Fix memory leak in AbstractEmbeddedChannel

- Allow a transport implementation to perform an arbitrary task when a channel has been deregistered completely

transport/src/main/java/io/netty/channel/AbstractChannel.java

@@ -741,8 +741,9 @@ public abstract class AbstractChannel extends DefaultAttributeMap implements Cha
                     return;
                 }
 
+                Runnable postTask = null;
                 try {
-                    doDeregister();
+                    postTask = doDeregister();
                 } catch (Throwable t) {
                     logger.warn("Unexpected exception occurred while deregistering a channel.", t);
                 } finally {
@@ -756,6 +757,10 @@ public abstract class AbstractChannel extends DefaultAttributeMap implements Cha
                         // close() calls deregister() again - no need to fire channelUnregistered.
                         promise.setSuccess();
                     }
+
+                    if (postTask != null) {
+                        postTask.run();
+                    }
                 }
             } else {
                 eventLoop().execute(new Runnable() {
@@ -973,11 +978,12 @@ public abstract class AbstractChannel extends DefaultAttributeMap implements Cha
 
     /**
      * Deregister the {@link Channel} from its {@link EventLoop}.
+     * You can return a {@link Runnable} which will be run as post-task of the registration process.
      *
      * Sub-classes may override this method
      */
-    protected void doDeregister() throws Exception {
-        // NOOP
+    protected Runnable doDeregister() throws Exception {
+        return null;
     }
 
     /**

transport/src/main/java/io/netty/channel/embedded/AbstractEmbeddedChannel.java

@@ -225,8 +225,13 @@ public abstract class AbstractEmbeddedChannel<O> extends AbstractChannel {
     }
 
     @Override
-    protected void doDeregister() throws Exception {
-        // NOOP
+    protected Runnable doDeregister() throws Exception {
+        return new Runnable() {
+            @Override
+            public void run() {
+                runPendingTasks();
+            }
+        };
     }
 
     @Override

transport/src/main/java/io/netty/channel/local/LocalChannel.java

@@ -26,8 +26,8 @@ import io.netty.channel.ChannelPipeline;
 import io.netty.channel.ChannelPromise;
 import io.netty.channel.DefaultChannelConfig;
 import io.netty.channel.EventLoop;
-import io.netty.util.concurrent.SingleThreadEventExecutor;
 import io.netty.channel.SingleThreadEventLoop;
+import io.netty.util.concurrent.SingleThreadEventExecutor;
 
 import java.net.SocketAddress;
 import java.nio.channels.AlreadyConnectedException;
@@ -201,11 +201,12 @@ public class LocalChannel extends AbstractChannel {
     }
 
     @Override
-    protected void doDeregister() throws Exception {
+    protected Runnable doDeregister() throws Exception {
         if (isOpen()) {
             unsafe().close(unsafe().voidFuture());
         }
         ((SingleThreadEventExecutor) eventLoop()).removeShutdownHook(shutdownHook);
+        return null;
     }
 
     @Override

transport/src/main/java/io/netty/channel/local/LocalServerChannel.java

@@ -22,8 +22,8 @@ import io.netty.channel.ChannelPipeline;
 import io.netty.channel.DefaultChannelConfig;
 import io.netty.channel.EventLoop;
 import io.netty.channel.ServerChannel;
-import io.netty.util.concurrent.SingleThreadEventExecutor;
 import io.netty.channel.SingleThreadEventLoop;
+import io.netty.util.concurrent.SingleThreadEventExecutor;
 
 import java.net.SocketAddress;
 
@@ -126,8 +126,9 @@ public class LocalServerChannel extends AbstractServerChannel {
     }
 
     @Override
-    protected void doDeregister() throws Exception {
+    protected Runnable doDeregister() throws Exception {
         ((SingleThreadEventExecutor) eventLoop()).removeShutdownHook(shutdownHook);
+        return null;
     }
 
     @Override

transport/src/main/java/io/netty/channel/nio/AbstractNioChannel.java

@@ -273,8 +273,9 @@ public abstract class AbstractNioChannel extends AbstractChannel {
     }
 
     @Override
-    protected void doDeregister() throws Exception {
+    protected Runnable doDeregister() throws Exception {
         eventLoop().cancel(selectionKey());
+        return null;
     }
 
     @Override