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Driver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！！！
文章来源: Spark源码解读之Worker剖析