If you do all the registry access in main before you load a level or do a wait then it should be ok. However you want fully locked access then just create a mutex and do a read modify write operation there then test the value after closing the mutex. The only way that an unprotected read modify write operation would fail is if you got a windows task switch in the middle AND your doing the same operation in another program at the same time. If it is limited to program start and program end then the chance of failure is minimal as it is very difficult to start or end programs at the same time.