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 //
 // impl/awaitable.hpp
 // ~~~~~~~~~~~~~~~~~~
 //
 // Copyright (c) 2003-2023 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_AWAITABLE_HPP
 #define BOOST_ASIO_IMPL_AWAITABLE_HPP
 
 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
 # pragma once
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
 #include <exception>
 #include <new>
 #include <tuple>
 #include <boost/asio/cancellation_signal.hpp>
 #include <boost/asio/cancellation_state.hpp>
 #include <boost/asio/detail/thread_context.hpp>
 #include <boost/asio/detail/thread_info_base.hpp>
 #include <boost/asio/detail/throw_error.hpp>
 #include <boost/asio/detail/type_traits.hpp>
 #include <boost/asio/error.hpp>
 #include <boost/asio/post.hpp>
 #include <boost/system/system_error.hpp>
 #include <boost/asio/this_coro.hpp>
 
 #if defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
 # if defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
 #  include <boost/asio/detail/source_location.hpp>
 # endif // defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
 #endif // defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
 
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
 namespace asio {
 namespace detail {
 
 struct awaitable_thread_has_context_switched {};
 template <typename, typename> class awaitable_async_op_handler;
 template <typename, typename, typename> class awaitable_async_op;
 
 // An awaitable_thread represents a thread-of-execution that is composed of one
 // or more "stack frames", with each frame represented by an awaitable_frame.
 // All execution occurs in the context of the awaitable_thread's executor. An
 // awaitable_thread continues to "pump" the stack frames by repeatedly resuming
 // the top stack frame until the stack is empty, or until ownership of the
 // stack is transferred to another awaitable_thread object.
 //
 //                +------------------------------------+
 //                | top_of_stack_                      |
 //                |                                    V
 // +--------------+---+                            +-----------------+
 // |                  |                            |                 |
 // | awaitable_thread |<---------------------------+ awaitable_frame |
 // |                  |           attached_thread_ |                 |
 // +--------------+---+           (Set only when   +---+-------------+
 //                |               frames are being     |
 //                |               actively pumped      | caller_
 //                |               by a thread, and     |
 //                |               then only for        V
 //                |               the top frame.)  +-----------------+
 //                |                                |                 |
 //                |                                | awaitable_frame |
 //                |                                |                 |
 //                |                                +---+-------------+
 //                |                                    |
 //                |                                    | caller_
 //                |                                    :
 //                |                                    :
 //                |                                    |
 //                |                                    V
 //                |                                +-----------------+
 //                | bottom_of_stack_               |                 |
 //                +------------------------------->| awaitable_frame |
 //                                                 |                 |
 //                                                 +-----------------+
 
 template <typename Executor>
 class awaitable_frame_base
 {
 public:
 #if !defined(BOOST_ASIO_DISABLE_AWAITABLE_FRAME_RECYCLING)
   void* operator new(std::size_t size)
   {
     return boost::asio::detail::thread_info_base::allocate(
         boost::asio::detail::thread_info_base::awaitable_frame_tag(),
         boost::asio::detail::thread_context::top_of_thread_call_stack(),
         size);
   }
 
   void operator delete(void* pointer, std::size_t size)
   {
     boost::asio::detail::thread_info_base::deallocate(
         boost::asio::detail::thread_info_base::awaitable_frame_tag(),
         boost::asio::detail::thread_context::top_of_thread_call_stack(),
         pointer, size);
   }
 #endif // !defined(BOOST_ASIO_DISABLE_AWAITABLE_FRAME_RECYCLING)
 
   // The frame starts in a suspended state until the awaitable_thread object
   // pumps the stack.
   auto initial_suspend() noexcept
   {
     return suspend_always();
   }
 
