把互斥锁改为读写锁也很简单，只需要把 sync.Mutex 换成 sync.RWMutex ，然后在读操作的地方改为 RLock()，释放读锁改为 RUnlock()：

package main

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

type Account struct {
    balance float64
    mux     sync.RWMutex // 读写锁
}

//
func (a *Account) Deposit(amount float64) {
    a.mux.Lock() // 写锁
    time.Sleep(time.Second * 2)
    a.balance += amount
    a.mux.Unlock() // 释放写锁
}

func (a *Account) Balance() (balance float64) {
    a.mux.RLock() // 读锁
    time.Sleep(time.Second * 2)
    balance = a.balance
    a.mux.RUnlock() // 释放读锁
    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("写：存款: %v", 1000)
            wg.Done()
        }()
    }

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

    wg.Wait()
}