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Singleton.hpp

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 * This file is part of openWNS (open Wireless Network Simulator)
 * _____________________________________________________________________________
 *
 * Copyright (C) 2004-2007
 * Chair of Communication Networks (ComNets)
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 * fax: ++49-241-80-22242
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 * www: http://www.openwns.org
 * _____________________________________________________________________________
 *
 * openWNS is free software; you can redistribute it and/or modify it under the
 * terms of the GNU Lesser General Public License version 2 as published by the
 * Free Software Foundation;
 *
 * openWNS is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 * A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
 * details.
 *
 * You should have received a copy of the GNU Lesser General Public License
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#ifndef WNS_SINGLETON_HPP
#define WNS_SINGLETON_HPP

#include <assert.h>
#include <cstdlib>
#include <WNS/NonCopyable.hpp>
#include <WNS/simulator/ISimulator.hpp>

namespace wns {

    struct AtSimulatorExit
    {
        static void
        scheduleDestruction(void (*functionPtr)())
        {
            wns::simulator::getShutdownSignal()->connect(functionPtr);
        }
    };

    struct AtApplicationExit
    {
        static void
        scheduleDestruction(void (*functionPtr)())
        {
            std::atexit(functionPtr);
        }
    };

    template <class T>
    struct DefaultCreation
    {
        static T*
        create()
        {
            return new T;
        }

        static void
        destroy(T* p)
        {
            delete p;
        }
    };

    template <class T>
    class SingletonHolderStaticData
    {
    public:
        static T* instance;
        static bool destroyed;
    };

    template<class T>
    T* SingletonHolderStaticData<T>::instance;

    template<class T>
    bool SingletonHolderStaticData<T>::destroyed;

    template<class T, 
        template <class> class CreationPolicy = DefaultCreation, 
        class DestructTimePolicy = AtSimulatorExit>
    class SingletonHolder :
        private NonCopyable
    {
        typedef SingletonHolderStaticData<T> Static;
    public:
        static T&
        Instance()
        {
            if (Static::instance == NULL)
            {
                Static::instance = CreationPolicy<T>::create();
                Static::destroyed = false;

                DestructTimePolicy::scheduleDestruction(&destroySingleton);
            }

            assert(Static::destroyed == false); // using a destroyed singleton

            return *Static::instance;
        }

        static T*
        getInstance()
        {
            return &Instance();
        }

        static void
        reset()
        {
            CreationPolicy<T>::destroy(Static::instance);
            Static::instance = CreationPolicy<T>::create();
        }

    private:
        static void
        destroySingleton()
        {
            assert(Static::destroyed == false); // using a destroyed singleton
            CreationPolicy<T>::destroy(Static::instance);
            Static::instance = NULL;
            Static::destroyed = true;
        }

        SingletonHolder();

        ~SingletonHolder(); // forbidden
    };
}
#endif // NOT defined WNS_SINGLETON_HPP

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