序
本文次要钻研一下 machinery 的 Lock
Lock
type Lock interface {
//Acquire the lock with retry
//key: the name of the lock,
//value: at the nanosecond timestamp that lock needs to be released automatically
LockWithRetries(key string, value int64) error
//Acquire the lock with once
//key: the name of the lock,
//value: at the nanosecond timestamp that lock needs to be released automatically
Lock(key string, value int64) error
}
Lock 接口定义了 LockWithRetries、Lock 办法
redis/Lock
var (ErrRedisLockFailed = errors.New("redis lock: failed to acquire lock")
)
type Lock struct {
rclient redis.UniversalClient
retries int
interval time.Duration
}
func New(cnf *config.Config, addrs []string, db, retries int) Lock {
if retries <= 0 {return Lock{}
}
lock := Lock{retries: retries}
var password string
parts := strings.Split(addrs[0], "@")
if len(parts) == 2 {password = parts[0]
addrs[0] = parts[1]
}
ropt := &redis.UniversalOptions{
Addrs: addrs,
DB: db,
Password: password,
}
if cnf.Redis != nil {ropt.MasterName = cnf.Redis.MasterName}
lock.rclient = redis.NewUniversalClient(ropt)
return lock
}
func (r Lock) LockWithRetries(key string, unixTsToExpireNs int64) error {
for i := 0; i <= r.retries; i++ {err := r.Lock(key, unixTsToExpireNs)
if err == nil {
// 胜利拿到锁,返回
return nil
}
time.Sleep(r.interval)
}
return ErrRedisLockFailed
}
func (r Lock) Lock(key string, unixTsToExpireNs int64) error {now := time.Now().UnixNano()
expiration := time.Duration(unixTsToExpireNs + 1 - now)
ctx := r.rclient.Context()
success, err := r.rclient.SetNX(ctx, key, unixTsToExpireNs, expiration).Result()
if err != nil {return err}
if !success {v, err := r.rclient.Get(ctx, key).Result()
if err != nil {return err}
timeout, err := strconv.Atoi(v)
if err != nil {return err}
if timeout != 0 && now > int64(timeout) {newTimeout, err := r.rclient.GetSet(ctx, key, unixTsToExpireNs).Result()
if err != nil {return err}
curTimeout, err := strconv.Atoi(newTimeout)
if err != nil {return err}
if now > int64(curTimeout) {
// success to acquire lock with get set
// set the expiration of redis key
r.rclient.Expire(ctx, key, expiration)
return nil
}
return ErrRedisLockFailed
}
return ErrRedisLockFailed
}
return nil
}
Lock 定义了 rclient、retries、interval 属性;New 办法依据 cnf、addrs、db、retries 创立 lock;LockWithRetries 办法依据 retries 次数来尝试 r.Lock(key, unixTsToExpireNs),都没有胜利则返回 ErrRedisLockFailed;Lock 办法执行 r.rclient.SetNX,如果不胜利则判断是否过期,过期的话执行执行 r.rclient.GetSet,若的确过期了则执行 r.rclient.Expire(ctx, key, expiration) 更新新的过期工夫
小结
machinery 的 Lock 接口定义了 LockWithRetries、Lock 办法;基于 redis 的实现则通过 r.rclient.SetNX、r.rclient.GetSet、r.rclient.Expire 实现。
doc
- machinery