docs: public void shutdown() {
          if (open == 0 || shutdown) {
              return;
          }
          shutdown = true;
          sink.getIoThread().execute(new Runnable() {
              @Override
              public void run() {
  
                  synchronized (ServerSentEventConnection.this) {
                      if (queue.isEmpty() && pooled == null) {
                          exchange.endExchange();
                      }
                  }
              }
          });
      }