/**
 * The main class used to talk to a Spark deploy cluster. Takes a master URL, an app description,
 * and a listener for cluster events, and calls back the listener when various events occur.
 */
private[spark] class Client(
    actorSystem: ActorSystem,
    masterUrl: String,
    appDescription: ApplicationDescription,
    listener: ClientListener)
  extends Logging {
  var actor: ActorRef = null
  var appId: String = null

  class ClientActor extends Actor with Logging {
    var master: ActorRef = null
    var masterAddress: Address = null
    var alreadyDisconnected = false  // To avoid calling listener.disconnected() multiple times

    override def preStart() {
      try {
        master = context.actorFor(Master.toAkkaUrl(masterUrl)) // 创建master ActorRef, 用于和master通信
        masterAddress = master.path.address
        master ! RegisterApplication(appDescription) // 向master注册该application
        context.system.eventStream.subscribe(self, classOf[RemoteClientLifeCycleEvent])
        context.watch(master)  // Doesn't work with remote actors, but useful for testing
      } catch {
        case e: Exception =>
          markDisconnected()
          context.stop(self)
      }
    }

    override def receive = { // 接收master发来的各种events
      case RegisteredApplication(appId_) =>
      case ApplicationRemoved(message) =>
      case ExecutorAdded(id: Int, workerId: String, hostPort: String, cores: Int, memory: Int) =>
      case ExecutorUpdated(id, state, message, exitStatus) =>
      case Terminated(actor_) if actor_ == master =>
      case RemoteClientDisconnected(transport, address) if address == masterAddress =>
      case RemoteClientShutdown(transport, address) if address == masterAddress =>
      case StopClient =>
    }

  }

  def start() {
    // Just launch an actor; it will call back into the listener.
    actor = actorSystem.actorOf(Props(new ClientActor))
  }

  def stop() {
    if (actor != null) {
      try {
        val future = actor.ask(StopClient)(timeout)
        Await.result(future, timeout)
      } catch {
        case e: TimeoutException =>
          logInfo("Stop request to Master timed out; it may already be shut down.")
      }
      actor = null
    }
  }
}

  override def receive = {
    case RegisterWorker(id, host, workerPort, cores, memory, worker_webUiPort, publicAddress) => {
      logInfo("Registering worker %s:%d with %d cores, %s RAM".format(
        host, workerPort, cores, Utils.megabytesToString(memory)))
      if (idToWorker.contains(id)) {
        sender ! RegisterWorkerFailed("Duplicate worker ID")
      } else {
        addWorker(id, host, workerPort, cores, memory, worker_webUiPort, publicAddress)
        context.watch(sender)  // This doesn't work with remote actors but helps for testing
        sender ! RegisteredWorker("http://" + masterPublicAddress + ":" + webUi.boundPort.get)
        schedule() // 重新schedule 
      }
    }

    case RegisterApplication(description) => {
      logInfo("Registering app " + description.name)
      val app = addApplication(description, sender)
      logInfo("Registered app " + description.name + " with ID " + app.id)
      waitingApps += app
      context.watch(sender)  // This doesn't work with remote actors but helps for testing
      sender ! RegisteredApplication(app.id)
      schedule() // 重新schedule
    }

    // 当executor的状态发生变化时, 这里只处理失败的case

    case ExecutorStateChanged(appId, execId, state, message, exitStatus) => {
      val execOption = idToApp.get(appId).flatMap(app => app.executors.get(execId))
      execOption match {
        case Some(exec) => { // 说明该executor是有记录的,合法的
          exec.state = state
          exec.application.driver ! ExecutorUpdated(execId, state, message, exitStatus) // 向driver actor发送ExecutorUpdated事件
          if (ExecutorState.isFinished(state)) { // isFinished, means KILLED, FAILED, LOST, 即失败的case,名字起的不好
            val appInfo = idToApp(appId)
            // 先删除该executor, 释放出coresLeft, 重新schedule

// Remove this executor from the worker and app
            logInfo("Removing executor " + exec.fullId + " because it is " + state)
            appInfo.removeExecutor(exec)
            exec.worker.removeExecutor(exec)

            // Only retry certain number of times so we don't go into an infinite loop.

