Using std::atomic<T> for thread-safe accesses

In C++11 and later, the <atomic> header contains the definition of class template std::atomic<T>. There are two different ways you can think about std::atomic: you can think of it as a class template just like std::vector, with overloaded operators that just happen to implement thread-safe operations; or you can think of it as a magical built-in family of types whose names just happen to contain angle brackets. The latter way of thinking about it is actually pretty useful, because it suggests--correctly--that std::atomic is partly built into the compiler, and so the compiler will usually generate optimal code for atomic operations. The latter also suggests a way in which atomic is different from vector: with std::vector<T>, the T can be pretty much anything you like. With std::atomic<T>, the T is can be...