Netty源码分析系列--1.NioEventLoopGroup

Netty服务器开发模式

public class MyServer {

    public static void main(String[] args) throws InterruptedException {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        ServerBootstrap serverBootstrap = new ServerBootstrap();
        serverBootstrap.group(bossGroup, workerGroup)
                        .channel(NioServerSocketChannel.class)
                        .childHandler(new MyServerInitializer());

        ChannelFuture channelFuture = serverBootstrap.bind(8899).sync();
        channelFuture.channel().closeFuture().sync();

        bossGroup.shutdownGracefully();
        workerGroup.shutdownGracefully();
    }
}

• 创建两个事件循环组EventLoopGroup，即bossGroup和workerGroup。

• bossGroup接收事件后，转发给workerGroup。

NioEventLoopGroup

• 构造函数如下：bossGroup的线程数通常指定为1

public NioEventLoopGroup() {
    this(0);
}

//指定线程个数
public NioEventLoopGroup(int nThreads) {
    this(nThreads, (Executor) null);
}

• NioEventLoopGroup实现了 EventLoopGroup接口， EventLoopGroup文档说明：

  // 提供将Channel可以注册到EventLoopGroup中的若干方法
  public interface EventLoopGroup extends EventExecutorGroup {
      //返回下一个即将被使用的EventLoop
      @Override
      EventLoop next();
  
      //将Channel注册到EventLoop中，注册完成后，返回的ChannelFuture对象会得到通知
      ChannelFuture register(Channel channel);
  
      //传入的ChannelPromise对象在注册完成后也会得到通知
      ChannelFuture register(ChannelPromise promise);
  }
  

  ChannelPromise接口继承了ChannelFuture接口。

• 构造函数中的其他参数的默认值：

1. selectorProvider: SelectorProvider.provider()
2. selectStrategyFactory:DefaultSelectStrategyFactory.INSTANCE
3. rejectedExecutionHandler:RejectedExecutionHandlers.reject()

• NioEventLoopGroup的父类MultithreadEventLoopGroup:

  ​ 当传入的nThreads线程数为0时，会使用默认线程数字段DEFAULT_EVENT_LOOP_THREADS，它的计算逻辑如下：

  public abstract class MultithreadEventLoopGroup extends MultithreadEventExecutorGroup implements EventLoopGroup {
  
      private static final int DEFAULT_EVENT_LOOP_THREADS;
  
      static {
          DEFAULT_EVENT_LOOP_THREADS = Math.max(1, SystemPropertyUtil.getInt(
                  "io.netty.eventLoopThreads", NettyRuntime.availableProcessors() * 2));
      }
  
    
      protected MultithreadEventLoopGroup(int nThreads, Executor executor, Object... args) {
          super(nThreads == 0 ? DEFAULT_EVENT_LOOP_THREADS : nThreads, executor, args);
      }
  }