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+//
+// experimental/promise.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2021 Klemens D. Morgenstern
+// (klemens dot morgenstern at gmx dot net)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXPERIMENTAL_PROMISE_HPP
+#define ASIO_EXPERIMENTAL_PROMISE_HPP
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/any_io_executor.hpp"
+#include "asio/associated_cancellation_slot.hpp"
+#include "asio/bind_executor.hpp"
+#include "asio/cancellation_signal.hpp"
+#include "asio/experimental/detail/completion_handler_erasure.hpp"
+#include "asio/experimental/impl/promise.hpp"
+#include "asio/post.hpp"
+
+#include <variant>
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace experimental {
+
+template <typename Executor = any_io_executor>
+struct use_promise_t {};
+
+constexpr use_promise_t<> use_promise;
+
+template <typename T>
+struct is_promise : std::false_type {};
+
+template <typename ... Ts>
+struct is_promise<promise<Ts...>> : std::true_type {};
+
+template <typename T>
+constexpr bool is_promise_v = is_promise<T>::value;
+
+template <typename T>
+concept is_promise_c = is_promise_v<std::remove_reference_t<T>>;
+
+template <typename ... Ts>
+struct promise_value_type
+{
+ using type = std::tuple<Ts...>;
+};
+
+template <typename T>
+struct promise_value_type<T>
+{
+ using type = T;
+};
+
+template <>
+struct promise_value_type<>
+{
+ using type = std::monostate;
+};
+
+#if defined(GENERATING_DOCUMENTATION)
+/// The primary template is not defined.
+template<typename Signature = void(), typename Executor = any_io_executor>
+struct promise
+{
+};
+#endif // defined(GENERATING_DOCUMENTATION)
+
+template <typename ... Ts, typename Executor>
+struct promise<void(Ts...), Executor>
+{
+ using value_type = typename promise_value_type<Ts...>::type;
+ using tuple_type = std::tuple<Ts...>;
+ using executor_type = Executor;
+
+ executor_type get_executor() const
+ {
+ if (impl_)
+ return impl_->executor;
+ else
+ return {};
+ }
+
+ void cancel(cancellation_type level = cancellation_type::all)
+ {
+ if (impl_ && !impl_->done)
+ {
+ asio::dispatch(impl_->executor,
+ [level, impl = impl_]{impl->cancel.emit(level);});
+ }
+ }
+
+ bool complete() const noexcept
+ {
+ return impl_ && impl_->done;
+ }
+
+ template <typename CompletionToken>
+ auto async_wait(CompletionToken&& token)
+ {
+ assert(impl_);
+
+ return async_initiate<CompletionToken, void(Ts...)>(
+ initiate_async_wait{impl_}, token);
+ }
+
+ promise() = delete;
+ promise(const promise& ) = delete;
+ promise(promise&& ) noexcept = default;
+
+ ~promise() { cancel(); }
+
+ template <execution::executor Executor1, is_promise_c ... Ps>
+ static auto race(Executor1 exec, Ps ... ps)
+ -> promise<void(std::variant<typename Ps::value_type...>), Executor1>
+ {
+ using var_t = std::variant<typename Ps::value_type...>;
+ using pi = detail::promise_impl<void(var_t), Executor1>;
+
+ struct impl_t : pi
+ {
+ impl_t(Executor1 exec, Ps&& ... ps)
+ : pi(std::move(exec)),
+ tup(std::move(ps)...)
+ {
+ this->slot.template emplace<cancel_handler>(this);
+ }
+
+ struct cancel_handler
+ {
+ impl_t* self;
+
+ cancel_handler(impl_t* self)
+ : self(self)
+ {
+ }
+
+ void operator()(cancellation_type ct)
+ {
+ [ct, s=self]<std::size_t... Idx>(std::index_sequence<Idx...>)
+ {
+ (std::get<Idx>(s->tup).cancel(ct), ... );
+ }(std::make_index_sequence<sizeof...(Ps)>{});
+ }
+ };
+
+ std::tuple<std::remove_reference_t<Ps>...> tup;
+ cancellation_slot slot{this->cancel.slot()};
+ };
+
+ auto impl = std::allocate_shared<impl_t>(
+ get_associated_allocator(exec), exec, std::move(ps)...);
+
+ impl->executor = exec;
+
+ [impl, exec]<std::size_t... Idx>(std::index_sequence<Idx...>)
+ {
+ auto step =
+ [&]<std::size_t I>(std::integral_constant<std::size_t, I>)
+ {
+ return [impl]<typename... Args > (Args&& ... args)
+ {
+ if (impl->done)
+ return;
+ impl->result = var_t(std::in_place_index<I>,
+ std::forward<Args>(args)...);
+ impl->done = true;
+ if (auto f = std::exchange(impl->completion, nullptr); !!f)
+ std::apply(std::move(f), std::move(*impl->result));
+
+ auto cancel =
+ [&]<std::size_t Id>(std::integral_constant<std::size_t, Id>)
+ {
+ if constexpr (I != Id)
+ get<I>(impl->tup).cancel();
+ };
+
+ (cancel(std::integral_constant<std::size_t, Idx>{}), ...);
+ };
+ };
+
+ (
+ std::get<Idx>(impl->tup).async_wait(
+ bind_executor(exec,
+ step(std::integral_constant<std::size_t, Idx>{}))),
+ ...
