java-topology/defects/xenia-0001/test/XeniaTest.java

import java.util.*;

/**
 * XeniaTest: unit test for xenia-0001
 *
 * Defect: ObjectTable::GetAllObjects() in
 * src/xenia/kernel/util/object_table.cc uses std::find on a growing
 * std::vector<object_ref<XObject>> to deduplicate objects while iterating
 * over all table slots. Each slot check is O(results.size()), making the
 * full scan O(S * R) where S = table slot count (starting at 16,384) and R
 * = unique object count (up to S/2 in the worst case). At S=16384 with a
 * full table of unique objects this yields ~134 million pointer comparisons.
 *
 * Fix: replace the results vector linear scan with an unordered_set<XObject*>
 * seen-pointer set, reducing each membership test from O(R) to O(1) and the
 * full scan from O(S*R) to O(S).
 *
 * This test simulates both implementations and confirms:
 * 1. Functional equivalence: same objects returned in same order.
 * 2. Performance ratio: patched version is faster by the expected factor.
 */
public class XeniaTest {

    // Simulates an XObject pointer (just an Integer ID here).
    static class XObject {
        final int id;
        XObject(int id) { this.id = id; }
    }

    // --- DEFECTIVE IMPLEMENTATION ---
    // Mirrors ObjectTable::GetAllObjects() before the patch.
    // table[slot] may hold duplicate pointers (multiple handles to same object).
    // Dedup is done via List.contains() -- O(results.size()) per slot.
    static List<XObject> getAllObjectsDefective(XObject[] table) {
        List<XObject> results = new ArrayList<>();
        for (XObject entry : table) {
            if (entry != null && !results.contains(entry)) {  // O(R) scan
                results.add(entry);
            }
        }
        return results;
    }

    // --- PATCHED IMPLEMENTATION ---
    // Mirrors ObjectTable::GetAllObjects() after the patch.
    // Dedup via HashSet<XObject> seen -- O(1) per slot.
    static List<XObject> getAllObjectsPatched(XObject[] table) {
        List<XObject> results = new ArrayList<>();
        Set<XObject> seen = new HashSet<>();
        for (XObject entry : table) {
            if (entry != null && seen.add(entry)) {  // O(1) hash test+insert
                results.add(entry);
            }
        }
        return results;
    }

    // Build a table where each object is referenced by DUPLICATE_FACTOR slots.
    // This matches xenia's handle table: one object can have multiple handles.
    static XObject[] buildTable(int uniqueObjects, int duplicateFactor) {
        XObject[] objs = new XObject[uniqueObjects];
        for (int i = 0; i < uniqueObjects; i++) {
            objs[i] = new XObject(i);
        }
        XObject[] table = new XObject[uniqueObjects * duplicateFactor];
        for (int slot = 0; slot < table.length; slot++) {
            table[slot] = objs[slot % uniqueObjects];
        }
        return table;
    }

    public static void main(String[] args) {
        // --- Correctness test ---
        // Small table: 8 unique objects, each referenced 3 times -> 24 slots
        XObject[] smallTable = buildTable(8, 3);
        List<XObject> defResult = getAllObjectsDefective(smallTable);
        List<XObject> patResult = getAllObjectsPatched(smallTable);

        assert defResult.size() == 8 :
            "defective: expected 8 unique objects, got " + defResult.size();
        assert patResult.size() == 8 :
            "patched: expected 8 unique objects, got " + patResult.size();
        for (int i = 0; i < defResult.size(); i++) {
            assert defResult.get(i) == patResult.get(i) :
                "result mismatch at index " + i;
        }
        System.out.println("PASS correctness: 8 unique objects, 24 slots, results match");

        // --- Empty table ---
        XObject[] emptyTable = new XObject[0];
        assert getAllObjectsDefective(emptyTable).isEmpty() : "defective: empty table non-empty";
        assert getAllObjectsPatched(emptyTable).isEmpty()   : "patched: empty table non-empty";
        System.out.println("PASS correctness: empty table");

        // --- All-null table ---
        XObject[] nullTable = new XObject[100];
        assert getAllObjectsDefective(nullTable).isEmpty() : "defective: all-null table non-empty";
        assert getAllObjectsPatched(nullTable).isEmpty()   : "patched: all-null table non-empty";
        System.out.println("PASS correctness: all-null table");

        // --- Performance benchmark ---
        // xenia initial table_capacity = 16 * 1024 = 16384 slots.
        // Simulate a loaded game: 1000 unique objects, each with 4 handle slots -> 4000 slots.
        // Then scale to 4000 unique objects in 16384 slots for O(N^2) stress.
        int UNIQUE = 4000;
        int SLOTS  = 16384;
        XObject[] bigTable = new XObject[SLOTS];
        XObject[] objs = new XObject[UNIQUE];
        for (int i = 0; i < UNIQUE; i++) objs[i] = new XObject(i);
        for (int s = 0; s < SLOTS; s++) bigTable[s] = objs[s % UNIQUE];

        int REPS = 20;

        long tDef = 0;
        for (int r = 0; r < REPS; r++) {
            long t0 = System.nanoTime();
            getAllObjectsDefective(bigTable);
            tDef += System.nanoTime() - t0;
        }

        long tPat = 0;
        for (int r = 0; r < REPS; r++) {
            long t0 = System.nanoTime();
            getAllObjectsPatched(bigTable);
            tPat += System.nanoTime() - t0;
        }

        double defMs = tDef / 1e6 / REPS;
        double patMs = tPat / 1e6 / REPS;
        double ratio = defMs / patMs;

        System.out.printf(
            "BENCH defective=%.3f ms  patched=%.3f ms  ratio=%.1fx%n",
            defMs, patMs, ratio);

        assert ratio >= 2.0 :
            "expected speedup >= 2x, got " + String.format("%.2f", ratio) + "x";

        System.out.println("PASS performance: patched is " +
            String.format("%.1f", ratio) + "x faster");

        System.out.println("ALL TESTS PASSED");
    }
}