Use the multi-user device resync to batch requests

synapse/handlers/e2e_keys.py

@@ -320,18 +320,25 @@ class E2eKeysHandler:
             destination,
         )
 
-        for user_id in users_to_resync_devices:
-            # We've decided we're sharing a room with this user and should
-            # probably be tracking their device lists. However, we haven't
-            # done an initial sync on the device list so we do it now.
         try:
-                resync_results = (
+            user_resync_results = (
-                    await self.device_handler.device_list_updater.user_device_resync(
+                await self.device_handler.device_list_updater.multi_user_device_resync(
-                        user_id
+                    list(users_to_resync_devices)
                 )
             )
+            for user_id in users_to_resync_devices:
+                resync_results = user_resync_results[user_id]
+
                 if resync_results is None:
-                    raise ValueError("Device resync failed")
+                    # TODO: It's weird that we'll store a failure against a
+                    #       destination, yet continue processing users from that
+                    #       destination.
+                    #       We might want to consider changing this, but for now
+                    #       I'm leaving it as I found it.
+                    failures[destination] = _exception_to_failure(
+                        ValueError(f"Device resync failed for {user_id!r}")
+                    )
+                    continue
 
                 # Add the device keys to the results.
                 user_devices = resync_results["devices"]