   // On final suspension the frame is popped from the top of the stack.
   auto final_suspend() noexcept
   {
     struct result
     {
       awaitable_frame_base* this_;
 
       bool await_ready() const noexcept
       {
         return false;
       }
 
       void await_suspend(coroutine_handle<void>) noexcept
       {
         this->this_->pop_frame();
       }
 
       void await_resume() const noexcept
       {
       }
     };
 
     return result{this};
   }
 
   void set_except(std::exception_ptr e) noexcept
   {
     pending_exception_ = e;
   }
 
   void set_error(const boost::system::error_code& ec)
   {
     this->set_except(std::make_exception_ptr(boost::system::system_error(ec)));
   }
 
   void unhandled_exception()
   {
     set_except(std::current_exception());
   }
 
   void rethrow_exception()
   {
     if (pending_exception_)
     {
       std::exception_ptr ex = std::exchange(pending_exception_, nullptr);
       std::rethrow_exception(ex);
     }
   }
 
   void clear_cancellation_slot()
   {
     this->attached_thread_->entry_point()->cancellation_state_.slot().clear();
   }
 
   template <typename T>
   auto await_transform(awaitable<T, Executor> a) const
   {
     if (attached_thread_->entry_point()->throw_if_cancelled_)
       if (!!attached_thread_->get_cancellation_state().cancelled())
         throw_error(boost::asio::error::operation_aborted, "co_await");
     return a;
   }
 
   template <typename Op>
   auto await_transform(Op&& op,
       constraint_t<is_async_operation<Op>::value> = 0
 #if defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
 # if defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
       , detail::source_location location = detail::source_location::current()
 # endif // defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
 #endif // defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
     )
   {
     if (attached_thread_->entry_point()->throw_if_cancelled_)
       if (!!attached_thread_->get_cancellation_state().cancelled())
         throw_error(boost::asio::error::operation_aborted, "co_await");
 
     return awaitable_async_op<
       completion_signature_of_t<Op>, decay_t<Op>, Executor>{
         std::forward<Op>(op), this
 #if defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
 # if defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
         , location
 # endif // defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
 #endif // defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
       };
   }
 
   // This await transformation obtains the associated executor of the thread of
   // execution.
   auto await_transform(this_coro::executor_t) noexcept
   {
     struct result
     {
       awaitable_frame_base* this_;
 
       bool await_ready() const noexcept
       {
         return true;
       }
 
       void await_suspend(coroutine_handle<void>) noexcept
       {
       }
 
       auto await_resume() const noexcept
       {
         return this_->attached_thread_->get_executor();
       }
     };
 
     return result{this};
   }
 
   // This await transformation obtains the associated cancellation state of the
   // thread of execution.
   auto await_transform(this_coro::cancellation_state_t) noexcept
   {
     struct result
     {
       awaitable_frame_base* this_;
 
       bool await_ready() const noexcept
       {
         return true;
       }
 
       void await_suspend(coroutine_handle<void>) noexcept
       {
       }
 
       auto await_resume() const noexcept
       {
         return this_->attached_thread_->get_cancellation_state();
       }
     };
 
     return result{this};
   }
 
   // This await transformation resets the associated cancellation state.
   auto await_transform(this_coro::reset_cancellation_state_0_t) noexcept
   {
     struct result
     {
       awaitable_frame_base* this_;
 
       bool await_ready() const noexcept
       {
         return true;
       }
 
       void await_suspend(coroutine_handle<void>) noexcept
       {
       }
 
       auto await_resume() const
       {
         return this_->attached_thread_->reset_cancellation_state();
       }
     };
 
     return result{this};
   }
 
   // This await transformation resets the associated cancellation state.
   template <typename Filter>
   auto await_transform(
       this_coro::reset_cancellation_state_1_t<Filter> reset) noexcept
   {
     struct result
     {
       awaitable_frame_base* this_;
       Filter filter_;
 
       bool await_ready() const noexcept
       {
         return true;
       }
 
       void await_suspend(coroutine_handle<void>) noexcept
       {
       }
 
       auto await_resume()
       {
         return this_->attached_thread_->reset_cancellation_state(
             static_cast<Filter&&>(filter_));
       }
     };
 
