Construct a signal set and add one signal.
basic_signal_set( const executor_type & ex, int signal_number_1);
This constructor creates a signal set and registers for one signal.
The I/O executor that the signal set will use, by default, to dispatch handlers for any asynchronous operations performed on the signal set.
The signal number to be added.
This constructor is equivalent to performing:
boost::asio::signal_set signals(ex); signals.add(signal_number_1);