Java多个OP代码的SocketChannel寄存器（）从不被选择

Question

我在Java构建了一个基于选择器的系统，可以接受多个客户端。它有一个在OP_ACCEPT下注册的ServerSocketChannel，它接受（）的传入连接，并再次用选择器注册结果的SocketChannel。这是一点：

ServerSocketChannel insock = ServerSocketChannel.open();
    insock.configureBlocking(false);
    insock.socket().bind(new InetSocketAddress(6789));

    Selector sel = Selector.open();
    SelectionKey joinchannel = insock.register(sel, SelectionKey.OP_ACCEPT);

    System.out.println("Ready to accept incoming connections.");

    while (true) {
        int ready = sel.selectNow();
        if (ready == 0)
            continue;
        Set<SelectionKey> selectedKeys = sel.selectedKeys();
        Iterator<SelectionKey> keyIterator = selectedKeys.iterator();
        while (keyIterator.hasNext()) {
            SelectionKey key = keyIterator.next();
            if(key.isAcceptable()){
                SocketChannel newConnection = insock.accept();
                System.out.println("New client "+newConnection+" connected.");
                newConnection.configureBlocking(false);
                newConnection.register(sel, SelectionKey.OP_READ).attach(new DGPlayer());
            }

如果我为OP_READ注册了新的SocketChannel，这很好。检查isReadable（）成功，读取数据。如下所示：

else if(key.isReadable()){
                ByteBuffer buf = ByteBuffer.allocate(1024);
                int trans = ((SocketChannel)key.channel()).read(buf); buf.flip();
                byte[] ba = new byte[buf.remaining()]; buf.get(ba);
                String msg = new String(ba, 0, ba.length, Charset.forName("UTF-8"));

                if(trans > 0){
                    DGPlayer client = (DGPlayer) key.attachment();
                    System.out.println(client.name+": "+msg.trim());
                }
            }
                //              else if(key.isWritable()){
//                  ByteBuffer buf = ByteBuffer.allocate(48);
//                  buf.clear();
//                  buf.put(((String)key.attachment()).getBytes());
//                  buf.flip();
//                  
//                  SocketChannel target = ((SocketChannel)key.channel());
//                  while(buf.hasRemaining()) {
//                      target.write(buf);
//                  }
//                  
//                  key.attach(null);
//              }

然而，如果我为OP_READ|OP_WRITE注册SocketChannel，什么也不会发生。据我所知，选择器从未发现该通道是可读的（）或可写的（）。唯一的变化是注册该通道以获得WRITE权限。

知道为什么会这样吗？

编辑-为了完整起见，这里有一些客户端代码：

while (true) {
        int readyChannels = sel.select();
        if (readyChannels == 0)
            continue;

        Set<SelectionKey> selectedKeys = sel.selectedKeys();
        Iterator<SelectionKey> keyIterator = selectedKeys.iterator();

        while (keyIterator.hasNext()) {
            SelectionKey key = keyIterator.next();

            if (key.isReadable()) {
                ByteBuffer buf = ByteBuffer.allocate(1024);
                int trans = ((SocketChannel)key.channel()).read(buf); buf.flip();
                byte[] ba = new byte[buf.remaining()]; buf.get(ba);
                String msg = new String(ba, 0, ba.length, Charset.forName("UTF-8"));

                if(msg.trim().length() != 0)
                    System.out.println("Response from server: "+msg.trim());
            }
            else if(key.isWritable() && messages.size() > 0){
                String message = messages.remove();
                ByteBuffer buf = ByteBuffer.allocate(48);
                buf.clear();
                buf.put(message.getBytes(Charset.forName("UTF-8")));

                buf.flip();

                int written = outsock.write(buf);
                while(buf.hasRemaining()){
                    outsock.write(buf);
                }

                System.out.println("Wrote '"+message+"' to server");
            }
            keyIterator.remove();
        }
    }

（客户端注册服务器进行操作读取|操作写入）

Answer 1

一般来说，如果你没有任何可以主动写入的内容，那么为OP_WRITE注册一个频道是个坏主意。大多数通道在大多数时间都可以写入，因此每次调用选择器。选择将返回而不阻塞并消耗资源。最好将写入标志添加到SelectionKey。当你准备好向频道写入内容时，删除该标志。