Java并发框架Disruptor教程（二）、快速入门

时间：2019-03-06作者：klpeng分类：IT综合浏览：7041评论：0

添加Maven依赖

将以下内容添加到pom.xml中

<!-- https://mvnrepository.com/artifact/com.lmax/disruptor -->
<dependency>
    <groupId>com.lmax</groupId>
    <artifactId>disruptor</artifactId>
    <version>3.4.2</version>
</dependency>

入门示例

为了开始使用Disruptor，我们将考虑一个非常简单和人为的例子，一个将生产者传递给消费者的单个长值，消费者只需打印出该值。

1、创建事件
首先，我们将定义将携带数据的事件。

public class LongEvent
{
    private long value;

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

2、创建EventFactory
为了让Disruptor为我们预先分配这些事件，我们需要一个将执行构造的EventFactory，

import com.lmax.disruptor.EventFactory;

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

3、创建事件的消费者
一旦我们定义了事件，我们需要创建一个处理这些事件的消费者。在我们的例子中，我们要做的就是从控制台中打印出值。

import com.lmax.disruptor.EventHandler;

public class LongEventHandler implements EventHandler<LongEvent>
{
    public void onEvent(LongEvent event, long sequence, boolean endOfBatch)
    {
        System.out.println("Event: " + event);
    }
}

我们需要这些事件的来源，为了举个例子，我假设数据来自某种I / O设备，例如网络或ByteBuffer形式的文件。

4、创建事件生产者
这里将介绍两种生产者的创建方式
1). 使用Translator创建

import com.lmax.disruptor.RingBuffer;
import com.lmax.disruptor.EventTranslatorOneArg;

public class LongEventProducerWithTranslator
{
    private final RingBuffer<LongEvent> ringBuffer;
    
    public LongEventProducerWithTranslator(RingBuffer<LongEvent> ringBuffer)
    {
        this.ringBuffer = ringBuffer;
    }
    
    private static final EventTranslatorOneArg<LongEvent, ByteBuffer> TRANSLATOR =
        new EventTranslatorOneArg<LongEvent, ByteBuffer>()
        {
            public void translateTo(LongEvent event, long sequence, ByteBuffer bb)
            {
                event.set(bb.getLong(0));
            }
        };

    public void onData(ByteBuffer bb)
    {
        ringBuffer.publishEvent(TRANSLATOR, bb);
    }
}

2). 使用传统API创建
其中只要有

import com.lmax.disruptor.RingBuffer;

public class LongEventProducer
{
    private final RingBuffer<LongEvent> ringBuffer;

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

    public void onData(ByteBuffer bb)
    {
        long sequence = ringBuffer.next();  // Grab the next sequence
        try
        {
            LongEvent event = ringBuffer.get(sequence); // Get the entry in the Disruptor
                                                        // for the sequence
            event.set(bb.getLong(0));  // Fill with data
        }
        finally
        {
            ringBuffer.publish(sequence);
        }
    }
}

显而易见的是，事件发布变得比使用简单队列更复杂。这是由于对事件预分配的需求。它需要（在最低级别）消息发布的两阶段方法，即声明环形缓冲区中的插槽然后发布可用数据。还必须将发布包装在try / finally块中。如果我们在Ring Buffer中声明一个插槽（调用RingBuffer.next（）），那么我们必须发布这个序列。如果不这样做可能会导致干扰者状态的腐败。具体而言，在多生产者的情况下，这将导致消费者停滞并且在没有重启的情况下无法恢复。因此，建议使用EventTranslator API。

5、启动任务

import com.lmax.disruptor.dsl.Disruptor;
import com.lmax.disruptor.RingBuffer;
import com.lmax.disruptor.util.DaemonThreadFactory;
import java.nio.ByteBuffer;

public class LongEventMain
{
    public static void main(String[] args) throws Exception
    {
        // The factory for the event
        LongEventFactory factory = new LongEventFactory();

        // Specify the size of the ring buffer, must be power of 2.
        int bufferSize = 1024;

        // Construct the Disruptor
        Disruptor<LongEvent> disruptor = new Disruptor<>(factory, bufferSize, DaemonThreadFactory.INSTANCE);

        // Connect the handler
        disruptor.handleEventsWith(new LongEventHandler());

        // Start the Disruptor, starts all threads running
        disruptor.start();

        // Get the ring buffer from the Disruptor to be used for publishing.
        RingBuffer<LongEvent> ringBuffer = disruptor.getRingBuffer();

        LongEventProducer producer = new LongEventProducer(ringBuffer);

        ByteBuffer bb = ByteBuffer.allocate(8);
        for (long l = 0; true; l++)
        {
            bb.putLong(0, l);
            producer.onData(bb);
            Thread.sleep(1000);
        }
    }
}