--- /dev/null
+//
+// experimental/impl/parallel_group.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2022 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// 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 BOOST_ASIO_IMPL_EXPERIMENTAL_PARALLEL_GROUP_HPP
+#define BOOST_ASIO_IMPL_EXPERIMENTAL_PARALLEL_GROUP_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <atomic>
+#include <memory>
+#include <new>
+#include <tuple>
+#include <boost/asio/associated_cancellation_slot.hpp>
+#include <boost/asio/detail/recycling_allocator.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/dispatch.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace experimental {
+namespace detail {
+
+// Stores the result from an individual asynchronous operation.
+template <typename T, typename = void>
+struct parallel_group_op_result
+{
+public:
+ parallel_group_op_result()
+ : has_value_(false)
+ {
+ }
+
+ parallel_group_op_result(parallel_group_op_result&& other)
+ : has_value_(other.has_value_)
+ {
+ if (has_value_)
+ new (&u_.value_) T(std::move(other.get()));
+ }
+
+ ~parallel_group_op_result()
+ {
+ if (has_value_)
+ u_.value_.~T();
+ }
+
+ T& get() noexcept
+ {
+ return u_.value_;
+ }
+
+ template <typename... Args>
+ void emplace(Args&&... args)
+ {
+ new (&u_.value_) T(std::forward<Args>(args)...);
+ has_value_ = true;
+ }
+
+private:
+ union u
+ {
+ u() {}
+ ~u() {}
+ char c_;
+ T value_;
+ } u_;
+ bool has_value_;
+};
+
+// Proxy completion handler for the group of parallel operatations. Unpacks and
+// concatenates the individual operations' results, and invokes the user's
+// completion handler.
+template <typename Handler, typename... Ops>
+struct parallel_group_completion_handler
+{
+ typedef typename decay<
+ typename prefer_result<
+ typename associated_executor<Handler>::type,
+ execution::outstanding_work_t::tracked_t
+ >::type
+ >::type executor_type;
+
+ parallel_group_completion_handler(Handler&& h)
+ : handler_(std::move(h)),
+ executor_(
+ boost::asio::prefer(
+ boost::asio::get_associated_executor(handler_),
+ execution::outstanding_work.tracked))
+ {
+ }
+
+ executor_type get_executor() const noexcept
+ {
+ return executor_;
+ }
+
+ void operator()()
+ {
+ this->invoke(std::make_index_sequence<sizeof...(Ops)>());
+ }
+
+ template <std::size_t... I>
+ void invoke(std::index_sequence<I...>)
+ {
+ this->invoke(std::tuple_cat(std::move(std::get<I>(args_).get())...));
+ }
+
+ template <typename... Args>
+ void invoke(std::tuple<Args...>&& args)
+ {
+ this->invoke(std::move(args), std::make_index_sequence<sizeof...(Args)>());
+ }
+
+ template <typename... Args, std::size_t... I>
+ void invoke(std::tuple<Args...>&& args, std::index_sequence<I...>)
+ {
+ std::move(handler_)(completion_order_, std::move(std::get<I>(args))...);
+ }
+
+ Handler handler_;
+ executor_type executor_;
+ std::array<std::size_t, sizeof...(Ops)> completion_order_{};
+ std::tuple<
+ parallel_group_op_result<
+ typename parallel_op_signature_as_tuple<
+ typename parallel_op_signature<Ops>::type
+ >::type
+ >...
+ > args_{};
+};
+
+// Shared state for the parallel group.
+template <typename Condition, typename Handler, typename... Ops>
+struct parallel_group_state
+{
+ parallel_group_state(Condition&& c, Handler&& h)
+ : cancellation_condition_(std::move(c)),
+ handler_(std::move(h))
+ {
+ }
+
+ // The number of operations that have completed so far. Used to determine the
+ // order of completion.
+ std::atomic<unsigned int> completed_{0};
+
+ // The non-none cancellation type that resulted from a cancellation condition.
+ // Stored here for use by the group's initiating function.
+ std::atomic<cancellation_type_t> cancel_type_{cancellation_type::none};
+
+ // The number of cancellations that have been requested, either on completion
+ // of the operations within the group, or via the cancellation slot for the
+ // group operation. Initially set to the number of operations to prevent
+ // cancellation signals from being emitted until after all of the group's
+ // operations' initiating functions have completed.
+ std::atomic<unsigned int> cancellations_requested_{sizeof...(Ops)};
+
+ // The number of operations that are yet to complete. Used to determine when
+ // it is safe to invoke the user's completion handler.
+ std::atomic<unsigned int> outstanding_{sizeof...(Ops)};
+
+ // The cancellation signals for each operation in the group.
