Spark源码解读之Worker剖析

在上一篇中我们剖析了Master的工作原理，这节我们接着来剖析Worker的工作员原理，Worker主要包括两部分的工作，启动Executor和启动Driver，然后向Master发送注册启动消息。

下面是Worker的工作流程图：

在Application向Master注册之后，Master会发出命令启动Wroker，在Worker节点启动之后，它会调动内部的两个方法LaunchDriver和LaunchExecutor分别启动Driver和Executor，它们的启动过程大致相同，都是先创建一个DriverRunnner或者ExecutorRunner来封装Driver或者Executor的信息来启动Driver或者Executor，先创建它们各自的工作目录，然后会调用内部的start的方法启动，在start方法中会创建ProcessBuilder来启动进程，最后它会等待Driver或者Executor工作完成退出，最后向它们各自所在的Worker节点发送DriverStateChanged消息，接着Worker向Master发送DriverStateChanged消息。

首先来看看Driver启动的LaunchDriver方法的源码：

/**
      * 启动Driver
      */
    case LaunchDriver(driverId, driverDesc) => {
      logInfo(s"Asked to launch driver $driverId")
      //将Driver的信息封装在一个线程中启动
      val driver = new DriverRunner(
        conf,
        driverId,
        workDir,
        sparkHome,
        driverDesc.copy(command = Worker.maybeUpdateSSLSettings(driverDesc.command, conf)),
        self,
        akkaUrl)
      //将Driver放入缓存中（HashMap中）
      drivers(driverId) = driver
      //启动Driver
      driver.start()
      //使用的CPU核数加上Driver使用的核数
      coresUsed += driverDesc.cores
      //使用的内存加上Driver的内存
      memoryUsed += driverDesc.mem
    }

内部的start启动方法：

 /** Starts a thread to run and manage the driver. */
  def start() = {
    //启动一个java线程
    new Thread("DriverRunner for " + driverId) {
      override def run() {
        try {
          //创建Driver的工作目录
          val driverDir = createWorkingDirectory()
          //加载启动Spark需要的jar包
          val localJarFilename = downloadUserJar(driverDir)

          def substituteVariables(argument: String): String = argument match {
            case "{{WORKER_URL}}" => workerUrl
            case "{{USER_JAR}}" => localJarFilename
            case other => other
          }

          //创建ProcessBuilder，传入driverDesc和driver需要的内存大小的参数等等
          // TODO: If we add ability to submit multiple jars they should also be added here
          val builder = CommandUtils.buildProcessBuilder(driverDesc.command, driverDesc.mem,
            sparkHome.getAbsolutePath, substituteVariables)
          //启动Driver进行成
          launchDriver(builder, driverDir, driverDesc.supervise)
        }
        catch {
          case e: Exception => finalException = Some(e)
        }

        val state =
          if (killed) {
            DriverState.KILLED
          } else if (finalException.isDefined) {
            DriverState.ERROR
          } else {
            finalExitCode match {
              case Some(0) => DriverState.FINISHED
              case _ => DriverState.FAILED
            }
          }

        finalState = Some(state)
        //向Driver所在的Worker发送DriverStateChanged
        worker ! DriverStateChanged(driverId, state, finalException)
      }
    }.start()
  }

/***
    * 启动Driver进程
    * @param builder
    * @param baseDir
    * @param supervise
    */
  private def launchDriver(builder: ProcessBuilder, baseDir: File, supervise: Boolean) {
    builder.directory(baseDir)
    def initialize(process: Process) = {
      //重定向stdout和stderr到文件中（将输出的日志和报错的日志写入磁盘文件中）
      // Redirect stdout and stderr to files
      val stdout = new File(baseDir, "stdout")
      CommandUtils.redirectStream(process.getInputStream, stdout)

      val stderr = new File(baseDir, "stderr")
      val header = "Launch Command: %s\n%s\n\n".format(
        builder.command.mkString("\"", "\" \"", "\""), "=" * 40)
      Files.append(header, stderr, UTF_8)
      CommandUtils.redirectStream(process.getErrorStream, stderr)
    }
    runCommandWithRetry(ProcessBuilderLike(builder), initialize, supervise)
  }

  case DriverStateChanged(driverId, state, exception) => {
      state match {
        case DriverState.ERROR =>
          logWarning(s"Driver $driverId failed with unrecoverable exception: ${exception.get}")
        case DriverState.FAILED =>
          logWarning(s"Driver $driverId exited with failure")
        case DriverState.FINISHED =>
          logInfo(s"Driver $driverId exited successfully")
        case DriverState.KILLED =>
          logInfo(s"Driver $driverId was killed by user")
        case _ =>
          logDebug(s"Driver $driverId changed state to $state")
      }
      //在Driver向Worker发来DriverStateChanged之后
      //Worker向Driver发送DriverStateChanged消息
      master ! DriverStateChanged(driverId, state, exception)
      //Driver工作完成之后从缓存中移除该Driver
      val driver = drivers.remove(driverId).get
      finishedDrivers(driverId) = driver
      memoryUsed -= driver.driverDesc.mem
      coresUsed -= driver.driverDesc.cores
    }

Worker类内部的LaunchExecutor方法源码：

 /**
      * 启动Executor进程
      */
    case LaunchExecutor(masterUrl, appId, execId, appDesc, cores_, memory_) =>
      if (masterUrl != activeMasterUrl) {
        logWarning("Invalid Master (" + masterUrl + ") attempted to launch executor.")
      } else {
        try {
          logInfo("Asked to launch executor %s/%d for %s".format(appId, execId, appDesc.name))

