text: // Licensed to the Apache Software Foundation (ASF) under one
  // or more contributor license agreements.  See the NOTICE file
  // distributed with this work for additional information
  // regarding copyright ownership.  The ASF licenses this file
  // to you under the Apache License, Version 2.0 (the
  // "License"); you may not use this file except in compliance
  // with the License.  You may obtain a copy of the License at
  //
  //   http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing,
  // software distributed under the License is distributed on an
  // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  // KIND, either express or implied.  See the License for the
  // specific language governing permissions and limitations
  // under the License.
  
  #pragma once
  
  #include "exec/exec_node.h"
  #include "runtime/row_batch.h"
  #include "runtime/runtime_state.h"
  
  namespace doris {
  
  class DescriptorTbl;
  class ExprContext;
  class Tuple;
  class TupleRow;
  class TPlanNode;
  
  /// Node that merges the results of its children by either materializing their
  /// evaluated expressions into row batches or passing through (forwarding) the
  /// batches if the input tuple layout is identical to the output tuple layout
  /// and expressions don't need to be evaluated. The children should be ordered
  /// such that all passthrough children come before the children that need
  /// materialization. The union node pulls from its children sequentially, i.e.
  /// it exhausts one child completely before moving on to the next one.
  class UnionNode : public ExecNode {
  public:
      UnionNode(ObjectPool* pool, const TPlanNode& tnode, const DescriptorTbl& descs);
  
      virtual Status init(const TPlanNode& tnode, RuntimeState* state = nullptr);
      virtual Status prepare(RuntimeState* state);
      virtual Status open(RuntimeState* state);
      virtual Status get_next(RuntimeState* state, RowBatch* row_batch, bool* eos);
      // virtual Status reset(RuntimeState* state);
      virtual Status close(RuntimeState* state);
  
  protected:
      void debug_string(int indentation_level, std::stringstream* out) const;
  
  private:
      /// Tuple id resolved in Prepare() to set tuple_desc_;
      const int _tuple_id;
  
      /// Descriptor for tuples this union node constructs.
      const TupleDescriptor* _tuple_desc;
  
      /// Index of the first non-passthrough child; i.e. a child that needs materialization.
      /// 0 when all children are materialized, '_children.size()' when no children are
      /// materialized.
      const int _first_materialized_child_idx;
  
      /// Const exprs materialized by this node. These exprs don't refer to any children.
      /// Only materialized by the first fragment instance to avoid duplication.
      std::vector<std::vector<ExprContext*>> _const_expr_lists;
  
      /// Exprs materialized by this node. The i-th result expr list refers to the i-th child.
      std::vector<std::vector<ExprContext*>> _child_expr_lists;
  
      /////////////////////////////////////////
      /// BEGIN: Members that must be Reset()
  
      /// Index of current child.
      int _child_idx;
  
      /// Current row batch of current child. We reset the pointer to a new RowBatch
      /// when switching to a different child.
      std::unique_ptr<RowBatch> _child_batch;
  
      /// Index of current row in child_row_batch_.
      int _child_row_idx;
  
      typedef void (*UnionMaterializeBatchFn)(UnionNode*, RowBatch*, uint8_t**);
      /// Vector of pointers to codegen'ed materialize_batch functions. The vector contains one
      /// function for each child. The size of the vector should be equal to the number of
      /// children. If a child is passthrough, there should be a nullptr for that child. If
      /// Codegen is disabled, there should be a nullptr for every child.
      std::vector<UnionMaterializeBatchFn> _codegend_union_materialize_batch_fns;
  
      /// Saved from the last to GetNext() on the current child.
      bool _child_eos;
  
      /// Index of current const result expr list.
      int _const_expr_list_idx;
  
      /// Index of the child that needs to be closed on the next GetNext() call. Should be set
      /// to -1 if no child needs to be closed.
      int _to_close_child_idx;
  
      // Time spent to evaluates exprs and materializes the results
      RuntimeProfile::Counter* _materialize_exprs_evaluate_timer = nullptr;
  
      /// END: Members that must be Reset()
      /////////////////////////////////////////
  
      /// The following GetNext* functions don't apply the limit. It must be enforced by the
      /// caller.
  
      /// GetNext() for the passthrough case. We pass 'row_batch' directly into the GetNext()
      /// call on the child.
      Status get_next_pass_through(RuntimeState* state, RowBatch* row_batch);
  
      /// GetNext() for the materialized case. Materializes and evaluates rows from each
      /// non-passthrough child.
      Status get_next_materialized(RuntimeState* state, RowBatch* row_batch);
  
      /// GetNext() for the constant expression case.
      Status get_next_const(RuntimeState* state, RowBatch* row_batch);
  
      /// Evaluates exprs for the current child and materializes the results into 'tuple_buf',
      /// which is attached to 'dst_batch'. Runs until 'dst_batch' is at capacity, or all rows
      /// have been consumed from the current child batch. Updates '_child_row_idx'.
      void materialize_batch(RowBatch* dst_batch, uint8_t** tuple_buf);
  
      /// Evaluates 'exprs' over 'row', materializes the results in 'tuple_buf'.
      /// and appends the new tuple to 'dst_batch'. Increments '_num_rows_returned'.
      void materialize_exprs(const std::vector<ExprContext*>& exprs, TupleRow* row,
                             uint8_t* tuple_buf, RowBatch* dst_batch);
  
      Status get_error_msg(const std::vector<ExprContext*>& exprs);
  
      /// Returns true if the child at 'child_idx' can be passed through.
      bool is_child_passthrough(int child_idx) const {
          DCHECK_LT(child_idx, _children.size());
          return child_idx < _first_materialized_child_idx;
      }
  
      /// Returns true if there are still rows to be returned from passthrough children.
      bool has_more_passthrough() const { return _child_idx < _first_materialized_child_idx; }
  
      /// Returns true if there are still rows to be returned from children that need
      /// materialization.
      bool has_more_materialized() const {
          return _first_materialized_child_idx != _children.size() && _child_idx < _children.size();
      }
  
      /// Returns true if there are still rows to be returned from constant expressions.
      bool has_more_const(const RuntimeState* state) const {
          return state->per_fragment_instance_idx() == 0 &&
                 _const_expr_list_idx < _const_expr_lists.size();
      }
  };
  
  } // namespace doris
  