hadoop-2

AsyncDispatcher，直接看代码

  @Override
  protected void serviceStart() throws Exception {
    //start all the components
    super.serviceStart();
    eventHandlingThread = new Thread(createThread());
    eventHandlingThread.setName(dispatcherThreadName);
    eventHandlingThread.start();
  }

  Runnable createThread() {
    return new Runnable() {
      @Override
      public void run() {
        while (!stopped && !Thread.currentThread().isInterrupted()) {
          drained = eventQueue.isEmpty();
          // blockNewEvents is only set when dispatcher is draining to stop,
          // adding this check is to avoid the overhead of acquiring the lock
          // and calling notify every time in the normal run of the loop.
          if (blockNewEvents) {
            synchronized (waitForDrained) {
              if (drained) {
                waitForDrained.notify();
              }
            }
          }
          Event event;
          try {
            event = eventQueue.take();
          } catch(InterruptedException ie) {
            if (!stopped) {
              LOG.warn("AsyncDispatcher thread interrupted", ie);
            }
            return;
          }
          if (event != null) {
            dispatch(event);
          }
        }
      }
    };
  }

  protected void dispatch(Event event) {
    //all events go thru this loop
    if (LOG.isDebugEnabled()) {
      LOG.debug("Dispatching the event " + event.getClass().getName() + "."
          + event.toString());
    }

    Class<? extends Enum> type = event.getType().getDeclaringClass();

    try{
      EventHandler handler = eventDispatchers.get(type);
      if(handler != null) {
        handler.handle(event);
      } else {
        throw new Exception("No handler for registered for " + type);
      }
    } catch (Throwable t) {
      //TODO Maybe log the state of the queue
      LOG.fatal("Error in dispatcher thread", t);
      // If serviceStop is called, we should exit this thread gracefully.
      if (exitOnDispatchException
          && (ShutdownHookManager.get().isShutdownInProgress()) == false
          && stopped == false) {
        stopped = true;
        Thread shutDownThread = new Thread(createShutDownThread());
        shutDownThread.setName("AsyncDispatcher ShutDown handler");
        shutDownThread.start();
      }
    }
  }

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一个handler的实现

public class JobHistoryEventHandler extends AbstractService implements EventHandler<JobHistoryEvent> {
      protected BlockingQueue<JobHistoryEvent> eventQueue = new LinkedBlockingQueue<JobHistoryEvent>();
      protected boolean handleTimelineEvent = false;
      protected AsyncDispatcher atsEventDispatcher = null;
  ......
  @Override
  public void handle(JobHistoryEvent event) {
    try {
      eventQueue.put(event);
      // Process it for ATS (if enabled)
      if (handleTimelineEvent) {
        atsEventDispatcher.getEventHandler().handle(event);
      }
    }
  }
}