//用于处理业务操作
ExecutorService executorService = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors() << 1);
//构建ServerBootstrap实例
ServerBootstrap bootstrap = new ServerBootstrap()
.group(new NioEventLoopGroup(), new NioEventLoopGroup())
.channel(NioServerSocketChannel.class)
.option(ChannelOption.SO_BACKLOG, 2 << 9)
.childOption(ChannelOption.SO_KEEPALIVE, true)
.childOption(ChannelOption.TCP_NODELAY, true)
.handler(new LoggingHandler(LogLevel.DEBUG))
.childHandler(new ChannelInitializer<Channel>() {
@Override
protected void initChannel(Channel ch) throws Exception {
ch.pipeline()
.addLast(new LoggingHandler(LogLevel.DEBUG))
.addLast(new LengthFieldBasedFrameDecoder(1024, 0, 2, 0, 2))
.addLast(new StringDecoder(Charset.defaultCharset()))
.addLast(new LengthFieldPrepender(2, 0))
.addLast(new StringEncoder(Charset.defaultCharset()))
.addLast(new SimpleChannelInboundHandler<String>() {
@Override
protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
log.info("received msg: {}", msg);
String result = executorService.submit(() -> {
String s = new StringBuffer(msg).reverse().toString();
log.info("handle msg: {}, result: {}", msg, s);
return s;
}).get();
ctx.writeAndFlush(result)
.addListener(future -> {
log.info("send msg: {}", result);
});
}
});
}
});
-
ServerBootstrap.group(EventLoopGroup parentGroup, EventLoopGroup childGroup)
parentGroup处理Tcp链接请求，并将链接交给childGroup处理。
childGroup处理Tcp链接上的通信，如读、写、编解码等。
-
AbstractBootstrap.channel(Class<? extends C> channelClass)
实际上这里创建了一个ChannelFactory<? extends C>实例，也就是new ReflectiveChannelFactory(channelClass)，用于后面创建NioServerSocketChannel实例。
这里使用了NioServerSocketChannel.class。
这里也可以调用AbstractBootstrap.channelFactory(ChannelFactory<? extends C> channelFactory)直接创建ChannelFactory<? extends C>实例。
-
AbstractBootstrap.option(ChannelOption option, T value)
设置服务端socket的tcp参数，如ChannelOption.SO_BACKLOG，具体有哪些参数可以看ChannelOption
-
ServerBootstrap.childOption(ChannelOption childOption, T value)
设置用户客户端socket的tcp参数，如ChannelOption.SO_KEEPALIVE，具体有哪些参数可以看ChannelOption
-
AbstractBootstrap.handler(ChannelHandler handler)
设置用于服务端的ChannelHandler
-
ServerBootstrap.childHandler(ChannelHandler childHandler)
设置用于处理客户端读、写、编解码的ChannelHandler
下面主要对group、channel、handler、childHandler四个方法进行说明
该方法在ServerBootstrap类中实现，有两个参数，都是NioEventLoopGroup的实例。其中，parentGroup处理Tcp链接请求，并将链接交给childGroup处理；childGroup处理Tcp链接上的通信，如读、写、编解码等。
Netty的Reactor线程模型也是在这里实现的。
从NioEventLoopGroup的无参构造器跟踪代码，最终会看到以下代码。其中，nThreads = cpu核心数 * 2，executor = null， chooserFactory = new DefaultSelectStrategyFactory()，args先不管。
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) {
//默认情况下，创建一个没有任务队列的线程池，每次提交给它任务时，都会创建一个线程并被立即执行
executor = new ThreadPerTaskExecutor(newDefaultThreadFactory());
}
//创建nThreads大小的EventExecutor数组，从后面代码可知，实际上数组元素是NioEventLoop的实例
//NioEventLoopGroup实例内有一组NioEventLoop的实例
children = new EventExecutor[nThreads];
for (int i = 0; i < nThreads; i ++) {
boolean success = false;
try {
//这里创建NioEventLoop实例
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 {
//如果EventExecutor数组未初始化成功，则逐个关闭EventExecutor
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;
}
}
}
}
}
//创建一个EventExecutor选择器
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);
}
}
};
//为EventExecutor数组中每一个NioEventLoop实例添加关闭时的listener
for (EventExecutor e: children) {
e.terminationFuture().addListener(terminationListener);
}
Set<EventExecutor> childrenSet = new LinkedHashSet<EventExecutor>(children.length);
Collections.addAll(childrenSet, children);
readonlyChildren = Collections.unmodifiableSet(childrenSet);
}
从图中可以看出，NioEventLoopGroup实现了ScheduledExecutorService、ExecutorService、Executor，这三个接口都是jdk线程池的接口，所以它是一个线程池，但是这个线程池是没有任务队列的，其关于线程池的execute、submit、scheduleXXX、invokeXXX方法都在其抽象父类AbstractEventExecutorGroup中做了实现。
以线程池最核心的execute方法为例。
io.netty.util.concurrent.AbstractEventExecutorGroup.execute
@Override
public void execute(Runnable command) {
next().execute(command);
}
next方法在MultithreadEventExecutorGroup中实现。
io.netty.util.concurrent.MultithreadEventExecutorGroup.next
@Override
public EventExecutor next() {
return chooser.next();
}
它使用构造NioEventLoopGroup实例时创建的EventExecutorChooser从NioEventLoop数组中选取一个NioEventLoop实例。也就是说，execute方法提交的任务最终都交给了NioEventLoop来执行，submit、scheduleXXX、invokeXXX方法也是同样的套路。
再来看一下前面构造NioEventLoopGroup实例时调用的newChild方法
io.netty.channel.nio.NioEventLoopGroup.newChild
@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]);
}
其中，this = 当前正在创建的NioEventLoopGroup实例的引用，executor就是刚刚创建的ThreadPerTaskExecutor实例。
到这里就可以看出NioEventLoop与NioEventLoopGroup的关系了：
- NioEventLoopGroup实例内有一组NioEventLoop的实例
- 而每个NioEventLoop都持有一个NioEventLoopGroup的引用
从图中可以看出NioEventLoop也实现了java线程池的ScheduledExecutorService、ExecutorService、Executor接口；并且它还继承了AbstractExecutorService，这个是jdk线程池的抽象实现。所以它也是一个线程池。
- execute方法在SingleThreadEventExecutor中实现
- submit方法在AbstractEventExecutor中实现，它直接调用了父类AbstractExecutorService的submit方法
- scheduleXXX方法在AbstractScheduledEventExecutor中实现
- invokeXXX方法在SingleThreadEventExecutor中实现，校验是否在Netty的IO线程内调用，如果是，抛出异常；否则直接使用父类AbstractExecutorService的实现。也就是说在Netty的IO线程内调用invokeXXX方法是不被支持的。
在NioEventLoop的构造器参数中，parent = 当前正在创建的NioEventLoopGroup实例的引用，executor就是刚刚创建的ThreadPerTaskExecutor实例。
NioEventLoop(NioEventLoopGroup parent, Executor executor, SelectorProvider selectorProvider,
SelectStrategy strategy, RejectedExecutionHandler rejectedExecutionHandler) {
super(parent, executor, false, DEFAULT_MAX_PENDING_TASKS, rejectedExecutionHandler);
if (selectorProvider == null) {
throw new NullPointerException("selectorProvider");
}
if (strategy == null) {
throw new NullPointerException("selectStrategy");
}
provider = selectorProvider;
final SelectorTuple selectorTuple = openSelector();
selector = selectorTuple.selector;
unwrappedSelector = selectorTuple.unwrappedSelector;
