Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/7774#discussion_r36128883
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/SparkPlan.scala ---
@@ -110,11 +121,30 @@ abstract class SparkPlan extends QueryPlan[SparkPlan]
with Logging with Serializ
"Operator will receive unsafe rows as input but cannot process
unsafe rows")
}
RDDOperationScope.withScope(sparkContext, nodeName, false, true) {
+ prepare()
doExecute()
}
}
/**
+ * Do the preparation for SparkPlan.
+ */
+ final def prepare(): Unit = {
+ doPrepare
+ }
+
+ /**
+ * Overridden by concrete implementations of SparkPlan. It is guaranteed
to run before any
+ * `execute` of SparkPlan. This is helpful when we want to launch some
background works, e.g.,
+ * `BroadcastHashJoin` uses it to broadcast asynchronously.
+ *
+ * This is lazy to make sure running doPrepare is called only once for
each SparkPlan.
+ */
+ protected lazy val doPrepare: Unit = {
--- End diff --
it's really strange for subclasses to override a lazy val that is really a
method call. I think instead this should be a normal `protected def
doPrepare(): Unit` and we should have another `private val prepareCalled`
somewhere to make sure we only call this once.
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