DefaultPromise LateListener Logic Issues

Motivation:
The LateListener logic is prone to infinite loops and relies on being processed in the EventExecutor's thread for synchronization, but this EventExecutor may not be constant. An infinite loop can occur if the EventExecutor's execute method does not introduce a context switch in LateListener.run. The EventExecutor can be changed by classes which inherit from DefaultPromise. For example the DefaultChannelPromise will return w/e EventLoop the channel is registered to, but this EventLoop can change (re-registration).

Modifications:
- Remove the LateListener concept and instead use a single Object to maintain the listeners while still preserving notification order
- Make the result member variable an atomic variable so it can be outside the synchronized(this) blocks
- Cleanup/simplify existing state management code

Result:
Fixes https://github.com/netty/netty/issues/5185

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

@@ -84,7 +84,7 @@ public class DefaultPromiseTest {
             p[i].addListener(new FutureListener<Void>() {
                 @Override
                 public void operationComplete(Future<Void> future) throws Exception {
-                    DefaultPromise.notifyListener(ImmediateEventExecutor.INSTANCE, future, new FutureListener<Void>() {
+                    future.addListener(new FutureListener<Void>() {
                         @Override
                         public void operationComplete(Future<Void> future) throws Exception {
                             if (finalI + 1 < p.length) {
@@ -192,8 +192,8 @@ public class DefaultPromiseTest {
      * <ol>
      * <li>A write is done</li>
      * <li>The write operation completes, and the promise state is changed to done</li>
-     * <li>A listener is added to the return from the write. The {@link FutureListener#operationComplete()} updates
+     * <li>A listener is added to the return from the write. The {@link FutureListener#operationComplete(Future)}
-     * state which must be invoked before the response to the previous write is read.</li>
+     * updates state which must be invoked before the response to the previous write is read.</li>
      * <li>The write operation</li>
      * </ol>
      */

transport/src/test/java/io/netty/channel/embedded/EmbeddedChannelTest.java

@@ -19,6 +19,7 @@ import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
 import io.netty.channel.Channel;
 import io.netty.channel.ChannelFuture;
+import io.netty.channel.ChannelFutureListener;
 import io.netty.channel.ChannelHandler;
 import io.netty.channel.ChannelHandlerAdapter;
 import io.netty.channel.ChannelHandlerContext;
@@ -39,10 +40,27 @@ import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicReference;
 
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
 
 public class EmbeddedChannelTest {
 
+    @Test(timeout = 2000)
+    public void promiseDoesNotInfiniteLoop() throws InterruptedException {
+        EmbeddedChannel channel = new EmbeddedChannel();
+        channel.closeFuture().addListener(new ChannelFutureListener() {
+            @Override
+            public void operationComplete(ChannelFuture future) throws Exception {
+                future.channel().close();
+            }
+        });
+
+        channel.close().syncUninterruptibly();
+    }
+
     @Test
     public void testConstructWithChannelInitializer() {
         final Integer first = 1;