Update boost to 1.71 and add asio

boost/asio/system_context.hpp

@@ -0,0 +1,83 @@
+//
+// system_context.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_SYSTEM_CONTEXT_HPP
+#define BOOST_ASIO_SYSTEM_CONTEXT_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/detail/scheduler.hpp>
+#include <boost/asio/detail/thread_group.hpp>
+#include <boost/asio/execution_context.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+class system_executor;
+
+/// The executor context for the system executor.
+class system_context : public execution_context
+{
+public:
+  /// The executor type associated with the context.
+  typedef system_executor executor_type;
+
+  /// Destructor shuts down all threads in the system thread pool.
+  BOOST_ASIO_DECL ~system_context();
+
+  /// Obtain an executor for the context.
+  executor_type get_executor() BOOST_ASIO_NOEXCEPT;
+
+  /// Signal all threads in the system thread pool to stop.
+  BOOST_ASIO_DECL void stop();
+
+  /// Determine whether the system thread pool has been stopped.
+  BOOST_ASIO_DECL bool stopped() const BOOST_ASIO_NOEXCEPT;
+
+  /// Join all threads in the system thread pool.
+  BOOST_ASIO_DECL void join();
+
+#if defined(GENERATING_DOCUMENTATION)
+private:
+#endif // defined(GENERATING_DOCUMENTATION)
+  // Constructor creates all threads in the system thread pool.
+  BOOST_ASIO_DECL system_context();
+
+private:
+  friend class system_executor;
+
+  struct thread_function;
+
+  // Helper function to create the underlying scheduler.
+  BOOST_ASIO_DECL detail::scheduler& add_scheduler(detail::scheduler* s);
+
+  // The underlying scheduler.
+  detail::scheduler& scheduler_;
+
+  // The threads in the system thread pool.
+  detail::thread_group threads_;
+};
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#include <boost/asio/impl/system_context.hpp>
+#if defined(BOOST_ASIO_HEADER_ONLY)
+# include <boost/asio/impl/system_context.ipp>
+#endif // defined(BOOST_ASIO_HEADER_ONLY)
+
+#endif // BOOST_ASIO_SYSTEM_CONTEXT_HPP