java-topology/defects/ogre/unit/OGRETest.java

package unit;

import java.util.*;

/**
 * OGRETest — Java analogs of three OGRE CWE-407 defects.
 *
 * Defect 1 (ogre-0001): Node::~Node — std::find on vector of queued-update nodes.
 *   Slow: ArrayList.remove(Object) — O(N) scan per node destroyed.
 *   Fast: LinkedHashSet.remove(Object) — O(1) per node destroyed.
 *
 * Defect 2 (ogre-0002): ResourceGroupManager::_notifyAllResourcesRemoved — std::find
 *   in nested loop erasing resources from a list.
 *   Slow: ArrayList.remove(Object) inside an erase loop — O(N²).
 *   Fast: Build HashSet of to-remove pointers, single-pass removeIf — O(N).
 *
 * Defect 3 (ogre-0003): RibbonTrail::clearChain — std::find on parallel index vector
 *   to reverse-map chain-index → node.
 *   Slow: ArrayList.indexOf(chainIndex) — O(N).
 *   Fast: HashMap<Integer,Object> reverse map — O(1).
 */
public class OGRETest {

    static void bench(String label, Runnable slow, Runnable fast, long sOps, long fOps) {
        // warmup
        slow.run();
        fast.run();
        long t0 = System.nanoTime();
        slow.run();
        long sMs = (System.nanoTime() - t0) / 1_000_000;
        long t1 = System.nanoTime();
        fast.run();
        long fMs = (System.nanoTime() - t1) / 1_000_000;
        double ratio = fOps > 0 ? (double) sOps / fOps : 0;
        System.out.printf("  %-56s  slow:%5dms (%,d ops)  fast:%5dms (%,d ops)  speedup:%.0fx%n",
                label, sMs, sOps, fMs, fOps, ratio);
    }

    // -----------------------------------------------------------------------
    // ogre-0001: Node queued-update removal during bulk destruction
    // -----------------------------------------------------------------------
    static void benchNodeQueuedUpdates(int N) {
        // SLOW: vector — O(N) scan per node destruction
        Runnable slow = () -> {
            List<Object> queue = new ArrayList<>(N);
            Object[] nodes = new Object[N];
            for (int i = 0; i < N; i++) {
                nodes[i] = new Object();
                queue.add(nodes[i]);
            }
            // simulate N node destructions: each does std::find + erase
            for (int i = 0; i < N; i++) {
                queue.remove(nodes[i]);  // O(N) scan
            }
        };

        // FAST: unordered_set — O(1) erase per node destruction
        Runnable fast = () -> {
            Set<Object> queue = new LinkedHashSet<>(N * 2);
            Object[] nodes = new Object[N];
            for (int i = 0; i < N; i++) {
                nodes[i] = new Object();
                queue.add(nodes[i]);
            }
            for (int i = 0; i < N; i++) {
                queue.remove(nodes[i]);  // O(1) hash remove
            }
        };

        long sOps = (long) N * N / 2;  // average scan length N/2 × N destructions
        long fOps = N;
        bench(String.format("ogre-0001 Node::~Node queued-update scan N=%d", N),
                slow, fast, sOps, fOps);
    }

    // -----------------------------------------------------------------------
    // ogre-0002: ResourceGroupManager notify-removed — nested find+erase
    // -----------------------------------------------------------------------
    static void benchResourceGroupRemove(int R) {
        // SLOW: std::find on list for each item in arDel — O(R²)
        Runnable slow = () -> {
            List<Object> resourceList = new ArrayList<>(R);
            for (int i = 0; i < R; i++) resourceList.add(new Object());
            List<Object> arDel = new ArrayList<>(resourceList);  // remove all

            for (Object item : arDel) {
                resourceList.remove(item);  // O(R) scan each time
            }
        };

        // FAST: build HashSet, single-pass removeIf — O(R)
        Runnable fast = () -> {
            List<Object> resourceList = new ArrayList<>(R);
            for (int i = 0; i < R; i++) resourceList.add(new Object());
            List<Object> arDel = new ArrayList<>(resourceList);

            Set<Object> toRemove = new HashSet<>(arDel);
            resourceList.removeIf(toRemove::contains);  // O(R) single pass
        };

        long sOps = (long) R * R;
        long fOps = R;
        bench(String.format("ogre-0002 ResourceGroupManager::_notifyRemoved R=%d", R),
                slow, fast, sOps, fOps);
    }

    // -----------------------------------------------------------------------
    // ogre-0003: RibbonTrail::clearChain — parallel-vector reverse lookup
    // -----------------------------------------------------------------------
    static void benchRibbonTrailClearChain(int K, int clears) {
        Object[] nodes = new Object[K];
        for (int i = 0; i < K; i++) nodes[i] = new Object();

        // SLOW: parallel arrays, indexOf for reverse lookup
        Runnable slow = () -> {
            List<Object> nodeList = new ArrayList<>(Arrays.asList(nodes));
            List<Integer> chainSegments = new ArrayList<>();
            for (int i = 0; i < K; i++) chainSegments.add(i);

            long dummy = 0;
            for (int c = 0; c < clears; c++) {
                int chainIndex = c % K;
                // std::find on mNodeToChainSegment — O(K)
                int pos = chainSegments.indexOf(chainIndex);
                if (pos >= 0) dummy += pos;
            }
            if (dummy < 0) System.out.println("never");
        };

        // FAST: HashMap for reverse lookup — O(1) per clear
        Runnable fast = () -> {
            Map<Integer, Object> chainToNode = new HashMap<>(K * 2);
            for (int i = 0; i < K; i++) chainToNode.put(i, nodes[i]);

            long dummy = 0;
            for (int c = 0; c < clears; c++) {
                int chainIndex = c % K;
                // HashMap.get — O(1)
                Object n = chainToNode.get(chainIndex);
                if (n != null) dummy++;
            }
            if (dummy < 0) System.out.println("never");
        };

        long sOps = (long) clears * K;
        long fOps = clears;
        bench(String.format("ogre-0003 RibbonTrail::clearChain K=%d clears=%d", K, clears),
                slow, fast, sOps, fOps);
    }

    public static void main(String[] args) {
        System.out.println("OGRE CWE-407 defect benchmarks");
        System.out.println("=".repeat(100));

        System.out.println("\n[ogre-0001] Node::~Node — msQueuedUpdates linear scan");
        benchNodeQueuedUpdates(500);
        benchNodeQueuedUpdates(2_000);
        benchNodeQueuedUpdates(10_000);

        System.out.println("\n[ogre-0002] ResourceGroupManager::_notifyAllResourcesRemoved");
        benchResourceGroupRemove(500);
        benchResourceGroupRemove(2_000);
        benchResourceGroupRemove(10_000);

        System.out.println("\n[ogre-0003] RibbonTrail::clearChain — parallel-vector reverse lookup");
        benchRibbonTrailClearChain(50, 100_000);
        benchRibbonTrailClearChain(200, 100_000);
        benchRibbonTrailClearChain(1_000, 100_000);
    }
}