JoshRosen commented on code in PR #37282:
URL: https://github.com/apache/spark/pull/37282#discussion_r929397395
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sql/core/src/main/scala/org/apache/spark/sql/util/QueryExecutionListener.scala:
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@@ -81,7 +83,10 @@ class ExecutionListenerManager private[sql](
loadExtensions: Boolean)
extends Logging {
- private val listenerBus = new ExecutionListenerBus(this, session)
+ // SPARK-39864: lazily create the listener bus on the first register() call
in order to
+ // avoid listener overheads when QueryExecutionListeners aren't used:
+ @GuardedBy("this")
Review Comment:
I don't think there's a deadlock risk here (something that I always want to
check whenever I'm adding synchronization to existing code).
The register(), unregister(), clear(), and listListeners() methods call
`ListenerBus` methods and those methods are synchronized. However, I don't
think they'll have circular waits because those methods are just updating
ListenerBus data structures and aren't running code which could call back into
ExecutionListenerManager.
I'm a bit less sure about clone(), though.
To play it safe, I'm going to see if I can remove the method-level
`synchronized` and instead do something more surgical.
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