NioServerSocketChannelFactory 是ChannelFactory的实现接口之一,负责创建并管理服务端Channel。
先来看下它的周边类图是怎样
下面针对核心的类做下讲解,然后就开始跟踪源码一步一步分析
NioServerSocketPipelineSink
接受和处理终端的下游ChannelEvent事件.
AbstractNioBossPool
处理socket accept、connect的工作线程池抽象类,提供了创建工作线程的模板方法newBoss
NioServerBossPool
继续自AbstractNioBossPool重写了newBoss方法创建Boss工作线程
AbstractNioSelector
它间接的实现了Runnable接口,负责执行内部的工作队列、处理Selector事件(抽象方法process)、关闭相关的Channel(抽象方法close)、关闭内部了Selector;值得注意的是这个类的register抽象方法,它的作用是将一个新的Channel注册到自身这个工作线程中完成Channel的绑定或连接工作,这个方法由sink调用。
NioServerBoss
继承自AbstractNioSelector,完成如下工作
1、把ServerSocketChannel绑定到SocketAddress并将Selector实例注册到ServerSocketChannel监听其SelectionKey.OP_ACCEPT事件(其内部类干的事RegisterTask)
2、处理OP_ACCEPT事件,将新Accpet的Channel注册到一个工作线程中去(workPool.nextWorker().register());(网络模型图中acceptor到subRecator的过程)
NioWorker
与NioServerBoss类似,继承自AbstractNioSelector,完成如下工作
1、处理OP_READ、OP_WRITE事件
2、将Selector实例注册到SocketChannel,并监听OP_READ、OP_WRITE事件(其内部类干的事RegisterTask)
下面是一段是简单的服务端代码,我们顺着代码中的关键类分析
public class ServerTest { private final ChannelFactory channelFactory = new NioServerSocketChannelFactory( Executors.newCachedThreadPool(), Executors.newCachedThreadPool()); private final ServerBootstrap bootstrap; public ServerTest() { this.bootstrap = new ServerBootstrap(channelFactory); this.bootstrap.setOption("child.tcpNoDelay", true); this.bootstrap.setOption("child.keepAlive", true); this.bootstrap.setPipelineFactory(new ChannelPipelineFactory() { @Override public ChannelPipeline getPipeline() throws Exception { ChannelPipeline pipeline=Channels.pipeline(); // pipeline.addFirst("encoder", new Encoder()); // pipeline.addFirst("decoder", new encoder()); // ... return pipeline; } }); } public void service(){ this.bootstrap.bind(new InetSocketAddress(9008)); } public static void main(String[] args){ new ServerTest().service(); } }NioServerSocketChannelFactory
这个类的代码非常简洁就4个实例变量和几个方法
private final WorkerPool<NioWorker> workerPool; private final NioServerSocketPipelineSink sink; private final BossPool<NioServerBoss> bossPool; private boolean releasePools;//标记当前ChannelFactory是否已还没有关闭或者说工作线程还没有被shutdown这个类有个BUG,在默认的构造方法中将releasePools置为true了,但是在其它构造方法中却没有,这意味着在它被关闭的时候可能无法释放某些扩展资源
public NioServerSocketChannelFactory() { this(Executors.newCachedThreadPool(), Executors.newCachedThreadPool()); releasePools = true; } public NioServerSocketChannelFactory( Executor bossExecutor, Executor workerExecutor) { this(bossExecutor, workerExecutor, getMaxThreads(workerExecutor));//调用此构造方法时,getMaxThreads控制着工作线程数小于等于CPU数*2 } public NioServerSocketChannelFactory( Executor bossExecutor, Executor workerExecutor, int workerCount) { this(bossExecutor, 1, workerExecutor, workerCount);//默认情况下boss线程的数量为1 } public NioServerSocketChannelFactory( Executor bossExecutor, int bossCount, Executor workerExecutor, int workerCount) { this(bossExecutor, bossCount, new NioWorkerPool(workerExecutor, workerCount)); } public NioServerSocketChannelFactory( Executor bossExecutor, WorkerPool<NioWorker> workerPool) { this(bossExecutor, 1 , workerPool); } public NioServerSocketChannelFactory( Executor bossExecutor, int bossCount, WorkerPool<NioWorker> workerPool) { this(new NioServerBossPool(bossExecutor, bossCount, null), workerPool); } public NioServerSocketChannelFactory(BossPool<NioServerBoss> bossPool, WorkerPool<NioWorker> workerPool) { if (bossPool == null) { throw