Simplified DefaultChannelPipeline by making its list head final

- Previously, head was a volatile field which is null at the beginning.
  While iterating over the pipeline, if the loop hits null, it called
  Channel.Unsafe explicitly.
- Instead, I created an outbound handler that redirects all requests
  to the unsafe and made it a final field of the pipeline.
- As a result, DefaultChannelPipeline code became much simpler.

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

@@ -72,7 +72,7 @@ public abstract class AbstractChannel extends DefaultAttributeMap implements Cha
     private final Channel parent;
     private final Integer id;
     private final Unsafe unsafe;
-    private final ChannelPipeline pipeline;
+    private final DefaultChannelPipeline pipeline;
     private final ChannelFuture succeededFuture = new SucceededChannelFuture(this);
     private final ChannelFuture voidFuture = new VoidChannelFuture(this);
     private final CloseFuture closeFuture = new CloseFuture(this);
@@ -82,7 +82,6 @@ public abstract class AbstractChannel extends DefaultAttributeMap implements Cha
     private volatile EventLoop eventLoop;
     private volatile boolean registered;
 
-    private final ChannelBufferHolder<Object> directOutbound;
     private ClosedChannelException closedChannelException;
     private final Deque<FlushCheckpoint> flushCheckpoints = new ArrayDeque<FlushCheckpoint>();
     private long writeCounter;
@@ -123,7 +122,7 @@ public abstract class AbstractChannel extends DefaultAttributeMap implements Cha
         this.parent = parent;
         this.id = id;
         unsafe = newUnsafe();
-        directOutbound = (ChannelBufferHolder<Object>) outboundBuffer;
+        pipeline = new DefaultChannelPipeline(this);
 
         closeFuture().addListener(new ChannelFutureListener() {
             @Override
@@ -132,7 +131,6 @@ public abstract class AbstractChannel extends DefaultAttributeMap implements Cha
             }
         });
 
-        pipeline = new DefaultChannelPipeline(this);
     }
 
     @Override
@@ -385,7 +383,7 @@ public abstract class AbstractChannel extends DefaultAttributeMap implements Cha
 
         @Override
         public final ChannelBufferHolder<Object> directOutbound() {
-            return directOutbound;
+            return pipeline.directOutbound;
         }
 
         @Override
@@ -628,7 +626,7 @@ public abstract class AbstractChannel extends DefaultAttributeMap implements Cha
             }
 
             inFlushNow = true;
-            final ChannelBufferHolder<Object> out = directOutbound;
+            final ChannelBufferHolder<Object> out = directOutbound();
             try {
                 Throwable cause = null;
                 int oldSize = out.size();

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

@@ -5,6 +5,8 @@ import io.netty.util.DefaultAttributeMap;
 
 import java.net.SocketAddress;
 import java.util.Queue;
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.atomic.AtomicReference;
 
 final class DefaultChannelHandlerContext extends DefaultAttributeMap implements ChannelInboundHandlerContext<Object>, ChannelOutboundHandlerContext<Object> {
     volatile DefaultChannelHandlerContext next;
@@ -17,7 +19,17 @@ final class DefaultChannelHandlerContext extends DefaultAttributeMap implements
     private final boolean canHandleInbound;
     private final boolean canHandleOutbound;
     final ChannelBufferHolder<Object> in;
-    private final ChannelBufferHolder<Object> out;
+    final ChannelBufferHolder<Object> out;
+
+    // When the two handlers run in a different thread and they are next to each other,
+    // each other's buffers can be accessed at the same time resuslting in a race condition.
+    // To avoid such situation, we lazily creates an additional thread-safe buffer called
+    // 'bridge' so that the two handlers access each other's buffer only via the bridges.
+    // The content written into a bridge is flushed into the actual buffer by flushBridge().
+    final AtomicReference<BlockingQueue<Object>> inMsgBridge;
+    final AtomicReference<BlockingQueue<Object>> outMsgBridge;
+    final AtomicReference<ChannelBuffer> inByteBridge;
+    final AtomicReference<ChannelBuffer> outByteBridge;
 
