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Fix sync tightloop bug. #5507

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Jul 1, 2019
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Fix sync tightloop bug. #5507

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8181e29
Fix sync tightloop bug.
erikjohnston Jun 21, 2019
8d452e0
Newsfile
erikjohnston Jun 21, 2019
915280f
Fixup comment
erikjohnston Jul 1, 2019
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1 change: 1 addition & 0 deletions changelog.d/5507.bugfix
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix bug where clients could tight loop calling `/sync` for a period.
14 changes: 12 additions & 2 deletions synapse/handlers/presence.py
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Expand Up @@ -1017,11 +1017,21 @@ def get_new_events(
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
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ok so I think this a bit confusing, since your fix is explicitly to stop the sync stream making progress.

perhaps you could spell out the situation as per #5507 (comment)?

# 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()
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