code: public static IntSet concurrentCopyFrom(IntSet intSet, int maxExclusive) {
        ConcurrentSmallIntSet cis = new ConcurrentSmallIntSet(maxExclusive);
        intSet.forEach((IntConsumer) cis::set);
        return cis;
     }
docs: Returns a copy of the given set that supports concurrent operations. The returned set will contain all of the
  ints the provided set contained. The returned set only supports up to the maximum size the previous int set
  supported when this method is invoked or the largest int it held.
  @param intSet set to copy from
  @param maxExclusive the maximum value - 1 that can be inserted into the set
  @return concurrent copy