Update boost to 1.71 and add asio

boost/asio/co_spawn.hpp

@@ -0,0 +1,90 @@
+//
+// co_spawn.hpp
+// ~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2019 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_CO_SPAWN_HPP
+#define BOOST_ASIO_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 <boost/asio/awaitable.hpp>
+#include <boost/asio/execution_context.hpp>
+#include <boost/asio/is_executor.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace detail {
+
+template <typename T>
+struct awaitable_signature;
+
+template <typename T, typename Executor>
+struct awaitable_signature<awaitable<T, Executor>>
+{
+  typedef void type(std::exception_ptr, T);
+};
+
+template <typename Executor>
+struct awaitable_signature<awaitable<void, Executor>>
+{
+  typedef void type(std::exception_ptr);
+};
+
+} // namespace detail
+
+/// Spawn a new thread of execution.
+/**
+ * The entry point function object @c f must have the signature:
+ *
+ * @code awaitable<void, E> f(); @endcode
+ *
+ * where @c E is convertible from @c Executor.
+ */
+template <typename Executor, typename F, typename CompletionToken>
+BOOST_ASIO_INITFN_RESULT_TYPE(CompletionToken,
+    typename detail::awaitable_signature<typename result_of<F()>::type>::type)
+co_spawn(const Executor& ex, F&& f, CompletionToken&& token,
+    typename enable_if<
+      is_executor<Executor>::value
+    >::type* = 0);
+
+/// Spawn a new thread of execution.
+/**
+ * The entry point function object @c f must have the signature:
+ *
+ * @code awaitable<void, E> f(); @endcode
+ *
+ * where @c E is convertible from @c ExecutionContext::executor_type.
+ */
+template <typename ExecutionContext, typename F, typename CompletionToken>
+BOOST_ASIO_INITFN_RESULT_TYPE(CompletionToken,
+    typename detail::awaitable_signature<typename result_of<F()>::type>::type)
+co_spawn(ExecutionContext& ctx, F&& f, CompletionToken&& token,
+    typename enable_if<
+      is_convertible<ExecutionContext&, execution_context&>::value
+    >::type* = 0);
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#include <boost/asio/impl/co_spawn.hpp>
+
+#endif // defined(BOOST_ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
+
+#endif // BOOST_ASIO_CO_SPAWN_HPP