How to get process PID for manual lock mechanism in Python?

Question

I would like to make a simple locking mechanism in Python without having to rely on the existing libraries for locking (namely fcntl and probably others)

I already have a small stub, but after searching for a bit I couldn't find a good on answer on how to manually create the lock file and put the process PID inside. Here is my stub:

dir_name = "/var/lock/mycompany"
file_name = "myapp.pid"
lock = os.path.join(dir_name, file_name)

if os.path.exists(lock):
    print >> sys.stderr, "already running under %s, exiting..." % lock
    # display process PID contained in the file, not relevant to my question
    sys.exit(ERROR_LOCK)
else:
    # create the file 'lock' and put the process PID inside

How can I get the current process PID and put it inside the lock file? I thought about looking at /proc filesystem but that seems a bit too much for such a simple task.

Thanks.

Perfect answer thanks, guess I don't need to bother with /proc after all... — Charles Menguy
– Charles Menguy, Commented Apr 18, 2012 at 19:24
just for your info- if you ever need to interrogate a process in proc, you can do it with /proc/self. /proc/self is always a symlink to the calling process. However, for just gleaning the PID, it is overkill. — tMC
– tMC, Commented Apr 18, 2012 at 19:28

balki · Accepted Answer · 2012-04-18 19:23:15Z

2

http://docs.python.org/library/os.html#os.getpid

answered Apr 18, 2012 at 19:23

balki

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tMC · Accepted Answer · 2012-04-18 19:26:35Z

1

open(lock, 'w').write(os.getpid())

answered Apr 18, 2012 at 19:26

tMC

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user1277476 · Accepted Answer · 2012-04-19 01:20:15Z

0

Don't neglect to convert the result of os.getpid() to a string with str(os.getpid()). write wants a string argument.

answered Apr 19, 2012 at 1:20

user1277476

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