JobManager类

JobManager类用于对提交的任务进行管理。

初始化

JobManager初始化的过程主要是从配置文件(server/conf/sqoop.properties)中读取配置信息，
相关的配置信息包括了：任务的提交引擎，任务的执行引擎，以及对任务的提交信息进行更新的时间间隔（默认的时间 为一天 即源代码中的 DEFAULT_PURGE_THRESHOLD）以及更新时间。
之后根据配置信息，实例化提交引擎和执行引擎。以及根据时间间隔 启动submission清理的线程。和更新的线程。
初始化的源代码如下：

public synchronized void initialize() {
    LOG.trace("Begin submission engine manager initialization");
    MapContext context = SqoopConfiguration.getInstance().getContext();

    // Let's load configured submission engine
    String submissionEngineClassName =
      context.getString(DriverConstants.SYSCFG_SUBMISSION_ENGINE);

    submissionEngine = (SubmissionEngine) ClassUtils
      .instantiate(submissionEngineClassName);
    if (submissionEngine == null) {
      throw new SqoopException(DriverError.DRIVER_0001,
        submissionEngineClassName);
    }

    submissionEngine.initialize(context,
        DriverConstants.PREFIX_SUBMISSION_ENGINE_CONFIG);

    // Execution engine
    String executionEngineClassName =
      context.getString(DriverConstants.SYSCFG_EXECUTION_ENGINE);

    executionEngine = (ExecutionEngine) ClassUtils
      .instantiate(executionEngineClassName);
    if (executionEngine == null) {
      throw new SqoopException(DriverError.DRIVER_0007,
        executionEngineClassName);
    }

    // We need to make sure that user has configured compatible combination of
    // submission engine and execution engine
    if (!submissionEngine
      .isExecutionEngineSupported(executionEngine.getClass())) {
      throw new SqoopException(DriverError.DRIVER_0008);
    }

    executionEngine.initialize(context,
        DriverConstants.PREFIX_EXECUTION_ENGINE_CONFIG);

    // Set up worker threads
    purgeThreshold = context.getLong(
      DriverConstants.SYSCFG_SUBMISSION_PURGE_THRESHOLD,
      DEFAULT_PURGE_THRESHOLD
      );
    purgeSleep = context.getLong(
      DriverConstants.SYSCFG_SUBMISSION_PURGE_SLEEP,
      DEFAULT_PURGE_SLEEP
      );

    purgeThread = new PurgeThread();
    purgeThread.start();

    updateSleep = context.getLong(
      DriverConstants.SYSCFG_SUBMISSION_UPDATE_SLEEP,
      DEFAULT_UPDATE_SLEEP
      );

    updateThread = new UpdateThread();
    updateThread.start();

    SqoopConfiguration.getInstance().getProvider()
      .registerListener(new CoreConfigurationListener(this));

    LOG.info("Submission manager initialized: OK");
  }