Fix typing being reset causing infinite syncs (#4127)

2 files changed, 24 insertions, 4 deletions

diff --git a/synapse/app/synchrotron.py b/synapse/app/synchrotron.py
index 3926c7f263..0354e82bf8 100644
--- a/synapse/app/synchrotron.py
+++ b/synapse/app/synchrotron.py
@@ -226,7 +226,15 @@ class SynchrotronPresence(object):
 class SynchrotronTyping(object):
     def __init__(self, hs):
         self._latest_room_serial = 0
+        self._reset()
+
+    def _reset(self):
+        """
+        Reset the typing handler's data caches.
+        """
+        # map room IDs to serial numbers
         self._room_serials = {}
+        # map room IDs to sets of users currently typing
         self._room_typing = {}
 
     def stream_positions(self):
@@ -236,6 +244,12 @@ class SynchrotronTyping(object):
         return {"typing": self._latest_room_serial}
 
     def process_replication_rows(self, token, rows):
+        if self._latest_room_serial > token:
+            # The master has gone backwards. To prevent inconsistent data, just
+            # clear everything.
+            self._reset()
+
+        # Set the latest serial token to whatever the server gave us.
         self._latest_room_serial = token
 
         for row in rows:
diff --git a/synapse/handlers/typing.py b/synapse/handlers/typing.py
index c610933dd4..a61bbf9392 100644
--- a/synapse/handlers/typing.py
+++ b/synapse/handlers/typing.py
@@ -63,11 +63,8 @@ class TypingHandler(object):
         self._member_typing_until = {}  # clock time we expect to stop
         self._member_last_federation_poke = {}
 
-        # map room IDs to serial numbers
-        self._room_serials = {}
         self._latest_room_serial = 0
-        # map room IDs to sets of users currently typing
-        self._room_typing = {}
+        self._reset()
 
         # caches which room_ids changed at which serials
         self._typing_stream_change_cache = StreamChangeCache(
@@ -79,6 +76,15 @@ class TypingHandler(object):
             5000,
         )
 
+    def _reset(self):
+        """
+        Reset the typing handler's data caches.
+        """
+        # map room IDs to serial numbers
+        self._room_serials = {}
+        # map room IDs to sets of users currently typing
+        self._room_typing = {}
+
     def _handle_timeouts(self):
         logger.info("Checking for typing timeouts")