8085978: LinkedTransferQueue<T>.spliterator can report LTQ.Node object, not T

Reviewed-by: psandoz, martin

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

@@ -780,7 +780,9 @@ public class LinkedTransferQueue<E> extends AbstractQueue<E>
     }
 
     /**
-     * Version of firstOfMode used by Spliterator
+     * Version of firstOfMode used by Spliterator. Callers must
+     * recheck if the returned node's item field is null or
+     * self-linked before using.
      */
     final Node firstDataNode() {
         for (Node p = head; p != null;) {
@@ -953,11 +955,12 @@ public class LinkedTransferQueue<E> extends AbstractQueue<E>
                 Object[] a = new Object[n];
                 int i = 0;
                 do {
-                    if ((a[i] = p.item) != null)
+                    Object e = p.item;
+                    if (e != p && (a[i] = e) != null)
                         ++i;
                     if (p == (p = p.next))
                         p = q.firstDataNode();
-                } while (p != null && i < n);
+                } while (p != null && i < n && p.isData);
                 if ((current = p) == null)
                     exhausted = true;
                 if (i > 0) {
@@ -980,11 +983,11 @@ public class LinkedTransferQueue<E> extends AbstractQueue<E>
                 exhausted = true;
                 do {
                     Object e = p.item;
+                    if (e != null && e != p)
+                        action.accept((E)e);
                     if (p == (p = p.next))
                         p = q.firstDataNode();
-                    if (e != null)
-                        action.accept((E)e);
-                } while (p != null);
+                } while (p != null && p.isData);
             }
         }
 
@@ -997,10 +1000,11 @@ public class LinkedTransferQueue<E> extends AbstractQueue<E>
                 ((p = current) != null || (p = q.firstDataNode()) != null)) {
                 Object e;
                 do {
-                    e = p.item;
+                    if ((e = p.item) == p)
+                        e = null;
                     if (p == (p = p.next))
                         p = q.firstDataNode();
-                } while (e == null && p != null);
+                } while (e == null && p != null && p.isData);
                 if ((current = p) == null)
                     exhausted = true;
                 if (e != null) {

test/java/util/concurrent/LinkedTransferQueue/SpliteratorTraverseAddRemoveTest.java

+/*
+ * Copyright (c) 2015, 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.
+ */
+
+/*
+ * @test
+ * @run testng SpliteratorTraverseAddRemoveTest
+ * @bug 8085978
+ * @summary repeatedly traverse the queue using the spliterator while
+ *          concurrently adding and removing an element to test that self-linked
+ *          nodes are never erroneously reported on traversal
+ */
+
+import org.testng.Assert;
+import org.testng.annotations.DataProvider;
+import org.testng.annotations.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Queue;
+import java.util.Spliterator;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.LinkedTransferQueue;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.function.Consumer;
+
+@Test
+public class SpliteratorTraverseAddRemoveTest {
+
+    static Object[] of(String desc, Consumer<Queue<?>> c) {
+        return new Object[]{desc, c};
+    }
+
+    static void assertIsString(Object e) {
+        Assert.assertTrue(e instanceof String,
+                          String.format("Object instanceof %s (actual: instanceof %s)",
+                                        String.class.getName(),
+                                        e.getClass().getName()));
+    }
+
+    @DataProvider()
+    public static Object[][] spliteratorTraversers() {
+        return new Object[][]{
+                of("forEachRemaining", q -> {
+                    q.spliterator().forEachRemaining(SpliteratorTraverseAddRemoveTest::assertIsString);
+                }),
+                of("tryAdvance", q -> {
+                    Spliterator<?> s = q.spliterator();
+                    while (s.tryAdvance(SpliteratorTraverseAddRemoveTest::assertIsString))
+                        ;
+                }),
+                of("trySplit then forEachRemaining", q -> {
+                    Spliterator<?> r = q.spliterator();
+
+                    List<Spliterator<?>> ss = new ArrayList<>();
+                    Spliterator<?> l;
+                    while ((l = r.trySplit()) != null) {
+                        ss.add(l);
+                    }
+                    ss.add(r);
+
+                    ss.forEach(s -> s.forEachRemaining(SpliteratorTraverseAddRemoveTest::assertIsString));
+                }),
+        };
+    }
+
+    @Test(dataProvider = "spliteratorTraversers")
+    public void testQueue(String desc, Consumer<Queue<String>> c)
+            throws InterruptedException {
+        AtomicBoolean done = new AtomicBoolean(false);
+        Queue<String> msgs = new LinkedTransferQueue<>();
+
+        CompletableFuture<Void> traversalTask = CompletableFuture.runAsync(() -> {
+            while (!done.get()) {
+                // Traversal will fail if self-linked nodes of
+                // LinkedTransferQueue are erroneously reported
+                c.accept(msgs);
+            }
+        });
+        CompletableFuture<Void> addAndRemoveTask = CompletableFuture.runAsync(() -> {
+            while (!traversalTask.isDone()) {
+                msgs.add("msg");
+                msgs.remove("msg");
+            }
+        });
+
+        Thread.sleep(TimeUnit.SECONDS.toMillis(1));
+        done.set(true);
+
+        addAndRemoveTask.join();
+        Assert.assertTrue(traversalTask.isDone());
+        traversalTask.join();
+    }
+}