JedisSentinelPool源码分析

1. 概述

    Redis-Sentinel作为官方推荐的HA解决方案，jedis也在客户端角度实现了对Sentinel的支持，主要实现在JedisSentinelPool这个类里。

2. 简单例子

import redis.clients.jedis.HostAndPort;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisSentinelPool;

import java.util.HashSet;
import java.util.Set;

public class RedisSentinelClient {

    /**
     * @param args
     */
    public static void main(String[] args) {
        Set sentinels = new HashSet();
        sentinels.add(new HostAndPort("192.168.58.99", 26379).toString());
        sentinels.add(new HostAndPort("192.168.58.100", 26380).toString());
        sentinels.add(new HostAndPort("192.168.58.101", 26381).toString());
        JedisSentinelPool sentinelPool = new JedisSentinelPool("master", sentinels);
        System.out.println("Current master: " + sentinelPool.getCurrentHostMaster().toString());
        Jedis master = sentinelPool.getResource();
        master.set("username","liangzhichao");
        sentinelPool.returnResource(master);

        Jedis master2 = sentinelPool.getResource();
        String value = master2.get("username");
        System.out.println("username: " + value);
        master2.close();
        sentinelPool.destroy();
    }

3 JedisSentinelPool字段

//基于apache的commom-pool2的对象池配置
protected GenericObjectPoolConfig poolConfig;

//超时时间，默认是2000
protected int timeout = Protocol.DEFAULT_TIMEOUT;

//sentinel的密码
protected String password;

//redis数据库的数目
protected int database = Protocol.DEFAULT_DATABASE;

//master监听器，当master的地址发生改变时，会触发这些监听者
protected Set masterListeners = new HashSet();

protected Logger log = Logger.getLogger(getClass().getName());

//Jedis实例创建工厂
private volatile JedisFactory factory;

//当前的master，HostAndPort是一个简单的包装了ip和port的模型类
private volatile HostAndPort currentHostMaster;

4 JedisSentinelPool构造器

public JedisSentinelPool(String masterName, Set sentinels, final GenericObjectPoolConfig poolConfig, int timeout, final String password, final int database) {

    this.poolConfig = poolConfig;
    this.timeout = timeout;
    this.password = password;
    this.database = database;

    HostAndPort master = initSentinels(sentinels, masterName);
    initPool(master);
}

    构造器一开始对实例变量进行赋值，参数sentinels是客户端需要打交道的Redis-Sentinel，允许多个，然后通过initSentinels与sentinel沟通后，确定所监视的master节点，接着通过masater节点来创建好对象池，方便后续从对象池中取出一个Jedis实例。

5 initSentinels方法

private HostAndPort initSentinels(Set sentinels, final String masterName) {

    HostAndPort master = null;
    boolean sentinelAvailable = false;

    log.info("Trying to find master from available Sentinels...");

    // 有多个sentinels,遍历这些个sentinels
    for (String sentinel : sentinels) {
        // host:port表示的sentinel地址转化为一个HostAndPort对象。
        final HostAndPort hap = toHostAndPort(Arrays.asList(sentinel.split(":")));

        log.fine("Connecting to Sentinel " + hap);

        Jedis jedis = null;
        try {
            // 连接到sentinel
            jedis = new Jedis(hap.getHost(), hap.getPort());

            // 根据masterName得到master的地址，返回一个list，host= list[0], port =
            // list[1]
            List masterAddr = jedis.sentinelGetMasterAddrByName(masterName);

            // connected to sentinel...
            sentinelAvailable = true;

            if (masterAddr == null || masterAddr.size() != 2) {
                log.warning("Can not get master addr, master name: " + masterName
                        + ". Sentinel: " + hap + ".");
                continue;
            }

            master = toHostAndPort(masterAddr);
            log.fine("Found Redis master at " + master);
            // 如果在任何一个sentinel中找到了master，不再遍历sentinels
            break;
        } catch (JedisConnectionException e) {
            log.warning("Cannot connect to sentinel running @ " + hap
                    + ". Trying next one.");
        } finally {
            // 关闭与sentinel的连接
            if (jedis != null) {
                jedis.close();
            }
        }
    }

    // 到这里，如果master为null，则说明有两种情况，一种是所有的sentinels节点都down掉了，一种是master节点没有被存活的sentinels监控到
    if (master == null) {
        if (sentinelAvailable) {
            // can connect to sentinel, but master name seems to not
            // monitored
            throw new JedisException("Can connect to sentinel, but " + masterName
                    + " seems to be not monitored...");
        } else {
            throw new JedisConnectionException(
                    "All sentinels down, cannot determine where is " + masterName
                            + " master is running...");
        }
    }

    //如果走到这里，说明找到了master的地址
    log.info("Redis master running at " + master + ", starting Sentinel listeners...");

    //启动对每个sentinels的监听
    for (String sentinel : sentinels) {
        final HostAndPort hap = toHostAndPort(Arrays.asList(sentinel.split(":")));
        MasterListener masterListener = new MasterListener(masterName, hap.getHost(),
                hap.getPort());
        masterListeners.add(masterListener);
        masterListener.start();
    }

    return master;
}

    initSentinels方法的masterName参数就是我们所需要查找的master的名字。一开始，遍历多个sentinels，一个一个连接到sentinel，通过jedis.sentinelGetMasterAddrByName()方法去连接sentinel，询问关于masterName的消息。

 public List sentinelGetMasterAddrByName(String masterName) {
    client.sentinel(Protocol.SENTINEL_GET_MASTER_ADDR_BY_NAME, masterName);
    final List