GATE | GATE CS 2008 | Question 66

A process executes the following code

for (i = 0; i < n; i++) fork();

The total number of child processes created is
(A) n
(B) 2ⁿ - 1
(C) 2ⁿ
(D) 2⁽ⁿ⁺¹⁾ - 1


Answer: (B)

Explanation:

         F0       // There will be 1 child process created by first fork
      /     \
    F1      F1    // There will be 2 child processes created by second fork
   /  \    /  \
 F2   F2  F2   F2  // There will be 4 child processes created by third fork
/ \   / \ / \  / \
 ...............   // and so on

If we sum all levels of above tree for i = 0 to n-1, we get 2ⁿ - 1. So there will be 2ⁿ – 1 child processes. On the other hand, the total number of process created are (number of child processes)+1.

Note:The maximum number of process is 2ⁿ and may vary due to fork failures.Also see this post for more details.

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