public async Task Invalidate()
        {
            await _syncLock.WaitAsync().ConfigureAwait(false);

            _value = default(ExpirationMetadata <T>);
            _syncLock.Release();
        }
        public async Task <T> Value()
        {
            await _syncLock.WaitAsync().ConfigureAwait(false);

            try
            {
                if (IsValueCreatedInternal)
                {
                    return(_value.Result);
                }

                var result = await _valueProvider(_value).ConfigureAwait(false);

                _value = result;
                return(_value.Result);
            }
            finally
            {
                _syncLock.Release();
            }
        }