Netty源码解析---服务端启动
一个简单的服务端代码:
public class SimpleServer {
public static void main(String[] args) {
NioEventLoopGroup boss = new NioEventLoopGroup(1);
NioEventLoopGroup worker = new NioEventLoopGroup();
try {
ServerBootstrap b = new ServerBootstrap();
b.group(boss,worker)
.channel(NioServerSocketChannel.class)
.handler(new ServerHandler())
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
}
});
ChannelFuture f = b.bind(8000).sync();
f.channel().closeFuture().sync();
} catch (InterruptedException e) {
e.printStackTrace();
}finally {
boss.shutdownGracefully();
worker.shutdownGracefully();
}
}
private static class ServerHandler extends ChannelInboundHandlerAdapter{
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
System.out.println("channelActive");
}
@Override
public void channelRegistered(ChannelHandlerContext ctx) throws Exception {
System.out.println("channelRegistered");
}
@Override
public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
System.out.println("handlerAdded");
}
}
}
我们从bind(...)方法开始
AbstractBootstrap.java
/**
* Create a new {@link Channel} and bind it.
*/
public ChannelFuture bind(int inetPort) {
return bind(new InetSocketAddress(inetPort));
}
/**
* Create a new {@link Channel} and bind it.
*/
public ChannelFuture bind(SocketAddress localAddress) {
validate();
if (localAddress == null) {
throw new NullPointerException("localAddress");
}
return doBind(localAddress);
}
然后我们调了doBind()方法:
AbstractBootstrap.java
private ChannelFuture doBind(final SocketAddress localAddress) {
final ChannelFuture regFuture = initAndRegister();//初始化及注册
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);//绑定端口
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;
}
}
我们继续断点进initAndRegister();这个方法内部
AbstractBootstrap.java
final ChannelFuture initAndRegister() {
Channel channel = null;
try {
//这里的channelFactory是ReflectiveChannelFactory
channel = channelFactory.newChannel();
//初始化参数
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);
}
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;
}
initAndRegister()做了几件事情
- new一个channel
- init这个channel
- 将这个channel register到某个对象
newChannel();我们先来分析一个
ReflectiveChannelFactory.java
@Override
public T newChannel() {
try {
return clazz.newInstance();
} catch (Throwable t) {
throw new ChannelException("Unable to create Channel from class " + clazz, t);
}
}
可以看到里面是通过反射创建了一个NioServerSocketChannel 这个对象
我们再来看看NioServerSocketChannel
NioServerSocketChannel.java
public NioServerSocketChannel() {
this(newSocket(DEFAULT_SELECTOR_PROVIDER));
}
/**
* Create a new instance using the given {@link ServerSocketChannel}.
*/
public NioServerSocketChannel(ServerSocketChannel channel) {
super(null, channel, SelectionKey.OP_ACCEPT);
config = new NioServerSocketChannelConfig(this, javaChannel().socket());
}
这里调用了父类的构造器
我们接下来跟踪一下父类
AbstractNioMessageChannel.java
/**
* @see {@link AbstractNioChannel#AbstractNioChannel(Channel, SelectableChannel, int)}
*/
protected AbstractNioMessageChannel(Channel parent, SelectableChannel ch, int readInterestOp) {
super(parent, ch, readInterestOp);
}
AbstractNioChannel.java
/**
* Create a new instance
*
* @param parent the parent {@link Channel} by which this instance was created. May be {@code null}
* @param ch the underlying {@link SelectableChannel} on which it operates
* @param readInterestOp the ops to set to receive data from the {@link SelectableChannel}
*/
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);
}
}
AbstractChannel.java
/**
* Creates a new instance.
*
* @param parent
* the parent of this channel. {@code null} if there's no parent.
*/
protected AbstractChannel(Channel parent) {
this.parent = parent;
// 创建 ChannelId 对象
id = newId();
// 创建 Unsafe 对象
unsafe = newUnsafe();
// 创建 DefaultChannelPipeline 对象
pipeline = newChannelPipeline();
}
通过不断跟踪我们把Channel对象创建完毕 , 它总共包含一下几个核心组件:
- ChannelId
- Unsafe
- Pipeline
- ChannelHandler
- ChannelConfig
- Java 原生 NIO Channel
接下来我们回到initAndRegister()这个方法,继续往下分析int(channel)这个方法
ServerBootstrap.java
@Override
void init(Channel channel) throws Exception {
final Map<ChannelOption<?>, Object> options = options0();
synchronized (options) {
channel.config().setOptions(options);
}
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(childOptions.size()));
}
synchronized (childAttrs) {
currentChildAttrs = childAttrs.entrySet().toArray(newAttrArray(childAttrs.size()));
}
p.addLast(new ChannelInitializer<Channel>() {
@Override
public void initChannel(Channel ch) throws Exception {
final ChannelPipeline pipeline = ch.pipeline();
ChannelHandler handler = config.handler();
if (handler != null) {
pipeline.addLast(handler);
}
// We add this handler via the EventLoop as the user may have used a ChannelInitializer as handler.
