Kill process if is modified

Autokill.php

<?php

class Autokill {
    var $start_mtime_included_files = array();

    function Autokill() { $this->__construct(); }
    function __construct() {
        clearstatcache();

        $files = get_included_files();
        foreach ((array)$files as $file)
            $this->start_mtime_included_files[$file] = filemtime($file);
    }

    function kill_if_modified() {
        clearstatcache();

        $modified = false;
        $files = get_included_files();
        foreach ((array)$files as $file) {
            if (!array_key_exists($file, $this->start_mtime_included_files))
                $this->start_mtime_included_files[$file] = filemtime($file);

            else if (filemtime($file) != $this->start_mtime_included_files[$file]) {
                echo $file."[".$this->start_mtime_included_files[$file]."<".filemtime($file)."] \n";
                $modified = true;
                break;
            }
        }

        if ($modified)
            $this->kill();

        return $modified;
    }

    function kill() {
        $pid = getmypid();
        $cmd = "kill -9 ".(int)$pid;
        echo $cmd."\n";
        shell_exec($cmd);
    }
}