Java NIO之多个Selector的实现
欢迎大家讨论，我也是接触时间不长，有问题欢迎大家指正。欢迎转载，转载请注明出处
楔子
最近在研究JAVA NIO的相关知识，发现网上多是三种类型的研究文章，一是单Reactor单Selector，二是主从Reactor单Selector，三就是无Reactor单Selector，有一篇是一个Selector绑定两个地址的文章。但是随着链接数增多，单Selector肯定不能满足对于系统性能的要求，所以必然会出现多个selector配合工作的情况。可是我找了很久，也只找到一篇讨论Mina和Grizzly的多selector的实现，并没有自己去实现一个简单的多selector的例子(文章地址： 点击打开链接)。这些天闲来无事，写成一个多selector配合工作的例子，与大家共享。本实例只是关注如何进行多selector配合工作，例子有很多不完美的地方，比如对于包拆分和包合并的判断处理还没有实现，如果错误之处，还请大家指正。
背景
直接来。最基本的Java NIO流程图，如下：
我们知道，如果连接数增多，并且读写量很大，那么服务器的压力会非常大。于是大师们研究出使用reactor模式来搞定。于是出现了下面的实现：
（图片来源： 点击打开链接）
Reactor负责Select，如果发现是OP_ACCEPT，则交给acceptor处理，如果发现是读写，则交给Thread Pool来处理。读写新开了线程，不会阻塞整个主线程的运行。我们今天的例子就是从这个架构发展而来。
实例
多selector，顾名思义，多个selector来配合完成NIO的操作。这样做的好处是可以最大限度的榨取服务器的资源。我们使用一个selector来处理accept的工作，完成绑定，监听，一个selector完成读写，发送的工作。我们称这个版本为V1.1。
首先来看Server.Java,这是Server端main函数的所在地，代码如下：
package com.jjzhk.NIOPractice.MultiSelector;
import java.io.IOException;
public class Server {
public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
int port = 8008;
new Thread(new ServerReactor(port)).start();
}
}
来看ServerReactor.java:
package com.jjzhk.NIOPractice.MultiSelector;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.channels.spi.SelectorProvider;
import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import org.apache.log4j.Logger;
public class ServerReactor implements Runnable {
static Logger logger = Logger.getLogger(ServerReactor.class);
private SelectorProvider selectorProvider = SelectorProvider.provider();
private ServerSocketChannel serverSocketChannel;
public ServerReactor(int port) throws IOException {
serverSocketChannel = selectorProvider.openServerSocketChannel(); //ServerSocketChannel.open();
ServerSocket serverSocket = serverSocketChannel.socket();
serverSocket.bind(new InetSocketAddress("localhost", port), 1024);
serverSocketChannel.configureBlocking(false);
logger.debug(String.format("Server : Server Start.----%d", port));
}
public void run() {
try {
new ServerDispatcher(serverSocketChannel, SelectorProvider.provider()).execute();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
package com.jjzhk.NIOPractice.MultiSelector;
import java.io.IOException;
import java.nio.channels.CancelledKeyException;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.channels.spi.SelectorProvider;
import java.util.Iterator;
import java.util.Set;
import java.util.logging.Level;
import org.apache.log4j.Logger;
public class ServerDispatcher{
private ServerSocketChannel ssc;
private Selector[] selectors = new Selector[3];
private SelectorProvider selectorProvider;
private final static Logger logger = Logger.getLogger(ServerDispatcher.class);
public ServerDispatcher(ServerSocketChannel ssc, SelectorProvider selectorProvider) throws IOException {
this.ssc = ssc;
this.selectorProvider = selectorProvider;
for (int i = 0; i < 3; i++)
{
selectors[i] = selectorProvider.openSelector();
}
}
public Selector getAcceptSelector()
{
return selectors[0];
}
public Selector getReadSelector()
{
return selectors[1];
}
public Selector getWriteSelector()
{
return selectors[1];
}
public void execute() throws IOException
{
SocketHandler r = new SocketAcceptHandler(this, ssc, getAcceptSelector());
new Thread(r).start();
r = new SocketReadHandler(this, ssc, getReadSelector());
new Thread(r).start();
r = new SocketWriteHandler(this, ssc, getWriteSelector());
new Thread(r).start();
}
}
package com.jjzhk.NIOPractice.MultiSelector;
import java.io.IOException;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import org.apache.log4j.Logger;
public abstract class SocketHandler implements Runnable{
protected Selector selector;
protected SocketChannel socketChannel = null;
protected ServerSocketChannel serverSocketChannel;
protected ServerDispatcher dispatcher;
protected final static Logger logger = Logger.getLogger(SocketHandler.class);
private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();;
public SocketHandler(ServerDispatcher dispatcher, ServerSocketChannel sc, Selector selector) throws IOException{
this.selector = selector;
this.serverSocketChannel = sc;
this.dispatcher = dispatcher;
}
public abstract void runnerExecute(int readyKeyOps) throws IOException;
public final void run()
{
while(true)
{
readWriteLock.readLock().lock();
try {
int keyOps = this.Select();
runnerExecute(keyOps);
Thread.sleep(1000);
} catch (Exception e) {
// TODO: handle exception
logger.debug(e.getMessage());
}
finally {
readWriteLock.readLock().unlock();
