ConcurrentValue

public class ConcurrentValue<T> {
    readonly object _sync;
    T _value;
    Func<T> _createValueFunc;
    bool _created;

    public ConcurrentValue() { _sync = new object(); }
    public ConcurrentValue(Func<T> valueFunction) : this() { _createValueFunc = valueFunction; }

    public T Value {
        get {
            bool locktaken = false;
            try {
                Monitor.Enter(_sync,ref  locktaken);
                if(_value == null) {
                    _value = _createValueFunc();
                    _created = true;
                }
            }
            finally {
                if(locktaken)
                    Monitor.Exit(_sync);
            }
            return _value;
        }
    }
    public void ResetValue() {
        bool locktaken = false;
        try {
            Monitor.Enter(_sync,ref  locktaken);
            _value = default(T);
            _created = false;
        }
        finally {
            if(locktaken)
                Monitor.Exit(_sync);
        }
    }
    public bool IsValueCreated {
        get {
            return _created;
        }
    }
}