          //创建Executor工作目录
          // Create the executor's working directory
          val executorDir = new File(workDir, appId + "/" + execId)
          if (!executorDir.mkdirs()) {
            throw new IOException("Failed to create directory " + executorDir)
          }

          // Create local dirs for the executor. These are passed to the executor via the
          // SPARK_LOCAL_DIRS environment variable, and deleted by the Worker when the
          // application finishes.
          /**
            * 创建executor的本地目录，它们可以通过SPARK_LOCAL_DIRS环境变量来指定，并且在application完成的时候被Worker删除
            */
          val appLocalDirs = appDirectories.get(appId).getOrElse {
            Utils.getOrCreateLocalRootDirs(conf).map { dir =>
              Utils.createDirectory(dir).getAbsolutePath()
            }.toSeq
          }
          appDirectories(appId) = appLocalDirs
          //启动Executor线程来启动Executor
          val manager = new ExecutorRunner(
            appId,
            execId,
            appDesc.copy(command = Worker.maybeUpdateSSLSettings(appDesc.command, conf)),
            cores_,
            memory_,
            self,
            workerId,
            host,
            webUi.boundPort,
            publicAddress,
            sparkHome,
            executorDir,
            akkaUrl,
            conf,
            appLocalDirs, ExecutorState.LOADING)
          executors(appId + "/" + execId) = manager
          //启动executor
          manager.start()
          //CPU核数加上executor使用的核数
          coresUsed += cores_
          //使用的内存加上executor使用的内存大小
          memoryUsed += memory_
          //executor向worker发送ExecutorStateChanged的状态改变消息
          //worker又向master发送ExecutorStateChanged状态改变的消息
          master ! ExecutorStateChanged(appId, execId, manager.state, None, None)
        } catch {
          case e: Exception => {
            logError(s"Failed to launch executor $appId/$execId for ${appDesc.name}.", e)
            if (executors.contains(appId + "/" + execId)) {
              executors(appId + "/" + execId).kill()
              executors -= appId + "/" + execId
            }
            master ! ExecutorStateChanged(appId, execId, ExecutorState.FAILED,
              Some(e.toString), None)
          }
        }
      }

 /**
    * 启动Executor进程
    */
  def start() {
    //创建JAVA线程
    workerThread = new Thread("ExecutorRunner for " + fullId) {
      override def run() { fetchAndRunExecutor() }
    }
    workerThread.start()
    // Shutdown hook that kills actors on shutdown.
    shutdownHook = new Thread() {
      override def run() {
        killProcess(Some("Worker shutting down"))
      }
    }
    Runtime.getRuntime.addShutdownHook(shutdownHook)
  }

 /**
   * Download and run the executor described in our ApplicationDescription
   */
  def fetchAndRunExecutor() {
    try {
      //创建ProcessBuilder
      // Launch the process
      val builder = CommandUtils.buildProcessBuilder(appDesc.command, memory,
        sparkHome.getAbsolutePath, substituteVariables)
      val command = builder.command()
      logInfo("Launch command: " + command.mkString("\"", "\" \"", "\""))

      builder.directory(executorDir)
      builder.environment.put("SPARK_LOCAL_DIRS", appLocalDirs.mkString(","))
      // In case we are running this from within the Spark Shell, avoid creating a "scala"
      // parent process for the executor command
      builder.environment.put("SPARK_LAUNCH_WITH_SCALA", "0")

      // Add webUI log urls
      val baseUrl =
        s"http://$publicAddress:$webUiPort/logPage/?appId=$appId&executorId=$execId&logType="
      builder.environment.put("SPARK_LOG_URL_STDERR", s"${baseUrl}stderr")
      builder.environment.put("SPARK_LOG_URL_STDOUT", s"${baseUrl}stdout")

      process = builder.start()
      val header = "Spark Executor Command: %s\n%s\n\n".format(
        command.mkString("\"", "\" \"", "\""), "=" * 40)
      //重定向stdout和stderr到文件中
      // Redirect its stdout and stderr to files
      val stdout = new File(executorDir, "stdout")
      stdoutAppender = FileAppender(process.getInputStream, stdout, conf)

      val stderr = new File(executorDir, "stderr")
      Files.write(header, stderr, UTF_8)
      stderrAppender = FileAppender(process.getErrorStream, stderr, conf)

      // Wait for it to exit; executor may exit with code 0 (when driver instructs it to shutdown)
      // or with nonzero exit code
      //等待executor完成任务退出
      val exitCode = process.waitFor()
      state = ExecutorState.EXITED
      val message = "Command exited with code " + exitCode
      //向executor所在的Worker节点发送ExecutorStateChanged消息
      worker ! ExecutorStateChanged(appId, execId, state, Some(message), Some(exitCode))
    } catch {
      case interrupted: InterruptedException => {
        logInfo("Runner thread for executor " + fullId + " interrupted")
        state = ExecutorState.KILLED
        killProcess(None)
      }
      case e: Exception => {
        logError("Error running executor", e)
        state = ExecutorState.FAILED
        killProcess(Some(e.toString))
      }
    }
  }

至此我们就剖析完了Worker节点的工作流程，如有任何问题，希望不吝赐教！！！

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