What is the os.fork() method in Python?

Overview

This os.fork() method in Python provides the implementation of the fork() system, which creates a child or a forked process. Calling fork() results in the creation of an exact copy of the parent process.

An OSError error may occur during the fork() execution due to multiple reasons, like an inaccessible or invalid file path or names, etc.

Syntax

# Signature
os.fork()

Parameters

This method doesn't take any argument value.

Return value

This method returns an integer value.

  • pidprocess id > 0: It returns greater than zero valule when fork() is successfully called in the parent process.
  • 0: It returns zero when fork() is successfully called in the child process.
  • -1: It returns negative one upon unsuccessful fork()call.

Code

# Program to test fork() method
import os
# Creating child process
# In main parent thread
pid = os.fork()
# It is a parent process when fork() returns pid > 0
if pid > 0 :
	print("Parent process here:")
	print("Process ID:", os.getpid())
	print("Child process ID:", pid)
if pid < 0: # pid is -1 means unable to create process
	print("Unable to create child process")
else: # fork() return value 0 meaning it was called in a child process
	print("Child process here:")
	print("Process ID:", os.getpid())
	print("Parent process ID:", os.getppid())

Explanation

  • Line 5: We invoke os.fork() to create a child process in the main parent process.
    • pid > 0 means fork() is called in the parent process.
    • pid < 0 means fork() is unable to create a child process.
    • pid = 0 means fork() is called in a child process.
  • Line 7: If pid > 0, fork() was called in the parent process. We print the parent and child process IDs.
  • Line 11: If pid < 0, fork()is unable to create a new process.
  • Line 13: If pid = 0, fork() is called in the child process. We print child and parent process IDs.
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