// singleton.hh - Copyright 2005, 2006, University
//               of Padova, dept. of Pure and Applied
//               Mathematics
//
// 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 2 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, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

#ifndef SINGLETON_HH
#define SINGLETON_HH 1

#include <glibmm/thread.h>
#include "config.h"

namespace sgpem
{

  /** \brief An abstract implementation of the Singleton design pattern.
   * 
   * Singleton implementers constuctor will have to declare friendliness 
   * to Singleton::get_instance(). This also attempts to achieve 
   * thread-safeness.
   */
  template<typename Instantiated_class>
  class SG_DLLEXPORT Singleton
  {
  public:

    /** \brief Ensures thread safety is respected, and returns the instantiated object
     *
     * This is done by locking _instance via a mutex, before intantiating the 
     * Instantiated_class attribute (if not done before).
     *
     * \return The instantiated object
     */
    static Instantiated_class& get_instance();

  protected:
    static Glib::RecMutex SG_DLLLOCAL _mutex;

  private:
    static SG_DLLLOCAL Instantiated_class* _instance;
  }
  ; //~ class Singleton

} //~ namespace sgpem

#endif //~ SINGLETON_HH

