Disruptor 框架源码分析

Disruptor 是一个高性能异步处理框架，也可以认为是一个消息通信框架，它本质上为生产者-消费者模型。

Disruptor消息处理流程

Disruptor核心类和接口

• EventHandler：用户提供具体的实现，在里面实现事件的处理逻辑。
• Sequence：代表事件序号或一个指向缓存某个位置的序号。
• WaitStrategy：功能包括：当没有可消费的事件时，根据特定的实现进行等待，有可消费事件时返回可事件序号；有新事件发布时通知等待的SequenceBarrier。
• Sequencer：生产者用于访问缓存的控制器，它持有消费者序号的引用；新事件发布后通过 WaitStrategy 通知正在等待的SequenceBarrier。
• SequenceBarrier：消费者关卡。消费者用于访问缓存的控制器，每个访问控制器还持有前置访问控制器的引用，用于维持正确的事件处理顺序；通过WaitStrategy获取可消费事件序号。
• EventProcessor：事件处理器，是可执行单元，运行在指定的Executor里；它会不断地通过SequenceBarrier获取可消费事件，当有可消费事件时调用用户提供的EventHandler实现处理事件。
• EventTranslator：事件转换器，由于Disruptor只会覆盖缓存，需要通过此接口的实现来更新缓存里的事件来覆盖旧事件。
• RingBuffer：基于数组的缓存实现，它内部持有对Executor、WaitStrategy、生产者和消费者访问控制器的引用。
• Disruptor：提供了对 RingBuffer 的封装，并提供了一些DSL风格的方法，方便使用。

Disruptor门面类

public class Disruptor
{
    private final RingBuffer ringBuffer;
    private final Executor executor;
    private final ConsumerRepository consumerRepository = new ConsumerRepository();
    private final AtomicBoolean started = new AtomicBoolean(false);
    private ExceptionHandler exceptionHandler;
}

EventHandler

public interface EventHandler
{
    /**
     * Called when a publisher has published an event to the {@link RingBuffer}
     *
     * @param event published to the {@link RingBuffer}
     * @param sequence of the event being processed
     * @param endOfBatch flag to indicate if this is the last event in a batch from the {@link RingBuffer}
     * @throws Exception if the EventHandler would like the exception handled further up the chain.
     */
    void onEvent(T event, long sequence, boolean endOfBatch) throws Exception;
}

EventProcessor

public interface EventProcessor extends Runnable
{
    /**
     * Get a reference to the {@link Sequence} being used by this {@link EventProcessor}.
     *
     * @return reference to the {@link Sequence} for this {@link EventProcessor}
     */
    Sequence getSequence();

    /**
     * Signal that this EventProcessor should stop when it has finished consuming at the next clean break.
     * It will call {@link SequenceBarrier#alert()} to notify the thread to check status.
     */
    void halt();

    boolean isRunning();
}

RingBuffer

public final class RingBuffer implements Cursored, DataProvider
{
    public static final long INITIAL_CURSOR_VALUE = Sequence.INITIAL_VALUE;

    private final int indexMask;
    private final Object[] entries;
    private final int bufferSize;
    private final Sequencer sequencer;
}

    RingBuffer(EventFactory eventFactory,
               Sequencer       sequencer)
    {
        this.sequencer    = sequencer;
        this.bufferSize   = sequencer.getBufferSize();

        if (bufferSize < 1)
        {
            throw new IllegalArgumentException("bufferSize must not be less than 1");
        }
        if (Integer.bitCount(bufferSize) != 1)
        {
            throw new IllegalArgumentException("bufferSize must be a power of 2");
        }

        this.indexMask = bufferSize - 1;
        this.entries   = new Object[sequencer.getBufferSize()];
        fill(eventFactory);
    }

Disruptor简单使用示例

 Disruptor disruptor = new Disruptor(MyEvent.FACTORY, 32, Executors.newCachedThreadPool());
 EventHandler handler1 = new EventHandler() { ... };
 EventHandler handler2 = new EventHandler() { ... };
 disruptor.handleEventsWith(handler1);
 disruptor.after(handler1).handleEventsWith(handler2);

 RingBuffer ringBuffer = disruptor.start();