/* sigAck.c
 *
 * Neal Nelson  2009.11.04
 *
 * Separate signal handlers for parent and child. Note that the child
 *   has to be created before it can register its signal handler.
 * Child exits on its own here instead of by termination by the parent.
 *
 * See man pause. pause waits for a signal before continuing.
 *
 *
 */

#include <stdio.h>
#include <unistd.h>     /* for pause() */
#include <stdlib.h>
#include <signal.h>

/* prototypes must occur before sig handlers are referenced */
static void parent_handler(int);
static void child_handler(int);

main()
{ int i, parent_pid, child_pid, status;

  /* prepare the parent_handler to catch SIGUSR1 */
  if (signal(SIGUSR1, parent_handler) == SIG_ERR)
    printf("Parent: Unable to create handler for SIGUSR1\n");


  parent_pid = getpid();
  if ((child_pid = fork()) == 0)      /* child */
  {
    /* prepare the child_handler to catch SIGUSR2 */
    if (signal(SIGUSR2, child_handler) == SIG_ERR)
      printf("Child: Unable to create handler for SIGUSR2\n");

    printf("Child: raising SIGUSR1 signal to parent\n");  
    kill(parent_pid, SIGUSR1);
    pause();                 /* child pause for SIGUSR2 */  
    printf("Child: OK, I'm back from the SIGUSR2\n");
    printf("Child: exit(0)\n");
    exit(0);

  } else                              /* parent */
  { printf("Parent: raising SIGUSR2 signal to child\n");  
    kill(child_pid, SIGUSR2);

    /* Child exits on its own, we don't kill, and now we don't need the sleep
     * sleep(1);
     * printf("Parent: terminating child ...\n");
     * kill(child_pid, SIGTERM);
     */

    wait(&status);                    /* parent wait for child termination */
    printf("Parent: we're done.\n");
  }
}

static void parent_handler(int signo)
{
  switch(signo)
  { case SIGUSR1:
      printf("Parent: received SIGUSR1 signal from child\n");
      break;
    default: break; /* should never get here */
  }
  return; 
}

static void child_handler(int signo)
{
  switch(signo)
  { case SIGUSR2:
      printf("Child: received SIGUSR2 signal from parent\n");
      break;
    default: break; /* should never get here */
  }
  return; 
}