Preventing a PHP Script From Running Multiple Times at Once in Cron

I'm building a database synchronization script that should run every 5 minutes in Linux's cron. The problem is that it can end up taking longer than five minutes, so while researching a way to prevent the script from running again before the previous one finishes, I found the solution at the link below and post it here with small changes:

http://abhinavsingh.com/blog/2009/12/how-to-use-locks-in-php-cron-jobs-to-avoid-cron-overlaps/

Create a file called CronHelper.php and add the code below (I put it in the same folder as my cron script):

<?php
define('LOCK_DIR', __DIR__ . '/');
define('LOCK_SUFFIX', '.lock');

class CronHelper {
    private static $pid;

    function __construct() {
        
    }

    function __clone() {
        
    }

    private static function isrunning() {
        $pids = explode(PHP_EOL, `ps -e | awk '{print $1}'`);
        if (in_array(self::$pid, $pids)) {
            return TRUE;
        }
        return FALSE;
    }

    public static function lock() {
        global $argv;
        
        $path_parts = pathinfo($argv[0]);

        $lock_file = LOCK_DIR . $path_parts['basename'] . LOCK_SUFFIX;

        if (file_exists($lock_file)) {
            //return FALSE;
            // Is running?
            self::$pid = file_get_contents($lock_file);
            if (self::isrunning()) {
                error_log("==" . self::$pid . "== Já está em progresso...");
                return FALSE;
            } else {
                error_log("==" . self::$pid . "== O job anterior foi interrompido abruptamente...");
            }
        }

        self::$pid = getmypid();
        file_put_contents($lock_file, self::$pid);
        error_log("==" . self::$pid . "== Trava adquirida, processando o job...");
        return self::$pid;
    }

    public static function unlock() {
        global $argv;

        $lock_file = LOCK_DIR . $argv[0] . LOCK_SUFFIX;

        if (file_exists($lock_file)) {
            unlink($lock_file);
        }

        error_log("==" . self::$pid . "== Soltando a trava...");
        return TRUE;
    }

}

To use it, put all the cron code inside the if:

<?php
require 'CronHelper.php';

if(($pid = cronHelper::lock()) !== FALSE) {
    /*
     * O código do seu cron job vai aqui!
     */

    cronHelper::unlock();
}

?>