Checking if specific user is online through php session variable - session

Question

I'm currently trying to display all online users on my webpage using the php session variables. To do this, whenever a user logs in or out, a column in a database gets set to "online" or "offline".. However this doesn't entirely work since the database doesn't get updated when the user closes their browser (and therefor destroys the session).
So is there another way of checking if a certain sessionid is set??
Currently I am setting the session like this:
session_start();
$_SESSION['username']="Example Username";
To check from the current users page if there is a session variable set we can simply use:
if(isset($_SESSION['username']))
{
//username is set
}
But if we need to check if a specific user is online, how do we get for instance an array of all the session variables that have been set? e.g.
//Get all $_SESSION['username'] vars
//loop through array and check for specific $_SESSION
for($i=0; ... )
{
if( $_SESSION['username'][$i] == "User 1" )
{
//do something
}
}
From all that I've read so far, there doesn't seem to be a way to get an array of all sessions on your page..
So is there a better way of doing it, e.g. how do facebook, twitter, etc handle this stuff?
Thanks for your help!

Answer 1

One solution is to store a timestamp in your database in addition to the online/offline flag that records the last time a user accessed any of your website resources. Then you might just consider them offline after 15 minutes or some other constant value.
The other solution is to play with the callbacks here http://php.net/manual/en/function.session-set-save-handler.php where I think you can handle the gc callback and set the offline flag in your database.
If you search on that page for class SessionDB or go here it looks like somebody has implemented some version of this already in a custom class!

Answer 2

you can use a simple update query
for example you have a table users and in that you have a column called status(online/offline)
on your login.php use
<?php
//your user verification code
if(variable that holds your sql query){
$user_status=('UPDATE user SET status= online WHERE email="'your user email selector'")
}
then on the logout do a similar script just change the online value to offline

Answer 3

You could try this:
foreach ($_SESSION as $sessionKey => $sessionValue)
{
if( $sessionKey == 'username' ) && ( $sessionValue == 'User 1' )
{
//do something
}
}