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Q258736: FIX: Multi-Threaded DLL Is Slow to Release Connection Under MTS

Article: Q258736
Product(s): Microsoft FoxPro
Version(s): WINDOWS:6.0
Operating System(s): 
Keyword(s): kbCOMt kbMTS kbvfp600 kbvfp600bug kbGrpDSFox kbDSupport kbVS600sp4fix kbVS600sp4 kbVS60
Last Modified: 20-AUG-2001

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 6.0 
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SYMPTOMS
========

A dynamic-link library (DLL) created with Visual FoxPro and running under
Microsoft Transaction Server is slow to release connections. This behavior
occurs when a DLL is running under Microsoft Transaction Server (MTS) or COM+
with Transaction Support marked as either "Required" or "Requires New."

CAUSE
=====

Releasing a COM server launched from a DLL under MTS or COM+ with Transaction
Support marked as either "Required" or "Requires New," initiates a call to
CoFreeUnusedLibraries. When CoFreeUnusedLibraries is called, COM+ calls the
DllCanUnloadNow function in every COM DLL in the process. If that call returns
TRUE, then COM unloads the DLL.

RESOLUTION
==========

Using Visual FoxPro 6.0 with Microsoft Visual Studio 6.0 Service Pack 4 or
later, add the following line of code to the Init method of the code used to
create the multi-threaded DLL:

  =SYS(2339,0)

STATUS
======

Microsoft has confirmed that this is a bug in the Microsoft products that are
listed at the beginning of this article. This bug was corrected in the latest
service pack for Visual Studio 6.0.

For additional information about Visual Studio service packs, click the following
article numbers to view the articles in the Microsoft Knowledge Base:

  Q194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why

  Q194295 HOWTO: Tell That a Visual Studio Service Pack Is Installed

To download the latest Visual Studio service pack, visit the following Microsoft
Web site:

  http://msdn.microsoft.com/vstudio/downloads/updates.asp

MORE INFORMATION
================

Visual Studio 6.0 Service Pack 4 and later for Visual FoxPro 6.0 include the
SYS(2339) function call. This function call may be used in single-threaded or
multi-threaded DLLs to toggle when COM servers are released. The syntax for
using SYS(2339) is:

  SYS(2339,1) && Default setting CoFreeUnusedLibraries called after a COM server is released.
  SYS(2339,0) && CoFreeUnusedLibraries is not called after a COM server is 
  released.

Setting SYS(2339,0) can improve scalability.

Steps to Reproduce Behavior
---------------------------

1. Create project named "SLOWDLL" (without the quotation marks).

2. Create a program file named SLOWDLL.PRG using the following code:

  DEFINE CLASS MTDLLDemo AS SESSION OLEPUBLIC

     PROCEDURE foot

        oMTX = CREATEOBJ('MTXAS.APPSERVER.1')
        oContext = oMTX.GetObjectContext()

        loCommand = CREATEOBJ('ADODB.Command')
        loRecordSet = CREATEOBJ('ADODB.RecordSet')
        loConnection = CREATEOBJ('ADODB.Connection')
        loConnection.CursorLocation = 3

        *!* Note Adjust the name of the server used in the next line
        lcConnectionStr = "Driver=SQL SERVER;SERVER=MY_SERVER;DATABASE=PUBS;UID=SA;PWD="
        lcCommandStr = [SELECT Authors.au_id, Authors.au_lname, Authors.au_fname ] + ;
           [FROM dbo.authors Authors]

        loConnection.OPEN(lcConnectionStr)
        loCommand.ActiveConnection = loConnection
        loCommand.CommandText = lcCommandStr

        IF loRecordSet.State = 1
           loRecordSet.CLOSE()
        ENDIF
        loRecordSet.OPEN(loCommand)

        loRecordSet.ActiveConnection = NULL
        loCommand.ActiveConnection = NULL
        loCommand = NULL
        loConnection.CLOSE

        lnStart = SECONDS()
        loConnection = NULL  &&problem here
        lnStop = SECONDS()

        oContext.SetComplete

        RETURN STR((lnStop-lnStart),6,2)+" seconds to disconnect"

     ENDPROC

  ENDDEFINE

3. Build either a single-threaded or multi-threaded DLL.

4. Open the Microsoft Transaction Server/COM+ Management Console and create a
  new COM+ package named SLOWDLL.

5. Open the Components folder of the SLOWDLL package.

6. Right-click on the Components folder, select New from the pop-up menu, and
  then select Component.

7. In the COM Component Install Wizard, select Import component(s) that are
  already registered and add the SLOWDLL.MTDLLDemo component.

8. After adding the component, right-click on the component and select the
  Properties option from the pop-up menu.

9. Select the Transactions tab and then select either the "Required" or
  "Requires New" button.

10. From the Visual FoxPro Command window, run the following code:

  OX=NEWOBJECT('SLOWDLL.MTDLLDemo')
  ? OX.FOOT
  RELEASE OX

(c) Microsoft Corporation 2000, All Rights Reserved. Contributions by John Desch,
Microsoft Corporation.


Additional query words: sp4

======================================================================
Keywords          : kbCOMt kbMTS kbvfp600 kbvfp600bug kbGrpDSFox kbDSupport kbVS600sp4fix kbVS600sp4 kbVS600sp5fix 
Technology        : kbVFPsearch kbAudDeveloper kbVFP600
Version           : WINDOWS:6.0
Issue type        : kbbug
Solution Type     : kbfix

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