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 //
 // spawn.hpp
 // ~~~~~~~~~
 //
 // Copyright (c) 2003-2024 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_SPAWN_HPP
 #define BOOST_ASIO_SPAWN_HPP
 
 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
 # pragma once
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
 #include <boost/asio/any_io_executor.hpp>
 #include <boost/asio/cancellation_signal.hpp>
 #include <boost/asio/cancellation_state.hpp>
 #include <boost/asio/detail/exception.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/type_traits.hpp>
 #include <boost/asio/io_context.hpp>
 #include <boost/asio/is_executor.hpp>
 #include <boost/asio/strand.hpp>
 
 #if defined(BOOST_ASIO_HAS_BOOST_COROUTINE)
 # include <boost/coroutine/all.hpp>
 #endif // defined(BOOST_ASIO_HAS_BOOST_COROUTINE)
 
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
 namespace asio {
 namespace detail {
 
 // Base class for all spawn()-ed thread implementations.
 class spawned_thread_base
 {
 public:
   spawned_thread_base()
     : owner_(0),
       has_context_switched_(false),
       throw_if_cancelled_(false),
       terminal_(false)
   {
   }
 
   virtual ~spawned_thread_base() {}
   virtual void resume() = 0;
   virtual void suspend_with(void (*fn)(void*), void* arg) = 0;
   virtual void destroy() = 0;
 
   void attach(spawned_thread_base** owner)
   {
     owner_ = owner;
     *owner_ = this;
   }
 
   void detach()
   {
     if (owner_)
       *owner_ = 0;
     owner_ = 0;
   }
 
   void suspend()
   {
     suspend_with(0, 0);
   }
 
   template <typename F>
   void suspend_with(F f)
   {
     suspend_with(&spawned_thread_base::call<F>, &f);
   }
 
   cancellation_slot get_cancellation_slot() const noexcept
   {
     return cancellation_state_.slot();
   }
 
   cancellation_state get_cancellation_state() const noexcept
   {
     return cancellation_state_;
   }
 
   void reset_cancellation_state()
   {
     cancellation_state_ = cancellation_state(parent_cancellation_slot_);
   }
 
   template <typename Filter>
   void reset_cancellation_state(Filter filter)
   {
     cancellation_state_ = cancellation_state(
         parent_cancellation_slot_, filter, filter);
   }
 
   template <typename InFilter, typename OutFilter>
   void reset_cancellation_state(InFilter in_filter, OutFilter out_filter)
   {
     cancellation_state_ = cancellation_state(
         parent_cancellation_slot_, in_filter, out_filter);
   }
 
   cancellation_type_t cancelled() const noexcept
   {
     return cancellation_state_.cancelled();
   }
 
   bool has_context_switched() const noexcept
   {
     return has_context_switched_;
   }
 
   bool throw_if_cancelled() const noexcept
   {
     return throw_if_cancelled_;
   }
 
   void throw_if_cancelled(bool value) noexcept
   {
     throw_if_cancelled_ = value;
   }
 
 protected:
   spawned_thread_base** owner_; // Points to data member in active handler.
   boost::asio::cancellation_slot parent_cancellation_slot_;
   boost::asio::cancellation_state cancellation_state_;
   bool has_context_switched_;
   bool throw_if_cancelled_;
   bool terminal_;
 
 private:
   // Disallow copying and assignment.
   spawned_thread_base(const spawned_thread_base&) = delete;
   spawned_thread_base& operator=(const spawned_thread_base&) = delete;
 
   template <typename F>
   static void call(void* f)
   {
     (*static_cast<F*>(f))();
   }
 };
 
 template <typename T>
 struct spawn_signature
 {
   typedef void type(exception_ptr, T);
 };
 
 template <>
 struct spawn_signature<void>
 {
   typedef void type(exception_ptr);
 };
 
 template <typename Executor>
 class initiate_spawn;
 
 } // namespace detail
 
 /// A @ref completion_token that represents the currently executing coroutine.
 /**
  * The basic_yield_context class is a completion token type that is used to
  * represent the currently executing stackful coroutine. A basic_yield_context
  * object may be passed as a completion token to an asynchronous operation. For
  * example:
  *
  * @code template <typename Executor>
  * void my_coroutine(basic_yield_context<Executor> yield)
  * {
  *   ...
  *   std::size_t n = my_socket.async_read_some(buffer, yield);
  *   ...
  * } @endcode
  *
  * The initiating function (async_read_some in the above example) suspends the
  * current coroutine. The coroutine is resumed when the asynchronous operation
  * completes, and the result of the operation is returned.
  */
 template <typename Executor>
 class basic_yield_context
 {
 public:
   /// The executor type associated with the yield context.
   typedef Executor executor_type;
 
