Initial Commit

include/asio/experimental/impl/as_single.hpp

@@ -0,0 +1,181 @@
+//
+// experimental/impl/as_single.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 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 ASIO_IMPL_EXPERIMENTAL_AS_SINGLE_HPP
+#define ASIO_IMPL_EXPERIMENTAL_AS_SINGLE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include <tuple>
+#include "asio/associator.hpp"
+#include "asio/async_result.hpp"
+#include "asio/detail/handler_cont_helpers.hpp"
+#include "asio/detail/initiation_base.hpp"
+#include "asio/detail/type_traits.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace experimental {
+namespace detail {
+
+// Class to adapt a as_single_t as a completion handler.
+template <typename Handler>
+class as_single_handler
+{
+public:
+  typedef void result_type;
+
+  template <typename CompletionToken>
+  as_single_handler(as_single_t<CompletionToken> e)
+    : handler_(static_cast<CompletionToken&&>(e.token_))
+  {
+  }
+
+  template <typename RedirectedHandler>
+  as_single_handler(RedirectedHandler&& h)
+    : handler_(static_cast<RedirectedHandler&&>(h))
+  {
+  }
+
+  void operator()()
+  {
+    static_cast<Handler&&>(handler_)();
+  }
+
+  template <typename Arg>
+  void operator()(Arg&& arg)
+  {
+    static_cast<Handler&&>(handler_)(static_cast<Arg&&>(arg));
+  }
+
+  template <typename... Args>
+  void operator()(Args&&... args)
+  {
+    static_cast<Handler&&>(handler_)(
+        std::make_tuple(static_cast<Args&&>(args)...));
+  }
+
+//private:
+  Handler handler_;
+};
+
+template <typename Handler>
+inline bool asio_handler_is_continuation(
+    as_single_handler<Handler>* this_handler)
+{
+  return asio_handler_cont_helpers::is_continuation(
+        this_handler->handler_);
+}
+
+template <typename Signature>
+struct as_single_signature
+{
+  typedef Signature type;
+};
+
+template <typename R>
+struct as_single_signature<R()>
+{
+  typedef R type();
+};
+
+template <typename R, typename Arg>
+struct as_single_signature<R(Arg)>
+{
+  typedef R type(Arg);
+};
+
+template <typename R, typename... Args>
+struct as_single_signature<R(Args...)>
+{
+  typedef R type(std::tuple<decay_t<Args>...>);
+};
+
+} // namespace detail
+} // namespace experimental
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename CompletionToken, typename Signature>
+struct async_result<experimental::as_single_t<CompletionToken>, Signature>
+{
+  template <typename Initiation>
+  struct init_wrapper : detail::initiation_base<Initiation>
+  {
+    using detail::initiation_base<Initiation>::initiation_base;
+
+    template <typename Handler, typename... Args>
+    void operator()(Handler&& handler, Args&&... args) &&
+    {
+      static_cast<Initiation&&>(*this)(
+          experimental::detail::as_single_handler<decay_t<Handler>>(
+            static_cast<Handler&&>(handler)),
+          static_cast<Args&&>(args)...);
+    }
+
+    template <typename Handler, typename... Args>
+    void operator()(Handler&& handler, Args&&... args) const &
+    {
+      static_cast<const Initiation&>(*this)(
+          experimental::detail::as_single_handler<decay_t<Handler>>(
+            static_cast<Handler&&>(handler)),
+          static_cast<Args&&>(args)...);
+    }
+  };
+
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<CompletionToken,
+        typename experimental::detail::as_single_signature<Signature>::type>(
+          init_wrapper<decay_t<Initiation>>(
+            static_cast<Initiation&&>(initiation)),
+          token.token_, static_cast<Args&&>(args)...))
