How to detect whether a PHP script is already running?

Question

I have a cron script that executes a PHP script every 10 minutes. The script checks a queue and processes the data in the queue. Sometimes the queue has enough data to last ov

Answer 1

This worked for me. Set a database record with a lock flag and a time stamp. My script should complete well within 15min so added that as a last locked feild to check:

       $lockresult = mysql_query("
       SELECT *
       FROM queue_locks
       WHERE `lastlocked` > DATE_SUB(NOW() , INTERVAL 15 MINUTE)    
       AND `locked` = 'yes'
       AND `queid` = '1'
       LIMIT 1
        "); 
$LockedRowCount = mysql_num_rows($lockresult);

if($LockedRowCount>0){
    echo "this script is locked, try again later";
    exit;   
}else{
//Set the DB record to locked and carry on son
$result = mysql_query("
            UPDATE `queue_locks` SET `locked` = 'yes', `lastlocked` = CURRENT_TIMESTAMP WHERE `queid` = 1;
            ");

}

Then unlock it at the end of the script:

    $result = mysql_query("UPDATE `queue_locks` SET `locked` = 'no' WHERE `queid` = 1;");