osg智能指针错误 - Warning deleting still referenced object

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1 osg智能指针错误 - Warning: deleting still referenced object

1.1 问题描述

类的定义如下：

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class QOsgWidget {
public:
    ///< essential widget, use this ptr to be the real widget
    osgQOpenGLWidget* pWidget = nullptr;
    // QOsgWidget(QWidget* parent = nullptr);
    QOsgWidget(const std::string& modelPath, QWidget* parent = nullptr);
    ~QOsgWidget();

    ///< osg base vars
    osg::ref_ptr<osg::Group>                        mRoot                = nullptr; // root node of the osg scene
    osg::ref_ptr<osg::Camera>                       camera               = nullptr; // osg camera
    osg::ref_ptr<osgViewer::Viewer>                 mViewer              = nullptr; // osg viewer
    osg::ref_ptr<osgGA::TrackballManipulator>       trackball            = nullptr;
    osg::ref_ptr<osgGA::KeySwitchMatrixManipulator> keyswitchManipulator = nullptr;
    osg::ref_ptr<osgViewer::StatsHandler>           stats                = nullptr;
    <被省略>
}

类的析构函数如下：

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QOsgWidget::~QOsgWidget() {
    // end the render thread and destroy the osgOpenglWidget
    std::this_thread::sleep_for(std::chrono::microseconds(1000));
    mViewer->setDone(true);
    std::this_thread::sleep_for(std::chrono::microseconds(1000));
    mViewer->stopThreading();

    //////////////////////////////////////////////////////////////////////////
    /// without folowing post process, u will crash with the bellowing warning when: delete pWidget
    /// Warning: deleting still referenced object 000002433CA59BB0 of type 'class osg::Referenced * __ptr64'
    ///     the final reference count was 1, memory corruption possible.
    ///
    /// the reason i guess is:
    /// the bellowing vars can not be automatically set to null when delete pWidget, because they does
    /// not belong to the pWidget, so u need to set them to null manually, otherwise when delete pWidget,
    /// the destructor of pWidget will try to free the bellowing vars, but their ref != 0
    ///////////////////////////////// PART 1 /////////////////////////////////
        mRoot = nullptr;
        mViewer = nullptr;
        camera = nullptr;
        trackball = nullptr;
        keyswitchManipulator = nullptr;
    //////////////////////////////////////////////////////////////////////////

    delete pWidget; // call the destructor of the osgOpenglWidge
}

问题描述，在执行类的析构的时候：
当没有PART1的时候，直接执行pWidget会出错

1.2 原因推测：

  • 1 osg::ref_ptr<> 是一种智能指针，自动计算指针的引用个数，当引用个数为0的时候，自动回收其指向的对象。
  • 2 于是出现一个大问题，当pWidget这个类指针所指向的类，里面很多组件（比如 camera，mViewer）是在QOsgWidget类中申明的，那么当析构pWidget的时候，它会去析构自己的组件，然后当它析构了自己类里面的那些指针后，发现QOsgWidget里面的智能指针不是null（这些指针很可能在被别的模块访问），所以引用计数不为0，所以无法删除，或者删除会crash

1.3 得出结论：

  • 1 如果类mon里面嵌套了类son，那么当mon的析构的时候，要注意如下两点：
    • 1.1 将son析构
    • 1.2 执行son的析构前，对son的析构可能产生影响的内存，指针，都要释放掉和置空