MembershipRegistry.java

/*
 * Copyright (c) 2008, 2009, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */

package sun.nio.ch;

import java.nio.channels.*;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.util.*;

/**
 * Simple registry of membership keys for a MulticastChannel.
 *
 * Instances of this object are not safe by multiple concurrent threads.
 */
// 组播Socket注册表，记录了某个组播Socket在其所有组播小组上的注册信息
class MembershipRegistry {
    
    /*
     * 记录某个组播Socket在其所有组播小组上的注册信息
     *
     * key  : 组播小组地址
     * value: 加入到上述组播小组的成员
     */
    private Map<InetAddress, List<MembershipKeyImpl>> groups = null;
    
    MembershipRegistry() {
    }
    
    /**
     * Add membership to the registry, returning a new membership key.
     */
    // 添加一条组播小组成员信息
    void add(MembershipKeyImpl key) {
        InetAddress group = key.group();
        
        List<MembershipKeyImpl> keys;
        
        if(groups == null) {
            groups = new HashMap<>();
            keys = null;
        } else {
            keys = groups.get(group);
        }
        
        if(keys == null) {
            keys = new LinkedList<>();
            groups.put(group, keys);
        }
        
        keys.add(key);
    }
    
    /**
     * Remove a key from the registry
     */
    // 移除一条组播小组成员信息
    void remove(MembershipKeyImpl key) {
        InetAddress group = key.group();
        
        List<MembershipKeyImpl> keys = groups.get(group);
        if(keys == null) {
            return;
        }
        
        Iterator<MembershipKeyImpl> iterator = keys.iterator();
        while(iterator.hasNext()) {
            if(iterator.next() == key) {
                iterator.remove();
                break;
            }
        }
        
        if(keys.isEmpty()) {
            groups.remove(group);
        }
    }
    
    /**
     * Invalidate all keys in the registry
     */
    // 将当前注册表内的所有组播小组成员标记为无效
    void invalidateAll() {
        if(groups == null) {
            return;
        }
        
        for(InetAddress group : groups.keySet()) {
            for(MembershipKeyImpl key : groups.get(group)) {
                // 将组播小组成员key设置为无效
                key.invalidate();
            }
        }
    }
    
    /**
     * Checks registry for membership of the group on the given network interface.
     */
    // 检查组播小组group上添加的组播小组成员；如果某个成员的属性与形参中给出的属性匹配，则返回该成员；否则，返回null
    MembershipKey checkMembership(InetAddress group, NetworkInterface interf, InetAddress source) {
        if(groups == null) {
            return null;
        }
        
        List<MembershipKeyImpl> keys = groups.get(group);
        if(keys == null) {
            return null;
        }
        
        // 遍历当前注册表内的所有组播小组成员
        for(MembershipKeyImpl key : keys) {
            // 忽略那些网络接口(网卡)不匹配的成员
            if(!key.networkInterface().equals(interf)) {
                continue;
            }
            
            // already a member to receive all packets so return existing key or detect conflict
            if(source == null) {
                if(key.sourceAddress() == null) {
                    return key;
                }
                throw new IllegalStateException("Already a member to receive all packets");
            }
            
            // already have source-specific membership so return key or detect conflict
            if(key.sourceAddress() == null) {
                throw new IllegalStateException("Already have source-specific membership");
            }
            
            if(source.equals(key.sourceAddress())) {
                return key;
            }
        }
        
        return null;
    }
    
}