8029164: Race condition in CompletableFuture.thenCompose with asynchronous task

Reviewed-by: dl, chegar, mduigou

Author: Paul Sandoz

jdk/src/share/classes/java/util/concurrent/CompletableFuture.java

@@ -2004,7 +2004,7 @@ else if (UNSAFE.compareAndSwapObject
             }
             if (dst == null)
                 dst = new CompletableFuture<U>();
-            if (e == null || ex != null)
+            if (ex != null)
                 dst.internalComplete(null, ex);
         }
         helpPostComplete();

jdk/test/java/util/concurrent/CompletableFuture/ThenComposeAsyncTest.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2013, 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.
+ */
+
+import org.testng.Assert;
+import org.testng.annotations.Test;
+
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CountDownLatch;
+
+
+/**
+ * @test
+ * @bug 8029164
+ * @run testng ThenComposeAsyncTest
+ * @run testng/othervm -Djava.util.concurrent.ForkJoinPool.common.parallelism=0 ThenComposeAsyncTest
+ * @summary Test that CompletableFuture.thenCompose works correctly if the
+ * composing task is complete before composition
+ */
+@Test
+public class ThenComposeAsyncTest {
+
+    public void testThenComposeAsync() throws Exception {
+        // Composing CompletableFuture is complete
+        CompletableFuture<String> cf1 = CompletableFuture.completedFuture("one");
+
+        // Composing function returns a CompletableFuture executed asynchronously
+        CountDownLatch cdl = new CountDownLatch(1);
+        CompletableFuture<String> cf2 = cf1.thenCompose(str -> CompletableFuture.supplyAsync(() -> {
+            while (true) {
+                try {
+                    cdl.await();
+                    break;
+                }
+                catch (InterruptedException e) {
+                }
+            }
+            return str + ", two";
+        }));
+
+        // Ensure returned CompletableFuture completes after call to thenCompose
+        // This guarantees that any premature internal completion will be
+        // detected
+        cdl.countDown();
+
+        String val = cf2.get();
+        Assert.assertNotNull(val);
+        Assert.assertEquals(val, "one, two");
+    }
+}