--- a/jdk/src/share/classes/sun/rmi/transport/ObjectTable.java	Wed Apr 13 11:21:36 2011 -0400
+++ b/jdk/src/share/classes/sun/rmi/transport/ObjectTable.java	Wed Apr 13 18:39:48 2011 +0100
@@ -175,25 +175,26 @@
             DGCImpl.dgcLog.log(Log.VERBOSE, "add object " + oe);
         }
 
-        Remote impl = target.getImpl();
-        if (impl == null) {
-            throw new ExportException(
-                "internal error: attempt to export collected object");
-        }
+        synchronized (tableLock) {
+            /**
+             * Do nothing if impl has already been collected (see 6597112). Check while
+             * holding tableLock to ensure that Reaper cannot process weakImpl in between
+             * null check and put/increment effects.
+             */
+            if (target.getImpl() != null) {
+                if (objTable.containsKey(oe)) {
+                    throw new ExportException(
+                        "internal error: ObjID already in use");
+                } else if (implTable.containsKey(weakImpl)) {
+                    throw new ExportException("object already exported");
+                }
 
-        synchronized (tableLock) {
-            if (objTable.containsKey(oe)) {
-                throw new ExportException(
-                    "internal error: ObjID already in use");
-            } else if (implTable.containsKey(weakImpl)) {
-                throw new ExportException("object already exported");
-            }
+                objTable.put(oe, target);
+                implTable.put(weakImpl, target);
 
-            objTable.put(oe, target);
-            implTable.put(weakImpl, target);
-
-            if (!target.isPermanent()) {
-                incrementKeepAliveCount();
+                if (!target.isPermanent()) {
+                    incrementKeepAliveCount();
+                }
             }
         }
     }

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/test/java/rmi/server/UnicastRemoteObject/exportObject/GcDuringExport.java	Wed Apr 13 18:39:48 2011 +0100
@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2011 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.
+ *
+ * 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.
+ */
+
+/*
+ * Portions Copyright (c) 2011 IBM Corporation
+ */
+
+/*
+ * @test
+ * @bug 6597112
+ * @summary GC'ing objects whilst being exported to RMI should not cause exceptions
+ * @author Neil Richards <neil.richards@ngmr.net>, <neil_richards@uk.ibm.com>
+ */
+
+import java.rmi.Remote;
+import java.rmi.server.UnicastRemoteObject;
+
+public class GcDuringExport {
+    private static final long MAX_EXPORT_ITERATIONS = 50000;
+
+    public static void main(String[] args) throws Exception {
+        Thread gcInducingThread = new Thread() {
+            public void run() {
+                while (true) {
+                    System.gc();
+                    try { Thread.sleep(1); } catch (InterruptedException e) { }
+                }
+            }
+        };
+        gcInducingThread.setDaemon(true);
+        gcInducingThread.start();
+
+        long i = 0;
+        try {
+            while (i < MAX_EXPORT_ITERATIONS) {
+                i++;
+                UnicastRemoteObject.exportObject(new Remote() { }, 0);
+            }
+        } catch (Throwable e) {
+            throw new RuntimeException("Test FAILED on iteration " + i + ".", e);
+        }
+
+        System.out.println("Test successfully exported " + i + " objects.");
+    }
+}