new NullPointerException("bossExecutor"); } if (workerPool == null) { throw new NullPointerException("workerPool"); } this.bossPool = bossPool; this.workerPool = workerPool; sink = new NioServerSocketPipelineSink(); } public ServerSocketChannel newChannel(ChannelPipeline pipeline) { return new NioServerSocketChannel(this, pipeline, sink, bossPool.nextBoss(), workerPool);//注意nextBoss方法,它选择一个工作线程来处理ServerSocketChannel的读写事件 }这个类主要依赖于这4个类的实例NioWorkerPool、NioServerBossPool、NioServerSocketPipelineSink、NioServerSocketChannel,关于它们的作用前面已经有说明了,在此不讲了。先来看下NioWorkerPool吧。
NioWorkerPool这个类也很简单,其内部主要维护了一个线程数组,它继承自AbstractNioWorkerPool并重写了createWorker方法
protected NioWorker createWorker(Executor executor) { return new NioWorker(executor, determiner); }再来看下它的父类AbstractNioWorkerPool
这个类也非常简单,它只做2件事——负载均衡和工作线程的创建
public abstract class AbstractNioWorkerPool<E extends AbstractNioWorker> implements WorkerPool<E>, ExternalResourceReleasable { private final AbstractNioWorker[] workers; private final AtomicInteger workerIndex = new AtomicInteger(); private final Executor workerExecutor; private volatile boolean initDone; //此处省略了部分代码 AbstractNioWorkerPool(Executor workerExecutor, int workerCount, boolean autoInit) { if (workerExecutor == null) { throw new NullPointerException("workerExecutor"); } if (workerCount <= 0) { throw new IllegalArgumentException( "workerCount (" + workerCount + ") " + "must be a positive integer."); } workers = new AbstractNioWorker[workerCount]; this.workerExecutor = workerExecutor; if (autoInit) { init(); } } protected void init() { if (initDone) { throw new IllegalStateException("Init was done before"); } initDone = true; for (int i = 0; i < workers.length; i++) { workers[i] = newWorker(workerExecutor); } protected E newWorker(Executor executor) { return createWorker(executor);//调用抽象方法,把具体的工作线程交由子类完成 } public E nextWorker() { return (E) workers[Math.abs(workerIndex.getAndIncrement() % workers.length)];//负载均衡 }下面来具体的工作线程NioWorker
NioWorker继承自AbstractNioWorker,AbstractNioWorker继承自AbstractNioSelector,还是先从最顶层父类AbstractNioSelector看起吧
AbstractNioSelector实现了NioSelector接口,而NioSelector接口继承自Runnable接口AbstractNioSelector实现run方法,Netty把这个线程叫做IO线程
AbstractNioSelector类的构造方法会调用openSelector方法来创建一个Selector,并执行当前线程(这段代码很简单,我们就跳过直接看run方法了)
public void run() { thread = Thread.currentThread();//将当前线程保存起来,用来区分调用该类其它某些方法的线程是否为IO线程,请参看它的isIoThread方法。其它线程会调用此方法来区分自己是不是IO线程,如果是,则直接调用此类的方法完成,否则把相关的操作添加到IO线程的工作队列中。这样做的好处是,避免IO线程与其它线程的同步操作,带来了效率的提升。 int selectReturnsImmediately = 0; Selector selector = this.selector; if (selector == null) { return; } // use 80% of the timeout for measure final long minSelectTimeout = SelectorUtil.SELECT_TIMEOUT_NANOS * 80 / 100; boolean wakenupFromLoop = false; for (;;) { wakenUp.set(false); try { long beforeSelect = System.nanoTime(); int selected = select(selector); if (SelectorUtil.EPOLL_BUG_WORKAROUND && selected == 0 && !wakenupFromLoop && !wakenUp.get()) {//看代码中的解释说jdk的epoll可能存在BUG,这个if用来处理这类错误的.看下面的代码冒似是说Channel被关闭后没有从Selector中移除相关的键而导致过多的垃圾键,当这类键超过1024个时,Selector将被重键. long timeBlocked = System.nanoTime() - beforeSelect; if (timeBlocked < minSelectTimeout) { boolean notConnected = false; for (SelectionKey key: selector.keys()) { SelectableChannel ch = key.channel(); try { if (ch instanceof DatagramChannel && !