process - Check to see if python script is running

Question

I have a python daemon running as a part of my web app/ How can I quickly check (using python) if my daemon is running and, if not, launch it?

I want to do it that way to fix any crashes of the daemon, and so the script does not have to be run manually, it will automatically run as soon as it is called and then stay running.

How can i check (using python) if my script is running?

Answer 1

A technique that is handy on a Linux system is using domain sockets:

import socket
import sys
import time

def get_lock(process_name):
    # Without holding a reference to our socket somewhere it gets garbage
    # collected when the function exits
    get_lock._lock_socket = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM)

    try:
        # The null byte () means the socket is created 
        # in the abstract namespace instead of being created 
        # on the file system itself.
        # Works only in Linux
        get_lock._lock_socket.bind('' + process_name)
        print 'I got the lock'
    except socket.error:
        print 'lock exists'
        sys.exit()


get_lock('running_test')
while True:
    time.sleep(3)

It is atomic and avoids the problem of having lock files lying around if your process gets sent a SIGKILL

You can read in the documentation for socket.close that sockets are automatically closed when garbage collected.