Only store data in caches, not "smart" objects (#9845)

Author: erikjohnston

changelog.d/9845.misc

@@ -0,0 +1 @@
+Only store the raw data in the in-memory caches, rather than objects that include references to e.g. the data stores.

synapse/push/bulk_push_rule_evaluator.py

@@ -106,6 +106,10 @@ def __init__(self, hs: "HomeServer"):
         self.store = hs.get_datastore()
         self.auth = hs.get_auth()
 
+        # Used by `RulesForRoom` to ensure only one thing mutates the cache at a
+        # time. Keyed off room_id.
+        self._rules_linearizer = Linearizer(name="rules_for_room")
+
         self.room_push_rule_cache_metrics = register_cache(
             "cache",
             "room_push_rule_cache",
@@ -123,7 +127,16 @@ async def _get_rules_for_event(
             dict of user_id -> push_rules
         """
         room_id = event.room_id
-        rules_for_room = self._get_rules_for_room(room_id)
+
+        rules_for_room_data = self._get_rules_for_room(room_id)
+        rules_for_room = RulesForRoom(
+            hs=self.hs,
+            room_id=room_id,
+            rules_for_room_cache=self._get_rules_for_room.cache,
+            room_push_rule_cache_metrics=self.room_push_rule_cache_metrics,
+            linearizer=self._rules_linearizer,
+            cached_data=rules_for_room_data,
+        )
 
         rules_by_user = await rules_for_room.get_rules(event, context)
 
@@ -142,17 +155,12 @@ async def _get_rules_for_event(
         return rules_by_user
 
     @lru_cache()
-    def _get_rules_for_room(self, room_id: str) -> "RulesForRoom":
-        """Get the current RulesForRoom object for the given room id"""
-        # It's important that RulesForRoom gets added to self._get_rules_for_room.cache
+    def _get_rules_for_room(self, room_id: str) -> "RulesForRoomData":
+        """Get the current RulesForRoomData object for the given room id"""
+        # It's important that the RulesForRoomData object gets added to self._get_rules_for_room.cache
         # before any lookup methods get called on it as otherwise there may be
         # a race if invalidate_all gets called (which assumes its in the cache)
-        return RulesForRoom(
-            self.hs,
-            room_id,
-            self._get_rules_for_room.cache,
-            self.room_push_rule_cache_metrics,
-        )
+        return RulesForRoomData()
 
     async def _get_power_levels_and_sender_level(
         self, event: EventBase, context: EventContext
@@ -282,11 +290,49 @@ def _condition_checker(
     return True
 
 
+@attr.s(slots=True)
+class RulesForRoomData:
+    """The data stored in the cache by `RulesForRoom`.
+
+    We don't store `RulesForRoom` directly in the cache as we want our caches to
+    *only* include data, and not references to e.g. the data stores.
+    """
+
+    # event_id -> (user_id, state)
+    member_map = attr.ib(type=Dict[str, Tuple[str, str]], factory=dict)
+    # user_id -> rules
+    rules_by_user = attr.ib(type=Dict[str, List[Dict[str, dict]]], factory=dict)
+
+    # The last state group we updated the caches for. If the state_group of
+    # a new event comes along, we know that we can just return the cached
+    # result.
+    # On invalidation of the rules themselves (if the user changes them),
+    # we invalidate everything and set state_group to `object()`
+    state_group = attr.ib(type=Union[object, int], factory=object)
+
+    # A sequence number to keep track of when we're allowed to update the
+    # cache. We bump the sequence number when we invalidate the cache. If
+    # the sequence number changes while we're calculating stuff we should
+    # not update the cache with it.
+    sequence = attr.ib(type=int, default=0)
+
+    # A cache of user_ids that we *know* aren't interesting, e.g. user_ids
+    # owned by AS's, or remote users, etc. (I.e. users we will never need to
+    # calculate push for)
+    # These never need to be invalidated as we will never set up push for
+    # them.
+    uninteresting_user_set = attr.ib(type=Set[str], factory=set)
+
+
 class RulesForRoom:
     """Caches push rules for users in a room.
 
     This efficiently handles users joining/leaving the room by not invalidating
     the entire cache for the room.
+
+    A new instance is constructed for each call to
+    `BulkPushRuleEvaluator._get_rules_for_event`, with the cached data from
+    previous calls passed in.
     """
 
     def __init__(
@@ -295,6 +341,8 @@ def __init__(
         room_id: str,
         rules_for_room_cache: LruCache,
         room_push_rule_cache_metrics: CacheMetric,
+        linearizer: Linearizer,
+        cached_data: RulesForRoomData,
     ):
         """
         Args:
@@ -303,38 +351,21 @@ def __init__(
             rules_for_room_cache: The cache object that caches these
                 RoomsForUser objects.
             room_push_rule_cache_metrics: The metrics object
+            linearizer: The linearizer used to ensure only one thing mutates
+                the cache at a time. Keyed off room_id
+            cached_data: Cached data from previous calls to `self.get_rules`,
+                can be mutated.
         """
         self.room_id = room_id
         self.is_mine_id = hs.is_mine_id
         self.store = hs.get_datastore()
         self.room_push_rule_cache_metrics = room_push_rule_cache_metrics
 
