【Zookeeper】源码分析之网络通信（一）

一、前言

　　前面已经分析了请求处理链中的多数类，接着继续分析Zookeeper中的网络通信模块。

二、总体框图

　　对于网络通信模块，其总体框图如下所示

　　

　　说明：

　　Stats，表示ServerCnxn上的统计数据。

　　Watcher，表示时间处理器。

　　ServerCnxn，表示服务器连接，表示一个从客户端到服务器的连接。

　　NettyServerCnxn，基于Netty的连接的具体实现。

　　NIOServerCnxn，基于NIO的连接的具体实现。

三、ServerCnxn源码分析

　　3.1 类的继承关系　

public abstract class ServerCnxn implements Stats, Watcher {}

　　说明：ServerCnxn为抽象类，其继承Stats和Watcher两个接口，表示客户端到服务端的连接。

　　3.2 类的内部类　　

    // 请求关闭异常类
    protected static class CloseRequestException extends IOException {
        private static final long serialVersionUID = -7854505709816442681L;

        public CloseRequestException(String msg) {
            super(msg);
        }
    }

    // 流结束异常类
    protected static class EndOfStreamException extends IOException {
        private static final long serialVersionUID = -8255690282104294178L;

        public EndOfStreamException(String msg) {
            super(msg);
        }

        public String toString() {
            return "EndOfStreamException: " + getMessage();
        }
    }

　　说明：ServerCnxn包含了两个异常类，用于表示在连接中发生的异常情况。

　　3.3 类的属性

public abstract class ServerCnxn implements Stats, Watcher {
    // This is just an arbitrary object to represent requests issued by
    // (aka owned by) this class
    // 代表由本类提出的请求
    final public static Object me = new Object();
    // 认证信息
    protected ArrayList<Id> authInfo = new ArrayList<Id>();

    /**
     * If the client is of old version, we don't send r-o mode info to it.
     * The reason is that if we would, old C client doesn't read it, which
     * results in TCP RST packet, i.e. "connection reset by peer".
     */
    // 是否为旧的C客户端
    boolean isOldClient = true;
    
    // Zookeeper的Sasl服务器
    protected ZooKeeperSaslServer zooKeeperSaslServer = null;
    
    
    /**
    * CMD命令
    **/
    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    // CMD命令
    protected final static int confCmd =
        ByteBuffer.wrap("conf".getBytes()).getInt();

    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    protected final static int consCmd =
        ByteBuffer.wrap("cons".getBytes()).getInt();

    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    protected final static int crstCmd =
        ByteBuffer.wrap("crst".getBytes()).getInt();

    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    protected final static int dumpCmd =
        ByteBuffer.wrap("dump".getBytes()).getInt();

    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    protected final static int enviCmd =
        ByteBuffer.wrap("envi".getBytes()).getInt();

    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    protected final static int getTraceMaskCmd =
        ByteBuffer.wrap("gtmk".getBytes()).getInt();

    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    protected final static int ruokCmd =
        ByteBuffer.wrap("ruok".getBytes()).getInt();
    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    protected final static int setTraceMaskCmd =
        ByteBuffer.wrap("stmk".getBytes()).getInt();

    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    protected final static int srvrCmd =
        ByteBuffer.wrap("srvr".getBytes()).getInt();

    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    protected final static int srstCmd =
        ByteBuffer.wrap("srst".getBytes()).getInt();

    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    protected final static int statCmd =
        ByteBuffer.wrap("stat".getBytes()).getInt();

    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    protected final static int wchcCmd =
        ByteBuffer.wrap("wchc".getBytes()).getInt();

    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    protected final static int wchpCmd =
        ByteBuffer.wrap("wchp".getBytes()).getInt();

    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    protected final static int wchsCmd =
        ByteBuffer.wrap("wchs".getBytes()).getInt();

    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    protected final static int mntrCmd = ByteBuffer.wrap("mntr".getBytes())
            .getInt();

    /*
     * See <a href="{@docRoot}/../../../docs/zookeeperAdmin.html#sc_zkCommands">
     * Zk Admin</a>. this link is for all the commands.
     */
    protected final static int isroCmd = ByteBuffer.wrap("isro".getBytes())
            .getInt();

    // 存储CMD的整形值与String的键值对
    protected final static HashMap<Integer, String> cmd2String =
        new HashMap<Integer, String>();

