[Interest] Memory Leak when instantiating QWidget based windows

Thu Sep 8 15:54:54 CEST 2016

I too am using valgrind-3.11.0 (on Mac OS X 10.10.5), but I've never seen
that in the Application Output window.  I don't usually look there when
using Memcheck.

Is there anything at all in the Memcheck panel?  Sometimes if your
application crashes when using valgrind there is useful info there.

Are you running on the debug or release version of your application?

Or could it be related this?:
https://bugreports.qt.io/browse/QTCREATORBUG-10163

---
Andy Maloney  //  https://asmaloney.com
twitter ~ @asmaloney <https://twitter.com/asmaloney>

On Thu, Sep 8, 2016 at 9:37 AM, Edward Sutton <edward.sutton at subsite.com>
wrote:

>
> On Sep 8, 2016, at 8:18 AM, Andy <asmaloney at gmail.com> wrote:
>
> Ah - sorry.  I can see how that's unclear (pre-coffee email).
>
> I meant the Debug section on the left-hand side of the main window:
> Welcome, Edit, Design, Debug,...
>
> >0Then the bottom pane pops up below the editor and has a dropdown at the
> top-left - Debugger, Clang Static Analyzer, Memcheck,…
>
>
> Found it! Thank you.
>
> 3.1 - Selected Memcheck in the drop-down at lower-left main edit window
> 3.2 - Press green play button to the *right* of the Memcheck drop-down
>
> Unfortunately it did not run for me.
>
> Application Output reported:
>
> Analyzing finished.
> ** Unknown error **
>
> Using valgrind-3.11.0
>
> -Ed
>
>
>
> ---
> Andy Maloney  //  https://asmaloney.com
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__asmaloney.com&d=DQMFaQ&c=G4BpsyPyB19LB50bn2swXw&r=cAG2c-SQES5P2qb8IW-uwnBOCX_f2qYJIlzenFnoHUc&m=6HvvOEegoKg93yk53OwceqGbTwWp3iEoQVNaZSRUkTM&s=bdAVC6-LbUYQycT9JFc91oa7YAOneh6j9LUG3pCqRmU&e=>
> twitter ~ @asmaloney
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__twitter.com_asmaloney&d=DQMFaQ&c=G4BpsyPyB19LB50bn2swXw&r=cAG2c-SQES5P2qb8IW-uwnBOCX_f2qYJIlzenFnoHUc&m=6HvvOEegoKg93yk53OwceqGbTwWp3iEoQVNaZSRUkTM&s=DErQyEPdZ-8bI_rhS90_nSKoH2XfmOa5EdwR_Dzu7pU&e=>
>
>
> On Thu, Sep 8, 2016 at 9:13 AM, Edward Sutton <edward.sutton at subsite.com>
> wrote:
>
>> 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> 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.
>>
>>
>>
>>
>> ---
>> Andy Maloney  //  https://asmaloney.com
>> <https://urldefense.proofpoint.com/v2/url?u=https-3A__asmaloney.com&d=DQMFaQ&c=G4BpsyPyB19LB50bn2swXw&r=cAG2c-SQES5P2qb8IW-uwnBOCX_f2qYJIlzenFnoHUc&m=c5VUb3aKymRQx0ih8A7yljotGOJbYdQ2iJ1PDgaS508&s=r8u8ZRFO-Qd4fneoIZohXBUjpcA_h7vjbk3y92UEclg&e=>
>> twitter ~ @asmaloney
>> <https://urldefense.proofpoint.com/v2/url?u=https-3A__twitter.com_asmaloney&d=DQMFaQ&c=G4BpsyPyB19LB50bn2swXw&r=cAG2c-SQES5P2qb8IW-uwnBOCX_f2qYJIlzenFnoHUc&m=c5VUb3aKymRQx0ih8A7yljotGOJbYdQ2iJ1PDgaS508&s=o5ozT95AtJLPuZ0_E6csAPsjuGwFJwioJcJtEJxKwNk&e=>
>>
>>
>> On Thu, Sep 8, 2016 at 6:55 AM, Konstantin Shegunov <kshegunov at gmail.com>
>> wrote:
>>
>>>
>>> On Wed, Sep 7, 2016 at 11:23 PM, Mike Jackson <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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