Netty Reactor 线程模型（随记）
Netty被称为一个高性能、高可扩展性能的异步事件驱动的网络应用程序框架，它极大地简化了TCP和UDP客户端和服务器开发等网络编程。
Netty的Reactor模型中有四个核心概念：
- Resources资源（请求和任务）
- Synchronous Event Demultiplexer同步事件复用器
- Dispatcher 分配器
- Request Handler请求处理器
Reactor 模式设计和实现，我们先了解下它两端的通信方式：
服务端通信序列图如下：
客户端通信方式：
Netty 的 IO 线程 NioEventLoop 由于聚合了多路复用器 Selector，可以同时并发处理成百上千个客户端 Channel，由于读写操作都是非阻塞的，这就可以充分提升 IO 线程的运行效率，避免由于频繁 IO 阻塞导致的线程挂起。
Reactor线程模型的两次转变：
Reactor 线程接收请求->分发给线程池处理请求
mainReactor接收->分发给subReactor读写->具体业务逻辑分发给单独的线程池处理
上图出自Doug Lea的著名文档《Scalable IO in java》，建议大家可以去看看。
下载地址：http://gee.cs.oswego.edu/dl/cpjslides/nio.pdf
刚开始自己也没太明白这种设计的好处，于是就深入了下源码，看了看设计思想，深有体会。看百遍不如动手写一遍，这样才会有深入体会。
UML图
代码如下
package com.wywhdgg.netty.example.demo.reactor;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.util.Iterator;
import java.util.Random;
import java.util.Set;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;
/***
*@author dzhbo
*@date 2019/12/5 23:07
*@Description: Reactorc线程模型
*@version 1.0.0
*/
public class ReactorServer {
/**
* 处理业务的线程池
**/
private static ExecutorService workThreadPool = Executors.newCachedThreadPool();
/**
* 封装了selector.select()等事件轮询的代码
*/
abstract class ReactorThread extends Thread {
/**
* 通道选择
**/
Selector selector;
/**
* 任务队列
**/
LinkedBlockingQueue taskQueue = new LinkedBlockingQueue<>();
/**
* Selector监听到有事件后,调用这个方法
*/
public abstract void handler(SelectableChannel channel) throws Exception;
private ReactorThread() throws IOException {
selector = Selector.open();
}
volatile boolean running = false;
@Override
public void run() {
// 轮询Selector事件
while (running) {
try {
/**执行队列中的任务**/
Runnable task;
/**非阻塞，如果获取到，就开始处理**/
while ((task = taskQueue.poll()) != null) task.run();
selector.select(1000);
/**获取查询结果 遍历查询结果**/
Set selected = selector.selectedKeys();
Iterator iter = selected.iterator();
while (iter.hasNext()) {
SelectionKey key = iter.next();
iter.remove();
int readyOps = key.readyOps();
// 关注 Read 和 Accept两个事件
if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
try {
SelectableChannel channel = (SelectableChannel) key.attachment();
channel.configureBlocking(false);
handler(channel);
if (!channel.isOpen()) {
key.cancel(); // 如果关闭了,就取消这个KEY的订阅
}
} catch (Exception ex) {
key.cancel(); // 如果有异常,就取消这个KEY的订阅
}
}
}
selector.selectNow();
} catch (IOException e) {
e.printStackTrace();
}
}
}
private SelectionKey register(SelectableChannel channel) throws Exception {
/***
register要以任务提交的形式，让reactor线程去处理的原因：
1.因为线程在执行channel注册到selector的过程中，会和调用selector.select()方法的线程争用同一把锁
2.select()方法实在eventLoop中通过while循环调用的，争抢的可能性很高，为了让register能更快的执行，就放到同一个线程来处理
*/
FutureTask futureTask = new FutureTask<>(() -> channel.register(selector, 0, channel));
taskQueue.add(futureTask);
return futureTask.get();
}
private void doStart() {
if (!running) {
running = true;
start();
}
}
}
private ServerSocketChannel serverSocketChannel;
// 1、创建多个线程 - accept处理reactor线程 (accept线程)
private ReactorThread[] mainReactorThreads = new ReactorThread[1];
// 2、创建多个线程 - io处理reactor线程 (I/O线程)
private ReactorThread[] subReactorThreads = new ReactorThread[8];
/**
* 初始化线程组
*/
private void newGroup() throws IOException {
// 创建IO线程,负责处理客户端连接以后socketChannel的IO读写
for (int i = 0; i < subReactorThreads.length; i++) {
subReactorThreads[i] = new ReactorThread() {
@Override
public void handler(SelectableChannel channel) throws IOException {
/**work线程只负责处理IO处理，不处理accept事件*/
SocketChannel socketChannel = (SocketChannel) channel;
ByteBuffer requestBuffer = ByteBuffer.allocate(1024);
while (socketChannel.isOpen() && socketChannel.read(requestBuffer) != -1) {
if (requestBuffer.position() > 0) break;
}