+  {
+    return async_initiate<CompletionToken,
+      typename experimental::detail::as_single_signature<Signature>::type>(
+        init_wrapper<decay_t<Initiation>>(
+          static_cast<Initiation&&>(initiation)),
+        token.token_, static_cast<Args&&>(args)...);
+  }
+};
+
+template <template <typename, typename> class Associator,
+    typename Handler, typename DefaultCandidate>
+struct associator<Associator,
+    experimental::detail::as_single_handler<Handler>, DefaultCandidate>
+  : Associator<Handler, DefaultCandidate>
+{
+  static typename Associator<Handler, DefaultCandidate>::type get(
+      const experimental::detail::as_single_handler<Handler>& h) noexcept
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(const experimental::detail::as_single_handler<Handler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<Handler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_EXPERIMENTAL_AS_SINGLE_HPP

include/asio/experimental/impl/channel_error.ipp

@@ -0,0 +1,61 @@
+//
+// experimental/impl/channel_error.ipp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 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 ASIO_EXPERIMENTAL_IMPL_CHANNEL_ERROR_IPP
+#define ASIO_EXPERIMENTAL_IMPL_CHANNEL_ERROR_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/experimental/channel_error.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace experimental {
+namespace error {
+namespace detail {
+
+class channel_category : public asio::error_category
+{
+public:
+  const char* name() const noexcept
+  {
+    return "asio.channel";
+  }
+
+  std::string message(int value) const
+  {
+    switch (value)
+    {
+    case channel_closed: return "Channel closed";
+    case channel_cancelled: return "Channel cancelled";
+    default: return "asio.channel error";
+    }
+  }
+};
+
+} // namespace detail
+
+const asio::error_category& get_channel_category()
+{
+  static detail::channel_category instance;
+  return instance;
+}
+
+} // namespace error
+} // namespace experimental
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXPERIMENTAL_IMPL_CHANNEL_ERROR_IPP

include/asio/experimental/impl/parallel_group.hpp

@@ -0,0 +1,789 @@
+//
+// experimental/impl/parallel_group.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 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 ASIO_IMPL_EXPERIMENTAL_PARALLEL_GROUP_HPP
+#define ASIO_IMPL_EXPERIMENTAL_PARALLEL_GROUP_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include <atomic>
+#include <deque>
+#include <memory>
+#include <new>
+#include <tuple>
+#include "asio/associated_cancellation_slot.hpp"
+#include "asio/detail/recycling_allocator.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/dispatch.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+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 operations. 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 decay_t<
+      prefer_result_t<
+        associated_executor_t<Handler>,
+        execution::outstanding_work_t::tracked_t
+      >
+    > executor_type;
+
+  parallel_group_completion_handler(Handler&& h)
+    : handler_(std::move(h)),
+      executor_(
+          asio::prefer(
+            asio::get_associated_executor(handler_),
+            execution::outstanding_work.tracked))
+  {
+  }
+
+  executor_type get_executor() const noexcept
+  {
+    return executor_;
+  }
+
+  void operator()()
+  {
+    this->invoke(asio::detail::make_index_sequence<sizeof...(Ops)>());
+  }
+
+  template <std::size_t... I>
+  void invoke(asio::detail::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),
+        asio::detail::index_sequence_for<Args...>());
+  }
+
+  template <typename... Args, std::size_t... I>
+  void invoke(std::tuple<Args...>&& args,
+      asio::detail::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<
+          completion_signature_of_t<Ops>
+        >::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.
+  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 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)
+      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 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())
+      {
+        asio::cancellation_signal* sig = &signal_;
+        asio::dispatch(executor_,
+            [state, sig, type]{ sig->emit(type); });
+      }
+    }
+
+    std::weak_ptr<parallel_group_state<Condition, Handler, Ops...>> state_;
+    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 associated_executor_t<Op> ex_type;
+    ex_type ex = 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,
+    enable_if_t<
+      is_same<
+        typename associated_executor<
+          Op>::asio_associated_executor_is_unspecialised,
+        void
+      >::value
+    >>
+{
+  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, asio::detail::index_sequence<I...>)
+{
+  // Get the user's completion handler's cancellation slot, so that we can allow
+  // cancellation of the entire group.
+  associated_cancellation_slot_t<Handler> slot
+    = 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>(
+      asio::detail::recycling_allocator<state_type,
+        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);
+}
+
+// Proxy completion handler for the ranged group of parallel operations.
+// Unpacks and recombines the individual operations' results, and invokes the
+// user's completion handler.
