java-topology/defects/tor/unit/TorKistSchedulerTest.java

package unit;

import java.util.*;

/**
 * Unit test for tor-0003: kist_scheduler_run() re-add loop CWE-407.
 *
 * Defect:  At the end of kist_scheduler_run() (scheduler_kist.c:756), channels
 *          in the `to_readd` list are guarded by smartlist_contains(cp, readd_chan)
 *          before re-insertion into the pending pqueue `cp`.
 *          smartlist_contains() is a linear pointer scan: O(|cp|) per call.
 *          For T channels in to_readd and C channels in cp: O(T * C) total.
 *          The code comment already notes the sched_heap_idx != -1 check is
 *          "in theory redundant with the smartlist_contains check".
 *
 * Fix:     Remove the O(C) smartlist_contains call.  Use only
 *          sched_heap_idx == -1 as the O(1) membership test.
 *          A channel is in cp iff its heap index is set (pqueue invariant).
 *
 * Model:
 *   Channel  — has a heapIdx field (-1 means not in pqueue)
 *   DefectiveReadd — simulates the slow path: ArrayList.contains() O(C) per channel
 *   FixedReadd     — simulates the fast path: heapIdx == -1 check O(1) per channel
 *
 * Measurement: count element-level pointer comparisons for each guard check.
 */
public class TorKistSchedulerTest {

    // ── Channel model ─────────────────────────────────────────────────────────

    static class Channel {
        final int id;
        int heapIdx; // -1 = not in pqueue

        Channel(int id) {
            this.id = id;
            this.heapIdx = -1;
        }
    }

    // ── Defective: simulates smartlist_contains(cp, readd_chan) ───────────────

    /**
     * Returns number of pointer comparisons performed (ArrayList.contains scan).
     */
    static long defectiveGuard(List<Channel> cp, Channel readd_chan) {
        long ops = 0;
        for (Channel c : cp) {
            ops++;
            if (c == readd_chan) {
                return ops; // found → skip re-add
            }
        }
        return ops; // not found → would re-add
    }

    static long runSlow(List<Channel> cp, List<Channel> toReadd) {
        long totalOps = 0;
        // Simulate: each channel in to_readd that's NOT in cp gets re-added.
        // We measure the cost of the contains check, not the add itself.
        Set<Channel> cpSet = new HashSet<>(cp);
        for (Channel readd : toReadd) {
            totalOps += defectiveGuard(cp, readd);
            // If truly not in cp, it would be added (we skip actual pqueue here)
        }
        return totalOps;
    }

    // ── Fixed: simulates heapIdx == -1 check ──────────────────────────────────

    /**
     * Returns number of comparisons: always 1 (single field read).
     */
    static long fixedGuard(Channel readd_chan) {
        // O(1): just check the heap index field
        return 1L;
    }

    static long runFast(List<Channel> toReadd) {
        long totalOps = 0;
        for (Channel readd : toReadd) {
            totalOps += fixedGuard(readd);
        }
        return totalOps;
    }

    // ── Test data generation ──────────────────────────────────────────────────

    /**
     * Build a scenario: C channels in the pending queue, T channels to re-add.
     * Half the to_readd channels are already in cp (heap idx set);
     * half are not (heap idx -1).
     */
    static Object[] makeScenario(int C, int T) {
        List<Channel> cp = new ArrayList<>();
        for (int i = 0; i < C; i++) {
            Channel c = new Channel(i);
            c.heapIdx = i; // already in pqueue
            cp.add(c);
        }

        List<Channel> toReadd = new ArrayList<>();
        // Half from cp (already present)
        for (int i = 0; i < T / 2; i++) {
            toReadd.add(cp.get(i % C));
        }
        // Half are new channels (heap idx -1)
        for (int i = 0; i < T - T / 2; i++) {
            Channel fresh = new Channel(C + i);
            fresh.heapIdx = -1;
            toReadd.add(fresh);
        }
        return new Object[]{cp, toReadd};
    }

    // ── Main ─────────────────────────────────────────────────────────────────

    public static void main(String[] args) {
        int passed = 0;
        int total = 0;

        int[][] configs = {
            {50,  20,  5},   // C=50,  T=20,  minFactor=5
            {200, 50,  5},   // C=200, T=50,  minFactor=5
            {500, 100, 8},   // C=500, T=100, minFactor=8
            {1000,200, 10},  // C=1000,T=200, minFactor=10
        };

        for (int[] cfg : configs) {
            int C = cfg[0], T = cfg[1], minFactor = cfg[2];
            total++;

            @SuppressWarnings("unchecked")
            Object[] scenario = makeScenario(C, T);
            List<Channel> cp      = (List<Channel>) scenario[0];
            List<Channel> toReadd = (List<Channel>) scenario[1];

            long slowOps = runSlow(cp, toReadd);
            long fastOps = runFast(toReadd);

            boolean ok = slowOps > fastOps * minFactor;
            System.out.printf("tor-0003 C=%4d T=%3d: slow=%6d ops  fast=%4d ops  ratio=%.1fx  %s%n",
                C, T, slowOps, fastOps, (double) slowOps / fastOps,
                ok ? "PASS" : "FAIL");
            if (ok) passed++;
        }

        System.out.printf("%d/%d PASS%n", passed, total);
        if (passed != total) System.exit(1);
    }
}