docs: public void shutdown(final long timeout, final TimeUnit timeUnit) throws TimeoutException
      {
          final long timeOutAt = System.currentTimeMillis() + timeUnit.toMillis(timeout);
          while (hasBacklog())
          {
              if (timeout >= 0 && System.currentTimeMillis() > timeOutAt)
              {
                  throw TimeoutException.INSTANCE;
              }
              // Busy spin
          }
          halt();
      }