title: Auto-Update Messaging in PHP without using set interval function
body: <p>I am trying to build a messaging environment in PHP and stuck with some issues. 
  I am facing difficulties in auto-update of user online-list and messages. I want to auto update the user-list without need of reloading page again and again as it is going to put load on our server. same problem is in messaging. I want messages to get auto updated but don't want to put load on my servers with multiple hits using set interval function. So, Is there any robust and feasible method or theory that could help me out here. </p>
  
  <p>Thanks in advance to those who are going to put any effort here.</p>