text: //  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
  //  This source code is licensed under both the GPLv2 (found in the
  //  COPYING file in the root directory) and Apache 2.0 License
  //  (found in the LICENSE.Apache file in the root directory).
  //
  // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file. See the AUTHORS file for names of contributors.
  
  #pragma once
  #include "rocksdb/iterator.h"
  #include "rocksdb/env.h"
  #include "table/iterator_wrapper.h"
  
  namespace rocksdb {
  
  struct ReadOptions;
  class InternalKeyComparator;
  
  // TwoLevelIteratorState expects iterators are not created using the arena
  struct TwoLevelIteratorState {
    TwoLevelIteratorState() {}
  
    virtual ~TwoLevelIteratorState() {}
    virtual InternalIterator* NewSecondaryIterator(const Slice& handle) = 0;
  };
  
  
  // Return a new two level iterator.  A two-level iterator contains an
  // index iterator whose values point to a sequence of blocks where
  // each block is itself a sequence of key,value pairs.  The returned
  // two-level iterator yields the concatenation of all key/value pairs
  // in the sequence of blocks.  Takes ownership of "index_iter" and
  // will delete it when no longer needed.
  //
  // Uses a supplied function to convert an index_iter value into
  // an iterator over the contents of the corresponding block.
  // Note: this function expects first_level_iter was not created using the arena
  extern InternalIterator* NewTwoLevelIterator(
      TwoLevelIteratorState* state, InternalIterator* first_level_iter);
  
  }  // namespace rocksdb
  