PBDLL 6 GDI.BAS hangs after a few minutes

[Lance Edmonds]

I've been a little busy, but I intent to follow up my original post as time permits...


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Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

Regarding the resource leak problem in the GDI.BAS code by Dave Navarro, I still
haven't found a solution. In your last reply, Lance, you point out that "the final
section of PLOT() that is supposed to release GDI objects is failing miserably", and
offered to revise the code and post the "amendments".

I'm really looking forward to that and hope to see them soon.

Thanks. Alan.

[Lance Edmonds]

Whew... there are certainly a few GDI resource leaks... as far as I remember, Dave's GDI code was never finished so it may be that you have inherited a bug or two.

The most obvious leak is in the PLOT() routine... the variable "hWndShow" should be "hWnd", which means that EndPaint() is failing on each iteration to release the device context successfully.

Also, the final section of PLOT() that is supposed to release GDI objects is failing miserably! I'll revise this section of code for you off-line and post the "amendments" back here later on when I'm back it my DEV PC.

-------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

Thanks for your help, Kev and Lance. I tried watching the Resource meter, and indeed,
the GDI resources drop, about 1% for each 20 redraws of the window. If I speed up the
Timer events, the resources leak away faster, but the relation to redraws seems to stay the
same. So I have a resource leak, but deleting objects and device contexts after each
use doesn't seem to cure the problem. I think most of the code is still the same as Dave
Navarro's original example, although I did try making hDC, and then other handles too, STATIC
instead of LOCAL. One more thing ... I can't seem to get a pen size of "1" to work, as it
does in the "COOL" example that came with my PBDLL 6.0. Dave's example was written for
PBDLL 5.0 ... would that make a difference? Here is the complete code with my modifications:

'
' GDI.BAS test code for PB/DLL 5.0
' by Dave Navarro, Jr. ([email protected]) modified by Alan Dalglies
'

$COMPILE EXE
$INCLUDE "WIN32API.INC"

DEFSNG A-Z

FUNCTION FF(x AS SINGLE, y AS SINGLE)
  GLOBAL W AS SINGLE
  FUNCTION = 14 * EXP(-.04*W)*COS(.15*W)
END FUNCTION

SUB PLOT(BYVAL hWnd AS LONG)

  LOCAL LpPaint   AS PaintStruct
'  LOCAL hMemDC    AS LONG
'  LOCAL hBmp      AS LONG
'  LOCAL hBrush    AS LONG
'  LOCAL hPen      AS LONG
  LOCAL WinX      AS LONG
  LOCAL WinY      AS LONG
  LOCAL r         AS RECT
  LOCAL i         AS LONG
  LOCAL FL        AS LONG
  LOCAL yOfs      AS LONG

  STATIC PHI AS SINGLE
  STATIC hDC       AS LONG      ' 2000/1/18 suggested by Kev G. Peel
  STATIC hMemDC    AS LONG      '
  STATIC hBmp      AS LONG      '
  STATIC hBrush    AS LONG      '
  STATIC hPen      AS LONG      '

  GetClientRect hWnd, r
  WinX = r.nRight - r.nLeft
  WinY = r.nBottom - r.nTop

  hDC = BeginPaint(hWnd, LpPaint)
  hMemDC = CreateCompatibleDC(hDC)
  hBmp = CreateCompatibleBitmap(hDC, WinX, WinY)

  SelectObject hMemDC, hBmp

  hBrush = CreateSolidBrush(%BLACK)
  FillRect hMemDC, r, hBrush
  DeleteObject hBrush

  yOfs = WinY * .3

  hPen = CreatePen(%PS_SOLID, 2, %GREEN) ' <---- can't get "1" to work here
  SelectObject hMemDC, hPen

  RHO = 300 - ((WinX / 800) * 300)
  D = 2000

  THETA = .1
  S1 = SIN(THETA)
  C1 = COS(THETA)

  IF PHI THEN
    PHI = PHI+0.1
  ELSE
    PHI = 1.3
  END IF
  S2 = SIN(PHI)
  C2 = COS(PHI)

  DIM YMIN(0 TO WinX), YMAX(0 TO WinX)
  FOR I = 0 TO WinX : YMIN(I) = WinY \ 2 : NEXT I

  FOR X = 12 TO -12 STEP -.5
    FL = 0
    FOR Y = -12 TO 12 STEP .2
      W = X*X + Y*Y
      Z = FF(X, Y)

      XE = -X*S1 + Y*C1
      YE = -X*C1*C2 - Y*S1*C2 + Z*S2
      ZE = -X*S2*C1 - Y*S1*S2 - Z*S2 + RHO
      SX = D*XE/ZE + (WinX \ 2)
      SY = (-5*D*YE/ZE/12) + 120

