Move invalidation cb to its own structure

synapse/push/bulk_push_rule_evaluator.py

@@ -24,6 +24,8 @@ from synapse.api.constants import EventTypes, Membership
 from synapse.util.caches.descriptors import cached
 from synapse.util.async import Linearizer
 
+from collections import namedtuple
+
 
 logger = logging.getLogger(__name__)
 
@@ -204,12 +206,7 @@ class RulesForRoom(object):
         # To get around this we pass a function that on invalidations looks ups
         # the RoomsForUser entry in the cache, rather than keeping a reference
         # to self around in the callback.
-        def invalidate_all_cb():
-            rules = rules_for_room_cache.get(room_id, update_metrics=False)
-            if rules:
-                rules.invalidate_all()
-
-        self.invalidate_all_cb = invalidate_all_cb
+        self.invalidate_all_cb = _Invalidation(rules_for_room_cache, room_id)
 
     @defer.inlineCallbacks
     def get_rules(self, context):
@@ -347,3 +344,15 @@ class RulesForRoom(object):
             self.member_map.update(members)
             self.rules_by_user = rules_by_user
             self.state_group = state_group
+
+
+class _Invalidation(namedtuple("_Invalidation", ("cache", "room_id"))):
+    # We rely on _CacheContext implementing __eq__ and __hash__ sensibly,
+    # which namedtuple does for us (i.e. two _CacheContext are the same if
+    # their caches and keys match). This is important in particular to
+    # dedupe when we add callbacks to lru cache nodes, otherwise the number
+    # of callbacks would grow.
+    def __call__(self):
+        rules = self.cache.get(self.room_id, None, update_metrics=False)
+        if rules:
+            rules.invalidate_all()