#fork #threads

Question

Consider the following program segment of C-programming language:

#include<stdio.h>

 

int main() {

 

if (fork() || fork())

 

fork();

 

printf("GATE\n");

 

return 0;

 

}

 

Number of times the above program prints 'GATE' is_?

Comments

is it 7?

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5 is the answer.

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Right, 2^nd fork wont be invoked due to short circuiting.

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Can you explain in detail?

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no 5 @palashbehra5

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See if you find anything incorrect.
https://www.geeksforgeeks.org/short-circuiting-in-c-and-linux/

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first say parent process P call first fork() in if statement.

it then create its its child c1 so till now we have P and C1. now P return some non zero number and C1 return 0 as child is C1 which return 0 after the fork() call.

now P has some non zero number and if has OR it will check the another fork() in if block.

now P call fork() again which is after the If statement.

now P will create another child C2 .

So as of now we have 3 process P,C1,C2.

now come to C1 which is still in if block . it return 0 so it will call the next fork() in if statement.

so C1 create another child C12  .

now C12 return 0 so it will not execute the fork() after if statement but C1 will execute the fork() after the If statement which will create another process C13.

So total we have 5 process P,C1,C2,C12,C13.

Each of them execute the print statement. so 5 is the answer.

you can try this using tree diagram but i like to do this way.

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 in child c1 why the first fork value which is in if statement will be 0 ? 

@Kabir5454  @palashbehra5

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Because C1 was created because of P’s fork() calling. So in the first fork() C1 being child  so return 0 and P which is parent return non zero value in the first fork().

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https://www.csl.mtu.edu/cs4411.ck/www/NOTES/process/fork/create.html

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Here in this problem the program counter stores the if statement for all child and parent process and both forks in if statement are executed by all child and parent process. Is it correct?

Answer 1

@jayadev

The answer is 5 ( 1 1 1 1 1 )...…

 

1. It will create two process one parent P (has process ID of child process)and other is child C1 (process ID = 0)....

2. In if statement we used OR operator( || ) and in this case second condition is evaluated when first condition is false....

3. Parent process P will return positive integer so it directly execute statement and create two more processes (one parent P and other is child C2)…

Child process C1 will return 0 so it checks for second condition and second condition again create two more processes(one parent C1 and other is child C3)…

 

4. C1 return positive integer so it will further create two more processes (one parent C1 and other is child C4). Child C3 return 0 so it will directly print 1…

 

Answer 2

p

                                 (>0) p--------------------------------c(=0)

                     (>0)p----------------c1(=0)-----------------c(>0)-----------------c2(=0)

                     print(gate)       print(gate)        c(>0)-----------c3(=0)     print(gate)  

                                                                  print(gate)      print(gate)  

5 times gate will be printed

Answer 3

Ans 7.....because we don't know which process execute first so  we must execute on both sides