{"id":18185,"date":"2021-06-17T16:51:41","date_gmt":"2021-06-17T16:51:41","guid":{"rendered":"https:\/\/www.askpython.com\/?p=18185"},"modified":"2021-06-17T17:02:04","modified_gmt":"2021-06-17T17:02:04","slug":"python-fork","status":"publish","type":"post","link":"https:\/\/www.askpython.com\/python-modules\/python-fork","title":{"rendered":"Python fork() – How to create child processes using the fork() method?"},"content":{"rendered":"\n

In this article, we’ll talk about the Python fork() method which allows us to create child processes using the processes through which it was called. Let’s look <\/p>\n\n\n\n

What is a system call?<\/strong><\/h2>\n\n\n\n

A system call<\/em><\/strong> is used to get access to the kernel mode. It is a way with which a program can interact with the operating system and request its services to perform specified tasks.<\/p>\n\n\n\n

Hence all the system calls are executed in the kernel (privileged) mode when the execution completes the control is returned to the user mode. Sometimes a system call is also called syscall<\/em><\/strong> in abbreviated form.<\/p>\n\n\n\n

In modern computer systems, there are generally two modes of operations – User mode<\/em> and Kernel mode<\/em>. <\/p>\n\n\n\n

All the user programs and processes run in User mode and they cannot access the kernel-mode directly. This is done to protect the operating system from the modifications or changes caused by any user program.<\/p>\n\n\n\n

If any user program needs to perform privileged work, it requires the support of the operating system which it can get only through the system calls<\/em><\/strong>. And it the system calls which provide the various services of the operating system to the user programs and processes via API (Application Program Interface).<\/p>\n\n\n\n

What is Python fork()?<\/strong><\/h2>\n\n\n\n

There are multiple system calls for managing different types of services provided by the operating system. Also, these are different for different operating systems.<\/p>\n\n\n\n

System calls are broadly classified into five main categories:<\/p>\n\n\n\n

  1. Files related system calls<\/li>
  2. Device related system calls<\/li>
  3. Process related system calls<\/strong><\/li>
  4. Information related system calls<\/strong><\/li>
  5. Communication-related system calls<\/li><\/ol>\n\n\n\n

    So, Python fork()<\/code><\/strong> is an example of Process related or Process control system call. It is a method used to create a Child process<\/em> of the process which calls it just like the clone of the original (calling) process. The process which makes a system call using the fork()<\/code> statement is called the Parent process<\/em>.<\/p>\n\n\n\n

    Importing the OS module <\/strong><\/h2>\n\n\n\n

    In order to use and implement the fork()<\/code> system call in Python, we require the os<\/code> module of Python<\/a>. This os module in Python allows us to use the various operating system-dependent functionality. It allows the user program to access the operating system functionality on which the Python is running. <\/p>\n\n\n\n

    We need not install the os<\/code> module as it comes under Python\u2019s standard utility modules and gets installed when Python is installed in our system.<\/p>\n\n\n\n