+template <typename Handler, typename Op, typename Allocator>
+struct ranged_parallel_group_completion_handler
+{
+  typedef decay_t<
+      prefer_result_t<
+        associated_executor_t<Handler>,
+        execution::outstanding_work_t::tracked_t
+      >
+    > executor_type;
+
+  typedef typename parallel_op_signature_as_tuple<
+      completion_signature_of_t<Op>
+    >::type op_tuple_type;
+
+  typedef parallel_group_op_result<op_tuple_type> op_result_type;
+
+  ranged_parallel_group_completion_handler(Handler&& h,
+      std::size_t size, const Allocator& allocator)
+    : handler_(std::move(h)),
+      executor_(
+          asio::prefer(
+            asio::get_associated_executor(handler_),
+            execution::outstanding_work.tracked)),
+      allocator_(allocator),
+      completion_order_(size, 0,
+          ASIO_REBIND_ALLOC(Allocator, std::size_t)(allocator)),
+      args_(ASIO_REBIND_ALLOC(Allocator, op_result_type)(allocator))
+  {
+    for (std::size_t i = 0; i < size; ++i)
+      args_.emplace_back();
+  }
+
+  executor_type get_executor() const noexcept
+  {
+    return executor_;
+  }
+
+  void operator()()
+  {
+    this->invoke(
+        asio::detail::make_index_sequence<
+          std::tuple_size<op_tuple_type>::value>());
+  }
+
+  template <std::size_t... I>
+  void invoke(asio::detail::index_sequence<I...>)
+  {
+    typedef typename parallel_op_signature_as_tuple<
+        typename ranged_parallel_group_signature<
+          completion_signature_of_t<Op>,
+          Allocator
+        >::raw_type
+      >::type vectors_type;
+
+    // Construct all result vectors using the supplied allocator.
+    vectors_type vectors{
+        typename std::tuple_element<I, vectors_type>::type(
+          ASIO_REBIND_ALLOC(Allocator, int)(allocator_))...};
+
+    // Reserve sufficient space in each of the result vectors.
+    int reserve_fold[] = { 0,
+      ( std::get<I>(vectors).reserve(completion_order_.size()),
+        0 )...
+    };
+    (void)reserve_fold;
+
+    // Copy the results from all operations into the result vectors.
+    for (std::size_t idx = 0; idx < completion_order_.size(); ++idx)
+    {
+      int pushback_fold[] = { 0,
+        ( std::get<I>(vectors).push_back(
+            std::move(std::get<I>(args_[idx].get()))),
+          0 )...
+      };
+      (void)pushback_fold;
+    }
+
+    std::move(handler_)(std::move(completion_order_),
+        std::move(std::get<I>(vectors))...);
+  }
+
+  Handler handler_;
+  executor_type executor_;
+  Allocator allocator_;
+  std::vector<std::size_t,
+    ASIO_REBIND_ALLOC(Allocator, std::size_t)> completion_order_;
+  std::deque<op_result_type,
+    ASIO_REBIND_ALLOC(Allocator, op_result_type)> args_;
+};
+
+// Shared state for the parallel group.
+template <typename Condition, typename Handler, typename Op, typename Allocator>
+struct ranged_parallel_group_state
+{
+  ranged_parallel_group_state(Condition&& c, Handler&& h,
+      std::size_t size, const Allocator& allocator)
+    : cancellations_requested_(size),
+      outstanding_(size),
+      cancellation_signals_(
+          ASIO_REBIND_ALLOC(Allocator,
+            asio::cancellation_signal)(allocator)),
+      cancellation_condition_(std::move(c)),
+      handler_(std::move(h), size, allocator)
+  {
+    for (std::size_t i = 0; i < size; ++i)
+      cancellation_signals_.emplace_back();
+  }
+
+  // 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_;
+
+  // 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_;
+
+  // The cancellation signals for each operation in the group.
+  std::deque<asio::cancellation_signal,
+    ASIO_REBIND_ALLOC(Allocator, asio::cancellation_signal)>
+      cancellation_signals_;
+
+  // 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.
+  ranged_parallel_group_completion_handler<Handler, Op, Allocator> handler_;
+};
+
+// Handler for an individual operation within the parallel group.
+template <typename Condition, typename Handler, typename Op, typename Allocator>
+struct ranged_parallel_group_op_handler
+{
+  typedef asio::cancellation_slot cancellation_slot_type;
+
+  ranged_parallel_group_op_handler(
+      std::shared_ptr<ranged_parallel_group_state<
+        Condition, Handler, Op, Allocator>> state,
+      std::size_t idx)
+    : state_(std::move(state)),
+      idx_(idx)
+  {
+  }
+
+  cancellation_slot_type get_cancellation_slot() const noexcept
+  {
+    return state_->cancellation_signals_[idx_].slot();
+  }
+
+  template <typename... Args>
+  void operator()(Args... args)
+  {
+    // Capture this operation into the completion order.
+    state_->handler_.completion_order_[state_->completed_++] = idx_;
+
+    // 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.
