src/pattern/Singleton.h

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/*
 *   MetriVis - Metrics Visualization Application
 *
 *
 *   License notice:
 *
 *   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 _METRIVIS_SINGLETON_H
#define _METRIVIS_SINGLETON_H


#include <boost/thread/mutex.hpp>

namespace metrivis {

template<class T>
class Singleton {

public:

  static T& Instance();

  static void Destroy();

private:
  Singleton();
  Singleton(const Singleton& singleton);
  Singleton& operator=(const Singleton& singleton);
  virtual ~Singleton();


private:
  static T* volatile singleton_instance_;  

  static boost::mutex instance_mutex_;    
};


template<class T>
T* volatile Singleton<T>::singleton_instance_ = 0;

template<class T>
boost::mutex Singleton<T>::instance_mutex_;


template<class T>
T& Singleton<T>::Instance() {
  if( singleton_instance_ == NULL) {
    boost::mutex::scoped_lock lock(instance_mutex_);
    if ( singleton_instance_ == NULL) {
      singleton_instance_ = new T;
    }
  }
  return *singleton_instance_;
}


template<class T>
void Singleton<T>::Destroy() {
  // Lock mutex since it is a critical section.
  boost::mutex::scoped_lock lock(instance_mutex_);

  // Delete the singleton instance.
  if( singleton_instance_ != NULL) {
    delete singleton_instance_;
    singleton_instance_ = NULL;
  }
}

} // namespace metrivis


#endif

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