CoInitialize()、CoInitializeEx()和AfxOleInit()区别联系

CoInitialize()和AfxOleInit()

都是初始化COM库,不同之处在与:

OLE是建立在COM之上的技术,层次比COM要高。AfxOleInit()调用的是OleInitialize(),而 OleInitialize()除了调用CoInitializeEx()来初始化COM库外,还进行一些其它的操作,这些操作对OLE应用来说是必须的,这些OLE应用包括:  
    (1)Clipboard;  
    (2)Drag   and   drop;  
    (3)Object   linking   and   embedding(现在的OLE,已不再仅仅是Object   linking   and   embedding的概念);  
    (4)In-place   activation;  
    与AfxOleInit()对应的是,AfxOleTerm()。  

    AfxOleInit()和AfxOleTerm()其实也是需要成对的,但是,在你的程序中,AfxOleTerm()可以不出现,这是因为,MFC已经帮你做好了(有兴趣的话,你可以仔细研究一下CWinThread::m_lpfnOleTermOrFreeLib,而CWinApp是从CWinThread继承的)。

注:但是当你的函数出现了重复调用AfxOleInit()时间便不能依靠mfc自动调用了,需要显式的调用AfxOleTerm清理com库

 

CoInitialize与AfxOleInit

使用MFC的控制台主程序中如果用AfxOleInit()初始化com就会出现DLL中调用wordApp.CreateDispatch("Word.Application",NULL)失败,而改用用CoInitialize()则会成功

在AfxOleInit()函数中设置断点调试之后可以知道:afxContextIsDLL这个标志的值为ture,因而它并不会去调用OleInitialize,进而不会调用CoInitialize.

MSDN(If AfxOleInit is called from an MFC DLL, the call will fail. The failure occurs because the function assumes that, if it is called from a DLL, the OLE system was previously initialized by the calling application.) 看来在这个函数中把当前项目当做DLL来处理了.^_^,不知是不是MFC本身的bug

 1 BOOL AFXAPI AfxOleInit()
 2 {
 3     _AFX_THREAD_STATE* pState = AfxGetThreadState();
 4     ASSERT(!pState->m_bNeedTerm);    // calling it twice?
 5 
 6     // Special case DLL context to assume that the calling app initializes OLE.
 7     // For DLLs where this is not the case, those DLLs will need to initialize
 8     // OLE for themselves via OleInitialize.  This is done since MFC cannot provide
 9     // automatic uninitialize for DLLs because it is not valid to shutdown OLE
10     // during a DLL_PROCESS_DETACH.
11     if (afxContextIsDLL)
12     {
13         pState->m_bNeedTerm = -1;  // -1 is a special flag
14         return TRUE;
15     }
16 
17     // first, initialize OLE
18     SCODE sc = ::OleInitialize(NULL);
19     if (FAILED(sc))
20     {
21         // warn about non-NULL success codes
22 #ifdef _DEBUG
23         TRACE(traceOle, 0, _T("Warning: OleInitialize returned scode = %s.\n"),
24             AfxGetFullScodeString(sc));
25 #endif
26         goto InitFailed;
27     }
28     // termination required when OleInitialize does not fail
29     pState->m_bNeedTerm = TRUE;
30 
31     // hook idle time and exit time for required OLE cleanup
32     CWinThread* pThread; pThread = AfxGetThread();
33     ASSERT(pThread);
34     pThread->m_lpfnOleTermOrFreeLib = AfxOleTermOrFreeLib;
35 
36     // allocate and initialize default message filter
37     if (pThread->m_pMessageFilter == NULL)
38     {
39         pThread->m_pMessageFilter = new COleMessageFilter;
40         ASSERT(AfxOleGetMessageFilter() != NULL);
41         AfxOleGetMessageFilter()->Register();
42     }
43     return TRUE;
44 
45 InitFailed:
46     AfxOleTerm();
47     return FALSE;
48 }

 

 

COM中CoInitializeEx 与CoInitialize的区别

CoInitialize、CoInitializeEx都是windows的API,主要是告诉windows以什么方式为程序创建COM对象,原因是程序调用com库函数(除CoGetMalloc和内存分配函数)之前必须初始化com库。
    CoInitialize指明以单线程方式创建。
    CoInitializeEx可以指定COINIT_MULTITHREADED以多线程方式创建。
    创建单线程方式的COM服务器时不用考虑串行化问题,多线程COM服务器就要考虑。

    CoInitialize并不装载com库,这个函数只是用来初始化当前线程使用什么样的套间。当使用这个函数以后,线程就和一个套间建立了对应关系。
    线程的套间模式决定了该线程如何调用com对象,是否需要列集等

    套间是com中用来解决并发调用冲突的很有效的办法
    Before calling any COM functions, a thread needs to call CoInitialize to load the COM infrastructure (and to enter an apartment). Once a thread calls CoInitialize, the thread is free to call COM APIs.

    CoInitializeEx provides the same functionality as CoInitialize and also provides a parameter to explicitly specify the thread's concurrency model. The current implementation of CoInitialize calls CoInitializeEx and specifies the concurrency model as single-thread apartment. Applications developed today should call CoInitializeEx rather than CoInitialize.

    注:新的应用程序应该调用CoInitializeEx而不是CoInitialize,否则就会有必要在之后每个调用Com的线程中调用CoInitialize来初始化出每个线程自己的套间。

 

posted @ 2013-11-29 14:54  木有Some  阅读(1408)  评论(0编辑  收藏  举报