natix.SimilaritySearch.PivotSelectorRandom.NextPivot C# (CSharp) Method

        public override int NextPivot()
        {
            int piv;
            lock (this) {
                piv = this.permutation [this.curr];
                ++this.curr;
            }
            return piv;
        }

 public EPListRandomPivotsPriorized(MetricDB DB, int seed, int num_pivs)
 {
     var n = DB.Count;
     this.Items = new ItemPair[n];
     var pivs = new List<EPivot> (32);
     var rand = new Random (seed);
     var pivsel = new PivotSelectorRandom (n, rand);
     var piv = pivsel.NextPivot ();
     var pivOBJ = DB [piv];
     for (int objID = 0; objID < n; ++objID) {
         var d = DB.Dist(pivOBJ, DB[objID]);
         this.Items[objID] = new ItemPair(0, d);
     }
     double mean, variance;
     this.Statistics (out mean, out variance);
     pivs.Add(new EPivot(piv, Math.Sqrt(variance), mean, 0, 0, 0, 0));
     var item_cmp = new Comparison<ItemPair>((x,y) => {
         var diff_x = Math.Abs (x.Dist - pivs[x.ObjID].mean);
         var diff_y = Math.Abs (y.Dist - pivs[y.ObjID].mean);
         return diff_x.CompareTo(diff_y);
     });
     var queue = new SkipList2<int> (0.5, (x,y) => item_cmp (this.Items [x], this.Items [y]));
     for (int objID = 0; objID < n; ++objID) {
         queue.Add(objID, null);
     }
     var max_review = 2 * n / num_pivs;
     var list = new List<int> ();
     for (int i = 0; i < num_pivs; ++i) {
         Console.WriteLine("XXXXXX BEGIN {0} i: {1}", this, i);
         piv = pivsel.NextPivot();
         double piv_mean, piv_variance, qrad;
         PivotSelector.EstimatePivotStatistics(DB, rand, DB[piv], 256, out piv_mean, out piv_variance, out qrad);
         var pivID = pivs.Count;
         pivs.Add(new EPivot(piv, Math.Sqrt(piv_variance), mean, 0, 0, 0, 0));
         list.Clear();
         for (int s = 0; s < max_review; ++s) {
             var objID = queue.RemoveFirst();
             var d = DB.Dist(DB[objID], pivOBJ);
             var new_item = new ItemPair(pivID, d);
             if (item_cmp(new_item, this.Items[objID]) > 0) {
                 this.Items[objID] = new_item;
             }
             list.Add (objID);
         }
         foreach (var objID in list) {
             queue.Add(objID, null);
         }
         Console.WriteLine("XXXXXX END {0} i: {1}", this, i);
     }
     this.Pivs = pivs.ToArray ();
     Console.WriteLine("Number of pivots per group: {0}", this.Pivs.Length);
 }