* Removed a solved question from the comment

* Applied the same optimization applied to the TCP transport to the UDP transport

src/main/java/org/jboss/netty/channel/socket/nio/NioDatagramChannel.java

@@ -114,7 +114,8 @@ class NioDatagramChannel extends AbstractChannel
     /**
      * Boolean that indicates that write operation is in progress.
      */
-    volatile boolean inWriteNowLoop;
+    boolean inWriteNowLoop;
+    boolean writeSuspended;
 
     private volatile InetSocketAddress localAddress;
     volatile InetSocketAddress remoteAddress;
@@ -316,7 +317,7 @@ class NioDatagramChannel extends AbstractChannel
 
         public void run() {
             writeTaskInTaskQueue.set(false);
-            worker.write(NioDatagramChannel.this, false);
+            worker.writeFromTaskLoop(NioDatagramChannel.this);
         }
     }
 

src/main/java/org/jboss/netty/channel/socket/nio/NioDatagramPipelineSink.java

@@ -108,7 +108,7 @@ class NioDatagramPipelineSink extends AbstractChannelSink {
             final MessageEvent event = (MessageEvent) e;
             final boolean offered = channel.writeBufferQueue.offer(event);
             assert offered;
-            channel.worker.write(channel, true);
+            channel.worker.writeFromUserCode(channel);
         }
     }
 

src/main/java/org/jboss/netty/channel/socket/nio/NioDatagramWorker.java

@@ -350,7 +350,7 @@ class NioDatagramWorker implements Runnable {
                     }
                 }
                 if ((readyOps & SelectionKey.OP_WRITE) != 0) {
-                    write(k);
+                    writeFromSelectorLoop(k);
                 }
             } catch (CancelledKeyException e) {
                 close(k);
@@ -371,10 +371,6 @@ class NioDatagramWorker implements Runnable {
         return false;
     }
 
-    private void write(SelectionKey k) {
-        write((NioDatagramChannel) k.attachment(), false);
-    }
-
     /**
      * Read is called when a Selector has been notified that the underlying channel
      * was something to be read. The channel would previously have registered its interest
@@ -437,8 +433,7 @@ class NioDatagramWorker implements Runnable {
         close(ch, succeededFuture(ch));
     }
 
-    void write(final NioDatagramChannel channel,
-            final boolean mightNeedWakeup) {
+    void writeFromUserCode(final NioDatagramChannel channel) {
         /*
          * Note that we are not checking if the channel is connected. Connected
          * has a different meaning in UDP and means that the channels socket is
@@ -449,15 +444,33 @@ class NioDatagramWorker implements Runnable {
             return;
         }
 
-        if (mightNeedWakeup && scheduleWriteIfNecessary(channel)) {
+        if (scheduleWriteIfNecessary(channel)) {
+            return;
+        }
+
+        // From here, we are sure Thread.currentThread() == workerThread.
+
+        if (channel.writeSuspended) {
             return;
         }
 
         if (channel.inWriteNowLoop) {
-            scheduleWriteIfNecessary(channel);
-        } else {
-            writeNow(channel, channel.getConfig().getWriteSpinCount());
+            return;
         }
+
+        write0(channel);
+    }
+
+    void writeFromTaskLoop(final NioDatagramChannel ch) {
+        if (!ch.writeSuspended) {
+            write0(ch);
+        }
+    }
+
+    void writeFromSelectorLoop(final SelectionKey k) {
+        NioDatagramChannel ch = (NioDatagramChannel) k.attachment();
+        ch.writeSuspended = false;
+        write0(ch);
     }
 
     private boolean scheduleWriteIfNecessary(final NioDatagramChannel channel) {
@@ -481,15 +494,15 @@ class NioDatagramWorker implements Runnable {
         return false;
     }
 
-    private void writeNow(final NioDatagramChannel channel,
-            final int writeSpinCount) {
+    private void write0(final NioDatagramChannel channel) {
 
         boolean addOpWrite = false;
         boolean removeOpWrite = false;
 
         int writtenBytes = 0;
 
-        Queue<MessageEvent> writeBuffer = channel.writeBufferQueue;
+        final Queue<MessageEvent> writeBuffer = channel.writeBufferQueue;
+        final int writeSpinCount = channel.getConfig().getWriteSpinCount();
         synchronized (channel.writeLock) {
             // inform the channel that write is in-progress
             channel.inWriteNowLoop = true;
@@ -501,6 +514,7 @@ class NioDatagramWorker implements Runnable {
                 if (evt == null) {
                     if ((channel.currentWriteEvent = evt = writeBuffer.poll()) == null) {
                         removeOpWrite = true;
+                        channel.writeSuspended = false;
                         break;
                     }
 
@@ -553,6 +567,7 @@ class NioDatagramWorker implements Runnable {
                     } else {
                         // Not written at all - perhaps the kernel buffer is full.
                         addOpWrite = true;
+                        channel.writeSuspended = true;
                         break;
                     }
                 } catch (final AsynchronousCloseException e) {

src/main/java/org/jboss/netty/channel/socket/nio/NioWorker.java

@@ -386,7 +386,6 @@ class NioWorker implements Runnable {
         }
 
         if (channel.inWriteNowLoop) {
-            // Need to update the queue?
             return;
         }