#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <sys/wait.h>

int
main(int argc, char * argv[])
{
  pid_t child, pid;
  int status;
  time_t starttime, lasttime, nowtime;
  unsigned long int n_forks = 0;

  starttime = lasttime = time (NULL);

  while (1)
    {
      child = fork();
#define CHILD_EXIT 42
      if (child == -1)
        {
          perror("fork");
          exit(EXIT_FAILURE);
        }
      if (child == 0)
        _exit(CHILD_EXIT);
      pid = waitpid(child, &status, 0);
      if (pid == -1
          || !WIFEXITED(status)
          || WEXITSTATUS(status) != CHILD_EXIT)
        {
          perror("waitpid");
          exit(EXIT_FAILURE);
        }
      n_forks++;

      nowtime = time (NULL);
      if (lasttime != nowtime)
        {
          printf ("%u: %lu\n", (unsigned int) (nowtime - starttime), n_forks);
          n_forks = 0;
          lasttime = nowtime;
        }
    }

  return 0;
}