Cache set of users whose presence the other user should see

synapse/handlers/presence.py

@@ -29,6 +29,7 @@ from synapse.api.errors import SynapseError
 from synapse.api.constants import PresenceState
 from synapse.storage.presence import UserPresenceState
 
+from synapse.util.caches.descriptors import cachedInlineCallbacks
 from synapse.util.logcontext import preserve_fn
 from synapse.util.logutils import log_function
 from synapse.util.metrics import Measure
@@ -1031,7 +1032,6 @@ class PresenceEventSource(object):
         # sending down the rare duplicate is not a concern.
 
         with Measure(self.clock, "presence.get_new_events"):
-            user_id = user.to_string()
             if from_key is not None:
                 from_key = int(from_key)
 
@@ -1040,18 +1040,7 @@ class PresenceEventSource(object):
 
             max_token = self.store.get_current_presence_token()
 
-            plist = yield self.store.get_presence_list_accepted(user.localpart)
-            users_interested_in = set(row["observed_user_id"] for row in plist)
-            users_interested_in.add(user_id)  # So that we receive our own presence
-
-            users_who_share_room = yield self.store.get_users_who_share_room_with_user(
-                user_id
-            )
-            users_interested_in.update(users_who_share_room)
-
-            if explicit_room_id:
-                user_ids = yield self.store.get_users_in_room(explicit_room_id)
-                users_interested_in.update(user_ids)
+            users_interested_in = yield self._get_interested_in(user, explicit_room_id)
 
             user_ids_changed = set()
             changed = None
@@ -1093,6 +1082,31 @@ class PresenceEventSource(object):
     def get_pagination_rows(self, user, pagination_config, key):
         return self.get_new_events(user, from_key=None, include_offline=False)
 
+    @cachedInlineCallbacks(num_args=2, cache_context=True)
+    def _get_interested_in(self, user, explicit_room_id, cache_context):
+        """Returns the set of users that the given user should see presence
+        updates for
+        """
+        user_id = user.to_string()
+        plist = yield self.store.get_presence_list_accepted(
+            user.localpart, on_invalidate=cache_context.invalidate,
+        )
+        users_interested_in = set(row["observed_user_id"] for row in plist)
+        users_interested_in.add(user_id)  # So that we receive our own presence
+
+        users_who_share_room = yield self.store.get_users_who_share_room_with_user(
+            user_id, on_invalidate=cache_context.invalidate,
+        )
+        users_interested_in.update(users_who_share_room)
+
+        if explicit_room_id:
+            user_ids = yield self.store.get_users_in_room(
+                explicit_room_id, on_invalidate=cache_context.invalidate,
+            )
+            users_interested_in.update(user_ids)
+
+        defer.returnValue(users_interested_in)
+
 
 def handle_timeouts(user_states, is_mine_fn, syncing_user_ids, now):
     """Checks the presence of users that have timed out and updates as