<slide title="Problem Solving Exercise">
<break />
<example title="Add Locking" result="1"><![CDATA[<?php
  $cnt_file = '/tmp/'.basename(__FILE__).'.cnt';;
  $fp = fopen($cnt_file, 'r+');
  flock($fp, LOCK_EX);
  $num = (int)@fgets($fp);
  $num++;
  rewind($fp);
  fputs($fp, $num); 
  flock($fp, LOCK_UN);
  fclose($fp);
  echo "File has been accessed $num times";
?>]]></example>
</slide>
