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netty--NioEventLoop滴干活

2024-07-09 23:08:59   222人阅读

netty是最近项目要用到的nio框架，找了各种资料，发现称赞它的有点多，所以决定用它：其实也就二选一嘛，mina或netty或自己写。对于mina，也不熟，不过看各种介绍，貌似netty干活还是很不错的，尤其是最新的4.x和5.x重构后，且使用结构清晰就先了解了解了。

首先要把应用跑起来啦（官网的例子比较多），我这是一个关于mqtt的一个例子：

 

 1 m_bossGroup = new NioEventLoopGroup(); 2         m_workerGroup = new NioEventLoopGroup(); 3          4         final NettyMQTTHandler handler = new NettyMQTTHandler(); 5         handler.setMessaging(messaging); 6  7         ServerBootstrap b = new ServerBootstrap(); 8             b.group(m_bossGroup, m_workerGroup) 9              .channel(NioServerSocketChannel.class) 10              .childHandler(new ChannelInitializer<SocketChannel>() { 11                  @Override12                  public void initChannel(SocketChannel ch) throws Exception {13                     ChannelPipeline pipeline = ch.pipeline();14                     //pipeline.addFirst("metrics", new BytesMetricsHandler(m_metricsCollector));15                     pipeline.addFirst("idleStateHandler", new IdleStateHandler(0, 0, Constants.DEFAULT_CONNECT_TIMEOUT));16                     pipeline.addAfter("idleStateHandler", "idleEventHandler", new MoquetteIdleTimoutHandler());17                     //pipeline.addLast("logger", new LoggingHandler("Netty", LogLevel.ERROR));18                     pipeline.addLast("decoder", new MQTTDecoder());19                     pipeline.addLast("encoder", new MQTTEncoder());20                     pipeline.addLast("metrics", new MessageMetricsHandler(m_metricsCollector));21                     pipeline.addLast("handler", handler);22                  }23              })24              .option(ChannelOption.SO_BACKLOG, 128)25              .option(ChannelOption.SO_REUSEADDR, true)26              .childOption(ChannelOption.SO_KEEPALIVE, true); 27         try {    28             // Bind and start to accept incoming connections.29             ChannelFuture f = b.bind(Constants.PORT);30             LOG.info("Server binded");31             f.sync();32         } catch (InterruptedException ex) {33             LOG.error(null, ex);34         }

再回想下，我们自己写serversocket的时候是怎么写的呢（这是一个笨拙的实例代码）：

    ServerSocket socket;        channel = ServerSocketChannel.open(); // 打开通道         socket = channel.socket(); //得到与通到相关的socket对象         socket.bind(new InetSocketAddress(port)); //将scoket榜定在制定的端口上         //配置通到使用非阻塞模式，在非阻塞模式下，可以编写多道程序同时避免使用复杂的多线程         channel.configureBlocking(false);        channel.register(selector, SelectionKey.OP_ACCEPT);        try {            while (true) {                this.selector.select();                Iterator<SelectionKey> iter = this.selector.selectedKeys().iterator();                while (iter.hasNext()) {                    SelectionKey key = iter.next();                    iter.remove();                    this.handleKey(key);                }            }        } catch (IOException ex) {            ex.printStackTrace();        }

原理还是那些，channel.open(),然后register key，然后遍历，再然后才进行handleKey()的干活。

那netty的写法为什么那么潇洒呢，怀着这个莫名的疑问，我先不管它的结构什么的，直接进行search，发现了这么个东东：

1   NioEventLoop(NioEventLoopGroup parent, ThreadFactory threadFactory, SelectorProvider selectorProvider) {2         super(parent, threadFactory, false);3         if (selectorProvider == null) {4             throw new NullPointerException("selectorProvider");5         }6         provider = selectorProvider;7         selector = openSelector();8     }

其中第8行从名称上来看，有点点意思了，往下看：

1  private Selector openSelector() {2         final Selector selector;3         try {4             selector = provider.openSelector();

其中的provider就是我们熟悉的:java.nio.channels.spi.SelectorProvider类。

所以这个就是做了selector.open的工作。

接下来能看到NioEventLoop：

1     protected void run() {2         for (;;) {3             oldWakenUp = wakenUp.getAndSet(false);4             try {5                 if (hasTasks()) {6                     selectNow();7                 } else {8                     select();

再继续看，该类中处理的selectedKey：

 1         final NioUnsafe unsafe = ch.unsafe(); 2         if (!k.isValid()) { 3             // close the channel if the key is not valid anymore 4             unsafe.close(unsafe.voidPromise()); 5             return; 6         } 7  8         try { 9             int readyOps = k.readyOps();10             if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {11                 unsafe.read();12                 if (!ch.isOpen()) {13                     // Connection already closed - no need to handle write.14                     return;15                 }16             }17             if ((readyOps & SelectionKey.OP_WRITE) != 0) {18                 // Call forceFlush which will also take care of clear the OP_WRITE once there is nothing left to write19                 ch.unsafe().forceFlush();20             }21             if ((readyOps & SelectionKey.OP_CONNECT) != 0) {22                 // remove OP_CONNECT as otherwise Selector.select(..) will always return without blocking23                 // See https://github.com/netty/netty/issues/92424                 int ops = k.interestOps();25                 ops &= ~SelectionKey.OP_CONNECT;26                 k.interestOps(ops);27 28                 unsafe.finishConnect();29             }30         } catch (CancelledKeyException e) {31             unsafe.close(unsafe.voidPromise());32         }33

现在明白了吧，其实netty也是走这么一套逻辑。

然后再网上看，逻辑是这样：

NioEventLoopGroup extends MultithreadEventExecutorGroup，其初始化了n个单线程的线程池(children = new SingleThreadEventExecutor[nThreads];)

每个单线程的对象child[i]=NioEventLoop对象，每个NioEventLoop有一个Selector字段。

其run方法是该group都需要干活的具体业务逻辑代码。

后续再加上别的类说明。


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