Cron Job Helper - Lock, PID

cron.helper.php

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

define('LOCK_DIR', '/tmp/');
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;

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

		if(file_exists($lock_file)) {
			//return FALSE;

			// Is running?
			self::$pid = file_get_contents($lock_file);
			if(self::isrunning()) {
				error_log("==".self::$pid."== Already in progress...");
				return FALSE;
			}
			else {
				error_log("==".self::$pid."== Previous job died abruptly...");
			}
		}

		self::$pid = getmypid();
		file_put_contents($lock_file, self::$pid);
		error_log("==".self::$pid."== Lock acquired, processing the 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."== Releasing lock...");
		return TRUE;
	}

}