CODEWITHSUNDEEP
goredisgo-redis
Yongqi Z
Yongqi Z

Reputation: 641

Redis distributed lock does not take effect

I am using go-redis distributed lock to realize mutual exclusion access, my server is a single thread server. But at the same time, many requests get the distributed lock.

func (redisMgrPtr *RedisMgr) getLock(key string) (int32) {
    encodeKey := transcoding.Base64Encode(key)
    _, err := redisMgrPtr.redisClient.SetNX(redisMgrPtr.ctx, 
    encodeKey, 1, TIMEOUT).Result()
    if err != nil {
        return -1
    }
    return 0
}

func (redisMgrPtr *RedisMgr) delLock(key string, sessionId string) {
    encodeKey := transcoding.Base64Encode(key)
    redisMgrPtr.redisClient.Del(redisMgrPtr.ctx, encodeKey)
    Log.Errorf("session[%s] del lock", sessionId)
}

Get lock code is like this:

func (redisMgrPtr *RedisMgr) GetServer(name string, session string) () {
    for { 
        locRes := redisMgrPtr.getLock(name) 
        if locRes == 0 {
            break
        } else {
            time.Sleep(5 * time.Millisecond)
            continue
        }
    }
    defer redisMgrPtr.delLock(sceneLock, sessionId)
    Log.Errorf("session[%s] get lock", sessionId)
    // do something
}

I find many requests get the lock at the same time, result is

2021-09-08T15:05:21.073+0800 session[51776955325] get lock
2021-09-08T15:05:21.073+0800 session[91776955325] get lock
2021-09-08T15:05:21.073+0800 session[71776955325] get lock

I think at the same time only one session can get the lock

Upvotes: 1

Views: 854

Answers (1)

TehSphinX
TehSphinX

Reputation: 7440

The problem seems to be with the lock function. It does not check if the value existed or not, it just checks the error.

func (redisMgrPtr *RedisMgr) getLock(key string) (int32) {
    encodeKey := transcoding.Base64Encode(key)
    wasSet, err := redisMgrPtr.redisClient.SetNX(redisMgrPtr.ctx, encodeKey, 1, TIMEOUT).Result()
    if err != nil || !wasSet {
        return -1
    }
    return 0
}

... or using a boolean to make it easier to reason about:

func (redisMgrPtr *RedisMgr) getLock(key string) (ok bool) {
    encodeKey := transcoding.Base64Encode(key)
    wasSet, err := redisMgrPtr.redisClient.SetNX(redisMgrPtr.ctx, encodeKey, 1, TIMEOUT).Result()
    return err == nil && wasSet
}

With the boolean version GetServer could look like this:

func (redisMgrPtr *RedisMgr) GetServer(name string, session string) () {
    for { 
        if ok := redisMgrPtr.getLock(name); ok {
            break
        }
        time.Sleep(5 * time.Millisecond)
    }
    defer redisMgrPtr.delLock(sceneLock, sessionId)
    Log.Errorf("session[%s] get lock", sessionId)
    // do something
}

Upvotes: 2

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