// In header: <boost/log/sinks/async_frontend.hpp>

// A scope guard that resets a flag on destructor.
class scoped_flag {
public:
  // construct/copy/destruct
  explicit scoped_flag(frontend_mutex_type &, condition_variable_any &, 
                       boost::atomic< bool > &);
  scoped_flag(scoped_flag const &) = delete;
  scoped_flag & operator=(scoped_flag const &) = delete;
  ~scoped_flag();
};