FIX: A memory leak that is related to ActiveX Data Object recordsets occurs (836863)


The information in this article applies to:

  • Microsoft Visual Basic, Scripting Edition 5.6
  • Microsoft Internet Explorer (Programming) 6 (SP1)

SYMPTOMS

A memory leak that is related to Microsoft ActiveX Data Object (ADO) recordsets may occur if all the following conditions are true:
  • The ADO recordset values are being concatenated together.
  • The code that concatenates the values is using the following syntax:
    rs.Field("FieldName")
    The code is not using the following syntax:
    rs.Field("FieldName").value
  • The ADO recordset is empty.

CAUSE

When the Microsoft Visual Basic scripting engine (Vbscript.dll) calls an ADO method, the EXCEPINFO information structure is also passed to ADO. ADO can fill out the EXCEPINFO structure and then return the structure to the scripting engine when an error occurs. In this scenario, Vbscript.dll does not free the error information that ADO returns when the recordset is empty.

RESOLUTION

Service pack information

To resolve this problem, obtain the latest service pack for Microsoft Windows XP. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

322389 How to obtain the latest Windows XP service pack

Hotfix information

A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Only apply it to systems that are experiencing this specific problem. This hotfix may receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next Microsoft Windows XP service pack that contains this hotfix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services telephone numbers and information about support costs, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

The English version of this hotfix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel. 
   Date         Time    Version    Size     File name
   -----------------------------------------------------
   20-Feb-2004  23:49  5.6.0.8822  413,696  Vbscript.dll

WORKAROUND

To work around this problem, when you concatenate recordset values, do not use the rs.Field("FieldName") syntax. Use the rs.Field("FieldName").value syntax instead.

STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section. This problem was first corrected in Microsoft Windows XP Service Pack 2.
If an ADO Field object is referenced by using the rs.Field("FieldName") syntax, the code is keeping a reference to the ADODB.Field object itself instead of a reference to the default value property of the object. When the Visual Basic scripting engine concatenates the values together, the IDispatch interface calls to ADO must be made internally to determine what the default property is.

For an ADODB.Field object, the default property is the value property. The value property contains the actual field value. The Visual Basic scripting engine passes an exception information structure to ADO as part of the IDispatch call so error information can be filled out by ADO and can be returned if an error occurs.

If the ADO recordset is empty, ADO allocates Source, HelpFile, and Description strings and then places the strings in the exception information structure. However, when the exception information structure is returned to the Visual Basic scripting engine indicating an ADO error (because the recordset was empty), the Visual Basic scripting engine does not free the strings that were returned to it by ADO. This behavior causes a memory leak in the default process heap. This leak will include strings that are similar to the following:
  • "ADODB.Field"
  • "Either BOF or EOF is True, or the current record has been deleted. Requested operation requires a current record."
  • "C:\WINNT\HELP\ADO270.CHM"

Steps to reproduce the problem

  1. Create a VBScript file that contains the following code:
    on error resume next 
Set conn = CreateObject("adodb.connection")
		  conn.open "provider=msdasql;driver=sql
		  server;server=YourServer;database=pubs;uid=YourUID;pwd=YourPassword;"

 Set cmdTemp = CreateObject("ADODB.Command") 
cmdTemp.CommandType = 1 
Set cmdTemp.ActiveConnection = conn 
cmdTemp.CommandText = "select au_id, au_lname,
		  au_fname from authors where 1 = 2" 
For i = 0 To 50000 
     Set rs =CreateObject("ADODB.Recordset") 
     rs.Open cmdTemp, , 0, 1 

' This code leaks memory.
		  x = rs("au_id") & rs("au_fname") & rs("au_lname") 

' This code does not leak memory.
x = rs("au_id").value & rs("au_fname").value & rs("au_lname").value
		  rs.Close 
set rs = Nothing 
Next 
conn.Close
  2. Modify the connection string appropriately for your environment.

REFERENCES

For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

824684 Description of the standard terminology that is used to describe Microsoft software updates

Modification Type:MajorLast Reviewed:4/7/2006
Keywords:kbQFE KBHotfixServer kbWinXPsp2fix kbfix kbBug KB836863 kbAudDeveloper
©2004 Microsoft Corporation. All rights reserved.