Spark2.1命令工具类CommandUtils的源码分析

注：本文是为了配合《Spark内核设计的艺术 架构设计与实现》一书的内容而编写，目的是为了节省成本、方便读者查阅。

书中附录F的内容都在本文呈现。

CommandUtils是Spark中最常用的工具类之一，其作用是为了构建进程。如果不太关心其实现也不影响对Spark源码的阅读和原理的学习。我们要介绍的方法如下：

buildProcessBuilder

功能描述：基于给定的参数创建ProcessBuilder。

  def buildProcessBuilder(
      command: Command,
      securityMgr: SecurityManager,
      memory: Int,
      sparkHome: String,
      substituteArguments: String => String,
      classPaths: Seq[String] = Seq[String](),
      env: Map[String, String] = sys.env): ProcessBuilder = {
    val localCommand = buildLocalCommand(
      command, securityMgr, substituteArguments, classPaths, env)
    val commandSeq = buildCommandSeq(localCommand, memory, sparkHome)
    val builder = new ProcessBuilder(commandSeq: _*)
    val environment = builder.environment()
    for ((key, value) <- localCommand.environment) {
      environment.put(key, value)
    }
    builder
  }

buildLocalCommand

功能描述：通过库路径、类路径、包路径、环境变量、Java选项参数等信息，在本地创建Command。

  private def buildLocalCommand(
      command: Command,
      securityMgr: SecurityManager,
      substituteArguments: String => String,
      classPath: Seq[String] = Seq[String](),
      env: Map[String, String]): Command = {
    val libraryPathName = Utils.libraryPathEnvName
    val libraryPathEntries = command.libraryPathEntries
    val cmdLibraryPath = command.environment.get(libraryPathName)

    var newEnvironment = if (libraryPathEntries.nonEmpty && libraryPathName.nonEmpty) {
      val libraryPaths = libraryPathEntries ++ cmdLibraryPath ++ env.get(libraryPathName)
      command.environment + ((libraryPathName, libraryPaths.mkString(File.pathSeparator)))
    } else {
      command.environment
    }

    if (securityMgr.isAuthenticationEnabled) {
      newEnvironment += (SecurityManager.ENV_AUTH_SECRET -> securityMgr.getSecretKey)
    }

    Command(
      command.mainClass,
      command.arguments.map(substituteArguments),
      newEnvironment,
      command.classPathEntries ++ classPath,
      Seq[String](), // library path already captured in environment variable
      command.javaOpts.filterNot(_.startsWith("-D" + SecurityManager.SPARK_AUTH_SECRET_CONF)))
  }

buildCommandSeq

功能描述：用于构建命令行参数序列。

  private def buildCommandSeq(command: Command, memory: Int, sparkHome: String): Seq[String] = {
    val cmd = new WorkerCommandBuilder(sparkHome, memory, command).buildCommand()
    cmd.asScala ++ Seq(command.mainClass) ++ command.arguments
  }

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