cron.helper.php

<?php
/*
 * https://gist.github.com/andergmartins/5066143
 * From: http://abhinavsingh.com/blog/2009/12/how-to-use-locks-in-php-cron-jobs-to-avoid-cron-overlaps/
 */

class CronHelper
{
	const LOCK_DIR     = '/tmp/';
	const LOCK_SUFFIX  = '.lock';
	const LOCK_AGE_MAX = 3600;

	private $pid    = false;
	private $file   = false;
	private $locked = false;

	/**
	 * @param string $file optional
	 */
	function __construct($file = '')
	{
		$this->initialize();

		global $argv;

		if (!$file && is_array($argv))
		{
			$file = implode('.', $argv);
		}

		$this->file = self::LOCK_DIR.$file.self::LOCK_SUFFIX;
	}

	/**
	 * @return bool
	 */
	public function isRunning()
	{
		if (!$this->pid)
		{
			return false;
		}

		$pids = explode(PHP_EOL, `ps -e | awk '{print $1}'`);
		if (in_array($this->pid, $pids))
		{
			return true;
		}
	}

	/**
	 * @return bool|int
	 */
	public function lock()
	{
		// unlock needs to be called before a new lock can be done
		if ($this->locked)
		{
			error_log("==$this->pid== Already locked, please wait...");
			return false;
		}

		if (file_exists($this->file))
		{
			$file_age = (time() - filemtime($this->file)); // in seconds

			// Is running?
			$this->pid = file_get_contents($this->file);
			if ($this->isRunning())
			{
				// check for staled locks
				if ($file_age > self::LOCK_AGE_MAX)
				{
					error_log("==$this->pid== Lock staled. Killing PID! Age: $file_age / ".self::LOCK_AGE_MAX." (Seconds)");

					// kill the running script
					exec('kill -9 ' .$this->pid);
					$this->unlock();

					return $this->lock();
				}

				error_log("==$this->pid== Already in progress...");

				return false;
			}
			else
			{
				error_log("==$this->pid== Previous job died abruptly...");
			}
		}

		$this->pid = getmypid();
		file_put_contents($this->file, $this->pid);
		error_log("==$this->pid== Lock acquired, processing the job...");

		$this->locked = true;

		return $this->pid;
	}

	/**
	 * @return bool
	 */
	public function unlock()
	{
		if (file_exists($this->file))
		{
			unlink($this->file);
		}

		if ($this->pid)
		{
			error_log("==$this->pid== Releasing lock...");
			$this->pid = false;
		}

		$this->locked = false;

		return true;
	}

	/**
	 * @return bool
	 * @throws Exception
	 */
	private function initialize()
	{
		if (!file_exists(self::LOCK_DIR))
		{
			if (!mkdir(self::LOCK_DIR))
			{
				throw new Exception(sprintf('Could not create folder LOCK_DIR (%s)', self::LOCK_DIR));
			}
		}

		if (!is_writable(self::LOCK_DIR))
		{
			throw new Exception(sprintf('Unable to write to LOCK_DIR (%s)', self::LOCK_DIR));
		}

		return true;
	}
}