code: public void start() {
      instanceLock.writeLock().lock();
      try {
        for (final Map.Entry<MongoNamespace, NamespaceChangeStreamListener> streamerEntry :
            nsStreamers.entrySet()) {
          streamerEntry.getValue().start();
        }
      } finally {
        instanceLock.writeLock().unlock();
      }
    }
docs: Starts all streams.