I am wondering about how to kill the processes - c

Question

I create child using the fork and I try to kill the generated child every 3 seconds. I also try to kill my parents using "raise or kill".
I don't know how to do to kill parent processor.
When I run my code except kill parent, unlike my expectations, so many child kill come out.
that's the code :
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
int main()
{
int ch[3];
int i;
for (i = 0; i < 3; i++) {
ch[i] = fork();
if (ch[i] == 0){
printf("child[%d]=%d\n",i,getpid());
exit(0); }
}
for(i = 0; i<3; i++) {
sleep(3);
kill(ch[i],SIGKILL);
printf("Killch[%d]=%d\n",i,ch[i]);
}
/* KILL or raise() parent kill */
}
How can I correct this code?

Answer 1

sleep() is not correct solution to collect child status, use wait() or waitpid() in parent.
when parent is in sleep
for(i = 0; i<3; i++) {
sleep(3);
kill(ch[i],SIGKILL);
printf("Killch[%d]=%d\n",i,ch[i]);
}
in your code child is not waiting for parent to kill ? child is killed by itself by exit(0) statement.
You(child) need to send it's exit status to parent and parent's need to collect the child's status using wait() or waitpid() and then kill ?
If you want to observe that whether parent is killing child or not, use delay in child and observe.
"I try to kill the generated child " I ? assuming parent,Here is my code
int a[3];
int temp[3]; //to set flag=1 , when child completes instruction and become zombie
//collect status in wait() in parent, so no need to further process in my_isr
void my_isr(int n) //if child has not completed instruction, i.e not removed by wait() in parent
{ //then remove it using my_isr
printf("in isr..\n");
static int i;
for(;i<3;i++)
if((temp[i]!=1) )//if first child "not turned into zombie and removed by parent" then kill it
{
printf("child %d killed \n",i+1);
kill(a[i],SIGKILL);
}
else
{
printf("zombie child %d has been terminated normally \n",i+1);
}
}
int main()
{
if( (a[0]=fork()) == 0)
{
int r;
srand(getpid());
r=rand()%10+1;
printf("child %d is going for sleep of %d sec\n",getpid(),r);
sleep(r);
exit(1);
}
else
{
if( (a[1]=fork()) == 0)
{
int r;
srand(getpid());
r=rand()%10+1;
printf("child %d is going for sleep of %d sec\n",getpid(),r);
sleep(r);
exit(2);
}
else
{
if( (a[3]=fork()) == 0)
{
int r;
srand(getpid());
r=rand()%10+1;
printf("in child %d is going for sleep of %d sec\n",getpid(),r);
sleep(r);
exit(3);
}
else
{
int s;
printf("in parent : %d \n",getpid());
signal(SIGALRM,my_isr);
//setting timer to tell child's that you need to completes within this duration
alarm(5);
while(wait(&s) != -1)//when there is no child left , wait returns -1
{
if( s>>8 == 1 )
temp[0]=1; //set the flag when exit status is received
else if( s>>8 == 2)
temp[1]=1; //set the flag when child completed work before
else if( s>>8 ==3)
temp[2]=1; //set the flags when zombies are removed
}
}
}
}
return 0;
}
I hope it help's you.