[hamete.org] Forker

forker.py

On the Python Package Index (PyPI) you can find an interesting tool transforming python code to html : py2html 0.62

So I looked for a piece of code to test this script. Here is forker.py, a one page code piece that permit to "daemonise" a programm by a function call.

This code is directly derivated from this recipe of the Python Cookbook.
It allows to "fork" the running process when calling a function, then the forked part runs in background in daemon mode. This example code is functionnal (I use it in several programs).

Source code

Here is the source :

#!/usr/bin/env python
# -*- coding: iso-8859-1 -*-
# $Source$

# _include_licence_

import os
import sys

__version__ = "$Id: forker.py.html 2337 2005-05-13 23:42:37Z jd $"

def raz_file_descriptor(): 
    try: 
        maxfd = os.sysconf("SC_OPEN_MAX")
    except (AttributeError, ValueError): 
        maxfd = 256 # default maximum

    for fd in range(0, maxfd): 
        try: 
            os.close(fd)
        except OSError: # ERROR (ignore)
            pass

    # Redirect the standard file descriptors to /dev/null.
    os.open("/dev/null", os.O_RDONLY)# standard input (0)
    os.open("/dev/null", os.O_RDWR)# standard output (1)
    os.open("/dev/null", os.O_RDWR)# standard error (2)

def forker(fonction, *args): 
    # first, let's fork
    pid = os.fork()
    if pid == 0: 
        #we are child
        os.setsid()
        # second fork
        mpid = os.fork()
        if mpid == 0: 
            # we are the second child
            raz_file_descriptor()
            fonction(*args)
            os._exit(0)
        else: 
            # still 1st child
            try: 
                os.waitpid(mpid, os.WNOHANG)
            except: 
                pass
            os._exit(0)
    else: 
        # we are still there, continue our duty
        try: 
            os.waitpid(pid, os.WNOHANG)
        except: 
            pass
        return

if __name__ == "__main__": 
    import time
    def forked_funct(delay): 
        "test fonction: open a file, wait delay second, close the file."
        pid = os.getpid()
        of = open("./test_forker_%s"%pid, "w")
        of.write("Start  %s\n"%time.asctime())
        of.write("waiting %s sec.\n"%delay)
        time.sleep(delay)
        of.write("End    %s\n"%time.asctime())
        of.close()
        return

    forker(forked_funct, 10)
    forker(forked_funct, 8)
    forker(forked_funct, 12)

forker.py

Source code

Files