Handling processes in C - c

Question

I have a problem when trying to handle a SIGUSR1 signal sent from a father process to all of his child's process. The handler on the child's does nothing. I checked for the result of the kill command and it returns 0 meaning that the message sent was ok . Can anyone help with this? Below is the code of the child process. I use execl to differ the childs code from the father. Note that the handler works well for alarm calls
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <string.h>
/*Global declerations*/
int alarmflag=0;
double result=0;
int fd[2];
/*Handler for the alarm and SIGUSR1 signal*/
void signal_handler (int sig)
{
printf("******************");
if(sig==SIGALRM)
{
printf("Im child with pid:%d im going to die my value is %lf \n",getpid(),result);
alarmflag=1;
}
if(sig==SIGUSR1)
{
printf("gotit!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!\n");
}
}
double p_calculation ()
{
int i=2;
result=3;
double prosimo=-1;
while(!alarmflag)
{
prosimo=prosimo*(-1);
result=result+(prosimo*(4/((double)i*((double)i+1)*((double)i+2))));
i=i+2;
}
}
main(int argc,char *argv[])
{
int fd[2];
/*handling signals*/
signal(SIGALRM,signal_handler);
signal(SIGUSR1,signal_handler);
/*Notify for execution time*/
printf("PID : %d with PPID : %d executing for %d seconds \n",getpid(),getppid(),atoi(argv[1]));
/*end this after the value passed as argument*/
alarm(atoi(argv[1]));
p_calculation();
/*Notify for finish*/
printf("Done!!!\n");
}
The code for the father follows :
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <sys/types.h>
pid_t *childs; //array for storing childs pids
int number_of_childs;//variable for the number of childs
int count_controls=0;
/*Handler for the SIGINT signal*/
void control_handler(int sig)
{
int j;
for (j=0;j<number_of_childs;j++)
{
kill(childs[j],SIGUSR1);
}
}
main (int argc,char *argv[]){
int i,child_status;
int fd[2];
char cast[512];
int pid;
number_of_childs=atoi(argv[1]);
signal(SIGINT,control_handler);
childs=malloc(number_of_childs*sizeof (pid_t));
if(pipe(fd)==-1)
{
perror("pipe");exit(1);
}
for (i=0;i<number_of_childs;i++){
pid=fork();
/*Create pipes to communicate with all children*/
/*Fathers code goes here*/
if(pid!=0)
{
printf("Parent process: PID= %d,PPID=%d, CPID=%d \n",getpid(),getppid(),pid);
childs[i]=pid; // Keep all your childs in an array
printf("Child:%d\n",childs[i]);
}
/*If you are a child*/
else
{
/*Change the code for the childs and set the time of execution*/
sprintf(cast,"%d",i+1);
execl("./Child.out","",cast,NULL);
}
}
/*Father should never terminate*/
while (1);
}

Answer 1

I cant see a problem with a child when I kill it from shell:
test]$ ./a.out 120
PID : 7406 with PPID : 7035 executing for 120 seconds
******************gotit!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
******************Im child with pid:7406 im going to die my value is -nan
Done!!!
and parent being killed with INT does kill children with USR1:
test]$ ./a.out 1 30
Parent process: PID= 7490,PPID=7035, CPID=7491
Child:7491
PID : 7491 with PPID : 7490 executing for 40 seconds
******************gotit!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
My problem is when i use control -c to the father process. It gets the
interrupt but the message from the handler that the child got the
message does not appear – Giannos 9 mins ago
The problem is that you get SIGINT in your child process.
Try to add a handler for SIGINT in the child, then run your test.
You can see what happens with your current implementation after you pressed ctrl-c:
serge 7685 7035 99 08:01 pts/3 00:00:08 ./a.out 1
serge 7686 7685 30 08:01 pts/3 00:00:02 [Child.out] <defunct>
Your child process got SIGINT and terminated. Also, it is necessary to handle the SIGCLD in the parent to get rid of all your children processes in a defunct state:
if (sig == SIGCLD)
{
// harvest terminated DEFUNCT child process
pid = waitpid(-1, &status, WNOHANG);
}