singleton.h

设计模式模板源码

/* -*- C++ -*- */


#ifndef _XP_SINGLETON_H
#define _XP_SINGLETON_H

/**
 * @class Singleton
 *
 * If you want to make sure that only the singleton instance of
 * <T> is created, and that users cannot create their own
 * instances of <T>, do the following to class <T>:
 * (a) Make the constructor of <T> private (or protected)
 * (b) Make Singleton a friend of <T>
 * Here is an example:
 * class foo
 * {
 * friend class Singleton<foo>;
 * private:
 * foo () { cout << "foo constructed" << endl; }
 * ~foo () { cout << "foo destroyed" << endl; }
 * };
 * typedef Singleton<foo> FOO;
 *
 */

template <typename TYPE,typename _A = std::allocator<TYPE> > 
class Singleton
{
public:
  /// Global access point to the Singleton.
  static TYPE *instance (void)
  {
	Singleton<TYPE> &singleton = Singleton<TYPE>::instance_i ();

	if (singleton.instance_ == 0)
	{
		_A a; 
		singleton.instance_ = a.allocate(1, NULL); 
		a.construct(singleton.instance_, TYPE()); 
	}

	return singleton.instance_;
  }
  /// Explicitly delete the Singleton instance.
  static void close (void)
  {
	Singleton<TYPE> &singleton = Singleton<TYPE>::instance_i ();	
	if (singleton.instance_) 
	{
		_A a; 
		a.destroy(singleton.instance_ );
		a.deallocate(singleton.instance_ , 1);
	}
  }
  
protected:
  

  /// Contained instance.
  TYPE *instance_;

  /// Get pointer to the Singleton instance.
  static Singleton<TYPE> &instance_i (void)
  {
	  static Singleton<TYPE> singleton_;
	  return singleton_;
	  
  }
  
};


#endif /* _XP_SINGLETON_H */