[GitHub] srowen commented on a change in pull request #23638: [SPARK-26713][CORE] Interrupt pipe IO threads in PipedRDD when task is finished

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srowen commented on a change in pull request #23638: [SPARK-26713][CORE] Interrupt pipe IO threads in PipedRDD when task is finished
URL: https://github.com/apache/spark/pull/23638#discussion_r250835149
 
 

 ##########
 File path: core/src/main/scala/org/apache/spark/rdd/PipedRDD.scala
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 @@ -156,7 +157,32 @@ private[spark] class PipedRDD[T: ClassTag](
           out.close()
         }
       }
-    }.start()
+    }
+    stdinWriterThread.start()
+
+    // interrupts stdin writer and stderr read threads when the corresponding task is finished as a
+    // safe belt. Otherwise, these threads could outlive the task's lifetime. For example:
+    //   val pipeRDD = sc.range(1, 100).pipe(Seq("cat"))
+    //   val abnormalRDD = pipeRDD.mapPartitions(_ => Iterator.empty)
+    // the iterator generated by PipedRDD is never involved. If the parent RDD's iterator is time
+    // consuming to generate(ShuffledRDD's shuffle operation for example), the outlived stdin writer
+    // thread will consume significant memory and cpu time. Also, there's race condition for
 
 Review comment:
   Does the second part of the comment, beginning at "Also,", belong below in the change to `ShuffleBlockFetcherIterator`?

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