fork_decorator.py

import os
import sys
import time

def detached(f):
    """Generator for creating a forked process
    from a function"""

    def wrapper(*args, **kwargs):
        """Wrapper function to be returned from generator.
        Executes the function bound to the generator and then
        exits the process"""
        
        # Perform double fork
        if os.fork(): # Parent
            os.wait()
            return

        # Perform second fork
        os.setsid()
        if os.fork():
            os._exit(0)
        
        # Generate pid file
        pid_name = f.__name__
        pid = str(os.getpid())
        file(pid_name, 'w+').write("{0}\n".format(pid))

        # Execute function
        f(*args, **kwargs)
        os._exit(0)

    return wrapper

@detached
def sleep_1():
    sys.stdout.write("sleep {0} s.\n".format(10))
    time.sleep(10)
    f = open('test_detach.txt', 'a')
    f.write("test {0}\n".format(10))
    f.close()
    sys.stdout.write("finish sleeping {0} s.\n".format(10))


@detached
def sleep_2():
    sys.stdout.write("sleep {0} s.\n".format(20))
    time.sleep(20)
    f = open('test_detach.txt', 'a')
    f.write("test {0}\n".format(20))
    f.close()
    sys.stdout.write("finish sleeping {0} s.\n".format(20))


@detached
def sleep_3():
    sys.stdout.write("sleep {0} s.\n".format(30))
    time.sleep(30)
    f = open('test_detach.txt', 'a')
    f.write("test {0}\n".format(30))
    f.close()
    sys.stdout.write("finish sleeping {0} s.\n".format(30))


if __name__ == '__main__':
    sleep_1()
    sleep_2()
    sleep_3()