Access Violations or Memory Leak May Occur with Tracing Enabled

• Microsoft SNA Server, version 3.0

This article describes the following problems that were found in SNA Server 3.0 and corrected:

1. Enabling SNA Server tracing may cause a process to encounter an access violation.

2. A memory leak may occur when SNA Server tracing is enabled.

3. Link service internal tracing is not fully implemented.

1. Enabling SNA Server tracing may cause a process to encounter an access violation.

SYMPTOMS

When you have enabled SNA Server tracing using the SNATRACE tool, the process that is being traced (for example, SNA Server, SNA Print Service, SnaBase, or link services) may encounter an access violation (AV). If you generate a Drwtsn32.log file, the following failures may occur:

   Exception number: c0000005 (access violation)

   Function: MSVCRT!rmtmp
   FAULT ->779f8bc7 803f00           cmp     byte ptr [edi],0x0

-or-

   Exception number: c0000005 (access violation)

   Function: MSVCRT!_vsnprintf+0x34

   Exception number: 80000003 (hardcoded breakpoint)

   function: DbgBreakPoint
   FAULT ->77f75d64 cc               int     3

CAUSE

The tracing code incorrectly handles a string buffer, which may lead to an access violation. Also, under some timing conditions, if two processes attempt to initialize tracing at the same time, an access violation may occur.

1. A memory leak may occur when SNA Server tracing is enabled.

SYMPTOMS

Enabling SNA Server tracing may lead to an internal memory leak, causing the server to eventually run out of virtual memory. This was observed by setting the trace file size to 10 MB and enabling full tracing on SNA Server, the SNA Print Service, and SNA Application APPC API tracing.

CAUSE

This problem may occur when the disk I/O cannot keep up with trace creation. Memory keeps growing until the system runs out of virtual memory. The solution is to limit the maximum size of the trace buffer pool, which by default is the same size as the multiple of the trace file size chosen in SNATRACE. For example, if the trace file size is 1 MB, (1,000,000, the default), with internal, message and API tracing enabled, the maximum trace buffer pool is 3 x 1 MB = 3 MB.

You can use the following registry setting to define the maximum trace buffer pool size:

   HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/SnaServer/CurrentVersion/Traces/
   MemoryBufferSize: REG_DWORD: <value>

1. Link service tracing is not fully implemented.

SYMPTOMS

When enabling link service full internal tracing using SNATRACE, third- party link trace statements that use the TRACEx macros are not traced to the trace files.

CAUSE

The TRACEx macro statements were not converted to use the new SNA Server 3.0 tracing functions.

RESOLUTION

To resolve these problems, obtain the hotfix mentioned below. The updated modules are:

   <Snaroot>\System\Snatrc.dll
   <Snaroot>\System\Dbgtrace.dll
   <Snaroot>\System\Snalink.dll

STATUS

Microsoft has confirmed this to be a problem in SNA Server version 3.0. This problem was corrected in the latest Microsoft SNA Server 3.0 U.S. Service Pack. For information on obtaining the service pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

   S E R V P A C K