+ );
+ }(std::make_index_sequence<sizeof...(Ps)>{});
+
+ return {impl};
+ }
+
+ template <execution::executor Executor1, is_promise_c ... Ps>
+ static auto all(Executor1 exec, Ps ... ps)
+ -> promise<void(typename Ps::value_type...), Executor1>
+ {
+ using pi = detail::promise_impl<
+ void(typename Ps::value_type...), Executor1>;
+
+ struct impl_t : pi
+ {
+ impl_t(Executor1 exec, Ps&& ... ps)
+ : pi(std::move(exec)),
+ tup(std::move(ps)...)
+ {
+ this->slot.template emplace<cancel_handler>(this);
+ }
+
+ struct cancel_handler
+ {
+ impl_t* self;
+
+ cancel_handler(impl_t* self)
+ : self(self)
+ {
+ }
+
+ void operator()(cancellation_type level)
+ {
+ [level, s=self]<std::size_t... Idx>(std::index_sequence<Idx...>)
+ {
+ (std::get<Idx>(s->tup).cancel(level), ... );
+ }(std::make_index_sequence<sizeof...(Ps)>{});
+ }
+ };
+
+ std::tuple<std::remove_reference_t<Ps>...> tup;
+ std::tuple<std::optional<typename Ps::value_type>...> partial_result;
+ cancellation_slot slot{this->cancel.slot()};
+ };
+
+ auto impl = std::allocate_shared<impl_t>(
+ get_associated_allocator(exec), exec, std::move(ps)...);
+ impl->executor = exec;
+
+ [impl, exec]<std::size_t... Idx>(std::index_sequence<Idx...>)
+ {
+ auto step =
+ [&]<std::size_t I>(std::integral_constant<std::size_t, I>)
+ {
+ return [impl]<typename... Args>(Args&& ... args)
+ {
+ std::get<I>(impl->partial_result).emplace(
+ std::forward<Args>(args)...);
+ if ((std::get<Idx>(impl->partial_result) && ...)) // we're done.
+ {
+ impl->result = {*std::get<Idx>(impl->partial_result)...};
+
+ impl->done = true;
+ if (auto f = std::exchange(impl->completion, nullptr); !!f)
+ std::apply(std::move(f), std::move(*impl->result));
+ }
+ };
+ };
+
+ (
+ std::get<Idx>(impl->tup).async_wait(
+ bind_executor(exec,
+ step(std::integral_constant<std::size_t, Idx>{}))),
+ ...
