Preventing grand children from forking in C

Question

I have the following code in which I'm trying to create sub processes by forking. I want that exactly 3 sub processes are made. However, when I run the code I seem to be getting more, probably because of the children processes forking grandchildren. What am I missing here, how can I prevent this.

Code:

   for(j = 0; j < 3 ; j++){
    if((pid = fork()) == 0){            // child process
        dosomething();
        exit(0);                // terminate child process
    }
    else if((pid = fork()) > 0){
        printf("I'm in parent of the client spawn loop\n");
//      exit(0);    
    } 
}

Output:

I'm in parent of the client spawn loop
I'm in parent of the client spawn loop
I'm in parent of the client spawn loop
I'm in parent of the client spawn loop
I'm in parent of the client spawn loop
I'm in parent of the client spawn loop
I'm in parent of the client spawn loop

yeah, got it! that was kind of careless on my part! gross case of copy pasting — Zahaib Akhtar, Sep 23 '13 at 18:19

score 5 · Accepted Answer · answered Sep 23 '13 at 18:10

Don't do the second fork call as it will create a new child. The first is enough:

for (j = 0; j < 3; ++j)
{
    pid_t pid = fork();
    if (pid == 0)
    {
        printf("In child (j = %d)\n", j);
        exit(0);
    }
    else if (pid > 0)
    {
        printf("In parent (j = %d)\n", j);
    }
}

Will print "In child" three times, with j equal to 0, 1 and 2. The same for the parent printing.

In your real code you should check for errors though.

score 1 · Answer 2 · answered Sep 23 '13 at 18:08

Don't call fork() more than once in the loop.

The parent shouldn't call fork() again, that will create yet another child and introduce another child-parent split point.

You should have, in the loop:

const int pid = fork();
if(pid == 0)
{
  doSomething();
  exit();
}

Preventing grand children from forking in C

2 Answers2