soloprocess

I finally got around to making code from this blog post into a package:

http://blog.tplus1.com/blog/2012/08/08/python-allow-only-one-running-instance-of-a-script/

Say you start a cron job every hour, and each time, the job runs for about 20 minutes. But every once in a while, the job runs for 90 minutes, or even 12 hours.

And in those cases, you don't want to start another redundant cron job, because the first one is still running.

That's what I wrote this for.

Install like this:

$ pip install soloprocess

Here's how to use it:

>>> import soloprocess

>>> soloprocess.write_pidfile_or_die("/tmp/process-one.pid")
'/tmp/process-one.pid'

>>> soloprocess.write_pidfile_or_die("/tmp/process-one.pid") # doctest: +ELLIPSIS
Traceback (most recent call last):
...
ProcessAlreadyRunning: Sorry, found a pidfile!  Process ... is still running.

TODO

• Write a few tests and hook this up to travis CI.
• Explore whether to add some atexit hooks to clean up pidfiles.
• Fill out the setup.py with boring crap like my email, a license, a link to the github repository, etc.
• Document the theoretical scenarios where this won't work. Maybe in addition to storing the PID, also use uptime to figure out when the box last rebooted.