Segmentation fault within some specific conditions

[Phil Thompson]

On 06/03/2024 14:17, Erwan Mathieu wrote:
> Hello,
> 
> I'm running into a segmentation fault when using PyQt 6.6.0/6.6.1. I 
> could
> reproduce it with a very basic project, here is how to make it happen:
> 
> // File test.py
> from PyQt6.QtCore import QObject
> from PyQt6.QtGui import QGuiApplication
> from PyQt6.QtQml import QQmlApplicationEngine, qmlRegisterType
> 
> class MyModel(QObject):
>     def __init__(self, parent = None):
>         super().__init__(parent = parent)
>         print("I am alive")
>     def __del__(self):
>         print("I am dead ")
> 
> app = QGuiApplication([])
> qmlRegisterType(MyModel, "Test", 1, 0, "MyModel")
> engine = QQmlApplicationEngine()
> engine.load("./Main.qml")
> app.exec()
> 
> // File Main.qml
> import QtQuick
> import QtQuick.Controls
> 
> import Test 1.0
> 
> Window
> {
>     width: 640
>     height: 480
>     visible: true
>     title: qsTr("Hello World")
> 
>     Loader { id: loader; sourceComponent: superComponent; }
> 
>     Button
>     {
>         anchors.centerIn: parent
>         text: "Unload"
>         onClicked: loader.sourceComponent = null
>     }
> 
>     Component
>     {
>         id: superComponent
> 
>         Item
>         {
>             MyModel
>             {
>                 property var superProperty: "hello"
>             }
>         }
>     }
> }
> 
> Now start the test.py file, and click on the "Unload" button. The 
> Component
> instance is destroyed, which also destroys the MyModel instance. We can 
> see
> the print instructions that says so. Just after that, I get a 
> segmentation
> fault.
> 
> For some reason, this happens only when declaring a property on the 
> MyModel
> instance. If you comment the superProperty declaration, everything is 
> fine.
> 
> We were previously working with version 6.4.2, and this caused no 
> issue. I
> have it starting from 6.6.0 (but didn't try intermediate versions).
> 
> I also tried to make this example directly in C++, and I don't get the
> error, so I think this is related to PyQt.
> 
> If it is of any help, gdb gives me the following crash point:
> 0x00007ffff636abb0 in QMetaObject::methodOffset() const () from
> /..../lib/python3.10/site-packages/PyQt6/Qt6/lib/libQt6Core.so.6
> 
> Any idea of why this is happening, and if there is a workaround/fix ?
> 
> Kind regards,
> 
> Erwan MATHIEU

Should be fixed in the next snapshot (and v6.7.0). However, as is usual 
with QML, fixes in one area may break it in other areas. Fingers 
crossed.

Phil