mirror of https://gitee.com/bigwinds/arangodb
114 lines
3.7 KiB
C++
114 lines
3.7 KiB
C++
////////////////////////////////////////////////////////////////////////////////
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/// DISCLAIMER
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///
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/// Copyright 2018 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 Jan Steemann
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////////////////////////////////////////////////////////////////////////////////
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#ifndef ARANGOD_AQL_SHARED_QUERY_STATE_H
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#define ARANGOD_AQL_SHARED_QUERY_STATE_H 1
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#include <condition_variable>
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#include "Basics/Common.h"
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namespace arangodb {
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namespace aql {
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class SharedQueryState {
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public:
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SharedQueryState(SharedQueryState const&) = delete;
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SharedQueryState& operator=(SharedQueryState const&) = delete;
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SharedQueryState() : _wasNotified(false), _hasHandler(false), _valid(true) {}
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~SharedQueryState() = default;
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void invalidate();
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/// @brief continueAfterPause is to be called on the query object to
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/// continue execution in this query part, if the query got paused
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/// because it is waiting for network responses. The idea is that a
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/// RemoteBlock that does an asynchronous cluster-internal request can
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/// register a callback with the asynchronous request and then return
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/// with the result `ExecutionState::WAITING`, which will bubble up
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/// the stack and eventually lead to a suspension of the work on the
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/// RestHandler. In the callback function one can first store the
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/// results in the RemoteBlock object and can then call this method on
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/// the query.
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/// This will lead to the following: The original request that led to
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/// the network communication will be rescheduled on the ioservice and
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/// continues its execution where it left off.
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template <typename F>
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bool execute(F&& cb) {
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std::lock_guard<std::mutex> guard(_mutex);
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if (!_valid) {
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return false;
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}
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bool res = std::forward<F>(cb)();
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if (_hasHandler) {
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if (ADB_UNLIKELY(!executeContinueCallback())) {
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return false; // likely shutting down
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}
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} else {
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_wasNotified = true;
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// simon: bad experience on macOS guard.unloack();
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_condition.notify_one();
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}
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return res;
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}
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/// this has to stay for a backwards-compatible AQL HTTP API (hasMore).
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void waitForAsyncResponse();
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/// @brief setter for the continue callback:
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/// We can either have a handler or a callback
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void setContinueCallback() noexcept;
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/// @brief setter for the continue handler:
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/// We can either have a handler or a callback
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void setContinueHandler(std::function<void()> const& handler);
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private:
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/// execute the _continueCallback. must hold _mutex
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bool executeContinueCallback() const;
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private:
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std::mutex _mutex;
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std::condition_variable _condition;
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/// @brief a callback function which is used to implement continueAfterPause.
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/// Typically, the RestHandler using the Query object will put a closure
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/// in here, which continueAfterPause simply calls.
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std::function<void()> _continueCallback;
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bool _wasNotified;
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/// @brief decide if the _continueCallback needs to be pushed onto the
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/// ioservice
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/// or if it has to be executed in this thread.
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bool _hasHandler;
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bool _valid;
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};
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} // namespace aql
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} // namespace arangodb
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#endif
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