private V More ...doPut(K kkey, V value, boolean onlyIfAbsent) {
890         Comparable<? super K> key = comparable(kkey);
891         for (;;) {
892             Node<K,V> b = findPredecessor(key);
893             Node<K,V> n = b.next;
894             for (;;) {
895                 if (n != null) {
896                     Node<K,V> f = n.next;
897                     if (n != b.next)               // inconsistent read
898                         break;;
899                     Object v = n.value;
900                     if (v == null) {               // n is deleted
901                         n.helpDelete(b, f);
902                         break;
903                     }
904                     if (v == n || b.value == null) // b is deleted
905                         break;
906                     int c = key.compareTo(n.key);
907                     if (c > 0) {
908                         b = n;
909                         n = f;
910                         continue;
911                     }
912                     if (c == 0) {
913                         if (onlyIfAbsent || n.casValue(v, value))
914                             return (V)v;
915                         else
916                             break; // restart if lost race to replace value
917                     }
918                     // else c < 0; fall through
919                 }
920 
921                 Node<K,V> z = new Node<K,V>(kkey, value, n);
922                 if (!b.casNext(n, z))
923                     break;         // restart if lost race to append to b
924                 int level = randomLevel();
925                 if (level > 0)
926                     insertIndex(z, level);
927                 return null;
928             }
929         }
930     }

int level = randomLevel();