     // Runnables that calls handlers
     final Runnable fireChannelRegisteredTask = new Runnable() {
@@ -73,6 +85,7 @@ final class DefaultChannelHandlerContext extends DefaultAttributeMap implements
         @SuppressWarnings("unchecked")
         public void run() {
             DefaultChannelHandlerContext ctx = DefaultChannelHandlerContext.this;
+            flushBridge();
             try {
                 ((ChannelInboundHandler<Object>) ctx.handler()).inboundBufferUpdated(ctx);
             } catch (Throwable t) {
@@ -135,8 +148,23 @@ final class DefaultChannelHandlerContext extends DefaultAttributeMap implements
             } catch (Exception e) {
                 throw new ChannelPipelineException("A user handler failed to create a new inbound buffer.", e);
             }
+
+            if (!in.isBypass()) {
+                if (in.hasByteBuffer()) {
+                    inByteBridge = new AtomicReference<ChannelBuffer>();
+                    inMsgBridge = null;
+                } else {
+                    inByteBridge = null;
+                    inMsgBridge = new AtomicReference<BlockingQueue<Object>>();
+                }
+            } else {
+                inByteBridge = null;
+                inMsgBridge = null;
+            }
         } else {
             in = null;
+            inByteBridge = null;
+            inMsgBridge = null;
         }
         if (canHandleOutbound) {
             try {
@@ -148,8 +176,38 @@ final class DefaultChannelHandlerContext extends DefaultAttributeMap implements
                     // TODO Release the inbound buffer once pooling is implemented.
                 }
             }
+
+            if (!out.isBypass()) {
+                if (out.hasByteBuffer()) {
+                    outByteBridge = new AtomicReference<ChannelBuffer>();
+                    outMsgBridge = null;
+                } else {
+                    outByteBridge = null;
+                    outMsgBridge = new AtomicReference<BlockingQueue<Object>>();
+                }
+            } else {
+                outByteBridge = null;
+                outMsgBridge = null;
+            }
         } else {
             out = null;
+            outByteBridge = null;
+            outMsgBridge = null;
+        }
+    }
+
+    void flushBridge() {
+        if (inMsgBridge != null) {
+            BlockingQueue<Object> bridge = inMsgBridge.get();
+            if (bridge != null) {
+                bridge.drainTo(in.messageBuffer());
+            }
+        }
+        if (outMsgBridge != null) {
+            BlockingQueue<Object> bridge = outMsgBridge.get();
+            if (bridge != null) {
+                bridge.drainTo(out.messageBuffer());
+            }
         }
     }
 
@@ -229,7 +287,7 @@ final class DefaultChannelHandlerContext extends DefaultAttributeMap implements
 
     @Override
     public Queue<Object> nextInboundMessageBuffer() {
-        return DefaultChannelPipeline.nextInboundMessageBuffer(next);
+        return DefaultChannelPipeline.nextInboundMessageBuffer(executor(), next);
     }
 
     @Override
@@ -239,7 +297,7 @@ final class DefaultChannelHandlerContext extends DefaultAttributeMap implements
 
     @Override
     public Queue<Object> nextOutboundMessageBuffer() {
-        return pipeline.nextOutboundMessageBuffer(prev);
+        return pipeline.nextOutboundMessageBuffer(executor(), prev);
     }
 
     @Override

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

@@ -18,6 +18,7 @@ package io.netty.channel;
 import io.netty.buffer.ChannelBuffer;
 import io.netty.logging.InternalLogger;
 import io.netty.logging.InternalLoggerFactory;
+import io.netty.util.internal.QueueFactory;
 
 import java.net.SocketAddress;
 import java.util.ArrayList;
@@ -28,6 +29,9 @@ import java.util.List;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Queue;
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.Executor;
+import java.util.concurrent.atomic.AtomicReference;
 
 /**
  * The default {@link ChannelPipeline} implementation.  It is usually created
@@ -39,9 +43,9 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     final Channel channel;
     private final Channel.Unsafe unsafe;
-    private final ChannelBufferHolder<Object> directOutbound;
+    final ChannelBufferHolder<Object> directOutbound;
 
