public void apply()

in gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/strategy/optimization/LazyBarrierStrategy.java [80:137]
43 lines of code
26 McCabe index (conditional complexity)

    public void apply(final Traversal.Admin<?, ?> traversal) {
        // drop()/element() is a problem for bulked edge/meta properties because of Property equality changes in TINKERPOP-2318
        // which made it so that a Property is equal if the key/value is equal. as a result, they bulk together which
        // is fine for almost all cases except when you wish to drop the property.
        if (TraversalHelper.onGraphComputer(traversal) ||
                traversal.getTraverserRequirements().contains(TraverserRequirement.PATH) ||
                TraversalHelper.hasStepOfAssignableClass(DropStep.class, traversal)||
                TraversalHelper.hasStepOfAssignableClass(ElementStep.class, traversal))
            return;

        boolean foundFlatMap = false;
        boolean labeledPath = false;
        for (int i = 0; i < traversal.getSteps().size(); i++) {
            final Step<?, ?> step = traversal.getSteps().get(i);

            if (step.getLabels().contains(BARRIER_PLACEHOLDER)) {
                TraversalHelper.insertAfterStep(new NoOpBarrierStep<>(traversal, MAX_BARRIER_SIZE), step, traversal);
                step.removeLabel(BARRIER_PLACEHOLDER);
                if (step.getLabels().contains(BARRIER_COPY_LABELS)) {
                    step.removeLabel(BARRIER_COPY_LABELS);
                    TraversalHelper.copyLabels(step, step.getNextStep(), true);
                }
            }

            if (step instanceof PathProcessor) {
                final Set<String> keepLabels = ((PathProcessor) step).getKeepLabels();
                if (null != keepLabels && keepLabels.isEmpty()) // if no more path data, then start barrier'ing again
                    labeledPath = false;
            }

            if (step instanceof FlatMapStep &&
                    !(step instanceof VertexStep && ((VertexStep) step).returnsEdge()) ||
                    (step instanceof GraphStep &&
                            (i > 0 || ((GraphStep) step).getIds().length >= BIG_START_SIZE ||
                                    (((GraphStep) step).getIds().length == 0 && !(step.getNextStep() instanceof HasStep))))) {

                // DiscardStep, EmptyStep signify the end of the traversal where no barriers are really going to be
                // helpful after that. ProfileSideEffectStep means the traversal had profile() called on it and if
                // we don't account for that a barrier will inject at the end of the traversal where it wouldn't
                // be otherwise. LazyBarrierStrategy executes before the finalization strategy of ProfileStrategy
                // so additionally injected ProfileSideEffectStep instances should not have effect here.
                if (foundFlatMap && !labeledPath &&
                        !(step.getNextStep() instanceof Barrier) &&
                        !(step.getNextStep() instanceof DiscardStep) &&
                        !(step.getNextStep() instanceof EmptyStep) &&
                        !(step.getNextStep() instanceof ProfileSideEffectStep)) {
                    final Step noOpBarrierStep = new NoOpBarrierStep<>(traversal, MAX_BARRIER_SIZE);
                    TraversalHelper.copyLabels(step, noOpBarrierStep, true);
                    TraversalHelper.insertAfterStep(noOpBarrierStep, step, traversal);
                } else
                    foundFlatMap = true;
            }

            if (!step.getLabels().isEmpty())
                labeledPath = true;

        }
    }