SocketChannel.write() 写入问题

Question

这里的问题是我可以看到数据正在写入套接字，但并不总是被发送。

这是一个代码片段

ByteBuffer writeBuffer = ByteBuffer.allocate(8192);
writeBuffer.clear();
writeBuffer.put("heartbeat".getBytes());


writeBuffer.flip();
LOG.debug("is connected: " + socketChannel.isConnected());
int bytesWritten = 0;
if (key.isWritable()) {
    while (writeBuffer.hasRemaining()) {
        bytesWritten += socketChannel.write(writeBuffer);
    }
}

我使用 TCPMon 来查看实际数据是否被写入套接字 - 它确实如此。

但是使用 WireShark（另一种网络监控工具）我看不到通过 NIC 的数据包。

任何帮助将不胜感激

Answer 1

无论如何，您的代码都是错误的。如果写入返回零，则套接字发送缓冲区已满，因此您应该注册 OP_WRITE 并返回选择循环，而不是浪费时间旋转直到再次有空间。您目前的技术使其他服务渠道饥饿并浪费 CPU 周期。

此外，此时测试isConnected() 是徒劳的。这是。你连接了它。该方法告诉您的是套接字的状态，而不是连接。

Answer 2

如下尝试

/**
 * @param socketChannel
 * @param buf
 * @return no. of bytes written to the socket
 * @throws IOException
 */
public static int writeByteBuffer(SocketChannel socketChannel, ByteBuffer buf) throws IOException {

    boolean blocking = socketChannel.isBlocking();
    Selector selector = Selector.open();
    int totalWritten = 0;
    try {

        socketChannel.configureBlocking(false);

        // pass SelectionKey.OP_READ | SelectionKey.OP_WRITE for read and
        // write
        socketChannel.register(selector, SelectionKey.OP_WRITE);

        selector.select();

        Set<SelectionKey> selectedKeys = selector.selectedKeys();

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

        outerOfWriting: while (keyIterator.hasNext()) {

            SelectionKey key = keyIterator.next();

            boolean writable = key.isWritable();

            if (writable) {

                SocketChannel channel = (SocketChannel) key.channel();

                boolean hasRemaining = false;
                while (hasRemaining = buf.hasRemaining()) {
                    int written = channel.write(buf);
                    totalWritten += written;

                    if (written == 0) {                         
                        selector.select();
                        selectedKeys = selector.selectedKeys();
                        keyIterator = selectedKeys.iterator();
                        continue outerOfWriting;
                    }
                }

                if (!hasRemaining) {
                    key.cancel();
                    break;
                }
            }
        }

    } finally {
        try {
            selector.close();
            socketChannel.configureBlocking(blocking);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    return totalWritten;
}

public static void main(String[] args) {

    try {
        ByteBuffer writeBuffer = ByteBuffer.allocate(8192);
        writeBuffer.clear();
        writeBuffer.put("heartbeat".getBytes());
        writeBuffer.flip();

        SocketChannel socketChannel = null;//initialize
        writeByteBuffer(socketChannel, writeBuffer);

    } catch (IOException e) {
        e.printStackTrace();
    }
}