Github user zsxwing commented on a diff in the pull request:
https://github.com/apache/spark/pull/3710#discussion_r22786638
--- Diff:
streaming/src/main/scala/org/apache/spark/streaming/scheduler/StreamingListenerBus.scala
---
@@ -17,20 +17,28 @@
package org.apache.spark.streaming.scheduler
+import java.util.concurrent.atomic.AtomicBoolean
+import java.util.concurrent.{LinkedBlockingQueue, CopyOnWriteArrayList}
+
+import scala.util.control.NonFatal
+
import org.apache.spark.Logging
-import scala.collection.mutable.{SynchronizedBuffer, ArrayBuffer}
-import java.util.concurrent.LinkedBlockingQueue
+import org.apache.spark.util.Utils
/** Asynchronously passes StreamingListenerEvents to registered
StreamingListeners. */
private[spark] class StreamingListenerBus() extends Logging {
- private val listeners = new ArrayBuffer[StreamingListener]()
- with SynchronizedBuffer[StreamingListener]
+ // `listeners` will be set up during the initialization of the whole
system and the number of
+ // listeners is small, so the copying cost of CopyOnWriteArrayList will
be little. With the help
+ // of CopyOnWriteArrayList, we can eliminate a lock during processing
every event comparing to
+ // SynchronizedBuffer.
+ private val listeners = new CopyOnWriteArrayList[StreamingListener]()
--- End diff --
It's usually not safe to have a lock when posting events to outer
listeners. I elimiated all locks during posting events to listeners in #4006
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