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+//
+// experimental/co_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 BOOST_ASIO_EXPERIMENTAL_CO_SPAWN_HPP
+#define BOOST_ASIO_EXPERIMENTAL_CO_SPAWN_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+
+#if defined(BOOST_ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
+
+#include <experimental/coroutine>
+#include <boost/asio/executor.hpp>
+#include <boost/asio/strand.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace experimental {
+namespace detail {
+
+using std::experimental::coroutine_handle;
+
+template <typename> class awaiter;
+template <typename> class awaitee_base;
+template <typename, typename> class awaitee;
+template <typename, typename> class await_handler_base;
+template <typename Executor, typename F, typename CompletionToken>
+auto co_spawn(const Executor& ex, F&& f, CompletionToken&& token);
+
+} // namespace detail
+
+namespace this_coro {
+
+/// Awaitable type that returns a completion token for the current coroutine.
+struct token_t {};
+
+/// Awaitable object that returns a completion token for the current coroutine.
+constexpr inline token_t token() { return {}; }
+
+/// Awaitable type that returns the executor of the current coroutine.
+struct executor_t {};
+
+/// Awaitable object that returns the executor of the current coroutine.
+constexpr inline executor_t executor() { return {}; }
+
+} // namespace this_coro
+
+/// A completion token that represents the currently executing coroutine.
+/**
+ * The await_token class is used to represent the currently executing
+ * coroutine. An await_token may be passed as a handler to an asynchronous
+ * operation. For example:
+ *
+ * @code awaitable<void> my_coroutine()
+ * {
+ *   await_token token = co_await this_coro::token();
+ *   ...
+ *   std::size_t n = co_await my_socket.async_read_some(buffer, token);
+ *   ...
+ * } @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 await_token
+{
+public:
+  /// The associated executor type.
+  typedef Executor executor_type;
+
+  /// Copy constructor.
+  await_token(const await_token& other) noexcept
+    : awaiter_(other.awaiter_)
+  {
+  }
+
+  /// Move constructor.
+  await_token(await_token&& other) noexcept
+    : awaiter_(std::exchange(other.awaiter_, nullptr))
+  {
+  }
+
+  /// Get the associated executor.
+  executor_type get_executor() const noexcept
+  {
+    return awaiter_->get_executor();
+  }
+
+private:
+  // No assignment allowed.
+  await_token& operator=(const await_token&) = delete;
+
+  template <typename> friend class detail::awaitee_base;
+  template <typename, typename> friend class detail::await_handler_base;
+
+  // Private constructor used by awaitee_base.
+  explicit await_token(detail::awaiter<Executor>* a)
+    : awaiter_(a)
+  {
+  }
+
+  detail::awaiter<Executor>* awaiter_;
+};
+
+/// The return type of a coroutine or asynchronous operation.
+template <typename T, typename Executor = strand<executor>>
+class awaitable
+{
+public:
+  /// The type of the awaited value.
+  typedef T value_type;
+
+  /// The executor type that will be used for the coroutine.
+  typedef Executor executor_type;
+
+  /// Move constructor.
+  awaitable(awaitable&& other) noexcept
+    : awaitee_(std::exchange(other.awaitee_, nullptr))
+  {
+  }
+
+  /// Destructor
+  ~awaitable()
+  {
+    if (awaitee_)
+    {
+      detail::coroutine_handle<
+        detail::awaitee<T, Executor>>::from_promise(
+          *awaitee_).destroy();
+    }
+  }
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+  // Support for co_await keyword.
+  bool await_ready() const noexcept
+  {
+    return awaitee_->ready();
+  }
+
+  // Support for co_await keyword.
+  void await_suspend(detail::coroutine_handle<detail::awaiter<Executor>> h)
+  {
+    awaitee_->attach_caller(h);
+  }
+
+  // Support for co_await keyword.
+  template <class U>
+  void await_suspend(detail::coroutine_handle<detail::awaitee<U, Executor>> h)
+  {
+    awaitee_->attach_caller(h);
+  }
+
+  // Support for co_await keyword.
+  T await_resume()
+  {
+    return awaitee_->get();
+  }
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+private:
+  template <typename, typename> friend class detail::awaitee;
+  template <typename, typename> friend class detail::await_handler_base;
+
+  // Not copy constructible or copy assignable.
+  awaitable(const awaitable&) = delete;
+  awaitable& operator=(const awaitable&) = delete;
+
+  // Construct the awaitable from a coroutine's promise object.
+  explicit awaitable(detail::awaitee<T, Executor>* a) : awaitee_(a) {}
+
+  detail::awaitee<T, Executor>* awaitee_;
+};
+
+/// Spawn a new thread of execution.
+template <typename Executor, typename F, typename CompletionToken,
+    typename = typename enable_if<is_executor<Executor>::value>::type>
+inline auto co_spawn(const Executor& ex, F&& f, CompletionToken&& token)
+{
+  return detail::co_spawn(ex, std::forward<F>(f),
+      std::forward<CompletionToken>(token));
+}
+
+/// Spawn a new thread of execution.
+template <typename ExecutionContext, typename F, typename CompletionToken,
+    typename = typename enable_if<
+      is_convertible<ExecutionContext&, execution_context&>::value>::type>
+inline auto co_spawn(ExecutionContext& ctx, F&& f, CompletionToken&& token)
+{
+  return detail::co_spawn(ctx.get_executor(), std::forward<F>(f),
+      std::forward<CompletionToken>(token));
+}
+
+/// Spawn a new thread of execution.
+template <typename Executor, typename F, typename CompletionToken>
+inline auto co_spawn(const await_token<Executor>& parent,
+    F&& f, CompletionToken&& token)
+{
+  return detail::co_spawn(parent.get_executor(), std::forward<F>(f),
+      std::forward<CompletionToken>(token));
+}
+
+} // namespace experimental
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#include <boost/asio/experimental/impl/co_spawn.hpp>
+
+#endif // defined(BOOST_ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
+
+#endif // BOOST_ASIO_EXPERIMENTAL_CO_SPAWN_HPP