Only fire events once Events.STARTUP has been seen

One part of fixing #2090

src/octoprint/events.py

@@ -132,9 +132,11 @@ class EventManager(object):
 		self._registeredListeners = collections.defaultdict(list)
 		self._logger = logging.getLogger(__name__)
 
+		self._startup_signaled = False
 		self._shutdown_signaled = False
 
 		self._queue = queue.Queue()
+		self._held_back = queue.Queue()
 
 		self._worker = threading.Thread(target=self._work)
 		self._worker.daemon = True
@@ -177,7 +179,30 @@ class EventManager(object):
 		payload being a payload object specific to the event.
 		"""
 
-		self._queue.put((event, payload))
+		send_held_back = False
+		if event == Events.STARTUP:
+			self._logger.info("Processing startup event, this is our first event")
+			self._startup_signaled = True
+			send_held_back = True
+
+		self._enqueue(event, payload)
+
+		if send_held_back:
+			self._logger.info("Adding {} events to queue that "
+			                  "were held back before startup event".format(self._held_back.qsize()))
+			while True:
+				try:
+					self._queue.put(self._held_back.get())
+				except queue.Empty:
+					break
+
+	def _enqueue(self, event, payload):
+		if self._startup_signaled:
+			q = self._queue
+		else:
+			q = self._held_back
+
+		q.put((event, payload))
 
 		if event == Events.UPDATED_FILES and "type" in payload and payload["type"] == "printables":
 			# when sending UpdatedFiles with type "printables", also send another event with deprecated type "gcode"
@@ -185,7 +210,7 @@ class EventManager(object):
 			import copy
 			legacy_payload = copy.deepcopy(payload)
 			legacy_payload["type"] = "gcode"
-			self._queue.put((event, legacy_payload))
+			q.put((event, legacy_payload))
 
 	def subscribe(self, event, callback):
 		"""