Question

我使用emr-5.4.0和Spark 2.1.0。我理解NullPointerException是什么，这个问题是关于为什么在这种特殊情况下抛出的。

无法弄清楚为什么我在驱动程序线程中得到了NullPointerException。

我得到了这个奇怪的工作失败了这个错误：

18/03/29 20:07:52 INFO ApplicationMaster: Starting the user application in a separate Thread
18/03/29 20:07:52 INFO ApplicationMaster: Waiting for spark context initialization...
Exception in thread "Driver" java.lang.NullPointerException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.apache.spark.deploy.yarn.ApplicationMaster$$anon$2.run(ApplicationMaster.scala:637)
18/03/29 20:07:52 ERROR ApplicationMaster: Uncaught exception:
java.lang.IllegalStateException: SparkContext is null but app is still running!
    at org.apache.spark.deploy.yarn.ApplicationMaster.runDriver(ApplicationMaster.scala:415)
    at org.apache.spark.deploy.yarn.ApplicationMaster.run(ApplicationMaster.scala:254)
    at org.apache.spark.deploy.yarn.ApplicationMaster$$anonfun$main$1.apply$mcV$sp(ApplicationMaster.scala:766)
    at org.apache.spark.deploy.SparkHadoopUtil$$anon$1.run(SparkHadoopUtil.scala:67)
    at org.apache.spark.deploy.SparkHadoopUtil$$anon$1.run(SparkHadoopUtil.scala:66)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:422)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1698)
    at org.apache.spark.deploy.SparkHadoopUtil.runAsSparkUser(SparkHadoopUtil.scala:66)
    at org.apache.spark.deploy.yarn.ApplicationMaster$.main(ApplicationMaster.scala:764)
    at org.apache.spark.deploy.yarn.ApplicationMaster.main(ApplicationMaster.scala)
18/03/29 20:07:52 INFO ApplicationMaster: Final app status: FAILED, exitCode: 10, (reason: Uncaught exception: java.lang.IllegalStateException: SparkContext is null but app is still running!)
18/03/29 20:07:52 INFO ApplicationMaster: Unregistering ApplicationMaster with FAILED (diag message: Uncaught exception: java.lang.IllegalStateException: SparkContext is null but app is still running!)
18/03/29 20:07:52 INFO ApplicationMaster: Deleting staging directory hdfs://<ip-address>.ec2.internal:8020/user/hadoop/.sparkStaging/application_1522348295743_0010
18/03/29 20:07:52 INFO ShutdownHookManager: Shutdown hook called
End of LogType:stderr

我提交了这份工作：

spark-submit --deploy-mode cluster --master yarn --num-executors 40 --executor-cores 16 --executor-memory 100g --driver-cores 8 --driver-memory 100g --class <package.class_name> --jars <s3://s3_path/some_lib.jar> <s3://s3_path/class.jar>

我的班级看起来像这样：

class MyClass {

  def main(args: Array[String]): Unit = {
    val c = new MyClass()
    c.process()
  }

  def process(): Unit = {
    val sparkConf = new SparkConf().setAppName("my-test")
    val sparkSession: SparkSession = SparkSession.builder().config(sparkConf).getOrCreate()
    import sparkSession.implicits._
    ....
  }

  ...
}

Answer 1

将class MyClass更改为object MyClass，您已完成。

在我们处理此问题时，我也将class MyClass更改为object MyClass extends App并删除def main(args: Array[String]): Unit（由extends App提供）。

我已经报告了Spark 2.3.0的改进 - [SPARK-23830] Spark on YARN in cluster deploy mode fail with NullPointerException when a Spark application is a Scala class not object - 让它很好地报告给最终用户。

深入研究YARN上的Spark如何工作，以下消息是ApplicationMaster of a Spark application starts the driver（您使用--deploy-mode cluster --master yarn spark-submit时）。

ApplicationMaster：在单独的线程中启动用户应用程序

在INFO消息之后，您应该看到另一个消息：

ApplicationMaster：等待火花上下文初始化......

这是driver initialization when the ApplicationMaster runs。

的一部分

异常Exception in thread "Driver" java.lang.NullPointerException的原因归因于following code：

val mainMethod = userClassLoader.loadClass(args.userClass)
  .getMethod("main", classOf[Array[String]])

我的理解是此时mainMethod为null，因此following line（其中mainMethod为null）＆＃34;触发＆＃34; NullPointerException：

mainMethod.invoke(null, userArgs.toArray)

该线程确实称为Driver（如Exception in thread "Driver" java.lang.NullPointerException中所述），如this line中所设置：

userThread.setContextClassLoader(userClassLoader)
userThread.setName("Driver")
userThread.start()

行号不同，因为我在使用emr-5.4.0和Spark 2.1.0时使用Spark 2.3.0引用行。

为什么集群模式下的YARN上的Spark会因为＆＃34;线程中的异常而失败＆＃34;驱动程序＆＃34;显示java.lang.NullPointerException＆＃34;

1 个答案: