freebsd/linux pidfile+lockfile

lockme.py

#!/usr/bin/env python

import os, fcntl, time

def locked(func):
    def wrapper(*args, **kwargs):
        with open('LOCKFILE','a+') as lf:
            try:
                fcntl.flock(lf.fileno(), fcntl.LOCK_EX|fcntl.LOCK_NB)
            except IOError:
                raise SystemExit('Cannot acquire lock')
            else:
                lf.truncate(0)
                lf.write('%d\n' % os.getpid())
                lf.flush()
                try:
                    func(*args, **kwargs)
                finally:
                    lf.truncate(0)
    return wrapper

@locked
def job(foo):
    print "Doing serious business"
    print foo
    time.sleep(15)
    print "Bye"

if __name__ == "__main__":
    job('yo, dawg!')

The wrapper doesn't return what the original function returns and also truncate won't happen if function raises an exception. What about changing lines 16-17 with

try:
    return func(*args, **kwargs)
finally:
    lf.truncate(0)

And take a look here. I'm not sure whether it works on FreeBSD though.

Thank you, I've updated the code with the snippet you suggested.