从一个通道读取的多个 goroutine 给出了错误的数据计数

Question

I'm working on a program where I read a csv file and do below operations:

Full Code is available at: Here

My CSV file is available at: CSV file

The problem is sometimes I get the correct count for A and B and sometimes I get the wrong count.

I think I'm doing something wrong in Goroutines and channels communication.

When I comment the 2nd goroutine, I get correct result of 1st Goroutine. But when I uncomment 2nd Goroutine, I get incorrect output of Goroutine 1 and 2 both.

Can anyone please explain what wrong I'm doing?

Also when I do go run -race main.go, the result shows me a race condition.

func main() {
    input, err := os.Open("CSV.csv")
    if err != nil {
        fmt.Println("Error while opening CSV file.")
        return
    }
    defer input.Close()

    formattedStartDateRange,err := time.Parse(time.RFC3339, startDateRange)
    if err != nil {
        fmt.Println(err)
    }

    formattedendDateRange,err := time.Parse(time.RFC3339, endDateRange)
    if err != nil {
        fmt.Println(err)
    }

    reader := csv.NewReader(input)
    reader.FieldsPerRecord = -1
    files := make(map[string]chan []string)

    wg := &sync.WaitGroup{}

    var line []string
    for line, err = reader.Read(); err == nil; line, err = reader.Read() {
        ch, ok := files[line[0]]
        if ok {
            ch <- line
        } else {
            ch = make(chan []string, 8)
            ch <- line
            wg.Add(2) // Must wait for 2 calls to 'done' before moving on

            go func() {
                UserMapMutex.Lock()
                if (findNumberOfBuilds(formattedStartDateRange, formattedendDateRange, ch, wg)) {
                    totalBuildCount++
                }
                UserMapMutex.Unlock()
                wg.Done()
            }()

            go func() {
                UserMapMutex.Lock()
                countUserBuildFrequency(ch, wg)
                UserMapMutex.Unlock()
                wg.Done()
            }()


            files[line[0]] = ch
        }
    }


    if err.Error() != "EOF" {
        fmt.Println("Error while reading CSV file.")
        return
    }
    for _, ch := range files {
        close(ch)
    }
    wg.Wait()

    fmt.Println("Total Build executed from 1st November to 30th November =", totalBuildCount)
    fmt.Println("Total Build", userBuildFreq["5c00a8f685db9ec46dbc13d7"])
    fmt.Println("Done!")
}

Answer 1

In both cases, your wg.Done() is being called immediately after you start the goroutine. This means that your WaitGroup is not waiting for the goroutine to finish. Remember that the calling process proceeds when you call a goroutine. Try putting the wg.Done() call inside the goroutine, when it's finished doing stuff.

go func(wg) {
    // do stuff
    wg.Done
}

OR

go func(wg) {
    defer wg.Done
    // do stuff
}