Reduce memory usage by EmbeddedChannel

Motivation:

When using an EmbeddedChannel often it either does inbound or outbound processing which means we only often need one queue.

Modifications:

Lazy init the inbound and outbound message queues.

Result:

Less memory usage.

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

@@ -57,8 +57,9 @@ public class EmbeddedChannel extends AbstractChannel {
 
     private final EmbeddedEventLoop loop = new EmbeddedEventLoop();
     private final ChannelConfig config = new DefaultChannelConfig(this);
-    private final Queue<Object> inboundMessages = new ArrayDeque<Object>();
+
-    private final Queue<Object> outboundMessages = new ArrayDeque<Object>();
+    private Queue<Object> inboundMessages;
+    private Queue<Object> outboundMessages;
     private Throwable lastException;
     private State state;
 
@@ -136,6 +137,9 @@ public class EmbeddedChannel extends AbstractChannel {
      * Returns the {@link Queue} which holds all the {@link Object}s that were received by this {@link Channel}.
      */
     public Queue<Object> inboundMessages() {
+        if (inboundMessages == null) {
+            inboundMessages = new ArrayDeque<Object>();
+        }
         return inboundMessages;
     }
 
@@ -151,6 +155,9 @@ public class EmbeddedChannel extends AbstractChannel {
      * Returns the {@link Queue} which holds all the {@link Object}s that were written by this {@link Channel}.
      */
     public Queue<Object> outboundMessages() {
+        if (outboundMessages == null) {
+            outboundMessages = new ArrayDeque<Object>();
+        }
         return outboundMessages;
     }
 
@@ -167,7 +174,7 @@ public class EmbeddedChannel extends AbstractChannel {
      */
     @SuppressWarnings("unchecked")
     public <T> T readInbound() {
-        return (T) inboundMessages.poll();
+        return (T) poll(inboundMessages);
     }
 
     /**
@@ -175,7 +182,7 @@ public class EmbeddedChannel extends AbstractChannel {
      */
     @SuppressWarnings("unchecked")
     public <T> T readOutbound() {
-        return (T) outboundMessages.poll();
+        return (T) poll(outboundMessages);
     }
 
     /**
@@ -188,7 +195,7 @@ public class EmbeddedChannel extends AbstractChannel {
     public boolean writeInbound(Object... msgs) {
         ensureOpen();
         if (msgs.length == 0) {
-            return !inboundMessages.isEmpty();
+            return isNotEmpty(inboundMessages);
         }
 
         ChannelPipeline p = pipeline();
@@ -198,7 +205,7 @@ public class EmbeddedChannel extends AbstractChannel {
         p.fireChannelReadComplete();
         runPendingTasks();
         checkException();
-        return !inboundMessages.isEmpty();
+        return isNotEmpty(inboundMessages);
     }
 
     /**
@@ -210,7 +217,7 @@ public class EmbeddedChannel extends AbstractChannel {
     public boolean writeOutbound(Object... msgs) {
         ensureOpen();
         if (msgs.length == 0) {
-            return !outboundMessages.isEmpty();
+            return isNotEmpty(outboundMessages);
         }
 
         RecyclableArrayList futures = RecyclableArrayList.newInstance(msgs.length);
@@ -235,7 +242,7 @@ public class EmbeddedChannel extends AbstractChannel {
 
             runPendingTasks();
             checkException();
-            return !outboundMessages.isEmpty();
+            return isNotEmpty(outboundMessages);
         } finally {
             futures.recycle();
         }
@@ -255,7 +262,15 @@ public class EmbeddedChannel extends AbstractChannel {
 
         checkException();
 
-        return !inboundMessages.isEmpty() || !outboundMessages.isEmpty();
+        return isNotEmpty(inboundMessages) || isNotEmpty(outboundMessages);
+    }
+
+    private static boolean isNotEmpty(Queue<Object> queue) {
+        return queue != null && !queue.isEmpty();
+    }
+
+    private static Object poll(Queue<Object> queue) {
+        return queue != null ? queue.poll() : null;
     }
 
     /**
@@ -378,7 +393,7 @@ public class EmbeddedChannel extends AbstractChannel {
             }
 
             ReferenceCountUtil.retain(msg);
-            outboundMessages.add(msg);
+            outboundMessages().add(msg);
             in.remove();
         }
     }
@@ -393,7 +408,7 @@ public class EmbeddedChannel extends AbstractChannel {
     private final class LastInboundHandler extends ChannelHandlerAdapter {
         @Override
         public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
-            inboundMessages.add(msg);
+            inboundMessages().add(msg);
         }
 
         @Override