     return result{this, static_cast<Filter&&>(reset.filter)};
   }
 
   // This await transformation resets the associated cancellation state.
   template <typename InFilter, typename OutFilter>
   auto await_transform(
       this_coro::reset_cancellation_state_2_t<InFilter, OutFilter> reset)
     noexcept
   {
     struct result
     {
       awaitable_frame_base* this_;
       InFilter in_filter_;
       OutFilter out_filter_;
 
       bool await_ready() const noexcept
       {
         return true;
       }
 
       void await_suspend(coroutine_handle<void>) noexcept
       {
       }
 
       auto await_resume()
       {
         return this_->attached_thread_->reset_cancellation_state(
             static_cast<InFilter&&>(in_filter_),
             static_cast<OutFilter&&>(out_filter_));
       }
     };
 
     return result{this,
         static_cast<InFilter&&>(reset.in_filter),
         static_cast<OutFilter&&>(reset.out_filter)};
   }
 
   // This await transformation determines whether cancellation is propagated as
   // an exception.
   auto await_transform(this_coro::throw_if_cancelled_0_t)
     noexcept
   {
     struct result
     {
       awaitable_frame_base* this_;
 
       bool await_ready() const noexcept
       {
         return true;
       }
 
       void await_suspend(coroutine_handle<void>) noexcept
       {
       }
 
       auto await_resume()
       {
         return this_->attached_thread_->throw_if_cancelled();
       }
     };
 
     return result{this};
   }
 
   // This await transformation sets whether cancellation is propagated as an
   // exception.
   auto await_transform(this_coro::throw_if_cancelled_1_t throw_if_cancelled)
     noexcept
   {
     struct result
     {
       awaitable_frame_base* this_;
       bool value_;
 
       bool await_ready() const noexcept
       {
         return true;
       }
 
       void await_suspend(coroutine_handle<void>) noexcept
       {
       }
 
       auto await_resume()
       {
         this_->attached_thread_->throw_if_cancelled(value_);
       }
     };
 
     return result{this, throw_if_cancelled.value};
   }
 
   // This await transformation is used to run an async operation's initiation
   // function object after the coroutine has been suspended. This ensures that
   // immediate resumption of the coroutine in another thread does not cause a
   // race condition.
   template <typename Function>
   auto await_transform(Function f,
       enable_if_t<
         is_convertible<
           result_of_t<Function(awaitable_frame_base*)>,
           awaitable_thread<Executor>*
         >::value
       >* = nullptr)
   {
     struct result
     {
       Function function_;
       awaitable_frame_base* this_;
 
       bool await_ready() const noexcept
       {
         return false;
       }
 
       void await_suspend(coroutine_handle<void>) noexcept
       {
         this_->after_suspend(
             [](void* arg)
             {
               result* r = static_cast<result*>(arg);
               r->function_(r->this_);
             }, this);
       }
 
       void await_resume() const noexcept
       {
       }
     };
 
     return result{std::move(f), this};
   }
 
   // Access the awaitable thread's has_context_switched_ flag.
   auto await_transform(detail::awaitable_thread_has_context_switched) noexcept
   {
     struct result
     {
       awaitable_frame_base* this_;
 
       bool await_ready() const noexcept
       {
         return true;
       }
 
       void await_suspend(coroutine_handle<void>) noexcept
       {
       }
 
       bool& await_resume() const noexcept
       {
         return this_->attached_thread_->entry_point()->has_context_switched_;
       }
     };
 
     return result{this};
   }
 
   void attach_thread(awaitable_thread<Executor>* handler) noexcept
   {
     attached_thread_ = handler;
   }
 
   awaitable_thread<Executor>* detach_thread() noexcept
   {
     attached_thread_->entry_point()->has_context_switched_ = true;
     return std::exchange(attached_thread_, nullptr);
   }
 
   void push_frame(awaitable_frame_base<Executor>* caller) noexcept
   {
     caller_ = caller;
     attached_thread_ = caller_->attached_thread_;
     attached_thread_->entry_point()->top_of_stack_ = this;
     caller_->attached_thread_ = nullptr;
   }
 
