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Q133312: SNA Server Win 3.x APPC/CPIC Apps Hang Using Blocking Hook

Article: Q133312
Product(s): Microsoft SNA Server
Version(s): WINDOWS:2.0,2.1,2.11,3.0,4.0
Operating System(s): 
Keyword(s): kbnetwork kbprogramming sna4
Last Modified: 12-JUN-2001

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The information in this article applies to:

- Microsoft SNA Server, versions 2.0, 2.1, 2.11, 3.0, 4.0 
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SUMMARY
=======

When using the SNA Server Windows 3.x client WinAPPCSetBlockingHook() or
WinCPICSetBlockingHook() calls from a Windows 3.x application, the blocking hook
function must call PeekMessage, or the Windows 3.x application will hang.

The SNA Server Windows 3.x CPIC and APPC API interfaces rely on the use of
Windows messages to process an API call on behalf of the calling application. If
the application registers it's own blocking hook function that blocks the
reception of Windows messages, the calling application will hang.

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

The SNA Server Windows 3.x APPC and CPIC interfaces have a default mechanism by
which blocking functions are implemented. This function gives the application
the ability to execute it's own function at blocking time in place of the
default function.

The default blocking function, documented in the SNA Server APPC and CPIC API
references (under WinCPICSetBlockingHook and WinAPPCSetBlockingHook) is
equivalent to:

     BOOL DefaultBlockingHook ( void ) {
        MSG msg;
        /*  get the next message if any */ 
        if ( PeekMessage ( &msg, NULL, 0, 0, PM_NOREMOVE) ) {
           if ( msg.message = WM_QUIT )
              return FALSE;   // let app process WM_QUIT
           PeekMessage ( &msg, NULL, 0, 0, PM_REMOVE) ;
           TranslateMessage (&msg) ;
           DispatchMessage (&msg) ;
       }
       /* TRUE if no WM_QUIT received */ 
       return TRUE;
     }

NOTE: The SNA Server 2.1 APPC and CPIC API references incorrectly omit the second
parameter on the PeekMessage call above (the NULL parameter).

The NULL (window handle) is critical here in order for the underlying SNA client
software to receive and process the Windows messages necessary to support the
API calls being made.

Additional query words: prodsna

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Keywords          : kbnetwork kbprogramming sna4 
Technology        : kbAudDeveloper kbSNAServSearch kbSNAServ300 kbSNAServ200 kbSNAServ211 kbSNAServ400 kbSNAServ210
Version           : WINDOWS:2.0,2.1,2.11,3.0,4.0

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