Limit concurrent AS joins

synapse/handlers/room_member.py

@@ -31,7 +31,7 @@ from synapse.api.constants import (
 )
 from synapse.api.errors import AuthError, SynapseError, Codes
 from synapse.types import UserID, RoomID
-from synapse.util.async import Linearizer
+from synapse.util.async import Linearizer, Limiter
 from synapse.util.distributor import user_left_room, user_joined_room
 
 
@@ -68,6 +68,7 @@ class RoomMemberHandler(object):
         self.event_creation_hander = hs.get_event_creation_handler()
 
         self.member_linearizer = Linearizer(name="member")
+        self.member_limiter = Limiter(3)
 
         self.clock = hs.get_clock()
         self.spam_checker = hs.get_spam_checker()
@@ -241,6 +242,11 @@ class RoomMemberHandler(object):
     ):
         key = (room_id,)
 
+        as_id = object()
+        if requester.app_service:
+            as_id = requester.app_service.id
+
+        with (yield self.member_limiter.queue(as_id)):
             with (yield self.member_linearizer.queue(key)):
                 result = yield self._update_membership(
                     requester,