The Bakery Everything CakePHP

It uses cake's cache to log the pid (and an optional user supplied prefix) of a current running shell. When that shell is executed it refers to the cache and checks with PS to see if that process is still running. If it is still running then it quits. I had a site that needed to generate thumbnails for uploaded files, the process sometimes took many minutes so I didn't want to tie it to the controller handling the upload. I made a task to do it but since the process was very resource intensive I only wanted to run one at one time. My host didn't appreciate me running more then one either and would kill my processes. This solved my problem.

Component Class:

Download code <?php 
class DaemonTask extends Shell {

   function execute($prefix = '') {
           //the key the pid is stored with - default to just 'pid'
           $pidstring = $prefix . 'pid';
        if(!Cache::read($pidstring)){
            Cache::write($pidstring, getmypid(), 3600);    
        }else{
            $ps = shell_exec('ps -o pid -A');
            $ps = explode("\n", trim($ps));
            foreach($ps as $key => &$value){
                $value = trim($value);
            }
            if(in_array(Cache::read($pidstring), $ps)){
                exit("already got a process running\n");
            }else{
                echo "replacing stale pid\n";
                Cache::write($pidstring, getmypid(), 3600);    
            }
        }
    }
}
?>
It should work with most flavors of unix/linux (works on my osx 10.4, 10.5 and on debian and ubuntu linux's, sometimes the ps command is a little different so you may have to tweak that if it doesn't work). Here is the basic usage.

Controller Class:

Download code <?php 
class ThumbShell extends Shell {
    var $uses = array('Thumb');
     var $tasks = array('Daemon');

    function generate(){
        $this->Daemon->execute('thumb');
        //Configure::write('debug', 0);
        $thumbs = $this->Thumb->findAll(array('status' => 'pending'));
        if(!$thumbs){$this->out("Processing 0 Thumbs");return true;}
        $this->out('Processing ' . count($thumbs) . ' thumbs');
        foreach($thumbs as $thumb){
            $thumb = $this->Thumb->read(null,$thumb['Thumb']['id']);
            $this->out('Processing thumb id ' . $this->Thumb->id); 
            if(!$this->Thumb->generate()){
                $this->out('Processing of thumb id ' . $this->Thumb->id . ' failed!');
            }
        }
    }

}
?>
Enjoy!