此章是pipeline的源码阅读，pipeline是Netty中负责读写事件的传播的组件
在之前的服务端启动中我们有看到在创建Channel的时候 pipeline被创建
代码如下
protected AbstractChannel(Channel parent) {
this.parent = parent;
id = newId();
unsafe = newUnsafe();
pipeline = newChannelPipeline();
}
protected DefaultChannelPipeline newChannelPipeline() {
return new DefaultChannelPipeline(this);
}
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;
}
在默认情况下 Pipeline新建时会创建两个节点，一个是tailContext 一个是HeadContext
最后通过head.next和tail.prev 将这两个节点变成一个双向链表的形式
接着我们进入tailContext类
final class TailContext extends AbstractChannelHandlerContext implements ChannelInboundHandler {
TailContext(DefaultChannelPipeline pipeline) {
super(pipeline, null, TAIL_NAME, true, false);
setAddComplete();
}
@Override
public ChannelHandler handler() {
return this;
}
@Override
public void channelRegistered(ChannelHandlerContext ctx) throws Exception { }
@Override
public void channelUnregistered(ChannelHandlerContext ctx) throws Exception { }
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
onUnhandledInboundChannelActive();
}
@Override
public void channelInactive(ChannelHandlerContext ctx) throws Exception {
onUnhandledInboundChannelInactive();
}
@Override
public void channelWritabilityChanged(ChannelHandlerContext ctx) throws Exception {
onUnhandledChannelWritabilityChanged();
}
@Override
public void handlerAdded(ChannelHandlerContext ctx) throws Exception { }
@Override
public void handlerRemoved(ChannelHandlerContext ctx) throws Exception { }
@Override
public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
onUnhandledInboundUserEventTriggered(evt);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
onUnhandledInboundException(cause);
}
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
onUnhandledInboundMessage(msg);
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
onUnhandledInboundChannelReadComplete();
}
}
此处可发现TailContext实现了接口ChannelInboundHandler 说明此节点会传播Inbound事件，此类同时继承了AbstractChannelHandlerContext类 说明此类是个pipeline的数据结构 进入AbstractChannelHandlerContext类
abstract class AbstractChannelHandlerContext extends DefaultAttributeMap
implements ChannelHandlerContext, ResourceLeakHint {}
public interface ChannelHandlerContext extends AttributeMap, ChannelInboundInvoker, ChannelOutboundInvoker {
/**
* Return the {@link Channel} which is bound to the {@link ChannelHandlerContext}.
*/
Channel channel();
/**
* Returns the {@link EventExecutor} which is used to execute an arbitrary task.
*/
EventExecutor executor();
/**
* The unique name of the {@link ChannelHandlerContext}.The name was used when then {@link ChannelHandler}
* was added to the {@link ChannelPipeline}. This name can also be used to access the registered
* {@link ChannelHandler} from the {@link ChannelPipeline}.
*/
String name();
/**
* The {@link ChannelHandler} that is bound this {@link ChannelHandlerContext}.
*/
ChannelHandler handler();
/**
* Return {@code true} if the {@link ChannelHandler} which belongs to this context was removed
* from the {@link ChannelPipeline}. Note that this method is only meant to be called from with in the
* {@link EventLoop}.
*/
boolean isRemoved();
@Override
ChannelHandlerContext fireChannelRegistered();
@Override
ChannelHandlerContext fireChannelUnregistered();
@Override
ChannelHandlerContext fireChannelActive();
@Override
ChannelHandlerContext fireChannelInactive();
@Override
ChannelHandlerContext fireExceptionCaught(Throwable cause);
@Override
ChannelHandlerContext fireUserEventTriggered(Object evt);
@Override
ChannelHandlerContext fireChannelRead(Object msg);
@Override
ChannelHandlerContext fireChannelReadComplete();
@Override
ChannelHandlerContext fireChannelWritabilityChanged();
@Override
ChannelHandlerContext read();
@Override
ChannelHandlerContext flush();
/**
* Return the assigned {@link ChannelPipeline}
*/
ChannelPipeline pipeline();
/**
* Return the assigned {@link ByteBufAllocator} which will be used to allocate {@link ByteBuf}s.
*/
ByteBufAllocator alloc();
/**
* @deprecated Use {@link Channel#attr(AttributeKey)}
*/
@Deprecated
@Override
Attribute attr(AttributeKey key);
/**
* @deprecated Use {@link Channel#hasAttr(AttributeKey)}
*/
@Deprecated
@Override
boolean hasAttr(AttributeKey key);
}
AbstractChannelHandlerContext 此类实现了ChannelHandlerContext方法 而ChannelHandlerContext接口代表了PipeLine的节点数据结构
ChannelHandlerContext继承了AttributeMap, ChannelInboundInvoker, ChannelOutboundInvoker
AttributeMap：存储属性判断属性是否存在
public interface AttributeMap {
/**
* Get the {@link Attribute} for the given {@link AttributeKey}. This method will never return null, but may return
* an {@link Attribute} which does not have a value set yet.
