Process in background (called from VB)

[Edwin Knoppert]

I know that.
The cb may not be invoked from inside the pb thread, that's all.

[John Petty]

OK we agree, thank you for helping Mike understand my posts which might have caused a problem due to lack of clarity

[John Petty]

Mike
I am probably out of my depth here and I am not sure I understand your problem but here goes. VB6 has no understanding of threads and cannot be used to control them. When you end a VB program by most means you can respond to a (from memory) Form Unload Event of the main form. In that event you should be quering the DLL as to whether all threads it has created have actually ended or Windows is going to do a dummy spit.
John

[Mike Doty]

John,
Having no problems in that area.
Actually, everything seems to be working after using
DIALOG DO EVENTS and not ending the function that created the thread.

I guess this forum thread could be closed, but the different ways to
return data from the DLL to VB are of the most interest now.
I will be using the code in post #10.

I'm trying to write all code in PB with a VB front end for COM.

Note: Just noted a potential problem, not shown.
I set a global gBusy if something is processing a request.
This will be modified because it is possible that another function
could reset the flag. The gBusy flag will become a counter that
is increased and decreased to indicate something is in progress.
Instead of setting gBusy = 1, gBusy = gBusy + 1
and gBusy = gBusy - 1 instead of gBusy = 0.

'PB
FUNCTION GetThreadCount EXPORT AS LONG 'VB uses to not end until threadcount = 1
  FUNCTION = THREADCOUNT
END FUNCTION 
'VB
Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer)
  If GETTHREADCOUNT > 1 Then
    Splash "Background function is processing", 1000
    Cancel = True
  ElseIf gBusy Then
    Splash "Processing a request", 1000
    Cancel = True
  End If
 
End Sub

[Michael Mattias]

>The cb may not be invoked from inside the pb thread, that's all.

??

Why not, if that call will not do anything which might itself cause an re-entrant call? This is really the crux of my question about how VB works.

Given:

' MY_VB_PROGRAM.BAS 
FUNCTION MainWindowProcedure (hWnd, uMSG, wParam, lparam) 
......
     hThread = CreateThread (params, calling MY_VB_FUNCTION ) 
     ' returns immediately with a thread handle 

....

FUNCTION My_VB_FUNCTION (params) 
   CALL MyFunctionInmyPBDLL (params) 
   PostMessage  primaryHWnd, private_message_no, _
      params  with results of MyFunctionInMyPbDLL
END FUNCTION

You don't even need a callback here. Since CreateThread returns essentially immediately, the primary GUI thread is not blocked and should run normally, shouldn't it?

???

It's really not a whole lot different from the "ALL PB" demo at GUI + Worker Thread + Abort Demo 11-24-07, at least as far as I can tell.

MCM

[Mike Doty]

Threads are working fine with VB6.

Now about callbacks.

http://www.thescarms.com/vbasic/subclassform.aspx 'subclassing code for VB6
http://www.thevbzone.com/secrets.htm 'pointers with VB6

[Mike Doty]

Read back strings from PB to VB using SendMesssage
Added Peeker function to DLL below.
s = PEEKER(lParam, wParam) 'in VB6 callback

 
 
GLOBAL gForm1 AS LONG
 
SUB Init(Form1 AS DWORD) EXPORT
  gForm1 =Form1
END SUB

SUB CallVb EXPORT
  LOCAL s AS STRING        'use STRPTR with dynamic strings
  LOCAL lResult   AS LONG
  LOCAL dwHandle  AS DWORD
  LOCAL dwMsg     AS DWORD
  LOCAL dwParam   AS DWORD
  LOCAL lParam    AS LONG
  dwHandle = gForm1
  dwMsg    = &H300
  s = "TEST COMPLETE"
  dwParam = LEN(s)      'length
  lParam = STRPTR(s)    'address
  lResult = SendMessage(dwHandle,dwMsg,dwParam,lParam)
END SUB

FUNCTION Peeker(Address AS DWORD, Characters AS LONG) EXPORT AS STRING
  FUNCTION  = PEEK$(address???, characters)
END FUNCTION

[Mike Doty]

CallBack to Visual Basic and SendMessage to Visual Basic

This shows how to directly SendMessage to a VB control.
It also shows how to use a callback.
All the code is in a PowerBASIC DLL.

