#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <stdio.h>
#include <string.h>

void signal_action(int signo, siginfo_t *info, void *extra)
{
  int int_val = info->si_value.sival_int;

  printf("Signal %d, value %d  received from parent\n", signo, int_val);
  
  if (int_val == 4) {
    exit(0);
  }
}

static void signal_send(int pid, int v)
{
  union sigval sval;

  sleep(1);
  sval.sival_int = v;
  printf("Parent - Sending %d\n", sval.sival_int);
  sigqueue(pid, SIGRTMIN + 1, sval);
}

int main(int argc, char *argv[])
{
  pid_t pid;
  sigset_t newmask, oldmask;
  int stat, res;
  
  pid = fork();
  if (pid == 0) {
    struct sigaction action;

    printf("I am the child, and I am blocking the signals!!!\n");
    sigemptyset(&newmask);
    sigaddset(&newmask, SIGRTMIN + 1);
    sigprocmask(SIG_BLOCK, &newmask, &oldmask);

    memset(&action, 0, sizeof(struct sigaction));
    action.sa_flags = SA_SIGINFO;
    action.sa_sigaction = signal_action;
    res = sigaction(SIGRTMIN + 1, &action, NULL);
    if (res < 0) {
      perror("Sigaction");
      return -1;
    }

    /* Wait 5 seconds, to show that signals are actually queued! */
    sleep(5);

    printf("I am the child, and I am now going to listen to the parent!!!\n");
    while(1) {
      sigsuspend(&oldmask);
    }

    printf("Child is exiting");

    return 0;
  }

  signal_send(pid, 6);
  signal_send(pid, 8);
  signal_send(pid, 4);
  
  pid = wait(&stat);
  printf("Child exit status = %d\n", WEXITSTATUS(stat));
  
  return 0;
}