MembershipKeyImpl 简介

MembershipKey定义:http://donald-draper.iteye.com/blog/2372947
MulticastChanne接口定义：http://donald-draper.iteye.com/blog/2373009

package sun.nio.ch;

import java.io.IOException;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.nio.channels.MembershipKey;
import java.nio.channels.MulticastChannel;
import java.util.HashSet;

// Referenced classes of package sun.nio.ch:
//            DatagramChannelImpl

class MembershipKeyImpl extends MembershipKey
{
    private final MulticastChannel ch;//多播通道
    private final InetAddress group;//多播分组地址
    private final NetworkInterface interf;//网络接口
    private final InetAddress source;//源地址
    private volatile boolean valid;//是否有效
    private Object stateLock;//状态锁
    private HashSet blockedSet;//阻塞地址集
    //Ip4多播关系key
    static class Type4 extends MembershipKeyImpl
    {
        private final int groupAddress;//多播组地址
        private final int interfAddress;//网络接口地址
        private final int sourceAddress;//源地址

        Type4(MulticastChannel multicastchannel, InetAddress inetaddress, NetworkInterface networkinterface, InetAddress inetaddress1, int i, int j, int k)
        {
            super(multicastchannel, inetaddress, networkinterface, inetaddress1, null);
            groupAddress = i;
            interfAddress = j;
            sourceAddress = k;
        }
        int groupAddress()
        {
            return groupAddress;
        }

        int interfaceAddress()
        {
            return interfAddress;
        }

        int source()
        {
            return sourceAddress;
        }

       
    }
    //Ip6多播关系key
    static class Type6 extends MembershipKeyImpl
    {
        private final byte groupAddress[];//多播组地址
        private final int index;//索引
        private final byte sourceAddress[];//源地址

        Type6(MulticastChannel multicastchannel, InetAddress inetaddress, NetworkInterface networkinterface, InetAddress inetaddress1, byte abyte0[], int i, byte abyte1[])
        {
            super(multicastchannel, inetaddress, networkinterface, inetaddress1, null);
            groupAddress = abyte0;
            index = i;
            sourceAddress = abyte1;
        }
        byte[] groupAddress()
        {
            return groupAddress;
        }

        int index()
        {
            return index;
        }

        byte[] source()
        {
            return sourceAddress;
        }

        
    }

    //根据多播通道，多播组地址，网络接口，源地址信息构造MembershipKeyImpl
    private MembershipKeyImpl(MulticastChannel multicastchannel, InetAddress inetaddress, NetworkInterface networkinterface, InetAddress inetaddress1)
    {
        valid = true;//默认创建后，有效
        stateLock = new Object();
        ch = multicastchannel;
        group = inetaddress;
        interf = networkinterface;
        source = inetaddress1;
    }

    public boolean isValid()
    {
        return valid;
    }
    //使多播关系key无效
    void invalidate()
    {
        valid = false;
    }
   //drop多播关系
    public void drop()
    {
        ((DatagramChannelImpl)ch).drop(this);
    }
   //获取多播关系key的多播通道
    public MulticastChannel channel()
    {
        return ch;
    }
   //获取多播组地址
    public InetAddress group()
    {
        return group;
    }
    //获取网络接口
    public NetworkInterface networkInterface()
    {
        return interf;
    }
    //获取源地址
    public InetAddress sourceAddress()
    {
        return source;
    }
    //阻塞源地址的报文
    public MembershipKey block(InetAddress inetaddress)
        throws IOException
    {
        if(source != null)
            throw new IllegalStateException("key is source-specific");
        Object obj = stateLock;//同步状态锁
        JVM INSTR monitorenter ;//进入同步try
	//已添加阻塞地址集合，则直接返回
        if(blockedSet != null && blockedSet.contains(inetaddress))
            return this;
	 //委托给DatagramChannelImpl的block
        ((DatagramChannelImpl)ch).block(this, inetaddress);
        if(blockedSet == null)
            blockedSet = new HashSet();
	//添加地址到多播关系key阻塞集
        blockedSet.add(inetaddress);
        obj;
        JVM INSTR monitorexit ;//退try
          goto _L1
        Exception exception;//有异常，则抛出
        exception;
        throw exception;
_L1:
        return this;
    }
    //解除源地址的报文
    public MembershipKey unblock(InetAddress inetaddress)
    {
        synchronized(stateLock)
        {
            if(blockedSet == null || !blockedSet.contains(inetaddress))
	        //如果多播关系key的阻塞集合为null或阻塞地址集不包含inetaddress，则抛出IllegalStateException
                throw new IllegalStateException("not blocked");
	    //委托给DatagramChannelImpl的unblock
            ((DatagramChannelImpl)ch).unblock(this, inetaddress);
	    //从阻塞地址集移除阻塞的源地址
            blockedSet.remove(inetaddress);
        }
        return this;
    }

    public String toString()
    {
        StringBuilder stringbuilder = new StringBuilder(64);
        stringbuilder.append('<');
        stringbuilder.append(group.getHostAddress());
        stringbuilder.append(',');
        stringbuilder.append(interf.getName());
        if(source != null)
        {
            stringbuilder.append(',');
            stringbuilder.append(source.getHostAddress());
        }
        stringbuilder.append('>');
        return stringbuilder.toString();
    }
}

总结：
MembershipKeyImpl内部有一个多播关系key关联的多播通道和多播分组地址，及多播报文源地址，及一个地址阻塞集。MembershipKeyImpl主要操作为drop关系key，直接委托个多播通道drop方法；block地址，首先判断多播关系key中的阻塞Set中是否包含对应的地址，有，则直接返回，否则委托给DatagramChannelImpl的block方法，完成实际的阻塞工作，然后添加地址的多播关系key阻塞set；unblock，首先判断多播关系key中的阻塞Set中是否包含对应的地址，无，则直接返回，有则委托给DatagramChannelImpl的unblock方法，完成实际的的解除阻塞工作，并从多播关系key中的阻塞Set移除对应的地址。