--- /dev/null	2010-12-13 15:40:14.841669000 +0000
+++ new/test/java/util/Hashtable/SerializationDeadlock.java	2011-01-10 10:52:06.000000000 +0000
@@ -0,0 +1,153 @@
+/*
+ * Copyright 2010-2011 IBM Corporation.  All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is licensed by Oracle to you under the terms of the GNU
+ * General Public License version 2 only.  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.
+ */
+
+/*
+ * @test
+ * @bug 6927486
+ * @summary Serializing Hashtable objects which refer to each other should not be able to deadlock.
+ * @author Neil Richards <neil.richards@ngmr.net>, <neil_richards@uk.ibm.com>
+ */
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.ObjectOutputStream;
+import java.io.PrintWriter;
+import java.io.Serializable;
+import java.io.StringWriter;
+import java.util.ArrayList;
+import java.util.Hashtable;
+import java.util.List;
+import java.util.concurrent.CyclicBarrier;
+
+public class SerializationDeadlock {
+    public static void main(final String[] args) throws Exception {
+        // Test for Hashtable serialization deadlock
+        final Hashtable<Object, Object> h1 = new Hashtable<>();
+        final Hashtable<Object, Object> h2 = new Hashtable<>();
+        final TestBarrier testStart = new TestBarrier(3);
+
+        // Populate the hashtables so that they refer to each other
+        h1.put(testStart, h2);
+        h2.put(testStart, h1);
+
+        final CyclicBarrier testEnd = new CyclicBarrier(3);
+        final TestThread t1 = new TestThread(h1, testEnd);
+        final TestThread t2 = new TestThread(h2, testEnd);
+
+        t1.start();
+        t2.start();
+
+        // Wait for both test threads to have initiated serialization
+        // of the 'testStart' object (and hence of both 'h1' and 'h2') 
+        testStart.await();
+
+        // Wait for both test threads to successfully finish serialization
+        // of 'h1' and 'h2'.
+        System.out.println("Waiting for Hashtable serialization to complete ...");
+        System.out.println("(This test will hang if serialization deadlocks)");
+        testEnd.await();
+        System.out.println("Test PASSED: serialization completed successfully");
+
+        TestThread.handleExceptions();
+    }
+
+    static final class TestBarrier extends CyclicBarrier 
+    implements Serializable {
+        public TestBarrier(final int count) {
+            super(count);
+        }
+
+        private void writeObject(final ObjectOutputStream oos) 
+        throws IOException {
+            oos.defaultWriteObject();
+            // Wait until all test threads have started serializing data
+            try {
+                await();
+            } catch (final Exception e) {
+                throw new IOException("Test ERROR: Unexpected exception caught", e);
+            }
+        }
+    }
+
+    static final class TestThread extends Thread {
+        private static final List<Exception> exceptions = new ArrayList<>();
+
+        private final Hashtable<Object, Object> hashtable;
+        private final CyclicBarrier testEnd;
+
+        public TestThread(final Hashtable<Object, Object> hashtable,
+                final CyclicBarrier testEnd) {
+            this.hashtable = hashtable;
+            this.testEnd = testEnd;
+            setDaemon(true);
+        }
+
+        public void run() {
+            try {
+                final ByteArrayOutputStream baos = new ByteArrayOutputStream();
+                final ObjectOutputStream oos = new ObjectOutputStream(baos);
+
+                oos.writeObject(hashtable);
+                oos.close();
+            } catch (final IOException ioe) {
+                addException(ioe);
+            } finally {
+                try {
+                    testEnd.await();
+                } catch (Exception e) {
+                    addException(e);
+                }
+            }
+        }
+
+        private static synchronized void addException(final Exception exception) {
+            exceptions.add(exception);
+        }
+
+        public static synchronized void handleExceptions() {
+            if (false == exceptions.isEmpty()) {
+                throw new RuntimeException(getErrorText(exceptions));
+            }
+        }
+
+        private static String getErrorText(final List<Exception> exceptions) {
+            final StringWriter sw = new StringWriter();
+            final PrintWriter pw = new PrintWriter(sw);
+
+            pw.println("Test ERROR: Unexpected exceptions thrown on test threads:");
+            for (Exception exception : exceptions) {
+                pw.print("\t");
+                pw.println(exception);
+                for (StackTraceElement element : exception.getStackTrace()) {
+                    pw.print("\t\tat ");
+                    pw.println(element);
+                }
+            }
+
+            pw.close();
+            return sw.toString();
+        }
+    }
+}
+