Caching parsed MediaItem using Sitecore revision

Prices.cs

private static List<Price> _prices;
private static string _pricesRevision;
private static readonly object _lock = new object();

public static List<Price> GetPrices(MediaItem mediaItem)
{
  var revision = mediaItem.Statistics.Revision;

  if (revision != _pricesRevision)
  {
    lock (_lock)
    {
      if (revision != _pricesRevision)
      {
        _prices = ReadPrices(mediaItem);
        _pricesRevision = revision;
      }
    }
  }
  return _prices;
}