code: void renewLease(String holder) throws IOException {
      readLock();
      try {
        if (isInSafeMode()) {
          throw new SafeModeException("Cannot renew lease for " + holder, safeMode);
        }
  
        leaseManager.renewLease(holder);
      } finally {
        readUnlock();
      }
    }
docs: Renew the lease(s) held by the given client