-    private volatile DefaultChannelHandlerContext head;
+    private final DefaultChannelHandlerContext head;
     private volatile DefaultChannelHandlerContext tail;
     private final Map<String, DefaultChannelHandlerContext> name2ctx =
         new HashMap<String, DefaultChannelHandlerContext>(4);
@@ -56,8 +60,14 @@ public class DefaultChannelPipeline implements ChannelPipeline {
             throw new NullPointerException("channel");
         }
         this.channel = channel;
+
+        HeadHandler headHandler = new HeadHandler();
+        head = new DefaultChannelHandlerContext(
+                this, null, null, null, generateName(headHandler), headHandler);
+        tail = head;
+
+        directOutbound = head.out;
         unsafe = channel.unsafe();
-        directOutbound = unsafe.directOutbound();
     }
 
     @Override
@@ -72,23 +82,20 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     @Override
     public synchronized ChannelPipeline addFirst(EventExecutor executor, String name, ChannelHandler handler) {
-        if (name2ctx.isEmpty()) {
-            init(executor, name, handler);
-        } else {
-            checkDuplicateName(name);
-            DefaultChannelHandlerContext oldHead = head;
-            DefaultChannelHandlerContext newHead =
-                    new DefaultChannelHandlerContext(this, executor, null, oldHead, name, handler);
+        checkDuplicateName(name);
+        DefaultChannelHandlerContext nextCtx = head.next;
+        DefaultChannelHandlerContext newCtx =
+                new DefaultChannelHandlerContext(this, executor, head, nextCtx, name, handler);
 
-            callBeforeAdd(newHead);
+        callBeforeAdd(newCtx);
 
-            oldHead.prev = newHead;
-            head = newHead;
-            name2ctx.put(name, newHead);
-
-            callAfterAdd(newHead);
+        if (nextCtx != null) {
+            nextCtx.prev = newCtx;
         }
+        head.next = newCtx;
+        name2ctx.put(name, newCtx);
 
+        callAfterAdd(newCtx);
         return this;
     }
 
@@ -99,23 +106,18 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     @Override
     public synchronized ChannelPipeline addLast(EventExecutor executor, String name, ChannelHandler handler) {
-        if (name2ctx.isEmpty()) {
-            init(executor, name, handler);
-        } else {
-            checkDuplicateName(name);
-            DefaultChannelHandlerContext oldTail = tail;
-            DefaultChannelHandlerContext newTail =
-                    new DefaultChannelHandlerContext(this, executor, oldTail, null, name, handler);
+        checkDuplicateName(name);
+        DefaultChannelHandlerContext oldTail = tail;
+        DefaultChannelHandlerContext newTail =
+                new DefaultChannelHandlerContext(this, executor, oldTail, null, name, handler);
 
-            callBeforeAdd(newTail);
+        callBeforeAdd(newTail);
 
-            oldTail.next = newTail;
-            tail = newTail;
-            name2ctx.put(name, newTail);
-
-            callAfterAdd(newTail);
-        }
+        oldTail.next = newTail;
+        tail = newTail;
+        name2ctx.put(name, newTail);
 
+        callAfterAdd(newTail);
         return this;
     }
 
@@ -127,22 +129,17 @@ public class DefaultChannelPipeline implements ChannelPipeline {
     @Override
     public synchronized ChannelPipeline addBefore(EventExecutor executor, String baseName, String name, ChannelHandler handler) {
         DefaultChannelHandlerContext ctx = getContextOrDie(baseName);
-        if (ctx == head) {
-            addFirst(name, handler);
-        } else {
-            checkDuplicateName(name);
-            DefaultChannelHandlerContext newCtx =
-                    new DefaultChannelHandlerContext(this, executor, ctx.prev, ctx, name, handler);
+        checkDuplicateName(name);
+        DefaultChannelHandlerContext newCtx =
+                new DefaultChannelHandlerContext(this, executor, ctx.prev, ctx, name, handler);
 
-            callBeforeAdd(newCtx);
+        callBeforeAdd(newCtx);
 
-            ctx.prev.next = newCtx;
-            ctx.prev = newCtx;
-            name2ctx.put(name, newCtx);
-
-            callAfterAdd(newCtx);
-        }
+        ctx.prev.next = newCtx;
+        ctx.prev = newCtx;
+        name2ctx.put(name, newCtx);
 
