monitor<T>

Atomic

template<class T> 
class Atomic {
private:
     mutable T t;
     mutable std::mutex m;
public:
     Atomic( T t_ ) : t( t_ ) { }

     template<typename F>
     auto operator()( F f ) const -> decltype(f(t))
     {  std::lock_guard<mutex> hold{m};  return f(t);  }
};

// C++ and Beyond 2012
// herb sutter