Github user squito commented on a diff in the pull request:
https://github.com/apache/spark/pull/11105#discussion_r56409456
--- Diff: core/src/main/scala/org/apache/spark/util/collection/Utils.scala
---
@@ -36,4 +36,21 @@ private[spark] object Utils {
}
ordering.leastOf(input.asJava, num).iterator.asScala
}
+
+ /**
+ * Signal when empty.
+ * Wraps an iterator and calls the provided call back when the iterator
is consumed. If provided
+ * iterator is empty when, calls func right away.
+ */
+ def signalWhenEmpty[T](itr: Iterator[T], func: () => Unit): Iterator[T]
= {
+ if (itr.isEmpty) {
+ func()
+ }
+ itr.map{x =>
+ if (itr.isEmpty) {
+ func()
+ }
+ x
--- End diff --
looks like its something weird w/ `itr.map` -- this seems to work:
```scala
def signalWhenEmpty[T](itr: Iterator[T], func: () => Unit): Iterator[T] =
{
new SignalWhenEmptyIterator(itr, func)
}
private class SignalWhenEmptyIterator[T](sub: Iterator[T], func: () =>
Unit) extends Iterator[T] {
def hasNext: Boolean = {
val r = sub.hasNext
if (!r) {
func()
}
r
}
def next(): T = {
sub.next()
}
}
```
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