+        callAfterAdd(newCtx);
         return this;
     }
 
@@ -250,10 +247,9 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     private DefaultChannelHandlerContext remove(DefaultChannelHandlerContext ctx) {
         if (head == tail) {
-            head = tail = null;
-            name2ctx.clear();
+            return null;
         } else if (ctx == head) {
-            removeFirst();
+            throw new Error(); // Should never happen.
         } else if (ctx == tail) {
             removeLast();
         } else {
@@ -272,55 +268,26 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     @Override
     public synchronized ChannelHandler removeFirst() {
-        if (name2ctx.isEmpty()) {
+        if (head == tail) {
             throw new NoSuchElementException();
         }
-
-        DefaultChannelHandlerContext oldHead = head;
-        if (oldHead == null) {
-            throw new NoSuchElementException();
-        }
-
-        callBeforeRemove(oldHead);
-
-        if (oldHead.next == null) {
-            head = tail = null;
-            name2ctx.clear();
-        } else {
-            oldHead.next.prev = null;
-            head = oldHead.next;
-            name2ctx.remove(oldHead.name());
-        }
-
-        callAfterRemove(oldHead);
-
-        return oldHead.handler();
+        return remove(head.next).handler();
     }
 
     @Override
     public synchronized ChannelHandler removeLast() {
-        if (name2ctx.isEmpty()) {
+        if (head == tail) {
             throw new NoSuchElementException();
         }
 
         DefaultChannelHandlerContext oldTail = tail;
-        if (oldTail == null) {
-            throw new NoSuchElementException();
-        }
-
         callBeforeRemove(oldTail);
 
-        if (oldTail.prev == null) {
-            head = tail = null;
-            name2ctx.clear();
-        } else {
-            oldTail.prev.next = null;
-            tail = oldTail.prev;
-            name2ctx.remove(oldTail.name());
-        }
+        oldTail.prev.next = null;
+        tail = oldTail.prev;
+        name2ctx.remove(oldTail.name());
 
         callBeforeRemove(oldTail);
-
         return oldTail.handler();
     }
 
@@ -343,8 +310,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     private ChannelHandler replace(DefaultChannelHandlerContext ctx, String newName, ChannelHandler newHandler) {
         if (ctx == head) {
-            removeFirst();
-            addFirst(newName, newHandler);
+            throw new IllegalArgumentException();
         } else if (ctx == tail) {
             removeLast();
             addLast(newName, newHandler);
@@ -472,20 +438,20 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     @Override
     public synchronized ChannelHandler first() {
-        DefaultChannelHandlerContext head = this.head;
-        if (head == null) {
+        DefaultChannelHandlerContext first = head.next;
+        if (first == null) {
             return null;
         }
-        return head.handler();
+        return first.handler();
     }
 
     @Override
     public synchronized ChannelHandler last() {
-        DefaultChannelHandlerContext tail = this.tail;
-        if (tail == null) {
+        DefaultChannelHandlerContext last = tail;
+        if (last == head || last == null) {
             return null;
         }
-        return tail.handler();
+        return last.handler();
     }
 
     @Override
@@ -548,7 +514,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
         if (name2ctx.isEmpty()) {
             return null;
         }
-        DefaultChannelHandlerContext ctx = head;
+        DefaultChannelHandlerContext ctx = head.next;
         for (;;) {
             if (handlerType.isAssignableFrom(ctx.handler().getClass())) {
                 return ctx;
@@ -569,7 +535,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
             return list;
         }
 
-        DefaultChannelHandlerContext ctx = head;
+        DefaultChannelHandlerContext ctx = head.next;
         for (;;) {
             list.add(ctx.name());
             ctx = ctx.next;
@@ -587,7 +553,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
             return map;
         }
 
-        DefaultChannelHandlerContext ctx = head;
+        DefaultChannelHandlerContext ctx = head.next;
         for (;;) {
             map.put(ctx.name(), ctx.handler());
             ctx = ctx.next;
@@ -606,7 +572,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
         StringBuilder buf = new StringBuilder();
         buf.append(getClass().getSimpleName());
         buf.append('{');
-        DefaultChannelHandlerContext ctx = head;
+        DefaultChannelHandlerContext ctx = head.next;
         for (;;) {
             buf.append('(');
             buf.append(ctx.name());
@@ -629,7 +595,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
             throw new NoSuchBufferException(
                     "The first inbound buffer of this channel must be a message buffer.");
         }
-        return nextInboundMessageBuffer(head);
+        return nextInboundMessageBuffer(null, head.next);
     }
 
