test/jdk/java/lang/StableValue/StableValuesSafePublicationTest.java

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/* @test
 * @summary Basic tests for making sure StableValue publishes values safely
 * @modules java.base/jdk.internal.misc
 * @enablePreview
 * @run junit StableValuesSafePublicationTest
 */

import org.junit.jupiter.api.Test;

import java.util.Arrays;
import java.util.List;
import java.util.Objects;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;

import static org.junit.jupiter.api.Assertions.*;

final class StableValuesSafePublicationTest {

    private static final int SIZE = 100_000;
    private static final int THREADS = Runtime.getRuntime().availableProcessors();
    private static final StableValue<Holder>[] STABLES = stables();

    static StableValue<Holder>[] stables() {
        @SuppressWarnings("unchecked")
        StableValue<Holder>[] stables = (StableValue<Holder>[]) new StableValue[SIZE];
        for (int i = 0; i < SIZE; i++) {
            stables[i] = StableValue.of();
        }
        return stables;
    }

    static final class Holder {
        // These are non-final fields but should be seen
        // fully initialized thanks to the HB properties of StableValue.
        int a, b, c, d, e;

        Holder() {
            a = b = c = d = e = 1;
        }
    }

    static final class Consumer implements Runnable {

        final int[] observations = new int[SIZE];
        final StableValue<Holder>[] stables = STABLES;
        int i = 0;

        @Override
        public void run() {
            for (; i < SIZE; i++) {
                StableValue<Holder> s = stables[i];
                Holder h;
                // Wait until the StableValue has a holder value
                while ((h = s.orElse(null)) == null) {}
                int a = h.a;
                int b = h.b;
                int c = h.c;
                int d = h.d;
                int e = h.e;
                observations[i] = a + (b << 1) + (c << 2) + (c << 3) + (d << 4) + (e << 5);
            }
        }
    }

    static final class Producer implements Runnable {

        final StableValue<Holder>[] stables = STABLES;

        @Override
        public void run() {
            StableValue<Holder> s;
            long deadlineNs = System.nanoTime();
            for (int i = 0; i < SIZE; i++) {
                s = stables[i];
                s.trySet(new Holder());
                deadlineNs += 1000;
                while (System.nanoTime() < deadlineNs) {
                    Thread.onSpinWait();
                }
            }
        }
    }

    @Test
    void main() {
        List<Consumer> consumers = IntStream.range(0, THREADS)
                .mapToObj(_ -> new Consumer())
                .toList();

        List<Thread> consumersThreads = IntStream.range(0, THREADS)
                .mapToObj(i -> Thread.ofPlatform()
                        .name("Consumer Thread " + i)
                        .start(consumers.get(i)))
                .toList();

        Producer producer = new Producer();

        Thread producerThread = Thread.ofPlatform()
                .name("Producer Thread")
                .start(producer);

        join(consumers, producerThread);
        join(consumers, consumersThreads.toArray(Thread[]::new));

        int[] histogram = new int[64];
        for (Consumer consumer : consumers) {
            for (int i = 0; i < SIZE; i++) {
                histogram[consumer.observations[i]]++;
            }
        }

        // unless a = 1, ..., e = 1, zero observations should be seen
        for (int i = 0; i < 63; i++) {
            assertEquals(0, histogram[i]);
        }
        // a = 1, ..., e = 1 : index 2^5-1 = 63
        // All observations should end up in this bucket
        assertEquals(THREADS * SIZE, histogram[63]);
    }

    static void join(List<Consumer> consumers, Thread... threads) {
        try {
            for (Thread t:threads) {
                long deadline = System.nanoTime() + TimeUnit.MINUTES.toNanos(1);
                while (t.isAlive()) {
                    t.join(TimeUnit.SECONDS.toMillis(10));
                    if (t.isAlive()) {
                        String stack = Arrays.stream(t.getStackTrace())
                                .map(Objects::toString)
                                .collect(Collectors.joining(System.lineSeparator()));
                        System.err.println(t + ": " + stack);
                        for (int i = 0; i < consumers.size(); i++) {
                            System.err.println("Consumer " + i + ": " + consumers.get(i).i);
                        }
                    }
                    if (System.nanoTime() > deadline) {
                        long nonNulls = CompletableFuture.supplyAsync(() ->
                                Stream.of(STABLES)
                                        .map(s -> s.orElse(null))
                                        .filter(Objects::nonNull)
                                        .count(), Executors.newSingleThreadExecutor()).join();
                        fail("Giving up! Set stables seen by a new thread: " + nonNulls);
                    }
                }
            }
        } catch (InterruptedException ie) {
            fail(ie);
        }
    }

}