@Override
    public void toData(DataOutput out,
        SerializationContext context) throws IOException {
      super.toData(out, context);
      out.writeInt(processorId);
    }
override in subclass to provide reply data. terminate by returning Token.END_OF_STREAM
geode-core/src/main/java/org/apache/geode/distributed/internal/streaming/StreamingOperation.java