text: /**
   *    Copyright (C) 2013 10gen Inc.
   *
   *    This program is free software: you can redistribute it and/or  modify
   *    it under the terms of the GNU Affero General Public License, version 3,
   *    as published by the Free Software Foundation.
   *
   *    This program is distributed in the hope that it will be useful,
   *    but WITHOUT ANY WARRANTY; without even the implied warranty of
   *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   *    GNU Affero General Public License for more details.
   *
   *    You should have received a copy of the GNU Affero General Public License
   *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
   *
   *    As a special exception, the copyright holders give permission to link the
   *    code of portions of this program with the OpenSSL library under certain
   *    conditions as described in each individual source file and distribute
   *    linked combinations including the program with the OpenSSL library. You
   *    must comply with the GNU Affero General Public License in all respects for
   *    all of the code used other than as permitted herein. If you modify file(s)
   *    with this exception, you may extend this exception to your version of the
   *    file(s), but you are not obligated to do so. If you do not wish to do so,
   *    delete this exception statement from your version. If you delete this
   *    exception statement from all source files in the program, then also delete
   *    it in the license file.
   */
  
  #pragma once
  
  #include <queue>
  #include <vector>
  
  #include "mongo/db/exec/plan_stage.h"
  #include "mongo/db/jsobj.h"
  #include "mongo/db/matcher/expression.h"
  #include "mongo/db/record_id.h"
  #include "mongo/platform/unordered_set.h"
  
  namespace mongo {
  
  /**
   * Reads from N children, each of which must have a valid RecordId.  Assumes each child produces
   * RecordIds in sorted order.  Outputs the intersection of the RecordIds outputted by the
   * children.
   *
   * Preconditions: Valid RecordId.  More than one child.
   *
   * Any RecordId that we keep a reference to that is invalidated before we are able to return it
   * is fetched and added to the WorkingSet as "flagged for further review."  Because this stage
   * operates with RecordIds, we are unable to evaluate the AND for the invalidated RecordId, and it
   * must be fully matched later.
   */
  class AndSortedStage : public PlanStage {
  public:
      AndSortedStage(WorkingSet* ws, const Collection* collection);
  
      void addChild(PlanStage* child);
  
      virtual StageState work(WorkingSetID* out);
      virtual bool isEOF();
  
      virtual void doInvalidate(OperationContext* txn, const RecordId& dl, InvalidationType type);
  
      virtual StageType stageType() const {
          return STAGE_AND_SORTED;
      }
  
      virtual std::unique_ptr<PlanStageStats> getStats();
  
      virtual const SpecificStats* getSpecificStats() const;
  
      static const char* kStageType;
  
  private:
      // Find a node to AND against.
      PlanStage::StageState getTargetLoc(WorkingSetID* out);
  
      // Move a child which hasn't advanced to the target node forward.
      // Returns the target node in 'out' if all children successfully advance to it.
      PlanStage::StageState moveTowardTargetLoc(WorkingSetID* out);
  
      // Not owned by us.
      const Collection* _collection;
  
      // Not owned by us.
      WorkingSet* _ws;
  
      // The current node we're AND-ing against.
      size_t _targetNode;
      RecordId _targetLoc;
      WorkingSetID _targetId;
  
      // Nodes we're moving forward until they hit the element we're AND-ing.
      // Everything in here has not advanced to _targetLoc yet.
      // These are indices into _children.
      std::queue<size_t> _workingTowardRep;
  
      // If any child hits EOF or if we have any errors, we're EOF.
      bool _isEOF;
  
      // Stats
      AndSortedStats _specificStats;
  };
  
  }  // namespace mongo
  