Redis实践(八)-Sentinal12 主从复制高可用?3 Redis Sentinel 架构4 安装与配置5 安装与演示6 客户端11 三个定时任务12 主观下线和客观下线13 领导者选举14

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

    HostAndPort master = null;
    boolean sentinelAvailable = false;

    log.info("Trying to find master from available Sentinels...");
    // 遍历所有 Sentinel 节点
    for (String sentinel : sentinels) {
      final HostAndPort hap = toHostAndPort(Arrays.asList(sentinel.split(":")));

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

      Jedis jedis = null;
      try {
        // 找到一个可运行的,并用jedis连接上去
        jedis = new Jedis(hap.getHost(), hap.getPort());

        // 通过 mastername 区分 sentinel 节点,得到其地址
        List<String> masterAddr = jedis.sentinelGetMasterAddrByName(masterName);

        // connected to sentinel...
        sentinelAvailable = true;
        //节点不可用继续遍历
        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);
        // 找到可用节点,结束遍历,跳出循环
        break;
      } catch (JedisException e) {
        // resolves #1036, it should handle JedisException there's another chance
        // of raising JedisDataException
        log.warning("Cannot get master address from sentinel running @ " + hap + ". Reason: " + e
            + ". Trying next one.");
      } finally {
        if (jedis != null) {
          jedis.close();
        }
      }
    }
    //无可用节点,抛异常
    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...");
      }
    }

    log.info("Redis master running at " + master + ", starting Sentinel listeners...");
    //当拿到master节点后,所要做的就是订阅那个消息,客户端只需订阅该频道即可
    for (String sentinel : sentinels) {
      final HostAndPort hap = toHostAndPort(Arrays.asList(sentinel.split(":")));
      MasterListener masterListener = new MasterListener(masterName, hap.getHost(), hap.getPort());
      // whether MasterListener threads are alive or not, process can be stopped
      masterListener.setDaemon(true);
      masterListeners.add(masterListener);
      masterListener.start();
    }

protected class MasterListener extends Thread {

    protected String masterName;
    protected String host;
    protected int port;
    protected long subscribeRetryWaitTimeMillis = 5000;
    protected volatile Jedis j;
    protected AtomicBoolean running = new AtomicBoolean(false);

    protected MasterListener() {
    }

    public MasterListener(String masterName, String host, int port) {
      super(String.format("MasterListener-%s-[%s:%d]", masterName, host, port));
      this.masterName = masterName;
      this.host = host;
      this.port = port;
    }

    public MasterListener(String masterName, String host, int port,
        long subscribeRetryWaitTimeMillis) {
      this(masterName, host, port);
      this.subscribeRetryWaitTimeMillis = subscribeRetryWaitTimeMillis;
    }

    @Override
    public void run() {

      running.set(true);

      while (running.get()) {

        j = new Jedis(host, port);

        try {
          // double check that it is not being shutdown
          if (!running.get()) {
            break;
          }

          j.subscribe(new JedisPubSub() {
            @Override
            public void onMessage(String channel, String message) {
              log.fine("Sentinel " + host + ":" + port + " published: " + message + ".");

              String[] switchMasterMsg = message.split(" ");

              if (switchMasterMsg.length > 3) {

                if (masterName.equals(switchMasterMsg[0])) {
                  initPool(toHostAndPort(Arrays.asList(switchMasterMsg[3], switchMasterMsg[4])));
                } else {
                  log.fine("Ignoring message on +switch-master for master name "
                      + switchMasterMsg[0] + ", our master name is " + masterName);
                }

              } else {
                log.severe("Invalid message received on Sentinel " + host + ":" + port
                    + " on channel +switch-master: " + message);
              }
            }
          }, "+switch-master");

        } catch (JedisConnectionException e) {

          if (running.get()) {
            log.log(Level.SEVERE, "Lost connection to Sentinel at " + host + ":" + port
                + ". Sleeping 5000ms and retrying.", e);
            try {
              Thread.sleep(subscribeRetryWaitTimeMillis);
            } catch (InterruptedException e1) {
              log.log(Level.SEVERE, "Sleep interrupted: ", e1);
            }
          } else {
            log.fine("Unsubscribing from Sentinel at " + host + ":" + port);
          }
        } finally {
          j.close();
        }
      }
    }

    public void shutdown() {
      try {
        log.fine("Shutting down listener on " + host + ":" + port);
        running.set(false);
        // This isn't good, the Jedis object is not thread safe
        if (j != null) {
          j.disconnect();
        }
      } catch (Exception e) {
        log.log(Level.SEVERE, "Caught exception while shutting down: ", e);
      }
    }
  }