DOCUMENT:Q133312 12-JUN-2001 [sna] TITLE :SNA Server Win 3.x APPC/CPIC Apps Hang Using Blocking Hook PRODUCT :Microsoft SNA Server PROD/VER:WINDOWS:2.0,2.1,2.11,3.0,4.0 OPER/SYS: KEYWORDS:kbnetwork kbprogramming sna4 ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft SNA Server, versions 2.0, 2.1, 2.11, 3.0, 4.0 ------------------------------------------------------------------------------- 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 sna4 Technology : kbAudDeveloper kbSNAServSearch kbSNAServ300 kbSNAServ200 kbSNAServ211 kbSNAServ400 kbSNAServ210 Version : WINDOWS:2.0,2.1,2.11,3.0,4.0 ============================================================================= 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. Copyright Microsoft Corporation 2001.