@Override
  public boolean hasNext() throws Exception {
    if (finished) {
      return false;
    }
    return !isEmpty(readyChildIndex)
        || (children.get(readyChildIndex) != null
            && children.get(readyChildIndex).hasNextWithTimer());
  }
Start index for each input TsBlocks and size of it is equal to inputTsBlocks.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/process/join/HorizontallyConcatOperator.java