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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