聊聊rocketmq-client-go的PullConsumer

type PullConsumer interface {
    // Start
    Start()
​
    // Shutdown refuse all new pull operation, finish all submitted.
    Shutdown()
​
    // Pull pull message of topic,  selector indicate which queue to pull.
    Pull(ctx context.Context, topic string, selector MessageSelector, numbers int) (*primitive.PullResult, error)
​
    // PullFrom pull messages of queue from the offset to offset + numbers
    PullFrom(ctx context.Context, queue *primitive.MessageQueue, offset int64, numbers int) (*primitive.PullResult, error)
​
    // updateOffset update offset of queue in mem
    UpdateOffset(queue *primitive.MessageQueue, offset int64) error
​
    // PersistOffset persist all offset in mem.
    PersistOffset(ctx context.Context) error
​
    // CurrentOffset return the current offset of queue in mem.
    CurrentOffset(queue *primitive.MessageQueue) (int64, error)
}

type defaultPullConsumer struct {
    *defaultConsumer
​
    option    consumerOptions
    client    internal.RMQClient
    GroupName string
    Model     MessageModel
    UnitMode  bool
​
    interceptor primitive.Interceptor
}

func NewPullConsumer(options ...Option) (*defaultPullConsumer, error) {
    defaultOpts := defaultPullConsumerOptions()
    for _, apply := range options {
        apply(&defaultOpts)
    }
​
    srvs, err := internal.NewNamesrv(defaultOpts.NameServerAddrs)
    if err != nil {
        return nil, errors.Wrap(err, "new Namesrv failed.")
    }
​
    dc := &defaultConsumer{
        client:        internal.GetOrNewRocketMQClient(defaultOpts.ClientOptions, nil),
        consumerGroup: defaultOpts.GroupName,
        cType:         _PullConsume,
        state:         int32(internal.StateCreateJust),
        prCh:          make(chan PullRequest, 4),
        model:         defaultOpts.ConsumerModel,
        option:        defaultOpts,
​
        namesrv: srvs,
    }
​
    c := &defaultPullConsumer{
        defaultConsumer: dc,
    }
    return c, nil
}

func (c *defaultPullConsumer) Start() error {
    atomic.StoreInt32(&c.state, int32(internal.StateRunning))
​
    var err error
    c.once.Do(func() {
        err = c.start()
        if err != nil {
            return
        }
    })
​
    return err
}

func (c *defaultPullConsumer) Pull(ctx context.Context, topic string, selector MessageSelector, numbers int) (*primitive.PullResult, error) {
    mq := c.getNextQueueOf(topic)
    if mq == nil {
        return nil, fmt.Errorf("prepard to pull topic: %s, but no queue is founded", topic)
    }
​
    data := buildSubscriptionData(mq.Topic, selector)
    result, err := c.pull(context.Background(), mq, data, c.nextOffsetOf(mq), numbers)
​
    if err != nil {
        return nil, err
    }
​
    c.processPullResult(mq, result, data)
    return result, nil
}

func (c *defaultPullConsumer) getNextQueueOf(topic string) *primitive.MessageQueue {
    queues, err := c.defaultConsumer.namesrv.FetchSubscribeMessageQueues(topic)
    if err != nil && len(queues) > 0 {
        rlog.Error("get next mq error", map[string]interface{}{
            rlog.LogKeyTopic:         topic,
            rlog.LogKeyUnderlayError: err.Error(),
        })
        return nil
    }
    var index int64
    v, exist := queueCounterTable.Load(topic)
    if !exist {
        index = -1
        queueCounterTable.Store(topic, 0)
    } else {
        index = v.(int64)
    }
​
    return queues[int(atomic.AddInt64(&index, 1))%len(queues)]
}

// PullFrom pull messages of queue from the offset to offset + numbers
func (c *defaultPullConsumer) PullFrom(ctx context.Context, queue *primitive.MessageQueue, offset int64, numbers int) (*primitive.PullResult, error) {
    if err := c.checkPull(ctx, queue, offset, numbers); err != nil {
        return nil, err
    }
​
    selector := MessageSelector{}
    data := buildSubscriptionData(queue.Topic, selector)
​
    return c.pull(ctx, queue, data, offset, numbers)
}

// updateOffset update offset of queue in mem
func (c *defaultPullConsumer) UpdateOffset(queue *primitive.MessageQueue, offset int64) error {
    return c.updateOffset(queue, offset)
}

// PersistOffset persist all offset in mem.
func (c *defaultPullConsumer) PersistOffset(ctx context.Context) error {
    return c.persistConsumerOffset()
}

// CurrentOffset return the current offset of queue in mem.
func (c *defaultPullConsumer) CurrentOffset(queue *primitive.MessageQueue) (int64, error) {
    v := c.queryOffset(queue)
    return v, nil
}

// Shutdown close defaultConsumer, refuse new request.
func (c *defaultPullConsumer) Shutdown() error {
    return c.defaultConsumer.shutdown()
}