How to limit 1 instance of a PHP script, what's wrong with my solution

Question

<?PHP
define('TEMPPATH', '/tmp/');
$fp = fopen(TEMPPATH.'abc.php.lock', 'a+');
if(!flock($fp, LOCK_EX | LOCK_NB))
    exit;

I use the above codes to limit the script from running multiple instances, and it's OK when I test it, but today when I logged in to my server (CentOS 6) and I saw two instances running, how could that happen?

[root@server user]# ps aux | grep abc
root     21061  0.0  0.1 103284  2016 pts/0    S+   15:45   0:00 grep abc
user     22560  0.0  1.2 154608 12788 ?        Ss   Nov10   1:35 /usr/bin/php /path/abc.php
user     25106  0.0  1.3 154896 13336 ?        Ss   Nov06   2:51 /usr/bin/php /path/abc.php

The script was started from crontab jobs, crontab tries to run it every minute, is there any better ways to do this ?

Answer 1

Very elaborate instance control :).

Take a look at mine:

function par_processes($name = null,$ownPids = array(),$dbg = false){
    exec("ps x | grep $name", $ProcessState);
    $modifier = 0;

    while (list($idp,$procs) = each($ProcessState)){
        if (preg_match("/grep/i",$procs)) {
            unset($ProcessState[$idp]);
        }else{
            if (!empty($ownPids)){
                if (in_array(strstr(trim($procs)," ",true),$ownPids)){
                    unset($ProcessState[$idp]);
                }
            }
        }
    }

    if (!$dbg){
        return (count($ProcessState) - $modifier);
    }else{
        return array(0=>(count($ProcessState) - $modifier),1=>$ProcessState,2=>$ownPids);
    }
}

And in the php daemon before I go any further I use this:

# INSTANCE CHECK    
if (par_processes("MYSOFTWARENAME",array(getmypid()))){
    error_log("SOME ERROR"); die();
}

Quite frankly it can be done quicker and more effective (probably) but it does the job. Of course you need to be able to run exec() for this to work.