Github user pwendell commented on a diff in the pull request: https://github.com/apache/spark/pull/126#discussion_r11263798 --- Diff: core/src/main/scala/org/apache/spark/ContextCleaner.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 + +import java.lang.ref.{ReferenceQueue, WeakReference} + +import scala.collection.mutable.{ArrayBuffer, SynchronizedBuffer} + +import org.apache.spark.broadcast.Broadcast +import org.apache.spark.rdd.RDD + +/** + * Classes that represent cleaning tasks. + */ +private sealed trait CleanupTask +private case class CleanRDD(rddId: Int) extends CleanupTask +private case class CleanShuffle(shuffleId: Int) extends CleanupTask +private case class CleanBroadcast(broadcastId: Long) extends CleanupTask + +/** + * A WeakReference associated with a CleanupTask. + * + * When the referent object becomes only weakly reachable, the corresponding + * CleanupTaskWeakReference is automatically added to the given reference queue. + */ +private class CleanupTaskWeakReference( + val task: CleanupTask, + referent: AnyRef, + referenceQueue: ReferenceQueue[AnyRef]) + extends WeakReference(referent, referenceQueue) + +/** + * An asynchronous cleaner for RDD, shuffle, and broadcast state. + * + * This maintains a weak reference for each RDD, ShuffleDependency, and Broadcast of interest, + * to be processed when the associated object goes out of scope of the application. Actual + * cleanup is performed in a separate daemon thread. + */ +private[spark] class ContextCleaner(sc: SparkContext) extends Logging { + + private val referenceBuffer = new ArrayBuffer[CleanupTaskWeakReference] + with SynchronizedBuffer[CleanupTaskWeakReference] + + private val referenceQueue = new ReferenceQueue[AnyRef] + + private val listeners = new ArrayBuffer[CleanerListener] + with SynchronizedBuffer[CleanerListener] + + private val cleaningThread = new Thread() { override def run() { keepCleaning() }} + + @volatile private var stopped = false + + /** Attach a listener object to get information of when objects are cleaned. */ + def attachListener(listener: CleanerListener) { + listeners += listener + } + + /** Start the cleaner. */ + def start() { + cleaningThread.setDaemon(true) + cleaningThread.setName("ContextCleaner") + cleaningThread.start() + } + + /** Stop the cleaner. */ + def stop() { + stopped = true + cleaningThread.interrupt() + } + + /** Register a RDD for cleanup when it is garbage collected. */ + def registerRDDForCleanup(rdd: RDD[_]) { + registerForCleanup(rdd, CleanRDD(rdd.id)) + } + + /** Register a ShuffleDependency for cleanup when it is garbage collected. */ + def registerShuffleForCleanup(shuffleDependency: ShuffleDependency[_, _]) { + registerForCleanup(shuffleDependency, CleanShuffle(shuffleDependency.shuffleId)) + } + + /** Register a Broadcast for cleanup when it is garbage collected. */ + def registerBroadcastForCleanup[T](broadcast: Broadcast[T]) { + registerForCleanup(broadcast, CleanBroadcast(broadcast.id)) + } + + /** Register an object for cleanup. */ + private def registerForCleanup(objectForCleanup: AnyRef, task: CleanupTask) { + referenceBuffer += new CleanupTaskWeakReference(task, objectForCleanup, referenceQueue) + } + + /** Keep cleaning RDD, shuffle, and broadcast state. */ + private def keepCleaning() { + while (!stopped) { + try { + val reference = Option(referenceQueue.remove(ContextCleaner.REF_QUEUE_POLL_TIMEOUT)) + .map(_.asInstanceOf[CleanupTaskWeakReference]) + reference.map(_.task).foreach { task => + logDebug("Got cleaning task " + task) + referenceBuffer -= reference.get + task match { + case CleanRDD(rddId) => doCleanupRDD(rddId) --- End diff -- From what I can tell here `doCleanupRDD` is not blocking and the other two are blocking. Is there any ways these could all be non-blocking? Otherwise if there is, e.g. GC on one of the slaves, or one of the shuffles takes a long time to delete all of the files, then you could end up in a situation where you are sitting in this loop for a long time. That doesn't seem super desirable.
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