The difference is it is encapsulated inside a function so only a call to this function can modify it. The use I cited was exactly what you mentioned - to achieve exclusivity for termination for every third thread (when and only when a sequence repeated 3 times there should be a viable result). Now I see it could probably be dealt with using first_match(). Thanks for your opinion. I will try to avoid static variables for communication between threads in any other circumstances than mentioned.