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GlobalFree crash

Once every few days my app crashes inside GlobalFree.

Before I call the function, I check that the memory is OK by IsBadWritePtr.
Is there a way to make sure that it will not crash?
Or is there a way like try{}catch() that will avoid the crash.

Thanks,
Shlomo;

ASKER CERTIFIED SOLUTION

jkr

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VapiSoft

ASKER

I already have

try
{
GlobalFree(hDIB);
}
catch(...)
{
}

What is the difference between try and __try ?

jkr

>>What is the difference between try and __try ?

'try' will catch ++ exceptions, but *no* SEH exceptions (unless you provide a translator, see http://msdn.microsoft.com/library/en-us/vclib/html/_CRT__set_se_translator.asp) - this applies to access violations also, whereas '__try' will only catch SEH exceptions. They simply belong to two absolutely different exception handling concepts.

VapiSoft

ASKER

Thank you very much.
I will try it.

VapiSoft

ASKER

I tried it, it doesn't work.
I load it with a debugger, and I changed the hDIB handle.
I expected the __except to catch the "crash", it did not.

jkr

>>I expected the __except to catch the "crash", it did not.

Wrong assumption. It is not to catch the exception, but to detect the cause. That's the interesting part.

VapiSoft

ASKER

I tried again, it does not get to the ExceptionFilter(DWORD dwCause) either.
Maybe because it is under the debugger?

jkr

Could you post the exact code how you're trying that?

VapiSoft

ASKER

Opps.
Now I did receive it, and it even helped me not to crash (it did get to the exception handler part).
So first, thank you very much.
Also, the dwCause was 5, what is 5?

jkr

That's odd, there is no such exception code....

VapiSoft

ASKER

Opps, the error code is 0xc0000005

jkr

Well, that's a plain EXCEPTION_ACCESS_VIOLATION.

VapiSoft

ASKER

What does it mean in relation to GlobalFree(hDIB)?
Does it mean that it is already free?

jkr

Good question. How are you allocating that memory?

VapiSoft

ASKER

First I do GlobalAlloc, and then GlobalReAlloc

jkr

Can you post the code where you create 'hDIB'?

VapiSoft

ASKER

HANDLE getPictureHandle(HBITMAP hBitmap, HDC hdc, int &nLines, int &nColumns, LPBYTE &start)
{
BITMAPINFOHEADER bih;
//HPALETTE hPal;
BITMAP Bitmap;
//HDC hDC;

      HANDLE hMem;
WORD biBits;
      LPBITMAPINFOHEADER lpbih;

      GetObject(hBitmap, sizeof(Bitmap), (LPSTR)&Bitmap);

int w2=Bitmap.bmWidth;
int h2=Bitmap.bmHeight;

      biBits = n_pixels; // Bitmap.bmPlanes * Bitmap.bmBitsPixel;

      bih.biSize = sizeof(BITMAPINFOHEADER);
      bih.biWidth = w2;
      bih.biHeight = h2;
      bih.biPlanes = Bitmap.bmPlanes;
      bih.biBitCount = n_pixels; // 32; // Bitmap.bmBitsPixel;
      bih.biCompression = 0;
      bih.biSizeImage = 0;
      bih.biXPelsPerMeter = 3780;
      bih.biYPelsPerMeter = 3780;
      bih.biClrUsed = 0;
      bih.biClrImportant = 0;
      bih.biSizeImage=0;

      int dwLen = bih.biSize + ColorTableSize(&bih);

      HANDLE hDIB = GlobalAlloc(GPTR, dwLen);

      if (!hDIB)
{
            return 0;
      }

      lpbih = (LPBITMAPINFOHEADER)hDIB;

      *lpbih = bih;

/// get the actual size
      nLines=GetDIBits(hdc,
            hBitmap,
            (UINT)0,
            (UINT)bih.biHeight,
(LPVOID)NULL,
            (LPBITMAPINFO)lpbih,
            DIB_RGB_COLORS);

      bih = *lpbih;

      if (bih.biSizeImage == 0)
{
            if(hDIB)
            {
                  GlobalFreeDIB(hDIB,5);
            }
            return 0;
      }

      dwLen = bih.biSize + ColorTableSize(&bih) + bih.biSizeImage;
      hMem = GlobalReAlloc(hDIB, dwLen, GMEM_MOVEABLE|GMEM_ZEROINIT);
if (!hMem) return 0;

      hDIB = hMem;
      //printDebugLog("GlobalReAlloc: hDIB=%x",hDIB);

lpbih = (LPBITMAPINFOHEADER)hDIB;
int color_table_size=ColorTableSize(lpbih);
start=(LPBYTE)lpbih + (WORD)lpbih->biSize + color_table_size;
nColumns=bih.biWidth;

      DWORD t1=GetTickCount();

nLines=GetDIBits(hdc,
            hBitmap,
            (UINT)0,
            (UINT)bih.biHeight,
start,
              (LPBITMAPINFO)lpbih,
            DIB_RGB_COLORS);

      //CreateDIBSection(hdc,(LPBITMAPINFO) &lpbih,DIB_RGB_COLORS,(void **) &start,0,0);
//memcpy(start,start1,bih.biSizeImage);

DWORD t2=GetTickCount();
      //DeleteObject(hbmp);
      printDebugLog("GetDIBits: dt=%d",t2-t1);

return hDIB;
}

HDC hdc=GetWindowDC(hwnd);
HDC memDC =CreateCompatibleDC(hdc);
HBITMAP hbmp=CreateCompatibleBitmap(hdc, wr.cx, wr.cy);
      DWORD t3=GetTickCount();
HBITMAP oldBmp=(HBITMAP) SelectObject(memDC,hbmp);
BitBlt(memDC,0,0, wr.cx, wr.cy, hdc, x_offset, y_offset, SRCCOPY);
//oldBmp=(HBITMAP) SelectObject(memDC,hbmp);
      DWORD t4=GetTickCount();

msg->hDIB=getPictureHandle(hbmp,hdc,wr.cy,wr.cx,msg->pixels);

SelectObject(memDC,oldBmp);
DeleteObject(hbmp);
DeleteObject(memDC);
ReleaseDC(hwnd, hdc);