谈谈java selector的机制

EPollSelectorImpl
维护了3个键set
keys【已经注册的键的集合】
selectedKeys【已选择的键的集合】
cancelledKeys【已取消的键的集合】
EPollArrayWrapper【真正的对linux epoll的封装】
包含了3个重要的native方法epollCreate、epollCtl、epollWait分别对应库函数epoll_create、epoll_ctl、epoll_wait
一个native实例pollArray模拟库中struct epoll_event
SelectionKeyImpl
表示了一个特定的通道对象和一个特定的选择器对象之间的注册 关系
包含两个以整数形式进行编码的比特掩码
关心的操作(interestOps)
表示通道准备好要执行的操作（readyOps）
SocketChannelImpl/ServerSocketChannelImpl: 分别是连接socket和监听socket
2）一段代码
有了上面的概念，接下来看一段简单的代码，采用select实现的echo server
[java]
<pre name="code" class="java">public class SelectTest { 
 
    public static int PORT_NUMBER = 1234; 
 
    public static void main(String args[]) throws Exception { 
        new SelectTest().go(); 
    } 
 
    public void go() throws Exception { 
        int port = PORT_NUMBER; 
 
        ServerSocketChannel serverChannel = ServerSocketChannel.open(); 
        ServerSocket serverSocket = serverChannel.socket(); 
        // Set the port the server channel will listen to 
        serverSocket.bind(new InetSocketAddress(port)); 
        // Set nonblocking mode for the listening socket 
        serverChannel.configureBlocking(false); 
 
        Selector selector = Selector.open(); 
 
        // Register the ServerSocketChannel with the Selector 
        serverChannel.register(selector, SelectionKey.OP_ACCEPT); 
        while (true) { 
            // This may block for a long time. Upon returning, the // selected 
            // set contains keys of the ready channels. 
            int n = selector.select(); 
            if (n == 0) { 
                // nothing to do 
                continue; 
            } 
 
            // Get an iterator over the set of selected keys 
            Iterator<SelectionKey> it = selector.selectedKeys().iterator(); 
            // Look at each key in the selected set while (it.hasNext()) { 
            SelectionKey key = (SelectionKey) it.next(); 
 
            // step1 Is a new connection coming in? 
            if (key.isAcceptable()) { 
                ServerSocketChannel server = (ServerSocketChannel) key 
                        .channel(); 
                SocketChannel channel = server.accept(); 
                registerChannel(selector, channel, SelectionKey.OP_READ); 
                sayHello(channel); 
            } 
 
            // step2 Is there data to read on this channel? 
            if (key.isReadable()) { 
                readDataFromSocket(key); 
            } 
 
            // step3 Remove key from selected set; it's been handled 
            it.remove(); 
 
        } 
 
    } 
 
    protected void registerChannel(Selector selector, 
            SelectableChannel channel, int ops) throws Exception { 
        if (channel == null) { 
 
            return; // could happen 
        } 
        // Set the new channel nonblocking 
        channel.configureBlocking(false); 
        // Register it with the selector 
        channel.register(selector, ops); 
    } 
 
    // Use the same byte buffer for all channels. A single thread is // 
    // servicing all the channels, so no danger of concurrent acccess. 
    private ByteBuffer buffer = ByteBuffer.allocateDirect(1024); 
 
    protected void readDataFromSocket(SelectionKey key) throws Exception { 
        SocketChannel socketChannel = (SocketChannel) key.channel(); 
        int count; 
        buffer.clear(); // Empty buffer 
        // Loop while data is available; channel is nonblocking 
        while ((count = socketChannel.read(buffer)) > 0) { 
            buffer.flip(); // Make buffer readable 
            // Send the data; don't assume it goes all at once 
        

补充：软件开发 , Java ,

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