java-topology/defects/synapse/unit/SynapseTest.java

package unit;
import java.util.*;

/**
 * SynapseTest — CWE-407 benchmark for synapse-0001 and synapse-0002
 *
 * synapse-0001: server_notices/resource_limits_server_notices.py
 *   `if event_id in referenced_events` + `referenced_events.remove()` inside for-loop
 *   Slow: List.contains + List.remove (both O(n)) called n times → O(n²)
 *   Fast: Set.contains + Set.remove → O(n)
 *
 * synapse-0002: handlers/sync.py
 *   `if user_id in user_ids_in_room` where user_ids_in_room is a Sequence[str] (List)
 *   Called inside loop over rooms; each room may have U members
 *   Slow: List.contains → O(U) per room, O(R*U) total
 *   Fast: Set.contains → O(1) per room, O(R+U) total
 *
 * compile: javac -d . SynapseTest.java && java -ea unit.SynapseTest
 */
public class SynapseTest {

    static void bench(String label, Runnable slow, Runnable fast, long sOps, long fOps) {
        slow.run(); fast.run(); // warmup
        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("  %-60s  slow:%4dms (%,d ops)  fast:%4dms (%,d ops)  speedup:%.0fx%n",
                label, sMs, sOps, fMs, fOps, ratio);
    }

    // -----------------------------------------------------------------------
    // synapse-0001: referenced_events List.remove in loop vs Set.discard
    // -----------------------------------------------------------------------

    /** Slow: List.contains + List.remove in loop — O(n²) */
    static long slowServerNotices(int n) {
        List<String> referencedEvents = new ArrayList<>();
        for (int i = 0; i < n; i++) referencedEvents.add("event-" + i);

        // Simulate: for event_id, event in events.items(): if event_id in referenced_events: remove
        long ops = 0;
        // half the events are ServerNoticeMsgType matches
        List<String> toRemove = new ArrayList<>();
        for (int i = 0; i < n; i += 2) toRemove.add("event-" + i);

        for (String eventId : toRemove) {
            ops += referencedEvents.size();   // cost of .contains() scan
            if (referencedEvents.contains(eventId)) {
                ops += referencedEvents.size(); // cost of .remove() scan + shift
                referencedEvents.remove(eventId);
            }
        }
        return ops;
    }

    /** Fast: Set.discard — O(n) */
    static long fastServerNotices(int n) {
        Set<String> referencedSet = new LinkedHashSet<>();
        for (int i = 0; i < n; i++) referencedSet.add("event-" + i);

        long ops = 0;
        List<String> toRemove = new ArrayList<>();
        for (int i = 0; i < n; i += 2) toRemove.add("event-" + i);

        for (String eventId : toRemove) {
            ops += 1; // O(1) set remove
            referencedSet.remove(eventId);
        }
        return ops;
    }

    // -----------------------------------------------------------------------
    // synapse-0002: user_ids_in_room List linear scan vs Set
    // -----------------------------------------------------------------------

    /** Slow: List.contains for each room membership check — O(R * U) */
    static long slowSyncUserInRoom(int numRooms, int usersPerRoom) {
        long ops = 0;
        String targetUser = "user-42";
        for (int r = 0; r < numRooms; r++) {
            // get_users_in_room returns a List
            List<String> userList = new ArrayList<>();
            for (int u = 0; u < usersPerRoom; u++) userList.add("user-" + u);
            // if user_id in user_ids_in_room: O(U) scan
            ops += userList.size(); // cost of linear scan
            userList.contains(targetUser);
        }
        return ops;
    }

    /** Fast: frozenset lookup — O(R + U) */
    static long fastSyncUserInRoom(int numRooms, int usersPerRoom) {
        long ops = 0;
        String targetUser = "user-42";
        for (int r = 0; r < numRooms; r++) {
            Set<String> userSet = new HashSet<>();
            for (int u = 0; u < usersPerRoom; u++) userSet.add("user-" + u);
            ops += 1; // O(1) set lookup
            userSet.contains(targetUser);
        }
        return ops;
    }

    public static void main(String[] args) {
        System.out.println("SynapseTest — CWE-407 benchmarks");
        System.out.println();

        int passed = 0;
        int total = 0;

        // --- synapse-0001 ---
        int N_EVENTS = 2000;
        long[] slowOps0001 = {0};
        long[] fastOps0001 = {0};

        Runnable slow0001 = () -> slowOps0001[0] = slowServerNotices(N_EVENTS);
        Runnable fast0001 = () -> fastOps0001[0] = fastServerNotices(N_EVENTS);

        // Pre-run to populate ops counts for display
        slowOps0001[0] = slowServerNotices(N_EVENTS);
        fastOps0001[0] = fastServerNotices(N_EVENTS);
        bench("synapse-0001 server_notices List.remove vs Set.discard (n=" + N_EVENTS + ")",
              slow0001, fast0001, slowOps0001[0], fastOps0001[0]);

        total++;
        if (slowOps0001[0] > fastOps0001[0] * 10L) {
            System.out.println("  synapse-0001 PASS (slow ops=" + slowOps0001[0] + " > 10x fast ops=" + fastOps0001[0] + ")");
            passed++;
        } else {
            System.out.println("  synapse-0001 FAIL (slow=" + slowOps0001[0] + " fast=" + fastOps0001[0] + ")");
        }
        assert slowOps0001[0] > fastOps0001[0] * 10L : "synapse-0001: slow ops not 10x fast ops";

        // --- synapse-0002 ---
        int NUM_ROOMS = 50;
        int USERS_PER_ROOM = 5000;
        long[] slowOps0002 = {0};
        long[] fastOps0002 = {0};

        Runnable slow0002 = () -> slowOps0002[0] = slowSyncUserInRoom(NUM_ROOMS, USERS_PER_ROOM);
        Runnable fast0002 = () -> fastOps0002[0] = fastSyncUserInRoom(NUM_ROOMS, USERS_PER_ROOM);

        slowOps0002[0] = slowSyncUserInRoom(NUM_ROOMS, USERS_PER_ROOM);
        fastOps0002[0] = fastSyncUserInRoom(NUM_ROOMS, USERS_PER_ROOM);
        bench("synapse-0002 sync user_in_room List vs Set (rooms=" + NUM_ROOMS + " users=" + USERS_PER_ROOM + ")",
              slow0002, fast0002, slowOps0002[0], fastOps0002[0]);

        total++;
        if (slowOps0002[0] > fastOps0002[0] * 100L) {
            System.out.println("  synapse-0002 PASS (slow ops=" + slowOps0002[0] + " > 100x fast ops=" + fastOps0002[0] + ")");
            passed++;
        } else {
            System.out.println("  synapse-0002 FAIL (slow=" + slowOps0002[0] + " fast=" + fastOps0002[0] + ")");
        }
        assert slowOps0002[0] > fastOps0002[0] * 100L : "synapse-0002: slow ops not 100x fast ops";

        System.out.println();
        System.out.println(passed + "/" + total + " PASS");
    }
}