     @Override
@@ -638,12 +604,12 @@ public class DefaultChannelPipeline implements ChannelPipeline {
             throw new NoSuchBufferException(
                     "The first inbound buffer of this channel must be a byte buffer.");
         }
-        return nextInboundByteBuffer(head);
+        return nextInboundByteBuffer(head.next);
     }
 
     @Override
     public Queue<Object> outboundMessageBuffer() {
-        return nextOutboundMessageBuffer(tail);
+        return nextOutboundMessageBuffer(null, tail);
     }
 
     @Override
@@ -690,14 +656,27 @@ public class DefaultChannelPipeline implements ChannelPipeline {
         }
     }
 
-    static Queue<Object> nextInboundMessageBuffer(DefaultChannelHandlerContext ctx) {
+    static Queue<Object> nextInboundMessageBuffer(
+            EventExecutor currentExecutor, DefaultChannelHandlerContext ctx) {
         for (;;) {
             if (ctx == null) {
                 throw new NoSuchBufferException();
             }
-            ChannelBufferHolder<Object> in = ctx.inbound();
-            if (in != null && !in.isBypass() && in.hasMessageBuffer()) {
-                return in.messageBuffer();
+
+            final AtomicReference<BlockingQueue<Object>> inMsgBridge = ctx.inMsgBridge;
+            if (inMsgBridge != null) {
+                if (currentExecutor == ctx.executor()) {
+                    return ctx.in.messageBuffer();
+                } else {
+                    BlockingQueue<Object> queue = inMsgBridge.get();
+                    if (queue == null) {
+                        queue = QueueFactory.createQueue();
+                        if (!inMsgBridge.compareAndSet(null, queue)) {
+                            queue = inMsgBridge.get();
+                        }
+                    }
+                    return queue;
+                }
             }
             ctx = ctx.next;
         }
@@ -706,11 +685,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
     boolean hasNextOutboundByteBuffer(DefaultChannelHandlerContext ctx) {
         for (;;) {
             if (ctx == null) {
-                if (directOutbound.hasByteBuffer()) {
-                    return true;
-                } else {
-                    return false;
-                }
+                return false;
             }
 
             ChannelBufferHolder<Object> out = ctx.outbound();
@@ -724,11 +699,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
     boolean hasNextOutboundMessageBuffer(DefaultChannelHandlerContext ctx) {
         for (;;) {
             if (ctx == null) {
-                if (directOutbound.hasMessageBuffer()) {
-                    return true;
-                } else {
-                    return false;
-                }
+                return false;
             }
 
             ChannelBufferHolder<Object> out = ctx.outbound();
@@ -742,11 +713,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
     ChannelBuffer nextOutboundByteBuffer(DefaultChannelHandlerContext ctx) {
         for (;;) {
             if (ctx == null) {
-                if (directOutbound.hasByteBuffer()) {
-                    return directOutbound.byteBuffer();
-                } else {
-                    throw new NoSuchBufferException();
-                }
+                throw new NoSuchBufferException();
             }
 
             ChannelBufferHolder<Object> out = ctx.outbound();
@@ -757,20 +724,28 @@ public class DefaultChannelPipeline implements ChannelPipeline {
         }
     }
 
-    Queue<Object> nextOutboundMessageBuffer(DefaultChannelHandlerContext ctx) {
+    Queue<Object> nextOutboundMessageBuffer(Executor currentExecutor, DefaultChannelHandlerContext ctx) {
         for (;;) {
             if (ctx == null) {
-                if (directOutbound.hasMessageBuffer()) {
-                    return directOutbound.messageBuffer();
+                throw new NoSuchBufferException();
+            }
+
+            final AtomicReference<BlockingQueue<Object>> outMsgBridge = ctx.outMsgBridge;
+            if (outMsgBridge != null) {
+                if (currentExecutor == ctx.executor()) {
+                    return ctx.out.messageBuffer();
                 } else {
-                    throw new NoSuchBufferException();
+                    BlockingQueue<Object> queue = outMsgBridge.get();
+                    if (queue == null) {
+                        queue = QueueFactory.createQueue();
+                        if (!outMsgBridge.compareAndSet(null, queue)) {
+                            queue = outMsgBridge.get();
+                        }
+                    }
+                    return queue;
                 }
             }
 
