crashes when adding series fast

    if ( m_view_cur->type==QAbstractSeries::SeriesTypeBoxPlot) {
        auto series_t = m_view_cur->chart()->series().count();
        if ( series_count == series_t) {
            return;
        }

        // append
        if (series_count > series_t) {
            for(int i = 0 ; i < series_count-series_t; ++i) {
                QList<int> list_x={0,1,2,3,4};
                QBoxPlotSeries * ser = new QBoxPlotSeries;
                foreach(auto x, list_x) {
                    QBoxSet * bs = new QBoxSet;
                    QList<qreal> set;
                    for(int j = 0 ; j < 5; ++j ) {
                        set.append(RANDOM_VAL);
                    }
                    std::sort(set.begin(), set.end());
                    bs->append(set);
                    bs->setLabel(QString::number(x));
                    ser->append(bs);
                }
                m_view_cur->chart()->addSeries(ser);


                if (m_view_cur->chart()->axes().isEmpty()) {
                    m_view_cur->chart()->createDefaultAxes();
                }
               else{
                          ser->attachAxis(m_view_cur->chart()->axisX());
                        ser->attachAxis(m_view_cur->chart()->axisY());
               }
            }
        }
        // delete
        else{
            for(int  i = 0 ; i < series_t-series_count; ++i) {
                m_view_cur->chart()->removeSeries(m_view_cur->chart()->series().last());
            }
        }