A debate formed about a lock statement in our team – I would appreciate some external feedback about this. The questionable code part is:

lock (IndexLock)
{
    currentIndex = Index;
}

You can see part of the class below:

public class BuilderService
{

    private ImmutableList<Model> Index { get; set; } = ImmutableList<Model>.Empty;
    private object IndexLock { get; } = new();

    public Add(Model item)
    {
        lock (IndexLock)
        {
           Index = Index.Add(item);
        }
    }


    public void GetFilterLinesExcluding()
    {
        var filters = new List<Model>();
        ImmutableList<FilterModel> currentIndex;
    
        lock (IndexLock)
        {
            currentIndex = Index;
        }
    
        foreach (var filter in currentIndex)
        {
            ...
    
    }

Without going into the details, the debate is around phenomenons like:

• memory visibility
• memory barriers
• stale values

Does it make sense to have a lock around currentIndex = Index?

I will provide more information if required.

Thank you in advance!