Introduced event queue to properly decouple event processing from firing

src/octoprint/events.py

@@ -7,6 +7,8 @@ __license__ = 'GNU Affero General Public License http://www.gnu.org/licenses/agp
 import datetime
 import logging
 import subprocess
+import Queue
+import threading
 
 from octoprint.settings import settings
 
@@ -28,6 +30,27 @@ class EventManager(object):
 		self._registeredListeners = {}
 		self._logger = logging.getLogger(__name__)
 
+		self._queue = Queue.PriorityQueue()
+		self._worker = threading.Thread(target=self._work)
+		self._worker.daemon = True
+		self._worker.start()
+
+	def _work(self):
+		while True:
+			(event, payload) = self._queue.get(True)
+
+			eventListeners = self._registeredListeners.get(event, None)
+			if eventListeners is None:
+				return
+			self._logger.debug("Firing event: %s (Payload: %r)" % (event, payload))
+
+			for listener in eventListeners:
+				self._logger.debug("Sending action to %r" % listener)
+				try:
+					listener(event, payload)
+				except:
+					self._logger.exception("Got an exception while sending event %s (Payload: %r) to %s" % (event, payload, listener))
+
 	def fire(self, event, payload=None):
 		"""
 		Fire an event to anyone subscribed to it
@@ -41,17 +64,8 @@ class EventManager(object):
 
 		if not event in self._registeredListeners.keys():
 			return
-		self._logger.debug("Firing event: %s (Payload: %r)" % (event, payload))
+		self._queue.put((event, payload), 0)
 
-		eventListeners = self._registeredListeners[event]
-		for listener in eventListeners:
-			self._logger.debug("Sending action to %r" % listener)
-			try:
-				listener(event, payload)
-			except:
-				self._logger.exception("Got an exception while sending event %s (Payload: %r) to %s" % (event, payload, listener))
-
-	
 	def subscribe(self, event, callback):
 		"""
 		Subscribe a listener to an event -- pass in the event name (as a string) and the callback object