[原]ACE_Singleton类学习
先看一下源代码。template <class TYPE, class ACE_LOCK>class ACE_Singleton : public ACE_Cleanup
{
public:
/// Global access point to the Singleton.
static TYPE *instance (void);
/// Cleanup method, used by <ace_cleanup_destroyer> to destroy the
/// ACE_Singleton.
virtual void cleanup (void *param = 0);
/// Dump the state of the object.
static void dump (void);
protected:
/// Default constructor.
ACE_Singleton (void);
/// Contained instance.
TYPE instance_;
#if !defined (ACE_LACKS_STATIC_DATA_MEMBER_TEMPLATES)
/// Pointer to the Singleton (ACE_Cleanup) instance.
static ACE_Singleton<TYPE, ACE_LOCK> *singleton_;
#endif /* ACE_LACKS_STATIC_DATA_MEMBER_TEMPLATES */
/// Get pointer to the Singleton instance.
static ACE_Singleton<TYPE, ACE_LOCK> *&instance_i (void);
};
实现文件：
// Singleton.cpp,v 4.54 2005/10/28 16:14:55 ossama Exp
#ifndef ACE_SINGLETON_CPP
#define ACE_SINGLETON_CPP
#include "ace/Singleton.h"
#if !defined (ACE_LACKS_PRAGMA_ONCE)
# pragma once
#endif /* ACE_LACKS_PRAGMA_ONCE */
#if !defined (__ACE_INLINE__)
#include "ace/Singleton.inl"
#endif /* __ACE_INLINE__ */
#include "ace/Object_Manager.h"
#include "ace/Log_Msg.h"
#include "ace/Framework_Component.h"
#include "ace/Guard_T.h"
ACE_RCSID (ace,
Singleton,
"Singleton.cpp,v 4.54 2005/10/28 16:14:55 ossama Exp")
ACE_BEGIN_VERSIONED_NAMESPACE_DECL
template <class TYPE, class ACE_LOCK> void
ACE_Singleton<TYPE, ACE_LOCK>::dump (void)
{
#if defined (ACE_HAS_DUMP)
ACE_TRACE ("ACE_Singleton<TYPE, ACE_LOCK>::dump");
#if !defined (ACE_LACKS_STATIC_DATA_MEMBER_TEMPLATES)
ACE_DEBUG ((LM_DEBUG,ACE_LIB_TEXT ("instance_ = %x"),
ACE_Singleton<TYPE, ACE_LOCK>::instance_i ()));
ACE_DEBUG ((LM_DEBUG, ACE_END_DUMP));
#endif /* ACE_LACKS_STATIC_DATA_MEMBER_TEMPLATES */
#endif /* ACE_HAS_DUMP */
}
template <class TYPE, class ACE_LOCK> ACE_Singleton<TYPE, ACE_LOCK> *&
ACE_Singleton<TYPE, ACE_LOCK>::instance_i (void)
{
#if defined (ACE_LACKS_STATIC_DATA_MEMBER_TEMPLATES)
// Pointer to the Singleton instance.This works around a bug with
// G++ and it's (mis-)handling of templates and statics...
static ACE_Singleton<TYPE, ACE_LOCK> *singleton_ = 0;
return singleton_;
#else
return ACE_Singleton<TYPE, ACE_LOCK>::singleton_;
#endif /* ACE_LACKS_STATIC_DATA_MEMBER_TEMPLATES */
}
template <class TYPE, class ACE_LOCK> TYPE *
ACE_Singleton<TYPE, ACE_LOCK>::instance (void)
{
ACE_TRACE ("ACE_Singleton<TYPE, ACE_LOCK>::instance");
ACE_Singleton<TYPE, ACE_LOCK> *&singleton =
ACE_Singleton<TYPE, ACE_LOCK>::instance_i ();
// Perform the Double-Check pattern...
if (singleton == 0)
{
if (ACE_Object_Manager::starting_up () ||
ACE_Object_Manager::shutting_down ())
{
// The program is still starting up, and therefore assumed
// to be single threaded.There's no need to double-check.
// Or, the ACE_Object_Manager instance has been destroyed,
// so the preallocated lock is not available.Either way,
// don't register for destruction with the
// ACE_Object_Manager:we'll have to leak this instance.
ACE_NEW_RETURN (singleton, (ACE_Singleton<TYPE, ACE_LOCK>), 0);
}
else
{
#if defined (ACE_MT_SAFE) && (ACE_MT_SAFE != 0)
// Obtain a lock from the ACE_Object_Manager.The pointer
// is static, so we only obtain one per ACE_Singleton
// instantiation.
static ACE_LOCK *lock = 0;
if (ACE_Object_Manager::get_singleton_lock (lock) != 0)
// Failed to acquire the lock!
return 0;
ACE_GUARD_RETURN (ACE_LOCK, ace_mon, *lock, 0);
if (singleton == 0)
{
#endif /* ACE_MT_SAFE */
ACE_NEW_RETURN (singleton, (ACE_Singleton<TYPE, ACE_LOCK>), 0);
// Register for destruction with ACE_Object_Manager.
ACE_Object_Manager::at_exit (singleton);
#if defined (ACE_MT_SAFE) && (ACE_MT_SAFE != 0)
}
#endif /* ACE_MT_SAFE */
}
}
return &singleton->instance_;
}
template <class TYPE, class ACE_LOCK> void
ACE_Singleton<TYPE, ACE_LOCK>::cleanup (void *)
{
delete this;
ACE_Singleton<TYPE, ACE_LOCK>::instance_i () = 0;
}
#if !defined (ACE_LACKS_STATIC_DATA_MEMBER_TEMPLATES)
// Pointer to the Singleton instance.
template <class TYPE, class ACE_LOCK> ACE_Singleton<TYPE, ACE_LOCK> *
ACE_Singleton<TYPE, ACE_LOCK>::singleton_ = 0;
class ACE_Singleton : public ACE_Cleanup 继承了ACE_Cleanup，这个类自动完成了对对象的清理工作。就是实现了
template <class TYPE, class ACE_LOCK> voidACE_Singleton<TYPE, ACE_LOCK>::cleanup (void *){delete this;ACE_Singleton<TYPE, ACE_LOCK>::instance_i () = 0;}
还有就是对程序的使用了ACE_Object_Manager 释放程序的实例。
ACE_Object_Manager::at_exit (singleton);
因此当你使用ACE_Singleton 大可以放心的使用，对象管理ACE经过自己的方法和类已经很好的解决了。
总之，不管他如何实现，我们完全就是直接简单的使用。
typedef ACE_Singleton<Class, ACE_Null_Mutex> instance;
更多文章，欢迎访问：http://blog.csdn.net/wallwind
ACE_Singleton对象的实例化和删除都处在你的程序、而不是平台的运行时环境的控制之下。和Boost的Singleton有所区别。:)
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