/* sigCross.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.
 *
 * 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();
static void child_handler();

static int sigusr1 = 0;
static int sigusr2 = 0;

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

  /* prepare the parent_handler to catch SIGUSR1 */
  signal(SIGUSR1, parent_handler);

  parent_pid = getpid();
  if ((child_pid = fork()) == 0)      /* child */
  {
    /* prepare the child_handler to catch SIGUSR2 */
    signal(SIGUSR2, child_handler);
    kill(parent_pid, SIGUSR1);
    pause();                 /* child pause for SIGUSR2 */  
    printf("Child: sigusr1, sigusr2: %d, %d\n",sigusr1, sigusr2); 
    exit(0);

  } else                              /* parent */
  { kill(child_pid, SIGUSR2);
    wait(&status);                    /* parent wait for child termination */
    printf("Parent: sigusr1, sigusr2: %d, %d\n",sigusr1, sigusr2); 
  }
}

static void parent_handler()
{
  sigusr1++;
  printf("parent_handler: incremented sigusr1 %d\n",sigusr1);
  return; 
}

static void child_handler()
{
  sigusr2++;
  printf("child_handler: incremented sigusr2 %d\n", sigusr2);
  return; 
}