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Fixup comment

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Erik Johnston 2019-07-01 10:22:42 +01:00
parent 8d452e0ca5
commit 915280f1ed
1 changed files with 13 additions and 6 deletions
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19
synapse/handlers/presence.py
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@ -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()