我应该用互斥保护结构对象吗？

Question

I use 4 go routines to assign different member variables of a struct instance. Each member variable is only accessed by one go routine.

Do I need to add mutex when accessing the struct instance?

I am not sure if the 4 go routines access the same memory. I feel I should be cause all of them accesses the holder.

This code demonstrates what I'm doing.

package main

import (
    "fmt"
    "sync"
)

func main() {
    var wg sync.WaitGroup
    var res Response

    var mu sync.Mutex

    wg.Add(1)
    go func() {

        defer wg.Done()
        mu.Lock()
        defer mu.Unlock()
        res.A = []string{"a"}
    }()

    wg.Add(1)
    go func() {
        defer wg.Done()
        mu.Lock()
        defer mu.Unlock()
        res.B = "b"
    }()

    wg.Add(1)
    go func() {
        defer wg.Done()
        mu.Lock()
        defer mu.Unlock()
        res.C = 100
    }()

    wg.Add(1)
    go func() {
        defer wg.Done()
        mu.Lock()
        defer mu.Unlock()
        res.D = map[string]string{
            "d": "dd",
        }
    }()

    wg.Wait()

    fmt.Println(res)

}

type Response struct {
    A []string
    B string
    C int
    D map[string]string
}

Answer 1

You do not need a mutex for this program. As far as the Go memory model is concerned, separate fields of a struct are separate variables. Since the four goroutines are accessing four separate (sub-)variables, there is no data race, even without the mutex.

You can verify this by removing the mutex and running your program with the race detector enabled: https://golang.org/doc/articles/race_detector.html