+ );
+ }(std::make_index_sequence<sizeof...(Ps)>{});
+
+ return {impl};
+ }
+
+ template <is_promise_c ... Ps>
+ static auto race(Ps ... ps)
+ {
+ auto exec = get<0>(std::tie(ps...)).get_executor();
+ return race(std::move(exec), std::move(ps)...);
+ }
+
+ template <is_promise_c ... Ps>
+ static auto all(Ps ... ps)
+ {
+ auto exec = get<0>(std::tie(ps...)).get_executor();
+ return all(std::move(exec), std::move(ps)...);
+ }
+
+ template <execution::executor Executor1, typename Range>
+#if !defined(GENERATING_DOCUMENTATION)
+ requires requires (Range r)
+ {
+ {*std::begin(r)} -> is_promise_c;
+ {*std:: end(r)} -> is_promise_c;
+ }
+#endif // !defined(GENERATING_DOCUMENTATION)
+ static auto race(Executor1 exec, Range range)
+ {
+ using var_t = typename std::decay_t<
+ decltype(*std::begin(range))>::value_type;
+ using signature_type = std::conditional_t<
+ std::is_same_v<var_t, std::monostate>,
+ void(std::size_t),
+ void(std::size_t, var_t)>;
+ using pi = detail::promise_impl<signature_type, Executor1>;
+ using promise_t = promise<signature_type, Executor1>;
+
+ struct impl_t : pi
+ {
+ impl_t(Executor1 exec, Range&& range)
+ : pi(std::move(exec)),
+ range(std::move(range))
+ {
+ this->slot.template emplace<cancel_handler>(this);
+ }
+
+ struct cancel_handler
+ {
+ impl_t* self;
+
+ cancel_handler(impl_t* self)
+ : self(self)
+ {
+ }
+
+ void operator()(asio::cancellation_type ct)
+ {
+ for (auto& r : self->range)
+ r.cancel(ct);
+ }
+ };
+
+ Range range;
+ cancellation_slot slot{this->cancel.slot()};
+ };
+
+ const auto size = std::distance(std::begin(range), std::end(range));
+ auto impl = std::allocate_shared<impl_t>(
+ get_associated_allocator(exec), exec, std::move(range));
+ impl->executor = exec;
+
+ if (size == 0u)
+ {
+ if constexpr (std::is_same_v<var_t, std::monostate>)
+ impl->result = {-1};
+ else
+ impl->result = {-1, var_t{}};
+
+ impl->done = true;
+ if (auto f = std::exchange(impl->completion, nullptr); !!f)
+ {
+ asio::post(exec,
+ [impl, f = std::move(f)]() mutable
+ {
+ std::apply(std::move(f), std::move(*impl->result));
+ });
+ }
+ return promise_t{impl};
+ }
+ auto idx = 0u;
+ for (auto& val : impl->range)
+ {
+ val.async_wait(
+ bind_executor(exec,
+ [idx, impl]<typename... Args>(Args&&... args)
+ {
+ if (impl->done)
+ return;
+ if constexpr (std::is_same_v<var_t, std::monostate>)
+ impl->result = idx;
+ else
+ impl->result = std::make_tuple(idx,
+ var_t(std::forward<Args>(args)...));
+ impl->done = true;
+ if (auto f = std::exchange(impl->completion, nullptr); !!f)
+ std::apply(std::move(f), std::move(*impl->result));
+
+ auto jdx = 0u;
+
+ for (auto &tc : impl->range)
+ if (jdx++ != idx)
+ tc.cancel();
+ }));
+ idx++;
+ }
+ return promise_t{impl};
+ }
+
+
+ template <execution::executor Executor1, typename Range>
+#if !defined(GENERATING_DOCUMENTATION)
+ requires requires (Range r)
+ {
+ {*std::begin(r)} -> is_promise_c;
+ {*std:: end(r)} -> is_promise_c;
+ }
+#endif // !defined(GENERATING_DOCUMENTATION)
+ static auto all(Executor1 exec, Range range)
+ -> promise<
+ void(
+ std::vector<
+ typename std::decay_t<
+ decltype(*std::begin(range))
+ >::value_type
+ >
+ ), Executor1>
+ {
+ using var_t = typename std::decay_t<
+ decltype(*std::begin(range))>::value_type;
+ using pi = detail::promise_impl<void(std::vector<var_t>), Executor1>;
+
+ struct impl_t : pi
+ {
+ impl_t(Executor1 exec, Range&& range)
+ : pi(std::move(exec)),
+ range(std::move(range))
+ {
+ this->slot.template emplace<cancel_handler>(this);
+ }
+
+ struct cancel_handler
+ {
+ impl_t* self;
+
+ cancel_handler(impl_t* self)
+ : self(self)
+ {
+ }
+
+ void operator()(cancellation_type ct)
+ {
+ for (auto& r : self->range)
+ r.cancel(ct);
+ }
+ };
+
+ Range range;
+ std::vector<std::optional<var_t>> partial_result;
+ cancellation_slot slot{this->cancel.slot()};
+ };
+
+ const auto size = std::distance(std::begin(range), std::end(range));
+ auto impl = std::allocate_shared<impl_t>(
+ get_associated_allocator(exec), exec, std::move(range));
+ impl->executor = exec;
+ impl->partial_result.resize(size);
+
+ if (size == 0u)
