Singleton.h

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/*
 Copyright (2016) Michael Baer, Daniel Bonrath, All rights reserved.

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at

 http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 */

#ifndef __M2ETIS_UTIL_SINGLETON_H__
#define __M2ETIS_UTIL_SINGLETON_H__

#include "m2etis/util/SystemParameters.h"

#include "boost/interprocess/sync/scoped_lock.hpp"
#include "boost/thread.hpp"

namespace m2etis {
namespace util {

        template<typename T>
        class Singleton {
        public:
                static inline T * GetSingletonPtr() {
                        Init();

                        return _ptrSingleton;
        }

                static inline T & GetSingleton() {
                        Init();

            return *_ptrSingleton;
        }

        protected:
                Singleton() {}
        virtual ~Singleton() {
                        boost::unique_lock<boost::mutex> lock(_objMutex);
                if (_ptrSingleton != NULL) {
                        delete _ptrSingleton;
                        _ptrSingleton = NULL;
                }
        }
                static T * _ptrSingleton;
                static boost::mutex _objMutex;

        private:
                static void Init() {
                        // Double check to avoid overhead locking
                        if (!_ptrSingleton) {
                                // no need to unlock, because the destructor of boost::unique_lock does this for us
                                boost::unique_lock<boost::mutex> lock(_objMutex);
                                if (!_ptrSingleton) {
                                        _ptrSingleton = new T();
                                }
                        }
                }

                Singleton(const Singleton &) {}
                const Singleton& operator=(const Singleton &) { return *this; }
        };

        template<typename T> T * Singleton<T>::_ptrSingleton = nullptr;
    template<typename T> boost::mutex  Singleton<T>::_objMutex;

} /* namespace util */
} /* namespace m2etis */

#endif /* __M2ETIS_UTIL_SINGLETON_H__ */