private Set<Shape> evalRoot(
            Model model,
            NeighborProviderIndex index,
            InternalSelector selector,
            List<Set<Shape>> results
    ) {
        Collection<? extends Shape> shapesToEmit = selector.getStartingShapes(model);
        Context isolatedContext = new Context(model, index, results);
        Set<Shape> captures = new HashSet<>();
        for (Shape rootShape : shapesToEmit) {
            isolatedContext.getVars().clear();
            selector.push(isolatedContext, rootShape, (c, s) -> {
                captures.add(s);
                return InternalSelector.Response.CONTINUE;
            });
        }

        return captures;
    }
Uses parallel streams when the model size exceeds this number.
smithy-model/src/main/java/software/amazon/smithy/model/selector/WrappedSelector.java