8004138: ForkJoinTask leaks exceptions

Reviewed-by: chegar, mduigou, psandoz, martin
Contributed-by: NDoug Lea <dl@cs.oswego.edu>

src/share/classes/java/util/concurrent/ForkJoinTask.java

@@ -439,11 +439,13 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
         final Throwable ex;
         ExceptionNode next;
         final long thrower;  // use id not ref to avoid weak cycles
+        final int hashCode;  // store task hashCode before weak ref disappears
         ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
             super(task, exceptionTableRefQueue);
             this.ex = ex;
             this.next = next;
             this.thrower = Thread.currentThread().getId();
+            this.hashCode = System.identityHashCode(task);
         }
     }
 
@@ -605,9 +607,9 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
     private static void expungeStaleExceptions() {
         for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
             if (x instanceof ExceptionNode) {
-                ForkJoinTask<?> key = ((ExceptionNode)x).get();
+                int hashCode = ((ExceptionNode)x).hashCode;
                 ExceptionNode[] t = exceptionTable;
-                int i = System.identityHashCode(key) & (t.length - 1);
+                int i = hashCode & (t.length - 1);
                 ExceptionNode e = t[i];
                 ExceptionNode pred = null;
                 while (e != null) {

test/java/util/concurrent/forkjoin/FJExceptionTableLeak.java

+/*
+ * 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.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+/*
+ * @test
+ * @author Doug Lea
+ * @bug 8004138
+ * @summary Check if ForkJoinPool table leaks thrown exceptions.
+ * @run main/othervm -Xmx32m FJExceptionTableLeak
+ */
+import java.util.concurrent.*;
+
+public class FJExceptionTableLeak {
+
+    // Run with TASKS_PER_STEP * 40 < Xmx < STEPS * TASKS_PER_STEP * 40
+    // These work for Xmx32m:
+    static final int STEPS = 2000;
+    static final int TASKS_PER_STEP = 1000;
+
+    static class FailingTaskException extends RuntimeException {}
+    static class FailingTask extends RecursiveAction {
+        public void compute() {
+            throw new FailingTaskException();
+        }
+    }
+
+    public static void main(String[] args) throws InterruptedException {
+        ForkJoinPool pool = new ForkJoinPool(4);
+        FailingTask[] tasks = new FailingTask[TASKS_PER_STEP];
+        for (int k = 0; k < STEPS; ++k) {
+            for (int i = 0; i < tasks.length; ++i)
+                tasks[i] = new FailingTask();
+            for (int i = 0; i < tasks.length; ++i)
+                pool.execute(tasks[i]);
+            for (int i = 0; i < tasks.length; ++i) {
+                try {
+                    tasks[i].join();
+                    throw new AssertionError("should throw");
+                } catch (FailingTaskException success) {}
+            }
+        }
+    }
+}