Windows – Page 2 – 0x2B|~0x2B

Category: Windows

GDI Leaks (2)

March 6, 2009 by gonwan·0 Comments

额.. 又漏了…

这次是GDI+ 的调用引起的, 看代码吧:

int main()
{
    Gdiplus::GdiplusStartupInput input;
    Gdiplus::GdiplusStartupOutput output;
    ULONG ulToken = 0;
    Gdiplus::GdiplusStartup(&ulToken, &input, &output);

    HWND hwndDesktop = ::GetDesktopWindow();
    HDC hdcDesktop = ::GetDC(hwndDesktop);
    HDC hdcMem = ::CreateCompatibleDC(hdcDesktop);
    for (int i = 0; i < 300; i++)
    {
        HBITMAP hbmpMem = ::CreateCompatibleBitmap(hdcMem, 1024, 768);
        HBITMAP hbmpOldMem = (HBITMAP)::SelectObject(hdcMem, hbmpMem);
        Gdiplus::Bitmap *bmpImage = new Gdiplus::Bitmap(L"C:\AmaneMisa1.jpg");
        //{
            Gdiplus::Graphics g(hdcMem);
            g.DrawImage(bmpImage, 0, 0, 1024, 768);
        //}
        delete bmpImage;
        ::SelectObject(hdcMem, hbmpOldMem);
        ::DeleteObject(hbmpMem);
    }
    ::DeleteDC(hdcMem);
    ::ReleaseDC(hwndDesktop, hdcDesktop);

    Gdiplus::GdiplusShutdown(ulToken);

    ::MessageBox(NULL, L"aa!", L"a", MB_OK);
    return 0;
}

int main()

{

Gdiplus::GdiplusStartupInput input;

Gdiplus::GdiplusStartupOutput output;

ULONG ulToken = 0;

Gdiplus::GdiplusStartup(&ulToken, &input, &output);

HWND hwndDesktop = ::GetDesktopWindow();

HDC hdcDesktop = ::GetDC(hwndDesktop);

HDC hdcMem = ::CreateCompatibleDC(hdcDesktop);

for (int i = 0; i < 300; i++)

{

HBITMAP hbmpMem = ::CreateCompatibleBitmap(hdcMem, 1024, 768);

HBITMAP hbmpOldMem = (HBITMAP)::SelectObject(hdcMem, hbmpMem);

Gdiplus::Bitmap *bmpImage = new Gdiplus::Bitmap(L"C:\AmaneMisa1.jpg");

//{

Gdiplus::Graphics g(hdcMem);

g.DrawImage(bmpImage, 0, 0, 1024, 768);

//}

delete bmpImage;

::SelectObject(hdcMem, hbmpOldMem);

::DeleteObject(hbmpMem);

}

::DeleteDC(hdcMem);

::ReleaseDC(hwndDesktop, hdcDesktop);

Gdiplus::GdiplusShutdown(ulToken);

::MessageBox(NULL, L"aa!", L"a", MB_OK);

return 0;

}

主要问题在于Graphics 那个对象. 实际上当前代码的SelectObject() 调用是错误的, 结果就是HBITMAP 对象又泄漏了. 解决的办法就是Graphics 对象用完了就删掉, 就不会锁住里面的HBITMAP 对象了. 方法有2 种: 1) 加一个作用域, 就是把上面的注释去掉. 2) new 一个Graphics 对象, 用完了直接delete 掉.

发现GDI+ 虽然封装了一些比较好用的函数, 但是很容易出错, 而且performance 也不太好. 以后还是少用为妙.

GDI Leaks

February 24, 2009 by gonwan·0 Comments

第一篇技术文…

内存泄漏, 句柄泄漏.. windows 编程中最头痛的事情. windows 提供了查看内存检测内存泄漏的API, 却没有提供检测句柄的, 至少我不知道. 第三方的工具如BoundsChecker 倒是异常强大.实在不行并且看得懂nc 堆栈信息的话, 可以用用看M$自家的 AppVerifier .

今天碰到的问题很诡异. 在用工具检查完GDI 句柄泄漏之后, 跑了一上午某个绘图程序, 内存居然涨到了100+M, ft 啊. 于是代码一段段注掉, 找到底哪里漏了… 最后定位到这样的一段代码:

HDC hMemDC = ::CreateCompatibleDC(...);
HBITMAP hBitmap = ::CreateCompatibleBitmap(...);
::DeleteObject(::SelectObject(hMemDC, hBitmap));
// draw something on hMemDC...
::DeleteObject(hBitmap);

HDC hMemDC = ::CreateCompatibleDC(...);

HBITMAP hBitmap = ::CreateCompatibleBitmap(...);

::DeleteObject(::SelectObject(hMemDC, hBitmap));

// draw something on hMemDC...

::DeleteObject(hBitmap);

问题在于, 最后的DeleteObject() 调用不正确. 应改为如下:

HDC hMemDC = ::CreateCompatibleDC(...);
HBITMAP hBitmap = ::CreateCompatibleBitmap(...);
HBITMAP hOldBitmap = (HBITMAP)::SelectObject(hMemDC, hBitmap));
// draw something on hMemDC...
::SelectObject(hMemDC, hOldBitmap);
::DeleteObject(hBitmap);

HDC hMemDC = ::CreateCompatibleDC(...);

HBITMAP hBitmap = ::CreateCompatibleBitmap(...);

HBITMAP hOldBitmap = (HBITMAP)::SelectObject(hMemDC, hBitmap));

// draw something on hMemDC...

::SelectObject(hMemDC, hOldBitmap);

::DeleteObject(hBitmap);

就是说, 一个HBITMAP 跟一个HDC 还有关联的时候, 不要调用DeleteObject(), 而应该先把原始的HBITMAP 句柄SelectObject() 还原回去. 有以下几条notes:

Bitmaps must be disconnected from a DC before being freed.
Menus must be freed before an application exits if the menu is not connected to any window.
A DC must be disconnected from bitmaps before being freed.
If a bitmap is specified for the Caret, it must be freed.
Calls to DeleteObject do not harm stock objects.