[SPARK-26713][CORE][2.4] Interrupt pipe IO threads in PipedRDD when t…

…ask is finished

### What changes were proposed in this pull request?
Manually release stdin writer and stderr reader thread when task is finished. This is the backport of apache#23638 including apache#25049.

### Why are the changes needed?
This is a bug fix. PipedRDD's IO threads may hang even the corresponding task is already finished. Without this fix,  it would leak resource(memory specially).

### Does this PR introduce any user-facing change?
No.

### How was this patch tested?
Add new test

Closes apache#25825 from advancedxy/SPARK-26713_for_2.4.

Authored-by: Xianjin YE <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

core/src/main/scala/org/apache/spark/rdd/PipedRDD.scala

@@ -113,7 +113,7 @@ private[spark] class PipedRDD[T: ClassTag](
     val childThreadException = new AtomicReference[Throwable](null)
 
     // Start a thread to print the process's stderr to ours
-    new Thread(s"stderr reader for $command") {
+    val stderrReaderThread = new Thread(s"${PipedRDD.STDERR_READER_THREAD_PREFIX} $command") {
       override def run(): Unit = {
         val err = proc.getErrorStream
         try {
@@ -128,10 +128,11 @@ private[spark] class PipedRDD[T: ClassTag](
           err.close()
         }
       }
-    }.start()
+    }
+    stderrReaderThread.start()
 
     // Start a thread to feed the process input from our parent's iterator
-    new Thread(s"stdin writer for $command") {
+    val stdinWriterThread = new Thread(s"${PipedRDD.STDIN_WRITER_THREAD_PREFIX} $command") {
       override def run(): Unit = {
         TaskContext.setTaskContext(context)
         val out = new PrintWriter(new BufferedWriter(
@@ -156,7 +157,28 @@ private[spark] class PipedRDD[T: ClassTag](
           out.close()
         }
       }
-    }.start()
+    }
+    stdinWriterThread.start()
+
+    // interrupts stdin writer and stderr reader threads when the corresponding task is finished.
+    // 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 takes a
+    // long time to generate(ShuffledRDD's shuffle operation for example), the stdin writer thread
+    // may consume significant memory and CPU time even if task is already finished.
+    context.addTaskCompletionListener[Unit] { _ =>
+      if (proc.isAlive) {
+        proc.destroy()
+      }
+
+      if (stdinWriterThread.isAlive) {
+        stdinWriterThread.interrupt()
+      }
+      if (stderrReaderThread.isAlive) {
+        stderrReaderThread.interrupt()
+      }
+    }
 
     // Return an iterator that read lines from the process's stdout
     val lines = Source.fromInputStream(proc.getInputStream)(encoding).getLines
@@ -219,4 +241,7 @@ private object PipedRDD {
     }
     buf
   }
+
+  val STDIN_WRITER_THREAD_PREFIX = "stdin writer for"
+  val STDERR_READER_THREAD_PREFIX = "stderr reader for"
 }

core/src/test/scala/org/apache/spark/rdd/PipedRDDSuite.scala

@@ -19,6 +19,7 @@ package org.apache.spark.rdd
 
 import java.io.File
 
+import scala.collection.JavaConverters._
 import scala.collection.Map
 import scala.io.Codec
 
@@ -83,6 +84,29 @@ class PipedRDDSuite extends SparkFunSuite with SharedSparkContext {
     }
   }
 
+  test("stdin writer thread should be exited when task is finished") {
+    assume(TestUtils.testCommandAvailable("cat"))
+    val nums = sc.makeRDD(Array(1, 2, 3, 4), 1).map { x =>
+      val obj = new Object()
+      obj.synchronized {
+        obj.wait() // make the thread waits here.
+      }
+      x
+    }
+
+    val piped = nums.pipe(Seq("cat"))
+
+    val result = piped.mapPartitions(_ => Array.emptyIntArray.iterator)
+
+    assert(result.collect().length === 0)
+
+    // collect stderr writer threads
+    val stderrWriterThread = Thread.getAllStackTraces.keySet().asScala
+      .find { _.getName.startsWith(PipedRDD.STDIN_WRITER_THREAD_PREFIX) }
+
+    assert(stderrWriterThread.isEmpty)
+  }
+
   test("advanced pipe") {
     assume(TestUtils.testCommandAvailable("cat"))
     val nums = sc.makeRDD(Array(1, 2, 3, 4), 2)