@Override
    public OpTreeSignature getSignature(Operator<? extends OperatorDesc> op) {
      return cache.computeIfAbsent(op, k -> OpTreeSignature.of(op, this));
    }
A simple cache backend to prevent repeated signature computations.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/signature/OpTreeSignatureFactory.java