GO Classes Test Series 2023 | Operating Systems | Test 4 | Question: 8

Answer 1

To solve this problem, we compute the number of processes that get created by calling the function $\textsf{forkthem()}.$ This can be given by the following equation:

• $n > 0:  \text{T}(n) = 2 \text{T}(n-1) + 1$
• $n = 0:  \text{T}(0) = 0$

where $\text{T}(n)$ is the number of processes created by the function. To see why this is the case, consider what happens when the function is called. The first statement calls the system call $\textsf{fork()}$ which creates a child in addition to the caller. Both the caller and the child then execute a recursive call to $\textsf{forkthem()}$ with an argument set to $n-1.$ Therefore, a call to $\textsf{forkthem()}$ creates one process of its own, and then is responsible for all the children that will get created by the function with $n-1.$ The solution to the recurrence equation is $2^n - 1.$

Comments

I didn't get it, @Kabir5454 bro.

These are my arguments : 

→ When we execute any user program its PCB enters the ready state and then it becomes a process. 

→ Initially we don't have any process(except process-0 [the shell itself – as per said by Vishal sir in OS lectures]).

Now, when we execute the above code, this will happen.

The answer they have mentioned is correct when the question is “How many new processes are created”.

@Deepak Poonia sir, @Sachin Mittal 1 sir, @Lakshman Patel RJIT sir.

@GO Classes sir, please resolve this ambiguity.

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Parents process was not created by the above piece of code that was created by OS to run the main function which created the other 31 child process which the question asked . We should start counting after the main started how many processes created.

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@Deepak Poonia  @Sachin Mittal 1  @Lakshman Patel RJIT 

In this video

https://www.youtube.com/watch?v=iZa2vm7A6mw

they are taking parent process also in counting total no. of processes. 

Answer 2

If the code is run, the function forkthem() will be called with the parameter n set to 5. Inside the function, the code checks whether n is greater than 0. Since 5 is greater than 0, the code will execute the following lines:

fork();
forkthem(n-1);
 

The fork() function creates a new process, which is a copy of the current process. This means that after the first call to fork(), there will be two processes running the same code. Each of these processes will then call forkthem() again, with n set to 4.

Since 4 is still greater than 0, the fork() function will be called again, creating two more processes. This means that there are now four processes running the same code. Each of these processes will call forkthem() again, with n set to 3.

This process will continue until n is no longer greater than 0. Since n is decremented by 1 each time forkthem() is called, the value of n will eventually become 0. At this point, the code inside the if statement will not be executed, and the recursive calls to forkthem() will stop.

In total, the code will create 2^5 = 32 processes.