   /// The cancellation slot type associated with the yield context.
   typedef cancellation_slot cancellation_slot_type;
 
   /// Construct a yield context from another yield context type.
   /**
    * Requires that OtherExecutor be convertible to Executor.
    */
   template <typename OtherExecutor>
   basic_yield_context(const basic_yield_context<OtherExecutor>& other,
       constraint_t<
         is_convertible<OtherExecutor, Executor>::value
       > = 0)
     : spawned_thread_(other.spawned_thread_),
       executor_(other.executor_),
       ec_(other.ec_)
   {
   }
 
   /// Get the executor associated with the yield context.
   executor_type get_executor() const noexcept
   {
     return executor_;
   }
 
   /// Get the cancellation slot associated with the coroutine.
   cancellation_slot_type get_cancellation_slot() const noexcept
   {
     return spawned_thread_->get_cancellation_slot();
   }
 
   /// Get the cancellation state associated with the coroutine.
   cancellation_state get_cancellation_state() const noexcept
   {
     return spawned_thread_->get_cancellation_state();
   }
 
   /// Reset the cancellation state associated with the coroutine.
   /**
    * Let <tt>P</tt> be the cancellation slot associated with the current
    * coroutine's @ref spawn completion handler. Assigns a new
    * boost::asio::cancellation_state object <tt>S</tt>, constructed as
    * <tt>S(P)</tt>, into the current coroutine's cancellation state object.
    */
   void reset_cancellation_state() const
   {
     spawned_thread_->reset_cancellation_state();
   }
 
   /// Reset the cancellation state associated with the coroutine.
   /**
    * Let <tt>P</tt> be the cancellation slot associated with the current
    * coroutine's @ref spawn completion handler. Assigns a new
    * boost::asio::cancellation_state object <tt>S</tt>, constructed as <tt>S(P,
    * std::forward<Filter>(filter))</tt>, into the current coroutine's
    * cancellation state object.
    */
   template <typename Filter>
   void reset_cancellation_state(Filter&& filter) const
   {
     spawned_thread_->reset_cancellation_state(
         static_cast<Filter&&>(filter));
   }
 
   /// Reset the cancellation state associated with the coroutine.
   /**
    * Let <tt>P</tt> be the cancellation slot associated with the current
    * coroutine's @ref spawn completion handler. Assigns a new
    * boost::asio::cancellation_state object <tt>S</tt>, constructed as <tt>S(P,
    * std::forward<InFilter>(in_filter),
    * std::forward<OutFilter>(out_filter))</tt>, into the current coroutine's
    * cancellation state object.
    */
   template <typename InFilter, typename OutFilter>
   void reset_cancellation_state(InFilter&& in_filter,
       OutFilter&& out_filter) const
   {
     spawned_thread_->reset_cancellation_state(
         static_cast<InFilter&&>(in_filter),
         static_cast<OutFilter&&>(out_filter));
   }
 
   /// Determine whether the current coroutine has been cancelled.
   cancellation_type_t cancelled() const noexcept
   {
     return spawned_thread_->cancelled();
   }
 
   /// Determine whether the coroutine throws if trying to suspend when it has
   /// been cancelled.
   bool throw_if_cancelled() const noexcept
   {
     return spawned_thread_->throw_if_cancelled();
   }
 
   /// Set whether the coroutine throws if trying to suspend when it has been
   /// cancelled.
   void throw_if_cancelled(bool value) const noexcept
   {
     spawned_thread_->throw_if_cancelled(value);
   }
 
   /// Return a yield context that sets the specified error_code.
   /**
    * By default, when a yield context is used with an asynchronous operation, a
    * non-success error_code is converted to system_error and thrown. This
    * operator may be used to specify an error_code object that should instead be
    * set with the asynchronous operation's result. For example:
    *
    * @code template <typename Executor>
    * void my_coroutine(basic_yield_context<Executor> yield)
    * {
    *   ...
    *   std::size_t n = my_socket.async_read_some(buffer, yield[ec]);
    *   if (ec)
    *   {
    *     // An error occurred.
    *   }
    *   ...
    * } @endcode
    */
   basic_yield_context operator[](boost::system::error_code& ec) const
   {
     basic_yield_context tmp(*this);
     tmp.ec_ = &ec;
     return tmp;
   }
 
