check_process.php

<?php
/**
 *
 * Thanks to Erickson Reyes ercbluemonday at yahoo dot com | so processes dont overlap
 * ref : http://www.php.net/manual/en/function.getmypid.php#94531*/

// Initialize variables
$found = 0;
$file = basename(__FILE__);
$commands = array();

// Get running processes.
exec("ps w", $commands);

// If processes are found
if (count($commands) > 0)
{

	foreach ($commands as $command)
	{
		if (strpos($command, $file) === false)
		{
			// Do nothin'
		}
		else
		{
			// Let's count how many times the file is found.
			$found++;
		}
	}
}

// If the instance of the file is found more than once.
if ($found > 1)
{
	echo "Another process is running.\n";
	die();
}