public long sum( ) {
      long sum = _next == null ? 0 : _next.sum(); // Recursively get cached sum
      final long[] t = _t;
      for( long cnt : t ) sum += cnt;
      return sum;
    }
Return the internal counter striping factor.  Useful for diagnosing
performance problems.
jctools-core/src/main/java/org/jctools/maps/ConcurrentAutoTable.java