// 在retry次数以内, 则重新schedule执行
            if (appInfo.incrementRetryCount < ApplicationState.MAX_NUM_RETRY) {
              schedule()
            } else { // 超过retry次数, 则整个application失败
              logError("Application %s with ID %s failed %d times, removing it".format(
                appInfo.desc.name, appInfo.id, appInfo.retryCount))
              removeApplication(appInfo, ApplicationState.FAILED)
            }
          }
        }
        case None =>
          logWarning("Got status update for unknown executor " + appId + "/" + execId)
      }
    }

    case Heartbeat(workerId) => { // 更新worker的hb
      idToWorker.get(workerId) match {
        case Some(workerInfo) =>
          workerInfo.lastHeartbeat = System.currentTimeMillis()
        case None =>
          logWarning("Got heartbeat from unregistered worker " + workerId)
      }
    }

    case Terminated(actor)

    case RemoteClientDisconnected(transport, address) 

    case RemoteClientShutdown(transport, address) 

    case RequestMasterState 

    case CheckForWorkerTimeOut 

    case RequestWebUIPort 

  }

  /**
   * Schedule the currently available resources among waiting apps. This method will be called
   * every time a new app joins or resource availability changes.
   */
  def schedule() {
    // Right now this is a very simple FIFO scheduler. We keep trying to fit in the first app
    // in the queue, then the second app, etc.
    if (spreadOutApps) { // 让app分布到尽可能多的worker上去
      // Try to spread out each app among all the nodes, until it has all its cores
      for (app <- waitingApps if app.coresLeft > 0) { // coresLeft表示该app是否还需要更多的cores, 表示并发度
        val usableWorkers = workers.toArray.filter(_.state == WorkerState.ALIVE) // 找出可以使用的workers,本身alive,可以run这个app,最终按coresFree排序
                                   .filter(canUse(app, _)).sortBy(_.coresFree).reverse // canUse的定义,worker.memoryFree >= app.desc.memoryPerSlave && !worker.hasExecutor(app)
        val numUsable = usableWorkers.length
        val assigned = new Array[Int](numUsable) // Number of cores to give on each node
        var toAssign = math.min(app.coresLeft, usableWorkers.map(_.coresFree).sum) // 一共可以分配的cores数,取需要的和可用的的min
        // 下面的过程是平均从每个可用的workers上获取cores

var pos = 0
        while (toAssign > 0) {
          if (usableWorkers(pos).coresFree - assigned(pos) > 0) { // 不能assign的比free的多 
            toAssign -= 1
            assigned(pos) += 1
          }
          pos = (pos + 1) % numUsable // 如果一轮不够,就需要循环分配
        }
        // Now that we've decided how many cores to give on each node, let's actually give them
        for (pos <- 0 until numUsable) {
          if (assigned(pos) > 0) {
            val exec = app.addExecutor(usableWorkers(pos), assigned(pos))
            launchExecutor(usableWorkers(pos), exec, app.desc.sparkHome) //launch executorbackend
            app.state = ApplicationState.RUNNING
          }
        }
      }
    } else { // 让app分配到尽可能少的workers上去, 逻辑更简单点
      // Pack each app into as few nodes as possible until we've assigned all its cores
      for (worker <- workers if worker.coresFree > 0 && worker.state == WorkerState.ALIVE) {
        for (app <- waitingApps if app.coresLeft > 0) {
          if (canUse(app, worker)) {
            val coresToUse = math.min(worker.coresFree, app.coresLeft)
            if (coresToUse > 0) {
              val exec = app.addExecutor(worker, coresToUse)
              launchExecutor(worker, exec, app.desc.sparkHome)
              app.state = ApplicationState.RUNNING
            }
          }
        }
      }
    }
  }

  def launchExecutor(worker: WorkerInfo, exec: ExecutorInfo, sparkHome: String) {
    logInfo("Launching executor " + exec.fullId + " on worker " + worker.id)
    worker.addExecutor(exec)
    worker.actor ! LaunchExecutor( // 向work actor发送LaunchExecutor事件
      exec.application.id, exec.id, exec.application.desc, exec.cores, exec.memory, sparkHome)
    exec.application.driver ! ExecutorAdded( // 向driver actor发送ExecutorAdded事件
      exec.id, worker.id, worker.hostPort, exec.cores, exec.memory)
  }

private[spark] class Worker(
    host: String,
    port: Int,
    webUiPort: Int,
    cores: Int,
    memory: Int,
    masterUrl: String,
    workDirPath: String = null)
  extends Actor with Logging {

  override def preStart() {
    sparkHome = new File(Option(System.getenv("SPARK_HOME")).getOrElse("."))
    logInfo("Spark home: " + sparkHome)
    createWorkDir() // 根据用户配置的sparkHome创建工作目录
    connectToMaster() // 向master注册自己
  }

  override def receive = {
    case RegisteredWorker(url) => // 注册成功,master的反馈
      masterWebUiUrl = url
      logInfo("Successfully registered with master")
      context.system.scheduler.schedule(0 millis, HEARTBEAT_MILLIS millis) {
        master ! Heartbeat(workerId) // 设置scheduler.schedule定期发送hb
      }

    case RegisterWorkerFailed(message) =>
      logError("Worker registration failed: " + message)
      System.exit(1)

