NioEventLoopGroup核心功能是管理多個NioEventLoop，似的channel均勻的注冊在多個NioEventLoop中，功能比較簡單，實現也比較簡單。

UML

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如上圖所示，NioEventLoopGroup基于netty的多線程框架實現，本文不相信介紹netty的多線程框架，所以不深入到其父類中。

NioEventLoopGroup自己的代碼非常簡單，如下:

public class NioEventLoopGroup extends MultithreadEventLoopGroup {

    /**
     * Create a new instance using the default number of threads, the default {@link ThreadFactory} and
     * the {@link SelectorProvider} which is returned by {@link SelectorProvider#provider()}.
     */
    public NioEventLoopGroup() {
        this(0);
    }

    /**
     * Create a new instance using the specified number of threads, {@link ThreadFactory} and the
     * {@link SelectorProvider} which is returned by {@link SelectorProvider#provider()}.
     */
    public NioEventLoopGroup(int nThreads) {
        this(nThreads, null);
    }

    /**
     * Create a new instance using the specified number of threads, the given {@link ThreadFactory} and the
     * {@link SelectorProvider} which is returned by {@link SelectorProvider#provider()}.
     */
    public NioEventLoopGroup(int nThreads, ThreadFactory threadFactory) {
        this(nThreads, threadFactory, SelectorProvider.provider());
    }

    /**
     * Create a new instance using the specified number of threads, the given {@link ThreadFactory} and the given
     * {@link SelectorProvider}.
     */
    public NioEventLoopGroup(
            int nThreads, ThreadFactory threadFactory, final SelectorProvider selectorProvider) {
        super(nThreads, threadFactory, selectorProvider);
    }

    /**
     * Sets the percentage of the desired amount of time spent for I/O in the child event loops.  The default value is
     * {@code 50}, which means the event loop will try to spend the same amount of time for I/O as for non-I/O tasks.
     */
    public void setIoRatio(int ioRatio) {
        for (EventExecutor e: children()) {
            ((NioEventLoop) e).setIoRatio(ioRatio);
        }
    }

    /**
     * Replaces the current {@link Selector}s of the child event loops with newly created {@link Selector}s to work
     * around the  infamous epoll 100% CPU bug.
     */
    public void rebuildSelectors() {
        for (EventExecutor e: children()) {
            ((NioEventLoop) e).rebuildSelector();
        }
    }

    @Override
    protected EventExecutor newChild(
            ThreadFactory threadFactory, Object... args) throws Exception {
        return new NioEventLoop(this, threadFactory, (SelectorProvider) args[0]);
    }
}

如上代碼所示，其都是一些初始化代碼和屬性設置方法，其核心方法應該是父類的next()方法，next()方法實現的功能是:每次選擇下一個ＮioEventLoop負責注冊channel和執行任務，達到所有的NioEventLoop負載均衡。