code: public synchronized List<Runnable> shutdownNow() {
      
      LOG.info("Shutting down all AsyncDiskService threads immediately...");
      
      List<Runnable> list = new ArrayList<Runnable>();
      for (Map.Entry<String, ThreadPoolExecutor> e
          : executors.entrySet()) {
        list.addAll(e.getValue().shutdownNow());
      }
      return list;
    }
docs: Shut down all ThreadPools immediately.