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+//
+// detail/std_global.hpp
+// ~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 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_DETAIL_STD_GLOBAL_HPP
+#define ASIO_DETAIL_STD_GLOBAL_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if defined(ASIO_HAS_STD_CALL_ONCE)
+
+#include <exception>
+#include <mutex>
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+template <typename T>
+struct std_global_impl
+{
+ // Helper function to perform initialisation.
+ static void do_init()
+ {
+ instance_.ptr_ = new T;
+ }
+
+ // Destructor automatically cleans up the global.
+ ~std_global_impl()
+ {
+ delete ptr_;
+ }
+
+ static std::once_flag init_once_;
+ static std_global_impl instance_;
+ T* ptr_;
+};
+
+template <typename T>
+std::once_flag std_global_impl<T>::init_once_;
+
+template <typename T>
+std_global_impl<T> std_global_impl<T>::instance_;
+
+template <typename T>
+T& std_global()
+{
+ std::call_once(std_global_impl<T>::init_once_, &std_global_impl<T>::do_init);
+ return *std_global_impl<T>::instance_.ptr_;
+}
+
+} // namespace detail
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // defined(ASIO_HAS_STD_CALL_ONCE)
+
+#endif // ASIO_DETAIL_STD_GLOBAL_HPP