QWebView for running D3 javascript is slow after reloading HTML.

CLang

I am using a QWebView to display plots using javascript and D3. There is a combobox to select different datasets. Each time a new dataset is selected, some calculations are done, then the javascript is reinitialized with the new data and set as an html string. Then the QWebview is reset using QWebView::setHtml().

If I change the combobox value a few times, the plots load exponentially slower each time until it eventually freezes. Sometimes it will eventually load and sometimes not.

(I'm not sure the javascript is relevant - it is not my area of expertise so I haven't taken the time to understand it yet. I'm hoping the problem can be resolved with Qt code)

From the QWebView documentation: "The html is loaded immediately; external objects are loaded asynchronously."

My guess is that the javascript continues to execute in the background and it doesn't stop when the html is updated and reloaded. Is there a way to stop this?

The code for initializing and updating are as follows:

dataView::dataView(QWidget* parent) : QWidget(parent)
{
  init();
}

void dataview::updatePlot()
{
  //Get new value and do some calculations

  // Update html string with new data
  std::string htmlString = "[new javascript]";

  webView->setHtml(QString::fromLocal8bit(htmlString.c_str()));
}

void dataView::init()
{
   webView = new QWebView();
  // Need path to exe as this is where the local copies of the js files are.
  QUrl path = webView->url();
  path.setUrl(QCoreApplication::applicationDirPath());
  m_jsPath = path.toString().toStdString();  

  // Initialise the html string
  htmlText=""

  webSetting = webView->settings();

   // Maybe doing nothing-----------------------
   webSetting->setObjectCacheCapacities(0, 0, 0);
   webSetting->setMaximumPagesInCache(1);    
   //--------------------------------------------

  QPointer<QVBoxLayout> mainLayout = new QVBoxLayout();
  mainLayout->addWidget(webView);
  setLayout(mainLayout);
}

Hopefully I have included all the relative information code.

CLang

The issue seems to be in Qt5.5 - I compiled with 5.3 and the issue is gone.

Konstantin Tokarev

Which version of QtWebKit are you using?
Does problem reproduce if you remove cache settings?

CLang

This post is deleted!

CLang

@Konstantin-Tokarev

I am using Qt 5.5

I am unsure how to remove the cache settings but I will try that right now.

Edit: It appears that

webSetting->setObjectCacheCapacities(0, 0, 0);

should disable cache, so I have tried this.

Konstantin Tokarev

Yep, try without this line

CLang

@Konstantin-Tokarev

I have tried it with all combinations of the following settings (one, other one, both, none)

webSetting->setObjectCacheCapacities(0, 0, 0);
webSetting->setMaximumPagesInCache(1);

I am going to try another Qt version and see if that has an effect.

Konstantin Tokarev

You should use qtwebkit from 5.212 branch, version coming with Qt 5.5 is obsolete

CLang

@Konstantin-Tokarev said in QWebView for running D3 javascript is slow after reloading HTML.:

5.212

Thanks for the advice. Is 5.212 > 5.10?

And why such a weird version number? Should I download form git or is the qt installer going to have it?

Konstantin Tokarev

@CLang For use with Qt 5.10, get binaries from http://download.qt.io/snapshots/ci/qtwebkit/5.212/latest/qtwebkit/

And why such a weird version number?

It isn't tied to particular Qt version, instead respective WebKitGTK's branch name is used as a basis

CLang

@Konstantin-Tokarev

Thanks for all your help.

Does this mean I could download the source, compile it with cmake and msvc2013_64 and use it with qt5.5?

Konstantin Tokarev

No, MSVC 2013 is not supported. You need MSVC >= 2015 or MinGW >= 4.9

CLang

@Konstantin-Tokarev I actually downgraded to 5.3 and the issue has resolved.

What's the best way to resolve this post? Reply to the initial post with the solution and change to 'solved'?

CLang

The issue seems to be in Qt5.5 - I compiled with 5.3 and the issue is gone.