Article ID: 191967 - Last Review: August 6, 1999 - Revision: 1.0

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

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This article was previously published under Q191967

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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.
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CAUSE

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

This behavior is by design.
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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.
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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.
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APPLIES TO
  • Microsoft Visual FoxPro 6.0 Professional Edition
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Keywords: 
kbcode kbprb KB191967
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Retired KB ArticleRetired KB Content Disclaimer
This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.
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