Run unsafe proces in a loop until we've caught up

and wrap unsafe process in a try block

synapse/push/httppusher.py

@@ -116,7 +116,16 @@ class HttpPusher(object):
             return
         try:
             self.processing = True
+            # if the max ordering changes while we're running _unsafe_process,
+            # call it again, and so on until we've caught up.
+            while True:
+                starting_max_ordering = self.max_stream_ordering
+                try:
                     yield self._unsafe_process()
+                except:
+                    logger.exception("Exception processing notifs")
+                if self.max_stream_ordering == starting_max_ordering:
+                    break
         finally:
             self.processing = False
 
@@ -127,7 +136,7 @@ class HttpPusher(object):
         Never call this directly: use _process which will only allow this to
         run once per pusher.
         """
-        starting_max_ordering = self.max_stream_ordering
+
         unprocessed = yield self.store.get_unread_push_actions_for_user_in_range(
             self.user_id, self.last_stream_ordering, self.max_stream_ordering
         )
@@ -188,8 +197,6 @@ class HttpPusher(object):
                     self.timed_call = reactor.callLater(self.backoff_delay, self.on_timer)
                     self.backoff_delay = min(self.backoff_delay * 2, self.MAX_BACKOFF_SEC)
                     break
-        if self.max_stream_ordering != starting_max_ordering:
-            self._unsafe_process()
 
     @defer.inlineCallbacks
     def _process_one(self, push_action):