+ boost::asio::cancellation_signal cancellation_signals_[sizeof...(Ops)];
+
+ // The cancellation condition is used to determine whether the results from an
+ // individual operation warrant a cancellation request for the whole group.
+ Condition cancellation_condition_;
+
+ // The proxy handler to be invoked once all operations in the group complete.
+ parallel_group_completion_handler<Handler, Ops...> handler_;
+};
+
+// Handler for an individual operation within the parallel group.
+template <std::size_t I, typename Condition, typename Handler, typename... Ops>
+struct parallel_group_op_handler
+{
+ typedef boost::asio::cancellation_slot cancellation_slot_type;
+
+ parallel_group_op_handler(
+ std::shared_ptr<parallel_group_state<Condition, Handler, Ops...> > state)
+ : state_(std::move(state))
+ {
+ }
+
+ cancellation_slot_type get_cancellation_slot() const noexcept
+ {
+ return state_->cancellation_signals_[I].slot();
+ }
+
+ template <typename... Args>
+ void operator()(Args... args)
+ {
+ // Capture this operation into the completion order.
+ state_->handler_.completion_order_[state_->completed_++] = I;
+
+ // Determine whether the results of this operation require cancellation of
+ // the whole group.
+ cancellation_type_t cancel_type = state_->cancellation_condition_(args...);
+
+ // Capture the result of the operation into the proxy completion handler.
+ std::get<I>(state_->handler_.args_).emplace(std::move(args)...);
+
+ if (cancel_type != cancellation_type::none)
+ {
+ // Save the type for potential use by the group's initiating function.
+ state_->cancel_type_ = cancel_type;
+
+ // If we are the first operation to request cancellation, emit a signal
+ // for each operation in the group.
+ if (state_->cancellations_requested_++ == 0)
+ for (std::size_t i = 0; i < sizeof...(Ops); ++i)
+ if (i != I)
+ state_->cancellation_signals_[i].emit(cancel_type);
+ }
+
+ // If this is the last outstanding operation, invoke the user's handler.
+ if (--state_->outstanding_ == 0)
+ boost::asio::dispatch(std::move(state_->handler_));
+ }
+
+ std::shared_ptr<parallel_group_state<Condition, Handler, Ops...> > state_;
+};
+
+// Handler for an individual operation within the parallel group that has an
+// explicitly specified executor.
+template <typename Executor, std::size_t I,
+ typename Condition, typename Handler, typename... Ops>
+struct parallel_group_op_handler_with_executor :
+ parallel_group_op_handler<I, Condition, Handler, Ops...>
+{
+ typedef parallel_group_op_handler<I, Condition, Handler, Ops...> base_type;
+ typedef boost::asio::cancellation_slot cancellation_slot_type;
+ typedef Executor executor_type;
+
+ parallel_group_op_handler_with_executor(
+ std::shared_ptr<parallel_group_state<Condition, Handler, Ops...> > state,
+ executor_type ex)
+ : parallel_group_op_handler<I, Condition, Handler, Ops...>(std::move(state))
+ {
+ cancel_proxy_ =
+ &this->state_->cancellation_signals_[I].slot().template
+ emplace<cancel_proxy>(this->state_, std::move(ex));
+ }
+
+ cancellation_slot_type get_cancellation_slot() const noexcept
+ {
+ return cancel_proxy_->signal_.slot();
+ }
+
+ executor_type get_executor() const noexcept
+ {
+ return cancel_proxy_->executor_;
+ }
+
+ // Proxy handler that forwards the emitted signal to the correct executor.
+ struct cancel_proxy
+ {
+ cancel_proxy(
+ std::shared_ptr<parallel_group_state<
+ Condition, Handler, Ops...> > state,
+ executor_type ex)
+ : state_(std::move(state)),
+ executor_(std::move(ex))
+ {
+ }
+
+ void operator()(cancellation_type_t type)
+ {
+ if (auto state = state_.lock())
+ {
+ boost::asio::cancellation_signal* sig = &signal_;
+ boost::asio::dispatch(executor_,
+ [state, sig, type]{ sig->emit(type); });
+ }
+ }
+
+ std::weak_ptr<parallel_group_state<Condition, Handler, Ops...> > state_;
+ boost::asio::cancellation_signal signal_;
+ executor_type executor_;
+ };
+
+ cancel_proxy* cancel_proxy_;
+};
+
+// Helper to launch an operation using the correct executor, if any.
+template <std::size_t I, typename Op, typename = void>
+struct parallel_group_op_launcher
+{
+ template <typename Condition, typename Handler, typename... Ops>
+ static void launch(Op& op,
+ const std::shared_ptr<parallel_group_state<
+ Condition, Handler, Ops...> >& state)
+ {
+ typedef typename associated_executor<Op>::type ex_type;
+ ex_type ex = boost::asio::get_associated_executor(op);
+ std::move(op)(
+ parallel_group_op_handler_with_executor<ex_type, I,
+ Condition, Handler, Ops...>(state, std::move(ex)));
+ }
+};
+
+// Specialised launcher for operations that specify no executor.
