聊聊rocketmq-client-go的QueueSelector

序

本文主要研究一下rocketmq-client-go的QueueSelector

QueueSelector

rocketmq-client-go-v2.0.0/producer/selector.go

type QueueSelector interface {
    Select(*primitive.Message, []*primitive.MessageQueue) *primitive.MessageQueue
}

• QueueSelector接口，定义了Select方法

manualQueueSelector

rocketmq-client-go-v2.0.0/producer/selector.go

type manualQueueSelector struct{}

func NewManualQueueSelector() QueueSelector {
    return new(manualQueueSelector)
}

func (manualQueueSelector) Select(message *primitive.Message, queues []*primitive.MessageQueue) *primitive.MessageQueue {
    return message.Queue
}

• manualQueueSelector的select方法直接返回message.Queue

NewRandomQueueSelector

rocketmq-client-go-v2.0.0/producer/selector.go

type randomQueueSelector struct {
    rander *rand.Rand
}

func NewRandomQueueSelector() QueueSelector {
    s := new(randomQueueSelector)
    s.rander = rand.New(rand.NewSource(time.Now().UTC().UnixNano()))
    return s
}

func (r randomQueueSelector) Select(message *primitive.Message, queues []*primitive.MessageQueue) *primitive.MessageQueue {
    i := r.rander.Intn(len(queues))
    return queues[i]
}

• NewRandomQueueSelector方法先创建randomQueueSelector，然后设置其rander；Select方法通过r.rander.Intn(len(queues))随机选择index，然后从queue取值

roundRobinQueueSelector

rocketmq-client-go-v2.0.0/producer/selector.go

type roundRobinQueueSelector struct {
    sync.Locker
    indexer map[string]*int32
}

func NewRoundRobinQueueSelector() QueueSelector {
    s := &roundRobinQueueSelector{
        Locker:  new(sync.Mutex),
        indexer: map[string]*int32{},
    }
    return s
}

func (r *roundRobinQueueSelector) Select(message *primitive.Message, queues []*primitive.MessageQueue) *primitive.MessageQueue {
    t := message.Topic
    if _, exist := r.indexer[t]; !exist {
        r.Lock()
        if _, exist := r.indexer[t]; !exist {
            var v = int32(0)
            r.indexer[t] = &v
        }
        r.Unlock()
    }
    index := r.indexer[t]

    i := atomic.AddInt32(index, 1)
    if i < 0 {
        i = -i
        atomic.StoreInt32(index, 0)
    }
    qIndex := int(i) % len(queues)
    return queues[qIndex]
}

• roundRobinQueueSelector的qIndex为int(i) % len(queues)

hashQueueSelector

rocketmq-client-go-v2.0.0/producer/selector.go

type hashQueueSelector struct {
    random QueueSelector
}

func NewHashQueueSelector() QueueSelector {
    return &hashQueueSelector{
        random: NewRandomQueueSelector(),
    }
}

// hashQueueSelector choose the queue by hash if message having sharding key, otherwise choose queue by random instead.
func (h *hashQueueSelector) Select(message *primitive.Message, queues []*primitive.MessageQueue) *primitive.MessageQueue {
    key := message.GetShardingKey()
    if len(key) == 0 {
        return h.random.Select(message, queues)
    }

    hasher := fnv.New32a()
    _, err := hasher.Write([]byte(key))
    if err != nil {
        return nil
    }
    queueId := int(hasher.Sum32()) % len(queues)
    if queueId < 0 {
        queueId = -queueId
    }
    return queues[queueId]
}

• hashQueueSelector通过int(hasher.Sum32()) % len(queues)来计算queue的index

小结

rocketmq-client-go的selector.go定义了manualQueueSelector、roundRobinQueueSelector、hashQueueSelector

doc

• selector.go