Question

Here’s my problem:

In my database I have a requests table, which has a status field.
A cronjob runs every minute, looking for every request with a “pending” status. WHen it’s done processing the request it sets the status to “finished”.

Sometimes this cronjob takes over a minute to run, so two of the same cronjob are running. I need to make sure they don’t process the same request.

Right now I’m doing this:

$requests = db_all($this->db->query('SELECT * FROM x__mx_request WHERE status="pending"'));
//few lines of code later
$this->db->query('UPDATE x__mx_request SET status="processing" WHERE id IN('.implode(',', $ids).')');

I set the status to processing after I select it, which stops other scripts from processing it too, but Isn’t it possible that one script selects all requests, then a 2nd script selects all requests before the 1st script sets them to processing?

I’d like a more secure way of doing this!

EDIT: Thanks for the great answers, I’ll have to actually try them out though before I can mark one as correct.

Answer 1

you can try to make a lock/unlock file so cronjobs can check to “know” if a job is/isn’t already running.
also process pid could be used for identifying status of process in case something failed, not responding etc..