source: liacs/os/assignment3/assignment3.c@ 144

/****************************
* March 5, 2008             *
* Operating Systems         *
* LIACS                     *
* Spring Semester 2008      *
* Assignment #3             *
* Written by Sjoerd Henstra *
****************************/

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

// printerror prints a custom error message followed by the error code and
// description to stderr
void printerror(const char* message) {
  fprintf(stderr, "%s\nERROR %i: %s\n", message, errno, strerror(errno));
}

// signal handler, handles SIGUSR1 and SIGUSR2 properly
static void handler(int signal) {
  int pid = getpid();
  switch(signal) {
    case SIGUSR1:
      printf("process %i received SIGUSR1\n", pid);
      break;
    case SIGUSR2:
      printf("process %i received SIGUSR2\n", pid);
      break;
    default:
      printf("process %i caught another signal, this shouldn't happen\n", pid);
      break;
  }
}

int main() {
  int parent_pid; // holds parent process id, used by child to signal parent
  int child_pid; // hold child process id, used by parent to signal child
  int status;

  // set signal handlers for signals SIGUSR1 and SIGUSR2
  if (signal(SIGUSR1, handler) == SIG_ERR) {
    printerror("Cannot set handler for SIGUSR1.");
  }
  if (signal(SIGUSR2, handler) == SIG_ERR) {
    printerror("Cannot set handler for SIGUSR2.");
  }

  parent_pid = getpid();
  printf("parent pid: %i\n", parent_pid);

  // split into parent and child
  if ((child_pid = fork()) == 0) {
    printf("child pid: %i\n", getpid());

    // send signal to parent
    kill(parent_pid, SIGUSR1);

    sleep(1);                  // LINE 51 <--------

    printf("child is done\n");
    
  } else {
    // send signals to child
    kill(child_pid, SIGUSR1);
    kill(child_pid, SIGUSR2); // LINE 59 <---------
    
    sleep(1);                 // LINE 61 <---------

    printf("parent is done\n");
    
    // reap child
    wait(&status);
    printf("child reaped\n");
  }
  return 0;
}