FIX: Multiple Opens of Memo File May Cause Corruption

ID: Q221732

The information in this article applies to:

Microsoft Visual FoxPro for Windows, version 6.0

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

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

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

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

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

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

Additional query words: KBDSE

Keywords : kbDatabase kbVFp600 kbVFp600bug KbDBFDBC kbVS600sp3fix kbGrpFox
Version : WINDOWS:6.0
Platform : WINDOWS
Issue type : kbbug