I am familiar with BindingOperations.EnableCollectionSynchronization to make WPF participate in locking access to an ObservableCollection for use on multiple threads.

But does this place the same restriction on my use of a CollectionViewSource.View that uses that ObservableCollection as its source? Or does the view contain its own internal list?

For example, consider the following simplified view-model (which I admit I have not compiled) with a protected list of shapes that is publicly exposed from a CollectionViewSource view. As long as I protect every use of the _shapes collection with the _lock object, I should be fine and WPF will like me.

But should I be locking the same _lock object in the DoesViewContainShape function?

public class MeasureVm
{
    public MeasureVm()
    {
        BindingOperations.EnableCollectionSynchronization(_shapes, _lock);  
        _cvsShapes = new CollectionViewSource() { Source = _shapes, Filter = FilterShapes };
    }

    // WPF Binds to this

    public ICollectionView Shapes => _cvsShapes.View;

    private  bool FilterShapes(object obj)
    {
         // Eventually some arbitrary code to filter out shapes
         return true.
    }
    public void AddShape(shape)
    {
        // Any use of _shapes requires locking.

        lock(_lock)
            _shapes.Add(shape);
    }

    public bool DoesViewContainShape(Shape shape)
    {
        // SHOULD I LOCK HERE?
        return _cvsShapes.View.Contains(shape);
    }

    private ObservableCollection<Shape> _shapes = new();
    private CollectionViewSource _cvsShapes;
    private object _lock                        = new();

}