Github user pwendell commented on a diff in the pull request:
https://github.com/apache/spark/pull/3518#discussion_r23051146
--- Diff: core/src/main/scala/org/apache/spark/util/ObjectWalker.scala ---
@@ -0,0 +1,105 @@
+/*
+ * 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.lang.reflect.{Modifier, Field}
+
+import com.google.common.collect.Queues
+
+import scala.collection.mutable
+
+
+/**
+ * This class permits traversing a generic Object's reference graph. This
is useful for debugging
+ * serialization errors. See SPARK-3694.
+ *
+ * This code is based on code written by Josh Rosen found here:
+ * https://gist.github.com/JoshRosen/d6a8972c99992e97d040
+ */
+object ObjectWalker {
+ def isTransient(field: Field): Boolean =
Modifier.isTransient(field.getModifiers)
+ def isStatic(field: Field): Boolean =
Modifier.isStatic(field.getModifiers)
+ def isPrimitive(field: Field): Boolean = field.getType.isPrimitive
+
+ /**
+ * Traverse the graph representing all references between the provided
root object, its
+ * members, and their references in turn.
+ *
+ * What we want to be able to do is readily identify un-serializable
components AND the path
+ * to those components. To do this, store the traversal of the graph as
a 2-tuple - the actual
+ * reference visited and its parent. Then, to get the path to the
un-serializable reference
+ * we can simply follow the parent links.
+ *
+ * @param rootObj - The root object for which to generate the reference
graph
+ * @return a new Set containing the 2-tuple of references from the
traversal of the
+ * reference graph along with their parent references. (self,
parent)
+ */
+ def buildRefGraph(rootObj: AnyRef): mutable.LinkedList[AnyRef] = {
+ val visitedRefs = mutable.Set[AnyRef]()
+ val toVisit = Queues.newArrayDeque[AnyRef]()
+ var results = mutable.LinkedList[AnyRef]()
+
+ toVisit.add(rootObj)
+
+ while (!toVisit.isEmpty) {
+ val obj : AnyRef = toVisit.pollFirst()
+ // Store the last parent reference to enable quick retrieval of the
path to a broken node
+
+ if (!visitedRefs.contains(obj)) {
+ results = mutable.LinkedList(obj).append(results)
+ visitedRefs.add(obj)
+
+ // Extract all the fields from the object that would be
serialized. Transient and
+ // static references are not serialized and primitive variables
will always be serializable
+ // and will not contain further references.
+
+ for (field <- getAllFields(obj.getClass)
--- End diff --
could you pull this expression out into it's own variable `val fieldsToTest
= getAllFields(...)`. We try not to nest expressions like this to make the code
more readable.
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