PRB: VFP ODBC Driver in COM DLL Under MTS Package May Hang (270106)


The information in this article applies to:

  • Microsoft Visual FoxPro for Windows 5.0
  • Microsoft Visual FoxPro for Windows 6.0
This article was previously published under Q270106

SYMPTOMS

A client application calls a FoxPro Component Object Model (COM) .dll file in an Microsoft Transaction Server (MTS)/COM+ package. Under certain circumstances, the client application may hang. This behavior can occur when:
  • The COM DLL accesses a FoxPro datasource through ODBC.
  • The Fetch Data In Background option is set to YES for the ODBC connection that is used by the .dll server.

RESOLUTION

To work around this problem, deselect the Fetch Data in Background option on the DSN, either visually or through code.

MORE INFORMATION

Steps to Reproduce Behavior

Create the COM Server:
  1. Copy the TESTDATA database to the computer that is running MTS/COM+.
  2. Create a new project in Microsoft Visual FoxPro called VFP_PROB.
  3. Save the following code to a new program and add it to the project. (Remember to change the DATA_PATH constant to a valid path. It needs to point to a local directory on your MTS/COM+ computer.)
    *********** START SERVER CODE **************
DEFINE CLASS SERVER AS CUSTOM OLEPUBLIC
	PROCEDURE GETDATA(lcSQLCmd, lcFetchOn)
		LOCAL lcDSN, lnSQLHand, lnSQLSuccess, lcFDIB, ;
			lcRetVal,lnStartTime,lnEndTime,lcQueryDuration

                *!* Change path appropriately for your computer.
		#DEFINE DATA_PATH "C:\DATA\TESTDATA.DBC"
		
		lcFDIB = IIF(lcFetchOn,"YES","NO")

		lcDSN = "DRIVER=Microsoft Visual FoxPro Driver;" + ;
			"UID=;Deleted=Yes;Null=Yes;Collate=Machine;BackgroundFetch=" + lcFDIB + ";" + ;
			"Exclusive=No;SourceType=DBC;SourceDB=" + DATA_PATH + ";"

		lnSQLHand = SQLSTRINGCONNECT(lcDSN)
		IF lnSQLHand < 0
			lcRetVal = THIS.RaiseError()
			RETURN lcRetVal
		ENDIF

		lnStartTime = DATETIME()
		lnSQLSuccess = SQLEXEC(lnSQLHand,lcSQLCmd,"ResultSet")
		lnEndTime = DATETIME()
		lcQueryDuration = TRANSFORM(ROUND(lnEndTime - lnStartTime,0)) + " seconds"
		IF lnSQLSuccess < 0
			lcRetVal = THIS.RaiseError()
			RETURN lcRetVal
		ENDIF

		lcRetVal = TRANSFORM(RECCOUNT("ResultSet")) + ;
			" Records Returned In ~ " + lcQueryDuration + ;
			". 'Fetch Data In Background' = " + lcFDIB + "."
		USE IN ResultSet
		SQLDISCONNECT(0)
		CLOSE DATABASES ALL
		RETURN lcRetVal
	ENDPROC

	PROCEDURE RaiseError
		LOCAL laErrArray[1], lcErrMsg
		AERROR(laErrArray)
		lcErrMsg = laErrArray(3)
		SQLDISCONNECT(0)
		RETURN lcErrMsg
	ENDPROC

ENDDEFINE
***************** END SERVER CODE ***********
  4. Build the project into a multi-threaded COM server (.dll).
  5. With a text editor, open the .vbr file that was generated when you built the .dll file (it is in the same directory as the .dll). Make note of the CLSID because you need it later.
  6. Take the .dll and .tlb files to your computer running MTS/COM+. Add them to a package.For additional information on this process, click the article numbers below to view the articles in the Microsoft Knowledge Base:

    191623 HOWTO: Distribute VFP COM Components used with MTS

    223406 HOWTO: Create an Empty MTS Package to Add Components for ASP

Create the Clients:
  1. Copy the following code to a program file in a new instance of Microsoft Visual FoxPro.
  2. Change the COM_CLSID and COM_SERVER constants to the CLSID you made note of earlier, and also change the name of your MTS/COM+ computer.
  3. Save the program as four different file names (1.prg, 2.prg, 3.prg, 4.prg, for example).
  4. Start three more instances of Microsoft Visual FoxPro, and then run the four separate programs, one in each instance. Eventually, all four instances of FoxPro stop processing queries. 
    *********** START CLIENT CODE ***********
LOCAL loVFPCOM, lnCaseNum, lcSQLCmd, lcExitKey, lcYear

#DEFINE FetchData 	.T.
#DEFINE lnLower 	1
#DEFINE lnUpper 	5
#DEFINE COM_CLSID	"{6F5C4280-C6B4-4D84-936D-57E4AFFB843F}"
#DEFINE COM_SERVER	"\\MYSERVER"

loVFPCOM = CREATEOBJECTEX(COM_CLSID,COM_SERVER)

DO WHILE .T.
	lnCaseNum = INT((lnUpper - lnLower + 1) * RAND( ) + lnLower)
	DO CASE
		CASE lnCaseNum = 1
			lcYEAR  = "1992"
		CASE lnCaseNum = 2
			lcYEAR = "1993"
		CASE lnCaseNum = 3
			lcYEAR = "1994"
		CASE lnCaseNum = 4
			lcYEAR = "1995"
		CASE lnCaseNum = 5
			lcYEAR = "1996"
	ENDCASE
	lcSQLCmd = "SELECT * " + ;
		"FROM  testdata!customer INNER JOIN testdata!orders " + ;
		"ON  Customer.cust_id = Orders.cust_id " + ;
		"WHERE YEAR( Orders.order_date) = " + lcYEAR 

	? "Starting query..."
	? loVFPCOM.GETDATA(lcSQLCmd,FetchData)
	WAIT "Requery in 3 seconds. Press 'q' to exit..." TO lcExitKey TIMEOUT 3
	? ""
	IF lcExitKey = "q"
		EXIT
	ENDIF
ENDDO
RELE ALL
*********** END CLIENT CODE ***********
    To see this work, edit the four client programs and change the #DEFINE FetchData to .F.

REFERENCES

For additional information about the Fetch Data In Background option on the Microsoft Visual FoxPro ODBC driver, click the article numbers below to view the articles in the Microsoft Knowledge Base:

236019 PRB: ASP App Using ADO with Visual FoxPro ODBC Driver Stops IIS

175801 PRB: Accessing FoxPro Table in ASP Returns Error 80040e14

269881 PRB: Problems with Visual FoxPro Driver Fetch Data In Background Option

(c) Microsoft Corporation 200, All Rights Reserved. Contributions by Trevor Hancock, Microsoft Corporation.

Modification Type:MajorLast Reviewed:10/15/2003
Keywords:kbprb KB270106
©2003 Microsoft Corporation. All rights reserved.