A tiny utility to help make sure only one cron job (or process) of the same kind is running at any given time.
As an example, if you have a cron job that depends on a database and hangs when the database is down, next cron jobs will hang as well when they're launched. This can possibly snowball into consuming all of the available resources.
A good design is to have a circuitbreaker in place.
In our case - fail the next cron job when an existing cron job is already running.
Download a binary release here:
https://github.com/jondot/cronlock/releases/tag/1.0.2
Cronlock is Unixy in that it does one thing and one thing well. Cronlock will
- Fail (exit(1)) when it cannot acquire an exclusive lock
- Succeed (exit(0)) when it acquired an exclusive lock
You can exploit these two properties in order to make sure your Cron job doesn't step on itself:
$ cronlock your required command && signal success command
you can also define your own lock with the CRONLOCK_LOCKFILE environment variable:
$ CRONLOCK_LOCKFILE=foobar.lock cronlock your required command && your
success command
Cronlock is build around flock internally and uses just the syscall package to stay lean and mean, which should be stable and reliable for this use case. That's basically it.
You got me. Cronlock isn't only useful for cron, it could have just been
called flock.
You can use it anywhere you want to make sure just one unix process is running, in the same way.
Fork, implement, add tests, pull request, get my everlasting thanks and a respectable place here :).
Copyright (c) 2014 Dotan Nahum @jondot. See MIT-LICENSE for further details.