整体类图参照

1. thread确定

NioEventLoopGroup() 这样的话，默认是cpu的核数*2

public NioEventLoopGroup() {
     this(0);
}


// MultithreadEventLoopGroup类
// 看这里如果thread=0 则默认是DEFAULT_EVENT_LOOP_THREADS
protected MultithreadEventLoopGroup(int nThreads, Executor executor, Object... args) {
     super(nThreads == 0 ? DEFAULT_EVENT_LOOP_THREADS : nThreads, executor, args);
}



// MultithreadEventLoopGroup类
// 默认是cpu核数*2，当前也可以配置这个属性io.netty.eventLoopThreads
 /** cpu核数*2  比如4核=4*2=8 */
private static final int DEFAULT_EVENT_LOOP_THREADS;

    static {
        DEFAULT_EVENT_LOOP_THREADS = Math.max(1, SystemPropertyUtil.getInt(
                "io.netty.eventLoopThreads", NettyRuntime.availableProcessors() * 2)); //availableProcessors=cpu核数*2  比如4核=4*2=8

        if (logger.isDebugEnabled()) {
            logger.debug("-Dio.netty.eventLoopThreads: {}", DEFAULT_EVENT_LOOP_THREADS);
        }
}

创建线程池(Acceptor线程、IO线程)

protected MultithreadEventExecutorGroup(int nThreads, Executor executor,
                                            EventExecutorChooserFactory chooserFactory, Object... args) {
        if (nThreads <= 0) {
            throw new IllegalArgumentException(String.format("nThreads: %d (expected: > 0)", nThreads));
        }

        if (executor == null) {
            executor = new ThreadPerTaskExecutor(newDefaultThreadFactory());
        }
        // 某种线程集合 accetpor线程集合 、 io线程集合
        children = new EventExecutor[nThreads];

        for (int i = 0; i < nThreads; i ++) {
            boolean success = false;
            try {
                children[i] = newChild(executor, args); //创建对象为NioEventLoop
                success = true;
            } catch (Exception e) {
                // TODO: Think about if this is a good exception type
                throw new IllegalStateException("failed to create a child event loop", e);
            } finally {
                if (!success) { // 如果不成功，所有已经实例化的线程优雅关闭
                    for (int j = 0; j < i; j ++) {
                        children[j].shutdownGracefully();
                    }
                    // 确保已经实例化的线程终止
                    for (int j = 0; j < i; j ++) {
                        EventExecutor e = children[j];
                        try {
                            while (!e.isTerminated()) {
                                e.awaitTermination(Integer.MAX_VALUE, TimeUnit.SECONDS);
                            }
                        } catch (InterruptedException interrupted) {
                            // Let the caller handle the interruption.
                            Thread.currentThread().interrupt();
                            break;
                        }
                    }
                }
            }
        }

}

protected EventLoop newChild(Executor executor, Object... args) throws Exception {
        return new NioEventLoop(this, executor, (SelectorProvider) args[0],
            ((SelectStrategyFactory) args[1]).newSelectStrategy(), (RejectedExecutionHandler) args[2]);
    }