lockfile in python

lockfile is one of my must haves, as it is a very useful semaphore lock file creator.

# lockfile --help
Usage: lockfile -v | -nnn | -r nnn | -l nnn | -s nnn | -! | -ml | -mu | file ...
# rpm -qf `which lockfile`
procmail-3.22-25.1.el6.x86_64

As can be seen above, /usr/bin/lockfile is part of procmail, which comes with its own dependencies (usually sendmail or postfix etc.). I did not like having to install those MTA type dependencies to setup procmail for locking purposes. This is the reason why I wrote lockfile.py.

lockfile.py

#!/usr/bin/python

# Author Evuraan Gmail dot com

import optparse,sys,os,time

def usage():
	print """
Usage   : lockfile.py 
Usage   : lockfile.py -l  
Example : lockfile.py -l 1300 /tmp/my.lockfile.txt
Example : lockfile.py /tmp/my.lockfile.txt

"""


def remove_lockfile(lock_file):
	os.remove(lock_file)


def set_lockfile(lock_file):
	write_file = open(lock_file,"w",)
	write_file.write(str(time.time()))
	write_file.close()
	if os.path.isfile(lock_file):
		# file exists, good enough for us.
		return 0
	else:
		return 1



#if the lockfile exists, check for locktimeout
def checklock(lock_file):
	if os.path.isfile(lock_file):
		# lock file exists. check how old etc.
		mtime = float(os.path.getmtime(lock_file))
		delta = time.time() - mtime
		if float(delta) >= float(locktimeout):
			# file is stale, over write it
			if set_lockfile(lock_file) != 0:
				sys.exit(1)
		else:
			#file is not stale. new. spanking new.
			sys.exit(1)
	else:
		# no lock file.
		if set_lockfile(lock_file) != 0:
			sys.exit(1)



if __name__ == "__main__":

	parser = optparse.OptionParser()
	parser.add_option('-l', '--locktimeout',
		dest="locktimeout",
		type="int",
		default="3489999999",
		help="""If you specify a locktimeout then a lockfile will be
removed by force after locktimeout seconds have passed since the lockfile was last
modified/created (most likely by some other program that unexpectedly
died a long time ago, and hence could not clean up any leftover lockfiles)."""
		)

	options,remainder = parser.parse_args()

	#print "locktimeout       :", options.locktimeout
	#print "remainder         :", remainder

	global locktimeout
	locktimeout = options.locktimeout

	try:
		if len(remainder) == 0:
			print "Invalid usage"
			usage()
			sys.exit(2)
		else:
			global lock_file
			lock_file = remainder[0]
	except:
		sys.exit(2)


	#print "Ahem", lock_file
	checklock(lock_file)

Download

lockfile.py can be downloaded as:

$ wget https://evuraan.info/evuraan/stuff/lockfile.py.txt --no-check-certificate -O lock.py

Usage:

$ ./lockfile.py
Invalid usage

Usage   : lockfile.py 
Usage   : lockfile.py -l  
Example : lockfile.py -l 1300 /tmp/my.lockfile.txt
Example : lockfile.py /tmp/my.lockfile.txt


$ ./lockfile.py --help
Usage: lockfile.py [options]

Options:
  -h, --help            show this help message and exit
  -l LOCKTIMEOUT, --locktimeout=LOCKTIMEOUT
                        If you specify a locktimeout then a lockfile will be
                        removed by force after locktimeout seconds have passed
                        since the lockfile was last modified/created (most
                        likely by some other program that unexpectedly  died a
                        long time ago, and hence could not clean up any
                        leftover lockfiles).


$ ./lockfile.py  /tmp/mylockfile ; echo $?
0

$ ./lockfile.py  /tmp/mylockfile ; echo $?
1

Feedback

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License

Software License:

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

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