code: func shouldAttemptUpdate(ai time.Duration, now, lastAccessed time.Time, rf randFunc) bool {
  	return xFetch(now, lastAccessed.Add(ai), (ai / accessUpdateDeltaFactor), 1, rf)
  }
docs: // shouldAttemptUpdate  returns true if a cache entry update should be attempted
  // given the supplied parameters.
  //
  // We probabilistically update the "last accessed" field based on how close we
  // are to the configured AccessUpdateInterval using the xFetch function.