evaluate_uid(void)
{
  uid_t ruid = getuid();
  uid_t euid = geteuid();

  /* if we're really root and aren't running setuid */
  return (uid_t) 0 == ruid && ruid == euid ? 0 : 1;
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.