      IF SX < 0 OR SX > WinX THEN OutOfRange
      IF FL = 0 THEN FL = 1 : F = 0 : GOTO OutOfRange
      DX = OLDX - SX : IF DX = 0 THEN DX = 1
      SL = (OLDY - SY) / DX
      YP = OLDY

      FOR XP = INT(OLDX) + 1 TO SX
        YP = YP + SL
        IF YP <= YMIN(XP) THEN
          YMIN(XP) = YP
          IF F = 0 THEN XX = XP: YY = YP : F = 1
          MoveToEx hMemDC, XX, YY+yOfs, BYVAL %NULL
          LineTo hMemDC, XP, YP+yOfs
          XX = XP
          YY = YP
        END IF
        IF YP >= YMAX(XP) THEN
          YMAX(XP) = YP
          IF F = 0 THEN XX = XP: YY = YP : F = 1
          MoveToEx hMemDC, XX, YY+yOfs, BYVAL %NULL
          LineTo hMemDC, XP, YP+yOfs
          XX = XP
          YY = YP
        END IF
        F = 0
      NEXT XP
OutOfRange:
      OLDX = SX : OLDY = SY
    NEXT Y
  NEXT X

  BitBlt hDC, r.nLeft, r.nTop, Winx, WinY, hMemDC, 0, 0, %SRCCOPY
  DeleteObject hPen
  DeleteObject hMemDC           ' 2000/1/17 added at Kev Peel's suggestion.
  DeleteObject hBmp             '
  DeleteDC hDC                 '  not ReleaseDC.
  EndPaint hWndShow, LpPaint


END SUB

FUNCTION WINMAIN (BYVAL hInstance     AS LONG, _
                  BYVAL hPrevInstance AS LONG, _
                  lpCmdLine           AS ASCIIZ PTR, _
                  BYVAL iCmdShow      AS LONG) AS LONG

  LOCAL Msg         AS tagMsg
  LOCAL wndclass    AS WndClassEx
  LOCAL szAppName   AS ASCIIZ * 80
  LOCAL hWnd        AS LONG
  LOCAL hTimer      AS LONG

  szAppName              = "GDIWINDOW"

  wndclass.cbSize        = SIZEOF(WndClass)
  wndclass.style         = %CS_HREDRAW OR %CS_VREDRAW

  wndclass.lpfnWndProc   = CODEPTR( WndProc )

  wndclass.cbClsExtra    = 0
  wndclass.cbWndExtra    = 0
  wndclass.hInstance     = hInstance
  wndclass.hIcon         = %NULL
  wndclass.hCursor       = LoadCursor( %NULL, BYVAL %IDC_ARROW )
  wndclass.hbrBackground = GetStockObject( %BLACK_BRUSH )
  wndclass.lpszMenuName  = %NULL
  wndclass.lpszClassName = VARPTR( szAppName )
  wndclass.hIconSm       = LoadIcon( hInstance, BYVAL %IDI_APPLICATION )

  RegisterClassEx wndclass

  ' Create a window using the registered class
  hWnd = CreateWindow("GDIWINDOW",_              ' window class name
                      "PowerBASIC GDI Test", _   ' window caption
                      %WS_OVERLAPPEDWINDOW, _    ' window style
                      %CW_USEDEFAULT, _          ' initial x position
                      %CW_USEDEFAULT, _          ' initial y position
                      %CW_USEDEFAULT, _          ' initial x size
                      %CW_USEDEFAULT, _          ' initial y size
                      %NULL, _                   ' parent window handle
                      %NULL, _                   ' window menu handle
                      hInstance, _               ' program instance handle
                      BYVAL %NULL)               ' creation parameters

  hTimer = SetTimer(hWnd, 0, 500, BYVAL %NULL) 'Timer event every .5 Secs
                                               'Alan Dalgliesh added this
  ShowWindow hWnd, iCmdShow
  UpdateWindow hWnd

  WHILE GetMessage(Msg, %NULL, 0, 0)
    TranslateMessage Msg
    DispatchMessage Msg
  WEND

  KillTimer hWnd, 0   ' Destroy the timer ... added by Alan Dalgliesh

  FUNCTION = msg.wParam

END FUNCTION  ' WinMain

'------------------------------------------------------------------------------

FUNCTION WndProc (BYVAL hWnd AS LONG, BYVAL wMsg AS LONG, _
                  BYVAL wParam AS LONG, BYVAL lParam AS LONG) EXPORT AS LONG

'  LOCAL hDC       AS LONG          2000/1/17 Kev Peel's comments,
'  LOCAL LpPaint   AS PaintStruct   I notice these aren't used
'  LOCAL tRect     AS Rect          so I'm commenting them out.

