Variable not updating

[NICON]

function callback($buffer) {
    global $user_class, $db, $m;
    if (!$m->get('membersonline.' . $user_class->gang)) {
        $db->query("SELECT COUNT(id) FROM grpgusers WHERE gang = ? AND lastactive >= ?");
        $db->execute(array(
            $user_class->gang, 
            time() - 900
        ));
        $membersonline = $db->fetch_single();
        $m->set('membersonline.' . $user_class->gang, $membersonline);
    } else
        $membersonline = $m->get('membersonline.' . $user_class->gang);
   
   $buffer = str_replace("<!_-monline-_!>", $membersonline ? "<font color='yellow'><strong>" . prettynum($membersonline) . "</strong></font>" : 0, $buffer);
   return $buffer;
}
ob_start("callback");

<a href="test.php">Test Line [<!_-monline-_!>]</a>

My problem is quite simple but yet I cant figure it out. I want $membersonline to update as people go inactive using the existing format for similar data. Above is just that but as the number increases it just holds to the highest number and never drops lower. i.e. if the value shown is 3 and I check who is online and its 1 why is 3 still showing? Thanks in advance.

Edited November 22, 2016 by NICON

[requinix]

What's $m->get/set? Caching? Is that working correctly? It doesn't look like the ->get is setting any sort of TTL or expiration time...

[NICON]

That was the issue. I had stored a permanent variable in the cache and of coarse it would not update. I fixed it though with this:

if (!$m->get('membersonline.' . $user_class->gang)) {
        $db->query("SELECT COUNT(id) FROM grpgusers WHERE gang = ? AND lastactive >= ?");
		$db->execute(array(
			$user_class->gang, 
			time() - 900
		));
        $membersonline = $db->fetch_single();
        $m->set('membersonline.' . $user_class->gang, $membersonline, 1);
    } else
        $membersonline = $m->get('membersonline.' . $user_class->gang);

of coarse I enabled this after destroying the old variable. Thanks for your reply!