[Development] [Qt-5.6] leak of QtSharedPointer::ExternalRefCountData objects

[Liang Jian]

    After some further investigation I can now confirm that one of the leak
is caused by the following code in QQmlObjectCreator::createInstance(),
qqmlobjectcreator.cpp:

    *sharedState->allJavaScriptObjects = QV4::QObjectWrapper::wrap(v4,
instance);

  ++sharedState->allJavaScriptObjects;


    But the reason is still unknown



On Sun, Nov 15, 2015 at 10:19 PM, Liang Jian <jianliang79 at gmail.com> wrote:

>       Hello everyone, I checkout qt 5.6 branch yesterday in my windows 10
> x64 machine, I build it and run my program and see many leaks. Then I use C++
> Memory Validator to find the source of the leaks, I can now confirm the
> leaked objects are QtSharedPointer::ExternalRefCountData which are created
> in QQmlObjectCreator::createInstance(), qqmlobjectcreator.cpp Line 1049,
> below is the call stack printed by C++ Memory Validator:
>
>    Qt5Cored.dll  QtSharedPointer::ExternalRefCountData::getAndRef :
> [d:\qt5\qtbase\src\corelib\tools\qsharedpointer.cpp Line 1337]
>
>    Qt5Qmld.dll  QWeakPointer<QObject>::QWeakPointer<QObject><QObject> :
> [d:\qt5\qtbase\src\corelib\tools\qsharedpointer_impl.h Line 706]
>
>    Qt5Qmld.dll  QPointer<QObject>::QPointer<QObject> :
> [d:\qt5\qtbase\src\corelib\kernel\qpointer.h Line 65]
>
>    Qt5Qmld.dll  QQmlObjectCreator::createInstance :
> [d:\qt5\qtdeclarative\src\qml\qml\qqmlobjectcreator.cpp Line 1049]
>     1044 :                 QQmlData *ddata = QQmlData::get(instance,
> /*create*/true);
>     1045 :                 ddata->rootObjectInCreation = true;
>     1046 :
> sharedState->rootContext->isRootObjectInCreation = false;
>     1047 :             }
>     1048 :
>     1049 :             sharedState->allCreatedObjects.push(instance);
>     1050 :         } else {
>     1051 :             Q_ASSERT(typeRef->component);
>     1052 :             Q_QML_OC_PROFILE(sharedState->profiler,
> profiler.update(typeRef->component->fileName(),
>     1053 :                     context->url(), obj->location.line,
> obj->location.column));
>     1054 :             if
> (typeRef->component->compilationUnit->data->isSingleton())
>    Qt5Qmld.dll  QQmlObjectCreator::create :
> [d:\qt5\qtdeclarative\src\qml\qml\qqmlobjectcreator.cpp Line 197]
>
>    Qt5Qmld.dll  QQmlComponentPrivate::beginCreate :
> [d:\qt5\qtdeclarative\src\qml\qml\qqmlcomponent.cpp Line 863]
>
>    Qt5Qmld.dll  QQmlComponent::beginCreate :
> [d:\qt5\qtdeclarative\src\qml\qml\qqmlcomponent.cpp Line 812]
>
>    Qt5Qmld.dll  QQmlComponent::create :
> [d:\qt5\qtdeclarative\src\qml\qml\qqmlcomponent.cpp Line 772]
>
>    Qt5Quickd.dll  QQuickView::continueExecute :
> [d:\qt5\qtdeclarative\src\quick\items\qquickview.cpp Line 486]
>
>    Qt5Quickd.dll  QQuickViewPrivate::execute :
> [d:\qt5\qtdeclarative\src\quick\items\qquickview.cpp Line 127]
>
>    Qt5Quickd.dll  QQuickView::setSource :
> [d:\qt5\qtdeclarative\src\quick\items\qquickview.cpp Line 256]
>
>
>     All the leaked QtSharedPointer::ExternalRefCountData objects are
> allocated in the line
>     sharedState->allCreatedObjects.push(instance);
>     then some other code path will also use QPointer (contained in some
> structures allocated by v4mm) to track the same object 'instance' and I
> guess the QPointer wasn't properly destructed which will cause the QtSharedPointer::ExternalRefCountData
> not deleted.
>     I have investigated this issue for nearly one day, but I can't find
> which code cause the leak, this is a non-trivial leak, I hope somebody can
> help to find the source of the leak. thanks!
>
>
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