SO_REUSEPORT学习笔记补遗

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前言

因为能力有限，还是有很多东西（SO_REUSEADDR和SO_REUSEPORT的区别等）没有能够在一篇文字中表达清楚，作为补遗，也方便以后自己回过头来复习。

SO_REUSADDR VS SO_REUSEPORT

两者不是一码事，没有可比性。有时也会被其搞晕，自己总结的不好，推荐StackOverflow的Socket options SO_REUSEADDR and SO_REUSEPORT, how do they differ?资料，总结的很全面。

简单来说：

设置了SO_REUSADDR的应用可以避免TCP 的 TIME_WAIT 状态时间过长无法复用端口，尤其表现在应用程序关闭-重启交替的瞬间
SO_REUSEPORT更强大，隶属于同一个用户（防止端口劫持）的多个进程/线程共享一个端口，同时在内核层面替上层应用做数据包进程/线程的处理均衡

若有困惑，推荐两者都设置，不会有冲突。

Netty多线程使用SO_REUSEPORT

上一篇讲到SO_REUSEPORT，多个程绑定同一个端口，可以根据需要控制进程的数量。这里讲讲基于Netty 4.0.25+Epoll navtie transport在单个进程内多个线程绑定同一个端口的情况，也是比较实用的。

TCP服务器，同一个进程多线程绑定同一个端口

这是一个PING-PONG示范应用：

     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下面运行，检查同一个端口所打开的文件句柄。

# lsof -i:8000COMMAND  PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAMEjava    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)

同一进程，但打开的文件句柄是不一样的。

UDP服务器，多个线程绑同一个端口

/** * UDP谚语服务器，单进程多线程绑定同一端口示范 */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();                  }            });      }}}@Sharableclass 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();      }}

同样也要检测一下端口文件句柄打开情况：

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

小结

以上为Netty+SO_REUSEPORT多线程绑定同一端口的一些情况，是为记载。

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