首页手记 Disruptor 实践：整合到现有的爬虫框架

Disruptor 实践：整合到现有的爬虫框架

标签：

Java 架构爬虫

一. Disruptor

Disruptor 是一个高性能的异步处理框架。

Disruptor 是 LMAX 在线交易平台的关键组成部分，LMAX平台使用该框架对订单处理速度能达到600万TPS，除金融领域之外，其他一般的应用中都可以用到Disruptor，它可以带来显著的性能提升。其实 Disruptor 与其说是一个框架，不如说是一种设计思路，这个设计思路对于存在“并发、缓冲区、生产者—消费者模型、事务处理”这些元素的程序来说，Disruptor提出了一种大幅提升性能（TPS）的方案。

二. 实践

NetDiscovery 是基于 Vert.x、RxJava 2 等框架实现的爬虫框架。

NetDiscovery 默认的消息队列采用 JDK 的 ConcurrentLinkedQueue，由于爬虫框架各个组件都可以被替换，所以下面基于 Disruptor 实现爬虫的 Queue。

2.1 事件的封装

将爬虫的 request 封装成一个 RequestEvent，该事件会在 Disruptor 中传输。

import com.cv4j.netdiscovery.core.domain.Request;
import lombok.Data;

/**
 * Created by tony on 2018/9/1.
 */
@Data
public class RequestEvent {

    private Request request;

    public String toString() {

        return request.toString();
    }
}

2.2 发布事件

下面编写事件的发布，从 RingBuffer 中获取下一个可写入事件的序号，将爬虫要请求的 request 设置到 RequestEvent 事件中，最后将事件提交到 RingBuffer。

import com.cv4j.netdiscovery.core.domain.Request;
import com.lmax.disruptor.RingBuffer;

import java.util.concurrent.atomic.AtomicInteger;

/**
 * Created by tony on 2018/9/2.
 */
public class Producer {

    private final RingBuffer<RequestEvent> ringBuffer;

    private AtomicInteger count = new AtomicInteger(0); // 计数器

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

    public void pushData(Request request){
        long sequence = ringBuffer.next();

        try{
            RequestEvent event = ringBuffer.get(sequence);
            event.setRequest(request);
        }finally {
            ringBuffer.publish(sequence);
            count.incrementAndGet();
        }
    }

    /**
     * 发送到队列中到Request的数量
     * @return
     */
    public int getCount() {

        return count.get();
    }
}

2.3 消费事件

RequestEvent 设置了 request 之后，消费者需要处理具体的事件。下面的 Consumer 仅仅是记录消费者的线程名称以及 request。真正的“消费”还是需要从 DisruptorQueue 的 poll() 中获取 request ，然后在 Spider 中进行“消费”。

import com.lmax.disruptor.WorkHandler;
import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.atomic.AtomicInteger;

/**
 * Created by tony on 2018/9/2.
 */
@Slf4j
public class Consumer implements WorkHandler<RequestEvent> {

    @Override
    public void onEvent(RequestEvent requestEvent) throws Exception {

        log.info("consumer:" + Thread.currentThread().getName() + " requestEvent: value=" + requestEvent.toString());
    }
}

2.4 DisruptorQueue 的实现

Disruptor 支持单生产者单消费者、多生产者、多消费者、分组等方式。

在 NetDiscovery 中采用多生产者多消费者。

在 RingBuffer 创建时，ProducerType 使用 MULTI 类型表示多生产者。创建 RingBuffer 采用了 YieldingWaitStrategy 。YieldingWaitStrategy 是一种WaitStrategy，不同的 WaitStrategy 会有不同的性能。

YieldingWaitStrategy 性能是最好的，适合用于低延迟的系统。在要求极高性能且事件处理线数小于CPU逻辑核心数的场景中，推荐使用此策略；例如，CPU开启超线程的特性。

        ringBuffer = RingBuffer.create(ProducerType.MULTI,
                new EventFactory<RequestEvent>() {
                    @Override
                    public RequestEvent newInstance() {
                        return new RequestEvent();
                    }
                },
                ringBufferSize ,
                new YieldingWaitStrategy());

