Problems when initialise COM in MFC SDI App with CoInitializeEx

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I have a MFC SDI GUI application in which I have a CMyApp member variable set at start-up which requires a COM interface.

So, in CMyApp::InitInstance() I have called:

CoInitializeEx(NULL, COINIT_MULTITHREADED);

However, when I shut down the app it crashes.

If I use

CoInitializeEx(NULL, COINIT_APARTMENTTHREADED)

it is fine.

Can anyone please tell me what the problem is? I have used

CoInitializeEx(NULL, COINIT_MULTITHREADED)

elsewhere in the application, e.g. in MyDoc.cpp and it does not cause any problem. I am not using multiple threads so I do not need to use the MULTITHREADED version, but i don't understand why it is causing the crash at shutdown (when it is trying to release an m_pInterace in the depths of microsoft's code).

Also, is CMyApp::InitInstance() the best place to initialise a member variable for the GUI that is not related to a document that is viewed. It stores an XMLDOMDocPtr to a file that contains a file path to some information that is used behind the GUI.

Many thanks.

Posted 20-Sep-11 23:56pm

Jackie Lloyd

Updated 21-Sep-11 0:13am

v2

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tolw · Answer 1 · 2011-09-21T00:34:00

The first thing to do would be to check what the call returns. You can find more details here[^] but the simple explanation is: you should only call CoUninitialise if your call to CoInitialize SUCCEEDED:
"To close the COM library gracefully on a thread, each successful call to CoInitialize or CoInitializeEx, including any call that returns S_FALSE, must be balanced by a corresponding call to CoUninitialize."

My guess would be that the XMLDOMDocPtr calls CoInitialize with the APARTMENTTHREADED model and you get a RPC_E_CHANGED_MODE from your call. If this is the case you should not call CoUninitialize.