Github user squito commented on a diff in the pull request:
https://github.com/apache/spark/pull/19211#discussion_r139787945
--- Diff:
core/src/main/scala/org/apache/spark/scheduler/AsyncEventQueue.scala ---
@@ -0,0 +1,196 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.scheduler
+
+import java.util.concurrent.LinkedBlockingQueue
+import java.util.concurrent.atomic.{AtomicBoolean, AtomicLong}
+
+import com.codahale.metrics.{Gauge, Timer}
+
+import org.apache.spark.{SparkConf, SparkContext}
+import org.apache.spark.internal.Logging
+import org.apache.spark.internal.config._
+import org.apache.spark.util.Utils
+
+/**
+ * An asynchronous queue for events. All events posted to this queue will
be delivered to the child
+ * listeners in a separate thread.
+ *
+ * Delivery will only begin when the `start()` method is called. The
`stop()` method should be
+ * called when no more events need to be delivered.
+ */
+private class AsyncEventQueue(val name: String, conf: SparkConf, metrics:
LiveListenerBusMetrics)
+ extends SparkListenerBus
+ with Logging {
+
+ import AsyncEventQueue._
+
+ // Cap the capacity of the 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 eventQueue = new LinkedBlockingQueue[SparkListenerEvent](
+ conf.get(LISTENER_BUS_EVENT_QUEUE_CAPACITY))
+
+ // Keep the event count separately, so that waitUntilEmpty() can be
implemented properly;
+ // this allows that method to return only when the events in the queue
have been fully
+ // processed (instead of just dequeued).
+ private val eventCount = new AtomicLong()
+
+ /** A counter for dropped events. It will be reset every time we log it.
*/
+ private val droppedEventsCounter = new AtomicLong(0L)
+
+ /** When `droppedEventsCounter` was logged last time in milliseconds. */
+ @volatile private var lastReportTimestamp = 0L
+
+ private val logDroppedEvent = new AtomicBoolean(false)
+
+ private var sc: SparkContext = null
+
+ private val started = new AtomicBoolean(false)
+ private val stopped = new AtomicBoolean(false)
+
+ private val droppedEvents =
metrics.metricRegistry.counter(s"queue.$name.numDroppedEvents")
+ private val processingTime =
metrics.metricRegistry.timer(s"queue.$name.listenerProcessingTime")
+
+ // Remove the queue size gauge first, in case it was created by a
previous incarnation of
+ // this queue that was removed from the listener bus.
+ metrics.metricRegistry.remove(s"queue.$name.size")
+ metrics.metricRegistry.register(s"queue.$name.size", new Gauge[Int] {
+ override def getValue: Int = eventQueue.size()
+ })
+
+ private val dispatchThread = new Thread(s"spark-listener-group-$name") {
+ setDaemon(true)
+ override def run(): Unit = Utils.tryOrStopSparkContext(sc) {
+ dispatch()
+ }
+ }
+
+ private def dispatch(): Unit =
LiveListenerBus.withinListenerThread.withValue(true) {
+ try {
+ var next: SparkListenerEvent = eventQueue.take()
+ while (next != POISON_PILL) {
+ val ctx = processingTime.time()
+ try {
+ super.postToAll(next)
+ } finally {
+ ctx.stop()
+ }
+ eventCount.decrementAndGet()
+ next = eventQueue.take()
+ }
+ eventCount.decrementAndGet()
+ } catch {
+ case ie: InterruptedException =>
+ logInfo(s"Stopping listener queue $name.", ie)
+ }
+ }
+
+ override protected def getTimer(listener: SparkListenerInterface):
Option[Timer] = {
+
metrics.getTimerForListenerClass(listener.getClass.asSubclass(classOf[SparkListenerInterface]))
+ }
+
+ /**
+ * Start an asynchronous thread to dispatch events to the underlying
listeners.
+ *
+ * @param sc Used to stop the SparkContext in case the async dispatcher
fails.
+ */
+ private[scheduler] def start(sc: SparkContext): Unit = {
+ if (started.compareAndSet(false, true)) {
+ this.sc = sc
+ dispatchThread.start()
+ } else {
+ throw new IllegalStateException(s"$name already started!")
--- End diff --
seems fine to me -- its only called in LiveListenerBus, where we guarantee
this is true. seems better to fail-fast if its messed up
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