Lockmagentoprocess.php

<?php

class Lockmagentoprocess
{
    /**
     * Our process ID.
     */
    const PROCESS_ID = 'ProcessId';

    /**
     * Mage_Index_Model_Process will provide us a lock file API.
     *
     * @var Mage_Index_Model_Process $indexProcess
     */
    private $indexProcess;

    /**
     * Constructor.  Instantiate the Process model, and set our custom
     * batch process ID.
     */
    public function __construct()
    {
        $this->indexProcess = new Mage_Index_Model_Process();

        $this->indexProcess->setId(self::PROCESS_ID);
    }

    /**
     * Process all the things!
     */
    public function changeEverything()
    {
        if ($this->indexProcess->isLocked())
        {
            $this->log(sprintf("Another %s process is running!  Abort", self::PROCESS_ID));
            return false;
        }

        // Set an exclusive lock.
        $this->indexProcess->lockAndBlock();

        $this->log("Starting...hold on to your hats.");

        for ($i = 1; $i < 1000; $i++)
        {
            // Do something complicated with $i.
        }

        $this->log("Finished!  Whew.");

        // Remove the lock.
        $this->indexProcess->unlock();

        return true;
    }

    /**
     * Log a message to stdout.
     *
     * @param $msg
     */
    public function log($msg)
    {
        echo $msg . PHP_EOL;
    }
}