摘要

本节开始，后面几节围绕单机服务器类ZooKeeperServer进行展开
ZooKeeperServer类图如下

ZooKeeperServer类图

本节讲解服务器启动器ServerStats源码，类图如下

ServerStats类图

主要讲解

    内部类Provider完成服务器状态，队列数量，client存活数量等信息
    属性，函数完成延迟，发送，接收量等信息

内部类

org.apache.zookeeper.server.ServerStats.Provider
Provider是一个接口，源码如下

   public interface Provider {
        public long getOutstandingRequests();//获取队列中还没有被处理的请求数量
        public long getLastProcessedZxid();//获取最后一个处理的zxid
        public String getState();//获取服务器状态
        public int getNumAliveConnections();//获取存活的客户端连接总数
    }

注意
Provider的实现类如下

Provider实现类

其中，getOutstandingRequests，getLastProcessedZxid，getNumAliveConnections就一种默认实现，在
ZooKeeperServer类中
getState有5种实现，用于区分单机，集群不同server的状态

getState5种实现

属性

    private long packetsSent;//发送包个数
    private long packetsReceived;//接收个数
    private long maxLatency;//最长延迟
    private long minLatency = Long.MAX_VALUE;//最短延迟
    private long totalLatency = 0;//总延迟
    private long count = 0;//延迟次数

    private final Provider provider;//Provider对象，提供部分统计数据

函数

分为几种，构造函数，获取信息函数，设置，重置信息函数

获取信息类

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

    synchronized public long getAvgLatency() {
        if (count != 0) {
            return totalLatency / count;
        }
        return 0;
    }

    synchronized public long getMaxLatency() {
        return maxLatency;
    }

    public long getOutstandingRequests() {
        return provider.getOutstandingRequests();
    }
    
    public long getLastProcessedZxid(){
        return provider.getLastProcessedZxid();
    }
    
    synchronized public long getPacketsReceived() {
        return packetsReceived;
    }

    synchronized public long getPacketsSent() {
        return packetsSent;
    }

    public String getServerState() {
        return provider.getState();
    }
    
    /** The number of client connections alive to this server */
    public int getNumAliveClientConnections() {
        return provider.getNumAliveConnections();
    }

比较简单，不展开
其中，getOutstandingRequests，getLastProcessedZxid，getServerState，getNumAliveClientConnections都是通过provider完成

设置，重置信息函数

    // mutators
    synchronized void updateLatency(long requestCreateTime) {//更新延迟统计数据
        long latency = System.currentTimeMillis() - requestCreateTime;
        totalLatency += latency;
        count++;
        if (latency < minLatency) {
            minLatency = latency;
        }
        if (latency > maxLatency) {
            maxLatency = latency;
        }
    }
    synchronized public void resetLatency(){//重置延迟数据
        totalLatency = 0;
        count = 0;
        maxLatency = 0;
        minLatency = Long.MAX_VALUE;
    }
    synchronized public void resetMaxLatency(){//重置max延迟
        maxLatency = getMinLatency();
    }
    synchronized public void incrementPacketsReceived() {//接受次数+1
        packetsReceived++;
    }
    synchronized public void incrementPacketsSent() {//发送次数+1
        packetsSent++;
    }
    synchronized public void resetRequestCounters(){//重置请求量统计
        packetsReceived = 0;
        packetsSent = 0;
    }
    synchronized public void reset() {
        resetLatency();
        resetRequestCounters();
    }

都比较好理解

构造函数

    public ServerStats(Provider provider) {
        this.provider = provider;
    }

是指provider来完成getOutstandingRequests,getLastProcessedZxid等调用

思考

什么时候用到了ServerStats对应的信息

jmx中，不过jmx怎么用目前还不清楚，后面学习了再说