    // specify all of the commands that are available
    static {
        cmd2String.put(confCmd, "conf");
        cmd2String.put(consCmd, "cons");
        cmd2String.put(crstCmd, "crst");
        cmd2String.put(dumpCmd, "dump");
        cmd2String.put(enviCmd, "envi");
        cmd2String.put(getTraceMaskCmd, "gtmk");
        cmd2String.put(ruokCmd, "ruok");
        cmd2String.put(setTraceMaskCmd, "stmk");
        cmd2String.put(srstCmd, "srst");
        cmd2String.put(srvrCmd, "srvr");
        cmd2String.put(statCmd, "stat");
        cmd2String.put(wchcCmd, "wchc");
        cmd2String.put(wchpCmd, "wchp");
        cmd2String.put(wchsCmd, "wchs");
        cmd2String.put(mntrCmd, "mntr");
        cmd2String.put(isroCmd, "isro");
    }
    
    
    /**
    * 服务器的统计数据
    **/
    // 创建连接的时间
    protected final Date established = new Date();

    // 接受的packet数量
    protected final AtomicLong packetsReceived = new AtomicLong();
    // 发送的packet数量
    protected final AtomicLong packetsSent = new AtomicLong();
    // 最小延迟
    protected long minLatency;
    // 最大延迟
    protected long maxLatency;
    // 最后操作类型
    protected String lastOp;
    // 最后的cxid
    protected long lastCxid;
    // 最后的zxid
    protected long lastZxid;
    // 最后的响应时间
    protected long lastResponseTime;
    // 最后的延迟
    protected long lastLatency;
    // 数量
    protected long count;
    // 总的延迟
    protected long totalLatency;
}

　　说明：可以看到，ServerCnxn类维护了很多属性，主要是服务器的统计信息和和命令行信息。

　　3.4 核心函数分析

　　1. 抽象方法　

    // 获取会话超时时间
    abstract int getSessionTimeout();

    // 关闭
    abstract void close();

    // 发送响应
    public abstract void sendResponse(ReplyHeader h, Record r, String tag)
        throws IOException;

    /* notify the client the session is closing and close/cleanup socket */
    // 关闭会话
    abstract void sendCloseSession();

    // 处理，Watcher接口中的方法
    public abstract void process(WatchedEvent event);

    // 获取会话id
    abstract long getSessionId();

    // 设置会话id
    abstract void setSessionId(long sessionId);

    // 设置缓冲
    abstract void sendBuffer(ByteBuffer closeConn);

    // 允许接收
    abstract void enableRecv();

    // 不允许接收
    abstract void disableRecv();

    // 设置会话超时时间
    abstract void setSessionTimeout(int sessionTimeout);
    
    // 获取服务器的统计数据
    protected abstract ServerStats serverStats();

　　说明：以上的方法均为抽象方法，需要具体子类实现，如process方法是Watcher接口中的方法，在ServerCnxn中并未实现，需要具体子类实现。

　　2. 具体方法

    /** auth info for the cnxn, returns an unmodifyable list */
    // 获取认证信息，返回不可修改的列表
    public List<Id> getAuthInfo() {
        return Collections.unmodifiableList(authInfo);
    }

    // 添加认证信息
    public void addAuthInfo(Id id) {
        if (authInfo.contains(id) == false) {
            authInfo.add(id);
        }
    }

    // 移除认证信息
    public boolean removeAuthInfo(Id id) {
        return authInfo.remove(id);
    }

    // 接收的packet
    protected void packetReceived() {
        incrPacketsReceived();
        ServerStats serverStats = serverStats();
        if (serverStats != null) {
            serverStats().incrementPacketsReceived();
        }
    }

    // 发送的packet
    protected void packetSent() {
        incrPacketsSent();
        ServerStats serverStats = serverStats();
        if (serverStats != null) {
            serverStats().incrementPacketsSent();
        }
    }
    
    
    // 重置统计数据
    public synchronized void resetStats() {
        packetsReceived.set(0);
        packetsSent.set(0);
        minLatency = Long.MAX_VALUE;
        maxLatency = 0;
        lastOp = "NA";
        lastCxid = -1;
        lastZxid = -1;
        lastResponseTime = 0;
        lastLatency = 0;

        count = 0;
        totalLatency = 0;
    }

    // 增加接收的packet数量
    protected long incrPacketsReceived() {
        return packetsReceived.incrementAndGet();
    }
    
    // 增加outstandingRequest数量
    protected void incrOutstandingRequests(RequestHeader h) {
    }
    
