L-1.8: Fork System call with Example | Fork() system call questions

Summary

In this video, the presenter delves into the fork system call in operating systems, explaining how it creates a child process from a parent process. They discuss the process's behavior, noting that fork returns 0 to the child and the child's PID to the parent. The video also covers the implications of multiple fork calls, illustrating how the number of 'Hello' prints and child processes can be calculated using the formula 2^n and 2^n - 1, respectively. Aimed at viewers preparing for competitive exams, the presenter emphasizes the importance of understanding fork for success in computer science quizzes.

Takeaways

• 🔑 The fork system call is used to create a child process from a parent process in C programming.
• 👥 A child process created by fork is an exact clone of the parent, but with its own unique process ID.
• 📈 The fork system call returns 0 to the child process, a positive number (often the child's PID) to the parent, and -1 in case of an error.
• 🤖 When fork is called, both the parent and child processes continue to execute the subsequent instructions in parallel.
• 🌐 The number of times 'Hello' will be printed when fork is used can be calculated as 2^n, where n is the number of fork calls.
• 💡 The total number of child processes created by multiple fork calls is given by the formula 2^n - 1.
• 🧩 Forking creates a full copy of the parent process, whereas threading involves sharing most resources but having separate threads of execution.
• 📚 Understanding fork and its behavior is crucial for computer science competitive exams like GATE and UGC NET.
• 🔍 The script emphasizes the importance of remembering the values returned by fork and the formulas for calculating the number of prints and child processes.
• 🎯 The video aims to clarify common misconceptions and provide a clear understanding of how fork operates in operating systems.

Q & A

What is the primary purpose of the fork system call in programming?

The primary purpose of the fork system call is to create a child process that is an exact clone of the parent process.

How does the fork system call differ from using threads?

Fork creates a completely new process with its own process ID, memory space, and resources, while threads share most of the resources but have their own stack and can perform tasks concurrently.

What is the significance of the return value of the fork system call?

The return value of the fork system call is significant as it returns 0 to the child process, the child's process ID to the parent process, and -1 upon failure.

What happens when the fork system call is executed within a program?

When the fork system call is executed, it creates a child process, and both the parent and child processes continue to execute concurrently from the point of the fork call.

How can you determine if a process is a child or parent after a fork call?

You can determine if a process is a child or parent by checking the return value of the fork call: 0 indicates the child process, and a positive value indicates the parent process.

What is the formula to calculate the number of times 'Hello' would be printed if the fork system call is used in a loop?

The number of times 'Hello' would be printed is calculated using the formula 2^n, where n is the number of times the fork system call is executed.

How many child processes are created when the fork system call is executed n times?

The total number of child processes created when the fork system call is executed n times is given by the formula 2^n - 1.

Why is it important to handle the return value of the fork system call in a program?

Handling the return value of the fork system call is important to differentiate the parent and child processes and to perform different actions based on whether the process is a parent or child.

What is the role of the operating system and kernel in the fork system call?

The operating system and kernel play a crucial role in the fork system call by managing the creation of the child process, allocating resources, and ensuring the child is an exact clone of the parent at the time of the fork.

Can the fork system call fail, and what could be the reason for failure?

Yes, the fork system call can fail, typically due to reasons such as the system being busy, reaching the maximum limit of processes, or insufficient memory to create a new process.

Outlines

00:00

🛠️ Understanding the Fork System Call

This paragraph introduces the concept of the fork system call in operating systems, specifically in the context of creating child processes. The fork system call is used to duplicate the parent process, resulting in a child process that is an exact clone of the parent, with its own unique process ID. The discussion highlights the difference between forking and threading, emphasizing that forking creates a full copy of the process, whereas threading involves sharing most resources and creating only a small, separate task. The paragraph also touches on the return values of the fork system call: zero for the child process, a positive value for the parent process, and -1 in case of an error. A simple example is given where the 'Hello World' program is used to illustrate how the fork system call would duplicate the process, leading to the 'Hello' message being printed twice if fork is called once.

05:04

📚 Deep Dive into Fork System Call Behavior

This paragraph delves deeper into the behavior of the fork system call, particularly focusing on the implications of calling fork multiple times within a program. It explains that each call to fork results in the creation of a new child process, and if a child process itself calls fork, it creates further child processes. The paragraph uses a step-by-step explanation to demonstrate how multiple fork calls lead to an exponential increase in the number of processes. It introduces the formulas 2^n to calculate the total number of times a statement following fork will be executed and 2^n - 1 to determine the total number of child processes created. The paragraph concludes with an emphasis on the importance of understanding these concepts, especially for competitive exams like GATE and UGC NET, and encourages viewers to practice solving problems based on these principles.

Keywords

💡fork system call

The 'fork system call' is a fundamental concept in operating systems, particularly in Unix-like systems. It is used to create a new process by duplicating the calling process, which is referred to as the parent. In the script, the fork system call is central to the discussion, as it is used to spawn a child process that is an exact clone of the parent process, except for its process ID. The video explains that when a program includes a fork call, it results in the creation of a child process that can execute concurrently with the parent, which is crucial for understanding multiprocessing and concurrency.

