[Interest] Memory Leak when instantiating QWidget based windows

[Edward Sutton]

Hi Andy,

Could you please elaborate on step #3?

I cannot find a Memcheck option under Preferences > Debugger.

Thanks for the tips!

-Ed
Qt Creator 4.01 with Qt 5.6.1


On Sep 8, 2016, at 7:56 AM, Andy <asmaloney at gmail.com<mailto:asmaloney at gmail.com>> wrote:

Mike:

If you haven't already tried it, using Qt Creator in combination with valgrind works really well to track these kinds of things down.

The basics:

  1) install valgrind (I used homebrew)
  2) point Qt Creator at it in the prefs (Analyzer->Valgrind)
  3) Click the Debug tab, set the tool to Memcheck, and click the start button (little green arrow)

After it runs your application (slowly), it will spit out a bunch of info about memory leaks that make it pretty easy to track down the problems.




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On Thu, Sep 8, 2016 at 6:55 AM, Konstantin Shegunov <kshegunov at gmail.com<mailto:kshegunov at gmail.com>> wrote:

On Wed, Sep 7, 2016 at 11:23 PM, Mike Jackson <imikejackson at gmail.com<mailto:imikejackson at gmail.com>> wrote:
We monitor the memory use before and after the loop using OS X's Activity monitor. At the end of the loop there is more memory being used than before the loop, by about 2~3MB worth.

This isn't reliable. Consider the following C++ only code:

int main(int argc, char ** argv)

{

    struct X;

    X * x = nullptr;


    struct X {

        int data[1024];

    };


    for (qint32 i = 0; i < 100000; i++)  {

        x = new X[1024];

        delete x;

    }


    return 0;

}


In the KSysGuard (KDE's system monitor) I observe for the memory consumption: 12 908k, 23 048k shared before the loop and 12 944k, 25 112k shared after the loop. There isn't a leak here, yet there's a difference. The OS's heap manager may free the memory immediately, may cache it, or hold on to it. Ultimately it's out of your control, that's why you should use a code analyzer (like valgrind to track leaks).


Kind regards.

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