selectStrategy = strategy;
}
protected SingleThreadEventLoop(EventLoopGroup parent, Executor executor,
boolean addTaskWakesUp, int maxPendingTasks,
RejectedExecutionHandler rejectedExecutionHandler) {
super(parent, executor, addTaskWakesUp, maxPendingTasks, rejectedExecutionHandler);
tailTasks = newTaskQueue(maxPendingTasks);
}
protected SingleThreadEventExecutor(EventExecutorGroup parent, Executor executor,
boolean addTaskWakesUp, int maxPendingTasks,
RejectedExecutionHandler rejectedHandler) {
super(parent);
this.addTaskWakesUp = addTaskWakesUp;
this.maxPendingTasks = Math.max(16, maxPendingTasks);
this.executor = ObjectUtil.checkNotNull(executor, "executor");
taskQueue = newTaskQueue(this.maxPendingTasks);
rejectedExecutionHandler = ObjectUtil.checkNotNull(rejectedHandler, "rejectedHandler");
}
看看它的execute方法，这个方法留在后面进行说明。
io.netty.util.concurrent.SingleThreadEventExecutor.execute
@Override
public void execute(Runnable task) {
if (task == null) {
throw new NullPointerException("task");
}
boolean inEventLoop = inEventLoop();
addTask(task);
if (!inEventLoop) {
startThread();
if (isShutdown() && removeTask(task)) {
reject();
}
}
if (!addTaskWakesUp && wakesUpForTask(task)) {
wakeup(inEventLoop);
}
}
addTaskWakesUp由构造器传入，值为false
wakesUpForTask方法在其子类SingleThreadEventLoop中进行了重写
@Override
protected boolean wakesUpForTask(Runnable task) {
return !(task instanceof NonWakeupRunnable);
}
wakeup方法在其子类NioEventLoop中进行了重写
@Override
protected void wakeup(boolean inEventLoop) {
if (!inEventLoop && wakenUp.compareAndSet(false, true)) {
selector.wakeup();
}
}
该方法在AbstractBootstrap中实现。这里会创建一个ReflectiveChannelFactory实例，这个方法通过反射创建Channel实例。 具体过程会在后面真正创建Channel实例时进行说明。
该方法在AbstractBootstrap中实现。handler参数用于处理NioServerSocketChannel。
该方法在ServerBootstrap中实现。childHandler参数用于处理NioSocketChannel。
Netty Server端的启动可以使用AbstractBootstrap类的bind方法的几个重载方法来执行。 以AbstractBootstrap.bind(SocketAddress localAddress)来说明。
io.netty.bootstrap.AbstractBootstrap.bind(java.net.SocketAddress)
public ChannelFuture bind(SocketAddress localAddress) {
validate();
if (localAddress == null) {
throw new NullPointerException("localAddress");
}
return doBind(localAddress);
}
它调用了doBind方法。
io.netty.bootstrap.AbstractBootstrap.doBind
private ChannelFuture doBind(final SocketAddress localAddress) {
final ChannelFuture regFuture = initAndRegister();
final Channel channel = regFuture.channel();
if (regFuture.cause() != null) {
return regFuture;
}
if (regFuture.isDone()) {
// At this point we know that the registration was complete and successful.
ChannelPromise promise = channel.newPromise();
doBind0(regFuture, channel, localAddress, promise);
return promise;
} else {
// Registration future is almost always fulfilled already, but just in case it's not.
final PendingRegistrationPromise promise = new PendingRegistrationPromise(channel);
regFuture.addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture future) throws Exception {
Throwable cause = future.cause();
if (cause != null) {
// Registration on the EventLoop failed so fail the ChannelPromise directly to not cause an
// IllegalStateException once we try to access the EventLoop of the Channel.
promise.setFailure(cause);
} else {
// Registration was successful, so set the correct executor to use.
// See https://github.com/netty/netty/issues/2586
promise.registered();
doBind0(regFuture, channel, localAddress, promise);
}
}
});
return promise;
}
}
该方法主要分为两个功能。主要看initAndRegister(...)和doBind0(...)两个方法。
io.netty.bootstrap.AbstractBootstrap.initAndRegister
final ChannelFuture initAndRegister() {
Channel channel = null;
try {
//Server创建NioServerSocketChannel实例，client创建的是NioSocketChannel实例。
channel = channelFactory.newChannel();
//Server设置ServerSocketChannel的属性，然后将channel添加到pipeline中。
init(channel);
} catch (Throwable t) {
if (channel != null) {
// channel can be null if newChannel crashed (eg SocketException("too many open files"))
channel.unsafe().closeForcibly();
// as the Channel is not registered yet we need to force the usage of the GlobalEventExecutor
return new DefaultChannelPromise(channel, GlobalEventExecutor.INSTANCE).setFailure(t);
}
// as the Channel is not registered yet we need to force the usage of the GlobalEventExecutor
return new DefaultChannelPromise(new FailedChannel(), GlobalEventExecutor.INSTANCE).setFailure(t);
}
ChannelFuture regFuture = config().group().register(channel);
if (regFuture.cause() != null) {
if (channel.isRegistered()) {
channel.close();
} else {
channel.unsafe().closeForcibly();
}
}
// If we are here and the promise is not failed, it's one of the following cases:
// 1) If we attempted registration from the event loop, the registration has been completed at this point.
// i.e. It's safe to attempt bind() or connect() now because the channel has been registered.
// 2) If we attempted registration from the other thread, the registration request has been successfully
// added to the event loop's task queue for later execution.
// i.e. It's safe to attempt bind() or connect() now:
// because bind() or connect() will be executed *after* the scheduled registration task is executed
// because register(), bind(), and connect() are all bound to the same thread.
return regFuture;
}
channel = channelFactory.newChannel();
这里使用反射技术调用了NioServerSocketChannel的默认构造方法
public NioServerSocketChannel() {
this(newSocket(DEFAULT_SELECTOR_PROVIDER));
}
newSocket(DEFAULT_SELECTOR_PROVIDER)返回了一个Java Nio的ServerSocketChannel实例。
private static ServerSocketChannel newSocket(SelectorProvider provider) {
try {
/**
* Use the {@link SelectorProvider} to open {@link SocketChannel} and so remove condition in
* {@link SelectorProvider#provider()} which is called by each ServerSocketChannel.open() otherwise.
