- std::unique_ptr<MIDIMappingProto> mapping_proto;
- int num_controller_banks;
- int current_controller_bank = 0;
+ mutable std::mutex mapping_mu;
+ std::unique_ptr<MIDIMappingProto> mapping_proto; // Under <mapping_mu>.
+ int num_controller_banks; // Under <mapping_mu>.
+ std::atomic<int> current_controller_bank{0};