Sort out error handling

synapse/storage/events.py

@@ -502,8 +502,8 @@ class EventsStore(SQLBaseStore):
 
     def _do_fetch(self, conn):
         event_list = []
-        try:
         while True:
+            try:
                 logger.debug("do_fetch getting lock")
                 with self._event_fetch_lock:
                     logger.debug("do_fetch go lock: %r", self._event_fetch_list)
@@ -561,7 +561,6 @@ class EventsStore(SQLBaseStore):
             defer.returnValue({})
 
         events_d = defer.Deferred()
-        try:
         logger.debug("enqueueueueue getting lock")
         with self._event_fetch_lock:
             logger.debug("enqueue go lock")
@@ -569,21 +568,19 @@ class EventsStore(SQLBaseStore):
                 (events, events_d)
             )
 
+            if self._event_fetch_ongoing < 1:
                 self._event_fetch_ongoing += 1
+                should_start = True
+            else:
+                should_start = False
 
+        if should_start:
             self.runWithConnection(
                 self._do_fetch
             )
 
-        except Exception as e:
-            if not events_d.called:
-                events_d.errback(e)
-
         logger.debug("events_d before")
-        try:
         rows = yield events_d
-        except:
-            logger.exception("events_d")
         logger.debug("events_d after")
 
         res = yield defer.gatherResults(