go-redis源码解析：如何实现sentinel高可用

go-redis里，sentinel只用来获取master和从节点的ip地址，在获取master和replica节点ip时，如果sentinel不可用，那么会换其他的sentinel重试，并将可用的sentinel换到第一个

1. 用于获取master节点

先通过读锁获取c.sentinel，使用c.sentinel获取主节点信息
如果上面sentinel为空或者出错未获取到主节点，那么可能在此中间有地方重新设置了c.sentinel，继续用读写锁，使用c.sentinel获取主节点信息
1. 分读锁和读写锁这两步的原因是，提高并发性能
如果以上两步的sentinel都有问题，那么遍历所有的sentinelAddr，创建sentinel进行处理
最后如果所有的sentinel都不可用，则报错

1.1. 核心高可用代码

1.2. 方法内所有处理逻辑

func (c *sentinelFailover) replicaAddrs(ctx context.Context, useDisconnected bool) ([]string, error) {// 1. 先通过读锁获取c.sentinel，使用c.sentinel获取主节点信息c.mu.RLock()sentinel := c.sentinelc.mu.RUnlock()if sentinel != nil {// 通过哨兵查询从节点addrs, err := c.getReplicaAddrs(ctx, sentinel)if err != nil {if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {return nil, err}// Continue on other errorsinternal.Logger.Printf(ctx, "sentinel: Replicas name=%q failed: %s",c.opt.MasterName, err)} else if len(addrs) > 0 {return addrs, nil}}// 2. 如果上面sentinel为空或者出错未获取到主节点，那么可能在此中间有地方重新设置了c.sentinel，继续用读写锁，使用c.sentinel获取主节点信息// 分读锁和读写锁这两步的原因是，提高并发性能c.mu.Lock()defer c.mu.Unlock()if c.sentinel != nil {addrs, err := c.getReplicaAddrs(ctx, c.sentinel)if err != nil {_ = c.closeSentinel()if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {return nil, err}// Continue on other errorsinternal.Logger.Printf(ctx, "sentinel: Replicas name=%q failed: %s",c.opt.MasterName, err)} else if len(addrs) > 0 {return addrs, nil} else {// No error and no replicas._ = c.closeSentinel()}}// 3. 如果以上两步的sentinel都有问题，那么遍历所有的sentinelAddr，创建sentinel进行处理var sentinelReachable boolfor i, sentinelAddr := range c.sentinelAddrs {sentinel := NewSentinelClient(c.opt.sentinelOptions(sentinelAddr))replicas, err := sentinel.Replicas(ctx, c.opt.MasterName, c.opt.ServerVersion).Result()if err != nil {_ = sentinel.Close()if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {return nil, err}internal.Logger.Printf(ctx, "sentinel: Replicas master=%q failed: %s",c.opt.MasterName, err)continue}sentinelReachable = trueaddrs := parseReplicaAddrs(replicas, useDisconnected)if len(addrs) == 0 {continue}// Push working sentinel to the top.c.sentinelAddrs[0], c.sentinelAddrs[i] = c.sentinelAddrs[i], c.sentinelAddrs[0]c.setSentinel(ctx, sentinel)return addrs, nil}if sentinelReachable {return []string{}, nil}// 4. 最后如果所有的sentinel都不可用，则报错return []string{}, errors.New("redis: all sentinels specified in configuration are unreachable")
}

2. 用于获取replica从节点

和获取主节点方法处理逻辑类似

先通过读锁获取c.sentinel，使用c.sentinel获取从节点信息
如果上面sentinel为空或者出错未获取到从节点，那么可能在此中间有地方重新设置了c.sentinel，继续用读写锁，使用c.sentinel获取从节点信息
1. 分读锁和读写锁这两步的原因是，提高并发性能
如果以上两步的sentinel都有问题，那么遍历所有的sentinelAddr，创建sentinel进行处理
最后如果所有的sentinel都不可用，则报错

func (c *sentinelFailover) replicaAddrs(ctx context.Context, useDisconnected bool) ([]string, error) {c.mu.RLock()sentinel := c.sentinelc.mu.RUnlock()if sentinel != nil {// 通过哨兵查询从节点addrs, err := c.getReplicaAddrs(ctx, sentinel)if err != nil {if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {return nil, err}// Continue on other errorsinternal.Logger.Printf(ctx, "sentinel: Replicas name=%q failed: %s",c.opt.MasterName, err)} else if len(addrs) > 0 {return addrs, nil}}c.mu.Lock()defer c.mu.Unlock()if c.sentinel != nil {addrs, err := c.getReplicaAddrs(ctx, c.sentinel)if err != nil {_ = c.closeSentinel()if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {return nil, err}// Continue on other errorsinternal.Logger.Printf(ctx, "sentinel: Replicas name=%q failed: %s",c.opt.MasterName, err)} else if len(addrs) > 0 {return addrs, nil} else {// No error and no replicas._ = c.closeSentinel()}}var sentinelReachable boolfor i, sentinelAddr := range c.sentinelAddrs {sentinel := NewSentinelClient(c.opt.sentinelOptions(sentinelAddr))replicas, err := sentinel.Replicas(ctx, c.opt.MasterName, c.opt.ServerVersion).Result()if err != nil {_ = sentinel.Close()if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {return nil, err}internal.Logger.Printf(ctx, "sentinel: Replicas master=%q failed: %s",c.opt.MasterName, err)continue}sentinelReachable = trueaddrs := parseReplicaAddrs(replicas, useDisconnected)if len(addrs) == 0 {continue}// Push working sentinel to the top.c.sentinelAddrs[0], c.sentinelAddrs[i] = c.sentinelAddrs[i], c.sentinelAddrs[0]c.setSentinel(ctx, sentinel)return addrs, nil}if sentinelReachable {return []string{}, nil}return []string{}, errors.New("redis: all sentinels specified in configuration are unreachable")
}