java NIO实现(一) ——ServerSocketChannel和Selector源码分析

概述

java NIO属于epoll水平触发

NIO调用	linux epoll实现
Selector.open()	epoll_create
ServerSocketChannel#register()	将事件存储EpollArrayWrapper的成员变量eventsLow和eventsHigh中
Selector#select()	从eventsLow和eventsHigh中取出事件,调用epoll_ctl ,设置为水平触发, 并epoll_wait

 

ServerSocketChannel的使用示例如下：

//1. 获取服务端通道
        ServerSocketChannel ssChannel = ServerSocketChannel.open();
        ssChannel.bind(new InetSocketAddress(9898));
        //2. 设置为非阻塞模式
        ssChannel.configureBlocking(false);
        
        //3. 打开一个监听器
        Selector selector = Selector.open();
        //4. 向监听器注册接收事件
        ssChannel.register(selector, SelectionKey.OP_ACCEPT);

        while (selector.select() > 0) {
            //5. 获取监听器上所有的监听事件值
            Iterator<SelectionKey> it = selector.selectedKeys().iterator();

            //6. 如果有值
            while (it.hasNext()) {
                //7. 取到SelectionKey
                SelectionKey key = it.next();

                //8. 根据key值判断对应的事件
                if (key.isAcceptable()) {
                    //9. 接入处理
                    SocketChannel socketChannel = ssChannel.accept();
                    socketChannel.configureBlocking(false);
                    socketChannel.register(selector, SelectionKey.OP_READ);
                } else if (key.isReadable()) {
                    //10. 可读事件处理
                    SocketChannel channel = (SocketChannel) key.channel();
                    readMsg(channel);
                }
                //11. 移除当前key
                it.remove();
            }
        }

ServerSocketChannel.open()方法源码分析

底层是调用SelectorProvider#openServerSocketChannel()方法

 /**
     * Opens a server-socket channel.
     *
     * <p> The new channel is created by invoking the {@link
     * java.nio.channels.spi.SelectorProvider#openServerSocketChannel
     * openServerSocketChannel} method of the system-wide default {@link
     * java.nio.channels.spi.SelectorProvider} object.
     *
     * <