  STATIC First    AS LONG

  SELECT CASE wMsg

    CASE %WM_CREATE

'    CASE %WM_LBUTTONDOWN  ... changed to line below by Alan Dalgliesh
    CASE %WM_Timer
      InvalidateRect hWnd, BYVAL %NULL, %TRUE

    CASE %WM_ERASEBKGND
      IF First = 0 THEN
        First = 1
      ELSE
        FUNCTION = 1
        EXIT FUNCTION
      END IF

    CASE %WM_PAINT
      Plot hWnd
      FUNCTION = 0
      EXIT FUNCTION

    CASE %WM_DESTROY
      PostQuitMessage 0
      FUNCTION = 0
      EXIT FUNCTION

  END SELECT

  FUNCTION = DefWindowProc(hWnd, wMsg, wParam, lParam)

END FUNCTION

[Lance Edmonds]

It is not usual to "hold" onto a DC as Kev suggests unless you are using a Private Device Context (the code snippet above suggests that a Common Device Context is in use). When dealing with a Common Device Context, you would normally only take ownership of the DC when responding to a
%WM_PAINT event, and then immediately release the DC back to the "pool" before leaving the %WM_PAINT handler.

However, it is likely that a resource leak is occurring, given the symptoms. If you install the Windows Resource Meter, you may be able to watch Resource Memory dropping as the app runs.

Alan, if you can post all of the code, we may be able to help you better.

-------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

Alan,
Since you haven't posted all the source, I can't figure out your problem. But I see you have the hDC as a LOCAL variable, usually I would declare hDC as STATIC LONG and initialize it in the WM_CREATE message, then use ReleaseDC in the WM_DESTROY message, also be sure to delete all created objects such as CreateSolidBrush with the DeleteObject Function.

To me it looks like a resource leak, but I could be wrong.

Regardz,


-------------
Kev G Peel
KGP Software
Bridgwater, UK.
mailto:[email protected][email protected]</A>

I modified Dave Navarro's GDI.BAS so that the window is repainted every
one or two seconds (instead of when the mouse is left-clicked), and just
let it run. After a few minutes (about 4 or 5) the app. froze. Sometimes
I can close it, no apparent harm, but other times everything is locked up
and I have to reboot. I'm using Windows 98SE, Pentium III 500 MHz, 128 MB
Ram. Here are the mods I inserted into Dave's code:
' GDI.BAS test code for PB/DLL 5.0
' by Dave Navarro, Jr. ([email protected])
..
FUNCTION WINMAIN (BYVAL hInstance AS LONG, _
BYVAL hPrevInstance AS LONG, _
lpCmdLine AS ASCIIZ PTR, _
BYVAL iCmdShow AS LONG) AS LONG

LOCAL Msg AS tagMsg
LOCAL wndclass AS WndClassEx
LOCAL szAppName AS ASCIIZ * 80
LOCAL hWnd AS LONG
LOCAL hTimer AS LONG
' my first added statement <------------------------------------- (1)
...
' Create a window using the registered class
hWnd = CreateWindow("GDIWINDOW",_ ' window class name
"PowerBASIC GDI Test", _ ' window caption
%WS_OVERLAPPEDWINDOW, _ ' window style
%CW_USEDEFAULT, _ ' initial x position
%CW_USEDEFAULT, _ ' initial y position
%CW_USEDEFAULT, _ ' initial x size
%CW_USEDEFAULT, _ ' initial y size
%NULL, _ ' parent window handle
%NULL, _ ' window menu handle
hInstance, _ ' program instance handle
BYVAL %NULL) ' creation parameters

hTimer = SetTimer(hWnd, 0, 1000, BYVAL %NULL) 'Timer event every 1 Secs
' my second added statement <---------------------------------------- (2)
ShowWindow hWnd, iCmdShow
UpdateWindow hWnd

WHILE GetMessage(Msg, %NULL, 0, 0)
TranslateMessage Msg
DispatchMessage Msg
WEND

' KillTimer hWnd, 0 ' Destroy the timer.. I tried with and without this
' my third added statement <--------------------------------------- (3)
FUNCTION = msg.wParam

END FUNCTION ' WinMain
...
FUNCTION WndProc (BYVAL hWnd AS LONG, BYVAL wMsg AS LONG, _
BYVAL wParam AS LONG, BYVAL lParam AS LONG) EXPORT AS LONG

LOCAL hDC AS LONG
LOCAL LpPaint AS PaintStruct
LOCAL tRect AS Rect

STATIC First AS LONG

SELECT CASE wMsg

CASE %WM_CREATE

' CASE %WM_LBUTTONDOWN this is Dave's CASE statement
CASE %WM_Timer
' my fourth and final added statement <---------------------------- (4)
InvalidateRect hWnd, BYVAL %NULL, %TRUE

I hope this is neither too short nor too long to explain what I am having
trouble with. PBDLL 6.0 is very impressive, compared to 2.0 which I was
able to use to replace slow code in a VB 3.0 program, but I'm having a
little difficulty getting up to speed in the 32-bit environment.

Thanks to Dave and others at PB for providing so many useful examples,
such as this one. I only wish I could understand it better.