KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q196836: PRB: MFC Socket Functions Fail from ExitInstance

Article: Q196836
Product(s): Microsoft C Compiler
Version(s): winnt:4.0,4.1,4.2,5.0,6.0
Operating System(s): 
Keyword(s): kbDLL kbMFC kbVC400 kbVC410 kbVC420 kbVC500 kbVC600 kbWinsock kbGrpDSMFCATL
Last Modified: 17-JUL-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

When you call MFC socket functions from ExitInstance of a DLL, the functions may
fail and return an error.

CAUSE
=====

In an MFC DLL, the CWinApp::ExitInstance function is called from the DllMain
function in response to the DLL_PROCESS_DETACH case.

The MFC socket functions call the WinSock APIs implemented in wsock32.dll. When
an application shuts down, the DllMain with DLL_PROCESS_DETACH of the WinSock
DLL may be called before the DllMain of the MFC regular DLL. This can cause some
process specific information to be lost.

NOTE: This problem applies to non-MFC DLLs and non-MFC sockets as well.

RESOLUTION
==========

Do not call socket functions from CWinApp::ExitInstance (DLL_PROCESS_DETACH).
Provide a cleanup function that the application can call to perform the last
socket functions.

STATUS
======

This behavior is by design.

MORE INFORMATION
================

A common mistake is to call the CSocket::Close (or CAsyncSocket::Close) function
in CWinApp::ExitInstance. This can generate an assertion in sockcore.cpp line
856 in Microsoft Visual C++ 5.0, and line 667 in Microsoft Visual C++ 6.0.

(c) Microsoft Corporation 1998, All Rights Reserved. Contributions by Adam Kim,
Microsoft Corporation.


Additional query words:

======================================================================
Keywords          : kbDLL kbMFC kbVC400 kbVC410 kbVC420 kbVC500 kbVC600 kbWinsock kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:4.0,4.1,4.2,5.0,6.0
Issue type        : kbprb

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.