Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/3233#discussion_r24305878
--- Diff:
core/src/main/scala/org/apache/spark/util/MutableURLClassLoader.scala ---
@@ -0,0 +1,103 @@
+/*
+ * 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.util
+
+import java.net.{URLClassLoader, URL}
+import java.util.Enumeration
+import java.util.concurrent.ConcurrentHashMap
+
+import scala.collection.JavaConversions._
+
+import org.apache.spark.util.ParentClassLoader
+
+/**
+ * URL class loader that exposes the `addURL` and `getURLs` methods in
URLClassLoader.
+ */
+private[spark] class MutableURLClassLoader(urls: Array[URL], parent:
ClassLoader)
+ extends URLClassLoader(urls, parent) {
+
+ override def addURL(url: URL): Unit = {
+ super.addURL(url)
+ }
+
+ override def getURLs(): Array[URL] = {
+ super.getURLs()
+ }
+
+}
+
+/**
+ * A mutable class loader that gives preference to its own URLs over the
parent class loader
+ * when loading classes and resources.
+ */
+private[spark] class ChildFirstURLClassLoader(urls: Array[URL], parent:
ClassLoader)
+ extends MutableURLClassLoader(urls, null) {
+
+ private val parentClassLoader = new ParentClassLoader(parent)
+
+ /**
+ * Used to implement fine-grained class loading locks similar to what is
done by Java 7. This
+ * prevents deadlock issues when using non-hierarchical class loaders.
+ *
+ * Note that due to Java 6 compatibility (and some issues with
implementing class loaders in
+ * Scala), Java 7's `ClassLoader.registerAsParallelCapable` method is
not called.
+ */
+ private val locks = new ConcurrentHashMap[String, Object]()
+
+ override def loadClass(name: String, resolve: Boolean): Class[_] = {
--- End diff --
also, should we override `findClass` instead? Quoting the docs from
`ClassLoader.java`
```
...
* <p> Subclasses of <tt>ClassLoader</tt> are encouraged to override {@link
* #findClass(String)}, rather than this method. </p>
...
protected Class<?> loadClass(String name, boolean resolve)
...
```
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