diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index e4ce037acf..7785417311 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -30,9 +30,10 @@ import synapse.metrics
from synapse.types import get_domain_from_id
from synapse.util import async
from synapse.util.caches.response_cache import ResponseCache
-from synapse.util.logcontext import make_deferred_yieldable, preserve_fn
from synapse.util.logutils import log_function
+from six import iteritems
+
# when processing incoming transactions, we try to handle multiple rooms in
# parallel, up to this limit.
TRANSACTION_CONCURRENCY_LIMIT = 10
@@ -212,16 +213,17 @@ class FederationServer(FederationBase):
if not in_room:
raise AuthError(403, "Host not in room.")
- result = self._state_resp_cache.get((room_id, event_id))
- if not result:
- with (yield self._server_linearizer.queue((origin, room_id))):
- d = self._state_resp_cache.set(
- (room_id, event_id),
- preserve_fn(self._on_context_state_request_compute)(room_id, event_id)
- )
- resp = yield make_deferred_yieldable(d)
- else:
- resp = yield make_deferred_yieldable(result)
+ # we grab the linearizer to protect ourselves from servers which hammer
+ # us. In theory we might already have the response to this query
+ # in the cache so we could return it without waiting for the linearizer
+ # - but that's non-trivial to get right, and anyway somewhat defeats
+ # the point of the linearizer.
+ with (yield self._server_linearizer.queue((origin, room_id))):
+ resp = yield self._state_resp_cache.wrap(
+ (room_id, event_id),
+ self._on_context_state_request_compute,
+ room_id, event_id,
+ )
defer.returnValue((200, resp))
@@ -425,9 +427,9 @@ class FederationServer(FederationBase):
"Claimed one-time-keys: %s",
",".join((
"%s for %s:%s" % (key_id, user_id, device_id)
- for user_id, user_keys in json_result.iteritems()
- for device_id, device_keys in user_keys.iteritems()
- for key_id, _ in device_keys.iteritems()
+ for user_id, user_keys in iteritems(json_result)
+ for device_id, device_keys in iteritems(user_keys)
+ for key_id, _ in iteritems(device_keys)
)),
)
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