Gc Crashes Qml-application

Do not fear! This is not production code. It is just to learn new things about QML! I do not seek 'you shall not do something like this - do it like that.' I am more interested

Solution 1:

What might be the reason for this? Is there a way to tell the GC to be mor proactive?

The reason for this is the buggy qtquick object lifetime implementation. At this point it doesn't look to be a JS thing, but a qtquick thing. It clearly doesn't abide to its own alleged rules - for example, it will delete an object with a parent while still in use, resulting in a hard crash. You cannot expect reference counting to work as well. This behavior can occur in a number of scenarios that employ dynamism, it generally does not manifest in trivial and static scenarios.

The solution, as already outlined in the linked question, is to use manual object lifetime management. Use a set of new functions for the creation and deletion of objects.

• for creation, you must pass the object to the C++ side in order to call QQmlEngine::setObjectOwnership(ojb, QQmlEngine::CppOwnership); on it, this basically tells qtquick "don't even bother trying", luckily at least this works as it is supposed
• for destruction, you must pass the object to the C++ side in order to call obj->deleteLater();

For me this does the trick, I no longer get crashes for no apparent reason. Use the custom lifetime management and stay away from the stock functions for that. It gives you guarantees, that the object will stay alive as long as you need it, but also that it will not stay past the point where you want it gone, which is another problem, albeit not that severe. Of course, this eliminates the convenience factor of using JS, as you have to give up on automatic lifetime management and be a little more diligent and explicit with your own code, but there isn't much you can do about it. Even though the bug was reported almost a year ago and deemed critical, not a shred of work has been done about it whatsoever. Thus I assume that as critical as it may be in its severity, it is more like lowest priority when it comes to finding its cause and fixing it.