code: public void start() {
      nsLock.writeLock().lock();
      try {
        if (runnerThread != null) {
          return;
        }
        runnerThread =
            new Thread(new NamespaceChangeStreamRunner(
                new WeakReference<>(this), networkMonitor, logger));
        runnerThread.start();
      } finally {
        nsLock.writeLock().unlock();
      }
    }
docs: Opens the stream in a background thread.