Java NIO 反应堆模式

Java NIO 反应堆模式简单模型

一般NIO里反应堆模式都是这样：一个Acceptor（当然多个也行，不过一般场景一个够了）负责accept事件，把接收到Socket CHannel注册到按某种算法从Reactor池中取出的一个Reactor上，注册的事件为读，写等，之后这个Socket Channel的所有IO事件都和Acceptor没关系，都由被注册到的那个Reactor来负责。

每个Acceptor和每个Reactor都各自持有一个Selector

当然每个Acceptor和Reactor都得是一个线程（起码在逻辑上得是线程）

简单实现，三个类NioAcceptor、NioReactor和ReactorPool：

package cc.lixiaohui.demo.dp.reator;

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.Objects;
import java.util.Set;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Acceptor负责处理SelectionKey.OP_ACCEPT事件, 将接收到的SocketChannel注册到Reactor上去
 */
public class NioAcceptor {
	
	private int port;
	
	private String host;
	
	private Selector selector; // Java NIO Selector
	
	private final ServerSocketChannel serverChannel; // Java NIO ServerSocketChannel
	
	private ReactorPool reactorPool; // NioReactor池
	
	private Thread thread; // 工作线程
	
	private volatile boolean stop = false;
	
	private static final Logger logger = LoggerFactory.getLogger(NioAcceptor.class);
	
	public NioAcceptor(int port, String host, int reactorPoolSize) throws IOException {
		this.port = port;
		this.host = Objects.requireNonNull(host);
		this.reactorPool = new ReactorPool(reactorPoolSize);
		
		selector = Selector.open(); // 创建selector
		serverChannel = ServerSocketChannel.open(); // new server socket channel
		serverChannel.configureBlocking(false); // in non-blocking mode
		serverChannel.bind(new InetSocketAddress(host, port)); // bind
		serverChannel.register(selector, SelectionKey.OP_ACCEPT); // 
	}
	
	public void stop() throws InterruptedException {
		stop = true;
		thread.join();
	}
	
	public void start() {
		thread = new Thread(new AcceptTask(this));
		thread.start();
	}
	
	private static class AcceptTask implements Runnable {
		
		NioAcceptor acceptor;
		
		AcceptTask(NioAcceptor acceptor) {
			this.acceptor = acceptor;
		}

		public void run() {
			final Selector selector = acceptor.selector;
			Set<SelectionKey> keys = null;
			while (!acceptor.stop) { // 运行中
				try {
					selector.select(1000L); // select, 最多等1秒
					keys = selector.selectedKeys();
					try {
						for (SelectionKey key : keys) {
							if (key.isValid() && key.isAcceptable()) { // 可accept
								SocketChannel channel = acceptor.serverChannel.accept();
								channel.configureBlocking(false);
								// 取下一个Reactor并把SocketChannel加入到Reactor的注册队列
								acceptor.reactorPool.nextReactor().postRegistry(channel);
							} else {
								key.cancel();
							}
						}
					} finally {
						keys.clear();
					}
				} catch (IOException e) {
					logger.error("", e);
				}
			}
		}
	}
}

/**
 * Reactor负责SelectionKey.OP_READ | SelectionKey.OP_WRITE等事件
 */
public class NioReactor {
	
	/** 待注册的{@link SocketChannel} 队列 */
	private Queue<SocketChannel> registerQueue = new ConcurrentLinkedQueue<SocketChannel>();
	
	private Selector selector;
	
	private volatile boolean stop = false;
	
	private Thread thread;
	
	private static final Logger logger = LoggerFactory.getLogger(NioReactor.class);
	
	public NioReactor() throws IOException {
		selector = Selector.open();
	}
	
	public void postRegistry(SocketChannel channel) {
		registerQueue.add(channel);
		selector.wakeup(); // 唤醒selector, 以便让其即时处理注册
	}
	
	public NioReactor start() {
		thread = new Thread(new ReactTask(this));
		thread.start();
		return this;
	}
	
	public void stop() throws InterruptedException {
		stop = true;
		thread.join();
	}
	
	/**
	 * 处理队列里面的待注册的SocketChannel
	 */
	private void doRegister(Selector selector) {
		while (!registerQueue.isEmpty()) {
			SocketChannel channel = registerQueue.poll();
			try {
				// 注册读事件, 写事件无需注册, 写事件是业务驱动的, 当往channel写入 数据未写完时再注册写事件
				channel.register(selector, SelectionKey.OP_READ); 
			} catch (ClosedChannelException e) {
				logger.error("", e);
			}
		}
	}
	
	private void handleWrite(SelectionKey key) {
		// TODO 业务写
	}

	private void handleRead(SelectionKey key) {
		// TODO 业务读
	}
	
	private static class ReactTask implements Runnable {
		
		NioReactor reactor;
		
		ReactTask(NioReactor reactor) {
			this.reactor = reactor;
		}
		
		public void run() {
			Set<SelectionKey> keys = null;
			while (!reactor.stop) {
				final Selector selector = reactor.selector;
				try {
					selector.select(500L);
					reactor.doRegister(selector); // 处理注册
					keys = selector.selectedKeys();
					
					for (SelectionKey key : keys) {
						try {
							if (!key.isValid()) { // not valid
								key.cancel();
								continue;
							}
							if (key.isReadable()) { // 可读
								reactor.handleRead(key);
							}
							if (key.isWritable()) { // 可写
								reactor.handleWrite(key);
							}
						} catch (Throwable t) {
							logger.error("", t);
							continue;
						}
					}
				} catch (IOException e) {
					logger.error("", e);
				}
			}
		}
	}
 }

ReactorPool用来管理Reactor：

public class ReactorPool extends LinkedList<NioReactor>{
	
	private static final long serialVersionUID = 6525233920805533099L;
	
	private final int capacity;
	
	public ReactorPool(int size) {
		this.capacity = size;
	}
	// 轮询算法取下一个Reactor
	public NioReactor nextReactor() throws IOException {
		// 新建或从头部拿一个Reactor
		NioReactor reactor = size() < capacity ? new NioReactor().start() : poll();
		add(reactor);// 加到尾部
		return reactor;
	}

}

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参考：

Netty的NIO模型

Mycat的NIO实现