why is std::shared_ptr using atomic cpu operations

Question

I have a problem understanding why shared_ptr is using atomic cpu instructions... I cant figure out the reasons because it is NOT thread safe. Can somebody please explain.

Answer 1

Herb Sutter just used shared_ptr as a nice example in his gotw 95, he goes there to elaborate on design decision:
https://herbsutter.com/2014/01/13/gotw-95-solution-thread-safety-and-synchronization/