-            ChannelBufferHolder<Object> out = ctx.outbound();
-            if (out != null && !out.isBypass() && out.hasMessageBuffer()) {
-                return out.messageBuffer();
-            }
             ctx = ctx.prev;
         }
     }
@@ -998,24 +973,20 @@ public class DefaultChannelPipeline implements ChannelPipeline {
         }
         validateFuture(future);
 
-        if (ctx != null) {
-            EventExecutor executor = ctx.executor();
-            if (executor.inEventLoop()) {
-                try {
-                    ((ChannelOutboundHandler<Object>) ctx.handler()).bind(ctx, localAddress, future);
-                } catch (Throwable t) {
-                    notifyHandlerException(t);
-                }
-            } else {
-                executor.execute(new Runnable() {
-                    @Override
-                    public void run() {
-                        bind(ctx, localAddress, future);
-                    }
-                });
+        EventExecutor executor = ctx.executor();
+        if (executor.inEventLoop()) {
+            try {
+                ((ChannelOutboundHandler<Object>) ctx.handler()).bind(ctx, localAddress, future);
+            } catch (Throwable t) {
+                notifyHandlerException(t);
             }
         } else {
-            unsafe.bind(localAddress, future);
+            executor.execute(new Runnable() {
+                @Override
+                public void run() {
+                    bind(ctx, localAddress, future);
+                }
+            });
         }
         return future;
     }
@@ -1036,24 +1007,20 @@ public class DefaultChannelPipeline implements ChannelPipeline {
         }
         validateFuture(future);
 
-        if (ctx != null) {
-            EventExecutor executor = ctx.executor();
-            if (executor.inEventLoop()) {
-                try {
-                    ((ChannelOutboundHandler<Object>) ctx.handler()).connect(ctx, remoteAddress, localAddress, future);
-                } catch (Throwable t) {
-                    notifyHandlerException(t);
-                }
-            } else {
-                executor.execute(new Runnable() {
-                    @Override
-                    public void run() {
-                        connect(ctx, remoteAddress, localAddress, future);
-                    }
-                });
+        EventExecutor executor = ctx.executor();
+        if (executor.inEventLoop()) {
+            try {
+                ((ChannelOutboundHandler<Object>) ctx.handler()).connect(ctx, remoteAddress, localAddress, future);
+            } catch (Throwable t) {
+                notifyHandlerException(t);
             }
         } else {
-            unsafe.connect(remoteAddress,  localAddress, future);
+            executor.execute(new Runnable() {
+                @Override
+                public void run() {
+                    connect(ctx, remoteAddress, localAddress, future);
+                }
+            });
         }
 
         return future;
@@ -1066,24 +1033,20 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     ChannelFuture disconnect(final DefaultChannelHandlerContext ctx, final ChannelFuture future) {
         validateFuture(future);
-        if (ctx != null) {
-            EventExecutor executor = ctx.executor();
-            if (executor.inEventLoop()) {
-                try {
-                    ((ChannelOutboundHandler<Object>) ctx.handler()).disconnect(ctx, future);
-                } catch (Throwable t) {
-                    notifyHandlerException(t);
-                }
-            } else {
-                executor.execute(new Runnable() {
-                    @Override
-                    public void run() {
-                        disconnect(ctx, future);
-                    }
-                });
+        EventExecutor executor = ctx.executor();
+        if (executor.inEventLoop()) {
+            try {
+                ((ChannelOutboundHandler<Object>) ctx.handler()).disconnect(ctx, future);
+            } catch (Throwable t) {
+                notifyHandlerException(t);
             }
         } else {
-            unsafe.disconnect(future);
+            executor.execute(new Runnable() {
+                @Override
+                public void run() {
+                    disconnect(ctx, future);
+                }
+            });
         }
 
