ReferenceQueue.cs

public class PhantomReference
{
    private readonly ReferenceQueue _queue;

    protected PhantomReference(ReferenceQueue queue)
    {
        _queue = queue;
    }
   
    ~PhantomReference()
    {
        _queue.Notify(this);
    }
}

public class ReferenceQueue
{
    private readonly ConcurrentQueue<PhantomReference> _references;

    public ReferenceQueue()
    {
        _references = new ConcurrentQueue<PhantomReference>();
    }
   
    public PhantomReference Poll()
    {
        return _references.TryDequeue(out var value) ? value : null;
    }
    
    internal void Notify(PhantomReference value)
    {
        _references.Enqueue(value);
    }
}