How to avoid multiple instances of a program?

Question

I need to find a right way to prevent two running instances of my (Python) program. I am currently using the following method.

On Windows,

os.popen('wmic process get caption,processid | findstr `programname.exe`')

On Linux,

os.popen('ps x | grep `programname`')

It seems to work fine for now. Is this method correct? Can someone suggest to me a better way?

edit: Thanks for the reply guys, Is anything wrong with the above methods? I tried the pid file way for linux. What if the pid file gets deleted somehow?

Duplicate: http://stackoverflow.com/questions/380870/python-single-instance-of-program — ire_and_curses, Dec 14 '09 at 16:18
Related: http://stackoverflow.com/questions/220525/ensuring-a-single-instance-of-an-application-in-linux#221159 — ire_and_curses, Dec 14 '09 at 16:20
This is basically a duplicate of the [python-single-instance-of-program](http://stackoverflow.com/questions/380870/python-single-instance-of-program) question. — Peter Hansen, Dec 14 '09 at 15:55

jldupont · Accepted Answer · 2009-12-14T13:50:08.537

5

There are numerous ways:

have an "instance file" in /var/run or similar (cross-platform)
use a fixed socket (cross-platform)
use DBus to register a name (linux)

What you need is a service (external to your application) that manages a namespace where unique ids are available & enforced.

edited Dec 14 '09 at 13:50

answered Dec 14 '09 at 13:41

jldupont

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score 2 · Answer 2 · answered Dec 14 '09 at 14:19

on Linux, I used to write a pidfile, roughly:

if (pidfile already exists)
    read pidfile content
    if (/proc/<pid>/exec == my executable)
        already running, exit
    else
        it´s a stale pidfile, delete it
write my own pid to pidfile
start the 'real' work

lately, i´ve heard of the flock(1) tool. it´s easier to use in bash scripts:

( flock -n 200 || exit
    # ... commands executed under lock ...
) 200>/var/lock/mylockfile

and not too hard to use from 'real' programming languages, just open a file and try to get a flock(2) on it.

score 1 · Answer 3 · answered Dec 14 '09 at 13:45

1

For linux, see the answer from jldupont. For windows, use the CreateMutex-method, to create a named mutex. See: http://msdn.microsoft.com/en-us/library/ms686927%28VS.85%29.aspx

answered Dec 14 '09 at 13:45

Sven Lilienthal

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This question is about Python, but that link seems to be all about C++ and so isn't relevant. Or am I missing something? – ArtOfWarfare Sep 03 '13 at 20:07

How to avoid multiple instances of a program?

3 Answers3

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