what is this code result? and why is like that?

Question

What is the reason for the code result? And what happens when an exception happens in the fork()?

#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/wait.h>
int main(){
    int pid=fork();
    if(pid==0){
        int child=getpid();
        printf("child: parent %d\n",getppid());
        sleep(4);
        printf("child: parent %d\n",getppid());
        sleep(100);
    }
    else{
        int parent=getpid();
        printf("parent: parent %d\n",getppid());
        sleep(2);
        int zero=0;
        int i=3/zero;
    }
    return 0;
}

And here's the output:

parent: parent 63742
child: parent 63825
Floating point exception (core dumped)
ubunto@ubuntu:~/Desktop$ child: parent 4497

Please [edit] your question to indent the code. While it doesn't matter for the compiler, it does for us humans trying to read and understand the code. — Some programmer dude, Oct 22 '20 at 08:15
When the parent dies, its chidren are "adopted" (the kernel forcibly sets their PPID) by `init` (PID 1) — pmg, Oct 22 '20 at 08:18
@pmg and what happens if we don't use sleep function? I mean why do we use sleep()? — Afrooz Sheikholeslami, Oct 22 '20 at 08:25
`sleep()`, in the posted code, forces the events in different processes to happen in the sequence expected by the programmer ... without it the order of events in different processes would be "random". — pmg, Oct 22 '20 at 08:30
The program is designed to demonstrate the "adoption" mechanism described by pmg. In order to do that, the parent needs to crash between the two `printf()` calls in the child. The easiest way to achieve that is to have a long sleep in the child, and a shorter sleep in the parent. — Felix G, Oct 22 '20 at 08:33

Roberto Caboni · Answer 1 · 2020-10-22T09:48:34.033

0

Here it is the time sequence of the execution:

Second 0:

fork() issued
The parent process prints its pid (63742)
The child process prints its pid (63825)
Both processes issue a sleep

Second 1:

Both processes are sleeping

Second 2:

Parent process wakes up. Child process will sleep for 2 further seconds
Parent process issues a division by 0 causing an exception and the program abnormal termination

In order to examine in depth what happens in case the parent process terminates before its child I suggest checking this question and this other one.

edited Oct 22 '20 at 09:48

answered Oct 22 '20 at 09:17

Roberto Caboni

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Hmmm ... **second 2: the parent wakes up and attempts to divide by zero** – pmg Oct 22 '20 at 09:43
1

@pmg you are right... I corrected it. In my defence it was correct in my brain but my fingers typed the opposite.. – Roberto Caboni Oct 22 '20 at 09:49
1

Fingers are awesome! ;-) – pmg Oct 22 '20 at 09:51

what is this code result? and why is like that?

1 Answers1