Method compare

fe/src/main/java/org/apache/impala/service/Frontend.java:1860–1863

(Function f1, Function f2)

    Collections.sort(fns,
        new Comparator<Function>() {
          @Override
          public int compare(Function f1, Function f2) {
            return f1.signatureString().compareTo(f2.signatureString());
          }
        });
    return fns;
  }