Merge pull request #3029 from matrix-org/erikj/linearize_generate_user_id

Linearize calls to _generate_user_id

synapse/handlers/register.py

@@ -24,7 +24,7 @@ from synapse.api.errors import (
 from synapse.http.client import CaptchaServerHttpClient
 from synapse import types
 from synapse.types import UserID
-from synapse.util.async import run_on_reactor
+from synapse.util.async import run_on_reactor, Linearizer
 from synapse.util.threepids import check_3pid_allowed
 from ._base import BaseHandler
 
@@ -46,6 +46,10 @@ class RegistrationHandler(BaseHandler):
 
         self.macaroon_gen = hs.get_macaroon_generator()
 
+        self._generate_user_id_linearizer = Linearizer(
+            name="_generate_user_id_linearizer",
+        )
+
     @defer.inlineCallbacks
     def check_username(self, localpart, guest_access_token=None,
                        assigned_user_id=None):
@@ -344,6 +348,8 @@ class RegistrationHandler(BaseHandler):
 
     @defer.inlineCallbacks
     def _generate_user_id(self, reseed=False):
+        if reseed or self._next_generated_user_id is None:
+            with (yield self._generate_user_id_linearizer.queue(())):
                 if reseed or self._next_generated_user_id is None:
                     self._next_generated_user_id = (
                         yield self.store.find_next_generated_user_id_localpart()

synapse/storage/registration.py

@@ -460,14 +460,12 @@ class RegistrationStore(RegistrationWorkerStore,
         """
         def _find_next_generated_user_id(txn):
             txn.execute("SELECT name FROM users")
-            rows = self.cursor_to_dict(txn)
 
             regex = re.compile("^@(\d+):")
 
             found = set()
 
-            for r in rows:
-                user_id = r["name"]
+            for user_id, in txn:
                 match = regex.search(user_id)
                 if match:
                     found.add(int(match.group(1)))