FIX: TABLEREVERT() Does Not Release Header Lock

The information in this article applies to:

• Microsoft Visual FoxPro for Windows, versions 3.0

SYMPTOMS

If Pessimistic locking is in use and an APPEND BLANK is canceled with a TABLEREVERT(), another user will not be able to add another record to the table. If an attempt is made either an "Attempting to Lock...Press ESC to Cancel" message is presented or a "File is in use by another" error is generated.

CAUSE

Visual FoxPro 3.0 TABLEREVERT() command is not releasing the header lock on the file.

WORKAROUND

The best workaround is to update to 3.0b. If this is not an option, follow the TABLEREVERT() command with an UNLOCK RECORD 0. This will force an unlock of the header.

STATUS

Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article. This problem was corrected in Microsoft Visual FoxPro 3.0b.

MORE INFORMATION

TABLEREVERT() does not release the header lock that has been applied by an APPEND BLANK under Pessimistic locking schemes.

For example, Pessimistic Table Buffering is in effect for a form. User A on workstation 1 appends a blank record then cancels the change by issuing a TABLEREVERT(). User B on workstation 2 then attempts to append a blank record to the same table. However, the attempt fails with an "Attempting to Lock...Press ESC to Cancel" error.

Steps to Reproduce Problem

1. Open the \Samples\Data\Testdata.dbc

2. Create a new form.

3. Add the Customer table to the form's DataEnvironment, and set the cursor's BufferModeOverride property to either 2 or 4. Drag a field from the customer table to the form.

4. Place a command button on the form, and change its caption to Add. Then place the following code its Click event:

   APPEND BLANK THISFORM.REFRESH

5. Add another command button to the form. Change its caption to Cancel, and place the following code in its Click event:

   =TABLEREVERT() THISFORM.REFRESH

6. Set the form's DataSession property to 2 - Private Data Session.

7. Save and run the form twice.

8. Click the Add button and then the Cancel button of one of the forms. Go to the Second form, and click the Add button. A "File is in use by another" error message is generated. of this form was run from two different workstations, the second user would have received an "Attempting to Lock...Press ESC to Cancel" message.