title: Visual "busy" indication in Primefaces
body: <p>I have a Primefaces-based application, in which there are some lengthy operations.</p>
  
  <p>When such operation is being executed, I want to indicate this somehow (like displaying an hourglass or a message, which appears at the center of the screen).</p>
  
  <p>What is the easiest way to do this in Primefaces/JSF?</p>