code: public static void closeAtShutdown(Closeable closeable) {
      if (SHUTDOWN_HOOK.addCloseable(closeable)) {
        try {
          Runtime.getRuntime().addShutdownHook(new Thread(SHUTDOWN_HOOK, "OryxShutdownHookThread"));
        } catch (IllegalStateException ise) {
          log.warn("Can't close {} at shutdown since shutdown is in progress", closeable);
        }
      }
    }
docs: Adds a shutdown hook that tries to call {@link Closeable#close()} on the given argument
  at JVM shutdown.
  
  @param closeable thing to close