Construct a signal set and add two signals.
basic_signal_set( boost::asio::io_service & io_service, int signal_number_1, int signal_number_2);
This constructor creates a signal set and registers for two signals.
io_service object that
the signal set will use to dispatch handlers for any asynchronous
operations performed on the set.
The first signal number to be added.
The second signal number to be added.
This constructor is equivalent to performing:
boost::asio::signal_set signals(io_service); signals.add(signal_number_1); signals.add(signal_number_2);