 #if !defined(GENERATING_DOCUMENTATION)
 //private:
   basic_yield_context(detail::spawned_thread_base* spawned_thread,
       const Executor& ex)
     : spawned_thread_(spawned_thread),
       executor_(ex),
       ec_(0)
   {
   }
 
   detail::spawned_thread_base* spawned_thread_;
   Executor executor_;
   boost::system::error_code* ec_;
 #endif // !defined(GENERATING_DOCUMENTATION)
 };
 
 /// A @ref completion_token object that represents the currently executing
 /// coroutine.
 typedef basic_yield_context<any_io_executor> yield_context;
 
 /**
  * @defgroup spawn boost::asio::spawn
  *
  * @brief Start a new stackful coroutine.
  *
  * The spawn() function is a high-level wrapper over the Boost.Coroutine
  * library. This function enables programs to implement asynchronous logic in a
  * synchronous manner, as illustrated by the following example:
  *
  * @code boost::asio::spawn(my_strand, do_echo, boost::asio::detached);
  *
  * // ...
  *
  * void do_echo(boost::asio::yield_context yield)
  * {
  *   try
  *   {
  *     char data[128];
  *     for (;;)
  *     {
  *       std::size_t length =
  *         my_socket.async_read_some(
  *           boost::asio::buffer(data), yield);
  *
  *       boost::asio::async_write(my_socket,
  *           boost::asio::buffer(data, length), yield);
  *     }
  *   }
  *   catch (std::exception& e)
  *   {
  *     // ...
  *   }
  * } @endcode
  */
 /*@{*/
 
 /// Start a new stackful coroutine that executes on a given executor.
 /**
  * This function is used to launch a new stackful coroutine.
  *
  * @param ex Identifies the executor that will run the stackful coroutine.
  *
  * @param function The coroutine function. The function must be callable the
  * signature:
  * @code void function(basic_yield_context<Executor> yield); @endcode
  *
  * @param token The @ref completion_token that will handle the notification
  * that the coroutine has completed. If the return type @c R of @c function is
  * @c void, the function signature of the completion handler must be:
  *
  * @code void handler(std::exception_ptr); @endcode
  * Otherwise, the function signature of the completion handler must be:
  * @code void handler(std::exception_ptr, R); @endcode
  *
  * @par Completion Signature
  * @code void(std::exception_ptr, R) @endcode
  * where @c R is the return type of the function object.
  *
  * @par Per-Operation Cancellation
  * The new thread of execution is created with a cancellation state that
  * supports @c cancellation_type::terminal values only. To change the
  * cancellation state, call the basic_yield_context member function
  * @c reset_cancellation_state.
  */
 template <typename Executor, typename F,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(typename detail::spawn_signature<
       result_of_t<F(basic_yield_context<Executor>)>>::type)
         CompletionToken = default_completion_token_t<Executor>>
 auto spawn(const Executor& ex, F&& function,
     CompletionToken&& token = default_completion_token_t<Executor>(),
 #if defined(BOOST_ASIO_HAS_BOOST_COROUTINE)
     constraint_t<
       !is_same<
         decay_t<CompletionToken>,
         boost::coroutines::attributes
       >::value
     > = 0,
 #endif // defined(BOOST_ASIO_HAS_BOOST_COROUTINE)
     constraint_t<
       is_executor<Executor>::value || execution::is_executor<Executor>::value
     > = 0)
   -> decltype(
     async_initiate<CompletionToken,
       typename detail::spawn_signature<
         result_of_t<F(basic_yield_context<Executor>)>>::type>(
           declval<detail::initiate_spawn<Executor>>(),
           token, static_cast<F&&>(function)));
 