((DatagramChannel) ch).isConnected() || ch instanceof SocketChannel && !((SocketChannel) ch).isConnected()) { notConnected = true; key.cancel(); } } catch (CancelledKeyException e) { } } if (notConnected) { selectReturnsImmediately = 0; } else { selectReturnsImmediately ++; } } else { selectReturnsImmediately = 0; } if (selectReturnsImmediately == 1024) { rebuildSelector(); selector = this.selector; selectReturnsImmediately = 0; wakenupFromLoop = false; continue; } } else { selectReturnsImmediately = 0; } //代码中这里的解释很清楚,请看代码 if (wakenUp.get()) { wakenupFromLoop = true; selector.wakeup(); } else { wakenupFromLoop = false; } cancelledKeys = 0; processTaskQueue();//执行队列中的任务 selector = this.selector; //因为rebuildSelector()方法是一个公共的方法,也许在上一步的processTaskQueue方法中这个方法被调了 if (shutdown) {//如果当前IO线程标记为关闭,则执行关闭逻辑 this.selector = null; processTaskQueue();//处理任务队列 for (SelectionKey k: selector.keys()) { close(k);//关闭相关的Channel,这里会执行Pipeline的Upstream直到sink中才关闭Channel } try { selector.close(); } catch (IOException e) { logger.warn( "Failed to close a selector.", e); } shutdownLatch.countDown();//shutdown方法必需等待相关的释放操作完成才能返回,此处唤醒调用shutdown方法的线程 break;//工作线程退出 } else { process(selector);//执行process抽象方法,SelectionKey的处理行为交给子类去完成 } } catch (Throwable t) { logger.warn( "Unexpected exception in the selector loop.", t); // Prevent possible consecutive immediate failures that lead to // excessive CPU consumption. try { Thread.sleep(1000); } catch (InterruptedException e) { } } } }这个类还有两个方法值得解释一下,看完这两个方法再看process方法
//这个方法在Boss线程中被调用在Channel被bind到本地端口(Server)或成功连接到服务器(Client端)的时候被调用 public void register(Channel channel, ChannelFuture future) { Runnable task = createRegisterTask(channel, future);//具体的注册操作交由子类去完成,透露一下 这个task面会有socketChannel.register方法的调用 registerTask(task); } protected final void registerTask(Runnable task) { taskQueue.add(task); Selector selector = this.selector; if (selector != null) { if (wakenUp.compareAndSet(false, true)) {//唤醒IO线程,这个CAS操作是防止Selector被过早的唤醒的情况下导致信号丢失.请参看AbstractNioSelector类源码282行上面的解释 selector.wakeup(); } } else { if (taskQueue.remove(task)) { // the selector was null this means the Worker has already been shutdown. throw new RejectedExecutionException("Worker has already been shutdown"); } } }子类AbstractNioWorker重写了process方法来处理SelectionKey
protected void process(Selector selector) throws IOException { Set<SelectionKey> selectedKeys = selector.selectedKeys(); if (selectedKeys.isEmpty()) { return; } for (Iterator<SelectionKey> i = selectedKeys.iterator(); i.hasNext();) { SelectionKey k = i.next(); i.remove(); try { int readyOps = k.readyOps(); if ((readyOps & SelectionKey.OP_READ) != 0 || readyOps == 0) { if (!read(k)) {//调用抽象方法读取数据,如果此方法返回false则表示连接已经被关闭,无需再做处理 continue; } } if ((readyOps & SelectionKey.OP_WRITE) != 0) { writeFromSelectorLoop(k);//如果该Selector中触发了写事件则写出数据。用户代码调用channel.write(obj)方法后数据并不是马上被写出,而是被提交Channel的writeBufferQueue队列中(sink放的)等待IO线程去完成写出,写操作实际上是由write0这个方法完成的. } } catch (CancelledKeyException e) { close(k);//出形异常关闭Channel并释放相关资源 } if (cleanUpCancelledKeys()) { break; // break the loop to avoid ConcurrentModificationException } } }先看该类的其它几个重要的方法再看NioWorker类的方法
