the bot's own identifier.
@@ -307,9 +310,14 @@ def background():
                 else:
                     log.debug('Received keep-alive on %s', room.name)
 
-        t = threading.Thread(target=background)
-        t.daemon = True
-        t.start()
+        with self._joined_rooms_lock:
+            if room._uri not in self._joined_rooms:
+                t = threading.Thread(target=background)
+                t.daemon = True
+                t.start()
+                self._joined_rooms.append(room._uri)
+            else:
+                log.info("Already joined %s", room.name)
 
     def rooms(self):
         json_rooms = self.readAPIRequest('rooms')