Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/18083#discussion_r120999648
--- Diff: core/src/main/scala/org/apache/spark/util/ListenerBus.scala ---
@@ -23,29 +23,41 @@ import scala.collection.JavaConverters._
import scala.reflect.ClassTag
import scala.util.control.NonFatal
+import com.codahale.metrics.Timer
+
import org.apache.spark.internal.Logging
/**
* An event bus which posts events to its listeners.
*/
private[spark] trait ListenerBus[L <: AnyRef, E] extends Logging {
+ private[this] val listenersPlusTimers = new CopyOnWriteArrayList[(L,
Timer)]
+
// Marked `private[spark]` for access in tests.
- private[spark] val listeners = new CopyOnWriteArrayList[L]
+ private[spark] def listeners =
listenersPlusTimers.asScala.map(_._1).asJava
+
+ /**
+ * Returns a CodaHale metrics Timer for measuring the listener's event
processing time.
+ * This method is intended to be overridden by subclasses.
+ */
+ protected def getTimer(listener: L): Option[Timer] = None
/**
* Add a listener to listen events. This method is thread-safe and can
be called in any thread.
*/
final def addListener(listener: L): Unit = {
- listeners.add(listener)
+ listenersPlusTimers.add((listener, getTimer(listener).orNull))
}
/**
* Remove a listener and it won't receive any events. This method is
thread-safe and can be called
* in any thread.
*/
final def removeListener(listener: L): Unit = {
- listeners.remove(listener)
+ listenersPlusTimers.asScala.find(_._1 eq listener).foreach {
listenerAndTimer =>
+ listenersPlusTimers.remove(listenerAndTimer)
--- End diff --
I think the only reason that `CopyOnWriteArrayList` was used was for
thread-safety and fast performance for readers interleaved with very rare
mutations / writes. If we were to replace the array list then we'd need to add
a `synchronized` to guard the `listenersPlusTimers` field itself.
Given the workload and access patterns here, I'm not sure that it's worth
it to attempt to optimize this `removeListener()` method any further.
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