EventProcessor 用于处理 Disruptor 中的事件。

EventProcessor 的实现类包括：BatchEventProcessor 用于单线程批量处理事件，WorkProcessor 用于多线程处理事件。

WorkerPool 管理着一组 WorkProcessor。创建完 ringBuffer 之后，创建 workerPool：

        SequenceBarrier barriers = ringBuffer.newBarrier();

        for (int i = 0; i < consumers.length; i++) {
            consumers[i] = new Consumer();
        }

        workerPool = new WorkerPool<RequestEvent>(ringBuffer,
                        barriers,
                        new EventExceptionHandler(),
                        consumers);

启动 workerPool：

        ringBuffer.addGatingSequences(workerPool.getWorkerSequences());
        workerPool.start(Executors.newFixedThreadPool(threadNum));

最后是 DisruptorQueue 完整的代码：

import com.cv4j.netdiscovery.core.domain.Request;
import com.cv4j.netdiscovery.core.queue.AbstractQueue;
import com.lmax.disruptor.*;
import com.lmax.disruptor.dsl.ProducerType;
import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * Created by tony on 2018/9/1.
 */
@Slf4j
public class DisruptorQueue extends AbstractQueue {

    private RingBuffer<RequestEvent> ringBuffer;

    private Consumer[] consumers = null;
    private Producer producer = null;
    private WorkerPool<RequestEvent> workerPool = null;
    private int ringBufferSize = 1024*1024; // RingBuffer 大小，必须是 2 的 N 次方

    private AtomicInteger consumerCount = new AtomicInteger(0);

    private static final int CONSUME_NUM = 2;
    private static final int THREAD_NUM = 4;

    public DisruptorQueue() {

        this(CONSUME_NUM,THREAD_NUM);
    }

    public DisruptorQueue(int consumerNum,int threadNum) {

        consumers = new Consumer[consumerNum];

        //创建ringBuffer
        ringBuffer = RingBuffer.create(ProducerType.MULTI,
                new EventFactory<RequestEvent>() {
                    @Override
                    public RequestEvent newInstance() {
                        return new RequestEvent();
                    }
                },
                ringBufferSize ,
                new YieldingWaitStrategy());

        SequenceBarrier barriers = ringBuffer.newBarrier();

        for (int i = 0; i < consumers.length; i++) {
            consumers[i] = new Consumer();
        }

        workerPool = new WorkerPool<RequestEvent>(ringBuffer,
                        barriers,
                        new EventExceptionHandler(),
                        consumers);

        ringBuffer.addGatingSequences(workerPool.getWorkerSequences());
        workerPool.start(Executors.newFixedThreadPool(threadNum));

        producer = new Producer(ringBuffer);
    }

    @Override
    protected void pushWhenNoDuplicate(Request request) {

        producer.pushData(request);
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    @Override
    public Request poll(String spiderName) {

        Request request = ringBuffer.get(ringBuffer.getCursor() - producer.getCount() +1).getRequest();
        ringBuffer.next();
        consumerCount.incrementAndGet();
        return request;
    }

    @Override
    public int getLeftRequests(String spiderName) {

        return producer.getCount()-consumerCount.get();
    }

    public int getTotalRequests(String spiderName) {

        return super.getTotalRequests(spiderName);
    }

    static class EventExceptionHandler implements ExceptionHandler {

        public void handleEventException(Throwable ex, long sequence, Object event) {

            log.debug("handleEventException：" + ex);
        }

        public void handleOnStartException(Throwable ex) {

            log.debug("handleOnStartException：" + ex);
        }

        public void handleOnShutdownException(Throwable ex) {

            log.debug("handleOnShutdownException：" + ex);
        }
    }
}