Disruptor（2）

版权声明： https://blog.csdn.net/ph3636/article/details/84635021

3. RingBuffer#addGatingSequences=》AbstractSequencer#addGatingSequences

public void addGatingSequences(Sequence... gatingSequences)
    {
        sequencer.addGatingSequences(gatingSequences);
    }

public final void addGatingSequences(Sequence... gatingSequences)
    {
        SequenceGroups.addSequences(this, SEQUENCE_UPDATER, this, gatingSequences);
    }

通过原子更新private static final AtomicReferenceFieldUpdater<AbstractSequencer, Sequence[]> SEQUENCE_UPDATER = AtomicReferenceFieldUpdater.newUpdater(AbstractSequencer.class, Sequence[].class, "gatingSequences");把每个消费端的定序器的下标都设置为提供端的定序器cursor对应的下标，之所以要保存消费端的下标，主要是因为当提供端设置数据的时候不能覆盖消费端还没有消费的对应下标，这个时候提供端就需要等待该下标被消费掉，才能用新的值覆盖旧值。

static <T> void addSequences(
        final T holder,
        final AtomicReferenceFieldUpdater<T, Sequence[]> updater,
        final Cursored cursor,
        final Sequence... sequencesToAdd)
    {
        long cursorSequence;
        Sequence[] updatedSequences;
        Sequence[] currentSequences;

        do
        {
            currentSequences = updater.get(holder);
            updatedSequences = copyOf(currentSequences, currentSequences.length + sequencesToAdd.length);
            cursorSequence = cursor.getCursor();

            int index = currentSequences.length;
            for (Sequence sequence : sequencesToAdd)
            {
                sequence.set(cursorSequence);
                updatedSequences[index++] = sequence;
            }
        }
        while (!updater.compareAndSet(holder, currentSequences, updatedSequences));

        cursorSequence = cursor.getCursor();
        for (Sequence sequence : sequencesToAdd)
        {
            sequence.set(cursorSequence);
        }
    }

4. 启动Disruptor，原子类型判断启动状态，ConsumerRepository实现了Iterable接口，则遍历的是consumerInfos集合

 public RingBuffer<T> start()
    {
        checkOnlyStartedOnce();
        for (final ConsumerInfo consumerInfo : consumerRepository)
        {
            consumerInfo.start(executor);
        }

        return ringBuffer;
    }

WorkerPoolInfo#start

 public void start(Executor executor)
    {
        workerPool.start(executor);
    }

原子类型判断设置状态，获取当前提供端的下标并设置到消费池的消费定序器下标中workSequence以及各个消费端的定序器

 public RingBuffer<T> start(final Executor executor)
    {
        if (!started.compareAndSet(false, true))
        {
            throw new IllegalStateException("WorkerPool has already been started and cannot be restarted until halted.");
        }

        final long cursor = ringBuffer.getCursor();
        workSequence.set(cursor);

        for (WorkProcessor<?> processor : workProcessors)
        {
            processor.getSequence().set(cursor);
            executor.execute(processor);
        }

        return ringBuffer;
    }

在BasicExecutor中创建消费线程并启动

  public void execute(Runnable command)
    {
        final Thread thread = factory.newThread(command);
        if (null == thread)
        {
            throw new RuntimeException("Failed to create thread to run: " + command);
        }

        thread.start();

        threads.add(thread);
    }

WorkProcessor#run，判断设置运行状态，清除警示标志，主体是个死循环，除非有异常产生，先获取本线程要处理的定序器下标，因为各个消费线程都是共用的一个workSequence，所以通过原子类型设置方法来获取各自消费线程所需要从头开始消费的下标，达到了互斥消费。

public void run()
    {
        if (!running.compareAndSet(false, true))
        {
            throw new IllegalStateException("Thread is already running");
        }
        sequenceBarrier.clearAlert();

        notifyStart();

        boolean processedSequence = true;
        long cachedAvailableSequence = Long.MIN_VALUE;
        long nextSequence = sequence.get();
        T event = null;
        while (true)
        {
            try
            {
                // if previous sequence was processed - fetch the next sequence and set
                // that we have successfully processed the previous sequence
                // typically, this will be true
                // this prevents the sequence getting too far forward if an exception
                // is thrown from the WorkHandler
                if (processedSequence)
                {
                    processedSequence = false;
                    do
                    {
                        nextSequence = workSequence.get() + 1L;
                        sequence.set(nextSequence - 1L);
                    }
                    while (!workSequence.compareAndSet(nextSequence - 1L, nextSequence));
                }

                if (cachedAvailableSequence >= nextSequence)
                {
                    event = ringBuffer.get(nextSequence);
                    workHandler.onEvent(event);
                    processedSequence = true;
                }
                else
                {
                    cachedAvailableSequence = sequenceBarrier.waitFor(nextSequence);
                }
            }
            catch (final TimeoutException e)
            {
                notifyTimeout(sequence.get());
            }
            catch (final AlertException ex)
            {
                if (!running.get())
                {
                    break;
                }
            }
            catch (final Throwable ex)
            {
                // handle, mark as processed, unless the exception handler threw an exception
                exceptionHandler.handleEventException(ex, nextSequence, event);
                processedSequence = true;
            }
        }

        notifyShutdown();

        running.set(false);
    }