/** * 这个方法是由sink调用的,sink将要写出的数据offer到writeBufferQueue中然后调用该方法(上面解释process方法中有提到) */ void writeFromUserCode(final AbstractNioChannel<?> channel) { if (!channel.isConnected()) { //如果Channel已经关闭则没必要继续写了 cleanUpWriteBuffer(channel); return; } if (scheduleWriteIfNecessary(channel)) { //这是个抽象方法,实现在NioWorker类中,这个方法中判断当前线程是否为IO线程,如果是则返回false,否则向IO线程的 任务队列添加一个写出任务并返回true return; } //到这里,就能确定当前线程是否是IO线程 if (channel.writeSuspended) {//如果写出通道被挂起,则返回 return; } if (channel.inWriteNowLoop) {//当前正在写数据,则返回 return; } write0(channel);//写出数据 } protected void write0(AbstractNioChannel<?> channel) { boolean open = true;//标记channel是否处理打开状态 boolean addOpWrite = false;//是否向此Channel关联的SelectionKey的interestOps添加SelectionKey.OP_WRITE,这会导致前面的process方法中这句代码“if ((readyOps & SelectionKey.OP_WRITE) != 0) ”返回true,然后再次触发写操作 boolean removeOpWrite = false;//与上面对应 boolean iothread = isIoThread(channel);//当前线程是否是该Channel的工作线程 long writtenBytes = 0; final SocketSendBufferPool sendBufferPool = this.sendBufferPool; final WritableByteChannel ch = channel.channel; final Queue<MessageEvent> writeBuffer = channel.writeBufferQueue; final int writeSpinCount = channel.getConfig().getWriteSpinCount();//最多尝试写的次数 List<Throwable> causes = null; synchronized (channel.writeLock) { channel.inWriteNowLoop = true;//上面提到过这个writeFromUserCode方法 for (;;) { MessageEvent evt = channel.currentWriteEvent; SendBuffer buf = null; ChannelFuture future = null; try { if (evt == null) { if ((channel.currentWriteEvent = evt = writeBuffer.poll()) == null) { //如果没有要写的东西,则打个标记,在后面向此Channel关联的SelectionKey的interestOps移除SelectionKey.OP_WRITE removeOpWrite = true; channel.writeSuspended = false; break; } future = evt.getFuture(); channel.currentWriteBuffer = buf = sendBufferPool.acquire(evt.getMessage()); } else { future = evt.getFuture(); buf = channel.currentWriteBuffer; } long localWrittenBytes = 0; //下面的代码尝试发送数据,直到有数据被写出,否则尽可能的尝试 for (int i = writeSpinCount; i > 0; i --) { localWrittenBytes = buf.transferTo(ch); if (localWrittenBytes != 0) { writtenBytes += localWrittenBytes; break; } if (buf.finished()) { break; } } if (buf.finished()) { //如果当前消息已经写完了释放资源,并准备下一条消息的写出 buf.release(); channel.currentWriteEvent = null; channel.currentWriteBuffer = null; // Mark the event object for garbage collection. //noinspection UnusedAssignment evt = null; buf = null; future.setSuccess(); } else { //没有全部写完,则打上addOpWrite标记,并设置写出进度 addOpWrite = true; channel.writeSuspended = true; if (localWrittenBytes > 0) { // Notify progress listeners if necessary. future.setProgress( localWrittenBytes, buf.writtenBytes(), buf.totalBytes()); } break; } } catch (AsynchronousCloseException e) { // Doesn't need a user attention - ignore. } catch (Throwable t) { if (buf != null) { buf.release(); } channel.currentWriteEvent = null; channel.currentWriteBuffer = null; // Mark the event object for garbage collection. //noinspection UnusedAssignment buf = null; //noinspection UnusedAssignment evt = null; if (future != null) { future.setFailure(t);//通知消息写出失败 } if (iothread) { // An exception was thrown from within a write in the iothread. We store a reference to it // in a list for now and notify the handlers in the chain after the writeLock was released // to prevent possible deadlock. // See #1310 //如果异常在IO线程中被抛出,则存储它的一个引用,待锁释放后触发pipeline的UpStream以防止死锁 if (causes == null) { causes = new ArrayList<Throwable>(1); } causes.add(t); } else { fireExceptionCaughtLater(channel, t); } if (t instanceof IOException) { // close must be handled from outside the write lock to fix a possible deadlock // which can happen when MemoryAwareThreadPoolExecutor is used and the limit is exceed // and a close is triggered while the lock is hold. This is because the close(..) // may try to submit a task to handle it via the ExecutorHandler which then deadlocks. // See #1310 open = false; } } } channel.inWriteNowLoop = false; // Initially, the following block was executed after releasing // the writeLock, but there was a race condition, and it has to be // executed before releasing the writeLock: // // https://issues.jboss.org/browse/NETTY-410 // //这个issues是说 之前下面这段代码是被放到同步段之外的,导致未完全写完的数据丢失的问题,所以移到同步块里面来了。 if (open) { if (addOpWrite) { setOpWrite(channel); } else if (removeOpWrite) { clearOpWrite(channel); } } } if (causes != null) { for (Throwable cause: causes) { // notify about cause now as it was triggered in the write loop fireExceptionCaught(channel, cause); } } if (!open) { // close the channel now close(channel, succeededFuture(channel)); } if (iothread) { fireWriteComplete(channel, writtenBytes); } else { fireWriteCompleteLater(channel, writtenBytes); } }AbstractNioSelector类把IO线程的构架搭起来, AbstractNioWorker类实现了数据的写出逻辑,只留下变化的部分交给子类去完成。现在来看来NioWorker类的几个比较重要的方法
protected boolean read(SelectionKey k) { final SocketChannel ch = (SocketChannel) k.channel(); final NioSocketChannel channel = (NioSocketChannel) k.attachment(); //获取缓存大小分配策略,Netty中缓存分配策略有2种,一种是自动扩展的缓存分配策略,另一种是固定大小的缓存分配策略。自动扩展的缓存分配策略内部维护了一个缓存大小的int数组,数组中的值分段按一定数量递增 final ReceiveBufferSizePredictor predictor = channel.getConfig().getReceiveBufferSizePredictor(); final int predictedRecvBufSize = predictor.nextReceiveBufferSize();//获取下一个接收缓冲区大小 final ChannelBufferFactory bufferFactory = channel.getConfig().getBufferFactory(); int ret = 0; int readBytes = 0; boolean failure = true; ByteBuffer bb = recvBufferPool.get(predictedRecvBufSize).order(bufferFactory.getDefaultOrder());//recvBufferPool目的是为了缓存重用 try { //读取Channel中的数据,直到缓冲区满或没有可读的字节 while ((ret = ch.read(bb)) > 0) { readBytes += ret; if (!bb.hasRemaining()) { break; } } failure = false; } catch (ClosedChannelException e) { // Can happen, and does not need a user attention. } catch (Throwable t) { fireExceptionCaught(channel, t); } if (readBytes > 0) { bb.flip(); final ChannelBuffer buffer = bufferFactory.getBuffer(readBytes); buffer.setBytes(0, bb); buffer.writerIndex(readBytes); //向缓存分配策略报告当前读到的缓存大小,以预计算下一次的缓存大小 predictor.previousReceiveBufferSize(readBytes); // 触发MessageReceive UpStream fireMessageReceived(channel, buffer); } if (ret < 0 || failure) {//如果代码执行到这,则表示此Channel不可用 k.cancel(); // Some JDK implementations run into an infinite loop without this. close(channel, succeededFuture(channel)); return false; } return true; } //这个方法实现父类的抽象方法,返回Channel注册到IO线程的Task.这个方法一定是在Boss线程中被调用的,当boss线程接收到新的连接或一条新的连接与服务端建立,则调用这个方法,这个方法创建的Task完成将Channel注册到工作线程的Selector上 protected Runnable createRegisterTask(Channel channel, ChannelFuture future) { boolean server = !