docs: public synchronized void sendRetry(long retry, EventCallback callback) {
  
          if (open == 0 || shutdown) {
              if (callback != null) {
                  callback.failed(this, null, null, null, new ClosedChannelException());
              }
              return;
          }
          queue.add(new SSEData(retry, callback));
          sink.getIoThread().execute(new Runnable() {
              @Override
              public void run() {
                  synchronized (ServerSentEventConnection.this) {
                      if (pooled == null) {
                          fillBuffer();
                          writeListener.handleEvent(sink);
                      }
                  }
              }
          });
      }