PHP Concurrency via Cron

Question

I have a few scripts that need to run concurrently as separate processes. My plan is to have a cron job that executes multiple instances of these scripts at a set interval. Is this a good idea? What are the pros/cons to this approach? Are there any other options I need to consider?

Bottomline: I'm trying to mimic multithreading. Any race conditions will be handled via code (e.g. setting statuses in DB, etc.). The scripts are supposed to do processing intensive tasks (e.g. creating thumbnails, etc.).

Answer 1

You can use forking. The startup script would load all the default configurations and initializations, then fork child processes to do the processing. It could then monitor the processes to see if they are still running. http://php.net/manual/en/function.pcntl-fork.php

Answer 2

Doesn't PHP have fork()? While that's not really multithreading, it is a basic way of co-routines.

Answer 3

Well, if you need it as a cronjob, go ahead. If you want multiple processes, you most likely want to use pcntl_fork to create multiple instances of the same script.

Answer 4

Depending on how quickly you want to react to those jobs and if you're looking to do processor intensive tasks then you can also spread out that processing using a queuing system. Check out Gearman or beanstalkd with multiple workers per machine if you have multiple cores/processors.

Answer 5

One con of using cron is that it will execute a copy of your script at the interval you set regardless of how many script processes are already running. This means the scripts need a way to communicate with each other so that a maximum of N scripts are kept running concurrently (excess scripts can just exit immediately).

An alternative to cron could be supervisord which will execute a configurable number of scripts and monitor each one so any that exit are respawned.