+    state_->handler_.args_[idx_].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 < state_->cancellation_signals_.size(); ++i)
+          if (i != idx_)
+            state_->cancellation_signals_[i].emit(cancel_type);
+    }
+
+    // If this is the last outstanding operation, invoke the user's handler.
+    if (--state_->outstanding_ == 0)
+      asio::dispatch(std::move(state_->handler_));
+  }
+
+  std::shared_ptr<ranged_parallel_group_state<
+    Condition, Handler, Op, Allocator>> state_;
+  std::size_t idx_;
+};
+
+// Handler for an individual operation within the parallel group that has an
+// explicitly specified executor.
+template <typename Executor, typename Condition,
+    typename Handler, typename Op, typename Allocator>
+struct ranged_parallel_group_op_handler_with_executor :
+  ranged_parallel_group_op_handler<Condition, Handler, Op, Allocator>
+{
+  typedef ranged_parallel_group_op_handler<
+    Condition, Handler, Op, Allocator> base_type;
+  typedef asio::cancellation_slot cancellation_slot_type;
+  typedef Executor executor_type;
+
+  ranged_parallel_group_op_handler_with_executor(
+      std::shared_ptr<ranged_parallel_group_state<
+        Condition, Handler, Op, Allocator>> state,
+      executor_type ex, std::size_t idx)
+    : ranged_parallel_group_op_handler<Condition, Handler, Op, Allocator>(
+        std::move(state), idx)
+  {
+    cancel_proxy_ =
+      &this->state_->cancellation_signals_[idx].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<ranged_parallel_group_state<
+          Condition, Handler, Op, Allocator>> state,
+        executor_type ex)
+      : state_(std::move(state)),
+        executor_(std::move(ex))
+    {
+    }
+
+    void operator()(cancellation_type_t type)
+    {
+      if (auto state = state_.lock())
+      {
+        asio::cancellation_signal* sig = &signal_;
+        asio::dispatch(executor_,
+            [state, sig, type]{ sig->emit(type); });
+      }
+    }
+
+    std::weak_ptr<ranged_parallel_group_state<
+      Condition, Handler, Op, Allocator>> state_;
+    asio::cancellation_signal signal_;
+    executor_type executor_;
+  };
+
+  cancel_proxy* cancel_proxy_;
+};
+
+template <typename Condition, typename Handler, typename Op, typename Allocator>
+struct ranged_parallel_group_cancellation_handler
+{
+  ranged_parallel_group_cancellation_handler(
+      std::shared_ptr<ranged_parallel_group_state<
+        Condition, Handler, Op, Allocator>> 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 < state->cancellation_signals_.size(); ++i)
+            state->cancellation_signals_[i].emit(cancel_type);
+  }
+
+  std::weak_ptr<ranged_parallel_group_state<
+    Condition, Handler, Op, Allocator>> state_;
+};
+
+template <typename Condition, typename Handler,
+    typename Range, typename Allocator>
+void ranged_parallel_group_launch(Condition cancellation_condition,
+    Handler handler, Range&& range, const Allocator& allocator)
+{
+  // Get the user's completion handler's cancellation slot, so that we can allow
+  // cancellation of the entire group.
+  associated_cancellation_slot_t<Handler> slot
+    = asio::get_associated_cancellation_slot(handler);
+
+  // The type of the asynchronous operation.
+  typedef decay_t<decltype(*declval<typename Range::iterator>())> op_type;
+
+  // Create the shared state for the operation.