    It is imported inside the program as follows:<\/p>\n\n\n

    \nimport os\n<\/pre><\/div>\n\n\n
    Working of Python fork()<\/strong><\/h2>\n\n\n\n
    Following are the key properties of fork()<\/code> method\/statement:<\/p>\n\n\n\n
    • It takes no argument\/parameter when it is being called inside any program.<\/li>
    • If the child process is created successfully then both the parent process and the child process will execute the next statement\/instruction followed by the fork()<\/code> statement.<\/li>
    • The number of child processes = 2N<\/sup> – 1<\/em><\/strong>; where N<\/em> = Number of fork()<\/code> statements used inside the main program.<\/li><\/ul>\n\n\n\n
      On execution of the Python fork() statement it returns three types of integer values:<\/strong><\/p>\n\n\n\n
      1. Zero<\/strong> (0<\/strong>) is returned to the child process if the child process is created successfully.<\/li>
      2. A positive <\/strong>(+ve<\/strong>) value is returned to the parent process if the child process is created successfully. This positive value is usually the PID<\/strong> that is the **<\/strong><\/sup>process ID<\/em> of the newly created child process.<\/li>
      3. A negative <\/strong>(-ve<\/strong>) value is returned to the parent process if some error occurs in the creation of the child process due to any reason.<\/li><\/ol>\n\n\n\n
        Process ID<\/strong> usually referred to as PID<\/strong> is a unique identifier associated with every process present inside the computer system. The process ID of any process can be accessed using another system call getpid()<\/code><\/em><\/strong> which is an example of Information related system calls. The getpid()<\/code> statement returns the process ID of the process which calls it.<\/p>\n\n\n\n
        It is called inside the program as follows:<\/p>\n\n\n
        \nos.fork()\n<\/pre><\/div>\n\n\n
        Creating child processes with the fork() method in Python<\/strong><\/h2>\n\n\n\n
        Example 1:<\/strong><\/p>\n\n\n
        \n# Importing os module\nimport os\n\n# Creating child processes using fork() method\nos.fork()\nos.fork()\n\n# This will be executed by both parent & child processes\nprint("AskPython")\n<\/pre><\/div>\n\n\n
        Output:<\/strong><\/p>\n\n\n\n
        \"Python<\/figure><\/div>\n\n\n\n
        The above python program has produced the correct output as there are two fork()<\/code> statements used inside the program. Hence the print()<\/code> statement executed four times (3 + 1) three (22<\/sup> -1 = 3<\/strong>) times by the three child processes and one time by the parent process.<\/p>\n\n\n\n
        Example 2:<\/strong><\/p>\n\n\n
        \n# Importing os module\nimport os\n\n# Creating a child process using fork() method\nval = os.fork()\n\n# Testing the values returned by fork() method\nif val == 0:\n    pid = os.getpid()\n    print(f"Hi I am Child Process and my PID is {pid}.")\nelif val > 0:\n    pid = os.getpid()\n    print(f"Hi I am Parent Process and my PID is {pid} and PID {val} is my Child Process.")\nelse:\n    print("Sorry!! Child Process creation has failed...")\n<\/pre><\/div>\n\n\n
        Output:<\/strong><\/p>\n\n\n\n
        \"Python<\/figure><\/div>\n\n\n\n
        The above python program has produced the correct output and clearly demonstrated the values returned by the fork()<\/code> statement.<\/p>\n\n\n\n
        Conclusion<\/strong><\/h2>\n\n\n\n
        In this tutorial, we have learned what is a system call, what a Python fork()<\/code> method is, its properties, and how to create child processes using the fork()<\/code> method in Python.<\/p>\n\n\n\n
        Note: <\/strong>fork()<\/code> method\/system call is available only for Linux\/Unix operating systems. If you try to run any Python program that calls the fork()<\/code> method on a Windows system then the following error will be produced:<\/p>\n\n\n\n
        \"Fork<\/figure><\/div>\n","protected":false},"excerpt":{"rendered":"
        In this article, we’ll talk about the Python fork() method which allows us to create child processes using the processes through which it was called. Let’s look What is a system call? A system call is used to get access to the kernel mode. It is a way with which a program can interact with […]<\/p>\n","protected":false},"author":33,"featured_media":18186,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-18185","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-python-modules"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/www.askpython.com\/wp-json\/wp\/v2\/posts\/18185","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.askpython.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.askpython.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.askpython.com\/wp-json\/wp\/v2\/users\/33"}],"replies":[{"embeddable":true,"href":"https:\/\/www.askpython.com\/wp-json\/wp\/v2\/comments?post=18185"}],"version-history":[{"count":0,"href":"https:\/\/www.askpython.com\/wp-json\/wp\/v2\/posts\/18185\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.askpython.com\/wp-json\/wp\/v2\/media\/18186"}],"wp:attachment":[{"href":"https:\/\/www.askpython.com\/wp-json\/wp\/v2\/media?parent=18185"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.askpython.com\/wp-json\/wp\/v2\/categories?post=18185"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.askpython.com\/wp-json\/wp\/v2\/tags?post=18185"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}