第25课：Spark Streaming的StreamingContext启动及JobScheduler启动源码图解

本期内容：
1. StreamingContext启动源码图解
2. JobScheduler启动源码图解
 
StreamingContext的start方法对INITIALIZED、ACTIVE、STOPPED等状态分别做不同处理。

 

/**
 * Start the execution of the streams.
 *
 * @throws IllegalStateException if the StreamingContext is already stopped.
 */
def start(): Unit = synchronized {
  state match {
    case INITIALIZED =>
      startSite.set(DStream.getCreationSite())
      StreamingContext.ACTIVATION_LOCK.synchronized {
        StreamingContext.assertNoOtherContextIsActive()
        try {
          validate()

          // Start the streaming scheduler in a new thread, so that thread local properties
          // like call sites and job groups can be reset without affecting those of the
          // current thread.
          ThreadUtils.runInNewThread("streaming-start") {
            sparkContext.setCallSite(startSite.get)
            sparkContext.clearJobGroup()
            sparkContext.setLocalProperty(SparkContext.SPARK_JOB_INTERRUPT_ON_CANCEL, "false")
            scheduler.start()
          }
          state = StreamingContextState.ACTIVE
        } catch {
          case NonFatal(e) =>
            logError("Error starting the context, marking it as stopped", e)
            scheduler.stop(false)
            state = StreamingContextState.STOPPED
            throw e
        }
        StreamingContext.setActiveContext(this)
      }
      shutdownHookRef = ShutdownHookManager.addShutdownHook(
        StreamingContext.SHUTDOWN_HOOK_PRIORITY)(stopOnShutdown)
      // Registering Streaming Metrics at the start of the StreamingContext
      assert(env.metricsSystem != null)
      env.metricsSystem.registerSource(streamingSource)
      uiTab.foreach(_.attach())
      logInfo("StreamingContext started")
    case ACTIVE =>
      logWarning("StreamingContext has already been started")
    case STOPPED =>
      throw new IllegalStateException("StreamingContext has already been stopped")
  }
}

 

 

 

 

JobScheduler中的eventLoop是带有一个消息队列的线程循环器。接收的消息有JobStarted、JobCompleted、ErrorReported等三种。eventLoop用start方法启动。

JobScheduler还把所有InputDStream的rateController放入监听器中。然后启动了listenerBus。

然后启动了receiverTracker、jobGenerator。这两个在JobScheduler中至关重要。

ReceiverTracker中有个适用于RPC的ReceiverTrackerEndpoint类型的消息循环体，用receive方法接收StartAllReceivers、RestartReceiver、CleanupOldBlocks、UpdateReceiverRteLimit等4种消息，用receiveAndREply方法接收RegisterReceiver、AddBlock、DeregisterReceiver、AllReceiverIds、StopAllReceivers等五种消息。消息有自己给自己发的消息，也有远程发来的消息。

shutdownHookManager用于关闭时。env.metricsSystem用于计量，注册的计量信息在StreamingSource中有定义。uiTab用于web界面。针对UI界面，定义有StreamingPage、BatchPage等WebUIPage的子类 ，做定制时也可定义自己的Page。

源码需要在细节上下工夫。深度决定广度。

JobGenerator中也有一个消息循环体。

 
所以，JobScheduler有3个消息循环体。如下图所示