(channel instanceof NioClientSocketChannel); return new RegisterTask((NioSocketChannel) channel, future, server); } private final class RegisterTask implements Runnable { private final NioSocketChannel channel; private final ChannelFuture future; private final boolean server; RegisterTask( NioSocketChannel channel, ChannelFuture future, boolean server) { this.channel = channel; this.future = future; this.server = server; } public void run() { SocketAddress localAddress = channel.getLocalAddress(); SocketAddress remoteAddress = channel.getRemoteAddress(); if (localAddress == null || remoteAddress == null) { if (future != null) { future.setFailure(new ClosedChannelException()); } close(channel, succeededFuture(channel)); return; } try { if (server) { channel.channel.configureBlocking(false); } channel.channel.register( selector, channel.getRawInterestOps(), channel);//注册感兴趣的事件(OP_READ),在write0方法中会添加或移除OP_WRITE(请参看上面的write0方法) if (future != null) { channel.setConnected(); future.setSuccess(); } if (server || !((NioClientSocketChannel) channel).boundManually) {//触发BOUND事件 fireChannelBound(channel, localAddress); } //触发Connected事件 fireChannelConnected(channel, remoteAddress); } catch (IOException e) { if (future != null) { future.setFailure(e); } close(channel, succeededFuture(channel)); if (!(e instanceof ClosedChannelException)) { throw new ChannelException( "Failed to register a socket to the selector.", e); } } } }到这里为止, NioWorker工作线程(IO线程)核心路径已经基本分析完毕,现在来看NioWorker它主要是做下面这两件事。
1、执行内部工作队列中的任务
2、处理SelectionKey的读写事件
我们知道如果Selector不被注册到java.nio.channels.SelectableChannel上,它是没有任何作用的。那什么时候将被注册到SelectableChannel上呢(上面提到过RegisterTask的职责)?Boss线程,我们来看下NioServerBoss这个类
NioServerBoss
该类继承自AbstractNioSelector类并且实现了process抽象方法处理SelectionKey关于AbstractNioSelector类前面已经提过了,process方法
protected void process(Selector selector) { Set<SelectionKey> selectedKeys = selector.selectedKeys(); if (selectedKeys.isEmpty()) { return; } for (Iterator<SelectionKey> i = selectedKeys.iterator(); i.hasNext();) { SelectionKey k = i.next(); i.remove(); NioServerSocketChannel channel = (NioServerSocketChannel) k.attachment(); try { for (;;) { //获取新连接到服务端的的SocketChannel SocketChannel acceptedSocket = channel.socket.accept(); if (acceptedSocket == null) { break; } //取出Channel,并注册到IO线程 registerAcceptedChannel(channel, acceptedSocket, thread); } } catch (CancelledKeyException e) { // Raised by accept() when the server socket was closed. k.cancel(); channel.close(); } catch (SocketTimeoutException e) { // Thrown every second to get ClosedChannelException // raised. } catch (ClosedChannelException e) { // Closed as requested. } catch (Throwable t) { if (logger.isWarnEnabled()) { logger.warn( "Failed to accept a connection.", t); } try { //避免在出现异常的情况下,无线循环导致cpu资源浪费 Thread.sleep(1000); } catch (InterruptedException e1) { // Ignore } } } } private static void registerAcceptedChannel(NioServerSocketChannel parent, SocketChannel acceptedSocket, Thread currentThread) { try { ChannelSink sink = parent.getPipeline().getSink(); ChannelPipeline pipeline = parent.getConfig().getPipelineFactory().getPipeline(); NioWorker worker = parent.workerPool.nextWorker();//获取一个工作线程 //NioWorker类的register方法完成注册,之前说过的 worker.register(new NioAcceptedSocketChannel( parent.getFactory(), pipeline, parent, sink , acceptedSocket, worker, currentThread), null); } catch (Exception e) { if (logger.isWarnEnabled()) { logger.warn( "Failed to initialize an accepted socket.", e); } try { acceptedSocket.close(); } catch (IOException e2) { if (logger.isWarnEnabled()) { logger.warn( "Failed to close a partially accepted socket.", e2); } } } }该类同样也有实现了父类的createRegisterTask方法来创建并返回一个Task,这个Task负责监听客户端连接Channel,并把Channel注册到IO线程上.在后面讲的NioServerSocketPipelineSink类会调用执行到这个方法
