Constructor notifies the io_service that work is starting.
boost::asio::io_service & io_service);
The constructor is used to inform the io_service that some work has
begun. This ensures that the io_service object's run()
function will not exit while the work is underway.
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)