private TsBlock constructTsBlock(long count) {
    TsBlockBuilder tsBlockBuilder = new TsBlockBuilder(OUTPUT_DATA_TYPES);
    tsBlockBuilder.getTimeColumnBuilder().writeLong(0L);
    tsBlockBuilder.getColumnBuilder(0).writeLong(count);
    tsBlockBuilder.declarePosition();
    return tsBlockBuilder.build();
  }
Try to get next TsBlock. If the next is not ready, return a future. After success, {@link
SchemaCountOperator#next} will be set.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/schema/SchemaCountOperator.java