Microsoft KB Archive/836863

= FIX: A memory leak that is related to ActiveX Data Object recordsets occurs =

Article ID: 836863

Article Last Modified on 11/15/2007

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APPLIES TO


 * Microsoft Visual Basic, Scripting Edition 5.5
 * Microsoft Internet Explorer (Programming) 6 (SP1)

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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(&quot;FieldName&quot;) The code is not using the following syntax: rs.Field(&quot;FieldName&quot;).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.



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. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next service pack that contains this hotfix.

To resolve this problem, submit a request to Microsoft Online Customer Services to obtain the hotfix. To submit an online request to obtain the hotfix, visit the following Microsoft Web site:

http://go.microsoft.com/?linkid=6294451

Note If additional issues occur or any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. To create a separate service request, visit the following Microsoft Web site:

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

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(&quot; &quot;) syntax. Use the rs.Field(&quot; &quot;).value syntax instead.



STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the &quot;Applies to&quot; 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(&quot; &quot;) 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:
 * &quot;ADODB.Field&quot;
 * &quot;Either BOF or EOF is True, or the current record has been deleted. Requested operation requires a current record.&quot;
 * &quot;C:\WINNT\HELP\ADO270.CHM&quot;

Steps to reproduce the problem
<ol>  Create a VBScript file that contains the following code: on error resume next Set conn = CreateObject(&quot;adodb.connection&quot;) conn.open &quot;provider=msdasql;driver=sql server;server=YourServer;database=pubs;uid=YourUID;pwd=YourPassword;&quot;

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

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

' This code does not leak memory. x = rs(&quot;au_id&quot;).value & rs(&quot;au_fname&quot;).value & rs(&quot;au_lname&quot;).value rs.Close set rs = Nothing Next conn.Close </li> Modify the connection string appropriately for your environment.</li></ol>

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