[编织消息框架][netty源码分析]5 EventLoopGroup 实现类NioEventLoopGroup职责与实现

分析NioEventLoopGroup最主有两个疑问

1.next work如何分配NioEventLoop

2.boss group 与child group 是如何协作运行的

从EventLoopGroup接口约定通过register方法从channel或promise转换成ChannelFuture对象

next方法就是用来分配NioEventLoop

public interface EventLoopGroup extends EventExecutorGroup {

    @Override
    EventLoop next();
    
    ChannelFuture register(Channel channel);
    ChannelFuture register(ChannelPromise promise);
    @Deprecated
    ChannelFuture register(Channel channel, ChannelPromise promise);
}

为了节省篇副，做了代码整理

1.NioEventLoopGroup构造时绑定SelectorProvider.provider()，通过newChild生成单个EventLoop

2.next实现是个环形循环

3.register方法是将channel转换成ChannelFuture

读者如果感兴趣可以在这几个方法打上断点看看

public class NioEventLoopGroup extends MultithreadEventLoopGroup {
    public NioEventLoopGroup(int nThreads, Executor executor) {
        this(nThreads, executor, SelectorProvider.provider());
    }
    @Override
    protected EventLoop newChild(Executor executor, Object... args) throws Exception {
        return new NioEventLoop(this, executor, (SelectorProvider) args[0],
            ((SelectStrategyFactory) args[1]).newSelectStrategy(), (RejectedExecutionHandler) args[2]);
    }
    /////////////////////////////GenericEventExecutorChooser实现next//////////////////////////////////
    @Override
    public EventExecutor next() {
        return executors[Math.abs(idx.getAndIncrement() % executors.length)];
    }
    
    /////////////////////////////SingleThreadEventLoop实现register//////////////////////////////////
 
    @Override
    public ChannelFuture register(Channel channel) {
        return register(new DefaultChannelPromise(channel, this));
    }

    @Override
    public ChannelFuture register(final ChannelPromise promise) {
        ObjectUtil.checkNotNull(promise, "promise");
        promise.channel().unsafe().register(this, promise);
        return promise;
    }
}

我们用过程的方式来模拟NioEventLoopGroup使用

如果读者有印象netty server 至少有两组NioEventLoopGroup 一个是boss 另一个是child

public class TestBossChildGroup {
    static SocketAddress address = new InetSocketAddress("localhost", 8877);

    @Test
    public void server() throws IOException {

        SelectorProvider bossProvider = SelectorProvider.provider();
        SelectorProvider childProvider = SelectorProvider.provider();

        int count = 2;
        AbstractSelector bossSelector = bossProvider.openSelector();
        AbstractSelector[] childSelectors = new AbstractSelector[count];
        for (int i = 0; i < count; i++) {
            childSelectors[i] = childProvider.openSelector();
        }

        //server绑定访问端口 并向Selector注册OP_ACCEPT
        ServerSocketChannel serverSocketChannel = bossProvider.openServerSocketChannel();
        serverSocketChannel.configureBlocking(false);
        serverSocketChannel.bind(address);
        serverSocketChannel.register(bossSelector, SelectionKey.OP_ACCEPT);  
        
        int i = 0;
        while (true) {
            int s = bossSelector.select(300);
            if (s > 0) {
            Set<SelectionKey> keys = bossSelector.selectedKeys();
            Iterator<SelectionKey> it = keys.iterator();
            while (it.hasNext()) {
                SelectionKey key = it.next();
                //为什么不用elseIf 因为 key interestOps 是多重叠状态，一次返回多个操作
                if (key.isAcceptable()) {
                System.out.println("isAcceptable");
                //这里比较巧妙，注册OP_READ交给别一个Selector处理
                key.channel().register(childSelectors[i++ % count], SelectionKey.OP_READ);
                }
                //这部分是child eventLoop处理
                if (key.isConnectable()) {
                System.out.println("isConnectable");
                }
                if (key.isWritable()) {
                System.out.println("isWritable");
                }
                if (key.isReadable()) {
                System.out.println("isReadable");
                }
                key.interestOps(~key.interestOps());
                it.remove();
            }
            }
        }
    }

    @Test
    public void client() throws IOException {
        SocketChannel clientSocketChannel = SelectorProvider.provider().openSocketChannel();
        clientSocketChannel.configureBlocking(true);
        clientSocketChannel.connect(address);
    }
}