synchronization between two process in c - c

Question

I am trying to send signals between two child in alternative way for 100 times.
Here is my snippet of code.
here is the link to the whole question:
sending signal between two child process
But i have synchronization issue in the loop.
where is the right position to put the sigsuspend()?
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <signal.h>
#include <ctype.h>
pid_t pid2;
struct sigaction act;
sigset_t mask,oldmask,temp;
void sighandler(int signum, siginfo_t *info, void *ptr)
{
printf("Received signal %d\n", signum);
printf("Signal originates from process %lu\n",
(unsigned long)info->si_pid);
pid2 = info->si_pid;
}
int main(int argc,char **argv)
{
int i,j,counter = 0,counter2 = 0;
sigemptyset(&mask);
sigemptyset(&temp);
//sigemptyset(&oldmask);
sigaddset(&mask,SIGUSR1);
//sigset_t mask;
memset(&act, 0, sizeof(act));
act.sa_sigaction = sighandler;
act.sa_flags = SA_SIGINFO;
if(sigaction(SIGUSR1, &act, NULL) == -1)
fprintf(stderr, "sigaction failed: %s\n", strerror(errno));
pid_t current, pidOther;
current = getpid();
pidOther = atol(argv[1]);
int k;
for(k = 0;k < 100;k++){
if(pidOther != 0){ // second child
kill(pidOther,SIGUSR1);
sigprocmask(SIG_BLOCK,&mask,&oldmask);
counter++;
printf("2nd child = %d sent signal to 1st child = %d signal number = %d\n",getpid(),pidOther,counter);
//sigprocmask(SIG_BLOCK,&mask,&oldmask);
sigsuspend(&temp);
}
if(pidOther == 0) // fisrt child
{
//pause();
kill(pid2,SIGUSR1);
sigprocmask(SIG_BLOCK,&mask,&oldmask); // was blank
counter++;
printf("\nj=%d 1st child = %d sent signal to 2nd child = %d signal counter = %d\n",j,getpid(),pid2,counter);
printf("test1\n");
sigsuspend(&temp); // was pause()
}
}
return 0;
}

Answer 1

I don't see you calling fork() anywhere. Also taking the process ID of the second process is not the way your program should know about the child process. Here's a simple example of how to use fork.
pid_t pid = fork();
if (pid == 0)
{
// executes only in child process..
// do stuff related what you need to do in child process
}
else
{
// executes only in parent process
// pid variable contains the child process's PID.
// do stuff related what you need to do in parent process
}
// runs in both parent and child.

Answer 2

The problem is that the first time the first child loops, pid2 is 0, so it sends the signal to every process in the process group (including itself), which means it will start looping immediately, sending signals (just) back to itself...