簡單的非阻塞服務器

Question

為了編寫即時消息程序，我試圖組成一個簡單的服務器類，它將在自己的線程中運行。

服務器應該做什么

• 接受來自/連接到服務器的其他實例的連接，並將Map<Integer, SelectionKey> keys的連接的Map<Integer, SelectionKey> keys與ID相關聯，以便信使線程可以通過ID訪問連接
• 讀/寫連接
• 將傳入的消息存儲在隊列中
• 信使線程可以
  • 獲取傳入的消息
  • 要發送的隊列消息： send_message(int id, String msg)

我目前的方法主要基於這個例子： 一個帶有Java nio的簡單非阻塞Echo服務器 。
我還使用了使用選擇器來管理非阻塞套接字和已編輯的頁面，以了解非阻塞套接字和選擇器。

目前的代碼

• EJP的建議已實施
• 微小的變化

package snserver;

/* imports */

//class SNServer (Simple non-blocking Server)

public class SNServer extends Thread {
    private int port;
    private Selector selector;
    private ConcurrentMap<Integer, SelectionKey> keys; // ID -> associated key
    private ConcurrentMap<SocketChannel,List<byte[]>> dataMap_out;
    ConcurrentLinkedQueue<String> in_msg; //incoming messages to be fetched by messenger thread

    public SNServer(int port) {
        this.port = port;
        dataMap_out = new ConcurrentHashMap<SocketChannel, List<byte[]>>();
        keys = new ConcurrentHashMap<Integer, SelectionKey>();
    }

    public void start_server() throws IOException {
        // create selector and channel
        this.selector = Selector.open();
        ServerSocketChannel serverChannel = ServerSocketChannel.open();
        serverChannel.configureBlocking(false);

        // bind to port
        InetSocketAddress listenAddr = new InetSocketAddress((InetAddress)null, this.port);
        serverChannel.socket().bind(listenAddr);
        serverChannel.register(this.selector, SelectionKey.OP_ACCEPT);

        log("Echo server ready. Ctrl-C to stop.");

        // processing
        while (true) {
            // wait for events
            this.selector.select();

            // wakeup to work on selected keys
            Iterator keys = this.selector.selectedKeys().iterator();
            while (keys.hasNext()) {
                SelectionKey key = (SelectionKey) keys.next();

                // this is necessary to prevent the same key from coming up 
                // again the next time around.
                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);
                }
                else if(key.isConnectable()) {
                    this.connect(key);
                }
            }
        }
    }

    private void accept(SelectionKey key) throws IOException {
        ServerSocketChannel serverChannel = (ServerSocketChannel) key.channel();
        SocketChannel channel = serverChannel.accept();
        channel.configureBlocking(false);
        send_message(key, "Welcome."); //DEBUG

        Socket socket = channel.socket();
        SocketAddress remoteAddr = socket.getRemoteSocketAddress();
        log("Connected to: " + remoteAddr);

        // register channel with selector for further IO
        dataMap_out.put(channel, new ArrayList<byte[]>());
        channel.register(this.selector, SelectionKey.OP_READ);

        //store key in 'keys' to be accessable by ID from messenger thread //TODO first get ID
        keys.put(0, key);
    }

    //TODO verify, test
    public void init_connect(String addr, int port){
        try {
            SocketChannel channel = createSocketChannel(addr, port);
            channel.register(this.selector, channel.validOps()/*, SelectionKey.OP_?*/);
        }
        catch (IOException e) {
            //TODO handle
        }
    }

    //TODO verify, test
    private void connect(SelectionKey key) {
        SocketChannel channel = (SocketChannel) key.channel();
        try {
            channel.finishConnect(); //try to finish connection - if 'false' is returned keep 'OP_CONNECT' registered
            //store key in 'keys' to be accessable by ID from messenger thread //TODO first get ID
            keys.put(0, key);
        }
        catch (IOException e0) {
            try {
                //TODO handle ok?
                channel.close();
            }
            catch (IOException e1) {
                //TODO handle
            }
        }

