Python: module for creating PID-based lockfile?

Question

I\'m writing a Python script that may or may not (depending on a bunch of things) run for a long time, and I\'d like to make sure that multiple instances (started via cron)

Answer 1

This might be of help to you: lockfile

Answer 2

There is a recipe on ActiveState on creating lockfiles.

To generate the filename you can use os.getpid() to get the PID.

Answer 3

If you can use GPLv2, Mercurial has a module for that:

http://bitbucket.org/mirror/mercurial/src/tip/mercurial/lock.py

Example usage:

from mercurial import error, lock

try:
    l = lock.lock("/path/to/lock", timeout=600) # wait at most 10 minutes
    # do something
except error.LockHeld:
     # couldn't take the lock
else:
    l.release()

Answer 4

I believe you will find the necessary information here. The page in question refers to a package for building daemons in python: this process involves creating a PID lockfile.

Answer 5

I know this is an old thread, but I also created a simple lock which only relies on python native libraries:

import fcntl
import errno


class FileLock:
    def __init__(self, filename=None):
        self.filename = os.path.expanduser('~') + '/LOCK_FILE' if filename is None else filename
        self.lock_file = open(self.filename, 'w+')

    def unlock(self):
        fcntl.flock(self.lock_file, fcntl.LOCK_UN)

    def lock(self, maximum_wait=300):
        waited = 0
        while True:
            try:
                fcntl.flock(self.lock_file, fcntl.LOCK_EX | fcntl.LOCK_NB)
                return True
            except IOError as e:
                if e.errno != errno.EAGAIN:
                    raise e
                else:
                    time.sleep(1)
                    waited += 1
                    if waited >= maximum_wait:
                        return False

Answer 6

You can try PID: https://pypi.org/project/pid/

As the documentation shows, you can lock a function simply adding the decorator @pidfile() on the top of function/method name.

from pid.decorator import pidfile


@pidfile()
def main():
  pass

if __name__ == "__main__":
  main()

The default location for pidfile self check (the file who says if you can execute the code or not) is '/var/run'. You can change it as follows:

@pidfile(piddir='/path/to/a/custom/location')

For other params, see: https://github.com/trbs/pid/blob/95499b30e8ec4a473c0e6b407c03ce644f61c643/pid/base.py#L41

Unfortunatly, this lib's documentation is a little bit poor.