// 核心是一个循环缓冲区。我们的循环缓冲区是一个LMAX Disruptor。当多个线程在单个WAL竞争append和sync时，它试图最小化同步与volatile写。
// Disruptor配置为处理多个生产者和仅有一个消费者（HBase中的生产者是调用append、sync的IPC Handlers）。单一的消费者从环形缓冲区中
// 拉去append和sync。
/**
* RingBufferTruck为事件--Event
* RingBufferTruck.EVENT_FACTORY为事件工厂--EventFactory
* preallocatedEventCount为RingBuffer大小，必须是2的N次方，默认为1024*16
* appendExecutor为事件处理的线程池--newSingleThreadExecutor
* ProducerType.MULTI为生产者类型，意思为多个生产者
* BlockingWaitStrategy为指定的等待策略
*/
this.disruptor =
new Disruptor<RingBufferTruck>(RingBufferTruck.EVENT_FACTORY, preallocatedEventCount,
this.appendExecutor, ProducerType.MULTI, new BlockingWaitStrategy());
// Advance the ring buffer sequence so that it starts from 1 instead of 0,
// because SyncFuture.NOT_DONE = 0.
// 请求下一个事件序号
// 让ring buffer sequence从1开始，而不是从0开始
this.disruptor.getRingBuffer().next();
// 构造事件处理器实例
this.ringBufferEventHandler =
new RingBufferEventHandler(conf.getInt("hbase.regionserver.hlog.syncer.count", 5),
maxHandlersCount);
// 添加异常处理器
this.disruptor.handleExceptionsWith(new RingBufferExceptionHandler());
// 添加事件处理器
this.disruptor.handleEventsWith(new RingBufferEventHandler [] {this.ringBufferEventHandler});
// Presize our map of SyncFutures by handler objects.
this.syncFuturesByHandler = new ConcurrentHashMap<Thread, SyncFuture>(maxHandlersCount);
// Starting up threads in constructor is a no no; Interface should have an init call.
// 启动disruptor
this.disruptor.start();
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