xahaud/modules/beast_basics/memory/beast_StaticObject.h

/*============================================================================*/
/*
  VFLib: https://github.com/vinniefalco/VFLib

  Copyright (C) 2008 by Vinnie Falco <vinnie.falco@gmail.com>

  This library contains portions of other open source products covered by
  separate licenses. Please see the corresponding source files for specific
  terms.

  VFLib is provided under the terms of The MIT License (MIT):

  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:

  The above copyright notice and this permission notice shall be included in
  all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  IN THE SOFTWARE.
*/
/*============================================================================*/

#ifndef BEAST_STATICOBJECT_BEASTHEADER
#define BEAST_STATICOBJECT_BEASTHEADER

#include "../threads/beast_SpinDelay.h"

//
// 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)];

//------------------------------------------------------------------------------

// Provides a thread safe flag for indicating if and when
// initialization is required for an object with static storage duration.
//
class Initializer
{
public:
    /*
    bool inited () const
    {
      return m_state.get () == stateInitialized;
    }
    */

    // If the condition is not initialized, the first caller will
    // receive true, while concurrent callers get blocked until
    // initialization completes.
    //
    bool begin ()
    {
        bool shouldInitialize;

        if (m_state.get () == stateUninitialized)
        {
            if (m_state.compareAndSetBool (stateInitializing, stateUninitialized))
            {
                shouldInitialize = true;
            }
            else
            {
                SpinDelay delay;

                do
                {
                    delay.pause ();
                }
                while (m_state.get () != stateInitialized);

                shouldInitialize = false;
            }
        }
        else
        {
            shouldInitialize = false;
        }

        return shouldInitialize;
    }

    // Called to signal that the initialization is complete
    //
    void end ()
    {
        m_state.set (stateInitialized);
    }

private:
    enum
    {
        stateUninitialized = 0, // must be zero
        stateInitializing,
        stateInitialized
    };

    Atomic <int> m_state;
};

}

#endif