在 Qt5.3(mingw32) 中删除 QQuickView 的内存管理问题

Question

我们正在开发一个带有Qt/Qml的应用程序（Qml嵌入在QWidget中）。删除包含 QQuickView（嵌入式）的 QWidget 时，分配的内存不会完全释放。

通过将QWidget添加到应用程序，将分配大约30MB的内存，但是当小部件删除时，只会释放大约20MB的内存。

在 QWidget 的析构函数中，我删除了 QQuickView 实例，并且没有其他大对象。

另外，我很确定QQuickView没有正确释放内存。

如何释放QQuickView分配的全部内存？

注意：代码真的很大（160000 行），因此我无法放置示例代码。

提前感谢...

Answer 1

我写了一个快速测试来确定在创建和删除QQUickWidget时是否存在实际泄漏：

class Widget : public QWidget {
    Q_OBJECT
public:
    Widget(QWidget *parent = 0) : QWidget(parent) {
        widget = 0;
        count = 0;
        resize(200, 200);
        layout = new QVBoxLayout(this);
        setLayout(layout);
        QTimer * t = new QTimer(this);
        t->setInterval(200);
        t->setSingleShot(false);
        t->start();
        connect (t, SIGNAL(timeout()), this, SLOT(toggleQuickView()));
    }
public slots:
    void toggleQuickView() {
        if (!widget) {
            widget = new QQuickWidget;
            widget->setSource(QUrl::fromLocalFile("d:\main.qml"));
            connect(widget, SIGNAL(destroyed()), this, SLOT(echo()));
            layout->addWidget(widget);
        } else {
            layout->removeWidget(widget);
            widget->deleteLater();
            widget = 0;
        }
    }
    void echo() {
        PROCESS_MEMORY_COUNTERS memcount;
        if (!GetProcessMemoryInfo(GetCurrentProcess(), &memcount, sizeof(memcount))) return;
        qDebug() << ++count << "created and destroyed," << memcount.WorkingSetSize / (1024 * 1024) << "MB memory used";
    }
private:
    QVBoxLayout * layout;
    QQuickWidget * widget;
    int count;
};

它有一个计时器，可以创建/销毁一个QQuickWidget，里面有一个加载的QML文件，虽然结果最初会增加，但内存使用量会及时稳定下来，这表明Qt代码中不太可能存在内存泄漏，如果你确实泄漏了内存，错误不在于Qt，而在于你自己的代码。

另外，值得一提的是，任务管理器实际上使用比GetProcessMemoryInfo()更少的内存显示了该过程，我认为后者是两者中更准确的度量。任务管理器读数也没有表明任何内存泄漏，尽管其值波动更大。

这是输出：

1 created and destroyed, 41 MB memory used
2 created and destroyed, 44 MB memory used
3 created and destroyed, 44 MB memory used
4 created and destroyed, 48 MB memory used
5 created and destroyed, 48 MB memory used
6 created and destroyed, 48 MB memory used
7 created and destroyed, 48 MB memory used
8 created and destroyed, 48 MB memory used
9 created and destroyed, 48 MB memory used
10 created and destroyed, 48 MB memory used
11 created and destroyed, 52 MB memory used
12 created and destroyed, 52 MB memory used
13 created and destroyed, 52 MB memory used
14 created and destroyed, 52 MB memory used
15 created and destroyed, 52 MB memory used
16 created and destroyed, 52 MB memory used
17 created and destroyed, 52 MB memory used
18 created and destroyed, 52 MB memory used
19 created and destroyed, 52 MB memory used
20 created and destroyed, 52 MB memory used
21 created and destroyed, 53 MB memory used
...
50 created and destroyed, 53 MB memory used
...
100 created and destroyed, 53 MB memory used
...
200 created and destroyed, 53 MB memory used
...
500 created and destroyed, 53 MB memory used