Single Instance App Singleton.

single_instance_no_root.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-


import sys, os, socket
import logging as log


def set_single_instance(name, single_instance=True, port=8888):
    """Set process name and cpu priority, return socket.socket object or None.

    >>> isinstance(set_single_instance("test"), socket.socket)
    True
    """
    __lock = None
    if single_instance:
        try:  # Single instance app ~crossplatform, uses udp socket.
            log.info("Creating Abstract UDP Socket Lock for Single Instance.")
            __lock = socket.socket(
                socket.AF_UNIX if sys.platform.startswith("linux")
                else socket.AF_INET, socket.SOCK_STREAM)
            __lock.bind(
                "\0_{name}__lock".format(name=str(name).lower().strip())
                if sys.platform.startswith("linux") else ("127.0.0.1", port))
        except socket.error as e:
            log.warning(e)
        else:
            log.info("Socket Lock for Single Instance: {}.".format(__lock))
    else:  # if multiple instance want to touch same file bad things can happen
        log.warning("Multiple instance on same file can cause Race Condition.")
    return __lock


if __name__ in '__main__':
    log.basicConfig(level=-1)  # basic logger
    set_single_instance("your_app_name_here")
    __import__("doctest").testmod(verbose=True, report=True, exclude_empty=1)

No multiple instances:

juan@z:~$ python prueba.py
Simulating an App running, run multiple instances to try.

juan@z:~$ python prueba.py
App already running, ([Errno 98] Address already in use,Reboot to Fix). Exiting.

juan@z:~$ 

juan@z:~$ python3 temp.py 
Creating Abstract UDP Socket Lock for Single Instance.
Socket Lock for Single Instance: <socket.socket fd=3, family=AddressFamily.AF_UNIX, type=SocketType.SOCK_STREAM, proto=0, laddr=b'\x00_your_app_name_here__lock'>.
Trying:
    isinstance(set_single_instance(), socket.socket)
Expecting:
    True
Creating Abstract UDP Socket Lock for Single Instance.
Socket Lock for Single Instance: <socket.socket fd=3, family=AddressFamily.AF_UNIX, type=SocketType.SOCK_STREAM, proto=0, laddr=b'\x00_your_app_name_here__lock'>.
ok
1 items passed all tests:
   1 tests in __main__.set_single_instance
1 tests in 1 items.
1 passed and 0 failed.
Test passed.

juan@z:~$ python2 temp.py
Creating Abstract UDP Socket Lock for Single Instance.
Socket Lock for Single Instance: <socket._socketobject object at 0x7f64886d3280>.
Trying:
    isinstance(set_single_instance(), socket.socket)
Expecting:
    True
Creating Abstract UDP Socket Lock for Single Instance.
Socket Lock for Single Instance: <socket._socketobject object at 0x7f6488585ec0>.
ok
1 items passed all tests:
   1 tests in __main__.set_single_instance
1 tests in 1 items.
1 passed and 0 failed.
Test passed.

juan@z:~/code$

Note:

• Edit the string "\0_your_app_name_here_lock", but do NOT remove the \0_ at the beginning 😃