   void pop_frame() noexcept
   {
     if (caller_)
       caller_->attached_thread_ = attached_thread_;
     attached_thread_->entry_point()->top_of_stack_ = caller_;
     attached_thread_ = nullptr;
     caller_ = nullptr;
   }
 
   struct resume_context
   {
     void (*after_suspend_fn_)(void*) = nullptr;
     void *after_suspend_arg_ = nullptr;
   };
 
   void resume()
   {
     resume_context context;
     resume_context_ = &context;
     coro_.resume();
     if (context.after_suspend_fn_)
       context.after_suspend_fn_(context.after_suspend_arg_);
   }
 
   void after_suspend(void (*fn)(void*), void* arg)
   {
     resume_context_->after_suspend_fn_ = fn;
     resume_context_->after_suspend_arg_ = arg;
   }
 
   void destroy()
   {
     coro_.destroy();
   }
 
 protected:
   coroutine_handle<void> coro_ = nullptr;
   awaitable_thread<Executor>* attached_thread_ = nullptr;
   awaitable_frame_base<Executor>* caller_ = nullptr;
   std::exception_ptr pending_exception_ = nullptr;
   resume_context* resume_context_ = nullptr;
 };
 
 template <typename T, typename Executor>
 class awaitable_frame
   : public awaitable_frame_base<Executor>
 {
 public:
   awaitable_frame() noexcept
   {
   }
 
   awaitable_frame(awaitable_frame&& other) noexcept
     : awaitable_frame_base<Executor>(std::move(other))
   {
   }
 
   ~awaitable_frame()
   {
     if (has_result_)
       static_cast<T*>(static_cast<void*>(result_))->~T();
   }
 
   awaitable<T, Executor> get_return_object() noexcept
   {
     this->coro_ = coroutine_handle<awaitable_frame>::from_promise(*this);
     return awaitable<T, Executor>(this);
   };
 
   template <typename U>
   void return_value(U&& u)
   {
     new (&result_) T(std::forward<U>(u));
     has_result_ = true;
   }
 
   template <typename... Us>
   void return_values(Us&&... us)
   {
     this->return_value(std::forward_as_tuple(std::forward<Us>(us)...));
   }
 
   T get()
   {
     this->caller_ = nullptr;
     this->rethrow_exception();
     return std::move(*static_cast<T*>(static_cast<void*>(result_)));
   }
 
 private:
   alignas(T) unsigned char result_[sizeof(T)];
   bool has_result_ = false;
 };
 
 template <typename Executor>
 class awaitable_frame<void, Executor>
   : public awaitable_frame_base<Executor>
 {
 public:
   awaitable<void, Executor> get_return_object()
   {
     this->coro_ = coroutine_handle<awaitable_frame>::from_promise(*this);
     return awaitable<void, Executor>(this);
   };
 
   void return_void()
   {
   }
 
   void get()
   {
     this->caller_ = nullptr;
     this->rethrow_exception();
   }
 };
 
 struct awaitable_thread_entry_point {};
 
 template <typename Executor>
 class awaitable_frame<awaitable_thread_entry_point, Executor>
   : public awaitable_frame_base<Executor>
 {
 public:
   awaitable_frame()
     : top_of_stack_(0),
       has_executor_(false),
       has_context_switched_(false),
       throw_if_cancelled_(true)
   {
   }
 
