Practical Session 2

#include<signal.h>

/* Description : This program runs a few processes which send to each other 
signals through the kill command. The signals activate the procedure 
sigCathcher which sends a signal to the next process. Each child process is
exiting after receiving the signal. The parent is collecting all the zombies 
and then exiting.
*/

int cpid[5];//holds the pids of the childs
int j;//pointer to cpid

int sigCatcher(){ // function to activate when a signal is caught
  printf("PID %d caught one\n",getpid());
  signal(SIGINT,sigCatcher); // reset the signal catcher
  if(j>-1)
    kill(cpid[j],SIGINT);// send signal to next child in cpid
}

int main(){
  int i;
  int zombie;
  int status;
  int pid

  signal(SIGINT,sigCatcher); // set the signal catcher  to sigCatcher
  for(i=0;i<5;i++){
    if((pid=fork())==0){ // create new child
      printf("PID %d ready\n",getpid());
      j=i-1;
      pause(); // wait for signal
      exit(0); // end proccess (become a zombie)
    } else
    			 // Only father update the cpid array.
     cpid[i]=pid;
    
  }
  sleep(2); // allow children time to enter pause
  kill(cpid[4],SIGINT); // send signal to first child
  sleep(2); // wait for children to become zombies
  for(i=0;i<5;i++){
    zombie=wait(&status); // collect zombies
    printf("%d is dead\n",zombie);
  }
  exit(0);
}