docs: private void close()
      {
          lock.lock();
          try {
              for (SocketBase s : sockets) {
                  try {
                      s.setSocketOpt(ZMQ.ZMQ_LINGER, 0);
                      s.close();
                  }
                  catch (Exception ignore) {
                  }
              }
              sockets.clear();
          }
          finally {
              lock.unlock();
          }
      }