   ~awaitable_frame()
   {
     if (has_executor_)
       u_.executor_.~Executor();
   }
 
   awaitable<awaitable_thread_entry_point, Executor> get_return_object()
   {
     this->coro_ = coroutine_handle<awaitable_frame>::from_promise(*this);
     return awaitable<awaitable_thread_entry_point, Executor>(this);
   };
 
   void return_void()
   {
   }
 
   void get()
   {
     this->caller_ = nullptr;
     this->rethrow_exception();
   }
 
 private:
   template <typename> friend class awaitable_frame_base;
   template <typename, typename> friend class awaitable_async_op_handler;
   template <typename, typename> friend class awaitable_handler_base;
   template <typename> friend class awaitable_thread;
 
   union u
   {
     u() {}
     ~u() {}
     char c_;
     Executor executor_;
   } u_;
 
   awaitable_frame_base<Executor>* top_of_stack_;
   boost::asio::cancellation_slot parent_cancellation_slot_;
   boost::asio::cancellation_state cancellation_state_;
   bool has_executor_;
   bool has_context_switched_;
   bool throw_if_cancelled_;
 };
 
 template <typename Executor>
 class awaitable_thread
 {
 public:
   typedef Executor executor_type;
   typedef cancellation_slot cancellation_slot_type;
 
   // Construct from the entry point of a new thread of execution.
   awaitable_thread(awaitable<awaitable_thread_entry_point, Executor> p,
       const Executor& ex, cancellation_slot parent_cancel_slot,
       cancellation_state cancel_state)
     : bottom_of_stack_(std::move(p))
   {
     bottom_of_stack_.frame_->top_of_stack_ = bottom_of_stack_.frame_;
     new (&bottom_of_stack_.frame_->u_.executor_) Executor(ex);
     bottom_of_stack_.frame_->has_executor_ = true;
     bottom_of_stack_.frame_->parent_cancellation_slot_ = parent_cancel_slot;
     bottom_of_stack_.frame_->cancellation_state_ = cancel_state;
   }
 
   // Transfer ownership from another awaitable_thread.
   awaitable_thread(awaitable_thread&& other) noexcept
     : bottom_of_stack_(std::move(other.bottom_of_stack_))
   {
   }
 
   // Clean up with a last ditch effort to ensure the thread is unwound within
   // the context of the executor.
   ~awaitable_thread()
   {
     if (bottom_of_stack_.valid())
     {
       // Coroutine "stack unwinding" must be performed through the executor.
       auto* bottom_frame = bottom_of_stack_.frame_;
       (post)(bottom_frame->u_.executor_,
           [a = std::move(bottom_of_stack_)]() mutable
           {
             (void)awaitable<awaitable_thread_entry_point, Executor>(
                 std::move(a));
           });
     }
   }
 
   awaitable_frame<awaitable_thread_entry_point, Executor>* entry_point()
   {
     return bottom_of_stack_.frame_;
   }
 
   executor_type get_executor() const noexcept
   {
     return bottom_of_stack_.frame_->u_.executor_;
   }
 
   cancellation_state get_cancellation_state() const noexcept
   {
     return bottom_of_stack_.frame_->cancellation_state_;
   }
 
   void reset_cancellation_state()
   {
     bottom_of_stack_.frame_->cancellation_state_ =
       cancellation_state(bottom_of_stack_.frame_->parent_cancellation_slot_);
   }
 
   template <typename Filter>
   void reset_cancellation_state(Filter&& filter)
   {
     bottom_of_stack_.frame_->cancellation_state_ =
       cancellation_state(bottom_of_stack_.frame_->parent_cancellation_slot_,
         static_cast<Filter&&>(filter));
   }
 
   template <typename InFilter, typename OutFilter>
   void reset_cancellation_state(InFilter&& in_filter,
       OutFilter&& out_filter)
   {
     bottom_of_stack_.frame_->cancellation_state_ =
       cancellation_state(bottom_of_stack_.frame_->parent_cancellation_slot_,
         static_cast<InFilter&&>(in_filter),
         static_cast<OutFilter&&>(out_filter));
   }
 
   bool throw_if_cancelled() const
   {
     return bottom_of_stack_.frame_->throw_if_cancelled_;
   }
 
   void throw_if_cancelled(bool value)
   {
     bottom_of_stack_.frame_->throw_if_cancelled_ = value;
   }
 
   cancellation_slot_type get_cancellation_slot() const noexcept
   {
     return bottom_of_stack_.frame_->cancellation_state_.slot();
   }
 