+  typedef ranged_parallel_group_state<Condition,
+    Handler, op_type, Allocator> state_type;
+  std::shared_ptr<state_type> state = std::allocate_shared<state_type>(
+      asio::detail::recycling_allocator<state_type,
+        asio::detail::thread_info_base::parallel_group_tag>(),
+      std::move(cancellation_condition),
+      std::move(handler), range.size(), allocator);
+
+  std::size_t idx = 0;
+  std::size_t range_size = range.size();
+  for (auto&& op : std::forward<Range>(range))
+  {
+    typedef associated_executor_t<op_type> ex_type;
+    ex_type ex = asio::get_associated_executor(op);
+    std::move(op)(
+        ranged_parallel_group_op_handler_with_executor<
+          ex_type, Condition, Handler, op_type, Allocator>(
+            state, std::move(ex), idx++));
+  }
+
+  // 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_ -= range_size) > 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<
+      ranged_parallel_group_cancellation_handler<
+        Condition, Handler, op_type, Allocator>>(state);
+}
+
+} // namespace detail
+} // namespace experimental
+
+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) noexcept
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(
+      const experimental::detail::parallel_group_completion_handler<
+        Handler, Ops...>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<Handler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+template <template <typename, typename> class Associator, typename Handler,
+    typename Op, typename Allocator, typename DefaultCandidate>
+struct associator<Associator,
+    experimental::detail::ranged_parallel_group_completion_handler<
+      Handler, Op, Allocator>,
+    DefaultCandidate>
+  : Associator<Handler, DefaultCandidate>
+{
+  static typename Associator<Handler, DefaultCandidate>::type get(
+      const experimental::detail::ranged_parallel_group_completion_handler<
+        Handler, Op, Allocator>& h) noexcept
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(
+      const experimental::detail::ranged_parallel_group_completion_handler<
+        Handler, Op, Allocator>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<Handler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_EXPERIMENTAL_PARALLEL_GROUP_HPP

include/asio/experimental/impl/promise.hpp

@@ -0,0 +1,255 @@
+//
+// experimental/impl/promise.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2021-2023 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_IMPL_PROMISE_HPP
+#define ASIO_EXPERIMENTAL_IMPL_PROMISE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/cancellation_signal.hpp"
+#include "asio/detail/utility.hpp"
+#include "asio/error.hpp"
+#include "asio/system_error.hpp"
+#include <tuple>
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace experimental {
+
+template<typename Signature = void(),
+    typename Executor = asio::any_io_executor,
+    typename Allocator = std::allocator<void>>
+struct promise;
+
+namespace detail {
+
+template<typename Signature, typename Executor, typename Allocator>
+struct promise_impl;
+
+template<typename... Ts, typename Executor, typename Allocator>
+struct promise_impl<void(Ts...), Executor, Allocator>
+{
+  using result_type = std::tuple<Ts...>;
+
+  promise_impl(Allocator allocator, Executor executor)
+    : allocator(std::move(allocator)), executor(std::move(executor))
+  {
+  }
+
+  promise_impl(const promise_impl&) = delete;
+
+  ~promise_impl()
+  {
+    if (completion)
+      this->cancel_();
+
+    if (done)
+      reinterpret_cast<result_type*>(&result)->~result_type();
+  }
+
+  aligned_storage_t<sizeof(result_type), alignof(result_type)> result;
+  std::atomic<bool> done{false};
+  cancellation_signal cancel;
+  Allocator allocator;
+  Executor executor;
+
+  template<typename Func, std::size_t... Idx>
+  void apply_impl(Func f, asio::detail::index_sequence<Idx...>)
+  {
+    auto& result_type = *reinterpret_cast<promise_impl::result_type*>(&result);
+    f(std::get<Idx>(std::move(result_type))...);
+  }
+
+  using allocator_type = Allocator;
+  allocator_type get_allocator() {return allocator;}
+
+  using executor_type = Executor;
+  executor_type get_executor() {return executor;}
+
+  template<typename Func>
+  void apply(Func f)
+  {
+    apply_impl(std::forward<Func>(f),
+        asio::detail::make_index_sequence<sizeof...(Ts)>{});
+  }
+
+  struct completion_base
+  {
+    virtual void invoke(Ts&&...ts) = 0;
