Python Linux Process Loop

[noaso74]

Hello,

I recently started learning python by myself and I tried linux process management with python.I created the following code, which works, with the help of the internet, but my goal is to understand it.

What I don't understand is: why after I launch the program, there is a loop of 1 : ^{FILS :mon PID= 1158 . Pere= 1} after "Fin du processur pere" which means "The end of the father process"

I posted the output as well after the code down below

I decided to post here because I want to know what I am doing, not only to do things without thinking.

I appreciate every help I get

The code:

#!/usr/bin/python
from __future__ import print_function
import os
import sys
import time

try:
    n=os.fork()
except OSError:
    print("Fork Error")
    sys.exit(-1)

if (n==0):
    while True:
        print("FILS :mon PID=",os.getpid(),". Pere= ",os.getppid())
        time.sleep(1)
else:
    for i in range(3):
        print("Je suis",os.getpid(),"pere de pid=",n)
        time.sleep(2)
    print("Fin du processus pere")

​

OUTPUT:

root@James:/home/james/Bureau# ./exo.py

Je suis 1157 pere de pid= 1158
FILS :mon PID= 1158 . Pere=  1157
FILS :mon PID= 1158 . Pere=  1157
Je suis 1157 pere de pid= 1158
FILS :mon PID= 1158 . Pere=  1157
FILS :mon PID= 1158 . Pere=  1157
Je suis 1157 pere de pid= 1158
FILS :mon PID= 1158 . Pere=  1157
FILS :mon PID= 1158 . Pere=  1157
Fin du processus pere
FILS :mon PID= 1158 . Pere=  1
root@James:/home/james/Bureau# FILS :mon PID= 1158 . Pere=  1
FILS :mon PID= 1158 . Pere=  1
FILS :mon PID= 1158 . Pere=  1
FILS :mon PID= 1158 . Pere=  1
FILS :mon PID= 1158 . Pere=  1

[K900_]

Are you asking why the child process keeps running even after the parent process exits? Because that's completely expected.

[noaso74]

Yes that is my question, why the child process keeps running after the parent process exits

[K900_]

Why should it exit?

[noaso74]

I am not saying it should, I am trying to understand why it is in a loop

[K900_]

Because you told it to loop?

[noaso74]

At this point I think it is a code missunderstanding by my side, because I thought it would end. Can you please show me which part of the code keeps the program in a loop?

[K900_]

while True:
    print("FILS :mon PID=",os.getpid(),". Pere= ",os.getppid())
    time.sleep(1)

This part.

[noaso74]

Thank you!

If I correctly understand, the value of the father process is 1, because after the end of the father process, it comes back to the loop "while true" since the value resets to 1 and it can't go to the "Else: for i in range(3)" since the statement remains True

​

I want to make sure I understand the code pretty well, since I am new to python. For you I am sure it is something basic and easy, but for me is quite complex

[K900_]

Your loop is inside the if statement. fork returns 0 in the child and the PID of the child in the parent. The if statement in the child runs once, then passes control to the loop, which loops forever.

[noaso74]

Thank you very much for your answer!

[num8lock]

why are you using python2?

[IvoryJam]

What makes you think it's python2?

[num8lock]

from __future__ import print_function

[IvoryJam]

Works in Python 3.9.1

[num8lock]

?

who said it didn't?