Question

I am writing a program that uses multiple worker processes (a pre-forking model) with the following code.

from  multiprocessing import Process
for i in range(0,3):
    Process(target=worker, args=(i,)).start()

I use Windows. I notice that they are run as separate processes when I wanted them to start as subprocesses instead. How do I make them subprocesses of the main process?

I am hesitant to use the subprocess module as it seems suited to run external processes (as far as I have used it).

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An update: It seems Windows does not launch new processes as sub-processes. Python doesnt support getppid() (get parent’s PID) in Windows.

Answer 1

What do you wall subprocess ? To me they are subprocess of your main process. Here my example and returned output.

import time, os
from  multiprocessing import Process

def worker():
    print "I'm process %s, my father is %s" % (os.getpid(), os.getppid())

print "I'm the main process %s" % os.getpid()
for i in range(0,3):
    Process(target=worker).start()

The output is :

I'm the main process 5897
I'm process 5898, my father is 5897
I'm process 5899, my father is 5897
I'm process 5900, my father is 5897

You have 3 subprocesses attached to a main process…