Invalid Page Fault in Wappc32.dll Using WinAPPCSetBlockingHook

• Microsoft SNA Server, versions 2.11, 2.11 Service Pack 1 (SP1), 2.11 Service Pack 2 (SP2), 3.0, 3.0 Service Pack 1 (SP1), and 3.0 Service Pack 2 (SP2)

SYMPTOMS

A 32-bit APPC application that initiates multiple conversations and uses the WinAPPCSetBlockingHook() call causes a general protection fault (GP fault) in Wappc32.dll on a computer running Windows 95 and using the SNA Server Client for Windows 95. The GP fault will be similar to the following:

   This program has performed an illegal operation and will be shut down.

   If the problem persists, contact the program vendor.

   <Program Name> caused an invalid page fault in module WAPPC32.DLL at
   <memory location>.

   Registers:

     ..data omitted..

CAUSE

The 32-bit APPC library does not correctly handle the case where the WinAPPCSetBlockingHook() call returns FALSE on multiple threads.

WORKAROUND

If the WinAPPCSetBlockingHook() call is being used to cancel one conversation when the MC_ALLOCATE() takes too long. The application should call WinAPPCCancelBlockingCall() from within the WinAPPCSetBlockingHook() call. If this is done, the WinAPPCSetBlockingHook() call would continue to return TRUE instead of FALSE.

Another alternative is to have the application use the Asynchronous APPC API and the WinAPPCCancelAsyncRequest() call.

Please refer to the SNA Server "APPC Programmer's Guide" for more details on the APPC functions mentioned in this article.

STATUS

Microsoft has confirmed this to be a problem in SNA Server versions 2.11, 2.11 Service Pack 1, 2.11 Service Pack 2, 3.0, 3.0 Service Pack 1, 3.0 Service Pack 2.

The 32-bit APPC library has been updated to correctly handle cases where a WinAPPCSetBlockingHook() call returns FALSE. The updated module is Wappc32.dll. A supported fix is now available, but has not been fully regression tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Technical Support for more information.