Netty服务器端启动流程分析

简介：上面一篇文章从宏观上介绍了netty各个组件之间的关系，会有一个大概的认识，这篇文章主要是从源码上来分析netty启动的过程。

这个是netty服务器启动的一段代码：

首先：创建了一个NioEventLoopGroup对象，我们先去看下这个对象主要的内容是什么

接下来在MultithreadEventLoopGroup中

从参数传递上来看，传入的是nThreads ==0

这段代码的意思就是，如果环境变量里面配置了io.netty.eventLoopThread这个属性，那么就拿这个配置的线程数来和1比较，两者之间比较大的，就是默认DEFAULT_EVENT_LOOP_THREADS 的值，否则的话，就去当前操作系统核心线程数*2 来作为这个数据的值。

继续往下进入，MultiThreadEventExectorGroup对象当中。

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());
    }

    children = new EventExecutor[nThreads]; //创建一个数组为n的NioEventLoop

    for (int i = 0; i < nThreads; i ++) {
        boolean success = false;
        try {
            children[i] = newChild(executor, args);
            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) {
                for (int j = 0; j < i; j ++) {
                    children[j].shutdownGracefully();
                }

                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;
                    }
                }
            }
        }
    }

    chooser = chooserFactory.newChooser(children);

    final FutureListener