-        self.linearizer = Linearizer(name="rules_for_room")
-
-        # event_id -> (user_id, state)
-        self.member_map = {}  # type: Dict[str, Tuple[str, str]]
-        # user_id -> rules
-        self.rules_by_user = {}  # type: Dict[str, List[Dict[str, dict]]]
-
-        # The last state group we updated the caches for. If the state_group of
-        # a new event comes along, we know that we can just return the cached
-        # result.
-        # On invalidation of the rules themselves (if the user changes them),
-        # we invalidate everything and set state_group to `object()`
-        self.state_group = object()
-
-        # A sequence number to keep track of when we're allowed to update the
-        # cache. We bump the sequence number when we invalidate the cache. If
-        # the sequence number changes while we're calculating stuff we should
-        # not update the cache with it.
-        self.sequence = 0
-
-        # A cache of user_ids that we *know* aren't interesting, e.g. user_ids
-        # owned by AS's, or remote users, etc. (I.e. users we will never need to
-        # calculate push for)
-        # These never need to be invalidated as we will never set up push for
-        # them.
-        self.uninteresting_user_set = set()  # type: Set[str]
+        # Used to ensure only one thing mutates the cache at a time. Keyed off
+        # room_id.
+        self.linearizer = linearizer
+
+        self.data = cached_data
 
         # We need to be clever on the invalidating caches callbacks, as
         # otherwise the invalidation callback holds a reference to the object,
@@ -352,25 +383,25 @@ async def get_rules(
         """
         state_group = context.state_group
 
-        if state_group and self.state_group == state_group:
+        if state_group and self.data.state_group == state_group:
             logger.debug("Using cached rules for %r", self.room_id)
             self.room_push_rule_cache_metrics.inc_hits()
-            return self.rules_by_user
+            return self.data.rules_by_user
 
-        with (await self.linearizer.queue(())):
-            if state_group and self.state_group == state_group:
+        with (await self.linearizer.queue(self.room_id)):
+            if state_group and self.data.state_group == state_group:
                 logger.debug("Using cached rules for %r", self.room_id)
                 self.room_push_rule_cache_metrics.inc_hits()
-                return self.rules_by_user
+                return self.data.rules_by_user
 
             self.room_push_rule_cache_metrics.inc_misses()
 
             ret_rules_by_user = {}
             missing_member_event_ids = {}
-            if state_group and self.state_group == context.prev_group:
+            if state_group and self.data.state_group == context.prev_group:
                 # If we have a simple delta then we can reuse most of the previous
                 # results.
-                ret_rules_by_user = self.rules_by_user
+                ret_rules_by_user = self.data.rules_by_user
                 current_state_ids = context.delta_ids
 
                 push_rules_delta_state_cache_metric.inc_hits()
@@ -393,24 +424,24 @@ async def get_rules(
                 if typ != EventTypes.Member:
                     continue
 
-                if user_id in self.uninteresting_user_set:
+                if user_id in self.data.uninteresting_user_set:
                     continue
 
                 if not self.is_mine_id(user_id):
-                    self.uninteresting_user_set.add(user_id)
+                    self.data.uninteresting_user_set.add(user_id)
                     continue
 
                 if self.store.get_if_app_services_interested_in_user(user_id):
-                    self.uninteresting_user_set.add(user_id)
+                    self.data.uninteresting_user_set.add(user_id)
                     continue
 
                 event_id = current_state_ids[key]
 
-                res = self.member_map.get(event_id, None)
+                res = self.data.member_map.get(event_id, None)
                 if res:
                     user_id, state = res
                     if state == Membership.JOIN:
-                        rules = self.rules_by_user.get(user_id, None)
+                        rules = self.data.rules_by_user.get(user_id, None)
                         if rules:
                             ret_rules_by_user[user_id] = rules
                     continue
@@ -430,7 +461,7 @@ async def get_rules(
             else:
                 # The push rules didn't change but lets update the cache anyway
                 self.update_cache(
-                    self.sequence,
+                    self.data.sequence,
                     members={},  # There were no membership changes
                     rules_by_user=ret_rules_by_user,
                     state_group=state_group,
@@ -461,7 +492,7 @@ async def _update_rules_with_member_event_ids(
                 for. Used when updating the cache.
             event: The event we are currently computing push rules for.
         """
-        sequence = self.sequence
+        sequence = self.data.sequence
 
         rows = await self.store.get_membership_from_event_ids(member_event_ids.values())
 
@@ -501,23 +532,11 @@ async def _update_rules_with_member_event_ids(
 
         self.update_cache(sequence, members, ret_rules_by_user, state_group)
 
-    def invalidate_all(self) -> None:
-        # Note: Don't hand this function directly to an invalidation callback
-        # as it keeps a reference to self and will stop this instance from being
-        # GC'd if it gets dropped from the rules_to_user cache. Instead use
-        # `self.invalidate_all_cb`
-        logger.debug("Invalidating RulesForRoom for %r", self.room_id)
-        self.sequence += 1
-        self.state_group = object()
-        self.member_map = {}
-        self.rules_by_user = {}
-        push_rules_invalidation_counter.inc()
-
     def update_cache(self, sequence, members, rules_by_user, state_group) -> None:
-        if sequence == self.sequence:
-            self.member_map.update(members)
-            self.rules_by_user = rules_by_user
-            self.state_group = state_group
+        if sequence == self.data.sequence:
+            self.data.member_map.update(members)
+            self.data.rules_by_user = rules_by_user
+            self.data.state_group = state_group
 
 
 @attr.attrs(slots=True, frozen=True)
@@ -535,6 +554,10 @@ class _Invalidation:
     room_id = attr.ib(type=str)
 
     def __call__(self) -> None:
-        rules = self.cache.get(self.room_id, None, update_metrics=False)
-        if rules:
-            rules.invalidate_all()
+        rules_data = self.cache.get(self.room_id, None, update_metrics=False)
+        if rules_data:
+            rules_data.sequence += 1
+            rules_data.state_group = object()
+            rules_data.member_map = {}
+            rules_data.rules_by_user = {}
+            push_rules_invalidation_counter.inc()