code: private void startupAcceptor() {
          if (!selectable) {
              registerQueue.clear();
              cancelQueue.clear();
              flushingSessions.clear();
          }
  
          synchronized (lock) {
              if (acceptor == null) {
                  acceptor = new Acceptor();
                  executeWorker(acceptor);
              }
          }
      }
docs: Starts the inner Acceptor thread.