--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/jdk/jdk/jfr/jvm/TestClearStaleConstants.java	Thu Oct 24 16:37:22 2019 +0200
@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package jdk.jfr.jvm;
+
+import java.time.Duration;
+import java.util.List;
+
+import jdk.jfr.consumer.RecordedClass;
+import jdk.jfr.consumer.RecordedClassLoader;
+import jdk.jfr.consumer.RecordedEvent;
+import jdk.jfr.internal.JVM;
+import jdk.jfr.Recording;
+import jdk.test.lib.Asserts;
+import jdk.test.lib.jfr.EventNames;
+import jdk.test.lib.jfr.Events;
+import jdk.test.lib.jfr.TestClassLoader;
+
+/**
+ * @test
+ * @bug 8231081
+ * @key jfr
+ * @requires vm.hasJFR
+ * @modules jdk.jfr/jdk.jfr.internal
+ * @library /test/lib /test/jdk
+ * @run main/othervm -Xlog:class+unload -Xlog:gc -Xmx16m jdk.jfr.jvm.TestClearStaleConstants
+ */
+
+/**
+ * System.gc() will trigger class unloading if -XX:+ExplicitGCInvokesConcurrent is NOT set.
+ * If this flag is set G1 will never unload classes on System.gc() and
+ * As far as the "jfr" key guarantees no VM flags are set from the outside
+ * it should be enough with System.gc().
+ */
+public final class TestClearStaleConstants {
+    static class MyClass {
+    }
+    private final static String TEST_CLASS_NAME = "jdk.jfr.jvm.TestClearStaleConstants$MyClass";
+    private final static String EVENT_NAME = EventNames.ClassDefine;
+
+    // to prevent the compiler to optimize away all unread writes
+    public static TestClassLoader firstClassLoader;
+    public static TestClassLoader secondClassLoader;
+
+    public static void main(String... args) throws Exception {
+        firstClassLoader = new TestClassLoader();
+        // define a  class using a class loader under a recording
+        Class<?> clz = recordClassDefinition(firstClassLoader);
+        JVM jvm = JVM.getJVM();
+        // we will now tag the defined and loaded clz as being in use (no recordings are running here)
+        jvm.getClassIdNonIntrinsic(clz);
+        // null out for unload to occur
+        firstClassLoader = null;
+        clz = null;
+        // provoke unload
+        System.gc();
+        // try to define another class _with the same name_ using a different class loader
+        secondClassLoader = new TestClassLoader();
+        // this will throw a NPE for 8231081 because it will reuse the same class name
+        // that symbol was  marked as already serialized by the unload, but since no recordings were running
+        // it was not written to any chunk. This creates a reference to a non-existing symbol, leading to an NPE (no symbol at the expected location).
+        recordClassDefinition(secondClassLoader);
+    }
+
+    private static Class<?> recordClassDefinition(TestClassLoader classLoader) throws Exception  {
+        try (Recording recording = new Recording())  {
+            recording.enable(EVENT_NAME);
+            recording.start();
+            Class<?> clz = classLoader.loadClass(TEST_CLASS_NAME);
+            recording.stop();
+            assertClassDefineEvent(recording);
+            return clz;
+        }
+    }
+
+    private static void assertClassDefineEvent(Recording recording) throws Exception {
+        boolean isAnyFound = false;
+        for (RecordedEvent event : Events.fromRecording(recording)) {
+            System.out.println(event);
+            RecordedClass definedClass = event.getValue("definedClass");
+            if (TEST_CLASS_NAME.equals(definedClass.getName())) {
+                RecordedClassLoader definingClassLoader = definedClass.getClassLoader();
+                String definingName = definingClassLoader.getType().getName();
+                String testName = TestClassLoader.class.getName();
+                String errorMsg = "Expected " + testName + ", got " + definingName;
+                Asserts.assertEquals(testName, definingName, errorMsg);
+                Asserts.assertFalse(isAnyFound, "Found more than 1 event");
+                isAnyFound = true;
+            }
+        }
+        Asserts.assertTrue(isAnyFound, "No events found");
+    }
+}