+  };
+
+  template<typename Alloc, typename WaitHandler_>
+  struct completion_impl final : completion_base
+  {
+    WaitHandler_ handler;
+    Alloc allocator;
+    void invoke(Ts&&... ts)
+    {
+      auto h = std::move(handler);
+
+      using alloc_t = typename std::allocator_traits<
+        typename asio::decay<Alloc>::type>::template
+          rebind_alloc<completion_impl>;
+
+      alloc_t alloc_{allocator};
+      this->~completion_impl();
+      std::allocator_traits<alloc_t>::deallocate(alloc_, this, 1u);
+      std::move(h)(std::forward<Ts>(ts)...);
+    }
+
+    template<typename Alloc_, typename Handler_>
+    completion_impl(Alloc_&& alloc, Handler_&& wh)
+      : handler(std::forward<Handler_>(wh)),
+        allocator(std::forward<Alloc_>(alloc))
+    {
+    }
+  };
+
+  completion_base* completion = nullptr;
+  typename asio::aligned_storage<sizeof(void*) * 4,
+    alignof(completion_base)>::type completion_opt;
+
+  template<typename Alloc, typename Handler>
+  void set_completion(Alloc&& alloc, Handler&& handler)
+  {
+    if (completion)
+      cancel_();
+
+    using impl_t = completion_impl<
+      typename asio::decay<Alloc>::type, Handler>;
+    using alloc_t = typename std::allocator_traits<
+      typename asio::decay<Alloc>::type>::template rebind_alloc<impl_t>;
+
+    alloc_t alloc_{alloc};
+    auto p = std::allocator_traits<alloc_t>::allocate(alloc_, 1u);
+    completion = new (p) impl_t(std::forward<Alloc>(alloc),
+        std::forward<Handler>(handler));
+  }
+
+  template<typename... T_>
+  void complete(T_&&... ts)
+  {
+    assert(completion);
+    std::exchange(completion, nullptr)->invoke(std::forward<T_>(ts)...);
+  }
+
+  template<std::size_t... Idx>
+  void complete_with_result_impl(asio::detail::index_sequence<Idx...>)
+  {
+    auto& result_type = *reinterpret_cast<promise_impl::result_type*>(&result);
+    this->complete(std::get<Idx>(std::move(result_type))...);
+  }
+
+  void complete_with_result()
+  {
+    complete_with_result_impl(
+        asio::detail::make_index_sequence<sizeof...(Ts)>{});
+  }
+
+  template<typename... T_>
+  void cancel_impl_(std::exception_ptr*, T_*...)
+  {
+    complete(
+        std::make_exception_ptr(
+          asio::system_error(
+            asio::error::operation_aborted)),
+        T_{}...);
+  }
+
+  template<typename... T_>
+  void cancel_impl_(asio::error_code*, T_*...)
+  {
+    complete(asio::error::operation_aborted, T_{}...);
+  }
+
+  template<typename... T_>
+  void cancel_impl_(T_*...)
+  {
+    complete(T_{}...);
+  }
+
+  void cancel_()
+  {
+    cancel_impl_(static_cast<Ts*>(nullptr)...);
+  }
+};
+
+template<typename Signature = void(),
+    typename Executor = asio::any_io_executor,
+    typename Allocator = std::allocator<void>>
+struct promise_handler;
+
+template<typename... Ts,  typename Executor, typename Allocator>
+struct promise_handler<void(Ts...), Executor, Allocator>
+{
+  using promise_type = promise<void(Ts...), Executor, Allocator>;
+
+  promise_handler(
+      Allocator allocator, Executor executor) // get_associated_allocator(exec)
+    : impl_(
+        std::allocate_shared<promise_impl<void(Ts...), Executor, Allocator>>(
+          allocator, allocator, executor))
+  {
+  }
+
+  std::shared_ptr<promise_impl<void(Ts...), Executor, Allocator>> impl_;
+
+  using cancellation_slot_type = cancellation_slot;
+
+  cancellation_slot_type get_cancellation_slot() const noexcept
+  {
+    return impl_->cancel.slot();
+  }
+
+  using allocator_type = Allocator;
+
+  allocator_type get_allocator() const noexcept
+  {
+    return impl_->get_allocator();
+  }
+
+  using executor_type = Executor;
+
+  Executor get_executor() const noexcept
+  {
+    return impl_->get_executor();
+  }
+
+  auto make_promise() -> promise<void(Ts...), executor_type, allocator_type>
+  {
+    return promise<void(Ts...), executor_type, allocator_type>{impl_};
+  }
+
+  void operator()(std::remove_reference_t<Ts>... ts)
+  {
+    assert(impl_);
+
+    using result_type = typename promise_impl<
+      void(Ts...), allocator_type, executor_type>::result_type ;
+
+    new (&impl_->result) result_type(std::move(ts)...);
+    impl_->done = true;
+
+    if (impl_->completion)
+      impl_->complete_with_result();
+  }
+};
+
+} // namespace detail
+} // namespace experimental
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXPERIMENTAL_IMPL_PROMISE_HPP

