[SPARK-5307] SerializationDebugger to help debug NotSerializableExcep…

…tion.

This patch adds a SerializationDebugger that is used to add more information to
a NotSerializableException. When a NotSerializableException is encountered, the
debugger tries to serialize the object one more time through a DebugStream that
hooks into the internals of ObjectOutputStream to get the serialization stack.

An example output looks like this:

org.apache.spark.serializer.NotSerializableClass
	Serialization stack (3):
	- org.apache.spark.serializer.NotSerializableClass@5e20dc10 (class org.apache.spark.serializer.NotSerializableClass)
	- org.apache.spark.serializer.SerializableClass2@521fb14e (class org.apache.spark.serializer.SerializableClass2)
	- org.apache.spark.serializer.SerializableClass1@5f54e92c (class org.apache.spark.serializer.SerializableClass1)
	Run the JVM with sun.io.serialization.extendedDebugInfo for more information.

core/src/main/scala/org/apache/spark/serializer/JavaSerializer.scala

@@ -39,7 +39,7 @@ private[spark] class JavaSerializationStream(out: OutputStream, counterReset: In
    * the stream 'resets' object class descriptions have to be re-written)
    */
   def writeObject[T: ClassTag](t: T): SerializationStream = {
-    objOut.writeObject(t)
+    SerializationDebugger.writeObject(objOut, t)
     counter += 1
     if (counterReset > 0 && counter >= counterReset) {
       objOut.reset()

core/src/main/scala/org/apache/spark/serializer/SerializationDebugger.scala

@@ -0,0 +1,128 @@
+/*
+ * 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.serializer
+
+import java.io._
+import java.lang.reflect.Field
+import java.security.AccessController
+
+import scala.collection.mutable
+import scala.util.control.NonFatal
+
+
+private[serializer]
+object SerializationDebugger {
+
+  /**
+   * Write an object to the [[ObjectOutputStream]]. If a NotSerializableException is encountered,
+   * use our debug stream to capture the serialization stack leading to the problematic object.
+   */
+  def writeObject(out: ObjectOutputStream, obj: Any): Unit = {
+    try {
+      out.writeObject(obj)
+    } catch {
+      case e: NotSerializableException =>
+        if (enableDebugging) throw improveException(obj, e) else throw e
+    }
+  }
+
+  /**
+   * Improve the given NotSerializableException with the serialization stack leading from the given
+   * object to the problematic object.
+   */
+  private def improveException(obj: Any, e: NotSerializableException): NotSerializableException = {
+    if (depthField != null) {
+      val out = new DebugStream(new ByteArrayOutputStream)
+      try {
+        out.writeObject(obj)
+        e
+      } catch {
+        case nse: NotSerializableException =>
+          new NotSerializableException(
+            nse.getMessage + "\n" +
+            s"\tSerialization stack (${out.stack.size}):\n" +
+            out.stack.map(o => s"\t- $o (class ${o.getClass.getName})").mkString("\n") + "\n" +
+            "\tRun the JVM with sun.io.serialization.extendedDebugInfo for more information.")
+        case _: Throwable => e
+      }
+    } else {
+      e
+    }
+  }
+
+  /** Reference to the private depth field in ObjectOutputStream. */
+  private val depthField: Field = try {
+    val f = classOf[ObjectOutputStream].getDeclaredField("depth")
+    f.setAccessible(true)
+    f
+  } catch {
+    case NonFatal(e) => null
+  }
+
+  /**
+   * Whether to enable this debugging or not. By default, the special debugging feature is disabled
+   * if the JVM is run with sun.io.serialization.extendedDebugInfo.
+   */
+  private[serializer] var enableDebugging: Boolean = {
+    !AccessController.doPrivileged(new sun.security.action.GetBooleanAction(
+      "sun.io.serialization.extendedDebugInfo")).booleanValue()
+  }
+
+  /**
+   * An [[ObjectOutputStream]] that collects the serialization stack when a NotSerializableException
+   * is thrown.
+   *
+   * This works by hooking into ObjectOutputStream internals using replaceObject method and the
+   * private depth field. Inspired by Bob Lee's DebuggingObjectOutputStream.
+   */
+  private class DebugStream(underlying: OutputStream) extends ObjectOutputStream(underlying) {
+
+    // Enable replacement so replaceObject is called whenever an object is being serialized.
+    enableReplaceObject(true)
+
+    val stack = new mutable.Stack[Object]
+
+    private var foundNotSerializableObject = false
+
+    /**
+     * Called when [[ObjectOutputStream]] tries to serialize any object.
+     */
+    override protected def replaceObject(obj: Object): Object = obj match {
+      case _: NotSerializableException if depth == 1 =>
+        // When an object is not serializable, ObjectOutputStream resets the depth to 1 and writes
+        // an NotSerializableException to the stream, and we will catch it here.
+        // Once we reach here, the stack is what we want to return back to the caller.
+        foundNotSerializableObject = true
+        obj
+      case _ =>
+        if (!foundNotSerializableObject) {
+          // Once ObjectOutputStream finishes serializing an object (and its fields), it will
+          // decrease the depth field and serialize the next object. We pop the stack since
+          // everything above depth has been successfully serialized.
+          while (depth < stack.size) {
+            stack.pop()
+          }
+          stack.push(obj)
+        }
+        obj
+    }
+
+    /** Return the value of the private depth field in [[ObjectOutputStream]]. */
+    private def depth: Int = SerializationDebugger.depthField.get(this).asInstanceOf[Int]
+  }
+}

core/src/test/scala/org/apache/spark/serializer/SerializationDebuggerSuite.scala

@@ -0,0 +1,53 @@
+/*
+ * 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.serializer
+
+import java.io.{NotSerializableException, ObjectOutputStream, ByteArrayOutputStream}
+
+import org.scalatest.FunSuite
+
+
+class SerializationDebuggerSuite extends FunSuite {
+
+  test("normal serialization") {
+    SerializationDebugger.enableDebugging = true
+    val out = new ObjectOutputStream(new ByteArrayOutputStream)
+    SerializationDebugger.writeObject(out, 1)
+    out.close()
+  }
+
+  test("NotSerializableException with stack") {
+    SerializationDebugger.enableDebugging = true
+    val out = new ObjectOutputStream(new ByteArrayOutputStream)
+    val obj = new SerializableClass1(new SerializableClass2(new NotSerializableClass))
+    val e = intercept[NotSerializableException] {
+      SerializationDebugger.writeObject(out, obj)
+    }
+    out.close()
+
+    assert(e.getMessage.contains("SerializableClass1"))
+    assert(e.getMessage.contains("SerializableClass2"))
+    assert(e.getMessage.contains("NotSerializableClass"))
+  }
+}
+
+class NotSerializableClass
+
+class SerializableClass1(val a: Object) extends Serializable
+
+class SerializableClass2(val b: Object) extends Serializable