使用ACE的Singleton(单体)设计模式的简捷方式

peakzhang

Singleton设计模式最简单,也用得常见, 下面是经典的使用示例:

1. * Here is an example:
2. * @verbatim
3. * class foo
4. * {
5. * friend class ACE_Singleton<foo, ACE_Null_Mutex>;
6. * private:
7. * foo () { cout << "foo constructed" << endl; }
8. * ~foo () { cout << "foo destroyed" << endl; }
9. * };
10. * typedef ACE_Singleton<foo, ACE_Null_Mutex> FOO;
11. * @endverbatim
12. *

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其实,还有一种更简单的方式,在JAWS3中用得更常见
下面是其中一例:

2. class JAWS_Export JAWS_Concurrency
3.   : public JAWS_Concurrency_Bridge<JAWS_CONCURRENCY_CONCRETE_IMPL>
4. {
5. public:
6.   static JAWS_Concurrency * instance (void)
7.   {
8.     return ACE_Singleton<JAWS_Concurrency, ACE_SYNCH_MUTEX>::instance ();
9.   }
10. };

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peakzhang

不错，但不知道有没有测试在不同dll中这个单体是否能正常工作呢？

我的意思是，在a.DLL中做了一个单体类A，

然后在b.dll和c.dll中使用这个单体类，然后在同一进程内调用b.dll和c.dll，

A这个单体是只有一个实例吗？

我以前一直用的楼主的第一种使用方式来做单体，但发现在我说的情况下，不能保证A只有一个实例！

peakzhang

Q:

How do I instantiate a singleton from a DLL?

A:

Singletons in DLLs on Windows If you want to instantiate a singleton in a DLL on Windows, follow these steps: Use generate_export_file.pl (found in ACE_wrappers/bin) to generate the proper Win32 export directives for your dll. For example, "perl generate_export_file.pl MyLib >MyLib_Export.h" generates the following output in the file "MyLib_Export.h":   // -*- C++ -*-   // generate_export_file.pl,v 1.8 2001/03/04 09:16:29 nanbor Exp   // Definition for Win32 Export directives.   // This file is generated automatically by generate_export_file.pl   // ------------------------------   #ifndef MYLIB_EXPORT_H   #define MYLIB_EXPORT_H   #include "ace/config-all.h"   #if !defined (MYLIB_HAS_DLL)   #  define MYLIB_HAS_DLL 1   #endif /* ! MYLIB_HAS_DLL */   #if defined (MYLIB_HAS_DLL) && (MYLIB_HAS_DLL == 1)   #  if defined (MYLIB_BUILD_DLL)   #    define MyLib_Export ACE_Proper_Export_Flag   #    define MYLIB_SINGLETON_DECLARATION(T)                 ACE_EXPORT_SINGLETON_DECLARATION (T)   #    define MYLIB_SINGLETON_DECLARE(SINGLETON_TYPE, CLASS, LOCK)                 ACE_EXPORT_SINGLETON_DECLARE(SINGLETON_TYPE, CLASS, LOCK)   #  else /* MYLIB_BUILD_DLL */   #    define MyLib_Export ACE_Proper_Import_Flag   #    define MYLIB_SINGLETON_DECLARATION(T)                 ACE_IMPORT_SINGLETON_DECLARATION (T)   #    define MYLIB_SINGLETON_DECLARE(SINGLETON_TYPE, CLASS, LOCK)                 ACE_IMPORT_SINGLETON_DECLARE(SINGLETON_TYPE, CLASS, LOCK)   #  endif /* MYLIB_BUILD_DLL */   #else /* MYLIB_HAS_DLL == 1 */   #  define MyLib_Export   #  define MYLIB_SINGLETON_DECLARATION(T)   #  define MYLIB_SINGLETON_DECLARE(SINGLETON_TYPE, CLASS, LOCK)   #endif /* MYLIB_HAS_DLL == 1 */   #endif /* MYLIB_EXPORT_H */   // End of auto generated file. When declaring your singleton, make sure and use the right export directive that you generated for your dll. For instance, if you create a class that is meant to be a singleton in MyLib.dll, you'd typically do this:   class MyLib_Export MyClass   {   };   typedef ACE_Singleton<MyClass, ACE_Null_Mutex> MY_CLASS_SINGLETON;   MYLIB_SINGLETON_DECLARE(ACE_Singleton, MyClass, ACE_Null_Mutex);

[ 本帖最后由 peakzhang 于 2008-1-15 21:26 编辑 ]