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

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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.