Question

This seems like a simple question, but I am having trouble finding the answer.

I am making a web app which would require the constant running of a task.

I’ll use sites like Pingdom or Twitterfeed as an analogy. As you may know, Pingdom checks uptime, so is constantly checking websites to see if they are up and Twitterfeed checks RSS feeds to see if they;ve changed and then tweet that. I too need to run a simple script to cycle through URLs in a database and perform an action on them.

My question is: how should I implement this? I am familiar with cron, currently using it to do my server backups. Would this be the way to go?

I know how to make a Python script which runs indefinitely, starting back at the beginning with the next URL in the database when I’m done. Should I just run that on the server? How will I know it is always running and doesn’t crash or something?

I hope this question makes sense and I hope I am not repeating someone else or anything.

Thank you,

Sam

Edit: To be clear, I need the task to run constantly. As in, check URL 1 in the database, check URl 2 in the database, check URL 3 and, when it reaches the last one, go right back to the beginning. Thanks!

Answer 1

If you need a repeatable running of the task which can be run from command line – that’s what the cron is ideal for.
I don’t see any demerits of this approach.

Update:
Okay, I saw the issue somewhat different. Now I see several solutions:

• run the cron task at set intervals, let it process the data once per run, next time it will process the data on another run; use PIDs/Database/semaphores to avoid parallel processes;
• update the processes that insert/update data in the database; let the information be processed when it is inserted/updated; c)
• write a demon process which will reside in memory and check the data in real time.