General refactoring of beast framework classes

modules/beast_core/memory/StaticObject.h

@@ -0,0 +1,197 @@
+//------------------------------------------------------------------------------
+/*
+    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_STATICOBJECT_H_INCLUDED
+#define BEAST_STATICOBJECT_H_INCLUDED
+
+//
+// A full suite of thread-safe objects designed for static storage duration.
+//
+// Wraps an object with a thread-safe initialization preamble so that it can
+// properly exist with static storage duration.
+//
+// Implementation notes:
+//
+//   This is accomplished by omitting the constructor and relying on the C++
+//   specification that plain data types with static storage duration are filled
+//   with zeroes before any other initialization code executes.
+//
+// Spec: N2914=09-0104
+//
+// [3.6.2] Initialization of non-local objects
+//
+//         Objects with static storage duration (3.7.1) or thread storage
+//         duration (3.7.2) shall be zero-initialized (8.5) before any
+//         other initialization takes place.
+//
+// Requirements:
+//
+//  Object must be constructible without parameters.
+//  The StaticObject must be declared with static storage duration or
+//    the behavior is undefined.
+//
+// Usage example:
+//
+// Object* getInstance ()
+// {
+//   static StaticObject <Object> instance;
+//   return instance->getObject ();
+// }
+//
+
+namespace Static
+{
+
+//------------------------------------------------------------------------------
+
+// Holds an object with static storage duration.
+// The owner determines if and when the object is constructed and destroyed.
+// Caller is responsible for synchronization.
+//
+template <class ObjectType, class Tag>
+class Storage
+{
+public:
+    static inline void construct ()
+    {
+        new (getObjectPtr ()) ObjectType;
+    }
+
+    static inline void destroy ()
+    {
+        getObjectPtr ()->~ObjectType ();
+    }
+
+    static inline ObjectType* getObjectPtr ()
+    {
+        return reinterpret_cast <ObjectType*> (s_storage);
+    }
+
+    static inline ObjectType& getObject ()
+    {
+        return *getObjectPtr ();
+    }
+
+    inline ObjectType* operator-> () const
+    {
+        return getObjectPtr ();
+    }
+
+    inline ObjectType& operator* () const
+    {
+        return getObject ();
+    }
+
+    inline operator ObjectType* () const
+    {
+        return getObjectPtr ();
+    }
+
+    // TODO: Crashes on iOS if not accessed before usage
+    static char s_storage [sizeof (ObjectType)];
+
+private:
+};
+
+template <class ObjectType, class Tag>
+char Storage <ObjectType, Tag>::s_storage [sizeof (ObjectType)];
+
+}
+
+//------------------------------------------------------------------------------
+
+namespace detail
+{
+
+extern void staticObjectWait (std::size_t n);
+
+}
+
+/** Wrapper to produce an object with static storage duration.
+    
+    The object is constructed in a thread-safe fashion when the get function
+    is first called. Note that the destructor for Object is never called. To
+    invoke the destructor, use the AtExitHook facility (with caution).
+
+    The Tag parameter allows multiple instances of the same Object type, by
+    using different tags.
+
+    Object must meet these requirements:
+        DefaultConstructible
+
+    @see AtExitHook
+*/
+template <class Object, typename Tag = void>
+class StaticObject
+{
+public:
+    static Object& get ()
+    {
+        StaticData& staticData (StaticData::get());
+
+        if (staticData.state.get() != initialized)
+        {
+            if (staticData.state.compareAndSetBool (initializing, uninitialized))
+            {
+                // Initialize the object.
+                ::new (&staticData.object) Object;
+                staticData.state = initialized;
+            }
+            else
+            {
+                for (std::size_t n = 0; staticData.state.get() != initialized; ++n)
+                {
+                    detail::staticObjectWait (n);
+                }
+            }
+        }
+
+        return staticData.object;
+    }
+
+private:
+    enum
+    {
+        uninitialized = 0,          // must be zero to function properly
+        initializing,
+        initialized
+    };
+
+    // This structure gets zero-filled at static initialization time.
+    // No constructors are called.
+    //
+    class StaticData : public Uncopyable
+    {
+    public:
+        Atomic <int> state;
+        Object object;
+
+        static StaticData& get ()
+        {
+            static uint8 storage [sizeof (StaticData)];
+            return *(reinterpret_cast <StaticData*> (&storage [0]));
+        }
+
+    private:
+        StaticData();
+        ~StaticData();
+    };
+};
+
+#endif