聶永的博客

前言

因為能力有限，還是有很多東西（SO_REUSEADDR和SO_REUSEPORT的區別等）沒有能夠在一篇文字中表達清楚，作為補遺，也方便以后自己回過頭來復習。

SO_REUSADDR VS SO_REUSEPORT

兩者不是一碼事，沒有可比性。有時也會被其搞暈，自己總結的不好，推薦StackOverflow的Socket options SO_REUSEADDR and SO_REUSEPORT, how do they differ?資料，總結的很全面。

簡單來說：

• 設置了SO_REUSADDR的應用可以避免TCP 的 TIME_WAIT 狀態 時間過長無法復用端口，尤其表現在應用程序關閉-重啟交替的瞬間
• SO_REUSEPORT更強大，隸屬于同一個用戶（防止端口劫持）的多個進程/線程共享一個端口，同時在內核層面替上層應用做數據包進程/線程的處理均衡

若有困惑，推薦兩者都設置，不會有沖突。

Netty多線程使用SO_REUSEPORT

上一篇講到SO_REUSEPORT，多個程綁定同一個端口，可以根據需要控制進程的數量。這里講講基于Netty 4.0.25+Epoll navtie transport在單個進程內多個線程綁定同一個端口的情況，也是比較實用的。

TCP服務器，同一個進程多線程綁定同一個端口

這是一個PING-PONG示范應用：

     public void run() throws Exception {
            final EventLoopGroup bossGroup = new EpollEventLoopGroup();
            final EventLoopGroup workerGroup = new EpollEventLoopGroup();
            ServerBootstrap b = new ServerBootstrap();

           b.group(bossGroup, workerGroup)
                     .channel(EpollServerSocketChannel. class)
                     .childHandler( new ChannelInitializer<SocketChannel>() {
                            @Override
                            public void initChannel(SocketChannel ch) throws Exception {
                                ch.pipeline().addLast(
                                            new StringDecoder(CharsetUtil.UTF_8 ),
                                            new StringEncoder(CharsetUtil.UTF_8 ),
                                            new PingPongServerHandler());
                           }
                     }).option(ChannelOption. SO_REUSEADDR, true)
                     .option(EpollChannelOption. SO_REUSEPORT, true)
                     .childOption(ChannelOption. SO_KEEPALIVE, true);

            int workerThreads = Runtime.getRuntime().availableProcessors();
           ChannelFuture future;
            for ( int i = 0; i < workerThreads; ++i) {
                future = b.bind( port).await();
                 if (!future.isSuccess())
                      throw new Exception(String. format("fail to bind on port = %d.",
                                 port), future.cause());
           }
           Runtime. getRuntime().addShutdownHook (new Thread(){
                 @Override
                 public void run(){
                     workerGroup.shutdownGracefully();
                     bossGroup.shutdownGracefully();
                }
           });
     }

打成jar包，在CentOS 7下面運行，檢查同一個端口所打開的文件句柄。

# lsof -i:8000
COMMAND  PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
java    3515 root   42u  IPv6  29040      0t0  TCP *:irdmi (LISTEN)
java    3515 root   43u  IPv6  29087      0t0  TCP *:irdmi (LISTEN)
java    3515 root   44u  IPv6  29088      0t0  TCP *:irdmi (LISTEN)
java    3515 root   45u  IPv6  29089      0t0  TCP *:irdmi (LISTEN)

同一進程，但打開的文件句柄是不一樣的。

UDP服務器，多個線程綁同一個端口

/**
 * UDP諺語服務器，單進程多線程綁定同一端口示范
 */
public final class QuoteOfTheMomentServer {

       private static final int PORT = Integer.parseInt(System. getProperty("port" ,
                   "9000" ));

       public static void main(String[] args) throws Exception {
             final EventLoopGroup group = new EpollEventLoopGroup();

            Bootstrap b = new Bootstrap();
            b.group(group).channel(EpollDatagramChannel. class)
                        .option(EpollChannelOption. SO_REUSEPORT, true )
                        .handler( new QuoteOfTheMomentServerHandler());

             int workerThreads = Runtime.getRuntime().availableProcessors();
             for (int i = 0; i < workerThreads; ++i) {
                  ChannelFuture future = b.bind( PORT).await();
                   if (!future.isSuccess())
                         throw new Exception(String.format ("Fail to bind on port = %d.",
                                     PORT), future.cause());
            }

            Runtime. getRuntime().addShutdownHook(new Thread() {
                   @Override
                   public void run() {
                        group.shutdownGracefully();
                  }
            });
      }
}
}

@Sharable
class QuoteOfTheMomentServerHandler extends
            SimpleChannelInboundHandler<DatagramPacket> {

       private static final String[] quotes = {
                   "Where there is love there is life." ,
                   "First they ignore you, then they laugh at you, then they fight you, then you win.",
                   "Be the change you want to see in the world." ,
                   "The weak can never forgive. Forgiveness is the attribute of the strong.", };

       private static String nextQuote() {
             int quoteId = ThreadLocalRandom.current().nextInt( quotes .length );
             return quotes [quoteId];
      }

       @Override
       public void channelRead0(ChannelHandlerContext ctx, DatagramPacket packet)
                   throws Exception {
             if ("QOTM?" .equals(packet.content().toString(CharsetUtil. UTF_8))) {
                  ctx.write( new DatagramPacket(Unpooled.copiedBuffer( "QOTM: "
                              + nextQuote(), CharsetUtil. UTF_8), packet.sender()));
            }
      }

       @Override
       public void channelReadComplete(ChannelHandlerContext ctx) {
            ctx.flush();
      }

       @Override
       public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
            cause.printStackTrace();
      }
}

同樣也要檢測一下端口文件句柄打開情況：

# lsof -i:9000
COMMAND  PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
java    3181 root   26u  IPv6  27188      0t0  UDP *:cslistener
java    3181 root   27u  IPv6  27217      0t0  UDP *:cslistener
java    3181 root   28u  IPv6  27218      0t0  UDP *:cslistener
java    3181 root   29u  IPv6  27219      0t0  UDP *:cslistener

小結

以上為Netty+SO_REUSEPORT多線程綁定同一端口的一些情況，是為記載。