asynchronous I/O (the POSIX aio_functions)—————异步IO模型最大的特点是 完成后发回通知。
与NIO不同，当进行读写操作时，只须直接调用API的read或write方法即可。这两种方法均为异步的，对于读操作而言，当有流可读取时，操作系统会将可读的流传入read方法的缓冲区，并通知应用程序；对于写操作而言，当操作系统将write方法传递的流写入完毕时，操作系统主动通知应用程序。
即可以理解为，accept,connect,read,write方法都是异步的，完成后会主动调用回调函数。
在JDK1.7中，这部分内容被称作NIO.2，主要在java.nio.channels包下增加了下面四个异步通道：- AsynchronousSocketChannel
- AsynchronousServerSocketChannel
- AsynchronousFileChannel
- AsynchronousDatagramChannel
其中的accept,connect,read,write方法，会返回一个带回调函数的对象，当执行完读取/写入操作后，直接调用回调函数。
1 public class ClientAio implements Runnable { 2 private final static int count = 50000; 3 private final static AsynchronousSocketChannel[] clients = new AsynchronousSocketChannel[count]; 4 private final static AtomicInteger ai = new AtomicInteger(); 5 6 private String host; 7 private int port; 8 private AsynchronousSocketChannel client; 9 10 public ClientAio(String host, int port) throws IOException {11 this.client = AsynchronousSocketChannel.open();12 this.host = host;13 this.port = port;14 }15 16 public static void main(String[] args) throws Exception {17 String addr = args.length > 0 ? args[0] : "192.168.56.122";18 while (ai.get() < count) {19 new ClientAio(addr, 8989).run();20 }21 System.in.read();22 }23 24 public void run() {25 client.connect(new InetSocketAddress(host, port), null, new CompletionHandler () {26 public void completed(Void result, Object attachment) {27 int i = ai.getAndIncrement();28 if (i < count) {29 clients[i] = client;30 }31 final ByteBuffer byteBuffer = ByteBuffer.allocate(512);32 client.read(byteBuffer, null, new CompletionHandler () {33 public void completed(Integer result, Object attachment) {34 35 //System.out.println("client read data: " + new String(byteBuffer.array()));36 }37 38 public void failed(Throwable exc, Object attachment) {39 System.out.println("read faield");40 }41 });42 }43 44 public void failed(Throwable exc, Object attachment) {45 System.out.println("client connect field...");46 try {47 if(client.isOpen()){48 client.close();49 }50 } catch (IOException e) {51 }52 }53 });54 }55 }
1 public class ServerAio implements Runnable { 2 private final static AtomicInteger ai = new AtomicInteger(); 3 private int port = 8889; 4 private int threadSize = 10; 5 private AsynchronousChannelGroup asynchronousChannelGroup; 6 private AsynchronousServerSocketChannel serverChannel; 7 8 public ServerAio(int port, int threadSize) { 9 this.port = port;10 this.threadSize = threadSize;11 }12 13 public static void main(String[] args) throws IOException {14 new ServerAio(8989, Runtime.getRuntime().availableProcessors() * 10).run();15 System.in.read();16 }17 18 public void run() {19 try {20 asynchronousChannelGroup = AsynchronousChannelGroup.withCachedThreadPool(Executors.newCachedThreadPool(), threadSize);21 serverChannel = AsynchronousServerSocketChannel.open(asynchronousChannelGroup);22 serverChannel.bind(new InetSocketAddress(port));23 System.out.println("listening on port: " + port);24 serverChannel.accept(this, new CompletionHandler () {25 26 public void completed(AsynchronousSocketChannel result, ServerAio attachment) {27 try {28 System.out.println(ai.getAndIncrement());29 ByteBuffer echoBuffer = ByteBuffer.allocateDirect(1024);30 result.read(echoBuffer, null, new CompletionHandler () {31 @Override32 public void completed(Integer result, Object attachment) {33 // System.out.println("received : " +34 // Charset.defaultCharset().decode(echoBuffer));35 }36 37 @Override38 public void failed(Throwable exc, Object attachment) {39 }40 });41 42 result.write(ByteBuffer.wrap("ok".getBytes()));43 } catch (Exception e) {44 e.printStackTrace();45 } finally {46 attachment.serverChannel.accept(attachment, this);// 监听新的请求，递归调用。47 }48 }49 50 public void failed(Throwable exc, ServerAio attachment) {51 System.out.println("received failed");52 exc.printStackTrace();53 attachment.serverChannel.accept(attachment, this);// 监听新的请求，递归调用。54 }55 });56 57 } catch (Exception e) {58 e.printStackTrace();59 }60 }61 } AIO与NIO对比，减少read阻塞等侍时间，速度非常之快，本人在window环境下测试瓶颈1.6W左右连接(后面会讲如何突破)