void bind(final NioServerSocketChannel channel, final ChannelFuture future, final SocketAddress localAddress) { registerTask(new RegisterTask(channel, future, localAddress));//这里会调父类的registerTask方法,父类的这个方法是个模板方法,具体bind任务的创建会调用该类的createRegisterTask方法 } protected Runnable createRegisterTask(Channel channel, ChannelFuture future) { return new RegisterTask((NioServerSocketChannel) channel, future, null); } private final class RegisterTask implements Runnable { private final NioServerSocketChannel channel; private final ChannelFuture future; private final SocketAddress localAddress; public RegisterTask(final NioServerSocketChannel channel, final ChannelFuture future, final SocketAddress localAddress) { this.channel = channel; this.future = future; this.localAddress = localAddress; } public void run() { boolean bound = false; boolean registered = false; try { channel.socket.socket().bind(localAddress, channel.getConfig().getBacklog());//绑定到本地 bound = true; future.setSuccess(); fireChannelBound(channel, channel.getLocalAddress()); channel.socket.register(selector, SelectionKey.OP_ACCEPT, channel);//将此IO线程的Selector注册到该ServerSocketChannel上 registered = true; } catch (Throwable t) { future.setFailure(t); fireExceptionCaught(channel, t); } finally { if (!registered && bound) { close(channel, future); } } } }现在知道IO线程(NioWorker)的Selector在什么时候被注册到SelectableChannel上了,那Boss线程的Selector是什么时候被注册到SelectableChannel呢?ServerBootstrap的bind方法。
public Channel bind(final SocketAddress localAddress) { ChannelFuture future = bindAsync(localAddress); // 等待完成 future.awaitUninterruptibly(); if (!future.isSuccess()) { future.getChannel().close().awaitUninterruptibly(); throw new ChannelException("Failed to bind to: " + localAddress, future.getCause()); } return future.getChannel(); } public ChannelFuture bindAsync(final SocketAddress localAddress) { if (localAddress == null) { throw new NullPointerException("localAddress"); } Binder binder = new Binder(localAddress); ChannelHandler parentHandler = getParentHandler(); ChannelPipeline bossPipeline = pipeline(); bossPipeline.addLast("binder", binder);//注意这个 if (parentHandler != null) { bossPipeline.addLast("userHandler", parentHandler); } //newChannel实际上是调用的NioServerSocketChannelFactory.newChannel方法new NioServerSocketChannel,NioServerSocketChannel构造方法创建完ServerSocketChannel后会触发UpStream(ChannelState.OPEN事件)这个事件被ServerBootstrap类的内部类Binder处理并完成Selector与Channel的注册操作 Channel channel = getFactory().newChannel(bossPipeline); final ChannelFuture bfuture = new DefaultChannelFuture(channel, false); binder.bindFuture.addListener(new ChannelFutureListener() { public void operationComplete(ChannelFuture future) throws Exception { if (future.isSuccess()) { bfuture.setSuccess(); } else { // Call close on bind failure bfuture.getChannel().close(); bfuture.setFailure(future.getCause()); } } }); return bfuture; } private final class Binder extends SimpleChannelUpstreamHandler { private final SocketAddress localAddress; private final Map<String, Object> childOptions = new HashMap<String, Object>(); private final DefaultChannelFuture bindFuture = new DefaultChannelFuture(null, false); Binder(SocketAddress localAddress) { this.localAddress = localAddress; } @Override public void channelOpen( ChannelHandlerContext ctx, ChannelStateEvent evt) { try { evt.getChannel().getConfig().setPipelineFactory(getPipelineFactory()); // Split options into two categories: parent and child. Map<String, Object> allOptions = getOptions(); Map<String, Object> parentOptions = new HashMap<String, Object>(); for (Entry<String, Object> e: allOptions.entrySet()) { if (e.getKey().startsWith("child.")) { childOptions.put( e.getKey().substring(6), e.getValue()); } else if (!"pipelineFactory".equals(e.getKey())) { parentOptions.put(e.getKey(), e.getValue()); } } // Apply parent options. evt.getChannel().getConfig().setOptions(parentOptions); } finally { ctx.sendUpstream(evt); } //这里将NioServerSocketChannel绑定到本地端口,并触发Downstream(ChannelState.BOUND)事件,最终被传递sin处理(NioServerSocketPipelineSink) evt.getChannel().bind(localAddress).addListener(new ChannelFutureListener() { public void operationComplete(ChannelFuture future) throws Exception { if (future.isSuccess()) { bindFuture.setSuccess(); } else { bindFuture.setFailure(future.getCause()); } } }); }
NioServerSocketPipelineSink类用来处理最底层的事件。
class NioServerSocketPipelineSink extends AbstractNioChannelSink { public void eventSunk( ChannelPipeline pipeline, ChannelEvent e) throws Exception { Channel channel = e.getChannel(); if (channel instanceof NioServerSocketChannel) { handleServerSocket(e);//处理服务端Channel } else if (channel instanceof NioSocketChannel) { handleAcceptedSocket(e);//处理客户端Channel } } private static void handleServerSocket(ChannelEvent e) { if (!(e instanceof ChannelStateEvent)) { return; } ChannelStateEvent event = (ChannelStateEvent) e; NioServerSocketChannel channel = (NioServerSocketChannel) event.getChannel(); ChannelFuture future = event.getFuture(); ChannelState state = event.getState(); Object value = event.getValue(); switch (state) { case OPEN://根据一个值标记是Open还是Close,其它case也是这样 if (Boolean.FALSE.equals(value)) { ((NioServerBoss) channel.boss).close(channel, future); } break; case BOUND: if (value != null) {//在ServerBootStraup内部类Binder中触发BOUND事件,传递此value的值为localAddress,所以进入这个if调用boss的bind方法(NioServerBoss类的)完成地址绑定与OP_ACCEPT的注册,请参见上面讲NioServerBoss中的bind方法 ((NioServerBoss) channel.boss).bind(channel, future, (SocketAddress) value); } else { ((NioServerBoss) channel.boss).close(channel, future); } break; default: break; } } private static void handleAcceptedSocket(ChannelEvent e) { if (e instanceof ChannelStateEvent) { ChannelStateEvent event = (ChannelStateEvent) e; NioSocketChannel channel = (NioSocketChannel) event.getChannel(); ChannelFuture future = event.getFuture(); ChannelState state = event.getState(); Object value = event.getValue(); switch (state) { case OPEN: if (Boolean.FALSE.equals(value)) { channel.worker.close(channel, future); } break; case BOUND: case CONNECTED: if (value == null) { channel.worker.close(channel, future); } break; case INTEREST_OPS: channel.worker.setInterestOps(channel, future, ((Integer) value).intValue()); break; } } else if (e instanceof MessageEvent) { MessageEvent event = (MessageEvent) e; NioSocketChannel channel = (NioSocketChannel) event.getChannel(); boolean offered = channel.writeBufferQueue.offer(event);//将消息提交到该Channel的writeBuffer中 assert offered; channel.worker.writeFromUserCode(channel);//写(不一定马上进行写入,它会把写入工作放到IO线程中去做) } } }
Netty的代码可以说是即漂亮又简单,了解实现原理后,再去看代码感觉很容易,发现没什么可讲的了...
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