1 files changed, 48 insertions, 0 deletions
diff --git a/synapse/notifier.py b/synapse/notifier.py
index 560866b26e..3c36a20868 100644
--- a/synapse/notifier.py
+++ b/synapse/notifier.py
@@ -159,6 +159,8 @@ class Notifier(object):
             self.remove_expired_streams, self.UNUSED_STREAM_EXPIRY_MS
         )
 
+        self.replication_deferred = ObservableDeferred(defer.Deferred())
+
         # This is not a very cheap test to perform, but it's only executed
         # when rendering the metrics page, which is likely once per minute at
         # most when scraping it.
@@ -207,6 +209,8 @@ class Notifier(object):
             ))
             self._notify_pending_new_room_events(max_room_stream_id)
 
+            self.notify_replication()
+
     def _notify_pending_new_room_events(self, max_room_stream_id):
         """Notify for the room events that were queued waiting for a previous
         event to be persisted.
@@ -276,6 +280,8 @@ class Notifier(object):
                 except:
                     logger.exception("Failed to notify listener")
 
+            self.notify_replication()
+
     @defer.inlineCallbacks
     def wait_for_events(self, user_id, timeout, callback, room_ids=None,
                         from_token=StreamToken("s0", "0", "0", "0", "0")):
@@ -479,3 +485,45 @@ class Notifier(object):
             room_streams = self.room_to_user_streams.setdefault(room_id, set())
             room_streams.add(new_user_stream)
             new_user_stream.rooms.add(room_id)
+
+    def notify_replication(self):
+        """Notify the any replication listeners that there's a new event"""
+        with PreserveLoggingContext():
+            deferred = self.replication_deferred
+            self.replication_deferred = ObservableDeferred(defer.Deferred())
+            deferred.callback(None)
+
+    @defer.inlineCallbacks
+    def wait_for_replication(self, callback, timeout):
+        """Wait for an event to happen.
+
+        :param callback:
+            Gets called whenever an event happens. If this returns a truthy
+            value then ``wait_for_replication`` returns, otherwise it waits
+            for another event.
+        :param int timeout:
+            How many milliseconds to wait for callback return a truthy value.
+        :returns:
+            A deferred that resolves with the value returned by the callback.
+        """
+        listener = _NotificationListener(None)
+
+        def timed_out():
+            listener.deferred.cancel()
+
+        timer = self.clock.call_later(timeout / 1000., timed_out)
+        while True:
+            listener.deferred = self.replication_deferred.observe()
+            result = yield callback()
+            if result:
+                break
+
+            try:
+                with PreserveLoggingContext():
+                    yield listener.deferred
+            except defer.CancelledError:
+                break
+
+        self.clock.cancel_call_later(timer, ignore_errs=True)
+
+        defer.returnValue(result)