private void bing(int port) {
    EventLoopGroup parentGroup = new NioEventLoopGroup(); 
    EventLoopGroup childGroup = new NioEventLoopGroup();
    try {
        ServerBootstrap b = new ServerBootstrap();
        b.group(parentGroup, childGroup)
                .channel(NioServerSocketChannel.class)    //非阻塞模式
                .option(ChannelOption.SO_BACKLOG, 128)
                .childHandler(new MyChannelInitializer());
        ChannelFuture f = b.bind(port).sync();
        System.out.println("itstack-demo-netty server start done. {关注公众号：bugstack虫洞栈，获取源码}");
        f.channel().closeFuture().sync();
    } catch (InterruptedException e) {
        e.printStackTrace();
    } finally {
        childGroup.shutdownGracefully();
        parentGroup.shutdownGracefully();
    }
}

/**
 * The {@link EventExecutorGroup} is responsible for providing the {@link EventExecutor}'s to use
 * via its {@link #next()} method. Besides this, it is also responsible for handling their
 * life-cycle and allows shutting them down in a global fashion.
 */
public interface EventExecutorGroup extends ScheduledExecutorService, Iterable<EventExecutor> {
    ...
    /**
     * Returns one of the {@link EventExecutor}s managed by this {@link EventExecutorGroup}.
     */
    EventExecutor next();
    ...
}

/**
 * Special {@link EventExecutorGroup} which allows registering {@link Channel}s that get
 * processed for later selection during the event loop.
 *
 */
public interface EventLoopGroup extends EventExecutorGroup {
    /**
     * Return the next {@link EventLoop} to use
     */
    @Override
    EventLoop next();
    /**
     * Register a {@link Channel} with this {@link EventLoop}. The returned {@link ChannelFuture}
     * will get notified once the registration was complete.
     */
    ChannelFuture register(Channel channel);
    /**
     * Register a {@link Channel} with this {@link EventLoop} using a {@link ChannelFuture}. The passed
     * {@link ChannelFuture} will get notified once the registration was complete and also will get returned.
     */
    ChannelFuture register(ChannelPromise promise);
    /**
     * Register a {@link Channel} with this {@link EventLoop}. The passed {@link ChannelFuture}
     * will get notified once the registration was complete and also will get returned.
     *
     * @deprecated Use {@link #register(ChannelPromise)} instead.
     */
    @Deprecated
    ChannelFuture register(Channel channel, ChannelPromise promise);
}

/**
 * {@link MultithreadEventLoopGroup} implementations which is used for NIO {@link Selector} based {@link Channel}s.
 */
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, (Executor) 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());
    }
    public NioEventLoopGroup(int nThreads, Executor executor) {
        this(nThreads, executor, 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) {
        this(nThreads, threadFactory, selectorProvider, DefaultSelectStrategyFactory.INSTANCE);
    }
    public NioEventLoopGroup(int nThreads, ThreadFactory threadFactory,
        final SelectorProvider selectorProvider, final SelectStrategyFactory selectStrategyFactory) {
        super(nThreads, threadFactory, selectorProvider, selectStrategyFactory, RejectedExecutionHandlers.reject());
    }
    public NioEventLoopGroup(
            int nThreads, Executor executor, final SelectorProvider selectorProvider) {
        this(nThreads, executor, selectorProvider, DefaultSelectStrategyFactory.INSTANCE);
    }
    public NioEventLoopGroup(int nThreads, Executor executor, final SelectorProvider selectorProvider,
                             final SelectStrategyFactory selectStrategyFactory) {
        super(nThreads, executor, selectorProvider, selectStrategyFactory, RejectedExecutionHandlers.reject());
    }
    public NioEventLoopGroup(int nThreads, Executor executor, EventExecutorChooserFactory chooserFactory,
                             final SelectorProvider selectorProvider,
                             final SelectStrategyFactory selectStrategyFactory) {
        super(nThreads, executor, chooserFactory, selectorProvider, selectStrategyFactory,
                RejectedExecutionHandlers.reject());
    }
    public NioEventLoopGroup(int nThreads, Executor executor, EventExecutorChooserFactory chooserFactory,
                             final SelectorProvider selectorProvider,
                             final SelectStrategyFactory selectStrategyFactory,
                             final RejectedExecutionHandler rejectedExecutionHandler) {
        super(nThreads, executor, chooserFactory, selectorProvider, selectStrategyFactory, rejectedExecutionHandler);
    }
    ...
}

public abstract class MultithreadEventLoopGroup extends MultithreadEventExecutorGroup implements EventLoopGroup {
private static final InternalLogger logger = InternalLoggerFactory.getInstance(MultithreadEventLoopGroup.class);
private static final int DEFAULT_EVENT_LOOP_THREADS;
static {
    DEFAULT_EVENT_LOOP_THREADS = Math.max(1, SystemPropertyUtil.getInt(
            "io.netty.eventLoopThreads", NettyRuntime.availableProcessors() * 2));
    if (logger.isDebugEnabled()) {
        logger.debug("-Dio.netty.eventLoopThreads: {}", DEFAULT_EVENT_LOOP_THREADS);
    }
}
...
}

EventLoopGroup parentGroup = new NioEventLoopGroup(1);  //单线程
EventLoopGroup parentGroup = new NioEventLoopGroup(4);  //多线程

if (executor == null) {
    executor = new ThreadPerTaskExecutor(newDefaultThreadFactory());
}

/**
* 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());
}

public static SelectorProvider provider() {
    synchronized (lock) {
        if (provider != null)
            return provider;
        return AccessController.doPrivileged(
            new PrivilegedAction<SelectorProvider>() {
                public SelectorProvider run() {
                        if (loadProviderFromProperty())
                            return provider;
                        if (loadProviderAsService())
                            return provider;
                        provider = sun.nio.ch.DefaultSelectorProvider.create();
                        return provider;
                    }
                });
    }
}

final class DefaultSelectStrategy implements SelectStrategy {
    static final SelectStrategy INSTANCE = new DefaultSelectStrategy();
    private DefaultSelectStrategy() { }
    @Override
    public int calculateStrategy(IntSupplier selectSupplier, boolean hasTasks) throws Exception {
        return hasTasks ? selectSupplier.get() : SelectStrategy.SELECT;
    }
}

private static final RejectedExecutionHandler REJECT = new RejectedExecutionHandler() {
    @Override
    public void rejected(Runnable task, SingleThreadEventExecutor executor) {
        throw new RejectedExecutionException();
    }
};

/**
 * Abstract base class for {@link EventExecutorGroup} implementations that handles their tasks with multiple threads at
 * the same time.
 */
public abstract class MultithreadEventExecutorGroup extends AbstractEventExecutorGroup {
    ...
    /**
     * Create a new instance.
     *
     * @param nThreads          the number of threads that will be used by this instance.
     * @param executor          the Executor to use, or {@code null} if the default should be used.
     * @param chooserFactory    the {@link EventExecutorChooserFactory} to use.
     * @param args              arguments which will passed to each {@link #newChild(Executor, Object...)} call
     */
    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];
        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<Object> terminationListener = new FutureListener<Object>() {
            @Override
            public void operationComplete(Future<Object> future) throws Exception {
                if (terminatedChildren.incrementAndGet() == children.length) {
                    terminationFuture.setSuccess(null);
                }
            }
        };
        for (EventExecutor e: children) {
            e.terminationFuture().addListener(terminationListener);
        }
        Set<EventExecutor> childrenSet = new LinkedHashSet<EventExecutor>(children.length);
        Collections.addAll(childrenSet, children);
        readonlyChildren = Collections.unmodifiableSet(childrenSet);
    }
    ...
}