YugabyteDB (2.13.1.0-b60, 21121d69985fbf76aa6958d8f04a9bfa936293b5)

//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.

//  This source code is licensed under the BSD-style license found in the

//  LICENSE file in the root directory of this source tree. An additional grant

//  of patent rights can be found in the PATENTS file in the same directory.

//

// The following only applies to changes made to this file as part of YugaByte development.

//

// Portions Copyright (c) YugaByte, Inc.

//

// Licensed 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 <deque>

#include <string>

#include "yb/util/slice.h"

namespace rocksdb {

const std::deque<std::string> empty_operand_list;

// The merge context for merging a user key.

// When doing a Get(), DB will create such a class and pass it when

// issuing Get() operation to memtables and version_set. The operands

// will be fetched from the context when issuing partial of full merge.

class MergeContext {

 public:

  // Clear all the operands

  void Clear() {

    if (operand_list) {

      operand_list->clear();

    }

  }

  // Replace all operands with merge_result, which are expected to be the

  // merge result of them.

  void PushPartialMergeResult(std::string&& merge_result) {

    assert (operand_list);

    operand_list->clear();

    operand_list->push_front(std::move(merge_result));

  }

  // Push a merge operand

  void PushOperand(const Slice& operand_slice) {

    Initialize();

    operand_list->push_front(operand_slice.ToString());

  }

  // return total number of operands in the list

  size_t GetNumOperands() const {

    if (!operand_list) {

      return 0;

    }

    return operand_list->size();

  }

  // Get the operand at the index.

  Slice GetOperand(int index) const {

    assert (operand_list);

    return (*operand_list)[index];

  }

  // Return all the operands.

  const std::deque<std::string>& GetOperands() const {

    if (!operand_list) {

      return empty_operand_list;

    }

    return *operand_list;

  }

 private:

  void Initialize() {

    if (!operand_list) {

      operand_list.reset(new std::deque<std::string>());

    }

  }

  std::unique_ptr<std::deque<std::string>> operand_list;

};

} // namespace rocksdb