title: Integrate boost::asio into file descriptor based eventloops (select/poll)
body: <p>If I want to integrate stuff from boost::asio into an eventloop that is based on file descriptors (select/poll), how can I achieve it? Other libraries with asynchronous functions offer to hand out a file descriptor that becomes readable as soon as there is work to be done, so that you can integrate it into the select/poll of the eventloop and let it call a processing callback of the library (like a single shot event processing).</p>
  
  <p>A great example would be an asynchronous name resolver in a thread pool, like discussed in <a href="https://stackoverflow.com/a/18832363/3750161">this question</a>.</p>