    case LaunchExecutor(appId, execId, appDesc, cores_, memory_, execSparkHome_) =>
      logInfo("Asked to launch executor %s/%d for %s".format(appId, execId, appDesc.name))
      val manager = new ExecutorRunner( // 创建ExecutorRunner, 并start
        appId, execId, appDesc, cores_, memory_, self, workerId, host, new File(execSparkHome_), workDir)
      executors(appId + "/" + execId) = manager
      manager.start()
      coresUsed += cores_
      memoryUsed += memory_
      master ! ExecutorStateChanged(appId, execId, ExecutorState.RUNNING, None, None) // 发送给master ExecutorStateChanged事件,汇报ExecutorState.RUNNING

    case ExecutorStateChanged(appId, execId, state, message, exitStatus) => // 接收ExecutorRunner发来的ExecutorStateChanged事件
      master ! ExecutorStateChanged(appId, execId, state, message, exitStatus) // 转发给master
      val fullId = appId + "/" + execId
      if (ExecutorState.isFinished(state)) {
        val executor = executors(fullId)
        logInfo("Executor " + fullId + " finished with state " + state +
          message.map(" message " + _).getOrElse("") +
          exitStatus.map(" exitStatus " + _).getOrElse(""))
        finishedExecutors(fullId) = executor
        executors -= fullId
        coresUsed -= executor.cores
        memoryUsed -= executor.memory
      }

    case KillExecutor(appId, execId) =>
      val fullId = appId + "/" + execId
      executors.get(fullId) match {
        case Some(executor) =>
          logInfo("Asked to kill executor " + fullId)
          executor.kill()
        case None =>
          logInfo("Asked to kill unknown executor " + fullId)
      }

    case Terminated(_) | RemoteClientDisconnected(_, _) | RemoteClientShutdown(_, _) =>
      masterDisconnected()

    case RequestWorkerState => {
      sender ! WorkerStateResponse(host, port, workerId, executors.values.toList,
        finishedExecutors.values.toList, masterUrl, cores, memory,
        coresUsed, memoryUsed, masterWebUiUrl)
    }
  }

val args = Seq(driverUrl, "{{EXECUTOR_ID}}", "{{HOSTNAME}}", "{{CORES}}")
val command = Command("org.apache.spark.executor.StandaloneExecutorBackend", args, sc.executorEnvs)

/**
 * Manages the execution of one executor process.
 */
private[spark] class ExecutorRunner(
    val appId: String,
    val execId: Int,
    val appDesc: ApplicationDescription,
    val cores: Int,
    val memory: Int,
    val worker: ActorRef,
    val workerId: String,
    val host: String,
    val sparkHome: File,
    val workDir: File)
  extends Logging {

  val fullId = appId + "/" + execId
  var workerThread: Thread = null
  var process: Process = null
  var shutdownHook: Thread = null

  def start() {
    workerThread = new Thread("ExecutorRunner for " + fullId) {
      override def run() { fetchAndRunExecutor() } // 创建线程执行fetchAndRunExecutor
    }
    workerThread.start()

  }

  def buildCommandSeq(): Seq[String] = {
    val command = appDesc.command
    val runner = getAppEnv("JAVA_HOME").map(_ + "/bin/java").getOrElse("java")
    // SPARK-698: do not call the run.cmd script, as process.destroy()
    // fails to kill a process tree on Windows
    Seq(runner) ++ buildJavaOpts() ++ Seq(command.mainClass) ++ //java执行command.mainClass
      command.arguments.map(substituteVariables)
  }

  /**
   * Download and run the executor described in our ApplicationDescription
   */
  def fetchAndRunExecutor() {
    try {
      //调用ProcessBuilder, 使用进程执行command

      //Launch the process
      val command = buildCommandSeq()
      val builder = new ProcessBuilder(command: _*).directory(executorDir)
      val env = builder.environment()
      for ((key, value) <- appDesc.command.environment) {
        env.put(key, value)
      }
      // In case we are running this from within the Spark Shell, avoid creating a "scala"
      // parent process for the executor command
      env.put("SPARK_LAUNCH_WITH_SCALA", "0")
      process = builder.start()

      // Wait for it to exit; this is actually a bad thing if it happens, because we expect to run
      // long-lived processes only. However, in the future, we might restart the executor a few
      // times on the same machine.
      val exitCode = process.waitFor()
      worker ! ExecutorStateChanged(appId, execId, ExecutorState.FAILED, Some(message), Some(exitCode))
    } catch {
        worker ! ExecutorStateChanged(appId, execId, ExecutorState.FAILED, Some(message), None)
      }
    }
  }
}

本文章摘自博客园，原文发布日期：2014-01-02