03-EventLoop通过Provider模式实现Selector

// EventLoopGroup传递SelectorProvider提供者给EventLoop
public class NioEventLoopGroup implements EventExecutorGroup {
    ...
    public NioEventLoopGroup(int nThreads) {
        // SelectorProvider提供者
        this(nThreads, SelectorProvider.provider());
    }

    public NioEventLoopGroup(int nThreads, final SelectorProvider selectorProvider) {
        this(nThreads == 0 ? DEFAULT_EVENT_LOOP_THREADS : nThreads, selectorProvider, DefaultEventExecutorChooserFactory.INSTANCE);
    }
}

// selector的实现: provider.openSelector() 通过提供者返回适配的selector实现
public class NioEventLoop extends SingleThreadEventLoop {

    private Selector selector;
    private final SelectorProvider provider;
    
    public NioEventLoop(SelectorProvider selectorProvider) {
        this.provider = selectorProvider;
        this.selector = openSelector();
    }

    private Selector openSelector() {
        try {
            return provider.openSelector();
        } catch (IOException e) {
            throw new ChannelException("failed to open a new selector", e);
        }
    }
}