Fix TaskMetrics not being serializable

core/src/main/scala/spark/executor/TaskMetrics.scala

 package spark.executor
 
-class TaskMetrics{
+class TaskMetrics extends Serializable {
   /**
    * Time taken on the executor to deserialize this task
    */
   var executorDeserializeTime: Int = _
+
   /**
    * Time the executor spends actually running the task (including fetching shuffle data)
    */
   var executorRunTime:Int = _
+
   /**
    * The number of bytes this task transmitted back to the driver as the TaskResult
    */
@@ -23,49 +25,54 @@ class TaskMetrics{
    * If this task writes to shuffle output, metrics on the written shuffle data will be collected here
    */
   var shuffleWriteMetrics: Option[ShuffleWriteMetrics] = None
-
 }
 
 object TaskMetrics {
-  private[spark] def empty() : TaskMetrics = new TaskMetrics
+  private[spark] def empty(): TaskMetrics = new TaskMetrics
 }
 
 
-class ShuffleReadMetrics {
+class ShuffleReadMetrics extends Serializable {
   /**
    * Total number of blocks fetched in a shuffle (remote or local)
    */
   var totalBlocksFetched : Int = _
+
   /**
    * Number of remote blocks fetched in a shuffle
    */
   var remoteBlocksFetched: Int = _
+
   /**
    * Local blocks fetched in a shuffle
    */
   var localBlocksFetched: Int = _
+
   /**
    * Total time to read shuffle data
    */
   var shuffleReadMillis: Long = _
+
   /**
    * Total time that is spent blocked waiting for shuffle to fetch remote data
    */
   var remoteFetchWaitTime: Long = _
+
   /**
    * The total amount of time for all the shuffle fetches.  This adds up time from overlapping
    *     shuffles, so can be longer than task time
    */
   var remoteFetchTime: Long = _
+
   /**
    * Total number of remote bytes read from a shuffle
    */
   var remoteBytesRead: Long = _
 }
 
-class ShuffleWriteMetrics {
+class ShuffleWriteMetrics extends Serializable {
   /**
    * Number of bytes written for a shuffle
    */
   var shuffleBytesWritten: Long = _
-}
+}
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