CODEWITHSUNDEEP
c++operating-system
ngunha02
ngunha02

Reputation: 1729

fork() in C++ Learning os development

I am learning OS development with C/C++ and i am using fork() method to experiment with process. I have the following code like this:

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char **argv) {
    fork(); //create a child process, currently total is 1 parent, 1 child
    fork(); //create a child process,currently total is 2 parents, 2 child
    pid_t pid;
    if((pid=fork()) == 0) { //fork() and assign to pid, now has 4 parents, 4 childs
        printf("I am the child: %u\n", getpid());
    else {
        printf("I am the parent: %u and my child is: %u\n", getpid(), pid);
    }
}

When i compile it, and run it, it shows 4 parents and 4 children as i expected, however the output looks strange to me (notice the bolded line below where i get the output after user@slacker:~$).

user@slacker:~$ gcc forktest.c -o forktest

user@slacker:~$ ./forktest

I am the parent: 1183 and my child is: 1186

user@slacker:~$ I am the parent: 1184 and my child is: 1188

I am the parent: 1185 and my child is: 1189

I am the parent: 1187 and my child is: 1190

I am the child: 1186

I am the child: 1189

I am the child: 1190

I am the child: 1191

When i tried with 3 fork(), the output is even stranger. Can someone explain to me please?

Upvotes: 2

Views: 293

Answers (1)

tristan
tristan

Reputation: 4332

         fork            fork            fork
  1183----+---------------+----------------+-------------------->
          |               |                |
          |               |           1186 +-------------------->
          |               |
          |         1185  +----------------+-------------------->
          |                                |
          |                           1189 +-------------------->
          |
  1184    +---------------+----------------+-------------------->
                          |                |
                          |           1188 +-------------------->
                          |
                  1187    +----------------+-------------------->
                                           |
                                      1190 +-------------------->

created with http://www.asciiflow.com/#Draw

Upvotes: 5

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