浅析Disruptor高性能线程消息传递并发框架

Disruptor是一个高性能线程消息传递并发框架，它的操作主要是在内存中进行，最早由LMAX Exchange公司开源，并且在金融领域得到广泛应用。Disruptor与传统的生产者/消费者模式相比，最大的优势在于它可以避免锁竞争、缓存不命中等问题，从而获得更高的性能。

Disruptor的核心概念

RingBuffer

RingBuffer是Disruptor的核心，它实际上就是一个环形的数组。生产者往其中不断写入数据，消费者从中不断读取数据，每个元素在有数据时只会被处理一次。

Sequence

Sequence是Disruptor用于保证序列的一致性，每个生产者和消费者都会维护一个序列。生产者在写入数据时会占用一个序列位置，而读取数据时会释放序列位置。消费者在读取数据时会占用一个序列位置，而处理完数据后会释放序列位置。

Event

Event是RingBuffer中存储的对象，代表生产者和消费者之间的数据交换单元。每个Event需实现Event接口的抽象方法，以供消费者处理数据。

WaitStrategy

WaitStrategy实际上就是一种等待策略，用于控制消费者的等待方式。Disruptor提供了多种等待策略，包括BlockingWaitStrategy、BusySpinWaitStrategy等。

Disruptor的使用

基本流程

Disruptor的基本流程分为3步：

1. 定义Event类：实现Event接口的抽象方法，以供消费者处理数据。

2. 定义EventFactory类：用于实例化Event对象。

3. 定义EventHandler类：用于处理Event对象。

public class LongEvent
{
    private long value;

    public void set(long value)
    {
        this.value = value;
    }

    public long get()
    {
        return value;
    }
}

public class LongEventFactory implements EventFactory<LongEvent>
{
    public LongEvent newInstance()
    {
        return new LongEvent();
    }
}

public class LongEventHandler implements EventHandler<LongEvent>
{
    public void onEvent(LongEvent event, long sequence, boolean endOfBatch)
    {
        // 处理Event对象
    }
}

1. 实例化Disruptor对象：

int bufferSize = 1024;
Disruptor<LongEvent> disruptor = new Disruptor<>(new LongEventFactory(), bufferSize, executor);

1. 实例化消费者：

EventHandler<LongEvent> handler = new LongEventHandler();
disruptor.handleEventsWith(handler);

1. 启动Disruptor：

disruptor.start();

1. 生产者写入数据：

RingBuffer<LongEvent> ringBuffer = disruptor.getRingBuffer();
long sequence = ringBuffer.next();
try
{
    LongEvent event = ringBuffer.get(sequence);
    event.set(value);
}
finally
{
    ringBuffer.publish(sequence);
}

批量消费

Disruptor支持批量处理消费者。

public class LongEventHandler implements EventHandler<LongEvent>, BatchStartAware, BatchEndAware
{
    private static final int BATCH_SIZE = 10;
    private int batchSize = BATCH_SIZE;
    private long[] events = new long[batchSize];
    private int count = 0;

    public void onEvent(LongEvent event, long sequence, boolean endOfBatch)
    {
        events[count++] = event.get();
        if (count == batchSize) {
            handleEvents(events);
            count = 0;
        }
    }

    public void onStart()
    {
        count = 0;
    }

    public void onEnd()
    {
        if (count > 0) {
            handleEvents(Arrays.copyOfRange(events, 0, count));
            count = 0;
        }
    }

    private void handleEvents(long[] events)
    {
        // 处理批量的Event对象
    }
}

并行消费

Disruptor支持并行处理消费者。

public class LongEventHandler implements EventHandler<LongEvent>
{
    private final int id;
    private final int total;

    public LongEventHandler(int id, int total)
    {
        this.id = id;
        this.total = total;
    }

    public void onEvent(LongEvent event, long sequence, boolean endOfBatch)
    {
        // 处理Event对象
    }
}

int consumerCount = 4;
WorkerPool<LongEvent> workerPool = new WorkerPool<>(disruptor.getRingBuffer(), disruptor.getSequenceBarrier(), new IgnoreExceptionHandler(), new LongEventHandler[consumerCount]);
for (int i = 0; i < consumerCount; i++)
{
    LongEventHandler handler = new LongEventHandler(i, consumerCount);
    workerPool.start(newWorkerPool(handler));
}
disruptor.handleEventsWithWorkerPool(workerPool.getWorkerSequences());