 /// Start a new stackful coroutine that executes on a given execution context.
 /**
  * This function is used to launch a new stackful coroutine.
  *
  * @param ctx Identifies the execution context that will run the stackful
  * coroutine.
  *
  * @param function The coroutine function. The function must be callable the
  * signature:
  * @code void function(basic_yield_context<Executor> yield); @endcode
  *
  * @param token The @ref completion_token that will handle the notification
  * that the coroutine has completed. If the return type @c R of @c function is
  * @c void, the function signature of the completion handler must be:
  *
  * @code void handler(std::exception_ptr); @endcode
  * Otherwise, the function signature of the completion handler must be:
  * @code void handler(std::exception_ptr, R); @endcode
  *
  * @par Completion Signature
  * @code void(std::exception_ptr, R) @endcode
  * where @c R is the return type of the function object.
  *
  * @par Per-Operation Cancellation
  * The new thread of execution is created with a cancellation state that
  * supports @c cancellation_type::terminal values only. To change the
  * cancellation state, call the basic_yield_context member function
  * @c reset_cancellation_state.
  */
 template <typename ExecutionContext, typename F,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(typename detail::spawn_signature<
       result_of_t<F(basic_yield_context<
         typename ExecutionContext::executor_type>)>>::type)
           CompletionToken = default_completion_token_t<
             typename ExecutionContext::executor_type>>
 auto spawn(ExecutionContext& ctx, F&& function,
     CompletionToken&& token
       = default_completion_token_t<typename ExecutionContext::executor_type>(),
 #if defined(BOOST_ASIO_HAS_BOOST_COROUTINE)
     constraint_t<
       !is_same<
         decay_t<CompletionToken>,
         boost::coroutines::attributes
       >::value
     > = 0,
 #endif // defined(BOOST_ASIO_HAS_BOOST_COROUTINE)
     constraint_t<
       is_convertible<ExecutionContext&, execution_context&>::value
     > = 0)
   -> decltype(
     async_initiate<CompletionToken,
       typename detail::spawn_signature<
         result_of_t<F(basic_yield_context<
           typename ExecutionContext::executor_type>)>>::type>(
             declval<detail::initiate_spawn<
               typename ExecutionContext::executor_type>>(),
             token, static_cast<F&&>(function)));
 
 /// Start a new stackful coroutine, inheriting the executor of another.
 /**
  * This function is used to launch a new stackful coroutine.
  *
  * @param ctx Identifies the current coroutine as a parent of the new
  * coroutine. This specifies that the new coroutine should inherit the executor
  * of the parent. For example, if the parent coroutine is executing in a
  * particular strand, then the new coroutine will execute in the same strand.
  *
  * @param function The coroutine function. The function must be callable the
  * signature:
  * @code void function(basic_yield_context<Executor> yield); @endcode
  *
  * @param token The @ref completion_token that will handle the notification
  * that the coroutine has completed. If the return type @c R of @c function is
  * @c void, the function signature of the completion handler must be:
  *
  * @code void handler(std::exception_ptr); @endcode
  * Otherwise, the function signature of the completion handler must be:
  * @code void handler(std::exception_ptr, R); @endcode
  *
  * @par Completion Signature
  * @code void(std::exception_ptr, R) @endcode
  * where @c R is the return type of the function object.
  *
  * @par Per-Operation Cancellation
  * The new thread of execution is created with a cancellation state that
  * supports @c cancellation_type::terminal values only. To change the
  * cancellation state, call the basic_yield_context member function
  * @c reset_cancellation_state.
  */
 template <typename Executor, typename F,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(typename detail::spawn_signature<
       result_of_t<F(basic_yield_context<Executor>)>>::type)
         CompletionToken = default_completion_token_t<Executor>>
 auto spawn(const basic_yield_context<Executor>& ctx, F&& function,
     CompletionToken&& token = default_completion_token_t<Executor>(),
 #if defined(BOOST_ASIO_HAS_BOOST_COROUTINE)
     constraint_t<
       !is_same<
         decay_t<CompletionToken>,
         boost::coroutines::attributes
       >::value
     > = 0,
 #endif // defined(BOOST_ASIO_HAS_BOOST_COROUTINE)
     constraint_t<
       is_executor<Executor>::value || execution::is_executor<Executor>::value
     > = 0)
   -> decltype(
     async_initiate<CompletionToken,
       typename detail::spawn_signature<
         result_of_t<F(basic_yield_context<Executor>)>>::type>(
           declval<detail::initiate_spawn<Executor>>(),
           token, static_cast<F&&>(function)));
 
 #if defined(BOOST_ASIO_HAS_BOOST_CONTEXT_FIBER) \
   || defined(GENERATING_DOCUMENTATION)
 
