java-topology/defects/wasmer/unit/SignalVecDedupTest.java

package unit;

import java.util.ArrayList;
import java.util.List;

/**
 * wasmer-0002: WasiThread signal Vec<Signal> O(n) dedup on every signal delivery.
 *
 * Models the thread.signal() hot path:
 *   slow: signals stored as Vec<Signal>, contains() used for dedup => O(n) per insert
 *   fast: signals stored as long bitmask => O(1) insert with automatic dedup
 *
 * Also models has_signal(query: &[Signal]):
 *   slow: O(S * Q) nested loop (S=pending signals, Q=query len)
 *   fast: O(Q) build query mask + O(1) bitmask AND
 *
 * The signal domain is bounded to POSIX signals 1..31 (~30 distinct values).
 * Benchmark: S signals pending, Q queries, N deliver calls.
 * slow: O(S) per deliver (contains check) + O(S*Q) per has_signal call
 * fast: O(1) per deliver + O(Q) per has_signal call
 */
public class SignalVecDedupTest {

    static final int MAX_SIGNAL = 31; // POSIX signals 1..31

    /** SLOW: Vec<Signal> with linear contains for dedup */
    static class SlowSignalSet {
        final List<Integer> signals = new ArrayList<>();

        /** Returns ops performed */
        long signal(int sig) {
            long ops = 0;
            for (int s : signals) { ops++; if (s == sig) return ops; } // contains check
            signals.add(sig);
            return ops + 1; // add op
        }

        /** Returns ops performed */
        long hasSignal(int[] query) {
            long ops = 0;
            for (int s : signals) {
                for (int q : query) {
                    ops++;
                    if (s == q) return ops;
                }
            }
            return ops;
        }
    }

    /** FAST: long bitmask — O(1) insert and O(Q) query */
    static class FastSignalSet {
        long mask = 0L;

        /** Returns ops performed (always 1: single bit-set) */
        long signal(int sig) {
            mask |= (1L << sig);
            return 1;
        }

        /** Returns ops performed: Q bit-set ops + 1 AND */
        long hasSignal(int[] query) {
            long qmask = 0L;
            for (int q : query) qmask |= (1L << q);
            return query.length + 1; // Q ops to build mask + 1 AND
        }
    }

    static long benchSignal(boolean slow, int N, int S) {
        // Deliver N signals cycling through S distinct signal values
        SlowSignalSet slowSet = slow ? new SlowSignalSet() : null;
        FastSignalSet fastSet = slow ? null : new FastSignalSet();

        long totalOps = 0;
        for (int i = 0; i < N; i++) {
            int sig = (i % S) + 1; // signals 1..S
            if (slow) totalOps += slowSet.signal(sig);
            else      totalOps += fastSet.signal(sig);
        }
        return totalOps;
    }

    static long benchHasSignal(boolean slow, int S, int Q, int calls) {
        // S signals pending, query Q signals, repeat 'calls' times
        SlowSignalSet slowSet = slow ? new SlowSignalSet() : null;
        FastSignalSet fastSet = slow ? null : new FastSignalSet();

        // Pre-fill with S pending signals (signals 1..S)
        for (int s = 1; s <= S; s++) {
            if (slow) slowSet.signal(s); else fastSet.signal(s);
        }
        // Query for signals that are NOT pending (worst-case: full scan required)
        // Use signals S+1..S+Q (not in the pending set)
        int[] queryArr = new int[Q];
        for (int q = 0; q < Q; q++) queryArr[q] = S + q + 1;

        long totalOps = 0;
        for (int c = 0; c < calls; c++) {
            if (slow) totalOps += slowSet.hasSignal(queryArr);
            else      totalOps += fastSet.hasSignal(queryArr);
        }
        return totalOps;
    }

    static void testSignal(String name, int N, int S, int minSpeedup) {
        long sOps = benchSignal(true,  N, S);
        long fOps = benchSignal(false, N, S);

        double speedup = (double) sOps / fOps;
        boolean pass = sOps >= fOps * minSpeedup;

        System.out.printf("  signal  %-42s  slow=%,d  fast=%,d  speedup=%.1fx  %s%n",
            name, sOps, fOps, speedup, pass ? "PASS" : "FAIL");
        assert pass : String.format(
            "signal %s: expected speedup >=%dx, got %.1fx", name, minSpeedup, speedup);
    }

    static void testHasSignal(String name, int S, int Q, int calls, int minSpeedup) {
        long sOps = benchHasSignal(true,  S, Q, calls);
        long fOps = benchHasSignal(false, S, Q, calls);

        double speedup = (double) sOps / fOps;
        boolean pass = sOps >= fOps * minSpeedup;

        System.out.printf("  has_sig %-42s  slow=%,d  fast=%,d  speedup=%.1fx  %s%n",
            name, sOps, fOps, speedup, pass ? "PASS" : "FAIL");
        assert pass : String.format(
            "has_signal %s: expected speedup >=%dx, got %.1fx", name, minSpeedup, speedup);
    }

    public static void main(String[] args) {
        System.out.println("wasmer-0002: Signal Vec dedup");
        System.out.println("=============================");
        System.out.println("-- signal() delivery --");

        // S=30 signals: after all 30 are in the set, each new deliver scans ~30 items
        // vs O(1) bitmask. With N=1000 delivers cycling through 30: slow costs ~15000 ops.
        testSignal("N=100  S=30  minSpeedup=10x",  100, 30, 10);
        testSignal("N=1000 S=30  minSpeedup=10x", 1000, 30, 10);

        System.out.println("-- has_signal() query --");
        // S=30 pending, Q=10 query: slow=S*Q=300 per call, fast=Q+1=11 per call => ~27x
        testHasSignal("S=30 Q=10 calls=100  minSpeedup=15x", 30, 10, 100, 15);
        testHasSignal("S=30 Q=30 calls=100  minSpeedup=15x", 30, 30, 100, 15);

        System.out.println("=============================");
        System.out.println("ALL PASS");
    }
}