title: What is the definition of a boost::asio::io_service ready handler?
body: <p>I am trying to understand the difference between io_service's poll()/poll_one() and run()/run_one(). The difference as stated in the documentation is that poll() executes ready handlers as opposed to run() which executes any handler.</p>
  
  <p>But nowhere in the boost documentation could I find the definition of a 'ready handler'.</p>
  
  <p>A valid answer to this question is one able to show, preferably with a code example, the difference between a ready and non-ready handler and the difference between how poll() and run() executes it.</p>
  
  <p>Thanks.</p>