CPIC/APPC Program May Hang Opening a Dependent APPC Session

• Microsoft SNA Server for Windows NT, versions 2.0, 2.1, and 2.11

SYMPTOMS

Under SNA Server 2.0 or 2.1, when a CPIC or APPC application allocates a dependent LU6.2 session where the dependent APPC LU is defined in SNA Server Admin to be a "Member of Default Outgoing Local APPC LU Pool", the allocate request may hang. Within an APPC application, the call to [MC_]ALLOCATE may not return. Within a CPIC application, the call to CMINIT may not return (since CPIC runs over APPC, the underlying APPC [MC_]ALLOCATE hangs).

CAUSE

SNA Server 2.0 and 2.1 do not correctly implement pooling of dependent APPC LU's, however, the SNA Server Admin program does not prevent it. The problem doesn't occur if independent APPC LU's are configured to be a member of the default outgoing APPC LU pool.

With dependent APPC LU's, SNA Server may have allocated the dependent APPC LU/LU session to another APPC or CPIC application. If a second APPC or CPIC application attempts to open the same dependent APPC LU (which can occur if a dependent APPC LU is configured to be a member of the default APPC LU pool), the second application's [MC_]ALLOCATE call will hang until the session becomes available.

RESOLUTION

This problem is fixed in SNA Server 2.11. The fix involves changes to the server and the client software, so both ends must be updated to SNA Server 2.11.

To solve the problem on SNA Server 2.0 or 2.1, each CPIC or APPC application must use a unique dependent Local APPC LU.

For an APPC application, the application must be predefined to use a specific dependent Local APPC LU alias. If the Local LU alias is left blank, the default Local APPC LU can be associated to a user or group within the "Users and Groups" window of SNA Server Admin.

For a CPIC application, the Local APPC LU alias must be preset within SNA Server by either:

   Defaulting the user/group to use a specific Local APPC LU alias:

      Within the "Users and Groups" window of SNA Admin, the user or group
      record can be configured with a default Local and Remote APPC LU
      aliases.

   -or-

   Defaulting the workstation to use a specific Local APPC LU alias:

      The SNA Server client software can be defined with a default Local
      APPC LU alias, as described in the CPI-C API section of Appendix C in
      the SNA Server Reference Guide:

         Windows NT clients (within the Registry):

            HKEY_LOCAL_MACHINE
             \SYSTEM
               \CurrentControlSet
                 \Services
                   \SnaBase
                     \Parameters
                       \Client

            application: REG_SZ: localLUalias

         Win 3.x clients (within WIN.INI) or OS/2 clients (within SNA.INI):

            [ApplicationName]
            APPCLLU=localLUalias

            where application is the name of the CPIC application (without
            the .EXE extension).