#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

static const int NOF_SIGNALS = 1000;
static volatile sig_atomic_t received_signals = 0;
static volatile sig_atomic_t terminated = 0;

static void count_signals(int sig) {
   ++received_signals;
}

void termination_handler(int sig) {
   terminated = 1;
}

int main() {
   sighold(SIGUSR1); sighold(SIGTERM);

   pid_t child = fork();
   if (child < 0) {
      perror("fork"); exit(1);
   }
   if (child == 0) {
      struct sigaction action = {0};
      action.sa_handler = count_signals;
      if (sigaction(SIGUSR1, &action, 0) != 0) {
         perror("sigaction"); exit(1);
      }
      action.sa_handler = termination_handler;
      if (sigaction(SIGTERM, &action, 0) != 0) {
         perror("sigaction"); exit(1);
      }
      sigrelse(SIGUSR1); sigrelse(SIGTERM);
      while (!terminated) pause();
      printf("[%d] received %d signals\n",
         (int) getpid(), received_signals);
      exit(0);
   }

   sigrelse(SIGUSR1); sigrelse(SIGTERM);
   for (int i = 0; i < NOF_SIGNALS; ++i) {
      kill(child, SIGUSR1);
   }
   printf("[%d] sent %d signals\n",
      (int) getpid(), NOF_SIGNALS);
   kill(child, SIGTERM); wait(0);
}