I'm pretty new in Go and need the answers to some of dilemmas while implementing small HTTP notifier than runs concurrently, sending message to the configured HTTP endpoint. For that purpose, I use the following structure:

type Notifier struct {
    url          string
    waitingQueue *list.List
    progress   *list.List

    errs chan NotificationError

    active sync.WaitGroup
    mu     sync.Mutex
}

Here is the notify method:

func (hn *Notifier) Notify(message string) {
    if hn.ProcessingCount() < hn.config.MaxActiveRequestsCount() && hn.checkIfOlderThanOldestWaiting(time.Now().Unix()) {
        element := hn.addToProgressQueue(message)
        hn.active.Add(1)
        go hn.sendNotification(element)
    } else {
        hn.waitingQueue.PushBack(QueueItem{message, time.Now().UnixNano()})
    }
}

And addToInProgressQueue:

func (hn *Notifier) addToProgressQueue(message string) *list.Element {
    hn.mu.Lock()
    defer hn.mu.Unlock()

    queueItem := QueueItem{message, time.Now().UnixNano()}
    element := hn.progress.PushBack(queueItem)
    return element
}

1. I guess this won't work as expected for concurrent reads/writes of queue? Is it enought to use RWMutex instead of Mutex to ensure the locks are working properly?

2. The code of ProcessingCount

func (hn *Notifier) ProcessingCount() int {
    hn.mu.Lock()
    defer hn.mu.Unlock()

    return hn.inProgress.Len()
}

Can there be a data race here?

Also, if you have some good resources on data race examples in Golang, it would be well appreciated.

Thanks in advance