// In this case the initChannel(...) method will only be called after this method returns. Because
// of this we need to ensure we add our handler in a delayed fashion so all the users handler are
// placed in front of the ServerBootstrapAcceptor.
ch.eventLoop().execute(new Runnable() {
@Override
public void run() {
pipeline.addLast(new ServerBootstrapAcceptor(
currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs));
}
});
}
});
}
看到这个方法, 我们大概知道以下几件事:
- 设置option和attr
- 设置新接入channel的option和attr
- 加入新连接处理器
接下来我们再分析
ChannelFuture regFuture = config().group().register(channel);
通过断点可以看到调用到:
SingleThreadEventLoop.java
@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;
}
在调用到:
AbstractChannel.java
@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;
}
AbstractChannel.this.eventLoop = eventLoop;
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);
}
}
}
这段这么长的代码,其实重点就两行代码:
@Override
public final void register(EventLoop eventLoop, final ChannelPromise promise) {
//...
AbstractChannel.this.eventLoop = eventLoop;
//...
register0(promise);
//...
}
我们断点进入到register0
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)) {// 确保 Channel 是打开的
return;
}
// 记录是否为首次注册
boolean firstRegistration = neverRegistered;
// 执行注册逻辑
doRegister();
// 标记首次注册为 false
neverRegistered = false;
// 标记 Channel 为已注册
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();
// 回调通知 `promise` 执行成功
safeSetSuccess(promise);
// 触发通知已注册事件
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);
}
}
最终我们在doRegister()里面看到了java NIO的注册方法
AbstractNioChannel.java
@Override
protected void doRegister() throws Exception {
boolean selected = false;
for (;;) {
try {
selectionKey = javaChannel().register(eventLoop().selector, 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;
}
}
}
}
至此我们分析完了doBind()里面的initAndRegister(),
接下来我们分析doBind0(regFuture, channel, localAddress, promise);
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() {
//注册成功,绑定端口
if (regFuture.isSuccess()) {
channel.bind(localAddress, promise).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
//注册失败,回调通知promise异常
} else {
promise.setFailure(regFuture.cause());
}
}
});
}
我们继续断点跟踪bind()方法:
最后我们调用到AbstractUnsafe 的bind()方法
@Override
public final void bind(final SocketAddress localAddress, final ChannelPromise promise) {
// 判断是否在 EventLoop 的线程中。
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.isRoot()) {
// 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.");
}
// 记录 Channel 是否激活
boolean wasActive = isActive();
try {
// 绑定 Channel 的端口
doBind(localAddress);
} catch (Throwable t) {
safeSetFailure(promise, t);
closeIfClosed();
return;
}
// 若 Channel 是新激活的，触发通知 Channel 已激活的事件。
if (!wasActive && isActive()) {
invokeLater(new Runnable() {
@Override
public void run() {
pipeline.fireChannelActive();
}
});
}
// 回调通知 promise 执行成功
safeSetSuccess(promise);
}
在dobind()方法里面终于用java NIO绑定了端口
NioServerSocketChannel.java
@Override
protected void doBind(SocketAddress localAddress) throws Exception {
if (PlatformDependent.javaVersion() >= 7) {
javaChannel().bind(localAddress, config.getBacklog());
} else {
javaChannel().socket().bind(localAddress, config.getBacklog());
}
}
在invokeLater里面加入了异步执行过程,通过提交一个新任务到EventLoop的线程中
private void invokeLater(Runnable task) {
try {
// This method is used by outbound operation implementations to trigger an inbound event later.
// They do not trigger an inbound event immediately because an outbound operation might have been
// triggered by another inbound event handler method. If fired immediately, the call stack
// will look like this for example:
//
// handlerA.inboundBufferUpdated() - (1) an inbound handler method closes a connection.
// -> handlerA.ctx.close()
// -> channel.unsafe.close()
// -> handlerA.channelInactive() - (2) another inbound handler method called while in (1) yet
//
// which means the execution of two inbound handler methods of the same handler overlap undesirably.
eventLoop().execute(task);
} catch (RejectedExecutionException e) {
logger.warn("Can't invoke task later as EventLoop rejected it", e);
}
}
通过断点跟踪,可以到AbstractUnsafe#beginRead()方法
@Override
public final void beginRead() {
// 判断是否在 EventLoop 的线程中。
assertEventLoop();
// Channel 必须激活
if (!isActive()) {
return;
}
// 执行开始读取
try {
doBeginRead();
} catch (final Exception e) {
invokeLater(new Runnable() {
@Override
public void run() {
pipeline.fireExceptionCaught(e);
}
});
close(voidPromise());
}
}
doBeginRead()方法,执行开始读取,对于NioServerSocketChannel 来说,实现如下:
AbstractNioMessageChannel.java
@Override
protected void doBeginRead() throws Exception {
if (inputShutdown) {
return;
}
super.doBeginRead();
}
AbstractNioChannel.java
@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);
}
}
selectionKey.interestOps()方法调用后,服务端可以开始处理客户端的连接事件.