// Tracks monotonic sequence numbers for graphs.
class ClusterSequenceNumberGenerator {
 public:
  void Reset() {
    mutex_lock lock(mu_);
    sequence_numbers_.clear();
  }

  int64 GetNext(uint64 key) {
    mutex_lock lock(mu_);
    return sequence_numbers_[key]++;
  }

  static ClusterSequenceNumberGenerator& Global() {
    static ClusterSequenceNumberGenerator* gen =

        final long seqNo = response.getSeqNo();
        if (seqNo != SequenceNumbers.UNASSIGNED_SEQ_NO) {
            esEntity.asDocMeta().seqNo(seqNo);
        }
        final long primaryTerm = response.getPrimaryTerm();
        if (primaryTerm != SequenceNumbers.UNASSIGNED_PRIMARY_TERM) {
            esEntity.asDocMeta().primaryTerm(primaryTerm);
        }

        return 1;

        final long seqNo = response.getSeqNo();
        if (seqNo != SequenceNumbers.UNASSIGNED_SEQ_NO) {
            esEntity.asDocMeta().seqNo(seqNo);
        }
        final long primaryTerm = response.getPrimaryTerm();
        if (primaryTerm != SequenceNumbers.UNASSIGNED_PRIMARY_TERM) {
            esEntity.asDocMeta().primaryTerm(primaryTerm);
        }

        return 1;

        final long seqNo = response.getSeqNo();
        if (seqNo != SequenceNumbers.UNASSIGNED_SEQ_NO) {
            esEntity.asDocMeta().seqNo(seqNo);
        }
        final long primaryTerm = response.getPrimaryTerm();
        if (primaryTerm != SequenceNumbers.UNASSIGNED_PRIMARY_TERM) {
            esEntity.asDocMeta().primaryTerm(primaryTerm);
        }

        return 1;