*
* See <a href="https://github.com/netty/netty/issues/2308">#2308</a>.
*/
return provider.openServerSocketChannel();
} catch (IOException e) {
throw new ChannelException(
"Failed to open a server socket.", e);
}
}
继续往深挖
public NioServerSocketChannel(ServerSocketChannel channel) {
super(null, channel, SelectionKey.OP_ACCEPT);
config = new NioServerSocketChannelConfig(this, javaChannel().socket());
}
这里的ServerSocketChannel就是Java NIO的ServerSocketChannel。创建了一个NioServerSocketChannelConfig，将netty的NioServerSocketChannel实例与java的ServerSocket包装进去。
protected AbstractNioMessageChannel(Channel parent, SelectableChannel ch, int readInterestOp) {
super(parent, ch, readInterestOp);
}
再挖，看super(null, channel, SelectionKey.OP_ACCEPT);
这里parent == null，readInterestOp == SelectionKey.OP_ACCEPT。然后配置ServerSocketChannel为非阻塞。
protected AbstractNioChannel(Channel parent, SelectableChannel ch, int readInterestOp) {
super(parent);
this.ch = ch;
this.readInterestOp = readInterestOp;
try {
ch.configureBlocking(false);
} catch (IOException e) {
try {
ch.close();
} catch (IOException e2) {
if (logger.isWarnEnabled()) {
logger.warn(
"Failed to close a partially initialized socket.", e2);
}
}
throw new ChannelException("Failed to enter non-blocking mode.", e);
}
}
还挖，看super(parent);，这里创建了NioMessageUnsafe实例、DefaultChannelPipeline实例、ChannelId实例。并且DefaultChannelPipeline通过持有一个当前所创建的channel引用进行关联。
protected AbstractChannel(Channel parent) {
this.parent = parent;
id = newId();
unsafe = newUnsafe();
pipeline = newChannelPipeline();
}
protected DefaultChannelPipeline(Channel channel) {
this.channel = ObjectUtil.checkNotNull(channel, "channel");
succeededFuture = new SucceededChannelFuture(channel, null);
voidPromise = new VoidChannelPromise(channel, true);
tail = new TailContext(this);
head = new HeadContext(this);
head.next = tail;
tail.prev = head;
}
final class TailContext extends AbstractChannelHandlerContext implements ChannelInboundHandler {
TailContext(DefaultChannelPipeline pipeline) {
super(pipeline, null, TAIL_NAME, true, false);
setAddComplete();
}
...
}
final class HeadContext extends AbstractChannelHandlerContext
implements ChannelOutboundHandler, ChannelInboundHandler {
private final Unsafe unsafe;
HeadContext(DefaultChannelPipeline pipeline) {
super(pipeline, null, HEAD_NAME, false, true);
unsafe = pipeline.channel().unsafe();
setAddComplete();
}
...
}
HeadContext、TailContext都继承了AbstractChannelHandlerContext。
HeadContext是outbound的、也是inbound的。TailContext是inbound的。
AbstractChannelHandlerContext持有pipeline的引用。
AbstractChannelHandlerContext是一个双向链表，而pipeline持有双向链表的头节点、尾节点的引用。
channel、pipeline互相持有对方的一个引用。
io.netty.bootstrap.ServerBootstrap.init
@Override
void init(Channel channel) throws Exception {
final Map<ChannelOption<?>, Object> options = options0();
synchronized (options) {
setChannelOptions(channel, options, logger);
}
final Map<AttributeKey<?>, Object> attrs = attrs0();
synchronized (attrs) {
for (Entry<AttributeKey<?>, Object> e: attrs.entrySet()) {
@SuppressWarnings("unchecked")
AttributeKey<Object> key = (AttributeKey<Object>) e.getKey();
channel.attr(key).set(e.getValue());
}
}
ChannelPipeline p = channel.pipeline();
final EventLoopGroup currentChildGroup = childGroup;
final ChannelHandler currentChildHandler = childHandler;
final Entry<ChannelOption<?>, Object>[] currentChildOptions;
final Entry<AttributeKey<?>, Object>[] currentChildAttrs;
synchronized (childOptions) {
currentChildOptions = childOptions.entrySet().toArray(newOptionArray(0));
}
synchronized (childAttrs) {
currentChildAttrs = childAttrs.entrySet().toArray(newAttrArray(0));
}
// 1
p.addLast(new ChannelInitializer<Channel>() {
@Override
public void initChannel(final Channel ch) throws Exception {
final ChannelPipeline pipeline = ch.pipeline();
ChannelHandler handler = config.handler();
if (handler != null) {
// 2
pipeline.addLast(handler);
}
ch.eventLoop().execute(new Runnable() {
@Override
public void run() {
// 3
pipeline.addLast(new ServerBootstrapAcceptor(
ch, currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs));
}
});
}
});
}
- 设置NioServerSocketChannel的TCP属性。
- 向NioServerSocketChannel的pipeline添加handler、childHandler
1处的addLast
@Override
public final ChannelPipeline addLast(EventExecutorGroup group, String name, ChannelHandler handler) {
final AbstractChannelHandlerContext newCtx;
synchronized (this) {
checkMultiplicity(handler);
//new DefaultChannelHandlerContext(this, childExecutor(group), name, handler);
//创建DefaultChannelHandlerContext实例，并将handler、pipeline与其相关联，即它持有了当前添加的handler以及当前pipeline的引用
newCtx = newContext(group, filterName(name, handler), handler);
//将刚创建的context添加到双向链表的尾节点之前
addLast0(newCtx);
// If the registered is false it means that the channel was not registered on an eventloop yet.
