G cluster_1 upb Arena cluster_python cluster_01 upb_msg upb Message upb_array upb Array upb_msg->upb_array upb_msg2 upb Message upb_msg->upb_msg2 py_upb_msg Python Message py_upb_msg->upb_msg py_upb_arena Python Arena py_upb_msg->py_upb_arena py_upb_msg2 Python Message py_upb_msg2->upb_msg2 py_upb_msg2->py_upb_arena py_upb_arena->dummy key raw ptr unique ptr shared (GC) ptr key2       key:e->key2:w key:e->key2:w key:e->key2:w