Q151841: PRB: FoxPro and Clipper Share the Same DBF Files on a Network

Article: Q151841
Product(s): Microsoft FoxPro
Version(s): 2.50 2.50a 2.50b 2.60 2.60a 3.00
Operating System(s): 
Keyword(s): kb3rdparty
Last Modified: 21-AUG-1999

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The information in this article applies to:

- Microsoft FoxPro for Windows, versions 2.5, 2.5a, 2.5b, 2.6, 2.6a 
- Microsoft FoxPro for MS-DOS, versions 2.0, 2.5, 2.5a, 2.5b, 2.6, 2.6a 
- Microsoft Visual FoxPro for Windows, versions 3.0, 3.0b 
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SYMPTOMS
========

RLOCK() will not function properly when a FoxPro Application and a Clipper
Application access the same table simultaneously.

CAUSE
=====

Both FoxPro and Clipper have their own Locking Mechanism. When applying a lock
to a table file on the Network, the function FLOCK() can be recognized by both
Foxpro and Clipper; it will return a TRUE (.T.) if the table is locked by any of
the applications. The function RLOCK() returns a TRUE only if a particular
record of a table is locked by the same application. In other words, if a record
was locked by Foxpro, Clipper can still lock the particular record without an
error, and it has the same behavior the other way around.

RESOLUTION
==========

Use FLOCK() instead of RLOCK().

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

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

Run the following code in Clipper:

     ** <Table_Field> is a numeric field in a Table

     USE <Table_Name> SHARED
     GOTO TOP
     REPLACE <Table_Field> WITH 100   && Initial Value of <Table_Field>

     DO WHILE RLOCK()                 && Record is Locked by Clipper
        ? <Table_Field>
        WAIT ?Hit a Key ...? TO M.temp
     ENDDO

and Run the following code in FoxPro:

     USE <Table_Name> SHARED
     GOTO TOP

     DO WHILE RLOCK()                 && Record is Locked by Foxpro
        REPLACE <Table_Field> WITH <Table_Field> + 1
        WAIT ?Hit a Key ...? TO M.temp
     ENDDO

Expected Behavior
-----------------

When the above code is executed by Foxpro and Clipper at the same time, the
expected behavior is:

- Clipper locks the record and displays the value of the field, which is 100.

- Foxpro cannot lock the same record, so it will keep on trying to lock the
  record and will not be able to add 1 to the field.

Actual Behavior
---------------

- Clipper locks the record and displays the value of the field, which is 100.

- FoxPro locks the record successfully and adds 1 to the field.

- Press a key on the Clipper machine, and it displays 101.

- Press a key on the Foxpro machine, and it locks the record successfully again
  and adds one more to the field.

- Press a key on the Clipper machine, and it displays 102.

Additional query words: FoxWin VFoxWin FoxDos

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Keywords          : kb3rdparty 
Technology        : kbVFPsearch kbAudDeveloper kbFoxproSearch kbZNotKeyword3 kbFoxPro200DOS kbFoxPro250DOS kbFoxPro250aDOS kbFoxPro250bDOS kbFoxPro260DOS kbFoxPro260aDOS kbFoxPro260 kbFoxPro250 kbFoxPro250a kbFoxPro250b kbFoxPro260a kbVFP300 kbVFP300b
Version           : 2.50 2.50a 2.50b 2.60 2.60a 3.00

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