把互斥鎖改為讀寫鎖也很簡(jiǎn)單，只需要把 sync.Mutex 換成 sync.RWMutex ，然后在讀操作的地方改為 RLock()，釋放讀鎖改為 RUnlock()：

package main

import (
    "log"
    "sync"
    "time"
)

type Account struct {
    balance float64
    mux     sync.RWMutex // 讀寫鎖
}

//
func (a *Account) Deposit(amount float64) {
    a.mux.Lock() // 寫鎖
    time.Sleep(time.Second * 2)
    a.balance += amount
    a.mux.Unlock() // 釋放寫鎖
}

func (a *Account) Balance() (balance float64) {
    a.mux.RLock() // 讀鎖
    time.Sleep(time.Second * 2)
    balance = a.balance
    a.mux.RUnlock() // 釋放讀鎖
    return balance
}

func main() {

    wg := &sync.WaitGroup{}
    user := &Account{}

    n := 5
    wg.Add(n)
    for i := 1; i <= n; i++ {
        go func() {
            user.Deposit(1000)
            log.Printf("寫：存款: %v", 1000)
            wg.Done()
        }()
    }

    wg.Add(n)
    for i := 1; i <= n; i++ {
        go func() {
            log.Printf("讀：余額: %v", user.Balance())
            wg.Done()
        }()
    }

    wg.Wait()
}