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

@@ -53,8 +53,8 @@ public class EmbeddedChannel extends AbstractChannel {
     private final ChannelConfig config = new DefaultChannelConfig(this);
     private final SocketAddress localAddress = new EmbeddedSocketAddress();
     private final SocketAddress remoteAddress = new EmbeddedSocketAddress();
-    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 int state; // 0 = OPEN, 1 = ACTIVE, 2 = CLOSED
 
@@ -125,6 +125,9 @@ 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;
     }
 
@@ -140,6 +143,9 @@ 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;
     }
 
@@ -155,14 +161,14 @@ public class EmbeddedChannel extends AbstractChannel {
      * Return received data from this {@link Channel}
      */
     public Object readInbound() {
-        return inboundMessages.poll();
+        return poll(inboundMessages);
     }
 
     /**
      * Read data froum the outbound. This may return {@code null} if nothing is readable.
      */
     public Object readOutbound() {
-        return outboundMessages.poll();
+        return poll(outboundMessages);
     }
 
     /**
@@ -175,7 +181,7 @@ public class EmbeddedChannel extends AbstractChannel {
     public boolean writeInbound(Object... msgs) {
         ensureOpen();
         if (msgs.length == 0) {
-            return !inboundMessages.isEmpty();
+            return isNotEmpty(inboundMessages);
         }
 
         ChannelPipeline p = pipeline();
@@ -185,7 +191,7 @@ public class EmbeddedChannel extends AbstractChannel {
         p.fireChannelReadComplete();
         runPendingTasks();
         checkException();
-        return !inboundMessages.isEmpty();
+        return isNotEmpty(inboundMessages);
     }
 
     /**
@@ -197,7 +203,7 @@ 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);
@@ -222,7 +228,7 @@ public class EmbeddedChannel extends AbstractChannel {
 
             runPendingTasks();
             checkException();
-            return !outboundMessages.isEmpty();
+            return isNotEmpty(outboundMessages);
         } finally {
             futures.recycle();
         }
@@ -242,7 +248,15 @@ 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;
     }
 
     /**
@@ -365,7 +379,7 @@ public class EmbeddedChannel extends AbstractChannel {
             }
 
             ReferenceCountUtil.retain(msg);
-            outboundMessages.add(msg);
+            outboundMessages().add(msg);
             in.remove();
         }
     }
@@ -380,7 +394,7 @@ public class EmbeddedChannel extends AbstractChannel {
     private final class LastInboundHandler extends ChannelInboundHandlerAdapter {
         @Override
         public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
-            inboundMessages.add(msg);
+            inboundMessages().add(msg);
         }
 
         @Override