// In this case we add the context to the pipeline and add a task that will call
// ChannelHandler.handlerAdded(...) once the channel is registered.
if (!registered) {
newCtx.setAddPending();
// registered = false，初始化pendingHandlerCallbackHead属性，即在这里会创建PendingHandlerAddedTask实例，pendingHandlerCallbackHead是一个链表，如果后续还有调用到这里，会在链表尾部追加元素
// 所以这里就返回了，2、3处对addLast方法的调用也没有在这里执行
callHandlerCallbackLater(newCtx, true);
return this;
}
EventExecutor executor = newCtx.executor();
if (!executor.inEventLoop()) {
newCtx.setAddPending();
executor.execute(new Runnable() {
@Override
public void run() {
//这里调用ChannelInitializer的initChannel方法，它将AbstractBootstrap.handler(ChannelHandler handler)的handler添加到pipeline，然后将ChannelInitializer实例从pipeline中移除
callHandlerAdded0(newCtx);
}
});
return this;
}
}
//这里调用ChannelInitializer的initChannel方法，它将AbstractBootstrap.handler(ChannelHandler handler)的handler添加到pipeline，然后将ChannelInitializer实例从pipeline中移除
callHandlerAdded0(newCtx);
return this;
}
这里创建了DefaultChannelHandlerContext实例，并将该实例添加到context双向链表的尾节点tail节点之前。该实例持有ChannelPipeline的实例引用。 由于当前registered = false，所以会调用callHandlerCallbackLater方法。
private void callHandlerCallbackLater(AbstractChannelHandlerContext ctx, boolean added) {
assert !registered;
PendingHandlerCallback task = added ? new PendingHandlerAddedTask(ctx) : new PendingHandlerRemovedTask(ctx);
PendingHandlerCallback pending = pendingHandlerCallbackHead;
if (pending == null) {
pendingHandlerCallbackHead = task;
} else {
// Find the tail of the linked-list.
while (pending.next != null) {
pending = pending.next;
}
pending.next = task;
}
}
PendingHandlerAddedTask继承了PendingHandlerCallback，实现了Runnable接口，而PendingHandlerCallback是一个单链表。 参数added = true，会创建一个PendingHandlerAddedTask实例，并把它添加到PendingHandlerCallback单链表中。
2处的addLast、3处的addLast会在后面执行。
将ServerBootstrapAcceptor添加到pipeline。它继承了ChannelInboundHandlerAdapter，包装了通过ServerBootstrap添加的channel、childGroup、childHandler、childOptions、childAttrs，并且添加了一个任务在异常时重新设置channel的config的autoRead属性。
@Override
public ChannelConfig setAutoRead(boolean autoRead) {
boolean oldAutoRead = AUTOREAD_UPDATER.getAndSet(this, autoRead ? 1 : 0) == 1;
if (autoRead && !oldAutoRead) {
channel.read();
} else if (!autoRead && oldAutoRead) {
autoReadCleared();
}
return this;
}
ChannelFuture regFuture = config().group().register(channel);
这里的group就是parentGroup，eventLoop就是从parentGroup的EventExecutor数组中选取的其中一个。
@Override
public final void register(EventLoop eventLoop, final ChannelPromise promise) {
if (eventLoop == null) {
throw new NullPointerException("eventLoop");
}
if (isRegistered()) {
promise.setFailure(new IllegalStateException("registered to an event loop already"));
return;
}
if (!isCompatible(eventLoop)) {
promise.setFailure(
new IllegalStateException("incompatible event loop type: " + eventLoop.getClass().getName()));
return;
}
// 给channel的eventLoop赋值，即将该eventLoop绑定到了channel上
AbstractChannel.this.eventLoop = eventLoop;
//currentThread = main，NioEventLoop.thread = null，所以走else分枝
if (eventLoop.inEventLoop()) {
register0(promise);
} else {
try {
eventLoop.execute(new Runnable() {
@Override
public void run() {
register0(promise);
}
});
} catch (Throwable t) {
logger.warn(
"Force-closing a channel whose registration task was not accepted by an event loop: {}",
AbstractChannel.this, t);
closeForcibly();
closeFuture.setClosed();
safeSetFailure(promise, t);
}
}
NioEventLoop的execute方法，将对register0的调用包装为一个task并将其添加到任务队列。任务
@Override
public void execute(Runnable task) {
if (task == null) {
throw new NullPointerException("task");
}
// currentThread = main，NioEventLoop.thread = null，false
boolean inEventLoop = inEventLoop();
// 将任务添加到队列
addTask(task);
if (!inEventLoop) {
//这里会给NioEventLoop.thread赋值，并调用NioEventLoop的run方法
startThread();
if (isShutdown() && removeTask(task)) {
reject();
}
}
if (!addTaskWakesUp && wakesUpForTask(task)) {
wakeup(inEventLoop);
}
}
由于这里的inEventLoop = false，所以会调用startThread方法
private void startThread() {
if (state == ST_NOT_STARTED) {
if (STATE_UPDATER.compareAndSet(this, ST_NOT_STARTED, ST_STARTED)) {
try {
doStartThread();
} catch (Throwable cause) {
STATE_UPDATER.set(this, ST_NOT_STARTED);
PlatformDependent.throwException(cause);
}
}
}
}
private void doStartThread() {
assert thread == null;
//这里的executor就是构建NioEventLoopGroup时创建的那个没有任务队列的线程池，提交一个任务就开启一个线程
executor.execute(new Runnable() {
@Override
public void run() {
// 给thread属性赋值，之后eventLoop.inEventLoop()就应该是true了
thread = Thread.currentThread();
if (interrupted) {
thread.interrupt();
}
boolean success = false;
updateLastExecutionTime();
try {
SingleThreadEventExecutor.this.run();
success = true;
} catch (Throwable t) {
logger.warn("Unexpected exception from an event executor: ", t);
} finally {
for (;;) {
int oldState = state;
if (oldState >= ST_SHUTTING_DOWN || STATE_UPDATER.compareAndSet(
SingleThreadEventExecutor.this, oldState, ST_SHUTTING_DOWN)) {
break;
}
}
// Check if confirmShutdown() was called at the end of the loop.
if (success && gracefulShutdownStartTime == 0) {
if (logger.isErrorEnabled()) {
logger.error("Buggy " + EventExecutor.class.getSimpleName() + " implementation; " +
SingleThreadEventExecutor.class.getSimpleName() + ".confirmShutdown() must " +
"be called before run() implementation terminates.");
}
}
try {
// Run all remaining tasks and shutdown hooks.
for (;;) {
if (confirmShutdown()) {
break;
}
}
} finally {
try {
cleanup();
} finally {
STATE_UPDATER.set(SingleThreadEventExecutor.this, ST_TERMINATED);
threadLock.release();
if (!taskQueue.isEmpty()) {
if (logger.isWarnEnabled()) {
logger.warn("An event executor terminated with " +
"non-empty task queue (" + taskQueue.size() + ')');
}
}
terminationFuture.setSuccess(null);
}
}
}
}
});
}
这里调用了NioEventLoop的run方法，用于nio的事件处理
@Override
protected void run() {
for (;;) {
try {
switch (selectStrategy.calculateStrategy(selectNowSupplier, hasTasks())) {
case SelectStrategy.CONTINUE:
continue;
case SelectStrategy.BUSY_WAIT:
// fall-through to SELECT since the busy-wait is not supported with NIO
case SelectStrategy.SELECT:
select(wakenUp.getAndSet(false));
// 'wakenUp.compareAndSet(false, true)' is always evaluated
// before calling 'selector.wakeup()' to reduce the wake-up
// overhead. (Selector.wakeup() is an expensive operation.)
//
// However, there is a race condition in this approach.
// The race condition is triggered when 'wakenUp' is set to
// true too early.
