Q221732: FIX: Multiple Opens of Memo File May Cause Corruption

Article: Q221732
Product(s): Microsoft FoxPro
Version(s): WINDOWS:6.0
Operating System(s): 
Keyword(s): kbDatabase kbvfp600 kbvfp600bug KbDBFDBC kbVS600sp3fix kbGrpDSFox
Last Modified: 02-OCT-1999

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The information in this article applies to:

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

You have an application that accesses tables in a multiuser environment. If one
of the clients performs an action that results in a table's memo file being
locked, and a second client attempts to open the same table and access the memo
field information, the second client may open the memo file with an incorrect
blocksize. This can result in incorrect information being read from the memo
field or memo file corruption.

STATUS
======

This bug was corrected in Visual Studio 6.0 Service Pack 3. For more information
about Visual Studio service packs, please see the following articles in the
Microsoft Knowledge Base:

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

  Q194295 HOWTO: Tell That Visual Studio 6.0 Service Packs Are Installed

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

This behavior requires the memo file (.fpt) to be locked in one instance of
Visual FoxPro. One mechanism which causes this locking to occur is a REPLACE on
a memo field within a transaction. This is described in Knowledge Base article:

  Q190066 - FIX: Table Can Not Be USED After REPLACE of Memo in TRANSACTION

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

1. Start two instances of Visual FoxPro. Make sure each uses the same default
  directory.

2. Run the following code from a program (.PRG) file in instance 1:

     CLEAR
     SET EXCLUSIVE OFF
     SET MULTILOCKS ON
     SET REPROCESS TO 5

     IF NOT FILE('MUTest.DBC')
        SET BLOCKSIZE TO 64
        WAIT WINDOW "Creating test data..." NOWAIT
        CREATE DATABASE MUTest
        CREATE TABLE MUTable (IntFld I, MemoFld M)
        FOR lni = 1 TO 5
           APPEND BLANK
           REPLACE MemoFld WITH REPLICATE(TRANS(lni), 10)
        ENDFOR
        CLOSE DATABASE
        WAIT CLEAR
     ENDIF

     USE MUTable
     ?'Blocksize is ',SYS(2012)
     ?'Contents of memo field in 1st record is ' + memofld

     SELECT MUTable
     LOCATE

     BEGIN TRANSACTION
     REPLACE MemoFld WITH SYS(3)
     =MESSAGEBOX('Before you click OK, go to the other '+ ;
     'instance of Visual FoxPro, and run the second test '+ ;
     'program from there. Come back and click OK when you are done.', 16)

     ROLLBACK
     CLOSE DATABASE ALL

3. Run the following code from a program (.PRG) file in instance 2:

     CLEAR
     SET EXCLUSIVE OFF
     SET MULTILOCKS ON
     SET REPROCESS TO 5

     WAIT WINDOW "Opening table..." NOWAIT
     USE MUTable 
     WAIT CLEAR
     ?'Blocksize is ',SYS(2012)
     ?'Contents of memo field is' + memofld
     CLOSE DATA ALL

4. The blocksize returned in instance 1 will be 64, and the memo field contents
  will be "1111111111".

5. The blocksize returned in instance 2 will be 512, and the memo field contents
  appears to be empty. This is incorrect, as the blocksize should be 64, and
  the memo field contents should appear as "1111111111".

REFERENCES
==========

Visual FoxPro Help, topics SET BLOCKSIZE, SYS(2012), SET REPROCESS.

(c) Microsoft Corporation 1999, All Rights Reserved. Contributions by Jim
Saunders, Microsoft Corporation.


Additional query words: KBDSE

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Keywords          : kbDatabase kbvfp600 kbvfp600bug KbDBFDBC kbVS600sp3fix kbGrpDSFox 
Technology        : kbVFPsearch kbAudDeveloper kbVFP600
Version           : WINDOWS:6.0
Issue type        : kbbug
Solution Type     : kbfix

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