         return future;
@@ -1096,24 +1059,20 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     ChannelFuture close(final DefaultChannelHandlerContext ctx, final ChannelFuture future) {
         validateFuture(future);
-        if (ctx != null) {
-            EventExecutor executor = ctx.executor();
-            if (executor.inEventLoop()) {
-                try {
-                    ((ChannelOutboundHandler<Object>) ctx.handler()).close(ctx, future);
-                } catch (Throwable t) {
-                    notifyHandlerException(t);
-                }
-            } else {
-                executor.execute(new Runnable() {
-                    @Override
-                    public void run() {
-                        close(ctx, future);
-                    }
-                });
+        EventExecutor executor = ctx.executor();
+        if (executor.inEventLoop()) {
+            try {
+                ((ChannelOutboundHandler<Object>) ctx.handler()).close(ctx, future);
+            } catch (Throwable t) {
+                notifyHandlerException(t);
             }
         } else {
-            unsafe.close(future);
+            executor.execute(new Runnable() {
+                @Override
+                public void run() {
+                    close(ctx, future);
+                }
+            });
         }
 
         return future;
@@ -1126,24 +1085,20 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     ChannelFuture deregister(final DefaultChannelHandlerContext ctx, final ChannelFuture future) {
         validateFuture(future);
-        if (ctx != null) {
-            EventExecutor executor = ctx.executor();
-            if (executor.inEventLoop()) {
-                try {
-                    ((ChannelOutboundHandler<Object>) ctx.handler()).deregister(ctx, future);
-                } catch (Throwable t) {
-                    notifyHandlerException(t);
-                }
-            } else {
-                executor.execute(new Runnable() {
-                    @Override
-                    public void run() {
-                        deregister(ctx, future);
-                    }
-                });
+        EventExecutor executor = ctx.executor();
+        if (executor.inEventLoop()) {
+            try {
+                ((ChannelOutboundHandler<Object>) ctx.handler()).deregister(ctx, future);
+            } catch (Throwable t) {
+                notifyHandlerException(t);
             }
         } else {
-            unsafe.deregister(future);
+            executor.execute(new Runnable() {
+                @Override
+                public void run() {
+                    deregister(ctx, future);
+                }
+            });
         }
 
         return future;
@@ -1156,20 +1111,16 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     ChannelFuture flush(final DefaultChannelHandlerContext ctx, final ChannelFuture future) {
         validateFuture(future);
-        if (ctx != null) {
-            EventExecutor executor = ctx.executor();
-            if (executor.inEventLoop()) {
-                flush0(ctx, future);
-            } else {
-                executor.execute(new Runnable() {
-                    @Override
-                    public void run() {
-                        flush(ctx, future);
-                    }
-                });
-            }
+        EventExecutor executor = ctx.executor();
+        if (executor.inEventLoop()) {
+            flush0(ctx, future);
         } else {
-            unsafe.flush(future);
+            executor.execute(new Runnable() {
+                @Override
+                public void run() {
+                    flush(ctx, future);
+                }
+            });
         }
 
         return future;
@@ -1177,6 +1128,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     private void flush0(final DefaultChannelHandlerContext ctx, ChannelFuture future) {
         try {
+            ctx.flushBridge();
             ((ChannelOutboundHandler<Object>) ctx.handler()).flush(ctx, future);
         } catch (Throwable t) {
             notifyHandlerException(t);
@@ -1204,16 +1156,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
         boolean msgBuf = false;
         for (;;) {
             if (ctx == null) {
-                executor = channel.eventLoop();
-                out = directOutbound;
-                if (out.hasByteBuffer()) {
-                    if(!(message instanceof ChannelBuffer)) {
-                        throw new NoSuchBufferException();
-                    }
-                } else {
-                    msgBuf = true;
-                }
-                break;
+                throw new NoSuchBufferException();
             }
 
             if (ctx.canHandleOutbound()) {
@@ -1238,11 +1181,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
                 ChannelBuffer buf = (ChannelBuffer) message;
                 out.byteBuffer().writeBytes(buf, buf.readerIndex(), buf.readableBytes());
             }
-            if (ctx != null) {
-                flush0(ctx, future);
-            } else {
-                unsafe.flush(future);
-            }
+            flush0(ctx, future);
             return future;
         } else {
             final DefaultChannelHandlerContext ctx0 = ctx;
@@ -1274,7 +1213,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
     }
 
     private DefaultChannelHandlerContext firstInboundContext() {
-        return nextInboundContext(head);
+        return nextInboundContext(head.next);
     }
 
     private DefaultChannelHandlerContext firstOutboundContext() {
@@ -1347,16 +1286,6 @@ public class DefaultChannelPipeline implements ChannelPipeline {
         return inExceptionCaught(cause.getCause());
     }
 
