Python context manager for managing pid files. Example usage:

import pidfile
import time
print('Starting process')
try:
 with pidfile.PIDFile("/var/run/example.pid"):
 print('Process started')
 time.sleep(30)
except pidfile.AlreadyRunningError:
 print('Already running.')
print('Exiting')

The context manager will take care of verifying the existence of a pid file, check its pid to see if it's alive, check the command line (which should be <something>/<python name>), and if all the conditions are met, rise a pidfile.AlreadyRunningError exception.

PIDFile() defaults to pidfile for the file name, but it's possible to specify another, e.g. PIDFile('foobar.pid').

The algorithm of the library is very simple, at startup, a file is created, and after checking that another instance of the program is not running, the current process ID is written to it.

The check works as follows:

• If the file does not exist, then the check is passed.
• An identifier is written in the file, it is read and checked that a process running with such an identifier exists, and has the same command line.