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.
   */
  
  #include <boost/optional.hpp>
  
  #include "mongo/db/catalog/collection.h"
  #include "mongo/db/clientcursor.h"
  
  namespace mongo {
  
  /**
   * A RangePreserver prevents the RangeDeleter from removing any new data ranges in a collection.
   * Previously queued ranges may still be deleted but the documents in those ranges will be
   * filtered by CollectionMetadata::belongsToMe.
   */
  class RangePreserver {
  public:
      /**
       * Sharding uses the set of active cursor IDs as the current state. We pin a dummy
       * ClientCursor, which creates an additional cursor ID. The cursor ID lasts as long as this
       * object does. The ClientCursorPin guarantees that the underlying ClientCursor is not deleted
       * until this object goes out of scope.
       */
      RangePreserver(const Collection* collection) {
          // Empty collections don't have any data we need to preserve
          if (collection) {
              // Pin keeps the CC from being deleted while it's in scope.  We delete it ourselves.
              _pin.emplace(collection->getCursorManager()->registerRangePreserverCursor(collection));
          }
      }
  
      void release() {
          if (_pin) {
              _pin->deleteUnderlying();
              _pin.reset();
          }
      }
  
      ~RangePreserver() {
          release();
      }
  
  private:
      boost::optional<ClientCursorPin> _pin;
  };
  
  }  // namespace mongo
  