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include/asio/detail/std_global.hpp

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+//
+// detail/std_global.hpp
+// ~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 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"
+#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 // ASIO_DETAIL_STD_GLOBAL_HPP