Q193953: PRB: COM .Dll In MTS ‘Sharing’ Datasessions Between Instances
Article: Q193953
Product(s): Microsoft FoxPro
Version(s): WINDOWS:6.0
Operating System(s):
Keyword(s):
Last Modified: 06-AUG-1999
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The information in this article applies to:
- Microsoft Visual FoxPro for Windows, version 6.0
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SYMPTOMS
========
Moving the record pointer of a table in one object instance of a Component
Object Model (COM) .dll file created in Visual FoxPro, moves the record pointer
in all instances of that object when running in Microsoft Transaction Server
(MTS).
CAUSE
=====
Using a table outside the data environment causes the cursor to be public to all
instances of that object.
RESOLUTION
==========
Open and access the table that uses a cursor object in a data environment with
the DataSession property set to two (2) Private.
In the example provided in the Steps To Reproduce Behavior section, change the
SERVER CODE to the following.
NOTE: After rebuilding the COM .dll, make sure to delete the Component object
from the MTS Package, then add it back using the Add Component/Add New Component
menu options.
***************Server Code With Dataenvironment******************
DEFINE CLASS MTSData AS FORM OLEPUBLIC
DATAENVIRONMENT=.NULL.
DATASESSION=2 &&PRIVATE
PROCEDURE LOAD
SET DEFAULT TO "c:\MTSTest"
THIS.DATAENVIRONMENT=CREATEOBJECT("MTSDataEnv")
ENDPROC
PROCEDURE movenext
SKIP 1
ENDPROC
PROCEDURE moveprev
SKIP -1
ENDPROC
PROCEDURE movefirst
GO TOP
ENDPROC
PROCEDURE movelast
GO BOTTOM
ENDPROC
PROCEDURE returnrec
LPARAMETER MyArray
EXTERNAL ARRAY MyArray
MyArray(1,1)=fld1
MyArray(2,1)=fld2
MyArray(3,1)=fld3
ENDPROC
ENDDEFINE
DEFINE CLASS MTSDataEnv AS DATAENVIRONMENT
ADD OBJECT cursor1 AS MTScursor
PROCEDURE INIT
THIS.OPENTABLES
ENDPROC
ENDDEFINE
DEFINE CLASS MTScursor AS CURSOR
PROCEDURE INIT
OPEN DATABASE MTSData SHARED
THIS.EXCLUSIVE=.F.
THIS.ALIAS="MTSTest"
THIS.DATABASE="c:\MTSTest\MTSData.dbc"
THIS.CURSORSOURCE="MTSTest"
ENDPROC
ENDDEFINE
****************End Server Code With Dataenvironment**************
STATUS
======
This behavior is by design.
MORE INFORMATION
================
NOTE: This happens with any COM server created in Microsoft Visual FoxPro where
multiple instantiations of a single object reside in the same process, and the
DataSession property is set to 1 - Default Datasession. The variations where
this happens are below:
- Multi-Use Local (.exe) COM Server.
- Multi-Use In Process (.dll) Server called twice in one session.
- Multi-Use In Process (.dll) Server in a MTS Package called twice from one
session, or once from multiple sessions.
The code in the Steps To Reproduce Behavior section requires a database with a
table. You can run the following code to create the database and table:
NOTE: Make sure to change the SET DEFAULT TO line in the SERVER CODE to point to
the directory that contains the database.
CREATE DATABASE MTSData
CREATE TABLE MTSTest (fld1 c(10) PRIMARY KEY,fld2 N(5,2),fld3 T)
FOR i=1 TO 4
INSERT INTO MTSTest VALUES (STR(i),i,DATETIME()+ (i*60))
ENDFOR
Steps to Reproduce Behavior
---------------------------
1. Build the Server Code into a COM .dll named MTSData.
2. Import the MTSData.dll and the MTSData.tlb as a component into a MTS Package.
Be sure to mark the component as "Requires A New Transaction".
3. Place the Client Code in a program file.
4. Run the ClientCode.prg in two instances of Visual FoxPro.
5. Issue the following commands in the Command window of the first instance of
Visual FoxPro:
x.MoveNext
x.ReturnRec(@aMTSRecord)
DISPLAY MEMORY LIKE aMTSRecord
6. Issue the following commands in the second instance of Visual FoxPro noting
that the x.MoveNext command in the first instance moved the record pointer in
this instance also.
x.ReturnRec(@aMTSRecord)
DISPLAY MEMORY LIKE aMTSRecord
********************Server Code********************************
DEFINE CLASS MTSData AS FORM OLEPUBLIC
PROCEDURE INIT
SET DEFAULT TO "C:\MTSTest"
OPEN DATABASE MTSData SHARED
USE MTSTest SHARED
ENDPROC
PROCEDURE movenext
SKIP 1
ENDPROC
PROCEDURE moveprev
SKIP -1
ENDPROC
PROCEDURE movefirst
GO TOP
ENDPROC
PROCEDURE movelast
GO BOTTOM
ENDPROC
PROCEDURE returnrec
LPARAMETER MyArray
EXTERNAL ARRAY MyArray
MyArray(1,1)=fld1
MyArray(2,1)=fld2
MyArray(3,1)=fld3
ENDPROC
ENDDEFINE
********************End Server Code****************************
********************Client Code********************************
PUBLIC x
PUBLIC aMTSRecord(3,1)
x=CREATEOBJECT("MTSData.MTSData")
COMARRAY(x,11) &&Sets the arrays passed to object X as 1 based
&&passed by reference.
x.movenext
x.returnrec(@aMTSRecord)
DISPLAY MEMORY LIKE aMTSRecord
********************End Client Code****************************
Additional query words: kbVFp kbVFp600 kbCOMt kbMTS200 kbDatabase
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Keywords :
Technology : kbVFPsearch kbAudDeveloper kbVFP600
Version : WINDOWS:6.0
Issue type : kbprb
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