VPN上的DatagramChannel.receive阻止

Question

我正在学习DatagramChannel Multicast，

我正在尝试执行以下操作，我注意到当我在VPN上并且没有收到任何内容时，DatagramChannel＃receive方法完全阻塞，但是当我断开VPN时，数据会被打印几次。

  

1。将数据发送到多播IP组：

import java.io.IOException;
import java.net.*;
import java.nio.ByteBuffer;
import java.nio.channels.DatagramChannel;
import java.util.Date;


public class MultiCastChannelThread extends Thread {
    DatagramChannel channel;
    ProtocolFamily family = StandardProtocolFamily.INET;


    MultiCastChannelThread(String name) throws IOException {
        super(name);
        configureChannel();
    }


    public static void main(String[] args) throws IOException {
        new MultiCastChannelThread("MultiCastChannel").start();
    }


    private void configureChannel() throws IOException {
        channel = DatagramChannel.open(family).setOption(StandardSocketOptions.SO_REUSEADDR, true).bind(null).setOption(
                  StandardSocketOptions.IP_MULTICAST_IF, NetworkInterface.getByName("wlan0"));
    }


    @Override
    public void run() {
        int i = 0;
        while (i++ < 6) {

            try {
                byte[] buff = new Date().toString().getBytes();

                ByteBuffer buffer = ByteBuffer.wrap(buff);
                InetAddress group = InetAddress.getByName("224.0.15.15");


                int sent = channel.send(buffer, new InetSocketAddress(group, 4466));
                System.out.format("Number of bytes sent :%s\n Data sent:%s\t\n", sent, new String(buff));

                try {
                    sleep(5 * 1000);
                } catch (InterruptedException e) {
                }

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

    }


}

  

2。加入和接收群组数据

import static java.lang.Thread.sleep;

    import java.io.IOException;
    import java.net.*;
    import java.nio.ByteBuffer;
    import java.nio.channels.DatagramChannel;
    import java.util.Enumeration;
    import java.util.HashMap;
    import java.util.Map;


    public class MulticastChannelClient {
        NetworkInterface networkInterface;
        InetAddress inetAddress;
        InetAddress group;
        ProtocolFamily family = StandardProtocolFamily.INET;


        public MulticastChannelClient() throws UnknownHostException, SocketException {
            group = InetAddress.getByName("224.0.15.15");
            networkInterface = NetworkInterface.getByName("wlan0");
        }


        public static void main(String[] args) throws IOException {
            new MulticastChannelClient().testMultiCastChannel();
        }


        private void testMultiCastChannel() throws IOException {
            new MultiCastChannelThread("MulticastChannelTest").start();

            DatagramChannel channel = DatagramChannel.open(family).setOption(StandardSocketOptions.SO_REUSEADDR, true).bind(
                      new InetSocketAddress((InetAddress) null, 4466));

            channel.join(group, networkInterface);


            for (int i = 0; i < 6; i++) {
                ByteBuffer received = ByteBuffer.allocate(250);
                SocketAddress socketAddress = channel.receive(received);
                System.out.println("Received  ::: " + i + " " + new String(received.array()));
                   try {
                        sleep(2 * 1000);
                    } catch (InterruptedException e) {
                    }

            }

        }


       }