实战示例

示例1：队列消费

我们用Disruptor实现一个简单的生产者/消费者模式，将数据插入到队列中并进行消费处理。

public class DisruptorQueueTest
{
    private static final int RING_BUFFER_SIZE = 1024;

    public static void main(String[] args)
    {
        DisruptorQueueTest test = new DisruptorQueueTest();
        test.test();
    }

    private void test()
    {
        Executor executor = Executors.newCachedThreadPool();
        Disruptor<LongEvent> disruptor = new Disruptor<>(new LongEventFactory(), RING_BUFFER_SIZE, executor);
        EventHandler<LongEvent> handler = new LongEventHandler();
        disruptor.handleEventsWith(handler);
        disruptor.start();

        RingBuffer<LongEvent> ringBuffer = disruptor.getRingBuffer();
        Producer producer = new Producer(ringBuffer);
        Consumer consumer = new Consumer(ringBuffer);
        Thread producerThread = new Thread(producer);
        Thread consumerThread = new Thread(consumer);
        producerThread.start();
        consumerThread.start();
        try {
            producerThread.join();
            consumerThread.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static class Producer implements Runnable
    {
        private final RingBuffer<LongEvent> ringBuffer;

        public Producer(RingBuffer<LongEvent> ringBuffer)
        {
            this.ringBuffer = ringBuffer;
        }

        @Override
        public void run()
        {
            for (long i = 0; i < Long.MAX_VALUE; i++)
            {
                long sequence = ringBuffer.next();
                try
                {
                    LongEvent event = ringBuffer.get(sequence);
                    event.set(i);
                } finally {
                    ringBuffer.publish(sequence);
                }
            }
        }
    }

    public static class Consumer implements Runnable
    {
        private final RingBuffer<LongEvent> ringBuffer;

        public Consumer(RingBuffer<LongEvent> ringBuffer)
        {
            this.ringBuffer = ringBuffer;
        }

        @Override
        public void run()
        {
            while (true)
            {
                long availableSequence = ringBuffer.getCursor();
                long currentSequence = 0;
                while (currentSequence < availableSequence)
                {
                    LongEvent event = ringBuffer.get(currentSequence);
                    long value = event.get();
                    System.out.println(value);
                    currentSequence++;
                }
                ringBuffer.publish(currentSequence - 1);
            }
        }
    }
}

示例2：并行消费

我们用Disruptor实现一个并行消费的示例，模拟电商秒杀活动的处理过程。

public class DisruptorSeckillTest {

    private static final Logger logger = LogManager.getLogger(DisruptorSeckillTest.class);
    private static final int RING_BUFFER_SIZE = 1024;

    public static void main(String[] args) {
        DisruptorSeckillTest test = new DisruptorSeckillTest();
        test.test();
    }

    private void test() {
        Executor executor = Executors.newCachedThreadPool();
        Disruptor<SeckillEvent> disruptor = new Disruptor<>(new SeckillEventFactory(), RING_BUFFER_SIZE, executor);
        SeckillHandler[] handlers = new SeckillHandler[4];
        for (int i = 0; i < handlers.length; i++) {
            handlers[i] = new SeckillHandler(i + 1, handlers.length);
        }
        WorkerPool<SeckillEvent> workerPool = new WorkerPool<>(disruptor.getRingBuffer(), disruptor.getSequenceBarrier(), new IgnoreExceptionHandler(), handlers);
        disruptor.handleEventsWithWorkerPool(workerPool);
        disruptor.start();

        for (int i = 1; i <= 100; i++) {
            SeckillEvent event = new SeckillEvent(i);
            disruptor.publishEvent((event1, sequence, value) -> event1.set(value), event.getSeckillId());
        }
    }

    public static class SeckillEvent {
        private int seckillId;

        public SeckillEvent(int seckillId) {
            this.seckillId = seckillId;
        }

        public int getSeckillId() {
            return seckillId;
        }

        public void setSeckillId(int seckillId) {
            this.seckillId = seckillId;
        }
    }

    public static class SeckillEventFactory implements EventFactory<SeckillEvent>
    {
        public SeckillEvent newInstance()
        {
            return new SeckillEvent(0);
        }
    }

    public static class SeckillHandler implements WorkHandler<SeckillEvent>
    {
        private final int id;
        private final int total;

        public SeckillHandler(int id, int total)
        {
            this.id = id;
            this.total = total;
        }

        public void onEvent(SeckillEvent event) throws Exception
        {
            logger.info("Consumer {} start seckill {}", id, event.getSeckillId());
            Thread.sleep(1000);
            logger.info("Consumer {} finish seckill {}", id, event.getSeckillId());
        }
    }
}

以上是Disruptor的简要介绍和两个简单示例。Disruptor实现了高性能的并发消息传递框架，因此在一些高性能的业务场景下被广泛使用和推广。但是，Disruptor也存在一些局限性，如果在处理数据时需要耗时的操作，会导致Disruptor的性能下降。因此，在使用Disruptor时，需要根据实际业务进行考虑和选择。