*/
Attribute attr(AttributeKey key);
/**
* Returns {@code} true if and only if the given {@link Attribute} exists in this {@link AttributeMap}.
*/
boolean hasAttr(AttributeKey key);
}
ChannelInboundInvoker:会触发一些事件，从类名可知 此接口是Inbound事件的传播 主要是传播读事件和注册事件
ChannelOutboundInvoker:同上 outBound事件的传播 主要是传播写事件
代码略过
接下来是往Pipeline中添加Handler的方法
public void run()throws Exception{
EventLoopGroup bossGroup = new NioEventLoopGroup();
try{
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup)
.channel(NioServerSocketChannel.class)
.childHandler(new ChannelInitializer() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new ObjectDecoder(1024*1024,ClassResolvers.weakCachingConcurrentResolver(this.getClass().getClassLoader())));
ch.pipeline().addLast(new ObjectEncoder());
ch.pipeline().addLast(new DubboServerHandler());
}
})
.option(ChannelOption.SO_BACKLOG,128)
.childOption(ChannelOption.SO_KEEPALIVE,true);
ChannelFuture f = b.bind(port).sync();
f.channel().closeFuture().sync();
}finally {
bossGroup.shutdownGracefully();
}
}
用户Handler添加调用的方法是pipeline中的addLast方法 下面我们进入addLast中看看
public final ChannelPipeline addLast(ChannelHandler... handlers) {
return addLast(null, handlers);
}
public final ChannelPipeline addLast(EventExecutorGroup executor, ChannelHandler... handlers) {
if (handlers == null) {
throw new NullPointerException("handlers");
}
for (ChannelHandler h: handlers) {
if (h == null) {
break;
}
addLast(executor, null, h);
}
return this;
}
public final ChannelPipeline addLast(EventExecutorGroup group, String name, ChannelHandler handler) {
final AbstractChannelHandlerContext newCtx;
synchronized (this) {
checkMultiplicity(handler);
newCtx = newContext(group, filterName(name, handler), handler);
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();
callHandlerCallbackLater(newCtx, true);
return this;
}
EventExecutor executor = newCtx.executor();
if (!executor.inEventLoop()) {
newCtx.setAddPending();
executor.execute(new Runnable() {
@Override
public void run() {
callHandlerAdded0(newCtx);
}
});
return this;
}
}
callHandlerAdded0(newCtx);
return this;
}
checkMultiplicity->判断handler是否被重复添加
newContext(group, filterName(name, handler), handler);->创建节点
addLast0(newCtx);->将创建的节点添加至列表
callHandlerAdded0(newCtx);->回调执行成功方法
checkMultiplicity newContext addLast0比较简单 就不列代码了
下面进入callHandlerAdded0方法
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));
}
}
}
final void setAddComplete() {
for (;;) {
int oldState = handlerState;
// Ensure we never update when the handlerState is REMOVE_COMPLETE already.
// oldState is usually ADD_PENDING but can also be REMOVE_COMPLETE when an EventExecutor is used that is not
// exposing ordering guarantees.
if (oldState == REMOVE_COMPLETE || HANDLER_STATE_UPDATER.compareAndSet(this, oldState, ADD_COMPLETE)) {
return;
}
}
}
此处就是通过CAS将状态设置为ADD_COMPLETE 然后回调到用户代码中 最常见的回调就是ChannelInitializer 下面进入ChannelInitializer handlerAdded方法，ChannelInitializer 被添加到pipeline后会调用这个方法
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);
}
}
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;
}
此处可以看到 当ChannelInitializer 被添加到pipeline后会调用initChannel方法 initChannel方法就是外面自己定义的那个InitChannel方法 执行用户代码，添加完成后执行remove方法 将自身删除
下面进入remove方法
private void remove(ChannelHandlerContext ctx) {
try {
ChannelPipeline pipeline = ctx.pipeline();
if (pipeline.context(this) != null) {
pipeline.remove(this);
}
} finally {
initMap.remove(ctx);
}
}
public final ChannelPipeline remove(ChannelHandler handler) {
//要么获取context 要么抛出异常
remove(getContextOrDie(handler));
return this;
}
private AbstractChannelHandlerContext remove(final AbstractChannelHandlerContext ctx) {
assert ctx != head && ctx != tail;
synchronized (this) {
remove0(ctx);
// If the registered is false it means that the channel was not registered on an eventloop yet.
