text: /**
   *    Copyright (C) 2014 MongoDB 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 "mongo/db/diskloc.h"
  #include "mongo/db/jsobj.h"
  #include "mongo/db/exec/plan_stage.h"
  #include "mongo/db/matcher/expression.h"
  
  namespace mongo {
  
      /**
       * KeepMutationsStage passes all of its child's data through until the child is EOF.
       * It then returns all flagged elements in the WorkingSet that pass the stage's filter.
       *
       * This stage is used to merge results that are invalidated mid-query back into the query
       * results when possible.  The query planner is responsible for determining when it's valid to
       * merge these results.
       */
      class KeepMutationsStage : public PlanStage {
      public:
          KeepMutationsStage(const MatchExpression* filter, WorkingSet* ws, PlanStage* child);
          virtual ~KeepMutationsStage();
  
          virtual bool isEOF();
          virtual StageState work(WorkingSetID* out);
  
          virtual void prepareToYield();
          virtual void recoverFromYield();
          virtual void invalidate(const DiskLoc& dl, InvalidationType type);
  
          virtual PlanStageStats* getStats();
  
      private:
          // Not owned here.
          WorkingSet* _workingSet;
  
          scoped_ptr<PlanStage> _child;
  
          // Not owned here.  Should be the full query expression tree.
          const MatchExpression* _filter;
  
          // We read from our child...
          bool _doneReadingChild;
  
          // ...until it's out of results, at which point we put any flagged results back in the query
          // stream.
          bool _doneReturningFlagged;
  
          // Stats
          CommonStats _commonStats;
  
          unordered_set<WorkingSetID>::const_iterator _flaggedIterator;
      };
  
  }  // namespace mongo
  