Reactor模型
有关Reactor模型结构，可以参考Doug Lea在 Scalable IO in Java 中的介绍。这里简单介绍一下Reactor模式的典型实现：
Reactor单线程模型
这是最简单的单Reactor单线程模型。Reactor线程负责多路分离套接字、accept新连接，并分派请求到处理器链中。该模型适用于处理器链中业务处理组件能快速完成的场景。不过，这种单线程模型不能充分利用多核资源，所以实际使用的不多。
image.png
这个模型和上面的NIO流程很类似，只是将消息相关处理独立到了Handler中去了。
代码实现如下：
public class Reactor implements Runnable {
final Selector selector;
final ServerSocketChannel serverSocketChannel;
public static void main(String[] args) throws IOException {
new Thread(new Reactor(1234)).start();
}
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 selectionKeys = selector.selectedKeys();
for (SelectionKey selectionKey : selectionKeys) {
dispatch(selectionKey);
}
selectionKeys.clear();
} catch (IOException e) {
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) {
e.printStackTrace();
}
}
}
}
class Handler implements Runnable {
private final static int DEFAULT_SIZE = 1024;
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) {
e.printStackTrace();
}
if (outIsComplete()) {
seletionKey.cancel();
}
}
}
private void write() {
try {
socketChannel.write(outputBuffer);
} catch (IOException e) {
e.printStackTrace();
}
while (outIsComplete()) {
seletionKey.cancel();
}
}
private void read() {
try {
socketChannel.read(inputBuffer);
if (inputIsComplete()) {
process();
System.out.println("接收到来自客户端（" + socketChannel.socket().getInetAddress().getHostAddress()
+ "）的消息：" + new String(inputBuffer.array()));
seletionKey.attach(new Sender());
seletionKey.interestOps(SelectionKey.OP_WRITE);
seletionKey.selector().wakeup();
}
} catch (IOException e) {
e.printStackTrace();
}
}
public boolean inputIsComplete() {
return true;
}
public boolean outIsComplete() {
return true;
}
public void process() {
// do something...
}
}
虽然上面说到NIO一个线程就可以支持所有的IO处理。但是瓶颈也是显而易见的。我们看一个客户端的情况，如果这个客户端多次进行请求，如果在Handler中的处理速度较慢，那么后续的客户端请求都会被积压，导致响应变慢！所以引入了Reactor多线程模型。
Reactor多线程模型
相比上一种模型，该模型在处理器链部分采用了多线程（线程池）：
image.png
Reactor多线程模型就是将Handler中的IO操作和非IO操作分开，操作IO的线程称为IO线程，非IO操作的线程称为工作线程。这样的话，客户端的请求会直接被丢到线程池中，客户端发送请求就不会堵塞。
可以将Handler做如下修改：
class Handler implements Runnable {
private final static int DEFAULT_SIZE = 1024;
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);
private Selector selector;
private static ExecutorService executorService = Executors.newFixedThreadPool(Runtime.getRuntime()
.availableProcessors());
private static final int PROCESSING = 3;
public Handler(Selector selector, SocketChannel channel) throws IOException {
this.selector = selector;
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) {
e.printStackTrace();
}
if (outIsComplete()) {
seletionKey.cancel();
}
}
}
private void write() {
try {
socketChannel.write(outputBuffer);
} catch (IOException e) {
e.printStackTrace();
}
if (outIsComplete()) {
seletionKey.cancel();
}
}
private void read() {
try {
socketChannel.read(inputBuffer);
if (inputIsComplete()) {
process();
executorService.execute(new Processer());
}
} catch (IOException e) {
e.printStackTrace();
}
}
public boolean inputIsComplete() {
return true;
}
public boolean outIsComplete() {
return true;
}
public void process() {
}
synchronized void processAndHandOff() {
process();
state = SENDING; // or rebind attachment
seletionKey.interestOps(SelectionKey.OP_WRITE);
selector.wakeup();
}
class Processer implements Runnable {
public void run() {
processAndHandOff();
}
}
}
但是当用户进一步增加的时候，Reactor会出现瓶颈！因为Reactor既要处理IO操作请求，又要响应连接请求。为了分担Reactor的负担，所以引入了主从Reactor模型。
主从Reactor多线程模型
主从Reactor多线程模型是将Reactor分成两部分，mainReactor负责监听server socket，accept新连接，并将建立的socket分派给subReactor。subReactor负责多路分离已连接的socket，读写网络数据，对业务处理功能，其扔给worker线程池完成。通常，subReactor个数上可与CPU个数等同：
image.png
这时可以把Reactor做如下修改：
public class Reactor {
final ServerSocketChannel serverSocketChannel;
Selector[] selectors; // also create threads
AtomicInteger next = new AtomicInteger(0);
ExecutorService sunReactors = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());
public static void main(String[] args) throws IOException {
new Reactor(1234);
}
public Reactor(int port) throws IOException {
serverSocketChannel = ServerSocketChannel.open();
serverSocketChannel.socket().bind(new InetSocketAddress(port));
serverSocketChannel.configureBlocking(false);
selectors = new Selector[4];
for (int i = 0; i < 4; i++) {
Selector selector = Selector.open();
selectors[i] = selector;
SelectionKey key = serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
key.attach(new Acceptor());
new Thread(() -> {
while (!Thread.interrupted()) {
try {
selector.select();
Set selectionKeys = selector.selectedKeys();
for (SelectionKey selectionKey : selectionKeys) {
dispatch(selectionKey);
}
selectionKeys.clear();
} catch (IOException e) {
e.printStackTrace();
}
}
}).start();
}
}
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 connection = serverSocketChannel.accept();
if (connection != null)
sunReactors.execute(new Handler(selectors[next.getAndIncrement() % selectors.length], connection));
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
可见，主Reactor用于响应连接请求，从Reactor用于处理IO操作请求。