Is an instance PHP script already running?

n4ows

I have been tasked to write an XML report dispatcher which will run as a cron job. I need to check a few things that I'm not sure about. I need to check to see if the script is already running and I need to check the state of the data coming in. Is it fresh or stale?

This is a whole new area for me. I'm not used to working at the cron level.

Any help would be greatly appreciated,

Thanks,
Alisa

NogDog

You could do some "down in the weeds" shell_exec() stuff to check for running processes, but it might be simpler to do something like having the script use [man]touch[/man] and [man]unlink[/man] to create an empty file while it's running, then deleting it when it's done.

<?php
if(file_exists('script_is_running'))
{
   die('Script is already running');
}
touch('script_is_running');
//
// body of script
//
unlink('script_is_running');
?>

n4ows

Thanks NogDog,

I've had a heck of a time figuring out how to google this problem. I have just about come to the same conclusion as your suggestion.

I have someone "helping me" on this project. He has set up a very similar web service in another language, but doesn't know too much about PHP syntax, so we are having a bit of a communication problem.

In the mean time, I've been studying online tutorials and the book "Pro PHP XML and Web Services" to get a handle on it. BTW, the publisher or author of that book should have hired an English teacher to "grade" it before it was published. Plus the code is pretty buggy.

Thanks,
Alisa

n4ows

Question...

Does 'script_is_running' need an extension, like .txt or something like that or will plain ol' 'script_is_running' work?

Thanks,
Alisa

NogDog

You can call it whatever you want with any suffix (or none), assuming it will just be an empty file. If for some reason you decide to put any data in it, then it might make sense to give it a suffix that matches that type of data.

Note that there is still a possibility of race condition, where two instances of the script start within microseconds of each other, and each does the file_exists() test before either does the touch(). If this nearly simultaneous running is a real possibility, then you might need a cleverer solution.

n4ows

I just talked to the guy that's helping me and he made the suggestion that I apend the file with a timestamp every x seconds so that I can take it's pulse and make sure the process hasn't died. That way, if there's no activity for x minutes, I can kill it and restart it or send out a failure message. He also suggested that I check the process status directly on the server so a) I know it's been kicked off and b) I know that progress is being made.

Not sure yet how to check the status. It is a *nix server, I think Linix, but not for sure.

Thanks,
Alisa

n4ows

This script will be launched from a cron with a timer. I can't imagine a case where it would be launched twice miliseconds apart.