//
// 'wakenUp' is set to true too early if:
// 1) Selector is waken up between 'wakenUp.set(false)' and
// 'selector.select(...)'. (BAD)
// 2) Selector is waken up between 'selector.select(...)' and
// 'if (wakenUp.get()) { ... }'. (OK)
//
// In the first case, 'wakenUp' is set to true and the
// following 'selector.select(...)' will wake up immediately.
// Until 'wakenUp' is set to false again in the next round,
// 'wakenUp.compareAndSet(false, true)' will fail, and therefore
// any attempt to wake up the Selector will fail, too, causing
// the following 'selector.select(...)' call to block
// unnecessarily.
//
// To fix this problem, we wake up the selector again if wakenUp
// is true immediately after selector.select(...).
// It is inefficient in that it wakes up the selector for both
// the first case (BAD - wake-up required) and the second case
// (OK - no wake-up required).
if (wakenUp.get()) {
selector.wakeup();
}
// fall through
default:
}
cancelledKeys = 0;
needsToSelectAgain = false;
final int ioRatio = this.ioRatio;
if (ioRatio == 100) {
try {
//处理nio事件
processSelectedKeys();
} finally {
// 执行所有已提交的task，前面else分枝添加的任务会在这里被执行
// Ensure we always run tasks.
runAllTasks();
}
} else {
final long ioStartTime = System.nanoTime();
try {
//处理nio事件
processSelectedKeys();
} finally {
// 执行所有已提交的task，前面else分枝添加的任务会在这里被执行
// Ensure we always run tasks.
final long ioTime = System.nanoTime() - ioStartTime;
runAllTasks(ioTime * (100 - ioRatio) / ioRatio);
}
}
} catch (Throwable t) {
handleLoopException(t);
}
// Always handle shutdown even if the loop processing threw an exception.
try {
if (isShuttingDown()) {
closeAll();
if (confirmShutdown()) {
return;
}
}
} catch (Throwable t) {
handleLoopException(t);
}
}
}
上面这块代码在else分枝调用runAllTasks方法时才会执行刚才addLast时添加的任务，即register0方法。
private void register0(ChannelPromise promise) {
try {
// check if the channel is still open as it could be closed in the mean time when the register
// call was outside of the eventLoop
if (!promise.setUncancellable() || !ensureOpen(promise)) {
return;
}
boolean firstRegistration = neverRegistered;
// 监听tcp读事件？？?
doRegister();
neverRegistered = false;
registered = true;
// Ensure we call handlerAdded(...) before we actually notify the promise. This is needed as the
// user may already fire events through the pipeline in the ChannelFutureListener.
pipeline.invokeHandlerAddedIfNeeded();
safeSetSuccess(promise);
pipeline.fireChannelRegistered();
// Only fire a channelActive if the channel has never been registered. This prevents firing
// multiple channel actives if the channel is deregistered and re-registered.
if (isActive()) {
if (firstRegistration) {
pipeline.fireChannelActive();
} else if (config().isAutoRead()) {
// This channel was registered before and autoRead() is set. This means we need to begin read
// again so that we process inbound data.
//
// See https://github.com/netty/netty/issues/4805
beginRead();
}
}
} catch (Throwable t) {
// Close the channel directly to avoid FD leak.
closeForcibly();
closeFuture.setClosed();
safeSetFailure(promise, t);
}
}
@Override
protected void doRegister() throws Exception {
boolean selected = false;
for (;;) {
try {
selectionKey = javaChannel().register(eventLoop().unwrappedSelector(), 0, this);
return;
} catch (CancelledKeyException e) {
if (!selected) {
// Force the Selector to select now as the "canceled" SelectionKey may still be
// cached and not removed because no Select.select(..) operation was called yet.
eventLoop().selectNow();
selected = true;
} else {
// We forced a select operation on the selector before but the SelectionKey is still cached
// for whatever reason. JDK bug ?
throw e;
}
}
}
}
这里就开始监听TCP读事件了
pipeline.invokeHandlerAddedIfNeeded();
final void invokeHandlerAddedIfNeeded() {
assert channel.eventLoop().inEventLoop();
if (firstRegistration) {
firstRegistration = false;
// We are now registered to the EventLoop. It's time to call the callbacks for the ChannelHandlers,
// that were added before the registration was done.
callHandlerAddedForAllHandlers();
}
}
firstRegistration默认值true，然后更新为false，也就是只有在第一次调用register0时才会执行callHandlerAddedForAllHandlers方法。callHandlerAddedForAllHandlers就是在执行刚才在addLast方法中创建的pendingHandlerCallbackHead链表中的任务了。
private void callHandlerAddedForAllHandlers() {
final PendingHandlerCallback pendingHandlerCallbackHead;
synchronized (this) {
assert !registered;
// This Channel itself was registered.
registered = true;
pendingHandlerCallbackHead = this.pendingHandlerCallbackHead;
// Null out so it can be GC'ed.
this.pendingHandlerCallbackHead = null;
}
// This must happen outside of the synchronized(...) block as otherwise handlerAdded(...) may be called while
// holding the lock and so produce a deadlock if handlerAdded(...) will try to add another handler from outside
// the EventLoop.
PendingHandlerCallback task = pendingHandlerCallbackHead;
while (task != null) {
task.execute();
task = task.next;
}
}
看看这些任务在干啥，实际上还是调用的callHandlerAdded0方法
private final class PendingHandlerAddedTask extends PendingHandlerCallback {
PendingHandlerAddedTask(AbstractChannelHandlerContext ctx) {
super(ctx);
}
@Override
public void run() {
callHandlerAdded0(ctx);
}
@Override
void execute() {
EventExecutor executor = ctx.executor();
// executor.inEventLoop() = true
if (executor.inEventLoop()) {
callHandlerAdded0(ctx);
} else {
try {
executor.execute(this);
} catch (RejectedExecutionException e) {
if (logger.isWarnEnabled()) {
logger.warn(
"Can't invoke handlerAdded() as the EventExecutor {} rejected it, removing handler {}.",
executor, ctx.name(), e);
}
remove0(ctx);
ctx.setRemoved();
}
}
}
}
io.netty.channel.DefaultChannelPipeline.callHandlerAdded0
private void callHandlerAdded0(final AbstractChannelHandlerContext ctx) {
try {
// We must call setAddComplete before calling handlerAdded. Otherwise if the handlerAdded method generates
// any pipeline events ctx.handler() will miss them because the state will not allow it.
ctx.setAddComplete();
ctx.handler().handlerAdded(ctx);
} catch (Throwable t) {
boolean removed = false;
try {
remove0(ctx);
try {
ctx.handler().handlerRemoved(ctx);
} finally {
ctx.setRemoved();
}
removed = true;
} catch (Throwable t2) {
if (logger.isWarnEnabled()) {
logger.warn("Failed to remove a handler: " + ctx.name(), t2);
}
}
if (removed) {
fireExceptionCaught(new ChannelPipelineException(
ctx.handler().getClass().getName() +
".handlerAdded() has thrown an exception; removed.", t));
} else {
fireExceptionCaught(new ChannelPipelineException(
ctx.handler().getClass().getName() +
".handlerAdded() has thrown an exception; also failed to remove.", t));
}
}
}
这里的ctx 就是刚才创建的newCtx，handler是1处的ChannelInitializer实例，看看ChannelInitializer的handlerAdded方法
@Override
public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
if (ctx.channel().isRegistered()) {
// This should always be true with our current DefaultChannelPipeline implementation.
