code: synchronized Lease reassignLease(Lease lease, String src, String newHolder) {
       assert newHolder != null : "new lease holder is null";
       LeaseOpenTime leaseOpenTime = null;
       if (lease != null) {
         leaseOpenTime = removeLease(lease, src);
       }
       return addLease(newHolder, src,
                       leaseOpenTime != null ?
                       leaseOpenTime.openTime :
                       System.currentTimeMillis());
     }
docs: Reassign lease for file src to the new holder.