title: The difference between wait_queue_head and wait_queue in linux kernel
body: <p>I can find many examples regarding <code>wait_queue_head</code>.
  It works as a signal, create a <code>wait_queue_head</code>, someone
  can sleep using it until someother kicks it up.</p>
  
  <p>But I can not find a good example of using <code>wait_queue</code> itself, supposedly very related to it.</p>
  
  <p>Could someone gives example, or under the hood of them?</p>