// The good thing about calling initChannel(...) in handlerAdded(...) is that there will be no ordering
// surprises if a ChannelInitializer will add another ChannelInitializer. This is as all handlers
// will be added in the expected order.
initChannel(ctx);
}
}
@SuppressWarnings("unchecked")
private boolean initChannel(ChannelHandlerContext ctx) throws Exception {
if (initMap.putIfAbsent(ctx, Boolean.TRUE) == null) { // Guard against re-entrance.
try {
initChannel((C) ctx.channel());
} catch (Throwable cause) {
// Explicitly call exceptionCaught(...) as we removed the handler before calling initChannel(...).
// We do so to prevent multiple calls to initChannel(...).
exceptionCaught(ctx, cause);
} finally {
remove(ctx);
}
return true;
}
return false;
}
调用了ChannelInitializer实例的initChannel方法，该方法以构建ServerBootstrap时传入的handler为参数再一次调用了addLast方法。然后在finally中将ctx从pipeline移除。也就是ChannelInitializer的context不会在pipeline中保留。 这里开始执行2处的addLast。
@Override
public final ChannelPipeline addLast(EventExecutorGroup group, String name, ChannelHandler handler) {
final AbstractChannelHandlerContext newCtx;
synchronized (this) {
checkMultiplicity(handler);
// 创建DefaultChannelHandlerContext实例，并将handler、pipeline与其相关联，即它持有了当前添加的handler以及当前pipeline的引用
newCtx = newContext(group, filterName(name, handler), handler);
// 将刚创建的context添加到双向链表的尾节点之前
addLast0(newCtx);
// If the registered is false it means that the channel was not registered on an eventloop yet.
// In this case we add the context to the pipeline and add a task that will call
// ChannelHandler.handlerAdded(...) once the channel is registered.
// 调用register0时，设置了registered = true
if (!registered) {
newCtx.setAddPending();
// registered = false，初始化pendingHandlerCallbackHead属性，即在这里会创建PendingHandlerAddedTask实例，pendingHandlerCallbackHead是一个链表，如果后续还有调用到这里，会在链表尾部追加元素
// 所以这里就返回了，2、3处对addLast方法的调用也没有在这里执行
callHandlerCallbackLater(newCtx, true);
return this;
}
// executor.inEventLoop() = true，所以也不会走这里
EventExecutor executor = newCtx.executor();
if (!executor.inEventLoop()) {
newCtx.setAddPending();
executor.execute(new Runnable() {
@Override
public void run() {
//这里调用ChannelInitializer的initChannel方法，它将AbstractBootstrap.handler(ChannelHandler handler)的handler添加到pipeline，然后将ChannelInitializer实例从pipeline中移除
callHandlerAdded0(newCtx);
}
});
return this;
}
}
// 实际上只添加了一个LoggingHandler，它的handlerAdded也没做什么事情
callHandlerAdded0(newCtx);
return this;
}
2处的addLast之后，会执行以下代码
ch.eventLoop().execute(new Runnable() {
@Override
public void run() {
// 3
pipeline.addLast(new ServerBootstrapAcceptor(
ch, currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs));
}
});
@Override
public void execute(Runnable task) {
if (task == null) {
throw new NullPointerException("task");
}
// true
boolean inEventLoop = inEventLoop();
addTask(task);
if (!inEventLoop) {
startThread();
if (isShutdown() && removeTask(task)) {
reject();
}
}
if (!addTaskWakesUp && wakesUpForTask(task)) {
wakeup(inEventLoop);
}
}
这段代码将对3处的addLast的调用包装成一个task添加到任务队列中。 任务
ServerBootstrapAcceptor实例的context被添加到双向链表尾节点的前面。
双向链表现在有四个节点，head、logging、acceptor、tail。
head： HeadContext， in & out logging： LoggingHandler， in & out acceptor： ServerBootstrapAcceptor， in tail： TailContext， in
AbstractBootstrap.doBind0(regFuture, channel, localAddress, promise);
AbstractBootstrap.doBind0，它将对channel.bind方法的调用包装成一个task添加到任务队列。任务
private static void doBind0(
final ChannelFuture regFuture, final Channel channel,
final SocketAddress localAddress, final ChannelPromise promise) {
// This method is invoked before channelRegistered() is triggered. Give user handlers a chance to set up
// the pipeline in its channelRegistered() implementation.
channel.eventLoop().execute(new Runnable() {
@Override
public void run() {
if (regFuture.isSuccess()) {
channel.bind(localAddress, promise).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
} else {
promise.setFailure(regFuture.cause());
}
}
});
}
AbstractChannel.bind(java.net.SocketAddress, io.netty.channel.ChannelPromise)
channel.bind(localAddress, promise).addListener(ChannelFutureListener.CLOSE_ON_FAILURE); 这里的channel是前面创建的NioServerSocketChannel实例。
@Override
public ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise) {
return pipeline.bind(localAddress, promise);
}
io.netty.channel.DefaultChannelPipeline.bind(java.net.SocketAddress, io.netty.channel.ChannelPromise)
@Override
public final ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise) {
return tail.bind(localAddress, promise);
}
tail是DefaultChannelPipeline的一个属性，是双向链表的尾节点，在实例化DefaultChannelPipeline时已被赋值。
tail = new TailContext(this);
io.netty.channel.AbstractChannelHandlerContext.bind(java.net.SocketAddress, io.netty.channel.ChannelPromise)
@Override
public ChannelFuture bind(final SocketAddress localAddress, final ChannelPromise promise) {
if (localAddress == null) {
throw new NullPointerException("localAddress");
}
if (isNotValidPromise(promise, false)) {
// cancelled
return promise;
}
final AbstractChannelHandlerContext next = findContextOutbound();
EventExecutor executor = next.executor();
if (executor.inEventLoop()) {
next.invokeBind(localAddress, promise);
} else {
safeExecute(executor, new Runnable() {
@Override
public void run() {
next.invokeBind(localAddress, promise);
}
}, promise, null);
}
return promise;
}
它从尾节点tail开始向前遍历双向链表，找到第一个是outbound的context并调用它的invokeBind方法。 所以这里首先会调用LoggingHandler、HeadContext。
HeadContext.bind(ChannelHandlerContext ctx, SocketAddress localAddress, ChannelPromise promise)
@Override
public void bind(
ChannelHandlerContext ctx, SocketAddress localAddress, ChannelPromise promise)
throws Exception {
unsafe.bind(localAddress, promise);
}
AbstractChannel.AbstractUnsafe.bind(final SocketAddress localAddress, final ChannelPromise promise)
@Override
public final void bind(final SocketAddress localAddress, final ChannelPromise promise) {
assertEventLoop();
if (!promise.setUncancellable() || !ensureOpen(promise)) {
return;
}
// See: https://github.com/netty/netty/issues/576
if (Boolean.TRUE.equals(config().getOption(ChannelOption.SO_BROADCAST)) &&
localAddress instanceof InetSocketAddress &&
!((InetSocketAddress) localAddress).getAddress().isAnyLocalAddress() &&
!PlatformDependent.isWindows() && !PlatformDependent.maybeSuperUser()) {
// Warn a user about the fact that a non-root user can't receive a
// broadcast packet on *nix if the socket is bound on non-wildcard address.
