Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/10779#discussion_r50048973
--- Diff:
core/src/main/scala/org/apache/spark/scheduler/LiveListenerBus.scala ---
@@ -17,24 +17,169 @@
package org.apache.spark.scheduler
+import java.util.concurrent._
import java.util.concurrent.atomic.AtomicBoolean
-import org.apache.spark.util.AsynchronousListenerBus
+import scala.util.DynamicVariable
+
+import org.apache.spark.SparkContext
+import org.apache.spark.util.Utils
/**
* Asynchronously passes SparkListenerEvents to registered SparkListeners.
*
- * Until start() is called, all posted events are only buffered. Only
after this listener bus
+ * Until `start()` is called, all posted events are only buffered. Only
after this listener bus
* has started will events be actually propagated to all attached
listeners. This listener bus
- * is stopped when it receives a SparkListenerShutdown event, which is
posted using stop().
+ * is stopped when `stop()` is called, and it will drop further events
after stopping.
*/
-private[spark] class LiveListenerBus
- extends AsynchronousListenerBus[SparkListener,
SparkListenerEvent]("SparkListenerBus")
- with SparkListenerBus {
+private[spark] class LiveListenerBus extends SparkListenerBus {
+
+ self =>
+
+ import LiveListenerBus._
+
+ private var sparkContext: SparkContext = null
+
+ /* Cap the capacity of the event queue so we get an explicit error
(rather than
+ * an OOM exception) if it's perpetually being added to more quickly
than it's being drained. */
+ private val EVENT_QUEUE_CAPACITY = 10000
+ private val eventQueue = new
LinkedBlockingQueue[SparkListenerEvent](EVENT_QUEUE_CAPACITY)
+
+ // Indicate if `start()` is called
+ private val started = new AtomicBoolean(false)
+ // Indicate if `stop()` is called
+ private val stopped = new AtomicBoolean(false)
+
+ // Indicate if we are processing some event
+ // Guarded by `self`
+ private var processingEvent = false
private val logDroppedEvent = new AtomicBoolean(false)
- override def onDropEvent(event: SparkListenerEvent): Unit = {
+ // A counter that represents the number of events produced and consumed
in the queue
+ private val eventLock = new Semaphore(0)
+
+ private val listenerThread = new Thread(name) {
+ setDaemon(true)
+ override def run(): Unit = Utils.tryOrStopSparkContext(sparkContext) {
+ LiveListenerBus.withinListenerThread.withValue(true) {
+ while (true) {
+ eventLock.acquire()
+ self.synchronized {
+ processingEvent = true
+ }
+ try {
+ val event = eventQueue.poll
+ if (event == null) {
+ // Get out of the while loop and shutdown the daemon thread
+ if (!stopped.get) {
+ throw new IllegalStateException("Polling `null` from
eventQueue means" +
+ " the listener bus has been stopped. So `stopped` must
be true")
+ }
+ return
+ }
+ postToAll(event)
+ } finally {
+ self.synchronized {
+ processingEvent = false
+ }
+ }
+ }
+ }
+ }
+ }
+
+ /**
+ * Start sending events to attached listeners.
+ *
+ * This first sends out all buffered events posted before this listener
bus has started, then
+ * listens for any additional events asynchronously while the listener
bus is still running.
+ * This should only be called once.
+ *
+ * @param sc Used to stop the SparkContext in case the listener thread
dies.
+ */
+ def start(sc: SparkContext) {
--- End diff --
`Unit` return type
---
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