 /// Start a new stackful coroutine that executes on a given executor.
 /**
  * This function is used to launch a new stackful coroutine using the
  * specified stack allocator.
  *
  * @param ex Identifies the executor that will run the stackful coroutine.
  *
  * @param stack_allocator Denotes the allocator to be used to allocate the
  * underlying coroutine's stack. The type must satisfy the stack-allocator
  * concept defined by the Boost.Context library.
  *
  * @param function The coroutine function. The function must be callable the
  * signature:
  * @code void function(basic_yield_context<Executor> yield); @endcode
  *
  * @param token The @ref completion_token that will handle the notification
  * that the coroutine has completed. If the return type @c R of @c function is
  * @c void, the function signature of the completion handler must be:
  *
  * @code void handler(std::exception_ptr); @endcode
  * Otherwise, the function signature of the completion handler must be:
  * @code void handler(std::exception_ptr, R); @endcode
  *
  * @par Completion Signature
  * @code void(std::exception_ptr, R) @endcode
  * where @c R is the return type of the function object.
  *
  * @par Per-Operation Cancellation
  * The new thread of execution is created with a cancellation state that
  * supports @c cancellation_type::terminal values only. To change the
  * cancellation state, call the basic_yield_context member function
  * @c reset_cancellation_state.
  */
 template <typename Executor, typename StackAllocator, typename F,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(typename detail::spawn_signature<
       result_of_t<F(basic_yield_context<Executor>)>>::type)
         CompletionToken = default_completion_token_t<Executor>>
 auto spawn(const Executor& ex, allocator_arg_t,
     StackAllocator&& stack_allocator, F&& function,
     CompletionToken&& token = default_completion_token_t<Executor>(),
     constraint_t<
       is_executor<Executor>::value || execution::is_executor<Executor>::value
     > = 0)
   -> decltype(
     async_initiate<CompletionToken,
       typename detail::spawn_signature<
         result_of_t<F(basic_yield_context<Executor>)>>::type>(
           declval<detail::initiate_spawn<Executor>>(),
           token, allocator_arg_t(),
           static_cast<StackAllocator&&>(stack_allocator),
           static_cast<F&&>(function)));
 
 /// Start a new stackful coroutine that executes on a given execution context.
 /**
  * This function is used to launch a new stackful coroutine.
  *
  * @param ctx Identifies the execution context that will run the stackful
  * coroutine.
  *
  * @param stack_allocator Denotes the allocator to be used to allocate the
  * underlying coroutine's stack. The type must satisfy the stack-allocator
  * concept defined by the Boost.Context library.
  *
  * @param function The coroutine function. The function must be callable the
  * signature:
  * @code void function(basic_yield_context<Executor> yield); @endcode
  *
  * @param token The @ref completion_token that will handle the notification
  * that the coroutine has completed. If the return type @c R of @c function is
  * @c void, the function signature of the completion handler must be:
  *
  * @code void handler(std::exception_ptr); @endcode
  * Otherwise, the function signature of the completion handler must be:
  * @code void handler(std::exception_ptr, R); @endcode
  *
  * @par Completion Signature
  * @code void(std::exception_ptr, R) @endcode
  * where @c R is the return type of the function object.
  *
  * @par Per-Operation Cancellation
  * The new thread of execution is created with a cancellation state that
  * supports @c cancellation_type::terminal values only. To change the
  * cancellation state, call the basic_yield_context member function
  * @c reset_cancellation_state.
  */
 template <typename ExecutionContext, typename StackAllocator, typename F,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(typename detail::spawn_signature<
       result_of_t<F(basic_yield_context<
         typename ExecutionContext::executor_type>)>>::type)
           CompletionToken = default_completion_token_t<
             typename ExecutionContext::executor_type>>
 auto spawn(ExecutionContext& ctx, allocator_arg_t,
     StackAllocator&& stack_allocator, F&& function,
     CompletionToken&& token
       = default_completion_token_t<typename ExecutionContext::executor_type>(),
     constraint_t<
       is_convertible<ExecutionContext&, execution_context&>::value
     > = 0)
   -> decltype(
     async_initiate<CompletionToken,
       typename detail::spawn_signature<
         result_of_t<F(basic_yield_context<
           typename ExecutionContext::executor_type>)>>::type>(
             declval<detail::initiate_spawn<
               typename ExecutionContext::executor_type>>(),
             token, allocator_arg_t(),
             static_cast<StackAllocator&&>(stack_allocator),
             static_cast<F&&>(function)));
 