logger.warn(
"A non-root user can't receive a broadcast packet if the socket " +
"is not bound to a wildcard address; binding to a non-wildcard " +
"address (" + localAddress + ") anyway as requested.");
}
boolean wasActive = isActive();
try {
doBind(localAddress);
} catch (Throwable t) {
safeSetFailure(promise, t);
closeIfClosed();
return;
}
if (!wasActive && isActive()) {
invokeLater(new Runnable() {
@Override
public void run() {
pipeline.fireChannelActive();
}
});
}
safeSetSuccess(promise);
}
NioServerSocketChannel.doBind(SocketAddress localAddress)
protected void doBind(SocketAddress localAddress) throws Exception {
if (PlatformDependent.javaVersion() >= 7) {
javaChannel().bind(localAddress, config.getBacklog());
} else {
javaChannel().socket().bind(localAddress, config.getBacklog());
}
}
到这里，javaChannel已经跟localAddress进行了绑定。
invokeLater将对 pipeline.fireChannelActive();的调用包装成task添加到任务队列。任务
再来看，pipeline.fireChannelActive();
@Override
public final ChannelPipeline fireChannelActive() {
AbstractChannelHandlerContext.invokeChannelActive(head);
return this;
}
static void invokeChannelActive(final AbstractChannelHandlerContext next) {
EventExecutor executor = next.executor();
if (executor.inEventLoop()) {
next.invokeChannelActive();
} else {
executor.execute(new Runnable() {
@Override
public void run() {
next.invokeChannelActive();
}
});
}
}
它调用了head节点的channelActive方法。
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
ctx.fireChannelActive();
readIfIsAutoRead();
}
这里的ctx.fireChannelActive();，它pipeline的head开始向后遍历链表，找到第一个inbound的context并调用channelActive方法，所以这里会先后经过head、logging、acceptor、tail节点。
logging、acceptor、tail这三个节点没做什么重要的事。
那就接着看看readIfIsAutoRead方法。
io.netty.channel.DefaultChannelPipeline.HeadContext.readIfIsAutoRead
private void readIfIsAutoRead() {
if (channel.config().isAutoRead()) {
channel.read();
}
}
io.netty.channel.AbstractChannel.read
@Override
public Channel read() {
pipeline.read();
return this;
}
io.netty.channel.DefaultChannelPipeline.read
@Override
public final ChannelPipeline read() {
tail.read();
return this;
}
这里调用了tail节点的read方法。
AbstractChannelHandlerContext.read
@Override
public ChannelHandlerContext read() {
final AbstractChannelHandlerContext next = findContextOutbound();
EventExecutor executor = next.executor();
if (executor.inEventLoop()) {
next.invokeRead();
} else {
Runnable task = next.invokeReadTask;
if (task == null) {
next.invokeReadTask = task = new Runnable() {
@Override
public void run() {
next.invokeRead();
}
};
}
executor.execute(task);
}
return this;
}
这里同样是从tail开始遍历链表找outbound的节点，依次为logging、head，logging依然是将调用向下一个节点传递。最终到HeadContext的read方法。
io.netty.channel.DefaultChannelPipeline.HeadContext.read
@Override
public void read(ChannelHandlerContext ctx) {
unsafe.beginRead();
}
io.netty.channel.AbstractChannel.AbstractUnsafe.beginRead
@Override
public final void beginRead() {
assertEventLoop();
if (!isActive()) {
return;
}
try {
doBeginRead();
} catch (final Exception e) {
invokeLater(new Runnable() {
@Override
public void run() {
pipeline.fireExceptionCaught(e);
}
});
close(voidPromise());
}
}
io.netty.channel.nio.AbstractNioChannel.doBeginRead
@Override
protected void doBeginRead() throws Exception {
// Channel.read() or ChannelHandlerContext.read() was called
final SelectionKey selectionKey = this.selectionKey;
if (!selectionKey.isValid()) {
return;
}
readPending = true;
final int interestOps = selectionKey.interestOps();
if ((interestOps & readInterestOp) == 0) {
selectionKey.interestOps(interestOps | readInterestOp);
}
}
这里interestOps=0，readInterestOp=OP_ACCEPT，所以这里注册了OP_ACCEPT事件。
到这里地址绑定算完事了。
processSelectedKeys
NioEventLoop的run方法调用了这个方法。
private void processSelectedKeys() {
if (selectedKeys != null) {
processSelectedKeysOptimized();
} else {
processSelectedKeysPlain(selector.selectedKeys());
}
}
private void processSelectedKeysOptimized() {
for (int i = 0; i < selectedKeys.size; ++i) {
final SelectionKey k = selectedKeys.keys[i];
// null out entry in the array to allow to have it GC'ed once the Channel close
// See https://github.com/netty/netty/issues/2363
selectedKeys.keys[i] = null;
final Object a = k.attachment();
if (a instanceof AbstractNioChannel) {
processSelectedKey(k, (AbstractNioChannel) a);
} else {
@SuppressWarnings("unchecked")
NioTask<SelectableChannel> task = (NioTask<SelectableChannel>) a;
processSelectedKey(k, task);
}
if (needsToSelectAgain) {
// null out entries in the array to allow to have it GC'ed once the Channel close
// See https://github.com/netty/netty/issues/2363
selectedKeys.reset(i + 1);
selectAgain();
i = -1;
}
}
}
processSelectedKey(k, (AbstractNioChannel) a);
private void processSelectedKey(SelectionKey k, AbstractNioChannel ch) {
final AbstractNioChannel.NioUnsafe unsafe = ch.unsafe();
if (!k.isValid()) {
final EventLoop eventLoop;
try {
eventLoop = ch.eventLoop();
} catch (Throwable ignored) {
// If the channel implementation throws an exception because there is no event loop, we ignore this
// because we are only trying to determine if ch is registered to this event loop and thus has authority
// to close ch.
return;
}
// Only close ch if ch is still registered to this EventLoop. ch could have deregistered from the event loop
// and thus the SelectionKey could be cancelled as part of the deregistration process, but the channel is
// still healthy and should not be closed.
