// CONTAINS_VALUE_RETRIES increases, though without locking it is theoretically possible.
    final Segment<K, V, E, S>[] segments = this.segments;
    long last = -1L;
    for (int i = 0; i < CONTAINS_VALUE_RETRIES; i++) {
      long sum = 0L;
      for (Segment<K, V, E, S> segment : segments) {
        // ensure visibility of most recent completed write
        int unused = segment.count; // read-volatile