public interface LifecycleAware {

  /**
   * <p>
   * Starts a service or component.
   * </p>
   * <p>
   * Implementations should determine the result of any start logic and effect
   * the return value of {@link #getLifecycleState()} accordingly.
   * </p>
   *
   * @throws LifecycleException
   * @throws InterruptedException
   */
  public void start();

  /**
   * <p>
   * Stops a service or component.
   * </p>
   * <p>
   * Implementations should determine the result of any stop logic and effect
   * the return value of {@link #getLifecycleState()} accordingly.
   * </p>
   *
   * @throws LifecycleException
   * @throws InterruptedException
   */
  public void stop();

  /**
   * <p>
   * Return the current state of the service or component.
   * </p>
   */
  public LifecycleState getLifecycleState();
}

生命周期的状态：

public enum LifecycleState {
  IDLE, START, STOP, ERROR;
}

SourceRunner

/**
 * A source runner controls how a source is driven.
 *
 * This is an abstract class used for instantiating derived classes.
 */
public abstract class SourceRunner implements LifecycleAware {

  private Source source;

  /**
   * Static factory method to instantiate a source runner implementation that
   * corresponds to the type of {@link Source} specified.
   *
   * @param source The source to run
   * @return A runner that can run the specified source
   * @throws IllegalArgumentException if the specified source does not implement
   * a supported derived interface of {@link SourceRunner}.
   */
  public static SourceRunner forSource(Source source) {
    SourceRunner runner = null;

    //根据source类型选择具体的SourceRunner
    if (source instanceof PollableSource) {
      runner = new PollableSourceRunner();
      ((PollableSourceRunner) runner).setSource((PollableSource) source);
    } else if (source instanceof EventDrivenSource) {
      runner = new EventDrivenSourceRunner();
      ((EventDrivenSourceRunner) runner).setSource((EventDrivenSource) source);
    } else {
      throw new IllegalArgumentException("No known runner type for source "
          + source);
    }

    return runner;
  }

  public Source getSource() {
    return source;
  }

  public void setSource(Source source) {
    this.source = source;
  }
}

PollableSourceRunner会驱动PollableSource。start方法通过调用source类的ChannelProcessor的initialize()，完成拦截器链的初始化，并调用source的start()。然后后台启动一个PollingRunner线程，完成轮询操作。如果未能拉取到数据，则会BACKOFF，线程sleep时间如下：

 Thread.sleep(Math.min(
                counterGroup.incrementAndGet("runner.backoffs.consecutive")
                * source.getBackOffSleepIncrement(), source.getMaxBackOffSleepInterval()));

/**
 * <p>
 * An implementation of {@link SourceRunner} that can drive a
 * {@link PollableSource}.
 * </p>
 * <p>
 * A {@link PollableSourceRunner} wraps a {@link PollableSource} in the required
 * run loop in order for it to operate. Internally, metrics and counters are
 * kept such that a source that returns a {@link PollableSource.Status} of
 * {@code BACKOFF} causes the run loop to do exactly that. There's a maximum
 * backoff period of 500ms. A source that returns {@code READY} is immediately
 * invoked. Note that {@code BACKOFF} is merely a hint to the runner; it need
 * not be strictly adhered to.
 * </p>
 */
public class PollableSourceRunner extends SourceRunner {
  private AtomicBoolean shouldStop;

  private CounterGroup counterGroup;//metrics以及计数信息
  private PollingRunner runner;
  private Thread runnerThread;
  private LifecycleState lifecycleState;

  public PollableSourceRunner() {
    shouldStop = new AtomicBoolean();
    counterGroup = new CounterGroup();
    lifecycleState = LifecycleState.IDLE;
  }

  @Override
  public void start() {
    PollableSource source = (PollableSource) getSource();
    ChannelProcessor cp = source.getChannelProcessor();
    cp.initialize();//拦截器链初始化
    source.start();

    runner = new PollingRunner();

    runner.source = source;
    runner.counterGroup = counterGroup;
    runner.shouldStop = shouldStop;

    runnerThread = new Thread(runner);
    runnerThread.setName(getClass().getSimpleName() + "-" + 
        source.getClass().getSimpleName() + "-" + source.getName());
    runnerThread.start();//启动PollingRunner线程

    lifecycleState = LifecycleState.START;
  }

  @Override
  public void stop() {

    runner.shouldStop.set(true);

    try {
      runnerThread.interrupt();
      runnerThread.join();
    } catch (InterruptedException e) {
      logger.warn("Interrupted while waiting for polling runner to stop. Please report this.", e);
      Thread.currentThread().interrupt();
    }

    Source source = getSource();
    source.stop();
    ChannelProcessor cp = source.getChannelProcessor();
    cp.close();

    lifecycleState = LifecycleState.STOP;
  }

  @Override
  public LifecycleState getLifecycleState() {
    return lifecycleState;
  }

  public static class PollingRunner implements Runnable {

    private PollableSource source;
    private AtomicBoolean shouldStop;
    private CounterGroup counterGroup;

    @Override
    public void run() {
      logger.debug("Polling runner starting. Source:{}", source);

      while (!shouldStop.get()) {//是否关闭
        counterGroup.incrementAndGet("runner.polls");

        try {
            //调用process()，尝试从source拉取item，并发送给channel
          if (source.process().equals(PollableSource.Status.BACKOFF)) {
            //没有拉取到item
            counterGroup.incrementAndGet("runner.backoffs");

            Thread.sleep(Math.min(
                counterGroup.incrementAndGet("runner.backoffs.consecutive")
                * source.getBackOffSleepIncrement(), source.getMaxBackOffSleepInterval()));
          } else {
            counterGroup.set("runner.backoffs.consecutive", 0L);
          }
        } catch (InterruptedException e) {
          logger.info("Source runner interrupted. Exiting");
          counterGroup.incrementAndGet("runner.interruptions");
        } catch (EventDeliveryException e) {
          logger.error("Unable to deliver event. Exception follows.", e);
          counterGroup.incrementAndGet("runner.deliveryErrors");
        } catch (Exception e) {
          counterGroup.incrementAndGet("runner.errors");
          logger.error("Unhandled exception, logging and sleeping for " +
              source.getMaxBackOffSleepInterval() + "ms", e);
          try {
            Thread.sleep(source.getMaxBackOffSleepInterval());
          } catch (InterruptedException ex) {
            Thread.currentThread().interrupt();
          }
        }
      }

      logger.debug("Polling runner exiting. Metrics:{}", counterGroup);
    }

  }

}