From: Paul Archer <paul@...>
Date: 2009-07-01T01:18:43+09:00
Subject: Re: locking a process

11:39am, Daniel DeLorme wrote:

> Paul Archer wrote:
>> I am in the process of developing a few scripts that:
>> 1) pull images off a CF card on my laptop
>> 2) move the images to a server
>> 3) rename the images on the server according to the EXIF info
>> 
>> 
>> I figure that for 2 & 3, the easiest way to make sure they work is to have 
>> them run in a cron job once a minute (or five). (Wake up, check to see if 
>> there's any work, either do it or quit.)
>> 
>> The problem is that I need to make sure that if the script starts while 
>> another copy of the script is running, it quits. I can work out how to 
>> create lock files, stick in PIDs to make sure the script is really there, 
>> etc. But it seems like someone must have tackled this problem already 
>> (IIRC, I ran across a Perl module that back in my misspent youth).
>
> What I do for this is simply rename the process:
>
>  abort("already running") if `pgrep -f my-wonderful-process` != ""
>  $0 = "my-wonderful-process"
>

Cool, thanks. I like this. Of course, it's still possible to have a race 
condition, but it should be pretty unlikely in my case.

Paul