Microsoft KB Archive/133312

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

Article ID: 133312

Article Last Modified on 2/11/2004

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APPLIES TO


 * Microsoft SNA Server 2.0
 * Microsoft SNA Server 2.1
 * Microsoft SNA Server 3.0
 * Microsoft SNA Server 3.0 Service Pack 4
 * Microsoft SNA Server 4.0

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This article was previously published under Q133312



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

Keywords: kbnetwork kbprogramming KB133312

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