如何在JAVA非阻塞I/O（NIO）API中使用多核？

Question

JAVA NIO提供了一个API使用NIO架构编写TCP服务器，如下

import java.io.IOException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketAddress;
import java.nio.Buffer;
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.text.ParseException;
import java.util.*;

public class NIOServer implements Runnable{
    private InetAddress addr;
    private int port;
    private Selector selector;

    public NIOServer(InetAddress addr, int port) throws IOException {
        this.addr = addr;
        this.port = port;
    }

    public void run(){
        try {
            startServer();
        }catch(IOException ex){
            System.out.println(ex.getMessage());
        }
    }

    private void startServer() throws IOException {

        this.selector = Selector.open();
        ServerSocketChannel serverChannel = serverSocketChannel.open();
        serverChannel.configureBlocking(false);
        InetSocketAddress listenAddr = new InetSocketAddress(this.addr, this.port);
        serverChannel.socket().bind(listenAddr);
        serverChannel.register(this.selector, SelectionKey.OP_ACCEPT);


        while (true) {

            this.selector.select();


            Iterator keys = this.selector.selectedKeys().iterator();
            while (keys.hasNext()) {
                SelectionKey key = (SelectionKey) keys.next();


                keys.remove();

                if (! key.isValid()) {
                    continue;
                }

                if (key.isAcceptable()) {
                    this.accept(key);
                }
                else if (key.isReadable()) {
                    this.read(key);
                }
                else if (key.isWritable()) {
                    this.write(key);
                }
            }
        }
    }
}

这使用单个线程来处理读取、写入和接受等事件。

与每个连接的阻塞线程架构相比，这是更受欢迎的，因为它的非阻塞性质导致最小的缓存未命中、线程开销、低 cpu 迁移。

但是，此架构仅使用单线程。在多进程环境下（比如4核cpu），NIO架构浪费了其他核。有没有我可以使用的设计方法来利用 NIO 架构的所有内核？

NIO2（基于前摄器模式）就是这样一种选择。但是底层架构和原来的NIO有很大的不同。

Answer 1

基本思路是拆分任务:

    ExecuterService workers = Executors.newFixedThreadPool(50);

    ....
    while (true) {

                this.selector.select();

                Iterator keys = this.selector.selectedKeys().iterator();
                while (keys.hasNext()) {
                    SelectionKey key = (SelectionKey) keys.next();

                    keys.remove();

                    if (! key.isValid()) {
                        continue;
                    }

                    if (key.isAcceptable()) {
                        this.accept(key);
                    }
                    else if (key.isReadable()) {
                        workers.execute(new ReadTaskHandler(key));
                    }
                    else if (key.isWritable()) {
                        workers.execute(new WriteTaskHandler(key));
                    }
                }
            }

class ReadTaskHandler implements Runnable {
    SelectionKey key;

    public ReadTaskHandler(SelectionKey key) {
        this.key = key;
    }

    @Override
    public void run() {
        ByteBuffer buffer = ByteBuffer.allocate(1024);
        SocketChannel channel = (SocketChannel) key.channel();

        int size = 0;
        try {
            while ((size = channel.read(buffer)) > 0) {
                System.out.println(new String(buffer.array()));
                buffer.flip();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

其实关于NIO的车型有很多。比如我们也可以使用多线程来处理accept任务（也叫多反应器模型或者多事件循环模型）。

BTW，Netty是一个很棒的event-driven网络应用框架封装javaNIO

如何在JAVA非阻塞I/O（NIO）API中使用多核？

How to use multiple cores in the JAVA Non Blocking I/O (NIO) API?

java

nio