   // Launch a new thread of execution.
   void launch()
   {
     bottom_of_stack_.frame_->top_of_stack_->attach_thread(this);
     pump();
   }
 
 protected:
   template <typename> friend class awaitable_frame_base;
 
   // Repeatedly resume the top stack frame until the stack is empty or until it
   // has been transferred to another resumable_thread object.
   void pump()
   {
     do
       bottom_of_stack_.frame_->top_of_stack_->resume();
     while (bottom_of_stack_.frame_ && bottom_of_stack_.frame_->top_of_stack_);
 
     if (bottom_of_stack_.frame_)
     {
       awaitable<awaitable_thread_entry_point, Executor> a(
           std::move(bottom_of_stack_));
       a.frame_->rethrow_exception();
     }
   }
 
   awaitable<awaitable_thread_entry_point, Executor> bottom_of_stack_;
 };
 
 template <typename Signature, typename Executor>
 class awaitable_async_op_handler;
 
 template <typename R, typename Executor>
 class awaitable_async_op_handler<R(), Executor>
   : public awaitable_thread<Executor>
 {
 public:
   struct result_type {};
 
   awaitable_async_op_handler(
       awaitable_thread<Executor>* h, result_type&)
     : awaitable_thread<Executor>(std::move(*h))
   {
   }
 
   void operator()()
   {
     this->entry_point()->top_of_stack_->attach_thread(this);
     this->entry_point()->top_of_stack_->clear_cancellation_slot();
     this->pump();
   }
 
   static void resume(result_type&)
   {
   }
 };
 
 template <typename R, typename Executor>
 class awaitable_async_op_handler<R(boost::system::error_code), Executor>
   : public awaitable_thread<Executor>
 {
 public:
   typedef boost::system::error_code* result_type;
 
   awaitable_async_op_handler(
       awaitable_thread<Executor>* h, result_type& result)
     : awaitable_thread<Executor>(std::move(*h)),
       result_(result)
   {
   }
 
   void operator()(boost::system::error_code ec)
   {
     result_ = &ec;
     this->entry_point()->top_of_stack_->attach_thread(this);
     this->entry_point()->top_of_stack_->clear_cancellation_slot();
     this->pump();
   }
 
   static void resume(result_type& result)
   {
     throw_error(*result);
   }
 
 private:
   result_type& result_;
 };
 
 template <typename R, typename Executor>
 class awaitable_async_op_handler<R(std::exception_ptr), Executor>
   : public awaitable_thread<Executor>
 {
 public:
   typedef std::exception_ptr* result_type;
 
   awaitable_async_op_handler(
       awaitable_thread<Executor>* h, result_type& result)
     : awaitable_thread<Executor>(std::move(*h)),
       result_(result)
   {
   }
 
   void operator()(std::exception_ptr ex)
   {
     result_ = &ex;
     this->entry_point()->top_of_stack_->attach_thread(this);
     this->entry_point()->top_of_stack_->clear_cancellation_slot();
     this->pump();
   }
 
   static void resume(result_type& result)
   {
     if (*result)
     {
       std::exception_ptr ex = std::exchange(*result, nullptr);
       std::rethrow_exception(ex);
     }
   }
 
 private:
   result_type& result_;
 };
 
 template <typename R, typename T, typename Executor>
 class awaitable_async_op_handler<R(T), Executor>
   : public awaitable_thread<Executor>
 {
 public:
   typedef T* result_type;
 
   awaitable_async_op_handler(
       awaitable_thread<Executor>* h, result_type& result)
     : awaitable_thread<Executor>(std::move(*h)),
       result_(result)
   {
   }
 
   void operator()(T result)
   {
     result_ = &result;
     this->entry_point()->top_of_stack_->attach_thread(this);
     this->entry_point()->top_of_stack_->clear_cancellation_slot();
     this->pump();
   }
 
   static T resume(result_type& result)
   {
     return std::move(*result);
   }
 
 private:
   result_type& result_;
 };
 
