protected function cleanup()
  {
    // Free/unlock caches
    $this->CookieCache->cleanup();
    $this->LinkCache->cleanup();

    // Delete working-dir
    PHPCrawlerUtils::rmDir($this->working_directory);
    
    // Remove semaphore (if multiprocess-mode)
    if ($this->multiprocess_mode != PHPCrawlerMultiProcessModes::MPMODE_NONE)
    {
      $sem_key = sem_get($this->crawler_uniqid);
      sem_remove($sem_key);
    }
  }