    // 增加发送的packet数量
    protected long incrPacketsSent() {
        return packetsSent.incrementAndGet();
    }

    // 更新响应的统计数据
    protected synchronized void updateStatsForResponse(long cxid, long zxid,
            String op, long start, long end)
    {
        // don't overwrite with "special" xids - we're interested
        // in the clients last real operation
        if (cxid >= 0) { 
            lastCxid = cxid;
        }
        lastZxid = zxid;
        lastOp = op;
        lastResponseTime = end;
        long elapsed = end - start;
        lastLatency = elapsed;
        if (elapsed < minLatency) {
            minLatency = elapsed;
        }
        if (elapsed > maxLatency) {
            maxLatency = elapsed;
        }
        count++;
        totalLatency += elapsed;
    }

    public Date getEstablished() {
        return (Date)established.clone();
    }

    public abstract long getOutstandingRequests();

    public long getPacketsReceived() {
        return packetsReceived.longValue();
    }

    public long getPacketsSent() {
        return packetsSent.longValue();
    }

    public synchronized long getMinLatency() {
        return minLatency == Long.MAX_VALUE ? 0 : minLatency;
    }

    public synchronized long getAvgLatency() {
        return count == 0 ? 0 : totalLatency / count;
    }

    public synchronized long getMaxLatency() {
        return maxLatency;
    }

    public synchronized String getLastOperation() {
        return lastOp;
    }

    public synchronized long getLastCxid() {
        return lastCxid;
    }

    public synchronized long getLastZxid() {
        return lastZxid;
    }

    public synchronized long getLastResponseTime() {
        return lastResponseTime;
    }

    public synchronized long getLastLatency() {
        return lastLatency;
    }

    /**
     * Prints detailed stats information for the connection.
     *
     * @see dumpConnectionInfo(PrintWriter, boolean) for brief stats
     */
    @Override
    public String toString() {
        StringWriter sw = new StringWriter();
        PrintWriter pwriter = new PrintWriter(sw);
        dumpConnectionInfo(pwriter, false);
        pwriter.flush();
        pwriter.close();
        return sw.toString();
    }

    public abstract InetSocketAddress getRemoteSocketAddress();
    public abstract int getInterestOps();
    
    /**
     * Print information about the connection.
     * @param brief iff true prints brief details, otw full detail
     * @return information about this connection
     */
    protected synchronized void
    dumpConnectionInfo(PrintWriter pwriter, boolean brief) {
        pwriter.print(" ");
        pwriter.print(getRemoteSocketAddress());
        pwriter.print("[");
        int interestOps = getInterestOps();
        pwriter.print(interestOps == 0 ? "0" : Integer.toHexString(interestOps));
        pwriter.print("](queued=");
        pwriter.print(getOutstandingRequests());
        pwriter.print(",recved=");
        pwriter.print(getPacketsReceived());
        pwriter.print(",sent=");
        pwriter.print(getPacketsSent());

        if (!brief) {
            long sessionId = getSessionId();
            if (sessionId != 0) {
                pwriter.print(",sid=0x");
                pwriter.print(Long.toHexString(sessionId));
                pwriter.print(",lop=");
                pwriter.print(getLastOperation());
                pwriter.print(",est=");
                pwriter.print(getEstablished().getTime());
                pwriter.print(",to=");
                pwriter.print(getSessionTimeout());
                long lastCxid = getLastCxid();
                if (lastCxid >= 0) {
                    pwriter.print(",lcxid=0x");
                    pwriter.print(Long.toHexString(lastCxid));
                }
                pwriter.print(",lzxid=0x");
                pwriter.print(Long.toHexString(getLastZxid()));
                pwriter.print(",lresp=");
                pwriter.print(getLastResponseTime());
                pwriter.print(",llat=");
                pwriter.print(getLastLatency());
                pwriter.print(",minlat=");
                pwriter.print(getMinLatency());
                pwriter.print(",avglat=");
                pwriter.print(getAvgLatency());
                pwriter.print(",maxlat=");
                pwriter.print(getMaxLatency());
            }
        }
        pwriter.print(")");
    }

　　说明：ServerCnxn实现了Stats接口中的很多方法，其相对简单，不再累赘。

四、总结

　　本篇博文分析了ServerCnxn的源码，其是抽象类，定义了子类需要实现的方法，较为简单，也谢谢各位园友的观看~