I have scheduled a cron job to run every minute but sometimes the script takes more than a minute to finish and I don't want the jobs to start "stacking up" over each other. I guess this is a concurrency problem - i.e. the script execution needs to be mutually exclusive.
To solve the problem I made the script look for the existence of a particular file ("lockfile.txt") and exit if it exists or touch it if it doesn't. But this is a pretty lousy semaphore! Is there a best practice that I should know about? Should I have written a daemon instead?
Answer
There are a couple of programs that automate this feature, take away the annoyance and potential bugs from doing this yourself, and avoid the stale lock problem by using flock behind the scenes, too (which is a risk if you're just using touch). I've used lockrun and lckdo in the past, but now there's flock(1) (in newish versions of util-linux) which is great. It's really easy to use:
* * * * * /usr/bin/flock -n /tmp/fcj.lockfile /usr/local/bin/frequent_cron_job
No comments:
Post a Comment