|  | 
            Run the io_service
            object's event processing loop to execute at most one handler.
          
std::size_t run_one();
            The run_one()
            function blocks until one handler has been dispatched, or until the
            io_service
            has been stopped.
          
            The number of handlers that were executed. A zero return value implies
            that the io_service
            object is stopped (the stopped() function returns true).
            Subsequent calls to run(), run_one(), poll() or poll_one() will return immediately unless there
            is a prior call to reset().
          
Thrown on failure.