VB code is in the second code window.

If no errors reported will post in source code forum.

#DIM ALL
#COMPILE DLL 'subDLL.bas
#INCLUDE "win32api.inc"
%CallBack = &H300
GLOBAL gControl    AS LONG
GLOBAL gPrevWndProc AS LONG
SUB TestCallBack EXPORT
  IF gControl = 0 THEN ? "Subclass is not on":EXIT SUB
  STATIC Counter AS LONG
  LOCAL s       AS STRING
  LOCAL wParam  AS DWORD
  LOCAL lParam  AS LONG
  INCR Counter
  s = "Callback string" + STR$(Counter)
  wParam = LEN(s)
  lParam = STRPTR(s)
  SendMessage gControl,%Callback,wParam,lParam 'let callback handle it
END SUB
SUB TestSendMessage(hControl AS LONG) EXPORT
  STATIC Counter AS LONG
  LOCAL s AS STRING
  INCR Counter
  s = "SendMessage direct to control" + STR$(counter)
  SendMessage(hControl,%LB_ADDSTRING,%NULL,STRPTR(s))
END SUB
FUNCTION Peeker(Address AS DWORD, Characters AS LONG) EXPORT AS STRING
  'Could be used by VB to read string in memory
  FUNCTION  = PEEK$(address???, characters)
END FUNCTION
SUB EndSubClass() EXPORT
  CALL SetWindowLong(gControl, %GWL_WNDPROC, gPrevWndProc)  'restore old address
END SUB
FUNCTION WindowProc(BYVAL hControl AS LONG, BYVAL uMsg AS LONG, _
    BYVAL wParam AS LONG, BYVAL lParam AS LONG) AS LONG
 
  DIM sPeekString AS STRING  'string already in memory
  IF uMsg = %CALLBACK THEN  'triggered callback
    sPeekString = PEEKER(lParam, wParam)
    SendMessage gControl,%LB_ADDSTRING,%NULL,STRPTR(sPeekString)
    EXIT FUNCTION
  END IF
  FUNCTION = CallWindowProc(gPrevWndProc, hControl, uMsg, wParam, lParam)
END FUNCTION
SUB StartSubClass(hControl AS LONG) EXPORT
  gControl = hControl
  gPrevWndProc = SetWindowLong(gControl, %GWL_WNDPROC, CODEPTR (WindowProc))
END SUB

#IF 0
 REM VB6
 REM  1. Add a Command button
 REM  2. Add a listbox
PRIVATE DECLARE SUB TESTSENDMESSAGE LIB "subdll" (hControl AS LONG)
PRIVATE DECLARE SUB TESTCALLBACK LIB "subdll" ()
PRIVATE DECLARE SUB STARTSUBCLASS LIB "subdll" (hControl AS LONG)
PRIVATE DECLARE FUNCTION ENDSUBCLASS LIB "subdll" () AS LONG
OPTION EXPLICIT
PRIVATE SUB Command1_Click()
  TESTSENDMESSAGE List1.hWnd
  TESTCALLBACK
END SUB
PRIVATE SUB Form_Load()
  CHDIR App.Path
  Command1.Caption = "Test"
  STARTSUBCLASS List1.hWnd
END SUB
PRIVATE SUB Form_QueryUnload(CANCEL AS INTEGER, UnloadMode AS INTEGER)
  ENDSUBCLASS 'required if subclassing
END SUB
#ENDIF

Can now work in the VB6 environment with threads, callbacks and sendmessage.