同时从两个不同的goroutine调用方法是否安全？

I have two goroutines go doProcess_A() and go doProcess_B(). Both can call saveData(), a non goroutine method.

should I use go saveData() instead of saveData() ? Which one is safe?

var waitGroup sync.WaitGroup

func main() {

    for i:=0; i<4; i++{
        waitGroup.Add(2)

        go doProcess_A(i)
        go doProcess_B(i)
    }
    waitGroup.Wait()
}

func doProcess_A(i int)  {
    // do process
    // the result will be stored in data variable
    data := "processed data-A as string"
    uniqueFileName := "file_A_"+strconv.Itoa(i)+".txt"
    saveData(uniqueFileName, data)

    waitGroup.Done()
}

func doProcess_B(i int) {
    // do some process
    // the result will be stored in data variable
    data := "processed data-B as string"
    uniqueFileName := "file_B_"+strconv.Itoa(i)+".txt"
    saveData(uniqueFileName, data)

    waitGroup.Done()
}

// write text file
func saveData(fileName ,dataStr string) {
    // file name will be unique.
    // there is no chance to be same file name
    err := ioutil.WriteFile("out/"+fileName, []byte(dataStr), 0644)
    if err != nil {
        panic(err)
    }
}

here, does one goroutine wait for disk file operation when other goroutine is doing? or, are two goroutine make there own copy of saveData() ?

Goroutines typically don't wait for anything except you explicitly tell them to or if an operation is waiting on a channel or other blocking operation. In your code there is a possibility of a race condition with unwanted results if multiple goroutines call the saveData() function with same filename. It appears that the two goroutines are writing to different files, therefore as long as the filenames are unique, the saveData operation will be safe in a goroutine. It doesn't make sense to use a go routine to call saveData(), don't unnecessarily complicate your life, just call it directly in the doProcess_X functions.

Read more about goroutines and make sure you are using it where it is absolutely necessary. - https://gobyexample.com/goroutines

Note: Just because you are writing a Go application doesn't mean you should litter it with goroutines. Read and understand what problem it solves so as to know the best time to use it.