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Fix sync tightloop bug.

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If, for some reason, presence updates take a while to persist then it
can trigger clients to tightloop calling `/sync` due to the presence
handler returning updates but not advancing the stream token.

Fixes #5503.
This commit is contained in:
Erik Johnston 2019-06-21 11:10:27 +01:00
parent 7456698241
commit 8181e290a9
1 changed files with 12 additions and 2 deletions
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14
synapse/handlers/presence.py
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@ -1017,11 +1017,21 @@ class PresenceEventSource(object):
if from_key is not None:
from_key = int(from_key)
max_token = self.store.get_current_presence_token()
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.
defer.returnValue(([], max_token))
presence = self.get_presence_handler()
stream_change_cache = self.store.presence_stream_cache
max_token = self.store.get_current_presence_token()
users_interested_in = yield self._get_interested_in(user, explicit_room_id)
user_ids_changed = set()