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Deleting QChart Causes 30+ Second Application Hang!

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  • JoeCFDJ JoeCFD

    @FleetingMemory Maybe try to delete it in a thread. Also a splash widget may be needed at exit.

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    FleetingMemory
    wrote on last edited by FleetingMemory
    #40

    @JoeCFD Can't delete in a thread, it calls on GUI functions because it loops across removeSeries(), which calls update. This causes a cross-thread exception in Qt. DeleteLater() doesn't actually delete immediately within your timer bounds in the code you posted above (that is just timing QT scheduling it), so it still freezes the program later on.

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    • JonBJ Online
      JonBJ Online
      JonB
      wrote on last edited by JonB
      #41

      @FleetingMemory
      As you have now discovered, it is the deleting of each series which is so time consuming (for unknown reasons). There is a huge difference between 10 series with 10,000 points each versus 10,000 series with 10 points each. (In fact, in latter case timing is same even if all series are empty/have no points.) There seems to be little you can do to affect that timing. I see no evidence it has anything to do with whether the view/chart/series are shown or not, have signals disabled or not, etc.

      Which takes me back to my question as to why you need 10,000 series or any such figure, which you did not answer. There is no chance the user can view or appreciate such a large number, so what is the point of adding that many onto the chart in the first place? That is where I would look for efficiency improvement.

      If you really are not prepared to reduce that, then: I presume any deleteLater() won't help as that just delays when the delay comes to a bit later. I assume you are right that series cannot or should not be deleted from a thread as they are some kind of UI object. Which would leave you with one possible "hack" to distribute the deletion time "nicely". Follow @JoeCFD's code to assign a new, blank chart to the view (chartView->setChart( new QChart() );). But do not immediately delete the original chart there: instead, keep it around in a suitable variable. In UI code thread set off a repeating timer every so often: in each timeout use removeSeries() to delete a few of the 10,000 series, example perhaps 100 at a time. You can do this because you are in the main/UI thread. Over time you will have deleted all the series from the old QChart object, at that point you can delete the (empty) chart and terminate the timer. Seems to me reducing the number of series in the first place is preferable, but there you are if you really want to do this.

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      • JonBJ JonB

        @FleetingMemory
        As you have now discovered, it is the deleting of each series which is so time consuming (for unknown reasons). There is a huge difference between 10 series with 10,000 points each versus 10,000 series with 10 points each. (In fact, in latter case timing is same even if all series are empty/have no points.) There seems to be little you can do to affect that timing. I see no evidence it has anything to do with whether the view/chart/series are shown or not, have signals disabled or not, etc.

        Which takes me back to my question as to why you need 10,000 series or any such figure, which you did not answer. There is no chance the user can view or appreciate such a large number, so what is the point of adding that many onto the chart in the first place? That is where I would look for efficiency improvement.

        If you really are not prepared to reduce that, then: I presume any deleteLater() won't help as that just delays when the delay comes to a bit later. I assume you are right that series cannot or should not be deleted from a thread as they are some kind of UI object. Which would leave you with one possible "hack" to distribute the deletion time "nicely". Follow @JoeCFD's code to assign a new, blank chart to the view (chartView->setChart( new QChart() );). But do not immediately delete the original chart there: instead, keep it around in a suitable variable. In UI code thread set off a repeating timer every so often: in each timeout use removeSeries() to delete a few of the 10,000 series, example perhaps 100 at a time. You can do this because you are in the main/UI thread. Over time you will have deleted all the series from the old QChart object, at that point you can delete the (empty) chart and terminate the timer. Seems to me reducing the number of series in the first place is preferable, but there you are if you really want to do this.

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        FleetingMemory
        wrote on last edited by
        #42

        @JonB said in Deleting QChart Causes 30+ Second Application Hang!:

        Which takes me back to my question as to why you need 10,000 series or any such figure, which you did not answer. There is no chance the user can view or appreciate such a large number, so what is the point of adding that many onto the chart in the first place? That is where I would look for efficiency improvement.

        The chart is to be used for displaying & isolating specific data/time frames, thus all data/lines need to be present, and each series is a line being displayed. By manipulating the X-Axis the user can zoom into/out of to a specific time frame. The idea of deleting a few at a time is something I have definitely been exploring as a possible solution however it doesn't fix the fact it will still hang the whole application when the window is closed or application exited as well.

        JoeCFDJ 1 Reply Last reply
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        • F FleetingMemory

          @JonB said in Deleting QChart Causes 30+ Second Application Hang!:

          Which takes me back to my question as to why you need 10,000 series or any such figure, which you did not answer. There is no chance the user can view or appreciate such a large number, so what is the point of adding that many onto the chart in the first place? That is where I would look for efficiency improvement.

          The chart is to be used for displaying & isolating specific data/time frames, thus all data/lines need to be present, and each series is a line being displayed. By manipulating the X-Axis the user can zoom into/out of to a specific time frame. The idea of deleting a few at a time is something I have definitely been exploring as a possible solution however it doesn't fix the fact it will still hang the whole application when the window is closed or application exited as well.

          JoeCFDJ Offline
          JoeCFDJ Offline
          JoeCFD
          wrote on last edited by JoeCFD
          #43

          @FleetingMemory that is why I wrote earlier that you need a splash widget with some nice animation at exit and make your app wait for these series to be cleared.

          You can also file a bug with Jon's test code to Qt for optimization in removeAllSeries call. I guess one update may be enough instead of one update after one deletion.

