网络编程基础(3) : IO多路复用(单线程)

1. 简介

IO多路复用(multiplexing)属于同步IO网络模型

是以Reactor模式实现

常见的IO多路复用应用有：select、poll、epoll

有关于select的应用方式，请参阅[C语言] 基于Linux的一对一Socket简易聊天程序实例

本篇文章采用Java的NIO框架来实现单线程的IO多路复用

2. Reactor模式的组成角色

1. Reactor：负责派发IO事件给对应的角色处理。为了监听IO事件，select必须实现在Reactor中。

2. Acceptor：负责接受client的连线，然后给client绑定一个Handler并注册IO事件到Reactor上监听。

3. Handler：负责处理与client交互的事件或行为。通常因为Handler要处理与所对应client交互的多个事件或行为，为了简化设计，会以状态模式来实现Handler。

3. 代码实现

[TCPReactor.java]

// Reactor線程package server;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.util.Iterator;import java.util.Set;public class TCPReactor implements Runnable {private final ServerSocketChannel ssc;private final Selector selector;public TCPReactor(int port) throws IOException {selector = Selector.open();ssc = ServerSocketChannel.open();InetSocketAddress addr = new InetSocketAddress(port);ssc.socket().bind(addr); // 在ServerSocketChannel綁定監聽端口ssc.configureBlocking(false); // 設置ServerSocketChannel為非阻塞SelectionKey sk = ssc.register(selector, SelectionKey.OP_ACCEPT); // ServerSocketChannel向selector註冊一個OP_ACCEPT事件，然後返回該通道的keysk.attach(new Acceptor(selector, ssc)); // 給定key一個附加的Acceptor對象}@Overridepublic void run() {while (!Thread.interrupted()) { // 在線程被中斷前持續運行System.out.println("Waiting for new event on port: " + ssc.socket().getLocalPort() + "...");try {if (selector.select() == 0) // 若沒有事件就緒則不往下執行continue;} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}Set<SelectionKey> selectedKeys = selector.selectedKeys(); // 取得所有已就緒事件的key集合Iterator<SelectionKey> it = selectedKeys.iterator();while (it.hasNext()) {dispatch((SelectionKey) (it.next())); // 根據事件的key進行調度it.remove();}}}/* * name: dispatch(SelectionKey key) * description: 調度方法，根據事件綁定的對象開新線程 */private void dispatch(SelectionKey key) {Runnable r = (Runnable) (key.attachment()); // 根據事件之key綁定的對象開新線程if (r != null)r.run();}}

[Acceptor.java]

// 接受連線請求線程package server;import java.io.IOException;import java.nio.channels.SelectionKey;import java.nio.channels.Selector;import java.nio.channels.ServerSocketChannel;import java.nio.channels.SocketChannel;public class Acceptor implements Runnable {private final ServerSocketChannel ssc;private final Selector selector;public Acceptor(Selector selector, ServerSocketChannel ssc) {this.ssc=ssc;this.selector=selector;}@Overridepublic void run() {try {SocketChannel sc= ssc.accept(); // 接受client連線請求System.out.println(sc.socket().getRemoteSocketAddress().toString() + " is connected.");if(sc!=null) {sc.configureBlocking(false); // 設置為非阻塞SelectionKey sk = sc.register(selector, SelectionKey.OP_READ); // SocketChannel向selector註冊一個OP_READ事件，然後返回該通道的keyselector.wakeup(); // 使一個阻塞住的selector操作立即返回sk.attach(new TCPHandler(sk, sc)); // 給定key一個附加的TCPHandler對象}} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}

我们先来简单点的，Handler不以​​状态模式实现，只以比较直觉的方式实现。

[TCPHandler.java]

// Handler線程package server;import java.io.IOException;import java.nio.ByteBuffer;import java.nio.channels.SelectionKey;import java.nio.channels.SocketChannel;import java.util.concurrent.LinkedBlockingQueue;import java.util.concurrent.ThreadPoolExecutor;import java.util.concurrent.TimeUnit;public class TCPHandler implements Runnable {private final SelectionKey sk;private final SocketChannel sc;int state; public TCPHandler(SelectionKey sk, SocketChannel sc) {this.sk = sk;this.sc = sc;state = 0; // 初始狀態設定為READING}@Overridepublic void run() {try {if (state == 0)read(); // 讀取網絡數據elsesend(); // 發送網絡數據} catch (IOException e) {System.out.println("[Warning!] A client has been closed.");closeChannel();}}private void closeChannel() {try {sk.cancel();sc.close();} catch (IOException e1) {e1.printStackTrace();}}private synchronized void read() throws IOException {// non-blocking下不可用Readers，因為Readers不支援non-blockingbyte[] arr = new byte[1024];ByteBuffer buf = ByteBuffer.wrap(arr);int numBytes = sc.read(buf); // 讀取字符串if(numBytes == -1){System.out.println("[Warning!] A client has been closed.");closeChannel();return;}String str = new String(arr); // 將讀取到的byte內容轉為字符串型態if ((str != null) && !str.equals(" ")) {process(str); // 邏輯處理System.out.println(sc.socket().getRemoteSocketAddress().toString()+ " > " + str);state = 1; // 改變狀態sk.interestOps(SelectionKey.OP_WRITE); // 通過key改變通道註冊的事件sk.selector().wakeup(); // 使一個阻塞住的selector操作立即返回}}private void send() throws IOException  {// get message from message queueString str = "Your message has sent to "+ sc.socket().getLocalSocketAddress().toString() + "\r\n";ByteBuffer buf = ByteBuffer.wrap(str.getBytes()); // wrap自動把buf的position設為0，所以不需要再flip()while (buf.hasRemaining()) {sc.write(buf); // 回傳給client回應字符串，發送buf的position位置 到limit位置為止之間的內容}state = 0; // 改變狀態sk.interestOps(SelectionKey.OP_READ); // 通過key改變通道註冊的事件sk.selector().wakeup(); // 使一個阻塞住的selector操作立即返回}void process(String str) {// do process(decode, logically process, encode)..// ..}}

最后是主程序代码

[Main.java]

package server;import java.io.IOException;public class Main {public static void main(String[] args) {// TODO Auto-generated method stubtry {TCPReactor reactor = new TCPReactor(1333);reactor.run();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}

下面附上客戶端代碼：

[Client.java]

package main.pkg;import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import java.io.PrintWriter;import java.net.Socket;import java.net.UnknownHostException;public class Client {/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubString hostname=args[0];int port = Integer.parseInt(args[1]);//String hostname="127.0.0.1";//int port=1333;System.out.println("Connecting to "+ hostname +":"+port);try {Socket client = new Socket(hostname, port); // 連接至目的地System.out.println("Connected to "+ hostname);PrintWriter out = new PrintWriter(client.getOutputStream());BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));String input;while((input=stdIn.readLine()) != null) { // 讀取輸入out.println(input); // 發送輸入的字符串out.flush(); // 強制將緩衝區內的數據輸出if(input.equals("exit")){break;}System.out.println("server: "+in.readLine());}client.close();System.out.println("client stop.");} catch (UnknownHostException e) {// TODO Auto-generated catch blockSystem.err.println("Don't know about host: " + hostname);} catch (IOException e) {// TODO Auto-generated catch blockSystem.err.println("Couldn't get I/O for the socket connection");}}}

下一篇将给出使用多线程的IO多路复用代码实现。