include/asio/experimental/impl/use_coro.hpp

@@ -0,0 +1,214 @@
+//
+// experimental/impl/use_coro.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2021-2023 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_IMPL_USE_CORO_HPP
+#define ASIO_EXPERIMENTAL_IMPL_USE_CORO_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/deferred.hpp"
+#include "asio/experimental/coro.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename Allocator, typename R>
+struct async_result<experimental::use_coro_t<Allocator>, R()>
+{
+  template <typename Initiation, typename... InitArgs>
+  static auto initiate_impl(Initiation initiation,
+      std::allocator_arg_t, Allocator, InitArgs... args)
+    -> experimental::coro<void() noexcept, void,
+      asio::associated_executor_t<Initiation>, Allocator>
+  {
+    co_await deferred_async_operation<R(), Initiation, InitArgs...>(
+        deferred_init_tag{}, std::move(initiation), std::move(args)...);
+  }
+
+  template <typename... InitArgs>
+  static auto initiate_impl(asio::detail::initiation_archetype<R()>,
+      std::allocator_arg_t, Allocator, InitArgs... args)
+    -> experimental::coro<void(), void,
+      asio::any_io_executor, Allocator>;
+
+  template <typename Initiation, typename... InitArgs>
+  static auto initiate(Initiation initiation,
+      experimental::use_coro_t<Allocator> tk, InitArgs&&... args)
+  {
+    return initiate_impl(std::move(initiation), std::allocator_arg,
+        tk.get_allocator(), std::forward<InitArgs>(args)...);
+  }
+};
+
+template <typename Allocator, typename R>
+struct async_result<
+    experimental::use_coro_t<Allocator>, R(asio::error_code)>
+{
+  template <typename Initiation, typename... InitArgs>
+  static auto initiate_impl(Initiation initiation,
+      std::allocator_arg_t, Allocator, InitArgs... args)
+    -> experimental::coro<void() noexcept, void,
+      asio::associated_executor_t<Initiation>, Allocator>
+  {
+    co_await deferred_async_operation<
+      R(asio::error_code), Initiation, InitArgs...>(
+        deferred_init_tag{}, std::move(initiation), std::move(args)...);
+  }
+
+  template <typename... InitArgs>
+  static auto initiate_impl(
+      asio::detail::initiation_archetype<R(asio::error_code)>,
+      std::allocator_arg_t, Allocator, InitArgs... args)
+    -> experimental::coro<void(), void,
+      asio::any_io_executor, Allocator>;
+
+  template <typename Initiation, typename... InitArgs>
+  static auto initiate(Initiation initiation,
+      experimental::use_coro_t<Allocator> tk, InitArgs&&... args)
+  {
+    return initiate_impl(std::move(initiation), std::allocator_arg,
+        tk.get_allocator(), std::forward<InitArgs>(args)...);
+  }
+};
+
+template <typename Allocator, typename R>
+struct async_result<
+    experimental::use_coro_t<Allocator>, R(std::exception_ptr)>
+{
+  template <typename Initiation, typename... InitArgs>
+  static auto initiate_impl(Initiation initiation,
+      std::allocator_arg_t, Allocator, InitArgs... args)
+    -> experimental::coro<void(), void,
+      asio::associated_executor_t<Initiation>, Allocator>
+  {
+    co_await deferred_async_operation<
+      R(std::exception_ptr), Initiation, InitArgs...>(
+        deferred_init_tag{}, std::move(initiation), std::move(args)...);
+  }
+
+  template <typename... InitArgs>
+  static auto initiate_impl(
+      asio::detail::initiation_archetype<R(std::exception_ptr)>,
+      std::allocator_arg_t, Allocator, InitArgs... args)
+    -> experimental::coro<void(), void,
+      asio::any_io_executor, Allocator>;
+
+  template <typename Initiation, typename... InitArgs>
+  static auto initiate(Initiation initiation,
+      experimental::use_coro_t<Allocator> tk, InitArgs&&... args)
+  {
+    return initiate_impl(std::move(initiation), std::allocator_arg,
+        tk.get_allocator(), std::forward<InitArgs>(args)...);
+  }
+};
+
+template <typename Allocator, typename R, typename T>
+struct async_result<experimental::use_coro_t<Allocator>, R(T)>
+{
+
+  template <typename Initiation, typename... InitArgs>
+  static auto initiate_impl(Initiation initiation,
+      std::allocator_arg_t, Allocator, InitArgs... args)
+    -> experimental::coro<void() noexcept, T,
+      asio::associated_executor_t<Initiation>, Allocator>
+  {
+    co_return co_await deferred_async_operation<R(T), Initiation, InitArgs...>(
+        deferred_init_tag{}, std::move(initiation), std::move(args)...);
+  }
+
