Microsoft KB Archive/258736

Knowledge Base

FIX: A DLL that was created by using Visual FoxPro 6.0 and that is running under Microsoft Transaction Server is slow to release connections

Article ID: 258736

Article Last Modified on 8/7/2007

---

APPLIES TO

• Microsoft Visual FoxPro 6.0 Professional Edition

---

This article was previously published under Q258736

SYMPTOMS

A dynamic-link library (DLL) created with Microsoft 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 Microsoft 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 problem in the Microsoft products that are listed in the "Applies to" section. 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:

194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why

194295 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://msdn2.microsoft.com/en-us/vstudio/Aa718353.aspx

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 the behavior

1. Create project named SLOWDLL.

2. Create a program file named SLOWDLL.PRG using the following code:
   Note The user, Username, must have permissions to perform these operations on the database.

   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=UserName;PWD=StrongPassword"
         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                  

Additional query words: sp4

Keywords: kbbug kbfix kbvs600sp4fix kbvs600sp5fix KB258736

---

Send feedback to Microsoft

© Microsoft Corporation. All rights reserved.