
@group
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
@end group

/* @r{When a @code{SIGUSR1} signal arrives, set this variable.} */
volatile sig_atomic_t usr_interrupt = 0;

void
synch_signal (int sig)
@{
  usr_interrupt = 1;
@}

/* @r{The child process executes this function.} */
void
child_function (void)
@{
  /* @r{Perform initialization.} */
  printf ("I'm here!!!  My pid is %d.\n", (int) getpid ());

  /* @r{Let parent know you're done.} */
  kill (getppid (), SIGUSR1);

  /* @r{Continue with execution.} */
  puts ("Bye, now....");
  exit (0);
@}

int
main (void)
@{
  struct sigaction usr_action;
  sigset_t block_mask;
  pid_t child_id;

  /* @r{Establish the signal handler.} */
  sigfillset (&block_mask);
  usr_action.sa_handler = synch_signal;
  usr_action.sa_mask = block_mask;
  usr_action.sa_flags = 0;
  sigaction (SIGUSR1, &usr_action, NULL);

  /* @r{Create the child process.} */
  child_id = fork ();
  if (child_id == 0)
    child_function ();          /* @r{Does not return.} */

@group
  /* @r{Busy wait for the child to send a signal.} */
  while (!usr_interrupt)
    ;
@end group

  /* @r{Now continue execution.} */
  puts ("That's all, folks!");

  return 0;
@}
