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+//
+// spawn.hpp
+// ~~~~~~~~~
+//
+// Copyright (c) 2003-2018 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_SPAWN_HPP
+#define ASIO_SPAWN_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include <boost/coroutine/all.hpp>
+#include "asio/bind_executor.hpp"
+#include "asio/detail/memory.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/detail/wrapped_handler.hpp"
+#include "asio/executor.hpp"
+#include "asio/io_context.hpp"
+#include "asio/is_executor.hpp"
+#include "asio/strand.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+/// Context object the represents the currently executing coroutine.
+/**
+ * The basic_yield_context class is used to represent the currently executing
+ * stackful coroutine. A basic_yield_context may be passed as a handler to an
+ * asynchronous operation. For example:
+ *
+ * @code template <typename Handler>
+ * void my_coroutine(basic_yield_context<Handler> 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 Handler>
+class basic_yield_context
+{
+public:
+  /// The coroutine callee type, used by the implementation.
+  /**
+   * When using Boost.Coroutine v1, this type is:
+   * @code typename coroutine<void()> @endcode
+   * When using Boost.Coroutine v2 (unidirectional coroutines), this type is:
+   * @code push_coroutine<void> @endcode
+   */
+#if defined(GENERATING_DOCUMENTATION)
+  typedef implementation_defined callee_type;
+#elif defined(BOOST_COROUTINES_UNIDIRECT) || defined(BOOST_COROUTINES_V2)
+  typedef boost::coroutines::push_coroutine<void> callee_type;
+#else
+  typedef boost::coroutines::coroutine<void()> callee_type;
+#endif
+  
+  /// The coroutine caller type, used by the implementation.
+  /**
+   * When using Boost.Coroutine v1, this type is:
+   * @code typename coroutine<void()>::caller_type @endcode
+   * When using Boost.Coroutine v2 (unidirectional coroutines), this type is:
+   * @code pull_coroutine<void> @endcode
+   */
+#if defined(GENERATING_DOCUMENTATION)
+  typedef implementation_defined caller_type;
+#elif defined(BOOST_COROUTINES_UNIDIRECT) || defined(BOOST_COROUTINES_V2)
+  typedef boost::coroutines::pull_coroutine<void> caller_type;
+#else
+  typedef boost::coroutines::coroutine<void()>::caller_type caller_type;
+#endif
+
+  /// Construct a yield context to represent the specified coroutine.
+  /**
+   * Most applications do not need to use this constructor. Instead, the
+   * spawn() function passes a yield context as an argument to the coroutine
+   * function.
+   */
+  basic_yield_context(
+      const detail::weak_ptr<callee_type>& coro,
+      caller_type& ca, Handler& handler)
+    : coro_(coro),
+      ca_(ca),
+      handler_(handler),
+      ec_(0)
+  {
+  }
+
+  /// Construct a yield context from another yield context type.
+  /**
+   * Requires that OtherHandler be convertible to Handler.
+   */
+  template <typename OtherHandler>
+  basic_yield_context(const basic_yield_context<OtherHandler>& other)
+    : coro_(other.coro_),
+      ca_(other.ca_),
+      handler_(other.handler_),
+      ec_(other.ec_)
+  {
+  }
+
+  /// 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 Handler>
+   * void my_coroutine(basic_yield_context<Handler> yield)
+   * {
+   *   ...
+   *   std::size_t n = my_socket.async_read_some(buffer, yield[ec]);
+   *   if (ec)
+   *   {
+   *     // An error occurred.
+   *   }
+   *   ...
+   * } @endcode
+   */
+  basic_yield_context operator[](asio::error_code& ec) const
+  {
+    basic_yield_context tmp(*this);
+    tmp.ec_ = &ec;
+    return tmp;
+  }
+
+#if defined(GENERATING_DOCUMENTATION)
+private:
+#endif // defined(GENERATING_DOCUMENTATION)
+  detail::weak_ptr<callee_type> coro_;
+  caller_type& ca_;
+  Handler handler_;
+  asio::error_code* ec_;
+};
+
+#if defined(GENERATING_DOCUMENTATION)
+/// Context object that represents the currently executing coroutine.
+typedef basic_yield_context<unspecified> yield_context;
+#else // defined(GENERATING_DOCUMENTATION)
+typedef basic_yield_context<
+  executor_binder<void(*)(), executor> > yield_context;
+#endif // defined(GENERATING_DOCUMENTATION)
+
+/**
+ * @defgroup spawn 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 asio::spawn(my_strand, do_echo);
+ *
+ * // ...
+ *
+ * void do_echo(asio::yield_context yield)
+ * {
+ *   try
+ *   {
+ *     char data[128];
+ *     for (;;)
+ *     {
+ *       std::size_t length =
+ *         my_socket.async_read_some(
+ *           asio::buffer(data), yield);
+ *
+ *       asio::async_write(my_socket,
+ *           asio::buffer(data, length), yield);
+ *     }
+ *   }
+ *   catch (std::exception& e)
+ *   {
+ *     // ...
+ *   }
+ * } @endcode
+ */
+/*@{*/
+
+/// 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<Handler> yield); @endcode
+ *
+ * @param attributes Boost.Coroutine attributes used to customise the coroutine.
+ */
+template <typename Function>
+void spawn(ASIO_MOVE_ARG(Function) function,
+    const boost::coroutines::attributes& attributes
+      = boost::coroutines::attributes());
+
+/// 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<Handler> yield); @endcode
+ *
+ * @param attributes Boost.Coroutine attributes used to customise the coroutine.
+ */
+template <typename Handler, typename Function>
+void spawn(ASIO_MOVE_ARG(Handler) handler,
+    ASIO_MOVE_ARG(Function) function,
+    const boost::coroutines::attributes& attributes
+      = boost::coroutines::attributes(),
+    typename enable_if<!is_executor<typename decay<Handler>::type>::value &&
+      !is_convertible<Handler&, execution_context&>::value>::type* = 0);
+
+/// 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<Handler> yield); @endcode
+ *
+ * @param attributes Boost.Coroutine attributes used to customise the coroutine.
+ */
+template <typename Handler, typename Function>
+void spawn(basic_yield_context<Handler> ctx,
+    ASIO_MOVE_ARG(Function) function,
+    const boost::coroutines::attributes& attributes
+      = boost::coroutines::attributes());
+
+/// 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 implicitly given its own 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,
+    ASIO_MOVE_ARG(Function) function,
+    const boost::coroutines::attributes& attributes
+      = boost::coroutines::attributes(),
+    typename enable_if<is_executor<Executor>::value>::type* = 0);
+
+/// 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,
+    ASIO_MOVE_ARG(Function) function,
+    const boost::coroutines::attributes& attributes
+      = boost::coroutines::attributes());
+
+/// 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 asio::io_context::strand& s,
+    ASIO_MOVE_ARG(Function) function,
+    const boost::coroutines::attributes& attributes
+      = boost::coroutines::attributes());
+
+/// 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,
+    ASIO_MOVE_ARG(Function) function,
+    const boost::coroutines::attributes& attributes
+      = boost::coroutines::attributes(),
+    typename enable_if<is_convertible<
+      ExecutionContext&, execution_context&>::value>::type* = 0);
+
+/*@}*/
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#include "asio/impl/spawn.hpp"
+
+#endif // ASIO_SPAWN_HPP