A new code example for the "Qt Performance" book

Recently I added a new example* to my "Qt5 Performance" book's resources that I didn't manage to include in the original release - the trace macros creating output in chrome:tracing format. 

I think it's a very cool technique - instrument your code and than inspect the result as a graphic! On Linux we have flame graph support in the standard tooling integrated with Qt Creator.

On Windows, however, we do not have such a thing! And because I decided to use Windows as the deveolpment platform for my book, we have a kind of problem here, so creative solutions are needed!

And I already came up with an idea for that in the book - we can use libraries (like minitrace, the library we are using in this example ) to generate profiling output in a format that the Chrome's** trace viewer will understand! You didn't know that Google's Chrome had a built-in profiler? Some people assume it’s only for profiling “web stuff” like JavaScript and DOM, but we can use it as a really nice frontend for our own profiling data.

However, due to lack of time I couldn't try it out when I was writing the book 😞, but with the new example I added  I was able to generate output you see visualizedin the figure below:

Here is the code example I used - as you can see, you have only to insert some MTR_() macros here and there:

  int main(int argc, char *argv[])
  {
    mtr_init("trace.json");

    MTR_META_PROCESS_NAME("QmlWithModel");
    MTR_META_THREAD_NAME("Main GUI tread");
    MTR_BEGIN("main", "main()");

    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QGuiApplication app(argc, argv);

    QStringList countryList;
    countryList << "Thinking...";

    MTR_BEGIN("main", "load QML View");
    QQuickView view;
    QQmlContext *ctxt = view.rootContext();
    ctxt->setContextProperty("myModel", QVariant::fromValue(countryList));

    view.setSource(QUrl("qrc:/main.qml"));
    view.show();
    MTR_END("main", "load QML View");

    // get country names from network
    MTR_BEGIN("main", "init NetworkMgr");
    QNetworkAccessManager networkManager;
    MTR_END("main", "init NetworkMgr");
 
    ....

PS: heob-3 (i.e the new version of the heob memory profiler we discussed in the book) has a sampling profiler with optional flame graph output!!! I think I have to try it out in the near future!

--
* you can find the new example here, and the generated JSON file here

** Chrome browser's about:tracing tool. You can use it like this:

• go to chrome://tracing in Chrome
• click “Load” and open your JSON file (or alternatively drag the file into Chrome)
• that's all