 template <typename R, typename T, typename Executor>
 class awaitable_async_op_handler<R(boost::system::error_code, T), Executor>
   : public awaitable_thread<Executor>
 {
 public:
   struct result_type
   {
     boost::system::error_code* ec_;
     T* value_;
   };
 
   awaitable_async_op_handler(
       awaitable_thread<Executor>* h, result_type& result)
     : awaitable_thread<Executor>(std::move(*h)),
       result_(result)
   {
   }
 
   void operator()(boost::system::error_code ec, T value)
   {
     result_.ec_ = &ec;
     result_.value_ = &value;
     this->entry_point()->top_of_stack_->attach_thread(this);
     this->entry_point()->top_of_stack_->clear_cancellation_slot();
     this->pump();
   }
 
   static T resume(result_type& result)
   {
     throw_error(*result.ec_);
     return std::move(*result.value_);
   }
 
 private:
   result_type& result_;
 };
 
 template <typename R, typename T, typename Executor>
 class awaitable_async_op_handler<R(std::exception_ptr, T), Executor>
   : public awaitable_thread<Executor>
 {
 public:
   struct result_type
   {
     std::exception_ptr* ex_;
     T* value_;
   };
 
   awaitable_async_op_handler(
       awaitable_thread<Executor>* h, result_type& result)
     : awaitable_thread<Executor>(std::move(*h)),
       result_(result)
   {
   }
 
   void operator()(std::exception_ptr ex, T value)
   {
     result_.ex_ = &ex;
     result_.value_ = &value;
     this->entry_point()->top_of_stack_->attach_thread(this);
     this->entry_point()->top_of_stack_->clear_cancellation_slot();
     this->pump();
   }
 
   static T resume(result_type& result)
   {
     if (*result.ex_)
     {
       std::exception_ptr ex = std::exchange(*result.ex_, nullptr);
       std::rethrow_exception(ex);
     }
     return std::move(*result.value_);
   }
 
 private:
   result_type& result_;
 };
 
 template <typename R, typename... Ts, typename Executor>
 class awaitable_async_op_handler<R(Ts...), Executor>
   : public awaitable_thread<Executor>
 {
 public:
   typedef std::tuple<Ts...>* result_type;
 
   awaitable_async_op_handler(
       awaitable_thread<Executor>* h, result_type& result)
     : awaitable_thread<Executor>(std::move(*h)),
       result_(result)
   {
   }
 
   template <typename... Args>
   void operator()(Args&&... args)
   {
     std::tuple<Ts...> result(std::forward<Args>(args)...);
     result_ = &result;
     this->entry_point()->top_of_stack_->attach_thread(this);
     this->entry_point()->top_of_stack_->clear_cancellation_slot();
     this->pump();
   }
 
   static std::tuple<Ts...> resume(result_type& result)
   {
     return std::move(*result);
   }
 
 private:
   result_type& result_;
 };
 
 template <typename R, typename... Ts, typename Executor>
 class awaitable_async_op_handler<R(boost::system::error_code, Ts...), Executor>
   : public awaitable_thread<Executor>
 {
 public:
   struct result_type
   {
     boost::system::error_code* ec_;
     std::tuple<Ts...>* value_;
   };
 
   awaitable_async_op_handler(
       awaitable_thread<Executor>* h, result_type& result)
     : awaitable_thread<Executor>(std::move(*h)),
       result_(result)
   {
   }
 
   template <typename... Args>
   void operator()(boost::system::error_code ec, Args&&... args)
   {
     result_.ec_ = &ec;
     std::tuple<Ts...> value(std::forward<Args>(args)...);
     result_.value_ = &value;
     this->entry_point()->top_of_stack_->attach_thread(this);
     this->entry_point()->top_of_stack_->clear_cancellation_slot();
     this->pump();
   }
 
   static std::tuple<Ts...> resume(result_type& result)
   {
     throw_error(*result.ec_);
     return std::move(*result.value_);
   }
 
