Have a PHP script run forever, access a queue

Question

See also Having a PHP script loop forever doing computing jobs from a queue system, but that doesn't answer all my questions.

If I want to run a PHP script forever, accessing a queue and doing jobs:

1. What is the potential for memory problems? How to avoid them? (any flush functions or something I should use?)

2. What if the script dies for some reason? What would be a good method to automatically start it up again?

3. What would be the best basic approach to start the script. Since it runs forever, I don't need cron. But how do I start it up? (See also 2.)

Answer 1

Set the queue up as a cron script. Have it execute every 10 seconds. When the script fires up, check if there's a lock file present (something like .lock). If there is, exit immediately. If not, create the .lock and start processing. If any errors occur, email/log these errors, delete .lock and exit. If there's no tasks, then exit.

I think this approach is ideal, since PHP isn't really designed to be able to run a script for extended periods of time like you're asking. To avoid potential memory leaks, crashes etc, continuously executing the script is a better approach.

Answer 2

While PHP can access (publish and consume) MQ's, if at all possible try to use a fully functional MQ application to do this.

A fully functional MQ application (in ruby, perl, .NET, java etc) will handle all of the concurrency, error logging, state management and scalability issues that you discuss.