python run once

common.py

import sys
import fcntl
import os

_run_once_file_handle = 0


def run_once():
    global _run_once_file_handle

    host_script_file_path = os.path.realpath(sys.argv[0])
    _run_once_file_handle = open(host_script_file_path, 'r')
    try:
        fcntl.flock(_run_once_file_handle, fcntl.LOCK_EX | fcntl.LOCK_NB)
    except:
        sys.exit('Another instance already running')

demo.py

import common
import time

common.run_once()

print ('sleeping')
time.sleep(10)
print ('done')

This does not appear to work on Debian 9 stretch. Both instances of script run and both acquire lock. I am executing the scripts from different SSH sessions.

The same behaviour experienced od Debian 11 as dachshund-digital described for Deb9.