java-topology/defects/loki/unit/LokiTest.java

import java.util.*;

/**
 * Java simulation unit test for Loki CWE-407 defect.
 * Simulates the O(E^2) edge dedup pattern in Loki's DAG implementation.
 *
 * loki-0001: DAG AddEdge slices.Contains on children/parents O(E^2)
 *
 * In practice, Loki query plans have small fan-out (1-3 children per node),
 * so this is LOW severity. The test uses synthetic high fan-out to
 * demonstrate the algorithmic defect.
 */
public class LokiTest {

    // ---------------------------------------------------------------
    // loki-0001: DAG AddEdge edge dedup O(E^2) vs O(E)
    // ---------------------------------------------------------------

    /** BEFORE: linear scan of children list for uniqueness */
    static class DagBefore {
        Map<String, List<String>> children = new HashMap<>();
        Map<String, List<String>> parents = new HashMap<>();

        void addEdge(String parent, String child) {
            children.computeIfAbsent(parent, k -> new ArrayList<>());
            parents.computeIfAbsent(child, k -> new ArrayList<>());

            List<String> ch = children.get(parent);
            if (!ch.contains(child)) {  // O(E) linear scan
                ch.add(child);
            }
            List<String> pa = parents.get(child);
            if (!pa.contains(parent)) {  // O(E) linear scan
                pa.add(parent);
            }
        }
    }

    /** AFTER: parallel set for O(1) membership */
    static class DagAfter {
        Map<String, List<String>> children = new HashMap<>();
        Map<String, List<String>> parents = new HashMap<>();
        Map<String, Set<String>> childrenSet = new HashMap<>();
        Map<String, Set<String>> parentSet = new HashMap<>();

        void addEdge(String parent, String child) {
            children.computeIfAbsent(parent, k -> new ArrayList<>());
            parents.computeIfAbsent(child, k -> new ArrayList<>());
            childrenSet.computeIfAbsent(parent, k -> new HashSet<>());
            parentSet.computeIfAbsent(child, k -> new HashSet<>());

            if (childrenSet.get(parent).add(child)) {
                children.get(parent).add(child);
            }
            if (parentSet.get(child).add(parent)) {
                parents.get(child).add(parent);
            }
        }
    }

    static void testLoki0001() {
        int E = 500;  // edges from one parent to many children
        String parent = "root";

        // Warm up
        for (int w = 0; w < 3; w++) {
            DagBefore db = new DagBefore();
            DagAfter da = new DagAfter();
            for (int i = 0; i < E; i++) {
                db.addEdge(parent, "child-" + i);
                da.addEdge(parent, "child-" + i);
            }
        }

        int ITER = 200;

        long t0 = System.nanoTime();
        for (int it = 0; it < ITER; it++) {
            DagBefore db = new DagBefore();
            for (int i = 0; i < E; i++) {
                db.addEdge(parent, "child-" + i);
            }
            // Also add duplicates to exercise the contains path
            for (int i = 0; i < E; i++) {
                db.addEdge(parent, "child-" + i);
            }
        }
        long befNs = System.nanoTime() - t0;

        t0 = System.nanoTime();
        for (int it = 0; it < ITER; it++) {
            DagAfter da = new DagAfter();
            for (int i = 0; i < E; i++) {
                da.addEdge(parent, "child-" + i);
            }
            for (int i = 0; i < E; i++) {
                da.addEdge(parent, "child-" + i);
            }
        }
        long aftNs = System.nanoTime() - t0;

        // Correctness check
        DagBefore db = new DagBefore();
        DagAfter da = new DagAfter();
        for (int i = 0; i < E; i++) {
            db.addEdge(parent, "child-" + i);
            da.addEdge(parent, "child-" + i);
        }
        assert db.children.get(parent).size() == da.children.get(parent).size()
                : "loki-0001 correctness: children sizes differ";
        assert db.children.get(parent).equals(da.children.get(parent))
                : "loki-0001 correctness: children order differs";

        double ratio = (double) befNs / aftNs;
        System.out.printf("loki-0001 dag-edge-dedup           BEFORE=%,dns  AFTER=%,dns  ratio=%.1fx  %s%n",
                befNs, aftNs, ratio, ratio > 2.0 ? "PASS" : "FAIL");
        assert ratio > 2.0 : "loki-0001: expected >2x speedup, got " + ratio;
    }

    // ---------------------------------------------------------------
    public static void main(String[] args) {
        testLoki0001();
        System.out.println("\nAll 1 Loki CWE-407 test PASSED.");
    }
}