sclass NLLogic_MultiThreadedEngine {
  bool unsafeEvals;
  MultiMap<Int, ExecutedRule> executedRules = treeMultiMap();
  new MultiThreadStepper stepper;
  LinkedHashSet<S> inputs = litorderedset(input);
  
  void processInput(S input) {
    temp tempSetTL(nlLogic_processInputOrFact_steppable_allowUnsafeEvals, unsafeEvals);
    stepper.add(nlLogic_processInputOrFact_steppable(input, inputAsFact, 
      or2(trim(source), "<default>"), new Collector<ExecutedRule>() {
        bool add(ExecutedRule r) {
          if (!showFailed && r.isFailed()) true;
          executedRules.put(ai_executedRuleScorer().get(r), r);
          for (S s : unnull(r.newInput))
            if (inputs.add(s))
              processInput(s);
          true;
        }
      }));
  };
  
  void seedInput(S input) { processInput(input); }
  
  void fullRun {
    stepAllWithStats_multiThreaded(stepper);
  }
  
  L<ExecutedRule> executedRules() { ret executedRules.allValues(); }
}