//
//  "$Id$"
//
//  Copyright (c)1992-2007, ZheJiang Dahua Technology Stock CO.LTD.
//  All Rights Reserved.
//
//	Description:
//	Revisions:		Year-Month-Day  SVN-Author  Modification
//


#ifndef DAHUA_MEMORY_SINGLETON_H__
#define DAHUA_MEMORY_SINGLETON_H__


namespace Dahua {
namespace Memory {
namespace Detail {


// T must be: no-throw default constructible and no-throw destructible
template <typename T>
struct singleton_default
{
  private:
	struct object_creator
	{
	  // This constructor does nothing more than ensure that instance()
	  //  is called before main() begins, thus creating the static
	  //  T object before multithreading race issues can come up.
	  object_creator() { singleton_default<T>::instance(); }
	  inline void do_nothing() const { }
	};
	static object_creator create_object;

	singleton_default();

  public:
	typedef T object_type;

	// If, at any point (in user code), singleton_default<T>::instance()
	//  is called, then the following function is instantiated.
	static object_type & instance()
	{
	  // This is the object that we return a reference to.
	  // It is guaranteed to be created before main() begins because of
	  //  the next line.
	  static object_type obj;

	  // The following line does nothing else than force the instantiation
	  //  of singleton_default<T>::create_object, whose constructor is
	  //  called before main() begins.
	  create_object.do_nothing();

	  return obj;
	}
};
template <typename T>
typename singleton_default<T>::object_creator
singleton_default<T>::create_object;

} // namespace Detail
} // namespace Memory
} // namespace Dahua

#endif // DAHUA_MEMORY_SINGLETON_H__