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public class CloseableThreadLocal {
    [ThreadStatic]
    public static Dictionary<int, object> slots;

    private static readonly List<Dictionary<int, object>> slotsContainers = new List<Dictionary<int, object>>();

    public static Dictionary<int, object> Slots {
        get {
            if (slots == null) {
                var container = new Dictionary<int, object>();
                slotsContainers.Add(container);
                return slots = container;
            }

            return slots;
        }
    }

    public /*protected internal*/ virtual Object InitialValue() {
        return null;
    }

    public virtual Object Get() {
        object val;

        if (Slots.TryGetValue(this.GetHashCode(), out val)) {
            return val;
        }
        val = InitialValue();
        Set(val);
        return val;
    }

    public virtual void Set(object val) {
        Slots[this.GetHashCode()] = val;
    }

    public virtual void Close() {
        if (slots != null)// intentionally using the field here, to avoid creating the instance
            slots.Remove(this.GetHashCode());
    }

    ~CloseableThreadLocal() {
        foreach (var container in slotsContainers)
            container.Remove(this.GetHashCode());
    }
}