code: public SequenceGenerator.SequenceBlock allocateBlock(int blockSize) {
          final long l = this.last;
          SequenceGenerator.SequenceBlock block =
                  new SequenceGenerator.SequenceBlock(l + 1, l + blockSize);
          this.last = l + blockSize;
  
          return block;
      }
docs: Allocate a block of sequence numbers, starting from the last allocated
  sequence value.
  
  @param blockSize the number of sequences to allocate
  
  @return allocated block of sequential numbers