php - Only two people on a certain page at a time? -

I'm not sure how much security I'll implement it. I want to know whether a person or two people on my line Based. These two people are completely anonymous. I have an XMPP server, but I'm not sure how it will integrate into MySQL and I have a separate login system for it. Server side is done with PHP

EDIT: I want to allow two people on a certain page only, but if they leave that page, then I need to determine that Have they left?

The issue is that if someone closes their browser, you are not being notified That they have left the page.

What you can do is an AJAX request on the page, so that every 10-15 seconds can be requested to log into the server timestamp and session ID in a table with a session ID, and then You can ask the database to ask what is requested in the last 15 seconds