    }

    private void read(SelectionKey key) throws IOException {
        SocketChannel channel = (SocketChannel) key.channel();

        ByteBuffer buffer = ByteBuffer.allocate(8192);
        int numRead = -1;
        try {
            numRead = channel.read(buffer);
        }
        catch (IOException e) {
            e.printStackTrace();
        }

        if (numRead == -1) {
            this.dataMap_out.remove(channel);
            Socket socket = channel.socket();
            SocketAddress remoteAddr = socket.getRemoteSocketAddress();
            log("Connection closed by client: " + remoteAddr); //TODO handle
            channel.close();
            return;
        }

        byte[] data = new byte[numRead];
        System.arraycopy(buffer.array(), 0, data, 0, numRead);
        in_msg.add(new String(data, "utf-8"));
    }

    private void write(SelectionKey key) throws IOException {
        SocketChannel channel = (SocketChannel) key.channel();
        List<byte[]> pendingData = this.dataMap_out.get(channel);
        Iterator<byte[]> items = pendingData.iterator();
        while (items.hasNext()) {
            byte[] item = items.next();
            items.remove();
            //TODO is this correct? -> re-doing write in loop with same buffer object
            ByteBuffer buffer = ByteBuffer.wrap(item);
            int bytes_to_write = buffer.capacity();
            while (bytes_to_write > 0) {
                bytes_to_write -= channel.write(buffer);
            }
        }
        key.interestOps(SelectionKey.OP_READ);
    }

    public void queue_data(SelectionKey key, byte[] data) {
        SocketChannel channel = (SocketChannel) key.channel();
        List<byte[]> pendingData = this.dataMap_out.get(channel);
        key.interestOps(SelectionKey.OP_WRITE);

        pendingData.add(data);
    }

    public void send_message(int id, String msg) {
        SelectionKey key = keys.get(id);
        if (key != null)
            send_message(key, msg);
        //else
            //TODO handle
    }

    public void send_message(SelectionKey key, String msg) {
        try {
            queue_data(key, msg.getBytes("utf-8"));
        }
        catch (UnsupportedEncodingException ex) {
            //is not thrown: utf-8 is always defined
        }
    }

    public String get_message() {
        return in_msg.poll();
    }

    private static void log(String s) {
        System.out.println(s);
    }

    @Override
    public void run() {
        try {
            start_server();
        }
        catch (IOException e) {
            System.out.println("IOException: " + e);
            //TODO handle exception
        }
    }    


    // Creates a non-blocking socket channel for the specified host name and port.
    // connect() is called on the new channel before it is returned.
    public static SocketChannel createSocketChannel(String hostName, int port) throws IOException {
        // Create a non-blocking socket channel
        SocketChannel sChannel = SocketChannel.open();
        sChannel.configureBlocking(false);

        // Send a connection request to the server; this method is non-blocking
        sChannel.connect(new InetSocketAddress(hostName, port));
        return sChannel;
    }
}

我的問題：上面的代碼是正確的還是好的，或者我應該改變什么？ 如何正確實現上面提到的要求？ 另請注意我的“TODO”。

感謝您的任何幫助！

Answer 1

這里有幾個問題。

1. 您沒有檢查write（）的結果。 它可以從零開始返回任何內容。 您可能不得不多次重做。

2. 如果finishConnect（）返回false則不是錯誤，它還沒有完成，所以只需保持OP_CONNECT注冊並等待它（再次）觸發。 您剛剛通過SocketChannel.open（）創建的SocketChannel的唯一validOps（）是OP_CONNECT。 如果finishConnect（）拋出異常，那就是錯誤，您應該關閉該通道。

3. 關閉頻道取消密鑰，您不必自己取消密鑰。

4. 通常，綁定時應使用null作為本地InetAddress。