-    private void init(EventExecutor executor, String name, ChannelHandler handler) {
-        DefaultChannelHandlerContext ctx =
-                new DefaultChannelHandlerContext(this, executor, null, null, name, handler);
-        callBeforeAdd(ctx);
-        head = tail = ctx;
-        name2ctx.clear();
-        name2ctx.put(name, ctx);
-        callAfterAdd(ctx);
-    }
-
     private void checkDuplicateName(String name) {
         if (name2ctx.containsKey(name)) {
             throw new IllegalArgumentException("Duplicate handler name: " + name);
@@ -1365,7 +1294,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     private DefaultChannelHandlerContext getContextOrDie(String name) {
         DefaultChannelHandlerContext ctx = (DefaultChannelHandlerContext) context(name);
-        if (ctx == null) {
+        if (ctx == null || ctx == head) {
             throw new NoSuchElementException(name);
         } else {
             return ctx;
@@ -1374,7 +1303,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     private DefaultChannelHandlerContext getContextOrDie(ChannelHandler handler) {
         DefaultChannelHandlerContext ctx = (DefaultChannelHandlerContext) context(handler);
-        if (ctx == null) {
+        if (ctx == null || ctx == head) {
             throw new NoSuchElementException(handler.getClass().getName());
         } else {
             return ctx;
@@ -1383,10 +1312,84 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     private DefaultChannelHandlerContext getContextOrDie(Class<? extends ChannelHandler> handlerType) {
         DefaultChannelHandlerContext ctx = (DefaultChannelHandlerContext) context(handlerType);
-        if (ctx == null) {
+        if (ctx == null || ctx == head) {
             throw new NoSuchElementException(handlerType.getName());
         } else {
             return ctx;
         }
     }
+
+    @SuppressWarnings("rawtypes")
+    private final class HeadHandler implements ChannelOutboundHandler {
+        @Override
+        public ChannelBufferHolder newOutboundBuffer(
+                ChannelOutboundHandlerContext ctx) throws Exception {
+            switch (channel.type()) {
+            case STREAM:
+                return ChannelBufferHolders.byteBuffer();
+            case MESSAGE:
+                return ChannelBufferHolders.messageBuffer();
+            default:
+                throw new Error();
+            }
+        }
+
+        @Override
+        public void beforeAdd(ChannelHandlerContext ctx) throws Exception {
+            // NOOP
+        }
+
+        @Override
+        public void afterAdd(ChannelHandlerContext ctx) throws Exception {
+            // NOOP
+        }
+
+        @Override
+        public void beforeRemove(ChannelHandlerContext ctx) throws Exception {
+            // NOOP
+        }
+
+        @Override
+        public void afterRemove(ChannelHandlerContext ctx) throws Exception {
+            // NOOP
+        }
+
+        @Override
+        public void bind(ChannelOutboundHandlerContext ctx,
+                SocketAddress localAddress, ChannelFuture future)
+                throws Exception {
+            unsafe.bind(localAddress, future);
+        }
+
+        @Override
+        public void connect(ChannelOutboundHandlerContext ctx,
+                SocketAddress remoteAddress, SocketAddress localAddress,
+                ChannelFuture future) throws Exception {
+            unsafe.connect(remoteAddress, localAddress, future);
+        }
+
+        @Override
+        public void disconnect(ChannelOutboundHandlerContext ctx,
+                ChannelFuture future) throws Exception {
+            unsafe.disconnect(future);
+        }
+
+        @Override
+        public void close(ChannelOutboundHandlerContext ctx,
+                ChannelFuture future) throws Exception {
+            unsafe.close(future);
+        }
+
+        @Override
+        public void deregister(ChannelOutboundHandlerContext ctx,
+                ChannelFuture future) throws Exception {
+            unsafe.deregister(future);
+        }
+
+        @Override
+        public void flush(ChannelOutboundHandlerContext ctx,
+                ChannelFuture future) throws Exception {
+            unsafe.flush(future);
+        }
+    }
 }