event processing loop for a specified duration to execute at most one handler.
template< typename Rep, typename Period> std::size_t run_one_for( const chrono::duration< Rep, Period > & rel_time);
run_one_for() function blocks until one handler has been
dispatched, until the
has been stopped, or until the specified duration has elapsed.
The duration for which the call may block.
The number of handlers that were executed.