// In this case we remove the context from the pipeline and add a task that will call
// ChannelHandler.handlerRemoved(...) once the channel is registered.
if (!registered) {
callHandlerCallbackLater(ctx, false);
return ctx;
}
EventExecutor executor = ctx.executor();
if (!executor.inEventLoop()) {
executor.execute(new Runnable() {
@Override
public void run() {
callHandlerRemoved0(ctx);
}
});
return ctx;
}
}
callHandlerRemoved0(ctx);
return ctx;
}
private static void remove0(AbstractChannelHandlerContext ctx) {
AbstractChannelHandlerContext prev = ctx.prev;
AbstractChannelHandlerContext next = ctx.next;
prev.next = next;
next.prev = prev;
}
最后进入了链表节点的删除
删除节点之后会回调删除事件
private void callHandlerRemoved0(final AbstractChannelHandlerContext ctx) {
// Notify the complete removal.
try {
try {
ctx.handler().handlerRemoved(ctx);
} finally {
ctx.setRemoved();
}
} catch (Throwable t) {
fireExceptionCaught(new ChannelPipelineException(
ctx.handler().getClass().getName() + ".handlerRemoved() has thrown an exception.", t));
}
}
此处的操作跟新增操作相同 不进行详解了
接着看看channelpipeline中的事件传播 先看看channelHandler的继承关系
image.png
先看看Channelhandler中有什么功能
public interface ChannelHandler {
/**
* Gets called after the {@link ChannelHandler} was added to the actual context and it's ready to handle events.
*/
void handlerAdded(ChannelHandlerContext ctx) throws Exception;
/**
* Gets called after the {@link ChannelHandler} was removed from the actual context and it doesn't handle events
* anymore.
*/
void handlerRemoved(ChannelHandlerContext ctx) throws Exception;
/**
* Gets called if a {@link Throwable} was thrown.
*
* @deprecated is part of {@link ChannelInboundHandler}
*/
@Deprecated
void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception;
/**
* Indicates that the same instance of the annotated {@link ChannelHandler}
* can be added to one or more {@link ChannelPipeline}s multiple times
* without a race condition.
*
* If this annotation is not specified, you have to create a new handler
* instance every time you add it to a pipeline because it has unshared
* state such as member variables.
*
* This annotation is provided for documentation purpose, just like
* the JCIP annotations.
*/
@Inherited
@Documented
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@interface Sharable {
// no value
}
}
handlerAdd、handlerRemove刚才我们说过 是新增或删除时间完成后进行的回调
exceptionCaught是异常时触发的方法
下面进入ChannelInboundHandler
public interface ChannelInboundHandler extends ChannelHandler {
/**
* The {@link Channel} of the {@link ChannelHandlerContext} was registered with its {@link EventLoop}
*/
void channelRegistered(ChannelHandlerContext ctx) throws Exception;
/**
* The {@link Channel} of the {@link ChannelHandlerContext} was unregistered from its {@link EventLoop}
*/
void channelUnregistered(ChannelHandlerContext ctx) throws Exception;
/**
* The {@link Channel} of the {@link ChannelHandlerContext} is now active
*/
void channelActive(ChannelHandlerContext ctx) throws Exception;
/**
* The {@link Channel} of the {@link ChannelHandlerContext} was registered is now inactive and reached its
* end of lifetime.
*/
void channelInactive(ChannelHandlerContext ctx) throws Exception;
/**
* Invoked when the current {@link Channel} has read a message from the peer.
*/
void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception;
/**
* Invoked when the last message read by the current read operation has been consumed by
* {@link #channelRead(ChannelHandlerContext, Object)}. If {@link ChannelOption#AUTO_READ} is off, no further
* attempt to read an inbound data from the current {@link Channel} will be made until
* {@link ChannelHandlerContext#read()} is called.
*/
void channelReadComplete(ChannelHandlerContext ctx) throws Exception;
/**
* Gets called if an user event was triggered.
*/
void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception;
/**
* Gets called once the writable state of a {@link Channel} changed. You can check the state with
* {@link Channel#isWritable()}.
*/
void channelWritabilityChanged(ChannelHandlerContext ctx) throws Exception;
/**
* Gets called if a {@link Throwable} was thrown.
*/
@Override
@SuppressWarnings("deprecation")
void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception;
}
channelRegistered、channelUnregistered、channelActive、channelInactive、channelReadComplete、exceptionCaught都是对应事件的回调方法
channelRead如果是服务器的话MSG参数代表一个链接 如果是客户端的话MSG代表消息
在pipeline中消息是通过流的形式
Inbound中 事件的传播是从head节点一直传播到tail节点中的 最后在节点中进行内存释放 但是若你在自定义的handler中定义了channelRead方法 并且未向后进行传播 最后未传播到tail节点 的话 内存就不会进行释放 最后会造成内存泄露 Netty中提供了SimpleInBoundHandler若使用了这个类 则会在Read之后自动释放内存 会比自己去释放内存要方便得多，这里不进行介绍
而OutBound中事件的传播是和Inbound相反的从tail节点开始一步步 往前传播 最终传播到Head节点
若直接使用context.write则会从当前节点向上传播而context.pipeline.write是从tail中开始传播