netty学习04

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1.网络服务一般的结构：

读取请求--->解码请求--->处理服务--->编码响应--->发送响应

经典的服务设计是“每一个请求一个线程”，如下图

2.Reactor模式

Reactor响应I/O事件，分发到合适的Handler处理。

Handler执行非阻塞的动作。

基本的Reactor设计，单线程版本

示例代码：

Java代码

package com.zhang.nio;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Set;
public class Reactor implements Runnable {
final Selector selector;
final ServerSocketChannel serverSocketChannel;
public Reactor(int port) throws IOException {
selector = Selector.open();
serverSocketChannel = ServerSocketChannel.open();
serverSocketChannel.socket().bind(new InetSocketAddress(port));
serverSocketChannel.configureBlocking(false);
SelectionKey key = serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
key.attach(new Acceptor());
}
@Override
public void run() {
while (!Thread.interrupted()) {
try {
selector.select();
Set<SelectionKey> selectionKeys = selector.selectedKeys();
for(SelectionKey selectionKey : selectionKeys){
dispatch(selectionKey);
}
selectionKeys.clear();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
private void dispatch(SelectionKey selectionKey) {
Runnable run = (Runnable) selectionKey.attachment();
if(run != null){
run.run();
}
}
class Acceptor implements Runnable{
@Override
public void run() {
try {
SocketChannel channel = serverSocketChannel.accept();
if(channel != null){
new Handler(selector,channel);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}

Java代码

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
public class Handler implements Runnable {
private final static int DEFAULT_SIZE = 8092;
private final SocketChannel socketChannel;
private final SelectionKey seletionKey;
private static final int READING = 0;
private static final int SENDING = 1;
private int state = READING;
ByteBuffer inputBuffer = ByteBuffer.allocate(DEFAULT_SIZE);
ByteBuffer outputBuffer = ByteBuffer.allocate(DEFAULT_SIZE);
public Handler(Selector selector, SocketChannel channel) throws IOException {
this.socketChannel = channel;
socketChannel.configureBlocking(false);
this.seletionKey = socketChannel.register(selector, 0);
seletionKey.attach(this);
seletionKey.interestOps(SelectionKey.OP_READ);
selector.wakeup();
}
@Override
public void run() {
if(state == READING){
read();
}else if(state == SENDING){
write();
}
}
class Sender implements Runnable {
@Override
public void run() {
try {
socketChannel.write(outputBuffer);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
if(outIsComplete()){
seletionKey.cancel();
}
}
}
private void write() {
try {
socketChannel.write(outputBuffer);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
while(outIsComplete()){
seletionKey.cancel();
}
}
private void read() {
try {
socketChannel.read(inputBuffer);
if(inputIsComplete()){
process();
seletionKey.attach(new Sender());
seletionKey.interestOps(SelectionKey.OP_WRITE);
seletionKey.selector().wakeup();
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public boolean inputIsComplete(){
return false;
}
public boolean outIsComplete(){
return false;
}
public void process(){
}
}

NIO支持的特性：

Channels，连接到文件、socket等等，支持非阻塞读。
Buffers，与数组相似的对象，能直接从Channels中读写。
Selectors，辨识哪一个通道的集合有IO事件。（Tell which of a set of Channels have IO events）
SelectionKeys，维护IO事件的状态和绑定。

多线程设计

添加线程增加可扩展性，主要应用在多核处理器中
Worker 线程，Reactors要快速出发handlers。handlers的处理降低了Reactor的速度。将非I/O操作分离到其他线程中处理。
Multiple Reactor Threads，多Reactor线程。Reactor线程可以使IO操作饱和，分布负载到其他的reactors，负载均衡来匹配CPU和IO之间的速度差异。

使用多个Reactors

文章转自：http://ryanflyer.iteye.com/blog/1672876

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