一个疑问
首先一切的一切，是从一次意外开始。
在写一个netty的server的时候，这里有四个handler，inboundHandler实现的类EchoInHandler1与EchoInHandler2，outboundHandler实现的类EchoOutHandler1与EchoOutHandler2；
在添加到pipeline的时候，如果这些handler的存放到pipeline的位置为EchoOutHandler1-EchoOutHandler2-EchoInHandler1-EchoInHandler2，那么一切就正常了。
开始监听，端口为：/127.0.0.1:20000
in1
in2
接收客户端数据:QUERY TIME ORDER
server向client发送数据
out2
out1
Complete1
但是如果存放的顺序是EchoInHandler1-EchoInHandler2-EchoOutHandler1-EchoOutHandler2，那么会出现在出站的时候，EchoOutHandler1与EchoOutHandler2却没有执行。
开始监听，端口为：/127.0.0.1:20000
in1
in2
接收客户端数据:QUERY TIME ORDER
server向client发送数据
Complete1
这是为什么呢？
PS：如果想知道答案可以直接看最后一节
public void start() throws Exception {
EventLoopGroup eventLoopGroup = null;
try {
//server端引导类
ServerBootstrap serverBootstrap = new ServerBootstrap();
//连接池处理数据
eventLoopGroup = new NioEventLoopGroup();
serverBootstrap.group(eventLoopGroup)
.channel(NioServerSocketChannel.class)
//指定通道类型为NioServerSocketChannel，一种异步模式，OIO阻塞模式为OioServerSocketChannel
.localAddress("localhost",port)
//设置InetSocketAddress让服务器监听某个端口已等待客户端连接。
.childHandler(new ChannelInitializer<Channel>() {
//设置childHandler执行所有的连接请求
@Override
protected void initChannel(Channel ch) throws Exception {
// 注册两个InboundHandler，执行顺序为注册顺序，所以应该是InboundHandler1 InboundHandler2
// 注册两个OutboundHandler，执行顺序为注册顺序的逆序，所以应该是OutboundHandler2 OutboundHandler1
ch.pipeline().addLast(new EchoInHandler1());
ch.pipeline().addLast(new EchoInHandler2());
ch.pipeline().addLast(new EchoOutHandler1());
ch.pipeline().addLast(new EchoOutHandler2());
}
});
// 最后绑定服务器等待直到绑定完成，调用sync()方法会阻塞直到服务器完成绑定,
// 然后服务器等待通道关闭，因为使用sync()，所以关闭操作也会被阻塞。
ChannelFuture channelFuture = serverBootstrap.bind().sync();
System.out.println("开始监听，端口为：" + channelFuture.channel().localAddress());
channelFuture.channel().closeFuture().sync();
} finally {
eventLoopGroup.shutdownGracefully().sync();
}
}
EchoInHandler1
package com.aguicode.practice.netty.mutilhandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
/**
* @author aguicode
* @since 2020-3-8
*/
public class EchoInHandler1 extends ChannelInboundHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg)
throws Exception {
System.out.println("in1");
// 通知执行下一个InboundHandler
ctx.fireChannelRead(msg);
//ctx.writeAndFlush(msg);
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
System.out.println("Complete1");
//ctx.flush();//刷新后才将数据发出到SocketChannel
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
throws Exception {
cause.printStackTrace();
ctx.close();
}
}
EchoInHandler2
package com.aguicode.practice.netty.mutilhandler;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import java.util.Date;
/**
* @author aguicode
* @since 2020-3-8
*/
public class EchoInHandler2 extends ChannelInboundHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg)
throws Exception {
System.out.println("in2");
ByteBuf buf = (ByteBuf) msg;
byte[] req = new byte[buf.readableBytes()];
buf.readBytes(req);
String body = new String(req, "UTF-8");
System.out.println("接收客户端数据:" + body);
//向客户端写数据
System.out.println("server向client发送数据");
String currentTime = new Date(System.currentTimeMillis()).toString();
ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());
//ctx.write(resp);
ctx.writeAndFlush(resp);
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
System.out.println("Complete2");
//ctx.flush();//刷新后才将数据发出到SocketChannel
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
throws Exception {
cause.printStackTrace();
ctx.close();
}
}
EchoOutHandler1
package com.aguicode.practice.netty.mutilhandler;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelOutboundHandlerAdapter;
import io.netty.channel.ChannelPromise;
import java.util.Date;
/**
* @author aguicode
* @since 2020-3-8
*/
public class EchoOutHandler1 extends ChannelOutboundHandlerAdapter {
@Override
// 向client发送消息
public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
System.out.println("out1");
/*System.out.println(msg);*/
String response = "\nI am ok!\n";
ByteBuf encoded = ctx.alloc().buffer(4 * response.length());
encoded.writeBytes(response.getBytes());
String currentTime = new Date(System.currentTimeMillis()).toString();
ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());
ctx.write(resp);
ctx.writeAndFlush(encoded);
ctx.flush();
}
}
EchoOutHandler2
package com.aguicode.practice.netty.mutilhandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelOutboundHandlerAdapter;
import io.netty.channel.ChannelPromise;
/**
* @author aguicode
* @since 2020-3-8
*/
public class EchoOutHandler2 extends ChannelOutboundHandlerAdapter {
@Override
public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
System.out.println("out2");
// 执行下一个OutboundHandler
/*System.out.println("at first..msg = "+msg);
msg = "hi newed in out2";*/
// 通知执行下一个OutboundHandler
super.write(ctx, msg, promise);
super.flush(ctx);
}
}
几个重要的概念
netty中有以下几个重要的概念，首先是server与client，它们中有channel、channelPipeline、channelHandler、channelHandlerContext、ServerBootStrap、bootStrap、channelFuture、selector、Eventloop；
关于Netty的组件中的介绍会安排到另外一篇详细解答，这里只是分析in与out boundHandler执行顺序
原理解析
channelHandler 中定义outboundhandler和inboundhandler，表示一个请求进来时通过入站inboundhandler，而内部进行一些业务的逻辑处理之后出站使用outboundhandler，
这里handler是定义在channelPipeline里边的，handler之间是一种双向链表的关系，inBound事件从head节点传播到tail节点，outBound事件从tail节点传播到head节点。
/**
* I/O Request
* via {@link Channel} or
* {@link ChannelHandlerContext}
* |
* +---------------------------------------------------+---------------+
* | ChannelPipeline | |
* | \|/ |
* | +---------------------+ +-----------+----------+ |
* | | Inbound Handler N | | Outbound Handler 1 | |
* | +----------+----------+ +-----------+----------+ |
* | /|\ | |
* | | \|/ |
* | +----------+----------+ +-----------+----------+ |
* | | Inbound Handler N-1 | | Outbound Handler 2 | |
* | +----------+----------+ +-----------+----------+ |
* | /|\ . |
* | . . |
* | ChannelHandlerContext.fireIN_EVT() ChannelHandlerContext.OUT_EVT()|
* | [ method call] [method call] |
* | . . |
* | . \|/ |
* | +----------+----------+ +-----------+----------+ |
* | | Inbound Handler 2 | | Outbound Handler M-1 | |
* | +----------+----------+ +-----------+----------+ |
* | /|\ | |
* | | \|/ |
* | +----------+----------+ +-----------+----------+ |
* | | Inbound Handler 1 | | Outbound Handler M | |
* | +----------+----------+ +-----------+----------+ |
* | /|\ | |
* +---------------+-----------------------------------+---------------+
* | \|/
* +---------------+-----------------------------------+---------------+
* | | | |
* | [ Socket.read() ] [ Socket.write() ] |
* | |
* | Netty Internal I/O Threads (Transport Implementation) |
* +-------------------------------------------------------------------+
*/
例如在建立三次握手之后，开始读数据，从head节点发起，准确来说是head的unsafe方法发起，inbound寻找下一个inbound时，调用invokeChannelActive(next)，一个个递归调用，直到最后一个inBound节点—即tail节点，并且tail节点作为尾节点，会终止inbound事件的传播，读事件就结束了，
这个时候，经过一段业务逻辑的处理，就需要处理outbound事件，转而反向传播，outbound则调用的是writeAndFlush()，直到head节点，数据最终会落在head节点的unsafe.write方法。
我是分割线
执行顺序的分析
那么原理都懂了，这里就重点分析一下inboundHandler与outboundHandler添加顺序不同，带来执行顺序的问题
- inbound事件在pipeline中传输方向是head->tail，即从头到尾，而且会忽略outbound事件
invokeChannelRead(findContextInbound(MASK_CHANNEL_READ), msg);
重要的是find方法
private AbstractChannelHandlerContext findContextInbound(int mask) {
AbstractChannelHandlerContext ctx = this;
do {
ctx = ctx.next;
} while ((ctx.executionMask & mask) == 0);
return ctx;
}
或者类似这样子：
- outbound事件在pipeline传输方向正好相反，会从tail->head，即从尾到头，同时也会忽略inbound事件
final AbstractChannelHandlerContext next = findContextOutbound(flush ?
(MASK_WRITE | MASK_FLUSH) : MASK_WRITE);
重要的是find方法
private AbstractChannelHandlerContext findContextOutbound(int mask) {
AbstractChannelHandlerContext ctx = this;
do {
ctx = ctx.prev;
} while ((ctx.executionMask & mask) == 0);
return ctx;
}
或者类似这样子：
但是 需要关注的是：AbstractChannelHandlerContext ctx = this;
其实AbstractChannelHandlerContext是上下文都共享的，所以，
如果是EchoInHandler1-EchoInHandler2-EchoOutHandler1-EchoOutHandler2，那么一开始入站执行了EchoInHandler1-EchoInHandler2，因为do-while循环跳出，ctx留在了EchoInHandler2的位置，在出站的时候，在EchoInHandler2的位置反向遍历，只会遍历EchoInHandler2-EchoInHandler1，那么自然就不会去读取-EchoOutHandler1-EchoOutHandler2了。
相反，如果是EchoOutHandler1-EchoOutHandler2-EchoInHandler1-EchoInHandler2的顺序，一开始入站ctx到了EchoInHandler2的位置，反向遍历就会经过EchoInHandler2-EchoInHandler1-EchoOutHandler2-EchoOutHandler1
