Q222676: HOWTO: Tell if a VFP COM DLL is Single- or Multi-threaded

Article: Q222676
Product(s): Microsoft FoxPro
Version(s): WINDOWS:6.0
Operating System(s): 
Keyword(s): kbCOMt kbvfp600 kbVS600sp2 kbVS600sp3
Last Modified: 20-MAY-1999

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 6.0 
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SUMMARY
=======

Starting with the Visual Studio 6.0 Service Pack 3 version of Visual FoxPro 6.0,
you now have the ability to create multi-threaded DLL COM components. There is
no obvious way to tell from the DLL file itself or its Property Sheet whether a
DLL is single-threaded or multi-threaded. This article demonstrates a technique
for determining whether a particular DLL is single- or multi-threaded.

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

This approach uses the FILETOSTR() function to transfer the contents of the DLL
to be tested into a string variable, then searches for the text "foxwt" or
"foxwd" within the string. The "foxwt" text will be contained in a
multi-threaded DLL and the "foxwd" text will be contained in a single- threaded
DLL.

The program below is an implementation of this approach. You can pass it a DLL
name if you want, or it will prompt you for a file to test.

It correctly calls a Visual FoxPro 5.0 or Visual FoxPro 6.0 pre-SP3 DLL
"single-threaded."

The program calls DLLs not built in Visual FoxPro "Non-FoxPro" DLLs.

STEPS TO USE THE PROGRAM
------------------------

1. Save the following code in a file called TestADLL.PRG:

  ****************************
  * Program TestADLL.PRG
  *
  * Parameters:
  *               tcFileName - Name of DLL file w/ or w/o extension
  *
  * Usage:        DO TestADLL with <dllname>
  *
  *                    OR
  *
  *               DO TestADll
  * 			Prompts for file name
  *
  ****************************
  #DEFINE 	MSGBOXTITLE 	'VFP COM DLL Tester'

  LPARA tcFileName, p2, p3, p4, p5, p6
  LOCAL lcType, lcFileContents

  * Parameter checking/cleanup

  DO CASE
     CASE PARA() > 1
        MESSAGEBOX([Too many parameters specified. Usage is:] + ;
           CHR(13)+CHR(13) + ;
           [DO TestDLL with 'filename'], 16, MSGBOXTITLE)
        RETURN
     CASE PARA() = 0
        tcFileName = GETFILE('dll','Open a DLL' , ;
           'Open', 0, 'Select a DLL to check')
        IF EMPTY(tcFileName)
           RETURN
        ENDIF
     CASE VARTYPE(tcFileName) # 'C'
        MESSAGEBOX([Incorrect parameter data type. Usage is:] + ;
           CHR(13)+CHR(13) + ;
           [DO TestDLL with 'filename'], 16, MSGBOXTITLE)
        RETURN

  ENDCASE

  * Drop trailing dot, if present
  IF ATC('.', tcFileName) = LEN(tcFileName)
     tcFileName = STRTRAN(tcFileName, '.', '')
  ENDIF

  * Append DLL extension if not there
  IF ATC('.', tcFileName) = 0
     tcFileName = tcFileName + '.dll'
  ENDIF

  tcFileName = PROPER(tcFileName)

  * See if file exists
  IF !FILE(tcFileName)
     MESSAGEBOX([File '] + tcFileName + ;
        [' does not exist.], 48, MSGBOXTITLE)
     RETURN
  ENDIF

  * Verify it is a DLL
  IF ATC('.dll', tcFileName) = 0
     MESSAGEBOX([File '] + tcFileName + ;
        [' is not a dll.], 48, MSGBOXTITLE)
     RETURN
  ENDIF

  lcFileContents = FILETOSTR(tcFileName)

  DO CASE
     CASE  ATC('foxwt',lcFileContents) <> 0
        lcType = 'Multi-threaded'
     CASE ATC('foxwd',lcFileContents) <> 0
        lcType = 'Single-threaded'
     OTHERWISE
        lcType = 'Non-FoxPro'
  ENDCASE

  MESSAGEBOX('File '+ tcFileName + ' is a '+ ;
     lcType + ' dll.', 64, MSGBOXTITLE)

2. To test a specific file, run the following code from the Command window:

  DO TestADLL.PRG with <path and filename>

3. To have the program prompt you for a file, run the following code from the
  Command window:

  DO TestADLL.PRG 

Additional query words: KBDSE

======================================================================
Keywords          : kbCOMt kbvfp600 kbVS600sp2 kbVS600sp3 
Technology        : kbVFPsearch kbAudDeveloper kbVFP600
Version           : WINDOWS:6.0
Issue type        : kbhowto

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