💡child process

A 'child process' is a process created by a parent process using the fork system call. The child process is a duplicate of the parent, but it runs as a separate entity with its own process ID. In the video, the concept is illustrated by explaining that if a parent process executes a fork, a child process is born, which can then independently execute further code, including additional forks. This leads to the creation of a process tree, which is essential for understanding how multiple processes can be managed and executed in an operating system.

💡parent process

The 'parent process' is the original process from which a child process is created using the fork system call. The parent continues to execute after the fork, often alongside its child. The video script uses the parent process as a reference point to explain how the fork system call works, noting that the parent process remains active and can also execute further forks, creating additional child processes. This distinction between parent and child processes is key to understanding process hierarchy and communication.

💡process ID

A 'process ID' (PID) is a unique identifier assigned to each process in an operating system. It is used to distinguish between different processes. In the context of the video, the script explains that each child process created by a fork call has its own PID, which is different from that of the parent process. This is important for process management, as it allows the operating system to track and manage each process individually.

💡thread

A 'thread' is the smallest unit of processing that can be scheduled by an operating system. Unlike a process, a thread shares the same memory space and resources with other threads within the same process. The video script contrasts threads with processes created by fork, highlighting that threads are a lighter-weight alternative for parallelism within a process, as they do not require the overhead of duplicating an entire process's memory and resources.

💡concurrency

Concurrency refers to the ability of an operating system to manage and execute multiple processes or threads simultaneously. The video script discusses how the fork system call enables concurrency by creating child processes that can run concurrently with the parent process. This is a fundamental concept in computer science, as it allows for efficient use of system resources and improved performance through parallel execution.

💡return value

In the context of the fork system call, the 'return value' is significant as it differentiates the view of the system call from the perspective of the parent and child processes. The script explains that in the child process, fork returns 0, while in the parent process, it returns the PID of the child. Understanding the return value is crucial for writing correct multi-process programs, as it allows the parent and child to perform different actions based on whether they are the parent or child.

💡multiprocessing

Multiprocessing is the use of multiple processing units to execute multiple processes simultaneously. The video script uses the fork system call as an example of how multiprocessing can be implemented in an operating system. By creating multiple child processes, each capable of running independently, the script illustrates the concept of multiprocessing and its role in allowing for parallel execution of tasks.

💡GATE and UGC NET

GATE (Graduate Aptitude Test in Engineering) and UGC NET (University Grants Commission National Eligibility Test) are competitive exams in India for postgraduate admissions and teaching positions, respectively. The script mentions that understanding the fork system call and related concepts is important for these exams, as they often include questions on operating systems and process management. This highlights the relevance of the topic in academic and professional contexts.

💡2^n

The '2^n' formula mentioned in the script is used to calculate the total number of times a certain operation, such as printing 'Hello', will occur when the fork system call is used multiple times within a program. The script explains that each fork creates a new process, and with each additional fork, the number of processes doubles, leading to a total number of processes and executions that can be calculated using the 2^n formula, where 'n' is the number of fork calls. This is a key concept for understanding the exponential growth of processes in a system.

Highlights

Introduction to the fork system call and its role in creating child processes.

Explanation of how the fork system call duplicates the parent process to create a child process.

Description of the child process as an exact clone of the parent with its own unique ID.

Comparison between creating a child process using fork and using threads.

Clarification that the forked child process continues execution from the point of the fork call.

The fork system call returns 0 in the child process and the child's PID in the parent process.

Discussion on the return value of -1 indicating a failure in creating the child process.

Example of a simple program demonstrating the fork system call and its output.

Explanation of how multiple fork calls lead to multiple child processes being created.

The concept that each additional fork doubles the number of processes executing concurrently.

Formula to calculate the total number of times a statement will be executed after multiple forks: 2^n.

Formula to calculate the total number of child processes created after multiple forks: 2^n - 1.

Emphasis on the importance of understanding fork for competitive exams like GATE and UGC NET.

Advice on remembering the key values returned by the fork system call for solving related problems.

Encouragement to practice solving problems related to the fork system call.

Conclusion and a call to action for viewers to like, share, and subscribe to the channel.

Transcripts

Hello Friends, Welcome to Gate Smashers

Today's topic is fork system call

We're going to discuss about fork system call in this video

And in the last of this video

you'll get two questions based on everything that we're going to discuss in this video

Whose answer you can share with me in the comment box

So first we are talking about fork, which is our system call

We use fork system call to create a child process

Means let's say there's a process Let's say I wrote a program in C... print F "Hello World"

So print F "Hello World" is a main program which we can call a parent program

But in the parent program if I would write fork anywhere,

then a child of that parent will get created

Let's say I want to place this marker from here to here

So let's say I'm the parent process If parent process is busy somewhere

Then we have to create a child process Child process means it'll be my exact clone

Child process will be parent's clone which will have its own ID

Means Child have its own ID and Parent have its own ID

And that child will pick it up from here and will place here

Or we have one more method We can use the method of thread

What we do in thread is We don't have to make full clone

Let's say My both hands are busy then I can create a third hand here

Third hand means that rest of the area is doing sharing,

means maximum things are getting shared just an extra thing is performing this task

But when we do fork then everything is new

Although we are doing little bit sharing there also, There also we are sharing code but...

