singleton.h

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
 
#ifndef COMMON_SINGLETON_H
#define COMMON_SINGLETON_H
 
#include "common/noncopyable.h"
 
namespace Common {
 
template<class T>
class Singleton : NonCopyable {
private:
    Singleton(const Singleton&);
    Singleton &operator=(const Singleton &);
 
    //template<class T>
#if defined(__WINS__)
//FIXME verify if __WINS__ needs this still
public:
#endif
    static T *makeInstance() {
        return new T();
    }
 
    static void destroyInstance() {
        delete _singleton;
        _singleton = 0;
    }
 
 
public:
    static bool hasInstance() {
        return _singleton != 0;
    }
 
    static T& instance() {
        // TODO: We aren't thread safe. For now we ignore it since the
        // only thing using this singleton template is the config manager,
        // and that is first instantiated long before any threads.
        // TODO: We don't leak, but the destruction order is nevertheless
        // semi-random. If we use multiple singletons, the destruction
        // order might become an issue. There are various approaches
        // to solve that problem, but for now this is sufficient
        if (!_singleton)
            _singleton = T::makeInstance();
        return *_singleton;
    }
 
    static void destroy() {
        T::destroyInstance();
    }
protected:
    Singleton()     { }
    virtual ~Singleton()    { }
 
    typedef T   SingletonBaseType;
 
    static T *_singleton;
};
 
#define DECLARE_SINGLETON(T) \
    template<> T *Singleton<T>::_singleton = 0
 
} // End of namespace Common
 
#endif