+template <std::size_t I, typename Op>
+struct parallel_group_op_launcher<I, Op,
+ typename enable_if<
+ is_same<
+ typename associated_executor<
+ Op>::asio_associated_executor_is_unspecialised,
+ void
+ >::value
+ >::type>
+{
+ template <typename Condition, typename Handler, typename... Ops>
+ static void launch(Op& op,
+ const std::shared_ptr<parallel_group_state<
+ Condition, Handler, Ops...> >& state)
+ {
+ std::move(op)(
+ parallel_group_op_handler<I, Condition, Handler, Ops...>(state));
+ }
+};
+
+template <typename Condition, typename Handler, typename... Ops>
+struct parallel_group_cancellation_handler
+{
+ parallel_group_cancellation_handler(
+ std::shared_ptr<parallel_group_state<Condition, Handler, Ops...> > state)
+ : state_(std::move(state))
+ {
+ }
+
+ void operator()(cancellation_type_t cancel_type)
+ {
+ // If we are the first place to request cancellation, i.e. no operation has
+ // yet completed and requested cancellation, emit a signal for each
+ // operation in the group.
+ if (cancel_type != cancellation_type::none)
+ if (auto state = state_.lock())
+ if (state->cancellations_requested_++ == 0)
+ for (std::size_t i = 0; i < sizeof...(Ops); ++i)
+ state->cancellation_signals_[i].emit(cancel_type);
+ }
+
+ std::weak_ptr<parallel_group_state<Condition, Handler, Ops...> > state_;
+};
+
+template <typename Condition, typename Handler,
+ typename... Ops, std::size_t... I>
+void parallel_group_launch(Condition cancellation_condition, Handler handler,
+ std::tuple<Ops...>& ops, std::index_sequence<I...>)
+{
+ // Get the user's completion handler's cancellation slot, so that we can allow
+ // cancellation of the entire group.
+ typename associated_cancellation_slot<Handler>::type slot
+ = boost::asio::get_associated_cancellation_slot(handler);
+
+ // Create the shared state for the operation.
+ typedef parallel_group_state<Condition, Handler, Ops...> state_type;
+ std::shared_ptr<state_type> state = std::allocate_shared<state_type>(
+ boost::asio::detail::recycling_allocator<state_type,
+ boost::asio::detail::thread_info_base::parallel_group_tag>(),
+ std::move(cancellation_condition), std::move(handler));
+
+ // Initiate each individual operation in the group.
+ int fold[] = { 0,
+ ( parallel_group_op_launcher<I, Ops>::launch(std::get<I>(ops), state),
+ 0 )...
+ };
+ (void)fold;
+
+ // Check if any of the operations has already requested cancellation, and if
+ // so, emit a signal for each operation in the group.
+ if ((state->cancellations_requested_ -= sizeof...(Ops)) > 0)
+ for (auto& signal : state->cancellation_signals_)
+ signal.emit(state->cancel_type_);
+
+ // Register a handler with the user's completion handler's cancellation slot.
+ if (slot.is_connected())
+ slot.template emplace<
+ parallel_group_cancellation_handler<
+ Condition, Handler, Ops...> >(state);
+}
+
+} // namespace detail
+} // namespace experimental
+
+template <typename R, typename... Args>
+class async_result<
+ experimental::detail::parallel_op_signature_probe,
+ R(Args...)>
+{
+public:
+ typedef experimental::detail::parallel_op_signature_probe_result<
+ void(Args...)> return_type;
+
+ template <typename Initiation, typename... InitArgs>
+ static return_type initiate(Initiation&&,
+ experimental::detail::parallel_op_signature_probe, InitArgs&&...)
+ {
+ return return_type{};
+ }
+};
+
+template <template <typename, typename> class Associator,
+ typename Handler, typename... Ops, typename DefaultCandidate>
+struct associator<Associator,
+ experimental::detail::parallel_group_completion_handler<Handler, Ops...>,
+ DefaultCandidate>
+ : Associator<Handler, DefaultCandidate>
+{
+ static typename Associator<Handler, DefaultCandidate>::type get(
+ const experimental::detail::parallel_group_completion_handler<
+ Handler, Ops...>& h,
+ const DefaultCandidate& c = DefaultCandidate()) BOOST_ASIO_NOEXCEPT
+ {
+ return Associator<Handler, DefaultCandidate>::get(h.handler_, c);
+ }
+};
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_IMPL_EXPERIMENTAL_PARALLEL_GROUP_HPP
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