Still it has it's own process ID, I'll have its own registers, there are a lot of values, that it does separately

That we'll discuss in the video where we'll talk about differences between fork and thread

But here we're talking about what is a fork system call,

then fork system call simply means to create a child process

So the moment we creates a child process then what happens is,

fork system call generally returns a value 0 + 1 or -1

You can say +1 or positive value also Zero means child process

Zero denotes child, it returns a child value

Positive means that process itself which you can call parent process

We denotes -1, if child process didn't get created because of some reason

Let's say operating system and kernel is busy, so child process didn't get created

But we do not consider this case because we are assuming that child process will surely create

means you just have to keep only two values in mind, zero means denotes child process

And positive value means we're denoting parent process

So let's say If I would write here If we'd write a simple program

Main()... If I'll write in main, fork() And in fork system call I'll write PrintF ("Hello")

PrintF ("Hello")... Now what is the meaning of this The moment I wrote fork...

Let's say if I won't write fork here then main()... printF ("Hello")

so hello will get printed once because this is a parent process

You can call main process, parent process also That process will get execute

And it'll print hello on the monitor

But, the moment you wrote fork here Fork means... If you wrote fork inside parent process

So a child process of parent process will create

Means it's already a parent, child process will generate and run in it's parallel and congruently

So the child process will create which I'm denoting from C1

So this child process and parent process will execute parallelly

Means how many times hello will print here? Two times

Reason... Child process will print hello and parent will definitely do it

So Hello will print 2 times here So that's the important point

Whenever you write fork and we are talking about child process in fork

so you can denote child with 0 and we generally denotes parent with positive number

If I would write two times fork here... let's say if I would write the fork statement two times

Writing fork statement two times means that one is parent process that's complete main process,

that's the general process or main process

The moment I wrote fork in that parent then fork means parent got a child

But parent is still there It didn't get killed... It's alive

A child process congruent to it has created here

Now next fork, this was the output of writing first fork

But the moment you wrote second fork second fork means

that this C1 is like a parent for second fork

Parent means C1 will create a further child process C2

and C1 is there already...

and this parent P will also create its own child process... let's say C3, and P is already there

So It means C2, C1, C3 and P All four will print Hello

Means these are four are running congruent,

out of which these three are child process and one parent process is also here

So there're three and one parent

This is a very very Important point

And talking from GATE and UGC NET point of view, or any other competitive exam in computer science

then fork in operating system is a frequently asked topic Many times question comes on fork

Let's check once more... Let's say if I will take fork three times here Fork... Fork... Fork

And below it let's say I wrote printF... Hello

So what it means is... It's a very simple thing

Again what we did here... P is a parent process

The moment I wrote fork in parent first time

Then a child process of parent i.e. C1 got created and parent is already there

Now in child I wrote fork once again The other fork will create a child of this child i.e. C2

And C1 will already get executed

Now this P which was running parallel to it

this fork will create another child of that P, let's say C3 and P is already there as we saw

Now when you'll write fork third time, what will happen is...

This C2 will create its child, Let's say C4 And this C2 is already there

This C1 will create its own child process let's say C5 and C1 is already there

Now C3 will create its own child process let's say C6 and C3 is already there

And this P will have its own child Let's say C7 and P is already there

So if we'll talk at leaf then 7 child processes are there

and one parent process that was the main program

So there's one main program that you can call parent, and 7 others are child

So how many times Hello will print It'll print total 8 times

So how can you calculate total times hello will be printed... 2^n

Means the no. of times fork is written, that's the number "n"

And many times they asks how many child process will be generated

Total no. of child processes are 2^n - 1

You can see when we used 3 Then these 7 are child processes from C1 to C7

But P is parent process, here if we'll say we wrote fork two times

So 2^2 - 1 i.e. 3... C1, C2, C3 which is child

and P is parent, but totally how many times hello will get print is 2^n

Means total execution will be 2^n and total child process will be 2^n - 1

This is a very important point guys, here first you have to remember this very important point in the video

Second, It always returns the ID of child process

The moment you'll write fork, it'll return child process's identity as zero

We write parent process's ID as positive You can get it as positive 1 at many places then it's fine

Here number is not important, here it's positive, negative or zero

So negative means child didn't even created

Don't consider this case, because we are using fork so child will definitely create

But in the worst case it may be possible that kernel is busy somewhere

If there's is any problem or error then maybe it won't create child process

But if this comes in question, then they'll mention it definitely

And in actual we have used fork to create child

so in this type of question you never have to use -1

Just remember these main two values and these two formulas

over this you'll get many questions that you can try

just by putting direct value you'll easily get the question solved

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