Process tree using fork()

Question

I am given the task of creating this process tree in C using fork, if and else:

|_____1___
|___2__   |
|_4_   |  |_3_
|   |  |  |   |

Or as a pstree like drawing:

p(0)─┬─p(1)───p(3)
     ├─p(2)
     └─p(4)

Is this code correct?

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main() {

    if(fork()){
        // 1
        if(fork()){
            // 2
            if(fork()){
                // 4
            }
            else{}
        }
        else{}
    }
    else{
        if(fork()){
            // 3}
        else{}
    }

    pause();
    return 0;
}

Solution

OK I understand your question now. Your answer is correct. All I will say is that you can just do

fork()

for the final forks instead of

if (fork()) {}
else {}

Comments

[gardenhead]

The question is unclear. This is clearly a homework problem: what were you give, and what do you have to find?

[Altair64]

Hmm - i need to programme this process tree using only fork()

[joepd]

Hi. It does not help if you use a non standard way to make a graph. Have a look at the output of pstree -ap to see how PIDs and relations are normaslly displayed. Also: Can't you just print out the pid that is returned by fork? You could use pstree to check your assumptions.

[Altair64]

Ok thank you. I think that our lecturer need to specify what he wants from us :) I have to create a process tree using fork() and if, else in C. The proc tree have to look like is shown above.

[Altair64]

Here is similar problem but different process tree. stackoverflow.com/questions/24082775/…

[Runium]

Added a pstree like drawing. Is it correct? If not edit question and remove it.

[gardenhead]

Could you elaborate The order of what?

[gardenhead]

No it can't. Besides the numbers don't matter -- only the structure of the tree.

[Runium]

Guess we're talking past each other. The point is that there is no guarantee 3 is forked before 4.

[gardenhead]

I don't think that diagram is meant to have a timeline to it. Whether 3 or 4 is forked first, the tree structure will be the same.

[Runium]

Yes, guess not. But then there is those dangling lines. Are those the forks and the pstree drawing wrong? (I added that one but perhaps I should not have. Did it as comments does not support that kind of drawings ...)

[gardenhead]

The only way to know what exactly the original drawing was intended to represent is to ask the professor :D I think the lines are confusing and your pstree drawing is better. The best way to visualize a process tree is as, well, a tree!

[Runium]

Ach. The update seems to never arrive. Was looking forward to this ...