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/***************************************************************************** |
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* vim:tw=78 |
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* |
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* Copyright (C) 2022 Bjarne von Horn (vh at igh dot de). |
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* |
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* This file is part of the PdCom library. |
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* |
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* The PdCom library is free software: you can redistribute it and/or modify |
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* it under the terms of the GNU Lesser General Public License as published by |
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* the Free Software Foundation, either version 3 of the License, or (at your |
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* option) any later version. |
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* |
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* The PdCom library is distributed in the hope that it will be useful, but |
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* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
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* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public |
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* License for more details. |
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* |
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* You should have received a copy of the GNU Lesser General Public License |
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* along with the PdCom library. If not, see <http://www.gnu.org/licenses/>. |
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* |
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*****************************************************************************/ |
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#ifndef PDCOM5_FUTURE_H |
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#define PDCOM5_FUTURE_H |
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#include <functional> |
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#include <memory> |
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#include <pdcom5_export.h> |
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namespace PdCom { |
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namespace impl { |
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template <class Exception, class... Result> |
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struct Promise; |
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} |
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/** Callback management handle. |
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* |
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* This class can save up to two callbacks for an asynchronous operation. |
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* When the result of the asynchronous operation arrives, |
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* the callback set by then() is called. |
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* On error, handle_exception() is invoked. |
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* |
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* Please note that this Future does not support fire-and-forget. |
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* The Future should be kept until one of the callback was called. |
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* If you're not interested in the result anymore, you can delete the future. |
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* In this case, no callbacks are run. |
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*/ |
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template <class Exception, class... Result> |
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class PDCOM5_PUBLIC Future |
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{ |
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public: |
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using ResolveFn = std::function<void(Result...)>; |
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using RejectFn = std::function<void(Exception)>; |
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/// Default Constructor. |
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Future() = default; |
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Future(std::shared_ptr<impl::Promise<Exception, Result...>> impl) noexcept : |
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impl_(std::move(impl)) |
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{} |
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Future(Future &&) = default; |
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Future(const Future &) = delete; |
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Future &operator=(Future &&) = default; |
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Future &operator=(const Future &) = delete; |
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/** Set continuation callback. |
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* |
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* \param resolve The callback to be invoked with the result. |
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* \return const Reference to \c this. |
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*/ |
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const Future &then(ResolveFn resolve) const &; |
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/** Set continuation callback. |
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* |
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* \param resolve The callback to be invoked with the result. |
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* \return a new Future. |
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*/ |
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Future then(ResolveFn resolve) &&; |
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/** Set error handling callback |
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* |
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* \param reject The callback to be invoked on error. |
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* \return const Reference to \c this. |
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*/ |
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const Future &handle_exception(RejectFn reject) const &; |
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/** Set error handling callback |
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* |
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* \param reject The callback to be invoked on error. |
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* \return a new Future. |
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*/ |
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Future handle_exception(RejectFn reject) &&; |
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/** |
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* \return true if the Future was default-constructed. |
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*/ |
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bool empty() const noexcept { return !impl_.operator bool(); } |
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/// Hash support, e.g. for \c std::unordered_set |
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struct Hash |
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{ |
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std::size_t operator()(Future const &future) const |
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{ |
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return std::hash< |
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std::shared_ptr<impl::Promise<Exception, Result...>>>()( |
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future.impl_); |
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} |
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}; |
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/// Less compare support, e.g. for \c std::set |
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struct Less |
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{ |
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bool operator()(const Future &lhs, const Future &rhs) const noexcept |
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{ |
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return std::owner_less< |
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std::shared_ptr<impl::Promise<Exception, Result...>>>()( |
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lhs.impl_, rhs.impl_); |
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} |
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}; |
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/// Equal comparsion. |
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bool operator==(const Future &other) const noexcept |
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{ |
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return other.impl_ == impl_; |
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} |
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private: |
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std::shared_ptr<impl::Promise<Exception, Result...>> impl_; |
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}; |
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} // namespace PdCom |
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namespace std { |
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template <class Exception, class... Result> |
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struct hash<PdCom::Future<Exception, Result...>> : |
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PdCom::Future<Exception, Result...>::Hash |
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{}; |
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template <class Exception, class... Result> |
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struct less<PdCom::Future<Exception, Result...>> : |
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PdCom::Future<Exception, Result...>::Less |
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{}; |
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} // namespace std |
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#endif // PDCOM5_FUTURE_H |
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