 /// Start a new stackful coroutine, inheriting the executor of another.
 /**
  * This function is used to launch a new stackful coroutine using the
  * specified stack allocator.
  *
  * @param ctx Identifies the current coroutine as a parent of the new
  * coroutine. This specifies that the new coroutine should inherit the
  * executor of the parent. For example, if the parent coroutine is executing
  * in a particular strand, then the new coroutine will execute in the same
  * strand.
  *
  * @param stack_allocator Denotes the allocator to be used to allocate the
  * underlying coroutine's stack. The type must satisfy the stack-allocator
  * concept defined by the Boost.Context library.
  *
  * @param function The coroutine function. The function must be callable the
  * signature:
  * @code void function(basic_yield_context<Executor> yield); @endcode
  *
  * @param token The @ref completion_token that will handle the notification
  * that the coroutine has completed. If the return type @c R of @c function is
  * @c void, the function signature of the completion handler must be:
  *
  * @code void handler(std::exception_ptr); @endcode
  * Otherwise, the function signature of the completion handler must be:
  * @code void handler(std::exception_ptr, R); @endcode
  *
  * @par Completion Signature
  * @code void(std::exception_ptr, R) @endcode
  * where @c R is the return type of the function object.
  *
  * @par Per-Operation Cancellation
  * The new thread of execution is created with a cancellation state that
  * supports @c cancellation_type::terminal values only. To change the
  * cancellation state, call the basic_yield_context member function
  * @c reset_cancellation_state.
  */
 template <typename Executor, typename StackAllocator, typename F,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(typename detail::spawn_signature<
       result_of_t<F(basic_yield_context<Executor>)>>::type)
         CompletionToken = default_completion_token_t<Executor>>
 auto spawn(const basic_yield_context<Executor>& ctx, allocator_arg_t,
     StackAllocator&& stack_allocator, F&& function,
     CompletionToken&& token = default_completion_token_t<Executor>(),
     constraint_t<
       is_executor<Executor>::value || execution::is_executor<Executor>::value
     > = 0)
   -> decltype(
     async_initiate<CompletionToken,
       typename detail::spawn_signature<
         result_of_t<F(basic_yield_context<Executor>)>>::type>(
           declval<detail::initiate_spawn<Executor>>(),
           token, allocator_arg_t(),
           static_cast<StackAllocator&&>(stack_allocator),
           static_cast<F&&>(function)));
 
 #endif // defined(BOOST_ASIO_HAS_BOOST_CONTEXT_FIBER)
        //   || defined(GENERATING_DOCUMENTATION)
 
 #if defined(BOOST_ASIO_HAS_BOOST_COROUTINE) \
   || defined(GENERATING_DOCUMENTATION)
 
 /// (Deprecated: Use overloads with a completion token.) Start a new stackful
 /// coroutine, calling the specified handler when it completes.
 /**
  * This function is used to launch a new coroutine.
  *
  * @param function The coroutine function. The function must have the signature:
  * @code void function(basic_yield_context<Executor> yield); @endcode
  * where Executor is the associated executor type of @c Function.
  *
  * @param attributes Boost.Coroutine attributes used to customise the coroutine.
  */
 template <typename Function>
 void spawn(Function&& function,
     const boost::coroutines::attributes& attributes
       = boost::coroutines::attributes());
 
 /// (Deprecated: Use overloads with a completion token.) Start a new stackful
 /// coroutine, calling the specified handler when it completes.
 /**
  * This function is used to launch a new coroutine.
  *
  * @param handler A handler to be called when the coroutine exits. More
  * importantly, the handler provides an execution context (via the the handler
  * invocation hook) for the coroutine. The handler must have the signature:
  * @code void handler(); @endcode
  *
  * @param function The coroutine function. The function must have the signature:
  * @code void function(basic_yield_context<Executor> yield); @endcode
  * where Executor is the associated executor type of @c Handler.
  *
  * @param attributes Boost.Coroutine attributes used to customise the coroutine.
  */
 template <typename Handler, typename Function>
 void spawn(Handler&& handler, Function&& function,
     const boost::coroutines::attributes& attributes
       = boost::coroutines::attributes(),
     constraint_t<
       !is_executor<decay_t<Handler>>::value &&
       !execution::is_executor<decay_t<Handler>>::value &&
       !is_convertible<Handler&, execution_context&>::value
     > = 0);
 
