bug修复，内存释放问题

碰到了一个内存释放的问题，在进行某个复杂的操作时内存释放后否则会造成崩溃。经过多方面调查发现此时根据就不能释放内存（历史原因），否则会造成不可预知的问题。所以我打算把要删除的指针暂时保存起来，并不立马delete，等到10秒钟还没有操作的时候（稍微空闲）再把保存的指针都销毁掉。

后来顺利的解决了问题，而且改动较小。

代码如下：

class DelayDestory : public QObject {
    Q_OBJECT
public:
    static DelayDestory* instance();
    void deleteItem(TreeItem *item);
    void deleteItem(const QList<TreeItem*> &items);

private slots:
    void onTimer();

private:
    DelayDestory();

private:
    static const int INTERVAL_SECOND = 5;
    static const int TIMEOUT_SECOND = 10;
    QList<TreeItem*> items_;
    class QTimer *timer_;
    QMutex mutex_;
    qint64 lastTime_;
};

DelayDestory* DelayDestory::instance()
{
    static DelayDestory s_inst;
    return &s_inst;
}

void DelayDestory::deleteItem(TreeItem *item)
{
    if (!item) {
        return;
    }

    lastTime_ = QDateTime::currentMSecsSinceEpoch();
    QMutexLocker lock(&mutex_);
    if (!items_.contains(item)) {
        items_.push_back(item);
    }
}

void DelayDestory::deleteItem(const QList<TreeItem*> &items)
{
    if (items.isEmpty()) {
        return;
    }

    lastTime_ = QDateTime::currentMSecsSinceEpoch();
    QMutexLocker lock(&mutex_);
    for (int i = 0; i < items.size(); i++) {
        if (items[i] && !items_.contains(items[i])) {
            items_.push_back(items[i]);
        }
    }
}

DelayDestory::DelayDestory()
    : mutex_(QMutex::Recursive), lastTime_(0)
{
    timer_ = new QTimer(this);
    connect(timer_, SIGNAL(timeout()), this, SLOT(onTimer()));
    timer_->start(INTERVAL_SECOND * 1000);
}

void DelayDestory::onTimer()
{
    qint64 currentTime = QDateTime::currentMSecsSinceEpoch();
    if (currentTime - lastTime_ >= TIMEOUT_SECOND * 1000 && !items_.isEmpty()) {
        QList<TreeItem*> tempList;
        {
            QMutexLocker lock(&mutex_);
            tempList = items_;
            items_.clear();
        }
        qDebug() << "delete tree items, size:" << tempList.size();
        for (int i = 0; i < tempList.size(); i++) {
            delete tempList[i];
        }
    }
}