Add static_initializer

beast/utility/static_initializer.h

@@ -0,0 +1,120 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of Beast: https://github.com/vinniefalco/Beast
+    Copyright 2013, Vinnie Falco <vinnie.falco@gmail.com>
+
+    Permission to use, copy, modify, and/or distribute this software for any
+    purpose  with  or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#ifndef BEAST_UTILITY_STATIC_INITIALIZER_H_INCLUDED
+#define BEAST_UTILITY_STATIC_INITIALIZER_H_INCLUDED
+
+#ifdef _MSC_VER
+
+#include <beast/utility/noexcept.h>
+#include <atomic>
+#include <chrono>
+#include <new>
+#include <thread>
+#include <type_traits>
+
+namespace beast {
+
+/** Returns an object with static storage duration.
+    This is a workaround for Visual Studio 2013 and earlier non-thread
+    safe initialization of function local objects with static storage duration.
+
+    Usage:
+    @code
+    my_class& foo()
+    {
+        static static_initializer <my_class> instance;
+        return *instance;
+    }
+    @endcode
+*/
+template <class T, class Tag = void>
+class static_initializer
+{
+private:
+    T* instance_;
+
+public:
+    template <class... Args>
+    static_initializer(Args&&... args)
+    {
+        static std::aligned_storage <sizeof(T),
+            std::alignment_of <T>::value>::type storage;
+        instance_ = reinterpret_cast<T*>(&storage);
+
+        // double checked lock
+        static bool volatile initialized;
+        if (! initialized)
+        {
+            static std::atomic_flag lock;
+            while (lock.test_and_set())
+                std::this_thread::sleep_for (
+                    std::chrono::milliseconds(10));
+            if (! initialized)
+            {
+                try
+                {
+                    ::new(instance_) T(std::forward<Args>(args)...);
+                    
+                    struct destroyer
+                    {
+                        T* t_;
+
+                        destroyer (T* t)
+                            : t_(t)
+                        {
+                        }
+
+                        ~destroyer()
+                        {
+                            t_->~T();
+                        }
+                    };
+
+                    static destroyer on_exit (instance_);
+                }
+                catch(...)
+                {
+                    lock.clear();
+                    throw;
+                }
+                initialized = true;
+            }
+            lock.clear();
+        }
+    }
+
+    T&
+    get() noexcept
+    {
+        return *instance_;
+    }
+
+    T&
+    operator*() noexcept
+    {
+        return *instance_;
+    }
+};
+
+}
+
+#endif
+
+#endif