FIX: Index Corruption Updating Same Record from Two FoxPro Instances (299020)


The information in this article applies to:

  • Microsoft Visual FoxPro for Windows 6.0
This article was previously published under Q299020

SYMPTOMS

When Buffering is set to 3 (Optimistic row) and two or more users edit a record and commit changes, the table index may become corrupt, causing blank ("phantom") records to appear.

CAUSE

Internally, FoxPro calls functions that lock a record and determine that the record was changed by another user. The status of current value of the record is adjusted, but the value for each index is not updated. As a result, an inconsistency is created between the index buffer and the new record.

STATUS

This problem was corrected in Microsoft Visual FoxPro version 7.0 for Windows.

MORE INFORMATION

Steps to Reproduce Behavior

  1. In Visual FoxPro version 6.0 (VFP6), paste the following code in a new program:
    ON ERROR *
TABLEREVERT(.T.)
ON ERROR
CLEAR ALL
CLEAR
SET MULTILOCKS ON
SET SAFETY OFF
PUBLIC mErr
mErr = 0

ON ERROR mErr = ERROR()
USE table1 EXCLUSIVE
ON ERROR

IF mErr  < 2
	DO maketable
	? "Making table."
ELSE
	? "Not making table."
	? mErr
ENDIF

USE table1 ORDER 1 SHARED
CURSORSETPROP("Buffering",3)
REPLACE NAME WITH ALLTRIM(NAME) + IIF(mErr < 2,"x","y")
IF mErr >2
	? "TableUpdate: ",TABLEUPDATE(0,.T.)
	CLOSE DATABASES ALL
	RETURN
ENDIF

PUBLIC ox
ox = NEWOBJECT("myform")
ox.SHOW

*~~~~~~~~~~~~~~~~~~~~~~~~~~~
DEFINE CLASS myform AS FORM
	AUTOCENTER = .T.
	WIDTH = 350
	HEIGHT = 300
	MINBUTTON = .F.
	MAXBUTTON = .F.
	BORDERSTYLE = 2
	CAPTION = []
	ADD OBJECT cmdUpdate AS COMMANDBUTTON
	ADD OBJECT grdMyGrid AS GRID
	PROCEDURE cmdUpdate.CLICK
		ACTIVATE SCRE
		?"TableUpdate: ",TABLEUPDATE(0,.T.)
	ENDPROC
	PROCEDURE INIT
		WITH THIS
			.grdMyGrid.TOP = 75
			.grdMyGrid.LEFT = 20
			.cmdUpdate.CAPTION = "TableUpdate(0,.T.)"
			.cmdUpdate.TOP = 10
			.cmdUpdate.WIDTH = 120
			.cmdUpdate.HEIGHT = 40
			.cmdUpdate.LEFT = 100
			IF mErr >2
				THIS.cmdUpdate.CLICK
			ENDIF
		ENDWITH
	ENDPROC
	PROCEDURE DESTROY
		ACTIVATE SCREEN
		LIST
		CLOSE DATABASES ALL
	ENDPROC
ENDDEFINE

PROCEDURE maketable
	CLOSE DATABASES ALL
	CREATE TABLE table1 (NAME c(10))
	INSERT INTO table1 VALUES ('John')
	INSERT INTO table1 VALUES ('Mary')
	INDEX ON NAME TAG NAME
ENDPROC
  2. Save the program as Repro1.prg. Then, save the program a second time as Repro2.prg. Be sure to save both programs to the same folder.
  3. Run Repro1.prg in this instance of VFP6.
  4. Open a second instance of VFP6 and run Repro2.prg.
  5. Return to the first instance of VFP6 and click the command button on the form that is displayed. Press the DOWN ARROW key to enter the grid.
You now see a blank, "phantom" record in the grid. If the Status bar is available, note that there are only two records in the table that the grid is displaying, although the grid seems to contain three records.
Modification Type:MajorLast Reviewed:10/15/2002
Keywords:kbBug kbDatabase kbDSupport kbvfp700fix KB299020
©2002 Microsoft Corporation. All rights reserved.