 /// (Deprecated: Use overloads with a completion token.) Start a new stackful
 /// coroutine, inheriting the execution context of another.
 /**
  * This function is used to launch a new coroutine.
  *
  * @param ctx Identifies the current coroutine as a parent of the new
  * coroutine. This specifies that the new coroutine should inherit the
  * execution context of the parent. For example, if the parent coroutine is
  * executing in a particular strand, then the new coroutine will execute in the
  * same strand.
  *
  * @param function The coroutine function. The function must have the signature:
  * @code void function(basic_yield_context<Executor> yield); @endcode
  *
  * @param attributes Boost.Coroutine attributes used to customise the coroutine.
  */
 template <typename Executor, typename Function>
 void spawn(basic_yield_context<Executor> ctx, Function&& function,
     const boost::coroutines::attributes& attributes
       = boost::coroutines::attributes());
 
 /// (Deprecated: Use overloads with a completion token.) Start a new stackful
 /// coroutine that executes on a given executor.
 /**
  * This function is used to launch a new coroutine.
  *
  * @param ex Identifies the executor that will run the coroutine. The new
  * coroutine is automatically given its own explicit strand within this
  * executor.
  *
  * @param function The coroutine function. The function must have the signature:
  * @code void function(yield_context yield); @endcode
  *
  * @param attributes Boost.Coroutine attributes used to customise the coroutine.
  */
 template <typename Function, typename Executor>
 void spawn(const Executor& ex, Function&& function,
     const boost::coroutines::attributes& attributes
       = boost::coroutines::attributes(),
     constraint_t<
       is_executor<Executor>::value || execution::is_executor<Executor>::value
     > = 0);
 
 /// (Deprecated: Use overloads with a completion token.) Start a new stackful
 /// coroutine that executes on a given strand.
 /**
  * This function is used to launch a new coroutine.
  *
  * @param ex Identifies the strand that will run the coroutine.
  *
  * @param function The coroutine function. The function must have the signature:
  * @code void function(yield_context yield); @endcode
  *
  * @param attributes Boost.Coroutine attributes used to customise the coroutine.
  */
 template <typename Function, typename Executor>
 void spawn(const strand<Executor>& ex, Function&& function,
     const boost::coroutines::attributes& attributes
       = boost::coroutines::attributes());
 
 #if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
 
 /// (Deprecated: Use overloads with a completion token.) Start a new stackful
 /// coroutine that executes in the context of a strand.
 /**
  * This function is used to launch a new coroutine.
  *
  * @param s Identifies a strand. By starting multiple coroutines on the same
  * strand, the implementation ensures that none of those coroutines can execute
  * simultaneously.
  *
  * @param function The coroutine function. The function must have the signature:
  * @code void function(yield_context yield); @endcode
  *
  * @param attributes Boost.Coroutine attributes used to customise the coroutine.
  */
 template <typename Function>
 void spawn(const boost::asio::io_context::strand& s, Function&& function,
     const boost::coroutines::attributes& attributes
       = boost::coroutines::attributes());
 
 #endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
 
 /// (Deprecated: Use overloads with a completion token.) Start a new stackful
 /// coroutine that executes on a given execution context.
 /**
  * This function is used to launch a new coroutine.
  *
  * @param ctx Identifies the execution context that will run the coroutine. The
  * new coroutine is implicitly given its own strand within this execution
  * context.
  *
  * @param function The coroutine function. The function must have the signature:
  * @code void function(yield_context yield); @endcode
  *
  * @param attributes Boost.Coroutine attributes used to customise the coroutine.
  */
 template <typename Function, typename ExecutionContext>
 void spawn(ExecutionContext& ctx, Function&& function,
     const boost::coroutines::attributes& attributes
       = boost::coroutines::attributes(),
     constraint_t<
       is_convertible<ExecutionContext&, execution_context&>::value
     > = 0);
 
 #endif // defined(BOOST_ASIO_HAS_BOOST_COROUTINE)
        //   || defined(GENERATING_DOCUMENTATION)
 
 /*@}*/
 
 } // namespace asio
 } // namespace boost
 
 #include <boost/asio/detail/pop_options.hpp>
 
 #include <boost/asio/impl/spawn.hpp>
 
 #endif // BOOST_ASIO_SPAWN_HPP

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