Github user srowen commented on the pull request:
https://github.com/apache/spark/pull/11628#issuecomment-196741708
Here's an alternate take in light of comments above, to illustrate what I'm
thinking of:
```
...
val proc = pb.start()
val env = SparkEnv.get
val childThreadException = new AtomicReference[Throwable]()
// Start a thread to print the process's stderr to ours
new Thread(s"stderr reader for $command") {
override def run(): Unit = {
val err = proc.getErrorStream
try {
for (line <- Source.fromInputStream(err).getLines) {
// scalastyle:off println
System.err.println(line)
// scalastyle:on println
}
} catch {
case t: Throwable => childThreadException.set(t)
} finally {
err.close()
}
}
}.start()
// Start a thread to feed the process input from our parent's iterator
new Thread(s"stdin writer for $command") {
override def run(): Unit = {
TaskContext.setTaskContext(context)
val out = new PrintWriter(proc.getOutputStream)
try {
// scalastyle:off println
// input the pipe context firstly
if (printPipeContext != null) {
printPipeContext(out.println)
}
for (elem <- firstParent[T].iterator(split, context)) {
if (printRDDElement != null) {
printRDDElement(elem, out.println)
} else {
out.println(elem)
}
}
// scalastyle:on println
} catch {
case t: Throwable => childThreadException.set(t)
} finally {
out.close()
}
}
}.start()
// Return an iterator that read lines from the process's stdout
val lines = Source.fromInputStream(proc.getInputStream).getLines()
new Iterator[String] {
def next(): String = {
if (!hasNext()) {
throw new NoSuchElementException()
}
lines.next()
}
def hasNext(): Boolean = {
propagateChildException()
if (lines.hasNext) {
true
} else {
val exitStatus = proc.waitFor()
cleanup()
if (exitStatus != 0) {
throw new IllegalStateException(s"Subprocess exited with status
$exitStatus")
}
false
}
}
private def cleanup(): Unit = {
// cleanup task working directory if used
if (workInTaskDirectory) {
scala.util.control.Exception.ignoring(classOf[IOException]) {
Utils.deleteRecursively(new File(taskDirectory))
}
logDebug(s"Removed task working directory $taskDirectory")
}
}
private def propagateChildException(): Unit = {
val t = childThreadException.get()
if (t != null) {
proc.destroy()
cleanup()
throw t
}
}
}
...
```
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