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GO Classes DPP | GATE CS | Operating System | Fork System Call

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3 3 votes

Assume that every $\texttt{fork()}$ call succeeds.

int main() {
    int a = 0;
    int rc = fork();

    a++;

    if (rc == 0) {
        rc = fork();
        a++;
    } else {
        a++;
    }

    printf("a is %d\n", a);
}

What is the largest value of $\texttt{a}$ printed by the program?

  1. The value may vary because of a race condition
     
  2. $2$
     
  3. $3$
     
  4. None of the above

1 Answer

0 0 votes

After the first $\texttt{fork()}$, the parent and child have separate copies of $\texttt{a}$.

Both processes execute the first increment, making their private value of $\texttt{a}$ equal to $1$.

In the parent:

$\texttt{a++;}$

Therefore, the parent prints $2$.

The first child executes another $\texttt{fork()}$. Both the child and the newly created grandchild then execute:

$\texttt{a++;}$

Their private value also becomes $2$.

Hence, every process prints $2$, and the largest value printed is $2$.

Answer : B

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