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

• 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

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

   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.