 private:
   result_type& result_;
 };
 
 template <typename R, typename... Ts, typename Executor>
 class awaitable_async_op_handler<R(std::exception_ptr, Ts...), Executor>
   : public awaitable_thread<Executor>
 {
 public:
   struct result_type
   {
     std::exception_ptr* ex_;
     std::tuple<Ts...>* value_;
   };
 
   awaitable_async_op_handler(
       awaitable_thread<Executor>* h, result_type& result)
     : awaitable_thread<Executor>(std::move(*h)),
       result_(result)
   {
   }
 
   template <typename... Args>
   void operator()(std::exception_ptr ex, Args&&... args)
   {
     result_.ex_ = &ex;
     std::tuple<Ts...> value(std::forward<Args>(args)...);
     result_.value_ = &value;
     this->entry_point()->top_of_stack_->attach_thread(this);
     this->entry_point()->top_of_stack_->clear_cancellation_slot();
     this->pump();
   }
 
   static std::tuple<Ts...> resume(result_type& result)
   {
     if (*result.ex_)
     {
       std::exception_ptr ex = std::exchange(*result.ex_, nullptr);
       std::rethrow_exception(ex);
     }
     return std::move(*result.value_);
   }
 
 private:
   result_type& result_;
 };
 
 template <typename Signature, typename Op, typename Executor>
 class awaitable_async_op
 {
 public:
   typedef awaitable_async_op_handler<Signature, Executor> handler_type;
 
   awaitable_async_op(Op&& o, awaitable_frame_base<Executor>* frame
 #if defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
 # if defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
       , const detail::source_location& location
 # endif // defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
 #endif // defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
     )
     : op_(std::forward<Op>(o)),
       frame_(frame),
       result_()
 #if defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
 # if defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
     , location_(location)
 # endif // defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
 #endif // defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
   {
   }
 
   bool await_ready() const noexcept
   {
     return false;
   }
 
   void await_suspend(coroutine_handle<void>)
   {
     frame_->after_suspend(
         [](void* arg)
         {
           awaitable_async_op* self = static_cast<awaitable_async_op*>(arg);
 #if defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
 # if defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
           BOOST_ASIO_HANDLER_LOCATION((self->location_.file_name(),
               self->location_.line(), self->location_.function_name()));
 # endif // defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
 #endif // defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
           std::forward<Op&&>(self->op_)(
               handler_type(self->frame_->detach_thread(), self->result_));
         }, this);
   }
 
   auto await_resume()
   {
     return handler_type::resume(result_);
   }
 
 private:
   Op&& op_;
   awaitable_frame_base<Executor>* frame_;
   typename handler_type::result_type result_;
 #if defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
 # if defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
   detail::source_location location_;
 # endif // defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
 #endif // defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
 };
 
 } // namespace detail
 } // namespace asio
 } // namespace boost
 
 #if !defined(GENERATING_DOCUMENTATION)
 # if defined(BOOST_ASIO_HAS_STD_COROUTINE)
 
 namespace std {
 
 template <typename T, typename Executor, typename... Args>
 struct coroutine_traits<boost::asio::awaitable<T, Executor>, Args...>
 {
   typedef boost::asio::detail::awaitable_frame<T, Executor> promise_type;
 };
 
 } // namespace std
 
 # else // defined(BOOST_ASIO_HAS_STD_COROUTINE)
 
 namespace std { namespace experimental {
 
 template <typename T, typename Executor, typename... Args>
 struct coroutine_traits<boost::asio::awaitable<T, Executor>, Args...>
 {
   typedef boost::asio::detail::awaitable_frame<T, Executor> promise_type;
 };
 
 }} // namespace std::experimental
 
 # endif // defined(BOOST_ASIO_HAS_STD_COROUTINE)
 #endif // !defined(GENERATING_DOCUMENTATION)
 
 #include <boost/asio/detail/pop_options.hpp>
 
 #endif // BOOST_ASIO_IMPL_AWAITABLE_HPP

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