code: public void shutdown() {
          try {
              executorService.shutdown();
              executorService.awaitTermination(10, TimeUnit.SECONDS);
          } catch (Throwable e) {
              log.error("Interrupted during shutdown.", e);
          }
      }
docs: Shuts down the executor service.
  Blocks and awaits termination for up to 10 seconds before returning.
  TODO Eike: should it be possible to pass in this timeout? The Duration class could be used for it.