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Merge pull request #5507 from matrix-org/erikj/presence_sync_tighloop

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Fix sync tightloop bug.
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Erik Johnston 2019-07-01 11:43:10 +01:00 committed by GitHub
commit 04196a4dae
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2 changed files with 20 additions and 2 deletions
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1
changelog.d/5507.bugfix Normal file
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@ -0,0 +1 @@
Fix bug where clients could tight loop calling `/sync` for a period.

21
synapse/handlers/presence.py
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@ -1017,11 +1017,28 @@ 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 (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()
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()