+  template <typename... InitArgs>
+  static auto initiate_impl(asio::detail::initiation_archetype<R(T)>,
+      std::allocator_arg_t, Allocator, InitArgs... args)
+    -> experimental::coro<void() noexcept, T,
+      asio::any_io_executor, Allocator>;
+
+  template <typename Initiation, typename... InitArgs>
+  static auto initiate(Initiation initiation,
+      experimental::use_coro_t<Allocator> tk, InitArgs&&... args)
+  {
+    return initiate_impl(std::move(initiation), std::allocator_arg,
+        tk.get_allocator(), std::forward<InitArgs>(args)...);
+  }
+};
+
+template <typename Allocator, typename R, typename T>
+struct async_result<
+    experimental::use_coro_t<Allocator>, R(asio::error_code, T)>
+{
+  template <typename Initiation, typename... InitArgs>
+  static auto initiate_impl(Initiation initiation,
+      std::allocator_arg_t, Allocator, InitArgs... args)
+    -> experimental::coro<void(), T,
+      asio::associated_executor_t<Initiation>, Allocator>
+  {
+    co_return co_await deferred_async_operation<
+      R(asio::error_code, T), Initiation, InitArgs...>(
+        deferred_init_tag{}, std::move(initiation), std::move(args)...);
+  }
+
+  template <typename... InitArgs>
+  static auto initiate_impl(
+      asio::detail::initiation_archetype<
+        R(asio::error_code, T)>,
+      std::allocator_arg_t, Allocator, InitArgs... args)
+    -> experimental::coro<void(), T, asio::any_io_executor, Allocator>;
+
+  template <typename Initiation, typename... InitArgs>
+  static auto initiate(Initiation initiation,
+      experimental::use_coro_t<Allocator> tk, InitArgs&&... args)
+  {
+    return initiate_impl(std::move(initiation), std::allocator_arg,
+        tk.get_allocator(), std::forward<InitArgs>(args)...);
+  }
+};
+
+template <typename Allocator, typename R, typename T>
+struct async_result<
+    experimental::use_coro_t<Allocator>, R(std::exception_ptr, T)>
+{
+  template <typename Initiation, typename... InitArgs>
+  static auto initiate_impl(Initiation initiation,
+      std::allocator_arg_t, Allocator, InitArgs... args)
+    -> experimental::coro<void(), T,
+      asio::associated_executor_t<Initiation>, Allocator>
+  {
+    co_return co_await deferred_async_operation<
+      R(std::exception_ptr, T), Initiation, InitArgs...>(
+        deferred_init_tag{}, std::move(initiation), std::move(args)...);
+  }
+
+  template <typename... InitArgs>
+  static auto initiate_impl(
+      asio::detail::initiation_archetype<R(std::exception_ptr, T)>,
+      std::allocator_arg_t, Allocator, InitArgs... args)
+    -> experimental::coro<void(), T, asio::any_io_executor, Allocator>;
+
+  template <typename Initiation, typename... InitArgs>
+  static auto initiate(Initiation initiation,
+      experimental::use_coro_t<Allocator> tk, InitArgs&&... args)
+  {
+    return initiate_impl(std::move(initiation), std::allocator_arg,
+        tk.get_allocator(), std::forward<InitArgs>(args)...);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXPERIMENTAL_IMPL_USE_CORO_HPP

include/asio/experimental/impl/use_promise.hpp

@@ -0,0 +1,66 @@
+//
+// experimental/impl/use_promise.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2021-2023 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_IMPL_USE_PROMISE_HPP
+#define ASIO_EXPERIMENTAL_IMPL_USE_PROMISE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include <memory>
+#include "asio/async_result.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace experimental {
+
+template <typename Allocator>
+struct use_promise_t;
+
+namespace detail {
+
+template<typename Signature, typename Executor, typename Allocator>
+struct promise_handler;
+
+} // namespace detail
+} // namespace experimental
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename Allocator, typename R, typename... Args>
+struct async_result<experimental::use_promise_t<Allocator>, R(Args...)>
+{
+  template <typename Initiation, typename... InitArgs>
+  static auto initiate(Initiation initiation,
+      experimental::use_promise_t<Allocator> up, InitArgs... args)
+    -> experimental::promise<void(decay_t<Args>...),
+      asio::associated_executor_t<Initiation>, Allocator>
+  {
+    using handler_type = experimental::detail::promise_handler<
+      void(decay_t<Args>...),
+      asio::associated_executor_t<Initiation>, Allocator>;
+
+    handler_type ht{up.get_allocator(), 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_IMPL_USE_PROMISE_HPP