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Q191967: PRB: Visual FoxPro In-Process Servers Do Not Run Concurrently

Article: Q191967
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
========

When a Visual FoxPro 6.0 Component Object Model (COM) component (DLL) is
accessed by multiple threads (or processes, if the Visual FoxPro component is
part of a Microsoft Transaction Server package), if one thread calls a method on
the component while another thread is already executing a method, the new method
call will not begin executing until the existing method call has finished.

CAUSE
=====

In the object implementation in Visual FoxPro, entry into the run-time is
blocked while another object is in execution.

STATUS
======

This behavior is by design.

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

In order to preserve data integrity of variables, Microsoft Visual FoxPro blocks
entry into the run-time while another object is in execution.

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

1. Create a Visual FoxPro COM .dll, called VFPMTS, by adding a program file with
  the following code to a project:

        DEFINE CLASS MTSServer as Custom OLEPUBLIC

        oAPPServer = .NULL.
        oObjectContext = .NULL.
        cErrorMsg = ""

        FUNCTION FastHit
           RETURN "Done. " + TIME()
        ENDFUNC
        FUNCTION SlowHit
        LPARAMETER lnSecs
           lnSecs=IIF(type("lnSecs")="N",lnSecs,5)

           THIS.oAppServer = CREATEOBJECT("MTXaS.Appserver.1")
           THIS.oObjectContext = THIS.oAppServer.GetObjectContext()

           lcOutput = ""

           FOR x = 1 to lnSecs * 300000
              i=1
           ENDFOR

           THIS.oObjectContext.SetComplete()
           RETURN lcOutput + "Done waiting for "+STR(lnSecs)+" secs"
        ENDFUNC
        FUNCTION Error
        LPARAMETER lnErrorNo, lcCode, lnLine

           THIS.cErrorMsg = THIS.cErrorMsg + STR(lnErrorNo)+ " - " ;
           + STR(lnLine) + " " + lcCode + " - " +Message()
        ENDFUNC
        ENDDEFINE

2. Build the project into a multi-use COM .dll then add it to Microsoft
  Transaction Server (MTS) using the Import Component option of an MTS package.

3. Start up two Visual FoxPro sessions.

In Session one, run the following code from the Command window:

     o=create("vfpmts.mtsserver")
     ? o.SlowHit(35)

In Session two run the following code from the Command window:

     o=create("vfpmts.mtsserver")
     ? o.FastHit()

Make sure you run the call to FastHit after SlowHit starts.

Notice that the FastHit does not start until after the SlowHit completes.

Additional query words: kbVFp600 kbCOMt kbMTS

======================================================================
Keywords          :  
Technology        : kbVFPsearch kbAudDeveloper kbVFP600
Version           : WINDOWS:6.0
Issue type        : kbprb

=============================================================================

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