Check if pid is not in use in Python

Question

Is there a way to check to see if a pid corrosponds to a valid process? I'm getting a pid from a different source other than from os.getpid() and I need to check to see if a process with that pid doesn't exist on the machine. Much thanks.

Update: I need it to be available in Unix and Windows.

Update #2: I should be more specific - I'm checking to see if the PID is NOT in use.

Answer 1

Sending signal 0 to a pid will raise an OSError exception if the pid is not running, and do nothing otherwise.

import os
import signal

def check_pid(pid):        
    """ Check For the existence of a unix pid. """
    try:
        os.kill(pid, 0)
    except OSError:
        return False
    else:
        return True

Answer 2

Look here for windows-specific way of getting full list of running processes with their IDs. It would be something like

from win32com.client import GetObject
def get_proclist():
    WMI = GetObject('winmgmts:')
    processes = WMI.InstancesOf('Win32_Process')
    return [process.Properties_('ProcessID').Value for process in processes]

You can then verify pid you get against this list. I have no idea about performance cost, so you'd better check this if you're going to do pid verification often.

For *NIx, just use mluebke's solution.

Answer 3

I'd say use the PID for whatever purpose you're obtaining it and handle the errors gracefully. Otherwise, it's a classic race (the PID may be valid when you check it's valid, but go away an instant later)