// See https://github.com/netty/netty/issues/5125
if (eventLoop != this || eventLoop == null) {
return;
}
// close the channel if the key is not valid anymore
unsafe.close(unsafe.voidPromise());
return;
}
try {
int readyOps = k.readyOps();
// We first need to call finishConnect() before try to trigger a read(...) or write(...) as otherwise
// the NIO JDK channel implementation may throw a NotYetConnectedException.
if ((readyOps & SelectionKey.OP_CONNECT) != 0) {
// remove OP_CONNECT as otherwise Selector.select(..) will always return without blocking
// See https://github.com/netty/netty/issues/924
int ops = k.interestOps();
ops &= ~SelectionKey.OP_CONNECT;
k.interestOps(ops);
unsafe.finishConnect();
}
// Process OP_WRITE first as we may be able to write some queued buffers and so free memory.
if ((readyOps & SelectionKey.OP_WRITE) != 0) {
// Call forceFlush which will also take care of clear the OP_WRITE once there is nothing left to write
ch.unsafe().forceFlush();
}
// Also check for readOps of 0 to workaround possible JDK bug which may otherwise lead
// to a spin loop
if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
unsafe.read();
}
} catch (CancelledKeyException ignored) {
unsafe.close(unsafe.voidPromise());
}
}
当有OP_ACCEPT事件时调用了unsafe.read();
public void read() {
assert eventLoop().inEventLoop();
final ChannelConfig config = config();
final ChannelPipeline pipeline = pipeline();
final RecvByteBufAllocator.Handle allocHandle = unsafe().recvBufAllocHandle();
allocHandle.reset(config);
boolean closed = false;
Throwable exception = null;
try {
try {
do {
int localRead = doReadMessages(readBuf);
if (localRead == 0) {
break;
}
if (localRead < 0) {
closed = true;
break;
}
allocHandle.incMessagesRead(localRead);
} while (allocHandle.continueReading());
} catch (Throwable t) {
exception = t;
}
int size = readBuf.size();
for (int i = 0; i < size; i ++) {
readPending = false;
pipeline.fireChannelRead(readBuf.get(i));
}
readBuf.clear();
allocHandle.readComplete();
pipeline.fireChannelReadComplete();
if (exception != null) {
closed = closeOnReadError(exception);
pipeline.fireExceptionCaught(exception);
}
if (closed) {
inputShutdown = true;
if (isOpen()) {
close(voidPromise());
}
}
} finally {
// Check if there is a readPending which was not processed yet.
// This could be for two reasons:
// * The user called Channel.read() or ChannelHandlerContext.read() in channelRead(...) method
// * The user called Channel.read() or ChannelHandlerContext.read() in channelReadComplete(...) method
//
// See https://github.com/netty/netty/issues/2254
if (!readPending && !config.isAutoRead()) {
removeReadOp();
}
}
}
}
调用了NioServerSocketChannel的doReadMessages方法。
@Override
protected int doReadMessages(List<Object> buf) throws Exception {
//调用了ServerSocketChannel的accept方法，获取一个客户端SocketChannel
SocketChannel ch = SocketUtils.accept(javaChannel());
try {
if (ch != null) {
buf.add(new NioSocketChannel(this, ch));
return 1;
}
} catch (Throwable t) {
logger.warn("Failed to create a new channel from an accepted socket.", t);
try {
ch.close();
} catch (Throwable t2) {
logger.warn("Failed to close a socket.", t2);
}
}
return 0;
}
readBuf里实际上存的时NioSocketChannel对象，它包装了Java Nio的SocketChannel。
接着使用pipeline触发了ChannelRead、ChannelReadComplete事件。
对于ChannelRead，先后通过head、logging、acceptor
看看acceptor的channelRead方法，msg是NioSocketChannel实例，childHandler是构建ServerBootstrap时创建的ChannelInitializer实例。addLast方法前面已介绍过过。register前面也已经介绍过。
@Override
@SuppressWarnings("unchecked")
public void channelRead(ChannelHandlerContext ctx, Object msg) {
final Channel child = (Channel) msg;
child.pipeline().addLast(childHandler);
setChannelOptions(child, childOptions, logger);
for (Entry<AttributeKey<?>, Object> e: childAttrs) {
child.attr((AttributeKey<Object>) e.getKey()).set(e.getValue());
}
try {
childGroup.register(child).addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture future) throws Exception {
if (!future.isSuccess()) {
forceClose(child, future.cause());
}
}
});
} catch (Throwable t) {
forceClose(child, t);
}
}
childGroup.register(child)这里跟前面的config().group().register(channel)一毛一样
new NioSocketChannel(this, ch)
它的unsafe是NioSocketChannelUnsafe的实例，pipeline还是DefaultChannelPipeline的实例。
还是这个方法processSelectedKey(k, (AbstractNioChannel) a);
当有OP_READ事件时调用了unsafe.read();
@Override
public final void read() {
final ChannelConfig config = config();
if (shouldBreakReadReady(config)) {
clearReadPending();
return;
}
final ChannelPipeline pipeline = pipeline();
final ByteBufAllocator allocator = config.getAllocator();
final RecvByteBufAllocator.Handle allocHandle = recvBufAllocHandle();
allocHandle.reset(config);
ByteBuf byteBuf = null;
boolean close = false;
try {
do {
byteBuf = allocHandle.allocate(allocator);
allocHandle.lastBytesRead(doReadBytes(byteBuf));
if (allocHandle.lastBytesRead() <= 0) {
// nothing was read. release the buffer.
byteBuf.release();
byteBuf = null;
close = allocHandle.lastBytesRead() < 0;
if (close) {
// There is nothing left to read as we received an EOF.
readPending = false;
}
break;
}
allocHandle.incMessagesRead(1);
readPending = false;
pipeline.fireChannelRead(byteBuf);
byteBuf = null;
} while (allocHandle.continueReading());
allocHandle.readComplete();
pipeline.fireChannelReadComplete();
if (close) {
closeOnRead(pipeline);
}
} catch (Throwable t) {
handleReadException(pipeline, byteBuf, t, close, allocHandle);
} finally {
// Check if there is a readPending which was not processed yet.
// This could be for two reasons:
// * The user called Channel.read() or ChannelHandlerContext.read() in channelRead(...) method
// * The user called Channel.read() or ChannelHandlerContext.read() in channelReadComplete(...) method
//
// See https://github.com/netty/netty/issues/2254
if (!readPending && !config.isAutoRead()) {
removeReadOp();
}
}
}
当有OP_WRITE事件时调用ch.unsafe().forceFlush();方法。