Upgrade netty to 4.0.23 enable epoll

Patch by tjake; reviewed by Jason Brown for CASSANDRA-7761

CHANGES.txt

@@ -1,4 +1,5 @@
 2.1.1
+ * Upgrade netty version and enable epoll event loop (CASSANDRA-7761)
  * Don't duplicate sstables smaller than split size when using
    the sstablesplitter tool (CASSANDRA-7616)
  * Avoid re-parsing already prepared statements (CASSANDRA-7923)

NEWS.txt

@@ -13,6 +13,15 @@ restore snapshots created with the previous major version using the
 'sstableloader' tool. You can upgrade the file format of your snapshots
 using the provided 'sstableupgrade' tool.
 
+2.1.1
+=====
+
+New features
+------------
+   - Netty support for epoll on linux is now enabled.  If for some
+     reason you want to disable it pass, the following system property
+     -Dcassandra.native.epoll.enabled=false
+
 2.1
 ===
 

build.xml

@@ -398,12 +398,12 @@
           <dependency groupId="com.addthis.metrics" artifactId="reporter-config" version="2.1.0" />
           <dependency groupId="org.mindrot" artifactId="jbcrypt" version="0.3m" />
           <dependency groupId="io.airlift" artifactId="airline" version="0.6" />
-          <dependency groupId="io.netty" artifactId="netty-all" version="4.0.20.Final" />
+          <dependency groupId="io.netty" artifactId="netty-all" version="4.0.23.Final" />
           <dependency groupId="com.google.code.findbugs" artifactId="jsr305" version="2.0.2" />
           <dependency groupId="com.clearspring.analytics" artifactId="stream" version="2.5.2" />
           <dependency groupId="com.datastax.cassandra" artifactId="cassandra-driver-core" version="2.0.5" />
           <dependency groupId="net.sf.supercsv" artifactId="super-csv" version="2.1.0" />
-	  <dependency groupId="net.ju-n.compile-command-annotations" artifactId="compile-command-annotations" version="1.2.0" />
+	      <dependency groupId="net.ju-n.compile-command-annotations" artifactId="compile-command-annotations" version="1.2.0" />
         </dependencyManagement>
         <developer id="alakshman" name="Avinash Lakshman"/>
         <developer id="aleksey" name="Aleksey Yeschenko"/>

src/java/org/apache/cassandra/transport/Server.java

@@ -29,6 +29,9 @@ import javax.net.ssl.SSLEngine;
 
 import io.netty.buffer.ByteBufAllocator;
 import io.netty.buffer.PooledByteBufAllocator;
+import io.netty.channel.epoll.Epoll;
+import io.netty.channel.epoll.EpollEventLoopGroup;
+import io.netty.channel.epoll.EpollServerSocketChannel;
 import io.netty.util.Version;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -61,6 +64,7 @@ public class Server implements CassandraDaemon.Server
     }
 
     private static final Logger logger = LoggerFactory.getLogger(Server.class);
+    private static final boolean enableEpoll = Boolean.valueOf(System.getProperty("cassandra.native.epoll.enabled", "true"));
 
     public static final int VERSION_3 = 3;
     public static final int CURRENT_VERSION = VERSION_3;
@@ -138,11 +142,23 @@ public class Server implements CassandraDaemon.Server
 
         // Configure the server.
         eventExecutorGroup = new RequestThreadPoolExecutor();
-        workerGroup = new NioEventLoopGroup();
+
+
+        boolean hasEpoll = enableEpoll ? Epoll.isAvailable() : false;
+        if (hasEpoll)
+        {
+            workerGroup = new EpollEventLoopGroup();
+            logger.info("Netty using native Epoll event loop");
+        }
+        else
+        {
+            workerGroup = new NioEventLoopGroup();
+            logger.info("Netty using Java NIO event loop");
+        }
 
         ServerBootstrap bootstrap = new ServerBootstrap()
                                     .group(workerGroup)
-                                    .channel(NioServerSocketChannel.class)
+                                    .channel(hasEpoll ? EpollServerSocketChannel.class : NioServerSocketChannel.class)
                                     .childOption(ChannelOption.TCP_NODELAY, true)
                                     .childOption(ChannelOption.SO_KEEPALIVE, DatabaseDescriptor.getRpcKeepAlive())
                                     .childOption(ChannelOption.ALLOCATOR, CBUtil.allocator)