mirror of https://gitee.com/bigwinds/arangodb
99 lines
3.4 KiB
C++
99 lines
3.4 KiB
C++
////////////////////////////////////////////////////////////////////////////////
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/// DISCLAIMER
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///
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/// Copyright 2019 ArangoDB GmbH, Cologne, Germany
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///
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/// Licensed under the Apache License, Version 2.0 (the "License");
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/// you may not use this file except in compliance with the License.
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/// You may obtain a copy of the License at
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///
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/// http://www.apache.org/licenses/LICENSE-2.0
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///
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/// Unless required by applicable law or agreed to in writing, software
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/// distributed under the License is distributed on an "AS IS" BASIS,
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/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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/// See the License for the specific language governing permissions and
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/// limitations under the License.
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///
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/// Copyright holder is ArangoDB GmbH, Cologne, Germany
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///
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/// @author Tobias Gödderz
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////////////////////////////////////////////////////////////////////////////////
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#ifndef ARANGOD_AQL_UNSORTINGGATHEREXECUTOR_H
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#define ARANGOD_AQL_UNSORTINGGATHEREXECUTOR_H
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#include "Aql/ExecutionState.h"
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#include "Aql/ExecutorInfos.h"
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#include "Aql/MultiDependencySingleRowFetcher.h"
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#include "Aql/types.h"
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#include <string>
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#include <unordered_set>
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namespace arangodb::aql {
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class NoStats;
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class InputAqlItemRow;
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class OutputAqlItemRow;
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class IdExecutorInfos;
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class SharedAqlItemBlockPtr;
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/**
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* @brief Produces all rows from its dependencies, which may be more than one,
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* in some unspecified order. It is, purposefully, strictly synchronous, and
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* always waits for an answer before requesting the next row(s).
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*
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* The actual implementation fetches all available rows from the first
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* dependency, then from the second, and so forth. But that is not guaranteed.
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*/
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class UnsortingGatherExecutor {
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public:
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struct Properties {
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static constexpr bool preservesOrder = false;
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static constexpr BlockPassthrough allowsBlockPassthrough = BlockPassthrough::Disable;
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// TODO I think we can set this to true (but needs to implement
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// hasExpectedNumberOfRows for that)
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static constexpr bool inputSizeRestrictsOutputSize = false;
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};
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using Fetcher = MultiDependencySingleRowFetcher;
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// TODO I should probably implement custom Infos, we don't need distributeId().
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using Infos = IdExecutorInfos;
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using Stats = NoStats;
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UnsortingGatherExecutor(Fetcher& fetcher, Infos&);
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~UnsortingGatherExecutor();
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/**
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* @brief produce the next Row of Aql Values.
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*
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* @return ExecutionState,
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* if something was written output.hasValue() == true
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*/
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[[nodiscard]] auto produceRows(OutputAqlItemRow& output)
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-> std::pair<ExecutionState, Stats>;
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[[nodiscard]] auto skipRows(size_t atMost) -> std::tuple<ExecutionState, NoStats, size_t>;
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private:
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[[nodiscard]] auto numDependencies() const
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noexcept(noexcept(static_cast<Fetcher*>(nullptr)->numberDependencies())) -> size_t;
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[[nodiscard]] auto fetcher() const noexcept -> Fetcher const&;
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[[nodiscard]] auto fetcher() noexcept -> Fetcher&;
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[[nodiscard]] auto done() const noexcept -> bool;
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[[nodiscard]] auto currentDependency() const noexcept -> size_t;
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[[nodiscard]] auto fetchNextRow(size_t atMost)
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-> std::pair<ExecutionState, InputAqlItemRow>;
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[[nodiscard]] auto skipNextRows(size_t atMost) -> std::pair<ExecutionState, size_t>;
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auto advanceDependency() noexcept -> void;
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private:
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Fetcher& _fetcher;
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size_t _currentDependency{0};
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size_t _skipped{0};
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};
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} // namespace arangodb::aql
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#endif // ARANGOD_AQL_UNSORTINGGATHEREXECUTOR_H
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