如何进行DAGScheduler源码解读

如何进行DAGScheduler源码解读，针对这个问题，这篇文章详细介绍了相对应的分析和解答，希望可以帮助更多想解决这个问题的小伙伴找到更简单易行的方法。

当构建完TaskScheduler之后，我们需要构建DAGScheduler这个核心对象：

进入其构造函数中：

可以看出构建DAGScheduler实例的时候需要把TaskScheduler实例对象作为参数传入。

LiveListenerBus：

BlockManagerMaster：

通过阅读代码，我们可以发现DAGScheduler实例化的时候，调用了initializeEventProcessActor()方法

private def initializeEventProcessActor() {  // blocking the thread until supervisor is started, which ensures eventProcessActor is  // not null before any job is submitted  // 阻塞当前线程，等待supervisor启动，这样可以确保Job提交时，eventProcessActor not null  implicit val timeout = Timeout(30 seconds)  val initEventActorReply =    dagSchedulerActorSupervisor ? Props(new DAGSchedulerEventProcessActor(this))  eventProcessActor = Await.result(initEventActorReply, timeout.duration).    asInstanceOf[ActorRef]}initializeEventProcessActor()

DAGSchedulerEventProcessActor：

private[scheduler] class DAGSchedulerEventProcessActor(dagScheduler: DAGScheduler)  extends Actor with Logging {  override def preStart() {    // set DAGScheduler for taskScheduler to ensure eventProcessActor is always    // valid when the messages arrive    // 设置taskScheduler对DAGScheduler的引用句柄。在此处设置保证了Job提交时候    // eventProcessActor已经准备就绪    dagScheduler.taskScheduler.setDAGScheduler(dagScheduler)  }  /**   * The main event loop of the DAG scheduler.   */  def receive = {    case JobSubmitted(jobId, rdd, func, partitions, allowLocal, callSite, listener, properties) =>      dagScheduler.handleJobSubmitted(jobId, rdd, func, partitions, allowLocal, callSite,        listener, properties)    case StageCancelled(stageId) =>      dagScheduler.handleStageCancellation(stageId)    case JobCancelled(jobId) =>      dagScheduler.handleJobCancellation(jobId)    case JobGroupCancelled(groupId) =>      dagScheduler.handleJobGroupCancelled(groupId)    case AllJobsCancelled =>      dagScheduler.doCancelAllJobs()    case ExecutorAdded(execId, host) =>      dagScheduler.handleExecutorAdded(execId, host)    case ExecutorLost(execId) =>      dagScheduler.handleExecutorLost(execId, fetchFailed = false)    case BeginEvent(task, taskInfo) =>      dagScheduler.handleBeginEvent(task, taskInfo)    case GettingResultEvent(taskInfo) =>      dagScheduler.handleGetTaskResult(taskInfo)    case completion @ CompletionEvent(task, reason, _, _, taskInfo, taskMetrics) =>      dagScheduler.handleTaskCompletion(completion)    case TaskSetFailed(taskSet, reason) =>      dagScheduler.handleTaskSetFailed(taskSet, reason)    case ResubmitFailedStages =>      dagScheduler.resubmitFailedStages()  }  override def postStop() {    // Cancel any active jobs in postStop hook    dagScheduler.cleanUpAfterSchedulerStop()  }}

可以看出核心在于实例化eventProcessActor对象，eventProcessActor会负责接收和发送DAGScheduler的消息，是DAGScheduler的通信载体。

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