netty学习记录

• NioEventLoopGroup

1. 线程数量默认为：处理器数量*2

        DEFAULT_EVENT_LOOP_THREADS = Math.max(1, SystemPropertyUtil.getInt(
                "io.netty.eventLoopThreads", NettyRuntime.availableProcessors() * 2));

• ChannelInboundHandlerAdapter

　　1.channelRead，msg正确处理

//方式一
public void channelRead(ChannelHandlerContext ctx, Object msg) {
    try {
        // Do something with msg
    } finally {
        ReferenceCountUtil.release(msg);
    }
}
//方式二
public void channelRead(ChannelHandlerContext ctx, Object msg) {　
    // Netty releases it for you when it is written out to the wire
    ctx.write(msg); // (1)
    ctx.flush(); // (2)
}

•  DefaultChannelGroup

1. 线程安全的channel集合，对channel提供多种操作
2. 广播一个消息到多个channels

    ChannelGroup recipients = new DefaultChannelGroup();
    recipients.add(channelA);
    recipients.add(channelB);
    //.. 
    recipients.write(ChannelBuffers.copiedBuffer(
            "Service will shut down for maintenance in 5 minutes.",
            CharsetUtil.UTF_8));

3. 简单关闭多个channels

    ChannelGroup allChannels = new DefaultChannelGroup();
    public static void main(String[] args) throws Exception {     
        ServerBootstrap b = new ServerBootstrap(..);
        //...
        // Start the server
        b.getPipeline().addLast("handler", new MyHandler());     
        Channel serverChannel = b.bind(..);     
        allChannels.add(serverChannel);
         
        //... Wait until the shutdown signal reception ...
        // Close the serverChannel and then all accepted connections.     
        allChannels.close().awaitUninterruptibly();
        b.releaseExternalResources();
    }
    public class MyHandler extends SimpleChannelUpstreamHandler {     
        @Override
        public void channelOpen(ChannelHandlerContext ctx, ChannelStateEvent e) {
            // Add all open channels to the global group so that they are
            // closed on shutdown.         
            allChannels.add(e.getChannel());
        }
    }

管理channels

    public void channelActive(ChannelHandlerContext ctx) throws Exception {
//        logger.debug("channelActive");
        NettyServer.ALL_CHANNELS.add(ctx.channel());
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
//        logger.debug("channelInactive");
        NettyServer.ALL_CHANNELS.remove(ctx.channel());
    }

• ChannelHandlerContext记录问题

1. 如果要在内存记下ctx，要注意记录的是哪一个

       protected void initChannel(SocketChannel ch) throws Exception {
           ChannelPipeline pipeline = ch.pipeline();
   
           // Add the message codec first,
           pipeline.addLast("decode", new NetDecodeHandler(serverManager.getConfig().baseProtocol));
           pipeline.addLast("encode", new NetEncodeHandler(serverManager.getConfig().baseProtocol));
   
           // and then business logic.
           pipeline.addLast("serverHandler", new NetServerHandler(serverManager));
           
           Glog.debug("NetServerInitializer:pipeline={}", pipeline);
   }

   假如在NetEncodeHandler中记录ctx，调用ctx.writeAndFlush将直接写入到pipeline中的headercontext，不会经过NetEncodeHandler处理。通常应该记录

   NetServerHandler中的ctx，这时候调用ctx.writeAndFlush将会经过

   NetEncodeHandler处理

   public class NetDecodeHandler extends ByteToMessageDecoder {
       private IProtocol baseProtocol;
   
       public NetDecodeHandler(IProtocol baseProtocol) {
           this.baseProtocol = baseProtocol;
       }
       
       @Override
       protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
           if(!in.isReadable() || in.readableBytes() < 4) {
               return;
           }
           while (in.readableBytes() >= 4) {
               in.markReaderIndex();
               int dataLength = in.readInt();
               if (in.readableBytes() < dataLength) {
                   in.resetReaderIndex();
                   return;
               }
               byte[] data = new byte[dataLength];
               in.readBytes(data);
               out.add(baseProtocol.decode(data));
           }
       }
   
   }