diff options
Diffstat (limited to 'synapse/handlers/presence.py')
| -rw-r--r-- | synapse/handlers/presence.py | 19 |
1 files changed, 13 insertions, 6 deletions
diff --git a/synapse/handlers/presence.py b/synapse/handlers/presence.py index 3edd359985..c80dc2eba0 100644 --- a/synapse/handlers/presence.py +++ b/synapse/handlers/presence.py @@ -1021,12 +1021,19 @@ class PresenceEventSource(object): if from_key == max_token: # This is necessary as due to the way stream ID generators work # we may get updates that have a stream ID greater than the max - # token. This is usually fine, as it just means that we may send - # down some presence updates multiple times. However, we need to - # be careful that the sync stream actually does make some - # progress, otherwise clients will end up tight looping calling - # /sync due to it returning the same token repeatedly. Hence - # this guard. C.f. #5503. + # token (e.g. max_token is N but stream generator may return + # results for N+2, due to N+1 not having finished being + # persisted yet). + # + # This is usually fine, as it just means that we may send down + # some presence updates multiple times. However, we need to be + # careful that the sync stream either actually does make some + # progress or doesn't return, otherwise clients will end up + # tight looping calling /sync due to it immediately returning + # the same token repeatedly. + # + # Hence this guard where we just return nothing so that the sync + # doesn't return. C.f. #5503. defer.returnValue(([], max_token)) presence = self.get_presence_handler() |