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          • Christian EhrlicherC Offline
            Christian EhrlicherC Offline
            Christian Ehrlicher
            Lifetime Qt Champion
            wrote on last edited by
            #44

            I've tested @JonB 's code with 12000 series / 40 data points each in debug mode:

            Starting to create
            Finished creating 32858
            Starting to delete
            Finished deleting 195421

            Digged a little bit around to see what happens during destruction. The most time the legend gets updated... so:
            I added this before delete chart;:
            delete chart->legend();

            -->
            Starting to create
            Finished creating 33861
            Starting to delete
            Finished deleting 27167

            The best thing I found is to add d_ptr->m_dataset->disconnect(); in QChart dtor. I doubt this will go in into official QtCharts since it's in maintainance mode only.

            -->
            Starting to create
            Finished creating 31901
            Starting to delete
            Finished deleting 16988

            Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
            Visit the Qt Academy at https://academy.qt.io/catalog

            JonBJ F 2 Replies Last reply
            1
            • Christian EhrlicherC Christian Ehrlicher

              I've tested @JonB 's code with 12000 series / 40 data points each in debug mode:

              Starting to create
              Finished creating 32858
              Starting to delete
              Finished deleting 195421

              Digged a little bit around to see what happens during destruction. The most time the legend gets updated... so:
              I added this before delete chart;:
              delete chart->legend();

              -->
              Starting to create
              Finished creating 33861
              Starting to delete
              Finished deleting 27167

              The best thing I found is to add d_ptr->m_dataset->disconnect(); in QChart dtor. I doubt this will go in into official QtCharts since it's in maintainance mode only.

              -->
              Starting to create
              Finished creating 31901
              Starting to delete
              Finished deleting 16988

              JonBJ Online
              JonBJ Online
              JonB
              wrote on last edited by JonB
              #45

              @Christian-Ehrlicher
              All I saw was all the time being spent in removeAllSeries(), or whichever you remove series if one by one. I looked at remoceSeries() source code online but I don't have sources to dig further. I don't know how that is affected by legend. Nothing struck me except however it is storing its model data. That could relate to your d_ptr->m_dataset. And d_ptr requires OP to change and compile Qt sources, right?

              It's taking 30 seconds to get rid of 10,000 series which it never took 30 seconds to create, it is a lot of time per series.

              P.S.
              Of course, as you say QtCharts is going so realise nothing is going to be done about sources.

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              • Christian EhrlicherC Christian Ehrlicher

                I've tested @JonB 's code with 12000 series / 40 data points each in debug mode:

                Starting to create
                Finished creating 32858
                Starting to delete
                Finished deleting 195421

                Digged a little bit around to see what happens during destruction. The most time the legend gets updated... so:
                I added this before delete chart;:
                delete chart->legend();

                -->
                Starting to create
                Finished creating 33861
                Starting to delete
                Finished deleting 27167

                The best thing I found is to add d_ptr->m_dataset->disconnect(); in QChart dtor. I doubt this will go in into official QtCharts since it's in maintainance mode only.

                -->
                Starting to create
                Finished creating 31901
                Starting to delete
                Finished deleting 16988

                F Offline
                F Offline
                FleetingMemory
                wrote on last edited by
                #46

                @Christian-Ehrlicher I currently have legend disabled, is it still updating in the background even with it off?

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                • JoeCFDJ JoeCFD

                  @FleetingMemory that is why I wrote earlier that you need a splash widget with some nice animation at exit and make your app wait for these series to be cleared.

                  You can also file a bug with Jon's test code to Qt for optimization in removeAllSeries call. I guess one update may be enough instead of one update after one deletion.

                  F Offline
                  F Offline
                  FleetingMemory
                  wrote on last edited by FleetingMemory
                  #47

                  original bug report was ignored, had to refile and explain more. Linked the new report below

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                  • JoeCFDJ JoeCFD

                    @FleetingMemory that is why I wrote earlier that you need a splash widget with some nice animation at exit and make your app wait for these series to be cleared.

                    You can also file a bug with Jon's test code to Qt for optimization in removeAllSeries call. I guess one update may be enough instead of one update after one deletion.

                    F Offline
                    F Offline
                    FleetingMemory
                    wrote on last edited by
                    #48

                    @JoeCFD Filed the bug report yesterday -- Feel free to add any findings to it!
                    https://bugreports.qt.io/browse/QTBUG-134490

                    JoeCFDJ 1 Reply Last reply
                    0
                    • Christian EhrlicherC Offline
                      Christian EhrlicherC Offline
                      Christian Ehrlicher
                      Lifetime Qt Champion
                      wrote on last edited by
                      #49

                      As I already said QtCharts is deprecated. Nothing will be changed there. I gave you two solutions...

                      Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
                      Visit the Qt Academy at https://academy.qt.io/catalog

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                      2
                      • F FleetingMemory

                        @JoeCFD Filed the bug report yesterday -- Feel free to add any findings to it!
                        https://bugreports.qt.io/browse/QTBUG-134490

                        JoeCFDJ Offline
                        JoeCFDJ Offline
                        JoeCFD
                        wrote on last edited by
                        #50

                        @FleetingMemory They will not fix it for you. Maybe you can dig into the source code of this module and try some fixes. Then build it for yourself.

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                        1
                        • F Offline
                          F Offline
                          FleetingMemory
                          wrote on last edited by
                          #51

                          @Christian-Ehrlicher @JoeCFD Thank you for helping find the fix will try what was submitted to the bug report.

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