}
}
}
private int Select() throws IOException
{
int keyOps = this.selector.selectNow();
boolean flag = keyOps > 0;
if (flag)
{
SetreadyKeySet = selector.selectedKeys();
Iterator iterator = readyKeySet.iterator();
while (iterator.hasNext()) {
SelectionKey key = iterator.next();
iterator.remove();
keyOps = key.readyOps();
if (keyOps == SelectionKey.OP_READ || keyOps == SelectionKey.OP_WRITE)
{
socketChannel = (SocketChannel)key.channel();
socketChannel.configureBlocking(false);
}
}
}
return keyOps;
}
}
大家看到这里，就会比较清楚了，每一个线程启动后，都会调用selector.selectNow方法来监听SelectionKey，找到了以后，就会进行处理。可是怎么叫accept处理OP_ACCEPT, read处理OP_READ,Write处理OP_WRITE呢。我都是放到了具体的子类的runnerExecute里面进行判断。
package com.jjzhk.NIOPractice.MultiSelector;
import java.io.IOException;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import org.apache.log4j.Logger;
public class SocketAcceptHandler extends SocketHandler{
private static final Logger logger = Logger.getLogger(SocketAcceptHandler.class);
public SocketAcceptHandler(ServerDispatcher dispatcher, ServerSocketChannel sc, Selector selector)
throws IOException {
super(dispatcher, sc, selector);
serverSocketChannel.register(this.selector, SelectionKey.OP_ACCEPT, this);
}
@Override
public void runnerExecute(int readyKeyOps) throws IOException {
// TODO Auto-generated method stub
if (readyKeyOps == SelectionKey.OP_ACCEPT)
{
socketChannel = serverSocketChannel.accept();
socketChannel.configureBlocking(false);
logger.debug("Server accept");
socketChannel.register(dispatcher.getReadSelector(), SelectionKey.OP_READ);
}
}
}
package com.jjzhk.NIOPractice.MultiSelector;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.CancelledKeyException;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set;
import org.apache.log4j.Logger;
public class SocketReadHandler extends SocketHandler{
static Logger logger = Logger.getLogger(SocketReadHandler.class);
private SelectionKey selectionKey;
private int BLOCK = 4096;
private ByteBuffer receivebuffer = ByteBuffer.allocate(BLOCK);
public SocketReadHandler(ServerDispatcher dispatcher, ServerSocketChannel sc, Selector selector) throws IOException{
super(dispatcher, sc, selector);
}
@Override
public void runnerExecute(int readyKeyOps) throws IOException {
// TODO Auto-generated method stub
int count = 0;
if (SelectionKey.OP_READ == readyKeyOps)
{
receivebuffer.clear();
count = socketChannel.read(receivebuffer);
if (count > 0) {
logger.debug("Server : Readable.");
receivebuffer.flip();
byte[] bytes = new byte[receivebuffer.remaining()];
receivebuffer.get(bytes);
String body = new String(bytes, "UTF-8");
logger.debug("Server : Receive :" + body);
socketChannel.register(dispatcher.getWriteSelector(), SelectionKey.OP_WRITE);
}
}
}
}
package com.jjzhk.NIOPractice.MultiSelector;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set;
import org.apache.log4j.Logger;
public class SocketWriteHandler extends SocketHandler{
static Logger logger = Logger.getLogger(SocketReadHandler.class);
private int BLOCK = 4096;
private ByteBuffer sendbuffer = ByteBuffer.allocate(BLOCK);
private static int Index = 1;
public SocketWriteHandler(ServerDispatcher dispatcher, ServerSocketChannel sc, Selector selector) throws IOException{
super(dispatcher, sc, selector);
}
@Override
public void runnerExecute(int readyKeyOps) throws IOException {
// TODO Auto-generated method stub
if (readyKeyOps == SelectionKey.OP_WRITE)
{
logger.debug("Server : Writable.");
String data = String.format("%d", Index);
byte[] req = data.getBytes();
sendbuffer.clear();
logger.debug(String.format("Server : Write %s", data));
sendbuffer = ByteBuffer.allocate(req.length);
sendbuffer.put(req);
sendbuffer.flip();
socketChannel.write(sendbuffer);
Index++;
socketChannel.register(dispatcher.getReadSelector(), SelectionKey.OP_READ);
}
}
}
扩展
首先，可以将Read和Write的Selector分开，这样理论上会更快，但是会出现一个问题。那就是服务器处理完OP_ACCEPT和第一次的read之后，就会一直处理写，直到接收到客户端的数据才开始读，这样客户端读取的东西就是错误的。我们需要加一个变量来控制，如果上一次是写，那么必须处理完读之后，才能开始第二次的写。
其次，我们可以改造ServerDispatcher，现在维护的是3个selector，其实，应该维护3个SocketHandler，每个Handler里面自己创建新的selector，或者维护两个SocketHandler，一个accept，一个Read/Write，那么这就是什么的架构？这就是Grizzly的核心架构。如果我们维护两个线程池，第一个池子里面 只有一个线程--accept，第二个池子里面，放入读写的Handler，那么这就是Mina或者是Netty的基础架构。对于Netty来说，accept就是父类的handler，读写Handler就是子类的handler。
参考及代码
代码地址：https://github.com/JJZHK/NIOPractice.git
参考了以下图书及文章：
1. 《Netty权威指南》
2.http://www.iteye.com/topic/482269
3.http://blog.csdn.net/thomescai/article/details/6865406