Don't wait for the process to exit

Question

I have a PHP script that is called from a cron job every minute. This script takes some info from the database and then calls another PHP script using the System function (p

Answer 1

You may be able to use proc_open(), stream_select() and stream_set_blocking() in concert to achieve this kind of thing.

If that sounds vague, I was going to paste a big chunk of code in here that I used in a recent project that did something similar, but then felt it may hinder rather than help! In summary though, the code worked like this:

1. cronjob calls cronjob_wrapper.php
2. cronjob_wrapper.php creates a new Manager class and then calls start on it.
3. Manager class start method check to see how many instances are running (looking for pid files in a particular location). If it's less than a given max number of instances it writes out it's own process id to a pid file and then carries on
4. Manage class creates an instance of an appropriate Encoder class and calls exec on it.
5. The exec method uses proc_open, stream_select and stream_set_blocking to run a system command in a non-blocking fashion (running ffmpeg in this case - and could take quite a while!)
6. When it has finally run it cleans up its PID file and bails out.

Now the reason I'm being vague and handwavy is that our multiple instances here are being handled by the cronjob not by PHP. I was trying to do very much the kind of thing you are talking about, and got something working pretty well with pcntl_fork() and friends, but in the end I encountered a couple of problems (if I recall at least one was a bug in PHP) and decided that this approach was a much more rock-solid way to achieve the same thing. YMMV.

Well worth a look at those functions though, you can achieve a lot with them. Though somehow I don't think PHP will ever become the sockets programming language of choice... :)