zsxwing commented on a change in pull request #30242:
URL: https://github.com/apache/spark/pull/30242#discussion_r530075736
##########
File path:
sql/core/src/main/scala/org/apache/spark/sql/execution/python/EvalPythonExec.scala
##########
@@ -137,3 +139,47 @@ trait EvalPythonExec extends UnaryExecNode {
}
}
}
+
+/**
+ * A TaskContext aware iterator.
+ *
+ * As the Python evaluation consumes the parent iterator in a separate thread,
+ * it could consume more data from the parent even after the task ends and the
parent is closed.
+ * Thus, we should use ContextAwareIterator to stop consuming after the task
ends.
+ */
+class ContextAwareIterator[IN](iter: Iterator[IN], context: TaskContext)
extends Iterator[IN] {
+
+ val thread = new AtomicReference[Thread]()
+
+ if (iter.hasNext) {
+ val failed = new AtomicBoolean(false)
+
+ context.addTaskFailureListener { (_, _) =>
+ failed.set(true)
+ }
+
+ context.addTaskCompletionListener[Unit] { _ =>
+ var thread = this.thread.get()
+
+ while (thread == null && !failed.get()) {
+ // Wait for a while since the writer thread might not reach to
consuming the iterator yet.
+ context.wait(10)
Review comment:
I didn't realize it. It's better to not rely on this in a listener. This
is something we should consider to improve in future. It's a bad idea to hold
an implicit lock when calling user's listener because it's pretty easy to cause
surprising deadlock.
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