recordme.php

<?php
// Look for token
$token = (isset($_GET['token']) && preg_match('/^[0-9a-f]{8}$/', $_GET['token'])) ? $_GET['token'] : false;
if (!$token) {
  $token = sprintf('%08x', crc32(microtime()));
}
// get current minute, build APC key
$quadrant = ceil(date_create()->format('s') / 15); // between 1-4
$previousQuadrant = $quadrant - 1 < 1 ? 4 : $quadrant - 1;
$key = 'pinger_'.$quadrant; 
$previousKey = 'pinger_'.$previousQuadrant;
// get tokens for the last 30 seconds
$current = apc_fetch($key);
$previous = apc_fetch($previousKey);
if (!is_array($current)) {
  $current = array();
}
if (!is_array($previous)) {
  $previous = array();
}
// Add current token if not found
if (count($current) < 250 && !in_array($token, $current)) {
  $current[] = $token;
  apc_store($key, $current, 31);
}
// Build return object: userCount, token
$output = array(
  'userCount' => count($current) > 250 ? '250+' : count(array_unique(array_merge($current, $previous))),
  'token' => $token,
);
header('Content-Type: application/json');
print json_encode($output);
exit;

?>