PromiseNotifier does not propagate cancel events

Motivation:
If the Future that the PromiseNotifier is listening to is cancelled, it does not propagate the cancel to all the promises it is expected to notify.

Modifications:
- If the future is cancelled then all the promises should be cancelled
- Add a UnaryPromiseNotifier if a collection of promises is not necessary

Result:
PromiseNotifier propagates cancel events to all promises

common/src/main/java/io/netty/util/concurrent/PromiseNotifier.java

@@ -57,13 +57,18 @@ public void operationComplete(F future) throws Exception {
                     logger.warn("Failed to mark a promise as success because it is done already: {}", p);
                 }
             }
-            return;
-        }
-
-        Throwable cause = future.cause();
-        for (Promise<? super V> p: promises) {
-            if (!p.tryFailure(cause)) {
-                logger.warn("Failed to mark a promise as failure because it's done already: {}", p, cause);
+        } else if (future.isCancelled()) {
+            for (Promise<? super V> p: promises) {
+                if (!p.cancel(false)) {
+                    logger.warn("Failed to cancel a promise because it is done already: {}", p);
+                }
+            }
+        } else {
+            Throwable cause = future.cause();
+            for (Promise<? super V> p: promises) {
+                if (!p.tryFailure(cause)) {
+                    logger.warn("Failed to mark a promise as failure because it's done already: {}", p, cause);
+                }
             }
         }
     }

common/src/main/java/io/netty/util/concurrent/UnaryPromiseNotifier.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2016 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+package io.netty.util.concurrent;
+
+import io.netty.util.internal.ObjectUtil;
+import io.netty.util.internal.logging.InternalLogger;
+import io.netty.util.internal.logging.InternalLoggerFactory;
+
+public final class UnaryPromiseNotifier<T> implements FutureListener<T> {
+    private static final InternalLogger logger = InternalLoggerFactory.getInstance(UnaryPromiseNotifier.class);
+    private final Promise<? super T> promise;
+
+    public UnaryPromiseNotifier(Promise<? super T> promise) {
+        this.promise = ObjectUtil.checkNotNull(promise, "promise");
+    }
+
+    @Override
+    public void operationComplete(Future<T> future) throws Exception {
+        cascadeTo(future, promise);
+    }
+
+    public static <X> void cascadeTo(Future<X> completedFuture, Promise<? super X> promise) {
+        if (completedFuture.isSuccess()) {
+            if (!promise.trySuccess(completedFuture.getNow())) {
+                logger.warn("Failed to mark a promise as success because it is done already: {}", promise);
+            }
+        } else if (completedFuture.isCancelled()) {
+            if (!promise.cancel(false)) {
+                logger.warn("Failed to cancel a promise because it is done already: {}", promise);
+            }
+        } else {
+            if (!promise.tryFailure(completedFuture.cause())) {
+                logger.warn("Failed to mark a promise as failure because it's done already: {}", promise,
+                            completedFuture.cause());
+            }
+        }
+    }
+}

common/src/test/java/io/netty/util/concurrent/PromiseNotifierTest.java

@@ -78,6 +78,7 @@ public void testListenerFailure() throws Exception {
         Future<Void> future = createStrictMock(Future.class);
         Throwable t = createStrictMock(Throwable.class);
         expect(future.isSuccess()).andReturn(false);
+        expect(future.isCancelled()).andReturn(false);
         expect(future.cause()).andReturn(t);
         expect(p1.tryFailure(t)).andReturn(true);
         expect(p2.tryFailure(t)).andReturn(true);