if (requestBuffer.position() == 0) {
return;
}
/**写模式切换读
初始位置等于限制
limit = position;
position = 0; //初始位置设置为0
mark = -1; //清除标记
* **/
requestBuffer.flip();
byte[] content = new byte[requestBuffer.limit()];
requestBuffer.get(content);
System.out.println(Thread.currentThread().getName() +
"收到数据,IP ADDRESS：" + socketChannel.getRemoteAddress()
+ " CONTENT:" + new String(content));
workThreadPool.submit(() -> {
System.out.println("---------------执行业务数据---------------");
});
// 响应结果 200
String response = "HTTP/1.1 200 OK\r\n" +
"Content-Length: 11\r\n\r\n" +
"Hello World";
ByteBuffer buffer = ByteBuffer.wrap(response.getBytes());
while (buffer.hasRemaining()) {
socketChannel.write(buffer);
}
}
};
}
// 创建mainReactor线程, 只负责处理serverSocketChannel
for (int i = 0; i < mainReactorThreads.length; i++) {
mainReactorThreads[i] = new ReactorThread() {
AtomicInteger incr = new AtomicInteger(0);
@Override
public void handler(SelectableChannel channel) throws Exception {
ServerSocketChannel serverSocketChannel = (ServerSocketChannel) channel;
SocketChannel socketChannel = serverSocketChannel.accept();
socketChannel.configureBlocking(false);
// 收到连接建立的通知之后，分发给I/O线程继续去读取数据
int index = incr.getAndIncrement() % subReactorThreads.length;
ReactorThread workEventLoop = subReactorThreads[index];
workEventLoop.doStart();
/**注册channel 信息**/
SelectionKey selectionKey = workEventLoop.register(socketChannel);
selectionKey.interestOps(SelectionKey.OP_READ);
System.out.println(Thread.currentThread().getName() + "收到新连接 : " + socketChannel.getRemoteAddress());
}
};
}
}
/**
* 初始化channel,并且绑定一个eventLoop线程
*
* @throws IOException IO异常
*/
private void initAndRegister() throws Exception {
// 1、 创建ServerSocketChannel
serverSocketChannel = ServerSocketChannel.open();
serverSocketChannel.configureBlocking(false);
// 2、 将serverSocketChannel注册到selector
int index = new Random().nextInt(mainReactorThreads.length);
mainReactorThreads[index].doStart();
SelectionKey selectionKey = mainReactorThreads[index].register(serverSocketChannel);
//注册接收事件
selectionKey.interestOps(SelectionKey.OP_ACCEPT);
}
/**
* 绑定端口
*
* @throws IOException IO异常
*/
private void bind() throws IOException {
// 1、 正式绑定端口，对外服务
serverSocketChannel.bind(new InetSocketAddress(8080));
System.out.println("启动完成，端口8080");
}
public static void main(String[] args) {
ReactorServer reactorServer = new ReactorServer();
try {
//初始化线程组
reactorServer.newGroup();
//初始化链接
reactorServer.initAndRegister();
//绑定端口号
reactorServer.bind();
} catch (Exception e) {
e.printStackTrace();
}
}
}
// Thread-8收到新连接 : /127.0.0.1:51577
// Thread-0收到数据,IP ADDRESS：/127.0.0.1:51577 CONTENT:GET / HTTP/1.1
// Host: 127.0.0.1:8080
// Connection: keep-alive
// Cache-Control: max-age=0
// Upgrade-Insecure-Requests: 1
// User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.88 Safari/537.36
// Sec-Fetch-User: ?1
// Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
//Sec-Fetch-Site: cross-site
//Sec-Fetch-Mode: navigate
//Accept-Encoding: gzip, deflate, br
//Accept-Language: zh-CN,zh;q=0.9
//
//
//Thread-8收到新连接 : /127.0.0.1:51578
//---------------执行业务数据---------------
//Thread-0收到数据,IP ADDRESS：/127.0.0.1:51577 CONTENT:GET /favicon.ico HTTP/1.1
//Host: 127.0.0.1:8080
//Connection: keep-alive
//Pragma: no-cache
//Cache-Control: no-cache
//User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.88 Safari/537.36
//Accept: image/webp,image/apng,image/*,*/*;q=0.8
// Sec-Fetch-Site: same-origin
// Sec-Fetch-Mode: no-cors
// Referer: http://127.0.0.1:8080/
// Accept-Encoding: gzip, deflate, br
// Accept-Language: zh-CN,zh;q=0.9
//
//
// ---------------执行业务数据---------------