fix(mgb/opr-mm): fix user_data thread safety in CollectiveComm

GitOrigin-RevId: b6d6184e91b254119a96c892a3c5a68b024729a2

src/opr-mm/impl/collective_comm.cpp

@@ -458,13 +458,16 @@ void CollectiveComm::opr_register() {
     auto hash = m_group_client->opr_register(m_key, m_nr_devices, m_rank,
             reinterpret_cast<uintptr_t>(cuda_env.stream));
 
-    auto megray_comm_builder =
-            owner_graph()
-                    ->options()
-                    .user_data
-                    .get_user_data_or_create<MegRayCommunicatorBuilder>();
+    MegRayCommunicatorBuilder* builder;
 
-    m_megray_comm = megray_comm_builder->get_megray_comm(
+    {
+        static std::mutex user_data_mtx;
+        std::unique_lock<std::mutex> lk(user_data_mtx);
+        builder = owner_graph()->options().user_data
+                .get_user_data_or_create<MegRayCommunicatorBuilder>();
+    }
+
+    m_megray_comm = builder->get_megray_comm(
             hash, m_key, m_nr_devices, m_rank,
             get_megray_backend(m_backend), m_group_client);