+ {
+ impl->result.emplace();
+ impl->done = true;
+ if (auto f = std::exchange(impl->completion, nullptr); !!f)
+ asio::post(exec, [impl, f = std::move(f)]() mutable
+ {
+ std::apply(std::move(f), std::move(*impl->result));
+ });
+ return {impl};
+ }
+ auto idx = 0u;
+ for (auto& val : impl->range) {
+ val.async_wait(bind_executor(
+ exec,
+ [idx, impl]<typename... Args>(Args&&... args) {
+
+ impl->partial_result[idx].emplace(std::forward<Args>(args)...);
+ if (std::all_of(impl->partial_result.begin(),
+ impl->partial_result.end(),
+ [](auto &opt) {return opt.has_value();}))
+ {
+ impl->result.emplace();
+ get<0>(*impl->result).reserve(impl->partial_result.size());
+ for (auto& p : impl->partial_result)
+ get<0>(*impl->result).push_back(std::move(*p));
+
+ impl->done = true;
+ if (auto f = std::exchange(impl->completion, nullptr); !!f)
+ std::apply(std::move(f), std::move(*impl->result));
+ }
+
+ }));
+ idx++;
+ }
+ return {impl};
+ }
+
+ template <typename Range>
+#if !defined(GENERATING_DOCUMENTATION)
+ requires requires (Range r)
+ {
+ {*std::begin(r)} -> is_promise_c;
+ {*std:: end(r)} -> is_promise_c;
+ }
+#endif // !defined(GENERATING_DOCUMENTATION)
+ static auto race(Range range)
+ {
+ if (std::begin(range) == std::end(range))
+ throw std::logic_error(
+ "Can't use race on an empty range with deduced executor");
+ else
+ return race(std::begin(range)->get_executor(), std::move(range));
+ }
+
+ template <typename Range>
+#if !defined(GENERATING_DOCUMENTATION)
+ requires requires (Range&& r)
+ {
+ {*std::begin(r)} -> is_promise_c;
+ {*std:: end(r)} -> is_promise_c;
+ }
+#endif // !defined(GENERATING_DOCUMENTATION)
+ static auto all(Range range)
+ {
+ if (std::begin(range) == std::end(range))
+ throw std::logic_error(
+ "Can't use all on an empty range with deduced executor");
+ else
+ return all(std::begin(range)->get_executor(), std::move(range));
+ }
+
+private:
+#if !defined(GENERATING_DOCUMENTATION)
+ template <typename, typename> friend struct promise;
+ friend struct detail::promise_handler<void(Ts...)>;
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+ std::shared_ptr<detail::promise_impl<void(Ts...), Executor>> impl_;
+ promise(std::shared_ptr<detail::promise_impl<void(Ts...), Executor>> impl)
+ : impl_(impl)
+ {
+ }
+
+ struct initiate_async_wait
+ {
+ std::shared_ptr<detail::promise_impl<void(Ts...), Executor>> self_;
+
+ template <typename WaitHandler>
+ void operator()(WaitHandler&& handler) const
+ {
+ const auto exec = get_associated_executor(handler, self_->executor);
+ auto cancel = get_associated_cancellation_slot(handler);
+ if (self_->done)
+ {
+ asio::post(exec,
+ [self = self_, h = std::forward<WaitHandler>(handler)]() mutable
+ {
+ std::apply(std::forward<WaitHandler>(h),
+ std::move(*self->result));
+ });
+ }
+ else
+ {
+ if (cancel.is_connected())
+ {
+ struct cancel_handler
+ {
+ std::weak_ptr<detail::promise_impl<void(Ts...), Executor>> self;
+
+ cancel_handler(
+ std::weak_ptr<detail::promise_impl<void(Ts...), Executor>> self)
+ : self(std::move(self))
+ {
+ }
+
+ void operator()(cancellation_type level) const
+ {
+ if (auto p = self.lock(); p != nullptr)
+ p->cancel.emit(level);
+
+ }
+ };
+
+ cancel.template emplace<cancel_handler>(self_);
+ }
+
+ self_->completion = {exec, std::forward<WaitHandler>(handler)};
+ }
+ }
+ };
+};
+
+} // namespace experimental
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename Executor, typename R, typename... Args>
+struct async_result<experimental::use_promise_t<Executor>, R(Args...)>
+{
+ using handler_type = experimental::detail::promise_handler<
+ void(typename decay<Args>::type...), Executor>;
+
+ template <typename Initiation, typename... InitArgs>
+ static auto initiate(Initiation initiation,
+ experimental::use_promise_t<Executor>, InitArgs... args)
+ -> typename handler_type::promise_type
+ {
+ handler_type ht{get_associated_executor(initiation)};
+ std::move(initiation)(ht, std::move(args)...);
+ return ht.make_promise();
+ }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXPERIMENTAL_PROMISE_HPP