PRB: Values Not Stored Correctly in a Multiuser Environment

• Microsoft Visual FoxPro for Windows, version 3.0
• Microsoft FoxPro for Windows, versions 2.5 and 2.5a
• Microsoft FoxPro for MS-DOS, versions 2.0, 2.5, and 2.5a

SYMPTOMS

In a multiuser environment, programs that assign values to memory variables from database fields may not have access to the most recent values of those database fields.

CAUSE

To reproduce this problem, create a database with a numeric field, named FIELD1, and one record. Assign an initial value of 1 to FIELD1. Start the following program on one workstation:

   SET EXCLUSIVE OFF
   SET TALK OFF
   USE <database>
   DO WHILE .T.
     m.memvar = field1
     WAIT WINDOW NOWAIT "Current value of FIELD1 is: " + ;
       LTRIM(STR(m.memvar))
   ENDDO

   SET EXCLUSIVE OFF
   SET TALK OFF
   USE <database>

   FOR i = 1 TO 2000
     REPLACE field1 WITH i
     WAIT WINDOW NOWAIT "Current value of FIELD1 is: " + ;
        LTRIM(STR(i))
   ENDFOR

NOTE: Unless an RLOCK() function is issued, FoxPro does not re-read the current record.

RESOLUTION

For memory variables to be assigned the most current information from a database record, an RLOCK() function should be issued before performing the assignment. In the code example above, the first workstation's code should be modified to read:

   SET EXCLUSIVE OFF
   SET TALK OFF
   SET REPROCESS TO <an appropriate interval>
   USE <database>
   DO WHILE .T.
     IF RLOCK()
       UNLOCK
       m.memvar = field1
       WAIT WINDOW NOWAIT "Current value of FIELD1 is: " + ;
         LTRIM(STR(m.memvar))
     ENDIF
   ENDDO

   SET EXCLUSIVE OFF
   SET TALK OFF
   SET REPROCESS TO <an appropriate interval>
   USE <database>

   FOR i = 1 TO 2000
     IF RLOCK()
       REPLACE field1 WITH i
       UNLOCK
       WAIT WINDOW NOWAIT "Current value of FIELD1 is: " + ;
         LTRIM(STR(i))
     ENDIF
   ENDFOR