Function double_fork

src/ckptserializer.cpp:110–143

returns FORKED_PARENT, FORKED_GRANDCHILD, FORKED_CKPT_FAILED

// returns FORKED_PARENT, FORKED_GRANDCHILD, FORKED_CKPT_FAILED
static forked_rc_t
double_fork()
{
  pid_t pid;
  // 0. This assumes SIGCHLD is already blocked.  This works during checkpoint.
  struct sigaction saved_sigchld_action;
  // 1. Set SIGCHLD handler to trivial handler; save original SIGCHLD handler
  // NOTE: allow_delivery_of_one_sigchld calls sigsuspend(). This is unblocked
  //       when SIGCHLD arrives, only for trivial_sigchld_action, not SIG_IGN.
  struct sigaction trivial_sigchld_action;
  set_trivial_sigchld_action(&trivial_sigchld_action);
  sigaction(SIGCHLD, &trivial_sigchld_action, &saved_sigchld_action);
  pid = _real_sys_fork();
  JASSERT(pid >= 0)(pid); // Or could do:  return FORKED_CKPT_FAILED;

  if (pid > 0) {
    // 2. Allow delivery of just one SIGCHLD (due to the child that did _exit())
    allow_delivery_of_one_sigchld();

    // 3. Next, we reap that child process (which is now a zombie).
    JWARNING(_real_waitpid(pid, NULL, 0) != -1) (pid) (JASSERT_ERRNO);

    // 4. ... and we then restore the original SIGCHLD handler
    sigaction(SIGCHLD, &saved_sigchld_action, NULL);
    return FORKED_CKPT_PARENT;
  } else {
    pid = _real_sys_fork();
    JASSERT(pid >= 0)(pid);
    if (pid > 0) {
      _exit(EXIT_SUCCESS); // Child process exits, delivers SIGCHLD
    }
    return FORKED_CKPT_GRANDCHILD;
  }
}

/*
 * This function returns the fd to which the checkpoint file should be written.