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Testing SequenceBarrier Coordination Mechanisms in LMAX-Disruptor

A comprehensive test suite for the SequenceBarrier component in the LMAX Disruptor library. This test class validates the critical synchronization and coordination mechanisms between producers and consumers in the ring buffer implementation.

Test Coverage Overview

The test suite provides thorough coverage of SequenceBarrier functionality in the LMAX Disruptor:

Work completion verification with different threshold scenarios
Thread synchronization and blocking behavior
Alert status management and interruption handling
Multiple worker coordination scenarios

Implementation Analysis

The testing approach employs JUnit Jupiter framework with systematic validation of concurrent operations:

Uses DummyEventProcessor and StubEvent for controlled testing
Implements CountDownLatch for thread coordination
Validates both synchronous and asynchronous barrier operations

Technical Details

Testing infrastructure includes:

JUnit Jupiter test framework
RingBuffer implementation with 64-slot capacity
Custom sequence tracking mechanisms
Thread management utilities
Assertion methods for concurrent operation validation

Best Practices Demonstrated

The test suite exemplifies high-quality testing practices:

Comprehensive edge case coverage
Proper resource cleanup and management
Clear test method naming conventions
Effective use of test fixtures and setup
Robust concurrent operation validation

lmax-exchange/disruptor

src/test/java/com/lmax/disruptor/SequenceBarrierTest.java

            
/*
 * Copyright 2011 LMAX Ltd.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.lmax.disruptor;

import com.lmax.disruptor.support.DummyEventProcessor;
import com.lmax.disruptor.support.StubEvent;
import com.lmax.disruptor.util.Util;
import org.junit.jupiter.api.Test;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

import static com.lmax.disruptor.RingBuffer.createMultiProducer;
import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertThrows;
import static org.junit.jupiter.api.Assertions.assertTrue;


public final class SequenceBarrierTest
{
    private final RingBuffer<StubEvent> ringBuffer = createMultiProducer(StubEvent.EVENT_FACTORY, 64);

    public SequenceBarrierTest()
    {
        ringBuffer.addGatingSequences(new NoOpEventProcessor(ringBuffer).getSequence());
    }

    @Test
    public void shouldWaitForWorkCompleteWhereCompleteWorkThresholdIsAhead() throws Exception
    {
        final long expectedNumberMessages = 10;
        final long expectedWorkSequence = 9;
        fillRingBuffer(expectedNumberMessages);

        final Sequence sequence1 = new Sequence(expectedNumberMessages);
        final Sequence sequence2 = new Sequence(expectedWorkSequence);
        final Sequence sequence3 = new Sequence(expectedNumberMessages);

        final SequenceBarrier sequenceBarrier = ringBuffer.newBarrier(sequence1, sequence2, sequence3);

        long completedWorkSequence = sequenceBarrier.waitFor(expectedWorkSequence);
        assertTrue(completedWorkSequence >= expectedWorkSequence);
    }

    @Test
    public void shouldWaitForWorkCompleteWhereAllWorkersAreBlockedOnRingBuffer() throws Exception
    {
        long expectedNumberMessages = 10;
        fillRingBuffer(expectedNumberMessages);

        final DummyEventProcessor[] workers = new DummyEventProcessor[3];
        for (int i = 0, size = workers.length; i < size; i++)
        {
            workers[i] = new DummyEventProcessor();
            workers[i].setSequence(expectedNumberMessages - 1);
        }

        final SequenceBarrier sequenceBarrier = ringBuffer.newBarrier(Util.getSequencesFor(workers));

        Runnable runnable = () ->
        {
            long sequence = ringBuffer.next();
            StubEvent event = ringBuffer.get(sequence);
            event.setValue((int) sequence);
            ringBuffer.publish(sequence);

            for (DummyEventProcessor stubWorker : workers)
            {
                stubWorker.setSequence(sequence);
            }
        };

        new Thread(runnable).start();

        long expectedWorkSequence = expectedNumberMessages;
        long completedWorkSequence = sequenceBarrier.waitFor(expectedNumberMessages);
        assertTrue(completedWorkSequence >= expectedWorkSequence);
    }

    @Test
    public void shouldInterruptDuringBusySpin() throws Exception
    {
        final long expectedNumberMessages = 10;
        fillRingBuffer(expectedNumberMessages);

        final CountDownLatch latch = new CountDownLatch(3);
        final Sequence sequence1 = new CountDownLatchSequence(8L, latch);
        final Sequence sequence2 = new CountDownLatchSequence(8L, latch);
        final Sequence sequence3 = new CountDownLatchSequence(8L, latch);

        final SequenceBarrier sequenceBarrier =
            ringBuffer.newBarrier(sequence1, sequence2, sequence3);

        Thread t = new Thread(
                () -> assertThrows(AlertException.class, () ->
                        sequenceBarrier.waitFor(expectedNumberMessages - 1)));

        t.start();
        latch.await(3, TimeUnit.SECONDS);
        sequenceBarrier.alert();
        t.join();
    }

    @Test
    public void shouldWaitForWorkCompleteWhereCompleteWorkThresholdIsBehind() throws Exception
    {
        long expectedNumberMessages = 10;
        fillRingBuffer(expectedNumberMessages);

        final DummyEventProcessor[] eventProcessors = new DummyEventProcessor[3];
        for (int i = 0, size = eventProcessors.length; i < size; i++)
        {
            eventProcessors[i] = new DummyEventProcessor();
            eventProcessors[i].setSequence(expectedNumberMessages - 2);
        }

        final SequenceBarrier sequenceBarrier = ringBuffer.newBarrier(Util.getSequencesFor(eventProcessors));

        Runnable runnable = () ->
        {
            for (DummyEventProcessor stubWorker : eventProcessors)
            {
                stubWorker.setSequence(stubWorker.getSequence().get() + 1L);
            }
        };

        Thread thread = new Thread(runnable);
        thread.start();
        thread.join();

        long expectedWorkSequence = expectedNumberMessages - 1;
        long completedWorkSequence = sequenceBarrier.waitFor(expectedWorkSequence);
        assertTrue(completedWorkSequence >= expectedWorkSequence);
    }

    @Test
    public void shouldSetAndClearAlertStatus()
    {
        SequenceBarrier sequenceBarrier = ringBuffer.newBarrier();

        assertFalse(sequenceBarrier.isAlerted());

        sequenceBarrier.alert();
        assertTrue(sequenceBarrier.isAlerted());

        sequenceBarrier.clearAlert();
        assertFalse(sequenceBarrier.isAlerted());
    }

    private void fillRingBuffer(final long expectedNumberMessages) throws InterruptedException
    {
        for (long i = 0; i < expectedNumberMessages; i++)
        {
            long sequence = ringBuffer.next();
            StubEvent event = ringBuffer.get(sequence);
            event.setValue((int) i);
            ringBuffer.publish(sequence);
        }
    }

    private static final class CountDownLatchSequence extends Sequence
    {
        private final CountDownLatch latch;

        private CountDownLatchSequence(final long initialValue, final CountDownLatch latch)
        {
            super(initialValue);
            this.latch = latch;
        }

        @Override
        public long get()
        {
            latch.countDown();
            return super.get();
        }
    }
}