GZ - online visitors counter

<?php
// two config lines

  $dataFile = "counter.txt";

  $sessionTime = 5; //this is the time in **minutes** to consider someone 

online before removing them from our file


if(!file_exists($dataFile)) {

  $fp = fopen($dataFile, "w+");

  fclose($fp);

  }
$ip = $_SERVER['REMOTE_ADDR'];

  $visitor = array();

  $onvisitor = array();
// insert new in counter.txt

  $fp = fopen($dataFile, "r");

  flock($fp, LOCK_SH);

  while(!feof($fp)) {

  $visitor[] = rtrim(fgets($fp, 32));

  }

  flock($fp, LOCK_UN);

  fclose($fp);


// removing old entries

  $x = 0;

  $old = FALSE;

  foreach($visitor as $key => $data) {

  list( , $last) = explode("|", $data);

  if(time() - $last >= $sessionTime * 60) {

  $visitor[$x] = "";

  } else {

  if(strpos($data, $ip) !== FALSE) {

  $old = TRUE;

  $visitor[$x] = "$ip|" . time();

  }

  }

  $x++;

  }
if($old == FALSE) {

  $visitor[] = "$ip|" . time();

  }
//writing

  $fp = fopen($dataFile, "w+");

  flock($fp, LOCK_EX);

  $i = 0;

  foreach($visitor as $single) {

  if($single != "") {

  fwrite($fp, $single . "\r\n");

  $i++;

  }

  }

  flock($fp, LOCK_UN);

  fclose($fp);

  echo '<strong>curently ' . $i . ' online</strong>';


?>